Protective role of M muscarinic acetylcholine receptor in indomethacin-induced small intestinal injury.

EP prostanoid receptor (EPR) contributes to the intestinal epithelial Cl secretion, and inhibition of prostaglandin E (PGE) production by non-steroidal anti-inflammatory drugs (NSAIDs) plays a central role in NSAID-induced enteropathy. Although M muscarinic acetylcholine receptor (MR) also contributes to the intestinal epithelial Cl secretion, it remains unclear whether MR is involved in NSAID-induced enteropathy due to a lack of selective agents. The present study explored how MR is involved in the regulation of the intestinal epithelial Cl secretion and its pathophysiological role in NSAID-induced enteropathy. Using the novel highly-selective M positive allosteric modulator PAM-369 that we recently developed, we evaluated the role of MR in the intestinal epithelial secretion ex vivo by measuring the short circuit current (Isc) of intestinal epithelium with a Ussing chamber system and examined whether or not MR protects against small intestinal injury in indomethacin-treated mice. Both the PGE derivative misoprostol and carbachol similarly increased the Isc in a concentration-dependent manner. The Isc increases were abolished either by receptor antagonists (an EPR antagonist and a MR antagonist, respectively) or by removal of extracellular Cl. PAM-369 enhanced the carbachol-induced Isc by potentiating MR, which could contribute to enhanced intestinal epithelial secretion. Treatment with PAM-369 ameliorated small intestinal injury in indomethacin-treated mice. Importantly, the MR expression was significantly up-regulated, and PAM-369 potentiation of MR was augmented in indomethacin-treated mice compared to untreated mice. These findings show that MR plays a role in maintaining the intestinal epithelial secretion, which could contribute to protection against indomethacin-induced small intestinal injury. MR is a promising target for treating or preventing NSAID-induced enteropathy. KEY MESSAGES: PAM-369, the M positive allosteric modulator, was used to potentiate MR. PAM-369 enhanced carbachol-induced Isc in mouse ileum. PAM-369 ameliorated small intestinal injury in indomethacin-treated mice. MR is a promising target for treating or preventing NSAID-induced enteropathy.