In vitro and in vivo oxidative stress associated with Alzheimer's amyloid β-peptide (1-42)

The amyloid β-peptide (Aβ)-associated free radical oxidative stress model for neuronal death in Alzheimer s disease (AD) brain predicts that neuronal protein oxidation is a consequence of Aβ-associated free radicals [8]. In this study we have used both in vitro and in vivo models of b-amyloid (Ab) toxicity to detect free radical induced oxidative stress by the measure of protein carbonyl levels. These model systems employed cultured hippocampal neurons exposed to exogenous synthetic Aβ(1-42) and transgenic Caenorhabditis elegans (C. elegans) animals expressing Aβ(1-42). We also investigated the importance of the Aβ(1-42) Met ³⁵ residue for free radical formation in peptide solution and for peptide-induced protein oxidation and neuronal toxicity in these model systems. Aβ(1-42) in solution yielded an EPR spectrum, suggesting that free radicals are associated with this peptide; however, neither the reverse [Aβ(42-1)] nor methionine-substituted peptide [Aβ(1-42)Met³⁵ Nle] gave significant EPR spectra, suggesting the importance of the methionine residue in free radical formation. Aβ(1-42) addition to cultured hippocampal neurons led to both neurotoxicity (30.1% cell death, p < 0.001) and increased protein oxidation (158% of controls, p < 0.001), and both of those effects were not observed with reverse or Met³⁵ Nle substituted peptides. C. elegans transgenic animals expressing human Aβ(1-42) also had significantly increased in vivo protein carbonyls (176% of control animals, p < 0.001), consistent with our model. In contrast, transgenic animals with a Met³⁵ cys substitution in Aβ(1-42) showed no increased protein carbonyls in vivo, in support of the hypothesis that methionine is important in Aβ-associated free radical oxidative stress. These results are discussed with reference to the Aβ-associated free radical oxidative stress model of neurotoxicity in AD brain. (C) 1999 Elsevier Science Inc. All rights reserved.