Missing links: Cytochrome P450 arachidonate products

Overexpression of Human Soluble Epoxide Hydrolase Exacerbates Coronary Reactive Hyperemia Reduction in Angiotensin-II-Treated Mouse Hearts

ABSTRACT

Coronary reactive hyperemia (CRH) is impaired in cardiovascular diseases, and angiotensin-II (Ang-II) exacerbates it. However, it is unknown how Ang-II affects CRH in Tie2-sEH Tr (human-sEH-overexpressed) versus wild-type (WT) mice. sEH-overexpression resulted in CRH reduction in Tie2-sEH Tr versus WT. We hypothesized that Ang-II exacerbates CRH reduction in Tie2-sEH Tr versus WT. The Langendorff system measured coronary flow in Tie2-sEH Tr and WT. The hearts were exposed to 15-second ischemia, and CRH was assessed in 10 mice each. Repayment volume was reduced by 40.50% in WT treated with Ang-II versus WT (7.42 ± 0.8 to 4.49 ± 0.8 mL/g) and 48% in Tie2-sEH Tr treated with Ang-II versus Tie2-sEH Tr (5.18 ± 0.4 to 2.68 ± 0.3 mL/g). Ang-II decreased repayment duration by 50% in WT-treated with Ang-II versus WT (2.46 ± 0.5 to 1.24 ± 0.4 minutes) and 54% in Tie2-sEH Tr treated with Ang-II versus Tie2-sEH Tr (1.66 ± 0.4 to 0.76 ± 0.2 minutes). Peak repayment flow was reduced by 11.2% in WT treated with Ang-II versus WT (35.98 ± 0.7 to 32.11 ± 1.4 mL/g) and 4% in Tie2-sEH Tr treated with Ang-II versus Tie2-sEH Tr (32.18 ± 0.6 to 30.89 ± 1.5 mL/g). Furthermore, coronary flow was reduced by 43% in WT treated with Ang-II versus WT (14.2 ± 0.5 to 8.15 ± 0.8 mL/min/g) and 32% in Tie2-sEH Tr treated with Ang-II versus Tie2-sEH Tr (12.1 ± 0.8 to 8.3 ± 1.2 mL/min/g). Moreover, the Ang-II-AT 1 -receptor and CYP4A were increased in Tie2-sEHTr. Our results demonstrate that Ang-II exacerbates CRH reduction in Tie2-sEH Tr mice.

Angiotensin II stimulation alters vasomotor response to adenosine in mouse mesenteric artery: role for A1 and A2B adenosine receptors

BACKGROUND AND PURPOSE

Stimulation of the A1 adenosine receptor and angiotensin II receptor type-1 (AT1 receptor) causes vasoconstriction through activation of cytochrome P450 4A (CYP4A) and ERK1/2. Thus, we hypothesized that acute angiotensin II activation alters the vasomotor response induced by the non-selective adenosine receptor agonist, NECA, in mouse mesenteric arteries (MAs).

EXPERIMENTAL APPROACH

We used a Danish Myo Technology wire myograph to measure muscle tension in isolated MAs from wild type (WT), A1 receptor and A2B receptor knockout (KO) mice. Western blots were performed to determine the expression of AT1 receptors and CYP4A.

KEY RESULTS

Acute exposure (15 min) to angiotensin II attenuated the NECA-dependent vasodilatation and enhanced vasoconstriction. This vasoconstrictor effect of angiotensin II in NECA-treated MAs was abolished in A1 receptor KO mice and in WT mice treated with the A1 receptor antagonist DPCPX, CYP4A inhibitor HET0016 and ERK1/2 inhibitor PD98059. In MAs from A2B receptor KO mice, the vasoconstrictor effect of angiotensin II on the NECA-induced response was shown to be dependent on A1 receptors. Furthermore, in A2B receptor KO mice, the expression of AT1 receptors and CYP4A was increased and the angiotensin II-induced vasoconstriction enhanced. In addition, inhibition of KATP channels with glibenclamide significantly reduced NECA-induced vasodilatation in WT mice.

CONCLUSIONS AND IMPLICATIONS

Acute angiotensin II stimulation enhanced A1 receptor-dependent vasoconstriction and inhibited A2B receptor-dependent vasodilatation, leading to a net vasoconstriction and altered vasomotor response to NECA in MAs. This interaction may be important in the regulation of BP.

