Background:
In vitro stimulation of mononuclear cells (peripheral blood mononuclear cells; pbmcs) with an endotoxin (lipopolysaccharide; lps) revealed elevated cell-associated levels of interleukin-1beta (il-1beta) in end-stage renal disease (esrd) patients on cuprophan hemodialysis (hd), suggesting a defect in the process of il-1beta's release from activated cells. il-1beta is initially synthesized as an inactive precursor called proil-1beta. proil-1beta is processed into the biologically active mature form of il-1beta (mil-1beta) requiring the specific il-1beta-converting enzyme (ice).
Methods:
Using specific immunoassays (enzyme-linked immunosorbent assays), we measured cell-associated and extracellular proil-1beta as well as mil-1beta in lps-stimulated pbmcs to test whether ice-dependent processing of proil-1beta and/or secretion of mil-1beta 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-1beta and mil-1beta were measured.
Results:
The total production (cell-associated plus extracellular) of lps-induced il-1beta (proil-1beta plus mil-1beta) 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 106 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-1beta was processed into mil-1beta, 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-1beta, pbmcs of normal controls secreted 82.2% of mil-1beta; 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-1beta production nor processing of il-1beta changed. however, secretion of mil-1beta 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-1beta in response to lps is normal in pd patients as well as in hd patients. ice-dependent processing of inactive proil-1beta into biologically active mil-1beta is reduced in pd patients, but not in hd patients. secretion of mil-1beta is impaired in pd and hd patients treated with cuprophan. this impaired ability to secrete active mil-1beta 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-1beta 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.