Peroxynitrite may affect clot retraction in human blood through the inhibition of platelet mitochondrial energy production.

Peroxynitrite (ONOO(-)) contributes to hemostasis abnormalities associated with inflammatory states by a poorly understood mechanism. Here we show that ONOO(-) may affect clot retraction (CR), an important step in hemostasis, by reducing contractility of human platelets resulting from the inhibition of mitochondrial energy production. Reduced CR may result in thromboembolic and hemorrhage events. The results show that in human blood, in vitro, physiologically relevant ONOO(-) concentrations reduce clot retraction rate and enlarge final clot size. The stressor was more effective in reconstituted system consisting of washed platelets and fibrinogen, (IC₅₀=25 nM) than in platelet rich plasma (IC₅₀=75 μM) or in whole blood (IC₅₀=120 μM), indicating that its effect depends on the number of targets. Retardation of CR by lower concentrations of ONOO(-) resulted in reduction of platelet energy production due to impairment of mitochondria but not from tyrosine nitration or inhibition of actin polymerization. In washed platelets nanomolar ONOO(-) concentrations produced a drop of the mitochondrial transmembrane potential (ΔΨm) explaining high sensitivity of CR (a large consumer of platelet energy) to stressor. Thromboelastometry measurements showed that ONOO(-) may diminish clot stability and elasticity through the reduction of platelet contractility. Our findings suggest that in humans ONOO(-)- altered platelet mitochondria represent a new link between inflammation and hemostasis.