Relationship between supersaturation and calcium oxalate crystallization in normals and idiopathic calcium oxalate stone formers

2022 Recommendations of the AFU Lithiasis Committee: Medical management - from diagnosis to treatment

The morphological-compositional analysis of urinary stones allows distinguishing schematically several situations: dietary, digestive, metabolic/hormonal, infectious and genetic problems. Blood and urine testing are recommended in the first instance to identify risk factors of urinary stone disease in order to avoid recurrence or progression. The other objective is to detect a potential underlying pathology associated with high risk of urinary stone disease (e.g. primary hyperparathyroidism, primary or enteric hyperoxaluria, cystinuria, distal renal tubular acidosis) that may require specific management. Lifestyle-diet measures are the basis of the management of all stone types, but pharmacological treatments may be required. METHODOLOGY: These recommendations were developed using two methods: the Clinical Practice Recommendation (CPR) method and the ADAPTE method, depending on whether the question was considered in the European Association of Urology (EAU) recommendations (https://uroweb.org/guidelines/urolithiasis) [EAU 2022] and their adaptability to the French context.

Oxalate disrupts monocyte and macrophage cellular function via Interleukin-10 and mitochondrial reactive oxygen species (ROS) signaling

Oxalate is a small compound found in certain plant-derived foods and is a major component of calcium oxalate (CaOx) kidney stones. Individuals that consume oxalate enriched meals have an increased risk of forming urinary crystals, which are precursors to CaOx kidney stones. We previously reported that a single dietary oxalate load induces nanocrystalluria and reduces monocyte cellular bioenergetics in healthy adults. The purpose of this study was to extend these investigations to identify specific oxalate-mediated mechanisms in monocytes and macrophages. We performed RNA-Sequencing analysis on monocytes isolated from healthy subjects exposed to a high oxalate (8 mmol) dietary load. RNA-sequencing revealed 1,198 genes were altered and Ingenuity Pathway Analysis demonstrated modifications in several pathways including Interleukin-10 (IL-10) anti-inflammatory cytokine signaling, mitochondrial metabolism and function, oxalic acid downstream signaling, and autophagy. Based on these findings, we hypothesized that oxalate induces mitochondrial and lysosomal dysfunction in monocytes and macrophages via IL-10 and reactive oxygen species (ROS) signaling which can be reversed with exogenous IL-10 or Mitoquinone (MitoQ; a mitochondrial targeted antioxidant). We exposed monocytes and macrophages to oxalate in an in-vitro setting which caused oxidative stress, a decline in IL-10 cytokine levels, mitochondrial and lysosomal dysfunction, and impaired autophagy in both cell types. Administration of exogenous IL-10 and MitoQ attenuated these responses. These findings suggest that oxalate impairs metabolism and immune response via IL-10 signaling and mitochondrial ROS generation in both monocytes and macrophages which can be potentially limited or reversed. Future studies will examine the benefits of these therapies on CaOx crystal formation and growth in vivo.

Comparison of two software programs used to determine the relative supersaturation of urine ions

Introduction

Relative supersaturation (RSS) values for urine crystals are a measure of the risk of urinary stone formation and have been shown to be lowered in foods shown to aid in the management of urolithiasis. In order to calculate RSS in pets, computer programs have been developed to calculate RSS and aid in the understanding of stone formation in veterinary medicine. However, some older programs have not been updated for use in animals, and the specific coefficients used are not publically available. One of the first RSS programs was developed in BASIC computer language and published in 1985 which was called EQUIL2. The EQUIL2 program was updated to a compiled version compatible with a PC platform. However, the formulas could not be read or altered.

Methods

This study evaluates a new program with known coefficients to the original EQUIL2 program. The RSS values of the two programs were compared through a t-test, calculating the r² from correlation analysis, Lin's concordance correlation coefficient, and by a Bland-Altman analysis of outputs from the two programs using urine samples from healthy dogs and cats.

Results and Discussion

Our results show that for both magnesium ammonium phosphate (struvite) and calcium oxalate, the RSS values of the original program could be calculated from the new programs RSS values. Although the actual RSS values were different (as might be expected through the use of the updated coefficients and different thermodynamic stability constants in the calculations) the results were highly correlated, finding elevations and reductions in RSS proportionally in the same urine samples. The current work creates a foundation for using the modernized program to calculate RSS and provides a shared method for understanding the risk of struvite and calcium oxalate stone formation.

