Glucose Output Research Articles

ERK2-Mediated Phosphorylation of Transcriptional Coactivator Binding Protein PIMT/NCoA6IP at Ser298 Augments Hepatic Gluconeogenesis

PRIP-Interacting protein with methyl transferase domain (PIMT) serves as a molecular bridge between CREB-binding protein (CBP)/ E1A binding protein p300 (Ep300) -anchored histone acetyl transferase and the Mediator complex sub-unit1 (Med1) and modulates nuclear receptor transcription. Here, we report that ERK2 phosphorylates PIMT at Ser298 and enhances its ability to activate PEPCK promoter. We observed that PIMT is recruited to PEPCK promoter and adenoviral-mediated over-expression of PIMT in rat primary hepatocytes up-regulated expression of gluconeogenic genes including PEPCK. Reporter experiments with phosphomimetic PIMT mutant (PIMTS298D) suggested that conformational change may play an important role in PIMT-dependent PEPCK promoter activity. Overexpression of PIMT and Med1 together augmented hepatic glucose output in an additive manner. Importantly, expression of gluconeogenic genes and hepatic glucose output were suppressed in isolated liver specific PIMT knockout mouse hepatocytes. Furthermore, consistent with reporter experiments, PIMTS298D but not PIMTS298A augmented hepatic glucose output via up-regulating the expression of gluconeogenic genes. Pharmacological blockade of MAPK/ERK pathway using U0126, abolished PIMT/Med1-dependent gluconeogenic program leading to reduced hepatic glucose output. Further, systemic administration of T4 hormone to rats activated ERK1/2 resulting in enhanced PIMT ser298 phosphorylation. Phosphorylation of PIMT led to its increased binding to the PEPCK promoter, increased PEPCK expression and induction of gluconeogenesis in liver. Thus, ERK2-mediated phosphorylation of PIMT at Ser298 is essential in hepatic gluconeogenesis, demonstrating an important role of PIMT in the pathogenesis of hyperglycemia.

Central visfatin potentiates glucose-stimulated insulin secretion and β-cell mass without increasing serum visfatin levels in diabetic rats

IntroductionOur previous study revealed that plasma visfatin levels were lower in pregnant women with gestational diabetes (GDM) than non-GDM independent of prepreganacy BMI. We examined whether central visfatin modulates energy and glucose homeostasis via altering insulin resistance, insulin secretion or islet morphometry in diabetic rats. MethodsPartial pancreatectomized, type 2 diabetic, rats were interacerbroventricularly infused with visfatin (100ng/rat/day, Px-VIS), visfatin+visfatin antagonist, CHS-828 (100μg/rat/day, Px-VIS-ANT), or saline (control, Px-Saline) via osmotic pump, respectively, for 4weeks. ResultsCentral visfatin improved insulin signaling (pAkt→pFOXO-1) but not pSTAT3 in the hypothalamus. Central visfatin did not alter serum visfatin levels in diabetic rats whereas the levels were higher in non-diabetic rats than diabetic rats. Body weight at the 2nd week was lowered in the Px-VIS group due to decreased food intake in the first two weeks compared to the Px-Saline group and energy expenditure was not significantly different among the treatment groups of diabetic rats. Visfatin antagonist treatment nullified the central visfatin effect. Px-VIS increased whole body glucose disposal rates in euglycemic hyperinsulinemic clamp compared to Px-Saline and lowered hepatic glucose output, whereas Px-VIS-ANT blocked the visfatin effect on insulin resistance (P<0.05). In hyperglycemic clamp study, the area under the curve of insulin in first and second phase were significantly higher in the Px-VIS group than the Px-Saline group without modifying insulin sensitivity at the hyperglycemic state, whereas the increase in serum insulin levels was blocked in the Px-VIS-ANT group. Central visfatin also increased β-cell mass by increasing β-cell proliferation. ConclusionsCentral visfatin improved glucose homeostasis by increasing insulin secretion and insulin sensitivity at euglycemia through the hypothalamus in diabetic rats. Therefore, visfatin is a positive modulator of glucose homeostasis by delivering the hypothalamic signals into the peripheries.

