Bypass surgery is performed so as to unclog arteries in one part of the body by using a vessel from elsewhere. But it seems that almost 40 percent of patients do not find vessels suitable for the procedure. To avoid such cases, scientists have created functional blood vessels that may prove helpful in replacing synthetic grafts during the surgeries.
During vascular bypass surgeries, surgeons make use of synthetic grafts that aide in clearing up the arteries. But sometimes it so happens that these artificial blood vessels clog within one to three years, which in comparison to natural arteries is quite fast. Moreover, such actions can even lead to sever infections.
Stephen E. McIlhenny, Ph.D., lead author of the research and tissue engineer of Thomas Jefferson University Hospital in Philadelphia, explains that “Our grafts have the potential to be used for peripheral artery disease bypass (mostly in the legs), and arteriovenous fistula (a type of vascular access for hemodialysis), and heart bypass surgery. However, the first uses of the grafts would be for treatment of peripheral artery disease and dialysis access grafting.”
McIlhenny and his team reported of interesting results acquired from the first pre-clinical test conducted by them, of the graphs.
McIlhenny further goes on to say that, “It was our idea to create a more biological conduit that would avoid the problems of synthetic grafts and give patients a better alternative. The significant finding is that we can build a blood vessel from donor tissue and an animal’s own adult stem cells. Potentially, patients requiring bypass surgery could receive optimized grafts that would reduce their future complications.”
For the research, the team grew rabbit adult stem cells on human vein scaffold in the laboratory. The team then moved on to remove all cells from sections of human saphenous veins, and was left with a tube that included the protein scaffolding which supported the cells. As the scaffolding contains no cells, the risk of the immune system disowning it, is minimized.
The scientists followed this up by deriving adult stem cells from the fat cells of each rabbit that were to receive the test graft. The stem cells were grown on pieces of the scaffolding whereby each rabbit received a graft with its own stem cells on it.
The team then cut the abdominal aorta of five male rabbits and implemented the graft into the large artery. The same procedure was followed for five other male rabbits with grafts of bare protein scaffolding. The animals were observed every two weeks for the next eight weeks with ultrasounds and monitoring to check on if the grafts were closing up. After the defined eight week period, the grafts from all ten rabbits were removed. The bare scaffolding grafts showed a thickening and blood clots similar to what is observed in human cardiovascular diseases.
Reporting about the other five grafts, McIlhenny said that, “We found that using the stem cells as a coating prevented clotting and thickening of the graft wall. I would say those grafts were significantly better.”
The team still needs to work on the research, which includes additional animal testing, before it can be administered on humans. Scientists have been trying to grow smooth muscle cells on the outer layer of the scaffolding. The smooth muscle cells apparently strengthens the blood vessels in the arteries and even helps them contract.
The team is simultaneously also examining a suspected but proven function of nitric oxide in the success of the adult stem cell graft. Nitric oxide, it seems inhibits platelet aggregation and blood-clot formation in blood vessels. McIlhenny and his team are focusing on proving that this molecule protects the graft against wall thickening.
The research was presented at the ‘American Heart Association’s Arteriosclerosis, Thrombosis and Vascular Biology Annual Conference’, 2010.