Aging is characterized by a progressive deterioration in physiological and metabolic processes. It has been extensively reported that reactive oxygen species can play a major role in neural damage associated with aging and aging-related neurodegenerative diseases. Previous results from our laboratory have shown alterations in reactive oxygen species in brain cortex synaptosomes and nonsynaptic mitochondria from animals of 14, 17 and 20 months of age. With the purpose of analyzing the effect of aging on oxidative stress in nerve terminals, male
Swiss mice of 3 and 24 months old were used. Brain cortex synaptosomes were isolated by Ficoll gradient procedures. Reactive oxygen species superoxide anion and hydrogen peroxide (H2O2) were measured. Superoxide anion levels were assayed by flow cytometry after synaptosomes loading with the fluorescent mitochondrial probe Mitosox and H2O2 production was determined by a fluorometric method with scopoletin and HRP. Also, the activity of enzymatic complexes I-III of the mitochondrial respiratory chain was determined. Finally, acetylcholinesterase activity was assayed as an indicator of synaptic neuronal function. Results show that levels of superoxide anion were increased by 18% in 24 months old animals as compared with 3 months old mice. An increase of 33% in basal H2O2 production was observed in old animals as compared with young mice. When measurements were performed in the presence of malate and glutamate, H2O2 production rates were increased by 45% in synaptosomes from young mice, while in old animals the increase was only of 16%. Therefore, this result suggests that the observed increase in hydrogen peroxide production in old animals would not be a consequence of mitochondrial respiratory chain activity. As a matter of fact, complex I-III activity declined by 20% in synaptosomes from 24 months old animals. Furthermore, the activity of acetylcholinesterase was diminished by 29% in old mice. From these results we can conclude that the decline of enzymatic activities
would be probably connected with the accumulation of protein damage during aging. Oxidative damage induced by reactive oxygen species could contribute to decrease mitochondrial bioenergetic function and impair neurotransmission in brain cortex with age.