Hyperoxaluric calcium nephrolithiasis

CAV1 unveils a novel therapeutic target for nephrolithiasis by modulating CaSR and ER stress

Nephrolithiasis is a complex disease resulted from abnormal crystal deposition in renal tissues. The crystal-cell interaction represents a critical step in kidney stone formation, involving numerous genes and proteins. We previously identified endoplasmic reticulum (ER) stress as a key biological process in the crystal-cell interactions, the precise mechanism of which has remained unclear. In the present study, we found that calcium oxalate monohydrate (COM) crystals induced an overload of intracellular Ca2+ and an upregulation of calcium-sensing receptor (CaSR) expression in the renal tubular epithelial cells HK-2, both of which were reversed by the CaSR inhibitor NPS2390 that also mitigated the COM-induced ER stress. The protein-protein interaction (PPI) network analysis of the genome-wide association studies (GWAS) data and the microarray data from kidney stone patients revealed that caveolin-1 (CAV1), epidermal growth factor receptor (EGFR), and the focal adhesion pathway formed a crucial intersection within the interactional networks. COM exposure induced HK-2 apoptosis, accompanied by a decrease in CAV1 protein levels and damage to EGFR-AKT signaling pathway, which was reversed by CAV1 overexpression. COM did not significantly affect CAV1 mRNA levels. Treatment with the proteasome inhibitor MG-132 prevented the downregulation of CAV1. CAV1 overexpression also inhibited ER stress and the upregulation of CaSR induced by COM. Similar results were observed in in vivo experiments. In conclusion, the present study suggests that CAV1 may be a promising target for nephrolithiasis therapy by modulating CaSR and ER stress.

Low Serum and Urine Fetuin-A Levels and High Composite Dietary Antioxidant Index as Risk Factors for Kidney Stone Formation

Background: Fetuin-A prevents the precipitation of hydroxyapatite in supersaturated solutions of calcium and phosphate; however, its relationship with nephrolithiasis has yet to be clarified. The aim of this study was to investigate the protective and predictive roles of serum and urine fetuin-A levels in nephrolithiasis and their relationships with the composite dietary antioxidant index (CDAI). Methods: This study involved 75 adult patients with kidney stone disease and 71 healthy adults without kidney stone disease in the control group. Participants had specific anthropometric measurements taken, and three-day food records were kept. The CDAI was calculated by summing six standard antioxidants, including vitamins A, C, and E, manganese, selenium, and zinc, representing participants' antioxidant profile. In addition to some analyzed serum and urine parameters of the participants, fetuin-A levels were measured using the enzyme-linked immunosorbent assay (ELISA) method. Results: In patients with kidney stones, both serum and urine fetuin-A levels (676.3 ± 160.14 ng/mL; 166.6 ± 128.13 ng/mL, respectively) were lower than in the control group (1455.6 ± 420.52 ng/mL; 2267.5 ± 1536.78 ng/mL, respectively) (p < 0.00001). In contrast, the CDAI was higher in patients with kidney stones compared to those without kidney stones (p < 0.001). Besides, several dietary parameters had significant positive correlations with serum and/or urinary fetuin-A. Conclusions: The present study suggests that serum and urinary fetuin-A levels may serve as protective factors against kidney stones and could potentially be used as predictive markers for the development of nephrolithiasis. Furthermore, our results suggest that the CDAI above a certain level may increase the risk of stone formation and that some dietary parameters may affect the levels of this biomarker in serum and urine.

Kukoamine A alleviates nephrolithiasis by inhibiting endogenous oxalate synthesis via the IL-6/JAK/STAT3/DAO signaling pathway

BACKGROUND

The recurrent nature and socioeconomic burden of nephrolithiasis demand effective treatments. Delineating the crosstalk between inflammatory processes and the endogenous oxalate metabolism pathway, which underpins nephrolithiasis pathogenesis, is essential for advancing treatment strategies.

PURPOSE

We aim to screen therapeutic Chinese herbal remedies and their bioactive constituents for kidney stone treatment using a fruit fly model, followed by efficacy and mechanism validation in a rodent nephrolithiasis model as well as in vitro human cell culture model.

STUDY DESIGN AND METHODS

We developed a fruit fly model to screen for efficient traditional Chinese medicine herbs and their active compounds for kidney stone treatment. Candidate active compounds from efficient herbs were separated and identified by solid-phase chromatography coupled with LC-MS analysis. Fruit fly genetic tools were employed to manipulate the expression of related genes to explore the therapeutic mechanisms of the Lycii Cortex and kukoamine A (KuA). To confirm the therapeutic effects and mechanisms of KuA for mammalian nephrolithiasis, mouse model of glyoxylate-induced kidney stone and human renal tubular cells were used. The therapeutic role of kukoamine A in nephrolithiasis was evaluated by assessing tubular injury, crystal deposition, and adhesion. The level of expression and phosphorylation in cells and mice was assessed using RT-qPCR and western blot.

RESULTS

Our findings indicate that Lycii Cortex potently inhibits calcium oxalate stone formation via activation of the JNK/Upd3/JAK/STAT signaling cascade, resulting in diminished endogenous oxalate synthesis by downregulating D-amino acid oxidase (DAO) gene expression, predominantly in fruit fly Malpighian tube stellate cells. KuA was identified as the principal bioactive constituent mediating these effects. Both mouse models and human cell assays confirmed KuA's efficacy in preventing calcium oxalate nephrolithiasis in mammals, through hepatic JAK/STAT3 pathway activation and upregulation of IL-6, culminating in reduced urinary crystal deposition.

CONCLUSION

Our research underscores the potential of kukoamine A as a lead compound in treating nephrolithiasis and reveals the interplay between the IL-6/JAK/STAT3 inflammatory pathway and endogenous oxalate metabolism in nephrolithiasis pathogenesis. Additionally, it highlights the utility of the fruit fly model as a powerful tool for deciphering the therapeutic mechanisms of traditional Chinese herbs.

Multiomics Assessment of the Gut Microbiome in Rare Hyperoxaluric Conditions

Introduction

Hyperoxaluria is a risk factor for kidney stone formation and chronic kidney disease progression. The microbiome is an important protective factor against oxalate accumulation through the activity of its oxalate-degrading enzymes (ODEs). In this cross-sectional study, we leverage multiomics to characterize the microbial community of participants with primary and enteric hyperoxaluria, as well as idiopathic calcium oxalate kidney stone (CKS) formers, focusing on the relationship between oxalate degrading functions of the microbiome.

Methods

Patients diagnosed with type 1 primary hyperoxaluria (PH), enteric hyperoxaluria (EH), and CKS were screened for inclusion in the study. Participants completed a food frequency questionnaire recording their dietary oxalate content while fecal oxalate levels were ascertained. DNA and RNA were extracted from stool samples and sequenced. Metagenomic (MTG) and metatranscriptomic (MTT) data were processed through our bioinformatics pipelines, and microbiome diversity, differential abundance, and networks were subject to statistical analysis in relationship with oxalate levels.

Results

A total of 38 subjects were recruited, including 13 healthy participants, 12 patients with recurrent CKS, 8 with PH, and 5 with EH. Urinary and fecal oxalate were significantly higher in the PH and the EH population compared to healthy controls. At the community level, alpha-diversity and beta-diversity indices were similar across all populations. The respective contributions of single bacterial species to the total oxalate degradative potential were similar in healthy and PH subjects. MTT-based network analysis identified the most interactive bacterial network in patients with PH. Patients with EH had a decreased abundance of multiple major oxalate degraders.

Conclusion

The composition and inferred activity of oxalate-degrading microbiota were differentially associated with host clinical conditions. Identifying these changes improves our understanding of the relationships between dietary constituents, microbiota, and oxalate homeostasis, and suggests new therapeutic approaches protecting against hyperoxaluria.

