Gut Microbiota's Oxalate-Degrading Activity and Its Implications on Cardiovascular Health in Patients with Kidney Failure: A Pilot Prospective Study

Background and Objectives: The present study aims to investigate the association between gut microbiota's oxalate-degrading activity (ODA) and the risk of developing cardiovascular disease (CVD) over a three-year follow-up period in a cohort of patients undergoing kidney replacement therapy (KRT). Additionally, various factors were examined to gain insight into the potential mechanisms underlying the ODA-CVD link. Materials and Methods: A cohort of 32 KRT patients and 18 healthy volunteers was enrolled in this prospective observational pilot study. Total fecal ODA, routine clinical data, plasma oxalic acid (POx), serum indoxyl sulfate, lipid profile, oxidative stress, and proinflammatory markers were measured, and the patients were followed up for three years to assess CVD events. Results: The results revealed that patients with kidney failure exhibited significantly lower total fecal ODA levels compared to the healthy control group (p = 0.017), with a higher proportion showing negative ODA status (≤-1% per 0.01 g) (p = 0.01). Negative total fecal ODA status was associated with a significantly higher risk of CVD events during the three-year follow-up period (HR = 4.1, 95% CI 1.4-16.3, p = 0.003), even after adjusting for potential confounders. Negative total fecal ODA status was significantly associated with elevated POx and indoxyl sulfate levels and linked to dyslipidemia, increased oxidative stress, and inflammation, which are critical contributors to CVD. Conclusions: The findings contribute novel insights into the relationship between gut microbiota's ODA and cardiovascular health in patients undergoing KRT, emphasizing the need for further research to elucidate underlying mechanisms and explore potential therapeutic implications of targeting gut microbiota's ODA in this vulnerable population.

Pre-existing serum indoxyl sulfate and COVID-19 outcomes in patients undergoing hemodialysis: A retrospective cohort study

Patients undergoing hemodialysis (HD) are at increased risk of severe complications from COVID-19 due to compromised immune function and comorbidities. This retrospective study aimed to investigate the association between pre-existing serum indoxyl sulfate (IS) concentrations and COVID-19 outcomes in HD patients. Methods. Data on pre-existing IS and proinflammatory cytokines, such as interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factor-alpha (TNF-α) were extracted from an existing patient database. The patients were followed up for 1.5 years and compared according to median serum IS concentration: low-IS (< 22.2 μg/mL) and high-IS (≥22.2 μg/mL) groups. The primary outcomes focused on assessing the risk and severity of COVID-19 infection. Results. A total of 56 patients aged 62 (56-67) years with a dialysis vintage of 37.5 (30-168) months were included in the analysis. Serum levels of IS were significantly correlated with Kt/V values (p = 0.043), arterial hypertension (p = 0.001), IL-6 (p = 0.023), MCP-1 (p = 0.023), and TNF-α (p = 0.033) concentrations. Elevated serum IS levels were significantly associated with an increased risk of COVID-19 infection (p < 0.0001) and a higher likelihood of hospitalization (p = 0.03). Patients with higher IS levels exhibited more severe lung involvement (p < 0.0001) and a greater need for respiratory support (p = 0.004). A serum IS concentration of 21.5 μg/mL was the optimal threshold for predicting COVID-19 infection in HD patients (sensitivity of 83.4% and specificity of 92.3%, p < 0.0001). Conclusion: Our study highlights the detrimental impact of serum IS on COVID-19 infection and its clinical outcomes in patients undergoing HD. Further research is warranted to elucidate the underlying mechanisms and explore potential therapeutic strategies targeting IS in this population.

