Activation of AMPK by chitosan oligosaccharide in intestinal epithelial cells: Mechanism of action and potential applications in intestinal disorders.

Chitosan oligosaccharide (COS), a biomaterial derived from chitin, is absorbed by intestinal epithelia without degradation and has diverse biological activities including intestinal epithelial function. However, the mode of action is still unclear. This study aimed to investigate the effect of COS on AMP-activated protein kinase (AMPK) in intestinal epithelial cells (IEC) and its potential applications in the intestinal diseases benefited from AMPK activation. COS with molecular weights (MW) from 5,000Da to 14,000Da induced AMPK activation in T84 cells. That with MW of 5,000-Da was the most potent polymer and was used in the subsequent experiments. COS also activated AMPK in other IEC including HT-29 and Caco-2 cells. Mechanism of COS-induced AMPK activation in T84 cells involves calcium-sensing receptor (CaSR)-phospholipase C (PLC)-IP3 receptor channel-mediated calcium release from endoplasmic reticulum (ER). In addition, COS promoted tight junction assembly in T84 cells in an AMPK-dependent manner. COS also inhibited NF-κB transcriptional activity and NF-κB-mediated inflammatory response and barrier disruption via AMPK-independent mechanisms. Interestingly, luminal exposure to COS suppressed cholera toxin-induced intestinal fluid secretion by ∼30% concurrent with AMPK activation in a mouse closed loop model. Importantly, oral administration of COS prevented the development of aberrant crypt foci in a mouse model of colitis-associated colorectal cancer (CRC) via a mechanism involving AMPK activation-induced β-catenin suppression and caspase-3 activation. Collectively, this study reveals a novel action of COS in activating AMPK via CaSR-PLC-IP3 receptor channel-mediated calcium release from ER. COS may be beneficial in the treatment of secretory diarrheas and CRC chemoprevention.