Renal cytochrome P4504A activity and salt sensitivity in spontaneously hypertensive rats

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.

Towards Precision Medicine for Hypertension: A Review of Genomic, Epigenomic, and Microbiomic Effects on Blood Pressure in Experimental Rat Models and Humans

Compelling evidence for the inherited nature of essential hypertension has led to extensive research in rats and humans. Rats have served as the primary model for research on the genetics of hypertension resulting in identification of genomic regions that are causally associated with hypertension. In more recent times, genome-wide studies in humans have also begun to improve our understanding of the inheritance of polygenic forms of hypertension. Based on the chronological progression of research into the genetics of hypertension as the "structural backbone," this review catalogs and discusses the rat and human genetic elements mapped and implicated in blood pressure regulation. Furthermore, the knowledge gained from these genetic studies that provide evidence to suggest that much of the genetic influence on hypertension residing within noncoding elements of our DNA and operating through pervasive epistasis or gene-gene interactions is highlighted. Lastly, perspectives on current thinking that the more complex "triad" of the genome, epigenome, and the microbiome operating to influence the inheritance of hypertension, is documented. Overall, the collective knowledge gained from rats and humans is disappointing in the sense that major hypertension-causing genes as targets for clinical management of essential hypertension may not be a clinical reality. On the other hand, the realization that the polygenic nature of hypertension prevents any single locus from being a relevant clinical target for all humans directs future studies on the genetics of hypertension towards an individualized genomic approach.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Evidence that 20-HETE contributes to the development of acute and delayed cerebral vasospasm

Recent studies have indicated that arachidonic acid (AA) is metabolized by the cytochrome P450 4A (CYP4A) enzymes in cerebral arteries to produce 20-hydroxyeicosatetraenoic acid (20-HETE) and that this compound has effects on cerebral vascular tone that mimic those seen following subarachnoid hemorrhage (SAH). In this regard, 20-HETE is a potent constrictor of cerebral arteries that decreases the open state probability of Ca(2+)-activated K(+) channels through activation of protein kinase C (PKC). It increases the sensitivity of the contractile apparatus to Ca(2+) by activating PKC and rho kinase. The formation of 20-HETE is stimulated by angiotensin II (AII), endothelin, adenosine triphosphate (ATP) and serotonin, and inhibited by NO, CO and superoxide radicals. Inhibitors of the formation of 20-HETE block the myogenic response of cerebral arterioles to elevations in transmural pressure in vitro and autoregulation of cerebral blood flow (CBF) in vivo. 20-HETE also plays an important role in modulating the cerebral vascular responses to vasodilators (NO and CO) and vasoconstrictors (AII, endothelin, serotonin). Recent studies have indicated that the levels of 20-HETE in cerebrospinal fluid (CSF) increase in rats, dogs and human patients following SAH and that inhibitors of the synthesis of 20-HETE prevent the acute fall in CBF in rats and reverse delayed vasospasm in both dogs and rats. This review examines the evidence that an elevation in the production of 20-HETE contributes to the initial fall in CBF following SAH and the later development of delayed vasospasm.

Elevated production of 20-HETE in the cerebral vasculature contributes to severity of ischemic stroke and oxidative stress in spontaneously hypertensive rats

Hypertension is a major risk factor for stroke, but the factors that contribute to the increased incidence and severity of ischemic stroke in hypertension remain to be determined. 20-hydroxyeicosatetraenoic acid (20-HETE) has been reported to be a potent constrictor of cerebral arteries, and inhibitors of 20-HETE formation reduce infarct size following cerebral ischemia. The present study examined whether elevated production of 20-HETE in the cerebral vasculature could contribute to the larger infarct size previously reported after transient middle cerebral artery occlusion (MCAO) in hypertensive strains of rat [spontaneously hypertensive rat (SHR) and spontaneously hypertensive stroke-prone rat (SHRSP)]. The synthesis of 20-HETE in the cerebral vasculature of SHRSP measured by liquid chromatography-tandem mass spectrometry was about twice that seen in Wistar-Kyoto (WKY) rats. This was associated with the elevated expression of cytochrome P-450 (CYP)4A protein and CYP4A1 and CYP4A8 mRNA. Infarct volume after transient MCAO was greater in SHRSP (36+/-4% of hemisphere volume) than in SHR (19+/-5%) or WKY rats (5+/-2%). This was associated with a significantly greater reduction in regional cerebral blood flow (rCBF) in SHR and SHRSP than in WKY rats during the ischemic period (78% vs. 62%). In WKY rats, rCBF returned to 75% of control following reperfusion. In contrast, SHR and SHRSP exhibited a large (166+/-18% of baseline) and sustained (1 h) postischemic hyperperfusion. Acute blockade of the synthesis of 20-HETE with N-hydroxy-N'-(4-butyl-2-methylphenyl)-formamidine (HET0016; 1 mg/kg) reduced infarct size by 59% in SHR and 87% in SHRSP. HET0016 had no effect on the fall in rCBF during MCAO but eliminated the hyperemic response. HET0016 also attenuated vascular O2*- formation and restored endothelium-dependent dilation in cerebral arteries of SHRSP. These results indicate the production of 20-HETE is elevated in the cerebral vasculature of SHRSP and contributes to oxidative stress, endothelial dysfunction, and the enhanced sensitivity to ischemic stroke in this hypertensive model.

Functional effects of 20-HETE on human bronchi: hyperpolarization and relaxation due to BKCa channel activation

Airway smooth muscle (ASM) metabolizes arachidonic acid (AA) through various enzymatic pathways, including cytochrome P-450 (CYP-450) omega-hydroxylase, which leads to the production of 20-hydroxyeicosatetraenoic acid (20-HETE). The goal of this study was to delineate the mode of action of 20-HETE in human ASM cells. Isometric tension measurements demonstrated that 20-HETE induced a concentration-dependent relaxant effect in ASM on bronchi precontracted with either methacholine or AA. Relaxing effects of 20-HETE on resting tone were prevented by 10 nM iberiotoxin (IbTx), a BK(Ca) channel inhibitor. Microelectrode measurements showed that exogenous additions of 20-HETE (0.1-10 microM) hyperpolarized the membrane potential of human ASM cells. This concentration-dependent electrophysiological effect induced by the eicosanoid was prevented by 10 nM IbTx. Complementary experiments, using the planar lipid bilayer reconstitution technique, demonstrated that 20-HETE activated reconstituted BK(Ca) channels at low free Ca(2+) concentrations. Together, these results indicate that 20-HETE-dependent activation of BK(Ca) channels is responsible for the hyperpolarization and controlled relaxation of ASM in human distal bronchi.

Cytochrome P450 4F subfamily: at the crossroads of eicosanoid and drug metabolism

The cytochrome P450 4F (CYP4F) subfamily has over the last few years come to be recognized for its dual role in modulating the concentrations of eicosanoids during inflammation as well as in the metabolism of clinically significant drugs. The first CYP4F was identified because it catalyzed the hydroxylation of leukotriene B(4) (LTB(4)) and since then many additional members of this subfamily have been documented for their distinct catalytic roles and functional significance. Recent evidence emerging in relation to the temporal change of CYP4F expression in response to injury and infection supports an important function for these isozymes in curtailing inflammation. Their tissue-dependent expression, isoform-based catalytic competence and unique response to the external stimuli imply a critical role for them to regulate organ-specific functions. From this standpoint variations in relative CYP4F levels in humans may have direct influence on the metabolic outcome through their ability to generate and/or degrade bioactive eicosanoids or therapeutic agents. This review covers the enzymatic characteristics and regulatory properties of human and rodent CYP4F isoforms and their physiological relevance to major pathways in eicosanoid and drug metabolism.

