Haemodiafiltration at increased plasma ionic strength for improved protein-bound toxin removal.

AIM: Protein-bound uraemic toxin accumulation causes uraemia-associated cardiovascular morbidity. Enhancing the plasma ionic strength releases toxins from protein binding and makes them available for removal during dialysis. This concept was implemented through high sodium concentrations ([Na+ ]) in the substituate of pre-dilution haemodiafiltration at increased plasma ionic strength (HDF-IPIS). METHODS: Ex vivo HDF-IPIS with blood tested increasing [Na+ ] to demonstrate efficacy and haemocompatibility. Haemocompatibility was further assessed in sheep using two different HDF-IPIS set-ups and [Na+ ] between 350 and 600 mmol L-1 . Safety and efficacy of para-cresyl sulphate (pCS) and indoxyl sulphate (IS) removal was further investigated in a randomized clinical pilot trial comparing HDF-IPIS to HD and HDF. RESULTS: Compared to [Na+ ] of 150 mmol L-1 , ex vivo HDF-IPIS at 500 mmol L-1 demonstrated up to 50% higher IS removal. Haemolysis in sheep was low even at [Na+ ] of 600 mmol L-1 (free Hb 0.016 ± 0.001 g dL-1 ). In patients, compared to HD, a [Na+ ] of 240 mmol L-1 in HDF-IPIS resulted in 40% greater reduction (48.7 ± 23.6 vs. 67.8 ± 7.9%; P = 0.013) in free IS. Compared to HD and HDF (23.0 ± 14.8 and 25.4 ± 10.5 mL min-1 ), the dialytic clearance of free IS was 31.6 ± 12.8 mL min-1 (P = 0.017) in HDF-IPIS, but [Na+ ] in arterial blood increased from 132 ± 2 to 136 ± 3 mmol L-1 (0 vs. 240 min; P < 0.001). CONCLUSION: HDF-IPIS is technically and clinically feasible. More effective HDF-IPIS requires higher temporary plasma [Na+ ], but dialysate [Na+ ] has to be appropriately adapted to avoid sodium accumulation.

Guanidinylations of albumin decreased binding capacity of hydrophobic metabolites.

AIM: 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. METHODS: Here, we analysed albumin - the most abundant plasma protein in human - isolated from patients with CKD and healthy controls by chromatographic steps and identified by MALDI mass spectrometry. Post-translational modifications of albumin were identified after digestion by analysing mass signal shifts of albumin peptides using pertinent mass databases. RESULTS: Albumin isolated from plasma of patients with CKD but not from healthy control subjects was specifically post-translationally modified by guanidinylation of lysines at positions 249, 468, 548, 565 and 588. After identification of guanidinylations as post-translational modifications of albumin isolated from patients with CKD, these modifications were quantified by mass spectrometry demonstrating a significant increase in the corresponding mass signal intensities in patients with CKD compared to healthy controls. The relative amount of guanidinylation of lysine at position 468 in patients with CKD was determined as 63 ± 32% (N = 3). Subsequently, we characterized the pathophysiological impact of the post-translational guanidinylation on the binding capacity of albumin for representative hydrophobic metabolic waste products. In vitro guanidinylation of albumin from healthy control subjects caused a decreased binding capacity of albumin in a time-dependent manner. Binding of indoxyl sulphate (protein-bound fraction) decreased from 82 ± 1% of not post-translationally modified albumin to 56 ± 1% after in vitro guanidinylation (P < 0.01), whereas the binding of tryptophan decreased from 20 to 4%. These results are in accordance with the binding of indoxyl sulphate to albumin from healthy control subjects and patients with CKD (88 ± 3 vs. 74 ± 10, P < 0.01). Thus, in vitro post-translational guanidinylation of albumin had a direct effect on the binding capacity of hydrophobic metabolites such as indoxyl sulphate and tryptophan. CONCLUSION: We used a mass spectrometry-based method for the characterization of post-translational modification and demonstrated the pathophysiological impact of a representative post-translational modification of plasma albumin. The data described in this study may help to elucidate the pathophysiological role of protein modifications.

Beta2-microglobulin, a uremic toxin with a double meaning.

beta(2)M is a strong and independent indicator of hemodialysis patient outcomes and an excellent surrogate for middle molecules, and deserves to be routinely monitored and incorporated into dialysis adequacy targets. beta(2)M has a double meaning, reflecting both dialysis efficacy in terms of solute mass transfer and patient bioactivity. The work of Ward et al. in this issue warrants a study to test the hypothesis that long daily hemodiafiltration treatment would be the optimal renal replacement modality to improve dialysis patient outcomes.

