Calcium Oxalate Kidney Stone Formation Research Articles

Carboxymethylated Desmodium styracifolium polysaccharide reduces the risk of calcium oxalate kidney stone formation by inhibiting crystal adhesion and promoting crystal endocytosis.

The inhibition of cell surface crystal adhesion and an appropriate increase in crystal endocytosis contribute to the inhibition of kidney stone formation. In this study, we investigated the effects of different degrees of carboxymethylation on these processes. An injury model was established by treating human renal proximal tubular epithelial (HK-2) cells with 98.3 ± 8.1 nm calcium oxalate dihydrate (nanoCOD) crystals. The HK-2 cells were protected with carboxy (-COOH) Desmodium styracifolium polysaccharides at 1.17% (DSP0), 7.45% (CDSP1), 12.2% (CDSP2), and 17.7% (CDSP3). Changes in biochemical indexes and effects on nanoCOD adhesion and endocytosis were detected. The protection of HK-2 cells from nanoCOD-induced oxidative damage by carboxymethylated Desmodium styracifolium polysaccharides (CDSPs) is closely related to the protection of subcellular organelles, such as mitochondria. CDSPs can reduce crystal adhesion on the cell surface and maintain appropriate crystal endocytosis, thereby reducing the risk of kidney stone formation. CDSP2 with moderate -COOH content showed the strongest protective activity among the CDSPs.

Size-Dependent Cytotoxicity, Adhesion, and Endocytosis of Micro-/Nano-hydroxyapatite Crystals in HK-2 Cells.

Nano-hydroxyapatite (nano-HAP) is often used as a crystal nest to induce calcium oxalate (CaOx) kidney stone formation, but the mechanism of interaction between HAP crystals of different properties and renal tubular epithelial cells remains unclear. In this study, the adhesion and endocytosis of HAP crystals with sizes of 40 nm, 70 nm, 1 μm, and 2 μm (HAP-40 nm, HAP-70 nm, HAP-1 μm, and HAP-2 μm, respectively) to human renal proximal tubular epithelial cells (HK-2) were comparatively studied. The results showed that HAP crystals of all sizes promoted the expression of osteopontin and hyaluronic acid on the cell surface, destroyed the integrity of the lysosomes, and induced the apoptosis and necrosis of cells. Nano-HAP crystals had a higher specific surface area, a smaller contact angle, a higher surface energy, and a lower Zeta potential than those of micro-HAP. Therefore, the abilities of HK-2 cells to adhere to and endocytose nano-HAP crystals were greater than their abilities to do the same for micro-HAP crystals. The order of the endocytosed crystals was as follows: HAP-40 nm > HAP-70 nm > HAP-1 μm > HAP-2 μm. The endocytosed HAP crystals entered the lysosomes. The more crystal endocytosis and adhesion there is, the more toxic it is to HK-2 cells. The results of this study showed that nanosized HAP crystals greatly promoted the formation of kidney stones than micrometer-sized HAP crystals.

FKBP5 deficiency attenuates calcium oxalate kidney stone formation by suppressing cell-crystal adhesion, apoptosis and macrophage M1 polarization via inhibition of NF-κB signaling.

Surgical crushing of stones alone has not addressed the increasing prevalence of kidney stones. A promising strategy is to tackle the kidney damage and crystal aggregation inherent in kidney stones with the appropriate therapeutic target. FKBP prolyl isomerase 5 (FKBP5) is a potential predictor of kidney injury, but its status in calcium oxalate (CaOx) kidney stones is not clear. This study attempted to elucidate the role and mechanism of FKBP5 in CaOx kidney stones. Lentivirus and adeno-associated virus were used to control FKBP5 expression in a CaOx kidney stone model. Transcriptomic sequencing and immunological assays were used to analyze the mechanism of FKBP5 deficiency in CaOx kidney stones. The results showed that FKBP5 deficiency reduced renal tubular epithelial cells (RTEC) apoptosis and promoted cell proliferation by downregulating BOK expression. It also attenuated cell-crystal adhesion by downregulating the expression of CDH4. In addition, it inhibited M1 polarization and chemotaxis of macrophages by suppressing CXCL10 expression in RTEC. Moreover, the above therapeutic effects were exerted by inhibiting the activation of NF-κB signaling. Finally, in vivo experiments showed that FKBP5 deficiency attenuated stone aggregation and kidney injury in mice. In conclusion, this study reveals that FKBP5 deficiency attenuates cell-crystal adhesion, reduces apoptosis, promotes cell proliferation, and inhibits macrophage M1 polarization and chemotaxis by inhibiting NF-κB signaling. This provides a potential therapeutic target for CaOx kidney stones.

