Glucose Production In Hepatocytes Research Articles

Serum visfatin in type 2 diabetes mellitus

Abstract Introduction Obesity is commonly associated with insulin resistance and hyperinsulinemia and is the most important risk factor for type 2 diabetes. Visfatin is an adipokine that exerts insulin-mimetic effects that stimulate muscle and adipocyte glucose transport and inhibit hepatocyte glucose production. Purpose The aim of this study was to assess levels of visfatin and its relationship to obesity and insulin resistance in type 2 diabetes mellitus. Patients and methods This study included 40 patients with type 2 diabetes as the patient group: 20 of them were obese (BMI ≥ 30) and 20 were not (BMI < 25). Forty apparently healthy individuals matched for age and sex were included as the control group: 20 of them were obese (BMI ≥ 30) and the other 20 were not (BMI < 25). All patients and controls underwent history taking, physical examination including determination of BMI, and the following laboratory investigations: determination of levels of fasting blood glucose, 2 h postprandial blood glucose, serum cholesterol, triglycerides, fasting insulin, and fasting visfatin; kidney and liver function tests and calculation of homeostasis model of assessment-insulin resistance (HOMA-IR) were also performed. Neither the patients nor controls suffered from any chronic disease other than diabetes. Results The results of this study revealed a highly significant increase in the fasting serum insulin level, HOMA-IR, and fasting serum visfatin level among diabetic patients (26.10 ± 6.04μIU/ml, 12.18 ± 5.24, 36.70 ± 6.86 ng/ml, respectively) when compared with controls (12.10 ± 3.45μIU/ml, 2.42 ± 0.79, 13.63 ± 3.98 ng/ml, respectively; P < 0.01). Fasting insulin levels, HOMA-IR, and visfatin levels were significantly higher in obese diabetic patients (31.13 ± 4.34μIU/ml, 14.71 ± 6.22, 42.36 ± 4.11 ng/ml, respectively) than in obese controls (14.31±3.11mIU/ml, 2.89±0.77, 16.72 ± 3.16 ng/ml, respectively; P < 0.01). Visfatin levels were higher in nonobese diabetic patients than in nonobese controls. Moreover, visfatin levels were higher in obese diabetic patients (31.04 ± 3.49 ng/ml) than in nonobese diabetic patients (10.54 ± 1.53 ng/ml; P < 0.01). The present study revealed a highly significant positive correlation between levels of visfatin and fasting insulin in both obese and nonobese diabetic patients. Although there was a significant positive correlation between visfatin levels and HOMA-IR, there was no significant correlation between visfatin levels and BMI in obese diabetic patients. Conclusion Visfatin levels are increased in patients with type 2 diabetes regardless the degree of adiposity.

B-cell translocation gene-2 increases hepatic gluconeogenesis via induction of CREB

Hepatic gluconeogenesis is mediated by the network of transcriptional factors and cofactors. Here, we show that B-cell translocation gene-2 (BTG2) plays a crucial cofactor in hepatic gluconeogenesis via upregulation of the cyclic AMP (cAMP) response element binding (CREB) in hepatocytes. cAMP/dexamethasone (Dex) significantly increased BTG2 and other gluconeogenic genes such as Nur77, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6Pase) in hepatocytes. In contrast, insulin treatment completely blocks their expressions. Interestingly, overexpression of BTG2 using adenoviral system (Ad-BTG2) significantly elevated hepatic glucose production via the increase of transcriptional activity and gene expression of CREB, PEPCK, and G6Pase in hepatocytes, suggesting that BTG2 is the key player on hepatic glucose production. Physiological interaction studies demonstrated that BTG2 correlated CREB recruitment on the PEPCK gene promoter via a direct interaction. Finally, knockdown of endogenous BTG2 expression markedly inhibits the cAMP/Dex-induced transcriptional activity of gluconeogenic genes and glucose production in hepatocytes. Overall, the present study provides us with a novel molecular mechanism of BTG2-mediated induction of hepatic gluconeogenesis and suggests that BTG2 plays an important role in hepatic glucose metabolism.

