Calcium oxalate crystal localization and osteopontin immunostaining in genetic hypercalciuric stone-forming rats

Oxalate Metabolism: From Kidney Stones to Cardiovascular Disease

Oxalate kidney stones are common and exert a huge burden of morbidity worldwide. However, circulating or excreted concentrations of oxalate are rarely measured. We argue that oxalate and its metabolism are important above and beyond kidney stone formation. There is emerging evidence that increased concentrations of oxalate could be a driver of chronic kidney disease progression. Furthermore, oxalate has been implicated in cardiovascular disease. Thus, the reduction of elevated plasma oxalate concentrations may represent a novel cardioprotective and nephroprotective strategy.

Association between aortic calcification and the presence of kidney stones: calcium oxalate calculi in focus

PURPOSE

The current research is aimed at analyzing the relationship between kidney stone (KS) and abdominal aortic calcification (AAC) and the relationship between KS components and AAC.

METHODS

This is a retrospective, case-control study. Kidney stone formers (KSFs) were treated at the Department of Urology, West China Hospital, Sichuan University for urological calculus disease from January 2014 to January 2020. Matched non-stone formers (non-SFs) were drawn from the same hospital for routine health examination from January 2018 to February 2019. Research-related information was collected and reviewed retrospectively from the hospital's computerized records. AAC were evaluated using available results of computed tomography imaging and abdominal vascular ultrasound. The relationships of AAC between KSFs and non-SFs were compared. The composition of renal calculi was analyzed by Fourier-transform infrared spectrophotometer. KSFs were divided into AAC groups and non-AAC based on AAC. The relationship of the composition of renal calculi between AAC and non-AAC were compared. The independent-sample t test, the chi-squared test and binary logistics regression were performed.

RESULTS

Altogether, 4516 people were included, with 1027 KSFs and 3489 non-SFs. There were no significant differences in the laboratory parameters between KSFs and non-SFs. The association between the presence of AAC and KS was significant in multivariable model 2 [adjusting hypertension, diabetes mellitus, fasting blood glucose, uric acid, serum triglyceride (TG), serum calcium, and urine pH] (OR 5.756, 95% CI 4.616-7.177, p < 0.001). The result of KSFs showed that calcium oxalate calculi (CaOx) was significantly associated with AAC in multivariable model 3 (adjusting age, hypertension, diabetes mellitus, drinking history, smoking history, and TG) (OR 1.351, 95% CI 1.002-1.822, p = 0.048).

CONCLUSIONS

The current study pioneered the revelation of the relationship between CaOx and AAC. Through an elimination of the confounding factors, the study demonstrated that KS and AAC were connected.

Calcium oxalate crystal deposition in the kidney: identification, causes and consequences

Calcium oxalate (CaOx) crystal deposition within the tubules is often a perplexing finding on renal biopsy of both native and transplanted kidneys. Understanding the underlying causes may help diagnosis and future management. The most frequent cause of CaOx crystal deposition within the kidney is hyperoxaluria. When this is seen in native kidney biopsy, primary hyperoxaluria must be considered and investigated further with biochemical and genetic tests. Secondary hyperoxaluria, for example due to enteric hyperoxaluria following bariatric surgery, ingested ethylene glycol or vitamin C overdose may also cause CaOx deposition in native kidneys. CaOx deposition is a frequent finding in renal transplant biopsy, often as a consequence of acute tubular necrosis and is associated with poorer long-term graft outcomes. CaOx crystal deposition in the renal transplant may also be secondary to any of the causes associated with this phenotype in the native kidney. The pathophysiology underlying CaOx deposition is complex but this histological phenotype may indicate serious underlying pathology and should always warrant further investigation.

Low Sodium Diet Decreases Stone Formation in Genetic Hypercalciuric Stone-Forming Rats

BACKGROUND

Urine (u) calcium (Ca) excretion is directly dependent on dietary sodium (Na) intake leading to the recommendation for Na restriction in hypercalciuric kidney stone formers. However, there is no direct evidence that limiting Na intake will reduce recurrent stone formation.

MATERIALS AND METHODS

We used genetic hypercalciuric stone-forming (GHS) rats, which universally form Ca phosphate (P) kidney stones, fed either a low Na (LNa, 0.05%) or normal Na (NNa, 0.4%) Na diet (D) for 18 weeks. Urine was collected at 6-week intervals. Radiographic analysis for stone formation and bone analyses were done at the conclusion of the study.

RESULTS

Mean uCa was lower with LNaD than NNaD as was uP and LNaD decreased mean uNa and uChloride. There were no differences in urine supersaturation (SS) with respect to calcium phosphate (CaP) or Ca oxalate (CaOx). However, stone formation was markedly decreased with LNaD by radiographic analysis. The LNaD group had significantly lower femoral anterior-posterior diameter and volumetric bone mineral density (vBMD), but no change in vertebral trabecular vBMD. There were no differences in the bone formation rate or osteoclastic bone resorption between groups. The LNaD group had significantly lower femoral stiffness; however, the ultimate load and energy to fail was not different.

CONCLUSION

Thus, a low Na diet reduced uCa and stone formation in GHS rats, even though SS with respect to CaP and CaOx was unchanged and effects on bone were modest. These data, if confirmed in humans, support dietary Na restriction to prevent recurrent Ca nephrolithiasis.

Urothelium proliferation is a trigger for renal crystal deposits in a murine lithogenesis model

Most mouse kidney stone models induce nephrocalcinosis rather than urolithiasis. The aim of our study was to find an accelerated experimental model in order to study the early events of stone formation, that is, at the time of crystal binding to intrarenal urothelium. C57B6 mice exposed to vitamin D supplements and water containing hydroxyl-L-proline, ammonium chloride and calcium chloride were studied for 42 days. A group receiving urothelial cell mitogen Fibroblast Growth Factor 7 (FGF7) was compared to control group receiving saline. Calcium oxalate monohydrate (COM) crystals were detected in urines by day 2 and within urinary spaces in specialized fornix areas in both groups as soon as day 14 with enhanced deposits in FGF7 group compared to controls at day 21. Urothelial cells proliferation, uroplakin III downregulation and de novo expression of osteopontin receptor CD44 detected in FGF7 group, were delayed in the control group (day 42). Crystal aggregates within specialized fornix areas by day 42 were located in urinary spaces but also within and under a multilayered metaplastic urothelium, simultaneous to macrophages influx. Point of note, administration of a normal diet by day 21 was responsible for a spontaneous crystal clearance. Our data show that under supersaturation conditions, urothelial cell proliferation and calcium oxalate crystal retention occur within specialized fornix areas. Enhanced crystal deposits following FGF7 administration suggest that urothelium proliferation would be a relevant trigger for renal stone formation.