Effects of lemon-tomato juice consumption on crystal formation in the urine of patients with calcium oxalate stones: A randomized crossover clinical trial

Background

Dietary supplementation with citrate-containing juices may serve as an effective alternative to potassium citrate therapy for preventing calcium oxalate stone recurrence. This study was performed to evaluate whether consumption of lemon-tomato juice can decrease the tendency for stone formation in the urine of calcium oxalate stone formers.

Materials and methods

The study was conducted as a prospective interventional randomized crossover clinical trial with a repeated-measures design. Twenty-two patients with calcium oxalate stones and no metabolic abnormalities in the urine treated with lithotripsy at a tertiary care center from August 2017 to July 2018 were recruited. After a 14-hour overnight fasting, urine samples were collected after the patients consumed either milk only or milk and lemon-tomato juice. Their urine was tested for multiple parameters, including urine pH, specific gravity, calcium-creatinine ratio, and supersaturation with sodium oxalate, followed by optical density measurement via spectrophotometry.

Results

There were no significant differences in the background characteristics between the 2 groups. The optical density of the urine samples obtained after consumption of milk only was significantly higher than that after consumption of milk and lemon-tomato juice (mean = 0.131 for milk only vs. 0.053 for milk and lemon-tomato juice, p < 0.001). The urine calcium-creatinine ratio was similar between the groups (mean = 0.141 for milk only vs. 0.076 for milk and lemon-tomato juice, p = 0.019).

Conclusions

The addition of lemon-tomato juice as a source of citrate in the diet significantly decreases the established risk factors for calcium oxalate stone formation in patients. This study was prospectively registered at CTRI under number CTRI/2017/04/008312 on April 7, 2017.

The role of microbiome: a novel insight into urolithiasis

Urolithiasis, referred to as the formation of stones in the urinary tract, is a common disease with growing prevalence and high recurrence rate worldwide. Although researchers have endeavoured to explore the mechanism of urinary stone formation for novel effective therapeutic and preventative measures, the exact aetiology and pathogenesis remain unclear. Propelled by sequencing technologies and culturomics, great advances have been made in understanding the pivotal contribution of the human microbiome to urolithiasis. Indeed, there are diverse and abundant microbes interacting with the host in the urinary tract, overturning the dogma that urinary system, and urine are sterile. The urinary microbiome of stone formers was clearly distinct from healthy individuals. Besides, dysbiosis of the intestinal microbiome appears to be involved in stone formation through the gut-kidney axis. Thus, the human microbiome has potential significant implications for the aetiology of urolithiasis, providing a novel insight into diagnostic, therapeutic, and prognostic strategies. Herein, we review and summarize the landmark microbiome studies in urolithiasis and identify therapeutic implications, challenges, and future perspectives in this rapidly evolving field. To conclude, a new front has opened with the evidence for a microbial role in stone formation, offering potential applications in the prevention, and treatment of urolithiasis.

The renal pelvis urobiome in the unilateral kidney stone patients revealed by 2bRAD-M

Background

The pathogenesis of kidney stone disease (KSD) is not fully understood, and potential contributing factors remain to be explored. Several studies have revealed that the urinary microbiome (urobiome) of stone formers was distinct from that of healthy individuals using 16S rRNA gene sequencing, most of which only provided microbial identification at the genus level. 2bRAD sequencing for Microbiome (2bRAD-M) is a novel sequencing technique that enables accurate characterization of the low-biomass microbiome at the species resolution. We aimed to apply 2bRAD-M to profile the renal pelvis urobiome of unilateral kidney stone patients and compared the urobiome with and without stone(s).

Method

A total of 30 patients with unilateral stones were recruited, and their renal pelvis urine from both sides was collected. A ureteroscope was inserted into the renal pelvis with stone(s) and a ureteral catheter was placed into the ureteroscope to collect renal pelvis urine. This procedure was repeated again with new devices to collect the urine of the other side. 2bRAD-M was performed to characterize the renal pelvis urobiome of unilateral stone formers to explore whether microbial differences existed between the stone side and the non-stone side.

