Induction of renal 20-hydroxyeicosatetraenoic acid by clofibrate attenuates high-fat diet-induced hypertension in rats

Update on current and potential application of extracellular vesicles in kidney transplantation

Kidney transplantation (KT) is the best treatment for end-stage kidney disease. However, early diagnosis of graft injury remains challenging, mainly because of the lack of accurate and noninvasive diagnostic techniques. Improving graft outcomes is equally demanding, as is the development of innovative therapies. Many research efforts are focusing on extracellular vesicles, cellular particles free in each body fluid that have shown promising results as precise markers of damage and potential therapeutic targets in many diseases, including the renal field. In fact, through their receptors and cargo, they act in damage response and immune modulation. In transplantation, they may be used to determine organ quality and aging, the presence of delayed graft function, rejection, and many other transplant-related pathologies. Moreover, their low immunogenicity and safe profile make them ideal for drug delivery and the development of therapies to improve KT outcomes. In this review, we summarize current evidence about extracellular vesicles in KT, starting with their characteristics and major laboratory techniques for isolation and characterization. Then, we discuss their use as potential markers of damage and as therapeutic targets, discussing their promising use in clinical practice as a form of liquid biopsy.

Bioactive lipids in hypertension

Hypertension is a major healthcare issue that afflicts one in every three adults worldwide and contributes to cardiovascular diseases, morbidity and mortality. Bioactive lipids contribute importantly to blood pressure regulation via actions on the vasculature, kidney, and inflammation. Vascular actions of bioactive lipids include blood pressure lowering vasodilation and blood pressure elevating vasoconstriction. Increased renin release by bioactive lipids in the kidney is pro-hypertensive whereas anti-hypertensive bioactive lipid actions result in increased sodium excretion. Bioactive lipids have pro-inflammatory and anti-inflammatory actions that increase or decrease reactive oxygen species and impact vascular and kidney function in hypertension. Human studies provide evidence that fatty acid metabolism and bioactive lipids contribute to sodium and blood pressure regulation in hypertension. Genetic changes identified in humans that impact arachidonic acid metabolism have been associated with hypertension. Arachidonic acid cyclooxygenase, lipoxygenase and cytochrome P450 metabolites have pro-hypertensive and anti-hypertensive actions. Omega-3 fish oil fatty acids eicosapentaenoic acid and docosahexaenoic acid are known to be anti-hypertensive and cardiovascular protective. Lastly, emerging fatty acid research areas include blood pressure regulation by isolevuglandins, nitrated fatty acids, and short chain fatty acids. Taken together, bioactive lipids are key contributors to blood pressure regulation and hypertension and their manipulation could decrease cardiovascular disease and associated morbidity and mortality.

The CYP/20-HETE/GPR75 axis in hypertension

20-Hydroxyeicosatetraenoic acid (20-HETE) is a bioactive lipid generated from the ω-hydroxylation of arachidonic acid (AA) by enzymes of the cytochrome P450 (CYP) family, primarily the CYP4A and CYP4F subfamilies. 20-HETE is most notably identified as a modulator of vascular tone, regulator of renal function, and a contributor to the onset and development of hypertension and cardiovascular disease. 20-HETE-mediated signaling promotes hypertension by sensitizing the vasculature to constrictor stimuli, inducing endothelial dysfunction, and potentiating vascular inflammation. These bioactions are driven by the activation of the G-protein coupled receptor 75 (GPR75), a 20-HETE receptor (20HR). Given the capacity of 20-HETE signaling to drive pro-hypertensive mechanisms, the CYP/20-HETE/GPR75 axis has the potential to be a significant therapeutic target for the treatment of hypertension and cardiovascular diseases associated with increases in blood pressure. In this chapter, we review 20-HETE-mediated cellular mechanisms that promote hypertension, highlight important data in humans such as genetic variants in the CYP genes that potentiate 20-HETE production and describe recent findings in humans with 20HR/GPR75 mutations. Special emphasis is given to the 20HR and respective receptor blockers that have the potential to pave a path to translational and clinical studies for the treatment of 20-HETE-driven hypertension, and obesity/metabolic syndrome.

Renal NKCC2 Is Dual Regulated by the Synergy of 20-HETE and High-Fat Diet in CYP4F2 Transgenic Mice

INTRODUCTION

20-Hydroxyeicosatetraenoic acid (20-HETE) is the metabolite of cytochrome P450, which modulates blood pressure by inhibiting renal sodium transport. However, the molecular mechanisms underlying the role of 20-HETE in the development of obesity-related hypertension remain unclear, necessitating this study.

METHODS

Cytochrome P450 4F2 (CYP4F2) transgenic mice fed high-fat diet (HFD) were used as research animal models. The expression of renal ion transport molecules targeted by 20-HETE was evaluated by real-time PCR and Western blot (WB). The regulatory effect of 20-HETE and HFD on renal Na+-K+-2Cl- cotransporter, isoform 2 (NKCC2) was explored by immunoprecipitation, WB, and luciferase assay.

