Decreased Renal Expression of the Putative Calcium Oxalate Inhibitor Tamm-Horsfall Protein in the Ethylene Glycol Rat Model of Calcium Oxalate Urolithiasis

Oxalobacter formigenes treatment confers protective effects in a rat model of primary hyperoxaluria by preventing renal calcium oxalate deposition

In primary hyperoxaluria, increased hepatic oxalate production sometimes leads to severe nephrocalcinosis and early end-stage kidney disease. Oral administration of Oxalobacter formigenes (O. formigenes), an oxalate-degrading bacterium, is thought to derive oxalate from systemic sources by inducing net enteric oxalate secretion. Here, the impact of O. formigenes on nephrocalcinosis was investigated in an ethylene glycol rat model mimicking hepatic oxalate overproduction in primary hyperoxaluria. Eighteen rats were administered ethylene glycol (0.75% in drinking water) for 6 weeks, of which 9 were treated by oral gavage with O. formigenes and 9 received vehicle. Five control rats did not receive ethylene glycol or O. formigenes. Plasma and urinary oxalate levels, calcium oxalate crystalluria, urinary volume, fluid intake, and serum creatinine were monitored during the study. On killing, nephrocalcinosis was quantified. Ethylene glycol intake induced pronounced hyperoxalemia, hyperoxaluria, calcium oxalate crystalluria and nephrocalcinosis. Concomitant O. formigenes treatment partially prevented the ethylene glycol-induced increase in plasma oxalate and completely prevented nephrocalcinosis. Urinary oxalate excretion was not reduced by O. formigenes treatment. Nevertheless, absence of crystals in renal tissue of O. formigenes-treated ethylene glycol animals indicates that the propensity for oxalate to crystallize in the kidneys was reduced compared to non-treated animals. This is supported by the lower plasma oxalate concentrations in O. formigenes-treated animals. This study shows a beneficial effect of O. formigenes treatment on ethylene glycol-induced hyperoxalemia and nephrocalcinosis, and thus supports a possible beneficial effect of O. formigenes in primary hyperoxaluria.

Antilithiatic effect of C. dactylon, E. officinalis, K. pinnata, and B. nutans ethyl acetate fraction on glyoxylate-induced nephrolithiasis

Background

The plants Cynodon dactylon (C. dactylon), Emblica officinalis (E. officinalis), Kalanchoe pinnata (K. pinnata), and Bambusa nutans (B. nutans) have been reported to possess diuretic and antiurolithiatic potential against ethylene glycol and ammonium chloride along with in vitro calcium oxalate (CaOx) crystal growth inhibition property. Our previous research publications reported a rich presence of antioxidative phytocompounds like polyphenols and flavonoids in ethyl acetate fractions of these plants. This present study aims to explore antiurolithiatic potential of C. dactylon, E. officinalis, K. pinnata, and B. nutans ethyl acetate fraction following 7 days of sodium glyoxalate treatment on mice.

Results

Sodium glyoxylate treatment caused significant (P < 0.01–0.001) reduction in the urine magnesium and creatinine and elevation in oxalate, citrate, calcium, and phosphate levels. Ethyl acetate fraction of K. pinnata and B. nutans showed a highly significant antilithiatic effect by increasing urine volume, normalizing disrupted urine parameters, increasing LDH level, and decreasing kidney tissue oxalate content. E. officinalis and K. pinnata ethyl acetate fraction treatment showed a pronounced reversal of tubular dilation and damage of epithelial cell in kidney tissue with very less inflammatory cell infiltration.

Conclusion

The results signify the protective effect of K. pinnata and B. nutans ethyl acetate fraction rich with polyphenol and flavonoid on glyoxylate induced oxidative cell damage and morphological changes in mouse kidneys.

