Urinary inhibitors of calcium oxalate crystallization and their potential role in stone formation

Oral supplementation with probiotics, potassium citrate, and magnesium in reducing crystalluria in stone formers: A phase II study

INTRODUCTION

Crystalluria is an important indicator of renal stone recurrence. Mechanisms underlying urinary stone formation are still not fully understood and raising interests has been giving to intestinal commensal bacteria for their contribute in maintaining urinary solutes equilibrium. The aim of our phase II study was to examine the administration of potassium citrate, magnesium and probiotics in order to reduce crystalluria.

MATERIALS AND METHODS

Since May 2021, we enrolled 23 patients candidates for ureterorenolithotripsy for calcium oxalate kidney stones with crystalluria and a normal metabolic profile. The analysis was validated by the Institution's Ethical Committee (no. approval STS CE Lazio 1/N-823). At discharge, patients were provided with daily food supplementation for 20 days of 1 billion Lactobacillus paracasei LPC09, 1 billion Lactobacillus plantarum LP01, 1 billion Bifidobacterium breve BR03, potassium (520 mg), citrate (1400 mg), and magnesium (80 mg). Crystalluria was re-assessed at 1, 3, 6, and 12-months follow-up by polarized light microscopy.

RESULTS

After one month from the oral supplementation, no patient reported crystalluria; at 3 months, among the 20 participants available for re-evaluation, still no patient reported crystalluria. Instead, crystalluria was reported in three patients (15%) at 6 months, and in five patients (25%) at 12 months follow-up.

CONCLUSIONS

The oral supplementation with Lactobacillus spp. and Bifidobacterium spp. was found able to reduce the prevalence of crystalluria in a cohort of patients with diagnosis of calcium oxalate kidney stones with crystalluria candidate to ureterorenolithotripsy.

Pediatric Nephrolithiasis

The prevalence of pediatric nephrolithiasis has increased dramatically in the past two decades for reasons that have yet to be fully elucidated. Workup of pediatric kidney stones should include metabolic assessment to identify and address any risk factors predisposing patients to recurrent stone formation, and treatment should aim to facilitate stone clearance while minimizing complications, radiation and anesthetic exposure, and other risks. Treatment methods include observation and supportive therapy, medical expulsive therapy, and surgical intervention, with choice of treatment method determined by clinicians' assessments of stone size, location, anatomic factors, comorbidities, other risk factors, and preferences and goals of patients and their families. Much of the current research into nephrolithiasis is restricted to adult populations, and more data are needed to better understand many aspects of the epidemiology and treatment of pediatric kidney stones.

Lime juice as a dietary alternative to mist potassium citrate for urine alkalinisation: A prospective, cross-over clinical trial

INTRODUCTION

Urinary citrate is a potent inhibitor of urinary crystallization that is freely filtered in the proximal tubule of the kidney. We aimed to investigate the effect of citrate supplementation with fresh lime juice on the urinary pH and calcium excretion level among healthy individuals compared with that of mist potassium citrate.

METHOD

In this prospective, cross-over single-centre study, 50 healthy medical student volunteers were randomly allocated to two treatment arms. One arm was prescribed with potassium citrate, while the other arm received citrate supplementation with a home preparation of fresh lime juice. The urinary pH and calcium-to-creatinine ratio (uCa/uCr) were measured at baseline and after 7 days of treatment. This was followed by a washout period of 2 weeks, after which each participant crossed over to the other treatment arm, and the urinary measurements were repeated.

RESULTS

Potassium citrate significantly increased the urinary pH among all participants, while fresh lime juice did not. Both fresh lime juice and potassium citrate reduced the uCa/uCr, although this effect was not significant.

CONCLUSION

Fresh lime juice is not as effective as potassium citrate in improving the urinary pH and calcium excretion level of healthy individuals. Therefore, it should be used as an adjunct rather than an alternative to potassium citrate.

Dietary management of hypocitraturia in children with urolithiasis: results from a systematic review

PURPOSE

Hypocitraturia is a low urinary excretion of citrate and a well-known risk factor for kidney stone development in children. This systematic review aimed to evaluate the dietary management of hypocitraturia in children with urolithiasis.

METHODS

Literature search was performed on 30th September 2022 using Embase, PubMed, and Cochrane Central Controlled Register of Trials. Studies were included if children with stones and hypocitraturia were managed with diet supplements.

RESULTS

Six papers were included. Four studies evaluated the role of oral potassium citrate associated with high fluid intake on stone resolution and recurrence. Two studies assessed the impact of oral potassium citrate on long-term stone recurrence after percutaneous nephrolithotomy and shock wave lithotripsy. All studies demonstrated that the association of potassium citrate and high fluid intake was well tolerated with no side effects and restored normal urine citrate excretion, allowed a reduction in stone size, and, following definitive treatments, was associated with a lower rate of stone regrowth and recurrence compared with controls. These effects were demonstrated across all pediatric ages.

CONCLUSIONS

Our review infers that oral potassium citrate and high fluid assumption are safe and effective in restoring urine citrate excretion, treating and preventing stone recurrence with no serious adverse events, and should probably be the first-line treatment of pediatric patients with asymptomatic stones and hypocitraturia.

Correlates of nephrolithiasis in US black women: data from the black women's health study

Nephrolithiasis is a common urologic condition and a significant source of patient morbidity and healthcare expenditure. There are few epidemiologic studies of kidney stones focusing exclusively on Black women. We retrospectively assessed the prevalence and correlates of self-reported kidney stones within the Black Women's Health Study (BWHS). Descriptive statistics and multivariable logistic regression models were used to explore factors associated with nephrolithiasis. As of the 2005 follow-up questionnaire, a cumulative total of 1063 women among 43,178 reported ever being diagnosed with kidney stones for a prevalence of 2.64%. Women with a history of nephrolithiasis were older, slightly heavier, and were more likely to have a comorbid condition (e.g., type-2 diabetes, gallstones), drink alcohol, and consume a Western-style diet. A history of gallstone disease was associated with an odds ratio (OR) of 3.59 (95% confidence interval (CI) 3.09-4.17). The OR for consuming ≥ 7 alcoholic beverages/week, compared to none was 0.61 (0.39-0.94), while the OR for high adherence to the Western diet, compared to low adherence was 1.53 (1.23-1.90). Our findings are consistent with previous studies of primarily white populations relating lifestyle-associated risk factors with nephrolithiasis. Despite their lower prevalence of kidney stones, it is important to focus on vulnerable populations such as Black women given their disproportionate burden of metabolic conditions (e.g., obesity, diabetes) related to kidney stone disease.