IL-33/ST2 axis mediates hyperplasia of intrarenal urothelium in obstructive renal injury

The monolayered intrarenal urothelium covers the renal papilla and ureteropelvic junction (UPJ). In response to increased renal pressure during obstruction or ischemic injuries, intrarenal urothelial cells begin to proliferate and form a multilayered urothelium. Little is known regarding the mechanism and pathophysiological role of urothelium hyperplasia during renal obstruction. In this study, we investigated the expression of interleukin (IL)-33, an IL-1 family cytokine, in kidneys with unilateral ureteral obstruction (UUO)-induced obstructive injury. IL-33 levels in hydronephrotic urine and serum were upregulated 2 days after UUO. The number of ST2-expressing immune cells was increased in the UUO kidney. We found that IL-33 was upregulated in vimentin-positive cells in the cortical and medullar layers and the UPJ stroma. Moreover, IL-33 expression was predominantly induced in multilayered keratin 5-positive urothelial cells in the UPJ. IL-33 was not detected in terminally differentiated superficial umbrella cells expressing uroplakin 3a. In vivo, we confirmed that deficiency of IL33 or its receptor ST2 attenuated UUO-induced hyperplasia of the UPJ urothelium. Deficiency of IL33 attenuated the expression of UUO-induced type 2 inflammatory cytokines and upregulated uroplakins and urothelial differentiation signaling in UPJ tissues. Our results collectively suggest that the IL-33/ST2 axis mediates the activation of innate immune responses and contributes to urothelial hyperplasia by regulating urothelial differentiation in obstructive kidney injury.

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

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

Animal models of urinary stone disease

The etiology of stone disease remains unknown despite the major technological advances in the treatment of urinary calculi. Clinically, urologists have relied on 24-h urine collections for the last 30-40 years to help direct medical therapy in hopes of reducing stone recurrence; yet little progress has been made in preventing stone disease. As such, there is an urgent need to develop reliable animal models to study the pathogenesis of stone formation and to assess novel interventions. A variety of vertebrate and invertebrate models have been used to help understand stone pathogenesis. Genetic knockout and exogenous induction models are described. Surrogates for an endpoint of stone formation have been urinary crystals on histologic examination and/or urinalyses. Other models are able to actually develop true stones. It is through these animal models that real breakthroughs in the management of urinary stone disease will become a reality.

A Comparison between Clinical and Metabolic Features of Renal Calyceal Microlithiasis and Overt Urolithiasis in Different Pediatric Age Groups

INTRODUCTION

This study assesses the differences in the presentations, complications and metabolic abnormalities of children with renal calyceal microlithiasis (RCM) and overt urolithiasis in different pediatric ages.

MATERIALS AND METHODS

A total of 465 children with urolithiasis were investigated retrospectively. Patients were categorized based on their ages to infancy, early childhood, middle childhood and adolescence. When the hyperechogenic spots on ultrasound imaging were <3 mm, they were considered RCM, and if they were ≥3 mm, they were considered overt urolithiasis.

RESULTS

Metabolic abnormalities were detected in 71%; hyperuricosuria in infants, hyperoxaluria in younger children and hypocitraturia in older children were the most common metabolic abnormalities. Hypercalciuria was the only metabolic abnormality that was significantly associated with overt urolithiasis in all pediatric ages (OR 2.25, 95% CI 1.21-4.19). The clinical presentations were not significantly different between RCM and overt urolithiasis; however, complications such as urinary tract infection was significantly higher with overt urolithiasis in infancy (p = 0.01), early childhood (p = 0.02), middle childhood (p = 0.007) and adolescence (p = 0.01). Also, growth retardation was significantly higher with overt urolithiasis in infancy and early childhood (p = 0.02).

CONCLUSIONS

Most children with urolithiasis have underlying urinary metabolic abnormalities that differ according to the child's age. Despite these differences, hypercalciuria is significantly associated with overt urolithiasis in all pediatric ages. Clinical and laboratory features cannot differentiate RCM and overt urolithiasis; however, complications are significantly higher with overt urolithiasis.

Modeling hypercalciuria in the genetic hypercalciuric stone-forming rat

PURPOSE OF REVIEW

In this review, we discuss how the genetic hypercalciuric stone-forming (GHS) rats, which closely model idiopathic hypercalciuria and stone formation in humans, provide insights into the pathophysiology and consequences of clinical hypercalciuria.

RECENT FINDINGS

Hypercalciuria in the GHS rats is due to a systemic dysregulation of calcium transport, as manifest by increased intestinal calcium absorption, increased bone resorption and decreased renal tubule calcium reabsorption. Increased levels of vitamin D receptor in intestine, bone and kidney appear to mediate these changes. The excess receptors are biologically active and increase tissue sensitivity to exogenous vitamin D. Bones of GHS rats have decreased bone mineral density (BMD) as compared with Sprague-Dawley rats, and exogenous 1,25(OH)2D3 exacerbates the loss of BMD. Thiazide diuretics improve the BMD in GHS rats.

SUMMARY

Studying GHS rats allows direct investigation of the effects of alterations in diet and utilization of pharmacologic therapy on hypercalciuria, urine supersaturation, stone formation and bone quality in ways that are not possible in humans.

