PPAR-alpha activator fenofibrate increases renal CYP-derived eicosanoid synthesis and improves endothelial dilator function in obese Zucker rats

Peroxisome proliferator-activated receptors, farnesoid X receptor, and dual modulating drugs in hypertension

Hypertension characterized by an elevated blood pressure is a cardiovascular disease that afflicts greater than one in every three adults worldwide. Nuclear receptors are large superfamily of DNA-binding transcription factors that target genes to regulate metabolic and cardiovascular function. Drugs have been developed for nuclear receptors such as peroxisome proliferator-activated receptors (PPARα and PPARγ) and farnesoid X receptor (FXR). PPARα, PPARγ, and FXR agonists are used clinically to treat lipid disorders and metabolic diseases. Evidence from clinical studies and animal hypertension models have demonstrated that PPARα, PPARγ, and FXR agonism can lower blood pressure and decrease end organ damage which could be useful for the treatment of hypertension in patients with metabolic diseases. Unfortunately, PPAR and FXR agonists have unwanted clinical side effects. There have been recent developments to limit side effects for PPAR and FXR agonists. Combining PPAR and FXR agonism with soluble epoxide hydrolase (sEH) inhibition or Takeda G protein receptor 5 (TGR5) agonism has been demonstrated in preclinical studies to have actions that would decrease clinical side effects. In addition, these dual modulating drugs have been demonstrated in preclinical studies to have blood pressure lowering, anti-fibrotic, and anti-inflammatory actions. There is now an opportunity to thoroughly test these novel dual modulators in animal models of hypertension associated with metabolic diseases. In particular, these newly developed dual modulating PPAR and FXR drugs could be beneficial for the treatment of metabolic diseases, organ fibrosis, and hypertension.

Effect of inflammation on cytochrome P450-mediated arachidonic acid metabolism and the consequences on cardiac hypertrophy

The incidence of heart failure (HF) is generally preceded by cardiac hypertrophy (CH), which is the enlargement of cardiac myocytes in response to stress. During CH, the metabolism of arachidonic acid (AA), which is present in the cell membrane phospholipids, is modulated. Metabolism of AA gives rise to hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs) via cytochrome P450 (CYP) ω-hydroxylases and CYP epoxygenases, respectively. A plethora of studies demonstrated the involvement of CYP-mediated AA metabolites in the pathogenesis of CH. Also, inflammation is known to be a characteristic hallmark of CH. In this review, our aim is to highlight the impact of inflammation on CYP-derived AA metabolites and CH. Inflammation is shown to modulate the expression of various CYP ω-hydroxylases and CYP epoxygenases and their respective metabolites in the heart. In general, HETEs such as 20-HETE and mid-chain HETEs are pro-inflammatory, while EETs are characterized by their anti-inflammatory and cardioprotective properties. Several mechanisms are implicated in inflammation-induced CH, including the modulation of NF-κB and MAPK. This review demonstrated the inflammatory modulation of cardiac CYPs and their metabolites in the context of CH and the anti-inflammatory strategies that can be employed in the treatment of CH and HF.

Differential contribution of renal cytochrome P450 enzymes to kidney endothelial dysfunction and vascular oxidative stress in obesity

Arachidonic acid (AA)-derived cytochrome P450 (CYP) derivatives, epoxyeicosatrienoic acids (EETs) and 20-hidroxyeicosatetranoic acid (20-HETE), play a key role in kidney tubular and vascular functions and blood pressure. Altered metabolism of CYP epoxygenases and CYP hydroxylases has differentially been involved in the pathogenesis of metabolic disease-associated vascular complications, although the mechanisms responsible for the vascular injury are unclear. The present study aimed to assess whether obesity-induced changes in CYP enzymes may contribute to oxidative stress and endothelial dysfunction in kidney preglomerular arteries. Endothelial function and reactive oxygen species (ROS) production were assessed in interlobar arteries of obese Zucker rats (OZR) and their lean counterparts lean Zucker rats (LZR) and the effects of CYP2C and CYP4A inhibitors sulfaphenazole and HET0016, respectively, were examined on the endothelium-dependent relaxations and O2- and H2O2 levels of preglomerular arteries. Non-nitric oxide (NO) non-prostanoid endothelium-derived hyperpolarization (EDH)-type responses were preserved but resistant to the CYP epoxygenase blocker sulfaphenazole in OZR in contrast to those in LZR. Sulfaphenazole did not further inhibit reduced arterial H2O2 levels, and CYP2C11/CYP2C23 enzymes were downregulated in intrarenal arteries from OZR. Renal EDH-mediated relaxations were preserved in obese rats by the enhanced activity and expression of endothelial calcium-activated potassium channels (KCa). CYP4A blockade restored impaired NO-mediated dilatation and inhibited augmented O2- production in kidney arteries from OZR. The current data demonstrate that both decreased endothelial CYP2C11/ CYP2C23-derived vasodilator H2O2 and augmented CYP4A-derived 20-HETE contribute to endothelial dysfunction and vascular oxidative stress in obesity. CYP4A inhibitors ameliorate arterial oxidative stress and restore endothelial function which suggests its therapeutic potential for the vascular complications of obesity-associated kidney injury.

