Interactions between stone-forming calcific crystals and macromolecules

Cucumis callosus (Rottl.) Cogn. fruit extract ameliorates calcium oxalate urolithiasis in ethylene glycol induced hyperoxaluric Rat model

Cucumis callosus dry fruits are traditionally used as folk remedy to treat conditions like urethral irritations, urine stoppage or dribbling and other urinary ailments of man in north-west India. But no study is reported to validate this ethnic practice of using Cucumis fruit in urolithiasis. To evaluate anti-urolithiatic potential of Cucumis, hyperoxaluria was induced in rats by supplying 0.75% ethylene glycol (EG) + 1% ammonium chloride (AC) in drinking water for 14 days. Anti-urolithiatic activity of Cucumis callosus hydro-ethanolic extract (CCHEE) was assessed by measuring blood and urine biochemical parameters, oxidative stress indices, histopathology and osteopontin (OPN) expression. Administration of EG-AC to rats caused hyperoxaluria, crystalluria, azotaemia, oxidant/antioxidant imbalance (increase in lipid peroxidation (LPO), and decrease in glutathione (GSH) and catalase (CAT)), up-regulation of OPN and calcium oxalate (CaOx) crystal deposition in kidney. Treatment of afflicted rats with Cucumis fruits extract restored renal function to a great extent (CCHEE group), testified by improvement of stated parameters. Findings demonstrate curative efficacy of Cucumis fruit extract in EG induced urolithiasis of rats. The restoration of renal function was possibly by regulating renal stone formation via reducing urinary oxalate excretion, correcting oxidant/antioxidant imbalances, and reduced expression of OPN. Hence, results of this study validate the ethnic practice of using Cucumis fruit and conclude that fruit extracts have beneficial effects on CaOx urolithiasis and renal function.

Cross-talk between renal lithogenesis and atherosclerosis: an unveiled link between kidney stone formation and cardiovascular diseases

The prevalence of kidney stones and cardiovascular diseases (CVDs) are increasing throughout the world. Both diseases are chronic and characterized by accumulation of oxidized proteins and lipids in the renal tissue and arterial wall, respectively. Emerging studies have revealed a positive association between nephrolithiasis and CVDs. Based on preclinical and clinical evidences, this review discusses: (i) stone forming risk factors, crystal nucleation, aggregation, injury-induced crystal retention, and stone formation, (ii) CVD risk factors such as dyslipidemia, perturbation of gut microbiome, obesity, free radical-induced lipoprotein oxidation, and retention in the arterial wall, subsequent foam cell formation, and atherosclerosis, (iii) mechanism by which stone forming risk factors such as oxalate, calcium, uric acid, and infection contribute toward CVDs, and (iv) how CVD risk factors, such as cholesterol, phospholipids, and uric acid, contribute to kidney stone formation are described.

Antiurolithiatic activity of ethanol leaf extract of Ipomoea eriocarpa against ethylene glycol-induced urolithiasis in male Wistar rats

Objective:

The objective of this study was to investigate the prophylactic and curative effect of the ethanol leaf extract of Ipomoea eriocarpa (Convolvulaceae) (IEE) in ethylene glycol-induced urolithiasis in rats.

Materials and Methods:

Thirty male Wistar rats were divided into five groups (n = 6). All the groups received stone-inducing treatment till 28^th day, comprising 1% ethylene glycol (v/v) with 1% ammonium chloride (w/v) for 4 days, followed by 1% ethylene glycol alone in water, except Group I (Control). Group II received only stone-inducing treatment till 28^th day. Group III (Standard) received cystone (500 mg/kg) from 15^th day till 28^th day. Group IV (Prophylactic) received IEE (200 mg/kg) from 1^st day till 28^th day and Group V (Curative) received IEE (200 mg/kg) from 15^th day till 28^th day. Various biochemical parameters such as phosphorus, calcium, magnesium, urea, and creatinine levels were evaluated using urine, serum, and kidney homogenate. The kidneys were also sectioned and examined histopathologically under light microscope to study the kidney architecture and calcium oxalate deposits.

Results:

The IEE treatment (prophylactic and curative) significantly (P < 0.001) restored the parameters in urine, serum, and kidney homogenate to near-normal level. The histopathological examinations revealed that calcium oxalate crystal deposits in the renal tubules and congestion and dilation of the parenchymal blood vessels were significantly reverted after IEE treatment.

Conclusions:

The leaf extract of I. eriocarpa reduces and inhibits the growth of urinary stones showing its effect as an antiurolithiatic agent.

Natural promoters of calcium oxalate monohydrate crystallization

Crystallization is often facilitated by modifiers that interact with specific crystal surfaces and mediate the anisotropic rate of growth. Natural and synthetic modifiers tend to function as growth inhibitors that hinder solute attachment and impede the advancement of layers on crystal surfaces. There are fewer examples of modifiers that operate as growth promoters, whereby modifier-crystal interactions accelerate the kinetic rate of crystallization. Here, we examine two proteins, lysozyme and lactoferrin, which are observed in the organic matrix of three types of pathological stones: renal, prostatic, and pancreatic stones. This work focuses on the role of these proteins in the crystallization of calcium oxalate monohydrate (COM), the most prominent constituent of human kidney stones. Using a combination of experimental techniques, we show that these proteins, which are rich in l-arginine and l-lysine amino acids, promote COM growth. The synthesis and testing of peptides derived from contiguous segments of lysozyme's primary amino acid sequence revealed subdomains within the protein that operate either as an inhibitor or promoter of COM growth, with the latter exhibiting efficacies that nearly match that of the protein. We observed that cationic proteins promote COM growth over a wide range of modifier concentration, which differs from calcification promoters in the literature that exhibit dual roles as promoters and inhibitors at low and high concentration, respectively. This seems to suggest a unique mechanism of action for lysozyme and lactoferrin. Possible explanations for their effects on COM growth and crystal habit are proposed on the basis of classical colloidal theories and the physicochemical properties of peptide subdomains, including the number and spatial location of charged or hydrogen-bonding moieties.

