Citrate inhibits growth of residual fragments in an in vitro model of calcium oxalate renal stones

Supramolecular citrate poly allylamine hydrochloride nanoparticles for citrate delivery and calcium oxalate nanocrystal dissolution

HYPOTHESIS

Renal calculi (kidney stones) are mainly made by calcium oxalate and can cause different complications including malfunction of the kidney. The most important urinary stone inhibitors are citrate molecules. Unfortunately, the amount of citrate reaching the kidney after oral ingestion is low. We hypothesized that nanoparticles of polyallylamine hydrochloride (CIT-PAH) carrying citrate ions could simultaneously deliver citrates while PAH would complex oxalate triggering dissolution and removal of CaOx nanocrystals.

EXPERIMENTS

We successfully prepared nanoparticles of citrate ions with polyallylamine hydrochloride (CIT-PAH), PAH with oxalate (OX-PAH) and characterize them by Small Angle X ray Scattering (SAXS), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) and NMR. Dissolution of CaOx nanocrystals in presence of CIT-PAH have been followed with Wide Angle Xray Scattering (WAXS), DLS and Confocal Raman Microscopy. Raman spectroscopy was used to study the dissolution of crystals in synthetic urine samples. The release of citrate from CIT-PAH was followed by diffusion NMR. Molecular dynamics (MD) simulations were carried out to study the interaction of CIT and OX ions with PAH.

FINDINGS

CIT-PAH nanoparticles dissolves CaOx nanocrystals as shown by NMR, DLS, TEM and WAXS in water and by Raman spectroscopy in artificial human urine. WAXS and Raman show that the crystal structure of CaOx disappears in the presence of CIT-PAH. DLS shows that the time required for CaOX dissolution will depend on the concentration of CIT-PAH NPs. NMR proves that citrate ions are released from the CIT PAH NPs during CaOX dissolution, MD simulations showed that oxalates exhibit a stronger interaction for PAH than citrate, explaining the removal of oxalate ions and replacement of the citrate in the polymer nanoparticles.

Resveratrol inhibits calcium oxalate crystal growth, reduces adhesion to renal cells and induces crystal internalization into the cells, but promotes crystal aggregation

Resveratrol is a natural phenolic compound that belongs to stilbenoid group found in diverse plants. Health benefits and therapeutic potentials of resveratrol have been widely recognized in various diseases. In kidney stone disease, it can alleviate oxalate-induced hyperproduction of free radicals in renal epithelial cells. Nevertheless, its direct effects on calcium oxalate (CaOx) crystal, which is the major stone component, remained unclear. This study therefore addressed the direct effects of resveratrol (at 1, 10 or 100 μM) on each step of CaOx kidney stone formation. The results revealed that resveratrol had no significant effects on CaOx crystallization. However, resveratrol significantly decreased CaOx crystal growth and adhesion to renal epithelial cells at all concentrations, and induced crystal internalization into the cells (a process related to crystal degradation by endolysosomes) in a concentration-dependent manner. On the other hand, resveratrol promoted crystal aggregation. These data indicate that resveratrol serves as a dual modulator on CaOx stone formation. While it inhibits CaOx stone development by reducing crystal growth and adhesion to renal cells and by inducing crystal internalization into the cells, resveratrol promotes crystal aggregation, which is one of the mechanisms leading to kidney stone formation.

The effectiveness of citrates and pyridoxine in the treatment of kidney stones

The prevalence of nephrolithiasis is increasing across all demographic groups. Apart from the morbidity associated with an acute occurrence, preventative treatment is essential for stone disease, which can become a long-term problem. Simple interventions like fluid intake optimization and dietary modification are effective for most stone types. However, patients with specific metabolic abnormalities may require pharmaceutical therapy if lifestyle changes are insufficient to reduce the risk of stone recurrence. The treatment of citrates and/or pyridoxines may help eliminate or prevent recurrences of kidney stones, especially when they are composed of uric acid, calcium oxalate, calcium phosphate, or the latter two together. In cases of struvite stones, which often necessitate a surgical approach, acetohydroxamic acid emerges as a valuable second-line treatment option. Thiol-binding agents may be needed for cystinuria, as well as lifestyle modifications. Successful treatment reduces stone recurrence and the need to remove stones surgically.

Incidence and Characteristics of Kidney Stones in Patients on Ketogenic Diet: A Systematic Review and Meta-Analysis

Very-low-carbohydrate diets or ketogenic diets are frequently used for weight loss in adults and as a therapy for epilepsy in children. The incidence and characteristics of kidney stones in patients on ketogenic diets are not well studied. Methods: A systematic literature search was performed, using MEDLINE, EMBASE, and Cochrane Database of Systematic Reviews from the databases’ inception through April 2020. Observational studies or clinical trials that provide data on the incidence and/or types of kidney stones in patients on ketogenic diets were included. We applied a random-effects model to estimate the incidence of kidney stones. Results: A total of 36 studies with 2795 patients on ketogenic diets were enrolled. The estimated pooled incidence of kidney stones was 5.9% (95% CI, 4.6–7.6%, I2 = 47%) in patients on ketogenic diets at a mean follow-up time of 3.7 +/− 2.9 years. Subgroup analyses demonstrated the estimated pooled incidence of kidney stones of 5.8% (95% CI, 4.4–7.5%, I2 = 49%) in children and 7.9% (95% CI, 2.8–20.1%, I2 = 29%) in adults, respectively. Within reported studies, 48.7% (95% CI, 33.2–64.6%) of kidney stones were uric stones, 36.5% (95% CI, 10.6–73.6%) were calcium-based (CaOx/CaP) stones, and 27.8% (95% CI, 12.1–51.9%) were mixed uric acid and calcium-based stones, respectively. Conclusions: The estimated incidence of kidney stones in patients on ketogenic diets is 5.9%. Its incidence is approximately 5.8% in children and 7.9% in adults. Uric acid stones are the most prevalent kidney stones in patients on ketogenic diets followed by calcium-based stones. These findings may impact the prevention and clinical management of kidney stones in patients on ketogenic diets.