Effect of Potassium Citrate on Calcium Phosphate Stones in a Model of Hypercalciuria

Potassium citrate is prescribed to decrease stone recurrence in patients with calcium nephrolithiasis. Citrate binds intestinal and urine calcium and increases urine pH. Citrate, metabolized to bicarbonate, should decrease calcium excretion by reducing bone resorption and increasing renal calcium reabsorption. However, citrate binding to intestinal calcium may increase absorption and renal excretion of both phosphate and oxalate. Thus, the effect of potassium citrate on urine calcium oxalate and calcium phosphate supersaturation and stone formation is complex and difficult to predict. To study the effects of potassium citrate on urine supersaturation and stone formation, we utilized 95th-generation inbred genetic hypercalciuric stone-forming rats. Rats were fed a fixed amount of a normal calcium (1.2%) diet supplemented with potassium citrate or potassium chloride (each 4 mmol/d) for 18 weeks. Urine was collected at 6, 12, and 18 weeks. At 18 weeks, stone formation was visualized by radiography. Urine citrate, phosphate, oxalate, and pH levels were higher and urine calcium level was lower in rats fed potassium citrate. Furthermore, calcium oxalate and calcium phosphate supersaturation were higher with potassium citrate; however, uric acid supersaturation was lower. Both groups had similar numbers of exclusively calcium phosphate stones. Thus, potassium citrate effectively raises urine citrate levels and lowers urine calcium levels; however, the increases in urine pH, oxalate, and phosphate levels lead to increased calcium oxalate and calcium phosphate supersaturation. Potassium citrate induces complex changes in urine chemistries and resultant supersaturation, which may not be beneficial in preventing calcium phosphate stone formation.

1,25(OH)₂D₃ induces a mineralization defect and loss of bone mineral density in genetic hypercalciuric stone-forming rats

Genetic hypercalciuric stone-forming (GHS) rats, bred to maximize urine (u) calcium (Ca) excretion, demonstrate increased intestinal Ca absorption, increased bone Ca resorption, and reduced renal Ca reabsorption, all leading to elevated uCa compared to the parental Sprague-Dawley (SD) rats. GHS rats have increased numbers of vitamin D receptors (VDRs) at each site, with normal levels of 1,25(OH)₂D₃ (1,25D), suggesting their VDR is undersaturated with 1,25D. We have shown that 1,25D induces a greater increase in uCa in GHS than SD rats. To examine the effect of the increased VDR on the osseous response to 1,25D, we fed GHS and SD rats an ample Ca diet and injected either 1,25D [low dose (LD) 12.5 or high dose (HD) 25 ng/100 g body weight/day] or vehicle (veh) daily for 16 days. Femoral areal bone mineral density (aBMD, by DEXA) was decreased in GHS+LD and GHS+HD relative to GHS+veh, while there was no effect on SD. Vertebral aBMD was lower in GHS compared to SD and further decreased in GHS+HD. Both femoral and L6 vertebral volumetric BMD (by μCT) were lower in GHS and further reduced by HD. Histomorphometry indicated a decreased osteoclast number in GHS+HD compared to GHS+veh or SD+HD. In tibiae, GHS+HD trabecular thickness and number increased, with a 12-fold increase in osteoid volume but only a threefold increase in bone volume. Bone formation rate was decreased in GHS+HD relative to GHS+veh, confirming the mineralization defect. The loss of BMD and the mineralization defect in GHS rats contribute to increased hypercalciuria; if these effects persist, they would result in decreased bone strength, making these bones more fracture-prone. The enhanced effect of 1,25D in GHS rats indicates that the increased VDRs are biologically active.

Osteopontin knockdown in the kidneys of hyperoxaluric rats leads to reduction in renal calcium oxalate crystal deposition

Osteopontin (OPN) expression is increased in kidneys of rats with ethylene glycol (EG) induced hyperoxaluria and calcium oxalate (CaOx) nephrolithiasis. The aim of this study is to clarify the effect of OPN knockdown by in vivo transfection of OPN siRNA on deposition of CaOx crystals in the kidneys. Hyperoxaluria was induced in 6-week-old male Sprague-Dawley rats by administering 1.5% EG in drinking water for 2 weeks. Four groups of six rats each were studied: Group A, untreated animals (tap water); Group B, administering 1.5% EG; Group C, 1.5% EG with in vivo transfection of OPN siRNA; Group D, 1.5% EG with in vivo transfection of negative control siRNA. OPN siRNA transfections were performed on day 1 and 8 by renal sub-capsular injection. Rats were killed at day 15 and kidneys were removed. Extent of crystal deposition was determined by measuring renal calcium concentrations and counting renal crystal deposits. OPN siRNA transfection resulted in significant reduction in expression of OPN mRNA as well as protein in group C compared to group B. Reduction in OPN expression was associated with significant decrease in crystal deposition in group C compared to group B. Specific suppression of OPN mRNA expression in kidneys of hyperoxaluric rats leads to a decrease in OPN production and simultaneously inhibits renal crystal deposition.

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.

Persistence of 1,25D-induced hypercalciuria in alendronate-treated genetic hypercalciuric stone-forming rats fed a low-calcium diet

Genetic hypercalciuric stone-forming (GHS) rats demonstrate increased intestinal Ca absorption, increased bone resorption, and reduced renal tubular Ca reabsorption leading to hypercalciuria and all form kidney stones. GHS have increased vitamin D receptors (VDR) at these sites of Ca transport. Injection of 1,25(OH)2D3 (1,25D) leads to a greater increase in urine (u)Ca in GHS than in control Sprague-Dawley (SD), possibly due to the additional VDR. In GHS the increased uCa persists on a low-Ca diet (LCD) suggesting enhanced bone resorption. We tested the hypothesis that LCD, coupled to inhibition of bone resorption by alendronate (alen), would eliminate the enhanced 1,25D-induced hypercalciuria in GHS. SD and GHS were fed LCD and half were injected daily with 1,25D. After 8 days all were also given alen until euthanasia at day 16. At 8 days, 1,25D increased uCa in SD and to a greater extent in GHS. At 16 days, alen eliminated the 1,25D-induced increase in uCa in SD. However, in GHS alen decreased, but did not eliminate, the 1,25D-induced hypercalciuria, suggesting maximal alen cannot completely prevent the 1,25D-induced bone resorption in GHS, perhaps due to increased VDR. There was no consistent effect on mRNA expression of renal transcellular or paracellular Ca transporters. Urine CaP and CaOx supersaturation (SS) increased with 1,25D alone in both SD and GHS. Alen eliminated the increase in CaP SS in SD but not in GHS. If these results are confirmed in humans with IH, the use of bisphosphonates, such as alen, may not prevent the decreased bone density observed in these patients.