Results

The microbial community composition of the stone side was similar to that of the non-stone side. Paired comparison showed that Corynebacterium was increased and Prevotella and Lactobacillus were decreased in the stone side. Four species (Prevotella bivia, Lactobacillus iners, Corynebacterium aurimucosum, and Pseudomonas sp_286) were overrepresented in the non-stone side. 24 differential taxa were also identified between two groups by linear discriminant analysis effect size (LEfSe). Extensive and close connections among genera and species were observed in the correlation analysis. Moreover, a random forest classifier was constructed using specific enriched species, which can distinguish the stone side from the non-stone side with an accuracy of 71.2%.

Conclusion

This first 2bRAD-M microbiome survey gave an important hint towards the potential role of urinary dysbiosis in KSD and provided a better understanding of mechanism of stone formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03639-6.

Pathophysiology and Management of Hyperoxaluria and Oxalate Nephropathy: A Review

Hyperoxaluria results from either inherited disorders of glyoxylate metabolism leading to hepatic oxalate overproduction (primary hyperoxaluria), or increased intestinal oxalate absorption (secondary hyperoxaluria). Hyperoxaluria may lead to urinary supersaturation of calcium oxalate and crystal formation, causing urolithiasis and deposition of calcium oxalate crystals in the kidney parenchyma, a condition termed oxalate nephropathy. Considerable progress has been made in the understanding of pathophysiological mechanisms leading to hyperoxaluria and oxalate nephropathy, whose diagnosis is frequently delayed and prognosis too often poor. Fortunately, novel promising targeted therapeutic approaches are on the horizon in patients with primary hyperoxaluria. Patients with secondary hyperoxaluria frequently have long-standing hyperoxaluria-enabling conditions, a fact suggesting the role of triggers of acute kidney injury such as dehydration. Current standard of care in these patients includes management of the underlying cause, high fluid intake, and use of calcium supplements. Overall, prompt recognition of hyperoxaluria and associated oxalate nephropathy is crucial because optimal management may improve outcomes.

Effect of calcium content of diet on crystal formation in urine of patients with calcium oxalate stones: a randomized crossover clinical trial

Background

Patients with idiopathic calcium oxalate stones are advised to consume a low-oxalate diet to prevent recurrence. In this study, on patients with calcium oxalate stones we have attempted to determine the effect of calcium content of diet on the formation of calcium oxalate crystals in urine by in vitro supersaturation study of fresh postprandial urine samples and observing the morphology of the crystals formed using polarized optical microscopy.

Methods

The trial was conducted as a prospective interventional randomised crossover clinical trial in a repeated measures design. Sixty patients with calcium oxalate stones and no metabolic abnormalities in urine treated by lithotripsy at a tertiary care centre during the period May 2016 to May 2019 were recruited. Following a 14 h overnight fasting, urine samples were collected after providing the patient with either a low- or high-calcium meal for breakfast followed four hours later, by high-oxalate meal for lunch. Urine was tested for multiple parameters including urine pH, specific gravity, calcium/creatinine ratio and supersaturation of urine with sodium oxalate followed by optical density measurement by spectrophotometry and microscopic analysis of crystals formed.

Results

Optical density values and calcium/creatinine ratio of urine samples obtained after high-calcium meal are significantly higher than in corresponding sample obtained after low-calcium meal (p < 0.001). These findings were reflected in the morphology of formed crystals in their size, shape and number. When urinary calcium levels were low, no crystals were formed during supersaturation study of postprandial urine samples following a high-oxalate diet.

Conclusions

High calcium content in diet significantly contributes to kidney stone formation. There is a lower risk of kidney stone formation with a low-calcium meal even on consumption of a high-oxalate diet.

Matting Calcium Crystals by Melamine Improves Stabilization and Prevents Dissolution

