Attenuation by monosodium urate of the inhibitory effect of glycosaminoglycans on calcium oxalate nucleation.

The interaction between mucopolysaccharide (glycosaminoglycans) and monosodium urate, with respect to their effects on spontaneous precipitation of calcium oxalate, was explored in vitro. Heparin and, to a lesser extent, chondroitin sulfate were found to inhibit calcium oxalate precipitation. The formation product ratio (FPR, limit of metastability or the minimum supersaturation required for spontaneous nucleation) of calcium oxalate was increased 29 per cent by 0.05 mg of heparin per liter, and by 70 per cent with 1 mg of heparin per liter. The increment produced by heparin was much less pronounced when the solution containing the mucopolysaccharide was preincubated with crystalline monosodium urate. Pretreatment of the solution containing heparin (0.05 mg per liter) by monosodium urate (0.5 mg per ml) virtually eliminated the inhibitory action of heparin. Studies with radioactive heparin indicated that monosodium urate binds heparin. In contrast, the inhibitory effect of chondroitin sulfate was unaltered by prior exposure to monosodium urate. The results indicated that monosodium urate may attenuate the inhibitor activity of certain mucopolysaccharides such as heparin and facilitate the calcium oxalate precipitation. The findings provide further support for the important etiologic role of hyperuricosuria in the formation of calcium oxalate stones.