25 March 2013

Nanoparticles will allow you to monitor the stem cells injected into the heart

The results of animal experiments and clinical studies, during which stem cells were injected for the treatment of severe myocardial infarction or subsequent heart failure, do not cause much enthusiasm. However, according to Professor Sam Gambhir from Stanford University School of Medicine, at least in part this is due to the suboptimal choice of the site of cell injection. Ultrasound allows you to see the injection site of a needle with a suspension of cells, but after the cells enter the tissue, it is impossible to track their fate.

As a result, the main questions of concern to researchers remain unanswered: have the cells really penetrated the heart wall? If this happened, did they stay there or did they leave the heart tissue? If they hit the heart wall and stayed there, how long did they remain viable? Did they divide and form a new myocardium?

A new imaging method developed by Professor Gambhir's group allows us to observe the process of introducing cells into tissue using ultrasound and, over the next few weeks, track their movement through the body using magnetic resonance imaging.

This became possible thanks to the labels developed by scientists – nanoparticles made of silicon oxide visualized by ultrasound with the addition of the rare-earth element gadolinium, which is a contrast agent for magnetic resonance imaging.

Experiments have shown that mesenchymal stem cells, most often used to repair damage to the heart muscle, are able to absorb and retain the developed nanoparticles without compromising their viability, as well as the ability to divide and differentiate into myocardial cells.

When inserting nanoparticle-labeled mesenchymal stem cells from mice, pigs and humans into the heart tissue of healthy mice, researchers could use ultrasound to observe the cells leaving the tip of the needle and correct the insertion zone. Two weeks later, during magnetic resonance imaging, they still registered a strong signal emitted by the injected cells. (Ultimately, cell division leads to a decrease in the concentration of contrast agent in their cytoplasm and attenuation of the signal to values below the detection limit.)

The introduction of nanoparticle-labeled stem cells was not accompanied by manifestations of toxicity or changes in animal behavior compared to control group animals that received injections of non-nanoparticle stem cells. The US Food and Drug Administration (FDA) has already approved the use of silicon oxide nanoparticles for other purposes. Gadolinium, toxic in high doses, is also approved by the FDA for clinical use in doses far exceeding the amount needed to label hundreds of millions of stem cells. However, scientists note that additional study of the potential toxicity of nanoparticles is still necessary.

In the near future, they plan to conduct experiments on mice and pigs with simulated heart damage, as well as a detailed study of the toxicity of nanoparticles. Within the next 3-5 years, they hope to start a clinical study of the technique.

Article by J.V. Jokerst et al. Intracellular Aggregation of Multimodal Silica Nanoparticles for Ultrasound-Guided Stem Cell is published in the journal Science Translational Medicine.

Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on Stanford University materials:
Stem cells entering heart can be tracked with nano-‘hitchhikers,’ scientists say.


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