LEISHMANICIDAL ACTIVITY OF PEROXYNITRITE

Nitric oxide reacts with superoxide to produce peroxynitrite which has been reported to be highly microbicidal to Trypanosoma cruzi in phosp hate buffer but ineffective against Leishmania major in culture medium . This contradiction and the potential importance of peroxynitrite as a cytotoxic effector molecule of both macrophages and neutrophils led us to re-examine its leishmanicidal effects. Our results demonstrate t hat peroxynitrite inhibits growth of Leishmania amazonensis promastigo tes in a concentration-dependent manner both in phosphate buffer and c ulture medium (DMEM containing 20% fetal calf serum). In the latter, 4 3% growth inhibition was observed with 4mM peroxynitrite whereas in bu ffer a 70% inhibition was already observed with 0.5 mM peroxynitrite. Treated parasites presented reduced motility and became round in shape further confirming the leishmanicidal activity of peroxynitrite. The latter was attenuated by reduced glutathione supporting the view that peroxynitrite-mediated oxidation of critical thiol groups is a major m echanism accounting for its trypanocidal activity.