Inhibition Of Gluconeogenesis Research Articles

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.

PPP1R3C mediates metformin-inhibited hepatic gluconeogenesis

BackgroundMetformin has been widely used to alleviate hyperglycemia in patients with type 2 diabetes mainly via suppressing hepatic gluconeogenesis. However, the underlying mechanism remains incompletely clear. Here, we aimed to explore the role of PPP1R3C in metformin-mediated inhibition of hepatic gluconeogenesis. MethodsThe differentially expressed genes in primary mouse hepatocytes incubated with 8-Br-cAMP and metformin were analyzed by microarrays. Hepatic glucose production and gluconeogenic gene expressions were detected after adenovirus-mediated overexpression or silence of PPP1R3C in vitro and in vivo. The phosphorylation level and location of transducer of regulated CREB activity 2 (TORC2) were determined by Western blot and immunofluorescence. ResultsMetformin and adenovirus-mediated activation of AMPK suppressed 8-Br-cAMP–stimulated Ppp1r3c mRNA expression in primary mouse hepatocytes. Overexpression of PPP1R3C in primary mouse hepatocytes or the livers of wild-type mice promoted hepatic glucose production and gluconeogenic gene expressions. On the contrary, adenovirus-mediated knockdown of PPP1R3C in primary mouse hepatocytes decreased hepatic gluconeogenesis, with the suppression of cAMP-stimulated gluconeogenic gene expressions and TORC2 dephosphorylation. Notably, Ppp1r3c expression was increased in the liver of db/db mice. After PPP1R3C silence in the livers of wild-type and db/db mice, blood glucose levels and hepatic glucose production were markedly lowered, with decreased expressions of key gluconeogenic enzymes and transcript factors as well as liver glycogen content. ConclusionMetformin-activated AMPK decreases hepatic PPP1R3C expression, leading to the suppression of hepatic gluconeogenesis through blocking cAMP-stimulated TORC2 dephosphorylation. Hepatic specific silence of PPP1R3C provides a promising therapeutic strategy for type 2 diabetes.

287-LB: Autophagic Degradation of CRY1 and Control of Gluconeogenesis

Cryptochrome 1 (CRY1) is a core clock repressor that maintains clock periodicity. CRY1 robustly suppresses hepatic gluconeogenesis by regulating CREB/cAMP and glucocorticoid receptor signaling and by reducing levels of FoxO1—a transcription factor that drives gluconeogenesis. Autophagy degrades cytoplasmic contents in lysosomes for maintenance of quality control and provision of energy. Since the liver clock and autophagy are each regulated by insulin and glucagon, we hypothesized that the control of autophagy, the circadian clock, and glucose homeostasis are interlinked. We have shown that induction of circadian autophagy between 3pm-7pm degrades CRY1, which releases its inhibition of gluconeogenesis and promotes glucose production. Acutely blocking autophagy or inactivating the LC3-Interacting-Region (LIR) motifs of CRY1, which allow it to interact with the autophagy marker LC3, led to accumulation of CRY1 and suppression of gluconeogenesis. Thus, autophagy drives glucose production in liver by timed degradation of CRY1. Interestingly, high-fat feeding accelerates the autophagic degradation of CRY1, which contributes to obesity-associated hyperglycemia. Since phosphorylation of CRY1 triggers its proteasomal degradation, and since phosphorylation in the vicinity of LIRs is thought to facilitate interaction with LC3, we hypothesized that phosphorylation of CRY1 leads to its degradation through autophagy and increases glucose production. Accordingly, we generated specific phosphorylation-resistant and constitutively-phosphorylated CRY1 mutants that were delivered to the liver. While the phosphorylation-resistant CRY1 mutant accumulated in liver and lowered blood glucose levels, the constitutively-phosphorylated CRY1 mutation that favors its rapid degradation resulted in increased blood glucose. Our results show that CRY1 phosphorylation couples its turnover by autophagy to regulation of gluconeogenesis—revealing novel targets to prevent obesity-associated hyperglycemia. Disclosure M. Toledo Soler: None. R. Singh: None. Funding American Diabetes Association (1-18-IBS-062 to R.S.)

