Hemoglobin oxidation products extract phospholipids from the membrane of human erythrocytes

Hydrogen peroxide oxidation of human erythrocytes induces a transfer of phospholipid from the membrane into the cytosol [Brunauer, L.S., Moxness, M.S., & Huestis, W.H. (1994) Biochemistry 33, 4527-4532]. The current study examines the mechanism of lipid reorganization in oxidized cells. Exogenous phosphatidylserine was introduced into the inner monolayer of erythrocytes, and its distribution was monitored by microscopy and radioisotopic labeling. Pretreatment of cells with carbon monoxide prevented both hemoglobin oxidation and the transfer of phosphatidyserine into the cytosolic compartment. The roles of the various hemoglobin oxidation products in lipid extraction were investigated using selective oxidants. Nitrite treatment of intact cells produced almost complete conversion to methemoglobin, but no detectable lipid extraction. Treatments designed to produce the green hemoglobin derivatives, sulfhemoglobin and choleglobin, resulted in cytosolic extraction of phosphatidylserine. Ion exchange and size exclusion chromatography of oxidized cytosolic components revealed a lipid-hemoglobin complex. The interaction between lipid and hemoglobin oxidation products was verified in a model system. Purified hemoglobin, enriched in sulfhemoglobin and choleglobin by treatment with H2O2, H2S, or ascorbate, extracted phospholipid from small unilamellar phospholipid vesicles. Electron paramagnetic resonance studies demonstrated that hemoglobin oxidation products also adsorb fatty acids from solution. This newly described activity of hemoglobin may play a role in the clearance of oxidatively damaged and senescent cells from circulation.