Diet in Different Calcium Oxalate Kidney Stones.

Diet can be a helpful tool to enhance the quality of urine and lower the likelihood and recurrence of kidney stones. This study set out to identify the foods and nutrients that are associated with each type of calcium oxalate kidney stone formation. A single-center, cross-sectional study was conducted. Between 2018 and 2021, a sample of 90 cases (13 cases with papillary COM, 27 with non-papillary COM, and 50 with COD kidney stones), as well as a control group of 50 people, were chosen. A food intake frequency questionnaire was completed by the study's participants, and the results were compared between groups. Additionally, a comparison of the 24 h urine analysis between stone groups was made. Processed food and meat derivatives were linked to COM papillary calculi (OR = 1.051, p = 0.032 and OR = 1.013, p = 0.012, respectively). Consuming enough calcium may offer protection against non-papillary COM stones (OR = 0.997; p = 0.002). Similarly, dairy product consumption was linked to COD calculi (OR = 1.005, p = 0.001). In conclusion, a diet high in animal items may increase the risk of developing papillary COM stones. Consuming calcium may be preventive against non-papillary COM calculi, and dairy product consumption may be a risk factor for COD stones.

Ferroptosis in calcium oxalate kidney stone formation and the possible regulatory mechanism of ANKRD1.

The objective of this study was to explore the role of ferroptosis in the formation of calcium oxalate (CaOx) kidney stones and the regulatory mechanism of the ankyrin repeat domain 1 (ANKRD1) gene. The study found that the Nrf2/HO-1 and p53/SLC7A11 signaling pathways were activated in the kidney stone model group, and the expression of the ferroptosis marker proteins SLC7A11 and GPX4 was significantly reduced, while the expression of ACSL4 was significantly increased. The expression of the iron transport-related proteins CP and TF increased significantly, and Fe2+ accumulated in the cell. The expression of HMGB1 increased significantly. In addition, the level of intracellular oxidative stress was increased. The gene with the most significant difference caused by CaOx crystals in HK-2 cells was ANKRD1. Silencing or overexpression of ANKRD1 by lentiviral infection technology regulated the expression of the p53/SLC7A11 signaling pathway, which regulated the ferroptosis induced by CaOx crystals. In conclusion, CaOx crystals can mediate ferroptosis through the Nrf2/HO-1 and p53/SLC7A11 pathways, thereby weakening the resistance of HK-2 cells to oxidative stress and other unfavorable factors, enhancing cell damage, and increasing crystal adhesion and CaOx crystal deposition in the kidney. ANKRD1 participates in the formation and development of CaOx kidney stones by activating ferroptosis mediated by the p53/SLC7A11 pathway.

Investigation the role of bacteria in calcium oxalate kidney stone formation.

Kidney stone disease is a serious health concern, with a high incidence rate of approximately 10% among North Americans and a high economic burden on the medical system exceedingly over $5 billion per year. Approximately 80% of kidney stones are composed of calcium oxalate (CaOx). While there are options for medical and surgical management of kidney stone disease, unfortunately, so far, no treatment has been developed to treat the cause of CaOx stone formation effectively. Thus, the rate of recurrence is high.(Lotan Y 2007) Recently, emerging clinical studies suggested that bacteria may play a critical role in stone formation, although the mechanism is not adequately studied (An et al. 2021). This study aims to investigate the role of bacteria in CaOx kidney stone formation and propagation. We hypothesize that inside the urinary tract, bacteria mediate the biocrystallization of CaOx, leading to the formation and development of kidney stones. Here, we will in-vitro study CaOx bacterial-induced crystallization using our developed microfluidic kidney model and under a continuous flow of artificial urine to mimic the unique physiological microenvironment of the urinary tract. In this regard, we will manipulate, monitor, and analyze the number, size, and morphology of the formed CaOx crystals in the presence of bacteria and under various urinary conditions (e.g., flow rate, pH, and chemistry) using high-resolution live microscopic, imaging, and spectroscopic approaches. Furthermore, we will elucidate the dominant molecular mechanism underlying the formation and propagation of CaOx stones at the single-bacterium level with a focus on the effect of bacterial secretion and sensing appendages.Investigation of the interaction at single and multi-cell levels allows us to accurately capture early aspects of the biocrystallization capabilities of bacteria.

