Enhancement by methylated oxypurines of the frequency of induced chromosomal aberrations

Effect of caffeine on induced damage in cells of Xenopus laevis

Xenopus laevis cells were treated with mitomycin C and subsequently treated with caffeine during either the S- or G2-phase of the cell cycle. The frequency of induced chromatid exchanges was especially increased by caffeine posttreatment during the S-phase. This increase took place at the expense of the frequency of isochromatid breaks, which was reduced, both when the caffeine posttreatment was given during the S- and G2-phase.

Effect of caffeine on G2 repair and its reversion by adenosine

Chromosome damage induced in root meristems of Allium cepa L. by an 18-h treatment with 5-aminouracil (AU) was enhanced by 2-h pulses with 5 mM caffeine, the most effective pulse being given from the 8th to the 10th h after AU. Chromosome damage was detected by the percentage of anaphases or telophases showing chromosomal aberrations. This caffeine effect was partially reversed by adenosine. We suggest that this caffeine anti-repair effect could be due to a competition between methylxanthine and an adenine-nucleotide derivative (ATP?) required for some step(s) of G2-prophase repair.

Cell-stage-specific enhancement by caffeine of the frequency of chromatid aberrations induced by X-rays in neural ganglia of Drosophila melanogaster

Caffeine (10(-2) M) induced a high level of chromatid aberrations in neural ganglia of third-instar larvae of Drosophila melanogaster only when it was added to cells in late G2 and mitotic prophase. No aberrations were observed after treatment in late S--middle G2 or C-mitosis. We observed that, in these stages, caffeine strongly increased X-ray-induced damage (500 R). This potentiation was quantitatively similar. But it involved all types of aberration after treatment in C-mitosis, and essentially isochromatid deletions and chromatid exchanges after treatment in S--G2. Some hypotheses are put forth to explain the possible mechanism of action of caffeine in the potentiation of X-ray-induced damage.

Genetic effects of dimethyl sulfate, diethyl sulfate, and related compounds

DMS and DES are monofunctional alkylating agents that have been shown to induce mutations, chromosomal aberrations, and other genetic alterations in a diversity of organisms. They have also been shown to be carcinogenic in animals. As an alkylating agent, DMS is a typical SN2 agent, attacking predominantly nitrogen sites in nucleic acids. DES is capable of SN1 alkylations as well as SN2 and thereby causes some alkylation on oxygen sites including the O6-position of guanine which is thought to be significant in mutagenesis by direct mispairing. The mutagenicity of DMS is better explained in terms of indirect, repair-dependent processes. With respect to both alkylating activity and genetic effects, striking similarities are found between DMS and MMS and between DES and EMS. In most systems where they have been tested, both DMS and DES are mutagenic. Results of many of the mutagenesis studies involving these compounds and other alkylating sulfuric acid esters are summarized in Tables 6, 7, 8, 9 and 10 of this review. Most data are consistent with these agents acting primarily as base-pair substitution mutagens. In the case of DES, strong specificity for G.C to A.T transitions has been reported in some systems but has not been clearly supported in some others. Low levels of frameshift mutations of the deletion type are also likely. In addition to the induction of mutations, recombinogenic and clastogenic effects have been described.

Caffeine

Most of the population of the world is exposed to caffeine to a greater or lesser extent since it occurs in a number of plants used in the preparation of widely consumed drinks, and has in addition a limited therapeutic use. Chromosomal abnormalities are induced by caffeine in both plant cells and in mammalian cells in culture and it also has some anti-mitotic activity. DNA-repair processes sensitive to caffeine have been demonstrated in a number of cell systems and it has been shown to affect a wide range of other cellular processes. Caffeine has potent mutagenic effects in Escherichia coli and other micro-organisms both when acting alone and in combination with other mutagens. However its mutagenic activity in Drosophila has been disputed and the available evidence suggests that it is neither mutagenic in mammals nor synergistic with other mutagens although at very high doses it appears to have some teratogenic activity in mammals.