Nitroarachidonic Acid, a Novel Peroxidase Inhibitor of Prostaglandin Endoperoxide H Synthases 1 and 2

Prostaglandin endoperoxide H synthase (PGHS) catalyzes the oxidation of arachidonate to prostaglandin H-2. We have previously synthesized and chemically characterized nitroarachidonic acid (AANO(2)), a novel anti-inflammatory signaling mediator. Herein, the interaction of AANO(2) with PGHS was analyzed. AANO(2) inhibited oxygenase activity of PGHS-1 but not PGHS-2. AANO(2) exhibited time- and concentration-dependent inhibition of peroxidase activity in both PGHS-1 and -2. The plot of k(obs) versus AANO(2) concentrations showed a hyperbolic function with k(inact) = 0.045 s(-1) and K-t(infinity aPP) = 0.019 mu m for PGHS-1 and k(inact) = 0.057 and K-t(infinity app) K-t(infinity aPP) = 0.020 mu m for PGHS-2. Kinetic analysis suggests that inactivation of PGHS by AANO(2) involves two sequential steps: an initial reversible binding event (described by K-t) followed by a practically irreversible event (K-t(infinity aPP)) leading to an inactivated enzyme. Inactivation was associated with irreversible disruption of heme binding to the protein. The inhibitory effects of AANO(2) were selective because other nitro-fatty acids tested, such as nitrooleic acid and nitrolinoleic acid, were unable to inhibit enzyme activity. In activated human platelets, AANO(2) significantly decreased PGHS-1-dependent thromboxane B-2 formation in parallel with a decrease in platelet aggregation, thus confirming the biological relevance of this novel inhibitory pathway.