Effects Of Peroxisome Proliferator-activated Receptors Agonists Research Articles

The Effects of PPAR Agonists on Atherosclerosis and Nonalcoholic Fatty Liver Disease in ApoE-/-FXR-/- Mice.

Background Farnesoid X receptor (FXR), a bile acid–activated nuclear receptor, is a potent regulator of glucose and lipid metabolism as well as of bile acid metabolism. Previous studies have demonstrated that FXR deficiency is associated with metabolic derangements, including atherosclerosis and nonalcoholic fatty liver disease (NAFLD), but its mechanism remains unclear. In this study, we investigated the role of FXR in atherosclerosis and NAFLD and the effect of peroxisome proliferator-activated receptor (PPAR) agonists in mouse models with FXR deficiency.Methods En face lipid accumulation analysis, liver histology, serum levels of glucose and lipids, and mRNA expression of genes related to lipid metabolism were compared between apolipoprotein E (ApoE)−/− and ApoE−/−FXR−/− mice. The effects of PPARα and PPARγ agonists were also compared in both groups of mice.Results Compared with ApoE−/− mice, ApoE−/−FXR−/− mice showed more severe atherosclerosis, hepatic steatosis, and higher levels of serum cholesterol, low-density lipoprotein cholesterol, and triglycerides, accompanied by increased mRNA expression of FAS, ApoC2, TNFα, IL-6 (liver), ATGL, TGH, HSL, and MGL (adipocytes), and decreased mRNA expressions of CPT2 (liver) and Tfam (skeletal muscle). Treatment with a PPARα agonist, but not with a PPARγ agonist, partly reversed atherosclerosis and hepatic steatosis, and decreased plasma triglyceride levels in the ApoE−/−FXR−/− mice, in association with increased mRNA expression of CD36 and FATP and decreased expression of ApoC2 and ApoC3 (liver).Conclusion Loss of FXR is associated with aggravation of atherosclerosis and hepatic steatosis in ApoE-deficient mice, which could be reversed by a PPARα agonist through induction of fatty acid uptake, β-oxidation, and triglyceride hydrolysis.

PPAR agonists reduce steatosis in oleic acid-overloaded HepaRG cells

Although non-alcoholic fatty liver disease (NAFLD) is currently the most common form of chronic liver disease there is no pharmacological agent approved for its treatment. Since peroxisome proliferator-activated receptors (PPARs) are closely associated with hepatic lipid metabolism, they seem to play important roles in NAFLD. However, the effects of PPAR agonists on steatosis that is a common pathology associated with NAFLD, remain largely controversial. In this study, the effects of various PPAR agonists, i.e. fenofibrate, bezafibrate, troglitazone, rosiglitazone, muraglitazar and tesaglitazar on oleic acid-induced steatotic HepaRG cells were investigated after a single 24-hour or 2-week repeat treatment. Lipid vesicles stained by Oil-Red O and triglycerides accumulation caused by oleic acid overload, were decreased, by up to 50%, while fatty acid oxidation was induced after 2-week co-treatment with PPAR agonists. The greatest effects on reduction of steatosis were obtained with the dual PPARα/γ agonist muraglitazar. Such improvement of steatosis was associated with up-regulation of genes related to fatty acid oxidation activity and down-regulation of many genes involved in lipogenesis. Moreover, modulation of expression of some nuclear receptor genes, such as FXR, LXRα and CAR, which are potent actors in the control of lipogenesis, was observed and might explain repression of de novo lipogenesis. ConclusionAltogether, our in vitro data on steatotic HepaRG cells treated with PPAR agonists correlated well with clinical investigations, bringing a proof of concept that drug-induced reversal of steatosis in human can be evaluated in in vitro before conducting long-term and costly in vivo studies in animals and patients.