Nuclear Receptors and Transcription Factors in Obesity-Related Kidney Disease

Both obesity and chronic kidney disease are increasingly common causes of morbidity and mortality worldwide. Although obesity often co-exists with diabetes and hypertension, it has become clear over the past several decades that obesity is an independent cause of chronic kidney disease, termed obesity-related glomerulopathy. This review defines the attributes of obesity-related glomerulopathy and describes potential pharmacologic interventions. Interventions discussed include peroxisome proliferator-activated receptors, the farnesoid X receptor, the Takeda G-protein-coupled receptor 5, and the vitamin D receptor.

Soluble epoxide hydrolase as a therapeutic target for obesity-induced disorders: roles of gut barrier function involved

Emerging research supports that soluble epoxide hydrolase (sEH), an enzyme involved in eicosanoid metabolism, could be a promising target for obesity-associated disorders. The sEH enzyme is overexpressed in many tissues of obese animals. Genetic ablation or pharmacological inhibition of sEH attenuates the development of a wide range of obesity-induced disorders, including endoplasmic reticulum stress, metabolic syndrome, kidney diseases, insulin resistance, fatty liver, hepatic steatosis, inflammation, and endothelial dysfunction. Furthermore, our recent research showed that genetic ablation or inhibition of sEH attenuated obesity-induced intestinal barrier dysfunction and its resulted bacterial translocation, which is widely regarded to be a central mechanism for the pathogenesis of various obesity-induced disorders. Together, these results support that targeting sEH could be a promising strategy to reduce risks of obesity-induced disorders, at least in part through blocking obesity-induced leaky gut syndrome.

Fenofibrate-induced renal dysfunction, yes or no?

In the treatment process of hypertriglyceridemia and diabetic nephropathy in type 2 diabetes, fenofibrate (FEN) is a well-known medication. FEN is from fibrate class drugs that using orally; however, as a side effect, it is associated with serum creatinine level increasing. The aim of this review was to determine the real effect of FEN therapy on renal functions based on both experimental and clinical studies. For this review, using the keywords of “fenofibrate” and “renal” and “function,” a variety of sources of information banks, including PubMed, Google Scholar, and Scopus, were used, and the published articles were considered and interpreted. Followed by searching in databases, 45 articles were collected. After screening these articles, based on the study source, they were devided into two parts: 23 articles on animal experiments and 22 articles clinical experiments. Based on this information, it seems that the protective mechanism of FEN is related to vascular endothelial functions. The increased creatinine by FEN is related to different sensitivities to FEN effects caused by a polymorphism in different patients. In patients with normal renal function, follow-up of serum creatinine would be necessary after FEN, but the discontinuation of FEN is not recommended. In addition, in diabetic patients with hypertriglyceridemia, FEN treatment would be suggested for protecting the kidney from diabetes-induced renal injury.

Effect of citral on mouse hepatic cytochrome P450 enzymes

CONTEXT

Citral is used as a potential natural treatment for various infectious diseases.

OBJECTIVE

To examine the effect of citral on the mRNA expression and activities of cytochrome P450 (CYP450) enzymes and establish the relationship between citral-induced liver injury and oxidative stress.

MATERIALS AND METHODS

ICR mice were randomly divided into citral (20, 200, and 2000 mg/kglow), Tween-80, and control groups (0.9% saline), 10 mice in each group. The citral-treated groups were intragastrically administered citral for 3 d, control groups treated with 0.5% Tween-80 and 0.9% saline in the same way. Liver injury and CYP450 enzymes were analyzed by analyzing the histopathological changes and the changes of related enzymes.

