A slippery slope: On the origin, role and physiology of mucus

Abstract

The mucosa of the gastrointestinal tract, eyes, nose, lungs, cervix and vagina is lined by epithelium interspersed with mucus-secreting goblet cells, all of which contribute to their unique functions. This mucus provides an integral defence to the epithelium against noxious agents and pathogens. However, it can equally act as a barrier to drugs and delivery systems targeting epithelial passive and active transport mechanisms. This review highlights the various mucins expressed at different mucosal surfaces on the human body, and their role in creating a mucoid architecture to protect epithelia with specialized functions. Various factors compromising the barrier properties of mucus have been discussed, with an emphasis on how disease states and microbiota can alter the physical properties of mucus. For instance, Akkermansia muciniphila, a bacterium found in higher levels in the gut of lean individuals induces the production of a thickened gut mucus layer. The aims of this article are to elucidate the different physiological, biochemical and physical properties of bodily mucus, a keen appreciation of which will help circumvent the slippery slope of challenges faced in achieving effective mucosal drug and gene delivery.

Immune exclusion by naturally acquired secretory IgA against pneumococcal pilus-1

“…The mucus is divided into 2 layers: an inner periciliary layer, which is relatively impenetrable to microbes, and an outer loose layer providing a niche for commensal bacteria that is continuously removed by ciliary activity (4). The nasal mucus is composed of 95% water, high-molecular weight glycoproteins (so called mucins, which confer the viscous properties of the mucus), lipids, proteins, and inorganic salts (5). Nearly all of the proteinaceous components present in the mucus harbor antibacterial activity (6)(7)(8).…”

Gastrointestinal Tracking and Gastric Emptying of Coated Capsules in Rats with or without Sedation Using CT imaging

“…Among the different animals used in preclinical research, rodents make up approximately 95% of all laboratory animals [2]. Specifically, rats are one of the most widely used small animal models for the assessment of new pharmaceutical entities during pre-clinical studies [3][4][5][6][7][8][9]. The oral route is the most preferred and convenient way to administer drugs which can either be formulated to act locally in the gastrointestinal (GI) tract or be absorbed to achieve a systemic effect [10].…”

Akkermansia and Microbial Degradation of Mucus in Cats and Dogs: Implications to the Growing Worldwide Epidemic of Pet Obesity

“…The digestive tract of humans and other animals is a muscular tube covered on the inside by epithelium containing mucus-secreting goblet cells [25][26][27]. This mucus has important protective, lubricative, and immune functions that are relevant to preserve health [28][29][30][31].…”