Intestinal Oxalate Absorption, Enteric Hyperoxaluria, and Risk of Urinary Stone Formation in Patients with Crohn's Disease

Nephrolithiasis is a common urologic manifestation of Crohn's disease. The purpose of this study was to investigate the clinical characteristics, intestinal oxalate absorption, and risk factors for urinary stone formation in these patients. In total, 27 patients with Crohn's disease and 27 healthy subjects were included in the present study. Anthropometric, clinical, and 24 h urinary parameters were determined, and the [13C2]oxalate absorption test was performed. Among all patients, 18 had undergone ileal resection, 9 of whom had a history of urinary stones. Compared to healthy controls, the urinary excretion values of calcium, magnesium, potassium, sulfate, creatinine, and citrate were significantly lower in patients with Crohn's disease. Intestinal oxalate absorption, the fractional and 24 h urinary oxalate excretion, and the risk of calcium oxalate stone formation were significantly higher in patients with urolithiasis than in patients without urolithiasis or in healthy controls. Regardless of the group, between 83% and 96% of the [13C2]oxalate was detected in the urine within the first 12 h after ingestion. The length of ileum resection correlated significantly with the intestinal absorption and urinary excretion of oxalate. These findings suggest that enteric hyperoxaluria can be attributed to the hyperabsorption of oxalate following extensive ileal resection. Oral supplementation of calcium and magnesium, as well as alkali citrate therapy, should be considered as treatment options for urolithiasis.

Qualitative assessment of the patient experience of primary hyperoxaluria type 1: an observational study

BACKGROUND

Without effective intervention, primary hyperoxaluria type 1 (PH1) causes oxalate-induced kidney damage, leading to end-stage kidney disease and serious complications throughout the body. Although PH1 carries a heavy burden that impacts quality of life, literature on the experiences of those living with PH1 and caring for patients with PH1 is limited. This study aimed to describe the diagnostic journey in PH1 and characterize patients' and caregivers' self-reported experiences throughout the disease course.

METHODS

This was an observational study involving in-depth, semi-structured telephone interviews. Dominant trends were assessed using constant comparative analysis to identify themes in interviewees' descriptions of their experiences. Individuals aged ≥ 12 years and caregivers of children aged 6-17 years with genetically confirmed PH1 were eligible. Informed consent/assent and ability to read and speak English were required.

RESULTS

Interviewees (16 patients, 12 caregivers) reported a prolonged diagnostic journey due to low disease awareness, among other factors. Upon diagnosis, PH1 was frequently symptomatic, typically involving kidney stone-related symptoms but also potentially symptoms arising beyond the kidneys. PH1 most commonly led to worry and social impairment in adolescents, impaired physical function in adults, and a range of impacts on caregivers. In late-stage disease, dialysis was the most burdensome aspect of living with PH1 (due to time requirements, limitations from living with a catheter, etc.), and this burden was exacerbated by the COVID-19 pandemic. Benefits desired from PH1 management included reductions in laboratory measures of oxalate burden, kidney stone and urination frequency, and oxalate-related skin ulcers.

CONCLUSIONS

PH1 greatly impacts patients' and caregivers' lives, primarily due to burdensome disease manifestations and associated emotional, physical, and practical impacts, as well as disease management challenges - particularly those related to dialysis in late-stage disease.

Oxalate (dys)Metabolism: Person-to-Person Variability, Kidney and Cardiometabolic Toxicity

Oxalate is a metabolic end-product whose systemic concentrations are highly variable among individuals. Genetic (primary hyperoxaluria) and non-genetic (e.g., diet, microbiota, renal and metabolic disease) reasons underlie elevated plasma concentrations and tissue accumulation of oxalate, which is toxic to the body. A classic example is the triad of primary hyperoxaluria, nephrolithiasis, and kidney injury. Lessons learned from this example suggest further investigation of other putative factors associated with oxalate dysmetabolism, namely the identification of precursors (glyoxylate, aromatic amino acids, glyoxal and vitamin C), the regulation of the endogenous pathways that produce oxalate, or the microbiota's contribution to oxalate systemic availability. The association between secondary nephrolithiasis and cardiovascular and metabolic diseases (hypertension, type 2 diabetes, and obesity) inspired the authors to perform this comprehensive review about oxalate dysmetabolism and its relation to cardiometabolic toxicity. This perspective may offer something substantial that helps advance understanding of effective management and draws attention to the novel class of treatments available in clinical practice.

Delta weight loss unlike genetic variation associates with hyperoxaluria after malabsorptive bariatric surgery

The risk of enteric hyperoxaluria is significantly increased after malabsorptive bariatric surgery (MBS). However, its underlying determinants are only poorly characterized. In this case-control study, we aimed at identifying clinical and genetic factors to dissect their individual contributions to the development of post-surgical hyperoxaluria. We determined the prevalence of hyperoxaluria and nephrolithiasis after MBS by 24-h urine samples and clinical questionnaires at our obesity center. Both hyperoxaluric and non-hyperoxaluric patients were screened for sequence variations in known and candidate genes implicated in hyperoxaluria (AGXT, GRHPR, HOGA1, SLC26A1, SLC26A6, SLC26A7) by targeted next generation sequencing (tNGS). The cohort comprised 67 patients, 49 females (73%) and 18 males (27%). While hyperoxaluria was found in 29 patients (43%), only one patient reported postprocedural nephrolithiasis within 41 months of follow-up. Upon tNGS, we did not find a difference regarding the burden of (rare) variants between hyperoxaluric and non-hyperoxaluric patients. However, patients with hyperoxaluria showed significantly greater weight loss accompanied by markers of intestinal malabsorption compared to non-hyperoxaluric controls. While enteric hyperoxaluria is very common after MBS, genetic variation of known hyperoxaluria genes contributes little to its pathogenesis. In contrast, the degree of postsurgical weight loss and levels of malabsorption parameters may allow for predicting the risk of enteric hyperoxaluria and consecutive kidney stone formation.

Anti-urolithiatic effect of Cucumis melo L. var inodorous in male rats with kidney stones

Melon seed extracts have high antioxidant activities and are effective against a variety of diseases, including kidney stones. In kidney stone model rats, the anti-urolithiatic effects of the hydro-ethanolic extract of melon seed and potassium citrate were studied and compared. After urolithiasis induction by ethylene glycol, the extract and potassium citrate were treated orally for 38 days concurrent with ethylene glycol. Then, urine and kidney sampling were done, and the urinary parameter levels were measured. The melon and potassium citrate treatments reduced the kidney index, the levels of urinary calcium and oxalate, calcium oxalate deposit numbers, the score of crystal deposits, histo-pathological damages, and the score of inflammation in the kidney sections, while elevating the urinary pH, magnesium, and citrate levels, and also the expression of the UMOD, spp1, and reg1 genes in the kidney of treated animals. The effect of potassium citrate is the same as the effect of melon in treated animals. So, their effects could be by normalizing urinary parameters, reducing crystal deposits, excreting small deposits from the kidney, reducing the chance of them being retained in the urinary tract, and elevating the expression of the UMOD, spp1, and reg1 genes, which are involved in kidney stone formation.

Oxalate secretion is stimulated by a cAMP-dependent pathway in the mouse cecum

Elevated levels of the intracellular second messenger cAMP can stimulate intestinal oxalate secretion however the membrane transporters responsible are unclear. Oxalate transport by the chloride/bicarbonate (Cl-/HCO3-) exchanger Slc26a6 or PAT-1 (Putative Anion Transporter 1), is regulated via cAMP when expressed in Xenopus oocytes and cultured cells but whether this translates to the native epithelia is unknown. This study investigated the regulation of oxalate transport by the mouse intestine focusing on transport at the apical membrane hypothesizing PAT-1 is the target of a cAMP-dependent signaling pathway. Adopting the Ussing chamber technique we measured unidirectional 14C-oxalate and 36Cl- flux ([Formula: see text] and [Formula: see text]) across distal ileum, cecum and distal colon, employing forskolin (FSK) and 3-isobutyl-1-methylxanthine (IBMX) to trigger cAMP production. FSK/IBMX initiated a robust secretory response by all segments but the stimulation of net oxalate secretion was confined to the cecum only involving activation of [Formula: see text] and distinct from net Cl- secretion produced by inhibiting [Formula: see text]. Using the PAT-1 knockout (KO) mouse we determined cAMP-stimulated [Formula: see text] was not directly dependent on PAT-1, but it was sensitive to mucosal DIDS (4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid), although unlikely to be another Cl-/HCO3- exchanger given the lack of trans-stimulation or cis-inhibition by luminal Cl- or HCO3-. The cAMP-activated oxalate efflux was reliant on CFTR (Cystic Fibrosis Transmembrane conductance Regulator) activity, but only in the presence of PAT-1, leading to speculation on the involvement of a multi-transporter regulatory complex. Further investigations at the cellular and molecular level are necessary to define the mechanism and transporter(s) responsible.