Over-the-counter alkali agents to raise urine pH and citrate excretion: a prospective crossover study in healthy adults

OBJECTIVE

To assess the effect of two over-the-counter alkalizing agents on 24-hour urinary parameters.

MATERIALS AND METHODS

Ten healthy volunteers without a history of kidney stones were recruited to complete a baseline 24-hour urinalysis with a four-day diet inventory. Participants then maintained the same diet on either LithoLyte® (20 mEq two times per day) or KSPtabs^TM (1 tablet two times per day) and submitted another 24-hour urinalysis. The process was repeated with the other supplement. Urinary alkali parameters were compared to baseline, and side effects were elicited with a questionnaire.

RESULTS

LithoLyte® intake resulted in a non-significant increase in citrate (597 to 758 mg/day, p=0.058, an increase in urine pH (6.46 to 6.66, p=0.028), and a decrease in urine ammonium (41 to 36 mmol/day, p=0.005) compared to baseline. KSPtabs^TM resulted in an increase in citrate (597 to 797 mg/day, p=0.037) and urine pH (6.46 to 6.86, p=0.037), with a non-significant decrease in ammonium (41 to 34 mmol/day, p=0.059). No significant differences were seen comparing urinary analytes between LithoLyte® and KSPtabs^TM. With Litholyte®, no side effects, mild, moderate, and severe side effects were seen in 50%, 40%, 10%, and 0%, respectively. With KSPtabs^TM, rates were 60%, 20%, 10%, and 10%, respectively.

CONCLUSIONS

In healthy participants without a history of kidney stones, LithoLyte® and KSPtabs^TM are effective over-the-counter alkali supplements, with a similar side effect profile to prescription potassium citrate.

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.

Human kidney stones: a natural record of universal biomineralization

GeoBioMed - a new transdisciplinary approach that integrates the fields of geology, biology and medicine - reveals that kidney stones composed of calcium-rich minerals precipitate from a continuum of repeated events of crystallization, dissolution and recrystallization that result from the same fundamental natural processes that have governed billions of years of biomineralization on Earth. This contextual change in our understanding of renal stone formation opens fundamentally new avenues of human kidney stone investigation that include analyses of crystalline structure and stratigraphy, diagenetic phase transitions, and paragenetic sequences across broad length scales from hundreds of nanometres to centimetres (five Powers of 10). This paradigm shift has also enabled the development of a new kidney stone classification scheme according to thermodynamic energetics and crystalline architecture. Evidence suggests that ≥50% of the total volume of individual stones have undergone repeated in vivo dissolution and recrystallization. Amorphous calcium phosphate and hydroxyapatite spherules coalesce to form planar concentric zoning and sector zones that indicate disequilibrium precipitation. In addition, calcium oxalate dihydrate and calcium oxalate monohydrate crystal aggregates exhibit high-frequency organic-matter-rich and mineral-rich nanolayering that is orders of magnitude higher than layering observed in analogous coral reef, Roman aqueduct, cave, deep subsurface and hot-spring deposits. This higher frequency nanolayering represents the unique microenvironment of the kidney in which potent crystallization promoters and inhibitors are working in opposition. These GeoBioMed insights identify previously unexplored strategies for development and testing of new clinical therapies for the prevention and treatment of kidney stones.

Seeking consistency for the role of urinary macromolecules and glycosaminoglycans in calcium oxalate crystallization processes pertaining to the risk of renal stone formation using a multi-faceted basic science approach

BACKGROUND

The roles of urinary macromolecules (UMMs) in calcium oxalate (CaOx) renal stone formation have not been consistently established.

AIM

To unravel these roles using a multi-faceted, multi-technique approach employing a wide range of experimental variables on a rotational basis in strategically chosen combinations.

METHODS

Endogenous urinary glycosaminoglycans (GAGs) were investigated in fractions obtained after ultrafiltration of pooled human urine (HU). Exogenous GAGs (chondroitin sulphate, CS, and hyaluronic acid, HA) were studied in artificial (AU) and in individual HUs. Experiments were conducted in a batch crystallizer and in a mixed suspension, mixed product removal flow system. Crystallization was quantitatively followed using Coulter multisizer and flow cytometer techniques. Crystal aggregation in the presence and absence of exogenous CS and HA was measured by Zeta potential and crystal sedimentation.

RESULTS

Total UMMs (endogenous) and individual GAGs (exogenous) consistently promoted CaOx crystallization and disaggregation. Evidence of UMM-UMM and UMM-solution synergistic effects was consistently observed for achieving modulation of crystallization processes.

CONCLUSIONS

Total UMMs, the main modulatory component of which is GAGs, are promoters of CaOx crystal nucleation and inhibitors of CaOx crystal aggregation. These results allow researchers to disregard alternative roles that have been advocated in such studies.

LITHOSCREEN: a comprehensive screening program and database for the assessment and treatment management of patients with kidney stones

The aim of the LITHOSCREEN project was to construct a comprehensive screening program and database for recording and assessing the various risk factors for stone-formation in patients with urolithiasis. It is intended for use in Stone Clinics and is now being made available free of charge to researchers in the field who wish to maintain a comprehensive record of their patients' medical histories, demographic backgrounds, lifestyle activities, metabolic abnormalities, biochemical risk of forming stones of various types, diet histories, stone analysis and long-term treatment records. From the recorded data for each patient, the program automatically calculates numerous functions important in the understanding of the clinical and chemical risk factors for stone-formation, including the renal handling of the ions involved, various metabolic functions, the biochemical risk of forming kidney stones (P_SF), the Tiselius Indices of the supersaturation of urine with respect to calcium oxalate and calcium phosphate, the projected effects of changing the composition of each patient's urinary composition on the risk of stone recurrence, and a program for analysing the diet of patients. It automatically produces one-page Summaries of each patient's biochemical and dietary records with abnormal values highlighted according to a "traffic-light" colour-coding system and generates charts designed to improve patient compliance with treatment in the form of colour-coded "Target Diagrams" showing (a) the patient's 24-h urine composition, (b) the patient's biochemical risk of forming stones of different types and (c) the composition of the patient's diet. The Summary pages and "Target Diagrams" are suitable for inclusion in the patient's Case Notes. LITHOSCREEN also produces charts projecting the effect of changing the composition of urine on the patient's biochemical risk of forming further stones. These graphs provide clues as to which urinary risk factors to target to reduce the patient's risk of stone recurrence.