Type 2 Diabetes Mellitus in Children and Adolescents

Type 2 Diabetes Mellitus in Children and Adolescents

Type 2 Diabetes Mellitus in Children and Adolescents

On the basis of strong research evidence and consensus, type 1 diabetes mellitus (DM) remains the most common form of DM in children and adolescents. The incidence of type 2 DM in the pediatric population is rapidly increasing because of the obesity epidemic, and minority groups are disproportionately affected. (2) (10) (19) On the basis of some research evidence and consensus, it can be challenging to initially differentiate between type 2 DM and type 1 DM clinically because of the increased prevalence of obesity, the complex interplay of autoimmunity and obesity, and common symptoms at presentation. (1) (10) (19) Significant evidence and consensus support a genetic basis for the development of type 2 DM in children. Physicians should routinely screen at risk children older than age 10 years for DM. Screening criteria include obesity, a family history of type 2 DM, a minority racial or ethnic background, acanthosis nigricans, or other diseases associated with insulin resistance, including polycystic ovary syndrome, hypertension, or dyslipidemia. (1) (10) (18) (19) On the basis of consensus, diagnosis of type 2 DM can be confirmed by an elevated fasting blood glucose level greater than 126 mg/dl (7.0 mmol/L), an elevated 2-hour plasma glucose greater than 200 mg/dL (11.1 mmol/L) on an oral glucose tolerance test, an elevated random blood glucose greater than 200 mg/dL (11.1 mmol/L), or a hemoglobin A1c level greater than 6.5% with suggestive symptoms. (10) According to strong research evidence and consensus, once the diagnosis has been made, treatment should be based on the acuity of presentation and should focus on lifestyle modification and on normalizing hyperglycemia to minimize complications. Metformin is currently first-line treatment for type 2 DM in children and adolescents older than age 10 years who present nonacutely. (18) (19) Strong research evidence and consensus demonstrate that because type 2 DM has an insidious onset, microvascular and macrovascular complications can be present at the time of diagnosis. Patients should be screened for the presence of complications when the diagnosis of type 2 DM is made and in follow-up. (6) (10).

Alteration of De Novo Glucose Production Contributes to Fasting Hypoglycaemia in Fyn Deficient Mice

Previous studies have demonstrated that glucose disposal is increased in the Fyn knockout (FynKO) mice due to increased insulin sensitivity. FynKO mice also display fasting hypoglycaemia despite decreased insulin levels, which suggested that hepatic glucose production was unable to compensate for the increased basal glucose utilization. The present study investigates the basis for the reduction in plasma glucose levels and the reduced ability for the liver to produce glucose in response to gluconeogenic substrates. FynKO mice had a 5-fold reduction in phosphoenolpyruvate carboxykinase (PEPCK) gene and protein expression and a marked reduction in pyruvate, pyruvate/lactate-stimulated glucose output. Remarkably, de novo glucose production was also blunted using gluconeogenic substrates that bypass the PEPCK step. Impaired conversion of glycerol to glucose was observed in both glycerol tolerance test and determination of the conversion of 13C-glycerol to glucose in the fasted state. α-glycerol phosphate levels were reduced but glycerol kinase protein expression levels were not changed. Fructose-driven glucose production was also diminished without alteration of fructokinase expression levels. The normal levels of dihydroxyacetone phosphate and glyceraldehyde-3-phosphate observed in the FynKO liver extracts suggested normal triose kinase function. Fructose-bisphosphate aldolase (aldolase) mRNA or protein levels were normal in the Fyn-deficient livers, however, there was a large reduction in liver fructose-6-phosphate (30-fold) and fructose-1,6-bisphosphate (7-fold) levels as well as a reduction in glucose-6-phosphate (2-fold) levels. These data suggest a mechanistic defect in the allosteric regulation of aldolase activity.

