Biliary bile acid profiles in familial adenomatous polyposis

Factors Determining Colorectal Cancer: The Role of the Intestinal Microbiota

The gastrointestinal tract, in particular the colon, holds a complex community of microorganisms, which are essential for maintaining homeostasis. However, in recent years, many studies have implicated microbiota in the development of colorectal cancer (CRC), with this disease considered a major cause of death in the western world. The mechanisms underlying bacterial contribution in its development are complex and are not yet fully understood. However, there is increasing evidence showing a connection between intestinal microbiota and CRC. Intestinal microorganisms cause the onset and progression of CRC using different mechanisms, such as the induction of a chronic inflammation state, the biosynthesis of genotoxins that interfere with cell cycle regulation, the production of toxic metabolites, or heterocyclic amine activation of pro-diet carcinogenic compounds. Despite these advances, additional studies in humans and animal models will further decipher the relationship between microbiota and CRC, and aid in developing alternate therapies based on microbiota manipulation.

The interrelationships of the gut microbiome and inflammation in colorectal carcinogenesis

The cause of colorectal cancer (CRC) is multifactorial, with genetic, molecular, inflammatory, and environmental risk factors. Recently, the gut microbiota has been recognized as a new environmental contributor to CRC in both animal models and human studies. An additional interplay of the gut microbiome with inflammation is also evident in studies that have shown that inflammation alone or the presence of bacteria/bacterial metabolites alone is not enough to promote tumorigenesis. Rather, complex interrelationships with the gut microbiome, inflammation, genetics, and other environmental factors are evident in progression of colorectal tumors.

The role of gut microbiota in the pathogenesis of colorectal cancer

The human gastrointestinal tract harbors a complex and abundant microbial community that can reach levels as high as 10(13)-10(14) microorganisms in the colon. These microorganisms are essential to a host's well-being in terms of nutrition and mucosa immunity. However, numerous studies have also implicated members of the colonic microbiota in the development of colorectal cancer (CRC). While CRC involves a genetic component where damaged DNA and genetic instability initiates a malignant transformation, environmental factors can also contribute to the onset of CRC. Furthermore, considering the constant exposure of the colonic mucosa to the microbiome and/or its metabolites, the mucosa has long been proposed to contribute to colon tumorigenesis. However, the mechanistic details of these associations remain unknown. Fortunately, due to technical and conceptual advances, progress in characterizing the taxonomic composition, metabolic capacity, and immunomodulatory activity of human gut microbiota have been made, thereby elucidating its role in human health and disease. Furthermore, the use of experimental animal models and clinical/epidemiological studies of environmental etiological factors has identified a correlation between gut microbiota composition and gastrointestinal cancers. Bacteria continuously stimulate activated immunity in the gut mucosa and also contribute to the metabolism of bile and food components. However, the highest levels of carcinogen production are also associated with gut anaerobic bacteria and can be lowered with live lactobacilli supplements. In this review, evidence regarding the relationship between microbiota and the development of CRC will be discussed, as well as the role for microbial manipulation in affecting disease development.