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

Declaration: Novel SLC3A1 mutation in a cystinuria patient with xanthine stones: a case report

BACKGROUND

Cystinuria and xanthinuria are both rare genetic diseases involving urinary calculi. However, cases combining these two disorders have not yet been reported.

CASE PRESENTATION

In this study, we report a case of cystinuria with xanthine stones and hyperuricemia. The 23-year-old male patient was diagnosed with kidney and ureteral stones, solitary functioning kidney and hyperuricemia after admission to the hospital. The stones were removed by surgery and found to be composed of xanthine.

CONCLUSION

Genetic testing by next-generation sequencing technology showed that the patient carried the homozygous nonsense mutation c.1113 C> A (p.Tyr371*) in the SLC3A1 gene, which was judged to be a functionally pathogenic variant. Sanger sequencing revealed that the patient's parents carried this heterozygous mutation, which is a pathogenic variant that can cause cystinuria. The 24-h urine metabolism analysis showed that the cystine content was 644 mg (<320 mg/24 h), indicating that the patient had cystinuria, consistent with the genetic test results. This case shows that cystinuria and xanthine stones can occur simultaneously, and provides evidence of a possible connection between the two conditions. Furthermore, our findings demonstrate the potential value of genetic testing using next-generation sequencing to effectively assist in the clinical diagnosis and treatment of patients with urinary calculi.

The ABCG2 rs2231142 polymorphism and the risk of nephrolithiasis: A case-control study from the Taiwan biobank

BACKGROUND

Hyperuricemia and gout are risk factors of nephrolithiasis. However, it is unclear whether the ABCG2 gene contributes to the development of nephrolithiasis. We aimed to investigate the interaction between the ABCG2 rs2231142 variant and incident nephrolithiasis in the Taiwanese population.

METHODS

A total of 120,267 adults aged 30-70 years were enrolled from the Taiwan Biobank data-base in this retrospective case-control study and genotyped for rs2231142. The primary outcome was the prevalence of self-reported nephrolithiasis. The odds ratio (OR) of incident nephrolithiasis was analyzed by multivariable logistic regression models with adjustment for multifactorial confounding factors. Associations of the ABCG2 rs2231142 variant with serum uric acid levels, and the incident nephrolithiasis were explored.

RESULTS

The frequency of rs2231142 T allele was 53%, and 8,410 participants had nephrolithiasis. The multivariable-adjusted OR (95% confidence interval) of nephrolithiasis was 1.18 (1.09-1.28) and 1.12 (1.06-1.18) for TT and GT genotypes, respectively, compared with the GG genotype (p<0.001), specifically in the male population with hyperuricemia. Higher age, male sex, hyperlipidemia, hypertension, diabetes mellitus, hyperuricemia, smoking and overweight were independent risk factors for nephrolithiasis. In contrast, regular physical exercise is a protective factor against nephrolithiasis.

CONCLUSIONS

ABCG2 genetic variation is a significant risk of nephrolithiasis, independent of serum uric acid levels. For rs2231142 T allele carriers, our result provides evidence for precision healthcare to tackle hyperuricemia, comorbidities, smoking, and overweight, and recommend regular physical exercise for the prevention of nephrolithiasis.

Update on Uric Acid and the Kidney

PURPOSE OF REVIEW

In this review, we report on new findings regarding associations of uric acid with kidney health. We discuss kidney stones, effects of uric acid in chronic kidney disease (CKD), and management of gout in CKD. Recent studies on neuroprotective effects of raising uric acid provide interesting data regarding nephrolithiasis.

RECENT FINDINGS

Elevated urate levels have been implicated in the progression of chronic kidney disease (CKD), but the results from PERL and CKD-FIX studies did not demonstrate that allopurinol slowed CKD progression. The SURE-PD3 sought to determine if increasing uric acid would slow the progression of Parkinson's disease. Results ultimately did not support this hypothesis, but high urinary uric acid levels caused uric acid stones, not calcium stones. Low urinary pH remains the key to the formation of uric acid stones. Thiazolidinediones improve insulin resistance, which is associated with an increase in urine pH. The most recent research has not supported the hypothesis that lowering serum uric acid levels will slow the progression of CKD or provide neuroprotection in Parkinson's disease. It is still unclear as to why uric acid stone formers have a high net acid excretion. The STOP-GOUT trial demonstrates that there was a lack of significant adverse events with higher urate-lowering dosages of allopurinol and febuxostat, despite patients' kidney function. This may push other studies to administer higher dosages per ACR guidelines. Future studies could then demonstrate decreased progression of CKD.

