Metabolic control analysis of hepatic glycogen synthesis in vivo

Effects of reducing sedentary behavior on liver insulin sensitivity, liver fat content, and liver enzyme levels: a six-month randomized controlled trial

Metabolic syndrome increases the risk of developing noncommunicable diseases such as metabolic dysfunction-associated steatotic liver disease. The aim was to investigate the effects of sedentary behavior (SB) reduction on liver glucose uptake (LGU), endogenous glucose production (EGP), liver fat content (LFC), and liver enzyme levels [alanine aminotransferase (ALT), aspartate aminotransferase, and γ-glutamyltransferase]. Forty-four sedentary (daily SB time ≥ 10 h), physically inactive middle-aged adults with metabolic syndrome were randomized into intervention (INT; n = 23, 21 completed) and control (CON; n = 21, 19 completed) groups. For 6 mo, INT aimed to limit SB by 1 h/day, whereas CON aimed to maintain usual habits. SB and physical activity (PA) were measured continuously with hip-worn accelerometers. Before and at the end of the intervention, LGU was measured using positron emission tomography during the hyperinsulinemic-euglycemic clamp. EGP was calculated, and LFC was measured by magnetic resonance spectroscopy. INT reduced SB by 51 [95% confidence interval (CI): 22, 78] min/day and increased moderate-to-vigorous physical activity (MVPA) by 22 (95% CI: 12, 33) min/day, with no significant change in CON. Differences in liver health markers between the groups were not significant. However, according to the exploratory analyses among participants who successfully reduced SB, ALT decreased (-1.1 [95% CI: 0.93, 1.36] U/L) compared with the continuously sedentary participants (+0.8 [95% CI: 0.65, 1.05] U/L) (group × time, P = 0.006). To enhance liver health, reducing SB for longer durations and/or increasing the intensity of PA may be necessary. However, successfully reducing SB may lead to better levels of circulating ALT liver enzymes.NEW & NOTEWORTHY Aiming to reduce sedentary behavior (SB) by 1 h/day did not significantly influence liver health markers, suggesting that more substantial reductions or a different approach might be necessary to see improvements. However, achieving the desired behavioral change could lead to improvements in ALT levels. This study is the first to analyze how reducing SB and replacing it with nonguided physical activity impacts liver health in adults with metabolic syndrome, offering insights for future intervention strategies.

Efficacy of Hypoglycemic Agents in Metabolic Dysfunction Associated Steatotic Liver Disease (MASLD): A Systematic Review and Network Meta-Analysis

AIMS

Metabolic dysfunction associated steatotic liver disease (MASLD) is a universal hepatic disease, and many recent randomized clinical trials (RCTs) have explored whether hypoglycemic agents may be beneficial for its treatment. This study aimed to assess the relative effectiveness of each hypoglycemic agent for MASLD.

METHODS

China National Knowledge Infrastructure（CNKI）, WanFang, Weipu, PubMed, Embase, The Cochrane Library, and Web of Science Core Collection were searched for RCTs on the efficacy of hypoglycemic agents in MASLD published up to December 31, 2024. All statistical analyses were performed using R version 4.3.3. The network meta-analysis was conducted using Bayesian statistical methods.

RESULTS

A total of 26 hypoglycemic agents for treating MASLD in 37 studies with 2406 participants were included. Empagliflozin was most effective in improving liver stiffness measurement (LSM), whereas liraglutide showed significant benefits in body weight, body mass index (BMI), and waist circumference. Both sodium-glucose co-transporter 2 (SGLT-2) inhibitors (e.g., empagliflozin) and glucagon-like peptide-1 (GLP-1) receptor agonists (e.g., liraglutide) improved liver enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], gamma-glutamyltransferase [GGT]), glucose metabolism (fasting plasma glucose [FPG], and homeostasis model assessment of insulin resistance [HOMA-IR]), and lipid profiles. Pioglitazone had limited benefits in these outcomes. Secondary outcomes such as inflammatory markers and fibrosis showed minimal changes.

CONCLUSIONS

Several hypoglycemic agents can improve laboratory and imaging indicators in adult patients with MASLD. Liraglutide is more effective than other agents, whereas empagliflozin emerged as the most effective for reducing LSM. However, different agents have different effects on the indicators; therefore, the relevant agents must be selected according to the specific patient condition.

The Counteracting Effect of Chrysin on Dietary Fructose-Induced Metabolic-Associated Fatty Liver Disease (MAFLD) in Rats with a Focus on Glucose and Lipid Metabolism

The prevalence of metabolic syndrome has been exponentially increasing in recent decades. Thus, there is an increasing need for affordable and natural interventions for this disorder. We explored the effect of chrysin, a dietary polyphenol, on hepatic lipid and glycogen accumulation, metabolic dysfunction-associated fatty liver disease (MAFLD) activity score and oxidative stress and on hepatic and adipose tissue metabolism in rats presenting metabolic syndrome-associated conditions. Rats fed a chow diet were separated into four groups: Control (tap water), Fructose (tap water with 10% fructose), Chrysin (tap water+ chrysin (100 mg/kg body weight/d)), and Fructose + Chrysin (tap water with 10% fructose + chrysin (100 mg/kg body weight/d, daily)) (for 18 weeks). When associated with the chow diet, chrysin reduced hepatic lipid and glycogen storage, increased the hepatic antioxidant potential of glutathione and reduced de novo lipogenesis in the adipose tissue. When associated with the high fructose-diet, chrysin attenuated the increase in lipid and glycogen hepatic storage, improved the MAFLD activity score, decreased hepatic lipid peroxidation, increased the antioxidant potential of glutathione, and improved lipid and glucose metabolic markers in the liver and adipose tissue. In conclusion, our results suggest that chrysin is a beneficial addition to a daily diet for improvement of hepatic metabolic health, particularly for individuals suffering from metabolic syndrome.

Metabolic phenotyping of patients with advanced chronic liver disease for better characterization of cirrhosis regression

BACKGROUND & AIMS

Regression of cirrhosis has been observed in patients with viral and non-viral etiologies of liver disease in whom the underlying cause of liver injury was effectively suppressed. However, the understanding of the factors contributing to reversibility of fibrosis and cirrhosis is limited. Our aims were to assess clinical factors, perform genotyping of known variants, and comprehensive metabolic phenotyping to characterize the regression of fibrosis in patients with compensated advanced chronic liver disease (cACLD).

METHODS

In a case-control pilot study of 81 patients with cACLD, we compared individuals exhibiting histological or clinical evidence of cACLD regression ("regressors"; n = 44) with those showing no improvement ("non-regressors"; n = 37) after a minimum of 24 months of successful treatment of the cause of liver disease. Data were validated using an external validation cohort (n = 30).

RESULTS

Regardless of the cause of cACLD, the presence of obesity (odds ratio [OR] 0.267 95% CI 0.072-0.882; p = 0.049), high liver stiffness (OR 0.960, 95% CI 0.925-0.995; p = 0.032), and carriage of GCKR variant rs1260326 (OR 0.148, 95% CI 0.030-0.773; p = 0.019) are associated with a reduced likelihood of fibrosis regression in a subgroup of 60 patients with ACLD genotyped for known genetic variants. Using liver tissue transcriptomics, we identified metabolic pathways differentiating regressors from non-regressors, with top pathways associated with lipid metabolism - especially fatty acids, bile acids, phospholipids, triacylglycerides (biosynthesis), and the carnitine shuttle. In the entire discovery cohort, we further measured metabolites within the defined pathways, which led to the identification of 33 circulating markers differentiating regressors from non-regressors after etiological therapy. The validation cohort confirmed 14 of the differentially expressed markers.

CONCLUSIONS

We identified and validated a group of lipid biomarkers associated with regression of fibrosis that could be used as non-invasive biomarkers for detecting regression of fibrosis in cACLD.

IMPACT AND IMPLICATIONS

Regression of cirrhosis/advanced chronic liver disease (ACLD) after removal of the underlying cause of liver injury has been observed in human cirrhosis. However, detailed characterization of ACLD regression remains an unmet need. In this study, we provide a comprehensive phenotyping of individuals likely to experience ACLD regression. While obesity, carriage of GCKR variant rs1260326 and high liver stiffness were associated with lower likelihood of regression of ACLD, a signature of circulating lipid metabolites enabled differentiation of regressors from non-regressors after effective etiologic therapy. The lipid signature we discovered and externally validated could be used as non-invasive biomarker to detect regression of fibrosis in patients with compensated ACLD.

Review on mechanisms of hypoglycemic effects of compounds from highland barley and potential applications

The rising prevalence of metabolic diseases, such as diabetes and obesity, presents a significant global health challenge. Dietary interventions, with their minimal side effects, hold great promise as effective strategies for blood sugar management. Highland barley (HB) boasts a comprehensive and unique nutritional composition, characterized by high protein, high fiber, high vitamins, low fat, low sugar, and diverse bioactive components. These attributes make it a promising candidate for alleviating high blood sugar. This review explores the mechanisms underlying the glucose-lowering properties of HB, emphasizing its nutritional profile and bioactive constituents. Additionally, it examines the impact of common HB processing techniques on its nutrient composition and highlights its applications in food products. By advancing the understanding of HB's value and mechanisms in diabetes prevention, this review aims to facilitate the development of HB-based foods suitable for diabetic patients.

