PANCREATIC ISLET TRANSPLANTATION
The pancreas is a complex organ located behind the stomach in the upper abdomen. It has two main functions:
1) To secrete enzymes that aid in digesting food, known as exocrine function
2) To secrete hormones like insulin and glucagon, which aid in the metabolism of blood glucose, known as endocrine function
Pancreatic islets consist of a cluster of different cells. One of the types is the beta cell that secretes the hormone insulin. The function of insulin is to help the cells throughout the body to absorb the glucose and use it for energy or store it for use later in the form of glycogen. A lack of insulin will cause the glucose to remain in the blood stream and increase the blood glucose level, a condition called diabetes mellitus. Diabetes is a serious illness that can lead to life threatening medical problems if not treated adequately and on time.
Type 1 diabetes is an autoimmune disorder, where the beta cells are destroyed by the body’s immune system. Type 2 diabetes usually begins with insulin resistance where the body is unable to use insulin effectively. Over a period of time, the insulin production slows down and therefore, many type 2 diabetics will also need insulin.
Pancreatic islet transplantation consists of separating and removing islets from a donor pancreas, purifying them and then transplanting them in a patient with diabetes. This procedure is still considered experimental in the US and is suitable for patients whose blood sugar is difficult to control with insulin given to them exogenously. Approximately, 450,000 to 500,000 islets are isolated from a single donor. Most patients will require two infusions of islets, approximately 1 million in total in order to get an adequate amount of insulin for them to be cured of diabetes.
After an adequate number of islets have been purified, they are transplanted in the recipient by placing a catheter into the portal vein of the liver and then infusing them. Once these islets are lodged in the liver, they begin to produce insulin. It will take a few days for new blood vessels to grow around these islets and therefore, insulin injections are still required initially after the procedure. Gradually, the transplanted islets will take over and the need for insulin injections will lessen over time. New research has identified the omentum, the apron of fat in the abdomen as a potential area for placing the islets and has shown encouraging initial results.
Benefits of islet transplants include better blood sugar control, especially in those patients who diabetes is difficult to control because of erratic blood sugar levels (brittle diabetes) and in patients who have hypoglycemic unawareness. An alternative to islet transplantation is whole organ pancreas transplantation. This is a major surgical procedure with a greater risk of complications and even death. Risks associated with islet transplantation include bleeding and blood clots. After the procedure, anti-rejection medications are required to be taken for life in order to prevent rejection. Risks of taking anti-rejection medications include infections, high blood pressure and increased risks of certain cancers, to name a few.
Long term results of islet transplantation remain unclear at the present time. While most islet cell recipients achieve better blood sugar control, very few patients have remained euglycemic without the use of external insulin beyond the four year mark. More research is needed in order to make islet transplantation a better alternative for long term cure of this dreaded disease.