N-acetylcysteine reverses existing cognitive impairment and increased oxidative stress in glutamate transporter type 3 deficient mice.

Oxidative stress contributes significantly to brain aging. Animals lacking glutamate transporter type 3 (EAAT3) have a decreased level of glutathione, the major intracellular anti-oxidant, in neurons, and present with early onset of brain aging including brain atrophy and cognitive impairment at 11 months of age. Here, 12-month-old male EAAT3 knockout mice received intraperitoneal injection of N-acetylcysteine (NAC) at 150 mg/kg once every day for 4 weeks. NAC is a membrane permeable cysteine precursor that can work as a substrate for glutathione synthesis. EAAT3 knockout mice that received saline injection or did not receive any injection were also included in the study. EAAT3 knockout mice had significantly less freezing behavior than age- and gender-matched wild-type mice in context- and tone-related fear conditioning tests. The knockout mice also had decreased levels of glutathione and increased levels of 4-hydroxy-2-nonenal and proteins containing nitrotyrosine, indicators of oxidative stress, in the cerebral cortex and hippocampus. NAC but not saline injection attenuated these behavioral and biochemical changes in the EAAT3 knockout mice. These results suggest that improvement of anti-oxidative capacity in neurons reverses the existing cognitive impairment in aging brains, implying a potential role of glutathione replacement in cognitive improvement of aging population.