The Wnt signaling pathway effector TCF7L2 is upregulated by insulin and represses hepatic gluconeogenesis

Certain single nucleotide polymorphisms (SNPs) in transcription factor 7-like 2 (TCF7L2) are strongly associated with the risk of type 2 diabetes. TCF7L2 and β-catenin (β-cat) form the bipartite transcription factor cat/TCF in stimulating Wnt target gene expression. cat/TCF may also mediate the effect of other signaling cascades, including that of cAMP and insulin in cell-type specific manners. As carriers of TCF7L2 type 2 diabetes risk SNPs demonstrated increased hepatic glucose production, we aimed to determine whether TCF7L2 expression is regulated by nutrient availability and whether TCF7L2 and Wnt regulate hepatic gluconeogenesis. We examined hepatic Wnt activity in the TOPGAL transgenic mouse, assessed hepatic TCF7L2 expression in mice upon feeding, determined the effect of insulin on TCF7L2 expression and β-cat Ser⁶⁷⁵ phosphorylation, and investigated the effect of Wnt activation and TCF7L2 knockdown on gluconeogenic gene expression and glucose production in hepatocytes. Wnt activity was observed in pericentral hepatocytes in the TOPGAL mouse, whereas TCF7L2 expression was detected in human and mouse hepatocytes. Insulin and feeding stimulated hepatic TCF7L2 expression in vitro and in vivo, respectively. In addition, insulin activated β-cat Ser⁶⁷⁵ phosphorylation. Wnt activation by intraperitoneal lithium injection repressed hepatic gluconeogenic gene expression in vivo, whereas lithium or Wnt-3a reduced gluconeogenic gene expression and glucose production in hepatic cells in vitro. Small interfering RNA-mediated TCF7L2 knockdown increased glucose production and gluconeogenic gene expression in cultured hepatocytes. These observations suggest that Wnt signaling and TCF7L2 are negative regulators of hepatic gluconeogenesis, and TCF7L2 is among the downstream effectors of insulin in hepatocytes.

Sodium caprate augments the hypoglycemic effect of berberine via AMPK in inhibiting hepatic gluconeogenesis

Berberine (BER), a natural product and active ingredient of genera Berberis and Coptis, has been demonstrated to possess anti-diabetic activities. However, the poor bioavailability of this agent greatly limits its clinical application. In our previous study, we demonstrated that co-administration of sodium caprate, an absorption enhancer, with BER could significantly increase the bioavailability of BER without any serious mucosal damage. Here, we investigated the effects of BER on AMP-activated protein kinase (AMPK)/gluconeogenesis pathway and the effects of sodium caprate on hypoglycemic action of BER. The ability of BER co-administered with sodium caprate to reduce insulin resistance was investigated in diabetic rat model induced by high-fat diet and low dose STZ. Western blot was performed to evaluate effects of BER on AMPK signaling proteins involved in hepatic gluconeogenesis in diabetic rat and HepG2 hepatocytes. BER reduced body weight and caused a significant improvement in glucose tolerance without altering food intake in diabetic rats. Similarly, BER reduced plasma triglycerides and improved insulin action in diabetic rats. BER down-regulated the elevated expressions of gluconeogenesis key enzymes PEPCK and G6Pase, inhibited the translocation of TORC2 from cytoplasm to nucleus and increased AMPK activity in liver tissues. The effect of BER was higher when co-administered with sodium caprate. BER treatment resulted in reduced glucose production in HepG2 hepatocytes. BER increased AMPK activity, reduced the expression of PEPCK, and the nuclear transcription factors PGC-1, HNF-4α and FOXO1. The effect of BER on gluconeogenesis could be partly blocked by AMPK inhibitor, Compound C. BER could suppress hepatic gluconeogenesis in rat model of diabetes at least in part via stimulation of AMPK activity and this action of BER is augmented by sodium caprate.

