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

Oxalate regulates crystal-cell adhesion and macrophage metabolism via JPT2/PI3K/AKT signaling to promote the progression of kidney stones

Oxalate is an organic dicarboxylic acid that is a common component of plant foods. The kidneys are essential organs for oxalate excretion, but excessive oxalates may induce kidney stones. Jupiter microtubule associated homolog 2 (JPT2) is a critical molecule in Ca2+ mobilization, and its intrinsic mechanism in oxalate exposure and kidney stones remains unclear. This study aimed to reveal the mechanism of JPT2 in oxalate exposure and kidney stones. Genetic approaches were used to control JPT2 expression in cells and mice, and the JPT2 mechanism of action was analyzed using transcriptomics and untargeted metabolomics. The results showed that oxalate exposure triggered the upregulation of JPT2, which is involved in nicotinic acid adenine dinucleotide phosphate (NAADP)-mediated Ca2+ mobilization. Transcriptomic analysis revealed that cell adhesion and macrophage inflammatory polarization were inhibited by JPT2 knockdown, and these were dominated by phosphatidylinositol 3-kinase (PI3K)/AKT signaling, respectively. Untargeted metabolomics indicated that JPT2 knockdown inhibited the production of succinic acid semialdehyde (SSA) in macrophages. Furthermore, JPT2 deficiency in mice inhibited kidney stones mineralization. In conclusion, this study demonstrates that oxalate exposure facilitates kidney stones by promoting crystal-cell adhesion, and modulating macrophage metabolism and inflammatory polarization via JPT2/PI3K/AKT signaling.

A Nuclear Magnetic Resonance (NMR)- and Mass Spectrometry (MS)-Based Saturation Kinetics Model of a Bryophyllum pinnatum Decoction as a Treatment for Kidney Stones

Bryophyllum pinnatum (BP) is a medicinal plant used to treat many conditions when taken as a leaf juice, leaves in capsules, as an ethanolic extract, and as herbal tea. These preparations have been chemically analyzed except for decoctions derived from boiled green leaves. In preparation for a clinical trial to validate BP tea as a treatment for kidney stones, we used NMR and MS analyses to characterize the saturation kinetics of the release of metabolites. During boiling of the leaves, (a) the pH decreased to 4.8 within 14 min and then stabilized; (b) regarding organic acids, citric and malic acid were released with maximum release time (tmax) = 35 min; (c) for glycoflavonoids, quercetin 3-O-α-L-arabinopyranosyl-(1 → 2)-α-L-rhamnopyranoside (Q-3O-ArRh), myricetin 3-O-α-L-arabinopyranosyl-(1 → 2)-α-L-rhamnopyranoside (M-3O-ArRh), kappinatoside, myricitrin, and quercitrin were released with tmax = 5-10 min; and (d) the total phenolic content (TPC) and the total antioxidant capacity (TAC) reached a tmax at 55 min and 61 min, respectively. In summary, 24 g of leaves boiled in 250 mL of water for 61 min ensures a maximal release of key water-soluble metabolites, including organic acids and flavonoids. These metabolites are beneficial for treating kidney stones because they target oxidative stress and inflammation and inhibit stone formation.

Corn Silk Polysaccharide Reduces the Risk of Kidney Stone Formation by Reducing Oxidative Stress and Inhibiting COM Crystal Adhesion and Aggregation

The aim of this study is to explore the inhibition of nanocalcium oxalate monohydrate (nano-COM) crystal adhesion and aggregation on the HK-2 cell surface after the protection of corn silk polysaccharides (CSPs) and the effect of carboxyl group (-COOH) content and polysaccharide concentration.

METHOD

HK-2 cells were damaged by 100 nm COM crystals to build an injury model. The cells were protected by CSPs with -COOH contents of 3.92% (CSP0) and 16.38% (CCSP3), respectively. The changes in the biochemical indexes of HK-2 cells and the difference in adhesion amount and aggregation degree of nano-COM on the cell surface before and after CSP protection were detected.

RESULTS

CSP0 and CCSP3 protection can obviously inhibit HK-2 cell damage caused by nano-COM crystals, restore cytoskeleton morphology, reduce intracellular ROS level, inhibit phosphoserine eversion, restore the polarity of the mitochondrial membrane potential, normalize the cell cycle process, and reduce the expression of adhesion molecules, OPN, Annexin A1, HSP90, HAS3, and CD44 on the cell surface. Finally, the adhesion and aggregation of nano-COM crystals on the cell surface were effectively inhibited. The carboxymethylated CSP3 exhibited a higher protective effect on cells than the original CSP0, and cell viability was further improved with the increase in polysaccharide concentration.

CONCLUSIONS

CSPs can protect HK-2 cells from calcium oxalate crystal damage and effectively reduce the adhesion and aggregation of nano-COM crystals on the cell surface, which is conducive to inhibiting the formation of calcium oxalate kidney stones.

Confining calcium oxalate crystal growth in a carbonated apatite-coated microfluidic channel to better understand the role of Randall's plaque in kidney stone formation

Effective prevention of recurrent kidney stone disease requires the understanding of the mechanisms of its formation. Numerous in vivo observations have demonstrated that a large number of pathological calcium oxalate kidney stones develop on an apatitic calcium phosphate deposit, known as Randall's plaque. In an attempt to understand the role of the inorganic hydroxyapatite phase in the formation and habits of calcium oxalates, we confined their growth under dynamic physicochemical and flow conditions in a reversible microfluidic channel coated with hydroxyapatite. Using multi-scale characterization techniques including scanning electron and Raman microscopy, we showed the successful formation of carbonated hydroxyapatite as found in Randall's plaque. This was possible due to a new two-step flow seed-mediated growth strategy which allowed us to coat the channel with carbonated hydroxyapatite. Precipitation of calcium oxalates under laminar flow from supersaturated solutions of oxalate and calcium ions showed that the formation of crystals is a substrate and time dependent complex process where diffusion of oxalate ions to the surface of carbonated hydroxyapatite and the solubility of the latter are among the most important steps for the formation of calcium oxalate crystals. Indeed when an oxalate solution was flushed for 24 h, dissolution of the apatite layer and formation of calcium carbonate calcite crystals occurred which seems to promote calcium oxalate crystal formation. Such a growth route has never been observed in vivo in the context of kidney stones. Under our experimental conditions, our results do not show any direct promoting role of carbonated hydroxyapatite in the formation of calcium oxalate crystals, consolidating therefore the important role that macromolecules can play in the process of nucleation and growth of calcium oxalate crystals on Randall's plaque.

