Photosensitization of the sunscreen octyl p-dimethylaminobenzoate by UVA in human melanocytes but not in keratinocytes

Sunscreens penetrate human epidermis and modify the biology of proliferatin g cells. This study addressed the question whether the UV response of cultu red human cells is affected by direct treatment with nontoxic levels of sun screens. Cell survival following exposure to UVC or unfiltered UVB was not altered by preincubation with 25 mug/mL of octyl p-dimethylaminobenzoate (o -PABA), 2-ethylhexyl p-methoxycinnamate (EHMC) or oxybenzone. However, UVA or UVB filtered to reproduce the solar UV spectrum penetrating to the basal layer of the epidermis, highly sensitized cells to killing by o-PABA but n ot by its hydrolysis product, 4-dimethylaminobenzoic acid. Sensitization wa s found in all cell types tested, except normal keratinocytes, and could be prevented by certain antioxidants particularly pyruvate and the hydroxyl r adical scavenger mannitol, o-PABA and EHMC applied without UV reduced the a dherence of cells. The results indicate that sunscreens may increase cell m obility and the combination of o-PABA with solar UV may selectively damage melanocytes in the skin.