Читать книгу The SAGE Encyclopedia of Stem Cell Research - Группа авторов - Страница 454

The World Health Organization (WHO) estimates that approximately 347 million people are currently afflicted with some form of diabetes. Diabetes is a disease that vastly diminishes the body’s ability to regulate blood sugar levels, in part due to a decrease in insulin production (type 1) or a metabolic disorder characterized by hyperglycemia in the context of insulin resistance and relative decrease in insulin (type 2).

The type 1 variant of the disease is not as easily managed. Since the body is unable to harness its own insulin reserves, external insulin must be administered daily. This administration can be in the form of an insulin pump or a hypodermic needle. The external insulin is derived from bacteria, which have been inserted with a gene to produce human insulin. These therapies are not a cure for the disease, however, and those with type 1 diabetes constantly struggle to maintain their glucose levels.

Type 2 diabetes is a chronic disease associated with a 10-year shorter life expectancy, partially due to the associated complications that include but are not limited to cardiovascular disease, stroke, lower-limb amputations, and damage to the blood vessels, eyes, kidneys, nerves, and other systems. Many lifestyle factors are associated with the development of type 2 diabetes, including obesity and overweight, sedentary lifestyle, stress, and poor diet. Current methods to circumvent the deleterious effects of the disease include a combination of diet, exercise, and weight loss. A sustained regimen of weight loss has shown signs of improved sensitivity of the tissues to insulin.

In order to gain a better understanding of the key role stem cells can play in the fight against diabetes, it is necessary to first provide a greater understanding of the physiology of the disease. The insulin produced by the body is derived directly from the pancreas. The specialized cells within the pancreas that secrete insulin are known as beta cells (β cells). In type 1 diabetes, the β cells are destroyed by an autoimmune response from the body, resulting in the decreased production of insulin by the body. The most successful interventions within the pancreas target these β cells, as a means to replace the inoperative cells with fully functioning substitutes. This will, hopefully, result in a full recovery of the individuals suffering from type 1 diabetes.

Prior to the advent of the mainstream feasibility of stem cells, scientists were relegated to simply transplanting the β cells of healthy individuals into the pancreases of those suffering from diabetes. Although the patients did show signs of insulin independence after the initial transplantation, it did not last. Due to the transient effects of the transplantation, multiple transplantations were required to produce the effects of insulin independence on a steady basis. However, a shortage of viable donors for the transplantation as well as an immune rejection on the part of the transplant recipients has stalled this avenue of research.

Stem cells have proven to possibly be a suitable replacement for these β cell transplantation therapies. Research in recent years has shown that it is possible to grow insulin-producing cells from embryonic stem cells. This is a very promising development in the search for a cure for type 1 diabetes. The research thus far has shown that it is possible to take murine embryonic stem cells and coax them into insulin-producing cells, ex vivo. These newly formed cells are subsequently reintroduced into the pancreases of diabetic mice and have shown to improve insulin efficiency within their bodies.

It is advantageous to upscale this method of manufacturing insulin-producing cells to the human level for a variety of reasons. First and foremost, a constant reserve of stem cell–derived pancreatic cells would do away with any need for multiple donors. This would expedite the transplantation process, vastly improving clinical outcomes.

Furthermore, embryonic stem cells are in essence a blank slate. Their undifferentiated qualities are a means to circumvent any adverse immune response that may be elicited from the transplant recipient’s body upon the cells. Growing these cells outside the body isolates them from adopting the unique histocompatibility markers that are so readily adopted by cells produced from within the body. Hence, when these cells are transplanted into an individual suffering from diabetes, that individual’s body will implant upon these cells markers that are inherently unique to that body. This process leaves no room for an immune rejection to the cells on the part of the patient’s body.

Years of research are still ahead to further elucidate any current unforeseen repercussions of this intervention. Positive showings in mice models are reassuring for the future of this avenue of research. A much wider consensus among the greater scientific community must be reached before large-scale human trials can begin. This burgeoning field of study is ever rapidly expanding, though; the leaps that have been made in the past 20 years may very well be outshined by advances that could be seen in the next five years.