RESULTS

A 2-week HFD feeding dramatically decreased protein abundance but increased renal NKCC2 mRNA expression in CYP4F2 transgenic mice. The decrease in NKCC2 protein was demonstrated to be due to ubiquitination induced by the synergy between 20-HETE and HFD. The increased PPAR-γ protein in CYP4F2 transgenic mice fed HFD and the activation of rosiglitazone on the luciferase reporter construct of the NKCC2 promoter demonstrated that the increase in NKCC2 mRNA in CYP4F2 transgenic mice fed HFD was a consequence of elevated PPAR-γ protein induced by the synergy between 20-HETE and HFD.

CONCLUSIONS

Our data demonstrated that the synergy between 20-HETE and HFD could decrease NKCC2 protein via posttranslational ubiquitination, which was thought to be the main mechanism underlying the short-term effect in response to HFD and might be responsible for the adaptive modulation of renal NKCC2 to resist sodium retention. Moreover, the increased NKCC2 mRNA expression via PPAR-γ-induced transcriptional regulation was thought to be the main mechanism underlying the long-term effect in response to HFD and plays a pivotal role in the development of obesity-related hypertension.

Role of the Peroxisome Proliferator Activated Receptors in Hypertension

Nuclear receptors represent a large family of ligand-activated transcription factors which sense the physiological environment and make long-term adaptations by mediating changes in gene expression. In this review, we will first discuss the fundamental mechanisms by which nuclear receptors mediate their transcriptional responses. We will focus on the PPAR (peroxisome proliferator-activated receptor) family of adopted orphan receptors paying special attention to PPARγ, the isoform with the most compelling evidence as an important regulator of arterial blood pressure. We will review genetic data showing that rare mutations in PPARγ cause severe hypertension and clinical trial data which show that PPARγ activators have beneficial effects on blood pressure. We will detail the tissue- and cell-specific molecular mechanisms by which PPARs in the brain, kidney, vasculature, and immune system modulate blood pressure and related phenotypes, such as endothelial function. Finally, we will discuss the role of placental PPARs in preeclampsia, a life threatening form of hypertension during pregnancy. We will close with a viewpoint on future research directions and implications for developing novel therapies.

New insights on association between circadian rhythm and lipid metabolism in spontaneously hypertensive rats

AIMS

The aim of this study is to provide new insights on the association of lipid metabolites, circadian genes and lipid metabolism associated genes in spontaneously hypertensive rats.

MATERIALS AND METHODS

An untargeted lipidomics using ultrahigh performance liquid chromatography-mass spectrometry metabolomics was used to identify the differentially expressed lipid metabolites over 24 h in Spontaneously hypertensive rats (SHR) with reference to Wistar-Kyoto rats (WKY). The expression of circadian clock genes (Bmal1, Clock, Per1, Per2, Cry1, Cry2) and lipid metabolism related genes (Rev-erbα, Pparα and Sirt1) was analysed RT-qPCR.

KEY FINDINGS

Ten lipid metabolites with significant differences in their levels in SHR compared to WKY were identified. The levels of MG (25:0), PA (36:3) and PE (38:2) were lower and the levels of LysoPCs (20:0 and 20:3) and TGs (54:5, 59:12, 28:0, 60:10 and 60:13) were found to be higher in SHR. SHR showed obvious disorders in the expression of circadian genes and lipid metabolism associated genes. A strong association between the levels of lipid metabolites and circadian genes and lipid metabolism associated genes was found.

SIGNIFICANCE

Rhythm genes may further affect the 24-hour lipid metabolism level of spontaneously hypertensive rats by mediating lipid metabolism associated genes. This research provides new insights on the association of lipid metabolites, circadian genes and lipid metabolism associated genes in SHR.

Proximal tubular-targeted overexpression of the Cyp4a12-20-HETE synthase promotes salt-sensitive hypertension in male mice

20-Hydroxyeicosatetraenoic acid (20-HETE) has been linked to blood pressure (BP) regulation via actions on the renal microvasculature and tubules. We assessed tubular 20-HETE contribution to hypertension by generating transgenic mice overexpressing the CYP4A12-20-HETE synthase (PT-4a12 mice) under the control of the proximal tubule (PT)-specific promoter, phosphoenolpyruvate carboxykinase (PEPCK). 20-HETE levels in the kidney cortex of male (967±210 vs. 249±69 pg/mg protein), but not female (121±15 vs. 92±11 pg/mg protein) PT-4a12 mice, showed a 2.5-fold increase compared to WT. Renal cortical Cyp4a12 mRNA and CYP4A12 protein in male, but not female PT-4a12 mice increased by 2-3-fold compared to WT. Male PT-4a12 mice displayed elevated BP (142±1 vs. 111±4 mmHg, p<0.0001), whereas BP in females PT-4a12 mice was not significantly different from WT (118±2 vs. 117±2 mmHg; p=0.98). In male PT-4a12 mice, BP decreased when transitioned from a control salt (0.4%) to a low-salt diet (0.075%) from 135±4 to 120±6 mmHg (p<0.01) and increased to 153±5 mmHg (p<0.05) when placed on a high-salt diet (4%). Female PT-4a12 mice did not show changes in BP on either low- or high-salt diet. In conclusion, the expression of Cyp4a12 driven by the PEPCK promoter is sex-specific probably due to its X-linkage. The salt-sensitive hypertension seen in PT-4a12 male mice suggests a potential anti-natriuretic activity of 20-HETE that needs to be further explored.

