Effects of PUVA therapy on skin surface lipids: skin surface lipid peroxidation in psoriasis vulgaris and its biological significance.

PUVA therapy (Psoralen + UVA irradiation) is an effective mode of photochemotherapy for psoriasis vulgaris. The biological significance of PUVA therapy for psoriasis vulgaris has mainly been considered to be based on DNA, especially the formation of DNA crosslinks between complementary DNA stands. On the other hand, we have already reported that skin surface lipids were oxidized by UVA irradiation in vitro and this reaction was enhanced in the presence of 8-methoxy-psoralen by a singlet oxygen mechanism. Keeping this in mind, we conducted an experiment to determine whether lipid peroxide can be formed in skin surface lipids following systemic PUVA therapy in psoriasis patients and the following results were obtained: 1) a marked increase of lipid peroxide values in skin surface lipids occurred following PUVA therapy; and 2) the amount of squalene in skin surface lipids was decreased by this treatment. These results indicate that skin surface lipids can be oxidized by PUVA therapy in vivo and this lipid peroxidation on the skin surface may be related to the effects of PUVA therapy on psoriasis vulgaris.