title: Improvement of impaired calcium and skeletal homeostasis in vitamin D receptor knockout mice by a high dose of calcitriol and maxacalcitol.
abstract: Vitamin D plays a major role in mineral and skeletal homeostasis through interaction with the nuclear vitamin D receptor (VDR) of target cells. Recent reports have indicated that some cellular effects of vitamin D may occur via alternative signaling pathways, but concrete evidence for mineral homeostasis has not been shown in vivo. To investigate this issue, the actions of calcitriol (1,25D) and maxacalcitol (OCT), which were developed for treatment of uremia-induced secondary hyperparathyroidism, were analyzed in VDR knockout (VDR(-/-)) mice. The VDR(-/-) mice were fed a rescue diet immediately after weaning. 1,25D, OCT or a control solution was administered intraperitoneally to these mice three times a week for eight weeks. Biological markers and bone growth were measured and bone histomorphometric analysis of the calcein-labeled tibia was performed 24 h after the final administration. Significantly higher levels of serum Ca(2+) were observed in 1,25D- and OCT-treated mice, but the serum parathyroid hormone level was unchanged by both agents. Impaired bone growth, enlarged and distorted cartilaginous growth plates, morphological abnormalities of cancellous and cortical bones; a morbid osteoid increase, lack of calcein labeling, and thinning of cortical bone, were all significantly improved by 1,25D and OCT. The significance of these effects was confirmed by bone histomorphometrical analysis. Upregulation of the calbindin D(9k) mRNA expression level in the duodenum may explain these findings, since this protein is a major modulator of Ca transport in the small intestine. We conclude that 1,25D and OCT both at a high dose exert significant effects on Ca and skeletal homeostasis with the principal improvement of Ca status in VDR(-/-) mice, and some of these effects may occur through an alternative vitamin D signaling pathway.
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan. shiizaki@jichi.ac.jp
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Shiizaki
authors.forename: Ikuji
authors.initials: I
authors.lastname: Hatamura
authors.forename: Ikuo
authors.initials: I
authors.lastname: Imazeki
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Moriguchi
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Sakaguchi
authors.forename: Fumie
authors.initials: F
authors.lastname: Saji
authors.forename: Eiko
authors.initials: E
authors.lastname: Nakazawa
authors.forename: Shigeaki
authors.initials: S
authors.lastname: Kato
authors.forename: Tadao
authors.initials: T
authors.lastname: Akizawa
authors.forename: Eiji
authors.initials: E
authors.lastname: Kusano
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001842:Bone and Bones / Q000002:abnormalities / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D064026:Calbindins; D002117:Calcitriol / Q000031:analogs & derivatives* / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004386:Duodenum / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D006132:Growth Plate / Q000187:drug effects / Q000473:pathology; D006706:Homeostasis / Q000187:drug effects*; D051379:Mice; D018345:Mice, Knockout; D010012:Osteogenesis / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000172:deficiency* / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000235:genetics / Q000378:metabolism; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism
chemical_list: D064026:Calbindins; D015220:Calcium Channels; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D064030:S100 Calcium Binding Protein G; D050916:TRPV Cation Channels; C446923:Trpv6 protein, mouse; D002117:Calcitriol; C051883:maxacalcitol; D002118:Calcium