Natural promoters of calcium oxalate monohydrate crystallization

Hydrogel Nanoparticles Enable Nucleation Barrier Regulation and Ion Anchoring as an Alternative Pathway for Monosodium Urate Monohydrate Crystallization Control

Gout flare-up, commonly resulting from monosodium urate monohydrate (MSUM) crystallization, has led to painful inflammatory arthritis among hundreds of millions of people. Herein, a kind of hydrogel nanoparticles (HNPs) with specific properties was developed, aimed at providing a promising pathway for MSUM crystallization control. The experimental and molecular dynamics simulation results synchronously indicate that the fabricated HNPs achieve efficient inhibition of MSUM crystallization governed by the mechanism of "host-guest interaction" even under very low-dose administration. HNPs as the host dispersed in the hyperuricemic model effectively lift the relative heterogeneous nucleation barrier of the MSUM crystal and hinder solute aggregation with strong electronegativity and hydrophobicity. The initial appearance of MSUM crystals was then delayed from 94 to 334 h. HNPs as the guest on the surface of the formed crystal can decelerate the growth rate by anchoring ions and occupying the active sites on the surface, and the terminal yield of the MSUM crystal declined to less than 1% of the control group. The good biocompatibility of HNPs (cell viability > 94%) renders it possible for future clinical applications. This study can guide the rational design of inhibitory nanomaterials and the development of their application in the control of relevant pathological crystallization.

The modulatory effects of large and small extracellular vesicles from normal human urine on calcium oxalate crystallization, growth, aggregation, adhesion on renal cells, and invasion through extracellular matrix: An in vitro study

Urinary extracellular vesicles (uEVs) play important roles in physiologic condition and various renal/urological disorders. However, their roles in kidney stone disease remain unclear. This study aimed to examine modulatory effects of large and small uEVs derived from normal human urine on calcium oxalate (CaOx) crystals (the main component in kidney stones). After isolation, large uEVs, small uEVs and total urinary proteins (TUPs) with equal (protein equivalent) concentration were added into various crystal assays to compare with the control (without uEVs or TUPs). TUPs strongly inhibited CaOx crystallization, growth, aggregation and crystal-cell adhesion. Large uEVs had lesser degree of inhibition against crystallization, growth and crystal-cell adhesion, and comparable degree of aggregation inhibition compared with TUPs. Small uEVs had comparable inhibitory effects as of TUPs for all these crystal assays. However, TUPs and large uEVs slightly promoted CaOx invasion through extracellular matrix, whereas small uEVs did not affect this. Matching of the proteins reported in six uEVs datasets with those in the kidney stone modulator (StoneMod) database revealed that uEVs contained 18 known CaOx stone modulators (mainly inhibitors). These findings suggest that uEVs derived from normal human urine serve as CaOx stone inhibitors to prevent healthy individuals from kidney stone formation.

Direct observations of nanoscale brushite dissolution by the concentration-dependent adsorption of phosphate or phytate

With the development of agricultural intensification, phosphorus (P) accumulation in croplands and sediments has resulted in the increasingly widespread interaction between inorganic and organic P species, which has been, previously, underestimated or even ignored. We quantified the nanoscale dissolution kinetics of sparingly soluble brushite (CaHPO4·2H2O, DCPD) over a broad range of phosphate and/or phytate concentrations by using in situ atomic force microscopy (AFM). Compared to water, we found that low concentrations of phosphate (1-1000 µM) or phytate (1-100 µM) inhibited brushite dissolution by slowing single step retraction. However, with increasing phosphate or phytate concentrations to 10 mM, there was a reverse effect of dissolution promotion at brushite-water interfaces. In situ observations of the coupled dissolution-reprecipitation showed that phosphate precipitated more readily than phytate on brushite surfaces, with the formation of amorphous calcium phosphate (ACP). For a fundamental understanding, zeta potential and in situ Raman spectroscopy (RS) revealed that the concentration-dependent dissolution is attributed to the reverse of outer-sphere to inner-sphere adsorption with increasing phosphate or phytate concentrations. In addition, the mineralization of phytate with outer-sphere adsorption by phytase was higher than that with inner-spere adsorption, and the presence of phytate delayed ACP phase transformation to hydroxylapatite (HAP). These in situ observations and analyses may fill the knowledge gaps of interaction between inorganic and organic P species in P-rich terrestrial and aquatic environments, thereby implicating their biogeochemical cycling and the associated availability.

