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Waterman HL, Moore MC, Smith MS, Farmer B, Scott M, Edgerton DS, Cherrington AD. Duration of Morning Hyperinsulinemia is Key to the Enhancement of Hepatic Glucose Uptake and Glycogen Storage Later in the Day. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.10.593551. [PMID: 38798653 PMCID: PMC11118521 DOI: 10.1101/2024.05.10.593551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2024]
Abstract
The second meal phenomenon refers to the improvement in glucose tolerance seen following a second identical meal. We previously showed that 4 hours of morning (AM) hyperinsulinemia, but not hyperglycemia, enhanced hepatic glucose uptake (HGU) and glycogen storage during an afternoon (PM) hyperinsulinemic hyperglycemic clamp (HIHG). Our current aim was to determine if the duration or pattern of morning hyperinsulinemia is important for the PM response to a HIHG clamp. To determine this, we administered the same total amount of insulin either over 2h in the first half of the morning (Ins2h-A), over 2h in the 2nd half of the morning (Ins2h-B), or over the entire 4h (Ins4h) of the morning. In the 4h PM period, all three groups had 4x basal insulin, 2x basal glycemia, and portal glucose infusion to simulate a meal. During the PM clamp, there was a marked increase in the mean hepatic glucose uptake and hepatic glycogen synthesis in the Ins4h group compared to the Ins2h-A and Ins2h-B groups, despite matched hepatic glucose and insulin loads. Thus, the longer duration (Ins4h) of mild hyperinsulinemia in the morning seems to be the key to much greater liver glucose uptake during the PM clamp.
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Affiliation(s)
- Hannah L Waterman
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine
| | - Mary Courtney Moore
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine
| | - Marta S Smith
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine
| | - Ben Farmer
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine
| | - Melanie Scott
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine
| | - Dale S Edgerton
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine
| | - Alan D Cherrington
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine
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2
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Paliwal A, Paliwal V, Jain S, Paliwal S, Sharma S. Current Insight on the Role of Glucokinase and Glucokinase Regulatory Protein in Diabetes. Mini Rev Med Chem 2024; 24:674-688. [PMID: 37612862 DOI: 10.2174/1389557523666230823151927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2023] [Revised: 06/19/2023] [Accepted: 07/13/2023] [Indexed: 08/25/2023]
Abstract
The glucokinase regulator (GCKR) gene encodes an inhibitor of the glucokinase enzyme (GCK), found only in hepatocytes and responsible for glucose metabolism. A common GCKR coding variation has been linked to various metabolic traits in genome-wide association studies. Rare GCKR polymorphisms influence GKRP activity, expression, and localization. Despite not being the cause, these variations are linked to hypertriglyceridemia. Because of their crystal structures, we now better understand the molecular interactions between GKRP and the GCK. Finally, small molecules that specifically bind to GKRP and decrease blood sugar levels in diabetic models have been identified. GCKR allelic spectrum changes affect lipid and glucose homeostasis. GKRP dysfunction has been linked to a variety of molecular causes, according to functional analysis. Numerous studies have shown that GKRP dysfunction is not the only cause of hypertriglyceridemia, implying that type 2 diabetes could be treated by activating liver-specific GCK via small molecule GKRP inhibition. The review emphasizes current discoveries concerning the characteristic roles of glucokinase and GKRP in hepatic glucose metabolism and diabetes. This information has influenced the growth of directed molecular therapies for diabetes, which has improved our understanding of lipid and glucose physiology.
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Affiliation(s)
- Ajita Paliwal
- Department of Pharmacy, Banasthali Vidyapith, Banasthali, Rajasthan, India
| | - Vartika Paliwal
- Department of Pharmacy, Banasthali Vidyapith, Banasthali, Rajasthan, India
| | - Smita Jain
- Department of Pharmacy, Banasthali Vidyapith, Banasthali, Rajasthan, India
| | - Sarvesh Paliwal
- Department of Pharmacy, Banasthali Vidyapith, Banasthali, Rajasthan, India
| | - Swapnil Sharma
- Department of Pharmacy, Banasthali Vidyapith, Banasthali, Rajasthan, India
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3
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Brouwers MCGJ. Fructose 1-phosphate, an evolutionary signaling molecule of abundancy. Trends Endocrinol Metab 2022; 33:680-689. [PMID: 35995682 DOI: 10.1016/j.tem.2022.07.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 07/27/2022] [Accepted: 07/27/2022] [Indexed: 11/18/2022]
Abstract
Evidence is accumulating that specifically fructose exerts adverse cardiometabolic effects in humans. Recent experimental studies have shown that fructose not only serves as a substrate for, among others, intrahepatic lipid formation, but also has a signaling function. It is postulated that fructose 1-phosphate (F1-P) has evolved as a signaling molecule of abundancy that stimulates nutrient absorption, lipid storage, and reproduction. Such a role would provide an explanation for why fructose contributes to the pathogenesis of evolutionary mismatch diseases, including nonalcoholic fatty liver disease (NAFLD), cardiovascular disease, polycystic ovary syndrome (PCOS), and colorectal cancer, in the current era of nutritional abundance. It is anticipated that reducing F1-P, by either pharmacological inhibition of ketohexokinase (KHK) or societal measures, will mitigate the risk of these diseases.
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Affiliation(s)
- Martijn C G J Brouwers
- Department of Internal Medicine, Division of Endocrinology and Metabolic Disease, Maastricht University Medical Centre, Maastricht, The Netherlands; CARIM School for Cardiovascular Disease, Maastricht University, Maastricht, The Netherlands.
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4
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Mora MR, Dando R. The sensory properties and metabolic impact of natural and synthetic sweeteners. Compr Rev Food Sci Food Saf 2021; 20:1554-1583. [PMID: 33580569 DOI: 10.1111/1541-4337.12703] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Revised: 11/12/2020] [Accepted: 12/13/2020] [Indexed: 12/11/2022]
Abstract
The global rise in obesity, type II diabetes, and other metabolic disorders in recent years has been attributed in part to the overconsumption of added sugars. Sugar reduction strategies often rely on synthetic and naturally occurring sweetening compounds to achieve their goals, with popular synthetic sweeteners including saccharin, cyclamate, acesulfame potassium, aspartame, sucralose, neotame, alitame, and advantame. Natural sweeteners can be further partitioned into nutritive, including polyols, rare sugars, honey, maple syrup, and agave, and nonnutritive, which include steviol glycosides and rebaudiosides, luo han guo (monk fruit), and thaumatin. We choose the foods we consume largely on their sensory properties, an area in which these sugar substitutes often fall short. Here, we discuss the most popular synthetic and natural sweeteners, with the goal of providing an understanding of differences in the sensory profiles of these sweeteners versus sucrose, that they are designed to replace, essential for the effectiveness of sugar reduction strategies. In addition, we break down the influence of these sweeteners on metabolism, and present results from a large survey of consumers' opinions on these sweeteners. Consumer interest in clean label foods has driven a move toward natural sweeteners; however, neither natural nor synthetic sweeteners are metabolically inert. Identifying sugar replacements that not only closely imitate the sensory profile of sucrose but also exert advantageous effects on body weight and metabolism is critical in successfully the ultimate goals of reducing added sugar in the average consumer's diet. With so many options for sucrose replacement available, consumer opinion and cost, which vary widely with suagr replacements, will also play a vital role in which sweeteners are successful in widespread adoption.
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Affiliation(s)
- Margaux R Mora
- Department of Food Science, Cornell University, Ithaca, New York
| | - Robin Dando
- Department of Food Science, Cornell University, Ithaca, New York
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Jiang S, Xiao W, Zhu X, Yang P, Zheng Z, Lu S, Jiang S, Zhang G, Liu J. Review on D-Allulose: In vivo Metabolism, Catalytic Mechanism, Engineering Strain Construction, Bio-Production Technology. Front Bioeng Biotechnol 2020; 8:26. [PMID: 32117915 PMCID: PMC7008614 DOI: 10.3389/fbioe.2020.00026] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 01/13/2020] [Indexed: 01/23/2023] Open
Abstract
Rare sugar D-allulose as a substitute sweetener is produced through the isomerization of D-fructose by D-tagatose 3-epimerases (DTEases) or D-allulose 3-epimerases (DAEases). D-Allulose is a kind of low energy monosaccharide sugar naturally existing in some fruits in very small quantities. D-Allulose not only possesses high value as a food ingredient and dietary supplement, but also exhibits a variety of physiological functions serving as improving insulin resistance, antioxidant enhancement, and hypoglycemic controls, and so forth. Thus, D-allulose has an important development value as an alternative to high-energy sugars. This review provided a systematic analysis of D-allulose characters, application, enzymatic characteristics and molecular modification, engineered strain construction, and processing technologies. The existing problems and its proposed solutions for D-allulose production are also discussed. More importantly, a green and recycling process technology for D-allulose production is proposed for low waste formation, low energy consumption, and high sugar yield.
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Affiliation(s)
- Suwei Jiang
- Department of Biological, Food and Environment Engineering, Hefei University, Hefei, China
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Wei Xiao
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Xingxing Zhu
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Peizhou Yang
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Zhi Zheng
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Shuhua Lu
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Shaotong Jiang
- Anhui Key Laboratory of Intensive Processing of Agricultural Products, College of Food and Biological Engineering, Hefei University of Technology, Hefei, China
| | - Guochang Zhang
- Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana–Champaign, Urbana, IL, United States
| | - Jingjing Liu
- Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana–Champaign, Urbana, IL, United States
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Salgado M, Ordenes P, Villagra M, Uribe E, García-Robles MDLA, Tarifeño-Saldivia E. When a Little Bit More Makes the Difference: Expression Levels of GKRP Determines the Subcellular Localization of GK in Tanycytes. Front Neurosci 2019; 13:275. [PMID: 30983961 PMCID: PMC6449865 DOI: 10.3389/fnins.2019.00275] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 03/08/2019] [Indexed: 01/01/2023] Open
Abstract
Glucose homeostasis is performed by specialized cells types that detect and respond to changes in systemic glucose concentration. Hepatocytes, β-cells and hypothalamic tanycytes are part of the glucosensor cell types, which express several proteins involved in the glucose sensing mechanism such as GLUT2, Glucokinase (GK) and Glucokinase regulatory protein (GKRP). GK catalyzes the phosphorylation of glucose to glucose-6-phosphate (G-6P), and its activity and subcellular localization are regulated by GKRP. In liver, when glucose concentration is low, GKRP binds to GK holding it in the nucleus, while the rise in glucose concentration induces a rapid export of GK from the nucleus to the cytoplasm. In contrast, hypothalamic tanycytes display inverse compartmentalization dynamic in response to glucose: a rise in the glucose concentration drives nuclear compartmentalization of GK. The underlying mechanism responsible for differential GK subcellular localization in tanycytes has not been described yet. However, it has been suggested that relative expression between GK and GKRP might play a role. To study the effects of GKRP expression levels in the subcellular localization of GK, we used insulinoma 832/13 cells and hypothalamic tanycytes to overexpress the tanycytic sequences of Gckr. By immunocytochemistry and Western blot analysis, we observed that overexpression of GKRP, independently of the cellular context, turns GK localization to a liver-like fashion, as GK is mainly localized in the nucleus in response to low glucose. Evaluating the expression levels of GKRP in relation to GK through RT-qPCR, suggest that excess of GKRP might influence the pattern of GK subcellular localization. In this sense, we propose that the low expression of GKRP (in relation to GK) observed in tanycytes is responsible, at least in part, for the compartmentalization pattern observed in this cell type. Since GKRP behaves as a GK inhibitor, the regulation of GKRP expression levels or activity in tanycytes could be used as a therapeutic target to regulate the glucosensing activity of these cells and consequently to regulate feeding behavior.
