Repeat treatment of obese mice with BRL 49653, a new potent insulin sensitizer, enhances insulin action in white adipocytes. Association with increased insulin binding and cell-surface GLUT4 as measured by photoaffinity labeling

Unraveling the rationale and conducting a comprehensive assessment of KD025 (Belumosudil) as a candidate drug for inhibiting adipogenic differentiation-a systematic review

Rho-associated kinases (ROCKs) are crucial during the adipocyte differentiation process. KD025 (Belumosudil) is a newly developed inhibitor that selectively targets ROCK2. It has exhibited consistent efficacy in impeding adipogenesis across a spectrum of in vitro models of adipogenic differentiation. Given the novelty of this treatment, a comprehensive systematic review has not been conducted yet. This systematic review aims to fill this knowledge void by providing readers with an extensive examination of the rationale behind KD025 and its impacts on adipogenesis. Preclinical evidence was gathered owing to the absence of clinical trials. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed, and the study's quality was assessed using the Joanna Briggs Institute (JBI) Checklist Critical Appraisal Tool for Systematic Reviews. In various in vitro models, such as 3T3-L1 cells, human orbital fibroblasts, and human adipose-derived stem cells, KD025 demonstrated potent anti-adipogenic actions. At a molecular level, KD025 had significant effects, including decreasing fibronectin (Fn) expression, inhibiting ROCK2 and CK2 activity, suppressing lipid droplet formation, and reducing the expression of proadipogenic genes peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα). Additionally, KD025 resulted in the suppression of fatty acid-binding protein 4 (FABP4 or AP2) expression, a decrease in sterol regulatory element binding protein 1c (SREBP-1c) and Glut-4 expression. Emphasis must be placed on the fact that while KD025 shows potential in preclinical studies and experimental models, extensive research is crucial to assess its efficacy, safety, and potential therapeutic applications thoroughly and directly in human subjects.

Chronic tissue inflammation and metabolic disease

In this review, Lee and Olefsky discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes.

Obesity is the most common cause of insulin resistance, and the current obesity epidemic is driving a parallel rise in the incidence of T2DM. It is now widely recognized that chronic, subacute tissue inflammation is a major etiologic component of the pathogenesis of insulin resistance and metabolic dysfunction in obesity. Here, we summarize recent advances in our understanding of immunometabolism. We discuss the characteristics of chronic inflammation in the major metabolic tissues and how obesity triggers these events, including a focus on the role of adipose tissue hypoxia and macrophage-derived exosomes. Last, we also review current and potential new therapeutic strategies based on immunomodulation.

Molecular Characterization of Constipation Disease as Novel Phenotypes in CRISPR-Cas9-Generated Leptin Knockout Mice with Obesity

(1) Background: We characterized a novel animal model with obesity-induced constipation because constipation is rarely known in genetically engineered mice (GEM); (2) Methods: The changes in the constipation parameters and mechanisms were analyzed in CRISPR-Cas9-mediated leptin (Lep) knockout (KO) mice from eight to 24 weeks; (3) Results: Significant constipation phenotypes were observed in the Lep KO mice since 16 weeks old. These mice showed a significant decrease in the gastrointestinal motility, mucosal layer thickness and ability for mucin secretion as well as the abnormal ultrastructure of Lieberkühn crypts in the transverse colon. The density or function of the enteric neurons, intestinal Cajal cells (ICC), smooth muscle cells, and the concentration of gastrointestinal (GI) hormones for the GI motility were remarkably changed in Lep KO mice. The downstream signaling pathway of muscarinic acetylcholine receptors (mAChRs) were activated in Lep KO mice, while the expression of adipogenesis-regulating genes were alternatively reduced in the transverse colon of the same mice; (4) Conclusions: These results provide the first strong evidence that Lep KO mice can represent constipation successfully through dysregulation of the GI motility mediated by myenteric neurons, ICC, and smooth muscle cells in the transverse colon during an abnormal function of the lipid metabolism.

A colorimetric bioassay for quantitation of both basal and insulin-induced glucose consumption in 3T3-L1 adipose cells

Introduction

The quantitation of glucose consumption in animal cell cultures is mainly based on the use of radiolabeled or fluorescent analogues, resulting in expensive and tedious procedures, requiring special equipment and, sometimes, with potential health and environmental risks.

Objectives

The objective of this work was to evaluate the application of a blood plasma colorimetric assay to quantify glucose consumption in in vitro cultures of adipose cells.

Methods

We worked with 3T3-L1 adipose cells differentiated by 7–8 days, which were exposed to different initial glucose concentrations (5.5, 2.8 and 1.4 mM) for variable times, either in the absence or the presence of 100 nM insulin. Using a commercial colorimetric glucose assay, extracellular glucose was determined, and glucose uptake was calculated as the difference between the initial and final glucose concentration.

Results

The colorimetric assay allowed us to quantify glucose uptake in our cell model, observing a linear response over time (r²≥0.9303) to the different glucose concentrations, both in the basal and insulin-induced condition. The insulin-stimulated glucose consumption was higher than basal consumption at all glucose concentrations evaluated, but significant differences were observed at 120-, 360- and 480-min in glucose 5.5 mM (p ≤ 0.01, n = 5), and 240 min in glucose 1.4 mM (p ≤ 0.01, n = 5). A V_max of 4.1 and 5.9 nmol/ml/min (basal and insulin-induced, respectively) and a K_m of 1.1 mM (same in basal vs insulin-stimulated) were calculated. The bioassay was also useful in a pharmacological context: in glucose 1.4 mM, glucose consumption showed an effect that depended on insulin concentration, with a calculated EC₅₀ of 18.4 ± 1.1 nM.

Conclusions

A simple and low-cost bioassay is proposed to quantify glucose consumption in 3T3-L1 adipose cells.

The Antagonist Effect of Arachidonic Acid on GLUT4 Gene Expression by Nuclear Receptor Type II Regulation

OBJECTIVES

Obesity is a complex disease that has a strong association with diet and lifestyle. Dietary factors can influence the expression of key genes connected to insulin resistance, lipid metabolism, and adipose tissue composition. In this study, our objective was to determine gene expression and fatty acid (FA) profiles in visceral adipose tissue (VAT) from lean and morbidly obese individuals. We also aimed to study the agonist effect of dietary factors on glucose metabolism.

DESIGN AND METHODS

Lean and low and high insulin resistance morbidly obese subjects (LIR-MO and HIR-MO) were included in this study. The gene expression of liver X receptor type alpha (LXR-α) and glucose transporter type 4 (GLUT4) and the FA profiles in VAT were determined. Additionally, the in vivo and in vitro agonist effects of oleic acid (OA), linoleic acid (LA), and arachidonic acid (AA) by peroxisome proliferator-activated receptor type gamma 2 (PPAR-γ2) on the activity of GLUT4 were studied.

RESULTS

Our results showed a dysregulation of GLUT4 and LXR-α in VAT of morbidly obese subjects. In addition, a specific FA profile for morbidly obese individuals was found. Finally, AA was an PPAR-γ2 agonist that activates the expression of GLUT4.

CONCLUSIONS

Our study suggests a dysregulation of LXR-α and GLUT4 expression in VAT of morbidly obese individuals. FA profiles in VAT could elucidate their possible role in lipolysis and adipogenesis. Finally, AA binds to PPAR-γ2 to activate the expression of GLUT4 in the HepG2 cell line, showing an alternative insulin-independent activation of GLUT4.

Molecular and Metabolic Markers of Fructose Induced Hepatic Insulin Resistance in Developing and Adult Rats are Distinct and Aegle marmelos is an Effective Modulator

The time course of pathogenesis of fructose mediated hepatic insulin resistance (HepIR) is not well-delineated and we chronicle it here from post-weaning to adulthood stages. Weaned rats were provided for either 4 or 8 weeks, i.e., upto adolescence or adulthood, chow + drinking water, chow + fructose, 15% or chow + fructose, 15% + hydroalcoholic extract of leaves of Aegle marmelos (AM-HM, 500 mg/kg/d, po) and assessed for feed intake, fructose intake, body weight, fasting blood sugar, oral glucose tolerance test, HOMA-IR, insulin tolerance test and lipid profile. Activities of enzymes (glucose-6-phosphatase, hexokinase, phosphofructokinase, aldehyde dehydrogenase), hormones (leptin, ghrelin, insulin), insulin signaling molecules (Akt-PI3k, AMPK, JNK) hallmarks of inflammation (TNF-α), angiogenesis (VEGF), hypoxia (HIF-1), lipogenesis (mTOR) and regulatory nuclear transcription factors of de novo lipogenesis and hepatic insulin resistance gene (SREBP-1, FoxO1) that together govern the hepatic fructose metabolism, were also studied. The effect of fructose-rich environment on metabolic milieu of hepatocytes was confirmed using (human hepatocellular carcinoma) HepG2 cells. Using in vitro model, fructose uptake and glucose output from isolated murine hepatocytes were measured to establish the HepIR under fructose environment and delineate the effect of AM-HM. The leaves from the plant Aegle marmelos (L) Correa were extracted, fractionated and validated for rutin content using LC-MS/MS. The rutin content of extract was quantified and correlated with oral pharmacokinetic parameters in rat. The outcomes of the study suggest that the molecular and metabolic markers of fructose induced HepIR in developing and adult rats are distinct. Further, AM-HM exerts a multi-pronged attack by raising insulin secretion, augmenting insulin action, improving downstream signaling of insulin, reducing overall requirement of insulin and modulating hepatic expression of glucose transporter (Glut2). The butanol fraction of AM-HM holds promise for future development.