Uric Acid and Urate in Urolithiasis: The Innocent Bystander, Instigator, and Perpetrator

Uric acid is an end product of purine metabolism in human beings. An unusual and still unexplained phenomenon is that higher primates have relatively high uric acid levels in body fluids owing to a combination of absence of degradation and renal retention. The physiologic purpose of high uric acid levels still is enigmatic, but the pathobiologic burden is a variety of crystallopathies owing to the low aqueous solubility of uric acid such as gouty arthritis and acute uric acid nephropathy. In the urinary space, three distinct conditions result from chronic uric acid and/or urate precipitation. The first and most common variety is uric acid urolithiasis. In this condition, urate is a victim of a systemic metabolic disease in which increased acid load to the kidney is coupled with diminished urinary buffer capacity owing to defective ammonium excretion, resulting in titration of urate to its sparingly soluble protonated counterpart, uric acid, and the formation of stones. Uric acid is the innocent bystander of the crime. The second variety is hyperuricosuric calcium urolithiasis, in which uric acid confers lithogenicity via promotion of calcium oxalate precipitation by multiple mechanisms involving soluble, colloidal, and crystalline urate salts. Uric acid is the instigator of the crime. The third and least common condition involves urate as an integral part of the urolith as an ammonium salt driven by high ammonium and high urate concentrations in urine. Here, uric acid is one of the perpetrators of the crime. Both known and postulated pathogenesis of these three types of urolithiasis are reviewed and summarized.

Urine and stone analysis for the investigation of the renal stone former: a consensus conference

The Consensus Group deliberated on a number of questions concerning urine and stone analysis over a period of months, and then met to develop consensus. The Group concluded that analyses of urine and stones should be routine in the diagnosis and treatment of urinary stone diseases. At present, the 24-h urine is the most useful type of urine collection, and accepted methods for analysis are described. Patient education is also important for obtaining a proper urine sample. Graphical methods for reporting urine analysis results can be helpful both for the physician and for educating the patient as to proper dietary changes that could be beneficial. Proper analysis of stones is also essential for diagnosis and management of patients. The Consensus Group also agreed that research has shown that evaluation of urinary crystals could be very valuable, but the Group also recognizes that existing methods for assessment of crystalluria do not allow this to be part of stone treatment in many places.

Isolation and Selection of Non-Saccharomyces Yeasts Being Capable of Degrading Citric acid and Evaluation Its Effect on Kiwifruit Wine Fermentation

High citric acid content in kiwifruit wine would lead to bad sensory experience and quality deterioration. It is opportune and crucial to develop an appropriate and feasible method to degrade citric acid for kiwifruit wine. The non-Saccharomyces yeasts confirmed to have the ability to degrade citric acid were screened and used in kiwifruit wine fermentation in the study. A representative number of 23 yeasts with a strong citric acid degradation ability was identified by molecular approaches. JT-1-3, identified to be Pichia fermentans, was preferred for high citric acid degradation and strong stress resistance in association with RV002 (commercial Saccharomyces cerevisiae). Then it was pure-cultured in kiwifruit juice, and the results indicated that citric, malic and tartaric acids declined significantly from 12.30, 3.09 and 0.61 g/L to 11.00, 2.02 and 0.41 g/L after fermentation, respectively, resulting in the significant decrease in total acid in kiwifruit wine. The analytical profiles for amino acids and volatile compounds showed that Pichia fermentans JT-1-3 could improve amino acids’ proportion and increase the volatile compounds of alcohols, esters and phenols. This work indicated that JT-1-3 has great potential to be applied for fruit wine with high level citric acid.

Urothelium proliferation is a trigger for renal crystal deposits in a murine lithogenesis model

Most mouse kidney stone models induce nephrocalcinosis rather than urolithiasis. The aim of our study was to find an accelerated experimental model in order to study the early events of stone formation, that is, at the time of crystal binding to intrarenal urothelium. C57B6 mice exposed to vitamin D supplements and water containing hydroxyl-L-proline, ammonium chloride and calcium chloride were studied for 42 days. A group receiving urothelial cell mitogen Fibroblast Growth Factor 7 (FGF7) was compared to control group receiving saline. Calcium oxalate monohydrate (COM) crystals were detected in urines by day 2 and within urinary spaces in specialized fornix areas in both groups as soon as day 14 with enhanced deposits in FGF7 group compared to controls at day 21. Urothelial cells proliferation, uroplakin III downregulation and de novo expression of osteopontin receptor CD44 detected in FGF7 group, were delayed in the control group (day 42). Crystal aggregates within specialized fornix areas by day 42 were located in urinary spaces but also within and under a multilayered metaplastic urothelium, simultaneous to macrophages influx. Point of note, administration of a normal diet by day 21 was responsible for a spontaneous crystal clearance. Our data show that under supersaturation conditions, urothelial cell proliferation and calcium oxalate crystal retention occur within specialized fornix areas. Enhanced crystal deposits following FGF7 administration suggest that urothelium proliferation would be a relevant trigger for renal stone formation.

Geobiology reveals how human kidney stones dissolve in vivo

More than 10% of the global human population is now afflicted with kidney stones, which are commonly associated with other significant health problems including diabetes, hypertension and obesity. Nearly 70% of these stones are primarily composed of calcium oxalate, a mineral previously assumed to be effectively insoluble within the kidney. This has limited currently available treatment options to painful passage and/or invasive surgical procedures. We analyze kidney stone thin sections with a combination of optical techniques, which include bright field, polarization, confocal and super-resolution nanometer-scale auto-fluorescence microscopy. Here we demonstrate using interdisciplinary geology and biology (geobiology) approaches that calcium oxalate stones undergo multiple events of dissolution as they crystallize and grow within the kidney. These observations open a fundamentally new paradigm for clinical approaches that include in vivo stone dissolution and identify high-frequency layering of organic matter and minerals as a template for biomineralization in natural and engineered settings.

Prevalence, pathophysiological mechanisms and factors affecting urolithiasis

The formation of urinary stone, urolithiasis, is one the oldest known disease affecting human throughout different civilizations and times. The exact pathophysiological mechanism of urolithiasis is not yet clear, as these calculi are of various types and too complex for simple understanding. A single theory cannot explain its formation; therefore, different theories are presented in various times for its explanation like free particle, fixed particle, Randall's plaque theory. In addition, various factors and components are identified that play an important role in the formation of these urinary calculi. In this review, composition of kidney stones, its prevalence/incidence, explanation of pathophysiological mechanisms and role of various factors; urinary pH, uric acid, parathyroid hormone, citrate, oxalate, calcium and macromolecules; osteopontin, matrix Gla protein, kidney injury molecules, urinary prothrombin fragment-1, Tamm-Horsfall protein, inter-α-inhibitors, have been discussed in detail.

