Removal of limulus reactivity and cytokine-inducing capacity from bicarbonate dialysis fluids by ultrafiltration.

Bicarbonate-based dialysate solutions support the rapid growth of bacteria. The long-term (360-h) efficacy of ultrafiltration by two polysulphone ultrafilters in removing not only endotoxin but also the cytokine(IL-1, TNF)-inducing capacity was evaluated using an experimental circuit contaminated with Pseudomonas aeruginosa filtrates. One of the polysulphone ultrafilters was submitted to a standard sanitization procedure every 12 h (hypochlorite 1.2% solution for 5 min and rinsing for 20 min). Endotoxin was detected by the kinetic quantitative chromogenic limulus amoebocyte lysate (LAL) assay. Immunoreactive IL-1 and TNF were evaluated in the lysates of peripheral blood mononuclear cells containing 5 x 10(5) human monocytes. The results of the present studies show that although LAL-reactive bacterial products were significantly removed in post-ultrafilter samples, they remained detectable, albeit below the upper limit accepted by the present European pharmacopeias (< 0.125 EU/ml). The removal of cytokine-inducing capacity was time-dependent and correlated with time of use in the case of the sanitized ultrafilter. Beyond the time of use, two other factors emerged as possibly capable of reducing the efficacy of the ultrafilter in removing LAL-reactive bacterial components, namely the pressure and the cytokine-inducing activity in pre-ultrafilter samples. Preincubation with polymyxin B, an agent that irreversibly binds lipid A and blocks lipid A-induced biological activities, did not abrogate the cytokine-inducing capacity in all post-ultrafilter samples; this suggests that either low-molecular-weight endotoxin subunits or lipid A-unrelated components may be responsible for the residual biological activity in post-ultrafilter samples.