Clastogenic interactions of γ radiation and caffeine in human peripheral blood cultures

Abstract

In order to determine whether the micronucleus test could be used as a rapid assay for mutagenic interactions, we studied the effect of 50–800 R of γ radiation in combination with 10 −6–10 −3 M caffeine in cultured human lymphocytes, with two treatment protocols. In one protocol (T 0), whole blood was irradiated with 50–800 R of γ radiation, then stimulated with PHA and cultured for 72, 96 or 120 h in the presence or absence of caffeine. Under these conditions, γ radiation produced micronuclei in proportion to dose but post-treatment with 1 mM caffeine significantly decreased the number of micronuclei observed. The effect of caffeine was greater with the higher radiation doses and at earlier fixation times. Caffeine also decreased the mitotic index which, in turn, decreased the number of micronuclei observed; but caffeine post-treatment still had a significant effect even after mitotic activity was taken into account. In a second protocol (T 48), PHA-stimulated (actively cycling) cultures were irradiated 48 h after innoculation, then treated with caffeine, and fixed at 72 h post-innoculation (PI). With this protocol γ radiation produced more micronuclei than at T 0; this suggests that many of the cells damaged at T 0 are either lost or repaired. At T 48 1 mM caffeine significantly increased the number of micronuclei observed after γ radiation at all doses except 50 and 200 R. The mitotic index increased after 400–600 R, but only in the absence of caffeine. These results indicate that caffeine can have paradoxical effects on micronucleus frequency, apparently by potentiation of both the lethal (at T 0) and clastogenic (at T 48) effects of γ radiation. Whether the mechanisms of action at T 0 and T 48 are the same awaits further research. We have thus shown that in this system the micronucleus test is a valuable assay for mutagenic interactions and may also indicate repair and cell cycle sensitivity.