This subgroup includesĪlong with the above-mentioned mucolytic action, N-acetylcysteine also has anti-inflammatory and antioxidative properties. This reaction disturbs the 3-D framework of mucus by reducing the S-S bond to an S-H (sulfhydryl) bond, rendering it incapable of anchoring the complex structure of the protein. The disulfide bonds are anchored on these residues to yield crosslinking of the polymer. The free thiol group in the structure of NAC hydrolyzes the disulfide bonds attached to cysteine residues. N-acetyl L-cysteine (NAC), the prototype drug of this class, reserves a reducing ability and works by the thiol-disulfide interchange mechanism. The mucin polymers have cysteine residues throughout their structure. Here, another class of mucolytics is helpful that targets the DNA polymers.ĭisulfide bonds are building blocks of many complex proteins, including mucus. These secretions are also thick and viscous and a frequent target of bacteria. In conditions like cystic fibrosis, mucus secretion is impaired, and thus the airway secretions mostly include filamentous actin polymers and inflammatory-cell derived DNA. Classic mucolytics like N-acetylcysteine are indicated in such conditions because they decrease mucus viscosity and increase its flowability, thereby improving its clearance. This condition is only worsened because this static mucus is invaded by bacteria like Pseudomonas aeruginosa and Staphylococcus aureus. Thus, a vicious cycle initiates, which invariably ends with an acute exacerbation of the condition. Unfortunately, this only worsens the condition as mucus viscosity increases, leading to further decreased clearance as well as the initiation of inflammation and fibrosis. The airways respond by secreting an excess of inflammatory mediators in an attempt to clear the obstruction. This leads to the formation of mucus plugs, which further decrease the clearance. Excessive mucus production overwhelms the mucociliary clearance mechanisms, thus leading to the accumulation of this excess mucus. In conditions like COPD and asthma, chronic irritation of the airways leads to mucus hypersecretion. However, there are some conditions where this regulation breaks down. The amount of mucus in our body is regulated chiefly by two mechanisms, which are the mucus-secreting cells and the mucociliary escalator. Goblet cells of the mucous membranes and the submucosal glands of the respiratory, GI, and reproductive systems are responsible for the secretion of mucus, and the mucociliary escalator is responsible for the clearance of mucus towards the pharynx, where it is eventually expectorated out by the cough reflex. The mucus layer also works as a physical barrier against respiratory irritants and prevents fluid loss as well. This layer is very protective against bacteria through bacterial growth inhibition and the prevention of biofilm formation. The cross-bridging of polymeric gel-forming mucins chiefly determines the biophysical properties of mucus. It houses an assemblage of proteins such as immunoglobulins, various glycoproteins, and even some antimicrobial enzymes like lysozyme. Its job also entails the protection of the epithelium from the excoriating irritants found in the gastrointestinal tract. They exert their effect on the mucus layer lining the respiratory tract with the motive of enhancing its clearance. Mucus is the first line of defense for the various epithelia inside our body against harmful pathogens. Mucolytics are drugs belonging to the class of mucoactive agents.
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