Involvement of ionic interactions in cytokine adsorption of polyethyleneimine-coated polyacrylonitrile and polymethyl methacrylate membranes in vitro

Polyethyleneimine-coated polyacrylonitrile (AN69ST) and polymethyl methacrylate (PMMA) membranes are effective cytokine-adsorbing hemofilters; however, the cytokine-adsorption mechanism remains elusive. This study investigated the involvement of ionic interactions in cytokine adsorption to a negatively charged AN69ST membrane and neutral-charged PMMA membrane. Experimental hemofiltration was performed for 30 min in a closed-loop circulation system using AN69ST and PMMA hemofilters. Tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-8 concentrations in the test solutions were measured at baseline and at 10 min and 30 min into hemofiltration. To investigate the involvement of ionic interactions in cytokine adsorption, cytokine clearance (CL) was calculated at 10 min into hemofiltration and with three types of solutions at various pH levels (7.6, 7.2, and 6.8). During AN69ST hemofiltration, the CLs of TNF-α, IL-6, and IL-8 were 38 ± 6 mL/min, 23 ± 7 mL/min, and 78 ± 3 mL/min, respectively, demonstrating a relationship with their respective isoelectric points. During PMMA hemofiltration, the CL of IL-6 peaked at 31 ± 76 mL/min, with no relationship observed between the CL and isoelectric point. When the pH of the test solution shifted from 7.6 to 6.8, the CLs of TNF-α, IL6, and IL-8 increased in the AN69ST hemofilter; whereas, no such trend was observed in the PMMA hemofilter. These results indicated that Ionic interactions play a role in cytokine adsorption by the AN69ST membrane but not the PMMA membrane and highlight the clinical relevance of this finding, as well as the potential practical applications for further hemofilter design.