Antispasmodic and Anti-inflammatory Effects of Kratom Leaf Extract on Acetic Acid-induced Ulcerative Colitis in Mice

Ulcerative colitis (UC) is colonic inflammation associated with increased production of pro-inflammatory cytokines, oxidative stress, and disturbances of immune responses. Mitragynine is the most abundant active alkaloid in Mitragyna speciosa (kratom) and may have anti-inflammatory, antioxidant, and antispasmodic properties. In this study, we investigated the palliative effects of mitragynine in kratom leaf extract on the symptoms of UC.

Mice were divided into six groups (n=9): control; colitis; colitis plus syrup with kratom extract containing 5, 10, or 20 mg/kg mitragynine; and a positive control group treated with 4 mg/kg loperamide. The treatments were orally administered for 5 days after colitis was induced by transrectal administration of 5% acetic acid.

The results showed that syrup with 10 and 20 mg/kg mitragynine significantly alleviated colonic tissue damage caused by acetic acid-induced colitis. Furthermore, the disease activity index, colonic weight, colonic lesions, and levels of malondialdehyde and inflammatory cytokines (tumor necrosis factor-α and interleukin-1β) decreased in these groups in comparison with the colitis-only group. With regard to antispasmodic activity, kratom extract significantly increased colonic smooth muscle relaxation by acting on μ-opioid receptor signaling and inhibited induced muscular contraction in mice with colitis. Moreover, kratom extract attenuated nitric oxide levels and enhanced the phagocytic activity of mouse peritoneal macrophages.

Kratom leaf extract, which contains mitragynine, alleviated acetic acid-induced colitis in mice by modulating immune responses and by its anti-inflammatory, antioxidative, and antispasmodic effects. Therefore, kratom leaves may be an effective therapeutic candidate for subsequent development as a multitarget drug for UC.