Plasma Oxalate Concentration Research Articles

Interleukin-16 is increased in dialysis patients but is not a cardiovascular risk factor.

Oxalate, a uremic toxin that accumulates in dialysis patients, is associated with cardiovascular disease. As oxalate crystals can activate immune cells, we tested the hypothesis that plasma oxalate would be associated with cytokine concentrations and cardiovascular outcomes in dialysis patients. In a cohort of 104 US patients with kidney failure requiring dialysis (cohort 1), we measured 21 inflammatory markers. As IL-16 was the only cytokine to correlate with oxalate, we focused further investigations on IL-16. We searched for associations between concentrations of IL-16 and mortality and cardiovascular events in the 4D cohort (1255 patients, cohort 2) and assessed further associations of IL-16 with other uremic toxins in this cohort. IL-16 levels were positively correlated with pOx concentrations (ρ = 0.39 in cohort 1, r = 0.35 in cohort 2) and were elevated in dialysis patients when compared to healthy individuals. No significant association could be found between IL-16 levels and cardiovascular events or mortality in the 4D cohort. We conclude that the cytokine IL-16 correlates with plasma oxalate concentrations and is substantially increased in patients with kidney failure on dialysis. However, no association could be detected between IL-16 concentrations and cardiovascular disease in the 4D cohort.

Lumasiran treatment in pediatric patients with PH1: real-world data within a compassionate use program in Italy.

Primary hyperoxaluria (PH) is a rare, severe genetic disorder, characterized by increased urinary excretion of calcium oxalate, which is responsible for kidney damage and systemic clinical manifestations. Since the year 2020, a new molecule, lumasiran, based on RNA interference (RNAi) technology, has been added to the traditional therapeutic approach. The aim of this analysis was to define the baseline characteristics of a PH1 pediatric population treated with lumasiran in a compassionate-use program setting, and to evaluate the medium-term efficacy of this drug in the routine clinical setting. A retrospective observational analysis was conducted in nine pediatric patients (male:female 5:4; median age at lumasiran start 1.9 years, range 0-14.1). Data concerning oxalate concentration in plasma and urine, kidney stones events, ultrasound and kidney function were collected during the study period (follow-up, mean±standard deviation: 15.3±5 months). In this analysis, a reduction in the urinary oxalate to creatinine ratio (reduction range within the sixth month of treatment from 25.8% to 69.6%, median 51.2%) as well as plasma oxalate concentration under the limit of supersaturation of oxalate in all the patients. Only one patient presented new stone events; kidney ultrasonographic findings related to nephrocalcinosis remained stable in eight out of nine patients. Glomerular filtration rate remained stable during treatment. No adverse events related to lumasiran were noted. Data from this analysis support the efficacy and safety of lumasiran in a pediatric clinical setting, especially if administrated in early life.

Primary Hyperoxaluria Screening and Monitoring: Quantitative Measurement of Plasma Oxalate by Gas Chromatography-Mass Spectrometry With High Sensitivity.

Plasma oxalate measurements can be used for the screening and therapeutic monitoring of primary hyperoxaluria. We developed a gas chromatography-mass spectrometry (GC-MS) assay for plasma oxalate measurements with high sensitivity and suitable testing volumes for pediatric populations. Plasma oxalate was extracted, derivatized, and analyzed by GC-MS. We measured the ion at m/z 261.10 to quantify oxalate and the 13C2-oxalate ion (m/z: 263.15) as the internal standard. Method validation included determination of the linear range, limit of blank, limit of detection, lower limit of quantification, precision, recovery, carryover, interference, and dilution effect. The cut-off value between primary and non-primary hyperoxaluria in a pediatric population was analyzed. The detection limit was 0.78 μmol/L, and the linear range was up to 80.0 μmol/L. The between-day precision was 5.7% at 41.3 μmol/L and 13.1% at 1.6 μmol/L. The carryover was <0.2%. The recovery rate ranged from 90% to 110%. Interference analysis showed that Hb did not interfere with plasma oxalate quantification, whereas intralipids and bilirubin caused false elevation of oxalate concentrations. A cut-off of 13.9 μmol/L showed 63% specificity and 77% sensitivity, whereas a cut-off of 4.15 μmol/L showed 100% specificity and 20% sensitivity. The minimum required sample volume was 250 μL. The detected oxalate concentrations showed interference from instrument conditioning, sample preparation procedures, medications, and various clinical conditions. GC-MS is a sensitive assay for quantifying plasma oxalate and is suitable for pediatric patients. Plasma oxalate concentrations should be interpreted in a clinical context.