Association of urinary citrate excretion, pH, and net gastrointestinal alkali absorption with diet, diuretic use, and blood glucose concentration

Urinary citrate (Ucit) protects against urinary stone formation. Acid base status and diet influence Ucit. However, the effect of demographics, diet, and glucose metabolism on Ucit excretion, urinary pH (U‐pH) and net gastrointestinal alkali absorption (NAA) are not known. Twenty‐four hour urine samples, blood glucose, creatinine, and cystatin C were obtained from non‐Hispanic white sibships in Rochester, MN (n = 446; 64.5 ± 9 years; 58% female). Diet was assessed by a food frequency questionnaire. The impact of blood glucose, demographics and dietary elements on Ucit excretion, U‐pH, and NAA were evaluated in bivariate and multivariable models and interaction models that included age, sex, and weight. NAA significantly associated with Ucit and U‐pH. In multivariate models Ucit increased with age, weight, eGFR_Cys, and blood glucose, but decreased with loop diuretic and thiazide use. U‐pH decreased with serum creatinine, blood glucose, and dietary protein but increased with dietary potassium. NAA was higher in males and increased with age, weight, eGFR_Cys and dietary potassium. Significant interactions were observed for Ucit excretion with age and blood glucose, weight and eGFR_Cys, and sex and thiazide use. Blood glucose had a significant and independent effect on U‐pH and also Ucit. This study provides the first evidence that blood glucose could influence urinary stone risk independent of urinary pH, potentially providing new insight into the association of obesity and urinary stone disease.

Probiotics for prevention of urinary stones

BACKGROUND

Urinary supersaturation is one key determinant of calcium oxalate (CaOx) urinary stone formation, and urinary excretions of oxalate and citrate are two key determinants. Each is influenced by gastrointestinal processes.

METHODS

Open label and randomized placebo studies have examined the effect of oral probiotic preparations on urinary supersaturation and oxalate excretion. Cross sectional studies in humans have studied the association of Oxalobacter formigenes colonization status and urinary oxalate excretion and prevalence of urinary stones. The intestinal microbiome of representative animals adapted to a high oxalate diet has been defined.

RESULTS

The fecal content of O. formigenes, the best studied oxalate-degrader, varies depending on stone status. However, trials with probiotics designed to degrade oxalate including those containing O. formigenes, Lactobacillus, and/or Bifidobacterium spp., have been disappointing. Multiple intestinal segments of animals on a high oxalate diet contains diverse communities of microorganisms that can function together to degrade and detoxify a large oxalate load.

CONCLUSIONS

Although the intestinal microbiome seems likely to play a role to modify gastrointestinal absorption of lithogenic substances and hence urinary stone risk, whether we can develop tools to manipulate it and decrease this kidney stone risk remains to be determined.

Effect of Potassium Citrate on Calcium Phosphate Stones in a Model of Hypercalciuria

Potassium citrate is prescribed to decrease stone recurrence in patients with calcium nephrolithiasis. Citrate binds intestinal and urine calcium and increases urine pH. Citrate, metabolized to bicarbonate, should decrease calcium excretion by reducing bone resorption and increasing renal calcium reabsorption. However, citrate binding to intestinal calcium may increase absorption and renal excretion of both phosphate and oxalate. Thus, the effect of potassium citrate on urine calcium oxalate and calcium phosphate supersaturation and stone formation is complex and difficult to predict. To study the effects of potassium citrate on urine supersaturation and stone formation, we utilized 95th-generation inbred genetic hypercalciuric stone-forming rats. Rats were fed a fixed amount of a normal calcium (1.2%) diet supplemented with potassium citrate or potassium chloride (each 4 mmol/d) for 18 weeks. Urine was collected at 6, 12, and 18 weeks. At 18 weeks, stone formation was visualized by radiography. Urine citrate, phosphate, oxalate, and pH levels were higher and urine calcium level was lower in rats fed potassium citrate. Furthermore, calcium oxalate and calcium phosphate supersaturation were higher with potassium citrate; however, uric acid supersaturation was lower. Both groups had similar numbers of exclusively calcium phosphate stones. Thus, potassium citrate effectively raises urine citrate levels and lowers urine calcium levels; however, the increases in urine pH, oxalate, and phosphate levels lead to increased calcium oxalate and calcium phosphate supersaturation. Potassium citrate induces complex changes in urine chemistries and resultant supersaturation, which may not be beneficial in preventing calcium phosphate stone formation.

Biomimetic synthesis of struvite with biogenic morphology and implication for pathological biomineralization

Recent studies have found that certain urinary proteins can efficiently inhibit stone formation. These discoveries are significant for developing effective therapies for stone disease, but the inhibition mechanism of crystallization remains elusive. In the present study, polyaspartic acid (PASP) was employed as a model peptide to investigate the effect of urinary proteins on the crystallization and morphological evolution of struvite. The results demonstrate that selective adsorption/binding of PASP onto the {010} and {101} faces of struvite crystals results in arrowhead-shaped morphology, which further evolves into X-shaped and unusual tabular structures with time. Noticeably, these morphologies are reminiscent of biogenic struvite morphology. Concentration-dependent experiments show that PASP can inhibit struvite growth and the inhibitory capacity increases with increasing PASP concentration, whereas aspartic acid monomers do not show a significant effect. Considering that PASP is a structural and functional analogue of the subdomains of aspartic acid-rich proteins, our results reveal that aspartic acid-rich proteins play a key role in regulating biogenic struvite morphology, and aspartic acid residues contribute to the inhibitory capacity of urinary proteins. The potential implications of PASP for developing therapeutic agents for urinary stone disease is also discussed.

Medical management of kidney stones: AUA guideline

PURPOSE

The purpose of this guideline is to provide a clinical framework for the diagnosis, prevention and follow-up of adult patients with kidney stones based on the best available published literature.

MATERIALS AND METHODS

The primary source of evidence for this guideline was the systematic review conducted by the Agency for Healthcare Research and Quality on recurrent nephrolithiasis in adults. To augment and broaden the body of evidence in the AHRQ report, the AUA conducted supplementary searches for articles published from 2007 through 2012 that were systematically reviewed using a methodology developed a priori. In total, these sources yielded 46 studies that were used to form evidence-based guideline statements. In the absence of sufficient evidence, additional statements were developed as Clinical Principles and Expert Opinions.

RESULTS

Guideline statements were created to inform clinicians regarding the use of a screening evaluation for first-time and recurrent stone formers, the appropriate initiation of a metabolic evaluation in select patients and recommendations for the initiation and follow-up of medication and/or dietary measures in specific patients.

