Murine Ileal Resection Model: Studying Ileectomy-Induced Bile Metabolism in Murine Model

- Enterohepatic circulation of bile acids, or BAs, maintains its homeostasis in the body. Liver cells or hepatocytes produce BAs from where they move towards the ileum and are actively transported inside intestinal cells or ileocytes. Inside ileocytes, BAs activate the synthesis of the Fibroblast Growth Factor, or FGF, hormone. FGF is transposed back to the liver by the hepatic portal vein and binds the receptors on hepatocytes, thus, sending a downstream negative feedback signal for shutting down the BA production.

Ileal resection is a common treatment strategy for colon cancer. Therefore, we prepare a murine ileal resection model to glean insights into ileum's role in colon cancer.

Begin by placing an anesthetized mouse on a dissection board and make a midline abdominal incision. Next, expose the ileum and resect the selected ileal segment and suture the ileal ends together. Finally, return the anastomotic intestine in the abdominal cavity and suture together the incised muscle and skin layer.

Allow the mouse to recover and analyze the effects of ileum removal, which may cause bile overaccumulation in the intestines. In the following protocol, we will prepare a murine ileal resection model to study the effects of the ileal FGF hormone on bile metabolism.

- Begin by confirming the appropriate level of sedation by toe pinch and applying depilatory cream to the mouse's abdomen. Remove the hair with surgical sponges and place the animal on a temperature-controlled, small-animal surgical table set to 37 degrees Celsius. Apply ointment to the animal's eyes and disinfect the exposed skin with a sequential povidone-iodine and 70% ethanol scrub.

Cover the surgical area of the abdomen with sterile surgical gauze and use a scalpel to make a midline incision in the abdomen and cut through the muscle layer. Using a cotton-tipped applicator to protect the intestines, fully open the mouse abdominal muscles with retractors to expose the abdominal cavity.

Starting from the cecum, carefully move the connected ileum and part of the jejunum out of the abdominal cavity and use a 7-0 silk suture to ligate the upper branch of the superior mesenteric artery. When the tissue color changes from pink to dark, indicating a full occlusion, use scissors to excise 50% or 90% of the ileum, depending on the parameters of the experiment.

Flush the lumen of both ileal ends with 0.9% saline. After locating the mesentery on the side of both ileal ends, align the mesenteries on both ends of the excised tissue and use an 8-0 suture to join the ends together. Suture the contralateral side of the ileum to keep the ileum anastomosed in a natural manner and suture the upper and lower sides between the two original sutures to thoroughly join the two ileal ends.

After confirming the lack of leakage from the anastomosis site, return the cecum and small intestine to their original anatomical locations and use a blunt needle to wash the surgical area with warm 0.9% saline. Close the abdominal muscle layer with a 6-0 suture and align the abdominal skin incision to close the skin and to facilitate optimal wound healing.

Then, transfer the mouse to an intensive care unit in a paper-bedding cage on a temperature-controlled heating pad for overnight recovery with soft food in addition to regular food and water.