C333H, a novel PPARalpha/gamma dual agonist, has beneficial effects on insulin resistance and lipid metabolism

Drug Discovery of Plausible Lead Natural Compounds That Target the Insulin Signaling Pathway: Bioinformatics Approaches

The growing smooth talk in the field of natural compounds is due to the ancient and current interest in herbal medicine and their potentially positive effects on health. Dozens of antidiabetic natural compounds were reported and tested in vivo, in silico, and in vitro. The role of these natural compounds, their actions on the insulin signaling pathway, and the stimulation of the glucose transporter-4 (GLUT4) insulin-responsive translocation to the plasma membrane (PM) are all crucial in the treatment of diabetes and insulin resistance. In this review, we collected and summarized a group of available in vivo and in vitro studies which targeted isolated phytochemicals with possible antidiabetic activity. Moreover, the in silico docking of natural compounds with some of the insulin signaling cascade key proteins is also summarized based on the current literature. In this review, hundreds of recent studies on pure natural compounds that alleviate type II diabetes mellitus (type II DM) were revised. We focused on natural compounds that could potentially regulate blood glucose and stimulate GLUT4 translocation through the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway. On attempt to point out potential new natural antidiabetic compounds, this review also focuses on natural ingredients that were shown to interact with proteins in the insulin signaling pathway in silico, regardless of their in vitro/in vivo antidiabetic activity. We invite interested researchers to test these compounds as potential novel type II DM drugs and explore their therapeutic mechanisms.

The Role of Peroxisome Proliferator-Activated Receptor Gamma and Atherosclerosis: Post-translational Modification and Selective Modulators

Atherosclerosis is the hallmark of cardiovascular disease (CVD) which is a leading cause of death in type 2 diabetes patients, and glycemic control is not beneficial in reducing the potential risk of CVD. Clinically, it was shown that Thiazolidinediones (TZDs), a class of peroxisome proliferator-activated receptor gamma (PPARγ) agonists, are insulin sensitizers with reducing risk of CVD, while the potential adverse effects, such as weight gain, fluid retention, bone loss, and cardiovascular risk, restricts its use in diabetic treatment. PPARγ, a ligand-activated nuclear receptor, has shown to play a crucial role in anti-atherosclerosis by promoting cholesterol efflux, repressing monocytes infiltrating into the vascular intima under endothelial layer, their transformation into macrophages, and inhibiting vascular smooth muscle cells proliferation as well as migration. The selective activation of subsets of PPARγ targets, such as through PPARγ post-translational modification, is thought to improve the safety profile of PPARγ agonists. Here, this review focuses on the significance of PPARγ activity regulation (selective activation and post-translational modification) in the occurrence, development and treatment of atherosclerosis, and further clarifies the value of PPARγ as a safe therapeutic target for anti-atherosclerosis especially in diabetic treatment.

A Network Pharmacology Study on the Active Components and Targets of the Radix Ginseng and Radix Bupleuri Herb Pair for Treating Nonalcoholic Fatty Liver Disease

OBJECTIVE

To explore the potential active components and corresponding target herb pairs of Radix Ginseng (Renshen) and Radix Bupleuri (Chaihu) in the treatment of nonalcoholic fatty liver disease (NAFLD) through network pharmacology and in vitro experiments.

METHODS

The active components and potential targets of the herb pair of Renshen and Chaihu were screened through a network database system, and Venn analysis was performed with the obtained NAFLD targets. The intersecting targets were analysed for gene ontology (GO) functions and Kyoto Encyclopedia of Genes and Genome (KEGG) pathways, and a protein-protein interaction (PPI) network was generated. Cytoscape software was used to construct active component-target networks of the Renshen and Chaihu herb pair. Free fatty acids were added to the HepG2 cell line to create high-fat models that were treated with different concentrations of stigmasterol. The effect of stigmasterol on the lipid metabolism in HepG2 cells and PPARγ-knockdown cells was determined by oil red O staining, Nile red staining, and TG level. PPARγ and UCP-1 mRNA, and protein expression levels were detected by qRT-PCR and Western blot analyses, respectively.

RESULTS

Twenty active components obtained from the Renshen and Chaihu herb pair were identified. The herb pair active component-target network showed that both Renshen and Chaihu contained stigmasterol and kaempferol as active components. The PPI network comprised 63 protein nodes. GO enrichment analysis and KEGG pathway enrichment analysis showed that the targets were mainly involved in lipid metabolism. Eight core targets were identified: AKT1, PPARG, MAPK3, TNF, TP53, SIRT1, STAT3, and PPARA. In vitro experiments demonstrated that stigmasterol reduced lipid accumulation and TG levels in HepG2 cells, and the mechanism may have been related to the activation of the PPARγ-UCP-1 signalling pathway.

