Presence of lipids in urine, crystals and stones: implications for the formation of kidney stones

Ab Initio Molecular Dynamics Simulations of Phosphocholine Interactions with a Calcium Oxalate Dihydrate (110) Surface

We use ab initio modeling (CASTEP) to help elucidate the crystallization phenomena and chemistry behind kidney stone composition and formation. To explore the stone formation process, we have constructed a surface model of calcium oxalate dihydrate-the mineral most commonly found in patients with hypercalciuria and modeled stone growth, by simulating further calcium oxalate adsorption onto the surface (-7.446 eV, -0.065 eV/atom). Furthermore, urine analysis of kidney stone patients has previously revealed that their urine contains higher concentrations of phospholipids compared to healthy individuals. Therefore, to investigate the interactions between urinary macromolecules and the growing crystal surfaces at an atomic level, we have performed ab initio molecular dynamics simulations of phosphocholine adsorption on calcium oxalate surfaces. We have shown that the phosphocholine headgroups become entrapped within the growing crystal and the lowest energy structures (-18.008 eV, -0.0396 eV/atom) are those where the calcium oxalate dihydrate surfaces have become disrupted, with reorganization of their crystallographic structure. Urinary calculi (kidney stones) are a common ailment affecting around 10% of the world's population and resulting in nearly 90,000 finished consultant episodes (FCE) each year in the United Kingdom [Hospital Episode Statistics, Admitted Patient Care-England, 2011-12 NHS Digital, 2021-2022. https://digital.nhs.uk/data-and-information/publications/statistical/hospital-admitted-patient-care-activity/hospital-episode-statistics-admitted-patient-care-england-2011-12].

Microbial communities, antibiotic resistance genes, and virulence factors in urinary infectious stone-associated urinary tract infections

Urinary infectious stones are challenging due to bacterial involvement, necessitating a comprehensive understanding of these conditions. Antibiotic-resistant urease-producing bacteria further complicate clinical management. In this study, analysis of urine and stone samples from urinary tract infection (UTI) patients revealed microbial shifts, gene enrichment in stones, and metabolic pathway disparities; antibiotic resistance gene trends were phylum-specific, urease-producing bacteria are at risk of acquiring AMR carried by Enterobacteriaceae under antibiotic, emphasizing potential AMR dissemination between them; Correlations of key pathogenic species in kidney stone and urine microbial communities highlight the need for targeted therapeutic strategies to manage complexities in UTIs; Stones and urine contain a variety of deleterious genes even before antibiotic use, and piperacillin/tazobactam better reduced the abundance of antibiotic resistance genes in stones and urine. The presence of diverse antibiotic resistance and virulence genes underscores challenges in clinical management and emphasizes the need for effective treatment strategies to mitigate risks associated with UTIs and urinary infectious stone formation. Ongoing research is vital for advancing knowledge and developing innovative approaches to address these urological conditions.

A cross-sectional analysis of the relationship between the non-high density to high density lipoprotein cholesterol ratio (NHHR) and kidney stone risk in American adults

BACKGROUND

Recent interest in the Non-High Density to High Density Lipoprotein Cholesterol ratio (NHHR) has emerged due to its potential role in metabolic disorders. However, the connection between NHHR and the development of kidney stones still lacks clarity. The primary goal of this research is to explore how NHHR correlates with kidney stone incidence.

METHODS

An analysis was conducted on the data collected by the National Health and Nutrition Examination Survey (NHANES) between 2007 and 2018, focusing on adults over 20 years diagnosed with kidney stones and those with available NHHR values. Employing weighted logistic regression and Restricted Cubic Spline (RCS) models, NHHR levels' correlation with kidney stone risk was examined. Extensive subgroup analyses were conducted for enhanced reliability of the findings.

RESULTS

The findings indicate a heightened kidney stone risk for those at the highest NHHR levels relative to those at the lowest (reference group). A notable non-linear correlation of NHHR with kidney stone incidence has been observed, with a significant P-value (< 0.001), consistent across various subgroups.

CONCLUSION

A clear link exists between high NHHR levels and increased kidney stone risk in the American adult population. This study highlights NHHR's significance as a potential indicator in kidney stone formation.

The association between non-high-density lipoprotein cholesterol to high-density lipoprotein cholesterol ratio (NHHR) and kidney stones: a cross-sectional study

BACKGROUND

The relationship between the NHHR and kidney stone risk remains unknown. The purpose of this study was to evaluate the association between adult NHHR and kidney stone occurrence in USA.

METHODS

This study used a variety of statistical techniques such as threshold effects, subgroup analysis, smooth curve fitting, multivariate logistic regression, and data from the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2014. We aimed to clarify the relationship between the NHHR and kidney stone risk.

RESULTS

The average age of the 21,058 individuals in this research was 49.70 ± 17.64 years. The mean NHHR was 3.00 ± 1.47, and the overall prevalence of kidney stone occurrence was 9.05%. The prevalence within the quartile ranges (Q1-Q4) was 7.01%, 8.71%, 9.98%, and 10.49%, respectively. The overall average recurrence rate of kidney stones was 3.05%, demonstrating a significant increase with increasing NHHR (Q1: 1.92%, Q2: 2.92%, Q3: 3.35%, Q4: 4.00%, P < 0.01). The occurrence of kidney stones increased by 4% (95% CI: 1.00-1.08, P = 0.0373) and the chance of recurrence increased by 9% (95% CI: 1.03-1.14, P < 0.01) with each unit increase in NHHR. The interaction analysis results demonstrated that the relationship between the NHHR and the risk of kidney stones was not significantly impacted by the following factors: sex, body mass index, poverty income ratio, diabetes, or hypertension. Curve fitting and threshold effect analysis also demonstrated a non-linear association, with a breakpoint found at 3.17, between the NHHR and the risk of kidney stones.

CONCLUSIONS

In adults in the USA, there is a substantial correlation between elevated NHHR levels and a higher probability of kidney stones developing and recurring. Timely intervention and management of NHHR may effectively mitigate the occurrence and recurrence of kidney stones.

Establishment and application of a nomogram diagram for predicting calcium oxalate stones in patients with urinary tract stones

This retrospective study aims to examine the correlation between calcium oxalate (CaOx) stones and common clinical tests, as well as urine ionic composition. Additionally, we aim to develop and implement a personalized model to assess the accuracy and feasibility of using charts to predict calcium oxalate stones in patients with urinary tract stones. A retrospective analysis was conducted on data from 960 patients who underwent surgery for urinary stones at the First Affiliated Hospital of Soochow University from January 1, 2010, to December 31, 2022. Among these patients, 447 were selected for further analysis based on screening criteria. Multivariate logistic regression analysis was then performed to identify the best predictive features for calcium oxalate stones from the clinical data of the selected patients. A prediction model was developed using these features and presented in the form of a nomogram graph. The performance of the prediction model was assessed using the C-index, calibration curve, and decision curve, which evaluated its discriminative power, calibration, and clinical utility, respectively. The nomogram diagram prediction model developed in this study is effective in predicting calcium oxalate stones which is helpful in screening and early identification of high-risk patients with calcium oxalate urinary tract stones, and may be a guide for urologists in making clinical treatment decisions.