Eicosanoids and renal vascular function in diseases

Arachidonic acid metabolites are vital for the proper control of renal haemodynamics and, when not properly controlled, can contribute to renal vascular injury and end-stage renal disease. Three major enzymatic pathways, COX (cyclo-oxygenase), CYP450 (cytochrome P450) and LOX (lipoxygenase), are responsible for the metabolism of arachidonic acid metabolites to bioactive eicosanoids. These eicosanoids can dilate or constrict the renal vasculature and maintain vascular resistance in the face of changing vasoactive hormones. Renal vascular generation of eicosanoids is altered in pathophysiological conditions such as hypertension, diabetes, metabolic syndrome and acute renal failure. Experimental evidence supports the concept that altered eicosanoid metabolism contributes to renal haemodynamic alterations and the development and progression of nephropathy. The possible beneficial renal vascular actions of enzymatic inhibitors, eicosanoid analogues and receptor antagonists have been examined in hypertension, diabetes and metabolic syndrome. This review highlights the roles of renal vascular eicosanoids in the pathogenesis of nephropathy and therapeutic targets for renal disease related to hypertension, diabetes, metabolic syndrome and acute renal failure.

Contribution of cytochrome P450 metabolites of arachidonic acid to hypertension and end-organ damage in spontaneously hypertensive rats treated with l-NAME

1 The purpose of this study was to examine the effect of inhibition of the formation of cytochrome P450 metabolites of arachidonic acid with 1-aminobenzotriazole (ABT) on the development of hypertension and end-organ damage in spontaneously hypertensive rats (SHR) chronically treated with nitric oxide synthesis inhibitor L-NAME (SHR-L-NAME). 2 Administration of L-NAME in drinking water (80 mg l(-1)) to SHR for 3 weeks significantly elevated mean arterial blood pressure (MABP) (223 +/- 4 mmHg) as compared to SHR controls drinking regular water (165 +/- 3 mmHg). The administration of ABT (50 mg kg(-1) i.p. alt diem) for 6 days significantly attenuated elevation of blood pressure in SHR-L-NAME (204 +/- 4 mmHg). 3 L-NAME-induced increase in urine volume and protein was significantly lower in ABT-treated animals. 4 The impaired vascular responsiveness to noradrenaline and isoprenaline in the perfused mesenteric vascular bed of SHR-L-NAME-treated animals was significantly improved by ABT treatment. 5 Morphological studies of the kidneys and hearts showed that treatment with ABT minimized the extensive arterial fibrinoid necrosis, arterial thrombosis, significant narrowing of arterial lumen with marked arterial hyperplastic arterial changes that were observed in vehicle treated SHR-L-NAME. 6 In isolated perfused hearts, recovery of left ventricular function from 40 min of global ischaemia was significantly better in ABT-treated SHR-L-NAME. 7 These results suggest that in hypertensive individuals with endothelial dysfunction and chronic NO deficiency, inhibitors of 20-HETE synthesis may be able to attenuate development of high blood pressure and end-organ damage.

Renal localization, expression, and developmental regulation of P450 4F cytochromes in three substrains of spontaneously hypertensive rats

Cytochrome P450 4F isoforms have been shown to metabolize arachidonic acid to generate 20-hydroxyeicosatetraenoic acid (20-HETE), a potent eicosanoid that modulates vascular tone and renal tubular function. 20-HETE production in the kidney is implicated in the development of essential hypertension in the spontaneously hypertensive rat (SHR). In this study, we determined CYP4F mRNA localization and distribution in rat liver and kidney by in situ hybridization and real time quantitative PCR. CYP4Fs are regionally distributed in the kidney with CYP4F1, 4F4, and 4F5 being expressed more in the renal cortex than medulla while CYP4F6 shows higher medullary expression. We investigated developmental CYP4F gene expression in three different substrains of SHR. Distinct age-dependent patterns of expression were seen for individual CYP4F isoforms in Wistar-Kyoto (WKY) and three SHR substrains (B2, C, and A3). A steady increase in CYP4F1 expression with age was seen in each of the three substrains which correlate well with increased 20-HETE levels and elevated blood pressure seen in these animals. CYP4F4 expression increased significantly at 8 weeks followed by a precipitous fall in WKY and A3 strains at 12 weeks of age. In strains B2 and C, CYP4F4 levels started declining as early as 8 weeks of age. CYP4F5 and 4F6 levels fluctuated with age in a biphasic manner with a different profile for each sub-strain. Based on the expression profile and catalytic activity, CYP4F1 seems to be the most critical 4F isoform involved in the production of 20-HETE in the SHR kidney.

Regulation and inhibition of arachidonic acid omega-hydroxylases and 20-HETE formation

Cytochrome P450-catalyzed metabolism of arachidonic acid is an important pathway for the formation of paracrine and autocrine mediators of numerous biological effects. The omega-hydroxylation of arachidonic acid generates significant levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in numerous tissues, particularly the vasculature and kidney tubules. Members of the cytochrome P450 4A and 4F families are the major omega-hydroxylases, and the substrate selectivity and regulation of these enzymes has been the subject of numerous studies. Altered expression and function of arachidonic acid omega-hydroxylases in models of hypertension, diabetes, inflammation, and pregnancy suggest that 20-HETE may be involved in the pathogenesis of these diseases. Our understanding of the biological significance of 20-HETE has been greatly aided by the development and characterization of selective and potent inhibitors of the arachidonic acid omega-hydroxylases. This review discusses the substrate selectivity and expression of arachidonic acid omega-hydroxylases, regulation of these enzymes during disease, and the application of enzyme inhibitors to study 20-HETE function.

Role of cytochrome P450-dependent arachidonic acid metabolites in liver physiology and pathophysiology

