Arachidonic acid in Alzheimer's disease

Abstract

Alzheimer's disease is a very complex disease in which neuroinflammation and synaptic dysfunctions play a critical role in association with the two well-known molecular agents of the disease, the Aβ 1-42 peptide oligomers and the hyperphosphorylated tau protein. Arachidonic acid, the main member of the ω-6 series, is quantitatively the second polyunsaturated fatty acid in brain and is mainly esterified in membrane phospholipids. It is specifically released by the cytosolic phospholipase A 2 whose inhibition or gene suppression counteract the deleterious effects of Aβ 1-42 peptide oligomers on cognitive abilities. Arachidonic acid can be reincorporated under the action of the acyl-CoA synthetase 4 and lysophospholipid acyltransferases which remain to be characterized. Free arachidonic acid can be involved in Alzheimer's disease through several mechanisms. First it is converted by cyclooxygenases-1/2 and the specific prostaglandin synthases into PGE2 and PGD2 which contributes to the occurrence and progression of neuroinflammation. Neuroinflammation has positive as well as negative effects, by favoring Aβ 1-42 peptide clearance on one hand and by increasing the production of neurotoxic compounds on the other hand. Second, free arachidonic acid is also involved in synaptic functions as a retrograde messenger and as a regulator of neuromediator exocytosis. Third, some studies indicated that free arachidonic acid and its derivatives activate kinases involved in tau hyperphosphorylation. In addition, the dietary intakes of arachidonic acid in western food increased in the last period. Taken together, these various reports support the hypothesis that arachidonic acid is interesting target in nutrition-based preventive strategies against this disease.