Uremic Toxin Concentrations Research Articles

Future of Uremic Toxin Management

During the progression of chronic kidney disease (CKD), the retention of uremic toxins plays a key role in the development of uremic syndrome. Knowledge about the nature and biological impact of uremic toxins has grown exponentially over the past decades. However, the science on reducing the concentration and effects of uremic toxins has not advanced in parallel. Additionally, the focus has remained for too long on dialysis strategies, which only benefit the small fraction of people with CKD who suffer from advanced kidney disease, whereas uremic toxicity effects are only partially prevented. This article reviews recent research on alternative methods to counteract uremic toxicity, emphasizing options that are also beneficial in the earlier stages of CKD, with a focus on both established methods and approaches which are still under investigation or at the experimental stage. We will consequently discuss the preservation of kidney function, the prevention of cardiovascular damage, gastro-intestinal interventions, including diet and biotics, and pharmacologic interventions. In the final part, we also review alternative options for extracorporeal uremic toxin removal. The future will reveal which of these options are valid for further development and evidence-based assessment, hopefully leading to a more sustainable treatment model for CKD than the current one.

The Effect of Renaltec on Serum Uremic Toxins in Cats with Experimentally Induced Chronic Kidney Disease.

Serum uremic toxins markedly increase in cats with chronic kidney disease (CKD) and have deleterious consequences. Renaltec is an oral adsorbent that binds uremic toxin precursors in the gut. In this prospective cohort study utilizing 13 purpose-bred cats with remnant kidney model-induced CKD (12 IRIS Stage 2, 1 IRIS Stage 3) eating a standardized renal diet, we aimed to assess the effect of Renaltec administration on serum indoxyl sulfate (IDS) and p-cresol sulfate (pCS) concentrations. Cats were sequentially treated with standard of care for 56 days, 500 mg Renaltec orally once daily for 56 days, and then three months later, 500 mg Renaltec orally twice daily for 56 days. Serum IDS and pCS concentrations were measured 28 and 56 days after the administration of Renaltec. Blood pressure and kidney function were measured before and 56 days after the administration of Renaltec. Significant decreases in serum IDS and pCS concentrations were observed for both once- and twice-daily dosing, particularly during the first 28 days of administration. More cats with BID dosing had clinically significant reductions in serum IDS and pCS concentrations than with SID dosing. Renaltec can reduce the serum concentrations of deleterious gut-derived uremic toxins in cats with CKD.

Assessment of Within- and Inter-Patient Variability of Uremic Toxin Concentrations in Children with CKD.

To promote improved trial design in upcoming randomized clinical trials in childhood chronic kidney disease (CKD), insight in the within- and inter-patient variability of uremic toxins with its nutritional, treatment- and patient-related confounding factors is of utmost importance. In this study, the within- and inter-patient variability of a selection of uremic toxins in a longitudinal cohort of children diagnosed with CKD was assessed, using the intraclass correlation coefficient (ICC) and the within-patient coefficient of variation (CV). Subsequently, the contribution of anthropometry, estimated glomerular filtration rate (eGFR), dietary fiber and protein, and use of (prophylactic) antibiotics to uremic toxin variability was evaluated. Based on 403 observations from 62 children (median seven visits per patient; 9.4 ± 5.3 years; 68% males; eGFR 38.5 [23.1; 64.0] mL/min/1.73 m2) collected over a maximum of 2 years, we found that the within-patient variability is high for especially protein-bound uremic toxins (PBUTs) (ICC < 0.7; within-patient CV 37-67%). Moreover, eGFR was identified as a predominant contributor to the within- and inter-patient variability for the majority of solutes, while the impact of the child's anthropometry, fiber and protein intake, and antibiotics on the variability of uremic toxin concentrations was limited. Based on these findings, we would recommend future intervention studies that attempt to decrease uremic toxin levels to select a (non-dialysis) CKD study population with a narrow eGFR range. As the expected effect of the selected intervention should exceed the inter-patient variability of the selected uremic toxins, a narrow eGFR range might aid in improving the trial design.

A Systematic Review of Uremic Toxin Concentrations and Cardiovascular Risk Markers in Pediatric Chronic Kidney Disease.

