Natural Promoters of Calcium Oxalate Monohydrate Crystallization

Abstract

Crystallization is often facilitated by modifiers that interact with specific crystal surfaces and mediate the anisotropic rate of growth. Natural and synthetic modifiers tend to function as growth inhibitors that hinder solute attachment and impede the advancement of layers on crystal surfaces. There are fewer examples of modifiers that operate as growth promoters, whereby modifier-crystal interactions accelerate the kinetic rate of crystallization. Here, we examine two proteins, lysozyme and lactoferrin, which are observed in the organic matrix of three types of pathological stones: renal, prostatic, and pancreatic stones. This work focuses on the role of these proteins in the crystallization of calcium oxalate monohydrate (COM), the most prominent constituent of human kidney stones. Using a combination of experimental techniques, we show that these proteins, which are rich in l-arginine and l-lysine amino acids, promote COM growth. The synthesis and testing of peptides derived from contiguous segments of lysozyme's primary amino acid sequence revealed subdomains within the protein that operate either as an inhibitor or promoter of COM growth, with the latter exhibiting efficacies that nearly match that of the protein. We observed that cationic proteins promote COM growth over a wide range of modifier concentration, which differs from calcification promoters in the literature that exhibit dual roles as promoters and inhibitors at low and high concentration, respectively. This seems to suggest a unique mechanism of action for lysozyme and lactoferrin. Possible explanations for their effects on COM growth and crystal habit are proposed on the basis of classical colloidal theories and the physicochemical properties of peptide subdomains, including the number and spatial location of charged or hydrogen-bonding moieties.

The role of macromolecules in the formation of kidney stones

“…On the other hand, equimolar (charge neutral) and polyR-rich mixtures apparently blocked growth related aggregation and shifted the predominant growth mechanism to secondary nucleation in the constant composition experiments [61] , along with promoting aggregation of COM seed crystals in saturated CaOx solutions [49] . The polyR-rich condition also appeared to increase crystal growth rates compared to the control, which may be analogous to reports of growth acceleration by selected native protein structures containing both anionic and cationic side chains [51] .…”

“…One recent report [17] described COM growth promotion by proteins extracted from stone matrix and purified by ion exchange chromatography and molecular sieving, though SDS-PAGE analyses suggested that some of these isolates contained more than one protein. Another report by Farmanesh et al described similar growth promotion for two proteins (lysozyme and lactoferrin) as well as peptide fragments of lysozyme containing both anionic and cationic residues [51] .…”

“…This is somewhat surprising given that CFM measurements reveal a similar strength of adhesive interaction for both amidinium and carboxylic acid functionalized AFM tips to CaOx crystal surfaces [52] . These polycations weakly disaggregated COM seed crystals compared to polyanions under near equilibrium conditions, and they exhibited little or no effect on growth, aggregation, or phase selectivity [61] , although weak growth promotion by proteins and peptides with cationic residues in the presence of nearby anionic residues has been reported [51] . Moreover, no discernible effect of these cationic polymers on COM morphology was observed in spontaneous nucleation experiments.…”

“…Conversely, few examples of cationic macromolecules interacting strongly with COM crystals have been reported [50] , though they play a critical role in polyanion-polycation aggregate formation which induces COM aggregation [49] . Also, cationic side chains appear to be critical to crystal growth acceleration, as observed with some amphiphilic proteins [51] . Collectively, in vitro studies suggest that both polymer-polymer and polymer-crystal interactions are important to stone formation.…”

Organic Mesopore Generating Agents (OMeGAs) for Hierarchical Zeolites: Combining Functions on Multiple Scales

“…[6] Usually this growth modification effect is to inhibit crystal growth, [22] but there are also a few examples of promotion effect on crystal growth. [23] In the study of zeolite growth modifiers, Lupulescu and Rimer first reported in 2012 the use of ZGMs, such as functional organic molecules found in silica proteins, termed silicateins or silaffins, to alter the anisotropic rate of step growth on the surface of crystals, thereby regulating the morphology of the synthesized silicalite-1 zeolite. [21] Zeolite growth modifiers can be added to the crystallization medium in small amounts without significantly altering the growth environment, while they can be designed to have specific binding to a particular crystal surfaces to enhance exposure of the desired crystallographic faces.…”