Xenobiotic Metabolising Enzymes: Impact on Pathologic Conditions, Drug Interactions and Drug Design

Background:

The biotransformation of xenobiotics is a homeostatic defensive response of the body against bioactive invaders. Xenobiotic metabolizing enzymes, important for the metabolism, elimination and detoxification of exogenous agents, are found in most tissues and organs and are distinguished into phase I and phase II enzymes, as well as phase III transporters. The cytochrome P450 superfamily of enzymes plays a major role in the biotransformation of most xenobiotics as well as in the metabolism of important endogenous substrates such as steroids and fatty acids. The activity and the potential toxicity of numerous drugs are strongly influenced by their biotransformation, mainly accomplished by the cytochrome P450 enzymes, one of the most versatile enzyme systems.

Objective:

In this review, considering the importance of drug metabolising enzymes in health and disease, some of our previous research results are presented, which, combined with newer findings, may assist in the elucidation of xenobiotic metabolism and in the development of more efficient drugs.

Conclusion:

Study of drug metabolism is of major importance for the development of drugs and provides insight into the control of human health. This review is an effort towards this direction and may find useful applications in related medical interventions or help in the development of more efficient drugs.

20-HETE in the regulation of vascular and cardiac function

20-HETE, the ω-hydroxylation product of arachidonic acid catalyzed by enzymes of the cytochrome P450 (CYP) 4A and 4F gene families, is a bioactive lipid mediator with potent effects on the vasculature including stimulation of smooth muscle cell contractility, migration and proliferation as well as activation of endothelial cell dysfunction and inflammation. Clinical studies have shown elevated levels of plasma and urinary 20-HETE in human diseases and conditions such as hypertension, obesity and metabolic syndrome, myocardial infarction, stroke, and chronic kidney diseases. Studies of polymorphic associations also suggest an important role for 20-HETE in hypertension, stroke and myocardial infarction. Animal models of increased 20-HETE production are hypertensive and are more susceptible to cardiovascular injury. The current review summarizes recent findings that focus on the role of 20-HETE in the regulation of vascular and cardiac function and its contribution to the pathology of vascular and cardiac diseases.

The role of 20-HETE in cardiovascular diseases and its risk factors

Arachidonic acid (AA) is metabolized in mammals by enzymes of the CYP4A and 4F families to 20-hydroxyeicosatetraeonic acid (20-HETE) which plays an important role in the regulation of renal function, vascular tone and arterial pressure. In the vasculature, 20-HETE is a potent vasoconstrictor, the up-regulation of which contributes to inflammation, oxidative stress, endothelial dysfunction and an increase in peripheral vascular resistance in models of obesity, diabetes, ischemia/reperfusion, and vascular oxidative stress. Recent studies have established a role for 20-HETE in normal and pathological angiogenic conditions. We discuss in this review the synthesis of 20-HETE and how it and various autacoids, especially the renin-angiotensin system, interact to promote hypertension, vasoconstriction, and vascular dysfunction. In addition, we examine the molecular mechanisms through which 20-HETE induces these actions and the clinical implication of inhibiting 20-HETE production and activity.

Alkaloids of Nitraria sibirica Pall. decrease hypertension and albuminuria in angiotensin II-salt hypertension

In traditional Chinese medicine, Nitraria sibirica Pall. (Nitrariaceae) is used to treat hypertension. This study determined the effects of the total alkaloids of the leaves of Nitraria sibirica (NSTA) on blood pressure and albuminuria in mice treated with angiotensin II and a high-salt diet (ANG/HS). Adult mice were divided into three groups: control; infused with angiotensin II and fed a diet containing 4% NaCl (ANG/HS; and ANG/HS plus injection of NSTA (1 mg·kg(-1)·d(-1), i.p.). After treatment of these regimens, daily water and food intake, kidney weight, blood pressure, urinary albumin excretion, renal concentrations of inflammatory markers, including soluble intercellular adhesion molecule-1 (sICAM-1) and monocyte chemoattractant protein-1 (MCP-1), and the expression of renal fibrosis markers were determined. Compared to the control group, the ANG/HS group had higher blood pressure and urinary albumin excretion. Treatment with NSTA in ANG/HS mice for three weeks significantly reduced blood pressure and urinary albumin excretion. ANG/HS treatment caused elevated levels of sICAM-1 and MCP-1, as well as increased fibrosis markers. Concurrent treatment with ANG/HS and NSTA attenuated the levels and expression of renal inflammatory and fibrosis markers. Treatment with NSTA effectively reduces hypertension-induced albuminuria through the reduction of renal inflammatory and fibrosis markers.

