Increased intestinal vitamin D receptor in genetic hypercalciuric rats. A cause of intestinal calcium hyperabsorption

The real-world analysis of adverse events with teduglutide: a pharmacovigilance study based on the FAERS database

Background

Teduglutide, the first glucagon-like peptide 2 analogue, has been demonstrated to facilitate the absorption of gut nutrient and lessen the need for parenteral assistance in patients with Short Bowel Syndrome (SBS). However, its adverse drug events (AEs) are primarily documented in clinical trials, with a deficit in real-world data. This study evaluates the AEs profile of teduglutide based on Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) data.

Method

A disproportionality analysis of FAERS data from Quarter 1 (Q1) 2013 to Quarter 3 (Q3) 2023 was conducted to examine the association between teduglutide and adverse events, employing Reporting Odds Ratio (ROR), Proportional Reporting Ratio (PRR), Bayesian Confidence Propagation Neural Network (BCPNN), and Empirical Bayesian Geometric Mean (EBGM) methods.

Results

Out of 13,809,302 reports in the FAERS database, 10,114 reports identified teduglutide as the "primary suspect" in AEs identification. During the dosing observation period, the median occurrence of adverse events was 393 days (interquartile range [IQR] 97-996 days). Teduglutide-associated AEs occurred in 27 System Organ Classes (SOC), of which renal and urinary disorders is not mentioned in the specification. Based on the four algorithms, a total of 260 major disproportionality preferred terms (PTs) were filtered out, including previously unreported AEs including weight decreased (n = 805), vascular device infection (n = 683), dehydration (n = 596) and nephrolithiasis (n = 146).

Conclusion

Our findings corroborate the AEs listed in the teduglutide prescribing information and additionally unveil new adverse reaction signals such as nephrolithiasis. These discoveries could aid in clinical monitoring and risk identification for teduglutide.

Hypouricemia with hypercalciuria: Longitudinal study and review of the topic

BACKGROUND AND OBJECTIVE

The association of hypouricemia and hypercalciuria is rare. In 1974 a new syndrome named Hypouricemia with hypercalciuria and decreased bone density was described. Afterwards, some cases with such association were published in which the fractional excretion of urate was higher than 20ml/100ml FGR. We have analyzed a series of children who were diagnosed with hypouricemia and hypercalciuria and who were monitored. The aim of this study was to determine whether our patients could be affected by the aforementioned syndrome or be carriers of a variant of idiopathic hypercalciuria.

PATIENTS AND METHODS

Retrospective longitudinal study in which the medical records of eight patients (5V, 3M) diagnosed with hypouricemia and hypercalciuria in childhood. Clinical features at diagnosis, ultrasound and densitometric findings and selected biochemical variables were noted, with special emphasis on renal tubular handling of urate. Results were compared with 36 children with idiopathic hypercalciuria without hypouricemia (14V, 22M).

RESULTS

In the hypouricemia group baseline urate levels were 1.9 (0.3) mg/dl (range: 1.5-2) and first day urine calcium/creatinine ratio 0.27 (0.05) mg/mg (range: 0.23-0.31). In all cases fractional urate excretion was less than 20ml/100ml FGR. The z-DMO values were less than -1 in 4/8 cases. At the last follow-up only three cases still had an elevated calcium/creatinine ratio and in all of them the urates levels was greater than 2mg/dl. The z-DMO value had improved in five cases and worsened in three others. In relation to the group without hypouricemia, no differences were observed between the various parameters studied including the z-DMO value, with the exception of fractional excretion and tubular urate reabsorption although plasmatic uric acid levels were still significantly lower.

CONCLUSION

Our patients with hypercalciuria and hypouricemia would be affected by a variant of idiopathic hypercalciuria in which, due to an unknown cause, the proximal tubular reabsorption of urate is modestly reduced and improves over time. Hypouricemia with hypercalciuria and decreased bone density may not be a specific entity.

Magnesium Decreases Urine Supersaturation but Not Calcium Oxalate Stone Formation in Genetic Hypercalciuric Stone-Forming Rats

BACKGROUND/AIMS

Hypercalciuria is the most common identifiable risk factor predisposing to CaOx stone formation. Increased oral magnesium intake may lead to decreased CaOx stone formation by binding intestinal Ox leading to decreased absorption and/or binding urinary Ox to decrease urinary supersaturation. This study assessed the effect of oral magnesium on 24-h urine ion excretion, supersaturation, and kidney stone formation in a genetic hypercalciuric stone-forming (GHS) rat model of human idiopathic hypercalciuria.

METHODS

When fed the oxalate precursor, hydroxyproline, every GHS rat develops CaOx stones. The GHS rats, fed a normal calcium and phosphorus diet supplemented with hydroxyproline to induce CaOx, were divided into three groups of ten rats per group: control diet with 4.0 g/kg MgO, low MgO diet (0.5 g/kg), and high MgO diet (8 g/kg). At 6 weeks, 24-h urines were collected, and urine chemistry and supersaturation were determined. Stone formation was quantified.

RESULTS

The GHS rats fed the low and high Mg diets had a significant reduction and increase, respectively, in urinary Mg compared to those fed the control diet. Dietary Mg did not alter urine Ca excretion while the low Mg diet led to a significant fall in urinary Ox. Urine supersaturation with respect to CaOx was significantly increased with low Mg, whereas urine supersaturation was significantly decreased with high Mg. There was no effect of dietary Mg on stone formation within 6 weeks of treatment.

