Dietary Calcium and Phosphorus Ratio Regulates Bone Mineralization and Turnover in Vitamin D Receptor Knockout Mice by Affecting Intestinal Calcium and Phosphorus Absorption

Abstract

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. Introduction: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. Materials and 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 ϭ 1). Group 2 was the control and was fed a similar diet (Ca/P ϭ 1). Groups 3, 4, 5, and 6 were fed the following diets:0.5% Ca and 1.0% P (Ca/P ϭ 0.5), 1.0% Ca and 1.0% P (Ca/P ϭ 1), 1.0% Ca and 0.5% P (Ca/P ϭ 2), and 0.5% Ca and 0.25% P (Ca/P ϭ 2). Results and 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.

Effects of calcium to non-phytate phosphorus ratio and different sources of vitamin D on growth performance and bone mineralization in broiler chickens

“…The dietary Ca to P ratio regulates bone mineralization and turnover by affecting the intestinal Ca and P transports in mice (Masuyama et al, 2003). The imbalance between Ca and P also impaired bone mineralization of pigs (Létourneau-Montminy et al, 2010).…”

Effects of Dietary Phosphorus Intake on Bone Mineralization and Calcium Absorption in Adult Female Rats

“…13) In this present study, we did not change the dietary Ca level in the dietary groups and maintained an adequate level in the diets (0.5%). However, a decreased dietary P level led to an increased dietary Ca/P ratio, and then to increased Ca absorption and bone mineralization in adult female rats.…”

“…Therefore, the low-P diet enhanced Ca absorption which was effective for bone mineralization in adult female rats, as well as in vitamin D receptor knockout male mice in our previous study. 13) In spite of the enhanced bone mineralization, the serum P concentration was lower in the rats fed the low-P diet than in those fed the control diet. Similarly to Ca, P is one of the important minerals for bone constitution.…”

The Effects of a Vitamin D–deficient Diet on Chronic Cadmium Exposure in Rats

“…The active metabolite has many functions related to Ca regulation and bone metabolism, including intestinal Ca and P absorption, Ca mobilization in the bone, and resorption of P and Ca in the renal tubular cells (Deluca 2004;Jones et al 1998;Lips 2006). Although vitamin D interacts with PTH (Deluca 2004;Jones et al 1998), hypovitaminosis D does not influence PTH under sufficient serum levels of Ca (Dabbagh et al 1989;Kollenkirchen et al 1991), and many researchers (Fox 1992;Lee et al 1991;Masuyama et al 2003) have reported a vitamin D-independent Ca homeostasis system. Therefore, hypovitaminosis D alone might not affect Ca homeostasis and bone remodeling owing to the vitamin D-independent system in the present experiment.…”