Anti-inflammatory properties of a dual PPARgamma/alpha agonist muraglitazar in in vitro and in vivo models

IntroductionPeroxisome proliferator-activated receptor (PPAR) agonists are widely used drugs in the treatment of diabetes and dyslipidemia. In addition to their metabolic effects, PPAR isoforms PPARα and PPARγ are also involved in the regulation of immune responses and inflammation. In the present study, we investigated the effects of a dual PPARγ/α agonist muraglitazar on inflammatory gene expression in activated macrophages and on carrageenan-induced inflammation in the mouse.MethodsJ774 murine macrophages were activated by lipopolysaccharide (LPS) and treated with dual PPARγ/α agonist muraglitazar, PPARγ agonist GW1929 or PPARα agonist fenofibrate. The effects of PPAR agonists on cytokine production and the activation of inducible nitric oxide synthase (iNOS) pathway were investigated by ELISA, Griess method, Western blotting and quantitative RT-PCR. Nuclear translocation, DNA-binding activity and reporter gene assays were used to assess the activity of nuclear factor kappa B (NF-kB) transcription factor. Carrageenan-induced paw oedema was used as an in vivo model of acute inflammation.ResultsMuraglitazar as well as PPARγ agonist GW1929 and PPARα agonist fenofibrate inhibited LPS-induced iNOS expression and NO production in activated macrophages in a dose-dependent manner. Inhibition of iNOS expression by muraglitazar included both transcriptional and post-transcriptional components; the former being shared by GW1929 and the latter by fenofibrate. All tested PPAR agonists also inhibited IL-6 production, while TNFα production was reduced by muraglitazar and GW1929, but not by fenofibrate. Interestingly, the anti-inflammatory properties of muraglitazar were also translated in vivo. This was evidenced by the finding that muraglitazar inhibited carrageenan-induced paw inflammation in a dose-dependent manner in mice as did iNOS inhibitor L-NIL and anti-inflammatory steroid dexamethasone.ConclusionsThese results show that muraglitazar has anti-inflammatory properties both in vitro and in vivo and these effects reflect the agonistic action through both PPARα and PPARγ.

Differential susceptibility to the PPAR-γ agonist pioglitazone in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 6-hydroxydopamine rodent models of Parkinson's disease

A growing body of evidence suggests that peroxisome proliferator-activated receptor (PPAR) agonists are valuable candidates as disease modifiers in Parkinson's disease (PD) and may thus enable neuroprotection and preserve motor function. The present study sought to evaluate the effect of the PPAR-gamma agonist pioglitazone in two different animal models of PD. The study was based on nigral dopaminergic neuron labelling and the assessment of motor behaviour in (i) the frequently investigated MPTP mouse model and (ii) the less well-known bilateral 6-OHDA rat model.In MPTP-injected mice, pioglitazone reversed body weight loss and the reduction in rearing frequency and induced significant neuroprotection of the nigrostriatal dopaminergic pathway (by 24%, compared with vehicle). In contrast, pioglitazone did not have any effect on the 73.5% loss of dopaminergic neurons or motor impairments (a reduced rearing frequency and a loss of strength in the forepaws) in bilateral 6-OHDA rats.The PPAR-gamma agonist pioglitazone had a significant neuroprotective effect in MPTP mice but not in bilateral 6-OHDA rats. The various effects of PPAR agonists in both models can be accounted by the different action mechanism of the 2 toxins or by the fact that 3μg 6-OHDA injection was too harmful to be alleviated by the compound. This work supports PPAR-agonists to be relevant in the therapeutic strategy research in Parkinson's disease and highlights the importance in evaluating neuroprotective agent in different models.

The subtypes of peroxisome proliferator-activated receptors expressed by human podocytes and their role in decreasing podocyte injury.

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors, and three subtypes (α, β and γ) have been identified. PPAR activation has been reported to decrease renal injury and markers of glomerular dysfunction in models of renal ischemia/reperfusion (I/R). However, both the I/R effects and the effects of PPAR agonists on podocytes, an integral cellular part of the glomerular filtration barrier, remain to be established. By using oxygen/glucose deprivation-reoxygenation as an in vitro model that mimics in vivo I/R, the effects of PPAR agonists on podocyte death were compared. Human immortalized podocytes were treated with gemfibrozil, GW0742, pioglitazone or rosiglitazone, as a single or repeated challenge. Cell loss, necrotic and apoptotic cell death were measured. Only the repeated treatment with each PPAR agonist significantly prevented cell death, mainly by decreasing apoptosis. In comparison, in a model of serum deprivation-induced apoptosis, both treatments were effective, although the repeated treatment achieved the more pronounced effect. Finally, our results showed that preservation of Bcl-2, Bax and nephrin expression accompanied the anti-apoptotic effects exerted by PPAR agonists in human podocytes. These findings contribute to clarification of the pathophysiological role of renal PPARs and suggest that selective PPARα, PPARβ or PPARγ agonists may exert similar protective effects on podocytes by decreasing apoptotic cell death.

