Influence of Amino Acids on Calcium Oxalate Precipitation in Systems of Different Chemical Complexity

Abstract

The mechanisms and conditions under which urinary stones, pathological biominerals in the kidneys and bladder, are formed have not yet been fully clarified. This study aims to understand the role of the system complexity and seven different amino acids (alanine, phenylalanine, glycine, serine, cysteine, histidine, and aspartic acid) in the spontaneous precipitation of calcium oxalate. To elucidate these effects, the conditions simulating hyperoxaluria (ci(Ca2+) = 7.5 mmol dm−3 and ci(C2O42−) = 6.0 mmol dm−3) were used for the first time. In this work, systematic research on calcium oxalate precipitation was performed in three systems of different chemical complexities: (a) only calcium and oxalate ions, (b) increased ionic strength, and (c) artificial urine at two initial pHs (pHi = 5.0 and 9.0). In all the investigated systems, the dominant precipitation of calcium oxalate monohydrate (COM) was observed, except in the artificial urine system at pHi = 9.0, in which a mixture of COM and calcium oxalate dihydrate (COD) was obtained. In all the investigated systems, a significant influence of the selected amino acids on the morphology and crystal growth of COM was observed, with more pronounced changes at pHi = 9.0. Overall, polar amino acids and nonpolar phenylalanine inhibit the growth of COM, which is a more pathogenic hydrate form. The artificial urine system proved to be more relevant for the observation of effects relevant to kidney stone formation in the human body.