1,25(OH)₂D₃-enhanced hypercalciuria in genetic hypercalciuric stone-forming rats fed a low-calcium diet

The inbred genetic hypercalciuric stone-forming (GHS) rats exhibit many features of human idiopathic hypercalciuria and have elevated levels of vitamin D receptors (VDR) in calcium (Ca)-transporting organs. On a normal-Ca diet, 1,25(OH)2D3 (1,25D) increases urine (U) Ca to a greater extent in GHS than in controls [Sprague-Dawley (SD)]. The additional UCa may result from an increase in intestinal Ca absorption and/or bone resorption. To determine the source, we asked whether 1,25D would increase UCa in GHS fed a low-Ca (0.02%) diet (LCD). With 1,25D, UCa in SD increased from 1.2 ± 0.1 to 9.3 ± 0.9 mg/day and increased more in GHS from 4.7 ± 0.3 to 21.5 ± 0.9 mg/day (P < 0.001). In GHS rats on LCD with or without 1,25D, UCa far exceeded daily Ca intake (2.6 mg/day). While the greater excess in UCa in GHS rats must be derived from bone mineral, there may also be a 1,25D-mediated decrease in renal tubular Ca reabsorption. RNA expression of the components of renal Ca transport indicated that 1,25D administration results in a suppression of klotho, an activator of the renal Ca reabsorption channel TRPV5, in both SD and GHS rats. This fall in klotho would decrease tubular reabsorption of the 1,25D-induced bone Ca release. Thus, the greater increase in UCa with 1,25D in GHS fed LCD strongly suggests that the additional UCa results from an increase in bone resorption, likely due to the increased number of VDR in the GHS rat bone cells, with a possible component of decreased renal tubular calcium reabsorption.

New insights into the pathogenesis of renal calculi

The pathophysiology of the various forms of urinary stone disease remains a complex topic. Epidemiologic research and the study of urine and serum chemistries have created an abundance of data to help drive the formulation of pathophysiologic theories. This article addresses the associations of urinary stone disease with hypertension, cardiovascular disease, atherosclerosis, obesity, dyslipidemia, diabetes, and other disease states. Findings regarding the impact of dietary calcium and the formation of Randall's plaques are also explored and their implications discussed. Finally, further avenues of research are explored, including genetic analyses and the use of animal models of urinary stone disease.

Increased biological response to 1,25(OH)(2)D(3) in genetic hypercalciuric stone-forming rats

Genetic hypercalciuric stone-forming (GHS) rats, bred to maximize urine (U) calcium (Ca) excretion, have increased intestinal Ca absorption and bone Ca resorption and reduced renal Ca reabsorption, leading to increased UCa compared with the Sprague-Dawley (SD) rats. GHS rats have increased vitamin D receptors (VDR) at each of these sites, with normal levels of 1,25(OH)(2)D(3) (1,25D), indicating that their VDR is undersaturated with 1,25D. We tested the hypothesis that 1,25D would induce a greater increase in UCa in GHS rats by feeding both strains ample Ca and injecting 1,25D (25 ng · 100 g body wt(-1) · day(-1)) or vehicle for 16 days. With 1,25D, UCa in SD increased from 1.7 ± 0.3 mg/day to 24.4 ± 1.2 (Δ = 22.4 ± 1.5) and increased more in GHS from 10.5 ± 0.7 to 41.9 ± 0.7 (Δ = 29.8 ± 1.8; P = 0.003). To determine the mechanism of the greater increase in UCa in GHS rats, we measured kidney RNA expression of components of renal Ca transport. Expression of transient receptor potential vanilloid (TRPV)5 and calbindin D(28K) were increased similarly in SD + 1,25D and GHS + 1,25D. The Na(+)/Ca(2+) exchanger (NCX1) was increased in GHS + 1,25D. Klotho was decreased in SD + 1,25D and GHS + 1,25D. TRPV6 was increased in SD + 1,25D and increased further in GHS + 1,25D. Claudin 14, 16, and 19, Na/K/2Cl transporter (NKCC2), and secretory K channel (ROMK) did not differ between SD + 1,25D and GHS + 1,25D. Increased UCa with 1,25D in GHS exceeded that of SD, indicating that the increased VDR in GHS induces a greater biological response. This increase in UCa, which must come from the intestine and/or bone, must exceed any effect of 1,25D on TRPV6 or NCX1-mediated renal Ca reabsorption.

Interaction between submicron COD crystals and renal epithelial cells

Objectives

This study aims to investigate the adhesion characteristics between submicron calcium oxalate dihydrate (COD) with a size of 150 ± 50 nm and African green monkey kidney epithelial cells (Vero cells) before and after damage, and to discuss the mechanism of kidney stone formation.

Methods

Vero cells were oxidatively injured by hydrogen peroxide to establish a model of injured cells. Scanning electron microscopy was used to observe Vero–COD adhesion. Inductively coupled plasma emission spectrometry was used to quantitatively measure the amount of adhered COD microcrystals. Nanoparticle size analyzer and laser scanning confocal microscopy were performed to measure the change in the zeta potential on the Vero cell surface and the change in osteopontin expression during the adhesion process, respectively. The level of cell injury was evaluated by measuring the changes in malonaldehyde content, and cell viability during the adhesion process.

Results

The adhesion capacity of Vero cells in the injury group to COD microcrystals was obviously stronger than that of Vero cells in the control group. After adhesion to COD, cell viability dropped, both malonaldehyde content and cell surface zeta potential increased, and the fluorescence intensity of osteopontin decreased because the osteopontin molecules were successfully covered by COD. Submicron COD further damaged the cells during the adhesion process, especially for Vero cells in the control group, leading to an elevated amount of attached microcrystals.

Conclusion

Submicron COD can further damage injured Vero cells during the adhesion process. The amount of attached microcrystals is proportional to the degree of cell damage. The increased amount of microcrystals that adhered to the injured epithelial cells plays an important role in the formation of early-stage kidney stones.

