Combining myeloperoxidase (MPO) with fluorogenic ZnSalen to detect lysosomal hydrogen peroxide in live cells

Accumulating evidence suggests that lysosomal H₂O₂ is closely associated with autophagy and apoptosis in normal and pathological processes. Imaging H₂O₂ in lysosomes is a powerful tool to elucidate its diverse roles, however, is limited by the lack of fluorescent probes capable of specifically detecting H₂O₂ under acidic conditions (pH 4.5-6). Herein we report the design and application of the “MPO-J-S” probe, a new combination of “peroxidase/fluorogenic substrate”, which is membrane-permeable and can be used to visualize exogenous or endogenous H₂O₂ confined to lysosomes via one and two photon fluorescence microscopies. The features of lysosomal H₂O₂ selectivity, high sensitivity, and live-cell compatibility offer new opportunities for luminescent ZnSalens and the related hypochlorite responsive fluorophores, combined with MPO, to decipher the physiological roles of lysosomal H₂O₂ in live cells.