The aim of this investigation was to examine whether macrophage and Leishma
nia major glutathione were involved in either host or parasite protection a
gainst NO cytotoxicity. Buthionine sulfoximine (BSO), an inhibitor of gamma
-glutamylcysteine synthase, caused a complete and irreversible depletion of
macrophage glutathione, but only a 20 % and reversible decrease in L. majo
r glutathione. Glutathione-depleted macrophages, when activated with IFN-ga
mma/LPS, released less than 60 % of the NO produced by untreated macrophage
s, resulting in a corresponding decrease in their leishmanicidal activity.
BSO-treated macrophages were more susceptible to the cytotoxic effects of t
he NO donor SNAP. Treatment of macrophages with 1,3-bis(chloroethyl)-1-nitr
osourea (BCNU), an inhibitor of glutathione reductase and trypanothione red
uctase or with Br-Octane, a glutathione-S-transferase substrate, resulted i
n a transient decrease in glutathione levels and did not increase the susce
ptibility of the macrophages to SNAP. Treatment of the promastigote forms o
f L. major with BCNU resulted in an 80 % decrease in total glutathione conc
entration with no concomitant change in viability. However, this treatment
rendered the parasites more susceptible to SNAP. Finally, macrophage glutat
hione 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.