Changes in antioxidant defense systems induced by thiram in V79 Chinese hamster fibroblasts

The role of antioxidant defence systems in protection against oxidative damage of lipids and proteins induced by fungicide thiram during in vitro exposure was investigated in cultured Chinese hamster V79 cells with normal, depleted, and elevated glutathione (GSH) levels. We analyzed the catalytic activities of superoxide dismutases (SOD1 and SOD2), Se-dependent and Se-independent glutathione peroxidases (GSH-Px), glutathione reductase (GR), and catalase (CAT), as well as total glutathione/glutathione disulfide ratio (GSHtotal/GSSG). Thiram treatment resulted in an increase in activities of SOD1, Se-dependent GSH-Px, and GR at the highest tested dose (150 μM). On the contrary, inhibition of CAT and Se-independent GSH-Px activities, and no significant changes in the level of SOD2 activity was observed at any tested doses (100–150 μM). GSHtotal/GSSG ratio in the 100 μM thiram treated cells was not significantly changed comparing to the control, despite significant decrease of GSH total (50%). In 150 μM thiram treated cells the ratio falls to 43% of control value. Pretreatment with l-buthionine sulfoximine (l-BSO), an inhibitor of GSH synthesis, significantly enhanced decrease in CAT and Se-independent GSH-Px activities, as well as GSHtotal/GSSG ratio, and reduced Se-dependent GSH-Px activity, following exposure to thiram. Simultaneously, l-BSO pretreatment enhanced increase in SOD1 activity, and had no effect on SOD2, following thiram exposure. Pretreatment with N-acetyl cysteine (NAC), a GSH precursor, prevented enzymatic changes in CAT, Se-dependent GSH-Px, GR, SOD1 activities, and significantly decreased SOD2 activity following exposure to thiram. GSHtotal/GSSG ratio was restored to the control value. This study suggests that following the changes in antioxidant defense systems thiram can act through the production of free radicals.