Levels Of Uremic Toxins Research Articles

Gut Microbiota and Their Derived Metabolites, a Search for Potential Targets to Limit Accumulation of Protein-Bound Uremic Toxins in Chronic Kidney Disease.

Chronic kidney disease (CKD) is characterized by gut dysbiosis with a decrease in short-chain fatty acid (SCFA)-producing bacteria. Levels of protein-bound uremic toxins (PBUTs) and post-translational modifications (PTMs) of albumin increase with CKD, both risk factors for cardiovascular morbidity and mortality. The relationship between fecal metabolites and plasma concentrations of PBUTs in different stages of CKD (n = 103) was explored. Estimated GFR tends to correlate with fecal butyric acid (BA) concentrations (rs = 0.212; p = 0.032), which, in its turn, correlates with the abundance of SCFA-producing bacteria. Specific SCFAs correlate with concentrations of PBUT precursors in feces. Fecal levels of p-cresol correlate with its derived plasma UTs (p-cresyl sulfate: rs = 0.342, p < 0.001; p-cresyl glucuronide: rs = 0.268, p = 0.006), whereas an association was found between fecal and plasma levels of indole acetic acid (rs = 0.306; p = 0.002). Finally, the albumin symmetry factor correlates positively with eGFR (rs = 0.274; p = 0.005). The decreased abundance of SCFA-producing gut bacteria in parallel with the fecal concentration of BA and indole could compromise the intestinal barrier function in CKD. It is currently not known if this contributes to increased plasma levels of PBUTs, potentially playing a role in the PTMs of albumin. Further evaluation of SCFA-producing bacteria and SCFAs as potential targets to restore both gut dysbiosis and uremia is needed.

Biotic Supplements in Patients With Chronic Kidney Disease: Meta-Analysis of Randomized Controlled Trials

Gut flora imbalance characterizes patients with chronic kidney disease (CKD). Although biotic supplementation has been proposed to lessen inflammation and oxidative stress and, thus, reduce the risk of progressive kidney damage and cardiovascular disease, the effects remain controversial. We conducted a meta-analysis to assess the therapeutic benefits of biotics in CKD. PubMed, Embase, and Cochrane databases were systematically searched for randomized controlled trials that evaluated any biotic (prebiotic, probiotic, synbiotics) supplements in patients with CKD (CKD, stage 3-4 to end-stage renal disease). Primary endpoints included changes in renal function, markers of inflammation, and oxidative stress. Secondary endpoints included changes in levels of uremic toxins and variations in lipid metabolism. Twenty-three eligible studies included 842 participants. In a pooled-analysis, biotics did not change estimated glomerular filtration rate (mean difference [MD] = 0.08, P=.92) or serum albumin (MD=-0.01, P=.86), although prebiotics reduced serum creatinine (standardized mean difference [SMD]=-0.23, P=.009) and blood urea nitrogen (MD=-6.05, P<.00001). Biotics improved total antioxidative capacity (SMD=0.37, P=.007) and malondialdehyde (SMD=-0.96, P=.006) and reduced the inflammatory marker interleukin-6 (SMD=-0.30, P=.01) although not C-reactive protein (SMD=-0.22, P=.20). Biotic intervention reduced some uremic toxins, including p-cresol sulfate (SMD=-2.18, P<.0001) and indoxyl sulfate (MD=-5.14, P=.0009), which decreased in dialysis-dependent patients. Another toxin, indole-3-acetic acid (MD=-0.22, P=.63), did not change. Lipids were unaffected by biotic intervention (total cholesterol: SMD=-0.01, P=.89; high-density lipoprotein: SMD=-0.08, P=.76; low-density lipoprotein: MD=3.54, P=.28; triglyceride: MD=-2.26, P=.58). The results highlight the favorable influence of biotics on circulating markers of creatinine, oxidant stress (malondialdehyde, total antioxidative capacity), inflammation (interleukin-6), and uremic toxins (p-cresol sulfate) in patients with CKD. Biotics did not affect estimated glomerular filtration rate, albumin, indole-3-acetic acid, or lipids in either predialysis or dialysis patients.

Effects of Probiotics, Prebiotics, and Synbiotics on Uremic Toxins, Inflammation, and Oxidative Stress in Hemodialysis Patients: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

