Peroxisome proliferator-activated receptor (PPAR) activation induces tissue-specific effects on fatty acid uptake and metabolism in vivo--a study using the novel PPARalpha/gamma agonist tesaglitazar

WJCPR11 reverses the TNF-α-induced inhibition of adipocyte differentiation and glucose uptake

Berberine is a natural isoquinoline alkaloid present in various herbs and is effective against metabolic syndrome in the pre-diabetic stage and high insulin resistance. The present study aimed to determine the effectiveness of WJCPR11, a berberine derivative that is commonly used for diabetes treatment, in ameliorating insulin resistance and diabetes treatment. WJCPR11 promoted adipocyte differentiation to a higher extent than other berberine derivatives and showed no noticeable toxicity in its effective concentration range. It increased the mRNA expression levels and protein abundance of adipogenic markers, including peroxisome proliferator-activated receptor γ (PPARγ), glucose transporter type 4 (GluT4), and fatty acid synthase (FAS), and markedly enhanced the level of adiponectin, a distinct marker of insulin sensitivity. Meanwhile, the mRNA levels of inflammatory markers such as plasminogen activator inhibitor-1 (PAI-1), monocyte chemoattractant protein-1 (MCP-1), and interleukin 6 (IL-6) were reduced after WJCPR11 treatment. Furthermore, the tumor necrosis factor-α (TNF-α)-induced inhibition of adipocyte differentiation and downregulation of glucose uptake were markedly reversed by WJCPR11 treatment. Collectively, the findings of this study indicate that WJCPR11 has great potential for diabetes treatment.

The Glitazars Paradox: Cardiotoxicity of the Metabolically Beneficial Dual PPARα and PPARγ Activation

The most common complications in patients with type-2 diabetes are hyperglycemia and hyperlipidemia that can lead to cardiovascular disease. Alleviation of these complications constitutes the major therapeutic approach for the treatment of diabetes mellitus. Agonists of peroxisome proliferator-activated receptor (PPAR) alpha and PPARγ are used for the treatment of hyperlipidemia and hyperglycemia, respectively. PPARs belong to the nuclear receptors superfamily and regulate fatty acid metabolism. PPARα ligands, such as fibrates, reduce circulating triglyceride levels, and PPARγ agonists, such as thiazolidinediones, improve insulin sensitivity. Dual-PPARα/γ agonists (glitazars) were developed to combine the beneficial effects of PPARα and PPARγ agonism. Although they improved metabolic parameters, they paradoxically aggravated congestive heart failure in patients with type-2 diabetes via mechanisms that remain elusive. Many of the glitazars, such as muraglitazar, tesaglitazar, and aleglitazar, were abandoned in phase-III clinical trials. The objective of this review article pertains to the understanding of how combined PPARα and PPARγ activation, which successfully targets the major complications of diabetes, causes cardiac dysfunction. Furthermore, it aims to suggest interventions that will maintain the beneficial effects of dual PPARα/γ agonism and alleviate adverse cardiac outcomes in diabetes.

Rethinking pioglitazone as a cardioprotective agent: a new perspective on an overlooked drug

Since 1985, the thiazolidinedione pioglitazone has been widely used as an insulin sensitizer drug for type 2 diabetes mellitus (T2DM). Although fluid retention was early recognized as a safety concern, data from clinical trials have not provided conclusive evidence for a benefit or a harm on cardiac function, leaving the question unanswered. We reviewed the available evidence encompassing both in vitro and in vivo studies in tissues, isolated organs, animals and humans, including the evidence generated by major clinical trials. Despite the increased risk of hospitalization for heart failure due to fluid retention, pioglitazone is consistently associated with reduced risk of myocardial infarction and ischemic stroke both in primary and secondary prevention, without any proven direct harm on the myocardium. Moreover, it reduces atherosclerosis progression, in-stent restenosis after coronary stent implantation, progression rate from persistent to permanent atrial fibrillation, and reablation rate in diabetic patients with paroxysmal atrial fibrillation after catheter ablation. In fact, human and animal studies consistently report direct beneficial effects on cardiomyocytes electrophysiology, energetic metabolism, ischemia–reperfusion injury, cardiac remodeling, neurohormonal activation, pulmonary circulation and biventricular systo-diastolic functions. The mechanisms involved may rely either on anti-remodeling properties (endothelium protective, inflammation-modulating, anti-proliferative and anti-fibrotic properties) and/or on metabolic (adipose tissue metabolism, increased HDL cholesterol) and neurohormonal (renin–angiotensin–aldosterone system, sympathetic nervous system, and adiponectin) modulation of the cardiovascular system. With appropriate prescription and titration, pioglitazone remains a useful tool in the arsenal of the clinical diabetologist.