Tailored hydrogel composite membrane for the regulated crystallization of monosodium urate monohydrate within coffee's metabolites system

Herein, a facile bionic research platform with fabricated hydrogel composite membrane (HCM) is constructed to uncover the effects of the main components of coffee's metabolites on MSUM crystallization. Tailored and biosafety polyethylene glycol diacrylate/N-isopropyl acrylamide (PEGDA/NIPAM) HCM allows the proper mass transfer of coffee's metabolites and can well simulate the process of coffee's metabolites acting in the joint system. With the validations of this platform, it is shown that chlorogenic acid (CGA) can hinder the MSUM crystals formation from 45 h (control group) to 122 h (2 mM CGA), which is the most likely reason that reduces the risk of gout after long-term coffee consumption. Molecular dynamics simulation further indicates that the high interaction energy (E_int) between CGA and MSUM crystal surface and the high electronegativity of CGA both contribute to the restraint of MSUM crystal formation. In conclusion, the fabricated HCM, as the core functional materials of the research platform, presents the understanding of the interaction between coffee consumption and gout control.

Untargeted and targeted metabolomics reveal bile acid profile changes in rats with ethylene glycol-induced calcium oxalate nephrolithiasis

Calcium oxalate (CaOx) nephrolithiasis is a prevalent disorder linked to metabolism. Examining metabolic alterations could potentially give an initial understanding of the origins of CaOx nephrolithiasis. This study aims to determine gut metabolic biomarkers differentiating CaOx nephrolithiasis utilizing untargeted and targeted metabolomics. CaOx nephrolithiasis model rats were built by 1% ethylene glycol administration. Histologic staining and renal function measurement revealed the presence of crystals in the lumen of the renal tubules, the renal injury and interstitial fibrosis in CaOx rats, demonstrating that the models of CaOx were established successfully. Hematoxylin & eosin (H&E) staining showed that CaOx group had inflammation and damage in the ileal tissue. Immunofluorescence and PCR results displayed that the tight junction proteins, ZO-1 and Occludin levels were decreased in the ileal tissues of the CaOx group. The untargeted metabolomic analysis revealed that 269 gut metabolites were differentially expressed between the CaOx group and the control group. Meanwhile, bile secretion, the main metabolic pathway in CaOx nephrolithiasis, was identified. Following, five significant bile acid metabolites were selected utilizing the targeted bile acid metabolomics, including Hyodeoxycholic acid (HDCA), Glycohyodeoxycholic acid (GHDCA), Nor-Deoxycholic Acid, omega-muricholic acid, and Taurolithocholic acid. Among these metabolites, HDCA and GHDCA presented the highest predictive accuracy with AUC = 1 to distinguish the CaOx group from the control group. As a result of network pharmacology, target genes of HDCA and GHDCA in CaOx nephrolithiasis were enriched in oxidative stress and apoptosis pathways. Conclusively, our study provides insight into bile acids metabolic changes related to CaOx nephrolithiasis. Although alterations in biochemical pathways indicate a complex pathology in CaOx rats, bile acid changes may serve as biomarkers of CaOx nephrolithiasis.

Purification of Intramineral Peptides from Cuttlebones and In Vitro Activity in CaCO3 Biomineralization

Living organisms develop functional hard structures such as teeth, bones, and shells from calcium salts through mineralization for managing vital functions to sustain life. However, the exact mechanism or role of biomolecules such as proteins and peptides in the biomineralization process to form defect-free hierarchical structures in nature is poorly understood. In this study, we have extracted, purified, and characterized five major peptides (CBP1-CBP5) from the soluble organic materials (SOMs) of cuttlefish bone (CB) and used for the in vitro mineralization of calcium carbonate crystals. The SOMs induced nucleation of the calcite phase at low concentrations and the vaterite phase at high concentrations. The purified peptides nucleated calcite crystals and enhanced aggregation under laboratory conditions. Among five peptides, only CBP2 and CBP3 showed concentration-dependent nucleation, aggregation, and morphological changes of the calcite crystals within 12 h. Circular dichroism studies showed that the peptides CBP2 and CBP3 are in alpha helix and β-sheet conformation, respectively, in solution. CBP1 and CBP4 and CBP5 are in random coil and β-sheet conformation, respectively. In addition, the peptides showed different sizes in solution in the absence (∼27 nm, low aggregation) and presence (∼118 nm, high aggregation) of calcium ions. Aragonite crystals with needle-type morphologies were nucleated in the presence of Mg²⁺ ions in solution. Overall, exploring the activities of such intramineral peptides from CB help to unravel the mechanism of calcium salt deposition in nature.

Himalayan Citrus jambhiri juice reduced renal crystallization in nephrolithiasis by possible inhibition of glycolate oxidase and matrix metalloproteinases

ETHNOPHARMACOLOGICAL RELEVANCE

Citrus fruits are a very rich source of electrolytes and citric acid. They have been used traditionally for treating urinary ailments and renal stones. Citrus jambhiri is indigenously used as a diuretic.

AIM OF THE STUDY

Present study aimed at establishing the antiurolithiatic potential of the juice of Citrus jambhiri fruits along with the elucidation of the mechanism involved in the urolithiasis disease defying activity.