The dysbiosis of gut microbiota may cause many complications in patients with end-stage renal disease, which may be alleviated by probiotic, prebiotic, and synbiotic supplementation. The aim of this systematic review and meta-analysis was to assess the effects of these supplementations on circulatory uremic toxins, biomarkers of inflammation, and oxidative stress in hemodialysis patients. We searched the EMBASE, MEDLINE, Web of Science, and Cochrane Library databases until 8 August 2021. Randomized controlled trials evaluating adult patients receiving hemodialysis were included. The pooled results from 23 studies with 931 hemodialysis patients indicated that interventions significantly decreased the circulating levels of p-cresyl sulfate (standardized mean difference (SMD): 0.38; 95% CI: −0.61, −0.15; p = 0.001), endotoxins (SMD: −0.58; 95% CI: −0.99, −0.18; p = 0.005), malondialdehyde (SMD: −1.16; 95% CI: −1.81, −0.52; p = 0.0004), C-reactive proteins (CRP) (SMD: −0.61; 95% CI: −0.99, −0.23; p = 0.002), and interleukin 6 (SMD: −0.92; 95% CI: −1.51, −0.33; p = 0.002), and improved the total antioxidant capacity (SMD: 0.89; 95% CI: 0.49, 1.30; p < 0.0001) and glutathione (SMD: 0.40; 95% CI: 0.14, 0.66; p = 0.003) when compared to the placebo group. Our results suggest that treatment with probiotics, prebiotics, and synbiotics may help alleviate uremic toxin levels, oxidative stress, and the inflammatory status in hemodialysis patients.

Is there an association between the plasma levels of uremic toxins from gut microbiota and anemia in patients on hemodialysis?

Anemia is one of the most frequent complications in patients with chronic kidney disease (CKD). Despite being multifactorial, the relative or absolute deficiency of erythropoietin production is the leading cause. Recent studies have shown that uremic toxins produced by the gut microbiota also may play a role in the genesis of anemia in these patients. To evaluate the possible association between uremic toxins plasma levels and anemia in patients with CKD on hemodialysis (HD). This cross-sectional study evaluated one hundred fifty-four patients (53.2% men, 51.2 ± 11.2years, hemoglobin (Hb) levels of 11.2 ± 1.6g/dL). Biochemical variables such as urea, creatinine, hemoglobin, hematocrit, were measured according to standard methods and uremic toxins such as indoxyl sulfate (IS), indole-3-acetic acid (IAA), p-cresyl sulfate (p-CS) plasma levels were measured by reverse-phase high-performance liquid chromatography (RP-HPLC). The levels of uremic toxins such as IS, IAA, p-CS were increased in all patients. However, no correlation was found between uremic toxins plasma levels and anemia parameters. Only patients with Hb < 11g/dL presented a negative correlation between hematocrit and IAA plasma levels. There is no strong evidence that uremic toxins produced by the gut microbiota may be associated with anemia in patients with CKD on HD.

Cytokines and chemokines systemic levels are related to dialysis adequacy and creatinine clearance in patients with end-stage renal disease undergoing hemodialysis

Although the clearance of low-molecular weight toxins is modulated by dialysis dose, the relationship between dialysis adequacy and middle systemic inflammatory mediators is often overlooked. Thus, the relationship between dialysis adequacy, pro- and anti-inflammatory cytokines and chemokines in hemodialysis (HD) patients was investigated. Forty-eight HD patients (19 women and 25 men) were investigated. Age, body mass index, time in HD, nutritional status, Kt/V and blood biochemical parameters was similar in patients of both sexes (P > 0.05). Thus, patients were stratified by dialysis adequacy measured by Kt/V method (adequate Kt/V ≥ 1.2). Post-HD urea, creatinine, cytokines (IFN-γ, IL-4 and IL-10) and chemokines (CCL-2, CCL-5, CXCL-8 and CXCL-10) were higher in patients with Kt/V < 1.2 (P < 0.05). Kt/V exhibited significant correlation with CXCL-10/IP-10 serum levels. Positive correlation between creatinine with IFN-γ, CCL-2/MCP-1, and CXCL-10/IP-10, and negative correlation with IL-10 was identified in patients with Kt/V < 1.2 (P < 0.05). In patients with Kt/V ≥ 1.2, only IL-10 was positively and CXCL-10/IP-10 negatively correlated with creatinine levels (P < 0.05). Kt/V and creatinine levels exhibited variable predictive value (Kt/V = 27% to 37%, creatinine = 29% to 47%) to explain cytokines and chemokines circulating levels in patients with adequate and inadequate dialysis dose. Taken together, our findings provide evidence that in addition to modulating uremic toxins levels, such as urea and creatinine, dialysis dose is associated with circulating levels of inflammatory mediators. Thus, low Kt/V results and creatinine accumulation are potential indicators of the systemic inflammatory stress determined by up-regulation of proinflammatory cytokines and chemokines, and downregulation of anti-inflammatory cytokines.

Gut Microbiome-Derived Uremic Toxin Levels in Hemodialysis Patients on Different Phosphate Binder Therapies

