Abstract
High intestinal availability of dietary phosphorus (P) may impair calcium (Ca) homeostasis and bone integrity. In the present study, we investigated the effect of phytase supplementation in comparison to the soaking of cereal grains in 2.5% lactic acid (LA) on intestinal Ca and P absorption; intestinal, renal, and bone gene expression regarding Ca and P homeostasis; bone parameters; and serum levels of regulatory hormones in growing pigs. Thirty-two pigs were randomly assigned to one of four diets in a 2 × 2 factorial design in four replicate batches for 19 days. The diets comprised either untreated or LA-treated wheat and maize without and with phytase supplementation (500 phytase units/kg). Although both treatments improved the P balance, phytase and LA-treated cereals differently modulated gene expression related to intestinal absorption, and renal and bone metabolism of Ca and P, thereby altering homeostatic regulatory mechanisms as indicated by serum Ca, P, vitamin D, and fibroblast growth factor 23 levels. Moreover, phytase increased the gene expression related to reabsorption of Ca in the kidney, whereas LA-treated cereals decreased the expression of genes for osteoclastogenesis in bones, indicating an unbalanced systemic availability of minerals. In conclusion, high intestinal availability of dietary P may impair Ca homeostasis and bone integrity.
Highlights
The majority of body phosphorus (P) can be found in bones and teeth, where it forms hydroxyapatite crystals with calcium (Ca) [1,2]
By using a 2 × 2 factorial design, we investigated the effects of phytase supplementation and lactic acid (LA) treatment of cereals on the intestinal uptake and retention of Ca and P; intestinal, renal, and bone gene expression related to Ca and P
Our findings demonstrated a positive correlation between serum levels of alkaline phosphatase (ALP) and fibroblast growth factor 23 (FGF23), suggesting that two opposing factors for the regulation of the P homeostasis were regulated
Summary
The majority of body phosphorus (P) can be found in bones and teeth, where it forms hydroxyapatite crystals with calcium (Ca) [1,2]. The most important organs involved in the P homeostasis regulating P absorption, excretion, and storage are the gastrointestinal tract, kidney, and bone [1,2,5]. Phosphorus and Ca homeostasis are closely linked as they are regulated by the same hormones, including vitamin D (VitD), parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23) [6,7,8,9]. Studies in mice and humans showed that the phosphaturic hormone FGF23 is primarily involved in P homeostasis and is produced by osteoblasts and osteocytes in the bone as well as by pericyte-like cells in the bone marrow as a response to high blood P and mainly suppresses P reabsorption and
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