The influence of dietary restriction on DNA repair in rodents: a preliminary study

A range study was undertaken to determine if dietary restriction (DR) affects DNA repair in rodents. Unscheduled DNA synthesis (UDS) was examined in two strains of rat (Brown Norway, BN and Brown Norway X Fischer 344 F1 hybrid, BNF) at 18 months of age. O(6)-Methylguanine-acceptor protein activity (MGAP) was measured across species using rat (Brown Norway X Fischer F-344 F1 hybrid, 18 months) and mouse (B6CB F1 hybrid, 30 months). The rodents were maintained on either an ad libitum (AL) or a restricted diet (60% of the caloric intake of AL rodents). UDS increased approximately 48-65% in freshly isolated skin cells from DR animals opposed to their AL controls after challenge with ultraviolet light (254 nm, 20 J/m2 UV). After treatment with methylmethane sulfonate (0.5 mM MMS), a significant increase in UDS was observed (P less than 0.01, approx, 55% for BN and 52% for BNF rats). Results of measurements for MGAP activity found levels to increase 73% in DR rats and approximately 28% in DR mice when compared to their AL counterparts. In addition MGAP levels in phase shifted mice were examined at three time points during a 24-h period where significant changes were found to occur in the metabolism of DR rodents. The activity of MGAP changed in a circadian fashion with significant increases in MGAP activity in DR mice occurring during the period of highest metabolic activity.