Effects of High Molecular Weight Urinary Macromolecules on Crystallization of Calcium Oxalate Dihydrate

Abstract

Timed urinary collections from 8 normal (N1) persons or 11 stone forming (SF) patients were passed through ultrafiltration apparatus to remove macromolecules in the ranges 1000–30,000d, 30,000–50,000d, and over 50,000d. No macromolecules could be recovered from either group in the 30,000–50,000d range, and no low molecular weight macromolecules (LMWMM) (<30,000d) were recovered from stone forming urines. Significant amounts of LMWMM (mean 105.8 ± 17.63mg./l.) were recovered from normal urine, but these extracts had no effects on calcium oxalate dihydrate (COD) nucleation (B°) or linear growth (G) rates in a continuous crystallization (MSMPR) system. Urines from SF contained nearly twice the concentration of high molecular weight macromolecules (HMWMM) when compared to N1 urines. SF HMWMM differed from N1 in Immunoelectrophoresis separation by absence of a dense band that was present in N1 extracts. This band reappeared in SF extract after boiling. Comparison of effects of addition of SF or N1 HMWMM to the COD-MSMPR crystallization system revealed no major quantitative differences in B° or G, but SF HMWMM had a remarkable stabilizing effect on total mass (MT) of COD crystals produced. This effect was confirmed by analysis of oxalate residual supersaturation after crystallization. We conclude that SF excrete higher concentrations of HMWMM and almost no LMWMM when compared to normals. This higher concentration of HMWMM must contribute to increased B° and decreased G noted in SF urine additive experiments previously reported. The mechanism of rapid removal of oxalate (i.e., stabilization) noted in experiments with SF HMWMM is not obvious at this time.