Calcitriol

Calcitriol is an active metabolite of vitamin D with 3 hydroxyl (OH) groups and is commonly referred to as 1,25-dihydroxycholecalciferol, or 1alpha,25-dihydroxyvitamin D, 1,25-dihydroxyvitamin D. It is produced in the body after series of conversion steps of 7-dehydrocholesterol from exposure to UV light. 7-dehydrocholesterol is converted to Vitamin D3 (vitamin D3) in the skin, which is then converted to Calcifediol in the liver and kidneys. Calcifediol undergoes hydroxylation to form calcitriol via 1α-hydroxylase (CYP27B1) activity . Calcitriol is considered to be the most potent metabolite of vitamin D in humans . Renal production of calcitriol is stimulated in response to PTH, low calcium and low phosphate . Calcitriol plays a role in plasma calcium regulation in concert with parathyroid hormone (PTH) by enhancing absorption of dietary calcium and phosphate from the gastrointestinal tract, promoting renal tubular reabsorption of calcium in the kidneys, and stimulating the release of calcium stores from the skeletal system. In addition to promoting fatty acid synthesis and inhibiting lipolysis, calcitriol has been demonstrated to increase energy efficiency by suppressing UCP2 expression, which is modulated by signaling pathways of classical nuclear receptors (nVDR), where calcitriol acts as a natural ligand . There is also evidence that calcitriol modulates the action of cytokines and may regulate immune and inflammatory response, cell turnover, cell differentiation . Administered orally and intravenously, calcitriol is commonly used as a medication in the treatment of secondary hyperparathyroidism and resultant metabolic bone disease, hypocalcemia in patients undergoing chronic renal dialysis, and osteoporosis. It is also available in topical form for the treatment of mild to moderate plaque psoriasis in adults. Calcitriol is marketed under various trade names including Rocaltrol (Roche), Calcijex (Abbott) and Decostriol (Mibe, Jesalis).