Contribution of Ras farnesyl transferase, MAP kinase and cytochrome P-450 metabolites to endothelin-1 induced hypertension

Endothelin 1 (ET-1) is vasoactive peptide that acts via ET-A receptors coupling inducing vascular smooth muscle cell proliferation and contraction. ET-1 is involved in the development and maintenance of hypertension. Aim of this study was to determine the contribution of Ras farnesyl transferase, mitogen activated protein kinase (MAP kinase) and cytochrome P¬450 (CYP450) metabolites to ET-1 induced hypertension. ET-1 (5 pmol/kg per minute) was chronically infused into to the jugular vein by use of mini-osmotic pump for 9 days in male Sprague-Dawley rats. Mean arterial blood pressure (MABP) in ET-1-treated rats was 154±2 mm Hg (hypertensive rats) compared with 98±3 mm Hg in control (normotensive) rats. Infusion of Ras farnesyl transferase inhibitor FPTIII (138 ng/min), MAP kinase inhibitor PD-98059 (694 ng/min) and CYP450 inhibitor 17-ODYA (189 ng/min) significantly attenuated MABP to 115±2.5 mm Hg, 109±3 mm Hg and 118±1.5 mm Hg, respectively. These results suggest that CYP-450 metabolites and Ras/MAP kinase pathway contribute to the development of ET-1 induced hypertension. Further investigation has to be done to confirm whether activation of RAS/MAP kinase pathway by arachidonic acid metabolites plays an important role in the development of ET-1 induced hypertension.

Endothelin-1 induced vascular smooth muscle cell proliferation is mediated by cytochrome p-450 arachidonic acid metabolites

Endothelins (ETs) are a family of three peptides (ET-1, ET-2, ET-3) that are implicated in the physiological control of vascular smooth muscle cell (VSMC) and myocardial contractility and growth. ET-1 is vasoactive peptide that acts via ET-A receptors coupling inducing vascular smooth muscle cell contraction. ET-1 is involved in the development and maintenance of hypertension. Aim of this study was to investigate whether ET-1 can induce vascular smooth muscle cell proliferation through arachidonic acid (AA) metabolites formed via cytochrome P¬450 (CYP-450). VSMC proliferation was measured by [3H]thymidine incorporation in cultured cells treated by ET-1 (10 to l00 nmol/L) in presence of different inhibitors of CYP-450 (17-ODYA 5 μmol/L), lipoxygenase (LO) (baicalein 20 μmol/L) and cyclooxygenase (COX) (indomethacin 5 μmol/L). ET-1 (10 to 100 nmol/L) induced VSMC proliferation and this effect was attenuated by CYP-450 inhibitor (17-ODYA) and lipoxygenase (LO) inhibitor (baicalein) but not by cyclooxygenase (COX) inhibitor (indomethacin). CYP-450 and LO metabolites of AA, 20-hydroxyeicosatetraenoic acid (HETE) and 12-HETE increased [3H]thymidine incorporation in VSMC. Inhibitors of MAP kinase (PD-98059 50 μmol/L) and cPLA2 (MAFP 50 μmol/L) attenuated ET-1 as well as 20-HETE induced VSMC proliferation. These results suggest AA metabolites via CYP-450 mediates ET-1 induce VSMC proliferation.

Endothelium-derived hyperpolarizing factor: is there a novel chemical mediator?

1. Endothelium-derived hyperpolarization (EDH) has been reported in many vessels and an extensive literature suggests that a novel, non-nitric oxide and non-prostanoid, endothelium-derived factor(s) may be synthesized in endothelial cells. 2. The endothelium-dependent hyperpolarizing factor, or EDHF, is synthesized by the putative EDHF synthase and mediates its cellular effects by either, directly or indirectly, opening K channels on vascular smooth muscle cells or, via hyperpolarization of the endothelial cell, by facilitating electrical coupling between the endothelial and the vascular smooth muscle cell. 3. The question of the chemical identity of EDHF has received considerable attention; however, no consensus has been reached. Tissue and species heterogeneity exists that may imply there are multiple EDHF. Leading candidate molecules for EDHF include an arachidonic acid product, possibly an epoxygenase product, or an endogenous cannabinoid, or simply an increase in extracellular K+. 4. An increasing body of evidence suggests that EDH, notably in the resistance vasculature, may be mediated via electrical coupling through myoendothelial gap junctions and the existence of electrical coupling may negate the need to hypothesize the existence of a true endothelium-derived chemical mediator. 5. In this paper we review the evidence that supports and refutes the existence of a novel EDHF versus a hyperpolarization event mediated solely by myoendothelial gap junctions.