Haemodialysis-membrane biocompatibility and mortality of patients with dialysis-dependent acute renal failure: a prospective randomised multicentre trial. International Multicentre Study Group.

BACKGROUND: There is controversy as to whether haemodialysis-membrane biocompatibility (ie, the potential to activate complement and neutrophils) influences mortality of patients with acute renal failure. We did a prospective randomised multicentre trial in patients with dialysis-dependent acute renal failure treated with two different types of low-flux membrane. METHODS: 180 patients with acute renal failure were randomly assigned bioincompatible Cuprophan (n=90) or polymethyl-methacrylate (n=90) membranes. The main outcome was survival 14 days after the end of therapy (treatment success). Odds ratios for survival were calculated and the two groups were compared by Fisher's exact test. Analyses were based on patients treated according to protocol (76 Cuprophan, 84 polymethyl methacrylate). FINDINGS: At the start of dialysis, the groups did not differ significantly in age, sex, severity of illness (as calculated by APACHE II scores), prevalence of oliguria, or biochemical measures of acute renal failure. 44 patients (58% [95% CI 46-69]) assigned Cuprophan membranes and 50 patients (60% [48-70]) assigned polymethyl-methacrylate membranes survived. The odds ratio for treatment failure on Cuprophan compared with polymethyl-methacrylate membranes was 1.07 (0.54-2.11; p=0.87). No difference between Cuprophan and polymethyl-methacrylate membranes was detected when the analysis was adjusted for age and APACHE II score. 18 patients in the Cuprophan group and 20 in the polymethyl-methacrylate group had clinical complications of therapy (mainly hypotension). INTERPRETATION: There were no differences in outcome for patients with dialysis-dependent acute renal failure between those treated with Cuprophan membranes and those treated with polymethyl-methacrylate membranes.

Autosomal dominant medullary cystic kidney disease: evidence of gene locus heterogeneity.

Autosomal dominant medullary cystic kidney disease (ADMCKD; synonym: medullary cystic disease, MCD) is an autosomal dominant kidney disorder, sharing morphological and clinical features with recessive juvenile nephronophthisis (NPH), such as reduced urinary concentration ability and multiple renal cysts at the corticomedullary junction. While in NPH end-stage renal disease (ESRD) occurs in adolescence, ADMCKD leads to ESRD in adulthood. Recently a gene locus for ADMCKD has been localized to chromosome 1q21 in two large Cypriot families. This prompted us to examine linkage in three ADMCKD-families, using the same set of polymorphic microsatellite markers spanning the critical region on chromosome 1q21. Haplotype analysis revealed that none of the three families showed linkage to this locus, thus demonstrating evidence for genetic locus heterogeneity. Additional linkage analysis studies need to be performed in order to identify further gene loci cosegregating with this autosomal dominant kidney disorder.

Anaphylactoid reactions during hemodialysis in sheep are ACE inhibitor dose-dependent and mediated by bradykinin.

Anaphylactoid reactions (AR) have been attributed to the generation of bradykinin (BK) when AN69 membranes are used together with angiotensin converting enzyme (ACE) inhibitors during hemodialysis. However, conclusive evidence for the involvement of the BK as the mediator of these AR is still lacking. This study examined the degree of contact activation in an animal model caused by three PAN membranes--AN69, PAN DX, and SPAN- and the effects of different doses of the ACE inhibitor enalapril (ENA) and the BK B2-receptor antagonist icatibant on AR during hemodialysis. Six sheep were dialyzed for one hour with or without ENA pre-treatment using the different membranes in random order. Severe AR were observed only during hemodialysis with AN69 dialyzers together with ENA pre-treatment; the severity of AR increased with the ENA dose. Mild hypotension was noted during hemodialysis with AN69 without ACE inhibition and with PAN DX and 20 mg ENA. Compared to pre-dialysis values, maximum generation of BK after blood passage through the dialyzer was found at five minutes: 73-fold (AN69 without ENA), 161-fold (AN69 with 10 mg ENA), 97-fold (AN69 with 20 mg ENA), 108-fold (AN69 with 30 mg ENA), 154-fold (AN69 with 30 mg ENA and 0.1 mg/kg icatibant), 18-fold (PAN DX without ENA), and 42-fold (PAN DX with 20 mg ENA). Elevated BK levels in arterial blood were detected during hemodialysis with AN69 membranes even without ACE inhibition (2.5-fold); pre-treatment with 20 mg ENA further increased arterial BK concentrations (4-fold). Furthermore, a marked decline of prekallikrein and high molecular weight kininogen concentrations was noted for both AN69 and PAN DX membranes. Anaphylactoid reactions during hemodialysis were completely prevented by icatibant even after pre-treatment with ENA and in the presence of high BK concentrations. Concentrations of prekallikrein, high molecular weight kininogen, and BK remained unchanged and no AR were observed during hemodialysis with SPAN and pre-treatment with 20 mg ENA. Our findings confirm that AR during hemodialysis with the negatively charged AN69 membrane are mediated by BK, since they can be prevented by the BK B2-receptor antagonist icatibant.

