P-cresyl Sulfate Concentrations Research Articles

#885 Combination of medium cut-off dialyzer membrane and diet modification to reduce serum concentrations of p-cresyl sulfate and indoxyl sulfate

Abstract Background and Aims Online hemodiafiltration (ol-HDF) may be considered currently as the best choice for chronic hemodialysis (HD) treatment, but medium cut-off (MCO) membranes may provide similar efficiency for larger and protein-bound toxin removal. P-cresyl sulfate (PCS) and indoxyl-sulfate (IS) concentration depends mainly on residual renal function and diet. Increased dietary fiber intake and short-chain fatty acid (SCFA) supplementation were associated with decreased production of PCS and IS. The aim of this study was to pragmatically combine MCO use with diet modification in an attempt to reduce serum concentration of PCS and IS and compare this strategy to online HDF use. Method We report preliminary results from a subset of a study sample with 42 chronic prevalent HD patients in a prospective randomized controlled interventional study. Two weeks after standard bicarbonate HD (BHD), patients were randomized to hemodialysis with MCO membrane (EXP group) or ol-HDF with a standard "high-flux" (HF) dialyzer membrane (CON group). After 4 weeks, both groups were supplemented by a change in the diet with increase of the daily intake of dietary fiber to 30g and addition of a SCFA propionate in the dose of 1g daily for 8 weeks. Two main outcomes were serum concentrations of PCS and IS. Measurements were taken at baseline (after 2 week wash-in period), after 4 weeks of the first intervention phase (MCO vs. ol-HDF; T1), after 8 weeks of the second intervention phase (fiber and SCFA supplementation; T2) and finally, after 4 weeks of wash-out period with BHD (T3). Results From 42 participants, 38 completed the study (63.2% men, 66.4±10.9 years, Charlson comorbidity index 5.7±2.3). In the CON group, serum concentrations of PCS (in μg/ml) were 36.8±19.6 (baseline), 36.9±20.8 (T1), 32.4±17.4 (T2) and 38.6±22.1 (T3). Serum concentrations of IS (in μg/ml) were 31.8±13.0 (baseline), 32.9±14.7 (T1), 29.5±9.1 (T2) and 35.5±16.8 (T3). In the EXP group, serum concentrations of PCS were 33.5± 16.6 (baseline), 35.9±17.8 (T1), 34.0±16.1 (T2) and 37.4±21.5 (T3). Serum concentrations for IS were 39.6±12.6 (baseline), 37.3±12.9 (T1), 42.3±13.5 (T2) and 41.0±12.8 (T3). Repeated measures ANOVA revealed no significant time*group interaction for PCS (F(1,33)=0.479, p=0.698, ŋ2=0.014) and IS (F(1,33)=2.392, p=0.073, ŋ2=0.068). There was a significant within-group increase in serum IS concentration between T2 and T3 in CON group (p=0.042). There was a trend towards a decrease in PCS concentration between T1 and T2 and increase between T2 and T3 in CON group. Conclusion The results of the study suggest both hemodialysis methods are equivalent in eliminating PCS and IS. Additional fiber and SCFA propionate supplementation did not decrease serum PCS and IS concentrations significantly, although there was a trend towards lower serums concentration of PCS after diet modification in CON group.

#2711 Cardiomyocytes exposed to medium conditioned by kidney cells treated with the uremic toxin p-cresyl sulfate undergo changes in cell viability

Abstract Background and Aims Cardiorenal Syndrome (CRS) is a condition involving the heart and the kidneys, where a disturbance in one of these organs can lead to alterations in the other. High levels of uremic toxins (UTs) such as p-Cresyl Sulfate (PCS) can induce renal injury. Furthermore, UTs play a crucial role in inflammatory status and cardiac function. Therefore, it is crucial that studies regarding the influence of uremic toxins in the context of cardiorenal syndrome be conducted. Nevertheless, few studies have been conducted in the context of Acute Kidney Injury (AKI) causing acute damage to the heart, and few mechanisms are still known. The objective of the study was to evaluate the role of PCS in cell viability and inflammatory genes in renal and cardiac cells, to simulate cardiorenal syndrome due to excessive PCS. Method The HEK293 (human epithelial renal cells) and H9c2 (murine cardiomyocyte cells) cell lines were used. HEK293 was treated with concentrations of 0.25 mM, 0.5 mM, 1 mM, and 1.5 mM PCS for 6, 24, and 48 hours. H9c2 was treated with PCS (1.5 mM) and conditioned media from PCS-treated renal cells (1.5 mM) for 6 and 24 hours. MTT assays, growth curve analysis, and Hoechst-PI staining were performed. Gene expression was evaluated by RT-qPCR. ANOVA followed by Bonferroni post-test was conducted, considering P < 0.05 as significant. Results PCS treatment led to a time and dose-dependent decrease in cell viability. The cell growth curve indicated a negative impact across time on renal cell proliferation at all different PCS concentrations. Hoechst-PI assay revealed increased cell death in the treatment with PCS (1.5 mM) for 24 hours. There was no change in the gene expression of IL-6, IL-1β, Bax, and Bcl-2 in renal cells. Cardiac cell viability decreased both after direct PCS treatment (85.3%) and exposure to PCS-conditioned media from renal cells for 24 hours (87.3%). Conclusion PCS reduces renal cell viability and inhibits cell proliferation without affecting the inflammatory status and apoptosis signaling within the evaluated time frames. Cardiac cell viability decreased after PCS treatment, either directly or indirectly, suggesting a cardiotoxic effect of PCS, independent of changes in renal cells.