CONCLUSION

Dietary magnesium decreases urine supersaturation but not CaOx stone formation in GHS rats.

Prevalence of osteoporosis in patients with nephrolithiasis and vice versa: a cumulative analysis

Purpose

Nephrolithiasis is thought to be a risk factor for osteoporosis, but data assessing if osteoporosis predisposes to the risk of nephrolithiasis are lacking. The present study aims to investigate whether patients with nephrolithiasis have a prominently higher prevalence of osteoporosis than the controls and vice versa via a cumulative analysis.

Methods

Four databases were used to detect the eligible studies. We calculated the relative risk (RR) with a 95% confidence interval (CI) to assess the combined effect. The methodologies for conducting this study followed the PRISMA guidelines and were registered in the PROSPERO (ID: CRD42023395875).

Results

Nine case-control or cohort studies with a total of 454,464 participants were finally included. Combined results indicated that there was a significantly higher prevalence of osteoporosis in patients with nephrolithiasis as compared to the general population without nephrolithiasis (overall RR from six studies= 1.204, 95%CI: 1.133 to 1.28, P< 0.001; heterogeneity: I2 = 34.8%, P= 0.162). Conversely, osteoporosis was significantly correlated to an increased risk of nephrolithiasis as compared to the controls without osteoporosis (overall RR from four studies= 1.505, 95%CI: 1.309 to 1.731, P< 0.001; I2 = 89.8%, P< 0.001). Sensitivity analysis on the two categories validated the above findings. No significant publication bias was identified in this study.

Conclusions

The present study highlighted a significantly high prevalence of osteoporosis in patients with nephrolithiasis and vice versa. This reciprocal association reminded the clinicians to conduct a regular follow-up assessment when managing patients with nephrolithiasis or osteoporosis, especially for the elderly.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/#searchadvanced, identifier CRD42023395875.

Calcium and Vitamin D Supplementation and Their Association with Kidney Stone Disease: A Narrative Review

Kidney stone disease is a multifactorial condition influenced by both genetic predisposition and environmental factors such as lifestyle and dietary habits. Although different monogenic polymorphisms have been proposed as playing a causal role for calcium nephrolithiasis, the prevalence of these mutations in the general population and their complete pathogenetic pathway is yet to be determined. General dietary advice for kidney stone formers includes elevated fluid intake, dietary restriction of sodium and animal proteins, avoidance of a low calcium diet, maintenance of a normal body mass index, and elevated intake of vegetables and fibers. Thus, balanced calcium consumption protects against the risk for kidney stones by reducing intestinal oxalate availability and its urinary excretion. However, calcium supplementation given between meals might increase urinary calcium excretion without the beneficial effect on oxalate. In kidney stone formers, circulating active vitamin D has been found to be increased, whereas higher plasma 25-hydroxycholecalciferol seems to be present only in hypercalciuric patients. The association between nutritional vitamin D supplements and the risk for stone formation is currently not completely understood. However, taken together, available evidence might suggest that vitamin D administration worsens the risk for stone formation in patients predisposed to hypercalciuria. In this review, we analyzed and discussed available literature on the effect of calcium and vitamin D supplementation on the risk for kidney stone formation.

Beyond kidney stones: Why pediatricians should worry about hypercalciuria

The incidence of urolithiasis (UL) is increasing, and it has become more common in children and adolescents over the past few decades. Hypercalciuria is the leading metabolic risk factor of pediatric UL, and it has high morbidity, with or without lithiasis as hematuria and impairment of bone mass. The reduction in bone mineral density has already been described in pediatric idiopathic hypercalciuria (IH), and the precise mechanisms of bone loss or failure to achieve adequate bone mass gain remain unknown. A current understanding is that hypercalciuria throughout life can be considered a risk of change in bone structure and low bone mass throughout life. However, it is still not entirely known whether hypercalciuria throughout life can compromise the quality of the mass. The peak bone mass is achieved by late adolescence, peaking at the end of the second decade of life. This accumulation should occur without interference in order to achieve the peak of optimal bone mass. The bone mass acquired during childhood and adolescence is a major determinant of adult bone health, and its accumulation should occur without interference. This raises the critical question of whether adult osteoporosis and the risk of fractures are initiated during childhood. Pediatricians should be aware of this pediatric problem and investigate their patients. They should have the knowledge and ability to diagnose and initially manage patients with IH, with or without UL.

The association between single nucleotide polymorphism in vitamin D receptor and calcium oxalate urolithiasis in dogs

Background

Polymorphisms of the vitamin D receptor (VDR) are associated with calcium oxalate (CaOx) nephrolithiasis in humans.

Objectives

To investigate the association between VDR polymorphisms and susceptibility to CaOx urolithiasis in dogs.

Animals

Thirty‐five dogs with CaOx urolithiasis were compared with 40 stone‐free dogs.

Methods

This was a case‐control study. Two VDR gene polymorphisms (rs851998024 and rs852900542) were detected by specific TaqMan real‐time polymerase chain reaction assay, and their relationship with serum 1,25‐dihydroxyvitamin D, serum and urinary electrolyte concentrations was evaluated.