Size-selective adhesion of calcium oxalate monohydrate crystals to lipid membranes

The retention of calcium oxalate monohydrate (COM) crystals on cell membranes is pivotal in kidney stone formation. However, the mechanisms underlying COM attachment to neutral lipid membranes remain unclear. In this study, we demonstrate that COM exhibits size-selective adhesion to fluid lipid membranes composed of lipids with distinct sizes. Specifically, the (100) facet of COM induces the formation of new domains and establishes strong adhesion in the 18:1 (Δ9-Cis) PC (DOPC) membrane, while the (010) facet induces domains with strong adhesion in the 16:0-14:0 PC membrane. This selectivity is linked to the compatibility of the area per lipid in DOPC with the unit cell area of the (100) facet and the area per lipid in 16:0-14:0 PC with the (010) facet. Our Raman spectroscopic analyses reveal that the lipid acyl chains within these induced domains exhibit a higher degree of ordering compared to the typical fluid state of the membrane. This ordered structural alignment, combined with the lateral size-matching effect, suggests the potential formation of molecular arrays within the lipid bilayer that are in harmony with the lattice dimension of COM. To elucidate the strong adhesion between calcium oxalate and the phospholipid head group in the absence of a direct molecular structural correspondence, we propose that crystal water associated with COM can form hydrogen bonds with the phospholipid head group. Using structure visualization software, we demonstrate the feasibility of such hydrogen bonding networks. The formation of this network could serve to stabilize and enhance the attachment of COM to the lipid membrane. This mediation by water molecules offers a plausible explanation for the pronounced affinity at the interface.

FKBP5 deficiency attenuates calcium oxalate kidney stone formation by suppressing cell-crystal adhesion, apoptosis and macrophage M1 polarization via inhibition of NF-κB signaling

Surgical crushing of stones alone has not addressed the increasing prevalence of kidney stones. A promising strategy is to tackle the kidney damage and crystal aggregation inherent in kidney stones with the appropriate therapeutic target. FKBP prolyl isomerase 5 (FKBP5) is a potential predictor of kidney injury, but its status in calcium oxalate (CaOx) kidney stones is not clear. This study attempted to elucidate the role and mechanism of FKBP5 in CaOx kidney stones. Lentivirus and adeno-associated virus were used to control FKBP5 expression in a CaOx kidney stone model. Transcriptomic sequencing and immunological assays were used to analyze the mechanism of FKBP5 deficiency in CaOx kidney stones. The results showed that FKBP5 deficiency reduced renal tubular epithelial cells (RTEC) apoptosis and promoted cell proliferation by downregulating BOK expression. It also attenuated cell-crystal adhesion by downregulating the expression of CDH4. In addition, it inhibited M1 polarization and chemotaxis of macrophages by suppressing CXCL10 expression in RTEC. Moreover, the above therapeutic effects were exerted by inhibiting the activation of NF-κB signaling. Finally, in vivo experiments showed that FKBP5 deficiency attenuated stone aggregation and kidney injury in mice. In conclusion, this study reveals that FKBP5 deficiency attenuates cell-crystal adhesion, reduces apoptosis, promotes cell proliferation, and inhibits macrophage M1 polarization and chemotaxis by inhibiting NF-κB signaling. This provides a potential therapeutic target for CaOx kidney stones.

Calcineurin B inhibits calcium oxalate crystallization, growth and aggregation via its high calcium-affinity property

Calcineurin inhibitors (CNIs) are widely used in organ transplantation to suppress immunity and prevent allograft rejection. However, some transplant patients receiving CNIs have hypocitraturia, hyperoxaluria and kidney stone with unclear mechanism. We hypothesized that CNIs suppress activities of urinary calcineurin, which may serve as the stone inhibitor. This study aimed to investigate effects of calcineurin B (CNB) on calcium oxalate monohydrate (COM) stone formation. Sequence and structural analyses revealed that CNB contained four EF-hand (Ca2+-binding) domains, which are known to regulate Ca2+ homeostasis and likely to affect COM crystals. Various crystal assays revealed that CNB dramatically inhibited COM crystallization, crystal growth and crystal aggregation. At an equal amount, degrees of its inhibition against crystallization and crystal growth were slightly inferior to total urinary proteins (TUPs) from healthy subjects that are known to strongly inhibit COM stone formation. Surprisingly, its inhibitory effect against crystal aggregation was slightly superior to TUPs. While TUPs dramatically inhibited crystal-cell adhesion, CNB had no effect on this process. Ca2+-affinity assay revealed that CNB strongly bound Ca2+ at a comparable degree as of TUPs. These findings indicate that CNB serves as a novel inhibitor of COM crystallization, growth and aggregation via its high Ca2+-affinity property.

A magnetic hydrogel for the efficient retrieval of kidney stone fragments during ureteroscopy

Only 60-75% of conventional kidney stone surgeries achieve complete stone-free status. Up to 30% of patients with residual fragments <2 mm in size experience subsequent stone-related complications. Here we demonstrate a stone retrieval technology in which fragments are rendered magnetizable with a magnetic hydrogel so that they can be easily retrieved with a simple magnetic tool. The magnetic hydrogel facilitates robust in vitro capture of stone fragments of clinically relevant sizes and compositions. The hydrogel components exhibit no cytotoxicity in cell culture and only superficial effects on ex vivo human urothelium and in vivo mouse bladders. Furthermore, the hydrogel demonstrates antimicrobial activity against common uropathogens on par with that of common antibiotics. By enabling the efficient retrieval of kidney stone fragments, our method can lead to improved stone-free rates and patient outcomes.

Valorisation of Three Underutilised Native Australian Plants: Phenolic and Organic Acid Profiles and In Vitro Antimicrobial Activity

Tasmannia lanceolata, Diploglottis bracteata and Syzygium aqueum are understudied native Australian plants. This study aimed to characterise the non-anthocyanin phenolic and organic acid profiles of the aqueous extracts obtained from the leaves of T. lanceolata and fruits of D. bracteata and S. aqueum by UHPLC-Q-Orbitrap-MS/MS and UHPLC-TQ-MS/MS. A total of 39, 22, and 27 non-anthocyanin polyphenols were tentatively identified in T. lanceolata, D. bracteata, and S. aqueum extracts, respectively. Furthermore, sugars and ascorbic acid contents as well as in vitro antioxidant and antimicrobial activities of the extracts were determined. Response surface methodology was applied to achieve an extract blend with a strong inhibitory effect against Pseudomonas viridiflava, the main cause of soft rot in vegetables, Bacillus subtilis, Rhodotorula diobovata and Alternaria alternata. The identified compounds including organic acids (e.g., quinic, citric and malic acids) and polyphenols (e.g., catechin, procyanidins, and ellagitannins) might contribute to the observed antimicrobial activity. Furthermore, this study provides the most comprehensive phenolic profiles of these three underutilised native Australian plants to date.

