Quantitative Assays for Catalytic Photo-Oxygenation of Alzheimer Disease-Related Tau Proteins

Catalytic photo-oxygenation of tau amyloid is a potentialtherapeuticapproach to tauopathies, including Alzheimer disease (AD). However,tau is a complex target containing great molecular size and heterogeneousisoforms/proteoforms. Although catalytic photo-oxygenation has beenconfirmed when using catalyst 1 and recombinant tau pretreatedwith heparin, its effects on tau from human patients have not yetbeen clarified. In this study, focusing on the histidine residuesbeing oxygenated, we have constructed two assay systems capable ofquantitatively evaluating the catalytic activity when used on humanpatient tau: (1) fluorescence labeling at oxygenated histidine sitesand (2) LC-MS/MS analysis of histidine-containing fragments.Using these assays, we identified 2 as a promising catalystfor oxygenation of human tau. In addition, our results suggest thataggregated tau induced by heparin is different from actual AD patienttau in developing effective photo-oxygenation catalysts.