Background: The artemisinin derivative artesunate is effective in the treatment of severe malaria and is considered for the treatment of malignancy. Artesunate triggers tumor cell apoptosis, an effect at least in part mediated by mitochondria. Even though lacking mitochondria, erythrocytes may similarly enter suicidal death or eryptosis, which is characterized by cell shrinkage and breakdown of the phospholipid asymmetry of the cell membrane with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include increase of cytosolic Ca(2+)-activity ([Ca(2+)]i), ceramide formation, and oxidative stress. The present study explored whether artesunate stimulates eryptosis.
Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin V binding, cell volume from forward scatter, [Ca(2+)]i from Fluo3-fluorescence, ceramide abundance from binding of specific antibodies, and oxidative stress from 2',7'-dichlorodihydrofluorescein-diacetate fluorescence.
Results: A 48 h exposure of human erythrocytes to artesunate significantly increased the percentage of annexin-V-binding cells (≥ 9 µg/ml) without significantly influencing forward scatter. Artesunate significantly increased [Ca(2+)]i. The stimulation of annexin-V-binding by artesunate (15 µg/ml) was significantly blunted but not abolished by removal of extracellular Ca(2+). Artesunate increased the ceramide abundance at the cell surface and the 2',7'-dichlorodihydrofluorescein-diacetate fluorescence.
Conclusions: Artesunate stimulates phosphatidylserine translocation at the erythrocyte cell membrane, an effect at least partially due to increase of [Ca(2+)]i, stimulation of ceramide formation and generation of oxidative stress.