Renal calcium stones: insights from the control of bone mineralization

Do pseudoxanthoma elasticum patients have higher prevalence of kidney stones on computed tomography compared to hospital controls?

BACKGROUND

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disease characterized by diminished inorganic plasma pyrophosphate (PPi), a strong calcification inhibitor. In addition to more typical calcification of skin, retina and arterial wall a diminished plasma PPi could lead to other ectopic calcification, such as formation of kidney stones.

OBJECTIVE

To compare the prevalence of kidney stones between PXE patients and hospital controls on computed tomography (CT).

METHOD

Low-dose CT images of PXE patients and controls were assessed by one radiologist, who was blinded for the diagnosis PXE. The number of kidney stones, and the size of the largest stone was recorded. Odds ratios (ORs) for having kidney stone were calculated using multivariable adjusted logistic regression.

RESULTS

Our study comprised 273 PXE patients and 125 controls. The mean age of PXE patients was 51.5 ± 15.9 years compared to 54.9 ± 14.2 in the control group (p = 0.04) and PXE patients more often were women (63 vs. 50%, p = 0.013). The prevalence of kidney stones on CT was similar: 6.9% in PXE patients, compared to 5.6% in controls (p = 0.6). In the multivariate analysis adjusting for age and sex, there was no significantly higher odds for PXE patients on having stones, compared to controls: OR 1.48 (95% CI 0.62-3.96).

CONCLUSION

There is no significant difference in the prevalence of incidental kidney stones on CT in PXE patients versus controls.

Transcriptomic response of Mytilus coruscus mantle to acute sea water acidification and shell damage

Mytilus coruscus is an economically important marine calcifier living in the Yangtze River estuary sea area, where seasonal fluctuations in natural pH occur owing to freshwater input, resulting in a rapid reduction in seawater pH. In addition, Mytilus constantly suffers from shell fracture or injury in the natural environment, and the shell repair mechanisms in mussels have evolved to counteract shell injury. Therefore, we utilized shell-complete and shell-damaged Mytilus coruscus in this study and performed transcriptomic analysis of the mantle to investigate whether the expression of mantle-specific genes can be induced by acute seawater acidification and how the mantle responds to acute acidification during the shell repair process. We found that acute acidification induced more differentially expressed genes than shell damage in the mantle, and the biomineralization-related Gene Ontology terms and KEGG pathways were significantly enriched by these DEGs. Most DEGs were upregulated in enriched pathways, indicating the activation of biomineralization-related processes in the mussel mantle under acute acidification. The expression levels of some shell matrix proteins and antimicrobial peptides increased under acute acidification and/or shell damage, suggesting the molecular modulation of the mantle for the preparation and activation of the shell repairing and anti-infection under adverse environmental conditions. In addition, morphological and microstructural analyses were performed for the mantle edge and shell cross-section, and changes in the mantle secretory capacity and shell inner film system induced by the two stressors were observed. Our findings highlight the adaptation of M. coruscus in estuarine areas with dramatic fluctuations in pH and may prove instrumental in its ability to survive ocean acidification.

Role of carboxylic organic molecules in interfibrillar collagen mineralization

Bone is a composite material made up of inorganic and organic counterparts. Most of the inorganic counterpart accounts for calcium phosphate (CaP) whereas the major organic part is composed of collagen. The interfibrillar mineralization of collagen is an important step in the biomineralization of bone and tooth. Studies have shown that synthetic CaP undergoes auto-transformation to apatite nanocrystals before entering the gap zone of collagen. Also, the synthetic amorphous calcium phosphate/collagen combination alone is not capable of initiating apatite nucleation rapidly. Therefore, it was understood that there is the presence of a nucleation catalyst obstructing the auto-transformation of CaP before entering the collagen gap zone and initiating rapid nucleation after entering the collagen gap zone. Therefore, studies were focused on finding the nucleation catalyst responsible for the regulation of interfibrillar collagen mineralization. Organic macromolecules and low-molecular-weight carboxylic compounds are predominantly present in the bone and tooth. These organic compounds can interact with both apatite and collagen. Adsorption of the organic compounds on the apatite nanocrystal governs the nucleation, crystal growth, lattice orientation, particle size, and distribution. Additionally, they prevent the auto-transformation of CaP into apatite before entering the interfibrillar compartment of the collagen fibril. Therefore, many carboxylic organic compounds have been utilized in developing CaP. In this review, we have covered different carboxylate organic compounds governing collagen interfibrillar mineralization.

Genetic Variants Involved in the Crystallization Pathway Are Associated with Calcium Nephrolithiasis in the Chinese Han Population

A genome-wide association analysis study (GWAS) in the Japanese population identified 14 significant loci associated with nephrolithiasis. Besides 4 novel loci related to metabolic traits, the 10 remaining loci were associated with kidney or electrolyte-related traits. We aimed to replicate the association of these loci with calcium nephrolithiasis in the Chinese Han population. A case–control association analysis was conducted involving 691 calcium nephrolithiasis patients and 1008 control subjects. We were able to genotype a total of 11 single-nucleotide polymorphisms (SNPs) previously identified as being correlated with nephrolithiasis in the Japanese population. SNP rs35747824 at PDILT was related to calcium nephrolithiasis in the Chinese Han population (p = 4.346 × 10⁻³, OR = 1.292). Moreover, four SNPs at four loci, rs6667242 at ALPL (p = 0.02999, OR = 0.8331), rs1544935 at KCNK5 (p = 0.01341, OR = 0.7804), rs7328064 at DGKH (p = 0.007452, OR = 1.211) and rs13041834 at BCAS1 (p = 0.03897, OR = 0.8409), were suggestively associated with calcium nephrolithiasis. Our results demonstrated that the genetic variants at 1p36.12, 6p21.2, 13q14.11, 16p12.3 and 20q13.2 are associated with calcium nephrolithiasis in the Chinese Han population. Furthermore, our study highlights the importance of genetic variance associated with the crystallization pathway in Chinese patients with calcium nephrolithiasis.