Melamine induces calcium phosphate (CaP) and calcium oxalate (CaOx) crystal formation; however, the physicochemical mechanism is not clear. Recently, we found that melamine has a discriminatory effect on CaP, CaOx, and CaP + CaOx (Mixed) crystal dissolution. Thus, to delineate the mechanism, we examined crystal interactions through birefringence analysis and found that CaP becomes increasingly birefringent when bound to melamine, while the birefringence of CaOx decreases when it forms CaOx-melamine cocrystals. We also confirmed the feasibility of such melamine-CaP/CaOx co-crystallization at the nanomicromolar range. Interestingly, ammeline, which is a similar triazine, did not accelerate CaP/CaOx/Mixed crystal formation and growth, indicating the specificity of crystal interaction by melamine. Furthermore, melamine stabilizes the CaP/CaOx/Mixed crystals when exposed to a crystal inhibitor (etidronic acid) or dissolution agents (citrate analogues), while it induces crystal growth by increasing crystal retention, suggesting melamine's interference with conventional dissolution remedies. Morphological and elemental analysis of melamine-CaP/CaOx/Mixed co-crystals using scanning electron microscopy further revealed that melamine harbors such crystals by creating a nucleation site. Finally, we confirmed the physiological relevance of melamine exposure using artificial urine to show the induction, stabilization, and retention of mixed crystals in the presence of crystal-inhibitor/dissolution agent and thus established potential causes of recurrence of kidney stones.

The microbiome of calcium-based urinary stones

Historically, the role of bacteria in urinary stone disease (USD) has been limited to urease-producing bacteria associated with struvite stone formation. However, growing evidence has revealed bacteria associated with stones of non-struvite composition. These bacteria may be derived from either urine or from the stones themselves. Using 16S rRNA gene sequencing and an enhanced culture technique (EQUC), we identified the urine and stone microbiota of USD patients and then determined if bacteria were statistically enriched in the stones relative to the urine. From 52 patients, bladder urine and urinary stones were collected intraoperatively during ureteroscopy. Stone homogenate and urine specimens were subjected to 16S rRNA gene sequencing and EQUC. Standard Chi-squared tests were applied to determine if the relative abundance of any bacterial taxon was significantly enriched in urinary stones compared to urine. Stones were primarily calcium-based. 29/52 (55.8%) stones had bacteria detected by 16S rRNA gene sequencing. Of these, dominant bacterial taxa were enriched from 12 stones. Bacterial taxa isolated by EQUC include members of the genera Staphylococcus, Enterobacter, Escherichia, Corynebacterium, and Lactobacillus. Dominant bacterial genera were enriched compared to paired bladder urine. Differences between the stone and urine microbiota may indicate that certain bacteria contribute to USD pathophysiology. Further investigation is warranted.

The Urological Association of Asia clinical guideline for urinary stone disease

The Urological Association of Asia, consisting of 25 member associations and one affiliated member since its foundation in 1990, has planned to develop Asian guidelines for all urological fields. The field of stone diseases is the third of its guideline projects. Because of the different climates, and social, economic and ethnic environments, the clinical practice for urinary stone diseases widely varies among the Asian countries. The committee members of the Urological Association of Asia on the clinical guidelines for urinary stone disease carried out a surveillance study to better understand the diversity of the treatment strategy among different regions and subsequent systematic literature review through PubMed and MEDLINE database between 1966 and 2017. Levels of evidence and grades of recommendation for each management were decided according to the relevant strategy. Each clinical question and answer were thoroughly reviewed and discussed by all committee members and their colleagues, with suggestions from expert representatives of the American Urological Association and European Association of Urology. However, we focused on the pragmatic care of patients and our own evidence throughout Asia, which included recent surgical trends, such as miniaturized percutaneous nephrolithotomy and endoscopic combined intrarenal surgery. This guideline covers all fields of stone diseases, from etiology to recurrence prevention. Here, we present a short summary of the first version of the guideline - consisting 43 clinical questions - and overview its key practical issues.

Water and other fluids in nephrolithiasis: State of the art and future challenges

Adequate hydration, as to maintain urinary volume over 2 L/day, has long been considered as the cornerstone medical prescription for preventing nephrolithiasis. However, scientific evidence about what kind of water stone formers should drink and about the effects of other beverages on urinary stone risk factors is sometimes unclear. Moreover, the recommendation that water therapy prevents kidney stone recurrence relies on only one randomized controlled trial, even if more epidemiologic and basic science studies seem to support this assumption. Therefore, in this review we analyze current evidence that support water therapy in nephrolithiasis and we highlight the possible effects of different types of water and other beverages on lithogenic risk, giving some practical recommendations for what stone formers should be advised to prevent recurrence.