Numerical characterization of astronaut CaOx renal stone incidence rates to quantify in-flight and post-flight relative risk

Changes in urine chemistry potentially alter the risk of renal stone formation in astronauts. Quantifying spaceflight renal stone incidence risk compared to pre-flight levels remains a significant challenge for assessing the appropriate vehicle, mission, and countermeasure design. A computational biochemistry model representing CaOx crystal precipitation, growth, and agglomeration is combined with a probabilistic analysis to predict the in- and post-flight CaOx renal stone incidence risk ratio (IRR) relative to pre-flight values using 1517 astronaut 24-h urine chemistries. Our simulations predict that in-flight fluid intake alone would need to increase from current prescriptions of 2.0–2.5 L/day to ~3.2 L/day to approach the CaOx IRR of the pre-flight population. Bone protective interventions would reduce CaOx risk to pre-flight levels if Ca excretion alone is reduced to <150 mg/day or if current levels are diminished to 190 mg/day in combination with increasing fluid intake to 2.5–2.7 L/day. This analysis provides a quantitative risk assessment that can influence the critical balance between engineering and astronaut health requirements.

Purification of quantum dot-based bioprobes with a salting out strategy

A salting out strategy is reported for purification of IgG-conjugated QD (IgG-QD) bioprobes. Adding NaCl can precipitate free IgG selectively, while the IgG-QD maintains good colloidal stability. The dynamic light scattering technique reveals that this is due to the relatively positive zeta potential of free IgG than that of the IgG-QD.

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.

Effects of high-dose uric acid on cellular proteome, intracellular ATP, tissue repairing capability and calcium oxalate crystal-binding capability of renal tubular cells: Implications to hyperuricosuria-induced kidney stone disease

Hyperuricosuria is associated with kidney stone disease, especially uric acid (UA) and calcium oxalate (CaOx) types. Nevertheless, detailed mechanisms of hyperuricosuria-induced kidney stone formation remained unclear. This study examined changes in cellular proteome and function of renal tubular cells after treatment with high-dose UA for 48-h. Quantitative proteomics using 2-DE followed by nanoLC-ESI-ETD MS/MS tandem mass spectrometry revealed significant changes in levels of 22 proteins in the UA-treated cells. These proteomic data could be confirmed by Western blotting. Functional assays revealed an increase in intracellular ATP level and enhancement of tissue repairing capability in the UA-treated cells. Interestingly, levels of HSP70 and HSP90 (the known receptors for CaOx crystals) were increased in apical membranes of the UA-treated cells. CaOx crystal-cell adhesion assay revealed significant increase in CaOx-binding capability of the UA-treated cells, whereas neutralization of the surface HSP70 and/or HSP90 using their specific monoclonal antibodies caused significant reduction in such binding capability. These findings highlighted changes in renal tubular cells in response to high-dose UA that may, at least in part, explain the pathogenic mechanisms of hyperuricosuria-induced mixed kidney stone disease.

Cystolitholapaxy and laparoscopic sacrocolpopexy in a case of multiple urinary bladder calculi & vault prolapse

Vesical calculi are more common in men than women. The prevalence in women is less than 2%. Multiple vesical calculi in chronic cases of utero vaginal prolapse or vault prolapse is rare. Urinary stasis, urethral kinking along with chronic infection are the probable predisposing factors for stone formation [2]. We report a case of 65 year old female, with mass per vagina since 10 years, who developed acute urinary retention due to impaction of vesical calculus at the external urethra meatus. Subsequently in a span of 12 h she passed 3 more vesical calculi. KUB X-ray failed to show any calculi but Computed Tomography(CT) Kidney Ureter Bladder (KUB) showed 2 vesical calculi. After cystolitholapaxy she underwent laparoscopic sacrocolpopexy for vault prolapse. In cases of chronic uterovaginal prolapse or vault prolapse X-Ray KUB should not miss the prolapsed part of the cystocele as calculi are present in the most redundant part. Chances of missing radiolucent uric acid calculi is high. In such cases CT KUB is essential.

