COPD: gut microbiota in the dock
Have you ever heard of chronic obstructive pulmonary disease, or COPD? This respiratory disease worsens over time and can be severely debilitating. We now know that COPD-associated inflammation affects not only the lungs, but other organs too. Moreover, a recent study has revealed that, like other respiratory diseases, COPD is associated to an imbalance in the gut microbiota1.
About this article
(sidenote: https://www.who.int/news-room/fact-sheets/detail/chronic-obstructive-pulmonary-disease-(copd). ) is a chronic respiratory disease characterized by increasing difficulty in breathing. In its “mild” stage, patients have limited respiratory discomfort. In the “very severe” stage, they are short of breath at the slightest effort – even when at rest – preventing normal activity. Today, we can slow the aggravation of COPD with anti-inflammatory drugs, (sidenote: Bronchodilators Drugs that reduce bronchial obstruction. https://www.who.int/news-room/fact-sheets/detail/chronic-obstructive-pulmonary-disease-(copd) ) , and breathing exercises, but we do not know how to cure it. While smoking and pollution are major risk factors for the disease, its mechanisms remain poorly understood.
3rd COPD is the 3rd leading cause of death worldwide
3.23 million COPD resulted in 3.23 million deaths in 2019
However, a link between gut microbiota imbalances and respiratory diseases such as allergic asthma or pneumonia has recently been discovered, part of what scientists refer to as the “gut-lung axis”. Could the gut-lung axis be involved in COPD?
A microbiota imbalance associated with inflammation in patients...
To answer this question, a team of Chinese researchers analyzed the gut microbiota of around a hundred COPD patients at various stages of severity and compared them with the microbiota of healthy subjects. They found that the gut flora of COPD patients differed from that of healthy subjects. Specifically, the bacterial species Prevotella, suspected of exacerbating inflammation, dominated their gut microbiota. In addition, they had lower levels of (sidenote: Short chain fatty acids (SCFA) Short chain fatty acids (SCFA) are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are involved in communication between the intestine and the brain. Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) , especially the most severely affected patients. SCFAs are produced by bacteria in the microbiota from dietary fiber and are known for their anti-inflammatory properties.
... that increases vulnerability to pollution
The researchers then performed a fecal microbiota transplant from the participants to mice. Four weeks later, the lungs of the mice receiving the transplant showed strong inflammation and mucus hypersecretion. Knowing that COPD is accompanied by hypersensitivity to air pollutants, they then exposed the mice to fuel smoke for 20 weeks. The researchers found that the lung function of these mice deteriorated faster than that of unexposed mice.
This study confirms that gut microbiota imbalances in COPD patients are associated with lung inflammation and accelerate the progression of COPD in mice. Do these results tell us we should increase our intake of SCFAs through a high-fiber diet to slow the progression of the disease? Like other researchers before them2, the authors consider the possibility, but it remains to be proven.
To be continued...
1 Li N, Dai Z, Wang Z. et al. Gut microbiota dysbiosis contributes to the development of chronic obstructive pulmonary disease. Respir Res 2021; 22, 274.
2 Kaluza J, Harris H, Wallin A, et al. Dietary Fiber Intake and Risk of Chronic Obstructive Pulmonary Disease: A Prospective Cohort Study of Men. Epidemiology. 2018 ;29(2):254-260.