Prospective Assessment of the Prevalence of Enter Hyperoxalosis in Kidney Transplant Candidates.

We prospectively measured POx among KT candidates evaluated at our center from 2017 to 2020 with risk factors for EH namely bariatric surgery, inflammatory bowel disease, or cystic fibrosis. EH was defined by a POx ≥10 μmol/L. Period-prevalence of EH was calculated. We compared mean POx across 5 factors: underlying condition, chronic kidney disease (CKD) stage, dialysis modality, phosphate binder type, and body mass index. Of 40 KT candidates screened, 23 had EH for a 4-y period prevalence of 58%. Mean POx was 21.6 ± 23.5 μmol/L ranging from 0 to 109.6 μmol/L. 40% of screened had POx >20 μmol/L. Sleeve gastrectomy was the most common underlying condition associated with EH. Mean POx did not differ by underlying condition (P = 0.27), CKD stage (P = 0.17), dialysis modality (P = 0.68), phosphate binder (P = 0.58), and body mass index (P = 0.56). Bariatric surgery and inflammatory bowel disease were associated with a high prevalence of EH among KT candidates. Contrary to prior studies, sleeve gastrectomy was also associated with hyperoxalosis in advanced CKD. POx concentrations observed in EH reached levels associated with tissue and potentially allograft deposition. Concentrations can be as high as that seen in primary hyperoxaluria. More studies are needed to assess if POx is indeed a modifiable factor affecting allograft function in patients with EH.

Plasma oxalate and glycolate concentrations in dialysis patients with and without primary hyperoxaluria type 1.

Plasma oxalate and glycolate concentrations in dialysis patients with and without primary hyperoxaluria type 1.

Oxalate homeostasis.

Oxalate homeostasis is maintained through a delicate balance between endogenous sources, exogenous supply and excretion from the body. Novel studies have shed light on the essential roles of metabolic pathways, the microbiome, epithelial oxalate transporters, and adequate oxalate excretion to maintain oxalate homeostasis. In patients with primary or secondary hyperoxaluria, nephrolithiasis, acute or chronic oxalate nephropathy, or chronic kidney disease irrespective of aetiology, one or more of these elements are disrupted. The consequent impairment in oxalate homeostasis can trigger localized and systemic inflammation, progressive kidney disease and cardiovascular complications, including sudden cardiac death. Although kidney replacement therapy is the standard method for controlling elevated plasma oxalate concentrations in patients with kidney failure requiring dialysis, more research is needed to define effective elimination strategies at earlier stages of kidney disease. Beyond well-known interventions (such as dietary modifications), novel therapeutics (such as small interfering RNA gene silencers, recombinant oxalate-degrading enzymes and oxalate-degrading bacterial strains) hold promise to improve the outlook of patients with oxalate-related diseases. In addition, experimental evidence suggests that anti-inflammatory medications might represent another approach to mitigating or resolving oxalate-induced conditions.

EPHex: a phase 3, double-blind, placebo-controlled, randomized study to evaluate long-term efficacy and safety of Oxalobacter formigenes in patients with primary hyperoxaluria

BackgroundPrimary hyperoxalurias (PHs) are rare genetic diseases that increase the endogenous level of oxalate, a waste metabolite excreted predominantly by the kidneys and also the gut. Treatments aim to improve oxalate excretion, or reduce oxalate generation, to prevent kidney function deterioration. Oxalobacter formigenes is an oxalate metabolizing bacterium. This Phase III, double-blind, placebo-controlled randomized trial investigated the effectiveness of orally administered Oxabact™, a lyophilized O. formigenes formulation, at reducing plasma oxalate levels in patients suffering from PH.MethodsSubjects (≥ 2 years of age) with a diagnosis of PH and maintained but suboptimal kidney function (mean estimated glomerular filtration rate at baseline < 90 mL/min/1.73 m2) were eligible to participate. Subjects were randomized to receive Oxabact or placebo twice daily for 52 weeks. Change from baseline in plasma oxalate concentration at Week 52 was the primary study endpoint.ResultsForty-three subjects were screened, 25 were recruited and one was discontinued. At Week 52, O. formigenes was established in the gut of subjects receiving Oxabact. Despite decreasing plasma oxalate level in subjects treated with Oxabact, and stable/increased levels with placebo, there was no significant difference between groups in the primary outcome (Least Squares mean estimate of treatment difference was − 3.80 μmol/L; 95% CI: − 7.83, 0.23; p-value = 0.064). Kidney function remained stable in both treatments.ConclusionsOxabact treatment may have stabilized/reduced plasma oxalate versus a rise with placebo, but the difference over 12 months was not statistically significant (p = 0.06). A subtle effect observed with Oxabact suggests that O. formigenes may aid in preventing kidney stones.Graphical abstractA higher resolution version of the Graphical abstract is available as Supplementary information.