Renal glomerular and tubular injury after gastric bypass in obese rats

OBJECTIVE

Roux-en-Y gastric bypass (RYGB) surgery is the most common surgical intervention for long-term weight loss in morbidly obese patients. By decreasing obesity-associated hyperfiltration, diabetes, and hypertension, RYGB is touted to stabilize, if not prevent, progression of chronic renal disease. To test this, the renal histology of diet-induced obese rats that underwent RYGB surgery was compared with that of pair-fed and sham obese controls.

METHODS

Sprague-Dawley rats, fed a high-fat, low-oxalate diet to induce gross obesity, were randomized to RYGB (n = 6), gastrointestinal-intact sham-operated obese controls (sham, n = 4), or gastrointestinal-intact sham-operated obese pair-fed controls (fed, n = 8). Daily body weight and food intake were recorded. On postoperative day 42, renal histology and immunohistochemistry were examined. Renal pathology was assessed by a categorical glomerular lesion score and a quantitative glomerular/tubular scoring system by experienced veterinary pathologists. Osteopontin and ED-1 (monocyte/macrophage cell) stainings were estimated by the percentage of stained area and the number of counted cells/high-power field, respectively.

RESULTS

Compared with sham and fed controls, RYGB rats had significant decreases in body weight (P < 0.001), more glomerular lesions (P = 0.02), and received higher glomerular and tubular lesion scores (P < 0.01). RYGB rodents had significantly stronger staining for osteopontin within the inner medullary region (P < 0.005) and ED-1 within the outer medullary region (P < 0.02) compared with sham and fed controls.

CONCLUSION

In this diet-induced obese rat model, RYGB is associated with chronic glomerulosclerosis and tubulointerstitial nephritis, confirmed by histology and immunohistochemistry. Prospective studies to better define the injurious mechanisms in this model are underway.

Chlorthalidone improves vertebral bone quality in genetic hypercalciuric stone-forming rats

We have bred a strain of rats to maximize urine (u) calcium (Ca) excretion and model hypercalciuric nephrolithiasis. These genetic hypercalciuric stone-forming (GHS) rats excrete more uCa than control Sprague-Dawley rats, uniformly form kidney stones, and similar to patients, demonstrate lower bone mineral density. Clinically, thiazide diuretics reduce uCa and prevent stone formation; however, whether they benefit bone is not clear. We used GHS rats to test the hypothesis that the thiazide diuretic chlorthalidone (CTD) would have a favorable effect on bone density and quality. Twenty GHS rats received a fixed amount of a 1.2% Ca diet, and half also were fed CTD (4 to 5 mg/kg/d). Rats fed CTD had a marked reduction in uCa. The axial and appendicular skeletons were studied. An increase in trabecular mineralization was observed with CTD compared with controls. CTD also improved the architecture of trabecular bone. Using micro-computed tomography (µCT), trabecular bone volume (BV/TV), trabecular thickness, and trabecular number were increased with CTD. A significant increase in trabecular thickness with CTD was confirmed by static histomorphometry. CTD also improved the connectivity of trabecular bone. Significant improvements in vertebral strength and stiffness were measured by vertebral compression. Conversely, a slight loss of bending strength was detected in the femoral diaphysis with CTD. Thus results obtained in hypercalciuric rats suggest that CTD can favorably influence vertebral fracture risk. CTD did not alter formation parameters, suggesting that the improved vertebral bone strength was due to decreased bone resorption and retention of bone structure.

Ethylene glycol induces calcium oxalate crystal deposition in Malpighian tubules: a Drosophila model for nephrolithiasis/urolithiasis

Several animal species are used to study calcium oxalate urolithiasis; however, an ideal model has yet to be identified. We used Drosophila as a model organism and fed the flies lithogenic agents such as ethylene glycol, hydroxyl-L-proline, and sodium oxalate. At different times, the Malpighian tubules, the kidney equivalent of insects, were dissected and a polarized light microscope used to highlight the birefringent crystals. Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed that the crystal composition was predominately calcium oxalate. Furthermore, administration of potassium citrate successfully reduced the quantity of and modulated the integrity of the ethylene glycol-induced crystals. Thus, the Drosophila model of bio-mineralization produces crystals in the urinary system through many lithogenic agents, permits observation of crystal formation, and is amenable to genetic manipulation. This model may mimic the etiology and clinical manifestations of calcium oxalate stone formation and aid in identification of the genetic basis of this disease.

Genetic hypercalciuric stone-forming rats have a primary decrease in BMD and strength

Kidney stone patients often have a decrease in BMD. It is unclear if reduced BMD is caused by a primary disorder of bone or dietary factors. To study the independent effects of hypercalciuria on bone, we used genetic hypercalciuric stone-forming (GHS) rats. GHS and control (Ctl) rats were fed a low Ca (0.02% Ca, LCD) or a high Ca (1.2% Ca, HCD) diet for 6 wk in metabolic cages. All comparisons are to Ctl rats. Urine Ca was greater in the GHS rats on both diets. GHS fed HCD had reduced cortical (humerus) and trabecular (L(1)-L(5) vertebrae) BMD, whereas GHS rats fed LCD had a reduction in BMD similar to Ctl. GHS rats fed HCD had a decrease in trabecular volume and thickness, whereas LCD led to a approximately 20-fold increase in both osteoid surface and volume. GHS rats fed HCD had no change in vertebral strength (failure stress), ductibility (failure strain), stiffness (modulus), or toughness, whereas in the humerus, there was reduced ductibility and toughness and an increase in modulus, indicating that the defect in mechanical properties is mainly manifested in cortical, rather than trabecular, bone. GHS rat cortical bone is more mineralized than trabecular bone and LCD led to a decrease in the mineralization profile. Thus, the GHS rats, fed an ample Ca diet, have reduced BMD with reduced trabecular volume, mineralized volume, and thickness, and their bones are more brittle and fracture prone, indicating that GHS rats have an intrinsic disorder of bone that is not secondary to diet.

Metabolic abnormalities in patients with nephrolithiasis: comparison of first-episode with recurrent cases in Southern Iran

BACKGROUND

Metabolic disorders are one of the etiologic factors in renal stone formation. The aim of present study was to evaluate prevalence of metabolic disorders in patients with renal stone.

