Lead toxicity in Saccharomyces cerevisiae : the role of glutathione

Lead is a non-essential metal for biological functions and is classified by the International Agency for Research on Cancer (IARC) as a probable human carcinogen. S. cerevisiae is a suitable model for studying Pb toxic effects since it is an eukaryote cell that can be easily manipulated and has a completely sequenced genome. In the present work, the role of reduced glutathione (GSH) as a defense mechanism against Pbinduced toxicity in S. cerevisiae was investigated. Yeast cells exposed to Pb (3h) lost cell viability (quantified by a clonogenic assay), accumulated intracellular reactive oxygen species (ROS) (evaluated by 2′,7′-dichlorodihydrofluorescein diacetate, H2 DCFDA) and decreased GSH level (assessed by monochlorobimane, mBCl). Yeast cells lacking the GSH1 (Dgsh1) or GSH2 (Dgsh2) genes were compared with wild type (WT) cells for loss of cell viability and Pb-induced ROS accumulation. We verified that Dgsh1 and Dgsh2 cells did not exhibit an increased loss of viability and did not experience ROS accumulation compared with WT cells. However, the treatment of WT cells with iodoacetamide (an alkylating agent which binds covalently to thiol groups) enhanced sensitivity to Pb. Incubation of WT cells with an amino acid mixture constituting GSH (L-glutamic acid, L-cysteine and glycine) reduced oxidative stress and loss of Pb-induced proliferation capacity. Together, the results suggest that intracellular GSH is involved in the defense against Pb-induced toxicity; however, it seems insufficient to sustain the oxidative stress and Pb-induced loss of cell viability