Kaempferol reduces hepatic triglyceride accumulation by inhibiting Akt

In this paper, we studied the mechanism of the triglyceride (TG)-lowering effect of kaempferol in vitro and in vivo. Kaempferol showed LXR agonistic activities without inducing TGs or the expression of several lipogenic genes in cultured cells. A luciferase and qPCR analysis showed that kaempferol increased the transactivation of PPARα and PPARδ and stimulated gene expression associated with fatty acid oxidation and uptake in hepatocytes. More importantly, kaempferol inhibited protein kinase B (Akt) activity and suppressed SREBP-1 activation via multiple mechanisms, including through increasing Insig-2a expression, reducing SREBP-1 phosphorylation, and increasing GSK-3 phosphorylation. Collectively, these actions inhibited the SREBP-1 activation process. Furthermore, as an Akt/mTOR pathway inhibitor, kaempferol led to the induction of hepatic autophagy and resulted in a decrease in lipid droplet formation in the mouse liver. These findings demonstrate that kaempferol exerts its TG-lowering effect via Akt inhibition and activation of PPARα and PPARδ. PRACTICAL APPLICATIONS: Kaempferol is a major dietary flavonoid in various plant-based foods, and it is used as a valuable ingredient in functional foods, with numerous beneficial properties such as anticancer, antioxidant, and anti-atherosclerotic activities. Kaempferol exerts its TG-lowering effect via Akt inhibition and activation of PPARα and PPARδ. Currently, the number of people with hyperlipidemia is rapidly growing in both developed and developing societies; thus, we propose that kaempferol could be used for therapeutic interventions aimed at the treatment of these individuals.

Chrysanthemum Leaf Ethanol Extract Prevents Obesity and Metabolic Disease in Diet-Induced Obese Mice via Lipid Mobilization in White Adipose Tissue

This study aimed to elucidate the molecular mechanism of Chrysanthemum morifolium Ramat. against obesity and diabetes, by comparing the transcriptional changes in epididymal white adipose tissue (eWAT) with those of the bioactive compound in C. morifolium, luteolin (LU). Male C57BL/6J mice were fed a normal diet, high-fat diet (HFD), and HFD supplemented with 1.5% w/w chrysanthemum leaf ethanol extract (CLE) for 16 weeks. Supplementation with CLE and LU significantly decreased the body weight gain and eWAT weight by stimulating mRNA expressions for thermogenesis and energy expenditure in eWAT via lipid mobilization, which may be linked to the attenuation of dyslipidemia. Furthermore, CLE and LU increased uncoupling protein-1 protein expression in brown adipose tissue, leading to energy expenditure. Of note, CLE and LU supplements enhanced the balance between lipid storage and mobilization in white adipose tissue (WAT), in turn, inhibiting adipocyte inflammation and lipotoxicity of peripheral tissues. Moreover, CLE and LU attenuated hepatic steatosis by suppressing hepatic lipogenesis, thereby ameliorating insulin resistance and dyslipidemia. Our data suggest that CLE helps inhibit obesity and its comorbidities via the complex interplay between liver and WAT in diet-induced obese mice.

The E3 ligase MARCH5 is a PPARγ target gene that regulates mitochondria and metabolism in adipocytes

Mitochondrial dynamics refers to the constant remodeling of mitochondrial populations by multiple cellular pathways that help maintain mitochondrial health and function. Disruptions in mitochondrial dynamics often lead to mitochondrial dysfunction, which is frequently associated with disease in rodents and humans. Consistent with this, obesity is associated with reduced mitochondrial function in white adipose tissue, partly via alterations in mitochondrial dynamics. Several proteins, including the E3 ubiquitin ligase membrane-associated RING-CH-type finger 5 (MARCH5), are known to regulate mitochondrial dynamics; however, the role of these proteins in adipocytes has been poorly studied. Here, we show that MARCH5 is regulated by peroxisome proliferator-activated receptor-γ (PPARγ) during adipogenesis and is correlated with fat mass across a panel of genetically diverse mouse strains, in ob/ob mice, and in humans. Furthermore, manipulation of MARCH5 expression in vitro and in vivo alters mitochondrial function, affects cellular metabolism, and leads to differential regulation of several metabolic genes. Thus our data demonstrate an association between mitochondrial dynamics and metabolism that defines MARCH5 as a critical link between these interconnected pathways.

Vascular endothelial growth factor-B: Impact on physiology and pathology

Angiogenesis plays an important role in controlling tissue development and maintaining normal tissue function. Dysregulated angiogenesis is implicated in the pathogenesis of a variety of diseases, particularly diabetes, cancers, and neurodegenerative disorders. As the major regulator of angiogenesis, the vascular endothelial growth factor (VEGF) family is composed of a group of crucial members including VEGF-B. While the physiological roles of VEGF-B remain debatable, increasing evidence suggests that this protein is able to protect certain type of cells from apoptosis under pathological conditions. More importantly, recent studies reveal that VEGF-B is involved in lipid transport and energy metabolism, implicating this protein in obesity, diabetes and related metabolic complications. This article summarizes the current knowledge and understanding of VEGF-B in physiology and pathology, and shed light on the therapeutic potential of this crucial protein.

Roles of Peroxisome Proliferator-Activated Receptor Gamma on Brain and Peripheral Inflammation

Peroxisome proliferator-activated receptor gamma (PPARγ) has been implicated in the pathology of numerous diseases involving diabetes, stroke, cancer, or obesity. It is expressed in diverse cell types, including vessels, immune and glial cells, and neurons. PPARγ plays crucial roles in the regulation of cellular differentiation, lipid metabolism, or glucose homeostasis. PPARγ ligands also exert effects on attenuating degenerative processes in the brain, as well as in peripheral systems, and it has been associated with the control of anti-inflammatory mechanisms, oxidative stress, neuronal death, neurogenesis, differentiation, and angiogenesis. This review will highlight key advances in the understanding of the PPARγ-related mechanisms responsible for neuroprotection after brain injuries, both ischemia and traumatic brain injury, and it will also cover the natural and synthetic agonist for PPARγ, angiotensin receptor blockers, and PPARγ antagonists, used in experimental and clinical research. A better understanding of the pleiotropic mechanisms and applications of these drugs to improve the recovery and to repair the acute and chronic induced neuroinflammation after brain injuries will pave the way for more effective therapeutic strategies after brain deficits.

