DALLAS, July 25 -- A biodegradable arterial stent, a tube that is inserted into clogged blood vessels to restore proper blood flow, has been successfully tested in human patients for the first time researchers report in today's Circulation: Journal of the American Heart Association.
The new stents could revolutionize coronary angioplasty, a procedure to re-open narrowed blood vessels that is performed thousands of times each day, says lead researcher Hideo Tamai, M.D., of the department of cardiology at Shiga Medical Center, Japan.
A traditional stent is a tube -- usually a cage of surgical-grade stainless steel somewhat resembling chicken wire -- that props open an artery that has become partially closed from the fatty build-up of atherosclerosis.
The Japanese study is the first to demonstrate the feasibility and safety of biodegradable stents in humans, Tamai says. He notes that no deaths, heart attacks, or bypass surgeries were recorded among the 15 study participants during a six-month monitoring period. Tamai says that one patient underwent a second angioplasty during the monitoring period.
A multi-center randomized U.S. study of biodegradable stents is now being planned as a follow-up to the Japanese research, according to Tamai. "If this study supports our findings about the efficacy of biodegradable stents, and if the FDA approves them, they could be in general use in America within a few years," he says.
"This study represents the first move toward a new concept of coronary stenting," says Antonio Colombo, M.D., of the Centro Cuore Columbus in Milan, Italy, author of an editorial accompanying the Circulation report. "It is a fresh departure from the traditional idea of stents as permanent replacements for a part of the body."
Because the new stents are fully absorbed and disappear within two years after implant, they allow medical science to "fulfill its mission and step away," rather than leave a permanently intrusive object behind, Colombo adds.
In the Japanese study, 25 biodegradable stents were implanted in 15 individuals undergoing angioplasty. Because there is a high risk of restenosis during the three to six months following coronary angioplasty, the participants' conditions were monitored for six months. Tamai says his results were "highly encouraging."
Although this number of patients is considered too small to draw definitive conclusions, researchers say the rate of restenosis, or re-narrowing of the arteries, was generally lower than that seen with metallic stents.
"Since metal is a foreign material for humans, traditional stents sometimes cause inflammatory reactions in patients, and there are many long-term safety concerns associated with metallic stents," says Tamai. The metal stent may also injure the artery wall when inserted, which would cause an inflammatory response.
During an inflammatory response the body's immune defenses are activated, causing immune cells to "pile up" at the site of the stent. This activity can cause restenosis, Tamai says.
"What is unique about the stent these researchers invented, compared with prior investigators, is the change in stent design from a knitted pattern to a zigzag coil design," says Colombo. He says the new design may be less traumatic to the artery wall, therefore reducing the chance of restenosis.
In addition, Tamai says that no one really knows the effects of metallic stents after 10 or more years of use. "Those that remain in place for long periods may become obstacles to additional treatments, such as repeat angioplasty or bypass grafting," he says.
Another advantage of the biodegradable stent is that it can self-expand gradually for at least three months, says Tamai. This allows stented sections of arteries to fully expand, which may be responsible for the low stenosis rate.
Colombo notes that a biodegradable stent may have an additional advantage as a vehicle for administering drug or gene therapy at the site where the stent is inserted.
Co-authors include Keiji Igaki, M.D.; Eisho Kyo, M.D.; Kunihiko Kosuga, M.D.; Akiyoshi Kawashima, M.D.; Shigeo Matsui, M.D.; Hidenori Komori, M.D.; Takafumi Tsuji, M.D.; Seiichiro Motohara, M.D.; and Hiromu Uehata, M.D. Editorial co-author is Evangelia Karvouni, M.D.
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Media Advisory: Dr. Tamai can be reached by phone at 81 77 582 5031; or by fax at 81 77 582 5426; Dr. Colombo can be reached by phone at 39 02 481 2920; or by email at columbus@micronet.it (Please do not publish numbers.)