Arachidonic acid (AA) can undergo monooxygenation or epoxidation by enzymes in the cytochrome P450 (CYP) family in the brain, kidney, lung, vasculature, and the liver. CYP-AA metabolites, 19- and 20-hydroxyeicosatetraenoic acids (HETEs), epoxyeicosatrienoic acids (EETs) and diHETEs have different biological properties based on sites of production and can be stored in tissue lipids and released in response to hormonal stimuli. 20-HETE is a vasoconstrictor, causing blockade of Ca(++)-activated K(+) (KCa) channels. Inhibition of the formation of nitric oxide (NO) by 20-HETE mediates most of the cGMP-independent component of the vasodilator response to NO. 20-HETE elicits a potent dilator response in human and rabbit pulmonary vascular and bronchiole rings that is dependent on an intact endothelium and COX. 20-HETE is also a vascular oxygen sensor, inhibits Na(+)/K(+)-ATPase activity, is an endogenous inhibitor of the Na(+)-K(+)-2Cl(-)cotransporter, mediates the mitogenic actions of vasoactive agents and growth factors in many tissues and plays a significant role in angiogenesis. EETs, produced by the vascular endothelium, are potent dilators. EETs hyperpolarize VSM cells by activating KCa channels. Several investigators have proposed that one or more EETs may serve as endothelial-derived hyperpolarizing factors (EDHF). EETs constrict human and rabbit bronchioles, are potent mediators of insulin and glucagon release in isolated rat pancreatic islets, and have anti-inflammatory activity. Compared with other organs, the liver has the highest total CYP content and contains the highest levels of individual CYP enzymes involved in the metabolism of fatty acids. In humans, 50-75% of CYP-dependent AA metabolites formed by liver microsomes are omega/omega-OH-AA, mainly w-OH-AA, i.e. 20HETE, and 13-28% are EETs. Very little information is available on the role of 19- and 20-HETE and EETs in liver function. EETs are involved in vasopressin-induced glycogenolysis, probably via the activation of phosphorylase. In the portal vein, inhibition of EETs exerts profound effects on a variety of K-channel activities in smooth muscles of this vessel. 20-HETE is a weak, COX-dependent, vasoconstrictor of the portal circulation. EETs, particularly 11,12-EET, cause vasoconstriction of the porto-sinusoidal circulation. Increased synthesis of EETs in portal vessels and/or sinusoids or increased levels in blood from the meseneric circulation may participate in the pathophysiology of portal hypertension of cirrhosis. CYP-dependent AA metabolites are involved in the pathophysiology of portal hypertension, not only by increasing resistance in the porto-sinusoidal circulation, but also by increasing portal inflow through mesenteric vasodilatation. In patients with cirrhosis, urinary 20-HETE is several-fold higher than PGs and TxB2, whereas in normal subjects, 20-HETE and PGs are excreted at similar rates. Thus, 20-HETE is probably produced in increased amounts in the preglomerular microcirculation accounting for the functional decrease of flow and increase in sodium reabsorption. In conclusion, CYP-AA metabolites represent a group of compounds that participate in the regulation of liver metabolic activity and hemodynamics. They appear to be deeply involved in abnormalities related to liver diseases, particularly cirrhosis, and play a key role in the pathophysiology of portal hypertension and renal failure.

Inhibition of the formation of EETs and 20-HETE with 1-aminobenzotriazole attenuates pressure natriuresis

This study examined the effects of chronic blockade of the renal formation of epoxyeicosatrienoic acids and 20-hydroxyeicosatetraenoic acid with 1-aminobenzotriazole (ABT; 50 mg·kg−1· day−1ip for 5 days) on pressure natriuresis and the inhibitory effects of elevations in renal perfusion pressure (RPP) on Na+-K+-ATPase activity and the distribution of the sodium/hydrogen exchanger (NHE)-3 in the proximal tubule of rats. In control rats ( n = 15), sodium excretion rose from 2.3 ± 0.4 to 19.4 ± 1.8 μeq·min−1·g kidney weight−1when RPP was increased from 114 ± 1 to 156 ± 2 mmHg. Fractional excretion of lithium rose from 28 ± 3 to 43 ± 3% of the filtered load. Chronic treatment of the rats with ABT for 5 days ( n = 8) blunted the natriuretic response to elevations in RPP by 75% and attenuated the increase in fractional excretion of lithium by 45%. In vehicle-treated rats, renal Na+-K+-ATPase activity fell from 31 ± 5 to 19 ± 2 μmol Pi·mg protein−1·h−1and NHE-3 protein was internalized from the brush border of the proximal tubule after an elevation in RPP. In contrast, Na+-K+-ATPase activity and the distribution of NHE-3 protein remained unaltered in rats treated with ABT. These results suggest that cytochrome P-450 metabolites of arachidonic acid contribute to pressure natriuresis by inhibiting Na+-K+-ATPase activity and promoting internalization of NHE-3 protein from the brush border of the proximal tubule.

Role of 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids in hypertension

PURPOSE OF REVIEW

Cytochrome P-450 metabolites of arachidonic acid have been reported to play an important role in the control of renal function and vascular tone, and in the long-term control of arterial pressure. In this regard, 20-hydroxyeicosatetraenoic acid is a potent vasoconstrictor that inhibits sodium reabsorption in the kidney. Epoxyeicosatrienoic acids are endothelium-derived relaxing factors that hyperpolarize vascular smooth muscle cells and also promote sodium excretion in the kidney.

RECENT FINDINGS

Studies have demonstrated that the expression of cytochrome P-450 enzymes and the synthesis of 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids in the kidney and peripheral vasculature are altered in many genetic and experimental models of hypertension. The production of these compounds is altered following exposure to high-salt or high-fat diets, in hepatorenal syndrome, in diabetes and in patients with toxemia of pregnancy. However, the functional significance of changes in the formation of 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids in the pathogenesis of hypertension are just being uncovered.

SUMMARY

This review summarizes recent findings that address the issue of whether cytochrome P-450 metabolites of arachidonic acid play an important role in the regulation of renal tubular and peripheral vascular function and contribute to the pathogenesis of hypertension.

20-HETE inotropic effects involve the activation of a nonselective cationic current in airway smooth muscle

20-Hydroxyeicosatetraenoic acid (20-HETE) controls several mechanisms such as vasoactivity, mitogenicity, and ion transport in various tissues. Our goal was to quantify the effects of 20-HETE on the electrophysiological properties of airway smooth muscle (ASM). Isometric tension measurements, performed on guinea pig ASM, showed that 20-HETE induced a dose-dependent inotropic effect with an EC50 value of 1.5 microM. This inotropic response was insensitive to GF-109203X, a PKC inhibitor. The sustained contraction, requiring Ca2+ entry, was partially blocked by either 100 microM Gd3+ or 1 microM nifedipine, revealing the involvement of noncapacitative Ca2+ entry and L-type Ca2+ channels, respectively. Microelectrode measurements showed that 3 microM 20-HETE depolarized the membrane potential in guinea pig ASM by 13 +/- 2mV(n = 7), as did 30 microM 1-oleoyl-2-acetyl-sn-glycerol. Depolarizing effects were also observed in the absence of epithelium. Patch-clamp recordings demonstrated that 1 microM 20-HETE activated a nonselective cationic inward current that may be supported by the activation of transient receptor potential channels. The presence of canonical transient receptor potential mRNA was confirmed by RT-PCR in guinea pig ASM cells.

Role of 20-hydroxyeicosatetraenoic acid in the renal and vasoconstrictor actions of angiotensin II

The present study examined the effects of ANG II on the renal synthesis of 20-hydroxyeicosatetraenoic acid (20-HETE) and its contribution to the renal vasoconstrictor and the acute and chronic pressor effects of ANG II in rats. ANG II (10(-11) to 10(-7) mol/l) reduced the diameter of renal interlobular arteries treated with inhibitors of nitric oxide synthase and cyclooxygenase, lipoxygenase, and epoxygenase by 81 +/- 8%. Subsequent blockade of the synthesis of 20-HETE with 17-octadecynoic acid (1 micromol/l) increased the ED(50) for ANG II-induced constriction by a factor of 15 and diminished the maximal response by 61%. Graded intravenous infusion of ANG II (5-200 ng/min) dose dependently increased mean arterial pressure (MAP) in thiobutylbarbitol-anesthetized rats by 35 mmHg. Acute blockade of the formation of 20-HETE with dibromododecenyl methylsulfimide (DDMS; 10 mg/kg) attenuated the pressor response to ANG II by 40%. An intravenous infusion of ANG II (50 ng. kg(-1). min(-1)) in rats for 5 days increased the formation of 20-HETE and epoxyeicosatrienoic acids (EETs) in renal cortical microsomes by 60 and 400%, respectively, and increased MAP by 78 mmHg. Chronic blockade of the synthesis of 20-HETE with intravenous infusion of DDMS (1 mg. kg(-1). h(-1)) or EETs and 20-HETE with 1-aminobenzotriazole (ABT; 2.2 mg. kg(-1). h(-1)) attenuated the ANG II-induced rise in MAP by 40%. Control urinary excretion of 20-HETE averaged 350 +/- 23 ng/day and increased to 1,020 +/- 105 ng/day in rats infused with ANG II (50 ng. kg(-1). min(-1)) for 5 days. In contrast, urinary excretion of 20-HETE only rose to 400 +/- 40 and 600 +/- 25 ng/day in rats chronically treated with ANG II and ABT or DDMS respectively. These results suggest that acute and chronic elevations in circulating ANG II levels increase the formation of 20-HETE in the kidney and peripheral vasculature and that 20-HETE contributes to the acute and chronic pressor effects of ANG II.

