Mucin-epithelial cell surfaces

An ideal bioadhesive should be nontoxic, nonabsorbable, and nonirritating to the mucus membrane, form a strong noncovalent bond with the mucin-epithelial cell surfaces, allow easy incorporation of drug and should not offer hindrance to drug release, and should not decompose on storage or during the shelf-life of the dosage form. Some of the other desirable characteristics of the polymer have been discussed under bioadhesion. 

The functions of the large gel-forming mucins include lubrication of the epithelial surfaces and protection from chemical and physical impact and microbial damage. Bacteria, viruses, and other microbes bind to mucin-type 0-glycans and are trapped by the viscous mucus layer. This may prevent their migration toward the epithelial cell surface and support their removal by ciliary action. Bacteria can also use the carbohydrate moieties of mucins as nutrients. 

Due to the high degree of glycosylation of mucins, they may form gels which protect underlying epithelial cell surfaces. Mucin O-glycans may be involved in the... 

Mucins are a class of O-linked glycoproteins that are distributed on the surfaces of epithelial cells of the respiratory, gastrointestinal, and reproductive tracts. The Golgi apparatus plays a major role in glycosyla-tion reactions involved in the biosynthesis of glycoproteins. 

A deep layer rich in mucus and the origin of which is to be found in the conjunctival calyciform cells. This mucus is in relation with the apical epithelial cells via the glycocalyx. This interface between the lacrymal secretion and the epithelium influences the quality of the corneal surface. Indeed, the stability of the lacrymal secretion and the epithelial absorption of its metabolites both depend on the mucin and the apical expansions of the epithelial cells [2]. 

The construction of the eye is completely different. The outer layer of this mucosa consists of a tiny tear layer of lipids and water which covers a superficial epithelium closed by double layer lipid membranes of 30-70 nm size interconnected by tight jnnctions. Three to seven layers of epithelial cells cover the stromal structures of conjunctiva or cornea. The conjnnctival surface has interposed cells secreting small amonnts of mucin, the so-called goblet cells, which are typically missing within the corneal epithelinm. The regeneration of epithelial structnres is dne to the limbal stem cells located deep in the Vogt s crypts, for the cornea. 

According to some authors, the success in the establishment of infection by the oral route is associated with the expression of gp82, a surface glycoprotein, which binds to mucin and gastric epithelial cells. This molecule promotes the entrance of trypomastigotes through a cascade reaction that culminates with the mobilization of intracellular calcium (Ruiz et al., 1998). 

Q9 The stomach secretes a very acid gastric juice with a pH of 1.5-2. The mucosa is normally protected from acid by a number of mechanisms. Mucus is produced by the large number of mucous cells in the body and fundus. It contains glycoproteins called mucins, and the mucus produced forms a kind of gel which coats the mucosal surface. In addition these cells secrete HCO3-, which is trapped in the mucus and increases the local pH to form a less acidic environment at the surface of the epithelial cells. 

P2Y2 receptors are present in the epithelial cells of the ocular surface and stimulation of them by ATP increases mucin-like glycoprotein secretions in conjunctival... 

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