Selective Vitamin D Receptor Modulators (SVIMS) as Potential Adjuvant Therapeutic Agents

Copyright: © 2013 Li W. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Vitamin D3 (cholecalciferol, D3) is one of the most important forms of vitamin D in human health [1-4]. There are two sources for human beings to obtain vitamin D3. The first source is the conversion of 7-dehydrocholesterol (7-DHC) in the skin to pre-vitamin D3 by UVB irradiation from the sunlight, followed by thermal isomerization to produce vitamin D3 (Figure 1) [5]. This is a tightly regulated process by the human body, and it is impossible to result in vitamin D3 overdose. The second source is through diet supplements. Human body cannot regulate this source of intake well, and vitamin D3 overdose and subsequent toxicity could occur. Interestingly, vitamin D3 itself is not the biologically active form. It must be first hydroxylated at the C25 position in the liver to produce 25-hydroxyvitamin D3 (25(OH)D3), followed by a second hydroxylation at the C1 position in the kidney or by monocyte-macrophages in the immune system to produce the biologically active form 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (Figure 1). 1,25(OH)2D3 binds to the Vitamin D Receptor (VDR) which ultimately lead to its various biological functions (Figure 1).