Effect of 20-hydroxyecdysone on glucose and lipid metabolism in vitro

Ecdysteroids such as 20-hydroxyecdysone (20HE) are commonly found in the highly nutritious Andean pseudocereal quinoa (Chenopodium quinoa Willd.). 20HE and an ecdysteroid-enriched extract from quinoa have been shown to improve insulin sensitivity and decrease adiposity in diet-induced obese mice. One proposed mechanism of action for this in vivo effect is 20HE's negative impact on hepatic glucose output. However, associated anti-diabetic and anti-obesity mechanims, including enhanced insulin sensitivity in peripheral tissues and changes to adipogenesis or lipid metabolism in adipose tissue, have not been reported. Here, we tested the effect of this molecule on these parameters by measuring (a) glucose uptake and insulin sensitivity in L6 rat myotubes, (b) lipid accumulation in 3T3-L1 mouse adipocytes, and (c) lipolysis in 3T3-L1 adipocytes. We also confirmed the impact of 20HE on glucose production in HII4E rat hepatocytes and showed that several fractions of a crude ethanolic extract from quinoa containing ecdysteroids similarly decrease glucose output in this model. Our data suggest that the complex mixture of secondary metabolites found in quinoa may play a synergistic role in the improvement of physiologic parameters associated with metabolic syndrome, and quinoa may be an important functional food for the treatment and prevention of diabetes and obesity.

The Influence of Social Status on Hepatic Glucose Metabolism in Rainbow TroutOncorhynchus mykiss

The effects of chronic social stress on hepatic glycogen metabolism were examined in rainbow trout Oncorhynchus mykiss by comparing hepatocyte glucose production, liver glycogen phosphorylase (GP) activity, and liver β-adrenergic receptors in dominant, subordinate, control, fasted, and cortisol-treated fish. Hepatocyte glucose production in subordinate fish was approximately half that of dominant fish, reflecting hepatocyte glycogen stores in subordinate trout that were just 16% of those in dominant fish. Fasting and/or chronic elevation of cortisol likely contributed to these differences based on similarities among subordinate, fasted, and cortisol-treated fish. However, calculation of the "glycogen gap"--the difference between glycogen stores used and glucose produced--suggested an enhanced gluconeogenic potential in subordinate fish that was not present in fasted or cortisol-treated trout. Subordinate, fasted, and cortisol-treated trout also exhibited similar GP activities (both total activity and that of the active or a form), and these activities were in all cases significantly lower than those in control trout, perhaps reflecting an attempt to protect liver glycogen stores or a modified capacity to activate GP. Dominant trout exhibited the lowest GP activities (20%-24% of the values in control trout). Low GP activities, presumably in conjunction with incoming energy from feeding, allowed dominant fish to achieve the highest liver glycogen concentrations (double the value in control trout). Liver membrane β-adrenoceptor numbers (assessed as the number of (3)H-CGP binding sites) were significantly lower in subordinate than in dominant trout, although this difference did not translate into attenuated adrenergic responsiveness in hepatocyte glucose production in vitro. Transcriptional regulation, likely as a result of fasting, was indicated by significantly lower β(2)-adrenoceptor relative mRNA levels in subordinate and fasted trout. Collectively, the data indicate that social status shapes liver metabolism and in particular glycogen metabolism, favoring accumulation of glycogen reserves from incoming energy in dominant fish and reliance on onboard fuels in subordinate fish.

Fatty acids-stress attenuates gluconeogenesis induction and glucose production in primary hepatocytes

BackgroundHepatic gluconeogenesis tightly controls blood glucose levels in healthy individuals, yet disorders of fatty acids (FAs) oxidation are characterized by hypoglycemia. We studied the ability of free-FAs to directly inhibit gluconeogenesis, as a novel mechanism that elucidates the hypoglycemic effect of FAs oxidation defects.MethodsPrimary rat hepatocytes were pre-treated with FAs prior to gluconeogenic stimuli with glucagon or dexamethasone and cAMP.ResultsPre-treatment with 1 mM FAs (mixture of 2:1 oleate:palmitate) for 1 hour prior to gluconeogenic induction, significantly decreases the induced expression of the gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6pase) as well as the induced glucose production by the cells. The inhibitory effect of FAs upon gluconeogenesis is abolished when pre-treatment is elongated to 18 hours, allowing clearance of FAs into triglycerides by the cells. Replacement of palmitate with the non-metabolic fatty acid 2-bromopalmitate inhibits esterification of FAs into triglycerides. Accordingly, the increased exposure to unesterified-FAs allows their inhibitory effect to be extended even when pre-treatment is elongated to 18 hours. Similar changes were caused by FAs to the induction of peroxisome-proliferator-activated receptor-γ coactivator 1α (PGC1α) expression, indicating this transcriptional coactivator as the mediating link of the effect. This inhibitory effect of FAs upon gluconeogenic induction is shown to involve reduced activation of cAMP response element-binding (CREB) transcription factor.ConclusionsThe present results demonstrate that free-FAs directly inhibit the induced gluconeogenic response in hepatocytes. Hence, high levels of free-FAs may attenuate hepatic gluconeogenesis, and liver glucose output.

