Serum total indoxyl sulfate levels and all-cause and cardiovascular mortality in maintenance hemodialysis patients: a prospective cohort study

The Prognostic Role of Serum β-Trace Protein Levels among Patients on Maintenance Hemodialysis

Cardiovascular (CV) diseases are the most commonly encountered etiology of mortality in patients having kidney failure. β-Trace protein (BTP) is a biomarker of glomerular filtration function as well as a potential predictor of adverse CV outcomes. This study aimed to determine the prognostic value of BTP in patients on chronic hemodialysis (HD). A total of 96 patients undergoing HD were enrolled. Baseline variables were collected, and the patients were tracked for 3 years. Twenty-five patients died at 3 years. Those who experienced mortality were noted to have higher serum concentrations of BTP and a higher incidence of diabetes mellitus (DM). The area under the receiver operating characteristic curve for serum BTP distinguishing mortality from survival was 0.659 (95% confidence interval [CI], 0.555-0.752; p = 0.027). After the adjustment of variables potentially affecting survival rates, BTP levels above the median (adjusted hazard ratio [aHR]: 2.913, 95% CI, 1.256-6.754; p = 0.013), the presence of DM (aHR: 2.474, 95% CI, 1.041-5.875; p = 0.040), and low serum albumin (aHR: 0.298, 95% CI, 0.110-0.806; p = 0.017) independently correlated with survival in HD patients. Serum BTP is a novel biomarker for predicting overall outcomes in HD patients.

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.

Preventive Action of Beta-Carotene against the Indoxyl Sulfate-Induced Renal Dysfunction in Male Adult Zebrafish via Regulations of Mitochondrial Inflammatory and β-Carotene Oxygenase-2 Actions

Indoxyl sulfate (IS) is a metabolic byproduct of indole metabolism. IS readily interacts with the mitochondrial redox metabolism, leading to altered renal function. The β-carotene oxygenase-2 (BCO2) enzyme converts carotenoids to intermediate products. However, the role of β-carotene (BC) in IS-induced renal dysfunction in zebrafish and their modulatory action on BCO2 and mitochondrial inflammations have not been explored yet. Hence, the present study is designed to investigate the role of BC in the attenuation of IS-induced renal dysfunction via regulations of mitochondrial redox balance by BCO2 actions. Renal dysfunction was induced by exposure to IS (10 mg/L/hour/day) for 4 weeks. BC (50 and 100 mg/L/hour/day) and coenzyme Q10 (CoQ10; 20 mg/L/hour/day) were added before IS exposure. BC attenuated the IS-induced increase in blood urea nitrogen (BUN) and creatinine concentrations, adenosine triphosphate (ATP), and complex I activity levels, and the reduction of renal mitochondrial biomarkers, i.e., BCO2, superoxide dismutase-2 (SOD2), glutathione peroxidase-1 (GPX1), reduced and oxidized glutathione (GSH/GSSG) ratio, and carbonylated proteins. Moreover, renal histopathological changes were analyzed by the eosin and hematoxylin staining method. As a result, the administration of BC attenuated the IS-induced renal damage via the regulation of mitochondrial function.

Gut Microbiome and Microbiome-Derived Metabolites in Patients with End-Stage Kidney Disease

The composition of the gut microbiome is altered in patients with chronic kidney disease (CKD). Dysbiosis leads to decreased levels of stool organic acids (OAs) and systemic inflammation, followed by accumulation of uremic toxins (UTs) and the development of end-stage kidney disease (ESKD). We assessed the relationship between the microbiome and UT levels or the development of ESKD by comparing patients undergoing hemodialysis (HD) and those with normal renal function (NRF). This cross-sectional study recruited 41 patients undergoing HD and 38 sex- and age-matched patients with NRF, and gut microbiome, levels of plasma UTs, inflammatory markers, and stool OAs were compared. The indices of beta-diversity differed significantly between patients with NRF and those undergoing HD, and between patients undergoing HD with and without type 2 diabetes. The levels of stool total OA, inflammatory markers, and UTs differed significantly between the patients with NRF and those undergoing HD. The combined main effects of type 2 diabetes and kidney function status were accumulation of indoxyl sulfate and p-cresyl sulfate. The relative abundances of Negativicutes and Megamonas were associated with development of ESKD and with the levels of UTs, even after adjustment for factors associated with the progression of ESKD. The present study indicates that the gut environment differs between patients with NRF and those undergoing HD and between patients undergoing HD with and without type 2 diabetes. Moreover, ESKD patients with diabetes accumulate more UTs derived from the gut microbiome, which might be associated with cardio-renal diseases and poor prognosis.

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.

Gut-Derived Uremic Toxins in CKD: An Improved Approach for the Evaluation of Serum Indoxyl Sulfate in Clinical Practice

In the past years, indoxyl sulfate has been strongly implicated in kidney disease progression and contributed to cardiovascular morbidity. Moreover, as a result of its elevated albumin affinity rate, indoxyl sulfate is not adequately cleared by extracorporeal therapies. Within this scenario, although LC-MS/MS represents the conventional approach for IS quantification, it requires dedicated equipment and expert skills and does not allow real-time analysis. In this pilot study, we implemented a fast and simple technology designed to determine serum indoxyl sulfate levels that can be integrated into clinical practice. Indoxyl sulfate was detected at the time of enrollment by Tandem MS from 25 HD patients and 20 healthy volunteers. Next, we used a derivatization reaction to transform the serum indoxyl sulfate into Indigo blue. Thanks to the spectral shift to blue, its quantity was measured by the colorimetric assay at a wavelength of 420-450 nm. The spectrophotometric analysis was able to discriminate the levels of IS between healthy subjects and HD patients corresponding to the LC-MS/MS. In addition, we found a strong linear relationship between indoxyl sulfate levels and Indigo levels between the two methods (Tandem MS and spectrophotometry). This innovative method in the assessment of gut-derived indoxyl sulfate could represent a valid tool for clinicians to monitor CKD progression and dialysis efficacy.