1886-P: Hepatic Type 2 Innate Lymphoid Cells Suppress Gluconeogenesis via the IL-33/GATA3/IL-13 Axis

Type 2 innate lymphoid cells (ILC2s) were recently identified as essential components of innate immunity. Besides, beneficial roles of ILC2s in metabolic diseases are attracting attentions. Although the liver contains various immune cells including T cells and ILC2s, little is known about ILC2s in hepatic gluconeogenesis. We therefore investigated the role of ILC2s and the effect of IL-33, a potent ILC2 activator, on hepatic gluconeogenesis in mice. We found that recombinant IL-33 injection decreased fasting blood glucose levels in wild type mice. This effect was not observed in NOD/SCID Il2rg null (NSG) mice lacking certain immune cells including ILC2s, whereas the similar response was seen in another immune deficient mice Foxnnu/nu (nude mice), which have normal development in ILC2s. IL-33 treatment also suppressed hepatic gluconeogenesis assessed by pyruvate tolerance test in wt mice, while there was no response in NSG. Moreover, ILC2 transplantation was able to rescue the absence of glucose response by IL-33 in NSG. We observed a marked increase of IL-13+ ILC2 population in liver after IL-33 treatment, and Il13-/- mice did not show the decrease of blood glucose or the suppression of gluconeogenesis by IL-33 treatment. Additionally, the transfer of Il13-/- ILC2 failed to gain IL-33 induced glucose response in NSG, suggesting that the hypoglycemic effect of IL-33/ILC2s depends on IL-13. In consistent with these results, the differentially expressed gene analysis revealed that IL-13 treatment mostly altered the gene expressions of glucose metabolic process in primary hepatocytes. Notably, we identified GATA3 as a direct regulator of the effecter molecules such as Il5, Il13 and I1rl1 in hepatic ILC2s. These phenomena were also reproducible in human ILC2s and primary hepatocyte. In conclusion, these findings indicate that hepatic ILC2s suppress hepatic gluconeogenesis via the IL-33/GATA3/IL-13 axis, thus reducing blood glucose levels. Disclosure M. Fujimoto: None. K. Yokote: None. T. Tanaka: None.

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.

Phytomedicines Used for Diabetes Mellitus in Ghana: A Systematic Search and Review of Preclinical and Clinical Evidence.

Background Available data indicate that diabetes mellitus leads to elevated cost of healthcare. This imposes a huge economic burden on households, societies, and nations. As a result many Ghanaians, especially rural folks, resort to the use of phytomedicine, which is relatively less expensive. This paper aims at obtaining information on plants used in Ghana to treat diabetes mellitus, gather and present evidence-based data available to support their uses and their mechanisms of action, and identify areas for future research. Method A catalogue of published textbooks, monographs, theses, and peer-reviewed articles of plants used in Ghanaian traditional medicine between 1987 and July 2018 for managing diabetes mellitus was obtained and used. Results The review identified 76 plant species belonging to 45 families that are used to manage diabetes mellitus. Leaves were the part of the plants frequently used for most preparation (63.8%) and were mostly used as decoctions. Majority of the plants belonged to the Euphorbiaceae, Lamiaceae, Asteraceae, and Apocynaceae families. Pharmacological data were available on 23 species that have undergone in vitro studies. Forty species have been studied using in vivo animal models. Only twelve plants and their bioactive compounds were found with data on both preclinical and clinical studies. The records further indicate that medicinal plants showing antidiabetic effects did so via biochemical mechanisms such as restitution of pancreatic β-cell function, improvement in insulin sensitivity by receptors, stimulating rate of insulin secretion, inhibition of liver gluconeogenesis, enhanced glucose absorption, and inhibition of G-6-Pase, α-amylase, and α-glucosidase activities. Conclusion This review contains information on medicinal plants used to manage diabetes mellitus, including their pharmacological properties and mechanisms of action as well as models used to investigate them. It also provides gaps that can form the basis for further investigations and development into useful medications for effective treatment of diabetes mellitus.

