Association of Plasma Uremic Solute Levels with Residual Kidney Function in Children on Peritoneal Dialysis

Background and objectives. Residual native kidney function confers health benefits in dialysis patients. It can facilitate control of extracellular volume and inorganic ion concentrations. Residual kidney function can also limit the accumulation of uremic solutes. This study assessed whether lower plasma concentrations of uremic solutes were associated with residual kidney function in pediatric patients on peritoneal dialysis. Design, setting, participants, and measurements. Samples were analyzed from 29 pediatric peritoneal dialysis patients including 13 without residual kidney function and 10 with residual kidney function. Metabolomic analysis by untargeted mass spectrometry compared plasma solute levels in patients with and without residual kidney function. Dialytic and residual clearances of selected solutes were also measured by assays employing chemical standards. Results. Metabolomic analysis showed that plasma levels of 256 uremic solutes in patients with residual kidney function averaged 64 (51-81 IQR) percent of the values in patients without residual kidney function who had similar total Kt/Vurea. The plasma levels were significantly lower for 59 of the 256 solutes in the patients with residual kidney function and significantly higher for none. Assays employing chemical standards showed that residual kidney function provides a higher portion of the total clearance for non-urea solutes than it does for urea. Conclusions. Concentrations of many uremic solutes are lower in peritoneal dialysis patients with residual kidney function than in those without residual kidney function receiving similar treatment as assessed by Kt/Vurea.

CE-MS-Based Identification of Uremic Solutes Specific to Hemodialysis Patients

Uremic toxins are suggested to be involved in the pathophysiology of hemodialysis (HD) patients. However, the profile of uremic solutes in HD patients has not been fully elucidated. In this study using capillary electrophoresis mass spectrometry (CE-MS), we comprehensively quantified the serum concentrations of 122 ionic solutes before and after HD in 11 patients. In addition, we compared the results with those in non-HD patients with chronic kidney disease (CKD) to identify HD patient-specific solutes. We identified 38 solutes whose concentrations were higher in pre-HD than in CKD stage G5. Ten solutes among them did not significantly accumulate in non-HD CKD patients, suggesting that these solutes accumulate specifically in HD patients. We also identified 23 solutes whose concentrations were lower in both pre- and post-HD than in CKD stage G5. The serum levels of 14 solutes among them were not affected by renal function in non-HD patients, suggesting that these solutes tend to be lost specifically in HD patients. Our data demonstrate that HD patients have a markedly different profile of serum uremic solute levels compared to that in non-HD CKD patients. The solutes identified in our study may contribute to the pathophysiology of HD patients.

Exploring blood alterations in chronic kidney disease and haemodialysis using metabolomics

Chronic kidney disease (CKD) is characterized by retention of uremic solutes. Compared to patients with non-dialysis dependent CKD, those requiring haemodialysis (HD) have increased morbidity and mortality. We wished to characterise metabolic patterns in CKD compared to HD patients using metabolomics. Prevalent non-HD CKD KDIGO stage 3b–4 and stage 5 HD outpatients were screened at a single tertiary hospital. Various liquid chromatography approaches hyphenated with mass spectrometry were used to identify 278 metabolites. Unsupervised and supervised data analyses were conducted to characterize metabolic patterns. 69 patients were included in the CKD group and 35 in the HD group. Unsupervised data analysis showed clear clustering of CKD, pre-dialysis (preHD) and post-dialysis (postHD) patients. Supervised data analysis revealed qualitative as well as quantitative differences in individual metabolites profiles between CKD, preHD and postHD states. An original metabolomics framework could discriminate between CKD stages and highlight HD effect based on 278 identified metabolites. Significant differences in metabolic patterns between CKD and HD patients were found overall as well as for specific metabolites. Those findings could explain clinical discrepancies between patients requiring HD and those with earlier stage of CKD.

