February 3, 2011
Researchers Grow Their Own Blood Vessels
Scientists reported on Wednesday that they have successfully grown bio-engineered blood vessels that surgeons could someday take off the shelf and implant into patients, something that could ultimately help people lacking healthy veins for coronary bypass surgery or dialysis.
The researchers employed a novel way of using human cells to generate the blood vessels that could allow them to function without triggering a patient's immune response. Furthermore, unlike other engineered vessels, these can be stored for up to one year, allowing hospitals to keep them on hand for immediate use.
"This new type of bioengineered vein allows them to be easily stored in hospitals so they are readily available to surgeons at the time of need," said Dr. Alan Kypson, Associate Professor of Cardiothoracic Surgery at East Carolina University, who authored a report about the findings.
"Currently, grafting using the patient's own veins remains the gold standard. But, harvesting a vein from the patient's leg can lead to complications, and for patients who don't have suitable veins, the bioengineered veins could serve as an important new way to provide a coronary bypass," Dr. Kypson said.
The bio-engineered vessels also have "decreased potential for infection, obstruction or clotting," wrote the researchers from Duke, Yale and East Carolina University.
The team created the bio-engineered blood vessels by taking smooth muscle cells from a human cadaver and grafting them onto tubes made of polyglycolic acid -- the material used in making dissolvable stitches.
Within eight to 10 weeks, the tubes degrade, leaving behind a "fully formed vascular graft".
The veins have been tested in dogs and baboons, and were not rejected by their bodies and functioned well for six months.
The vessels can be stored in saline solution for up to 12 months, which would allow surgeons to select an "off the shelf" vessel for use in a sick patient, the researchers said.
"These can be made ahead of time and then are ready to go whenever they are needed," the researchers said.
According to the National Kidney Foundation, 320,000 patients require dialysis, more than half of which lack the healthy veins necessary for the procedure and must therefore undergo arteriovenous graft (AV graft) placement.
"Most AV grafts that are placed for hemodialysis access are comprised of a synthetic material, which suffers from significant drawbacks including a high rate of infection, or a propensity for occlusion due to thrombosis and intimal hyperplasia," said Dr. Jeffrey Lawson, Associate Professor of Surgery at Duke University School of Medicine and an author of the research.
"Due to high complication rates, each AV dialysis graft requires an average of 2.8 interventions over its lifetime just to keep it functioning. Hence, there is a huge clinical need for a functionally superior, off-the-shelf, AV graft that suffers from fewer complications than current materials."
Humacyte, a North Carolina-based regenerative medicine firm that funded and contributed to the research, said clinical trials in humans would begin soon.
Shannon Dahl, Humacyte's co-founder and senior director of scientific operations, said veins can be constructed in different sizes according to the type of operation required.
"We can make the bio-engineered veins in large and small diameter, which means they can be used for procedures ranging from hemodialysis for patients with kidney failure and for coronary by-pass."
Around 400,000 coronary bypass procedures are performed each year in the U.S., according to the American Heart Association.
"Not only are bioengineered veins available at the time of patient need, but the ability to generate a significant number of grafts from a cell bank will allow for a reduction in the final production costs, as compared to other regenerative medicine strategies," Dahl said.
"While there is still considerable research to be done before a product is available for widespread use, we are highly encouraged by the results outlined in this paper and eager to move forward with additional study."
The study was published February 2 in the journal Science Translational Medicine.
Image 2: This is a 6 mm-diameter decellularized human bioengineered vein before implant. Credit: Science/AAAS
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