Oral-Intestinal Microbiota in Colorectal Cancer: Inflammation and Immunosuppression

Abstract

It is widely recognized that microbial disorders are involved in the pathogenesis of many malignant tumors. The oral and intestinal tract are two of the overriding microbial habitats in the human body. Although they are anatomically and physiologically continuous, belonging to the openings at both ends of the digestive tract, the oral and intestinal microbiome do not cross talk with each other due to a variety of reasons, including intestinal microbial colonization resistance and chemical barriers in the upper digestive tract. However, this balance can be upset in certain circumstances, such as disruption of colonization resistance of gut microbes, intestinal inflammation, and disruption of the digestive tract chemical barrier. Evidence is now accruing to suggest that the oral microbiome can colonize the gut, leading to dysregulation of the gut microbes. Furthermore, the oral-gut microbes create an intestinal inflammatory and immunosuppressive microenvironment conducive to tumorigenesis and progression of colorectal cancer (CRC). Here, we review the oral to intestinal microbial transmission and the inflammatory and immunosuppressive microenvironment, induced by oral-gut axis microbes in the gut. A superior comprehension of the contribution of the oral-intestinal microbes to CRC provides new insights into the prevention and treatment of CRC in the future.

Emerging role of human microbiome in cancer development and response to therapy: special focus on intestinal microflora

“…This imbalanced gut microbiota may have been attributed to gastrointestinal diseases and cancer. The association between oral microbiota and tumor development is documented by several reports [ 48 , 49 ]. For instance, the genomic analysis of colorectal adenocarcinoma tissue revealed the F. nucleatum and other Fusobacterium species enrichment [ 50 ].…”

The Urinary Microbiome: Role in Bladder Cancer and Treatment

“…Because the NF-κB cascade is a central link in the communication within host-microbial interactions during the occurrence and development of BC, it induces an inflammatory microenvironment by promoting the production of pro-inflammatory cytokines, containing TNF-α, IL-1β, IL-6, and IL-8 [ 135 , 136 ]. An epidemiologic study of bladder carcinoma patients from ten geographic areas of the United States demonstrated that urinary tract infections were strongly related to squamous cell carcinoma [ 137 ].…”

New Insights into the Relationship between Gut Microbiota and Radiotherapy for Cancer

“…Overall, oral and gut microbes interact through gut-oral and fecal-oral pathways, which, in turn, can form and/or reshape the microbial ecosystems in both habitats, ultimately regulating the body’s physiological and pathological processes. The oral pathogen(s) can disturb the barrier function of the intestine and invade the gut mucosa, which causes intestinal dysbacteriosis and chronic inflammation, eventually resulting in inflammatory bowel disease (IBD) [ 107 , 108 ]. A number of studies have also found that a series of oral bacteria are closely associated with CRC, by analyzing the microbial composition of the oral cavity, colonic mucosal tissue, and fecal samples from patients with CRC [ 109 ], implying that the cross-talk between microbes may also be an important mechanism of tumorigenesis in the digestive system.…”

“…The intestinal inflammatory and immunosuppressive microenvironment created by oral-gut microbes is a key factor in the development and progression of CRC [ 108 ]. Wang et al [ 156 ] investigated the theory that sodium butyrate (NaB), a major product of gut microbial fermentation, could modulate the gut microbiota in mice with CRC liver metastasis (CLM) and improve the host immune response.…”