Comparison of cat and human calcium oxalate monohydrate kidney stone matrix proteomes

Despite its critical nature, the role of matrix in calcium oxalate stone formation is poorly understood. The wide diversity of proteins comprising matrix has contributed to the ambiguity. This study compares the protein distributions measured by mass spectrometry in human calcium oxalate stone matrix to that observed in cat stone matrix, because cats share many clinical characteristics of their stone disease with humans. The observed protein distributions were analyzed in the context of a recent model based on the aggregation of strongly anionic and strongly cationic proteins which includes selective adsorption of other proteins based on total charge. Matrix protein distributions shared many common features between species, including enrichment of both strongly anionic and strongly cationic proteins, increased total charge in matrix proteins compared to urine proteins, and a high degree of similarity of prominent strongly anionic proteins in the matrix of both species. However, there was weaker overlap of the specific dominant proteins in other regions of the net charge distribution. Collectively, these observations support the conceptual model where the strongly anionic proteins associate most strongly with the calcium oxalate crystal surfaces, while the other proteins associate with the strongly anionic proteins through non-specific, charge interactions with each other to create stones. Also, cats appear to be the best animal model of human stone disease identified to date based on these similarities.

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.

Method for CaOx crystals isolation from plant leaves

Although calcium oxalate (CaOx) crystals are present in many plants they are poorly studied. A possible limitation is the lack of methods for CaOx crystals isolation at high concentration and high purity, which is required for the analysis of their associated biomolecules such as proteins. To our knowledge, there are only four works that have isolated proteins from CaOx crystals. Those methods basically consist of grinding the plant material, filtration steps, enzymatic digestions, and density-based separation. However, they lack of steps to evaluate the quality and purity of the isolated crystals. Likewise, those works do not evaluate whether the crystals obtained carry contaminating proteins.

In the present work a detailed method for CaOx crystals isolation from amaranth leaves is described, which can be used to isolate crystals from other plant leaves. The present method is based on previous works with the addition of cleaning steps to removal contaminating protein, separation of crystals by size, and microscopic monitoring to validate the purification efficiency.

Main steps for CaOx crystals isolation:•

Plant leaves are ground and several washing steps, including enzymatic digestions and centrifugation, are carried out to remove cellular debris and contaminating proteins.

•

CaOx crystals are enriched by centrifugation in sodium polytungstate.

•

The different forms of crystals are separated by filtration.

Protein primary structure correlates with calcium oxalate stone matrix preference

Despite the apparent importance of matrix proteins in calcium oxalate kidney stone formation, the complexity of the protein mixture continues to elude explanation. Based on a series of experiments, we have proposed a model where protein aggregates formed from a mixture containing both strongly charged polyanions and strongly charged polycations could initiate calcium oxalate crystal formation and crystal aggregation to create a stone. These protein aggregates also preferentially adsorb many weakly charged proteins from the urine to create a complex protein mixture that mimics the protein distributions observed in patient samples. To verify essential details of this model and identify an explanation for phase selectivity observed in weakly charged proteins, we have examined primary structures of major proteins preferring either the matrix phase or the urine phase for their contents of aspartate, glutamate, lysine and arginine; amino acids that would represent fixed charges at normal urine pH of 6-7. We verified enrichment in stone matrix of proteins with a large number of charged residues exhibiting extreme isoelectric points, both low (pI<5) and high (pI>9). We found that the many proteins with intermediate isoelectric points exhibiting preference for stone matrix contained a smaller number of charge residues, though still more total charges than the intermediate isoelectric point proteins preferring the urine phase. While other sources of charge have yet to be considered, protein preference for stone matrix appears to correlate with high total charge content.

Phytochemical Composition, Antibacterial Activity, and Antioxidant Properties of the Artocarpus altilis Fruits to Promote Their Consumption in the Comoros Islands as Potential Health-Promoting Food or a Source of Bioactive Molecules for the Food Industry

The present study aimed to evaluate the health-promoting potential of breadfruit (Artocarpus altilis (Parkinson) Fosberg, Moraceae family), a traditional Comorian food, considering the sample variability according to geographic localisation. Moreover, the main aims of this research were also to promote its consumption in the Comoros Islands as potential health-promoting food and evaluate it as a source of bioactive molecules for the food industry thanks to its antioxidant and antibacterial properties. Investigations on biologically active substances were carried out on the extracts obtained from breadfruit flours from five regions of Grande Comore (Ngazidja), the main island in Comoros. Phytochemical screening revealed the presence of tannins and polyphenols, flavonoids, leucoanthocyanins, steroids, and triterpenes. The considered secondary metabolites were phenolic compounds, vitamin C, monoterpenes, and organic acids. The contents of total phenolic compounds (mgGAE/100 g of dry weight—DW) in the extracts ranged from 29.69 ± 1.40 (breadfruit from Mbadjini—ExMBA) to 96.14 ± 2.07 (breadfruit from Itsandra—ExITS). These compounds included flavanols, flavonols, cinnamic acid and benzoic acid derivatives, and tannins which were detected at different levels in the different extracts. Chlorogenic acid presented the highest levels between 26.57 ± 0.31 mg/100 g DW (ExMIT) and 43.80 ± 5.43 mg/100 g DW (ExMBA). Quercetin was by far the most quantitatively important flavonol with levels ranging from 14.68 ± 0.19 mg/100 g DW (ExMIT) to 29.60 ± 0.28 mg/100 g DW (ExITS). The extracts were also rich in organic acids and monoterpenes. Quinic acid with contents ranging from 77.25 ± 6.04 mg/100 g DW (ExMBA) to 658.56 ± 0.25 mg/100 g DW of ExHAM was the most important organic acid in all the breadfruit extracts, while limonene was quantitatively the main monoterpene with contents between 85.86 ± 0.23 mg/100 g DW (ExMIT) and 565.45 ± 0.24 mg/100 g DW (ExITS). The antibacterial activity of the extracts was evaluated on twelve pathogens including six Gram (+) bacteria and six Gram (−) bacteria. By the solid medium disc method, except for Escherichia coli and Pseudomonas aeruginosa, all the bacteria were sensitive to one or more extracts. Inhibitory Halo Diameters (IHDs) ranged from 8 mm to 16 mm. Salmonella enterica, Clostridium perfringens, and Vibrio fischeri were the most sensitive with IHD > 14 mm for ExITS. By the liquid microdilution method, MICs ranged from 3.12 mg/mL to 50 mg/mL and varied depending on the extract. Bacillus megaterium was the most sensitive with MICs ≤ 12.5 mg/mL. Pseudomonas aeruginosa, Shigella flexneri, and Vibrio fischeri were the least sensitive with all MICs ≥ 12.5 mg/mL. ExHAM was most effective with a MIC of 3.12 mg/mL on Staphylococcus aureus and 6.25 mg/mL on Salmonella enterica. The antioxidant power of the extracts was evaluated by the FRAP method. The activity ranged from 5.44 ± 0.35 (ExMBA) to 14.83 ± 0.11 mmol Fe²⁺/kg DW (ExHAM). Breadfruit from different regions of Comoros contained different classes of secondary metabolites well known for their important pharmacological properties. The results of this study on phenolics, monoterpenes, and organic acids have provided new data on these fruits. The obtained results showed that breadfruit from the biggest island of the Union of Comoros also presented antimicrobial and antioxidant properties, even if some differences in effectiveness existed between fruits from different regions.

