Renal cell osteopontin production is stimulated by calcium oxalate monohydrate crystals

The protective effect of allium cepa against ethylene glycol-induced kidney stones in rats

1Background

Kidney stones is one of the serious medical conditions affecting populations worldwide. So, we aimed in this study to investigate the protective effect of allium cepa administration against KSD.

2Methods

24 adult male albino rats were assigned into 3 groups; group I: control group; group II: received ethylene glycol (EG) in the drinking water for 4 weeks; and group III received EG in the drinking water plus freshly prepared allium cepa extract (ACE) for 4 weeks. Renal function tests and urine analysis were done. Tissue oxidative stress markers (SOD and MDA) were assessed, and kidney expression of SIRT-1, Beclin, LC3, osteopontin, and Regucalcin were measured by RT-qPCR. Histopathological assessment and immunohistochemistry for Bax, Beclin-1 and TNF-α were performed.

3Results

There was a significant improved kidney function tests in the ACE received group compared to EG group (P < 0.001). The present study showed less stones formation and apoptosis with decreased osteopontin and autophagy genes expression in the ACE received group compared to EG group (P < 0.001). While, regucalcin and SIRT-1 genes showed higher expression in the former group than the later group (P < 0.001).

4 Conclusion

Alium Cepa extract administration has a significant protective effect against kidney stones formation.

Inhibition of AT1R/IP3/IP3R-mediated Ca2+ release protects against calcium oxalate crystals-induced renal oxidative stress

Calcium oxalate (CaOx) stones are the most prevalent type of kidney stones. CaOx crystals can stimulate reactive oxygen species (ROS) generation and induce renal oxidative stress to promote stone formation. Intracellular Ca2+ is an important signaling molecule, and an elevation of cytoplasmic Ca2+ levels could trigger oxidative stress. Our previous study has revealed that upregulation of Ang II/AT1R promoted renal oxidative stress during CaOx exposure. IP3/IP3R/Ca2+ signaling pathway activated via Ang II/AT1R is involved in several diseases, but its role in stone formation has not been reported. Herein, we focus on the role of AT1R/IP3/IP3R-mediated Ca2+ release in CaOx crystals-induced oxidative stress and explore whether inhibition of this pathway could alleviate renal oxidative stress. NRK-52E cells were exposed to CaOx crystals pretreated with AT1R inhibitor losartan or IP3R inhibitor 2-APB, and glyoxylic acid monohydrate-induced CaOx stone-forming rats were treated with losartan or 2-APB. The intracellular Ca2+ levels, ROS levels, oxidative stress indexes, and the gene expression of this pathway were detected. Our results showed that CaOx crystals activated AT1R to promote IP3/IP3R-mediated Ca2+ release, leading to increased cytoplasmic Ca2+ levels. The Ca2+ elevation was able to stimulate NOX2 and NOX4 to generate ROS, induce oxidative stress, and upregulate the expression of stone-related proteins. 2-APB and losartan reversed the referred effects, reduced CaOx crystals deposition and alleviated tissue injury in the rat kidneys. In summary, our results indicated that CaOx crystals promoted renal oxidative stress by activating the AT1R/IP3/IP3R/Ca2+ pathway. Inhibition of AT1R/IP3/IP3R-mediated Ca2+ release protected against CaOx crystals-induced renal oxidative stress. 2-APB and losartan might be promising preventive and therapeutic agents for the treatment of kidney stone disease.

The Protective Role of Dietary Polyphenols in Urolithiasis: Insights into Antioxidant Effects and Mechanisms of Action

Urolithiasis is a common urological disease with increasing prevalence and high recurrence rates around the world. Numerous studies have indicated reactive oxygen species (ROS) and oxidative stress (OS) were crucial pathogenic factors in stone formation. Dietary polyphenols are a large group of natural antioxidant compounds widely distributed in plant-based foods and beverages. Their diverse health benefits have attracted growing scientific attention in recent decades. Many literatures have reported the effectiveness of dietary polyphenols against stone formation. The antiurolithiatic mechanisms of polyphenols have been explained by their antioxidant potential to scavenge free radicals and ROS, modulate the expression and the activity of endogenous antioxidant and prooxidant enzymes, regulate signaling pathways associated with OS, and maintain cell morphology and function. In this review, we first describe OS and its pathogenic effects in urolithiasis and summarize the classification and sources of dietary polyphenols. Then, we focus on the current evidence defining their antioxidant potential against stone formation and put forward challenges and future perspectives of dietary polyphenols. To conclude, dietary polyphenols offer potential applications in the treatment and prevention of urolithiasis.

Opportunities for future therapeutic interventions for hyperoxaluria: targeting oxidative stress

INTRODUCTION

Oxalate is a toxic byproduct of metabolism and is normally produced in quantities easily removed from the body. However, under specific circumstances oxalate production is increased resulting in deposition of calcium oxalate (CaOx) crystals in the kidneys as well as other organs causing inflammation and injury. Excessive buildup of crystal deposits in the kidneys causes eventual loss of renal function requiring renal transplantation. Areas covered: Cellular exposure to CaOx crystals induces the production of reactive oxygen species (ROS) with the involvement of renin-angiotensin aldosterone system (RAAS), mitochondria, and NADPH oxidase. Inflammasomes are activated and pro-inflammatory cytokines, such as IL-1β and IL-18 are produced. We reviewed results of experimental and clinical studies of crystal renal epithelial cell interactions with emphasis on cellular injury and ROS production. Expert opinion: Treatment should depend upon the level of hyperoxaluria and whether it is associated with CaOx crystal deposition. Persistent low grade or intermittent hyperoxaluria can be treated with antioxidants, free radical scavengers. Hyperoxaluria associated with CaOx crystal deposition will require administration of angiotensin II receptor blockers, and NADPH oxidase or NLRP3 inflammasome inhibitors. DASH-style diet will be beneficial in both cases.

Protective effect of dietary polyphenol caffeic acid on ethylene glycol-induced kidney stones in rats

Dietary polyphenol caffeic acid (1) has been reported for various pharmacological activities. The aim of the current study was to investigate the effect of caffeic acid (1) on ethylene glycol-induced renal stones in rats. For the study, male Wistar rats were divided into seven groups; normal, pathological, and standard drug controls, and preventive and curative groups. Normal control group received drinking water for 8 weeks. Pathological, standard drug, preventive, and curative groups received 0.75% ethylene glycol in drinking water for the induction of calcium oxalate stone formation, along with the regular diet. Standard drug group received Urocit-K by gavage from day 1, while preventive and curative groups received caffeic acid (1) by gavage at doses of 20 and 40 mg/kg on day 1 and day 14, respectively. At the end of the experiment, urine analysis and kidney histopathology were performed. Real-time PCR was performed to evaluate the renal expression of the most important genes involved in urolithiasis, i.e., osteopontin, Tamm-Horsfall, prothrombin fragment 1, and bikunin genes. The results indicated that in both the preventive and curative groups, treatment of rats with caffeic acid (1) significantly regulated the altered biochemical parameters, along with the remarkable reduction of calcium oxalate deposits in the kidneys, as compared to the pathological group. Treatment with compound 1 also resulted in down-regulation of the osteopontin gene, and up-regulation of the prothrombin fragment 1, Tamm-Horsfall, and bikunin genes. These results suggest that caffeic acid (1) can be further investigated for the prevention, and treatment of kidney stones.