Chronic kidney disease (CKD) can lead to cardiac dysfunction in a condition known as cardiorenal syndrome (CRS). It is postulated that the accumulation of uremic toxins in the bloodstream, as a consequence of declining kidney function, may contribute to these adverse cardiac effects. While CRS in adults has been extensively studied, there is a significant knowledge gap with pediatric patients. Uremic toxin levels in children remain inadequately characterized and quantified compared to adults. This review aims to systematically evaluate the association between uremic toxin concentrations and cardiac changes in pediatric CRS and to examine the impact of different dialysis modalities, specifically hemodialysis and peritoneal dialysis, on uremic toxin clearance and cardiovascular parameters. To address this, we conducted a systematic literature search of PubMed, following PRISMA guidelines. We used the terms "uremic toxins" and "cardiorenal syndrome" with variations in syntax to search for studies discussing the relationship between uremic toxin levels in CKD, the subsequent impact on cardiac parameters, and the emergence of cardiac dysfunction. Full-text articles written in English, conducted on humans aged from birth to 18 years, and published until December 2021 were included. A comprehensive literature search yielded six studies, and their risk of bias was assessed using JBI Critical Appraisal Checklists. Our systematic review is registered on PROSPERO, number CRD42023460072. This synthesis intends to provide an understanding of the role of uremic toxins in pediatric CRS. The findings reveal that pediatric patients with end-stage CKD on dialysis exhibit elevated uremic toxin levels, which are significantly associated with cardiovascular disease parameters. Additionally, the severity of CKD correlated with higher uremic toxin levels. No conclusive evidence was found to support the superiority of either hemodialysis or peritoneal dialysis in terms of uremic toxin clearance or cardiovascular outcomes. More pediatric-specific standardized and longitudinal studies are needed to develop targeted treatments and improve clinical outcomes and the quality of life for affected children.

Reduction in Serum Concentrations of Uremic Toxins Driven by Bifidobacterium Longum Subsp. Longum BL21 is Associated with Gut Microbiota Changes in a Rat Model of Chronic Kidney Disease.

Gut microbiota dysbiosis and consequent impairment of gut barrier function, culminating in elevated levels of uremic toxins, are prevalent in chronic kidney disease (CKD) patients. These toxins, notably indoxyl sulphate (IS), indole-3-acetic acid (IAA), and trimethylamine oxide (TMAO), are implicated in a spectrum of CKD-related complications, including cardiovascular disease, bone and mineral disorders, and inflammation. The specific impacts of various probiotics on these CKD manifestations remain unexplored. This study delved into the potential of dietary probiotic interventions, particularly Bifidobacterium longum subsp. longum BL21, to modulate gut microbiota and mitigate metabolic disorders in a CKD rat model. Over a six-week period, we administered a dietary regimen of BL21 and conducted comprehensive analyses, including serum uremic toxin quantification and 16S rRNA gene sequencing, to systematically profile gut microbial alterations at the phylogenetic level. Our findings reveal that BL21 intervention significantly ameliorated CKD-induced disruptions in gut microbial populations, enhancing both microbial richness and the relative abundance of key taxa. Importantly, BL21 appeared to exert its beneficial effects by modulating the abundance of crucial species such as Barnesiella and Helicobacter. Functionally, the intervention markedly normalized serum levels of IS, IAA, and TMAO, while potentially attenuating p-cresol sulphate (PCS) and p-cresol glucuronide (PCG) concentrations. Consequently, BL21 demonstrated efficacy in regulating gut microbiota and curtailing the accumulation of uremic toxins. Our results advocate for the utilization of BL21 as a dietary intervention to diminish serum uremic toxins and re-establish gut microbiota equilibrium at the phylogenetic level, underscoring the promise of probiotic strategies in the management of CKD.

Changes in the composition of the gut microbiota and content of microbial-derived uremic toxins in patients undergoing hemodialysis