Various vascular malformations are prevalent in Finnish pseudoxanthoma elasticum (PXE) patients: a national registry study

Background

Pseudoxanthoma elasticum (PXE, OMIM# 264800) is an inborn error of metabolism causing ectopic soft tissue calcification due to low plasma pyrophosphate concentration. We aimed to assess the prevalence of PXE in Finland and to characterize the Finnish PXE population. A nationwide registry search was performed to identify patients with ICD-10 code Q82.84. Information was gathered from available medical records which were requisitioned from hospitals and health centers. Misdiagnosed patients and patients with insufficient records were excluded.

Results

The prevalence of PXE in Finland was 1:260,000 with equal sex distribution. Patients with high conventional cardiovascular risk had more visual and vascular complications than patients with low risk. Four patients (19%) had at least one vascular malformation. A high proportion (33%) of ABCC6 genotypes were of the common homozygous c.3421C > T, p.Arg1141Ter variant. Nine other homozygous or compound heterozygous allelic variants were found.

Conclusions

The prevalence of diagnosed PXE appears to be lower in Finland than in estimates from other countries. Decreased visual acuity is the most prevalent complication. We suggest that various vascular malformations may be an unrecognized feature of PXE.

TNAP as a therapeutic target for cardiovascular calcification: a discussion of its pleiotropic functions in the body

Cardiovascular calcification (CVC) is associated with increased morbidity and mortality. It develops in several diseases and locations, such as in the tunica intima in atherosclerosis plaques, in the tunica media in type 2 diabetes and chronic kidney disease, and in aortic valves. In spite of the wide occurrence of CVC and its detrimental effects on cardiovascular diseases (CVD), no treatment is yet available. Most of CVC involve mechanisms similar to those occurring during endochondral and/or intramembranous ossification. Logically, since tissue-nonspecific alkaline phosphatase (TNAP) is the key-enzyme responsible for skeletal/dental mineralization, it is a promising target to limit CVC. Tools have recently been developed to inhibit its activity and preclinical studies conducted in animal models of vascular calcification already provided promising results. Nevertheless, as its name indicates, TNAP is ubiquitous and recent data indicate that it dephosphorylates different substrates in vivo to participate in other important physiological functions besides mineralization. For instance, TNAP is involved in the metabolism of pyridoxal phosphate and the production of neurotransmitters. TNAP has also been described as an anti-inflammatory enzyme able to dephosphorylate adenosine nucleotides and lipopolysaccharide. A better understanding of the full spectrum of TNAP's functions is needed to better characterize the effects of TNAP inhibition in diseases associated with CVC. In this review, after a brief description of the different types of CVC, we describe the newly uncovered additional functions of TNAP and discuss the expected consequences of its systemic inhibition in vivo.

The Physiological and Pathological Role of Tissue Nonspecific Alkaline Phosphatase beyond Mineralization

Tissue-nonspecific alkaline phosphatase (TNAP) is a key enzyme responsible for skeletal tissue mineralization. It is involved in the dephosphorylation of various physiological substrates, and has vital physiological functions, including extra-skeletal functions, such as neuronal development, detoxification of lipopolysaccharide (LPS), an anti-inflammatory role, bile pH regulation, and the maintenance of the blood brain barrier (BBB). TNAP is also implicated in ectopic pathological calcification of soft tissues, especially the vasculature. Although it is the crucial enzyme in mineralization of skeletal and dental tissues, it is a logical clinical target to attenuate vascular calcification. Various tools and studies have been developed to inhibit its activity to arrest soft tissue mineralization. However, we should not neglect its other physiological functions prior to therapies targeting TNAP. Therefore, a better understanding into the mechanisms mediated by TNAP is needed for minimizing off targeted effects and aid in the betterment of various pathological scenarios. In this review, we have discussed the mechanism of mineralization and functions of TNAP beyond its primary role of hard tissue mineralization.

Ectopic biomineralization in kidney stone formers compared to non-stone formers

Background

Kidney stone formers (SFs) are at increased risk of stroke, myocardial infarction, and atherosclerosis of the carotid and coronary arteries. These cardiovascular and urologic pathologies can result from ectopic biomineral deposition. The objectives of this study are: (I) to evaluate risk factors for ectopic biomineralization, and (II) to characterize the overall burden of ectopic minerals in known SFs compared to non-stone formers (NSFs) matched for these risk factors.

Methods

Presence and quantity of biominerals at eight anatomic locations (abdominal aorta, common iliac arteries, pelvic veins, prostate or uterus, mesentery, pancreas, and spleen) were determined in a case control study by retrospective analysis of clinical non-contrast computed tomography scans obtained from 190 SFs and 190 gender- and age-matched NSFs (renal transplant donors). Predictors of biomineralization were determined using negative binomial regression. A subgroup of 140 SFs and 140 NSFs were matched for risk factors for systemic biomineralization, and mineralization was compared between these matched SFs and NSFs using ordinal logistic regression.

Results

Hypertension, hyperlipidemia, diabetes mellitus, and smoking were more common amongst SFs. Risk factors for increased systemic biomineralization included history of nephrolithiasis, male gender, older age, and history of hyperlipidemia. When controlling for these comorbidities, SFs had significantly increased biomineralization systemically and at the abdominal aorta, iliac arteries, prostate, mesentery, pancreas, and spleen compared to NSFs.

Conclusions

The current study provides evidence that SFs are at increased risk of biomineralization systemically, independent of common risk factors of atherosclerosis.

Genetic polymorphisms in CLDN14 (rs219780) and ALP (rs1256328) genes are associated with risk of nephrolithiasis in Egyptian children

OBJECTIVE

Nephrolithiasis results from metabolic and anatomic abnormalities together with genetic factors. Claudin 14 (CLDN14) is a protein that regulates the passage of small solutes through the kidneys. Alkaline phosphatase (ALPL) hydrolyzes the pyrophosphate to free phosphate, proposing its enabling role in nephrolithiasis development. Solute carrier family 13 member 2 (SLC13A2) encodes Na+-Pi cotransporter 2a, which is responsible for the renal absorption of phosphate. We aimed to detect the association between CLDN14, ALPL, and SLC13A2 genetic variants and susceptibility to nephrolithiasis in the Egyptian pediatric population.

MATERIAL AND METHODS

We enrolled 204 consecutive pediatric patients with nephrolithiasis, and 126 normal individuals served as controls. Real-time polymerase chain reaction analysis of CLDN14 rs219780, ALPL rs1256328, and SLC34A1 rs11746443 single-nucleotide polymorphisms (SNPs) was performed.