Abstract 18968: Bromocriptine-QR: A Potential Novel Strategy for Cardiovascular Risk Reduction in Type 2 Diabetes

Type 2 diabetes (T2D) is associated with a substantially increased risk of cardiovascular disease (CVD). Of the available therapies for T2D, none have been conclusively shown to reduce CVD risk. Metformin has long been considered the only agent with some evidence, albeit limited, of a potential CVD benefit. Bromocriptine-QR (BQR), a quick release sympatholytic dopamine agonist, is a newer FDA-approved therapy for T2D. Based on preclinical and clinical study findings, it is postulated that BQR restores the normal circadian peak in central dopaminergic tone diminished in insulin resistant states, which in turn reduces hyperactive sympathetic tone and improves central fuel sensing thereby reducing postprandial hepatic glucose and lipid output as well as reduces vascular resistance, oxidative stress, and inflammation. In a one-year randomized trial of BQR vs. placebo added to standard therapy (diet and/or ≤ 2 diabetes medications including sulfonylureas, TZD, metformin, or insulin) in 3070 T2D subjects (average duration of T2D: 7.9 years), including individuals with pre-existing CVD, BQR therapy resulted in a 40% hazard rate reduction (HRR) in major CVD events, pre-specified as a composite of time to first myocardial infarction, stroke, coronary revascularization, hospitalization for angina or congestive heart failure. In the present study, this CVD effect of BQR was evaluated in a subset of this original study population on metformin +/- another anti-diabetes therapy at baseline (N = 1791). The composite CVD end point occurred in 16/1208 BQR-treated (1.3%) and 18/583 placebo-treated (3.1%) subjects resulting in a 53% CVD HRR (ITT group, Cox regression analysis; HR 0.47, 95% CI 0.24, 0.92, P = 0.028) adjusted by age (HR 1.08, 95% C.I. 1.04, 1.12, P = 0.0003) and pre-existing CVD (HR 2.27, 95% C.I. 1.02, 5.07, P = 0.041). Kaplan-Meier Curves of the cumulative incidence rate yielded a CVD HRR of 58% (HR 0.42, 95% C.I. 0.21, 0.85, Log-Rank = 0.017). These findings reaffirm prior observations of CVD risk reduction with BQR therapy and further demonstrate the potential for a marked additive effect of BQR above any derived from metformin, suggesting a potential novel strategy for CVD risk reduction in T2D.

Hepatic Notch Signaling Correlates With Insulin Resistance and Nonalcoholic Fatty Liver Disease

Hepatic Notch signaling is inappropriately activated in obese/insulin-resistant mouse models. Genetic or pharmacologic inhibition of hepatic Notch signaling in obese mice simultaneously improves glucose tolerance and reduces hepatic triglyceride content. As such, we predicted that Notch signaling in human liver would be positively associated with insulin resistance and hepatic steatosis. Here, we systematically survey Notch signaling in liver biopsy specimens, and show active Notch signaling in lean and obese adults, with expression of multiple Notch receptors and ligands. In morbidly obese patients undergoing bariatric surgery, we show that Notch activation positively correlates with glucose-6-phosphatase (G6PC) and phosphoenolpyruvate carboxykinase (PCK1) expression, key regulators of hepatic glucose output. We used immunofluorescence to identify active Notch signaling in hepatocytes and show highest activity in hyperglycemia, which we confirmed is a direct effect of hyperglycemia and insulin resistance. In a validation cohort of leaner individuals undergoing percutaneous liver biopsy for suspected nonalcoholic fatty liver disease (NAFLD), Notch activity showed independent positive association with insulin resistance and hepatic steatosis. Notably, Notch activity showed stronger correlation with the NAFLD activity score and alanine aminotransferase levels than with steatosis alone, suggesting that Notch activity is associated with nonalcoholic steatohepatitis. In summary, this study establishes that Notch signaling is activated in and may represent a therapeutic target for patients with obesity-related liver disease.

Periodic-Zone Model Predictive Control for Diurnal Closed-Loop Operation of an Artificial Pancreas

The objective of this research is an artificial pancreas (AP) that performs automatic regulation of blood glucose levels in people with type 1 diabetes mellitus. This article describes a control strategy that performs algorithmic insulin dosing for maintaining safe blood glucose levels over prolonged, overnight periods of time and furthermore was designed with outpatient, multiday deployment in mind. Of particular concern is the prevention of nocturnal hypoglycemia, because during sleep, subjects cannot monitor themselves and may not respond to alarms. An AP intended for prolonged and unsupervised outpatient deployment must strategically reduce the risk of hypoglycemia during times of sleep, without requiring user interaction. A diurnal insulin delivery strategy based on predictive control methods is proposed. The so-called "periodic-zone model predictive control" (PZMPC) strategy employs periodically time-dependent blood glucose output target zones and furthermore enforces periodically time-dependent insulin input constraints to modulate its behavior based on the time of day. The proposed strategy was evaluated through an extensive simulation-based study and a preliminary clinical trial. Results indicate that the proposed method delivers insulin more conservatively during nighttime than during daytime while maintaining safe blood glucose levels at all times. In clinical trials, the proposed strategy delivered 77% of the amount of insulin delivered by a time-invariant control strategy; specifically, it delivered on average 1.23 U below, compared with 0.31 U above, the nominal basal rate overnight while maintaining comparable, and safe, blood glucose values. The proposed PZMPC algorithm strategically prevents nocturnal hypoglycemia and is considered a significant step toward deploying APs into outpatient environments for extended periods of time in full closed-loop operation.

