Epitaxial deposition of calcium oxalate on uric acid rich stone matrix is induced by a 29 kDa protein

Protein content of human apatite and brushite kidney stones: significant correlation with morphologic measures

Apatite and brushite kidney stones share calcium and phosphate as their main inorganic components. We tested the hypothesis that these stone types differ in the amount of proteins present in the stones. Intact stones were intensively analyzed by microcomputed tomography (micro CT) for both morphology (including the volume of voids, i.e., space devoid of X-ray dense material) and mineral type. To extract all proteins present in kidney stones in soluble form we developed a three-step extraction procedure using the ground stone powder. Apatite stones had significantly higher levels of total protein content and void volume compared to brushite stones. The void volume was highly correlated with the total protein contents in all stones (r2 = 0.61, P < 0.0001), and brushite stones contained significantly fewer void regions and proteins than did apatite stones (3.2 +/- 4.5% voids for brushite vs. 10.8 +/- 11.2% for apatite, P < 0.005; 4.1 +/- 1.6% protein for brushite vs. 6.0 +/- 2.4% for apatite, P < 0.03). Morphological observations other than void volume did not correlate with protein content of stones, and neither did the presence or absence of minor mineral components. Our results show that protein content of brushite and apatite stones is higher than that was previously thought, and also suggest that micro CT-visible void regions are related to the presence of protein.

Pathogenesis of renal calculi

Recent reports suggest that kidney stone disease prevalence is increasing. Despite significant treatment advances, the inciting factor and sequence of events leading to kidney stone formation remain elusive; however, recent efforts to understand the pathogenesis of nephrolithiasis have led to a delineation of the human surgical anatomy, histopathology, and metabolic factors in a variety of kidney stone formers. This article reviews the fundamental concepts of calculus formation, and the leading theories of stone pathogenesis, focusing on recent data from human papillary and renal cortical biopsies in stone formers that provide evidence for the role of Randall's plaque in kidney stone disease pathogenesis. These data suggest there are individual stone-forming phenotypes with unique surgical anatomy, histology, and metabolic profiles.

Identification of myeloperoxidase, alpha-defensin and calgranulin in calcium oxalate renal stones

BACKGROUND

In order to understand the mechanism of stone genesis, it is essential to determine the characteristics of macromolecules constituting the urinary stones. We characterized proteins from the inner core and outer matrix of calcium oxalate (CaOx) renal stones.

METHODS

Inner core and outer matrix of CaOx renal stones were separated and proteins were extracted with a buffer containing SDS and beta-mercaptoethanol. Proteins were analyzed and purified by SDS-PAGE and RP-HPLC respectively. The protein bands from gel and protein fractions were sequenced by MALDI TOF mass spectrometry. ELISA, western and slot blot immunoassays were performed to confirm the identity of the proteins in stones and urine of the stone formers. The potential of the identified protein as an effective promoter or inhibitor was assessed by observing their effects on CaOx crystallization using aggregometer.

RESULTS

The inner core extract predominantly exhibited protein species in the molecular weight range of 12-14 kDa. However, a 66 kDa band, identified as osteopontin was also detected in the inner core along with outer matrix and in the urine of stone formers and non stone formers. Purification of low molecular weight proteins was carried out by reversed phase HPLC. Tandem mass spectrometry analysis identified them as myeloperoxidase chain A (MPO-A), alpha-defensin, and calgranulin. ELISA, western blot and slot-blot immuno-assays further confirmed their presence restricted to the inner core and not in the outer matrix. Turbidity assays showed that low molecular weight renal stone proteins promoted the aggregation of CaOx crystals.

CONCLUSIONS

Persistent hyperoxaluria leads to tubular epithelial injury, resulting in the release of these anti-inflammatory proteins. These proteins could have been first adsorbed on CaOx crystals thereby become a part of nucleation process leading to inner matrix formation.