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PAIN MEDICINE

The Antiinflammatory and Analgesic Effects of Baicalin in Carrageenan-Evoked Thermal Hyperalgesia

Tz-Chong Chou, PhD^*, Li-Ping Chang, MD PhD, Chi-Yuan Li, MD, Chih-Shung Wong, MD PhD, and Shih-Ping Yang, MD PhD

*Department of Physiology and Biophysics, National Defense Medical Center, Taipei, Taiwan, Republic of China; and Department of Radiation Oncology, Department of Anesthesiology, and Division of Cardiology, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan, Republic of China

Address correspondence and reprint requests to Tz-Chong Chou, PhD, Department of Physiology and Biophysics, National Defense Medical Center, No. 161, Min-Chuan E. Rd., Sec. 6, Taipei, Taiwan, ROC. Address e-mail to tcchou{at}ms5.hinet.net

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- (from 3510 ± 150 pg/mL to 2860 ± 148 pg/mL to 1480 ± 210 pg/mL), interleukin (IL)-1ß (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 E₂ (PGE₂) and nitrate formation in the carrageenan-injected paws were dose-dependently inhibited by baicalin (10–100 mg/kg intraperitoneally) (PGE₂: 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 µM to 27.5 ± 3.0 µM to 17.2 ± 1.6 µM) 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, PGE₂, and proinflammatory cytokines, accompanied by an increase in IL-10 production, as well as neutrophil infiltration at sites of inflammation.

IMPLICATIONS: 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 E₂, as well as neutrophil infiltration. This implies that baicalin may be a potential therapeutic analgesic for inflammatory pain.

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