Demonstration of calcium oxalate crystallization-enhancing activity of urinary macromolecules with a gel model

Abstract

The influence of urinary macromolecules of nucleating calcium oxalate crystallites trapped in a matrix was studied in an agarose gel medium. The mean inhibitory activity (I) of concentrated whole urine (1,200 mOsmol/kg) differentiates the population into two groups: a high activity groups (H, 63% of stone formers, 23% of normal controls; I = 0.64) and a low activity group (L, 37% of stone formers, 77% of normal controls: I = 0.27). Urinary macromolecules concentrated by ultrafiltration at a nominal cutoff of 5 kDa resulted in increased crystallization. This contrasts with the purely inhibitory activity of the dextrans. The overall crystallization activity of whole urine is due therefore to the composite action of inhibiting as well as enhancing factors.