Suppression of superoxide production by chlorothalonil in striped bass (Morone saxatilus) macrophages: the role of cellular sulfhydryls and oxidative stress.
Chlorothalonil (TCIN) is the most commonly applied fungicide in the USA, with substantial use in the Chesapeake Bay area. Little is known about the sublethal toxicity of TCIN to fish, but since it is structurally similar to the immunotoxicant pentachlorophenol, the potential for immunomodulation exists. Previous studies have indicated that in vitro exposure of macrophages to TCIN modulates immunostimulated reactive oxygen species (H(2)O(2)/hypochlorous acid) and NADPH production in striped bass (Morone saxatilus). The goals of this study were to determine if TCIN inhibits superoxide (O(2)(-)) production by macrophage NADPH oxidase, to examine the role of cellular sulfhydryl groups in TCIN-induced macrophage dysfunction, and to identify the extent to which lipid peroxidation contributes to the observed toxic effects. The results of lucigenin-augmented chemiluminescence assays indicated that TCIN suppressed both baseline and stimulated O(2)(-) production in a dose-dependent manner. Similar results were obtained using both the particulate stimulant zymosan and the lipid-soluble stimulant phorbol 12-myristate-13-acetate. Inhibition of glutathione synthesis by pre-treatment with buthionine sulfoximine (BSO) enhanced the suppression of O(2)(-) production. The protection of sulfhydryl groups by culturing macrophages with dithiothreitol (DTT) reduced TCIN-induced macrophage dysfunction. TCIN did not initiate lipid peroxidation in macrophages, as measured by the thiobarbituric acid reactive substances (TBARS) assay, nor did pre-treatment with BSO potentiate lipid peroxidation. Because the observed TCIN-induced suppression of O(2)(-) was modulated by altering cellular sulfhydryl status with BSO and DTT, it is possible that toxicity results from the inhibition of NADPH oxidase activity by TCIN binding to its functional sulfhydryl groups.