Topical treatment of psoriatic plaques with 1,25-dihydroxyvitamin D3: a cell biological study.

Calcitriol, 1 alpha,25 dihydroxycholecalciferol (1 alpha,25 (OH)2 D3) is a natural active vitamin D3 metabolite, which has been shown to have antipsoriatic efficacy. In vitro studies have demonstrated that calcitriol influences various aspects of inflammation, epidermal proliferation and keratinization. The aim of the present study was to determine to what extent calcitriol (3 micrograms/g in white petrolatum) affects these parameters in vivo. Using an immunohistochemical assessment of recruitment of cycling epidermal cells, filaggrin and involucrin expression, T-cell accumulation, polymorphonuclear neutrophil (PMN) accumulation, amount of endothelium and ICAM-1 expression, we demonstrated that: (i) modulation of all these parameters occurred during calcitriol treatment; (ii) there was early reduction of epidermal proliferation and PMN accumulation; (iii) the order of changes was comparable with the response to treatment with calcipotriol. In conclusion, at the cell biological level, calcitriol (3 micrograms/g in white petrolatum) has a substantial effect on various elements of the psoriatic lesion.