RESULTS

Citral treatment (2000 mg/kg) for 3 d increased serum glutamic pyruvic transaminase and glutamic oxaloacetic transaminase levels, as well as glutathione, gydroxyl radicals, malonaldehyde and total superoxide dismutase contents, but decreased the content of total antioxidant capacity. In doses of 20 and 200 mg/kg groups mice, the contents of NO were decreased significantly and other changes were similar to the 2000 mg/kg group mice, but the liver damage was most severe in the 2000 mg/kg group. Citral induced the mRNA expression and activities of CYP450 1A2, 2D22, and 2E1 in the liver of mice at doses of 20 and 200 mg/kg. There were no changes in testing indexes in Tween-80 treated group mice. Due to its toxic effects, the CYP induction effect of citral negatively correlated with its dose. Although the mRNA expression of CYP450 3A11 was induced by citral, its activity was not affected by low and moderate doses of citral. CYP450 3A11 activity was significantly decreased by high-dose citral.

CONCLUSIONS

Citral is hepatotoxic and induced oxidative stress in higher dose, which has a negative effect on CYP450 enzymes. These data suggest caution needs to be taken in order to avoid citral-drug interactions in human beings.

Altered Protein Expression of Cardiac CYP2J and Hepatic CYP2C, CYP4A, and CYP4F in a Mouse Model of Type II Diabetes-A Link in the Onset and Development of Cardiovascular Disease?

Arachidonic acid can be metabolized by cytochrome P450 (CYP450) enzymes in a tissue- and cell-specific manner to generate vasoactive products such as epoxyeicosatrienoic acids (EETs-cardioprotective) and hydroxyeicosatetraenoic acids (HETEs-cardiotoxic). Type II diabetes is a well-recognized risk factor for developing cardiovascular disease. A mouse model of Type II diabetes (C57BLKS/J-db/db) was used. After sacrifice, livers and hearts were collected, washed, and snap frozen. Total proteins were extracted. Western blots were performed to assess cardiac CYP2J and hepatic CYP2C, CYP4A, and CYP4F protein expression, respectively. Significant decreases in relative protein expression of cardiac CYP2J and hepatic CYP2C were observed in Type II diabetes animals compared to controls (CYP2J: 0.80 ± 0.03 vs. 1.05 ± 0.06, n = 20, p < 0.001); (CYP2C: 1.56 ± 0.17 vs. 2.21 ± 0.19, n = 19, p < 0.01). In contrast, significant increases in relative protein expression of both hepatic CYP4A and CYP4F were noted in Type II diabetes mice compared to controls (CYP4A: 1.06 ± 0.09 vs. 0.18 ± 0.01, n = 19, p < 0.001); (CYP4F: 2.53 ± 0.22 vs. 1.10 ± 0.07, n = 19, p < 0.001). These alterations induced by Type II diabetes in the endogenous pathway (CYP450) of arachidonic acid metabolism may increase the risk for cardiovascular disease by disrupting the fine equilibrium between cardioprotective (CYP2J/CYP2C-generated) and cardiotoxic (CYP4A/CYP4F-generated) metabolites of arachidonic acid.

Endothelial dysfunction in renal arcuate arteries of obese Zucker rats: The roles of nitric oxide, endothelium-derived hyperpolarizing factors, and calcium-activated K+ channels

The roles of nitric oxide (NO), endothelium-derived hyperpolarizing factors (EDHF), and calcium-activated K⁺ (K_Ca) channels in diabetes-associated endothelial dysfunction of small renal arteries are not clear. The present study investigated acetylcholine (ACh)-induced vasorelaxation of renal arcuate arteries from obese Zucker (OZ) rats at different diabetes durations, and the relative contribution of NO, EDHF, and K_Ca channels to the endothelial dysfunction. OZ rats of 7 weeks (prediabetic stage), 12 weeks (early diabetic stage), and 20 weeks (late diabetic stage), and time-matched lean control rats, were studied. Segments of arcuate arteries (130 to 180 μm) were isolated, cannulated and pressurized. Vascular endothelial functions were tested using ACh-induced vasodilation. Our experiments demonstrated: (1) ACh-elicited vasodilation was impaired in OZ rats of 20 weeks, but not in rats of 7 and 12 weeks; (2) inhibition of NO or EDHF (contributed by epoxyeicosatrienoic acids [EETs]) production significantly decreased ACh-induced vasodilation in both lean and OZ rats of 20 weeks. The reduction of ACh-induced vasodilation by inhibition of NO or EDHF formation was less in OZ rats, as compared to lean rats; and (3) inhibition of K_Ca channels markedly reduced ACh-induced vasodilation in lean control rats, but not in OZ rats of 20 weeks. Our observations indicated that endothelium-dependent vasodilation in renal arcuate arteries is impaired in diabetes mellitus; NO and EDHF, mainly EETs, dominate the ACh-induced vasodilation in renal arcuate arteries; the contribution of NO and EETs is impaired in diabetic rats; K_Ca channels are involved in ACh-induced vasodilation; and the activity of K_Ca channels is downregulated in diabetes mellitus.

