Naringenin Inhibits Superoxide Anion-Induced Inflammatory Pain: Role of Oxidative Stress, Cytokines, Nrf-2 and the NO-cGMP-PKG-K.sub.ATPChannel Signaling Pathway

In the present study, the effect and mechanism of action of the flavonoid naringenin were evaluated in superoxide anion donor (KO.sub.2 )-induced inflammatory pain in mice. Naringenin reduced KO.sub.2 -induced overt-pain like behavior, mechanical hyperalgesia, and thermal hyperalgesia. The analgesic effect of naringenin depended on the activation of the NO-cGMP-PKG-ATP-sensitive potassium channel (K.sub.ATP) signaling pathway. Naringenin also reduced KO.sub.2 -induced neutrophil recruitment (myeloperoxidase activity), tissue oxidative stress, and cytokine production. Furthermore, naringenin downregulated KO.sub.2 -induced mRNA expression of gp91phox, cyclooxygenase (COX)-2, and preproendothelin-1. Besides, naringenin upregulated KO.sub.2 -reduced nuclear factor (erythroid-derived 2)-like 2 (Nrf2) mRNA expression coupled with enhanced heme oxygenase (HO-1) mRNA expression. In conclusion, the present study demonstrates that the use of naringenin represents a potential therapeutic approach reducing superoxide anion-driven inflammatory pain. The antinociceptive, anti-inflammatory and antioxidant effects are mediated via activation of the NO-cGMP-PKG-K.sub.ATP channel signaling involving the induction of Nrf2/HO-1 pathway.