Inhibition of smooth muscle proliferation by urea-based alkanoic acids via peroxisome proliferator-activated receptor alpha-dependent repression of cyclin D1

An insight to treat cardiovascular diseases through phytochemicals targeting PPAR-α

Peroxisome proliferator-activated receptor-α (PPAR-α) belonging to the nuclear hormone receptor superfamily is a promising target for CVDs which mechanistically improves the production of high-density lipid as well as inhibit vascular smooth muscle cell proliferation. PPAR-α mainly interferes with adenosine monophosphate-activated protein kinase, transforming growth factor-β-activated kinase, and nuclear factor-κB pathways to protect against cardiac complications. Natural products/extracts could serve as a potential therapeutic strategy in CVDs for targeting PPAR-α with broad safety margins. In recent years, the understanding of naturally derived PPAR-α agonists has considerably improved; however, the information is scattered. In vitro and in vivo studies on acacetin, apigenin, arjunolic acid, astaxanthin, berberine, resveratrol, vaticanol C, hispidulin, ginsenoside Rb3, and genistein showed significant effects in CVDs complications by targeting PPAR-α. With the aim of demonstrating the tremendous chemical variety of natural products targeting PPAR-α in CVDs, this review provides insight into various natural products that can work to prevent CVDs by targeting the PPAR-α receptor along with their detailed mechanism.

Molecular mechanisms and therapeutic perspectives of peroxisome proliferator-activated receptor α agonists in cardiovascular health and disease

The prevalence of cardiovascular disease (CVD) has been rising due to sedentary lifestyles and unhealthy dietary patterns. Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor regulating multiple biological processes, such as lipid metabolism and inflammatory response critical to cardiovascular homeostasis. Healthy endothelial cells (ECs) lining the lumen of blood vessels maintains vascular homeostasis, where endothelial dysfunction associated with increased oxidative stress and inflammation triggers the pathogenesis of CVD. PPARα activation decreases endothelial inflammation and senescence, contributing to improved vascular function and reduced risk of atherosclerosis. Phenotypic switch and inflammation of vascular smooth muscle cells (VSMCs) exacerbate vascular dysfunction and atherogenesis, in which PPARα activation improves VSMC homeostasis. Different immune cells participate in the progression of vascular inflammation and atherosclerosis. PPARα in immune cells plays a critical role in immunological events, such as monocyte/macrophage adhesion and infiltration, macrophage polarization, dendritic cell (DC) embedment, T cell activation, and B cell differentiation. Cardiomyocyte dysfunction, a major risk factor for heart failure, can also be alleviated by PPARα activation through maintaining cardiac mitochondrial stability and inhibiting cardiac lipid accumulation, oxidative stress, inflammation, and fibrosis. This review discusses the current understanding and future perspectives on the role of PPARα in the regulation of the cardiovascular system as well as the clinical application of PPARα ligands.

Soluble Epoxide Hydrolase as an Important Player in Intestinal Cell Differentiation

There is growing evidence that soluble epoxide hydrolase (sEH) may play a role in cell differentiation. sEH metabolizes biologically highly active and generally cytoprotective epoxyeicosatrienoic acids (EETs), generated from arachidonic acid metabolism by CYP epoxygenases (CYP2C and CYP2J subfamilies), to less active corresponding diols. We investigated the effect of sEH inhibitor (TPPU) on the expression of villin, CYP2C8, CYP2C9, CYP2J2, and sEH in undifferentiated and in vitro differentiated HT-29 and Caco2 cell lines. The administration of 10 μM TPPU on differentiated HT-29 and Caco2 cells resulted in a significant decrease in expression of villin, a marker for intestinal cell differentiation. It was accompanied by a disruption of the brush border when microvilli appeared sparse and short in atomic force microscope scans of HT-29 cells. Although inhibition of sEH in differentiated HT-29 and Caco2 cells led to an increase in sEH expression in both cell lines, this treatment had an opposite effect on CYP2J2 expression in HT-29 and Caco2 cells. In addition, tissue samples of colorectal carcinoma and adjacent normal tissues from 45 patients were immunostained for sEH and villin. We detected a significant decrease in the expression of both proteins in colorectal carcinoma in comparison to adjacent normal tissue, and the decrease in both sEH and villin expression revealed a moderate positive association. Taken together, our results showed that sEH is an important player in intestinal cell differentiation.