The association between bacteria and urinary stones

Urinary stone disease (USD) is an increasing clinical problem in both children and adults. One in ten individuals will experience a urinary stone, yet the mechanisms responsible for urinary stones remain largely unknown. Bacteria have long been recognized to contribute to struvite urinary stones; however, the role of bacteria in the development of the more common calcium oxalate (CaOx) and calcium phosphate (CaPhos) stones has not been extensively investigated. However, several findings do indicate a possible association between urinary stones and bacteria, including the high rate of urinary tract infections (UTI) in urinary stone patients and multiple case series of culture-positive urinary stones, including stones composed of CaOx or CaPhos. New technology, such as next generation sequencing, may be used to lend additional insight regarding the association between urinary stones and bacteria. In 2015, we published the initial bacterial sequencing results from five urinary stones, from which we sequenced multiple types of bacterial DNA. Whether these bacteria are causal, disease modifying or passively present remains to be determined. However, initial exploration of underlying mechanisms for this association indicate that bacteria aggregate selectively to crystals, that their presence is associated with increased clumping of crystals, and that they stimulate incorporation of proteins into the stone matrix.

Clinical relevance of seasonal changes in the prevalence of ureterolithiasis in the diagnosis of renal colic

Ureterolithiasis is one of the most frequently diagnosed urologic diseases worldwide. Its annual incidence in Japan increased three-fold from 1965 to 2005. Ureterolithiasis incidence is affected by numerous factors, including race, sex, body weight, fluid intake, and climate. Here, we aimed to address the latter by considering the effect of seasonal variation on stone incidence and incorporating this information into a predictive model for differential diagnosis of ureteral stone from other conditions with similar presentations. We retrospectively identified 491 patients in our emergency department computer database who complained of back, flank, or lower abdominal pain during 2007-2015. Among them, 358 had stones, as confirmed by computerized tomography or plain abdominal X-ray of kidney-ureter-bladder. We also charted the mean ambient temperatures in our city for a year. The cases of ureteral stones paralleled the ambient temperatures, peaking during the hottest weather. Univariate analysis identified 13 factors associated with ureteral stones. Multivariate analysis narrowed the number to eight: age <60 years, male sex, short duration of pain (<6 h), nausea/vomiting, hydronephrosis, hematuria, history of urinary stone(s), and summer (July-September in Japan). Pain appearing during summer was nine times more likely to be due to a ureteral stone than was pain appearing during other seasons. We incorporated the eight variables identified into a predictive logistic regression model, which yielded good prediction of ureteral stones. Awareness that hot weather is associated with increased incidence of ureterolithiasis could facilitate differential diagnosis, and our prediction model could be useful for screening for ureterolithiasis.

Nutritional Management of Kidney Stones (Nephrolithiasis)

The incidence of kidney stones is common in the United States and treatments for them are very costly. This review article provides information about epidemiology, mechanism, diagnosis, and pathophysiology of kidney stone formation, and methods for the evaluation of stone risks for new and follow-up patients. Adequate evaluation and management can prevent recurrence of stones. Kidney stone prevention should be individualized in both its medical and dietary management, keeping in mind the specific risks involved for each type of stones. Recognition of these risk factors and development of long-term management strategies for dealing with them are the most effective ways to prevent recurrence of kidney stones.

Self-Fluid Management in Prevention of Kidney Stones: A PRISMA-Compliant Systematic Review and Dose-Response Meta-Analysis of Observational Studies

Epidemiologic studies have suggested that daily fluid intake that achieves at least 2.5 L of urine output per day is protective against kidney stones. However, the precise quantitative nature of the association between fluid intake and kidney stone risk, as well as the effect of specific types of fluids on such risk, are not entirely clear.We conducted a systematic review and dose-response meta-analysis to quantitatively assess the association between fluid intake and kidney stone risk. Based on a literature search of the PubMed, Embase, and Cochrane Library databases, 15 relevant studies (10 cohort and 5 case-control studies) were selected for inclusion in the meta-analysis with 9601 cases and 351,081 total participants.In the dose-response meta-analysis, we found that each 500 mL increase in water intake was associated with a significantly reduced risk of kidney stone formation (relative risk (RR) = 0.93; 95% CI: 0.87, 0.98; P < 0.01). Protective associations were also found for an increasing intake of tea (RR = 0.96; 95% CI: 0.93, 0.99; P = 0.02) and alcohol (RR = 0.80, 95% CI: 0.75, 0.85; P < 0.01). A borderline reverse association were observed on coffee intake and risk of kidney stone (RR = 0.88; 95% CI: 0.76, 1.00; P = 0.05). The risk of kidney stones was not significantly related to intake of juice (RR = 1.02, 95% CI: 0.95, 1.10; P = 0.64), soda (RR = 1.03; 95% CI: 0.90, 1.17; P = 0.65), or milk (RR = 0.96; 95% CI: 0.88, 1.03; P = 0.21). Subgroup analysis and sensitivity analyses showed inconsistent results on coffee, alcohol, and milk intake.Increased water intake is associated with a reduced risk of kidney stones; increased consumption of tea and alcohol may reduce kidney stone risk. An average daily water intake was recommended for kidney stone prevention.

