EFFECT OF UVA AND BLUE-LIGHT ON PORPHYRIN BIOSYNTHESIS IN EPIDERMAL-CELLS

To study porphyrin biosynthesis in normal human keratinocytes and A431 cells derived from human epidermoid carcinoma, cultured cells were in cubated with delta-aminolevulinic acid (ALA), the precursor of porphyr in synthesis, and accumulation of porphyrins was measured spectrofluor ometrically. Both human keratinocytes and A431 cells accumulated porph yrins in a time-dependent and a dose-dependent fashion. Protoporphyrin was the predominant porphyrin accumulated by both cell types. Porphyr in accumulation was enhanced by Ca Mg ethylenediaminetetraacetic acid, a ferrochelatase inhibitor, and the enhancement was reversed by the a ddition of iron, suggesting the utilization of iron by ferrochelatase. The effect of light on porphyrin accumulation was evaluated by exposi ng the ALA-loaded A431 cells to ultraviolet-A (UVA) and blue light rad iation, followed by continued incubation with ALA for 2-48 h. There wa s an enhancement of porphyrin accumulation 2-48 h after the radiation as compared with nonirradiated controls. Consistent with this finding, ferrochelatase activity decreased in these cells at 24 h and 48 h. Th ese data demonstrate that human keratinocytes and A431 cells are capab le of porphyrin biosynthesis, and that exposure of porphyrin-containin g A431 cells to light, which includes the Soret band spectrum, decreas es the ferrochelatase activity, which is responsible, at least in part , for the further increase in porphyrin level.