PPARγ as a therapeutic target to rescue mitochondrial function in neurological disease

There is increasing evidence for the involvement of mitochondrial dysfunction and oxidative stress in the pathogenesis of many of the major neurodegenerative and neuroinflammatory diseases, suggesting that mitochondrial and antioxidant pathways may represent potential novel therapeutic targets. Recent years have seen a rapidly growing interest in the use of therapeutic strategies that can limit the defects in, or even to restore, mitochondrial function while reducing free radical generation. The peroxisome proliferation-activated receptor gamma (PPARγ), a ligand-activated transcription factor, has a wide spectrum of biological functions, regulating mitochondrial function, mitochondrial turnover, energy metabolism, antioxidant defence and redox balance, immune responses and fatty acid oxidation. In this review, we explore the evidence for potential beneficial effects of PPARγ agonists in a number of neurological disorders, including Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis and Huntington's disease, ischaemia, autoimmune encephalomyelitis and neuropathic pain. We discuss the mechanisms underlying those beneficial effects in particular in relation to mitochondrial function, antioxidant defence, cell death and inflammation, and suggest that the PPARγ agonists show significant promise as therapeutic agents in otherwise intractable neurological disease.

Palmitoylethanolamide treatment reduces blood pressure in spontaneously hypertensive rats: involvement of cytochrome p450-derived eicosanoids and renin angiotensin system

Palmitoylethanolamide (PEA), a peroxisome proliferator-activated receptor-α agonist, has been demonstrated to reduce blood pressure and kidney damage secondary to hypertension in spontaneously hypertensive rat (SHR). Currently, no information is available concerning the putative effect of PEA on modulating vascular tone. Here, we investigate the mechanisms underpinning PEA blood pressure lowering effect, exploring the contribution of epoxyeicosatrienoic acids, CYP-dependent arachidonic acid metabolites, as endothelium-derived hyperpolarizing factors (EDHF), and renin angiotensin system (RAS) modulation. To achieve this aim SHR and Wistar-Kyoto rats were treated with PEA (30 mg/kg/day) for five weeks. Functional evaluations on mesenteric bed were performed to analyze EDHF-mediated vasodilation. Moreover, mesenteric bed and carotid were harvested to measure CYP2C23 and CYP2J2, the key isoenzymes in the formation of epoxyeicosatrienoic acids, and the soluble epoxide hydrolase, which is responsible for their degradation in the corresponding diols. Effect of PEA on RAS modulation was investigated by analyzing angiotensin converting enzyme and angiotensin receptor 1 expression. Here, we showed that EDHF-mediated dilation in response to acetylcholine was increased in mesenteric beds of PEA-treated SHR. Western blot analysis revealed that the increase in CYP2C23 and CYP2J2 observed in SHR was significantly attenuated in mesenteric beds of PEA-treated SHR, but unchanged in the carotids. Interestingly, in both vascular tissues, PEA significantly decreased the soluble epoxide hydrolase protein level, accompanied by a reduced serum concentration of its metabolite 14-15 dihydroxyeicosatrienoic acid, implying a reduction in epoxyeicosatrienoic acid hydrolisis. Moreover, PEA treatment down-regulated angiotensin receptor 1 and angiotensin converting enzyme expression, indicating a reduction in angiotensin II-mediated effects. Consistently, a damping of the activation of angiotensin receptor 1 underlying pathways in mesenteric beds was shown in basal conditions in PEA-treated SHR. In conclusion, our data demonstrate the involvement of epoxyeicosatrienoic acids and renin angiotensin system in the blood pressure lowering effect of PEA.

CYP2J2 targeting to endothelial cells attenuates adiposity and vascular dysfunction in mice fed a high-fat diet by reprogramming adipocyte phenotype

