Pancreatic Islets Isolation through Collagenase Perfusion: An Enzymatic Method to Isolate Pancreatic Islet Cells

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

The surgical tools needed are shown in Figure 1 and the schematic diagram of the procedure is shown in Figure 2.

1. Solutions

1. Prepare Hank’s Balanced Salt Solution (HBSS) by adding 100 mL of 10X HBSS (from stock) to 900 mL of distilled water to make 1 L HBSS (1X).
2. Prepare STOP solution (must be made fresh and should be used within 1 h) by adding 50 mL of 100X fetal bovine serum (FBS) to 450 mL of ice cold 1X HBSS; this makes 500 mL STOP solution. Keep the STOP solution at 4 °C.
3. Prepare collagenase P solution (must be made fresh within 1 h of being used) by adding 1 mg/mL of collagenase P to ice cold 1X HBSS; use 6 mL/mouse.
   1. Add 0.05% (w/v) bovine serum albumin (BSA) to collagenase P solution (this provides nutrients to the isolated islets). For example, use 3 mg BSA in 6 mL collagenase P solution. Keep on ice.
   2. Calculate and prepare the amount of collagenase P needed for all mice in one 50 mL tube.
4. Prepare complete RPMI 1640 medium by adding 10% FBS, 100 U/mL penicillin, 100 µg/mL streptomycin, INS-1 cell supplement (10 mM HEPES, 2 mM L-glutamine, 1 mM sodium pyruvate, and 0.05 mM 2-mercaptoethanol) to 500 mL RPMI 1640 media containing 5.5 mM glucose to be used for overnight culture and incubation.

2. Preparation

1. Fill three 50 mL tubes of 25 mL RNase inhibiting solution, 70% ethanol or distilled H₂O. These solutions will be used for cleaning surgical tools prior and during the procedure.
2. Soak the tips of the tools in RNase inhibiting solution for 30 min before starting the protocol; this eliminates any potential RNase on the tools.
3. Pre-cut absorbent pads to 6 in x 6 in size for use during surgery.
4. Prepare 1X HBSS solution in advance and store at 4 °C. Prepare STOP solution prior to surgery. Store at 4 °C.
5. Prepare collagenase P solution immediately prior to surgery and store on ice.
   NOTE: This should be used within 2 h of preparation.
6. Label 50 mL tubes for digestion and purification; prepare 2 tubes for each mouse, one for digestion and the other for islet purification. Ensure that the animal ID is on both tubes.
7. Add 3 mL of collagenase P solution into the first 50 mL tube. The remaining 3 mL of collagenase P will be injected.
8. Draw the remaining 3 mL of collagenase solution into a 3 mL syringe mounted with 30 G ½ in needle. Place the syringe on ice.

