Inhibition Of Hepatic Gluconeogenesis Research Articles

Insulin resistance and iatrogenic hyperinsulinemia in type 1 diabetes - norm or complication? Role of metformin in type 1 diabetes mellitus

There is a rising trend of overweight and obesity among individuals with type 1 diabetes. This is often associated with decreased insulin sensitivity, increased insulin dose requirements and poor glycemic control. Insulin resistance is a state of diminished effect of insulin on target tissues, despite normal or elevated serum insulin levels. Metformin as an adjunct to insulin in treating overweight or also not specific image of insulin resistance (without overweight or hormonal disorders) adults with type 1 diabetes is increasingly used. The main goal of this off-label type 1 diabetes treatment method is to improve insulin signaling leading to a subsequent increase in glucose uptake by skeletal myocytes, inhibition of hepatic gluconeogenesis and, as a result, a reduction in the need for a daily dose of insulin. The use of metformin as an addition to insulin may increase the chance of achieving target glucose control and reduce the anabolic effect of this hormone. Metformin can improve insulin sensitivity, glycemia and modulate cardiovascular disease risk factors or nonalcoholic fatty liver disease. In the vast majority of clinical trials conducted with metformin in type 1 diabetes, the effect of the drug on daily insulin doses, improvement in lipid parameters, and decline in body fat was assessed without correlating pre-specified outcomes with drug plasma concentrations.

222-OR: Metformin Reduces Fasting Glycemia in Well-Controlled Type 2 Diabetes by Promoting Aerobic Glycolysis Independent of Decreasing Endogenous Glucose Production

It is well established that metformin improves glycemic control in individuals with poorly-controlled type 2 diabetes (T2D) by reducing rates of endogenous glucose production (EGP) mediated by inhibition of hepatic gluconeogenesis. However, the mechanism by which metformin reduces blood glucose levels in well-controlled individuals with T2D is still unknown. To address this question, we examined rates of EGP, lactate turnover and hepatic triglyceride (TAG), ATP and glycogen content in near-normoglycemic individuals with T2D (n=10, HbA1c 7±1%) with (M+; 1000 mg bid x 2 wks) and without (M-; 2 wks) metformin treatment using the PINTA method with [2H7]glucose and [3-13C]lactate tracer infusions in combination with 1H- /31P- /13C- magnetic resonance spectroscopy. Metformin treatment did not affect rates of EGP, but reduced fasting plasma glucose concentrations by 30% (p<0.01 vs. M-), which could be attributed to increased rates of glucose clearance (+18%, p<0.005 vs. M-) resulting in increased lactate production (+14%, p<0.01 vs. M-). These changes were associated with decreased hepatic ATP content (-20%, p<0.05 vs. M-), increased hepatic glycogen content (+40%, p<0.05 vs. M-) and no changes in hepatic TAG content. Conclusion: In contrast to the glucose-lowering effect of metformin in poorly-controlled T2D, which is due to reductions in gluconeogenesis, this study demonstrates that in well-controlled T2D metformin reduces fasting glycemia - independent of reductions in EGP - primarily by increasing rates of aerobic glycolysis as reflected by increased peripheral glucose clearance and lactate production as well as reduced hepatic ATP content, which is consistent with metformin-induced inhibition of mitochondrial electron transport chain activity. Disclosure T.Sarabhai: None. T.E.Lamoia: None. S.Friesl: None. M.Jonuscheit: None. K.Petersen: Advisory Panel; Novo Nordisk, Research Support; Merck Sharp & Dohme Corp., Gilead Sciences, Inc. G.I.Shulman: Consultant; Novo Nordisk, DiCerna Pharmaceuticals, Inc., Bayer Consumer Care AG, Kriya Therapeutics, Arrowhead Pharmaceuticals, Inc., ESPERION Therapeutics, Inc., Other Relationship; AstraZeneca, Merck & Co., Inc., Janssen Research & Development, LLC, iMetabolic Biopharma Corporation, Maze Therapeutics, 89bio, Inc., Equator Therapeutics, Inc., Generian Pharmaceuticals, Fortress Biotech, Inc., OrsoBio, Aro Biotherapeutics Company, Stock/Shareholder; Levels Health, Inc. M.Roden: Advisory Panel; Eli Lilly and Company, Consultant; TARGET PharmaSolutions, Inc., Research Support; Boehringer-Ingelheim, Novo Nordisk, Novartis, Sanofi.

