gw9662 and Insulin-Resistance

Proline-serine-threonine phosphatase-interacting protein 2 (PSTPIP2) plays a role in inflammatory disease. In diabetes, very little is known about PSTPIP2 until now. Hence, this study aimed to determine PSTPIP2 functional role in diabetes.. Diabetes mouse model was constructed by feeding high fat diet (HFD). Intraperitoneal glucose tolerance test and intraperitoneal insulin tolerance test were examined the glucose and insulin tolerance. The expression of genes and proteins was detected by quantitative real time PCR, immunohistochemistry and western blotting. The pathological changes of epididymal adipose tissues were examined by hematoxylin-eosin staining. RAW264.7 macrophages were treated with GW9662 (PPARγ antagonist). Flow cytometry examined the proportion of M1/M2 macrophages.. HFD enhanced the body weight, glucose and insulin tolerance, and inhibited PSTPIP2 expression in mice. PSTPIP2 overexpression alleviated glucose and insulin tolerance, reduced inflammation and macrophage accumulation in the epididymal adipose tissues of diabetic mice. The expression of iNOS and TNF-α was increased, the expression of IL-10 and Arg-1 was decreased in diabetic mice, which was abrogated by PSTPIP2 overexpression. In vitro, PSTPIP2 overexpression reduced the proportions of iNOS-positive cells and enhanced the proportions of CD206-positive cells in RAW264.7 cells. PPARγ and p-STAT6 were up-regulated, STAT6 was down-regulated in RAW264.7 cells. GW9662 impaired PSTPIP2 overexpression-mediated up-regulation of Arg-1, YM-1 and FIZZ1 in RAW264.7 cells.. PSTPIP2 alleviates obesity associated adipose tissue inflammation and insulin resistance in diabetic mice through promoting M2 macrophage polarization via activation of PPARγ, suggesting that PSTPIP2 is a prospective target for diabetes treatment.

Topics: Adipose Tissue; Animals; Diabetes Mellitus, Experimental; Diet, High-Fat; Glucose; Inflammation; Insulin Resistance; Insulins; Macrophage Activation; Macrophages; Mice; Mice, Inbred C57BL; Obesity; PPAR gamma

Insulin resistance is among the key risk factors for the development of non-alcoholic fatty liver disease (NAFLD). Recently, it has been reported that GW9662, shown to be a potent peroxisome proliferator-activated receptor gamma (PPARγ) antagonist, may improve insulin sensitivity in settings of type 2 diabetes. Here, we determined the effects of GW9662 on the development of NAFLD and molecular mechanisms involved.. Female C57BL/6J mice were pair-fed either a liquid control diet (C) or a fat-, fructose- and cholesterol-rich diet (FFC) for 8 weeks while either being treated with GW9662 (1 mg/kg body weight; C+GW9662 and FFC+GW9662) or vehicle (C and FFC) i.p. three times weekly. Indices of liver damage and inflammation, parameters of glucose metabolism and portal endotoxin levels were determined. Lipopolysaccharide (LPS)-challenged J774A.1 cells were treated with 10 μM GW9662.. Despite similar caloric intake the development of NAFLD and insulin resistance were significantly attenuated in FFC+GW9662-treated mice when compared to FFC-fed animals. Bacterial endotoxin levels in portal plasma were almost similarly increased in both FFC-fed groups while expressions of toll-like receptor 4 (Tlr4), myeloid differentiation primary response 88 (Myd88) and interleukin 1 beta (Il1b) as well as nitrite (NO. In summary, our data suggest that the PPARγ antagonist GW9662 attenuates the development of a diet-induced NAFLD and that this is associated with a protection against the activation of the TLR4 signaling cascade.

Topics: Anilides; Animals; Diabetes Mellitus, Type 2; Endotoxins; Female; Insulin Resistance; Lipopolysaccharides; Liver; Mice; Mice, Inbred C57BL; Nitrogen Dioxide; Non-alcoholic Fatty Liver Disease; PPAR gamma; Toll-Like Receptor 4