Optimized thiol derivatizing reagent for the mass spectral analysis of disubstituted epoxy fatty acids

A novel procedure is described for the derivatization of fatty acid epoxides in the presence of their corresponding diols. The acidic character of 2,3,5,6-tetrafluorobenzenethiol promotes favorable mass fragmentation of linoleate and arachidonate derived epoxide derivatives and reduces alkene isomerization to a manageable side reaction, eliminated through the addition of a thiol scavenger. After silylation, regioisomeric mixtures of epoxy- and dihydroxylipids are simultaneously detected and discriminated using gas chromatography with electron impact mass spectral detection. Silylated hydroxysulfanyloctadecanoids yielded instrumental detection limits of 5 pg/microl, sufficient sensitivity for the quantification of endogenous epoxylipids.

Endothelium-derived relaxing factors: A focus on endothelium-derived hyperpolarizing factor(s)

Endothelium-derived hyperpolarizing factor (EDHF) is defined as the non-nitric oxide (NO) and non-prostacyclin (PGI2) substance that mediates endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells (VSMC). Although both NO and PGI2 have been demonstrated to hyperpolarize VSMC by cGMP- and cAMP-dependent mechanisms, respectively, and in the case of NO by cGMP-independent mechanisms, a considerable body of evidence suggests that an additional cellular mechanism must exist that mediates EDH. Despite intensive investigation, there is no agreement as to the nature of the cellular processes that mediates the non-NO/PGI2 mediated hyperpolarization. Epoxyeicosatrienoic acids (EET), an endogenous anandamide, a small increase in the extracellular concentration of K+, and electronic coupling via myoendothelial cell gap junctions have all been hypothesized as contributors to EDH. An attractive hypothesis is that EDH is mediated via both chemical and electrical transmissions, however, the contribution from chemical mediators versus electrical transmission varies in a tissue- and species-dependent manner, suggesting vessel-specific specialization. If this hypothesis proves to be correct then the potential exists for the development of vessel and organ-selective vasodilators. Because endothelium-dependent vasodilatation is dysfunctional in disease states (i.e., atherosclerosis), selective vasodilators may prove to be important therapeutic agents.Key words: endothelium, nitric oxide, potassium channels, hyperpolarization, gap junctions.

Evaluation of fish models of soluble epoxide hydrolase inhibition

Substituted ureas and carbamates are mechanistic inhibitors of the soluble epoxide hydrolase (sEH). We screened a set of chemicals containing these functionalities in larval fathead minnow (Pimphales promelas) and embryo/larval golden medaka (Oryzias latipes) models to evaluate the utility of these systems for investigating sEH inhibition in vivo. Both fathead minnow and medaka sEHs were functionally similar to the tested mammalian orthologs (murine and human) with respect to substrate hydrolysis and inhibitor susceptibility. Low lethality was observed in either larval or embryonic fish exposed to diuron [N-(3,4-dichlorophenyl), N'-dimethyl urea], desmethyl diuron [N-(3,4-dichlorophenyl), N'-methyl urea], or siduron [N-(1-methylcyclohexyl), N'-phenyl urea]. Dose-dependent inhibition of sEH was a sublethal effect of substituted urea exposure with the potency of siduron < desmethyl diuron = diuron, differing from the observed in vitro sEH inhibition potency of siduron > desmethyl diuron > diuron. Further, siduron exposure synergized the toxicity of trans-stilbene oxide in fathead minnows. Medaka embryos exposed to diuron, desmethyl diuron, or siduron displayed dose-dependent delays in hatch, and elevated concentrations of diuron and desmethyl diuron produced developmental toxicity. The dose-dependent toxicity and in vivo sEH inhibition correlated, suggesting a potential, albeit undefined, relationship between these factors. Additionally, the observed inversion of in vitro to in vivo potency suggests that these fish models may provide tools for investigating the in vivo stability of in vitro inhibitors while screening for untoward effects.