HNF4α contributes to glucose formation in aged rat hepatocytes

Aging-dependent physiological conditions are attributed to parenchymal structural changes to cellular functions in aged organisms. Compared to the young animals, the primary hepatocytes from old rats showed a higher glucose output and a higher expression of the key gluconeogenesis-regulating enzyme, phosphoenol pyruvate carboxykinase (PEPCK). The primary hepatocytes from old rats showed a higher glucose output and a higher expression of the key gluconeogenesis-regulating enzyme, phosphoenol pyruvate carboxykinase (PEPCK), compared with those from the young animals. The in situ hybridization study showed increased PEPCK mRNA expression in the aged liver tissues. The livers from old rats showed loosened hexagonal hepatic lobular structures, increased collagen accumulation, and high expression of the hypoxia marker hypoxia-inducible factor 1α (HIF1α). Hypoxia increased the PEPCK mRNA and protein expression levels in accordance with the HIF1α expression. PEPCK promoter luciferase reporter assay showed that hypoxia increased PEPCK through transcriptional activation. Furthermore, the hepatocyte nuclear factor α (HNF4α) protein, but not the HNF4α mRNA level, increased in parallel with the PEPCK mRNA expression under hypoxic conditions. Glucose production increased under hypoxic conditions, but this increment diminished by HNF4α siRNA in young hepatocytes. Moreover, increased glucose production from old rat hepatocytes was reversed by the down-regulation of HNF4α through a specific siRNA. This study suggests that the mild hypoxic conditions in response to aging-dependent hepatic structural changes may contribute to the induction of the gluconeogenic enzyme PEPCK through HNF4α protein stabilization.

Hepatocyte nuclear factors 1α/4α and forkhead box A2 regulate the solute carrier 2A2 (Slc2a2) gene expression in the liver and kidney of diabetic rats

AimsSolute carrier 2a2 (Slc2a2) gene codifies the glucose transporter GLUT2, a key protein for glucose flux in hepatocytes and renal epithelial cells of proximal tubule. In diabetes mellitus, hepatic and tubular glucose output has been related to Slc2a2/GLUT2 overexpression; and controlling the expression of this gene may be an important adjuvant way to improve glycemic homeostasis. Thus, the present study investigated transcriptional mechanisms involved in the diabetes-induced overexpression of the Slc2a2 gene. Main methodsHepatocyte nuclear factors 1α and 4α (HNF-1α and HNF-4α), forkhead box A2 (FOXA2), sterol regulatory element binding protein-1c (SREBP-1c) and the CCAAT-enhancer-binding protein (C/EBPβ) mRNA expression (RT-PCR) and binding activity into the Slc2a2 promoter (electrophoretic mobility assay) were analyzed in the liver and kidney of diabetic and 6-day insulin-treated diabetic rats. Key findingsSlc2a2/GLUT2 expression increased by more than 50% (P<0.001) in the liver and kidney of diabetic rats, and 6-day insulin treatment restores these values to those observed in non-diabetic animals. Similarly, the mRNA expression and the binding activity of HNF-1α, HNF-4α and FOXA2 increased by 50 to 100% (P<0.05 to P<0.001), also returning to values of non-diabetic rats after insulin treatment. Neither the Srebf1 and Cebpb mRNA expression, nor the SREBP-1c and C/EBP-β binding activity was altered in diabetic rats. SignificanceHNF-1α, HNF-4α and FOXA2 transcriptional factors are involved in diabetes-induced overexpression of Slc2a2 gene in the liver and kidney. These data point out that these transcriptional factors are important targets to control GLUT2 expression in these tissues, which can contribute to glycemic homeostasis in diabetes.

