Induction of Cyp1a and Cyp2-Mediated Arachidonic Acid Epoxygenation and Suppression of 20-Hydroxyeicosatetraenoic Acid by Imidazole Derivatives Including the Aromatase Inhibitor Vorozole

Abstract

ABSTRACT:Cytochrome P450 (P450) enzymes metabolize the membrane lipid arachidonic acid to stable biologically active epoxides [eicosatrienoic acids (EETs)] and 20-hydroxyeicosatetraenoic acid (20-HETE). These products have cardiovascular activity, primarily acting as vasodilators and vasoconstrictors, respectively. EET formation can be increased by the prototype CYP1A or CYP2 inducers, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or phenobarbital (PB), respectively. We report here that imidazole derivative drugs: the anthelminthics, albendazole and thiabendazole; the proton pump inhibitor, omeprazole; the thromboxane synthase inhibitor, benzylimidazole; and the aromatase (CYP19) inhibitor vorozole (R76713, racemate; and R83842, (؉) enantiomer) increased hepatic microsomal EET formation in a chick embryo model. Albendazole increased EETs by transcriptional induction of CYP1A5 and the others by combined induction of CYP1A5 and CYP2H, the avian orthologs of mammalian CYP1A2 and CYP2B, respectively. All inducers increased formation of the four EET regioisomers, but TCDD and albendazole had preference for 5,6-EET and PB and omeprazole for 14,15-EET. Vorozole, benzylimidazole, and TCDD also suppressed 20-HETE formation. Vorozole was a remarkably effective and potent inducer of multiple hepatic P450s at a dose range which overlapped its inhibition of ovarian aromatase. Increased CYP1A activity in mouse Hepa 1-6 and human HepG2 cells by vorozole and other imidazole derivatives demonstrated applicability of the findings to mammalian cells. The findings suggest that changes in P450-dependent arachidonic acid metabolism may be a new source of side effects for drugs that induce CYP1A or CYP2. They demonstrate further that in vivo induction of multiple hepatic P450s produces additive increases in arachidonic acid epoxygenase activity and can occur concurrently with inhibition of ovarian aromatase activity.

Mitochondrial P450-dependent arachidonic acid metabolism by TCDD-induced hepatic CYP1A5; conversion of EETs to DHETs by mitochondrial soluble epoxide hydrolase

“…20-HETE (ω), essentially the sole P450 aa product in livers of control CE, was suppressed by TCDD treatment in mitochondria, as previously observed in microsomes [12,13], here by means of 27.5 ± 2% in microsomes and 25 ± 8% in mitochondria (p = 0.001 and 0.045, respectively; n = 3).…”

“…TCDD has been found to suppress formation of 20-HETE in mammalian and avian liver microsomes [12,13] and is shown here also to suppress 20-HETE in mitochondria. Notwithstanding the dominant role of 20-HETE as virtually the only constitutive P450 product in CE liver microsomes and mitochondria, hepatic effects of 20-HETE are unknown.…”

“…Further, TCDD treatment suppressed formation of another P450 aa metabolite, 20-HETE, in both mammalian and CE liver microsomes [12,13].…”

Increases in Levels of Epoxyeicosatrienoic and Dihydroxyeicosatrienoic Acids (EETs and DHETs) in Liver and Heart in Vivo by 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and in Hepatic EET:DHET Ratios by Cotreatment with TCDD and the Soluble Epoxide Hydrolase Inhibitor AUDA

“…Interestingly, Bui et al (2012) also reported that TCDD increased 20-HETE in vivo in mouse liver. The finding also seems to contradict the substantial evidence that AHR activation by diverse agents, including TCDD, b-naphthoflavone, planar PCBs, and imidazole drugs, suppresses hepatic 20-HETE formation by microsomes in in vitro experiments in many species, including chick embryo, mouse, scup, rats, and guinea pigs (Huang and Gibson, 1991;Nakai et al, 1992;Lee et al, 1998;Schlezinger et al, 1998;Diani-Moore et al, 2006b) (also see Fig. 1).…”

“…CYP2B (avian 2H) arachidonic acid epoxygenases are induced by phenobarbital, an activator of different nuclear receptors, i.e., constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) (Nakai et al, 1992;Gilday et al, 1996;Gannon et al, 2000;Willson and Kliewer, 2002;Diani-Moore et al, 2006a;Rifkind, 2006). Imidazole-based drugs (i.e., vorozole, omeprazole, benzylimidazole) increase arachidonic acid metabolism by mixed induction of CYP1 and CYP2 family P450s (Diani-Moore et al, 2006b). Significantly, the different P450 epoxygenases all produce the same arachidonic acid products: four regioisomeric epoxides, 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatetraenoic acids, and terminal hydroxyeicosatetraenoic acids (HETEs), i.e., 16-19 HETE (Capdevila et al, 1981), although the relative amounts of the products can vary for different P450s.…”