High Plasma Oxalate Levels Early After Kidney Transplantation Are Associated With Impaired Long-Term Outcomes.

Background: Elevated levels of oxalate are common in renal failure patients and non-hyperoxaluria disease, and may cause damage after transplantation. We examined outcomes after 15 years for 167 kidney transplant recipients who had plasma oxalate measured early after transplantation. Analyses included plasma oxalate, recipient age, donor age, live donor, HLA-DR mismatch, mGFR, and smoking. Results: Median age was 52 years (range 18–81), 63% were male and 38% had live donors. Median plasma oxalate concentration 10 weeks after transplantation was 9.0 μmol/L (range 2.7–53.0), one third above the upper reference limit (11.0 μmol/L). Multivariable analysis revealed upper quartile plasma oxalate (>13.0 μmol/L, p = 0.008), recipient age (p < 0.001), deceased donor (p = 0.003), and current smoking (p < 0.001) as significant factors associated with patient survival. Upper quartile plasma oxalate (p = 0.021), recipient age (p = 0.001), deceased donor kidney (p = 0.001), HLA-DR mismatch (p = 0.015), and current smoking (p = 0.014) were also associated with graft loss. Factors associated with death censored graft losses were donor age (p = 0.012), deceased donor (p = 0.032), and HLA-DR mis-matched kidneys (p = 0.005) but plasma oxalate was not (p = 0.188). Conclusions: Plasma oxalate in the upper quartile early after transplantation was significantly associated with impaired long-term patient survival and graft losses, but not when censored for death.

New therapeutics for primary hyperoxaluria type 1.

Primary hyperoxaluria type 1 (PH1) is a rare genetic disorder that causes hepatic overproduction of oxalate and, often, nephrocalcinosis, nephrolithiasis, chronic kidney disease, and kidney failure. The purpose of the review is to provide an update on current emerging therapies for the treatment of PH1. Use of ribonucleic acid interference (RNAi) therapeutics that target the liver to block production of key enzymes along pathways that generate oxalate is a promising approach. Available evidence supports the efficacy of both Lumasiran (targeting glycolate oxidase) and Nedosiran (targeting hepatic lactate dehydrogenase (LDHa)) to reduce urinary oxalate excretion in PH1. The efficacy of alternative approaches including stiripentol (an anticonvulsant drug that also targets LDHa), lanthanum (a potential gastrointestinal oxalate binder), and Oxalobacter formigenes (a bacterium that can degrade oxalate within the gastrointestinal tract and may also increase its secretion from blood) are all also under study. Genetic editing tools including clustered regularly interspaced short palindromic repeats/Cas9 are also in preclinical study as a potential PH1 therapeutic. Novel treatments can reduce the plasma oxalate concentration and urinary oxalate excretion in PH1 patients. Thus, it is possible these approaches will reduce the need for combined kidney and liver transplantation to significantly decrease the morbidity and mortality of affected patients.

