1. The binding of heparin, chondroitin sulphate and the low molecular weight heparin analogue pentosan polysulphate to sodium urate and uric acid crystals was studied by the use of competitive binding technique. Trace amounts of radioactively labelled glycosaminoglycans were used in the binding step, and varying amounts of unlabelled glycosaminoglycans for the competition experiments.
2. The experiments were carried out in 140 mmol/l NaCl at pH 6, with or without 5 mmol/l CaCl2 in the solution.
3. A reversible and almost complete binding of heparin and chondroitin sulphate to sodium urate crystals did occur in the presence of calcium, whereas pentosan polysulphate bound incompletely. The binding was much less pronounced in the calcium-free conditions.
4. Uric acid crystals did not bind any of the three inhibitors, not even with calcium present.
5. The clinical relevance depends on whether sodium urate microcrystals are present in the urine of calcium stone patients, to cause a binding and thereby a masking or inactivation of these inhibitors in the urine, which seems to be possible in the presence of calcium. However, the potential of pentosan polysulphate for the treatment of calcium stone patients does not seem to be at risk from this effect.