title: Caffeine inhibition of the metabolic activation of a carcinogen, 4-nitroquinoline-1-oxide, in cultured Chinese hamster cells.
abstract: The cytotoxic effect of 4-nitroquinoline-1-oxide (4NQO) on cultured Chinese hamster cells was drastically reduced by the presence of caffeine (0.2-1 mM). Caffeine, however, did not reduce the cytotoxicity of 4-hydroxyaminoquinoline-1-oxide (4HAQO), an active metabolite of 4NQO. The 105 000 g supernatant from the cell homogenate could catalyze the conversion of 4NQO to 4HAQO in the presence of NADPH or NADH as a hydrogen donor. This enzyme activity was strongly inhibited by caffeine (0.1-10 mM) or dicumarol (10(-8)-10(-6) M), an inhibitor of DT diaphorase (E.C.1.6.99.2). Dicumarol also reduced the cytotoxicity of 4NQO. These results clearly suggest that caffeine inhibits the conversion step of 4NQO to 4HAQO, resulting in a decrease in the cytotoxicity of 4NQO. Furthermore, the frequency of 6-thioguanine-resistant mutation by 4NQO was also strongly reduced by the presence of caffeine (1 mM) in cultured Chinese hamster cells, being consistent with the results of cytotoxicity.
mesh_terms: D015112:4-Nitroquinoline-1-oxide / Q000378:metabolism / Q000633:toxicity*; D000818:Animals; D001711:Biotransformation; D002110:Caffeine / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D001728:Dicumarol / Q000494:pharmacology; D007700:Kinetics; D008168:Lung; D009152:Mutagenicity Tests; D009153:Mutagens; D009154:Mutation; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009600:Nitroquinolines / Q000633:toxicity*; D010084:Oxidation-Reduction
chemical_list: D009153:Mutagens; D009600:Nitroquinolines; D009243:NAD; D002110:Caffeine; D009249:NADP; D015112:4-Nitroquinoline-1-oxide; D001728:Dicumarol