Christensenella regulated by Huang-Qi-Ling-Hua-San is a key factor by which to improve type 2 diabetes.

There is a lot of evidence that oral hypoglycemic drugs work by affecting gut microbes, but the key strains responsible for this effect are not well known. Huang-Qi-Ling-Hua-San (HQLHS), composed of Astragalus Membranaceus, Ganoderma lucidum, Inonotus obliquus, and Momordica charantia L., is a specially designed Chinese medicine formula to treat type 2 diabetes (T2D). In this study, a mouse model of T2D induced by high-fat diet and streptozotocin was used to explore the mechanism of HQLHS in improving hyperglycemia and hyperlipidemia through multiple rounds of animal experiments, such as HQLHS feeding, fecal microbiota transplantation (FMT), and live bacteria feeding, so as to explore the potential target intestinal flora in its hypoglycemic effect. Results show that such specific taxa as Bifidobacterium, Turicibacter, Alistipes, Romboutsia, and Christensenella were identified to be preferably enriched by HQLHS and then assumed to be the target microbes. Herein, FMT was used to test if the upregulated beneficial bacteria by HQLHS play a therapeutic role. The strain Christensenella minuta DSM 22607 and the strain Christensenella timonensis DSM 102800 were selected to test the beneficial effect of Christensenella taxa on T2D. Diabetic animals supplemented with these strains showed the improvement in blood glucose and lipid metabolism, the promotion of GLP-1 secretion, the increase in antioxidant capacity, the inhibition of hepatic gluconeogenesis, the suppression of intestinal glucose absorption, the enhancement of intestinal barrier, reduced LPS-induced inflammation, and the reduction of branched amino acids (BCAAs) content in the liver. Overall, these data demonstrate that Christensenella plays a beneficial role in T2D and is a target for the action of HQLHS therapy.

Semaglutide for the treatment of obesity

Introduction and purpose
 Due to the growing tendency to diagnose obesity in patients, scientists are trying to find drugs that facilitate weight reduction. 
 An example of such a formulation is the GLP-1 analogue semaglutide. The following article is an analysis of the current knowledge on the effectiveness and safety of obesity treatment with semaglutide based on available publications in Pubmed and Google Scholar databases.
 State of knowledge
 The main mechanism of semaglutide is based on a stimulation of insulin secretion from pancreatic beta cells, and inhibition of glucagon from alpha cells, inhibition of hepatic gluconeogenesis, and reduction of energy consumption with minimal impact on energy expenditure. In clinical trials, it showed the best results compared to placebo and other drugs used in weight reduction. Participants treated with semaglutide achieved a reduction in waist circumference, improvements in blood pressure parameters, HbA1c levels, total cholesterol, LDL cholesterol, triglycerides, and CRP protein, and increased HDL cholesterol levels. Semaglutide is well tolerated by patients, and its main side effects come from the gastrointestinal tract, including nausea, emesis, diarrhea.
 Summary
 The analysis of the latest publications and meta-analyzes of the literature shows that the use of semaglutide is safe and effective in the treatment of obesity. The positive effect of semaglutide on weight reduction also contributes to the reduction of the risk of cardiovascular events and other obesity-related complications. It is also well tolerated by patients, which translates into possible longer use, and weekly subcutaneous injections are not burdensome for patients.
 Key words: semaglutide; obesity; GLP-1 analogue; overweight

Chitosan Oligosaccharide Alleviates Abnormal Glucose Metabolism without Inhibition of Hepatic Lipid Accumulation in a High-Fat Diet/Streptozotocin-Induced Diabetic Rat Model.

This study investigated the effects of chitosan oligosaccharide (COS) on glucose metabolism and hepatic steatosis in a high-fat (HF) diet/streptozotocin-induced diabetic rat model. Male Wistar rats were divided into: (1) normal control (NC group), (2) HF diet (HF group), (3) streptozotocin (STZ)-induced diabetes with HF diet (DF group), and DF group supplemented with (4) 0.5% COS (D0.5F group), (5) 1% COS (D1F group), and (6) 5% COS (D5F group) for 4 weeks. COS supplementation significantly decreased the plasma glucose, BUN, creatinine, uric acid, triglyceride (TG), and total cholesterol (TC) levels, and hepatic glucose-6-phosphatase activity, and significantly increased hepatic hexokinase activity and glycogen content in diabetic rats; but the increased hepatic TG and TC levels could not be significantly decreased by COS supplementation. Supplementation of COS increased superoxide dismutase activity and decreased lipid peroxidation products in the diabetic rat livers. COS supplementation significantly increased phosphorylated AMP-activated protein kinase (AMPK) protein expression, and attenuated protein expression of hepatic phosphoenolpyruvate carboxykinase (PEPCK) and phosphorylated p38 and renal sodium-glucose cotransporter-2 (SGLT2) in diabetic rats. These results suggest that COS may possess a potential for alleviating abnormal glucose metabolism in diabetic rats through the inhibition of hepatic gluconeogenesis and lipid peroxidation and renal SGLT2 expression.