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Affiliation(s)
- Magdiel Salgado
- Department of Cellular Biology, Faculty of Biological Sciences, University of Concepción, Concepción, Chile
| | - Patricio Ordenes
- Department of Cellular Biology, Faculty of Biological Sciences, University of Concepción, Concepción, Chile
| | - Marcos Villagra
- Department of Cellular Biology, Faculty of Biological Sciences, University of Concepción, Concepción, Chile
| | - Elena Uribe
- Department of Biochemistry and Molecular Biology, Faculty of Biological Sciences, University of Concepción, Concepción, Chile
| | | | - Estefanía Tarifeño-Saldivia
- Department of Biochemistry and Molecular Biology, Faculty of Biological Sciences, University of Concepción, Concepción, Chile
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7
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O'Brien TP, Jenkins EC, Estes SK, Castaneda AV, Ueta K, Farmer TD, Puglisi AE, Swift LL, Printz RL, Shiota M. Correcting Postprandial Hyperglycemia in Zucker Diabetic Fatty Rats With an SGLT2 Inhibitor Restores Glucose Effectiveness in the Liver and Reduces Insulin Resistance in Skeletal Muscle. Diabetes 2017; 66:1172-1184. [PMID: 28246292 PMCID: PMC5399614 DOI: 10.2337/db16-1410] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 02/17/2017] [Indexed: 12/11/2022]
Abstract
Ten-week-old Zucker diabetic fatty (ZDF) rats at an early stage of diabetes embody metabolic characteristics of obese human patients with type 2 diabetes, such as severe insulin and glucose intolerance in muscle and the liver, excessive postprandial excursion of plasma glucose and insulin, and a loss of metabolic flexibility with decreased lipid oxidation. Metabolic flexibility and glucose flux were examined in ZDF rats during fasting and near-normal postprandial insulinemia and glycemia after correcting excessive postprandial hyperglycemia using treatment with a sodium-glucose cotransporter 2 inhibitor (SGLT2-I) for 7 days. Preprandial lipid oxidation was normalized, and with fasting, endogenous glucose production (EGP) increased by 30% and endogenous glucose disposal (E-Rd) decreased by 40%. During a postprandial hyperglycemic-hyperinsulinemic clamp after SGLT2-I treatment, E-Rd increased by normalizing glucose effectiveness to suppress EGP and stimulate hepatic glucose uptake; activation of glucokinase was restored and insulin action was improved, stimulating muscle glucose uptake in association with decreased intracellular triglyceride content. In conclusion, SGLT2-I treatment improves impaired glucose effectiveness in the liver and insulin sensitivity in muscle by eliminating glucotoxicity, which reinstates metabolic flexibility with restored preprandial lipid oxidation and postprandial glucose flux in ZDF rats.
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Affiliation(s)
- Tracy P O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Erin C Jenkins
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Shanea K Estes
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Antonio V Castaneda
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Kiichiro Ueta
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Tiffany D Farmer
- Diabetes Research Training Center, Vanderbilt University School of Medicine, Nashville, TN
| | - Allison E Puglisi
- Diabetes Research Training Center, Vanderbilt University School of Medicine, Nashville, TN
| | - Larry L Swift
- Department of Pathology, Vanderbilt University School of Medicine, Nashville, TN
| | - Richard L Printz
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
| | - Masakazu Shiota
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN
- Diabetes Research Training Center, Vanderbilt University School of Medicine, Nashville, TN
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8
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Affiliation(s)
- Loranne Agius
- Institutes of Cellular Medicine and Ageing and Health, Medical School, Newcastle University, Newcastle upon Tyne, NE2 4HH United Kingdom;
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9
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A new level of regulation in gluconeogenesis: metabolic state modulates the intracellular localization of aldolase B and its interaction with liver fructose-1,6-bisphosphatase. Biochem J 2015; 472:225-37. [PMID: 26417114 DOI: 10.1042/bj20150269] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Accepted: 09/25/2015] [Indexed: 11/17/2022]
Abstract
Understanding how glucose metabolism is finely regulated at molecular and cellular levels in the liver is critical for knowing its relationship to related pathologies, such as diabetes. In order to gain insight into the regulation of glucose metabolism, we studied the liver-expressed isoforms aldolase B and fructose-1,6-bisphosphatase-1 (FBPase-1), key enzymes in gluconeogenesis, analysing their cellular localization in hepatocytes under different metabolic conditions and their protein-protein interaction in vitro and in vivo. We observed that glucose, insulin, glucagon and adrenaline differentially modulate the intracellular distribution of aldolase B and FBPase-1. Interestingly, the in vitro protein-protein interaction analysis between aldolase B and FBPase-1 showed a specific and regulable interaction between them, whereas aldolase A (muscle isozyme) and FBPase-1 showed no interaction. The affinity of the aldolase B and FBPase-1 complex was modulated by intermediate metabolites, but only in the presence of K(+). We observed a decreased association constant in the presence of adenosine monophosphate, fructose-2,6-bisphosphate, fructose-6-phosphate and inhibitory concentrations of fructose-1,6-bisphosphate. Conversely, the association constant of the complex increased in the presence of dihydroxyacetone phosphate (DHAP) and non-inhibitory concentrations of fructose-1,6-bisphosphate. Notably, in vivo FRET studies confirmed the interaction between aldolase B and FBPase-1. Also, the co-expression of aldolase B and FBPase-1 in cultured cells suggested that FBPase-1 guides the cellular localization of aldolase B. Our results provide further evidence that metabolic conditions modulate aldolase B and FBPase-1 activity at the cellular level through the regulation of their interaction, suggesting that their association confers a catalytic advantage for both enzymes.
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10
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Guzman G, Chennuri R, Chan A, Rea B, Quintana A, Patel R, Xu PZ, Xie H, Hay N. Evidence for heightened hexokinase II immunoexpression in hepatocyte dysplasia and hepatocellular carcinoma. Dig Dis Sci 2015; 60:420-6. [PMID: 25381201 PMCID: PMC4323170 DOI: 10.1007/s10620-014-3364-3] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 09/08/2014] [Indexed: 02/07/2023]
Abstract
BACKGROUND Normal hepatocytes exhibit low-affinity hexokinase (glucokinase [HKIV]), but during oncogenesis, there is a switch from HKIV to HKII expression. The aims of this study were to compare the immunoexpression of HKII in non-dysplastic cirrhosis (NDC), liver cell change/dysplasia in cirrhosis (LCD), HCC, and normal liver control tissues, and to correlate HKII expression with clinical and histopathological parameters. DESIGN Immunohistochemistry was performed on a liver cancer progression tissue array consisting of specimens from explants with cirrhosis, including 45 tissue samples with HCC, 108 without HCC, 143 with LCD, and 8 normal liver control tissues. HKII expression was quantified as positive pixel counts/square millimeter (ppc/mm(2)) by image analysis. RESULTS There was a stepwise increase in HKII level from normal liver tissue to NDC, to LCD, and to HCC (p = 0.001). HKII levels were significantly higher in areas of LCD versus NDC (p ≤ 0.001), and in LCD and HCC versus NDC (p = 0.007). HKII levels were similar in LCD and HCC (p = 0.124). HKII levels were higher in grade 2-4 versus grade 1 HCCs (p = 0.044), and in pleomorphic versus non-pleomorphic HCC variants (p = 0.041). Higher levels of HKII expression in LCD and HCC versus NDC and in higher tumor grade remained significant in multivariate analysis. CONCLUSIONS Higher levels of HKII immunoexpression in LDC and HCC compared with NDC suggest that upregulation of HKII occurs during the process of hepatocarcinogenesis in humans. In HCC, higher levels of HKII are associated with more aggressive histological features.
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Affiliation(s)
- Grace Guzman
- Pathology, College of Medicine, Cancer Center, University of Illinois Hospital and Health Science System, 840 South Wood Street Room 130M/C 847, Chicago, IL 60612, USA
| | - Rohini Chennuri
- Pathology, College of Medicine, Cancer Center, University of Illinois Hospital and Health Science System, 840 South Wood Street Room 130M/C 847, Chicago, IL 60612, USA
| | - Alexander Chan
- Pathology, College of Medicine, Cancer Center, University of Illinois Hospital and Health Science System, 840 South Wood Street Room 130M/C 847, Chicago, IL 60612, USA
| | - Bryan Rea
- Pathology, College of Medicine, Cancer Center, University of Illinois Hospital and Health Science System, 840 South Wood Street Room 130M/C 847, Chicago, IL 60612, USA
| | - Ada Quintana
- Pathology, College of Medicine, Cancer Center, University of Illinois Hospital and Health Science System, 840 South Wood Street Room 130M/C 847, Chicago, IL 60612, USA
| | - Roshan Patel
- Pathology, College of Medicine, Cancer Center, University of Illinois Hospital and Health Science System, 840 South Wood Street Room 130M/C 847, Chicago, IL 60612, USA
| | - Pei-Zhang Xu
- Biochemistry and Molecular Genetics, College of Medicine, University of Illinois Hospital and Health Science System, Chicago, IL 60612, USA
| | - Hui Xie
- Epidemiology and Biostatistics, School of Public Health, University of Illinois Hospital and Health Science System, Chicago, IL 60612, USA
| | - Nissim Hay
- Biochemistry and Molecular Genetics, College of Medicine, University of Illinois Hospital and Health Science System, Chicago, IL 60612, USA
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11
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Farmer TD, Jenkins EC, O'Brien TP, McCoy GA, Havlik AE, Nass ER, Nicholson WE, Printz RL, Shiota M. Comparison of the physiological relevance of systemic vs. portal insulin delivery to evaluate whole body glucose flux during an insulin clamp. Am J Physiol Endocrinol Metab 2015; 308:E206-22. [PMID: 25516552 PMCID: PMC4312835 DOI: 10.1152/ajpendo.00406.2014] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
To understand the underlying pathology of metabolic diseases, such as diabetes, an accurate determination of whole body glucose flux needs to be made by a method that maintains key physiological features. One such feature is a positive differential in insulin concentration between the portal venous and systemic arterial circulation (P/S-IG). P/S-IG during the determination of the relative contribution of liver and extra-liver tissues/organs to whole body glucose flux during an insulin clamp with either systemic (SID) or portal (PID) insulin delivery was examined with insulin infusion rates of 1, 2, and 5 mU·kg(-1)·min(-1) under either euglycemic or hyperglycemic conditions in 6-h-fasted conscious normal rats. A P/S-IG was initially determined with endogenous insulin secretion to exist with a value of 2.07. During an insulin clamp, while inhibiting endogenous insulin secretion by somatostatin, P/S-IG remained at 2.2 with PID, whereas, P/S-IG disappeared completely with SID, which exhibited higher arterial and lower portal insulin levels compared with PID. Consequently, glucose disappearance rates and muscle glycogen synthetic rates were higher, but suppression of endogenous glucose production and liver glycogen synthetic rates were lower with SID compared with PID. When the insulin clamp was performed with SID at 2 and 5 mU·kg(-1)·min(-1) without managing endogenous insulin secretion under euglycemic but not hyperglycemic conditions, endogenous insulin secretion was completely suppressed with SID, and the P/S-IG disappeared. Thus, compared with PID, an insulin clamp with SID underestimates the contribution of liver in response to insulin to whole body glucose flux.