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.

Asymmetric depth-filtration: A versatile and scalable method for high-yield isolation of extracellular vesicles with low contamination

We developed a novel asymmetric depth filtration (DF) approach to isolate extracellular vesicles (EVs) from biological fluids that outperforms ultracentrifugation and size-exclusion chromatography in purity and yield of isolated EVs. By these metrics, a single-step DF matches or exceeds the performance of multistep protocols with dedicated purification procedures in the isolation of plasma EVs. We demonstrate the selective transit and capture of biological nanoparticles in asymmetric pores by size and elasticity, low surface binding to the filtration medium, and the ability to cleanse EVs held by the filter before their recovery with the reversed flow all contribute to the achieved purity and yield of preparations. We further demonstrate the method's versatility by applying it to isolate EVs from different biofluids (plasma, urine, and cell culture growth medium). The DF workflow is simple, fast, and inexpensive. Only standard laboratory equipment is required for its implementation, making DF suitable for low-resource and point-of-use locations. The method may be used for EV isolation from small biological samples in diagnostic and treatment guidance applications. It can also be scaled up to harvest therapeutic EVs from large volumes of cell culture medium.

Probiotics in the Prevention of the Calcium Oxalate Urolithiasis

Nephrolithiasis ranks third among urological diseases in terms of prevalence, making up about 15% of cases. The continued increase in the incidence of nephrolithiasis is most probably due to changes in eating habits (high protein, sodium, and sugar diets) and lifestyle (reduced physical activity) in all developed countries. Some 80% of all kidney stones cases are oxalate urolithiasis, which is also characterized by the highest risk of recurrence. Frequent relapses of nephrolithiasis contribute to severe complications and high treatment costs. Unfortunately, there is no known effective way to prevent urolithiasis at present. In cases of diet-related urolithiasis, dietary changes may prevent recurrence. However, in some patients, the condition is unrelated to diet; in such cases, there is evidence to support the use of stone-related medications. Interestingly, a growing body of evidence indicates the potential of the microbiome to reduce the risk of developing renal colic. Previous studies have primarily focused on the use of Oxalobacterformigenes in patients with urolithiasis. Unfortunately, this bacterium is not an ideal probiotic due to its antibiotic sensitivity and low pH. Therefore, subsequent studies sought to find bacteria which are capable of oxalate degradation, focusing on well-known probiotics including Lactobacillus and Bifidobacterium strains, Eubacterium lentum, Enterococcus faecalis, and Escherichia coli.

Differential biomolecular recognition by synthetic vs. biologically-derived components in the stone-forming process using 3D microfluidics

Calcium phosphate (CaP) biomineralization is the hallmark of extra-skeletal tissue calcification and renal calcium stones. Although such a multistep process starts with CaP crystal formation, the mechanism is still poorly understood due to the complexity of the in vivo system and the lack of a suitable approach to simulate a truly in vivo-like environment. Although endogenous proteins and lipids are engaged with CaP crystals in such a biological process of stone formation, most in vitro studies use synthetic materials that can display differential bioreactivity and molecular recognition by the cellular component. Here, we used our in vitro microfluidic (MF) tubular structure, which is the first completely cylindrical platform, with renal tubular cellular microenvironments closest to the functional human kidney tubule, to understand the precise role of biological components in this process. We systematically evaluated the contribution of synthetic and biological components in the stone-forming process in the presence of dynamic microenvironmental cues that originated due to cellular pathophysiology, which are critical for the nucleation, aggregation, and growth of CaP crystals. Our results show that crystal aggregation and growth were enhanced by immunoglobulin G (IgG), which was further inhibited by etidronic acid due to the chelation of extracellular Ca²⁺. Interestingly, biogenic CaP crystals from mice urine, when applied with cell debris and non-specific protein (bovine serum albumin), exhibited a more discrete crystal growth pattern, compared to exposure to synthetic CaP crystals under similar conditions. Furthermore, proteins found on those calcium crystals from mice urine produced discriminatory effects on crystal-protein attachment. Specifically, such biogenic crystals exhibited enhanced affinity to the proteins inherent to those crystals. More importantly, a physiological comparison of crystal induction in renal tubular cells revealed that biogenic crystals are less effective at producing a sustained rise in cytosolic Ca²⁺ compared to synthetic crystals, suggesting a milder detrimental effect to downstream signaling. Finally, synthetic crystal-internalized cells induced more oxidative stress, inflammation, and cellular damage compared to the biogenic crystal-internalized cells. Together, these results suggest that the intrinsic nature of biogenically derived components are appropriate to generate the molecular recognition needed for spatiotemporal effects and are critical towards understanding the process of kidney stone formation.

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.

Randall's plaque and calcium oxalate stone formation: role for immunity and inflammation

Idiopathic calcium oxalate (CaOx) stones often develop attached to Randall's plaque present on kidney papillary surfaces. Similar to the plaques formed during vascular calcification, Randall's plaques consist of calcium phosphate crystals mixed with an organic matrix that is rich in proteins, such as inter-α-trypsin inhibitor, as well as lipids, and includes membrane-bound vesicles or exosomes, collagen fibres and other components of the extracellular matrix. Kidney tissue surrounding Randall's plaques is associated with the presence of classically activated, pro-inflammatory macrophages (also termed M1) and downregulation of alternatively activated, anti-inflammatory macrophages (also termed M2). In animal models, crystal deposition in the kidneys has been associated with the production of reactive oxygen species, inflammasome activation and increased expression of molecules implicated in the inflammatory cascade, including osteopontin, matrix Gla protein and fetuin A (also known as α2-HS-glycoprotein). Many of these molecules, including osteopontin and matrix Gla protein, are well known inhibitors of vascular calcification. We propose that conditions of urine supersaturation promote kidney damage by inducing the production of reactive oxygen species and oxidative stress, and that the ensuing inflammatory immune response promotes Randall's plaque initiation and calcium stone formation.

Sphingomyelin and Medullary Sponge Kidney Disease: A Biological Link Identified by Omics Approach

Background: Molecular biology has recently added new insights into the comprehension of the physiopathology of the medullary sponge kidney disease (MSK), a rare kidney malformation featuring nephrocalcinosis and recurrent renal stones. Pathogenesis and metabolic alterations associated to this disorder have been only partially elucidated.