Urinary saturation: casual or causal risk factor in urolithiasis?

OBJECTIVE

To assess (i) the extent to which urinary supersaturation (SS) has successfully discriminated between stone formers and healthy individuals (N), (ii) whether absolute SS has diagnostic worth and (iii) whether high SS is the fundamental cause of stone formation per se.

MATERIALS AND METHODS

Google Scholar was used to identify studies in which urinary compositional data had been determined. In those cases where SS values were not given, or where other risk indices had been reported, they were (re-)calculated. Collected data were termed 'global' but were then 'filtered' according to stone type and protocols used for SS calculations. SS distribution plots for calcium oxalate, brushite and uric acid were constructed. Data were statistically analysed using the unpaired t-test and Mann-Whitney test.

RESULTS

In all, 47 studies yielded 123 SS values for healthy individuals and 122 values for stone formers. The mean and median SS values were significantly greater in stone formers compared with healthy individuals in all but one of the comparisons. Wide variations in SS occurred for healthy individuals and stone formers. The two groups could not be separated.

CONCLUSIONS

Absolute SS has no diagnostic worth. It is impossible to quantify the meaning of a 'high' SS value. Urines cannot be identified as originating from healthy individuals or stone formers based on their SS. SS should be determined in clinical and research settings for relative comparisons during the assessment of treatment efficacies. This study provides a compelling argument for SS being a casual factor rather than a causal one.

Lifestyle recommendations to reduce the risk of kidney stones

Kidney stones are increasingly common in wealthy industrialized countries. The most frequent form (80%) is idiopathic calcium stone disease. Eating habits and lifestyle have a direct effect on the lithogenic urinary risk factors and the pathogenesis of this condition. A diet characterized by a high intake of fluids, fruits, and vegetables; a low consumption of salt and protein; and a balanced intake of calcium, fats, and carbohydrates constitutes an efficacious approach to the prevention and treatment of this illness. A correct body weight, regular exercise, and a reduction in stressful life events are also useful preventive actions.

Do weather conditions influence the onset of renal colic? A novel approach to analysis

BACKGROUND/AIM

To investigate the seasonal variations of the incidence of renal colic by a computerized analysis of cyclic climatic features.

METHODS

1,163 consecutive patients with acute renal colic were studied. Eigendecomposition and signal reconstruction of district temperature and humidity were performed to establish any cyclic variation. Average temperatures and humidity values were calculated at time periods of 15, 30, 45 and 60 days preceding each renal colic.

RESULTS

Patients were allocated to groups every 30 days, since eigendeanalysis suggested that intervals of this duration have homogeneous climatic features. With an average time period of 15 days preceding each renal colic, a positive correlation coefficient of temperature (r = +0.75 with CI 0.31-0.93, p < 0.005) and a cubic relationship at the regression analysis (R = 82.4%, p = 0.015) were found with the onset of colics. We observed a negative correlation between humidity and renal colic (rho = -0.70 with CI -0.92 to -0.21, p < 0.01), with an inverse relation as regression model (R = 57.9%, p < 0.05).

CONCLUSIONS

We demonstrated an association between the onset of renal colics and exposure to hot and dry weather, particularly when temperatures rose above 27 degrees C and relative humidity fell below 45%.