Dose-response relationship between higher serum calcium level and higher prevalence of hyperuricemia: A cross-sectional study

The aim of the study was to examine the relationship between serum calcium (Ca) levels and the prevalence of hyperuricemia (HU).The data included in this analysis were extracted from a population-based study conducted at the Xiangya Hospital Health Management Centre. Serum Ca levels were measured using the Arsenazo III method. HU was defined as the uric acid ≥416 μmol/L for male subjects, and ≥360 μmol/L for female subjects. The association between serum Ca levels and the prevalence of HU was evaluated using logistic and spline regression.The present study included a total of 6337 subjects. The overall prevalence of HU for the target population was 17.5%. Compared with the lowest quintile, the odds ratios adjusted by age, sex, body mass index, smoking, and drinking for HU were 1.51 [95% confidence interval (CI): 1.20-1.91], 1.43 (95% CI: 1.13-1.82), 2.02 (95% CI: 1.61-2.54), and 2.54 (95% CI: 2.02-3.18) for the second, third, fourth, and fifth quintiles of serum Ca levels, respectively (P for trend <.001), and a positive dose-response relationship was observed. Similar results were observed for men and women, respectively. The findings were not materially altered by the adjustment for further potential confounders.Subjects with higher serum Ca levels are subject to a higher prevalence of HU in a dose-response relationship manner.

Development of Nephrolithiasis in Asymptomatic Hyperuricemia: A Cohort Study

BACKGROUND

Although the association between gout and nephrolithiasis is well known, the relationship between asymptomatic hyperuricemia and the development of nephrolithiasis is largely unknown.

STUDY DESIGN

Cohort study.

SETTING & PARTICIPANTS

239,331 Korean adults who underwent a health checkup examination during January 2002 to December 2014 and were followed up annually or biennially through December 2014.

PREDICTOR

Baseline serum uric acid levels of participants.

OUTCOME

The development of nephrolithiasis during follow-up.

MEASUREMENTS

Nephrolithiasis is determined based on ultrasonographic findings. A parametric Cox model was used to estimate the adjusted HRs of nephrolithiasis according to serum uric acid level.

RESULTS

During 1,184,653.8 person-years of follow-up, 18,777 participants developed nephrolithiasis (incidence rate, 1.6/100 person-years). Elevated uric acid level was significantly associated with increased risk for nephrolithiasis in a dose-response manner (P for trend < 0.001) in men. This dose-response association was not observed in women. In male participants, multivariable-adjusted HRs for incident nephrolithiasis comparing uric acid levels of 6.0 to 6.9, 7.0 to 7.9, 8.0 to 8.9, 9.0 to 9.9, and ≥10.0mg/dL with uric acid levels < 6.0mg/dL were 1.06 (95% CI, 1.02-1.11), 1.11 (95% CI, 1.05-1.16), 1.21 (95% CI, 1.13-1.29), 1.31 (95% CI, 1.17-1.46), and 1.72 (95% CI, 1.44-2.06), respectively. This association was observed in all clinically relevant subgroups and persisted even after adjustment for homeostasis model assessment of insulin resistance and high-sensitivity C-reactive protein level.

LIMITATIONS

Dietary information and computed tomographic diagnosis of nephrolithiasis were unavailable.

CONCLUSIONS

In this large cohort study, increased serum uric acid level was modestly and independently associated with increased risk for the development of nephrolithiasis in a dose-response manner in apparently healthy men.

