Enhancement and reduction by methylated oxypurines of the frequencies of chromatid aberrations induced by camptothecin in root-tip cells of Vicia faba

Abstract

In root-tip cells of Vicia faba the frequencies of chromatid aberrations induced by 3-h treatments with 0.05 μM camptothecin were strongly modified when the treatments were carried out in the presence of caffeine at concentrations above 1 mM. Depending in the concentration of caffeine, the clastogenic effect of camptothecin was either enhanced or reduced. At concentrations between 1 and 6 mM, caffeine increased the camptothecin-induced chromosome damage, the strongest enhancement being obtained at 5 mM. A reduction of the chromosome damage was apparent at caffeine concentrations above 10 mM, and in the presence of 20 mM caffeine the clastogenic effect of camptothecin was almost completely suppressed. When present during the camptothecin treatment, theophylline, 8-chlorocaffeine and 1,3,7,9-tetramethyluric acid influenced the induced chromosome damage in a similar way as caffeine, although with varying efficiency. If the concentrations required to produce the two types of modifying effect are used as a criterion, 8-chlorocaffeine was the most effective and 1,3,7,9-tetramethyluric acid the least, whereas caffeine and theophylline were about equally effective.