Heme-Aβ compound 0: a common intermediate in ROS generation and peroxidase activity

Oxidative stress is a key factor in neurodegenerative diseases, particularly in Alzheimer's disease (AD) which is the leading cause of dementia. A hallmark of AD is the accumulation of amyloid β (Aβ) peptides, along with redox-active metal ions and heme cofactors, all of which significantly contribute to disease progression. When heme binds to Aβ, it can drive oxidative stress through two primary pathways: firstly, reduced high-spin ferrous heme-Aβ active sites may generate H₂O₂ through oxygen reduction, leading to the oxidation of biomolecules and lipid membranes; secondly, this H₂O₂ can react with the oxidised form of high-spin ferric heme-Aβ, initiating peroxidase-like activity that can catalyse the oxidation of neurotransmitters. These pathways converge at a crucial intermediate i.e. the heme-Aβ-peroxo complex, which serves as the final intermediate in the ROS cycle and the first in the peroxidase cycle. Although, we have previously characterized other intermediates in these pathways, compound 0 resulting from the reaction of a high-spin heme-Aβ species with peroxides has remained elusive due to its rapid hydrolysis in an aqueous environment. In this study, we report the oxidation of dopamine by peroxides catalyzed by ferric heme-Aβ species and successfully stabilised and characterized compound 0 of high-spin heme-Aβ in dimethylformamide, an organic aprotic solvent. This stabilization enables detection through stopped-flow, EPR and resonance Raman spectroscopy, thereby facilitating a deeper understanding of the oxidative stress caused by high-spin heme-Aβ.