Abstract: This study expanded on previous research by focusing on the regulatory effect of extracellular vesicles (Baevs) of Bifidobacterium animalis on the polarization of colorectal cancer cells and macrophages and the related mechanisms. The results showed that Baevs not only effectively inhibited the proliferation of HT-29 cells in a concentration-dependent manner, but also induced cell apoptosis and increased the level of reactive oxygen species (ROS). In the co-culture environment of HT-29 cells with RAW264.7 macrophages, Baevs reduced the ratio of interleukin-6 (IL-6) to IL-10, indicating that it might reduce the risk of tumor metastasis and recurrence by regulating the tumor immune microenvironment. In addition, through cell transcriptomics analysis, it was found that tumor suppressor genes such as DUSP10 and SOCS1, the mitogen-activated protein kinase (MAPK) pathway and the peroxisome proliferator-activated receptor (PPAR) signaling pathway under co-culture conditions, and inflammatory factors such as IL-17 were all up-regulated, indicating that Baevs could inhibit the proliferation of HT-29 cells, prevent their metastasis, and promote the transformation of tumor-associated macrophages (TAMs) to M1-like phenotype. The findings from this research showed that Baevs could exert its anti-tumor effect by regulating the metabolic pathways of tumor cells and regulating the polarization of TAMs, providing a scientific and theoretical basis for the development of anti-tumor preparations based on probiotic bacterial extracellular vesicles.

Key words: Bifidobacterium animalis; extracellular vesicles; colorectal cancer; macrophages; polarization