Future trends in biocompatibility aspects of hemodialysis and related therapies.

Biocompatibility is redefined as the quality of being mutually tolerant with life. In so far as this represents a quality which is as likely to be achieved as is the alchemist's dream of turning lead into gold, a compromise approach is recommended. It is suggested that all extracorporeal or body invasive procedures stimulate the inflammatory defense mechanism of the body by stimulating the monocyte to produce a family of polypeptides currently known collectively as Interleukin-1 (IL-1). So far two dissimilar gene products have been cloned and there are probably more. The IL-1 group of polypeptides possess hormonal functions which orchestrate nearly every instrument of the body's defense system. Inducers of IL-1 are present in dialysate and include bacterial pyrogen and acetate. In addition bacterial cell wall glycoprotein may be cleaved into muramyl dipeptides by the release of granulocyte lysozyme at the membrane interface. Muramyl dipeptides have been found in CAPD drain fluid and are more potent inducers of IL-1 than endotoxin. Membrane activation of the fifth component of complement with the release of C5a will also induce monocytes to produce IL-1. The consequences of repeated stimulation of the acute phase response are undesirable and may include muscle wasting, osteopenia and bone cysts (Shrinking man syndrome), fibrosis of scapulo-humeral joints and the carpal-tunnel syndrome. These latter lesions are often associated with deposition of amyloid fibrils related to beta 2 microglobulin. Efforts to reduce these complications are urgently required.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in the permeability of high-flux dialyzer membranes for bacterial pyrogens.

AIMS: The increasing use of high-flux membranes for hemodialysis has raised concerns that patients dialyzed with these membranes may be at higher risk of being exposed to cytokine-inducing bacterial substances in the dialysate than patients dialyzed with low-flux membranes. We investigated the permeability of various high-flux membranes for both purified E. coli lipopolysaccharide (LPS) as well as for LPS derived from Stenotrophomonas (Sten.) maltophilia. MATERIALS AND METHODS: An in vitro dialysis circuit with saline in the blood compartment of 3 dialyzers containing different membranes (polysulfone, helixone and Diapes) was employed. The dialysate was challenged with increasing doses of sterile filtrates derived from Sten. maltophilia cultures or with purified LPS from E. coli. Samples from the blood compartment were tested for cytokine induction (IL-1beta, IL-6 and TNF) in mononuclear cells as well as for LPS by limulus amebocyte lysate test (LAL). RESULTS: IL-6 induction above sterile controls (< 0.02 ng/ml IL-6) was observed by samples from the blood side of DIAPES dialyzers (1.2 +/- 0.7 ng/ml IL-6) after challenging the dialysate with 4.1 +/- 3.6 U/ml E. coli LPS (9.9 +/- 4.5 ng/ml IL-6). In contrast, at the same challenge dose no significant IL-6 induction above sterile controls was observed by blood side samples of polysulfone (0.15 +/- 0.07 ng/ml) and helixone (0.09 +/- 0.05 ng/ml) dialyzers. Increasing the amount of E. coli LPS in the dialysate further augmented IL-6 induction by blood side samples of Diapes but not of polysulfone and helixone dialyzers. Similar results were obtained for IL-1beta and TNF. After challenging the dialysate with E. coli LPS as well as with cultures of Sten. maltophilia, significantly more LAL reactivity was observed in the blood compartment of Diapes compared to polysulfone and helixone. CONCLUSIONS: There are considerable differences between high-flux membranes regarding their permeability for cytokine-inducing substances from E. coli as well as for LPS derived from E. coli and Sten. maltophilia. Dialyzers that leak CIS under aqueous conditions in vivo should not be used unless the dialysate has passed through an ultrafilter.

Plasma levels of bactericidal/permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP) during hemodialysis.

