The contribution of cerebral vascular semicarbazide-sensitive amine oxidase to cerebral amyloid angiopathy in Alzheimer's disease

Semicarbazide‐sensitive amine oxidase (SSAO) catalyses the oxidative deamination of a variety of endogenous substrates, such as methylamine and aminoacetone, to produce highly reactive aldehydes, which are capable of inducing protein cross‐linkage, beta amyloid (Aβ) aggregation and advanced glycation end‐product formation. In the brain, SSAO is exclusively located on the blood vessels. Deposits of Aβ, the hallmark of Alzheimer's disease (AD), are closely associated with cerebral blood vessels, that is, cerebral amyloid angiopathy (CAA). In the present study, we examined whether SSAO‐mediated deamination contributes to CAA in AD. We employed immunohistochemistry to examine the colocalization of SSAO and Aβ in post mortem brains of AD patients. To assess the role of SSAO‐mediated deamination in the deposition of Aβ on blood vessel walls, we developed an in vitro blood vessel model using sections of human umbilical cord. We found a strong expression of SSAO colocalized with Aβ deposits on the blood vessels in AD brains. We also demonstrated that SSAO‐mediated deamination increases the deposition of Aβ onto blood vessel walls. Our results support the hypothesis that cerebral vascular SSAO‐catalysed deamination contributes to CAA in AD brains.