piperidines and 20-hydroxy-5-8-11-14-eicosatetraenoic-acid

The cytochrome P-450 arachidonic acid metabolite 20-HETE is central to the regulation of vascular tone, renal function, and blood pressure and is synthesized in the rat kidney in response to angiotensin II (ANG II) and endothelin-1 (ET-1). There are very few studies examining the cellular synthesis of 20-HETE in humans. We aimed to measure human neutrophil and platelet 20-HETE levels under basal conditions and after ANG II, ET-1, and calcium ionophore (CaI). 20-HETE was measured in human platelets and neutrophils after saline (control), CaI (2.5 μg/ml), and ANG II or ET-1 (10 nmol/l-1 μmol/l) incubations. The effect of cells, which were preincubated with the ω-hydroxylase inhibitor N-hydroxy-N'-(4-butyl-2-methylphenyl) (HET0016, 10 nM), ANG II types 1 or 2 (AT(1) or AT(2)) receptor inhibition with irbesartan (1 μmol/l) or PD-123319 (1 μmol/l), or endothelin receptor subtypes A or B (ET(A) or ET(B)) receptor inhibition with BQ-123 or BQ-778 (100 nmol/l), was studied. Neutrophil and platelet content and release of 20-HETE was significantly increased by CaI and blocked by the ω-hydroxylase inhibitor HET0016. ANG II and ET-1 significantly increased neutrophil and platelet content and release of 20-HETE. ANG II increased 20-HETE via the AT(2) receptor. ET-1 increased 20-HETE through the ET(B) receptor in platelets and both the ET(A) and ET(B) receptors in neutrophils. These studies show that human platelets and neutrophils synthesize 20-HETE in response to ANG II and ET-1. 20-HETE synthesis in both cell types was predominantly mediated via the AT(2) and ET(B) receptors. Stimulation via these receptor pathways has generally been thought to be cardioprotective and requires further studies in clinical situations associated with low-grade inflammation or where ANG II and ET-1 are elevated to clarify the role of 20-HETE.

Topics: Adult; Aged; Amidines; Angiotensin II; Angiotensin Receptor Antagonists; Biphenyl Compounds; Blood Platelets; Calcium Channels; Cells, Cultured; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Endothelin-1; Humans; Hydroxyeicosatetraenoic Acids; Imidazoles; Ionophores; Irbesartan; Male; Middle Aged; Neutrophils; Oligopeptides; Peptides, Cyclic; Piperidines; Pyridines; Tetrazoles; Young Adult

CYP4F enzymes, including CYP4F2 and CYP4F3B, were recently shown to be the major enzymes catalyzing the initial oxidative O-demethylation of the antiparasitic prodrug pafuramidine (DB289) by human liver microsomes. As suggested by a low oral bioavailability, DB289 could undergo first-pass biotransformation in the intestine, as well as in the liver. Using human intestinal microsomes (HIM), we characterized the enteric enzymes that catalyze the initial O-demethylation of DB289 to the intermediate metabolite, M1. M1 formation in HIM was catalyzed by cytochrome P450 (P450) enzymes, as evidenced by potent inhibition by 1-aminobenzotriazole and the requirement for NADPH. Apparent K(m) and V(max) values ranged from 0.6 to 2.4 microM and from 0.02 to 0.89 nmol/min/mg protein, respectively (n = 9). Of the P450 chemical inhibitors evaluated, ketoconazole was the most potent, inhibiting M1 formation by 66%. Two inhibitors of P450-mediated arachidonic acid metabolism, HET0016 (N-hydroxy-N'-(4-n-butyl-2-methylphenyl)formamidine) and 17-octadecynoic acid, inhibited M1 formation in a concentration-dependent manner (up to 95%). Immunoinhibition with an antibody raised against CYP4F2 showed concentration-dependent inhibition of M1 formation (up to 92%), whereas antibodies against CYP3A4/5 and CYP2J2 had negligible to modest effects. M1 formation rates correlated strongly with arachidonic acid omega-hydroxylation rates (r(2) = 0.94, P < 0.0001, n = 12) in a panel of HIM that lacked detectable CYP4A11 protein expression. Quantitative Western blot analysis revealed appreciable CYP4F expression in these HIM, with a mean (range) of 7 (3-18) pmol/mg protein. We conclude that enteric CYP4F enzymes could play a role in the first-pass biotransformation of DB289 and other xenobiotics.