Orphan Nuclear Receptor Estrogen-Related Receptor γ (ERRγ) Is Key Regulator of Hepatic Gluconeogenesis

Glucose homeostasis is tightly controlled by hormonal regulation of hepatic glucose production. Dysregulation of this system is often associated with insulin resistance and diabetes, resulting in hyperglycemia in mammals. Here, we show that the orphan nuclear receptor estrogen-related receptor γ (ERRγ) is a novel downstream mediator of glucagon action in hepatic gluconeogenesis and demonstrate a beneficial impact of the inverse agonist GSK5182. Hepatic ERRγ expression was increased by fasting-dependent activation of the cAMP-response element-binding protein-CRTC2 pathway. Overexpression of ERRγ induced Pck1 and G6PC gene expression and glucose production in primary hepatocytes, whereas abolition of ERRγ gene expression attenuated forskolin-mediated induction of gluconeogenic gene expression. Deletion and mutation analyses of the Pck1 promoter showed that ERRγ directly regulates the Pck1 gene transcription via ERR response elements of the Pck1 promoter as confirmed by ChIP assay and in vivo imaging analysis. We also demonstrate that GSK5182, an inverse agonist of ERRγ, specifically inhibits the transcriptional activity of ERRγ in a PGC-1α dependent manner. Finally, the ERRγ inverse agonist ameliorated hyperglycemia through inhibition of hepatic gluconeogenesis in db/db mice. Control of hepatic glucose production by an ERRγ-specific inverse agonist is a new potential therapeutic approach for the treatment of type 2 diabetes.

Abstract 5155: Suppression of gluconeogenesis in hepatocellular carcinoma by miR-23 directed downregulation of key gluconeogenic enzymes and the transcription factor PGC-1α

Abstract Although the mechanism and functional significance of high levels of aerobic glycolysis in cancer cells (Warburg effect) have been extensively studied, the possibility of altered gluconeogenesis that could potentially facilitate glycolytic pathway has not been explored. To examine this possibility, we investigated the potential alteration in expression of the key enzymes in gluconeogenesis pathway and its underlying mechanism using a mouse HCC model and primary human HCC. In the mouse model, C57/BL6 mice fed choline deficient and amino acid defined (CDAA) diet progressively develop nonalcoholic steatohepatitis (NASH), foci of altered hepatocytes (FAH) and ultimately hepatocellular carcinoma (HCC). The expression of genes encoding glucose-6-phosphatase (G6PC), phosphoenolpyruvate carboxykinase (PEPCK), fructose-1,6-bisphosphatase (FBP1), and pyruvate carboxylase (PC), key enzymes involved in gluconeogenesis, as well as PGC-1α, a transcription factor that regulates G6PC and PEPCK expression, was drastically reduced in the tumors. Increased serum ALT and decreased serum glucose levels correlated well with the liver damage and inhibition of gluconeogenesis in the tumor bearing mice. The mRNA levels G6PC, PEPCK, FBP1 and PGC-1α were also curtailed by ∼80% in the majority of primary human HCCs compared to matching peritumoral livers. Further, the glucose 6-phosphatase activity was markedly diminished in the mouse liver tumors and human primary HCCs, and G6PC expression correlated with tumor grade in human primary HCCs. The expression of miR-23a, a candidate microRNA targeting PGC-1α and G6PC, was significantly elevated in mouse and human HCCs. We established that PGC-1α and G6PC are direct targets of miR-23a and demonstrated that their expressions are inversely related to miR-23a expression in human HCCs. Furthermore, miR-23a negatively regulates glucose production in mouse hepatocytes in culture. The miR-23a level was upregulated following treatment of hepatic cells with IL-6 and significantly reduced by phospho-Stat3 inhibitor or siRNA-mediated depletion of Stat3, demonstrating the involvement of IL-6 signaling pathway in miR-23a expression. Positive regulation of miR-23a expression by IL-6-Stat3 signaling was further confirmed by ChIP analysis and miR-23a promoter-luciferase assay. This study has convincingly demonstrated severe compromise of gluconeogenesis in hepatocellular carcinoma in both mouse HCC model and primary HCC and elucidated its mechanism involving IL-Stat3-mediated activation of miR-23a, resulting in hypoglycemia (supported, in part, by the grant CA 086978-10 from the National Institutes of Health). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5155. doi:1538-7445.AM2012-5155

