Quantification of beta 2-microglobulin and albumin in plasma and peritoneal dialysis fluid by a noncompetitive immunoenzymometric assay.

An enzyme-linked immunosorbent assay (ELISA) was developed for measuring beta 2-microglobulin (beta 2m) and albumin in continuous ambulatory peritoneal dialysis (CAPD) fluid. Plasma concentrations of beta 2m were twofold greater in hemodialysis patients (41.3 +/- 13.3 mg/L) than in CAPD patients (23.6 +/- 5.5 mg/L) matched for duration of treatment. Measurement of beta 2m in CAPD fluid showed a substantial loss of this protein, approximately 31% of total body beta 2m, compared with a 5% loss of a protein of middle molecular mass (albumin). Because of the molecular sieving effects of the peritoneal membrane, peritoneal clearance of beta 2m was sixfold greater than that of albumin. Whether beta 2m losses prevent or delay the incidence of dialysis-induced amyloidosis in these patients remains to be established.

Lipoprotein particles in homozygous familial hypercholesterolemic patients treated with portacaval shunt and LDL apheresis.

Lipoprotein particles containing apolipoproteins (Apo) were studied by enzyme-linked-immunosorbent assay in two homozygous familial hypercholesterolemic patients (1 male and 1 female) with portacaval shunts, and in controls. Total Apo B, total cholesterol and LDL cholesterol were increased in both patients while complex Apo B containing particles, Lp CIII: B, were not increased in these FH patients. The dextran-sulfate cellulose columns (Liposorber LA-40) had an excellent adsorption selectivity and adsorption capacity for lipoprotein particles containing Apo B and a minimum adsorption capacity in Apo AI and Apo AII-containing particles. This apheresis technique selectively depleted plasma of atherogenic Apo B-containing particles with a minimal loss of antiatherogenic Apo AI-containing particles.

[Application of the immunoenzyme technic in double determination of antibodies for the study of hyperlipoproteinemia]. / Application de la méthode immunoenzymatique à double détermination d'anticorps à l'exploration des hyperlipoprotéinémies.

Antibodies directed against designed apolipoprotein, were absorbed on microtiter plates, the other apolipoprotein present on the retained particles was evaluated by using corresponding peroxidase labeled antibodies. This differential antibody immunosorbent assay was applied to evaluate lipoprotein particles concentration in familial type IIa, IIb, III, IV, and in the type IV secondary to chronic renal failure. Type IIa and IIb, were characterized by the increasing plasma concentration of lipoprotein particles containing both apo B and apo E (LpE-B). Although type IIa have high level of apo CIII, the plasma concentration of lipoprotein containing both apo B and apo CIII was within the normal range. The high concentration of apo E in type III hyperlipoproteinemia, revealed the accumulation of LpB-CIII-E but mainly lipoproteins containing both apo B and apo E (LpE-B). The latter represents 0.94 +/- 0.51 g/l when compared to normolipidemic subjects: 0.29 +/- 0.06 g/l. The decrease concentration of apo AI affects essentially lipoprotein containing apo AI without apo AII (LpAI) in primary type IV hyperlipoproteinemic patients, while in chronic renal failure, both populations of apo AI (with and without apo AII) were affected. The differential antibody immunosorbent assay may be used in the future as a new approach to classify lipid transport disorders.

Antipeptide antibody against the human low-density-lipoprotein receptor. Characterization and cross-reactivity with bovine lymphocytes.

A dodecapeptide corresponding to the external N-terminal sequence of the human low-density-lipoprotein (LDL) receptor was synthesized. Antibodies raised in rabbits against the peptide were purified and were shown to react specifically with the peptide and with human LDL receptor of fibroblasts, HeLa cells and lymphocytes using binding studies and immunoblotting. By indirect immunogold analysis, antibodies bound to the LDL receptor of human lymphocytes could be revealed as clusters. Anti-receptor peptide immunoglobulins specifically bound to the human HeLa cell's LDL receptor with a lower affinity than LDL (Kd x 3). The anti-receptor peptide immunoglobulins and 125I-labelled-LDL competed with each other for the LDL-receptor sites. Antibodies failed to react with lymphocytes of subjects with the homozygous form of familial hypercholesterolaemia. Cross-reactivity with the dodecapeptide of the bovine LDL receptor was limited, but this cross-reactivity was confirmed by the binding of anti-receptor peptide immunoglobulins to the LDL receptor from bovine lymphocytes.

Apolipoprotein B immunochemical heterogeneity in dialysed patients with chronic renal failure and patients with coronary artery stenosis.

Serum cholesterol, triglyceride, apolipoprotein B (apo B) and the cholesterol and phospholipid content of apo-B-containing particles was determined in 41 male patients on dialysis for chronic renal failure, in 41 male patients with coronary artery disease selected on the basis of a total cholesterol level below 6.72 mmol/l and in 41 male control subjects of similar age. Apo B was assessed as total B protein determined using polyclonal antibodies and also by measuring the expression of epitopes recognized by three different monoclonal antibodies (BL3, BL5 and BL7). Triglyceride was increased (p less than 0.01) and cholesterol was decreased (p less than 0.01) in the dialysed patients with chronic renal failure. Total apo B was similar in the three tested groups while the expression of the BL7 epitope was increased in the group of dialysed patients with chronic renal failure (p less than 0.001). The expression of BL3 and BL5 epitopes was increased in patients with coronary artery disease (BL3: p less than 0.05; BL5: p less than 0.02) but not in dialysed patients with chronic renal failure. These results suggest an abnormal composition and an immunological heterogeneity of apo-B-containing lipoprotein particles in patients with coronary artery stenosis and in dialysed patients with chronic renal failure.

Enzyme-linked immunosorbent assay for human proapolipoprotein A-I using specific antibodies against synthetic peptide.

Apolipoprotein A-I (apoA-I), the major protein component of human high density lipoprotein, appears intracellularly as an intermediate precursor (proapoA-I) with a hexapeptide extension (Arg-His-Phe-Trp-Gln-Gln) at its amino terminus. To investigate the regulation of processes that regulate plasma apoA-I levels, a sensitive and simple assay for proapoA-I is required. We describe a specific enzyme-linked immunosorbent assay (ELISA) for quantification of proapoA-I using monospecific rabbit antibodies raised against the peptide: Arg-His-Phe-Trp-Gln-Gln-Asp-Glu-Pro. The monospecificity of antibodies to propeptide has been checked and no cross-reaction with mature apoA-I has been found although three first mature apoA-I amino acids (Asp-Glu-Pro) were included in the immunizing peptide. The assay is a non-competitive sandwich ELISA in which polystyrene microtiter plates were used with antibodies to propeptide adsorbed on the wells. After incubation with plasma samples, the bound proapoA-I was revealed by labeled rabbit polyclonal antibodies directed against mature apoA-I. The working range was 10 to 100 ng/ml, recovery of proapoA-I added to plasma was 94.6 to 106.5%, and the intra- and interassay coefficients of variation were 3.8% and 7.9%, respectively. A delipidation step using diisopropylether-n-butanol was necessary to expose antigen sites of proapoA-I in native lipoproteins. Mean level of proapoA-I in normal subjects was 87 +/- 15 micrograms/ml. It represented 7.1% of total apoA-I while in Tangier serum it represented 29%.