A growing body of evidence suggests that soluble oligomeric forms of the amyloid beta peptide known as amyloid-derived diffusible ligands (ADDLs) are the toxic species responsible for neurodegeneration associated with Alzheimer's disease. Accurate biophysical characterization of ADDL preparations is hampered by the peptide's strong tendency to self-associate and the effect of factors such as ionic strength, temperature, and pH on its behavior. In addition, amyloid peptides are known to interact with common laboratory excipients, specifically detergents, further complicating the results from standard analytical methods such as denaturing polyacrylamide gel electrophoresis. We have studied the solution behavior of various amyloid peptide preparations using analytical ultracentrifugation and size exclusion chromatography coupled with multiangle laser light scattering. Our results indicate that ADDL preparations exist in solution primarily as a binary mixture of a monomeric peptide and high-molecular mass oligomers. We relate our findings to previously described characterizations utilizing atomic force microscopy and electrophoretic methods and demonstrate that low-molecular mass oligomers identified by gel electrophoresis likely represent artifacts induced by the peptide's interaction with detergent, while atomic force microscopy results are likely skewed by differential binding of monomeric and oligomeric peptide species. Finally, we confirm that only the high-molecular mass oligomeric components of an ADDL preparation are capable of binding to subpopulations of primary hippocampal neurons in vitro.

The amyloid-beta (Abeta) cascade hypothesis of Alzheimer's disease (AD) has dominated research and subsequent therapeutic drug development for over two decades. Central to this hypothesis is the observation that Abeta is elevated in AD patients and that the disease is ultimately characterized by the central deposition of insoluble senile plaques. More recent evidence, however, suggests that the presence or absence of plaque is insufficient to fully account for the deleterious role of elevated Abeta in AD. Such studies support the basis for an alternate interpretation of the Abeta cascade hypothesis. Namely, that soluble oligomers of Abeta (i.e., ADDLs) accumulate and cause functional deficits prior to overt neuronal cell death or plaque deposition. Accordingly, the following review focuses on research describing the preparation and functional activity of ADDLs in vitro and in vivo. These studies provide the basis for an alternate, ADDL-based, view of the Abeta cascade hypothesis and accounts for the disconnect between plaque burden and cognitive deficits. Possible therapeutic approaches aimed at lowering ADDLs in AD patients are also considered.

Extracellular deposits of aggregated amyloid-␤ (A␤)peptides are a hallmark of Alzheimer disease; thus, inhibition of A␤ production and/or aggregation is an appealing strategy to thwart the onset and progression of this disease. The release of A␤ requires processing of the amyloid precursor protein (APP) by both ␤-and ␥-secretase. Using an assay that incorporates full-length recombinant APP as a substrate for ␤-secretase (BACE), we have identified a series of compounds that inhibit APP processing, but do not affect the cleavage of peptide substrates by BACE1. These molecules also inhibit the processing of APP and A␤ by BACE2 and selectively inhibit the production of A␤ 42 species by ␥-secretase in assays using CTF99. The compounds bind directly to APP, likely within the A␤ domain, and therefore, unlike previously described inhibitors of the secretase enzymes, their mechanism of action is mediated through APP. These studies demonstrate that APP binding agents can affect its processing through multiple pathways, providing proof of concept for novel strategies aimed at selectively modulating A␤ production. Alzheimer disease (AD)1 is the leading cause of senile dementia. AD currently affects 4.5 million people in the United States and is anticipated to increase to more than 13 million by the year 2050 (1, 2). Histopathologically, AD is characterized by the prevalence of senile plaques, as well as neocortical atrophy, neuronal and synaptic loss, and the formation of neuritic tangles of the microtubule-associated protein tau (3). Senile plaques consist predominantly of fibrils of amyloid ␤ (A␤), a 39 -43-amino acid peptide generated by proteolysis of the amyloid precursor protein (APP) (4). Production of A␤ has been linked genetically to AD. Recent studies (5-7) have shown that A␤ multimerizes into neurotoxic oligomers that target the synapse, leading to disruption of long term potentiaton, cell death, and memory loss. These oligomers then coalesce into fibrils, ultimately forming the plaques originally used to characterize the disease (5-7).To produce A␤, APP, a type I single-transmembrane glycoprotein, is sequentially cleaved by two aspartyl proteases, ␤-and ␥-secretase. The initial cleavage is mediated by ␤-secretase (BACE1) on the luminal side of the endosomal membrane or at the cell surface (8). BACE1 cleavage generates a secreted Nterminal product (sAPP␤) and a transmembrane N-terminal product (CTF99). Processing of CTF99 within the transmembrane domain by the ␥-secretase enzyme complex generates the C-terminal end of A␤ and results in its release (9). The ␥-secretase enzyme is known to cleave CTF99 at any of several discrete positions, generating A␤ peptides that range in length from 38 to 42 amino acids. Although A␤ 40 is the predominant species produced both in vitro and in vivo, A␤ 42 is the more aggregenic species and the major component of amyloid plaques. The release of A␤ 42 and subsequent aggregation into insoluble fibrils are believed to lead to the formation of the dense plaques characteristic of AD (1...

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Poloxamers are water-soluble polymers that are widely used in cell culture bioprocessing to protect cells against shearing forces. Use of poor-quality poloxamers may lead to a drastic reduction in cell growth, viabilities and productivities in cell culture-based manufacturing. In order to evaluate poloxamer quality and promote more consistent performance, a rapid cell membrane adhesion to hydrocarbon assay was developed based on the adhesive properties of cell membranes to selective hydrocarbons. The assay can identify a poor-performing poloxamer characterized by significant drop in viable cell density and percent viability. The assay was verified across multiple good and bad poloxamer lots, and the results were in agreement with established cell growth and high-performance liquid chromatography assays.