Glutathione precursors protect M
s from lethal toxin
(A) Cellular levels of glutathione, an endogenous antioxidant, were increased by preincubating RAW 264.7 cultures with the indicated concentrations of precursor (N-acetyl-L-cysteine or methionine) for 16 hr prior to LeTx challenge (PA = 0.1 µg/ml, LF = 0.1 µg/ml). Cytotoxicity was scored using the 51Cr-release assay described in Materials and Methods. Control amino acids did not protect Mϗs from LeTx challenge. Experiments were run in triplicate with two experimental series. SEM values for each data point were <11% of the indicated value. (B) Preventing precursor incorporation into glutathione by buthionine sulfoximine (BSO), a competitive inhibitor of glutathione synthetase, blocks the protective ability of N-acetyl-L-cysteine. Mϕ cultures were preincubated in the presence or absence of the N-acetyl-L-cysteine (50 mM), in the presence of the indicated amounts of BSO (0–200 mM) for 16 hr prior to LeTx challenge (PA = 0.1 µg/ml, LF = 0.1 µg/ml). LeTx toxicity was assayed by 51Cr-release as previously described. Experiments were run in duplicate with two experimental series. SEM values for each point were <12% of the indicated value.