Glutathione export by human lymphoid cells: depletion of glutathione by inhibition of its synthesis decreases export and increases sensitivity to irradiation.

Glutathione (in the form of GSH) is transported out of cultured human lymphoid cells at rates proportional to the intracellular glutathione levels. Inhibition of glutathione synthesis by buthionine sulfoximine, a potent selective inhibitor of gamma-glutamylcysteine synthetase, leads to exponential decrease in intracellular glutathione, a large fraction of which appears extracellularly, indicating that glutathione turnover is associated with its export. Although cells with 0.09 mM glutathione (4% of controls) were 85% viable, further decrease was associated with marked loss of viability. Cells with 4-5% of control glutathione levels were much more sensitive than control cells to the effects of gamma radiation and of 5,5'-dithiobis(2-nitrobenzoate). Depletion of glutathione by use of buthionine sulfoximine has advantages over other reagents (such as diamide, other oxidizing agents, and diethylmaleate, which affect other cellular components and may increase glutathione disulfide levels) and therefore has potential usefulness in sensitizing cells to the effects of radiation and to therapeutic agents that are detoxified by reactions involving glutathione.