Ageing in vivo does not influence micronucleus induction in human lymphocytes by X-irradiation

To test the hypothesis that the age-related decline in the stability of the genome is the consequence of an increasing deficiency in DNA repair we compared the extent of chromosome damage, after X-irradiation, in lymphocytes from healthy young and old individuals, using the expression of micronuclei as the end-point. Micronuclei have been shown to increase in number with age and they were enumerated using a recently described and improved technique which involves measurement of micronuclei in cells that were blocked from performing cytokinesis. The level of X-ray-induced micronuclei in cytokinesis-blocked cells, after exposure to 75 cGy and 150 cGy, was measured by subtracting the base-line micronucleus frequency in the control unirradiated cultures from the observed micronucleus frequency in the irradiated cultures. There was no difference between the results for the young and old subjects thus indicating that cells from the aged subjects do not exhibit increased chromosomal instability following X-irradiation. These results suggest that repair of those DNA lesions that lead to chromosome breakage does not decline with age.