Specificity of growth inhibitors and their cooperative effects in calcium oxalate monohydrate crystallization

The molecular recognition and interactions governing site-specific adsorption of growth inhibitors on crystal surfaces can be tailored in order to control the anisotropic growth rates and physical properties of crystalline materials. Here we examine this phenomenon in calcium oxalate monohydrate (COM) crystallization, a model system of calcification with specific relevance for pathological mineralization. We analyzed the effect of three putative growth inhibitors--chondroitin sulfate, serum albumin, and transferrin--using analytical techniques capable of resolving inhibitor-crystal interactions from interfacial to bulk scales. We observed that each inhibitor alters surface growth by adsorbing on to distinct steps emanating from screw dislocations on COM surfaces. Binding of inhibitors to different crystallographic faces produced morphological modifications that are consistent with classical mechanisms of layer-by-layer crystal growth inhibition. The site-specific adsorption of inhibitors on COM surfaces was confirmed by bulk crystallization, fluorescent confocal microscopy, and atomic force microscopy. Kinetic studies of COM growth at varying inhibitor concentrations revealed marked differences in their efficacy and potency. Systematic analysis of inhibitor combinations, quantified via the combination index, identified various binary pairings capable of producing synergistic, additive, and antagonistic effects. Collectively, our investigation of physiologically relevant biomolecules suggests potential roles of COM inhibitors in pathological crystallization and provides guiding principles for biomimetic design of molecular modifiers for applications in crystal engineering.

Study of antiurolithiatic activity of Asparagus racemosus on albino rats

Aims:

The aim of this study was to investigate the effect of ethanolic extract of Asparagus racemosus on urolithiasis in rats.

Materials and Methods:

Thirty-six male Wistar albino rats were randomly divided into six groups (n = 6). Ethylene glycol (EG) 0.75% and ammonium chloride (AC) 2% in drinking water were fed to all groups (Groups II–VI) except normal control (Group I) rats for 10 days to induce urolithiasis. Group III–VI rats were treated with ethanolic extract of Asparagus racemosus at doses 200, 400, 800, and 1600 mg/kg, respectively, for 10 days. Positive control (Group II) rats were treated with EG/AC alone. Group I rats were administered drinking water and distilled water (6 μl/g) by gavage. After 10 days, blood samples were collected and analyzed for serum concentrations of calcium, phosphorus, urea, and creatinine. The kidneys were removed and sectioned for histopathological examination. The data were presented as mean ± standard error of mean and analyzed using one-way analysis of variance and Student's “t”-test. P < 0.05 was considered statistically significant. Conventional windows software was used for statistical analysis.

Results:

The rats treated with ethanolic extract of A. racemosus at doses 800 and 1600 mg/ kg significantly (P < 0.05) reduced the serum concentrations of calcium, phosphorus, urea, and creatinine. Histopathology of the kidneys in Groups V and VI revealed less tissue damage and were almost similar to Group I rats.

Conclusions:

The ethanolic extract of A. racemosus has protective effect against urolithiasis.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Prophylaxis and therapeutic effects of raspberry (Rubus idaeus) on renal stone formation in Balb/c mice

PURPOSE

To evaluate the prophylactic potential of herbal decoction from Rubus idaeus, a medicinal plant widely used in the Middle East to treat kidney stones, by assessing the effect of administration in experimentally induced calcium oxalate (CaOx) nephrolithiasis in mice.

MATERIALS AND METHODS

This study was based on administration of glyoxylate and/or herbal treatments simultaneously for 12 days, followed by histological and biochemical tests. Group I was used as a negative control. Group II was only given daily intra-abdominal injection of glyoxylate (80 mg/Kg). Group III and IV were given 100 mg/kg/day and 200 mg/kg/day of aqueous extract of R. idaeus by gavage, respectively in addition to glyoxylate injection. To examine the effect of anti-oxidants on hyperoxaluria-induced changes in kidney, the enzymatic and non-enzymatic anti-oxidant levels were assessed.

RESULTS

Significant reductions were obtained in the urinary oxalate, calcium and phosphorus values in the herbal-treated groups relative to untreated animals while creatinine excretion increased. Serum oxalate, calcium and creatinine were significantly reduced, while phosphorus was not significantly changed. Kidney content of calcium was higher in the untreated group. Mice in treated groups at 12 days had significantly more superoxide dismutase, catalase, glutathione reductase (GSH) and G6PD activities than the untreated group. Hyperoxaluria-induced generation of malondialdehyde (MDA) and protein carbonyls was significantly prevented in the treated groups. R. idaeus had a significantly high content of vitamin E in the herbal treated groups. The histology showed more CaOx deposition in the kidneys of untreated animals.

CONCLUSION

Rubus idaeus has an impressive prophylactic effect on CaOx stones in nephrolithic mice. There is a possible role of lipid peroxidation in CaOx stone formation which may has a relationship with the major risk factors in urine including oxalate, calcium, phosphorus and MDA. Further experimental studies are required to elucidate the chemical constituents of the active ingredients of this interesting plant.

Antiurolithiatic and antioxidant activity of Mimusops elengi on ethylene glycol-induced urolithiasis in rats

Objective:

To evaluate the potential of Mimusops elengi in the treatment of renal calculi.

Materials and Methods:

Petroleum ether, chloroform, and alcohol extracts of Mimusops elengi bark were evaluated for antiurolithiatic and antioxidant activity in male albino Wistar rats. Ethylene glycol (0.75%) in drinking water was fed to all the groups (Groups II–IX) except normal control (Group I) for 28 days to induce urolithiasis for curative (CR) and preventive (PR) regimen. Groups IV, V, and VI served as CR, and groups VII, VIII, and IX as PR were treated with different extracts of M. elengi bark. Groups I, II, and III served as normal control, positive control (hyperurolithiatic), and standard (cystone 750 mg/kg), respectively. Oxalate, calcium, and phosphate were monitored in the urine and kidney. Serum BUN, creatinine, and uric acid were also recorded. In vivo antioxidant parameters such as lipid peroxidation (MDA), glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) were also monitored.

Results:

All the extracts of M. elengi were safe orally and exhibited no gross behavioral changes in the rats. In hypercalculi animals, the oxalate, calcium, and phosphate excretion grossly increased. However, the increased deposition of stone forming constituents in the kidneys of calculogenic rats were significantly (P < 0.001) lowered by curative and preventive treatment with alcohol extract (AlE) of M. elengi. It was also observed that alcoholic extract of M. elengi produced significant (P < 0.001) decrease in MDA, and increased GSH, SOD, and CAT. These results confirm that AlE of M. elengi possess potent antiurolithiatic activity.

Conclusion:

The results obtained suggest potential usefulness of the AlE of M. elengi bark as an antiurolithiatic agent.

