Effects of dialyzer membrane on interleukin-1β (IL-1β) and IL-1β-converting enzyme in mononuclear cells

Background. In vitro stimulation of mononuclear cells (peripheral blood mononuclear cells; PBMCs) with an endotoxin (lipopolysaccharide; LPS) revealed elevated cell-associated levels of interleukin-1 beta (IL-1 beta) in end-stage renal disease (ESRD) patients on Cuprophan hemodialysis (HD), suggesting a defect in the process of IL-1 beta 's release from activated cells. IL-1 beta is initially synthesized as an inactive precursor called proIL-1 beta. ProIL-1 beta is processed into the biologically active mature form of IL-1 beta (mIL-1 beta) requiring the specific IL-1 beta -converting enzyme (ICE). Methods. Using specific immunoassays (enzyme-linked immunosorbent assays), we measured cell-associated and extracellular proIL-1 beta as well as mIL-1 beta in LPS-stimulated PBMCs to test whether ICE-dependent processing of proIL-1 beta and/or secretion of mIL-1 beta was impaired in ESRD patients compared with healthy controls. PBMCs of healthy controls (N = 9), of ESRD patients on peritoneal dialysis (PD, N = 10), and of those patients on intermittent HD (N = 8) were studied. The same HD patients were studied three times with low-flux Cuprophan (GFS 12), low-flux polysulfon (F6 HPS), and high-flux polysulfon (F60S) in randomized order. PBMCs were separated from whole blood by Ficoll-Hypaque centrifugation and incubated in vitro for 18 hours in the presence LPS (10 ng/mL). Extracellular (PBMC culture supernatants) and cell-associated (cell lysates) levels of proIL-1 beta and mIL-1 beta were measured. Results. The total production (cell-associated plus extracellular) of LPS-induced IL-1 beta (proIL-1 beta plus mIL-1 beta) was similar in healthy controls (25.96 +/- 0.84 ng/2.5 x 10(6) PBMC), PD patients (29.53 +/- 1.31 ng/2.5 x 10(6) PBMC), and in Cuprophan-treated HD patients (23.28 +/- 1.24 ng/2.5 x 10(6) PBMC). In normal controls, 43.6% of the total IL-1 beta was processed into mIL-1 beta, which was significantly more than that in PD patients (27.3%, P < 0.02) but was similar to that in Cuprophan-treated HD patients (37.1%). Comparing cell-associated and extracellular concentrations of mIL-1<beta>, PBMCs of normal controls secreted 82.2% of mIL-1 beta; this was significantly more than that in PD patients (59.4%, P < 0.01) and that in Cuprophan HD patients (54.2%, P < 0.01). When HD patients were switched from Cuprophan to F6 HPS or F60S, neither total IL-1 beta production nor processing of IL-1 beta changed. However, secretion of mIL-1 beta increased significantly with F6 HPS (80.6%, P < 0.01) as well as with F60S (76.6%, P < 0.02) compared with Cuprophan. Conclusion. We conclude that the ability of PBMCs to produce IL-1 beta in response to LFS is normal in PD patients as well as in I-ID patients. ICE-dependent processing of inactive proIL-1 beta into biologically active mIL-1 beta is reduced in PD patients, but not in IID patients. Secretion of mIL-1 beta is impaired in PD and IID patients treated with Cuprophan. This impaired ability to secrete active mIL-1 beta seems to be independent of ICE activity and is normalized when HD-patients are switched from Cuprophan to low- or high-flux polysulfon. Increased cell-associated levels of biologically active mIL-1 beta in circulating PBMCs represent a state of inflammation that may contribute to chronic inflammatory diseases such as beta2-microglobulin amyloidosis. Replacement of Cuprophan by synthetic membranes normalizes PBMC function and reduces the state of inflammation in ESRD patients.