Tangeretin mitigates ulcerative colitis by improving BMAL1-mediated intestinal barrier function

Ulcerative colitis (UC), a chronic inflammatory bowel disease associated with circadian rhythm disruption, presents a critical need for novel therapeutic strategies. While the natural flavonoid tangeretin (TAN) exhibits anti-inflammatory properties, its effect of alleviating UC and the mechanism through intestinal circadian clock modulation remains unclear. Using a dextran sulfate sodium (DSS)-induced murine colitis model, we demonstrated that Prophylactic TAN administration significantly alleviated colitis severity, restored locomotor rhythms, and reversed UC-induced disruptions in colonic clock gene oscillations (Bmal1, Per1/2, Cry1/2, Dbp, Rev-erbα, and Rorα), inflammatory cytokines (Il-6 and Il-1β), and tight junction proteins (ZO-1 and Occludin). Importantly, TAN robustly enhanced the expression and rhythmicity of BMAL1, which mechanistically drove its therapeutic effects. The critical role of BMAL1 was confirmed by the abolished protective effect of TAN in intestine specific Bmal1 knockout (Bmal1^iKO) mice. In vitro studies in MODE-K cells further demonstrated that siRNA-mediated Bmal1 knockdown abolished TAN-mediated suppression of inflammation and barrier repair in lipopolysaccharide (LPS) treated MODE-K cells. Dual-luciferase reporter assays validated that BMAL1 directly enhanced the Zo-1 and Occludin promoter activities. Notably, TAN exhibited chronotherapeutic efficacy, with ZT2 administration significantly improving UC symptoms, whereas ZT14 dosing showed minimal benefits. In conclusion, TAN ameliorates UC by upregulating BMAL1-dependent inflammation suppression and barrier integrity enhancement. This study underscores circadian clock modulation as a promising strategy for UC management and provides a mechanistic foundation for optimizing timed dosing regimens in clinical translation.