Advantages of isovolemic large-volume erythrocytapheresis as a rapidly effective and long-lasting treatment modality for red blood cell depletion in patients with polycythemia vera.

Long-term survival of patients with polycythemia vera (PV) is essentially determined by the ability to reduce the risk of thromboembolic complications resulting from the altered rheological conditions by the high red blood cell (RBC) mass of these patients. RBC depletion to normal hematocrit (Hct) values is the first line therapy and should be preferred to chemotherapy (or P32) because of the long-term risk of acute leukemia or other secondary malignancies. RBC depletion is accomplished much more effectively and rapidly by erythrocytapheresis (EA) than by repeated phlebotomies and has been shown to be well tolerated and accepted by the patients (8). The main indications for EA for a PV patient (often newly diagnosed) are high risk Hct values of >55-60% that can be reduced to the normal range within 1-2 h. The long-lasting effect (median interval between 2 EA treatments: ca. 6 months) is partially the result of the massive loss of iron, a growth factor for erythropoesis. This has been shown by in vitro studies in erythroid progenitor cells of PV patients before and after EA (11). The advantages and possible disadvantages of EA treatment are discussed.

[Terminal kidney insufficiency in tuberous sclerosis]. / Terminale Niereninsuffizienz bei tuberöser Sklerose.

A now 33-year-old woman first had psychomotor seizures at the age of 3 years. At 9 years tuberous sclerosis (Bourneville-Pringle disease) was diagnosed, on the basis of sebaceous adenoma, white spots of the skin and periventricular cerebral calcifications. Later she developed hyperostoses of the cranium and two periungual fibromas. When aged 23 years she was first noted to have borderline hypertension (145/95 mmHg) and signs of renal insufficiency which, over the subsequent 10 years, gradually worsened: computed tomography and magnetic resonance imaging demonstrated angiolipomas and cysts. Haemodialysis became necessary when serum creatinine level had risen to 9.0 mg/dl, creatinine clearance to 8 ml/min, with proteinuria of 2660 mg/24 h and metabolic acidosis (pH 7.17, base excess -8.1 mmol). She had no mental retardation nor other neurological deficits and is scheduled to have renal transplantation. There were no hamartomas in other organs.

Anaphylactoid reactions during haemodialysis in sheep are associated with bradykinin release.

Anaphylactoid reactions have been observed in patients treated with AN69 dialysers and ACE inhibitors. Recently, it has been shown in vitro that AN69 membranes induce the release of high amounts of bradykinin in plasma. To verify the possible role of bradykinin in these shock-like reactions, six sheep were dialysed in a random fashion using AN69 or the new SPAN membrane with and without pretreatment with captopril. All animals were dialysed for 60 min via double-lumen Shaldon catheters. Blood samples were drawn at 0, 5, 10, 15, 30, and 60 min from the venous line. A total of 24 haemodialysis procedures was carried out: group A (n = 6), AN69 without captopril; group B (n = 6), SPAN without captopril; group C (n = 6), AN69 with captopril; group D (n = 6), SPAN with captopril. A significant bradykinin release was observed only in groups A and C, reaching peak values already after 5 min. Animals in group C showed the highest bradykinin values. In four of six animals in group C anaphylactoid reactions with severe hypotension were noted. From this animal model we conclude that dialysis with the AN69 membrane is associated with bradykinin release. Pretreatment with ACE inhibitors results in further increasing bradykinin levels, which lead to anaphylactoid reactions. In contrast, the new SPAN membrane was well tolerated without detectable changes in bradykinin concentrations.