Permeability of the small intestinal mucus for physiologically relevant studies: Impact of mucus location and ex vivo treatment

Abstract

The small intestinal mucus is a complex colloidal system that coats the intestinal mucosa. It allows passage on nutrients/pharmaceuticals from the gut lumen towards the epithelium, whilst preventing it from direct contact with luminal microorganisms. Mucus collected from intestinal tissue is often used in studies looking at inter-mucosal transport of food particulates, drug carriers, etc. However, detaching the highly hydrated native mucus from the tissue and storing it frozen prior to use may disrupt its physiological microstructure, and thus selective barrier properties. Multiple-particle tracking experiments showed that microstructural organisation of native, jejunal mucus depends on its spatial location in the intestinal mucosa. The inter-villus mucus was less heterogeneous than the mucus covering villi tips in the pig model used. Collecting mucus from tissue and subjecting it to freezing and thawing did not significantly affect (P > 0.05) its permeability to model, sub-micron sized particles, and the microviscosity profile of the mucus reflected the overall profiles recorded for the native mucus in the tissue. This implies the method of collecting and storing mucus is a reliable ex vivo treatment for the convenient planning and performing of mucus-permeability studies that aim to mimic physiological conditions of the transport of molecules/particles in native mucus.

Comparing the permeability of human and porcine small intestinal mucus for particle transport studies

“…Mucus was incubated for 10 min at RT before use. As reported previously 22,28 , the freezing, storing and thawing cause no substantial differences in the macro-and microrheological properties of small intestinal mucus.…”

“…Porcine small intestinal mucus collection. A detailed procedure of collecting porcine mucus, including the ex vivo handling of intestinal tissue, was described previously 9,22 . In brief, mucus was gently removed with a soft-rubber scraper from the mucosal surface ( Fig.…”

“…The fresh adult pig small intestines 22 were obtained from a local abattoir (H. G. Blakes Ltd, Costessey, Norfolk, UK), from five healthy animals (7-10-month old) that were slaughtered for a commercial meat production process, and therefore any ethical requirements that would be specific for this study were not necessary. The authors obtained permission from the abattoir to collect and use these samples for scientific research.…”

“…Multiple-particle tracking in mucus. Specimen preparation for confocal laser scanning microscopy (CLSM) and the particle tracking were done according to the method described recently 22 . Briefly, 500 nm redfluorescent, carboxylate-modified latex beads (L3280, Sigma-Aldrich, Poole, UK) were used to probe permeability of mucus.…”

“…A recent study 22 has shown that removing mucus from the mucosal tissue of porcine jejunum does not considerably affect the microstructure of mucus with regard to the diffusivity of penetrating particles. The microviscosity of the collected mucus was very similar to the microviscosity of the intact mucus attached to mucosal tissue.…”