Recent data highlight a significant role of the gut microbiota in the pathogenesis of chronic kidney disease, particularly in its terminal stage. However, little is known about the features of intestinal dysbiosis in people undergoing programed hemodialysis. Changes in the intestinal microbiota and blood levels of uremic toxins of microbial origin in patients with terminal renal insufficiency receiving hemodialysis were analyzed. This cross-sectional study included 80 patients receiving hemodialysis and 20 individuals with normal kidney function. The state of the microbiocenosis of the colon was studied using a polymerase chain reaction with a commercial set Colonoflor 16 (premium) manufactured by Alfalab (Russia). Serum levels of trimethylamine and its metabolite trimethylamine-N-oxide were determined by liquid chromatography/mass spectrometry. The concentrations of indoxyl sulfate and p-cresyl sulfate were evaluated by enzyme immunoassay according to the instructions of a commercial kit. In patients undergoing programed hemodialysis, increased colonization of enterococci was combined with the reduction of lacto and bifidophlora, E. coli, ruminococci, bacteria producing short-chain fatty acids (Faecalibacterium prausnitzii, Eubacterium rectale, Roseburia inulinivorans, and Blautia spp.) and microorganisms involved in maintaining the integrity of the intestinal barrier (Bacteroides thetaomicron and Akkermansia muciniphila). In addition, high titer levels of representatives of opportunistic and even pathogenic flora were often found in this group. Intestinal dysbiosis in patients undergoing programed hemodialysis was accompanied by a significant increase in the concentration of uremic toxins in the blood. Compared with individuals with normal renal function, the trimethylamine level in patients undergoing programed hemodialysis was increased 22 times; trimethylamine-N-oxide, 23 times; indoxyl sulfate, 21 times; and p-cresyl sulfate, 5 times. Thus, patients receiving hemodialysis exhibited pronounced pathological changes in intestinal microbiocenosis, accompanied by a significant increase in serum levels of uremic toxins of microbial origin.

Indoxyl Sulfate Contributes to Impaired Height Velocity in (Pre)School Children

IntroductionGrowth failure is considered the most important clinical outcome parameter in childhood chronic kidney disease (CKD). Central in the pathophysiology of growth failure is the presence of a chronic pro-inflammatory state, presumed partly driven by the accumulation of uremic toxins. In this study, we assessed the association between uremic toxin concentrations and height velocity in a longitudinal multicentric prospective pediatric CKD cohort of (pre-)school aged children and children during pubertal stages. MethodsIn a prospective, multicentric observational study, a selection of uremic toxin levels of children (0-18y) with CKD stage 1-5D was assessed every 3 months (max 2 years) along with clinical growth parameters. Linear mixed models with a random slope for age and a random intercept for child were fitted for height (in cm and SDS). A piecewise linear association between age and height was assumed. ResultsData-analysis included data from 560 visits of 81 children (median age 9.4 years; 2/3 male). In (pre-)school aged children (2-12 years), a 10% increase in concurrent indoxyl sulfate (IxS, total) concentration resulted in an estimated mean height velocity decrease of 0.002 SDS/year (p<.05), given that CKD stage, growth hormone, bicarbonate concentration, and dietary protein intake are held constant. No significant association with height velocity was found in children during pubertal stages (>12years). ConclusionsThe present study demonstrated that especially IxS contributes to a lower height velocity in (pre-)school children, while we could not find a role for uremic toxins with height velocity during pubertal stages.

Canagliflozin attenuates kidney injury, gut-derived toxins, and gut microbiota imbalance in high-salt diet-fed Dahl salt-sensitive rats

Purpose To investigate the effects of canagliflozin (20 mg/kg) on Dahl salt-sensitive (DSS) rat gut microbiota and salt-sensitive hypertension-induced kidney injury and further explore its possible mechanism. Methods Rats were fed a high-salt diet to induce hypertension and kidney injury, and physical and physiological indicators were measured afterwards. This study employed 16S rRNA sequencing technology and liquid chromatography–tandem mass spectrometry (LC–MS/MS)-based metabolic profiling combined with advanced differential and association analyses to investigate the correlation between the microbiome and the metabolome in male DSS rats. Results A high-salt diet disrupted the balance of the intestinal flora and increased toxic metabolites (methyhistidines, creatinine, homocitrulline, and indoxyl sulfate), resulting in severe kidney damage. Canagliflozin contributed to reconstructing the intestinal flora of DSS rats by significantly increasing the abundance of Corynebacterium spp., Bifidobacterium spp., Facklamia spp., Lactobacillus spp., Ruminococcus spp., Blautia spp., Coprococcus spp., and Allobaculum spp. Moreover, the reconstruction of the intestinal microbiota led to significant changes in host amino acid metabolite concentrations. The concentration of uremic toxins, such as methyhistidines, creatinine, and homocitrulline, in the serum of rats was decreased by canagliflozin, which resulted in oxidative stress and renal injury alleviation. Conclusion Canagliflozin may change the production of metabolites and reduce the level of uremic toxins in the blood circulation by reconstructing the intestinal flora of DSS rats fed a high-salt diet, ultimately alleviating oxidative stress and renal injury.

Continuous intake of galacto-oligosaccharides containing syrup contributes to maintaining the health of household dogs by modulating their gut microbiota.

