Oral Administration of Hydrogel-Embedding Silk Sericin Alleviates Ulcerative Colitis through Wound Healing, Anti-Inflammation, and Anti-Oxidation

Silk sericin (SS) is abundant in silk industry wastewater, and it has emerged as a promising natural protein for biomedical research. However, its therapeutic potential against ulcerative colitis (UC) has not been exploited. The objective of this study is to investigate the therapeutic effects of SS in a dextran sulfate sodium-induced UC mouse model, and further discover its underlying mechanisms. The purified SS molecules showed negative cytotoxicity, and could be efficiently internalized by colonic epithelial cells and macrophages. In vitro experiments revealed that it could accelerate the mucosal healing, down-regulate the production of pro-inflammatory factors, increase the secretion of anti-inflammatory cytokines, and eliminate the intracellular reactive oxygen species. Finally, animal experiments confirmed that oral administration of hydrogel (chitosan/alginate)-embedding SS molecules attenuated UC-induced symptoms (e.g., body weight loss, colon shortening, increase of spleen weight, and histopathological appearance), which was supported by signs of mucosal healing, anti-inflammation, and elevation of the amounts of tight junction proteins (occludin and zonula occludens-1) and mucin protein (MUC2). Taken together, our results demonstrate that SS can be exploited as a promising oral natural therapeutic for UC treatment with the aid of hydrogel.