Long-Term Effects of Bariatric Surgery on Meal Disposal and β-Cell Function in Diabetic and Nondiabetic Patients

Gastric bypass surgery leads to marked improvements in glucose tolerance and insulin sensitivity in obese type 2 diabetes (T2D); the impact on glucose fluxes in response to a physiological stimulus, such as a mixed meal test (MTT), has not been determined. We administered an MTT to 12 obese T2D patients and 15 obese nondiabetic (ND) subjects before and 1 year after surgery (10 T2D and 11 ND) using the double-tracer technique and modeling of β-cell function. In both groups postsurgery, tracer-derived appearance of oral glucose was biphasic, a rapid increase followed by a sharp drop, a pattern that was mirrored by postprandial glucose levels and insulin secretion. In diabetic patients, surgery lowered fasting and postprandial glucose levels, peripheral insulin sensitivity increased in proportion to weight loss (∼30%), and β-cell glucose sensitivity doubled but did not normalize (compared with 21 nonsurgical obese and lean controls). Endogenous glucose production, however, was less suppressed during the MMT as the combined result of a relative hyperglucagonemia and the rapid fall in plasma glucose and insulin levels. We conclude that in T2D, bypass surgery changes the postprandial response to a dumping-like pattern and improves glucose tolerance, β-cell function, and peripheral insulin sensitivity but worsens endogenous glucose output in response to a physiological stimulus.

The Short Isoform of the Ubiquitin Ligase NEDD4L Is a CREB Target Gene in Hepatocytes

During cycles of fasting and feeding, liver function is regulated by both transcriptional and post-translational events. Regulated protein degradation has recently emerged as a key mechanism to control abundance of specific hepatic proteins under different nutritional conditions. As glucagon signaling through cAMP and PKA is central to glucose output during fasting, we hypothesized that this signaling pathway may also regulate ubiquitin ligases in the fasted state. Here we show that fasting stimuli promote expression of the short isoform of the E3 ubiquitin ligase Nedd4l in primary mouse hepatocytes. Nedd4l-short mRNA and NEDD4L (short isoform) protein accumulate in glucagon-treated primary mouse hepatocytes and in liver tissues during fasting. We identified a functional cAMP response element in the alternate Nedd4l-short promoter; mutation of this element blunts cAMP-induced expression of a Nedd4l reporter construct. CREB occupies the endogenous Nedd4l locus near this element. CREB and its co-activator CRTC2, both activated by fasting stimuli, contribute to glucagon-stimulated Nedd4l-short expression in primary hepatocytes. siRNA-mediated Nedd4l depletion in primary hepatocytes did not affect gluconeogenic gene expression, glucose output or glycogen synthesis. Our findings reveal a new mechanism of Nedd4l transcriptional regulation in liver cells.

Antihyperglycemic effect of a natural chicoric acid extract of chicory (Cichorium intybus L.): A comparative in vitro study with the effects of caffeic and ferulic acids

Ethnopharmacological relevanceIn Eurasia folk medicine, roots of chicory (Cichorium intybus L.) have been reported to exert antidiabetic benefits. In vitro, a natural chicoric acid extract (NCRAE) from Cichorium intybus root has been shown to increase insulin secretion by pancreatic β-cells and glucose uptake by muscle cells. Materials and methodsIn vitro experiments were designed to compare the effects of two hydroxycinnamic acids, caffeic and ferulic acids, to those obtained with NCRAE (50 and 100µg.mL−1) on the three major tissues implicated in glycemic regulation (pancreas, muscle and liver). In vivo experiments were performed in Wistar rats submitted to a daily intraperitoneal injection of NCRAE (3, 15 or 30mgkg−1) for 4 days. On the fourth day, an intraperitoneal glucose tolerance test (IPGTT; 1gkg−1) was carried out. ResultsOur results show that the three compounds we used are able each to induce an original response. Caffeic acid mainly promotes a decrease in hepatic glycogenolysis. Ferulic acid elicits a clear increase of insulin release and a reduction of hepatic glycogenolysis. However, this compound induces an inhibition of muscle glucose uptake. NCRAE provokes an increase of insulin release and glucose uptake without any effect on hepatic glycogenolysis. We could also show that none of these compounds implicates hepatic glucose 6-phosphatase in contrast to chlorogenic acid, known as an inhibitor of glucose 6-phosphatase and which is able to decrease glucose output from hepatocytes. Our results point out that NCRAE is able to decrease blood glucose without any effect hepatic effect. Our in vivo experiments bring evidence that 4 daily IP administrations of NCRAE improve IP glucose tolerance in a dose-dependent manner and mainly via an insulin sensitizing effect. ConclusionsWe conclude that NCRAE presents an antihyperglycemic effect essentially due to a peripheral effect on muscle glucose uptake.

