Gastrointestinal Mucus

Enhancement of Mucus Production in Eukaryotic Cells and Quantification of Adherent Mucus by ELISA

The mucosal surfaces of the gastrointestinal, respiratory, reproductive, and urinary tracts, and the surface of the eye harbor a resident microflora that lives in symbiosis with their host and forms a complex ecosystem. The protection of the vulnerable epithelium is primarily achieved by mucins that form a gel-like structure adherent to the apical cell surface. This mucus layer constitutes a physical and chemical barrier between the microbial flora and the underlying epithelium. Mucus is critical to the maintenance of a homeostatic relationship between the microbiota and its host. Subtle deviations from this dynamic interaction may result in major implications for health. The protocol in this article describes the procedures to grow low mucus-producing HT29 and high mucus-producing HT29-MTX-E12 cells, maintain cells and use them for mucus quantification by ELISA. Additionally, it is described how to assess the amount of secreted adherent mucus. This system can be used to study the protective effect of mucus, e.g., against bacterial toxins, to test the effect of different culture conditions on mucus production or to analyze diffusion of molecules through the mucus layer. Since the ELISA used in this protocol is available for different species and mucus proteins, also other cell types can be used.

The gastric mucus layers: constituents and regulation of accumulation

The mucus layer continuously covering the gastric mucosa consists of a loosely adherent layer that can be easily removed by suction, leaving a firmly adherent mucus layer attached to the epithelium. These two layers exhibit different gastroprotective roles; therefore, individual regulation of thickness and mucin composition were studied. Mucus thickness was measured in vivo with micropipettes in anesthetized mice [isoflurane; C57BL/6, Muc1-/-, inducible nitric oxide synthase (iNOS)-/-, and neuronal NOS (nNOS)-/-] and rats (inactin) after surgical exposure of the gastric mucosa. The two mucus layers covering the gastric mucosa were differently regulated. Luminal administration of PGE(2) increased the thickness of both layers, whereas luminal NO stimulated only firmly adherent mucus accumulation. A new gastroprotective role for iNOS was indicated since iNOS-deficient mice had thinner firmly adherent mucus layers and a lower mucus accumulation rate, whereas nNOS did not appear to be involved in mucus secretion. Downregulation of gastric mucus accumulation was observed in Muc1-/- mice. Both the firmly and loosely adherent mucus layers consisted of Muc5ac mucins. In conclusion, this study showed that, even though both the two mucus layers covering the gastric mucosa consist of Muc5ac, they are differently regulated by luminal PGE(2) and NO. A new gastroprotective role for iNOS was indicated since iNOS-/- mice had a thinner firmly adherent mucus layer. In addition, a regulatory role of Muc1 was demonstrated since downregulation of gastric mucus accumulation was observed in Muc1-/- mice.

Gastroduodenal mucus bicarbonate barrier: protection against acid and pepsin

Secretion of bicarbonate into the adherent layer of mucus gel creates a pH gradient with a near-neutral pH at the epithelial surfaces in stomach and duodenum, providing the first line of mucosal protection against luminal acid. The continuous adherent mucus layer is also a barrier to luminal pepsin, thereby protecting the underlying mucosa from proteolytic digestion. In this article we review the present state of the gastroduodenal mucus bicarbonate barrier two decades after the first supporting experimental evidence appeared. The primary function of the adherent mucus gel layer is a structural one to create a stable, unstirred layer to support surface neutralization of acid and act as a protective physical barrier against luminal pepsin. Therefore, the emphasis on mucus in this review is on the form and role of the adherent mucus gel layer. The primary function of the mucosal bicarbonate secretion is to neutralize acid diffusing into the mucus gel layer and to be quantitatively sufficient to maintain a near-neutral pH at the mucus-mucosal surface interface. The emphasis on mucosal bicarbonate in this review is on the mechanisms and control of its secretion and the establishment of a surface pH gradient. Evidence suggests that under normal physiological conditions, the mucus bicarbonate barrier is sufficient for protection of the gastric mucosa against acid and pepsin and is even more so for the duodenum.

Bioadhesive oesophageal bandages: protection against acid and pepsin injury

The rate of acid and pepsin diffusion through solutions of sodium alginate was measured using in vitro techniques. Previous work has demonstrated that solutions of alginate may adhere to the oesophagus for up to 60 min; this work measured their ability to protect the oesophageal epithelial surface from damage caused by refluxed acid and pepsin. Franz diffusion cells were used to measure the rate of acid and pepsin diffusion through an alginate layer. The effect of the type of alginate, alginate concentration and depth of alginate applied were investigated. The rate of both acid and pepsin diffusion was significantly reduced (ANOVA analysis; P<0.05) in the presence of an alginate solution compared to the control. A 2% (w/v) alginate solution with a high guluronic acid component, in a layer of 0.44 mm depth, demonstrated the greatest reduction in acid diffusion with a permeation coefficient 14% than that of a control value. All three alginates demonstrated significant reductions in acid diffusion with both increasing depth and increasing concentration, as expected. Pepsin diffusion was also significantly reduced as the depth and concentration of applied alginate increased. This study demonstrates that an adhesive layer of alginate present within the oesophagus will limit the contact of refluxed acid and pepsin with the epithelial surface.