20-HETE and blood pressure regulation: clinical implications

20-Hydroxy-5, 8, 11, 14-eicosatetraenoic acid (20-HETE) is a cytochrome P450 (CYP)-derived omega-hydroxylation metabolite of arachidonic acid. 20-HETE has been shown to play a complex role in blood pressure regulation. In the kidney tubules, 20-HETE inhibits sodium reabsorption and promotes natriuresis, thus, contributing to antihypertensive mechanisms. In contrast, in the microvasculature, 20-HETE has been shown to play a pressor role by sensitizing smooth muscle cells to constrictor stimuli and increasing myogenic tone, and by acting on the endothelium to further promote endothelial dysfunction and endothelial activation. In addition, 20-HETE induces endothelial angiotensin-converting enzyme, thus, setting forth a potential feed forward prohypertensive mechanism by stimulating the renin-angiotensin-aldosterone system. With the advancement of gene sequencing technology, numerous polymorphisms in the regulatory coding and noncoding regions of 20-HETE-producing enzymes, CYP4A11 and CYP4F2, have been associated with hypertension. This in-depth review article discusses the biosynthesis and function of 20-HETE in the cardiovascular system, the pharmacological agents that affect 20-HETE action, and polymorphisms of CYP enzymes that produce 20-HETE and are associated with systemic hypertension in humans.

Peroxisome proliferator-activated receptors for hypertension

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear receptor superfamily, which is composed of four members encoded by distinct genes (α, β, γ, and δ). The genes undergo transactivation or transrepression under specific mechanisms that lead to the induction or repression of target gene expression. As is the case with other nuclear receptors, all four PPAR isoforms contain five or six structural regions in four functional domains; namely, A/B, C, D, and E/F. PPARs have many functions, particularly functions involving control of vascular tone, inflammation, and energy homeostasis, and are, therefore, important targets for hypertension, obesity, obesity-induced inflammation, and metabolic syndrome in general. Hence, PPARs also represent drug targets, and PPARα and PPARγ agonists are used clinically in the treatment of dyslipidemia and type 2 diabetes mellitus, respectively. Because of their pleiotropic effects, they have been identified as active in a number of diseases and are targets for the development of a broad range of therapies for a variety of diseases. It is likely that the range of PPARγ agonist therapeutic actions will result in novel approaches to lifestyle and other diseases. The combination of PPARs with reagents or with other cardiovascular drugs, such as diuretics and angiotensin II receptor blockers, should be studied. This article provides a review of PPAR isoform characteristics, a discussion of progress in our understanding of the biological actions of PPARs, and a summary of PPAR agonist development for patient management. We also include a summary of the experimental and clinical evidence obtained from animal studies and clinical trials conducted to evaluate the usefulness and effectiveness of PPAR agonists in the treatment of lifestyle-related diseases.

Intrarenal ghrelin receptor antagonism prevents high-fat diet-induced hypertension in male rats

Excess weight gain contributes up to 65% of the risk of primary hypertension, and the increase in blood pressure in response to high-fat diet (HFD) is preceded by significant increases in renal tubular sodium (Na(+)) reabsorption. In normal rats, intrarenal ghrelin infusion increases distal nephron-dependent Na(+) reabsorption via activation of the intrarenal ghrelin receptor (GHSR). This study focusses on the role of intrarenal GHSR-mediated Na(+) reabsorption in HFD-induced hypertension. Dahl salt-sensitive rats received standard diet or HFD for 6 weeks. Rats underwent uninephrectomy and osmotic minipump implantation for chronic intrarenal delivery of vehicle (0.25 μL/h × 28 d), selective GHSR antagonist [D-Lys-3]-growth hormone releasing peptide-6 (0.2μM/d), or GHSR inverse agonist [D-Arg(1), D-Phe(5), D-Trp(7,9), Leu(11)]-substance P (SUB-P) (3.6μM/d). HFD rats with vehicle pumps had significantly increased renal GHSR expression compared with standard diet (0.092 ± 0.005 vs 0.065 ± 0.004 arbitrary units; P < .05), whereas acyl ghrelin levels were similar (16.3±6.2 vs 15.7±8.7 pg/g tissue). HFD rats with vehicle pumps became hypertensive after 2 weeks (P < .05) and showed a significant reduction in 24-hour urine Na(+) before hypertension. At this time, these rats showed an increase in collecting duct α-epithelial Na(+) channel, thereby providing a potential mechanism for the excess Na(+) reabsorption. In contrast, HFD rats with [D-Lys-3]-growth hormone releasing peptide-6 or SUB-P pumps never became hypertensive and did not show the reduction in urine Na(+). Because SUB-P blocks the constitutive, but not ghrelin-dependent, activity of the GHSR, and HFD-induced α-epithelial Na(+) channel up-regulation was abolished during GHSR antagonism, these data suggest that HFD increases the constitutive activity of renal GHSR to increase Na(+) reabsorption and induce hypertension in rats.