Pilot testing for long-term impact of glycerol-induced acute kidney injury on oxalate homeostasis in rats

Abstract. There is a general lack of research on the long-term effects of acute kidney injury (AKI) on oxalate-degrading bacteria (ODB) and their total oxalate-degrading activity (ODA) in fecal microbiota. In the present pilot study, we separately evaluated the changes in the ODB number and their total ODA in fecal microbiota at 3-time points after glycerol-induced AKI. In addition, we assessed the interactions between AKI-induced renal histopathological changes and ODB, total fecal ODA, and plasma and urine oxalate concentrations in rats. Methods. The male Wistar rats (200-300 g, n = 20) on oxalate-free diet were randomly divided into 2 groups. After 24-h of water deprivation, experimental group 1 (n = 10) received an intramuscular injection of 50% glycerol (10 ml/kg of body weight), and group 2 (n = 10) served as a control. The numbers of ODB (incubated in a highly selective Oxalate Medium and determined using the culture method), total fecal ODA and urinary oxalate (UOx) excretion were measured after injection on days 8, 22 and 70. The method of redoximetric titration with a KMnO4 solution was adopted to evaluate total ODA in fecal microbiota. Renal injury was assessed by histopathology examination, serum creatinine plasma oxalic acid (POx) concentration and daily proteinuria levels after removing the animals from the experiment on day 70. Results. After glycerol injection on days 8 and 22, no differences were found in the numbers of ODB, their total fecal ODA, and UOx excretion level between the experimental and control groups. However, after AKI initiation on day 70, the numbers of ODB, total fecal ODA, and daily UOx excretion were significantly lower in the experimental group as compared with the control group. In addition, in 10 weeks following AKI, the number of ODB had a direct correlation with UOx excretion and an inverse correlation with POx and serum creatinine concentrations and daily proteinuria. Total ODA in fecal microbiota was directly associated with the percentage of renal interstitial fibrosis and the average glomerular volumes in the experimental rats. Conclusions: AKI had long-term negative effects on the quantitative and qualitative characteristics of ODB in fecal microbiota in rats. Moreover, the results of our study confirmed an increasing trend in total fecal ODA according to the aggravation of renal interstitial fibrosis and glomerular volume in rats’ kidneys. Further studies are warranted to gain more insight into the mechanism of oxalate homeostasis impairment in AKI.

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

BACKGROUND

Little evidence is available on oxalate balance in peritoneal dialysis (PD) patients.

PATIENTS AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

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 (200-300 g) were randomly divided into four groups (n = 7). Group 1 was treated with vehicle sterile water (0.1 ml, i.m., 14 days); Group 2 received synbiotic (30 mg/kg, per os, 14 days); Group 3 was treated with ceftriaxone (300 mg/kg, i.m., 7 days); 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.

FC 044THE LONG-TERM EFFECTS OF ACUTE KIDNEY INJURY ON INTESTINAL OXALATE-DEGRADING BACTERIA IN RATS

Background and Aims

Gut microbiota is considered an important factor affecting oxalate handling in the intestine. It has been demonstrated that intestinal oxalate secretion provides a complementary route of excretion, and it becomes more evident when kidney function declines. A diversity of gut oxalate-degrading bacteria (ODB) has been hypothesized to play a role in this process. However, there is a general lack of research on the long-term effects of acute kidney injury (AKI) on ODB and their total oxalate-degrading activity (ODA) in fecal microbiota. In this study, we evaluated whether renal dysfunction could affect intestinal ODB and their total ODA in a rat model of glycerol-induced AKI.

Method

The Male Wistar rats (200-300 g, n=20) on oxalate-free diet were randomly divided into 2 groups. After 24-h of water deprivation, Group 1 (n=10) received an intramuscular injection of 50% glycerol (10 ml/kg of body weight), and Group 2 (n=10) served as control. The numbers of ODB (incubated in a highly selective Oxalate Medium and determined using culture method) and total fecal ODA were measured after injection on days 7 and 70. The method of redoximetric titration with a KMnO4 solution was adopted to evaluate total ODA in fecal microbiota; the results were expressed as % of oxalate degradation per 0.01 g of feces.

