Comparison of Monoamine Oxidase-A, Aβ Plaques, Tau, and Translocator Protein Levels in Postmortem Human Alzheimer’s Disease Brain

Abstract

Increased monoamine oxidase-A (MAO-A) activity in Alzheimer's disease (AD) may be detrimental to the point of neurodegeneration. To assess MAO-A activity in AD, we compared four biomarkers, Aβ plaques, tau, translocator protein (TSPO), and MAO-A in postmortem AD. Radiotracers were [¹⁸F]FAZIN3 for MAO-A, [¹⁸F]flotaza and [¹²⁵I]IBETA for Aβ plaques, [^124/125I]IPPI for tau, and [¹⁸F]FEPPA for TSPO imaging. Brain sections of the anterior cingulate (AC; gray matter GM) and corpus callosum (CC; white matter WM) from cognitively normal control (CN, <i>n</i> = 6) and AD (<i>n</i> = 6) subjects were imaged using autoradiography and immunostaining. Using competition with clorgyline and (<i>R</i>)-deprenyl, the binding of [¹⁸F]FAZIN3 was confirmed to be selective to MAO-A levels in the AD brain sections. Increases in MAO-A, Aβ plaque, tau, and TSPO activity were found in the AD brains compared to the control brains. The [¹⁸F]FAZIN3 ratio in AD GM versus CN GM was 2.80, suggesting a 180% increase in MAO-A activity. Using GM-to-WM ratios of AD versus CN, a >50% increase in MAO-A activity was observed (AD/CN = 1.58). Linear positive correlations of [¹⁸F]FAZIN3 with [¹⁸F]flotaza, [¹²⁵I]IBETA, and [¹²⁵I]IPPI were measured and suggested an increase in MAO-A activity with increases in Aβ plaques and tau activity. Our results support the finding that MAO-A activity is elevated in the anterior cingulate cortex in AD and thus may provide a new biomarker for AD in this brain region.