The Bidirectional Gut–Lung Axis in Chronic Obstructive Pulmonary Disease

Abstract Epidemiological studies indicate that chronic obstructive pulmonary disease (COPD) is associated with the incidence of changes in intestinal health. Cigarette smoking, as one of the major causes of COPD, can have an impact on the gastrointestinal system and promotes intestinal diseases. This points to the existence of gut–lung interactions, but an overview of the underlying mechanisms of the bidirectional connection between the lungs and the gut in COPD is lacking. The interaction between the lungs and the gut can occur through circulating inflammatory cells and mediators. Moreover, gut microbiota dysbiosis, observed in both COPD and intestinal disorders, can lead to a disturbed mucosal environment, including the intestinal barrier and immune system, and hence may negatively affect both the gut and the lungs. Furthermore, systemic hypoxia and oxidative stress that occur in COPD may also be involved in intestinal dysfunction and play a role in the gut–lung axis. In this review, we summarize data from clinical research, animal models, and in vitro studies that may explain the possible mechanisms of gut–lung interactions associated with COPD. Interesting observations on the possibility of promising future add-on therapies for intestinal dysfunction in patients with COPD are highlighted.