Obesity is a global epidemic and a common risk factor for endothelial dysfunction and the subsequent development of diabetes mellitus and vascular diseases such as hypertension. Epoxyeicosatrienoic acids (EETs) are cytochrome P450 (CYP)-derived metabolites of arachidonic acid that contribute to vascular protection by stimulating vasodilation and inhibiting inflammation. Heme oxygenase-1 is a stress response protein that plays an important cytoprotective role against oxidative insult in diabetes mellitus and cardiovascular disease. We recently demonstrated interplay between EETs and heme oxygenase-1 in the attenuation of adipogenesis. We examined whether adipocyte dysfunction in mice fed a high-fat diet could be prevented by endothelial-specific targeting of the human CYP epoxygenase, CYP2J2. Tie2-CYP2J2 transgenic mice, fed a high-fat diet, had a reduction in body weight gain, blood glucose, insulin levels, and inflammatory markers. Tie2-CYP2J2 gene targeting restored HF-mediated decreases in vascular heme oxygenase-1, Cyp2C44, soluble epoxide hydrolase, phosphorylated endothelial nitric oxide synthase, phosphorylated protein kinase B, and phosphorylated adenosine monophosphate protein kinase protein expression, thus improving vascular function. These changes translated into decreased inflammation and oxidative stress within adipose tissue and decreased peroxisome proliferator-activated receptor-γ, CCAAT/enhancer binding protein alpha, mesoderm-specific transcript, and adipocyte 2 expression and increased uncoupling protein 1 and uncoupling protein 2 expression, reflecting the effect of vascular EET overproduction on adipogenesis. The current study documents a direct link between endothelial-specific EET production and adipogenesis, further implicating the EET-heme oxygenase-1 crosstalk as an important cytoprotective mechanism in the amelioration of vascular and adipocyte dysfunction resulting from diet-induced obesity.

Pharmacological manipulation of arachidonic acid-epoxygenase results in divergent effects on renal damage

Kidney damage is markedly accelerated by high-salt (HS) intake in stroke-prone spontaneously hypertensive rats (SHRSP). Epoxyeicosatrienoic acids (EETs) are epoxygenase products of arachidonic acid which possess vasodepressor, natriuretic, and anti-inflammatory activities. We examined whether up-regulation (clofibrate) or inhibition [N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH)] of epoxygenase would alter systolic blood pressure (SBP) and/or renal pathology in SHRSP on HS intake (1% NaCl drinking solution). Three weeks of treatment with clofibrate induced renal cortical protein expression of CYP2C23 and increased urinary excretion of EETs compared with vehicle-treated SHRSP. SBP and urinary protein excretion (UPE) were significantly lowered with clofibrate treatment. Kidneys from vehicle-treated SHRSP, which were on HS intake for 3 weeks, demonstrated focal lesions of vascular fibrinoid degeneration, which were markedly attenuated with clofibrate treatment. In contrast, 2 weeks of treatment with the selective epoxygenase inhibitor, MS-PPOH, increased UPE without significantly altering neither urinary EET levels nor SBP. Kidneys from vehicle-treated SHRSP, which were on HS intake for 11 days, demonstrated occasional mild damage whereas kidneys from MS-PPOH-treated rats exhibited widespread malignant nephrosclerosis. These results suggest that pharmacological manipulation of epoxygenase results in divergent effects on renal damage and that interventions to increase EET levels may provide therapeutic strategies for treating salt-sensitive hypertension and renal damage.

Mechanism of the sex difference in endothelial dysfunction after stroke

Stroke, the number four cause of death in the United States, is a greatly debilitating event resulting from insufficient blood supply to the brain (cerebral ischemia). Endothelial dysfunction, primarily characterized by dampened endothelial- dependent vasodilation, is a major contributor to the development and outcome of stroke. This review discusses the role of soluble epoxide hydrolase (sEH), an enzyme responsible for the degradation of vasoprotective eicosatrienoic acids (EETs), in the context of the cerebral vasculature and its contribution to the sexual dimorphic nature of stroke.

Role of cytochrome P450-mediated arachidonic acid metabolites in the pathogenesis of cardiac hypertrophy

A plethora of studies have demonstrated the expression of cytochrome P450 (CYP) and soluble epoxide hydrolase (sEH) enzymes in the heart and other cardiovascular tissues. In addition, the expression of these enzymes is altered during several cardiovascular diseases (CVDs), including cardiac hypertrophy (CH). The alteration in CYP and sEH expression results in derailed CYP-mediated arachidonic acid (AA) metabolism. In animal models of CH, it has been reported that there is an increase in 20-hydroxyeicosatetraenoic acid (20-HETE) and a decrease in epoxyeicosatrienoic acids (EETs). Further, inhibiting 20-HETE production by CYP ω-hydroxylase inhibitors and increasing EET stability by sEH inhibitors have been proven to protect against CH as well as other CVDs. Therefore, CYP-mediated AA metabolites 20-HETE and EETs are potential key players in the pathogenesis of CH. Some studies have investigated the molecular mechanisms by which these metabolites mediate their effects on cardiomyocytes and vasculature leading to pathological CH. Activation of several intracellular signaling cascades, such as nuclear factor of activated T cells, nuclear factor kappa B, mitogen-activated protein kinases, Rho-kinases, Gp130/signal transducer and activator of transcription, extracellular matrix degradation, apoptotic cascades, inflammatory cytokines, and oxidative stress, has been linked to the pathogenesis of CH. In this review, we discuss how 20-HETE and EETs can affect these signaling pathways to result in, or protect from, CH, respectively. However, further understanding of these metabolites and their effects on intracellular cascades will be required to assess their potential translation to therapeutic approaches for the prevention and/or treatment of CH and heart failure.