Hypoxia Stimulates PYGB Enzymatic Activity to Promote Glycogen Metabolism and Cholangiocarcinoma Progression

Cholangiocarcinoma (CCA) displays enhanced glycolysis, pivotal for fulfilling the heightened energy demands intrinsic to its malignant progression. Recent research has indicated that endogenous glycogen rather than exogenous glucose acts as the major carbon source for glycolysis, highlighting the need to better understand the regulation of glycogen homeostasis in CCA. Here, through comprehensive integrative analysis, we identified that glycogen phosphorylase brain form (PYGB), the main enzyme involved in glycogen homeostasis, was markedly upregulated in CCA tissues, serving as an independent prognostic indicator for human patients with CCA. Moreover, elevated PYGB expression potentiated cholangiocarcinogenesis and augmented CCA cell proliferation in both organoid and xenograft models. Hypoxia stimulated PYGB activity in a phosphoglycerate kinase 1-dependent manner, leading to glycogenolysis and the subsequent release of glucose-6-phosphate (G6P) and thereby facilitating aerobic glycolysis. Notably, a virtual screening pinpointed the β-blocker carvedilol as a potent pharmacologic inhibitor of PYGB that could attenuate CCA progression. Collectively, these findings position PYGB as a promising prognostic biomarker and therapeutic target for CCA.  Significance: Cholangiocarcinoma cells exhibit high glycogen phosphorylase activity under hypoxic conditions that mediates metabolic reprograming to promote glycolysis and support tumor development.

High-fat-diet-induced hepatic insulin resistance per se attenuates murine de novo lipogenesis

Hepatic insulin resistance (IR) is often said to be "pathway-selective" with preserved insulin stimulation of de novo lipogenesis (DNL) despite attenuated insulin signaling toward glucose metabolism. However, DNL has not been assessed in models of liver-specific IR. We studied mice with differential tissue-specific lipid-induced IR achieved by different durations of high-fat diet (HFD) feeding. Mice with isolated hepatic IR demonstrated markedly reduced DNL, with a rebound seen in mice with whole-body IR. Insr T1150A mice (protected against diacylglycerol-PKCε-induced hepatic IR) maintained normal DNL with HFD feeding. During hyperinsulinemic clamps, hepatic IR reduced DNL, but hyperglycemia augmented DNL in both resistant and sensitive animals. Regulation through SREBP1c did not consistently correlate with changes in DNL. These results demonstrate that hepatic IR is not pathway-selective, highlighting the primacy of lipogenic substrate in stimulation of DNL. Future therapeutics to reduce lipogenesis should target substrate drivers of DNL rather than targeting plasma insulin levels.

Molecular exploration of the diurnal alteration of glycogen structural fragility and stability in time-restricted-feeding mouse liver

The structure of glycogen α particles in healthy mouse liver has two states: stability and fragility. In contrast, glycogen α particles in diabetic liver present consistent fragility, which may exacerbate hyperglycemia. Currently, the molecular mechanism behind glycogen structural alteration is still unclear. In this study, we characterized the fine molecular structure of liver glycogen α particles in healthy mice under time-restricted feeding (TRF) mode during a 24-h cycle. Then, differentially expressed genes (DEGs) in the liver during daytime and nighttime were revealed via transcriptomics, which identified that the key downregulated DEGs were mainly related to insulin secretion in daytime. Furthermore, GO annotation and KEGG pathway enrichment found that negative regulation of the glycogen catabolic process and insulin secretion process were significantly downregulated in the daytime. Therefore, transcriptomic analyses indicated that the structural stability of glycogen α particles might be correlated with the glycogen degradation process via insulin secretion downregulation. Further molecular experiments confirmed the significant upregulation of glycogen phosphorylase (PYGL), phosphorylated PYGL (p-PYGL), and glycogen debranching enzyme (AGL) at the protein level during the daytime. Overall, we concluded that the downregulation of insulin secretion in the daytime under TRF mode facilitated glycogenolysis, contributing to the structural stability of glycogen α-particles.

Time and dose selective glucose metabolism for glucose homeostasis and energy conversion in the liver

Hepatic glucose metabolism serves dual purposes: maintaining glucose homeostasis and converting glucose into energy sources; however, the underlying mechanisms are unclear. We quantitatively measured liver metabolites, gene expression, and phosphorylated insulin signaling molecules in mice orally administered varying doses of glucose, and constructed a transomic network. Rapid phosphorylation of insulin signaling molecules in response to glucose intake was observed, in contrast to the more gradual changes in gene expression. Glycolytic and gluconeogenic metabolites and expression of genes involved in glucose metabolism including glucose-6-phosphate, G6pc, and Pck1, demonstrated high glucose dose sensitivity. Whereas, glucokinase expression and glycogen accumulation showed low glucose dose sensitivity. During the early phase after glucose intake, metabolic flux was geared towards glucose homeostasis regardless of the glucose dose but shifted towards energy conversion during the late phase at higher glucose doses. Our research provides a comprehensive view of time- and dose-dependent selective glucose metabolism.

Effects of Obesity and Exercise on Hepatic and Pancreatic Lipid Content and Glucose Metabolism: PET Studies in Twins Discordant for BMI

Obesity and sedentarism are associated with increased liver and pancreatic fat content (LFC and PFC, respectively) as well as impaired organ metabolism. Exercise training is known to decrease organ ectopic fat but its effects on organ metabolism are unclear. Genetic background affects susceptibility to obesity and the response to training. We studied the effects of regular exercise training on LFC, PFC, and metabolism in monozygotic twin pairs discordant for BMI. We recruited 12 BMI-discordant monozygotic twin pairs (age 40.4, SD 4.5 years; BMI 32.9, SD 7.6, 8 female pairs). Ten pairs completed six months of training intervention. We measured hepatic insulin-stimulated glucose uptake using [18F]FDG-PET and fat content using magnetic resonance spectroscopy before and after the intervention. At baseline LFC, PFC, gamma-glutamyl transferase (GT), and hepatic glucose uptake were significantly higher in the heavier twins compared to the leaner co-twins (p = 0.018, p = 0.02 and p = 0.01, respectively). Response to training in liver glucose uptake and GT differed between the twins (Time*group p = 0.04 and p = 0.004, respectively). Liver glucose uptake tended to decrease, and GT decreased only in the heavier twins (p = 0.032). In BMI-discordant twins, heavier twins showed higher LFC and PFC, which may underlie the observed increase in liver glucose uptake and GT. These alterations were mitigated by exercise. The small number of participants makes the results preliminary, and future research with a larger pool of participants is warranted.

Hesperetin-loaded chitosan nanoparticles ameliorate hyperglycemia by regulating key enzymes of carbohydrate metabolism in a diabetic rat model

The study aimed to investigate the potential of hesperetin-loaded chitosan nanoparticles (HSPCNPs) in alleviating hyperglycemia by modulating key enzymes in diabetic rats. Chitosan nanoparticles loaded with hesperetin were prepared using the ionic gelation method and characterized with Electron microscope (SEM), zeta potential, particle size analysis, Fourier-transform infrared (FT-IR), Energy dispersive spectroscopy (EDS) and Encapsulation efficiency and Loading efficiency. To induce diabetes, rats were fed a high-fat beef tallow diet for 28 days, then given a single dose of streptozotocin (STZ) at 35 mg/kg b.w in 0.1 M citrate buffer (pH 4.0). Rats were treated with HSPCNPs at doses of 10, 20, and 40 mg/kg b.w. The analyzed parameters included body weight, food and water intake, plasma glucose and insulin, liver and skeletal muscle glycogen levels, and carbohydrate metabolism. SEM imaging revealed dimensions between 124.2 and 251.6 nm and a mean particle size of 145.0 nm. FT-IR analysis confirmed the presence of functional groups in the chitosan nanoparticles, and the zeta potential was 35.5 mV. HSPCNP 40 mg/kg b.w significantly (p < 0.05) reduced blood glucose levels and glycosylated hemoglobin, improving body weight, food intake, and reducing water intake. In diabetic rats, enzymes for carbohydrate metabolism like fructose 1,6-bisphosphatase, phosphoenolpyruvate carboxykinase, and glucose 6-phosphatase are evaluated in the liver, while glucose 6 phosphate dehydrogenase and hexokinase activity were significantly lower. Additionally, plasma insulin levels increased, indicating enhanced insulin sensitivity. The results show that HSPCNPs at 40 mg/kg b.w. ameliorate hyperglycemia to provide robust protection against diabetic complications and significantly improve metabolic health.