Association between OPN genetic variations and nephrolithiasis risk

Osteopontin (OPN) has an important role in urolithiasis. However, few studies have explored the association between OPN genetic variants and urolithiasis risk. In the present study, three single-nucleotide polymorphisms (SNPs) (rs28357094, rs11439060 and rs11730582) located on the promoter of OPN were genotyped in a total of 480 individuals, including 230 nephrolithiasis patients and 250 matched healthy controls, and the associations between these SNPs and nephrolithiasis risk in different genetic models was assessed. No significant differences were identified in the genotype and allele frequencies of OPN rs28357094 or rs11730582 (P=0.805 for rs28357094; P=0.577 for rs11730582, respectively). However, carriers with the OPN rs11439060 insertion (ins) types (ins/deletion and ins/ins) were overrepresented in urolithiasis patients compared with the controls [odds ratio (OR), 1.55; 95% confidence interval (CI), 1.08-2.22]. In the stratified analysis, the increased risk was more evident among younger subjects (adjusted OR, 1.68; 95% CI, 1.01-2.81), females (2.15; 1.14-4.08), overweight subjects (1.80; 1.07-3.05), normotensive subjects (2.48; 1.02-6.00), abnormal blood sugar subjects (1.58; 1.08-2.30), smokers (1.63; 1.02-2.60), and ever-drinkers (1.98; 1.10-3.60).. These findings revealed that the OPN rs11439060 polymorphism may act as genetic biomarker for the detection of high-risk nephrolithiasis patients.

Analysis of altered microRNA expression profiles in proximal renal tubular cells in response to calcium oxalate monohydrate crystal adhesion: implications for kidney stone disease

BACKGROUND

Calcium oxalate monohydrate (COM) is the major crystalline component in kidney stones and its adhesion to renal tubular cells leads to tubular injury. However, COM-induced toxic effects in renal tubular cells remain ambiguous. MicroRNAs (miRNAs) play an important role in gene regulation at the posttranscriptional levels.

OBJECTIVE

The present study aimed to assess the potential changes in microRNAs of proximal renal tubular cells in response to the adhesion of calcium oxalate monohydrate (COM) crystals.

METHODOLOGY

Lactate dehydrogenase (LDH) activity and DAPI staining were used to measure the toxic effects of HK-2 cells exposed to COM crystals. MicroRNA microarray and mRNA microarray were applied to evaluate the expression of HK-2 cells exposed to COM crystals. Quantitative real-time PCR (qRT-PCR) technology was used to validate the microarray results. Target prediction, Gene Ontology (GO) analysis and pathway analysis were applied to predict the potential roles of microRNAs in biological processes.

PRINCIPAL FINDINGS

Our study showed that COM crystals significantly altered the global expression profile of miRNAs in vitro. After 24 h treatment with a dose (1 mmol/L), 25 miRNAs were differentially expressed with a more than 1.5-fold change, of these miRNAs, 16 were up-regulated and 9 were down-regulated. A majority of these differentially expressed miRNAs were associated with cell death, mitochondrion and metabolic process. Target prediction and GO analysis suggested that these differentially expressed miRNAs potentially targeted many genes which were related to apoptosis, regulation of metabolic process, intracellular signaling cascade, insulin signaling pathway and type 2 diabetes.

CONCLUSION

Our study provides new insights into the role of miRNAs in the pathogenesis associated with nephrolithiasis.

Anti-nephrolithic potential of resveratrol via inhibition of ROS, MCP-1, hyaluronan and osteopontin in vitro and in vivo

BACKGROUND

Though resveratrol is known to have anti-cancer, anti-diabetic, anti-oxidant and anti-inflammatory activities, the inhibitory mechanism of resveratrol in kidney stone formation has not been elucidated so far.

METHOD

ELISA, flow cytometry, RT-PCR, and western blotting were performed. Human renal epithelial cells (HRCs) and rats with ethylene glycol (EG)-induced kidney stones were used.

RESULTS

A wound healing assay revealed that resveratrol significantly inhibited the oxalate-mediated migration of HRCs, considering oxalate mediates kidney stone formation. Also, resveratrol suppressed the mRNA expression of nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) oxidase subunits such as p22(phox) and p47(phox), monocyte chemoattractant protein 1 (MCP-1) and osteopontin (OPN) in oxalate-treated HRCs. Furthermore, western blotting showed that resveratrol downregulated the expression of MCP-1-related proteins including transforming growth factor(TGF-β1), TGFR-I or II and hyaluronan in oxalate-treated HRCs. Consistently, resveratrol reduced oxalate-mediated production of reactive oxygen species (ROS) and malondialdehyde (MDA) in oxalate-treated HRCs, while the activities of anti-oxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were enhanced by resveratrol in HRCs and EG-treated kidneys of rats. Consistently, resveratrol significantly reduced the number of urine calcium oxalate crystals and serum MDA, and attenuated the expression of OPN and hyaluroran in EG-treated rats.

CONCLUSIONS

Our findings suggest that resveratrol exerts anti-nephrolithic potential via inhibition of ROS, MCP-1 hyaluronan and OPN signaling.

Immunohistochemical localization and mRNA quantification of osteopontin and Tamm-Horsfall protein in canine renal tissue after potassium oxalate injection

Background

Urinary macromolecules contribute to promoting or inhibiting crystal retention in renal tissue and stone formation. Osteopontin (OPN) and Tamm-Horsfall protein (THP) are the most important proteins involved in this process. Although these two proteins were discovered a long time ago, their role in setting kidney stone formation has not yet been fully investigated. We conducted a study to explore the role of OPN and THP in canine renal oxalosis. Ten dogs were carefully examined prior to the study. Six dogs were assigned to the treatment group and were injected intravenously with 0.5 M potassium oxalate (KOx). The other four dogs were assigned to a control group and were injected intravenously with 0.9% NaCl three times a day (tid) for 7 consecutive days. Then kidneys were harvested for pathological, immunohistochemical examination and OPN and THP mRNA expression levels were quantified by quantitative real-time PCR.

Results

Calcium oxalate crystals deposition was observed in both renal cortex and medulla. Immunohistochemistry examination revealed increased tissue expression of OPN in the renal tissue while THP was significantly decreased. OPN mRNA expression level significantly increased in treated dogs compared to that in the controls, while THP mRNA level significantly decreased.

Conclusion

Together, these results suggest that THP and OPN are both involved in the pathogenesis and response to oxalate exposure.

Regulation of macromolecular modulators of urinary stone formation by reactive oxygen species: transcriptional study in an animal model of hyperoxaluria

We used an unbiased approach of gene expression profiling to determine differential gene expression of all the macromolecular modulators (MMs) considered to be involved in stone formation, in hyperoxaluric rats, with and without treatment with the NADPH oxidase inhibitor apocynin. Male rats were fed rat chow or chow supplemented with 5% wt/wt hydroxy-l-proline (HLP) with or without apocynin-supplemented water. After 28 days, rats were euthanized and their kidneys explanted. Total RNA was isolated and microarray analysis was conducted using the Illumina bead array reader. Gene ontology analysis and the pathway analyses of the genes were done using Database for Annotation, Visualization of Integrated Discovery enrichment analysis tool. Quantitative RT-PCR of selected genes was carried out to verify the microarray results. Expression of selected gene products was confirmed using immunohistochemistry. Administration of HLP led to crystal deposition. Genes encoding for fibronectin, CD 44, fetuin B, osteopontin, and matrix-gla protein were upregulated while those encoding for heavy chains of inter-alpha-inhibitor 1, 3, and 4, calgranulin B, prothrombin, and Tamm-Horsfall protein were downregulated. HLP-fed rats receiving apocynin had a significant reversal in gene expression profiles: those that were upregulated came down while those that were downregulated stepped up. Apocynin treatment resulted in near complete absence of crystals. Clearly, there are two types of MMs; one is downregulated while the other is upregulated during hyperoxaluria and crystal deposition. Apparently gene and protein expressions of known macromolecular modulators of CaOx crystallization are likely regulated by ROS produced in part through the activation of NADPH oxidase.