Transcriptional study of hyperoxaluria and calcium oxalate nephrolithiasis in male rats: Inflammatory changes are mainly associated with crystal deposition

Hyperoxaluria associated with renal deposition of calcium oxalate (CaOx) crystals causes renal injury and inflammation leading to number of diseases including chronic kidney disease (CKD). It is however, not been possible to separate the renal consequences of hyperoxaluria from that of CaOx crystal deposition. We decided to utilize ethylene glycol (EG) model where hyperoxaluria and CaOx crystal deposition can be separated in time. To test our hypothesis, male rats were made hyperoxaluric by administering EG, rats were euthanized and kidneys were extracted on day 14, when occasional crystal is seen in the kidneys and day 28, when all animals have developed renal CaOx crystal deposits. Total RNA was extracted for microarray analysis and genome wide analysis of differentially expressed genes was performed to investigate differences between hyperoxaluria and crystal induced alterations in the kidneys. Immunohistochemical and Hematoxylin and Eosin (H&E) staining was also done for macromolecules with significant role in stone formation. All EG fed rats became hyperoxaluric by day 7, showed a few crystal deposits on day 14, and had heavy crystal deposition by day 28. There were significant changes in the expression of genes encoding for NADPH Oxidases; macromolecular crystallization modulators; genes involved in inflammasome activation; and osteogenic marker genes. Results demonstrate major differences between hyperoxaluria and CaOx crystal induced changes in the kidneys. Injury and inflammation are mainly associated with crystal deposition indicating significant role played by crystal retention.

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.

What is nephrocalcinosis?

The available publications on nephrocalcinosis are wide-ranging and have documented multiple causes and associations of macroscopic or radiological nephrocalcinosis, most often located in the renal medulla, with various metabolic and genetic disorders; in fact, so many and various are these that it is difficult to define a common underlying mechanism. We have reviewed nephrocalcinosis in relation to its definition, genetic associations, animal models, and putative mechanisms. We have concluded, and hypothesized, that nephrocalcinosis is primarily a renal interstitial process, resembling metastatic calcification, and that it may have some features in common with, and pathogenic links to, vascular calcification.

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.

Nephrolithiasis: molecular mechanism of renal stone formation and the critical role played by modulators

Urinary stone disease is an ailment that has afflicted human kind for many centuries. Nephrolithiasis is a significant clinical problem in everyday practice with a subsequent burden for the health system. Nephrolithiasis remains a chronic disease and our fundamental understanding of the pathogenesis of stones as well as their prevention and cure still remains rudimentary. Regardless of the fact that supersaturation of stone-forming salts in urine is essential, abundance of these salts by itself will not always result in stone formation. The pathogenesis of calcium oxalate stone formation is a multistep process and essentially includes nucleation, crystal growth, crystal aggregation, and crystal retention. Various substances in the body have an effect on one or more of the above stone-forming processes, thereby influencing a person's ability to promote or prevent stone formation. Promoters facilitate the stone formation while inhibitors prevent it. Besides low urine volume and low urine pH, high calcium, sodium, oxalate and urate are also known to promote calcium oxalate stone formation. Many inorganic (citrate, magnesium) and organic substances (nephrocalcin, urinary prothrombin fragment-1, osteopontin) are known to inhibit stone formation. This review presents a comprehensive account of the mechanism of renal stone formation and the role of inhibitors/promoters in calcium oxalate crystallisation.

A comparative study of experimental rat models of renal calcium oxalate stone formation

PURPOSE

The aim of this study was to design a simple and convenient rat model with significant calcium oxalate crystal deposition in the kidney.

MATERIALS AND METHODS

Sprague-Dawley rats were divided into seven groups of 30 rats each. One group of rats was untreated to serve as controls. Two of the groups of rats were provided with drinking water supplemented with 1% ethylene glycol (EG), and of these two groups, one group was also administered vitamin D. Two groups of rats received intraperitoneal injections of EG, and of these two groups, one group also received vitamin D. Two groups of rats received intraperitoneal injections of glyoxylate, and of these two groups, one group also received vitamin D. We analyzed 24-hour urine samples for urinary constituents for all experimental groups, including calcium, oxalate, citrate, uric acid, pH, and urine volume. The kidneys were examined for crystal deposition using histologic examination and for osteopontin expression using immunohistochemical staining.

