Docosahexaenoic acid induces apoptosis in the human PaCa-44 pancreatic cancer cell line by active reduced glutathione extrusion and lipid peroxidation

We investigated the ability of fatty acids to induce growth inhibition and apoptosis in the human PaCa-44 pancreatic cancer cell line and the mechanism(s) underlying apoptosis. Butyric acid, alpha-linoleic acid, and docosahexaenoic acid (DHA) were supplemented at 200 mu M concentration in the medium of cell cultures. Our results showed that all fatty acids inhibited cell growth, whereas only DHA induced cell apoptosis. An oxidative process was implicated in apoptosis induced by DHA because butylated hydroxytoluene and vitamin E prevented lipid peroxidation and reversed apoptosis. Intracellular and extracellular glutathione [reduced glutathione (GSH) and oxidized glutathione (GSSG)] concentrations were measured following DHA treatment in the presence or in the absence of GSH extrusion inhibitors such as cystathionine or methionine. DHA induced intracellular GSH depletion without affecting intracellular GSSG concentration and increased extracellular GSH and GSSG levels. Intracellular GSH depletion and extracellular GSH increase were both reversed by cystathionine. Inhibition of active GSH extrusion from the cell by cystathionine or methionine completely reversed lipid peroxidation and apoptosis. These data document the antiproliferative and apoptotic activities of DHA. The date provide evidence that intracellular GSH depletion represents an active extrusion process rather than a consequence of an oxidative stress, suggesting a causative role of GSH depletion in DHA-induced apoptosis.