Lack of correlation between apoptosis and DNA single-strand breaks in X-irradiated human peripheral blood mononuclear cells in the course of ageing

Abstract

The dependence on age of both the basal and the X-radiation-induced levels of apoptosis was examined in human peripheral blood mononuclear cells (PBMC). In the same samples, the base value and the extent of induced DNA single-strand breaks were determined, using a sensitive and fast microplate assay. PBMC were isolated from blood of donors of various age groups (20–30, 40–60 and >70 years of age) and X-irradiated ex vivo using a 6 MV linear accelerator to give a total exposure of 4 Gy. The mean basal levels of apoptosis in PBMC from donors in the 40–60 year age group and the >70 year age group were found to be only slightly higher (by 20–10%) compared to that of the 20–30 year age group, whereas the extent of DNA damage strongly and significantly ( P<0.01) increased with age by up to 2-fold. In contrast to the extent of induced DNA damage, which steadily increased in the course of ageing by up to 1.8-fold, there was only a transient increase in the level of induced apoptosis to 1.5-fold in PBMC from X-irradiated blood (4 Gy photons) from donors aged 40–60 followed by a decrease to 0.9-fold in PBMC from old donors (>70), compared to age group 20–30. The results show that X-ray-induced apoptosis and DNA damage in PBMC are not correlated during ageing.