Protective Effect of TRPM8 against Indomethacin-Induced Small Intestinal Injury via the Release of Calcitonin Gene-Related Peptide in Mice.

Transient receptor potential melastatin 8 (TRPM8) is a non-selective cation channel activated by mild cooling and chemical agents including menthol. Nonsteroidal anti-inflammatory drugs have antipyretic, analgesic effects, and they can cause stomach and small intestinal injury. The current study investigated the role of TRPM8 in the pathogenesis of indomethacin-induced small intestinal injury. In male TRPM8-deficient (TRPM8KO) and wild-type (WT) mice, intestinal injury was induced via the subcutaneous administration of indomethacin. In addition, the effect of WS-12, a specific TRPM8 agonist, was examined in TRPM8KO and WT mice with indomethacin-induced intestinal injury. TRPM8KO mice had a significantly higher intestinal ulcerogenic response to indomethacin than WT mice. The repeated administration of WS-12 significantly attenuated the severity of intestinal injury in WT mice. However, this response was abrogated in TRPM8KO mice. Furthermore, in TRPM8-enhanced green fluorescent protein (EGFP) transgenic mice, which express EGFP under the direction of TRPM8 promoter, the EGFP signals in the indomethacin-treated intestinal mucosa were upregulated. Further, the EGFP signals were commonly found in calcitonin gene-related peptide (CGRP)-positive sensory afferent neurons and partly colocalized with substance P (SP)-positive neurons in the small intestine. The intestinal CGRP-positive neurons were significantly upregulated after the administration of indomethacin in WT mice. Nevertheless, this response was abrogated in TRPM8KO mice. In contrast, indomethacin increased the expression of intestinal SP-positive neurons in not only WT mice but also TRPM8KO mice. Thus, TRPM8 has a protective effect against indomethacin-induced small intestinal injury. This response may be mediated by the upregulation of CGRP, rather than SP.