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

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. MR inhibited Trypanosoma cruzi trypanothione reductase (TR) (K-i = 1.9 mu M), and served as a significant subversive substrate of this enzyme (K-M = 30 mu M, 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, 14202 or superoxide, is produced in each cycle. Since MR is an affordable, available, and accessible drug it might be tested - alone or in drug combinations - against trypanosomatid-casused diseases of animal and man. (C) 2008 Elsevier B.V. All rights reserved.