PPARδ agonists suppress angiogenesis in a VEGFR2-dependent manner

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that have a pleiotropic impact on the regulation of differentiation, cell growth, and the metabolism of lipids and glucose. PPARδ agonists display a variety of effects on pro- and anti-tumor processes, and seem to have pro-angiogenic activity at very low concentrations. We analyzed the influence of higher concentrations of PPARδ agonists on angiogenesis and its underlying mechanisms. We found that treatment with PPARδ agonists inhibited the formation of capillary-like structures and endothelial cell migration. Since signaling via the vascular endothelial growth factor receptor-2 (VEGFR2) pathway is critical for angiogenic responses during chronic inflammation and tumor development, we explored whether PPARδ agonist inhibition acted by diminishing VEGFR2 expression. PPARδ agonists inhibited endothelial VEGFR2 protein expression in a time- and concentration-dependent manner. In contrast, neither tie-2, neuropilin-1 nor VEGFR1 expression was significantly affected by PPARδ agonist treatment. We also demonstrated that PPARδ agonists significantly suppressed accumulation of VEGFR2 mRNA. Consistent with these results, promoter luciferase assays showed that the inhibitory effects of PPAR agonists occur through suppression of VEGFR2 promoter activity. Hence, VEGFR-2 expression may be a critical molecular target of PPAR δ agonists, which may be responsible for their anti-angiogenic effects. These results may help to define the optimal therapeutic doses of PPARδ agonists in prospective therapeutic applications.

Peroxisome proliferator-activated receptors as stimulants of angiogenesis in cardiovascular disease and diabetes

The incidence of diabetes is directly related to the incidence of obesity, which is at epidemic proportions in the US. Cardiovascular disease is a common complication of diabetes, which results in high morbidity and mortality. Peroxisome proliferator-activated receptors (PPARs) are a group of nuclear hormone receptors that regulate lipid and glucose metabolism. PPAR-α agonists such as fenofibrate and PPAR-γ agonists such as the thiozolidinediones have been used to treat dyslipidemia and insulin resistance in diabetes. Over the past few years research has discovered the role of PPARs in the regulation of inflammation, proliferation, and angiogenesis. Clinical trials looking at the effect of PPAR agonists on cardiovascular outcomes have produced controversial results. Studies looking at angiogenesis and proliferation in various animal models and cell lines have shown a wide variation in results. This may be due to the differential effects of PPARs on proliferation and angiogenesis in various tissues and pathologic states. This review discusses the role of PPARs in stimulating angiogenesis. It also reviews the settings in which stimulation of angiogenesis may be either beneficial or harmful.

Effects of PPAR agonists on proliferation and differentiation in human urothelium

Systemic treatment of rats with peroxisome proliferator-activated receptor (PPAR) agonists (mainly of dual α/ γ activity) has indicated that they may invoke non-genotoxic carcinogenesis in the epithelial lining of the urinary tract (urothelium). Although there is evidence in the male rat to support an indirect effect via a crystaluria-induced urothelial damage response, there is other evidence to indicate a direct signalling effect on the urothelium and hence the full implication for using these drugs in man is unclear. Numerous reports have demonstrated that PPARs are expressed within the urothelium of different species, including man, and from an early developmental stage. We have developed methods to maintain normal human urothelial (NHU) cells in culture, where the cells retain PPAR expression and express a highly proliferative phenotype, mediated via autocrine stimulation of the epidermal growth factor (EGF) receptor. We have shown that specific activation of PPAR γ results in a programme of gene expression changes associated with late/terminal cytodifferentiation, including induction of cytokeratins CK13 and CK20, tight junction-associated claudin 3, and uroplakins UPK1a and UPK2, but this is dependent upon inhibition of the signalling cascade downstream of the EGF receptor. This indicates a subtle balance in the regulation of proliferation and differentiation in urothelium, with PPAR γ agonists promoting differentiation. Our data indicate that human urothelium is a target tissue for PPAR γ signalling, but it has yet to be determined whether dual agonists could have a modulatory effect on the proliferation/differentiation balance.

