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Oguri Y, Fujita Y, Abudukadier A, Ohashi A, Goto T, Furuya F, Obara A, Fukushima T, Matsuo N, Kim M, Hosokawa M, Kawada T, Hasegawa H, Inagaki N. Tetrahydrobiopterin activates brown adipose tissue and regulates systemic energy metabolism. JCI Insight 2017; 2:91981. [PMID: 28469071 DOI: 10.1172/jci.insight.91981] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 03/29/2017] [Indexed: 12/12/2022] Open
Abstract
Brown adipose tissue (BAT) is a central organ that acts to increase energy expenditure; its regulatory factors could be clinically useful in the treatment of obesity. Tetrahydrobiopterin (BH4) is an essential cofactor of tyrosine hydroxylase and nitric oxide synthase (NOS). Although BH4 regulates the known regulatory factors of BAT, such as noradrenaline (NA) and NO, participation of BH4 in BAT function remains unclear. In the present study, we investigate the role of BH4 in the regulation of BAT. Hph-1 mice, a mouse model of BH4 deficiency, exhibit obesity, adiposity, glucose intolerance, insulin resistance, and impaired BAT function. Impaired BAT function was ameliorated together with systemic metabolic disturbances by BAT transplantation from BH4-sufficient mice (control mice) into BH4-deficient mice, strongly suggesting that BH4-induced BAT has a critical role in the regulation of systemic energy metabolism. Both NA derived from the sympathetic nerve and NO derived from endothelial NOS in the blood vessels participate in the regulation of BH4. In addition, a direct effect of BH4 in the stimulation of brown adipocytes via NO is implicated. Taken together, BH4 activates BAT and regulates systemic energy metabolism; this suggests an approach for metabolic disorders, such as obesity and diabetes.
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Affiliation(s)
- Yasuo Oguri
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan.,Japan Society for the Promotion of Science, Tokyo, Japan
| | - Yoshihito Fujita
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Abulizi Abudukadier
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Akiko Ohashi
- Department of Anatomy, Nihon University School of Dentistry, Tokyo, Japan
| | - Tsuyoshi Goto
- Laboratory of Molecular Function of Food, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Futoshi Furuya
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Akio Obara
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Toru Fukushima
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Naomi Matsuo
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Minji Kim
- Laboratory of Molecular Function of Food, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Masaya Hosokawa
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan.,Faculty of Human Sciences, Tezukayama Gakuin University, Osaka, Japan
| | - Teruo Kawada
- Laboratory of Molecular Function of Food, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
| | - Hiroyuki Hasegawa
- Department of Anatomy, Nihon University School of Dentistry, Tokyo, Japan
| | - Nobuya Inagaki
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
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Popov VB, Jornayvaz FR, Akgul EO, Kanda S, Jurczak MJ, Zhang D, Abudukadier A, Majumdar SK, Guigni B, Petersen KF, Manchem VP, Bhanot S, Shulman GI, Samuel VT. Second-generation antisense oligonucleotides against β-catenin protect mice against diet-induced hepatic steatosis and hepatic and peripheral insulin resistance. FASEB J 2015; 30:1207-17. [PMID: 26644352 DOI: 10.1096/fj.15-271999] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 11/16/2015] [Indexed: 12/24/2022]
Abstract
Although mutations in the Wnt/β-catenin signaling pathway are linked with the metabolic syndrome and type 2 diabetes in humans, the mechanism is unclear. High-fat-fed male C57BL/6 mice were treated for 4 wk with a 2'-O-methoxyethyl chimeric antisense oligonucleotide (ASO) to decrease hepatic and adipose expression of β-catenin. β-Catenin mRNA decreased by ≈80% in the liver and by 70% in white adipose tissue relative to control ASO-treated mice. β-Catenin ASO improved hepatic insulin sensitivity and increased insulin-stimulated whole body glucose metabolism, as assessed during hyperinsulinemic-euglycemic clamp in awake mice. β-Catenin ASO altered hepatic lipid composition in high-fat-fed mice. There were reductions in hepatic triglyceride (44%, P < 0.05) and diacylglycerol content (60%, P < 0.01) but a 30% increase in ceramide content (P < 0.001). The altered lipid content was attributed to decreased expression of sn-1,2 diacylglycerol acyltransferase and mitochondrial acyl-CoA:glycerol-sn-3-phosphate acyltransferase and an increase in serine palmitoyl transferase. The decrease in cellular diacyglycerol was associated with a 33% decrease in PKCε activation (P < 0.05) and 64% increase in Akt2 phosphorylation (P < 0.05). In summary, Reducing β-catenin expression decreases expression of enzymes involved in hepatic fatty acid esterification, ameliorates hepatic steatosis and lipid-induced insulin resistance.
