MO660: Medium Chain Fatty Acids used as Binding Competitors of Albumin Improve the Dialytic Clearance of Protein-Bound Uraemic Toxins

Abstract

Abstract BACKGROUND AND AIMS Protein-bound uraemic toxins (PBUTs) remain a concerning burden in patients with end-stage renal disease (ESRD) since their removal in haemodialysis (HD) is limited by their strong binding to plasma proteins. By increasing their circulating free fraction during HD, "binding competitors" of albumin could be used to increase their dialytic clearance. Medium-chain fatty acids (MCFAs, 4–10 carbon length) are potent candidates for that purpose. The aim of this work was to evaluate the displacing capacities of MCFAs. METHOD Sodium salts of butanoic acid (C4), hexanoic acid (C6), octanoic acid (C8) and decanoic acid (C10) were purchased from Sigma-Aldrich. The interaction between MCFAs and serum albumin was explored using two fluorescent probes: warfarin (specific to Sudlow's site I) and dansylsarcosine (specific to Sudlow's site II). Indoxyl-sulfate (IS, final concentration 212 µM) and p-cresyl sulfate (p-CS, final concentration 250 µM) were added to a 600 µM bovine serum albumin-phosphate buffered saline solution. The free fractions of IS and p-CS were assayed with or without MCFAs (1–2 mM) using ultrafiltration devices. To mimic the removal of PBUTs during an HD session, batches of 2L of fresh bovine blood were loaded with IS and p-CS (final concentration 200 µM). A 2-h closed-loop HD session was performed using a Fresenius 5008 CorDiax HD generator (Fresenius, Germany). A solution of 224 mM of sodium octanoate (C8) was perfused using the electric syringe pump at the rate of 150 µL/min; a solution of saline 0.9% was used as a control. A total of 1 mL of blood was sampled every 15 min through the arterial sampling port and concentrations of IS and pCS were assayed by HPLC coupled with fluorescence detection. The haemolytic effect of MCFAs was evaluated in vitro by assaying the free haemoglobin concentration. RESULTS Among the short-chain fatty acids tested, octanoic (C8) and decanoic (C10), acids were more prone to displace dansylsarcosine from Sudlow's site II of albumin (which is the main binding site of IS and p-CS). In vitro, the incubation with 2 mM of sodium octanoate or decanoate increased the free fraction of PBUTs from 12 to 53% for p-CS (4.4 folds change, P < .05) and from 11 to 45% for IS (4.1 folds change, P < .05). The per-dialytic infusion of sodium octanoate significantly increased the fractional removal of p-CS (from 38 to 88%, P < .001) and IS (from 36 to 91%, P < .001) (Figure 1). No significant haemolysis was observed for the concentration of MCFAs ˂ 2 mmol/L. CONCLUSION MCFAs and especially C8 and C10 are serious candidates to displace the binding of PBUTs such as p-CS and IS. The per-dialytic administration of MCFA significantly increased the removal of PBUTs and could constitute a new strategy to get rid of these compounds and prevent their accumulation in end-stage kidney disease patients. Due to their safeness (toxicity and metabolism profiles in vivo), MCFAs could be better tolerated than other chemical compounds that have already been tested clinically such as ibuprofen. Further in vivo studies are, however needed to carefully evaluate this potentially new therapeutic option.