Probing the Mechanism of the Carcinogenic Activation of <i>N</i>-Nitrosodiethanolamine with Deuterium Isotope Effects: In Vivo Induction of DNA Single-Strand Breaks and Related in Vitro Assays
作者:Richard N. Loeppky、Anne Fuchs、Christine Janzowski、Christina Humberd、Petra Goelzer、Heiko Schneider、Gerhard Eisenbrand
DOI:10.1021/tx9801716
日期:1998.12.1
A series of bioassays, including in vivo induction of DNA single-strand breaks (SSB) and cytotoxicity in cytochrome P450 2E1-transfected cells, were utilized with N-nitrosodiethanolamine (NDELA), its deuterated isotopomers (alpha-D(4)NDELA and beta-D(4)NDELA), N-nitroso-2-hydroxymorpholine (NHMOR), and two of its deuterated isotopomers (2-D-NHMOR and 5,5-D-2-NHMOR) to probe the mechanism of carcinogenic activation of NDELA and the role of its metabolite NHMOR. DNA samples, taken from the livers of male Wistar rats 4 h after the administration of NDELA, exhibited dose-dependent DNA SSB levels over the range of 0.08-0.75 mmol/kg (body weight), with the greatest SSB level at the highest dose. Deuterium isotope effects on DNA SSB levels were inversely dependent on dose: alpha-D(4)NDELA, 3.22-1.37; and beta-D(4)NDELA, 1.38-0.79, At the lowest dose of 0.15 mmol/kg (body weight), 5,5-D-2-NHMOR gave an isotope effect for DNA SSB of 2.8 while that for 2-D-NHMOR was 0.7, NDELA and beta-D(4)NDELA were equally cytotoxic to human P450 2E1-transfected V79 Chinese hamster cells, while alpha-D(4)NDELA was not. Significant DNA SSR levels were observed in these cells for NDELA and beta-D(4)NDELA but not for alpha-D(4)NDELA. A kinetic deuterium isotope effect of 2.6 NDELA to NHMOR, while k(II)/k(D) for alpha-D(4)NDELA was 1.05, These data provide the first definitive evidence fur the activation of NDELA by a pathway involving the scission of the alpha-CH bond and are consistent with P450 2E1-mediated alpha-hydroxylation of NDELA producing the corresponding reactive alpha-hydroxynitrosamine.