CONCLUSIONS

A variety of medications and dietary measures have been evaluated with greater or less rigor for their efficacy in reducing recurrence rates in stone formers. The guideline statements offered in this document provide a simple, evidence-based approach to identify high-risk or interested stone-forming patients for whom medical and dietary therapy based on metabolic testing and close follow-up is likely to be effective in reducing stone recurrence.

[Nephrolithiasis: metabolic defects and terapeutic implications]

Over the past 10 years, major progress has been made in the knowledge of urinary lithogenesis, including the potential pathogenetic role of Randall's plaques and renal tubular crystal retention. Urine supersaturation is the driving force of this process and can be induced by some risk factors, including low urine volume, high urinary excretion of calcium oxalate and uric acid and low urinary excretion of citrate. Primary hypercalciuria can be due to intestinal overabsorption renal leak and bone reabsorption of calcium. Prophilaxis is mainly conducted with thiazides and low calcium diet which is indicated only in the intestinal form. Primary hyperoxaluria is treated with pyridoxine and may require in the severe forms simultaneous renal and liver transplantation. Enteric hyperoxaluria is secondary to fatty acids malabsorption and requires diet, oral calcium and cholestiramine. Hyperuricosuria is caused by diet endogenous overproduction, mainly due to enzymatic defects or high renal excretion of uric acid. Urine alkalinization with K or K and Mg citrate can prevent stone formation even in idiopathic uric acid nephrolithiasis, in which a defect of urine acidification is supposed to be the main abnormality, and in hypocitraturic patients. Cystinuria is a rare inherited defect with an intense clinical impact. It can be classified in three forms and urinary stone formation is the role. Increased solubility and conversion of cystine in a more soluble form are the main goals of the prophylaxis which includes K citrate and thiol agents administration. Tiopronin is preferred to D-penicillamine due to its lower side effects.

Association between human prothrombin variant (T165M) and kidney stone disease

We previously reported the association between prothrombin (F2), encoding a stone inhibitor protein - urinary prothrombin fragment 1 (UPTF1), and the risk of kidney stone disease in Northeastern Thai patients. To identify specific F2 variation responsible for the kidney stone risk, we conducted sequencing analysis of this gene in a group of the patients with kidney stone disease. Five intronic SNPs (rs2070850, rs2070852, rs1799867, rs2282687, and rs3136516) and one exonic non-synonymous single nucleotide polymorphism (nsSNP; rs5896) were found. The five intronic SNPs have no functional change as predicted by computer programs while the nsSNP rs5896 (c.494 C>T) located in exon 6 results in a substitution of threonine (T) by methionine (M) at the position 165 (T165M). The nsSNP rs5896 was subsequently genotyped in 209 patients and 216 control subjects. Genotypic and allelic frequencies of this nsSNP were analyzed for their association with kidney stone disease. The frequency of CC genotype of rs5896 was significantly lower in the patient group (13.4%) than that in the control group (22.2%) (P = 0.017, OR 0.54, 95% CI 0.32–0.90), and the frequency of C allele was significantly lower in the patient group (36.1%) than that in the control group (45.6%) (P = 0.005, OR 0.68, 95% CI 0.51–0.89). The significant differences of genotype and allele frequencies were maintained only in the female group (P = 0.033 and 0.003, respectively). The effect of amino-acid change on UPTF1 structure was also examined by homologous modeling and in silico mutagenesis. T165 is conserved and T165M substitution will affect hydrogen bond formation with E180. In conclusion, our results indicate that prothrombin variant (T165M) is associated with kidney stone risk in the Northeastern Thai female patients.

Genetic determinants of urolithiasis

Urolithiasis affects approximately 10% of individuals in Western societies by the seventh decade of life. The most common form, idiopathic calcium oxalate urolithiasis, results from the interaction of multiple genes and their interplay with dietary and environmental factors. To date, considerable progress has been made in identifying the metabolic risk factors that predispose to this complex trait, among which hypercalciuria predominates. The specific genetic and epigenetic factors involved in urolithiasis have remained less clear, partly owing to the candidate gene and linkage methods that have been available until now, being inherently low in their power of resolution and in assessing modest effects in complex traits. However, together with investigations of rare, Mendelian forms of urolithiasis associated with various metabolic risk factors, these methods have afforded insights into biological pathways that seem to underlie the development of stones in the urinary tract. Monogenic diseases account for a greater proportion of stone formers in children and adolescents than in adults. Early diagnosis of monogenic forms of urolithiasis is of importance owing to associated renal injury and other potentially treatable disease manifestations, but diagnosis is often delayed because of a lack of familiarity with these rare disorders. In this Review, we will discuss advances in the understanding of the genetics underlying polygenic and monogenic forms of urolithiasis.

Label-free quantitative proteomics reveals differentially regulated proteins influencing urolithiasis

Urinary proteins have been implicated as inhibitors of kidney stone formation (urolithiasis). As a proximal fluid, prefiltered by the kidneys, urine is an attractive biofluid for proteomic analysis in urologic conditions. However, it is necessary to correct for variations in urinary concentration. In our study, individual urine samples were normalized for this variation by using a total protein to creatinine ratio. Pooled urine samples were compared in two independent experiments. Differences between the urinary proteome of stone formers and nonstone-forming controls were characterized and quantified using label-free nano-ultraperformance liquid chromatography high/low collision energy switching analysis. There were 1063 proteins identified, of which 367 were unique to the stone former groups, 408 proteins were unique to the control pools, and 288 proteins were identified for comparative quantification. Proteins found to be unique in stone-formers were involved in carbohydrate metabolism pathways and associated with disease states. Thirty-four proteins demonstrated a consistent >twofold change between stone formers and controls. For ceruloplasmin, one of the proteins was shown to be more than twofold up-regulated in the stone-former pools, this observation was validated in individuals by enzyme-linked immunosorbent assay. Moreover, in vitro crystallization assays demonstrated ceruloplasmin had a dose-dependent increase on calcium oxalate crystal formation. Taken together, these results may suggest a functional role for ceruloplasmin in urolithiasis.

Prothrombin haplotype associated with kidney stone disease in Northeastern Thai patients

OBJECTIVE

To evaluate genetic variations associated with kidney stone disease in Northeastern Thai patients.

METHODS

Altogether, 67 single nucleotide polymorphisms (SNP) distributed within 8 candidate genes, namely TFF1, S100A8, S100A9, S100A12, AMBP, SPP1, UMOD, and F2, which encode stone inhibitor proteins, including trefoil factor 1, calgranulin (A, B, and C), bikunin, osteopontin, tamm-Horsfall protein, and prothrombin, respectively, were initially genotyped in 112 individuals each and in additional subjects to consist of 164 patients and 216 control subjects in total.

