Photoinactivation and recovery in skin fibroblasts after formation of mono- and bifunctional adducts by furocoumarins-plus-UVA.

Cultured skin fibroblasts from young male guinea pigs were irradiated with UVA light in the presence of 8-methoxypsoralen (8-MOP) or angelicin. As compared to 8-MOP 30 times higher concentrations of angelicin were needed to obtain comparative inhibition rates of DNA-synthesis. Complete cellular recovery could be observed when the cell cultures were treated with angelicin-plus-UVA (320-400 nm) or 8-MOP-plus-395 nm. Both treatment schedules are known to cause monofunctional photoreactions. In contrast to this, bifunctional photoreactions caused by 8-MOP-plus-365 nm produced an inhibition of DNA synthesis which lasted more than four days. Also, UVA (320-400 nm) applied to cells treated with 3H-labeled 8-MOP resulted in a dose-dependent binding of 8-MOP molecules again lasting several days. Application of 8-MOP-plus-UVA (320-400 nm) to cells growing in log-phase showed a characteristic change in morphology. An increasing number of polynuclear and hyperchromatic cells appeared with time after treatment. In this subpopulation of cells DNA synthesis continued without division as revealed by DNA measurements and autoradiography. It is concluded that monofunctional adducts caused by angelicin-plus-UVA as well as 8-MOP-plus-395 nm permit cellular recovery whereas bifunctional photoadducts remained without recovery. In the latter case semiconservative DNA synthesis continued leading to hyperchromatic cells which could serve as a parameter for the presence of cross-linked nuclear DNA strands.