Accumulating evidence suggests that inhibition of mitogen-activated protein kinase signalling can reduce phosphorylation of peroxisome proliferator-activated receptor γ (PPARγ) at serine 273, which mitigates obesity-associated insulin resistance and might be a promising treatment for type 2 diabetes. Dihydromyricetin (DHM) is a flavonoid that has many beneficial pharmacological properties. In this study, mouse fibroblast 3T3-L1 cells were used to investigate whether DHM alleviates insulin resistance by inhibiting PPARγ phosphorylation at serine 273 via the MEK/ERK pathway. 3T3-L1 pre-adipocytes were differentiated, and the effects of DHM on adipogenesis and glucose uptake in the resulting adipocytes were examined. DHM was found to dose dependently increase glucose uptake and decrease adipogenesis. Insulin resistance was then induced in adipocytes using dexamethasone, and DHM was shown to dose and time dependently promote glucose uptake in the dexamethasone-treated adipocytes. DHM also inhibited phosphorylation of PPARγ and ERK. Inhibition of PPARγ activity with GW9662 potently blocked DHM-induced glucose uptake and adiponectin secretion. Interestingly, DHM showed similar effects to PD98059, an inhibitor of the MEK/ERK pathway. DHM acted synergistically with PD98059 to improve glucose uptake and adiponectin secretion in dexamethasone-treated adipocytes. In conclusion, our findings indicate that DHM improves glucose uptake in adipocytes by inhibiting ERK-induced phosphorylation of PPARγ at serine 273.

Topics: 3T3-L1 Cells; Adipocytes; Adipogenesis; Adiponectin; Anilides; Animals; Cell Survival; Dexamethasone; Down-Regulation; Fibroblast Growth Factors; Flavonoids; Flavonols; Glucose; Insulin Resistance; MAP Kinase Signaling System; Mice; Mitogen-Activated Protein Kinase Kinases; Phosphorylation; Phosphoserine; PPAR gamma

Ampelopsin (APL), a major bioactive constituent of Ampelopsis grossedentata, exerts a number of biological effects. Here, we explored the anti-diabetic activity of APL and elucidate the underlying mechanism of this action. In palmitate-induced insulin resistance of L6 myotubes, APL treatment markedly up- regulated phosphorylated insulin receptor substrate-1 and protein kinase B, along with a corresponding increase of glucose uptake capacity. APL treatment also increased expressions of fibroblast growth factor (FGF21) and phosphorylated adenosine 5'-monophosphate -activated protein kinase (p-AMPK), however inhibiting AMPK by Compound C or AMPK siRNA, or blockage of FGF21 by FGF21 siRNA, obviously weakened APL -induced increases of FGF21 and p-AMPK as well as glucose uptake capacity in palmitate -pretreated L6 myotubes. Furthermore, APL could activate PPAR γ resulting in increases of glucose uptake capacity and expressions of FGF21 and p-AMPK in palmitate -pretreated L6 myotubes, whereas all those effects were obviously abolished by addition of GW9662, a specific inhibitor of peroxisome proliferator- activated receptor -γ (PPARγ), and PPARγsiRNA. Using molecular modeling and the luciferase reporter assays, we observed that APL could dock with the catalytic domain of PPARγ and dose-dependently up-regulate PPARγ activity. In summary, APL maybe a potential agonist of PPARγ and promotes insulin sensitization by activating PPARγ and subsequently regulating FGF21- AMPK signaling pathway. These results provide new insights into the protective health effects of APL, especially for the treatment of Type 2 diabetes mellitus.

Topics: AMP-Activated Protein Kinases; Anilides; Animals; Blotting, Western; Cell Line; Fibroblast Growth Factors; Flavonoids; Glucose; Insulin Resistance; Muscle Fibers, Skeletal; PPAR gamma; Rats; RNA Interference; RNA, Small Interfering; Signal Transduction

Epoxyeicosatrienoic acids (EETs) and arachidonic acid-derived cytochrome P450 (CYP) epoxygenase metabolites have diverse biological effects, including anti-inflammatory properties in the vasculature. Increasing evidence suggests that inflammation in type 2 diabetes is a key component in the development of insulin resistance. In this study, we investigated whether CYP epoxygenase expression and exogenous EETs can attenuate insulin resistance in diabetic db/db mice and in cultured hepatic cells (HepG2). In vivo, CYP2J2 expression and the accompanying increase in EETs attenuated insulin resistance, as determined by plasma glucose levels, glucose tolerance test, insulin tolerance test, and hyperinsulinemic euglycemic clamp studies. CYP2J2 expression reduced the production of proinflammatory cytokines in liver, including CRP, IL-6, IL-1β, and TNFα, and decreased the infiltration of macrophages in liver. CYP2J2 expression also decreased activation of proinflammatory signaling cascades by decreasing NF-κB and MAPK activation in hepatocytes. Interestingly, CYP2J2 expression and exogenous EET treatment increased glucose uptake and activated the insulin-signaling cascade both in vivo and in vitro, suggesting that CYP2J2 metabolites play a role in glucose homeostasis. Furthermore, CYP2J2 expression upregulated PPARγ, which has been shown to induce adipogenesis, which attenuates dyslipidemias observed in diabetes. All of the findings suggest that CYP2J2 expression attenuates the diabetic phenotype and insulin resistance via inhibition of NF-κB and MAPK signaling pathways and activation of PPARγ.