Gluconeogenesis is reduced from alanine, lactate and pyruvate, but maintained from glycerol, in liver perfusion of rats with early and late sepsis.

Sepsis induces several metabolic abnormalities, including hypoglycaemia in the most advanced stage of the disease, a risk factor for complications and death. Although hypoglycaemia can be caused by inhibition of hepatic gluconeogenesis, decreased and increased gluconeogenesis were reported in sepsis. Furthermore, gluconeogenesis from glycerol was not yet evaluated in this disease. The main purpose of this study was to investigate the gluconeogenesis from alanine, lactate, pyruvate and glycerol in rats with early (8 hours) and late (18 hours) sepsis. Parameters related to the characterization of sepsis were also evaluated. Sepsis was induced by cecal ligation and puncture and gluconeogenesis was assessed in liver perfusion. Rats with early and late sepsis showed increased lactataemia, depletion of liver glycogen and peripheral insulin resistance, characterizing the establishment of sepsis. Rats with early and late sepsis showed decreased gluconeogenesis from alanine, lactate and pyruvate. Interestingly, gluconeogenesis from glycerol, a precursor that enters in the pathway at a later step, subsequent to the entry of alanine, lactate and pyruvate, was maintained in rats with early and late sepsis. In conclusion, gluconeogenesis is decreased from alanine, lactate and pyruvate, but maintained from glycerol, in liver perfusion of rats with early and late sepsis. SIGNIFICANCE OF THE STUDY: The maintenance of gluconeogenesis from glycerol, but not from alanine, lactate and pyruvate, together with the liver glycogen depletion, points the glycerol as an important precursor for the maintenance of glycaemic homeostasis in sepsis. The findings open the possibility of further investigation on the administration of glycerol in the treatment of hypoglycaemia associated with more advanced sepsis.

Metformin - its anti-cancer effects in hematologic malignancies.

The main anti-diabetic effect of metformin mediated through stimulation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) is the inhibition of hepatic gluconeogenesis and triggering glucose uptake in skeletal muscles. Additionally, some new pathways, besides the AMPK activation, were discovered, that can explain wide-range properties of metformin. All these properties are now attracting the attention of researchers in the fields other than diabetes and the drug has been reported to have anti-cancer, immunoregulatory and anti-aging effects. Among others, the beneficial effects of metformin in hematological disorders like leukemias, lymphomas, and multiple myeloma were reported. Despite a great progress in therapy, these diseases are still incurable in most cases. Thus, there is an urgent need to discover novel, less toxic and more effective drugs especially for older or chemotherapy-resistant patients. In this review article, the current findings on the anti-cancer effect of metformin together with underlying possible mechanisms in blood cancers are discussed. However. to evaluate precisely these promising effects of metformin, more studies are required, because many of the published results are preclinical.

The Hypoglycemic Effect of Berberine and Berberrubine Involves Modulation of Intestinal Farnesoid X Receptor Signaling Pathway and Inhibition of Hepatic Gluconeogenesis.

