title: Free radical-mediated platelet activation by hemoglobin released from red blood cells.
abstract: It is known that the rate of thrombus formation depends on interaction between platelets and erythrocytes, but the mechanism of this process has remained obscure. We here show that nanomolar levels of hemoglobin released from damaged red blood cells can induce platelet aggregation. The molecular mechanism is not receptor-based, but involves oxidation of oxyhemoglobin by platelet-derived hydrogen peroxide, with subsequent generation of a small unknown free radical species, detected by ESR spectroscopy. Methemoglobin and carbon monoxide-treated hemoglobin are unable to cause platelet activation or radical formation. The aggregation of platelets induced by hemoglobin is completely blocked by catalase or radical scavengers. These findings indicate a role for a novel extracellular free radical second messenger in the activation of platelets.
authors.affiliation: Institute of 1st Clinical Medicine, University of Rome La Sapienza, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Iuliano
authors.forename: F
authors.initials: F
authors.lastname: Violi
authors.forename: J Z
authors.initials: JZ
authors.lastname: Pedersen
authors.forename: D
authors.initials: D
authors.lastname: Praticò
authors.forename: G
authors.initials: G
authors.lastname: Rotilio
authors.forename: F
authors.initials: F
authors.lastname: Balsano
mesh_terms: D002248:Carbon Monoxide / Q000494:pharmacology; D004492:Edetic Acid / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004912:Erythrocytes / Q000737:chemistry*; D005609:Free Radicals; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D007501:Iron / Q000737:chemistry; D015539:Platelet Activation; D010974:Platelet Aggregation; D017382:Reactive Oxygen Species
chemical_list: D005609:Free Radicals; D006454:Hemoglobins; D017382:Reactive Oxygen Species; D002248:Carbon Monoxide; D004492:Edetic Acid; D007501:Iron