Associations of Indoxyl Sulfate and p-cresyl Sulfate with Serum Uncarboxylated Matrix γ-carboxyglutamate Protein in Chronic Kidney Disease Patients.

Indoxyl sulfate (IS) and p-cresyl sulfate (PCS) are two important protein-bound uremic retention solutes. Increased serum levels of IS and PCS are associated with cardiovascular calcification. Matrix γ-carboxyglutamate protein (MGP) is a potent inhibitor of vascular calcification and inactivated uncarboxylated MGP (ucMGP) is related to vascular calcification. Nevertheless, whether serum levels of IS and PCS are associated with the serum ucMGP level in chronic kidney disease (CKD) patients with different stages is unknown. This cross-sectional study enrolled 90 patients in different stages of chronic kidney disease. Serum levels of IS and PCS were determined. The serum concentration of ucMGP was measured with an enzyme-linked immunosorbent assay. Independent associations between serum total IS and PCS with ucMGP were evaluated. The mean serum level of ucMGP in participants of this study is 10.78±5.22 μg/mL. Serum levels of the two above-mentioned uremic toxins and ucMGP were elevated commensurately with deteriorating renal function. The serum level of ucMPG was associated with total IS (r = 0.456, p < 0.001) and total PCS (r =0.413, p < 0.001) levels. Multiple linear regression analysis showed that ucMGP was significantly related to levels of IS (β = 0.442, p <0.001), but not the level of PCS concentrations after adjusting for other confounding variables. Our study showed that a higher serum IS level was independently associated with ucMGP in deteriorating CKD. Therefore, it would be worthwhile to investigate the effect of IS on ucMGP in the pathogenesis of vascular calcification in future studies.

Protein/Fiber Index Modulates Uremic Toxin Concentrations in Hemodialysis Patients.

Background: Indoxyl sulfate (IS) and p-cresyl sulfate (PCS), two uremic toxins (UTs), are associated with increased mortality in patients with chronic kidney disease (CKD). These toxins are produced by the microbiota from the diet and excreted by the kidney. The purpose of this study was to analyze the effect of diet on IS and PCS concentration in hemodialysis (HD) patients. Methods: We performed a prospective monocentric study using a seven-day diet record and determination of serum IS and PCS levels in HD patients. We tested the association between toxin concentrations and nutritional data. Results: A total of 58/75 patients (77%) completed the diet record. Mean caloric intake was 22 ± 9.2 kcal/kg/day. The protein/fiber index was 4.9 ± 1.8. No correlation between IS or PCS concentration and protein/fiber index was highlighted. In the 18 anuric patients (31%) in whom residual renal function could not affect toxin concentrations, IS and PCS concentrations were negatively correlated with fiber intake and positively correlated with the protein/fiber index. In a multivariate analysis, IS serum concentration was positively associated with the protein/fiber index (p = 0.03). Conclusions: A low protein/fiber index is associated with low concentrations of uremic toxins in anuric HD patients. Diets with an increased fiber intake must be tested to determine whether they reduce PCS and IS serum concentrations.

Circulating p-Cresyl Sulfate, Non-Hepatic Alkaline Phosphatase and Risk of Bone Fracture Events in Chronic Kidney Disease-Mineral Bone Disease.

