| MadSci Network: Medicine |
Dear Alex, Thanks for your question! It is a very insightful one. As you may know, diabetes mellitus is a disease characterized by abnormally high blood glucose levels. Glucose is a carbohydrate, or sugar, that is released from ingested food and absorbed into the blood. It is important for maintaining energy levels, especially during the periods between meals. Under normal circumstances, insulin, a hormone produced by the pancreas, is released when there is a large amount of glucose in the blood. This causes the tissues in the body to store the glucose so it can be used at a later time. What leads to unusually high blood glucose levels in diabetic patients is a lack of insulin, a reduced effectiveness of this hormone, or a combination of these two situations. Diabetes essentially comes in two types. One form is called type I diabetes, or insulin-dependent diabetes mellitus (IDDM). Patients with this form usually develop the disease when they are young, often due to the destruction of the cells in the pancreas which produce insulin. These cells are called beta cells and are found in specialized structures in the pancreas called islets of Langerhans. It is not entirely clear why these cells are selectively destroyed in these patients. However, one theory is that the patients' immune systems recognize the beta cells as "foreign" and therefore, destroy these cells as they would a bacterium or other invader. Therefore, without any beta cells, these patients cannot produce insulin. The other form of diabetes is referred to as type II, or non-insulin-dependent diabetes mellitus (NIDDM). Patients with this form are frequently older, and often, their beta cells are intact. Exactly what causes this form is also not well understood. It seems that many of these patients produce insulin, but it effectiveness is reduced. This means that, although the beta cells produce insulin normally, the tissues that usually respond to this hormone aren't doing so. This phenomenon is sometimes described as "insulin resistance". Although I have described these two forms of diabetes as being very distinct, the truth is that this is not always the case. Diabetes mellitus is a very complex disease and does not easily fit into distinct categories. Okay, so on to your question: why don't diabetic patients get pancreas transplants? Well, the truth is that they sometimes do. However, this is not a routine treatment for diabetes. As it stands now, the patients who normally receive pancreas transplants usually have some very serious complications from their disease. High glucose levels in the blood can ultimately damage tissues in the body, such as the kidney, the eyes, as well as nerves. Although many diabetics receive treatment to control their blood glucose levels, this control is not always perfect, and can still result in organ damage after many years of living with the disease. For instance, some diabetic patients sustain serious kidney damage and need to undergo a kidney transplant. Many of these patients receive a pancreas at the same time. The rationale is that although medical therapy can control blood glucose rather well, the pancreas does it better. However, receiving a new pancreas (and kidney) is not without cost--like other patients who receive organ transplants, these patients will have to take drugs which suppress their immune system for the rest of their lives. Transplanted organs, even from a blood-related donor, are perceived by the recipient's immune system as foreign and therefore, destoyed. Thus, unless a patient has an identical twin, they will need immunosuppressive drugs in order for the graft to survive. This is a very serious situation--people who are on immunosuppressive therapy are at a much higher risk for life-threatening infections as well as some cancers because their defenses against these insults are weakened. The standard treatments for diabetes (insulin, diet control, etc.) are effective in controlling the disease, and they are getting even better. It is true that they are not always perfect. But, unless a diabetic patient must receive an organ transplant and therefore, will need to be on immunosuppressive drugs anyway, pancreatic transplants are a very risky treatment option An emerging therapy for diabetes is islet transplantation. Although it is still in an experimental stage, it may one day be an important therapeutic option for diabetic patients. The idea is that, rather than transplanting the entire pancreas, the islets themselves are transplanted. This approach provides three main advantages over traditional pancreas transplants. First, although patients still need to take immunosuppressive drugs, they don't require the high doses that traditional pancreas recipients need. Second, these islets can be transplanted in any region of the body that has a rich blood supply and don't necessarily have to be put into the recipient's pancreas. In fact, islets are often placed in the kidney! This means a less invasive surgical procedure and a speedier recovery for the patient. Finally, since the islets are quite small relative to the entire pancreas, this means that the procedure is easier. In addition to producing hormones like insulin, the pancreas is also responsible for making digestive enzymes and then releasing them into the intestine. When the pancreas is transplanted, these intestinal connections need to be handled appropriately. However, this is not necessary for islet transplantation. I hope this information is helpful to you. If you are interested, there is a ton of information about diabetes mellitus on the Web. Here are a few sites that I think might be useful: On-line Diabetes Resources http://www.mendosa.com/diabetes.htm Juvenile Diabetes Foundation http://www.jdfcure.org/ Joslin Diabetes Center http://www.joslin.org/ If you have further questions, feel free to email me! Nikki nmdavis@fas.harvard.edu
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