Abstract
Caffeine induced a high frequency of chromatid aberrations in the cultured human leucocytes and the human embryonic cells in culture. The chromatid aberrations were predominantly gaps and breaks, and no exchange aberrations were observed. Experiments made by varying the interim between treatment and fixation, accompanied by the 3H-TdR labelling technique, showed that induction of damage was confined to the DNA-synthesis phase, in which the later part of the S phase was the most sensitive. Caffeine had no effect on the G1 and G2 phases. The rarity of exchange aberrations and the restriction of sensitivity to the DNA-synthesis phase may relate to the ambiguous results on the effectiveness of caffeine in the induction of dominant lethal mutations in laboratory animals.
