Increased reduction of dimethylarginines and lowered interdialytic blood pressure by the use of biocompatible membranes.

Hypertension contributes to cardiac and cerebrovascular complications in HD patients. Endogenous inhibitors of nitric oxide synthase accumulate in renal failure and may interfere with the regulation of vascular tone. We investigated the elimination of asymmetric dimethylarginine (ADMA) by using biocompatible Polyamide Strade mark membranes in low-flux (Polyflux 6L) or high-flux (Polyflux 14S) hemodialysis or hemodiafiltration (HDF) compared with hemodialysis with cellulosic membranes. Removal rates for ADMA, symmetric dimethylarginine (SDMA), and beta2-microglobulin significantly increased in HDF. The plasma total amino acid concentration and the arginine/ADMA ratio increased, and the mean 24-hour blood pressure decreased during the study. In a second study, we investigated whether plasma amino acids and interdialytic blood pressure are influenced by the use of a biocompatible membrane and HDF. Seventeen end-stage renal disease patients were treated for six weeks with hemodialysis using cellulosic membranes, six weeks with low-flux hemodialysis using Polyflux 6L, and six weeks with HDF using Polyflux 14S. Only in the diabetic patients were the hemoglobin concentration (from 10.6 +/- 1.5 to 11.9 +/- 0.6 mg/dL) and hematocrit (from 33.6 +/- 1.9 to 36.2 +/- 1.5%) increased significantly, whereas the mean 24-hour systolic blood pressure decreased (from 154 +/- 22 to 129 +/- 18 mm Hg). No significant changes were observed in nondiabetic patients. We conclude that primarily diabetic patients seem to benefit from the use of biocompatible membranes--most in HDF--after a period of six weeks. The regulation of nitric oxide pathways by ADMA removal and changed ADMA/arginine ratio might be contributing factors. Further prospective studies are required to show whether the long-term application of HDF or other changes of dialysis treatment modalities may help to improve well-being, morbidity, and mortality in hemodialysis patients.

Expression of beta2-microglobulin and c-fos mRNA: is there an influence of high- or low-flux dialyzer membranes?

BACKGROUND: Dialysis-related amyloidosis is an important complication of long-term hemodialysis (HD) therapy with several pathogenetic factors. One of them is the influence of the dialyzer membrane type on the synthesis of beta2-microglobulin (beta2m). In vitro results are controversial. Thus, the hypothesis of whether in vivo beta2m generation is induced by the HD procedure and whether this induction depends on the type of the used dialyzer membrane should be tested. The aim of the present study was to investigate the influence of "biocompatible" high-flux versus "bioincompatible" low-flux HD on in vivo beta2m generation as well as the induction of the early activation gene c-fos in peripheral blood cells. METHODS: Six nondiabetic HD patients [mean age 46 (21 to 69) years; Kt/V> 1.2] were included in a randomized crossover study using either a low-flux (cellulosic/cuprophan) or a high-flux (polyamide) dialyzer membrane. At the end of a four-week run-in period for each membrane, whole blood samples were taken before, immediately at, and four hours after the end of the dialysis session. MRNA was extracted, and after transcription to cDNA, quantitative polymerase chain reaction was performed for the beta2m gene, the early response gene c-fos, and the GAP-DH housekeeping gene. RESULTS: Based on the applied method for detection of specific mRNA, the results were given as ratio of beta2m or c-fos cDNA per GAP-DH cDNA. General cell activation during HD was indicated by increasing mRNA expression of c-fos related to the time course of the dialysis session, whereas beta2m did not change significantly. However, no difference was found when comparing the low-flux and the high-flux dialyzer membranes. Despite the evidence for activation of peripheral blood cells, as indicated by increasing c-fos message, no sign of beta2m mRNA induction during HD procedure with different dialyzer membranes was seen. CONCLUSIONS: Our results suggest that there is post-transcriptional regulation of beta2m generation and/or release as well as the influence of the dialyzer membrane type on post-translational processes, that is, advance glycation end products (AGE) or conformational modification of the beta2m protein. Furthermore, our data demonstrate that gene expression patterns during dialysis and/or uremia are not homogenous and need to be investigated further, especially with respect to the proinflammatory role of early leukocyte activation signals.

Complement components as uremic toxins and their potential role as mediators of microinflammation.