Results

The distribution of the rs852900542 polymorphism was significantly different between the case and the control dogs (x² = 6.369, P = .04). Dogs with a CC or CT genotype had an increased risk of CaOx stones than those with the TT genotype (odds ratio = 3.82, 95% confidence interval 1.04‐13.98). The CaOx dogs with the TT genotype had a significantly lower urinary calcium‐to‐creatinine ratio than the CT+CC genotypes. 1,25‐(OH)2D concentrations did not differ between the cases and the controls (308.7 ± 217.4 vs 286.7 ± 185.1 pg/mL, P = .45).

Conclusions and Clinical Importance

This finding suggests that vitamin D metabolism might play a role in CaOx stone formation in dogs.

Chlorthalidone with potassium citrate decreases calcium oxalate stones and increases bone quality in genetic hypercalciuric stone-forming rats

To study human idiopathic hypercalciuria we developed an animal model, genetic hypercalciuric stone-forming rats, whose pathophysiology parallels that of human idiopathic hypercalciuria. Fed the oxalate precursor, hydroxyproline, every rat in this model develops calcium oxalate stones. Using this rat model, we tested whether chlorthalidone and potassium citrate combined would reduce calcium oxalate stone formation and improve bone quality more than either agent alone. These rats (113 generation) were fed a normal calcium and phosphorus diet with hydroxyproline and divided into four groups: diets plus potassium chloride as control, potassium citrate, chlorthalidone plus potassium chloride, or potassium citrate plus chlorthalidone. Urine was collected at six, 12, and 18 weeks and kidney stone formation and bone parameters were determined. Compared to potassium chloride, potassium citrate reduced urinary calcium, chlorthalidone reduced it further and potassium citrate plus chlorthalidone even further. Potassium citrate plus chlorthalidone decreased urine oxalate compared to all other groups. There were no significant differences in calcium oxalate supersaturation in any group. Neither potassium citrate nor chlorthalidone altered stone formation. However, potassium citrate plus chlorthalidone significantly reduced stone formation. Vertebral trabecular bone increased with chlorthalidone and potassium citrate plus chlorthalidone. Cortical bone area increased with chlorthalidone but not potassium citrate or potassium citrate plus chlorthalidone. Mechanical properties of trabecular bone improved with chlorthalidone, but not with potassium citrate plus chlorthalidone. Thus in genetic hypercalciuric stone-forming rats fed a diet resulting in calcium oxalate stone formation, potassium citrate plus chlorthalidone prevented stone formation better than either agent alone. Chlorthalidone alone improved bone quality, but adding potassium citrate provided no additional benefit.

Vitamin D receptor (VDR) contributes to the development of hypercalciuria by sensitizing VDR target genes to vitamin D in a genetic hypercalciuric stone-forming (GHS) rat model

Human idiopathic hypercalciuria (IH) is the most common cause of calcium oxalate nephrolithiasis with perturbed calcium metabolism with increased bone resorption and decreased renal calcium reabsorption, which can be phenotype-copied in the genetic hypercalciuric stone-forming (GHS) rat model. We previously demonstrated that high VDR expression plays important roles in the development of hypercalciuria in the GHS rats. However, the underlying mechanism through which VDR impact hypercalciuria development remains to be fully understood. Here, we sought to determine how VDR regulated its target genes that are implicated in calcium homeostasis and potentially hypercalciuria. We found that VDR expression in the GHS rats was elevated in the calcium transporting tissues, as well as in the thymus and prostate, but not in lung, brain, heart, liver and spleen, when compared with control SD rats. Snail expression in the GHS rats was significantly downregulated in kidney, intestine, thymus and testis. Intraperitoneal injection of 1,25(OH)₂D₃ significantly upregulated the expression of renal calcium sensing receptor (CaSR), intestinal calcium transporters transient receptor potential vanilloid type 6 (TRPV6), and VDR in GHS rats, compared with that in control SD rats. ChIP assays revealed that VDR specifically bound to the proximal promoters of target genes, followed by histone H3 hyperacetylation or hypermethylation. Collectively, our results suggest that elevated VDR expression may contribute to the development of hypercalciuria by sensitizing VDR target genes to 1,25(OH)₂D₃ through histone modifications at their promoter regions in a genetic hypercalciuric stone-forming (GHS) rat model.

Intestinal responses to 1,25 dihydroxyvitamin D are not improved by higher intestinal VDR levels resulting from intestine-specific transgenic expression of VDR in mice