Characterizations of urinary sediments precipitated after freezing and their effects on urinary protein and chemical analyses

One of the obstacles in analyzing frozen urine samples is the formation of uncharacterized precipitates. Frequently, these precipitates are discarded before analysis. Some laboratory data may be erroneous if these precipitates contain important compounds. In the present study, we examined urinary sediments precipitated after overnight storage at -20 degrees C. Although cells and debris were removed before freezing, the precipitates remained, whereas storing the centrifuged urine overnight at 4 degrees C did not result in precipitate formation. There were no significant differences observed among 10 healthy individuals (5 men and 5 women). EDTA (5 mM) could efficiently reduce the amount of precipitates to approximately 25% of the initial amount. The addition of exogenous CaCl2, but not sodium oxalate and NaCl, significantly increased the amount of precipitates in a dose-dependent manner. Linear regression analysis revealed a significant correlation between endogenous urinary calcium level and the amount of precipitates (r = 0.894; P < 0.001). Urine pH also had some effects on the type and amount of precipitates. These precipitates were composed mainly of calcium oxalate dihydrate and amorphous calcium crystals. The results also showed that these precipitates could deplete urinary proteins and calcium ions (23.6 +/- 1.1% decrease). Therefore, these freezer-induced urinary sediments significantly affect protein analysis and measurement of calcium levels in the urine. However, vigorous shaking of the sample at room temperature could redissolve these precipitates. Our data strongly indicate that these freezer-induced precipitates must be taken into account when the frozen urine samples are analyzed.

1,2,3,4,6-penta-O-galloyl-beta-D-glucose attenuates renal cell migration, hyaluronan expression, and crystal adhesion

Calcium oxalate monohydrate (COM) crystals bind avidly to the surface of proliferating and migrating renal endothelial cells, and oxalate-induced peroxidative injury can promote crystal attachment to renal epithelial cells. 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG), isolated from a traditional herbal remedy, inhibits vascular endothelial growth factor (VEGF) stimulated proliferation and migration of human umbilical vein endothelial cells (HUVECs) and has antioxidant activity. This study was performed to determine if PGG altered calcium oxalate monohydrate (COM) crystal adhesion to cells, perhaps via a change in cell surface properties. PGG significantly decreased COM crystal adhesion to cultured MDCK I cells at a low concentration (<10 microM) which was not cytotoxic. PGG exerted anti-adhesion effects whether cells or crystals were pre-coated. PGG also inhibited cell migration after scrape-wounding, decreased subsequent adhesion of crystals to proliferating and migrating cells, and decreased expression of the crystal binding molecule hyaluronan. These findings suggest that PGG represents a potential urolithiasis prevention compound. Anti-crystal adhesion effects appear multifaceted involving crystal coating by PGG, as well as decreased cell migration and the associated surface expression of hyaluronan. The latter represents a novel mechanism of nephrolithiasis prevention.

Acidic polyanion poly(acrylic acid) prevents calcium oxalate crystal deposition

Acidic macromolecules inhibit calcium oxalate nucleation, growth, aggregation and attachment to cells in vitro. To test for such an effect in vivo we used osmotic minipumps to continuously infuse several doses of the 5.1 kDa poly(acrylic acid) (pAA(5.1)) into rats fed a diet which causes renal calcium oxalate crystal deposition. Although kidneys of rats receiving the saline control contained calcium oxalate crystals, measured by polarized light microscopy, those of animals given pAA(5.1) had significantly lower numbers of crystals in various zones of the kidney. Delivery of pAA(5.1) to urine was confirmed by measuring excretion of infused biotinylated pAA(5.1). Both the derivatized and unlabelled pAA(5.1) had the same effects on crystallization in vitro. Our study shows that acidic polymers hold promise as effective therapies for kidney stones likely through prevention of calcium oxalate crystal aggregate formation.

Direct AFM measurements of adhesion forces between calcium oxalate monohydrate and kidney epithelial cells in the presence of Ca2+ and Mg2+ ions

Adhesion forces between the calcium oxalate monohydrate (COM, whewellite) crystal and the layer of the epithelial kidney cells have been directly measured under buffer solutions by using atomic force microscope (AFM). Two renal epithelial lines, MDCK (a collecting duct line) and LLC-PK1 (a proximal tubular line), were used. All experiments were conducted in buffer solutions containing additional Ca(2+) and Mg(2+) ions in the various concentrations. For MDCK-cells, the obtained values of the adhesion force were in the range 0.12-0.51 nN and 0.12-0.20 nN for Ca(2+) and Mg(2+), respectively. No adhesion force (larger than 0.05 nN) has been found for LLC-PK1 cells. The "critical" concentrations of ions, near which the adhesion force (for MDCK-cells) was maximal, were found to be 100 mM. The "critical" concentration of ions and the tendency of the adhesion forces with the changing ions concentration, confirm earlier results of Lieske et al. [J.C. Lieske, G. Farell, S. Deganello, Urol. Res. 32 (2004) 117-123], in which the affinity (rather than the adhesion force) between the COM micro-crystals and the layer of the MDCK-cells were measured, calculating the radioactive signal of radioactive (14)C COM-crystals stuck to the cells. We believe that the aggregation of the COM crystals does not occur in the bulk urine due to short travel time through the nephron. If so, the kidney stone formation is determined by COM-seeding on the tubules walls. The further growth of the stone on the seed can take practically unlimited time because the COM crystal is practically is not soluble in water or urine solutions. The value of the adhesion force can be useful for evaluation of the adhesion energy or probability of the COM-aggregates to stick to the kidney epithelium under the urine flow. This probability is calculated taking into account the adhesion force, F(ad), and hydrodynamic driving force of the flow. This probability reflects the opportunity of the small aggregates to grow and form the kidney stones.

Prophylaxis effect of Trigonella foenum graecum L. seeds on renal stone formation in rats

Despite considerable progress in medical therapy, there is no satisfactory drug to treat kidney stones. Therefore, the current study aimed to look for an alternative by using Trigonella foenum graecum (Tfg) on nephrolithiasic rats as a preventive agent against the development of kidney stones, which is commonly used in Morocco as a phytotherapeutic agent. The inhibitory effect of the aqueous extract of Tfg seeds was examined on the formation of calcium oxalate renal stones induced by ethylene glycol (EG) with ammonium chloride. At the end of the experiment all kidneys were removed and examined microscopically for possible crystal/stone locations and the total calcium amount in the renal tissue was evaluated. The blood was recovered to determine the levels of calcium, phosphorus, creatinine and urea. The results showed that the amount of calcification in the kidneys and the total calcium amount of the renal tissue in rats treated with Tfg were significantly reduced compared with the untreated group. Consequently, Tfg may be a useful agent in the treatment of patients with calcic urolithiasis.

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.

Comparison of urinary proteins in calcium stone formers and healthy individuals: a case-control study

OBJECTIVE

This study aimed at comparing the urinary protein levels in calcium stone formers with those of healthy individuals.

