Activation Of Peroxisome Proliferator-activated Receptor Alpha Research Articles

Modulation of receptor phosphorylation contributes to activation of peroxisome proliferator activated receptor alpha by dehydroepiandrosterone and other peroxisome proliferators.

Dehydroepiandrosterone (DHEA), a C19 human adrenal steroid, activates peroxisome proliferator-activated receptor alpha (PPARalpha) in vivo but does not ligand-activate PPARalpha in transient transfection experiments. We demonstrate that DHEA regulates PPARalpha action by altering both the levels and phosphorylation status of the receptor. Human hepatoma cells (HepG2) were transiently transfected with the expression plasmid encoding PPARalpha and a plasmid containing two copies of fatty acyl coenzyme oxidase (FACO) peroxisome-proliferator activated receptor responsive element consensus oligonucleotide in a luciferase reporter gene. Nafenopin treatment increased reporter gene activity in this system, whereas DHEA treatment did not. Okadaic acid significantly decreased nafenopin-induced reporter activity in a concentration-dependent manner. Okadaic acid treatment of primary rat hepatocytes decreased both DHEA- and nafenopin-induced FACO activity in primary rat hepatocytes. DHEA induced both PPARalpha mRNA and protein levels, as well as PP2A message in primary rat hepatocytes. Western blot analysis showed that the serines at positions 12 and 21 were rapidly dephosphorylated upon treatment with DHEA and nafenopin. Results using specific protein phosphatase inhibitors suggested that protein phosphatase 2A (PP2A) is responsible for DHEA action, and protein phosphatase 1 might be involved in nafenopin induction. Mutation of serines at position 6, 12, and 21 to an uncharged alanine residue significantly increased transcriptional activity, whereas mutation to negative charged aspartate residues (mimicking receptor phosphorylation) decreased transcriptional activity. DHEA action involves induction of PPARalpha mRNA and protein levels as well as increased PPARalpha transcriptional activity through decreasing receptor phosphorylation at serines in the AF1 region.

Peroxisome Proliferator-Activated Receptor Down-Regulation Is Associated With Enhanced Ceramide Levels in Age-Associated Cardiac Hypertrophy

We used an experimental murine model of accelerated aging, the senescence-accelerated mouse (SAM), to examine the effect of age-associated cardiac hypertrophy on peroxisome proliferator-activated receptor alpha (PPARalpha) expression and activity in the heart. Senescence-accelerated prone mice (SAM-P8) showed cardiac hypertrophy compared with senescence-accelerated resistant mice (SAM-R1). Furthermore, a decrease in PPARalpha messenger RNA (mRNA; 28% reduction, p<.001) and protein (47%, p<.05) levels and in PPAR DNA-binding activity was observed in SAM-P8 hearts. Increased protein-protein interaction between PPARalpha and the p65 subunit of nuclear factor-kappaB (NF-kappaB) was found, suggesting that this mechanism may prevent PPARalpha from binding to its response elements. The mRNA levels of PPARalpha target genes involved in fatty acid use were strongly suppressed in SAM-P8, which was consistent with the accumulation of ceramide in SAM-P8 hearts (2.5-fold induction, p<.05). These findings suggest that NF-kappaB activation in SAM-P8 heart prevents PPARalpha from binding to its response elements leading to changes in gene expression that may lead to ceramide accumulation in the aged heart.