Intestinal calcium (Ca) absorption depends upon vitamin D signaling through the vitamin D receptor (VDR) in the proximal and distal intestine while lower VDR content causes intestinal resistance to 1,25 dihydroxyvitamin D (1,25(OH)₂ D) action. We tested whether intestinal responsiveness to 1,25(OH)₂ D is increased in mice with higher than normal VDR levels resulting from transgenic VDR expression in the whole intestine (villin promoter-human VDR transgene, HV2). Wild type (WT) and HV2 mice were treated with 0, 0.15, or 0.3 ng 1,25(OH)₂ D/g body weight (BW) (n = 6/dose) for 6 h. 1,25(OH)₂ D significantly induced Cyp24a1, Trpv6, and S100 g mRNA in duodenum (Dd) of WT mice but induction was not higher in HV2 mice. We next tested whether higher intestinal VDR could protect mice from the consequences of low dietary Ca intake. WT and HV2 mice were fed diets with 0.125, 0.25, 0.5 (reference), or 1% Ca from weaning to 3 months of age (n = 9/diet/genotype). Dietary Ca restriction caused a dose dependent increase in serum 1,25(OH)₂ D, Dd TRPV6, and Dd S100 g mRNA in WT mice and the effect was greater in HV2 mice. While Ca absorption was increased by low Ca intake, there was no difference in Ca absorption between HV2 and WT mice. Similarly, while bone density and microstructure were reduced by low Ca intake in WT mice, high intestinal VDR in HV2 mice did not protect bone in mice fed low Ca diets. Thus, while intestinal VDR and vitamin D signaling are essential for normal Ca metabolism during growth, our data demonstrate that higher than normal intestinal VDR levels do not improve the intestinal response to either 1,25(OH)₂ D injection or to elevated 1,25(OH)₂ D levels resulting from the physiologic adaptation to low Ca diets.

Increased Osteoclast and Decreased Osteoblast Activity Causes Reduced Bone Mineral Density and Quality in Genetic Hypercalciuric Stone-Forming Rats

To study human idiopathic hypercalciuria (IH), we developed an animal model, genetic hypercalciuric stone-forming (GHS) rats, whose pathophysiology parallels that in IH. All GHS rats form kidney stones and have decreased BMD and bone quality compared with the founder Sprague-Dawley (SD) rats. To understand the bone defect, we characterized osteoclast and osteoblast activity in the GHS compared with SD rats. Bone marrow cells were isolated from femurs of GHS and SD rats and cultured to optimize differentiation into osteoclasts or osteoblasts. Osteoclasts were stained for TRAcP (tartrate resistant acid phosphatase), cultured to assess resorptive activity, and analyzed for specific gene expression. Marrow stromal cells or primary neonatal calvarial cells were differentiated to osteoblasts, and osteoblastic gene expression as well as mineralization was analyzed. There was increased osteoclastogenesis and increased resorption pit formation in GHS compared with SD cultures. Osteoclasts had increased expression of cathepsin K, Tracp, and MMP9 in cells from GHS compared with SD rats. Osteoblastic gene expression and mineralization was significantly decreased. Thus, alterations in baseline activity of both osteoclasts and osteoblasts in GHS rats, led to decreased BMD and bone quality, perhaps because of their known increase in vitamin D receptors. Better understanding of the role of GHS bone cells in decreased BMD and quality may provide new strategies to mitigate the low BMD and increased fracture risk found in patients with IH. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Longitudinal study of kidney water management in patients diagnosed with idiopathic hypercalciuria in childhood

INTRODUCTION

There is much debate about whether idiopathic hypercalciuria (IH) affects kidney water management. For the first time in the literature, we carried out a longitudinal study of kidney water management (KWM) in patients diagnosed with IH in childhood and followed-up until adulthood (mean follow-up 17.7±1.4 years).

METHODS

Twenty-nine patients (7 M, 22 F) over the age of 24 years (mean 28.2±2.9 years, range: 24.1-35.9) who were diagnosed with IH in childhood (mean 7.6±3.2 years, range: 1-14) were included. Maximum urine osmolality (UO) and/or urine volume adjusted for 100ml of glomerular filtration rate (V/GFR) in both age groups (paediatric and adult) were determined. Moreover, whenever possible, in both age groups plasma creatinine levels, plasma sodium levels, uric acid levels, the citrate/creatinine ratio and the calcium/citrate ratio were recorded and a renal and bladder ultrasound was performed.

RESULTS

In the paediatric age group, KWM was altered in 9/29 cases (31%) (4 with reduced maximum UO and 5 with elevated V/GFR). In adulthood, KWM was found to be affected in 7/29 cases (24.1%) (6 with reduced UO and one with elevated V/GFR). Compared to the paediatric age group, adult patients had lower V/GFR, calcium/creatinine and citrate/creatinine values, as well as higher plasma creatinine, uric acid and calcium/citrate. There were no differences in the maximum UO in both age groups. However, UO in adulthood was significantly lower in subjects who had renal colic compared to those who did not (P=.04).

CONCLUSIONS

KWM was affected in approximately one third of patients with IH, which persisted 20 years after diagnosis. We think that these results may be due to adherence to the recommended protective diet and to the pharmacological treatment administered at the diagnosis of IH during childhood.

