title: 24R,25-dihydroxyvitamin D3 promotes bone formation without causing excessive resorption in hypophosphatemic mice.
abstract: To clarify the differences in the action of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and 24,25-(OH)2D3 in hypophosphatemic (Hyp) mice, a model for familial X-linked hypophosphatemic rickets in humans, we carried out histomorphometric examinations of the effects of these agents in the lumbar vertebra of these mice. The Hyp mice received 1-1000 micrograms/kg.day 24,25-(OH)2D3, 0.01-0.1 micrograms/kg.day 1,25.(OH)2D3, or vehicle alone given daily for 28 days by ip injection. Histomorphometrically, 1,25-(OH)2D3 and 24,25-(OH)2D3 showed similar effects on bone formation. The parameters of bone formation, mineralized bone volume/bone volume, mineral apposition rate, and bone formation rate/bone surface, were improved to a similar extent in a dose-dependent manner by 1,25-(OH)2D3 and 24,25-(OH)2D3, but there were remarkable differences in the indexes of the bone resorption between these two metabolites. In 24,25-(OH)2D3-treated Hyp mice, osteoclast number/bone perimeter and osteoclast surface/bone surface, the parameters of bone resorption, increased to control levels and did not change according to the dose of 24,25-(OH)2D3. However, in 1,25-(OH)2D3-treated Hyp mice, these values increased remarkably, exceeding the control level. That is, 24,25-(OH)2D3 normalized bone resorption in the rachitic mice, whereas 1,25-(OH)2D3 caused excessive stimulation of bone resorption. This qualitative difference between the two compounds contributes to the superior effects exerted by 24,25-(OH)2D3 in improving the bone lesion in Hyp mice. At doses from 1-1000 micrograms/kg.day, 24,25-(OH)2D3 had dose-dependent effects in increasing bone formation without promoting excessive bone resorption, as shown by histomorphometric analysis.
authors.affiliation: Department of Pediatrics, Okayama University Medical School, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ono
authors.forename: H
authors.initials: H
authors.lastname: Tanaka
authors.forename: T
authors.initials: T
authors.lastname: Yamate
authors.forename: Y
authors.initials: Y
authors.lastname: Nagai
authors.forename: T
authors.initials: T
authors.lastname: Nakamura
authors.forename: Y
authors.initials: Y
authors.lastname: Seino
mesh_terms: D015650:24,25-Dihydroxyvitamin D 3 / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D000818:Animals; D015519:Bone Density / Q000187:drug effects; D001846:Bone Development / Q000187:drug effects*; D001862:Bone Resorption; D002117:Calcitriol / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D007015:Hypophosphatemia, Familial / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*; D051379:Mice; D008817:Mice, Mutant Strains; D013131:Spine / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology
chemical_list: D015650:24,25-Dihydroxyvitamin D 3; D002117:Calcitriol