Dietary calcium and phosphorus ratio regulates bone mineralization and turnover in vitamin D receptor knockout mice by affecting intestinal calcium and phosphorus absorption.
The effects of the dietary Ca and P ratio, independent of any vitamin D effects, on bone mineralization and turnover was examined in 60 VDRKO mice fed different Ca/P ratio diets. High dietary Ca/P ratio promoted bone mineralization and turnover with adequate intestinal Ca and P transports in VDRKO mice.


BACKGROUND
To clarify the effects of the dietary calcium (Ca) and phosphorus (P) ratio (Ca/P ratio) on bone mineralization and turnover in null-vitamin D signal condition, vitamin D receptor knockout (VDRKO) mice were given diets containing different Ca/P ratios.


METHODS
Five groups of 4-week-old VDRKO mice, 10 animals each, were fed diets for 4 weeks. Group 1 was wild-type littermate mice, fed the diet containing 0.5% Ca and P (Ca/P = 1). Group 2 was the control and was fed a similar diet (Ca/P = 1). Groups 3, 4, 5, and 6 were fed the following diets: 0.5% Ca and 1.0% P (Ca/P = 0.5), 1.0% Ca and 1.0% P (Ca/P = 1), 1.0% Ca and 0.5% P (Ca/P = 2), and 0.5% Ca and 0.25% P (Ca/P = 2).


CONCLUSIONS
Compared with group 2, serum calcium and phosphorus levels in groups 4-6 significantly increased. Serum parathyroid hormone levels increased in group 3 and decreased in group 5. The amounts of intestinal calcium absorption decreased in groups 3 and 4. Phosphorus absorption increased in group 3 and decreased in groups 4-6. Bone mineral content (BMC) and bone mineral density (BMD) of the femur in group 3 significantly decreased and increased in group 5. In the primary spongiosa of the proximal tibia, the trabecular bone volume (BV/TV) and osteoid thickness (O.Th) in group 3 significantly increased, and decreased in group 6. In groups 5 and 6, the numbers of the trabecular osteoclasts increased. In groups 2 and 4, and the secondary spongiosa was identified in 5 of 10 mice. In group 3, there was no secondary spongiosa in either mouse. Osteoid maturation time (OMT) significantly decreased, and bone formation rate (BFR/BS) increased in groups 4-6. These data indicate that the dietary Ca/P ratio regulates bone mineralization and turnover by affecting the intestinal calcium and phosphorus transports in VDRKO mice. They may suggest the existence of Ca/P ratio-dependent, vitamin D-independent calcium and phosphorus transport system in the intestine.
Masuyama
Ritsuko
R
Department of Nutritional Science, Tokyo University of Agriculture, Tokyo, Japan. rmasu@nodai.ac.jp
Nakaya
Yumi
Y
Katsumata
Shinichi
S
Kajita
Yasutaka
Y
Uehara
Mariko
M
Tanaka
Shinya
S
Sakai
Akinori
A
Kato
Shigeaki
S
Nakamura
Toshitaka
T
Suzuki
Kazuharu
K
D000818:Animals; D015519:Bone Density / Q000187:drug effects; D001842:Bone and Bones / Q000187:drug effects* / Q000378:metabolism*; D002113:Calcification, Physiologic / Q000187:drug effects*; D002118:Calcium / Q000097:blood / Q000378:metabolism; D002136:Calcium, Dietary / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D004435:Eating; D005243:Feces / Q000737:chemistry; D005260:Female; D005269:Femur / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D017353:Gene Deletion; D006132:Growth Plate / Q000187:drug effects / Q000254:growth & development; D007408:Intestinal Absorption / Q000187:drug effects*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010281:Parathyroid Hormone / Q000097:blood; D016226:Phosphorus, Dietary / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D018167:Receptors, Calcitriol / Q000172:deficiency* / Q000235:genetics; D015430:Weight Gain / Q000187:drug effects
D002136:Calcium, Dietary; D010281:Parathyroid Hormone; D016226:Phosphorus, Dietary; D018167:Receptors, Calcitriol; D002118:Calcium