Evaluations of the curative efficacy of G. fruticosus solvent extracts in experimentally induced nephrolithiatic Wistar male rats

BACKGROUND

In Ethiopian folk medicine, there is a claim that medicinal plants can treat urolithiasis although there is insufficient scientific evidence. The objective of this study was to evaluate the curative efficacy of Gomphocarpus fruticosus extracts in experimentally induced nephrolithiatic rats.

METHODS

Urolithiasis was induced in male Wistar rats by feeding ethylene glycol in drinking water for 28 days. The curative effects were evaluated after oral administrations of 200 mg/kg of the extracts from 15 to 28 days. Urine samples were collected 1 day before sacrificing the rats. Blood, liver and kidney samples were gathered under anaesthetic condition at day 28. Crystals in the urine were also analyzed by light microscopy.

RESULTS

G. fruticosus EtOAc extract reduced significantly the level of sodium (P < 0.001), whereas it was significantly elevated the levels of magnesium and citrate (P < 0.01) compared to lithiatic control. G. fruticosus BuOH extract lowered the levels of potassium (P < 0.01), calcium and phosphate in urolithiatic rats. It was also observed that G. fruticosus EtOAc extract decreased the level of oxalate in the urine (P < 0.001), whereas it was increased the levels of magnesium (P < 0.05) and citrate (P < 0.01) in serum analysis after exposure to BuOH extract. In the kidneys, CaOx crystal deposits were reduced significantly by G. fruticosus EtOAc extract (P < 0.01).

CONCLUSION

It has been noted that G. fruticosus EtOAc extract was potent in treating urolithiasis. However, further study is required to assess the efficacy of the active compounds against urolithiasis.

Demineralization and sectioning of human kidney stones: A molecular investigation revealing the spatial heterogeneity of the stone matrix

The molecular mechanisms by which kidney stones grow are largely unknown. Organic molecules from the urine combine with mineral crystals to form stones, but analysis of the stone matrix has revealed over a thousand different proteins, with no clues as to which are important for stone growth. Molecules that are present in every layer of a stone would be candidates for having an essential function, and thus the analysis of the stone matrix at a microscopic level is necessary. For this purpose, kidney stones were demineralized, sectioned, stained, and imaged by microscopy, using micro CT for precise orientation. Histological staining demonstrated heterogeneity in the density of adjacent layers within stones. Additional results also showed brilliant and unique autofluorescence patterns in decalcified nephroliths, indicating heterogeneous organic composition in adjacent layers. Regions of calcium oxalate (CaOx) stones were dissected using laser microdissection (LMD) for protein analysis. LMD of broad regions of demineralized CaOx stone sections yielded the same proteins as those found in different specimens of pulverized CaOx stones. These innovative methodologies will allow spatial mapping of protein composition within the heterogeneous stone matrix. Proteins that consistently coincide spatially with mineral deposition would be candidates for molecules essential for stone growth. This kind of analysis will be required to assess which of the thousand proteins in the stone matrix may be fundamental for stone growth.

Lower Socioeconomic Status is Associated With Adverse Urinary Markers and Surgical Complexity in Kidney Stone Patients

OBJECTIVE

To determine if socioeconomic status (SES) correlates with severity of kidney stone disease and 24-hour urine parameters.

MATERIALS AND METHODS

An IRB approved prospectively maintained database for nephrolithiasis was retrospectively analyzed for both 24-hour urine results and surgical procedures performed from 2009 to 2019. Severely distressed communities (SDC) were categorized as those with a Distressed Communities Index (DCI), a composite measure of SES, score in the top quartile (lowest for SES). Univariate and multivariate analyses were performed to evaluate the strength of the association of DCI on: stone size at presentation, need for and type of surgical procedure, need for staged surgery and specific stone risk factors in 24-hour urine collections.

RESULTS

Surgical procedures were performed on 3939 patients (1978 women) who were not from SDC and 200 (97 women) from SDC. Patients from SDC were older (57.1 years vs 54.2 years; P = .009). Patients from SDC were more likely to undergo proportionally more invasive procedures (17.5% vs 11.6%; P = .011) and require staged surgery at a higher rate (13.0% vs 8.5%; P = .028). Men from SDC had larger stones (12.5 mm vs 9.7 mm; P = .001). Among 24-hour urine results from 2454 patients (1187 women), DCI was not correlated with sodium, calcium, magnesium, volume, oxalate, phosphate, and pH levels. Higher DCI (lower SES) correlated with lower urine citrate (P = .001) and lower urine potassium (P = .002).

CONCLUSION

SES correlates with larger stone burden at the time of urologic intervention, requires proportionally more invasive procedures and more staged procedures. Lower SES correlated with lower urine citrate and potassium.

