A pharmacokinetic study of ethanol inhibition of micronuclei induction by urethane in mouse bone marrow erythrocytes

Modulation of Urethane (Ethyl Carbamate) Carcinogenicity by Ethyl Alcohol: A Review

Urethane (ethyl carbamate) is a carcinogen that has been detected as a contaminant in certain foods and alcoholic beverages. The carcinogenicity of urethane appears to be mediated through a metabolic pathway involving sequential cytochrome P-450-catalyzed oxidation to vinyl carbamate and vinyl carbamate epoxide, the latter of which reacts with DNA to yield etheno-type DNA adducts. The interactions of ethanol on urethane metabolism and carcinogenicity are varied and complex. Urethane is oxidized by cytochrome P-450 IIE1, an isoform induced by ethanol, which suggests that chronic ethanol consumption could increase the oxidation of urethane to its epoxide derivative. On the other hand, ethanol coadministration is known to inhibit the elimination and hydrolysis of urethane. Ethanol has decreased the tumorigenicity of urethane in two bioassays, but did not have an effect in a third. While the results to date suggest that ethanol will decrease the metabolic activation of urethane, with a resultant decrease in tumorigenicity, additional studies are clearly necessary to elucidate the mechanisms by which ethanol influences the carcinogenicity of urethane.

Micronuclei in genotoxicity assessment: from genetics to epigenetics and beyond

Micronuclei (MN) are extra-nuclear bodies that contain damaged chromosome fragments and/or whole chromosomes that were not incorporated into the nucleus after cell division. MN can be induced by defects in the cell repair machinery and accumulation of DNA damages and chromosomal aberrations. A variety of genotoxic agents may induce MN formation leading to cell death, genomic instability, or cancer development. In this review, the genetic and epigenetic mechanisms of MN formation after various clastogenic and aneugenic effects on cell division and cell cycle are described. The knowledge accumulated in literature on cytotoxicity of various genotoxins is precisely reflected and individual sensitivity to MN formation due to single gene polymorphisms is discussed. The importance of rapid MN scoring with respect to the cytokinesis-block micronucleus assay is also evaluated.

Genotoxicity of ethyl carbamate (urethane) in Salmonella, yeast and human lymphoblastoid cells

Ethyl carbamate is a known carcinogen occurring in fermented food and beverages and is therefore of interest for food safety assurance. We studied the genotoxicity of ethyl carbamate in Salmonella typhimurium, in Saccharomyces cerevisiae and in human lymphoblastoid TK6 cells. In absence of cytochrome P450 enzymes, no ethyl carbamate-mediated genotoxicity was observed in any of the three test systems in the non-cytotoxic range. In the presence of an activating system, ethyl carbamate was found to be mutagenic in Salmonella typhimurium strain TA100 but not in strains TA98 and TA102, indicating base-pair substitutions at G-C base pairs. In contrast, no significant mutagenicity of ethyl carbamate could be detected in human lymphoblastoid TK6 cells. However, applied in cytotoxic concentrations, ethyl carbamate was genotoxic for Saccharomyces cerevisiae in the absence of P450-mediated metabolic activation. Inhibitors of P450IIE1 (DMSO, ethanol and dithiodiethylcarbamate) diminished ethyl carbamate-mediated mutagenicity in Salmonella typhimurium strain TA100 in a dose dependent manner, suggesting that P450IIE1 is the activating enzyme.

Co-administration of ethanol transiently inhibits urethane genotoxicity as detected by a kinetic study of micronuclei induction in mice

Urethane (ethyl carbamate) is a genotoxic carcinogen that requires metabolic activation. Ethanol is known to inhibit urethane metabolism and genotoxicity. Since ethanol is eliminated rapidly in animals, the persistence of ethanol inhibition was studied in a mouse bone marrow and a peripheral blood micronucleus assays. In the bone marrow assay, male CD-1 mice were injected intraperitoneally (i.p.) with water (vehicle), urethane (1000 mg/kg), ethanol (2500 mg/kg) or urethane and ethanol (1000 and 2500 mg/kg, respectively) in single injections. Polychromatic erythrocytes (PCE) from bone marrow were obtained at 24 and 48 h after injection and scored for micronuclei. Urethane induced an increase of micronucleated PCE (MN PCE) frequency from 0.19% in the control to 8.63% at 24 h, followed by a decrease to 6.98% at 48 h. When urethane was co-administered with ethanol, the MN PCE frequency was suppressed to 0.49% at 24 h, but markedly increased to 7.35% at 48 h. This delay of MN PCE occurrence indicated that ethanol inhibition was transient. To pinpoint the duration of this delay, a peripheral blood micronucleus assay was conducted to monitor the kinetics of MN PCE induction. In this assay, male CD-1 mice were injected i.p. with water, ethanol, urethane, or urethane and ethanol as described above. Peripheral blood was scored for MN PCE at 8-h intervals for 4 days. Two additional dose groups injected with urethane or urethane and ethanol were also scored for MN PCE at 8 h intervals, but each blood sampling time was staggered 4 h later from the first four dose groups. The combined data provided MN PCE frequencies at 4-h intervals from 24 to 100 h after injection. Urethane alone induced a peak MN PCE frequency of 11.6% at 52 h. Urethane and ethanol induced a peak MN PCE frequency of 11.2% at 64 h, a delay of 12 h. Thus, ethanol delays but does not diminish urethane genotoxicity.