MON-159 Increased Gluconeogenesis and Lower Glycogenolysis in Patients with Non-Selective Compared Selective Insulin Resistance

Type 2 diabetes is characterized by increased hepatic glucose production and selective insulin resistance that occurs downstream of the insulin receptor. However, the differential pathways and exact molecules implicated in selective insulin signaling are unclear. To elucidate the hepatic mechanistic pathways affected by selective versus non-selective insulin resistance, we compared basal rates of hepatic glucose production and its components, gluconeogenesis and glycogenolysis, in patients with severe non-selective insulin resistance (insulin receptor mutations (INSR)) to patients with selective insulin resistance (lipodystrophy and type 2 diabetes). In 7 patients with INSR, 14 with lipodystrophy and 9 with type 2 diabetes, we measured rates of hepatic glucose production (via [6,6-2H2] glucose) and fractional gluconeogenesis (via 2H2O) after an overnight fast. Absolute rates of gluconeogenesis were calculated as the product of fractional gluconeogenesis and hepatic glucose production, and glycogenolysis were calculated as hepatic glucose production minus gluconeogenesis. In patients with INSR, lipodystrophy and type 2 diabetes, HbA1c (8.2 ± 2.8, 8.4 ± 1.9, 7.4 ± 0.9%) and fasting glucose (120 ± 70, 159 ± 55, 127 ± 32 mg/dl) were comparable (P>0.05). Fasting serum insulin was higher in INSR vs. lipodystrophy and type 2 diabetes (332 ± 355, 48 ± 50, 50 ± 16 μU/ml; P<0.01). Patients with INSR and lipodystrophy had higher hepatic glucose production vs. type 2 diabetes (24.0 ± 4.0, 24.1 ± 6.2, 15.8 ± 4.3 µmol/kgLEAN/min; P<0.01). Fractional gluconeogenesis was higher in INSR vs. lipodystrophy and type 2 diabetes (77.1 ± 9.4, 55.4 ± 11.5, 59.1 ± 5.9%; P<0.01). Absolute gluconeogenesis was highest in INSR, intermediate in lipodystrophy, and lowest in type 2 diabetes (19.1 ± 4.4, 13.5 ± 4.2, 9.5 ± 1.9 µmol/kgLEAN/min; P<0.01). Glycogenolysis was lowest in INSR, highest in lipodystrophy, and intermediate in type 2 diabetes (4.9 ± 2.2 vs. 10.6 ± 4.8, 6.3 ± 2.6 µmol/kgLEAN/min; P<0.01). Higher hepatic glucose production in lipodystrophy vs. type 2 diabetes is consistent with higher hepatic insulin resistance in patients with lipodystrophy, but comparable fractional rates of gluconeogenesis and glycogenolysis confirm similar mechanisms of selective post-receptor insulin resistance. By contrast, the markedly higher contribution of gluconeogenesis to hepatic glucose production in INSR may reflect complete loss of insulin signaling for glycogen accumulation and/or suppression of gluconeogenesis. Further studies should evaluate whether greater substrate and fuel availability for gluconeogenesis, and/or lower hepatic glycogen stores are important determinants of the components of glucose production in patients with non-selective insulin resistance due to INSR mutation.

Low metformin causes a more oxidized mitochondrial NADH/NAD redox state in hepatocytes and inhibits gluconeogenesis by a redox-independent mechanism

The mechanisms by which metformin (dimethylbiguanide) inhibits hepatic gluconeogenesis at concentrations relevant for type 2 diabetes therapy remain debated. Two proposed mechanisms are 1) inhibition of mitochondrial Complex 1 with consequent compromised ATP and AMP homeostasis or 2) inhibition of mitochondrial glycerophosphate dehydrogenase (mGPDH) and thereby attenuated transfer of reducing equivalents from the cytoplasm to mitochondria, resulting in a raised lactate/pyruvate ratio and redox-dependent inhibition of gluconeogenesis from reduced but not oxidized substrates. Here, we show that metformin has a biphasic effect on the mitochondrial NADH/NAD redox state in mouse hepatocytes. A low cell dose of metformin (therapeutic equivalent: <2 nmol/mg) caused a more oxidized mitochondrial NADH/NAD state and an increase in lactate/pyruvate ratio, whereas a higher metformin dose (≥5 nmol/mg) caused a more reduced mitochondrial NADH/NAD state similar to Complex 1 inhibition by rotenone. The low metformin dose inhibited gluconeogenesis from both oxidized (dihydroxyacetone) and reduced (xylitol) substrates by preferential partitioning of substrate toward glycolysis by a redox-independent mechanism that is best explained by allosteric regulation at phosphofructokinase-1 (PFK1) and/or fructose 1,6-bisphosphatase (FBP1) in association with a decrease in cell glycerol 3-phosphate, an inhibitor of PFK1, rather than by inhibition of transfer of reducing equivalents. We conclude that at a low pharmacological load, the metformin effects on the lactate/pyruvate ratio and glucose production are explained by attenuation of transmitochondrial electrogenic transport mechanisms with consequent compromised malate-aspartate shuttle and changes in allosteric effectors of PFK1 and FBP1.