Interest is growing in the relationship of the microbiota and intestinal environment with health in companion animals. Galacto-oligosaccharides (GOS), typical prebiotics, are expected to provide benefits in dogs. Previous studies of GOS in dogs have involved dogs with similar rearing conditions and diets, which may have biased the results. We conducted an open study of 26 healthy dogs kept in households with diverse rearing environments in order to evaluate how the intake of a GOS-containing syrup affects the intestinal microbiota and its metabolites. Each dog was fed 1.2-4.8 g of the GOS-containing syrup (GOS 0.5-2.0 g equivalent) for 8 weeks. Fecal microbiota, fecal concentrations of organic acids and putrefactive products, fecal odor, and serum uremic toxin concentrations were evaluated before intake (0 weeks), during the 8-week intake period (4 and 8 weeks), and 4 weeks after intake (12 weeks). The activity of N-benzoyl-DL-arginine peptidase in dental plaque, which may be associated with periodontal disease, was evaluated at 0 and 8 weeks. Continuous intake of GOS resulted in changes in fecal microbiota, with a particularly marked increase in the abundance of Megamonas, which produces propionic acid. Other findings included a significant increase in the fecal acetic, propionic, and n-butyric acid concentrations. Additionally, significant decreases in fecal odor, fecal phenol concentration, and serum indoxyl sulfate concentration. Intake of GOS was also associated with a significant decrease in N-benzoyl-DL-arginine peptidase activity in dental plaques. These results suggest that continuous intake of GOS may contribute to canine health.

Chronic kidney disease may evoke anxiety by altering CRH expression in the amygdala and tryptophan metabolism in rats

Chronic kidney disease (CKD) is associated with anxiety; however, its exact mechanism is not well understood. Therefore, the aim of the present study was to assess the effect of moderate CKD on anxiety in rats. 5/6 nephrectomy was performed in male Wistar rats. 7 weeks after, anxiety-like behavior was assessed by elevated plus maze (EPM), open field (OF), and marble burying (MB) tests. At weeks 8 and 9, urinalysis was performed, and blood and amygdala samples were collected, respectively. In the amygdala, the gene expression of Avp and the gene and protein expression of Crh, Crhr1, and Crhr2 were analyzed. Furthermore, the plasma concentration of corticosterone, uremic toxins, and tryptophan metabolites was measured by UHPLC-MS/MS. Laboratory tests confirmed the development of CKD. In the CKD group, the closed arm time increased; the central time and the total number of entries decreased in the EPM. There was a reduction in rearing, central distance and time in the OF, and fewer interactions with marbles were detected during MB. CKD evoked an upregulation of gene expression of Crh, Crhr1, and Crhr2, but not Avp, in the amygdala. However, there was no alteration in protein expression. In the CKD group, plasma concentrations of p-cresyl-sulfate, indoxyl-sulfate, kynurenine, kynurenic acid, 3-hydroxykynurenine, anthranilic acid, xanthurenic acid, 5-hydroxyindoleacetic acid, picolinic acid, and quinolinic acid increased. However, the levels of tryptophan, tryptamine, 5-hydroxytryptophan, serotonin, and tyrosine decreased. In conclusion, moderate CKD evoked anxiety-like behavior that might be mediated by the accumulation of uremic toxins and metabolites of the kynurenine pathway, but the contribution of the amygdalar CRH system to the development of anxiety seems to be negligible at this stage.

Metagenome-wide analysis uncovers gut microbial signatures and implicates taxon-specific functions in end-stage renal disease

BackgroundThe gut microbiota plays a crucial role in regulating host metabolism and producing uremic toxins in patients with end-stage renal disease (ESRD). Our objective is to advance toward a holistic understanding of the gut ecosystem and its functional capacity in such patients, which is still lacking.ResultsHerein, we explore the gut microbiome of 378 hemodialytic ESRD patients and 290 healthy volunteers from two independent cohorts via deep metagenomic sequencing and metagenome-assembled-genome-based characterization of their feces. Our findings reveal fundamental alterations in the ESRD microbiome, characterized by a panel of 348 differentially abundant species, including ESRD-elevated representatives of Blautia spp., Dorea spp., and Eggerthellaceae, and ESRD-depleted Prevotella and Roseburia species. Through functional annotation of the ESRD-associated species, we uncover various taxon-specific functions linked to the disease, such as antimicrobial resistance, aromatic compound degradation, and biosynthesis of small bioactive molecules. Additionally, we show that the gut microbial composition can be utilized to predict serum uremic toxin concentrations, and based on this, we identify the key toxin-contributing species. Furthermore, our investigation extended to 47 additional non-dialyzed chronic kidney disease (CKD) patients, revealing a significant correlation between the abundance of ESRD-associated microbial signatures and CKD progression.ConclusionThis study delineates the taxonomic and functional landscapes and biomarkers of the ESRD microbiome. Understanding the role of gut microbiota in ESRD could open new avenues for therapeutic interventions and personalized treatment approaches in patients with this condition.

