Oral-Gut Microbiome Axis in Gastrointestinal Disease and Cancer

Abstract

It is well-known that microbiota dysbiosis is closely associated with numerous diseases in the human body. The oral cavity and gut are the two largest microbial habitats, playing a major role in microbiome-associated diseases. Even though the oral cavity and gut are continuous regions connected through the gastrointestinal tract, the oral and gut microbiome profiles are well-segregated due to the oral-gut barrier. However, the oral microbiota can translocate to the intestinal mucosa in conditions of the oral-gut barrier dysfunction. Inversely, the gut-to-oral microbial transmission occurs as well in inter- and intrapersonal manners. Recently, it has been reported that oral and gut microbiomes interdependently regulate physiological functions and pathological processes. Oral-to-gut and gut-to-oral microbial transmissions can shape and/or reshape the microbial ecosystem in both habitats, eventually modulating pathogenesis of disease. However, the oral-gut microbial interaction in pathogenesis has been underappreciated to date. Here, we will highlight the oral-gut microbiome crosstalk and its implications in the pathogenesis of the gastrointestinal disease and cancer. Better understanding the role of the oral-gut microbiome axis in pathogenesis will be advantageous for precise diagnosis/prognosis and effective treatment.

Keywords: GI cancer; GI disease; gut microbiome; oral microbiome; oral–gut microbiome axis.

Figure 1

Local and systemic effects of oral microbiome. The oral dysbiosis can regulate the pathological processes in the oral cavity, such as dental caries, periodontitis, and OSCC. The altered oral microbiota profiles can further modulate systemic diseases, including Alzheimer’s disease, diabetes, and cardiovascular disease, beyond the local impacts.

Figure 2

Oral–gut microbiome axis. The oral microbiota can translocate to the gut in conditions of the oral–gut barrier disruption. Likewise, the gut microbes transmit to the oral cavity in both intra- and interpersonal manners, particularly related to poor hygienic conditions. This bidirectional interaction between oral and gut microbiomes develops the microbial ecosystems in both habitats through either competition or cooperation, eventually regulating the pathophysiological processes in the gastrointestinal (GI) tract.