Calcium-acidic phospholipid-phosphate complexes in human hydroxyapatite-containing pathologic deposits

Abstract

The deposition of calcium-containing crystals in tissues is due to a combination of factors: elevation in the concentrations of precipitating ions, formation of specific nucleators, and removal of macromolecules that inhibit crystal deposition. This study tested the hypothesis that calcium acidic phospholipid phosphate complexes, which promote hydroxyapatite deposition both in vitro and in vivo, are associated only with hydroxyapatite deposits, and furthermore, that the presence of these complexes is associated with all such hydroxyapatite deposits. Lipid analysis of 76 surgical specimens containing evidence of pathologic calcification (35 hydroxyapatite, 35 calcium pyrophosphate dihydrate, and 6 containing other crystalline materials) had mean complexed acidic phospholipid contents of 8.7, 1, and 0.012, (microgram/mg demineralized dry weight) respectively. Tissues that contained larger, more perfect hydroxyapatite crystals based on x-ray diffraction analyses, had a higher complexed acidic phospholipid content (7.5 +/- 4 micrograms/mg demineralized dry weight, N = 16) than tissues with poorly crystallized hydroxyapatite (3.9 +/- 2 micrograms/mg, N = 11). Histologically, tissues containing larger crystals were characterized by cell or tissue necrosis. Poorly crystalline deposits were found in tissues showing little or no evidence of cell necrosis or tissue degeneration.