Gut microbiota and carcinogenesis: actual aspects

The microbiota, together with the host, form a symbiotic relationship in which the microbiota plays a key role in maintaining the homeostasis of the human body, performing a number of significant functions such as energy metabolism, maturation and maintenance of the immune system, vitamin synthesis, regulation of bile acid reabsorption in the intestine, and much more. Scientific research in recent years has made a significant contribution to understanding the complex relationship between the microbiota and a range of human pathologies, including malignant neoplasms. The review considers the mechanisms of the possible influence of bacteria on the development and progression of cancer with an emphasis on the procarcinogenic properties of the microbiota. The most important factor in the mechanism of influence of the microbiota on carcinogenesis are toxins produced by microorganisms that induce direct damage to host cell DNA, causing DNA mutations, disruption of its exact replication, and also provoke an imbalance in the proliferation and apoptosis of host cells, their rapid aging and oncogenesis. The probable mechanisms of participation of microorganisms in the development of cancer through the activation of TLRs and NLRs receptors, which have a tumor-activating effect, are considered. A brief review is given on the mechanisms of carcinogenesis associated with the metabolic activity of the microbiota due to the processes of regulation of the production of secondary bile acids, activation of pro-carcinogenic compounds: phenols, ethanol, sulfides, ammonia, nitrosamines. The influence of the microbiota on the metabolism of sex hormones and the development of hormone-dependent cancers mediated by the mechanisms of enterohepatic circulation and estrogen deconjugation is described. The study of the carcinogenic mechanisms of action of the microbiota in the host organism opens up prospects for the development of new successful personalized approaches to the diagnosis, treatment, and prevention of cancer. Changing the composition of the microbiota should become a way to fight cancer, along with surgical treatment, chemotherapy, radiation therapy, targeted therapy and immunotherapy.