Association Study of Reported Significant Loci at 5q35.3, 7p14.3, 13q14.1 and 16p12.3 with Urolithiasis in Chinese Han Ethnicity

In this study, we aimed to validate the association of 8 reported significant loci at 5q35.3, 7p14.3, 13q14.1 and 16p12.3 with urolithiasis in Chinese Han population. We performed case-control association analysis using 624 patients with nephrolithiasis and 1008 control subjects. We selected single-nucleotide polymorphism (SNPs) including rs12654812 and rs11746443 from 5q32.3; rs12669187 and rs1000597 from 7q14.3; rs7981733, rs4142110 and rs17646069 from 13q14.1 and rs4293393 from 16p12.3 which were previously reported to be associated with nephrolithiasis. We found none of these eight reported SNPs were significant associated with urolithiasis risk in Chinese Han population, which suggested that differences could exist in the mechanisms of calcium urolithiasis between Chinese and Japanese Ethnics. The A allele of rs12669187 was significantly correlated with increased level of serum magnesium. The C allele of rs1000597 was associated with higher levels of serum creatinine, uric acid, calcium and lower urine pH level. The T allele of rs4142110 was correlated with higher levels of serum magnesium, phosphorus, and lower AKP level. The G alleles of rs4293393 was associated with higher serum CO₂ level. The risk alleles of these SNPs were proved to be associated with the electrolytes metabolism that may result in the formation of urolithiasis.

Metabolic diagnosis and medical prevention of calcium nephrolithiasis and its systemic manifestations: a consensus statement

BACKGROUND

Recently published guidelines on the medical management of renal stone disease did not address relevant topics in the field of idiopathic calcium nephrolithiasis, which are important also for clinical research.

DESIGN

A steering committee identified 27 questions, which were proposed to a faculty of 44 experts in nephrolithiasis and allied fields. A systematic review of the literature was conducted and 5216 potentially relevant articles were selected; from these, 407 articles were deemed to provide useful scientific information. The Faculty, divided into working groups, analysed the relevant literature. Preliminary statements developed by each group were exhaustively discussed in plenary sessions and approved.

RESULTS

Statements were developed to inform clinicians on the identification of secondary forms of calcium nephrolithiasis and systemic complications; on the definition of idiopathic calcium nephrolithiasis; on the use of urinary tests of crystallization and of surgical observations during stone treatment in the management of these patients; on the identification of patients warranting preventive measures; on the role of fluid and nutritional measures and of drugs to prevent recurrent episodes of stones; and finally, on the cooperation between the urologist and nephrologist in the renal stone patients.

CONCLUSIONS

This document has addressed idiopathic calcium nephrolithiasis from the perspective of a disease that can associate with systemic disorders, emphasizing the interplay needed between urologists and nephrologists. It is complementary to the American Urological Association and European Association of Urology guidelines. Future areas for research are identified.

Hyperuricemia, the kidneys, and the spectrum of associated diseases: a narrative review

Hyperuricemia (elevated serum uric acid) is prevalent, and an important mediator of gout, an increasingly common condition. In addition, hyperuricemia is associated with metabolic syndrome, diabetes, hypertension, and kidney and cardiovascular diseases. Although it remains controversial whether hyperuricemia is a causal factor for kidney disease, the kidneys play a major role in the regulation of serum uric acid levels. Approximately two-thirds of the uric acid produced in humans is excreted by the kidneys. The handling of urate in the renal proximal tubule is extensive, as uric acid undergoes filtration, reabsorption, and secretion. Variations in renal urate handling have been shown to influence the risk of gout. In observational studies, hyperuricemia has been shown to predict kidney disease onset and progression, with a variety of mechanisms implicated. Because of this close association between hyperuricemia and kidney disease, and due to limited studies on the topic, it is important to conduct future studies on the treatment of hyperuricemia to slow kidney disease progression and improve cardiovascular survival in patients with chronic kidney disease. Furthermore, it is important to monitor for gout in patients with kidney disease and to follow the guidelines for treatment of hyperuricemia in this group of patients. This narrative review provides an in-depth discussion of the link between serum uric acid levels, renal handling of uric acid, and diseases associated with dysfunction in uric acid homeostasis.

