Calcium phosphate saturation levels in ultrafiltered serum

Area of Science:

• Biochemistry
• Materials Science
• Pathology

Background:

• Pathological calcifications in arteriosclerotic plaque are a significant health concern.
• Understanding the formation mechanisms of these calcium phosphate deposits is essential.

Purpose of the Study:

• To investigate the solubility of calcium phosphates in undiluted ultrafiltered human serum (u.f.s.).
• To compare the apparent ion activity products of calcium phosphates in u.f.s. with their known solubility products.

Main Methods:

• Equilibration of dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP), and hydroxyapatite (OHAp) crystals with u.f.s. at 37°C.
• Analysis of calcium, phosphate, and pH in serum samples under a 5.5% CO2 atmosphere.
• Calculation of apparent ion activity products to assess saturation levels.

Main Results:

• Native u.f.s. was substantially undersaturated for DCPD (ion activity product 2.4 x 10⁻⁷ vs. Ksp 2.3 x 10⁻⁷).
• Native u.f.s. was slightly supersaturated for OCP (ion activity product 4 x 10⁻⁴⁹ vs. Ksp 2.5 x 10⁻⁴⁹).
• Native u.f.s. remained highly supersaturated for OHAp even after 2 months.

Conclusions:

• The low concentrations of calcium and phosphate complexing agents in u.f.s. (excluding bicarbonate) were inferred from DCPD and OCP saturation levels.
• The high supersaturation with respect to OHAp suggests its potential role in pathological calcification processes.
• These findings provide insights into the biomineralization processes relevant to vascular diseases.