Cannabinoid activation of PPARα; a novel neuroprotective mechanism

Although CB(1) receptor activation evokes neuroprotection in response to cannabinoids, some cannabinoids have been reported to be peroxisome proliferator activated receptor (PPAR) ligands, offering an alternative protective mechanism. We have, therefore, investigated the ability of a range of cannabinoids to activate PPAR alpha and for N-oleoylethanolamine (OEA), an endogenous cannabinoid-like compound (ECL), to evoke neuroprotection. Assays of PPAR alpha occupancy and gene transactivation potential were conducted in cell-free and transfected HeLa cell preparations, respectively. In vivo estimates of PPAR alpha activation through fat mobilization and gene transcription were conducted in mice. Neuroprotection in vivo was investigated in wild-type and PPAR alpha gene-disrupted mice. The ECLs OEA, anandamide, noladin ether and virodhamine were found to bind to the purified PPAR alpha ligand binding domain and to increase PPAR alpha-driven transcriptional activity. The high affinity synthetic CB(1/2) cannabinoid agonist WIN 55212-2 bound to PPAR alpha equipotently with the PPARalpha agonist fenofibrate, and stimulated PPARalpha-mediated gene transcription. The phytocannabinoid delta 9 tetrahydrocannabinol was without effect. OEA and WIN 55212-2 induced lipolysis in vivo, while OEA pre-treatment reduced infarct volume from middle cerebral artery occlusion in wild-type, but not in PPAR alpha-null mice. OEA treatment also led to increased expression of the NFkappa B-inhibitory protein, Ikappa B, in mouse cerebral cortex, while expression of the NFkappa B-regulated protein COX-2 was inhibited. These data demonstrate the potential for a range of cannabinoid compounds, of diverse structures, to activate PPAR alpha and suggest that at least some of the neuroprotective properties of these agents could be mediated by nuclear receptor activation.

The role of fenofibrate in clinical practice

Clinical guidelines highlight the importance of dyslipidaemia management for reducing the risk of cardiovascular disease in patients with type 2 diabetes and metabolic syndrome. While statins represent the main focus of therapy, there is increasing evidence that the addition of a fibrate such as fenofibrate provides further reduction in risk. Fenofibrate also offers a number of benefits beyond lipid modification; these are mediated by peroxisome proliferator-activated receptor-alpha (PPARalpha) activation and appear to be independent of effects of glucose and lipid metabolism. Furthermore, as shown by the Fenofibrate Intervention for Event Lowering in Diabetes (FIELD) study, fenofibrate treatment has promising effects in preventing progression of diabetes-related microvascular complications. PPARalpha is critical to lipid metabolism in the liver. Recent findings which showed that pioglitazone, a PPARgamma agonist with weak PPARalpha activity, improved fatty liver disease in patients with non-alcoholic steatohepatitis (NASH) and metabolic syndrome or type 2 diabetes have prompted interest in whether more potent PPARalpha agonists, such as fenofibrate, may have a role in the management of non-alcoholic fatty liver disease (NAFLD). The combination of fenofibrate and a statin is well tolerated, with no apparent increase in the risk of myopathy, unlike gemfibrozil-statin combination therapy. In overview, the available evidence indicates that the combination of fenofibrate with a statin is a useful approach for optimising reduction in the risk of cardiovascular disease in patients with type 2 diabetes and metabolic syndrome, as well as delaying the progression of diabetes-related microvascular complications. Data are awaited from the ongoing Action to Control Cardiovascular Risk in Diabetes (ACCORD) study to evaluate the outcome benefits of this approach.

Gemfibrozil Ameliorates Relapsing-Remitting Experimental Autoimmune Encephalomyelitis Independent of Peroxisome Proliferator-Activated Receptor-α

The present study underlines the importance of gemfibrozil, a lipid-lowering drug and an activator of peroxisome proliferator-activated receptor-alpha (PPAR-alpha), in inhibiting the disease process of adoptively transferred experimental allergic encephalomyelitis (EAE), an animal model of relapsing-remitting multiple sclerosis. Clinical symptoms of EAE, infiltration of mononuclear cells, and demyelination were significantly lower in SJL/J female mice receiving gemfibrozil through food chow than those without gemfibrozil. It is noteworthy that the drug was equally effective in treating EAE in PPAR-alpha wild-type as well as knockout mice. Gemfibrozil also inhibited the encephalitogenicity of MBP-primed T cells and switched the immune response from a Th1 to a Th2 profile independent of PPAR-alpha. Gemfibrozil consistently inhibited the expression and DNA-binding activity of T-bet, a key regulator of interferon-gamma (IFN-gamma) expression and stimulated the expression and DNA-binding activity of GATA3, a key regulator of IL-4. Gemfibrozil treatment decreased the number of T-bet-positive T cells and increased the number of GATA3-positive T cells in spleen of donor mice. The histological and immunohistochemical analyses also demonstrate the inhibitory effect of gemfibrozil on the invasion of T-bet-positive T cells into the spinal cord of EAE mice. Furthermore, we demonstrate that the differential effect of gemfibrozil on the expression of T-bet and GATA3 was due to its inhibitory effect on NO production. Although excess NO favored the expression of T-bet, scavenging of NO stimulated the expression of GATA-3. Taken together, our results suggest gemfibrozil, an approved drug for hyperlipidemia in humans, may find further therapeutic use in multiple sclerosis.