Introduction: Constipation is prevalent in patients with kidney failure partly due to the use of medication, such as phosphate binders. We hypothesized that serum levels of gut microbiome-derived uremic toxins (UTOX) may be affected by the choice of phosphate binder putatively through its impact on colonic transit time. We investigated two commonly prescribed phosphate binders, sevelamer carbonate (SEV) and sucroferric oxyhydroxide (SFO), and their association with gut microbiome-derived UTOX levels in hemodialysis (HD) patients. Methods: Weekly blood samples were collected from 16 anuric HD participants during the 5-week observational period. All participants were on active phosphate binder monotherapy with either SFO or SEV for at least 4 weeks prior to enrollment. Eight UTOX (7 gut microbiome-derived) and tryptophan were quantified using liquid chromatography-mass spectrometry. Serum phosphorus, nutritional, and liver function markers were also measured. For each substance, weekly individual levels, the median concentration per participant, and differences between SFO and SEV groups were reported. Patient-reported bowel movements, by the Bristol Stool Scale (BSS), and pill usage were assessed weekly. Results: The SEV group reported a 3.3-fold higher frequency of BSS stool types 1 and 2 (more likely constipated, p < 0.05), whereas the SFO group reported a 1.5-fold higher frequency of BSS stool types 5–7 (more likely loose stool and diarrhea, not significant). Participants in the SFO group showed a trend toward better adherence to phosphate binder therapy (SFO: 87.6% vs. SEV: 66.6%, not significant). UTOX, serum phosphorus, nutritional and liver function markers, and tryptophan were not different between the two groups. Conclusion: There was no difference in the gut microbiome-derived UTOX levels between phosphate binders (SFO vs. SEV), despite SFO therapy resulting in fewer constipated participants. This pilot study may inform study design of future clinical trials and highlights the importance of including factors beyond bowel habits and their association with UTOX levels.

Melatonin Prevents Chronic Kidney Disease-Induced Hypertension in Young Rat Treated with Adenine: Implications of Gut Microbiota-Derived Metabolites.

Melatonin, a signaling hormone with pleiotropic biofunctions, has shown health benefits. Trimethylamine-N-oxide (TMAO) and asymmetric dimethylarginine (ADMA) are uremic toxins involved in the development of hypertension. TMAO originates from trimethylamine (TMA), a gut microbial product. ADMA is an endogenous nitric oxide (NO) synthase inhibitor. We examined whether melatonin therapy could prevent hypertension and kidney disease by mediating gut microbiota-derived metabolites and the NO pathway using an adenine-induced chronic kidney disease (CKD) young rat model. Six-week-old young Sprague Dawley rats of both sexes were fed a regular diet (C group), a diet supplemented with 0.5% adenine (CKD group), or adenine plus 0.01% melatonin in their drinking water (CKD + M group) for three weeks (N = 8/group). Adenine-fed rats developed renal dysfunction, hypertension, renal hypertrophy and increased uremic toxin levels of TMAO and ADMA. Melatonin therapy prevented hypertension in both sexes and attenuated kidney injury in males. Melatonin reversed the changes to the plasma TMAO-to-TMA ratio induced by CKD in both sexes. Besides, the protective effects of melatonin were associated with restoration of gut microbiota alterations, including increased α-diversity, and enhancement of the abundance of the phylum Proteobacteria and the genus Roseburia in male rats. Melatonin therapy also partially prevented the increases in ADMA in male CKD rats. Melatonin sex-specifically protected young rats against hypertension and kidney injury induced by CKD. The results of this study contribute toward a greater understanding of the interaction between melatonin, gut microbiota-derived metabolites, and the NO pathway that is behind CKD, which will help to prevent CKD-related disorders in children.

Uremic toxins levels from the gut microbiota seem not to be altered by physical exercise in hemodialysis patients.

Regular physical exercise may result in many benefits to patients with chronic kidney disease (CKD) on hemodialysis (HD), including gut microbiota modulation and solute removal. The study aimed to evaluate the effects of two programs of intradialytic exercises on uremic toxins plasma levels in HD patients. In experiment 1, twenty HD patients [12 men, 44.1 ± 8.9years, BMI of 23.4 ± 2.4kg/m2] were randomized into two groups: Aerobic exercise group (AEG, n = 11) that performed aerobic exercise on an adapted exercise bike three times a week for three months (36 sessions) and Control group (CG, n = 9). In experiment 2, twenty-six HD patients [19 men, 47.6 ± 11.0years, BMI of 25.9 ± 3.6kg/m2] were randomized into Resistance exercise group (REG, n = 14) that performed a resistance exercise program (using elastic bands and ankle cuffs with both lower limbs) monitored three times a week, during six months (72 sessions) and CG (n = 12). P-cresyl sulfate (p-CS), indoxyl sulfate (IS), and indol-3-acetic acid (IAA) plasma levels were determined by high-performance liquid chromatography (HPLC) with fluorescent detection. The uremic toxins plasma levels did not reduce in both exercise programs, aerobic exercise (IS: 32.7 ± 14.0 vs 33.0 ± 15.4mg/L, p = 0.86; p-CS: 59.9 ± 39.3 vs 60.0 ± 41.2mg/L, p = 0.99; IAA: 2233 [1488-2848] vs 2227 [1275-2824] µg/L, p = 0.72) and resistance exercise (IS: 28.3 ± 11.3 vs 29.1 ± 9.7mg/L, p = 0.77; p-CS: 31.4 ± 21.3 vs 34.2 ± 19.8mg/L, p = 0.63; IAA: 1628 [1330-3530] vs 2000 [971-3085] µg/L, p = 0.35) in HD patients. According to our findings, physical exercise does not appear to alter the levels of uremic toxins produced by the gut microbiota in HD patients.

