[NO-dependent pathway of the modifying of the cellular sensitivity to gamma- and neutron irradiation]

The modifying effect of L-NAME, the NO-synthase inhibitor and D-NAME, the inactive enantiomer was investigated in human carcinoma cells (HeLa) and Chinese hamster fibroblasts (V-79) exposed to different doses of gamma-rays and 0.85 MeV neutrons. We estimated the level of the chromosome aberrations manifested as the bridges and fragments in anaphases. Radioprotective effect of L-NAME showed the inverse dependence on the exposure dose and at low doses (1 Gy) it was higher in the V-79 cells, than in the HeLa cells. However, at high doses (3, 4, 6 Gy) the efficiency of L-NAME for these cellular lines was almost equal (DFR = 2). The modifying effect of L-NAME was almost equal for gamma-irradiation and neutrons, although the exposure of V-79 cells to neutrons induced more the asymmetric chromosome aberrations (RBE = 4). The D-NAME had no effect on the level of the radiation-induced chromosome aberrations, although D-NAME treatment of cells increased the chromatin condensation, as well as L-NAME. The counteractive condensation does not play the major role in the radioprotective effect of L-NAME. We suggest that the radioprotective effect of L-NAME resulted from the action on the generation reactive radicals due to the inhibition of the inducible NO-synthase.