Differential Effects of sEH Inhibitors on the Proliferation and Migration of Vascular Smooth Muscle Cells

Epoxyeicosatrienoic acid (EET) is a cardioprotective metabolite of arachidonic acid. It is known that soluble epoxide hydrolase (sEH) is involved in the metabolic degradation of EET. The abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) play important roles in the pathogenesis of atherosclerosis and restenosis. Thus, the present study investigated the effects of the sEH inhibitor 12-(((tricyclo(3.3.1.13,7)dec-1-ylamino)carbonyl)amino)-dodecanoic acid (AUDA) on platelet-derived growth factor (PDGF)-induced proliferation and migration in rat VSMCs. AUDA significantly inhibited PDGF-induced rat VSMC proliferation, which coincided with Pin1 suppression and heme oxygenase-1 (HO-1) upregulation. However, exogenous 8,9-EET, 11,12-EET, and 14,15-EET treatments did not alter Pin1 or HO-1 levels and had little effect on the proliferation of rat VSMCs. On the other hand, AUDA enhanced the PDGF-stimulated cell migration of rat VSMCs. Furthermore, AUDA-induced activation of cyclooxygenase-2 (COX-2) and subsequent thromboxane A2 (TXA₂) production were required for the enhanced migration. Additionally, EETs increased COX-2 expression but inhibited the migration of rat VSMCs. In conclusion, the present study showed that AUDA exerted differential effects on the proliferation and migration of PDGF-stimulated rat VSMCs and that these results may not depend on EET stabilization.

Aberrant soluble epoxide hydrolase and oxylipin levels in a porcine arteriovenous graft stenosis model

Synthetic arteriovenous grafts (AVGs) used for hemodialysis frequently fail due to the development of neointimal hyperplasia (NH) at the vein-graft anastomosis. Inflammation and smooth-muscle cell (SMC) and myofibroblast proliferation and migration likely play an important role in the pathogenesis of NH. Epoxyeicosatrienoic acids (EETs), the products of the catabolism of arachidonic acid by cytochrome P450 enzymes, possess anti-inflammatory, antiproliferative, antimigratory and vasodilatory properties that should reduce NH. The degradation of vasculoprotective EETs is catalyzed by the enzyme, soluble epoxide hydrolase (sEH). sEH upregulation may thus contribute to NH development by the enhanced removal of vasculoprotective EETs. In this study, sEH, cytochrome P450 and EETs were examined after AVG placement in a porcine model to explore their potential roles in AVG stenosis. Increased sEH protein expression, decreased P450 epoxygenase activity and dysregulation of 5 oxylipin mediators were observed in the graft-venous anastomotic tissues when compared to control veins. Pharmacological inhibitors of sEH decreased the growth factor-induced migration of SMCs and fibroblasts, although they had no significant effect on the proliferation of these cells. These results provide insights on epoxide biology in vascular disorders and a rationale for the development of novel pharmacotherapeutic strategies to prevent AVG failure due to NH and stenosis.

Quercetin prevents liver carcinogenesis by inducing cell cycle arrest, decreasing cell proliferation and enhancing apoptosis

SCOPE

Quercetin is the most abundant flavonoid in human diet. It has special interest as it holds anticancerous properties. This study aims to clarify the mechanisms involved in quercetin effects during the occurrence of preneoplastic lesions in rat liver.

METHODS AND RESULTS

Adult male Wistar rats were subjected to a two-phase model of hepatocarcinogenesis (initiated-promoted group). Initiated-promoted animals also received quercetin 10 and 20 mg/kg body weight (IPQ10 and IPQ20 groups, respectively). Antioxidant defenses were modified by quercetin administration at both doses. However, only IPQ20 group showed a reduction in number and volume of preneoplastic lesions. This group showed increased apoptosis and a reduction in the proliferative index. In addition, IPQ20 group displayed a reduction of cell percentages in G₁ and S phases, accumulation in G₂, and decrease in M phase, with reduced expression of cyclin D1, cyclin A, cyclin B, and cyclin-dependent kinase 1. Interestingly, peroxisome proliferator activated receptor-α levels were reduced in IPQ20 group.

CONCLUSION

The outcomes of this study represent a significant contribution to the current understanding on the preventive mechanisms of quercetin during the early stages of liver cancer development, demonstrating that in addition to its known proapoptotic characteristics, the flavonoid modulates the expression of critical cell cycle regulators and peroxisome proliferator activated receptor-α activity.