METHODS

From 572 patients referring to our urologic clinics, 376 patients participated in the study. Patients were divided to first time stone former (group A) and recurrent renal stone (group B). Twenty-four hour urine specimens were obtained for urinary calcium, oxalate, magnesium, citrate, uric acid, phosphor and 24-h urine volume. Venous blood samples were obtained evaluating serum phosphate, uric acid, and calcium. The prevalence of each metabolic disorder was detected, and two groups were compared regarding metabolic disorders.

RESULTS

The prevalence of renal stone in male patients was 63.04% versus 36.96% in female patients (P < 0.05). The most common abnormality observed in patients was low 24-h urine volume (58.24%) followed by hypercalciuria (17.18%) and hyperuricosuria (15.15%). Hyperuricemia was found in 6 first time stone former patients and 14 patients with recurrent renal stone (P = 0.04). There was no statistically significant difference between group A and B in other metabolic abnormalities (P > 0.05).

CONCLUSION

Low 24-h urine volume was the most common abnormalities in patients with nephrolithiasis in our region. Metabolic evaluation must be performed in all patients with renal stone even those with first time stone formation.

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

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

Calcium oxalate crystal deposition in kidneys of hypercalciuric mice with disrupted type IIa sodium-phosphate cotransporter

The most common theories about the pathogenesis of idiopathic kidney stones consider precipitation of calcium phosphate (CaP) within the kidneys critical for the development of the disease. We decided to test the hypothesis that a CaP substrate can promote the deposition of calcium oxalate (CaOx) in the kidneys. Experimental hyperoxaluria was induced by feeding glyoxylate to male mice with knockout (KO) of NaP(i) IIa (Npt2a), a sodium-phosphate cotransporter. Npt2a KO mice are hypercalciuric and produce CaP deposits in their renal tubules. Experimental hyperoxaluria led to CaOx crystalluria in both the hypercalciuric KO mice and the normocalciuric control B6 mice. Only the KO mice produced CaOx crystal deposits in their kidneys, but the CaOx crystals deposited separately from the CaP deposits. Perhaps CaP deposits were not available for a CaOx overgrowth. These results also validate earlier animal model observations that showed that CaP substrate is not required for renal deposition of CaOx and that other factors, such as local supersaturation, may be involved. The absence of CaOx deposition in the B6 mice despite extreme hyperoxaluria also signifies the importance of both calcium and oxalate in the development of CaOx nephrolithiasis.

Effect of bolus and divided feeding on urine ions and supersaturation in genetic hypercalciuric stone-forming rats

Because urine ion excretion varies throughout the day, clinicians monitor 24 h urine samples to measure ion excretion and supersaturation in kidney stone patients. However, these results are averages and may not reflect maximal supersaturation which drives stone formation. We measured ion excretion and saturation in genetic hypercalciuric stone-forming rats on both a normal or low calcium diet over 0-3, 3-6 and 6-24 h using two feeding protocols, where the daily food allotment was fed either as a bolus or divided into three portions. With a normal calcium diet, urine calcium, oxalate, volume, and calcium oxalate supersaturation were significantly greater on the bolus compared to the divided feeds in the prandial and postprandial periods. Bolus eaters also excreted more calcium and oxalate and had increased volume over 24 h. Maximal calcium oxalate supersaturation was greater during the initial time periods than during the entire 24 h, regardless of the feeding schedule. With the low calcium diet, the effect of bolus feeding was reduced. Thus, urine ion excretion and supersaturation vary with the type of feeding. If these results are confirmed in man, it suggests that eating as a bolus may result in greater prandial and postprandial calcium oxalate supersaturation. This may increase growth on Randall's plaques and promote stone disease.

Idiopathic hypercalciuria

Hypercalcuria is the most common metabolic disorder found in patients with nephrolithiasis. As the prevalence of kidney stones rises in industrialized nations, understanding the pathogenesis and treatment of hypercalciuria becomes increasingly important. Idiopathic hypercalciuria (IH), defined as an excess urine calcium excretion without an apparent underlying etiology, is the most frequent cause of hypercalciuria and will be the focus of this paper. Calcium homeostasis is tightly controlled and slight disturbances in transport at the level of the intestine, bone, and/or kidney can lead to excessive urine calcium excretion and promote stone formation. IH is a systemic disorder with dysregulation of calcium transport at a combination of these calcium regulatory sites. The goal of treatment is to prevent stone formation and relies on a combination of dietary and pharmaceutical interventions. Dietary management includes increasing fluid intake, salt restriction, animal protein restriction, and maintaining a normal calcium intake. Thiazide diuretics have proven effective in preventing calcium stone formation by reducing the urinary excretion of calcium. It is important to note that while decreasing urinary calcium excretion is important the clinician should focus primarily on reducing the supersaturation of calcium oxalate as this determines the true tendency for stone formation.

Genetic hypercalciuric stone-forming rats

PURPOSE OF REVIEW

We will describe the pathophysiology of hypercalciuria and the mechanism of the resultant stone formation in a rat model and draw parallels to human hypercalciuria and stone formation.

RECENT FINDINGS

Through inbreeding we have established a strain of rats that excrete 8-10 times more urinary calcium than control rats. These genetic hypercalciuric rats absorb more dietary calcium at lower 1,25-dihydroxyvitamin D3 levels. Elevated urinary calcium excretion on a low-calcium diet indicated a defect in renal calcium reabsorption and/or an increase in bone resorption. Bone from hypercalciuric rats released more calcium when exposed to 1,25-dihydroxyvitamin D3. Bisphosphonate significantly reduced urinary calcium excretion in rats fed a low-calcium diet. Clearance studies showed a primary defect in renal calcium reabsorption. The intestine, bone and kidneys of the hypercalciuric rats had increased numbers of vitamin D receptors. When hydroxyproline is added to their diet they form calcium oxalate stones, the most common stone type in humans. Increased numbers of vitamin D receptors may cause hypercalciuria in these rats and humans.

SUMMARY

Understanding the mechanism of hypercalciuria and stone formation in this animal model will help clinicians devise effective treatment strategies for preventing recurrent stone formation in humans.

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.