Our previous study suggests that berberine (BBR) lowers lipids by modulating bile acids and activating intestinal farnesoid X receptor (FXR). However, to what extent this pathway contributes to the hypoglycemic effect of BBR has not been determined. In this study, the glucose-lowering effects of BBR and its primary metabolites, berberrubine (M1) and demethyleneberberine, in a high-fat diet-induced obese mouse model were studied, and their modulation of the global metabolic profile of mouse livers and systemic bile acids was determined. The results revealed that BBR (150 mg/kg) and M1 (50 mg/kg) decreased mouse serum glucose levels by 23.15% and 48.14%, respectively. Both BBR and M1 markedly modulated the hepatic expression of genes involved in gluconeogenesis and metabolism of amino acids, fatty acids, and purine. BBR showed a stronger modulatory effect on systemic bile acids than its metabolites. Moreover, molecular docking and gene expression analysis in vivo and in vitro suggest that BBR and M1 are FXR agonists. The mRNA levels of gluconeogenesis genes in the liver, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, were significantly decreased by BBR and M1. In summary, BBR and M1 modulate systemic bile acids and activate the intestinal FXR signaling pathway, which reduces hepatic gluconeogenesis by inhibiting the gene expression of gluconeogenesis genes, achieving a hypoglycemic effect. BBR and M1 may function as new, natural, and intestinal-specific FXR agonists with a potential clinical application to treat hyperglycemia and obesity. SIGNIFICANCE STATEMENT: This investigation revealed that BBR and its metabolite, berberrubine, significantly lowered blood glucose, mainly through activating intestinal farnesoid X receptor signaling pathway, either directly by themselves or indirectly by modulating the composition of systemic bile acids, thus inhibiting the expression of gluconeogenic genes in the liver and, finally, reducing hepatic gluconeogenesis and lowering blood glucose. The results will help elucidate the mechanism of BBR and provide a reference for mechanism interpretation of other natural products with low bioavailability.

Cellular and Molecular Mechanisms of Metformin Action.

Metformin is a first-line therapy for the treatment of type 2 diabetes, due to its robust glucose-lowering effects, well-established safety profile, and relatively low cost. While metformin has been shown to have pleotropic effects on glucose metabolism, there is a general consensus that the major glucose-lowering effect in patients with type 2 diabetes is mostly mediated through inhibition of hepatic gluconeogenesis. However, despite decades of research, the mechanism by which metformin inhibits this process is still highly debated. A key reason for these discrepant effects is likely due to the inconsistency in dosage of metformin across studies. Widely studied mechanisms of action, such as complex I inhibition leading to AMPK activation, have only been observed in the context of supra-pharmacological (>1 mM) metformin concentrations, which do not occur in the clinical setting. Thus, these mechanisms have been challenged in recent years and new mechanisms have been proposed. Based on the observation that metformin alters cellular redox balance, a redox-dependent mechanism of action has been described by several groups. Recent studies have shown that clinically relevant (50-100 μM) concentrations of metformin inhibit hepatic gluconeogenesis in a substrate-selective manner both in vitro and in vivo, supporting a redox-dependent mechanism of metformin action. Here, we review the current literature regarding metformin’s cellular and molecular mechanisms of action.

Determination of the antidiabetic chemical basis of Phellodendri Chinensis Cortex by integrating hepatic disposition in vivo and hepatic gluconeogenese inhibition in vitro

Ethnopharmacological relevancePhellodendri Chinensis Cortex (PCC) has been an herb clinically used to treat diabetes, but the chemical basis of its antidiabetic effects has remained unclear. Aim of this studyBased on the efficacy of herbal medicine resulting from the cooperative response of the effective compounds in the target organs with sufficient exposure, the in vivo hepatic disposition and in vitro hepatic gluconeogenesis inhibition were integrated to elucidate the chemical basis for the antidiabetic effect of orally administered PCC from a target organ, liver, perspective. Materials and methodsWith a developed and validated HPLC-MS/MS method, three alkaloids and five metabolites were determined in the portal vein plasma, liver, and systemic plasma of rats orally administered PCC. The inhibition of hepatic gluconeogenesis by the eight compounds was evaluated in primary hepatocytes. ResultsThe in vivo results showed that magnoflorine was present at the highest concentration among the target constituents in the plasma, where berberine showed a low concentration. In contrast, berberine showed the highest concentration in the liver, and its five metabolites exhibited substantial hepatic accumulation. This discrepancy was strongly associated with the hepatic disposition of the compounds. The hepatic disposition prevented the transfer of 96.1% of the phellodendrine, 71.1% of the berberine and 47.5% of the magnoflorine from the portal vein plasma to the systemic plasma, which corresponded to their hepatic distribution and hepatic metabolism. In vitro, berberine, M1, M4 and M5 significantly and dose-dependently inhibited hepatic glucose production. By integrating the hepatic exposure and inhibitory activity data, we estimated that berberine contributed the most (74%) to the total glucose production inhibition of the orally administered PCC decoction, followed by M4 (14%), M1 (11%) and M5 (1%). ConclusionThis study was the first to comprehensively describe the pharmacokinetic profiles and hepatic disposition of alkaloids in PCC, and concluded that berberine and its metabolites contributed the most to the total hepatic gluconeogenesis inhibition by orally administered PCC. These results reveal the chemical basis for the antidiabetic effect of orally administered PCC decoction, providing scientific evidence to support the clinical usage of PCC in diabetes treatment.