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.

Exploring mechanisms of protein influence on calcium oxalate kidney stone formation

Calcium oxalate monohydrate (COM) crystals are the primary constituent of most kidney stones, but urine proteins in stone matrix are believed to be critical elements for stone formation from these crystals. Recent data have shown that hundreds of proteins appear in the stone matrix with no explanation for inclusion of so many proteins. We have proposed a stone formation model with protein stimulated COM aggregation based on polyanion-polycation aggregation, which is supported by finding that matrix is highly enriched in strongly anionic and strongly cationic proteins. Many other proteins may be drawn to such aggregates due to their limited solubility in water or charge effects. Finding similar protein enrichment in both polyarginine (pR) induced aggregates of urine proteins and COM stone matrix would support this hypothesis. Purified proteins (PP) were obtained from random urine samples of six healthy adults by ultradiafiltration. Protein aggregation was induced by adding pR to PP solutions at two concentrations; 0.25 and 0.5 µg pR/µg of PP. Samples of each fraction and the original PP mixture were lyophilized and analyzed by tandem mass spectrometry. Aggregates induced by pR addition to PP samples collected a protein mixture that mimicked the protein distribution observed in COM matrix, supporting our hypothesis. The apparently discordant behavior of certain abundant anionic proteins preferentially joining the pR aggregate, when they had demonstrated reduced abundance in COM stone matrix, suggests that this model was overdriven to aggregate. The reversal of aggregate preference of albumin at low pR addition supports this interpretation.

Small intestine resection increases oxalate and citrate transporter expression and calcium oxalate crystal formation in rat hyperoxaluric kidneys

Short bowel (SB) increases the risk of kidney stones. However, the underlying mechanism is unclear. Here, we examined how SB affected renal oxalate and citrate handlings for in vivo hyperoxaluric rats and in vitro tubular cells. SB was induced by small intestine resection in male Wistar rats. Sham-operated controls had no resection. After 7 days of recovery, the rats were divided into control, SB (both fed with distilled water), ethylene glycol (EG), and SB+EG (both fed with 0.75% EG for hyperoxaluric induction) groups for 28 days. We collected the plasma, 24 h of urine, kidney, and intestine tissues for analysis. Hypocitraturia was found and persisted up to 28 days for the SB group. Hypocalcemia and high plasma parathyroid hormone (PTH) levels were found in the 28-day SB rats. SB aggravated EG-mediated oxalate nephropathy by fostering hyperoxaluria and hypocitraturia, and increasing the degree of supersaturation and calcium oxalate (CaOx) crystal deposition. These effects were associated with renal up-regulations of the oxalate transporter solute carrier family 26 (Slc26)a6 and citrate transporter sodium-dependent dicarboxylate cotransporter-1 (NaDC-1) but not Slc26a2. The effects of PTH on the SB kidneys were then examined in NRK-52E tubular cells. Recombinant PTH attenuated oxalate-mediated cell injury and up-regulated NaDC-1 via protein kinase A (PKA) activation. PTH, however, showed no additive effects on oxalate-induced Slc26a6 and NaDC-1 up-regulation. Together, these results demonstrated that renal NaDC-1 upregulation-induced hypocitraturia weakened the defense against Slc26a6-mediated hyperoxaluria in SB kidneys for excess CaOx crystal formation. Increased tubular NaDC-1 expression caused by SB relied on PTH.

Metabolic assessment in pure struvite stones formers: is it necessary?

BACKGROUND AND OBJECTIVE

Magnesium ammonium phosphate stones (MAP), also known as struvite stones, are associated with urinary infection and impairment of renal unit. The aim of this study is to evaluate the urinary metabolic risk factors for recurrence of renal calculi in patients submitted to nephrectomy due to MAP stones.

METHODS

We retrospectively reviewed the charts of patients > 18 years old submitted to total nephrectomy due to pure MAP stones and pure calcium oxalate (CaOx) stones from July 2006 to July 2016. Urinary metabolic parameters were assessed through 24-hour urine exams ≥ 3 months after nephrectomy. Urinary metabolic parameters and new event related to lithiasis were compared.

RESULTS

Twenty-eight and 39 patients were included in MAP and CaOx group, respectively. Abnormalities in 24-hour urine samples were similar between groups. Hypercalciuria occurred in 7.1 and 10.3% of patients in MAP and CaOx group, respectively (p = 0.66), whereas hypocitraturia was present in 65.2 and 59.0% of patients with MAP and CaOx group, respectively (p = 0.41). No significant difference in new events was found between MAP and CaOx groups (17.9 vs. 23.1%, respectively; p = 0.60).

CONCLUSION

A 24-hour urine evaluation should be offered to patients submitted to nephrectomy due to pure MAP stones in order to detect metabolic risk, improve treatment, and prevent stone recurrence.

