Oxidative stress in models of Alzheimer's disease: I. Roles of peroxynitrite, amyloid beta-peptide, and 4-hydroxy-2-nonenal. II. Modulation by gamma-glutamylcysteine ethyl ester

The studies presented in this work were completed with the goal of understanding better the role of oxidative stress in neurodegenerative disorders, specifically Alzheimer's disease (AD). AD is characterized pathologically by senile plaques, neurofibrillary tangles, and synapse loss. Additionally, the AD brain is under significant oxidative stress, evidenced by various protein oxidation, lipid peroxidation, and DNA oxidation parameters. Senile plaques are rich in amyloid β-peptide (Aβ), which our laboratory has provided evidence for Aβ-associated oxidative stress. This dissertation examines the role of peroxynitrite, Aβ, and the lipid peroxidation product 4-hydroxynonenal in AD models and neurodegenerative processes. Further, modulation of these processes by γ-glutamylcysteine ethyl ester (GCEE) was determined.; The novel compound GCEE proved to be an effective antioxidant strategy against ONOO-induced damage in synaptosomal and brain mitochondrial suspensions. Upon i.p. injection of gerbils, GCEE increased whole brain and mitochondrial glutathione levels by providing the limiting amino acid of GSH biosynthesis and bypassing feedback inhibition of the enzyme γ-glutamylcysteine synthetase. The in vivo administration of the compound GCEE protected brain from ONOO- protein modification and mitochondrial damage.; An in vivo model of Aβ toxicity was used to determine the temporal relationship between Aβ fibril formation and protein carbonyl formation, an indicator of protein oxidation. Caenorhabditis elegans (C. elegans) were made to express human Aβ(1–42) through a body-wall muscle myosin promoter and through a temperature-inducible system of an Aβ minigene. We found that oxidative stress, evidenced by increased protein carbonyl formation, occurred prior to Aβ fibril deposition, suggesting that soluble Aβ aggregates are the toxic species of this peptide and not fibrillar Aβ.; Aβ has been shown to cause lipid peroxidation in vitro, causing formation of the HNE. This alkenal has been found to be increased in AD brain compared to control subjects. The AD brain is under extensive oxidative stress, evidenced by oxidation of several DNA bases and deficient DNA base repair mechanisms. Histones are DNA binding proteins that are lysine rich, which may make these proteins susceptible to HNE damage. We found that HNE binds histones, altering histone protein conformation and compromising the ability of histones to bind DNA. Additionally, acetylated histones, an indicator of transcriptional activity, are more susceptible to HNE damage. These results provide a potential mechanism by which increased DNA oxidation in AD brain could occur.