Caffeine pretreatment enhances the unscheduled DNA synthesis in spermatids of mice exposed to methyl methanesulfonate

Abstract

The effect of caffeine on unscheduled DNA synthesis (UDS) induced by methyl methanesulfonate (MMS) was studied in the germ cells of male mice. The concentration of caffeine in the testes was found to be greatest about 0.5 h after i.p. injection. Therefore, caffeine exposures were given 0.5 h before i.p. injection with MMS. DNA repair in early spermatids was measured by the unscheduled incorporation of [ 3h]dThd into the germ cells, which were then recovered from the caudal epididymides 16 days after chemical treatment. Pretreatment of the mice with 100 mg caffeine/kg resulted in approximately a 60% increase in the unscheduled uptake of [ 3]H]dThd into the MMS-damaged germ cells, compared with that observed with MMS treatment alone ( P < 0.0001). However, caffeine alone did not induce any measurable UDS. Further studies showed that caffeine enhancement of UDS response of germ cells to MMS damage was not due to a reduction in the endogenous dThd pool. Also, chemical dosimetry studies using [ 3H]MMS did not show any difference in the level of testicular DNA methylation in caffeine-pretreated animals compared with controls. To explain the increased UDS response of the germ cells to MMS-induced DNA damage following caffeine pretreatment, we suggest a model in which the average patch size resulting from the excision of methylated DNA is increased in the presence of caffeine (or possibly its metabolites). Thus, for example, pretreatment with 100 mg caffeine/kg results in a DNA repair patch ≈60% larger than that resulting from MMS treatment alone.