Methods: Plasma and urine samples were collected from 15 MSK patients and 15 controls affected by idiopathic calcium nephrolithiasis (ICN). Plasma metabolomic profile of 7 MSK and 8 ICN patients was performed by liquid chromatography combined with electrospray ionization tandem mass spectrometry (UHPLC–ESI-MS/MS). Subsequently, we reinterrogated proteomic raw data previously obtained from urinary microvesicles of MSK and ICN focusing on proteins associated with sphingomyelin metabolism. Omics results were validated by ELISA in the entire patients' cohort.

Results: Thirteen metabolites were able to discriminate MSK from ICN (7 increased and 6 decreased in MSK vs. ICN). Sphingomyelin reached the top level of discrimination between the two study groups (FC: −1.8, p < 0.001). Ectonucleotide pyrophophatase phosphodiesterase 6 (ENPP6) and osteopontin (SPP1) resulted the most significant deregulated urinary proteins in MSK vs. ICN (p < 0.001). ENPP6 resulted up-regulated also in plasma of MSK by ELISA.

Conclusion: Our data revealed a specific high-throughput metabolomics signature of MSK and indicated a pivotal biological role of sphingomyelin in this disease.

Calcium oxalate kidney stones, where is the organic matter?: A synchrotron based infrared microspectroscopy study

Kidney stones are collections of microcrystals formed inside the kidneys, which affect 6% to 12% of the population worldwide, with an increasing recurrence (50%-72%) after the first episode. The most abundant type is calcium oxalate (66%), described as monohydrated (COM) and dihydrated (COD). An issue in their chemistry is the transformation process of the metastable specie (COD) into the stable one, which is chemically, and in appearance, monohydrated. Since the origin of these species is different, it is important to differentiate between the transformation stage (and what stabilize COD) to understand the physiopathology and prevent the patients' recurrence. This work focuses on the organic matter distribution along these nephroliths by synchrotron radiation-based infrared microspectroscopy. Differences in the asymmetric stretching of the aliphatic hydrocarbons suggest that lipids may participate in the stabilization of COD and as inhibitors of COM formation/development; however, the presence of proteins in the nucleus could indicate a promoting role.

Immunotherapy for stone disease

PURPOSE OF REVIEW

In addition to traditional risk factors such as low urine volume or hypercalciuria, emerging data suggest that calcium oxalate (CaOx), one of the most common mineral complexes in the urine, elicits a strong immunologic response. This review highlights those studies and projects how future therapies may be directed for kidney stone prevention.

RECENT FINDINGS

Over the last 2 years, several groups have studied the response of the immune system to CaOx crystals using cell culture and animal models. Dominguez et al. found that CaOx crystals were recognized by monocytes through an lipopolysaccharide-mediated mechanism, leading to M1 'inflammatory' macrophage phenotype. Patel et al. proposed excessive oxalate-mediated reactive oxygen species within macrophage mitochondria may impair their ability to properly clear stones. Two other groups developed mouse models (an androgen receptor knock-out and an overexpression of Sirtuin 3 protein) and demonstrated increased renal anti-inflammatory macrophage differentiation and decreased CaOx deposition in experimental compared with controls. Anders et al. fed hyperoxaluric mice 1,3-butanediol, which blocks an inflammatory form of cell death called NLRP3 inflammasome and found less intrarenal oxidative damage and higher anti-inflammatory renal infiltrates in experimentals. Finally, monocytes exposed to CaOx crystals followed by hydroxyapatite had reduced inflammatory cytokine and chemokine production compared with those without hydroxyapatite, suggesting that Randall's plaque may play a role in dampening M1-mediatiated CaOx inflammation.

SUMMARY

By modulating the immune response, immunotherapy could provide the means to prevent stone recurrences in certain individuals. The promotion of M2 over M1 macrophages and inhibition of inflammation could prevent the cascade that leads to CaOx nucleation. Future therapies may target the ability of macrophages to degrade CaOx crystals to prevent stones.

SMolESY: an efficient and quantitative alternative to on-instrument macromolecular 1H-NMR signal suppression

One-dimensional (1D) proton-nuclear magnetic resonance (1H-NMR) spectroscopy is an established technique for measuring small molecules in a wide variety of complex biological sample types. It is demonstrably reproducible, easily automatable and consequently ideal for routine and large-scale application. However, samples containing proteins, lipids, polysaccharides and other macromolecules produce broad signals which overlap and convolute those from small molecules. NMR experiment types designed to suppress macromolecular signals during acquisition may be additionally performed, however these approaches add to the overall sample analysis time and cost, especially for large cohort studies, and fail to produce reliably quantitative data. Here, we propose an alternative way of computationally eliminating macromolecular signals, employing the mathematical differentiation of standard 1H-NMR spectra, producing small molecule-enhanced spectra with preserved quantitative capability and increased resolution. Our approach, presented in its simplest form, was implemented in a cheminformatic toolbox and successfully applied to more than 3000 samples of various biological matrices rich or potentially rich with macromolecules, offering an efficient alternative to on-instrument experimentation, facilitating NMR use in routine and large-scale applications.

Current insights into the mechanisms and management of infection stones

Infection stones are complex aggregates of crystals amalgamated in an organic matrix that are strictly associated with urinary tract infections. The management of patients who form infection stones is challenging owing to the complexity of the calculi and high recurrence rates. The formation of infection stones is a multifactorial process that can be driven by urine chemistry, the urine microenvironment, the presence of modulator substances in urine, associations with bacteria, and the development of biofilms. Despite decades of investigation, the mechanisms of infection stone formation are still poorly understood. A mechanistic understanding of the formation and growth of infection stones - including the role of organics in the stone matrix, microorganisms, and biofilms in stone formation and their effect on stone characteristics - and the medical implications of these insights might be crucial for the development of improved treatments. Tools and approaches used in various disciplines (for example, engineering, chemistry, mineralogy, and microbiology) can be applied to further understand the microorganism-mineral interactions that lead to infection stone formation. Thus, the use of integrated multidisciplinary approaches is imperative to improve the diagnosis, prevention, and treatment of infection stones.

UPLC/MS-Based Metabolomics Investigation of the Protective Effect of Hydrogen Gas Inhalation on Mice with Calcium Oxalate-Induced Renal Injury

Hydrogen has a significant protective effect on calcium oxalate-induced renal injury, but its effect on metabolic profiles is unknown. This study showed the effects of hydrogen on serum and urine metabolites in a renal injury model. Ultra-HPLC quadrupole time-of-flight-MS-based metabolomics was used to characterise metabolic variations. Twenty-five serum metabolites and 14 urine metabolites showed differences in the the nitrogen and oxygen inhalation (NO), nitrogen and oxygen inhalation combined with calcium oxalate induction (CaOx), and hydrogen inhalation combined with calcium oxalate induction (HO+CaOx) groups. Nineteen serum metabolites and 7 urine metabolites showed significant restoration to normal levels after hydrogen gas (H₂) treatment. These metabolites are primarily related to amino acid metabolism, fatty acid metabolism, and phospholipid metabolism. This study showed that a comprehensive metabolomics approach is an effective strategy to elucidate the mechanisms underlying the effects of hydrogen treatment on calcium oxalate-induced renal injury.