The crystallization of monosodium urate

Gout is a common crystal-induced arthritis, in which monosodium urate (MSU) crystals precipitate within joints and soft tissues and elicit an inflammatory response. The causes of elevated serum urate and the inflammatory pathways activated by MSU crystals have been well studied, but less is known about the processes leading to crystal formation and growth. Uric acid, the final product of purine metabolism, is a weak acid that circulates as the deprotonated urate anion under physiologic conditions, and combines with sodium ions to form MSU. MSU crystals are known to have a triclinic structure, in which stacked sheets of purine rings form the needle-shaped crystals that are observed microscopically. Exposed, charged crystal surfaces are thought to allow for interaction with phospholipid membranes and serum factors, playing a role in the crystal-mediated inflammatory response. While hyperuricemia is a clear risk factor for gout, local factors have been hypothesized to play a role in crystal formation, such as temperature, pH, mechanical stress, cartilage components, and other synovial and serum factors. Interestingly, several studies suggest that MSU crystals may drive the generation of crystal-specific antibodies that facilitate future MSU crystallization. Here, we review MSU crystal biology, including a discussion of crystal structure, effector function, and factors thought to play a role in crystal formation. We also briefly compare MSU biology to that of uric acid stones causing nephrolithasis, and consider the potential treatment implications of MSU crystal biology.

Comparison of the metabolic profile of mixed calcium oxalate/uric acid stone formers to that of pure calcium oxalate and pure uric acid stone formers

OBJECTIVE

To compare the metabolic profile of patients who form mixed calcium oxalate (CaOx)/uric acid (UA) stones to those of pure CaOx and pure UA stone formers.

METHODS

We performed a retrospective review of 232 patients, with both stone composition analysis and 24-hour urine collection, seen between March 2002 and April 2012. Analysis of 24-hour urine constituents across the 3 stone groups (pure UA, pure CaOx, and mixed CaOx/UA) was performed using univariate analysis of variance and multivariate linear regression models adjusting for clinical and demographic factors and 24-hour urine collection elements.

RESULTS

A total of 27 patients (11.6%) had mixed CaOx/UA, 122 (52.6%) had pure CaOx, and 83 (35.8%) had pure UA calculi. Univariate analysis demonstrated significant differences between mixed CaOx/UA patients and pure CaOx patients for urine pH (mixed, 5.63 ± 0.49 vs pure, CaOx 5.93 ± 0.51; P = .009) and supersaturation (SS) UA (mixed, 1.84 ± 1.09 vs pure, CaOx 1.26 ± 0.93; P = .01), and a significant difference between mixed CaOx/UA patients and pure UA patients for SS CaOx (mixed, 7.18 ± 4.23 vs pure, UA 4.90 ± 2.96; P = .005). Multivariate analysis demonstrated that mixed CaOx/UA patients had no significant difference in SS CaOx as compared with pure CaOx patients (difference, -0.27; P = .66), whereas at the same time had no significant difference in SS UA as compared with pure UA patients (-0.07; P = .69).

CONCLUSION

The metabolic profile of patients who form mixed CaOx/UA stones demonstrates abnormalities that promote both CaOx and UA stone formation. Dietary and medical management for this group of patients should address treatment of both defects.

Treatment of calcium nephrolithiasis in the patient with hyperuricosuria

Nearly one-third of patients with calcium stones have hyperuricosuria. In vitro studies and clinical trials have investigated the relationship between uric acid and calcium stones, but the association between hyperuricosuria and calcium stone formation in patients is still being debated. Uric acid appears to cause salting out of calcium oxalate in human urine. However, the importance of this in vitro phenomenon to the proposed association is not supported in cross-sectional observational studies. A small placebo-controlled randomized clinical trial showed that allopurinol decreased the rate of recurrent calcium oxalate calculi in patients with hyperuricosuria and normocalciuria. An assessment of the effect of combination therapy of allopurinol with indapamide showed no additive effect. Allopurinol may have antioxidant effects that are responsible for its reducing calcium stone formation, which are independent of xanthine oxidase inhibition. In addition, a newer xanthine oxidoreductase inhibitor, febuxostat, may also be effective in the prevention of calcium stones, as it reduces urinary uric acid excretion.

Effect of magnesium on calcium and oxalate ion binding

BACKGROUND AND PURPOSE

Magnesium (Mg(2+)) has been shown to be a kidney stone inhibitor; however, the exact mechanism of its effect is unknown. Using theoretical models, the interactions of calcium and oxalate were examined in the presence of Mg(2+).

