Phosphate status impacts bone integrity and stem cell proliferation in neonatal pigs

Mesenchymal stem cells (MSC) are essential to postnatal bone growth and a previous research indicates that dietary phosphate (PO₄) level impacts proliferation of these cells in vivo. To determine the effect of early PO₄ nutrition on bone integrity and MSC activity, fifteen pigs (1.5 + 0.2 kg) between 24 and 36 hr old were divided into 3 dietary treatment groups. Over a 12 d period, pigs were either fed a PO₄ adequate diet or 1 of 2 diets that exceeded PO₄ requirements. Blood collected at d 6 and d 12 was analyzed for sera PO₄, Ca, and PTH concentrations. Remaining sera was pooled from each treatment group to determine the impact of sera on MSC proliferation in vitro. At the conclusion of the trial, tibias were collected for bone measures and MSC were isolated from bone marrow of individual animals.

While sera PO₄ did not differ between treatment groups at either time point, a dose response was noted in sera Ca (P < 0.05) and PTH (P < 0.05) concentrations at d 6, with adequate animals having the lowest sera PTH concentrations and correspondingly higher circulating Ca when compared to the other groups. Although, the tibias of animals receiving the PO₄ adequate diet were larger (P < 0.05) and thicker (P < 0.1) than the bones of those animals receiving excess PO₄, ash percentage did not differ between groups. Proliferation of MSC treated for 24 h in sera from each group was effected by PO4 status (P < 0.1) of the animal and tended to be influenced by PO₄ status of the sera. Because circulating PO₄ did not differ between groups, the changes in bone measures, sera mineral and hormone concentrations, and MSC proliferation would suggest possible differences in PO₄ utilization. Additional research is needed to further clarify how PO₄ status affects MSC activity and the subsequent alterations in bone integrity.