Porous Se@SiO2 nanospheres inhibit calcium oxalate kidney stone formation by oxidation resistance

The prevalence of kidney stones continues to increase worldwide, however, there are still short of effective drugs against urinary stones. In our study, we developed and utilized porous Se@SiO2 nanospheres as the novel antioxidant agent to detect its potential effects on crystallization inhibition. Porous Se@SiO2 nanospheres enable to deliver Se sustainably with lower cytotoxicity and preferred biocompatibility. In vivo, we found that porous Se@SiO2 nanospheres markedly decreased CaOX crystal deposition in renal parenchyma and alleviated kidney oxidative damage. In vitro, we found that the antioxidant effects of porous Se@SiO2 nanospheres were mediated by upregulation of HO-1 and activation of Keap1/Nrf2 pathway. These results suggests that porous Se@SiO2 nanospheres may be a new promising therapeutic option for stone formers.

Hyaluronic acid promotes calcium oxalate crystal growth, crystal-cell adhesion, and crystal invasion through extracellular matrix

Hyaluronic acid (HA), a macromolecule in glycosaminoglycans family, is normally excreted into the urine with a small amount, but with much greater level in the urine from stone patients (formers). However, its precise roles in kidney stone pathogenesis remained unclear. This study examined its roles in calcium oxalate (CaOx) kidney stone formation processes, including neocrystallization, crystal growth, adhesion, internalization, aggregation and invasion. The results showed that HA (1, 10, 100, 1000, or 10,000 ng/ml) did not affect CaOx neocrystallization, aggregation, and internalization into MDCK distal renal tubular cells. However, HA significantly promoted CaOx crystal growth (at 10–10,000 ng/ml), adhesion onto renal tubular cells (at 1000–10,000 ng/ml), and invasion through extracellular matrix (ECM) (at 1–10,000 ng/ml). Analysis of the plasminogen sequence revealed six sites with the HA-binding motif “B(X7)B" that explained the HA ability to trigger the plasminogen-plasmin system required for crystal invasion. In summary, our systematic analysis highlights the promoting effects of HA on CaOx crystal growth, crystal-cell adhesion and invasion through the ECM. These effects of HA may explain its high level in the stone patients' urine, thereby promoting the stone formation.

MicroRNA-204 attenuates oxidative stress damage of renal tubular epithelial cells in calcium oxalate kidney-stone formation via MUC4-mediated ERK signaling pathway.

Oxalate-induced oxidative stress causes damage to cells, accompanied with renal deposition of calcium oxalate crystals. Recent studies have highlighted the extensive functions of microRNAs (miRNAs) in various processes, including cellular responses to oxidative stress. Hence, this study was intended to analyze the role of miR-204 in the calcium oxalate kidney-stone formation and the underlying mechanism. In silico analysis was performed to determine the miRNA/mRNA interaction involved in calculus, while dual-luciferase reporter assay was conducted for validation. A calcium oxalate kidney-stone model was established by H2O2 induction in RTEC HK-2 cells, in which the expression of miR-204 was examined. Gain- and loss-of-function approaches were employed to alter the expression of miR-204/MUC4 so as to assess the detailed role of miR-204 in oxidative stress injury in renal tubular epithelial cells (RTECs) and calcium oxalate kidney-stone formation. MUC4, an up-regulated gene in H2O2-induced HK-2 cells, was a target of MUC4. miR-204 functionally targeted MUC4 and blocked the ERK pathway activation. Furthermore, up-regulated miR-204 contributed to promotion of RTEC proliferation and suppression of ROS levels, RTEC apoptosis as well as formation of calcium oxalate crystal. Taken together, miR-204 impairs MUC4-dependent activation of the ERK signaling pathway and consequently ameliorates oxidative stress damage to RTECs and prevents calcium oxalate kidney-stone formation.

Protein primary structure correlates with calcium oxalate stone matrix preference.

