title: A High-Calcium and Phosphate Rescue Diet and VDR-Expressing Transgenes Normalize Serum Vitamin D Metabolite Profiles and Renal Cyp27b1 and Cyp24a1 Expression in VDR Null Mice.
abstract: Vitamin D receptor (VDR)-mediated 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-dependent gene expression is compromised in the VDR null mouse. The biological consequences include: hypocalcemia, hypophosphatemia, elevated parathyroid hormone (PTH) and 1,25(OH)2D3, and consequential skeletal abnormalities. CYP24A1 is a cytochrome P450 enzyme that is involved in the side chain oxidation and destruction of both 1,25(OH)2D3 and 25-hydroxyvitamin D3 (25-OH-D3). In the current studies, we used liquid chromatography-tandem mass spectrometry technology to compare the metabolic profiles of VDR null mice fed either a normal or a calcium and phosphate-enriched rescue diet and to assess the consequence of transgenic expression of either mouse or human VDR genes in the same background. Serum 1,25(OH)2D3 levels in VDR null mice on normal chow were highly elevated (>3000 pg/mL) coincident with undetectable levels of catabolites such as 24,25-(OH)2D3 and 25-OH-D3-26,23-lactone normally observed in wild-type mice. The rescue diet corrected serum Ca(++), PTH, and 1,25(OH)2D3 values and restored basal expression of Cyp24a1 as evidenced by both renal expression of Cyp24a1 and detection of 24,25-(OH)2D3 and the 25-OH-D3-26,23-lactone. Unexpectedly, this diet also resulted in supranormal levels of 3-epi-24,25-(OH)2D3 and 3-epi-25-OH-D3-26,23-lactone. The reappearance of serum 24,25-(OH)2D3 and renal Cyp24a1 expression after rescue suggests that basal levels of Cyp24a1 may be repressed by high PTH. Introduction of transgenes for either mouse or human VDR also normalized vitamin D metabolism in VDR null mice, whereas this metabolic pattern was unaffected by a transgene encoding a ligand binding-deficient mutant (L233S) human VDR. We conclude that liquid chromatography-tandem mass spectrometry-based metabolic profiling is an ideal analytical method to study mouse models with alterations in calcium/phosphate homeostasis.
authors.affiliation: Department of Biomedical and Molecular Sciences (M.K., G.J.), Queen's University, Kingston, Ontario, Canada K7L3N6; and Department of Biochemistry (S.M.L., J.W.P.), University of Wisconsin-Madison, Madison, Wisconsin 53706.
authors.forename: Martin
authors.initials: M
authors.lastname: Kaufmann
authors.affiliation: Department of Biomedical and Molecular Sciences (M.K., G.J.), Queen's University, Kingston, Ontario, Canada K7L3N6; and Department of Biochemistry (S.M.L., J.W.P.), University of Wisconsin-Madison, Madison, Wisconsin 53706.
authors.forename: Seong Min
authors.initials: SM
authors.lastname: Lee
authors.affiliation: Department of Biomedical and Molecular Sciences (M.K., G.J.), Queen's University, Kingston, Ontario, Canada K7L3N6; and Department of Biochemistry (S.M.L., J.W.P.), University of Wisconsin-Madison, Madison, Wisconsin 53706.
authors.forename: J Wesley
authors.initials: JW
authors.lastname: Pike
authors.affiliation: Department of Biomedical and Molecular Sciences (M.K., G.J.), Queen's University, Kingston, Ontario, Canada K7L3N6; and Department of Biochemistry (S.M.L., J.W.P.), University of Wisconsin-Madison, Madison, Wisconsin 53706.
authors.forename: Glenville
authors.initials: G
authors.lastname: Jones
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002112:Calcifediol / Q000031:analogs & derivatives / Q000378:metabolism; D002117:Calcitriol / Q000378:metabolism; D002136:Calcium, Dietary / Q000494:pharmacology*; D002853:Chromatography, Liquid; D004032:Diet; D005786:Gene Expression Regulation; D006801:Humans; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010710:Phosphates / Q000494:pharmacology*; D018167:Receptors, Calcitriol / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053719:Tandem Mass Spectrometry; D014807:Vitamin D / Q000031:analogs & derivatives / Q000378:metabolism; D065668:Vitamin D3 24-Hydroxylase / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D002136:Calcium, Dietary; D010710:Phosphates; D018167:Receptors, Calcitriol; C579457:VDR protein, human; C118756:dihydroxy-vitamin D3; D014807:Vitamin D; C026396:calcifediol lactone; C585550:Cyp24a1 protein, mouse; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002117:Calcitriol; D002112:Calcifediol