The Key to Implanting an Artificial Pancreas? Add a Matrix for Vascularization

The Key to Implanting an Artificial Pancreas? Add a Matrix for Vascularization

The insulin-producing cells survive longer in the engineered tissue, and produce more insulin and other essential hormones, Levenberg and colleagues said. When they transplanted the tissue into diabetic mice, the cells began functioning well enough to lower blood sugar levels in the mice.

Transplantation of islets, the pancreatic tissue that contains hormone-producing cells, is one therapy considered for people with type 1 diabetes, who produce little or no insulin because their islets are destroyed by their own immune systems. But as with many tissue and organ transplants, donors are scarce, and there is a strong possibility that the transplantation will fail.

The well-developed blood vessel network built into the engineered tissue is key to its success, the researchers concluded. The blood vessels encourage cell-to-cell communication, by secreting growth hormones and other molecules, that significantly improve the odds that transplanted tissue will survive and function normally.

The findings confirm that the blood vessel network “provides key survival signals to pancreatic, hormone-producing cells even in the absence of blood flow,” Levenberg and colleagues concluded in their study published in the journal PLoS One.

One reason transplants fail, Levenberg said, “is that the islets are usually transplanted without any accompanying blood vessels.” Until the islets begin to connect with a person’s own vascular system, they are vulnerable to starvation.

The 3-D system developed by the Technion researchers tackled this challenge by bringing together several different cell types to form a new transplantable tissue. Using a porous plastic material as the scaffold for the new tissue, the scientists seeded the scaffold with mouse islets, tiny blood vessel cells taken from human umbilical veins, and human foreskin cells that encouraged the blood vessels to develop a tube-like structure.

“The advantages provided by this type of environment are really profound,” said Xunrong Luo, an islet transplantation specialist at the Northwestern University Feinberg School of Medicine. She noted that the number of islets used to lower blood sugar levels in the mice was nearly half the number used in a typical islet transplant.

Islets grown in these rich, multicellular environments lived three times as long on average as islets grown by themselves, Levenberg and colleagues found.

The technology “is still far from tests in humans,” Levenberg said, but she noted that she and her colleagues are beginning to test the 3-D tissue scaffolds using human instead of mouse islets.

According to Northwestern’s Luo, the 3-D model demonstrated in the study “will have important and rapid clinical implications” if the same results can be replicated with human cells. “This model system also provides a good platform to study the details and mechanisms that underlie successful transplantation.”

The Technion-Israel Institute of Technology is a major source of the innovation and brainpower that drives the Israeli economy, and a key to Israel’s renown as the world’s “Start-Up Nation.” Its three Nobel Prize winners exemplify academic excellence. Technion people, ideas and inventions make immeasurable contributions to the world including life-saving medicine, sustainable energy, computer science, water conservation and nanotechnology.

American Technion Society (ATS) donors provide critical support for the Technion—more than $1.7 billion since its inception in 1940. Based in New York City, the ATS and its network of chapters across the U.S. provide funds for scholarships, fellowships, faculty recruitment and chairs, research, buildings, laboratories, classrooms and dormitories, and more.

The mechanisms underlying early islet graft failure are not entirely clear, but are thought to involve ischemic injury due to delayed vascularization. We hypothesize that blood vessels play an active role in cell-cell communications supporting islet survival and engraftment. To test this hypothesis and to uncouple endothelial cell (EC)-generated signaling stimuli from their nutritional and gas exchange functions, we developed three dimensional (3D) endothelial vessel networks in engineered pancreatic tissues prepared from islets, fibroblasts and ECs. The tri-culture setup, seeded on highly porous biocompatible polymeric scaffolds closely mimics the natural anatomical context of pancreatic vasculature. Enhanced islet survival correlating with formation of functional tube-like endothelial vessels was demonstrated. Addition of foreskin fibroblasts to islet-endothelial cultures promoted tube-like structure formation, which further supported islet survival as well as insulin secretion. Gene expression profiles of EC growth factors, extracellular matrix (ECM), morphogenes and differentiation markers were significantly different in 2D versus 3D culture systems and were further modified upon addition of fibroblasts. Implantation of prevascularized islets into diabetic mice promoted survival, integration and function of the engrafted engineered tissue, supporting the suggested role of ECs in islet survival. These findings present potential strategies for preparation of transplantable islets with increased survival prospects.

In the quest to develop a lab-grown artificial pancreas, researchers have realized that simply implanting islets (insulin-producing pancreatic cells) into a patient isn’t very effective. The implanted cells tend to die off and the overall benefit of the procedure is negligible.

A team of Israeli scientists has been working to overcome the problem by building a network of blood vessels around the islets to help these cells interact with their new environment. The 3D vessel structure, when implanted into diabetic mice, showed a considerably higher effectiveness over simple islet transplantation. Moreover, and somewhat surprisingly, the researchers report in PLoS ONE that the vessel network “provides key survival signals to pancreatic, hormone-producing cells even in the absence of blood flow.”

From the study abstract:

The tri-culture setup, seeded on highly porous biocompatible polymeric scaffolds closely mimics the natural anatomical context of pancreatic vasculature. Enhanced islet survival correlating with formation of functional tube-like endothelial vessels was demonstrated. Addition of foreskin fibroblasts to islet-endothelial cultures promoted tube-like structure formation, which further supported islet survival as well as insulin secretion. Gene expression profiles of EC growth factors, extracellular matrix (ECM), morphogenes and differentiation markers were significantly different in 2D versus 3D culture systems and were further modified upon addition of fibroblasts. Implantation of prevascularized islets into diabetic mice promoted survival, integration and function of the engrafted engineered tissue, supporting the suggested role of ECs in islet survival. These findings present potential strategies for preparation of transplantable islets with increased survival prospects.

Source : http://www.ats.org/site/News2?page=NewsArticle&id=7567&news_iv_ctrl=1161

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