Time dependent effects of caffeine on the frequency of N-methyl-N'-nitro-N-nitrosoguanidine-induced mutation in chinese hamster cells in vitro.

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Abstract
The effect of caffeine on the frequency of 8-azaguanine (8AG) resistant mutations in Chinese hamster cells (V79 [lung] cells) treated with N-methyl-N''-nitro-N-nitrosoguanidine (MNNG) was investigated. The effects of caffeine appeared to differ depending on the time and duration of caffeine exposure after MNNG treatment. When cells were exposed to caffeine during the 1st half of mutation expression time (0-24 h after MNNG treatment), the mutation frequency was slightly enhanced compared to MNNG treatment alone. Mutation frequency was reduced if caffeine was present during the latter half of expression time (24-48 h after MNNG treatment). Caffeine drastically reduced the frequency of mutation if the cells were exposed to caffeine for the whole mutation selection period from 48-240 h after MNNG treatment.