CKD273, a new proteomics classifier assessing CKD and its prognosis

National Kidney Foundation CKD staging has allowed uniformity in studies on CKD. However, early diagnosis and predicting progression to end stage renal disease are yet to be improved. Seventy six patients with different levels of CKD, including outpatients and dialysed patients were studied for transcriptome, metabolome and proteome description. High resolution urinary proteome analysis was blindly performed in the 53 non-anuric out of the 76 CKD patients. In addition to routine clinical parameters, CKD273, a urinary proteomics-based classifier and its peptides were quantified. The baseline values were analyzed with regard to the clinical parameters and the occurrence of death or renal death during follow-up (3.6 years) as the main outcome measurements. None of the patients with CKD273<0.55 required dialysis or died while all fifteen patients that reached an endpoint had a CKD273 score >0.55. Unsupervised clustering analysis of the CKD273 peptides separated the patients into two main groups differing in CKD associated parameters. Among the 273 biomarkers, peptides derived from serum proteins were relatively increased in patients with lower glomerular filtration rate, while collagen-derived peptides were relatively decreased (p<0.05; Spearman). CKD273 was different in the groups with different renal function (p<0.003). The CKD273 classifier separated CKD patients according to their renal function and informed on the likelihood of experiencing adverse outcome. Recently defined in a large population, CKD273 is the first proteomic-based classifier successfully tested for prognosis of CKD progression in an independent cohort.

Genome wide analysis of differentially expressed genes in HK-2 cells, a line of human kidney epithelial cells in response to oxalate

Nephrolithiasis is a multi-factorial disease which, in the majority of cases, involves the renal deposition of calcium oxalate. Oxalate is a metabolic end product excreted primarily by the kidney. Previous studies have shown that elevated levels of oxalate are detrimental to the renal epithelial cells; however, oxalate renal epithelial cell interactions are not completely understood. In this study, we utilized an unbiased approach of gene expression profiling using Affymetrix HG_U133_plus2 gene chips to understand the global gene expression changes in human renal epithelial cells [HK-2] after exposure to oxalate. We analyzed the expression of 47,000 transcripts and variants, including 38,500 well characterized human genes, in the HK2 cells after 4 hours and 24 hours of oxalate exposure. Gene expression was compared among replicates as per the Affymetrix statistical program. Gene expression among various groups was compared using various analytical tools, and differentially expressed genes were classified according to the Gene Ontology Functional Category. The results from this study show that oxalate exposure induces significant expression changes in many genes. We show for the first time that oxalate exposure induces as well as shuts off genes differentially. We found 750 up-regulated and 2276 down-regulated genes which have not been reported before. Our results also show that renal cells exposed to oxalate results in the regulation of genes that are associated with specific molecular function, biological processes, and other cellular components. In addition we have identified a set of 20 genes that is differentially regulated by oxalate irrespective of duration of exposure and may be useful in monitoring oxalate nephrotoxicity. Taken together our studies profile global gene expression changes and provide a unique insight into oxalate renal cell interactions and oxalate nephrotoxicity.

Kidney injury molecule-1 is up-regulated in renal epithelial cells in response to oxalate in vitro and in renal tissues in response to hyperoxaluria in vivo

Oxalate is a metabolic end product excreted by the kidney. Mild increases in urinary oxalate are most commonly associated with Nephrolithiasis. Chronically high levels of urinary oxalate, as seen in patients with primary hyperoxaluria, are driving factor for recurrent renal stones, and ultimately lead to renal failure, calcification of soft tissue and premature death. In previous studies others and we have demonstrated that high levels of oxalate promote injury of renal epithelial cells. However, methods to monitor oxalate induced renal injury are limited. In the present study we evaluated changes in expression of Kidney Injury Molecule-1 (KIM-1) in response to oxalate in human renal cells (HK2 cells) in culture and in renal tissue and urine samples in hyperoxaluric animals which mimic in vitro and in vivo models of hyper-oxaluria. Results presented, herein demonstrate that oxalate exposure resulted in increased expression of KIM-1 m RNA as well as protein in HK2 cells. These effects were rapid and concentration dependent. Using in vivo models of hyperoxaluria we observed elevated expression of KIM-1 in renal tissues of hyperoxaluric rats as compared to normal controls. The increase in KIM-1 was both at protein and mRNA level, suggesting transcriptional activation of KIM-1 in response to oxalate exposure. Interestingly, in addition to increased KIM-1 expression, we observed increased levels of the ectodomain of KIM-1 in urine collected from hyperoxaluric rats. To the best of our knowledge our studies are the first direct demonstration of regulation of KIM-1 in response to oxalate exposure in renal epithelial cells in vitro and in vivo. Our results suggest that detection of KIM-1 over-expression and measurement of the ectodomain of KIM-1 in urine may hold promise as a marker to monitor oxalate nephrotoxicity in hyperoxaluria.

Relative deficiency of acidic isoforms of osteopontin from stone former urine

We have tested the relative electrophoretic mobility of osteopontin (OPN) isolated from urine obtained from normal individuals (NU) against similar samples derived from the urine of stone formers (SFU) using high-resolution isoelectric focusing (isoelectric point, pI range 3.5-4.5) in 2D electrophoresis, with Western blot detection. We also report the results from competitive ELISA analyses of these samples. We demonstrated that human urinary OPN has a discrete four band separation pattern that conforms to four previously documented OPN isoforms. The lower two M(r) isoforms migrate to a greater degree toward the acidic end of the gel than do the higher two M(r) isoforms. Densitometry of the signal reveals significant difference in the migration pattern of OPN from SFU as compared to that from NU based on an analysis of the spot intensities grouped in 0.1 pI unit increments. A novel method for the calculation of a weight-averaged pI based on the relative signal strength in an OPN 2D Western blot was developed. The analysis revealed a significantly increased weight-averaged pI values for the higher M(r) forms of OPN in the stone former compared to normal population. Additionally, alkaline phosphatase-treated NU samples resulted in a significant average pI shift of 0.05 units in the alkaline direction, suggesting that a decrease in the average degree of phosphorylation could be responsible for the difference between NU and SFU pI.

Urinary glycosaminoglycans and glycoproteins in a calcium oxalate crystallization system

This study measures the effects of total urinary glycosaminoglycans (GAGs), glycoproteins (GPs) and individual GAGs on the nucleation rates (Bo), growth rates (G) and suspension densities (Mт) of calcium oxalate (CaOx) crystallization by the mixed suspension mixed product removal (MSMPR) system. Total urinary GAGs, glycoproteins and individual GAGs including heparan sulfate (HS), chondroitin sulfate (CS) and Hyaluronic acid (HA) were added into the artificial urine (AU) and then introduced into the MSMPR test chamber and the crystal sizes and numbers were analyzed by a particle counter. The effects of added GAGs and GPs on CaOx crystallization were reflected by the changes on the crystallization indexes including the Bo, G and Mт of CaOx that were calculated based on the crystal size and numbers. Total urinary GAGs showed no statistical significance on CaOx crystallization. However, individual GAGs such as HA, CS and HS enhanced Bo and suppressed the G when measured individually. CS and HS enhanced the Mт while HA shown no significant change in the Mт of CaOx. Total urinary GPs showed an increase in the G and Mт of crystals. Although total urinary GAGs showed no statistically significant effect on CaOx crystallization, individual GAGs (CS, HS) promoted the CaOx crystallization by increasing the suspension density of smaller crystals, indicative of reduced risk of stones while HA showed no significance in the M(T) of CaOx formed. Urinary GPs indicated increased sizes and M(T) suggesting larger crystals and/or aggregates.