Cardiovascular disease is the major cause of death in end-stage renal disease (ESRD) patients. There is growing evidence that atherogenesis is an inflammatory rather than a purely degenerative process leading to a state of microinflammation. This raises the issue of whether treatment modalities of ESRD contribute to the microinflammatory state. One potential candidate in this context is the complement system. Here we consider three potential pathways linking complement activation to progression of atherosclerosis: (1) complement activation on artificial surfaces depends on their physicochemical characteristics, the effect of which is amplified because of the accumulation of complement factor D; (2) the exposure of ESRD patients to endotoxin creates a microinflammatory state, and this may amplify complement-induced damage; exposure to endotoxin may result from frequent infections because of the impairment of host-defense mechanisms or from transfer of bacterial contaminants across dialysis membranes into the blood stream; and (3) direct transduction of proinflammatory signals from blood-material interactions to the vascular system. We conclude that the complement system is an important candidate system in the genesis of microinflammation and accelerated atherogenesis in ESRD. We advance the hypothesis that the generation of proinflammatory signals, in which the complement system appears to be involved--both through systemic and local activation--plays a role in the development of late complications of uremia, including coronary heart disease. This hypothesis provides a rationale to maximize the biocompatibility of the dialysis procedure, that is, selection of nonactivating materials, use of ultrapure dialysis fluid, and--still theoretical--high-flux dialysis to remove factor D.

Hepatotoxic substance(s) removed by high-flux membranes enhances the positive acute phase response.

BACKGROUND: Acute phase proteins (APPs) are enhanced in end-stage renal disease patients (ESRD) requiring dialysis treatment. They are involved in a variety of pathologic processes like muscle proteolysis, cachexia, regulation of appetite, and atherosclerosis. They are predictive for mortality. APPs are not only makers but also active substances. They are mainly produced in liver cells and are primarily, but not exclusively, regulated by proinflammatory cytokines. To what extent hepatic APPs are influenced by uremic toxins is still unclear. Therefore, we investigated the effects of different ultrafiltrates (UFs) on the synthesis of alpha1-acid glycoprotein (AGP) in HepG2 cells. METHODS: A cross-sectional as well as a crossover study with high-/low-flux membranes was conducted to investigate the impact of UFs on bioactivity of liver cell cultures. Metabolic activity (MTT test), cytotoxicity (lactate dehydrogenase release), and the positive APP AGP were measured in HepG2 cells. RESULTS: Cultured hepatocytes treated with UFs from high-flux membranes exhibited a higher cytotoxicity (18.6 +/- 0.3% high-flux vs. 13.9 +/- 0.2% low-flux, P < 0.001) and a lower metabolic activity (29.3% high-flux vs. 50.3% low-flux, P < 0.001) in comparison with low-flux UFs. In addition, enhanced APP secretion could be observed under costimulatory conditions (high-flux 5.0 +/- 0.7 vs. low-flux 3.1 +/- 0.6 ng/microg protein, P < 0.05). The effects of high- and low-flux UFs were strongly expressed at the beginning and were still significantly different after 120 minutes of hemodialysis (HD) treatment. The crossover experiments confirmed that UFs collected during high-flux HD had a higher capacity to stimulate AGP synthesis in liver cells. CONCLUSION: The effects of UFs from dialysis patients demonstrate that hepatotoxic substances can be removed by dialysis. Stimulating the acute phase response UF collected during high-flux HD had a higher impact on liver cells in comparison with low-flux UF. These substances are putative cofactors involved in cytokine regulation.

Surface modifying additives for improved device-blood compatibility.

Copolymers composed of polar and nonpolar blocks, when blended with a base polymer in low concentrations, migrate to the base polymer surface during and after fabrication. Migration of these surface modifying additives (SMAs) dramatically changes the outermost surface molecular layers that comprise the region that determines biocompatibility. The blood compatibility of cardiopulmonary bypass and hemodialysis components have been improved by using SMA blended polymers or SMA coated surfaces. The particular SMAs used were a series of triblock copolymers with a general formulation of polycaprolactone-polydimethylsiloxane-polycaprolactone. X-ray fluorescence (XRF), fourier transform infrared (FTIR), refractive increments (RI), and gel permeation chromatography (GPC) were used to characterize the molecular weight of SMA and the bulk concentration of SMA after blending. Electron spectroscopy for chemical analysis (ESCA) proved that the surface of blended polymers was highly saturated with SMA. Results of in vitro experiments with human blood demonstrated that SMA blended polymers delay contact activation (kallikrein-like activity), reduce coagulation activity (thrombin-antithrombin [TAT] generation), and do not adversely affect complement activation (terminal complement complex [TCC] generation) or mononuclear cells activation (IL-1 beta production). Ex vivo canine AV shunt studies showed improvement of platelet compatibility of SMA blended polymers. Reduction of cellular and protein system activation by using components fabricated with SMA blood contacting surfaces can potentially result in reduced morbidity associated with extracorporeal circulation.