The Effect of Lemonade and Diet Lemonade Upon Urinary Parameters Affecting Calcium Urinary Stone Formation

PURPOSE

To determine the effects of regular and diet lemonade upon urinary parameters affecting kidney stone formation.

METHODS

In this prospective blinded crossover study, 12 healthy participants consumed either 2 L of regular or diet lemonade daily while on a standardized low sodium moderate calcium diet. Twenty four-hour urine collections were obtained at baseline on the controlled diet only and on days 4 and 5 of each treatment phase. There was a 1-week washout period between regular and diet lemonade treatments. Primary outcomes were urine citrate, pH, and volume determined by 24-hour urine collections. Secondary outcomes included the supersaturation of calcium oxalate, calcium phosphate, and uric acid.

RESULTS

Urine volume was significantly higher with both regular and diet lemonade consumption compared with baseline values. Urinary citrate significantly increased from baseline with diet lemonade only. Urine pH was unchanged with both beverages. The supersaturation of calcium oxalate significantly decreased with diet lemonade only, whereas supersaturation of calcium phosphate decreased with both beverages. Daily consumption of 2 L of regular and diet lemonade resulted in an intake of 168.4 and 170.2 mEq of citrate but a total alkali intake of 12.2 and 16.0 mEq, respectively. Compared with diet lemonade, regular lemonade provided subjects with 805 additional calories and 225 g of sugar per day.

CONCLUSIONS

Diet lemonade may provide a low-calorie sugar-free cost-effective option for decreasing the risk of recurrent calcium nephrolithiasis through a significant increase in urine volume, increase in urinary citrate, and reduction in supersaturation of calcium oxalate and calcium phosphate.

Current insights into the mechanisms and management of infection stones

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

Signification of distal urinary acidification defects in hypocitraturic patients

BACKGROUND AND OBJECTIVES

Hypocitraturia has been associated with metabolic acidosis and mineral disorders. The aim of this study was to investigate the occurrence of urinary acidification defects underlying hypocitraturia.

MATERIALS AND METHODS

This retrospective observational study included 67 patients (32 men), aged 40.7±15.1 years with hypocitraturia (<1.67 mmol/24-h) and nephrolithiasis, nephrocalcinosis, and/or bone demineralization, referred to our center from 2000 to 2015. We aimed to assess renal distal acidification capacity, prevalence and mechanisms of urinary acidification defects. Patients with low baseline plasma HCO3- (<22 mmol/L) were studied by bicarbonate loading or furosemide/fludrocortisone tests. Patients with normal baseline plasma HCO3- had an ammonium-chloride challenge test. A normal response was a decrease in urinary pH <5.3 and an increase in urinary NH4+ ≥33 μmol/min and defined idiopathic hypocitraturia.

RESULTS

Eleven patients (16.4%) had low HCO3- and overt distal acidification defect. Three had a mutation in the gene encoding AE1, 4 had Gougerot-Sjögren syndrome and no cause was found in the remaining 4 cases. Fifty-six patients (83.6%) had normal HCO3-; of those, 33 (58.9%) had idiopathic hypocitraturia. Among the 23 (41%) remaining patients, 12 were unable to increase urinary NH4+ excretion (among them, 8 were able to decrease urinary pH and 4 were not) whereas 11 were able to increase urinary NH4+ excretion but unable to decrease urinary pH. These 11 patients had higher fasting urinary calcium, reflecting bone resorption, than the other 12 patients: median 0.41 [0.24-0.47] vs. 0.22 [0.08-0.37] mmol/mmol creatinine (P = 0.04).

CONCLUSIONS

Patients with hypocitraturia and normal plasma HCO3- frequently show a latent acidification defect that can be further dissected into one of several subtypes based on urinary pH and NH4+ response to the acid load. Those patients with impaired urine acidification capacity but preserved NH4+ excretion exhibit particularly high calciuria and should be identified to optimize nephrolithiasis prevention.

Potential Mechanisms Responsible for the Antinephrolithic Effects of an Aqueous Extract of Fructus Aurantii

The potential effects of Fa extract on the prevention and treatment of CaOx nephrolithiasis were analyzed in an ethylene glycol- (EG-) induced CaOx crystallization model in rats and an in vitro assay. Multiple biochemical variables were measured in the urine and kidney. Kidney sections were subjected to histopathological and immunohistochemical analyses. Urolithiasis-related osteopontin (OPN) was evaluated by Western blotting. The in vitro assay revealed the significant inhibition of crystal formation (3.50 ± 1.43) and dilution of formed crystals (12.20 ± 3.35) in the group treated with 1 mg/mL Fa extract compared with the control group (52.30 ± 4.71 and 53.00 ± 4.54, resp.) (p < 0.05). The in vivo experiments showed that prophylactic treatment with Fa aqueous extract significantly prevented EG-induced renal crystallization and pathological alterations compared with nephrolithic rats (p < 0.05). Significantly lower levels of oxidative stress, oxalate, and OPN expression as well as increased citrate and urine output levels were observed in both the low- and high-dose prophylactic groups (p < 0.05). However, in the low- and high-dose therapeutic groups, none of these indexes were significantly improved (p > 0.05) except for urinary oxalate in the high-dose therapeutic groups (p < 0.05). Fa extract prevented CaOx crystallization and promoted crystal dissolution in vitro. Additionally, it was efficacious in preventing the formation of CaOx nephrolithiasis in rats.