The impact of metaphylaxis of kidney stone disease in the renal function at long term in active kidney stone formers patients

A total of 150 patients were included in the analysis. Through chart review, we estimated glomerular filtration rate in the first visit and, at least, 5 years later. All patients were divided into two groups: (1) metaphylaxis adherents (n = 74) and (2) metaphylaxis non-adherents (n = 76). We followed all patients for at least 5 years. The Scr percentage of patients and GFR <60 mL/min was compared between groups. Variables were compared between groups using t test, χ(2) tests, odds ratios with 95% confidence intervals. There were no differences at baseline between groups. After 5 years of follow-up, GFR was 77.9 mL/min in non-adherent-metaphylaxis group and in the adherent-metaphylaxis group was 87.3 mL/min, with p value of 0.02. After 5 years of follow-up, we had a GFR <60 mL/min in the adherent-metaphylaxis group (4.89 vs. 21.95%) with p value of 0.001 and OR = 5.36; IC-95% = 1.95-14.8. Metaphylaxis of kidney stone disease could prevent chronic kidney disease.

A comparison of the binding of urinary calcium oxalate monohydrate and dihydrate crystals to human kidney cells in urine

OBJECTIVE

To compare the binding kinetics of urinary calcium oxalate monohydrate (COM) and dihydrate (COD) crystals to human kidney (HK-2) cells in ultra-filtered (UF), and centrifuged and filtered (CF) human urine; and to quantify the binding of COM and COD crystals to cultured HK-2 cells in UF and CF urine samples collected from different individuals.

MATERIALS AND METHODS

Urine was collected from healthy subjects, pooled, centrifuged and filtered. (14) C-oxalate-labelled COM and COD crystals were precipitated from the urine by adding oxalate after adjustment of two aliquots of the urine to 2 and 8 mm Ca(2+), respectively. For the kinetic study, the crystals were incubated with HK-2 cells for up to 120 min in pooled CF urine adjusted to 2 and 8 mm Ca(2+). Identical experiments were also carried out in UF urine samples collected from the same individuals. For the quantitative study, the same radioactively labelled COM and COD crystals were incubated with HK-2 cells for 50 min in separate CF and UF urines collected from eight healthy individuals at the native Ca(2+) concentrations of the urines. Field emission electron microscopy and Fourier transform-infrared spectroscopy were used to confirm crystal morphology.

RESULTS

COM and COD crystals generally bound more strongly at 8 mm than at 2 mm Ca(2+). The kinetic binding curves of COM were smooth, while those of COD were consistently biphasic, suggesting that the two crystal types induce different cellular metabolic responses: HK-2 cells crystals appear to possess a transitory mechanism for detaching COD, but not COM crystals. In UF urine, COM binding was significantly greater than that of COD at 2 mm Ca(2+), but at 8 mm Ca(2+) the binding of COD was greater at early and late time points. COD also bound significantly more strongly at early time points in CF urine at both 2 and 8 mm Ca(2+). In both CF and UF urine, there was no difference between the binding affinity of urinary COM and COD crystals.

CONCLUSION

Binding of both COM and COD crystals to cultured human renal epithelial cells is influenced by urinary macromolecules and ambient Ca(2+) concentration. HK-2 cells appear to possess a mechanism for the rapid detachment of bound COD crystals, making it difficult to show any unambiguous overall difference between the binding affinity of COM and COD crystals.

The impact of osteopontin promoter polymorphisms on the risk of calcium urolithiasis

BACKGROUND

Osteopontin (OPN) is an important modulator of urolithiasis formation. Three functional polymorphisms (-66T/G, -156delG/G, and -443T/G) on the promoter region of the OPN gene have been found to affect the gene expression and transcriptional activity. This study investigated the association of those three functional polymorphisms with the risk of calcium urolithiasis.

METHODS

A total of 249 cases diagnosed with calcium urolithiasis and 247 age- and sex-matched healthy controls were recruited from Kaohsiung Medical University Hospital between June, 2003 and February, 2007. All subjects completed a detailed questionnaire survey, and provided blood and urine samples for biochemical evaluations. Three single nucleotide polymorphisms were determined by using TaqMan 5' allelic discrimination assay.

RESULTS

In-156delG/G polymorphism, subjects who carried delG allele had a significantly higher risk of developing calcium urolithiasis than those with G allele (odds ratio=1.39; 95% confidence interval=1.02-1.90; P=0.037). In stone cases, subjects with delG/G and delG/delG genotypes also had significantly higher urinary ratio of calcium to OPN than those with G/G genotype (11.8+/-15.9 vs 7.08+/-5.26, P=0.021).

CONCLUSIONS

The -156 delG/G polymorphism of OPN gene could serve as a candidate genetic marker used to evaluate the risk of calcium urolithiasis.

Increased expression of heparan sulfate proteoglycan on the cultured renal epithelial cells during oxalate exposure

We have previously reported that heparan sulfate (HS) / heparan sulfate proteoglycan (HSPG, syndecan-1) expression significantly increased in the rat kidney during calcium oxalate (CaOx) nephrolithiasis. Although the exact mechanism of the increased syndecan expression still remains unclear, HS/syndecan is thought to have some important roles in CaOx crystal formation. The present study examined the role of HS during oxalate exposure by using a newly developed cell line (KIC-synd-1) that expresses human heparan sulfate proteoglycan (syndecan-1). Quantitative competitive (QC)-RT-PCR was used to examine change of syndecan-1 mRNA expression in KIC-synd-1 cells. Production of syndecan-1 core protein and glycosaminoglycans (GAGs) were also confirmed by Western blot, immunohistochemistry and HPLC, respectively. Wild type Mardin-Darby canine kidney (MDCK) cells were also examined in the same manner. The stable expression of syndecan-1 gene and production of both core protein and HS chains were confirmed in the newly developed KIC-synd-1 cell line. Increased syndecan-1 mRNA expression and production of core proteins were confirmed in KIC-synd-1 cells during oxalate exposure. MTT assay revealed that the cell viability decreased significantly in the MDCK cells after 1 mM oxalate exposure (p<0.05). On the other hand, there was no significant difference in the oxalate exposed KIC-synd-1 cells. However, the cell viability in KIC-synd-1 cells pretreated with heparitinase digestion decreased significantly before oxalate exposure (p<0.05). The present data suggests that both exogenous and endogenous HS exerts protective effect against oxalate-induced cell injuries. Previous studies in our laboratory have indicated that hyperoxaluria and deposition of CaOx crystals resulted in renal tubular cellular injury inducing the synthesis of HSPG to protect and repair the damaged epithelial cell surface. The present data offers strong support for this hypothesis. Finally, HS could be potent inhibitor of CaOx nephrolithiasis and the absence of this substance on the tubular surface may increase the risk of CaOx crystal formation and retention.