Topics: Anilides; Animals; Benzamides; C-Reactive Protein; Cytochrome P-450 CYP2J2; Cytochrome P-450 Enzyme System; Cytokines; Diabetes Mellitus, Type 2; Down-Regulation; Genetic Therapy; Hep G2 Cells; Humans; Insulin Resistance; Liver; Macrophages; Male; MAP Kinase Signaling System; Mice, Inbred C57BL; Mice, Mutant Strains; NF-kappa B; PPAR gamma; Recombinant Proteins; Up-Regulation

Fetuin-A, a circulating glycoprotein synthesized in the liver, is involved in insulin resistance and type 2 diabetes. However, regulation of fetuin-A synthesis has remained obscure. We previously reported that pioglitazone treatment significantly reduced serum fetuin-A levels in patients with type 2 diabetes. To clarify whether pioglitazone can directory inhibit hepatic fetuin-A synthesis, we investigated the effects of pioglitazone on fetuin-A expression both in vitro and in vivo. Pioglitazone treatment suppressed mRNA and protein expression of fetuin-A in Fao hepatoma cells. Interestingly, rosiglitazone but not metformin, also inhibited fetuin-A expression. In addition, GW 9662, an inhibitor of peroxisome proliferator-activated receptor (PPAR) γ, reversed pioglitazone-induced suppression of fetuin-A, suggesting that thiazolidinedione derivatives may have common characteristics with regard to fetuin-A suppression, possibly through PPARγactivation. Finally, oral administration of pioglitazone to mice for 8 weeks resulted in suppression of hepatic fetuin-A mRNA. These findings suggest that pioglitazone may partially ameliorate insulin resistance through its direct inhibitory effects on fetuin-A expression in the liver.

Topics: alpha-2-HS-Glycoprotein; Anilides; Animals; Cell Line, Tumor; Diabetes Mellitus, Type 2; Gene Expression; Hepatocytes; Humans; Hypoglycemic Agents; Insulin Resistance; Liver; Male; Metformin; Mice; Mice, Inbred C57BL; Pioglitazone; PPAR gamma; RNA, Messenger; Rosiglitazone; Thiazolidinediones

This study aimed to investigate the influence of rosiglitazone on hepatic insulin resistance and the expressions of IκB kinase-β (IKK-β)/nuclear factor-κB (NF-κB) in chronic pancreatitis (CP).. After CP was induced in rats, rosiglitazone and GW9662 were administered at the doses of 4 and 2 mg/kg per day for 4 weeks, respectively. Then, glucose and insulin tolerance tests were performed. Hepatocytes were isolated for the glucose release experiments. Determination of the IKK-β, NF-κB, and Ser307p-insulin receptor substrates-1 (Ser307p-IRS-1) expression in the liver was performed.. The increased plasma glucose, reduced insulin sensitivity, and the capacity of insulin to suppress glucose release in hepatocytes were observed in CP rats. The IKK-β, NF-κB, and Ser307p-IRS-1 expressions were significantly higher in the liver of CP rats than in sham-operated rats (P < 0.05). Rosiglitazone treatment significantly improved hepatic insulin sensitivity and inhibited the IKK-β, NF-κB, and Ser307p-IRS-1 expressions in the liver (P < 0.05). Counteraction with peroxisome proliferator-activated receptor-γ by GW9662 attenuated the aforementioned effects of rosiglitazone.. Rosiglitazone attenuates hepatic insulin resistance induced by CP. The inhibition of hepatic IKK-β and NF-κB expressions via peroxisome proliferator-activated receptor-γ may be involved in the therapeutic effect of rosiglitazone.