Epoxides and soluble epoxide hydrolase in cardiovascular physiology

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites that importantly contribute to vascular and cardiac physiology. The contribution of EETs to vascular and cardiac function is further influenced by soluble epoxide hydrolase (sEH) that degrades EETs to diols. Vascular actions of EETs include dilation and angiogenesis. EETs also decrease inflammation and platelet aggregation and in general act to maintain vascular homeostasis. Myocyte contraction and increased coronary blood flow are the two primary EET actions in the heart. EET cell signaling mechanisms are tissue and organ specific and provide significant evidence for the existence of EET receptors. Additionally, pharmacological and genetic manipulations of EETs and sEH have demonstrated a contribution for this metabolic pathway to cardiovascular diseases. Given the impact of EETs to cardiovascular physiology, there is emerging evidence that development of EET-based therapeutics will be beneficial for cardiovascular diseases.

Reno-protective mechanisms of epoxyeicosatrienoic acids in cardiovascular disease

Cardiovascular disease (CVD) is the leading cause of mortality worldwide, and it is well known that end-stage renal disease (ESRD) is a profound consequence of the progression of CVD. Present treatments only slow CVD progression to ESRD, and it is imperative that new therapeutic strategies are developed to prevent the incidence of ESRD. Because epoxyeicosatrienoic acids (EETs) have been shown to elicit reno-protective effects in hypertensive animal models, the current review will focus on addressing the reno-protective mechanisms of EETs in CVD. The cytochrome P-450 epoxygenase catalyzes the oxidation of arachidonic acid to EETs. EETs have been identified as endothelium-derived hyperpolarizing factors (EDHFs) with vasodilatory, anti-inflammatory, antihypertensive, and antiplatelet aggregation properties. EETs also have profound effects on vascular migration and proliferation and promote angiogenesis. The progression of CVD has been linked to decreased EETs levels, leading to the concept that EETs should be therapeutically targeted to prevent end-organ damage associated with CVD. However, EETs are quickly degraded by the enzyme soluble epoxide hydrolase (sEH) to their less active diols, dihydroxyeicosatrienoic acids (DHETs). As such, one way to increase EETs level is to inhibit their degradation to DHETs by using sEH inhibitors. Inhibition of sEH has been shown to effectively reduce blood pressure and organ damage in experimental models of CVD. Another approach to target EETs is to develop EET analogs with improved solubility and resistance to auto-oxidation and metabolism by sEH. For example, stable ether EET analogs dilate afferent arterioles and lower blood pressure in hypertensive rodent animal models. EET agonists also improve insulin signaling and vascular function in animal models of metabolic syndrome.

The PPAR-RXR Transcriptional Complex in the Vasculature

The peroxisome proliferator-activated receptors (PPARs) and the retinoid X receptors (RXRs) are ligand-activated transcription factors that coordinately regulate gene expression. This PPAR-RXR transcriptional complex plays a critical role in energy balance, including triglyceride metabolism, fatty acid handling and storage, and glucose homeostasis: processes whose dysregulation characterize obesity, diabetes, and atherosclerosis. PPARs and RXRs are also involved directly in inflammatory and vascular responses in endothelial and vascular smooth muscle cells. New insights into fundamental aspects of PPAR and RXR biology, and their actions in the vasculature, continue to appear. Although RXRs are obligate heterodimeric partners for PPAR action, the part that RXRs, and their endogenous retinoid mediators, exert in the vessel wall is less well understood. Biological insights into PPAR-RXRs may help inform interpretation of clinical trials with synthetic PPAR agonists and prospects for future PPAR therapeutics. Importantly, the extensive data establishing a key role for PPARs and RXRs in energy balance, inflammation, and vascular biology stands separately from the clinical experience with any given synthetic PPAR agonist. Both the basic science data and the clinical experience with PPAR agonists identify the need to better understand these important transcriptional regulators.