Patients with chronic kidney disease (CKD), especially those undergoing hemodialysis, are at a considerably high risk of bone fracture events. Experimental data indicate that uremic toxins intricately involved in bone-related proteins exert multi-faced toxicity on bone cells and tissues, leading to chronic kidney disease–mineral and bone disorder (CKD-MBD). Nonetheless, information regarding the association between p-cresyl sulfate (PCS), non-hepatic alkaline phosphatase (NHALP) and skeletal events remains elusive. We aim to explore the association between PCS, NHALP and risk of bone fracture (BF) in patients with hemodialysis. Plasma concentrations of PCS and NHALP were ascertained at study entry. Cox proportional hazard regression analyses were used to determine unadjusted and adjusted hazard ratios (aHRs) of PCS for BF risk. In multivariable analysis, NHALP was associated with incremental risks of BFs [aHR: 1.06 (95% CI: 1.01–1.11)]. The association between the highest PCS tertile and BF risk remained robust [aHR: 2.87 (95% CI: 1.02–8.09)]. With respect to BF events, the interaction between NHALP and PCS was statistically significant (p value for the interaction term < 0.05). In addition to mineral dysregulation and hyperparathyroidism in hemodialysis patients, higher circulating levels of PCS and NHALP are intricately associated with incremental risk of BF events, indicating that a joint evaluation is more comprehensive than single marker. In light of the extremely high prevalence of CKD-MBD in the hemodialysis population, PCS may act as a pro-osteoporotic toxin and serve as a potential surrogate marker for skeletal events.

Inverted U-Curve Association between Serum Indoxyl Sulfate Levels and Cardiovascular Events in Patients on Chronic Hemodialysis.

Background: Protein-bound uremic toxins are associated with cardiovascular disease and mortality in patients with chronic kidney disease. We investigated their association with clinical outcomes in patients undergoing chronic hemodialysis (CHD). Methods: A prospective cohort study was conducted on 86 Taiwanese patients undergoing CHD. The predictors were indoxyl sulfate and p-cresyl sulfate concentrations, with each analyzed as three tertiles. Outcomes were cardiovascular events and all-cause mortality. Results: During a 25-month follow up period, there were 23 cardiovascular events and seven all-cause mortality events. In the crude survival analysis, the second indoxyl sulfate tertile was shown to be a powerful predictor of cardiovascular events compared with the third tertile (hazard ratio (HR), 3.14; 95% confidence interval (CI), 1.10–8.94), and the first tertile was shown to have a poor but insignificant cardiovascular outcome (HR, 1.09; 95% CI, 0.30–4.00). Moreover, the predictive power of the second indoxyl sulfate tertile for cardiovascular events remained after adjustment for confounders (HR, 5.42; 95% CI, 1.67–17.60). Conclusions: An inverse U-curve relationship was observed between the total serum indoxyl sulfate level and cardiovascular events in our CHD patients. A large-scale study is needed to confirm this relationship.

Associations among total p-cresylsulfate, indoxyl sulfate and hippuric acid levels with hemodialysis quality indicators in maintenance hemodialysis patients

BackgroundTotal p-cresylsulfate (PCS), indoxyl sulfate (IS) and hippuric acid (HA) are harmful uremic toxins known to be elevated in patients with uremia. Serum total PCS, IS and HA levels have been associated with coronary atherosclerosis, left ventricular hypertrophy, metabolic acidosis, neurological symptoms, and accelerated renal damage associated with chronic kidney disease; however, no study has examined the effect of total PCS, IS and HA on hemodialysis (HD) quality indicators. The aim of this study was to examine associations among total PCS, IS and HA with HD quality indicators in patients undergoing HD treatment. MethodsThis study included 264 consecutive patients at a single HD center who assessed using previously demonstrated HD quality indicators including anemia, bone-mineral metabolism, dialysis dose, cardiovascular risk, and middle molecule removal area. Serum HA was measured using a capillary electrophoresis method. Serum total PCS and IS concentrations were measured using an Ultra Performance LC System. ResultsMultiple regression analysis showed that sex, potassium, systolic blood pressure (SBP), average BP, β2-microglobulin, and creatinine were independently positively associated with IS level, and that age, total cholesterol, and estimated glomerular filtration rate (eGFR) was independently negatively associated with IS level. In addition, β2-microglobulin was independently positively associated with total PCS. Moreover, potassium, diastolic blood pressure, average BP, β2-microglobulin, dialysis vintage, and albumin were independently positively associated with HA level, and age, transferrin saturation, fasting glucose, and eGFR were independently negatively associated with HA level. When the patients were stratified by age and sex, serum IS and HA levels were still independently associated with some hemodialysis quality indicators. In addition, canonical correlation analysis also confirmed the relationship between uremic toxins (IS and HA) and HD quality indicators (potassium, β2-microglobulin, average BP, creatinine, and eGFR). ConclusionThis study demonstrated that uremic toxins (IS and HA) and HD quality indicators (potassium, β2-microglobulin, average BP, creatinine, and eGFR) constructs were correlated with each other, and that there were sex and age differences in these associations among maintenance HD patients.

Scavenging Intracellular ROS Attenuates p-Cresyl Sulfate-Triggered Osteogenesis through MAPK Signaling Pathway and NF-κB Activation in Human Arterial Smooth Muscle Cells.