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Affiliation(s)
- Tiffany D Farmer
- Diabetes Research Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Erin C Jenkins
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee; and
| | - Tracy P O'Brien
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee; and
| | - Gregory A McCoy
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee; and
| | - Allison E Havlik
- Diabetes Research Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Erik R Nass
- Diabetes Research Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Wendell E Nicholson
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Richard L Printz
- Diabetes Research Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee; Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee; and
| | - Masakazu Shiota
- Diabetes Research Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee; Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee; and
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12
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Nakamura A, Terauchi Y. Present status of clinical deployment of glucokinase activators. J Diabetes Investig 2014; 6:124-32. [PMID: 25802718 PMCID: PMC4364845 DOI: 10.1111/jdi.12294] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Revised: 09/24/2014] [Accepted: 09/25/2014] [Indexed: 12/14/2022] Open
Abstract
Glucokinase is one of four members of the hexokinase family of enzymes. Its expression is limited to the major organs (such as the pancreas, liver, brain and the gastrointestinal tract) that are thought to have an integrated role in glucose sensing. In the liver, phosphorylation of glucose by glucokinase promotes glycogen synthesis, whereas in the β-cells, it results in insulin release. Studies of glucokinase-linked genetically-modified mice and mutations in humans have illustrated the important roles played by glucokinase in whole-body glucose homeostasis, and suggest that the use of pharmacological agents that augment glucokinase activity could represent a viable treatment strategy in patients with type 2 diabetes. Since 2003, many glucokinase activators (GKAs) have been developed, and their ability to lower the blood glucose has been shown in several animal models of type 2 diabetes. Also, we and others have shown in mouse models that GKAs also have the effect of stimulating the proliferation of β-cells. However, the results of recent phase II trials have shown that GKAs lose their efficacy within several months of use, and that their use is associated with a high incidence of hypoglycemia; furthermore, patients treated with GKAs frequently developed dyslipidemia. A better understanding of the role of glucokinase in metabolic effects is required to resolve several issues identified in clinical trials.
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Affiliation(s)
- Akinobu Nakamura
- Division of Immunology and Metabolism, Hokkaido University Graduate School of Medicine Sapporo, Japan
| | - Yasuo Terauchi
- Department of Endocrinology and Metabolism, Graduate School of Medicine, Yokohama City University Yokohama, Japan
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13
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Edgerton DS, Moore MC, Winnick JJ, Scott M, Farmer B, Naver H, Jeppesen CB, Madsen P, Kjeldsen TB, Nishimura E, Brand CL, Cherrington AD. Changes in glucose and fat metabolism in response to the administration of a hepato-preferential insulin analog. Diabetes 2014; 63:3946-54. [PMID: 24947349 PMCID: PMC4392933 DOI: 10.2337/db14-0266] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Endogenous insulin secretion exposes the liver to three times higher insulin concentrations than the rest of the body. Because subcutaneous insulin delivery eliminates this gradient and is associated with metabolic abnormalities, functionally restoring the physiologic gradient may provide therapeutic benefits. The effects of recombinant human insulin (HI) delivered intraportally or peripherally were compared with an acylated insulin model compound (insulin-327) in dogs. During somatostatin and basal portal vein glucagon infusion, insulin was infused portally (PoHI; 1.8 pmol/kg/min; n = 7) or peripherally (PeHI; 1.8 pmol/kg/min; n = 8) and insulin-327 (Pe327; 7.2 pmol/kg/min; n = 5) was infused peripherally. Euglycemia was maintained by glucose infusion. While the effects on liver glucose metabolism were greatest in the PoHI and Pe327 groups, nonhepatic glucose uptake increased most in the PeHI group. Suppression of lipolysis was greater during PeHI than PoHI and was delayed in Pe327 infusion. Thus small increments in portal vein insulin have major consequences on the liver, with little effect on nonhepatic glucose metabolism, whereas insulin delivered peripherally cannot act on the liver without also affecting nonhepatic tissues. Pe327 functionally restored the physiologic portal-arterial gradient and thereby produced hepato-preferential effects.
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Affiliation(s)
- Dale S Edgerton
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN
| | - Mary C Moore
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN
| | - Jason J Winnick
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN
| | - Melanie Scott
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN
| | - Ben Farmer
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN
| | | | | | | | | | | | | | - Alan D Cherrington
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, TN
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14
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Abstract
The glucokinase (GK) enzyme (EC 2.7.1.1.) is essential for the use of dietary glucose because it is the first enzyme to phosphorylate glucose in excess in different key tissues such as the pancreas and liver. The objective of the present review is not to fully describe the biochemical characteristics and the genetics of this enzyme but to detail its nutritional regulation in different vertebrates from fish to human. Indeed, the present review will describe the existence of the GK enzyme in different animal species that have naturally different levels of carbohydrate in their diets. Thus, some studies have been performed to analyse the nutritional regulation of the GK enzyme in humans and rodents (having high levels of dietary carbohydrates in their diets), in the chicken (moderate level of carbohydrates in its diet) and rainbow trout (no carbohydrate intake in its diet). All these data illustrate the nutritional importance of the GK enzyme irrespective of feeding habits, even in animals known to poorly use dietary carbohydrates (carnivorous species).
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15
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Ueta K, O'Brien TP, McCoy GA, Kim K, Healey EC, Farmer TD, Donahue EP, Condren AB, Printz RL, Shiota M. Glucotoxicity targets hepatic glucokinase in Zucker diabetic fatty rats, a model of type 2 diabetes associated with obesity. Am J Physiol Endocrinol Metab 2014; 306:E1225-38. [PMID: 24714398 PMCID: PMC4042096 DOI: 10.1152/ajpendo.00507.2013] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A loss of glucose effectiveness to suppress hepatic glucose production as well as increase hepatic glucose uptake and storage as glycogen is associated with a defective increase in glucose phosphorylation catalyzed by glucokinase (GK) in Zucker diabetic fatty (ZDF) rats. We extended these observations by investigating the role of persistent hyperglycemia (glucotoxicity) in the development of impaired hepatic GK activity in ZDF rats. We measured expression and localization of GK and GK regulatory protein (GKRP), translocation of GK, and hepatic glucose flux in response to a gastric mixed meal load (MMT) and hyperglycemic hyperinsulinemic clamp after 1 or 6 wk of treatment with the sodium-glucose transporter 2 inhibitor (canaglifrozin) that was used to correct the persistent hyperglycemia of ZDF rats. Defective augmentation of glucose phosphorylation in response to a rise in plasma glucose in ZDF rats was associated with the coresidency of GKRP with GK in the cytoplasm in the midstage of diabetes, which was followed by a decrease in GK protein levels due to impaired posttranscriptional processing in the late stage of diabetes. Correcting hyperglycemia from the middle diabetic stage normalized the rate of glucose phosphorylation by maintaining GK protein levels, restoring normal nuclear residency of GK and GKRP under basal conditions and normalizing translocation of GK from the nucleus to the cytoplasm, with GKRP remaining in the nucleus in response to a rise in plasma glucose. This improved the liver's metabolic ability to respond to hyperglycemic hyperinsulinemia. Glucotoxicity is responsible for loss of glucose effectiveness and is associated with altered GK regulation in the ZDF rat.
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Affiliation(s)
- Kiichiro Ueta
- Department of Molecular Physiology and Biophysics and
| | | | | | - Kuikwon Kim
- Department of Molecular Physiology and Biophysics and
| | - Erin C Healey
- Department of Molecular Physiology and Biophysics and
| | - Tiffany D Farmer
- Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - E Patrick Donahue
- Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | | | - Richard L Printz
- Department of Molecular Physiology and Biophysics and Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Masakazu Shiota
- Department of Molecular Physiology and Biophysics and Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee
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16
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Salgado M, Tarifeño-Saldivia E, Ordenes P, Millán C, Yañez MJ, Llanos P, Villagra M, Elizondo-Vega R, Martínez F, Nualart F, Uribe E, de los Angeles García-Robles M. Dynamic localization of glucokinase and its regulatory protein in hypothalamic tanycytes. PLoS One 2014; 9:e94035. [PMID: 24739934 PMCID: PMC3989220 DOI: 10.1371/journal.pone.0094035] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Accepted: 03/11/2014] [Indexed: 11/28/2022] Open
Abstract
Glucokinase (GK), the hexokinase involved in glucose sensing in pancreatic β cells, is also expressed in hypothalamic tanycytes, which cover the ventricular walls of the basal hypothalamus and are implicated in an indirect control of neuronal activity by glucose. Previously, we demonstrated that GK was preferentially localized in tanycyte nuclei in euglycemic rats, which has been reported in hepatocytes and is suggestive of the presence of the GK regulatory protein, GKRP. In the present study, GK intracellular localization in hypothalamic and hepatic tissues of the same rats under several glycemic conditions was compared using confocal microscopy and Western blot analysis. In the hypothalamus, increased GK nuclear localization was observed in hyperglycemic conditions; however, it was primarily localized in the cytoplasm in hepatic tissue under the same conditions. Both GK and GKRP were next cloned from primary cultures of tanycytes. Expression of GK by Escherichia coli revealed a functional cooperative protein with a S0.5 of 10 mM. GKRP, expressed in Saccharomyces cerevisiae, inhibited GK activity in vitro with a Ki 0.2 µM. We also demonstrated increased nuclear reactivity of both GK and GKRP in response to high glucose concentrations in tanycyte cultures. These data were confirmed using Western blot analysis of nuclear extracts. Results indicate that GK undergoes short-term regulation by nuclear compartmentalization. Thus, in tanycytes, GK can act as a molecular switch to arrest cellular responses to increased glucose.
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Affiliation(s)
- Magdiel Salgado
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Estefanía Tarifeño-Saldivia
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Patricio Ordenes
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Carola Millán
- Facultad de Artes Liberales, Universidad Adolfo Ibañez, Viña del Mar, Chile
| | - María José Yañez
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Paula Llanos
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Marcos Villagra
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Roberto Elizondo-Vega
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Fernando Martínez
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Francisco Nualart
- Departamento de Biología Celular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
| | - Elena Uribe
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Biológicas, Universidad de Concepción, Concepción, Chile
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17
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Rees MG, Davis MI, Shen M, Titus S, Raimondo A, Barrett A, Gloyn AL, Collins FS, Simeonov A. A panel of diverse assays to interrogate the interaction between glucokinase and glucokinase regulatory protein, two vital proteins in human disease. PLoS One 2014; 9:e89335. [PMID: 24586696 PMCID: PMC3929664 DOI: 10.1371/journal.pone.0089335] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Accepted: 01/19/2014] [Indexed: 12/02/2022] Open
Abstract
Recent genetic and clinical evidence has implicated glucokinase regulatory protein (GKRP) in the pathogenesis of type 2 diabetes and related traits. The primary role of GKRP is to bind and inhibit hepatic glucokinase (GCK), a critically important protein in human health and disease that exerts a significant degree of control over glucose metabolism. As activation of GCK has been associated with improved glucose tolerance, perturbation of the GCK-GKRP interaction represents a potential therapeutic target for pharmacological modulation. Recent structural and kinetic advances are beginning to provide insight into the interaction of these two proteins. However, tools to comprehensively assess the GCK-GKRP interaction, particularly in the context of small molecules, would be a valuable resource. We therefore developed three robust and miniaturized assays for assessing the interaction between recombinant human GCK and GKRP: an HTRF assay, a diaphorase-coupled assay, and a luciferase-coupled assay. The assays are complementary, featuring distinct mechanisms of detection (luminescence, fluorescence, FRET). Two assays rely on GCK enzyme activity modulation by GKRP while the FRET-based assay measures the GCK-GKRP protein-protein interaction independent of GCK enzymatic substrates and activity. All three assays are scalable to low volumes in 1536-well plate format, with robust Z’ factors (>0.7). Finally, as GKRP sequesters GCK in the hepatocyte nucleus at low glucose concentrations, we explored cellular models of GCK localization and translocation. Previous findings from freshly isolated rat hepatocytes were confirmed in cryopreserved rat hepatocytes, and we further extended this study to cryopreserved human hepatocytes. Consistent with previous reports, there were several key differences between the rat and human systems, with our results suggesting that human hepatocytes can be used to interrogate GCK translocation in response to small molecules. The assay panel developed here should help direct future investigation of the GCK-GKRP interaction in these or other physiologically relevant human systems.
