A pivotal study (73) demonstrated that 5-hydroxyindoleacetic acid (5-HIAA), the primary metabolite of serotonin, significantly reduces amyloid-beta (Aβ) levels in the brain of a mouse model of AD, as well as in a mouse model with phosphoramidon-induced neprilysin (NEP) inhibition in the brain. Here, MME is linked to Alzheimer disease.