Is there correlation between Aβ-heme peroxidase activity and the peptide aggregation state? A literature review combined with hypothesis

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by aggregation of amyloid-β (Aβ) peptide, formation of neurofibrillary tangles, synaptic loss and neuronal cell death, and is manifested clinically by progressive cognitive dysfunction and memory loss. Disease pathogenesis is mainly linked to the formation of Aβ insoluble or soluble oligomeric assemblies. Binding of heme to Aβ has been suggested as the origin of the heme deficiency, peroxidase activity, as well as some oxidative stress-mediated AD pathologies, and then differential affinity of heme for human and rodent Aβ peptide has been proposed to account for the susceptibility of humans to AD. This review highlights whether there is any dependency of peroxidase activity of heme-bound Aβ on the Aβ aggregation state or not, with focusing on emerging role of heme in neurodegeneration. Here, several lines of evidence supporting existing contradictory conjectures are discussed.