Osteogenesis in human arterial smooth muscle cell (HASMC) is a key feature of uremic vascular calcification (UVC). Concerning pro-oxidant properties of p-cresyl sulfate (PCS), the therapeutic effect of reactive oxygen species (ROS) scavenger on PCS triggered inflammatory signaling transduction in osteogenesis was investigated in this translational research. Based on severity level of chronic kidney disease (CKD), arterial specimens with immunohistochemistry stain were quantitatively analyzed for UVC, oxidative injury and osteogenesis along with PCS concentrations. To mimic human UVC, HASMC model was used to explore whether PCS-induced ROS could trigger mitogen-activated protein kinase (MAPK) pathways with nuclear factor-κB (NF-κB) translocation that drive context-specific gene/protein expression, including Runt-related transcription factor 2 (Runx2) and alkaline phosphatase (ALP). In parallel with PCS accumulation, CKD arteries corresponded with UVC severity, oxidative DNA damage (8-hydroxy-2′-deoxyguanosine), Runx2 and ALP. PCS directly phosphorylated extracellular signal-regulated kinase (ERK)/c-Jun N-terminal kinase (JNK)/P38 (pERK/pJNK/pP38) and modulated NF-κB translocation to promote expressions of Runx2 and ALP in HASMC. Notably, intracellular ROS scavenger attenuated pERK signaling cascade and downstream osteogenic differentiation. Collectively, our data demonstrate PCS induces osteogenesis through triggering intracellular ROS, pERK/pJNK/pP38 MAPK pathways and NF-κB translocation to drive Runx2 and ALP expressions, culminating in UVC. Beyond mineral dysregulation, osteocytic conversion in HASMC could be the stimulation of PCS. Thus PCS may act as a pro-osteogenic and pro-calcific toxin. From the perspective of translational medicine, PCS and intracellular ROS could serve as potential therapeutic targets for UVC in CKD patients.

The Arrhythmogenic Effect of Protein-Bound Uremic Toxin p-Cresylsulfate: An In Vitro Study.

p-Cresylsulfate (PCS) is a protein-bound uremic toxin that accumulates in patients with chronic kidney disease. Previous studies have indicated that serum total PCS levels are significantly increased in the presence of abnormal corrected QT (QTc) intervals, and that they are associated with QTc prolongation. However, the QTc prolongation effect of PCS remains unclear. The current study aimed to investigate the arrhythmogenic effect of PCS using in vitro experiments and computer simulation. The arrhythmogenic effect of PCS was evaluated by incubating H9c2 rat ventricular cardiomyocytes in vitro with increasing concentrations of PCS. Electrophysiological studies and mathematical computer simulations were performed. in vitro, the delayed rectifier potassium current (IK ) was significantly decreased in a dose-dependent manner after treatment with PCS. The modulation of PCS on IK was through regulation of the phosphorylation of the major potassium ion channel protein Kv2.1. In computer simulations, the decrease in IK induced by PCS prolonged the action potential duration (APD) and sped up the re-entrant wave, which is known to be a trigger mechanism for lethal ventricular arrhythmias. PCS significantly downregulated the phosphorylation of the IK channel protein Kv2.1 and IK current activity, which increased the cardiomyocyte APD. This was observed both in vitro and in the computer O'Hara-Rudy dynamic human ventricular model. These findings suggest that PCS may play a key role in the development of cardiac arrhythmias.

Dysbiosis of the gut microbiome is associated with CKD5 and correlated with clinical indices of the disease: a case\u2013controlled study

BackgroundChronic kidney disease (CKD) is a universal chronic disease in China. The balance of the gut microbiome is highly crucial for a healthy human body, especially for the immune system. However, the relationship between the gut microbiome and CKD has not yet been clarified.MethodsA total of 122 patients were recruited for this study. Among them, 24 patients were diagnosed with CKD5 but did not receive hemodialysis therapy, 29 patients were diagnosed with CKD5 and received hemodialysis therapy and 69 were matched healthy controls. The gut microbiome composition was analyzed by a 16S rRNA (16S ribosomal RNA) gene-based sequencing protocol. High-performance liquid chromatography–electrospray ionization-tandem mass spectrometry (HPLC/ESI-MS/MS) technology was used to evaluate the levels of microbiome-related protein-binding uremic toxins level, indoxyl sulfate (IS) and p-cresyl sulfate (PCS), in the patients.ResultsWe compared the gut microbiome results of 122 subjects and established a correlation between the gut microbiome and IS and PCS levels. The results indicated that alpha and beta diversity were different in patients with CKD5 than in the healthy controls (p < 0.01). In comparison to healthy controls, CKD5 patients exhibited a significantly higher relative abundance of Neisseria (p < 0.001), Lachnoclostridium (p < 0.001) and Bifidobacterium (p < 0.001). Faecalibacterium (p < 0.001) displayed a notably lower relative abundance for CKD5 patients both with and without hemodialysis than for controls. It was also found that the concentrations of IS and PCS were correlated with the gut microbiome.ConclusionsOur results indicate that CKD5 patients both with and without hemodialysis had dysbiosis of the gut microbiome and that this dysbiosis was associated with an accumulation of IS and PCS. These results may support further clinical diagnosis to a great extent and help in developing potential probiotics to facilitate the treatment of CKD5.