Peroxisome proliferator-activated receptor α polymorphisms and postprandial lipemia in healthy men

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a ligand-dependent transcription factor that plays a key role in lipid and glucose homeostasis. This study evaluated whether variants of PPARalpha are associated with postprandial lipemia. Subjects were given a single fat load composed of 60% calories as fat, 15% as protein, and 25% as carbohydrate. Blood was drawn every hour from baseline to 6 h, then every 2.5 h to 11 h to determine triglyceride (TG) levels. The minor allele of the nonsynonymous p.Leu162Val variant was associated with higher fasting total cholesterol, LDL-cholesterol, and apolipoprotein B. There were no significant associations with all of the postprandial parameters examined. Conversely, the noncoding variant c.140+5435T>C was not associated with fasting lipid concentrations but was significantly associated with decreased postprandial TG and cholesterol in the small TG-rich lipoprotein particle. Although the minor allele carriers displayed lower mean concentrations of TG and cholesterol throughout the postprandial period, the differences were most pronounced in the latter period. These data suggest that PPARalpha variants may modulate the risk of cardiovascular disease by influencing both fasting and postprandial lipid concentrations.

Cardiovascular Actions of the Peroxisome Proliferator‐Activated Receptor‐Alpha (PPARα) Agonist Wy14,643

This review examines the various effects of Wy14,643, a hypolipidemic agent that activates peroxisome proliferator-activated receptor-alpha (PPARalpha), on the cardiovascular system. An emphasis has been placed on the specific cellular processes affected by Wy14,643 as they relate to vascular and cardiac function. Although the topic of this discussion is limited to vascular and cardiac tissues, the importance of circulating lipids on cardiovascular disease requires that a description of the indirect actions of this compound on liver metabolism also be included. Finally, the pharmacology of Wy14,643 is discussed within the context of PPARalpha-dependent and -independent mechanisms.

Activation of peroxisome proliferator-activated receptor-α by fenofibrate prevents myocardial dysfunction during endotoxemia in rats*

To investigate the effects of fenofibrate, an activator of peroxisome proliferator-activated receptor-alpha, on cardiac function in a rat endotoxemia model. Prospective, randomized, controlled study. University research laboratory. Three-month-old male Wistar rats. Animals were fed with standard diet containing no drug or fenofibrate (0.2%) for 14 days. They were then injected intravenously with either 5 mg/kg lipopolysaccharide (LPS and fenofibrate + LPS groups) or saline (control and fenofibrate groups). In the LPS group, body weight loss, metabolic acidosis, and thrombocytopenia confirmed presence of systemic endotoxemia. LPS administration resulted in an early peak in plasma tumor necrosis factor-alpha, decreased cardiac contractility (isolated and perfused heart), reduced myofilament Ca2+ sensitivity (Triton-skinned cardiac fibers), and increased left ventricular nitric oxide (NO) end-oxidation products (NO(x) and NO2), without evidence of myocardial oxidative stress (thiobarbituric acid-reactive substances and antioxidant enzyme activities). Fenofibrate pretreatment (fenofibrate + LPS group) did not alter signs of endotoxemia but prevented reductions in both cardiac contractility and myofilament Ca2+ sensitivity. The peak of plasma tumor necrosis factor-alpha was attenuated, whereas myocardial NO(x) and NO2 remained similar to the LPS group. Oxidative stress was suggested from moderate increase in cardiac thiobarbituric acid-reactive substances and reduced glutathione peroxidase activity. Fenofibrate, an activator of peroxisome proliferator-activated receptor-alpha, may prevent endotoxemia-induced cardiac dysfunction and reduction in myofilament Ca2+ sensitivity. Our data also suggest a mediating role for early peak plasma tumor necrosis factor-alpha, but not for myocardial NO production or oxidative stress.