The Hepatic Plasma Membrane Citrate Transporter NaCT (SLC13A5) as a Molecular Target for Metformin

Metformin is the first-line treatment for type 2 diabetes. Inhibition of hepatic gluconeogenesis is the primary contributor to its anti-diabetic effect. Metformin inhibits complex I and α-glycerophosphate shuttle, and the resultant increase in cytoplasmic NADH/NAD+ ratio diverts glucose precursors away from gluconeogenesis. These actions depend on metformin-mediated activation of AMP kinase (AMPK). Here we report on a hitherto unknown mechanism. Metformin inhibits the expression of the plasma membrane citrate transporter NaCT in HepG2 cells and decreases cellular levels of citrate. 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMPK activator, elicits a similar effect. The process involves a decrease in maximal velocity with no change in substrate affinity. The decrease in NaCT expression is associated with decreased mRNA levels. AMPK inhibits mTOR, and the mTOR inhibitor rapamycin also decreases NaCT expression. The transcription factor downstream of AMPK that is relevant to cAMP signaling is CREB; decreased levels of phospho-CREB seem to mediate the observed effects of metformin on NaCT. Citrate is known to suppress glycolysis by inhibiting phosphofructokinase-1 and activate gluconeogenesis by stimulating fructose-1,6-bisphophatase; therefore, the decrease in cellular levels of citrate would stimulate glycolysis and inhibit gluconeogenesis. These studies uncover a novel mechanism for the anti-diabetic actions of metformin.

Glucagon up-regulates hepatic mitochondrial pyruvate carrier 1 through cAMP-responsive element-binding protein; inhibition of hepatic gluconeogenesis by ginsenoside Rb1.

Hepatic mitochondrial pyruvate carrier (MPC) transports pyruvate into mitochondria. This study investigated the involvement of MPC1 in hepatic glucagon response, in order to identify a possible pharmacological intervention. The correlation between hepatic glucagon response and MPC1 induction was investigated in fasted mice and primary hepatocytes. The effects of ginsenoside Rb1 on MPC1 function were observed. Glucagon challenge raised blood glucose with hepatic MPC1 induction, and inhibition of MPC induction coincided with a reduced rise in blood glucose. cAMP-responsive element-binding protein (CREB) knockdown blocked glucagon-induced MPC1 expression, while CREB overexpression increased MPC1 expression. Luciferase reporter, chromatin immunoprecipitation assay, and promoter mutation confirmed that CREB increased MPC1 transcription through gene promoter induction. CREB regulated transcription co-activator 2 nuclear translocation was also required for CREB to promote MPC1 induction. Glucagon shifted mitochondrial pyruvate towards carboxylation for gluconeogenesis via the opposite regulation of pyruvate dehydrogenase and carboxylase with respect to MPC1 induction. MPC1 induction was necessary for glucagon to promote pyruvate-driven hepatic glucose production (HGP), but glucagon failed to influence HGP from other gluconeogenic substrates routed into the tricarboxylic acid cycle, independent of MPC. Rb1 blocked cAMP signalling by inhibiting AC activity and deactivated CREB by dephosphorylation, possibly contributing to inhibiting MPC1 induction to reduce HGP. CREB transcriptionally up-regulates MPC1 to provide pyruvate for gluconeogenesis. Rb1 reduced cAMP formation which consequently reduced CREB-mediated MPC1 induction and thereby might contribute to limiting pyruvate-dependent HGP. These results suggest a therapeutic strategy to reduce hyperglycaemia in diabetes.

