Intestinal and Hepatic CYP3A4 Catalyze Hydroxylation of 1α,25-Dihydroxyvitamin D₃: Implications for Drug-Induced Osteomalacia

Abstract

The decline in bone mineral density that occurs after longterm treatment with some antiepileptic drugs is thought to be mediated by increased vitamin D 3 metabolism. In this study, we show that the inducible enzyme CYP3A4 is a major source of oxidative metabolism of 1␣,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] in human liver and small intestine and could contribute to this adverse effect. Heterologously-expressed CYP3A4 catalyzed the 23-and 24-hydroxylation of 1,25(OH) 2 D 3 . No human microsomal cytochrome P450 enzyme tested, other than CYP3A5, supported these reactions. CYP3A4 exhibited opposite product stereochemical preference compared with that of CYP24A1, a known 1,25(OH) 2 D 3 hydroxylase. The three major metabolites generated by CYP3A4 were 1,23R,25(OH) 3 D 3 , 1,24S,25(OH) 3 D 3 , and 1,23S,25(OH) 3 D 3 . Although the metabolic clearance of CYP3A4 was less than that of CYP24A1, comparison of metabolite profiles and experiments using CYP3A-specific inhibitors indicated that CYP3A4 was the dominant source of 1,25(OH) 2 D 3 23-and 24-hydroxylase activity in both human small intestine and liver. Consistent with this observation, analysis of mRNA isolated from human intestine and liver (including samples from donors treated with phenytoin) revealed a general absence of CYP24A1 mRNA. In addition, expression of CYP3A4 mRNA in a panel of duodenal samples was significantly correlated with the mRNA level of a known vitamin D receptor gene target, calbindin-D9K. These and other data suggest that induction of CYP3A4-dependent 1,25(OH) 2 D 3 metabolism by antiepileptic drugs and other PXR ligands may diminish intestinal effects of the hormone and contribute to osteomalacia.

25-Hydroxyvitamin D concentration and all-cause mortality: the Melbourne Collaborative Cohort Study

“…While the microsomal vitamin D 25-hydroxylase, CYP2R1, 25-hydroxylates both ergocalciferol and cholecalciferol equally well (29,30) , mitochondrial CYP27A1 25-hydroxylates cholecalciferol (31) , but not ergocalciferol (32) . Another enzyme, CYP3A4, 25-hydroxylates ergocalciferol and not cholecalciferol, but also 24-hydroxylates several vitamin D metabolites (33)(34)(35) . In particular, CYP3A4 plays a major role in 23-and 24-hydroxylation of the biologically active form of cholecalciferol, 1,25-dihydroxycholecalciferol (1,25(OH) 2 D 3 ), in the liver and small intestine (35) .…”

“…Another enzyme, CYP3A4, 25-hydroxylates ergocalciferol and not cholecalciferol, but also 24-hydroxylates several vitamin D metabolites (33)(34)(35) . In particular, CYP3A4 plays a major role in 23-and 24-hydroxylation of the biologically active form of cholecalciferol, 1,25-dihydroxycholecalciferol (1,25(OH) 2 D 3 ), in the liver and small intestine (35) . CYP3A4 is the most abundant liver cytochrome P450 enzyme and has broad specificity, catabolising more than 50 % of known drugs (34,36) .…”

“…CYP3A4 is the most abundant liver cytochrome P450 enzyme and has broad specificity, catabolising more than 50 % of known drugs (34,36) . Many drugs inhibit or induce CYP3A4, thereby potentially increasing vitamin D turnover (33,35) . It is possible that ergocalciferol similarly induces CYP3A4, leading to enhanced 23-and 24-hydroxylation of 1,25(OH) 2 D 3 ; inactivating cholecalciferol and ultimately eliminating it from the body.…”

Can Vitamin D Slow Progression of Osteoarthritis?

“…CYP2R1 is the important 25-hydroxylase. [14]. CYP3A4 was reported in drug-drug interactions involving Vit-D, in which coadministered drug causes accelerated degradation of Vitamin D 2 over D 3 .…”

Identification of human UDP-glucuronosyltransferases catalyzing hepatic 1α,25-dihydroxyvitamin D3 conjugation

“…The intestinal mucosa is an important target tissue for 1,25(OH) 2 D 3 , where it regulates the expression of calcium binding and transport proteins and helps maintain calcium homeostasis throughout the body [7,8,9]. In addition, we have recently shown that up-regulation of CYP3A4 gene expression by 1,25(OH) 2 D 3 may provide negative feedback control of the hormone's biological effects in the intestine through CYP3A4-catalyzed metabolism of 1,25(OH) 2 D 3 to inactive oxidation products [10].…”