RESULTS

Calcium-oxalate crystals were found in all rats injected with glyoxylate after 1 week. The degree of crystal deposition in rats injected with glyoxylate for 1 week was significantly increased compared with rats fed EG for 4 weeks.

CONCLUSIONS

Intraperitoneal injection of glyoxylate is a faster, more exact, and more reliable method to produce calcium oxalate crystal deposition in the kidney than previous urolithiasis animal models.

Nephrocalcinosis in animal models with and without stones

Nephrocalcinosis is the deposition of calcium salts in renal parenchyma and can be intratubular or interstitial. Animal model studies indicate that intratubular nephrocalcinosis is a result of increased urinary supersaturation. Urinary supersaturation with respect to calcium oxalate (CaOx) and calcium phosphate (CaP) are generally achieved at different locations in the renal tubules. As a result experimental induction of hyperoxaluria in animals with CaP deposits does not lead to growth of CaOx over CaP. Interstitial nephrocalcinosis has been seen in mice with lack of crystallization modulators Tamm-Horsfall protein and osteopontin. Sodium phosphate co-transporter or sodiumhydrogen exchanger regulator factor-1 null mice also produced interstitial nephrocalcinosis. Crystals plug the tubules by aggregating and attaching to the luminal cell surface. Structural features of the renal tubules also play a role in crystal retention. The crystals plugging the terminal collecting ducts when exposed to the metastable pelvic urine may promote the formation of stone.

Uromodulin is expressed in renal primary cilia and UMOD mutations result in decreased ciliary uromodulin expression

Uromodulin (UMOD) mutations are responsible for three autosomal dominant tubulo-interstitial nephropathies including medullary cystic kidney disease type 2 (MCKD2), familial juvenile hyperuricemic nephropathy and glomerulocystic kidney disease. Symptoms include renal salt wasting, hyperuricemia, gout, hypertension and end-stage renal disease. MCKD is part of the 'nephronophthisis-MCKD complex', a group of cystic kidney diseases. Both disorders have an indistinguishable histology and renal cysts are observed in either. For most genes mutated in cystic kidney disease, their proteins are expressed in the primary cilia/basal body complex. We identified seven novel UMOD mutations and were interested if UMOD protein was expressed in the primary renal cilia of human renal biopsies and if mutant UMOD would show a different expression pattern compared with that seen in control individuals. We demonstrate that UMOD is expressed in the primary cilia of renal tubules, using immunofluorescent studies in human kidney biopsy samples. The number of UMOD-positive primary cilia in UMOD patients is significantly decreased when compared with control samples. Additional immunofluorescence studies confirm ciliary expression of UMOD in cell culture. Ciliary expression of UMOD is also confirmed by electron microscopy. UMOD localization at the mitotic spindle poles and colocalization with other ciliary proteins such as nephrocystin-1 and kinesin family member 3A is demonstrated. Our data add UMOD to the group of proteins expressed in primary cilia, where mutations of the gene lead to cystic kidney disease.

Are calcium oxalate crystals involved in the mechanism of acute renal failure in ethylene glycol poisoning?

INTRODUCTION

Ethylene glycol (EG) poisoning often results in acute renal failure, particularly if treatment with fomepizole or ethanol is delayed because of late presentation or diagnosis. The mechanism has not been established but is thought to result from the production of a toxic metabolite.

METHODS

A literature review utilizing PubMed identified papers dealing with renal toxicity and EG or oxalate. The list of papers was culled to those relevant to the mechanism and treatment of the renal toxicity associated with either compound. ROLE OF METABOLITES: Although the "aldehyde" metabolites of EG, glycolaldehyde, and glyoxalate, have been suggested as the metabolites responsible, recent studies have shown definitively that the accumulation of calcium oxalate monohydrate (COM) crystals in kidney tissue produces renal tubular necrosis that leads to kidney failure. In vivo studies in EG-dosed rats have correlated the severity of renal damage with the total accumulation of COM crystals in kidney tissue. Studies in cultured kidney cells, including human proximal tubule (HPT) cells, have demonstrated that only COM crystals, not the oxalate ion, glycolaldehyde, or glyoxylate, produce a necrotic cell death at toxicologically relevant concentrations. COM CRYSTAL ACCUMULATION: In EG poisoning, COM crystals accumulate to high concentrations in the kidney through a process involving adherence to tubular cell membranes, followed by internalization of the crystals. MECHANISM OF TOXICITY: COM crystals have been shown to alter membrane structure and function, to increase reactive oxygen species and to produce mitochondrial dysfunction. These processes are likely to be involved in the mechanism of cell death.