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Affiliation(s)
- Violeta B Popov
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Francois R Jornayvaz
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Emin O Akgul
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Shoichi Kanda
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Michael J Jurczak
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Dongyan Zhang
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Abulizi Abudukadier
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Sachin K Majumdar
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Blas Guigni
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Kitt Falk Petersen
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Vara Prasad Manchem
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Sanjay Bhanot
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Gerald I Shulman
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
| | - Varman T Samuel
- *Department of Internal Medicine, Department of Cellular and Molecular Physiology, and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA; West Haven Veterans Affairs Medical Center, West Haven, Connecticut, USA; and ISIS Pharmaceuticals, Carlsbad, California, USA
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Obara A, Fujita Y, Abudukadier A, Fukushima T, Oguri Y, Ogura M, Harashima SI, Hosokawa M, Inagaki N. DEPTOR-related mTOR suppression is involved in metformin's anti-cancer action in human liver cancer cells. Biochem Biophys Res Commun 2015; 460:1047-52. [PMID: 25843797 DOI: 10.1016/j.bbrc.2015.03.148] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Accepted: 03/26/2015] [Indexed: 10/23/2022]
Abstract
Metformin, one of the most commonly used drugs for patients with type 2 diabetes, recently has received much attention regarding its anti-cancer action. It is thought that the suppression of mTOR signaling is involved in metformin's anti-cancer action. Although liver cancer is one of the most responsive types of cancer for reduction of incidence by metformin, the molecular mechanism of the suppression of mTOR in liver remains unknown. In this study, we investigated the mechanism of the suppressing effect of metformin on mTOR signaling and cell proliferation using human liver cancer cells. Metformin suppressed phosphorylation of p70-S6 kinase, and ribosome protein S6, downstream targets of mTOR, and suppressed cell proliferation. We found that DEPTOR, an endogenous substrate of mTOR suppression, is involved in the suppressing effect of metformin on mTOR signaling and cell proliferation in human liver cancer cells. Metformin increases the protein levels of DEPTOR, intensifies binding to mTOR, and exerts a suppressing effect on mTOR signaling. This increasing effect of DEPTOR by metformin is regulated by the proteasome degradation system; the suppressing effect of metformin on mTOR signaling and cell proliferation is in a DEPTOR-dependent manner. Furthermore, metformin exerts a suppressing effect on proteasome activity, DEPTOR-related mTOR signaling, and cell proliferation in an AMPK-dependent manner. We conclude that DEPTOR-related mTOR suppression is involved in metformin's anti-cancer action in liver, and could be a novel target for anti-cancer therapy.
