Incidence of Micronuclei inversly relates with apoptosis in human circulating lymphocytes

In this study relationship between chromosome aberrations, micronuclei, radiosensitivity and apoptosis of circulating lymphocytes of radiation workers was evaluated. Exposed group comprises 34 individuals, radiology sts, of mean age 43,35±6.02; with 14.9±5.2 years of occupational exposition to ionizing radiation. In 10 out of 34 exchange aberrations were found (dicentrics and ring chromosomes). According to chromosomal findings exposed groups was divided on two subgroups:>> dicentric positive<< and >>dicentric negative<<. The induction of micronuclei in circulating lymphocytes was used as indicator of radiation sensitivity in vitro (challenge dose of 2 Gy; 60Co g-rays). Apoptosis was assessed by flow cytometric identification of cells displaying apoptosis-associated DNA condensation. Three parameters were measured: cell size, granularity and DNA content. Each sample was analyzed using 10.000 events. Both subgroups of exposures are matched with controls (44persons). Dicentric chromosomes were not found in lymphocytes of control subjects: mean value of baseline micronuclei was 14±4, percent of apoptosis cells was 80±16, and mean incidence of radiation induced micronuclei was 195±31. In exposed group 10 out of 34 were dicentric positive. Mean value of baseline micronuclei in>> dicentric positive << group was 33±7; 23±7 in>>dicentric<< negative, (statistically unsignifficant, t=0.2, p<0,2). Mean value of radiation induced micronuclei was 187±29 in >>dicentric<< positive group, 177±34 in >>dicentric<< negative (statistically un significant, t=1,3, p<0,2). Mean percent of apoptosis cells was 41±20 in >>dicentric<< positive group, 62±24 in >>dicentric<< negative respectively. Baseline micronuclei correlates negatively with apoptosis in both exposed groups (r=0.55m p<0.45) suggesting that chronical exposure to low doses of ionizing radiation disturb the balance between pro apoptotic and anti apoptotic signals in cells. Results of our study have shown that effects of radiation-induced cytotoxicity could be characterised employing flow cytometry as precise method for measuring degradation of internucleosaomal DNA. Inversly relationship between baseline micronuclei and percent of lymphocytes undergoing apoptosis is the most important finding in this study, suggesting that assay can discriminate differences in radiation-induced cytotoxicity between individuals occupationally exposed to low doses of ionising radiation. (Author)