The antiinflammatory and analgesic effects of baicalin in carrageenan-evoked thermal hyperalgesia.

Abstract

We tested baicalin for its antiinflammatory and analgesic effects (and the mechanisms) in a rat model of carrageenan-evoked thermal hyperalgesia. Pre- or posttreatment with baicalin (10, 30, or 100 mg/kg intraperitoneally) caused a significant analgesic effect with a similar effect of dose-matched ibuprofen. Furthermore, baicalin dose-dependently attenuated tumor necrosis factor-alpha (from 3510 +/- 150 pg/mL to 2860 +/- 148 pg/mL to 1480 +/- 210 pg/mL), interleukin (IL)-1beta (from 3210 +/- 210 pg/mL to 2200 +/- 140 pg/mL to 750 +/- 95 pg/mL), and IL-6 (from 58.5 +/- 9.8 pg/mL to 38.5 +/- 9.0 to 21.0 +/- 8.1 ng/mL) formation but enhanced IL-10 (from 18.1 +/- 2.5 pg/mL to 36.1 +/- 5.5 pg/mL to 71.2 +/- 9.5 pg/mL) production in paw exudates at 4 h after carrageenan injection. Prostaglandin E(2) (PGE(2)) and nitrate formation in the carrageenan-injected paws were dose-dependently inhibited by baicalin (10-100 mg/kg intraperitoneally) (PGE(2): from 15.9 +/- 2.1 ng/mL to 12.1 +/- 1.6 ng/mL to 6.2 +/- 1.8 ng/mL; nitrate: from 39.8 +/- 4.8 microM to 27.5 +/- 3.0 microM to 17.2 +/- 1.6 microM) at 4 h but not at 1.5 h after carrageenan injection. Increased myeloperoxidase activity in carrageenan-injected paws was also dose-dependently reduced by baicalin. These findings suggest that the antiinflammatory and analgesic mechanisms of baicalin may be associated with the inhibition of critical inflammatory mediators, including nitric oxide, PGE(2), and proinflammatory cytokines, accompanied by an increase in IL-10 production, as well as neutrophil infiltration at sites of inflammation. Our results showed that baicalin possesses an analgesic effect in carrageenan-evoked thermal hyperalgesia. The possible mechanisms of action of baicalin may be associated with the inhibition of proinflammatory mediator overproduction, including cytokines, nitric oxide, and prostaglandin E(2), as well as neutrophil infiltration. This implies that baicalin may be a potential therapeutic analgesic for inflammatory pain.