Topics: Amidines; Antibodies; Antiparasitic Agents; Arachidonic Acid; Benzamidines; Benzoflavones; Butyrophenones; Chromatography, High Pressure Liquid; Cytochrome P-450 CYP2J2; Cytochrome P-450 CYP3A; Cytochrome P-450 CYP4A; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Cytochrome P450 Family 4; Enzyme Inhibitors; Fatty Acids, Unsaturated; Humans; Hydroxyeicosatetraenoic Acids; Intestinal Mucosa; Intestines; Kinetics; Methylation; Microsomes; Oxygenases; Piperidines; Prodrugs; Recombinant Proteins; Stereoisomerism

Myogenic constriction describes the innate ability of resistance arteries to constrict in response to elevations in intraluminal pressure and is a fundamental determinant of peripheral resistance and, hence, organ perfusion and systemic blood pressure. However, the receptor/cell-type that senses changes in pressure on the blood vessel wall and the pathway that couples this to constriction of vascular smooth muscle remain unclear. In this study, we show that elevation of intraluminal transmural pressure of mesenteric small arteries in vitro results in a myogenic response that is profoundly suppressed following ablation of sensory C-fiber activity (using in vitro capsaicin desensitization resulted in 72.8+/-10.3% inhibition, n=8; P<0.05). Activation of C-fiber nerve endings by pressure was attributable to stimulation of neuronal vanilloid receptor, TRPV1, because blockers of this channel, capsazepine (71.9+/-11.1% inhibition, n=9; P<0.001) and ruthenium red (46.1+/-11.7% inhibition, n=4; P<0.05), suppressed the myogenic constriction. In addition, this C-fiber dependency is likely related to neuropeptide substance P release and activity because blockade of tachykinin NK1 receptors (66.3+/-13.7% inhibition, n=6; P<0.001), and not NK2 receptors (n=4, NS), almost abolished the myogenic response. Previous studies support a role for 20-hydroxyeicosatetraenoic acid (20-HETE) in myogenic constriction responses; herein, we show that 20-HETE-induced constriction of mesenteric resistance arteries is blocked by capsazepine. Together, these results suggest that elevation of intraluminal pressure is associated with generation of 20-HETE that, in turn, activates TRPV1 on C-fiber nerve endings resulting in depolarization of nerves and consequent vasoactive neuropeptide release. These findings identify a novel mechanism contributing to Bayliss' myogenic constriction and highlights an alternative pathway that may be targeted in the therapeutics of vascular disease, such as hypertension, where enhanced myogenic constriction plays a role in the pathogenesis.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Capsaicin; Cation Transport Proteins; CHO Cells; Cricetinae; Endothelium, Vascular; Gadolinium; Ganglia, Sympathetic; Guanethidine; Hydroxyeicosatetraenoic Acids; Ion Channels; Male; Mesenteric Arteries; Mice; Mice, Knockout; Models, Cardiovascular; Models, Neurological; Nerve Fibers, Unmyelinated; Nociceptors; Peptides, Cyclic; Piperidines; Pressure; Quinuclidines; Rats; Rats, Sprague-Dawley; Receptors, Neurokinin-1; Ruthenium Red; Sodium Channel Blockers; Splanchnic Circulation; Stress, Mechanical; Sympathectomy, Chemical; Tetrodotoxin; TRPV Cation Channels; Vascular Resistance; Vasoconstriction