Recent advances in the pathophysiology of nephrolithiasis

Over the past 10 years, major progress has been made in the pathogenesis of uric acid and calcium stones. These advances have led to our further understanding of a pathogenetic link between uric acid nephrolithiasis and the metabolic syndrome, the role of Oxalobacter formigenes in calcium oxalate stone formation, oxalate transport in Slc26a6-null mice, the potential pathogenetic role of Randall's plaque as a precursor for calcium oxalate nephrolithiasis, and the role of renal tubular crystal retention. With these advances, we may target the development of novel drugs including (1) insulin sensitizers; (2) probiotic therapy with O. formigenes, recombinant enzymes, or engineered bacteria; (3) treatments that involve the upregulation of intestinal luminal oxalate secretion by increasing anion transporter activity (Slc26a6), luminally active nonabsorbed agents, or oxalate binders; and (4) drugs that prevent the formation of Randall's plaque and/or renal tubular crystal adhesions.

cDNA macroarray analysis of genes in renal epithelial cells exposed to calcium oxalate crystals

Kidney stone formation is a complex process, and numerous genes participate in this cascade. The binding and internalization of calcium oxalate monohydrate (COM) crystals, the most common crystal in renal stones by renal epithelial cells may be a critical step leading to kidney stone formation. Exposure to COM crystals alters the expression of various genes, but previous studies on gene expression have generally been limited. To obtain more detailed insight into gene expression, we examined gene expression profiles in renal epithelial cells exposed to COM crystals using cDNA macroarray. NRK-52E cells were exposed to COM crystals for 60 and 120 min. Poly (A)(+) RNA was isolated and converted into (32)P-labeled first-strand cDNA, then the cDNA probe was hybridized to the membrane. Hybridization images were scanned and the signal intensities were quantified. Expression of mRNA of 1,176 genes was analyzed with global sum normalization methods. Exposure to COM crystals altered the expression of some of the genes reported previously. Furthermore, novel genes were also identified. Over 20 genes were found to be regulated at least twofold. We performed a large-scale analysis of gene expression in renal epithelial cells exposed to COM crystals, and identified the genes differentially regulated. cDNA macroarray is a useful tool for evaluating gene expression in urolithiasis research.

High calcium concentration and calcium oxalate crystals cause significant inaccuracies in the measurement of urinary osteopontin by enzyme linked immunosorbent assay

Strong evidence that osteopontin (OPN) is a determinant of urolithiasis has prompted studies comparing the protein's urinary excretion in healthy subjects and stone formers. However, reported mean urinary values have varied widely, from <1 microg/mL to more than 20 times that value. Since OPN binds to CaOx crystals, the presence of crystals in urine may cause underestimation of its urinary levels. Using a commercial ELISA, we measured urinary OPN levels in the presence of endogenous or exogenous CaOx monohydrate (COM) and dihydrate (COD) crystals. OPN concentrations decreased in the presence of endogenous and exogenous CaOx crystals, but never below 2 microg/mL. Increasing the urinary calcium concentration decreased detectable OPN levels, possibly as a result of changes in the three-dimensional conformation of the protein. Because calcium concentration and the formation of CaOx crystals cannot be controlled in urine, the use of urinary OPN levels as a biomarker for any human pathology must be seriously questioned, but particularly for the investigation of stone formers in whom hypercalciuria and crystalluria are more common than in healthy subjects.

Oxalate exposure provokes HSP 70 response in LLC-PK1 cells, a line of renal epithelial cells: protective role of HSP 70 against oxalate toxicity

We investigated the effects of oxalate on immediate early genes (IEGs) and stress protein HSP 70, commonly induced genes in response to a variety of stresses. LLC-PK1 cells were exposed to oxalate. Gene transcription and translation were monitored by Northern and Western blot analysis. RNA and DNA synthesis were assessed by [(3)H]-uridine and [(3)H]-thymidine incorporation, respectively. Oxalate exposure selectively increased the levels of mRNA encoding IEGs c-myc and c-jun as well as stress protein HSP 70. While expression of c-myc and c-jun was rapid (within 15 min to 2 h) and transient, HSP 70 expression was delayed (approximately 8 h) and stable. Furthermore, oxalate exposure resulted in delayed induction of generalized transcription by 18 h and reinitiation of the DNA synthesis by 24 h of oxalate exposure. Moreover, we show that prior induction of HSP 70 by mild hypertonic exposure protected the cells from oxalate toxicity. To the best of our knowledge this is the first study to demonstrate rapid IEG response and delayed heat-shock response to oxalate toxicity and protective role of HSP 70 against oxalate toxicity to renal epithelial cells. Oxalate, a metabolic end product, induces IEGs c-myc and c-jun and a delayed HSP 70 expression; While IEG expression may regulate additional genetic responses to oxalate, increased HSP 70 expression would serve an early protective role during oxalate stress.

Preliminary observations of urinary calcium and osteopontin excretion in premature infants, term infants and adults

Osteopontin is an acidic glycoprotein which may prevent nephrocalcinosis and nephrolithiasis by inhibiting the growth and retention of calcium oxalate crystals within the tubular lumen. The purpose of this study was to obtain preliminary data regarding urinary osteopontin in premature infants at risk for nephrocalcinosis. We examined urinary osteopontin concentration in premature infants, term infants and adults, and examined the relationship between urinary calcium and osteopontin concentration in these groups. The urinary osteopontin concentration of 17 premature infants of 3.7 +/- 1.2 microg/ml was not significantly different from the urinary osteopontin concentration of 12 term infants of 6 +/- 6 microg/ml, while the urinary osteopontin concentration in 23 urine specimens from adults of 27 +/- 15 microg/ml was significantly higher than premature infants and term infants (p < 0.05). Urinary osteopontin concentration did not correlate with urinary calcium concentration in premature infants, while there was a correlation between the osteopontin/creatinine ratio and calcium/creatinine ratios in premature infants. Diminished urinary concentration of osteopontin may enhance the risk for nephrocalcinosis in premature infants.

Idiopathic hypercalciuria associated with urinary tract infection in children

The aim of this study was to evaluate the association between idiopathic hypercalciuria (IH) and urinary tract infection (UTI) in children. This prospective clinical study included 75 patients with UTI (without urinary tract malformations and lithiasis) and a control group of 30 healthy children. Of the total number of patients with UTI, 21% (n = 16/75) had IH, but only 7% (n = 2/30) with IH were reported in the control group (p < 0.05). Recurrent UTI affected 33% (n = 25/75) of patients , and in 67% (n = 50/75) of patients, UTI was diagnosed for the first time. In the group of patients with recurrent UTI, 44% (n = 11/25) had IH, but only 10% (n = 5/50) were reported in the group of patients with first-time UTI (p < 0.05). The results of multifactorial logistic regression analysis showed that clinical and laboratory parameters (recurrent UTI, dysuria, and microscopic hematuria) may predict the diagnosis of IH in 80% of patients and absence of IH in 87% of cases. In our opinion, IH is a major contributing factor to UTI, especially to recurrent UTI in children.

