Triggering of Erythrocyte Death by Triparanol
The cholesterol synthesis inhibitor Triparanol has been shown to induce apoptosis in various malignancies. In a manner similar to nucleated cells undergoing apoptosis, erythrocytes can undergo eryptosis—a form of programmed cell death characterized by cell shrinkage and the scrambling of the cell membrane, resulting in the translocation of phosphatidylserine to the erythrocyte surface. Eryptosis can be triggered by oxidative stress, which may activate unselective cation channels that are permeable to Ca(2+), leading to increased cytosolic Ca(2+) levels.
This study investigated whether and how Triparanol induces eryptosis. We assessed phosphatidylserine exposure at the cell surface using annexin-V binding, measured cell volume through forward scatter analysis, evaluated hemolysis by quantifying hemoglobin release, and determined cytosolic Ca(2+) levels via Fluo3 fluorescence. Additionally, we measured reactive oxygen species (ROS) formation using 2′,7′-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence.
Our findings revealed that a 48-hour exposure of human erythrocytes to Triparanol (20 µM) significantly increased DCFDA fluorescence and Fluo3 fluorescence. Furthermore, treatment with Triparanol (15 µM) led to a significant rise in the percentage of annexin-V-binding cells and a notable decrease in forward scatter. The effect of Triparanol on annexin-V binding was significantly reduced, but not completely eliminated, when extracellular Ca(2+) was removed.
In conclusion, Triparanol induces eryptosis in erythrocytes, characterized by cell shrinkage and phospholipid scrambling of the cell membrane. Its effects are partially mediated by the stimulation of ROS formation and the entry of Ca(2+).