Several proteins modify the biological response to lipopolysaccharide (LPS). Both bactericidal/permeability-increasing factor (BPI), a protein stored in neutrophils, and the acute phase protein LPS-binding protein (LBP) bind to LPS; however, BPI inhibits while LBP enhances binding of LPS to leukocytes and subsequent induction of cytokines. We investigated plasma levels of BPI, LBP, elastase and C5a before, during and after hemodialysis (HD). Six patients were dialysed with Cuprophane (Cup) and polysulfone (PS) low-flux dialyzers on two consecutive HD sessions. There was a significant, 10.9 +/- 2.8-fold increase in BPI after 4-hour HD compared to predialysis and a 4.4 +/- 1.6-fold increase in elastase after 4-hour HD using Cup. Plasma levels of BPI and elastase decreased rapidly after the dialysis session. HD with PS resulted in a smaller, but still significant rise in BPI (3.7 +/- 1.6-fold at 4 hours) and elastase (1.69 +/- 0.2-fold at 4 hours). Levels for BPI and elastase were similar in the arterial and venous blood lines of the dialyzer. Plasma levels of LBP did not change during or after the HD session. These data indicate that BPI, but not LBP is released during HD with Cup and to a lesser extent with PS. Activation of neutrophils and release of BPI during HD may influence the biological response to bacterial products possibly introduced during HD.

Hemodialysis-related induction of beta 2-microglobulin synthesis and release by mononuclear phagocytes.

We have investigated beta 2-microglobulin (beta 2M) synthesis and release by blood leukocytes and isolated mononuclear phagocytes. Since beta 2M was discovered to form amyloid fibrils in patients undergoing long term, chronic hemodialysis and monomeric beta 2M levels in plasma of these patients are highly elevated, and since hemodialysis-related factors that increase beta 2M production are unknown, we evaluated beta 2M production by mononuclear phagocytes under a variety of conditions. We utilized a novel enzyme-lined immunoabsorbant assay to quantitate beta 2M release. Adherence of macrophages onto polystyrene or Cuprophan membranes does not induce beta 2M synthesis or release. In contrast, interaction of macrophages with lipopolysaccharide, gamma-interferon, tumor necrosis factor, or interleukin 1 induces synthesis or release. In contrast, interaction of macrophages with lipopolysaccharide, gamma-interferon, tumor necrosis factor, or interleukin 1 induces synthesis and release of beta 2M, indicating that beta 2M synthesis is increased during macrophage activation. Exposing leukocytes or macrophages to changes in osmotic or oncotic pressure induces a rapid release of beta 2M and interleukin 1 into the cellular medium. These results suggest that during hemodialysis, beta 2M production is more likely to result from endotoxin contamination, or osmotic and oncotic changes, rather than direct interaction of mononuclear phagocytes with cellulosic membranes.

Detection of endotoxin antibody in long-term dialysis patients.

Endotoxins are often seen in dialysate. They are derived from Gram-negative bacteria especially Pseudomonas, E. coli and Serratia. Endotoxins are large-molecular-weight substances with an average molecular weight of 10(8). These large units can be divided into subunits down to a molecular weight of 10,000 which are thought to pass through dialyzer membranes. To investigate this, endotoxin antibody levels were measured in two groups of patients on chronic regular hemodialysis, a low-flux group using cellulosic membrane dialyzers (cuprophan and cuproammonium rayon (CAR) and a high-flux group using synthetic polymer membrane dialyzers (PMMA, EVAL). Using an ELISA based on standard endotoxin antibodies the percentages of patients in the low flux group with endotoxin antibodies were 26.9% with Cuprophan and 25% with CAR, not significantly different from a normal control group. In the PMMA and EVAL groups, it was 53.6% and 68.4% respectively. Back filtration of dialysate into blood is understood as the main reason for the entry of endotoxin in patients treated with high-flux dialyzers.

The relationship between biocompatibility and interleukin-1.

