Effects of metronidazole on colorectal cancer occurrence and colorectal cancer liver metastases by regulating Fusobacterium nucleatum in mice.

OBJECTIVE: Colorectal cancer (CRC) represents a leading cause of cancer-related deaths. Metronidazole (MNZ) is exceedingly implicated in CRC. This study explored the roles of MNZ in mouse CRC occurrence and liver metastasis (CRLM). METHODS: Male BALB/c nude mice were subjected to CRC and CRLM modeling, orally administration with MNZ (1 g/L) 1 week before modeling, and disease activity index (DAI) evaluation. Fresh stool and anal swab samples were collected on the morning of the 28th day after modeling. The relative expression of Fusobacterium nucleatum (F. nucleatum) DNA was assessed by quantitative polymerase chain reaction. After euthanasia, tumor tissues and liver tissues were separated and the tumor volume and weight change were measured. The liver tissues were stained with hematoxylin-eosin to quantitatively analyze the metastatic liver nodules. Malignant tumor biomarker Ki67 protein levels in liver tissues/DNA from stool samples were detected by immunohistochemistry/high-throughput 16S rRNA gene sequencing. Bioinformatics analysis was performed on the raw sequence data to analyze microbial community richness (Chao1 index, ACE index) and microbial community diversity (Shannon index). RESULTS: The DAI and F. nucleatum DNA relative expression in feces and anal swabs of the CRC and CRLM groups were raised and repressed after MNZ intervention. MNZ repressed tumor occurrence and growth in mice to a certain extent, alleviated CRLM malignant degree (reduced liver metastases and Ki67-positive cell density/number), and suppressed CRC liver metastasis by regulating intestinal flora structure, which affected the intestinal characteristic flora of CRC and CRLM mice. CONCLUSION: MNZ suppressed CRC occurrence and CRLM in mice by regulating intestinal F. nucleatum.