Host genes shape the gut microbiota

Microbiota and Aging. A Review and Commentary

Although there is a consensus that the dominant species that make up the adult microbiota remains unchanged in elderly people, it has been reported that there are significant alterations in the proportion and composition of the different taxa, leading to reduced microbiota diversity, as well as an increase of enteropathogens that may lead to chronic inflammation. The ageing of mucosal immune and motor systems also contributes to these changes. As the individual ages, there is a loss in the number of Peyer's patches, an altered local capacity of T and B cell functions as well as chronic macrophage activation. Also, environment, diet, place of residence and biogeography are regulatory factors of the microbiota. Communication in the gut-brain-axis is regulated by many intermediaries including diverse metabolites of the microbiota. Microbial changes have been observed in several geriatric diseases, like Parkinson's and Alzheimer's. In addition, evidence has shown that individuals with high frailty scores had a significant reduction on lactobacilli species when compared to non-frail individuals. Oral microbiota may be also especially important because of the opportunities for access to the brain through the olfactory nerve at the roof of the nose or through the abundant innervations of the oral cavity by the trigeminal and other cranial nerves. Also, there are an increasing number of reports that have suggested potential mechanisms by which the microbiota promote human health span and aging. The study of the microbiota represents an important advance in the understanding of the aging process.

Irinotecan (CPT-11) chemotherapy alters intestinal microbiota in tumour bearing rats

Intestinal microbiota mediate toxicity of irinotecan (CPT-11) cancer therapies and cause systemic infection after CPT-11-induced loss of barrier function. The intestinal microbiota and their functions are thus potential targets for treatment to mitigate CPT-11 toxicity. However, microbiota changes during CPT-11 therapy remain poorly described. This study analysed changes in intestinal microbiota induced by CPT-11 chemotherapy. Qualitative and quantitative taxonomic analyses, and functional analyses were combined to characterize intestinal microbiota during CPT-11-based chemotherapy, and in presence or absence of oral glutamine, a treatment known to reduce CPT-11 toxicity. In the first set of experiments tumour-bearing rats received a dose-intensive CPT-11 regimen (125 mg kg⁻¹×3 days), with or without oral glutamine bolus (0.75 g kg⁻¹). In a subsequent more clinically-oriented chemotherapy regimen, rats received two cycles of CPT-11 (50 mg kg⁻¹) followed by 5-flurouracil (50 mg kg⁻¹). The analysis of fecal samples over time demonstrated that tumours changed the composition of intestinal microbiota, increasing the abundance of clostrridial clusters I, XI, and Enterobacteriaceae. CPT-11 chemotherapy increased cecal Clostridium cluster XI and Enterobacteriaceae, particularly after the dose-intensive therapy. Glutamine treatment prevented the reduced abundance of major bacterial groups after CPT-11 administration; i.e. total bacteria, Clostridium cluster VI, and the Bacteroides-group. Virulence factor/toxin genes of pathogenic Escherichia coli and Clostridium difficile were not detected in the cecal microbiota. In conclusion, both colon cancer implantation and CPT-11-based chemotherapies disrupted the intestinal microbiota. Oral glutamine partially mitigated CPT-11 toxicity and induced temporary changes of the intestinal microbiota.