CONCLUSIONS

Accumulation of COM crystals in the kidney is responsible for producing the renal toxicity associated with EG poisoning. The development of a pharmacological approach to reduce COM crystal adherence to tubular cells and its cellular interactions would be valuable as this would decrease the renal toxicity not only in late treated cases of EG poisoning, but also in other hyperoxaluric diseases such as primary hyperoxaluria and kidney stone formation.

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.

Oxalate in renal stone disease: the terminal metabolite that just won't go away

The incidence of calcium oxalate nephrolithiasis in the US has been increasing throughout the past three decades. Biopsy studies show that both calcium oxalate nephrolithiasis and nephrocalcinosis probably occur by different mechanisms in different subsets of patients. Before more-effective medical therapies can be developed for these conditions, we must understand the mechanisms governing the transport and excretion of oxalate and the interactions of the ion in general and renal physiology. Blood oxalate derives from diet, degradation of ascorbate, and production by the liver and erythrocytes. In mammals, oxalate is a terminal metabolite that must be excreted or sequestered. The kidneys are the primary route of excretion and the site of oxalate's only known function. Oxalate stimulates the uptake of chloride, water, and sodium by the proximal tubule through the exchange of oxalate for sulfate or chloride via the solute carrier SLC26A6. Fecal excretion of oxalate is stimulated by hyperoxalemia in rodents, but no similar phenomenon has been observed in humans. Studies in which rats were treated with (14)C-oxalate have shown that less than 2% of a chronic oxalate load accumulates in the internal organs, plasma, and skeleton. These studies have also demonstrated that there is interindividual variability in the accumulation of oxalate, especially by the kidney. This Review summarizes the transport and function of oxalate in mammalian physiology and the ion's potential roles in nephrolithiasis and nephrocalcinosis.

Pathogenesis of renal calculi

Recent reports suggest that kidney stone disease prevalence is increasing. Despite significant treatment advances, the inciting factor and sequence of events leading to kidney stone formation remain elusive; however, recent efforts to understand the pathogenesis of nephrolithiasis have led to a delineation of the human surgical anatomy, histopathology, and metabolic factors in a variety of kidney stone formers. This article reviews the fundamental concepts of calculus formation, and the leading theories of stone pathogenesis, focusing on recent data from human papillary and renal cortical biopsies in stone formers that provide evidence for the role of Randall's plaque in kidney stone disease pathogenesis. These data suggest there are individual stone-forming phenotypes with unique surgical anatomy, histology, and metabolic profiles.

Successful formation of calcium oxalate crystal deposition in mouse kidney by intraabdominal glyoxylate injection

The establishment of an experimental animal model would be useful to study the mechanism of kidney stone formation. A calcium kidney stone model in rats induced by ethylene glycol has been used for research; however, to investigate the genetic basis affecting kidney stone formation, which will contribute to preventive medicine, the establishment of a kidney stone model in mice is essential. This study indicates the optimum conditions for inducing calcium oxalate stones in normal mouse kidney. Various doses of oxalate precursors, ethylene glycol, glycolate and glyoxylate, were administered either by free drinking or intraabdominal injection for 2 months as a preliminary study. Stone formation was detected with light microscopy, polarized light optical microscopy and electron microscopy. Stone components were detected with X-ray diffraction analysis. The expression of osteopontin (OPN), a major stone-related protein, was detected with immunohistochemical staining, in situ hybridization and quantitative reverse transcriptase polymerase chain reaction. Kidney stones were not detected in ethylene glycol- or glycolate-treated groups even at the highest dose of LD(50). Whereas, numerous kidney stones were detected in glyoxylate-treated mice (more than 60 mg/kg) at 3, 6 and 9 days after glyoxylate were administered intraabdominally. However, the number of kidney stones decreased gradually at day 12, and was hardly detected at day 15. The stone component was further analyzed as calcium oxalate monohydrate. A dramatic increase in the expression of OPN was observed by the administration of glyoxylate. We established a mouse kidney stone experimental system in this study. The difficulty of inducing kidney stones suggested that mice have greater intrinsic ability to prevent stone formation with hyperoxaluric stress than rats. The differing response to hyperoxaluric stress between mice and rats possibly contributes to the molecular mechanism of kidney stone formation and will aid preventive medicine in the future.