Naturally produced crystals obtained from kidney stones are less injurious to renal tubular epithelial cells than synthetic crystals

OBJECTIVE

To determine the differences in cell responses to synthetic and biological crystals of calcium oxalate (CaOx) and brushite

MATERIALS AND METHODS

Nephrolithiasis depends on crystal retention within the kidneys, often promoted by crystal attachment to the injured renal epithelium; studies often use various crystals that might be injurious to cells and cause the exposure of crystal binding molecules on cell surfaces, thus promoting crystal attachment and retention. The synthetic crystals used in these studies might be more injurious than the biological crystals naturally produced in the kidneys and that form kidney stones. We exposed the renal epithelial cell line NRK 52E in vitro to CaOx or brushite crystals at 67 or 133 microg/cm(2) for 3 or 6 h. Synthetic crystals were purchased and the biocrystals were obtained by pulverizing CaOx and brushite stones. We determined the release of lactate dehydrogenase (LDH), hydrogen peroxide (H(2)O(2)) and 8-isoprostane (8-IP), and monocyte chemoattractant protein-1 (MCP-1), as markers of injury, oxidative stress and inflammation, respectively. Cells were also examined after trypan blue staining to determine their membrane integrity. We also examined crystals of CaOx by scanning electron microscopy both in the native state as well as after decalcification.

RESULTS

Exposure to both the synthetic and biological crystals resulted in a significant increase in LDH release and trypan blue staining, as a sign of crystal-induced injury. There was increased production of H(2)O(2) and 8-IP, suggesting the development of oxidative stress. In addition MCP-1 production was also significantly increased. However, the synthetic crystals caused significantly higher increases in all the indicators than the biological crystals.

CONCLUSIONS

These results indicate that even though both synthetic and naturally produced biocrystals invoke a response from the renal epithelial cells, the latter are significantly less injurious and inflammatory. Exposure to low concentrations of these crystals alone might not invoke an inflammatory response, cause the uncovering of crystal binding molecules on epithelial cell surfaces, and promote crystal attachment and retention.

Proposed mechanisms in renal tubular crystal retention

The production of concentrated urine inevitably leads to the precipitation of poorly soluble waste salts in the renal tubular fluid. These crystallization processes are physiologic and without consequences as long as all crystals are excreted with the urine. The retention of crystals in the renal tubules, however, may lead to tubular nephrocalcinosis. Here, we present a brief survey of the possible mechanisms involved in this process, which seems to depend predominantly on the presence of regenerating/(re)differentiating cells in the renal tubules. Crystal binding to the surface of these cells can be mediated by a number of luminal membrane molecules, including acidic fragment of nucleolin-related protein, annexin-II, osteopontin, and hyaluronan.

Oxalate ions and calcium oxalate crystal-induced up-regulation of osteopontin and monocyte chemoattractant protein-1 in renal fibroblasts

OBJECTIVE

To examine the responses of renal fibroblasts to high oxalate (Ox) and calcium Ox (CaOx) crystals, as the latter are found in the renal interstitium of patients with primary or enteric hyperoxaluria, and in animals with experimental CaOx nephrolithiasis, and are associated with tubulointerstitial inflammation (TI). TI might begin with the production of chemoattractants by the renal epithelial cells exposed to high Ox and/or CaOx crystals; as Ox levels are also high in the renal interstitium and crystal deposition in nephrolithiasis might start in the interstitium, we hypothesized that renal fibroblasts might also be involved in the development of TI.

MATERIALS AND METHODS

We exposed renal fibroblast cells of line NRK 49F in vitro to Ox ions (500 micromol/L) or CaOx monohydrate crystals (67 microg/cm(2)). We assessed the production of osteopontin and monocyte chemoattractant protein-1 (MCP-1), and expression of their mRNA, in the cells. We also determined the cellular malondialdehyde content as a marker of reactive oxygen species (ROS)-induced lipid peroxidation, and Trypan blue staining and the release of lactate dehydrogenase as markers of injury.

RESULTS

Similar to renal epithelial cells, renal fibroblasts were stimulated by exposure to Ox and CaOx crystals. They showed signs of injury and ROS-induced lipid peroxidation. The mRNA expression and production of osteopontin and MCP-1 increased significantly.

CONCLUSIONS

These results indicate that fibroblasts respond to high Ox and CaOx crystals by up-regulating specific pathways producing pro-inflammatory conditions. Migration of monocytes/macrophages to sites of interstitial crystal deposits can lead to localized interstitial inflammation and fibrosis.

Modeling of hyperoxaluric calcium oxalate nephrolithiasis: experimental induction of hyperoxaluria by hydroxy-L-proline

A number of animal models have been developed to investigate calcium oxalate (CaOx) nephrolithiasis. Ethylene glycol (EG)-induced hyperoxaluria in rats is most common, but is criticized because EG and some of its metabolites are nephrotoxic and EG causes metabolic acidosis. Both oxalate (Ox) and CaOx crystals are also injurious to renal epithelial cells. Thus, it is difficult to distinguish the effects of EG and its metabolites from those induced by Ox and CaOx crystals. This study was performed to investigate hydroxy-L-proline (HLP), a common ingredient of many diets, as a hyperoxaluria-inducing agent. In rats, HLP has been shown to induce CaOx nephrolithiasis in only hypercalciuric conditions. Five percent HLP mixed with chow was given to male Sprague-Dawley rats for 63 days, resulting in hyperoxaluria, CaOx crystalluria, and nephrolithiasis. Crystal deposits were surrounded by ED-1-positive inflammatory cells. Cell injury and death was followed by regeneration, as suggested by an increase in proliferating cell nuclear antigen-positive cells. Both osteopontin (OPN) and CD44 were upregulated. Staining for CD44 and OPN was intense in cells lining the tubules that contained crystals. Along with a rise in urinary Ox and lactate dehydrogenase, there were significant increases in 8-isoprostane and hydrogen peroxide excretion, indicating that the oxidative stress induced cell injury. Thus, HLP-induced hyperoxaluria alone can induce CaOx nephrolithiasis in rats.

Crystal Retention in Renal Stone Disease: A Crucial Role for the Glycosaminoglycan Hyaluronan?

The mechanisms that are involved in renal stone disease are not entirely clear. In this article, the various concepts that have been proposed during the past century are reviewed briefly and integrated into current insights. Much attention is dedicated to hyaluronan (HA), an extremely large glycosaminoglycan that may play a central role in renal stone disease. The precipitation of poorly soluble calcium salts (crystal formation) in the kidney is the inevitable consequence of producing concentrated urine. HA is a major constituent of the extracellular matrix in the renal medullary interstitium and the pericellular matrix of mitogen/stress-activated renal tubular cells. HA is an excellent crystal-binding molecule because of its size, negative ionic charge, and ability to form hydrated gel-like matrices. Crystal binding to HA leads to crystal retention in the renal tubules (nephrocalcinosis) and to the formation of calcified plaques in the renal interstitium (Randall's plaques). It remains to be determined whether one or both forms of renal crystal retention are involved in the development of kidney stones (nephrolithiasis).

Preconditioning of the distal tubular epithelium of the human kidney precedes nephrocalcinosis

BACKGROUND

Preterm neonates and renal transplant patients frequently develop nephrocalcinosis. Experimental studies revealed that crystal retention in the distal nephron, a process that may lead to nephrocalcinosis, is limited to proliferating/regenerating tubular cells expressing hyaluronan and osteopontin at their luminal surface. Fetal and transplant kidneys contain proliferating and/or regenerating cells since nephrogenesis is not completed until 36 weeks of gestation, while ischemia and nephrotoxic immunosuppressants may lead to injury and repair in renal transplants. This prompted us to investigate the expression of hyaluronan and osteopontin and to correlate this to the appearance of tubular calcifications both in fetal/preterm and transplanted kidneys.

