INTERACTION OF CULTURED RAT OSTEOBLASTS WITH 8-METHOXYPSORALEN DURINGIRRADIATION WITH LONG-WAVE ULTRAVIOLET-LIGHT

Rat osteoblasts in monolayer cell cultures have been irradiated with l ong-wave ultraviolet light (UVA) in the presence and without 8-methoxy psoralen (8-MOP). In the absence of 8-MOP, the exposures to UVA (3x10( -3)W.cm(-2)) for up to 30 min have not affected cellular viability, th e rate of C-14-acetate incorporation, and alkaline phosphatase (AP) ac tivity. However, it depressed H-3-TdR incorporation rates by osteoblas ts. In the presence of 15 to 100ng of 8-MOP/ml, even 5-min irradiation of osteoblasts was sufficient to reduce DNA synthesis. Much higher (0 .5 to 1.0 mu g/ml) 8-MOP concentrations were required to depress lipid synthesis, AP activity, and the viability of irradiated cells. These results suggest that in osteoblasts the machinery of DNA synthesis is especially labile to photosensitization with 8-MOP and UVA, whereas UV A light by itself exerts a less potent inhibitory effect. (C) 1995 Aca demic Press, Inc.