PHOSPHOLIPID CHANGES IN THE BONES OF THE HYPOPHOSPHATEMIC MOUSE

The mineral and lipid composition of the bones of 35 day old hypophosphatemic (Hyp/Y) and control (+/Y) mice were compared in order to test the hypothesis that phosphate status has an effect on the complexed acidic phospholipid content of developing bones. The Hyp/Y bones were found to be rachitic and osteomalacic, having significantly reduced mineral content. That mineral was shown by X-ray diffraction to consist of larger/more perfect crystals than that in +/Y animals, indicating either a preference for crystal growth rather than new mineral deposition, or an increased mineral turnover. The increased crystal perfection was confirmed by chemical analyses which showed an increased calcium to phosphorus ratio in the Hyp/Y bones. The bones of Hyp/Y animals had significantly reduced complexed acidic phospholipid contents relative to those of control animals. Since these complexes are believed to play a role in vitro and in vivo mineral deposition, it is suggested that the deficiency of these complexes contributes to the mineralization defect. The magnitude of the complexed acidic phospholipid deficiency in the Hyp/Y animals indicates the importance of phosphate for the formation of these lipids. Although the proportion of phosphatidylserine and phosphatidylinositol and lysophospholipids tended to be reduced in the Hyp/Y bones, the absence of other statistically significant phospholipid abnormalities in the bones and brains of these animals suggests that the lipid defect is not systemic, but is associated with a decrease in phosphate at the site of bone formation.