RESULTS

We found that minor allele and homozygous genotype frequencies of 8 of 10 SNPs distributed within the F2 gene were significantly higher in the control group than in the patient group. Two F2 haplotypes were found to be dually associated with kidney stone risk, one (TGCCGCCGCG) with increased disease risk and the other (CGTTCCGCTA) with decreased disease risk. However, these 2 haplotypes were associated with the disease risks in only the female, not the male, group.

CONCLUSIONS

The results of our study indicate that genetic variation of F2 is associated with kidney stone risk in Northeastern Thai female patients.

The effects of intracrystalline and surface-bound proteins on the attachment of calcium oxalate monohydrate crystals to renal cells in undiluted human urine

OBJECTIVE

To compare the binding to Madin-Darby canine kidney (MDCK)-II cells of: (i) inorganic calcium oxalate monohydrate (iCOM) crystals and COM crystals precipitated from urine containing different concentrations of protein; and (ii) urinary COM crystals containing intracrystalline and intracrystalline + surface-bound protein.

MATERIALS AND METHODS

Urinary COM crystals were generated in sieved (sCOM), centrifuged and filtered (cfCOM), and ultrafiltered (ufCOM) portions of a pooled human urine and their adhesion to MDCK-II cells was compared using six different ultrafiltered urine samples as the binding medium. Crystal matrix extract (CME) was prepared by demineralizing calcium oxalate crystals precipitated from human urine and used to prepare COM crystals with intracrystalline, and intracrystalline + surface-bound CME at protein concentrations of 0, 0.05, 0.1, 0.5 and 5.0 mg/L. The amount of protein associated with the crystals was qualitatively assessed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and Western blotting, using prothrombin fragment 1 (PTF1) as a marker. Protein concentration was determined in sieved, centrifuged and filtered, and ultrafiltered fractions of 10 additional urine samples.

RESULTS

The median crystal attachment in the six urine types decreased in the order iCOM > ufCOM > cfCOM = sCOM, in inverse proportion to the concentration of protein in the solution or urine from which they were precipitated. sCOM and cfCOM crystals bound approximately 23% less than iCOM crystals. The attachment of COM crystals generated in the presence of increasing concentrations of CME proteins was unaffected up to a concentration of 5 mg/L, but binding of crystals containing the same concentrations of intracrystalline + surface-bound proteins decreased proportionally at protein concentrations from 0 to 5.0 mg/L.

CONCLUSION

Inorganic COM crystals bind significantly more strongly to MDCK-II cells than urinary crystals precipitated from sieved, centrifuged and filtered, and ultrafiltered urine, and binding affinity is inversely related to the concentration of protein in the urine in which they are formed. While both intracrystalline and superficial CME proteins reduce the attachment of COM crystals to MDCK-II cells, those located on the crystal surface have a greater influence than those incarcerated within the mineral bulk. Future cell-crystal interaction studies should use urinary crystals and be performed in human urine.

Recurrence of renal lithiasis

OBJECTIVE

It is well known that all renal stones are associated with a high recurrence rate. The aim of this paper is to study the different types of renal calculi recurrence.

MATERIAL AND METHODS

The study included 220 patients who had produced two or more renal calculi over a period of <5 years (total 634 calculi). The procedure used to study renal calculi involved appropriate combinations of stereoscopic microscopy with infrared spectrometry and scanning electron microscopy coupled with X-ray microanalysis.

RESULTS AND CONCLUSION

Recurrent stone-formers can be classified into two large groups: those who always produce the same type of calculus (the most common type of recurrence was calcium oxalate dihydrate, followed by calcium oxalate monohydrate non-papillary and calcium oxalate monohydrate papillary calculi); and those who produce different types of renal calculi (the most frequent recurrences in this group were the changes calcium oxalate dihydrate-->calcium oxalate dihydrate/hydroxyapatite and calcium oxalate monohydrate-->calcium oxalate dihydrate).

Quantitative assessment of citric acid in lemon juice, lime juice, and commercially-available fruit juice products

BACKGROUND AND PURPOSE

Knowledge of the citric acid content of beverages may be useful in nutrition therapy for calcium urolithiasis, especially among patients with hypocitraturia. Citrate is a naturally-occurring inhibitor of urinary crystallization; achieving therapeutic urinary citrate concentration is one clinical target in the medical management of calcium urolithiasis. When provided as fluids, beverages containing citric acid add to the total volume of urine, reducing its saturation of calcium and other crystals, and may enhance urinary citrate excretion. Information on the citric acid content of fruit juices and commercially-available formulations is not widely known. We evaluated the citric acid concentration of various fruit juices.

MATERIALS AND METHODS

The citric acid content of 21 commercially-available juices and juice concentrates and the juice of three types of fruits was analyzed using ion chromatography.

RESULTS

Lemon juice and lime juice are rich sources of citric acid, containing 1.44 and 1.38 g/oz, respectively. Lemon and lime juice concentrates contain 1.10 and 1.06 g/oz, respectively. The citric acid content of commercially available lemonade and other juice products varies widely, ranging from 0.03 to 0.22 g/oz.

CONCLUSIONS

Lemon and lime juice, both from the fresh fruit and from juice concentrates, provide more citric acid per liter than ready-to-consume grapefruit juice, ready-to-consume orange juice, and orange juice squeezed from the fruit. Ready-to-consume lemonade formulations and those requiring mixing with water contain < or =6 times the citric acid, on an ounce-for-ounce basis, of lemon and lime juice.

Evaluation of Sesbania grandiflora for antiurolithiatic and antioxidant properties

In the indigenous system of medicine in India, the plant Sesbania grandiflora is claimed to be useful for various ailments, and one such use is for the treatment of renal calculi. The major purpose of this study is to investigate the potential of S. grandiflora in the treatment of renal calculi. The leaf juice of S. grandiflora was evaluated for median lethal dose, gross behavioral changes, antiurolithiatic and antioxidant activities. The antiurolithiatic activity was evaluated by a calculi-producing diet model, using gentamicin (subcutaneously) and 5% ammonium oxalate in rat feed to induce calcium oxalate-type stones. The parameters monitored in the present study are calcium and oxalate deposition in the kidney, kidney weights, urinary excretion of calcium and oxalate. The in vivo antioxidant parameters lipid peroxidation, glutathione reductase and catalase were monitored. The plant juice was also evaluated for scavenging of nitric oxide and 2-diphenyl-2-picryl hydrazyl free radicals. The leaf juice of S. grandiflora was safe orally and exhibited no gross behavioral changes except for an increase in urination. The leaf juice of S. grandiflora showed significant antiurolithiatic activity against calcium oxalate-type stones and also exhibited antioxidant properties. The results obtained in this study provide evidence for the efficacy of the leaf juice of S. grandiflora as antiurolithiatic agent.