Indanylacetic Acid Derivatives Carrying 4-Thiazolyl-phenoxy Tail Groups, a New Class of Potent PPAR α/γ/δ Pan Agonists: Synthesis, Structure−Activity Relationship, and In Vivo Efficacy

Compounds that simultaneously activate the three peroxisome proliferator-activated receptor (PPAR) subtypes alpha, gamma, and delta hold potential to address the adverse metabolic and cardiovascular conditions associated with diabetes and the metabolic syndrome. We recently identified the indanylacetic acid moiety as a well-tunable PPAR agonist head group. Here we report the synthesis and structure-activity relationship (SAR) studies of novel aryl tail group derivatives that led to a new class of potent PPAR pan agonists. While most of the tail group modifications imparted potent PPAR delta agonist activity, improvement of PPAR alpha and gamma activity required the introduction of new heterocyclic substituents that were not known in the PPAR literature. Systematic optimization led to the discovery of 4-thiazolyl-phenyl derivatives with potent PPAR alpha/gamma/delta pan agonistic activity. The lead candidate from this series was found to exhibit excellent ADME properties and superior therapeutic potential compared to known PPAR gamma activating agents by favorably modulating lipid levels in hApoA1 mice and hyperlipidemic hamsters, while normalizing glucose levels in diabetic rodent models.

Fenofibrate

Fenofibrate is a fibric acid derivative indicated for use in the treatment of primary hypercholesterolaemia, mixed dyslipidaemia and hypertriglyceridaemia in adults who have not responded to nonpharmacological measures. Its lipid-modifying effects are mediated by activation of peroxisome proliferator-activated receptor-alpha. Fenofibrate also has nonlipid (i.e. pleiotropic) effects (e.g. it reduces fibrinogen, C-reactive protein and uric acid levels and improves flow-mediated dilatation). Fenofibrate improves lipid levels (in particular triglyceride [TG] and high-density lipoprotein-cholesterol [HDL-C] levels) in patients with primary dyslipidaemia. Its lipid-lowering profile means that fenofibrate is particularly well suited for use in atherogenic dyslipidaemia (characterised by high TG levels, low HDL-C levels and small, dense low-density lipoprotein [LDL] particles), which is commonly seen in patients with the metabolic syndrome and type 2 diabetes mellitus. Indeed, fenofibrate improves the components of atherogenic dyslipidaemia in patients with these conditions, including a shift from small, dense LDL particles to larger, more buoyant LDL particles. Greater improvements in lipid levels are seen when fenofibrate is administered in combination with an HMG-CoA reductase inhibitor (statin) or in combination with ezetimibe, compared with monotherapy with these agents. In the DAIS study, fenofibrate significantly slowed the angiographic progression of focal coronary atherosclerosis in patients with type 2 diabetes. In terms of clinical outcomes, although no significant reduction in the risk of coronary events was seen with fenofibrate in the FIELD trial in patients with type 2 diabetes, treatment was associated with a significantly reduced risk of total cardiovascular disease (CVD) events, primarily through the prevention of non-fatal myocardial infarction and coronary revascularisation. Subgroup analyses revealed significant reductions in total CVD events and coronary heart disease events in patients with no previous CVD, suggesting a potential role for primary prevention with fenofibrate in patients with early type 2 diabetes. Improvements were also seen in microvascular outcomes with fenofibrate in the FIELD trial. Fenofibrate is generally well tolerated, both as monotherapy and when administered in combination with a statin. Combination therapy with fenofibrate plus a statin appears to be associated with a low risk of rhabdomyolysis; no cases of rhabdomyolysis were reported in patients receiving such therapy in the FIELD trial. Thus, fenofibrate is a valuable lipid-lowering agent, particularly in patients with atherogenic dyslipidaemia.