Efficacy of Mixtures of Magnesium, Citrate and Phytate as Calcium Oxalate Crystallization Inhibitors in Urine

PURPOSE

The main aim of the current study was to evaluate the effectiveness of mixtures of magnesium, citrate and phytate as calcium oxalate crystallization inhibitors.

MATERIALS AND METHODS

A turbidimetric assay in synthetic urine was performed to obtain induction times for calcium oxalate crystallization in the absence and presence of different mixtures of inhibitors. The morphology of calcium oxalate crystals in the absence or presence of inhibitors and mixtures of the inhibitors was evaluated in 2 crystallization experiments at low and high calcium oxalate supersaturation. The crystals formed were examined using scanning electron microscopy.

RESULTS

Examination of crystallization induction times revealed clear inhibitory effects of magnesium, citrate and phytate on calcium oxalate crystallization, supporting usefulness in the treatment and prevention of calcium oxalate nephrolithiasis. Significant synergistic effects between magnesium and phytate were observed. Scanning electron microscopy images revealed that phytate is a powerful crystal growth inhibitor of calcium oxalate, totally preventing the formation of trihydrate and monohydrate. In addition to crystallization inhibition capacity, citrate and magnesium avoided calcium oxalate crystallization by decreasing its supersaturation.

CONCLUSIONS

The synergistic effect between magnesium and phytate on calcium oxalate crystallization suggests that a combination of these 2 compounds may be highly useful as antilithiasis therapy.

Theobromine inhibits uric acid crystallization. A potential application in the treatment of uric acid nephrolithiasis

PURPOSE

To assess the capacity of methylxanthines (caffeine, theophylline, theobromine and paraxanthine) to inhibit uric acid crystallization, and to evaluate their potential application in the treatment of uric acid nephrolithiasis.

MATERIALS AND METHODS

The ability of methylxathines to inhibit uric acid nucleation was assayed turbidimetrically. Crystal morphology and its modification due to the effect of theobromine were evaluated by scanning electron microscopy (SEM). The ability of theobromine to inhibit uric acid crystal growth on calculi fragments resulting from extracorporeal shock wave lithotripsy (ESWL) was evaluated using a flow system.

RESULTS

The turbidimetric assay showed that among the studied methylxanthines, theobromine could markedly inhibit uric acid nucleation. SEM images showed that the presence of theobromine resulted in thinner uric acid crystals. Furthermore, in a flow system theobromine blocked the regrowth of post-ESWL uric acid calculi fragments.

CONCLUSIONS

Theobromine, a natural dimethylxanthine present in high amounts in cocoa, acts as an inhibitor of nucleation and crystal growth of uric acid. Therefore, theobromine may be clinically useful in the treatment of uric acid nephrolithiasis.

The inhibitory effect of an ethanol extract of the spores of Lygodium japonicum on ethylene glycol-induced kidney calculi in rats

We investigated the effect of an ethanol extract of Lygodii spora (LS) as a preventive and therapeutic agent for experimentally induced calcium oxalate nephrolithiasis with ethylene glycol (EG) in rats. Male Wistar rats were randomly divided into preventive (n = 18, for 28 days) and therapeutic (n = 24, for 42 days) groups. The preventive group was further subdivided into three groups of six rats each: preventive control, preventive lithiatic control (EG) and preventive lithiatic LS (EG + 400 mg/kg LS). Similarly, the therapeutic group was subdivided into four groups of six rats each: therapeutic control, therapeutic lithiatic control, therapeutic lithiatic untreated, and therapeutic lithiatic LS. Lithiasis was induced by adding 0.75% EG to the drinking water of all groups except the preventive and therapeutic control groups. Preventive and therapeutic subjects also received the LS ethanol extract in drinking water at a dose of 400 mg/kg, since day 0 or day 28, respectively. At the end of the each experimental period, various biochemical parameters were measured in urine and kidney homogenates. The kidneys were subjected to histopathological analysis. The results revealed that treatment with the LS preventive protocol significantly decreased the levels of urinary calcium, oxalate and uric acid, and increased the levels of urinary citrate as compared to those in the EG control. No significant changes in the urinary parameters except oxalate and citrate levels were observed in the rats in the therapeutic protocol. In both preventive and therapeutic protocols, the extract significantly decreased kidney peroxides, renal calcium, oxalate content, and the number of kidney oxalate deposits as compared to those in the EG group. We conclude that LS is useful as a preventive and therapeutic agent against the formation of oxalate kidney stones.

Citrate occurs widely in healthy and pathological apatitic biomineral: mineralized articular cartilage, and intimal atherosclerotic plaque and apatitic kidney stones

There is continuing debate about whether abundant citrate plays an active role in biomineralization of bone. Using solid state NMR dipolar dephasing, we examined another normally mineralized hard tissue, mineralized articular cartilage, as well as biocalcifications arising in pathological conditions, mineralized intimal atherosclerotic vascular plaque, and apatitic uroliths (urinary stones). Residual nondephasing ¹³C NMR signal at 76 ppm in the spectra of mineralized cartilage and vascular plaque indicates that a quaternary carbon atom resonates at this frequency, consistent with the presence of citrate. The presence, and as yet unproven possible mechanistic involvement, of citrate in tissue mineralization extends the compositional, structural, biogenetic, and cytological similarities between these tissues and bone itself. Out of 10 apatitic kidney stones, five contained NMR-detectable citrate. Finding citrate in a high proportion of uroliths may be significant in view of the use of citrate in urolithiasis therapy and prophylaxis. Citrate may be essential for normal biomineralization (e.g., of cartilage), play a modulatory role in vascular calcification which could be a target for therapeutic intervention, and drive the formation of apatitic rather than other calcific uroliths, including more therapeutically intractable forms of calcium phosphate.