Herbal constituent sequoyitol improves hyperglycemia and glucose intolerance by targeting hepatocytes, adipocytes, and β-cells.

The prevalence of insulin resistance and type 2 diabetes increases rapidly; however, treatments are limited. Various herbal extracts have been reported to reduce blood glucose in animals with either genetic or dietary type 2 diabetes; however, plant extracts are extremely complex, and leading compounds remain largely unknown. Here we show that 5-O-methyl-myo-inositol (also called sequoyitol), a herbal constituent, exerts antidiabetic effects in mice. Sequoyitol was chronically administrated into ob/ob mice either orally or subcutaneously. Both oral and subcutaneous administrations of sequoyitol decreased blood glucose, improved glucose intolerance, and enhanced insulin signaling in ob/ob mice. Sequoyitol directly enhanced insulin signaling, including phosphorylation of insulin receptor substrate-1 and Akt, in both HepG2 cells (derived from human hepatocytes) and 3T3-L1 adipocytes. In agreement, sequoyitol increased the ability of insulin to suppress glucose production in primary hepatocytes and to stimulate glucose uptake into primary adipocytes. Furthermore, sequoyitol improved insulin signaling in INS-1 cells (a rat β-cell line) and protected INS-1 cells from streptozotocin- or H₂O₂-induced injury. In mice with streptozotocin-induced β-cell deficiency, sequoyitol treatments increased plasma insulin levels and decreased hyperglycemia and glucose intolerance. These results indicate that sequoyitol, a natural, water-soluble small molecule, ameliorates hyperglycemia and glucose intolerance by increasing both insulin sensitivity and insulin secretion. Sequoyitol appears to directly target hepatocytes, adipocytes, and β-cells. Therefore, sequoyitol may serve as a new oral diabetes medication.

Venlafaxine and atenolol disrupt epinephrine-stimulated glucose production in rainbow trout hepatocytes

The beta-blocker atenolol (ATEN), and the selective serotonin and norepinephrine reuptake inhibitor, venlafaxine (VEN) are found in municipal wastewater effluents, but little is known about the effect of these pharmaceuticals on aquatic animals. We tested the hypothesis that VEN and ATEN disrupt acute stress mediated glucose production in fish liver. To this end, rainbow trout ( Oncorhynchus mykiss) hepatocytes were exposed in vitro to different concentrations (0, 0.1, 10, 1000 nM) of VEN or ATEN and glucose production in response to either cortisol or epinephrine (two key stress hormones) was ascertained. Both VEN and ATEN did not affect either the unstimulated or cortisol (100 ng/mL)-stimulated glucose release over a 24 h period. The acute (3 h) unstimulated glucose production by isolated hepatocytes in suspension was also not modified by ATEN, while VEN (100 and 1000 nM) reduced basal glucose release. However, ATEN, even at concentration as low as 0.01 nM completely abolished epinephrine (1 μM)-induced glucose production in trout hepatocytes. Interestingly, VEN also suppressed epinephrine-induced glucose production but only at higher concentrations (100 and 1000 nM). Neither VEN nor ATEN significantly impacted the glucose production in response to either 8-bromo-cAMP (cAMP analogue) or glucagon (a metabolic hormone that increases glucose production) stimulation. ATEN but not VEN attenuated the epinephrine-induced increase in glucose transporter 2 (GLUT2) mRNA abundance in trout hepatocytes. Taken together, our results suggest that the impact of ATEN and VEN on glucose production involves inhibition of β-adrenoceptor signaling in trout hepatocytes. Overall, VEN and ATEN are beta-blockers and may disrupt the adaptive acute glucose response to a secondary stressor in rainbow trout.

