The emergence of vitamin D as a first-line treatment for psoriasis

Vitamin D first became available during the 1930s and it was soon reported that psoriasis could respond to this drug. It was recognized that vitamin D analogues (secosteroids) were potent hormones with a major role in the regulation of calcium homeostasis. Further study revealed that specific receptors for secosteroids were present not only in organs regulating calcium metabolism but in virtually all types of cells. The secosteroid receptor is part of the steroid/retinoid/thyroid hormone receptor superfamily. It is most active in dimeric forms either as a homodimer or combined with other receptors in this family as heterodimers. Dimeric hormone/receptor complexes combine with a range of response elements on segments of DNA upstream of regulated genes and are involved in the control of gene transcription. Functions of secosteroids include regulation of proliferation and differentiation. They also have immunosuppressant properties. It has not proved simple to produce an analogue suitable for systemic use which will retain antipsoriatic activity without having a significant effect on calcium metabolism. However, topical vitamin D analogues, especially calcitriol, tacalcitol and calcipotriol have proved effective in psoriasis vulgaris. Tacalcitol and calcipotriol have become first-line treatments for this disease