Post-extracorporeal shockwave lithotripsy residual stone fragments: clinical significance and management

Although extracorporeal shockwave lithotripsy (ESWL) is one of the primary treatments for urolithiasis, very often residual fragments of the calculi are still present for a long time after the ESWL session. These fragments are usually asymptomatic and can be managed expectantly, but sometimes they can cause symptoms and require intervention. Secondary procedures are not routinely applied to all patients with residual fragments, but only to those with significant symptoms. Medical therapy may play an important role in the management of residual fragments, by correcting an underlying metabolic disorder and by preventing the growth of residual calculi and the formation of new ones.

Drosophila: a fruitful model for calcium oxalate nephrolithiasis?

Even though the prevalence of nephrolithiasis is increasing, our understanding of the pathophysiology has not kept pace and new therapeutic approaches have not emerged. The potential of a new physiological model (the fruitfly) is exciting. The model has strengths, namely the low cost of maintaining colonies and rapid deployment of new transgenic lines, but also weaknesses that may ultimately limit its usefulness, such as the mechanism of tubular fluid formation and difficulties in following plasma and urine biochemistries.

The effects of the hydroalcohol extract of Rosa canina L. fruit on experimentally nephrolithiasic Wistar rats

This research evaluated the possible therapeutic potential of Rosa canina (RC) as a preventive agent in experimentally induced calcium oxalate (CaOx) nephrolithiasis with ethylene glycol (1% EG) in rats. In this experiment, 50 Wistar rats were divided randomly into five groups (n = 10). These groups received tap drinking water (group I), 1% EG (group II), 250 mg/kg RC + 1% EG (group III), 500 mg/kg RC + 1% EG (group IV), or 2.5 g/kg potassium citrate + 1% EG (group V) for a period of 30 days. Blood and urine were collected for biochemical analysis, and the liver and kidneys were prepared for total lipid peroxides, calcium content and histological evaluation. The extract was analysed for total phenolics, flavonoids, ascorbic acid, citric acid and radical scavenger activity. The supplementation of the hydromethanol RC extract contributed to reducing the kidney and liver lipid peroxides to optimum levels in rats that had been treated with EG-induced CaOx lithiasis. The extract also decreased renal and urinary calcium contents, decreased the size and number of CaOx calculi in the kidneys, and significantly increased citrate excretion without changing the volume, pH, or urinary concentrations of oxalate in comparison with the control group. According to these results, RC can be useful as a preventive agent against the formation of CaOx kidney stones.

Nephrolithiasis: evaluation and management

Nephrolithiasis is a major cause of morbidity involving the urinary tract. The prevalence of this disease in the United States has increased from 3.8% in the 1970s to 5.2% in the 1990s. There were nearly two million physician-office visits for nephrolithiasis in the year 2000, with estimated annual costs totaling $2 billion. New information has become available on the clinical presentation, epidemiologic risk factors, evaluative approach, and outcome of various therapeutic strategies. In this report, we will review the epidemiology and mechanisms of kidney-stone formation and outline management aimed at preventing recurrences. Improved awareness and education in both the general population and among health-care providers about these modifiable risk factors has the potential to improve general health and decrease morbidity and mortality secondary to renal-stone disease.

Dietary therapy for patients with hypocitraturic nephrolithiasis

Citrate is an inhibitor of urinary stone formation. Clinical and in vitro data suggest that increasing urine citrate levels will decrease the precipitation of calcium stones. Historically, low urinary citrate has been treated with oral potassium citrate or sodium citrate supplementation, but recent studies have shown the potential of dietary interventions to raise urine citrate levels. Dietary therapy with commercial or homemade beverages is attractive to patients who would prefer nonpharmacological intervention. To date, several drinks have shown promise but no single beverage has been found to consistently raise urine citrate levels in a reproducible fashion. Further research is necessary to develop the ideal dietary therapy for hypocitraturic calcium nephrolithiasis.

Prevention of renal crystal deposition by an extract of Ammi visnaga L. and its constituents khellin and visnagin in hyperoxaluric rats

In Egypt, teas prepared from the fruits of Ammi visnaga L. (syn. "Khella") are traditionally used by patients with urolithiasis. The aim of this study was to evaluate whether oral administration of an aqueous extract prepared from the fruits of A. visnaga as well as two major constituents khellin and visnagin could prevent crystal deposition in stone-forming rats. Hyperoxaluria was induced in male Sprague-Dawley rats by giving 0.75% ethylene glycol and 1% ammonium chloride via the drinking water. The Khella extract (KE; 125, 250 or 500 mg/kg) was orally administered for 14 days. The histopathological examination of the kidneys revealed that KE significantly reduced the incidence of calcium oxalate (CaOx) crystal deposition. In addition, KE significantly increased urinary excretion of citrate along with a decrease of oxalate excretion. Comparable to the extract, khellin and visnagin significantly reduced the incidence of CaOx deposition in the kidneys. However, both compounds did not affect urinary citrate or oxalate excretion indicating a mechanism of action that differs from that of the extract. For KE, a reasonably good correlation was observed between the incidence of crystal deposition, the increase in citrate excretion and urine pH suggesting a mechanisms that may interfere with citrate reabsorption. In conclusion, our data suggest that KE and its compounds, khellin and visnagin, may be beneficial in the management of kidney stone disease caused by hyperoxaluria but that it is likely that different mechanism of action are involved in mediating these effects.

