Proteomic identification of nitrated brain proteins in traumatic brain-injured rats treated postinjury with gamma-glutamylcysteine ethyl ester: Insights into the role of elevation of glutathione as a potential therapeutic strategy for traumatic brain injury

Traumatic brain injury (TBI) occurs suddenly and has damaging effects to the brain that are dependent on the severity of insult. Symptoms can be mild, moderate, or severe. Oxidative damage is associated with traumatic brain injury through reactive oxygen/nitrogen species production. One such species, peroxynitrite, is elevated in TBI brain tissue (Orihara et al. [2001] Forensic Sci. Int. 123:142-149; Deng et al. [2007] Exp. Neurol. 205:154-165). Peroxynitrite can react with carbon dioxide and decompose to produce NO₂ and carbonate radicals, which in turn can lead to 3-nitrotyrosine, an index of protein nitration. Gamma-glutamylcysteine ethyl ester (GCEE) is an ethyl ester moiety of gammaglutamylcysteine, an agent that up-regulates glutathione (GSH) production in brain (Drake et al. [2002] J. Neurosci. Res. 68:776-784). Many preclinical studies of TBI have employed pretreatment of animals with proposed beneficial agents prior to the injury itself. However, in the real world of TBI, treatment begins postinjury. Hence, insights into agents that improve outcome following injury are desperately needed. This study is one of the first to investigate a potential GSH-based therapy for TBI postinjury, Protein carbonyls, an index of protein oxidation, were significantly elevated in brain of animals subjected to TBI. However, if, after TBI, GCEE was administered i.p., protein carbonyl levels were significantly reduced. Similarly, 3-nitrotyrosine levels were elevated in brain following TBI but significantly decreased following TBI if GCEE was administered i.p. Redox proteomics analysis showed that several brain proteins were nitrated after TBI. However, if GCEE was given i.p. following TBI, many of these proteins were protected from nitration. The results are encouraging and are discussed with reference to potential therapeutic strategies for TBI involving elevated GSH.