Effects of ultrapure and non-sterile dialysate on the inflammatory response during in vitro hemodialysis

Several studies support the hypothesis that bacterial contamination of the dialysate stimulates the inflammatory response to hemodialysis (HD) and increases the long-term morbidity of HD patients; this phenomenon could also be modulated by the nature of the HD membrane. Therefore, this study was designed to compare the effects of non-sterile (NSBD, mean endotoxin content +/- SEM 97 +/- 22 EU/ml) and ultrapure bicarbonate dialysate (UPBD, sterile and pyrogen-free, obtained by ultrafiltration through polyamide) on several aspects of the inflammatory reaction during in vitro HD. The HD sessions (7 in each experimental group) were performed using miniaturized new cuprophane (CU) and polyacrylonitrile (PAN) hollow fiber dialyzers, and closed dialysate and blood circuits (the latter filled with heparinized blood from healthy donors). Plasma C3aDesarg levels were significantly increased after 15 minutes (t1) and increased further after three hours (t2) of CU HD, while during PAN dialysis they decreased from t0 to t1 and t2; however, no difference appeared between experiments with NSBD and UPBD. Granulocyte (PMN) and monocyte (MNC) expression of LFA-1, Mac-1, and CD45 at the start (t0), t1 and t2 was quantitated by flow cytometry analysis, after staining of the cells with specific fluorescinated monoclonal antibodies. In contrast with published data of in vivo HD, LFA-1 was overexpressed at t1 and peaked at t2, which suggests that the leukocytes expressing more LFA-1 leave the systemic circulation during in vivo HD. During CU HD, Mac-1 and CD45 on PMN and MNC were significantly increased at t1, and still more at t2. During PAN HD, Mac-1 and CD45 remained unchanged at t1, but increased significantly at t2 on PMN as on MNC. Again, no significant difference was found between NSBD and UPBD in LFA-1, Mac-1 and CD45 expression on PMN and MNC, during both CU and PAN HD. AFter three hours of dialysis, plasma levels of TNF-alpha, but not of IL-6, were significantly increased with CU and PAN. Again, no difference appeared when NSBD and UPBD were compared. Moreover, the lack of influence of bacterial contamination of the dialysate on TNF-alpha production was confirmed when MNC were cultured up to 24 hours after the end of the HD session. We conclude that complement activation products, either in plasma (CU) of those adsorbed on the HD membrane (CU and PAN) play the major role in the overexpression of beta 2-integrins and CD45 by PMN and MNC during HD. Also, bacterial products (at the levels that can be found in clinical conditions) do not influence either beta 2-integrin overexpression or TNF-alpha production induced by the dialysis membrane.