Objective:To investigate the effects of propionic acid produced by Akkermansia muciniphila on the radiosensitivity of colorectal cancer and the underlying mechanism. Methods:Normal human colon mucosal epithelial cells (NCM460) were used to determine the appropriate concentration of propionic acid. Human colorectal cancer cells (HCT-8) were treated with A. muciniphila-conditioned medium or propionic acid, followed by exposure to 6 Gy γ-ray irradiation, and cell survival and proliferation were measured by clone formation assay and Cell Counting Kit-8 (CCK-8) assay, respectively. A mouse model of colorectal cancer was established using azoxymethane/dextran sodium sulfate. The mice were divided into control model group, irradiation group, and irradiation+ propionic acid group. Their body weight, colorectal length, tumor count, and tumor area were recorded. The radiosensitizing effect of propionic acid was assessed with HE staining, immunohistochemical staining, and enzyme-linked immunosorbent assay. The mechanism was explored by using RT-PCR and flow cytometry. Results:CCK-8 assay showed that 1-mmol/L propionic acid had no significant effect on the proliferation of NCM460 cells ( P>0.05), which was used for subsequent experiments. Pretreated with A. muciniphila-conditioned medium or propionic acid, the survival and proliferation abilities of irradiated HCT cells were significantly decreased ( t=3.14-34.98, P<0.05). Compared with the irradiation group, the colorectal cancer mice in the irradiation+ propionic acid group showed a significantly longer colorectal length ( t=3.50, P<0.05) and a significantly smaller number of tumors ( t=3.48, P<0.05); the two groups had significantly smaller tumor areas than the control model group ( t=5.97, 7.30, P<0.05). HE staining and immunohistochemical staining showed that propionic acid restored colorectal structure, and decreased Ki67 expression in colorectal tissue ( t=14.50, 3.40, P<0.05). Propionic acid treatment significantly reduced the levels of the inflammatory factors interleukin-6 and tumor necrosis factor-α, as compared with the mice receiving irradiation alone ( t=4.86, 5.06, P<0.05). Irradiation plus propionic acid treatment significantly increased p53 expression and significantly aggravated G 2/M phase block and cell apoptosis ( t=20.35, 13.05, P<0.05). Conclusions:The A. muciniphila metabolite propionic acid plays a sensitizing role in radiation therapy for colorectal cancer by promoting G 2/M phase block and apoptosis in colorectal cancer cells.

Objective:To investigate the effects of propionic acid produced by Akkermansia muciniphila on the radiosensitivity of colorectal cancer and the underlying mechanism. Methods:Normal human colon mucosal epithelial cells (NCM460) were used to determine the appropriate concentration of propionic acid. Human colorectal cancer cells (HCT-8) were treated with A. muciniphila-conditioned medium or propionic acid, followed by exposure to 6 Gy γ-ray irradiation, and cell survival and proliferation were measured by clone formation assay and Cell Counting Kit-8 (CCK-8) assay, respectively. A mouse model of colorectal cancer was established using azoxymethane/dextran sodium sulfate. The mice were divided into control model group, irradiation group, and irradiation+ propionic acid group. Their body weight, colorectal length, tumor count, and tumor area were recorded. The radiosensitizing effect of propionic acid was assessed with HE staining, immunohistochemical staining, and enzyme-linked immunosorbent assay. The mechanism was explored by using RT-PCR and flow cytometry. Results:CCK-8 assay showed that 1-mmol/L propionic acid had no significant effect on the proliferation of NCM460 cells ( P>0.05), which was used for subsequent experiments. Pretreated with A. muciniphila-conditioned medium or propionic acid, the survival and proliferation abilities of irradiated HCT cells were significantly decreased ( t=3.14-34.98, P<0.05). Compared with the irradiation group, the colorectal cancer mice in the irradiation+ propionic acid group showed a significantly longer colorectal length ( t=3.50, P<0.05) and a significantly smaller number of tumors ( t=3.48, P<0.05); the two groups had significantly smaller tumor areas than the control model group ( t=5.97, 7.30, P<0.05). HE staining and immunohistochemical staining showed that propionic acid restored colorectal structure, and decreased Ki67 expression in colorectal tissue ( t=14.50, 3.40, P<0.05). Propionic acid treatment significantly reduced the levels of the inflammatory factors interleukin-6 and tumor necrosis factor-α, as compared with the mice receiving irradiation alone ( t=4.86, 5.06, P<0.05). Irradiation plus propionic acid treatment significantly increased p53 expression and significantly aggravated G 2/M phase block and cell apoptosis ( t=20.35, 13.05, P<0.05). Conclusions:The A. muciniphila metabolite propionic acid plays a sensitizing role in radiation therapy for colorectal cancer by promoting G 2/M phase block and apoptosis in colorectal cancer cells.