Pioglitazone ameliorates the lowered exercise capacity and impaired mitochondrial function of the skeletal muscle in type 2 diabetic mice

We have reported that exercise capacity is reduced in high fat diet (HFD)-induced diabetic mice, and that this reduction is associated with impaired mitochondrial function in skeletal muscle (SKM). However, it remains to be clarified whether the treatment of diabetes ameliorates the reduced exercise capacity. Therefore, we examined whether an insulin-sensitizing drug, pioglitazone, could improve exercise capacity in HFD mice. C57BL/6J mice were fed a normal diet (ND) or HFD, then treated with or without pioglitazone (3 mg/kg/day) to yield the following 4 groups: ND+vehicle, ND+pioglitazone, HFD+vehicle, and HFD+pioglitazone (n=10 each). After 8 weeks, body weight, plasma glucose, and insulin in the HFD+vehicle were significantly increased compared to the ND+vehicle group. Pioglitazone normalized the insulin levels in HFD-fed mice, but did not affect the body weight or plasma glucose. Exercise capacity determined by treadmill tests was significantly reduced in the HFD+vehicle, and this reduction was almost completely ameliorated in HFD+pioglitazone mice. ADP-dependent mitochondrial respiration, complex I and III activities, and citrate synthase activity were significantly decreased in the SKM of the HFD+vehicle animals, and these decreases were also attenuated by pioglitazone. NAD(P)H oxidase activity was significantly increased in the HFD+vehicle compared with the ND+vehicle, and this increase was ameliorated in HFD+pioglitazone mice. Pioglitazone improved the exercise capacity in diabetic mice, which was due to the improvement in mitochondrial function and attenuation of oxidative stress in the SKM. Our data suggest that pioglitazone may be useful as an agent for the treatment of diabetes mellitus.

Estrogen increases ENaC activity via PKCδ signaling in renal cortical collecting duct cells

The most active estrogen, 17β‐estradiol (E2), has previously been shown to stimulate a female sex‐specific antisecretory response in the intestine. This effect is thought to contribute to the increase in whole body extracellular fluid (ECF) volume which occurs in high estrogen states, such as in the implantation window during estrous cycle. The increased ECF volume may be short‐circuited by a renal compensation unless estrogen exerts a proabsorptive effect in the nephron. Thus, the effect of E2 on ENaC in kidney cortical collecting duct (CCD) cells is of interest to understand estrogen regulation of ECF volume. Previous studies showed a rapid stimulatory effect of estrogen on ENaC in bronchial epithelium. In this study we examined if such a rapid effect on Na⁺ absorption could occur in the kidney. Experiments were carried out on murine M1‐CCD cell cultures. E2 (25 nmol/L) treatment caused a rapid‐onset (<15 min) and sustained increase in the amiloride‐sensitive Na⁺ current (I_Na) in CCD monolayers mounted in Ussing chambers (control, 1.9 ± 0.2 μA/cm²; E2, 4.7 ± 0.3 μA/cm²; n = 43, P < 0.001), without affecting the ouabain‐sensitive Na⁺/K⁺ pump current. The I_Na response to E2 was inhibited by PKCδ activity antagonism with rottlerin (5 μmol/L), inhibition of matrix metalloproteinases activity with GM6001 (1 μmol/L), inhibition of EGFR activity with AG1478 (10 μmol/L), inhibition of PLC activity with U‐73122 (10 μmol/L), and inhibition of estrogen receptors with the general ER antagonist ICI‐182780 (100 nmol/L). The estrogen activation of I_Na could be mimicked by the ERα agonist PPT (1 nmol/L). The nuclear excluded estrogen dendrimer conjugate (EDC) induced similar stimulatory effects on I_Na comparable to free E2. The end target for E2 stimulation of PKCδ was shown to be an increased abundance of the γ‐ENaC subunit in the apical plasma membrane of CCD cells. We have demonstrated a novel rapid “nongenomic” function of estrogen to stimulate ENaC via ERα‐EGFR transactivation in kidney CCD cells. We propose that the salt‐retaining effect of estrogen in the kidney together with its antisecretory action in the intestine are the molecular mechanisms causing the expanded ECF volume in high‐estrogen states.

Estrogen stimulates sodium absorption in kidney cells. This rapid “nongenomic” response to estrogen is transduced via estrogen receptor transactivation of the epidermal growth factor receptor. The ER‐EGFR transactivation triggers a protein kinase signaling cascade which culminates in the insertion of sodium channel subunits into the cell membrane. Estrogen is a novel salt‐retaining hormone with proabsorptive effects in kidney and antisecretory actions in intestine.

