Cytotoxic interactions of methylene blue with trypanosomatid-specific disulfide reductases and their dithiol products.

Abstract Methylene blue (MB) is known to have trypanocidal activity. We tested the interactions of MB with a number of trypanosomatid-specific molecules of the antioxidant metabolism. At pH 7, trypanothione and other (di)thiols were oxidized to disulfides by the phenothiazine drug. MB inhibited Trypanosoma cruzi trypanothione reductase (TR) ( K i  = 1.9 μM), and served as a significant subversive substrate of this enzyme ( K M  = 30 μM, k cat  = 4.9 s −1 ). With lipoamide dehydrogenase, the second thiol-generating flavoenzyme of T. cruzi , the catalytic efficiency for MB reduction was found to be almost 10 6  M −1  s −1 . When the system MB-enzyme-molecular oxygen acts as a NAD(P)H-driven redox cycler, a reactive oxygen species, H 2 O 2 or superoxide, is produced in each cycle. Since MB is an affordable, available, and accessible drug it might be tested – alone or in drug combinations – against trypanosomatid-caused diseases of animal and man.