Excess mucus production is a common problem in people with Allergic Bronchopulmonary Aspergillosis (ABPA), and chronic pulmonary aspergillosis (CPA). Mucus is a thick mixture of water, cellular debris, salt, lipids, and proteins. It lines our airways, trapping and removing foreign particles from the lungs. The gel-like thickness of mucus is caused by a family of proteins called mucins. In individuals with asthma, genetic changes to these mucin proteins can thicken the mucus, making it more difficult to clear from the lungs. This thick and dense mucous builds up and can lead to mucus plugs, blocking the airways and causing breathing difficulties, wheezing, coughing, and other respiratory symptoms.

Doctors usually treat these symptoms with inhalable medications such as bronchodilators and corticosteroids to open the airways and reduce inflammation. Mucolytics can also be used to break down mucus plugs, but the only available medication, N-Acetylcysteine (NAC), is not very effective and can cause unwanted side effects. While current treatments can help manage symptoms, there is a need for effective and safe treatments to directly address the issue of mucus plugs.

 

To address this issue, 3 approaches are being explored:

  1. Mucolytics to dissolve mucus plugs

Researchers at the University of Colorado are testing new mucolytics such as tris (2-carboxyethyl) phosphine. They gave this mucolytic to a group of asthmatic mice experiencing inflammation and excess mucus production. After treatment, mucus flow improved, and the asthmatic mice could clear mucus just as effectively as the non-asthmatic mice.

However, mucolytics work by breaking the bonds which hold mucins together, and these bonds are found in other proteins in the body. If the bonds are broken in these proteins, it could lead to unwanted side effects. Therefore, further research is needed to discover a drug that will only target the bonds in mucins, reducing the risk of side effects.

2. Clearing crystals

In another approach, Helen Aegerter and her team at the University of Belgium are studying protein crystals which they believe drive mucus overproduction in asthma. These crystals, known as Charcot-Leyden crystals (CLC’s) cause mucus to become thicker, therefore harder to clear from the airways.

To address the crystals directly, the team developed antibodies that attack the proteins in the crystals. They tested the antibodies on mucus samples collected from individuals with asthma.  They found that the antibodies effectively dissolved the crystals by attaching themselves to the specific regions of the CLC proteins that hold them together. In addition, the antibodies dampened inflammatory reactions in mice. Based on these findings, the researchers are now working on a drug that could have the same effect in humans. Aegerter believes that this approach could be used to treat a variety of inflammatory diseases that involve excessive mucus production, including sinus inflammation and certain allergic reactions to fungal pathogens (such as ABPA).

  1. Preventing excess secretion of mucus

In a third approach, pulmonologist Burton Dickey of the University of Texas is working to prevent mucus plugs by reducing the overproduction of mucus. Dickey’s team identified a specific gene, Syt2, that is only involved in excessive mucus production and not in normal mucus production. To inhibit excess mucus production, they developed a drug called PEN-SP9-Cy that blocks Syt2’s action. This approach is particularly promising as it targets mucus overproduction without interfering with the vital functions of normal mucus. Normal mucus production plays a critical role in protecting and maintaining the health of the respiratory and digestive systems. Although the initial results are promising, further research is necessary to evaluate the efficacy and safety of these drugs in clinical trials.

In summary, mucus plugs present uncomfortable symptoms in ABPA, CPA and asthma. Current treatments focus on symptom management rather than directly addressing reduction or removal of mucus plugs. However, researchers are exploring 3 potential approaches, involving mucolytics, clearing crystals, and preventing excess mucus secretion. Additional research is required to confirm their effectiveness and safety, but approaches have shown promising results and may in future be one way we can prevent mucus plugs.

 

Further information:

Phlegm, mucus and asthma | Asthma + Lung UK

How to loosen and clear mucus 

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