Human kidney stone matrix proteins alleviate hyperoxaluria induced renal stress by targeting cell-crystal interactions

Increased levels of urinary oxalate also known as hyperoxaluria, increase the likelihood of kidney stone formation through enhanced calcium oxalate (CaOx) crystallization. The management of lithiatic renal pathology requires investigations at the initial macromolecular stages. Hence, the current study was designed to unravel the protein make-up of human kidney stones and its impact on renal cells' altered proteome, induced as the consequence of CaOx injury. CaOx kidney stones were collected from patients; stones were pooled for entire cohort, followed by protein extraction. Immunocytochemistry, RT-PCR and flow-cytometric analysis revealed the promising antilithiatic activity of kidney stone matrix proteins. The iTRAQ analysis of renal cells showed up-regulation of 12 proteins and down-regulation of 41 proteins due to CaOx insult, however, this differential expression was normalized in the presence of kidney stone matrix proteins. Protein network analysis revealed involvement of up-regulated proteins in apoptosis, calcium-binding, inflammatory and stress response pathways. Moreover, seven novel antilithiatic proteins were identified from human kidney stones' matrix: Tenascin-X-isoform2, CCDC-144A, LIM domain kinase-1, Serine/Arginine receptor matrix protein-2, mitochondrial peptide methionine sulfoxide reductase, volume-regulated anion channel subunit-LRRC8A and BMPR2. In silico analysis concluded that these proteins exert antilithiatic potential through crystal binding, thereby inhibiting the crystal-cell interaction, a pre-requisite to initiate inflammatory response. Thus, the outcomes of this study provide insights into the molecular events of CaOx induced renal toxicity and subsequent progression into nephrolithiasis.

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.

Assessing the Role of Light Absorption in Laser Lithotripsy by Isotopic Substitution of Kidney Stone Materials

Understanding the chemical characteristics of kidney stones and how the stone composition affects their fragmentation is key to improving clinical laser lithotripsy. During laser lithotripsy, two mechanisms may be responsible for stone fragmentation: a photothermal mechanism and/or microexplosion mechanism. Herein, we carry out an isotopic substitution of crystal H₂O with D₂O in calcium oxalate monohydrate and struvite stones to alter their optical properties to study the relationship between the absorption of the stones, at the wavelength of the Ho:YAG (2.12 μm) laser, and the fragmentation behavior. Changing the absorption of the stones at 2.12 μm changes the extent of fragmentation, whereas changing the absorption of the bulk medium has a negligible effect on fragmentation, leading to the conclusion that kidney stone ablation is dominated by a photothermal mechanism.

Preparation and characterization of abalone shells derived biological mesoporous hydroxyapatite microspheres for drug delivery

The rapid growth of the abalone industry has brought a great burden to the environment because of their inedible shells. Aiming at environmental and resource sustainability, porous microspheres of carbonate-substituted hydroxyapatite (HAP) were prepared by a hydrothermal method using abalone shells; then, they were further used as a carrier for doxorubicin (DOX) in a drug delivery system. The porous HAP microspheres were approximately 6 μm in size with a considerable specific surface area and average pore size (128.6659 cm²/g and 9.064 nm, respectively), which ensured excellent drug-handling capacity (95.542%). In addition, the pH responsiveness of the drug release system was favorable for effective in vivo drug release in an acidic tumor microenvironment. Moreover, the drug-loaded microspheres could effectively induce apoptosis of MCF-7 cells but were less cytotoxic to MC3T3-E1 cells. Because of its good biocompatibility, high drug loading capacity and controlled drug release property, the porous microspheres prepared in this experiment have potential application value in drug delivery and tumor therapy; furthermore, they make full use of abalone shells, providing environmental sustainability.

In situ flow cell platform for examining calcium oxalate and calcium phosphate crystallization on films of basement membrane extract in the presence of urinary 'inhibitors'

A significant portion of the population suffers from idipoathic calcium oxalate (CaOx) kidney stones, and current clinical treatments of stones have limited lasting success with a high rate of patients suffering from reoccurring stones. Understanding the role of physiologically relevant urinary species on the formation, aggregation, and growth of CaOx crystals can allow for better understanding of this complex biomineralization process and lead to more effective clinical treatments. Our prior work has focused on developing a two-stage model system, where the first stage emulates the formation of Randall's plaque, and the second stage examines the influence of the plaque on overgrowth of CaOx into a stone. Herein, we report on the development of an easy-to-use flow-cell platform that utilizes basement membrane extract (BME) as a biologically relevant crystallization substrate to study the influence of urinary 'inhibitors' on the in situ formation and growth of CaOx on BME under flow conditions. Magnesium, citrate, and osteopontin were studied because of their known ability to inhibit CaOx formation, but their influence also led to interesting modifications to the terminal crystal habit. Magnesium had little to no effect on the CaOx crystallization, but both citrate and osteopontin resulted in significant changes to the crystallization kinetics and the terminal crystal habits. Triply inhibited artificial urine solutions resulted in CaOx monohydrate formations that resembled physiological stones, and the in situ platform allowed for morphogenesis to be dynamically monitored. The BME was also used in a two-stage model system to first grow CaP that mimicked Randall's plaques, whereby the impact of the CaP crystallizing surface on CaOx formation could be studied. It was found that the CaP surface did not result in any significant changes in CaOx crystal formation or growth indicating that the urinary inhibitors and the basement membrane substrate were the dominant factors in modulating CaOx crystallization. It was also found that the basement membrane surface promoted the attachment and/or nucleation and growth of both CaOx and CaP crystals compared to bare glass surfaces, thereby enabling easy study of the urinary inhibitors. The work presented here has elucidated the terminal growth habit of different COM structures and has provided an easy to use platform that can be widely adopted by the kidney stone and other crystallization communities.

Molecular Understanding of Humic Acid-Limited Phosphate Precipitation and Transformation

Phosphorus (P) availability is widely assumed to be limited by the formation of metal (Ca, Fe, or Al) phosphate precipitates that are modulated by soil organic matter (SOM), but the SOM-precipitate interactions remain uncertain because of their environmental complexities. Here, we present a model system by quantifying the in situ nanoscale nucleation kinetics of calcium phosphates (Ca-Ps) on mica in environmentally relevant aqueous solutions by liquid-cell atomic force microscopy. We find that Ca-P precipitate formation is slower when humic acid (HA) concentration is higher. High-resolution transmission electron microscopy observations demonstrate that HA strongly stabilizes amorphous calcium phosphate (ACP), delaying its subsequent transformation to thermodynamically more stable phases. Consistent with the formation of molecular organo-mineral bonding, dynamic force spectroscopy measurements display larger binding energies of organic ligands with certain chemical functionalities on HA to the initially formed ACP than to mica that are responsible for stabilization of ACP through stronger HA-ACP interactions. Our results provide direct evidence for the proposed importance of SOM in inhibiting Ca-P precipitation/transformation. We suggest that similar studies of binding strength in SOM-Fe/Al-P may reveal how both organic matter and metal ions control P availability and fate, and thus the eventual P management for agronomical and environmental sustainability.

