Colorectal Cancer

Metallomic Signature#

The metallomic profile of CRC from^{[1]Recent advances in the application of metallomics in diagnosis and prognosis of human cancerYan Zhang, Jie He, Jiao Jin et al. · 2022Open reference 1 ↓} and supporting literature:

The Cu/Zn Ratio#

The copper/zinc ratio was first proposed as a CRC biomarker and captures the two most consistent metallomic changes—copper elevation and zinc depletion. Elevated copper displaces zinc from metallothionein due to higher binding affinity, simultaneously impairing copper/zinc superoxide dismutase (Cu/Zn-SOD) antioxidant defense and creating a pro-oxidant environment favorable to carcinogenesis.

This ratio is now documented as elevated across breast, prostate, lung, and thyroid cancers as well.

Metal-Carcinogenesis Mechanisms#

^{[2]Adverse Human Health Effects of Chromium by Exposure Route: A Comprehensive Review Based on Toxicogenomic ApproachDong Yeop Shin, Sang Min Lee, Yujin Jang et al. · 2023Open reference 2 ↓} demonstrated that chromium (Cr)(VI) ingestion causes DNA damage and metastasis through hub genes VEGFA, EGFR, APP, SGK1, JUN, and TLR2—directly relevant to colorectal carcinogenesis. Cadmium and arsenic converge on similar pathways of oxidative DNA damage, epigenetic modification, and DNA repair disruption.

Heavy metal exposure also depletes SCFA-producing bacteria, removing a key protective mechanism against carcinogenesis.

Microbiome Signatures#

Fusobacterium nucleatum as Key Pathobiont#

Fusobacterium nucleatum is the most consistently enriched bacterium in CRC across global cohorts.^{[3]Towards the Human Colorectal Cancer MicrobiomeMarchesi JR, Dutilh BE, Hall N et al. · 2011Open reference 3 ↓[4]Microbiota disbiosis is associated with colorectal cancerZhiguang Gao, Bomin Guo, Renyuan Gao et al. · 2015Open reference 4 ↓} Its pro-tumorigenic mechanisms are multifaceted. FadA adhesin disrupts E-cadherin, activating beta-catenin/Wnt signaling and promoting proliferation.^{[5]Immune System, Microbiota, and Microbial Metabolites: The Unresolved Triad in Colorectal Cancer MicroenvironmentHanus M, Parada-Venegas D, Landskron G et al. · 2021Open reference 5 ↓}

Fap2 protein binds TIGIT receptor on NK cells, inhibiting anti-tumor immunity, and binds Gal-GalNAc on tumor cells for selective colonization.^{[5]Immune System, Microbiota, and Microbial Metabolites: The Unresolved Triad in Colorectal Cancer MicroenvironmentHanus M, Parada-Venegas D, Landskron G et al. · 2021Open reference 5 ↓}

LPS–TLR4 interaction activates NF-kB signaling, autophagy, and chemotherapy resistance (5-FU). miR21/TLR4/NF-kB axis and ULK1/ATG7 autophagy pathway activation.

F. nucleatum abundance increases progressively through the adenoma-carcinoma sequence, validated by qPCR in cohorts exceeding 400 patients.^{[6]Features of combined gut bacteria and fungi from a Chinese cohort of colorectal cancer, colorectal adenoma, and post-operative patientsXiaopeng Li, Jiahui Feng, Zhanggui Wang et al. · 2023Open reference 6 ↓}

Bile Acid-Microbiome-Cancer Axis#

Secondary bile acids (deoxycholic acid/DCA and lithocholic acid/LCA), converted from primary bile acids by gut bacterial 7-alpha dehydroxylation, are potent CRC promoters. Their carcinogenic mechanisms include.

ROS/RNS generation via NAD(P)H oxidase activation and mitochondrial membrane disruption. NF-kB activation determining intestinal epithelial cell fate; persistent activation drives colitis-associated CRC. DNA damage through oxidative base modification and disruption of base excision repair.

Cancer stem cell induction: DCA/LCA induce CSC markers (CD44, CD166, ALDHA1) and pluripotency genes (KLF4, Nanog, OCT4, SOX2) through M3R/Wnt/beta-catenin signaling, with 12-15 fold increases in c-Myc.

EMT promotion: MMP upregulation (MMP1, MMP3, MMP10) and mesenchymal marker activation. Drug resistance: upregulation of ABCB1 and ABCG2 transporters in bile acid-exposed colonocytes.

High dietary fat and red meat consumption increase secondary bile acid levels. Western diet populations bear up to 60% of the global CRC burden. Vitamin D deficiency compounds the risk, as VDR functions as a secondary bile acid receptor (LCA) and activates detoxification pathways via PXR/SXR.

SCFA Receptor Network#

Three GPCRs mediate SCFA tumor suppression. FFAR2/GPR43: promotes IL-18 secretion via NLRP3 inflammasome; enhances Treg differentiation; deficiency promotes tumorigenesis via Wnt/beta-catenin. FFAR3/GPR41: expressed on intestinal epithelial and immune cells.