METHODS

Molecular dynamics simulations were performed with NAMD and CHARMM27 force field. The interaction between calcium (Ca(2+)) and oxalate (Ox(2-)) ions was examined with and without magnesium. Concentrations of calcium and oxalate were 0.1 M and 0.03 M, respectively, and placed in a cubic box of length ~115 Angstrom. Na(+) and Cl(-) ions were inserted to meet system electroneutrality. Mg(2+) was then placed into the box at physiologic concentrations and the interaction between calcium and oxalate was observed. In addition, the effect of citrate and pH were examined in regard to the effect of Mg(2+) inhibition. Each system was allowed to run until a stable crystalline structure was formed.

RESULTS

The presence of Mg(2+) reduces the average size of the calcium oxalate and calcium phosphate aggregates. This effect is found to be Mg(2+) concentration-dependent. It is also found that Mg(2+) inhibition is synergistic with citrate and continues to be effective at acidic pH levels.

CONCLUSION

The presence of magnesium ions tends to destabilize calcium oxalate ion pairs and reduce the size of their aggregates. Mg(2+) inhibitory effect is synergistic with citrate and remains effective in acidic environments. Further studies are needed to see if this can be applied to in vivo models as well as extending this to other stone inhibitors and promoters.

Randomized controlled trial of febuxostat versus allopurinol or placebo in individuals with higher urinary uric acid excretion and calcium stones

BACKGROUND AND OBJECTIVES

Higher urinary uric acid excretion is a suspected risk factor for calcium oxalate stone formation. Febuxostat, a xanthine oxidoreductase inhibitor, is effective in lowering serum urate concentration and urinary uric acid excretion in healthy volunteers and people with gout. This work studied whether febuxostat, compared with allopurinol and placebo, would reduce 24-hour urinary uric acid excretion and prevent stone growth or new stone formation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this 6-month, double-blind, multicenter, randomized controlled trial, hyperuricosuric participants with a recent history of calcium stones and one or more radio-opaque calcium stone ≥ 3 mm (as seen by multidetector computed tomography) received daily febuxostat at 80 mg, allopurinol at 300 mg, or placebo. The primary end point was percent change from baseline to month 6 in 24-hour urinary uric acid. Secondary end points included percent change from baseline to month 6 in size of index stone and change from baseline in the mean number of stones and 24-hour creatinine clearance.

RESULTS

Of 99 enrolled participants, 86 participants completed the study. Febuxostat led to significantly greater reduction in 24-hour urinary uric acid (-58.6%) than either allopurinol (-36.4%; P=0.003) or placebo (-12.7%; P<0.001). Percent change from baseline in the size of the largest calcium stone was not different with febuxostat compared with allopurinol or placebo. There was no change in stone size, stone number, or renal function. No new safety concerns were noted for either drug.

CONCLUSIONS

Febuxostat (80 mg) lowered 24-hour urinary uric acid significantly more than allopurinol (300 mg) in stone formers with higher urinary uric acid excretion after 6 months of treatment. There was no change in stone size or number over the 6-month period.

Pathogenesis of bladder calculi in the presence of urinary stasis

PURPOSE

Although minimal evidence exists, bladder calculi in men with benign prostatic hyperplasia are thought to be secondary to bladder outlet obstruction induced urinary stasis. We performed a prospective, multi-institutional clinical trial to determine whether metabolic differences were present in men with and without bladder calculi undergoing surgical intervention for benign prostatic hyperplasia induced bladder outlet obstruction.

MATERIALS AND METHODS

Men who elected surgery for bladder outlet obstruction secondary to benign prostatic hyperplasia with and without bladder calculi were assessed prospectively and compared. Men without bladder calculi retained more than 150 ml urine post-void residual urine. Medical history, serum electrolytes and 24-hour urinary metabolic studies were compared.