METHODS

The antiurolithiatic activity was established by means of nucleation, growth and aggregation assay in the in vitro settings and by means of ethylene glycol mediated calcium oxalate urolithiasis in the male Wistar rats. Docking studies were performed in an attempt to determine the mechanism of the antiurolithiatic action.

RESULTS

Present study revealed the role of C. jambhiri fruit juice in reducing nucleation, growth and aggregation of calcium oxalate crystals by possible reduction in the urinary supersaturation relative to calcium oxalate and raising the zeta potential of the calcium oxalate crystals. C. jambhiri fruit juice treatment in experimental rats produced significant amelioration of hypercalciuria, hyperoxaluria, hyperphosphaturia, hyperproteinuria, hyperuricosuria, hypocitraturia and hypomagnesiuria and ion activity product of calcium oxalate. It exhibited nephroprotection against calcium oxalate crystals induced renal tubular dilation and renal tissue deterioration. Docking studies further revealed high binding potential of the phytoconstituents of C. jambhiri viz. narirutin, neohesperidin, hesperidin, rutin and citric acid with glycolate oxidase and matrix metalloproteinase-9.

CONCLUSION

C. jambhiri fruit juice possesses excellent antiurolithiatic activity. The study reveals antiurolithiatic mechanism that involves restoration of equilibrium between the promoters and inhibitors of stone formation; and inhibition of matrix metalloproteinases and glycolate oxidase.

Bioinformatics and computational analyses of kidney stone modulatory proteins lead to solid experimental evidence and therapeutic potential

In recent biomedical research, bioinformatics and computational analyses have played essential roles for examining experimental findings and database information. Several bioinformatic tools have been developed and made publicly available for analyzing protein sequence, structure, functional motif/domain, and interactions network. Such properties are very helpful to define biochemical and functional roles of the protein(s) of interest. During the past few decades, bioinformatics and computational biotechnology have been widely applied to kidney stone research. This review summarizes commonly used tools and evidence of bioinformatics and computational biotechnology applied to kidney stone disease (KSD) with special emphasis on analyses of the stone modulatory proteins that play critical roles in kidney stone formation. Such analyses lead to solid experimental evidence to demonstrate mechanisms underlying their stone modulatory activities. The findings obtained from such analyses may also lead to better understanding of KSD pathogenesis and to further development of new therapeutic and preventive strategies.

Roles of heat-shock protein 90 and its four domains (N, LR, M and C) in calcium oxalate stone-forming processes

Human heat-shock protein 90 (HSP90) has four functional domains, including NH₂-terminal (N), charged linker region (LR), middle (M) and COOH-terminal (C) domains. In kidney stone disease (or nephrolithiasis/urolithiasis), HSP90 serves as a receptor for calcium oxalate monohydrate (COM), which is the most common crystal to form kidney stones. Nevertheless, roles of HSP90 and its four domains in kidney stone formation remained unclear and under-investigated. We thus examined and compared their effects on COM crystals during physical (crystallization, growth and aggregation) and biological (crystal–cell adhesion and crystal invasion through extracellular matrix (ECM)) pathogenic processes of kidney stone formation. The analyses revealed that full-length (FL) HSP90 obviously increased COM crystal size and abundance during crystallization and markedly promoted crystal growth, aggregation, adhesion onto renal cells and ECM invasion. Comparing among four individual domains, N and C domains exhibited the strongest promoting effects, whereas LR domain had the weakest promoting effects on COM crystals. In summary, our findings indicate that FL-HSP90 and its four domains (N, LR, M and C) promote COM crystallization, crystal growth, aggregation, adhesion onto renal cells and invasion through the ECM, all of which are the important physical and biological pathogenic processes of kidney stone formation.

Discovering inhibitor molecules for pathological crystallization of CaOx kidney stones from natural extracts of medical herbs

ETHNOPHARMACOLOGICAL RELEVANCE

Kidney stones is one of the common diseases of the urinary system. The primary cause of kidney stone formation is the thermodynamic supersaturation of lithogenic solutes in urine, which desaturates by nucleation, crystal growth and aggregation of minerals and salts, mainly Calcium oxalate (CaOx). One of the potential therapies is to develop drug molecules to inhibit or prevent CaOx crystallization in urine. Traditional Chinese medicines (TCMs) provided an efficient approach for the treatment of kidney stones with a specialized-designed recipe of medicinal herbs. But the action details of these herbs were poorly understood due to their complex components, and whether the effective constituents of herbs have an inhibitory effect on the process of stone formation has not been evaluated.

AIM OF THE STUDY

This study aims to develop and identify inhibitor substitutes from a library of kidney stone prescriptions in traditional Chinese medicines to prevent pathological kidney stone formation.