Interactions of PPAR-alpha and adenosine receptors in hypoxia-induced angiogenesis

Hypoxia and adenosine are known to upregulate angiogenesis; however, the role of peroxisome proliferator-activated receptor alpha (PPARα) in angiogenesis is controversial. Using transgenic Tg(fli-1:EGFP) zebrafish embryos, interactions of PPARα and adenosine receptors in angiogenesis were evaluated under hypoxic conditions. Epifluorescent microscopy was used to assess angiogenesis by counting the number of intersegmental (ISV) and dorsal longitudinal anastomotic vessel (DLAV) at 28 h post-fertilization (hpf). Hypoxia (6h) stimulated angiogenesis as the number of ISV and DLAV increased by 18-fold (p<0.01) and 100 ± 8% (p<0.001), respectively, at 28 hpf. Under normoxic and hypoxic conditions, WY-14643 (10 μM), a PPARα activator, stimulated angiogenesis at 28 hpf, while MK-886 (0.5 μM), an antagonist of PPARα, attenuated these effects. Compared to normoxic condition, adenosine receptor activation with NECA (10 μM) promoted angiogenesis more effectively under hypoxic conditions. Involvement of A2B receptor was implied in hypoxia-induced angiogenesis as MRS-1706 (10nM), a selective A2B antagonist attenuated NECA (10 μM)-induced angiogenesis. NECA- or WY-14643-induced angiogenesis was also inhibited by miconazole (0.1 μM), an inhibitor of epoxygenase dependent production of eicosatrienoic acid (EET) epoxide. Thus, we conclude that: activation of PPARα promoted angiogenesis just as activation of A2B receptors through an epoxide dependent mechanism.

Peroxisome Proliferator Activated Receptor-α Agonist Slows the Progression of Hypertension, Attenuates Plasma Interleukin-6 Levels and Renal Inflammatory Markers in Angiotensin II Infused Mice

The anti-inflammatory properties of PPAR-α plays an important role in attenuating hypertension. The current study determines the anti-hypertensive and anti-inflammatory role of PPAR-α agonist during a slow-pressor dose of Ang II (400 ng/kg/min). Ten to twelve week old male PPAR-α KO mice and their WT controls were implanted with telemetry devices and infused with Ang II for 12 days. On day 12 of Ang II infusion, MAP was elevated in PPAR-α KO mice compared to WT (161 ± 4 mmHg versus 145 ± 4 mmHg) and fenofibrate (145 mg/kg/day) reduced MAP in WT + Ang II mice (134 ± 7 mmHg). Plasma IL-6 levels were higher in PPAR-α KO mice on day 12 of Ang II infusion (30 ± 4 versus 8 ± 2 pg/mL) and fenofibrate reduced plasma IL-6 in Ang II-treated WT mice (10 ± 3 pg/mL). Fenofibrate increased renal expression of CYP4A, restored renal CYP2J expression, reduced the elevation in renal ICAM-1, MCP-1 and COX-2 in WT + Ang II mice. Our results demonstrate that activation of PPAR-α attenuates Ang II-induced hypertension through up-regulation of CYP4A and CYP2J and an attenuation of inflammatory markers such as plasma IL-6, renal MCP-1, renal expression of ICAM-1 and COX-2.

Acute arsenic toxicity alters cytochrome P450 and soluble epoxide hydrolase and their associated arachidonic acid metabolism in C57Bl/6 mouse heart

Acute arsenic (As(III)) exposure has been reported to cause cardiac toxicity, however this toxicity was never linked to the disturbance in cytochrome P450 (P450)-mediated arachidonic acid metabolism. Therefore, we investigated the effect of acute As(III) toxicity on the expression of P450 and soluble epoxide hydrolase (sEH) and their associated arachidonic acid metabolism in mice hearts. As(III) toxicity was induced by a single intraperitoneal injection of 12.5 mg/kg of As(III). Our results showed that As(III) treatment caused a significant induction of the cardiac hypertrophic markers in addition to Cyp1b1, Cyp2b, Cyp2c, Cyp4f, and sEH gene expression in mice hearts. Furthermore, As(III) increased sEH protein expression and activity in hearts with a consequent decrease in 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs) formation. Whereas the formation of 8,9-, 11,12-, 14,15-dihydroxyeicosatrienoic acids (DHETs) was significantly increased. As(III) also increased sEH mRNA and protein expression levels in addition to the hypertrophic markers which was reversed by knockdown of sEH in H9c2 cells. In conclusion, acute As(III) toxicity alters the expression of several P450s and sEH enzymes with a consequent decrease in the cardioprotective EETs which may represent a novel mechanism by which As(III) causes progressive cardiotoxicity. Furthermore, inhibiting sEH might represent a novel therapeutic approach to prevent As(III)-induced hypertrophy.