Hypoglycaemic activity of Bauhinia holophylla through GSK3-β inhibition and glycogenesis activation

Context: Bauhinia L. species, including Bauhinia holophylla (Bong.) Steud. (Fabaceae), have traditionally been used to treat diabetes. Bauhinia is a complex botanical genus, and the indiscriminate use of the diverse Bauhinia species is reflected in the experimental divergence of their medicinal potential.Objective: The hypoglycaemic and hypolipidaemic effects, molecular mechanism of action and phytochemical properties of an authentic extract of B. holophylla leaves were evaluated.Materials and methods: A phytochemical study of a 70% EtOH extract was performed using FIA-ESI-IT-MS/MSn and HPLC-PAD-ESI-IT-MS. The extract (200 or 400 mg/kg b.w.) was administered for 14 days to streptozotocin-induced diabetic Swiss mice. Glucose tolerance and insulin sensitivity, blood parameters, gene and protein expression, and the in vivo and in vitro inhibition of intestinal glucosidases were assessed.Results: HPLC-PAD-ESI-IT-MS analysis identified flavonoid derivatives of quercetin, myricetin, luteolin and kaempferol. Treatment with 400 mg/kg of the extract reduced blood glucose (269.0 ± 32.4 mg/dL vs. 468.0 ± 32.2 mg/dL for diabetic animals), improved glucose tolerance, decreased cholesterol and triglyceride levels, and increased the mRNA expression of proteins involved in glucogenesis in the liver and muscle, such as PI3-K/Akt, GS, GSK3-β (ser-9), AMPK and Glut4. The activity of intestinal maltase was inhibited in vitro (IC50: 43.0 µg/mL for the extract compared to 516.4 µg/mL for acarbose) and in vivo.Discussion and conclusions: Treatment with B. holophylla was associated with a marked hypoglycaemic effect through the stimulation of glycogenesis and inhibition of gluconeogenesis and intestinal glucose absorption, without increasing basal insulinaemia.

Effects of sodium salicylate on glucose kinetics and insulin signaling in postpartum dairy cows

Low-grade inflammation has been implicated as a contributor to metabolic disease during the transition to lactation. In previous work, administration of sodium salicylate (SS) for 7 d led to hypoglycemia in mature dairy cows in early lactation. The purpose of this study was to identify the mode of action underlying this response to SS. Twenty mature (parity 3) cows were assigned alternately at time of calving to either control or SS treatments; the control received a molasses placebo in drinking water, whereas SS received 2.3 g/L of SS with the molasses carrier in drinking water for 7 d after parturition. Blood samples were collected daily. A glucose turnover assay was performed on d 7, followed by liver, muscle, and adipose tissue biopsies. There were no treatment effects on intake of dry matter or water. Tumor necrosis factor α mRNA abundance tended to be decreased by SS in adipose tissue but not in muscle or liver, and plasma haptoglobin and adiponectin concentrations were not altered by treatment. Treatment did not significantly alter plasma glucose or insulin concentrations, but plasma glucagon concentration tended to be increased by SS and the insulin:glucagon molar ratio was significantly decreased. Cows on SS had a tendency for a 25% decrease in glucose turnover rate compared with control cows. However, there were no differences in transcript abundance of pyruvate carboxylase (PC) or glucose-6-phosphatase (G6PC) in liver or of glucose transporter 4 (GLUT4) in any of the tissues. Finally, SS did not alter insulin receptor substrate-1 phosphorylation in muscle or adipose, but tended to increase phosphorylation of AMP-activated protein kinase and decrease protein kinase B phosphorylation in adipose tissue. These findings may be explained by enhanced hepatic insulin sensitivity leading to posttranscriptional suppression of gluconeogenesis and adaptive responses to decreased glucose supply in the pancreas and adipose tissue.