Participation of renal and circulating endothelin in salt-sensitive essential hypertension

Salt sensitivity of blood pressure is a cardiovascular risk factor, independent of and in addition to hypertension. In essential hypertension, a conglomerate of clinical and biochemical characteristics defines a salt-sensitive phenotype. Despite extensive research on multiple natriuretic and antinatriuretic systems, there is no definitive answer yet about the major causes of salt-sensitivity, probably reflecting the complexity of salt-balance regulation. The endothelins, ubiquitous peptides first described as potent vasoconstrictors, also have vasodilator, natriuretic and antinatriuretic actions, depending on their site of generation and binding to different receptors. We review the available data on endothelin in salt-sensitive essential hypertension and conclude that abnormalities of renal endothelin may play a primary role. More importantly, the salt-sensitive patient may have blood pressure-dependency on endothelin in all states of salt balance, thus predicting that endothelin receptor blockers will have a major therapeutic role in salt-sensitive essential hypertension.

Two closely linked interactive blood pressure QTL on rat chromosome 5 defined using congenic Dahl rats

Previously we reported the construction of a congenic strain, S.LEW, spanning a large region of rat chromosome 5. The Lewis (LEW) strain was the donor, and the Dahl salt-sensitive (S) strain was the recipient. The congenic strain included a blood pressure quantitative trait locus (QTL). In the present work, a series of nine congenic substrains were constructed from S.LEW which defined two closely linked blood pressure QTL in the region previously thought to contain only one. LEW low-blood-pressure alleles at both QTL were required for a major effect on blood pressure. Neither LEW allele alone had a significant effect on blood pressure. The two QTL were localized to regions 6.3 and 4.6 cM, and these were 1.0 cM apart.

P-450 metabolites of arachidonic acid in the control of cardiovascular function

Recent studies have indicated that arachidonic acid is primarily metabolized by cytochrome P-450 (CYP) enzymes in the brain, lung, kidney, and peripheral vasculature to 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) and that these compounds play critical roles in the regulation of renal, pulmonary, and cardiac function and vascular tone. EETs are endothelium-derived vasodilators that hyperpolarize vascular smooth muscle (VSM) cells by activating K(+) channels. 20-HETE is a vasoconstrictor produced in VSM cells that reduces the open-state probability of Ca(2+)-activated K(+) channels. Inhibitors of the formation of 20-HETE block the myogenic response of renal, cerebral, and skeletal muscle arterioles in vitro and autoregulation of renal and cerebral blood flow in vivo. They also block tubuloglomerular feedback responses in vivo and the vasoconstrictor response to elevations in tissue PO(2) both in vivo and in vitro. The formation of 20-HETE in VSM is stimulated by angiotensin II and endothelin and is inhibited by nitric oxide (NO) and carbon monoxide (CO). Blockade of the formation of 20-HETE attenuates the vascular responses to angiotensin II, endothelin, norepinephrine, NO, and CO. In the kidney, EETs and 20-HETE are produced in the proximal tubule and the thick ascending loop of Henle. They regulate Na(+) transport in these nephron segments. 20-HETE also contributes to the mitogenic effects of a variety of growth factors in VSM, renal epithelial, and mesangial cells. The production of EETs and 20-HETE is altered in experimental and genetic models of hypertension, diabetes, uremia, toxemia of pregnancy, and hepatorenal syndrome. Given the importance of this pathway in the control of cardiovascular function, it is likely that CYP metabolites of arachidonic acid contribute to the changes in renal function and vascular tone associated with some of these conditions and that drugs that modify the formation and/or actions of EETs and 20-HETE may have therapeutic benefits.

Quantitative trait loci for body weight, blood pressure, blood glucose, and serum lipids: linkage analysis with wild rats (Rattus norvegicus)

To study polygenetically inherited human diseases like hypertension, inbred rat strains are usually the preferred models. Because many inbred generations under optimized environmental conditions may have led to the survival of "silent" disease genes, we used a cross between one wild rat and genetically hypertensive SHR rats to analyze quantitative trait loci (QTLs) of blood pressure and related traits. The (Wild x SHR)F1 hybrids were transferred into a pathogen-free environment by wet-hysterectomy and were backcrossed onto SHR to generate first backcross hybrids (BC1). Progeny from one F1 female (n = 72) were phenotypically and genetically characterized to map QTLs. Significant, subsignificant, and suggestive evidence was found for more sex-specific than common linkage of blood pressure and most blood-pressure-related traits. Male- and female-specific regions were determined on different chromosomes for blood pressures (Chrs. 2 and 7 vs 5 and 11), body weight (Chrs. 10 vs 18), and blood glucose (Chr. 17 vs 20). A linkage in both males and females was shown for serum triglycerides on chromosomes 6 and 17, respectively, and blood glucose on chromosome 15. For serum total cholesterol, a significant linkage was found on chromosome 14 only in males. Our findings not only indicate the complex character of quantitative traits per se but also show impressively their dependence on sex, age, and strains in cosegregation analysis.

Effects of converting enzyme inhibitors on renal P-450 metabolism of arachidonic acid

The effects of blockade of the renin-angiotensin system on the renal metabolism of arachidonic acid (AA) were examined. Male Sprague-Dawley rats were treated with vehicle, captopril (25 mg x kg(-1) x day(-1)), enalapril (10 mg x kg(-1) x day(-1)), or candesartan (1 mg x kg(-1) x day(-1)) for 1 wk. The production of 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) by renal cortical microsomes increased in rats treated with captopril by 59 and 24% and by 90 and 58% in rats treated with enalapril. Captopril and enalapril increased 20-HETE production in the outer medulla by 100 and 143%, respectively. In contrast, blockade of ANG II type 1 receptors with candesartan had no effect on the renal metabolism of AA. Captopril and enalapril increased cytochrome P-450 (CYP450) reductase protein levels in the renal cortex and outer medulla and the expression of CYP450 4A protein in the outer medulla. The effects of captopril on the renal metabolism of AA were prevented by the bradykinin-receptor antagonist, HOE-140, or the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester. These results suggest that angiotensin-converting enzyme inhibitors may increase the formation of 20-HETE and EETs secondary to increases in the intrarenal levels of kinins and NO.

