Italian scientists from Milan have used skin-derived stem cells in combination with a previously developed collagen tube to successfully bridge the gaps in injured nerves in a rat model, On the strength of that animal model system, the Italian group successfully used this procedure to heal the damaged peripheral nerves in the upper arms of a patient whose only other option was limb amputation.
“Peripheral nerve repair with satisfactory functional remains a great surgical challenge, especially for severe nerve injuries resulting in extended nerve defects,” said the corresponding author of this study Dr, Yvan Torrente of the Department of Pathophysiology and Transplantation at the University of Milan. “However, we hypothesized that the combination of autologous (self donated) stem cells placed in collagen tubes to bridge gaps in the damaged nerves would restore the continuity of injured nerves and save from amputation the upper arms of a patient with poly-injury to motor and sensory nerves.”
Although autologous nerve grafting has been the “gold standard” for reconstructive surgeries, these researchers recognized the disadvantages of such a procedure. Graft availability is the first drawback of autologous nerve grafting. Secondly, the condition of the donor site or “donor site morbidity.” If the donor site is in bad shape, taking a nerve from that site will probably make the donor site worse and provide a nerve that does not work as well. Finally, neuropathic pain is also an issue.
Autologous skin-derived stem cells have several advantages over autologous nerve grafts. First, the skin provides an accessible source of stem cells that are rapidly expandable in culture. Secondly, these skin-derived cells are capable of survival and integration within host tissues.
The NeuraGen nerve guide is a tiny collagen tube that connects the two damaged ends of a nerve together to mediate and expedite nerve healing. NeuraGen tubes guide the transplanted stem cells to the gaps in the damaged nerves. Torrente and his co-workers developed and tested the NeuraGen tubes in rats, and the US Food and Drug Administration (FDA) has approved NeuraGen for use in human patients. See this figure from the NeuraGen web site:
Torrente and others successfully used skin-derived stem cells and NeuraGen tubes to heal the severed sciatic nerves in rats. Therefore, once the FDA approved NeuraGen tubes, Torrente tried NeuraGen tubes in human patients with severe peripheral nerve damage.
A three-year follow-up on one particular patient showed that injured median and ulnar nerves showed extensive healing as ascertained by magnetic resonance imaging. Functional tests, such as pinch gauge tests, static two-point discrimination and monofilament touch tests established the functional recovery of these peripheral nerves in the patient.
“Our three-year follow-up has witnesses nerve regeneration with suitable functional recovery in the patient and the salvage of upper arms from amputation,” said researchers from Torrente’s group. “This finding opens an alternative avenue for patients who are at-risk of amputation after the injury to important nerves.”
Globally, thousands of heart patients have been treated with stem cells from bone marrow and other sources. While many of these patients have been helped by these treatments, the results have been inconsistent, and most patients only show a modest improvement in heart function.
The reason for these sometimes underwhelming results seems to result from the fact that implanted stem cells either die soon after they are delivered to the heart or washed out. Since the heart is a pump, it is constantly contracting and having fluid (blood) wash through it. Therefore, it is one of the last places in the body we should expect implanted stem cells to stay put.
To that end, cardiology researchers a Emory University in Atlanta, Georgia have packaged stem cells into small capsules made of alginate (a molecule from seaweed) to keep them in the heart once they are implanted there.
W. Robert Taylor, professor of medicine and director of the cardiology division at Emory University School of Medicine, and his group encapsulated mesenchymal stem cells in alginate and used them to male a “patch” that was applied to the hearts of rats after a heart attack. Taylor’s group compared the recovery of these animals to those rats that had suffered heart attacks, but were treated with non-encapsulated cells, or no cells at all. The rats treated with encapsulated cells not only showed a more robust recovery, but they had larger numbers of stem cells in their hearts and showed better survival.
Of this work, Taylor said, “This approach appears to be an effective way to increase cell retention and survival in the context of cardiac cell therapy. It may be a strategy applicable to many cell types for regenerative therapy in cardiovascular medicine.
Readers of this blog might remember that I have detailed before the inhospitable environment inside the heart after a heart attack. Oxygen levels are low because blood vessels have died, and roving white blood cells are gobbling up cell debris and releasing toxic molecules while they do it. Also the dying cells have released a toxic cocktail of molecules that make the infarcted area very inhospitable. Injecting stem cells into this region is an invitation for more cells to die. Previous experiments have shown that preconditioning stem cells either by genetically engineering them to withstand high stress levels of by growing them in high-stress conditions prior to implantation can increase their survival in the heart.
Taylor also pointed out that the mechanical forces of the contracting heart can squeeze them and displace them from the heart, much like pinching a watermelon seed between your fingers causes it to slip out. “These cells are social creatures and like to be together,” said Taylor. “From some studies of cell therapy after myocardial infarction, one can estimate that more than 90 percent of the cells are lost in the first hour. With numbers like that, it’s easy to make the case that retention is the first place to look to boost effectiveness.”
Encapsulation keeps the mesenchymal stem cells together in the heart and “keeps them happy.” Encapsulation, however, does not completely cut off the cells from their environment. They can still sense the cardiac milieu and release growth factors and cytokines while they are protected from marauding white blood cells and antibodies that might damage, destroy, or displace them.
Alginate already has an impressive medical pedigree as a biomaterial. It is completely non-toxic, and chefs use it to make edible molds to encase other types of tasty morsels. Dentists use alginate to take impressions of a patient’s teeth and it is also used a component of wound dressings. One of Taylor’s co-authors, an Emory University colleague named Collin Weber has used alginate to encapsulate insulin-producing islet-cells that are being tested in clinical trials with diabetics.
Encasing cells in alginate prevents them from replacing dead cells, but mesenchymal stem cells tend to do the majority of their healing by means of “paracrine” mechanisms; that is to say, mesenchymal stem cells tend to secrete growth factors, cytokines and other healing molecules rather than differentiating into heart cells. Mesenchymal stem cells can be isolated from bone marrow or fat.
One month after suffering from a heart attack, those rats that had suffered a heart attack saw their ejection fractions (a measure of how much volume the heart pumps out with every beat) fell from an average of 72% to 34%. However, rats treated with encapsulated mesenchymal stem cells saw an increase in their ejection fractions from 34% to 56%. Those treated with unencapsulated mesenchymal stem cells saw their ejection fractions rise to 39%.
One of the main effects of implanted stem cells is the promotion of the growth of new blood vessels. In capsule-treated rats, the damaged area of the heart had a blood vessel density that was several times that of the hearts of control animals. Also, the area of cell death was much lower in the hearts treated with encapsulated MSCs.
The encapsulated stem cells seem to stay in the heart for just over ten days, which is the time is takes for the alginate hydrogels to break down. Taylor said that he and his lab would like to test several different materials to determine how long these capsules remain bound to the patch.
The goal is to use a patient’ own stem cells as a source for stem cell therapy. Whatever the source of stem cells, a patient’s own stem cells must be grown outside the body for several days in a stem cell laboratory, much like Emory Personalized Immunotherapy Center in order to have enough material for a therapeutic effect.