The method of inducing acute pancreatitis by retrograde sodium taurocholate infusion has already been shown in rats22,23,24. Three similar works, published in 2008, 2010 and 2015, served as a reference for the protocol3,14,15. In this work, we list all the critical steps for reproducing this method in C57BL/6 mice and some possibilities for validating it.
A critical step in this test is blocking the bile duct at the level of the hilum with a microvessel clip (step 3.1) to avoid sodium taurocholate reflux into the liver. This step requires much attention, since the portal vein is next to the duct (Figure 1D), so care must be taken to not block it together. The needle should be inserted only into the most distal duct portion. If it is introduced deeply into the duct, it can cause a rupture with the acid overflowing to the glandular parenchyma and/or to other ducts14. Check that the polyethylene tube has air inside to prevent the obstruction of the common bile duct.
This model requires an incision in the mouse abdomen. Inserting the cannula through the pancreatic duct orifice requires experience but that can be achieved with training15,25. It is important to highlight that the severity of pancreatitis in this model is proportionally dependent on the concentration, volume of the infusion, pressure of the infusion, and the time of AP induction. Thus, a constant infusion machine with controlled volume and pressure must be used.
For this study, we standardized a concentration of 2.5%, with an infusion speed of 10 µL/min, for 3 min and constant pressure. At 12 h of AP, increased inflammatory parameters and necrosis of the pancreatic tissues were observed, with animals dying within 16 h after AP induction.
Although the main causes of AP are alcohol consumption or gallstones, these models are not experimentally reproducible26. Currently, the most used protocol for AP induction in mice involves 7 intraperitoneal injections of cerulein (50 µg/kg body weight) at 1 h intervals27. Cerulein has been used to induce a mild or moderate acute pancreatitis as well. The variability in this model limits its use in studying the destructive effects of the disease, which confer clinical morbidity and mortality10. Models that trigger high mortality in a short time are relevant for the study of severe AP (necrotizing), as they can evaluate the effectiveness of new drugs or interventions. Among these models are hemorrhagic AP induction in young female rodents (between 4 and 6 weeks) by a choline-deficient diet28 and L-arginine (e.g., 3 x 3 g/kg or 2 x 4 g/kg) based acute pancreatitis induction in mice but the proper dosing of L-arginine to induce AP should be tested by each laboratory and in each mouse strain29. In 2015, a study showed that an intra-ductal taurocholate infusion followed by distal common bile duct ligation leads to a severe, necrotic model of pancreatitis in mice3. However, this model is not useful for testing drug efficacy and interventions due to its irreversible condition.
The outcomes found in this study correlate with recent literature such as the elevation of serum amylase concentration and IL-6 being associated with disease progression. It is possible that in the future, the measurement of proteins such as TNF-α, IL-1β and myeloperoxidase will be a clinical prognostic parameter for severe acute pancreatitis30,31,32.
In conclusion, the protocol used in the present study to induce AP in mice by the infusion of sodium taurocholate directly into the common bile duct results in severe acute pancreatitis with necrosis of pancreatic tissue that can be observed even at 12 h after the induction with elevation of IL-6 cytokine in the serum and peritoneal fluid and with high lethality (100% mortality in 16 h, data not shown).