Phenylacetylglutamine and trimethylamine N-oxide: Two uremic players, different actions.

Chronic kidney disease (CKD) patients exhibit a heightened cardiovascular (CV) risk which may be partially explained by increased medial vascular calcification. Although gut-derived uremic toxin trimethylamine N-oxide (TMAO) is associated with calcium-phosphate deposition, studies investigating phenylacetylglutamine's (PAG) pro-calcifying potential are missing. The effect of TMAO and PAG in vascular calcification was investigated using 120 kidney failure patients undergoing living-donor kidney transplantation (LD-KTx), in an observational, cross-sectional manner. Uremic toxin concentrations were related to coronary artery calcification (CAC) score, epigastric artery calcification score, and markers of established non-traditional risk factors that constitute to the 'perfect storm' that drives early vascular aging in this patient population. Vascular smooth muscle cells were incubated with TMAO or PAG to determine their calcifying effects in vitro and analyse associated pathways by which these toxins may promote vascular calcification. TMAO, but not PAG, was independently associated with CAC score after adjustment for CKD-related risk factors in kidney failure patients. Neither toxin was associated with epigastric artery calcification score; however, PAG was independently, positively associated with 8-hydroxydeoxyguanosine. Similarly, TMAO, but not PAG, promoted calcium-phosphate deposition in vitro, while both uremic solutes induced oxidative stress. In conclusion, our translational data confirm TMAO's pro-calcifying effects, but both toxins induced free radical production detrimental to vascular maintenance. Our findings suggest these gut-derived uremic toxins have different actions on the vessel wall and therapeutically targeting TMAO may help reduce CV-related mortality in CKD.

The Effect of Dietary Protein Concentration on the Fecal Microbiome and Serum Concentrations of Gut-Derived Uremic Toxins in Healthy Adult Cats.

The purpose of this study was to evaluate the effect of feeding healthy adult cats with foods containing variable protein concentrations on the fecal microbiome and serum concentrations of the gut-derived uremic toxins indoxyl sulfate, p-cresol sulfate (pCS), and trimethylamine-n-oxide. Twenty healthy young adult cats were randomized into two groups and fed either a low-protein diet (LPD; 7.4 g/100 kcal ME) or a high-protein diet (HPD; 11.0 g/100 kcal ME) for a 12-week period. Serum uremic toxin concentrations were measured via liquid chromatography tandem mass spectrometry, and the fecal microbiome was characterized using shallow sequence shotgun metagenomics. Cats that consumed the HPD had higher pCS concentrations at 8 weeks (p = 0.028) when compared to baseline. After 12 weeks, cats fed the HPD had higher fecal alpha diversity indices at both the taxonomic and functional levels and lower fecal Bifidobacterium relative abundance compared to those cats fed the LPD. In conclusion, a change in diet and dietary protein concentration shifted the fecal microbial community and microbial function. Feeding cats a high amount of protein increased serum concentrations of the uremic toxin pCS; however, the effect was short-lived.