Polymer-Mineral Composites Mimic Human Kidney Stones in Laser Lithotripsy Experiments

Despite the widespread use of laser lithotripsy to fragment kidney stones in vivo, there is a lack of robust artificial stone models to replicate the behavior of human stones during lithotripsy procedures. This need for accurate stone models is particularly important as novel laser technologies are introduced in the field of lithotripsy. In this work, we present a method to prepare composite materials that replicate the properties of human kidney stones during laser lithotripsy. Their behavior is understood through the lens of near-IR spectroscopy and helps to elucidate the mechanism of laser lithotripsy in kidney stone materials.

Biominerals Formed by DNA and Calcium Oxalate or Hydroxyapatite: A Comparative Study

Biominerals formed by DNA and calcium oxalate (CaOx) or hydroxyapatite (HAp), the most important and stable phase of calcium phosphate) have been examined and compared using a synergistic combination of computer simulation and experimental studies. The interest of this comparison stems from the medical observation that HAp- and CaOx-based microcalcifications are frequently observed in breast cancer tissues, and some of their features are used as part of the diagnosis. Molecular dynamics simulations show that (1) the DNA double helix remains stable when it is adsorbed onto the most stable facet of HAp, whereas it undergoes significant structural distortions when it is adsorbed onto CaOx; (2) DNA acts as a template for the nucleation and growth of HAp but not for the mineralization of CaOx; and (3) the DNA double helix remains stable when it is encapsulated inside HAp nanopores, but it becomes destabilized when the encapsulation occurs into CaOx nanopores. Furthermore, CaOx and HAp minerals containing DNA molecules inside and/or adsorbed on the surface have been prepared in the lab by mixing solutions containing the corresponding ions with fish sperm DNA. Characterization of the formed minerals, which has been focused on the identification of DNA using UV-vis spectroscopy, indicates that the tendency to adsorb and, especially, encapsulate DNA is much smaller for CaOx than for HAp, which is in perfect agreement with results from molecular dynamics simulations. Finally, quantum mechanical calculations have been performed to rationalize these results in terms of molecular interactions, evidencing the high affinity of Ca²⁺ toward oxalate anions in an aqueous environment.

A Short Review on the Relationships Between Nephrolithiasis and Myocardial Infarction

The interaction between organs is a crucial part of modern medicine. As a very prerequisite to manage a disease, practitioners should have a full awareness of the related organs. Kidney and heart are two vital organs that are closely interconnected in various fields. These two organs have a lot of common risk factors for making a person unhealthy; therefore, if you prevent the disease in one of them, the other's morbidity might be alleviated as well. Among them, nephrolithiasis and myocardial infarction (MI) have more risk factors in common, and both could be fatal. Also, these two diseases are important regarding the prevalence, incidence, and burden of disease. Some studies confirm the relationship between MI and nephrolithiasis; however, further researches are needed to discover the exact direction of their relationship. The present review aims to explain the mechanism of MI and nephrolithiasis; clarify the relationship between these two disease based on physiological, pathological, and clinical studies; and propose some solutions for the prevention and treatment of such diseases.

In Vitro Studies Reveal Antiurolithic Effect of Antioxidant Sulfated Polysaccharides from the Green Seaweed Caulerpa cupressoides var flabellata

Urolithiasis affects approximately 10% of the world population and is strongly associated with calcium oxalate (CaOx) crystals. Currently, there is no efficient compound that can be used to prevent this disease. However, seaweeds' sulfated polysaccharides (SPs) can change the CaOx crystals surface's charge and thus modify the crystallization dynamics, due to the interaction of the negative charges of these polymers with the crystal surface during their synthesis. We observed that the SPs of Caulerpa cupressoides modified the morphology, size and surface charge of CaOx crystals. Thus, these crystals became similar to those found in healthy persons. In the presence of SPs, dihydrate CaOx crystals showed rounded or dumbbell morphology. Infrared analysis, fluorescence microscopy, flow cytometry (FITC-conjugated SPs) and atomic composition analysis (EDS) allowed us to propose the mode of action between the Caulerpa's SPs and the CaOx crystals. This study is the first step in understanding the interactions between SPs, which are promising molecules for the treatment of urolithiasis, and CaOx crystals, which are the main cause of kidney stones.

Selective protein enrichment in calcium oxalate stone matrix: a window to pathogenesis?

Urine proteins are thought to control calcium oxalate stone formation, but over 1000 proteins have been reported in stone matrix obscuring their relative importance. Proteins critical to stone formation should be present at increased relative abundance in stone matrix compared to urine, so quantitative protein distribution data were obtained for stone matrix compared to prior urine proteome data. Matrix proteins were isolated from eight stones (> 90% calcium oxalate content) by crystal dissolution and further purified by ultradiafiltration (> 10 kDa membrane). Proteomic analyses were performed using label-free spectral counting tandem mass spectrometry, followed by stringent filtering. The average matrix proteome was compared to the average urine proteome observed in random urine samples from 25 calcium oxalate stone formers reported previously. Five proteins were prominently enriched in matrix, accounting for a mass fraction of > 30% of matrix protein, but only 3% of urine protein. Many highly abundant urinary proteins, like albumin and uromodulin, were present in matrix at reduced relative abundance compared to urine, likely indicating non-selective inclusion in matrix. Furthermore, grouping proteins by isoelectric point demonstrated that the stone matrix proteome was highly enriched in both strongly anionic (i.e., osteopontin) and strongly cationic (i.e., histone) proteins, most of which are normally found in intracellular or nuclear compartments. The fact that highly anionic and highly cationic proteins aggregate at low concentrations and these aggregates can induce crystal aggregation suggests that protein aggregation may facilitate calcium oxalate stone formation, while cell injury processes are implicated by the presence of many intracellular proteins.