METHODS

Sections of fetal/preterm kidneys and protocol biopsies of transplanted kidneys (12 and 24 weeks posttransplantation from the same patients) were stained for osteopontin, hyaluronan, and calcifications (von Kossa).

RESULTS

Hyaluronan and osteopontin were expressed at the luminal surface of the epithelial cells lining the distal tubules of all fetal kidneys at birth and in all kidney graft protocol biopsies 12 and 24 weeks posttransplantation. In 7 out of 18 surviving (at least 4 days) preterm neonates crystal retention developed. In renal allografts a striking increase (from 2/10 to 6/10) in tubular crystal retention between 12 and 24 weeks posttransplantation was observed. In addition, crystals were selectively retained in distal renal tubules containing cells with hyaluronan and osteopontin at their luminal surface.

CONCLUSION

The results of this study show that luminal expression of hyaluronan and osteopontin preceded renal distal tubular retention of crystals in preterm neonates and renal transplant patients. We propose that the presence of this crystal binding phenotype may play a general role in renal calcification processes.

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Diphenyleneiodium (DPI) reduces oxalate ion- and calcium oxalate monohydrate and brushite crystal-induced upregulation of MCP-1 in NRK 52E cells

BACKGROUND

Our earlier studies have demonstrated upregulation of monocyte chemoattractant protein-1 (MCP-1) in NRK52E rat renal epithelial cells by exposure to oxalate (Ox) ions and crystals of calcium oxalate monohydrate (COM) or the brushite (Br) form of calcium phosphate. The upregulation was mediated by reactive oxygen species (ROS). This study was performed to investigate whether NADPH oxidase is involved in ROS production.

METHODS

Confluent cultures of NRK52E cells were exposed to Ox ions or COM and Br crystals. They were exposed for 1, 3, 6, 12, 24 and 48 h for isolation of MCP-1 mRNA and 24 h for enzyme-linked immunosorbent assay (ELISA) to determine the secretion of protein into the culture medium. We also investigated the effect of free radical scavenger, catalase, and the NADPH oxidase inhibitor diphenyleneiodium (DPI) chloride, on the Ox- and crystal-induced expression of MCP-1 mRNA and protein. The transcription of MCP-1 mRNA in the cells was determined using real-time polymerase chain reaction. Hydrogen peroxide and 8-isoprostane were measured to investigate the involvement of ROS.

RESULTS

Exposure of NRK52E cells to Ox ions as well as the crystals resulted in increased expression of MCP-1 mRNA and production of the chemoattractant. Treatment with catalase reduced the Ox- and crystal-induced expression of both MCP-1 mRNA and protein. DPI reduced the crystal-induced gene expression and protein production but not Ox-induced gene expression and protein production.

CONCLUSIONS

Exposure to Ox ions, and COM and Br crystals stimulates a ROS-mediated increase in MCP-1 mRNA expression and protein production. Reduction in ROS production, lipid peroxidation, low-density lipoprotein release, and inducible MCP-1 gene and protein in the presence of DPI indicates an involvement of NADPH oxidase in the production of ROS.

Nuclear pore complex oxalate binding protein p62: expression in different kidney disorders

BACKGROUND

Urolithiasis is a multifactorial process that starts with the formation of microcrystals in the urine and terminates as mature renal calculi. The oxalate binding protein plays a vital role in the transport of oxalate. The physiological significance of the presence of oxalate binding protein in the nuclear pore complex is not well understood.

METHODS

The nuclear envelope was extracted from human cadaver kidneys. 14C oxalate was labeled, nuclear pore complex proteins were extracted and loaded onto Sephadex G-200, and further purified in DEAE-Sephadex A-50 column. The radioactive protein peak was pooled, concentrated and checked for purity in SDS-PAGE. The purified protein showed cross-reactivity with the monoclonal antibody (MAb 414) and was homogeneous. Urine samples of healthy individuals with no history of kidney disease served as control. Blood and urine samples were collected from kidney and autoimmune disorder patients and checked for the expression of p62 protein by ELISA.

RESULTS

Extracted and purified nuclear pore complex oxalate binding protein had a molecular weight of 62 kDa. A threefold increase in oxalate excretion was observed in hyperoxaluric patients compared to control subjects. The protein expression was found to be higher in hyperoxaluric patients vs. controls, chronic renal failure (CRF) and acute renal failure (ARF), whereas decreased expression was observed in nephrotic syndrome (NS) patients. p62 autoantibodies was observed in hyperoxaluria (HO), systemic lupus erythematosus (SLE) and primary biliary cirrhosis (PBC), whereas it was absent in controls.

CONCLUSION

Increased expression of p62 may be due to membrane damage induced by oxalate stress, and may be used as a diagnostic marker. This study also confirms the presence of p62 autoantibodies in HO patients.

Calcium Oxalate Crystal Adherence to Hyaluronan-, Osteopontin-, and CD44-Expressing Injured/Regenerating Tubular Epithelial Cells in Rat Kidneys

ABSTRACT. Retention of crystals in the kidney is an essential early step in renal stone formation. Studies with renal tubular cells in culture indicate that hyaluronan (HA) and osteopontin (OPN) and their mutual cell surface receptor CD44 play an important role in calcium oxalate (CaOx) crystal binding during wound healing. This concept was investigated in vivo by treating rats for 1, 4, and 8 d with ethylene glycol (0.5 and 0.75%) in their drinking water to induce renal tubular cell damage and CaOx crystalluria. Tubular injury was morphologically scored on periodic acid-Schiff–stained renal tissue sections and tissue repair assessed by immunohistochemical staining for proliferating cell nuclear antigen. CaOx crystals were visualized in periodic acid-Schiff–stained sections by polarized light microscopy, and renal calcium deposits were quantified with von Kossa staining. HA was visualized with HA-binding protein and OPN and CD44 immunohistochemically with specific antibodies and quantified with an image analyzer system. Already after 1 d of treatment, both concentrations of ethylene glycol induced hyperoxaluria and CaOx crystalluria. At this point, there was neither tubular injury nor crystal retention in the kidney, and expression of HA, OPN, and CD44 was comparable to untreated controls. After 4 and 8 d of ethylene glycol, however, intratubular crystals were found adhered to injured/regenerating (proliferating cell nuclear antigen positive) tubular epithelial cells, expressing HA, OPN, and CD44 at their luminal membrane. In conclusion, the expression of HA, OPN, and CD44 by injured/regenerating tubular cells seems to play a role in retention of crystals in the rat kidney.

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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Protective role of heparin/heparan sulfate on oxalate-induced changes in cell morphology and intracellular Ca2+

Alterations in intracellular Ca2+ ([Ca2+]i) are generally associated with cellular distress. Oxalate-induced cell injury of the renal epithelium plays an important role in promoting CaOx nephrolithiasis. However, the degree of change in intracellular free calcium ions in renal epithelial cells during oxalate exposure remains unclear. The aim of this study is to determine whether acute short-term exposure to oxalate produces morphological changes in the cells, induces a change in cytosolic Ca2+ levels in renal tubular epithelial cells and whether the application of extracellular glycosaminoglycans (GAGs) prevents these changes. Cultured Mardin-Darby canine kidney cells were exposed to oxalate, and changes in cytosolic Ca2+ were determined under various conditions. The effect of heparin and heparan sulfate (HS) during oxalate exposure was examined. The change in the GAG contents of the culture medium was also determined. Transmission electron microscopy (TEM) was performed for morphological analysis. The degree of change in cytosolic Ca2+ strongly correlated with oxalate concentration. Cytosolic Ca2+ levels decreased in parallel with an increase in the concentration of oxalate. However, this decrease was strongly inhibited by pretreatment with heparin or HS. TEM revealed cytoplasmic vacuolization, the appearance of flocculent material and mitochondrial damage after oxalate exposure. On the other hand, pretreatment with heparin or HS completely blocked these morphological changes. The present data suggest that acute exposure to a high concentration of oxalate challenges the renal cells, diminishes their viability and induces changes in cytosolic Ca2+ levels. Heparin and HS, which are known as potent inhibitors of CaOx crystallization, may also prevent oxalate-induced cell changes by stabilizing the cytosolic Ca2+ level.