PATIENTS AND METHODS

From January 2002 until June 2004, 100 calcium stone formers (mean age 38.6 +/- 10.3 years), who had at least two episodes of calcium stone formation, were compared with 100 healthy individuals (mean age 33.8 +/- 9.7 years). Their 24-hour urinary protein levels, using SDS-PAGE, were measured.

RESULTS

The mean 24-hour urinary Tamm-Horsfall protein (THP) levels were 3.3 +/- 0.8 mg in the case group and 4.6 +/- 1.9 mg in the controls, and the difference was not statistically significant (p = 0.53). However, the THP levels in individuals with and without bacteriuria were significantly different (15.8 +/- 3.3 mg vs. 2.6 +/- 1.0 mg, p = 0.0001). The mean 24-hour urinary albumin concentrations were 163.31 +/- 15.1 mg in the case group and 74.26 +/- 4.6 mg in the controls. The mean 24-hour urinary transferrin levels were 8.09 +/- 2.7 mg in the case group and 0.40 +/- 0.3 mg in the controls. The differences were statistically significant for both albumin and transferrin (p < 0.0001 and p = 0.0063, respectively). There were no significant differences in any other mean urinary protein concentrations between cases and controls.

CONCLUSIONS

The THP level in the urine of stone formers is not quantitatively different from that of healthy individuals, but it increases in association with bacteriuria. Albumin and transferrin may play a presumptive role in stone formation.

Vitamin E attenuates crystal formation in rat kidneys: Roles of renal tubular cell death and crystallization inhibitors

We previously reported that oxidative stress and renal tubular damage occur in chronic hyperoxaluric rats. However, the in vivo responses of renal epithelial cells after vitamin E administration and their correlations with calcium oxalate (CaOx) crystal formation have not been evaluated. Male Wistar rats received 0.75% ethylene glycol (EG) for 7, 21, or 42 days to induce CaOx deposition (EG group). Another group of EG-treated rats received 200 mg kg(-1) of vitamin E intraperitoneally (EG+E group) to evaluate its effect on hyperoxaluria. Urinary electrolytes and biochemistry and levels of lipid peroxides and enzymes were examined, together with serum vitamin E levels. Levels of the tubular markers, alpha and mu glutathione S-transferase, proliferating cell nuclear antigen (PCNA), osteopontinin (OPN), and Tamm-Horsfall protein (THP) were also measured, and TUNEL staining was performed to examine the viability of the tubular epithelium. There were no significant differences between the two age-matched controls either untreated or given vitamin E. Compared to untreated controls, tubular cell death was increased at all time points in EG rats with a gradual increase in CaOx crystals, whereas the number of PCNA-positive cells was only significantly increased on day 21. In EG+E rats, tubular cell death was decreased compared to the EG group, and cell proliferation was seen at all time points, while CaOx crystal deposition was decreased, but hyperoxaluria, urinary lipid peroxides, and enzymuria were unaffected. Vitamin E supplement prevented the loss of OPN and THP in renal tissues by EG and the reduction in their levels in the urine. The beneficial effect of vitamin E in reducing CaOx accumulation is due to attenuation of tubular cell death and enhancement of the defensive roles of OPN and THP.

Mixing model systems: using zebrafish and mouse inner ear mutants and other organ systems to unravel the mystery of otoconial development

Human vestibular dysfunction is an increasing clinical problem. Degeneration or displacement of otoconia is a significant etiology of age-related balance disorders and Benign Positional Vertigo (BPV). In addition, commonly used antibiotics, such as aminoglycoside antibiotics, can lead to disruption of otoconial structure and function. Despite such clinical significance, relatively little information has been compiled about the development and maintenance of otoconia in humans. Recent studies in model organisms and other mammalian organ systems have revealed some of the proteins and processes required for the normal biomineralization of otoconia and otoliths in the inner ear of vertebrates. Orchestration of extracellular biomineralization requires bringing together ionic and proteinaceous components in time and space. Coordination of these events requires the normal formation of the otocyst and sensory maculae, specific secretion and localization of extracellular matrix proteins, as well as tight regulation of the endolymph ionic environment. Disruption of any of these processes can lead to the formation of abnormally shaped, or ectopic, otoconia, or otoconial agenesis. We propose that normal generation of otoconia requires a complex temporal and spatial control of developmental and biochemical events. In this review, we suggest a new hypothetical model for normal otoconial and otolith formation based on matrix vesicle mineralization in bone which we believe to be supported by information from existing mutants, morphants, and biochemical studies.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Oral L-arginine supplementation ameliorates urinary risk factors and kinetic modulation of Tamm-Horsfall glycoprotein in experimental hyperoxaluric rats

BACKGROUND

Oral supplementation of l-arginine (l-arg) is found to be beneficial in many kidney disorders. We determined whether l-arg supplementation safeguards the renal epithelial cell damage induced by hyperoxaluria with excretion of urinary marker enzymes and lithogenic salts with special reference to Tamm-Horsfall glycoprotein (THP).

METHODS

Hyperoxaluria was induced by 0.75% ethylene glycol (EG) in drinking water. l-Arg was co-supplemented at the dose of 1.25 g/kg b.w. orally for 28 days. At the end of experimental period, 24-h urine samples were collected in all the experimental groups. Isolation and purification of THP was carried in rat urine and were subjected to spectrophotometric crystallization assay and calcium-(14)C-oxalate binding studies. Determination of the lithogenic risk factors like calcium, oxalate, phosphorus, citrate, and marker enzymes such as lactate dehydrogenase (LDH) and gamma-glutamyltransferase (gamma-GT) were carried out in the collected urine sample.

RESULTS

Urinary excretion of calcium and oxalate was significantly increased in EG-treated rats. In l-arg supplemented hyperoxaluric rats, these concentrations were significantly (p<0.001) decreased when compared to that of hyperoxaluric rats, and were moderately elevated from that of control rats. The activities of urinary marker enzymes, both LDH and gamma-GT were 2-fold increased in EG-treated rats, when compared to control rats, but these values were maintained near normal in l-arg supplemented EG-treated rats. Citrate excretion was enhanced in the l-arg co-supplemented hyperoxaluric rats. In spectrophotometric crystallization assay system, l-arg supplemented rat THP showed inhibition in nucleation and aggregation phases, whereas EG-treated rat THP showed promotion of both calcium oxalate nucleation and aggregation phases. In calcium-(14)C-oxalate binding assay, THP derived from hyperoxaluric rats exhibited 2-fold increase (p<0.001) in the Ca*Ox binding when compared to control and l-arg supplemented animals.

