Prostaglandin and cannabinoid receptors in EoE

Eosinophilic esophagitis (EoE) is a chronic, antigen- and immune cell-mediated inflammation of the esophagus. The disease is characterized by intense infiltration of eosinophils into the esophageal mucosa. Eosinophils belong to the group of white blood cells with cytotoxic enzymes. Dysphagia is one of the early symptoms of EoE. It has been long regarded as a rare disease but through advanced diagnostic methods and actual higher number of cases, the incidence of EoE has increased in the past years. Although thought to be induced primarily by an aberrant immune response the exact cause of EoE remains unclear. A compound inhibiting the prostaglandin (PG) D2 receptor has been recently shown to improve disease symptoms of EoE suggesting a regulatory role for bioactive lipids like prostaglandins and endocannabinoids in the development of disease. These mediators are key players in inflammation. Similar to prostaglandins, endocannabinoids regulate tissue homeostasis. The project, therefore, explores the role of PGD2, PGE2 and endocannabinoids, and of their receptors in white blood cells of subjects with and without EoE. Esophageal mucosal biopsies from patients with EoE and gastro-esophageal reflux, and from subjects with no esophageal disease are collected and used to study expression of PGD2, PGE2 and cannabinoid receptors. In biopsies, the content of PGD2, PGE2 and endocannabinoids are measured by mass spectrometry. In cell culture experiments, we will explore whether eosinophils interact with mucosal epithelial cells of the esophagus. Prostaglandin-producing enzymes and receptors of the endocannabinoid system are highly amenable to pharmacological treatment. Since the role of the two systems in EoE are hardly known, the proposal explores new ground. The prostaglandin and the endocannabinoid system could reveal much needed biomarkers of disease while investigating the two systems could open up new therapeutical possibilities of EoE treatment.

Inflammation of the esophagus: a role for the endocannabinoid system Similar to the Cannabis plant, humans and animals produce molecules (so-called endocannabinoids) that activate receptors of the endocannabinoid system (ECS). Endocannabinoids and receptors of the ECS regulate many aspects, such as mood and appetite, but also inflammation. After the legalization of "medical marijuana" in many countries, Cannabis is now widely used as an alternative form of treatment. However, the use of Cannabis may also increase the risk of cardiovascular events calling out for a deeper knowledge on the effects of cannabinoids in different disease conditions. In our project we investigated whether the ECS could play a role in a once rare but now more frequent disease, namely, in eosinophilic esophagitis (EoE), a specific type of inflammation of the esophageal mucosa characterized by high presence of certain immune cells of the mucosa - the eosinophils. We recruited EoE patients and control subjects at the Medical University of Graz, and took biopsies from the esophageal mucosa and collected blood samples. We first compared immune cells from blood and esophageal mucosal tissue and detected differences in the expression of cell membrane activation markers in mucosal tissue, but not in the blood, between subjects with active and no EoE. We further noticed that many ECS components were differentially regulated. While many receptors of the ECS were up in esophageal mucosal biopsies of patients with active EoE, enzymes were down. One of these enzymes, monoacylglycerol lipase (MGL), which is responsible for the breakdown of the endocannabinoid 2-arachidonoylglycerol (2-AG), displayed significantly low expression, and we, therefore, investigated it further. The downregulation of MGL seems to be very specific for eosinophilic EoE disease, but not for other forms of esophagitis. At the same time, the levels of 2-AG were higher in mucosal biopsies of EoE patients than control subjects. We found out that MGL was present in the epithelial cells of the mucosa and that 2-AG was also released from epithelial cells. Inhibition of MGL in esophageal epithelial cells caused increased levels of inflammatory mediators that are typical of EoE. Finally, we proved that 2-AG helped recruiting eosinophils to the tissue via the actions of cannabinoid receptor 2, which is found on eosinophils. From our results we concluded that components of the ECS such as MGL, 2-AG and cannabinoid receptor 2 play an important role in EoE pathogenesis. Phytocannabinoids could increase infiltration of eosinophils to the esophagus, potentially exacerbating EoE disease. Our project coincides with a publication reporting that Cannabis users have worse outcomes after treatment of EoE than non-users. Our results may, therefore, represent a mechanism for the clinical data. Pharmacological compounds that influence the ECS could represent valuable tools for the treatment of EoE.