Ying Leng

Downregulation of diacylglycerol kinase delta contributes to hyperglycemia-induced insulin resistance.

Type 2 (non-insulin-dependent) diabetes mellitus is a progressive metabolic disorder arising from genetic and environmental factors that impair beta cell function and insulin action in peripheral tissues. We identified reduced diacylglycerol kinase delta (DGKdelta) expression and DGK activity in skeletal muscle from type 2 diabetic patients. In diabetic animals, reduced DGKdelta protein and DGK kinase activity were restored upon correction of glycemia. DGKdelta haploinsufficiency increased diacylglycerol content, reduced peripheral insulin sensitivity, insulin signaling, and glucose transport, and led to age-dependent obesity. Metabolic flexibility, evident by the transition between lipid and carbohydrate utilization during fasted and fed conditions, was impaired in DGKdelta haploinsufficient mice. We reveal a previously unrecognized role for DGKdelta in contributing to hyperglycemia-induced peripheral insulin resistance and thereby exacerbating the severity of type 2 diabetes. DGKdelta deficiency causes peripheral insulin resistance and metabolic inflexibility. These defects in glucose and energy homeostasis contribute to mild obesity later in life.

Role of AMP kinase and PPAR delta in the regulation of lipid and glucose metabolism in human skeletal muscle

The peroxisome proliferator-activated receptor (PPAR)δ has been implicated in the regulation of lipid metabolism in skeletal muscle. Furthermore, activation of PPARδ has been proposed to improve insulin sensitivity and reduce glucose levels in animal models of type 2 diabetes. We recently demonstrated that the PPARδ agonist GW501516 activates AMP-activated protein kinase (AMPK) and stimulates glucose uptake in skeletal muscle. However, the underlying mechanism remains to be clearly identified. In this study, we first confirmed that incubation of primary cultured human muscle cells with GW501516 induced AMPK phosphorylation and increased fatty acid transport and oxidation and glucose uptake. Using small interfering RNA, we have demonstrated that PPARδ expression is required for the effect of GW501516 on the intracellular accumulation of fatty acids. Furthermore, we have shown that the subsequent increase in fatty acid oxidation induced by GW501516 is dependent on both PPARδ and AMPK. Concomitant with these metabolic changes, we provide evidence that GW501516 increases the expression of key genes involved in lipid metabolism (FABP3, CPT1, and PDK4) by a PPARδ-dependent mechanism. Finally, we have also demonstrated that the GW501516-mediated increase in glucose uptake requires AMPK but not PPARδ. In conclusion, the PPARδ agonist GW501516 promotes changes in lipid/glucose metabolism and gene expression in human skeletal muscle cells by PPARδ- and AMPK-dependent and -independent mechanisms.

Emodin, a natural product, selectively inhibits 11β-hydroxysteroid dehydrogenase type 1 and ameliorates metabolic disorder in diet-induced obese mice

BACKGROUND AND PURPOSE 11β‐Hydroxysteroid dehydrogenase type 1 (11β‐HSD1) is an attractive therapeutic target of type 2 diabetes and metabolic syndrome. Emodin, a natural product and active ingredient of various Chinese herbs, has been demonstrated to possess multiple biological activities. Here, we investigated the effects of emodin on 11β‐HSD1 and its ability to ameliorate metabolic disorders in diet‐induced obese (DIO) mice.

Role of AMP-activated protein kinase in the coordinated expression of genes controlling glucose and lipid metabolism in mouse white skeletal muscle

Aims/hypothesisAMP-activated protein kinase (AMPK) regulates metabolic adaptations in skeletal muscle. The aim of this study was to investigate whether AMPK modulates the expression of skeletal muscle genes that have been implicated in lipid and glucose metabolism under fed or fasting conditions.MethodsTwo genetically modified animal models were used: AMPK γ3 subunit knockout mice (Prkag3−/−) and skeletal muscle-specific transgenic mice (Tg-Prkag3225Q) that express a mutant (R225Q) γ3 subunit. Levels of mRNA transcripts of genes involved in lipid and glucose metabolism in white gastrocnemius muscles of these mice (under fed or 16-h fasting conditions) were assessed by quantitative real-time PCR.ResultsWild-type mice displayed a coordinated increase in the transcription of skeletal muscle genes encoding proteins involved in lipid/oxidative metabolism (lipoprotein lipase, fatty acid transporter, carnitine palmitoyl transferase-1 and citrate synthase) and glucose metabolism (glycogen synthase and lactate dehydrogenase) in response to fasting. In contrast, these fasting-induced responses were impaired in Prkag3−/− mice. The transcription of genes involved in lipid and oxidative metabolism was increased in the skeletal muscle of Tg-Prkag3225Q mice compared with that in wild-type mice. Moreover, the expression of the genes encoding hexokinase II and 6-phosphofrucktokinase was decreased in Tg-Prkag3225Q mice after fasting.Conclusions/interpretationAMPK is involved in the coordinated transcription of genes critical for lipid and glucose metabolism in white glycolytic skeletal muscle.

Insulin signaling defects in type 2 diabetes.

