Inhibition of renal arachidonic acid omega-hydroxylase activity with ABT reduces blood pressure in the SHR

P450-dependent arachidonic acid metabolism and angiotensin II-induced renal damage

Transgenic rats overexpressing both human renin and angiotensinogen genes (dTGR) develop hypertension, inflammation, and renal failure. We tested the hypothesis that these pathological features are associated with changes in renal P450-dependent arachidonic acid (AA) metabolism. Samples were prepared from 5- and 7-week-old dTGR and from normotensive Sprague-Dawley (SD) rats, ie, before and after the dTGR developed severe hypertension and albuminuria. At both stages, dTGR showed significantly lower renal microsomal AA epoxygenase and hydroxylase activities that reached 63% and 76% of the control values at week 7. Furthermore, the protein levels of several potential AA epoxygenases (CYP2C11, CYP2C23, and CYP2J) were significantly reduced. Immunoinhibition studies identified CYP2C23 as the major AA epoxygenase, both in dTGR and SD rats. Immunohistochemistry showed that CYP2C23 was localized in cortical and outer medullary tubules that progressively lost this enzyme from week 5 to week 7 in dTGR. CYP2C11 expression occurred only in the outer medullary tubules and was markedly reduced in dTGR compared with age-matched SD rats. These findings indicate site-specific decreases in the availability of AA epoxygenase products in the kidney of dTGR. In contrast to renal microsomes, liver microsomes of dTGR and SD rats showed no change in the expression and activity of AA epoxygenases and hydroxylases. We conclude that hypertension and end-organ damage in dTGR is associated with kidney-specific downregulation of P450-dependent AA metabolism. Because the products of AA epoxygenation have anti-inflammatory properties, this alteration may contribute to uncontrolled renal inflammation, which is a major cause of renal damage in dTGR.

Antihypertensive effect of mechanism-based inhibition of renal arachidonic acid omega-hydroxylase activity

The cytochrome P-450 eicosanoid 20-hydroxyeicosatetraenoic acid (20-HETE) is a potent vasoconstrictor that is implicated in the regulation of blood pressure. The identification of selective inhibitors of renal 20-HETE formation for use in vivo would facilitate studies to determine the systemic effects of this eicosanoid. We characterized the acetylenic fatty acid sodium 10-undecynyl sulfate (10-SUYS) as a potent and selective mechanism-based inhibitor of renal 20-HETE formation. A single dose of 10-SUYS caused an acute reduction in mean arterial blood pressure in 8-wk-old spontaneously hypertensive rats. The decrease in mean arterial pressure was maximal 6 h after 10-SUYS treatment (17.9 +/- 3.2 mmHg; P < 0.05), and blood pressure returned to baseline levels within 24 h after treatment. Treatment with 10-SUYS was associated with a decrease in urinary 20-HETE formation in vivo and attenuation of the vasoconstrictor response of renal interlobar arteries to ANG II in vitro. These results provide further evidence that 20-HETE plays an important role in the regulation of blood pressure in the spontaneously hypertensive rat.

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.

Renal 20-hydroxyeicosatetraenoic acid synthesis during pregnancy

We examined whether renal 20-hydroxyeicosatetraenoic acid (20-HETE) synthesis is altered during gestation. Renal microsomal arachidonic acid omega-hydroxylase activity increased by 50 and 48% in rats on days 12 and 19 of gestation, respectively. Renal microvessel 20-HETE synthesis increased by 50 and 82% in rats on days 6 and 12 of gestation, respectively, and returned to control levels at day 19 of gestation. In contrast, 20-HETE synthesis in isolated medullary thick ascending limb was unchanged from control levels on days 6 and 12 of gestation, but it increased twofold on day 19 of gestation. This increase on day 19 of gestation was associated with a twofold increase in urinary 20-HETE excretion, and it coincided with a 23-mmHg fall in blood pressure. Moreover, change in the rate of 20-HETE synthesis in microvessels was consistent with the level of expression of cytochrome P450 (CYP)4A proteins. Administration of the CYP4A inhibitor 1-aminobenzotriazole (ABT) for 2 days on day 12 of pregnancy or for 5 days starting on day 15 of pregnancy caused a transient but significant reduction in systolic blood pressure. ABT treatment also decreased urinary sodium, urinary 20-HETE, and renal and microvessel 20-HETE synthesis. This study, to our knowledge, is the first to demonstrate that 20-HETE synthesis in the kidney is altered in time- and site-specific manners during pregnancy. The localized pattern of changes suggests that there are distinct regulatory mechanisms for 20-HETE synthesis in the kidney during pregnancy.