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.

Cress and potato soluble epoxide hydrolases: purification, biochemical characterization, and comparison to mammalian enzymes

Affinity chromatographic methods were developed for the one-step purification to homogeneity of recombinant soluble epoxide hydrolases (sEHs) from cress and potato. The enzymes are monomeric, with masses of 36 and 39 kDa and pI values of 4.5 and 5.0, respectively. In spite of a large difference in sequence, the two plant enzymes have properties of inhibition and substrate selectivity which differ only slightly from mammalian sEHs. Whereas mammalian sEHs are highly selective for trans- versus cis-substituted stilbene oxide and 1,3-diphenylpropene oxide (DPPO), plant sEHs exhibit far greater selectivity for trans- versus cis-stilbene oxide, but little to no selectivity for DPPO isomers. The isolation of a covalently linked plant sEH-substrate complex indicated that the plant and mammalian sEHs have a similar mechanism of action. We hypothesize an in vivo role for plant sEH in cutin biosynthesis, based on relatively high plant sEH activity on epoxystearate to form a cutin precursor, 9,10-dihydroxystearate. Plant sEHs display a high thermal stability relative to mammalian sEHs. This stability and their high enantioselectivity for a single substrate suggest that their potential as biocatalysts for the preparation of enantiopure epoxides should be evaluated.

Biochemical characterization of rat P450 2C11 fused to rat or bacterial NADPH-P450 reductase domains

cDNAs coding for rat P450 2C11 fused to either a bacterial (the NADPH-cytochrome P450 BM3 reductase domain of P450 BM3) or a truncated form of rat NADPH-P450 reductases were expressed in Escherichia coli and characterized enzymatically. Measurements of NADPH cytochrome c reductase activity showed fusion-dependent increases in the rates of cytochrome c reduction by the bacterial or the mammalian flavoprotein (21 and 48%, respectively, of the rates observed with nonfused enzymes). Neither the bacterial flavoprotein nor the truncated rat reductase supported arachidonic acid metabolism by P450 2C11. In contrast, fusion of P450 2C11 to either reductase yielded proteins that metabolized arachidonic acid to products similar to those obtained with reconstituted systems containing P450 2C11 and native rat P450 reductase. Addition of a 10-fold molar excess of rat P450 reductase markedly increased the rates of metabolism by both fused and nonfused P450s 2C11. These increases occurred with preservation of the regioselectivity of arachidonic acid metabolism. The fusion-independent reduction of P450 2C11 by bacterial P450 BM3 reductase was shown by measurements of NADPH-dependent H(2)O(2) formation [73 +/- 10 and 10 +/- 1 nmol of H(2)O(2) formed min(-)(1) (nmol of P450)(-)(1) for the reconstituted and fused protein systems, respectively]. These studies demonstrate that (a) a self-sufficient, catalytically active arachidonate epoxygenase can be constructed by fusing P450 2C11 to mammalian or bacterial P450 reductases and (b) the P450 BM3 reductase interacts efficiently with mammalian P450 2C11 and catalyzes the reduction of the heme iron. However, fusion is required for metabolism and product formation.

TCDD induces CYP1A4 and CYP1A5 in chick liver and kidney and only CYP1A4, an enzyme lacking arachidonic acid epoxygenase activity, in myocardium and vascular endothelium

The toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other Ah receptor ligands, species differences in sensitivity and the relationship of CYP1A induction to the toxicity, are poorly understood. Ah receptor ligands induce formation of CYP1A1 and 1A2 in mammals and of a different set of enzymes, CYP1A4 and 1A5, in chicks. We examined induction by TCDD of CYP1A4 and 1A5 mRNA and protein in chick embryo liver, heart, kidney, lung, intestine, bursa, spleen, thymus, brain, and muscle by in situ hybridization and immunohistochemistry and verified the histochemical findings by CYP-specific assays, 7-ethoxyresorufin deethylase for CYP1A4 and arachidonic acid epoxygenation for CYP1A5. CYP1A4 alone was extensively induced in the cardiovascular system, in cardiac myocytes, in perivascular cells having the same location as impulse-conducting Purkinje cells, and like CYP1A1, in vascular endothelium in every organ examined. Unlike mammalian CYP1A, CYP1A4 and 1A5 were both substantially induced in kidney proximal tubules as well as liver, and neither enzyme was induced in kidney glomeruli or lung or brain parenchymal cells. The findings demonstrate (a) a route for CYP1A4 to affect cardiac function, (b) that vascular endothelium is a major site of CYP1A induction across species, and (c) that CYP1A induced in heart or endothelial cells cannot affect cardiac or vascular function via generation of arachidonic acid epoxides because the CYP1A enzymes induced in those organs are not arachidonic acid epoxygenases. Further, the specificity of CYP1A induction sites and of the catalytically active enzymes induced at each site support a significant role for CYP1A induction in Ah receptor ligand toxicity and species differences in sensitivity.