Microbiome perturbation by oral vancomycin reduces plasma concentration of two gut-derived uremic solutes, indoxyl sulfate and p-cresyl sulfate, in end-stage renal disease.

Observational studies have suggested a relationship between the plasma concentration of indoxyl sulfate (IS) and p-cresyl sulfate (PCS), small gut-derived 'uremic solutes', and the high incidence of uremic cardiomyopathy in patients with end-stage renal disease (ESRD). IS and PCS are derived from the metabolism of dietary components (tryptophan and tyrosine) by gut bacteria. This pilot study was designed to examine the effects of a poorly absorbable antibiotic (vancomycin) on the plasma concentration of two gut-derived 'uremic solutes', IS and PCS, and on the composition of the gut microbiome. Plasma concentrations of IS and PCS were measured by MS-HPLC. The gut microbiome was assessed in stool specimens sequenced for the 16S rRNA gene targeting the V4 region. The pre-dialysis mean plasma concentrations of both IS and PCS were markedly elevated. Following the administration of vancomycin (Day 0), the IS and PCS concentrations decreased at Day 2 or Day 5 and returned to baseline by Day 28. Following vancomycin administration, several changes in the gut microbiome were observed. Most striking was the decrease in diversity, a finding that was evident on Day 7 and was still evident at Day 28. There was little change at the phylum level but at the genus level, broad population changes were noted. Changes in the abundance of several genera appeared to parallel the concentration of IS and PCS. These findings suggest that alteration of the gut microbiome, by an antibiotic, might provide an important strategy in reducing the levels of IS and PCS in ESRD.

Increased Levels of Total p-Cresylsulfate Are Associated with Pruritus in Patients with Chronic Kidney Disease

Background: Pruritus is a common and distressing symptom that affects patients with chronic kidney disease (CKD). Indoxyl sulfate (IS) and p-cresylsulfate (PCS) are uremic toxins with similar protein binding, dialytic clearance, and proinflammatory features. Pruritus in CKD may correlate better with uremic toxins than the glomerular filtration rate (GFR), suggesting that uremic toxins either in the central nervous system or peripherally may play an important role in the pathophysiology. Objective: We sought to investigate the potential contribution of serum total IS and PCS to the pathogenesis of pruritus. Methods: The serum levels of total IS and PCS concentrations were measured in all patients by using the Ultra Performance LC System. The characteristics of pruritus were assessed using a visual analog scale score and an interview questionnaire. Results: Among the 320 CKD patients, 35% had pruritus. The patients with pruritus were older and had a higher frequency of diabetes mellitus, higher uric acid, calcium, phosphorus, creatinine, high-sensitivity C-reactive protein, and total IS and PCS levels, and lower albumin concentrations and estimated GFR (eGFR) than those without pruritus. Increasing concentrations of total PCS were independently and significantly associated with pruritus. Multiple logistic regression analysis revealed total PCS as an independent association factor for pruritus, even after full adjustment of known biomarkers. Furthermore, serum total PCS levels were positively associated with calcium, phosphorus, blood urea nitrogen, creatinine, and white blood cell count, and negatively associated with eGFR, hemoglobin, and hematocrit. Conclusion: Our results indicate that total PCS may play a role in the pathogenesis of pruritus.

Reduced protein bound uraemic toxins in vegetarian kidney failure patients treated by haemodiafiltration.

