The broad and well-funded field of regenerative medicine is giving rise many new and varied areas of development, one of which is the engineering of stem cells to make them perform more effectively following transplantation. This includes a range of additions that do not occur in nature. For example, in past years, researchers have enhanced stem cells with add-ons such as timed release packages of supportive molecules to steer their behavior and sustain their activities for longer in the patient. In the research presented here, scientists instead coat stem cells with particles based on the exterior of platelets, causing the cells to adhere to tissues in areas of damage, where they can do the most good via signaling and other mechanisms. In effect, it is a way to improve the localization of delivery and activity of stem cells, even when lacking information on the exact location of damage in the patient. As might be expected, that turns out to improve the end result in terms of regeneration and restoration of tissue function.
Although cardiac stem cell therapy is a promising treatment for heart attack patients, directing the cells to the site of an injury - and getting them to stay there - remains challenging. In a new pilot study using an animal model, researchers show that "decorating" cardiac stem cells with platelet nanovesicles can increase the stem cells' ability to find and remain at the site of heart attack injury and enhance their effectiveness in treatment. "Platelets can home in on an injury site and stay there, and even in some cases recruit a body's own naturally occurring stem cells to the site, but they are a double-edged sword. That's because once the platelets arrive at the site of injury, they trigger the coagulation processes that cause clotting. In a heart-attack injury, blood clots are the last thing that you want."
The researchers wondered if it would be possible to co-opt a platelet's ability to locate and stick to an injury site without inducing clotting. They found that adhesion molecules (a group of glycoproteins) located on the platelet's surface were responsible for its ability to find and bind to an injury. So the team created platelet nanovesicles from these molecules, and then decorated the surface of cardiac stem cells with the nanovesicles, "The nanovesicle is like the platelet's coat. There isn't any internal cellular machinery that could activate clotting. When you place the nanovesicle on the stem cell, it's like giving the stem cell a tiny GPS that helps it locate the injury so it can do its repair work without any of the side effects associated with live platelets."
In a proof-of-concept study involving a rat model of myocardial infarction, twice as many platelet nanovesicle (PNV) decorated cardiac stem cells (CSCs) were retained in the heart than non-decorated cardiac stem cells. The rodents were monitored for four weeks. Overall, the rats in the PNV-CSC group showed nearly 20 percent or higher cardiac function than the control CSC group. A small pilot study in a pig model also demonstrated higher rates of stem cell retention with PNV-CSCs, though the team did not perform functional studies. A future follow-up study is planned.