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 ml, 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 ml 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.

Intrapancreatic activation of trypsinogen is believed to play a critical role in the initiation of acute pancreatitis, but mechanisms responsible for intrapancreatic trypsinogen activation during pancreatitis have not been clearly defined. In previous in vitro studies, we have shown that intra-acinar cell activation of trypsinogen and acinar cell injury in response to supramaximal secretagogue stimulation could be prevented by the cell permeant cathepsin B inhibitor E64d (Saluja A, Donovan EA, Yamanaka K, Yamaguchi Y, Hofbauer B, and Steer ML. Gastroenterology 113: 304-310, 1997). The present studies evaluated the role of intrapancreatic trypsinogen activation, this time under in vivo conditions, in two models of pancreatitis by using another highly soluble cell permeant cathepsin B inhibitor, L-3-trans-(propylcarbamoyl)oxirane-2-carbonyl-L-isoleucyl-L-proline methyl ester (CA-074me). Intravenous administration of CA-074me (10 mg/kg) before induction of either secretagogue-elicited pancreatitis in mice or duct infusion-elicited pancreatitis in rats markedly reduced the extent of intrapancreatic trypsinogen activation and substantially reduced the severity of both pancreatitis models. These observations support the hypothesis that, during the early stages of pancreatitis, trypsinogen activation in the pancreas is mediated by the lysosomal enzyme cathepsin B. Our findings also suggest that pharmacological interventions that inhibit cathepsin B may prove useful in preventing acute pancreatitis or reducing its severity.

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Mechanistic studies of acute pancreatitis require animal models because clinical material is generally not available during the early phases of the disease. Here we describe a protocol to induce biliary pancreatitis by retrogradely infusing bile acids into the pancreatic duct of anesthetized mice. The resulting model replicates events believed to be responsible for the onset of clinical biliary (i.e., gallstone) pancreatitis and creates highly reproducible pancreatitis with a severity that depends on the concentration of infused bile acid. Pancreatitis reaches its maximal level of severity within 24 h of induction, and it resolves over the subsequent week. This protocol enables the investigator to use genetically modified strains of mice, and it requires only relatively simple and easily learned techniques of small animal surgery. With practice and gentle technique, the surgery (from induction of anesthesia to completion of the infusion) can be completed within 25 min per animal.