Tanshinone IIA Stimulates Erythrocyte Phosphatidylserine Exposure
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Tanshinone IIA, an antimicrobial, antioxidant, antianaphylactic, antifibrotic, vasodilating, antiatherosclerotic, organo-protective and antineoplastic component from the rhizome of Salvia miltiorrhiza, is known to trigger apoptosis of tumor cells. Tanshinone IIA is effective in part through mitochondrial depolarization and altered gene expression. Erythrocytes lack mitochondria and nuclei but may undergo eryptosis, an apoptosis-like suicidal cell death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine exposure at the cell surface. Eryptosis is triggered by increase of cytosolic Ca(2+) activity, ATP depletion and ceramide formation. The present study explored, whether tanshinone IIA elicits eryptosis. Cytosolic Ca(2+)-concentration was determined from Fluo3-fluorescence, cell volume from forward scatter, phosphatidylserine exposure from binding of fluorescent annexin V, hemolysis from hemoglobin concentration in the supernatant, ATP concentration utilizing luciferin-luciferase and ceramide formation utilizing fluorescent anticeramide antibodies. Clearance of circulating erythrocytes was estimated by CFSE-labeling. A 48 h exposure to tanshinone IIA (≥10 µM) significantly increased cytosolic Ca(2+)-concentration, decreased ATP concentration (25 µM), increased lactate concentration (25 µM), increased ceramide formation (25 µM), decreased forward scatter, increased annexin-V-binding and increased (albeit to a much smaller extent) hemolysis. The effect of 25 µM tanshinone IIA on annexin-V binding was partially reversed in the nominal absence of Ca(2+). Labelled tanshinone IIA-treated erythrocytes were more rapidly cleared from the circulating blood in comparison to untreated erythrocytes. The present observations reveal a completely novel effect of tanshinone IIA, i.e. triggering of Ca(2+) entry, ATP depletion and ceramide formation in erythrocytes, events eventually leading to eryptosis with cell shrinkage and cell membrane scrambling.
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