AbstractG-protein coupled receptors (GPCRs) play an essential role in the ability of a cell to react to its environment. The presence of these receptors on the cell membrane allow the external environment of a cell to affect the intracellular signalling that takes place. For this reason GPCRs are an attractive drug target. Targeting of class B GPCRs through the GLP-1 receptor (GLP1R) agonists is an already approved therapy for the treatment of Type 2 Diabetes. Class A rhodopsin-like GPCRs are currently the most popular drug targets for current FDA approved drugs. GPCRs are also attractive drug targets due to the wide range of ligands that bind to GPCRs such as free fatty acids during digestion.
This thesis examined the effects of activation of both synthetic and endogenous ligands for GPR39, GPR55, GPR75, GPR119 and GPR120 on the secretion of the incretin hormones GLP-1 and GIP. The insulinotropic effects of these receptors was also investigated. GLP-1 and GIP secretion were studied using GLUTag and pGIPneo STC-1 cells respectively while insulin secretion was assessed in BRIN-BD11 cells and isolated pancreatic islets. The cytotoxicity of GPCR agonists was determined using MTT assay in GLUTag and pGIPneo STC-1 cells and Alamar blue assay in BRINBD11 cells. Membrane integrity was further studied using LDH assay. The expression and cellular localisation of GPCRs and intestinal hormones was determined using qPCR and double immunohistochemistry in both cell lines and small intestine. The acute in vivo effects of intestinal GPCR activation on blood glucose as well as plasma GLP-1, GIP and insulin were examined in male Swiss TO mice. The chronic effects biological effects of GPR55 agonist Abn-CBD and GPR119 agonist GPR119 as a monotherapy and combination therapy with the DPP-IV inhibitor Sitagliptin were assessed.
GPCR agonists were able to demonstrate GLP-1, GIP and insulin secretory ability both in vitro and in vivo. The expression of GPCRs in the L and K cells of the intestine were confirmed using immunohistochemistry. Oral administration of GPCR agonists as a monotherapy or combination therapy resulted increased incretin hormone and insulin secretion as well as reduced blood glucose. The effects of chronic treatment of AS1269574 and Abn-CBD in streptozotocin induced diabetic mice improved glucose homeostasis.
Overall this thesis identified the ability of GPCR ligands to affect glucose homeostasis through the incretin hormone pathway as well as through direct action on the pancreas. The work carried out in this thesis demonstrates that GPCR based therapies have anti-diabetic potential and may be an important therapeutic strategy in the treatment of diabetes in the future.
|Date of Award||May 2018|
|Sponsors||Department of Education and Learning (DEL)|
|Supervisor||Peter Flatt (Supervisor) & Aine Mc Killop (Supervisor)|
- unified receptors
- Type 2 Diabetes
- gastro intestinal