MATERIALS AND METHODS

As many as twenty Chinese medicines were extracted and separated into five different polar extracts, the inhibition performance of which on CaOx crystallization was explored by recording and comparing crystallization kinetics. The potential inhibitor molecules in the inhibitory extracts were confirmed by HPLC and their retardation efficacy was evaluated by quantifying nucleation and growth kinetics using colorimetry. Then the inhibitor-COM crystal interactions and specificity were examined by morphology evolution and surface structure analysis. In vitro inhibition performance of inhibitors on crystal growth and attachment of CaOx crystals to human renal epithelial cells were further evaluated by recording the nucleation and adhesive crystal numbers.

RESULTS AND CONCLUSION

Water- and n-butanol- soluble extracts from 20 kinds of herbs show almost 100% inhibition percentage, and the n-butanol extracts was found better than commercial drug citrate. Twenty-one molecule substitutes were identified from these extracts, and among them polyphenols display the best inhibition efficacy to retard CaOx crystallization. The high-throughput colorimetric assay and morphology examinations reveals thirteen out of 21 molecules show inhibition potential and disrupt growth of CaOx monohydrate crystals by interacting with exposed Ca²⁺ and C₂O₄^2- on the (100) and (010) surfaces. Moreover, these inhibitors also display pronounced performance in protecting renal epithelial cells by inhibiting nucleation and adhesion of CaOx crystals to cells, thus reducing stone formation. The structure-performance correlation among 19 screened molecules that inhibitors having pKa<3.5, logD (pH = 6) <0, H-number>0.1 mmol are the best in suppressing CaOx crystallization. Our findings provide a novel solution to design and manufacture inhibitor drugs from Chinese medicines for preventing pathological kidney stones formation.

Crystallization of zeolite Beta in the presence of an anionic surfactant AESA

Organic molecules are widely used as structure directing agents, mesopore generating agents or zeolite growth modifiers in the synthesis of various zeolites. However, the organic molecules used in zeolite synthesis...

What roles do alkali metal ions play in the pathological crystallization of uric acid?

Na+ and K+ regulate the crystal growth of uric acid dihydrate by kink blocking and rough growth mechanisms.

Natural inhibitors from earthworms for the crystallization of calcium oxalate monohydrate

Two proteins are proposed as CaOx nucleation and crystal growth regulators. The site-specific adsorption of inhibitors is confirmed from both macroscopic and microscopic perspectives.

Intrinsically Disordered Osteopontin Fragment Orders During Interfacial Calcium Oxalate Mineralization

Calcium oxalate (CaC2 O4 ) is the major component of kidney stone. The acidic osteopontin (OPN) protein in human urine can effectively inhibit the growth of CaC2 O4 crystals, thereby acting as a potent stone preventer. Previous studies in bulk solution all attest to the importance of binding and recognition of OPN at the CaC2 O4 mineral surface, yet molecular level insights into the active interface during CaC2 O4 mineralization are still lacking. Here, we probe the structure of the central OPN fragment and its interaction with Ca2+ and CaC2 O4 at the water-air interface using surface-specific non-linear vibrational spectroscopy. While OPN peptides remain largely disordered in solution, our results reveal that the bidentate binding of Ca2+ ions refold the interfacial peptides into well-ordered and assembled β-turn motifs. One critical intermediate directs mineralization by releasing structural freedom of backbone and binding side chains. These insights into the mineral interface are crucial for understanding the pathological development of kidney stones and possibly relevant for calcium oxalate biomineralization in general.

Escherichia coli Aggravates Calcium Oxalate Stone Formation via PPK1/Flagellin-Mediated Renal Oxidative Injury and Inflammation

Escherichia coli (E. coli) is closely associated with the formation of kidney stones. However, the role of E. coli in CaOx stone formation is not well understood. We explored whether E. coli facilitate CaOx stone formation and its mechanism. Stone and urine cultures were reviewed from kidney stone formers. The ability of calcium oxalate monohydrate (COM) aggregation was detected to evaluate the influence of uropathogenic E. coli, then gel electrophoresis and nanoLC-MS/MS to detect the crystal-adhered protein. Flagellin (Flic) and polyphosphate kinase 1 (PPK1) were screened out following detection of their role on crystal aggregation, oxidative injury, and inflammation of HK-2 cell in vitro. By transurethral injection of wild-type, Ppk1 mutant and Flic mutant strains of E. coli and intraperitoneally injected with glyoxylate in C57BL/6J female mice to establish an animal model. We found that E. coli was the most common bacterial species in patients with CaOx stone. It could enhance CaOx crystal aggregation both in vitro and in vivo. Flagellin was identified as the key molecules regulated by PPK1, and both of them could facilitate the crystal aggregation and mediated HK-2 cell oxidative injury and activated the inflammation-related NF-κB/P38 signaling pathway. Wild-type strain of E. coli injection significantly increased CaOx deposition and enhanced oxidative injury and inflammation-related protein expression, and this effect could be reversed by Ppk1 or Flic mutation. In conclusion, E. coli promotes CaOx stone formation via enhancing oxidative injury and inflammation regulated by the PPK1/flagellin, which activated NF-κB/P38 pathways, providing new potential drug targets for the renal CaOx calculus precaution and treatment.

