High Zn content of Randall's plaque: a µ-X-ray fluorescence investigation.

Kidney stone disease, or nephrolithiasis, is a common ailment. Among the different risk factors usually associated with nephrolithiasis are dehydration, metabolic defects (especially with regard to calcium and oxalate). The presence of a mineral deposit at the surface of the renal papilla (termed Randall's plaque) has all been recently underlined. Of note, Randall's plaque is made of the calcium phosphate, carbapatite, and serves as a nucleus for kidney stone formation. The process by which apatite nanocrystals nucleate and form Randall's plaque remains unclear. This paper deals with the possible relationship between trace elements and the formation of this mineral. The investigation has been performed on a set of Randall's plaques, extracted from human kidney stones, through µ-X-ray diffraction and µ-X-ray fluorescence analyses in order to determine the chemical composition of the plaque as well as the nature and the amount of trace elements. Our data provide evidence that Zn levels are dramatically increased in carbapatite of RP by comparison to carbapatite in kidney stones, suggesting that calcified deposits within the medullar interstitium are a pathological process involving a tissue reaction. Further studies, perhaps including the investigation of biomarkers for inflammation, are necessary for clarifying the role of Zn in Randall's plaque formation.

Relationships between carbonation rate of carbapatite and morphologic characteristics of calcium phosphate stones and etiology.

OBJECTIVES: To examine the significance of the carbonation rate (CR) in carbonated apatite (carbapatite [CA]) stones and its relationships with the morphologic characteristics of CA and etiology. CA stones without struvite can result from metabolic disorders or urinary tract infection, but the latter etiology is still debated. Infection stones caused by urea-splitting bacteria are made of CA admixed with struvite and exhibit a high CO(3)(2-)/PO(4)(3-) ratio (CR). However, little is known as to the significance of the CR of CA in the absence of struvite in idiopathic calcium phosphate stones. METHODS: We studied 39 urinary calculi mainly composed of CA without struvite. Of the 39 patients, 13 had a past or present history of urinary tract infection, 24 had hypercalciuria, and 2 had medullary sponge kidney. The stones were examined by Fourier transform infrared spectroscopy and scanning electron microscopy. The presence of amorphous carbonated calcium phosphate or whitlockite was also considered. RESULTS: The CR of CA was 14% +/- 9%. On scanning electron microscopy, the CA particles appeared as spherules of 4.5 +/- 3.0 mum in diameter and were significantly larger in females than in males. In 16 cases, scanning electron microscopy showed bacterial imprints. In these calculi, the CR was significantly greater (22% +/- 7%) than in those without a visible bacterial imprint (8% +/- 5%, P < .0001). Amorphous carbonated calcium phosphate was found in 15 of 16 stones (93.8%) with imprints and in none of the 23 stones without imprints (P < .0001). CONCLUSIONS: A close relationship was observed between the presence of bacterial imprints, indicative of past or current urinary tract infection, and both the presence of amorphous carbonated calcium phosphate (or whitlockite) and a high CR of CA.