Age-related differences in glycaemic control in diabetes

Age-related differences in glycaemic control in diabetes

Intermittent Hypoxia Impairs Glucose Homeostasis in C57BL6/J Mice: Partial Improvement with Cessation of the Exposure

Obstructive sleep apnea is associated with insulin resistance, glucose intolerance, and type 2 diabetes mellitus. Although several studies have suggested that intermittent hypoxia in obstructive sleep apnea may induce abnormalities in glucose homeostasis, it remains to be determined whether these abnormalities improve after discontinuation of the exposure. The objective of this study was to delineate the effects of intermittent hypoxia on glucose homeostasis, beta cell function, and liver glucose metabolism and to investigate whether the impairments improve after the hypoxic exposure is discontinued. C57BL6/J mice were exposed to 14 days of intermittent hypoxia, 14 days of intermittent air, or 7 days of intermittent hypoxia followed by 7 days of intermittent air (recovery paradigm). Glucose and insulin tolerance tests were performed to estimate whole-body insulin sensitivity and calculate measures of beta cell function. Oxidative stress in pancreatic tissue and glucose output from isolated hepatocytes were also assessed. Intermittent hypoxia increased fasting glucose levels and worsened glucose tolerance by 67% and 27%, respectively. Furthermore, intermittent hypoxia exposure was associated with impairments in insulin sensitivity and beta cell function, an increase in liver glycogen, higher hepatocyte glucose output, and an increase in oxidative stress in the pancreas. While fasting glucose levels and hepatic glucose output normalized after discontinuation of the hypoxic exposure, glucose intolerance, insulin resistance, and impairments in beta cell function persisted. Intermittent hypoxia induces insulin resistance, impairs beta cell function, enhances hepatocyte glucose output, and increases oxidative stress in the pancreas. Cessation of the hypoxic exposure does not fully reverse the observed changes in glucose metabolism.

Effects of small interfering RNA-mediated hepatic glucagon receptor inhibition on lipid metabolism in db/db mice

Hepatic glucose overproduction is a major characteristic of type 2 diabetes. Because glucagon is a key regulator for glucose homeostasis, antagonizing the glucagon receptor (GCGR) is a possible therapeutic strategy for the treatment of diabetes mellitus. To study the effect of hepatic GCGR inhibition on the regulation of lipid metabolism, we generated siRNA-mediated GCGR knockdown (si-GCGR) in the db/db mouse. The hepatic knockdown of GCGR markedly reduced plasma glucose levels; however, total plasma cholesterol was increased. The detailed lipid analysis showed an increase in the LDL fraction, and no change in VLDL HDL fractions. Further studies showed that the increase in LDL was the result of over-expression of hepatic lipogenic genes and elevated de novo lipid synthesis. Inhibition of hepatic glucagon signaling via siRNA-mediated GCGR knockdown had an effect on both glucose and lipid metabolism in db/db mice.

Cynara Scolymus Leaf Extract Stimulates Adipogenesis in 3T3-L1 Preadipocytes and Suppresses Hepatic Glucose Output in H4IIE Hepatocytes