Correlates of nephrolithiasis in US black women: data from the black women's health study

Nephrolithiasis is a common urologic condition and a significant source of patient morbidity and healthcare expenditure. There are few epidemiologic studies of kidney stones focusing exclusively on Black women. We retrospectively assessed the prevalence and correlates of self-reported kidney stones within the Black Women's Health Study (BWHS). Descriptive statistics and multivariable logistic regression models were used to explore factors associated with nephrolithiasis. As of the 2005 follow-up questionnaire, a cumulative total of 1063 women among 43,178 reported ever being diagnosed with kidney stones for a prevalence of 2.64%. Women with a history of nephrolithiasis were older, slightly heavier, and were more likely to have a comorbid condition (e.g., type-2 diabetes, gallstones), drink alcohol, and consume a Western-style diet. A history of gallstone disease was associated with an odds ratio (OR) of 3.59 (95% confidence interval (CI) 3.09-4.17). The OR for consuming ≥ 7 alcoholic beverages/week, compared to none was 0.61 (0.39-0.94), while the OR for high adherence to the Western diet, compared to low adherence was 1.53 (1.23-1.90). Our findings are consistent with previous studies of primarily white populations relating lifestyle-associated risk factors with nephrolithiasis. Despite their lower prevalence of kidney stones, it is important to focus on vulnerable populations such as Black women given their disproportionate burden of metabolic conditions (e.g., obesity, diabetes) related to kidney stone disease.

Identification of Biomarkers for Methamphetamine Exposure Time Prediction in Mice Using Metabolomics and Machine Learning Approaches

Methamphetamine (METH) abuse has become a global public health and safety problem. More information is needed to identify the time of drug abuse. In this study, methamphetamine was administered to male C57BL/6J mice with increasing doses from 5 to 30 mg kg^-1 (once a day, i.p.) for 20 days. Serum and urine samples were collected for metabolomics studies using gas chromatography-mass spectrometry (GC-MS). Six machine learning models were used to infer the time of drug abuse and the best model was selected to predict administration time preliminarily. The metabolic changes caused by methamphetamine were explored. As results, the metabolic patterns of methamphetamine exposure mice were quite different from the control group and changed over time. Specifically, serum metabolomics showed enhanced amino acid metabolism and increased fatty acid consumption, while urine metabolomics showed slowed metabolism of the tricarboxylic acid (TCA) cycle, increased organic acid excretion, and abnormal purine metabolism. Phenylalanine in serum and glutamine in urine increased, while palmitic acid, 5-HT, and monopalmitin in serum and gamma-aminobutyric acid in urine decreased significantly. Among the six machine learning models, the random forest model was the best to predict the exposure time (serum: MAE = 1.482, RMSE = 1.69, R squared = 0.981; urine: MAE = 2.369, RMSE = 1.926, R squared = 0.946). The potential biomarker set containing four metabolites in the serum (palmitic acid, 5-hydroxytryptamine, monopalmitin, and phenylalanine) facilitated the identification of methamphetamine exposure. The random forest model helped predict the methamphetamine exposure time based on these potential biomarkers.

Lumasiran in the Management of Patients with Primary Hyperoxaluria Type 1: From Bench to Bedside

Primary hyperoxaluria (PH) is a rare genetic disease caused by excessive hepatic production and elevated urinary excretion of oxalate that leads to recurrent nephrolithiasis, nephrocalcinosis and, eventually, kidney failure. As glomerular filtration rate declines, oxalate accumulates leading to systemic oxalosis, a debilitating condition with high morbidity and mortality. Although PH is usually diagnosed during infancy, it can present at any age with different phenotypes, ranging from mild symptoms to extremely debilitating manifestations. PH is an autosomal recessive disorder and, to date, three types have been identified: PH1, PH2 and PH3. PH1 is the most common and most aggressive type, accounting for almost 80% of primary hyperoxaluria diagnoses. Until 2020, general treatment for PH1 consisted mainly in high fluid intake, urine alkalization, surgical management of recurrent nephrolithiasis and eventually, if and when kidney failure occurred, intensive dialysis regimens and transplantation strategies (simultaneous or sequential liver-kidney transplant or isolated liver/kidney transplant in carefully selected patients). Specific treatment did and still consists in administration of pyridoxine hydrochloride, although it is only effective in a subset of PH1 patients. Lumasiran, a novel biological drug based on mRNA interference that has been recently approved in the US and European Union, showed promising results and is set to be a turning point in the management of PH1. This literature review aims to summarize the available evidence on PH1 treatment with lumasiran, in order to provide both pediatric and adult nephrologists and clinicians with the knowledge for the identification and management of PH1 patients suitable for treatment.

Calcium oxalate crystallization in synthetic urinary medium: the impact of resorcinares and calixarenes

The impact of macrocycles on calcium oxalate formation. Calcium oxalate is a major component of kidney stones, an ailment that affects many people globally.

Oxalate Flux Across the Intestine: Contributions from Membrane Transporters

Epithelial oxalate transport is fundamental to the role occupied by the gastrointestinal (GI) tract in oxalate homeostasis. The absorption of dietary oxalate, together with its secretion into the intestine, and degradation by the gut microbiota, can all influence the excretion of this nonfunctional terminal metabolite in the urine. Knowledge of the transport mechanisms is relevant to understanding the pathophysiology of hyperoxaluria, a risk factor in kidney stone formation, for which the intestine also offers a potential means of treatment. The following discussion presents an expansive review of intestinal oxalate transport. We begin with an overview of the fate of oxalate, focusing on the sources, rates, and locations of absorption and secretion along the GI tract. We then consider the mechanisms and pathways of transport across the epithelial barrier, discussing the transcellular, and paracellular components. There is an emphasis on the membrane-bound anion transporters, in particular, those belonging to the large multifunctional Slc26 gene family, many of which are expressed throughout the GI tract, and we summarize what is currently known about their participation in oxalate transport. In the final section, we examine the physiological stimuli proposed to be involved in regulating some of these pathways, encompassing intestinal adaptations in response to chronic kidney disease, metabolic acid-base disorders, obesity, and following gastric bypass surgery. There is also an update on research into the probiotic, Oxalobacter formigenes, and the basis of its unique interaction with the gut epithelium. © 2021 American Physiological Society. Compr Physiol 11:1-41, 2021.

Perspectives in primary hyperoxaluria - historical, current and future clinical interventions

Primary hyperoxalurias are a devastating family of diseases leading to multisystem oxalate deposition, nephrolithiasis, nephrocalcinosis and end-stage renal disease. Traditional treatment paradigms are limited to conservative management, dialysis and combined transplantation of the kidney and liver, of which the liver is the primary source of oxalate production. However, transplantation is associated with many potential complications, including operative risks, graft rejection, post-transplant organ failure, as well as lifelong immunosuppressive medications and their adverse effects. New therapeutics being developed for primary hyperoxalurias take advantage of biochemical knowledge about oxalate synthesis and metabolism, and seek to specifically target these pathways with the goal of decreasing the accumulation and deposition of oxalate in the body.

Primary hyperoxalurias are a devastating family of diseases that eventually lead to end-stage renal disease. In this Review, Shee and Stoller discuss current treatment paradigms for primary hyperoxalurias, new therapeutics and their mechanisms of action, and future directions for novel research in the field.

Primary hyperoxalurias (PHs) are a devastating family of rare, autosomal-recessive genetic disorders that lead to multisystem oxalate deposition, nephrolithiasis, nephrocalcinosis and end-stage renal disease.