Functional significance of activation of calcium/calmodulin-dependent protein kinase II in angiotensin II--induced vascular hyperplasia and hypertension

We have reported that norepinephrine (NE) and angiotensin II (Ang II) increase CaM kinase II activity, which, in turn, activates cytosolic phospholipase A(2) (PLA(2)) and releases arachidonic acid. The products of arachidonic acid generated via cytochrome P-450 and lipoxygenase contribute to the development of hypertension and vascular smooth muscle cell (VSMC) hyperplasia. The purpose of this study was to investigate whether CaM kinase II contributes to VSMC proliferation elicited by NE and Ang II and to hypertension induced by Ang II. NE (1 micromol/L) and Ang II (1 micromol/L) increased proliferation of rabbit aortic VSMC as measured by increased [(3)H]-thymidine incorporation; this effect of NE and Ang II was attenuated 88 +/- 10% and 64 +/- 11% by the CaM kinase II inhibitor KN-93, respectively. Infusion of Ang II with miniosmotic pumps (350 ng/min for 6 days) in rats elevated mean arterial pressure (MABP), which was reduced by simultaneous infusion of KN-93 (578 ng/min, for 6 days) (Ang II alone: MABP =174 +/- 3 mm Hg, n=12 versus Ang II + KN-93: MABP 123 +/- 5 mm Hg, n=4, P<0.05). Administration of KN-93 as a single bolus injection (16 mg/Kg), but not its vehicle, in Ang II--infused hypertensive animals also decreased MABP from 179 +/- 9 mm Hg to 109 +/- 6 mm Hg (n=5, P<0.05). CaM kinase II activity was increased in the kidney of Ang II--infused hypertensive animals compared with normotensive controls. Treatment with KN-93 reduced CaM kinase II activity and ameliorated the intravascular injury in the kidneys of Ang II--infused hypertensive rats. Our data indicate that CaM kinase activation represents an important component of the mechanism(s) initiating VSMC proliferation and the development and maintenance of Ang II--induced hypertension in rat.

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.

Modulation by 20-HETE of phenylephrine-induced mesenteric artery contraction in spontaneously hypertensive and Wistar-Kyoto rats

Small mesenteric arteries of spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY) were compared for the production of 20-HETE and the effects of 20-HETE and N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS, 30 micromol/L), a 20-HETE synthesis inhibitor, on contractile responsiveness to phenylephrine (0.1 to 50.0 micromol/L). 20-HETE production was higher in vessels of SHR compared with WKY (1.34+/-0.16 versus 0.27+/-0.09 pmol/mg tissue, P<0.05). Phenylephrine elicited concentration-dependent vascular contraction; the R(max) was similar in vessels of SHR and WKY, but the former were more sensitive as denoted by the lower EC(50) (1.10+/-0.14 versus 1.89+/-0.33 micromol/L, P<0.05). DDMS caused a rightward shift in the concentration-response curve to phenylephrine, increasing (P<0.05) the EC(50) by 258% and 134% in vessels of SHR and WKY, respectively. In contrast, in DDMS-treated vessels, 20-HETE (0.01 to 10.0 micromol/L) caused a leftward shift in the phenylephrine concentration-response curve, decreasing (P<0.05) the EC(50) without affecting the R(max). Importantly, the minimal concentration of 20-HETE that decreased the EC(50) of phenylephrine was much smaller in vessels of SHR that of WKY (0.01 versus 1.0 micromol/L). We conclude that 20-HETE increases the sensitivity of mesenteric arterial vessels to phenylephrine, vessels of SHR are more sensitive to this action of the eicosanoid than vessels of WKY, and vessels of SHR produce more 20-HETE than do vessels of WKY. Hence, 20-HETE of vascular origin may be a determinant of the increased reactivity to constrictor agonists in the vasculature of SHR.

