The role of gut microbiota in the pathogenesis of colorectal cancer

The gut microbiota and the metabolic health of the host

PURPOSE OF REVIEW

It is clear that the metabolic activities of the gut microbiota significantly impact upon human health and disease.

RECENT FINDINGS

Recent analyses have correlated alterations in microbial community structure with the onset of diabetes, obesity and cardiovascular disease as well as inflammatory conditions of the intestine. This work has demonstrated the influence of diet upon the microbiota in disease states and has identified a number of microbial metabolites that orchestrate the crucial aspects of the host-microbe dialog. The microbial production of short-chain fatty acids, trimethylamine, acetaldehyde and inflammatory mediators has been shown to significantly impact upon the metabolic health of the host through pathways that influence satiety, gut permeability and immune function. In the small intestine, microbial metabolism alters the host bile acid profile affecting the interactions with dedicated bile acid receptors (including FXR and TGR5) to influence both local and systemic cellular responses. Recent findings have, therefore, identified specific microbiota profiles and metabolites as predictors of disease risk as well as determining the microbial species (such as Akkermansia muciniphila and Bilophila wadsworthia) which correlate with health and disease.

SUMMARY

This work identifies the microbiota as an important target for new diagnostic and therapeutic approaches in metabolic disease.

β-Glucuronidase and β-glucosidase activity and human fecal water genotoxicity in the presence of probiotic lactobacilli and the heterocyclic aromatic amine IQ in vitro

The aim of the study was to assess the genotoxicity of fecal water (FW) and the activity of fecal enzymes (β-glucuronidase and β-glucosidase) after incubation with 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ) and probiotic lactobacilli: Lb. casei 0900, Lb. casei 0908, and Lb. paracasei 0919. Our results show that the carcinogen IQ greatly increased FW genotoxicity (up to 16.92 ± 3.03 U/mg) and the activity of fecal enzymes (up to even 1.4 ± 0.16 U/mg) in 15 individuals (children, adults and elderly). After incubation with IQ, the activity of β-glucuronidase was reduced by Lactobacillus bacteria by 76.0% (Lb. paracasei 0908) in the FW of children, and by 82.0% (Lb. paracasei 0919) in the elderly; while that of β-glucosidase was reduced by 55.0% in children (Lb. casei 0908) and 90.0% (Lb. paracasei 0919) in elderly subjects. Lactobacilli decreased the genotoxicity of FW after incubation with IQ to the greatest extent in adults (by 64.5%). Probiotic lactobacilli, in the presence of IQ, efficiently inhibits activity of fecal enzymes to the level of control. Genotoxicity inhibition depends on the person's age, its individual microbiota and diet.

Review of mass spectrometry-based metabolomics in cancer research

Metabolomics, the systematic investigation of all metabolites present within a biologic system, is used in biomarker development for many human diseases, including cancer. In this review, we investigate the current role of mass spectrometry-based metabolomics in cancer research. A literature review was carried out within the databases PubMed, Embase, and Web of Knowledge. We included 106 studies reporting on 21 different types of cancer in 7 different sample types. Metabolomics in cancer research is most often used for case-control comparisons. Secondary applications include translational areas, such as patient prognosis, therapy control and tumor classification, or grading. Metabolomics is at a developmental stage with respect to epidemiology, with the majority of studies including less than 100 patients. Standardization is required especially concerning sample preparation and data analysis. In the second part of this review, we reconstructed a metabolic network of patients with cancer by quantitatively extracting all reports of altered metabolites: Alterations in energy metabolism, membrane, and fatty acid synthesis emerged, with tryptophan levels changed most frequently in various cancers. Metabolomics has the potential to evolve into a standard tool for future applications in epidemiology and translational cancer research, but further, large-scale studies including prospective validation are needed.

A potential role of probiotics in colorectal cancer prevention: review of possible mechanisms of action

A number of investigations, mainly using in vitro and animal models, have demonstrated a wide range of possible mechanisms, by which probiotics may play a role in colorectal cancer (CRC) prevention. In this context, the most well studied probiotics are certain strains from the genera of lactobacilli and bifidobacteria. The reported anti-CRC mechanisms of probiotics encompass intraluminal, systemic, and direct effects on intestinal mucosa. Intraluminal effects detailed in this review include competitive exclusion of pathogenic intestinal flora, alteration of intestinal microflora enzyme activity, reduction of carcinogenic secondary bile acids, binding of carcinogens and mutagens, and increasing short chain fatty acids production. Reduction of DNA damage and suppression of aberrant crypt foci formation have been well demonstrated as direct anti-CRC effects of probiotics on intestinal mucosa. Existing evidence clearly support a multifaceted immunomodulatory role of probiotics in CRC, particularly its ability to modulate intestinal inflammation, a well known risk factor for CRC. The effectiveness of probiotics in CRC prevention is dependent on the strain of the microorganism, while viability may not be a prerequisite for certain probiotic anticancer mechanisms, as indicated by several studies. Emerging data suggest synbiotic as a more effective approach than either prebiotics or probiotics alone. More in vivo especially human studies are warranted to further elucidate and confirm the potential role of probiotics (viable and non-viable), prebiotics and synbiotics in CRC chemoprevention.

The role of gut microbiota in nutritional status

PURPOSE OF REVIEW

The objective of this review is to outline the contribution of the gut microbiota to nutritional status and to highlight the mechanisms by which this can occur.

RECENT FINDINGS

Historically, research linking intestinal bacteria with nutritional status focused on the degradation of indigestible food components by bacterial enzymes and metabolites. Of late, emerging evidence suggests an independent role of the gut microbiota in the regulation of glucose and energy homeostasis via complex interactions between microbially derived metabolites and specific target tissue cells. In addition, novel findings highlight specific microbial species involved in the production of a number of micronutrient components, which could potentially improve nutritional status in certain population groups, if available to the host at sufficiently abundant levels.

SUMMARY

New insights into the role of the gut microbiota and its holistic effects on the host are now emerging. High-throughput technologies allow for a greater insight into the role of the intestinal microbiota and the mechanisms by which it can contribute to overall nutritional status. Further, exploration of this evolving field of research will advance our understanding of how this complex ecosystem could advance the area of personalized nutrition in the future.

Intestinal iron homeostasis and colon tumorigenesis

Colorectal cancer (CRC) is the third most common cause of cancer-related deaths in industrialized countries. Understanding the mechanisms of growth and progression of CRC is essential to improve treatment. Iron is an essential nutrient for cell growth. Iron overload caused by hereditary mutations or excess dietary iron uptake has been identified as a risk factor for CRC. Intestinal iron is tightly controlled by iron transporters that are responsible for iron uptake, distribution, and export. Dysregulation of intestinal iron transporters are observed in CRC and lead to iron accumulation in tumors. Intratumoral iron results in oxidative stress, lipid peroxidation, protein modification and DNA damage with consequent promotion of oncogene activation. In addition, excess iron in intestinal tumors may lead to increase in tumor-elicited inflammation and tumor growth. Limiting intratumoral iron through specifically chelating excess intestinal iron or modulating activities of iron transporter may be an attractive therapeutic target for CRC.