Effect of supplementing lysins and methionine to low-protein diets on growth performance, hepatic antioxidant capacity, immune status, and glycolytic activity of tibetan sheep

Reducing the levels of dietary protein is an effective nutritional approach in lowering feed cost and nitrogen emissions in ruminants. The purpose of this study was to evaluate the effects of dietary Lys/Met ratio in a low protein diet (10%, dry matter basis) on the growth performance and hepatic function (antioxidant capacity, immune status, and glycolytic activity) in Tibetan lambs. Ninety two-month-old rams with an average weight of 15.37 ± 0.92 kg were randomly assigned to LP-L (dietary Lys/Met = 1:1), LP-M (dietary Lys/Met = 2:1) and LP-H (dietary Lys/Met = 3:1) treatments. The trial was conducted over 100 d, including 10 d of adaption to the diets. Hepatic phenotypes, antioxidant capacity, immune status, glycolytic activity and gene expression profiling was detected after the conclusion of the feeding trials. The results showed that the body weight was higher in the LP-L group when compared to those on the LP-M group (P < 0.05). In addition, the activities of the catalase (CAT) and glutathione peroxidase (GSH-Px) in the LP-L group were significantly increased compared with the LP-M group (P < 0.05), while the malondialdehyde (MDA) levels in LP-H group were significantly decreased (P < 0.05). Compared with LP-H group, both hepatic glycogen (P < 0.01) and lactate dehydrogenase (LDH) (P < 0.05) were significantly elevated in LP-L group. For the LP-L group, the hepatocytes were arranged radially with the central vein in the center, and hepatic plates exhibited tight arrangement. Transcriptome analysis identified 29, 179, and 129 differentially expressed genes (DEGs) between the LP-M vs. LP-L, LP-H vs. LP-M, and LP-H vs. LP-L groups, respectively (Q-values < 0.05 and |log2Fold Change| > 1). Gene Ontology (GO) and correlation analyses showed that in the LP-L group, core genes (C1QA and JUNB) enriched in oxidoreductase activity were positively correlated with antioxidant indicators, while the MYO9A core gene enriched in the immune response was positively associated with immune indicators, and core genes enriched in molecular function (PDK3 and PDP2) were positively correlated with glycolysis indicators. In summary, low-protein diet with a low Lys/Met ratio (1:1) could reduce the hepatic oxidative stress and improve the glycolytic activity by regulating the expression of related genes of Tibetan sheep.

miR-141/200c contributes to ethanol-mediated hepatic glycogen metabolism

OBJECTIVE

Hepatic glucose metabolism is profoundly perturbed by excessive alcohol intake. miR-141/200c expression is significantly induced by chronic ethanol feeding. This study aimed at identifying the role of miR-141/200c in glucose homeostasis during chronic ethanol exposure.

METHODS

WT and miR-141/200c KO mice were fed a control or an ethanol diet for 30 days, followed by a single binge of maltose dextrin or ethanol, respectively. Untargeted metabolomics analysis of hepatic primary metabolites was performed along with analyses for liver histology, gene expression, intracellular signaling pathways, and physiological relevance. Primary hepatocytes were used for mechanistic studies.

RESULTS

miR-141/200c deficiency rewires hepatic glucose metabolism during chronic ethanol feeding, increasing the abundance of glucose intermediates including G6P, an allosteric activator for GS. miR-141/200c deficiency replenished glycogen depletion during chronic ethanol feeding accompanied by reduced GS phosphorylation in parallel with increased expression of PP1 glycogen targeting subunits. Moreover, miR-141/200c deficiency prevented ethanol-mediated increases in AMPK and CaMKK2 activity. Ethanol treatment reduced glycogen content in WT-hepatocytes, which was reversed by dorsomorphin, a selective AMPK inhibitor, while KO-hepatocytes displayed higher glycogen content than WT-hepatocytes in response to ethanol treatment. Furthermore, treatment of hepatocytes with A23187, a calcium ionophore activating CaMKK2, lowered glycogen content in WT-hepatocytes. Notably, the suppressive effect of A23187 on glycogen deposition was reversed by dorsomorphin, demonstrating that the glycogen depletion by A23187 is mediated by AMPK. KO-hepatocytes exhibited higher glycogen content than WT-hepatocytes in response to A23187. Finally, miR-141/200c deficiency led to improved glucose tolerance and insulin sensitivity during chronic ethanol feeding.

CONCLUSIONS

miR-141/200c deficiency replenishes ethanol-mediated hepatic glycogen depletion through the regulation of GS activity and calcium signaling coupled with the AMPK pathway, improving glucose homeostasis and insulin sensitivity. These results underscore miR-141/200c as a potential therapeutic target for the management of alcohol intoxication.

From NAFLD to NASH: Understanding the spectrum of non-alcoholic liver diseases and their consequences

Non-alcoholic fatty liver disease (NAFLD) has become one of the most frequent chronic liver diseases worldwide in recent decades. Metabolic diseases like excessive blood glucose, central obesity, dyslipidemia, hypertension, and liver function abnormalities cause NAFLD. NAFLD significantly increases the likelihood of liver cancer, heart disease, and mortality, making it a leading cause of liver transplants. Non-alcoholic steatohepatitis (NASH) is a more advanced form of the disease that causes scarring and inflammation of the liver over time and can ultimately result in cirrhosis and hepatocellular carcinoma. In this review, we briefly discuss NAFLD's pathogenic mechanisms, their progression into NASH and afterward to NASH-related cirrhosis. It also covers disease epidemiology, metabolic mechanisms, glucose and lipid metabolism in the liver, macrophage dysfunction, bile acid toxicity, and liver stellate cell stimulation. Additionally, we consider the contribution of intestinal microbiota, genetics, epigenetics, and ecological factors to fibrosis progression and hepatocellular carcinoma risk in NAFLD and NASH patients.

Hepatic extracellular ATP/adenosine dynamics in zebrafish models of alcoholic and metabolic steatotic liver disease

Steatotic liver disease (SLD) is a burgeoning health problem predominantly associated with excessive alcohol consumption, which causes alcohol-related liver disease (ALD), and high caloric intake, which results in metabolic dysfunction-associated SLD (MASLD). The pathogenesis of ALD and MASLD, which can progress from steatohepatitis to more severe conditions such as liver fibrosis, cirrhosis, and hepatocellular carcinoma, is complicated by several factors. Recently, extracellular ATP and adenosine (Ado), as damage-associated molecular patterns, were reported to promote inflammation and liver fibrosis, contributing to SLD pathogenesis. Here, we explored the in vivo dynamics of hepatic extracellular ATP and Ado during the progression of steatohepatitis using a genetically encoded GPCR-activation-based sensor (GRAB) in zebrafish models. We established hepatocyte-specific GRABATP and GRABAdo in zebrafish and investigated the changes in in vivo hepatic extracellular ATP and Ado levels under ALD or MASLD conditions. Disease-specific changes in hepatocyte extracellular ATP and Ado levels were observed, clearly indicating a correlation between hepatocyte extracellular ATP/Ado dynamics and disease progression. Furthermore, clodronate, a vesicular nucleotide transporter inhibitor, alleviated the MASLD phenotype by reducing the hepatic extracellular ATP and Ado content. These findings provide deep insights into extracellular ATP/Ado dynamics in disease progression, suggesting therapeutic potential for ALD and MASLD.

Excessive Tryptophan and Phenylalanine Induced Pancreatic Injury and Glycometabolism Disorder in Grower-finisher Pigs

BACKGROUND

The increase in circulating insulin levels is associated with the onset of type 2 diabetes (T2D), and the levels of branched-chain amino acids and aromatic amino acids (AAAs) are altered in T2D, but whether AAAs play a role in insulin secretion and signaling remains unclear.

OBJECTIVES

This study aimed to investigate the effects of different AAAs on pancreatic function and on the use of insulin in finishing pigs.

METHODS

A total of 18 healthy finishing pigs (Large White) with average body weight of 100 ± 1.15 kg were randomly allocated to 3 dietary treatments: Con, a normal diet supplemented with 0.68% alanine; Phe, a normal diet supplemented with 1.26% phenylalanine; and Trp, a normal diet supplemented with 0.78% tryptophan. The 3 diets were isonitrogenous. There were 6 replicates in each group.

RESULTS

Herein, we investigated the effects of tryptophan and phenylalanine on pancreatic function and the use of insulin in finishing pigs and found that the addition of tryptophan and phenylalanine aggravated pancreatic fat deposition, increased the relative content of saturated fatty acids, especially palmitate (C16:0) and stearate (C18:0), and the resulting lipid toxicity disrupted pancreatic secretory function. We also found that tryptophan and phenylalanine inhibited the growth and secretion of β-cells, downregulated the gene expression of the PI3K/Akt pathway in the pancreas and liver, and reduced glucose utilization in the liver.

CONCLUSIONS

Using fattening pigs as a model, multiorgan combined analysis of the insulin-secreting organ pancreas and the main insulin-acting organ liver, excessive intake of tryptophan and phenylalanine will aggravate pancreatic damage leading to glucose metabolism disorders, providing new evidence for the occurrence and development of T2D.

Hyperglycemia - A culprit of podocyte pathology in the context of glycogen metabolism

Prolonged disruption in the balance of glucose can result in metabolic disorders. The kidneys play a significant role in regulating blood glucose levels. However, when exposed to chronic hyperglycemia, the kidneys' ability to handle glucose metabolism may be impaired, leading to an accumulation of glycogen. Earlier studies have shown that there can be a significant increase in glucose storage in the form of glycogen in the kidneys in diabetes. Podocytes play a crucial role in maintaining the integrity of filtration barrier. In diabetes, exposure to elevated glucose levels can lead to significant metabolic and structural changes in podocytes, contributing to kidney damage and the development of diabetic kidney disease. The accumulation of glycogen in podocytes is not a well-established phenomenon. However, a recent study has demonstrated the presence of glycogen granules in podocytes. This review delves into the intricate connections between hyperglycemia and glycogen metabolism within the context of the kidney, with special emphasis on podocytes. The aberrant storage of glycogen has the potential to detrimentally impact podocyte functionality and perturb their structural integrity. This review provides a comprehensive analysis of the alterations in cellular signaling pathways that may potentially lead to glycogen overproduction in podocytes.

