Withaferin A-stimulated Ca2+ entry, ceramide formation and suicidal death of erythrocytes

Withaferin A, a triterpenoid component from Withania somnifera, counteracts malignancy, an effect attributed to stimulation of apoptosis. Withaferin A is partially effective through induction of oxidative stress, altered gene expression and mitochondrial depolarization. Erythrocytes lack mitochondria and nuclei but may enter apoptosis-like eryptosis, a suicidal cell death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the cell surface. Triggers of eryptosis include increase of cytosolic Ca2+-activity [ Ca 2 + ] i following activation of oxidant-sensitive Ca2+-permeable cation channels, ceramide formation and/or ATP-depletion. The present study explored, whether withaferin A triggers eryptosis. To this end, [ Ca 2 + ] i was estimated from Fluo3-fluorescence, cell volume from forward scatter, phosphatidylserine exposure from annexin-V-binding, hemolysis from hemoglobin release, oxidative stress from DCFDA-fluorescence and ceramide abundance utilizing antibodies. A 48 h exposure to withaferin A significantly decreased forward scatter (at ⩾ 10 μM withaferin concentration) and increased [ Ca 2 + ] i (⩾5 μM), ROS-formation (⩾10 μM) ceramide-formation (⩾10 μM) as well as annexin-V-binding (⩾5 μM). Withaferin A treatment was followed by slight but significant increase of hemolysis. Extracellular Ca2+ removal, amiloride, and the antioxidant N-acetyl- l -cysteine significantly blunted withaferin A-triggered annexin-V-binding. The present observations reveal that withaferin A triggers suicidal erythrocyte death despite the absence of gene expression and key elements of apoptosis such as mitochondria.