Geraniol, a natural monoterpene, ameliorates hyperglycemia by attenuating the key enzymes of carbohydrate metabolism in streptozotocin-induced diabetic rats

CONTEXT

Geraniol, an acyclic monoterpene alcohol is found in medicinal plants, is used traditionally for several medical purposes including diabetes.

OBJECTIVES

The present study evaluates the antihyperglycemic potential of geraniol on key enzymes of carbohydrate metabolism in streptozotocin (STZ)-induced diabetic rats.

MATERIALS AND METHODS

Diabetes was induced in experimental rats, by a single intraperitoneal (i.p) injection of STZ [40 mg/kg body weight (b.w.)]. Different doses of geraniol (100, 200 and 400 mg/kg b.w.) and glyclazide (5 mg/kg b.w.) were administrated orally to diabetic rats for 45 days. Body weight, food intake, plasma glucose, insulin, blood haemoglobin (Hb), glycosylated haemoglobin (HbA_1c), hepatic glucose metabolic enzymes and glycogen were examined.

RESULTS

The LD₅₀ value of geraniol is 3600 mg/kg b.w. at oral administration in rats. Administration of geraniol in a dose-dependent manner (100, 200, 400 mg/kg b.w.) and glyclazide (5 mg/kg b.w.) for 45 days significantly improved the levels of insulin, Hb and decreased plasma glucose, HbA_1C in diabetic-treated rats. Geraniol at its effective dose (200 mg/kg b.w.) ameliorated the altered activities of carbohydrate metabolic enzymes near normal effects compared with two other doses (100 and 400 mg/kg b.w.). Geraniol treatment to diabetic rats improved hepatic glycogen content suggesting its anti-hyperglycemic potential. Geraniol supplement was found to preserve the normal histological appearance of hepatic cells and pancreatic β-cells in diabetic rats.

DISCUSSION AND CONCLUSIONS

The present findings suggest that geraniol can potentially ameliorate key enzymes of glucose metabolism in experimental diabetes even though clinical studies used to evaluate this possibility are warranted.

Troglitazone suppresses glutamine metabolism through a PPAR-independent mechanism

Enhanced glutamine metabolism is required for tumor cell growth and survival, which suggests that agents targeting glutaminolysis may have utility within anti-cancer therapies. Troglitazone, a PPARγ agonist, exhibits significant anti-tumor activity and can alter glutamine metabolism in multiple cell types. Therefore, we examined whether troglitazone would disrupt glutamine metabolism in tumor cells and whether its action was reliant on PPARγ activity. We found that troglitazone treatment suppressed glutamine uptake and the expression of the glutamine transporter, ASCT2, and glutaminase. In addition, troglitazone reduced 13C-glutamine incorporation into the TCA cycle, decreased [ATP], and resulted in an increase in reactive oxygen species (ROS). Further, troglitazone treatment decreased tumor cell growth, which was partially rescued with the addition of the TCA-intermediate, α-ketoglutarate, or the antioxidant N-acetylcysteine. Importantly, troglitazone's effects on glutamine uptake or viable cell number were found to be PPARγ-independent. In contrast, troglitazone caused a decrease in c-Myc levels, while the proteasomal inhibitor, MG132, rescued c-Myc, ASCT2 and GLS1 expression, as well as glutamine uptake and cell number. Lastly, combinatorial treatment of troglitazone and metformin resulted in a synergistic decrease in cell number. Therefore, characterizing new anti-tumor properties of previously approved FDA therapies supports the potential for repurposing of these agents.

Dual Peroxisome Proliferator-Activated Receptor-alpha/gamma Agonists : In the Treatment of Type 2 Diabetes Mellitus and the Metabolic Syndrome

The metabolic syndrome consists of a combination of cardiovascular risk factors that include hyperglycemia with or without type 2 diabetes mellitus, visceral obesity, elevated blood pressure, and atherogenic dyslipidemia. These interrelated disorders and their associated lipotoxicity, oxidative stress, and inflammatory state predispose to a constellation of cardiovascular conditions leading to high risk of heart attack, stroke, renal failure, blindness, and lower extremity amputation. Visceral obesity, a prime risk factor for type 2 diabetes and a major component of the metabolic syndrome, potentiates atherogenesis, atherosclerosis, organ lipotoxicity, and oxidative tissue damage.Peroxisome proliferator-activated receptors (PPARs) are relatively recently discovered nuclear transcription factors that are modulated by dietary fatty acids, including the essential polyunsaturated fatty acids, arachidonic acid and its metabolites, and are essential to the control of energy metabolism. Of the three PPAR isoforms (alpha, gamma, and delta), synthetic pharmaceutical ligands that activate PPARalpha (the antidyslipidemic fibric acid derivatives ['fibrates']) and PPARgamma (the antidiabetic thiazolidinediones) have been studied extensively. Recently developed dual PPARalpha/gamma agonists may combine the therapeutic effects of these drugs, creating the expectation of greater efficacy, and perhaps other advantages in the treatment of type 2 diabetes and the metabolic syndrome. However, thiazolidinediones are hampered by adverse effects related to increased weight gain and fluid overload. It remains to be seen whether the dual PPARalpha/gamma agonists currently under development have similar limitations. Nevertheless, existing clinical data imply that the combined effects of thiazolidinediones and fibrates are likely to be emulated by dual PPARalpha/gamma agonists, providing superior efficacy to these classes for the treatment of type 2 diabetes, the metabolic syndrome, and their cardiovascular and other end-organ complications.

A phase II clinical trial to investigate the effect of pioglitazone on (18)F-FDG uptake in malignant lesions

BACKGROUND

We found that (18)F-2-fluoro-2-deoxy-D-glucose ((18)F-FDG) uptake in malignant lesion was enhanced, and it was decreased in the inflammatory lesion after the use of peroxisome proliferator activated receptor-γ (PPAR-γ) agonist in our previous preclinical study. The purpose of this study was to investigate the effect of PPAR-γ agonist on malignant lesions in clinical (18)F-FDG positron emission tomography/computed tomography (PET/CT) imaging.

METHODS

Forty-three patients were enrolled in this prospective study. We received the approval for the investigator-initiated trials for a phase II human clinical trial from the Korean Food and Drug Administration. On the first day, (18)F-FDG PET/CT images were acquired from patients without administration of pioglitazone (PIO), which is a PPAR-γ agonist. On the next day, (18)F-FDG PET/CT images were acquired once again from the same patients after administration of PIO. We measured the (18)F-FDG uptake in malignant lesions or inflammatory lesions from two (18)F-FDG PET/CT images. Four different PET parameters were used to compare between the two studies: SUVmax, SUVmean, average activity over 30 % of the isocontour (isocontour, Bq/mL), and isocontour-mediastinal activity (Bq/mL). Additionally, we classified the patients into two groups: the responder or non-responder group according to the presence of PIO effect on skeletal muscle. Furthermore, PET parameters of malignant lesions were analyzed based on the type of malignancy and were compared with those of inflammatory lesions.

RESULTS

All four PET parameters of malignant lesions in the responder group showed increasing patterns after the use of PIO. In the subgroup analysis, the similar pattern was observed in gastrointestinal cancer. In hepatobiliary and pancreatic cancer, SUVmean and isocontour showed statistically significant increase in the presence of PIO. On the other hand, in the non-responder group, all four PET parameters showed decreasing patterns in both malignant and inflammatory lesions after the use of PIO. There was no statistically significant difference in PET parameters of malignant lesions in the non-responder group.

CONCLUSIONS

In this study, we found that PIO had the potential to increase (18)F-FDG uptake of malignant lesions in the patients who showed PIO effect on skeletal muscle. Contrary to our preclinical studies, clinical results had limitations to evaluate malignant lesions in non-responder group. Further larger-scale studies are necessary to elucidate the potential role of PIO on (18)F-FDG uptake in malignant or inflammatory lesions.

TRIAL REGISTRATION

The test for safety and effectiveness of the new efficacy of Pioglitazone to diagnose the malignant tumor and inflammation in F-18 FDG positron emission tomography (PET) study, 12029.