The role of various peroxisome proliferator-activated receptors and their ligands in clinical practice

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors involved in several physiological processes including modulation of cellular differentiation, development, metabolism of carbohydrates, lipids, proteins, and tumorigenesis. The aim of this review is to examine how different PPAR ligands act, and discuss their use in clinical practice. PPAR ligands have a lot of effects and applications in clinical practice. Some PPAR ligands such as fibrates (PPAR-α ligands) are currently used for the treatment of dyslipidemia, while pioglitazone and rosiglitazone (PPAR-γ ligands) are anti-diabetic and insulin-sensitizing agents. Regarding new generation drugs, acting on both α/γ, β/δ, or α/δ receptors simultaneously, preliminary data on PPAR-α/γ dual agonists revealed a positive effect on lipid profile, blood pressure, atherosclerosis, inflammation, and anti-coagulant effects, while the overexpression of PPAR-β/δ seems to prevent obesity and to decrease lipid storage in cardiac cells. Finally, PPAR-α/δ dual agonist induces resolution of nonalcoholic steatohepatitis without fibrosis worsening.

Design, synthesis and biological evaluation of a class of bioisosteric oximes of the novel dual peroxisome proliferator-activated receptor α/γ ligand LT175

The effects resulting from the introduction of an oxime group in place of the distal aromatic ring of the diphenyl moiety of LT175, previously reported as a PPARα/γ dual agonist, have been investigated. This modification allowed the identification of new bioisosteric ligands with fairly good activity on PPARα and fine-tuned moderate activity on PPARγ. For the most interesting compound (S)-3, docking studies in PPARα and PPARγ provided a molecular explanation for its different behavior as full and partial agonist of the two receptor isotypes, respectively. A further investigation of this compound was carried out performing gene expression studies on HepaRG cells. The results obtained allowed to hypothesize a possible mechanism through which this ligand could be useful in the treatment of metabolic disorders. The higher induction of the expression of some genes, compared to selective agonists, seems to confirm the importance of a dual PPARα/γ activity which probably involves a synergistic effect on both receptor subtypes.

trans-Caryophyllene is a natural agonistic ligand for peroxisome proliferator-activated receptor-α

Intake of dietary aroma compounds may regulate cellular lipid metabolism. We demonstrated that trans-caryophyllene, a flavor compound in plant foods and teas, activates peroxisome proliferator-activated receptor (PPAR)-α through direct interaction with the ligand-binding domain of PPAR-α. The agonistic activity of trans-caryophyllene was investigated by the luciferase reporter assay, surface plasmon resonance, and time-resolved fluorescence resonance energy transfer assay. Following the stimulation of cells with trans-caryophyllene, intracellular triglyceride concentrations were significantly reduced by 17%, and hepatic fatty acid uptake was significantly increased by 31%. The rate of fatty acid oxidation was also significantly increased. The expressions of PPAR-α and its target genes and proteins in fatty acid uptake and oxidation were significantly up-regulated as well. In HepG2 cells transfected with small interfering RNA of PPAR-α, the effects of trans-caryophyllene on PPAR-α responsive gene expressions, intracellular triglyceride, fatty acid uptake and oxidation were disappeared. These results indicate that the aroma compound, trans-caryophyllene, is PPAR-α agonist thus regulates cellular lipid metabolism in PPAR-α dependent manners.

Potent anti-diabetic effects of MHY908, a newly synthesized PPAR α/γ dual agonist in db/db mice

Peroxisome proliferator-activated receptor (PPAR) α/γ dual agonists have been developed to alleviate metabolic disorders and have the potential to be used as therapeutic agents for the treatment of type 2 diabetes. In this study, we investigated the effects of a newly synthesized PPAR α/γ dual agonist, 2-[4-(5-chlorobenzo [d] thiazol-2-yl) phenoxy]-2-methylpropanoic acid (MHY908) on type 2 diabetes in vitro and in vivo. To obtain initial evidence that MHY908 acts as a PPAR α/γ dual agonist, ChIP and reporter gene assays were conducted in AC2F rat liver cells, and to investigate the anti-diabetic effects and molecular mechanisms, eight-week-old, male db/db mice were allowed to eat ad libitum, placed on calorie restriction, or administered MHY908 (1 mg or 3 mg/kg/day) mixed in food for 4 weeks. Age-matched male db/m lean mice served as non-diabetic controls. It was found that MHY908 enhanced the binding and transcriptional activity of PPAR α and γ in AC2F cells, and it reduced serum glucose, triglyceride, and insulin levels, however increased adiponectin levels without body weight gain. In addition, MHY908 significantly improved hepatic steatosis by enhancing CPT-1 levels. Remarkably, MHY908 reduced endoplasmic reticulum (ER) stress and c-Jun N-terminal kinase (JNK) activation in the livers of db/db mice, and subsequently reduced insulin resistance. The study shows MHY908 has beneficial effects on type 2 diabetes by simultaneously activating PPAR α/γ and improving ER stress, and suggests that MHY908 could have a potent anti-diabetic effect as a PPAR α/γ dual agonist, and potential for the treatment of type 2 diabetes.