Protective potential of Angelica sinensis polysaccharide extract against ethylene glycol-induced calcium oxalate urolithiasis

Purpose: To evaluate a Angelica sinensis polysaccharide aqueous extract as a preventive agent in experimentally induced urolithiasis using in- vitro and vivo models.

Material and methods:Angelica sinensis polysaccharide was investigated in vitro to determine its antilithiatic effects on the formation and morphology of calcium oxalate (CaOx) crystals and was analyzed in vivo to determine its ability to prevent CaOx urolithiasis in rats subjected to ethylene glycol-induced urolithiasis. Potassium citrate administration was used in the positive control group. The urolithiasis-related biochemical parameters were evaluated in the rats urine, serum and kidney homogenates. Kidney sections were subjected to histopathological and immunohistochemical analyses, and urolithiasis-related phospho-c-Jun NH2-terminal protein kinase and kidney injury molecule-1proteins were evaluated by Western blot analyses.

Results:Angelica sinensis polysaccharide exhibited concentration-dependent inhibition of CaOx crystal formation. The in vitro assay revealed significant inhibition of crystal formation (6.99 ± 1.07) in the group treated with 4.0 mg/mL Angelica sinensis polysaccharide extract compared with the control group (58.38 ± 5.63; p < .05). In vivo, after treatment with ethylene glycol for 28 days, urinary oxidative stress, oxalate, creatinine, urea and urolithiasis-related protein were significantly increased (p < .05), except for serum oxidative stress (p > .05). The rats administered the extract of Angelica sinensis polysaccharide showed significantly decreased pathological change and CaOx deposition (p < .05) compared with the urolithiatic rats. Significantly reduced levels of urinary oxidative stress, oxalate, creatinine, urea and urolithiasis-related protein were observed in the Angelica sinensis polysaccharide treatment groups (p < .05) compared with the nephrolithic rats.

Conclusion: The results presented here suggest that Angelica sinensis polysaccharide has the potential to inhibit CaOx crystallization in vitro and may present anti-urolithiatic effects in vivo.

Computer-Assisted Quantitative Assessment of Prostatic Calcifications in Patients with Chronic Prostatitis

BACKGROUND

The aim of this study was the development of quantitative assessment of prostatic calcifications at prostatic ultrasound examination by the use of an image analyzer.

MATERIALS AND METHODS

A group of 82 patients was evaluated by medical history, physical, and transrectal ultrasound examination. Patients had a urethral swab, a 4-specimen study and culture of the seminal fluid. Patients were classified according to National Institute of Diabetes and Digestive and Kidney Diseases/National Institutes of Health. Subjective symptoms were scored by Chronic Prostatitis Symptom Index (CPSI) questionnaire. Ultrasound images were analyzed by the digital processing software Image J to quantitatively assess the presence of calcifications.

RESULTS

Computer-assessed calcified areas were significantly higher in chronic bacterial prostatitis (n = 18; group II; 6.76 ± 8.09%) than in the chronic pelvic pain syndrome group IIIa (n = 26; 2.07 ± 1.01%) and IIIb (n = 38; 2.31 ± 2.18%). The area of calcification of the prostate was significantly related to the CPSI score for domains of micturition (r = 0.278, p = 0.023), Prostatic Specific Antigen values (r = 0341, p = 0.005), postvoiding residual urine (r = 0.262, p = 0.032), total prostate volume (r = 0.592, p = 0.000), and adenoma volume (r = 0.593; p = 0.000).

CONCLUSIONS

The presence of calcifications is more frequently observed in patients with chronic bacterial prostatitis and is related to urinary symptoms.

Shape and structure controlling of calcium oxalate crystals by a combination of additives in the process of biomineralization

The origin of complex hierarchical superstructures of biomaterials and their unique self-assembly mechanisms of formation are important in biological systems and have attracted considerable attention. In the present study, we investigated the morphological changes of calcium oxalate (CaO x ) crystals induced by additives including chiral aspartic acid, sodium citrate, Mg2+, casein and combinations of these molecules. The morphology and structure of CaO x were identified with the use of various techniques. The morphogenesis of CaO x crystals were significantly affected by chiral aspartic acid, sodium citrate or Mg2+. However, they only formed calcium oxalate monohydrate (COM). It was observed that the chiral aspartic acid, sodium citrate and casein adhered to the surface of the crystals. The adherence of Mg2+ to crystals was not evident. Casein significantly affected the formation of COM and calcium oxalate dihydrate (COD). The ratio of different CaO x crystal forms is associated with the casein concentration. In combination with Mg2+ or citrate ions, casein showed improved formation of COD. The present study mimics biomineralization with a simple chemical approach and provides insight into the complicated system of CaO x biomineralization as well as facilitates the understanding of urinary stone treatment.

Kidney Stone Disease: An Update on Current Concepts

Kidney stone disease is a crystal concretion formed usually within the kidneys. It is an increasing urological disorder of human health, affecting about 12% of the world population. It has been associated with an increased risk of end-stage renal failure. The etiology of kidney stone is multifactorial. The most common type of kidney stone is calcium oxalate formed at Randall's plaque on the renal papillary surfaces. The mechanism of stone formation is a complex process which results from several physicochemical events including supersaturation, nucleation, growth, aggregation, and retention of urinary stone constituents within tubular cells. These steps are modulated by an imbalance between factors that promote or inhibit urinary crystallization. It is also noted that cellular injury promotes retention of particles on renal papillary surfaces. The exposure of renal epithelial cells to oxalate causes a signaling cascade which leads to apoptosis by p38 mitogen-activated protein kinase pathways. Currently, there is no satisfactory drug to cure and/or prevent kidney stone recurrences. Thus, further understanding of the pathophysiology of kidney stone formation is a research area to manage urolithiasis using new drugs. Therefore, this review has intended to provide a compiled up-to-date information on kidney stone etiology, pathogenesis, and prevention approaches.

Non-alcoholic fatty liver disease and the development of nephrolithiasis: A cohort study

Background

Non-alcoholic fatty liver disease (NAFLD), a hepatic manifestation or precursor of metabolic syndrome, may increase nephrolithiasis, a renal manifestation of insulin resistance, but the prospective association between NAFLD and incident nephrolithiasis has not been evaluated. We examined the association of NAFLD with the development of nephrolithiasis in a large cohort of Korean men and women.

