Melatonin receptor expression in the normal human gastrointestinal tract and in gastrointestinal neuroendocrine tumors
Abstract
Melatonin is present in peripheral tissues and regulates many functions. The largest source, according to animal studies, is the gastrointestinal tract (GIT). Melatonin receptors, MT1 and MT2 have been identified in rat intestine, but in humans receptor expression has not been thoroughly characterized.
This study aims to map the expression of melatonin and its two receptors both in normal human GIT as well as in small intestine neuroendocrine tumors (SI-NETs) derived from enterochromaffin cells.
Biopsies from normal GIT from 21 individuals and from SI-NETs from 39 patients were immunohistochemically stained for melatonin, MT1 and MT2. Melatonin levels in plasma from 20 patients with SI-NETs were measured.
Melatonin stainings were not complete due to methodological problems. Positive expression of both MT1 and MT2 was found in the epithelium of the normal GIT, in sections representing stomach (n=5), small intestine (n=4) and large intestine (n=12). Positive expression was also found for MT2 in endocrine cells in crypts throughout the GIT. In the tumor sections, positive expression for MT1 was rare, while the majority of sections studied were positive for MT2. The intensity of the staining was not related to clinical parameters but MT2 expression was stronger in primary tumors than in metastases (p=0,01).
Receptor expression indicates a role for melatonin signaling in the epithelium and in endocrine cells of the GIT. Melatonin has well documented anti-proliferative effects and melatonin receptor expression in tumors may provide a target for therapy.
NOTE: This publication/thesis cites (Ref. N.58): Di Bella G., Mascia F., Gualano L., Di Bella L. - Melatonin anticancer effect: review. Int J Mol Sci. 2013;14:2410–2430
See also About Melatonin.