Cuprammonium membranes stimulate interleukin 1 release and arachidonic acid metabolism in monocytes in the absence of complement

Evaluation of phagocytic cell function in an ex vivo model of hemodialysis

An ex vivo model of hemodialysis was used to evaluate the effect of dialysis membranes on phagocytic cell function. Blood was withdrawn continuously from healthy, non-uremic donors, heparinized, and pumped, single pass, through membrane modules under conditions which simulated normal dialysis conditions. The membrane modules contained membranes of cellulose, DEAE-substituted cellulose, or polysulfone. Blood was obtained from the module outlets for determination of complement activation, phagocyte elastase release, zymosan-induced phagocyte chemiluminescence, and monocyte interleukin-1 production. Significantly less complement activation occurred with the polysulfone and DEAE-substituted cellulose membranes than with cellulose membranes. Normal monocyte interleukin-1 production was not stimulated by any of the membranes used. In contrast, the cellulosic, but not the polysulfone, membranes primed the oxidative burst of the phagocytes and caused them to release elastase. DEAE-substituted cellulose had a lesser effect on elastase release than did cellulose and elastase release correlated significantly with the degree of complement activation. However, the correlation between complement activation and priming of phagocyte oxidative burst was weak, suggesting that membranes affect phagocyte oxidative metabolism through more than one mechanism. We conclude that some dialysis membranes stimulate the bacteriacidal functions of normal phagocytic cells, in part through complement-dependent mechanisms.

Differential activation of monocytes in haemodialysis patients exposed to different types of membranes

Peripheral blood mononuclear cells (PBMC) from haemodialysis patients treated with different types of membranes were isolated, incubated in vitro, and extracellular and cell-associated interleukin I (IL-1) assayed by radioimmunological methods. Extracellular IL-1 was low and not different from controls, regardless of the dialyser used. In contrast, cell-associated IL-1 was increased in patients treated with dialysers containing low-flux Cuprophan (CU, n = 5) and polyacrylonitrile sheet membrane (AN69, n = 5). Patients treated with dialysers containing high-flux polysulphone (PS, n = 7), and polymethylmethacrylate (PMMA, n = 8), exhibited no increase in cell-associated IL-1 under these conditions. To elucidate the mechanism of the activation, aqueous extracts of dialysers containing CU, PS, and AN69 were tested for their ability to induce IL-1 generation in PBMC from healthy donors. Extracts from unrinsed CU-containing dialysers caused significant IL-1 synthesis and release, whereas incubation with extracts from dialysers containing PS and AN69 sheet membranes did not. Hence, although both CU and AN69 sheet-type dialysers result in activation of blood monocytes the mechanism of action appears to be different. We speculate that functional signs of PBMC activation as evidenced by increased spontaneous IL-1 production observed in some patients on long-term haemodialysis may result from extractable dialyser membrane material while in other instances direct cell membrane interactions or endotoxin transfer from the dialysate may be relevant.

Influence of uremia and hemodialysis on circulating interleukin-1 and tumor necrosis factor alpha

Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) were determined in the plasma of long-term hemodialysis (HD) patients and uremic (UR) patients undergoing their first dialysis session using either cellulosic (CUP) or synthetic (PAN-AN 69) membrane-equipped dialyzers. In long-term HD patients, plasma IL-1 and TNF alpha levels were significantly increased compared to their levels in normal subjects. During a single dialysis session, a significant increase in IL-1 but not in TNF alpha was observed. In not yet dialyzed UR patients, IL-1 plasma levels did not differ from those observed in normal subjects. By contrast, TNF alpha was found significantly increased although less than in long-term HD patients. During the first dialysis session, no significant increase was observed in the levels of either monokine. Lastly, regardless of the group of patients, no significant influence of the dialysis membrane could be detected, suggesting that the observed changes are not exclusively secondary to the activation of complement. Altogether, these results suggest that the passage of the blood through the extracorporeal dialysis circuit triggers the secretion of IL-1 and further exacerbates that of TNF alpha by monocytes. The presence of increased TNF alpha in the plasma of first-dialysis UR patients suggests that factors unrelated to dialysis contribute to the activation of monocytes in these patients. Lastly, the concomitant presence of IL-1 and TNF alpha in the plasma of long-term HD patients could be responsible for some of the clinical features observed in these patients, and provides strong evidence favoring the concept that HD can be assimilated to a recurrent acute-phase inflammatory response.

Transcription, not synthesis, of interleukin-1 and tumor necrosis factor by complement

Stimulation of interleukin-1 beta (IL-1 beta) and tumor necrosis factor (TNF alpha) production was studied during in vitro hemodialysis (HD) of whole blood using cuprammonium (Cup) or polysulfone (PS) dialyzers. In the absence of LPS, circulation of whole blood for two hours through Cup or PS dialyzers was not sufficient to induce production of IL-1 beta or TNF alpha in peripheral blood mononuclear cells (PBMC) during subsequent 24 hour culture. However, compared to freshly isolated cells, post-HD PBMC were primed to produce more IL-1 beta and TNF alpha when subsequently stimulated with LPS. Despite the lack of spontaneous monokine synthesis after HD, we observed transcription of mRNA coding for IL-1 beta and TNF alpha after two hours of LPS-free HD. When compared to levels of mRNA induced by 5 ng/ml LPS (100%), Cup induced 27 +/- 6% whereas PS did not induce detectable transcription of IL-1 beta. In the case of TNF alpha mRNA, Cup induced 26 +/- 8% and PS 13 +/- 3%. Recombinant C5a induced mRNA for IL-1 beta in PBMC without detectable IL-1 beta protein synthesis. We conclude that transcription of mRNA for IL-1 beta and TNF alpha during HD is primarily caused by complement activation by Cup, but that LPS or other factors are required for translation of IL-1 beta and TNF alpha mRNA transcribed during HD.

Induction of leukotriene B4 formation by dialyzer membranes

Interactions between blood and dialysis membranes lead to activation of the 5-lipoxygenase pathway of the arachiodonic acid metabolism during hemodialysis. Newly generated leukotriene B4 (LTB4) may contribute to the multifaceted granulocyte abnormalities of uremic patients.

Neutrophil activation during hemodialysis

Oxidative metabolism of PMNs of uremic patients is enhanced due to unknown serum (plasma) factors which are removed during hemodialysis. Respiratory burst activity is diminished in both PMA-stimulated and unstimulated states compared to healthy controls. Hemodialysis normalizes stimulated and decreases unstimulated hydrogen peroxide production. Several authors found that resting and stimulated chemiluminescence (CL) during hemodialysis correlates with complement activation, whereas other authors describe CL using dialyzer membranes with only mild anaphylatoxin formation. Alterations of PMN carbohydrate metabolism in uremic patients improves during HD with polysulfone. HD with PMMA, however, activates glycogenolysis. These alterations may be responsible for disturbance in phagocytosis. Degranulation during HD also occurs in absence of complement activation. Calcium channel blockers decrease activation of PMNs using dialyzers with only little anaphylatoxin formation.