[Current Topics on Vitamin D. Protein interaction and biological action of active vitamin D compounds]

To express its biological action, active vitamin D3 (1α,25-dihydroxyvitamin D3) interacts with three proteins : vitamin D binding protein (DBP), vitamin D receptor (VDR), and CYP24A1. This article explains how eldecalcitol interacts with these three proteins to achieve its mode of action. The main feature of eldecalcitol's molecular structure is the 3-hydroxypropyloxy group (3-HP group) at the 2β-position. When interacting with DBP, eldecalcitol tightly binds to DBP via the 3-HP group and enhances systemic stability of eldecalcitol. By binding to VDR, the 3-HP group stabilizes the eldecalcitol-VDR complex, which leads to high efficacy. The 3-HP group also interferes with the binding to CYP24A1, which induces residence to CYP24A1 and liver metabolism. These protein interactions constitute the mode of action of eldecalcitol.