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.

Inhibition of pressure natriuresis in mice lacking the AT2 receptor

Inhibition of pressure natriuresis in mice lacking the AT2 receptor.

BACKGROUND

Angiotensin II type 2 (AT2) receptor knockout mice have higher blood pressures than wild-type mice; however, the hypertension is imperfectly defined. We tested the hypothesis that renal mechanisms could be contributory.

METHODS

We conducted pressure-natriuresis-diuresis experiments, measured renal cortical and medullary blood flow by laser Doppler methods, and explored cytochrome P450-dependent arachidonic acid metabolism by means of reverse transcription-polymerase chain reaction.

RESULTS

Blood pressure was 15 mm Hg higher in AT2 receptor knockout mice than in controls, and pressure diuresis and natriuresis curves were shifted rightward. At similar renal perfusion pressures (113 to 118 mm Hg), wild-type mice excreted threefold more sodium and water than AT2 receptor knockout mice. Fractional sodium and water excretion curves were shifted rightward in parallel. Renal blood flow ranged between 6.72 and 7.88 mL/min/g kidney wet weight (kwt) in wild-type and between 5.84 and 6.15 mL/min/g kwt in AT2 receptor knockout mice. Renal vascular resistance was increased in AT2A receptor knockout mice. Cortical blood flow readings leveled at 2.5 V in wild-type and 1.5 V in AT2 receptor knockout mice. Medullary blood flow readings ranged between 0.8 and 1.0 V and increased 116% in wild-type mice as renal perfusion pressure was increased. This increase did not occur in AT2 receptor knockout mice. The glomerular filtration rate (GFR) was similar in both groups at approximately 1 mL/min/g kwt. Renal microsomes from AT2 receptor knockout mice had less activity in hydroxylating arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-meter) than controls, whereas renal AT1 receptor gene expression was increased in AT2 receptor knockout mice.

CONCLUSIONS

Hemodynamic and tubular factors modify renal sodium handling in AT2 receptor knockout mice and may cause hypertension. AT2 receptor disruption induces alterations of other regulatory systems, including altered arachidonic acid metabolism, that may contribute to the intrarenal differences observed between AT2 receptor knockout and wild-type mice.

The kidney cytochrome P-450 2C23 arachidonic acid epoxygenase is upregulated during dietary salt loading

Excess dietary salt intake induces the activity of the kidney arachidonate epoxygenase and markedly increases the urinary excretion of its metabolites. The epoxyeicosatrienoic acids, products of the kidney P-450 arachidonate epoxygenase, inhibit distal nephron Na(+) reabsorption. Nucleic acid hybridization studies demonstrated the expression of P-450s 2C23, 2C24, and 2C11 as the predominant kidney 2C isoforms and the lack of significant dietary salt-dependent transcriptional regulation of these proteins. Recombinant P-450s 2C11, 2C23, and 2C24 catalyze arachidonate metabolism to mixtures of epoxy- and monohydroxylated acids. Whereas the arachidonate 11,12-olefin was the preferred target for epoxidation by P-450 2C23 (57% of total products), P-450s 2C11 and 2C24 epoxidized the 11,12-olefins and 14,15-olefins with nearly equal efficiency. Stereochemical comparisons demonstrated that the regiochemical and enantiofacial selectivity of P-450 2C23 matched that of the kidney microsomal epoxygenase and that excess dietary salt does not alter the regiochemical or stereochemical selectivity of the kidney arachidonate epoxygenase. Inhibition and immunoelectrophoresis experiments using antibodies raised against recombinant P-450s 2C11 and 2C23 demonstrated that P-450 2C23 is the major 2C arachidonic acid epoxygenase in the rat kidney and the renal P-450 isoform regulated by excess dietary salt intake.

