Mucin (MUC) (MUC)

Respiratory mucus is a complex viscoelastic hydrogel primarily composed of high-molecular-weight glycoproteins known as mucins, which were historically characterized in pharmacological literature as mucopolysaccharide fibers (Thornton & Sheehan, 2004). These fibers form an extensive cross-linked network through disulfide bonds and non-covalent interactions, serving as a critical physical barrier that traps pathogens and particulates for removal via mucociliary clearance (Balsamo et al., 2010). In chronic respiratory conditions such as COPD, asthma, and cystic fibrosis, the overproduction and altered chemical structure of these fibers lead to mucus hyperviscosity and impaired clearance, contributing to airway obstruction and recurrent infections (Fahy & Dickey, 2010). Therapeutic agents known as mucolytics target these fibers to restore normal mucus rheology; for example, N-acetylcysteine reduces viscosity by cleaving disulfide bridges, while secretolytic agents like bromhexine and ambroxol are described as fragmenting the mucopolysaccharide chains and stimulating surfactant production (Zanasi et al., 2017). Understanding the molecular architecture of these fibers is essential for developing treatments that can effectively liquefy pathological mucus without compromising its protective functions (StatPearls, 2023).

Other names

Mucopolysaccharide fibersAcid mucopolysaccharidesMucus glycoproteinsMucin networkRespiratory mucus gelMUC5ACMUC5B

Mucolytics reduce the viscosity of respiratory secretions by depolymerizing the mucin network; this is achieved through the cleavage of disulfide bonds (e.g., N-acetylcysteine) or the fragmentation of the carbohydrate-rich mucopolysaccharide chains (e.g., bromhexine) (Zanasi et al., 2017; StatPearls, 2023).