Filtration of native and glycated beta2-microglobulin by charged and neutral dialysis membranes.

BACKGROUND: It has been postulated that protein glycation and formation of advanced glycation end products (AGE) are among toxic factors in chronic uremia, whether the renal disease is of diabetic or nondiabetic origin. In this setting, AGE-modified beta2-microglobulin (beta2m) may favor dialysis beta2m-related dialysis amyloidosis. Consequently, efficient removal of modified beta2m by highly permeable dialysis membranes is as important as removal of native beta2m to postpone the development of dialysis amyloidosis. METHODS: To define the role of dialysis membrane surface electronegativity on plasma protein transfer, an in vitro model was used to test the interactions of native and glycated beta2m with various highly permeable dialysis membranes. An experimental circuit with minidialyzers was used. The neutral high-flux polysulfone membrane (PS), the electronegative polymethylmetacrylate membrane (PMMA), the electronegative AN69 membrane and a modified AN69 membrane, the surface of which was neutralized with polyethyleneimine (AN69-PEI), were tested using both native beta2m and the more acidic glycated beta2m. Protein mass transfer and binding to the membrane were measured. RESULTS: Mass transfer of glycated beta2m was significantly decreased through all membranes tested when compared with native beta2m. This result was due to the increased molecular weight of beta2m, which became less permeable to porous membranes, whereas adsorption of both native and glycated beta2m to membranes, due to ionic interactions, decreased similarly with AN69 and AN69-PEI, but remained unchanged with PS and PMMA. Moreover, surface neutralization of AN69 membrane did not alter its core binding capacity, since beta2m absorption accounted for 98 and 97% and glycated beta2m for 83.7 and 81.4% of the protein removed with AN69 and AN69-PEI, respectively. CONCLUSION: Clearance of glycated beta2m through highly permeable neutral and negatively charged membranes was lower than that of native beta2m, reflecting a decreased sieving coefficient for the neoformed higher molecular weight and conformationally altered molecule. The binding capacity of the neutral PS was roughly half that of the charged membranes. Neutralizing surface electronegativity of the AN69 membrane with PEI did not alter its binding capacity. These results suggest that it would be useful for dialysis protocols to include comparative studies of both serum native and modified beta2m in order to prevent beta2m-amyloidosis.

Detection of subclinical abdominal hernia by peritoneal scintigraphy.

This study investigated the incidence of subclinical abdominal hernia in patients starting peritoneal dialysis (PD). From April 1995 to August 1999, every new patient without clinical evidence of abdominal leakage underwent peritoneal scintigraphy. A total of 59 patients were enrolled in the study. Imaging of the peritoneal cavity was performed by mixing 74 MBq (2 mCi) of 99 m technetium sulfur colloid with 2 L of 1.36% dextrose peritoneal dialysis solution. Sequential gamma camera static images were obtained at 0 minutes, 60 minutes, and after drainage. Ten abdominal hernias (2 diaphragmatic leaks, 8 inguinal hernias) were observed in ten patients (6 males, 4 females; mean age: 65.1 years). One patient with diaphragmatic leak recovered partial renal function and stopped continuous ambulatory peritoneal dialysis (CAPD); the other was switched to automated peritoneal dialysis (APD). Among the eight patients with inguinal hernia, six had no clinical manifestations within eight months of follow-up. Two patients became symptomatic at 15 months and 25 months respectively. They underwent surgical repair. In CAPD patients without obvious abdominal hernias, peritoneal scintigraphy at onset of dialysis discovered 17% positive cases. The technique of scintigraphy is safe, with a low radiation exposure. Surgical repair for maintenance on CAPD is not always necessary, and a change in the PD strategy may be useful.

Influence of in vivo hemoglobin carbamylation on HbA1c measurements by various methods.

Increased carbamylated hemoglobin formed in erythrocytes during uremia may interfere with HbA1c assays, but few studies compared directly both parameters. We measured carbamylated hemoglobin by HPLC in 45 non-diabetic uremic patients (16 with acute and two with chronic renal failure, 27 with transplant recipients) as 57.8 +/- 22.3 microg carbamylvaline/g Hb (mean +/- standard deviation) vs. 31.6 +/- 5.1 in 15 controls (+83%, p < 0.001). In these samples, HbA1c was evaluated by three ion-exchange HPLC methods, 1: Diamat (BioRad), 2: A1c2.2 (Tosoh) and 3: HA8140 (Menarini), and one immunoassay method (Tinaquant II Roche). Whichever the method, mean HbA1c values obtained increased in patients with high (> 60 microg carbamylvaline/g Hb) vs. low (< 45) carbamylated hemoglobin values (+0.08 to 0.25% of total Hb), but differences were not significant. Minor peaks on the chromatograms were however increased in parallel to carbamylated hemoglobin. HbA1c values over 6% were found in 4, 1, 2 and 0 samples, with HPLC 1, 2, 3 and immunoassay, respectively. Fructosamine values were not significantly altered. Our results show that Hb adducts, whether due to carbamylation or to other chemical reactions, interfere to a variable extent with different HbA1c assay methods, and confirm that HbA1c values should be interpreted with caution in uremic patients.