The PPAR α / γ Agonist, Tesaglitazar, Improves Insulin Mediated Switching of Tissue Glucose and Free Fatty Acid Utilization In Vivo in the Obese Zucker Rat

Metabolic flexibility was assessed in male Zucker rats: lean controls, obese controls, and obese rats treated with the dual peroxisome proliferator activated receptor (PPAR) α/γ agonist, tesaglitazar, 3 μmol/kg/day for 3 weeks. Whole body glucose disposal rate (R_d) and hepatic glucose output (HGO) were assessed under basal fasting and hyperinsulinemic isoglycemic clamp conditions using [3,³H]glucose. Indices of tissue specific glucose utilization (R_g′) were measured at basal, physiological, and supraphysiological levels of insulinemia using 2-deoxy-D-[2,6-³H]glucose. Finally, whole body and tissue specific FFA and glucose utilization and metabolic fate were evaluated under basal and hyperinsulinemic conditions using a combination of [U-¹³C]glucose, 2-deoxy-D-[U-¹⁴C]glucose, [U-¹⁴C]palmitate, and [9,10-³H]-(R)-bromopalmitate. Tesaglitazar improved whole body insulin action by greater suppression of HGO and stimulation of R_d compared to obese controls. This involved increased insulin stimulation of R_g′ in fat and skeletal muscle as well as increased glycogen synthesis. Tesaglitazar dramatically improved insulin mediated suppression of plasma FFA level, whole body turnover (R_fa), and muscle, liver, and fat utilization. At basal insulin levels, tesaglitazar failed to lower HGO or R_fa compared to obese controls. In conclusion, the results demonstrate that tesaglitazar has a remarkable ability to improve insulin mediated control of glucose and FFA fluxes in obese Zucker rats.

Pathogenic role of diabetes-induced PPAR-α down-regulation in microvascular dysfunction

Two independent clinical studies have reported that fenofibrate, a peroxisome proliferator-activated receptor α (PPARα) agonist, has robust therapeutic effects on microvascular complications of diabetes, including diabetic retinopathy (DR) in type 2 diabetic patients. However, the expression and function of PPARα in the retina are unclear. Here, we demonstrated that PPARα is expressed in multiple cell types in the retina. In both type 1 and type 2 diabetes models, expression of PPARα, but not PPARβ/δ or PPARγ, was significantly down-regulated in the retina. Furthermore, high-glucose medium was sufficient to down-regulate PPARα expression in cultured retinal cells. To further investigate the role of PPARα in DR, diabetes was induced in PPARα knockout (KO) mice and wild-type (WT) mice. Diabetic PPARα KO mice developed more severe DR, as shown by retinal vascular leakage, leukostasis, pericyte loss, capillary degeneration, and over-expression of inflammatory factors, compared with diabetic WT mice. In addition, overexpression of PPARα in the retina of diabetic rats significantly alleviated diabetes-induced retinal vascular leakage and retinal inflammation. Furthermore, PPARα overexpression inhibited endothelial cell migration and proliferation. These findings revealed that diabetes-induced down-regulation of PPARα plays an important role in DR. Up-regulation or activation of PPARα may represent a novel therapeutic strategy for DR.

Adiposopathy: sick fat causes high blood sugar, high blood pressure and dyslipidemia

Adiposopathy is defined as pathological adipose tissue function that may be promoted and exacerbated by fat accumulation (adiposity) and sedentary lifestyle in genetically susceptible patients. Adiposopathy is a root cause of some of the most common metabolic diseases observed in clinical practice, including Type 2 diabetes mellitus, hypertension and dyslipidemia. The most common term for the metabolic consequences of adiposopathy is currently 'the metabolic syndrome'. Drug usage to treat the metabolic syndrome has focused on the safety and efficacy of treatments directed towards individual components of the metabolic syndrome, and not so much upon adiposopathy itself. However, enough is known about the pathophysiology of adiposopathy to propose diagnostic criteria. Regulatory issues are important obstacles to the research and development of new drug treatments for the metabolic syndrome. It is hoped that these obstacles can, to some extent, be addressed and overcome by clearly defining and increasing our understanding of adiposopathy.

Ursolic acid is a PPAR-α agonist that regulates hepatic lipid metabolism

In this study, we confirmed that ursolic acid, a plant triterpenoid, activates peroxisome proliferator-activated receptor (PPAR)-α in vitro. Surface plasmon resonance and time-resolved fluorescence resonance energy transfer analyses do not show direct binding of ursolic acid to the ligand-binding domain of PPAR-α; however, ursolic acid enhances the binding of PPAR-α to the peroxisome proliferator response element in PPAR-α-responsive genes, alters the expression of key genes in lipid metabolism, significantly reducing intracellular triglyceride and cholesterol concentrations in hepatocytes. Thus, ursolic acid is a PPAR-α agonist that regulates the expression of lipid metabolism genes, but it is not a direct ligand of PPAR-α.

