Direct observation of urinary stone ultrastructure

The density and protein content of calcium oxalate crystals precipitated from human urine: a tool to investigate ultrastructure and the fractional volume occupied by organic matrix

One of the key debates in biomineralisation studies is the extent to which components of the organic matrix become occluded into the crystal lattice during growth. Here, the relationship between protein content and density of calcium oxalate crystals grown in human urine has been investigated in order to determine which fraction of crystal volume is non-mineral. The density of crystals varied from 1.84 to 2.08 g/cm3 while the protein content ranged from 0.1 to 2.1% (w/w). There was an inverse relationship between measured density and protein content which was qualitatively and quantitatively consistent with predictions based on reasonable densities for the mineral and non-mineral components. The coefficients of the fitted equation suggest that, at 2% protein (w/w), the volume of non-mineral would be 5.0% (v/v). The density values we observed are incompatible with fractional volumes of 20%. The results confirm that the occlusion of a small but possibly significant amount of protein into a crystal lattice is possible, but cast doubt on the hypothesis that protein acts as a major intracrystalline ultrastructural element. Moreover, the methodology developed for this study offers a simple and robust method for interrogating organic/inorganic associations in a range of biological and medical systems.

Experimental model to study sedimentary kidney stones

An experimental model to reproduce, to some extent, the conditions prevailing during the formation of the so-called sedimentary urinary stones, was developed. The results obtained demonstrated that in the absence of organic matter no calcium phosphate crystals were deposited in cavities with scarce liquid renovation. Nevertheless, in such case a regular hydroxyapatite layer was developed on the walls around the cavity. The presence of crystallization inhibitors cannot stop indefinitely the crystal development. Therefore, phytate manifested important inhibitory effects in concentrations normally found in urine (0.77-1.54 x 10(-6) mol/l), whereas citrate only manifested important inhibitory effects when found at high urinary concentrations (2.64 x 10(-3) mol/l). When mucin (a glycoprotein) was present in the urine, a clear deposit of calcified organic material was formed. The organic matter appeared mixed with the spherulites of hydroxyapatite, this demonstrating the capacity of the glycoprotein agglomerates to act as heterogeneous nucleants of calcium salts and their important role in the formation of sedimentary stones. The structural features of the obtained in vitro deposits were compared with the fine structure of human sedimentary phosphate calculi. Scanning electron microscopy images demonstrated a good correspondence between in vitro experiments and in vivo observations.

Phosphates precipitating from artificial urine and fine structure of phosphate renal calculi

Phosphates precipitating from artificial urine in the pH range 6-8 were identified using X-ray diffraction, chemical analysis and scanning electron microscopy. The influence of magnesium and citrate on phases precipitating from urine was established. From urine containing a normal quantity of magnesium (around 70 ppm), brushite accompanied by hydroxyapatite (HAP) precipitated at pH < or = 7.0 and struvite with HAP at pH > 7.0. HAP was formed exclusively from magnesium deficient urine at pH 7.0. Newberyite, octacalcium phosphate and whitlockite were not identified. The chemical and phase composition and inner fine structure of 14 phosphate calculi were studied. Three types of stones were distinguished based on their magnesium content: (i) stones rich in magnesium composed of struvite, hydroxyapatite and abundant organic matter, (ii) stones with low magnesium content constituted by calcium deficient hydroxyapatite, up to 5% of struvite, considerable amount of organic matter and occasionally brushite, and (iii) calculi without magnesium consisting of brushite, hydroxyapatite and little organic matter. Conditions prevaling during stone-formation assessed for each type of stone were confirmed by corresponding urinary biochemical data and corroborate the in vitro studies of phosphates precipitation.

Study on calcium oxalate monohydrate renal uroliths. III. Composition and density

Density and content of mineral constituents were determined for 33 human calcium oxalate monohydrate (hereafter COM) uroliths whose external appearance and inner structure were described in part I and II respectively. Studied stones contained 0.13-0.42 wt.% of struvite, 0.68-4.12 wt.% of hydroxyapatite, 73-96 wt.% of COM and 3-10 wt.% of water unbound in a crystallohydrate 10 to 20 wt.% of calculus mass is not accounted for by chemical analysis. Density of COM calculi varying between 1.67 and 2.06 g cm-3 is not a function of any single stone parameter. Around 30% of stone volume is not occupied by crystalline components. The mulberry stones of sedimentary origin contained higher amount of organic matter than papillar and mulberry stones displaying site of attachment to epithelium.

