Diphenyleneiodonium triggers the efflux of glutathione from cultured cells.

Diphenyleneiodonium (DPI) is a broad-spectrum flavoprotein inhibitor commonly used to inhibit oxidant production by the NADPH oxidase of phagocytic and nonphagocytic cells. A previous study has shown that DPI can sensitize T24 bladder carcinoma cells to Fas-mediated apoptosis. We observed DPI to deplete intracellular reduced glutathione (GSH) in T24 cells and a range of other primary and transformed cell types. The effect was immediate, with 50% loss of intracellular GSH within 2 h of treatment with DPI. The glutathione was quantitatively recovered in the extracellular medium, indicating that efflux was occurring. The loss of GSH was blocked with bromosulfophthalein, an inhibitor of the canalicular GSH transporters. We conclude that DPI induces a dramatic efflux of cellular GSH from T24 cells via a specific transport channel. This provides a potential mechanism for its proapoptotic effect, and it also has important implications for the regulation of glutathione homeostasis in cells.