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

Abstract

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 organic matrix present in the stones. Intact stones were intensively analyzed by micro-computed tomography (micro CT) for both morphology (including the volume of voids, i.e., regions without mineral) and mineral type. In order 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 was previously thought, and also suggest that micro CT-visible void regions are related to the presence of protein.

Papillary Ductal Plugging is a Mechanism for Early Stone Retention in Brushite Stone Disease

“…This is much as has been described for the variation in morphology of kidney stones formed from apatite. 20 One stone in patient 3 contained apatite and CaOx as part of the apparent ductal plug (fig. 1).…”

Stability of the Infection Marker Struvite in Urinary Stone Samples

“…17 Surface areas of the pieces were measured in a similar fashion, by summing perimeter measures on each thresholded image slice and multiplying this by the slice thickness.…”

Micro-CT imaging of Randall’s plaques

“…The micro-CT reconstruction of the densest portion of the mineralized regions in this biopsy reveals several features that we regularly see with Randall’s plaque: first, the interstitial mineralization shows no layering in the accumulation of apatite that occurs (which is quite unlike what has been seen in apatite stones [15], as described below). It would seem that an entire region of interstitial connective tissue becomes mineralized, with the density of apatite reaching some maximum value that remains uniform with the densest portions of Randall’s plaque.…”