Acute effect of 8-methoxypsoralen and ultraviolet light on sister chromatid exchange.

The acute effect of 8-methoxypsoralen (8-MOP) and 8-MOP + long wave ultraviolet light (UVA) on sister chromatid exchange (SCE) has been examined in an in vitro experiment. The SCE count was significantly increased by 8-MOP without light, but the effect was substantially greater (50%) by 8-MOP + UVA. In addition, mitoses with banded staining of the chromosomes were seen after 8-MOP and UVA. These changes were dose dependent, and they might be responsible for the reduced cell turnover in psoriasis plaque after PUVA.