Abstract
The cholesterol synthesis inhibitor Triparanol has been shown to trigger apoptosis in several malignancies. Similar to the apoptosis of nucleated cells, erythrocytes may enter eryptosis, the suicidal death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include oxidative stress which may activate erythrocytic Ca2+ permeable unselective cation channels with subsequent Ca2+ entry and increase of cytosolic Ca2+ activity ([Ca2+]i). The present study explored whether and how Triparanol induces eryptosis. To this end, phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, hemolysis from hemoglobin release, [Ca2+]i from Fluo3-fluorescence, and ROS formation from 2’,7’-dichlorodihydrofluorescein diacetate (DCFDA) dependent fluorescence. As a result, a 48 h exposure of human erythrocytes to Triparanol (20 µM) significantly increased DCFDA fluorescence and significantly increased Fluo3-fluorescence. Triparanol (15 µM) significantly increased the percentage of annexin-V-binding cells, and significantly decreased the forward scatter. The effect of Triparanol on annexin-V-binding was significantly blunted, but not abolished by removal of extracellular Ca2+. In conclusion, Triparanol leads to eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane. Triparanol is at least in part effective by stimulating ROS formation and Ca2+ entry.
Highlights
Triparanol, a 3β-hydroxysterol-Δ24-reductase inhibitor and inhibitor of cholesterol synthesis [1,2,3,4], has been shown to inhibit proliferation and trigger apoptosis in several malignancies including leukemia, melanoma, chondrosarcoma, and cancer of lung, breast, liver, pancreas, or prostate [5,6,7]
Triparanol leads to eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane
Human erythrocytes from healthy volunteers were treated with Triparanol and phosphatidylserine surface abundance, cell volume, [Ca2+]i and reactive oxygen species (ROS) formation determined by flow cytometry
Summary
Triparanol, a 3β-hydroxysterol-Δ24-reductase inhibitor and inhibitor of cholesterol synthesis [1,2,3,4], has been shown to inhibit proliferation and trigger apoptosis in several malignancies including leukemia, melanoma, chondrosarcoma, and cancer of lung, breast, liver, pancreas, or prostate [5,6,7]. Triparanol has further been shown to increase cytosolic Ca2+ activity ([Ca2+]i), an effect attributed to Ca2+ release from intracellular stores [9]. Similar to apoptosis of nucleated cells, erythrocytes may enter eryptosis, the suicidal death of erythrocytes characterized by cell shrinkage [14] and phosphatidylserine translocation from the inner cell membrane leaflet to the cell surface [15]. Triggers of eryptosis include oxidative stress, opening of oxidant sensitive cation channels, Ca2+ entry and increase of [Ca2+]i. The present study explored whether Triparanol triggers eryptosis. To this end, human erythrocytes from healthy volunteers were treated with Triparanol and phosphatidylserine surface abundance, cell volume, [Ca2+]i and ROS formation determined by flow cytometry
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