Effect of covalently bound fatty acids and associated lipids on the viscosity of gastric mucus glycoprotein in cystic fibrosis

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

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.

Solid liquid liquid extraction of porcine gastric mucins from homogenized animal material

With solid liquid liquid extraction as a new capture step for the purification of porcine gastric mucins from crude homogenate, yield and productivity was optimized.

Dietary nitrite induces nitrosation of the gastric mucosa: the protective action of the mucus and the modulatory effect of red wine

The stomach chemical environment promotes the production of new molecules that can induce post-translational modifications of endogenous proteins with physiological impact. The nitrate-nitrite-nitric oxide pathway is relevant in this process via production of nitric oxide ((•)NO) and nitric oxide-derived nitrogen oxides (NOx) at high concentrations. Using a highly sensitive and selective chemiluminescence approach, we found that exposure the stomach of rats to nitrite yielded S- and N-nitroso derivatives in gastric mucus cysteine-rich glycoproteins (mucins). To lesser extent, the underlying epithelial cell layers also suffered nitrite-driven S- and N-nitroso modifications which increased upon mucus removal, indicating that, under normal nitrite load, (•)NO and NOx can reach inner layers of the stomach wall and locally modify proteins. S-nitrosation was by large the predominant modification. In vitro and ex vivo experiments indicated that the gastric nitrosation pattern is triggered by dietary nitrite in a concentration dependent manner, encompassing the intermediary formation of (•)NO and is susceptible to modulation by dietary reductants, notably red wine polyphenols. Collectively, these results suggest a protective action of the mucus and potential (•)NO-dependent biochemical effects at deeper cells layers of the mucosa.

Digestive system dysfunction in cystic fibrosis: challenges for nutrition therapy

Cystic fibrosis can affect food digestion and nutrient absorption. The underlying mutation of the cystic fibrosis trans-membrane regulator gene depletes functional cystic fibrosis trans-membrane regulator on the surface of epithelial cells lining the digestive tract and associated organs, where Cl(-) secretion and subsequently secretion of water and other ions are impaired. This alters pH and dehydrates secretions that precipitate and obstruct the lumen, causing inflammation and the eventual degradation of the pancreas, liver, gallbladder and intestine. Associated conditions include exocrine pancreatic insufficiency, impaired bicarbonate and bile acid secretion and aberrant mucus formation, commonly leading to maldigestion and malabsorption, particularly of fat and fat-soluble vitamins. Pancreatic enzyme replacement therapy is used to address this insufficiency. The susceptibility of pancreatic lipase to acidic and enzymatic inactivation and decreased bile availability often impedes its efficacy. Brush border digestive enzyme activity and intestinal uptake of certain disaccharides and amino acids await clarification. Other complications that may contribute to maldigestion/malabsorption include small intestine bacterial overgrowth, enteric circular muscle dysfunction, abnormal intestinal mucus, and intestinal inflammation. However, there is some evidence that gastric digestive enzymes, colonic microflora, correction of fatty acid abnormalities using dietary n-3 polyunsaturated fatty acid supplementation and emerging intestinal biomarkers can complement nutrition management in cystic fibrosis.

Barrier properties of mucus

Mucus is tenacious. It sticks to most particles, preventing their penetration to the epithelial surface. Multiple low-affinity hydrophobic interactions play a major role in these adhesive interactions. Mucus gel is also shear-thinning, making it an excellent lubricant that ensures an unstirred layer of mucus remains adherent to the epithelial surface. Thus nanoparticles (NP) must diffuse readily through the unstirred adherent layer if they are to contact epithelial cells efficiently. This article reviews some of the physiological and biochemical properties that form the mucus barrier. Capsid viruses can diffuse through mucus as rapidly as through water and thereby penetrate to the epithelium even though they have to diffuse 'upstream' through mucus that is being continuously secreted. These viruses are smaller than the mucus mesh spacing, and have surfaces that do not stick to mucus. They form a useful model for developing NP for mucosal drug delivery.

Enhancement of the lipid content and physical properties of gastric mucus by geranylgeranylacetone

The effects of intragastric administration of geranylgeranylacetone (GGA) on the content, composition and physical properties of the mucus component of the gastric mucosal barrier were investigated. One group of rats received twice daily for 3 consecutive days a dose of 100 mg/kg body weight of GGA, while the control group was subjected to daily doses of the vehicle. Sixteen hours following the last dose, the animals were killed, and their stomach was cut open and subjected to measurements of the adherent mucus gel content, analysis of its lipids and molecular forms of elaborated mucin, and evaluation of the viscosity and H+ retardation capacity. The results revealed that GGA elicited a 62% increase in the adherent mucus gel and caused a marked decrease in the proportion of the lower molecular weight mucin. Furthermore, the mucus of the GGA group exhibited a 67% higher content of covalently bound fatty acids and contained 46% more total lipids which were greatly (143%) enriched in phospholipids. The physical measurements demonstrated that mucus elaborated in the presence of GGA also exhibited 2.3 times higher viscosity and had a 32% greater ability to retard the diffusion of H+ than the mucus of the control group. The results suggest that GGA exerts a profound effect on the lipid content and the properties of gastric mucus associated with the maintenance of the mucosal integrity.

Role of carbohydrates in the viscosity and permeability of gastric mucin to hydrogen ion

The effect of carbohydrate removal on the viscosity of gastric mucin and its ability to impede the diffusion of hydrogen ion was investigated. The mucin, purified from dog gastric mucus, was subjected to partial or extensive deglycosylation with specific exoglycosidases and then used in the measurements. The obtained results revealed that removal of peripheral fucose or N-acetylglucosamine caused in each case only about 5% reduction of the glyco-protein viscosity. An 18% drop in the viscosity, however, occurred following removal of sialic acid, while extensive deglycosylation (removal of 86% carbohydrate) reduced the glycoprotein viscosity by 40%. The ability of mucin to retard the diffusion of hydrogen ion increased by 7% following removal of fucose or N-acetylgalactosamine, a 28% increase was obtained following removal of sialic acid, while the permeability to hydrogen ion of the extensively deglycosylated glycoprotein decreased by 42%. The results suggest that carbohydrates contribute significantly to the viscoelastic and permselective properties of gastric mucin.