Synbiotic supplementation and oxalate homeostasis in rats: focus on microbiota oxalate-degrading activity

The present study aimed (i) to evaluate whether ceftriaxone treatment could affect not only intestinal oxalate-degrading bacteria number but also their total activity to degrade oxalate and influence oxalate homeostasis in rats, (ii) and to estimate the ability of commercially available inulin-contained synbiotic to restore fecal oxalate-degrading activity and ceftriaxone-induced disruption of oxalate homeostasis in rats. Twenty-eight female Wistar rats (200-300g) were randomly divided into four groups (n = 7). Group 1 was treated with vehicle sterile water (0.1ml, i.m., 14days); Group 2 received synbiotic (30mg/kg, per os, 14days); Group 3 was treated with ceftriaxone (300mg/kg, i.m., 7days); Group 4 was supplemented with ceftriaxone and synbiotic. Oxalate-degrading bacteria number and their total activity, urinary and plasma oxalate concentrations were measured on days 1 and 57 after the treatment withdrawal. The redoximetric titration with KMnO4 was adopted to evaluate the total oxalate-degrading activity in highly selective Oxalate Medium. Ceftriaxone treatment reduced total fecal oxalate-degrading activity independently on oxalate-degrading bacteria number and increased urinary and plasma oxalate concentrations. The synbiotic had higher oxalate-degrading activity vs probiotics and was able to restore fecal oxalate-degrading activity and significantly decrease urinary oxalate excretion in antibiotic-treated rats. Total fecal oxalate-degrading activity but not oxalate-degrading bacteria number should be thoroughly examined in the future to develop predictive diagnostics methods, targeted prevention and personalized treatment in kidney stone disease. Synbiotic supplementation had a beneficial effect on the total oxalate-degrading activity of gut microbiota, which resulted in decreased UOx excretion in rats.

Oxalobacter formigenes treatment confers protective effects in a rat model of primary hyperoxaluria by preventing renal calcium oxalate deposition.

In primary hyperoxaluria, increased hepatic oxalate production sometimes leads to severe nephrocalcinosis and early end-stage kidney disease. Oral administration of Oxalobacter formigenes (O. formigenes), an oxalate-degrading bacterium, is thought to derive oxalate from systemic sources by inducing net enteric oxalate secretion. Here, the impact of O. formigenes on nephrocalcinosis was investigated in an ethylene glycol rat model mimicking hepatic oxalate overproduction in primary hyperoxaluria. Eighteen rats were administered ethylene glycol (0.75% in drinking water) for 6weeks, of which 9 were treated by oral gavage with O. formigenes and 9 received vehicle. Five control rats did not receive ethylene glycol or O. formigenes. Plasma and urinary oxalate levels, calcium oxalate crystalluria, urinary volume, fluid intake, and serum creatinine were monitored during the study. On killing, nephrocalcinosis was quantified. Ethylene glycol intake induced pronounced hyperoxalemia, hyperoxaluria, calcium oxalate crystalluria and nephrocalcinosis. Concomitant O. formigenes treatment partially prevented the ethylene glycol-induced increase in plasma oxalate and completely prevented nephrocalcinosis. Urinary oxalate excretion was not reduced by O. formigenes treatment. Nevertheless, absence of crystals in renal tissue of O. formigenes-treated ethylene glycol animals indicates that the propensity for oxalate to crystallize in the kidneys was reduced compared to non-treated animals. This is supported by the lower plasma oxalate concentrations in O. formigenes-treated animals. This study shows a beneficial effect of O. formigenes treatment on ethylene glycol-induced hyperoxalemia and nephrocalcinosis, and thus supports a possible beneficial effect of O. formigenes in primary hyperoxaluria.

POS-432 PRIMARY HYPEROXALURIA, A TOO OFTEN MISSED DIAGNOSIS AND CAUSE OF END STAGE KIDNEY DISEASE IN ADULTS : A MONOCENTRIC TUNISIAN STUDY