Association of vitamin D receptor gene polymorphisms and risk of urolithiasis: results of a genetic epidemiology study and comprehensive meta-analysis

Polymorphisms of vitamin D receptor (VDR) gene have been associated with risk of urolithiasis, but, with inconsistent results and lack data from Pakistani population. Therefore, after including our indigenous study data, a comprehensive meta-analysis was performed to provide an evidence-based estimate of any association between VDR polymorphisms and urolithiasis risk. A total of 483 Pakistani subjects, comprising 235 urolithiasis patients and 248 healthy controls, were genotyped for 6 VDR polymorphisms. Additionally, a systematic literature search with subsequent meta-analysis was conducted and pooled odds ratios (ORs) were used to determine the strength of any existent associations. Trial sequential analysis (TSA) was also performed. Results revealed no significant association of any VDR polymorphism and urolithiasis risk in indigenous Pakistani patients. However, meta-analysis of 29 relevant studies indicated that VDR FokI polymorphism significantly increased the risk of urolithiasis in allelic (f vs. F: OR = 1.13; 95% CI = 1.05-1.22; p ≤ 0.01) and recessive (ff vs. FF + Ff: OR = 1.20; 95% CI = 1.05-1.38; p = 0.01) models with no significant heterogeneity. No associations were evident for VDR ApaI, BsmI and TaqI polymorphic variants and urolithiasis risk after correction for multiple testing. Subgroup analysis by ethnicity suggested significant association for FokI variant among Asians. The TSA results demonstrated that the evidence reflecting association of FokI polymorphism and urolithiasis risk was sufficient and conclusive. In conclusion, this meta-analysis suggests that VDR FokI polymorphism is significantly associated with urolithiasis risk, especially in Asians, whereas ApaI, BsmI and TaqI polymorphisms are not associated.

The idiopathic hypercalciuria reviewed. Metabolic abnormality or disease?

Idiopathic hypercalciuria (IH) is defined as that clinical situation in which an increase in urinary calcium excretion is observed, in the absence of hypercalcemia and other known causes of hypercalciuria. In recent years, its diagnosis in pediatric age has been more frequent because it has been known that it can debut with very different symptoms, in the absence of kidney stone formation. The discovery of genetic hypercalciuric stone-forming rats has allowed us to glimpse the pathophysiological mechanism of IH since they show many data in common with humans with IH as normal levels of blood calcium, intestinal calcium hyperabsorption, increased bone resorption and a defect in the renal tubular calcium reabsorption. In 1993, it was shown that in these animals there is an increase in the number of vitamin D receptors (VDR) in the intestine, which favors an increase in the functional capacity of calcitriol-VDR complexes that explains the increase in intestinal transport of calcium. The same happens at the bone level producing a greater resorption. In our opinion, IH is a 'metabolic anomaly' or, better, an inheritable constitutive metabolic characteristic. In this sense, what patients with IH would inherit is the availability of having a greater number of VDRs in their cells than those with normal urinary calcium excretion. IH cannot be considered a sensu stricto disease, so pharmacological treatment must be individualized.

Chlorthalidone Is Superior to Potassium Citrate in Reducing Calcium Phosphate Stones and Increasing Bone Quality in Hypercalciuric Stone-Forming Rats

BACKGROUND

The pathophysiology of genetic hypercalciuric stone-forming rats parallels that of human idiopathic hypercalciuria. In this model, all animals form calcium phosphate stones. We previously found that chlorthalidone, but not potassium citrate, decreased stone formation in these rats.

METHODS

To test whether chlorthalidone and potassium citrate combined would reduce calcium phosphate stone formation more than either medication alone, four groups of rats were fed a fixed amount of a normal calcium and phosphorus diet, supplemented with potassium chloride (as control), potassium citrate, chlorthalidone (with potassium chloride to equalize potassium intake), or potassium citrate plus chlorthalidone. We measured urine every 6 weeks and assessed stone formation and bone quality at 18 weeks.

RESULTS

Potassium citrate reduced urine calcium compared with controls, chlorthalidone reduced it further, and potassium citrate plus chlorthalidone reduced it even more. Chlorthalidone increased urine citrate and potassium citrate increased it even more; the combination did not increase it further. Potassium citrate, alone or with chlorthalidone, increased urine calcium phosphate supersaturation, but chlorthalidone did not. All control rats formed stones. Potassium citrate did not alter stone formation. No stones formed with chlorthalidone, and rats given potassium citrate plus chlorthalidone had some stones but fewer than controls. Rats given chlorthalidone with or without potassium citrate had higher bone mineral density and better mechanical properties than controls, whereas those given potassium citrate did not.

CONCLUSIONS

In genetic hypercalciuric stone-forming rats, chlorthalidone is superior to potassium citrate alone or combined with chlorthalidone in reducing calcium phosphate stone formation and improving bone quality.

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.

Efficacy and safety of alfacalcidol in Chinese postmenopausal women aged over 65 with osteoporosis or osteopenia: An open label, non-comparative, post marketing observational study

This study aimed to explore the therapeutic efficacy and safety of alfacalcidol among Chinese postmenopausal women (age >65 years) with osteoporosis or osteopenia.A total of 62 postmenopausal women with osteoporosis or osteopenia (>65 years) were recruited from urban residential community of Beijing. The patients daily took oral calcium and alfacalcidol (Alpha D3, 1 μg) for 9 months. Safety and efficacy assessments were performed at baseline and regular intervals. Alfacalcidol was adjusted to a daily dose of 0.5 μg in case of hypercalcemia or hypercalciuria.A significant improvement in "timed up and go test" and "chair rising test" was achieved 3 months after treatment. Significant decreases in bone turnover markers were observed 3 months after the treatment and lasted throughout the study. Nineteen patients discontinued due to adverse events (17 hypercalciuria, 1 hydronephrosis, and 1 stomach ache), while alfacalcidol was adjusted to a daily dose of 0.5 μg in 18 patients (29.0%). Increased serum creatinine was observed when compared to baseline (P <.001), but all the values were in normal range.The treatment with 1 μg alfacalcidol can significantly improve muscle function and bone metabolism. Regular monitoring of urine calcium and timely dosage-adjustments are very important to guarantee the safety of alfacalcidol treatment in Chinese menopausal women.

