Vitamin D receptor (VDR), via conversion to calcitriol

Class

Vitamin D receptor activator / prohormone (extended-release calcifediol, 25-hydroxyvitamin D3)

Pathway

Vitamin D / calcium-phosphate-PTH regulatory axis

Notes

original target text: Vitamin D receptor (VDR), via conversion to calcitriol (1,25-dihydroxyvitamin D3)

The vitamin D receptor (VDR) is a nuclear receptor found in intestine, bone, parathyroid gland, and kidney. It is switched on by calcitriol, the fully activated hormonal form of vitamin D, and once activated it turns on genes that govern calcium and phosphate absorption from the gut, calcium handling in the kidney, bone remodeling, and suppression of parathyroid hormone (PTH) release. Calcitriol itself is made in two steps: the liver converts vitamin D3 to calcifediol (25-hydroxyvitamin D3), and the kidney then converts calcifediol to calcitriol. Extended-release calcifediol supplies this intermediate prohormone directly, raising circulating substrate so that whatever hydroxylation capacity a person retains can generate calcitriol at a steadier, more physiological pace, rather than giving the active hormone outright. This approach is used when vitamin D activation is impaired or when its precursor pool is depleted, most notably in chronic kidney disease, where the kidney's converting enzyme is reduced, and in more general vitamin D insufficiency affecting bone mineralization. The broader therapeutic aim across this pathway is to restore adequate VDR signaling so that calcium and phosphate balance is preserved and PTH remains appropriately suppressed, since chronic imbalance in this axis drives secondary hyperparathyroidism, bone disease, and disturbances in mineral metabolism.