Primary hyperoxaluria (PH) is a rare hereditary metabolic disorder of oxalate overproduction. Persistently high plasma oxalate concentrations lead to potential life-threatening complications. The major objective of this study is to investigate this condition which is frequent in our country but under diagnosed. In a retrospective descriptive study, we reviewed the record of 9 patients who were diagnosed with primary hyperoxaluria hospitalized at a nephrology department during the period 2001-2020. Their demographics, clinical and investigations parameters were documented. Nine patients were enrolled and followed up. Mean age of patients was 21, 2 ± 12, 3 years with predominance of male (88, 8%). Consanguinity was noted in 28, 5%. All our patients were from Tunisian center (55, 5% were from Gafsa). Renal colic and urolithiasis were the most common symptoms in our study (100%). Ultrasonography and CT scans showed nephrocalcinosis in 5 cases (55, 55%). Urinary tract infections were observed in 2 cases (22, 2%). Renal failure was noted in almost all cases; serum creatinine level ranged from 144 to 986 µmol/L. Seven patients reached end-stage renal disease and were treated with hemodialysis at a median age of 23 years. The extra renal manifestations were bone impairment (4 cases), bone marrow fibrosis (2 cases), cardiac dysfunction (1case), digestive wall calcifications (1 case) and adrenal insufficiency (1 case). The diagnosis was based on Hyperoxaluria (1 case), positive crystalluria (1 case), kidney stone analysis (2 cases) and oxalate crystal deposition identified in both renal and bone marrow biopsy respectively in one and four cases. Mutational analysis of AGXT gene was carried out in five out of nine patients. We identified a novel frameshift mutation in the AGXT gene, the c.406_410dupACTGC resulting in a truncated protein (p.Gln137Hisfs*19). It was found in homozygous state in two related patients from the Tunisian center. Primary hyperoxaluria is not rare in the Tunisian population. In our study it was lately diagnosed in most cases. Awareness campaign to change attitude of family members to screening should be conducted.

Oxalate Balance in Peritoneal Dialysis Patients: A Potential Role of Dialysis-related Peritonitis.

Little evidence is available on oxalate balance in peritoneal dialysis (PD) patients. We performed a cross-sectional observational pilot study with 62 adult PD patients to document oxalate balance and explore its association with PD-related peritonitis. Plasma oxalate concentration, levels of oxalate excretion in 24-h urine, and peritoneal dialysis effluent were evaluated. The peritoneal oxalate transport status and renal and peritoneal oxalate clearances were calculated according to the PD-related peritonitis history. PD patients with a history of peritonitis had a statistically significantly lower peritoneal oxalate clearance, daily peritoneal oxalate excretion, and overall oxalate removal rate compared with the peritonitis-free PD patients. They had a 4-fold risk of plasma oxalic acid increase, and even a single episode of dialysis-related peritonitis resulted in plasma oxalate elevation. Peritoneal oxalate clearance plays an important role in oxalate balance in PD patients and, therefore, dialysis-related peritonitis is a significant predictor for hyperoxalemia. Further well-designed clinical trials need to be undertaken before the association between peritonitis and oxalate balance in PD patients is more clearly understood.

MO692COULD THE RESIDUAL RENAL FUNCTION REMAIN A KEY DETERMINANT OF PLASMA OXALIC ACID CONCENTRATION IN PERITONEAL DIALYSIS PATIENTS?

Abstract Background and Aims Under physiological conditions, the bulk of circulating oxalate (90% to 95%) is ultimately excreted by the kidneys. Under uremic and/or anuric conditions, dialysis is considered to be the main method of oxalate removal. Nevertheless, little evidence is available on oxalate balance in peritoneal dialysis (PD) patients. The present study aimed to evaluate the separate contribution of residual renal and peritoneal oxalate clearances to oxalate balance in PD patients. Method We performed a cross-sectional observational study involving 62 PD patients with the average age of 50.5±13.5 years and PD vintage of 37±24 months. Plasma oxalate (POx) concentration, levels of daily urinary (UOx) and peritoneal dialysis effluent oxalate (PDEOx) excretion were evaluated. POx concentration was measured spectrophotometrically using MAK315 kit (Sigma, Spain); UOx and PDEOx concentrations were determined using an oxalate oxidase/peroxidase reagent (BioSystems, Spain). In addition, oxalate transport status (4-hour D/P oxalate ratio), renal oxalate clearance (ROxCL) and peritoneal oxalate clearance (PerOxCL) were calculated. Results Among the examined PD patients were 41 (66%) patients with preserved diuresis and 21 (34%) patients with anuria. The anuric PD patients had lower PerOxCL and, accordingly, peritoneal and overall oxalate removal levels compared with the patients with preserved diuresis (Table 1). Conclusion The results of our research demonstrated an important role of the residual renal function in oxalate balance in PD patients. However, the decline in RRF could partially (but not completely) contribute to the increase in POx in PD patients. Thus, PerOxCL but not ROxCL could significantly affect oxalate balance in PD patients.