373-P: Recurrent Insulin-Induced Hypoglycaemia Leads to Weight Gain in Association with Increased Adiposity and Reduced Basal Metabolic Rate

Intensification of insulin therapy in type 1 diabetes is associated with significant weight gain. Several mechanisms have been proposed to account for this weight gain including reduced glucosuria and suppression of hepatic gluconeogenesis and glucose production however the precise mechanisms responsible for this remain unclear. This study examined the hypothesis that recurrent hypoglycaemia (RH) might contribute, at least in part, to this phenomenon. Male C57BL6J mice (n=12/group) received either RH (1mU/g insulin i.p. 3 per week for 12 weeks to achieve glucose of approximately 2.8mmol/l) or Vehicle (saline i.p in equivalent volume). Body composition and energy homeostasis were assessed using EchoMRI and CLAMS systems respectively. Hypothalamic transcript abundance was assessed using Taqman real time PCR. Data are expressed as mean+/-SEM. RH animals were 43% heavier and had increased fat mass compared to Control animals (8.49+/-0.64 v 16.6+/-1.38% body weight) despite comparable food intake (p=ns). Energy expenditure was significantly lower (53% decrease) in RH animal (0.414+/-0.006 v 0.218+/-0.004 kcal/min; p<0.01) and was associated with a decrease in the respiratory exchange ratio (RER: 0.98+/-0.01 v 0.96+/-0.01;p<0.05). There was no difference in locomotor activity. These changes were associated with suppression of genes involved in thermogenesis, mitochondrial energetics and lipolysis within the brown adipose tissue. Consistent with our hypothesis, RH leads to increased accumulation of fat stored which is associated with reduced energy expenditure and RER. These results suggest that RH induces a state of hypometabolism that may contribute to weight gain observed with intensification of insulin therapy in type 1 diabetes. Disclosure A.D. McNeilly: None. J. Gallagher: None. R.J. McCrimmon: Advisory Panel; Self; Eli Lilly and Company, Novo Nordisk A/S, Sanofi-Aventis. Research Support; Self; The Leona M. and Harry B. Helmsley Charitable Trust. Funding JDRF; Diabetes UK

Role of Mitochondria in the Mechanism(s) of Action of Metformin.

Metformin is a drug from the biguanide family that is used for decades as the first-line therapeutic choice for the treatment of type 2 diabetes. Despite its worldwide democratization, owing to its clinical efficacy, high safety profile and cheap cost, the exact mechanism(s) of action of this anti-hyperglycemic molecule with pleiotropic properties still remains to be fully elucidated. The concept that metformin would exert some of its actions though modulation of the mitochondrial bioenergetics was initially forged in the 50s but undeniably revived at the beginning of the twenty-first century when it was shown to induce a weak but specific inhibition of the mitochondrial respiratory-chain complex 1. Furthermore, metformin has been reported to reduce generation of reactive oxygen species at the complex 1 and to prevent mitochondrial-mediated apoptosis, suggesting that it can protect against oxidative stress-induced cell death. Nevertheless, despite some recent progress and the demonstration of its key role in the inhibition of hepatic gluconeogenesis, the exact nature of the mitochondrial interaction between the drug and the complex 1 is still poorly characterized. Recent studies reported that metformin may also have anti-neoplastic properties by inhibiting cancer cell growth and proliferation, at least partly through its mitochondrial action. As such, many trials are currently conducted for exploring the repositioning of metformin as a potential drug for cancer therapy. In this mini-review, we discuss both historical and more recent findings on the central role played by the interaction between metformin and the mitochondria in its cellular mechanism of action.

Unraveling the Regulation of Hepatic Gluconeogenesis.

Hepatic gluconeogenesis, de novo glucose synthesis from available precursors, plays a crucial role in maintaining glucose homeostasis to meet energy demands during prolonged starvation in animals. The abnormally increased rate of hepatic gluconeogenesis contributes to hyperglycemia in diabetes. Gluconeogenesis is regulated on multiple levels, such as hormonal secretion, gene transcription, and posttranslational modification. We review here the molecular mechanisms underlying the transcriptional regulation of gluconeogenesis in response to nutritional and hormonal changes. The nutrient state determines the hormone release, which instigates the signaling cascades in the liver to modulate the activities of various transcriptional factors through various post-translational modifications like phosphorylation, methylation, and acetylation. AMP-activated protein kinase (AMPK) can mediate the activities of some transcription factors, however its role in the regulation of gluconeogenesis remains uncertain. Metformin, a primary hypoglycemic agent of type 2 diabetes, ameliorates hyperglycemia predominantly through suppression of hepatic gluconeogenesis. Several molecular mechanisms have been proposed to be metformin's mode of action.

