Evaluation of Two Non-Invasive Extracorporeal Strategies for Enhancing Protein-Bound Uremic Toxin Removal During Hemodialysis

Current hemodialysis (HD) methods inefficiently remove protein-bound uremic toxins (PBUTs) due to their high binding affinity to plasma proteins, mainly albumin. This study aimed to investigate electromagnetic (EM) fields and temperature as potential extracorporeal, non-systemic methods to increase HD PBUT clearance. PBUT release was measured in infusible (caprylate-stabilized) albumin solutions spiked with indoxyl sulfate (IS) using an in vitro dialysis setup including a real-time, in-line IS-sensor. No measurable influence on PBUT release was observed during EM field-tests (f = 1–600 MHz, E <= 1 kV/m), but temperature tests (35–40 °C range) showed an absolute increase in IS free fraction of 0.7%/°C. Furthermore, static equilibrium dialysis tests, including IS, p-cresyl sulfate (pCS) and hippuric acid (HA), showed a free fraction increase for all three PBUTs upon a temperature increase from 37 °C to 43 °C (IS 1.30-fold, pCS 1.12-fold, HA 1.15-fold). Mathematical modeling showed a 1.14-fold decrease in plasma IS concentration after 5 weeks of HD, and exploratory hemocompatibility tests did not reveal pronounced changes over 15 heating cycles at 43 °C under static conditions. Extracorporeal temperature elevation is a promising technique to enhance PBUT removal during hemodialysis, which may be easily combined with current HD machines, does not break sterility, and avoids elevating free PBUTs inside the body.