Increasing the removal of protein-bound uremic toxins by liposome-supported hemodialysis.

Protein-bound uremic toxins (PBUTs) accumulate at high plasma levels and cause various deleterious effects in end-stage renal disease patients because their removal by conventional hemodialysis is severely limited by their low free-fraction levels in plasma. Here, we assessed the extent to which solute removal can be increased by adding liposomes to the dialysate. The uptake of liposomes by direct incubation in vitro showed an obvious dose-response relationship for p-cresyl sulfate (PCS) and indoxyl sulfate (IS) but not for hippuric acid (HA). The percent removal of both PCS and IS but not of HA was gradually increased with the increased concentration of liposomes in a rapid equilibrium dialysis setup. In vitro closed circulation showed that adding liposomes to the dialysate markedly increased the dialysances of PBUTs without greatly altering that of urea and creatinine. In vivo experiments in uremic rats demonstrated that adding liposomes to the dialysate resulted in higher reduction ratios (RRs) and more total solute removal (TSR) for several PBUTs compared to the conventional dialysate, which was approximately similar to the addition of bovine serum albumin to the dialysate. These findings highlight that as an adjunct to conventional hemodialysis, addition of liposomes to the dialysate could significantly improve the removal of protein-bound uremic solutes without greatly altering the removal of small, water-soluble solutes.

Carbon Nanotube/Conducting Polymer Hybrid Nanofibers as Novel Organic Bioelectronic Interfaces for Efficient Removal of Protein-Bound Uremic Toxins.

Protein-bound uremic toxins (PBUTs) can cause noxious effects in patients suffering from renal failure as a result of inhibiting the transport of proteins and inducing their structural modification. They are difficult to remove through standard hemodialysis (HD) treatment. Herein, we report an organic bioelectronic HD device system for the effective removal of PBUTs through electrically triggered dissociation of protein-toxin complexes. To prepare this system, we employed electrospinning to fabricate electrically conductive quaternary composite nanofiber mats-comprising multiwalled carbon nanotubes (MWCNTs), poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), poly(ethylene oxide) (PEO), and (3-glycidyloxypropyl)trimethoxysilane (GOPS)-on conventional polyethersulfone (PES) dialysis membranes. These composite nanofiber platforms exhibited (i) long-term water resistance (due to cross-linking among PSS, PEO, and GOPS), (ii) high adhesion strength on the PES membrane (due to GOPS functioning as an adhesion promoter), (iii) enhanced electrical properties [due to the MWCNTs and PEDOT:PSS promoting effective electrical stimulation (ES) operation in devices containing bioelectronic interfaces (BEI)], and (iv) good anticoagulant ability and negligible hemolysis of red blood cells. We employed this organic BEI electronic system as a novel single-membrane HD device to study the removal efficiency of four kinds of uremic toxins [p-cresol (PC), indoxyl sulfate, and hippuric acid as PBUTs; creatinine as a non-PBUT] as well as the effects of ES on lowering the protein binding ratio. Our organic BEI devices provided a high rate of removal of PC with low protein loss after 4 h of a simulated dialysis process. It also functioned with low complement activation, low contact activation levels, and lower amounts of platelet adsorption, suggesting great suitability for use in developing next-generation bioelectronic medicines for HD.

Behavior of non-protein-bound and protein-bound uremic solutes during daily hemodialysis.