RESULTS

Of the men 27 had bladder calculi and 30 did not. Bladder calculi were associated with previous renal stone disease in 36.7% of patients (11 of 30) vs 4% (2 of 27) and gout was associated in 13.3% (4 of 30) vs 0% (0 of 27) (p <0.01 and 0.05, respectively). There was no observed difference in the history of other medical conditions or in serum electrolytes. Bladder calculi were associated with lower 24-hour urinary pH (median 5.9 vs 6.4, p = 0.02), lower 24-hour urinary magnesium (median 106 vs 167 mmol, p = 0.01) and increased 24-hour urinary uric acid supersaturation (median 2.2 vs 0.6, p <0.01).

CONCLUSIONS

In this comparative prospective analysis patients with bladder outlet obstruction and benign prostatic hyperplasia with bladder calculi were more likely to have a renal stone disease history, low urinary pH, low urinary magnesium and increased urinary uric acid supersaturation. These findings suggest that, like the pathogenesis of nephrolithiasis, the pathogenesis of bladder calculi is likely complex with multiple contributing lithogenic factors, including metabolic abnormalities and not just urinary stasis.

Urine risk factors in children with calcium kidney stones and their siblings

Calcium nephrolithiasis in children is increasing in prevalence and tends to be recurrent. Although children have a lower incidence of nephrolithiasis than adults, its etiology in children is less well understood; hence, treatments targeted for adults may not be optimal in children. To better understand metabolic abnormalities in stone-forming children, we compared chemical measurements and the crystallization properties of 24-h urine collections from 129 stone formers matched to 105 non-stone-forming siblings and 183 normal, healthy children with no family history of stones, all aged 6 to 17 years. The principal risk factor for calcium stone formation was hypercalciuria. Stone formers have strikingly higher calcium excretion along with high supersaturation for calcium oxalate and calcium phosphate, and a reduced distance between the upper limit of metastability and supersaturation for calcium phosphate, indicating increased risk of calcium phosphate crystallization. Other differences in urine chemistry that exist between adult stone formers and normal individuals such as hyperoxaluria, hypocitraturia, abnormal urine pH, and low urine volume were not found in these children. Hence, hypercalciuria and a reduction in the gap between calcium phosphate upper limit of metastability and supersaturation are crucial determinants of stone risk. This highlights the importance of managing hypercalciuria in children with calcium stones.

Potential pharmacologic treatments for cystinuria and for calcium stones associated with hyperuricosuria

Two new potential pharmacologic therapies for recurrent stone disease are described. The role of hyperuricosuria in promoting calcium stones is controversial with only some but not all epidemiologic studies demonstrating associations between increasing urinary uric acid excretion and calcium stone disease. The relationship is supported by the ability of uric acid to "salt out" (or reduce the solubility of) calcium oxalate in vitro. A randomized, controlled trial of allopurinol in patients with hyperuricosuria and normocalciuria was also effective in preventing recurrent stones. Febuxostat, a nonpurine inhibitor of xanthine oxidase (also known as xanthine dehydrogenase or xanthine oxidoreductase) may have advantages over allopurinol and is being tested in a similar protocol, with the eventual goal of determining whether urate-lowering therapy prevents recurrent calcium stones. Treatments for cystinuria have advanced little in the past 30 years. Atomic force microscopy has been used recently to demonstrate that effective inhibition of cystine crystal growth is accomplished at low concentrations of l-cystine methyl ester and l-cystine dimethyl ester, structural analogs of cystine that provide steric inhibition of crystal growth. In vitro, l-cystine dimethyl ester had a significant inhibitory effect on crystal growth. The drug's safety and effectiveness will be tested in an Slc3a1 knockout mouse that serves as an animal model of cystinuria.

Management of Cystinuria

Cystinuria is a monogenic disorder in which there is a transepithelial transport defect of di-basic amino acids, including cystine, ornithine, lysine, and arginine (COLA). This results in diminished reabsorption of these amino acids in both the intestine and renal proximal tubule. This article describes the disorder, reviews the mechanisms of normal COLA renal transport, and summarizes issues related to the disorder, such as the role of mutations, associated diseases, clinical manifestations, therapies, the renal impact, and handling of pediatric patients.

