Triggering of eryptosis, the suicidal erythrocyte death, by phenoxodiol

Phenoxodiol is used for the treatment of malignancy. The substance is effective by triggering suicidal tumor cell death or apoptosis. At least in theory, phenoxodiol could similarly stimulate suicidal erythrocyte death or eryptosis. Eryptosis is characterized by cell shrinkage and breakdown of cell membrane asymmetry with phosphatidylserine translocation to the erythrocyte surface. Signaling of eryptosis includes increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), formation of reactive oxygen species (ROS), and increase of ceramide abundance at the cell surface. The present study explored whether phenoxodiol induces eryptosis and whether it modifies Ca²⁺ entry, ROS, and ceramide. Using flow cytometry, phosphatidylserine exposure at the cell surface was quantified from annexin V binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3 fluorescence, ROS from DCFDA-dependent fluorescence, and ceramide abundance utilizing specific antibodies. A 48-h exposure of human erythrocytes to phenoxodiol (100 μg/ml [416 μM]) significantly increased the percentage of annexin V binding cells, significantly decreased average forward scatter and Fluo3 fluorescence and significantly increased ceramide abundance, but did not significantly modify DCFDA fluorescence. The effect of phenoxodiol on annexin V binding tended to decrease following removal of extracellular Ca²⁺, an effect, however, not reaching statistical significance. In conclusion, phenoxodiol triggers eryptosis, an effect paralleled by increase of ceramide abundance.