Background & aims: The mechanisms by which reflux of bile acids into the pancreas induces pancreatitis are unknown. We reasoned that key events responsible for this phenomenon might be mediated by Gpbar1, a recently identified and widely expressed G-protein-coupled, cell surface bile acid receptor.
Methods: Acute pancreatitis was induced in wild-type and Gpbar1(-/-) mice by either retrograde ductal infusion of taurolithocholic acid-3-sulfate (TLCS) or supramaximal secretagogue stimulation with caerulein. In vitro experiments were performed in which acini obtained from wild-type and Gpbar1(-/-) mice were exposed to either submicellar concentrations of TLCS (200-500 microM) or a supramaximally stimulating concentration of caerulein (10 nM).
Results: Gpbar1 is expressed at the apical pole of acinar cells and its genetic deletion is associated with reduced hyperamylasemia, edema, inflammation, and acinar cell injury in TLCS-induced, but not caerulein-induced, pancreatitis. In vitro, genetic deletion of Gpbar1 is associated with markedly reduced generation of pathological calcium transients, intracellular activation of digestive zymogens, and cell injury when these responses are induced by exposure to TLCS, but not when they are induced by exposure to caerulein.
Conclusions: Gpbar1 may play a critical role in the evolution of bile-acid-induced pancreatitis by coupling exposure to bile acids with generation of pathological intracellular calcium transients, intra-acinar cell zymogen activation, and acinar cell injury. Acute biliary pancreatitis may be a "receptor-mediated" disease and interventions that interfere with Gpbar1 function might prove beneficial in the treatment and/or prevention of biliary acute pancreatitis.