Secondary Oxalate Nephropathy: Causes and Clinicopathological Characteristics of a Case Series

INTRODUCTION

Secondary oxalate nephropathy (OxN) is associated with a variety of causes and has not been well characterized in Chinese population. To investigate the etiology, clinicopathological features, and outcomes of secondary OxN, we report a case series from a single center in China.

METHODS

A retrospective analysis of 68 patients diagnosed with secondary OxN by renal biopsy from January 2013 to February 2019 in Jinling Hospital was performed.

RESULTS

Secondary OxN accounted for 0.23% of the renal biopsies and 2.31% of patients who received renal biopsies due to acute kidney injury (AKI). A total of 49 men and 19 women with an average age of 51.6 ± 11.8 years were enrolled. The most common cause was iatrogenic medication, followed by oxalate-rich diet and industry exposure. Stage 1, 2, and 3 AKI and AKI on chronic kidney disease (ACKD) were found in 4.4, 8.8, 69.1, and 17.6% of the patients, respectively. The peak serum creatinine during hospitalization was 8.62 ± 4.67 mg/dL. The median urinary oxalate excretion was 51.5 (23.2-147.1) mg/24 h. Kidney biopsy showed extensive calcium oxalate crystal deposits with acute tubulointerstitial nephritis. Thirty-four patients (50.0%) required renal replacement therapy. At the end of a follow-up that lasted 8.7 (0.1-72.1) months, 81.0% of patients achieved renal function recovery in 50 (14-432) days. Patients with renal function recovery had a lower rate of ACKD, a higher level of hemoglobin, a lower level of urine lysozyme, and a lower degree of interstitial fibrosis/tubular atrophy, interstitial inflammation, and global glomerulosclerosis than those in the nonrecovery group.

CONCLUSIONS

In this case series of secondary OxN, the most common cause was iatrogenic medication, and it presented with AKI or ACKD. Half of the patients required renal replacement therapy, and in most of them, the renal function was reversible. Renal biopsy played an important role in diagnosis and prognosis evaluation.

Recent advances on the mechanisms of kidney stone formation (Review)

Kidney stone disease is one of the oldest diseases known to medicine; however, the mechanisms of stone formation and development remain largely unclear. Over the past decades, a variety of theories and strategies have been developed and utilized in the surgical management of kidney stones, as a result of recent technological advances. Observations from the authors and other research groups suggest that there are five entirely different main mechanisms for kidney stone formation. Urinary supersaturation and crystallization are the driving force for intrarenal crystal precipitation. Randall's plaques are recognized as the origin of calcium oxalate stone formation. Sex hormones may be key players in the development of nephrolithiasis and may thus be potential targets for new drugs to suppress kidney stone formation. The microbiome, including urease-producing bacteria, nanobacteria and intestinal microbiota, is likely to have a profound effect on urological health, both positive and negative, owing to its metabolic output and other contributions. Lastly, the immune response, and particularly macrophage differentiation, play crucial roles in renal calcium oxalate crystal formation. In the present study, the current knowledge for each of these five aspects of kidney stone formation is reviewed. This knowledge may be used to explore novel research opportunities and improve the understanding of the initiation and development of kidney stones for urologists, nephrologists and primary care.

Kaempferol alleviates calcium oxalate crystal-induced renal injury and crystal deposition via regulation of the AR/NOX2 signaling pathway

BACKGROUND

Calcium oxalate (CaOx) crystal deposition and crystal-induced renal tubular epithelial cell injury have been found to fundamentally contribute to the formation of CaOx nephrolithiasis.

PURPOSE

In the current work, we aim to study the role and mechanism of kaempferol in CaOx crystal kidney deposition and crystal-induced renal injury.

STUDY DESIGN

Mice models and HK-2 cells were used to investigate the effect of kaempferol in CaOx crystal-induced renal injury and crystal deposition in the kidney and its underlying mechanism by a series of experiments.

METHODS

CaOx crystal deposition in mice renal tubulars and tubular damage were evaluated. And crystal adhesion to HK-2 cells, as well as cellular injury were identified. Furthermore, the effect of kaempferol on the expression of androgen receptor (AR) in renal tubular epithelial cells was assessed. The interaction between AR and nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2), and the intrinsic molecular mechanism of how AR regulated NOX2 in HK-2 cells were dissected. Additionally, several different assays were applied to analyze the expression levels of various related genes in this study.