Cytochrome p450 and vascular homeostasis

Since the initial reports that renal cytochrome P450 (CYP) enzymes can metabolize arachidonic acid to substances which affect arterial tone, it has become increasingly clear that CYP enzymes expressed within the cardiovascular system play a crucial role in the modulation of vascular homeostasis. There is strong evidence suggesting that the activation of a CYP epoxygenase in endothelial cells is an essential step in nitric oxide and prostacyclin-independent vasodilatation of several vascular beds, particularly in the heart and kidney. A smooth muscle CYP omega-hydroxylase, on the other hand, generates a vasoconstrictor eicosanoid that is central to the myogenic response. Moreover, CYP epoxygenase and omega-hydroxylase products, as well as CYP-derived reactive oxygen species, are intracellular signal transduction molecules involved in several signaling cascades affecting numerous cellular processes, including vascular cell proliferation and angiogenesis. This review summarizes the vascular effects of epoxyeicosatrienoic acids and 20-hydroxyeicosatetraenoic acid, both of which are CYP-derived metabolites of arachidonic acid, endogenously generated within endothelial and vascular smooth muscle cells. Although the link between CYP expression/activity and cardiovascular disease is currently tentative, the evidence being accumulated to suggest that CYP pathways are altered in animal models of hypertension and atherosclerosis can no longer be ignored. The development of selective pharmacological tools is, however, a prerequisite for the analysis of the involvement of specific CYP isoforms in the regulation of vascular homeostasis in human subjects.

Role of guanylyl cyclase and cytochrome P-450 on renal response to nitric oxide

The present study evaluated whether inhibition of guanylyl cyclase (GC) with 1H-(1,2,4)oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) and methylene blue (MB) or inhibition of the renal metabolism of arachidonic acid by cytochrome P-450 (CYP450) enzymes with 1-aminobenzotriazole (ABT) and N-hydroxy-N'-(4 butyl-2-methyl phenyl)formamidine (HET0016) alters the renal tubular and vascular effects of a nitric oxide (NO) donor in vivo. Intrarenal infusion of ODQ or MB at a dose of 170 nmol. kg(-1). min(-1) lowered renal blood flow (RBF) by 30 and 15%, respectively; glomerular filtration rate (GFR) by 26 and 18%, respectively; and sodium and water excretion by approximately 35%. In rats pretreated with nitro-L-arginine methyl ester (37 nmol. kg(-1). min(-1)) to block the endogenous production of NO, intrarenal infusion of the NO donor S-nitroso-N-acetylcysteine (S-NO-NAC; 50 nmol. kg(-1). min(-1)) increased RBF (18%), sodium (73%), and water excretion (61%). ODQ or MB administration blocked the effect of S-NO-NAC on RBF but not the diuretic and natriuretic response. Pretreatment of rats with ABT or HET0016 also abolished the renal vasodilatory response to the NO donor and reduced its diuretic and natriuretic effect. These results indicate that both activation of GC and inhibition of CYP450 enzymes contribute to the renal vascular actions of NO, whereas the natriuretic and diuretic actions of NO appear to be largely CYP450 dependent.

HET0016, a potent and selective inhibitor of 20-HETE synthesizing enzyme

The present study examined the inhibitory effects of N-hydroxy-N'-(4-butyl-2-methylphenyl)-formamidine (HET0016) on the renal metabolism of arachidonic acid by cytochrome P450 (CYP) enzymes. HET0016 exhibited a high degree of selectivity in inhibiting the formation of 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE) in rat renal microsomes. The IC(50) value averaged 35+/-4 nM, whereas the IC(50) value for inhibition of the formation of epoxyeicosatrienoic acids by HET0016 averaged 2800+/-300 nM. In human renal microsomes, HET0016 potently inhibited the formation of 20-HETE with an IC(50) value of 8.9+/-2.7 nM. Higher concentrations of HET0016 also inhibited the CYP2C9, CYP2D6 and CYP3A4-catalysed substrates oxidation with IC(50) values of 3300, 83,900 and 71,000 nM. The IC(50) value for HET0016 on cyclo-oxygenase activity was 2300 nM. These results indicate that HET0016 is a potent and selective inhibitor of CYP enzymes responsible for the formation of 20-HETE in man and rat.

