Hypochlorite-induced oxidation promotes aggregation and reduces toxicity of amyloid beta 1-42

Exacerbated hypochlorite (OCl(−)) production is linked to neurodegenerative processes, but there is growing evidence that lower levels of hypochlorite activity are important to protein homeostasis. In this study we characterise the effects of hypochlorite on the aggregation and toxicity of amyloid beta peptide 1–42 (Aβ(1-42)), a major component of amyloid plaques that form in the brain in Alzheimer's disease. Our results demonstrate that treatment with hypochlorite promotes the formation of Aβ(1-42) assemblies ≥100 kDa that have reduced surface exposed hydrophobicity compared to the untreated peptide. This effect is the result of the oxidation of Aβ(1-42) at a single site as determined by mass spectrometry analysis. Although treatment with hypochlorite promotes the aggregation of Aβ(1-42), the solubility of the peptide is enhanced and amyloid fibril formation is inhibited as assessed by filter trap assay, thioflavin T assay and transmission electron microscopy. The results of in vitro assays using SH-SY5Y neuroblastoma cells show that pre-treatment of Aβ(1-42) with a sub-stoichiometric amount of hypochlorite substantially reduces its toxicity. The results of flow cytometry analysis and internalisation assays indicate that hypochlorite-induced modification of Aβ(1-42) reduces its toxicity via at least two-distinct mechanism, reducing the total binding of Aβ(1-42) to the surface of cells and facilitating the cell surface clearance of Aβ(1-42) to lysosomes. Our data is consistent with a model in which tightly regulated production of hypochlorite in the brain is protective against Aβ-induced toxicity.