20-Hydroxyeicosatetraenoic acid mediates calcium/calmodulin-dependent protein kinase II-induced mitogen-activated protein kinase activation in vascular smooth muscle cells

Norepinephrine (NE) and angiotensin II (Ang II), by promoting extracellular Ca2+ influx, increase Ca2+/calmodulin-dependent kinase II (CaMKII) activity, leading to activation of mitogen-activated protein kinase (MAPK) and cytosolic phospholipase A2 (cPLA2), resulting in release of arachidonic acid (AA) for prostacyclin synthesis in rabbit vascular smooth muscle cells. However, the mechanism by which CaMKII activates MAPK is unclear. The present study was conducted to determine the contribution of AA and its metabolites as possible mediators of CaMKII-induced MAPK activation by NE, Ang II, and epidermal growth factor (EGF) in vascular smooth muscle cells. NE-, Ang II-, and EGF-stimulated MAPK and cPLA2 were reduced by inhibitors of cytochrome P450 (CYP450) and lipoxygenase but not by cyclooxygenase. NE-, Ang II-, and EGF-induced increases in Ras activity, measured by its translocation to plasma membrane, were abolished by CYP450, lipoxygenase, and farnesyltransferase inhibitors. An AA metabolite of CYP450, 20-hydroxyeicosatetraenoic acid (20-HETE), increased the activities of MAPK and cPLA2 and caused translocation of Ras. These data suggest that activation of MAPK by NE, Ang II, and EGF is mediated by a signaling mechanism involving 20-HETE, which is generated by stimulation of cPLA2 by CaMKII. Activation of Ras/MAPK by 20-HETE amplifies cPLA2 activity and releases additional AA by a positive feedback mechanism. This mechanism of Ras/MAPK activation by 20-HETE may play a central role in the regulation of other cellular signaling molecules involved in cell proliferation and growth.

Mechanism of mammalian soluble epoxide hydrolase inhibition by chalcone oxide derivatives

A series of substituted chalcone oxides (1,3-diphenyl-2-oxiranyl propanones) and structural analogs was synthesized to investigate the mechanism by which they inhibit soluble epoxide hydrolases (sEH). The inhibitor potency and inhibition kinetics were evaluated using both murine and human recombinant sEH. Inhibition kinetics were well described by the kinetic models of A. R. Main (1982, in Introduction to Biochemical Toxicology, pp. 193-223, Elsevier, New York) supporting the formation of a covalent enzyme-inhibitor intermediate with a half-life inversely proportional to inhibitor potency. Structure-activity relationships describe active-site steric constraints and support a mechanism of inhibition consistent with the electronic stabilization of the covalent enzyme-inhibitor intermediate. The electronic effects induced by altering the ketone functionality and the para-substitution of the phenyl attached to the epoxy C1 (i.e., the alpha-carbon) had the greatest influence on inhibitor potency. The direction of the observed influence was reversed for the inhibitory potency of glycidol (1-phenyl-2-oxiranylpropanol) derivatives. Recent insights into the mechanism of epoxide hydrolase activity are combined with these experimental results to support a proposed mechanism of sEH inhibition by chalcone oxides.

Role of inducible nitric oxide synthase and cyclooxygenase-2 in endotoxin-induced cerebral hyperemia

BACKGROUND AND PURPOSE

Bacterial lipopolysaccharide (LPS), an endotoxin, has been reported to induce the expression of inducible isoforms of both nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) in various cell types. LPS is also known to dilate systemic vasculature, including cerebral vessels. This study aimed to determine to what extent LPS induces iNOS and COX-2 expression in the brain and whether NO and/or cyclooxygenase metabolites derived from iNOS and/or COX-2 contribute to the LPS-induced cerebral hyperemia.

METHODS

Regional cerebral blood flow (rCBF) was measured by laser-Doppler flowmetry in halothane-anesthetized, artificially ventilated rats for 4 hours after intracerebroventricular administration of LPS.

