Vitamin D Related

Vitamin D was first identified as a cure for nutritional rickets, a disease of bone growth caused by an inadequate uptake of dietary calcium. Vitamin D refers collectively to vitamin D3 and vitamin D2. Biologically active vitamin D is generated via largely hepatic 25-hydroxylation catalyzed by CYP2R1, CYP27A1, and possibly other enzymes to produce 25-hydroxvitamin D (25D), which has a long half-life and is the major circulating vitamin D metabolite. 25D is modified by 1α-hydroxylation catalyzed by CYP27B1, which produces hormonal 1,25-dihydroxyvitamin D (1,25D).

The biological actions of 1,25(OH)2D3 are mediated by the VDR. VDR belongs to the steroid receptor family which includes receptors for retinoic acid, thyroid hormone, sex hormones, and adrenal steroids. The genomic mechanism of 1,25(OH)2D3 action involves the direct binding of the 1,25(OH)2D3 activated vitamin D receptor/retinoic X receptor (VDR/RXR) heterodimeric complex to specific DNA sequences. 1,25(OH)2D3 action regulates renal calcium reabsorption and phosphate loss, and thus control bone metabolism mainly indirectly by regulating mineral homeostasis.

Vitamin D deficiency increases rates of cancer, as well as autoimmune and infectious diseases. More than 3,000 vitamin D analogs are developed worldwide and several analogs demonstrated more potent antiproliferative and prodifferentating effects on cancer cell lines compared with 1,25(OH)2D3, which may lead to the development of new therapies to prevent and treat diseases.

References:
[1] White JH. Infect Immun. 2008 Sep;76(9):3837-43.
[2] Christakos S, et al. Physiol Rev. 2016 Jan;96(1):365-408.