The effect of urine, pyrophosphate, citrate, magnesium and glycosaminoglycans on the growth and aggregation of calcium oxalate crystals in vitro

Kidney stones, aggregates of microcrystals, most commonly contain calcium oxalate monohydrate (COM) as the primary constituent. The aggregation of COM microcrystals and their attachment to epithelial cells are thought to involve adhesion at COM crystal surfaces, mediated by anionic molecules or urinary macromolecules. Identification of the most important functional group-crystal face adhesive combinations is crucial to understanding the stability of COM aggregates and the strength of their attachments to epithelial cell surfaces under flow in the renal tubules of the kidney. Here, we describe direct measurements of adhesion forces, by atomic force microscopy, between various functional groups and select faces of COM crystals immersed in aqueous media. Tip-immobilized carboxylate and amidinium groups displayed the largest adhesion forces, and the adhesive strength of the COM crystal faces decreased in the order (100) > (121) > (010), demonstrating that adhesion is sensitive to the structure and composition of crystal faces. The influence of citrate and certain urinary proteins on adhesion was examined, and it was curious that osteopontin, a suspected regulator of stone formation, increased the adhesion force between a carboxylate tip and the (100) crystal face. This behavior was unique among the various combinations of additives and COM crystal faces examined here. Collectively, the force measurements demonstrate that adhesion of functional groups and binding of soluble additives, including urinary macromolecules, to COM crystal surfaces are highly specific in nature, suggesting a path toward a better understanding of kidney stone disease and the eventual design of therapeutic agents.

https://www.pnas.org/content/pnas/102/2/267.full.pdf

Adhesion at calcium oxalate crystal surfaces and the effect of urinary constituents

Urease activity is a physiological function of many bacteria that enables these organisms to utilize urea as a source of nitrogen. The association of ureolytic bacteria with human or animal hosts varies widely from a commensal relationship as demonstrated with skin microflora, a symbiotic relationship in the gastrointestinal tract, to a pathogenic relationship in the urinary tract. Since similar or identical species of bacteria such as Staphylococcus aureus are found in all three environments, the effect of urease activity on the host must be solely a function of the environment of these organisms. In this review, the importance of urease to bacteria is discussed, identifying the gastrointestinal tract as a major reservoir of ureolytic bacteria and investigating the urinary tract environment and the infectious struvite stone production that often accompanies urease-producing bacteria there. Finally, an infection model is presented which explains the development and growth of these urinary calculi and their remarkable persistence in spite of modern urological treatments.

The Ecology and Pathogenicity of Urease-Producing Bacteria in the Urinary Tract

Factors influencing the crystallisation of calcium oxalate in urine - critique

Polyelectrolytes and protein molecules appear to be able to act not only as crystallization inhibitors when present in solution, but also as promoters of crystal growth when immobilized onto surfaces. Because this is especially relevant for systems in which heterogeneous nucleation can occur, the influence of poly-L-glutamic (PGlu) acid, poly-L-aspartic (PAsp) acid, and human serum albumin (HSA) on the nucleation and growth inhibition of calcium oxalate monohydrate (COM) was studied using the Constant Composition (CC) kinetics technique. The overgrowth of COM on hydroxyapatite (HAP) seed crystals pretreated with HSA was also investigated. Pronounced differences in inhibiting and nucleating potential were found for the various additives. HSA, a relatively poor growth inhibitor when present in solution, was found to nucleate very regular, hexagonal COM crystals when immobilized on a surface and to enhance the overgrowth of COM when adsorbed on HAP surfaces.

R.K. McCulloh

Papers

Glycosaminoglycans as inhibitors of calcium oxalate crystal growth and aggregation