Influence of gold nanoparticle surface chemistry and diameter upon Alzheimer's disease amyloid-ß protein aggregation.

BACKGROUND: Deposits of aggregated amyloid-ß protein (Aß) are a pathological hallmark of Alzheimer's disease (AD). Thus, one therapeutic strategy is to eliminate these deposits by halting Aß aggregation. While a variety of possible aggregation inhibitors have been explored, only nanoparticles (NPs) exhibit promise at low substoichiometric ratios. With tunable size, shape, and surface properties, NPs present an ideal platform for rationally designed Aß aggregation inhibitors. In this study, we characterized the inhibitory capabilities of gold nanospheres exhibiting different surface coatings and diameters. RESULTS: Both NP diameter and surface chemistry were found to modulate the extent of aggregation, while NP electric charge influenced aggregate morphology. Notably, 8 nm and 18 nm poly(acrylic acid)-coated NPs abrogated Aß aggregation at a substoichiometric ratio of 1:2,000,000. Theoretical calculations suggest that this low stoichiometry could arise from altered solution conditions near the NP surface. Specifically, local solution pH and charge density are congruent with conditions that influence aggregation. CONCLUSIONS: These findings demonstrate the potential of surface-coated gold nanospheres to serve as tunable therapeutic agents for the inhibition of Aß aggregation. Insights gained into the physiochemical properties of effective NP inhibitors will inform future rational design of effective NP-based therapeutics for AD.

Inhibition of amyloid-ß aggregation by coumarin analogs can be manipulated by functionalization of the aromatic center.

Aggregation of the amyloid-ß protein (Aß) plays a pathogenic role in the progression of Alzheimer's disease, and small molecules that attenuate Aß aggregation have been identified toward a therapeutic strategy that targets the disease's underlying cause. Compounds containing aromatic structures have been repeatedly reported as effective inhibitors of Aß aggregation, but the functional groups that influence inhibition by these aromatic centers have been less frequently explored. The current study identifies analogs of naturally occurring coumarin as novel inhibitors of Aß aggregation. Derivatization of the coumarin structure is shown to affect inhibitory capabilities and to influence the point at which an inhibitor intervenes within the nucleation dependent Aß aggregation pathway. In particular, functional groups found within amyloid binding dyes, such as benzothiazole and triazole, can improve inhibition efficacy. Furthermore, inhibitor intervention at early or late stages within the amyloid aggregation pathway is shown to correlate with the ability of these functional groups to recognize and bind amyloid species that appear either early or late within the aggregation pathway. These results demonstrate that functionalization of small aromatic molecules with recognition elements can be used in the rational design of Aß aggregation inhibitors to not only enhance inhibition but to also manipulate the inhibition mechanism.

Activation of brain endothelium by soluble aggregates of the amyloid-ß protein involves nuclear factor-κB.

Cerebrovascular accumulation of amyloid-ß protein (Aß) aggregates in Alzheimer's disease (AD) is proposed to contribute to disease progression and brain inflammation as a result of Aß-induced increases in endothelial monolayer permeability and stimulation of the endothelium for cellular adhesion and transmigration. These deficiencies facilitate the entry of serum proteins and monocyte-derived microglia into the brain. In the current study, a role for nuclear factor-κB (NF-κB) in the activation of cerebral microvascular endothelial cells by Aß is explored.Quantitative immunocytochemistry is employed to demonstrate that Aß(1-40) preparations containing isolated soluble aggregates elicit the most pronounced activation and nuclear translocation of NF-κB. This rapid and transient response is observed down to physiological Aß concentrations and parallels phenotypic changes in endothelial monolayers that are selectively elicited by soluble Aß(1-40) aggregates. While monomeric and fibrillar preparations of Aß(1-40) also activated NF-κB, this response was less pronounced, limited to a small cell population, and not coupled with phenotypic changes. Soluble Aß(1-40) aggregate stimulation of endothelial monolayers for adhesion and subsequent transmigration of monocytes as well as increases in permeability were abrogated by inhibition of NF-κB activation. Together, these results provide additional evidence indicating a role for soluble Aß aggregates in the activation of the cerebral microvascular endothelium and implicate the involvement of NF-κB signaling pathways in Aß stimulation of endothelial dysfunction associated with AD.

Comparative study of inhibition at multiple stages of amyloid-beta self-assembly provides mechanistic insight.

The "amyloid cascade hypothesis," linking self-assembly of the amyloid-beta protein (Abeta) to the pathogenesis of Alzheimer's disease, has led to the emergence of inhibition of Abeta self-assembly as a prime therapeutic strategy for this currently unpreventable and devastating disease. The complexity of Abeta self-assembly, which involves multiple reaction intermediates related by nonlinear and interconnected nucleation and growth mechanisms, provides multiple points for inhibitor intervention. Although a number of small-molecule inhibitors of Abeta self-assembly have been identified, little insight has been garnered concerning the point at which these inhibitors intervene within the Abeta assembly process. In the current study, a julolidine derivative is identified as an inhibitor of Abeta self-assembly. To gain insight into the mechanistic action of this inhibitor, the inhibition of fibril formation from monomeric protein is assessed quantitatively and compared with the inhibition of two distinct mechanisms of growth for soluble Abeta aggregation intermediates. This compound is observed to significantly inhibit soluble aggregate growth by lateral association while having little effect on soluble aggregate elongation via monomer addition. In addition, inhibition of soluble Abeta aggregate association exhibits an IC(50) with a somewhat lower stoichiometric ratio than the IC(50) determined for inhibition of fibril formation from monomeric Abeta. This quantitative comparison of inhibition within multiple Abeta self-assembly assays suggests that this compound binds the lateral surface of on-pathway intermediates exhibiting a range of sizes to prevent their association with other aggregates, which is required for further assembly into mature fibrils.