Biocompatibility is redefined as the quality of being mutually tolerant with life. In so far as this represents a quality which is as likely to be achieved as is the alchemist's dream of turning lead into gold, a compromise approach is recommended. It is suggested that all extracorporeal or body invasive procedures stimulate the inflammatory defence mechanism of the body by stimulating the monocyte to produce a family of polypeptides currently known collectively as Interleukin-1 (IL-1). So far two dissimilar gene products have been cloned and there are probably more. The IL-1 group of polypeptides possess hormonal functions which orchestrate nearly every instrument of the body's defence system. Inducers of IL-1 are present in dialysate and induce bacterial pyrogen and acetate. In addition bacterial cell wall glycoprotein may be cleaved into muramyl peptides by the release of granulocyte lysozyme at the membrane interface. Muramyl dipeptides have been found in CAPD drain fluid and are more potent inducers of IL-1 than endotoxin. Membrane activation of the fifth component of the complement with the release of C5a will also induce monocytes to produce IL-1. The consequences of repeated stimulation of the acute phase response are undesirable and may include muscle wasting, osteopenia and bone cysts (Shrinking man syndrome), fibrosis of scapulo-humeral joints and the carpal-tunnel syndrome. These latter lesions are often associated with deposition of amyloid fibrils related to beta 2-microglobulin. Efforts to reduce these complications are urgently required.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatibility in hemodialysis: clinical relevance in 1995.

Hemodialysis therapy for end-stage renal disease is still empirical even after more than 30 years of experience. Although long-term survival can now be assured in selected patients, clinical results tend to be disappointing. Hemodialysis therapy needs to be improved. Zealots of the biocompatibility school believe that this improvement will come from reducing undesirable consequences of blood membrane interaction, particularly complement activation. However, there is controversy over the clinical meaningfulness of biocompatibility when exclusively related to blood membrane interactions. Another dimension needs to be added, namely ultrapure dialysate to avoid subclinical chronic effects of activation of the cytokine cascade by bacterial fragments present in dialysate. While the pathogenesis of acute anaphylactoid reactions are understood and largely preventable, the relation of the chronic syndromes such as amyloidosis to the use of a particular membrane remain unproven. Prospective studies that will occupy at least a decade will be necessary to decide these issues.

Bacterial challenge of NISSHO ultrafilter ETF 609: results of in vitro testing.

In hemodialysis, a certain degree of bacterial contamination on the dialysate side is a regular finding. Concern has been growing that this contamination may lead to a chronic inflammatory response in the patient. Ultrafiltration of dialysate can be used to reduce bacterial content and levels of cytokine-inducing substances upstream of the patient's dialyzer. The aim of this study was to test in vitro the rejection capacity of a polysulfone hollow-fiber ultrafilter (ETF 609, NISSHO Co., Osaka, Japan) challenged with bacterial filtrates derived from Pseudomonas aeruginosa PA103. Results showed a reduction of interleukin-1 beta-inducing activity (measured on peripheral blood mononuclear cells) from 5,035 +/- 394 pg/ml prefilter to nondetectable levels postfilter and endotoxin levels (limulus amebocyte lysate assay) of 4,167 +/- 1,079 versus 12 +/- 2 pg/ml, respectively. In conclusion, ultrafiltration of dialysate with the polysulfone ultrafilter ETF 609 leads to a potent reduction of cytokine-inducing activity.

The role of plasma coating on the permeation of cytokine-inducing substances through dialyser membranes.

We studied the effects of coating of dialyser membranes with plasma proteins on the permeation of bacteria-derived cytokine-inducing substances (CIS). An in vitro dialysis circuit using polysulphone (PS) or modified cellulose triacetate (mCT) dialysers was used. Precoating of the dialysers was performed by recirculation of 10% normal human plasma for 30 min in the blood compartment and subsequent rinse with pyrogen-free saline. Samples from the blood compartment were tested for induction of interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta) and tumour necrosis factor (TNF alpha) at various time points after challenging the dialysate with sterile culture supernatants from Pseudomonas aeruginosa. Contamination of the dialysate resulted in the appearance of CIS in the blood compartment of both polysuphone modified cellulose triacetate (IL-1 alpha: PS, time 0: 81 +/- 11 pg/ml, time 60 min: 4747 +/- 1822 pg/ml, P < 0.05; mCT, time 0: 235 +/- 141 pg/ml, time 60 min: 1632 +/- 531 pg/ml, P < 0.05). The plasma protein layer reduced the penetration of CIS significantly only for polysulphone (IL-1 alpha: PS, time 60: 4747 +/- 1822 versus 880 +/- 525 pg/ml, P < 0.05; modified cellulose triacetate, time 60 min: 1632 +/- 531 pg/ml versus 930 +/- 326 pg/ml). Samples from the blood compartment contained < 6 pg/ml LAL-reactive material at all time points. We conclude that plasma coating of polysulphone dialysers reduces the permeability for CIS derived from Pseudomonas, either by reducing the effective pore size or by adsorption of proteins that bind CIS.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the ability of hemodialysis membranes to induce, bind, and clear human interleukin-1.