PPARα ligand clofibrate ameliorates blood pressure and vascular reactivity in spontaneously hypertensive rats

AIM

Peroxisome proliferator activated receptors (PPARs) are nuclear transcription factors that regulate numerous genes influencing blood pressure. The aim of this study was to examine the effects of clofibrate, a PPARα ligand, on blood pressure in spontaneously hypertensive rats (SHR).

METHODS

Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR), 8-9 weeks old, were randomly allocated into groups treated with vehicle or clofibrate (250 mg·kg(-1)·d(-1), ip for 21 d). Systolic blood pressure (SBP) was measured before and after the study period using tail-cuff plethysmography. Rats were sacrificed under anesthesia and blood, urine and tissue samples were processed for subsequent analysis.

RESULTS

SHR rats showed significantly higher SBP compared with WKY rats (198±6 mmHg vs 93±7 mmHg), and a 3-fold increase in urinary protein excretion. Clofibrate treatment reduced SBP by 26%±2% and proteinuria by 43%±9% in SHR but not in WKY rats. The urinary nitrite/nitrate excretion in SHR rats was nearly 2-fold greater than that in WKY, and was further increased by 30%±4% and 48%±3%, respectively, following clofibrate treatment. In addition, PPARα protein expression and PPARα activity were significantly lower in SHR than that in WKY rats. Clofibrate treatment significantly increased PPARα protein expression and PPARα activity in SHR rats, but not in WKY rats. Moreover, the vasoconstrictor response of aortic ring was markedly increased in SHRs, which was blunted after clofibrate treatment.

CONCLUSION

PPARα contributes to regulation of blood pressure and vascular reactivity in SHR, and clofibrate-mediated reduction in blood pressure and proteinuria is probably through increased NO production.

Beneficial effects of inhibition of soluble epoxide hydrolase on glucose homeostasis and islet damage in a streptozotocin-induced diabetic mouse model

Soluble epoxide hydrolase (sEH) is an enzyme involved in the metabolism of endogenous inflammatory and anti-apoptotic mediators. In the present study, we determined the effects of the inhibition of sEH on glucose homeostasis and islet damage in mice treated with streptozotocin (STZ), a model of chemical-induced diabetes. STZ increased daily water intake and decreased visceral (spleen and pancreas) weight in mice; sEH inhibition in STZ mice decreased water intake, but did not affect visceral weight. Hyperglycemia induced by STZ treatment in mice was attenuated by inhibiting sEH. The beneficial effects of sEH inhibition were accompanied, after 2 and 4 weeks of initial administration, by improving glucose tolerance. In contrast, sEH inhibition did not affect insulin tolerance. Using LC/MS analysis, neither STZ nor STZ plus sEH inhibition affected pancreatic and plasma ratios of epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs), an index of EETs levels. Western blot analysis showed that mouse cytochrome P450 (CYP) 2C enzymes are the major epoxygenases in islets. On day 5 after initial STZ treatment, STZ induced islet cell apoptosis, while sEH inhibition in STZ mice significantly reduced islet cell apoptosis. These studies provide pharmacological evidence that inhibiting sEH activity provides significant protection against islet β-cell damage and improves glucose homeostasis in STZ-induced diabetes.

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.

Protective effect of 20-hydroxyeicosatetraenoic acid (20-HETE) on adriamycin-induced toxicity of human renal tubular epithelial cell (HK-2)

20-Hydroxyeicosatetraenoic acid is a cytochrome P4504A11 metabolite of arachidonic acid that plays an important role in the regulation of human renal functions. In the present study, we investigated the role of 20-hydroxyeicosatetraenoic acid on adriamycin induced toxicity in human renal tubular epithelial cells. Results showed that cell viability was decreased significantly and lactate dehydrogenase activity was increased significantly in a concentration-dependent manner when human renal tubular epithelial cells were incubated with adriamycin (10⁻⁷-10⁻³ mol/l) for 24h. In contrast, 20-hydroxyeicosatetraenoic acid (0.1, 1, 10, 50 μmol/l) increased cell survival and decreased lactate dehydrogenase activity concentration dependently in human renal tubular epithelial cells. When 20-hydroxyeicosatetraenoic acid (10, 50 μmol/l) was co-administered with adriamycin (10⁻³ mol/l), it significantly increased cell viability and decreased lactate dehydrogenase activity. On the other hand, N-hydroxy-N'-(4-butyl-2-methylphenyl)formamidine (HET-0016) (1 μM), a selective inhibitor of 20-hydroxyeicosatetraenoic acid synthesizing enzyme exaggerated cell viability reduction and lactate dehydrogenase activity augmentation induced by adriamycin. Adriamycin suppressed the expression of cytochrome P4504A11 gene and its protein production in human renal tubular epithelial cells. Furthermore, adriamycin was more effective than N-hydroxy-N'-(4-butyl-2-methylphenyl)formamidine at lowering the expression of cytochrome P4504A11 gene and its protein. These results suggest that 20-hydroxyeicosatetraenoic acid may protect adriamycin-induced toxicity of human renal tubular epithelial cells, meanwhile, adriamycin-induced toxicity of human renal tubular epithelial cells possibly involves inhibiting cytochrome P4504A11 expression.