The preglomerular arteriole of the rat was used to evaluate the contribution of cytochrome P450-derived eicosanoids to the vasoconstrictor effect of endothelin (ET)-1 and to determine the receptors mediating the response. ET-1 (4 x 10(-11) to 2 x 10(-9) M) produced dose-dependent reductions in the intraluminal diameter of the renal arteriole ranging from 25 +/- 8 to 142 +/- 16 micrometer. BMS182874 [(5-dimethylamino)-N-(3, 4-dimethyl-5-isoxazolyl)-1-naphthalenesulfonamide; 3 microM], an ET(A) receptor antagonist, or BQ788 (N-cis-2, 6-dimethyl-piperidino-carbonyl-L-gamma-methylleucyl-D-1-methoxy carbonyl-tryptophanyl-D-norleucine; 1 microM), an ET(B) receptor antagonist, attenuated ET-1 vasoconstriction by 59 +/- 4 and 50 +/- 10%, respectively. The combined administration of both ET receptor antagonists increased inhibition of ET-1 vasoconstriction to 75 +/- 4%. 17-Octadecynoic acid (17-ODYA, 2 microM) or 12, 12-dibromododec-enoic acid (2 microM), inhibitors of 20-hydroxyeicosatetraenoic acid (20-HETE) production, attenuated ET-1-induced vasoconstriction by 50 +/- 6 and 40 +/- 3%, respectively, as did indomethacin (10 microM), an inhibitor of cyclooxygenase. Miconazole (2 microM), the epoxygenase inhibitor, was without effect. 20-HETE (10(-8) and 2 x 10(-8) M) elicited a dose-related vasoconstriction that was inhibited by 10 microM, but not 5 microM, indomethacin. The inhibition by 17-ODYA of ET-1 vasoconstriction was not greater when combined with BMS182874 or BQ788. Moreover, vasoconstriction induced by ET-3, an ET(B)-selective agonist, was inhibited by 17-ODYA. These data indicate that both ET(A) and ET(B) receptors mediate ET-1 vasoconstriction and that 20-HETE production linked to both receptors makes a major contribution to ET-1-induced renal arteriolar vasoconstriction in the rat.

Topics: 5,8,11,14-Eicosatetraynoic Acid; Animals; Arachidonic Acid; Arterioles; Cytochrome P-450 CYP4A; Cytochrome P-450 Enzyme System; Dansyl Compounds; Endothelin-1; Hydroxyeicosatetraenoic Acids; Kidney; Male; Mixed Function Oxygenases; Oligopeptides; Piperidines; Prostaglandin-Endoperoxide Synthases; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptor, Endothelin B; Receptors, Endothelin; Vasoconstriction

Endothelin-1 (ET-1) produces potent renal effects that we have previously shown to be dependent on cytochrome P-450 (CYP450) metabolites of aracidonic acid (24) This study evaluated the role of these metabolites in the effects produced by ET-1 on renal blood flow (RBF), cortical blood flow (CBF), medullary blood flow (MBF), and mean arterial blood pressure (MBP). ET-1 (20-200 pmol/kg) increased MBP, renal vascular resistance (RVR), and MBF but reduced CBF and RBF in a dose-dependent manner. The decreases in CBF and RBF, and increases in MBP and RVR were blunted by BMS-182874, an ET(A) receptor antagonist or BQ-788, an ET(B) receptor antagonist. Similarly, indomethacin, an inhibitor of cyclooxygenase activity, or 12,12-dibromododecenoic acid (DBDD), a CYP450-dependent inhibitor of production of 20-hydroxyeicosatetraenoic acid (20-HETE), blunted these effects. ET-3 elicited dose-related reduction in CBF and increase in MBF. Indomethacin accentuated the reduction in CBF and attenuated the increase in MBF, as did DBDD. ET-1-induced increase in MBF was attenuated by BQ-788, N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, indomethacin, or DBDD. DBDD inhibited the hemodynamic effects of L-NAME. Miconazole, the inhibitor of CYP450-dependent epoxygenase activity, was without effect. These results indicate that hemodynamic changes produced by ET-1 are mediated by vasoconstrictor prostanoids and/or prostanoid-like substances, possibly, 20-HETE via activation of ET(A) and ET(B) receptors. However, the increase in MBF is mediated by vasodilator prostanoids or by NO via ET(B) receptor activation.

Topics: Animals; Blood Pressure; Cytochrome P-450 Enzyme System; Dansyl Compounds; Eicosanoids; Endothelin Receptor Antagonists; Endothelin-1; Endothelin-3; Hemodynamics; Hydroxyeicosatetraenoic Acids; Indomethacin; Kidney Cortex; Kidney Medulla; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide; Oligopeptides; Piperidines; Rats; Rats, Sprague-Dawley; Receptor, Endothelin A; Receptor, Endothelin B; Regional Blood Flow; Renal Artery; Renal Circulation; Vascular Resistance