Cytochrome P450 eicosanoids and cerebral vascular function

The eicosanoids 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs), which are generated from the metabolism of arachidonic acid by cytochrome P450 (CYP) enzymes, possess a wide array of biological actions, including the regulation of blood flow to organs. 20-HETE and EETs are generated in various cell types in the brain and cerebral blood vessels, and contribute significantly to cerebral blood flow autoregulation and the coupling of regional brain blood flow to neuronal activity (neurovascular coupling). Investigations are beginning to unravel the molecular and cellular mechanisms by which these CYP eicosanoids regulate cerebral vascular function and the changes that occur in pathological states. Intriguingly, 20-HETE and the soluble epoxide hydrolase (sEH) enzyme that regulates EET levels have been explored as molecular therapeutic targets for cerebral vascular diseases. Inhibition of 20-HETE, or increasing EET levels by inhibiting the sEH enzyme, decreases cerebral damage following stroke. The improved outcome following cerebral ischaemia is a consequence of improving cerebral vascular structure or function and protecting neurons from cell death. Thus, the CYP eicosanoids are key regulators of cerebral vascular function and novel therapeutic targets for cardiovascular diseases and neurological disorders.

Soluble epoxide hydrolase inhibition modulates vascular remodeling

The soluble epoxide hydrolase enzyme (SEH) and vascular remodeling are associated with cardiovascular disease. Although inhibition of SEH prevents smooth muscle cell proliferation in vitro, the effects of SEH inhibition on vascular remodeling in vivo and mechanisms of these effects remain unclear. Herein we determined the effects of SEH antagonism in an endothelium intact model of vascular remodeling induced by flow reduction and an endothelium denuded model of vascular injury. We demonstrated that chronic treatment of spontaneously hypertensive stroke-prone rats with 12-(3-adamantan-1-yl-ureido) dodecanoic acid, an inhibitor of SEH, improved the increment of inward remodeling induced by common carotid ligation to a level that was comparable with normotensive Wistar Kyoto rats. Similarly, mice with deletion of the gene responsible for the production of the SEH enzyme (Ephx2(-/-)) demonstrated enhanced inward vascular remodeling induced by carotid ligation. However, the hyperplastic response induced by vascular injury that denudes the endothelium was unabated by SEH inhibition or Ephx2 gene deletion. These results suggest that SEH inhibition or Ephx2 gene deletion antagonizes neointimal formation in vivo by mechanisms that are endothelium dependent. Thus SEH inhibition may have therapeutic potential for flow-induced remodeling and neointimal formation.

Inhibition of soluble epoxide hydrolase enhances the anti-inflammatory effects of aspirin and 5-lipoxygenase activation protein inhibitor in a murine model

Inflammation is a multi-staged process whose expansive phase is thought to be driven by acutely released arachidonic acid (AA) and its metabolites. Inhibition of cyclooxygenase (COX), lipoxygenase (LOX), or soluble epoxide hydrolase (sEH) is known to be anti-inflammatory. Inhibition of sEH stabilizes the cytochrome P450 (CYP450) products epoxyeicosatrienoic acids (EETs). Here we used a non-selective COX inhibitor aspirin, a 5-lipoxygenase activation protein (FLAP) inhibitor MK886, and a sEH inhibitor t-AUCB to selectively modulate the branches of AA metabolism in a lipopolysaccharide (LPS)-challenged murine model. We used metabolomic profiling to simultaneously monitor representative AA metabolites of each branch. In addition to the significant crosstalk among branches of the AA cascade during selective modulation of COX, LOX, or sEH, we demonstrated that co-administration of t-AUCB enhanced the anti-inflammatory effects of aspirin or MK886, which was evidenced by the observations that co-administration resulted in favorable eicosanoid profiles and better control of LPS-mediated hypotension as well as hepatic protein expression of COX-2 and 5-LOX. Targeted disruption of the sEH gene displayed a parallel profile to that produced by t-AUCB. These observations demonstrate a significant level of crosstalk among the three major branches of the AA cascade and that they are not simply parallel pathways. These data illustrate that inhibition of sEH by both pharmacological intervention and gene knockout enhances the anti-inflammatory effects of aspirin and MK886, suggesting the possibility of modulating multiple branches to achieve better therapeutic effects.