Proteomic Analysis of GLUT4 Storage Vesicles Reveals Tumor Suppressor Candidate 5 (TUSC5) as a Novel Regulator of Insulin Action in Adipocytes

Insulin signaling augments glucose transport by regulating glucose transporter 4 (GLUT4) trafficking from specialized intracellular compartments, termed GLUT4 storage vesicles (GSVs), to the plasma membrane. Proteomic analysis of GSVs by mass spectrometry revealed enrichment of 59 proteins in these vesicles. We measured reduced abundance of 23 of these proteins following insulin stimulation and assigned these as high confidence GSV proteins. These included established GSV proteins such as GLUT4 and insulin-responsive aminopeptidase, as well as six proteins not previously reported to be localized to GSVs. Tumor suppressor candidate 5 (TUSC5) was shown to be a novel GSV protein that underwent a 3.7-fold increase in abundance at the plasma membrane in response to insulin. siRNA-mediated knockdown of TUSC5 decreased insulin-stimulated glucose uptake, although overexpression of TUSC5 had the opposite effect, implicating TUSC5 as a positive regulator of insulin-stimulated glucose transport in adipocytes. Incubation of adipocytes with TNFα caused insulin resistance and a concomitant reduction in TUSC5. Consistent with previous studies, peroxisome proliferator-activated receptor (PPAR) γ agonism reversed TNFα-induced insulin resistance. TUSC5 expression was necessary but insufficient for PPARγ-mediated reversal of insulin resistance. These findings functionally link TUSC5 to GLUT4 trafficking, insulin action, insulin resistance, and PPARγ action in the adipocyte. Further studies are required to establish the exact role of TUSC5 in adipocytes.

Rosiglitazone enhances apolipoprotein M (Apom) expression in rat's liver

Apolipoprotein M (APOM) has been suggested as a vasculoprotective constituent of high density lipoprotein (HDL), which plays a crucial role behind the mechanism of HDL-mediated anti-atherosclerosis. Previous studies demonstrated that insulin resistance could associate with decreased APOM expressions. In agreement with our previous reports, here, we further confirmed that the insulin sensitivity was also reduced in rats treated with high concentrations of glucose; such effect could be reversed by administration of rosiglitazone, a peroxisome proliferator-activated receptor-γ (PPARγ). The present study shows that Apom expression is significantly affected by either rosiglitazone or hyperglycemia alone without cross interaction with each other, which indicates that the pathway of Apom expression regulating by hyperglycemia might be differed from that by rosiglitazone. Further study indicated that hyperglycemia could significantly inhibit mRNA levels of Lxrb (P=0.0002), small heterodimer partner 1 (Shp1) (P<0.0001), liver receptor homologue-1 (Lrh1) (P=0.0012), ATP-binding cassette transporter 1 (Abca1) (P=0.0012) and Pparb/d (P=0.0043). Two-way ANOVA analysis demonstrated that the interactions between rosiglitazone and infusion of 25% glucose solution on Shp1 (P=0.0054) and Abca1 (4E, P=0.0004) mRNA expression was statistically significant. It is concluded that rosiglitazone could increase Apom expression, of which the detailed mechanism needs to be further investigated. The downregulation of Apom by hyperglycemia might be mainly through decreasing expression of Pparg and followed by inhibiting Lxrb in rats.

SDF7, a group of Scoparia dulcis Linn. derived flavonoid compounds, stimulates glucose uptake and regulates adipocytokines in 3T3-F442a adipocytes

ETHNOPHARMACOLOGY RELEVANCE

Adipocytes are major tissues involved in glucose uptake second to skeletal muscle and act as the main adipocytokines mediator that regulates glucose uptake mechanism and cellular differentiation. The objective of this study were to examine the effect of the SDF7, which is a fraction consists of four flavonoid compounds (quercetin: p-coumaric acid: luteolin: apigenin=8: 26: 1: 3) from Scoparia dulcis Linn., on stimulating the downstream components of insulin signalling and the adipocytokines expression on different cellular fractions of 3T3-F442a adipocytes.

MATERIAL AND METHODS

Morphology and lipid accumulation of differentiated 3T3-F442a adipocytes by 100 nM insulin treated with different concentrations of SDF7 and rosiglitazone were examined followed by the evaluation of glucose uptake activity expressions of insulin signalling downstream components (IRS-1, PI3-kinase, PKB, PKC, TC10 and GLUT4) from four cellular fractions (plasma membrane, cytosol, high density microsome and low density microsome). Next, the expression level of adipocytokines (TNF-α, adiponectin and leptin) and immunoblotting of treated 3T3-F442 adipocytes was determined at 30 min and 480 min. Glucose transporter 4 (GLUT4) translocation of 3T3-F442a adipocytes membrane was also determined. Lastly, mRNA expression of adiponectin and PPAR-γ of 3T3-F442a adipocytes were induced and compared with basal concentration.

RESULTS

It was found that SDF7 was able to induce adipocytes differentiation with great extends of morphological changes, lipid synthesis and lipid stimulation in vitro. SDF7 stimulation of glucose transport on 3T3-F442a adipocytes are found to be dose independent, time-dependent and plasma membrane GLUT4 expression-dependent. Moreover, SDF7 are observed to be able to suppress TNF-α and leptin expressions that were mediated by 3T3-F442a adipocytes, while stimulated adiponectin secretion on the cells. There was a significant expression (p<0.01) of protein kinase C and small G protein TC10 on 3T3-F442a adipocytes upon treatment with SDF7 as compared to the control. SDF7 was also found to be effective in stimulating adiponectin and PPAR-γ mRNA upregulation at 50 µg/ml.

CONCLUSION

SDF7 exhibited good lipogenesis, adiponectinesis and glucose uptake stimulatory properties on 3T3-F442a adipocytes.

Proteomic analysis of rosiglitazone and guggulsterone treated 3T3-L1 preadipocytes

Adipogenesis is the differentiation of preadipocytes to adipocytes which is marked by the accumulation of lipid droplets. Adipogenic differentiation of 3T3-L1 cells is achieved by exposing the cells to Insulin, Dexamethasone and IBMX for 5-7 days. Thiazolidinedione drugs, like rosiglitazone are potent insulin sensitizing agents and have been shown to enhance lipid droplet formation in 3T3-L1 cells, a model cell line for preadipocyte differentiation. Guggulsterone is a natural drug extracted from the gum resin of tree Commiphora mukul. Guggulsterone has been shown to inhibit adipogenesis and induce apoptosis in 3T3-L1 cells. In this study we treated the 3T3-L1 preadipocytes with rosiglitazone and guggulsterone and assessed the protein expression profile using 2D gel electrophoresis-based proteomics to find out differential target proteins of these drugs. The proteins that were identified upon rosiglitazone treatment generally regulate cell proliferation and/or exhibit anti-inflammatory effect which strengthens its differentiation-inducing property. Guggulsterone treatment resulted in the identification of the apoptosis-inducing proteins to be up regulated which rightly is in agreement with the apoptosis-inducing property of guggulsterone in 3T3-L1 cells. Some of the proteins identified in our proteomic screen such as Galectin1, AnnexinA2 & TCTP were further confirmed by Real Time qPCR. Thus, the present study provides a better outlook of proteins being differentially regulated/expressed upon treatment with rosiglitazone and guggulsterone. The detailed study of the differentially expressed proteins identified in this proteomic screen may further provide the better molecular insight into the mode of action of these anti-diabetic drugs rosiglitazone and guggulsterone.

Effects of Combination of Thiazolidinediones with Melatonin in Dexamethasone-induced Insulin Resistance in Mice

In type 2 Diabetes, oxidative stress plays an important role in development and aggregation of insulin resistance. In the present study, long term administration of the dexamethasone led to the development of insulin resistance in mice. The effect of thiazolidinediones pioglitazone and rosiglitazone, with melatonin on dexamethasone-induced insulin resistance was evaluated in mice. Insulin resistant mice were treated with combination of pioglitazone (10 mg/kg/day, p.o.) or rosiglitazone (5 mg/kg/day, p.o.) with melatonin 10 mg/kg/day p.o. from day 7 to day 22. In the biochemical parameters, the serum glucose, triglyceride levels were significantly lowered (P<0.05) in the combination groups as compared to dexamethasone treated group as well as with individual groups of pioglitazone, rosiglitazone, and melatonin. There was also, significant increased (P<0.05) in the body weight gain in combination treated groups as compared to dexamethasone as well as individual groups. The combination groups proved to be effective in normalizing the levels of superoxide dismutase, catalase, glutathione reductase and lipid peroxidation in liver homogenates may be due to antioxidant effects of melatonin and decreased hyperglycemia induced insulin resistance by thiazolidinediones. The glucose uptake in the isolated hemidiaphragm of mice was significantly increased in combination treated groups (PM and RM) than dexamethasone alone treated mice as well as individual (pioglitazone, rosiglitazone, melatonin) treated groups probably via increased in expression of GLUT-4 by melatonin and thiazolidinediones as well as increased in insulin sensitivity by thiazolidinediones. Hence, it can be concluded that combination of pioglitazone and rosiglitazone, thiazolidinediones, with melatonin may reduces the insulin resistance via decreased in oxidative stress and control on hyperglycemia.