Introduction Indoxyl sulfate (IS) and p cresyl sulfate (PCS) are protein bound toxins which accumulate with chronic kidney disease. Haemodiafiltration (HDF) increases middle molecule clearances and has been suggested to increase IS and PCS clearance. We therefore wished to establish whether higher convective clearances with HDF would reduce IS and PCS concentrations. Methods We measured total plasma IS and PCS in a cohort of 138 CKD5d patients treated by On-line HDF (Ol-HDF), by high pressure liquid chromatography. Findings Mean patient age was 64.6 ± 16.5 years, 60.1% male, 57.3% diabetic, median dialysis vintage 25.9 months (12.4-62.0). The mean ICS concentration was 79.8 ± 56.4 umol/L and PCS 140.3 ± 101.8 umol/L. On multivariate analysis, IS was associated with serum albumin (β 4.31,P < 0.001), and negatively with residual renal function (β-4.1,P = 0.02) and vegetarian diet(β-28.3, P = 0.048) and PCS negatively with log C reactive protein (β-75.8, P < 0.001) and vegetarian diet (β-109, P = 0.001). Vegetarian patients had lower IS and PCS levels (median 41.5 (24.2-71.9) vs. 78.1 (49.5-107.5) and PCS (41.6 (14.2-178.3) vs. 127.3 (77.4-205.6) µmol/L, respectively, P < 0.05. Vegetarian patients had lower preOl-HDF serum urea, and phosphate (13.8 ±3.8 vs. 18.4 ± 5.2 mmol/L, and 1.33 ± 0.21 vs. 1.58 ± 0.45 mmol/L), and estimated urea nitrogen intake (1.25 ± 0.28 vs. 1.62 ± 0.5 g/kg/day), respectively, all P < 0.05. Discussion Plasma IS and PCS concentrations were not lower with Ol-HDF compared to previous studies in haemodialysis patients. However those eating a vegetarian diet had reduced IS and PCS concentrations. Although this could be due to differences in dietary protein intake, a vegetarian diet may also potentially reduce IS and PCS production by the intestinal microbiome.

Associations among chronic kidney disease, high total p-cresylsulfate and left ventricular systolic dysfunction

BackgroundA significant number of patients with chronic kidney disease (CKD) have cardiac abnormalities, and left ventricular systolic dysfunction (LVSD) is a common manifestation. p-Cresylsulfate (PCS), a protein-bound uraemic retention solute, is known to cause endothelial dysfunction and possibly plays a role in coronary atherosclerosis. Furthermore, the associations among serum total PCS, major adverse cardiovascular events, all-cause mortality, and QTc prolongation have also been found in previous studies. We thus investigated the association of total PCS and CKD with LVSD in the clinical setting. MethodsWe included 403 consecutive patients with stable angina. To evaluate LV function, all patients underwent echocardiography. To measure the serum total PCS concentrations and estimated glomerular filtration rate (eGFR), blood samples were obtained. ResultsMultiple regression analysis showed that left atrium diameter, left ventricular mass index, end diastolic interventricular septal thickness, left ventricular end-systolic diameter, left ventricular end-systolic volume, stroke volume, left ventricular end-systolic volume index, left ventricular ejection fraction (LVEF), and the interventricular septum/posterior wall of the left ventricle were independently associated with total PCS (all p<0.05). In addition, a significantly decreased LVEF was present in patients with lower and higher serum total PCS and with CKD, and with higher serum total PCS and without CKD than from those with lower serum total PCS concentrations and without CKD (p=0.004). In the multivariate logistic regression analysis, when patients without CKD and lower PCS were used as reference group, patients with the higher total PCS concentration and without CKD had an odds ratio of 3.59 for the risk of LVSD, the lower total PCS concentration and with CKD had an odds ratio of 3.89 for the risk of LVSD, and the higher total PCS concentration and with CKD had an odds ratio of 4.04 for the risk of LVSD (p=0.039, p=0.038, and p=0.020, respectively). ConclusionsHigh serum concentrations of total PCS or CKD, or both, represent an increased risk of impaired LV systolic function in stable angina patients.

Synbiotics Easing Renal Failure by Improving Gut Microbiology (SYNERGY): A Randomized Trial.

The generation of key uremic nephrovascular toxins, indoxyl sulfate (IS), and p-cresyl sulfate (PCS), is attributed to the dysbiotic gut microbiota in CKD. The aim of our study was to evaluate whether synbiotic (pre- and probiotic) therapy alters the gut microbiota and reduces serum concentrations of microbiome-generated uremic toxins, IS and PCS, in patients with CKD. Predialysis adult participants with CKD (eGFR=10-30 ml/min per 1.73 m(2)) were recruited between January 5, 2013 and November 12, 2013 to a randomized, double-blind, placebo-controlled, crossover trial of synbiotic therapy over 6 weeks (4-week washout). The primary outcome was serum IS. Secondary outcomes included serum PCS, stool microbiota profile, eGFR, proteinuria-albuminuria, urinary kidney injury molecule-1, serum inflammatory biomarkers (IL-1β, IL-6, IL-10, and TNF-α), serum oxidative stress biomarkers (F2-isoprostanes and glutathione peroxidase), serum LPS, patient-reported health, Gastrointestinal Symptom Score, and dietary intake. A prespecified subgroup analysis explored the effect of antibiotic use on treatment effect. Of 37 individuals randomized (age =69±10 years old; 57% men; eGFR=24±8 ml/min per 1.73 m(2)), 31 completed the study. Synbiotic therapy did not significantly reduce serum IS (-2 μmol/L; 95% confidence interval [95% CI], -5 to 1 μmol/L) but did significantly reduce serum PCS (-14 μmol/L; 95% CI, -27 to -2 μmol/L). Decreases in both PCS and IS concentrations were more pronounced in patients who did not receive antibiotics during the study (n=21; serum PCS, -25 μmol/L; 95% CI, -38 to -12 μmol/L; serum IS, -5 μmol/L; 95% CI, -8 to -1 μmol/L). Synbiotics also altered the stool microbiome, particularly with enrichment of Bifidobacterium and depletion of Ruminococcaceae. Except for an increase in albuminuria of 38 mg/24 h (P=0.03) in the synbiotic arm, no changes were observed in the other secondary outcomes. In patients with CKD, synbiotics did not significantly reduce serum IS but did decrease serum PCS and favorably modified the stool microbiome. Large-scale clinical trials are justified.