BACKGROUND: In the last few years, renewed interest in daily short hemodialysis (DHD; six 2-hour sessions per week) has become apparent as a consequence of the better clinical outcome of patients treated by this schedule. Uremic syndrome is characterized by the retention of a large number of toxins with different molecular masses and chemical properties. Some toxins are water soluble and non-protein bound, whereas others are partially lipophilic and protein bound. There is increased evidence that protein-bound toxins are responsible for the biochemical and functional alterations present in uremic syndrome, and the kinetics of urea is not applicable to these substances for their removal. The aim of this study is to investigate whether DHD is accompanied by increased removal of non-protein-bound and protein-bound toxins and a decrease in their prehemodialysis (pre-HD) serum levels. PATIENTS AND METHODS: We studied 14 patients with end-stage renal disease treated by standard HD (SHD; three 4-hour sessions per week) for at least 6 months and randomly assigned them to a two-period crossover study (SHD to DHD and DHD to SHD). Patients maintained the same dialyzer, dialysate, and Kt/V during the entire study. At the end of 6 months of SHD and 6 months of DHD, we evaluated hemoglobin levels, hematocrits, recombinant human erythropoietin doses, and pre-HD and post-HD concentrations of serum urea, creatinine, uric acid, and the following protein-bound toxins: 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid, p-cresol, indole-3-acetic acid, indoxyl sulfate, and hippuric acid. RESULTS: Values for hemoglobin, hematocrit, and recombinant human erythropoietin dose did not change during the two study periods. Pre-HD concentrations of creatinine, urea, and uric acid decreased on DHD (creatinine, from 8.7 +/- 1.9 to 7.8 +/- 1.6 mg/dL; P < 0.05; urea, from 149.4 +/- 28.8 to 132.7 +/- 40 mg/dL; P = 0.05; uric acid, from 9.14 +/- 1.49 to 8.16 +/- 1.98 mg/dL; P = 0.06). Concerning protein-bound toxins, lower pre-HD levels during DHD were reported for indole-3-acetic acid (SHD, 0.16 +/- 0.04 mg/dL; DHD, 0.13 +/- 0.03 mg/dL; P = 0.01), indoxyl sulfate (SHD, 3.35 +/- 1.68 mg/dL; DHD, 2.85 +/- 1.08 mg/dL; P = 0.02), and p-cresol at the borderline of significance (SHD, 0.96 +/- 0.59 mg/dL; DHD, 0.78 +/- 0.33 mg/dL; P = 0.07). CONCLUSION: Such non-protein-bound compounds as uric acid, creatinine, and urea were removed significantly better by DHD, and pre-HD serum levels were reduced. Furthermore, pre-HD concentrations of some protein-bound solutes, such as indole-3-acetic acid, indoxyl sulfate, and p-cresol, also were lower during DHD.

In vivo clearance and elimination of nine marker substances during hemofiltration with different membranes.

The handling of low, middle and high molecular weight markers was examined in seven stable dialysis patients during hemofiltration with different membranes. Four membranes were examined in a randomized, crossover order (polysulfone, polyamide, AN69 polyacrylonitrile, Asahi polyacrylonitrile) by measuring plasma and dialysate concentrations of phosphate, creatinine, vitamin B12, beta 2-microglobulin, furanic acid, hippuric acid, retinol-binding protein, alpha-1-antitrypsin, and albumin. Sieving coefficients and plasma clearances of beta 2-microglobulin or retinol-binding protein were markedly or slightly lower during hemofiltration with the Asahi polyacrylonitrile membrane than with the other membranes (highest removal with polysulfone/AN69 polyacrylonitrile membranes). No differences of obvious clinical relevance could be seen between the four membranes. A high beta 2-microglobulin removal rate might be important to prevent dialysis-associated amyloidosis.

Mixed matrix hollow fiber membranes for removal of protein-bound toxins from human plasma.

In end stage renal disease (ESRD) waste solutes accumulate in body fluid. Removal of protein bound solutes using conventional renal replacement therapies is currently very poor while their accumulation is associated with adverse outcomes in ESRD. Here we investigate the application of a hollow fiber mixed matrix membrane (MMM) for removal of these toxins. The MMM hollow fiber consists of porous macro-void free polymeric inner membrane layer well attached to the activated carbon containing outer MMM layer. The new membranes have permeation properties in the ultrafiltration range. Under static conditions, they adsorb 57% p-cresylsulfate, 82% indoxyl sulfate and 94% of hippuric acid from spiked human plasma in 4 h. Under dynamic conditions, they adsorb on average 2.27 mg PCS/g membrane and 3.58 mg IS/g membrane in 4 h in diffusion experiments and 2.68 mg/g membrane PCS and 12.85 mg/g membrane IS in convection experiments. Based on the dynamic experiments we estimate that our membranes would suffice to remove the daily production of these protein bound solutes.

New approaches to the removal of protein-bound toxins from blood plasma of uremic patients.