Effect of cinacalcet on urine calcium excretion and supersaturation in genetic hypercalciuric stone-forming rats

Idiopathic hypercalciuria is the most common metabolic abnormality in patients with nephrolithiasis. Through successive inbreeding, we have developed a strain of rats whose urine calcium (UCa) excretion is approximately 8-10-fold greater than that of control rats and who spontaneously form kidney stones. We have termed these rats genetic hypercalciuric stone-forming (GHS) rats. The physiology of the hypercalciuria in the GHS rats closely parallels that of man. We have recently shown that the GHS rat kidneys have an increased number of receptors for calcium (CaR) compared to Sprague-Dawley rats, the strain of rats originally bred to develop the GHS rats. Calcimimetics, such as cinacalcet (Cin), increase the sensitivity of the CaR to Ca. The effects of Cin on UCa are complex and difficult to predict. We tested the hypothesis that Cin would alter urinary (U) Ca and supersaturation with respect to calcium hydrogen phosphate (CaHPO(4)) and calcium oxalate (CaOx). GHS or control rats were fed a normal Ca diet (0.6% Ca) for 28 days with Cin (30 mg/kg/24 h) added to the diet of half of each group for the last 14 days. The protocol was then repeated while the rats were fed a low Ca (0.02% Ca) diet. We found that Cin led to a marked reduction in circulating parathyroid hormone and a modest reduction in serum Ca. Cin did not alter UCa when the GHS rats were fed the normal Ca diet but lowered UCa when they were fed the low Ca diet. However, Cin did not alter U supersaturation with respect to either CaOx or CaHPO(4) on either diet. If these findings in GHS rats can be confirmed in man, it suggests that Cin would not be an effective agent in the treatment of human idiopathic hypercalciuria and resultant stone formation.

Isolation and confirmation of a calcium excretion quantitative trait locus on chromosome 1 in genetic hypercalciuric stone-forming congenic rats

Hypercalciuria is the most common risk factor for kidney stones and has a substantial genetic component. The genetic hypercalciuric stone-forming (GHS) rat model displays complex changes in physiology involving intestine, bone, and kidney and overexpression of the vitamin D receptor, thereby reproducing the human phenotype of idiopathic hypercalciuria. Through quantitative trait locus (QTL) mapping of rats that were bred from GHS female rats and normocalciuric Wistar Kyoto (WKY) male rats, loci that are linked to hypercalciuria and account for a 6 to eight-fold phenotypic difference between the GHS and WKY progenitors were mapped. GHS x WKY rats were backcrossed to breed for congenic rats with the chromosome 1 QTL HC1 on a normocalciuric WKY background. Ten generations of backcrosses produced N10F1 rats, which were intercrossed to produce rats that were homozygous for GHS loci in the HC1 region between markers D1Mit2 and D1Mit32. On a high-calcium diet (1.2% calcium), significantly different levels of calcium excretion were found between male congenic (1.67 +/- 0.71 mg/24 h) and male WKY control rats (0.78 +/- 0.19 mg/24 h) and between female congenic (3.11 +/- 0.90 mg/24 h) and female WKY controls (2.11 +/- 0.50 mg/24 h); the congenics preserve the calcium excretion phenotype of the GHS parent strain. Microarray expression analyses of the congenic rats, compared with WKY rats, showed that of the top 100 most changed genes, twice as many as were statistically expected mapped to chromosome 1. Of these, there is a clear bias in gene expression change for genes in the region of the HC1. Of >1100 gene groups analyzed, one third of the 50 most differentially expressed gene groups have direct or secondary action on calcium metabolism or transport. This is the first QTL for hypercalciuria to be isolated in a congenic animal.

Proposed pathogenesis of idiopathic loin pain-hematuria syndrome

BACKGROUND

To study loin pain-hematuria syndrome (LPHS) pathogenesis, we evaluated 43 consecutive patients for whom urological evaluation failed to disclose the cause of their recurrent flank pain and hematuria. Each underwent percutaneous kidney biopsy. In 9 patients, the biopsy specimen showed immunoglobulin A nephritis, an established cause of LPHS. We suggest these cases be designated secondary LPHS. They are not included in this analysis. The remaining patients (N = 34) are designated idiopathic (primary) LPHS. They are the basis of this report.

METHODS

Demographics of patients with primary LPHS are mean age of 30.8 +/- 10.3 years; 74% women; 94% white; and history of kidney stones, 47%, although none was obstructing.

RESULTS

Primary LPHS kidney biopsy specimens showed red blood cells (RBCs) in multiple tubules, consistent with glomerular hematuria. Glomeruli were normal by means of light and immunofluorescent microscopy; however, more than 50% of biopsy specimens showed unusually thin or thick glomerular basement membranes. To assess whether the biopsy itself caused RBCs in tubules, we compared RBCs in renal tubular cross-sections from primary LPHS biopsies with those of normal kidneys (donors, n = 10). The mean percentage of tubular cross-sections containing RBCs was greater in primary LPHS than normal specimens (7.2% +/- 6.5% versus 1.6% +/- 1.0% [SD]; P < 0.0001), confirming glomerular hematuria in patients with primary LPHS.

CONCLUSION

Primary LPHS pathogenesis includes glomerular hematuria, apparently from structurally abnormal glomerular basement membrane. Primary LPHS pain may be initiated by obstructing RBC casts and perhaps microcrystals in those with a history of urolithiasis. Nevertheless, other factors are needed to explain the severe pain in patients with primary LPHS.