In vivo kinetics of the uremic toxin p-cresyl sulfate in mice with variable renal function.

Uremic toxins such as p-cresyl sulfate (PCS) are associated with increased mortality for chronic kidney disease (CKD) patients, but in vivo PCS toxicity studies are limited due to the lack of a standard animal model. To establish such a model, we measured the pharmacokinetics of PCS in mice with variable renal function. Male Balb/c mice subjected to 5/6 nephrectomy (CRF), unilateral nephrectomy (UNX), or no surgery (controls) were given PCS (po, 50 mg/kg). Blood samples were collected over time and plasma PCS concentrations were measured. Over 4 h, PCS was significantly higher in the plasma of CRF mice (63.28 ± 2.76 mg/L), compared to UNX mice (3.11 ± 0.64 mg/L) and controls (0.39 ± 0.12 mg/L). The PCS half-life was greatest in CRF mice (12.07 ± 0.12 h), compared to 0.79 ± 0.04 h in UNX mice and 0.48 ± 0.02 h in control mice. However, the potential presence of additional uremic toxins along with PCS in CRF mice and rapid PCS clearance in control mice suggest that the UNX mouse would be a better PCS model to study toxicity.

CKD NUTRITION, INFLAMMATION AND OXIDATIVE STRESS

Introduction and Aims: Serum p-cresyl sulfate associates with cardiovascular disease in patients at different stages of chronic kidney disease. p-Cresyl sulfate concentrations are determined by intestinal uptake of p-cresol, human metabolism to p-cresyl sulfate and renal clearance. Whether intestinal uptake of p-cresol itself is associated with cardiovascular disease in patients with renal disease has not been studied to date. Methods: We performed a prospective study in patients with chronic kidney disease stage 1-5 (clinicaltrials.gov NCT00441623). Intestinal uptake of p-cresol, under steady state conditions, was estimated from 24h urinary excretion of p-cresyl sulfate. Primary endpoint was time to first cardiovascular event, i.e. cardiac death, myocardial infarction/ischemia, ventricular arythmia, cardiovascular surgery, cerebrovascular accident or symptomatic peripheral arterial disease. Statistical analysis was done using Kaplan Meier estimates and Cox proportional hazard analyses. Results: In a cohort of 200 patients, median 24h urinary excretion of p-cresyl sulfate was 457.47 µmol (IQR 252.68-697.17). After a median follow-up of 52 months, 25 patients reached the primary endpoint (tertile 1/2/3: 5/6/14 events, log rank P 0.0368, see figure). Higher urinary excretion of p-cresyl sulfate was related with cardiovascular events (univariate hazard ratio per 100 µmol increase: 1.112, P 0.0015). In multivariate analysis, urinary excretion of p-cresyl sulfate remained a predictor of cardiovascular events, independent of markers of renal function (Hazard ratio 1.120, P 0.0022) and in different models with other cardiovascular risk factors (Framingham risk factors, cardiovascular history, diabetes mellitus and biochemical parameters). The independent association between urinary excretion of p-cresyl sulfate and outcome persisted after correction for serum p-cresyl sulfate. Conclusions: Intestinal uptake of p-cresol associates with cardiovascular disease independent of renal function. Insights into mechanisms governing intestinal generation and absorption of p-cresol may lead to identification of novel therapeutic targets to reduce cardiovascular disease risk in patients with chronic kidney disease.