Uremic solutes of indoxyl sulfate and p-cresol enhance protease-activated receptor-2 expression in vitro and in vivo in keratinocytes

Objectives: Uremic pruritus is common in patients with chronic kidney disease (CKD). The retention of uremic solutes is thought to be associated with uremic pruritus. Meanwhile, activation of protease-activated receptor-2 (PAR-2) has been suggested to play an important role in pruritus. The present study was performed to investigate the effects of uremic solutes on the expression of PAR-2 in the skin. Methods: Indoxyl sulfate (IS), p-cresol (PC), and uremic sera from CKD patients were used to stimulate PAR-2 expression in normal human epidermal keratinocytes (NHEKs). Also, NHEKs were additionally pretreated with soybean trypsin inhibitor to evaluate its inhibitory effect on PAR-2 expression. Patterns of cutaneous PAR-2 expression were investigated in skin samples from five CKD patients and CKD mice. Results: In NHEKs, IS, PC, and sera from CKD patients significantly induced PAR-2 mRNA and protein expression. Soybean trypsin inhibitor significantly decreased PAR-2 mRNA and protein expression in NHEKs treated with IS, PC, and CKD sera. NHEKs treated with IS and PC exhibited significant increases in protease activity. Skin from both CKD patients and mice exhibited marked upregulation of PAR-2 expression compared to control skin. Conclusions: Results from the present study suggest that uremic solutes either directly or indirectly affect PAR-2 expression in the skin of CKD subjects, potentially playing an important role in the pathogenesis of uremic pruritus.

P1059REMOVAL OF LOW MOLECULAR WEIGHT AND PROTEIN-BOUND UREMIC RETENTION SOLUTES WITH ALLO-HEMODIALYSIS: RESULTS FROM EX VIVO STUDY

Background and Aims It is projected that in 2030, 14.5 million people will have end stage kidney disease and need kidney replacement therapy, yet only 5.4 million will receive it due to economic, social, and political factors. We have proposed allo-hemodialysis (alloHD) as a simple and low-cost HD alternative (https://www.kidneynews.org/kidney-news/features/buddy-dialysis-probed-hemodialysis-alternative). In alloHD, the patient’s blood is dialyzed against the blood of a healthy subject (‘buddy’), who receives the excess fluid and uremic solutes and excretes them via his/her healthy kidneys. Method We conducted ex vivo experiment with bovine whole blood, 4L in a patient and buddy bucket, respectively. In this setup, buddy blood flows through the dialyzer fiber lumen, while patient blood flows in the dialysate space (Nipro Cellentia 17H dialyzer). The patient blood was spiked with urea, creatinine, potassium chloride, indoxyl sulfate (IS), and p-cresyl sulfate (pCS); solute levels on the buddy side were not altered. The alloHD session lasted for 3 hours, the ultrafiltration (UF) volume was 750 mL. The blood flow rates were kept constant at 150 and 200 mL/min on the patient and buddy side, respectively. Heparin (5000 IU/L) was added to either bucket. The alloHD machine prototype comprises 2 pumps on the buddy side and one on patient side (Figure 1A). UF is controlled by the blood flow rate differential between the buddy-sided arterial and venous pumps, respectively. Results The levels of small unbound solutes (urea, creatinine, potassium) equilibrate quickly between patient and buddy buckets (Fig. 1B, top panel). Of note, the buddy-sided potassium equilibrium concentration is lower, because ongoing UF dilutes albumin in the buddy bucket and concentrates it in the patient bucket, resulting in a Gibbs-Donnan potential. The protein-bound uremic solutes IS and pCS equilibrate towards lower total concentrations on the buddy side due to the earlier mentioned UF-induced albumin dilution. Of note, the levels of free IS and pCS, respectively, converge on both sides of the dialyzer membrane (Fig 1B, bottom panel). Conclusion Our ex vivo data suggest that alloHD can be used to treat hyperkalemia, a major cause of death in acute and chronic kidney failure. Both unbound and protein-bound low molecular weight uremic solutes are also removed. With elimination of “classical” dialysate, we simplify the HD procedure and reduce machine size and costs significantly, making it an affordable HD alternative. Feasibility and efficacy studies in animal models are the next step.