In recent years, type 2 diabetes mellitus has been recognized as one of the most common metabolic disorders, affecting millions of people worldwide. The pathogenesis of type 2 diabetes involves a combination of genetic and environmental factors, which cause insulin resistance in target tissues and impaired insulin secretion from the pancreatic β-cells. Skeletal muscle accounts for the largest fraction of insulin-stimulated glucose disposal. Insulin resistance in skeletal muscle is characterized by an impairment in insulin regulated metabolic actions, including glucose transport, glycogen synthesis and gene expression [1,2]. In normal glucose-tolerant relatives of type 2 diabetic patients, insulin resistance in skeletal muscle has been observed several years before the development of overt diabetes [3]. Thus, insulin resistance in skeletal muscle might be an early defect in the pathogenesis of type 2 diabetes. During the past decade, intense interest has been focused on identifying the molecular defects responsible for insulin resistance in skeletal muscle in an effort to describe the pathogenesis of type 2 diabetes and to provide clues to the identity of new targets for drug therapy. This review will summarize the current understanding of the nature of the insulin signaling defects present in skeletal muscle from type 2 diabetic patients (Table 1) and current therapeutic approaches to improve insulin action in skeletal muscle.

Discovery of novel inhibitors of 11β-hydroxysteroid dehydrogenase type 1 by docking and pharmacophore modeling

11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) is a potential target for treatment of diabetes and metabolic syndrome. Docking and pharmacophore modeling have been used to discover novel inhibitors of 11beta-HSD1. Several compounds, with large structural diversity and good potency against 11beta-HSD1, have been found and their potency was determined by the enzyme assay. New scaffolds of 11beta-HSD1 inhibitors are also reported.

Arctigenin, a natural compound, activates AMP-activated protein kinase via inhibition of mitochondria complex I and ameliorates metabolic disorders in ob/ob mice

Aims/hypothesisArctigenin is a natural compound that had never been previously demonstrated to have a glucose-lowering effect. Here it was found to activate AMP-activated protein kinase (AMPK), and the mechanism by which this occurred, as well as the effects on glucose and lipid metabolism were investigated.Methods2-Deoxyglucose uptake and AMPK phosphorylation were examined in L6 myotubes and isolated skeletal muscle. Gluconeogenesis and lipid synthesis were evaluated in rat primary hepatocytes. The acute and chronic effects of arctigenin on metabolic abnormalities were observed in C57BL/6J and ob/ob mice. Changes in mitochondrial membrane potential were measured using the J-aggregate-forming dye, JC-1. Analysis of respiration of L6 myotubes or isolated mitochondria was conducted in a channel oxygen system.ResultsArctigenin increased AMPK phosphorylation and stimulated glucose uptake in L6 myotubes and isolated skeletal muscles. In primary hepatocytes, it decreased gluconeogenesis and lipid synthesis. The enhancement of glucose uptake and suppression of hepatic gluconeogenesis and lipid synthesis by arctigenin were prevented by blockade of AMPK activation. The respiration of L6 myotubes or isolated mitochondria was inhibited by arctigenin with a specific effect on respiratory complex I. A single oral dose of arctigenin reduced gluconeogenesis in C57BL/6J mice. Chronic oral administration of arctigenin lowered blood glucose and improved lipid metabolism in ob/ob mice.Conclusions/interpretationThis study demonstrates a new role for arctigenin as a potent indirect activator of AMPK via inhibition of respiratory complex I, with beneficial effects on metabolic disorders in ob/ob mice. This highlights the potential value of arctigenin as a possible treatment of type 2 diabetes.

Design, Synthesis, and Antidiabetic Activity of 4-Phenoxynicotinamide and 4-Phenoxypyrimidine-5-carboxamide Derivatives as Potent and Orally Efficacious TGR5 Agonists

4-Phenoxynicotinamide and 4-phenoxypyrimidine-5-carboxamide derivatives as potent and orally efficacious TGR5 agonists are reported. Several 4-phenoxynicotinamide derivatives were found to activate human and mouse TGR5 (hTGR5 and mTGR5) with EC50 values in the low nanomolar range. Compound 23g, with an EC50 value of 0.72 nM on hTGR5 and an EC50 value of 6.2 nM on mTGR5, was selected for further in vivo efficacy studies. This compound exhibited a significant dose-dependent glucagon-like peptide-1 (GLP-1) secretion effect. A single oral dose of 23g (50 mg/kg) significantly reduced blood glucose levels in db/db mice and caused a 49% reduction in the area under the blood glucose curve (AUC)0-120 min following an oral glucose tolerance test (OGTT) in imprinting control region (ICR) mice. However, 23g stimulated gallbladder filling, which might result in side effects to the gallbladder.

Structure-based virtual screening for identification of novel 11β-HSD1 inhibitors

Structure-based pharmacophore models were built by using LigandScout and used for virtual screening of the SPECS database to identify new potential 11beta-HSD1 inhibitors. As a refinement of the results obtained from virtual 3D pharmacophore screening, the best fitting virtual hits were subjected to docking study. The resulting compounds were tested in an enzyme assay and revealed several compounds with novel scaffolds that show sub-micromolar activity and high selectivity for 11beta-HSD1 against 11beta-HSD2.

Segetoside F a new triterpenoid saponin with inhibition of luteal cell from the seeds of Vaccaria segetalis

Abstract A new triterpenoid saponin, named segetoside F, showing strong inhibition of luteal cell activity, has been isolated from the seeds of Vaccaria segetalis. Its structure has been established by chemical reactions and spectral analyses.