title: Increased bioaccumulation of urethane in CYP2E1-/- versus CYP2E1+/+ mice.
abstract: Urethane is a fermentation by-product and a potent animal carcinogen. Human exposure to urethane occurs through consumption of alcoholic beverages and fermented foods. Recently, CYP2E1 was identified as the primary enzyme responsible for the metabolism of [(14)C]carbonyl-labeled urethane. Subsequently, attenuation of urethane-induced cell proliferation and genotoxicity in CYP2E1-/- mice was reported. The present work compares the metabolism of single versus multiple exposures of CYP2E1-/- and CYP2E1+/+ mice to (14)C-ethyl-labeled urethane. Urethane was administered as a single 10 or 100 mg/kg gavage dose or at 100 mg/kg/day for 5 consecutive days. CYP2E1+/+ mice administered single or multiple doses exhaled 78 to 88% of dose as (14)CO(2)/day. CYP2E1-/- mice eliminated 30 to 38% of a single dose as (14)CO(2) in 24 h and plateaued after day 3 at approximately 52% of dose/day. The concentrations of urethane-derived radioactivity in plasma and tissues were dose-dependent, increased as a function of the number of doses administered, and were significantly higher in CYP2E1-/- versus CYP2E1+/+ mice. Whereas urethane was the main chemical found in the plasma and tissues of CYP2E1-/- mice, it was not detectable in CYP2E1+/+ mice. In conclusion, multiple dosing led to considerable bioaccumulation of urethane in mice of both genotypes; however, greater retention occurred in CYP2E1-/- versus CYP2E1+/+ mice. Furthermore, greater bioaccumulation of (14)C-ethyl-labeled than [(14)C]carbonyl-labeled urethane was observed in mice. Comparison of the metabolism of ethyl-versus carbonyl-labeled urethane was necessary for tracing the source of CO(2) and led us to propose for the first time that C-hydroxylation is a likely pathway of urethane metabolism.
authors.affiliation: Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
authors.forename: Undi
authors.initials: U
authors.lastname: Hoffler
authors.forename: Burhan I
authors.initials: BI
authors.lastname: Ghanayem
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000378:metabolism; D002250:Carbon Radioisotopes; D002273:Carcinogens / Q000633:toxicity; D019392:Cytochrome P-450 CYP2E1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004032:Diet; D004305:Dose-Response Relationship, Drug; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009153:Mutagens / Q000633:toxicity; D014018:Tissue Distribution; D014520:Urethane / Q000378:metabolism* / Q000493:pharmacokinetics / Q000633:toxicity
chemical_list: D002250:Carbon Radioisotopes; D002273:Carcinogens; D009153:Mutagens; D002245:Carbon Dioxide; D014520:Urethane; D019392:Cytochrome P-450 CYP2E1