Cannabinoid Receptor Type 1 (CB1R) Signaling Regulates Hepatic Gluconeogenesis via Induction of Endoplasmic Reticulum-bound Transcription Factor cAMP-responsive Element-binding Protein H (CREBH) in Primary Hepatocytes

Activated cannabinoid 1 receptor (CB1R) signaling has been implicated in the development of phenotypes associated with fatty liver, insulin resistance, and impaired suppression of hepatic glucose output. Endoplasmic reticulum stress-associated liver-specific transcription factor CREBH is emerging as a critical player in various hepatic metabolic pathways and regulates hepatic gluconeogenesis in diet-induced obese settings. In this study, we elucidated the critical role of CREBH in mediating CB1R signaling to regulate glucose homeostasis in primary rat and human hepatocytes. mRNA and protein levels and glucose production were analyzed in primary rat and human hepatocytes. ChIP assays were performed together with various transcriptional analyses using standard techniques. CB1R activation by 2-arachidonoylglycerol (2-AG) specifically induced CREBH gene expression via phosphorylation of the JNK signaling pathway and c-Jun binding to the AP-1 binding site in the CREBH gene promoter. 2-AG treatment significantly induced hepatic gluconeogenic gene expression and glucose production in primary hepatocytes, and we demonstrated that the CREBH binding site mutant significantly attenuated 2-AG-mediated activation of the gluconeogenic gene promoter. Endogenous knockdown of CREBH led to ablation of 2-AG-induced gluconeogenic gene expression and glucose production, and the CB1R antagonist AM251 or insulin exhibited repression of CREBH gene induction and subsequently inhibited gluconeogenesis in both rat and human primary hepatocytes. These results demonstrate a novel mechanism of action of activated CB1R signaling to induce hepatic gluconeogenesis via direct activation of CREBH, thereby contributing to a better understanding of the endocannabinoid signaling mechanism involved in regulating the hepatic glucose metabolism.

Regulator of G Protein Signaling (RGS16) Inhibits Hepatic Fatty Acid Oxidation in a Carbohydrate Response Element-binding Protein (ChREBP)-dependent Manner

G protein-coupled receptor (GPCR) pathways control glucose and fatty acid metabolism and the onset of obesity and diabetes. Regulators of G protein signaling (RGS) are GTPase-activating proteins (GAPs) for G(i) and G(q) α-subunits that control the intensity and duration of GPCR signaling. Herein we determined the role of Rgs16 in GPCR regulation of liver metabolism. Rgs16 is expressed during the last few hours of the daily fast in periportal hepatocytes, the oxygen-rich zone of the liver where lipolysis and gluconeogenesis predominate. Rgs16 knock-out mice had elevated expression of fatty acid oxidation genes in liver, higher rates of fatty acid oxidation in liver extracts, and higher plasma β-ketone levels compared with wild type mice. By contrast, transgenic mice that overexpressed RGS16 protein specifically in liver exhibited reciprocal phenotypes as well as low blood glucose levels compared with wild type littermates and fatty liver after overnight fasting. The transcription factor carbohydrate response element-binding protein (ChREBP), which induces fatty acid synthesis genes in response to high carbohydrate feeding, was unexpectedly required during fasting for maximal Rgs16 transcription in liver and in cultured primary hepatocytes during gluconeogenesis. Thus, RGS16 provides a signaling mechanism for glucose production to inhibit GPCR-stimulated fatty acid oxidation in hepatocytes.