CONCLUSIONS

l-Arg could act as a potent antilithic agent, by increasing the level of citrate in the hyperoxaluria-induced rats and decreasing calcium oxalate binding to the THP. l-Arg also effectively prevents the deposition of calcium oxalate crystals by curtailing the renal epithelial damage and protein oxidation as evidenced by the normal activities of urinary marker enzymes in l-arg supplemented hyperoxaluric rats.

The association of different urinary proteins with calcium oxalate hydromorphs. Evidence for non-specific interactions

It has been proposed that various urinary proteins interact specifically with different calcium oxalate hydromorphs and these interactions have important implications regarding the understanding of the onset and progress of kidney stone disease. Calcium oxalate monohydrate and dihydrate crystals were grown and characterised thoroughly to establish sample purity. These crystals were then incubated in artificial urine samples containing isolated urinary macromolecules. Crystal growth was prevented by saturating the incubation mix with calcium oxalate, and this was confirmed through electron microscopy and calcium measurements of the incubation mix. The surface interactions between the different calcium oxalate hydrates and urinary proteins were investigated by the use of Western blots and immunoassays. The same proteins, notably albumin, Tamm-Horsfall protein, osteopontin and prothrombin fragment 1, associated with both hydrates. There was a trend for more protein to associate with calcium oxalate dihydrate, and greater quantities of different proteins associated with both hydrates when Tamm-Horsfall protein was removed from the incubation mix. There is no evidence from this study to indicate that particular proteins interact with specific calcium oxalate hydrates, which in turn suggests that these protein-mineral interactions are likely to be mediated through non-specific charge interactions.

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.

Otopetrin 1 is required for otolith formation in the zebrafish Danio rerio

Orientation with respect to gravity is essential for the survival of complex organisms. The gravity receptor is one of the phylogenetically oldest sensory systems, and special adaptations that enhance sensitivity to gravity are highly conserved. The fish inner ear contains three large extracellular biomineral particles, otoliths, which have evolved to transduce the force of gravity into neuronal signals. Mammalian ears contain thousands of small particles called otoconia that serve a similar function. Loss or displacement of these structures can be lethal for fish and is responsible for benign paroxysmal positional vertigo (BPPV) in humans. The distinct morphologies of otoconial particles and otoliths suggest divergent developmental mechanisms. Mutations in a novel gene Otopetrin 1 (Otop1), encoding multi-transmembrane domain protein, result in nonsyndromic otoconial agenesis and a severe balance disorder in mice. Here we show that the zebrafish, Danio rerio, contains a highly conserved gene, otop1, that is essential for otolith formation. Morpholino-mediated knockdown of zebrafish Otop1 leads to otolith agenesis without affecting the sensory epithelium or other structures within the inner ear. Despite lack of otoliths in early development, otolith formation partially recovers in some fish after 2 days. However, the otoliths are malformed, misplaced, lack an organic matrix, and often consist of inorganic calcite crystals. These studies demonstrate that Otop1 has an essential and conserved role in the timing of formation and the size and shape of the developing otolith.

Effect of aqueous extract from Herniaria hirsuta L. on experimentally nephrolithiasic rats

Despite considerable progress in medical therapy, there is no satisfactory drug to treat kidney stones. Therefore, this current study is aimed to look for an alternative treatment by using Herniaria hirsuta on nephrolithiasic rats as a preventive agent against the development of kidney stones. The experiment was conducted in normal and calcium oxalate (CaOx) nephrolithiasic rats during 3 weeks. Several parameters were followed weekly including water intake, urinary volume and pH, some urinary chemistries, and crystalluria. At the end, kidneys were analyzed by light microscope. The results showed that water intake and urinary volume increased in nephrolithiasic rats, but their urinary pH decreased especially in the third week of treatment. Urinary oxalate increased significantly during the second week for untreated rats and remained constant in rats treated with Herniaria decoction. However, urinary calcium decreased significantly in week 2 in untreated rats and remained constant in treated rats. Qualitative analysis of crystalluria showed that untreated rats excreted large CaOx monohydrate and few dihydrate crystals while treated animals excreted mostly small CaOx dihydrate crystals. The examination of kidney sections revealed that CaOx deposition was limited in treated rats when compared to untreated ones. These results obtained in vivo confirmed the beneficial effect of Herniaria hirsuta and may justify its use as a preventive agent against the formation of calcium oxalate kidney stones.

Calcium oxalate monohydrate binding protein: a diagnostic biomarker for calcium oxalate kidney stone formers

Urinary oxalate is a biomarker for calcium oxalate kidney stone disease; however, its assay is insensitive and nonspecific. Calcium oxalate monohydrate (COM) binding protein (45 kDa) is a promoter of calcium oxalate kidney disease, which is markedly upregulated by oxalate induced oxidative stress. The current study was carried out to evaluate whether COM binding protein can serve as a diagnostic marker for calcium oxalate kidney stone formers. COM binding protein was isolated, purified and antibody was raised against it in rabbits. Urine samples (24 h) were collected from patients suffering from various kidney diseases such as acute nephritis, chronic nephritis, nephrotic syndrome, calcium oxalate (CaOx) stone formers, uric acid stone formers, struvite stone formers and calcium phosphate stone formers. This COM binding protein was quantified by an in house ELISA method and the excretion was found to lie between 2 and 3 mg in control samples, while in CaOx stone formers it was detected between 11 and 19 mg. Urinary risk factors were assayed. We conclude that COM binding protein can serve as a diagnostic marker for CaOx stone formers.

Tamm-Horsfall protein is a critical renal defense factor protecting against calcium oxalate crystal formation

BACKGROUND

The tubular fluid of the mammalian kidney is often supersaturated with mineral salts, but crystallization rarely occurs under normal conditions. The unique ability of the kidney to avoid harmful crystal formation has long been attributed to the inhibitory activity of the urinary macromolecules, although few in vivo studies have been carried out to examine this hypothesis. Here we examined the role of Tamm-Horsfall protein (THP), the principal urinary protein, in urinary defense against renal calcium crystal formation, using a THP knockout model that we recently developed.

METHODS

Wild-type and THP knockout mice were examined for the spontaneous formation of renal calcium crystals using von Kossa staining. The susceptibility of these mice to experimentally induced renal crystal formation was evaluated by administering mice with ethylene glycol, a precursor of oxalate, and vitamin D(3), which increases calcium absorption. Renal calcium crystals were visualized by von Kossa stain, dark field microscopy with polarized light and scanning electron microscopy.