TO015INTRADIALYTIC ON-LINE MULTICOMPONENT TOTAL REMOVED SOLUTE MONITORING IN SPENT DIALYSATE BY A NOVEL MINIATURIZED OPTICAL SENSOR

Background and Aims Urea is the most commonly exploited marker of dialysis adequacy. Plenty of other uremic retention solutes with a deleterious effect on morbidity and mortality of uremic patients accumulate in ESKD patients [1]. Commonly, the uremic solutes are divided into three physicochemical types [2] with the representative markers urea, uric acid (UA),indoxyl sulfate (IS), and β2-Microglobulin (B2M). Optical monitoring of the uremic marker molecules has been proposed [3]. Despite being cumbersome as a clinical routine, direct dialysis quantification from total dialysate collection (TDC) is as the ‘gold standard’ for measuring the total amount of uremic solutes removed [4]. A robust and compact optical on-line dialysis monitoring device is a step closer to automatic assessment of removal of uremic toxins in dialysis. The aim of this study was to evaluate intradialytic on-line multicomponent Total Removed Solute (TRS) monitoring in the spent dialysate by a novel miniaturized optical sensor during hemodialysis (HD) and hemodiafiltration (HDF) with different settings. Method Ten ESKD patients (6 male and 4 female, 60.2±16.8 years) on chronic HDF were enrolled into the study (fistula N=9, graft N=1). For each patient 5 midweek dialysis sessions (length 240min, HD: N=1, Qb=200ml/min, Qd=300ml/min, 1,5m2; HDF: N=4, Qb≥300ml/min, Qd≥500ml/min, Vsubst≥15l, 1,8m2 and 2,2m2) were included. Spent dialysate from the drain was monitored on-line by a miniaturized sensor prototype (Optofluid Technologies OÜ, Estonia). For the reference, the samples from the spent dialysate drain tube of the HD machine were taken as 7, 60, 120 and 180min after the start and at the end of the session (240min). The concentrations of urea and B2M in dialysate were determined in the clinical laboratory. Concentration of IS and UA was determined utilizing the HPLC. TRS values were calculated using the tank weight and the lab or optical tank solute concentrations. t-test was used to determine significant differences between the methods (P≤0.05). Results The laboratory and optical TRS values were 489±112mM and 512±87mM for urea (R2=0.870), 4232±712µM and 4331±756µM for UA (R2=0.985), 230±47mg and 231±40mg for B2M (R2=0.906), 606±339µM and 616±321µM for IS (R2=0.969) (Fig. 1), being not statistically different for any uremic solutes. The reason for higher correlation for UA and IS is direct measurements of UA and IS by the optical sensor whereas urea and B2M are estimated indirectly. Conclusion Novel miniaturized optical sensor successfully carried out intradialytic on-line multicomponent TRS monitoring for the uremic solutes urea, UA, B2M and IS in the spent dialysate.

Serum Levels and Removal by Haemodialysis and Haemodiafiltration of Tryptophan-Derived Uremic Toxins in ESKD Patients

Tryptophan is an essential dietary amino acid that originates uremic toxins that contribute to end-stage kidney disease (ESKD) patient outcomes. We evaluated serum levels and removal during haemodialysis and haemodiafiltration of tryptophan and tryptophan-derived uremic toxins, indoxyl sulfate (IS) and indole acetic acid (IAA), in ESKD patients in different dialysis treatment settings. This prospective multicentre study in four European dialysis centres enrolled 78 patients with ESKD. Blood and spent dialysate samples obtained during dialysis were analysed with high-performance liquid chromatography to assess uremic solutes, their reduction ratio (RR) and total removed solute (TRS). Mean free serum tryptophan and IS concentrations increased, and concentration of IAA decreased over pre-dialysis levels (67%, 49%, −0.8%, respectively) during the first hour of dialysis. While mean serum total urea, IS and IAA concentrations decreased during dialysis (−72%, −39%, −43%, respectively), serum tryptophan levels increased, resulting in negative RR (−8%) towards the end of the dialysis session (p < 0.001), despite remarkable Trp losses in dialysate. RR and TRS values based on serum (total, free) and dialysate solute concentrations were lower for conventional low-flux dialysis (p < 0.001). High-efficiency haemodiafiltration resulted in 80% higher Trp losses than conventional low-flux dialysis, despite similar neutral Trp RR values. In conclusion, serum Trp concentrations and RR behave differently from uremic solutes IS, IAA and urea and Trp RR did not reflect dialysis Trp losses. Conventional low-flux dialysis may not adequately clear Trp-related uremic toxins while high efficiency haemodiafiltration increased Trp losses.