Priming of Platelet α _IIb β ₃ by Oxidants Is Associated With Tyrosine Phosphorylation of β ₃

Abstract

Abstract-Reactive oxygen species play an important role at the site of vascular injuries and arterial thromboses. We studied the mechanism mediating platelet aggregation induced by H 2 O 2 , a major cellular oxidant. Exposure to H 2 O 2 triggered platelet aggregation, but only when the platelets were stirred. Strong platelet aggregation induced by H 2 O 2 required the presence of the tyrosine phosphatase inhibitor sodium orthovanadate (NaVO 4 ) and was dependent on the participation of integrin ␣ IIb ␤ 3 (glycoprotein IIb-IIIa 2 Leukocytes and platelets have been found adjacent during acute coronary syndromes and even circulate as clusters in the blood of patients with unstable angina.3-5 Leukocytes and, in particular, neutrophils produce large amounts of reactive oxygen species (ROS), which could influence platelet function in a paracrine fashion. 6 Moreover, superoxide and hydroxyl radicals have been shown to be produced by anoxic and subsequently reoxygenated platelets.7 Previous studies on the effects of ROS and, in particular, hydrogen peroxide (H 2 O 2 ) on platelets indicated that ROS might exert a dual effect on platelets. In the presence of nitric oxide (NO), H 2 O 2 seems to potentiate the inhibitory effect of NO on agonist-mediated platelet activation. 8 In contrast, in the presence of arachidonate, H 2 O 2 enhances aggregation induced by phospholipid-derived arachidonate.9,10 To further characterize the effect of H 2 O 2 on platelet reactivity, we sought to characterize the effect of ROS and, in particular, of H 2 O 2 on platelet signaling pathways.Integrin ␣ IIb ␤ 3 , the classic platelet fibrinogen receptor, can exist in resting or activated states, and the latter can occur with or without ligand engagement. Activation corresponds to a structural change, whereby the affinity of ␣ IIb ␤ 3 for fibrinogen and other adhesive molecules in solution is markedly increased.11 Moreover, integrin ␣ IIb ␤ 3 can be found in 2 different compartments relative to extracellular ligands: exposed (to extracellular ligands) or cryptic (not accessible to extracellular ligands).12 Receptor molecules can be recruited from cryptic storage to the platelet surface or removed from the surface through a process of endocytosis.12-14 The molecular reactions that lead to receptor activation have been studied: ␤ 3 seems to play the role of a regulatory subunit of the receptor, whereas ␣ IIb appears to mediate receptor specificity. 15,16 There is good evidence that the activation process utilizes ATP 15 and involves interaction of the short cytoplasmic domain of ␤ 3 with a regulatory factor. 15,17,18 H 2 O 2 can induce a strong tyrosine kinase response in smooth muscle cells, especially in cells whose tyrosine phosphatases are concurrently inhibited with orthovanadate.

d-glucaro 1,4-lactone and resveratrol as antioxidants in blood platelets

“…Tyrosine phosphorylation of GPIIIa (regulatory subunit of the classical platelet fibrinogen receptor) after thrombin-induced platelet aggregation occurs. Irani et al (1998) found that GPIIIa was phosphorylated on tyrosine also in platelets exposed to H 2 O 2 . In the platelet aggregation induced by free radicals, tyrosine kinase pathways are involved, and it seems that p72 syk may be an important kinase in tyrosine phosphorylation of phospholipase C (Nagai et al 1994).…”

“…H 2 O 2 enhances platelet aggregation induced by phospholipid-derived arachidonate. Several reports indicate a role of ROS in regulation of tyrosine phosphorylation in platelet proteins by inhibiting phosphatase(s) (Hernandez-Hernandez et al 1999;Irani et al 1998). Tyrosine phosphorylation of GPIIIa (regulatory subunit of the classical platelet fibrinogen receptor) after thrombin-induced platelet aggregation occurs.…”

Treatment of Platelet Concentrates with the Mirasol Pathogen Inactivation System Modulates Platelet Oxidative Stress and NF-κB Activation

“…ROS are intimately involved in the process of oxidative metabolism, the process by which platelets obtain the majority of their energy supply when stored under ideal ex vivo conditions [33]. Hydrogen peroxide has also been shown to trigger platelet aggregation [17,19,34,35], as well as inhibit aggregation, depending on the presence of other mediators, such as NO and the type of agonists used [36]. ROS may also play a role in the generation of platelet microparticles and subsequent procoagulant effects [37] as well as in regulating tyrosine phosphorylation of many key proteins involved in platelet signal transduction, including vasodilator-stimulated phosphoprotein (VASP) [34,38].…”

“…Hydrogen peroxide has also been shown to trigger platelet aggregation [17,19,34,35], as well as inhibit aggregation, depending on the presence of other mediators, such as NO and the type of agonists used [36]. ROS may also play a role in the generation of platelet microparticles and subsequent procoagulant effects [37] as well as in regulating tyrosine phosphorylation of many key proteins involved in platelet signal transduction, including vasodilator-stimulated phosphoprotein (VASP) [34,38]. Similarly, increased metabolism, a reduced ability to aggregate in response to agonists, and increased expression of platelet signaling proteins, including VASP, have been observed in Mirasol- treated platelets [5,9,39,40].…”

Ageing, Oestrogen, Platelets and Thrombotic Risk

“…apoptosis) 62,70 . In the future, it will be important to determine what factors and mechanisms control aerobic respiration because lactate production is greater in platelets derived from aged (reproductively senescent) compared with younger (reproductively competent) individuals 71,72 and to determine whether hormonal status affects energy pathways independent of chronological age.…”