CHICAGO — We’ve heard the prediction often — biological materials will ultimately replace metal and plastic in medical devices.
Instead of getting much too old, that mantra has gotten renewed promise with the development of stem cell technology. Even so, it seems rather clear that the road from stem cell research bench to commercialization and clinical bedside for such products is still going to be lengthy.
A research effort that appears tantalizingly possible was described during a press conference at the scientific sessions of the American Heart Association (Dallas), that effort, if viable, perhaps taking only a few years to see clinical use. Put it under the category, “Grow-your-own heart valves.”
Simon Hoerstrup, MD, PhD, professor of biomedical engineering and director of cardiovascular research and the division of regenerative medicine at University Hospital (Zurich, Switzerland), described the use of a pregnant woman’s amniotic fluid to produce heart valves that can then be used to repair her baby’s defective heart valve.
Researchers at the University of Zurich harvested stem cells from the amniotic fluid and “seeded” them on heart valve-shaped polymeric scaffolds. The result was the creation of biological heart valves that the researchers hope will be able to replace a defective heart valve of the mother’s baby, once born.
Hoerstrup said the stem cell-produced valves were then placed in a biological environment simulating the pulsatile flow of the real heart and they showed the characteristics of healthy valves, chiefly the ability to naturally open and close.
Replacement of the defective valve would be made at a time determined by the degree of the baby’s defect, Hoerstrup told Medical Device Daily.
He said this has not yet been done. The next step in the research, he said, will be to replace the valves of sheep and follow these for two years to determine their ability to grow and change with the animal.
This ability is the essential key benefit of the amniotic fluid stem cell use, he said, because mechanical and biological valves don’t grow as a child matures — though the attempt to achieve this with biological valves is ongoing. Thus, babies with these defects must have repeat replacements as they grow older, the repeat procedures greatly shortening their life span.
How to decide when this is required?
Hoerstrup said that 1% of all babies have a heart valve defect and one-third of these need valve replacement. He suggested the need to target women determined to have high genetic risk factors for their babies to have such defects, but that ultimately all women might be encouraged to have samples of their amniotic fluid cryopreserved for future use.
These processes, of course, provide a fairly large barrier given the infrequency of such preservation and the still embryonic sector of the companies providing this type of service.
Three other potential uses for stem cells for cardiovascular applications were also described at the press conference.
• The use of stem cells harvested from adipose tissue isn’t a new idea. But Paul DiMuzio, MD, associate professor of surgery at Thomas Jefferson University (Philadelphia), said in his presentation that this harvesting has been done from “young and healthy” patients, primarily as part of a cosmetic surgery procedure.
In this study, it was determined that adipose stem cells can be collected from the elderly patients with cardiovascular disease — that is, those most likely to benefit from stem cell treatment for heart damage.
The researchers isolated stem cells from fat collected via standard liposuction from 49 patients undergoing cardiovascular procedures; the cells are then cultured for seven days. The resulting stem cells were determined to be healthy and viable and “not affected by the presence of associated disease, such as end-stage renal disease.” In his presentation though, DiMuzio did qualify this by saying that the number of stem cells was not as great when taken from diabetic patients.
He said that the next step in the research was to determine the level of viable usefulness in the stem cells taken from older patients.
• Thorsten Dill, MD, of the Department of Cardiology and Cardiac Imaging, Kerckhoff-Heart Center (Bad Nauheim, Germany), presented research demonstrating that bone marrow stem cells could be used to improve the repair of left ventricular strength and function after serious heart attacks, those described as ST-segment elevation of myocardial infarction.
MRI analysis demonstrated that the treatment with the bone marrow stem cells — via injection into the patients’ coronary arteries — produced functional improvement in ejection fraction of the left ventricle after four months, compared to those receiving a placebo treatment.
The improvement was shown to be greatest in those hearts with the more severe damage, Dill said.
• The development of what researchers termed “universal donor” stem cells was described by Ray Chiu, MD, PhD, professor of surgery and chair, emeritus, cardiothoracic surgery division, McGill University Health Center (Montreal).
The research team collected human bone marrow stromal stem cells and introduced them into rats with induced heart attacks, and they found that these cells could grow into various different types of tissues. Importantly, the cells survived in the rat myocardium without producing an immune rejection response.
The implanted cells “differentiated,” Chiu said, and within eight weeks produced significant improvements in heart function in the rats.
The significance of the findings, he said, is that the bone marrow stem cells offered the possibility of providing an “off-the-shelf” supply of stem cells for a variety of uses in heart repair.
The main benefit, Chiu said: they could be placed “in the refrigerator” and offer a great decrease “in time and money spent.”