The aim of this investigation was to examine whether macrophage and Leishmania major glutathione were involved in
either host or parasite protection against NO cytotoxicity. Buthionine sulfoximine (BSO), an inhibitor of γ-glutamyl-cysteine synthase, caused a complete and irreversible depletion of macrophage glutathione, but only a 20% and reversible
decrease in L. major glutathione. Glutathione-depleted macrophages, when activated with IFN-γ/LPS, released less than
60% of the NO produced by untreated macrophages, resulting in a corresponding decrease in their leishmanicidal activity.
BSO-treated macrophages were more susceptible to the cytotoxic effects of the NO donor SNAP. Treatment of macrophages
with 1,3-bis(chloroethyl)-1-nitrosourea (BCNU), an inhibitor of glutathione reductase and trypanothione
reductase or with Br-Octane, a glutathione-S-transferase substrate, resulted in a transient decrease in glutathione levels
and did not increase the susceptibility of the macrophages to SNAP. Treatment of the promastigote forms of L. major
with BCNU resulted in an 80% decrease in total glutathione concentration with no concomitant change in viability.
However, this treatment rendered the parasites more susceptible to SNAP. Finally, macrophage glutathione protected the
internalized L. major from SNAP. Overall, these results demonstrate that glutathione is an essential protective component
against NO cytotoxicity on both macrophages and parasites.