RESULTS

LPS at doses of 0.01 mg/kg to 1 mg/kg caused dose-dependent, progressive increases in rCBF at 1 to 4 hours after administration. The increase in rCBF was attenuated by systemic administration of the selective iNOS inhibitor aminoguanidine (100 mg/kg IP) or the selective COX-2 inhibitor NS-398 (5 mg/kg IP), and it was abolished by preventing induction of these isoforms with dexamethasone (4 mg/kg IP). LPS significantly increased iNOS and COX-2 mRNA, iNOS protein, and iNOS and cyclooxygenase enzyme activity. The increases in iNOS and cyclooxygenase enzyme activity were eliminated by aminoguanidine and NS-398, respectively. Dexamethasone also prevented the increase in iNOS and cyclooxygenase activity.

CONCLUSIONS

These results indicate that induction of iNOS and COX-2 expression and the increased production of NO and vasodilator prostanoids in the brain contribute to the elevation in CBF after intracerebroventricular administration of LPS.

Cytochrome P-450 metabolites mediate norepinephrine-induced mitogenic signaling

Norepinephrine (NE) stimulates release of arachidonic acid (AA) from tissue lipids in blood vessels, which is metabolized via cyclooxygenase, lipoxygenase (LO), and cytochrome P-450 (CYP-450) pathways to biologically active products. Moreover, NE and AA have been shown to stimulate proliferation of vascular smooth muscle cells (VSMCs) of rat aorta. The purpose of this study was to determine the possible contribution of AA and its metabolites to NE-induced mitogenesis in VSMCs of rat aorta and the underlying mechanism of their actions. NE (0.1 to 10 micromol/L) increased DNA synthesis as measured by [3H]thymidine incorporation in VSMCs, and this effect was attenuated by inhibitors of CYP-450 (17-octadecynoic acid, 5 micromol/L; 12-diabromododec-11-enoic acid, 10 micromol/L; and dibromo-dodecenyl-methylsulfimide, 10 micromol/L) and by the LO inhibitor (baicalein, 20 micromol/L), but not by the cyclooxygenase inhibitor (indomethacin, 5 micromol/L). CYP-450 and LO metabolites of AA, 20-hydroxyeicosatetraenoic acid (HETE) (0.1 to 0.5 micromol/L) and 12(S)-HETE, respectively, increased [3H]thymidine incorporation in VSMCs. Both NE and 20-HETE increased mitogen activated protein (MAP) kinase activity as measured by the in-gel kinase assay. The inhibitor of MAP kinase kinase, PD-98059 (50 micromol/L), attenuated NE as well as 20-HETE induced [3H]thymidine incorporation and MAP kinase activation in VSMCs. These data suggest that products of AA formed via CYP-450, most likely 20-HETE, and via LO mediate NE induced mitogenesis in VSMCs.

Perivascular sensory nerve Ca2+ receptor and Ca2+-induced relaxation of isolated arteries

The present study tested two hypotheses: (1) that a receptor for extracellular Ca2+ (Ca2+ receptor [CaR]) is located in the perivascular sensory nerve system and (2) that activation of this receptor by physiological concentrations of extracellular Ca2+ results in the release of vasodilator substance that mediates Ca2+-induced relaxation. Reverse transcription-polymerase chain reaction using primers derived from rat kidney CaR cDNA sequence showed that mRNA encoding a CaR is present in dorsal root ganglia but not the mesenteric resistance artery. Western blot analysis using monoclonal anti-CaR showed that a 140-kD protein that comigrates with the parathyroid CaR is present in both the dorsal root ganglia and intact mesenteric resistance artery. Immunocytochemical analysis of whole mount preparations of mesenteric resistance arteries showed that the anti-CaR-stained perivascular nerves restricted to the adventitial layer. Biophysical analysis of mesenteric resistance arteries showed that cumulatively raising Ca2+ from 1 to 1.25 mol/L and above relaxes precontracted arteries with an ED50 value of 2.47+/-0.17 mmol/L (n=12). The relaxation is endothelium independent and is unaffected by blockade of nitric oxide synthase but is completely antagonized by acute and subacute phenolic destruction of perivascular nerves. A bioassay showed further that superfusion of Ca2+ across the adventitial surface of resistance arteries releases a diffusible vasodilator substance. Pharmacological analysis indicates that the relaxing substance is not a common sensory nerve peptide transmitter but is a phospholipase A2/cytochrome P450-derived hyperpolarizing factor that we have classified as nerve-derived hyperpolarizing factor. These data demonstrate that a CaR is expressed in the perivascular nerve network, show that raising Ca2+ from 1 to 1.25 mol/L and above causes nerve-dependent relaxation of resistance arteries, and suggest that activation of the CaR induces the release of a diffusible hyperpolarizing vasodilator. We propose that this system could serve as a molecular link between whole-animal Ca2+ balance and arterial tone.