20-hydroxyeicosatetraeonic acid: a new target for the treatment of hypertension

Arachidonic acid is metabolized by enzymes of the CYP4A and 4F families to 20-hydroxyeicosatetraeonic acid (20-HETE), which plays an important role in the regulation of renal function, vascular tone, and the long-term control of arterial pressure. In the vasculature, 20-HETE is a potent vasoconstrictor, and upregulation of the production of this compound contributes to the elevation in oxidative stress and endothelial dysfunction and the increase in peripheral vascular resistance associated with some forms of hypertension. In kidney, 20-HETE inhibits Na transport in the proximal tubule and thick ascending loop of Henle, and deficiencies in the renal formation of 20-HETE contributes to sodium retention and development of some salt-sensitive forms of hypertension. 20-HETE also has renoprotective actions and opposes the effects of transforming growth factor β to promote proteinuria and renal end organ damage in hypertension. Several new inhibitors of the synthesis of 20-HETE and 20-HETE agonists and antagonists have recently been developed. These compounds along with peroxisome proliferator-activated receptor-α agonists that induce the renal formation of 20-HETE seem to have promise as antihypertensive agents. This review summarizes the rationale for the development of drugs that target the 20-HETE pathway for the treatment of hypertension and associated cardiovascular complications.

Glomerular 20-HETE, EETs, and TGF-beta1 in diabetic nephropathy

The early stage of diabetic nephropathy (DN) is linked to proteinuria. Transforming growth factor (TGF)-beta1 increases glomerular permeability to albumin (P(alb)), whereas 20-HETE and EETs reduce P(alb). To investigate the impact of hyperglycemia and hyperlipidemia on 20-HETE, EETs, and TGF-beta1 in the glomeruli, rats were divided into four groups: ND rats were fed a normal diet, HF rats were fed a high-fat diet, STZ rats were treated with 35 mg/kg of streptozotocin, and HF/STZ rats were fed a HF diet and treated with STZ. After 10 wk on these regimens, blood glucose, urinary albumin, serum cholesterol, serum triglyceride levels, and the kidney-to-body weight ratio were significantly elevated in STZ and HF/STZ rats compared with HF and ND rats. STZ and HF/STZ rats had histopathologic changes and abnormal renal hemodynamics. Expression of glomerular CYP4A, enzymes for 20-HETE production, was significantly decreased in STZ rats, whereas expression of glomerular CYP2C and CYP2J, enzymes for EETs production, was significantly decreased in both STZ and HF/STZ rats. Moreover, glomerular TGF-beta1 levels were significantly greater in STZ and HF/STZ rats than in HF and ND rats. Five-week treatment of STZ rats with clofibrate induced glomerular CYP4A expression and 20-HETE production, but reduced glomerular TGF-beta1 and urinary protein excretion. These results demonstrate that hyperglycemia increases TGF-beta1 but decreases 20-HETE and EETs production in the glomeruli, changes that may be important in causing glomerular damage in the early stage of DN.

Colfibrate attenuates blood pressure and sodium retention in DOCA-salt hypertension

Clofibrate, a peroxisome proliferator-activated receptor-alpha (PPAR alpha) agonist, increases renal tubular cytochrome P450 4a (Cyp4a) expression thereby increasing 20-hydroxyeicosatetraenoic acid (20-HETE) production. To determine if clofibrate affects blood pressure regulation we studied mice with DOCA-salt induced hypertension in wild-type and PPAR alpha knockout mice. Wild-type mice treated with DOCA-salt had higher mean arterial pressures and higher cumulative sodium balance, but lower renal 20-HETE production than did vehicle-treated mice. Treating DOCA-salt mice with clofibrate attenuated the increase in mean arterial pressure and cumulative sodium balance while increasing 20-HETE production and renal Cyp4a expression. In contrast the PPAR alpha knockout mice treated with clofibrate and DOCA-salt showed no attenuation in the increase of blood pressure, cumulative sodium balance, renal 20-HETE production or Cyp4a protein expression. Expression of the PPAR alpha protein was greater in proximal tubules than in renal microvessels. Our results show that PPAR alpha pathway induces renal tubular 20-HETE production which affects sodium retention and blood pressure regulation in DOCA-salt-treated mice.

