The gastrointestinal microbiota and colorectal cancer

Abstract

The human gut is home to a complex and diverse microbiota that contributes to the overall homeostasis of the host. Increasingly, the intestinal microbiota is recognized as an important player in human illness such as colorectal cancer (CRC), inflammatory bowel diseases, and obesity. CRC in itself is one of the major causes of cancer mortality in the Western world. The mechanisms by which bacteria contribute to CRC are complex and not fully understood, but increasing evidence suggests a link between the intestinal microbiota and CRC as well as diet and inflammation, which are believed to play a role in carcinogenesis. It is thought that the gut microbiota interact with dietary factors to promote chronic inflammation and CRC through direct influence on host cell physiology, cellular homeostasis, energy regulation, and/or metabolism of xenobiotics. This review provides an overview on the role of commensal gut microbiota in the development of human CRC and explores its association with diet and inflammation.

Gut microbiome compositional and functional differences between tumor and non-tumor adjacent tissues from cohorts from the US and Spain

“…These results correlate with our hypothesis that the specific tumor microenvironment could modulate the tumor microbiome resulting in the selection of similar taxa resistant to conditions of hypoxia, occurring due to the insufficient vascularization, low pH and depletion of glucose and other nutrients. 51,52 A number of research studies have analyzed the microbiome composition of tissue and fecal samples from CRC patients 41 and our study alineates in general with their findings. In our study, however, although we observed a lower phylogenetic diversity and richness in tumor tissues compared to adjacent tissues, Principal Coordinate Analysis of weighted and unweight Unifrac matrices and ANOSIM analysis showed no extensive differences in composition between adjacent and tumor microbial communities in both cohorts, which could be due in part to the fact that adjacent tissues, although non-tumoral, are in close proximity to tumors sharing the same intestinal microenvironment.…”

“…Studies have increasingly addressed the role of the gut microbiome in CRC since a dysbiotic state has been reported in the stools and tissue-adherent microbiome of adenoma and CRC patients (recently reviewed by Keku et al 41 ). Our study aimed to test the hypothesis that, regardless of the geographic origin, the tumor microenvironment could modulate the microbiota in situ generating compositional and functional similarities in the tumor microbiomes.…”

Luminally expressed gastrointestinal biomarkers

“…A biomarker is defined as an objectively measurable characteristic that is objectively measured and evaluated as an indicator of normal biologic or pathogenic processes, or pharmacological responses to a specified therapeutic intervention [1]- [3]. Ideally it should be measured from easily obtained bodily fluids and waste such as plasma, serum, urine and faecal matter for improved patient acceptance; if not feasible then invasive techniques such as tissue biopsy are acceptable.…”

Historical perspective: gut dysbiosis and hypertension

“…The microbiome influences Phase I and Phase II drug metabolism (43) . In recent years, a number of studies have pointed to links between the gut microbiota and pathophysiology of diabetes (8,36), cancer (27), bowel disorders (9,15), liver disease (46), immune conditions (33), and the metabolic syndrome (12). Increased understanding of these processes may unravel tremendous potential for therapeutics.…”