Permeability of dialyzer membranes to TNFα-inducing substances derived from water bacteria

Abstract

Pro-inflammatory cytokine-inducing substances derived from cultured E. coli have previously been shown to pass across low-flux regenerated cellulosic dialyzer membranes. In the present study, a sterile filtrate of Pseudomonas maltophilia grown from standard bicarbonate dialysis fluid was used to test the permeability of various dialyzer membranes (regenerated cellulose, cellulose triacetate, polyacrylonitrile, polysulfone and polyamide) to TNFα-inducing bacterial substances. Pyrogen-free tissue culture medium (MEM) was recirculated for 60 minutes in the dialysate compartment of a closed-loop dialysis system, then P. maltophilia filtrate was added and recirculation was continued for a further hour. Samples from the dialysate (MEM) and the blood side (containing 10% human plasma in MEM) were incubated with donor mononuclear cells (MNC) for 18 hours and TNFα release was measured in MNC supernatants by radioimmunoassay. Five minutes after the addition of P. maltophilia filtrate, mean TNFα-inducing activity in the dialysate increased from (mean ± SEM) 0.10 ± 0.02 to 18.2 ± 1.5(ng/2.5 x 106 MNC/18 hr). TNFα-inducing activity in the blood side increased with regenerated cellulose from 0.10 ± 0.01 to 4.57 ± 1.55 (N = 8; P < 0.001); with cellulose triacetate from 0.20 ± 0.05 to 0.44 ± 0.10 (N = 5; P < 0.05), and with polyacrylonitrile from 0.10 ± 0.02 to 1.16 ± 0.45 (N = 5; P < 0.03). No increased TNFα-inducing activity was observed in the blood side of polysulfone (N = 5) or polyamide dialyzers (N = 5). Polymyxin B reduced dialysate TNFα-inducing activity by 40%, but had no effect on the TNFα-inducing activity of samples derived from the blood compartments. We conclude that the permeability of dialyzer membranes to cytokine-inducing substances derived from water bacteria is influenced by the physicochemical nature of the membrane rather than its pore size. Backfiltration was ≤1.2 ml/min with all dialyzers, suggesting that the sport of cytokine-inducing substances was predominantly by diffusion. As the cytokine-inducing material passed through low-flux regenerated cellulose, our data suggest that the molecular weight of the material is less than 5 kD.