Despite the apparent importance of matrix proteins in calcium oxalate kidney stone formation, the complexity of the protein mixture continues to elude explanation. Based on a series of experiments, we have proposed a model where protein aggregates formed from a mixture containing both strongly charged polyanions and strongly charged polycations could initiate calcium oxalate crystal formation and crystal aggregation to create a stone. These protein aggregates also preferentially adsorb many weakly charged proteins from the urine to create a complex protein mixture that mimics the protein distributions observed in patient samples. To verify essential details of this model and identify an explanation for phase selectivity observed in weakly charged proteins, we have examined primary structures of major proteins preferring either the matrix phase or the urine phase for their contents of aspartate, glutamate, lysine and arginine; amino acids that would represent fixed charges at normal urine pH of 6-7. We verified enrichment in stone matrix of proteins with a large number of charged residues exhibiting extreme isoelectric points, both low (pI<5) and high (pI>9). We found that the many proteins with intermediate isoelectric points exhibiting preference for stone matrix contained a smaller number of charge residues, though still more total charges than the intermediate isoelectric point proteins preferring the urine phase. While other sources of charge have yet to be considered, protein preference for stone matrix appears to correlate with high total charge content.

Dual modulatory effects of diosmin on calcium oxalate kidney stone formation processes: Crystallization, growth, aggregation, crystal-cell adhesion, internalization into renal tubular cells, and invasion through extracellular matrix

Diosmin is a natural flavone glycoside (bioflavonoid) found in fruits and plants with several pharmacological activities. It has been widely used as a dietary supplement or therapeutic agent in various diseases/disorders. Although recommended, evidence of its protective mechanisms against kidney stone disease (nephrolithiasis/urolithiasis), especially calcium oxalate (CaOx) monohydrate (COM) that is the most common type, remained unclear. In this study, we thus systematically evaluated the effects of diosmin (at 2.5–160 nM) on various stages of kidney stone formation processes, including COM crystallization, crystal growth, aggregation, crystal-cell adhesion, internalization into renal tubular cells and invasion through extracellular matrix (ECM). The results showed that diosmin had dose-dependent modulatory effects on all the mentioned COM kidney stone processes. Diosmin significantly increased COM crystal number and mass during crystallization, but reduced crystal size and growth. While diosmin promoted crystal aggregation, it inhibited crystal-cell adhesion and internalization into renal tubular cells. Finally, diosmin promoted crystal invasion through the ECM. Our data provide evidence demonstrating both inhibiting and promoting effects of diosmin on COM kidney stone formation processes. Based on these dual modulatory activities of diosmin, its anti-urolithiasis role is doubtful and cautions should be made for its use in kidney stone disease.

Urine osmolality predicts calcium-oxalate crystallization risk in patients with recurrent urolithiasis.

Our aim was to investigate the validity of osmolality from 24-h urine collection in examining the risk for calcium-oxalate (CaOx) kidney stone formation in patients with recurrent urolithiasis. Three hundred and twelve subjects (males/females: 184/128) from France with a history of recurrent kidney stones from confirmed or putative CaOx origin were retrospectively included in the study (46 ± 14 years, BMI: 25.3 ± 5.0kg·m-2). Tiselius' crystallization risk index (CRI) was calculated based on urinary calcium, oxalate, citrate, magnesium, and volume from 24-h samples. The diagnostic ability of 24-h urine osmolality to classify patients as high risk for kidney stone crystallization was examined through the receivers operating characteristics analysis. High risk for CaOx crystallization was defined as CRI > 1.61 and > 1.18, for males and females, respectively. The accuracy of urine osmolality to diagnose risk of CaOx stone formation (AUC, area under the curve) for females was 84.6%, with cut-off point of 501mmol·kg-1 (sensitivity: 83.3%, specificity: 76.0%). Males had AUC of 85.8% with threshold of 577mmo·kg-1 (sensitivity: 85.5%, specificity: 77.6%). A negative association was found between 24-h urine volume and osmolality (r = -0.63, P < 0.001). Also, a positive association was found between 24-h urine osmolality and CRI (r = 0.65, P < 0.001), as well as urea excretion with CRI (r = 0.37, P < 0.001). In conclusion, urine osmolality > 501 and > 577mmol·kg-1, infemale and in male, respectively, was associated with a risk for CaOx kidney stone formation in patients with a history of recurrent urolithiasis. Thus, when CaOx origin is confirmed or suspected, 24-h urine osmolality provides a simple way to define individualized target of urine dilution to prevent urine crystallization and stone formation.

Exploring mechanisms of protein influence on calcium oxalate kidney stone formation.