Effects of Probiotic Preparations on Inflammatory Cytokines in Chronic Kidney Disease Patients: A Systematic Review and Meta-Analysis.

To summarize and assess the effects of probiotic preparations on inflammatory cytokine levels in patients with Chronic Kidney Disease (CKD). We searched through the PubMed, Cochrane Library, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), Chinese Biomedical Literature Database (CBM), and Wan Fang databases for Randomized Controlled Trials (RCTs) that report the impact of probiotic preparations on inflammatory cytokines in CKD patients. Outcomes were composed of serum levels of CReactive Protein (CRP), Interleukin 6 (IL-6), Tumor Necrosis Factor-α (TNF-α), serum urea, creatinine, uric acid, Para-Cresol Sulfate (PCS), and Indoxyl-Sulfate (IS). The Mean Differences (MDs) with 95% Confidence Intervals (CIs) were considered as effect estimates. Sensitivity analysis and Egger's linear regression test were performed to evaluate the stability of results and publication bias. This study was registered with PROSPERO number CRD42020176557. Sixteen studies met the inclusion criteria. Evidence showed that serum CRP levels were decreased in the intervention group (WMD, -12.29, 95% CI, -16.41 to -8.16, p = 0). The IL-6 was significantly reduced only in the prebiotic group (SMD, -0.73, 95% CI, -1.3 to -0.16, p = 0.012). However, no reduction was observed in TNF-α (SMD, -0.07, 95% CI, -0.51 to 0.38, p = 0.772). Moreover, there was no significant change in serum uremic toxin, including creatine, urea, uric acid, PCS, and IS. Probiotic preparations decrease the serum levels of inflammatory cytokines in CKD patients but do not affect the serum uremic toxin levels. The results of this meta-analysis suggest essential guidance for treatment decisions in clinical practice.

Myeloid cell-derived coagulation tissue factor is associated with renal tubular damage in mice fed an adenine diet

Patients with chronic kidney disease (CKD) commonly exhibit hypercoagulability. Increased levels of uremic toxins cause thrombogenicity by increasing tissue factor (TF) expression and activating the extrinsic coagulation cascade. TF is induced in monocytes and macrophages under pathological conditions, such as inflammatory diseases. However, the role of monocyte myeloid cell TF in CKD progression remains unclear. We aimed to clarify this issue, and the present study found that patients with CKD had elevated levels of D-dimer, a marker of fibrin degradation, which was associated with decreased estimated glomerular filtration rate and increased serum levels of uremic toxins, such as indoxyl sulfate. In vitro studies showed that several uremic toxins increased cellular TF levels in monocytic THP-1 cells. Mice with TF specifically deleted in myeloid cells were fed an adenine diet to cause uremic kidney injury. Myeloid TF deletion reduced tubular injury and pro-inflammatory gene expression in the kidneys of adenine-induced CKD but did not improve renal function as measured by plasma creatinine or blood urea nitrogen. Collectively, our findings suggest a novel concept of pathogenesis of coagulation-mediated kidney injury, in which elevated TF levels in monocytes under uremic conditions is partly involved in the development of CKD.

Effect of Pea Hull Fiber on Uremic Metabolites and Gut Microbiota Composition in Individuals Undergoing Hemodialysis

ObjectivesThe objective was to determine the effects of pea hull fiber intake on serum uremic molecules and microbiota composition of individuals undergoing hemodialysis. MethodsA randomized, double-blind, placebo-control, crossover study was conducted with individuals undergoing hemodialysis. Following a 1-week baseline, participants consumed muffins with added pea hull fiber (15 g/d) and control muffins daily for 4 weeks in random order, separated by a 4-week washout. Blood and stool samples were collected during each period. Serum p-cresol sulfate (PCS), indoxyl sulfate (IS) and trimethylamine N-oxide (TMAO) were analyzed by LC–MS/MS and fecal microbiome profile by 16S rRNA gene amplicon sequencing. qPCR for taxa of interest (Akkermansia muciniphila, Faecalibacterium prausnitzii, Bifidobacterium, and Roseburia) was performed. QIIME 2 sample-classifier was used to discover a unique microbiota profile due to the consumption of pea hull fiber. ResultsOf the 18 participants randomized (50 ± 4 y; eGFR 6.6 ± 0.7 ml/min/1.73m2), 13 completed the study. No significant changes from baseline were observed in serum PCS (3256 ± 505 μmol/L), IS (166 ± 23 μmol/L) or TMAO (96 ± 12 μmol/L), or for the relative quantification of A. muciniphila, F. prausnitzii, Bifidobacterium, and Roseburia, taxa thought to be health enhancing. Taxa that most distinguished the microbiota composition during the pea hull fiber intervention from usual diet periods were enriched Gemmiger, Collinsella and depleted Lactobacillus, Ruminococcus, Coprococcus and Mogibacteriaceae. Given that abundance of Collinsella has been inversely associated with dietary fiber, this finding was unexpected. ConclusionsIn dialysis patients, added pea hull fiber did not reduce the serum levels of targeted uremic molecules but did alter fecal microbiota composition. Future research in this patient population should explore the efficacy of alternate fiber sources or plant-based dietary patterns for reducing serum levels of uremic toxins. Funding SourcesSaskatchewan Pulse Growers.