The role of osteopontin on calcium oxalate crystal formation

OBJECTIVE

We evaluated whether osteopontin (OPN) and other proteins with the RGD sequence as in OPN (RGD family proteins) that are present in renal tubular cells (fibronectin [FN], Tamm-Horsfall glycoprotein [THP], vitronectin [VN], and laminin [LN]) inhibit the aggregation and growth of calcium oxalate (CaOx) crystals by a novel seed crystal method using collagen granules (CG) with and without OPN adhered on the surface. We also evaluated the effect of solid phase OPN, FN and THP in which the relationship between their proteins and CaOx crystallization was reported. Moreover, the state and time-course changes in CaOx crystals adhered to CG were observed under scanning electron microscopy (SEM).

METHODS

The inhibitory activity (IA) on the aggregation and growth of CaOx crystals was measured in vitro by the conventional seed crystal method using isotopes. In this study, the following nine samples were used: OPN alone; FN alone; THP alone; VN alone; LN alone; CG alone; and CG with OPN, FN, or THP adhered on the surface (OPN/FN/THP-immobilized CG). In addition, the state and time-course changes in CaOx crystals adhered to CG were evaluated by SEM.

RESULTS

Using the conventional seed crystal method, the following values of IA were obtained: 91.7% (37.5 micro g/ml) for OPN, 5.0% (100 micro g/ml) for FN, 2.0% (100 micro g/ml) for THP, 3.0% (100 micro g/ml) for VN, and 1.0% (100 micro g/ml) for LN. However, the value of IA obtained by our seed crystal method using CG was 92.1% (180cm(2)/5ml PBS) when CG alone was used. Although the value of IA was decreased by 33.6% when OPN-immobilized CG was used, it did not significantly change when FN/THP-immobilized CG was used. When CG alone was used, the evaluation of CaOx crystallization by SEM demonstrated mild adherence and aggregation of CaOx crystal suspension (seed crystals) on the CG surface, although newly formed crystals only slightly adhered to the CG surface. When OPN-immobilized CG was used, marked adherence and aggregation of seed crystals were observed, in addition to the relatively increased adherence of newly formed crystals. When FN/THP-immobilized CG was used, newly formed crystals only slightly adhered to the CG surface, although the degree of seed crystal adherence and aggregation did not significantly change.

CONCLUSIONS

These findings suggest that the immobilization of OPN to the CG surface enhances the adherence and aggregation of seed crystals, as well as enhancing the adherence of newly formed crystals, resulting in decreased IA of CG (overall promotion of crystal deposition). Therefore, the results of this study clarified that OPN enhances the formation and aggregation of CaOx crystals in this experimental system.

Osteopontin is a critical inhibitor of calcium oxalate crystal formation and retention in renal tubules

Calcium nephrolithiasis is the most common form of renal stone disease, with calcium oxalate (CaOx) being the predominant constituent of renal stones. Current in vitro evidence implicates osteopontin (OPN) as one of several macromolecular inhibitors of urinary crystallization with potentially important actions at several stages of CaOx crystal formation and retention. To determine the importance of OPN in vivo, hyperoxaluria was induced in mice targeted for the deletion of the OPN gene together with wild-type control mice. Both groups were given 1% ethylene glycol, an oxalate precursor, in their drinking water for up to 4 wk. At 4 wk, OPN-deficient mice demonstrated significant intratubular deposits of CaOx crystals, whereas wild-type mice were completely unaffected. Retained crystals in tissue sections were positively identified as CaOx monohydrate by both polarized optical microscopy and x-ray powder diffraction analysis. Furthermore, hyperoxaluria in the OPN wild-type mice was associated with a significant 2- to 4-fold upregulation of renal OPN expression by immunocytochemistry, lending further support to a renoprotective role for OPN. These data indicate that OPN plays a critical renoprotective role in vivo as an inhibitor of CaOx crystal formation and retention in renal tubules.

Crystal retention capacity of cells in the human nephron: involvement of CD44 and its ligands hyaluronic acid and osteopontin in the transition of a crystal binding- into a nonadherent epithelium

Nephrolithiasis requires formation of crystals followed by their retention and accumulation in the kidney. Crystal retention can be caused by the association of crystals with the epithelial cells lining the renal tubules. The present study investigated the interaction between calcium oxalate monohydrate (COM) crystals and primary cultures of human proximal (PTC) and distal tubular/collecting duct cells (DTC). Both PTC and DTC were susceptible to crystal binding during the first days post-seeding (4.9 +/- 0.8 micro g COM/cm2), but DTC lost this affinity when the cultures developed into confluent monolayers with functional tight junctions (0.05 +/- 0.02 micro g COM/cm2). Confocal microscopy demonstrated the expression of the transmembrane receptor protein CD44 and its ligands osteopontin (OPN) and hyaluronic acid (HA) at the apical membrane of proliferating tubular cells; at confluence, CD44 was expressed at the basolateral membrane and OPN and HA were no longer detectable. In addition, a particle exclusion technique revealed that proliferating cells were surrounded by HA-rich pericellular matrices or "cell coats" extending several microns from the cell surface. Disintegration of these coats with hyaluronidase significantly decreased the cell surface affinity for crystals. Furthermore, CD44, OPN, and HA were also expressed in vivo at the luminal side of tubular cells in damaged kidneys. These results suggest (1) that the intact distal tubular epithelium of the human kidney does not bind crystals, and (2) that crystal retention in the human kidney may depend on the expression of CD44-, OPN-, and-HA rich cell coats by damaged distal tubular epithelium.

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.

Osteopontin expression and regulation in the testis, efferent ducts, and epididymis of rats during postnatal development through to adulthood

Osteopontin (OPN), a multifunctional phosphoprotein found in both hard and soft tissues, was examined in the male reproductive tract. The expression and regulation of OPN in the rat testis, efferent ducts, and epididymis was examined during postnatal development through to adulthood using immunocytochemistry at the light- and electron-microscopic level. Immunoblot analysis revealed a major 30-kDa band for epididymal tissue and a major 60-kDa band for the testis. In the testis, immunostaining of OPN was noted in early germ cells from spermatogonia to early pachytene spermatocytes, suggesting a role for OPN as an adhesive protein binding these cells to the basement membrane and adjacent Sertoli cells. Nonciliated cells of the efferent ducts expressed OPN, whereas a cell- and region-specific distribution of OPN was observed in the epididymis. Reactivity of OPN in the apical region of the cell corresponded to labeling of microvilli, small endocytic vesicles, and endosomes, where OPN may serve to remove calcium from the epididymal lumen and, thus, prevent mineral accumulation and subsequent decrease in sperm fertility. Regulation and postnatal studies revealed that circulating androgens regulate OPN expression in principal cells of the epididymis only. Taken together, the data reveal cell- and region-specific expression and regulation of OPN in the epididymis.