Rat brain and liver mitochondria develop oxidative stress and lose enzymatic activities on aging.

The mitochondrial mass of rat brain and liver remained unchanged on aging in young adults, old adults, and senescent animals (28, 60, and 92 wk of age); the values were 15-17 and 29-31 mg protein/g for brain and liver, respectively. The whole aging process was associated with an increased content of the oxidation products, thiobarbituric acid-reactive substances and protein carbonyls, by 61-69% in brain and 36-45% in liver, respectively. The activities of critical enzymes for mitochondrial function, mitochondrial nitric oxide synthase, Mn-superoxide dismutase, complex I, and complex IV, decreased progressively during aging with activity losses of 73, 37, 29, and 28%, respectively, in the brain and 47, 46, 30, and 24% in the liver of senescent rats compared with young adults. Brain mitochondria isolated from aged rats showed increased mitochondrial fragility, as assayed by mitochondrial marker enzyme activities in the postmitochondrial supernatant, and increased volume and water permeability, as assayed by light scattering. Liver mitochondria isolated from young and old rats did not show differences in fragility and water permeability. A subpopulation of brain mitochondria with increased size and fragility was differentiated in aging rats, whereas liver showed a homogeneous mitochondrial population.