RESULTS

We found that individuals carrying the T allele of CLDN14 rs219780 and ALPL rs1256328 SNPs had a significantly higher risk of nephrolithiasis than the controls (p=0.001 and 0.001, respectively). Genetic association analyses identified that CLDN14 rs219780 and ALPL rs1256328SNPs were significantly associated with the nephrolithiasis status (odds ratio [OR] =4.51; 95% confidence interval [CI]=2.758-7.374; p=0.001 and OR=6.088; 95% CI=3.651-10.152; p=0.001, respectively). The sequence variant ALPL rs1256328 T allele had a significant correlation with the increased serum alkaline phosphatase levels in children with nephrolithiasis (p=0.02). No significant association was found between SLC34A1 rs11746443 SNP and the risk of nephrolithiasis (p=0.5).

CONCLUSION

CLDN14 rs219780 and ALPL rs1256328 SNPs might raise the risk of nephrolithiasis in Egyptian children, and might be used as genetic markers in these patients.

Conversion of extracellular ATP into adenosine: a master switch in renal health and disease

ATP and its ultimate degradation product adenosine are potent extracellular signalling molecules that elicit a variety of pathophysiological functions in the kidney through the activation of P2 and P1 purinergic receptors, respectively. Extracellular purines can modulate immune responses, balancing inflammatory processes and immunosuppression; indeed, alterations in extracellular nucleotide and adenosine signalling determine outcomes of inflammation and healing processes. The functional activities of ectonucleotidases such as CD39 and CD73, which hydrolyse pro-inflammatory ATP to generate immunosuppressive adenosine, are therefore pivotal in acute inflammation. Protracted inflammation may result in aberrant adenosinergic signalling, which serves to sustain inflammasome activation and worsen fibrotic reactions. Alterations in the expression of ectonucleotidases on various immune cells, such as regulatory T cells and macrophages, as well as components of the renal vasculature, control purinergic receptor-mediated effects on target tissues within the kidney. The role of CD39 as a rheostat that can have an impact on purinergic signalling in both acute and chronic inflammation is increasingly supported by the literature, as detailed in this Review. Better understanding of these purinergic processes and development of novel drugs targeting these pathways could lead to effective therapies for the management of acute and chronic kidney disease.

The rs1256328 (ALPL) and rs12654812 (RGS14) Polymorphisms are Associated with Susceptibility to Calcium Nephrolithiasis in a Taiwanese population

Nephrolithiasis is a common disease affecting almost all populations, with an increasing prevalence over the past decades. Previous studies revealed several functional polymorphisms associated with the pathogenesis of nephrolithiasis. However, data on Asian populations are limited. In this study, three candidate polymorphisms were selected from previous studies to investigate the correlations with nephrolithiasis in a Taiwanese population. In total, 454 nephrolithiasis patients were recruited from Kaohsiung Medical University Hospital, with SNP frequency for 1513 subjects of general population from the Taiwan Biobank (TWB) as a genotypic reference. Results revealed that subjects with minor TT genotype at rs1256328 (alkaline phosphatase, liver/bone/kidney (ALPL)) have higher susceptibility to nephrolithiasis (odds ratio (OR) = 2.03, p = 0.0013). In addition, subjects carrying the minor AA genotype at rs12654812 (regulator of G protein signaling 14 (RGS14)) have higher susceptibility to nephrolithiasis (OR = 1.91, p = 0.0017). Among nephrolithiasis patients, subjects with GG at rs7627468 (calcium-sensing receptor (CASR)) have lower pH level in urine (p = 0.0088). Importantly, rs7627468 is associated with the expressions of IQCB1 and EAF2. rs12654812 could influence the expression of RGS14 itself, MXD3, and FGFR4. In summary, this study successfully validated the genetic roles of rs1256328 and rs12654812 in human nephrolithiasis.

Novel Risk Loci Identified in a Genome-Wide Association Study of Urolithiasis in a Japanese Population

BACKGROUND

A family history of urolithiasis is associated with a more than doubling of urolithiasis risk, and a twin study estimating 56% heritability of the condition suggests a pivotal role for host genetic factors. However, previous genome-wide association studies (GWAS) have identified only six risk-related loci.

METHODS

To identify novel urolithiasis-related loci in the Japanese population, we performed a large-scale GWAS of 11,130 cases and 187,639 controls, followed by a replication analysis of 2289 cases and 3817 controls. Diagnosis of urolithiasis was confirmed either by a clinician or using medical records or self-report. We also assessed the association of urolithiasis loci with 16 quantitative traits, including metabolic, kidney-related, and electrolyte traits (such as body mass index, lipid storage, eGFR, serum uric acid, and serum calcium), using up to 160,000 samples from BioBank Japan.

RESULTS

The analysis identified 14 significant loci, including nine novel loci. Ten regions showed a significant association with at least one quantitative trait, including metabolic, kidney-related, and electrolyte traits, suggesting a common genetic basis for urolithiasis and these quantitative traits. Four novel loci were related to metabolic traits, obesity, hypertriglyceridemia, or hyperuricemia. The remaining ten loci were associated with kidney- or electrolyte-related traits; these may affect crystallization. Weighted genetic risk score analysis indicated that the highest risk group (top 20%) showed an odds ratio of 1.71 (95% confidence interval, 1.42 to 2.06) - 2.13 (95% confidence interval, 2.00 to 2.27) compared with the reference group (bottom 20%).

CONCLUSIONS

Our findings provide evidence that host genetic factors related to regulation of metabolic and crystallization pathways contribute to the development of urolithiasis.

