P1321 Emulsifier carboxymethylcellulose ameliorates high-fat diet-associated colitis via inhibition of deoxycholic acid and regulation of mitochondrial oxidative phosphorylation of colonic macrophages

Background High-fat diet (HFD) is closely associated with the development and progression of Inflammatory Bowel Disease (IBD), with bile acids metabolism playing a critical role in this process. Safe and effective intervention strategies are urgently needed in clinic. This study investigates the effects and underlying mechanisms of food emulsifier carboxymethylcellulose (CMC) on HFD-associated colitis. Methods We investigated the actions of CMC on HFD-associated colitis mouse models through in vivo/in vitro experiments, multi-omics integrated with bioinformatics analysis, utilizing various colitis mouse models, and a monocyte/macrophage-specific Ndufs4 knockout mouse model (NDUFS4: a subunit of mitochondrial respiratory chain Complex I). Results In vivo: CMC significantly ameliorated HFD-associated acute colitis phenotypes. And CMC induces a significant decrease in gut microbiota Bacteroides acidifaciens and its metabolite secondary bile acids, especially deoxycholic acid (DCA). Antibiotics-treated model and Bacteroides acidifaciens transfer model supported a microbiota-dependent effect of CMC. Furthermore, CMC reversed the DCA-aggravated acute colitis phenotype. Single-cell sequencing revealed that in HFD-associated colitis, macrophages were among the increased immune cells, contributing the most to changes in the numbers of pathways and inflammatory factors. Mechanistically, single-cell sequencing revealed a significant increase in M1-like macrophages (Mac_CD86hiS100a8hi and Mac_CD86hi), accompanied by downregulation of the oxidative phosphorylation (OXPHOS) pathway. Further validation using IF and RT-qPCR revealed that CMC decreased the infiltration of M1 macrophages and associated cytokines Nos2 and IL-1β, while M2 macrophages and cytokines Arg2 and IL-10 showed no change. Meanwhile, CMC elevated colonic mucosal oxidative phosphorylation, increasing ATP levels and reducing ROS. In the Ndufs4fl/fl LysM-Cre +/- knockout mice, the protective effect of CMC against HFD-associated colitis phenotypes was abolished. In vitro: Mechanistically, RNA sequencing demonstrated that DCA downregulated the oxidative phosphorylation pathway in LPS-treated primary bone marrow-derived macrophages (BMDMs). Further validation using Seahorse and biochemical assays revealed that DCA damaged oxidative phosphorylation in LPS-treated Raw264.7 cells, decreasing OCR and ATP levels. Additionally, DCA decreased the Ndufs4 mRNA expression. Conclusion Collectively, our findings demonstrated that CMC alleviates HFD-associated colitis via reducing DCA levels and restoring mitochondrial oxidative phosphorylation of colonic macrophages, providing new insights into diet-related bile acids dysregulation in IBD. References: none Conflict of interest: Dr. Shao, Limei: No conflict of interest Liu, Yingying: No conflict of interest Lv, Wei: No conflict of interest Liu, Ling: No conflict of interest Graphical abstract