Reduction of mononuclear cytokine production in hemodialysis patients treated with steam-sterilized low-flux polysulphone membranes.

An increased cytokine production, correlated with long term complications of uremic disease, has been described during hemodialysis. To identify possible differences in the cytokine release of differently sterilized membranes, we enrolled six uremic patients on chronic hemodialysis. The patients underwent dialysis with ETO-sterilized low-flux polysulphone membranes (F6, Fresenius AG) for at least three months (A1), they were then switched to steam-sterilized polysulphone membranes (F6-HPS Fresenius AG) and further evaluations after one (B1) and two months (B2) were carried out. A final evaluation (A2) was made one month after switching back to F6 dialyzers. At each time period, samples were drawn to measure IL-1beta released by cultured mononuclear cells (MN). Moreover, dialysate samples were collected to test endotoxin levels. C3a and C5a levels were assessed at 0, 5, 15 and 60 min from starting hemodialysis. Anti-ETO IgE levels were also assayed at A1, B1 and A2. The LAL test revealed a good quality dialysate. The mean pre-dialysis IL-1beta levels were 215 pg/million cells at A1; falling to 49 at B1, and 54 at B2 (p<0.01); there was then a sharp rebound at A2: 284, p<0.01. Post-dialysis levels followed the same pattern. No correlation between the dialysate endotoxin level and cytokine release was found. Complement activation did not change and in all the phases of the study no anti-ETO IgE was detected in any of the subjects. Our data suggest that the steam sterilized polysulphone membrane induces a lower cytokine release than the ETO sterilized membrane, although the mechanism by which it does so remains to be clarified.

Is steam sterilization really making any difference in dialysis-induced cytokine release?

Ethylene oxide (ETO) is presently the most commonly used sterilization method for medical devices. Although alternative sterilization modes such as steam sterilization have been suggested, the effect of steam on dialysis-induced cytokine release is unknown. We enrolled 9 patients on chronic hemodialysis and evaluated at different intervals IL-1beta production while treated with ETO (NC 1785-Bellco) and steam sterilized NC 1785S-Bellco) Synthetically Modified Cellulose (SMC). A basal test during treatment with NC 1785 was performed (A); the same test was set up 4 weeks after treatment with NC 1785S (B) and, lastly, 4 weeks after returning to NC 1785 (C). Peripheral blood mononuclear cells (PBMC) were purified before and after the dialysis session, were isolated on a Ficoll/Hypaque gradient and incubated for 24 h. Spontaneous IL-1beta release was evaluated in the supernatant and in the lysate. In A, IL-1beta levels were (in pg/ml/10(6) cells, in supematant and lysate, respectively): 5.8 +/- 4.8 and 7.6+/-5.2 in pre-HD and 4.68 +/- 3.6 and 9.7 +/- 6.65 in post-HD. These levels showed a clear reduction in B: 2.5 +/- 2.2 and 4.4 +/- 3.1 in pre-HD, and 4.35+/- 6.6 and 7.52 +/- 7.22 in post-HD. In the C test, 4 weeks after the return to the ETO membrane, IL-1beta levels remained unchanged: 2.9 +/- 1.8 and 4.5 +/- 3.1 in pre-HD; and 2.6 +/- 3 and 5.7 +/- 6.6 in post-HD. Statistical analysis showed significant changes in the pre-HD levels both in supematant (p < 0.04) and in lysate (p < 0.04). Steam sterilization of SMC induced a lower spontaneous IL-1beta release, but this effect was not statistically significant due to the large inter-individual variation. Hence, contrary to claims of better biocompatibility, steam sterilization does not result in a reduced production of pro-inflammatory IL-1beta.