The DRG Amyloid _ 1-40 (human) ELISA (Abeta-40 ELISA) is an enzyme immunoassay for the quantitative in vitro measurement of human Amyloid _ peptide 1-40 in serum, plasma and CSF.
The pathological hallmarks ofAlzheimerÕs disease (AD) are amyloid plaques, neurofibrillary tangles, synapticdegeneration and neuronal loss (1). Amyloid plaques are mainly composed ofamyloid-beta (A_) 40 and 42peptides derived from the proteolytic cleavage of amyloid precursor protein(APP) by _-site APP cleavageenzyme 1 (BACE1) (2,3) and the _-secretase (4). The endosomeand the endocytic pathway have been proposed as possible sites for the _ and _cleavage sites of APP (5), and the resulting A_peptides are secreted by both neuronal and non-neuronal cells (6). Recently,soluble forms of A_ have been implicated in neurotoxicity(7), and may correlate better with cognition than amyloid plaque burden(8). As A_ is considered toplay an early and pivotal role in AD pathogenesis, it may be a useful tool indiagnosing AD in the preclinical/early stages, as well as for monitoring potential A_ modifying therapies (9). While human CSF A_ levels have mostlyshown reduction with disease progression (10), much of the data on human plasmaA_ remain unclear. Studies have shown that subjects who exhibit overproductionof A_ such as individuals with familial forms of AD and DownÕs syndrome havehigher plasma A_ levels compared to controls (11). In addition to variabilityfound with age and disease severity (12), A_ plasma levels are furthermodulated by production in large peripheral organs such as skeletal muscle,liver, kidney, skin, and lung (13,14), movement from brain interstitial fluidinto blood stream (15), and peripheral uptake and clearance of A_ in theliver by presence of low densitylipoprotein receptor-related protein-1 (16) andreceptors for advanced glycation end products (RAGE) (17). This mayexplain why much of the plasma A_ data in cross-sectional studies do not showsignificant differences between sporadic AD and controls. Longitudinal studiesseem more promising, showing initially elevated A_42 levels in those thateventually develop AD in the future (18). Furthermore, subjects who manifestsporadic AD within the time frame of the study start with higher plasma A_42levels, and the A_42/A_40 ratios also appear to be significantly different fromthose who remain asymptomatic (19).2
The DRG Abeta-40ELISA Kit is a solid phase enzyme-linked immunosorbent assay (ELISA) basedon the sandwich principle. The microtiter wells are coated with a monoclonal[mouse] antibody directed towards a unique antigenic site on the Abeta-40peptide. An aliquot of patient samplecontaining endogenous Abeta-40 peptide is incubated in the coated well withenzyme conjugate, which is a biotinylated anti-Abeta-40 antibody. Afterincubation the unbound conjugate is washed off. Finally, Enzyme Complex, whichis streptavidin conjugated with horseradish peroxidase is added, and after incubation,unbound enzyme complex is washed off.The amount of bound peroxidase is proportional to theconcentration of Abeta-40 peptide in the sample. Having added the substrate solution, the intensityof colour developed is proportional to the concentration of Abeta-40 in thepatient sample.