RESULTS

It was revealed that kaempferol reduced CaOx crystal deposition in renal tubulars and crystal adhesion to HK-2 cells. Meanwhile, the results of in vivo and in vitro experiments corroborated that crystal-associated cellular injury, oxidative stress, inflammation and over-expression of OPN and CD44 in the kidney were ameliorated by kaempferol. Moreover, kaempferol functioned on inhibiting the expression of AR in renal tubular epithelial cells, and AR was able to up-regulate the expression of NOX2 at the transcriptional level by directly binding to the promoter of NOX2. Kaempferol decreased crystal deposition and crystal-induced renal oxidative and inflammatory injury by the down-regulation of AR/NOX2 signaling pathway.

CONCLUSION

Taken together, our study findings suggest that kaempferol has a suppressive effect on renal AR expression, which can attenuate CaOx crystal deposition and crystal-induced kidney injury through repressing oxidative stress and inflammation in the kidney by modulating the AR/NOX2 signaling pathway. It demonstrates that kaempferol may have preventive and therapeutic potential for CaOx nephrolithiasis.

Opposite effects of cations in enhancing and suppressing nucleation in the pathological crystallization of gout

“Opposite effects” were shown by cations, enhancing nucleation followed by suppressing nucleation at physiological pH and ionic strength.

Differential bound proteins and adhesive capabilities of calcium oxalate monohydrate crystals with various sizes

Adhesion of calcium oxalate (CaOx) crystals onto renal tubular epithelial cells is one of the critical steps in kidney stone formation. However, effects of crystal size on the crystal adhesive capability remained unclear. This study compared the adhesive capabilities of CaOx monohydrate (COM) crystals with various sizes (<10 μm, 20-30 μm, 50-60 μm, and > 80 μm). Crystal-cell adhesion assay showed size-dependent increase of COM crystal adhesion onto epithelial cell surface using the larger crystals. Identification of apical membrane proteins that could bind to COM crystals by tandem mass spectrometry (nanoLC-ESI-ETD MS/MS) demonstrated size-specific sets of the COM crystal-binding proteins. Among these, numbers of known oxalate-binding proteins and COM crystal receptors were greatest in the set of the largest size (>80 μm). Atomic force microscopy (AFM) revealed that adhesive forces between carboxylic-immobilized AFM tip and COM crystal surface and between COM-mounted AFM tip and renal epithelial cell surface were size-dependent (greater for the larger crystals). In summary, the adhesive capability of COM crystals is size-dependent - the larger the greater adhesive capability. These data may help better understanding of the pathogenic mechanisms of kidney stone formation at an initial stage when renal tubular cells are exposed to various sizes of COM crystals.

Inhibitors of Calcium Oxalate Crystallization for the Treatment of Oxalate Nephropathies

Calcium oxalate (CaOx) crystal-induced nephropathies comprise a range of kidney disorders, for which there are no efficient pharmacological treatments. Although CaOx crystallization inhibitors have been suggested as a therapeutic modality already decades ago, limited progress has been made in the discovery of potent molecules with efficacy in animal disease models. Herein, an image-based machine learning approach to systematically screen chemically modified myo-inositol hexakisphosphate (IP6) analogues is utilized, which enables the identification of a highly active divalent inositol phosphate molecule. To date, this is the first molecule shown to completely inhibit the crystallization process in the nanomolar range, reduce crystal-cell interactions, thereby preventing CaOx-induced transcriptomic changes, and decrease renal CaOx deposition and kidney injury in a mouse model of hyperoxaluria. In conclusion, IP6 analogues based on such a scaffold may represent a new treatment option for CaOx nephropathies.

Cooperative effects of Na+ and citrates on the dissolution of calcium oxalate crystals

Cooperative role of sodium and citrate ions in the dissolution of calcium oxalate crystals.

Exploring the effect of a peptide additive on struvite formation and morphology: a high-throughput method

Precipitation of struvite (MgNH₄PO₄·6H₂O), a slow-release fertilizer, provides a means of recycling phosphate from wastewater streams. In this work, a high-throughput struvite precipitation method is developed to investigate the effects of a peptide additive. The reactions occurred in small volumes (300 μL or less) in a 96-well plate for 45 minutes. The formation of struvite was monitored by fitting absorbance at 600 nm over time to a first order model with induction time, with the addition of peptide inducing significant changes to the yield parameter and formation constant in that model. The impact of struvite seed dosing was also investigated, highlighting the importance of optimization when peptide is present. The composition of the precipitate was confirmed through Fourier-transform infrared spectroscopy, while morphology and crystal size were analyzed through optical microscopy. Crystals had a higher aspect ratio when precipitated with the peptide. Finally, the utility of the high-throughput platform was demonstrated with a 2⁵ full factorial design to capture the effects and interactions of: magnesium dose, mixing time, seed dose, pH, and temperature. Overall, this study quantifies novel effects of a sequence-defined peptide on struvite formation and morphology via a newly developed high throughput platform.

A high-throughput platform was developed to analyze struvite formation, finding that peptide addition modulates growth in a potentially favorable way.

