Abstract
Mucositis, also referred to as mucosal barrier injury, is one of the most debilitating side effects of radiotherapy and chemotherapy treatment. Clinically, mucositis is associated with pain, bacteremia, and malnutrition. Furthermore, mucositis is a frequent reason to postpone chemotherapy treatment, ultimately leading towards a higher mortality in cancer patients. According to the model introduced by Sonis, both inflammation and apoptosis of the mucosal barrier result in its discontinuity, thereby promoting bacterial translocation. According to this five-phase model, the intestinal microbiota plays no role in the pathophysiology of mucositis. However, research has implicated a prominent role for the commensal intestinal microbiota in the development of several inflammatory diseases like inflammatory bowel disease, pouchitis, and radiotherapy-induced diarrhea. Furthermore, chemotherapeutics have a detrimental effect on the intestinal microbial composition (strongly decreasing the numbers of anaerobic bacteria), coinciding in time with the development of chemotherapy-induced mucositis. We hypothesize that the commensal intestinal microbiota might play a pivotal role in chemotherapy-induced mucositis. In this review, we propose and discuss five pathways in the development of mucositis that are potentially influenced by the commensal intestinal microbiota: 1) the inflammatory process and oxidative stress, 2) intestinal permeability, 3) the composition of the mucus layer, 4) the resistance to harmful stimuli and epithelial repair mechanisms, and 5) the activation and release of immune effector molecules. Via these pathways, the commensal intestinal microbiota might influence all phases in the Sonis model of the pathogenesis of mucositis. Further research is needed to show the clinical relevance of restoring dysbiosis, thereby possibly decreasing the degree of intestinal mucositis.
Highlights
Mucositis, referred to as mucosal barrier injury, is one of the most debilitating side effects of radiotherapy and chemotherapy treatment [1]
According to the model introduced by Sonis, five phases are important in the pathophysiology of mucositis: (1) the formation of reactive oxygen species leading to the activation of nuclear factor kappa B (NFkB) during the initiation phase, (2) the induction of messenger molecules such as tumor necrosis factor alpha (TNFa), resulting in treatment-related tissue inflammation and apoptosis during the upregulation/message generation phase, (3) the amplification of messenger molecules in the amplification/ signaling phase, leading to more inflammation and apoptosis, (4) discontinuity of the epithelial barrier resulting from apoptosis during the ulcerative phase, thereby promoting bacterial translocation, and (5) a spontaneous healing phase, characterized by cell proliferation [3]
According to this five-phase model, the intestinal microbiota plays no role in the pathophysiology of mucositis
Summary
Referred to as mucosal barrier injury, is one of the most debilitating side effects of radiotherapy and chemotherapy treatment [1]. PLoS Pathogens | www.plospathogens.org potentially influenced by the commensal intestinal microbiota: 1) the inflammatory process and oxidative stress, 2) intestinal permeability, 3) the composition of the mucus layer, 4) the resistance towards harmful stimuli and epithelial repair mechanisms, and 5) the activation and release of immune effector molecules (Figures 1 and 2). Butyrate attenuates inflammation, and reduces intestinal permeability and stimulates the activation of immune effector molecules.
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