Inhibitors of oxalocalcic lithiasis: Effects of their interactions on calcium oxalate crystallization

Objective: To study the possible effects caused by the interaction of some urinary components on the inhibition of calcium oxalate crystallization. Such interactions are susceptible to importantly change the inhibitory behavior of some urinary components by producing either positive (synergistic) or negative effects on preventing crystallization. Methods: A urinary lithogenic risk (ULR) test was used to follow the crystallization of calcium oxalate from artificial urine in the presence of binary mixtures of known inhibitors of its crystallization (phytate, pyrophosphate, citrate, and chondroitin sulfate), which were assayed in physiological concentrations. Results: Only the mixtures phytate + pyrophosphate and phytate + citrate manifested interaction effects on the calcium oxalate crystallization. Although the former exhibited synergistic effects, the latter showed negative effects on the inhibition. These effects are explained in terms of the affinity of the inhibitors for the calcium oxalate crystals surface and their concentrations in urine. Conclusion: The crystallization inhibitory capacity of target urine is explained by the combined effect of the compounds present in the complex urine matrix rather than the individual action of each compound. This kind of interactions is of key value in designing prophylactic treatments of urolithiasis based on inhibitors intake. © 2012 Elsevier Inc.