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 microM) 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(5+) [Fe(III)5,10,15,20-tetrakis(
N-methylpyridinium-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 microM) 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-kappaB 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-nitrophenyl)
methanesulfonamide; 10 mg/kg] a selective
COX-2 inhibitor, as well as by an anti-
prostaglandin (PG) E(2) antibody (200 microg). 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.