Kinetics of carbamylated haemoglobin in acute renal failure.

BACKGROUND: Carbamylation of proteins by isocyanic acid, the reactive form of cyanate derived from urea, is increased in uraemia and may contribute to uraemic toxicity. Kinetics of carbamylation that may reflect uraemic toxicity is not clearly defined in acute renal failure (ARF). METHODS: Twenty-eight patients with ARF and 13 with chronic renal failure (CRF) were included in the study in order to determine changes in carbamylated haemoglobin concentration (CarHb) in ARF. The usefulness of this parameter for differentiating ARF from CRF was also investigated. CarHb was measured by high-performance liquid chromatography after acid hydrolysis. RESULTS: Mean CarHb level (expressed as microg carbamyl valine per gram (CV/g) Hb) was significantly higher in ARF (54.3+/-5.2) than in normal subjects (31.6+/-1.3). On admission, CarHb level was correlated with duration of ARF prior to hospitalization in the intensive care unit (r(2)=0.723, P<0.001). CarHb was significantly higher at recovery in the subgroup of patients requiring haemodialysis than in the subgroup not requiring haemodialysis (82. 4+/-11.3 vs 46.7+/-5.2, P<0.01). Similarly dialysis patients lost more weight (8.6+/-1.4 vs 2.7+/-0.5 kg, P<0.005) and had higher averaged blood urea levels in the 20 days prior to recovery (17. 6+/-1.9 vs 11.3+/-1.8 mol/l, P<0.05). After recovery, CarHb level decreased at a rate of 0.219 microg CV/g Hb per day in patients with reversible renal insufficiency. CarHb concentration was higher in patients with CRF. A cut-off CarHb value of 100 microg CV/g Hb had a sensitivity of 94% and a positive predictive value of 94% for differentiating ARF from CRF. CONCLUSIONS: Kinetics of CarHb showed a near normal red blood cell life span in ARF. Changes in CarHb enabled, with a good sensitivity, the distinction to be made between patients who recovered from ARF and those with sustained renal impairment, whether due to prior CRF or resulting from parenchymal sequelae. Measurement of CarHb is valuable at clinical presentation of ARF in patients with an unknown medical history of renal disease.

Alpha-1-microglobulin: inhibitory effect on calcium oxalate crystallization in vitro and decreased urinary concentration in calcium oxalate stone formers.

In the past few years, alpha-1-microglobulin (alpha1m) has been copurified from human urine with bikunin, a potent inhibitor of calcium oxalate (CaOx) crystallization in vitro. In this study, we have purified alpha1m without bikunin contamination and investigated its possible role in CaOx crystallization by in vitro and in vivo studies. Alpha-1m was purified with an anti-alpha1m antibodies CNBr-activated sepharose column. Two molecular species of alpha1m of respectively 30 and 60 kDa were purified. For each protein, two blots of 30 and 60 kDa cross-reacted with anti-alpha1m antibodies, suggesting that these two forms were derived one from the other. Both protein species inhibited CaOx crystallization in a dose-dependent manner in two in vitro tests. In the first test, the presence of alpha1m of 30 kDa (8 microg/ml) in a medium containing 0. 76 mM CaCl(2) (with (45)Ca) and 0.76 mM Ox(NH(4))(2) inhibited CaOx crystallization by 38% as estimated by supernatant radioactivity after 1 h of agitation. In the second test, CaOx kinetics were examined for 3 to 10 min in a turbidimetric model at 620 nm. The presence of alpha1m of 30 kDa in a medium containing 4 mM CaCl(2) and 0.5 mM Na(2)Ox inhibited CaOx crystallization by 41.5%, as estimated by the slope modification of turbidimetric curve. Alpha-1m can be considered as another inhibitor of urinary CaOx crystal formation, as shown by the present in vitro studies. Using an ELISA assay, we found that urinary alpha1m concentration was significantly lower in 31 CaOx stone formers than in 18 healthy subjects (2.95 +/- 0.29 vs 5.34 +/- 1.08 mg/l respectively, P = 0.01). The decreased concentration of alpha1m in CaOx stone formers could be responsible in these patients, at least in part, for an increased risk of CaOx crystalluria.

Assessment of acetate free continuous veno-venous hemofiltration in acute renal failure.