Flagellum Is Responsible for Promoting Effects of Viable Escherichia coli on Calcium Oxalate Crystallization, Crystal Growth, and Crystal Aggregation

Urease-producing bacteria (especially Proteus mirabilis) can cause infection kidney stone. However, recent studies have shown that intact viable non-urease-producing bacteria such as Escherichia coli might also promote calcium oxalate (CaOx) kidney stone formation but with unclear mechanism. We thus hypothesized that some relevant bacterial components might be responsible for such promoting effects of the intact viable E. coli. Flagella, capsule, lipopolysaccharide (LPS), and outer membrane vesicles (OMVs) were isolated/purified and their stone modulatory activities were evaluated using CaOx crystallization, crystal growth, and crystal aggregation assays. Among these, flagella had the most potent promoting effects on CaOx crystallization, crystal growth, and crystal aggregation. Validation was performed by deflagellation demonstrating that the deflagellated intact viable E. coli had markedly reduced CaOx crystal modulatory activities in all aspects (comparable to those of the negative controls). Similarly, neutralization of the isolated/purified flagella using a specific anti-flagellin antibody, not an isotype control, could abolish the promoting effects of flagella. These findings provide direct evidence indicating that flagellum is responsible for the promoting effects of the viable E. coli on CaOx crystallization, crystal growth and aggregation.

Studying biomineralization pathways in a 3D culture model of breast cancer microcalcifications

Microcalcifications serve as diagnostic markers for breast cancer, yet their formation pathway(s) and role in cancer progression are debated due in part to a lack of relevant 3D culture models that allow studying the extent of cellular regulation over mineralization. Previous studies have suggested processes ranging from dystrophic mineralization associated with cell death to bone-like mineral deposition. Here, we evaluated microcalcification formation in 3D multicellular spheroids, generated from non-malignant, pre-cancer, and invasive cell lines from the MCF10A human breast tumor progression series. The spheroids with greater malignancy potential developed necrotic cores, thus recapitulating spatially distinct viable and non-viable areas known to regulate cellular behavior in tumors in vivo. The spatial distribution of the microcalcifications, as well as their compositions, were characterized using nanoCT, electron-microscopy, and X-ray spectroscopy. Apatite microcalcifications were primarily detected within the viable cell regions and their number and size increased with malignancy potential of the spheroids. Levels of alkaline phosphatase decreased with malignancy potential, whereas levels of osteopontin increased. These findings support a mineralization pathway in which cancer cells induce mineralization in a manner that is linked to their malignancy potential, but that is distinct from physiological osteogenic mineralization.

Deconstructing Quinoline-Class Antimalarials to Identify Fundamental Physicochemical Properties of Beta-Hematin Crystal Growth Inhibitors

A versatile approach to control crystallization involves the use of modifiers, which are additives that interact with crystal surfaces and alter their growth rates. Elucidating a modifier's binding specificity to anisotropic crystal surfaces is a ubiquitous challenge that is critical to their design. In this study, we select hematin, a byproduct of malaria parasites, as a model system to examine the complementarity of modifiers (i.e., antimalarial drugs) to β-hematin crystal surfaces. We divide two antimalarials, chloroquine and amodiaquine, into segments consisting of a quinoline base, common to both drugs, and side chains that differentiate their modes of action. Using a combination of scanning probe microscopy, bulk crystallization, and analytical techniques, we show that the base and side chain work synergistically to reduce the rate of hematin crystallization. In contrast to general observations that modifiers retain their function upon segmentation, we show that the constituents do not act as modifiers. A systematic study of quinoline isomers and analogues shows how subtle rearrangement and removal of functional moieties can create effective constituents from previously ineffective modifiers, along with tuning their inhibitory modes of action. These findings highlight the importance of specific functional moieties in drug compounds, leading to an improved understanding of modifier-crystal interactions that could prove to be applicable to the design of new antimalarials.

Urinary supersaturation as a diagnostic measure in urolithiasis

AIM

To demonstrate that urinary supersaturation per se is not a reliable diagnostic measure of the risk for stone formation.

METHODS

Available physical and chemical data for calcium oxalate monohydrate (COM) and calcium hydrogen phosphate dihydrate (brushite, BRU), and urinary supersaturations with respect to COM and BRU in healthy individuals and stone formers, were obtained from the literature. Classical theory of nucleation was used for calculations.

RESULTS

It was found that the rate of homogeneous nucleation (unaided by substrates) of COM and BRU is nil at all conceivable supersaturations of urine. Consequently spontaneous formation of crystals in urine requires the presence of nucleation substrates for (heteronuclei).

CONCLUSION

Urinary supersaturation with respect to lithiatic compounds is a necessary, but not a sufficient condition for nephrolithiasis. The absence of crystallization inhibitors and the presence of efficient nucleation promoters (heteronuclei) in urine are further necessary conditions of urolithiasis occurrence. Urinary supersaturation per se is not a reliable diagnostic measure of the risk of kidney stone formation.