Methods

We performed a cohort study of 208,578 Korean adults who underwent a health checkup examination between January 2002 and December 2014 and were followed-up annually or biennially through December 2014. NAFLD was defined as the presence of fatty liver in the absence of excessive alcohol use or other identifiable causes. Fatty liver and nephrolithiasis were determined based on ultrasonographic findings. We used a parametric Cox model to estimate the adjusted hazard ratios (HRs) of nephrolithiasis according to the presence of NAFLD.

Results

During 1,054,887.6 person-year of follow-up, 16,442 participants developed nephrolithiasis. After adjusting for age, center, year of screening exam, smoking status, alcohol intake, physical activity, education level, body mass index, history of hypertension and diabetes, HOMA-IR, uric acid and C-reactive protein, male participants with NAFLD had a significantly increased risk of nephrolithiasis than those without NAFLD (adjusted HR 1.17, 95% CI 1.06–1.30). However, no association between NAFLD and nephrolithiasis was observed in women (adjusted HR 0.97, 95% CI 0.81–1.16).

Conclusions

In this large cohort study of young and middle-aged Koreans, NAFLD was significantly associated with an increased incidence of nephrolithiasis in men but not in women.

Marked increase in urinary excretion of apolipoproteins in children with nephrolithiasis associated with hypercalciuria

BACKGROUND

Using a proteomic approach, we aimed to identify and compare the urinary excretion of proteins involved in lipid transport and metabolism in children with kidney stones and hypercalciuria (CAL), hypocitraturia (CIT), and normal metabolic work-up (NM), and in healthy controls (HCs). Additionally, we aimed to confirm these results using ELISA, and to examine the relationship between the urinary excretion of selected proteins with demographic, dietary, blood, and urinary parameters.

METHODS

Prospective, controlled, pilot study of pooled urine from CAL, CIT, and NM versus age- and gender-matched HCs, using liquid chromatography-mass spectrometry. Relative protein abundance was estimated using spectral counting. Results were confirmed by ELISA performed on individual samples.

RESULTS

Of the 1,813 proteins identified, 230 met the above criteria. Of those, 5 proteins (apolipoprotein A-II [APOA2]; apolipoprotein A-IV [APOA4]; apolipoprotein C-III [APOA3]; fatty acid-binding protein, liver [FABPL]; fatty acid-binding protein, adipocyte [FABP4]) involved in lipid metabolism and transport were found in the CAL group, with significant differences compared with HCs. ELISA analysis indicated statistically significant differences in the urinary excretion of APOC3, APOA4, and FABPL in the CAL group compared with HCs. Twenty-four-hour urinary calcium excretion correlated significantly with concentrations of ApoC3 (r = 0.77, p < 0.001), and FABPL (r = 0.80, p = 0.005).

CONCLUSIONS

We provide proteomic data showing increased urinary excretion of lipid metabolism/transport-related proteins in children with kidney stones and hypercalciuria. These findings suggest that abnormalities in lipid metabolism might play a role in kidney stone formation.

Antioxidant and Renoprotective Effects of Mushroom Extract: Implication in Prevention of Nephrolithiasis

Background

The pathogenesis of nephrolithiasis (kidney stone) remains elusive, while several therapeutic options are available but not effective as we expected. Accumulating data yet suggest that oxidative stress (generation of oxygen free radicals) may play a primary role in its occurrence. Particularly, calcium oxalate (CaOx) is a key element in the most common form (> 75%) of kidney stones, and its crystal form known as CaOx monohydrate (COM) has been shown to exert oxidative stress, facilitating CaOx stone formation. Hence, diminishing oxidative stress with certain antioxidants could be a potential strategic approach. We are interested in a bioactive extract of Poria mushroom, PE, which has been shown to have antioxidant and renoprotective activities. Accordingly, we investigated if PE might have antioxidant activity that would have implication in prevention of kidney stone formation.

Methods

Renal epithelial LLC-PK₁ cells were employed and exposed to COM or hydrogen peroxide (H₂O₂) as a positive control capable of exerting oxidative stress. Possible antioxidant and protective effects of PE against oxidative stress (exerted by COM or H₂O₂) were assessed by cell viability test and lipid peroxidation (LPO) assay. To explore its protective mechanism, two glycolytic parameters, hexokinase (HK) activity and ATP synthesis, were examined and cell cycle analysis was also performed.

Results

Both H₂O₂ and COM led to a significant (P < 0.05) reduction in cell viability, accompanied by severe oxidative stress assessed by LPO assay. Such oxidative stress also caused the significant decline in HK activity and cellular ATP level, indicating the inhibition of glycolysis. Cell cycle analysis further indicated that oxidative stress interfered with cell cycle, inducing a G₁ cell cycle arrest that presumably results in the cessation of cell proliferation. However, PE was capable of significantly preventing or diminishing all these cellular effects mediated through oxidative stress (exerted by H₂O₂ and COM).

Conclusions

The present study shows that the mushroom extract PE appears to have antioxidant and renoprotective effects against oxidative stress exerted by COM in renal cells. Therefore, PE with antioxidant activity is considered a promising natural agent that may have clinical implications in prevention of nephrolithiasis primarily induced by oxidative stress.

Differential human urinary lipid profiles using various lipid-extraction protocols: MALDI-TOF and LIFT-TOF/TOF analyses

Changes in lipid levels/profiles can reflect health status and diseases. Urinary lipidomics, thus, has a great potential in clinical diagnostics/prognostics. Previously, only chloroform and methanol were used for extracting lipids from the urine. The present study aimed to optimize lipid extraction and examine differential lipid classes obtained by various extraction protocols. Urine samples were collected from eight healthy individuals and then pooled. Lipids were extracted by six solvent protocols, including (i) chloroform/methanol (1:1, v/v), (ii) chloroform/methanol (2:1, v/v), (iii) hexane/isopropanol (3:2, v/v), (iv) chloroform, (v) diethyl ether, and (vi) hexane. Lipid profiles of the six extracts were acquired by MALDI-TOF mass spectrometry (MS) and some lipid classes were verified by LIFT-TOF/TOF MS/MS. The data revealed that phosphatidylglycerol (PG) and phosphatidylinositol (PI) could be detected by all six protocols. However, phosphatidylcholine (PC) and sphingomyelin (SM) were detectable only by protocols (i)–(iv), whereas phosphatidylserine (PS) was detectable only by protocols (iii)–(vi), and phosphatidylethanolamine (PE) was detectable only by protocols (v)–(vi). In summary, we have demonstrated differential lipidome profiles yielded by different extraction protocols. These data can serve as an important source for selection of an appropriate extraction method for further highly focused studies on particular lipid classes in the human urine.