Confirmatory studies on the antioxidant and antidiabetic effect of quercetin in rats

Quercetin (QE), one of natural flavanoid group, was widely distributed as a secondary metabolite in plant kingdom. It has been believed that oxidative stress plays a role in the pathogenesis of diabetes mellitus (DM). The aim of the present study was the evaluation of possible effects of QE on blood glucose and antioxidant enzymes in experimental streptozotocin (STZ)-induced diabetes in rats. STZ was injected intraperitoneally with single dose of 50 mg/kg for diabetes induction. QE (15 mg/kg bw day, intraperitoneal (i.p.) injection) was injected for 3 days prior to STZ administration; these injections were continued to the end of the study (for 25 days). Glucose tolerance test and random plasma glucose were done for all animals. Cellular antioxidant enzymes such as glutathione peroxidase (GSHPx), superoxide dismutase (SOD) and catalase (CAT) activities were measured in pancreatic homogenates. Quercetin had no effect on plasma glucose level of normal animals but its pre- treatment was able to prevent diabetes induced by single intraperitoneal injection of streptozocintreated rats. Antioxidant enzyme activity significantly decreased in STZ induced diabetic group. QE treatment significantly increased the antioxidant enzyme activities. It could be concluded that quercetin, a flavonoid with antioxidant properties, exerting its beneficial antidiabetic effects.

Metabolic effects of various antidiabetic and hypolipidaemic agents on a high-fat diet and multiple low-dose streptozocin (MLDS) mouse model of diabetes

Insulin resistance and subsequent insulin secretory defect are two main features of type 2 diabetes and associated metabolic disorders. The animal models of type 2 diabetes are very complex and are as heterogeneous as the disease. We have evaluated the effect of various antidiabetic and lipid lowering agents (fenofibrate, rosiglitazone, glimepiride, metformin and simvastatin) on the metabolic abnormalities induced by combining a high-fat diet and multiple low-dose streptozocin (MLDS) in mice. Male Swiss albino mice were orally treated with the above agents and fed with a diet containing high fat for 28 days. On day 15 the animals were injected intraperitoneally with low-dose streptozocin (40 mg kg−1), which was administered for five consecutive days. At the end of the 28-day treatment plasma metabolic parameters (glucose, triglyceride and immunoreactive insulin) were estimated. The antidiabetic and hypolipidaemic agents exhibited differential effects on these metabolic parameters. With the exception of fenofibrate all these agents reduced the plasma glucose levels, and the effects of metformin and rosiglitazone on glucose were found to be statistically significant. Although the effect of the test drugs on cholesterol was modest, a significant decrease in triglyceride levels was observed with sub-chronic treatment with these agents. Interestingly, glimepiride mildly elevated the insulin levels while the other antidiabetics and hypolipidaemics reduced the insulin levels, with metformin and rosiglitazone exhibiting statistically significant effects on insulin. To our knowledge this is the first report on the effect of various peroxisome proliferator-activated receptor modulators and newer antidiabetics on the metabolic effects induced by the combined high-fat diet and MLDS model of type 2 diabetes in Swiss albino mice. The results suggested the complexity of the hyperglycaemia, hyperinsulinaemia and hypertriglyceridaemia induced by the high-fat diet and MLDS mouse model, and their correction by various antidiabetics and antihyperlipidaemics may have involved diverse mechanisms.

Rosiglitazone increases cell surface GLUT4 levels in 3T3-L1 adipocytes through an enhancement of endosomal recycling

Insulin induces a translocation of the glucose transporter GLUT4 from intracellular storage compartments towards the cell surface in adipocytes and skeletal muscle cells, allowing the cells to take up glucose. In type 2 diabetes-associated insulin resistance, the efficiency of this process is reduced. The thiazolidinediones, widely prescribed as anti-diabetic therapy, are generally regarded as insulin-sensitizers. The aim of this study was to evaluate the effect of the thiazolidinedione rosiglitazone (BRL 49653) on GLUT4 in adipocytes. When applied during differentiation, rosiglitazone dose dependently augmented GLUT4 expression along with the formation of lipid droplets. Intriguingly, its presence during differentiation led to increases in both cell surface GLUT4 levels and insulin sensitivity of GLUT4 translocation in mature adipocytes. Treatment of fully differentiated adipocytes with rosiglitazone also led to increases in GLUT4 at the plasma membrane. Rosiglitazone similarly affected cell surface levels of the endosomal transferrin receptor, but did not alter the GLUT4 internalization rate. The augmentation in cell surface GLUT4 levels was maintained in adipocytes that were rendered insulin-resistant in vitro by a 24h insulin treatment and moreover in these cells rosiglitazone also fully restored insulin-induced GLUT4 translocation. We conclude that in adipocytes, rosiglitazone increases cell surface GLUT4 levels by increasing its endosomal recycling and restores insulin-induced GLUT4 translocation in insulin resistance. These results implicate novel modes of action on GLUT4 that are all likely to contribute to the insulin-sensitizing effect of rosiglitazone in type 2 diabetes.

Treatment with a peroxisomal proliferator activated receptor gamma agonist has a modest effect in the allergen challenge model in asthma: a randomised controlled trial

PURPOSE

A considerable body of non clinical evidence has accumulated to support peroxisomal proliferator-activated receptor gamma agonists as candidate anti-inflammatory drugs in asthma. We utilized rosiglitazone as a tool compound in the inhaled allergen challenge model of asthma.

METHODS

A single centre, double-blind, randomised, placebo controlled, two period cross-over study. Subjects received rosiglitazone 4mg and placebo twice daily for 28 days in random order. On day 28, inhaled allergen challenge was performed 1 hour post-dose. A methacholine challenge was performed on day 29 and an adenosine monophosphate challenge on day 14. Exhaled nitric oxide was measured on days 1, 14, 28, 29. Blood was collected pre dose on days 1, 14 and 28 and analysed for markers associated with PPAR activity and systemic markers of inflammation.

RESULTS

The late asthmatic reaction (LAR) change from post saline FEV(1) from 4-10 hrs post allergen on day 28 was statistically significant for the weighted mean LAR. The difference in weighted mean was 0.06 L (95% CI 0.01 to 0.11) which equates to a 15% attenuation of the response during placebo treatment. This was accompanied by trends in other markers of efficacy and anti-inflammatory activity but none were considered major effects.

DISCUSSION

Treatment with a PPARgamma agonist (rosiglitazone) was associated with a modest (15%) reduction in the late asthmatic reaction in the allergen challenge model of asthma. Based on the results of this study, PPARgamma agonist monotherapy is unlikely to represent a clinically useful intervention in human asthma. Registered with www.clinicaltrials.gov (NCT00318630).

Inhibition of protein tyrosine phosphatase-1B with antisense oligonucleotides improves insulin sensitivity and increases adiponectin concentrations in monkeys

Protein tyrosine phosphatase (PTP)-1B antagonizes insulin signaling and is a potential therapeutic target for insulin resistance associated with obesity and type 2 diabetes. To date, studies of PTP-1B have been limited by the availability of specific antagonists; however, treatment of rodents with antisense oligonucleotides (ASOs) directed against PTP-1B improves insulin sensitivity, inhibits lipogenic gene expression, and reduces triglyceride accumulation in liver and adipose tissue. Here we investigated ASO-mediated PTP-1B inhibition in primates. First, PTP-1B ASO (ISIS 113715) dose-dependently inhibited PTP-1B mRNA and protein expression in cultured monkey hepatocytes. Subcutaneous administration of ISIS 113715 reduced PTP-1B mRNA expression in liver and adipose tissue of normal-weight monkeys by 40-50% and improved insulin sensitivity during an iv glucose tolerance test (IVGTT). In obese, insulin-resistant rhesus monkeys, treatment with 20 mg/kg ISIS 113715 for 4 wk reduced fasting concentrations of insulin and glucose and reduced insulin responses during an IVGTT. In these animals, adiponectin concentrations were also increased by 70%, most of which was an increase of high-molecular-weight oligomers. These effects were not observed in monkeys on a lower, dose-escalation regimen (1-10 mg/kg over 9 wk). Overall, the increase of adiponectin concentrations during ISIS 113715 treatment was correlated with the lowering of insulin responses during IVGTT (r = -0.47, P = 0.042). These results indicate that inhibition of PTP-1B with ASOs such as ISIS 113715 may be a viable approach for the treatment and prevention of obesity-associated insulin resistance and type 2 diabetes because they potently increase adiponectin concentrations in addition to improving insulin sensitivity.