Traditional treatment paradigms are limited to conservative management, dialysis and inevitably transplantation of the kidney and liver, which is associated with high morbidity and the need for lifelong immunosuppression.

New therapeutics being developed for PHs take advantage of biochemical knowledge about oxalate synthesis and metabolism to specifically target these pathways, with the goal of decreasing the accumulation and deposition of plasma oxalate in the body.

New therapeutics can be divided into classes, and include substrate reduction therapy, intestinal oxalate degradation, chaperone therapy, enzyme restoration therapy and targeting of the inflammasome.

Lumasiran, a mRNA therapeutic targeting glycolate oxidase, was the first primary hyperoxaluria-specific therapeutic approved by the European Medicines Agency and the FDA in 2020.

Future work includes further clinical trials for promising therapeutics in the pipeline, identification of biomarkers of response to PH-directed therapy, optimization of drug development and delivery of new therapeutics.

Chemical modification of enzymes to improve biocatalytic performance

Improvement in intrinsic enzymatic features is in many instances a prerequisite for the scalable applicability of many industrially important biocatalysts. To this end, various strategies of chemical modification of enzymes are maturing and now considered as a distinct way to improve biocatalytic properties. Traditional chemical modification methods utilize reactivities of amine, carboxylic, thiol and other side chains originating from canonical amino acids. On the other hand, noncanonical amino acid- mediated 'click' (bioorthogoal) chemistry and dehydroalanine (Dha)-mediated modifications have emerged as an alternate and promising ways to modify enzymes for functional enhancement. This review discusses the applications of various chemical modification tools that have been directed towards the improvement of functional properties and/or stability of diverse array of biocatalysts.

Any Role of High-Dose Vitamin C for Septic Shock in 2021?

While the use of vitamin C as a therapeutic agent has been investigated since the 1950s, there has been substantial recent interest in the role of vitamin C supplementation in critical illness and particularly, sepsis and septic shock. Humans cannot synthesize vitamin C and rely on exogenous intake to maintain a plasma concentration of approximately 70 to 80 μmol/L. Vitamin C, in healthy humans, is involved with antioxidant function, wound healing, endothelial function, and catecholamine synthesis. Its function in the human body informs the theoretical basis for why vitamin C supplementation may be beneficial in sepsis/septic shock.Critically ill patients can be vitamin C deficient due to low dietary intake, increased metabolic demands, inefficient recycling of vitamin C metabolites, and loss due to renal replacement therapy. Intravenous supplementation is required to achieve supraphysiologic serum levels of vitamin C. While some clinical studies of intravenous vitamin C supplementation in sepsis have shown improvements in secondary outcome measures, none of the randomized clinical trials have shown differences between vitamin C supplementation and standard of care and/or placebo in the primary outcome measures of the trials. There are some ongoing studies of high-dose vitamin C administration in patients with sepsis and coronavirus disease 2019; the majority of evidence so far does not support the routine supplementation of vitamin C in patients with sepsis or septic shock.

β-Caryophyllene may attenuate hyperoxaluria-induced kidney dysfunction in rats by regulating stress marker KIM-1/MCP-1 and NF-κB signaling pathway

β-Caryophyllene (BCP), a bicyclic sesquiterpene, has proved to exhibit antioxidant and anti-inflammatory activities. The present study is carried out to investigate BCP impact on hyperoxaluria-induced kidney dysfunction in male Wistar rats. The animals were categorized into four groups, namely, Group I, control rats; Group II, ethylene glycol (inducer); Group III, inducer + BCP (100 µM/kg bw); Group IV, BCP alone. After the treatment period, the rate of creatinine clearance and the concentration of urea in urine and serum were assessed. Histopathology reports were conducted to study renal and liver tissues, while the reverse transcription-polymerase chain reaction studies were carried out for messenger RNA expression of inflammatory (nuclear factor kappa B) and endoplasmic reticulum (ER) stress (kidney dysfunction molecule-1, monocyte chemoattractant protein-1, glucose binding protein 78, CHOP, activating factor 4, and X-box binding protein-1) markers as well as antioxidant activity for the hyperoxaluric rats. Western blot was performed to investigate the level of protein expression by the treatment group on apoptotic (Bcl-2, Bax, caspase-3, and caspase-9) proteins. The results show BCP to possess a renoprotective effect under hyperoxaluric conditions by decreasing the level of the inflammatory and ER stress markers and restoring the enzymes' antioxidant activities. The histology reports depicted the satisfactory morphology of glomerulus in diseased rats. Furthermore, the results of Western blot suggested that BCP may possess inhibitory action on apoptosis by affecting the mitochondrial-dependent apoptotic pathway. Therefore, BCP can be considered as a potential candidate for the therapy of hyperoxaluric-induced kidney complications.

Association between intelectin-1 variation and human kidney stone disease in northeastern Thai population

An interplay of multiple genetic and environmental factors implicates an incidence of human kidney stone disease (KSD). However, the genetic factors associated with KSD are not completely known or understood. To identify KSD-associated genetic variations among the northeastern Thai patients, a genome-wide association study (GWAS) was conducted. We initially employed genotyping of single nucleotide polymorphism (SNP) using Genome-Wide Human SNP Array 6.0 in 105 patients and in 105 normal control subjects. To overcome the limitation of small sample size, we set forth to analyze SNPs as clusters based on the concept of linkage disequilibrium (LD) and haplotype. Using this analysis, 29 genes were identified. Three candidate SNPs, including rs2039415, rs2274907, and rs3747515, were selected on the basis of haplotype analysis, potentially functional SNPs, and the functions of associated genes. Further genotyping of these SNPs in a larger sample size (altogether 216 patients and 216 control subjects) showed that the candidate SNP rs2274907 remained significantly different between case and control subjects in both genotype frequencies (OR 2.44, 95% CI 1.38-4.30; p = 0.0015) and allele frequencies (OR 1.54, 95% CI 1.17-2.03; p = 0.0021). The non-synonymous SNP rs2274907 (c.326T > A) located in exon 4 of the ITLN1 gene results in a substitution of valine (V) by aspartate (D) at position 109 (p.V109D). This substitution could affect the predicted hydrogen (H)-bonds between lysine (K) 107 and glutamine (Q) 104, which supports its association with KSD in this population.

The role of NHE3 (Slc9a3) in oxalate and sodium transport by mouse intestine and regulation by cAMP

Intestinal oxalate transport involves Cl⁻/HCO₃⁻ exchangers but how this transport is regulated is not currently known. NHE3 (Slc9a3), an apical Na⁺/H⁺ exchanger, is an established target for regulation of electroneutral NaCl absorption working in concert with Cl⁻/HCO₃⁻ exchangers. To test whether NHE3 could be involved in regulation of intestinal oxalate transport and renal oxalate handling we compared urinary oxalate excretion rates and intestinal transepithelial fluxes of ¹⁴C‐oxalate and ²²Na⁺ between NHE3 KO and wild‐type (WT) mice. NHE3 KO kidneys had lower creatinine clearance suggesting reduced GFR, but urinary oxalate excretion rates (µmol/24 h) were similar compared to the WT but doubled when expressed as a ratio of creatinine. Intestinal transepithelial fluxes of ¹⁴C‐oxalate and ²²Na⁺ were measured in the distal ileum, cecum, and distal colon. The absence of NHE3 did not affect basal net transport rates of oxalate or sodium across any intestinal section examined. Stimulation of intracellular cAMP with forskolin (FSK) and 3‐isobutyl‐1‐methylxanthine (IBMX) led to an increase in net oxalate secretion in the WT distal ileum and cecum and inhibition of sodium absorption in the cecum and distal colon. In NHE3 KO cecum, cAMP stimulation of oxalate secretion was impaired suggesting the possibility of a role for NHE3 in this process. Although, there is little evidence for a role of NHE3 in basal intestinal oxalate fluxes, NHE3 may be important for cAMP stimulation of oxalate in the cecum and for renal handling of oxalate.