Dynamic Assessment of Functional Lipidomic Analysis in Human Urine

The development of enabling mass spectrometry platforms for the quantification of diverse lipid species in human urine is of paramount importance for understanding metabolic homeostasis in normal and pathophysiological conditions. Urine represents a non-invasive biofluid that can capture distinct differences in an individual's physiological status. However, currently there is a lack of quantitative workflows to engage in high throughput lipidomic analysis. This study describes the development of a MS/MS(ALL) shotgun lipidomic workflow and a micro liquid chromatography-high resolution tandem mass spectrometry (LC-MS/MS) workflow for urine structural and mediator lipid analysis, respectively. This workflow was deployed to understand biofluid sample handling and collection, extraction efficiency, and natural human variation over time. Utilization of 0.5 mL of urine for structural lipidomic analysis resulted in reproducible quantification of more than 600 lipid molecular species from over 20 lipid classes. Analysis of 1 mL of urine routinely quantified in excess of 55 mediator lipid metabolites comprised of octadecanoids, eicosanoids, and docosanoids generated by lipoxygenase, cyclooxygenase, and cytochrome P450 activities. In summary, the high-throughput functional lipidomics workflow described in this study demonstrates an impressive robustness and reproducibility that can be utilized for population health and precision medicine applications.

Kidney stones

Kidney stones are mineral deposits in the renal calyces and pelvis that are found free or attached to the renal papillae. They contain crystalline and organic components and are formed when the urine becomes supersaturated with respect to a mineral. Calcium oxalate is the main constituent of most stones, many of which form on a foundation of calcium phosphate called Randall's plaques, which are present on the renal papillary surface. Stone formation is highly prevalent, with rates of up to 14.8% and increasing, and a recurrence rate of up to 50% within the first 5 years of the initial stone episode. Obesity, diabetes, hypertension and metabolic syndrome are considered risk factors for stone formation, which, in turn, can lead to hypertension, chronic kidney disease and end-stage renal disease. Management of symptomatic kidney stones has evolved from open surgical lithotomy to minimally invasive endourological treatments leading to a reduction in patient morbidity, improved stone-free rates and better quality of life. Prevention of recurrence requires behavioural and nutritional interventions, as well as pharmacological treatments that are specific for the type of stone. There is a great need for recurrence prevention that requires a better understanding of the mechanisms involved in stone formation to facilitate the development of more-effective drugs.

Monosodium glutamate-induced oxidative kidney damage and possible mechanisms: a mini-review

Animal studies suggest that chronic monosodium glutamate (MSG) intake induces kidney damage by oxidative stress. However, the underlying mechanisms are still unclear, despite the growing evidence and consensus that α-ketoglutarate dehydrogenase, glutamate receptors and cystine-glutamate antiporter play an important role in up-regulation of oxidative stress in MSG-induced renal toxicity. This review summaries evidence from studies into MSG-induced renal oxidative damage, possible mechanisms and their importance from a toxicological viewpoint.

Antimicrobial lipids: Emerging effector molecules of innate host defense

The antimicrobial properties of host derived lipids have become increasingly recognized and evidence is mounting that antimicrobial lipids (AMLs), like antimicrobial peptides, are effector molecules of the innate immune system and are regulated by its conserved pathways. This review, with primary focus on the human body, provides some background on the biochemistry of lipids, summarizes their biological functions, expands on their antimicrobial properties and site-specific composition, presents modes of synergism with antimicrobial peptides, and highlights the more recent reports on the regulation of AML production as well as bacterial resistance mechanisms. Based on extant data a concept of innate epithelial defense is proposed where epithelial cells, in response to microbial products and proinflammatory cytokines and through activation of conserved innate signaling pathways, increase their lipid uptake and up-regulate transcription of enzymes involved in lipid biosynthesis, and induce transcription of antimicrobial peptides as well as cytokines and chemokines. The subsequently secreted antimicrobial peptides and lipids then attack and eliminate the invader, assisted by or in synergism with other antimicrobial molecules delivered by other defense cells that have been recruited to the site of infection, in most of the cases. This review invites reconsideration of the interpretation of cholesteryl ester accumulation in macrophage lipid droplets in response to infection as a solely proinflammatory event, and proposes a direct antimicrobial role of lipid droplet- associated cholesteryl esters. Finally, for the interested, but new- to- the-field investigator some starting points for the characterization of AMLs are provided. Before it is possible to utilize AMLs for anti-infectious therapeutic and prophylactic approaches, we need to better understand pathogen responses to these lipids and their role in the pathogenesis of chronic infectious disease.

Osteogenic changes in kidneys of hyperoxaluric rats

Many calcium oxalate (CaOx) kidney stones develop attached to renal papillary sub-epithelial deposits of calcium phosphate (CaP), called Randall's plaque (RP). Pathogenesis of the plaques is not fully understood. We hypothesize that abnormal urinary environment in stone forming kidneys leads to epithelial cells losing their identity and becoming osteogenic. To test our hypothesis male rats were made hyperoxaluric by administration of hydroxy-l-proline (HLP). After 28days, rat kidneys were extracted. We performed genome wide analyses of differentially expressed genes and determined changes consistent with dedifferentiation of epithelial cells into osteogenic phenotype. Selected molecules were further analyzed using quantitative-PCR and immunohistochemistry. Genes for runt related transcription factors (RUNX1 and 2), zinc finger protein Osterix, bone morphogenetic proteins (BMP2 and 7), bone morphogenetic protein receptor (BMPR2), collagen, osteocalcin, osteonectin, osteopontin (OPN), matrix-gla-protein (MGP), osteoprotegrin (OPG), cadherins, fibronectin (FN) and vimentin (VIM) were upregulated while those for alkaline phosphatase (ALP) and cytokeratins 10 and 18 were downregulated. In conclusion, epithelial cells of hyperoxaluric kidneys acquire a number of osteoblastic features but without CaP deposition, perhaps a result of downregulation of ALP and upregulation of OPN and MGP. Plaque formation may additionally require localized increases in calcium and phosphate and decrease in mineralization inhibitory potential.

Unified theory on the pathogenesis of Randall's plaques and plugs

Kidney stones develop attached to sub-epithelial plaques of calcium phosphate (CaP) crystals (termed Randall's plaque) and/or form as a result of occlusion of the openings of the Ducts of Bellini by stone-forming crystals (Randall's plugs). These plaques and plugs eventually extrude into the urinary space, acting as a nidus for crystal overgrowth and stone formation. To better understand these regulatory mechanisms and the pathophysiology of idiopathic calcium stone disease, this review provides in-depth descriptions of the morphology and potential origins of these plaques and plugs, summarizes existing animal models of renal papillary interstitial deposits, and describes factors that are believed to regulate plaque formation and calcium overgrowth. Based on evidence provided within this review and from the vascular calcification literature, we propose a "unified" theory of plaque formation-one similar to pathological biomineralization observed elsewhere in the body. Abnormal urinary conditions (hypercalciuria, hyperoxaluria, and hypocitraturia), renal stress or trauma, and perhaps even the normal aging process lead to transformation of renal epithelial cells into an osteoblastic phenotype. With this de-differentiation comes an increased production of bone-specific proteins (i.e., osteopontin), a reduction in crystallization inhibitors (such as fetuin and matrix Gla protein), and creation of matrix vesicles, which support nucleation of CaP crystals. These small deposits promote aggregation and calcification of surrounding collagen. Mineralization continues by calcification of membranous cellular degradation products and other fibers until the plaque reaches the papillary epithelium. Through the activity of matrix metalloproteinases or perhaps by brute physical force produced by the large sub-epithelial crystalline mass, the surface is breached and further stone growth occurs by organic matrix-associated nucleation of CaOx or by the transformation of the outer layer of CaP crystals into CaOx crystals. Should this theory hold true, developing an understanding of the cellular mechanisms involved in progression of a small, basic interstitial plaque to that of an expanding, penetrating plaque could assist in the development of new therapies for stone prevention.

