Gijs J.D. Van Acker

A mouse model of acute biliary pancreatitis induced by retrograde pancreatic duct infusion of na-taurocholate

Objective: Most mechanistic studies of pancreatitis in mice employ the secretagogue-induced model. The currently reported studies were designed to develop an alternative, and possibly more clinically relevant, mouse model of pancreatitis. Design: Na-taurocholate (10–50 &mgr;l, 1–5%) in saline, or saline alone, was retrogradely infused into the mouse pancreatic duct. The animals were killed 6–24 hours later and the severity of pancreatitis in the pancreatic head and tail was examined by quantitating hyperamylasemia, pancreatic edema, acinar cell necrosis, and pancreatic inflammation. In addition, intrapancreatic activation of trypsinogen, generation of IL-6, intrapulmonary sequestration of neutrophils, and alterations in lung compliance were evaluated. The effects of Na-taurocholate on in-vitro acinar cell calcium transients, viability, and trypsinogen activation were examined. Results: Little or no evidence of pancreatitis was observed in mice infused with saline alone or in the tail of pancreata removed from animals infused with Na-taurocholate. In the head of the pancreas, evidence of pancreatitis was observed 12–24 hours after infusion of 20–50 &mgr;l 2–5% Na-taurocholate and the earliest morphological changes involved terminal duct and acinar cells. Intrapancreatic trypsin activity was transiently elevated within 5 minutes of Na-taurocholate infusion and pancreatic IL-6 levels were elevated 24 hours later. Under in-vitro conditions, Na-taurocholate triggered pathological acinar cell calcium transients, cell death, and calcium-dependent trypsinogen activation. Conclusion: This clinically relevant model of acute biliary pancreatitis yields reproducible results and its severity can be easily manipulated. It is ideally suited for use in mechanistic studies employing genetically modified mouse strains.

Protease-activated Receptor-2 Exerts Contrasting Model-specific Effects on Acute Experimental Pancreatitis

Protease-activated receptor-2 (PAR2) is a 7-transmembrane G-protein-coupled tethered ligand receptor that is expressed by pancreatic acinar and ductal cells. It can be physiologically activated by trypsin. Previously reported studies (Namkung, W., Han, W., Luo, X., Muallem, S., Cho, K. H., Kim, K. H., and Lee, M. G. (2004) Gastroenterology 126, 1844–1859; Sharma, A., Tao, X., Gopal, A., Ligon, B., Andrade-Gordon, P., Steer, M. L., and Perides, G. (2005) Am. J. Physiol. 288, G388–G395) have shown that PAR2 activation exerts a protective effect on the experimental model of pancreatitis induced by supramaximal secretagogue (caerulein) stimulation. We now show that PAR2 exerts a worsening effect on a different model of experimental pancreatitis, i.e. one induced by retrograde pancreatic ductal infusion of bile salts. In vitro studies using freshly prepared pancreatic acini show that genetic deletion of PAR2 reduces bile salt-induced pathological calcium transients, acinar cell injury, and activation of c-Jun N-terminal kinase, whereas genetic deletion of PAR2 has the opposite or no effect on these pancreatitis-related events when they are elicited, in vitro, by caerulein stimulation. Studies employing a combination of trypsin inhibition and activation of PAR2 with the activating peptide SLIGRL show that all these differences indeed depend on the activation of PAR2. These studies are the first to report that a single perturbation can have model-specific and opposite effects on pancreatitis, and they underscore the importance of performing mechanistic pancreatitis studies using two dissimilar models of the disease to detect idiosyncratic, model-specific events. We suggest PAR2 activation exerts a worsening effect on the severity of clinical pancreatitis and that interventions interfering with PAR2 activation may be of benefit in the treatment of patients with severe pancreatitis.

Tumor Progression Locus-2 Is a Critical Regulator of Pancreatic and Lung Inflammation during Acute Pancreatitis

Pancreatic and lung inflammation during acute pancreatitis is a poorly understood, but clinically important, phenomenon. The proto-oncogene Tpl2 (tumor progression locus-2) has recently been shown to have important immunomodulatory effects on some inflammatory processes, but its importance to pancreatitis has not been previously examined. Our studies were designed to (a) define the effects of Tpl2 on pancreatic and lung inflammation during pancreatitis and (b) identify mechanisms and cell types responsible for those effects. We examined pancreatitis-associated Tpl2 effects in wild type and Tpl2-/- mice subjected to either secretagogue-induced or bile salt-induced pancreatitis. To determine the myeloid or non-myeloid lineage of cells responsible for the Tpl2 effects, we used Tpl2-/- chimeric mice generated by lethal irradiation followed by bone marrow transplantation. Mechanisms responsible for the effects of Tpl2 ablation on caerulein-induced proinflammatory events were evaluated under in vivo and in vitro conditions using the techniques of electrophoretic mobility shift assay, immunoblot analysis, and quantitative reverse transcription-PCR. We found that Tpl2 ablation markedly reduced pancreatic and lung inflammation in these two dissimilar models of pancreatitis, but it did not alter pancreatic injury/necrosis in either model. The reduction in caerulein-induced pancreatic inflammation is dependent upon Tpl2 ablation in non-myeloid cells and is associated with both in vivo and in vitro inhibition of MEK, JNK, and AP-1 activation and the expression of MCP-1, MIP-2, and interleukin-6. Non-myeloid cell expression of Tpl2 regulates pancreatic inflammation during pancreatitis by mediating proinflammatory signals and the generation of neutrophil chemoattracting factors.