MO977POTENTIAL INTERACTIONS BETWEEN UREMIC TOXINS AND DRUGS: AN APPLICATION IN KIDNEY TRANSPLANT RECIPIENTS TREATED WITH CALCINEURIN INHIBITORS*

Abstract Background and Aims In addition to affecting glomerular filtration rate, chronic kidney disease (CKD) changes the absorption, distribution and nonrenal clearance of a number of drugs. The uremic toxins that accumulate with as renal function deteriorates can potentially affect drug pharmacokinetics. Given the requirement for therapeutic drug monitoring (TDM) with most immunosuppressants, the latter are good models for understanding the potential impact of uremic toxins on blood concentrations of drugs. We focused on two calcineurin inhibitors (tacrolimus and cyclosporine) with similar pharmacological properties: low but variable oral bioavailability, strong binding to plasma proteins (albumin for tacrolimus and lipoproteins for cyclosporine), metabolism by cytochrome P450 3A4/5, and excretion in the bile. Our starting hypothesis was that uremic toxins influence the exposure of immunosuppressants. The study’s objective was to determine whether plasma concentrations of certain uremic toxins were correlated with blood concentrations of the two immunosuppressants. Method DRUGTOX was a cross-sectional study of 403 adult patients followed up after kidney transplantation at Amiens University Medical Center (Amiens, France) and who had undergone TDM of calcineurin inhibitors between August 4th, 2019, and March 11th, 2020. The patients had been treated daily with oral tacrolimus or cyclosporine. Two groups were constituted: 203 patients with low uremic toxin levels (estimated glomerular filtration rate (eGFR) according to the Modification of Diet in Renal Disease equation &amp;gt;40 mL/min/1.73m2) and 200 patients with high uremic toxin levels (eGFR &amp;lt;40 mL/min/1.73m2). For each patient, immunosuppressant trough concentrations (C0) were measured in whole-blood samples and then normalized against the total daily dose: C0/D ratio. After centrifugation, the sample was assayed for five uremic toxins (urea, trimethylamine N-oxide (TMAO), indole acetic acid (IAA), para-cresylsulfate (PCS), and indoxylsulfate (IxS)) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Univariate and multivariate logistic regressions were used to evaluate the associations between plasma uremic toxin levels and the blood tacrolimus or cyclosporine C0/D ratio. Results The median [interquartile range] age was 56 [48-66] and the median eGFR was 41 [30-57] ml/min/1.73 m2. The majority of the patients (56.5%) were at CKD stage 3. A total of 248 (61.5%) patients were being treated with tacrolimus and 155 (38.5%) were being treated with cyclosporine. The median time between transplantation and study inclusion was 6.5 years. Plasma urea, TMAO, IAA, PCS and IxS levels rose progressively with the CKD stage. In a univariate logistic analysis, age, sex, BMI, urea, IxS and PCS were significantly associated with an increment in the tacrolimus C0/D ratio. A multivariate analysis revealed an independent association with IxS (odds ratio [95% confidence interval]: 1.36 [1.00; 1.85], after adjustment for sex, age and BMI, whereas adjustment for age weakened the association for PCS (OR: 1.22 (0.99; 1.55)) and urea (OR: 1.71 (0.93; 3.16)). In a univariate logistic analysis, age, sex, BMI, and the TMAO level (but neither PCS, IxS, IAA nor urea) were significantly associated with an increment in the cyclosporine C0/D ratio. Conclusion Even though TDM and dose adaptation of immunosuppressants keeps levels within the therapeutic window, elevated exposure to tacrolimus (but not cyclosporine) is associated with an accumulation of PCS, IxS and urea. This might be explained by an interaction between tacrolimus and highly albumin-bound uremic toxins. Our findings may have implications for other drugs that bind with high affinity to albumin (since an elevated free fraction might lead to unexpected exposures, which can alter their efficacy and/or tolerance).