Rosiglitazone modulates insulin-induced plasma membrane area changes in single 3T3-L1 adipocytes

In this study we hypothesized that rosiglitazone, an antidiabetic high-affinity agonist for the peroxisome proliferator-activated receptor gamma, affects the plasma membrane (PM) turnover in single 3T3-L1 adipocytes. To study the PM turnover, the patch-clamp electrophysiological method was used to measure changes in membrane capacitance (Cm), a parameter linearly related to the PM area. Microscopy results show that the presence of rosiglitazone in the differentiating medium significantly increased the differentiation of 3T3-L1 adipocytes in cell culture, based on oil red O-stained area (11.4 +/- 1.2%) vs. controls (3.1 +/- 0.5%). Moreover, rosiglitazone treatment significantly reduced the size of single 3T3-L1 adipocytes; their average radius of 21.1 +/- 1.1 microm in controls was reduced to 17.5 +/- 0.5 microm in rosiglitazone-treated cells. Consistent with this, insulin application increased the rate of Cm increase to 2.34 +/- 0.10%/min, which was significantly different from controls (0.12 +/- 0.08%/min). However, pretreatment of cells with rosiglitazone prior to the treatment with insulin resulted in an attenuated rate of Cm increase. These data support the involvement of insulin in the modulation of membrane area and show that treatment by rosiglitazone reduced the insulin-mediated membrane area increase in 3T3-L1 adipocytes.

The effects of obesity-associated insulin resistance on mRNA expression of peroxisome proliferator-activated receptor-γ target genes, in dogs

Visceral adipose tissue and skeletal muscle have central roles in determining whole-body insulin sensitivity. The peroxisome proliferator-activated receptor-γ (PPARγ) is a potential mediator of insulin sensitivity. It can directly modulate the expression of genes that are involved in glucose and lipid metabolism, including GLUT4, lipoprotein lipase (LPL) and adipocytokines (leptin and adiponectin). In this study, we aimed to determine the effects of obesity-associated insulin resistance on mRNA expression of PPARγ and its target genes. Dogs were studied when they were lean and at the end of an overfeeding period when they had reached a steady obese state. The use of a sensitive, real-time PCR assay allowed a relative quantification of mRNA expression for PPARγ, LPL, GLUT4, leptin and adiponectin, in adipose tissue and skeletal muscle. In visceral adipose tissue and/or skeletal muscle, mRNA expression of PPARγ, LPL and GLUT4 were at least 2-fold less in obese and insulin-resistant dogs compared with the same animals when they were lean and insulin-sensitive. The mRNA expression and plasma concentration of leptin was increased, whereas the plasma level and mRNA expression of adiponectin was decreased, by obesity. In adipose tissue, PPARγ expression was correlated with leptin and adiponectin. These findings, in an original model of obesity induced by a prolonged period of overfeeding, showed that insulin resistance is associated with a decrease in PPARγ mRNA expression that could dysregulate expression of several genes involved in glucose and lipid metabolism.

The different mechanisms of insulin sensitizers to prevent type 2 diabetes in OLETF rats

OBJECTIVE

To investigate the effects of pioglitazone and metformin treatment during pre-diabetic period for the prevention of diabetes in a rat model.

METHODS

OLETF rats aged 18-weeks, were treated with pioglitazone (10 mg/kg/day) and metformin (300 mg/kg/day) for 10 weeks from their pre-diabetic period. We measured weight, lipid profiles, fat distribution, glucose tolerance, and pancreatic insulin content.

RESULTS

Prominent weight gain (mostly subcutaneous fat area) was observed in the pioglitazone-treated OLETF (O-P) rats versus significant weight loss was observed in the metformin-treated OLETF (O-M) rats. Pioglitazone reversed the serum triglyceride (TG) and FFAs levels to normal (TG 0.46 +/- 0.04 vs 0.88 +/- 0.05 mmol/l in LETO). At the age of 28 weeks, the O-P rats showed completely normal glucose tolerance, and the glucose disposal rate (GDR) was markedly improved (25.6 +/- 0.4 vs 20.6 +/- 0.5 mg/min/kg in O-C, p < 0.05). The O-M rats also showed an improved fasting glucose and GDR level, but not as much as those with O-P rats. The pancreas insulin contents were much improved in the O-P rats (22.9 +/- 1.2 vs 18.8 +/- 1.3 nmol/pancreas in O-M rats, p < 0.05) with histological improvement.

CONCLUSION

The pre-diabetic treatment with pioglitazone, despite significant weight gain, completely prevents to develop diabetes and enhances beta cell function with preservation of islet cell changes. Metformin treatment was also effective, but mainly by ameliorating the insulin resistance with marked reduction in body weight. The reversal of dyslipidaemia and the fat redistribution might contribute to the greater improvement of pioglitazone treatment compared to metformin in OLETF rats.

Antidiabetic effect of a novel non-thiazolidinedione PPAR gamma/alpha agonist on ob/ob mice

AIM

To study whether T33, a new synthesized non-thiazolidinedione (TZD) peroxisome proliferator-activated receptor (PPAR) gamma/alpha dual agonist has an antidiabetic effect on ob/ob mice.

METHODS

Ob/ob mice were treated with 4 mg/kg or 8 mg/kg T33 by gavage for 20 d. Blood glucose levels were measured regularly. An oral glucose tolerance test (OGTT) and an insulin tolerance test (ITT) were preformed on d 8 and d 12, respectively. The levels of insulin, triglyceride and free fatty acid (FFA) in the serum were measured at the end of administration. The intramuscular and liver triglyceride content was also determined.

RESULTS

T33 reduced the hyperglycemia, hyperinsulinemia and hyperlipidemia of the ob/ob mice. The OGTT and ITT showed that the insulin resistance state of the ob/ob mice was obviously ameliorated after T33 treatment. After 20 d treatment with 8 mg/kg T33, the triglyceride content in the gastrocnemius muscle decreased significantly. T33 did not have any effect on triglyceride content in the liver, whereas rosiglitazone significantly increased the hepatocyte lipid deposition.

CONCLUSION

The PPARgamma/alpha dual agonist T33 has antidiabetic and insulin-sensitizing effects in ob/ob mice. It has the potential to be a new therapeutic candidate for the treatment of type 2 diabetes.

Rosiglitazone versus bedtime insulin in the treatment of patients with conventional oral antidiabetic drug failure: a 1-year randomized clinical trial

This study was conducted to evaluate the efficacy and tolerability of rosiglitazone in the treatment of patients with secondary oral antidiabetic drug (OAD) failure and to directly compare its use with bedtime insulin. A total of 112 Chinese patients with type 2 diabetes and conventional OAD failure were recruited. Patients were randomly assigned to treatment with rosiglitazone or bedtime isophane insulin; they continued to take their original oral antidiabetic drugs. Glycemic index, other clinical profiles, and tolerability were assessed during treatment and 1 y after add-on treatment was provided. Among the 112 patients, mean age (+/-SD) was 58.2+/-11.0 y (median, 58 y; range, 37 to 84 y). Both rosiglitazone (n=56) and insulin (n=56) significantly improved fasting glucose (2.4 and 3.7 mmol/L, respectively) and hemoglobin A1c concentrations (1.1% and 1.3%, respectively). Both therapies increased body mass index after 1 y of treatment (0.9 and 0.8 kg/m2, respectively). Only rosiglitazone increased high-density lipoprotein cholesterol concentrations (0.1 mmol/L). Four patients (7.1%) who were given rosiglitazone developed adverse effects (2, ankle edema, and 2, gastrointestinal disturbance). Six insulin-treated patients (10.7%) described adverse effects (5, early morning hypoglycemia, and 1, anxiety). Investigators concluded that in Chinese patients with type 2 diabetes and secondary conventional OAD failure, 1 y of treatment with rosiglitazone or bedtime insulin added to the regular regimen resulted in similar improvements in glycemic control. Rosiglitazone was also associated with improved high-density lipoprotein cholesterol levels. The addition of rosiglitazone may offer a safe and effective alternative to bedtime insulin treatment.

Cardioprotection mediated by rosiglitazone, a peroxisome proliferator-activated receptor gamma ligand, in relation to nitric oxide

Activation of peroxisome proliferator-activated receptor (PPAR) gamma protects from myocardial ischemia/reperfusion injury. The aim of the study was to investigate whether the cardioprotective effect of PPARgamma is related to nitric oxide (NO).

METHODS

Wild type (WT) and endothelial NO synthase (eNOS) knockout (KO) mice received 3 mg/kg of the PPARgamma agonist rosiglitazone or vehicle (n = 6-9 in each group) i. p. 45 min before anesthesia. The hearts were isolated, perfused in a Langendorff mode and subjected to global ischemia and 30 min reperfusion. The hearts of another two groups of WT mice received the NOS inhibitor L-NNA (100 micromol/l) or vehicle in addition to pre-treatment with vehicle or rosiglitazone.

