Liver nuclear and microsomal CYP2E1-mediated metabolism of xenobiotics in rats chronically drinking an alcohol-containing liquid diet

Abstract

In previous studies from our laboratory, the presence in highly purified liver nuclei of metabolic pathways for processing ethanol (EtOH), N-nitrosodimethylamine (NDMA), carbon tetrachloride and chloroform was reported. All these chemicals are known to be metabolized in liver microsomes, via cytochrome P450 2E1 (CYP2E)-mediated processes. In the present work we checked whether rat liver nuclei from rats chronically drinking an alcohol-containing liquid diet exhibited an enhanced ability to metabolize chemicals known to require CYP2E1 participation for given metabolic transformations. The nicotinamide adenosine dinucleotide phosphate (NADPH)-requiring metabolism of p-nitrophenol to p-nitrocathecol; the activation of carbon tetrachloride to trichloromethyl radicals, covalently binding to proteins; and the ring hydroxylation of aniline and o-toluidine were studied. Comparison of the obtained nuclear activities against the one present in the microsomal counterpart, and their respective response to the EtOH inductive effect after repetitive exposure to it, was studied. The obtained results showed that rat liver nuclei exhibited less p-nitrophenol hydroxylase activity than microsomes, but it was inducible by repetitive alcohol drinking to equivalent levels of those of microsomes from control animals. Nuclei exhibited the ability to activate CCl4, which was significantly enhanced by alcohol drinking. Aniline was ring hydroxylated in liver microsomes but not in nuclei from either control or EtOH-treated animals. In contrast, nuclei and microsomes metabolized o-toluidine to ring hydroxylated products. They are considered less toxic in nature but other authors reported a genotoxic effect for one of them. The production of the ring hydroxylated metabolites was enhanced by repetitive EtOH drinking. Results suggest that nuclear metabolism of xenobiotics might be relevant for either activations or detoxications mediated by CYP2E1 and that repetitive exposure to EtOH might significantly modulate those processes.

Roles of EXTL2, a member of the EXT family of tumour suppressors, in liver injury and regeneration processes

“…We first checked expression levels of CYP2E1, which is the primary cytochrome P450 that catalyses CCl 4 metabolism. CCl 4 is a prototypical inducer of pericentral liver damage and causes hepatocytes close to the central vein to die [17]. We next examined the ratio of liver weight to body weight 5 days after a single administration of CCl 4 .…”

Renal Function in Male Sprague-Dawley Rats Concurrently Exposed to Long-Term Nicotine (3-{1-Methyl-2-Pyrrolidinyl}Pyridine) and Methylated Spirits (Methyl Alcohol)

“…Indeed, methanol stimulates CYP2E1. [32] Plausible explanations for the reduction of plasma ethanol levels in the combined treatments (see Table 3) may be due to increased ethanol metabolism via CYP2E1, an isoform inducible by ethanol, [33,34] and/or increased elimination of ethanol through nicotine-induced metabolic stimulation. [31] Plasma nicotine concentrations rose by approximately 33% in week 4 after the sacrifice of rats concurrently administered nicotine and methylated spirits (see Table 2) and remained elevated by about 30% during vehicle infusion (see Table 3), by comparison with rats administered nicotine alone.…”

Establishing a total allowable concentration of o-toluidine in drinking water incorporating early lifestage exposure and susceptibility

“…8-Oxo-7,8-dihydro-2 0 -deoxyguanosine is formed efficiently in vitro by o-toluidine metabolites (4-amino-3-methylphenol and o-nitrosotoluene plus NADH) in the presence of Cu(II) and is known to cause GC to TA transversions, a common DNA mutation found in bladder carcinoma (Ohkuma et al, 1999). It is of interest that ring hydroxylation of o-toluidine to 2-amino-m-cresol and 4-amino-m-cresol can be catalyzed by rat liver nuclei as well as microsomes (Diaz Gomez et al, 2006). Thus o-toluidine metabolites and reactive oxygen species might be generated in proximity to potential DNA targets.…”

“…CYP2E1 is implicated in the ring-hydroxylation of o-toluidine at positions para-and ortho-to the amine. Ring-hydroxylation reactions are catalyzed by liver microsomes and liver nuclei from naïve rats, and induced by ethanol treatment (Diaz Gomez et al, 2006). The major pathway of o-toluidine metabolism is ring hydroxylation in the para (4)-position to form 4-amino-m-cresol, and N-acetylation of the latter to form N-acetyl-4-amino-m cresol; both metabolites are excreted as sulfates and glucuronides in the urine (Cheever et al, 1980;Son et al, 1980;Williamson et al, 1995).…”

“…The production of ring-hydroxylated metabolites of o-toluidine was enhanced approximately 8-fold in rats given an ethanol liquid diet for 28 days as compared with rats given the control diet (Diaz Gomez et al, 2006), suggesting that ring-hydroxylation pathways may be catalyzed by CYP2E1.…”