Role of 20-HETE in mediating the effect of dietary K intake on the apical K channels in the mTAL

We have used the patch-clamp technique to study the effect of dietary K intake on the apical K channels in the medullary thick ascending limb (mTAL) of rat kidneys. The channel activity, defined by the number of channels in a patch and the open probability (NPo), of the 30- and 70-pS K channels, was 0.18 and 0.11, respectively, in the mTAL from rats on a K-deficient diet. In contrast, NPo of the 30- and 70-pS K channels increased to 0.60 and 0.80, respectively, in the tubules from animals on a high-K diet. The concentration of 20-hydroxyeicosatetraenoic acid (20-HETE) measured with gas chromatography-mass spectrometry was 0.8 pg/microg protein in the mTAL from rats on a high-K diet and increased significantly to 4.6 pg/microg protein in the tubules from rats on a K-deficient diet. Addition of N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS) or 17-octadecynoic acid (17-ODYA), agents that inhibit the formation of 20-HETE, had no significant effect on the activity of the 30-pS K channels. However, DDMS/17-ODYA significantly increased the activity of the apical 70-pS K channel from 0.11 to 0.91 in the mTAL from rats on a K-deficient diet. In contrast, inhibition of the cytochrome P-450 metabolism of arachidonic acid increased NPo from 0.64 to 0.81 in the tubules from animals on a high-K diet. Furthermore, the sensitivity of the 70-pS K channel to 20-HETE was the same between rats on a high-K diet and on a K-deficient diet. Finally, the pretreatment of the tubules with DDMS increased NPo of the 70-pS K channels in the mTAL from rats on a K-deficient diet to 0.76. We conclude that an increase in 20-HETE production is involved in reducing the activity of the apical 70-pS K channels in the mTAL from rats on a K-deficient diet.

The lung HETEs (and EETs) up

Arachidonic acid metabolites of the cyclooxygenase and lipoxygenase pathways have a variety of important lung functions. Recent observations indicate that cytochrome P-450 (P-450) monooxygenases are also expressed in the lung, localized to specific pulmonary cell types (e.g., epithelium, endothelium, and smooth muscle), and may modulate critical lung functions. This review summarizes recent data on the presence and biological activity of P-450-derived eicosanoids in the pulmonary vasculature and airways, including effects on pulmonary vascular and bronchial smooth muscle tone and airway epithelial ion transport. We hypothesize a number of potential functions of P-450-derived arachidonate metabolites in the lungs such as contribution to hypoxic pulmonary vasoconstriction, regulation of bronchomotor tone, control of the composition of airway lining fluid, and limitation of pulmonary inflammation. Finally, we describe a number of emerging technologies, including congenic and transgenic strains of experimental animals, P-450 isoform-specific inhibitors and inhibitory antibodies, eicosanoid analogs, and vectors for delivery of P-450 cDNAs and antisense oligonucleotides. These tools will facilitate further studies on the contribution of endogenously formed P-450 eicosanoid metabolites to lung function, under both normal and pathological conditions.

Cytochrome P450 metabolites of arachidonic acid in the control of renal function

Recent studies indicate that arachidonic acid is primarily metabolized by cytochrome P450 enzymes of the 4A and 2C families in the kidney to 20-hydroxyeicosatetraenoic acid (HETE), epoxyeicosatrienoic acids (EETs) and dihydroxyeicosatrienoic acids. These compounds play central roles in the regulation of renal tubular and vascular function. 20-HETE is produced by renal vascular smooth muscle (VSM) cells and is a potent constrictor that depolarizes VSM cells by blocking the calcium-activated potassium channel. Inhibition of the formation of 20-HETE blocks the myogenic response of isolated renal arterioles in vitro, and autoregulation of renal blood flow and tubuloglomerular feedback responses in vivo. EETs are products formed in the endothelium and are potent dilators that activate the calcium-activated potassium channel in renal VSM. Endothelial-dependent vasodilators stimulate the release of EETs, and these compounds appear to serve as an endothelial-derived hyperpolarizing factor. EETs and 20-HETE are produced in the proximal tubule. There, they regulate sodium/potassium-ATPase activity and serve as second messengers for the natriuretic effects of dopamine, parathyroid hormone and angiotensin II. 20-HETE is also produced in the thick ascending loop of Henle. It regulates sodium-potassium-chloride transport in this nephron segment. The renal production of cytochrome P450 metabolites of arachidonic acid is altered in hypertension, diabetes, toxemia of pregnancy, and hepatorenal syndrome. Given the importance of cytochrome P450 metabolites of arachidonic acid in the control of renal function, it is likely that changes in this system contribute to the abnormalities in renal function that are associated with many of these conditions.

Targeted disruption of soluble epoxide hydrolase reveals a role in blood pressure regulation

Renal microsomal cytochrome P-450 monooxygenase-dependent metabolism of arachidonic acid generates a series of regioisomeric epoxyeicosatrienoic acids that can be further metabolized by soluble epoxide hydrolase to the corresponding dihydroxyeicosatrienoic acids. Evidence exists that these metabolites affect renal function and, in particular, blood pressure regulation. To examine this possibility, blood pressure and renal arachidonic acid metabolism were examined in mice with a targeted disruption of the soluble epoxide hydrolase gene. Systolic blood pressure of male soluble epoxide hydrolase-null mice was lower compared with wild-type mice in both the absence and presence of dietary salt loading. Both female soluble epoxide hydrolase-null and wild-type female mice also had significantly lower systolic blood pressure than male wild-type mice. Renal formation of epoxyeicosatrienoic and dihydroxyeicosatrienoic acids was markedly lower for soluble epoxide hydrolase-null versus wild-type mice of both sexes. Although disruption of soluble epoxide hydrolase in female mice had minimal effects on blood pressure, deletion of this gene feminized male mice by lowering systolic blood pressure and altering arachidonic acid metabolism. These data provide the first direct evidence for a role for soluble epoxide hydrolase in blood pressure regulation and identify this enzyme as a novel and attractive target for therapeutic intervention in hypertension.

Renal and cardiovascular actions of 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids

1. Arachidonic acid (AA) is metabolized by cytochrome P450 (CYP)-dependent pathways to epoxyeicosatrienoic acids (EET) and 20-hydroxyeicosatetraenoic acid (20-HETE) in the kidney and the peripheral vasculature. 2. The present short review summarizes the renal and cardiovascular actions of these important mediators. 3. Epoxyeicosatrienoic acids are vasodilators produced by the endothelium that hyperpolarize vascular smooth muscle (VSM) cells by opening Ca2+-activated K+ (KCa) channels. 20-Hydroxyeicosatetraenoic acid is a vasoconstrictor that inhibits the opening of KCa channels in VSM cells. Cytochrome P450 4A inhibitors block the myogenic response of small arterioles to elevations in transmural pressure and autoregulation of renal and cerebral blood flow in vivo. Cytochrome P450 4A blockers also attenuate the vasoconstrictor response to elevations in tissue PO2, suggesting that this system may serve as a vascular oxygen sensor. Nitric oxide and carbon monoxide inhibit the formation of 20-HETE and a fall in 20-HETE levels contributes to the activation of KCa channels in VSM cells and the vasodilator response to these gaseous mediators. 20-Hydroxyeicosatetraenoic acid also mediates the inhibitory actions of peptide hormones on sodium transport in the kidney and the mitogenic effects of growth factors in VSM and mesangial cells. A deficiency in the renal production of 20-HETE is associated with the development of hypertension in Dahl salt-sensitive rats. 4. In summary, the available evidence indicates that CYP metabolites of AA play a central role in the regulation of renal, pulmonary and vascular function and that abnormalities in this system may contribute to the pathogenesis of cardiovascular diseases.