CONCLUSION

This study preliminarily illustrated the potential components and corresponding core targets of the Renshen and Chaihu herb pair in treating NAFLD. The effect of stigmasterol on the PPARγ-UCP-1 signalling pathway in enhancing lipid metabolism may represent one of the mechanisms of the Renshen and Chaihu herb pair in the treatment of NAFLD. The results provide new evidence and research insights to reveal the roles of Renshen and Chaihu in the management of NAFLD.

Hengshun Aromatic Vinegar Improves Glycolipid Metabolism in Type 2 Diabetes Mellitus via Regulating PGC-1α/PGC-1β Pathway

Hengshun aromatic vinegar (HSAV), produced by typical solid-state or liquid-state fermentation techniques, is consumed worldwide as a food condiment. HSAV shows multiple bioactivities, but its activity in type 2 diabetes mellitus (T2DM) and possible mechanisms have not been reported. In this study, the effects of HSAV against T2DM were evaluated in insulin-induced HepG2 cells and high-fat diet (HFD) and streptozotocin (STZ) induced T2DM rats. Then, the mechanisms of HSAV against T2DM were explored by Real-time PCR, Western blot, immunofluorescence assays, siRNA transfection and gene overexpression experiments. Results indicated that HSAV significantly improved glucose consumption and reduced triglycerides (TG) contents in metabolic disordered HepG2 cells. Meanwhile, HSAV obviously alleviated general status, liver and kidney functions of T2DM rats, and decreased hyperglycemia and hyperlipidemia, improved insulin resistance, and reduced lipid accumulation in liver. Mechanism studies indicated that HSAV markedly down-regulated the expression of proliferator-activated receptor γ coactivator-1α (PGC-1α), then regulated peroxisome proliferators-activated receptor α (PPAR-α)/protein kinase B (AKT) signal pathway mediated gluconeogenesis and glycogen synthesis. Meanwhile, HSAV significantly up-regulated proliferator-activated receptor γ coactivator-1β (PGC-1β), and subsequently decreased sterol regulatory element binding protein-1c (SREBP-1c) pathway mediated lipogenesis. In conclusion, HSAV showed potent anti-T2DM activity in ameliorating dysfunction of glycolipid metabolism through regulating PGC-1α/PGC-1β pathway, which has a certain application prospect as an effective diet supplement for T2DM therapy in the future.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Adipocyte-Derived Exosomal MiR-27a Induces Insulin Resistance in Skeletal Muscle Through Repression of PPARγ

The mechanism by which adipocyte-derived endocrine factors promote insulin resistance in skeletal muscle are not fully understood. MiR-27a is highly expressed in sera of obese individuals with prediabetes and T2DM, and mainly derived by adipose tissues. Thus, miR-27a secreted into circulation by adipose tissue may regulate insulin resistance in skeletal muscle.

Methods: The association between miR-27a and insulin resistance in skeletal muscle was determined in obese children, high-fat diet-induced miR-27a knockdown obese mice, db/db mice and C2C12 cells overexpressing miR-27a. The crosstalk mediated by exosomal miR-27a between adipose tissue and skeletal muscle was determined in C2C12 cells incubated with conditioned medium prepared from palmitate-treated 3T3-L1 adipocytes.

Results: We showed that serum miR-27a level correlated positively with obesity and insulin resistance in obese children, and that elevated serum miR-27a levels correlated with insulin resistance in leptin receptor-deficient db/db mice, and with obesity and insulin resistance in high-fat diet-fed C57BL/6J mice. MiR-27a released from adipocytes of high-fat diet-fed C57BL/6J mice was associated with triglyceride accumulation. MiR-27a derived from these adipocytes induced insulin resistance in C2C12 skeletal muscle cells through miR-27a-mediated repression of PPARγ and its downstream genes involved in the development of obesity.

Conclusions: These results identify a novel crosstalk signaling pathway between adipose tissue and skeletal muscle in the development of insulin resistance, and indicate that adipose tissue-derived miR-27a may play a key role in the development of obesity-triggered insulin resistance in skeletal muscle.

