Fenofibrate Attenuates Hypertension in Goldblatt Hypertensive Rats: Role of 20-Hydroxyeicosatetraenoic Acid in the Nonclipped Kidney.

BACKGROUND: There is vast evidence that the renin-angiotensin system is not the sole determinant of blood pressure (BP) elevation in human renovascular hypertension or the relevant experimental models. This study tested the hypothesis that kidney deficiency of 20-hydroxyeicosatetraenoic acid (20-HETE), a product of cytochrome P450 (CYP)-dependent ω-hydroxylase pathway of arachidonic acid metabolism, is important in the pathophysiology of the maintenance phase of 2-kidney, 1-clip (2K1C) Goldblatt hypertension. MATERIALS AND METHODS: In 2K1C Goldblatt rats with established hypertension, angiotensin II, angiotensin 1-7, 20-HETE concentrations and gene expression of CYP4A1 enzyme (responsible for 20-HETE formation) of the nonclipped kidney were determined. We examined if 14 days׳ administration of fenofibrate, a lipid-lowering drug, would increase CYP4A1 gene expression and renal 20-HETE formation, and if increased 20-HETE concentrations in the nonclipped kidney would decrease BP (telemetric measurements). RESULTS: CYP4A1 gene expression, 20-HETE and angiotensin 1-7 concentrations were lower and angiotensin II levels were higher in the nonclipped kidney of 2K1C rats than in sham-operated rats. Fenofibrate increased CYP4A1 gene expression and 20-HETE concentration in the nonclipped kidney and significantly decreased BP in 2K1C rats but did not restore it to normotensive range. The treatment did not change BP in sham-operated rats. CONCLUSIONS: Our results suggest that alterations in the RAS and CYP-dependent ω-hydroxylase metabolites of arachidonic acid in the nonclipped kidneys are both important in the pathophysiology of the maintenance phase of 2K1C Goldblatt hypertension. Therefore, fenofibrate treatment effectively attenuated hypertension, probably via stimulation of 20-HETE formation in the nonclipped kidney.

Deficiency in the Formation of 20-Hydroxyeicosatetraenoic Acid Enhances Renal Ischemia-Reperfusion Injury.

Ischemia-reperfusion (IR) injury is the most common cause of AKI. The susceptibility to develop AKI varies widely among patients. However, little is known about the genes involved. 20-Hydroxyeicosatetraenoic acid (20-HETE) has an important role in the regulation of renal tubular and vascular function and has been implicated in IR injury. In this study, we examined whether a deficiency in the renal formation of 20-HETE enhances the susceptibility of Dahl salt-sensitive (SS) rats to ischemic AKI. Transfer of chromosome 5 containing the CYP4A genes responsible for the formation of 20-HETE from the Brown Norway (BN) rat onto the SS genetic background increased renal 20-HETE levels after ischemia and reduced plasma creatinine levels (±SEM) 24 hours after IR from 3.7±0.1 to 2.0±0.2 mg/dl in an SS.5(BN)-consomic strain. Transfer of this chromosome also prevented the secondary decline in medullary blood flow and ischemia that develops 2 hours after IR in the susceptible SS strain. Blockade of the synthesis of 20-HETE with HET0016 reversed the renoprotective effects in SS.5(BN) rats. Similar results were observed in an SS.5(Lew)-congenic strain, in which a smaller region of chromosome 5 containing the CYP4A genes from a Lewis rat was introgressed onto the SS genetic background. These results indicate that 20-HETE has a protective role in renal IR injury by maintaining medullary blood flow and that a genetic deficiency in the formation of 20-HETE increases the susceptibility of SS rats to ischemic AKI.

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.

Contribution of 20-HETE to augmented myogenic constriction in coronary arteries of endothelial NO synthase knockout mice.

Previous studies suggested an important role for 20-HETE in the regulation of myogenic responses. Thus, pressure-diameter relationships were investigated in isolated, cannulated coronary arteries (approximately 100 microm) from male endothelial NO synthase knockout (eNOS-KO) and wild-type (WT) mice. All arteries constricted in response to step increases in perfusate pressure from 20 to 100 mm Hg. This constriction was significantly enhanced from 40 to 100 mm Hg in arteries of eNOS-KO compared with those of WT mice. For example, at 60 and 100 mm Hg, respectively, the normalized diameter (expressed as a percentage of the corresponding passive diameter) of arteries of eNOS-KO mice was 10% and 12% smaller than that of WT mice. Removal of the endothelium did not significantly affect the responses of vessels from either strain of mice. However, N-methylsulfonyl-12,12-dibromododec-11-enamide (5x10(-6) M), an inhibitor of cytochrome P-450 (CYP)/omega-hydroxylase, significantly attenuated the greater myogenic constriction of arteries from eNOS-KO mice by approximately 12% at each pressure step but did not significantly affect responses of those from WT mice, leading to a comparable myogenic response in the 2 strains. Western blot analysis demonstrated a comparable CYP4A protein content in coronary arteries of the 2 strains of mice. However, production of 20-HETE, measured by fluorescent high-performance liquid chromatography assay was approximately 2.7-fold greater in eNOS-KO compared to WT mice. Thus, as a function of eNOS deficiency, the enhanced coronary artery constriction to pressure is attributable to an increased activity of omega-hydroxylase, which, consequently, increases the synthesis of 20-HETE in vascular smooth muscle.

Decreased levels of cytochrome P450 2E1-derived eicosanoids sensitize renal arteries to constrictor agonists in spontaneously hypertensive rats.

We compared renal interlobar arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) in terms of cytochrome P450 (CYP) 4A and CYP2E1 protein expression; levels of 20-HETE, 19-HETE, and 18-HETE; and responsiveness to phenylephrine in the absence and presence of N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS; 30 mumol/L), a CYP4A inhibitor. Relative to data in WKY, arteries of SHR exhibited diminished (P<0.05) CYP2E1 and levels of 19-HETE (66.7+/-6.0 versus 44.9+/-2.8 pmol/mg) and 18-HETE (13.8+/-1.6 versus 7.9+/-0.5 pmol/mg), whereas CYP4A and 20-HETE levels (99.3+/-9.1 versus 98.9+/-12.8 pmol/mg) were unchanged. Phenylephrine contracted vascular rings of SHR and WKY; the R(max) was similar in both strains, but SHR vessels were more sensitive as denoted by the lower (P<0.05) EC50 (0.28+/-0.07 versus 0.71+/-0.12 mumol/L). DDMS decreased 20-HETE and, to a lesser extent, 19-HETE, while increasing (P<0.05) the EC50 for phenylephrine by 475% and 54% in vessels of SHR and WKY, respectively. The desensitizing effect of DDMS was reversed by 20-HETE. Notably, the minimal concentration of 20-HETE that decreased the EC50 for phenylephrine in DDMS-treated vessels was smaller in SHR (0.1 micromol/L) than WKY (10 micromol/L), and the sensitizing effect of 20-HETE was blunted (P<0.05) by the (R) stereoisomers of 19-HETE and 18-HETE. We conclude that the increased sensitivity to phenylephrine in arteries of SHR is attributable to a vasoregulatory imbalance produced by a deficit in vascular CYP2E1-derived products, most likely 19(R)-HETE and 18(R)-HETE, which condition amplification of the sensitizing action of 20-HETE.