FRUCTOSE INDUCES GLUCONEOGENESIS AND LIPOGENESIS THROUGH A SIRT1-DEPENDENT MECHANISM

Consumption of a fructose-rich diet leads to insulin resistance and dyslipidemia in part due to elevated gluconeogenesis and lipogenesis. SIRT1, an NAD(+)-dependent protein deacetylase, can induce gluconeogenesis and lipogenesis. The aim of this study was to determine whether fructose increased hepatic SIRT1, leading to induction of gluconeogenesis and lipogenesis. Rat hepatocytes were incubated with fructose (1-5 mM). SIRT1 protein, SIRT1 activity, and NAD(+)/NADH ratio were measured. The effects of SIRT1 inhibitors (EX-527 and nicotinamide) and activators (SIRT1 activator 3 and SRT1720) and the mitochondrial complex I inhibitor rotenone were examined on fructose-induced increases in gluconeogenesis and lipogenesis. Fructose increased SIRT1 protein, SIRT1 activity, and NAD(+)/NADH ratio. Fructose also induced gluconeogenesis, with increases in peroxisome proliferator-activated receptor coactivator 1-alpha (PGC1α) and phosphoenolpyruvate carboxykinase (PEPCK; gene code Pck1) gene expression, PEPCK activity, and hepatocyte glucose production. In addition, levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmgcr) and acetyl-coA carboxylase (Acc) mRNA, and intracellular cholesterol were increased. Increases in gluconeogenesis, Hmgcr, Acc, and cholesterol were abolished by SIRT1 inhibitors and rotenone, while SIRT1 activators increased gluconeogenesis, Hmgcr, Acc, Pgc1β, and sterol regulatory element-binding protein 1c (Srebp1c) gene expression. In conclusion, fructose induces gluconeogenesis and lipogenesis through a SIRT1-dependent mechanism, suggesting that induction of hepatic SIRT1 could play a pivotal role in the metabolic changes observed in humans and animals consuming a fructose-rich diet. These results highlight the need for a greater understanding of the role of SIRT1 in metabolic regulation and indicate the potential for adverse effects of SIRT1 activators if used therapeutically.

Inhibition of Glycogen Phosphorylase in the Context of Type 2 Diabetes, with Focus on Recent Inhibitors Bound at the Active Site

Among the variety of approaches for pharmacological intervention in T2DM, the inhibition of GP with the aim of reducing hepatic glucose output is a validated and thoroughly investigated strategy. Both the academia and health companies participate in the search of potent inhibitors, that might be suitable for long-term treatment. As several inhibitory sites have been identified for GP, interest focuses mainly on structures that can bind at either the catalytic, the allosteric, or the new allosteric sites. Glucose-based motifs and azasugars that bind at the active site constitute the most populated class of GPis. During the last two years, significant progresses have been made, since newly proposed motifs have K(i) values in the low micromolar and even sub- micromolar range. Without ignoring previously reported structures, new series based on β-D-glucopyranosyl-pyrimidine, D-glucopyranosylidene-spiro-isoxazoline and D-glucopyranosylidene-spiro-oxathiazole motifs appear promising. A representative from this last series, with a 2-naphthyl residue was identified as the most potent GPi to date (K(i) = 0.16 µM). While no inhibition was found for sulfonium analogs, D-DAB remains the best inhibitor among five and six-membered iminosugars that showed inhibitory properties toward GP. A study of glucagon-induced glucose production in primary rat hepatocytes has suggested that amylo-1,6-glucosidase inhibitors in combination with GPis may lower glucose level in T2DM. Considering the limitations found for other potent GPis binding at other sites and the complexity of pharmacological development, the potential of glucose-based GPis is still not established firmly and more tests with cells, tissues, animals are required to better establish the risks and merits of these structures, as antidiabetic drugs. Further studies might also confirm other directions where glucose-based GPis could be useful.

Discovery of potent and orally active tricyclic-based FBPase inhibitors

With the aim of exploring the effect of tricyclic-based FBPase inhibitors in cells and in vivo, a series of prodrugs of tricyclic phosphonates was designed and synthesized. Introducing prodrug moieties into tricyclic-based phosphonates led to the discovery of prodrug 15c, which strongly inhibited glucose production in monkey hepatocytes. Furthermore, prodrug 15c lowered blood glucose levels in fasted cynomolgus monkeys.