Peroxisome proliferator-activated receptors: Targets for the treatment of metabolic illnesses (Review)

Peroxisome proliferator-activated receptors (PPARs) belong to a family of transcription factors of which three isotypes, PPARα, PPARδ (β) and PPARγ, are known. These play a central role in regulating intermediate metabolism and in incidences of inflammation. In recent years, a greater understanding of their mechanisms of action and their effects, principally in the management of cardiovascular disease, has been achieved. PPAR agonists, catalysts and agents have been used since the 1990s, when it was confirmed that fibrates possess lipid modifying properties when selectively activating PPARα. In addition, thiazolidinediones, structures analogous to fibrates, showed PPARγ activity with an insulin-sensitizing effect, leading to their use in the control and even prevention of diabetes mellitus type 2. Currently, studies are oriented to the development of agents that activate multiple PPAR isoforms - not only dual (PPARα/γ), but also PPAR panagonists (α/γ/δ). The purpose of this review is to explain the mechanisms of the molecular action and the effects of PPAR agonists, and also to analyze existing and current studies concerning their use in cardiovascular and metabolic illnesses.

EVALUATION OF THE ANTI-ISCHEMIC EFFECT OF THE PPARy AGONIST, (ROSIGLITAZONE) IN PERMANENT FOCAL CEREBRAL ISCHEMIA IN DIABETIC RATS.

Diabetes mellitus (DM) is a clear risk factor for stroke. Furthermore, di­abetes has been shown to be a strong determinant for the presence of multiple lacunar infarcts in stroke patients. There has been a recent ap­preciation that peroxisome prolifera-tor-activated receptors (PPARs) and their ligands may play an important role in the brain. An increasing num­ber of studies have reported on the effects of PPAR agonists in animal models of neurological damage and disease, including the excitatory dam­age that occurs in stroke. The PPARy agonist, rosiglitazone, a synthetic li-gand of the thiazolidinedione class was currently used as an antidiabetic agent because of its insulin- sensitizing effect. So, the purpose of this study was to determine whether rosigiitazone may be neuroprotective in a model of permanent focal cerer-bral ischemia in diabetic rats. Meth­ods: This study was carried on 96 al­bino rats. Rats were divided into 8 equal groups: Group (1): Control group, Group (2): Diabetic control group, Group (3): Non-treated is-chemic group, Group (4): Diabetic and non-treated sham operated group, Group (5): Diabetic and non-treated permanent left middle cere­bral artery occlusion group, Group (6): Treated ischemic group, Group (7): Diabetic and treated sham oper­ated group, Group (8): Diabetic and treated permanent middle cerebral ar­tery occlusion group.

PPAR agonists modulate human osteoclast formation and activity in vitro

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear steroid hormone superfamily and exist in three isoforms: PPARα, β and γ, each with specific functions. In this study, we have investigated the expression of PPARs by human osteoclast precursors and osteoclasts generated in vitro. In addition, the effects of fibrates and isoform-specific PPAR agonists on osteoclast formation and resorption in vitro were determined. Human peripheral blood mononuclear cells (PBMCs) were stimulated with human recombinant RANKL and M-CSF to generate osteoclasts. RNA was extracted at days 0, 7, 14 and 21 and RT-PCR for all three PPAR isoforms demonstrated their expression throughout this culture period. To determine the effect on osteoclast formation, PPAR agonists (10 − 8 M to 10 − 5 M) were added from the beginning of the culture until day 14 and the number of multinucleated osteoclasts counted. The effect of PPAR agonists on osteoclast function was similarly determined by treating mature, multinucleated osteoclasts cultured on dentine wafers with PPAR agonists (10 − 8 M to 10 − 5 M) for 7 days and quantifying resorption. Bezafibrate and fenofibrate, which non-discriminately activate all PPAR isoforms, significantly inhibited the formation of multinucleated osteoclasts from PBMC in vitro. Bezafibrate treatment of mature osteoclast resulted in 50% inhibition (at 10 − 8 M and 10 − 7 M) of resorption, yet fenofibrate had no significant effect. Activation of individual PPARs with isoform-specific agonist (GW9578, L165041 and ciglitizone which preferentially activate PPARα, β and γ respectively) resulted in significant dose-dependent inhibition of multinucleated osteoclast formation. Divergent effects on osteoclast resorption were observed; GW9578 had no significant effect on resorption, whereas ciglitizone and L165041 dose-dependently inhibited and stimulated resorption, respectively. These data show for the first time expression of all three PPAR isoforms throughout the development and maturation period of osteoclasts generated from human PBMCs. In addition, we demonstrate that isoform-specific PPAR agonists have strong effects on multinucleation and highly variable effects on bone resorption. In conclusion, this study highlights the potential of PPARs as therapeutic targets in diseases with accelerated osteoclast formation and resorption.

