Vitamin D Basics

CYP24 Catabolism

Excessive intracellular levels of 1,25-dihydroxyvitamin D stimulate the expression of a cytochrome P450 enzyme known as CYP24 in cells which contain the vitamin D receptor (VDR). The CYP24 enzyme catabolizes 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D and vitamin D with high specificity, thereby restoring normal intracellular vitamin D hormone levels.  This is an important feedback mechanism that limits excessive local exposure to vitamin D hormones. In CKD, CYP24 can be aberrantly elevated due to processes related to kidney damage and by bolus high-dose treatment with current vitamin D hormone replacement therapies.  Aberrant elevations in CYP24 may contribute to vitamin D insufficiency and exacerbate SHPT in CKD patients.