Dual acting and pan-PPAR activators as potential anti-diabetic therapies

The thiazolidinedione PPAR-γ activator drugs rosiglitazone and pioglitazone suppress insulin resistance in type 2 diabetic patients. They lock lipids into adipose tissue triglyceride stores, thereby preventing lipid metabolites from causing insulin resistance in liver and skeletal muscle and β-cell failure. They also reduce the secretion of inflammatory cytokines such as TNFα and increase the plasma level of adiponectin, which increases insulin sensitivity in liver and skeletal muscle. However, they have only a modest effect on dyslipidaemia, and they increase fat mass and plasma volume. Fibrate PPAR-α activator drugs decrease plasma triglycerides and increase HDL-cholesterol levels. PPAR-δ activators increase the capacity for fat oxidation in skeletal muscle.Clinical experience with bezafibrate, which activates PPAR-δ and -α, and studies on the PPAR-α/δ activator tetradecylthioacetic acid, the PPAR-δ activator GW501516, and combinations of the PPAR-α activator fenofibrate with rosiglitazone or pioglitazone have encouraged attempts to develop single molecules that activate two or all three PPARs. Most effort has focussed on dual PPAR-α/γ activators. These reduce both hyperglycaemia and dyslipidaemia, but their development has been terminated by issues such as increased weight gain, oedema, plasma creatinine and myocardial infarction or stroke. In addition, the FDA has stated that many PPAR ligands submitted to it have caused increased numbers of tumours in carcinogenicity studies.Rather than aiming for full potent agonists, it may be best to identify subtype-selective partial agonists or compounds that selectively activate PPAR signalling pathways and use these in combination. Nutrients or modified lipids that are low-affinity agonists may also have potential.

Simple modeling allows prediction of steady-state glucose disposal rate from early data in hyperinsulinemic glucose clamps

After a constant insulin infusion is initiated, determination of steady-state conditions for glucose infusion rates (GIR) typically requires >or=3 h. The glucose infusion follows a simple time-dependent rise, reaching a plateau at steady state. We hypothesized that nonlinear fitting of abbreviated data sets consisting of only the early portion of the clamp study can provide accurate estimates of steady-state GIR. Data sets from two independent laboratories were used to develop and validate this approach. Accuracy of the predicted steady-state GDR was assessed using regression analysis and Altman-Bland plots, and precision was compared by applying a calibration model. In the development data set (n = 88 glucose clamp studies), fitting the full data set with a simple monoexponential model predicted reference GDR values with good accuracy (difference between the 2 methods -0.37 mg x kg(-1) x min(-1)) and precision [root mean square error (RMSE) = 1.11], validating the modeling procedure. Fitting data from the first 180 or 120 min predicted final GDRs with comparable accuracy but with progressively reduced precision [fitGDR-180 RMSE = 1.27 (P = NS vs. fitGDR-full); fitGDR-120 RMSE = 1.56 (P < 0.001)]. Similar results were obtained with the validation data set (n = 183 glucose clamp studies), confirming the generalizability of this approach. The modeling approach also derives kinetic parameters that are not available from standard approaches to clamp data analysis. We conclude that fitting a monoexponential curve to abbreviated clamp data produces steady-state GDR values that accurately predict the GDR values obtained from the full data sets, albeit with reduced precision. This approach may help reduce the resources required for undertaking clamp studies.

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

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

Crocetin improves the insulin resistance induced by high-fat diet in rats

BACKGROUND AND PURPOSE

The amelioration of insulin resistance by treatment with crocetin is closely related to the hypolipidaemic effect. The present study is designed to clarify the insulin-sensitizing mechanism of crocetin by elucidating the mechanism of regulation of lipid metabolism by crocetin.

EXPERIMENTAL APPROACH

Rats given a high-fat diet were treated with crocetin for 6 weeks before hyperinsulinaemic-euglycaemic clamp. 14C-palmitate was used as tracer to track the fate of non-esterified fatty acids or as substrate to measure beta-oxidation rate. Triglyceride clearance in plasma and lipoprotein lipase activity in tissues were tested. Content of lipids in plasma and tissues was determined. Real-time PCR was used to assay the level of mRNA from genes involved in non-esterified fatty acid and triglyceride uptake and oxidation.

KEY RESULTS

Crocetin prevented high-fat-diet induced insulin resistance (increased clamp glucose infusion rate), raised hepatic non-esterified fatty acid uptake and oxidation, accelerated triglyceride clearance in plasma, enhanced lipoprotein lipase activity in liver, and reduced the accumulation of detrimental lipids (DAG and long-chain acyl CoA) in liver and muscle. Genes involved in hepatic lipid metabolism which are regulated by peroxisome proliferator-activated receptor-alpha, were modulated to accelerate lipid uptake and oxidation.

CONCLUSIONS AND IMPLICATIONS

Through regulating genes involved in lipid metabolism, crocetin accelerated hepatic uptake and oxidation of non-esterified fatty acid and triglyceride, and reduced lipid availability to muscle, thus decreasing lipid accumulation in muscle and liver, and consequently improving sensitivity to insulin.

Long chain fatty acid uptake in vivo: comparison of [125I]-BMIPP and [3H]-bromopalmitate