#3367 NON-INVASIVE OPTICAL ESTIMATION OF INTRADIALYTIC CONCENTRATIONS OF UREMIC TOXINS IN BLOOD OF HEMODIALYSIS PATIENTS

Abstract Background and Aims Hemodialysis (HD) adequacy is generally estimated by the dialysis adequacy marker Kt/V urea that poorly describes removal of uremic toxins with different removal kinetics, such as protein bound or middle molecule uremic toxins, which have direct effect on morbidity and mortality of end stage kidney disease (ESKD) patients. We have recently shown the feasibility of estimating an alternative dialysis adequacy marker that can be applied to dialysis sessions with varying settings and different uremic toxins, intradialytic time average concentration (TAC) of uremic toxins, such as urea, uric acid (UA), indoxyl sulfate (IS) and beta-2-microglobulin in blood of ESKD patients, from spent dialysate concentrations determined by laboratory methods [1]. The aim of this retrospective observational study was to estimate intradialytic TAC of uremic toxins UA and IS non-invasively from spent dialysate concentrations determined by optical methods. Method Twenty-two ESKD patients on chronic HD were enrolled into the study. For each patient 4 midweek dialysis sessions with different treatment settings were included (1 HD: Qb = 200 mL/min, Qd = 300 mL/min, dialyzer 1,5m2; 3 HDF: median (interquartile range) Qb = 298 (296-356) mL/min, Qd = 795 (500–800) mL/min, Vsubst = 21.8 (15–24.5) L, dialyzers 1,8 m2 and 2,2 m2). During each dialysis session, blood samples were taken at 0 min (start) and 240 min after the start from the arterial blood line and dialysate samples were taken at 7 min and 240 min after the start from the outlet of the dialysis machine. Concentrations of UA and IS in serum and spent dialysate samples were determined with HPLC. In addition, UV absorbance and fluorescence of the spent dialysate samples were measured with spectrophotometer UV-3600 and spectrofluorometer RF-6000 (both from Shimadzu Corp., Japan), after which concentrations of UA and IS in spent dialysate samples were determined based on the optical properties of samples. Stability of HD treatment settings were monitored online and dialysis sessions with unstable blood and dialysate flow rates were excluded. TAC of UA and IS were calculated from serum concentrations and evaluated from laboratory and optically estimated logarithmic mean concentrations (Mln D) of spent dialysate. Results Mean intradialytic serum TAC values of UA and IS were 198.4±44.0 μmol/L and 69.5 ± 37.8 μmol/L and strongly correlated to those estimated from optically determined Mln D 198.0±38.9 μmol/L (R2 = 0.75) and 69.5 ± 37.8 μmol/L (R2 = 0.81), respectively. Mln D of UA and IS in spent dialysate based on laboratory methods were 102.2 ± 22.8 μmol/L and 5.9 ± 3.5 μmol/L and strongly correlated with the optically determined concentrations of 102.7 ± 23.1 μmol/L (R2 = 0.97) and 6.1 ± 3.4 μmol/L (R2 = 0.97), respectively. Conclusion Intradialytic serum TAC of UA and IS can be estimated non-invasively with optical methods from their concentration in spent dialysate independent of treatment modality. Optical online monitoring of spent dialysate in real-time could therefore provide additional information about treatment adequacy regarding the removal of uremic toxins’ other than urea. In future, TAC estimation models should be optimized for each uremic toxin to establish higher accuracy, considering real-time treatment settings, recirculation etc.

#3386 PROTON-PUMP INHIBITORS AND SERUM CONCENTRATIONS OF UREMIC TOXINS IN PATIENTS WITH CHRONIC KIDNEY DISEASE

Abstract Background and Aims Use of proton-pump inhibitors (PPIs) is common in patients with chronic kidney disease (CKD). PPIs and many uremic toxins (UTs) are eliminated by a kidney tubular organic anion transporter system. In a cross-sectional study, we sought to evaluate the association between PPI prescription and serum concentrations of various UTs. Method We studied a randomly selected subgroup of participants in the CKD-REIN prospective cohort (adult patients with a confirmed diagnosis of CKD and estimated glomerular filtration rate (eGFR) &amp;lt;60ml/min/1.73m²) with available frozen samples collected at baseline. PPI prescription was recorded at baseline. Serum concentrations of 10 UTs were measured using a validated liquid chromatography tandem mass spectrometry technique. Multiple linear regression was performed, with the log UT concentration as the dependent variable. Results Of the 680 included patients [median age: 68 years; median eGFR: 32 ml/min/1.73 m2], 31% had PPI prescriptions at baseline. Patients using PPIs had higher levels of certain UTs in comparison to other patients, including total and free indoxyl sulfate (IS), total and free p-cresylsulfate, total and free p-cresylglucuronide (PCG), phenylacetylglutamine (PAG), free kynurenine, and free hippuric acid. After adjustment for baseline comorbidities, number of co-prescribed drugs and laboratory data including eGFR, associations between PPI prescription and elevated serum concentrations of free and total IS, free and total PCG, and PAG remained significant. Conclusion Our results indicate that PPI prescription is independently associated with serum UT retention. These findings indicate a potential mechanism for side effect of PPIs in CKD patients that will need to be confirmed by longitudinal studies.