Should we modify the principles of risk evaluation and recurrence preventive treatment of patients with calcium oxalate stone disease in view of the etiologic importance of calcium phosphate?

Prevention of recurrent calcium oxalate (CaOx) stone formation in the urinary tract is important to avoid negative effects on renal function, patient suffering and to reduce health care cost. Present shortcomings in this regard can be explained both by insufficient understanding of the mechanisms of stone formation and by poor patient compliance to those regimens that nevertheless have proven effective. During the past years, we have got increased insights in the nature of CaOx stone formation and it is suggested that the improved understanding of this process can be used for a more dynamic risk evaluation and treatment regimen directed to specific risk periods that can be identified in the individual patients. Some of the possibilities with regard to the important role of calcium phosphate are discussed in this article.

Nephrolithiasis: molecular mechanism of renal stone formation and the critical role played by modulators

Urinary stone disease is an ailment that has afflicted human kind for many centuries. Nephrolithiasis is a significant clinical problem in everyday practice with a subsequent burden for the health system. Nephrolithiasis remains a chronic disease and our fundamental understanding of the pathogenesis of stones as well as their prevention and cure still remains rudimentary. Regardless of the fact that supersaturation of stone-forming salts in urine is essential, abundance of these salts by itself will not always result in stone formation. The pathogenesis of calcium oxalate stone formation is a multistep process and essentially includes nucleation, crystal growth, crystal aggregation, and crystal retention. Various substances in the body have an effect on one or more of the above stone-forming processes, thereby influencing a person's ability to promote or prevent stone formation. Promoters facilitate the stone formation while inhibitors prevent it. Besides low urine volume and low urine pH, high calcium, sodium, oxalate and urate are also known to promote calcium oxalate stone formation. Many inorganic (citrate, magnesium) and organic substances (nephrocalcin, urinary prothrombin fragment-1, osteopontin) are known to inhibit stone formation. This review presents a comprehensive account of the mechanism of renal stone formation and the role of inhibitors/promoters in calcium oxalate crystallisation.

The role of calcium phosphate in the development of Randall's plaques

Results of research carried out during recent years have shown that papillary subepithelial and intratubular deposits of calcium phosphate have important roles in the formation of calcium oxalate stones. In this article, the mechanisms of calcium oxalate stone formation are briefly reviewed and the background to formation of Randall's plaques type I and II discussed. Although some of the conclusions are difficult to prove, it stands to reason that improved understanding of how calcium phosphate is deposited in the interstitial tissue as well as in the collecting ducts will be of great importance for design of rational and individualized recurrence prevention.

Peeping into human renal calcium oxalate stone matrix: characterization of novel proteins involved in the intricate mechanism of urolithiasis

BACKGROUND

The increasing number of patients suffering from urolithiasis represents one of the major challenges which nephrologists face worldwide today. For enhancing therapeutic outcomes of this disease, the pathogenic basis for the formation of renal stones is the need of hour. Proteins are found as major component in human renal stone matrix and are considered to have a potential role in crystal-membrane interaction, crystal growth and stone formation but their role in urolithiasis still remains obscure.

METHODS

Proteins were isolated from the matrix of human CaOx containing kidney stones. Proteins having MW>3 kDa were subjected to anion exchange chromatography followed by molecular-sieve chromatography. The effect of these purified proteins was tested against CaOx nucleation and growth and on oxalate injured Madin-Darby Canine Kidney (MDCK) renal epithelial cells for their activity. Proteins were identified by Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF MS) followed by database search with MASCOT server. In silico molecular interaction studies with CaOx crystals were also investigated.

RESULTS

Five proteins were identified from the matrix of calcium oxalate kidney stones by MALDI-TOF MS followed by database search with MASCOT server with the competence to control the stone formation process. Out of which two proteins were promoters, two were inhibitors and one protein had a dual activity of both inhibition and promotion towards CaOx nucleation and growth. Further molecular modelling calculations revealed the mode of interaction of these proteins with CaOx at the molecular level.

CONCLUSIONS

We identified and characterized Ethanolamine-phosphate cytidylyltransferase, Ras GTPase-activating-like protein, UDP-glucose:glycoprotein glucosyltransferase 2, RIMS-binding protein 3A, Macrophage-capping protein as novel proteins from the matrix of human calcium oxalate stone which play a critical role in kidney stone formation. Thus, these proteins having potential to modulate calcium oxalate crystallization will throw light on understanding and controlling urolithiasis in humans.

Plasmodium falciparum-derived uric acid precipitates induce maturation of dendritic cells

Malaria is characterized by cyclical fevers and high levels of inflammation, and while an early inflammatory response contributes to parasite clearance, excessive and persistent inflammation can lead to severe forms of the disease. Here, we show that Plasmodium falciparum-infected erythrocytes contain uric acid precipitates in the cytoplasm of the parasitophorous vacuole, which are released when erythrocytes rupture. Uric acid precipitates are highly inflammatory molecules that are considered a danger signal for innate immunity and are the causative agent in gout. We determined that P. falciparum-derived uric acid precipitates induce maturation of human dendritic cells, increasing the expression of cell surface co-stimulatory molecules such as CD80 and CD86, while decreasing human leukocyte antigen-DR expression. In accordance with this, uric acid accounts for a significant proportion of the total stimulatory activity induced by parasite-infected erythrocytes. Moreover, the identification of uric acid precipitates in P. falciparum- and P. vivax-infected erythrocytes obtained directly from malaria patients underscores the in vivo and clinical relevance of our findings. Altogether, our data implicate uric acid precipitates as a potentially important contributor to the innate immune response to Plasmodium infection and may provide a novel target for adjunct therapies.