Hexokinase-linked glycolytic overload and unscheduled glycolysis in hyperglycemia-induced pathogenesis of insulin resistance, beta-cell glucotoxicity, and diabetic vascular complications

Hyperglycemia is a risk factor for the development of insulin resistance, beta-cell glucotoxicity, and vascular complications of diabetes. We propose the hypothesis, hexokinase-linked glycolytic overload and unscheduled glycolysis, in explanation. Hexokinases (HKs) catalyze the first step of glucose metabolism. Increased flux of glucose metabolism through glycolysis gated by HKs, when occurring without concomitant increased activity of glycolytic enzymes-unscheduled glycolysis-produces increased levels of glycolytic intermediates with overspill into effector pathways of cell dysfunction and pathogenesis. HK1 is saturated with glucose in euglycemia and, where it is the major HK, provides for basal glycolytic flux without glycolytic overload. HK2 has similar saturation characteristics, except that, in persistent hyperglycemia, it is stabilized to proteolysis by high intracellular glucose concentration, increasing HK activity and initiating glycolytic overload and unscheduled glycolysis. This drives the development of vascular complications of diabetes. Similar HK2-linked unscheduled glycolysis in skeletal muscle and adipose tissue in impaired fasting glucose drives the development of peripheral insulin resistance. Glucokinase (GCK or HK4)-linked glycolytic overload and unscheduled glycolysis occurs in persistent hyperglycemia in hepatocytes and beta-cells, contributing to hepatic insulin resistance and beta-cell glucotoxicity, leading to the development of type 2 diabetes. Downstream effector pathways of HK-linked unscheduled glycolysis are mitochondrial dysfunction and increased reactive oxygen species (ROS) formation; activation of hexosamine, protein kinase c, and dicarbonyl stress pathways; and increased Mlx/Mondo A signaling. Mitochondrial dysfunction and increased ROS was proposed as the initiator of metabolic dysfunction in hyperglycemia, but it is rather one of the multiple downstream effector pathways. Correction of HK2 dysregulation is proposed as a novel therapeutic target. Pharmacotherapy addressing it corrected insulin resistance in overweight and obese subjects in clinical trial. Overall, the damaging effects of hyperglycemia are a consequence of HK-gated increased flux of glucose metabolism without increased glycolytic enzyme activities to accommodate it.

Effects of monochromatic light on hepatic glycogen and lipid synthesis in broilers

Animal growth is closely related to glycolipid metabolism, and the liver is the main organ for glycogen storage and fat synthesis in birds, but whether monochromatic light affects glycogen and lipid synthesis in the liver is unclear. Therefore, in this study, a total of 96 Arbor Acre (AA) broilers at posthatching d 0 (P0) were raised under 4 kinds of light-emitting diode (LED) lights, white light (WL), red light (RL), green light (GL), and blue light (BL), to posthatching d 21 (P21) and 35 (P35). The results showed that the liver, abdominal fat, and abdominal fat indices gradually increased with increasing age under monochromatic light treatments. The liver glycogen and triglyceride (TG) contents also showed an increasing trend. Furthermore, compared with those at P21, the mRNA levels of glycogen synthase (GS), glycogen synthase kinase-3β (GSK-3β), and protein kinase B (AKT1) in the liver were increased in the WL and RL groups at P35, and the mRNA levels of acetyl-CoA carboxylase (ACC) and apolipoprotein B (APOB) increased in all groups at P35. At the same time, the total antioxidant capacity (T-AOC) and liver superoxide dismutase (SOD) contents increased in all groups at P35 compared with those at P21. In addition, at P21, compared with WL, GL and BL promoted the serum glucose (GLU) and TG contents by increasing the mRNA levels of GS, GSK-3β, glucose-6-phosphatase (G6PC), ACC, and fatty acid synthase (FAS), but no effect on the proliferative ability and damage of hepatocytes. At P35, RL promoted the hepatic glycogen and TG contents by increasing GSK-3β, AKT1, ACC, and APOB mRNA levels, and the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were increased than in the WL group. These results suggest that the effects of light color on liver glycogen and lipid synthesis in broilers changed with age, and also provide a theoretical guidance for scientific use of color of light information to improve productive performance in broilers.

Estimation of fatty liver disease clinical role on glucose metabolic remodelling phenotypes and T2DM onset

INTRODUCTION

Metabolic syndrome (MetS), prediabetes (PreDM) and Fatty Liver Disease (FLD) share pathophysiological pathways concerning type 2 diabetes mellitus (T2DM) onset. The non-invasive assessment of fatty liver combined with PreDM and MetS features screening might provide further accuracy in predicting hyperglycemic status in the clinical setting with the putative description of singular phenotypes. The objective of the study is to evaluate and describe the links of a widely available FLD surrogate -the non-invasive serological biomarker Hepatic Steatosis Index (HSI)- with previously described T2DM risk predictors, such as preDM and MetS in forecasting T2DM onset.

PATIENTS AND METHODS

A retrospective ancillary cohort study was performed on 2799 patients recruited in the Vascular-Metabolic CUN cohort. The main outcome was the incidence of T2DM according to ADA criteria. MetS and PreDM were defined according to ATP III and ADA criteria, respectively. Hepatic steatosis index (HSI) with standardized thresholds was used to discriminate patients with FLD, which was referred as estimated FLD (eFLD).

RESULTS

MetS and PreDM were more common in patients with eFLD as compared to those with an HSI < 36 points (35% vs 8% and 34% vs. 18%, respectively). Interestingly, eFLD showed clinical effect modification with MetS and PreDM in the prediction of T2DM [eFLD-MetS interaction HR = 4.48 (3.37-5.97) and eFLD-PreDM interaction HR = 6.34 (4.67-8.62)]. These findings supported the description of 5 different liver status-linked phenotypes with increasing risk of T2DM: Control group (1,5% of T2DM incidence), eFLD patients (4,4% of T2DM incidence), eFLD and MetS patients (10,6% of T2DM incidence), PreDM patients (11,1% of T2DM incidence) and eFLD and PreDM patients (28,2% of T2DM incidence). These phenotypes provided independent capacity of prediction of T2DM incidence after adjustment for age, sex, tobacco and alcohol consumption, obesity and number of SMet features with a c-Harrell=0.84.

CONCLUSION

Estimated Fatty Liver Disease using HSI criteria (eFLD) interplay with MetS features and PreDM might help to discriminate patient risk of T2DM in the clinical setting through the description of independent metabolic risk phenotypes. [Correction added on 15 June 2023, after first online publication: The abstract section was updated in this current version.].

Hepatic insulin receptor: new views on the mechanisms of liver disease

Over 65 % of people with obesity display the metabolic-associated fatty liver disease (MAFLD), which can manifest as steatohepatitis, fibrosis, cirrhosis, or liver cancer. The development and progression of MAFLD involve hepatic insulin resistance and reduced insulin clearance. This review discusses the relationships between altered insulin signaling, hepatic insulin resistance, and reduced insulin clearance in the development of MAFLD and how this provides the impetus for exploring the use of insulin sensitizers to curb this disease. The review also explores the role of the insulin receptor in hepatocytes and hepatic stellate cells and how it signals in metabolic and end-stage liver diseases. Finally, we discuss new research findings that indicate that advanced hepatic diseases may be an insulin-sensitive state in the liver and deliberate whether insulin sensitizers should be used to manage late-stage liver diseases.

Increased cardiac PFK-2 protects against high-fat diet-induced cardiomyopathy and mediates beneficial systemic metabolic effects

A healthy heart adapts to changes in nutrient availability and energy demands. In metabolic diseases like type 2 diabetes (T2D), increased reliance on fatty acids for energy production contributes to mitochondrial dysfunction and cardiomyopathy. A principal regulator of cardiac metabolism is 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2), which is a central driver of glycolysis. We hypothesized that increasing PFK-2 activity could mitigate cardiac dysfunction induced by high-fat diet (HFD). Wild type (WT) and cardiac-specific transgenic mice expressing PFK-2 (GlycoHi) were fed a low fat or HFD for 16 weeks to induce metabolic dysfunction. Metabolic phenotypes were determined by measuring mitochondrial bioenergetics and performing targeted quantitative proteomic and metabolomic analysis. Increasing cardiac PFK-2 had beneficial effects on cardiac and mitochondrial function. Unexpectedly, GlycoHi mice also exhibited sex-dependent systemic protection from HFD, including increased glucose homeostasis. These findings support improving glycolysis via PFK-2 activity can mitigate mitochondrial and functional changes that occur with metabolic syndrome.

Modeling and therapeutic targeting of inflammation-induced hepatic insulin resistance using human iPSC-derived hepatocytes and macrophages

Hepatic insulin resistance is recognized as a driver of type 2 diabetes and fatty liver disease but specific therapies are lacking. Here we explore the potential of human induced pluripotent stem cells (iPSCs) for modeling hepatic insulin resistance in vitro, with a focus on resolving the controversy about the impact of inflammation in the absence of steatosis. For this, we establish the complex insulin signaling cascade and the multiple inter-dependent functions constituting hepatic glucose metabolism in iPSC-derived hepatocytes (iPSC-Heps). Co-culture of these insulin-sensitive iPSC-Heps with isogenic iPSC-derived pro-inflammatory macrophages induces glucose output by preventing insulin from inhibiting gluconeogenesis and glycogenolysis and activating glycolysis. Screening identifies TNFα and IL1β as the mediators of insulin resistance in iPSC-Heps. Neutralizing these cytokines together restores insulin sensitivity in iPSC-Heps more effectively than individual inhibition, reflecting specific effects on insulin signaling and glucose metabolism mediated by NF-κB or JNK. These results show that inflammation is sufficient to induce hepatic insulin resistance and establish a human iPSC-based in vitro model to mechanistically dissect and therapeutically target this metabolic disease driver.