Renal injury was assessed by histopathological examination, serum creatinine and daily proteinuria levels after removing the animals from the experiment on day 70. Cortical interstitial fibrosis was measured by computerized image analysis on sections stained with picrosirius red. The median (Me) and the interquartile ranges (Q25; Q75) were calculated and compared using the nonparametric Mann-Whitney test. The Spearman correlation coefficient was used to evaluate association between the examined parameters.

Results

The obtained results demonstrated: 1) after glycerol injection on day 7, no differences were found in the numbers of ODB and total fecal ODA between the experimental and control groups: 5.9 (5.4-6.0) vs 6.0 (5.4-6.4) CFU/g, p=0.65 and 2.0 (0.1-5.0) vs 2.5 (2.0-9.0) %/0.01g, p=0.24, respectively; 2) after AKI initiation on day 70, the numbers of ODB and total fecal ODA were significantly lower in Group I compared with control Group II (Fig. 1); 3) the higher percentage of renal interstitial fibrosis was, the higher total fecal ODA occurred in the experimental rats (Fig. 2). In addition, the number of ODB in feces in Group 1 had an inverse association with serum creatinine (r=-0.52, p=0.006) and 24-h proteinuria levels (r=-0.86, p&lt;0.0001).

Conclusion

AKI had the long-term negative effects on the quantitative and qualitative characteristics of ODB in fecal microbiota in rats. Moreover, the results of our study confirmed an increasing trend in total fecal ODA according to the aggravation of renal interstitial fibrosis in rats.

MO311THE ASSOCIATION BETWEEN NEPHROTIC-RANGE PROTEINURIA AND OXALATE METABOLISM VIOLATION IN PATIENTS WITH PRIMARY GLOMERULONEPHRITIS

Background and Aims

There is a general lack of scientific research on oxalate metabolism in primary glomerulonephritis (PGN) patients. The present study aimed to evaluate plasma oxalic acid (POx) concentration and urinary oxalate (UOx) excretion in PGN patients and determine the role of nephrotic syndrome in oxalate metabolism, which has never before been reported.

Method

A total of 100 participants were enrolled in this cross-sectional single-center study, including 76 PGN patients aged 41 ± 1.83 years and 24 healthy volunteers on a free-choice diet who served as a control reference group to evaluate POx concentration. Among the patients were 53 (69.7 %) patients with nephrotic syndrome (NS) and biopsy-proven PGN and 23 (30.3 %) patients with a clinical diagnosis of PGN. All patients were treated according to KDIGO Clinical Practice Guidelines for Glomerulonephritis.

In addition to routine hematological and biochemical tests, POx concentration and UOx excretion were found in all study participants. POx was measured spectrophotometrically using a commercially available kit (MAK315, Sigma, Spain). Daily UOx excretion was determined using an oxalate oxidase/peroxidase reagent (BioSystems, Spain). Urine protein excretion (UPE) was measured in a 24-h urine collection. The glomerular filtration rate (GFR) was calculated using the CKD-EPI formula.

The data were presented as the median and the interquartile ranges [Me (Q25-Q75)] and compared using the Mann-Whitney test. The Spearman correlation test and the partial correlation coefficient were used to evaluate the association between the examined markers.

Results

POx concentration was significantly higher in the patients with PGN compared with the healthy volunteers: 29.9 (14.9-51.7) vs 18.9 (16.2-23.8) µmol/L, p = 0.01. Although the patients with NS demonstrated a statistically higher GFR level compared with the patients with mild proteinuria [70.5 (47-87) vs 50 (22-76.2) mL/min/1.73 m2, p = 0.01], these patients also had the highest POx level (Fig. 1). Moreover, POx concentration was significantly associated with GFR (r = -0.27, p = 0.005), serum phosphate (r = 0.26, p = 0.007) and UPE (Fig. 2) levels. No significant differences were found in UOx excretions between the groups. However, the higher level of UPE was, the higher level of UOx was observed in the PGN patients with NS (Fig. 3). The partial correlation analysis confirmed a strong association between UPE and POx concentration independently of the patients’ age, gender, GFR and serum phosphate levels (r = 0.22, p = 0.04).

