Stability of early-stage amyloid-β(1-42) aggregation species

Accumulation of aggregated amyloid-beta protein (A beta) is an important feature of Alzheimer's disease. There is significant interest in understanding the initial steps of A beta aggregation due to the recent focus on soluble A beta oligomers. In vitro studies of A beta aggregation have been aided by the use of conformation-specific antibodies which recognize shape rather than sequence. One of these, OC antiserum, recognizes certain elements of fibrillar A beta across a broad range of sizes. We have observed the presence of these fibrillar elements at very early stages of A beta incubation. Using a dot blot assay, OC-reactivity was found in size exclusion chromatography (SEC)-purified A beta(1-42) monomer fractions immediately after isolation (early-stage). The OC-reactivity was not initially observed in the same fractions for A beta(1-40) or the aggregation-restricted A beta(1-42) L34P but was detected within 1-2 weeks of incubation. Stability studies demonstrated that early-stage OC-positive A beta(1-42) aggregates were resistant to 4 M urea or guanidine hydrochloride but sensitive to 1% sodium dodecyl sulfate (SDS). Interestingly, the sensitivity to SDS diminished over time upon incubation of the SEC-purified A beta(1-42) solution at 4 degrees C. Within 6-8 days the OC-positive A beta 42 aggregates were resistant to SDS denaturation. The progression to, and development of, SOS resistance for A beta(1-42) occurred prior to thioflavin T fluorescence. In contrast, A beta(1-40) aggregates formed after 6 days of incubation were sensitive to both urea and SDS. These findings reveal information on some of the earliest events in A beta aggregation and suggest that it may be possible to target early-stage aggregates before they develop significant stability. (C) 2012 Elsevier B.V. All rights reserved.