An N-Ethyl-N-Nitrosourea (ENU)-Induced Tyr265Stop Mutation of the DNA Polymerase Accessory Subunit Gamma 2 (Polg2) Is Associated With Renal Calcification in Mice

Renal calcification (RCALC) resulting in nephrolithiasis and nephrocalcinosis, which affects ∼10% of adults by 70 years of age, involves environmental and genetic etiologies. Thus, nephrolithiasis and nephrocalcinosis occurs as an inherited disorder in ∼65% of patients, and may be associated with endocrine and metabolic disorders including: primary hyperparathyroidism, hypercalciuria, renal tubular acidosis, cystinuria, and hyperoxaluria. Investigations of families with nephrolithiasis and nephrocalcinosis have identified some causative genes, but further progress is limited as large families are unavailable for genetic studies. We therefore embarked on establishing mouse models for hereditary nephrolithiasis and nephrocalcinosis by performing abdominal X-rays to identify renal opacities in N-ethyl-N-nitrosourea (ENU)-mutagenized mice. This identified a mouse with RCALC inherited as an autosomal dominant trait, designated RCALC type 2 (RCALC2). Genomewide mapping located the Rcalc2 locus to a ∼16-Mbp region on chromosome 11D-E2 and whole-exome sequence analysis identified a heterozygous mutation in the DNA polymerase gamma-2, accessory subunit (Polg2) resulting in a nonsense mutation, Tyr265Stop (Y265X), which co-segregated with RCALC2. Kidneys of mutant mice (Polg2^+/Y265X ) had lower POLG2 mRNA and protein expression, compared to wild-type littermates (Polg2^+/+ ). The Polg2^+/Y265X and Polg2^+/+ mice had similar plasma concentrations of sodium, potassium, calcium, phosphate, chloride, urea, creatinine, glucose, and alkaline phosphatase activity; and similar urinary fractional excretion of calcium, phosphate, oxalate, and protein. Polg2 encodes the minor subunit of the mitochondrial DNA (mtDNA) polymerase and the mtDNA content in Polg2^+/Y265X kidneys was reduced compared to Polg2^+/+ mice, and cDNA expression profiling revealed differential expression of 26 genes involved in several biological processes including mitochondrial DNA function, apoptosis, and ubiquitination, the complement pathway, and inflammatory pathways. In addition, plasma of Polg2^+/Y265X mice, compared to Polg2^+/+ littermates had higher levels of reactive oxygen species. Thus, our studies have identified a mutant mouse model for inherited renal calcification associated with a Polg2 nonsense mutation. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.

The Boolean logic tree of molecular self-assembly system based on cobalt oxyhydroxide nanoflakes for three-state logic computation, sensing and imaging of pyrophosphate in living cells and in vivo

Sensing of pyrophosphate (PPi) is helpful to better understand many life processes and diagnose various early-stage diseases. However, many traditional reported methods based on artificial receptors for sensing of PPi exhibit some disadvantages including difficulties in designing appropriate binding sites and complicated multi-step assembly/functionalization. Thus, it is significantly important and a big challenge to know how to use a simple molecular self-assembly or an interaction system to solve the above-mentioned limits to achieve the quantitative analysis of specific substances in the system. Based on the natural connection and similarity (such as stimulus responsiveness) between sensing and logic computing, in this study, the Boolean logic tree of molecular self-assembly system based on the cobalt oxyhydroxide (CoOOH) nanoplatform is constructed and applied to organize and connect "plug and play" molecular events (fluorescent dye, acridine orange and anion, PPi). By using molecules as inputs and the corresponding fluorescence signal as the output, the CoOOH-based molecular self-assembly system can be programmed for three-input fluorescent Boolean logic computation, fluorescent three-state logic computation, detection of PPi (linear range from 50 to 6400 nM with a detection limit of 20 nM) and even for imaging in living cancer cells and in vivo (in systems such as Zebrafish and Carassius auratus). Our approach adds a new dimension for expanding molecular logic computing and sensing systems, which will not only provide more opportunities for developing novel logic computing paradigms, but also be helpful in promoting the development and applications of intelligent molecular computing and sensing systems.

Genetics of common complex kidney stone disease: insights from genome-wide association studies

Kidney stone disease is a common disorder in Western countries that is associated with significant suffering, morbidity, and cost for the healthcare system. Numerous studies have demonstrated familial aggregation of nephrolithiasis and a twin study estimated the heritability to be 56%. Over the past decade, genome-wide association studies have uncovered several sequence variants that confer increased risk of common complex kidney stone disease. The first reported variants were observed at the CLDN14 locus in the Icelandic population. This finding has since been replicated in other populations. The CLDN14 gene is expressed in tight junctions of the thick ascending limb of the loop of Henle, where the protein is believed to play a role in regulation of calcium transport. More recent studies have uncovered variants at the ALPL, SLC34A1, CASR, and TRPV5 loci, the first two genes playing a role in renal handling of phosphate, while the latter two are involved in calcium homeostasis. Although genetic data have provided insights into the molecular basis of kidney stone disease, much remains to be learned about the contribution of genetic factors to stone formation. Nevertheless, the progress made in recent years indicates that exciting times lie ahead in genetic research on kidney stone disease.

Precision medicine in renal stone-formers

Here we define precision medicine approaches and discuss how these may be applied to renal stone-formers to optimise diagnosis and a management. Using the gene discovery of monogenic stone disorders as examples, we discuss the benefits of personalising therapies for renal stone-formers to provide improved prevention and treatment of these disorders.

Precipitation SELEX: identification of DNA aptamers for calcium phosphate materials synthesis

DNA aptamers that enhance calcium phosphate mineral formation were identified using a novel precipitation SELEX method. The evolved DNA library was substantially enriched in G nucleotides and in predicted G-quadruplex structures, suggesting their importance in the mechanism of mineralization. This work could readily be extended to provide additional novel DNA aptamers for materials synthesis.

Antiurolithiatic effect of the taraxasterol on ethylene glycol induced kidney calculi in male rats

