Interaction of cultured rat osteoblasts with 8-methoxypsoralen during irradiation with long-wave ultraviolet light.

Rat osteoblasts in monolayer cell cultures have been irradiated with long-wave ultraviolet light (UVA) in the presence and without 8-methoxypsoralen (8-MOP). In the absence of 8-MOP, the exposures to UVA (3 x 10(-3)W.cm-2) for up to 30 min have not affected cellular viability, the rate of 14C-acetate incorporation, and alkaline phosphatase (AP) activity. However, it depressed 3H-TdR incorporation rates by osteoblasts. 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 micrograms/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 UVA light by itself exerts a less potent inhibitory effect.