MAOB and Alzheimer disease: Utilizing a ligand with a high affinity/specificity for monoamine oxidase B (MAO-B), an enzyme expressed primarily on the mitochondrial membrane of reactive astrocytes,80,81 PET imaging using the carbon-11 labeled L-deprenyl ([11C]DED) has revealed increased binding in patients with MCI, suggesting that astrocytosis is an early event in AD pathophysiology.82