Tannic Acid Induced Suicidal Erythrocyte Death

Abstract

Background: The polyphenol tannic acid with antioxidant and antimicrobial potency may trigger suicidal death of nucleated cells or apoptosis and thus may counteract tumor growth. In analogy to apoptosis of nucleated cells, erythrocytes may undergo eryptosis, a suicidal death characterized by cell shrinkage and cell membrane scrambling with appearance of phosphatidylserine at the erythrocyte surface. A major trigger of eryptosis is increase of cytosolic Ca²⁺-activity ([Ca²⁺]_i). Erythrocytes could be sensitized to the eryptotic effect of cytosolic Ca²⁺ by ceramide. Methods: Cell volume has been estimated from forward scatter, phosphatidylserine abundance at the erythrocyte surface from annexin V binding, hemolysis from hemoglobin release, [Ca²⁺]_i from Fluo3-fuorescence and ceramide utilizing fluorescent antibodies. Results: A 48 h treatment with tannic acid was followed by significant decrease of forward scatter (≥ 1 µg/ml) and significant increase of annexin-V-binding (≥ 10 µg/ml). Tannic acid did not significantly modify [Ca²⁺]_i (up to 50 µM) but significantly increased ceramide formation (50 µM). The annexin-V-binding following tannic acid treatment (50 µM) was significantly blunted in the nominal absence of extracellular Ca²⁺. Conclusions: Tannic acid stimulates eryptosis, an effect at least partially due to ceramide formation with subsequent sensitization of erythrocytes to cytosolic Ca²⁺.