Tu1841 Investigation of Indomethacin-Induced Small Intestinal Mucosal Damage in Atg5-Knock-out Mice, and the Molecular Mechanisms of Autophagy and Apoptosis

Background: In recent years, it has been shown that nonsteroidal anti-inflammatory drugs (NSAIDs) damage the mucosa of both the stomach and the small intestine. Various points are still unclear with respect to the pathology of NSAID-induced small intestinal mucosal damage, but attention has been given to the type of pathology that involves autophagy and cell death. For the present study, mice were prepared in which the Atg5 gene, essential for autophagy induction, was knocked out, in the small intestine only[w1] . Small intestinal mucosal damage induced by oral administration of indomethacin, an NSAID, was then compared between knock-out and normal mice. In addition, in order to elucidate the molecular mechanism, a study was carried out with IEC-6 cells, which are normal rat epithelial cells. Methods: Indomethacin was administered to normal mice and knock-out mice in the non-fasted state, and after 24 hours the entire damaged area of the small intestine was measured. In addition, Atg5-knock-out IEC-6 cells were administered indomethacin, and cell viability was determined. Furthermore, LC3, PARP1, Erk1/2, Nrf2, and HO-1 expression was investigated by the Western blot method. Results: The mean surface areas of small intestinal damage in normal mice and Atg5-knock-out mice were 16.26 ± 3.24 mm2 and 7.09 ± 2.24 mm2, respectively. Indomethacin-induced damage was also lower in Atg5-knock-out IEC-6 cells than in normal IEC-6 cells, and ERK, Nrf2, and HO-1 expression was higher in the former. Conclusions: It was confirmed that loss of autophagy results in reduction of indomethacin-induced small intestinal mucosal damage both in vivo and in vitro. It is known that HO-1 is induced by Nrf2, and Nrf2 is induced via the Erk pathway, suggesting the possibility that increased HO-1 expression mediated by the Erk-Nrf2 pathway, due to inhibition of autophagy, is the mechanism by which cytotoxicity is inhibited.