Fatty acid metabolization and insulin regulation prevent liver injury from lipid accumulation in Himalayan marmots

Fat storage and weight gain are dominant traits for hibernating mammals. However, excessive fat accumulation may cause liver damage. Here, we explore the lipid accumulation and metabolic processes of the Himalayan marmot (Marmota himalayana), a hibernating rodent species. We find that the unsaturated fatty acid (UFA) content in food was consistent with a large increase in the body mass of Himalayan marmots. Metagenomic analysis shows that Firmicutes Bacterium CAG:110 plays a synergistic role by synthesizing UFAs, which is demonstrated by fecal transplantation experiments, indicating that the gut microbiome promotes fat storage in Himalayan marmots for hibernation. Microscopic examination results indicate that the risk of fatty liver appears at maximum weight; however, liver function is not affected. Upregulations of UFA catabolism and insulin-like growth factor binding protein genes provide an entry point for avoiding liver injury.

The impact of metabolism on the adaptation of organisms to environmental change

Since Jacob and Monod's discovery of the lac operon ∼1960, the explanations offered for most metabolic adaptations have been genetic. The focus has been on the adaptive changes in gene expression that occur, which are often referred to as "metabolic reprogramming." The contributions metabolism makes to adaptation have been largely ignored. Here we point out that metabolic adaptations, including the associated changes in gene expression, are highly dependent on the metabolic state of an organism prior to the environmental change to which it is adapting, and on the plasticity of that state. In support of this hypothesis, we examine the paradigmatic example of a genetically driven adaptation, the adaptation of E. coli to growth on lactose, and the paradigmatic example of a metabolic driven adaptation, the Crabtree effect in yeast. Using a framework based on metabolic control analysis, we have reevaluated what is known about both adaptations, and conclude that knowledge of the metabolic properties of these organisms prior to environmental change is critical for understanding not only how they survive long enough to adapt, but also how the ensuing changes in gene expression occur, and their phenotypes post-adaptation. It would be useful if future explanations for metabolic adaptations acknowledged the contributions made to them by metabolism, and described the complex interplay between metabolic systems and genetic systems that make these adaptations possible.

Adverse effects and potential mechanisms of fluxapyroxad in Xenopus laevis on carbohydrate and lipid metabolism

Fungicides are one of significant contributing factors to the rapid decline of amphibian species worldwide. Fluxapyroxad (FLX), an effective and broad-spectrum succinate dehydrogenase inhibitor fungicide, has attracted major concerns due to its long-lasting in the environment. However, the potential toxicity of FLX in the development of amphibians remains mostly unknown. In this research, the potential toxic effects and mechanisms of FLX on Xenopus laevis were investigated. In the acute toxicity test, the 96 h median lethal concentration (LC₅₀) of FLX to X. laevis tadpoles was 1.645 mg/L. Based on the acute toxicity result, tadpoles at the stage 51 were exposed to 0, 0.00822, 0.0822, and 0.822 mg/L FLX during 21 days. Results demonstrated that FLX exposure led to an apparent delay in the growth and development of tadpoles and associated with severe liver injury. Additionally, FLX induced glycogen depletion and lipid accumulation in the liver of X. laevis. The biochemical analysis of plasma and liver indicated that FLX exposure could perturb liver glucose and lipid homeostasis by altering enzyme activity related to glycolysis, gluconeogenesis, fatty acid synthesis, and oxidation. Consistent with the biochemical result, FLX exposure altered the liver transcriptome profile, and the enrichment analysis of differential expression genes highlighted the adverse effects of FLX exposure on steroid biosynthesis, PPAR signaling pathway, glycolysis/gluconeogenesis, and fatty acid metabolism in the tadpole liver. Overall, our study was the first to reveal that sub-lethal concentrations of FLX could induce liver damage and produce obvious interference effects on carbohydrate and lipid metabolism of Xenopus, providing new insight into the potential chronic hazards of FLX for amphibians.

Hepatic Insulin Resistance Model in the Male Wistar Rat Using Exogenous Insulin Glargine Administration

Metabolic diseases are a worldwide health problem. Insulin resistance (IR) is their distinctive hallmark. For their study, animal models that provide reliable information are necessary, permitting the analysis of the cluster of abnormalities that conform to it, its progression, and time-dependent molecular modifications. We aimed to develop an IR model by exogenous insulin administration. The effective dose of insulin glargine to generate hyperinsulinemia but without hypoglycemia was established. Then, two groups (control and insulin) of male Wistar rats of 100 g weight were formed. The selected dose (4 U/kg) was administered for 15, 30, 45, and 60 days. Zoometry, a glucose tolerance test, insulin response, IR, and the serum lipid profile were assessed. We evaluated insulin signaling, glycogenesis and lipogenesis, redox balance, and inflammation in the liver. Results showed an impairment of glucose tolerance, dyslipidemia, hyperinsulinemia, and peripheral and time-dependent selective IR. At the hepatic level, insulin signaling was impaired, resulting in reduced hepatic glycogen levels and triglyceride accumulation, an increase in the ROS level with MAPK-ERK1/2 response, and mild pro-oxidative microenvironmental sustained by MT, GSH, and GR activity. Hepatic IR coincides with additions in MAPK-p38, NF-κB, and zoometric changes. In conclusion, daily insulin glargine administration generated a progressive IR model. At the hepatic level, the IR was combined with oxidative conditions but without inflammation.

Dysregulated Liver Metabolism and Polycystic Ovarian Syndrome

A significant fraction of couples around the world suffer from polycystic ovarian syndrome (PCOS), a disease defined by the characteristics of enhanced androgen synthesis in ovarian theca cells, hyperandrogenemia, and ovarian dysfunction in women. Most of the clinically observable symptoms and altered blood biomarker levels in the patients indicate metabolic dysregulation and adaptive changes as the key underlying mechanisms. Since the liver is the metabolic hub of the body and is involved in steroid-hormonal detoxification, pathological changes in the liver may contribute to female endocrine disruption, potentially through the liver-to-ovary axis. Of particular interest are hyperglycemic challenges and the consequent changes in liver-secretory protein(s) and insulin sensitivity affecting the maturation of ovarian follicles, potentially leading to female infertility. The purpose of this review is to provide insight into emerging metabolic mechanisms underlying PCOS as the primary culprit, which promote its incidence and aggravation. Additionally, this review aims to summarize medications and new potential therapeutic approaches for the disease.

The Liver and Glycogen: In Sickness and in Health

The liver is a major store of glycogen and is essential in maintaining systemic glucose homeostasis. In healthy individuals, glycogen synthesis and breakdown in the liver are tightly regulated. Abnormal glycogen metabolism results in prominent pathological changes in the liver, often manifesting as hepatic glycogenosis or glycogen inclusions. This can occur in genetic glycogen storage disease or acquired conditions with insulin dysregulation such as diabetes mellitus and non-alcoholic fatty liver disease or medication effects. Some primary hepatic tumors such as clear cell hepatocellular carcinoma also demonstrate excessive glycogen accumulation. This review provides an overview of the pathological manifestations and molecular mechanisms of liver diseases associated with abnormal glycogen accumulation.

Hepatic Leucine Carboxyl Methyltransferase 1 (LCMT1) contributes to high fat diet-induced glucose intolerance through regulation of glycogen metabolism

Impaired glucose regulation is one of the most important risk factors for type 2 diabetes mellitus (T2DM) and cardiovascular diseases, which have become a major public health issue worldwide. Dysregulation of carbohydrate metabolism in liver has been shown to play a critical role in the development of glucose intolerance but the molecular mechanism has not yet been fully understood. In this study, we investigated the role of hepatic LCMT1 in the regulation of glucose homeostasis using a liver-specific LCMT1 knockout mouse model. The hepatocyte-specific deletion of LCMT1 significantly upregulated the hepatic glycogen synthesis and glycogen accumulation in liver. We found that the liver-specific knockout of LCMT1 improved high fat diet-induced glucose intolerance and insulin resistance. Consistently, the high fat diet-induced downregulation of glucokinase (GCK) and other important glycogen synthesis genes were reversed in LCMT1 knockout liver. In addition, the expression of GCK was significantly upregulated in MIHA cells treated with siRNA targeting LCMT1 and improved glycogen synthesis. In this study, we provided evidences to support the role of hepatic LCMT1 in the development of glucose intolerance induced by high fat diet and demonstrated that inhibiting LCMT1 could be a novel therapeutic strategy for the treatment of glucose metabolism disorders.

Whole grains-derived functional ingredients against hyperglycemia: targeting hepatic glucose metabolism

Type 2 diabetes mellitus (T2DM) is characterized by the dysregulation of glucose homeostasis, resulting in hyperglycemia. However, concerns have been raised about the safety and efficacy of current hypoglycemic drugs due to undesirable side effects. Increasing studies have shown that whole grains (WG) consumption is inversely associated with the risk of T2DM and its subsequent complications. Thus, dietary strategies involving functional components from the WG provide an intriguing approach to restoring and maintaining glucose homeostasis. This review provides a comprehensive understanding of the major functional components derived from WG and their positive effects on glucose homeostasis, demonstrates the underlying molecular mechanisms targeting hepatic glucose metabolism, and discusses the unclear aspects according to the latest viewpoints and current research. Improved glycemic response and insulin resistance were observed after consumption of WG-derived bioactive ingredients, which are involved in the integrated, multi-factorial, multi-targeted regulation of hepatic glucose metabolism. Promotion of glucose uptake, glycolysis, and glycogen synthesis pathways, while inhibition of gluconeogenesis, contributes to amelioration of abnormal hepatic glucose metabolism and insulin resistance by bioactive components. Hence, the development of WG-based functional food ingredients with potent hypoglycemic properties is necessary to manage insulin resistance and T2DM.

