title: Altered pharmacokinetics of 1alpha,25-dihydroxyvitamin D3 and 25-hydroxyvitamin D3 in the blood and tissues of the 25-hydroxyvitamin D-24-hydroxylase (Cyp24a1) null mouse.
abstract: The 25-hydroxyvitamin D-24-hydroxylase (CYP24A1) plays an important role in regulating concentrations of both the precursor 25-hydroxyvitamin D3 [25(OH)D3] and the hormone 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)(2)D3]. Previous studies suggest that Cyp24a1-null mice cannot clear exogenous 1alpha,25(OH)2D3 efficiently. Here, we examined the metabolic clearance in Cyp24a1-null mice in vivo and in vitro using a physiological dose of [1beta-3H]1alpha,25(OH)2D3 or [26,27-methyl-3H]25(OH)D3. Cyp24a1-null mice showed difficulty in eliminating [1beta-3H]1alpha,25(OH)2D3 from the bloodstream and tissues over a 96-h time course, whereas heterozygotic mice eliminated the hormone within 6-12 h, although there was clearance of labeled hormone into water-soluble products involving liver in both genotypes. RT-PCR showed that Cyp24a1-null mice have decreased expression of 25-hydroxyvitamin D-1alpha-hydroxylase that must play a role in their survival. After the administration of [26,27-methyl-3H]25(OH)D3, Cyp24a1-null mice showed higher [26,27-methyl-3H]25(OH)D3 levels and no [26,27-methyl-3H]24,25(OH)2D3 formation, whereas heterozygotic mice showed significant [26,27-methyl-3H]24,25(OH)2D3 production. Based upon in vitro experiments, keratinocytes from Cyp24a1-null mice fail to synthesize [1beta-3H]calcitroic acid from [1beta-3H]1alpha,25(OH2D3 or [26,27-methyl-3H]24,25(OH)2D3 from [26,27-methyl-3H]25(OH)D3 as do control mice, confirming the target cell catabolic role of CYP24A1 in these processes. Finally, the role of vitamin D receptor (VDR) in the vitamin D catabolic cascade was examined using VDR-null mice. Keratinocytes from VDR-null mice failed to metabolize [1beta-3H]1alpha,25(OH)2D3 confirming the importance of vitamin D-inducible, VDR-mediated, C24 oxidation pathway in target cells. These results suggest that the absence of CYP24A1 or VDR retards catabolism of 1alpha,25(OH)2D3 and 25(OH)D3, reinforcing the physiological importance of CYP24A1 in vitamin D homeostasis.
authors.affiliation: Department of Biochemistry, Queen's University, Kingston Ontario, Canada K7L 3N6.
authors.forename: Sonoko
authors.initials: S
authors.lastname: Masuda
authors.forename: Valarie
authors.initials: V
authors.lastname: Byford
authors.forename: Alice
authors.initials: A
authors.lastname: Arabian
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Sakai
authors.forename: Marie B
authors.initials: MB
authors.lastname: Demay
authors.forename: René
authors.initials: R
authors.lastname: St-Arnaud
authors.forename: Glenville
authors.initials: G
authors.lastname: Jones
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000235:genetics; D000818:Animals; D002112:Calcifediol / Q000097:blood / Q000493:pharmacokinetics*; D002117:Calcitriol / Q000097:blood / Q000493:pharmacokinetics*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology; D066298:In Vitro Techniques; D015603:Keratinocytes / Q000201:enzymology; D051379:Mice; D018345:Mice, Knockout; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013250:Steroid Hydroxylases / Q000235:genetics* / Q000378:metabolism*; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D018167:Receptors, Calcitriol; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C585550:Cyp24a1 protein, mouse; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002117:Calcitriol; D002112:Calcifediol