The effect of caffeine and adenine on radiation induced suppresion of DNA synthesis and cell survival
Wilcoxson, Lesley Taylor
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Exposure of cultured mammalian cells to either UV light or ionizing radiation results in a transient decrease in the rate of DNA synthesis. The proposed function of this inhibition in synthesis is to allow cells time to repair inflicted damage, prior to replication. The effect of exposure to UV light or gamma-irradiation, and post-irradiation incubation with caffeine or adenine, upon rate of DNA synthesis was examined in two cell lines exhibiting normal sensitivity to UV light, BALB/3T3 and CHO AA8, and in two UV-sensitive cell lines, CHO UV5 and CHO UV20. The effect of caffeine and adenine post-irradiation treatment on cell survival was also investigated. Results indicate that both caffeine and adenine attenuate the post-irradiation depression in DNA synthetic rate. Differences in the effects of the two chemical agents on the depression in DNA synthesis may be due to differences in the exact mechanism by which each chemical agent exerts its action. After exposure to ionizing radiation, both caffeine and adenine enhance cell killing, suggesting that attenuation of the inhibition of DNA synthesis may increase fixation of damage by preventing repair. Following exposure to UV light, post-irradiation incubation with either caffeine or adenine has little effect on cell survival. Thus, it appears that the depression in rate of DNA synthesis is not the sole factor involved in the ultimate survival of cells following irradiation.