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.

Enalapril reverses high-fat diet-induced alterations in cytochrome P450-mediated eicosanoid metabolism

Metabolism of arachidonic acid by cytochrome P450 (CYP) to biologically active eicosanoids has been recognized increasingly as an integral mediator in the pathogenesis of cardiovascular and metabolic disease. CYP epoxygenase-derived epoxyeicosatrienoic and dihydroxyeicosatrienoic acids (EET + DHET) and CYP ω-hydroxylase-derived 20-hydroxyeicosatetraenoic acid (20-HETE) exhibit divergent effects in the regulation of vascular tone and inflammation; thus, alterations in the functional balance between these parallel pathways in liver and kidney may contribute to the pathogenesis and progression of metabolic syndrome. However, the impact of metabolic dysfunction on CYP-mediated formation of endogenous eicosanoids has not been well characterized. Therefore, we evaluated CYP epoxygenase (EET + DHET) and ω-hydroxylase (20-HETE) metabolic activity in liver and kidney in apoE(-/-) and wild-type mice fed a high-fat diet, which promoted weight gain and increased plasma insulin levels significantly. Hepatic CYP epoxygenase metabolic activity was significantly suppressed, whereas renal CYP ω-hydroxylase metabolic activity was induced significantly in high-fat diet-fed mice regardless of genotype, resulting in a significantly higher 20-HETE/EET + DHET formation rate ratio in both tissues. Treatment with enalapril, but not metformin or losartan, reversed the suppression of hepatic CYP epoxygenase metabolic activity and induction of renal CYP ω-hydroxylase metabolic activity, thereby restoring the functional balance between the pathways. Collectively, these findings suggest that the kinin-kallikrein system and angiotensin II type 2 receptor are key regulators of hepatic and renal CYP-mediated eicosanoid metabolism in the presence of metabolic syndrome. Future studies delineating the underlying mechanisms and evaluating the therapeutic potential of modulating CYP-derived EETs and 20-HETE in metabolic diseases are warranted.

Evaluation of the incidence and risk factors for development of fenofibrate-associated nephrotoxicity

BACKGROUND

Fenofibrate-associated nephrotoxicity has been described in two randomized controlled trials and several observational studies. However, little is known regarding its incidence and the population(s) at risk.

OBJECTIVE

This study aims to quantify the incidence and identify potential risk factors for development of nephrotoxicity in patients receiving fenofibrate.

METHODS

A retrospective, observational study was conducted in the South Texas Veterans Health Care System. Data were collected regarding baseline demographics, concurrent medical conditions, medications, laboratory results, and fenofibrate use.

RESULTS

Within 6 months after initiation of fenofibrate in 428 patients, 115 (27%) experienced an increase in serum creatinine of ≥ 0.3 mg/dL. Any renal disease (P = .001), chronic kidney disease (P = .01), and diabetes (P = .02) were significantly more prevalent in patients with fenofibrate-associated nephrotoxicity. Patients with nephrotoxicity had significantly greater serum creatinine (1.2 [SD 0.3] vs. 1.1 mg/dL [SD 0.3], P = .0002) and lower estimated glomerular filtration rate (72 [SD 20] vs 81 mL/min/1.73 m² [SD 20], P < .0001) at baseline. These patients also had greater use of calcium channel blockers (P = .0003), furosemide (P = .02), and angiotensin-converting enzyme inhibitors (P = .02). The incidence of nephrotoxicity was significantly greater in patients initiated on high-dose versus those on low-dose fenofibrate (P = .002). In a multivariable regression model, renal disease (P = .02), high-dose fenofibrate (P = .001), and dihydropyridine calcium channel blocker use (P = .02) were determined to be independent predictors of development of increased serum creatinine on fenofibrate.

CONCLUSION

This observational study suggests fenofibrate-associated nephrotoxicity occurs more frequently than previously reported, particularly in patients with renal disease and in those receiving high-dose fenofibrate or concomitant calcium channel blockers.