Taraxasterol is one of the important constituents of Taraxacum officinale L. (Compositae) with antioxidant potential. The present study was designed to evaluate and compare the antiurolithiatic effects of taraxasterol and potassium citrate in the ethylene glycol induced urolithiatic rat. Urolithiasis was induced by ammonium chloride and ethylene glycol in adult male rats. Taraxasterol (2, 4 and 8 mg/kg) and potassium citrate (2.5 g/kg) were treated for 33 days by gavage. Then, the animals were anesthetized and weighted and blood, urine, liver and kidney sampling were done. The kidney sections were prepared by hematoxylin & eosin staining. The liver and kidney coefficients, urine pH, calcium, magnesium, oxalate and citrate levels, serum albumin, calcium and magnesium levels, serum alanine aminotransferase, aspartate aminotransferase and lactate dehydrogenase activities, superoxide dismutase and glutathione peroxidase activities in serum, kidney and liver, number of calcium oxalate crystal deposits, score of crystal deposits, score of histopathological damages and score of inflammation in kidney sections were evaluated. The results showed that taraxasterol decreased liver and kidney coefficients (p < 0.001), serum calcium (p < 0.01) level, serum alanine aminotransferase (p < 0.001), aspartate aminotransferase (p < 0.001), lactate dehydrogenase (p < 0.05) activities, urine magnesium (p < 0.05) and oxalate (p < 0.001) levels, number of crystal deposits (p < 0.001), score of crystal deposits (p < 0.01), score of histopathological damages (p < 0.001) and score of inflammation (p < 0.01) in kidney sections, while increased urine pH (p < 0.01), calcium (p < 0.001) and citrate (p < 0.05), serum magnesium (p < 0.001) and albumin (p < 0.01) levels, superoxide dismutase and glutathione peroxidase in serum (p < 0.01), kidney (p < 0.05 and p < 0.001, respectively) and liver (p < 0.01 and p < 0.001, respectively) tissue homogenates in treated urolithiatic rats in comparison to the control urolithiatic rats. The effect of potassium citrate is the same as taraxasterol in treated urolithiatic rats. In conclusion, the effect of taraxasterol could be by improving liver function, changing serum and urine parameters, maintaining the antioxidant environment, reducing crystal deposition, excretion of small deposits from kidney and reducing the chance of them being retained in the urinary tract.

Pyrophosphate Recognition and Sensing in Water Using Bis[zinc(II)dipicolylamino]-Functionalized Peptides

Phosphate oxoanions and phosphorylated biomolecules (such as nucleotides, lipids, and proteins) play key roles in a wide range of biological processes. The ability to selectively detect these ions in the presence of each other has numerous applications in biochemistry and biomedicine. However, receptors and sensors that can discriminate between polyphosphate species with high selectivity and in biologically relevant conditions are rare. In this Account, we show how peptides (both cyclic and linear) can be used to position two zinc(II)dipicolylamine [Zn(II)DPA] binding sites in an appropriate arrangement to provide selective binding of pyrophosphate (PPi) in the presence of other polyphosphate species, including ATP, and in complex media such as cell growth buffer. The use of peptide scaffolds to position the Zn(II)DPA anion binding sites allowed the synthesis of small receptor libraries in which the arrangement of the two binding sites could be subtly altered to evaluate the factors affecting both binding selectivity and affinity for PPi. We altered a number of structural elements including peptide length, cyclic peptide ring size, amino acid composition, the positioning of the binding sites with respect to one another, and the relative stereochemistry of the peptides. Backbone modified cyclic peptides based on the Lissoclinum class of natural products were initially employed to provide an added degree of preorganization to the receptors, although it was subsequently found that short, flexible bis[Zn(II)DPA]-functionalized linear peptides are also effective scaffolds for selective pyrophosphate recognition. The peptidic receptors were successfully employed for the detection of PPi in aqueous media by indicator displacement assays using both colorimetric and fluorescent indicators, with the best compounds able to bind to PPi selectively in both cell growth media and artificial urine and also allow the accurate determination of PPi concentrations in physiologically relevant ranges (micromolar concentrations) in these complex media. Improved pyrophosphate selectivity was observed upon increasing the complexity of the media from HEPES buffer to cell growth media (Krebs saline). Pyrophosphate sensors in which a fluorescent indicator was covalently attached to either a linear or cyclic peptide scaffold through a flexible linker were then constructed. When the Zn(II)DPA binding sites and the indicator were suitably placed with respect to one another on the peptide scaffold, these 'intramolecular indicator displacement assays' showed improved selectivity for PPi over other polyphosphate anions, such as ATP, when compared to the intermolecular indicator displacement assays. This observation provides the basis for the design and application of future PPi sensors in biochemistry and biomedicine.

Intraperitoneal pyrophosphate treatment reduces renal calcifications in Npt2a null mice

Mutations in the proximal tubular sodium-dependent phosphate co-transporters NPT2a and NPT2c have been reported in patients with renal stone disease and nephrocalcinosis, however the relative contribution of genotype, dietary calcium and phosphate, and modifiers of mineralization such as pyrophosphate (PPi) to the formation of renal mineral deposits is unclear. In the present study, we used Npt2a^-/- mice to model the renal calcifications observed in these disorders. We observed elevated urinary excretion of PPi in Npt2a^-/- mice when compared to WT mice. Presence of two hypomorphic Extracellular nucleotide pyrophosphatase phosphodiesterase 1 (Enpp1^asj/asj) alleles decreased urine PPi and worsened renal calcifications in Npt2a^-/- mice. These studies suggest that PPi is a thus far unrecognized factor protecting Npt2a^-/- mice from the development of renal mineral deposits. Consistent with this conclusion, we next showed that renal calcifications in these mice can be reduced by intraperitoneal administration of sodium pyrophosphate. If confirmed in humans, urine PPi could therefore be of interest for developing new strategies to prevent the nephrocalcinosis and nephrolithiasis seen in phosphaturic disorders.

Association Study of Reported Significant Loci at 5q35.3, 7p14.3, 13q14.1 and 16p12.3 with Urolithiasis in Chinese Han Ethnicity

In this study, we aimed to validate the association of 8 reported significant loci at 5q35.3, 7p14.3, 13q14.1 and 16p12.3 with urolithiasis in Chinese Han population. We performed case-control association analysis using 624 patients with nephrolithiasis and 1008 control subjects. We selected single-nucleotide polymorphism (SNPs) including rs12654812 and rs11746443 from 5q32.3; rs12669187 and rs1000597 from 7q14.3; rs7981733, rs4142110 and rs17646069 from 13q14.1 and rs4293393 from 16p12.3 which were previously reported to be associated with nephrolithiasis. We found none of these eight reported SNPs were significant associated with urolithiasis risk in Chinese Han population, which suggested that differences could exist in the mechanisms of calcium urolithiasis between Chinese and Japanese Ethnics. The A allele of rs12669187 was significantly correlated with increased level of serum magnesium. The C allele of rs1000597 was associated with higher levels of serum creatinine, uric acid, calcium and lower urine pH level. The T allele of rs4142110 was correlated with higher levels of serum magnesium, phosphorus, and lower AKP level. The G alleles of rs4293393 was associated with higher serum CO₂ level. The risk alleles of these SNPs were proved to be associated with the electrolytes metabolism that may result in the formation of urolithiasis.

