INVESTIGATION OF ANTIOXIDANT STATUS, DNA-REPAIR CAPACITY AND MUTATIONAS A FUNCTION OF AGE IN HUMANS

We are constantly exposed, throughout life, to a wide variety of extri nsic and intrinsic agents which have the potential to damage cellular biomolecules, including DNA. Imperfections in cellular defence systems which protect against the fixation of DNA damage can lead to an accum ulation of mutations which on their own, or in combination with other age-related changes, may contribute to ageing and the development of a ge-related pathologies. We have previously reported an increase in fre quency of mutation with age in human lymphocytes taken from healthy ma les in the age groups, 35-39, 50-54 and 65-69 years. In this article w e report on the findings of a recent study which was designed to asses s whether the age-related increase in frequency of mutation was due to a decreased efficacy of the defence systems against ROS-induced DNA d amage, namely antioxidant status and DNA repair processes, in the same study subjects. In vivo antioxidant status was assessed in each of th e study subjects by measuring blood levels of; superoxide dismutase (S OD; EC 1.15.1.1), glutathione peroxidase (GPx; EC 1.11.1.9), catalase (EC 1.11.1.6), caeruloplasmin (CPL), uric acid and bilirubin. We did n ot find any statistically significant differences in the mean levels o f these antioxidants between the three different age groups. To invest igate the efficacy of DNA repair processes against ROS-induced DNA dam age, an ELISA was used to quantitate DNA damage (as % single-stranded DNA; %SS-DNA) at various times following treatment of peripheral blood lymphocytes with hydrogen peroxide (H2O2). The results of this part o f the study showed that in untreated lymphocytes, basal levels of %SS- DNA were significantly higher in individuals from the 65-69 years age group compared to the 35-39 years age group (p = 0.039, 0.0013; at 5% level of significance). No significant differences were found in H2O2 susceptibility with age immediately following treatment (p = 0.71, 1.0 0; at 5% level of significance) but a consistent and significant incre ase was observed in %SS-DNA remaining 90 min post-treatment in lymphoc ytes from subjects in the 65-69 years age group, compared to %SS-DNA p resent in lymphocytes from the 35-39 years age group (p = 0.013, 0.024 ; at 5% level of significance). The results of this study suggest that the age-related increase in frequency of mutations is not contributed to by alterations of in vivo antioxidant status with age but is by a decreased efficacy of the repair of ROS-induced DNA damage with age. T he biological implications of somatic mutations in the ageing process are discussed.