Physiological and Pathological Functions of SLC26A6

Solute Carrier Family 26 (SLC26) is a conserved anion transporter family with 10 members in human (SLC26A1-A11, A10 being a pseudogene). All SLC26 genes except for SLC26A5 (prestin) are versatile anion exchangers with notable ability to transport a variety of anions. SLC26A6 has the most extensive exchange functions in the SLC26 family and is widely expressed in various organs and tissues of mammals. SLC26A6 has some special properties that make it play a particularly important role in ion homeostasis and acid-base balance. In the past few years, the function of SLC26A6 in the diseases has received increasing attention. SLC26A6 not only participates in the development of intestinal and pancreatic diseases but also serves a significant role in mediating nephrolithiasis, fetal skeletal dysplasia and arrhythmia. This review aims to explore the role of SLC26A6 in physiology and pathophysiology of relative mammalian organs to guide in-depth studies about related diseases of human.

Medical evaluation and pharmacotherapeutical strategies in management of urolithiasis

Treatment of urolithiasis depends on several important factors which include stone location, size, composition, and patient symptoms. Although significant advancements have been made in the surgical management of urolithiasis in the last decade, pharmacotherapy which can prevent the formation of new stones and decrease the recurrence of urolithiasis has not experienced the same level of success. Currently, urolithiasis is regarded as a complicated syndrome that is determined by numerous factors, and any treatment plan for urolithiasis should be individualized while considering any potential damage arising from stone-forming factors. This review introduces the most popular methods currently used to evaluate urolithiasis and the pharmacotherapy of urolithiasis based on patient-specific factors.

Effects of fetuin-A with diverse functions and multiple mechanisms on human health

Fetuin-A (Alfa 2-Heremans-Schmid) is a glycoprotein that is mainly synthesized by hepatocytes and then released into the bloodstream. While fetuin-A, a multifunctional protein, has inhibitory effects on health in the processes of calcification, mineralization, coronary artery calcification (CAC), and kidney stone formation by various mechanisms, it has such stimulatory effects as obesity, diabetes, and tumor progression processes. Fetuin-A produces these effects on the organism mainly by playing a role in the secretion levels of some inflammatory cytokines and exosomes, preventing unwanted calcification, inhibiting the autophosphorylation of tyrosine kinase, suppressing the release of adiponectin and peroxisome proliferator-activated receptor-γ (PPARγ), activating the toll-like receptor 4 (TLR-4), triggering the phosphatidylinositol 3 (PI3) kinase/Akt signaling pathway and cell proliferation, and mimicking the transforming growth factor-beta (TGF-β) receptor. In the present review, fetuin-A was examined in a wide perspective from the structure and release of fetuin-A to its effects on health.

The anion exchanger PAT-1 (Slc26a6) does not participate in oxalate or chloride transport by mouse large intestine

The membrane-bound transport proteins responsible for oxalate secretion across the large intestine remain unidentified. The apical chloride/bicarbonate (Cl^-/HCO₃^-) exchanger encoded by Slc26a6, known as PAT-1 (putative anion transporter 1), is a potential candidate. In the small intestine, PAT-1 makes a major contribution to oxalate secretion but whether this role extends into the large intestine has not been directly tested. Using the PAT-1 knockout (KO) mouse, we compared the unidirectional absorptive ([Formula: see text]) and secretory ([Formula: see text]) flux of oxalate and Cl^- across cecum, proximal colon, and distal colon from wild-type (WT) and KO mice in vitro. We also utilized the non-specific inhibitor DIDS (4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid) to confirm a role for PAT-1 in WT large intestine and (in KO tissues) highlight any other apical anion exchangers involved. Under symmetrical, short-circuit conditions the cecum and proximal colon did not transport oxalate on a net basis, whereas the distal colon supported net secretion. We found no evidence for the participation of PAT-1, or indeed any other DIDS-sensitive transport mechanism, in oxalate or Cl^- by the large intestine. Most unexpectedly, mucosal DIDS concurrently stimulated [Formula: see text] and [Formula: see text] by 25-68% across each segment without impacting net transport. For the colon, these changes were directly proportional to increased transepithelial conductance suggesting this response was the result of bidirectional paracellular flux. In conclusion, PAT-1 does not contribute to oxalate or Cl^- transport by the large intestine, and we urge caution when using DIDS with mouse colonic epithelium.

Dietary Oxalate Intake and Kidney Outcomes

Oxalate is both a plant-derived molecule and a terminal toxic metabolite with no known physiological function in humans. It is predominantly eliminated by the kidneys through glomerular filtration and tubular secretion. Regardless of the cause, the increased load of dietary oxalate presented to the kidneys has been linked to different kidney-related conditions and injuries, including calcium oxalate nephrolithiasis, acute and chronic kidney disease. In this paper, we review the current literature on the association between dietary oxalate intake and kidney outcomes.

Associations between nephrolithiasis and diabetes mellitus, hypertension and gallstones: A meta-analysis of cohort studies

AIM

To review and clarify the strengths and directions of associations between nephrolithiasis and hypertension (HTN), diabetes mellitus (DM) and gallstones (GS) given the inconsistent results reported in cohort studies.

METHODS

Relevant literature was searched in PubMed and EMBASE from inception to July 2019, for cohort studies that examined the relationships between kidney stones and these three diseases among adults. Pooled relative risks (RRs) were calculated by maximally adjusted risk estimates using a random effect model. Subgroup analysis, meta-regression and sensitivity analysis were conducted whenever appropriate.

RESULTS

Of 3537 papers, 21 articles with each including 1 to 3 cohorts were identified. In this meta-analysis, nephrolithiasis was reciprocally linked to HTN, DM and GS. Kidney stones were significantly associated with 31%, 33% and 46% higher risks of incident HTN, DM and GS whereas GS was associated with a significantly higher risk of nephrolithiasis (RR: 1.49; 95% CI, 1.28-1.73), followed by HTN (RR: 1.30; 95% CI, 1.11-1.52) and DM (RR: 1.18; 95% CI, 1.07-1.29). Also, females with DM (RR: 1.29; 95% CI, 1.08-1.55) were more likely to develop kidney stones than diabetic male patients (RR: 0.91; 95% CI, 0.75-1.10).

CONCLUSION

Although additional studies are needed to confirm these findings and elucidate the mechanisms, this study revealed possible bidirectional associations between nephrolithiasis and HTN, diabetes and GS, which reinforced the notion of nephrolithiasis as a systemic disease that requires comprehensive investigations.

A novel loss-of-function mutation of PBK associated with human kidney stone disease

Kidney stone disease (KSD) is a prevalent disorder that causes human morbidity worldwide. The etiology of KSD is heterogeneous, ranging from monogenic defect to complex interaction between genetic and environmental factors. Since mutations of genes responsible for KSD in a majority of families are still unknown, our group is identifying mutations of these genes by means of genomic and genetic analyses. In this study, we identified a novel loss-of-function mutation of PBK, encoding the PDZ binding kinase, that was found to be associated with KSD in an affected Thai family. Glycine (Gly) substituted by arginine (Arg) at position 43 (p.Gly43Arg) in PBK cosegregated with the disease in affected members of this family, but was absent in 180 normal control subjects from the same local population. Gly43 is highly evolutionarily conserved in vertebrates, and its substitution affects protein structure by alterations in H-bond forming patterns. This p.Gly43Arg substitution results in instability of the variant PBK protein as examined in HEK293T cells. The variant PBK protein (p.Gly43Arg) demonstrated decreased kinase activity to phosphorylate p38 MAPK as analyzed by immunoblotting and antibody microarray techniques. Taken together, these findings suggest a possible new mechanism of KSD associated with pathogenic PBK variation.

The teleost fish intestine is a major oxalate-secreting epithelium

Oxalate is a common constituent of kidney stones, but the mechanism of its transport across epithelia is not well understood. With prior research on the role of the intestine focused on mammals, the present study considered oxalate handling by teleost fish. Given the osmotic challenge of seawater (SW), marine teleosts have limited scope for urinary oxalate excretion relative to freshwater (FW) taxa. The marine teleost intestine was hypothesized as the principal route for oxalate elimination, thus demanding epithelial secretion. To test this, intestinal 14C-oxalate flux was compared between FW- and SW-acclimated sailfin molly (Poecilia latipinna). In SW, oxalate was secreted at remarkable rates (367.90±22.95 pmol cm-2 h-1), which were similar following FW transfer (387.59±27.82 pmol cm-2 h-1), implying no regulation by salinity. Nevertheless, this ability to secrete oxalate at rates 15-19 times higher than the mammalian small intestine supports this proposal of the teleost gut as a major, previously unrecognized excretory pathway.