RESULTS

In the WT heart, rosiglitazone increased the recovery of left ventricular function and coronary flow following ischemia in comparison with the vehicle group.L-NNA did not affect recovery per se but significantly blunted the improvement in the recovery of left ventricular function induced by rosiglitazone. In the KO group rosiglitazone suppressed the recovery of myocardial function following ischemia. Expression of eNOS was not affected, but phosphorylated eNOS was significantly increased by rosiglitazone in the WT hearts (P < 0.05).

CONCLUSION

These results suggest that the cardioprotective effect of the PPARgamma agonist rosiglitazone is mediated via NO by phosphorylation of eNOS.

Atypical diabetes associated with inclusion formation in the R6/2 mouse model of Huntington's disease is not improved by treatment with hypoglycaemic agents

The R6/2 transgenic mouse model of Huntington's disease (HD) develops a progressive neurological phenotype that involves severe motor and cognitive dysfunctions. Although not a cardinal sign, diabetes has been described in R6/2 mice. It is not clear, however, whether the diabetes contributes to the HD-like phenotype of R6/2 mice. In our study we found that the severity of diabetes in R6/2 mice was associated with the progressive formation of ubiquinated inclusions in pancreatic beta cells. Diabetes is dissociated from early motor and cognitive dysfunctions and did not correlate with motor impairment and survival of R6/2 mice. However, chronic behavioural testing (at a level higher than that which is reported to improve several aspects of the R6/2 phenotype) exacerbated the onset of diabetes. Pharmacological treatment of the diabetes was attempted using two oral hypoglycaemic agents commonly used by diabetics. The mice responded acutely to glibenclamide (which induces exocytosis of insulin) but not to rosiglitazone (which induces sensitization to insulin). This supports the suggestion that the diabetes in R6/2 mice is caused by an impairment in insulin release rather than insulin insensitivity. However, chronic treatment with these hypoglycaemic agents had no effect on either the course of the diabetes or the disease in R6/2 mice.

Weight Loss–Associated Induction of Peroxisome Proliferator–Activated Receptor-α and Peroxisome Proliferator–Activated Receptor-γ Correlate With Reduced Atherosclerosis and Improved Cardiovascular Function in Obese Insulin-Resistant Mice

Background— Weight loss in obese insulin-resistant but not in insulin-sensitive persons reduces coronary heart disease risk. To what extent changes in gene expression are related to atherosclerosis and cardiovascular function is unknown.

Methods and Results— We studied the effect of diet restriction–induced weight loss on gene expression in the adipose tissue, the heart, and the aortic arch and on atherosclerosis and cardiovascular function in mice with combined leptin and LDL-receptor deficiency. Obesity, hypertriglyceridemia, and insulin resistance are associated with hypertension, impaired left ventricular function, and accelerated atherosclerosis in those mice. Compared with lean mice, peroxisome proliferator–activated receptors (PPAR)-α and PPAR-γ expression was downregulated in obese double-knockout mice. Diet restriction caused a 45% weight loss, an upregulation of PPAR-α and PPAR-γ, and a change in the expression of genes regulating glucose transport and insulin sensitivity, lipid metabolism, oxidative stress, and inflammation, most of which are under the transcriptional control of these PPARs. Changes in gene expression were associated with increased insulin sensitivity, decreased hypertriglyceridemia, reduced mean 24-hour blood pressure and heart rate, restored circadian variations of blood pressure and heart rate, increased ejection fraction, and reduced atherosclerosis. PPAR-α and PPAR-γ expression was inversely related to plaque volume and to oxidized LDL content in the plaques.

Conclusions— Induction of PPAR-α and PPAR-γ in adipose tissue, heart, and aortic arch is a key mechanism for reducing atherosclerosis and improving cardiovascular function resulting from weight loss. Improved lipid metabolism and insulin signaling is associated with decreased tissue deposition of oxidized LDL that increases cardiovascular risk in persons with the metabolic syndrome.

Effect of thalidomide and rosiglitazone on the prevention of diabetic retinopathy in streptozotocin-induced diabetic rats

AIMS/HYPOTHESIS

Our aim was to compare the therapeutic effect of thalidomide and rosiglitazone on the prevention of diabetic retinopathy in streptozotocin-induced diabetic rats.

METHODS

Male Holtzman rats of 6 to 8 weeks of age and weighing 170+/-30 g were randomly divided into four groups: control ( n=13), untreated diabetic ( n=17) and diabetic rats treated with thalidomide (200 mg kg(-1) day(-1)) ( n=8) or rosiglitazone (1 mg kg(-1) day(-1)) ( n=22) for 3 months. Diabetes was induced by streptozotocin with the rats having a body weight of 70 mg/kg. After treatment, vascular endothelial growth factor (VEGF) concentrations in ocular fluid were compared between the different groups, and retinal capillary basement membrane thickness was measured by electron microscopy.

RESULTS

Higher VEGF concentrations in ocular fluid and thicker basement membranes were observed in untreated diabetic rats compared to the control rats. Similar VEGF concentrations and basement membrane thickness were observed for the thalidomide-treated group compared with the control group, whereas no difference in these parameters was observed between the rosiglitazone-treated rats and the control or untreated diabetic rats.

CONCLUSIONS/INTERPRETATION

Our findings confirm the association between VEGF concentrations and diabetic retinopathy as suggested by other investigators. Thalidomide, but not rosiglitazone, was associated with the inhibition of basement membrane thickening and the blockade of the increase of VEGF in ocular fluid, thus representing a potential therapeutic drug for the prevention of diabetic retinopathy.

Expression of the insulin-responsive glucose transporter GLUT4 in adipocytes is dependent on liver X receptor alpha

The insulin-responsive glucose transporter GLUT4 plays a crucial role in insulin-mediated facilitated glucose uptake into adipose tissue and muscle, and impaired expression of GLUT4 has been linked to obesity and diabetes. In this study, we demonstrate that liver X receptors (LXRs) regulate the expression of GLUT4 through direct interaction with a conserved LXR response element in the GLUT4 promoter. The expression of GLUT4 in WAT is induced by a potent LXR agonist in wild type, LXR alpha-/-, and LXR beta-/- mice but not in LXR alpha-/-beta-/- mice, demonstrating that both LXRs are able to mediate ligand activated transcription of the GLUT4 gene. However, basal and insulin stimulated expression of GLUT4 in epididymal WAT is reduced only in mice carrying ablation of the LXR alpha isoform. The expression of GLUT4 is furthermore correlated to the induction of LXR alpha during mouse and human adipocyte differentiation. LXR beta is thus apparently not able to rescue basal expression of GLUT4 in the absence of LXR alpha. We have previously demonstrated that LXR alpha is down-regulated in animal models of obesity and diabetes, thus revealing a striking correlation between GLUT4 and LXR alpha expression in insulin-resistant conditions. This suggests that the LXR alpha isoform has a unique role in adipose expression of GLUT4 and suggests that alteration of adipose tissue expression of LXR alpha might be a novel tool to normalize the expression of a gene that is dysregulated in diabetic and insulin-resistant conditions.

Muscle-specific Pparg deletion causes insulin resistance

Thiazolidinediones (TZDs) are insulin-sensitizing drugs and are potent agonists of the nuclear peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Although muscle is the major organ responsible for insulin-stimulated glucose disposal, PPAR-gamma is more highly expressed in adipose tissue than in muscle. To address this issue, we used the Cre-loxP system to knock out Pparg, the gene encoding PPAR-gamma, in mouse skeletal muscle. As early as 4 months of age, mice with targeted disruption of PPAR-gamma in muscle showed glucose intolerance and progressive insulin resistance. Using the hyperinsulinemic-euglycemic clamp technique, the in vivo insulin-stimulated glucose disposal rate (IS-GDR) was reduced by approximately 80% and was unchanged by 3 weeks of TZD treatment. These effects reveal a crucial role for muscle PPAR-gamma in the maintenance of skeletal muscle insulin action, the etiology of insulin resistance and the action of TZDs.

PPARgamma and metabolism: insights from the study of human genetic variants

Diabetes, obesity, atherosclerosis and cancer are the principal contributors to morbidity and mortality in Western society. Emerging evidence indicates that a nuclear receptor, the peroxisome proliferator-activated receptor gamma (PPARgamma), plays a role in these pathological processes. Furthermore, modulation of receptor action in these diseases may be of therapeutic value, as exemplified by the recent introduction of the thiazolidinediones, a novel class of insulin-sensitizing agent for the treatment of type 2 diabetes mellitus. The availability of such high-affinity ligands has facilitated the study of signalling pathways through which PPARgamma regulates metabolic processes; these analyses have been complemented by the study of human subjects harbouring (naturally occurring) mutations and polymorphisms within the receptor. The latter have provided unique genetic evidence for a link between PPARgamma and mammalian glucose homeostasis, lipid metabolism and regulation of fat mass. This review highlights recent studies which have advanced our understanding of the pivotal role that this receptor plays in metabolism, with particular reference to the consequences of inherited variation in the human receptor gene.

