Noncovalent interaction between amyloid-β-peptide (1-40) and oleuropein studied by electrospray ionization mass spectrometry

Beta amyloid peptide (A beta) is the major proteinaceous component of senile plaques formed in Alzheimer's disease (AD) brain. The aggregation of A beta is associated with neurodegeneration, loss of cognitive ability, and premature death. It has been suggested that oxidative stress and generation of free radical species have implications in the fibrillation of A beta and its subsequent neurotoxicity. For this reason, it is proposed that antioxidants may offer a protective or therapeutic alternative against amyloidosis. This study is the first report of the formation of the noncovalent complex between A beta or its oxidized form and the natural derived antioxidant oleuropein (OE) by electrospray ionization mass spectrometry (ESI MS). ESI MS allowed the real time monitoring of the complex formation between A beta, OE, and variants thereof. Several experimental conditions, such as elevated orifice potential, low pH values, presence of organic modifier, and ligand concentration were examined, to assess the specificity and the stability of the formed noncovalent complexes.