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Affiliation(s)
- Matthew G. Rees
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, Maryland, United States of America
- National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America
- Oxford Centre for Diabetes Endocrinology & Metabolism, University of Oxford, United Kingdom
| | - Mindy I. Davis
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, Maryland, United States of America
| | - Min Shen
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, Maryland, United States of America
| | - Steve Titus
- GE Healthcare, Life Sciences, Piscataway, New Jersey, United States of America
| | - Anne Raimondo
- Oxford Centre for Diabetes Endocrinology & Metabolism, University of Oxford, United Kingdom
| | - Amy Barrett
- Oxford Centre for Diabetes Endocrinology & Metabolism, University of Oxford, United Kingdom
| | - Anna L. Gloyn
- Oxford Centre for Diabetes Endocrinology & Metabolism, University of Oxford, United Kingdom
- NIHR Oxford Biomedical Research Centre, ORH Trust, OCDEM, Churchill Hospital, Oxford, United Kingdom
| | - Francis S. Collins
- National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Anton Simeonov
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, Maryland, United States of America
- * E-mail:
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18
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Schermerhorn T. Normal glucose metabolism in carnivores overlaps with diabetes pathology in non-carnivores. Front Endocrinol (Lausanne) 2013; 4:188. [PMID: 24348462 PMCID: PMC3847661 DOI: 10.3389/fendo.2013.00188] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Accepted: 11/19/2013] [Indexed: 12/15/2022] Open
Abstract
Carnivores, such as the dolphin and the domestic cat, have numerous adaptations that befit consumption of diets with high protein and fat content, with little carbohydrate content. Consequently, nutrient metabolism in carnivorous species differs substantially from that of non-carnivores. Important metabolic pathways known to differ between carnivores and non-carnivores are implicated in the development of diabetes and insulin resistance in non-carnivores: (1) the hepatic glucokinase (GCK) pathway is absent in healthy carnivores yet GCK deficiency may result in diabetes in rodents and humans, (2) healthy dolphins and cats are prone to periods of fasting hyperglycemia and exhibit insulin resistance, both of which are risk factors for diabetes in non-carnivores. Similarly, carnivores develop naturally occurring diseases such as hemochromatosis, fatty liver, obesity, and diabetes that have strong parallels with the same disorders in humans. Understanding how evolution, environment, diet, and domestication may play a role with nutrient metabolism in the dolphin and cat may also be relevant to human diabetes.
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Affiliation(s)
- Thomas Schermerhorn
- Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, KS, USA
- *Correspondence: Thomas Schermerhorn, Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, 1800 Denison Avenue, Manhattan, KS 66506-5606, USA e-mail:
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19
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Abstract
Whether dietary fructose (as sucrose or high fructose corn syrup) has unique effects separate from its role as carbohydrate, or, in fact, whether it can be considered inherently harmful, even a toxin, has assumed prominence in nutrition. Much of the popular and scientific media have already decided against fructose and calls for regulation and taxation come from many quarters. There are conflicting data, however. Outcomes attributed to fructose — obesity, high triglycerides and other features of metabolic syndrome — are not found in every experimental test and may be more reliably caused by increased total carbohydrate. In this review, we try to put fructose in perspective by looking at the basic metabolic reactions. We conclude that fructose is best understood as part of carbohydrate metabolism. The pathways of fructose and glucose metabolism converge at the level of the triose-phosphates and, therefore, any downstream effects also occur with glucose. In addition, a substantial part of ingested fructose is turned to glucose. Regulation of fructose metabolism per se, is at the level of substrate control — the lower Km of fructokinase compared to glucokinase will affect the population of triose-phosphates. Generally deleterious effects of administering fructose alone suggest that fructose metabolism is normally controlled in part by glucose. Because the mechanisms of fructose effects are largely those of a carbohydrate, one has to ask what the proper control should be for experiments that compare fructose to glucose. In fact, there is a large literature showing benefits in replacing total carbohydrate with other nutrients, usually fat, and such experiments sensibly constitute the proper control for comparisons of the two sugars. In terms of public health, a rush to judgement analogous to the fat-cholesterol-heart story, is likely to have unpredictable outcome and unintended consequences. Popular opinion cannot be ignored in this problem and comparing fructose to ethanol, for example, is without biochemical correlates. Also, nothing in the biochemistry suggests that sugar is a toxin. Dietary carbohydrate restriction remains the best strategy for obesity, diabetes and metabolic syndrome. The specific contribution of the removal of fructose or sucrose to this effect remains unknown.
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Affiliation(s)
- Richard D Feinman
- State University of New York Downstate Medical Center, Brooklyn, NY, USA.
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20
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Coate KC, Kraft G, Irimia JM, Smith MS, Farmer B, Neal DW, Roach PJ, Shiota M, Cherrington AD. Portal vein glucose entry triggers a coordinated cellular response that potentiates hepatic glucose uptake and storage in normal but not high-fat/high-fructose-fed dogs. Diabetes 2013; 62:392-400. [PMID: 23028137 PMCID: PMC3554368 DOI: 10.2337/db12-0417] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The cellular events mediating the pleiotropic actions of portal vein glucose (PoG) delivery on hepatic glucose disposition have not been clearly defined. Likewise, the molecular defects associated with postprandial hyperglycemia and impaired hepatic glucose uptake (HGU) following consumption of a high-fat, high-fructose diet (HFFD) are unknown. Our goal was to identify hepatocellular changes elicited by hyperinsulinemia, hyperglycemia, and PoG signaling in normal chow-fed (CTR) and HFFD-fed dogs. In CTR dogs, we demonstrated that PoG infusion in the presence of hyperinsulinemia and hyperglycemia triggered an increase in the activity of hepatic glucokinase (GK) and glycogen synthase (GS), which occurred in association with further augmentation in HGU and glycogen synthesis (GSYN) in vivo. In contrast, 4 weeks of HFFD feeding markedly reduced GK protein content and impaired the activation of GS in association with diminished HGU and GSYN in vivo. Furthermore, the enzymatic changes associated with PoG sensing in chow-fed animals were abolished in HFFD-fed animals, consistent with loss of the stimulatory effects of PoG delivery. These data reveal new insight into the molecular physiology of the portal glucose signaling mechanism under normal conditions and to the pathophysiology of aberrant postprandial hepatic glucose disposition evident under a diet-induced glucose-intolerant condition.
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Affiliation(s)
- Katie C. Coate
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Guillaume Kraft
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Jose M. Irimia
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Marta S. Smith
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Ben Farmer
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Doss W. Neal
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Peter J. Roach
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Masakazu Shiota
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Alan D. Cherrington
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee
- Corresponding author: Alan D. Cherrington,
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21
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Winnick JJ, An Z, Kraft G, Ramnanan CJ, Irimia JM, Smith M, Lautz M, Roach PJ, Cherrington AD. Liver glycogen loading dampens glycogen synthesis seen in response to either hyperinsulinemia or intraportal glucose infusion. Diabetes 2013; 62:96-101. [PMID: 22923473 PMCID: PMC3526057 DOI: 10.2337/db11-1773] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The purpose of this study was to determine the effect of liver glycogen loading on net hepatic glycogen synthesis during hyperinsulinemia or hepatic portal vein glucose infusion in vivo. Liver glycogen levels were supercompensated (SCGly) in two groups (using intraportal fructose infusion) but not in two others (Gly) during hyperglycemic-normoinsulinemia. Following a 2-h control period during which fructose infusion was stopped, there was a 2-h experimental period in which the response to hyperglycemia plus either 4× basal insulin (INS) or portal vein glucose infusion (PoG) was measured. Increased hepatic glycogen reduced the percent of glucose taken up by the liver that was deposited in glycogen (74 ± 3 vs. 53 ± 5% in Gly+INS and SCGly+INS, respectively, and 72 ± 3 vs. 50 ± 6% in Gly+PoG and SCGly+PoG, respectively). The reduction in liver glycogen synthesis in SCGly+INS was accompanied by a decrease in both insulin signaling and an increase in AMPK activation, whereas only the latter was observed in SCGly+PoG. These data indicate that liver glycogen loading impairs glycogen synthesis regardless of the signal used to stimulate it.
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Affiliation(s)
- Jason J Winnick
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
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22
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Kraft G, Coate KC, Dardevet D, Farmer B, Donahue EP, Williams PE, Cherrington AD, Moore MC. Portal glucose delivery stimulates muscle but not liver protein metabolism. Am J Physiol Endocrinol Metab 2012; 303:E1202-11. [PMID: 23011060 PMCID: PMC3774325 DOI: 10.1152/ajpendo.00140.2012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Portal vein glucose delivery (the portal glucose signal) stimulates glucose uptake and glycogen storage by the liver, whereas portal amino acid (AA) delivery (the portal AA signal) induces an increase in protein synthesis by the liver. During a meal, both signals coexist and may interact. In this study, we compared the protein synthesis rates in the liver and muscle in response to portal or peripheral glucose infusion during intraportal infusion of a complete AA mixture. Dogs were surgically prepared with hepatic sampling catheters and flow probes. After a 42-h fast, they underwent a 3-h hyperinsulinemic (4× basal) hyperglucagonemic (3× basal) hyperglycemic (≈160 mg/dl) hyperaminoacidemic (hepatic load 1.5× basal; delivered intraportally) clamp (postprandial conditions). Glucose was infused either via a peripheral (PeG; n = 7) or the portal vein (PoG; n = 8). Protein synthesis was assessed with a primed, continuous [(14)C]leucine infusion. Net hepatic glucose uptake was stimulated by portal glucose infusion (+1 mg·kg(-1)·min(-1), P < 0.05) as expected, but hepatic fractional AA extraction and hepatic protein synthesis did not differ between groups. There was a lower arterial AA concentration in the PoG group (-19%, P < 0.05) and a significant stimulation (+30%) of muscle protein synthesis associated with increased expression of LAT1 and ASCT2 AA transporters and p70S6 phosphorylation. Concomitant portal glucose and AA delivery enhances skeletal muscle protein synthesis compared with peripheral glucose and portal AA delivery. These data suggest that enteral nutrition support may have an advantage over parenteral nutrition in stimulating muscle protein synthesis.
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Affiliation(s)
- Guillaume Kraft
- Dept. of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232-6015, USA
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23
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Bertinat R, Pontigo JP, Pérez M, Concha II, San Martín R, Guinovart JJ, Slebe JC, Yáñez AJ. Nuclear accumulation of fructose 1,6-bisphosphatase is impaired in diabetic rat liver. J Cell Biochem 2012; 113:848-56. [PMID: 22021109 DOI: 10.1002/jcb.23413] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Using a streptozotocin-induced type 1 diabetic rat model, we analyzed and separated the effects of hyperglycemia and hyperinsulinemia over the in vivo expression and subcellular localization of hepatic fructose 1,6-bisphosphatase (FBPase) in the multicellular context of the liver. Our data showed that FBPase subcellular localization was modulated by the nutritional state in normal but not in diabetic rats. By contrast, the liver zonation was not affected in any condition. In healthy starved rats, FBPase was localized in the cytoplasm of hepatocytes, whereas in healthy re-fed rats it was concentrated in the nucleus and the cell periphery. Interestingly, despite the hyperglycemia, FBPase was unable to accumulate in the nucleus in hepatocytes from streptozotocin-induced diabetic rats, suggesting that insulin is a critical in vivo modulator. This idea was confirmed by exogenous insulin supplementation to diabetic rats, where insulin was able to induce the rapid accumulation of FBPase within the hepatocyte nucleus. Besides, hepatic FBPase was found phosphorylated only in the cytoplasm, suggesting that the phosphorylation state is involved in the nuclear translocation. In conclusion, insulin and not hyperglycemia plays a crucial role in the nuclear accumulation of FBPase in vivo and may be an important regulatory mechanism that could account for the increased endogenous glucose production of liver of diabetic rodents.
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Affiliation(s)
- Romina Bertinat
- Instituto de Bioquímica y Microbiología, Universidad Austral de Chile, Valdivia, Chile
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24
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Ramnanan CJ, Edgerton DS, Cherrington AD. Evidence against a physiologic role for acute changes in CNS insulin action in the rapid regulation of hepatic glucose production. Cell Metab 2012; 15:656-64. [PMID: 22560218 PMCID: PMC3348512 DOI: 10.1016/j.cmet.2012.03.006] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
This Perspective will discuss the physiologic relevance of data that suggest CNS insulin action is required for the rapid suppression of hepatic glucose production. It will also review data from experiments on the conscious dog, which show that although the canine brain can sense insulin and, thereby, regulate hepatic glucoregulatory enzyme expression, CNS insulin action is not essential for the rapid suppression of glucose production caused by the hormone. Insulin's direct hepatic effects are dominant, thus it appears that insulin's central effects are redundant in the acute regulation of hepatic glucose metabolism.