Alcohol-induced ketonemia is associated with lowering of blood glucose, downregulation of gluconeogenic genes, and depletion of hepatic glycogen in type 2 diabetic db/db mice

Alcoholic ketoacidosis and diabetic ketoacidosis are life-threatening complications that share the characteristic features of high anion gap metabolic acidosis. Ketoacidosis is attributed in part to the massive release of ketone bodies (e.g., β-hydroxybutyrate; βOHB) from the liver into the systemic circulation. To date, the impact of ethanol consumption on systemic ketone concentration, glycemic control, and hepatic gluconeogenesis and glycogenesis remains largely unknown, especially in the context of type 2 diabetes. In the present study, ethanol intake (36% ethanol- and 36% fat-derived calories) by type 2 diabetic db/db mice for 9 days resulted in significant decreases in weight gain (∼19.5% ↓) and caloric intake (∼30% ↓). This was accompanied by a transition from macrovesicular-to-microvesicular hepatic steatosis with a modest increase in hepatic TG (∼37% ↑). Importantly, ethanol increased systemic βOHB concentration (∼8-fold ↑) with significant decreases in blood glucose (∼4-fold ↓) and plasma insulin and HOMA-IR index (∼3-fold ↓). In addition, ethanol enhanced hepatic βOHB content (∼5-fold ↑) and hmgcs2 mRNA expression (∼3.7-fold ↑), downregulated key gluconeogenic mRNAs (e.g., Pcx, Pck1, and G6pc), and depleted hepatic glycogen (∼4-fold ↓). Furthermore, ethanol intake led to significant decreases in the mRNA/protein expression and allosteric activation of glycogen synthase (GS) in liver tissues regardless of changes in the phosphorylation of GS, GSK-3β, or Akt. Together, our findings suggest that ethanol-induced ketonemia may occur in concomitance with significant lowering of blood glucose concentration, which may be attributed to suppression of gluconeogenesis in the setting of glycogen depletion in type 2 diabetes.

Metformin associated lactic acidosis in the setting of acute kidney injury: a case report

Metformin is often a first choice medication for patients with type 2 diabetes mellitus. It is considered to have a high efficacy as well as a mild adverse drug effect profile, and can be used in both monotherapy and polytherapy regimens. The drug is not altered at the molecular level during metabolism, and is cleared almost entirely through the renal system, so the major comorbidity that practitioners consider when starting Metformin is renal disease. As a patient’s renal function declines, there can be a build-up of unaltered and active Metformin that can lead to toxic events. Metformin toxicity leads to a build-up of lactic acid, primarily through its inhibition of gluconeogenesis. The FDA has guidelines for Metformin use in patients with chronic kidney disease, but at this time, no guidelines exist for patients with acute kidney injury. We present a report on a sixty-four year old female with a long-standing history of diabetes type 2 on Metformin therapy who experienced an acute kidney injury secondary to dehydration as a sequlae of acute gastrointestinal upset. This case illustrates the toxic effects that Metformin can have at supratherapeutic levels, as well as the importance of the discontinuation of Metformin in circumstances that may lead to acute kidney injury.

Estrogen Improves Insulin Sensitivity and Suppresses Gluconeogenesis via the Transcription Factor Foxo1.