Deficient renal 20-HETE release in the diabetic rat is not the result of oxidative stress

We confirmed that release of 20-hydroxyeicosatetraenoic acid (20-HETE) from the isolated perfused kidney of diabetic rats is greatly reduced compared with age-matched control rats. The present studies were undertaken to examine potential mechanisms for the deficit in renal 20-HETE in rats with streptozotocin-induced diabetes of 3-4 wk duration. A role for oxidative stress was excluded, inasmuch as treatment of diabetic rats with tempol, an SOD mimetic, for 4 wk did not affect the renal release of 20-HETE. Similarly, chronic inhibition of nitric oxide formation with nitro-l-arginine methyl ester or aldose reductase with zopolrestat failed to alter the release of 20-HETE from the diabetic rat kidney. Inasmuch as 20-HETE may be metabolized by cyclooxygenase (COX), the expression/activity of which is increased in diabetes, we included indomethacin in the perfusate of the isolated kidney to inhibit COX but found no effect on 20-HETE release. Diabetic rats were treated for 3 wk with fenofibrate to increase expression of cytochrome P-450 (CYP4A) in an attempt to find an intervention that would restore release of 20-HETE from the diabetic rat kidney. However, fenofibrate reduced 20-HETE release in diabetic and control rat kidneys but increased expression of CYP4A. Only insulin treatment of diabetic rats for 2 wk to reverse the hyperglycemia and maintain blood glucose levels at <200 mg/dl reversed the renal deficit in 20-HETE. We conclude that oxidative stress, increased aldose reductase activity, or increased COX activity does not contribute to the renal deficit of 20-HETE in diabetes, which may be directly related to insulin deficiency.

Functional polymorphism in human CYP4F2 decreases 20-HETE production

20-Hydroxyeicosatetraenoic acid (20-HETE) plays an important role in the regulation of renal tubular and vascular function and a deficiency in the renal formation of 20-HETE has been linked to the development of hypertension. The cytochrome P450 4F2 ( CYP4F2) gene encodes for the major CYP enzyme responsible for the synthesis of 20-HETE in the human kidney. We screened two human sampling panels (African and European Americans: n = 24 and 23 individuals, respectively) using PCR and DNA resequencing to identify informative SNPs in the coding region of the CYP4F2 gene. Two nonsynonymous SNPs that lead to amino acid changes at position 12 (W12G) and 433 (V433M), were identified. Both of these variants were found to be frequent in both African and European American sampling panels (9–21% minor allele frequency), and the W12G polymorphism exhibited extensive linkage disequilibrium with surrounding SNPs. To determine the functional significance of these mutations on the ability of the CYP4F2 enzyme to metabolize arachidonic acid and leukotriene B4(LTB4), recombinant baculoviruses containing four different human CYP4F2 variants (i.e., W12/V433, W12/M433, G12/V433, G12/M433) were generated and the proteins were expressed in Sf9 insect cells. The presence of the M433 allele, W12/M433, or G12/M433 decreased 20-HETE production to 56–66% of control. In contrast these variants had no effect on the ω-hydroxylation of LTB4. These findings are the first to identify a functional variant in the human CYP4F2 gene that alters the production of 20-HETE.

Increasing or stabilizing renal epoxyeicosatrienoic acid production attenuates abnormal renal function and hypertension in obese rats

Since epoxyeicosatrienoic acids (EETs) affect sodium reabsorption in renal tubules and dilate the renal vasculature, we have examined their effects on renal hemodynamics and sodium balance in male rats fed a high-fat (HF) diet by fenofibrate, a peroxisome proliferator-activated receptor-alpha (PPAR-alpha) agonist and an inducer of cytochrome P-450 (CYP) epoxygenases; by N-methanesulfonyl-6-(2-proparyloxyphenyl)hexanamide (MSPPOH), a selective EET biosynthesis inhibitor; and by 12-(3-adamantane-1-yl-ureido)dodecanoic acid (AUDA), a selective inhibitor of soluble epoxide hydrolase. In rats treated with fenofibrate (30 mg.kg(-1).day(-1) ig) or AUDA (50 mg/l in drinking water) for 2 wk, mean arterial pressure, renal vascular resistance, and glomerular filtration rate were lower but renal blood flow was higher than in vehicle-treated control rats. In addition, fenofibrate and AUDA decreased cumulative sodium balance in the HF rats. Treatment with MSPPOH (20 mg.kg(-1).day(-1) iv) + fenofibrate for 2 wk reversed renal hemodynamics and sodium balance to the levels in control HF rats. Moreover, fenofibrate caused a threefold increase in renal cortical CYP epoxygenase activity, whereas the fenofibrate-induced elevation of this activity was attenuated by MSPPOH. Western blot analysis showed that fenofibrate induced the expression of CYP epoxygenases in renal cortex and microvessels and that the induction effect of fenofibrate was blocked by MSPPOH. These results demonstrate that the fenofibrate-induced increase of CYP epoxygenase expression and the AUDA-induced stabilization of EET production in the kidneys cause renal vascular dilation and reduce sodium retention, contributing to the improvement of abnormal renal hemodynamics and hypertension in HF rats.