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Affiliation(s)
- Christopher J Ramnanan
- Vanderbilt University School of Medicine, Department of Molecular Physiology and Biophysics, Nashville, TN 37232, USA
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25
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Bechmann LP, Gastaldelli A, Vetter D, Patman GL, Pascoe L, Hannivoort RA, Lee UE, Fiel I, Muñoz U, Ciociaro D, Lee YM, Buzzigoli E, Miele L, Hui KY, Bugianesi E, Burt AD, Day CP, Mari A, Agius L, Walker M, Friedman SL, Reeves HL. Glucokinase links Krüppel-like factor 6 to the regulation of hepatic insulin sensitivity in nonalcoholic fatty liver disease. Hepatology 2012; 55:1083-93. [PMID: 22095588 PMCID: PMC3295906 DOI: 10.1002/hep.24793] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Accepted: 10/27/2011] [Indexed: 12/23/2022]
Abstract
UNLABELLED The polymorphism, KLF6-IVS1-27A, in the Krüppel-like factor 6 (KLF6) transcription factor gene enhances its splicing into antagonistic isoforms and is associated with delayed histological progression of nonalcoholic fatty liver disease (NAFLD). To explore a potential role for KLF6 in the development of insulin resistance, central to NAFLD pathogenesis, we genotyped KLF6-IVS1-27 in healthy subjects and assayed fasting plasma glucose (FPG) and insulin sensitivities. Furthermore, we quantified messenger RNA (mRNA) expression of KLF6 and glucokinase (GCK), as an important mediator of insulin sensitivity, in human livers and in liver tissues derived from a murine Klf6 knockdown model (DeltaKlf6). Klf6 overexpression studies in a mouse hepatocyte line were utilized to mechanistically link KLF6 with Gck promoter activity. KLF6-IVS1-27Gwt (i.e., less KLF6 splicing) was associated with stepwise increases in FPG and insulin and reduced hepatic insulin sensitivity. KLF6 binds to the liver-specific Gck promoter and activates a GCK promoter-reporter, identifying GCK as a KLF6 direct transcriptional target. Accordingly, in DeltaKlf6 hepatocytes Gck expression was reduced and stable transfection of Klf6 led to up-regulation of Gck. GCK and KLF6 mRNAs correlate directly in human NAFLD tissues and immunohistochemistry studies confirm falling levels of both KLF6 and GCK in fat-laden hepatocytes. In contrast to full-length KLF6, splice variant KLF6-SV1 increases in NAFLD hepatocytes and inversely correlates with glucokinase regulatory protein, which negatively regulates GCK activity. CONCLUSION KLF6 regulation of GCK contributes to the development of hepatic insulin resistance. The KLF6-IVS1-27A polymorphism, which generates more KLF6-SV1, combats this, lowering hepatic insulin resistance and blood glucose.
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Affiliation(s)
- Lars P Bechmann
- Division of Liver Diseases, Mount Sinai School of Medicine, New York, NY,Department of Gastroenterology and Hepatology; University Hospital Essen, Germany
| | - Amalia Gastaldelli
- Institute of Clinical Physiology, National Research Council, Pisa, Italy,RISC Consortium, Pisa, Italy
| | - Diana Vetter
- Division of Liver Diseases, Mount Sinai School of Medicine, New York, NY
| | - Gillian L Patman
- Northern Institute for Cancer Research, Newcastle University, UK
| | - Laura Pascoe
- RISC Consortium, Pisa, Italy,Institute of Cellular Medicine, Newcastle University, UK
| | - Rebekka A Hannivoort
- Division of Liver Diseases, Mount Sinai School of Medicine, New York, NY,Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands
| | - Ursula E Lee
- Division of Liver Diseases, Mount Sinai School of Medicine, New York, NY
| | - Isabel Fiel
- Lillian and Henry M. Stratton-Hans Popper Department of Pathology; Mount Sinai School of Medicine; New York, NY
| | - Ursula Muñoz
- Division of Liver Diseases, Mount Sinai School of Medicine, New York, NY
| | - Demetrio Ciociaro
- Institute of Clinical Physiology, National Research Council, Pisa, Italy,RISC Consortium, Pisa, Italy
| | - Young-Min Lee
- Division of Liver Diseases, Mount Sinai School of Medicine, New York, NY
| | - Emma Buzzigoli
- Institute of Clinical Physiology, National Research Council, Pisa, Italy,RISC Consortium, Pisa, Italy
| | - Luca Miele
- Northern Institute for Cancer Research, Newcastle University, UK,Department of Internal Medicine, Policlinico Gemelli Hospital and Catholic University of the Sacred Heart, Rome, Italy
| | - Kei Y Hui
- Northern Institute for Cancer Research, Newcastle University, UK
| | | | | | | | - Andrea Mari
- RISC Consortium, Pisa, Italy,Institute of Biomedical Engineering, National Research Council, Padua, Italy
| | - Loranne Agius
- Institute of Cellular Medicine, Newcastle University, UK
| | - Mark Walker
- RISC Consortium, Pisa, Italy,Institute of Cellular Medicine, Newcastle University, UK
| | - Scott L Friedman
- Division of Liver Diseases, Mount Sinai School of Medicine, New York, NY
| | - Helen L Reeves
- Northern Institute for Cancer Research, Newcastle University, UK,The Hepatopancreatobiliary Group, Freeman Hospital, Newcastle-upon-Tyne, UK
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Bechmann LP, Hannivoort RA, Gerken G, Hotamisligil GS, Trauner M, Canbay A. The interaction of hepatic lipid and glucose metabolism in liver diseases. J Hepatol 2012; 56:952-64. [PMID: 22173168 DOI: 10.1016/j.jhep.2011.08.025] [Citation(s) in RCA: 643] [Impact Index Per Article: 53.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Revised: 08/09/2011] [Accepted: 08/10/2011] [Indexed: 12/31/2022]
Abstract
It is widely known that the liver is a central organ in lipogenesis, gluconeogenesis and cholesterol metabolism. However, over the last decades, a variety of pathological conditions highlighted the importance of metabolic functions within the diseased liver. As observed in Western societies, an increase in the prevalence of obesity and the metabolic syndrome promotes pathophysiological changes that cause non-alcoholic fatty liver disease (NAFLD). NAFLD increases the susceptibility of the liver to acute liver injury and may lead to cirrhosis and hepatocellular cancer. Alterations in insulin response, β-oxidation, lipid storage and transport, autophagy and an imbalance in chemokines and nuclear receptor signaling are held accountable for these changes. Furthermore, recent studies revealed a role for lipid accumulation in inflammation and ER stress in the clinical context of liver regeneration and hepatic carcinogenesis. This review focuses on novel findings related to nuclear receptor signaling - including the vitamin D receptor and the liver receptor homolog 1 - in hepatic lipid and glucose uptake, storage and metabolism in the clinical context of NAFLD, liver regeneration, and cancer.
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Affiliation(s)
- Lars P Bechmann
- Department of Gastroenterology and Hepatology, University Hospital Essen, University of Duisburg-Essen, Essen, Germany
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Chung MY, Oh DK, Lee KW. Hypoglycemic health benefits of D-psicose. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2012; 60:863-9. [PMID: 22224918 DOI: 10.1021/jf204050w] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Diabetes is an emerging health problem worldwide. The incidence of type 2 diabetes has dramatically increased and is expected to increase more rapidly in the future. Most patients with type 2 diabetes suffer from obesity and diabetes-related complications, including cardiovascular disease and hepatic steatosis. It has been proposed that simple sugar consumption is one of the major risk factors in the development of diabetes. Hence, the replacement of sugars with a low glycemic response would be an effective strategy to prevent type 2 diabetes. Accumulating evidence demonstrates that D-psicose, which has 70% the sweetness of sucrose and no calories, is a functional sugar exerting several health benefits preventing the development of diabetes. Although D-psicose presents in small amounts in natural products, a recent new technique using biocatalyst sources enables large-scale D-psicose production. More importantly, several clinical and animal studies demonstrated that D-psicose has hypoglycemic, hypolipidemic, and antioxidant activities, which make it an ideal candidate for preventing diabetes and related health concerns. This review will summarize the protective effects of D-psicose against type 2 diabetes and its complications, suggesting its potential benefits as a sucrose substitute.
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Affiliation(s)
- Min-Yu Chung
- Center for Agricultural Biomaterials, Seoul National University, Seoul, South Korea
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Abstract
Male Zucker diabetic fatty fa/fa (ZDF) rats develop obesity and insulin resistance at a young age, and then with aging, progressively develop hyperglycemia. This hyperglycemia is associated with impaired pancreatic β-cell function, loss of pancreatic β-cell mass, and decreased responsiveness of liver and extrahepatic tissues to the actions of insulin and glucose. Of particular interest are the insights provided by studies of these animals into the mechanism behind the progressive impairment of carbohydrate metabolism. This feature among others, including the development of obesity- and hyperglycemia-related complications, is common between male ZDF rats and humans with type 2 diabetes associated with obesity. We discuss the diabetic features and complications found in ZDF rats and why these animals are widely used as a genetic model for obese type 2 diabetes.
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Affiliation(s)
- Masakazu Shiota
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, USA.
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Shiota M. Measurement of glucose homeostasis in vivo: combination of tracers and clamp techniques. Methods Mol Biol 2012; 933:229-53. [PMID: 22893411 DOI: 10.1007/978-1-62703-068-7_15] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
A tracer technique referred to as "pancreatic-blood glucose clamp" allows assessment in response to a change in blood glucose, insulin, and/or glucagon of whole body glucose disposal, endogenous glucose production, specific tissue/organ glucose uptake and storage, and insulin secretion. This technique is currently considered the optimal method for measurement of insulin sensitivity and glucose effectiveness. We describe here, for use in conscious-unrestrained mice and rats, the pancreatic-blood glucose clamp technique and its associated methods; which include catheterization of blood vessels; a clamp of plasma insulin, glucagon, and glucose; analyses of metabolites and tracers; and calculations.
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Affiliation(s)
- Masakazu Shiota
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, USA.
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30
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Ling Y, Li X, Gu Q, Chen H, Lu D, Gao X. Associations of common polymorphisms in GCKR with type 2 diabetes and related traits in a Han Chinese population: a case-control study. BMC MEDICAL GENETICS 2011; 12:66. [PMID: 21569451 PMCID: PMC3112072 DOI: 10.1186/1471-2350-12-66] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/20/2010] [Accepted: 05/13/2011] [Indexed: 12/02/2022]
Abstract
Background Several studies have shown that variants in the glucokinase regulatory protein gene (GCKR) were associated with type 2 diabetes and dyslipidemia. The purpose of this study was to examine whether tag single nucleotide polymorphisms (SNPs) in the GCKR region were associated with type 2 diabetes and related traits in a Han Chinese population and to identify the potential mechanisms underlying these associations. Methods We investigated the association of polymorphisms in the GCKR gene with type 2 diabetes by employing a case-control study design (1118 cases and 1161 controls). Four tag SNPs (rs8179206, rs2293572, rs3817588 and rs780094) with pairwise r2 > 0.8 and minor allele frequency > 0.05 across the GCKR gene and its flanking regions were studied and haplotypes were constructed. Genotyping was performed by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy using a MassARRAY platform. Results The G alleles of GCKR rs3817588 and rs780094 were associated with an increased risk of type 2 diabetes after adjustment for year of birth, sex and BMI (OR = 1.24, 95% CI 1.08-1.43, p = 0.002 and OR = 1.22, 95% CI 1.07-1.38, p = 0.002, respectively). In the non-diabetic controls, the GG carriers of rs3817588 and rs780094 were nominally associated with a lower plasma triglyceride level compared to the AA carriers after adjustment for year of birth, sex and BMI (p for trend = 0.00004 and 0.03, respectively). Furthermore, the association of rs3817588 with plasma triglyceride level was still significant after correcting for multiple testing. Conclusions The rs3817588 A/G polymorphism of the GCKR gene was associated with type 2 diabetes and plasma triglyceride level in the Han Chinese population.
