| Background.Protein-bound uremic toxins(PBUTs)accumulate at high plasma levels and cause pleiotropic toxic biological effects in end-stage renal disease(ESRD)patients because their removal by any dialytic procedure is severely limited by their low free-fraction levels in plasma.Here,this study aimed to(1)assess the extent to which PBUTs removal can be increased by hemodislysis(HD)with liposomes added to the standard bicarbonate dialysate;(2)enhance PBUTs removal in routine peritoneal dialysis(PD)by adding a binder to the peritoneal dialysate and evaluate the feasibility and efficacy of liposome-supported PD(LSPD)to increase the removal of PBUTs compared to albumin PD;(3)evaluated the effects of ionic strength,p H change and chemical displacers on the dissociation of PBUTs from human serum albumin(HSA);(4)examine whether increased removal of PBUTs could be achieved with intravenous lipid emulsion(ILE).Method.(1)A reservoir containing PBUTs and artificial plasma was used for determining the adsorption capacity of liposomes for p-cresyl sulfate(PCS),indoxyl sulfate(IS),hippuric acid(HA)and 3-Carboxy-4-methyl-5-propyl-2-furan-propanoic acid(CMPF).The effect of adding liposomes to the dialysate was then quantified and compared with the effect of adding albumin to the dialysate and with the dialysate without addition of any binder in a rapid equilibrium dialysis(RED)setup and in an in vitro closed HD model,respectively.Male Sprague-Dawley rats were subjected to 5/6nephrectomy and fed for 20 weeks to a model of ESRD.They received HD for 240 min at a blood and dialysate flow rate of 1.0 and 5.0 m L/min,respectively.Removal of solutes was determined by the reduction ratios(RRs)in the serum and total solute removal(TSR)in the dialysate;(2)Removal of PCS,IS and indole-3-acetic acid(3-IAA)was first evaluated in an in vitro PD model using artificial plasma preloaded with test solutes.ESRD rats were then treated with either conventional glucose-based PD,albumin-based PD,or liposome-based PD.Removal of PBUTs and small water-soluble solutes was then determined during a 6 h PD dwell;(3)PBUTs,such as CMPF,PCS,IS and IAA,were spiked with HSA solution prepared either with different Nacl concentrations and p H values or in the presence of a series of chemical displacers.Ultrafiltration was performed to separate the free and bound fractions,and the percentage protein binding(% PB)of each PBUT was calculated;(4)PBUTs such as CMPF,PCS,IS and IAA were spiked with HSA solution,and the inhibitory effects of free fatty acid(FFA)on the binding of CMPF,PCS and IS to HSA were examined separately in vitro by ultrafiltration.In vitro dialysis of albumin solution was then performed to investigate the effects of fatty acid mixtures(FAs)infusion on the fractional removal of PBUTs.Finally,the inhibitory effect of FFA on the binding of PBUTs to albumin was examined in ESRD rats,and blood purification therapy was conducted to calculate the RR and TSR of solutes after 3 h HD treatment.Results.(1)The uptake of liposomes showed an obvious dose-response relationship for PCS and IS but not for HA by direct incubation in vitro.The percent removal of both PCS and IS but not of HA was gradually increased with the increased concentration of liposomes in the RED setup.In vitro closed HD showed that adding liposomes to the dialysate markedly increased the clearance of PBUTs without greatly altering that of urea and creatinine.The difference was more noticeable for strongly albumin-bound compounds.In vivo experiments demonstrated that adding liposomes to the dialysate resulted in higher RRs and more TSR for several PBUTs compared to conventional dialysate,which was approximately similar to the addition of albumin to the dialysate;(2)In vitro PD experiments showed that adding albumin as a toxin binder to the peritoneal dialysate markedly increased the removal of PCS,IS,and3-IAA compared to control.The uptake capacity of liposomes was comparable to that of albumin for PCS and 3-IAA.In vivo PD in ESRD rats demonstrated that LSPD resulted in higher intraperitoneal concentrations and more total mass removal for PBUTs compared to the conventional glucose-based PD,which were comparable to albumin PD.(3)For CMPF,PCS,IS and IAA,their % PB decreased with increasing ionic strength while only slight changes occurred when the p H of the test solution increased from p H 6.0 to p H 8.5;PCS,IS and 3-IAA were relatively easily dissociated from albumin by drug displacement,while CMPF was difficultly released from HSA by all studied drugs;the PB % for CMPF,PCS,IS and 3-IAA decreased most remarkably in the presence of free fatty acids,such as oleic acid(41.73% for CMPF,29.9% for PCS,23.22% for IS,and 20.34% for 3-IAA)and linoleic acid(43.12% for CMPF,16.65% for PCS,29.99% for IS,and 16.29% for 3-IAA);(4)The PB % of CMPF,PCS and IS decreased significantly with increasing FFAs concentrations,and the inhibitory effect was more remarkable with the addition of oleic acid or linoleic acid than that of eicosapentaenoic acid and docosahexaenoic acid.Infusion of FAs increased the fractional removal of CMPF to 14.40 ± 2.38%.PCS,IS and indole-3-acetic acid(3-IAA)removal rose from 8.00 ± 2.43%,11.68 ± 1.54% and15.38 ± 3.97%,respectively,at baseline to 28.21 ± 5.99%,35.42 ± 5.27% and 40.18 ±5.05%,respectively,when FAs were present.In vivo,serum concentrations of free PBUTs were significantly higher in the ILE group than in the control group,and administration of ILE resulted in higher RRs and more TSRs for PBUTs after 3 h of HD therapy compared with the control group.Conclusion.(1)As an adjunct to conventional HD,addition of liposomes to the dialysate could significantly improve the removal of PBUTs without greatly altering the removal of small,water-soluble solutes;(2)Supplementing conventional glucose-based PD solutions with a binder could efficiently increase the removal of PBUTs.LSPD may be a promising alternative to albumin PD for increasing PBUTs removal in the development of next-generation PD solutions for PD patients;(3)The protein binding of PBUTs can be decreased by higher ionic strength,increased p H and the presence of some chemical displacers,including free fatty acids;(4)Administration of ILE effectively increased the dialytic removal of PBUTs.This method could be applied to current HD therapy. |
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