Mechanisms and kinetics of the synthesis and release of platelet-activating factor (PAF) by polyacrylonitrile membranes.

Platelet-activating factor is a recognized mediator of anaphylaxis and bioincompatibility. Here, the mechanisms and the kinetics of the production of platelet-activating factor were studied in vivo during high-flux hemodialysis and in vitro in a recirculation model with polyacrylonitrile membranes, the AN-69 and the more recent SPAN, where the Na-metallilsulfonate group is partially substituted with the less polar methacrylate group. In in vivo studies, eleven patients were studied in cross over. Patients were randomly allocated to the AN-69 (5 patients) and to the SPAN membrane (6 patients) for two weeks. Measurements were made in the second week of use. After completion of the second week, the patients were switched to the other membrane for a further two weeks. Samples for leukocyte and platelet counts, PAF in whole blood or bound to platelets, the C3a des Arg and the C5b-C9 membrane attack complex as well as samples for clearances of urea, creatinine and phosphates were taken at different time intervals during treatment. PAF was detected by biological assay after methanol extraction of whole blood or of platelet pellets obtained by sequential centrifugation. C3a des Arg and the C5b-C9 fraction were detected by commercially available immunoassays. Results were analyzed by Minitab statistical package. PAF was detectable only during treatment with AN-69 but not with SPAN 1 min after start of the extracorporeal circulation in both whole blood (4.5 +/- 2.7 ng/ml) and on platelet surface (4.1 +/- 1.2 ng/ml). No statistical significant differences were observed between AN-69 and SPAN with regard to leukocyte and platelet counts, plasma C3a des Arg and C5b-C9 levels. The structure modification did not alter functional performances as indicated by the lack of statistically significant differences in clearance values between the two membranes. In in vitro experiments performed with normal washed and whole blood recirculated in a closed circuit demonstrated the presence of a plasma-dependent, complement-independent mechanisms responsible for the triggering of PAF synthesis and release with AN-69 but not SPAN membrane. PAF was extractable from the inner and outer side of both polyacrylonitrile membranes (AN-69: inner, 4.9 +/- 0.5 ng/ml; outer, 0.1 +/- 0.05 ng/ml; SPAN: inner, 5.5 +/- 0.6 ng/ml, outer: 3.3 +/- 0.7 ng/ml, SPAN vs. p < 0.001), suggesting that absorption may be relevant with both membranes.