Cytoplasmic RIP140 negatively modulates adiponectin secretion in adipocytes

Receptor‐interacting protein 140 (RIP140) is known as a nuclear co‐repressor for various nuclear receptors. Recently, we identified a PKC epsilon‐triggered post‐translational modification pathway promotes RIP140 cytoplasmic accumulation which in turn blocks GLUT4 trafficking in adipocytes. Here we further examined the roles of cytoplasmic RIP140 in modulating adipokine secretion in adipocytes. We found that silencing RIP140 or PKC epsilon up‐regulated adiponectin secretion but did not affect its mRNA levels. Conditional medium from RIP140‐ or PKC epsilon‐knockdown 3T3‐L1 adipocytes increased glucose uptake in muscle cells as well as decreased glucose production in hepatocytes by promoting AMPK phosphorylation. However, adiponectin neutralized antibody can reverse conditional medium's effect on glucose uptake in muscle cells and glucose production in hepatocytes. Besides, we identified that endothelin‐1 (ET1) enhanced nuclear PKC epsilon activity resulted in RIP140 export from nucleus to cytoplasm, thus exerting its effect on inhibition of adiponectin secretion in adipocytes. Taken together, we demonstred that cytoplasmic RIP140 negatively modulates adiponectin secretion in adipocytes and provided evidence for targeting cytoplasmic RIP140 in adipocytes in promoting systemic insulin sensitivity.NIH grants DK54733, DK60521, DA11190 and K02‐DA13926 to L.‐N.W.

A prodrug approach towards the development of tricyclic-based FBPase inhibitors

For the purpose of reducing the strong CYP3A4 inhibitory potency of diamide prodrug 4, cyclic prodrugs of tricyclic-based FBPase inhibitors were synthesized. Extensive SAR studies led to the discovery of pyridine-containing cyclic prodrug 20, which strongly inhibited glucose production in monkey hepatocytes and also showed weak CYP3A4 inhibitory potency.

Fructose-1,6-bisphosphatase Inhibitors. 1. Purine Phosphonic Acids as Novel AMP Mimics

Inhibition of FBPase is considered a promising way to reduce hepatic gluconeogenesis and therefore could be a potential approach to treat type 2 diabetes. Herein we report the discovery of a series of purine phosphonic acids as AMP mimics targeting the AMP site of FBPase, which was achieved using a structure-guided drug design approach. These non-nucleotide purine analogues inhibit FBPase in a similar manner and with similar potency as AMP. More importantly, several purine analogues exhibited potent cellular and in vivo glucose-lowering activities, thus achieving proof-of-concept for inhibiting FBPase as a drug discovery target. For example, compounds 4.11 and 4.13 are as equipotent as AMP with regard to FBPase inhibition. Furthermore, compound 4.11 inhibited glucose production in primary rat hepatocytes and significantly lowered blood glucose levels in fasted rats.

Enhanced glucose synthesis in three-dimensional hepatocyte collagen matrix

Three-dimensional (3D) cell culture model offers a unique opportunity to study hepatocytes that require extracellular matrix to keep the cells at the differentiated state. In this report, we cultured isolated mouse hepatocytes in a 3D collagen matrix system and developed a protocol to measure glucose production at 3 h, 6 h, 18 h and 24 h after culture. The results demonstrated that hepatocytes cultured under 3D collagen matrix condition consistently produced glucose at 240–290 mg/10 6 cells for up to 24 h. Contrarily, hepatocytes cultured under traditional monolayer condition produced less than 50 mg/10 6 cells glucose. We demonstrated higher expression of phosphoenolpyruvate carboxykinase (PEPCK), a key enzyme for the synthesis of glucose from pyruvate, and CCAAT/enhancer-binding protein α (C/EBPα), an important liver-specific transcription factor, under the 3D collagen matrix culture condition in comparison to the monolayer condition. Thus, the 3D collagen matrix system preserved metabolic function of hepatocytes and can be used as an in vitro model for studying hepatocyte glucose production and gluconeogenesis.