Topics: Anilides; Animals; Drug Evaluation, Preclinical; Gene Expression Regulation; Glucose; Glucose Tolerance Test; Hepatocytes; I-kappa B Kinase; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Liver; Male; Pancreatitis, Chronic; PPAR gamma; Rats; Rats, Wistar; Rosiglitazone; Thiazolidinediones; Transcription Factor RelA

Activation of central PPARγ promotes food intake and body weight gain; however, the identity of the neurons that express PPARγ and mediate the effect of this nuclear receptor on energy homeostasis is unknown. Here, we determined that selective ablation of PPARγ in murine proopiomelanocortin (POMC) neurons decreases peroxisome density, elevates reactive oxygen species, and induces leptin sensitivity in these neurons. Furthermore, ablation of PPARγ in POMC neurons preserved the interaction between mitochondria and the endoplasmic reticulum, which is dysregulated by HFD. Compared with control animals, mice lacking PPARγ in POMC neurons had increased energy expenditure and locomotor activity; reduced body weight, fat mass, and food intake; and improved glucose metabolism when exposed to high-fat diet (HFD). Finally, peripheral administration of either a PPARγ activator or inhibitor failed to affect food intake of mice with POMC-specific PPARγ ablation. Taken together, our data indicate that PPARγ mediates cellular, biological, and functional adaptations of POMC neurons to HFD, thereby regulating whole-body energy balance.

Topics: Anilides; Animals; Diet, High-Fat; Energy Metabolism; Female; Glucose; Hyperphagia; Insulin Resistance; Leptin; Male; Mice; Motor Activity; Neurons; PPAR gamma; Pro-Opiomelanocortin; Reactive Oxygen Species; Rosiglitazone; Thiazolidinediones

Chrysin and luteolin are two flavonoids with Peroxisome proliferators-activated receptor γ (PPAR-γ) stimulating activity. Here, we investigated the protective effect of chrysin and luteolin from vascular complications associated with insulin resistance (IR). IR was induced in rats by drinking fructose for 12 weeks while chrysin and luteolin were given for 6 weeks with or without PPAR-γ antagonist, bisphenol A diglycidyl ether (BADGE). Then, blood pressure (BP) was recorded and serum levels of glucose, insulin, advanced glycation end products (AGEs) and lipids were measured. Concentration response curves for phenylephrine (PE), KCl, and acetylcholine (ACh) were obtained in thoracic aorta rings. Aortic reactive oxygen species (ROS) and nitric oxide (NO) generation were also studied. Chrysin and luteolin significantly alleviated systolic BP elevations caused by IR, while the co-administration of BADGE prevented chrysin alleviation. Although, neither chrysin nor luteolin affected ACh impaired vasodilatation, they both alleviated exaggerated vasoconstrictions to PE and KCl in IR animals. In addition, incubation of the aorta from IR animals with chrysin or luteolin prevented exaggerated vasoconstrictions to PE and KCl. On the other hand, co-administration of BADGE or co-incubation with GW9662, the selective PPAR-γ antagonist, prevented chrysin alleviation. Both chrysin and luteolin inhibited the developed hyperinsulinemia and increases in serum AGEs, lipids while, BADGE reduced the effect of chrysin on hyperinsulinemia and dyslipidemia. Chrysin and luteolin markedly inhibited elevated NO and ROS in IR aortae while BADGE did not change their effect on NO and ROS. In conclusion, chrysin and luteolin alleviate vascular complications associated with IR mainly through PPAR-γ dependent pathways.

Topics: Anilides; Animals; Aorta, Thoracic; Benzhydryl Compounds; Blood Glucose; Blood Pressure; Epoxy Compounds; Flavonoids; Glycation End Products, Advanced; Hyperinsulinism; In Vitro Techniques; Insulin; Insulin Resistance; Lipids; Luteolin; Male; Muscle, Smooth, Vascular; Nitric Oxide; PPAR gamma; Rats; Reactive Oxygen Species; Vasoconstriction

