Horst-Dieter Lemke

Plasma interleukin-6 is independently associated with mortality in both hemodialysis and pre-dialysis patients with chronic kidney disease

Chronic inflammation associated with chronic kidney disease predicts all-cause and cardiovascular mortality in hemodialysis patients. Here we sought to evaluate the association between plasma levels of the inflammatory mediator interleukin-6 (IL-6) and mortality and aortic calcification/stiffness in 125 patients at different stages (2-5D) of chronic kidney disease. Using multivariate linear regression, we found that plasma IL-6 was independently associated with C-reactive protein, albumin and the stage of chronic kidney disease, but not the aortic calcification score or pulse wave velocity. During follow-up studies (median of 829 days), 38 patients died, 22 from cardiovascular events. Plasma IL-6 significantly predicted overall and cardiovascular mortality; this association persisted after multiple adjustments or restricting the analysis to pre-dialysis patients. Moreover, IL-6 was a significantly better predictor of mortality than C-reactive protein, albumin or tumor necrosis factor-alpha. Hence, plasma IL-6 independently predicted overall and cardiovascular mortality in patients at different stages of chronic kidney disease; however, whether lowering plasma IL-6 will affect the outcome of chronic kidney disease will require more direct evaluation.

Protein-bound uraemic toxin removal in haemodialysis and post-dilution haemodiafiltration

BACKGROUND The accumulation of larger and protein-bound toxins is involved in the uraemic syndrome but their elimination by dialysis therapy remains difficult. In the present study, the impact of the albumin permeability of recently introduced advanced high-flux dialysis membranes on the removal of such substances was tested in haemodialysis and online post-dilution haemodiafiltration. METHODS Two types of polyethersulfone membranes only differing in albumin permeability (referred as PU- and PU+) were compared in eight patients on maintenance dialysis in a prospective cross-over manner. Treatment settings were identical for individual patients: time 229 +/- 22 min; blood flow rate 378 +/- 33 mL/min; dialysate flow rate 500 mL/min; substitution flow rate in haemodiafiltration 94 +/- 9 mL/min. Removal of the protein-bound compounds p-cresyl sulfate (pCS) and indoxyl sulfate (IS) was determined by reduction ratios (RRs), dialytic clearances and mass in continuously collected dialysate. In addition, the elimination of the low-molecular weight (LMW) proteins beta(2)-microglobulin, cystatin c, myoglobin (myo), free retinol-binding protein (rbp) and albumin was measured. RESULTS Plasma levels of the protein-bound toxins were significantly decreased by all treatment forms. However, the decreases were comparable between dialysis membranes and between haemodialysis and haemodiafiltration. The RRs of total pCS ranged between 40.4 +/- 25.3 and 47.8 +/- 10.3% and of total IS between 50.4 +/- 2.6 and 54.6 +/- 8.7%. Elimination of free protein-bound toxins as assessed by their mass in dialysate closely correlated positively with the pre-treatment plasma concentrations being r = 0.920 (P < 0.001) for total pCS and r = 0.906 (P < 0.001) for total IS, respectively. Compared to haemodialysis, much higher removal of all LMW proteins was found in haemodiafiltration. Dialysis membrane differences were only obvious in haemodialysis for the larger LMW proteins myo and rbp yielding significantly higher RRs for PU+ (myo 46 +/- 9 versus 37 +/- 9%; rbp 18 +/- 5 versus 15 +/- 5%; P < 0.05). Additionally, the albumin loss varied between membranes and treatment modes being undetectable with PU- in haemodialysis and highest with PU+ in haemodiafiltration (1430 +/- 566 mg). CONCLUSIONS The elimination of protein-bound compounds into dialysate is predicted by the level of pre-treatment plasma concentrations and depends particularly on diffusion. Lacking enhanced removal in online post-dilution haemodiafiltration emphasizes the minor significance of convection for the clearance of these solutes. Compared to LMW proteins, the highly protein-bound toxins pCS and IS are less effectively eliminated with all treatment forms. For a sustained decrease of pCS and IS plasma levels, alternative strategies promise to be more efficient therapy forms.