Presence of pyrophosphate in bone from an atypical femoral fracture site: A case report

Long-term antiresorptives use has been linked to atypical subtrochanteric and diaphyseal femoral fractures (AFF), the pathogenesis of which is still unknown. In the present case report we present the results of analysis of bone chips from a 74-year old female patient that had been on alendronate, ibandronate and denosumab treatment, and who sustained an atypical femoral fracture, by histology, quantitative backscattered electron imaging, and Raman spectroscopic analysis.

The results indicate ongoing osteoclastic resorption, but also several abnormalities: 1) an altered arrangement of osteons; 2) impaired mineralization; 3) the presence of pyrophosphate, which might contribute to the impaired mineralization evident in the present case. Taken together, these changes may contribute to the focally reduced bone strength of this patient.

Progress in Understanding the Genetics of Calcium-Containing Nephrolithiasis

Renal stone disease is a frequent condition, causing a huge burden on health care systems globally. Calcium-based calculi account for around 75% of renal stone disease and the incidence of these calculi is increasing, suggesting environmental and dietary factors are acting upon a preexisting genetic background. The familial nature and significant heritability of stone disease is known, and recent genetic studies have successfully identified genes that may be involved in renal stone formation. The detection of monogenic causes of renal stone disease has been made more feasible by the use of high-throughput sequencing technologies and has also facilitated the discovery of novel monogenic causes of stone disease. However, the majority of calcium stone formers remain of undetermined genotype. Genome-wide association studies and candidate gene studies implicate a series of genes involved in renal tubular handling of lithogenic substrates, such as calcium, oxalate, and phosphate, and of inhibitors of crystallization, such as citrate and magnesium. Additionally, expression profiling of renal tissues from stone formers provides a novel way to explore disease pathways. New animal models to explore these recently-identified mechanisms and therapeutic interventions are being tested, which hopefully will provide translational insights to stop the growing incidence of nephrolithiasis.

Diuretic and antiurolithiatic activities of an ethanolic extract of Acorus calamus L. rhizome in experimental animal models

Acorus calamus is a plant commonly used as a traditional herbal medicine and possesses the wide range of pharmacological applications. The present study investigated the diuretic and antiurolithiatic activities of an ethanolic extract of Acorus calamus L. (Family: Araceae) rhizome (EEAC). For diuretic activity, three doses of EEAC (250, 500 and 750 mg/kg) were studied, and measurement of the urinary volume and electrolytes (Na⁺ and K⁺) concentration were taken as evaluation parameters. On the other hand, ethylene glycol induced urolithiasis (0.75% v/v in drinking water for 28 days) was used to study the antiurolithiatic effect of EEAC at the oral dose of 750 mg/kg in male Wistar albino rats. CYSTONE (750 mg/kg, p.o.) was used as a standard reference drug in the present study. After completion of the 28-days respective treatments, the level of various urolithiatic promoters in the biological samples (urine, serum and kidney homogenate) and renal function were used as criteria for assessing the antiurolithiatic effect of EEAC. Results indicate that, the EEAC (750 mg/kg, p.o.) produced significant increase in urine volume (p < 0.001) and urinary excretion of Na⁺ and K⁺ electrolytes (p < 0.05) in a pattern comparable to that of furosemide. In ethylene glycol induced urolithiatic model, EEAC significantly (p < 0.05) decreased excretion and deposition of various urolithiatic promoters as compared to urolithiatic control in a pattern comparable to that of CYSTONE. The EEAC supplementation also prevents the impairment of renal functions. The antiurolithiatic mechanism is mediated possibly through diuretic and nephroprotective actions of the active compounds of rhizomes.

Common and rare variants associated with kidney stones and biochemical traits

Kidney stone disease is a complex disorder with a strong genetic component. We conducted a genome-wide association study of 28.3 million sequence variants detected through whole-genome sequencing of 2,636 Icelanders that were imputed into 5,419 kidney stone cases, including 2,172 cases with a history of recurrent kidney stones, and 279,870 controls. We identify sequence variants associating with kidney stones at ALPL (rs1256328[T], odds ratio (OR)=1.21, P=5.8 × 10⁻¹⁰) and a suggestive association at CASR (rs7627468[A], OR=1.16, P=2.0 × 10⁻⁸). Focusing our analysis on coding sequence variants in 63 genes with preferential kidney expression we identify two rare missense variants SLC34A1 p.Tyr489Cys (OR=2.38, P=2.8 × 10⁻⁵) and TRPV5 p.Leu530Arg (OR=3.62, P=4.1 × 10⁻⁵) associating with recurrent kidney stones. We also observe associations of the identified kidney stone variants with biochemical traits in a large population set, indicating potential biological mechanism.

Kidney stone formation is influenced by genetic factors and recurrent stone formation places a significant burden on health care systems. Here Oddsson et al. perform a large-scale genome-wide association study and uncover new genetic variants associated with kidney stone susceptibility and associated biochemical traits.

Calcium nephrolithiasis and bone demineralization: pathophysiology, diagnosis, and medical management

PURPOSE OF REVIEW

To establish the relationship between calcium nephrolithiasis, bone densitometry scoring, and bone mineral density (BMD) loss according to bone turnover markers (BTMs) and urinary metabolites.

RECENT FINDINGS

Patients with recurrent calcium nephrolithiasis and idiopathic fasting hypercalciuria (urinary calcium/creatinine ratio >0.11) are more likely to have BMD loss that may lead to osteopenia or osteoporosis. In these patients, BTMs may be used as a surrogate for both bone health and stone recurrence. Suspect higher lithogenic states when calcium stone formers have serum beta-crosslaps (resorptive marker) greater than 0.311 ng/ml, serum osteocalcin (formative marker) greater than 13.2 ng/ml, and beta-crosslaps/osteocalcin ratio greater than 0.024.

