Peroxynitrite‐mediated oxidation of fibrinogen inhibits clot formation

The clotting activity of human fibrinogen was fully inhibited in vitro by peroxynitrite. The decrease of activity followed an exponential function and the concentration of peroxynitrite needed to inhibit 50% of fibrinogen clotting was 22 μM at 25°C. The oxidative modification(s) induced by the peroxynitrite system (i.e. ONOO−, ONOOH and ONOOH*) appeared specifically to affect fibrin clot formation (through the inhibition of fibrinogen polymerization) since the interaction of peroxynitrite‐modified fibrinogen with thrombin appeared to be unaffected. The addition of NaHCO3decreased the peroxynitrite effect on fibrinogen clotting, suggesting that the reactive species formed by the reaction of CO2with peroxynitrite are less efficient oxidants of peroxynitrite itself. Similar effects were observed after addition of bilirubin, which also exerted a significant protection against peroxynitrite‐mediated modification of fibrinogen.