Identification of urinary stone and sediment crystals by scanning electron microscopy and x-ray microanalysis

A procedure based on scanning electron microscopic techniques is described for the identification of crystals in urinary sediments and stones. The crystals are identified by their morphology and elemental composition using scanning electron microscopy and x-ray microanalysis. The procedure has a number of advantages over conventional methods. It is easy to use. It is non-destructive so that both the exterior and interior of the same stone can be separately analyzed. It is the only technique in which information about spatial relationships between various crystals in a stone can be obtained easily. Scanning electron microscopic techniques can detect minor components, and analysis of a wide variety of materials ranging from amorphous substances to microcrystals to macroscopic stones is possible.

Ultrastructural microbial ecology of infection-induced urinary stones

With advanced techniques of scanning and transmission electron microscopy we studied the ultrastructural ecology of bacteria associated with struvite calculi on catheter surfaces, and in the bladder, ureter and renal pelvis. These detailed morphological data indicate that the interstices, core and external surface of such struvite aggregates contain large numbers of bacterial cells that grow as microcolonies and thick biofilms within extensive fibrous organic matrices. These bacterial cells and their secreted products (glycocalyx or biofilm matrix) appear to provide initial foci for crystal development and aggregation of crystals to form macroscopic struvite stones. The protective glycocalyx-enclosed microcolonial mode of bacterial growth also may explain the relative resistance to antibiotics observed in bacteria associated with infection stones.

Agar-embedded urinary stones: a technique useful for studying microscopic architecture

A procedure for studying urinary stones by various microscopic techniques is described. The stones are sectioned into approximately 0.2 to 1.0 mm. thick pieces using a low-speed saw. The sections are then embedded in agar and decalcified using 0.25 M ethylenediaminetetracetic acid at pH 7.2. The decalcified residue is then processed for light microscopy and scanning and transmission electron microscopy as with any other biological tissue. The results indicate that the ethylenediaminetetracetic acid-insoluble stone matrix keeps its architectural integrity and can be studied like other biological materials.

Growth and characterization of calcium oxalate dihydrate crystals (weddellite)

Conditions are given for the growth of calcium oxalate dihydrate crystals (weddellite) in aqueous solution. The crystals obtained were characterized by scanning electron microscopic, spectroscopic, and thermal methods. The dissolution kinetics and electrophoretic mobility were determined; the thermodynamically unstable calcium oxalate dihydrate had a higher dissolution rate and a lower zeta potential than the monohydrate and underwent a phase transformation into the more stable calcium oxalate monohydrate. The results obtained on the chemical stability and the surface charge of calcium oxalate dihydrate offered additional information for assessing the current theories on the formation of calcium oxalate renal stones.

Ultrastructural study of apatites in human urinary calculi

Using transmission and scanning electron microscopy, we have studied the ultrastructure of a number of urinary calculi, mainly composed of calcium phosphate. Three fundamental kinds of calcium phosphates were detected: nonstoichiometric carbonate apatite, nonhexagonal octacalcium phosphate, and calcium-magnesium whitlockite. The influence that the organic matter, substitutions in the phosphate lattice of CO3 and Mg, and apatitic stoichiometry have on the ultrastructure of the calcium phosphate calculi has been detailed. An originating apatitic unity named U2 is assumed to be the responsible for all the different structures of calcium apatites appearing in renal calculi. On the basis of our observations, a mechanism whereby apatites grow is postulated; magnesium functions as an inhibitor for the growing mechanism.

Ultrastructure and pathogenesis of human urinary calculi

The ultrastructure of human urinary calculi was studied using scanning and transmission electron microscopy. The hydroxyapatite constituent of the stones was often present in the form of sperical aggregates of the minute apatite crystallites (1 to 10 mu in diameter). In most cases, the sperical apatite deposits consisted of concentric lamellae of crystallites. The spherical apatite deposits, described in detail for the first time in urolithiasis, were similar to those found in a variety of calcified tissues including nephrocalcinosis and malakoplakia.