Involvement of AMPK activation in the inhibition of hepatic gluconeogenesis by Ficus carica leaf extract in diabetic mice and HepG2 cells

The aim of this study was to explore the possible mechanisms of Ficus carica leaf (FCL) extract in suppressing hepatic gluconeogenesis in diabetic mice. Diabetic mice (streptozotocin-induced) received 1 g/kg of FCL extract twice a day for 6 weeks. Fasting blood glucose levels were measured and a 2-h oral glucose tolerance test was conducted. AMP-activated protein kinase (AMPK), phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6Pase), and peroxisome proliferator activated receptor-γ coactivator-1α (PGC-1α) expression was examined. HepG2 hepatocytes were treated with FCL extract and an AMPK inhibitor (compound C) or agonist (AICAR), and PEPCK, G6pase, PGC-1α, AMPK, forkhead transcription factor O1 (FOXO1), and hepatic nuclear factor 4α (HNF4α) expression was determined. The results showed that FCL extract inhibited the expression of PEPCK and G6Pase in the liver of diabetic mice and HepG2 hepatocytes. FCL extract activated AMPK and decreased PGC-1α, HNF4α, and FOXO1 expression. The AMPK inhibitor attenuated those effects through inhibiting gluconeogenesis, while the AMPK agonist partially enhanced gluconeogenesis. In conclusion, FCL extract inhibits hepatic gluconeogenesis via activation of AMPK and down-regulation of gluconeogenic enzymes.

Baicalin regulates SirT1/STAT3 pathway and restrains excessive hepatic glucose production.

Sirtuin 1 (SirT1) and signal transducer and activator of transcription 3 (STAT3) oppositely regulate hepatic gluconeogenic genes and the association remains to be elucidated. Baicalin is a natural flavonoid with beneficial effects on glucose and lipid metabolism. This study aims to investigate the effect of baicalin on hepatic gluconeogenesis with focus on the regulation of fatty acid mobilization and SirT1/STAT3 pathway. In HFD feeding or fasting state, hepatic gluconeogenesis and fatty acid oxidation induced SirT1 expression due to the increased nicotinamide adenine dinucleotide+ (NAD+) contents. Baicalin reduces endogenous glucose production via suppression of hepatic gluconeogenesis and decreased SirT1 induction via reducing NAD+ accumulation in an energy-sensing way. Fasting increased SirT1 protein in STAT3 immunoprecipitation products and less in the liver of baicalin-treated mice, indicating that baicalin blocked the binding of SirT1 to STAT3 and thus preserved STAT3 acetylation. SirT1 knockdown enhanced the protective effect of baicalin on pyruvate-induced STAT3 phosphorylation and acetylation, these results further indicated that the regulation of STAT3 activity by baicalin was dependent on SirT1. Moreover, HFD feeding increased gene expression for PGC-1α in the liver, but the transcriptional regulation was inhibited by baicalin treatment. SirT1 overexpression and STAT3 inhibition enhanced pyruvate-mediated PGC-1α gene expression, suggesting that deacetylation of STAT3 by SirT1 is required for PGC-1α activity on hepatic gluconeogenesis. Taken together, these results showed that baicalin restrained HGP via inhibiting SirT1 activity coupled with STAT3 acetylation and subsequent PGC-1α suppression, suggesting that hepatic SirT1 and STAT3 pathway may provide therapeutic advantages for the control of hyperglycemia.

Effect of Metformin on Mitochondrial Pathways in Human Skeletal Muscle Cells

Metformin (Met) is the most commonly prescribed antidiabetic agent worldwide. Although it has been marketed in the U.S. for over two decades, the exact molecular mechanisms of Met remain controversial. In addition to suppression of hepatic gluconeogenesis, increasing evidence suggests Met induces extrahepatic tissue-specific effects, such as in skeletal muscle (SKM), where the mitochondrion is believed to be the primary cellular target. We investigated the effects of Met on mitochondrial pathways in human SKM cells isolated by percutaneous needle biopsy from lean control, obese nondiabetic, and type 2 diabetic (T2D) volunteers. Mitochondrial function was assessed by Seahorse XF24 analyzer in SKM cells treated with or without Met for 24 hours. Glycolytic rate increased in Met-treated SKM cells from lean (P<0.01), obese (P<0.0001), and T2D subjects (P<0.01) compared to untreated cells. In contrast, basal respiration and ATP production were dramatically reduced in SKM cells treated with Met (P<0.0001 for all phenotypes). Evaluation of the insulin signaling pathway revealed increased Akt phosphorylation at Ser473 (P<0.05) and Thr308 (P<0.01) in cells pre-treated with Met compared to insulin stimulation alone, indicating an additive effect of Met on insulin action. As expected, muscle cells incubated with Met showed enhanced AMPK phosphorylation at Thr172 (P<0.001). Recent studies have identified a direct link between AMPK activation and mitochondrial dynamics pathways. We therefore assessed changes in markers of mitochondrial fission and fusion and found that Met treatment significantly induced phosphorylation of mitochondrial fission factor (MFF; P<0.01) in human SKM cells. Our data suggest Met may mediate improvements in glycemic control by activating AMPK to directly regulate the mitochondrial fission machinery and alter cellular bioenergetics. Functional morphometric and biochemical studies are ongoing to validate mechanisms by which Met exerts its antihyperglycemic effects in SKM. Disclosure J. Sacks: None. A. Mulya: None. C.E. Fealy: None. K.M. Fitzgerald: None. E. Huang: None. J.P. Kirwan: None.

