In vitro benchmark of cytokine removal by dialyzers with various permeability profiles

Removal of cytokines is relevant for dialysis patients as they are suspected to promote cardiovascular complications. The objective of this study was to benchmark membranes with different permeability profiles under standardized in vitro test conditions using miniaturized devices with respect to their ability to remove cytokines from human serum and to lower cell activating potential.

In vitro dialysis was used to dialyze cytokine enriched serum in 3 independent experiments per tested membrane. IL-6 in the serum and dialysate was measured at defined times by enzyme-linked immunosorbent assay. IL-8, IL-1β, IL-6 and TNF-α in dialysate were measured by immunoassay. Dialysate samples were subjected to cultured tubular epithelial cells or human fibroblasts to study cell activation via IL-6 generation. Dialysate samples were added to human whole blood with subsequent analysis of granulocyte and monocyte activation by detection of CD11b.

IL-6 decreased in serum and increased in dialysate during in vitro dialysis. IL-8, IL-1β, and TNF-α were identified in dialysate. Dialysate added to cell cultures increased IL-6 concentration in culture medium or increased expression of CD11b. High cut-off membranes showed the strongest transfer of cytokines, albumin and total proteins from serum to dialysate and led to strongest cell activation. This effect was lower for medium cut-off membranes and lowest for conventional high-flux membranes.

This study demonstrated an in vitro test by which membranes were benchmarked with respect to cytokine and cell activation removal capacity. Cell activation levels could be influenced by the choice of membrane by altering cytokine concentration levels.