Current insights into the mechanisms and management of infection stones

Infection stones are complex aggregates of crystals amalgamated in an organic matrix that are strictly associated with urinary tract infections. The management of patients who form infection stones is challenging owing to the complexity of the calculi and high recurrence rates. The formation of infection stones is a multifactorial process that can be driven by urine chemistry, the urine microenvironment, the presence of modulator substances in urine, associations with bacteria, and the development of biofilms. Despite decades of investigation, the mechanisms of infection stone formation are still poorly understood. A mechanistic understanding of the formation and growth of infection stones - including the role of organics in the stone matrix, microorganisms, and biofilms in stone formation and their effect on stone characteristics - and the medical implications of these insights might be crucial for the development of improved treatments. Tools and approaches used in various disciplines (for example, engineering, chemistry, mineralogy, and microbiology) can be applied to further understand the microorganism-mineral interactions that lead to infection stone formation. Thus, the use of integrated multidisciplinary approaches is imperative to improve the diagnosis, prevention, and treatment of infection stones.

Vitamin K1 Inhibition of Renal Crystal Formation through Matrix Gla Protein in the Kidney

BACKGROUND AND OBJECTIVES

Vitamin K (VK) plays a major role in modifying the binding of calcium in bones and blood vessels. Understanding the effect of VK on crystal formation in the kidney would contribute to advancing the treatment and prevention of kidney stones.

METHODS

Rats were treated with vitamin K1 (VK1) for 8 weeks. VK1 levels were detected and crystal formation were observed. HK2 cells were exposed to calcium oxalate monohydrate crystals. Apoptosis and cell viability were detected. Crystal deposition was analyzed using atomic absorption assay. The adenovirus vectors expressing matrix Gla protein (MGP) and siMGP were constructed to elucidate the effect and mechanism of VK1 on crystal formation. MGP expression in vivo and in vitro was analyzed by Western blot. The mRNA levels of monocyte chemoattractant protein-1 (MCP-1) and collagen I was measured by semiquantitative RT-PCR.

RESULTS

The concentrations of VK1 in whole blood and kidney tissues rose under treatment with VK1. Crystal formation was inhibited from the second to the 6th week, the frequency and quality of crystal formation decreased significantly, and the location of crystal formation was limited to a greater extent in the rats treated by VK1 compared to the control group. Warfarin treatment in the crystals-exposed HK2 cells significantly increased the number of crystals adhering to cells and the number of apoptotic cells and reduced cell viability. VK1 treatment reversed warfarin's above influence. VK1 inhibited the upregulations of MCP-1 and collagen I in kidney tissues under crystal load. VK1 treatment increased MGP expression in vivo and in vitro, and MGP is necessary for VK1 to play a role in crystal deposition in cells.

CONCLUSIONS

VK1 treatment can inhibit the formation of renal crystals in vivo. VK1 increases MGP expression and functions through MGP to reduce crystal deposition in cells and provide cell protection. Our findings suggest that VK1 treatment could be a potential strategy for the treatment and prevention of nephrolithiasis.

Metabolism of Oxalate in Humans: A Potential Role Kynurenine Aminotransferase/Glutamine Transaminase/Cysteine Conjugate Beta-lyase Plays in Hyperoxaluria

Hyperoxaluria, excessive urinary oxalate excretion, is a significant health problem worldwide. Disrupted oxalate metabolism has been implicated in hyperoxaluria and accordingly, an enzymatic disturbance in oxalate biosynthesis can result in the primary hyperoxaluria. Alanine glyoxylate aminotransferase-1 and glyoxylate reductase, the enzymes involving glyoxylate (precursor for oxalate) metabolism, have been related to primary hyperoxalurias. Some studies suggest that other enzymes such as glycolate oxidase and alanine glyoxylate aminotransferase-2 might be associated with primary hyperoxaluria as well, but evidence of a definitive link is not strong between the clinical cases and gene mutations. There are still some idiopathic hyperoxalurias, which require a further study for the etiologies. Some aminotransferases, particularly kynurenine aminotransferases, can convert glyoxylate to glycine. Based on biochemical and structural characteristics, expression level, subcellular localization of some aminotransferases, a number of them appear able to catalyze the transamination of glyoxylate to glycine more efficiently than alanine glyoxylate aminotransferase-1. The aim of this minireview is to explore other undermining causes of primary hyperoxaluria and stimulate research toward achieving a comprehensive understanding of underlying mechanisms leading to the disease. Herein, we reviewed all aminotransferases in the liver for their functions in glyoxylate metabolism. Particularly, kynurenine aminotransferase-I and III were carefully discussed regarding their biochemical and structural characteristics, cellular localization, and enzyme inhibition. Kynurenine aminotransferase-III is, so far, the most efficient putative mitochondrial enzyme to transaminate glyoxylate to glycine in mammalian livers, might be an interesting enzyme to look over in hyperoxaluria etiology of primary hyperoxaluria and should be carefully investigated for its involvement in oxalate metabolism.

Biochemical properties and oxalate-degrading activity of oxalate decarboxylase from bacillus subtilis at neutral pH

Oxalate decarboxylase (OxDC) from Bacillus subtilis is a Mn-dependent hexameric enzyme that converts oxalate to carbon dioxide and formate. OxDC has greatly attracted the interest of the scientific community, mainly due to its biotechnological and medical applications in particular for the treatment of hyperoxaluria, a group of pathologic conditions caused by oxalate accumulation. The enzyme has an acidic optimum pH, but most of its applications involve processes occurring at neutral pH. Nevertheless, a detailed biochemical characterization of the enzyme at neutral pH is lacking. Here, we compared the structural-functional properties at acidic and neutral pH of wild-type OxDC and of a mutant form, called OxDC-DSSN, bearing four amino acid substitutions in the lid (Ser161-to-Asp, Glu162-to-Ser, Asn163-toSer, and Ser164-to-Asn) that improve the oxalate oxidase activity and almost abolish the decarboxylase activity. We found that both enzymatic forms do not undergo major structural changes as a function of pH, although OxDC-DSSN displays an increased tendency to aggregation, which is counteracted by the presence of an active-site ligand. Notably, OxDC and OxDC-DSSN at pH 7.2 retain 7 and 15% activity, respectively, which is sufficient to degrade oxalate in a cellular model of primary hyperoxaluria type I, a rare inherited disease caused by excessive endogenous oxalate production. The significance of the data in the light of the possible use of OxDC as biological drug is discussed. © 2019 IUBMB Life, 1-11, 2019.

Bidirectional association between gallstones and renal stones: Two longitudinal follow-up studies using a national sample cohort

The present study evaluated the associations between gallstones and renal stones using a national sample cohort of the Korean population. The Korean National Health Insurance Service-National Sample Cohort was collected from 2002 to 2013. We designed two different longitudinal follow-up studies. In study I, we extracted gallstone patients (n = 20,711) and 1:4-matched control I subjects (n = 82,844) and analyzed the occurrence of renal stones. In study II, we extracted renal stone patients (n = 23,615) and 1:4-matched control II subjects (n = 94,460) and analyzed the occurrence of gallstones. Matching was performed for age, sex, income, region of residence, and history of hypertension, diabetes mellitus, and dyslipidemia. Crude and adjusted hazard ratios (HRs) were calculated using a Cox proportional hazards model, and the 95% confidence intervals (CIs) were calculated. Subgroup analyses were performed according to age and sex. The adjusted HR of renal stones was 1.93 (95% CI = 1.75–2.14) in the gallstone group (P < 0.001). The adjusted HR of gallstones was 1.97 (95% CI = 1.81–2.15) in the renal stone group (P < 0.001). The results were consistent in all subgroup analyses. Gallstones increased the risk of renal stones, and renal stones increased the risk of gallstones.

