GPR39 receptors and actions of trace metals on pancreatic beta cell function and glucose homoeostasis.

Abstract

G-protein-coupled receptor 39 (GPR39) has been implicated in glucose homoeostasis, appetite control and gastrointestinal tract function. This study used clonal BRIN-BD11 cells and mouse pancreatic islets to assess the insulin-releasing actions of trace metals believed to act via GPR39, and the second messenger pathways involved in mediating their effects. Micromolar concentrations of Zn(2+), Cu(2+), Ni(2+) and Co(2+) were examined under normoglycaemic and hyperglycaemic conditions. Mechanistic studies investigated changes of intracellular Ca(2+), cAMP generation and assessment of cytotoxicity by LDH release. Cellular localisation of GPR39 was determined by double immunohistochemical staining. All trace metals (7.8-500µmol/l) stimulated insulin release with Cu(2+) being the most potent in isolated islets, with an EC50 value of 87μmol/l. Zn(2+) was the most selective with an EC50 value of 125μmol/l. Enhancement of insulin secretion was also observed with Ni(2+) (179μmol/l) and Co(2+) (190μmol/l). These insulin-releasing effects were confirmed using clonal BRIN-BD11 cells which exhibited enhanced intracellular Ca(2+) (p<0.05-p<0.001) and cAMP generation (p<0.05-p<0.001) in response to trace metals. Oral administration of Zn(2+), Ni(2+) and Cu(2+) (50µmol/kg together with 18mmol/kg glucose) decreased the glycaemic excursion (p<0.05-p<0.01) and augmented insulin secretion (p<0.05-p<0.01) in NIH Swiss mice. This study has demonstrated the presence of GPR39 and the insulinotropic actions of trace metals on BRIN-BD11 cells and pancreatic beta cells, together with their antihyperglycaemic actions in vivo. These data suggest that development of agonists capable of specifically activating GPR39 may be a useful new therapeutic approach for diabetes management.