Para-nitrophenol hydroxylation by fish liver microsomes: kinetics and effect of selective cytochrome P450 inhibitors

Abstract

The study investigated the kinetics of p-nitrophenol hydroxylase (PNPH) in hepatic microsomes obtained from Atlantic salmon (Salmo salar). The selective inhibitors for some major mammalian cytochrome P450 (CYP450) were used to investigate the potential inhibitory effect on enzymes involved in p-nitrophenol hydroxylation. The following inhibitors were used: α-naphtoflavone (CYP1A), ellipticine (CYP1A1), furafylline (CYP1A2), 8-methoxypsoralen (8MOP, CYP2A6), 4-methylpyrazole (4MP, CYP2A6/2E1), diallyl sulfide (DAS, CYP2E1), and ketoconazole (CYP3A4). Additionally, the natural steroids 17-beta-oestraiol (E2) and testosterone were investigated as potential inhibitors of PNPH activity. It was found that formation of 4-nitrocatechol from p-nitrophenol followed monophasic kinetics with K(m) = 0.17 ± 0.03 mM and V(max) = 21.8 ± 1.05 pmol/min/mg. PNPH activity was competitively inhibited by diallyle sulfide with the K(i) value of 285.1 ± 94.2 μM μM and uncompetitively by ellipticine with K(i) value of 65.7 ± 7.8 μM. Moreover, E2 showed an ability to reduce PNPH activity through the mechanism-based inhibition mode. Our results suggest that hepatic microsomes from Atlantic salmon possess CYP2E1-like activity. However, specific isoform-mediated PNPH activity should be identified.

Acute and Subchronic Toxicity Studies of Aqueous Extract of Desmodium adscendens (Sw) DC

“…In contrast, the extract may also alter levels or activities of certain isozymes of CYPs as demonstrated by the inhibition of p-nitrophenol hydroxylation (Figure 3B), which is mediated by CYP2E, responsible for the metabolism of isoniazid and other drugs. [33][34][35][36] The absence of any significant effects of the plant extract on ethoxyresorufin-O-deethylase activity mediated by CYP1A/1A2 isozymes (Figure 3C) would suggest that the plant extract would not impair the clearance of drugs that are metabolized by CYP1A/1A2 isozymes. 14,15…”

Does dexamethasone affect hepatic CYP450 system of fish? Semi-static in-vivo experiment on juvenile rainbow trout

“…The CYP2E1-like protein activity has also been identified in fish (Kaplan et al, 1999;Wall and Crivello, 1999;Zamaratskaia and Zlabek, 2011). To date, there are no reports on the in vivo effect of DEX on PNPH activity.…”