Impairment of flow-induced dilation of skeletal muscle arterioles with elevated oxygen in normotensive and hypertensive rats

The effects of elevated PO(2) on flow-induced dilation of in situ skeletal muscle arterioles was assessed in cremaster muscle preparations from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Blood flow increases in selected arterioles were initiated by occlusion of a parallel daughter branch from a parent arteriole. Changes in the diameter of the perfused arteriole were measured with a video micrometer and erythrocyte velocity was measured using optical Doppler velocimetry. Superfusate PO(2) was controlled by changing the O(2) concentration (0% O(2) or 21% O(2)) of the equilibration gas mixture. The increase in arteriolar diameter during occlusion was reduced in SHR compared to WKY rats, resulting in an elevated wall shear rate in SHR. Elevated PO(2) decreased flow-induced dilation in both groups and increased wall shear rate during parallel occlusion. An inhibitor of the formation of 20-HETE via cytochrome P450-4A enzymes (P450), dibromododecenyl methylsulfimide, minimized O(2)-induced constriction of arterioles and prevented the O(2)-induced decrease in flow-induced dilation and the increase in wall shear rate in both SHR and WKY rats. These results suggest that: (1) flow-induced dilation of in situ skeletal muscle arterioles is impaired in SHR compared to WKY, (2) elevated O(2) compromises flow-induced dilation in both groups, (3) 20-HETE contributes to both the O(2)-induced increases in resting tone and the reduced flow-induced dilation of cremasteric arterioles with elevated PO(2).

Formation of 20-hydroxyeicosatetraenoic acid, a vasoactive and natriuretic eicosanoid, in human kidney. Role of Cyp4F2 and Cyp4A11

20-hydroxyeicosatetraenoic acid (20-HETE), an omega-hydroxylated arachidonic acid (AA) metabolite, elicits specific effects on kidney vascular and tubular function that, in turn, influence blood pressure control. The human kidney's capacity to convert AA to 20-HETE is unclear, however, as is the underlying P450 catalyst. Microsomes from human kidney cortex were found to convert AA to a single major product, namely 20-HETE, but failed to catalyze AA epoxygenation and midchain hydroxylation. Despite the monophasic nature of renal AA omega-hydroxylation kinetics, immunochemical studies revealed participation of two P450s, CYP4F2 and CYP4A11, since antibodies to these enzymes inhibited 20-HETE formation by 65. 9 +/- 17 and 32.5 +/- 14%, respectively. Western blotting confirmed abundant expression of these CYP4 proteins in human kidney and revealed that other AA-oxidizing P450s, including CYP2C8, CYP2C9, and CYP2E1, were not expressed. Immunocytochemistry showed CYP4F2 and CYP4A11 expression in only the S2 and S3 segments of proximal tubules in cortex and outer medulla. Our results demonstrate that CYP4F2 and CYP4A11 underlie conversion of AA to 20-HETE, a natriuretic and vasoactive eicosanoid, in human kidney. Considering their proximal tubular localization, these P450 enzymes may partake in pivotal renal functions, including the regulation of salt and water balance, and arterial blood pressure itself.

Genetic analysis of inherited hypertension in the rat

Blood pressure is a quantitative trait that has a strong genetic component in humans and rats. Several selectively bred strains of rats with divergent blood pressures serve as an animal model for genetic dissection of the causes of inherited hypertension. The goal is to identify the genetic loci controlling blood pressure, i.e., the so-called quantitative trait loci (QTL). The theoretical basis for such genetic dissection and recent progress in understanding genetic hypertension are reviewed. The usual paradigm is to produce segregating populations derived from a hypertensive and normotensive strain and to seek linkage of blood pressure to genetic markers using recently developed statistical techniques for QTL analysis. This has yielded candidate QTL regions on almost every rat chromosome, and also some interactions between QTL have been defined. These statistically defined QTL regions are much too large to practice positional cloning to identify the genes involved. Most investigators are, therefore, fine mapping the QTL using congenic strains to substitute small segments of chromosome from one strain into another. Although impressive progress has been made, this process is slow due to the extensive breeding that is required. At this point, no blood pressure QTL have met stringent criteria for identification, but this should be an attainable goal given the recently developed genomic resources for the rat. Similar experiments are ongoing to look for genes that influence cardiac hypertrophy, stroke, and renal failure and that are independent of the genes for hypertension.

20-HETE agonists and antagonists in the renal circulation

The present study examined the effects of a series of 20-hydroxyeicosatetraenoic acid (20-HETE) derivatives on the diameter of renal arterioles to determine the structural requirements of the vasoconstrictor response to 20-HETE. The vascular responses to 5-, 8-, 12-, 15-, 19-, 20-, 21-HETEs, arachidonic acid (AA), and saturated, partially saturated, dimethyl, carboxyl, and 19-carbon derivatives of 20-HETE (10(-8) to 10(-6) M) were assessed in rat renal interlobular arteries (65-125 micrometer). 20-HETE, 21-HETE, dimethyl-20-HETE, and a partially saturated derivative of 20-HETE, 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid, reduced vessel diameter by 19 +/- 3, 17 +/- 3, 16 +/- 2, and 28 +/- 2%, respectively. In contrast, 5-, 8-, 12-, 15-, and 19-HETE, AA, saturated, partially saturated, carboxyl, and the 19-carbon derivatives of 20-HETE had no effect on vessel diameter. Pretreatment with 5-, 15-, and 19-HETE, the 19-carbon derivative or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (1 microM) completely blocked the vasoconstrictor response to 20-HETE in renal arterioles. Pretreatment with AA, carboxyl, saturated 19-carbon, and saturated 20-HETE derivatives (1 microM) partially blocked the response, whereas 8- and 12-HETE (1 microM) had no effect on the vasoconstrictor response to 20-HETE. These findings suggest that 20-HETE agonists and antagonists require a carboxyl or an ionizable group on carbon 1 and a double bond near the 14 or 15 carbon. 20-HETE agonists also require a functional group capable of hydrogen bonding on carbon 20 or 21, whereas antagonists lack this reactive group.

Renal cytochrome P450 omega-hydroxylase and epoxygenase activity are differentially modified by nitric oxide and sodium chloride

Renal function is perturbed by inhibition of nitric oxide synthase (NOS). To probe the basis of this effect, we characterized the effects of nitric oxide (NO), a known suppressor of cytochrome P450 (CYP) enzymes, on metabolism of arachidonic acid (AA), the expression of omega-hydroxylase, and the efflux of 20-hydroxyeicosatetraenoic acid (20-HETE) from the isolated kidney. The capacity to convert [(14)C]AA to HETEs and epoxides (EETs) was greater in cortical microsomes than in medullary microsomes. Sodium nitroprusside (10-100 microM), an NO donor, inhibited renal microsomal conversion of [(14)C]AA to HETEs and EETs in a dose-dependent manner. 8-bromo cGMP (100 microM), the cell-permeable analogue of cGMP, did not affect conversion of [(14)C]AA. Inhibition of NOS with N(omega)-nitro-L-arginine-methyl ester (L-NAME) significantly increased conversion of [(14)C]AA to HETE and greatly increased the expression of omega-hydroxylase protein, but this treatment had only a modest effect on epoxygenase activity. L-NAME induced a 4-fold increase in renal efflux of 20-HETE, as did L-nitroarginine. Oral treatment with 2% sodium chloride (NaCl) for 7 days increased renal epoxygenase activity, both in the cortex and the medulla. In contrast, cortical omega-hydroxylase activity was reduced by treatment with 2% NaCl. Coadministration of L-NAME and 2% NaCl decreased conversion of [(14)C]AA to HETEs without affecting epoxygenase activity. Thus, inhibition of NOS increased omega-hydroxylase activity, CYP4A expression, and renal efflux of 20-HETE, whereas 2% NaCl stimulated epoxygenase activity.