Regulation of peroxisome proliferator-activated receptors (PPAR) α and -γ of rat brain astrocytes in the course of activation by toll-like receptor agonists

Peroxisome proliferator-activated receptors (PPAR)-α and -γ in astrocytes play important roles in inflammatory brain pathologies. Understanding the regulation of both activity and expression levels of PPARs is an important neuroscience issue. Toll-like receptor (TLR) agonists are inflammatory stimuli that could modulate PPAR, but the mechanisms of their control in astrocytes are poorly understood. In the present study, we report that lipopolysaccharide, peptidoglycan, and flagellin, which are agonists of TLR4, TLR1/2, and TLR5, respectively, exert time- and nuclear factor kappa-light-chain-enhancer of activated B cells-dependent suppression of mRNA, protein and activity of PPARα and PPARγ. In naïve astrocytes, PPARα and PPARγ mRNA have short turnover time (half-life about 30 min for PPARα, 75 min for PPARγ) with a nearly two-fold stabilization after TLR-activation. p38 inhibition abolished TLR-induced stabilization. The levels of PPARα and PPARγ mRNA, and protein and DNA-binding activity could be modified using c-Jun N-terminal Kinase and p38 inhibitors. In addition, the expression levels of both PPARα and PPARγ isotypes were induced after inhibition of protein synthesis. This induction signifies participation of additional regulatory proteins with short life-time. They are p38-sensitive for PPARα and c-Jun N-terminal Kinase-sensitive for PPARγ. Thus, PPARα and PPARγ are regulated in astrocytes on mRNA and protein levels, mRNA stability, and DNA-binding activity during TLR-mediated responses. Astrocytes have the triad of PPARα, PPARβ/δ, and PPARγ in regulation of proinflammatory responses. Activation of Toll-like receptors (TLR) leads to PPARβ/δ overexpression, PPARα and PPARγ suppression via TLR/NF-κB pathway on mRNA, protein and activity levels. Mitogen-activated protein kinases (MAPK) p38 and JNK are involved in regulation of PPAR expression. p38 MAPK plays a special role in stabilization of PPAR mRNA.

Addressing unmet medical needs in type 2 diabetes: a narrative review of drugs under development

The global burden of type 2 diabetes is increasing worldwide, and successful treatment of this disease needs constant provision of new drugs. Twelve classes of antidiabetic drugs are currently available, and many new drugs are under clinical development. These include compounds with known mechanisms of action but unique properties, such as once-weekly DPP4 inhibitors or oral insulin. They also include drugs with new mechanisms of action, the focus of this review. Most of these compounds are in Phase 1 and 2, with only a small number having made it to Phase 3 at this time. The new drug classes described include PPAR agonists/modulators, glucokinase activators, glucagon receptor antagonists, anti-inflammatory compounds, G-protein coupled receptor agonists, gastrointestinal peptide agonists other than GLP-1, apical sodium-dependent bile acid transporter (ASBT) inhibitors, SGLT1 and dual SGLT1/SGLT2 inhibitors, and 11beta- HSD1 inhibitors.

The roots of Atractylodes japonica Koidzumi promote adipogenic differentiation via activation of the insulin signaling pathway in 3T3-L1 cells

BACKGROUND

Type 2 diabetes (T2D) is a complex metabolic disorder characterized by insulin resistance and hyperglycemia. Peroxisome proliferator-activated receptor gamma (PPARγ) is a key transcription factor and plays an important role in the regulation of genes involved in adipogenic differentiation, glucose metabolism and insulin signal transduction.

METHODS

In this study, the effects of the root extract of Atractylodes japonica Koidzumi (Atractylodis Rhizoma Alba, ARA) on the differentiation of 3T3-L1 preadipocytes and the possible mechanism of glucose transport were investigated. 3T3-L1 cells were cultured with insulin and ARA extract.

RESULTS

In 3T3-L1 cells, ARA extract significantly enhanced adipogenic differentiation and upregulated the expression of PPARγ genes and protein in a dose-dependent manner. ARA also promoted glucose transport by increasing the glucose transporter 4 (GLUT-4), phosphatidylinositol 3-kinase (PI3K) and insulin receptor substrates-1 (IRS-1) levels.

CONCLUSION

Our results suggest that ARA extract may be an attractive therapeutic agent for managing T2D via promoting the differentiation of adipocytes with the upregulation of PPARγ levels and the activation of the insulin signaling pathway.