Alterations in the regulation of androgen-sensitive Cyp 4a monooxygenases cause hypertension

Hypertension is a leading cause of cardiovascular, cerebral, and renal disease morbidity and mortality. Here we show that disruption of the Cyp 4a14 gene causes hypertension, which is, like most human hypertension, more severe in males. Male Cyp 4a14 (-/-) mice show increases in plasma androgens, kidney Cyp 4a12 expression, and the formation of prohypertensive 20-hydroxyarachidonate. Castration normalizes the blood pressure of Cyp 4a14 (-/-) mice and minimizes Cyp 4a12 expression and arachidonate omega-hydroxylation. Androgen replacement restores hypertensive phenotype, Cyp 4a12 expression, and 20-hydroxy-arachidonate formation. We conclude that the androgen-mediated regulation of Cyp 4a arachidonate monooxygenases is an important component of the renal mechanisms that control systemic blood pressures. These results provide direct evidence for a role of Cyp 4a isoforms in cardiovascular physiology, establish Cyp 4a14 (-/-) mice as a monogenic model for the study of cause/effect relationships between blood pressure, sex hormones, and P450 omega-hydroxylases, and suggest the human CYP 4A homologues as candidate genes for the analysis of the genetic and molecular basis of human hypertension.

Epoxyeicosatrienoic acid-mediated renal vasodilation to arachidonic acid is enhanced in SHR

We tested the hypothesis that cyclooxygenase-independent vasodilation produced by arachidonic acid (AA) is mediated by epoxyeicosatrienoic acids (EETs) and is blunted in the spontaneously hypertensive rat (SHR). At normal perfusion pressure (PP; 70 to 90 mm Hg), AA constricted the renal vasculature in both SHR and normotensive Wistar-Kyoto rats, an effect abolished by cyclooxygenase inhibition, and converted to vasodilation when PP was raised to approximately 200 mm Hg. Unexpectedly, renal vasodilation elicited by AA was greater in the SHR at high PP; for example, 2.5, 5, and 10 microg of AA produced PP declines of 54+/-9, 92+/-10, and 112+/-5 mm Hg, respectively, in SHR compared with 26+/-3, 45+/-5, and 77+/-6 mm Hg in Wistar-Kyoto rats (P:<0.01). However, the renal vasodilator responses to acetylcholine (0.1 microg) and sodium nitroprusside (1 microg) did not differ between strains, indicating that vascular responsiveness to AA was independent of intrinsic changes in vascular smooth muscle. Hyperresponsiveness of the renal vasculature to AA may be unique for the SHR, because it did not occur in Sprague-Dawley rats with angiotensin II-induced hypertension. 5,8,11,14-Eicosatetraynoic acid (ETYA; 4 micromol/L), an inhibitor of all AA pathways, attenuated the vasodilator responses to AA, as did treatment with stannous chloride, which depletes cytochrome P450 enzymes, suggesting that a cytochrome P450 AA metabolite mediated the renal vasodilation. N:-Methylsulfonyl-12,12-dibromododec-11-en-amide (DDMS; 2 micromol/L), a selective omega-hydroxylase inhibitor, did not affect AA-induced vasodilation, whereas selective inhibition of epoxygenases with either miconazole (0.3 micromol/L) or N:-methylsulfonyl-6-(2-propargyloxyphenyl) hexanamide (MS-PPOH; 12 micromol/L) did, indicating that one or more EETs were involved in the renal vasodilator action of AA at high PP. This conclusion was supported by the demonstration that AA greatly enhanced the renal efflux of EETs at high PP but not at basal PP.

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.