Ontogenetic aspects of hypertension development: analysis in the rat

In this review, we attempt to outline the age-dependent interactions of principal systems controlling the structure and function of the cardiovascular system in immature rats developing hypertension. We focus our attention on the cardiovascular effects of various pharmacological, nutritional, and behavioral interventions applied at different stages of ontogeny. Several distinct critical periods (developmental windows), in which particular stimuli affect the further development of the cardiovascular phenotype, are specified in the rat. It is evident that short-term transient treatment of genetically hypertensive rats with certain antihypertensive drugs in prepuberty and puberty (at the age of 4-10 wk) has long-term beneficial effects on further development of their cardiovascular apparatus. This juvenile critical period coincides with the period of high susceptibility to the hypertensive effects of increased salt intake. If the hypertensive process develops after this critical period (due to early antihypertensive treatment or late administration of certain hypertensive stimuli, e.g., high salt intake), blood pressure elevation, cardiovascular hypertrophy, connective tissue accumulation, and end-organ damage are considerably attenuated compared with rats developing hypertension during the juvenile critical period. As far as the role of various electrolytes in blood pressure modulation is concerned, prohypertensive effects of dietary Na+ and antihypertensive effects of dietary Ca2+ are enhanced in immature animals, whereas vascular protective and antihypertensive effects of dietary K+ are almost independent of age. At a given level of dietary electrolyte intake, the balance between dietary carbohydrate and fat intake can modify blood pressure even in rats with established hypertension, but dietary protein intake affects the blood pressure development in immature animals only. Dietary protein restriction during gestation, as well as altered mother-offspring interactions in the suckling period, might have important long-term hypertensive consequences. The critical periods (developmental windows) should be respected in the future pharmacological or gene therapy of human hypertension.

20-Hydroxyeicosatetraenoic acid and renal function in Lyon hypertensive rats

To evaluate the contribution of cytochrome P450 (CYP450) metabolites of arachidonic acid in the increased renal vascular resistance and blunted pressure-natriuresis response exhibited by Lyon hypertensive (LH) rats, the effects of an intrarenal infusion of 17-octadecynoic acid (3 microM), an inhibitor of the formation of epoxyeicosatrienoic and 20-hydroxyeicosatetraenoic acids, were compared in 8-week-old LH and low blood pressure (LL) control rats. 17-Octadecynoic acid failed to affect renal function in LL rats. In contrast, it reduced renal vascular resistance and shifted the pressure-natriuresis relationship to lower pressures in LH rats. Blockade of thromboxane-endoperoxide (TP) receptors with GR 32191B prevented the renal vasodilator response to 17-octadecynoic acid but not its natriuretic action. Miconazole (1 microM), an inhibitor of epoxygenase activity, had no effect on renal function in LH rats. These results indicate that CYP450 metabolites of arachidonic acid, likely 20-hydroxyeicosatetraenoic acid, contribute to the resetting of the pressure-natriuresis relation in LH rats and that the renal vasoconstrictor effects of 20-hydroxyeicosatetraenoic acid in LH rats may be related to activation of TP receptors.

Molecular cloning, enzymatic characterization, developmental expression, and cellular localization of a mouse cytochrome P450 highly expressed in kidney

A cDNA encoding a new cytochrome P450 was isolated from a mouse liver library. Sequence analysis reveals that this 1,886-base pair cDNA encodes a 501-amino acid polypeptide that is 69-74% identical to CYP2J subfamily P450s and is designated CYP2J5. Recombinant CYP2J5 was co-expressed with NADPH-cytochrome P450 oxidoreductase in Sf9 cells using a baculovirus system. Microsomal fractions of CYP2J5/NADPH-cytochrome P450 oxidoreductase-transfected cells metabolize arachidonic acid to 14,15-, 11,12-, and 8, 9-epoxyeicosatrienoic acids and 11- and 15-hydroxyeicosatetraenoic acids (catalytic turnover, 4.5 nmol of product/nmol of cytochrome P450/min at 37 degrees C); thus CYP2J5 is enzymologically distinct. Northern analysis reveals that CYP2J5 transcripts are most abundant in mouse kidney and present at lower levels in liver. Immunoblotting using a polyclonal antibody against a CYP2J5-specific peptide detects a protein with the same electrophoretic mobility as recombinant CYP2J5 most abundantly in mouse kidney microsomes. CYP2J5 is regulated during development in a tissue-specific fashion. In the kidney, CYP2J5 is present before birth and reaches maximal levels at 2-4 weeks of age. In the liver, CYP2J5 is absent prenatally and during the early postnatal period, first appears at 1 week, and then remains relatively constant. Immunohistochemical staining of kidney sections with anti-human CYP2J2 IgG reveals that CYP2J protein(s) are present primarily in the proximal tubules and collecting ducts, sites where the epoxyeicosatrienoic acids are known to modulate fluid/electrolyte transport and mediate hormonal action. In situ hybridization confirms abundant CYP2J5 mRNA within tubules of the renal cortex and outer medulla. Epoxyeicosatrienoic acids are endogenous constituents of mouse kidney thus providing direct evidence for the in vivo metabolism of arachidonic acid by the mouse renal epoxygenase(s). Based on these data, we conclude that CYP2J5 is an enzymologically distinct, developmentally regulated, protein that is localized to specific nephron segments and contributes to the oxidation of endogenous renal arachidonic acid pools. In light of the well documented effects of epoxyeicosatrienoic acids in modulating renal tubular transport processes, we postulate that CYP2J5 products play important functional roles in the kidney.

Regulation of P-450 4A activity in the glomerulus of the rat

We recently reported that an enzyme of the cytochrome P-450 4A family is expressed in the glomerulus, but there is no evidence that 20-hydroxyeicosatetraenoic acid (20-HETE) can be produced by this tissue. The purpose of present study was to determine whether glomeruli isolated from the kidney of rats can produce 20-HETE and whether the production of this metabolite is regulated by nitric oxide (NO) and dietary salt intake. Isolated glomeruli produced 20-HETE, dihydroxyeicosatrienoic acids, and 12-hydroxyeicosatetraenoic acid (4.13 +/- 0.38, 4.20 +/- 0.38, and 2. 10 +/- 0.20 pmol. min-1. mg protein-1, respectively) when incubated with arachidonic acid (10 microM). The formation of 20-HETE was dependent on the availability of NADPH and the PO2 of the incubation medium. The formation of 20-HETE was inhibited by NO donors in a concentration-dependent manner. The production of 20-HETE was greater in glomeruli isolated from the kidneys of rats fed a low-salt diet than in kidneys of rats fed a high-salt diet (5.67 +/- 0.32 vs. 2.83 +/- 0.32 pmol. min-1. mg protein-1). Immunoblot experiments indicated that the expression of P-450 4A protein in glomeruli from the kidneys of rats fed a low-salt diet was sixfold higher than in kidneys of rats fed a high-salt diet. These results indicate that arachidonic acid is primarily metabolized to 20-HETE and dihydroxyeicosatrienoic acids in glomeruli and that glomerular P-450 activity is modulated by NO and dietary salt intake.