MO460ASSOCIATION BETWEEN CARBAMYLATED ALBUMIN, GUT MICROBIOTA AND THEIR DERIVED METABOLITES IN CHRONIC KIDNEY DISEASE

Abstract Background and Aims Chronic kidney disease (CKD) is characterized by gut dysbiosis. We recently demonstrated a decrease of short-chain fatty acid (SCFA) producing bacterial species with the progression of CKD. Besides, levels of protein-bound uremic toxins (PBUTs) and post-translational modifications of protein are increased in CKD, both are risk factors for accelerated cardiovascular morbidity and mortality. The link between the gut-kidney axis and protein carbamylation is unclear. The aim of the study was to explore the relation between carbamylated albumin, estimated by the albumin symmetry factor, and plasma levels of PBUTs, fecal levels of SCFAs (ongoing), and the abundance of related gut microbiota in different stages of CKD (1-5). Method The study cohort includes 103 non-dialyzed CKD patients (stages 1-5). Serum proteins were detected by capillary electrophoresis and UV absorbance at 214 nm with the symmetry factor as a marker of albumin carbamylation [the lower the symmetry factor, the more carbamylated albumin]. The quantification of PBUTs and SCFAs in plasma and fecal samples, respectively, using validated UPLC methods. Results The Pearson correlation coefficient (r) shows a positive correlation between the albumin symmetry factor and the estimated glomerular filtration rate (eGFR) (r=0.3025; p=0.0019). The albumin symmetry factor correlates positively with the abundance of Butyricicoccus spp. (r= 0.3211; p=0.0009), Faecalibacterium prausnitzii (r=0.2765; p=0.0047) and Roseburia spp. (r=0.2527; p=0.0100) and negatively with the PBUTs, p-cresyl sulfate (pCS) (r=-0.2819; p=0.0039), p-cresyl glucuronide (pCG) (r=-0.2819; p=0.0039) and indoxyl sulfate (IxS) (r=-0.2650; p=0.0068). Conclusion The decreased abundance of SCFA producing gut bacteria with the progression of CKD can evoke unfavorable conditions in the gut. This can contribute to increased plasma levels of PBUTs potentially (indirectly) playing a role in albumin carbamylation. It will be further explored whether fecal levels of SCFAs are affected in parallel and could be potential targets to restore gut dysbiosis and uremia.

MO550INDOXYL SULFATE AFFECTS ERYTHROPOIESIS DURING THE COURSE OF CHRONIC KIDNEY DISEASE: A MOLECULAR STUDY

Abstract Background and Aims Chronic kidney disease (CKD) is a global health condition characterized by a progressive deterioration of renal function due to high serum levels of uremic toxins. Anemia is a major trouble in CKD patients that contributes to a faster deterioration of renal failure, leading to cardiovascular disease and increasing morbimortality. Erythropoietin (EPO) is known to contribute to CKD-associated anemia. Thus, accumulation of uremic toxins in blood impairs EPO synthesis, leading to a subsequent impairment of erythropoiesis in the bone marrow. Very few molecular clues explain why erythropoiesis is affected in CKD or explain why erythropoiesis-stimulating agents (ESA) are not efficient in some patients with CKD. The current study aims to characterize the impact of one of the most representative uremic toxins, Indoxyl Sulfate (IS), in CKD-related anemia. IS is a protein-bound uremic toxin derived from the tryptophan dietary metabolism which is difficult to remove by dialysis. Our study demonstrates the molecular effects of IS on the growth and the differentiation of red blood cells in an erythroid cell line and in primary cell cultures CD34+. Method Firstly, we examined in vitro the time-courses of IS under clinically relevant concentrations of IS (250 µM -1 mM) in a human leukemic cell line in which proliferation is induced by EPO, the UT7/EPO cell line. Cell apoptosis, proliferation, differentiation and cell cycle analysis were assessed by the MACSQuant flow cytometry. Erythroid gene expression analysis was assessed by RT-qPCR (Quantstudio 7 flex). The ratio A260/280 assessed the quality of nucleic acids. Western blotting experiments were performed to study protein expression. Human primary CD34+ cells were obtained from mobilized peripheral blood mononuclear cells (MNC) of healthy subjects and were isolated by magnetic microbeads separation on MACS columns. Results IS at 250 µM and 1 mM increased apoptosis of UT7/EPO cell line at 48h compared to control condition. On the other hand, we found no significant effect of IS on the phenotype of UT7/EPO, when using CD235a (Glycophorin A), as a marker for the detection of the erythroid cell lineage. Ki67 cellular levels, a cell proliferation marker, was not altered between control and IS experiments. This indicated that IS did not affect proliferation in UT7/EPO. At 48h, at the clinically relevant concentration of IS (250 µM), we observed an increase of the cell phase cycle Sub-G1. The analysis of erythropoiesis related genes shows that HIF2α was deregulated with IS (250 µM). Finally, in the Epo-EpoR signalling pathway, we studied the activation of the Jak2/Stat5 proteins. Results in human primary CD34+ cells confirmed the apoptotic effect of IS observed in UT7/EPO. Conclusion Our findings suggest that IS, a representative protein-bound uremic toxin, could affect cell viability, apoptosis and the cell cycle. This study suggests clues to develop new therapies for CKD-associated anemia.

Metabolomics Analysis Reveals Deranged Energy Metabolism and Amino Acid Metabolic Reprogramming in Dogs With Myxomatous Mitral Valve Disease.