The Long Pentraxin PTX3 Is an Endogenous Inhibitor of Hyperoxaluria-Related Nephrocalcinosis and Chronic Kidney Disease

The long pentraxin 3 (PTX3) exerts a variety of regulatory functions in acute and chronic tissue inflammation. In particular, PTX3 acts as an opsonin for a variety of pathogens and endogenous particles. We hypothesized that PTX3 would exhibit opsonin-like functions toward calcium oxalate crystals, too, and inhibit crystal growth. This process is fundamental in kidney stone disease as well as in hyperoxaluria-related nephrocalcinosis, the paradigmatic cause of chronic kidney disease (CKD) in children with primary hyperoxaluria type I due to genetic defects in oxalate metabolism. Direct effects of PTX3 on calcium oxalate crystals were investigated in chemico by adding recombinant PTX3 to supersaturated calcium and oxalate solutions. PTX3, but not isomolar concentrations of albumin, dose-dependently inhibited crystal growth. In vivo, the PTX3 protein was undetectable in tubular epithelial cells and urine of wild-type mice under physiological conditions. However, its levels increased within 3 weeks of feeding an oxalate-rich diet, an exposure inducing hyperoxaluria-related nephrocalcinosis and CKD in selected mouse strains (male and female C57BL/6N and male Balb/c mice) but not in others (male and female 129SV and CD-1, male and female Balb/c mice). Genetic ablation of ptx3 in nephrocalcinosis un-susceptible B6;129 mice was sufficient to raise the oxalate nephropathy phenotype observed in susceptible strains. We conclude that PTX3 is an endogenous inhibitor of calcium oxalate crystal growth. This mechanism limits hyperoxaluria-related nephrocalcinosis, e.g., in primary or secondary hyperoxaluria, and potentially also in the more prevalent kidney stone disease.

Modulation of calcium oxalate dihydrate growth by phosphorylated osteopontin peptides

Osteopontin (OPN) is a significant component of kidney stone matrix and a key modulator of stone formation. Here, we investigated the effects of different phosphorylated states of a synthesized peptide of OPN (the ASARM peptide; acidic, serine- and aspartate-rich motif) on calcium oxalate dihydrate (COD) crystals, a major mineral phase of kidney stones. In vitro, phosphorylated OPN-ASARM peptides strongly inhibited COD crystal growth in solution as compared to the nonphosphorylated state, with increasing inhibitory potency correlating with the degree of peptide phosphorylation. Scanning electron microscopy revealed that the inhibition from the phosphopeptides resulted in distinctive, rosette-like crystal aggregates called spherulites. The OPN-ASARM peptides preferentially bound and specifically inhibited the {1 1 0} crystallographic faces of COD, as identified by combining atomic force microscopy and computational simulation approaches. These {1 1 0} surfaces of COD have high lattice calcium occupancy (exposure), providing preferential binding sites for the highly acidic peptides; binding and inhibition by OPN-ASARM peptides at the {1 1 0} faces led to crystal aggregation and intergrowth. The crystal spherulite formations obtained in vitro when using the most phosphorylated form of OPN-ASARM peptide at a high concentration, resembled crystal morphologies observed in vivo in a rat model of urolithiasis, in which crystal deposits in the kidney contain abundant OPN as revealed by immunogold labeling. A mechanistic model for spherulite formation is proposed based on the symmetry and crystallographic structure of COD, where the phosphate groups of OPN-ASARM bind to calcium atoms at [1 1 1] step risers on the COD {1 1 0} surface, inducing the periodic emergence of new COD crystals to form spherulites.

Development of a two-stage in vitro model system to investigate the mineralization mechanisms involved in idiopathic stone formation: stage 1-biomimetic Randall's plaque using decellularized porcine kidneys

Idiopathic calcium oxalate (CaOx) stone formers form stones that are commonly attached to calcium phosphate (CaP) deposits in the renal tissue, known as Randall's plaques (RP). Plaques are suggested to originate in the renal tubular basement membrane, where they exhibit a morphology of concentrically laminated apatitic spherules, while in the interstitial regions, the collagen fibrils and vesicles become mineralized. We hypothesize that these minerals might form by non-classical crystallization mechanisms, such as via amorphous precursors, some of which might originate from a polymer-induced liquid-precursor (PILP) process. Thus, our goal is to identify mineralogical 'signatures' of various stone formation mechanisms. To do this for idiopathic CaOx stones, we are developing a two-stage model system of CaP-CaOx composite stones, consisting of stage (1) CaP mineralized plaque, followed by stage (2) CaOx overgrowth into a stone. For the studies presented here, decellularized porcine kidneys were mineralized with CaP using polyaspartic acid or the protein osteopontin (OPN) to induce the PILP process and create biomimetic RP. Analysis of the PILP-mineralized tissues shows features that resemble the native plaques, including mineral spherules and collagen with intrafibrillar mineral. In contrast, the classical crystallization produced large apatitic spherulites, which is a very different morphology, but one which is also found in some stones. An alternative hypothesis regarding Randall's plaque, and if or when it becomes pathological, is discussed.

Probing Anisotropic Surface Properties and Surface Forces of Fluorite Crystals

Fluorite is the most important mineral source for producing fluorine-based chemicals and materials in a wide range of engineering and technological applications. In this work, atomic force microscopy was employed, for the first time, to probe the surface interactions and adhesion energy of model oleic acid (a commonly used surface modification organics for fluorite) molecules on fluorite surfaces with different orientations in both air and aqueous solutions at different pH conditions. Fitted with the Derjaguin-Landau-Verwey-Overbeek theory, the force results during surface approaching demonstrate the anisotropy in the surface charge of different orientations, with the {111} surface exhibiting a higher magnitude of surface charge, which could be attributed to the difference in the atomic composition. The adhesion measured during surface retraction shows that model oleic acid molecules have a stronger adhesion with the {100} surface than with the {111} surface in both air and aqueous solutions. The anisotropic adhesion energy was analyzed in relation to the surface atom (especially calcium) activity, which was supported by the surface free energy results calculated based on a three-probe-liquid method. Each calcium atom on the {100} surface with four dangling bonds is more active than the calcium atom on the {111} surface with only one dangling bond, supported by a larger value of the Lewis acid component for the {100} surface. The model oleic acid molecules present in the ionic form at pH 9 exhibit a higher adhesion energy with fluorite surfaces as compared to their molecular form at pH 6, which was related to the surface activity of different forms. The adhesion energy measured in solution is much lower than that in air, indicating that the solvent exerts an important influence on the interactions of organic molecules with mineral surfaces. The results provide useful information on the fundamental understanding of surface interactions and adhesion energy of organic molecules on mineral surfaces with different orientations, and the methodology can be extended to many other crystal surfaces in various interfacial processes.