The Uromodulin C744G mutation causes MCKD2 and FJHN in children and adults and may be due to a possible founder effect

Autosomal dominant medullary cystic kidney disease type 2 (MCKD2) is a tubulo-in terstitial nephropathy that causes renal salt wasting, hyperuricemia, gout, and end-stage renal failure in the fifth decade of life. This disorder was described to have an age of onset between the age of 20-30 years or even later. Mutations in the Uromodulin (UMOD) gene were published in patients with familial juvenile hyperuricemic nephropathy (FJHN) and MCKD2. Clinical data and blood samples of 16 affected individuals from 11 different kindreds were collected. Mutational analysis of the UMOD gene was performed by exon polymerase chain reaction (PCR) and direct sequencing. We found the heterozygous C744G (Cys248Trp) mutation, which was originally published by our group, in an additional four kindreds from Europe and Turkey. Age of onset ranged from 3 years to 39 years. The phenotype showed a variety of symptoms such as urinary concentration defect, vesicoureteral reflux, urinary tract infections, hyperuricemia, hypertension, proteinuria, and renal hypoplasia. Haplotype analysis showed cosegragation with the phenotype in all eight affected individuals indicating that the C744G mutation may be due to a founder effect. Moreover, we describe a novel T229G (Cys77Gly) mutation in two affecteds of one kindred. Three of the affected individuals were younger than 10 years at the onset of MCKD2/FJHN. Symptoms include recurrent urinary tract infections compatible with the published phenotype of the Umod knockout mouse model. This emphasizes that MCKD2 is not just a disease of the young adult but is also relevant for children.

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.

Medullary cystic kidney disease type 1: mutational analysis in 37 genes based on haplotype sharing

Medullary cystic kidney disease type 1 (MCKD1) is an autosomal dominant, tubulo-interstitial nephropathy that causes renal salt wasting and end-stage renal failure in the fourth to seventh decade of life. MCKD1 was localized to chromosome 1q21. We demonstrated haplotype sharing and confirmed the telomeric border by a recombination of D1S2624 in a Belgian kindred. Since the causative gene has been elusive, high resolution haplotype analysis was performed in 16 kindreds. Clinical data and blood samples of 257 individuals (including 75 affected individuals) from 26 different kindreds were collected. Within the defined critical region mutational analysis of 37 genes (374 exons) in 23 MCKD1 patients was performed. In addition, for nine kindreds RT-PCR analysis for the sequenced genes was done to screen for mutations activating cryptic splice sites. We found consistency with the haplotype sharing hypothesis in an additional nine kindreds, detecting three different haplotype subsets shared within a region of 1.19 Mb. Mutational analysis of all 37 positional candidate genes revealed sequence variations in 3 different genes, AK000210, CCT3, and SCAMP3, that were segregating in each affected kindred and were not found in 96 healthy individuals, indicating, that a single responsible gene causing MCKD1 remains elusive. This may point to involvement of different genes within the MCKD1 critical region.

