Enhanced Eryptosis Following Exposure to Carnosic Acid

Abstract

Background/Aims: The phenolic abietane diterpene component of rosemary and sage, carnosic acid, may either induce or inhibit apoptosis of nucleated cells. The mechanisms involved in the effects of carnosic acid include altered mitochondrial function and gene expression. Human erythrocytes lack mitochondria and nuclei but are nevertheless able to enter suicidal death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Cellular mechanisms involved in the stimulation of eryptosis include oxidative stress, increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), and ceramide formation. The present study explored, whether and how carnosic acid induces eryptosis. Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin V binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, ROS formation from DCFDA dependent fluorescence and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to carnosic acid significantly increased the percentage of annexin-V-binding cells (2.5 µg/ml), significantly decreased forward scatter (10 µg/ml), significantly increased Fluo3 fluorescence (10 µg/ml), significantly increased ceramide abundance (10 µg/ml), significantly increased hemolysis (10 µg/ml), but significantly decreased DCFDA fluorescence (10 µg/ml). The effect of carnosic acid on annexin-V-binding was significantly blunted, but not abolished by removal of extracellular Ca²⁺. Conclusion: Carnosic acid triggers cell shrinkage and phospholipid scrambling of the human erythrocyte cell membrane, an effect paralleled by and/or in part due to Ca²⁺ entry and increased ceramide abundance.