Premenopausal women exhibit enhanced insulin sensitivity and reduced incidence of type 2 diabetes (T2D) compared with age-matched men, but this advantage disappears after menopause with disrupted glucose homeostasis, in part owing to a reduction in circulating 17β-estradiol (E2). Fasting hyperglycemia is a hallmark of T2D derived largely from dysregulation of hepatic glucose production (HGP), in which Foxo1 plays a central role in the regulation of gluconeogenesis. Here, we investigated the action of E2 on glucose homeostasis in male and ovariectomized (OVX) female control and liver-specific Foxo1 knockout (L-F1KO) mice and sought to understand the mechanism by which E2 regulates gluconeogenesis via an interaction with hepatic Foxo1. In both male and OVX female control mice, subcutaneous E2 implant improved insulin sensitivity and suppressed gluconeogenesis; however, these effects of E2 were abolished in L-F1KO mice of both sexes. In our use of mouse primary hepatocytes, E2 suppressed HGP and gluconeogenesis in hepatocytes from control mice but failed in hepatocytes from L-F1KO mice, suggesting that Foxo1 is required for E2 action on the suppression of gluconeogenesis. We further demonstrated that E2 suppresses hepatic gluconeogenesis through activation of estrogen receptor (ER)α-phosphoinositide 3-kinase-Akt-Foxo1 signaling, which can be independent of insulin receptor substrates 1 and 2 (Irs1 and Irs2), revealing an important mechanism for E2 in the regulation of glucose homeostasis. These results may help explain why premenopausal women have lower incidence of T2D than age-matched men and suggest that targeting ERα can be a potential approach to modulate glucose metabolism and prevent diabetes.

Effect of oral magnesium sulfate administration on blood glucose hemostasis via inhibition of gluconeogenesis and FOXO1 gene expression in liver and muscle in diabetic rats

The present study was designed to investigate the possible role of Mg2+ in suppression of phosphoenolpyruvate carboxy kinase (PEPCK) enzyme via inhibition of FOXO1gene expression in liver and we also examined whether Mg contributes to decrease blood glucose in muscle via inhibiting FOXO1 gene and protein expression. Fifty rats in five groups of experiment were considered as; non-diabetic control (NDC), Mg2+-treated non-diabetic control (Mg2+-NDC), chronic diabetic (CD), Mg2+-treated chronic diabetic (Mg2+-CD), and insulin-treated chronic diabetic (Ins-CD). Streptozotocin (STZ) was used for diabetes induction. The Mg2+-CD and Mg2+-NDC groups received 10 g/l of magnesium sulfate (MgSO4) added to drinking water, and Ins-CD group received 2.5 U/kg of insulin. The blood glucose level and body weight were measured weekly. After 16 weeks, intraperitoneal glucose tolerance test (IPGTT) was done and blood samples were taken to determine the plasma levels of Mg and gastrocnemius muscle legs, and liver were isolated for both Forkhead transcription factor (FOXO1) and PEPCK enzyme genes and proteins expression. Administration of MgSO4 improved IPGTT, lowered blood glucose levels and decreased FOXO1 and PEPCK genes and proteins expression in muscle and liver, while insulin just could decrease FOXO1 gene and protein expression in the muscle. These findings illustrated that MgSO4 improved hyperglycemia via inhibition of FOXO1 gene and protein level in the muscle and liver, and it also decreased blood glucose level by prohibition of gluconeogenesis pathway in the liver. However, long time administration of insulin did not have any effect on liver.

Effect of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes.

We investigated the effects of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes (T2DM). Empagliflozin (OLETF-EMPA) or voglibose (OLETF-VOG) was administered to Otsuka Long-Evans Tokushima fatty (OLETF) rats once daily for 12 weeks. Control Long-Evans Tokushima Otsuka (LETO) and OLETF (OLETF-C) rats received saline. Blood glucose levels were significantly suppressed in OLETF-EMPA and OLETF-VOG compared with the OLETF-C group. The liver fat content was significantly higher in the OLETF-C group than in the OLETF-EMPA and OLETF-VOG. Hepatic gene expressions involved in gluconeogenesis (glucose 6-phosphatase [G6Pase], fructose-1,6-bisphosphatase [FBP1], and phosphoenolpyruvate carboxykinase [PEPCK]) and lipogenesis (acetyl-CoA carboxylase [ACC], fatty acid synthase [FAS], and sterol regulatory element-binding transcription factor 1c [SREBP-1c]) were significantly decreased in the OLETF-EMPA group compared with other OLETF groups (OLETF-C and OLETF-VOG). Sirtuin 1 (SIRT1) expression level and SIRT1 activity were markedly reduced in OLETF-C rats; however, its expression increased in the OLETF-EMPA and OLETF-VOG. AMP-activated protein kinase (AMPK) phosphorylation level was remarkably increased by empagliflozin treatment in OLETF rats compared with other OLETF groups. Long-term empagliflozin and voglibose treatment reduced hepatic steatosis with suppression of gluconeogenesis and lipogenesis pathway in OLETF rats. We suggest that this metabolic improvement might be related to SIRT1 and AMPK pathway in T2DM. But empagliflozin is thought to have more advantage to prevent hepatic steatosis than voglibose in T2DM.

