Docosahexaenoic Acid Protects from Amyloid and Dendritic Pathology in an Alzheimer's Disease Mouse Model

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Abstract
Genetic data argues that Alzheimer's disease (AD) can be initiated by aggregates of a 42 amino acid beta amyloid peptide (Aβ42). The Aβ aggregates, notably small oligomer species, cause a cascade of events including oxidative damage, inflammation, synaptic toxicity and accumulation of intraneuronal inclusions; notably neurofibrillary tangles. Cognitive deficits are likely to begin with a failure of synaptogenesis and synaptic plasticity with dendritic spine loss and dying back of dendritic arbor. This is followed by neuron loss in key areas involved in learning and memory. Significant prevention or delay of clinical onset may be achievable by modifying environmental risk factors that impact the underlying pathogenic pathways. Because low fish intake and low blood levels of the marine lipid, docosahexaenoic acid (DHA) have been associated with increased AD risk we have tested the impact of depleting or supplementing with dietary DHA on AD pathogenesis in transgenic mice bearing a mutant human gene known to cause AD in people. We reported that even with intervention late in life dietary DHA depletion dramatically enhanced oxidative damage and the loss of dendritic markers, while DHA supplementation markedly reduced Aβ42 accumulation and oxidative damage, corrected many synaptic deficits and improved cognitive function. Loss of brain DHA was exacerbated in mice expressing the mutant human AD transgene, this is consistent with evidence for increased oxidative attack on DHA oxidation in AD. Treatment with the curry spice extract curcumin, a polyphenolic antioxidant that inhibits AP aggregation, has been strongly protective in the same mouse model. Many Western diets are typically deficient in DHA and low in polyphenolic antioxidant intake. These and other data argue that increasing dietary intake of both DHA and polyphenolic antioxidants may be useful for AD prevention.