Evidence of oxidative stress and in vivo neurotoxicity of β-amyloid in a transgenic mouse model of Alzheimer's disease: A chronic oxidative paradigm for testing antioxidant therapies in vivo

Increased expression of antioxidant enzymes and heat-shock proteins are key markers of oxidative stress. Such proteins are abnormally present within the neuropathological lesions of Alzheimer's disease (AD), suggesting that oxidative stress may play significant but yet undefined roles in this disorder. To gain further insight into the role of oxidative stress in AD, we studied the expression of CuZn superoxide dismutase (SOD) and hemoxygenase-1 (HO-1), two established markers of oxidative stress, in a transgenic mouse model of AD. Immunohistochemistry with anti-SOD and anti-HO-1 antibodies revealed a very pronounced increase of these proteins only in aged transgene- positive mice. Interestingly, the distribution of the oxidative burden was largely overlapping with dystrophic neuritic elements in the mice as highlighted with anti-ubiquitin antibodies. Because the most conspicuous alterations were identified around amyloid (Aβ) deposits, our results provide strong support for the hypothesis that Aβ is neurotoxic in vivo and that such toxicity is mediated by free radicals. To obtain additional experimental evidence for such an interpretation (ie, a cause-effect relationship between Aβ and oxidative neurotoxicity), PC12 cells were exposed to increasing concentrations of Aβ or to oxidative stress. In agreement with the in vivo findings, either treatment caused marked induction of SOD or HO-1 in a dose-dependent fashion. These results validate the transgenic approach for the study of oxidative stress in AD and for the evaluation of antioxidant therapies in vivo.