BackgroundMyxomatous mitral valve disease (MMVD), a naturally occurring heart disease, affects 10% to 15% of the canine population. Canine MMVD shares many similarities with human MMVD. Untargeted metabolomics was performed to identify changes in metabolic pathways and biomarkers with potential clinical utilities.Methods and ResultsSerum samples from 27 healthy, 22 stage B1, 18 stage B2 preclinical MMVD dogs, and 17 MMVD dogs with a history of congestive heart failure (CHF) were analyzed. Linear regression analysis identified 173 known metabolites whose concentrations were different among the 4 groups (adjusted P<0.05), of which 40% belonged to amino acid super pathways, while 30% were lipids. More than 50% of significant metabolites were correlated with left atrial diameter but not left ventricular dimension. Acylcarnitines, tricarboxylic acid cycle intermediates, and creatine accumulated in proportion to MMVD severity. α‐Ketobutyrate and ketone bodies were increased as MMVD advanced. Nicotinamide, a key substrate of the main nicotinamide adenine dinucleotide (NAD+) salvage pathway, was decreased, while quinolinate of the de novo NAD+ biosynthesis was increased in CHF dogs versus healthy dogs. 3‐Methylhistidine, marker for myofibrillar protein degradation, was higher in CHF dogs than non‐CHF dogs. Trimethylamine N‐oxide (TMAO) and TMAO–producing precursors, including carnitine, phosphatidylcholine, betaine, and trimethyllysine, were increased in CHF dogs versus non‐CHF dogs. Elevated levels of uremic toxins, including guanidino compounds, TMAO, and urea, were observed in CHF dogs. Pathway analysis highlighted the importance of bioenergetics and amino acid metabolism in canine MMVD.ConclusionsOur study revealed altered energy metabolism, amino acid metabolic programming, and reduced renal function in the development of MMVD and CHF. Complex interplays along the heart‐kidney‐gut axis were implicated.

Dietary Fibre Intake Is Associated with Serum Levels of Uraemic Toxins in Children with Chronic Kidney Disease.

Imbalanced colonic microbial metabolism plays a pivotal role in generating protein-bound uraemic toxins (PBUTs), which accumulate with deteriorating kidney function and contribute to the uraemic burden of children with chronic kidney disease (CKD). Dietary choices impact the gut microbiome and metabolism. The aim of this study was to investigate the relation between dietary fibre and gut-derived PBUTs in paediatric CKD. Sixty-one (44 male) CKD children (9 ± 5 years) were prospectively followed for two years. Dietary fibre intake was evaluated by either 24-h recalls (73%) or 3-day food records (27%) at the same time of blood sampling for assessment of total and free serum levels of different PBUTs using liquid chromatography. We used linear mixed models to assess associations between fibre intake and PBUT levels. We found an inverse association between increase in fibre consumption (g/day) and serum concentrations of free indoxyl sulfate (−3.1% (−5.9%; −0.3%) (p = 0.035)), free p-cresyl sulfate (−2.5% (−4.7%; −0.3%) (p = 0.034)), total indole acetic acid (IAA) (−1.6% (−3.0%; −0.3%) (p = 0.020)), free IAA (−6.6% (−9.3%; −3.7%) (p < 0.001)), total serum p-cresyl glucuronide (pCG) (−3.0% (−5.6%; −0.5%) (p = 0.021)) and free pCG levels (−3.3% (−5.8%; −0.8%) (p = 0.010)). The observed associations between dietary fibre intake and the investigated PBUTs highlight potential benefits of fibre intake for the paediatric CKD population. The present observational findings should inform and guide adaptations of dietary prescriptions in children with CKD.

The Role of Dietary Fiber Supplementation in Regulating Uremic Toxins in Patients With Chronic Kidney Disease: A Meta-Analysis of Randomized Controlled Trials

The results of previously published meta-analyses showed that dietary fiber could reduce the levels of p-cresyl sulfate, blood urea nitrogen, and creatinine in patients with chronic kidney disease (CKD). However, these results were based on some trials with pre-post design and randomized controlled trials of low quality. Additionally, it has been suggested that the dosage and duration of fiber supplementation and patients' characteristics potentially influence the effect of dietary fiber in reducing uremic toxins, but it would appear that no research has provided reliable evidence. We searched PubMed, Web of Science, and Cochrane Library. Data were pooled by the generic inverse variance method using random effects models and expressed as standardized mean difference (SMD) with 95% confidence interval (CI). Heterogeneity was quantified by I2. Publication bias was evaluated by Egger's test. Ten randomized controlled trials involving 292 patients with CKD were identified. Dietary fiber supplementation can significantly reduce the levels of indoxyl sulfate (SMD=-0.55, 95% CI=-1.04, -0.07, P=.03), p-cresyl sulfate (SMD=-0.47, 95% CI=-0.82, -0.13, P<.01), blood urea nitrogen (SMD=-0.31, 95% CI=-0.58, -0.03, P=.03), and uric acid (SMD=-0.60, 95% CI=-1.02, -0.18, P<.01), but not on reducing creatinine (SMD=-0.31, 95% CI=-0.73, 0.11, P=.14). In subgroup analyses, the reduction of indoxyl sulfate was more obvious among patients on dialysis than patients not on dialysis (P for interaction=.03); the reduction of creatinine was more obvious among patients without diabetes than those with diabetes (P for interaction <.01). This meta-analysis indicates that dietary fiber supplementation can significantly reduce the levels of uremic toxins in patients with CKD, with evidence for a more obvious effect of patients on dialysis and without diabetes. These findings inform recommendations for using dietary fiber to reducing the uremic toxin among CKD patients in clinical practice.

