Triggering of Suicidal Erythrocyte Death by Penta- O-galloyl-β-d-glucose

Abstract

The polyphenolic 1,2,3,4,6-penta- O-galloyl-beta- d-glucose from several medicinal herbs triggers apoptosis and has, thus, been proposed for treatment of malignancy. The substance is at least partially effective through caspase activation. In analogy to apoptosis of nucleated cells, erythrocytes may enter suicidal death or eryptosis, which is characterized by cell shrinkage and by phosphatidylserine translocation to the erythrocyte surface. Eryptosis is triggered by increase of cytosolic Ca ²⁺-activity ([Ca ²⁺]i). The sensitivity to [Ca ²⁺]i is enhanced by ceramide. The present study explored whether penta- O-galloyl-β- d-glucose stimulates eryptosis. Cell volume was estimated from forward scatter, phosphatidylserine exposure from annexin V binding, hemolysis from hemoglobin-release, [Ca ²⁺]i from Fluo3-fluorescence and ceramide abundance from fluorescent antibodies. A 48-h exposure of human erythrocytes to penta- O-galloyl-β- d-glucose significantly decreased forward scatter (50 µM) and significantly increased annexin V binding (10 µM). Up to 50 µM penta- O-galloyl-β- d-glucose did not significantly modify [Ca ²⁺]i. However, the effect of penta- O-galloyl-β- d-glucose (25 µM) induced annexin V binding was slightly, but significantly, blunted by removal of extracellular Ca ²⁺, pointing to sensitization of erythrocytes to the scrambling effect of Ca ²⁺. Penta- O-galloyl-β- d-glucose (25 µM) further increased ceramide formation. In conclusion, penta- O-galloyl-β- d-glucose stimulates suicidal erythrocyte death or eryptosis, an effect partially due to stimulation of ceramide formation with subsequent sensitization of erythrocytes to Ca ²⁺.