3. Procedure

1. Remove all the tools from RNase inhibiting solution, then dip them first in the tube with 70% ethanol, then in the tube containing distilled H₂O, then air-dry on clean paper towel.
2. Place the mouse in a chamber containing 0.5 mL of isoflurane until mouse is deeply anaesthetized.
3. Remove mouse from the chamber and check the state of anesthesia by pinching a foot pad with forceps. Deep anesthetization is based on the observation that breathing become steadily slow and mouse is unreactive to foot pinching. After confirming that the mouse is deeply anaesthetized, euthanize the mouse with cervical dislocation, and then place the mouse on the absorbent pad.
   1. Place anaesthetized mouse on its stomach, applying pressure to the neck and dislocating the spinal column from the brain by pulling tail.
4. Tape the limbs of the mouse in supine position to the absorbent pad, spray the body with 70% ethanol, and wipe excess off the excess ethanol.
5. Use cover glass forceps and curved surgical scissors to make incisions. First make a horizontal incision on the skin of the abdominal area (~3 cm), pull the skin wide open to expose the abdominal wall. Then make a vertical incision (~3–4cm) on the abdominal peritoneum to fully expose the pancreas in abdominal cavity (Figure 3).
6. Push the lobes of the liver superiorly to expose the bile duct, it will appear as a pale pink tube (Figure 3).
7. Carefully move the intestines from the right lumbar/iliac region of the abdominal cavity to the right, exposing the bile duct and hepatic artery (Figure 3).
8. Carefully clamp the common bile duct using the Schwartz micro serrefines (Figure 1) as close to the liver as possible.
9. Identify the ampulla of Vater, which is located at the duodenal papilla, formed by the union of the pancreatic duct and the common bile duct. The ampulla of Vater appears swollen when viewed under a dissection microscope which is the entry point to the common bile duct (Figure 4).
   NOTE: Adjusting intensity/angle of light of the dissection microscope can make it easier to locate.
10. Insert the syringe with 3 mL of the collagenase P solution into the ampulla of Vater. Push the needle into the duct for about 1/4 of the length of the common bile duct (ampulla leads into duct) as shown in Figure 5.
11. Once the needle is in the ampulla, ensure that the orientation of the needle is such that it is parallel with the duct.
12. Stabilize the needle by clamping with micro Adson forceps to prevent it from puncturing the duct (Figure 5).
13. Slowly and steadily inject 3 mL of the collagenase P solution from the syringe into the common bile duct (enough to feel resistance) as shown in Figure 6. The goal is to create backflow pressure to force the collagenase to enter the pancreatic duct. Injection is considered successful if the head, neck, body and tail region of the pancreas are all fully inflated.
    NOTE: Islet yield will be low if either the pancreas is not fully inflated, or the splenic area is not fully inflated. The splenic area contains the highest number of islets⁶. Inflation can be confirmed by the appearance of open spaces between pancreatic tissue that are filled with solution.
14. Carefully dissect out the inflated pancreas and place it in a 50 mL digestion tube containing 3 mL of ice-cold collagenase P solution.
    1. Remove the pancreas using 2 forceps (curved and Micro Adson; See Figure 1): (starting from the spleen, pull the pancreas away from spleen and continue removing from the stomach and along the duodenum.
       NOTE: No incisions required.
    2. Chop pancreas for 3–5 s in the digestion tube with 3 mL of ice-cold collagenase P solution using fine surgical scissors (Figure 7A).
15. Secure the tube to a rack in 37 °C water bath and shake at 100–120 rpm for approximately 12–13 min.
16. After incubation, gently shake the tubes by hand to disrupt the tissue until the collagenase P digestion solution becomes homogenous (Figure 7B). Homogeneity is confirmed by a sand-like appearance of fine particles of pancreas. About 30 s of gentle hand-shaking is usually enough. Hold the tube up to light to examine if the tissue is well homogenized; shake for another ~15 s if needed.
17. Once digested, immediately place the tubes on ice and add 40 mL of ice-cold STOP solution to terminate the enzymatic digestion.
    NOTE: At this point digestion tubes can be left on ice up to 2 h, if working on multiple mice.
18. Centrifuge the tube in a swinging-bucket centrifuge at 300 x g for 30 s (temperature of centrifuge is flexible).
    NOTE: Use a swinging-bucket centrifuge so that the tissue pellet is formed at the bottom of the 50 mL tube and not on the wall of the tube; this is critical for better islet yield.
