Multiple mechanisms of age-dependent accumulation of amyloid beta protein in rat brain: Prevention by dietary supplementation with N-acetylcysteine, α-lipoic acid and α-tocopherol.

The aged brain may be used as a tool to investigate altered metabolism of amyloid beta protein (Aß42) that may have implications in the pathogenesis of Alzheimer's disease (AD). In the present study, we have observed a striking increase in the amyloid precursor protein (APP) level in the brain cortex of aged rats (22-24 months) along with a mild but statistically significant increase in the level of APP mRNA. Moreover, the activity of ß secretase is elevated (nearly 55%) and that of neprilysin diminished (48%) in brain cortex of aged rats compared to that in young rats (4-6 months). All these changes lead to a markedly increased accumulation of Aß42 in brain cortical tissue of aged rats. Long-term dietary supplementation of rats with a combination of N-acetylcysteine, α-lipoic and α-tocopherol from 18 months onwards daily till the sacrifice of the animals by 22-24 months, attenuates the age-related alterations in amyloid beta metabolism. In separate experiments, a significant impairment of spatial learning and memory has been observed in aged rats, and the phenomenon is remarkably prevented by the dietary supplementation of the aged animals by the same combination of N-acetylcysteine, α-lipoic acid and α-tocopherol. The results call for further explorations of this combination in suitable animal models in ameliorating AD related brain deficits.

Aging and antioxidants modulate rat brain levels of homocysteine and dehydroepiandrosterone sulphate (DHEA-S): implications in the pathogenesis of Alzheimer's disease.

The study has shown that in aged (22-24 months) rat brains an elevation of homocysteine level (42%) and a decrease in dehydroepiandrosterone sulphate (DHEA-S) content (32%) occur compared to those in the brains of young rats (4-6 months). Such changes in the brain levels of homocysteine and DHEA-S in aged rats are prevented, when the diet daily of the rats is supplemented with a combination of antioxidants (N-acetyl cysteine 50 mg, alpha-lipoic acid 3 mg and alpha-tocopherol 1.5 mg - each per 100 g of body weight) starting from 18 months until these are sacrificed between 22 and 24 months. The brain content of reduced glutathione is also decreased in aged rats as compared to that in young ones and the phenomenon can again be prevented completely by the same regimen of antioxidant supplementation. The changes in the levels of homocysteine and DHEA-S in aged rat brain have been related to associated glutathione depletion and oxidative stress and the implications of the results highlighted in the pathogenesis of Alzheimer's disease.