Peroxynitrite-induced alterations in synaptosomal membrane proteins: Insight into oxidative stress in Alzheimer's disease

Peroxynitrite (ONOO-) is a highly reactive, oxidizing anion with a half-lif e of <1 s that is formed by reaction of superoxide radical anion with nitri c oxide. Several reports of ONOO--induced oxidation of lipids, proteins, DN A, sulfhydryls, and inactivation of key enzymes have appeared. ONOO- has al so been implicated as playing a role in the pathology of several neurodegen erative disorders, such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis, among others. Continuing our laboratory's interest in free radi cal oxidative stress in brain cells in AD, the present study was designed t o investigate the damage to brain neocortical synaptosomal membrane protein s and the oxidation-sensitive enzyme glutamine synthetase (GS) caused by ex posure to ONOO-. These synaptosomal proteins and GS have previously been sh own by us and others to have been oxidatively damaged in AD brain and also following treatment of synaptosomes with amyloid beta-peptide. The results of the current study showed that exposure to physiological levels of ONOO- induced significant protein conformational changes, demonstrated using elec tron paramagnetic resonance in conjunction with a protein-specific spin lab el, and caused oxidation of proteins, measured by the increase in protein c arbonyls. ONOO- also caused inactivation of GS and led to neuronal cell dea th examined in a hippocampal cell culture system. All these detrimental eff ects of ONOO- were successfully attenuated by the thiol-containing antioxid ant tripeptide glutathione. This research shows that ONOO- can oxidatively modify both membranous and cytosolic proteins, affecting both their physica l and chemical nature. These findings are discussed with reference to the p otential involvement of ONOO- in AD neurodegeneration.