<i>In vitro</i> and <i>in vivo</i> anti-inflammatory activity of oenothein B from <i>Eucalyptus</i> leaves and its amelioration mechanism on colitis in mice by regulating fecal microbiota and metabolism

Nonvolatile extracts from <i>Eucalyptus</i> leaves possess diverse bioactivities; however, their anti-inflammatory potential and key active components remain insufficiently characterized. In this study, we demonstrated that antioxidant polyphenols extracted from <i>Eucalyptus grandis</i> × <i>E. urophylla</i> (EPEGU) using low-temperature continuous phase transformation extraction (LCPTE) exhibited significant anti-inflammatory effects by suppressing the secretion of nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6). Furthermore, oenothein B (OEB), isolated from EPEGU, markedly reduced pro-inflammatory cytokine levels and their corresponding mRNA expression in LPS-stimulated RAW264.7 macrophages. <i>In vivo</i>, OEB administration alleviated ulcerative colitis (UC) symptoms in mice, evidenced by attenuation of body weight loss, prevention of colon shortening, reduction of pro-inflammatory mediator secretion, and improvement in spleen weight, disease activity index (DAI), histopathological damage, and oxidative stress markers. Gut microbiota analysis revealed that OEB mitigated dysbiosis by increasing the abundance of beneficial taxa such as <i>Firmicutes</i>, <i>Akkermansia</i>, <i>Lactobacillus</i>, and <i>Ruminococcus</i>, while reducing potentially pathogenic genera including <i>Proteobacteria</i>, <i>Bacteroides</i>, and <i>Escherichia</i>-<i>Shigella.</i> These microbial shifts were associated with alterations in colonic metabolites, primarily involving arachidonic acid and bile acid metabolism. Collectively, these findings indicate that OEB is a promising natural anti-inflammatory agent and potential adjuvant for the prevention and management of inflammatory bowel diseases.