Kinetic profile of the rat CYP4A isoforms: arachidonic acid metabolism and isoform-specific inhibitors

20-Hydroxyeicosatetraenoic acid (HETE), the cytochrome P-450 (CYP) 4A omega-hydroxylation product of arachidonic acid, has potent biological effects on renal tubular and vascular functions and on the control of arterial pressure. We have expressed high levels of the rat CYP4A1, -4A2, -4A3, and -4A8 cDNAs, using baculovirus and Sf 9 insect cells. Arachidonic acid omega- and omega-1-hydroxylations were catalyzed by three of the CYP4A isoforms; the highest catalytic efficiency of 947 nM-1. min-1 for CYP4A1 was followed by 72 and 22 nM-1. min-1 for CYP4A2 and CYP4A3, respectively. CYP4A2 and CYP4A3 exhibited an additional arachidonate 11,12-epoxidation activity, whereas CYP4A1 operated solely as an omega-hydroxylase. CYP4A8 did not catalyze arachidonic or linoleic acid but did have a detectable lauric acid omega-hydroxylation activity. The inhibitory activity of various acetylenic and olefinic fatty acid analogs revealed differences and indicated isoform-specific inhibition. These studies suggest that CYP4A1, despite its low expression in extrahepatic tissues, may constitute the major source of 20-HETE synthesis. Moreover, the ability of CYP4A2 and -4A3 to catalyze the formation of two opposing biologically active metabolites, 20-HETE and 11, 12-epoxyeicosatrienoic acid, may be of great significance to the regulation of vascular tone.

Effects of intrarenal infusion of 17-octadecynoic acid on renal antihypertensive mechanisms in anesthetized rabbits

To characterize the role of cytochrome P450 metabolism of fatty acids in the renal response to increased renal perfusion pressure, we tested the effects of renal arterial infusion of 17-octadecynoic acid (17-ODYA, 450 nmol/min) on renal and systemic hemodynamic, and renal excretory responses to step-wise increases in renal perfusion pressure (RPP) in anesthetized rabbits, using an extracorporeal circuit for renal autoperfusion. Inhibition of cytochrome P450-dependent fatty acid metabolism was estimated by comparing the metabolism of arachidonic acid in microsomes prepared from the kidneys of control and 17-ODYA-treated animals. Step-wise increases in RPP decreased mean arterial pressure, which previous studies have indicated is attributable to the release of a depressor hormone from the renal medulla. Elevations in RPP also increased renal blood flow and glomerular filtration rate, and the absolute and fractional excretions of urine and sodium. Intrarenal infusion of 17-ODYA reduced the metabolism of arachidonic acid to 20-hydroxyeicosatetraenoic acid by 41%, but it did not significantly influence the responses to increased renal perfusion pressure. We conclude that either the responses elicited by increased renal perfusion pressure in anesthetized rabbits do not depend on cytochrome P450-dependent fatty acid metabolism, or that cytochrome P450 activity must be inhibited by more than was achieved in the present study (41%), before functional effects on the response to increased renal perfusion pressure are observed.

Localization of cytochrome P-450 4A isoforms along the rat nephron

The expression of P-450 4A isoforms responsible for the formation of 20-hydroxyeicosatetraenoic acid (20-HETE) was examined using the reverse transcription and polymerase chain reaction in various nephron segments and preglomerular arterioles microdissected from the kidneys of Sprague-Dawley rats. Expression of cytochrome P-450 4A1, 4A2, 4A3, and 4A8 mRNA could be detected in RNA extracted from the whole kidney. The expression of P-450 4A1, 4A3, and 4A8 mRNA was similar in the kidney of male and female rats, whereas the expression of 4A2 mRNA was fourfold greater in the kidney of male vs. female rats. At the single-nephron level, P-450 4A1 mRNA could not be detected in either preglomerular arterioles or any nephron segments. P-450 4A2 mRNA was readily detected in preglomerular arterioles, glomeruli, proximal convoluted tubule (PCT), proximal straight tubule (PST), medullary thick ascending limb (MTAL), cortical thick ascending limb (CTAL), cortical collecting duct (CCD), outer medullary collecting duct (OMCD), and inner medullary collecting duct (IMCD). P-450 4A3 mRNA was also detected in every nephron segment, but the expression of this isoform was barely detectable in preglomerular arterioles. The expression of P-450 4A8 mRNA was detected in the glomerulus, PCT, PST, CTAL, and CCD. It was not detectable in preglomerular arterioles, MTAL, OMCD, or IMCD. Immunoblot analysis using a P-450 4A antibody exhibited a strong signal for P-450 4A protein in the proximal tubule. Smaller signals were also observed in glomerulus, MTAL, and preglomerular arterioles, but no signal could be detected in the IMCD. A similar pattern of P-450 4A protein expression was seen in kidney sections immunostained with this antibody. These results indicate that the expression of P-450 4A isoforms in the kidney of rats is sex dependent and that different P-450 4A isoforms are expressed throughout various nephron segments and the renal vasculature of rats.

Developmentally regulated expression of the CYP4A genes in the spontaneously hypertensive rat kidney

The CYP4A enzymes catalyze the formation of 20-hydroxyeicosatetraenoic acid (20-HETE), which has potent effects on the renal vasculature and tubular ion transport. Based on an increased 20-HETE formation in renal microsomes from spontaneously hypertensive rats, it has been proposed that increased expression of the CYP4A genes is an early event in the development of hypertension in these animals. To test this hypothesis, we developed RNase protection assays for specific detection of the individual CYP4A genes in the kidneys of spontaneously hypertensive and Wistar-Kyoto rats. Distinct age-dependent patterns of expression were observed for the individual CYP4A genes, with only CYP4A3 mRNA measurable in the kidneys of 1-week-old rats. CYP4A1 and CYP4A8 mRNA were detectable by 3 weeks of age and CYP4A2 mRNA at 5 weeks of age. The expression of CYP4A1 and CYP4A3 varied 4-5-fold throughout development and was highest between 3 and 5 weeks of age, declining steadily thereafter to 20% of their maximal level by 9 weeks of age. CYP4A2 mRNA levels increased steadily between 5 and 9 weeks of age, whereas CYP4A8 mRNA levels were relatively constant throughout development. The CYP4A3 mRNA level was significantly increased 1. 6-2-fold in the cortex and outer medulla of 1-4-week-old spontaneously hypertensive rat kidneys relative to the corresponding level in the Wistar-Kyoto. A similar 1.4-1.7-fold increase in CYP4A8 mRNA was also found in 3- and 4-week-old spontaneously hypertensive kidneys. Accompanying the increased expression of CYP4A3 and CYP4A8 mRNA in the prehypertensive rats were corresponding changes in functional CYP4A measured as either arachidonic acid or lauric acid omega-hydroxylase activity (1.4-2.0-fold increases) and CYP4A protein levels. After 4 weeks of age, the level of CYP4A mRNA, enzyme activity, and protein were similar in the kidneys of Wistar-Kyoto and spontaneously hypertensive rats. The findings suggest that the expression of CYP4A3 and CYP4A8 may be critical to the early changes in eicosanoid formation and renal function in the young spontaneously hypertensive rat.