Plasma beta-2 microglobulin is associated with cardiovascular disease in uremic patients.

Since beta-2 microglobulin (B2M) is a surrogate marker for middle molecular weight uremic toxins and the major protein component in dialysis-related amyloidosis, it has been frequently studied in dialysis patients. It is not known, however, whether B2M has an impact in patients with chronic kidney disease (CKD) not yet on dialysis. Here we studied the relationship of plasma B2M levels to clinical and cardiovascular outcomes in 142 patients (mean age of 67 years) at different stages of CKD. B2M levels increased with CKD stage and thus were highest in hemodialysis patients. Baseline B2M levels were associated with vascular calcification but not with arterial stiffness or bone density. During a mean follow-up of 969 days, 44 patients died and 49 suffered a cardiovascular event. Higher B2M levels were independently associated with overall and cardiovascular mortality and cardiovascular events in the whole cohort and with cardiovascular events in the predialysis cohort. Moreover, B2M appeared to be a better predictor than well-established factors associated with outcomes in this population, such as estimated glomerular filtration rate ((eGFR), only for predialysis patients), inflammation biomarkers, and other factors included in a propensity score. Thus, we confirm the strong relationship between B2M levels and eGFR and confirm the power of B2M to predict overall and cardiovascular mortality and cardiovascular events in patients at different stages of CKD.

Comparison of removal capacity of two consecutive generations of high-flux dialysers during different treatment modalities

BACKGROUND Innovative modifications have been introduced in several types of dialyser membranes to improve adequacy and permselectivity. Which aspects of removal are modified and how this relates to different diffusive or convective strategies has, however, been insufficiently investigated. METHODS In a prospective cross-over study, 14 chronic kidney disease (Stage 5D) patients were dialysed with a second-generation high-flux dialyser (Polynephron) in comparison to a first-generation type (DIAPES-HF800). Both dialysers were assessed in haemodialysis, in online pre-dilution and in post-dilution haemodiafiltration. Reduction ratio (RR, %) of small water-soluble compounds (urea and uric acid), low-molecular weight proteins (LMWPs) (β(2)-microglobulin, cystatin C, myoglobin and retinol-binding protein) and protein-bound solutes (hippuric acid, indole acetic acid, indoxylsulphate and p-cresylsulphate) was assessed, together with albumin losses into the dialysate. RESULTS Comparing the two types of membranes, the second-generation dialyser demonstrated a higher RR for LMWPs, whilst at the same time exhibiting lower albumin losses but only during post-dilution haemodiafiltration. No differences in RR were detected for both the small water-soluble and the protein-bound compounds. Comparing dialysis strategies, convection removed the same amount of solute or more as compared to diffusion. CONCLUSIONS The second-generation membrane resulted in a higher removal of LMWPs compared to the first-generation membrane, but for the other solutes, differences were less prominent. Convection was superior in removal of a broad range of uraemic retention solutes especially with the first-generation membrane.

NMR imaging of flow in hollow fiber hemodialyzers

Abstract In this paper, we report the use of NMR (nuclear magnetic resonance) imaging for the investigation of flow profiles and flow-velocity distributions in hemodialyzers containing hollow-fiber membranes. For this purpose, we calculated a velocity-encoding and velocity-compensated spin echo NMR imaging sequence. The performance of the sequence was tested on a simple flow phantom and the results were compared with simulated data showing good agreement regarding the geometry of the velocity profiles as well as the maximum flow velocities. Two different small-scale model hemodialyzers were investigated by means of NMR imaging to gather information about flow-velocity distributions in the two compartments of hemodialyzers. The results show that the incorporation of textile fibers as spacer yarn in one of these model hemodialyzers strongly narrowed the flow-velocity distribution in the dialysate compartment. Additionally, the spatial flow-velocity distribution was measured in a clinical-scale hemodialyzer to compare the results from model and clinical systems. Flow velocities were measured in the potting region of one of the model hemodialyzers and at a short distance downstream in the dialysate compartment. It was shown that swelling of the membranes in the potting region leads to higher flow velocities of the inner membrane flow.