HCAR2/GPR109A: butyrate-specific; suppresses carcinogenesis; knockdown accelerates colonic Metal-Driven Inflammation and cancer progression.

Fungal Microbiome (Mycobiome) in CRC#

Fungi represent ~0.1% of gut microorganisms but play important roles in CRC.

Candida albicans and Saccharomyces cerevisiae show significantly increasing abundance in CRC vs healthy controls, validated by qPCR (n=402). Basidiomycota/Ascomycota ratio increases with disease progression through the adenoma-carcinoma sequence. Bacterial-fungal antagonistic interactions (R = -0.17 to -0.32) suggest disruption of cross-kingdom balance contributes to CRC.

Fungal beta-glucans can be protective (upregulating tight junction proteins Claudin-1 and ZO-1), while C. albicans can be destructive (GelE-mediated E-cadherin degradation). Dectin-1 and TLR4 signaling are essential for anti-fungal immunity in the gut; C. albicans can inhibit NLRP3/NLRP6 inflammasomes.

Iron and Ferroptosis in CRC#

Iron intersects with CRC through multiple pathways.

Heme iron from red meat generates N-nitroso compounds (NOCs) causing KRAS mutations (G>A transitions at codons 12/13) and oxidative DNA damage. Ferroptosis (iron-dependent lipid peroxidation cell death) represents both a vulnerability and a defense mechanism in CRC cells; GPX4 is the key ferroptosis regulator.

Iron dysregulation parallels the mitochondrial membrane disruption caused by secondary bile acids. Metal-induced dysbiosis depletes butyrate-producing Firmicutes, reducing antioxidant defenses that normally protect against iron-mediated lipid peroxidation.

Protective Factors#

Dietary fiber: metabolized by gut microbiome into SCFAs (butyrate, propionate, acetate); maintains microbial diversity; 20-30g daily recommended.^{[10]Emerging Evidence on the Effects of Dietary Factors on the Gut Microbiome in Colorectal CancerAppunni S, Rubens M, Ramamoorthy V et al. · 2021Open reference 10 ↓[11]Diet, microbiota, and dysbiosis: a 'recipe' for colorectal cancerKishore Vipperla, Stephen J. O'Keefe · 2016Open reference 11 ↓}

Mediterranean diet: multi-component protection via n-3 fatty acids (COX-2/TNF-alpha suppression), fiber/butyrate (NF-kB inhibition), olive oil (COX-2/iNOS/STAT3 reduction), and polyphenols (IL-1beta/IL-6/TNF-alpha reduction).^{[12]Mediterranean Diet: Prevention of Colorectal CancerMicah G. Donovan, Ornella I. Selmin, Tom C. Doetschman et al. · 2017Open reference 12 ↓[13]Design of the Building Research in CRC Prevention (BRIDGE-CRC) Trial: A 6-Month, Parallel Group Mediterranean Diet and Weight Loss Randomized Controlled Lifestyle Intervention Targeting the Bile Acid-Gut Microbiome Axis to Reduce Colorectal Cancer Risk Among African American/Black Adults with ObesityAndrew McLeod, Patricia Wolf, Robert S. Chapkin et al. · 2023Open reference 13 ↓}

Polyphenols: function as prebiotics increasing Bifidobacterium, Lactobacillus, and Akkermansia; curcumin increases Lactobacillales and decreases Coriobacteriales in CRC models.^{[10]Emerging Evidence on the Effects of Dietary Factors on the Gut Microbiome in Colorectal CancerAppunni S, Rubens M, Ramamoorthy V et al. · 2021Open reference 10 ↓}

Risk Factors#

Red and processed meat: generates NOCs, heterocyclic amines, and heme iron-mediated genotoxicity; gut microbiome metabolizes these into more harmful compounds. High-fat diet: increases secondary bile acid production via microbial 7-alpha dehydroxylation. Alcohol: metabolized to acetaldehyde (DNA-damaging intermediate) via gut microbiome pathways; increases Bacteroidetes and Ruminococcaceae.

Low-fiber Western diet: predisposes to CRC via reduced SCFA production and increased pathobiont abundance.

Comorbidities#

Inflammatory Bowel Disease (IBD)—IBD is the strongest established risk factor for CRC; chronic colonic inflammation drives the inflammation-dysplasia-carcinoma sequence; shared Fusobacterium nucleatum enrichment and SCFA producer depletion.

Crohn's Disease—Crohn's colitis confers a 2-3x increased CRC risk; shared NF-kB/Wnt signaling crosstalk, barrier dysfunction, and Enterobacteriaceae bloom; the same metal-driven dysbiosis cascade underlies both.

Obesity—obesity increases CRC risk by 30%; shared high-fat diet, elevated secondary bile acids (DCA/LCA), and gut dysbiosis; adipokine dysregulation promotes tumor microenvironment inflammation.

Type 2 Diabetes—T2D increases CRC risk by 20-30%; shared insulin resistance, hyperinsulinemia (IGF-1 axis promotes cell proliferation), and SCFA depletion; metformin may be protective through AMPK activation and microbiome modulation.