Thursday, March 29, 2007

Stem Cell Therapies for Weakened Hearts

Now that the American College of Cardiology meeting has come to a close, a number of interesting reports have surfaced that promise to attack the weakened heart using stem cells. Even stem cells on stents are being evaluated.

While the results are exciting, careful evaluation of the very preliminary data is warranted. For instance, echo measurements demonstrating improvements of "1 mm" more of systolic contraction in 23 patients can hardly be classified as significant, since the resolution of reproducible measurement exceeds this amount. Also, the data suggest a trend (though again, not significant), of other possible issues with immune disorders or infections. Nonetheless, what was encouraging was that the authors found that their data did not demonstrate a worstened outcome in any patient so far.

Perhaps the best review of the current state of the art in this area has appeared recently in the New England Journal of Medicine. This report sheds light on the difficulties demonstrating long-term improvement in patients to date. Additionally, delivery of cells to their target has also been complicated:
Some of the complications of delivering cells or drugs locally to the heart are the inherent motion of the organ, the compatibility of the device with the treatment being injected, and the distribution of the therapy within the tissue. Other potential routes of cardiac delivery include intracoronary injection, adventitial delivery, epicardial injection, and pericardial injection.

The development of methods for delivering stem cell therapies to the heart is not straightforward. There are many complications and contradictions. Animal studies show that the success of a delivery method is different for a healthy heart than it is for a diseased heart.

There may be an additional mechanism where cells can find their way into the heart, which is not available for a normal heart, said Dr. Palasis. Many delivery devices in development for cardiac cell therapy are actually angioplasty catheters, and these devices come with their own complications.

If angioplasty catheters are going to be used for cell therapies, its important to look at potential for catheter materials to affect viability of cells. Guidewire lumens could be covered with lubricants. The FDA is aware of the compatibility issues. Both acute cell delivery and cell engraftment depend on the delivery method used.
And while early results of the more recent works may suggest a benefit to these therapies, they certainly have a long way to go before they can be applied to the populace at large. Perhaps the best advise came from the NEJM article:
Recent randomized studies of cell therapy for heart disease represent a milestone in this rapidly developing field while serving as a cogent reminder that many important clinical and fundamental questions have yet to be addressed. We should guard against both premature declarations of victory and premature abandonment of a promising therapeutic strategy. The ultimate success of this strategy is likely to depend on continued and effective coordination of rigorous basic and clinical investigations.


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