Heart-related diseases are the leading cause of death in the industrialized world. Cardiac stem cell therapy is a promising new way of reducing those numbers, but its application has proven to be less effective than hoped. Now researchers at Stanford University have developed nanoparticles that can be used to image stem cells implanted into the heart. They claim this will help improve the efficiency of these transplants drastically.

Stem cell therapy uses cells that have the ability to transform into a wide variety of mature cell types. When implanted in the heart, for instance, they can transform into heart cells. This ability can be used to repair injured or diseased parts of the heart. Sadly, current methods of introducing stem cells rely on trial and error.

Let’s say, for instance, that a patient suffers a heart attack, which leaves some of his heart cells injured. To help the heart heal, the patient is first put into an MRI scanner to locate the areas of the heart that need repair. Once those are determined, doctors use the scan to implant new stem cells into these regions. After implantation, the patient is returned to the MRI to determine the location and number of implanted cells—if they’re not where they need to be, the patient is returned to surgery. This is exhaustively repeated.

Jesse Jokerst and colleagues at Stanford’s Bio-X lab wanted a better solution. They chose to approach the problem using ultrasound imaging, which relies on sound waves that have a frequency much higher than the human ear can detect. When these wave hit something “big” enough (like an internal organ), they get reflected back. Measuring these reflections with the help of special instruments helps researchers image internal parts of the human body.

In the case of these tiny stem cells, however, Jokerst had to use a contrast agent that would improve the resolution of ultrasound. For that, he developed silica nanoparticles, which, despite their very small size, can be detected by ultrasound. These nanoparticles are then embedded into stem cells prior to transplant. Their inclusion enables real-time footage of stem cells as they are injected. As the video shows (at 0:11), despite the small number of stem cells, nanoparticles help track their placement in the injured area.

This imaging technique has two benefits. First, Jokerst says, it avoids the need for MRI, which “allows the entire procedure to be done in the operating room in real time. Thus, there is no need to move the patient because of the instant knowledge of cell location and number that ultrasound provides”. Second, it makes the use of needle-mediated implantation easier than the less precise catheter-mediated method that inserts stem cells via the heart’s coronary artery.

But that’s not all. Jokerst gave the nanoparticles two more properties. First, he linked them to a fluorescent dye, which he used to ensure that the nanoparticles were firmly embedded within the stem cells before implantation. Second, he doped the nanoparticles with gadolinium, which helps when the stem cells are imaged using an MRI scanner. Jokerst found that he could track the injected stem cells for up to two weeks after implantation by using an MRI scanner to follow the progress of the treatment.

As reported in Science Translational Medicine, the initial studies, done in mice, have given promising results. All the ingredients used in the nanoparticles (silica, fluorescent dye, gadolinium in small amounts) have individually been approved by the US Food and Drug Administration, which means that if it proves effective in clinical trials, this method should not hit too many hurdles before it makes its way into clinical practice.

Science Translational Medicine, 2013. DOI: 10.1126/scitranslmed.3005228 (About DOIs).