Concentrated urine and diluted urine: the effects of citrate and magnesium on the crystallization of calcium oxalate induced in vitro by an oxalate load

Supplementation of certain calcium crystallization inhibitors, such as citrate and magnesium, and the dilution of urine with water are now considered consolidated practice for the prevention of calcium kidney stones. The aim of this study is to verify, using tried and true in vitro methods, whether the effect of these inhibitors can manifest itself in different ways depending on whether the urine is concentrated or diluted. Calcium oxalate crystallization was studied on 4-h urine of 20 male idiopathic calcium oxalate stone formers, first under low hydration conditions (non-diluted urine) and then under high hydration conditions (diluted urine). Both the diluted and the non-diluted urine samples were subjected to three types of load: (a) an oxalate concentration increment of 1.3 mmol/l only; (b) an oxalate concentration increment of 1.3 mmol/l with a citrate concentration increment of 1.56 mmol/l; (c) an oxalate concentration increment of 1.3 mmol/l with a magnesium concentration increment of 2.08 mmol/l. In non-diluted urine, the addition of the citrate and magnesium did not modify the crystallization parameters under study. In contrast, in the diluted urine the addition of the citrate and magnesium led to a reduction in the total quantity of crystals (equivalent to 35-45%) and their aggregates (equivalent to 30-40%); at the same time, there was an increase in the diameter of the monohydrate calcium oxalate crystals, which also underwent a morphological change. In conclusion, the inhibitory effects of citrate and magnesium on the crystallization of calcium oxalate do not manifest themselves in highly concentrated urine.

Dietary therapy in idiopathic nephrolithiasis

Like other diseases striking predominantly the affluent societies, idiopathic nephrolithiasis is increasing in rich countries and appears to be closely related to dietary habits. In this review we summarize the latest evidence about the efficacy of dietary treatment for idiopathic calcium and uric acid stones, dealing especially with its effect on the urinary stone risk factors, stone recurrences, and clinical limitations. After a short introduction on epidemiology and pathogenesis, we review the role of the most important foods and nutrients in stone formation and protection: water and other fluids, proteins, carbohydrates, fats, salt, milk and dairy products, fruits and vegetables, and vitamins. The final part of the paper will provide practical guidelines for pursuing an anti-lithogenic diet in idiopathic calcium and uric acid stones.

Sialylation of urinary prothrombin fragment 1 is implicated as a contributory factor in the risk of calcium oxalate kidney stone formation

Urinary glycoproteins are important inhibitors of calcium oxalate crystallization and adhesion of crystals to renal cells, both of which are key mechanisms in kidney stone formation. This has been attributed to glycosylation of the proteins. In South Africa, the black population rarely form stones (incidence < 1%) compared with the white population (incidence 12-15%). A previous study involving urinary prothrombin fragment 1 from both populations demonstrated superior inhibitory activity associated with the protein from the black group. In the present study, we compared N-linked and O-linked oligosaccharides released from urinary prothrombin fragment 1 isolated from the urine of healthy and stone-forming subjects in both populations to elucidate the relationship between glycosylation and calcium oxalate stone pathogenesis. The O-glycans of both control groups and the N-glycans of the black control samples were significantly more sialylated than those of the white stone-formers. This demonstrates a possible association between low-percentage sialylation and kidney stone disease and provides a potential diagnostic method for a predisposition to kidney stones that could lead to the implementation of a preventative regimen. These results indicate that sialylated glycoforms of urinary prothrombin fragment 1 afford protection against calcium oxalate stone formation, possibly by coating the surface of calcium oxalate crystals. This provides a rationale for the established roles of urinary prothrombin fragment 1, namely reducing the potential for crystal aggregation and inhibiting crystal-cell adhesion by masking the interaction of the calcium ions on the crystal surface with the renal cell surface along the nephron.

High kidney stone risk in men working in steel industry at hot temperatures

OBJECTIVES

To study the incidence of urinary lithiasis and metabolic alterations among male employees from a steel industry who were exposed to high temperatures in the work environment.

METHODS

A retrospective cross-sectional study was performed and consisted of two stages. First, the incidence of urolithiasis among the industry's 10,326 employees was assessed. These employees were divided into two group's: group 1 (n = 1289) consisted of the hot-area workers (temperature greater than 45 degrees C) and group 2 (n = 9037) consisted of those working in areas at room temperature. In the second stage, 59 workers without urolithiasis who underwent a metabolic evaluation were divided into two group's: group 3 (n = 34) consisted of hot-area workers and group 4 (n = 25) consisted of those working in areas at room temperature. Evaluations were made of calcium, creatinine, and uric acid in serum; in the 24-hour urine samples, we assessed the volume, calcium, uric acid, citrate, and oxalate.