Renal prothrombin mRNA is significantly decreased in a hyperoxaluric rat model of nephrolithiasis

Although urinary prothrombin fragment 1 (UPTF1) possesses several hallmarks expected of a regulatory protein in urolithiasis, its precise role remains unknown. To determine the relationship between renal prothrombin (PT), the parent molecule of UPTF1, and lithogenesis, this study quantified and compared levels of renal PT mRNA in healthy rats (n = 10) and rats rendered lithogenic (n = 10) by ingestion of 0.75% ethylene glycol for 8 weeks. Studies included morphological and histological examination of the kidneys with scanning electron microscopy of the urinary filtrates of control and experimental animals. Haematuria and calcium oxalate (CaOx) crystals occurred in the urine of all experimental rats, but not in those of controls. Histological examination showed birefringent nephroliths and associated damage in kidneys of lithogenic rats, which were not seen in the control group. The amounts of total RNA extracted from both groups of rats were similar, but the median ratio of PT to beta-actin transcript of 11.14 x 10(-4) (10.65 x 10(-4) +/- 2.24 x 10(-4)) in the control rats was significantly (p < or = 0.001) reduced to 6.47 x 10(-4) (6.57 x 10(-4) +/- 2.72 x 10(-4)) in the lithogenic group. These results demonstrate that renal PT mRNA is reduced by approximately 42% in lithogenic rats and confirm the existence of a direct association between renal PT synthesis and calculogenesis. Attempts to compare renal PT and urinary levels of PTF1 were unsuccessful because of interference from hepatic PT circulating in the blood, haematuria, and the presence of urinary CaOx crystals. This is the first report of a significant reduction in the renal expression of a urinary protein well documented to inhibit CaOx crystal growth and aggregation in undiluted human urine in vitro.

N-Glycans carried by Tamm-Horsfall glycoprotein have a crucial role in the defense against urinary tract diseases

Tamm-Horsfall glycoprotein (THGP), produced exclusively by renal cells from the thick ascending limb of Henle's loop, is attached by a glycosyl-phosphatidylinositol (GPI)-anchor to the luminal face of the cells. Urinary excretion of THGP (50-100 mg/day) occurs upon proteolytic cleavage of the large ectodomain of the GPI-anchored form. N-Glycans, consisting of a large repertoire of sialylated polyantennary chains and high-mannose structures, account for approximately 30% of the weight of human urinary THGP. We describe: (i) the involvement of urinary THGP high-mannose glycans in defense against infections of the urinary tract, caused by type-1 fimbriated Escherichia coli, which recognize high-mannose structures, (ii) the role of GalNAcbeta1-4(NeuAcalpha2-3)Galbeta1-4GlcNAcbeta1-3Gal (Sd(a) determinant) carried by human THGP in protecting the distal nephron from colonization of type-S fimbriated E. coli which recognise NeuAcalpha2-3Gal, (iii) the inhibitory effect of sialylated THGP on crystal aggregation of calcium oxalate and calcium phosphate, thus preventing nephrolithiasis. Finally, we outline the importance of N-glycans in promoting the polymerization of THGP, a process resulting in the formation of homopolymers with an M(r) of several million in urine. Since THGP defense against diseases of the urinary tract mainly consists in binding damaging agents, its ability to behave as a multivalent ligand significantly enhances this protective role.

Microarray analysis of changes in renal phenotype in the ethylene glycol rat model of urolithiasis: potential and pitfalls

OBJECTIVES

To investigate, in an initial study, the use of microarray analysis (MA) to develop an information base for urolithiasis. MA enables the screening of thousands of genes simultaneously making it the technique of choice for situations where the results are known, but the underlying mechanisms are not. Little is known about the pathological changes occurring in the kidney during urolithiasis and this has severely hampered efforts to develop effective therapeutics.

MATERIALS AND METHODS

Male rats were treated with 0.75% ethylene glycol for 2, 4 or 8 weeks; after death the kidneys were processed for RNA isolation and MA, conducted using a rat-based chip (one kidney/chip) and the results confirmed by reverse transcription-polymerase chain reaction (RT-PCR, 21 probe sets; control, four rats; treated, five rats). Targets were defined as different by the software if the fold change (FC) was >or= 2, and sorted into functional categories using a data-mining tool. The repeatability of MA was investigated by subjecting the 4-week samples to MA in two independent runs.