Soluble epoxide hydrolase regulates hydrolysis of vasoactive epoxyeicosatrienoic acids

The cytochrome P450-derived epoxyeicosatrienoic acids (EETs) have potent effects on renal vascular reactivity and tubular sodium and water transport; however, the role of these eicosanoids in the pathogenesis of hypertension is controversial. The current study examined the hydrolysis of the EETs to the corresponding dihydroxyeicosatrienoic acids (DHETs) as a mechanism for regulation of EET activity and blood pressure. EET hydrolysis was increased 5- to 54-fold in renal cortical S9 fractions from the spontaneously hypertensive rat (SHR) relative to the normotensive Wistar-Kyoto (WKY) rat. This increase was most significant for the 14,15-EET regioisomer, and there was a clear preference for hydrolysis of 14, 15-EET over the 8,9- and 11,12-EETs. Increased EET hydrolysis was consistent with increased expression of soluble epoxide hydrolase (sEH) in the SHR renal microsomes and cytosol relative to the WKY samples. The urinary excretion of 14,15-DHET was 2.6-fold higher in the SHR than in the WKY rat, confirming increased EET hydrolysis in the SHR in vivo. Blood pressure was decreased 22+/-4 mm Hg (P:<0.01) 6 hours after treatment of SHRs with the selective sEH inhibitor N:, N:'-dicyclohexylurea; this treatment had no effect on blood pressure in the WKY rat. These studies identify sEH as a novel therapeutic target for control of blood pressure. The identification of a potent and selective inhibitor of EET hydrolysis will be invaluable in separating the vascular effects of the EET and DHET eicosanoids.

Cytochrome P450-dependent renal arachidonic acid metabolism in desoxycorticosterone acetate-salt hypertensive mice

Cytochrome P450 (P450)-dependent arachidonic acid metabolites may act as mediators in the regulation of vascular tone and renal function. We studied arachidonic acid hydroxylase activities in renal microsomes from normotensive NMRI mice, desoxycorticosterone acetate (DOCA)-salt hypertensive mice, and DOCA-salt mice treated with either lovastatin or bezafibrate, both of which improve hemodynamics in this model. Control renal microsomes had arachidonic acid hydroxylase activities of 175+/-12 pmol. min(-1). mg(-1). The metabolites formed were 20- and 19-hydroxyarachidonic acid, representing approximately 80% and approximately 20% of the total hydroxylation. Treatment with DOCA-salt resulted in significantly decreased hydroxylase activities (to 84+/-4 pmol. min(-1). mg(-1)) of the total microsomal P450 content and a decrease in immunodetectable Cyp4a proteins. Lovastatin had no effect on these variables, whereas bezafibrate increased arachidonic acid hydroxylase activities to 163+/-12 pmol. min(-1). mg(-1). In situ hybridization with probes for Cyp4a-10, 12, and 14 revealed that Cyp4a-14 was the P450 isoform most strongly induced by bezafibrate. The expression was concentrated in the cortical medullary junction and was localized predominantly in the proximal tubules. In conclusion, these results suggest that the capacity to produce 20-hydroxyarachidonic acid is impaired in the kidneys of DOCA-salt hypertensive mice. Furthermore, bezafibrate may ameliorate hemodynamics in this model by restoring P450-dependent arachidonic acid hydroxylase activities. Lovastatin, on the other hand, exerts its effects via P450-independent mechanisms.

Angiotensin II-induced hypertension: contribution of Ras GTPase/Mitogen-activated protein kinase and cytochrome P450 metabolites

