#2765 Medium chain fatty acids are potent binding competitors to improve protein-bound uremic toxin clearance in hemodialysis
Authors: Raillon Laure-Anne , Florens Nans , Guebre-Egziabher Fitsum , Soulage Christophe 
Published: May 2024

Abstract

Background and Aims
Protein-bound uremic toxins (PBUTs) remain a concerning burden in patients with end-stage renal disease (ESRD) since their removal during hemodialysis is limited due to their tight binding to albumin. 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, 6 to 12 carbon length) are potent candidates for that purpose. The present study aims to investigate whether MCFAs could serve as potential binding competitors of albumin to enhance the removal of PBUTs, specifically IS and p-CS, during hemodialysis.

Method
Hexanoate (C6), octanoate (C8), and decanoate (C10) were purchased from Sigma-Aldrich. The binding of MCFAs to albumin was investigated in silico and using fluorescent probes: warfarin (specific of Sudlow's site I) and dansylsarcosine (specific of 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 in this solutions and in patients uremic plasma. To mimic the removal of PBUTs during a HD session, batches of 2 liters of fresh bovine blood were loaded with IS and p-CS (final concentration 200 µM). A 2-hours closed-loop HD session was performed using a Fresenius 5008 CorDiax HD generator (Fresenius, Germany). A solution of 224 mM of octanoate was perfused at the rate of 150 µL/min; A solution of saline 0.9% was used as a control. One milliliter of blood was sampled every 15 minutes through the arterial sampling port and concentration of IS and p-CS were assayed by HPLC coupled with fluorescence detection. The hemolytic effect of MCFAs was evaluated in vitro by assaying the free hemoglobin concentration.

Results
According to the in silico prediction, the binding was predicted to be almost complete for MCFAs ≥ C8 (Fig. 1). The enhanced protein binding appeared to be inversely correlated with water solubility, which became particularly low for MCFAs ≥ C10. Octanoate and decanoate were the 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 octanoate and decanoate increased the free fraction of PBUTs from 12% to 53% for p-CS (4.4 fold, p &lt; 0.05) and from 11% to 45% for IS (4.1 fold, p &lt; 0.05). Octanoate was also able to increase the free fraction of PBUTs in patients uremic plasma (1.6-fold for IS, p &lt; 0.05 and 4.8 fold for p-CS, &lt;0.01). The per-dialytic infusion of octanoate significantly increased the fractional removal of p-CS (from 38% to 88%, p &lt; 0.001) and IS (from 36% to 91%, p &lt; 0.001). No significant hemolysis was observed for concentration of MCFAs lower than 2 mmol/L.

Conclusion
MCFAs and especially octanoate and decanoate are serious candidates to displace the binding of PBUTs such as p-CS and IS. The per-dialytic administration of octanoate significantly increased the removal of PBUTs and could constitute a new strategy to prevent their accumulation in end-stage kidney disease patients. Due to their good safety profile, MCFAs could be better tolerated than other chemical compounds that has already been tested in a clinical setting such as ibuprofen. Further in vivo studies are however needed to carefully evaluate this potentially new therapeutic option.