COPD: gut microbiota in the dock

COPD (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, bronchodilators (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.

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 short-chain fatty acid (SCFAs) (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.