Interleukin-1 (IL-1) is a polypeptide cytokine predominantly produced by monocytes in response to injury or infection. Effects of IL-1 such as fever, acute phase protein synthesis, hypotension, and loss of body mass are complications of hemodialysis. Endotoxin-contaminated dialysate fluid, sodium acetate as a dialysate buffer, and activated complement can induce IL-1 during hemodialysis. In the present study, we investigated the intrinsic property of hemodialysis membranes to stimulate human blood mononuclear cells (MNC) to produce IL-1. Incubation of MNC on sheets of two commonly used hemodialysis membranes, regenerated cellulose (RC) and polyacrylonitrile (PAN) resulted in significant induction of IL-1 in the absence of endotoxin or complement. Production of intracellular and extracellular IL-1 was greater in MNC exposed to PAN compared with RC (p less than 0.01). Similar results were obtained when MNC were exposed to strips of hemodialysis membranes in rotating tubes. However, compared with RC, PAN binds significant amounts of human IL-1. In a model of in vitro hemodialysis, radiolabeled recombinant human IL-1 was added to the blood compartment of a PAN and a RC dialyzer. Forty percent of radiolabeled IL-1 bound to the PAN dialyzer membrane compared with 10% to the membrane of a RC dialyzer. In addition, 22% of radiolabeled IL-1 was found in the dialysate compartment of a PAN dialyzer after 1 hour whereas 1% was found in the dialysate side of a RC dialyzer; these results were confirmed by measuring bioactivity of IL-1. These studies demonstrate the intrinsic property of hemodialysis membranes to stimulate human IL-1 production; in addition they establish that dialysis membranes differ in their ability to bind and clear IL-1.

Plasma interleukin-1 activity during hemodialysis: the influence of dialysis membranes.

Plasma interleukin-1 (IL-1) activity was measured in 7 stable ESRD patients on regular hemodialysis for no less than 5 months. Predialysis levels were significantly raised compared to 8 normal control subjects. During hemodialysis with four different membranes, plasma IL-1 activity rose with Cuprophan and Hemophan and was unchanged or reduced with Gambrane and Polysulfon. In spite of these differences, body temperature rose in all forms of hemodialysis. Factors responsible for the predialysis elevation included the absence of renal function and/or the repeated stimulus of human blood monocytes by hemodialysis. In view of the uniform increase of body temperature during hemodialysis, the differences in changes of plasma IL-1 activity observed with the various membranes may not be caused by a variable stimulation of monocytes but rather by the presence or absence of the membrane's ability to remove and/or absorb IL-1. Thus, the consequences of monocyte hemodialysis stimulation may be obtained locally, even in the presence of unchanged or reduced plasma IL-1 activity.

Enhancement of in-vitro human interleukin-1 production by sodium acetate.

Human blood monocytes were incubated in vitro in the presence of various concentrations of sodium acetate or sodium chloride or with medium alone. Intracellular and extracellular levels of interleukin-1 (IL-1) were measured. The production of intracellular IL-1 and the release of extracellular IL-1 were higher in the presence of acetate than in the presence of chloride or in medium alone. The concentrations of acetate used were comparable to those encountered by blood monocytes on the surface of haemodialysis membranes. Since complications of peritoneal dialysis, such as loss of ultrafiltration and progressive fibrosis of the peritoneum, have been associated with the use of sodium acetate as the exchange-fluid buffer, these results suggest that the widespread use of sodium acetate as a buffer during haemodialysis may be contraindicated.