Insulin resistance is characterized by increased metabolic uptake of fatty acids. Accordingly, techniques to examine in vivo shifts in fatty acid metabolism are of value in both clinical and experimental settings. Partially metabolizable long chain fatty acid (LCFA) tracers have been recently developed and employed for this purpose: [9,10-3H]-(R)-2-bromopalmitate ([3H]-BROMO) and [125I]-15-(rho-iodophenyl)-3-R,S-methylpentadecanoic acid ([125I]-BMIPP). These analogues are taken up like native fatty acids, but once inside the cell do not directly enter beta-oxidation. Rather, they become trapped in the slower processes of omega and alpha-oxidation. Study aims were to (1) simultaneously assess and compare [3H]-BROMO and [125I]-BMIPP and (2) determine if tracer breakdown is affected by elevated metabolic demands. Catheters were implanted in a carotid artery and jugular vein of Sprague-Dawley rats. Following 5 days recovery, fasted animals (5 h) underwent a rest (n = 8) or exercise (n = 8) (0.6 mi/h) protocol. An instantaneous bolus containing both [3H]-BROMO and [125I]-BMIPP was administered to determine LCFA uptake. No significant difference between [125I]-BMIPP and [3H]-BROMO uptake was found in cardiac or skeletal muscle during rest or exercise. In liver, rates of uptake were more than doubled with [3H]-BROMO compared to [125I]-BMIPP. Analysis of tracer conversion by TLC demonstrated no difference at rest. Exercise resulted in greater metabolism and excretion of tracers with approximately 37% and approximately 53% of [125I]-BMIPP and [3H]-BROMO present in conversion products at 40 min. In conclusion, [3H]-BROMO and [125I]-BMIPP are indistinguishable for the determination of tissue kinetics at rest in skeletal and cardiac muscle. Exercise preferentially exacerbates the breakdown of [3H]-BROMO, making [125I]-BMIPP the analogue of choice for prolonged (>30 min) experimental protocols with elevated metabolic demands.

Peroxisome proliferator activated receptor alpha/gamma dual agonist tesaglitazar attenuates diabetic nephropathy in db/db mice

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors and play a central role in insulin sensitivity, lipid metabolism, and inflammation. Both PPARalpha and -gamma are expressed in the kidney, and their agonists exhibit renoprotective effects in type 2 diabetes. In the present studies, we investigated the effect of the PPARalpha/gamma dual agonist tesaglitazar on diabetic nephropathy in type 2 diabetic db/db mice. Treatment of db/db mice with tesaglitazar for 3 months significantly lowered fasting plasma glucose and homeostasis model assessment of insulin resistance levels but had little effect on body weight, adiposity, or cardiac function. Treatment with tesaglitazar was associated with reduced plasma insulin and total triglyceride levels and increased plasma adiponectin levels. Notably, tesaglitazar markedly attenuated albuminuria and significantly lowered glomerulofibrosis, collagen deposition, and transforming growth factor-beta1 expression in renal tissues of db/db mice. In cultured mesangial cells and proximal tubule cells, where both PPARalpha and -gamma were expressed, tesaglitazar treatment abolished high glucose-induced total collagen protein production and type I and IV collagen gene expression. Collectively, tesaglitazar treatment not only improved insulin resistance, glycemic control, and lipid profile but also markedly attenuated albuminuria and renal glomerular fibrosis in db/db mice. These findings support the utility of dual PPARalpha/gamma agonists in treating type 2 diabetes and diabetic nephropathy.

Drug Insight: mechanisms of action and therapeutic applications for agonists of peroxisome proliferator-activated receptors

Intensive preclinical investigations have delineated a role for peroxisome proliferator-activated receptors (PPARs) in energy metabolism and inflammation. PPARs are activated by natural lipophilic ligands such as fatty acids and their derivatives. Normalization of lipid and glucose metabolism is achieved via pharmacological modulation of PPAR activity. PPARs may also alter atherosclerosis progression through direct effects on the vascular wall. PPARs regulate genes involved in the recruitment of leukocytes to endothelial cells, in vascular inflammation, in macrophage lipid homeostasis, and in thrombosis. PPARs therefore modulate metabolic and inflammatory perturbations that predispose to cardiovascular diseases and type 2 diabetes. The hypolipidemic fibrates and the antidiabetic thiazolidinediones are drugs that act via PPARalpha and PPARgamma, respectively, and are used in clinical practice. PPARbeta/delta ligands are currently in clinical evaluation. The pleiotropic actions of PPARs and the fact that chemically diverse PPAR agonists may induce distinct pharmacological responses have led to the emergence of new concepts for drug design. A more precise understanding of the molecular pathways implicated in the response to chemically distinct PPAR agonists should provide new opportunities for targeted therapeutic applications in the management of the metabolic syndrome, type 2 diabetes, and cardiovascular diseases.

Increase in weight induced by muraglitazar, a dual PPARalpha/gamma agonist, in db/db mice: adipogenesis/or oedema?

BACKGROUND AND PURPOSE

Muraglitazar, a dual PPARalpha/gamma agonist, caused a robust increase in body weight in db/db mice. The purpose of the study was to see if this increase in weight was due to oedema and/or adipogenesis.

EXPERIMENTAL APPROACH

The affinity of muraglitazar at PPARalpha/gamma receptors was characterized using transactivation assays. Pre-adipocyte differentiation, expression of genes for adipogenesis (aP2), fatty acid oxidation (ACO) and sodium reabsorption (ENaCgamma and Na+, K+-ATPase); haemodilution parameters and serum electrolytes were measured to delineate the role of muraglitazar in causing weight gain vis a vis rosiglitazone.

KEY RESULTS

Treatment with muraglitazar (10 mg kg(-1)) for 14 days significantly reduced plasma glucose and triglycerides. Reduction in plasma glucose was significantly greater than after similar treatment with rosiglitazone (10 mg kg(-1)). A marked increase in weight was also observed with muraglitazar that was significantly greater than with rosiglitazone. Muraglitazar increased aP2 mRNA and caused adipocyte differentiation in 3T3-L1 cells similar to rosiglitazone. It also caused a marked increase in ACO mRNA in the liver of the treated mice. Expression of mRNA for ENaCgamma and Na+, K+-ATPase in kidneys was up-regulated after either treatment. Increased serum electrolytes and decreased RBC count, haemoglobin and haematocrit were observed with both muraglitazar and rosiglitazone.