Mechanisms of Modulation of Calcium Phosphate Pathological Mineralization by Mobile and Immobile Small-Molecule Inhibitors

Potential pathways for inhibiting crystal growth are via either disrupting local microenvironments surrounding crystal-solution interfaces or physically blocking solute molecule attachment. However, the actual mode of inhibition may be more complicated due to the characteristic time scale for the inhibitor adsorption and relaxation to a well-bound state at crystal surfaces. Here we demonstrate the role of citrate (CA) and hydroxycitrate (HCA) in brushite (DCPD, CaHPO₄·2H₂O) crystallization over a broad range of both inhibitor concentrations and supersaturations by in situ atomic force microscopy (AFM). We observed that both inhibitors exhibit two distinct actions: control of surface crystallization by the decrease of step density at high supersaturations and the decrease of the [1̅00]_Cc step velocity at high inhibitor concentration and low supersaturation. The switching of the two distinct modes depends on the terrace lifetime, and the slow kinetics along the [1̅00]_Cc step direction provides specific sites for the newly formed dislocations. Molecular modeling shows the strong HCA-crystal interaction by molecular recognition, explaining the AFM observations for the formation of new steps and surface dissolution along the [101]_Cc direction due to the introduction of strong localized strain in the crystal lattice. These direct observations highlight the importance of the inhibitor coverage on mineral surfaces, as well as the solution supersaturation in predicting the inhibition efficacy, and reveal an improved understanding of inhibition of calcium phosphate biomineralization, with clinical implications for the full therapeutic potential of small-molecule inhibitors for kidney stone disease.

Preparation, properties, formation mechanisms, and cytotoxicity of calcium oxalate monohydrate with various morphologies

Calcium oxalate monohydrate (COM) crystals with various morphologies, such as elliptical, hexagonal, peanut-like, spherical and flower-like structures with a size of about 10 μm, were prepared through varying the reactant concentration, stirring speed, reaction temperature, and additive.

Effect of Crystal Shape and Aggregation of Calcium Oxalate Monohydrate on Cellular Toxicity in Renal Epithelial Cells

Renal epithelial cell injury is a key step in inducing kidney stone formation. This injury induced by crystallites with different shapes and aggregation states has been receiving minimal research attention. To compare the shape and aggregation effects of calcium oxalate crystals on their toxicity, we prepared calcium oxalate monohydrate (COM) crystals with the morphology of a hexagonal lozenge, a thin hexagonal lozenge, and their corresponding aggregates. We then compared their toxicities toward human kidney proximal tubular epithelial (HK-2) cells. All four shapes of COM crystals caused cell-membrane rupture, upregulated intracellular reactive oxygen, and decreased mitochondrial membrane potential. This series of phenomena ultimately led to necrotic cell death. The overall damage in cells was determined in terms of both exterior and interior damage. Crystals with a large Ca2+ ion-rich (1̅01) active face showed the greatest toxicity in HK-2 cells and the largest extent of adhesion onto the cell surface. Crystals with sharp edges easily caused cell-membrane ruptures. The aggregation of sharp crystals aggravated cell injury, whereas the aggregation of blunt crystals weakened cell injury. Therefore, crystal shapes and aggregation states were important factors that affected crystal toxicity in renal epithelial cells. All of these findings elucidated the relationship between the physical properties of crystals and cytotoxicity and provided theoretical references for inhibiting stone formation.

Protective Effects of Pistacia lentiscus L. fruit extract against calcium oxalate monohydrate induced proximal tubular injury

ETHNOPHARMACOLOGICAL RELEVANCE

The world prevalence of kidney stones is increasing and plants are frequently used to treat urolithiasis. Pistacia lentiscus L, a plant which freely grows around the Mediterranean basin areas, is widely used for various pathologies. P. lentiscus has an important impact as it has economical value on top of its pharmacological interest. Decoctions of its aerial parts and/or resin are used to treat kidney stones.

AIM OF THE STUDY

To in vitro assess the potential nephroprotective effect of Pistacia lentiscus ethanolic fruit extract (PLEF) on proximal tubular cells in response to the adhesion of calcium oxalate monohydrate (COM) crystals.

MATERIALS AND METHODS

Human Kidney [HK]-2 cells were incubated with and without COM in the presence or absence of PLEF. Cell viability was measured by the resazurin assay. The expression of E-cadherin was analyzed by PCR. The extracellular production of H₂O₂ was measured by Amplex® Red H₂O₂ Assay. The numbers of detached or non-adherent COM crystals in the presence of PLEF were microscopically captured and counted using ImageJ software. The interaction of PLEF with COM and the effect of PLEF on crystal size were analyzed by flow cytometry. The spectrophotometric measurement of turbidity was performed for assessing the COM concentration.

RESULTS

PLEF incubated with COM was able to increase the cell viability. The decrease of E-cadherin expression after incubation with COM was counteracted by PLEF. Overproduction of H₂O₂ induced by COM was also inhibited by PLEF. Observations using flow cytometry showed that interactions between PLEF and the COM crystals occurred. PLEF was also effective in reducing the particles size and in lowering COM concentration.

CONCLUSION

Our data show that COM tubulotoxicity can be significantly reversed by PLEF -at least in part- via an inhibition of COM crystals adhesion onto the apical membrane. This early beneficial effect of PLEF needs to be further investigated as a useful strategy in nephrolithiasis prevention.

Developing a molecular picture of soil organic matter-mineral interactions by quantifying organo-mineral binding

Long residence times of soil organic matter have been attributed to reactive mineral surface sites that sorb organic species and cause inaccessibility due to physical isolation and chemical stabilization at the organic–mineral interface. Instrumentation for probing this interface is limited. As a result, much of the micron- and molecular-scale knowledge about organic–mineral interactions remains largely qualitative. Here we report the use of force spectroscopy to directly measure the binding between organic ligands with known chemical functionalities and soil minerals in aqueous environments. By systematically studying the role of organic functional group chemistry with model minerals, we demonstrate that chemistry of both the organic ligand and mineral contribute to values of binding free energy and that changes in pH and ionic strength produce significant differences in binding energies. These direct measurements of molecular binding provide mechanistic insights into organo–mineral interactions, which could potentially inform land-carbon models that explicitly include mineral-bound C pools.

Most molecular scale knowledge on soil organo–mineral interactions remains qualitative due to instrument limitations. Here, the authors use force spectroscopy to directly measure free binding energy between organic ligands and minerals and find that both chemistry and environmental conditions affect binding.

Growth mechanism study of clustered aggregates of dirithromycin crystals in N,N-dimethylformamide solvent

A growth mechanism of novel clusters of the pharmaceutical compound dirithromycin was investigated by combining experimental crystallization and computational simulation.

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.