Triphenyl phosphate proved more potent than its metabolite diphenyl phosphate in inducing hepatic insulin resistance through endoplasmic reticulum stress

Triphenyl phosphate (TPHP) is a widely used flame retardant and plasticizer and has been detected extensively in environmental media, wildlife and human bodies. Several epidemiological and animal studies have revealed that TPHP exposure is positively associated with glucose homeostasis disruption and diabetes. However, the effects of TPHP on hepatic glucose homeostasis and the underlying mechanisms remain unclear. The present work aimed to investigate the cytotoxicity and glucose metabolism disruption of TPHP and its metabolite diphenyl phosphate (DPHP) within hepatocytes. The cell viability assay undertaken on human normal liver (L02) cells showed that TPHP exhibited more potent hepatotoxicity than DPHP. RNA sequencing (RNA-seq) data showed that TPHP and DPHP presented different modes of toxic action. Insulin resistance is one of the predominant toxicities for TPHP, but not for DPHP. The insulin-stimulated glucose uptake and glycogen synthesis were impaired by TPHP, while DPHP exhibited no significant impairment on these factors. TPHP exposure induced endoplasmic reticulum (ER) stress, and the ER stress antagonist 4-PBA restored the impairment of insulin-stimulated glucose uptake and glycogen synthesis induced by TPHP. TPHP could also induce liver ER stress and insulin resistance in mice. Taken together, the results suggested that TPHP induces more potent insulin resistance through ER stress than its metabolite DPHP.

Chronic lead exposure disrupts neurometabolic activity in mouse brain: An ex vivo1H-[13C]-NMR study

Lead poisoning has been identified as a problem in adults as well as in children. Chronic exposure to lead has been implicated in neurological disorders such as amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer's disease. In the present study, we evaluated the impact of chronic lead exposure on cerebral glutamatergic and GABAergic metabolic activity in mice. C57BL6 mice were provided lead acetate in drinking water for two months. The regional cerebral metabolic activity was measured using ¹H-[¹³C]-NMR spectroscopy in conjunction with infusion of [1,6-¹³C₂]glucose. The blood Pb²⁺ increased significantly in lead acetate treated mice. Concomitantly, there was a significant reduction in the forelimb strength. The level of myo-inositol was elevated in the cerebral cortex of mice chronically exposed to lead. The glutamatergic neurometabolic activity was found to be reduced following chronic lead exposure in the cerebral cortex, hippocampus, and striatum. In contrast, the GABAergic fluxes were impaired in the hippocampus and thalamus only. The metabolic fluxes in the cerebellum were unperturbed to Pb²⁺ toxicity. In conclusion, we report that chronic lead exposure in mice leads to an impairment in forelimb strength, and a perturbation in neurometabolism in brain regions involving cognition and movement.

Novel lipid emulsion for total parenteral nutrition based on 18-carbon n-3 fatty acids elicits a superior immunometabolic phenotype in a murine model compared with standard lipid emulsions

BACKGROUND

While lipid emulsions in modern formulations for total parenteral nutrition (TPN) provide essential fatty acids and dense calories, they also promote inflammation and immunometabolic disruptions.

OBJECTIVES

We aimed to develop a novel lipid emulsion for TPN use with superior immunometabolic actions compared with available standard lipid emulsions.

METHODS

A novel lipid emulsion [Vegaven (VV)] containing 30% of 18-carbon n-3 fatty acids (α-linolenic acid and stearidonic acid) was developed for TPN (VV-TPN) and compared with TPN containing soybean oil-based lipid emulsion (IL-TPN) and fish-oil-based lipid emulsion (OV-TPN). In vivo studies were performed in instrumented male C57BL/6 mice subjected to 7-d TPN prior to analysis of cytokines, indices of whole-body and hepatic glucose metabolism, immune cells, lipid mediators, and mucosal bowel microbiome.

RESULTS

IL-6 to IL-10 ratios were significantly lower in liver and skeletal muscle of VV-TPN mice when compared with IL-TPN or OV-TPN mice. VV-TPN and OV-TPN each increased hepatic insulin receptor abundance and resulted in similar HOMA-IR values, whereas only VV-TPN increased hepatic insulin receptor substrate 2 and maintained normal hepatic glycogen content, effects that were IL-10-dependent and mediated by glucokinase activation. The percentages of IFN-γ- and IL-17-expressing CD4+ T cells were increased in livers of VV-TPN mice, and liver macrophages exhibited primed phenotypes when compared with IL-TPN. This immunomodulation was associated with successful elimination of the microinvasive bacterium Akkermansia muciniphila from the bowel mucosa by VV-TPN as opposed to standard lipid emulsions. Assay of hepatic lipid mediators revealed a distinct profile with VV-TPN, including increases in 9(S)-hydroxy-octadecatrienoic acid. When co-administered with IL-TPN, hydroxy-octadecatrienoic acids mimicked the VV-TPN immunometabolic phenotype.

CONCLUSIONS

We here report the unique anti-inflammatory, insulin-sensitizing, and immunity-enhancing properties of a newly developed lipid emulsion designed for TPN use based on 18-carbon n-3 fatty acids.

Protein Targeting to Glycogen (PTG): A Promising Player in Glucose and Lipid Metabolism

Protein phosphorylation and dephosphorylation are widely considered to be the key regulatory factors of cell function, and are often referred to as "molecular switches" in the regulation of cell metabolic processes. A large number of studies have shown that the phosphorylation/dephosphorylation of related signal molecules plays a key role in the regulation of liver glucose and lipid metabolism. As a new therapeutic strategy for metabolic diseases, the potential of using inhibitor-based therapies to fight diabetes has gained scientific momentum. PTG, a protein phosphatase, also known as glycogen targeting protein, is a member of the protein phosphatase 1 (PP1) family. It can play a role by catalyzing the dephosphorylation of phosphorylated protein molecules, especially regulating many aspects of glucose and lipid metabolism. In this review, we briefly summarize the role of PTG in glucose and lipid metabolism, and update its role in metabolic regulation, with special attention to glucose homeostasis and lipid metabolism.

Mutations in GCK May Lead to MODY2 by Reducing Glycogen Synthesis

Dysfunction of glucokinase (GCK) caused by mutations in the GCK gene is the main cause of maturity-onset diabetes of the young type-2 (MODY2, also known as GCK-MODY), which is usually present in adolescence or young adulthood. MODY2 is characterized by mild, stable fasting hyperglycemia that presents at birth, usually 5.4-8.3 mmol L^-1 , and rarely develops complications from diabetes. The treatment of MODY2 prefers a manageable diet rather than the use of insulin. Previous studies have identified GCK mutations only by online software prediction or enzyme kinetic analysis and thermolability assays which are complicated to be conducted. In this study, six mutations in the GCK gene, including four novel mutations and two mutations that are previously reported, are identified. All the six locations are highly conserved according to the sequencing alignment. Moreover, missense mutations are strongly predicted to be pathogenic using online programs. Functional studies show that mutations in GCK mutation do not affect insulin secretion but affect glycogen synthesis. These findings demonstrate that GCK mutations decrease glycogen synthesis, which leads to hyperglycemia in MODY2. Meanwhile, this study provides a new perspective and methods for identifying pathogenic mutations in GCK.

Protein succinylation associated with the progress of hepatocellular carcinoma

Although post‐translational modification is critical to tumorigenesis, how succinylation modification of lysine sites influences hepatocellular carcinoma (HCC) remains obscure. 90 tumours and paired adjacent normal tissue of liver cancer were enrolled for succinylation staining. 423 HCC samples with 20 genes related to succinylation modification from TCGA were downloaded for model construction. Statistical methods were employed to analyse the data, including the Non‐Negative Matrix Factorization (NMF) algorithm, t‐Distributed Stochastic Neighbour Embedding (t‐SNE) algorithm, and Cox regression analysis. The staining pan‐succinyllysine antibody staining indicated that tumour tissues had a higher succinyllysine level than adjacent tissues (p < 0.001), which could be associated with a worse prognosis (p = 0.02). The survival was associated with pathological stage, tumour recurrence status and succinyllysine intensity in the univariate or multivariable cox survival analysis model. The risk model from 20 succinyllysine‐related genes had the best prognosis prediction. The high expression of succinylation modification in HCC contributed to the worse patient survival prognosis. Model construction of 20 genes related to succinylation modification (MEAF6, OXCT1, SIRT2, CREBBP, KAT5, SIRT4, SIRT6, SIRT7, CPT1A, GLYATL1, SDHA, SDHB, SDHC, SDHD, SIRT1, SIRT3, SIRT5, SUCLA2, SUCLG1 and SUCLG2) could be reliable in predicting prognosis in HCC.