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Affiliation(s)
- Akio Obara
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Yoshihito Fujita
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Abulizi Abudukadier
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Toru Fukushima
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Yasuo Oguri
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Masahito Ogura
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Shin-Ichi Harashima
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Masaya Hosokawa
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Nobuya Inagaki
- Department of Diabetes, Endocrinology and Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
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Perry RJ, Camporez JPG, Kursawe R, Titchenell PM, Zhang D, Perry CJ, Jurczak MJ, Abudukadier A, Han MS, Zhang XM, Ruan HB, Yang X, Caprio S, Kaech SM, Sul HS, Birnbaum MJ, Davis RJ, Cline GW, Petersen KF, Shulman GI. Hepatic acetyl CoA links adipose tissue inflammation to hepatic insulin resistance and type 2 diabetes. Cell 2015; 160:745-758. [PMID: 25662011 DOI: 10.1016/j.cell.2015.01.012] [Citation(s) in RCA: 489] [Impact Index Per Article: 54.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2014] [Revised: 11/10/2014] [Accepted: 01/05/2015] [Indexed: 01/15/2023]
Abstract
Impaired insulin-mediated suppression of hepatic glucose production (HGP) plays a major role in the pathogenesis of type 2 diabetes (T2D), yet the molecular mechanism by which this occurs remains unknown. Using a novel in vivo metabolomics approach, we show that the major mechanism by which insulin suppresses HGP is through reductions in hepatic acetyl CoA by suppression of lipolysis in white adipose tissue (WAT) leading to reductions in pyruvate carboxylase flux. This mechanism was confirmed in mice and rats with genetic ablation of insulin signaling and mice lacking adipose triglyceride lipase. Insulin's ability to suppress hepatic acetyl CoA, PC activity, and lipolysis was lost in high-fat-fed rats, a phenomenon reversible by IL-6 neutralization and inducible by IL-6 infusion. Taken together, these data identify WAT-derived hepatic acetyl CoA as the main regulator of HGP by insulin and link it to inflammation-induced hepatic insulin resistance associated with obesity and T2D.
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Affiliation(s)
- Rachel J Perry
- Howard Hughes Medical Institute, Yale University, New Haven, CT 06519, USA; Department of Internal Medicine, Yale University, New Haven, CT 06520, USA; Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520, USA
| | | | - Romy Kursawe
- Department of Internal Medicine, Yale University, New Haven, CT 06520, USA
| | - Paul M Titchenell
- The Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Dongyan Zhang
- Howard Hughes Medical Institute, Yale University, New Haven, CT 06519, USA
| | - Curtis J Perry
- Department of Immunobiology, Yale University, New Haven, CT 06520, USA
| | - Michael J Jurczak
- Department of Internal Medicine, Yale University, New Haven, CT 06520, USA
| | | | - Myoung Sook Han
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Xian-Man Zhang
- Howard Hughes Medical Institute, Yale University, New Haven, CT 06519, USA
| | - Hai-Bin Ruan
- Department of Comparative Medicine, Yale University, New Haven, CT 06520, USA
| | - Xiaoyong Yang
- Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520, USA; Department of Comparative Medicine, Yale University, New Haven, CT 06520, USA
| | - Sonia Caprio
- Department of Pediatrics, Yale University, New Haven, CT 06520, USA
| | - Susan M Kaech
- Department of Immunobiology, Yale University, New Haven, CT 06520, USA
| | - Hei Sook Sul
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Morris J Birnbaum
- The Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Roger J Davis
- Howard Hughes Medical Institute, Yale University, New Haven, CT 06519, USA; Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
| | - Gary W Cline
- Department of Internal Medicine, Yale University, New Haven, CT 06520, USA
| | - Kitt Falk Petersen
- Department of Internal Medicine, Yale University, New Haven, CT 06520, USA
| | - Gerald I Shulman
- Howard Hughes Medical Institute, Yale University, New Haven, CT 06519, USA; Department of Internal Medicine, Yale University, New Haven, CT 06520, USA; Department of Cellular and Molecular Physiology, Yale University, New Haven, CT 06520, USA.