Pathophysiology and Management of Calcium Stones

Nephrolithiasis is a common disorder that accounts for significant cost, morbidity, and loss of work. There is a one in eight lifetime chance of being diagnosed with urinary stones. Calcium is the most common component of renal stones in individuals in industrialized nations. Calcium stones form as a result of a variety of environmental and metabolic abnormalities that change the urinary environment and increase supersaturation of stone-forming salts. Understanding the pathophysiology of stone disease can help direct treatment toward correction of the underlying abnormalities. Current medical and dietary therapeutic regimens have been shown to significantly reduce the risk of recurrent stone formation.

Uric acid as inducer of calcium oxalate crystal development

OBJECTIVE

This paper deals with the mechanism by which uric acid affects calcium oxalate crystallization and the role of crystallization inhibitors in this process.

MATERIAL AND METHODS

Pure uric acid crystals and fragments of uric acid renal calculi were used to induce calcium oxalate crystal formation and development. These studies were performed in flow systems, using synthetic urine and similar conditions to those found in real renal situations. The type and size of the developed crystals were evaluated by scanning electron microscopy and the amount of calcium oxalate crystallized was quantitated by means of inductively coupled plasma atomic emission spectroscopy.

RESULTS

The presence of uric acid crystals in a flow system provoked calcium oxalate monohydrate (COM) crystallization at a rate of 3.3 microg/h/mg uric acid. When uric acid renal calculi fragments were used, the amount of COM crystallized varied between 0.048 and 0.161 microg/h/mg of renal calculi depending on the porosity of the calculus. At particular concentrations (3.03 microM phytate, 28.75 microM pyrophosphate, 40 mg/l chondroitin sulphate) the crystallization inhibitors assayed produced a maximum decrease of approximately 50% in the amount of COM crystallized on uric acid crystals. Mucin (a glycoprotein) caused only slight effects.

CONCLUSION

Uric acid crystals can clearly induce the development of COM crystals on them through a heterogeneous nucleation process and some crystallization inhibitors can notably delay such a process.

Epitaxial deposition of calcium oxalate on uric acid rich stone matrix is induced by a 29 kDa protein

BACKGROUND

Association of macromolecules particularly the role of proteins in urolithiasis has been studied for last few centuries, but still a complete profile of stone matrix proteins that mediate co-precipitation of uric acid and calcium oxalate has not been characterized. We isolated and characterize proteins from uric acid rich stone matrix, which have oxalate binding activity.

METHODS

Matrix proteins were isolated from uric acid rich stone matrix using EDTA as a demineralizing agent. The radiolabelled solubilized proteins were fractionated with increasing ionic concentration by DEAE cellulose column chromatography to identify the oxalate binding protein. It was purified using Sephadex G-200 column chromatography. Amino acid composition was determined and monoclonal antibody was produced against the oxalate binding uric acid rich stone matrix protein. Urinary uric acid binding proteins were isolated from stone formers urine, their oxalate binding activity assayed and cross reactivity with the produced monoclonal antibody were checked using ELISA and Western blotting.

RESULTS

Matrix on DEAE column chromatography elution yielded 3 protein peaks and they were named as fraction I, II and III among which fraction I had higher oxalate binding activity which was further purified with Sephadex G-200 column which yielded 2 protein peaks designated as Ia and Ib. Fraction Ib with molecular weight 29 kDa exhibited the maximum oxalate binding activity. Forty percent of this 29 kDa protein is comprised of basic amino acids. Monoclonal antibody (IgG1) was produced against the 29 kDa stone matrix protein. Urinary uric acid binding proteins were isolated from stone formers, 4 protein peaks were obtained named as fraction I to IV. Among them, fraction IV having molecular weight of approximately 29 kDa cross reacted up to 85.6% with 29 kDa stone matrix protein. Moreover, urinary 29 kDa protein exhibited oxalate binding activity of 94.16 +/- 6.08 pmol/mg protein at pH 5.5.

CONCLUSION

The 29 kDa protein isolated from uric acid rich stone matrix and urine are one and the same, thereby insinuating that 29 kDa protein might play a major role in epitaxial deposition of calcium oxalate over uric acid core, consequently favoring the lithogenic events like uric acid and calcium oxalate nucleation, aggregation and retention.

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.