Role of Fusobacterium nucleatum in intestinal tumorigenesis

BACKGROUND Colorectal cancer is one of the most common malignant tumors and an important associated-factor is intestinal microbiota. This may enhance the carcinogenicity by proliferation and differentiation of epithelial cells and by decreasing immune response to pathogenic organisms. The aim of the study is to analyze the link between the presence of Fusobacterium nucleatum (FN) in a series of matched oral brushing, colon adenomas/carcinomas and adjacent mucosa, and finally to elucidate the FN dissemination mechanism from oral cavity to colon. FN is detected in saliva, especially in smokers, with its quantities increased in patients with gingivitis and periodontitis, compared to the healthy controls. METHODS Patients are recruited at endoscopy or surgery in private Hospital “Villa Serena. Three questionnaires are administered to patients: about lifestyle, food and oral health. Intestinal colon adenomas or carcinomas biopsies are obtained from patients undergoing to colonscopy or surgery. At same time adjacent colonic mucosa was collected. As negative control we recruited normal colon mucosa from individuals undergoing to control colonscopy. The day before endoscopy or surgery a brushing of the oral cavity from patients is carried out. Genomic DNAs from brushing and tissue are extracted using a DNA kit (Zymo). PCR amplifications of bacterial 16S rDNA and FN fadA gene, a region identified to bind host cells and considered the best-characterized virulence factor identified, are performed. RESULTS The molecular analysis revealed FN presence in 50% of colon adenomas/carcinomas analyzed (6/12); similarly in adjacent mucosa. FN was also detected in 2 out of 5 oral swabs analyzed, but at first analysis in a more abundant way compared to tissues. Intriguingly these 2 patients are smokers and affected by perodontal disease. The quantitative analysis of the abundance of FN by Real-Time PCR is in progress. Normal colonic mucosa analyzed showed FN absence. CONCLUSIONS These results show FN presence in patients oral cavity and colon tumor tissue, and absence in control individuals normal colonic mucosa. The progress of patients recruitment will allow to shed light on fadA levels and their field effect. The final data may lead to the identification of biomarkers for the early diagnosis and prevention of CRC.