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Affiliation(s)
- Yan Ling
- Department of Endocrinology and Metabolism, Zhongshan Hospital, Fudan University, Shanghai 200032, China
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31
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Cao F, Wang X, Lu M, Yang Y, An Y, Zhang J, Chen X, Li L, Li S, Jiang J, Ye W, Jin L. Glucokinase regulatory protein (GCKR) gene rs4425043 polymorphism is associated with overweight and obesity in Chinese women. Lipids 2011; 46:357-63. [PMID: 21318467 DOI: 10.1007/s11745-011-3533-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2010] [Accepted: 01/22/2011] [Indexed: 11/30/2022]
Abstract
The aim of this study was to investigate the effects of GCKR polymorphism on the prevalence of overweight and obesity in Chinese female subjects using a gene-wide tagging- single nucleotide polymorphism (tSNP) strategy. We conducted a genetic association study in the Taizhou Retiree Women Cohort, a sub-cohort of the Taizhou longitudinal study. We genotyped four tSNPs (rs4425043, rs780094, rs814295, and rs8179206) of the GCKR gene using the Taqman assay in 2,851 female subjects and investigated their associations with overweight and obesity. Odds ratios and their 95% confidence intervals (CIs) were derived from ordered logistic regression model. We observed significant association between rs4425043 and body-mass-index-defined overweight and obesity. The frequencies of A allele of the rs4425043 exhibited a significant increasing trend from normal weight (13.20%), overweight (15.08%), to obese subjects (17.10%) (P = 0.006). Individuals with the GA or AA genotypes showed a 31% excessive risk to develop overweight or obesity (95% CI: 1.12-1.52, P = 0.001). In addition, we observed significantly increased levels of fasting plasma glucose associated with variations of both rs780094 and rs814295 (5.03, 5.09, and 5.15 mmol/L for rs780094 AA, GA and GG genotypes, respectively, and 5.03, 5.11, and 5.20 mmol/L for rs814295 AA, GA and GG genotypes, respectively). In conclusion, a novel polymorphism (rs4425043) in the GCKR gene increases the risk of overweight and obesity in Chinese women. Previous report that other polymorphisms in the GCKR gene are associated with glucose levels have also been confirmed.
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Affiliation(s)
- Feifei Cao
- Clinical Epidemiology Unit, Qilu Hospital of Shandong University, Jinan, Shandong, People's Republic of China
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Hossain MA, Kitagaki S, Nakano D, Nishiyama A, Funamoto Y, Matsunaga T, Tsukamoto I, Yamaguchi F, Kamitori K, Dong Y, Hirata Y, Murao K, Toyoda Y, Tokuda M. Rare sugar D-psicose improves insulin sensitivity and glucose tolerance in type 2 diabetes Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Biochem Biophys Res Commun 2010; 405:7-12. [PMID: 21187061 DOI: 10.1016/j.bbrc.2010.12.091] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Accepted: 12/18/2010] [Indexed: 02/07/2023]
Abstract
A rare sugar, D-psicose has progressively been evaluated as a unique metabolic regulator of glucose and lipid metabolism, and thus represents a promising compound for the treatment of type 2 diabetes mellitus (T2DM). The present study was undertaken to examine the underlying effector organs of D-psicose in lowering blood glucose and abdominal fat by exploiting a T2DM rat model, Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Rats were fed 5% D-psicose or 5% D-glucose supplemented in drinking water, and only water in the control for 13 weeks and the protective effects were compared. A non-diabetic Long-Evans Tokushima Otsuka (LETO), fed with water served as a counter control of OLETF. After 13 weeks feeding, D-psicose treatment significantly reduced the increase in body weight and abdominal fat mass. Oral glucose tolerance test (OGTT) showed the reduced blood glucose and insulin levels suggesting the improvement of insulin resistance in OLETF rats. Oil-red-O staining elucidated that D-psicose significantly reduced lipid accumulation in the liver. Immunohistochemical analysis showed D-psicose induced glucokinase translocation from nucleus to cytoplasm of the liver which enhances glucokinase activity and subsequent synthesis of glycogen in the liver. D-psicose also protected the pathological change of the β-cells of pancreatic islets. These data demonstrate that D-psicose controls blood glucose levels by reducing lipotoxicity in liver and by preserving pancreatic β-cell function.
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Affiliation(s)
- Mohammad A Hossain
- Department of Cell Physiology, Faculty of Medicine, Kagawa University, Kita, Kagawa, Japan
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Winnick JJ, An Z, Moore MC, Ramnanan CJ, Farmer B, Shiota M, Cherrington AD. A physiological increase in the hepatic glycogen level does not affect the response of net hepatic glucose uptake to insulin. Am J Physiol Endocrinol Metab 2009; 297:E358-66. [PMID: 19470836 PMCID: PMC2724107 DOI: 10.1152/ajpendo.00043.2009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To determine the effect of an acute increase in hepatic glycogen on net hepatic glucose uptake (NHGU) and disposition in response to insulin in vivo, studies were performed on two groups of dogs fasted 18 h. During the first 4 h of the study, somatostatin was infused peripherally, while insulin and glucagon were replaced intraportally in basal amounts. Hyperglycemia was brought about by glucose infusion, and either saline (n = 7) or fructose (n = 7; to stimulate NHGU and glycogen deposition) was infused intraportally. A 2-h control period then followed, during which the portal fructose and saline infusions were stopped, allowing NHGU and glycogen deposition in the fructose-infused animals to return to rates similar to those of the animals that received the saline infusion. This was followed by a 2-h experimental period, during which hyperglycemia was continued but insulin infusion was increased fourfold in both groups. During the initial 4-h glycogen loading period, NHGU averaged 1.18 +/- 0.27 and 5.55 +/- 0.53 mg x kg(-1) x min(-1) and glycogen synthesis averaged 0.72 +/- 0.24 and 3.98 +/- 0.57 mg x kg(-1) x min(-1) in the saline and fructose groups, respectively (P < 0.05). During the 2-h hyperinsulinemic period, NHGU rose from 1.5 +/- 0.4 and 0.9 +/- 0.2 to 3.1 +/- 0.6 and 2.5 +/- 0.5 mg x kg(-1) x min(-1) in the saline and fructose groups, respectively, a change of 1.6 mg x kg(-1) x min(-1) in both groups despite a significantly greater liver glycogen level in the fructose-infused group. Likewise, the metabolic fate of the extracted glucose (glycogen, lactate, or carbon dioxide) was not different between groups. These data indicate that an acute physiological increase in the hepatic glycogen content does not alter liver glucose uptake and storage under hyperglycemic/hyperinsulinemic conditions in the dog.
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Affiliation(s)
- Jason J Winnick
- Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6015, USA.
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Qi Q, Wu Y, Li H, Loos RJF, Hu FB, Sun L, Lu L, Pan A, Liu C, Wu H, Chen L, Yu Z, Lin X. Association of GCKR rs780094, alone or in combination with GCK rs1799884, with type 2 diabetes and related traits in a Han Chinese population. Diabetologia 2009; 52:834-43. [PMID: 19241058 DOI: 10.1007/s00125-009-1290-2] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Accepted: 01/19/2009] [Indexed: 10/21/2022]
Abstract
AIMS/HYPOTHESIS The GCKR rs780094 and GCK rs1799884 polymorphisms have been reported to be associated with dyslipidaemia and type 2 diabetes in white Europeans. The aim of this study was to replicate these associations in Han Chinese individuals and to identify the potential mechanisms underlying these associations. METHODS The single nucleotide polymorphisms rs780094 and rs1799884 were genotyped in a population-based sample of Han Chinese individuals (n = 3,210) and tested for association with risk of type 2 diabetes and related phenotypes. RESULTS The GCKR rs780094 A allele was marginally associated with reduced risk of type 2 diabetes (OR 0.85, 95% CI 0.73-1.00, p value under an additive model [p((add))] = 0.05) and significantly associated with reduced risk of impaired fasting glucose (IFG) or type 2 diabetes (OR 0.86, 95% CI 0.77-0.96, p([add]) = 0.0032). It was also significantly associated with decreased fasting glucose and increased HOMA of beta cell function (HOMA-B) and fasting triacylglycerol levels (p([add]) = 0.0169-5.3 x 10(-6)), but not with HOMA of insulin sensitivity (HOMA-S). The associations with type 2 diabetes and IFG remained significant after adjustment for BMI, while adjustment for HOMA-B abolished the associations. The GCKR rs780094 was also associated with obesity and BMI, independently of its association with type 2 diabetes. The GCK rs1799884 A allele was significantly associated with decreased HOMA-B (p([add]) = 0.0005), but not with type 2 diabetes or IFG. Individuals with increasing numbers of risk alleles for both variants had significantly lower HOMA-B (p([add]) = 5.8 x 10(-5)) in the combined analysis. CONCLUSIONS/INTERPRETATION Consistent with observations in white Europeans, the GCKR rs780094 polymorphism contributes to the risk of type 2 diabetes and dyslipidaemia in Han Chinese individuals. In addition, we showed that the effect on type 2 diabetes is probably mediated through impaired beta cell function rather than through obesity.
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Affiliation(s)
- Q Qi
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, People's Republic of China
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Polakof S, Míguez JM, Soengas JL. A hepatic protein modulates glucokinase activity in fish and avian liver: a comparative study. J Comp Physiol B 2009; 179:643-52. [DOI: 10.1007/s00360-009-0346-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Revised: 01/28/2009] [Accepted: 02/06/2009] [Indexed: 10/21/2022]
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Zheng D, Ionut V, Mooradian V, Stefanovski D, Bergman RN. Exenatide sensitizes insulin-mediated whole-body glucose disposal and promotes uptake of exogenous glucose by the liver. Diabetes 2009; 58:352-9. [PMID: 19011168 PMCID: PMC2628608 DOI: 10.2337/db08-0875] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
OBJECTIVE Recent progress suggests that exenatide, a mimetic of glucagon-like peptide-1 (GLP-1), might lower glycemia independent of increased beta-cell response or reduced gastrointestinal motility. We aimed to investigate whether exenatide stimulates glucose turnover directly in insulin-responsive tissues dependent or independent of insulinemia. RESEARCH DESIGN AND METHODS An intraportal glucose infusion clamp was used in dogs to measure glucose turnover to encompass potent activation of the putative glucose/GLP-1 sensor in the porto-hepatic circulation with exenatide. The modified glucose clamp was performed in the presence of postprandial hyperinsulinemia and hyperglycemia with exenatide (20 microg) or saline injected at 0 min. Furthermore, the role of hyperglycemia versus hyperinsulinemia in exenatide-mediated glucose disposal was studied. RESULTS With hyperinsulinemia and hyperglycemia, exenatide produced a significant increase in total glucose turnover by approximately 30%, as indicated by portal glucose infusion rate (saline 15.9 +/- 1.6 vs. exenatide 20.4 +/- 2.1 mg x kg(-1) x min(-1), P < 0.001), resulting from increased whole-body glucose disposal (R(d), approximately 20%) and increased net hepatic uptake of exogenous glucose ( approximately 80%). Reducing systemic hyperglycemia to euglycemia, exenatide still increased total glucose turnover by approximately 20% (saline 13.2 +/- 1.9 vs. exenatide 15.6 +/- 2.1 mg x kg(-1) x min(-1), P < 0.05) in the presence of hyperinsulinemia, accompanied by smaller increments in R(d) (12%) and net hepatic uptake of exogenous glucose (45%). In contrast, reducing hyperinsulinemia to basal levels, exenatide-increased total glucose turnover was completely abolished despite hyperglycemia (saline 2.9 +/- 0.6 vs. exenatide 2.3 +/- 0.3 mg x kg(-1) x min(-1), P = 0.29). CONCLUSIONS Exenatide directly stimulates glucose turnover by enhancing insulin-mediated whole-body glucose disposal and increasing hepatic uptake of exogenous glucose, contributing to its overall action to lower postprandial glucose excursions.
