Synergistic effects of long-term antioxidant diet and behavioral enrichment on β-amyloid load and non-amyloidogenic processing in aged canines

A long-term intervention (2.69 years) with an antioxidant diet, behavioral enrichment, or the combined treatment preserved and improved cognitive function in aged canines. Although each intervention alone provided cognitive benefits, the combination treatment was additive.Weevaluate the hypothesis that antioxidants, enrichment, or the combination intervention reduces age-related β-amyloid (Aβ) neuropathology, as one mechanism mediating observed functional improvements. Measures assessed were Aβ neuropathology in plaques, biochemically extractable Aβ₄₀ and Aβ₄₂ species, soluble oligomeric forms of Aβ, and various proteins in the β-amyloid precursor protein (APP) processing pathway. The strongest and most consistent effects on Aβ pathology were observed in animals receiving the combined antioxidant and enrichment treatment. Specifically, Aβ plaque load was significantly decreased in several brain regions, soluble Aβ₄₂ was decreased selectively in the frontal cortex, and a trend for lower Aβ oligomer levels was found in the parietal cortex. Reductions in Aβ may be related to shifted APP processing toward the non-amyloidogenic pathway, because α-secretase enzymatic activity was increased in the absence of changes in β-secretase activity. Although enrichment alone had no significant effects on Aβ, reduced Aβ load and plaque maturation occurred in animals receiving antioxidants as a component of treatment. Aβ measures did not correlate with cognitive performance on any of the six tasks assessed, suggesting that modulation of Aβ alone may be a relatively minor mechanism mediating cognitive benefits of the interventions. Overall, the data indicate that multidomain treatments may be a valuable intervention strategy to reduce neuropathology and improve cognitive function in humans.