Crosstalk between proteinuria, plasma oxalic acid and inflammation in glomerulonephritis patients: an exploratory study

Abstract. In the present exploratory cross-sectional cohort study, we evaluated whether plasma and urine oxalate concentrations in patients with primary glomerulonephritis depend not only on the glomerular filtration rate but also on the proteinuria level and influence the inflammatory response.&#x0D; Methods. We enrolled 100 participants, including 76 patients with glomerulonephritis having chronic kidney disease stage (CKD) 1–3b (69.7% of them with nephrotic syndrome) and 24 healthy volunteers. We excluded patients with diabetes, cardiovascular disease and those with glomerulonephritis with an estimated GFR (eGFR) &lt; 30 mL/min/1.73 m2. In addition to routine hematological and biochemical tests, plasma oxalate concentration, urinary oxalate excretion, and serum interleukin (IL)-6 and monocyte chemoattractant protein-1 (MCP-1) levels were assessed in all study participants.&#x0D; Results. We observed that plasma oxalic acid concentration was significantly higher in patients with glomerulonephritis (19.0 [5.9–45.2] µmol/L) than in healthy volunteers (5.5 [3.8–7.3] µmol/L, p &lt; 0.0001). Moreover, nephrotic proteinuria was significantly associated with plasma oxalic acid elevation independent of the patients’ age, sex, glomerular filtration rate, and body mass index (odds ratio = 1.42, 95% confidence interval = 1.13–1.77, p = 0.002). In turn, the increased plasma oxalic acid concentration was associated with high levels of serum IL-6 and MCP-1, which may be cardiovascular risk factors in patients with primary glomerulonephritis.&#x0D; Conclusions. Nephrotic proteinuria was significantly associated with the elevation of plasma oxalic acid concentration and hyperoxaluria in glomerulonephritis patients with CKD stages 1–3b. Plasma oxalate at least partly promotes inflammation, which may be a cardiovascular risk factor in patients with glomerulonephritis in the early stages of CKD. Future studies should recruit at least 156 participants to confirm our preliminary results, validate nephrotic proteinuria as a risk factor for oxalate metabolism violation or determine the role of impaired oxalate homeostasis in clinical outcomes in patients with glomerulonephritis.

Assessment of Plasma Oxalate Concentration in Patients With CKD

IntroductionAlterations in oxalate homeostasis are associated with kidney stone disease and progression of chronic kidney disease (CKD). However, accurate measurement of plasma oxalate (POx) concentrations in large patient cohorts is challenging as prompt acidification of samples has been deemed necessary. In the present study, we investigated the effects of variations in sample handling on POx results and examined an alternative strategy to the established preanalytical procedures.MethodsThe effect of storage time at room temperature (RT) and maintenance of samples at −80°C was tested. POx was measured in 1826 patients enrolled in the German Chronic Kidney Disease (GCKD) study, an ongoing multicenter, prospective, observational cohort study.ResultsWe demonstrate that POx concentrations increased rapidly when samples were maintained at RT. This was most relevant for POx <10 μM, as concentrations more than doubled within a few hours. Immediate freezing on dry ice and storage at −80°C provided stable results and allowed postponement of acidification for >1 year. In the patients of the lowest estimated glomerular filtration rate (eGFR) quartile, median POx was 2.7 μM (interquartile range [IQR] <2.0–4.2) with a median eGFR of 25.1 ml/min per 1.73 m2 (IQR 20.3–28.1).ConclusionWe conclude that immediate freezing and maintenance of plasma samples at -80°C facilitates the sample collection process and allows accurate POx assessment in large cohorts. The present study may serve as a reference for sample handling to assess POx in clinical trials and to determine its role in CKD progression.

Enteric Oxalate Secretion Mediated by Slc26a6 Defends against Hyperoxalemia in Murine Models of Chronic Kidney Disease.

