Reinforcing Mucus Barrier Properties with Low Molar Mass Chitosans

The mucus gel covers the wet epithelia that forms the inner lining of the body. It constitutes our first line of defense protecting the body from infections and other deleterious molecules. Failure of the mucus barrier can lead to the inflammation of the mucosa such as in inflammatory bowel diseases. Unfortunately, there are no effective strategies that reinforce the mucus barrier properties to recover or enhance its ability to protect the epithelium. Herein, we describe a mucus engineering approach that addresses this issue where we physically cross-link the mucus gel with low molar mass chitosan variants to reinforce its barrier functions. We tested the effect of these chitosans on mucus using in-lab purified porcine gastric mucins, which mimic the native properties of mucus, and on mucus-secreting HT29-MTX epithelial cell cultures. We found that the lowest molar mass chitosan variant (degree of polymerization of 8) diffuses deep into the mucus gels while physically cross-linking the mucin polymers, whereas the higher molar mass chitosan variants (degree of polymerization of 52 and 100) interact only superficially. The complexation resulted in a tighter mucin polymer mesh that slowed the diffusion of dextran polymers and of the cholera toxin B subunit protein through the mucus gels. These results uncover a new use for low molar mass mucoadhesive polymers such as chitosans as noncytotoxic mucosal barrier enhancers that could be valuable in the prevention and treatment of mucosal diseases.

黏液凝胶覆盖于构成机体内部衬里的湿润上皮组织(epithelia)之上，是机体抵御感染与其他有害分子的第一道防线。黏液屏障功能受损可引发黏膜炎症，例如炎症性肠病(inflammatory bowel diseases)。遗憾的是，目前尚无有效策略可强化黏液屏障特性，以恢复或增强其保护上皮组织的能力。本文报道一种可解决该问题的黏液工程学方法：通过低摩尔质量壳聚糖(chitosan)变体与黏液凝胶进行物理交联，强化其屏障功能。我们利用实验室纯化的猪胃黏蛋白(mucins)（其特性可模拟天然黏液）以及分泌黏液的HT29-MTX上皮细胞培养物，测试了这些壳聚糖对黏液的作用效果。研究发现，聚合度为8的最低摩尔质量壳聚糖变体可深入扩散至黏液凝胶内部，同时对黏蛋白聚合物进行物理交联；而摩尔质量更高的壳聚糖变体（聚合度分别为52和100）仅能产生表面相互作用。这种复合作用使黏蛋白聚合物网格变得更为紧密，延缓了葡聚糖聚合物(dextran polymers)与霍乱毒素B亚基蛋白(cholera toxin B subunit protein)在黏液凝胶中的扩散过程。上述研究结果揭示了低摩尔质量黏膜黏附聚合物(mucoadhesive polymers)（如壳聚糖）的全新用途：作为无细胞毒性(noncytotoxic)的黏膜屏障强化剂，有望在黏膜疾病的预防与治疗中发挥重要价值。