Ignored roles of gases in digestive diseases

Complexities of the intestine have brought enormous controversy and discussions to the research on the digestive diseases. The neglected gas environment is crucial in shaping the dynamic intestinal microenvironment. Many gases are involved in the biological activities within the intestinal anaerobic environment, including oxygen, hydrogen, carbon monoxide, ammonia, methane, hydrogen sulfide, carbon dioxide, and nitrogen. These gases participate in the regulation of systemic inflammation and metabolism via different pathways, thereby alleviating or promoting the development of intestinal disease. Meanwhile, the constitution and changes of gases reflect the intestinal environment, which could be utilized to monitor the variation in local metabolism and imply the progress of digestive disorders. However, individual gas has intrinsic functions in maintaining a healthy intestinal microenvironment or causing digestive diseases, and the underlying mechanisms are still unclear. Therefore, exploring the profile of gases in the digestive tract and their extraordinary impact on the intestinal microenvironment will be of great value in understanding the interplay between intestinal health and diseases. By reviewing the research progress of gases in the digestive tract, we anticipate that a better understanding of the roles of gases would promote the research and application transformation in this field as well as the diagnostics and treatment of clinical diseases.