Table 2

- Bacterial metabolites and colorectal cancer.

Bacterial metabolitesExamplesEffect on CRC
SCFAsButyrate, propionate, and acetate- Immunomodulation via regulation of AhR
- Rebalance gut microbiota diversity and composition
- Inhibit NF-kB and activate apoptosis
- Antitumor effect via modulation of Tc17 cells and CTLs
- Inhibit ERK1/2, causing tumor growth disruption
- Induce ROS activity and decrease glucose oxidation
- Induce HDAC
Bile acidPrimary and secondary bile acids- Bind to FXR as CRC inhibitor
- Promote cancer initiation by upregulating IL-8, ERK1/2, and inhibiting STAT3 phosphorylation
- Activate MAPK pathway via upregulation of uPAR and calcium signaling
Lactate- Creates an acidification environment
- Stimulates angiogenic response to oxygen transfer, glucose delivery and nutrition delivery that promote CRC invasion, proliferation, and migration
Succinate- Inhibits CRC proliferation and induces CRC metastasis via SUCNR1 signaling
Protein-derived metabolitesHO-PAA, PAA, phenol (produced from tyrosine), acetaldehyde, H2S, and NOCs- Hydrogen sulfide inhibits the anti-inflammatory outcome in CRC cell lines by activating NF-kB pathway signaling
- NOCs contribute to K-ras mutation, which drives CRC proliferation

SCFAs: short-chain fatty acids, HO-PAA: 4-hydroxyphenylacetic acid, PAA: phenylacetic acid, H2S: hydrogen sulfide, NOCs: N-nitroso compounds, AhR: aryl hydrocarbon receptor, NF-kB: nuclear factor kappa B, Tc17: IL-17-secreting CD8 T cells), CTLs: cytotoxic T lymphocytes, ERK1/2: protein kinases 1 and 2, ROS: reactive oxygen species, HDAC: histone deacetylases, FXR: farnesoid X receptor, CRC: colorectal cancer, IL: interleukin, STAT3: Signal Transducer and Activator of Transcription 3, MAPK: mitogen-activated protein kinase, uPAR: urokinase plasminogen activator, SUCNR1: succinate receptor 1, K-ras: Kirsten rat sarcoma viral oncogene homolog