Renal stones

Renal stone disease is a worldwide problem which carries significant morbidity. It frequently requires specialist urology intervention. Patients with recurrent disease and those at high risk require specialist investigations and review. Certain cases benefit from medical and surgical intervention. In this review, we discuss the pathophysiology, risk assessment, specialist investigations and various interventions, their rationale and evidence base. This review aims to provide an update of the previous publication in 2001 in this journal on this topic.

Vitamin D, Hypercalciuria and Kidney Stones

The estimated lifetime risk of nephrolithiasis is growing nowadays, and the formation of kidney stones is frequently promoted by hypercalciuria. Vitamin D, and especially its active metabolite calcitriol, increase digestive calcium absorption—as urinary calcium excretion is directly correlated with digestive calcium absorption, vitamin D metabolites could theoretically increase calciuria and promote urinary stone formation. Nevertheless, there was, until recently, low evidence that 25-hydroxyvitamin D serum levels would be correlated with kidney stone formation, even if high calcitriol concentrations are frequently observed in hypercalciuric stone formers. Low 25-hydroxyvitamin D serum levels have been associated with a broad spectrum of diseases, leading to a huge increase in vitamin D prescription in the general population. In parallel, an increased frequency of kidney stone episodes has been observed in prospective studies evaluating vitamin D alone or in association with calcium supplements, and epidemiological studies have identified an association between high 25-hydroxyvitamin D serum levels and kidney stone formation in some groups of patients. Moreover, urinary calcium excretion has been shown to increase in response to vitamin D supplements, at least in some groups of kidney stone formers. It seems likely that predisposed individuals may develop hypercalciuria and kidney stones in response to vitamin D supplements.

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.

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.

Association between vitamin D receptor gene polymorphisms (Fok1 and Bsm1) and osteoporosis: a systematic review

Osteoporosis is a health concern characterized by reduced bone mineral density (BMD) and increased risk of fragility fractures. Many studies have investigated the association between genetic variants and osteoporosis. Polymorphism and allelic variations in the vitamin D receptor gene (VDR) have been found to be associated with bone mineral density. However, many studies have not been able to find this association. Literature review was conducted in several databases, including MEDLINE/Pubmed, Scopus, EMBASE, Ebsco, Science Citation Index Expanded, Ovid, Google Scholar, Iran Medex, Magiran and Scientific Information Database (SID) for papers published between 2000 and 2013 describing the association between Fok1 and Bsm1 polymorphisms of the VDR gene and osteoporosis risk. The majority of the revealed papers were conducted on postmenopausal women. Also, more than 50% studies reported significant relation between Fok1, Bsm1 and osteoporosis. Larger and more rigorous analytical studies with consideration of gene-gene and gene-environment interactions are needed to further dissect the mechanisms by which VDR polymorphisms influence osteoporosis.

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.

Expression of fibroblast growth factor 23, vitamin D receptor, and sclerostin in bone tissue from hypercalciuric stone formers

BACKGROUND AND OBJECTIVES

Increased bone resorption, low bone formation, and abnormal mineralization have been described in stone formers with idiopathic hypercalciuria. It has been previously shown that the receptor activator of NF-κB ligand mediates bone resorption in idiopathic hypercalciuria (IH). The present study aimed to determine the expression of fibroblast growth factor 23 (FGF-23), vitamin D receptor (VDR), and sclerostin in bone tissue from IH stone formers.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Immunohistochemical analysis was performed in undecalcified bone samples previously obtained for histomorphometry from 30 transiliac bone biopsies of idiopathic hypercalciuria stone-forming patients between 1992 and 2002 and 33 healthy individuals (controls). Serum parameters were obtained from their medical records.

RESULTS

Histomorphometry disclosed 21 IH patients with high and 9 IH patients with normal bone resorption. Importantly, eroded surfaces (ES/BS) from IH patients but not controls were significantly correlated with VDR immunostaining in osteoblasts (r=0.51; P=0.004), sclerostin immunostaining in osteocytes (r=0.41; P=0.02), and serum 1,25-dihydroxyvitamin D (r=0.55; P<0.01). Of note, both VDR and sclerostin immunostaining were significantly correlated with serum 1,25-dihydroxyvitamin D in IH patients (r=0.52; P=0.01 and r=0.53; P=0.02, respectively), although VDR and sclerostin expression did not differ between IH and controls. IH patients with high bone resorption exhibited a significantly stronger sclerostin immunostaining than IH patients with normal bone resorption. FGF-23 expression in osteocytes from IH patients did not differ from controls and was not correlated with any histomorphometric parameter.

CONCLUSIONS

These findings suggest the contribution of VDR and sclerostin, as well as 1,25-dihydroxyvitamin D, to increase bone resorption in idiopathic hypercalciuria but do not implicate FGF-23 in the bone alterations seen in these patients.