Activation of liver X receptor suppresses osteopontin expression and ameliorates nephrolithiasis

Nephrolithiasis is a common disease of the urinary system, of which idiopathic calcium oxalate (CaOx) kidney stones, in particular, are one of the special types. In the initial stages of CaOx kidney stone formation, Randall's plaques (RPs) develop. Liver X receptors (LXRs) inhibit oxidative stress and inflammatory in other diseases; nevertheless, the role of LXRs in nephrolithiasis has yet to be elucidated. In this study, the role of LXRs in the progression of RP formation was investigated. Microarray analysis revealed that LXR/RXR levels were significantly greater in low-plaque tissues (<5%) than in high-plaque tissues (>5%), confirming the link between LXR activation and RP formation. Correspondingly, expression levels of two LXR target genes, LXRα and LXRβ, were lower in high-plaque tissues than in low-plaque tissues. In vitro, LXR agonist alleviated calcium oxalate monohydrate-induced cellular calcium deposits and apoptosis. LXR activation decreased reactive oxygen species production and gene expression of inflammatory mediators, including osteopontin that has recently been demonstrated to correlate with the development of RPs. Moreover, p38 MAPK and JNK signaling may mediate LXR-regulated expression in HK-2 cells. In an animal model, the deposition was reduced by activating LXR, and osteopontin expression was also inhibited. Our findings suggest a role for LXRs in the progression of idiopathic CaOx kidney stones; LXR agonists may have therapeutic potential for the treatment of nephrolithiasis.

Seasonal variation in occurrence of oxalate nephrosis in South Australian koalas (Phascolarctos cinereus)

Many koalas (Phascolarctos cinereus) in the Mount Lofty Ranges, South Australia, are affected by oxalate nephrosis, in which renal calcium oxalate deposition occurs. In other species, suboptimal water intake increases the risk of urinary calcium oxalate crystal formation. Koalas principally rely on eucalypt leaf moisture content to maintain hydration but the Mount Lofty Ranges region has hot, dry summers. This study investigates the association between temperature, rainfall and eucalypt leaf moisture and the occurrence of oxalate nephrosis in this population of koalas. Koalas from the Mount Lofty Ranges population that had died or were euthanased between 2008 and 2016 were necropsied and oxalate nephrosis was determined by histopathology (n=50). Leaf moisture content of Mount Lofty eucalypts was determined seasonally. It was found that increased numbers of koalas with oxalate nephrosis died in the months following high mean maximal temperature and in the months following low rainfall. Eucalypt leaf moisture content was not significantly associated with koala deaths. These findings suggest that hot and dry summer/autumn periods contribute to an increased incidence of koala deaths due to oxalate nephrosis. This is probably due to the effects of evaporative water loss and/or lack of access to supplementary drinking water at this time.

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, ³⁵SO42- , 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.

Molecular basis of primary hyperoxaluria: clues to innovative treatments

Primary hyperoxalurias (PHs) are rare inherited disorders of liver glyoxylate metabolism, characterized by the abnormal production of endogenous oxalate, a metabolic end-product that is eliminated by urine. The main symptoms are related to the precipitation of calcium oxalate crystals in the urinary tract with progressive renal damage and, in the most severe form named Primary Hyperoxaluria Type I (PH1), to systemic oxalosis. The therapies currently available for PH are either poorly effective, because they address the symptoms and not the causes of the disease, or highly invasive. In the last years, advances in our understanding of the molecular bases of PH have paved the way for the development of new therapeutic strategies. They include (i) substrate-reduction therapies based on small-molecule inhibitors or the RNA interference technology, (ii) gene therapy, (iii) enzyme administration approaches, (iv) colonization with oxalate-degrading intestinal microorganisms, and, in PH1, (v) design of pharmacological chaperones. This paper reviews the basic principles of these new therapeutic strategies and what is currently known about their application to PH.

Functional eubacteria species along with trans-domain gut inhabitants favour dysgenic diversity in oxalate stone disease

Analyses across all three domains of life are necessary to advance our understanding of taxonomic dysbiosis in human diseases. In the present study, we assessed gut microbiota (eubacteria, archaea, and eukaryotes) of recurrent oxalate kidney stone suffers to explore the extent of trans-domain and functional species dysbiosis inside the gut. Trans-domain taxonomic composition, active oxalate metabolizer and butyrate-producing diversity were explored by utilizing frc-, but-, and buk- functional gene amplicon analysis. Operational taxonomic units (OTUs) level analyses confound with the observation that dysbiosis in gut microbiota is not just limited to eubacteria species, but also to other domains like archaea and eukaryotes. We found that some of healthy eubacterial population retained together with Oxalobacter formigenes and Lactobacillus plantarum colonization in disease condition (p < 0.001 & FDR = 0.05). Interestingly, trans-domain species diversity has been less shared and dysgenic taxa augmentation was found to be higher. Oxalate metabolizing bacterial species (OMBS) and butyrate-producing eubacteria species were found to be decreased in Oxalobacter non-colonizers; and Prevotella and Ruminococcus species which may contribute to oxalate metabolism and butyrate synthesis as well. Our study underscores fact that microbial dysbiosis is not limited to eubacteria only hence suggest the necessity of the trans-domain surveillance in metabolic diseases for intervention studies.

Loss-of-function mutations of SCN10A encoding NaV1.8 α subunit of voltage-gated sodium channel in patients with human kidney stone disease

Human kidney stone disease (KSD) causes significant morbidity and public health burden worldwide. The etiology of KSD is heterogeneous, ranging from monogenic defects to complex interaction between genetic and environmental factors. However, the genetic defects causing KSD in the majority of affected families are still unknown. Here, we report the discovery of mutations of SCN10A, encoding Na_V1.8 α subunit of voltage-gated sodium channel, in families with KSD. The region on chromosome 3 where SCN10A locates was initially identified in a large family with KSD by genome-wide linkage analysis and exome sequencing. Two mutations (p.N909K and p.K1809R) in the same allele of SCN10A co-segregated with KSD in the affected family. Additional mutation (p.V1149M) of SCN10A was identified in another affected family, strongly supporting the causal role of SCN10A for KSD. The amino acids at these three positions, N909, K1809, and V1149, are highly conserved in vertebrate evolution, indicating their structural and functional significances. Na_V1.8 α subunit mRNA and protein were found to express in human kidney tissues. The mutant proteins expressed in cultured cells were unstable and causing reduced current density as analyzed by whole-cell patch-clamp technique. Thus, loss-of-function mutations of SCN10A were associated with KSD in the families studied.

Renal stones

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

Vitamin C Pharmacokinetics in Critically Ill Patients: A Randomized Trial of Four IV Regimens

BACKGROUND

Early high-dose IV vitamin C is being investigated as adjuvant therapy in patients who are critically ill, but the optimal dose and infusion method are unclear. The primary aim of this study was to describe the dose-plasma concentration relationship and safety of four different dosing regimens.

METHODS

This was a four-group randomized pharmacokinetic trial. Patients who were critically ill with multiple organ dysfunction were randomized to receive 2 or 10 g/d vitamin C as a twice daily bolus infusion or continuous infusion for 48 h. End points were plasma vitamin C concentrations during 96 h, 12-h urine excretion of vitamin C, and oxalate excretion and base excess. A population pharmacokinetic model was developed using NONMEM.

RESULTS

Twenty patients were included. A two-compartment pharmacokinetic model with creatinine clearance and weight as independent covariates described all four regimens best. With 2 g/d bolus, plasma vitamin C concentrations at 1 h were 29 to 50 mg/L and trough concentrations were 5.6 to 16 mg/L. With 2 g/d continuous, steady-state concentrations were 7 to 37 mg/L at 48 h. With 10 g/d bolus, 1-h concentrations were 186 to 244 mg/L and trough concentrations were 14 to 55 mg/L. With 10 g/d continuous, steady-state concentrations were 40 to 295 mg/L at 48 h. Oxalate excretion and base excess were increased in the 10 g/d dose. Forty-eight hours after discontinuation, plasma concentrations declined to hypovitaminosis levels in 15% of patients.