PPARs and the cardiovascular system

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone-receptor superfamily. Originally cloned in 1990, PPARs were found to be mediators of pharmacologic agents that induce hepatocyte peroxisome proliferation. PPARs also are expressed in cells of the cardiovascular system. PPAR gamma appears to be highly expressed during atherosclerotic lesion formation, suggesting that increased PPAR gamma expression may be a vascular compensatory response. Also, ligand-activated PPAR gamma decreases the inflammatory response in cardiovascular cells, particularly in endothelial cells. PPAR alpha, similar to PPAR gamma, also has pleiotropic effects in the cardiovascular system, including antiinflammatory and antiatherosclerotic properties. PPAR alpha activation inhibits vascular smooth muscle proinflammatory responses, attenuating the development of atherosclerosis. However, PPAR delta overexpression may lead to elevated macrophage inflammation and atherosclerosis. Conversely, PPAR delta ligands are shown to attenuate the pathogenesis of atherosclerosis by improving endothelial cell proliferation and survival while decreasing endothelial cell inflammation and vascular smooth muscle cell proliferation. Furthermore, the administration of PPAR ligands in the form of TZDs and fibrates has been disappointing in terms of markedly reducing cardiovascular events in the clinical setting. Therefore, a better understanding of PPAR-dependent and -independent signaling will provide the foundation for future research on the role of PPARs in human cardiovascular biology.

Soluble epoxide inhibition is protective against cerebral ischemia via vascular and neural protection

Inhibition of soluble epoxide hydrolase (SEH), the enzyme responsible for degradation of vasoactive epoxides, protects against cerebral ischemia in rats. However, the molecular and biological mechanisms that confer protection in normotension and hypertension remain unclear. Here we show that 6 weeks of SEH inhibition via 2 mg/day of 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) in spontaneously hypertensive stroke-prone (SHRSP) rats protects against cerebral ischemia induced by middle cerebral artery occlusion, reducing percent hemispheric infarct and neurodeficit score without decreasing blood pressure. This level of cerebral protection was similar to that of the angiotensin-converting enzyme inhibitor, enalapril, which significantly lowered blood pressure. SEH inhibition is also protective in normotensive Wistar-Kyoto (WKY) rats, reducing both hemispheric infarct and neurodeficit score. In SHRSP rats, SEH inhibition reduced wall-to-lumen ratio and collagen deposition and increased cerebral microvessel density, although AUDA did not alter middle cerebral artery structure or microvessel density in WKY rats. An apoptosis mRNA expression microarray of brain tissues from AUDA-treated rats revealed that AUDA modulates gene expression of mediators involved in the regulation of apoptosis in neural tissues of both WKY and SHRSP rats. Hence, we conclude that chronic SEH inhibition protects against cerebral ischemia via vascular protection in SHRSP rats and neural protection in both the SHRSP and WKY rats, indicating that SEH inhibition has broad pharmacological potential for treating ischemic stroke.

Pharmacokinetic optimization of four soluble epoxide hydrolase inhibitors for use in a murine model of inflammation

BACKGROUND AND PURPOSE

Early soluble epoxide hydrolase inhibitors (sEHIs) such as 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA) are effective anti-hypertensive and anti-inflammatory agents in various animal models. However, their poor metabolic stability and limited water solubility make them difficult to use pharmacologically. Here we present the evaluation of four sEHIs for improved pharmacokinetic properties and the anti-inflammatory effects of one sEHI.

EXPERIMENTAL APPROACH

The pharmacokinetic profiles of inhibitors were determined following p.o. (oral) administration and serial bleeding in mice. Subsequently the pharmacokinetics of trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB), the most promising inhibitor, was further studied following s.c. (subcutaneous), i.v. (intravenous) injections and administration in drinking water. Finally, the anti-inflammatory effect of t-AUCB was evaluated by using a lipopolysaccharide (LPS)-treated murine model.

KEY RESULTS

Better pharmacokinetic parameters (higher C(max), longer t(1/2) and greater AUC) were obtained from the tested inhibitors, compared with AUDA. Oral bioavailability of t-AUCB (0.1 mg.kg(-1)) was 68 +/- 22% (n = 4), and giving t-AUCB in drinking water is recommended as a feasible, effective and easy route of administration for chronic studies. Finally, t-AUCB (p.o.) reversed the decrease in plasma ratio of lipid epoxides to corresponding diols (a biomarker of soluble epoxide hydrolase inhibition) in lipopolysaccharide-treated mice. The in vivo potency of 1 mg.kg(-1) of t-AUCB (p.o.) was better in this inflammatory model than that of 10 mg.kg(-1) of AUDA-butyl ester (p.o) at 6 h after treatment.

CONCLUSIONS AND IMPLICATIONS

t-AUCB is a potent sEHI with improved pharmacokinetic properties. This compound will be a useful tool for pharmacological research and a promising starting point for drug development.

