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Melatonin and its receptors in the normal human gastrointestinal tract, pancreas and in small intestinal neuroendocrine tumours
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Psychiatry, University Hospital.
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Melatonin, “the hormone of darkness” is well known to regulate sleep and circadian rhythm. However, melatonin is also present in numerous peripheral tissues and the number of actions assigned to this neurohormone is growing steadily. Based on animal studies, it has been proposed that gastrointestinal melatonin is produced in enterochromaffin cells.

The aims were to characterise the expression of melatonin and its receptors MT1 and MT2 in normal human gastrointestinal tract and pancreas as well as in tumours derived from enterochromaffin cells, small intestinal neuroendocrine tumours (SI-NET), using immunohistochemistry. Melatonin and receptor expression was furthermore compared to clinical symptoms, tumour prognostic factors and treatment response.

In enterochromaffin cells from normal gastrointestinal tissue and in SI-NETs a strong immunoreactivity (IR) for melatonin and MT2 was found, while MT1 IR was low or absent. Melatonin, MT1 and MT2 IR was also seen in the large intestinal epithelium of normal gastrointestinal tract and in pancreatic islets, although the expression of MT1 in pancreatic tissue varied. Analyses of mRNA data confirmed the expression of the enzymes needed for melatonin synthesis as well as MT1 and MT2 in small intestine and pancreas.

The intensity of melatonin IR in SI-NETs correlated to lower proliferation index and less symptoms of diarrhoea, which is well in line with the proposed actions of melatonin described in nimal studies. The intensity of MT2 IR was generally lower in metastases than in primary tumours. Plasma levels of melatonin in patients with SI-NETs and disease stabilisation/remission were reduced after treatment and higher levels were associated with nausea.

In conclusion, melatonin and its receptors are present in the normal human gastrointestinal tract, pancreas and in SI-NETs. Melatonin IR intensity in tumours correlated significantly to less diarrhoea and to lower proliferation index. Plasma levels of melatonin in patients with SI-NETs were reduced with treatment response, indicating a possible tumour-derived origin of circulating melatonin levels.

These results are in agreement with the suggested actions of melatonin on gastrointestinal motility and tumour growth.

Place, publisher, year, edition, pages
Uppsala: Uppsala University, 2017. , p. 31
National Category
Clinical Medicine
Identifiers
URN: urn:nbn:se:uu:diva-319920OAI: oai:DiVA.org:uu-319920DiVA, id: diva2:1088036
Presentation
2017-04-25, Lilla konferensrummet, Blå korset, Akademiska sjukhuset, 75185, Uppsala, 09:15 (Swedish)
Supervisors
Available from: 2017-04-11 Created: 2017-04-11 Last updated: 2017-04-27Bibliographically approved
List of papers
1. Human Gastroenteropancreatic Expression of Melatonin and Its Receptors MT1 and MT2
Open this publication in new window or tab >>Human Gastroenteropancreatic Expression of Melatonin and Its Receptors MT1 and MT2
2015 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 3, article id e0120195Article in journal (Refereed) Published
Abstract [en]

Background and Aim The largest source of melatonin, according to animal studies, is the gastrointestinal (GI) tract but this is not yet thoroughly characterized in humans. This study aims to map the expression of melatonin and its two receptors in human GI tract and pancreas using microarray analysis and immunohistochemistry. Method Gene expression data from normal intestine and pancreas and inflamed colon tissue due to ulcerative colitis were analyzed for expression of enzymes relevant for serotonin and melatonin production and their receptors. Sections from paraffin-embedded normal tissue from 42 individuals, representing the different parts of the GI tract (n= 39) and pancreas (n= 3) were studied with immunohistochemistry using antibodies with specificity for melatonin, MT1 and MT2 receptors and serotonin. Results Enzymes needed for production of melatonin are expressed in both GI tract and pancreas tissue. Strong melatonin immunoreactivity (IR) was seen in enterochromaffin (EC) cells partially co-localized with serotonin IR. Melatonin IR was also seen in pancreas islets. MT1 and MT2 IR were both found in the intestinal epithelium, in the submucosal and myenteric plexus, and in vessels in the GI tract as well as in pancreatic islets. MT1 and MT2 IR was strongest in the epithelium of the large intestine. In the other cell types, both MT2 gene expression and IR were generally elevated compared to MT1. Strong MT2, IR was noted in EC cells but not MT1 IR. Changes in gene expression that may result in reduced levels of melatonin were seen in relation to inflammation. Conclusion Widespread gastroenteropancreatic expression of melatonin and its receptors in the GI tract and pancreas is in agreement with the multiple roles ascribed to melatonin, which include regulation of gastrointestinal motility, epithelial permeability as well as enteropancreatic cross-talk with plausible impact on metabolic control.

National Category
Neurosciences
Identifiers
urn:nbn:se:uu:diva-252709 (URN)10.1371/journal.pone.0120195 (DOI)000352134700057 ()25822611 (PubMedID)
Available from: 2015-05-12 Created: 2015-05-11 Last updated: 2018-01-11Bibliographically approved
2. Melatonin Immunoreactivity in Malignant Small Intestinal Neuroendocrine Tumours
Open this publication in new window or tab >>Melatonin Immunoreactivity in Malignant Small Intestinal Neuroendocrine Tumours
Show others...
2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 10, article id e0164354Article in journal (Refereed) Published
Abstract [en]

Background/ Aims Small intestinal neuroendocrine tumours (SI-NETs) are derived from enterochromaffin cells. After demonstrating melatonin in enterochromaffin cells, we hypothesized that SI-NETs may express and secrete melatonin, which may have an impact on clinical factors and treatment response. Methods Tumour tissue from 26 patients with SI-NETs, representing paired sections of primary tumour and metastasis, were immunohistochemically stained for melatonin and its receptors, MT1 and MT2. Plasma melatonin and immunoreactivity (IR) for melatonin, MT1 and MT2 in tumour cells were compared to other tumour markers and clinical parameters. Melatonin was measured at two time points in fasting morning plasma from 43 patients with SI-NETs. Results Melatonin IR was found in all SI-NETS. Melatonin IR intensity in primary tumours correlated inversely to proliferation index (p = 0.022) and patients reported less diarrhoea when melatonin IR was high (p = 0.012). MT1 IR was low or absent in tumours. MT2 expression was medium to high in primary tumours and generally reduced in metastases (p = 0.007). Plasma-melatonin ranged from 4.5 to 220.0 pg/L. Higher levels were associated with nausea at both time points (p = 0.027 and p = 0.006) and flush at the second sampling. In cases with disease stabilization or remission (n = 34), circulating melatonin levels were reduced in the second sample (p = 0.038). Conclusion Immunoreactive melatonin is present in SI-NETs. Circulating levels of melatonin in patients with SI-NETs are reduced after treatment. Our results are congruent with recent understanding of melatonin's endocrine and paracrine functions and SI-NETs may provide a model for further studies of melatonin function.

National Category
Cancer and Oncology Neurology
Identifiers
urn:nbn:se:uu:diva-310013 (URN)10.1371/journal.pone.0164354 (DOI)000385505800057 ()27736994 (PubMedID)
Funder
Swedish Society of MedicineSwedish Cancer Society
Available from: 2016-12-12 Created: 2016-12-09 Last updated: 2018-07-13Bibliographically approved

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