A state of oxalate homeostasis is maintained in patients with healthy kidney function. However, as GFR declines, plasma oxalate (Pox) concentrations start to rise. Several groups of researchers have described augmentation of oxalate secretion in the colon in models of CKD, but the oxalate transporters remain unidentified. The oxalate transporter Slc26a6 is a candidate for contributing to the extrarenal clearance of oxalate via the gut in CKD. Feeding a diet high in soluble oxalate or weekly injections of aristolochic acid induced CKD in age- and sex-matched wild-type and Slc26a6-/- mice. qPCR, immunohistochemistry, and western blot analysis assessed intestinal Slc26a6 expression. An oxalate oxidase assay measured fecal and Pox concentrations. Fecal oxalate excretion was enhanced in wild-type mice with CKD. This increase was abrogated in Slc26a6-/- mice associated with a significant elevation in plasma oxalate concentration. Slc26a6 mRNA and protein expression were greatly increased in the intestine of mice with CKD. Raising Pox without inducing kidney injury did not alter intestinal Slc26a6 expression, suggesting that changes associated with CKD regulate transporter expression rather than elevations in Pox. Slc26a6-mediated enteric oxalate secretion is critical in decreasing the body burden of oxalate in murine CKD models. Future studies are needed to address whether similar mechanisms contribute to intestinal oxalate elimination in humans to enhance extrarenal oxalate clearance.

SO011OXALATE-DEGRADING ACTIVITY IN FECAL MICROBIOTA ASSOCIATED WITH BLOOD LIPID PROFILE IN DIALYSIS PATIENTS

Abstract Background and Aims Cardiovascular disease (CVD) remains the leading cause of morbidity and death in end-stage renal disease (ESRD) patients. Thus, the accumulation of oxalate due to ESRD can increase the risk of CVD. Also, the ability of fecal oxalate-degrading activity (ODA) to reduce plasma oxalate levels has been discussed. On the other hand, despite a key role of atherogenic dyslipidemia in the development of CVD, only a few studies have shown a potential role of microbiota in the regulation of blood lipid profiles in the general population. However, at present, there is a general lack of research on this topic in dialysis patients. The present study aimed to investigate the association between oxalate-degrading activity (ODA) in fecal microbiota and blood lipid profiles in ESRD patients. Method We represented the data of a cross-sectional pilot study examining ODA in fecal microbiota, plasma oxalate concentration (POx) and blood lipid profile markers in 32 ESRD patients. Among the patients, there were 21 hemodialysis (HD) patients and 11 peritoneal dialysis (PD) patients. The average age of the patients was 52.5 [39; 65] years. The redoximetric titration with KMnO4 was adopted to evaluate total ODA in fecal microbiota. The results were expressed in % oxalate degradation per 0.01 g of feces. The blood lipid spectrum was determined in all patients: total cholesterol level (TC), high (HDL), low (LDL) and very low (VLDL) density cholesterol, triglycerides (TG) and atherogenic index of plasma (AIP). The median (Me) and interquartile ranges [Q25; Q75] were calculated using the nonparametric Kruskal-Wallis test. The Spearman test was used for the correlation analysis. Chi-square tests were used for comparison of 2 proportions. All statistical analyses were performed using MedCalc. Results Dyslipidemia defined as an increase in atherogenic lipoprotein fractions and inhibition of HDL cholesterol was identified in 13/32 (40.6%) ESRD patients. Negative ODA in fecal microbiota (≤ 0 % /0.01 g) was observed in 14/32 (43.7%) patients. Among them, there were 5/21 (23.8%) HD patients and 7/11 (63.6%) PD patients (χ2=3.9, p=0.04). Significantly lower ODA in fecal microbiota was observed in the patients with atherogenic dyslipidemia in comparison with dyslipidemia-free patients (-5.0 [-8.7; 3.7] vs 3.0 [0.5; 9] %/0.01 g of feces, p=0.02) (Fig. 1). Less ODA in fecal microbiota was, higher levels of TG (r=-0.5, p=0.004) (Fig. 2), VLDL (r=-0.34, p=0.05) (Fig. 3) and, accordingly, AIP (r=-0.38, p=0.03) (Fig. 4) occurred. Conclusion The results of our study have provided preliminary evidence on the fact that a decrease in total ODA in fecal microbiota is associated with atherogenic dyslipidemia. Further studies are needed to determine the role of fecal ODA in the formation of dyslipidemia.