The role of insulin resistance in the pathogenesis of Alzheimer's disease: implications for treatment

An emerging body of evidence suggests that an increased prevalence of insulin abnormalities and insulin resistance in Alzheimer's disease may contribute to the disease pathophysiology and clinical symptoms. It has long been known that insulin is essential for energy metabolism in the periphery. In the past 2 decades, convergent findings have begun to demonstrate that insulin also plays a role in energy metabolism and other aspects of CNS function. Investigators reported 20 years ago that insulin and insulin receptors were densely but selectively expressed in the brain, including the medial temporal regions that support the formation of memory. It has recently been demonstrated that insulin-sensitive glucose transporters are localised to the same regions supporting memory and that insulin plays a role in memory functions. Collectively, these findings suggest that insulin may contribute to normal cognitive functioning and that insulin abnormalities may exacerbate cognitive impairments, such as those associated with Alzheimer's disease. Insulin may also play a role in regulating the amyloid precursor protein and its derivative beta-amyloid (Abeta), which is associated with senile plaques, a neuropathological hallmark of Alzheimer's disease. It has been proposed that insulin can accelerate the intracellular trafficking of Abeta and interfere with its degradation. These findings are consistent with the notion that insulin abnormalities may potentially influence levels of Abeta in the brains of patients with Alzheimer's disease. The increased occurrence of insulin resistance in Alzheimer's disease and the numerous mechanisms through which insulin may affect clinical and pathological aspects of the disease suggest that improving insulin effectiveness may have therapeutic benefit for patients with Alzheimer's disease. The thiazolidinedione rosiglitazone has been shown to have a potent insulin-sensitising action that appears to be mediated through the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). PPAR-gamma agonists, such as rosiglitazone, also have anti-inflammatory effects that may be of therapeutic benefit in patients with Alzheimer's disease. This review presents evidence suggesting that insulin resistance plays a role in the pathophysiology and clinical symptoms of Alzheimer's disease. Based on this evidence, we propose that treatment of insulin resistance may reduce the risk or retard the development of Alzheimer's disease.

Reduction of intramyocellular lipid following short-term rosiglitazone treatment in Zucker fatty rats: an in vivo nuclear magnetic resonance study

The aim of the study was to characterize the effects of rosiglitazone, an oral insulin sensitizer, on intramyocellular lipid (IMCL) content in tibialis anterior muscle and whole body lipid deposition in Zucker fatty rats using in vivo (1)H nuclear magnetic resonance (NMR) spectroscopy. The IMCL/EMCL (extramyocellular) ratio was significantly lower in the rosiglitazone (FRSG) group at 7, 14, 21, and 28 days of treatment at 3 mg/kg/d (0.04 +/- 0.01, 0.09 +/- 0.03, 0.11 +/- 0.02, and 0.07 +/- 0.02, respectively) versus baseline (0.43 +/- 0.12, P <.01 v all time points), whereas there was no difference in the control (FC) group at these time points (0.31 +/- 0.08, 0.36 +/- 0.08, 0.40 +/- 0.14, and 0.49 +/- 0.18, respectively) versus baseline (0.37 +/- 0.07). Absolute IMCL content was also lower at 28 days in the FRSG (0.41 +/- 0.09 micromol/g) versus FC (2.13 +/- 0.40 micromol/g, P <.005) group. To further characterize the temporal nature of this change, the IMCL/EMCL ratio was examined in the FRSG group on each of the first 4 days of treatment, and a steady decline was observed (0.38 +/- 0.12, 0.21 +/- 0.08, 0.12 +/- 0.04, 0.09 +/- 0.04, 0.05 +/- 0.03 at baseline and days 1, 2, 3, and 4 respectively, P <.05 baseline v all time points). To examine the relationship between IMCL and insulin sensitivity, a euglycemic-hyperinsulinemic clamp and IMCL measurement was performed on 7-day treated FRSG and FC groups. There was a negative correlation between absolute IMCL content and glucose infusion rate (r = -0.47, P <.04). The FRSG and the FC groups had similar whole body lipid content (expressed as a percentage of whole body water content) at baseline (48% +/- 5% and 44% +/- 2%, respectively), but the value was greater in the FRSG group following 28 days of treatment (103% +/- 4 v 84% +/- 6%, respectively, P <.02). In summary, there was a rapid (days) and pronounced reduction ( downward arrow approximately 70%) in IMCL content in tibialis anterior muscle following rosiglitazone treatment. Additionally, the increase in whole body lipid in the FRSG group suggests that there was increased adipocyte lipid storage following long-term rosiglitazone treatment. These results support the hypothesis that rosiglitazone indirectly increases peripheral insulin sensitivity by decreasing adipocyte lipolysis, thereby lowering IMCL content.

Rosiglitazone but not metformin enhances insulin- and exercise-stimulated skeletal muscle glucose uptake in patients with newly diagnosed type 2 diabetes

Rosiglitazone, a thiazolidinedione, enhances peripheral insulin sensitivity in patients with type 2 diabetes. Because the synergic action of insulin and exercise has been shown to be decreased in insulin resistance, the aim of this study was to compare the effects of rosiglitazone and metformin on muscle insulin responsiveness at rest and during exercise in patients with type 2 diabetes. Therefore, 45 patients with newly diagnosed or diet-treated type 2 diabetes were randomized for treatment with rosiglitazone (4 mg b.i.d.), metformin (1 g b.i.d.), or placebo in a 26-week double-blind trial. Skeletal muscle glucose uptake was measured using fluorine-18-labeled fluoro-deoxy-glucose and positron emission tomography (PET) during euglycemic-hyperinsulinemic clamp and one-legged exercise before and after the treatment period. Rosiglitazone (P < 0.05) and metformin (P < 0.0001) treatment lowered the mean glycosylated hemoglobin. The skeletal muscle glucose uptake was increased by 38% (P < 0.01) and whole-body glucose uptake by 44% in the rosiglitazone group. Furthermore, the exercise-induced increment during insulin stimulation was enhanced by 99% (P < 0.0001). No changes were observed in skeletal muscle or whole-body insulin sensitivity in the metformin group. In conclusion, rosiglitazone but not metformin 1) improves insulin responsiveness in resting skeletal muscle and 2) doubles the insulin-stimulated glucose uptake rate during physical exercise in patients with type 2 diabetes. Our results suggest that rosiglitazone improves synergic action of insulin and exercise.

Rosiglitazone: a review of its use in the management of type 2 diabetes mellitus

Rosiglitazone, a thiazolidinedione with a different side chain from those of troglitazone and pioglitazone, reduces plasma glucose levels and glucose production and increases glucose clearance in patients with type 2 diabetes mellitus. Insulin sensitivity, pancreatic beta-cell function and surrogate markers of cardiovascular risk factors are significantly improved by rosiglitazone. Double-blind trials of 8 to 26 weeks of rosiglitazone 4 or 8 mg/day monotherapy indicate significant decreases in fasting plasma glucose (-2 to -3 mmol/L with 8 mg/day) and glycosylated haemoglobin levels [HbA(1c); -0.6 to -0.7% (-0.8 to -1.1% in drug-naive patients) with 8 mg/day]. Significant decreases in hyperglycaemic markers occurred when rosiglitazone was combined with metformin (HbA(1c) -0.8 to -1.0%), a sulphonylurea (-1.4%) or insulin (-1.2%) for 26 weeks versus little change with active comparator monotherapy. Efficacy was maintained in trials of < or = 2 years, and was also apparent in various ethnic subgroups, elderly patients, and both obese and nonobese patients. Rosiglitazone is currently not indicated in combination with injected insulin. It should be administered in conjunction with diet and exercise regimens. Rosiglitazone is generally well tolerated. Despite rare individual reports of liver function abnormalities in rosiglitazone recipients, the incidence of these in clinical trials (< or = 2 years' duration) was similar to that in placebo and active comparator groups. Fluid retention associated with rosiglitazone may be the cause of the increased incidence of anaemia in clinical trials, and also means that patients should be monitored for signs of heart failure during therapy. Although bodyweight is increased overall with rosiglitazone therapy, increases are in subcutaneous, not visceral, fat; hepatic fat is decreased. The pharmacokinetic profile of rosiglitazone is not substantially altered by age or renal impairment, nor are there important drug interactions. Rosiglitazone is not indicated in patients with active liver disease or increased liver enzymes.

CONCLUSIONS

Oral rosiglitazone 4 or 8 mg/day provides significant antihyperglycaemic efficacy and is generally well tolerated, both as monotherapy and in combination with other antihyperglycaemic agents, in patients with type 2 diabetes mellitus who do not have active liver disease. Long-term data are required before conclusions can be drawn about the clinical significance of positive changes to surrogate markers of cardiovascular disease risk and improvements to pancreatic beta-cell function. Rosiglitazone significantly improves insulin sensitivity and, as such, is a welcome addition to the treatment options for patients with type 2 diabetes mellitus.