Among the limitations of continuous renal replacement therapy (CRRT) in patients with severe acute renal failure (ARF) and cardiovascular instability is the use of acetate in the substitution fluid. Acetate is required to maintain acidity of the polyelectrolytic solution to avoid calcium carbonate precipitation in the presence of bicarbonate. In addition, in patients with cardiovascular instability, acetate metabolism is impaired and further compromises hemodynamics. A new CRRT technique is proposed in which bicarbonate is used as a buffer, but the acetate requirements are cancelled: acetate free veno-venous hemofiltration (AF-CVVH). This technique allows control of acid-base disturbances independent of urea removal. This preliminary report describes the feasibility of the technique based on separate infusion of water and electrolytes administered prefiltration, and isotonic sodium bicarbonate administered post filtration. The setting of the technique, adapted to the PRISMA device (Hospal, Lyon, France), was based on a model predicting the bicarbonate infusion rate for a target plasma bicarbonate level. The AF-CVVH was compared with conventional, continuous veno-venous hemofiltration (CVVH) in a crossover study that showed AF-CVVH allowed fastest control of acidosis, avoiding 70 to 80 mmol/d of acetate transfer to the patient. Urea removal was similar with both techniques. It was concluded that AF-CVVH, when compared with CVVH, has the main advantage of separately controlling urea retention and metabolic acidosis in patients with severe ARF and cardiovascular instability.

Long-term follow-up of acute renal failure caused by angiotensin converting enzyme inhibitors.

Angiotensin converting enzyme (ACE) inhibitors are useful in the treatment of hypertension and heart failure. However, acute renal failure (ARF) may occur in patients who are taking these drugs in situations associated with decreased glomerular filtration pressure, such as dehydration caused by acute diarrhea or diuretic therapy. Sixty-four patients who were admitted to the intensive care unit for ARF associated with ACE inhibitor therapy were followed for more than 5 years. In this historical retrospective study, we documented that 45 patients were treated for hypertension (group I) and 19 were treated for heart failure (group II). Their mean age was 71.2+/-11.6 years. Patients with ARF presented with overt dehydration in 91% and 84% of the cases in groups I and II, respectively. Hypovolemia was caused by diuretics or gastrointestinal fluid loss. Bilateral artery-renal stenosis or stenosis in a solitary kidney was documented in 22% and 10% of patients in groups I and II, respectively. The probability of survival was 91% and 49% at 1 year and 64% and 18% at 5 years, for groups I and II, respectively. Acute renal failure required hemodialysis in seven patients, but none of them became dialysis dependent. In the subgroup of patients with preexisting chronic renal failure, all the patients except for one who belonged to group II died within 2 years. In both groups, after resolution of ARF, plasma creatinine concentration returned to baseline level and the course of renal function was not significantly worsened. In conclusion, ARF associated with ACE inhibitors is likely to occur in many patients without renal artery stenosis after unexpected dehydration, especially in older patients with congestive heart failure. In both groups of patients, in the absence of preexisting chronic uremia, recovery of renal function occurred without sequelae, even after an episode of acute tubular necrosis requiring dialysis.

Kinetics of 131I-beta2 microglobulin in hemodialysis patients: assessment using total body counting.

The kinetics of 131I-beta2-microglobulin (beta2-M) were studied using external total body gamma counting in a low noise chamber after administration of trace doses of radioactivity (4 microCi) in 14 uremic patients treated by either hemodialysis or hemofiltration. Data were collected over a 1 week period that included 3 dialysis sessions. The following artificial membranes were used: Cuprophan, polyacrylonitrile AN69, polysulfone, polymethylmethacrylate (PMMA), and polyamide. Radiolabeled beta2-M excretion by an extrarenal route was nearly nonexistent. The 131I-beta2-M half-life was between 2.4 and 8 days, shorter in patients with residual diuresis. A mean removal of 153+/-33 mg/L of beta2-M was obtained per dialysis session with a highly permeable membrane. A hemofiltration session (25 L exchange per session) was slightly more efficient in removing beta2-M than a 4 h hemodialysis session with the same AN69 highly permeable membrane. The amounts of 131I-beta2-M binding on the membranes, expressed as beta2-M equivalents, were 0, 16, 54, 58, and 59 mg/m2 for Cuprophan, polysulfone, polyacrylonitrile AN69, polyamide, and PMMA, respectively. In conclusion, the decrease of total body gamma counting directly reflected the beta2-M breakdown and removal in hemodialysis patients. Intact beta2-M was removed by convection with synthetic, highly permeable membranes. In addition, membrane adsorption accounted for 15% (polysulfone) to near 100% (PMMA) of the beta2-M removal per session. Adsorption was of the same magnitude regardless of the dialysis technique in use, indicating a membrane saturability process. None of the currently available dialysis procedures based on a 3 sessions per week schedule can balance beta2-M generation.