The clastogenic effect of 5-methoxypsoralen plus UV-A in human lymphocytes in vitro and its modification by the anticlastogen beta-aminoethylisothiouronium.

The treatment of human lymphocytes in vitro with 5-methoxypsoralen (5-MOP) plus UV-A induces a dose-dependent increase in the SCE rate and in structural chromosome aberrations. We carried out tests to see whether the clastogenic effect of 5-MOP plus UV-A could be reduced by the anticlastogen beta-aminoethylisothiouronium (AET). The occurrence of a protective effect proved to be dependent upon the conditions of treatment. When AET was present over a long period of time (22 h) in cultures with 5-MOP, the number of breaks was reduced compared with such cultures without AET (reduction factor 0.5-0.6). On the other hand, a short period of action by AET (1.5 h) in the presence of 5-MOP produced no reduction of breaks. Posttreatment with AET (20 h) yielded an obvious protective effect (reduction factor 0.2-0.4). The possible mechanisms of the protective effect of AET are discussed.