Morphology, particle size distribution, aggregation, and crystal phase of nanocrystallites in the urine of healthy persons and lithogenic patients

BACKGROUND

The first step in urinary stone formation is the nucleation of urinary mineral from supersaturated urine. The formed nuclei then grow or/and aggregate to a pathological size. Thus, the nanocrystallites in urine may be related to the formation of urinary stones.

METHODS

Nanocrystallites with a size of less than 1000 nm in the urine samples of 85 healthy persons and 65 lithogenic patients were comparatively investigated using laser scattering spectroscopy, TEM, and X-ray diffraction.

RESULTS

Most of the nanocrystallites in healthy urine samples were spheroidal, less aggregated, well-dispersed, and with a narrow particle size distribution from about 20 to 350 nm. In contrast, most of the particles in lithogenic urines had sharply angled edges and tips, were aggregated, and had a broad particle size distribution from 1.1 to 1000 nm. More calcium oxalate dihydrate (COD) nanocrystallites were found in healthy urine; however, more calcium oxalate monohydrate (COM) nanocrystallites were found in lithogenic urine.

CONCLUSIONS

The morphology, particle size, aggregation, and crystal phase of nanocrystallites in the urine of lithogenic patients are pronouncedly different from those of healthy persons. The results suggest, in ascending order of importance, that making nanocrystallites rounded, diminishing their size differentiation, and decreasing their aggregation in urine by physical and chemical methods maybe the means to prevent urinary stone formation. The most crucial among the four differences is the crystal phase differential of calcium oxalate (CaOxa). That is, the formation of COD nanocrystallites in urine can be considered as being relatively more favorable in preventing stone formation than the formation of COM nanocrystallites, which are in accord with those found for larger crystallites.

Inhibitions of urinary oxidative stress and renal calcium level by an extract of Quercus salicina Blume/Quercus stenophylla Makino in a rat calcium oxalate urolithiasis model

OBJECTIVES

To clarify the mechanism of Urocalun, an extract of Quercus salicina Blume/Quercus stenophylla Makino (QS), in the treatment of urolithiasis.

METHODS

Rat calcium oxalate urolithiasis was induced by oral administration of ethylene glycol and the vitamin D3 analog alfa-calcidol for 14 days. QS extract was repeatedly given to rats. After the last administration, biochemistries in urine and plasma, renal calcium, and urinary malondialdehyde (an oxidative stress marker) were measured.

RESULTS

Ethylene glycol and alfa-calcidol treatment increased urinary malondialdehyde and renal calcium levels. This increase was significantly suppressed by the administration of QS extract, suggesting that the inhibition of renal calcium accumulation by QS extract is due to its antioxidative activity.

CONCLUSIONS

These findings suggest that the antioxidative activity of QS extract plays a role in the prevention of stone formation and recurrence in urolithiasis.

Strain differences in urinary factors that promote calcium oxalate crystal formation in the kidneys of ethylene glycol-treated rats

Ethylene glycol (EG)-induced hyperoxaluria is the most commonly employed experimental regimen as an animal model of calcium oxalate (CaOx) stone formation. The variant sensitivity to CaOx among different rat strains has not been fully explored, although the Wistar rat is known to accumulate more CaOx in kidney tissue after low-dose EG exposure than in the Fischer 344 (F344) rats. Supersaturation of CaOx in tubular fluid contributes to the amount of CaOx crystal formation in the kidney. We hypothesized that the urinary supersaturation of CaOx in Wistar rats is higher than that of F344 rats, thereby allowing for greater CaOx crystal deposition in the Wistar rat. Age-matched male Wistar and F344 rats were treated with 0.75% EG or drinking water for 8 wk. Twenty-four-hour urine was collected at 0, 2, 4, 6, and 8 wk for analysis of key electrolytes to calculate the CaOx supersaturation. Plasma oxalate level was also measured. Our data confirmed the different sensitivity to renal toxicity from EG between the two rat strains (Wistar > F344). After EG treatment, the plasma oxalate level and urine oxalate excretion were markedly greater in the Wistar rats than in the F344 rats, while urine calcium was slightly decreased in Wistars. Thus, the CaOx supersaturation in urine of Wistar rats was higher, which led to a greater crystal deposition in kidney in Wistar rats. These studies suggest that during EG treatment, changes in urine electrolytes and in CaOx supersaturation occur to a greater extent in the Wistar rat, in agreement with its greater sensitivity to EG toxicity.

Citrate levels in fresh tomato juice: a possible dietary alternative to traditional citrate supplementation in stone-forming patients

OBJECTIVES

To detect citrate levels in fresh tomato juice, to reveal whether it can be studied for prevention of recurrent hypocitraturic nephrolithiasis.

METHODS

Juices of tomato, orange, lemon, and mandarin were extracted and blended with a hand blender, and 10 samples of 100 mL were taken from each. Citrate, oxalate, calcium, phosphorus, magnesium, sodium, potassium, chloride, and pH levels were examined in these. The same variables were re-evaluated after the samples were stored at +4 degrees C for 1 week.