SUMMARY

Patients with recurrent calcium nephrolithiasis and fasting hypercalciuria have a higher incidence of osteopenia and osteoporosis, measured by the dual-energy X-ray absorptiometry. These patients present not only with hypercalciuria and increased BTMs (mainly resorptive), but also up to 30% have hypocitraturia and increased urinary calcium/citrate ratio (>0.25). On the basis of these results, a diagnostic algorithm was created, classifying hypercalciurics according to their fasting calcium/creatinine and calcium/citrate ratio. Medical therapy for these patients is aimed at improving the dietary habits (normocalcemic, low salt, low animal protein diet), prescribing combinations of potassium citrate, thiazides, and bisphosphonates, and correcting bone and urinary abnormalities that may lower future skeletal and kidney stone risk.

Multisystemic functions of alkaline phosphatases

Human and mouse alkaline phosphatases (AP) are encoded by a multigene family expressed ubiquitously in multiple tissues. Gene knockout (KO) findings have helped define some of the precise exocytic functions of individual isozymes in bone, teeth, the central nervous system, and in the gut. For instance, deficiency in tissue-nonspecific alkaline phosphatase (TNAP) in mice (Alpl (-/-) mice) and humans leads to hypophosphatasia (HPP), an inborn error of metabolism characterized by epileptic seizures in the most severe cases, caused by abnormal metabolism of pyridoxal-5'-phosphate (the predominant form of vitamin B6) and by hypomineralization of the skeleton and teeth featuring rickets and early loss of teeth in children or osteomalacia and dental problems in adults caused by accumulation of inorganic pyrophosphate (PPi). Enzyme replacement therapy with mineral-targeting TNAP prevented all the manifestations of HPP in mice, and clinical trials with this protein therapeutic are showing promising results in rescuing life-threatening HPP in infants. Conversely, TNAP induction in the vasculature during generalized arterial calcification of infancy (GACI), type II diabetes, obesity, and aging can cause medial vascular calcification. TNAP inhibitors, discussed extensively in this book, are in development to prevent pathological arterial calcification. The brush border enzyme intestinal alkaline phosphatase (IAP) plays an important role in fatty acid (FA) absorption, in protecting gut barrier function, and in determining the composition of the gut microbiota via its ability to dephosphorylate lipopolysaccharide (LPS). Knockout mice (Akp3 (-/-)) deficient in duodenal-specific IAP (dIAP) become obese, and develop hyperlipidemia and hepatic steatosis when fed a high-fat diet (HFD). These changes are accompanied by upregulation in the jejunal-ileal expression of the Akp6 IAP isozyme (global IAP, or gIAP) and concomitant upregulation of FAT/CD36, a phosphorylated fatty acid translocase thought to play a role in facilitating the transport of long-chain fatty acids into cells. gIAP, but not dIAP, is able to modulate the phosphorylation status of FAT/CD36. dIAP, even though it is expressed in the duodenum, is shed into the gut lumen and is active in LPS dephosphorylation throughout the gut lumen and in the feces. Akp3 (-/-) mice display gut dysbiosis and are more prone to dextran sodium sulfate-induced colitis than wild-type mice. Of relevance, oral administration of recombinant calf IAP prevents the dysbiosis and protects the gut from chronic colitis. Analogous to the role of IAP in the gut, TNAP expression in the liver may have a proactive role from bacterial endotoxin insult. Finally, more recent studies suggest that neuronal death in Alzheimer's disease may also be associated with TNAP function on certain brain-specific phosphoproteins. This review recounts the established roles of TNAP and IAP and briefly discusses new areas of investigation related to multisystemic functions of these isozymes.

Association of severe calcium lithogenic activity and bone remodeling markers

OBJECTIVE

To establish cutoff points for markers of bone remodeling that allow for screening of patients at risk for serious lithogenic activity.

MATERIALS AND METHODS

We conducted a cross-sectional study with 182 patients (aged between 25 and 60 years) divided into 3 groups: group 1, 56 patients without lithiasis; group 2, 67 patients with light calcium lithiasis; and group 3, 59 patients with severe calcium lithiasis. The criteria for inclusion in and exclusion from the study were established, and light and severe lithogenic activity were defined. Metabolic variables in blood and urine, along with bone densitometry, were studied for the groups. Statistical analysis of the results and preparation of receiver operating characteristic curves to establish optimal cutoff points were performed.

RESULTS

The patients in group 3 showed the greatest bone mineral density loss and the highest values for markers of bone remodeling, together with increased 24-hour calciuria. Using the receiver operating characteristic curves developed and based on statistical significance (P = .0001), the following cutoff points for severe lithogenic activity, with a sensitivity between 75% and 85%, were established: β-crosslaps >0.331 ng/mL; osteocalcin >13.2 ng/mL; β-crosslaps/osteocalcin >0.024; 24-hour calciuria >306.6 mg; and fasting urine calcium/creatinine >0.105.

CONCLUSION

Patients with calcium lithiasis and elevated values for osteocalcin, β-crosslaps, β-crosslaps/osteocalcin, 24-hour calciuria, and fasting urine calcium/creatinine may present a high risk of severe lithogenic activity.

Bone formation controlled by biologically relevant inorganic ions: role and controlled delivery from phosphate-based glasses

The role of metal ions in the body and particularly in the formation, regulation and maintenance of bone is only just starting to be unravelled. The role of some ions, such as zinc, is more clearly understood due to its central importance in proteins. However, a whole spectrum of other ions is known to affect bone formation but the exact mechanism is unclear as the effects can be complex, multifactorial and also subtle. Furthermore, a significant number of studies utilise single doses in cell culture medium, whereas the continual, sustained release of an ion may initiate and mediate a completely different response. We have reviewed the role of the most significant ions that are known to play a role in bone formation, namely calcium, zinc, strontium, magnesium, boron, titanium and also phosphate anions as well as copper and its role in angiogenesis, an important process interlinked with osteogenesis. This review will also examine how delivery systems may offer an alternative way of providing sustained release of these ions which may effect and potentiate a more appropriate and rapid tissue response.