En masse organoid phenotyping informs metabolic-associated genetic susceptibility to NASH

Genotype-phenotype associations for common diseases are often compounded by pleiotropy and metabolic state. Here, we devised a pooled human organoid-panel of steatohepatitis to investigate the impact of metabolic status on genotype-phenotype association. En masse population-based phenotypic analysis under insulin insensitive conditions predicted key non-alcoholic steatohepatitis (NASH)-genetic factors including the glucokinase regulatory protein (GCKR)-rs1260326:C>T. Analysis of NASH clinical cohorts revealed that GCKR-rs1260326-T allele elevates disease severity only under diabetic state but protects from fibrosis under non-diabetic states. Transcriptomic, metabolomic, and pharmacological analyses indicate significant mitochondrial dysfunction incurred by GCKR-rs1260326, which was not reversed with metformin. Uncoupling oxidative mechanisms mitigated mitochondrial dysfunction and permitted adaptation to increased fatty acid supply while protecting against oxidant stress, forming a basis for future therapeutic approaches for diabetic NASH. Thus, "in-a-dish" genotype-phenotype association strategies disentangle the opposing roles of metabolic-associated gene variant functions and offer a rich mechanistic, diagnostic, and therapeutic inference toolbox toward precision hepatology. VIDEO ABSTRACT.

HM-Chromanone, a Major Homoisoflavonoid in Portulaca oleracea L., Improves Palmitate-Induced Insulin Resistance by Regulating Phosphorylation of IRS-1 Residues in L6 Skeletal Muscle Cells

This study investigated the effect of (E)-5-hydroxy-7-methoxy-3-(2-hydroxybenzyl)-4-chromanone (HM-chromanone) on palmitate-induced insulin resistance and elucidated the underlying mechanism in L6 skeletal muscle cells. Glucose uptake was markedly decreased due to palmitate-induced insulin resistance in these cells; however, 10, 25, and 50 µM HM-chromanone remarkably improved glucose uptake in a concentration-dependent manner. HM-chromanone treatment downregulated protein tyrosine phosphatase 1B (PTP1B) and phosphorylation of c-Jun N-terminal kinase (JNK) and inhibitor of nuclear factor kappa-B kinase subunit beta (IKKβ), which increased because of palmitate mediating the insulin-resistance status in cells. HM-chromanone promoted insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation and suppressed palmitate-induced phosphorylation of IRS-1 serine. This activated phosphoinositide 3-kinase (PI3K) and stimulated protein kinase B (AKT) phosphorylation. Phosphorylated AKT promoted the translocation of Glucose transporter type 4 to the plasma membrane and significantly enhanced glucose uptake into muscle cells. Additionally, HM-chromanone increased glycogen synthesis through phosphorylating glycogen synthase kinase 3 alpha/beta (GSK3 α/β) via AKT. Consequently, HM-chromanone may improve insulin resistance by downregulating the phosphorylation of IRS-1 serine through inhibition of negative regulators of insulin signaling and inflammation-activated protein kinases in L6 skeletal muscle cells.

Estradiol (E2) Improves Glucose-Stimulated Insulin Secretion and Stabilizes GDM Progression in a Prediabetic Mouse Model

Female New Zealand obese (NZO) mice are an established model of preconceptional (pc.) prediabetes that progresses as gestational diabetes mellitus (GDM) during gestation. It is known that NZO mice show improvement in insulin sensitivity and glucose-stimulated insulin secretion (GSIS) during gestation in vivo. The latter is no longer detectable in ex vivo perifusion experiments in isolated islets of Langerhans, suggesting a modulation by extrapancreatic factors. Here, we demonstrated that plasma 17β-estradiol (E2) levels increased markedly in NZO mice during gestation. The aim of this work was to determine whether these increased E2 levels are responsible for the improvement in metabolism during gestation. To achieve this goal, we examined its effects in isolated islets and primary hepatocytes of both NZO and metabolically healthy NMRI mice. E2 increased GSIS in the islets of both strains significantly. Hepatic glucose production (HGP) failed to be decreased by insulin in NZO hepatocytes but was reduced by E2 in both strains. Hepatocytes of pregnant NZO mice showed significantly lower glucose uptake (HGU) compared with NMRI controls, whereby E2 stimulation diminished this difference. Hepatocytes of pregnant NZO showed reduced glycogen content, increased cyclic adenosine monophosphate (cAMP) levels, and reduced AKT activation. These differences were abolished after E2 stimulation. In conclusion, our data indicate that E2 stabilizes and prevents deterioration of the metabolic state of the prediabetic NZO mice. E2 particularly increases GSIS and improves hepatic glucose utilization to a lower extent.

Role of Serotonin (5-HT) in GDM Prediction Considering Islet and Liver Interplay in Prediabetic Mice during Gestation

Gestational diabetes (GDM) is characterized by a glucose tolerance disorder. This may first appear during pregnancy or pre-exist before conception as a form of prediabetes, but there are few data on the pathogenesis of the latter subtype. Female New Zealand obese (NZO) mice serve as a model for this subpopulation of GDM. It was recently shown that GDM is associated with elevated urinary serotonin (5-hydroxytryptamine, 5-HT) levels, but the role of the biogenic amine in subpopulations with prediabetes remains unclear. 5-HT is synthesized in different tissues, including the islets of Langerhans during pregnancy. Furthermore, 5-HT receptors (HTRs) are expressed in tissues important for the regulation of glucose homeostasis, such as liver and pancreas. Interestingly, NZO mice showed elevated plasma and islet 5-HT concentrations as well as impaired glucose-stimulated 5-HT secretion. Incubation of isolated primary NZO islets with 5-HT revealed an inhibitory effect on insulin and glucagon secretion. In primary NZO hepatocytes, 5-HT aggravated hepatic glucose production (HGP), decreased glucose uptake (HGU), glycogen content, and modulated AKT activation as well as cyclic adenosine monophosphate (cAMP) increase, indicating 5-HT downstream modulation. Treatment with an HTR2B antagonist reduced this 5-HT-mediated deterioration of the metabolic state. With its strong effect on glucose metabolism, these data indicate that 5-HT is already a potential indicator of GDM before conception in mice.

Conjunctional Relationship between Serum Uric Acid and Serum Nickel with Non-Alcoholic Fatty Liver Disease in Men: A Cross-Sectional Study

Serum uric acid (SUA) and heavy metals are closely related to non-alcoholic fatty liver disease (NAFLD). Yet, the conjunctional relationship between SUA and serum nickel (Ni) concentrations with the risk of NAFLD in men has not yet been investigated. Therefore, we designed this cross-sectional study to investigate the association of SUA or serum Ni with NAFLD in men. The cross-sectional study was based on data obtained from a prospective cohort study of common chronic non-communicable diseases in Central China, conducted in Xinxiang city, Central China's Henan Province, between April and June 2017. A total of 1709 male participants completed the physical examination. B-ultrasound was used to examine the liver and to diagnose NAFLD. Binary logistic regression models and restricted cubic splines were performed to estimate the association of the SUA and serum Ni with NAFLD. The prevalence of NAFLD among 1709 male participants was 46.6%. After adjusting for potential confounders, with the highest quartile compared to those with the lowest quartile, SUA (OR = 1.579, 95% CI: 1.140-2.189) and serum Ni (OR = 1.896, 95% CI: 1.372-2.625) were associated with NAFLD, respectively. At the same time, the associations for the second and third SUA quartiles were null. Restricted cubic splines showed a positive linear relationship between serum Ni (ln-transformed) and NAFLD risk. Intriguingly, high SUA and high Ni (OR = 2.370, 95% CI: 1.577-3.597) increased the risk of NAFLD, compared with those with low SUA and low Ni. Our findings demonstrate a positive linear trend between serum Ni concentrations and NAFLD risk. Men with elevated serum Ni had a higher risk of developing NAFLD when compared to those with high SUA. Furthermore, the conjunctional relationship of SUA and serum Ni with NAFLD risk was observed in men.

Organ fat in Latino youth at risk for type 2 diabetes

PURPOSE

Obesity in youth increases the risk for type 2 diabetes (T2D) and elevated abdominal adipose tissue and organ fat may be particularly deleterious. The purpose of this study was to examine associations among measures of adiposity including total, visceral, and organ fat (hepatic and pancreatic) and whether these measures were independently associated with glycemia in Latino youth at risk for diabetes.

METHODS

Latino adolescents (47 boys and 32 girls, 13.7 ± 1.4 years) with obesity (BMIz 2.3 ± 0.3) were assessed for total fat by DXA and visceral and organ fat by 3 T magnetic resonance imaging. Glycemic indicators included HbA1c, fasting glucose (FG), and 2-h glucose (2-HrG) following an oral glucose tolerance test. Pearson correlations and stepwise linear regression analyses controlling for age and sex were used to examine independent associations between adiposity and glycemia.

RESULTS

Total fat was associated with visceral (r = 0.66, p = 0.001) and hepatic fat (r = 0.34, p < 0.01) while visceral fat was associated with hepatic (r = 0.42, p < 0.001) and pancreatic fat (r = 0.36, p < 0.001). In stepwise linear regression analysis, hepatic and pancreatic fat were significant predictors of FG, explaining 4.7% and 5.2% of the variance, respectively (total R²  = 0.14, p = 0.02). Hepatic fat was the only significant predictor of 2-HrG explaining 9.9% of the variance in the model (total R²  = 0.12, p = 0.03). No measure of adiposity was retained as a significant predictor of HbA1c.

