Removal of cytokine inducing substances by polymyxin-B immobilized polystyrene-derivative fibers during in vitro hemoperfusion of 10% human plasma containing Staphylococcus aureus challenge

Staphylococcus aureus (S. aureus) is frequently isolated from blood cultures in the hospital setting. The pathogenesis of S. aureus bacteremia probably replicates mechanisms implicated in gram negative bacterial infections. Cell wall components, such as peptidoglycans and lipoteichoic acids (LTA), can trigger cytokine production. Polymyxin-B (PMX-B) is a cationic peptide that binds endotoxin (ET) and inhibits its activity. Based on this principle, PMX-B was incorporated in polystyrene-derivative fibers, creating a hemoperfusion column (PMX-20R) that removes ET. The authors assessed whether S. aureus possesses PMX-B suppressible cytokine-inducing substances, and whether LTA, an anionic molecule, is one such substance. Heparinized blood was obtained from healthy volunteers, peripheral blood mononuclear cells (PBMC) were isolated by Ficoll-Hypaque separation, and 10% human plasma prepared. PBMC were incubated with 1, 5, or 10 mu g/ml of S. aureus LTA, with and without 10 mu g/ml of PMX-B. Also, using PMX-20R, in vitro hemoperfusion (IVH) was performed with 10% human plasma containing 1:1,000 dilution of S. aureus challenge at 100 ml/min for 2 hours at 37 degrees C, and plasma obtained before and after IVH was incubated with PBMC. After a 24 hour incubation at 37 degrees C, PBMC were subjected to three freeze-thaw cycles, and total TNF alpha was measured by radioimmunoassay. TNF alpha production by PBMC incubated with LTA was 164 +/- 4 pg, 324 +/- 54 pg, 657 +/- 55 pg, and 1143 +/- 215 pg in control, and LTA 1, 5, and 10 mu g/ml, respectively. The addition of PMX-B resulted in a 40 +/- 12% (p = 0.02), 61 +/- 6% (p = 0.002), and 62 +/- 14% (p = 0.02) decrease in TNF alpha production, respectively. Before IVH, TNF alpha production by PBMC incubated with 10% plasma containing S. aureus challenge was 1275 +/- 70 pg. After 2 hours of IVH, the decrease in TNF alpha production was 20 +/- 4% (p = 0.002). In conclusion, S. aureus LTA induces TNF alpha production that is significantly suppressed by PMX-B. Consequently, S. aureus cytokine-inducing substances are removed during IVH with PMX-20R, and this may be due to stoichiometric binding of LTA to PMX-B.