CONCLUSIONS AND IMPLICATIONS

Although muraglitazar has a better glucose lowering profile, it also has a greater potential for weight gain than rosiglitazone. In conclusion, muraglitazar causes both robust adipogenesis and oedema in a 14-day treatment of db/db mice as observed in humans.

Selective PPAR modulators, dual and pan PPAR agonists: multimodal drugs for the treatment of Type 2 diabetes and atherosclerosis

More than 70% of patients with Type 2 diabetes mellitus (T2DM) die because of cardiovascular diseases. Current therapeutic strategies are based on separate treatment of insulin resistance and dyslipidaemia. Development of drugs with multimodal activities should improve management of the global cardiovascular risk of T2DM patients and result in better patient compliance. New therapeutic strategies are aimed at targeting the entire spectrum of dysfunctioning organs, cells and regulatory pathways implicated in the pathogenesis of T2DM, dyslipidaemia and atherosclerosis. PPAR family members play major roles in the regulation of lipid metabolism, glucose homeostasis and inflammatory processes, making these transcription factors ideal targets for therapeutic strategies against these diseases. This review discusses why PPARs and development of novel selective PPAR modulators, dual and pan PPAR agonists constitute promising approaches for the treatment of diabetes, dyslipidaemia and atherosclerosis.

Structure-Based Drug Design of a Novel Family of PPARγ Partial Agonists: Virtual Screening, X-ray Crystallography, and in Vitro/in Vivo Biological Activities

Peroxisome proliferator-activated receptor gamma (PPARgamma) is well-known as the receptor of thiazolidinedione antidiabetic drugs. In this paper, we present a successful example of employing structure-based virtual screening, a method that combines shape-based database search with a docking study and analogue search, to discover a novel family of PPARgamma agonists based upon pyrazol-5-ylbenzenesulfonamide. Two analogues in the family show high affinity for, and specificity to, PPARgamma and act as partial agonists. They also demonstrate glucose-lowering efficacy in vivo. A structural biology study reveals that they both adopt a distinct binding mode and have no H-bonding interactions with PPARgamma. The absence of H-bonding interaction with the protein provides an explanation why both function as partial agonists since most full agonists form conserved H-bonds with the activation function helix (AF-2 helix) which, in turn, enhances the recruitment of coactivators. Moreover, the structural biology and computer docking studies reveal the specificity of the compounds for PPARgamma could be due to the restricted access to the binding pocket of other PPAR subtypes, i.e., PPARalpha and PPARdelta, and steric hindrance upon the ligand binding.

Differential effects of isoflavones, from Astragalus membranaceus and Pueraria thomsonii, on the activation of PPARalpha, PPARgamma, and adipocyte differentiation in vitro

Compounds that target the peroxisome proliferator-activated receptors PPARalpha and PPARgamma are used to correct dyslipidemia and to restore glycemic balance, respectively. Because the majority of diabetic patients suffer from atherogenic lipid abnormalities, in addition to insulin resistance, ligands are required that can activate both PPARalpha and PPARgamma. In this study, we used chimeric PPARalpha/gamma reporter-gene bioassays to screen herbal extracts with purported antidiabetic properties. Extracts of Astragalus membranaceus and Pueraria thomsonii significantly activated PPARalpha and PPARgamma. Bioassay-guided fractionation resulted in the isolation of the isoflavones, formononetin, and calycosin from Astragalus membranaceus, and daidzein from Pueraria thomsonii as the PPAR-activating compounds. We investigated the effects of these and 2 common isoflavones, genistein and biochanin A, using chimeric and full-length PPAR constructs in vitro. Biochanin A and formononectin were potent activators of both PPAR receptors (EC50 = 1-4 micromol/L) with PPARalpha/PPARgamma activity ratios of 1:3 in the chimeric and almost 1:1 in the full-length assay, comparable to those observed for synthetic dual PPAR-activating compounds under pharmaceutical development. There was a subtle hierarchy of PPARalpha/gamma activities, indicating that biochanin A, formononetin, and genistein were more potent than calycosin and daidzein in chimeric as well as full-length receptor assays. At low doses, only biochanin A and formononetin, but not genistein, calycosin, or daidzein, activated PPARgamma-driven reporter-gene activity and induced differentiation of 3T3-L1 preadipocytes. Our data suggest the potential value of isoflavones, especially biochanin A and their parent botanicals, as antidiabetic agents and for use in regulating lipid metabolism.

PEROXISOME PROLIFERATOR-ACTIVATED RECEPTORS: How Their Effects on Macrophages Can Lead to the Development of a New Drug Therapy Against Atherosclerosis

Peroxisome proliferator-activated receptors (PPARs) alpha (alpha), beta/delta (beta/delta), and gamma (gamma) are members of the nuclear receptor superfamily, which also includes the estrogen, androgen, and glucocorticoid receptors. Recent evidence suggests that PPARs regulate genes involved in lipid metabolism, glucose homeostasis, and inflammation in various tissues; however, the mechanisms involved are not completely understood. Anti-diabetic drugs, called glitazones, can selectively activate PPARgamma, and hypolipidemic drugs, called fibrates, can weakly activate PPARalpha. Both classes of drugs can decrease insulin resistance and dyslipidemias, which also makes them attractive for treating the metabolic syndrome. The metabolic syndrome exhibits a constellation of risk factors for atherosclerosis that include obesity, insulin resistance, dyslipidemias, and hypertension. Interestingly, all three PPARs are present in macrophages and can therefore have a profound effect on several disease processes, including atherosclerosis. Macrophages are key players in atherosclerotic lesion development. Currently, the first line of defense in reducing the risk of atherosclerosis is aimed at lowering low-density lipoproteins (LDL) and raising high-density lipoproteins (HDL), but a large percentage of patients on statins still succumb to coronary artery disease. However, with the development of drugs selectively activating PPARs, a new arsenal of drugs specifically targeting to the macrophage/foam cell may potentially have a profound impact on how we treat cardiovascular disease.

