Analgesic and anti-inflammatory effects of ethyl acetate fraction of Polygonum cuspidatum in experimental animals

Polygonum cuspidatum (PC) has been used for the treatment of arthritis and urinary diseases in traditional medicine. Despite recent evidence that PC has anti-oxidant, anti-tumoral, and anti-inflammatory effects, analgesic and anti-inflammatory effects of PC have not been elucidated yet in vivo. Thus, in the present study, analgesic and anti-inflammatory effects of ethyl acetate extract of PC (EAPC) were investigated in vivo for the first time. Hot plate test and tail-flick test revealed that EAPC at 200 mg/kg exerts analgesic effect (p < 0.05). In contrast, EAPC did not show significant analgesic effect in acetic acid-induced writhing test. Serotonin-induced paw edema model and Freund's complete adjuvant (FCA)-induced adjuvant arthritis model were used to examine anti-inflammatory effect of EAPC in vivo. In serotonin-induced paw edema model, EAPC suppressed swelling inflammatory response within 12 min after serotonin injection, at both 100- and 200-mg/kg dose (p < 0.05). Consistently, in FCA-induced adjuvant arthritis model, FCA at 200 mg/kg significantly suppressed FCA-induced joint swelling within 3 days (p < 0.05), whereas FCA at 100 mg/kg showed the similar result within 5 days (p < 0.05). Furthermore, EAPC effectively inhibited positive responses of c-reactive protein and rheumatoid factor compared to untreated control. Taken together, our findings suggest that EAPC can be a potent candidate for rheumatoid arthritis treatment.