Effects of Aqueous and Methanolic Extracts of Stem Bark of <i>Alstonia boonei</i> De Wild. (Apocynaceae) on Dextran Sodium Sulfate‐Induced Ulcerative Colitis in Wistar Rats

Abstract

Among the most exploited species in Cameroon, <i>Alstonia boonei</i> is widely used in African medicine for the relief of several pathologies including gastrointestinal disorders. This study was conducted in order to assess the effects of aqueous and methanol stem-bark extracts of <i>Alstonia boonei</i> on DSS- (dextran sodium sulfate-) induced intestinal colitis and to determine its antioxidant potential. The classes of secondary metabolites present in these extracts were determined by chemical screening. The production of TNF-<i>α</i>, IL-6, IL-1<i>β</i>, and PGE2 was performed by <i>in vitro</i> ELISA analysis. Anticolitis effects were determined using an <i>in vivo</i> model of ulcerative colitis induced by DSS. The colitis was induced with a double dose of DSS (3% and 1%), and the aqueous and methanol extracts were administered orally from the 6^th day after commencement of induction. The phytochemical screening revealed the presence of six classes of secondary metabolites in these crude extracts: tannins, saponins, alkaloids, steroids, flavonoids, and phenols. Methanol and aqueous extracts of <i>Alstonia boonei</i> significantly (<i>P</i> < 0.001) inhibited TNF-<i>α</i>, IL-6, IL-1<i>β</i>, and PGE2 production stimulated by LPS. Both extracts at all doses significantly reduced (<i>P</i> < 0.01, <i>P</i> < 0.001) the signs of DSS-induced colitis in the Wistar rats by decreasing inflammation and chronic colon damage. In addition, the extracts significantly (<i>P</i> < 0.001) reduced malondialdehyde and nitric oxide levels in the colon and significantly (<i>P</i> < 0.01) increased superoxide dismutase and catalase and reduced glutathione (<i>P</i> < 0.05). Both extracts showed greater activity than the reference substance (prednisolone 4 mg/kg) used in this study. This study has demonstrated that aqueous and methanol extracts of <i>Alstonia boonei</i> stem bark have healing properties against colitis experimentally induced by DSS in rats.