Arachidonic acid cytochrome P450 epoxygenase pathway

Cytochrome P450 (CYP) epoxygenases convert arachidonic acid to four epoxyeicosatrienoic acid (EET) regioisomers, 5,6-, 8,9-, 11,12-, and 14,15-EET, that function as autacrine and paracrine mediators. EETs produce vascular relaxation by activating smooth muscle large-conductance Ca2+-activated K+ channels (BKCa). In addition, they have anti-inflammatory effects on blood vessels and in the kidney, promote angiogenesis, and protect ischemic myocardium and brain. CYP epoxygenases also convert eicosapentaenoic acid to vasoactive epoxy-derivatives, and endocannabinoids containing 11,12- and 14,15-EET are formed. Many EET actions appear to be initiated by EET binding to a membrane receptor that activates ion channels and intracellular signal transduction pathways. However, EETs also are taken up by cells, are incorporated into phospholipids, and bind to cytosolic proteins and nuclear receptors, suggesting that some functions may occur through direct interaction of the EET with intracellular effector systems. Soluble epoxide hydrolase (sEH) converts EETs to dihydroxyeicosatrienoic acids (DHETs). Because this attenuates many of the functional effects of EETs, sEH inhibition is being evaluated as a mechanism for increasing and prolonging the beneficial actions of EETs.

PPAR-alpha agonist fenofibrate induces renal CYP enzymes and reduces blood pressure and glomerular hypertrophy in Zucker diabetic fatty rats

We have previously shown that fenofibrate, a peroxisome proliferator-activated receptor-alpha activator, increases renal cytochrome P450 (CYP)-derived eicosanoids and improves endothelial function in pre-diabetic obese rats. The present study was designed to explore the efficacy of fenofibrate on blood pressure and renal injury in the advanced stage of type-2 diabetes. 26-week-old male Zucker diabetic fatty rats (ZDF) were fed fenofibrate (100 mg/kg/day) for 6 weeks. Chronic treatment with fenofibrate normalized systolic blood pressure and reduced glomerular size by 19% in diabetic rats. Western blot and fluorescent immunostaining revealed that the over-expression of collagen type IV and alpha-smooth muscle actin was significantly attenuated in the kidney of fenofibrate-treated ZDF (F-ZDF) rats. In addition, fenofibrate administration dramatically decreased the cyclin D1 protein level in the kidney of diabetic rats. In contrast, renal CYP2C23 and CYP4A proteins were significantly increased in F-ZDF rats. These fenofibrate effects were observed in the absence of significant changes in glucose, insulin or lipid levels. Taken together, our results demonstrate that fenofibrate may lower blood pressure and attenuate glomerular hypertrophy and collagen accumulation through the downregulation of cyclin D1 and upregulation of CYP monooxygenases in the late stage of type-2 diabetes.

Cardiovascular Actions of the Peroxisome Proliferator-Activated Receptor-Alpha (PPAR?) 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.

Cytochrome P450 eicosanoids are activators of peroxisome proliferator-activated receptor alpha

Cytochrome P450 (P450) eicosanoids regulate vascular tone, renal tubular transport, cellular proliferation, and inflammation. Both the CYP4A omega-hydroxylases, which catalyze 20-hydroxyeicosatetraenoic acid (20-HETE) formation, and soluble epoxide hydrolase (sEH), which catalyzes epoxyeicosatrienoic acid (EET) degradation to the dihydroxyeicosatrienoic acids (DHETs), are induced upon activation of peroxisome proliferator-activated receptor alpha (PPARalpha) by fatty acids and fibrates. In contrast, the CYP2C epoxygenases, which are responsible for EET formation, are repressed after fibrate treatment. We show here that P450 eicosanoids can bind to and activate PPARalpha and result in the modulation of PPARalpha target gene expression. In transactivation assays, 14,15-DHET, 11,2-EET, and 20-HETE were potent activators of PPARalpha. Gel shift assays showed that EETs, DHETs, and 20-HETE induced PPARalpha-specific binding to its cognate response element. Expression of apolipoprotein A-I was decreased 70% by 20-HETE, whereas apolipoprotein A-II expression was increased up to 3-fold by 11,12-EET, 14,15-DHET, and 20-HETE. In addition, P450 eicosanoids induced CYP4A1, sEH, and CYP2C11 expression, suggesting that they can regulate their own levels. Given that P450 eicosanoids have multiple cardiovascular effects, pharmacological modulation of their formation and/or degradation may yield therapeutic benefits.