A multiphysics model of in vitro transcription coupling enzymatic reaction and precipitation formation

Multiphysics modeling, which integrates the models studied in different disciplines so far, is an indispensable approach toward a comprehensive understanding of biological systems composed of diverse phenomena. However, the variety of the models is narrower than the actual diverse phenomena because of the difficulty in coupling independent models separately studied in different disciplines for the actual coupled phenomena. In this study, we develop a mathematical model coupling an enzymatic reaction and mineralization formation. As a test case, we selected an in vitro transcription system where a transcription reaction occurs along with the precipitation formation of magnesium pyrophosphate (Mg(2)PPi). To begin, we experimentally elucidated how the transcription reaction and the precipitation formation are coupled. In the analysis, we applied a Michaelis-Menten-type equation to the transcription reaction and a semiempirical equation describing the correlation between the induction period and the supersaturation ratio to the precipitation formation, respectively. Based on the experimental results, we then integrated these two models. These models were connected by supersaturation that increases as the transcription reaction proceeds and becomes the driving force of the precipitation. We believe that our modeling approach could significantly contribute to the development of newer multiphysics models in systems biology such as bone metabolic networks.

Key role of alkaline phosphatase in the development of human-derived nanoparticles in vitro

Alkaline phosphatase (ALP) is an enzyme critical for physiological and pathological biomineralization. Experiments were designed to determine whether ALP participates in the formation of calcifying nanometer sized particles (NPs) in vitro. Filtered homogenates of human calcified carotid artery, aorta and kidney stones were inoculated into cell culture medium containing 10% fetal bovine serum in the absence or presence of inhibitors of ALP or pyrophosphate. A calcific NP biofilm developed within 1 week after inoculation and their development was reduced by pyrophosphate and inhibitors of ALP. ALP protein and enzymatic activity were detected in washed NPs, whether calcified or decalcified. Therefore, ALP activity is required for the formation of calcifying NPs in vitro, as has previously been implicated during pathological calcification in vivo.

The Medical Management of Urolithiasis

Urolithiasis is increasing in prevalence and causes substantial morbidity and economic burden. Aside from “acute” stone episodes, urolithiasis should be regarded as a systemic disorder and investigated fully. Practical guidance is given for the medical investigation, diagnosis and treatment of urolithiasis. A single episode of urolithiasis should prompt a review of potential risk factors for recurrent disease and appropriate baseline investigations should be performed. Further biochemical tests may then be directed appropriately and allow individualised advice and treatment to be given to the patient with urolithiasis.

Localization, etiology and impact of calcium phosphate deposits in renal allografts

Hypercalcemia, hypophosphatemia and renal phosphate wasting are common after kidney transplantation. Animal data suggest that these alterations in mineral metabolism may contribute to calcium phosphate (CaPhos) deposition in the kidney and renal dysfunction. We tested the hypothesis that CaPhos deposition is highly prevalent in the early posttransplant period and is related to a disturbed mineral metabolism. For this purpose, biomarkers of mineral metabolism and renal calcium and phosphorus handling were prospectively assessed in 201 renal transplant recipients. CaPhos deposits were observed in 4.6, 30.4 and 24.7% of protocol biopsies obtained at the time of engraftment, and 3 and 12 months thereafter, respectively. In multivariate logistic regression analysis, high calcium and low serum phosphorus levels were independently associated with renal CaPhos deposition at month 3. The extent of CaPhos deposition correlated significantly with the severity of mineral metabolism disturbances. Renal function after a mean follow-up of 33 months was similar in patients with and without CaPhos deposition at month 3. In conclusion, our data demonstrate that CaPhos deposition is highly prevalent in the early posttransplant period and suggest that a disordered mineral metabolism is implicated in its pathogenesis. The clinical relevance of CaPhos deposition remains to be established.

Anthropometric and bone-related biochemical factors are associated with different haplotypes of ANKH locus

BACKGROUND

The human homologue of the mouse progressive ankylosis (ANKH) gene is one of the key genetic factors involved in bone mineralization. Previous studies have shown that plasma levels of osteoprotegerin (OPG) and parathyroid hormone (PTH) are associated with the distal region of the ANKH gene, whereas skeletal size measurements are associated with the promoter region.

AIM

The present study examines the possible phenotype-haplotype specificity of the associations in these two gene regions.

SUBJECTS AND METHODS

The total sample consists of 1249 healthy individuals (mean age = 47.7, SD = 16.8) from 404 nuclear families. Fifteen interrelated anthropometric measurements were transformed into two principal components, reflecting body size and mass. Those, plus circulating levels of PTH and OPG, were subjected to association analysis, using transmission disequilibrium tests (TDTs) with ANKH gene. From 805 to 1150 individuals per SNP were genotyped.

RESULTS

In the proximal region (rs3006069-rs835154-rs835141), associations were found between the A-A-C haplotype and the first principal component reflecting body size (p < or = 0.048), whereas another haplotype, G-G-C, was associated with the first principal component, reflecting the body mass (p < or = 0.008). In the distal region of ANKH (rs39968-rs696294-rs875525), the A-A-C haplotype was found to be associated with OPG plasma levels (p < or = 0.001), whereas the G-A-C haplotype was associated with PTH circulating concentrations (p < or = 0.025).

CONCLUSION

Taken together, the results show discrimination between the corresponding regions and haplotypes, suggesting trait-specific gene variants that influenced bone-related phenotypic variation in the studied population.

Serum alkaline phosphatase predicts mortality among maintenance hemodialysis patients

Several observational studies have demonstrated that serum levels of minerals and parathyroid hormone (PTH) have U- or J-shaped associations with mortality in maintenance hemodialysis patients, but the relationship between serum alkaline phosphatase (AlkPhos) and risk for all-cause or cardiovascular death is unknown. In this study, a 3-yr cohort of 73,960 hemodialysis patients in DaVita outpatient dialysis were studied, and the hazard ratios for all-cause and cardiovascular death were higher across 20-U/L increments of AlkPhos, including within the various strata of intact PTH and serum aspartate aminotransferase. In the fully adjusted model, which accounted for demographics, comorbidity, surrogates of malnutrition and inflammation, minerals, PTH, and aspartate aminotransferase, AlkPhos > or =120 U/L was associated with a hazard ratio for death of 1.25 (95% confidence interval 1.21 to 1.29; P < 0.001). This association remained among diverse subgroups of hemodialysis patients, including those positive for hepatitis C antibody. A rise in AlkPhos by 10 U/L during the first 6 mo was incrementally associated with increased risk for death during the subsequent 2.5 yr. In summary, high levels of serum AlkPhos, especially >120 U/L, are associated with mortality among hemodialysis patients. Prospective controlled trials will be necessary to test whether serum AlkPhos measurements could be used to improve the management of renal osteodystrophy.

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

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