Markers of vascular disease in plasma from patients with chronic kidney disease identified by proteomic analysis.

Objectives Chronic kidney disease (CKD) patients belong to the group of patients with a high prevalence of cardiovascular disease (CVD). Arterial calcification and aortic stiffness are currently used as surrogates for vascular alterations. However, still little is known about prediction and the patho-physiologic mechanisms leading to CVD. Methods We applied capillary electrophoresis coupled mass spectrometry profiling to blood specimens collected from 34 CKD stage 5D patients suffering from vascular alterations to allow insights into the molecular pathology of the disease. Results Statistical comparison of plasma profiles from mild and severe CVD cases according to either arterial calcification or aortic stiffness unveiled 13 novel biomarkers for vascular disease. Tandem mass spectrometry identified four of these as fragments of collagen alpha-1 type I and III and one as fragment of apolipoprotein CIII. Integrated in a distinct pattern the candidates were validated using the moderate CVD cases among the 34 CKD patients (N = 11) and an additional independent blinded cohort of CKD stage 4–5 patients (N = 21), who all had not been considered during biomarker discovery. The panel distinguished mild and severe CVD with sensitivity of 89% and specificity of 67% in this independent cohort. Conclusion This diagnostic phase I/II study supports the notion that vascular alterations are reflected by distinct changes in plasma profiles of CKD patients.

Bisphenol A in Chronic Kidney Disease: Bisphenol A in CKD

The estrogenic endocrine-disrupting substance bisphenol A (BPA) is extensively used as a starting material for a variety of consumer plastic products including dialyzer materials. The present study was performed to explore plasma BPA levels in patients with impaired renal function and to investigate if dialyzers differing in elutable BPA influence plasma levels in patients on maintenance hemodialysis. In vitro BPA was eluted from high-flux polyethersulfone (PUREMA H, referred as PUR-H), high-flux polysulfone (referred as HF-PSu), and low-flux polysulfone (referred as LF-PSu) dialyzers by recirculation with water for 180 min. In a cross-sectional clinical study, plasma BPA levels of outpatients with different stages of chronic kidney disease (CKD) from four different centers were determined. Furthermore, in a prospective, randomized, and crossover setting, 18 maintenance dialysis patients were subjected successively to 4 weeks of thrice-weekly hemodialysis with each LF-PSu, HF-PSu, and PUR-H. In addition, the fractions of protein-bound and free BPA were determined in a subset of dialysis patients. The mass of BPA eluted from the blood compartments in vitro under aqueous conditions varied for the three dialyzers being very low for PUR-H (6.2 ± 2.5 ng; P < 0.001), intermediate for HF-PSu (48.1 ± 7.7 ng), and highest for LF-PSu (140.8 ± 38.7 ng; P < 0.01). In 152 prevalent patients with CKD enrolled in the cross-sectional trial, plasma BPA started to rise after stage 3. Maintenance hemodialysis patients had more than six times higher BPA concentrations than patients with CKD stage 5 not yet on dialysis (10.0 ± 6.6 vs. 1.6 ± 1.8 ng/mL; P < 0.001). The BPA concentrations highly and inversely correlated with renal function. In the randomized controlled study, the plasma BPA concentrations were highly elevated compared with healthy controls (range 9.1 ± 4.5-12.0 ± 6.0 ng/mL vs. ≤0.2 ± 0.1 ng/mL; P < 0.001), but no change of the plasma levels was observed during hemodialysis with any of the three dialyzers in the course of a single treatment and over a period of 4 weeks. The protein-bound fraction of plasma BPA in the dialysis patients was 74 ± 5%. Renal function and, most likely, the total quantity of ingested BPA are essential parameters affecting plasma BPA concentrations. Dialyzers are one additional source of BPA, but differences in the elutable BPA content are not associated with a significant effect on BPA plasma levels in Western European maintenance dialysis patients. Due to high protein binding, the removal of BPA by hemodialysis is limited.