RESULTS

In fresh tomato juice, higher citrate and magnesium levels as well as lower sodium and oxalate levels were detected as compared with the other juices. No differences were observed with regard to all variables among fresh orange, lemon, and mandarin juices. The level of citrate in the fresh tomato juice was higher at a statistically significant level than that in tomato juice that was stored for 1 week. The amount of oxalate increased in stored tomato juice.

CONCLUSIONS

Fresh tomato juice is considered a rich source of citrate. Furthermore, a high level of magnesium and a low level of sodium and oxalate content were detected in fresh tomato juice, the usability of which in recurrent hypocitraturic nephrolithiasis can be investigated in clinical studies.

A nidus, crystalluria and aggregation: key ingredients for stone enlargement

The in vitro study of calcium oxalate (CaOx) stone formation is usually based on crystallisation models but it is recognised that both healthy individuals and stone formers have crystalluria. We have established a robust in vitro stone growth model based on the principle of mixed suspension, mixed product removal system (MSMPR). Utilising this technique we studied the influence of CaOx crystallisation kinetics and the variation of calcium and oxalate concentrations on CaOx stone growth in vitro. Six stones received standard concentration of Ca (6 mM) and Ox (1.2 mM) in the medium while another six received variable concentrations of both Ca and Ox at various intervals. Stone mass was plotted against the experiment duration (typically 5-7 weeks). The stone growth was dependent on sufficient input calcium and oxalate concentrations and once triggered, stone growth could not be maintained at reduced calcium and oxalate inputs. The stone growth rate was positively correlated to the number of crystals in suspension around the stone and to the crystal nucleation rate and negatively correlated to the crystal growth rates. This leads to the conclusion that aggregation of crystals from the surrounding suspension was the dominant mechanism for stone enlargement.

Lemonade therapy increases urinary citrate and urine volumes in patients with recurrent calcium oxalate stone formation

OBJECTIVES

Potassium citrate is prescribed to patients with calcium oxalate (CaOx) stone formation to increase urinary citrate and pH, thus reducing CaOx crystal formation. Lemonade therapy (LT) might also increase urinary citrate and the total urine volume. We compared the effects of LT alone (group 1, n = 63) and potassium citrate plus LT (group 2, n = 37) in patients with CaOx stone formation on the urinary citrate and total urine volume to determine the efficacy of LT.

METHODS

Adult patients with CaOx stone formation and three or more clinic visits from 1996 to 2005 and three or more UroRisk profiles were included in our retrospective analysis.

RESULTS

Urinary citrate increased maximally by 203 and 346 mg/day for groups 1 and 2, respectively. The maximal total urine volume increase was 763 and 860 mL/day for groups 1 and 2, respectively. The urinary citrate and total urine volume increased sooner during follow-up for group 1. By the last clinic visit, the urinary citrate and total urine volume had decreased in both groups. However, group 1 sustained a greater total urine volume than did group 2 (2.35 +/- 0.10 standard error versus 2.17 +/- 0.12 L/day). Urinary citrate was greater in group 1 (765 +/- 56 standard error versus 548 +/- 56 mg/day for group 2), but the change from baseline to the last visit was significant (P = 0.008) only in group 2.

CONCLUSIONS

LT resulted in favorable changes in urinary citrate and total urine volume in our series. Potassium citrate with LT was more effective than LT alone at increasing urinary citrate. Because maximal changes for urinary citrate and total urine volume were achieved earlier in follow-up, individualized encouragement and motivation should be provided to patients at each visit for sustained prevention.

Effects of Inositol Hexaphosphate (Phytate) on Calcium Binding, Calcium Oxalate Crystallization and In Vitro Stone Growth

PURPOSE

We measured and compared 3 activities of inositol hexaphosphate, also known as phytate, to explore their importance in relation to antilithogenic potential.

MATERIALS AND METHODS

Calcium binding activity by inositol hexaphosphate was measured with a calcium electrode in artificial and whole urine. Calcium oxalate crystallization inhibition was measured by a 96-well plate turbidimetric method with artificial and whole urine. Effects on stone growth were measured in an in vitro system of 12 stones grown simultaneously (a stone farm) using artificial urine alone or supplemented with urinary macromolecules.

RESULTS

Phytate decreased ionized calcium, increased the metastable limit, decreased the crystallization turbidity rate index and decreased the in vitro stone growth rate. The effective concentration for calcium binding reduction was about 2 orders of magnitude higher than that required for crystallization inhibition, which in turn was about 2 orders of magnitude higher than that required for stone growth inhibition. When human urine or artificial urine supplemented with urinary macromolecules was used, the effective concentration of phytate for inhibiting crystallization and stone growth was increased by about 1 order of magnitude.

CONCLUSIONS

Inhibition of crystallization by phytate does not depend on decreasing the effective ionized calcium concentration and inhibition of in vitro stone growth does not depend on inhibiting crystallization of the suspended crystals. To our knowledge this is the first demonstration of a quantitative distinction between the inhibition of crystallization and stone growth. Inhibition of in vitro stone growth in the presence of macromolecules occurred at concentrations consistent with urinary phytate excretion.

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.

Factors affecting calcium oxalate dihydrate fragmented calculi regrowth

Background

The use of extracorporeal shock wave lithotripsy (ESWL) to treat calcium oxalate dihydrate (COD) renal calculi gives excellent fragmentation results. However, the retention of post-ESWL fragments within the kidney remains an important health problem. This study examined the effect of various urinary conditions and crystallization inhibitors on the regrowth of spontaneously-passed post-ESWL COD calculi fragments.

