Ultraviolet irradiation depletes cellular retinol and alters the metabolism of retinoic acid in cultured human keratinocytes and melanocytes

Vitamin A is an intrinsic modulator of proliferation and differentiation in human epidermis, and may be destroyed by ultraviolet radiation (UVR) impin ging on the skin. To identify the deleterious effects of a perturbed cellul ar vitamin A status, we investigated the endogenous retinoid concentrations and the metabolism of [H-3]retinol and all-trans [H-3]retinoic acid in cul tured human keratinocytes and melanocytes exposed to UVR, using high perfor mance liquid chromatography, Before UVR the retinoid content was similar in keratinocytes and melanocytes, but the uptake of [H-3]retinol was three-fo ld higher and the uptake of [H-3]retinoic acid was 10-fold higher in the me lanocytes. In both cell types, UVR (UVA 360 mJ/cm(2) plus UVB 140 mJ/cm(2)) instantaneously reduced the concentration of retinol by about 50% and that of 3,4-didehydroretinol by about 20%, The retinoid concentrations returned to normal within 1-2 days post-irradiation, despite there being no evert i ncrease in the uptake of [H-3]retinol or the biosynthesis of 3,4-didehydror etinol. However, in both types of irradiated cells, the accumulation of the biologically most active metabolite, all-trans [H-3]retinoic acid, was abo ut 60% higher than in control cells. Furthermore, the metabolism of authent ically supplied [H-3]retinoic acid was reduced, especially in irradiated ke ratinocytes, which probably contributed to the restoration of retinoid leve ls after UV exposure. (C) 1999 Lippincott Williams & Wilkins.