Radiation-induced clastogenic plasma factors

Ionizing irradiation induces chromosomal aberrations in directly exposed cells and is known to have mutagenic and carcinogenic potential for the exposed host. Under controlled conditions, we examined whether such clastogenic effects of irradiation might be due in part to radiation-induced plasma factors. Irradiated cells and sera from CF-Nelson rats were used at 15 min, and 1, 7, 14, and 56–70 days after total body irradiation (250 R, n = 67 or 400 R, n=39). Control rats (n=44) served as donors of nonirradiated sera and cells. In addition, sera from six rats were irradiated (250 R or 400 R) in vitro. On the average, 298 metaphases from six rats were studied at each time-point. Cytogenetic abnormalities observed included chromatid- and chromosome-type lesions and hyperdiploidy. The frequency of abnormalities was comparable at both radiation doses. Nonirradiated cells exposed in vitro to irradiated serum (15 min postirradiation) exhibited a 36- to 48-fold increment in hyperdiploidy (p = 0.0001) and a 2.- to 2.2-fold rise in chromatid gaps and breaks (p < 0.01), but none of the chromosome-type aberrations seen in cells exposed to radiation. The clastogenic activity of irradiated plasma persisted in circulation for the 10-wk duration of the study and was not abrogated by dilution with nonirradiated serum. Serum irradiated in vitro was not clastogenic. This study shows that irradiation of rats results in the prompt appearance of clastogenic activity in their plasma. This activity is not due to radiation-induced depletion of protective factors nor to chemical-physical changes of normal plasma components, but results from circulating factors released by irradiated cells.