Keeping Implanted Stem Cells in the Heart


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.

alginate_formel

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.

Histological appearance of encapsulated human mesenchymal stem cells (hMSCs). Light microscopic appearance of encapsulated hMSCs at the time of implantation with approximately 200 cells within each 250 μm capsule. (Scale bar=100 μm)
Histological appearance of encapsulated human mesenchymal stem cells (hMSCs). Light microscopic appearance of encapsulated hMSCs at the time of implantation with approximately 200 cells within each 250 μm capsule. (Scale bar=100 μm)

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%.

Detailed cardiac functional analysis by cardiac magnetic resonance imaging (CMR) and transthoracic echocardiography (TTE) showed improvement in animals treated with encapsulated human mesenchymal stem cells (hMSCs). A, Representative short axis CMR at end systole of animals treated with encapsulated hMSCs or controls. Myocardial thinning and chamber dilation, delineated by traced endocardium (red) and epicardium (green) was reduced in the encapsulated hMSC group (arrow). Quantification of end systolic volume (B) and ejection fraction (C) by CMR at day 28 showed improved contractile function in the encapsulated hMSC treated group (n=4 per group). D, TTE comparison of untreated animals (n=9) to animals treated with encapsulated hMSCs (n=7) or hMSCs delivered by direct injection (n=7) into the infarcted myocardium showed greater benefit of treatment with encapsulated cells. Data represent mean±SEM. *P<0.05 by Dunnett's test of multiple comparisons; #P<0.05 by analysis of variance (ANOVA). LVESV indicates left ventricular end systolic volume; MI, myocardial infarction.
Detailed cardiac functional analysis by cardiac magnetic resonance imaging (CMR) and transthoracic echocardiography (TTE) showed improvement in animals treated with encapsulated human mesenchymal stem cells (hMSCs). A, Representative short axis CMR at end systole of animals treated with encapsulated hMSCs or controls. Myocardial thinning and chamber dilation, delineated by traced endocardium (red) and epicardium (green) was reduced in the encapsulated hMSC group (arrow). Quantification of end systolic volume (B) and ejection fraction (C) by CMR at day 28 showed improved contractile function in the encapsulated hMSC treated group (n=4 per group). D, TTE comparison of untreated animals (n=9) to animals treated with encapsulated hMSCs (n=7) or hMSCs delivered by direct injection (n=7) into the infarcted myocardium showed greater benefit of treatment with encapsulated cells. Data represent mean±SEM. *P

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.

Treatment of hearts with encapsulated human mesenchymal stem cells (hMSC) post myocardial infarction reduced myocardial scarring at 28 days. A, Representative sections of infarcted hearts stained with Masson's Trichrome and treated with encapsulated hMSCs or control gels. Blue indicates fibrotic scar. ×15, scale bar=1 mm. B, Animals treated with encapsulated hMSCs showed reduced scar area (7±1%; n=6) at 28 days compared to control treated hearts (MI: 12±1%, n=8; MI+Gel: 14±2%, n=7; MI+Gel+hMSC: 14±1%, n=7; MI+Gel+Empty Caps: 12±2%, n=5). Data represent mean±SEM. *P<0.05. MI indicates myocardial infarction.
Treatment of hearts with encapsulated human mesenchymal stem cells (hMSC) post myocardial infarction reduced myocardial scarring at 28 days. A, Representative sections of infarcted hearts stained with Masson’s Trichrome and treated with encapsulated hMSCs or control gels. Blue indicates fibrotic scar. ×15, scale bar=1 mm. B, Animals treated with encapsulated hMSCs showed reduced scar area (7±1%; n=6) at 28 days compared to control treated hearts (MI: 12±1%, n=8; MI+Gel: 14±2%, n=7; MI+Gel+hMSC: 14±1%, n=7; MI+Gel+Empty Caps: 12±2%, n=5). Data represent mean±SEM. *P

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.

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mburatov

Professor of Biochemistry at Spring Arbor University (SAU) in Spring Arbor, MI. Have been at SAU since 1999. Author of The Stem Cell Epistles. Before that I was a postdoctoral research fellow at the University of Pennsylvania in Philadelphia, PA (1997-1999), and Sussex University, Falmer, UK (1994-1997). I studied Cell and Developmental Biology at UC Irvine (PhD 1994), and Microbiology at UC Davis (MA 1986, BS 1984).

2 thoughts on “Keeping Implanted Stem Cells in the Heart”

  1. As well, I can appreciate your comments about the inhospitable environment for the Stem Cells after an MI. There are so many factors that go ‘unaccounted for’ as well.

    Pre-treatment of the Patient with Hyperbaric Oxygen has the potential to stimulate angiogenesis – as it is well known to be effective in the treatment of many other ‘circulation impaired’ (ex: Diabetic) wounds. It has also been documented to stimulate endogenous release of the Patient’s own Stem Cells 800% (Heart & Circulatory Physiology – November ’05).

    Additionally, the heavy metal burden of the individual Patient is not accounted for, and has been readily been shown to affect Stem Cells in the mouse embryo – it is not a tremendous ‘leap’ to imply that this would/could affect the ‘newly-implanted’ Stem Cells in the Adult, and should be evaluated.

    Typically, the person with Cardiac Disease often times has co-existing Blood Sugar difficulties (elevated Sugars impairing Stem Cell engraftment) and Gastrointestinal issues (Dysbiosis creating Endotoxins and Afalatoxins released into the circulation) which impair Stem Cell chances at engraftment, replication, and differentiation.

    The simplistic picture of “plant Stem Cells here” and expect “X-results” is just not a reality, as is the case in all ‘other’ disease processes and treatments. Co-morbid factors need thorough assessment and need to be addressed if we attempt to quantify treatment results in this / or any other disease process.

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