The role of the angiotensin system in cardiac glucose homeostasis: therapeutic implications

Resistance to the metabolic actions of insulin is thought to play a determining role in the aetiology of a great variety of disorders, including essential hypertension, accelerated atherosclerosis and cardiomyopathies. ACE inhibitors are recognised as being highly effective therapy for hypertension and cardiac insufficiency, and have a more beneficial effect on survival rate than expected on the basis of known mechanisms of action. The mechanism responsible for these extremely positive effects are just beginning to be understood and appear to be linked to the effects these drugs have on metabolism. The relationship between the insulin and angiotensin II (Ang II) signalling pathways needs to be fully clarified in order to prevent or correct the target organ damage resulting from changes in the cross-talk of these two hormonal systems. In recent years, Ang II has been shown to play a central role in cardiovascular and neuroendocrine physiology as well as in cellular cycle control. Moreover, the fact that Ang II utilises the insulin-receptor substrate (IRS)-1 to relay signals towards their intracellular destination, provides the biochemical explanation of how these two systems interact in a healthy organism and in a diseased one. Since it is overactivity of the renin-angiotensin system that seems to impair the intracellular response to insulin signalling, cardiovascular drugs that modulate the cellular transmission of Ang II have attracted particular interest. As well as the already widely-used ACE inhibitors, selective blockers of the Ang II type 1 receptor (AT(1)) have been shown to be clinically effective in the control of haemodynamic parameters, but with perhaps a less striking effect on glucose homeostasis. Many trials have investigated the effect of Ang II blockade on systemic glucose homeostasis. The inhibition of Ang II by ACE-inhibitors frequently showed a positive effect on glycaemia and insulin sensitivity, while information on the effects of AT(1) receptor antagonists on glucose homeostasis is more limited and controversial. An important limitation of these studies has been the short treatment and follow-up periods, even for the 'so called' long-term studies which were only 6 months. Several investigators have focused on the effects of the nuclear factors involved in gene transcriptions, especially with respect to the agonists/antagonists of peroxisome proliferator-activated receptors (PPARs) and their intriguing interconnections with the insulin and Ang II subcellular pathways. In fact, in vitro and in vivo experimental studies have shown that thiazolidinediones (selective PPAR-gamma ligands) are not only powerful insulin sensitisers, but also have anti-hypertensive and anti-atherosclerotic properties. In addition to conventional pharmacological approaches, attempts have been made to use genetic transfer in the treatment of cardiovascular and metabolic disorders. The development of powerful viral vectors carrying target genes has allowed us to restore the expression/function of specific proteins involved in the cellular mechanism of insulin resistance, and research now needs to move beyond animal models. Although a clearer picture is now emerging of the pathophysiological interaction between insulin and Ang II, especially from pre-clinical studies, there is much to be done before experimental findings can be used in daily clinical practice.

Normalization of skeletal muscle glycogen synthesis and glycolysis in rosiglitazone-treated Zucker fatty rats: an in vivo nuclear magnetic resonance study

The aim of this study was to characterize insulin-stimulated skeletal muscle glucose metabolism in Zucker fatty rats and to provide insight into the therapeutic mechanism by which rosiglitazone increases insulin-stimulated glucose disposal in these rats. Metabolic parameters were measured using combined in vivo (13)C nuclear magnetic resonance (NMR) spectroscopy to measure skeletal muscle glucose uptake and its distributed fluxes (glycogen synthesis and glycolysis), and (31)P NMR was used to measure simultaneous changes in glucose-6-phosphate (G-6-P) during a euglycemic-hyperinsulinemic clamp in awake Zucker fatty rats. Three groups of Zucker fatty rats (fatty rosiglitazone [FRSG], fatty control [FC], lean control [LC]) were treated for 7 days before the experiment (3 mg/kg rosiglitazone or vehicle via oral gavage). Rates of glycolysis and glycogen synthesis were assessed after treatment by monitoring 1,6-(13)C(2) glucose label incorporation into 1-(13)C glycogen, 3-(13)C lactate, and 3-(13)C alanine during a euglycemic ( approximately 7-8 mmol/l)-hyperinsulinemic (10 mU. kg(-1). min(-1)) clamp. The FRSG group exhibited a significant increase in insulin sensitivity, reflected by an increased whole-body glucose disposal rate during the clamp (24.4 +/- 1.9 vs. 17.6 +/- 1.4 and 33.2 +/- 2.0 mg. kg(-1). min(-1) in FRSG vs. FC [P < 0.05] and LC [P < 0.01] groups, respectively). The increased insulin-stimulated glucose disposal in the FRSG group was associated with a normalization of the glycolytic flux (52.9 +/- 9.1) to LC (56.2 +/- 16.6) versus FC (18.8 +/- 8.6 nmol. g(-1). min(-1), P < 0.02) and glycogen synthesis flux (56.3 +/- 11.5) to LC (75.2 +/- 15.3) versus FC (16.6 +/- 12.8 nmol. g(-1). min(-1), P < 0.05). [G-6-P] increased in the FRSG and LC groups versus baseline during the clamp (13.0 +/- 11.1 and 16.9 +/- 5.8%, respectively), whereas [G-6-P] in the FC group decreased (-23.3 +/- 13.4%, P < 0.05). There were no differences between groups in intramyocellular glucose, as measured by biochemical assay. These data suggest that the increased insulin-stimulated glucose disposal in muscle after rosiglitazone treatment can be attributed to a normalization of glucose transport and metabolism.

Rosiglitazone, a peroxisome proliferator-activated receptor-gamma, inhibits the Jun NH(2)-terminal kinase/activating protein 1 pathway and protects the heart from ischemia/reperfusion injury

This study was conducted to evaluate whether treatment of normal and diabetic rat hearts with rosiglitazone, a high-affinity ligand of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) used for the treatment of type 2 diabetes, improves postischemic functional recovery. The effects of acute rosiglitazone administration were investigated using working hearts isolated from normal rat or rats diabetic for 4 weeks after streptozotocin (STZ) injection. Hearts were subjected to 30 min of normothermic, zero-flow ischemia followed by 30-min reperfusion. Rosiglitazone (1 micromol/l) administered before ischemia had no effect on cardiac function during baseline perfusion, but it significantly improved aortic flow during reperfusion in both normal and diabetic hearts. In a chronic protocol in which rosiglitazone was given by daily gavage (10 micromol/kg body wt) immediately after STZ injection, rosiglitazone also prevented postischemic injury and significantly improved functional recovery. Using Western immunoblotting, it was demonstrated that the acute cardioprotective effect of rosiglitazone is associated with an inhibition of Jun NH(2)-terminal kinase phosphorylation in both normal and diabetic rat hearts. Furthermore, rosiglitazone also inhibited activating protein-1 DNA-binding activity. These data, demonstrating that rosiglitazone limits postischemic injury in isolated hearts, suggest an important function for PPAR-gamma in the heart.

The role of peroxisome proliferator-activated receptor gamma in diabetes and obesity

Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a nuclear receptor, which upon activation with various natural and synthetic ligands, stimulates the transcription of genes responsible for growth and differentiation of adipocytes. Furthermore, PPAR gamma is the receptor for the insulin-sensitizing thiazolidinediones, which are commonly used for the treatment of type 2 diabetes. Rare inactivating mutations of the gene encoding PPAR gamma are associated with insulin resistance type 2 diabetes, and hypertension, whereas a rare gain of function mutation causes extreme obesity. A common polymorphism (Pro12Ala) of the adipose tissue-specific gamma 2 isoform is associated with increased insulin sensitivity and decreased risk of developing type 2 diabetes. These findings indicate a central role of PPAR gamma in fat cell biology and in the pathophysiology of obesity, diabetes, and insulin resistance.

Where thiazolidinediones will fit

Individuals with type 2 diabetes have two defects: insulin resistance, which occurs in the first stages of disease progression, and pancreatic beta-cell failure, which occurs later in the disease. Insulin resistance is the major pathological defect. During the course of the disease, insulin levels are initially elevated to compensate for the increased insulin resistance and then decline as the disease progresses and beta-cells become less responsive. It is necessary to change antidiabetic therapies to address this progression. Current management of type 2 diabetes follows a stepwise treatment program of diet and exercise, monotherapy with oral antidiabetic agents, combination oral therapy and, ultimately, combination therapy with insulin to control blood glucose levels. While control of blood glucose will reduce the risk of microvascular complications, such as microalbuminuria and retinopathy, the incidence of macrovascular complications is not significantly reduced. The introduction of the thiazolidinediones (TZDs) or 'glitazones', a class of agents that offer effective glycemic control and work through the reduction of insulin resistance, offers a new strategy in the management of this condition. These agents have beneficial effects on the pancreatic beta-cell and, in addition, may have potential benefits on the macrovascular complications that commonly occur in these patients.