CONCLUSION

Hepatic and pancreatic fat were the only adiposity measures independently associated with glycemia but the small amount of variance explained underscores the need for additional T2D biomarkers in high risk youth.

Vitamin D regulates insulin pathway and glucose metabolism in zebrafish (Danio rerio)

1,25-dihydroxyvitamin D₃ [1,25(OH)₂ D₃ ], the most active vitamin D (VD) metabolite, is a steroid hormone playing an important role in many physiological functions in addition to maintaining mineral homeostasis. In this study, we explored the mechanism that the VD regulated insulin pathway and glucose metabolism in zebrafish in vitro and in vivo. Our results show that 1,25(OH)₂ D₃  significantly enhances the expression of insulin receptor a (insra), insulin receptor substrate 1 (irs1) and glucose transporter 2 (glut2), and promotes glycolysis and glycogenesis, while suppressing gluconeogenesis in zebrafish liver cell line (ZFL) under the condition of high glucose (20 mM), instead of the normal glucose (10 mM). Moreover, consistent results were obtained from the zebrafish fed with VD₃ -deficient diet, as well as the cyp2r1^-/- zebrafish, in which endogenous VD metabolism is blocked. Furthermore, results from dual-luciferase reporting system exhibited that 1,25(OH)₂ D₃ directly activated the transcription of insra, rather than insrb in zebrafish by binding to vitamin D response element (VDRE) located at -181 to -167 bp in the promoter region of insra. Importantly, the 1,25(OH)₂ D₃ treatment significantly alleviated the symptoms of hyperglycemia in diabetic zebrafish. In conclusion, our study demonstrated that VD activates VDRE located in the promoter area of insra in zebrafish to promote insulin/insra signaling pathway, thereby contributing to the maintenance of glucose homeostasis.

Hepatic Positron Emission Tomography: Applications in Metabolism, Haemodynamics and Cancer

Evaluating in vivo the metabolic rates of the human liver has been a challenge due to its unique perfusion system. Positron emission tomography (PET) represents the current gold standard for assessing non-invasively tissue metabolic rates in vivo. Here, we review the existing literature on the assessment of hepatic metabolism, haemodynamics and cancer with PET. The tracer mainly used in metabolic studies has been [¹⁸F]2-fluoro-2-deoxy-D-glucose (¹⁸F-FDG). Its application not only enables the evaluation of hepatic glucose uptake in a variety of metabolic conditions and interventions, but based on the kinetics of ¹⁸F-FDG, endogenous glucose production can also be assessed. 14(R,S)-[¹⁸F]fluoro-6-thia-Heptadecanoic acid (¹⁸F-FTHA), ¹¹C-Palmitate and ¹¹C-Acetate have also been applied for the assessment of hepatic fatty acid uptake rates (¹⁸F-FTHA and ¹¹C-Palmitate) and blood flow and oxidation (¹¹C-Acetate). Oxygen-15 labelled water (¹⁵O-H₂O) has been used for the quantification of hepatic perfusion. ¹⁸F-FDG is also the most common tracer used for hepatic cancer diagnostics, whereas ¹¹C-Acetate has also shown some promising applications in imaging liver malignancies. The modelling approaches used to analyse PET data and also the challenges in utilizing PET in the assessment of hepatic metabolism are presented.

Hepatic deficiency of selenoprotein S exacerbates hepatic steatosis and insulin resistance

Nonalcoholic fatty liver disease (NAFLD) is closely associated with insulin resistance (IR) and type 2 diabetes mellitus (T2DM), which are all complex metabolic disorders. Selenoprotein S (SelS) is an endoplasmic reticulum (ER) resident selenoprotein involved in regulating ER stress and has been found to participate in the occurrence and development of IR and T2DM. However, the potential role and mechanism of SelS in NAFLD remains unclear. Here, we analyzed SelS expression in the liver of high-fat diet (HFD)-fed mice and obese T2DM model (db/db) mice and generated hepatocyte-specific SelS knockout (SelS^H-KO) mice using the Cre-loxP system. We showed that hepatic SelS expression levels were significantly downregulated in HFD-fed mice and db/db mice. Hepatic SelS deficiency markedly increased ER stress markers in the liver and caused hepatic steatosis via increased fatty acid uptake and reduced fatty acid oxidation. Impaired insulin signaling was detected in the liver of SelS^H-KO mice with decreased phosphorylation levels of insulin receptor substrate 1 (IRS1) and protein kinase B (PKB/Akt), which ultimately led to disturbed glucose homeostasis. Meanwhile, our results showed hepatic protein kinase Cɛ (PKCɛ) activation participated in the negative regulation of insulin signaling in SelS^H-KO mice. Moreover, the inhibitory effect of SelS on hepatic steatosis and IR was confirmed by SelS overexpression in primary hepatocytes in vitro. Thus, we conclude that hepatic SelS plays a key role in regulating hepatic lipid accumulation and insulin action, suggesting that SelS may be a potential intervention target for the prevention and treatment of NAFLD and T2DM.

Liver fibrosis alters the molecular structures of hepatic glycogen

Liver fibrosis (LF) leads to liver failure and short survival. Liver glycogen is a hyperbranched glucose polymer, comprising individual β particles, which can bind together to form aggregated α particles. Glycogen functionality depends on its molecular structure. This study compared the molecular structure of liver glycogen from both LF and healthy rats, and explored underlying mechanisms for observed differences. Glycogen from both groups contained α and β particles; the LF group contained a higher proportion of β particles, with the glycogen containing fewer long chains than seen in the control group. Both glycogen branching enzyme and glycogen phosphorylase showed a significant decrease of activity in the LF group. Transcriptomics and proteomics revealed a functional deficiency of mitochondria in the LF group, which may lead to changes in glycogen structure. These results provide for the first time an understanding of how liver fibrosis affects liver glycogen metabolism and glycogen structure. HYPOTHESIS: We hypothesized that the molecular structure of liver glycogen from a rat model of liver fibrosis would be altered compared to the control group.

Riligustilide alleviates hepatic insulin resistance and gluconeogenesis in T2DM mice through multitarget actions

Riligustilide (RG), one of the dimeric phthalides of Angelica sinensis and Ligusticum chuanxiong, was confirmed effective against many diseases. However, its effects on type 2 diabetes mellitus (T2DM) and the underlying molecular mechanisms have not been clearly elucidated yet. The current study was designed to investigate the hypoglycemic potential by which RG affects the pathogenesis of T2DM. Comprehensive insights into the effects and underlying molecular mechanisms of RG on attenuating aberrant metabolism of glucose were determined in high-fat diet-induced T2DM mice and insulin-resistant (IR) HepG2 cells. In high-fat diet-induced C57BL/6J mice, RG administration significantly reduced hyperglycemia, decreased hyperinsulinemia, and ameliorated glucose intolerance. Mechanistically, RG activated PPARγ and insulin signaling pathway to improve insulin sensitivity, and increase glucose uptake as well as glycogenesis. In addition, RG also upregulated AMPK-TORC2-FoxO1 axis to attenuate gluconeogenesis in vivo and in vitro. According to the findings, RG may be a promising candidate for the treatment of T2DM.

Impaired glucocorticoid receptor expression in liver disrupts feeding-induced gene expression, glucose uptake, and glycogen storage

The transition from a fasted to a fed state is associated with extensive transcriptional remodeling in hepatocytes facilitated by hormonal- and nutritional-regulated transcription factors. Here, we use a liver-specific glucocorticoid receptor (GR) knockout (L-GRKO) model to investigate the temporal hepatic expression of GR target genes in response to feeding. Interestingly, in addition to the well-described fasting-regulated genes, we identify a subset of hepatic feeding-induced genes that requires GR for full expression. This includes Gck, which is important for hepatic glucose uptake, utilization, and storage. We show that insulin and glucocorticoids cooperatively regulate hepatic Gck expression in a direct GR-dependent manner by a 4.6 kb upstream GR binding site operating as a Gck enhancer. L-GRKO blunts preprandial and early postprandial Gck expression, which ultimately affects early postprandial hepatic glucose uptake, phosphorylation, and glycogen storage. Thus, GR is positively involved in feeding-induced gene expression and important for postprandial glucose metabolism in the liver.

Measurement of Pulsatile Insulin Secretion: Rationale and Methodology

Pancreatic β-cells are responsible for the synthesis and exocytosis of insulin in response to an increase in circulating glucose. Insulin secretion occurs in a pulsatile manner, with oscillatory pulses superimposed on a basal secretion rate. Insulin pulses are a marker of β-cell health, and secretory parameters, such as pulse amplitude, time interval and frequency distribution, are impaired in obesity, aging and type 2 diabetes. In this review, we detail the mechanisms of insulin production and β-cell synchronization that regulate pulsatile insulin secretion, and we discuss the challenges to consider when measuring fast oscillatory secretion in vivo. These include the anatomical difficulties of measuring portal vein insulin noninvasively in humans before the hormone is extracted by the liver and quickly removed from the circulation. Peripheral concentrations of insulin or C-peptide, a peptide cosecreted with insulin, can be used to estimate their secretion profile, but mathematical deconvolution is required. Parametric and nonparametric approaches to the deconvolution problem are evaluated, alongside the assumptions and trade-offs required for their application in the quantification of unknown insulin secretory rates from known peripheral concentrations. Finally, we discuss the therapeutical implication of targeting impaired pulsatile secretion and its diagnostic value as an early indicator of β-cell stress.