Inhibition of soluble epoxide hydrolase attenuates endothelial dysfunction in animal models of diabetes, obesity and hypertension

Endothelial dysfunction is a hallmark of, and plays a pivotal role in the pathogenesis of cardiometabolic diseases, including type II diabetes, obesity, and hypertension. It has been well established that epoxyeicosatrienoic acids (EETs) act as an endothelial derived hyperpolarization factor (EDHF). Soluble epoxide hydrolase (s-EH) rapidly hydrolyses certain epoxylipids (e.g. EETs) to less bioactive diols (DHETs), thereby attenuating the evoked vasodilator effects. The aim of the present study was to examine if inhibition of s-EH can restore impaired endothelial function in three animal models of cardiometabolic diseases. Isolated vessel rings of the aorta and/or mesenteric artery from mice or rats were pre-contracted using phenylephrine or U46619. Endothelium-dependent and independent vasorelaxation to acetylcholine and sodium nitroprusside (SNP) were measured using wire myography in vessels isolated from db/db or diet-induced obesity (DIO) mice, and angiotensin II-induced hypertensive rats treated chronically with s-EH inhibitors AR9281 or AR9276 or with vehicle. Vasorelaxation to acetylcholine, but not to SNP was severely impaired in all three animal models. Oral administration of AR9281 or AR9276 abolished whole blood s-EH activity, elevated epoxy/diol lipid ratio, and abrogated endothelial dysfunction in all three models. Incubating the mesenteric artery of db/db mice with L-NAME and indomethacin to block nitric oxide (NO) and prostacyclin formation did not affect AR9821-induced improvement of endothelial function. These data indicate that inhibition of s-EH ameliorates endothelial dysfunction and that effects in the db/db model are independent of the presence of NO and cyclooxygenase derived prostanoids. Thus, preserving vasodilator EETs by inhibition of s-EH may be of therapeutic benefit by improving endothelial function in cardiometabolic diseases.

Soluble Epoxide Hydrolase Inhibition: Targeting Multiple Mechanisms of Ischemic Brain Injury with a Single Agent

Soluble epoxide hydrolase (sEH) is a key enzyme in the metabolic conversion and degradation of P450 eicosanoids called epoxyeicosatrienoic acids (EETs). Genetic variations in the sEH gene, designated EPHX2, are associated with ischemic stroke risk. In experimental studies, sEH inhibition and gene deletion reduce infarct size after focal cerebral ischemia in mice. Although the precise mechanism of protection afforded by sEH inhibition remains under investigation, EETs exhibit a wide array of potentially beneficial actions in stroke, including vasodilation, neuroprotection, promotion of angiogenesis and suppression of platelet aggregation, oxidative stress and post-ischemic inflammation. Herein we argue that by capitalizing on this broad protective profile, sEH inhibition represents a prototype "combination therapy" targeting multiple mechanisms of stroke injury with a single agent.

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.

PPAR activation: a new target for the treatment of hypertension

Hypertensive patients are at increased risk for cardiovascular complications. Inhibition of different pathophysiological mechanisms involved in hypertension and hypertension-related target organ damage may revert or prevent the progression of the pathological changes observed and reduce the occurrence of cardiovascular events. One of the new targets that may prevent or regress hypertensive vascular, renal, and perhaps brain changes in hypertension is the activation of nuclear receptors that have metabolic effects but also exert antiinflammatory action, the peroxisome proliferator activator receptor (PPAR) activators alpha and gamma. This review will discuss some of the evidence, both experimental and clinical, that suggests that activation of PPAR alpha and/or gamma in hypertension may exert beneficial cardiovascular protective effects.

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.

Beyond vasodilatation: non-vasomotor roles of epoxyeicosatrienoic acids in the cardiovascular system

Epoxyeicosatrienoic acids (EETs), derived from arachidonic acid by cytochrome P450 epoxygenases, are potent vasodilators that function as endothelium-derived hyperpolarizing factors in some vascular beds. EETs are rapidly metabolized by soluble epoxide hydrolase to form dihydroxyeicosatrienoic acids (DHETs). Recent reports indicate that EETs have several important non-vasomotor regulatory roles in the cardiovascular system. EETs are potent anti-inflammatory agents and might function as endogenous anti-atherogenic compounds. In addition, EETs and DHETs might stimulate lipid metabolism and regulate insulin sensitivity. Thus, pharmacological inhibition of soluble epoxide hydrolase might be useful not only for hypertension but also for abating atherosclerosis, diabetes mellitus and the metabolic syndrome. Finally, although usually protective in the systemic circulation, EETs might adversely affect the pulmonary circulation.