Stem Cells Used to Create Heart Valves
CHICAGO, Nov. 17 (AP) — Scientists for the first time have grown human heart valves using stem cells from the fluid that cushions babies in the womb, offering an approach that may be used to repair defective hearts.
The idea is to create new valves in the laboratory while a pregnancy progresses and have them ready to implant in a baby with heart defects after it is born.
The Swiss experiment follows recent successes at growing bladders and blood vessels and suggests that people may one day be able to grow their own replacement heart parts, in some cases, even before they are born.
It is one of several tissue engineering advances that could lead to homegrown heart valves that are more durable and effective than artificial or cadaver valves.
“This may open a whole new therapy concept to the treatment of congenital heart defects,” said Dr. Simon Hoerstrup of the University of Zurich.
Dr. Hoerstrup led the work, which was presented Wednesday at an American Heart Association conference.
Also at the meeting, Japanese researchers said they had grown new heart valves in rabbits using cells from the animals’ own tissue. It was the first time replacement heart valves had been created in this manner, said the lead author, Dr. Kyoko Hayashida.
Dr. Ziyad Hijazi, a University of Chicago cardiologist, said the results of the two studies were “very promising.”
“I don’t doubt” that it will be applied one day in humans, Dr. Hijazi said.
One percent of all newborns, or more than one million babies born worldwide each year, have heart problems. Such defects kill more babies in the United States in the first year of life than any other birth defects, according to the National Institutes of Health.
Defects in heart valves can be detected during pregnancy with ultrasound tests at about 20 weeks. At least one-third of afflicted infants have problems that could be treated with replacement valves, Dr. Hoerstrup said.
Conventional procedures to fix faulty heart valves have drawbacks. Artificial valves are prone to blood clots, and patients must take anti-clotting drugs for life.
Valves from human cadavers or animals can deteriorate, requiring repeated open-heart surgeries to replace them, Dr. Hijazi said. That is especially true in children because such valves do not grow along with the body.
Valves made from the patient’s own cells are living tissue and might be able to grow with the patient, said Dr. Hayashida, who is with the National Cardiovascular Center Research Institute in Osaka.
The Swiss procedure has an additional advantage. Using cells the fetus sheds in amniotic fluid avoids controversy because it does not involve destroying embryos to get stem cells.
“This is an ethical advantage,” Dr. Hoerstrup said.
Here is how the experiment worked: Amniotic fluid was obtained through a needle inserted into the womb during amniocentesis, a prenatal test for birth defects. Fetal stem cells were isolated from the fluid, cultured in a laboratory dish, then placed on a mold shaped like a small ink pen and made of biodegradable plastic.
It took four to six weeks to grow each of the 12 valves created in the experiment. The researchers said laboratory tests showed they appeared to function normally.
The next step is to see if they work in sheep, a two-year experiment that Dr. Hoerstrup said was under way.
He and his co-researcher, Dorthe Schmidt, called their method “a promising, low-risk approach enabling the prenatal fabrication of heart valves ready to use at birth.”
Dr. Hoerstrup said amniotic stem cells could also be frozen for years and could potentially be used to create replacement parts for aging or diseased valves in adults, too.
The research is preliminary, and experts say implanting tissue-engineered valves in human hearts is probably years away. But it is not far-fetched. Earlier this year, American scientists reported re-engineering diseased bladders with tissue grown from the patients’ own cells.
And last year, researchers reported that two kidney dialysis patients from Argentina had received the world’s first tissue-engineered blood vessels, fashioned from their own skin and vein tissue.
Dr. John E. Mayer Jr., a Children’s Hospital Boston heart surgeon and a pioneer in tissue engineering, said scientists were optimistic that research would revolutionize care for people with valve disease.
About 250,000 patients worldwide have surgery to replace heart parts each year, Dr. Mayer said.
In one of Dr. Mayer’s experiments, heart valves fashioned from stem cells harvested from sheep bone marrow appeared to function normally when implanted in sheep. A similar experiment used cells harvested from sheep arteries.
Dr. Hoerstrup said amniotic fluid was potentially a richer source of stem cells than other sources. Dr. Mayer said the big question was whether stem cells from amniotic fluid could create valves superior to those made from other cell types.
“I’m pretty sure the ball will continue to be advanced down the field,” he said. “We’ll get there one way or the other.”