Dual PPAR α/γ Agonists: Promises and Pitfalls in Type 2 Diabetes

Type 2 diabetes mellitus is a disease of complex pathogenesis and pleiotropic clinical manifestations. The greatest clinical challenge in this disease is the prevention of the long-term complications, many of which involve cardiovascular outcomes. The peroxisome proliferator-activated receptor (PPAR) alpha and gamma isoforms of the family of nuclear transcription factors are pharmaceutical targets for therapeutic intervention because they can potentially ameliorate not only the hyperglycemia of diabetes, but also the dyslipidemia that is characteristic of this disorder (low high-density lipoprotein cholesterol, high triglycerides, small, dense low-density lipoprotein particles). Novel drugs with dual PPAR alpha and gamma activity have been under clinical development for type 2 diabetes, and they have shown promise in early studies with regard to glucose lowering and improved lipid profile when compared with the PPAR-gamma-specific thiazolidinediones. Unfortunately, the dual PPARs available to date have some of the PPAR-gamma-associated side effect profile, including fluid retention and weight gain, which have limited the further clinical development of higher doses that show improved efficacy. This review will briefly summarize our understanding of the pathogenesis of type 2 diabetes, the role of the PPAR family of receptors, and the potential for clinical use of this novel emerging class of agents that serve as dual activators of both PPAR-alpha and PPAR-gamma.

Action of epoxyeicosatrienoic acids on cellular function.

Epoxyeicosatrienoic acids (EETs), which function primarily as autocrine and paracrine mediators in the cardiovascular and renal systems, are synthesized from arachidonic acid by cytochrome P-450 epoxygenases. They activate smooth muscle large-conductance Ca(2+)-activated K(+) channels, producing hyperpolarization and vasorelaxation. EETs also have anti-inflammatory effects in the vasculature and kidney, stimulate angiogenesis, and have mitogenic effects in the kidney. Many of the functional effects of EETs occur through activation of signal transduction pathways and modulation of gene expression, events probably initiated by binding to a putative cell surface EET receptor. However, EETs are rapidly taken up by cells and are incorporated into and released from phospholipids, suggesting that some functional effects may occur through a direct interaction between the EET and an intracellular effector system. In this regard, EETs and several of their metabolites activate peroxisome proliferator-activated receptor alpha (PPARalpha) and PPARgamma, suggesting that some functional effects may result from PPAR activation. EETs are metabolized primarily by conversion to dihydroxyeicosatrienoic acids (DHETs), a reaction catalyzed by soluble epoxide hydrolase (sEH). Many potentially beneficial actions of EETs are attenuated upon conversion to DHETs, which do not appear to be essential under routine conditions. Therefore, sEH is considered a potential therapeutic target for enhancing the beneficial functions of EETs.

Peroxisome Proliferator-Activated Receptor (PPAR)-α Agonism Prevents the Onset of Type 2 Diabetes in Zucker Diabetic Fatty Rats: A Comparison with PPARγ Agonism

Peroxisome proliferator-activated receptor (PPAR)-gamma agonists are insulin sensitizers, whereas PPAR alpha agonists are lipid-lowering agents in humans. Chronic treatment with PPAR gamma agonists has been shown to prevent the onset of diabetes in young Zucker diabetic fatty (ZDF) rats; however, the effects of PPAR alpha agonists have not been well characterized in this model. Here we investigated chronic efficacy of PPAR alpha and nonthiazolidinedione (nTZD) PPAR gamma agonists on the onset of diabetes in 6-wk-old male ZDF rats. Whereas treatment with the nTZD PPAR gamma agonist completely prevented development of hyperglycemia, PPAR alpha activation was associated with lowering of food intake and body weight and reductions in fed and fasting hyperglycemia, with prevention of the hyperinsulinemic peak preceding the development of hyperglycemia in ZDF rats. Both compounds improved glucose tolerance during an oral glucose tolerance test with concomitant increases in insulin response. Such improvements of insulin secretion were associated with increased islet to total pancreatic area ratio and pancreatic insulin contents. Hyperinsulinemic-euglycemic clamp studies demonstrated that nTZD PPAR gamma reduced basal endogenous glucose production and increased insulin-stimulated glucose disposal, consistent with an improved insulin action as a cause of the improved glucose homeostasis. In contrast, activation of PPAR alpha did not significantly improve glucose metabolism during the hyperinsulinemic-euglycemic clamp. In conclusion, chronic treatment of ZDF rats with a PPAR gamma agonist completely prevented the onset of diabetes by improving both insulin action and secretion, whereas PPAR alpha agonism was partially effective, primarily by improving the pancreatic islet insulin response. Unlike the PPAR gamma agonist, the PPAR alpha agonist demonstrated efficacy without inducing body weight gain and cardiomegaly. This study suggests a possible role for PPAR alpha agonists in the prevention of type 2 diabetes mellitus.