Serum Concentrations of p-Cresyl Sulfate and Indoxyl Sulfate, But Not Inflammatory Markers, Increase in Incident Peritoneal Dialysis Patients in Parallel with Loss of Residual Renal Function

High serum concentrations of the protein-bound uremic retention solutes p-cresyl sulfate (PCS) and indoxyl sulfate (IndS) and inflammation are associated with increased cardiovascular morbidity and mortality in chronic kidney disease. Renal clearance contributes to up to 80% of the total clearance of PCS and IndS in peritoneal dialysis (PD) patients. Cross-sectional studies evaluating the impact of residual renal function (RRF) on serum concentrations of PCS, IndS, and circulating inflammatory markers have yielded conflicting results. ♢ To clarify this issue, we carried out a prospective observational cohort study in incident PD patients (n = 35; 19 men; mean age: 55 ± 17 years). Midday blood samples were collected and analyzed for total serum PCS, IndS, C-reactive protein, and high-sensitivity interleukin 6. Peritoneal and renal clearances were calculated from urine and dialysate collections, and RRF was calculated as the mean of renal urea nitrogen and creatinine clearances. Patients were assessed 1, 6, 12, and 24 months after PD start. Differences between time points were analyzed using linear mixed models (LMMs). ♢ Residual renal function declined significantly over time (LMM p < 0.0001). Peritoneal clearances of both toxins tended to increase, but did not compensate for the declining renal clearances. Serum concentrations of PCS and IndS increased significantly over time (LMM p = 0.01; p = 0.0009). In contrast, total mass removal of both toxins remained stable. Circulating inflammatory markers did not change over time. ♢ Our data indicate that serum concentrations of PCS and IndS, but not inflammatory markers, increase in incident PD patients in parallel with loss of RRF.

Renal Clearance and Intestinal Generation of p-Cresyl Sulfate and Indoxyl Sulfate in CKD

p-Cresyl sulfate and indoxyl sulfate contribute to cardiovascular disease and progression of renal disease. Renal clearance of both solutes mainly depends on tubular secretion, and serum concentrations are widely dispersed for any given stage of CKD. From this information, it is inferred that estimated GFR is not a suitable proxy of the clearance of these solutes. Formal clearance studies have, however, not been performed to date. This study analyzed renal clearances of p-cresyl sulfate and indoxyl sulfate in the Leuven CKD cohort (NCT00441623; inclusion between November of 2005 and September of 2006) and explored their relationship with estimated GFR. Multivariate linear regression models were built to evaluate contributions of estimated GFR, demographics, and generation rates to p-cresyl sulfate and indoxyl sulfate serum concentrations. Renal clearances were analyzed in 203 patients with CKD stages 1-5. Indoxyl sulfate clearances (median=17.7, interquartile range=9.4-33.2 ml/min) exceeded p-cresyl sulfate clearances (median=6.8, interquartile range=3.4-12.0 ml/min) by about threefold. A linear relationship was observed between estimated GFR and clearances of p-cresyl sulfate (R(2)=0.50, P<0.001) and indoxyl sulfate (R(2)=0.55, P<0.001). In multivariate regression, p-cresyl sulfate concentrations were associated (R(2)=0.75) with estimated GFR and generation rate (both P<0.001). Indoxyl sulfate concentrations were associated (R(2)=0.74) with estimated GFR, generation rate (both P<0.001), age (P<0.05), and sex (P<0.05). Estimated GFR provides an acceptable estimate of renal clearance of p-cresyl sulfate and indoxyl sulfate. Remarkably, clearances of indoxyl sulfate exceed clearances of p-cresyl sulfate by approximately threefold, suggesting substantial differences between tubular transporter affinities and/or involvement of separate transporter systems for p-cresyl sulfate and indoxyl sulfate.

P-Cresyl Sulfate Promotes Insulin Resistance Associated with CKD

The mechanisms underlying the insulin resistance that frequently accompanies CKD are poorly understood, but the retention of renally excreted compounds may play a role. One such compound is p-cresyl sulfate (PCS), a protein-bound uremic toxin that originates from tyrosine metabolism by intestinal microbes. Here, we sought to determine whether PCS contributes to CKD-associated insulin resistance. Administering PCS to mice with normal kidney function for 4 weeks triggered insulin resistance, loss of fat mass, and ectopic redistribution of lipid in muscle and liver, mimicking features associated with CKD. Mice treated with PCS exhibited altered insulin signaling in skeletal muscle through ERK1/2 activation. In addition, exposing C2C12 myotubes to concentrations of PCS observed in CKD caused insulin resistance through direct activation of ERK1/2. Subtotal nephrectomy led to insulin resistance and dyslipidemia in mice, and treatment with the prebiotic arabino-xylo-oligosaccharide, which reduced serum PCS by decreasing intestinal production of p-cresol, prevented these metabolic derangements. Taken together, these data suggest that PCS contributes to insulin resistance and that targeting PCS may be a therapeutic strategy in CKD.