RESULTS

Inactivating the THP gene in mouse embryonic stem cells results in spontaneous formation of calcium crystals in adult kidneys. Excessive intake of calcium and oxalate, precursors of the most common type of human renal stones, dramatically increases both the frequency and the severity of renal calcium crystal formation in THP-deficient, but not in wild-type mice. Under high calcium/oxalate conditions, the absence of THP triggers a marked, adaptive induction in renal epithelial cells of osteopontin (OPN), a potent inhibitor of bone mineralization and vascular calcification. Thus, OPN may serve as an inducible inhibitor of calcium crystallization, whereas THP can serve as a constitutive and apparently more effective inhibitor.

CONCLUSION

These results provide the first in vivo evidence that THP is a critical urinary defense factor and suggest that its deficiency could be an important contributing factor in human nephrolithiasis, a condition afflicting tens of millions of people in the world annually.

Apoptosis and its related genes in renal epithelial cells of the stone-forming rat

Experimental hyperoxaluria and calcium oxalate (CaOx) crystals are associated with renal epithelial injury and cell death. A recent study has demonstrated an oxalate-induced increase in cellular apoptosis in vitro, and speculates that this phenomenon may contribute to stone formation. We investigated the incidence of apoptotic cells and the expression of apoptosis related genes in the kidneys of stone-forming rats. Male Wistar rats were administrated ethylene glycol in drinking water and force fed with 1alpha-OH-D3. Apoptosis was detected as a ladder of fragmented DNA in agarose gels of electrophoresed genomic DNA. Apoptotic cells were localized by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) method. The expression of apoptosis-related genes was analyzed by both reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry. While no labeling was detected in the controls or on the first day of administration by the TUNEL method, labeling began to be detected in the renal tubular epithelium of the outer medulla at day 3, and the number of labeled cells increased progressively during the observation period. A ladder of DNA fragments was demonstrated in the kidneys of rats after 2 weeks. Immunohistochemical studies revealed the expression of Fas ligand (Fas L), Bax and interleukin-1 beta converting enzyme (ICE) in the renal tubular epithelium of the descending limb of loop of Henle and the distal convoluted tubules. mRNA of the ICE, c-myc, p53 and Fas L genes was also upregulated in the kidneys of the stone-forming rats.

Modulatory Effect of the 23-kD Calcium Oxalate Monohydrate Binding Protein on Calcium Oxalate Stone Formation during Oxalate Stress

AIMS

To isolate, characterize, and quantify the 23-kD calcium oxalate monohydrate (COM) binding protein in the urine of controls and calcium oxalate stone formers and to study its role in kidney stone formation.

METHODS

Calcium oxalate crystals were prepared and allowed to interact with human control kidney homogenate as well as urine of controls and calcium oxalate stone formers. EDTA extract was used for the separation of the 23-kD COM-binding protein (partially purified). This partially purified 23-kD COM-binding protein was further separated by DEAE-cellulose column chromatography. SDS-PAGE confirmed the molecular weight. An antibody was raised against the renal 23-kD COM-binding protein in rabbits. The 23-kD COM-binding protein was quantified in the urine from controls and stone formers by ELISA. Thiol group quantification, oxalate-binding assay, and calcium oxalate crystal nucleation and aggregation were performed. Morphological changes of the calcium oxalate crystals induced by the urinary 23-kDa protein were determined using scanning electron microscopy. The expression of this protein using different concentrations of oxalate was also determined in an in vitro model.

RESULTS

The urinary excretion of the 23-kD COM-binding protein varies between 0.5 and 1.5 mg/24 h in controls, while in stone former its excretion was found to range from 5 to 7 mg/24 h. The protein isolated from urine was found to inhibit crystal nucleation and aggregation in controls, while the protein isolated from stone formers exhibited less inhibitory activity with reduced thiol groups. The 23-kD COM-binding protein derived from control urine formed COM crystals and intertwined calcium oxalate dihydrate crystals in a crystal growth system, while protein isolated from stone formers' urine induced aggregation of COM crystals. This protein expression was found to be increased with increasing concentration of oxalate in renal epithelial cells of the African green monkey kidney (VERO) cell line.

CONCLUSIONS

Increased expression and excretion of the 23-kD protein was observed in oxalate stress conditions, and in stone formers this protein exhibited a promoting activity. The increased excretion of this protein with promoting activity favors the lithogenic process in stone formers.

Oxalate binding proteins in calcium oxalate nephrolithiasis

The existence of several oxalate specific binding proteins have been demonstrated in human and rat kidney. These occur in both cortical and medullary cells and are distributed mostly in the subcellular organelles. About 1/3 of the total cellular oxalate binding was localised in the inner mitochondrial membrane while the rest was in the nucleus. The purified mitochondrial oxalate binding protein (62 kDa) was composed, with a higher molar proportion, of basic amino acids, and could accumulate oxalate on incorporation into liposomes. In the nucleus, histone H(1B) (27.5 kDa), nuclear membrane protein (68 kDa) and nuclear pore complex protein (205 kDa) were present with oxalate binding activities. In addition, a 45 kDa calcium oxalate binding protein was identified in most of the subcellular organelles. Both mitochondrial and nuclear oxalate binding proteins and calcium oxalate binding protein have shown the kinetic properties of specificity, saturability, pH and temperature dependency, energy of activation and inhibition by substrate analogues. All oxalate binding proteins were sensitive to the transport inhibitor 4'-4' diisothiocyano stilbene-2-2 disulphonic acid (DIDS), which is known to interact with the lysine moiety of the proteins. Calcium oxalate monohydrate (COM) crystals adsorbed oxalate binding proteins from human and rat kidney, and oxalate binding proteins isolated from human kidney stone matrix also exhibited the above kinetic properties. In experimental hyperoxaluria, all of the renal oxalate binding proteins showed enhanced oxalate binding activity with increased protein concentration. This enhanced oxalate binding activity was also attributed to increased lipid peroxidation, which correlated positively, and to decreased thiol status, which correlated negatively. A positive correlation was observed between the lipid peroxidation and both the oxalate binding activity of the in vitro peroxidised subcellular organelles and the purified protein. Similarly, in an in vivo hyperoxaluric condition, a negative correlation was observed between thiol content and both the oxalate binding activity of the peroxidised subcellular organelles and the purified protein. In the calcium oxalate crystal growth system, the oxalate binding proteins behaved either as promoters or inhibitors of the nucleation and aggregation of crystals. Following the peroxidation of the proteins, the degree of effect of the promoter protein was further stimulated while the degree of inhibition caused by the inhibitor protein further declined. Similar observations were duplicated with the proteins derived from hyperoxaluric rat kidney or kidney homogenate subjected to in vitro lipid peroxidation. The oxalate binding proteins were thought to modulate the crystallisation process in an hyperoxaluric condition similar to calcium specific binding protein modulators.