Pharmacological Characterization of Hydrolysis-Resistant Analogs of Oleoylethanolamide with Potent Anorexiant Properties

Oleoylethanolamide (OEA) is an endogenous lipid mediator that reduces food intake, promotes lipolysis, and decreases body weight gain in rodents by activating peroxisome proliferator-activated receptor-alpha (PPAR-alpha). The biological effects of OEA are terminated by two intracellular lipid hydrolase enzymes, fatty-acid amide hydrolase and N-acylethanolamine-hydrolyzing acid amidase. In the present study, we describe OEA analogs that resist enzymatic hydrolysis, activate PPAR-alpha with high potency in vitro, and persistently reduce feeding when administered in vivo either parenterally or orally. The most potent of these compounds, (Z)-(R)-9-octadecenamide,N-(2-hydroxyethyl,1-methyl) (KDS-5104), stimulates transcriptional activity of PPAR-alpha with a half-maximal effective concentration (EC50) of 100 +/- 21 nM (n = 11). Parenteral administration of KDS-5104 in rats produces persistent dose-dependent prolongation of feeding latency and postmeal interval (half-maximal effective dose, ED50 = 2.4 +/- 1.8 mg kg(-1) i.p.; n = 18), as well as increased and protracted tissue exposure compared with OEA. Oral administration of the compound also results in a significant tissue exposure and reduction of food intake in free-feeding rats. These results suggest that the endogenous high-affinity PPAR-alpha agonist OEA may provide a scaffold for the discovery of novel orally active PPAR-alpha ligands.

Differential effects of contraction and PPAR agonists on the expression of fatty acid transporters in rat skeletal muscle

We have examined over the course of a 1-week period the independent and combined effects of chronically increased muscle contraction and the peroxisome proliferator-activated receptor (PPAR)alpha and PPARgamma activators, Wy 14,643 and rosiglitazone, on the expression and plasmalemmal content of the fatty acid transporters, FAT/CD36 and FABPpm, as well as on the rate of fatty acid transport. In resting muscle, the activation of either PPARalpha or PPARgamma failed to induce the protein expression of FAT/CD36. PPARalpha activation also failed to induce the protein expression of FABPpm. In contrast, PPARgamma activation induced the expression of FABPpm protein (40%; P < 0.05). Chronic muscle contraction increased the protein expression of FAT/CD36 (approximately 50%; P < 0.05), whereas FABPpm was slightly increased (12%; P < 0.05). Neither PPARalpha nor PPARgamma activation altered the contraction-induced expression of FAT/CD36 or FABPpm. Changes in protein expression of FAT/CD36 or FABPpm, induced by either contractions or by administration of rosiglitazone, were largely attributable to increased transcription. The contraction-induced increments in FAT/CD36 were accompanied by parallel increments in plasmalemmal FAT/CD36 and in rates of fatty acid transport (P < 0.05). Up-regulation of FABPpm expression was, however, accompanied by a reduction in plasmalemmal FABPpm, which did not affect the rates of long chain fatty acid (LCFA) transport. These studies have shown that in skeletal muscle (i) neither PPARalpha nor PPARgamma activation alters FAT/CD36 expression, (ii) PPARgamma activation selectively up-regulates FABPpm expression and (iii) contraction-induced up-regulation of LCFA transport does not appear to occur via activation of either PPARalpha or PPARgamma.

