title: Lipid antioxidant, etoposide, inhibits phosphatidylserine externalization and macrophage clearance of apoptotic cells by preventing phosphatidylserine oxidation.
abstract: Apoptosis is associated with the externalization of phosphatidylserine (PS) in the plasma membrane and subsequent recognition of PS by specific macrophage receptors. Selective oxidation of PS precedes its externalization/recognition and is essential for the PS-dependent engulfment of apoptotic cells. Because etoposide is a potent and selective lipid antioxidant that does not block thiol oxidation, we hypothesized that it may affect PS externalization/recognition without affecting other features of the apoptotic program. We demonstrate herein that etoposide induced apoptosis in HL-60 cells without the concomitant peroxidation of PS and other phospholipids. HL-60 cells also failed to externalize PS in response to etoposide treatment. In contrast, oxidant (H2O2)-induced apoptosis was accompanied by PS externalization and oxidation of different phospholipids, including PS. Etoposide potentiated H2O2-induced apoptosis but completely blocked H2O2-induced PS oxidation. Etoposide also inhibited PS externalization as well as phagocytosis of apoptotic cells by J774A.1 macrophages. Integration of exogenous PS or a mixture of PS with oxidized PS in etoposide-treated HL-60 cells reconstituted the recognition of these cells by macrophages. The current data demonstrate that lipid antioxidants, capable of preventing PS peroxidation, can block PS externalization and phagocytosis of apoptotic cells by macrophages and hence dissociate PS-dependent signaling from the final common pathway for apoptosis.
authors: Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
authors: Yulia Y
authors: YY
authors: Tyurina
authors: F Behice
authors: FB
authors: Serinkan
authors: Vladimir A
authors: VA
authors: Tyurin
authors: Vidisha
authors: V
authors: Kini
authors: Jack C
authors: JC
authors: Yalowich
authors: Alan J
authors: AJ
authors: Schroit
authors: Bengt
authors: B
authors: Fadeel
authors: Valerian E
authors: VE
authors: Kagan
mesh_terms: D000818:Animals; D017304:Annexin A5 / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D000975:Antioxidants / Q000737:chemistry*; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology*; D005434:Flow Cytometry; D005450:Fluorescamine / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D018922:HL-60 Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007202:Indicators and Reagents / Q000494:pharmacology; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry*; D008163:Luminescent Measurements; D008264:Macrophages / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D010100:Oxygen / Q000378:metabolism; D010587:Phagocytosis; D010718:Phosphatidylserines / Q000737:chemistry*; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000737:chemistry; D013481:Superoxides / Q000378:metabolism; D013997:Time Factors
chemical_list: D017304:Annexin A5; D000972:Antineoplastic Agents, Phytogenic; D000975:Antioxidants; D002352:Carrier Proteins; D007202:Indicators and Reagents; D008055:Lipids; D008565:Membrane Proteins; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D013481:Superoxides; D005450:Fluorescamine; D005047:Etoposide; D006861:Hydrogen Peroxide; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D005978:Glutathione; D010100:Oxygen