The density and protein content of calcium oxalate crystals precipitated from human urine: a tool to investigate ultrastructure and the fractional volume occupied by organic matrix

One of the key debates in biomineralisation studies is the extent to which components of the organic matrix become occluded into the crystal lattice during growth. Here, the relationship between protein content and density of calcium oxalate crystals grown in human urine has been investigated in order to determine which fraction of crystal volume is non-mineral. The density of crystals varied from 1.84 to 2.08 g/cm3 while the protein content ranged from 0.1 to 2.1% (w/w). There was an inverse relationship between measured density and protein content which was qualitatively and quantitatively consistent with predictions based on reasonable densities for the mineral and non-mineral components. The coefficients of the fitted equation suggest that, at 2% protein (w/w), the volume of non-mineral would be 5.0% (v/v). The density values we observed are incompatible with fractional volumes of 20%. The results confirm that the occlusion of a small but possibly significant amount of protein into a crystal lattice is possible, but cast doubt on the hypothesis that protein acts as a major intracrystalline ultrastructural element. Moreover, the methodology developed for this study offers a simple and robust method for interrogating organic/inorganic associations in a range of biological and medical systems.

Crystal attachment to injured renal collecting duct cells: influence of urine proteins and pH

BACKGROUND

The attachment of crystals to injured kidney epithelium is thought to be a necessary event in the development of urolithiasis. In vivo, the crystals are coated with urinary macromolecules that define the surface properties of the crystals. The present study examines the influence of coating of calcium oxalate crystals with urinary macromolecules on their attachment to both healthy (polarized) and injured (nonpolarized) primary inner medullary collecting duct (IMCD) cells.

METHODS

Calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) crystals were coated with urine macromolecules by incubating the crystals in urine from normal healthy volunteers at pH 5, 6, and 7. The level of attachment of the coated crystals to IMCD cells was also determined at pH 5, 6, and 7. The adsorbed proteins were extracted from the crystal surfaces and separated by gel electrophoresis.

RESULTS

The coating of calcium oxalate crystals with urine proteins greatly reduced the attachment of crystals to both control and injured IMCD cells. At pH levels below 6, the crystals readily attached to injured cells. Extraction and separation of the adsorbed proteins showed that both COM and COD crystals adsorbed a similar array of proteins. At pH 5 and 6, several trace proteins were adsorbed to the crystals and were not apparent at pH 7.

CONCLUSION

The coating of crystals with urine macromolecules greatly reduces the attachment of the crystals to normal healthy epithelia. The coating and attachment of the crystals below pH 6 enhances the attachment to injured cells. The enhanced crystal attachment could possibly be associated with one or more proteins adsorbed to the crystal surface that are not adsorbed to the crystals at higher pH.

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

BACKGROUND

Cell membranes and their lipids play critical roles in calcification. Specific membrane phospholipids promote the formation of calcium phosphate and become a part of the organic matrix of growing calcification. We propose that membrane lipids also promote the formation of calcium oxalate (CaOx) and calcium phosphate (CaP) containing kidney stones, and become a part of their stone matrix.

METHODS

Human urine, crystals of CaOx and CaP produced in the urine of healthy individuals, and urinary stones containing struvite, uric acid, CaOx and CaP crystals for the presence of membrane lipids were analyzed. Crystallization of CaOx monohydrate at Langmuir monolayers of dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylserine (DPPS), dioleoylphosphatidylglycerol (DOPG), palmitoyloleoylphosphatidylglycerol (POPG) and dimyristoylphosphatidylglycerol (DMPG) was investigated to directly demonstrate that phospholipid assemblies can catalyze CaOx nucleation.

RESULTS

Urine as well as CaOx and CaP crystals made in the urine and various types of urinary stones investigated contained some lipids. Urine of both CaOx and uric acid stone formers contained significantly more cholesterol, cholesterol ester and triglycerides than urine of healthy subjects. However, urine of CaOx stone formers contained more acidic phospholipids. The organic matrix of calcific stones contained significantly more acidic and complexed phospholipids than uric acid and struvite stones. For each Langmuir monolayer precipitation was heterogeneous and selective with respect to the orientation and morphology of the CaOx crystals. Crystals were predominantly monohydrate, and most often grew singly with the calcium rich (10-1) face toward the monolayer. The number of crystals/mm2 decreased in the order DPPG> DPPC and was inversely proportional to surface pressure and mean molecular area/molecule.

CONCLUSIONS

Stone forming conditions in the kidneys greatly impact their epithelial cells producing significant differences in the urinary lipids between healthy and stone forming individuals. Altered membrane lipids promote face selective nucleation and retention of calcium oxalate crystals, and in the process become a part of the growing crystals and stones.

Expression of osteopontin in rat kidneys: induction during ethylene glycol induced calcium oxalate nephrolithiasis

PURPOSE

Osteopontin is a well-known component of stone matrix and a strong inhibitor of the nucleation, growth and aggregation of calcium oxalate crystals in vitro. To understand its involvement in vivo in calcium oxalate nephrolithiasis we investigated the renal expression and urinary excretion of osteopontin in normal rats, and rats with hyperoxaluria and calcium oxalate crystal deposits in the kidneys.

MATERIALS AND METHODS

Calcium oxalate nephrolithiasis was induced by administering ethylene glycol. Immunohistochemistry and in situ hybridization were done to localize osteopontin and osteopontin messenger RNA in the kidneys, while sensitive reverse transcriptase quantitative competitive template polymerase chain reaction was performed to detect and quantify osteopontin messenger RNA expression. Urinary excretion was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis, and then quantified by densitometry of the Western blots.

RESULTS

Osteopontin expression in the kidneys was significantly increased after hyperoxaluria and it increased further after the deposition of calcium oxalate crystals in the kidneys. Urinary excretion of osteopontin increased concomitantly. The results reveal differences in renal responses after exposure to oxalate and calcium oxalate crystals. In normal kidneys osteopontin expression was limited to a small number of cells of the thin limbs of the loop of Henle and papillary surface epithelium. During hyperoxaluria osteopontin expression in the kidneys was increased but still mostly limited to cells of the thin limb and papillary surface epithelium. However, after calcium oxalate crystal deposition osteopontin expression was observed throughout the kidneys, including segments of the proximal tubules.

CONCLUSIONS

In response to exposure to oxalate and calcium oxalate crystals renal epithelial cells increase the production of osteopontin, which may have a significant role in calcium oxalate nephrolithiasis.