19. Decant and repeat the centrifugation with STOP solution 2 more times, decanting the solution after each spin. Use 20 mL of STOP solution for each subsequent wash.
    1. Before each spin, disrupt the pellet by gently shaking the tissue pellet in the 50 mL tube in 20 mL STOP solution.
20. Re-suspend the tissue pellet with 40 mL of ice cold HBSS and centrifuge at 300 x g for 30 s.
21. Decant and repeat the centrifugation using a swinging-bucket centrifuge with HBSS solution two more times, decanting the solution after each spin. Use 20 mL of HBSS for each wash.
    1. Before each spin, disrupt the pellet, to detach it from the bottom of the tube by gently shaking the tube containing 20 mL HBSS solution.
22. After the last centrifugation remove all HBSS.
23. Then add 5 mL of room temperature density gradient to the 50 mL tube containing the pellet. Vortex briefly at low speed until homogenized.
24. Add another 5 mL of the room temperature density gradient to the 50 mL tube. Do not vortex/mix.
    NOTE: It is critical to remain steady and still so as to allow better gradient to form without disruption.
25. Pipette 10 mL of room temperature HBSS buffer into the tube (containing the density gradient), drop-by-drop gently and slowly to allow a gradient to form. Use a pipette gun with a 10 mL pipette to add HBSS dropwise.
26. Using a swinging-bucket centrifuge, spin tubes at 1700 x g for 15 min. Make sure to change the speed of both acceleration/deceleration to the lowest setting to maintain the gradient (Figure 7C).
27. After the spin, carefully remove the tubes without disturbing the gradient. Using a pipette gun pre-wetted with cold HBSS (pipette HBSS up and down), pipette out the layer of islets (5–10 mL) formed between the density gradient and HBSS into the new 50 mL islet collection tube.
    NOTE: It is helpful to wet the pipette with cold HBSS prior to pipetting the islets to prevent the islets from sticking to the inner walls of the pipette.
    1. In case the separation is incomplete, islets would be visible in the density gradient layer, pipette out the entire 10 mL of the density gradient (bottom layer) along with the islet layer formed at the interface (only to leave about 8–10 mL of the HBSS top layer behind).
       NOTE: Collecting both the islet layer and the density gradient layer (bottom layer) can result in the collection of debris which may lengthen the islet picking time, but no other steps will be altered. Collecting both these layers is not necessary when islet layer is well formed.
28. Add 20 mL of ice cold HBSS to the new 50 mL tube containing islets, then centrifuge at 350 x g for 3 min in a swinging-bucket centrifuge.
29. After the spin, carefully pipette (do not decant) out the supernatant (leave ~3 mL at the bottom) without disturbing the pellet containing the islets at the bottom. Discard the supernatant.
30. Repeat washing and centrifuging at least 3 times. Add 20 mL of HBSS each time, and be sure to suspend the pellet before each spin.
31. Warm the RPMI-1640 complete media bottle in a water bath at 37 °C prior to use. After the last centrifugation, remove all of the HBSS and add 4 mL of previously prepared complete RPMI-1640 media (containing FBS, INS-1 cell supplement and penicillin/streptomycin) to the pellet.
32. Dislodge the pellet by gently swirling the tube and immediately pour the RPMI-1640 media into a 100 mm Petri dish. Add another 5 mL of RPMI-1640 media to the tube and gently swirl it to wash off any remaining islets, then also pour the media into the same Petri dish.
    1. Under a dissection microscope, pick healthy islets from the Petri dish using a 20 µL pipette, and put them in a new Petri dish containing 10 mL of complete RPMI 1640 media. When viewed under a dissection microscope, islets should appear spherical/oblong and golden-brown color with a smooth surface compared to the relatively transparent, wispy exocrine tissue.
       NOTE: Magnification of dissection microscope is usually set at 12.5–16x. Islet yield will vary depending on various factors including strain, age and sex of mouse. This protocol usually yields 250–350 healthy islets from healthy C57BL/6J mouse age 4–10 months old.
33. Incubate the islets in a sterile incubator at 37 °C with 5% CO₂ infusion and 95% humidified air overnight for experiments the next day, or freeze the islets for desired analysis at a later time.
    1. Once islets are frozen, they cannot be used for secretion assays, only RNA or protein quantification. To collect cells to freeze, place them in HBSS buffer, collect all islets in 200–500 µL of buffer, transfer to 1.5 mL tube, centrifuge 350 x g for 1–2 min, remove the supernatant leaving no more than 30–40 µL solution, place in -20 °C for short term storage (several days) or -80 °C for long term storage.