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Abudukadier A, Fujita Y, Obara A, Ohashi A, Fukushima T, Sato Y, Ogura M, Nakamura Y, Fujimoto S, Hosokawa M, Hasegawa H, Inagaki N. Tetrahydrobiopterin has a glucose-lowering effect by suppressing hepatic gluconeogenesis in an endothelial nitric oxide synthase-dependent manner in diabetic mice. Diabetes 2013; 62:3033-43. [PMID: 23649519 PMCID: PMC3749361 DOI: 10.2337/db12-1242] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Accepted: 04/27/2013] [Indexed: 12/01/2022]
Abstract
Endothelial nitric oxide synthase (eNOS) dysfunction induces insulin resistance and glucose intolerance. Tetrahydrobiopterin (BH4) is an essential cofactor of eNOS that regulates eNOS activity. In the diabetic state, BH4 is oxidized to 7,8-dihydrobiopterin, which leads to eNOS dysfunction owing to eNOS uncoupling. The current study investigates the effects of BH4 on glucose metabolism and insulin sensitivity in diabetic mice. Single administration of BH4 lowered fasting blood glucose levels in wild-type mice with streptozotocin (STZ)-induced diabetes and alleviated eNOS dysfunction by increasing eNOS dimerization in the liver of these mice. Liver has a critical role in glucose-lowering effects of BH4 through suppression of hepatic gluconeogenesis. BH4 activated AMP kinase (AMPK), and the suppressing effect of BH4 on gluconeogenesis was AMPK-dependent. In addition, the glucose-lowering effect and activation of AMPK by BH4 did not appear in mice with STZ-induced diabetes lacking eNOS. Consecutive administration of BH4 in ob/ob mice ameliorated glucose intolerance and insulin resistance. Taken together, BH4 suppresses hepatic gluconeogenesis in an eNOS-dependent manner, and BH4 has a glucose-lowering effect as well as an insulin-sensitizing effect in diabetic mice. BH4 has potential in the treatment of type 2 diabetes.
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Affiliation(s)
- Abulizi Abudukadier
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Yoshihito Fujita
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Akio Obara
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Akiko Ohashi
- Department of Functional Morphology, Nihon University School of Medicine, Tokyo, Japan
| | - Toru Fukushima
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Yuichi Sato
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Masahito Ogura
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Yasuhiko Nakamura
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Shimpei Fujimoto
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Masaya Hosokawa
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Hiroyuki Hasegawa
- Department of Functional Morphology, Nihon University School of Medicine, Tokyo, Japan
| | - Nobuya Inagaki
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Kyoto, Japan
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Fujita Y, Hosokawa M, Fujimoto S, Mukai E, Abudukadier A, Obara A, Ogura M, Nakamura Y, Toyoda K, Nagashima K, Seino Y, Inagaki N. Metformin suppresses hepatic gluconeogenesis and lowers fasting blood glucose levels through reactive nitrogen species in mice. Diabetologia 2010; 53:1472-81. [PMID: 20349346 DOI: 10.1007/s00125-010-1729-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Accepted: 02/24/2010] [Indexed: 02/08/2023]
Abstract
AIMS/HYPOTHESIS Metformin, the major target of which is liver, is commonly used to treat type 2 diabetes. Although metformin activates AMP-activated protein kinase (AMPK) in hepatocytes, the mechanism of activation is still not well known. To investigate AMPK activation by metformin in liver, we examined the role of reactive nitrogen species (RNS) in suppression of hepatic gluconeogenesis. METHODS To determine RNS, we performed fluorescence examination and immunocytochemical staining in mouse hepatocytes. Since metformin is a mild mitochondrial complex I inhibitor, we compared its effects on suppression of gluconeogenesis, AMPK activation and generation of the RNS peroxynitrite (ONOO(-)) with those of rotenone, a representative complex I inhibitor. To determine whether endogenous nitric oxide production is required for ONOO(-) generation and metformin action, we used mice lacking endothelial nitric oxide synthase (eNOS). RESULTS Metformin and rotenone significantly decreased gluconeogenesis and increased phosphorylation of AMPK in wild-type mouse hepatocytes. However, unlike rotenone, metformin did not increase the AMP/ATP ratio. It did, however, increase ONOO(-) generation, whereas rotenone did not. Exposure of eNOS-deficient hepatocytes to metformin did not suppress gluconeogenesis, activate AMPK or increase ONOO(-) generation. Furthermore, metformin lowered fasting blood glucose levels in wild-type diabetic mice, but not in eNOS-deficient diabetic mice. CONCLUSIONS/INTERPRETATION Activation of AMPK by metformin is dependent on ONOO(-). For metformin action in liver, intra-hepatocellular eNOS is required.
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Affiliation(s)
- Y Fujita
- Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, 54 Shogoin, Kawahara-cho, Sakyo-ku, Kyoto, 606-8507, Japan
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