In vitro and in vivo protein oxidation induced by Alzheimer's disease amyloid beta-peptide (1-42).

Amyloid β-peptide (Aβ) is thought by many researchers to be central to the pathogenesis of Alzheimer’s disease (AD) (reviewed in Ref. 1). In addition, oxidative stress, manifested by protein oxidation and lipid peroxidation, is apparent in AD brain.2,3 Our laboratory developed a comprehensive hypothesis for neurotoxicity in AD brain that unites these two observations and provides a testable framework for much of the AD literature. We proposed an Aβ-associated free radical oxidative stress model for neuronal death in AD brain2 (FIG. 1). In AD brain, the predominant forms of Aβ are Aβ(1-40) and Aβ(1-42). Consistent with our model and in ways completely inhibited by free radical scavengers (antioxidants), Aβ leads to lipid peroxidation4,5 and protein oxidation6–8 in various brain membrane systems; generates reactive oxygen species (ROS);7,8 inhibits hippocampal neuronal and cortical synaptosomal membrane ion-motive ATPases, including Na+/K+-ATPase and Ca2+ATPase; blocks glutamate uptake and inhibits the activity of glutamine synthetase (both of the latter Aβ-induced alterations have the effect of increasing excitotoxic glutamate levels); causes intracellular Ca2+ levels to increase dramatically;8 and leads to neurotoxicity in hippocampal neuronal or astrocytic cultures (reviewed in Ref. 2). A prediction of the Aβ-associated free radical oxidative stress model for neurotoxicity in AD brain is that Aβ(1-42), the predominant form of Aβ found in AD, will induce protein oxidation. A key marker of protein oxidation is protein carbonyl content.9 Previous studies showed increased antioxidant-inhibited protein oxidation in hippocampal neuronal cultures induced by Aβ(1-40)8 and Aβ(25-35).6,7 In the current study, we provide evidence for Aβ(1-42)–induced ROS generation in vitro and protein oxidation in vitro and in vivo. In agreement with our model (FIG. 1), 10 μM Aβ(1-42) added to cultured hippocampal neurons led to ROS formation that was inhibited by vitamin E (Fig. 2A) and induced significantly greater protein oxidation than in controls (Fig. 2B). In addition to the in vitro studies, in vivo studies were carried out. We reported earlier that AD brain regions rich in Aβ-containing senile plaques had significantly increased protein oxidation but Aβ-poor cerebellum did