Fibrate prevents cisplatin-induced proximal tubule cell death

In previous studies we have shown that cisplatin inhibits peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activity and consequently fatty acid oxidation, and these events precede proximal tubule cell death. In addition the use of fibrate class of PPAR-alpha ligands ameliorate renal function by preventing both inhibition of fatty acid oxidation and proximal tubule cell death. LLC-PK1 cells were treated with cisplatin and apoptosis was established by the presence of nuclear fragmentation and by cell cycle analysis. Proximal tubular cells treated with cisplatin and bezafibrate were subjected to sub cellular fractionation and the presence of Bax, Bcl-2, cytochrome c, and active caspase-3 in the cytosolic and mitochondrial membrane fractions was determined by Western blot analysis. PPAR-alpha activity was measured by determining luciferase activity after transfection of LLC-PK1 cells with TK-Luc 3x PPAR response elements (PPRE), and the accumulation of nonesterified free fatty acids was measured in lysates obtained from cells treated with cisplatin and bezafibrate. Incubation of LLC-PK1 cells with 25 micromol/L cisplatin for 18 hours induced 41.5% apoptosis measured by cell cycle analysis. Cisplatin-induced apoptosis was significantly suppressed by bezafibrate, a fibrate class of PPAR-alpha ligand. Bezafibrate treatment of LLC-PK1 cells prevented cisplatin-induced translocation of proapoptotic Bax from the cytosol to the mitochondrial fraction, and increased the expression of antiapoptotic molecule Bcl-2. Cisplatin-induced inhibition of PPAR-alpha activity was accompanied by increased accumulation of nonesterified free fatty acids. Pretreatment with bezafibrate prevented both the inhibition of PPAR-alpha activity and the accumulation of nonesterified free fatty acids induced by cisplatin. Finally, bezafibrate prevented cisplatin-induced release of cytochrome c from the mitochondria to the cytosol, and the cleavage of procaspase-3 to active caspase-3. Bezafibrate treatment inhibits cisplatin-mediated tubular injury by preventing the activation of various cellular mechanisms that lead to proximal tubule cell death. These findings support our previous observations where the use of fibrates represents a novel strategy to ameliorate proximal tubule cell death in cisplatin-induced acute renal failure.

Monocyte Release of Tumor Necrosis Factor-α and Interleukin-1β in Primary Type IIa and IIb Dyslipidemic Patients Treated With Statins or Fibrates

Both 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) as well as peroxisome proliferator-activated receptor (PPAR)alpha activators (fibrates) proved to be effective in the primary and secondary prevention of cardiovascular diseases. The benefits of hypolipemic therapy in cardiovascular diseases cannot be explained only by the lipid-lowering potential of these agents. The aim of this study was to clarify the effect of hypolipemic agents on proinflammatory cytokine release from human monocytes in relationship with their action on plasma levels of sensitive systemic marker of low-grade vascular inflammation. Plasma lipid and high-sensitivity C-reactive protein (hsCRP) levels, and the release of tumor necrosis factor-alpha (TNFalpha) and interleukin-1beta from monocytes were assessed at baseline and 30 and 90 days following randomization of IIa dyslipidemic patients into fluvastatin or simvastatin groups and randomization of type IIb dyslipidemic patients to the micronized form of either ciprofibrate or fenofibrate. Lipopolysaccharide-stimulated monocytes from dyslipidemic patients released significantly more TNFalpha (types IIa and IIb dyslipidemias) and interleukin-1beta (type IIa dyslipidemia) in comparison with monocytes in 59 age-, sex-, and weight-matched control subjects. Their baseline hsCRP levels were also higher. Both statins and fibrates reduced the release of TNFalpha and interleukin-1beta, and lowered plasma hsCRP levels. The effects of hypolipemic agents on cytokine release and plasma hsCRP were unrelated to their lipid-lowering action. Our results have demonstrated that type IIa and IIb dyslipidemic patients exhibit the abnormal pattern of TNFalpha and interleukin-1beta production by activated monocytes. Both HMG-CoA reductase inhibitors and PPARalpha activators normalize monocytic secretion of these cytokines, and this action may partially contribute to the systemic antiinflammatory effect of hypolipemic agents. The statin- and fibrate-induced suppression of proinflammatory cytokine release from monocytes seems to play a role in their beneficial effect on the incidence of cardiovascular events.