Macromolecules and urolithiasis: parallels and paradoxes

Long-standing interest in the possible role of macromolecules in urolithiasis stems from the observation that all human kidney stones consist of a complex amalgam of mineral and organic material. This review summarises what is currently known or is hypothesised about the influences of urinary macromolecules, especially proteins, on the formation of calcium oxalate crystals, their attachment to renal epithelial cells, and their subsequent destruction within those cells. Although a list is provided of proteins that have either been detected in stones or have been implicated by virtue of their effects on crystallization, only a select handful, which have been intensively studied, have been singled out for individual discussion. The review ends with a speculative discussion of the applicability of current knowledge to the investigation and treatment of urolithiasis.

Intracrystalline proteins and urolithiasis: a comparison of the protein content and ultrastructure of urinary calcium oxalate monohydrate and dihydrate crystals

OBJECTIVE

To compare the ultrastructure and protein content, particularly prothrombin fragment 1 and osteopontin, of calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) crystals precipitated from human urine, and their susceptibility to proteolysis, to try to clarify the role of intracrystalline proteins in urolithiasis, as differences between these types of crystal may determine whether calcium oxalate crystals nucleated in urine progress to stone formation.

MATERIALS AND METHODS

Sodium dodecyl sulphate gel electrophoresis and Western blotting were used to analyse demineralized extracts of COM and/or COD crystals deposited from the same centrifuged and filtered urine (which contains abundant urinary proteins) by adjusting the calcium concentration to 2 and 7 mmol/L, respectively. Similar analyses were performed on COM and COD crystals deposited from ultrafiltered urine (which contains only proteins of < 10 kDa) and then incubated in centrifuged and filtered urine, as well as crystals generated in the presence of increasing concentrations of proteins derived from the organic matrix of urinary calcium oxalate crystals. Field-emission scanning electron microscopy was used to assess effects of proteinase K and cathepsin D on internal and superficial crystal structure.

RESULTS

Osteopontin was undetectable in COM extracts, but clearly visible in COD. Prothrombin fragment 1 was abundant in COM, but present in COD in lesser amounts than osteopontin. The selectivity was also the same with crystals from ultrafiltered urine that were incubated in centrifuged and filtered urine: prothrombin fragment 1 binding was favoured by low calcium concentration, while osteopontin bound at higher levels. Scanning electron microscopy of COM and COD digested with proteinase K and cathepsin D revealed superficial and internal texture, as wells as surface erosion, in crystals from centrifuged and filtered urine, thus confirming the presence of intracrystalline proteins. Such features were absent from crystals precipitated from ultrafiltered urine.

CONCLUSION

Binding of osteopontin and prothrombin fragment 1 to calcium oxalate is dictated primarily by ambient calcium concentration. Each protein may inhibit urolithiasis by inhibiting crystallization of its preferred crystal habit, and by facilitating the intracellular disintegration and dissolution of crystals attached to and internalized by renal epithelial cells.

Uric acid: an abettor or protector in calcium oxalate urolithiasis? Biochemical study in stone formers

BACKGROUND

Free radical induced renal damage leads to crystal retention and formation of large stones. However, the scenario behind uric acid (UA) stone formation is still a mystery, as uric acid, a risk factor of stone formation, seems to be a potent antioxidant that can protect cells from damage by reactive oxygen species. This study was intended to evaluate the role of uric acid in stone formers by assessing the oxidative stress status of the stone patients.

METHODS

Determination of urinary stone forming risk factors and oxidative stress factors like plasma lipid peroxidation, protein carbonyls of stone formers and histopathological changes and uric acid deposition in stone patients kidney biopsy were studied.

RESULTS

Increased concentrations of urinary uric acid and oxalate in both uric acid as well as calcium oxalate stone formers were observed, whereas calcium is increased in calcium stone formers and not in the uric acid stone patients. Inhibitors such as citrate and glycosaminoglycans (GAGs) were found to be significantly decreased in all the stone patients. Histopathological studies confirmed the deposition of crystals in the damaged tubules and De Galantha staining authenticates that the damage is caused due to uric acid crystals. Increased oxidative stress is dictated by the concentrations of lipid peroxidation and protein carbonyls in stone formers. Moreover, increased activities of urinary marker enzymes substantiate the tubular damage.

CONCLUSION

We speculated that uric acid acts as a calculi forming salt rather than an antioxidant and it has no role in preventing oxidative stress pertaining to urolithiasis.

Nucleation of calcium oxalate crystals on an imprinted polymer surface from pure aqueous solution and urine

Calcium oxalate (CaOx) is the most common component of human kidney stones. Heterogeneous nucleation is regarded as the key mechanism in this process. In this study, we have used an imprinted 6-methacrylamidohexanoic acid/divinylbenzene co-polymer as a biomimetic surface to nucleate CaOx crystal formation. The polymer was imprinted with either calcium oxalate monohydrate (COM) or dihydrate (COD) template crystals. These were washed out of the polymer, which was then immersed in various test solutions. The test solutions were an aqueous solution of calcium chloride and sodium oxalate, artificial urine and a sample of real urine. Crystals that formed on the polymer surface were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy, atomic absorption spectroscopy and scanning electron microscopy. Results showed that in the aqueous solution the COM-imprinted polymer induced the nucleation of COM. The COD-imprinted polymer induced only trace amounts of COD crystallization, together with larger quantities of COM. In artificial and real urines, COM also specifically precipitated on the COM-imprinted surface. The results show that, at least to some extent, the imprinted polymers direct formation of their morphologically matched crystals. In the case of COD, however, it appears that either rapid hydrate transformation of COD to COM occurs, or the more stable COM polymorph is directly co-precipitated by the polymer. Our results support the hypothesis that heterogeneous nucleation plays a key role in CaOx stone formation and that the imprinted polymer model could provide an additional and superior diagnostic tool for stone researchers to assess stone-risk in urine.

Intracrystalline proteins and urolithiasis: a synchrotron X-ray diffraction study of calcium oxalate monohydrate

The existence of intracrystalline proteins and amino acids in calcium oxalate monohydrate was demonstrated by X-ray synchrotron diffraction studies. Their presence has implications for the destruction of calcium oxalate crystals formed in the urinary tract and the prevention of kidney stones.