Palmitic Acid Esters of Hydroxy Stearic Acids Are Hepatic Insulin Sensitizers in Chow and High-Fat Diet (HFD)–Fed Mice

Palmitic Acid esters of Hydroxy Stearic Acids (PAHSAs), bioactive lipids with potent anti-inflammatory and antidiabetic effects, reduce ambient glycemia and improve glucose tolerance and insulin sensitivity in insulin resistant HFD-fed mice. We aimed to determine the mechanisms by which PAHSAs improve insulin sensitivity. We treated chow- and HFD-fed mice with 5-PAHSA (0.1 mg/day) and 9-PAHSA (0.4 mg/day) by SQ osmotic minipumps for 13 weeks. Serum 5-PAHSA levels increased 3.5 fold and 9-PAHSA 2.5 fold in chow-fed mice, while 5-PAHSA levels increased 17 fold and 9-PAHSA 6 fold in HFD-fed mice. PAHSAs had no effect on weight gain or fat mass. We performed hyperinsulinemic euglycemic clamps (2.5 mU/Kg/min insulin infusion rate). PAHSA treatment increased systemic insulin sensitivity in both chow- [glucose infusion rate (GIR): vehicle 13±2 vs. PAHSA 27±4 mg/kg/min] and HFD-fed mice (GIR: vehicle 2±0.5 vs. PAHSA 10±3 mg/kg/min). Endogenous glucose production (EGP) was suppressed 28% by insulin in vehicle-treated mice and 55% in PAHSA-treated mice on chow diet. Remarkably, while insulin failed to suppress EGP in vehicle-treated HFD-fed mice, PAHSA treatment led to a 37% reduction in EGP. PAHSAs also decreased glycemia during a pyruvate tolerance test, indicating that suppression of hepatic gluconeogenesis contributes to the EGP improvement. Mechanistic studies showed that PAHSAs inhibit basal and glucagon-stimulated EGP and reduce cAMP in isolated hepatocytes. This effect is blocked by pertussis toxin indicating it is mediated by Gα/i protein-coupled receptors. PAHSAs also reduce G6pase activity and phosphorylation of CREB in liver. Sum: PAHSAs are systemic insulin sensitizers and augment insulin action on EGP in vivo. In vitro, PAHSAs reduce EGP through a cAMP dependent pathway involving Gα/i protein-coupled receptors. Thus, PAHSAs could be effective antidiabetic agents and the pathways they engage could provide novel drug targets for type 2 diabetes. Disclosure A. Santoro: None. P. Zhou: None. O.D. Peroni: None. I. Syed: None. A.T. Nelson: None. D. Siegel: None. A. Saghatelian: None. B. Kahn: Advisory Panel; Self; Janssen Research & Development. Research Support; Self; Janssen Research & Development. Advisory Panel; Self; Alterna Biotech.

Potential hypoglycemic effect of acetophenones from the root bark of Cynanchum wilfordii

Three new acetophenones, named cynwilforones A–C (1–3), together with cynandione A (4) were isolated from the root bark of Cynanchum wilfordii (Maxim.) Hemsl. Their structures were deduced based on spectroscopic analysis and chemical methods. Compounds 1 and 4 exhibited potential hypoglycemic effects through inhibition of hepatic gluconeogenesis by down-regulating the expression of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase. This is the first report that acetophenones from the root bark of C. wilfordii possesses potential hypoglycemic activity in vitro.