Cyclooxygenases 1 and 2 contribute to peroxynitrite‐mediated inflammatory pain hypersensitivity

Peroxynitrite (ONOO − ), the reaction product of the interaction between superoxide (O 2 · − ) and nitric oxide (·NO), is a potent proinflammatory and cytotoxic nitrooxidative species. Its role as a mediator of hyperalgesia (clinically defined as an augmented sensitivity to painful stimuli) is not known. In light of the known proinflammatory properties of ONOO − , our study addressed its potential involvement in the development of hyperalgesia associated with tissue damage and inflammation. Intraplantar injection in rats of the ONOO − precursor O 2 · − (1 εM) led to the development of thermal hyperalgesia associated with a profound localized inflammatory response. Both events were blocked by L‐NAME (N G ‐nitro‐L‐arginine methyl ester, 3–30 mg/kg), a nitric oxide synthase inhibitor, or by FeTM‐4‐PyP + [Fe(III)5,10,15,20‐tetrakis( N ‐meth‐ylpyridinium‐4‐yl)porphyrin, 3–30 mg/kg], an ONOO − decomposition catalyst. These results suggested that locally synthesized ONOO − produced in situ by O 2 · − and ·NO is key in the development of inflammatory hyperalgesia. The direct link between ONOO − and hyperalgesia was further supported by demonstrating that intraplantar injection of soluble ONOO − itself (1 εM) similarly led to inflammatory hyperalgesia. ONOO − generated by the interaction between exogenous administration of O 2 · − and endogenous ·NO, or provided by direct injection of ONOO − , activated the transcription factor NF‐κB in paw tissues, enhancing expression of the inducible but not the constitutive cyclooxygenase enzyme (COX‐2 and COX‐1, respectively). ONOO − ‐mediated hyperalgesia was blocked in a dose‐dependent manner by intraperitoneal injections of indomethacin (10 mg/kg), a nonselective COX‐1/ COX‐2 inhibitor, or NS398 [ N ‐(2‐cyclohexyloxy‐4‐nitro‐phenyl)methanesulfonamide; 10 mg/kg] a selective COX‐2 inhibitor, as well as by an anti‐prostaglandin (PG) E 2 antibody (200 pg). In another established model of inflammation‐related hyperalgesia by intraplantar injection of carrageenan in rats, inhibition of ONOO − with FeTM‐4‐PyP 5+ (3–30 mg/kg) inhibited the development of hyperalgesia and the release of PGE 2 in paw tissue exudates. Furthermore, FeTM‐4‐PyP 5+ synergized with indomethacin and NS397 (1–10 mg/kg) to block both hyperalgesia and edema. Taken together, these data show for the first time that ONOO − is a potent mediator of inflammation‐derived hyperalgesia operating via the COX‐to‐PGE 2 pathway. These results provide a pharmacological rationale for the development of inhibitors of peroxynitrite biosynthesis as novel nonnarcotic analgesics. The broad implications of our study are that dual inhibition of both ONOO − formation and COX activity may provide an alternative therapeutic approach to the management of pain: effective analgesia with reduced side‐effects typically associated with the use of COX inhibitors.—Ndengele, M. N., Cuzzocrea, S., Esposito, E., Mazzon, E., Di Paola, R., Matuschak, G. M., Salvemini, D. Cyclooxygenases 1 and 2 contribute to peroxynitritemediated inflammatory pain hypersensitivity. FASEB J. 22, 3154–3164 (2008)