[New relevance of vitamin D3 metabolism in the skin].

Epidermal keratinocytes are the site of both UVB-induced photochemical conversion of 7-dehydrocholesterol to vitamin D(3) (25 OHD(3)) and the enzymatically controlled hydroxylation via 25-hydroxyvitamin D(3) to the biologically active final product 1alpha,25-dihydroxy vitamin D(3) (1alpha,25(OH)(2)D(3), calcitriol). The epidermal synthesis of calcitriol is of fundamental relevance because calcitriol regulates important cellular functions in keratinocytes and dermal immunocompetent cells. Calcitriol and other vitamin D-analogues are effective in the treatment of psoriasis because of their anti-proliferative and pro-differentiation effects. One mechanism for UVB-light therapy in psoriasis could be the induction of calcitriol synthesis. A better understanding of the metabolism of vitamin D(3) in the skin opens new perspectives for potential therapeutic applications of vitamin D analogues in inflammatory skin diseases. Further studies investigating the role of vitamin D(3) metabolism in the prevention of malignant skin disorders are needed.