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 microM 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.

Polyunsaturated fatty acids have been indicated to induce anti-proliferative and/or apoptotic effects in various tumor cells. We showed that, at a 200- micro M concentration, both alpha-linoleic (18:2 n-6; LA) or docosahexaenoic (22:6 n-3; DHA) acid inhibited cell growth, while only DHA induced apoptosis in the human Paca-44 pancreatic cancer cell line. Investigating the mechanism underlying DHA-induced apoptosis, we showed that DHA induced a rapid and dramatic (>60%) intracellular depletion of reduced glutathione (GSH), without affecting oxidized glutathione (GSSG). Moreover, using two specific inhibitors of carrier-mediated GSH extrusion, cystathionine or methionine, we observed that GSH depletion occurred via an active GSH extrusion, and that inhibition of GSH efflux completely reversed apoptosis. These results provide the first evidence for a possible causative role of GSH depletion in DHA-induced apoptosis.