Fig. 3

Schematic presentation of HNE modification of amino acids using Michael’s addition concept and Schiff’s base formation concept. HNE is 9-carbon-atom long, with a double bond between carbon atoms 2 and 3 (C2 and C3). These atoms interact with the head aldehyde group at carbon atom 1 (C1) and the hydroxyl group at carbon atom 4 (C4). Carbon atoms 5 through to 9 (C5, C9) are hydrophobic. Michael’s addition to HNE occurs at the double bond (C=C) and carbonyl group (C=O) [136]. Amino acids interacting with HNE at C=C and C=O, consist of His, Cys and Lys. In Schiff’s base formation, HNE-His modification, a product of Michael’s addition, can interact with Lys. As a result of Michael’s addition and Schiff’s base adduction, HNE-IDE and HNE-NEP adducts cause impaired Aβ clearance