P0176REGULATION OF OXALATE HOMEOSTASIS BY OXALATE-DEGRADING ACTIVITY IN FECAL MICROBIOTA IN DIALYSIS PATIENTS

Abstract Background and Aims Despite evidence suggesting that a lack of fecal oxalate-degrading bacteria colonization is a risk factor for calcium oxalate stone formation, little is known about the oxalate-degrading activity (ODA) in fecal microbiota in end-stage renal disease (ESRD) patients. In addition, to date, there has been a general lack of research on the effect of fecal ODA on oxalate homeostasis in dialysis patients. The present pilot cross-sectional study was performed to compare the oxalate homeostasis profiles depending on ODA in fecal microbiota in ESRD patients. Method The data of a cross-sectional pilot study examining ODA in fecal microbiota, plasma oxalate concentration (POx) and urinary oxalate excretion (UOx) in 32 ESRD patients were represented in this study. Among the patients, there were 21 hemodialysis (HD) patients and 11 peritoneal dialysis (PD) patients. The average age of the patients was 52.5 [39; 65] years. The redoximetric titration with KMnO4 was adopted to evaluate total ODA in fecal microbiota. The results were expressed in % oxalate degradation per 0.01 g of feces. POx concentration and UOx excretion were measured spectrophotometrically using a commercially available kit (MAK-315, Sigma, Spain) and an oxalate oxidase/peroxidase reagent (BioSystems, Spain), respectively. Predialysis plasma samples were collected from HD patients. For further analysis, the patients were allocated to 2 groups according to ODA in feces. Group 1 included the patients with ≥ 1 % oxalate degradation per 0.01 g of feces. Group 2 included the patients with negative ODA (≤ 0 % /0.01 g). For the statistical analysis, we used the nonparametric Kruskal-Wallis test. The median (Me) and interquartile ranges [Q25; Q75] were calculated. The Spearman test was used for the correlation analysis. Univariate logistic regression analysis was used for predicting hyperoxalemia. All statistical analyses were performed using MedCalc. Results ODA in fecal microbiota ranged from -23 to 24 %/0.01 g of feces in ESRD patients and was statistically higher in HD patients compared with PD patients (3.2 [-0.5; 16] vs -4 [-6.5; 6.2], p=0.05). Negative ODA in fecal microbiota (≤ 0 % /0.01 g) was observed in 5/21 (23.8%) HD patients and 7/11 (63.6%) PD patients (χ2=3.9, p=0.04). Consequently, it might be associated with the negative effects of peritoneal dialysis solution. High POx concentration and low UOx excretion were diagnosed in patients with negative ODA in fecal microbiota (Group 2): 30.7 [25.5; 41.5] vs 50 [43.3; 75.5] μmol/L, p=0.01 and 60.9 [51; 65] vs 34.2 [24.4; 39] mg/d, p=0.0002, respectively (Fig. 1). Fecal ODA was directly associated with daily UOx excretion (r=0.85; p&amp;lt;0.0001) (Fig. 2) and had an inverse correlation with POx concentration (r=-0.36; p=0.04) (Fig. 3). In univariate logistic regression analysis, negative fecal ODA was determined as an independent risk factor for high POx concentration (OR: 40; 95% CI: 4.8-331, p&amp;lt;0.0001). Conclusion Our pilot cross-sectional study firstly demonstrated a close association between ODA in fecal microbiota and oxalate homeostasis in ESRD patients: less ODA in fecal microbiota was, higher POx concentration and lower UOx excretion occurred. We suppose that the potential significance of our findings provides preliminary information on the feasibility and necessity of further research in this area.

Plasma oxalate: comparison of methodologies

Measurement of oxalate in the blood is essential for monitoring primary hyperoxaluria patients with progressive renal impairment and on dialysis prior to transplantation. As no external quality assurance scheme is available for this analyte, we conducted a sample exchange scheme between six laboratories specifically involved with the investigation of primary hyperoxaluria to compare results. The methodologies compared were gas chromatography/mass spectrometry (GCMS), ion chromatography with mass spectrometry (ICMS), and enzymatic methods using oxalate oxidase and spectrophotometry. Although individual laboratories performed well in terms of reproducibility and linearity, there was poor agreement (absolute values) between centres as illustrated by a longer-term comparison of patient results from two of the participating laboratories. This situation was only partly related to differences in calibration and mainly reflected the lower recoveries seen with the ultrafiltration of samples. These findings lead us to conclude that longitudinal monitoring of primary hyperoxaluria patients with deteriorating kidney function should be performed by a single consistent laboratory and the methodology used should always be defined. In addition, plasma oxalate concentrations reported in registry studies and those associated with the risk of systemic oxalosis in published studies need to be interpreted in light of the methodology used. A reference method and external quality assurance scheme for plasma oxalate analysis would be beneficial.