Didymin ameliorates ulcerative colitis-associated secondary liver damage by facilitating Notch1 degradation

Didymin is a dietary flavonoid originally discovered by our group as a potent anti-ulcerative colitis (UC) agent. However, whether didymin plays a protective role in UC-associated inflammatory liver injury is still unclear. This study aimed to evaluate the therapeutic potential of didymin on UC-associated inflammatory liver injury and explore the underlying mechanism. Colitis model was established in C57BL/6 mice by exposure to DSS, and didymin was administrated intragastrically for consecutive 10 days. The inflammatory liver injury was assessed by levels of alanine aminotransferase (ALT) and aspartate transaminase (AST) in serum and histopathological damage in the liver. In vitro Kupffer cells and RAW264.7 cells challenged with lipopolysaccharides (LPS) were used to explore the modulatory activity of didymin on pro-inflammatory cytokines secretion and Notch1 signaling pathway activation. Didymin significantly mitigated liver coefficiency, ALT and AST levels in serum, and the hepatic histopathological damage caused by DSS-induced acute and chronic colitis. The mRNA expressions of pro-inflammatory factors including Tnf, Il1, and Il6 in liver tissues, Kupffer cells, and RAW264.7 cells stimulated by the influx of LPS was significantly deprived after didymin treatment. Mechanistically, didymin obstructed the protein expression, nuclear translocation of notch intracellular domain 1 (Notch1-ICD) and mRNA expression of hairy and enhancer of split 1 (Hes1). Further, the inhibitory mechanism of the Notch1-Hes1 pathway was dependent on c-Cbl-mediated Notch1-ICD lysosomal degradation. Our study verified for the first time that didymin could prevent UC-associated diseases, such as inflammatory liver injury, and the mechanism was related to facilitating Notch1 lysosomal degradation rather than proteasome degradation via promoting protein expression of c-Cbl in macrophages. Our findings that the inhibition of Notch1 signaling transduction helps to alleviate UC-associated liver injury provides possible therapeutics for the treatment of colitis and also furnishes a research paradigm for the study of flavonoids with similar structures.