Peroxisome proliferator-activated receptor alpha activation promotes neurological recovery and exerts anti-edematous effect in a model of traumatic brain injury

Peroxisome proliferator-activated receptor alpha activation promotes neurological recovery and exerts anti-edematous effect in a model of traumatic brain injury

Activation of Peroxisome Proliferator-Activated Receptor α by Substituted Urea-Derived Soluble Epoxide Hydrolase Inhibitors

Soluble epoxide hydrolase (sEH) plays a major role in regulating vascular epoxyeicosatrienoic acid metabolism and function, and substituted urea derivatives that inhibit sEH activity reduce blood pressure in hypertensive rats. We found that substituted urea derivatives containing a dodecanoic acid group, besides effectively inhibiting sEH, increased peroxisome proliferator-activated receptor (PPAR) alpha activity. In PPARalpha transfected COS-7 cells, treatment with 10 microM N-cyclohexyl-N'-dodecanoic acid urea (CUDA) or N-adamantanyl-N'-dodecanoic acid urea (AUDA) produced 6- and 3-fold increases, respectively, in PPARalpha activation. Neither CUDA nor AUDA activated PPARdelta or PPARgamma directly, indicating selectivity for PPARalpha. CUDA did not alter PPARalpha protein expression, and it competitively inhibited the binding of Wy-14643 (pirinixic acid) to the ligand binding domain of PPARalpha, suggesting that it functions as a PPARalpha ligand. CUDA and AUDA were metabolized to chain-shortened beta-oxidation products, a process that reduced their potency as sEH inhibitors and their ability to bind and activate PPARalpha. N,N'-Dicylclohexylurea and N-cyclohexyl-N'-dodecylurea, sEH inhibitors that do not contain a carboxylic acid group, did not activate PPARalpha. In HepG2 cells, CUDA increased the expression of the PPARalpha-responsive gene carnitine palmitoyltransferase 1A. We conclude that CUDA and AUDA, by virtue of their carboxylic acid substitution, activate PPARalpha in addition to potently inhibiting sEH. Further development of these compounds could lead to a class of agents with hypotensive and lipid-lowering properties that may be valuable for the prevention and treatment of cardiovascular disease.

Sixteen hours of fasting differentially affects hepatic and muscle insulin sensitivity in mice

Fasting readily induces hepatic steatosis. Hepatic steatosis is associated with hepatic insulin resistance. The purpose of the present study was to document the effects of 16 h of fasting in wild-type mice on insulin sensitivity in liver and skeletal muscle in relation to 1) tissue accumulation of triglycerides (TGs) and 2) changes in mRNA expression of metabolically relevant genes. Sixteen hours of fasting did not show an effect on hepatic insulin sensitivity in terms of glucose production in the presence of increased hepatic TG content. In muscle, however, fasting resulted in increased insulin sensitivity, with increased muscle glucose uptake without changes in muscle TG content. In liver, fasting resulted in increased mRNA expression of genes promoting gluconeogenesis and TG synthesis but in decreased mRNA expression of genes involved in glycogenolysis and fatty acid synthesis. In muscle, increased mRNA expression of genes promoting glucose uptake, as well as lipogenesis and beta-oxidation, was found. In conclusion, 16 h of fasting does not induce hepatic insulin resistance, although it causes liver steatosis, whereas muscle insulin sensitivity increases without changes in muscle TG content. Therefore, fasting induces differential changes in tissue-specific insulin sensitivity, and liver and muscle TG contents are unlikely to be involved in these changes.