Therapeutical effects of PPAR agonists assessed by biomarker modulation

The metabolic syndrome is defined as the clustering of cardiovascular risk factors, such as glucose intolerance, hyperinsulinemia, dyslipidemia, coagulation disturbances and hypertension. Activators of the nuclear receptors peroxisome proliferator-activated receptors (PPARs) modulate several of the metabolic risk factors pre-disposing to atherosclerosis. Fibrates are hypolipidemic drugs operating through activation of PPARα, whereas glitazones are insulin sensitizers activating PPARγ. In addition, these drugs exert pleiotropic and anti-inflammatory actions. This review will focus on the different effects of fibrates and glitazones, as measured by biomarker modulation, on the development of atherosclerosis and cardiovascular disease.

Differential effects of peroxisome proliferator activated receptor-γ (PPARγ) ligands in proximal tubular cells: Thiazolidinediones are partial PPARγ agonists

Background. Peroxisome proliferator activated receptors (PPARs) are ligand-activated transcription factors with multiple effects on target cell function. PPAR gamma activity is regulated by extracellular signal-regulated protein kinase (ERK), mitogen-activated protein (MAP) kinase, and PPAR gamma ligands have varying effects on activity of ERK. Different PPAR gamma ligands have been shown to have both protective and detrimental effects in the kidney. Since transcriptional activation by different PPAR agonists is ligand- and depot-specific PPAR gamma, we have examined the effects of different agonists on PPAR activity in the proximal tubule. Opossum kidney cells were used in all experiments, transiently transfected with a PPAR response element luciferase reporter and subject to stimulation with various PPAR ligands. The role of ERK and phosphorylation in PPAR gamma activation were studied, as were the effects of PPAR agonists on ERK activation and cell proliferation. Transcriptional activity of PPAR was not stimulated by PPAR alpha agonists, and only very modestly stimulated by a PPAR beta agonist. The PPAR gamma agonists 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), ciglitazone, and troglitazone stimulated significant transcriptional activation and phosphorylation of PPAR gamma. These effects were more marked with 15d-PGJ(2). Thiazolidinediones attenuated 15d-PGJ(2) evoked PPAR gamma activation and phosphorylation. ERK activity positively regulated PPAR activation. Only 15d-PGJ(2) stimulated ERK activity and cell proliferation, and these effects were also inhibited by thiazolidinediones. PPAR gamma agonists exert differential effects in proximal tubule cells with thiazolidinediones behaving as partial agonists.

Combination therapy with PPARγ and PPARα agonists increases glucose-stimulated insulin secretion in db/dbmice

Although peroxisome proliferator-activated receptor (PPAR)gamma agonists ameliorate insulin resistance, they sometimes cause body weight gain, and the effect of PPAR agonists on insulin secretion is unclear. We evaluated the effects of combination therapy with a PPARgamma agonist, pioglitazone, and a PPARalpha agonist, bezafibrate, and a dual agonist, KRP-297, for 4 wk in male C57BL/6J mice and db/db mice, and we investigated glucose-stimulated insulin secretion (GSIS) by in situ pancreatic perfusion. Body weight gain in db/db mice was less with KRP-297 treatment than with pioglitazone or pioglitazone + bezafibrate treatment. Plasma glucose, insulin, triglyceride, and nonesterified fatty acid levels were elevated in untreated db/db mice compared with untreated C57BL/6J mice, and these parameters were significantly ameliorated in the PPARgamma agonist-treated groups. Also, PPARgamma agonists ameliorated the diminished GSIS and insulin content, and they preserved insulin and GLUT2 staining in db/db mice. GSIS was further increased by PPARgamma and -alpha agonists. We conclude that combination therapy with PPARgamma and PPARalpha agonists may be more useful with respect to body weight and pancreatic GSIS in type 2 diabetes with obesity.