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

Background. In vitro stimulation of mononuclear cells (peripheral blood mon onuclear cells; PBMCs) with an endotoxin (lipopolysaccharide; LPS) revealed elevated cell-associated levels of interleukin-1 beta (IL-1 beta) in end-s tage renal disease (ESRD) patients on Cuprophan hemodialysis (HD), suggesti ng 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 be ta. ProIL-1 beta is processed into the biologically active mature form of I L-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 p roIL-1 beta and/or secretion of mIL-1 beta was impaired in ESRD patients co mpared with healthy controls. PBMCs of healthy controls (N = 9), of ESRD pa tients on peritoneal dialysis (PD, N = 10), and of those patients on interm ittent HD (N = 8) were studied. The same HD patients were studied three tim es with low-flux Cuprophan (GFS 12), low-flux polysulfon (F6 HPS), and high -flux polysulfon (F60S) in randomized order. PBMCs were separated from whol e blood by Ficoll-Hypaque centrifugation and incubated in vitro for 18 hour s 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 w ere measured. Results. The total production (cell-associated plus extracellular) of LPS-i nduced IL-1 beta (proIL-1 beta plus mIL-1 beta) was similar in healthy cont rols (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 proc essed into mIL-1 beta, which was significantly more than that in PD patient s (27.3%, P < 0.02) but was similar to that in Cuprophan-treated HD patient s (37.1%). Comparing cell-associated and extracellular concentrations of mI L-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 C uprophan 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 proces sing of IL-1 beta changed. However, secretion of mIL-1 beta increased signi ficantly with F6 HPS (80.6%, P < 0.01) as well as with F60S (76.6%, P < 0.0 2) compared with Cuprophan. Conclusion. We conclude that the ability of PBMCs to produce IL-1 beta in r esponse to LFS is normal in PD patients as well as in I-ID patients. ICE-de pendent 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 impai red ability to secrete active mIL-1 beta seems to be independent of ICE act ivity 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 t hat may contribute to chronic inflammatory diseases such as beta2-microglob ulin amyloidosis. Replacement of Cuprophan by synthetic membranes normalize s PBMC function and reduces the state of inflammation in ESRD patients.