[Nephrolithiasis: metabolic defects and terapeutic implications]

Over the past 10 years, major progress has been made in the knowledge of urinary lithogenesis, including the potential pathogenetic role of Randall's plaques and renal tubular crystal retention. Urine supersaturation is the driving force of this process and can be induced by some risk factors, including low urine volume, high urinary excretion of calcium oxalate and uric acid and low urinary excretion of citrate. Primary hypercalciuria can be due to intestinal overabsorption renal leak and bone reabsorption of calcium. Prophilaxis is mainly conducted with thiazides and low calcium diet which is indicated only in the intestinal form. Primary hyperoxaluria is treated with pyridoxine and may require in the severe forms simultaneous renal and liver transplantation. Enteric hyperoxaluria is secondary to fatty acids malabsorption and requires diet, oral calcium and cholestiramine. Hyperuricosuria is caused by diet endogenous overproduction, mainly due to enzymatic defects or high renal excretion of uric acid. Urine alkalinization with K or K and Mg citrate can prevent stone formation even in idiopathic uric acid nephrolithiasis, in which a defect of urine acidification is supposed to be the main abnormality, and in hypocitraturic patients. Cystinuria is a rare inherited defect with an intense clinical impact. It can be classified in three forms and urinary stone formation is the role. Increased solubility and conversion of cystine in a more soluble form are the main goals of the prophylaxis which includes K citrate and thiol agents administration. Tiopronin is preferred to D-penicillamine due to its lower side effects.

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.

The relation between bone and stone formation

Hypercalciuria is the most common metabolic abnormality found in patients with calcium-containing kidney stones. Patients with hypercalciuria often excrete more calcium than they absorb, indicating a net loss of total-body calcium. The source of this additional urinary calcium is almost certainly the skeleton, the largest repository of calcium in the body. Hypercalciuric stone formers exhibit decreased bone mineral density (BMD), which is correlated with the increase in urine calcium excretion. The decreased BMD also correlates with an increase in markers of bone turnover as well as increased fractures. In humans, it is difficult to determine the cause of the decreased BMD in hypercalciuric stone formers. To study the effect of hypercalciuria on bone, we utilized our genetic hypercalciuric stone-forming (GHS) rats, which were developed through successive inbreeding of the most hypercalciuric Sprague-Dawley rats. GHS rats excrete significantly more urinary calcium than similarly fed controls, and all the GHS rats form kidney stones while control rats do not. The hypercalciuria is due to a systemic dysregulation of calcium homeostasis, with increased intestinal calcium absorption, enhanced bone mineral resorption, and decreased renal tubule calcium reabsorption associated with an increase in vitamin D receptors in all these target tissues. We recently found that GHS rats fed an ample calcium diet have reduced BMD and that their bones are more fracture-prone, indicating an intrinsic disorder of bone not secondary to diet. Using this model, we should better understand the pathogenesis of hypercalciuria and stone formation in humans to ultimately improve the bone health of patients with kidney stones.

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.

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.

Idiopathic hypercalciuria and bone health

Calcium is an important participant in many physiologic processes including coagulation, cell membrane transfer, hormone release, neuromuscular activation, and myocardial contraction. The body cooperates in a sophisticated web of hormonally mediated interactions to maintain stable extracellular calcium levels. Calcium is vital for skeletal mineralization, and perturbations in extracellular calcium may be corrected at the expense of bone strength and integrity. The aim of this review is to delineate our current understanding of idiopathic hypercalciuria in the context of bone health, specifically its definition, etiology, epidemiology, laboratory evaluation, and potential therapeutic management.

Sex modifies genetic effects on residual variance in urinary calcium excretion in rat (Rattus norvegicus)

Conventional genetics assumes common variance among alleles or genetic groups. However, evidence from vertebrate and invertebrate models suggests that residual genotypic variance may itself be under partial genetic control. Such a phenomenon would have great significance: high-variability alleles might confound the detection of "classically" acting genes or scatter predicted evolutionary outcomes among unpredicted trajectories. Of the few works on this phenomenon, many implicate sex in some aspect of its control. We found that female genetic hypercalciuric stone-forming (GHS) rats (Rattus norvegicus) had higher coefficients of variation (CVs) for urinary calcium (CV = 0.14) than GHS males (CV = 0.06), and the reverse in normocalciuric Wistar-Kyoto rats (WKY) (CV(♂) = 0.14; CV(♀) = 0.09), suggesting sex-by-genotype interaction on residual variance. We therefore investigated the effect of sex on absolute-transformed residuals in urinary calcium in an F(2) GHS × WKY mapping cohort. Absolute residuals were associated with genotype at two microsatellites, D3Rat46 (RNO3, 33.9 Mb) and D4Mgh1 (RNO4, 84.8 MB) at Bonferroni thresholds across the entire cohort, and with the microsatellites D3Rat46, D9Mgh2 (RNO9, 84.4 Mb), and D12Rat25 (RNO12, 40.4 Mb) in females (P < 0.05) but not males. In GHS chromosome 1 congenic lines bred onto a WKY genomic background, we found that congenic males had significantly (P < 0.0001) higher CVs for urinary calcium (CV = 0.25) than females (CV = 0.15), supporting the hypothesis of the inheritance of sex-by-genotype interaction on this effect. Our findings suggest that genetic effects on residual variance are sex linked; heritable, sex-specific residuals might have great potential implications for evolution, adaptation, and genetic analysis.

