The role of macromolecules in the formation of kidney stones

Abstract

The formation of crystal aggregates, one of the critical processes in kidney stone pathogenesis, involves interactions between crystals (predominantly calcium oxalate monohydrate, COM) and urinary constituents (e.g. proteins), which serve as an adhesive “glue” between crystals in stones. To develop a better understanding of the protein-crystal interactions that lead to crystal aggregation, we have measured the effect of model proteins on bulk COM crystal properties as well as their adsorption on crystal surfaces using three synthetic polyanions: poly(aspartic acid) (polyD), poly(glutamic acid) (polyE), and poly(acrylic acid) (polyAA). These anionic macromolecules reduced the amount of COM crystal aggregation in bulk solution to an extent similar to that observed for mixture of proteins from normal urine, with little difference between the polymers. In contrast, the polymers exhibited differences in measures of COM crystal growth. Polycations such as poly(arginine) (polyR) and poly(lysine) (polyK) reduced aggregation weakly and exerted negligible effects on crystal growth. All polyions were found to associate with COM crystal surfaces, as evidenced by changes in the zeta potential of COM crystals in electrophoretic mobility measurements. On the other hand, COM aggregation and possibly growth can be promoted by many binary mixtures of polycations and polyanions, which appeared to be mediated by polymer aggregate formation rather than loss of crystal charge stabilization. Similarly, crystal aggregation promotion behavior can be driven by forming aggregates of weakly charged polyanions, like Tamm-Horsfall Protein, suggesting that polymer (protein) aggregation may play a critical role in stone formation. Sensitivity of polyanion–COM crystal surface interactions to the chemical composition of polymer side groups were demonstrated by large differences in crystal aggregation behavior between polyD and polyE, which correlated with atomic force microscopy (AFM) measurements of growth inhibition on various COM surfaces and chemical force microscopy (CFM) measurements of unbinding forces between COM crystal surfaces and AFM tips decorated with either carboxylate or amidinium moieties (mimicking polyanion and polyR side chains, respectively). The lack of strong interaction for polyE at the COM (100) surface compared to polyD appeared to be the critical difference. Finally, the simultaneous presence of polyanions and polycations appeared to alter the ability of polycations to mediate unbinding forces in CFM and promote crystal growth. In summary, polyanions strongly associated with COM surfaces and influenced crystallization, while polycations did not, though important differences were observed based on the physicochemical properties of polyanions. Observations suggest that COM aggregation with both polyanion–polycation mixtures and weakly charged polyanions is promoted by polymer aggregate formation, which plays a critical role in bridging crystal surfaces.

Stone former urine proteome demonstrates a cationic shift in protein distribution compared to normal

“…[12, 20, 21, 23, 24, 29] Observations of stone morphology over many years have shown that aggregation of preformed crystals with an existing stone must play a significant role in stone growth. [47] Unfortunately, the absence of data on post-translational modifications in this study prevents us from testing for the loss of anionic side chains (i.e., glycosyl or phosphoryl), as suggested in our earlier work,[12] so our data are insufficient to truly distinguish between the two prior protein aggregation models; the electrostatically driven association between strong polyanions and strong polycations[20, 21] versus the inherent solution instability of weak polyanions in salt solutions. [12] Nevertheless, we conclude that the observed cationic shift in protein distribution suggests a role for protein aggregation in stone formation.…”

“…[20, 21] Furthermore, de-glycosylated UROM induced crystal aggregation when mixed with CaOx crystals in the appropriate proportions, which correlated with self-aggregation at physiologically relevant protein and salt concentrations. [12] Removing glycosyl side chains reduced the number of anionic charges on UROM, so both of these examples illustrated the link between reduced net negative charge in the mixture and protein destabilization in solution (aggregation), which correlated with CaOx crystal aggregation.…”

The Phosphates ‐ Skipped Reaction Products in the Octahedron‐like Yb and Lu‐Doped Ceria Synthesis.

“…In the literature, the cases where two‐dimensional structures are formed on the support‐ are well‐known. Interestingly, the concept of the “glue” for crystals could be found in the numerous papers One of the most popular compounds used as a “glue” are carbonates ,.…”

Understanding the Pathophysiology of Nephrocalcinosis

“…The formation of crystal aggregates involves interaction between crystals and urinary macromolecules (UMs) that serve as an adhesive. Updates and Advances in Nephrolithiasis -Pathophysiology, Genetics, and Treatment Modalities steadily increasing, and they now form a large group of proteins and some glycosaminoglycans [48,49]. The main macromolecules involved in crystallization are summarized in Table 7.…”