Effects of chronic PPAR-agonist treatment on cardiac structure and function, blood pressure, and kidney in healthy sprague-dawley rats

PPAR-γ agonists have been associated with heart failure (HF) in diabetic patients. These incidences have been reported mostly in patient populations who were at high risk for HF or had pre-existing impaired cardiovascular function. However, whether there are similar effects of these agents in subjects with no or reduced cardiovascular pathophysiology is not clear. In this study, the effects of chronic treatment with PD168, a potent peroxisome proliferator activated receptor (PPAR) subtype-γ agonist with weak activity at PPAR-α, and rosiglitazone (RGZ), a less potent PPAR-γ agonist with no PPAR-α activity, were evaluated on the cardiovascular-renal system in healthy male Sprague-Dawley (SD) rats by serial echocardiography and radiotelemetry. Rats were treated with vehicle (VEH), PD168, @ 10 or 50 mg/kg.bw/day (PD-10 or PD-50, resp.) or RGZ @ 180 mg/kg.bw/day for 28 days (n = 10/group). Relative to VEH, RGZ, and both doses of PD168 resulted in a significant fall in blood pressure. Furthermore, RGZ and PD168 increased plasma volume (% increase from baseline) 18%, 22%, and 48% for RGZ, PD-10, and PD-50, respectively. PD168 and RGZ significantly increased urinary aldosterone excretion and heart-to-body weight ratio relative to VEH. In addition, PD168 significantly decreased (10-16%) cardiac ejection fraction (EF) and increased left ventricular area (LVA) in systole (s) and diastole (d) in PD-10 and -50 rats. RGZ significantly increased LVAd; however, it did not affect EF relative to VEH. In conclusion, chronic PPAR-γ therapy may predispose the cardiorenal system to a potential sequela of structural and/or functional changes that may be deleterious with regard to morbidity and mortality.

P633H, a novel dual agonist at peroxisome proliferator-activated receptors alpha and gamma, with different anti-diabetic effects in db/db and KK-Ay mice

BACKGROUND AND PURPOSE

Peroxisome proliferator-activated receptors (PPARs) are attractive targets for the treatment of type 2 diabetes and the metabolic syndrome. P633H (2-[4-(2-Fluoro-benzenesulphonyl)-piperazin-1-yl]-3-{4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-phenyl}-propionic acid), a novel PPARalpha/gamma dual agonist, was investigated for its very different effects on insulin resistance and dyslipidemia in db/db and KK-A(y) mice.

EXPERIMENTAL APPROACH

The action of P633H at PPARalpha/gamma was characterized by using transactivation assays. Functional activation of PPARalpha/gammain vitro was confirmed by pre-adipocyte differentiation and regulation of target gene expression. Anti-diabetic studies were performed in two different diabetic mice models in vivo.

KEY RESULTS

P633H activated both PPARalpha and PPAR gamma, (with EC(50) values of 0.012 micromol and 0.032 micromol respectively). Additionally, P633H promoted pre-adipocyte differentiation, up-regulated expression of adipose specific transport protein (aP2) mRNA (3T3-Ll cells) and acyl-CoA oxidase mRNA (LO2 cells). In db/db mice, P633H reduced serum glucose, insulin, triglycerides, non-esterified fatty acids and liver triglycerides. It also improved glucose intolerance without affecting food intake and body weight after 15 days of treatment. However in KK-A(y) mice, hyperglycaemia, dyslipidemia and impaired glucose tolerance were not relieved even after a 25 day treatment with P633H. Further studies with real-time PCR and electron microscopy revealed that P633H promoted progression of diabetes in KK-A(y) mice by increasing hepatic gluconeogenesis and exacerbating pancreatic pathology.

CONCLUSION AND IMPLICATIONS

Although P633H was a high-potency PPARalpha/gamma dual agonist, with good functional activity in vitro, it produced opposing anti-diabetic effects in db/db and KK-A(y) mice.

Activation of peroxisome proliferator-activated receptor gamma inhibits endothelin-1-induced cardiac hypertrophy via the calcineurin/NFAT signaling pathway

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) has been described as a negative regulator of cardiac hypertrophy. A better understanding of PPAR-gamma and cardiac hypertrophy may facilitate the development of novel therapeutic strategies to treat heart diseases related to cardiac hypertrophy by mimicking the naturally preferred mechanisms. In the present study, we investigated the interaction between PPAR-gamma and calcineurin/nuclear factor of activated T-cells (NFAT) in endothelin-1 (ET-1)-induced hypertrophy of neonatal rat cardiac myocytes. The results suggest that the treatment of cultured cardiac myocytes with a PPAR-gamma ligand, rosiglitazone, inhibited the ET-1-induced increase in protein synthesis, surface area, calcineurin enzymatic activity, and protein expression. Both the application of rosiglitazone and overexpression of the PPAR-gamma inhibited the nuclear translocation of NFATc4. Moreover, co-immunoprecipitation studies showed that rosiglitazone enhanced the association between PPAR-gamma and calcineurin/NFAT. These results suggest that ET-1-induced cardiac hypertrophy is inhibited by activation of PPAR-gamma, which is at least partly due to cross-talk between PPAR-gamma and calcineurin/NFAT.