CONCLUSIONS

The 2 g/d dose was associated with normal plasma concentrations, and the 10 g/d dose was associated with supranormal plasma concentrations, increased oxalate excretion, and metabolic alkalosis. Sustained therapy is needed to prevent hypovitaminosis.

TRIAL REGISTRY

ClinicalTrials.gov; No.: NCT02455180; URL: www.clinicaltrials.gov.

The relationship between serum and urinary Fetuin-A levels and kidney stone formation among kidney stone patients

Introduction

Mineralization inhibitors are required to prevent the precipitation of minerals and inhibit the formation of kidney stones and other ectopic calcifications. In laboratory studies, Fetuin-A as a glycoprotein has inhibited hydroxyapatite precipitation in calcium and phosphate supersaturated solutions; however, information about patients with kidney stones is limited. The aim of this study was to investigate the association of serum and urinary Fetuin-A levels with calcium oxalate kidney stones.

Material and methods

In this case-control study, 30 patients with kidney stones and 30 healthy individuals without any history of urolithiasis who were referred to the urology ward of Sina Hospital of Tehran, Iran, in 2015 were entered into the study. All patients underwent computerized tomography scans. After collecting demographic information, serum and urine levels of Fetuin-A and some other calcification inhibitors and promoters, were measured and compared using T-test, Mann-Whitney and logistic regression between the two study groups.

Results

Patients with kidney stones, on average, had lower levels of Serum Fetuin-A (1522.27 ±755.39 vs. 1914.64 ±733.76 μg/ml; P = 0.046) as well as lower levels of Urine Fetuin-A (944.62 ±188.5 vs. 1409.68 ±295.26 μg/ml; P <0.001). Multivariate logistic analysis showed that urinary calcium and serum creatinine are the risk factors and Fetuin-A is a urinary protective factor for kidney stones.

Conclusions

PFC Our study showed that patients with kidney stones had lower serum and urinary levels of Fetuin-A. In the logistic regression model, urinary Fetuin-A was reported as a protective factor for kidney stones.

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

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

In vitro and in vivo safety evaluation of Nephure™

Nephure™ is a proprietary oxalate decarboxylase (OxDC) enzyme being developed as a food ingredient. In this study, the safety of Nephure™ was evaluated in a bacterial mutagenicity assay and in a sub-chronic (13-week) oral toxicity study in rats. Nephure™ did not show any mutagenic properties in the mutagenicity assay. In the 13-week sub-chronic oral toxicity study in which 10 Sprague Dawley rats per sex were administered 0, 118, 235 and 475 mg/kg bw/day (8260, 16450 and 33,250 Units/kg bw/day, respectively) of Nephure™ by gavage, male and female rats did not show any test article-related clinical observations or effects on body weight, body weight gain, food consumption, food efficiency, ophthalmology, functional observational battery parameters or motor activity. Furthermore, there were no changes in coagulation, clinical chemistry, urinalysis or hematology parameters, macroscopic/microscopic findings or organ weights that could be attributed to the test article. Based on these results, Nephure™ was not mutagenic and the no-adverse-effect level (NOAEL) in the 13-week study was determined to be 475 mg/kg bw/day (33,250 Units/kg bw/day). Evaluation of the estimated consumption of Nephure™, generation of the metabolite formate, and the current safety studies resulted in a conclusion of a tolerable upper limit of 3450 Units of OxDC activity/day (57.5 Units activity/kg bw/day), when Nephure™ is added to food to decrease dietary oxalate.

Hyperoxaluria leads to dysbiosis and drives selective enrichment of oxalate metabolizing bacterial species in recurrent kidney stone endures

Hyperoxaluria due to endogenously synthesized and exogenously ingested oxalates is a leading cause of recurrent oxalate stone formations. Even though, humans largely rely on gut microbiota for oxalate homeostasis, hyperoxaluria associated gut microbiota features remain largely unknown. Based on 16S rRNA gene amplicons, targeted metagenomic sequencing of formyl-CoA transferase (frc) gene and qPCR assay, we demonstrate a selective enrichment of Oxalate Metabolizing Bacterial Species (OMBS) in hyperoxaluria condition. Interestingly, higher than usual concentration of oxalate was found inhibitory to many gut microbes, including Oxalobacter formigenes, a well-characterized OMBS. In addition a concomitant enrichment of acid tolerant pathobionts in recurrent stone sufferers is observed. Further, specific enzymes participating in oxalate metabolism are found augmented in stone endures. Additionally, hyperoxaluria driven dysbiosis was found to be associated with oxalate content, stone episodes and colonization pattern of Oxalobacter formigenes. Thus, we rationalize the first in-depth surveillance of OMBS in the human gut and their association with hyperoxaluria. Our findings can be utilized in the treatment of hyperoxaluria associated recurrent stone episodes.

In Silico Modeling of Liver Metabolism in a Human Disease Reveals a Key Enzyme for Histidine and Histamine Homeostasis

Primary hyperoxaluria type I (PH1) is an autosomal-recessive inborn error of liver metabolism caused by alanine:glyoxylate aminotransferase (AGT) deficiency. In silico modeling of liver metabolism in PH1 recapitulated accumulation of known biomarkers as well as alteration of histidine and histamine levels, which we confirmed in vitro, in vivo, and in PH1 patients. AGT-deficient mice showed decreased vascular permeability, a readout of in vivo histamine activity. Histamine reduction is most likely caused by increased catabolism of the histamine precursor histidine, triggered by rerouting of alanine flux from AGT to the glutamic-pyruvate transaminase (GPT, also known as the alanine-transaminase ALT). Alanine administration reduces histamine levels in wild-type mice, while overexpression of GPT in PH1 mice increases plasma histidine, normalizes histamine levels, restores vascular permeability, and decreases urinary oxalate levels. Our work demonstrates that genome-scale metabolic models are clinically relevant and can link genotype to phenotype in metabolic disorders.

•

In silico model of liver metabolism reveals global metabolic alterations in PH1

•

Changes in amino acid metabolism in PH1 result in a reduction of histidine and histamine

•

GPT overexpression normalizes histamine levels and reduces oxalate in PH1 mice

Role of mitochondria and NADPH oxidase derived reactive oxygen species in hyperoxaluria induced nephrolithiasis: therapeutic intervention with combinatorial therapy of N-acetyl cysteine and Apocynin

The interactions between the main cellular sources of ROS, such as mitochondria and NADPH oxidase, are known to play an imperative role in the pathogenesis of hyperoxaluria-induced nephrolithiasis. The present study was designed to investigate the protective effect of a combinatorial therapy based on the attenuation of oxidative stress with antioxidant (N-acetyl cysteine), and NADPH oxidase inhibitor (apocynin), that might be required to effectively eliminate hyperoxaluric manifestations. Hyperoxaluria was induced in male Wistar rats by administering 0.4% ethylene glycol with 1% ammonium chloride in drinking water for 9 days. Hyperoxaluria accentuated renal oxidative stress in terms of increased ROS production and lipid peroxidation. Mitochondrial dysfunction, a central deleterious event in renal stone crystallization, was evident by decreased activities of electron transport chain complex I, II and IV, augmented mitochondrial ROS, reduced GSH/GSSG ratio, which resulted in the mitochondrial permeability transition pore (mPTP) opening as indicated by increased mitochondrial swelling in hyperoxaluric rats. Furthermore, NADPH oxidase activity was significantly increased, with raised expression of NOX1, NOX2, NOX4, p38MAPK and MnSOD, in the renal tissue of hyperoxaluric rats compared to control. However, combinatorial therapy with N-acetyl cysteine (50mg/kg/day) and apocynin (200mg/kg/day), intraperitoneally, significantly improved renal functions in hyperoxaluric rats and considerably ameliorated mitochondrial dysfunction. NAC with apocynin was also found to be effective in reducing the redundant activity of NADPH oxidase in renal tissue of hyperoxaluric rats. Hence, our investigation provides novel mechanistic insights that combinatorial approaches using targeted modulators of ROS offer therapeutic benefits in hyperoxaluria-induced nephrolithiasis.