Clinical review. Kidney stones 2012: pathogenesis, diagnosis, and management

CONTEXT

The pathogenetic mechanisms of kidney stone formation are complex and involve both metabolic and environmental risk factors. Over the past decade, major advances have been made in the understanding of the pathogenesis, diagnosis, and treatment of kidney stone disease.

EVIDENCE ACQUISITION AND SYNTHESIS

Both original and review articles were found via PubMed search reporting on pathophysiology, diagnosis, and management of kidney stones. These resources were integrated with the authors' knowledge of the field.

CONCLUSION

Nephrolithiasis remains a major economic and health burden worldwide. Nephrolithiasis is considered a systemic disorder associated with chronic kidney disease, bone loss and fractures, increased risk of coronary artery disease, hypertension, type 2 diabetes mellitus, and the metabolic syndrome. Further understanding of the pathophysiological link between nephrolithiasis and these systemic disorders is necessary for the development of new therapeutic options.

Bone disease in pediatric idiopathic hypercalciuria

Idiopathic hypercalciuria (IH) is the leading metabolic risk factor for urolithiasis and affects all age groups without gender or race predominance. IH has a high morbidity with or without lithiasis and reduced bone mineral density (BMD), as described previously in pediatric patients as well as in adults. The pathogenesis of IH is complex and not completely understood, given that urinary excretion of calcium is the end result of an interplay between three organs (gut, bone and kidney), which is further orchestrated by hormones, such as 1,25 dihydroxyvitamin D, parathyroid hormone, calcitonin and fosfatonins (i.e., fibroblast growth-factor-23). Usually, a primary defect in one organ induces compensatory mechanisms in the remaining two organs, such as increased absorption of calcium in the gut secondary to a primary renal loss. Thus, IH is a systemic abnormality of calcium homeostasis with changes in cellular transport of this ion in intestines, kidneys and bones. Reduced BMD has been demonstrated in pediatric patients diagnosed with IH. However, the precise mechanisms of bone loss or failure of adequate bone mass gain are still unknown. The largest accumulation of bone mass occurs during childhood and adolescence, peaking at the end of the second decade of life. This accumulation should occur without interference to achieve the peak of optimal bone mass. Any interference may be a risk factor for the reduction of bone mass with increased risk of fractures in adulthood. This review will address the pathogenesis of IH and its consequence in bone mass.

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.

Elevated vitamin D receptor levels in genetic hypercalciuric stone-forming rats are associated with downregulation of Snail

Patients with idiopathic hypercalciuria (IH) and genetic hypercalciuric stone-forming (GHS) rats, an animal model of IH, are both characterized by normal serum Ca, hypercalciuria, Ca nephrolithiasis, reduced renal Ca reabsorption, and increased bone resorption. Serum 1,25-dihydroxyvitamin D [1,25(OH)(2)D] levels are elevated or normal in IH and are normal in GHS rats. In GHS rats, vitamin D receptor (VDR) protein levels are elevated in intestinal, kidney, and bone cells, and in IH, peripheral blood monocyte VDR levels are high. The high VDR is thought to amplify the target-tissue actions of normal circulating 1,25(OH)(2)D levels to increase Ca transport. The aim of this study was to elucidate the molecular mechanisms whereby Snail may contribute to the high VDR levels in GHS rats. In the study, Snail gene expression and protein levels were lower in GHS rat tissues and inversely correlated with VDR gene expression and protein levels in intestine and kidney cells. In human kidney and colon cell lines, ChIP assays revealed endogenous Snail binding close to specific E-box sequences within the human VDR promoter region, whereas only one E-box specifically bound Snail in the rat promoter. Snail binding to rat VDR promoter E-box regions was reduced in GHS compared with normal control intestine and was accompanied by hyperacetylation of histone H(3). These results provide evidence that elevated VDR in GHS rats likely occurs because of derepression resulting from reduced Snail binding to the VDR promoter and hyperacetylation of histone H(3).

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.

Thiosulfate reduces calcium phosphate nephrolithiasis

An uncontrolled trial reported that sodium thiosulfate reduces formation of calcium kidney stones in humans, but this has not been established in a controlled human study or animal model. Using the genetic hypercalciuric rat, an animal model of calcium phosphate stone formation, we studied the effect of sodium thiosulfate on urine chemistries and stone formation. We fed genetic hypercalciuric rats normal food with or without sodium thiosulfate for 18 wk and measured urine chemistries, supersaturation, and the upper limit of metastability of urine. Eleven of 12 untreated rats formed stones compared with only three of 12 thiosulfate-treated rats (P < 0.002). Urine calcium and phosphorus were higher and urine citrate and volume were lower in the thiosulfate-treated rats, changes that would increase calcium phosphate supersaturation. Thiosulfate treatment lowered urine pH, which would lower calcium phosphate supersaturation. Overall, there were no statistically significant differences in calcium phosphate supersaturation or upper limit of metastability between thiosulfate-treated and control rats. In vitro, thiosulfate only minimally affected ionized calcium, suggesting a mechanism of action other than calcium chelation. In summary, sodium thiosulfate reduces calcium phosphate stone formation in the genetic hypercalciuric rat. Controlled trials testing the efficacy and safety of sodium thiosulfate for recurrent kidney stones in humans are needed.