The effect of Phyllanthus niruri on urinary inhibitors of calcium oxalate crystallization and other factors associated with renal stone formation

OBJECTIVE

To evaluate the effect of an aqueous extract of Phyllanthus niruri (Pn), a plant used in folk medicine to treat lithiasis, on the urinary excretion of endogenous inhibitors of lithogenesis, citrate, magnesium and glycosaminoglycans (GAGs).

MATERIALS AND METHODS

The effect of chronic (42 days) administration of Pn (1.25 mg/mL/day, orally) was evaluated in a rat model of urolithiasis induced by the introduction of a calcium oxalate (CaOx) seed into the bladder of adult male Wistar rats. The animals were divided into four groups: a sham control (16 rats); a control+Pn (six); CaOx+water instead of Pn (14); and CaOx+Pn (22). Plasma and urine were collected after 42 days of treatment for biochemical analysis and the determination of urinary excretion of citrate, magnesium and GAGs. The animals were then killed and the calculi analysed.

RESULTS

The creatinine clearance or urinary and plasma concentrations of Na+, K+, Ca2+, oxalate, phosphate and uric acid were unaffected by Pn or the induction of lithiasis. Treatment with Pn strongly inhibited the growth of the matrix calculus and reduced the number of stone satellites compared with the group receiving water. The calculi were eliminated or dissolved in some treated animals (three of 22). The urinary excretion of citrate and magnesium was unaffected by Pn treatment. However, the mean (sd) urinary concentration of GAGs was significantly lower in rats treated with CaOx+Pn, at 5.64 (0.86) mg/g creatinine, than when treated with CaOx + water, at 11.78 (2.21) mg/g creatinine. In contrast, the content of GAGs in the calculi was higher in the CaOx + Pn rats, at 48.0 (10.4) g/g calculus, than in the CaOx + water group, at 16.6 (9.6) g/g calculus.

CONCLUSION

These results show that Pn has an inhibitory effect on crystal growth, which is independent of changes in the urinary excretion of citrate and Mg, but might be related to the higher incorporation of GAGs into the calculi.

Determinants of urinary excretion of Tamm-Horsfall protein in non-selected kidney stone formers and healthy subjects

BACKGROUND

The aim of the study was to measure urinary excretion of Tamm-Horsfall protein (THP), an important inhibitor of crystallization, and to identify possible determinants of urinary THP excretion in non-selected kidney stone formers (SF) and healthy subjects (C).

METHODS

By means of a commercially available ELISA (Pharmacia and Upjohn/Elias, Germany), we measured THP in 24-h urines of 104 SF (74 males/30 females, age 16-74 years) who had formed 8.7+/-2.4 stones (range 1-240), and of 71 C (41 males/30 females, age 22-62 years). Types of stones formed by SF were 88 calcium, eight uric acid, six infection, and two cystine. All values are means+/-SE.

RESULTS

The normal range (5th to 95th percentile) of U(THP)xV was 9.3-35.0 mg/day in males and 9.0-36.3 mg/day in females respectively. Mean U(THP)xV was 21.3+/-1.2 mg/day (range 3. 4-51.6) in male and 15.2+/-1.6 mg/day (range 1.8-32.3) in female SF (P=0.008 vs male SF). Since U(THP)xV was positively correlated with C(Crea) (r=0.312, P=0.001) in SF as well as with U(Crea)xV (r=0.346, P=0.0001) and with body surface (r=0.271, P=0.0003) in all study subjects, mean THP/Crea (mg/mmol) was used for all further calculations. Overall, THP/Crea was lower in SF (1.42+/-0.07 vs 1. 68+/-0.08, P:=0.015), mainly due to increased THP/Crea in female C (2.08+/-0.11, P=0.0036 vs female SF, P=0.0001 vs male C and vs male calcium SF), which also explains decreased THP/Crea values in calcium SF (1.46+/-0.08, P=0.041 vs C). In addition, THP/Crea was reduced in uric acid SF (1.11+/-0.21, P=0.049 vs C). Whereas THP/Crea was not related to age, urine volume, intake of dairy calcium, or urinary markers of protein intake, either in C or in SF, it correlated significantly with urinary Citrate/Crea, both in C (r=0.523, P=0.0001) and in SF (r=0.221, P=0.025). In C only, but not in SF, THP/Crea was correlated with urinary Calcium/Crea (r=0. 572, P=0.0001) and with Oxalate/Crea (r=0.274, P=0.022).

CONCLUSIONS

Both in C and SF, urinary THP excretion is related to body size, renal function and urinary citrate excretion, whereas dietary habits apparently do not affect THP excretion. Uric acid and calcium stone formation predict reduced THP excretion in comparison with C, whereas female gender goes along with increased urinary THP excretion in C. Possibly most relevant to kidney stone formation is the fact that THP excretion rises only in C in response to increasing urinary calcium and oxalate concentrations, whereas this self-protective mechanism appears to be missing in SF.

The otoconia of the guinea pig utricle: internal structure, surface exposure, and interactions with the filament matrix

A unique feature of the vertebrate gravity receptor organs, the saccule and utricle, is the mass of biomineral structures, the otoconia, overlying a gelatinous matrix also called "otoconial membrane" on the surface of the sensory epithelium. In mammals, otoconia are deposits of calcium carbonate in the form of composite calcite crystals. We used quick-freezing, deep etching to examine the otoconial mass of the guinea pig utricle. The deep-etching step exposed large expanses of intact and fractured otoconia, showing the fine structure and relationship between their internal crystal structure, their surface components, and the filament matrix in which they are embedded. Each otoconium has a compact central core meshwork of filaments and a composite outer shell of ordered crystallites and macromolecular aggregates. A distinct network of 20-nm beaded filaments covers the surface of the otoconia. The otoconia are interconnected and secured to the gelatinous matrix by surface adhesion and by confinement within a loose interotoconial filament matrix. The gelatinous matrix is a dense network made of yet another type of filament, 22 nm in diameter, which are cross-linked by shorter filaments, characteristically 11 nm in diameter. Our freeze-etching data provide a structural framework for considering the molecular nature of the components of the otoconial complex, their mechanical properties, and the degree of biological versus chemical control of otoconia biosynthesis.

Crystal±macromolecule interactions in urolithiasis: lessons from healthy biomineralization systems

Recent advances in understanding the molecular level mechanisms that control biomineralization and organic-inorganic interactions in urolithiasis are reviewed, and the validity of drawing parallels between them are considered. The multifunctional nature of many biomineralization molecules, particularly proteins, and the different roles they play in and out of solution suggest avenues for resolving the apparent paradox that urinary macromolecules have been observed both to inhibit and to promote stone formation.