Randall's plaque: Pathogenesis and role in calcium oxalate nephrolithiasis

The purpose of these studies was to test the hypothesis that Randall's plaque develops in unique anatomical sites of the kidney and their formation is conditioned by specific stone-forming pathophysiologies. We performed intraoperative papillary biopsies from kidneys of idiopathic-calcium oxalate (CaOx), intestinal bypass for obesity, brushite (BR) and cystine stone formers (SF) during percutaneous nephrolithotomy. Tissues were examined by infrared analysis and light and electron microscopy. Our analysis revealed a distinct pattern of mineral deposition and papillary pathology for each type of SF. CaOx SF had interstitial apatite crystals beginning at thin loops of Henle. These deposits termed Randall's plaque are thought to serve as sites for stone attachment. No tubular injury was noted. Intestinal bypass patients possessed intraluminal apatite deposits in inner medullary collecting ducts (IMCD) with associated cell injury. BR SF showed the most severe form of cortical and medullary changes with sites of Randall's plaque, and yellowish intraluminal deposits of apatite in IMCD. Cystine SF had plugging of ducts of Bellini with cystine crystals and apatite deposits in IMCD and loops of Henle. Intratubular sites of crystalline deposits were always associated to adjacent regions of interstitial fibrosis. The metabolic, anatomic, and surgical pathologic findings in four distinct groups of SF clearly show that 'the histology of the renal papilla from a stone former, is particular to the clinical setting'. We believe our approach to studying stone disease will provide insights into the pathogenesis of stone formation for each type of SF that will lead to improved clinical treatment.

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.

Apatite plaque particles in inner medulla of kidneys of calcium oxalate stone formers: osteopontin localization

BACKGROUND

We have previously shown that interstitial plaque particles appear first in the basement membranes of thin loops of Henle and then in the interstitial space. However, it is not known if the plaque in the basement membrane of thin loops of Henle is of the same or different form than the interstitial plaque. Thus our purpose here is to detail the structure of the interstitial and membrane-bound plaque and explore the relationship of plaque apatite to osteopontin, a well-known crystal-associated urine protein.

METHODS

Deep papillary biopsy tissue was studied from all 15 calcium oxalate stone formers and four nonforming subjects that we previously reported on [Evan et al, J Clin Ivest, 2003]. Routine light and transmission electron microscopy (TEM) as well as light microscopy and TEM immunohistochemical localization of osteopontin antibody were performed on all 19 subjects.

RESULTS

In the basement membrane, plaque particles are individual and appear laminated with alternating light regions of crystal and electron-dense organic layers. In the interstitium, individual particles are not abundant but are instead aggregated to form regions of attached particles and in some regions what appears to be a fusion or syncytium in which crystal islands float in an organic sea. By light microscopy immunohistochemistry, osteopontin was localized to cells of the loops of Henle and collecting ducts as well as on sites of plaque. By immunoelectron microscopy, osteopontin immunogold label was found mainly on the surfaces of apatite crystal phase, at the junction of the crystal/organic layers. A similar immunogold labeling pattern was seen in the particles forming the syncytial islands of interstitial plaque.

CONCLUSION

If indeed we accept the hypothesis that apatite plaque may be an anchored site on which calcium oxalate stones form and grow, the present work makes clear that it is unlikely that the surface of plaque presented to the final urine will be apatite crystal per se. However, our findings clearly show osteopontin is one of the crystal-associated urine proteins involved in the formation of the organic layers of the plaque particles.

Ethylene glycol induces hyperoxaluria without metabolic acidosis in rats

Ethylene glycol (EG) consumption is commonly employed as an experimental regimen to induce hyperoxaluria in animal models of calcium oxalate nephrolithiasis. This approach has, however, been criticized because EG overdose induces metabolic acidosis in humans. We tested the hypothesis that EG consumption (0.75% in drinking water for 4 wk) induces metabolic acidosis by comparing arterial blood gases, serum electrolytes, and urinary chemistries in five groups of Sprague-Dawley rats: normal controls (CON), those made hyperoxaluric (HYP) with EG administration, unilaterally nephrectomized controls (UNI), unilaterally nephrectomized rats fed EG (HRF), and a metabolic acidosis (MA) reference group imbibing sweetened drinking water (5% sucrose) containing 0.28 M NH4Cl. Arterial pH, plasma bicarbonate concentrations, anion gap, urinary pH, and the excretion of titratable acid, ammonium, phosphate, citrate, and calcium in HYP rats were not significantly different from CON rats, indicating that metabolic acidosis did not develop in HYP rats with two kidneys. Unilateral nephrectomy alone (UNI group) did not significantly affect arterial pH, plasma bicarbonate, anion gap, or urinary pH compared with CON rats; however, HRF rats exhibited some signs of a nascent acidosis in having an elevated anion gap, higher phosphate excretion, lower urinary pH, and an increase in titratable acid. Frank metabolic acidosis was observed in the MA rats: decreased arterial pH and plasma HCO3−concentration with lower urinary pH and citrate excretion with elevated excretion of ammonium, phosphate and, hence, titratable acid. We conclude that metabolic acidosis does not develop in conventional EG treatments but may ensue with renal insufficiency resulting from an oxalate load.

Thiazides Reduce Brushite, but not Calcium Oxalate, Supersaturation, and Stone Formation in Genetic Hypercalciuric Stone–Forming Rats

Over 59 generations, a strain of rats has been inbred to maximize urine calcium excretion. The rats now excrete eight to 10 times as much calcium as controls. These rats uniformly form calcium phosphate (apatite) kidney stones and have been termed genetic hypercalciuric stone-forming (GHS) rats. The addition of a common amino acid and oxalate precursor, hydroxyproline, to the diet of the GHS rats leads to formation of calcium oxalate (CaOx) kidney stones. Hydroxyproline-supplemented GHS rats were used to test the hypothesis that the thiazide diuretic chlorthalidone would decrease urine calcium excretion, supersaturation, and perhaps stone formation. All GHS rats received a fixed amount of a standard 1.2% calcium diet with 5% trans-4-hydroxy-l-proline (hydroxyproline) so that the rats would exclusively form CaOx stones. Half of the rats had chlorthalidone (Thz; 4 to 5 mg/kg per d) added to their diets. Urine was collected weekly, and at the conclusion of the study, the kidneys, ureters, and bladders were radiographed for the presence of stones. Compared with control, the addition of Thz led to a significant reduction of urine calcium and phosphorus excretion, whereas urine oxalate excretion increased. Supersaturation with respect to the calcium hydrogen phosphate fell, whereas supersaturation with respect to CaOx was unchanged. Rats that were fed Thz had fewer stones. As calcium phosphate seems to be the preferred initial solid phase in patients with CaOx kidney stones, the reduction in supersaturation with respect to the calcium phosphate solid phase may be the mechanism by which thiazides reduce CaOx stone formation.