#3048 INDOXYL SULFATE INHIBITS OSTEOGENESIS OF BONE MARROW DERIVED MESENCHYMAL STEM CELLS THROUGH AHR/HES1/BMP2 PATHWAY

Abstract Background and Aims There is a high global burden of chronic kidney disease (CKD). The increased risk of bone fracture in patients with CKD suggests that CKD-associated factors, such as uremic toxins, might be the cause. Recent studies demonstrated that low turnover osteodystrophy and bone formation defect develop in early CKD, which indicates that uremic toxins, particularly in relatively low concentrations, can potentially be a cause. Thus far, studies about defected osteogenesis adopted high concentrations of uremic toxins (for example, indoxyl sulfate (ISx) &amp;gt;100 μM). Furthermore, the pathology is not yet fully investigated. Uremic toxin induced aryl hydrocarbon receptor (AHR) has been linked to bone formation defect, however, the mechanisms are incompletely understood. AHR inhibit osteogenesis during early processes of differentiation of early cells (stem cells), but whether uremic toxins induced AHR to affect stem cell in osteogenesis lineage has yet to be studied. The present study aims to clarify whether ISx at concentrations approximate to average in CKD patients (20 μM in free form) affect osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs), and further survey the underline signal transduction of AHR-induced defected osteogenesis. Method Mineralization of D1 cells (mouse BMSCs) was evaluated by alizarin red S staining (ARS). The mRNA expressions and protein levels of osteogenic markers including Runx2, BMP2, ALP, and osteocalcin were determined by quantitative real-time polymerase chain reaction (RT-PCR) and western blotting. AHR translocation into the nucleus was evaluated by an immunofluorescence confocal microscope. Reporter gene assays were adopted to study the transcriptional regulation of Runx2 and BMP2. Results ISx at concentrations ≤50 μM significantly downregulated mineralization of BMSCs with the most influence in the early stage of osteogenesis. ISx decreased the mRNA expressions and protein levels of osteogenic markers Runx2, BMP2, ALP, and osteocalcin. ISx of 50 μM induced AHR translocation into the nucleus and upregulated AHR target genes CYP1a1 and CYP1b1. The ISx-induced mineralization defects of BMSCs were counteracted by AHR antagonist CH223191, while downregulated gene expressions of osteogenic markers were recovered by AHR antagonist and knockdown (KD) of AHR. In mechanistic studies, ISx upregulated mRNA levels of hairy and enhancer of split (HES1), which is a primary target of NOTCH signaling. Although there were no significant differences in expressions of Notch1∼4, the upregulated Hes1 was attenuated by the antagonist and KD of AHR, which indicated that Hes1 was directly regulated by AHR. We identified putative binding sites of transcription repressor Hes1 in the promoter area of BMP2 and Runx2. Following experimental treatment of ISx, expression levels of BMP2 and Runx2 monitored by reporter assays were downregulated, which indicated that Hes1 plays as a transcription repressor to downregulated BMP2 and Runx2. Conclusion ISx under clinically relevant concentrations attenuated mineralization of BMSCs, particularly in the early stage of osteogenesis. ISx-induced AHR upregulated Hes1, which inhibited expressions of not only Runx2, but also BMP2, which has not been published before. A study of the underline signal transduction pathways relevant to the AHR genomic control system may provide potential therapy for low bone formation in early CKD.

Proton-Pump Inhibitors and Serum Concentrations of Uremic Toxins in Patients with Chronic Kidney Disease.

Use of proton-pump inhibitors (PPIs) is common in patients with chronic kidney disease (CKD). PPIs and many uremic toxins (UTs) are eliminated by the kidney's tubular organic anion transporter system. In a cross-sectional study, we sought to evaluate the association between PPI prescription and serum concentrations of various UTs. We studied a randomly selected sub-group of participants in the CKD-REIN cohort (adult patients with a confirmed diagnosis of CKD and estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2) with available frozen samples collected at baseline. PPI prescription was recorded at baseline. Serum concentrations of 10 UTs were measured using a validated liquid chromatography tandem mass spectrometry technique. Multiple linear regression was performed, with the log UT concentration as the dependent variable. Of the 680 included patients (median age: 68 years; median eGFR: 32 mL/min/1.73 m2), 31% had PPI prescriptions at baseline. Patients using PPIs had higher levels of certain UTs in comparison to other patients, including total and free indoxyl sulfate (IS), total and free p-cresylsulfate, total and free p-cresylglucuronide (PCG), phenylacetylglutamine (PAG), free kynurenine, and free hippuric acid. After adjustment for baseline co-morbidities, number of co-prescribed drugs, and laboratory data, including eGFR, associations between PPI prescription and elevated serum concentrations of free and total IS, free and total PCG, and PAG remained significant. Our results indicate that PPI prescription is independently associated with serum UT retention. These findings are interesting to better understand the factors that may modulate serum UT concentration in CKD patients, however, they will need to be confirmed by longitudinal studies.