Intestinal Chelators, Sorbants, and Gut-Derived Uremic Toxins

Chronic kidney disease (CKD) is a highly prevalent condition and is associated with a high comorbidity burden, polymedication, and a high mortality rate. A number of conventional and nonconventional risk factors for comorbidities and mortality in CKD have been identified. Among the nonconventional risk factors, uremic toxins are valuable therapeutic targets. The fact that some uremic toxins are gut-derived suggests that intestinal chelators might have a therapeutic effect. The phosphate binders used to prevent hyperphosphatemia in hemodialysis patients act by complexing inorganic phosphate in the gastrointestinal tract but might conceivably have a nonspecific action on gut-derived uremic toxins. Since phosphorous is a major nutrient for the survival and reproduction of bacteria, changes in its intestinal concentration may impact the gut microbiota’s activity and composition. Furthermore, AST-120 is an orally administered activated charcoal adsorbent that is widely used in Asian countries to specifically decrease uremic toxin levels. In this narrative review, we examine the latest data on the use of oral nonspecific and specific intestinal chelators to reduce levels of gut-derived uremic toxins.

Protein-bound uremic toxin lowering strategies in chronic kidney disease: asystematic review and meta-analysis.

Accumulation of protein-bound uremic toxins, including indoxyl sulfate and p-cresyl sulfate, are associated with increased cardiovascular disease and mortality in chronic kidney disease (CKD). We performed a systematic review and meta-analysis to synthesize the available strategies for lowering protein-bound uremic toxin levels in CKD patients. We conducted a meta-analysis by searching the databases of MEDLINE, Scopus, and the Cochrane Central Register of Controlled Trials for observational studies and randomized controlled trials (RCTs) that examined the effect of dietary protein restrictions, biotic supplements (including prebiotics, probiotics, and synbiotics), AST-120, dialysis techniques, and the outcome of preservation of residual renal function (RRF) on indoxyl sulfate and p-cresyl sulfate levels. Random-effect model meta-analyses were used to compute changes in the outcomes of interest. A total of 38 articles (2,492 patients), comprising 28 RCTs, 8 single-arm or prospective cohort studies, and 2 cross-sectional studies were included in this meta-analysis. When compared with placebo, prebiotics, synbiotics, and AST-120 provided significantly lower levels of both serum indoxyl sulfate and p-cresyl sulfate. There were no significant reductions in serum indoxyl sulfate and p-cresyl sulfate levels in patients receiving probiotics. Preservation of RRF in dialysis patients resulted in lower levels of both of the protein-bound uremic toxins. When compared with conventional hemodialysis, hemodiafiltration significantly decreased serum p-cresyl sulfate alone, whereas a significant change in serum indoxyl sulfate levels was observed only in studies with long-term observation periods. Very low protein diet (VLPD) and other oral medications yielded insignificant differences in protein-bound uremic toxins. The present meta-analysis demonstrated that prebiotics, synbiotics, and AST-120 can effectively reduce both serum indoxyl sulfate and p-cresyl sulfate in CKD patients when compared with placebo. Preservation of RRF was associated with lower serum indoxyl sulfate and p-cresyl sulfate levels. The effect of biotic supplements was detected only in dialysis patients. For non-dialysis CKD patients, the results were limited due to the small number of studies. Further studies are needed to determine the efficacy in these populations.

Can curcumin supplementation reduce plasma levels of gut-derived uremic toxins in hemodialysis patients? A pilot randomized, double-blind, controlled study.

Gut dysbiosis is common in patients with chronic kidney disease (CKD) and is closely related to inflammatory processes. Some nutritional strategies, such as bioactive compounds present in curcumin, have been proposed as an option to modulate the gut microbiota and decrease the production of uremic toxins such as indoxyl sulfate (IS), p-cresyl sulfate (pCS) and indole-3 acetic acid (IAA). To evaluate the effects of curcumin supplementation on uremic toxins plasma levels produced by gut microbiota in patients with CKD on hemodialysis (HD). Randomized, double-blind trial in 28 patients [53.6 ± 13.4years, fourteen men, BMI 26.7 ± 3.7kg/m2, dialysis vintage 37.5 (12-193) months]. Fourteen patients were randomly allocated to the curcumin group and received 100mL of orange juice with 12g carrot and 2.5g of turmeric and 14 patients to the control group who received the same juice but without turmeric three times per week after HD sessions for three months. IS, pCS, IAA plasma levels were measured by reverse-phase high-performance liquid chromatography RESULTS: After three months of supplementation, the curcumin group showed a significant decrease in pCS plasma levels [from 32.4 (22.1-45.9) to 25.2 (17.9-37.9) mg/L, p = 0.009], which did not occur in the control group. No statistical difference was observed in IS and IAA levels in both groups. The oral supplementation of curcumin for three months seems to reduce p-CS plasma levels in HD patients, suggesting a gut microbiota modulation.