Palmitate induces insulin resistance and apoptosis in insulin target tissues. Rosiglitazone (RSG), a peroxisome proliferator-activated receptor γ (PPARγ) agonist, can activate both pro-apoptotic and anti-apoptotic pathways in different cells; however, its effect on palmitate-induced apoptosis in skeletal muscle cells remains to be elucidated. After differentiation of C2C12 cells, myotubes were treated with palmitate, RSG and GW9662 (PPARγ antagonist). MTT and terminal deoxynucleotide transferase dUTP nick end labelling (TUNEL) assays and caspase-3 activity were used to investigate the apoptosis. To study the underlying mechanism, glucose uptake, gene expression and protein levels were evaluated. A total of 0.75 mM palmitate reduced cell viability by 43% and increased TUNEL-positive cells and caspase-3 activity by 15-fold and 6.6-fold, respectively. RSG (10 μM) could markedly decrease the level of TUNEL-positive cells and caspase-3 activity in palmitate-treated cells. The protective effect of RSG on apoptosis was abrogated by GW9662. To investigate the molecular mechanism of this effect, gene expression and protein level of protein tyrosine phosphatase 1B (PTP1B) were evaluated. Palmitate and RSG individually increased the expression and protein level of PTP1B, whereas combined treatment (palmitate and RSG) were able to further increase the expression of PTP1B in C2C12 cells. We also evaluated the effect of RSG on palmitate-induced insulin resistance in muscle cells. RSG could significantly improve glucose uptake by 0.4-fold in myotubes treated with palmitate. Moreover, RSG could restore the phosphorylation of Akt in palmitate-treated cells. These data suggest that RSG protects skeletal muscle cells against palmitate-induced apoptosis and this effect appears to be mediated via the PPARγ-dependent and PTP1B-independent mechanisms.. Saturated free fatty acids (FFAs), such as palmitate, have been shown to induce cellular apoptosis. Strategies for preventing the cytotoxic effect of palmitate are useful in reduction of diabetes complications. In this study, we introduced RSG as an agent that protects skeletal muscle cells against palmitate-induced apoptosis and insulin resistance. It appears that RSG protects skeletal muscle cells against palmitate-induced apoptosis via the PPARγ-dependent and PTP1B-independent mechanisms. Given the role of FFAs in skeletal muscle apoptosis, these findings support the idea that RSG can ameliorate diabetes complications such as skeletal muscle loss.

Topics: Anilides; Animals; Apoptosis; Cell Line; Cell Survival; Enzyme Inhibitors; Hypoglycemic Agents; Insulin Resistance; Mice; Myoblasts, Skeletal; Palmitates; PPAR gamma; Protein Tyrosine Phosphatase, Non-Receptor Type 1; Rosiglitazone; Thiazolidinediones

TNFα plays an important role in the adipocyte dysfunction, including lipolysis acceleration, insulin resistance and changes of adipokines. Recently, we showed that paeoniflorin attenuates adipocyte lipolysis and inhibits the phosphorylation of ERK, JNK, IKK stimulated by TNFα. However, the effects of paeoniflorin on adipocytes insulin resistance and changes of adipokines remain unknown. The aim of the current study was to investigate the role of paeoniflorin in preventing insulin resistance or inflammation in 3T3-L1 adipocytes treated with TNFα. Our results showed that paeoniflorin restored insulin-stimulated [(3)H]2-DOG uptake, which was reduced by TNFα, with concomitant restoration in serine phosphorylation of IRS-1 and insulin-stimulated phosphorylation of AKT in adipocytes. Paeoniflorin attenuated TNFα-mediated suppression of the expressions of PPARγ and PPARγ target genes, and the improvement of paeoniflorin on TNFα-induced insulin resistance was attenuated by GW9662, an antagonist of PPARγ activity. Moreover, paeoniflorin could inhibit the expressions and secretions of IL-6 and MCP-1 from adipocytes induced by TNFα. These results, together with our previous data, indicate that paeoniflorin exerts a beneficial effect on adipocytes to prevent TNFα-induced insulin resistance and inflammatory adipokine release. Our studies provide important evidence for an ability of paeoniflorin in amelioration of TNFα-induced adipocyte dysfunction, which would be helpful to clarify its potential role in the treatment of obesity.

Topics: 3T3-L1 Cells; Adipocytes; Adipokines; Anilides; Animals; Benzoates; Bridged-Ring Compounds; Chemokine CCL2; Drugs, Chinese Herbal; Gene Expression; Glucose; Glucosides; Inflammation; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Interleukin-6; Mice; Monoterpenes; Obesity; Paeonia; Phosphorylation; PPAR gamma; Proto-Oncogene Proteins c-akt; Tumor Necrosis Factor-alpha