Calcium oxalate monohydrate (COM) crystals are the primary constituent of most kidney stones, but urine proteins in stone matrix are believed to be critical elements for stone formation from these crystals. Recent data have shown that hundreds of proteins appear in the stone matrix with no explanation for inclusion of so many proteins. We have proposed a stone formation model with protein stimulated COM aggregation based on polyanion-polycation aggregation, which is supported by finding that matrix is highly enriched in strongly anionic and strongly cationic proteins. Many other proteins may be drawn to such aggregates due to their limited solubility in water or charge effects. Finding similar protein enrichment in both polyarginine (pR) induced aggregates of urine proteins and COM stone matrix would support this hypothesis. Purified proteins (PP) were obtained from random urine samples of six healthy adults by ultradiafiltration. Protein aggregation was induced by adding pR to PP solutions at two concentrations; 0.25 and 0.5µg pR/µg of PP. Samples of each fraction and the original PP mixture were lyophilized and analyzed by tandem mass spectrometry. Aggregates induced by pR addition to PP samples collected a protein mixture that mimicked the protein distribution observed in COM matrix, supporting our hypothesis. The apparently discordant behavior of certain abundant anionic proteins preferentially joining the pR aggregate, when they had demonstrated reduced abundance in COM stone matrix, suggests that this model was overdriven to aggregate. The reversal of aggregate preference of albumin at low pR addition supports this interpretation.

Mutations in HOGA1 do Not Confer a Dominant Phenotype Manifesting as Kidney Stone Disease.

The etiology of calcium-oxalate kidney stone formation remains elusive. Biallelic mutations in HOGA1 are responsible for primary hyperoxaluria type 3 and result in oxalate overproduction and kidney stone disease. Our previous study showed that carriers of HOGA1 mutations have elevated urinary levels of oxalate precursors. In this study we explored the possibility that mutations in HOGA1 confer a dominant phenotype in the form of kidney stone disease or hyperoxaluria. An observational analytic case control study was designed to determine the prevalence of pathogenic HOGA1 mutations among adults with calcium-oxalate kidney stone disease. Given the high prevalence of HOGA1 mutations among Ashkenazi Jews, this group was evaluated separately. Carrier frequency of any of the 52 reported pathogenic mutations was compared to data derived from gnomAD for the corresponding ethnic group. Sanger sequencing of HOGA1 gene was performed on DNA samples from the following groups: 60 Ashkenazi Jews and 86 nonAshkenazi calcium-oxalate stone formers, 150 subjects with low and 150 with high urinary oxalate levels. The carrier prevalence of pathogenic mutations among the Ashkenazi Jews was 1.7% compared to 2.8% in the corresponding control group (p=0.9 OR=0.6 95% CI 0.01-3.51). We did not detect any mutation among the nonAshkenazi study group. No correlation was detected between hyperoxaluria and HOGA1 variants. This study shows that mutations in HOGA1 do not confer a dominant phenotype in the form of calcium-oxalate kidney stone disease or hyperoxaluria.

Interactions Between Phytochemicals and Minerals in Terminalia ferdinandiana and Implications for Mineral Bioavailability.

Oxalic and phytic acid are phytochemicals considered to be anti-nutritional factors as they are predominantly found as oxalates and phytates bound to minerals like calcium and potassium. Studies have associated excessive oxalate consumption with increased urinary excretion of oxalate (hyperoxaluria) and calcium oxalate kidney stone formation, and excessive phytate consumption with decreased bioaccessibility and bioavailability of certain minerals and reduced utilization of dietary protein. However, other studies suggest that dietary consumption of phytate may be beneficial and inhibit formation of calcium oxalate kidney stones. In light of these conflicting reports, dietary intake of oxalate and phytate enriched plants should be considered in relation to potential health outcomes following consumption. Terminalia ferdinandiana is one such plant and is investigated here with respect to oxalate, phytate, and mineral contents. Assessment of oxalate and phytate contents in T. ferdinandiana fruit, leaf, and seedcoat tissues through hydrolysis into acid forms revealed oxalic acid contents ranging from 327 to 1,420 mg/100 g on a dry weight (DW) basis whilst phytic acid contents ranged from 8.44 to 121.72 mg/100 g DW. Calcium content in the different tissues ranged from 131 to 1,343 mg/100 g. There was no correlation between oxalic acid and calcium, however a significant, positive correlation was observed between phytic acid and calcium (r = 0.9917; p < 0.001), indicating that tissues rich in phytic acid also contain higher levels of calcium. The high content of phytic acid in comparison to oxalic acid in T. ferdinandiana fruit found in this study and the dietary significance of this in terms of calcium bioavailability, needs to be investigated further.