We reported that norepinephrine and angiotensin II (Ang II) activate the Ras/mitogen-activated protein (MAP) kinase pathway primarily through the generation of cytochrome P450 (CYP450) metabolites. The purpose of the present study was to determine the contribution of Ras and CYP450 to Ang II-dependent hypertension in rats. Infusion of Ang II (350 ng/min for 6 days) elevated mean arterial blood pressure (MABP) (171+/-3 mm Hg for Ang II versus 94+/-5 for vehicle group, P<0.05). Ras is activated on farnesylation by farnesyl protein transferase (FPT). When Ang II was infused in combination with FPT inhibitor FPT III (232 ng/min) or BMS-191563 (578 ng/min), the development of hypertension was attenuated (171+/-3 mm Hg for Ang II plus vehicle versus 134+/-5 mm Hg for Ang II plus FPT III and 116+/-6 mm Hg for Ang II plus BMS-191563, P<0.05). Treatment with the MAP kinase kinase inhibitor PD-98059 (5 mg SC) reduced MABP. The CYP450 inhibitor aminobenzotriazole (50 mg/kg) also diminished the development of Ang II-induced hypertension to 113+/-8 mm Hg. The activities of Ras, MAP kinase, and CYP450 measured in the kidney were elevated in hypertensive animals. The infusion of FPT III, BMS-191563, or aminobenzotriazole reduced the elevation in Ras and MAP kinase activity. Morphological studies of the kidney showed that FPT III treatment ameliorated the arterial injury, vascular lesions, fibrinoid necrosis, focal hemorrhage, and hypertrophy of muscle walls observed in hypertensive animals. These data suggest that the activation of Ras and CYP450 contributes to the development of Ang II-dependent hypertension and associated vascular pathology.

Fluorescent HPLC assay for 20-HETE and other P-450 metabolites of arachidonic acid

This study describes a fluorescent HPLC assay for measuring 20-hydroxyeicosatetraenoic acid (20-HETE) and other cytochrome P-450 metabolites of arachidonic acid in urine, tissue, and interstitial fluid. An internal standard, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid, was added to samples, and the lipids were extracted and labeled with 2-(2,3-naphthalimino)ethyl trifluoromethanesulfonate. P-450 metabolites were separated on a C18 reverse-phase HPLC column. Coelution and gas chromatography-mass spectrometry studies confirmed the identity of the 20-HETE peak. The 20-HETE peak can be separated from those for dihydroxyeicosatrienoic acids, other HETEs, and epoxyeicosatrienoic acids. Known amounts of 20-HETE were used to generate a standard curve (range 1-10 ng, r(2) = 0.98). Recovery of 20-HETE from urine averaged 95%, and the intra-assay variation was <5%. Levels of 20-HETE were measured in 100 microliter of urine and renal interstitial fluid or 0.1 mg of renal tissue. The assay was evaluated by studying the effects of 1-aminobenzotriazole (ABT) on the excretion of 20-HETE in rats. ABT reduced excretion of 20-HETE by >65% and inhibited the formation of 20-HETE by renal microsomes. The availability of this assay should facilitate work in this field.

Contribution of Ras GTPase/MAP kinase and cytochrome P450 metabolites to deoxycorticosterone-salt-induced hypertension

We recently reported that norepinephrine and angiotensin II activate the Ras/mitogen-activated protein (MAP) kinase pathway through generation of a cytochrome P450 (CYP450) and lipoxygenase metabolites. The purpose of this study was to determine the contribution of Ras/MAP kinase to deoxycorticosterone acetate (DOCA)-salt-induced hypertension in rats. Administration of DOCA and 1% saline drinking water to uninephrectomized rats for 6 weeks significantly elevated mean arterial blood pressure (MABP) (166+/-5 mm Hg, n=19) compared with that of normotensive controls (95+/-5 mm Hg, n=7) (P<0.05). The activity of Ras and MAP kinase measured in the heart was increased in DOCA-salt hypertensive rats. Infusion of the Ras farnesyl transferase inhibitors FPT III (138 ng/min) and BMS-191563 (694 ng/min) significantly (P<0.05) attenuated MABP to 139+/-4 mm Hg (n=14) and 126+/-1 mm Hg (n=4), respectively. Moreover, infusion of MAP kinase kinase inhibitor PD-98059 (694 ng/min) also reduced MABP in hypertensive rats. Morphological studies of the kidney showed that treatment of rats with FPT III, which reduced Ras activity, minimized the hyperplastic occlusive arteriosclerosis and fibrinoid vasculitis observed in untreated hypertensive rats. In addition, the rise in CYP450 activity and MABP in hypertensive rats was prevented by the CYP450 inhibitor aminobenzotriazole (50 mg/kg) and was associated with a decrease in Ras and MAP kinase activity in the heart. These data suggest that the Ras/MAP kinase pathway contributes to DOCA-salt-induced hypertension and associated vascular pathology consequent to activation of CYP450.