The role of macromolecules in the formation of kidney stones

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.

Do "inhibitors of crystallisation" play any role in the prevention of kidney stones? A critique

A critical examination of data in the literature and in as yet unpublished laboratory records on the possible role of so-called inhibitors of crystallisation in preventing the formation of calcium-containing kidney stones leads to the following conclusions. So-called inhibitors of spontaneous "self-nucleation" are unlikely to play any role in the initiation of the crystallisation of CaOx or CaP in urine because excessive urinary supersaturation of urine with respect to these salts dominates the onset of "self-nucleation" within the normal time frame of the transit of tubular fluid through the nephron (3-4 min). Inhibitors of the crystal growth of CaOx crystals may or may not play a significant role in the prevention of CaOx stone-formation since once again excessive supersaturation of urine can overwhelm any potential effect of the inhibitors on the growth process. However, they may play a role as inhibitors of crystal growth at lower levels of metastable supersaturation when the balance between supersaturation and inhibitors is more equal. Inhibitors of CaOx crystal aggregation may play a significant role in the prevention of stones, since they do not appear to be strongly affected by excessive supersaturation, either in vitro or in vivo. Inhibitors of CaOx crystal binding to renal tubular epithelium may exist but further studies are necessary to elucidate their importance in reducing the risk of initiating stones in the renal tubules. Inhibitors of CaOx crystal binding to Randall's Plaques and Randall's Plugs may exist but further studies are necessary to elucidate their importance in reducing the risk of initiating stones on renal papillae. There may be an alternative explanation other than a deficiency in the excretion of inhibitors for the observations that there is a difference between CaOx crystal size and degree of aggregation in the fresh, warm urines of normal subjects compared those in urine from patients with recurrent CaOx stones. This difference may depend more on the site of "self-nucleation" of CaOx crystals in the renal tubule rather than on a deficiency in the excretion of so-called inhibitors of crystallisation by patients with CaOx stones. The claim that administration of potassium citrate, potassium magnesium citrate or magnesium hydroxide reduces the rate of stone recurrence may be due to the effect of these forms of medication on the supersaturation of urine with respect to CaOx and CaP rather than to any increase in "inhibitory activity" attributed to these forms of treatment. In summary, there is a competition between supersaturation and so-called inhibitors of crystallisation which ultimately determines the pattern of crystalluria in stone-formers and normals. If the supersaturation of urine with respect to CaOx reaches or exceeds the 3-4 min formation product of that salt, then it dominates the crystallisation process both in terms of "self-nucleation" and crystal growth but appears to have little or no effect on the degree of aggregation of the crystals produced. At supersaturation levels of urine with respect to CaOx well below the 3-4 min formation product of that salt, the influence of inhibitors increases and some may affect not only the degree of aggregation but also the crystal growth of any pre-formed crystals of CaOx at these lower levels of metastability.

Molecular modifiers reveal a mechanism of pathological crystal growth inhibition

Crystalline materials are crucial to the function of living organisms, in the shells of molluscs, the matrix of bone, the teeth of sea urchins, and the exoskeletons of coccoliths. However, pathological biomineralization can be an undesirable crystallization process associated with human diseases. The crystal growth of biogenic, natural and synthetic materials may be regulated by the action of modifiers, most commonly inhibitors, which range from small ions and molecules to large macromolecules. Inhibitors adsorb on crystal surfaces and impede the addition of solute, thereby reducing the rate of growth. Complex inhibitor-crystal interactions in biomineralization are often not well elucidated. Here we show that two molecular inhibitors of calcium oxalate monohydrate crystallization--citrate and hydroxycitrate--exhibit a mechanism that differs from classical theory in that inhibitor adsorption on crystal surfaces induces dissolution of the crystal under specific conditions rather than a reduced rate of crystal growth. This phenomenon occurs even in supersaturated solutions where inhibitor concentration is three orders of magnitude less than that of the solute. The results of bulk crystallization, in situ atomic force microscopy, and density functional theory studies are qualitatively consistent with a hypothesis that inhibitor-crystal interactions impart localized strain to the crystal lattice and that oxalate and calcium ions are released into solution to alleviate this strain. Calcium oxalate monohydrate is the principal component of human kidney stones and citrate is an often-used therapy, but hydroxycitrate is not. For hydroxycitrate to function as a kidney stone treatment, it must be excreted in urine. We report that hydroxycitrate ingested by non-stone-forming humans at an often-recommended dose leads to substantial urinary excretion. In vitro assays using human urine reveal that the molecular modifier hydroxycitrate is as effective an inhibitor of nucleation of calcium oxalate monohydrate nucleation as is citrate. Our findings support exploration of the clinical potential of hydroxycitrate as an alternative treatment to citrate for kidney stones.