The role of reactive oxygen species in platelet signal transduction

Platelet activation is triggered by numerous agonists, including small and soluble molecules and different adhesive proteins. How the signals integrate themselves to lead to the functional platelet response is so far unknown. This review focuses on the role of reactive oxygen species on platelet functions. In fact, reactive oxygen species modulate platelet responses. These species may be generated by several systems, but it must be stressed that platelets possess a NADH-dependent H2O2-producing system on plasma membrane, and this compound seems to be a physiologic intermediate of transductional events in these cells. Actually the H2O2-generating system is stimulated by tyrosine kinases, since genestein, a tyrosine kinase inhibitor, can abolish H2O2 production. On the contrary, inhibition of H2O2 formation by iodonium compounds causes a decrease in platelet tyrosine phosphorylation. The NAD(P)H oxidase is present in plasma membrane of various cells and its activation by many stimuli such as hormones and cytokines has been demonstrated. The H2O2-generating system meets the criteria of a universal transducing system and in human platelets it regulates platelet response to adhesive proteins.