Conclusion

Nephrotic-range proteinuria was significantly associated with the elevation of POx concentration and UOx excretion in the PGN patients. More research with a larger cohort is needed to confirm this preliminary evidence and validate NS as a risk factor for oxalate metabolism violation in PGN patients.

Serum uric acid and renal survival prognosis in primary glomerulonephritis patients in a retrospective single-center cohort

Introduction: The role of serum uric acid (SUA) concentration in primary glomerulonephritis (PGN) aggravation is currently under active discussion. Objectives: This study primarily aimed to analyze the association between SUA concentration and renal survival prognosis in PGN patients and secondarily to determine whether hyperuricemia is an independent risk factor for reduced glomerular filtration rate (GFR) in the presence of nephrotic syndrome. Patients and Methods: We performed a retrospective observational single-center study involving 344 patients with biopsy-proved or clinically diagnosed PGN with the mean follow-up period of 5.3 [3.8-6.2] years. The rate of annual decline in estimated GFR (eGFR) was used to assess chronic kidney disease progression. Primary outcome measures were eGFR decline or transfer to renal replacement therapy (RRT) during the 5-year follow-up period. Results: There were 78/344 (22.7%) patients who eventually progressed to eGFR <15 mL/min/1.73 m2 or started RRT. In multivariate logistic regression analysis eGFR at diagnosis, proteinuria and hyperuricemia were associated with increased renal risk in PGN patients during the 5-year follow-up period. However, a less significant effect of SUA on rapid eGFR decline was found in the patients with nephrotic-range proteinuria compared with the patients with mild proteinuria. Conclusion: Our study revealed that a higher level of SUA was significantly associated with a greater annual decline in GFR and, consequently, a worse 5-year renal survival prognosis in PGN patients. The effect of hyperuricemia on the risk of rapid CKD progression was greater in PGN patients with mild proteinuria compared with the patients with nephrotic-range proteinuria.

Dyslipidemia and Intraperitoneal Inflammation Axis in Peritoneal Dialysis Patients: A Cross-Sectional Pilot Study

Background

We have hypothesized that the problem of dyslipidemia in peritoneal dialysis (PD) patients lies beyond certain levels of plasma lipoprotein and involves cardiovascular risk, but can also influence the development of chronic intraperitoneal inflammation.

Objectives

The aim of our work was to define whether the association of dyslipidemia with intraperitoneal inflammation really exists and if it could it be used in a prospective cohort of PD patients.

Patients and Methods

We performed a cross-sectional, single-center, pilot study involving 40 nondiabetic PD patients (27 men and 13 women with an average age of 49.3 ± 12.2 years). The median time on PD was 29 (18.5-37) months. The parameters dialysis adequacy, blood lipid profile, and the concentrations of tumor necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP)-1, and interleukin (IL)-10 in peritoneal dialysate effluent (PDE) were determined. Cohen's d effect size was computed post hoc to determine the differences between groups in the concentrations of pro- and anti-inflammatory mediators.

Results

PD patients with atherogenic dyslipidemia had significantly high levels of MCP-1 compared with dyslipidemia-free patients (Cohen's d = 1.32). A reduced high-density lipoprotein cholesterol level was associated with a high intraperitoneal production of the proinflammatory mediator TNF-α (p < 0.0001) and anti-inflammatory IL-10 (p < 0.0001). Atherogenic index of plasma was directly correlated with MCP-1 (p < 0.0001) and TNF-α (p < 0.0001). In multiple regression analysis, MCP-1 appeared to predict PD inadequacy (R ² = 0.58; F ratio = 9.4; p = 0.006) independently of age and blood C-reactive protein level. Effect size was 1.38 with α = 0.05, n = 40, and 3 predictors.

Conclusions

Our cross-sectional pilot study first demonstrated a close interaction between the atherogenic lipid profile and a high concentration of MCP-1 in PDE; this might be a prognostic marker for PD inadequacy. The potential significance of our finding is that it provides useful preliminary information necessary for further research into this area.