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.

Lipid deposition pattern and adaptive strategy in response to dietary fat in Chinese perch (Siniperca chuatsi)

BackgroundPrevious studies in teleost have demonstrated the adaptive strategy to maintain hepatic lipid homeostasis within certain limit. The excess of fat-intake could induce abnormal lipid deposition in liver but not adipose tissue. However, the molecular mechanism between the impaired lipid homeostasis and the aggravated lipid deposition in liver has not been elucidated well in fish.MethodsFour isonitrogenous diets with different fat levels (2, 7, 12 and 17%) were formulated, named L2, L7, L12 and L17 respectively, and fed Chinese perch (44.50 ± 0.25 g) to apparent satiation for five weeks. Growth index, triglyceride concentrations and expression of genes involved in lipid metabolism were measured.ResultsThe maximal growth performance and food intake were observed in L12 group. The lipid content in liver and serum were comparable in L2, L7 and L12 groups, while they were increased significantly in L17 group. Histology analysis also demonstrated that mass lipid droplets emerged in hepatocyte and then induced hepatic steatosis in L17 group. Compared to L2 group, the lipolytic genes related to fatty acids (FAs) transport (lpl & hl) and FAs β-oxidation (cpt1 & cs) were increased in L7 and L12 group. Relative mRNA levels of the gluconeogenesis (pc, pepck & g6pase) were also increased, in contrast, the lipogenic genes (srebp1, accα & fas) were decreased. Compared to L12 group, L17 group had higher mRNA levels of the FAs transport and the lipogenesis. But the lipolytic genes related to FAs β-oxidation were steady and the mRNA levels of gluconeogenesis were down-regulated instead.ConclusionsWithin certain limit, the increase of dietary fat in L7 and L12 group was propitious to reduce the consumption of protein and improve growth performance in Chinese perch. It was due to the homeostasis of hepatic triglyceride (TG) pool and serum glucose through promoting the FAs β-oxidation and gluconeogenesis respectively. Both the increase of lipogenesis and the absence of FAs β-oxidation in L17 group could trigger the esterification of FAs, indeed, the inhibition of gluconeogenesis could also aggravate triglyceride accumulation in liver and induce hepatic steatosis.

The food additive BHA modifies energy metabolism in the perfused rat liver

A study of the effects of butylated hydroxyanisole (BHA) on the hepatic metabolism was conducted with emphasis on parameters linked to energy metabolism and mitochondrial reactive oxygen species production. The experimental systems were the isolated perfused rat liver and isolated mitochondria. It was found that BHA inhibits biosynthetic pathways (gluconeogenesis) and ammonia detoxification, which are dependent on ATP generated within the mitochondria. Conversely, the compound stimulated glycolysis and fructolysis, which are compensatory phenomena for an inhibited mitochondrial ATP generation. Furthermore, BHA diminished the cellular ATP content under conditions where the mitochondrial respiratory chain was the only source of this compound. Inhibition of gluconeogenesis started at the concentration of 50 μM and was generally pronounced at concentrations under 200 μM. Several effects, however, were prominent only at the concentrations of 500 and 750 μM. BHA can be considered, thus, a mild metabolic agent that becomes toxic only at high doses. An aggravating factor could be the observation that BHA exerts a net stimulating action on reactive oxygen species (ROS) production in isolated mitochondria, an observation that contradicts the general notion that the compound acts primarily as an antioxidant. Considerable time was required for the reversion of most effects after removal of the compound from the circulation. In toxicological terms, besides the lack of circulating glucose, one can expect metabolic acidosis due to excess lactate production, impairment of ammonia detoxification and cell damage due to a deficient maintenance of its homeostasis and possible excessive ROS production.

