Effects of docosahexaenoic acid on in vitro amyloid beta peptide 25-35 fibrillation

Amyloid beta peptide(25-35) (A beta(25-35)) encompasses one of the neurotoxic domains of full length A(1-40/42) the major proteinaceous component of amyloid deposits in Alzheimer's disease (AD). We investigated the effect of docosahexaenoic acid (DHA, 22:6, n-3), an essential brain polyunsaturated fatty acid, on the in vitro fibrillation of A beta(25-35) and found that it significantly reduced the degree of fibrillation, as shown by a decrease in the intensity of both the thioflavin T and green fluorescence in confocal microscopy. Transmission electron microscopy revealed that DHA-incubated samples were virtually devoid of structured fibrils but had an amorphous-like consistency, whereas the controls contained structured fibers of various widths and lengths. The in vitro fibrillation Of A beta(25-35) appeared to be pH-dependent, with the strongest effect seen at pH 5.0. DHA inhibited fibrillation at all pHs, with the strongest effect at pH 7.4. It also significantly decreased the levels of A beta(25-35) oligomers. Nonreductive gradient gel electrophoresis revealed that the molecular size of the oligomers of A beta(25-35) was 10 kDa (equivalent to decamers of A beta(25-35) and that DHA dose-dependently reduced these decamers. These results suggest that DHA decreases the in vitro fibrillation of A beta(25-35) by inhibiting the oligomeric amyloid species and, therefore, A beta(25-35) related neurotoxicity or behavioral impairment could be restrained by DHA. (c) 2009 Elsevier B.V. All rights reserved.