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Affiliation(s)
- Dan Zheng
- Department of Physiology and Biophysics, University of Southern California Keck School of Medicine, Los Angeles, California, USA
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Torres TP, Catlin RL, Chan R, Fujimoto Y, Sasaki N, Printz RL, Newgard CB, Shiota M. Restoration of hepatic glucokinase expression corrects hepatic glucose flux and normalizes plasma glucose in zucker diabetic fatty rats. Diabetes 2009; 58:78-86. [PMID: 18952838 PMCID: PMC2606896 DOI: 10.2337/db08-1119] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Accepted: 10/11/2008] [Indexed: 11/13/2022]
Abstract
OBJECTIVE We examined in 20-week-old Zucker diabetic fatty (ZDF) rats whether restoration of hepatic glucokinase (GK) expression would alter hepatic glucose flux and improve hyperglycemia. RESEARCH DESIGN AND METHODS ZDF rats were treated at various doses with an adenovirus that directs the expression of rat liver GK (AdvCMV-GKL) dose dependently, and various metabolic parameters were compared with those of nondiabetic lean littermates (ZCL rats) before and during a hyperglycemic clamp. Viral infection per se did not affect hepatic GK activity, since expression of a catalytically inactive form of GK did not alter endogenous hepatic GK activity. RESULTS ZDF rats compared with ZCL rats have lower hepatic GK activity (11.6 +/- 1.9 vs. 32.5 +/- 3.2 mU/mg protein), marked hyperglycemia (23.9 +/- 1.2 vs. 7.4 +/- 0.3 mmol/l), higher endogenous glucose production (80 +/- 3 vs. 38 +/- 3 micromol x kg(-1) x min(-1)), increased glucose-6-phosphatase flux (150 +/- 11 vs. 58 +/- 8 micromol x kg(-1) x min(-1)), and during a hyperglycemic clamp, a failure to suppress endogenous glucose production (80 +/- 7 vs. -7 +/- 4 micromol x kg(-1) x min(-1)) and promote glucose incorporation into glycogen (15 +/- 5 vs. 43 +/- 3 micromol/g liver). Treatment of ZDF rats with different doses of AdvCMV-GKL, which restored hepatic GK activity to one to two times that of ZCL rats, normalized plasma glucose levels and endogenous glucose production. During a hyperglycemic clamp, glucose production was suppressed and glucose incorporation into glycogen was normal. CONCLUSIONS Alteration of hepatic GK activity in ZDF rats has profound effects on plasma glucose and hepatic glucose flux.
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Affiliation(s)
- Tracy P Torres
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
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Springer N, Lindbloom-Hawley S, Schermerhorn T. Tissue expression of ketohexokinase in cats. Res Vet Sci 2008; 87:115-7. [PMID: 19108855 DOI: 10.1016/j.rvsc.2008.11.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2008] [Revised: 10/30/2008] [Accepted: 11/10/2008] [Indexed: 11/15/2022]
Abstract
Ketohexokinase (KHK) metabolizes dietary fructose and is an important regulator of hepatic glucose metabolism. The veterinary literature contains conflicting data regarding the role of KHK in feline fructose metabolism. The study objectives were to determine tissue expression of KHK mRNA and protein in cats, with special emphasis on hepatic expression. KHK mRNA and protein expression were determined using routine RT-PCR and immunoblot techniques. KHK mRNA was detected in feline liver, pancreas, spleen and striated muscle but not in lung. The partial sequence of feline KHK mRNA obtained was highly similar to known KHK mRNA sequences. Immunoblot studies confirmed KHK protein expression in the feline liver. The tissue distribution of KHK mRNA in cats is similar to KHK expression in other species. KHK mRNA and protein expression in feline liver is consistent with previous reports of hepatic fructokinase activity in this species.
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Affiliation(s)
- Nora Springer
- Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, 1800 Denison Avenue, Manhattan, KS 66506-5606, Manhattan, USA
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39
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Buettner C, Camacho RC. Hypothalamic control of hepatic glucose production and its potential role in insulin resistance. Endocrinol Metab Clin North Am 2008; 37:825-40. [PMID: 19026934 DOI: 10.1016/j.ecl.2008.09.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The liver plays a pivotal role in the regulation of glucose metabolism because it is the key organ that maintains glucose levels during fasting. An emerging body of literature has demonstrated the important role of the hypothalamus in controlling hepatic glucose production (HGP). The hypothalamus senses circulating nutrients and hormones, conveying the energy status to the central nervous system, which, in turn, controls HGP in part by way of the autonomic nervous system. Overfeeding results in the failure of the hypothalamus to sense circulating nutrients and hormones, and in a loss of the central control of HGP.
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Affiliation(s)
- Christoph Buettner
- Department of Medicine and Neuroscience, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA.
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40
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Anderka O, Boyken J, Aschenbach U, Batzer A, Boscheinen O, Schmoll D. Biophysical characterization of the interaction between hepatic glucokinase and its regulatory protein: impact of physiological and pharmacological effectors. J Biol Chem 2008; 283:31333-40. [PMID: 18809676 DOI: 10.1074/jbc.m805434200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucokinase (GK) is a key enzyme of glucose metabolism in liver and pancreatic beta-cells, and small molecule activators of GK (GKAs) are under evaluation for the treatment of type 2 diabetes. In liver, GK activity is controlled by the GK regulatory protein (GKRP), which forms an inhibitory complex with the enzyme. Here, we performed isothermal titration calorimetry and surface plasmon resonance experiments to characterize GK-GKRP binding and to study the influence that physiological and pharmacological effectors of GK have on the protein-protein interaction. In the presence of fructose-6-phosphate, GK-GKRP complex formation displayed a strong entropic driving force opposed by a large positive enthalpy; a negative change in heat capacity was observed (Kd = 45 nm, DeltaH = 15.6 kcal/mol, TDeltaS = 25.7 kcal/mol, DeltaCp = -354 cal mol(-1) K(-1)). With k(off) = 1.3 x 10(-2) s(-1), the complex dissociated quickly. The thermodynamic profile suggested a largely hydrophobic interaction. In addition, effects of pH and buffer demonstrated the coupled uptake of one proton and indicated an ionic contribution to binding. Glucose decreased the binding affinity between GK and GKRP. This decrease was potentiated by an ATP analogue. Prototypical GKAs of the amino-heteroaryl-amide type bound to GK in a glucose-dependent manner and impaired the association of GK with GKRP. This mechanism might contribute to the antidiabetic effects of GKAs.
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Affiliation(s)
- Oliver Anderka
- Sanofi Aventis Deutschland GmbH, Research and Development, D-65926 Frankfurt am Main, Germany.
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41
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Bishop AC, Chen VL. Brought to life: targeted activation of enzyme function with small molecules. J Chem Biol 2008; 2:1-9. [PMID: 19568788 DOI: 10.1007/s12154-008-0012-4] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2008] [Accepted: 09/04/2008] [Indexed: 11/30/2022] Open
Abstract
Cell-permeable small molecules that are capable of activating particular enzymes would be invaluable tools for studying protein function in complex cell-signaling cascades. But, is it feasible to identify compounds that allow chemical-biology researchers to activate specific enzymes in a cellular context? In this review, we describe some recent advances in achieving targeted enzyme activation with small molecules. In addition to surveying progress in the identification and targeting of enzymes that contain natural allosteric-activation sites, we focus on recently developed protein-engineering strategies that allow researchers to render an enzyme of interest "activatable" by a pre-chosen compound. Three distinct strategies for targeting an engineered enzyme are discussed: direct chemical "rescue" of an intentionally inactivated enzyme, activation of an enzyme by targeting a de novo small-molecule-binding site, and the generation of activatable enzymes via fusion of target enzymes to previously characterized small-molecule-binding domains.
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Affiliation(s)
- Anthony C Bishop
- Department of Chemistry, Amherst College, Amherst, MA, 01002, USA,
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42
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Hiskett EK, Suwitheechon OU, Lindbloom-Hawley S, Boyle DL, Schermerhorn T. Lack of glucokinase regulatory protein expression may contribute to low glucokinase activity in feline liver. Vet Res Commun 2008; 33:227-40. [PMID: 18780155 DOI: 10.1007/s11259-008-9171-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2008] [Accepted: 08/14/2008] [Indexed: 11/30/2022]
Abstract
In most mammals, glucokinase (GK) acts as a hepatic "glucose sensor" that permits hepatic metabolism to respond appropriately to changes in plasma glucose concentrations. GK activity is potently regulated by the glucokinase regulatory protein (GKRP), which is encoded by the GCKR gene. GKRP binds GK in the nucleus and inhibits its activity. GK becomes active when it is released from GKRP and translocates to the cytosol. Low glucokinase (GK) activity is reported to be a principal feature of feline hepatic carbohydrate metabolism but the molecular pathways that regulate GK activity are not known. This study examined the hypothesis that species-specific differences in GKRP expression parallel the low GK activity observed in feline liver. Hepatic GKRP expression was examined using RT-PCR, immunoblot, and confocal immunomicroscopy. The results show that the GCKR gene is present in the feline genome but GCKR mRNA and the GKRP protein were absent in feline liver. The lack of GKRP expression in feline liver indicates that the low GK activity cannot be the result of GKRP-mediated inhibition of the GK enzyme. However, the absence of the permissive effects of GCKR expression on GK expression and activity may contribute to reduced GK enzyme activity in feline liver. The study results show that the cat is a natural model for GCKR knockout and may be useful to study regulation of GCKR expression and its role in hepatic glucose-sensing and carbohydrate metabolism.
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Affiliation(s)
- Erin K Hiskett
- Department of Clinical Sciences, Kansas State University, Manhattan, KS, 66506-5606, USA
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Donati A, Recchia G, Cavallini G, Bergamini E. Effect of aging and anti-aging caloric restriction on the endocrine regulation of rat liver autophagy. J Gerontol A Biol Sci Med Sci 2008; 63:550-5. [PMID: 18559627 DOI: 10.1093/gerona/63.6.550] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Autophagy is a process that sequesters and degrades altered organelles and macromolecular cytoplasmic constituents for cellular restructuring and repair, and as a source of nutrients for metabolic use in early starvation it may be involved in anti-aging mechanisms of caloric restriction. The effects of 40% daily dietary restriction (DR) and intermittent feeding (EOD) on the age-related changes in the endocrine regulation of autophagic proteolysis were studied by monitoring the rate of valine release from isolated rat liver cells. Results show that in ad libitum-fed rats sensitivity of autophagy to glucagon and insulin declines by one order of magnitude in older rats. Both DR and EOD maintain the sensitivity to glucagon at juvenile levels, whereas only EOD can fully maintain response to insulin. It is concluded that changes in the sensitivity to glucagon may have a role in the aging process.
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Affiliation(s)
- Alessio Donati
- Università di Pisa, Centro di Ricerca Biologia e Patologia dell'Invecchiamento, Roma 55, Pisa, Italy 56126.