Molecular Mechanisms of the Effects of Metformin on the Functional Activity of Brain Neurons

Metformin (MF) is the most widely used drug for the treatment of type 2 diabetes mellitus and metabolic syndrome (MS). In the peripheral tissues, MF inhibits mitochondrial respiratory chain complex I and increases the activity of AMP-activated protein kinase (AMPK), leading to suppression of gluconeogenesis in the liver, increased insulin sensitivity, increased glucose utilization, and normalization of lipid metabolism. Recent years have seen the appearance of experimental and clinical evidence showing that the CNS is also a major target of MF, such that the action of MF on the functional state of neurons can be mediated both via AMPK-dependent and via AMPK-independent signal cascades. In contrast to the periphery, MF does not activate but suppresses AMPK activity in hypothalamic neurons, this influencing the ratio of anorexigenic (melanocortin peptides) and orexigenic (neuropeptide Y) factors and altering feeding behavior. A significant contribution to this effect is made by MF-induced activation of the leptin-dependent STAT3 signal cascade. As the leptin and melanocortin systems targeted by MF interact closely with the insulin and monoamine systems, MF, acting through them, affects the entire integrative signal system of the brain, on which the functioning of the nervous, endocrine, cardiovascular, and other body systems depend. This review analyzes and systematizes data on the molecular mechanisms and targets of the action of MF in brain neurons, and the effects of this drug, which are mediated or may be mediated by the interactions of MF with the CNS.

Synergistic effects of dietary carbohydrate and taurine on growth performance, digestive enzyme activities and glucose metabolism in juvenile turbot Scophthalmus maximus L.

A 10-week feeding trial was conducted to evaluate the effects of taurine on growth performance, digestive enzyme activities and glucose metabolism of juvenile turbot Scophthalmus maximus (initial body weight, 3.66 ± 0.02 g) fed diets with different carbohydrate level. With a 2 × 3 two factoral experimental design, two levels of dietary carbohydrate (15% and 21%, respectively) with three levels of taurine (0.4%, 1.2%, and 2.0%, respectively) were used. In addition, the diet with 15% carbohydrate and without taurine supplementation was used as the control. The results showed that, compared with the control group, 1.2% of dietary taurine supplementation significantly increased the specific growth rate, the activities of amylase and lipase in intestine, glycogen content and the mRNA levels of glucokinase, phosphofructokinase, pyruvate kinase, glucose-6-phosphate dehydrogenase (G6PD), glycogen synthase (GS) and glucose transporter 2 in liver at 15% of dietary carbohydrate level. Meanwhile, it significantly decreased the blood glucose concentration and the mRNA levels of cytosolic phosphoenolpyruvate carboxykinase (cPEPCK) in liver. In addition, significant interaction between dietary carbohydrate and taurine were observed in blood glucose level. Compared to 15% dietary carbohydrate, 21% dietary carbohydrate significantly increased the blood glucose level at 1.2% and 2.0% dietary taurine level, whereas it had no significant effect at 0.4% dietary taurine supplementation level. At 21% of dietary carbohydrate level, although 1.2% and 2.0% of dietary taurine supplementation had no significant effects on blood glucose level, it significantly decreased the advanced glycationend products level in plasma and the fructose-1, 6-bisphosphatase mRNA level in liver. Moreover, compared to that fed diet with 15% carbohydrate, fish fed diet with 21% carbohydrate had lower activities of amylase and lipase in intestine and lower mRNA levels of G6PD, mitochondrial phosphoenolpyruvate carboxykinase and cPEPCK in liver. Furthermore, significant interactions between dietary carbohydrate and taurine were also observed in the expression of the genes involved in liver glucose metabolism above in addition to GS and cPEPCK. Overall, this study indicated that taurine had a beneficial effect on glucose homeostasis through enhancement of glycolysis, glucose transport, glycogen synthesis and the inhibition of gluconeogenesis in liver of turbot, thus decreased blood glucose level. However, the beneficial effect of taurine on glucose metabolism was affected by dietary carbohydrate level.