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The influence of small intestinal mucus structure on particle transport ex vivo

Bajka, Balázs H., Rigby, Neil M., Cross, Kathryn L., Macierzanka, Adam, Mackie, Alan R.
Colloids and Surfaces B: Biointerfaces 2015 v.135 pp. 73-80
absorption, bacteria, colloids, drug delivery systems, ileum, immunohistochemistry, inflammatory bowel disease, jejunum, latex, mucins, mucus, porosity, scanning electron microscopy, staining, swine, toxins, ultrastructure, villi
Mucus provides a barrier to bacteria and toxins while allowing nutrient absorption and waste transport. Unlike colonic mucus, small intestinal mucus structure is poorly understood. This study aimed to provide evidence for a continuous, structured mucus layer and assess the diffusion of different sized particles through it.Mucus structure was assessed by histology and immunohistochemistry. Ultra-structure was assessed by scanning electron microscopy. Tracking of 100nm and 500nm latex beads was conducted using ex vivo porcine mucus.The porcine jejunum and ileum were filled with mucus. Layered MUC2 staining was visible throughout the small intestine, covering villus tips. Scanning electron microscopy showed net-like mucin sheets covering villi (211±7nm pore diameter). Particle tracking of 100nm latex beads, showed no inhibition of diffusion through mucus while 500nm beads displayed limited diffusion.These results suggest a continuous mucus layer exists throughout the small intestine, which is highly stratified adjacent to the epithelium. The network observed is consistent with previous observations and correlates with stratified MUC2 staining. Mucin pore size is consistent with free diffusion of 100nm and limited diffusion of 500nm particles. Small Intestinal mucus structure has important implications for drug delivery systems and prevention and treatment of conditions like mucositis and inflammatory bowel disease.