Stem cells hold the promise of treating a variety of diseases, and while techniques that differentiate these cells into wanted types are regularly making waves in the news, effectively depositing them where needed in the body remains a challenge.
Now a team from Emory University and Georgia Tech has developed a technique of injecting magnetized particles of iron oxide into mesenchymal stem cells. The technique involves coating the particles with polyethylene glycol to keep them non-toxic and then using a magnetic field to push them into the interior of cells. Once inside the cell walls, the magnetized particles provide the levers by which an external magnet can pull the cells to gather precisely where needed.
More details from Emory:
“We were able to load the cells with a lot of these nanoparticles and we showed clearly that the cells were not harmed,” [W. Robert Taylor, MD, PhD] says. “The coating is unique and thus there was no change in viability and perhaps even more importantly, we didn’t see any change in the characteristics of the stem cells, such as their capacity to differentiate. This was essentially a proof of principle experiment. Ultimately, we would target these to a particular limb, an abnormal blood vessel or even the heart.”
The particles are coated with the nontoxic polymer polyethylene glycol, and have an iron oxide core that is about 15 nanometers across. For comparison, a DNA molecule is 2 nanometers wide and a single influenza virus is at least 100 nanometers wide.
The particles appear to become stuck in cells’ lysosomes, which are parts of the cell that break down waste. The particles stay put for at least a week and leakage cannot be detected. The scientists measured the iron content in the cells once they were loaded up and determined that each cell absorbed roughly 1.5 million particles.
Once cells were loaded with iron oxide particles, the Emory/Tech team tested the ability of magnets to nudge the cells both in cell culture and in living animals. In mice, a bar-shaped rare earth magnet could attract injected stem cells to the tail (see photo). The magnet was applied to the part of the tail close to the body while the cells were being injected. Normally most of the mesenchymal stem cells would become deposited in the lungs or the liver.
To track where the cells went inside the mice, the scientists labeled the cells with a fluorescent dye. They calculated that the bar magnet made the stem cells 6 times more abundant in the tail. In addition, the iron oxide particles themselves could potentially be used to follow cells’ progress through the body.