Sodium alginate decreases the permeability of intestinal mucus

In the small intestine the nature of the environment leads to a highly heterogeneous mucus layer primarily composed of the MUC2 mucin. We set out to investigate whether the soluble dietary fibre sodium alginate could alter the permeability of the mucus layer. The alginate was shown to freely diffuse into the mucus and to have minimal effect on the bulk rheology when added at concentrations below 0.1%. Despite this lack of interaction between the mucin and alginate, the addition of alginate had a marked effect on the diffusion of 500 nm probe particles, which decreased as a function of increasing alginate concentration. Finally, we passed a protein stabilised emulsion through a simulation of oral, gastric and small intestinal digestion. We subsequently showed that the addition of 0.1% alginate to porcine intestinal mucus decreased the diffusion of fluorescently labelled lipid present in the emulsion digesta. This reduction may be sufficient to reduce problems associated with high rates of lipid absorption such as hyperlipidaemia

The impact of oat structure and β-glucan on in vitro lipid digestion

Oat β-glucan has been shown to play a positive role in influencing lipid and cholesterol metabolism. However, the mechanisms behind these beneficial effects are not fully understood. The purpose of the current work was to investigate some of the possible mechanisms behind the cholesterol lowering effect of oat β-glucan, and how processing of oat modulates lipolysis. β-Glucan release, and the rate and extent of lipolysis measured in the presence of different sources of oat β-glucan, were investigated during gastrointestinal digestion. Only a fraction of the original β-glucan content was released during digestion. Oat flakes and flour appeared to have a more significant effect on lipolysis than purified β-glucan. These findings show that the positive action of β-glucan is likely to involve complex processes and interactions with the food matrix. This work also highlights the importance of considering the structure and physicochemical properties of foods, and not just the nutrient content

Transport of Particles in Intestinal Mucus under Simulated Infant and Adult Physiological Conditions: Impact of Mucus Structure and Extracellular DNA

The final boundary between digested food and the cells that take up nutrients in the small intestine is a protective layer of mucus. In this work, the microstructural organization and permeability of the intestinal mucus have been determined under conditions simulating those of infant and adult human small intestines. As a model, we used the mucus from the proximal (jejunal) small intestines of piglets and adult pigs. Confocal microscopy of both unfixed and fixed mucosal tissue showed mucus lining the entire jejunal epithelium. The mucus contained DNA from shed epithelial cells at different stages of degradation, with higher amounts of DNA found in the adult pig. The pig mucus comprised a coherent network of mucin and DNA with higher viscosity than the more heterogeneous piglet mucus, which resulted in increased permeability of the latter to 500-nm and 1-µm latex beads. Multiple-particle tracking experiments revealed that diffusion of the probe particles was considerably enhanced after treating mucus with DNase. The fraction of diffusive 500-nm probe particles increased in the pig mucus from 0.6% to 64% and in the piglet mucus from ca. 30% to 77% after the treatment. This suggests that extracellular DNA can significantly contribute to the microrheology and barrier properties of the intestinal mucus layer. To our knowledge, this is the first time that the structure and permeability of the small intestinal mucus have been compared between different age groups and the contribution of extracellular DNA highlighted. The results help to define rules governing colloidal transport in the developing small intestine. These are required for engineering orally administered pharmaceutical preparations with improved delivery, as well as for fabricating novel foods with enhanced nutritional quality or for controlled calorie uptake

Enzyme kinetic approach for mechanistic insight and predictions of in vivo starch digestibility and the glycaemic index of foods

BACKGROUND: Starch is a principal dietary source of digestible carbohydrate and energy. Glycaemic and insulinaemic responses to foods containing starch vary considerably and glucose responses to starchy foods are often described by the glycaemic index (GI) and/or glycaemic load (GL). Low GI/GL foods are beneficial in the management of cardiometabolic disorders (e.g., type 2 diabetes, cardiovascular disease). Differences in rates and extents of digestion of starch-containing foods will affect postprandial glycaemia. SCOPE AND APPROACH: Amylolysis kinetics are influenced by structural properties of the food matrix and of starch itself. Native (raw) semi-crystalline starch is digested slowly but hydrothermal processing (cooking) gelatinises the starch and greatly increases its digestibility. In plants, starch granules are contained within cells and intact cell walls can limit accessibility of water and digestive enzymes hindering gelatinisation and digestibility. In vitro studies of starch digestion by α-amylase model early stages in digestion and can suggest likely rates of digestion in vivo and expected glycaemic responses. Reports that metabolic responses to dietary starch are influenced by α-amylase gene copy number, heightens interest in amylolysis. KEY FINDINGS AND CONCLUSIONS: This review shows how enzyme kinetic strategies can provide explanations for differences in digestion rate of different starchy foods. Michaelis-Menten and Log of Slope analyses provide kinetic parameters (e.g., K(m) and k(cat)/K(m)) for evaluating catalytic efficiency and ease of digestibility of starch by α-amylase. Suitable kinetic methods maximise the information that can be obtained from in vitro work for predictions of starch digestion and glycaemic responses in vivo

Thin section of pig small intestinal (jejunal) mucosa fixed with Carnoy’s solution.

<p>(A, B) Confocal microscopy of a villus tip (V) separated from intestinal lumen (L) with a mucus layer (M). The specimen was stained for mucin with WGA-Alexa633 and with DAPI for DNA (individual channels are shown in (B) and (C), respectively).</p

Effect of the extracellular DNA on diffusion in the mucus.

<p>Impact of the DNase treatment of the <i>ex vivo</i> intestinal mucus from pig and piglet on transport rates and distributions of 500-nm latex beads: (A) proportions of the diffusive particles in the two types of mucus (data shown as mean ± SD), (B) Ensemble mean-square displacements () as a function of time scale (Δt), (C) distributions of MSD values obtained for individual beads at the time scale Δt = 50 s, and (D) ensemble diffusivities (eff>) as a function of Δt calculated for the populations of diffusive particles (n = 3 with 100–150 beads per experiment). All measurements were done at 37±0.1°C.</p

The ζ-potential of colloidal particles. Data are presented as means ± SD.

<p>The ζ-potential of colloidal particles. Data are presented as means ± SD.</p

Microviscosity of the mucus.

<p>Distribution of the apparent viscosity for the <i>ex vivo</i> small intestinal mucus as determined from the motion of 1-µm and/or 500-nm latex beads freely diffusing in the mucus (diffusive fractions; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095274#pone-0095274-g005" target="_blank">Figures 5</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095274#pone-0095274-g007" target="_blank">7</a>): (A) results obtained for the native piglet mucus; (B) results obtained for the piglet and pig mucus samples pre-treated with DNase.</p

Comparison of the <i>ex vivo</i> mucus structures from pig and piglet.

<p>Confocal microscopy images of the <i>ex vivo</i> small intestinal (jejunal) mucus from (A) pig and (B) piglet, acquired at two magnifications. The upper images show a green channel for mucin stained with WGA-Oregon green, the red-channel images show DNA stained with TO-PRO-3 iodine, and the bottom images are merged views of the two channels. The magnified image (A, DNA staining) highlights a progressive degradation of nuclear DNA into fine particulates. The white asterisks (B, merge) indicate the areas in the piglet mucus with apparent lower local amounts of mucin and DNA as compared to the adjacent aggregates of the two polymers.</p