Ankaflavin (AK) is an active compound having anti-inflammatory, anti-cancer, antiatherosclerotic, and hypolipidemic effects. We have previously reported that AK acts as an antioxidant and antidiabetic drug; however, the mechanism by which AK prevents diabetes remains unknown. Hyperglycemia is associated with protein glycation, which produces advanced glycation end-products (AGEs). Methylglyoxal (MG)-a metabolite of carbohydrates-is believed to cause insulin resistance by inducing inflammation and pancreas damage. In this work, diabetes was induced in Wistar rats (4 weeks of age) by treating them with MG (600 mg/kg bw) for 4 weeks. We observed that AK (10mg/kg bw) exerted peroxisome proliferator-activated receptor-γ (PPARγ) agonist activity, thereby enhancing insulin sensitivity (as indicated by hepatic GLUT2 translocation, PTP1B suppression, and glucose uptake) by downregulating blood glucose and upregulating pancreatic and duodenal homeobox-1 and Maf-A expression and increasing insulin production in MG-induced rats. However, these effects were abolished by the administration of GW9662 (PPARγ antagonist), but the expression of hepatic heme oxygenase-1 (HO-1) and glutamate-cysteine ligase (GCL) was not suppressed in MG-induced rats. Therefore, the nuclear factor erythroid-related factor-2 (Nrf2) activation was investigated. AK did not affect hepatic Nrf2 mRNA or protein expression but significantly increased Nrf2 phosphorylation (serine 40), which was accompanied by increased transcriptional activation of hepatic HO-1 and GCL. These data indicated that AK protected rats from oxidative stress resulting from MG-induced insulin resistance. In contrast, these effects were not detected when the rats were treated with the antidiabetic drug rosiglitazone (10mg/kg bw). Moreover, we found that AK did not inhibit the generation of AGEs in vitro; however, the glutathione (GSH) levels in liver and pancreas of MG-induced rats were elevated in rats administered AK. Therefore, we believe that GSH may lower the MG level, which attenuates the formation of AGEs in the serum, kidney, liver, and pancreas of MG-induced rats. We also found that AK treatment reduced the production of inflammatory factors, such as tumor necrosis factor-α and interleukin-1β. Taken together, the results of our mechanistic study of MG-induced rats suggest that the protective effects of AK against diabetes are mediated by the upregulation of the signaling pathway of Nrf2, which enhances antioxidant a

Topics: Anilides; Animals; Anti-Inflammatory Agents; Blood Glucose; Cytokines; Diabetes Mellitus, Experimental; Flavins; Gene Expression; Gene Expression Regulation; Glycation End Products, Advanced; Heme Oxygenase-1; Hypoglycemic Agents; Insulin; Insulin Resistance; Leukocytes, Mononuclear; Liver; Male; NF-E2-Related Factor 2; Oxidative Stress; Pancreas; Phosphorylation; PPAR gamma; Protein Processing, Post-Translational; Pyruvaldehyde; Rats; Rats, Wistar; Receptor for Advanced Glycation End Products; Receptors, Immunologic; Up-Regulation

The role of angiotensin II type 2 (AT(2)) receptor stimulation in the pathogenesis of insulin resistance is still unclear. Therefore we examined the possibility that direct AT(2) receptor stimulation by compound 21 (C21) might contribute to possible insulin-sensitizing/anti-diabetic effects in type 2 diabetes (T2DM) with PPARγ activation, mainly focusing on adipose tissue.. T2DM mice, KK-Ay, were subjected to intraperitoneal injection of C21 and/or a PPARγ antagonist, GW9662 in drinking water for 2 weeks. Insulin resistance was evaluated by oral glucose tolerance test, insulin tolerance test, and uptake of 2-[(3)H] deoxy-D-glucose in white adipose tissue. Morphological changes of adipose tissues as well as adipocyte differentiation and inflammatory response were examined.. Treatment with C21 ameliorated insulin resistance in KK-Ay mice without influencing blood pressure, at least partially through effects on the PPARγ pathway. C21 treatment increased serum adiponectin concentration and decreased TNF-α concentration; however, these effects were attenuated by PPARγ blockade by co-treatment with GW9662. Moreover, we observed that administration of C21 enhanced adipocyte differentiation and PPARγ DNA-binding activity, with a decrease in inflammation in white adipose tissue, whereas these effects of C21 were attenuated by co-treatment with GW9662. We also observed that administration of C21 restored β cell damage in diabetic pancreatic tissue.. The present study demonstrated that direct AT(2) receptor stimulation by C21 accompanied with PPARγ activation ameliorated insulin resistance in T2DM mice, at least partially due to improvement of adipocyte dysfunction and protection of pancreatic β cells.

