Abstract
Crohn’s disease and ulcerative colitis (UC), two types of inflammatory bowel disease (IBD), and idiopathic slow transit constipation (ISTC) are serious diseases of the digestive system with unknown aetiologies. Since it is well known that opioids have a profound effect on the gastrointestinal tract, and also play an important role in immune regulation, it is postulated that they may be involved in the pathophysiology of these debilitating disorders. In this investigation immunohistochemical techniques were used to determine a potential role for opioids in intestinal disease by evaluating the abundance and localisation of the four opioid receptors; DOR, KOR, MOR and ORL1, in full thickness sections of colon from Crohn’s disease, UC and ISTC patients, compared to healthy specimens. The endogenous ligand for ORL1, nociceptin, was also investigated, and Tiffalyzer software was used for semi-quantification of the areas of immunoreactivity in the submucosal and myenteric plexuses.Each of the ORs was found to be present in a subpopulation of neuronal cells in the submucosal and myenteric plexuses of the enteric nervous system. Investigations using a neuronal marker - anti-neurofilament antibody - showed a decrease in the neuronal population of the ganglia of these plexuses in both forms of IBD and in ISTC (P < 0.001). There were apparent decreases in the areas with OR-like IR in disease, however, when the reduction in neurofilament-like IR was taken into account it was found that these were largely attributable to the decrease in overall neuronal population. The remaining differences were an increase in MOR-like IR in Crohn’s disease (P < 0.05) and in ISTC (P< 0.0001) submucosal plexuses and an increase in nociceptin-like IR in ISTC (PO.01). In the myenteric plexus there was a significant increase in ORLl-like IR in Crohn’s disease (P < 0.05), UC (P < 0.001) and ISTC (P < 0.01), and a significant decrease in DOR-like IR in UC (P < 0.05). KOR-like IR was unchanged throughout.
OR-like IR was also noted in other areas of the gut wall, including putative nerve fibres or interstitial cells of cajal in the muscularis mucosae and muscularis externa, however this was not quantified. In the mucosa each of the ORs except for KOR were observed in neuroendocrine cells, confirmed by co-localisation with an anti-chromogranin A antibody. There was a significant decrease in the number of these cells in both forms of IBD (P < 0.001) but not in ISTC. Although differences in the number of OR-like IR cells were found in disease compared to health, when the overall decrease in neuroendocrine cells was taken into account the only significant difference was an increase in DOR-like IR neuroendocrine cells in ISTC (P<0.001).
ORs were also observed in cells throughout the colon wall, and these were particularly prevalent in IBD tissue. A number of these IR cells were confirmed to be macrophages, using a macrophage marker antibody. In order to determine a possible function of opioid receptors on inflammatory cells a chemotaxis assay was attempted. However it was not possible to optimise the technique within the time limit, therefore further work is required here.
The results of this study support a role for ORs in the pathophysiology of the conditions investigated, with regard to both the chronic inflammation observed in IBD and the disruption in function found in each of the conditions. Further investigation, particularly with functional studies, will illuminate this role and how it can be applied to therapeutics.
| Date of Award | 2009 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Alistair Corbett (Supervisor) & Douglas Bovell (Supervisor) |