Insulin resistance is the hallmark of type 2 diabetes and is characterized by ectopic fat accumulation in insulin-sensitive tissues, including liver and skeletal muscle. Artichoke (Cynara scolymus) is 1 of the most commonly consumed foods around the world. Leaf extract of C. scolymus is reported to have important therapeutic activities. However, few studies have assessed the possible antidiabetic effects of artichoke extracts. In this study, we investigated the effects of artichoke leaf extract on adipogenesis in 3T3-L1 cells and on glucose-6-phosphatase (G6Pase) activity in H4IIE hepatocytes. Preadipocytes were incubated with 25 μg/ mL of the leaf extract and lipid accumulation was assessed by AdipoRed assay. Rosiglitazone (10 μM), an oral hypoglycemic thiazolidinedione PPAR-γ agonist, was used as a positive control. Hepatic insulin resistance results in increased hepatic glucose output, the main factor behind fasting hyperglycemia in type 2 diabetes. G6Pase is the rate-limiting enzyme of gluconeogenesis, hence its inhibition reduces hepatic glucose production. We tested the effect of artichoke leaf extract (25 μg/mL) on the production of glucose by H4IIE, insulin (100 nM) being used as the positive control. Our results show that C. scolymus leaf extract significantly stimulated adipogenesis in 3T3-L1 adipocytes by 4 fold, as compared to 7.8-fold increase by rosiglitazone. The artichoke extract also inhibited G6Pase activity by 30% in H4IIE hepatocytes, as compared to 60% for insulin. These findings support the antidiabetic potential of this plant product.

Identification of a New Class of Glucokinase Activators through Structure-Based Design

Glucose flux through glucokinase (GK) controls insulin release from the pancreas in response to high glucose concentrations. Glucose flux through GK also contributes to reducing hepatic glucose output. Because many individuals with type 2 diabetes appear to have an inadequacy or defect in one or both of these processes, compounds that can activate GK may serve as effective treatments for type 2 diabetes. Herein we report the identification and initial optimization of a novel series of allosteric glucokinase activators (GKAs). We discovered an initial thiazolylamino pyridine-based hit that was optimized using a structure-based design strategy and identified 26 as an early lead. Compound 26 demonstrated a good balance of in vitro potency and enzyme kinetic parameters and demonstrated blood glucose reductions in oral glucose tolerance tests in both C57BL/6J mice and high-fat fed Zucker diabetic fatty rats.

Tff3, as a novel peptide, regulates hepatic glucose metabolism.

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder strongly associated with hepatic glucose intolerance and insulin resistance. The trefoil peptides are a family of small regulatory proteins and Tff3 is widely expressed in multiple tissues including liver. But the roles of Tff3 in regulation of glucose metabolism and insulin sensitivity in liver remain unclear. Here we show that the hepatic Tff3 expression levels were decreased in ob/ob and high-fat diet-induced obese mice. Overexpression of Tff3 in primary mouse hepatocytes inhibited the expression of gluconeogenic genes, including G6pc, PEPCK and PGC-1α, subsequently decreasing cellular glucose output. GTT and ITT experiments revealed that adenovirus-mediated overexpression of Tff3 in diabetic or obese mice improved glucose tolerance and insulin sensitivity. Collectively, our results indicated that Tff3 peptides are involved in glucose homeostasis and insulin sensitivity, providing a promising peptide on new therapies against the metabolic disorders associated with T2DM.

Novel small-molecule AMPK activator orally exerts beneficial effects on diabetic db/db mice

AMP-activated protein kinase (AMPK), which is a pivotal guardian of whole-body energy metabolism, has become an attractive therapeutic target for metabolic syndrome. Previously, using a homogeneous scintillation proximity assay, we identified the small-molecule AMPK activator C24 from an optimization based on the original allosteric activator PT1. In this paper, the AMPK activation mechanism of C24 and its potential beneficial effects on glucose and lipid metabolism on db/db mice were investigated. C24 allosterically stimulated inactive AMPK α subunit truncations and activated AMPK heterotrimers by antagonizing autoinhibition. In primary hepatocytes, C24 increased the phosphorylation of AMPK downstream target acetyl-CoA carboxylase dose-dependently without changing intracellular AMP/ATP ratio, indicating its allosteric activation in cells. Through activating AMPK, C24 decreased glucose output by down-regulating mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) in primary hepatocytes. C24 also decreased the triglyceride and cholesterol contents in HepG2 cells. Due to its improved bioavailability, chronic oral treatment with multiple doses of C24 significantly reduced blood glucose and lipid levels in plasma, and improved the glucose tolerance of diabetic db/db mice. The hepatic transcriptional levels of PEPCK and G6Pase were reduced. These results demonstrate that this orally effective activator of AMPK represents a novel approach to the treatment of metabolic syndrome.