The article is devoted to the theoretical aspects of the development of the effective method for the removal of protein-bound uremic toxins. It is shown that the methods of flow and differential scanning microcalorimetry are sufficient enough for the evaluation of the degree of ligand loading of human serum albumin with protein-bound uremic toxins. The molecules of albumin isolated from blood plasma of the patients being kept on chronic dialysis are demonstrating significant alterations of conformation and complex-forming properties, the correction of which by conventional methods of extracorporeal detoxification (exhaustive dialysis, treatment on synthetic SCN carbons) are practically ineffective. Deliganding of uremic albumin may be successfully performed on conventional carbon haemosorbents upon preliminary separation of blood plasma and its dilution with acetate buffer 1:1 at pH = 5.08. Treatment of the whole blood of patients onto new mass-fractal deliganding carbon, i.e., hemosorbents of HSGD trademark. These HSGD haemosorbents quite effectively could be used for restoration of main parameters of uremic HAS molecules conformation and ligand-binding activity simultaneously with hemodialysis upon the protection by locally performed citrate anticoagulation as an easier and cheaper method for the removal of protein-bound uremic toxins.

Intradialytic removal of protein-bound uraemic toxins: role of solute characteristics and of dialyser membrane.

BACKGROUND: The efficiency of dialysis membranes is generally evaluated by assessing their capacity to remove small, water-soluble and non-protein-bound reference markers such as urea or creatinine. However, recent data suggest that protein-bound and/or lipophilic substances might be responsible for biochemical alterations characterizing the uraemic syndrome. METHODS: In the present study, the total concentrations of four uraemic retention compounds (indoxyl sulphate, hippuric acid, 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid (CMPF) and p-cresol) and of tryptophan, the only protein-bound amino acid and a precursor of indoxyl sulphate, were compared with those of urea and creatinine in pre- and post-dialysis serum and in dialysate of 10 patients; two high-flux (HF) membranes (cellulose triacetate (CTA) and polysulphone (PS)) and a low-flux polysulphone (LFPS) membrane were compared in a crossover design, using HPLC. RESULTS: Except for hippuric acid (67.3+/-17.5% decrease), major differences were found in the percentage removal of the classical uraemic markers on one hand (creatinine 66.6+/-7.0% and urea 75.5+/-5.8% decrease) and the studied protein-bound and/or lipophilic substances on the other (indoxyl sulphate, 35.4+/-15.3% and p-cresol 29.0+/-14.2% decrease; tryptophan, 27.5+/-40.3%, and CMPF, 22.4+/-17.5% increase; P<0.01 vs urea and creatinine in all cases). Hippuric acid removal was more pronounced than that of the remaining protein-bound compounds (P<0. 01). After correction for haemoconcentration, per cent increase of tryptophan and CMPF was less substantial, while per cent negative changes for the remaining compounds became more important. There was a correlation between creatinine and urea per cent removal at min 240 (r=0.51, P<0.01), but all the other compounds showed no significant correlation with either of these two. The three membranes were similar regarding the changes of total solute concentrations from the start to the end of dialysis. CONCLUSIONS: Urea and creatinine are far more efficiently removed than the other compounds under study, except for hippuric acid. There are no striking differences between the HF membranes. Moreover, compared with the LF membrane these HF membranes do not appear to be superior in removing the studied compounds.

Polyphenols from alcoholic apple cider are absorbed, metabolized and excreted by humans.

We determined the uptake and excretion of low doses of polyphenols in six subjects who each consumed 1.1 L of an alcoholic cider beverage. Over a 24-h period, no phloretin was detected in plasma (detection limit = 0.036 micromol/L), but 21 +/- 5% of the dose (4.8 mg) was excreted in the urine. In contrast, from a low dose of 1.6-mg quercetin equivalents, no quercetin was found in urine or plasma, but 3'-methyl quercetin was detected in plasma [C(max) (maximum concentration) = 0.14 +/- 0.19 micromol/L; range: 0 to 0.44 micromol/L]. No flavanol monomers (dose of free (+)-catechin and (-)-epicatechin = 3.5 mg) were detected in urine or plasma (detection limit: 0.01 micromol/L). Caffeic acid (total dose including esters = 11 mg) was detected only in plasma within 2 h, with C(max) = 0.43 +/- 0.3 micromol/L (range: 0.18 to 0.84 micromol/L). An almost 3-fold increase in hippuric acid was detected in 24-h urine (74 +/- 29 micromol/L; range: 38-116 micromol/L), compared with a prestudy value of 19 +/- 9 micromol/L. These data show that polyphenols are taken up from cider, that phloretin is excreted in the urine and suggest that low doses of quercetin are extensively methylated in humans.