Emerging Roles of Uremic Toxins and Inflammatory Cytokines in the Alteration of Hepatic Drug Disposition in Patients with Kidney Dysfunction.

Patients with kidney dysfunction exhibit distinct pharmacokinetic profiles compared to those with normal kidney function. Hence, it is desirable to monitor the drug efficacy and toxicity caused by fluctuations in plasma drug concentrations associated with kidney dysfunction. Recently, pharmacokinetic information of drugs excreted mainly through the urine of patients with kidney dysfunction has been reported via drug-labeling information. Pharmacokinetic changes in drugs mainly eliminated by the liver cannot be overlooked as drug metabolism and/or transport activity in the liver may also be altered in patients with kidney dysfunction; however, the underlying mechanisms remain unclear. To plan an appropriate dosage regimen, it is necessary to clarify the underlying processes of functional changes in pharmacokinetic proteins. In recent years, uremic toxins have been shown to reduce the activity and/or expression of renal and hepatic transporters. This inhibitory effect has been reported to be time-dependent. In addition, inflammatory cytokines, such as interleukin-6, released from immune cells activated by uremic toxins and/or kidney injury can reduce the expression levels of drug-metabolizing enzymes and transporters in human hepatocytes. In this mini-review, we have summarized the renal and hepatic pharmacokinetic changes as well as the potential underlying mechanisms in kidney dysfunction, such as the chronic kidney disease and acute kidney injury. SIGNIFICANCE STATEMENT: Patients with kidney dysfunction exhibit distinct pharmacokinetic profiles compared to those with normal kidney function. Increased plasma concentrations of uremic toxins and inflammatory cytokines during kidney disease may potentially affect the activities and/or expression levels of drug-metabolizing enzymes and transporters in the liver and kidneys.

Adsorption- and Displacement-Based Approaches for the Removal of Protein-Bound Uremic Toxins.

End-stage renal disease (ESRD) patients rely on renal replacement therapies to survive. Hemodialysis (HD), the most widely applied treatment, is responsible for the removal of excess fluid and uremic toxins (UTs) from blood, particularly those with low molecular weight (MW < 500 Da). The development of high-flux membranes and more efficient treatment modes, such as hemodiafiltration, have resulted in improved removal rates of UTs in the middle molecular weight range. However, the concentrations of protein-bound uremic toxins (PBUTs) remain essentially untouched. Due to the high binding affinity to large proteins, such as albumin, PBUTs form large complexes (MW > 66 kDa) which are not removed during HD and their accumulation has been strongly associated with the increased morbidity and mortality of patients with ESRD. In this review, we describe adsorption- and displacement-based approaches currently being studied to enhance the removal of PBUTs. The development of mixed matrix membranes (MMMs) with selective adsorption properties, infusion of compounds capable of displacing UTs from their binding site on albumin, and competitive binding membranes show promising results, but the road to clinical application is still long, and further investigation is required.

Canagliflozin protects the cardiovascular system through effects on the gut environment in non-diabetic nephrectomized rats.

The gut produces toxins that contribute to the cardiovascular complications of chronic kidney disease. Canagliflozin, a sodium glucose cotransporter (SGLT) 2 inhibitor that is used as an anti-diabetic drug, has a weak inhibitory effect against SGLT1 and may affect the gut glucose concentration and environment. Here, we determined the effect of canagliflozin on the gut microbiota and the serum gut-derived uremic toxin concentrations in 5/6th nephrectomized (Nx) rats. Canagliflozin increased the colonic glucose concentration and restored the number of Lactobacillus bacteria, which was low in Nx rats. In addition, the expression of tight junction proteins in the ascending colon was low in Nx rats, and this was partially restored by canagliflozin. Furthermore, the serum concentrations of gut-derived uremic toxins were significantly increased by Nx and reduced by canagliflozin. Finally, the wall of the thoracic aorta was thicker and there was more cardiac interstitial fibrosis in Nx rats, and these defects were ameliorated by canagliflozin. The increases in colonic glucose concentration, Lactobacillus numbers and tight junction protein expression, and the decreases in serum uremic toxin concentrations and cardiac interstitial fibrosis may have been caused by the inhibition of SGLT1 by canagliflozin because similar effects were not identified in tofogliflozin-treated rats.