RESULTS

The results for targets with a FC of >or= 2 were plotted (y = 1.01x - 0.75; r(2) 0.84). Comparing the results obtained by RT-PCR and MA showed a good qualitative correlation for those targets having a FC of >or= 5 as determined by MA. Changes in the expression of genes associated with tubule function and regulation, oxidative damage, and inflammation were the most common in the functional categories. Changes in the expression of tubule-specific markers indicated that there was damage to the proximal (gamma-adducin, organic anion and cation transporters, sodium-hydrogen exchange protein-isoform 3) and distal tubules (gamma-adducin, kallikrein) at 2 and 4 weeks. Increased expression of mitochondrial uncoupling protein indicated that there were changes to the mitochondria and oxidative stress at 2 and 4 weeks.

CONCLUSION

This study shows the power of MA as an exploratory technique, and changes in the expression of several physiologically important genes whose expression has not previously been reported to be affected by hyperoxaluria or calcium oxalate crystalluria.

Mutations of the Uromodulin gene in MCKD type 2 patients cluster in exon 4, which encodes three EGF-like domains

BACKGROUND

Autosomal-dominant medullary cystic kidney disease type 2 (MCKD2) is a tubulointerstitial nephropathy that causes renal salt wasting, hyperuricemia, gout, and end-stage renal failure in the fifth decade of life. The chromosomal locus for MCKD2 was localized on chromosome 16p12. Within this chromosomal region, Uromodulin (UMOD) was located as a candidate gene. UMOD encodes the Tamm-Horsfall protein. By sequence analysis, one group formerly excluded UMOD as the disease-causing gene. In contrast, recently, another group described mutations in the UMOD gene as responsible for MCKD2 and familial juvenile hyperuricemic nephropathy (FJHN).

METHODS

Haplotype analysis for linkage to MCKD2 was performed in 25 MCKD families. In the kindreds showing linkage to the MCKD2 locus on chromosome 16p12, mutational analysis of the UMOD gene was performed by exon polymerase chain reaction (PCR) and direct sequencing.

RESULTS

In 19 families, haplotype analysis was compatible with linkage to the MCKD2 locus. All these kindreds were examined for mutations in the UMOD gene. In three different families, three novel heterozygous mutations in the UMOD gene were found and segregated with the phenotype in affected individuals. Mutations were found only in exon 4.

CONCLUSION

We confirm the UMOD gene as the disease-causing gene for MCKD2. All three novel mutations were found in the fourth exon of UMOD, in which all mutations except one (this is located in the neighboring exon 5) published so far are located. These data point to a specific role of exon 4 encoded sequence of UMOD in the generation of the MCKD2 renal phenotype.

Tamm-Horsfall glycoprotein: biology and clinical relevance

Tamm-Horsfall glycoprotein (THP) is the most abundant urinary protein in mammals. Urinary excretion occurs by proteolytic cleavage of the large ectodomain of the glycosyl phosphatidylinositol-anchored counterpart exposed at the luminal cell surface of the thick ascending limb of Henle's loop. We describe the physical-chemical structure of human THP and its biosynthesis and interaction with other proteins and leukocytes. The clinical relevance of THP reported here includes: (1) involvement in the pathogenesis of cast nephropathy, urolithiasis, and tubulointerstitial nephritis; (2) abnormalities in urinary excretion in renal diseases; and (3) the recent finding that familial juvenile hyperuricemic nephropathy and autosomal dominant medullary cystic kidney disease 2 arise from mutations of the THP gene. We critically examine the literature on the physiological role and mechanism(s) that promote urinary excretion of THP. Some lines of research deal with the in vitro immunoregulatory activity of THP, termed uromodulin when isolated from urine of pregnant women. However, an immunoregulatory function in vivo has not yet been established. In the most recent literature, there is renewed interest in the capacity of urinary THP to compete efficiently with urothelial cell receptors, such as uroplakins, in adhering to type 1 fimbriated Escherichia coli. This property supports the notion that abundant THP excretion in urine is promoted in the host by selective pressure to obtain an efficient defense against urinary tract infections caused by uropathogenic bacteria.