Topics: Adiponectin; Adipose Tissue; Anilides; Animals; Blood Glucose; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Inflammation; Insulin; Insulin Resistance; Male; Mice; Pancreas; PPAR gamma; Receptor, Angiotensin, Type 2; Sulfonamides; Thiophenes; Tumor Necrosis Factor-alpha

Microvascular dysfunction occurs in insulin resistance and/or hyperinsulinaemia. Enhanced uptake of free fatty acids (FFA) and oxidised low-density lipoproteins (oxLDL) may lead to oxidative stress and microvascular dysfunction interacting with CD36, a PPARα/γ-regulated scavenger receptor and long-chain FFA transporter. We investigated CD36 expression and CD36-mediated oxLDL uptake before and after insulin treatment in human dermal microvascular endothelial cells (HMVECs), ± different types of fatty acids (FA), including palmitic, oleic, linoleic, arachidonic, eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids. Insulin (10(-8) and 10(-7) M) time-dependently increased DiI-oxLDL uptake and CD36 surface expression (by 30 ± 13%, p<0.05 vs. untreated control after 24 hours incubation), as assessed by ELISA and flow cytometry, an effect that was potentiated by the PI3-kinase inhibitor wortmannin and reverted by the ERK1/2 inhibitor PD98059 and the PPARα/γ antagonist GW9662. A ≥ 24 hour exposure to 50 μM DHA or EPA, but not other FA, blunted both the constitutive (by 23 ± 3% and 29 ± 2%, respectively, p<0.05 for both) and insulin-induced CD36 expressions (by 45 ± 27 % and 12 ± 3 %, respectively, p<0.05 for both), along with insulin-induced uptake of DiI-oxLDL and the downregulation of phosphorylated endothelial nitric oxide synthase (P-eNOS). At gel shift assays, DHA reverted insulin-induced basal and oxLDL-stimulated transactivation of PPRE and DNA binding of PPARα/γ and NF-κB. In conclusion, omega-3 fatty acids blunt the increased CD36 expression and activity promoted by high concentrations of insulin. Such mechanisms may be the basis for the use of omega-3 fatty acids in diabetic microvasculopathy.

Topics: Androstadienes; Anilides; Calcium-Calmodulin-Dependent Protein Kinases; CD36 Antigens; Cell Line; Dermis; Endothelial Cells; Fatty Acids, Omega-3; Flavonoids; Gene Expression Regulation; Humans; Insulin; Insulin Resistance; Oxidative Stress; Phosphoinositide-3 Kinase Inhibitors; PPAR alpha; PPAR gamma; Receptors, Scavenger; Wortmannin

The plant alkaloid berberine (BBR) has been reported to have antidiabetic effect in humans and animals. However, the mechanism of action is not well understood. The present study was conducted to determine the effect and mechanism of action of BBR on the free-fatty-acid (FFA)-induced insulin resistance in muscle cells. The FFA-induced insulin-resistant cell model was established in L6 myotubes by treating them with 250 mumol/L of palmitic acid. The inclusion of FFA in the medium increased peroxisome proliferator-activated receptor gamma (PPARgamma) and fatty acid transferase (FAT/CD36) expressions by 26% and 50% and decreased glucose consumption by 43% and insulin-mediated glucose uptake by 63%, respectively. Berberine treatment increased the glucose consumption and insulin-stimulated glucose uptake in normal cells and improved glucose uptake in the FFA-induced insulin-resistant cells. The improved glucose uptake by BBR was accompanied with a dose-dependent decrease in PPARgamma and FAT/CD36 protein expressions. In insulin-resistant myotubes, BBR (5 micromol/L) decreased PPARgamma and FAT/CD36 proteins by 31% and 24%, whereas PPARgamma antagonist GW9662 reduced both proteins by 56% and 46%, respectively. In contrast, PPARgamma agonist rosiglitazone increased the expression of PPARgamma and FAT/CD36 by 34% and 21%, respectively. Our results suggest that BBR improves the FFA-induced insulin resistance in myotubes through inhibiting fatty acid uptake at least in part by reducing PPARgamma and FAT/CD36 expressions.

Topics: Anilides; Berberine; Blotting, Western; Carnitine O-Palmitoyltransferase; CD36 Antigens; Cell Line; Cell Survival; Fatty Acids; Fatty Acids, Nonesterified; Gene Expression; Glucose; Humans; Hypoglycemic Agents; Insulin Resistance; Muscle Fibers, Skeletal; PPAR alpha; PPAR gamma; Rosiglitazone; Thiazolidinediones