Kidney Disease and the Metabolic Syndrome

The epidemic of metabolic syndrome contributes to the rapid growth of cardiovascular and renal diseases. Hyper-hemodynamics, impaired pressure natriuresis, excess excretory load, insulin resistance, endothelial dysfunction, chronic inflammation, and prothrombotic status individually and interdependently initiate renal injury in metabolic syndrome. The prevention and treatment of kidney disease require a multifactorial approach. Weight loss through diet control and exercise can reverse many pathophysiologic processes. Pharmacologic intervention includes insulin sensitizers, tight glycemic and lipid control, blockage of renin angiotensin aldosterone system, and anti-inflammatory and antithrombotic therapies. Each peroxisome proliferator-activated receptor isoform plays a distinct role in metabolic syndrome, and their agonists may prevent or reverse the early renal injuries.

Drug Insight: thiazolidinediones and diabetic nephropathy—relevance to renoprotection

Up to a third of people with diabetes mellitus suffer end-stage renal failure due to diabetic nephropathy. Strategies to delay progression of diabetic nephropathy-including glycemic and blood pressure control, modification of the renin-angiotensin system and management of lipid levels with statins-have been effective, but development of new strategies is essential if the ever-increasing burden of this disease is to be minimized. Thiazolidinediones (TZDs) are a family of compounds used as oral hypoglycemic agents in patients with type 2 diabetes mellitus. The therapeutic effects of TZDs are largely a function of their activity as ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), a transcription factor that has a central role in adipogenesis and insulin sensitization. In vitro animal and clinical studies have shown that TZDs ameliorate symptoms and pathogenic mechanisms of diabetic and nondiabetic nephropathy, including proteinuria, excessive deposition of glomerular matrix, cellular proliferation, inflammation and fibrosis. Many of these favorable effects occur under both normal and high-glucose conditions. The mechanisms responsible probably involve both PPARgamma-dependent and PPARgamma-independent pathways. So, TZDs and other agonists of PPARgamma offer promise for treatment of diabetic nephropathy; however, before their putative renoprotective effects can be translated into clinical practice, the complex mechanisms of PPARgamma activity and regulation will need to be investigated further.

Tesaglitazar, a dual PPARα/γ agonist, ameliorates glucose and lipid intolerance in obese Zucker rats

Insulin resistance, impaired glucose tolerance, high circulating levels of free fatty acids (FFA), and postprandial hyperlipidemia are associated with the metabolic syndrome, which has been linked to increased risk of cardiovascular disease. We studied the metabolic responses to an oral glucose/triglyceride (TG) (1.7/2.0 g/kg lean body mass) load in three groups of conscious 7-h fasted Zucker rats: lean healthy controls, obese insulin-resistant/dyslipidemic controls, and obese rats treated with the dual peroxisome proliferator-activated receptor α/γ agonist, tesaglitazar, 3 μmol·kg−1·day−1for 4 wk. Untreated obese Zucker rats displayed marked insulin resistance, as well as glucose and lipid intolerance in response to the glucose/TG load. The 2-h postload area under the curve values were greater for glucose (+19%), insulin (+849%), FFA (+53%), and TG (+413%) compared with untreated lean controls. Treatment with tesaglitazar lowered fasting plasma glucose, improved glucose tolerance, substantially reduced fasting and postload insulin levels, and markedly lowered fasting TG and improved lipid tolerance. Fasting FFA were not affected, but postprandial FFA suppression was restored to levels seen in lean controls. Mechanisms of tesaglitazar-induced lowering of plasma TG were studied separately using the Triton WR1339 method. In anesthetized, 5-h fasted, obese Zucker rats, tesaglitazar reduced hepatic TG secretion by 47%, increased plasma TG clearance by 490%, and reduced very low-density lipoprotein (VLDL) apolipoprotein CIII content by 86%, compared with obese controls. In conclusion, the glucose/lipid tolerance test in obese Zucker rats appears to be a useful model of the metabolic syndrome that can be used to evaluate therapeutic effects on impaired postprandial glucose and lipid metabolism. The present work demonstrates that tesaglitazar ameliorates these abnormalities and enhances insulin sensitivity in this animal model.

Tratamiento médico de la hepatopatía grasa no alcohólica primaria

The need for an effective and safe medical treatment of nonalcoholic fatty liver disease is urgent due to its high prevalence and progressive character. At the moment, therapeutic strategies are largely empirical and based on the control of associated clinical conditions (especially obesity, type 2 diabetes mellitus, and hypertriglyceridemia) and the use of some specific drugs (insulin sensitizing agents, cytoprotectives, antioxidants, and anticytokines) as an attempt to counteract known elements of the pathogenesis. None of these specifics measures have been found to display enough evidence to recommend their clinical use. It is indispensable to join efforts in coordinated networks to define, as soon as possible, the best treatment and the best time to start it.