Bacteria can promote calcium oxalate crystal growth and aggregation

Our previous report showed that uropathogenic bacteria, e.g., Escherichia coli, are commonly found inside the nidus of calcium oxalate (CaOx) kidney stones and may play pivotal roles in stone genesis. The present study aimed to prove this new hypothesis by direct examining CaOx lithogenic activities of both Gram-negative and Gram-positive bacteria. CaOx was crystallized in the absence (blank control) or presence of 10(5) CFU/ml E. coli, Klebsiella pneumoniae, Staphylococcus aureus, or Streptococcus pneumoniae. Fragmented red blood cell membranes and intact red blood cells were used as positive and negative controls, respectively. The crystal area and the number of aggregates were measured to initially screen for effects of bacteria on CaOx crystal growth and aggregation. The data revealed that all the bacteria tested dramatically increased the crystal area and number of crystal aggregates. Validation assays (spectrophotometric oxalate-depletion assay and an aggregation-sedimentation study) confirmed their promoting effects on both growth (20.17 ± 3.42, 17.55 ± 2.27, 16.37 ± 1.38, and 21.87 ± 0.85 % increase, respectively) and aggregation (57.45 ± 2.08, 51.06 ± 5.51, 55.32 ± 2.08, and 46.81 ± 3.61 % increase, respectively) of CaOx crystals. Also, these bacteria significantly enlarged CaOx aggregates, with the diameter greater than the luminal size of distal tubules, implying that tubular occlusion might occur. Moreover, these bacterial effects were dose-dependent and specific to intact viable bacteria, not intact dead or fragmented bacteria. In summary, intact viable E. coli, K. pneumoniae, S. aureus, and S. pneumoniae had significant promoting effects on CaOx crystal growth and aggregation. This functional evidence supported the hypothesis that various types of bacteria can induce or aggravate metabolic stone disease, particularly the CaOx type.

Biomolecular mechanism of urinary stone formation involving osteopontin

Urinary stones consist of two phases-an inorganic (mineral) phase and an organic (matrix) phase. Studies on the organic components of kidney stones have been undertaken later than those on the inorganic components. After osteopontin was identified as one of the matrix components, the biomolecular mechanism of urinary stone formation became clearer. It also triggered the development of new preventive treatments. Osteopontin expression is sporadically observed in normal distal tubular cells and is markedly increased in stone-forming kidneys. Calcium oxalate crystals adhering to renal tubular cells are incorporated into cells by the involvement of osteopontin. Stimulation of crystal-cell adhesion impairs the opening of mitochondrial permeability transition pores (mPTP) in tubular cells and produces oxidative stress, apoptosis, and osteopontin expression. Macrophages phagocytose and digest a small amount of crystals, but many crystals aggregate into a mass containing osteopontin and epithelial cell debris and are excreted into the renal tubular lumen, becoming nuclei of urinary stones. This biomolecular mechanism is similar to atherosclerotic calcification. Based on these findings, new preventive treatments have been developed. Dietary control such as low-cholesterol intake and the ingestion of antioxidative foods and vegetables have successfully reduced the 5-year recurrence rate. Osteopontin antibodies and cyclosporine A, which blocks the opening of mPTP, have markedly inhibited the expression of osteopontin and urinary stone formation in animal models.

Crucial role of the cryptic epitope SLAYGLR within osteopontin in renal crystal formation of mice

Osteopontin plays a crucial role in the formation of renal calcium crystals, which are primarily induced by renal tubular cell injury, especially mitochondrial damage. We have previously shown that the impaired Arg-Gly-Asp (RGD) sequence of osteopontin inhibits renal crystal formation by using OPN-transgenic mice and OPN-knockout (OPN-KO) mice. Here, we investigated the effects of an antimurine osteopontin antibody (35B6-Ab) that specifically reacts with the (162) SLAYGLR(168) sequence, which is exposed by thrombin cleavage and is located adjacent to the RGD sequence, on renal crystal formation. Renal crystals induced by daily administration of glyoxylate over 9 days (from days 1 to 9) in a murine model were sporadically detected in the renal tubular cells at the corticomedullary junction, where thrombin-cleaved osteopontin expression was also coincidentally detected. On days 0, 3, 6, and 9, 35B6-Ab administration inhibited renal crystal formation and induced significant morphological changes in a dose-dependent manner (250, 500, and 1000 µg per mouse). Scanning electron microscopy showed that the crystals in 35B6-Ab-treated mice were aberrantly formed and their density was low; in contrast, the crystals in untreated mice that were not administered 35B6-Ab had a radial pattern of growth (rosette petal-like crystals), and their density was high. Microstructure analysis of renal tubular cells by transmission electron microscopy revealed that untreated mice showed collapsed mitochondria in the flattened cytoplasm of renal tubular cells, unlike the corresponding structures in 35B6-Ab-treated mice, in which renal tubular cell injury was inhibited. In vitro, 35B6-Ab was found to inhibit the attachment of (14) C-labeled crystals to renal tubular culture cells and reduce morphological damage to these cells. We conclude that thrombin-cleaved osteopontin plays an important role in formation of renal calcium crystals and that 35B6-Ab contributes to the remarkable inhibition of early-stage renal crystal formation by preventing renal tubular cell injury and crystal-cell attachment.

Ultrastructural investigation of crystal deposits in Npt2a knockout mice: are they similar to human Randall's plaques?

PURPOSE

Idiopathic Ca oxalate stones may develop with attachment to renal interstitial Ca phosphate deposits (Randall's plaques). Sodium phosphate cotransporter (Npt2a) null mice have hypercalciuria and hyperphosphaturia, and produce tubular and interstitial Ca phosphate deposits. To determine whether this mouse is suitable for Randall's plaque investigations we chronologically studied Ca phosphate deposit sites, structure and composition.

MATERIALS AND METHODS

The kidneys of Npt2a null mice 2 days to 1 year old were examined by light, scanning and transmission electron microscopy. Electron diffraction and energy dispersive x-ray microanalyses were done to determine mineral composition.

RESULTS

Poorly crystalline, biological apatite deposits were seen in collecting duct lumina. Deposits consisted of aggregates approximately 5 μm in diameter appearing as microspheres of concentrically organized needle or plate-like, matrix rich crystals. Epithelium/crystal interfaces were filled with membrane bound vesicles. Some tubules were completely occluded by crystals and occasionally lost the epithelium while crystals moved into the interstitium.

CONCLUSIONS

Ca phosphate crystals formed in the tubular lumina and were organized as microspheres. The aggregation of Ca phosphate crystals produced nuclei, which grew by adding crystals at the periphery. They eventually became large enough to occlude the tubular lumina and obliterate the tubular epithelium, leading to the relocation of microliths into the interstitium. The pathogenesis of interstitial deposits in Npt2a null mice appears different from that proposed for Randall's plaques. Since Npt2a null mice purge the renal crystal deposits, these mice may serve as a model in which to investigate the elimination of crystal deposits in children and adults with nephrocalcinosis.