Stimulation of Erythrocyte Phosphatidylserine Exposure by Paclitaxel

Side effects of cytostatic treatment include development of anemia resulting from either decreased generation or accelerated clearance of circulating erythrocytes. Recent experiments revealed a novel kind of stress-induced erythrocyte death, i.e. eryptosis, which is characterized by enhanced cytosolic Ca 2+ levels, increased ceramide formation and exposure of phosphatidylserine at the cell surface. The present study explored whether cytostatic treatment with paclitaxel (Taxol®) triggers eryptosis. Blood was drawn from cancer patients before and after infusion of 175 mg/m2 Taxol®. The treatment significantly decreased the hematocrit and significantly increased the percentage of annexin-Vbinding erythrocytes in vivo (by 37%). In vitro incubation of human erythrocytes with 10 μM paclitaxel again significantly increased annexin-V-binding (by 129%) and augmented the increase of annexin-Vbinding following cellular stress. The enhanced phosphatidylserine exposure was not dependent on caspase-activity but paralleled by erythrocyte shrinkage, increase of cytosolic Ca 2+ activity, ceramide formation and activation of calpain. Phosphatidylserine exposure was similarly induced by docetaxel but not by carboplatin or doxorubicin. Moreover, eryptosis was triggered by the Ca 2+ ionophore ionomycin (10 μM). In mice, ionomycintreated eryptotic erythrocytes were rapidly cleared from circulating blood and sequestrated into the spleen. In conclusion, our data strongly suggest that paclitaxel-induced anemia is at least partially due to induction of eryptosis.