Toxicity in Rat Primary Neurons through the Cellular Oxidative Stress Induced by the Turn Formation at Positions 22 and 23 of Aβ42

The 42-mer amyloid beta-protein (A beta 42) aggregates to form soluble oligomers that cause memory loss and synaptotoxicity in Alzheimer's disease (AD). Oxidative stress is closely related to the pathogenesis of AD. We previously identified the toxic conformer of A beta 42 with a turn at positions 22 and 23 ("toxic turn") by solid-state NMR and demonstrated that a monoclonal antibody (11A1) against the toxic turn in A beta 42 mainly detected the oligomer in the brains of AD patients. Our recent study suggested that oxidative stress is a key factor of the oligomerization and cognitive impairment induced by A beta overproduction in vivo. However, the involvement of the toxic conformer in A beta 42-induced oxidative damage remains unclear. To investigate this mechanism, we examined the levels of intracellular reactive oxygen species (ROS) and neurotoxicity in rat primary neurons using E22P-A beta 42, a mutant that induces a turn at positions 22 and 23, and E22V-A beta 42, a turn-preventing mutant. E22P-A beta 42, but not E22V-A beta 42, induced greater ROS production than Wt-A beta 42 in addition to potent neurotoxicity. Interestingly, the formation of the toxic conformer in both E22P-A beta 42 and Wt-A beta 42 probed by the 11A1 antibody preceded A beta 42-induced neurotoxicity. Trolox (a radical scavenger) and Congo red (an aggregation inhibitor) significantly prevented the neurotoxicity and intracellular ROS induced by E22P-A beta 42 and Wt-A beta 42, respectively. These results