INTRODUCTION

Although proteins are present in human kidney stones, their role in stone pathogenesis remains unknown. This investigation aimed to characterize the nature of the relationship between the organic and mineral phases in calcium oxalate monohydrate (COM) crystals grown in human urine and in aqueous solutions of proteins and amino acids to clarify the function of proteins in urolithiasis.

METHODS

COM crystals were grown in human urine and in aqueous solutions containing either human prothrombin (PT), Tamm-Horsfall glycoprotein (THG), aspartic acid (Asp), aspartic acid dimer (AspAsp), glutamic acid (Glu), glutamic acid dimer (GluGlu), or gamma-carboxyglutamic acid (Gla). Controls consisted of COM crystals precipitated from pure inorganic solutions or from human urine that had been ultrafiltered to remove macromolecules. Synchrotron X-ray diffraction with Rietveld whole-pattern peak fitting and profile analysis was used to determine nonuniform crystal strain and crystallite size in polycrystalline samples.

RESULTS

Crystals precipitated from ultrafiltered urine had lower nonuniform strain than those grown in urine or in aqueous PT solution. Nonuniform strain was much lower in crystals grown in distilled water or in the presence of THG. For the amino acids, the highest nonuniform strain was exhibited by crystals grown in Gla solution, followed by Glu. Crystallite size was inversely related to nonuniform strain, with the effect being significantly less for amino acids than for macromolecules.

CONCLUSIONS

Selected proteins and amino acids associated with COM crystals are intracrystalline. Although their incorporation into the mineral bulk would be expected to affect the rate of crystal growth, they also have the potential to influence the phagocytosis and intracellular destruction of any crystals nucleated and trapped within the renal collecting system. Crystals impregnated with protein would be more susceptible to digestion by cellular proteases, which would provide access to the crystal core, thereby facilitating further proteolytic degradation and mineral dissolution. We therefore propose that intracrystalline proteins may constitute a natural form of defense against renal stone formation.

Epidemiology and medical management of stone disease

Recurrent stone formation in the urinary tract is a common and important problem that must be considered in daily urological practice. With a prevalence of> 10% and an expected recurrence rate of approximately 50%, stone disease has an important effect on the healthcare system. It is generally agreed that patients with uric acid/urate, cystine or infection stones always should be treated pharmacologically. For calcium stone formers the treatment should be chosen according to the severity of the disease. Recurrence in patients with calcium-stone disease can be prevented with general or specific dietary and drinking advice, and with pharmacological therapy. For idiopathic calcium stone formers the most convincing therapeutic effects have been reported with thiazide and alkaline citrate.

Dissolved urate salts out calcium oxalate in undiluted human urine in vitro: implications for calcium oxalate stone genesis

Hyperuricosuria has long been documented as a predisposing factor to calcium oxalate (CaOx) stone pathogenesis. However, its mechanism is still without sound scientific foundation. Previously, we showed that hyperuricosuria, simulated by the addition of dissolved sodium urate, promotes the crystallization of CaOx. In the present study, we demonstrate that the urate's effect on the crystallization is attributable to its salting out CaOx from solution. Furthermore, analysis of urines revealed that their metastable limit decreased with increases in the product of the prevailing concentrations of calcium and urate: this has implications for CaOx stone genesis. We also outline anti-salting out strategies for future research for the prevention and/or treatment of CaOx calculi.

Medical evaluation of nephrolithiasis

A careful and individualized evaluation of risk factors is a fundamental part of the management of patients with urinary tract stone disease. Identification and correction of important abnormalities provide the basis for designing an efficient and rational treatment program, aiming at an arrest or at least reduction of recurrent stone formation. It is beyond doubt that appropriate therapeutic steps in this regard are of great benefit for the patient. It needs to be emphasized, however, that no success will be obtained unless the patient is willing and able to follow the ensuing dietary recommendations and medical advice.

Simple classification of renal calculi closely related to their micromorphology and etiology

BACKGROUND

Classification of renal calculi with clear correlation with the main urinary etiological conditions has been previously established. However, such information is complex and difficult to adapt to clinical routine practice.

METHODS

A simple classification of renal calculi based on their structure and composition is proposed and applied to 2500 renal calculi to achieve the percentage of each category. The urines of 700 individuals chosen randomly have been analyzed and the results compared with those obtained with 51 healthy subjects.

RESULTS

12.9% calculi corresponded to calcium oxalate monohydrate papillary calculi, 16.4% to calcium oxalate monohydrate unattached calculi, 33.8% to calcium oxalate dihydrate calculi, 11.2% calcium oxalate dihydrate/hydroxyapatite mixed calculi, 7.1% hydroxyapatite calculi, 4.1% struvite calculi, 0.6% brushite calculi, 8.2% uric acid calculi, 2.6% calcium oxalate/uric acid mixed calculi, 1.1% cystine calculi and 1.9% various infrequent calculi. Based on the corresponding urinary analytical studies, each kind of calculus is related with the more frequently associated urinary alterations.

CONCLUSIONS

An important aspect of this classification is the possibility to establish, by means of the correct study of the calculus, some of the main possible etiologic factors closely related to its formation.

Intracrystalline proteins and the hidden ultrastructure of calcium oxalate urinary crystals: implications for kidney stone formation

The external appearance of urinary calcium oxalate (CaOx) crystals suggests that they are solid, homogeneous structures, despite their known association with proteins. Our aim was to determine whether proteins comprising the organic matrix of CaOx crystals are superficial or intracrystalline in order to clarify the role of urinary proteins in the formation of kidney stones. CaOx crystals were precipitated from centrifuged and filtered, or ultrafiltered, healthy human urine. They were then treated with dilute NaOH to remove bound proteins, partially demineralized with EDTA, or fractured and subjected to limited proteolysis before examination by low-resolution scanning electron microscopy or field emission scanning electron microscopy. Crystals precipitated from centrifuged and filtered urine had a complex interior network of protein distributed throughout the mineral phase, which appeared to comprise closely packed subcrystalline particles stacked in an orderly array among an amorphous organic matrix. This ultrastructure was not evident in crystals deposited in the absence of macromolecules, which were completely solid. This is the first direct evidence that crystals generated from cell-free systems contain significant amounts of protein distributed throughout a complex internal cribriform ultrastructure. Combined with mineral erosion in the acidic lysosomal environment, proteins inside CaOx crystals would render them susceptible to attack by urinary and intracellular renal proteases and facilitate their further dissolution or disruption into small particles and ions for removal by exocytosis. The findings also have broader ramifications for industry and the materials sciences, as well as the development and resorption of crystals in biomineralization systems throughout nature.