Differential effects of sulindac on renal hemodynamics and function in the rat

Renal hemodynamics were studied using an electromagnetic perivascular flow sensor in anesthetized rats injected i.v. with vehicle, 5 or 10 mg/kg body weight (b.w.) sulindac. No hemodynamic changes occurred with vehicle (n = 6), but mean arterial pressure was significantly decreased (by 15 mmHg) with sulindac (n = 12). In the 5 mg/kg b.w. sulindac group (n = 7), renal blood flow progressively and significantly increased from 7.88 +/- 0.36 to 8.98 +/- 0.58 ml/min, except during concomitant intrarenal infusion of 3 mg/kg b.w. per h proadifen (n = 7). The pressure limits for efficient and no renal blood flow autoregulation remained unchanged (approx. 100 and 80 mmHg, respectively). In the 10 mg/kg b.w. sulindac group (n = 5), renal blood flow did not change but autoregulatory pressure limits were lowered by 10 mmHg 2 h after treatment (P < 0.025). Also, Na+ retention was marked. Prostanoid excretion in urine was significantly reduced with either dose but basal plasma renin activity was not (about 8 ng/ml per h; n = 15). When plasma renin activity was enhanced after a reduction in renal perfusion pressure (n = 21), it was decreased from 11.5 +/- 1.2 to 7.4 +/- 0.2 ng/ml per h only by 10 mg/kg b.w. sulindac (P < 0.05; n = 6). In conclusion, differential effects of sulindac on renal hemodynamics, Na+ excretion and plasma renin activity were demonstrated. Renal hemodynamic changes could be related in part to the cytochrome P-450 arachidonic acid pathway.

Alteration of cytochrome P-450 isozymes by captopril and idrapril in hepatic and renal microsomes of normotensive and spontaneously hypertensive rats

To examine the effects of angiotensin-converting enzyme (ACE)inhibitors such as captopril and idrapril on the P-450 system, these compounds were administered 100 mg/kg i.p. for 4 days to spontaneously hypertensive (SHRs) and normotensive Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats; thereafter, the principal hepatic and renal microsomal monooxygenase activities were determined. In all the rat strains used, both captopril and idrapril decreased only the P-450 2C11, (as determined by immunoblotting) and its linked activities such as 16alpha-, 2alpha- and 17-testosterone hydroxylases. These changes were accompanied by a significant decrease of blood testosterone levels both in normotensive and, more markedly, in hypertensive rats and by a reduction of systolic blood pressure, but only in SHRs. Only in SHRs as well, the renal immunodetectable P-450 4A content and the P-450 4A-dependent activities, such as the (omega)-lauric acid hydroxylase, diminished after captopril or idrapril treatment. These data suggest that the decrease of increased blood pressure in hypertensive SHRs by the ACE inhibitors may be linked to the downregulation of the circulating testosterone level, the renal P-450 4A expression, and the related formation of the potent vasoconstrictor (omega)-hydroxy arachidonic acid.

Something completely different?

Three cDNAs clones, designated 4f-8, 4f-34 and 4f- 41, coding for three new forms of cytochrome P450 belonging to the CYP4F subfamily were isolated from an untreated rat brain cDNA library. CDNA 4f- 8, 4f-34 and 4f-41 coded for proteins of 522, 526 and 537 amino acids, respectively, and their amino acid sequence similarity to CYP4F ranged from 71 to 80%. These new P450s were thus named CYP4F4, 4F5 and 4F6, respectively. Northern blot analysis revealed that the expression levels of these forms of P450 in the brain were somewhat low and that similar forms of subfamily 4F P450 were expressed in liver and kidney at a relatively high level compared with brain. No CYP4A expression was detected by Northern blot analysis in untreated rat brain mRNA. All three clones were in vitro- translatable using a reticulocyte lysate system. These results show that multiple forms of subfamily 4F P450 exist in the brain and that the subfamily 4F P450 may be one of the major forms of P450 in the brain.