The effects of the inactivation of Hydroxyproline dehydrogenase on urinary oxalate and glycolate excretion in mouse models of primary hyperoxaluria

The major clinical manifestation of the Primary Hyperoxalurias (PH) is increased production of oxalate, as a consequence of genetic mutations that lead to aberrant glyoxylate and hydroxyproline metabolism. Hyperoxaluria can lead to the formation of calcium-oxalate kidney stones, nephrocalcinosis and renal failure. Current therapeutic approaches rely on organ transplants and more recently modifying the pathway of oxalate synthesis using siRNA therapy. We have recently reported that the metabolism of trans-4-hydroxy-L-proline (Hyp), an amino acid derived predominantly from collagen metabolism, is a significant source of oxalate production in individuals with PH2 and PH3. Thus, the first enzyme in the Hyp degradation pathway, hydroxyproline dehydrogenase (HYPDH), represents a promising therapeutic target for reducing endogenous oxalate production in these individuals. This is supported by the observation that individuals with inherited mutations in HYPDH (PRODH2 gene) have no pathological consequences. The creation of mouse models that do not express HYPDH will facilitate research evaluating HYPDH as a target. We describe the phenotype of the Prodh2 knock out mouse model and show that the lack of HYPDH in PH mouse models results in lower levels of urinary oxalate excretion, consistent with our previous metabolic tracer and siRNA-based knockdown studies. The double knockout mouse, Grhpr KO (PH2 model) and Prodh2 KO, prevented calcium-oxalate crystal deposition in the kidney, when placed on a 1% Hyp diet. These observations support the use of the Grhpr KO mice to screen HYPDH inhibitors in vivo. Altogether these data support HYPDH as an attractive therapeutic target for PH2 and PH3 patients.

Flagellum Is Responsible for Promoting Effects of Viable Escherichia coli on Calcium Oxalate Crystallization, Crystal Growth, and Crystal Aggregation.

Urease-producing bacteria (especially Proteus mirabilis) can cause infection kidney stone. However, recent studies have shown that intact viable non-urease-producing bacteria such as Escherichia coli might also promote calcium oxalate (CaOx) kidney stone formation but with unclear mechanism. We thus hypothesized that some relevant bacterial components might be responsible for such promoting effects of the intact viable E. coli. Flagella, capsule, lipopolysaccharide (LPS), and outer membrane vesicles (OMVs) were isolated/purified and their stone modulatory activities were evaluated using CaOx crystallization, crystal growth, and crystal aggregation assays. Among these, flagella had the most potent promoting effects on CaOx crystallization, crystal growth, and crystal aggregation. Validation was performed by deflagellation demonstrating that the deflagellated intact viable E. coli had markedly reduced CaOx crystal modulatory activities in all aspects (comparable to those of the negative controls). Similarly, neutralization of the isolated/purified flagella using a specific anti-flagellin antibody, not an isotype control, could abolish the promoting effects of flagella. These findings provide direct evidence indicating that flagellum is responsible for the promoting effects of the viable E. coli on CaOx crystallization, crystal growth and aggregation.

Theoretical and laboratory investigations of the effects of hydroxyproline ingestion on the metabolic and physicochemical risk factors for calcium oxalate kidney stone formation in a small group of healthy subjects.

Dietary hydroxyproline may be involved in the endogenous synthesis of oxalate. Glycolate, produced during the metabolism of hydroxyproline, may exert physicochemical effects on urinary calcium by virtue of its dihydroxycarboxylic acid structure. The aim of this study was to investigate these possible stone-risk scenarios. We modelled the effect of different glycolic acid concentrations on ionized calcium (iCa2+) and relative supersaturation (RSS) of calcium oxalate (CaOx) using the program JESS. Thereafter, three healthy white males and two healthy black males ingested 30g gelatin for 3days. 24-h urines were collected at baseline and after completion of the protocol. Urines were analysed for physicochemical risk factors and for iCa2+ and glycolic acid. Speciation concentrations and RSS values were calculated. Theoretical modelling showed that binding between calcium and glycolate does not occur and that iCa2+ and RSS CaOx are unaffected. However, after ingestion of hydroxyproline, iCa2+ decreased significantly. Urinary pH and glycolate increased significantly. Oxalate excretion and RSS CaOx did not change CONCLUSIONS: We attribute the decrease in iCa2+ to increases in the concentrations of several Ca-phosphate species, the formation of which is due to the increase in pH. We speculate that the absence of an increase in oxalate excretion despite an increase in glycolate excretion may be due to the mixed racial composition of our test group in which some pathways may be preferred to others. Our findings alert stone researchers to the importance of measuring urinary pH in their workup of subjects and to select racially homogenous groups for investigation.

