Apigenin-Induced Suicidal Erythrocyte Death

Apigenin, a flavone in fruits and vegetables, stimulates apoptosis and thus counteracts cancerogenesis. Erythrocytes may similarly undergo suicidal cell death or eryptosis, characterized by cell shrinkage and phosphatidylserine exposure at the cell surface. Triggers of eryptosis include increase of cytosolic Ca2+ activity ([Ca2+](i)), ceramide formation and ATP depletion. The present study explored the effect of apigenin on eryptosis. [Ca2+](i) was estimated from Fluo3-fluorescence, cell volume from forward scatter, phosphatidylserine exposure from annexin V binding, hemolysis from hemoglobin release, ceramide utilizing antibodies, and cytosolic ATP with luciferin luciferase. A 48 h exposure to apigenin significantly increased [Ca2+](i) (>= 1 mu M), increased ceramide formation (15 mu M), decreased ATP concentration (15 mu M), decreased forward scatter (>= 1 mu M), and increased annexin V binding (>= 5 mu M) but did not significantly modify hemolysis. The effect of 15 mu M apigenin on annexin V binding was blunted by Ca2+ removal. The present observations reveal novel effects of apigenin, i.e. stimulation of Ca2+ entry, ceramide formation and ATP depletion in erythrocytes with subsequent triggering of suicidal erythrocyte death, paralleled by cell shrinkage and phosphatidylserine exposure.