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.