Regulation of cytochrome P-450j, a high-affinity N-nitrosodimethylamine demethylase, in rat hepatic microsomes

Abstract

Polyclonal antibodies were produced in rabbits against purified cytochrome P-450j isolated from isoniazid-treated adult male rats. The monospecificity of immunoadsorbed antibody to cytochrome P-450j was demonstrated by Ouchterlony double diffusion analyses, enzyme-linked immunosorbent assays, and immunoblots. Immunoquantitation results indicated that rat liver microsomal cytochrome P-450j content decreases between 3 and 6 weeks of age in both the male and female animal. Several xenobiotics, such as Aroclor 1254, mirex, and 3-methylcholanthrene, repressed cytochrome P-450j levels when administered to male rats. Isoniazid, dimethyl sulfoxide, pyrazole, 4-methylpyrazole, and ethanol were inducers of cytochrome P-450j in rat liver although these compounds showed different inducing potencies. Microsomes from adult male rats with chemically induced diabetes also contained elevated levels of cytochrome P-450j compared to untreated animals. Cytochrome P-450j levels were measurable in kidney, whereas this isozyme was barely detectable in lung, ovaries, and testes; however, extrahepatic cytochrome P-450j was inducible by isoniazid. Approximately 80-90% of microsomal N-nitrosodimethylamine demethylation was inhibited by antibody to cytochrome P-450j whether the microsomes were isolated from untreated rats or animals administered inducers or repressors of cytochrome P-450j. The residual catalytic activity resistant to antibody inhibition may be a reflection of the inaccessibility of a certain amount of cytochrome P-450j due to interference by NADPH-cytochrome P-450 reductase based on results obtained with the reconstituted system. There was a good correlation (r2 = 0.87) between cytochrome P-450j content and N-nitrosodimethylamine demethylase activity in microsomes from rats of different ages and treated with various xenobiotics. The evidence presented indicates that cytochrome P-450j is the primary, and perhaps sole, microsomal catalyst of N-nitrosodimethylamine demethylation at substrate concentrations relevant to hepatocarcinogenesis induced by N-nitrosodimethylamine.

In Vivo Oxidative Damage in Rats Is Associated with Barbiturate Response but Not Other Cytochrome P450 Inducers

“…S1). Induction of P450 2E1 by PB had not been observed in another study (Thomas et al, 1987) but was confirmed by assays of liver microsomal chlorzoxazone 6-hydroxylation (Supplemental Fig. S2).…”

Decreased sensitivity in adolescent vs. adult rats to the locomotor activating effects of toluene

“…Since pharmacokinetic parameters were not measured in the present study, their influence cannot be completely eliminated. For example, levels of CYP2E1, the P450 isoenzyme most commonly associated with toluene metabolism, decrease between the ages of 3 and 8 weeks in both male and female and levels of CYP2C11, which is associated with toluene metabolism in male rats only, increase [57], suggesting that younger rats might metabolize toluene more quickly. Several other findings, however, argue against age-related pharmacokinetic differences as a sole explanation for the observed age differences in toluene's effects on activity.…”

<i>N</i>–nitrosodiethylamine cytochrome P450 induction and cytotoxicity evaluation in primary cultures of rat hepatocytes

“…3-MC and PB supp otein and metabolic activity in rats [34][35][36]. We observed a decrease on the CYP2E1 mRNA levels in the presence of NDEA for ETH, PYR and PB inducer treatments.…”