Absence of the sulfate transporter SAT-1 has no impact on oxalate handling by mouse intestine and does not cause hyperoxaluria or hyperoxalemia.

The anion exchanger SAT-1 [sulfate anion transporter 1 (Slc26a1)] is considered an important regulator of oxalate and sulfate homeostasis, but the mechanistic basis of these critical roles remain undetermined. Previously, characterization of the SAT-1-knockout (KO) mouse suggested that the loss of SAT-1-mediated oxalate secretion by the intestine was responsible for the hyperoxaluria, hyperoxalemia, and calcium oxalate urolithiasis reportedly displayed by this model. To test this hypothesis, we compared the transepithelial fluxes of 14C-oxalate, 35 , and 36Cl- across isolated, short-circuited segments of the distal ileum, cecum, and distal colon from wild-type (WT) and SAT-1-KO mice. The absence of SAT-1 did not impact the transport of these anions by any part of the intestine examined. Additionally, SAT-1-KO mice were neither hyperoxaluric nor hyperoxalemic. Instead, 24-h urinary oxalate excretion was almost 50% lower than in WT mice. With no contribution from the intestine, we suggest that this may reflect the loss of SAT-1-mediated oxalate efflux from the liver. SAT-1-KO mice were, however, profoundly hyposulfatemic, even though there were no changes to intestinal sulfate handling, and the renal clearances of sulfate and creatinine indicated diminished rates of sulfate reabsorption by the proximal tubule. Aside from this distinct sulfate phenotype, we were unable to reproduce the hyperoxaluria, hyperoxalemia, and urolithiasis of the original SAT-1-KO model. In conclusion, oxalate and sulfate transport by the intestine were not dependent on SAT-1, and we found no evidence supporting the long-standing hypothesis that intestinal SAT-1 contributes to oxalate and sulfate homeostasis. NEW & NOTEWORTHY SAT-1 is a membrane-bound transport protein expressed in the intestine, liver, and kidney, where it is widely considered essential for the excretion of oxalate, a potentially toxic waste metabolite. Previously, calcium oxalate kidney stone formation by the SAT-1-knockout mouse generated the hypothesis that SAT-1 has a major role in oxalate excretion via the intestine. We definitively tested this proposal and found no evidence for SAT-1 as an intestinal anion transporter contributing to oxalate homeostasis.

Oxalobacter formigenes-associated host features and microbial community structures examined using the American Gut Project

BackgroundIncreasing evidence shows the importance of the commensal microbe Oxalobacter formigenes in regulating host oxalate homeostasis, with effects against calcium oxalate kidney stone formation, and other oxalate-associated pathological conditions. However, limited understanding of O. formigenes in humans poses difficulties for designing targeted experiments to assess its definitive effects and sustainable interventions in clinical settings. We exploited the large-scale dataset from the American Gut Project (AGP) to study O. formigenes colonization in the human gastrointestinal (GI) tract and to explore O. formigenes-associated ecology and the underlying host–microbe relationships.ResultsIn >8000 AGP samples, we detected two dominant, co-colonizing O. formigenes operational taxonomic units (OTUs) in fecal specimens. Multivariate analysis suggested that O. formigenes abundance was associated with particular host demographic and clinical features, including age, sex, race, geographical location, BMI, and antibiotic history. Furthermore, we found that O. formigenes presence was an indicator of altered host gut microbiota structure, including higher community diversity, global network connectivity, and stronger resilience to simulated disturbances.ConclusionsThrough this study, we identified O. formigenes colonizing patterns in the human GI tract, potential underlying host–microbe relationships, and associated microbial community structures. These insights suggest hypotheses to be tested in future experiments. Additionally, we proposed a systematic framework to study any bacterial taxa of interest to computational biologists, using large-scale public data to yield novel biological insights.