Methods

Post-ESWL COD calculi fragments were incubated in chambers containing synthetic urine varying in pH and calcium concentration: pH = 5.5 normocalciuria (3.75 mM), pH = 5.5 hypercalciuria (6.25 mM), pH = 6.5 normocalciuria (3.75 mM) or pH = 6.5 hypercalciuria (6.25 mM). Fragment growth was evaluated by measuring increases in weight. Fragment growth was standardized by calculating the relative mass increase.

Results

Calcium oxalate monohydrate (COM) crystals formed on COD renal calculi fragments under all conditions. Under pH = 5.5 normocalciuria conditions, only COM crystals formed (growth rate = 0.22 ± 0.04 μg/mg·h). Under pH = 5.5 hypercalciuria and under pH = 6.5 normocalciuria conditions, COM crystals and a small number of new COD crystals formed (growth rate = 0.32 ± 0.03 μg/mg·h and 0.35 ± 0.05 μg/mg·h, respectively). Under pH = 6.5 hypercalciuria conditions, large amounts of COD, COM, hydroxyapatite and brushite crystals formed (growth rate = 3.87 ± 0. 34 μg/mg·h). A study of three crystallization inhibitors demonstrated that phytate completely inhibited fragment growth (2.27 μM at pH = 5.5 and 4.55 μM at pH = 6.5, both under hypercalciuria conditions), while 69.0 μM pyrophosphate caused an 87% reduction in mass under pH = 6.5 hypercalciuria conditions. In contrast, 5.29 mM citrate did not inhibit fragment mass increase under pH = 6.5 hypercalciuria conditions.

Conclusion

The growth rate of COD calculi fragments under pH = 6.5 hypercalciuria conditions was approximately ten times that observed under the other three conditions. This observation suggests COD calculi residual fragments in the kidneys together with hypercalciuria and high urinary pH values may be a risk factor for stone growth. The study also showed the effectiveness of specific crystallization inhibitors in slowing calculi fragment growth.

In vitro calcium oxalate crystallisation methods

In vitro calcium oxalate crystallisation has been, and will continue to be, of fundamental importance to urolithiasis research. Many different methods have been employed which differ qualitatively and quantitatively in the extent that they reproduce aspects of the renal system or in their ability to distinguish different aspects of crystallisation activity. Whatever system is used there are three key aspects that are worth bearing in mind. Firstly, a major controlling factor will be the prevailing supersaturation and other physicochemical considerations, secondly, during the course of the reaction different processes may come into play and thirdly, the processes we are trying to model take place in a dynamic biological environment. Different approaches to the study of crystallisation can be classified in many ways, such as the process or analytical technique but at a more fundamental level it is helpful to focus on the changes in supersaturation during the course of the reaction. A steady state supersaturation is more likely to be representative of the intra-renal situation than a system which decays to the equilibrium position. The constant composition method and the mixed suspension mixed product removal method both achieve a steady supersaturation.

How significant are clinically insignificant residual fragments following lithotripsy?

PURPOSE OF REVIEW

Extracorporeal shock-wave lithotripsy had revolutionized the treatment of kidney stones. Residual fragments smaller than 4 or 5 mm which are asymptomatic and likely to pass spontaneously are termed as clinically insignificant residual fragments. This article reviews the current literature with regards to the management of clinically insignificant residual fragments.

RECENT FINDINGS

However, the term is controversial because no consensus has been reached regarding its exact definition or interval after extracorporeal shock-wave lithotripsy to evaluate its presence. While most small residual stone fragments might be managed expectantly, a significant number of patients might become symptomatic or require intervention. These so-called clinically insignificant residual fragments have the potential to cause obstruction and are important risk factors for stone recurrence and re-growth.

SUMMARY

Residual fragments require close monitoring for stone growth, potential complications and subsequent intervention. Secondary procedures may be applied selectively to those patients who have significant symptoms of obstruction associated with the residual stone. Medical therapy might play an important role in the management of residual fragments.

An experimental study on residual lithiasis after shock wave lithotripsy

The main objective of this paper was to study residual lithiasis after extracorporeal shock wave lithotripsy (post-ESWL), with the aim of contributing to the development of effective prophylactic measures. In vivo regrown calcium oxalate monohydrate (COM) post-ESWL residual fragments were studied by stereoscopic microscopy, infrared spectroscopy and scanning electron microscopy with an energy dispersive X-ray analyzer. An in vitro system was also used to study the regrowth of post-ESWL fragments of COM calculi. The regrowth was evaluated as the relative increase in the weight of the fragments. The effects of a calcium oxalate crystallization inhibitor (phytate) were also evaluated. All of the in vivo regrown COM real residual post-ESWL fragments exhibited practically the same internal structural features. The in vitro studies demonstrated that the regrowth of post-ESWL residual fragments, in the absence of crystallization inhibitors, occurred even using normocalciuric/normooxaluric urine and could be detected at 24 h. At 144-240 h, the formation of new COM columnar zones was observed. The presence of 1.5 mg/l of phytate totally blocked the growth process. When hypercalciuric/normooxaluric urine was used, significant amounts of disorganized calcium oxalate dihydrate (COD) crystals were formed. The in vitro regrowth of post-ESWL COM fragments was clearly influenced by the presence of crystallization inhibitors. These data also demonstrate the importance that effective prophylactic therapies could exert on preventing recurrence.