The effect of methylxanthines on chromosomes of human lyphocytes in culture.

The effect of caffeine (I,3,7-trimethylxanthine), theophylline (I,3-dimethylxanthine), theobromine (3,7-dimethylxanthine), paraxanthine (I,7-dimethylxanthine) I-methylxanthine, 3-methylxanthine, and 7-methylxanthine added at the 48th h on the chromosomes of human lymphocytes in 72-h cultures has been investigated. Caffeine and the dimethylxanthines cause breakage at 750 mug/ml, with caffeine the most, and paraxanthine the least clastogenic. I-Methylxanthine and dimethylxanthines with a methyl group in the I-position are the most effective in depressing mitotic indices. No chromosome damage was exhibited by the monomethylxanthines.