Guanidinylations of albumin decreased binding capacity of hydrophobic metabolites.

As post‐translational modifications of proteins may have an impact on the pathogenesis of diseases such as atherosclerosis, diabetes mellitus and chronic kidney disease (CKD), post‐translational modifications are currently gaining increasing interest. In this study, a comprehensive method for analysis of these post‐translational modifications is established for the clinical diagnostic routine.

A New Synthetic Dialyzer With Advanced Permselectivity for Enhanced Low-molecular Weight Protein Removal

Optimizing solute removal at minimized albumin loss is a major goal of dialyzer engineering. In a prospective, randomized, crossover study on eight patients (age 63 +/- 14 years) on maintenance hemodialysis, the new Baxter Xenium 170 high-flux dialyzer (BX), which contains a 1.7-m(2) PUREMA H dialysis membrane, was compared with two widely used reference high-flux dialyzers currently available for hemodialysis in North America, the Fresenius Optiflux 180 NR (FO) and the Gambro Polyflux 170 H (GP). Solute removal and biocompatibility were assessed in hemodialysis for 240 min at blood and dialysate flow rates of 300 and 500 mL/min, respectively. Additional ex vivo experiments detecting the interleukin-1beta (IL-1b) generation in recirculated donor blood were performed to demonstrate the pyrogen retention properties of the dialyzers. The instantaneous plasma clearances were similar for the three dialyzers except for cystatin c (cysc), for which a lower clearance was measured with FO as compared with BX and GP after 30 and 180 min of hemodialysis. The reduction ratios (RRs) corrected for the hemoconcentration of beta(2)-microglobulin and cysc were lower in FO (44 +/- 9 and 35 +/- 9%, respectively) versus BX (62 +/- 6 and 59 +/- 7%, respectively) and GP (61 +/- 7 and 56 +/- 8%, respectively). The RRs of the cytokine tumor necrosis factor alpha and interleukin-6 were not different between the dialyzers. The albumin loss was <300 mg for all filters. No differences between the dialyzers were found in the biocompatibility parameters showing very low leukocyte and complement activation. The ex vivo recirculation experiments revealed a significantly higher IL-1b generation for GP (710 +/- 585 pg/mL) versus BX (317 +/- 211 pg/mL) and FO (151 +/- 38 pg/mL). BX is characterized by a steep solute sieving profile with high low-molecular weight protein removal at virtually no albumin loss and an excellent biocompatibility. This improved performance may be regarded as a contribution to optimal dialysis therapy.

Cellulose-Ester as Membrane Materials for Hemodialysis

The majority of dialysis membranes are fabricated from regenerated unmodified cellulose. This standard type of cellulosic membrane is frequently under attack because of its alleged lack of biocompatibility. Recent developments, however, have proven that a chemical modification of the reactive surface groups of regenerated cellulose, the hydroxylgroups, limits the complement-activating potential of these materials and thus improves its blood-compatibility. We extended the idea of modifying cellulose for improved blood-compatibility to a series of different cellulose esters. Special focus was directed towards the question whether a variation of the type of substituent and degree of substitution could influence the blood-compatibility pattern of these materials: the analysis of blood-compatibility profiles showed a direct dependency on the type of substituent and the degree of substitution (DS). As an example, it was found that the DS, necessary for a complete reduction of complement activation, decreases with increasing chain lengths of aliphatic substituents. Optimal degrees of substitution are characteristic of the type of substituents and enable us to tailor materials specifically for optimized blood compatibility.