Licochalcone A Induced Suicidal Death of Human Erythrocytes

Abstract

Background: The anti-inflammatory, immunomodulatory, and antimicrobial Glycyrrhiza inflata extract component licochalcone A triggers apoptosis of tumor cells and is thus considered for the treatment of malignancy. Similar to apoptosis of nucleated cells, erythrocytes may enter eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Signaling involved in the triggering of eryptosis includes Ca²⁺ entry with increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), and ceramide. The present study explored, whether and how licochalcone A induces eryptosis. Methods: Human erythrocytes drawn from healthy individuals were exposed for 24 hours to 1-10 µg/ml licochalcone A. Flow cytometry was subsequently employed to estimate phosphatidylserine exposure at the cell surface from annexin V binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, and ceramide utilizing specific antibodies. In addition, hemolysis was quantified from hemoglobin release. Results: Licochalcone A significantly increased the percentage of annexin-V-binding cells (≥ 5 µg/ml), significantly decreased forward scatter (2.5 - 5 µg/ml), significantly increased Fluo3-fluorescence (≥ 7.5 µg/ml), and significantly increased ceramide abundance (10 µg/ml). The effect of licochalcone on annexin-V-binding was not significantly modified, but hemolysis significantly enhanced by removal of extracellular Ca²⁺. Conclusions: Licochalcone triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect independent from Ca²⁺ entry and presumably in part due to ceramide.