Inhibitors of Catalase-Amyloid Interactions Protect Cells from β-Amyloid-Induced Oxidative Stress and Toxicity

Lila K Habib,Michelle T.C Lee,Jerry Yang

doi:10.1074/jbc.m110.132860

Lila K Habib, Michelle T.C Lee + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m110.132860

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Abstract

Compelling evidence shows a strong correlation between accumulation of neurotoxic β-amyloid (Aβ) peptides and oxidative stress in the brains of patients afflicted with Alzheimer disease (AD). One hypothesis for this correlation involves the direct and harmful interaction of aggregated Aβ peptides with enzymes responsible for maintaining normal, cellular levels of reactive oxygen species (ROS). Identification of specific, destructive interactions of Aβ peptides with cellular anti-oxidant enzymes would represent an important step toward understanding the pathogenicity of Aβ peptides in AD. This report demonstrates that exposure of human neuroblastoma cells to cytotoxic preparations of aggregated Aβ peptides results in significant intracellular co-localization of Aβ with catalase, an anti-oxidant enzyme responsible for catalyzing the degradation of the ROS intermediate hydrogen peroxide (H(2)O(2)). These catalase-Aβ interactions deactivate catalase, resulting in increased cellular levels of H(2)O(2). Furthermore, small molecule inhibitors of catalase-amyloid interactions protect the hydrogen peroxide-degrading activity of catalase in Aβ-rich environments, leading to reduction of the co-localization of catalase and Aβ in cells, inhibition of Aβ-induced increases in cellular levels of H(2)O(2), and reduction of the toxicity of Aβ peptides. These studies, thus, provide evidence for the important role of intracellular catalase-amyloid interactions in Aβ-induced oxidative stress and propose a novel molecular strategy to inhibit such harmful interactions in AD.

Highlights

BTA-EGx Molecules Reduce the Toxicity of A␤ Peptides— We hypothesized that small molecules (e.g. BTA-EGx, Fig. 1A) with the capability of forming protein-resistant surface coatings on aggregated A␤ peptides [55] could protect cells from A␤ toxicity
We mimicked the heterogeneous population of aggregated A␤ species in Alzheimer disease (AD) brains (44 – 46) by using a preparation of A␤ peptides that contained ϳ15% small oligomers (MW ϳ15 kDa corresponding to trimers), ϳ25% medium-sized oligomers (MW 20 – 65 kDa corresponding to 5–15 mers), and ϳ60% soluble protofibrils (MW Ͼ 150 kDa corresponding to Ͼ 30 mers)
Because we used a mixture of aggregated A␤ species in these experiments, the results shown in Fig. 1C suggest that the BTA-EGx molecules could simultaneously protect cells from several potentially toxic forms of aggregated A␤ peptides that are present in this mixture [47,48,49,50,51,52,53]

Summary

Introduction

Additional control experiments showed that 40 ␮M solutions of the BTA-EGx molecules by themselves (i.e. in the absence of A␤) did not affect cellular H2O2 levels compared with cells that were not exposed to these small molecules (Fig. 2A). BTA-EGx Molecules Readily Internalize in Cells and Reduce the Intracellular Co-localization of A␤ and Catalase—To test the hypothesis that intracellular protein-amyloid interactions contribute to A␤-induced increases in H2O2 levels and to A␤ toxicity in live cells, we exposed SH-SY5Y cells to a solution containing N-terminal, fluorescently labeled 〈␤ peptides.

Results

Conclusion