The Gut–Lung Axis, Epigenetics and Respiratory Disease

The first and second phases of the human microbiome project provided a view of mucosal surfaces and the skin of humans that mapped an abundant and complex ecosystem (microbiota) that is composed of bacteria (bacteriobiota), fungi (mycobiota), viruses (virobiota), enteric phages, archaea, protists, and helminths. Intestinal dysbiosis describes an adverse shift in microbial homeostasis in the gut that enhances intestinal epithelial permeability, translocating toxins that may lead to endotoxemia. Numerous intestinal and extra-intestinal illnesses have been linked to gut dysbiosis, including inflammatory bowel disease, infections, food allergies, asthma, diabetes, obesity, multiple sclerosis, autism, periodontitis, and colorectal cancer. The gut-lung axis is a bidirectional communication network between the lungs and the intestines mediated by bacterial elaborated products (e.g., butyrate), immune cells and neural pathways influencing health and disease at both sites. This review has focused on the gut-lung axis and the role that probiotics, prebiotics and postbiotics may play on the amelioration of respiratory symptoms that may result from viral and/or bacterial lung infections. Clinicians have for some time focused on treating inflammatory lung disorders such as asthma and chronic obstructive pulmonary disease by encouraging beneficial effects on the intestinal microbiome through the gut-lung axis with orally administered probiotics and pre- and/or postbiotics. The purpose is to restore gut microbial homeostasis. Developing novel delivery platforms to administer probiotics directly to the airways or as adjunctive systemic modulators is a plausible and increasingly supported hypothesis, with careful strain selection, formulation to preserve viability, targeted delivery, and rigorous safety and efficacy testing before clinical use. It is posited that such adjunctive treatments may significantly influence the lung microbiota epigenome by positively impacting the balance of microorganisms within the lung, restoring eubiosis and consequently health.