Hoffler Undi, Ghanayem Burhan I
Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Drug Metab Dispos. 2005 Aug;33(8):1144-50. doi: 10.1124/dmd.105.003806. Epub 2005 May 6.
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.
氨基甲酸乙酯是一种发酵副产物，也是一种强效动物致癌物。人类通过饮用酒精饮料和食用发酵食品接触氨基甲酸乙酯。最近，细胞色素P450 2E1（CYP2E1）被确定为负责[(14)C]羰基标记氨基甲酸乙酯代谢的主要酶。随后，有报道称在CYP2E1基因敲除小鼠中，氨基甲酸乙酯诱导的细胞增殖和遗传毒性有所减弱。本研究比较了CYP2E1基因敲除小鼠和CYP2E1基因正常小鼠单次和多次接触(14)C-乙基标记氨基甲酸乙酯后的代谢情况。氨基甲酸乙酯以单次10或100 mg/kg的灌胃剂量给药，或连续5天以100 mg/kg/天的剂量给药。单次或多次给药的CYP2E1基因正常小鼠每天呼出剂量的78%至88%作为(14)CO(2)。CYP2E1基因敲除小鼠在24小时内将单次剂量的30%至38%以(14)CO(2)形式排出，在第3天后趋于平稳，约为每天剂量的52%。血浆和组织中氨基甲酸乙酯衍生放射性的浓度呈剂量依赖性，随给药次数增加而升高，且CYP2E1基因敲除小鼠中的浓度显著高于CYP2E1基因正常小鼠。虽然氨基甲酸乙酯是在CYP2E1基因敲除小鼠的血浆和组织中发现的主要化学物质，但在CYP2E1基因正常小鼠中未检测到。总之，多次给药导致两种基因型小鼠体内氨基甲酸乙酯大量生物蓄积；然而，CYP2E1基因敲除小鼠比CYP2E1基因正常小鼠的蓄积量更大。此外，在小鼠中观察到(14)C-乙基标记的氨基甲酸乙酯比[(14)C]羰基标记的氨基甲酸乙酯有更大的生物蓄积。比较乙基标记和羰基标记氨基甲酸乙酯的代谢情况对于追踪CO(2)的来源很有必要，这使我们首次提出C-羟基化可能是氨基甲酸乙酯代谢的一条途径。
