Islet Cell Transplant: Still Promising?
This experimental pancreas procedure might eliminate the need for insulin injections in some people with diabetes. But it isn't easy, so other islet-cell alternatives are being researched.
A slightly less invasive alternative to pancreas transplantation is islet-cell transplantation alone. In this experimental procedure, beta-islet cells are identified, isolated, and removed from donor pancreases and are injected into a major vein connected to the liver. The injected islets find their way into microscopic blood vessels and become surrounded and fixed in place by liver tissue. Once there, the cells take over insulin production and secretion, effectively turning the liver into a substitute pancreas.
One problem with this approach is that human beta-islets are few and hard to find; they actually comprise only 1% of all cells in the pancreas (most of the remaining cells produce and secrete enzymes that aid in digestion). In addition some of the islets are inevitably damaged or destroyed during the harvesting process, explains a diabetes researcher in an interview with WebMD.
"The process of harvesting the pancreas, isolating the cells, and then transplanting them all in one day is pretty tough, especially when you also take into account the situation that you might actually spend that entire day trying to isolate cells and never come up with enough cells from that procedure," says Emmanuel Opara, PhD, associate research professor in the department of experimental surgery and assistant research professor in the department of cell biology at Duke University Medical Center in Durham, North Carolina.
Opara and colleagues are looking at alternatives to human islet cells, including the use of islets taken from pig pancreases. Although the use of animal organs in humans is controversial, insulin derived from pig and cow pancreases has been in use since the early 1920s, when commercial insulin production began; the use of human insulin is a relatively recent development.
Pig islet cells are very similar in nature and function to human islets, but because they come from an animal they are seen as foreign invaders by the patient's immune system, which sends out specialized cells to hunt them down, tag them for removal, and kill them.
To get around this problem, Opara and colleagues at Duke have developed special drug-delivery spheres made up of a complex carbohydrate called alginate. The spheres surround, or "encapsulate" the islet cells, and are reported to be porous enough to let blood sugar come in and insulin go out while protecting the islet cells from immune-system act. The spheres are a little like the arrow slits used by archers defending ancient castles.