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44
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Abstract
Conversion of glucose into glycogen is a major pathway that contributes to the removal of glucose from the portal vein by the liver in the postprandial state. It is regulated in part by the increase in blood-glucose concentration in the portal vein, which activates glucokinase, the first enzyme in the pathway, causing an increase in the concentration of glucose 6-P (glucose 6-phosphate), which modulates the phosphorylation state of downstream enzymes by acting synergistically with other allosteric effectors. Glucokinase is regulated by a hierarchy of transcriptional and post-transcriptional mechanisms that are only partially understood. In the fasted state, glucokinase is in part sequestered in the nucleus in an inactive state, complexed to a specific regulatory protein, GKRP (glucokinase regulatory protein). This reserve pool is rapidly mobilized to the cytoplasm in the postprandial state in response to an elevated concentration of glucose. The translocation of glucokinase between the nucleus and cytoplasm is modulated by various metabolic and hormonal conditions. The elevated glucose 6-P concentration, consequent to glucokinase activation, has a synergistic effect with glucose in promoting dephosphorylation (inactivation) of glycogen phosphorylase and inducing dephosphorylation (activation) of glycogen synthase. The latter involves both a direct ligand-induced conformational change and depletion of the phosphorylated form of glycogen phosphorylase, which is a potent allosteric inhibitor of glycogen synthase phosphatase activity associated with the glycogen-targeting protein, GL [hepatic glycogen-targeting subunit of PP-1 (protein phosphatase-1) encoded by PPP1R3B]. Defects in both the activation of glucokinase and in the dephosphorylation of glycogen phosphorylase are potential contributing factors to the dysregulation of hepatic glucose metabolism in Type 2 diabetes.
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Stafford JM, Yu F, Printz R, Hasty AH, Swift LL, Niswender KD. Central nervous system neuropeptide Y signaling modulates VLDL triglyceride secretion. Diabetes 2008; 57:1482-90. [PMID: 18332095 PMCID: PMC3968924 DOI: 10.2337/db07-1702] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
OBJECTIVE Elevated triglyceride (TG) is the major plasma lipid abnormality in obese and diabetic patients and contributes to cardiovascular morbidity in these disorders. We sought to identify novel mechanisms leading to hypertriglyceridemia. Resistance to negative feedback signals from adipose tissue in key central nervous system (CNS) energy homeostatic circuits contributes to the development of obesity. Because triglycerides both represent the largest energy depot in the body and are elevated in both the plasma and adipose in obesity and diabetes, we hypothesized that the same neural circuits that regulate energy balance also regulate the secretion of TGs into plasma. RESEARCH DESIGN AND METHODS In normal fasting rats, the TG secretion rate was estimated by serial blood sampling after intravascular tyloxapol pretreatment. Neuropeptide Y (NPY) signaling in the CNS was modulated by intracerebroventricular injection of NPY, receptor antagonist, and receptor agonist. RESULTS A single intracerebroventricular injection of NPY increased TG secretion by 2.5-fold in the absence of food intake, and this was determined to be VLDL by fast performance liquid chromatography (FPLC). This effect was recapitulated by activating NPY signaling in downstream neurons with an NPY-Y5 receptor agonist. An NPY-Y1 receptor antagonist decreased the elevated TGs in the form of VLDL secretion rate by 50% compared with vehicle. Increased TG secretion was due to increased secretion of VLDL particles, rather than secretion of larger particles, because apolipoprotein B100 was elevated in FPLC fractions corresponding to VLDL. CONCLUSIONS We find that a key neuropeptide system involved in energy homeostasis in the CNS exerts control over VLDL-TG secretion into the bloodstream.
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Affiliation(s)
- John M Stafford
- Division of Diabetes, Endocrinology, and Metabolism, Department of Internal Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
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Jurczak MJ, Danos AM, Rehrmann VR, Brady MJ. The role of protein translocation in the regulation of glycogen metabolism. J Cell Biochem 2008; 104:435-43. [DOI: 10.1002/jcb.21634] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Payne VA, Arden C, Lange AJ, Agius L. Contributions of glucokinase and phosphofructokinase-2/fructose bisphosphatase-2 to the elevated glycolysis in hepatocytes from Zucker fa/fa rats. Am J Physiol Regul Integr Comp Physiol 2007; 293:R618-25. [PMID: 17553851 DOI: 10.1152/ajpregu.00061.2007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The insulin-resistant Zucker fa/fa rat has elevated hepatic glycolysis and activities of glucokinase and phosphofructokinase-2/fructose bisphosphatase-2 (PFK2). The latter catalyzes the formation and degradation of fructose-2,6-bisphosphate (fructose-2,6-P2) and is a glucokinase-binding protein. The contributions of glucokinase and PFK2 to the elevated glycolysis in fa/fa hepatocytes were determined by overexpressing these enzymes individually or in combination. Metabolic control analysis was used to determine enzyme coefficients on glycolysis and metabolite concentrations. Glucokinase had a high control coefficient on glycolysis in all hormonal conditions tested, whereas PFK2 had significant control only in the presence of glucagon, which phosphorylates PFK2 and suppresses glycolysis. Despite the high control strength of glucokinase, the elevated glycolysis in fa/fa hepatocytes could not be explained by the elevated glucokinase activity alone. In hepatocytes from fa/fa rats, glucokinase translocation between the nucleus and the cytoplasm was refractory to glucose but responsive to glucagon. Expression of a kinase-active PFK2 variant reversed the glucagon effect on glucokinase translocation and glucose phosphorylation, confirming the role for PFK2 in sequestering glucokinase in the cytoplasm. Glucokinase had a high control on glucose-6-phosphate content; however, like PFK2, it had a relative modest effect on the fructose-2,6-P2 content. However, combined overexpression of glucokinase and PFK2 had a synergistic effect on fructose-2,6-P2 levels, suggesting that interaction of these enzymes may be a prerequisite for formation of fructose-2,6-P2. Cumulatively, this study provides support for coordinate roles for glucokinase and PFK2 in the elevated hepatic glycolysis in fa/fa rats.
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Affiliation(s)
- Victoria A Payne
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK
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48
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Shin JS, Torres TP, Catlin RL, Donahue EP, Shiota M. A defect in glucose-induced dissociation of glucokinase from the regulatory protein in Zucker diabetic fatty rats in the early stage of diabetes. Am J Physiol Regul Integr Comp Physiol 2007; 292:R1381-90. [PMID: 17204595 DOI: 10.1152/ajpregu.00260.2006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Effect of stimulation of glucokinase (GK) export from the nucleus by small amounts of sorbitol on hepatic glucose flux in response to elevated plasma glucose was examined in 6-h fasted Zucker diabetic fatty rats at 10 wk of age. Under basal conditions, plasma glucose, insulin, and glucagon were ∼8 mM, 2,000 pmol/l, and 60 ng/l, respectively. Endogenous glucose production (EGP) was 44 ± 4 μmol·kg−1·min−1. When plasma glucose was raised to ∼17 mM, GK was still predominantly localized with its inhibitory protein in the nucleus. EGP was not suppressed. When sorbitol was infused at 5.6 and 16.7 μmol·kg−1·min−1, along with the increase in plasma glucose, GK was exported to the cytoplasm. EGP (23 ± 19 and 12 ± 5 μmol·kg−1·min−1) was suppressed without a decrease in glucose 6-phosphatase flux (145 ± 23 and 126 ± 16 vs. 122 ± 10 μmol·kg−1·min−1without sorbitol) but increased in glucose phosphorylation as indicated by increases in glucose recycling (122 ± 17 and 114 ± 19 vs. 71 ± 11 μmol·kg−1·min−1), glucose-6-phosphate content (254 ± 32 and 260 ± 35 vs. 188 ± 20 nmol/g liver), fractional contribution of plasma glucose to uridine 5′-diphosphate-glucose flux (43 ± 8 and 42 ± 8 vs. 27 ± 6%), and glycogen synthesis from plasma glucose (20 ± 4 and 22 ± 5 vs. 9 ± 4 μmol glucose/g liver). The decreased glucose effectiveness to suppress EGP and stimulate hepatic glucose uptake may result from failure of the sugar to activate GK by stimulating the translocation of the enzyme.
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Affiliation(s)
- Jun-Seop Shin
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, 702 Light Hall, Nashville, TN 37232-0615, USA
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49
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Vagn Korsgaard T, Colding-Jørgensen M. Time-dependent mechanisms in beta-cell glucose sensing. J Biol Phys 2006; 32:289-306. [PMID: 19669468 DOI: 10.1007/s10867-006-9017-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2006] [Revised: 04/21/2006] [Accepted: 04/28/2006] [Indexed: 12/22/2022] Open
Abstract
The relation between plasma glucose and insulin release from pancreatic beta-cells is not stationary in the sense that a given glucose concentration leads to a specific rate of insulin secretion. A number of time-dependent mechanisms appear to exist that modify insulin release both on a short and a longer time scale. Typically, two phases are described. The first phase, lasting up to 10 min, is a pulse of insulin release in response to fast changes in glucose concentration. The second phase is a more steady increase of insulin release over minutes to hours, if the elevated glucose concentration is sustained. The paper describes the glucose sensing mechanism via the complex dynamics of the key enzyme glucokinase, which controls the first step in glucose metabolism: phosphorylation of glucose to glucose-6-phosphate. Three time-dependent phenomena (mechanisms) are described. The fastest, corresponding to the first phase, is a delayed negative feedback regulating the glucokinase activity. Due to the delay, a rapid glucose increase will cause a burst of activity in the glucose sensing system, before the glucokinase is down-regulated. The second mechanism corresponds to the translocation of glucokinase from an inactive to an active form. As the translocation is controlled by the product(s) of the glucokinase reaction rather than by the substrate glucose, this mechanism gives a positive, but saturable, feedback. Finally, the release of the insulin granules is assumed to be enhanced by previous glucose exposure, giving a so-called glucose memory to the beta-cells. The effect depends on the insulin release of the cells, and this mechanism constitutes a second positive, saturable feedback system. Taken together, the three phenomena describe most of the glucose sensing behaviour of the beta-cells. The results indicate that the insulin release is not a precise function of the plasma glucose concentration. It rather looks as if the beta-cells just increase the insulin production, until the plasma glucose has returned to normal. This type of integral control has the advantage that the precise glucose sensitivity of the beta-cells is not important for normal glucose homeostasis.
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Affiliation(s)
- Thomas Vagn Korsgaard
- Development Projects Management, Novo Nordisk A/S, Novo Allè, 2880 Bagsvaerd, Denmark
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50
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Futamura M, Hosaka H, Kadotani A, Shimazaki H, Sasaki K, Ohyama S, Nishimura T, Eiki JI, Nagata Y. An allosteric activator of glucokinase impairs the interaction of glucokinase and glucokinase regulatory protein and regulates glucose metabolism. J Biol Chem 2006; 281:37668-74. [PMID: 17028192 DOI: 10.1074/jbc.m605186200] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucokinase (GK) plays a key role in the control of blood glucose homeostasis. We identified a small molecule GK activator, compound A, that increased the glucose affinity and maximal velocity (V(max)) of GK. Compound A augmented insulin secretion from isolated rat islets and enhanced glucose utilization in primary cultured rat hepatocytes. In rat oral glucose tolerance tests, orally administrated compound A lowered plasma glucose elevation with a concomitant increase in plasma insulin and hepatic glycogen. In liver, GK activity is acutely controlled by its association to the glucokinase regulatory protein (GKRP). In order to decipher the molecular aspects of how GK activator affects the shuttling of GK between nucleus and cytoplasm, the effect of compound A on GK-GKRP interaction was further investigated. Compound A increased the level of cytoplasmic GK in both isolated rat primary hepatocytes and the liver tissues from rats. Experiments in a cell-free system revealed that compound A interacted with glucose-bound free GK, thereby impairing the association of GK and GKRP. On the other hand, compound A did not bind to glucose-unbound GK or GKRP-associated GK. Furthermore, we found that glucose-dependent GK-GKRP interaction also required ATP. Given the combined prominent role of GK on insulin secretion and hepatic glucose metabolism where the GK-GKRP mechanism is involved, activation of GK has a new therapeutic potential in the treatment of type 2 diabetes.
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Affiliation(s)
- Mayumi Futamura
- Tsukuba Research Institute, Banyu Pharmaceutical Co., Ltd., Tsukuba, Ibaraki 300-2611, Japan
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