RESULTS

Of the 10,326 workers, 181 (1.75%) had presented with at least one episode of urinary stones. Of these, 103 were among the hot-area workers (8.0%) and 78 among the room-temperature workers (0.9%; P <0.001). The metabolic evaluation showed that the hot-area group (group 3), compared with the room-temperature group (group 4), presented more frequently with hypocitraturia (55.8% versus 28%, P = 0.03) and low urinary volume (79.4% versus 48%, P = 0.01).

CONCLUSIONS

Workers exposed to high temperatures presented with a ninefold risk of lithiasis. Hypocitraturia and low urine volumes were the metabolic alterations observed.

Effects of urine dilution on quantity, size and aggregation of calcium oxalate crystals induced in vitro by an oxalate load

Increasing urinary volume is an important tool in the prevention of calcium renal stones. However, the mechanism of how it actually works is only partially understood. This study aimed at assessing how urine dilution affects urinary calcium oxalate crystallization. A total of 16 male idiopathic calcium oxalate (CaOx) stone-formers and 12 normal male subjects were studied and 4 h urine samples were taken twice, under low (undiluted urine) and high hydration conditions (diluted urine). An equal oxalate load (1.3mmol/L) was added to both types of urine and the crystallization parameters were assessed. In both stone-formers and normal subjects, the crystallization processes were significantly (p<0.05 or less) more marked in the undiluted urine than in the diluted urine in terms of: a) total quantity of calcium oxalate dihydrate (COD) and calcium oxalate monohydrate (COM) crystals; b) total quantity of crystalline aggregates; and c) aggregation index (i.e., ratio between the area occupied by crystalline aggregates and the area occupied by all the crystals present). The comparison between stone-formers and normal subjects showed that the greatest difference was for the size of COD crystals, which were larger in the urine of the stone-formers. A further important finding was an inverse relationship between changes in urinary volume and in the aggregation index (r=–0.53, p=0.004). In conclusion, urine dilution considerably reduces crystallization phenomena induced in vitro by an oxalate load in both calcium stone-formers and normal subjects.

Body weight, diet and water intake in preventing stone disease

Nutrition plays a major role in the pathogenesis of the most widespread forms of nephrolithiasis, i.e. calcium (calcium oxalate and phosphate) and uric acid stone disease. For this reason, dietary measures are the first level of intervention in primary prevention, as well as in secondary prevention of recurrences. An unbalanced diet or particular sensitivity to various foods in stone formers can lead to urinary alterations such as hypercalciuria, hyperoxaluria, hyperuricosuria, hypocitraturia and an excessively acid urinary pH. Over the course of time, these conditions contribute to the formation or recurrence of kidney stones, due to the effect they exert on the lithogenous salt profile. The fundamental aspects of the nutritional approach to the treatment of idiopathic nephrolithiasis are body weight, diet and water intake. This paper will present data resulting from our own investigations and the most significant evidence in literature.

Calcium oxalate crystallization in untreated urine, centrifuged and filtered urine and ultrafiltered urine

Centrifuged and filtered urine is often used to evaluate in vitro the crystallization processes of calcium oxalate (CaOx), but even such simple manipulations can alter the composition of the urine, as regards its protein and lipid concentrations. In urine samples taken from 17 normal male adults, we evaluated CaOx crystallization by simultaneously using three different types of urine: untreated (U), centrifuged at 2000 rpm (800

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.

Medical treatment of nephrolithiasis

The medical treatment of nephrolithiasis is aimed in particular at the prevention of relapses, even though in some cases, such as cystine or uric acid lithiasis, the calculi also can be dissolved on site. When the diagnosis and metabolic profile have been performed correctly, medical treatment is effective in a large number of patients. The greatest difficulty is the patient's compliance with the most suitable prevention measures and the frequency of follow-up controls. This compliance can be influenced significantly by the amount of time that the doctor spends to explain the origin of the disease. This article reviews the main methods available for the medical treatment of various nephrolithiasis types, namely water intake, diet, and drugs, supplying the relevant information about the mechanism of action, metabolic consequences, indications, evidence provided from studies, dosage, efficacy, and side-effects. Finally, brief simplified guidelines are given for the medical treatment of stone disease caused by calcium oxalate or calcium phosphate, uric acid, cystine, and struvite.