Using tiny rust-containing spheres to tag cells, scientists from Johns Hopkins and elsewhere have successfully used magnetic resonance imaging to track stem cells implanted into a living animal, believed to be a first.
In the December issue of the journal Nature Biotechnology, the team said the neuronal stem cells take up and hold onto the spheres, which contain a compound of iron and oxygen. The iron-laden cells create a magnetic black hole easily spotted by magnetic resonance imaging, or MRI, they report.
"Until now, tissue had to be removed from an animal to see where stem cells were going, so this gives us an important tool," says author Jeff Bulte, Ph.D., associate professor of radiology at the Johns Hopkins School of Medicine. "Tracking stem cells non-invasively will likely be required as research advances, although human studies are still some time away."
Scientists at the University of Wisconsin School of Veterinary Medicine mixed the magnetic spheres, made by Trevor Douglas at Temple University, with stem cells that make the white matter, or neuronal covering, of the brain. Then they injected the iron-laden cells into the brains of rats that lack that covering. Using MRI scanners at the National Institutes of Health, Bulte watched the cells travel away from the injection site. The research was funded by the National Science Foundation, the Oscar Rennebohm Foundation and the Keck Foundation.
The rusty spheres, known as magnetic dendrimers, represent an important improvement over other magnetic tags, Bulte says. And even though the amount of iron used to label the cells is tiny compared to the total amount of iron in the body, the labeled cells stand out from other cells, magnetically speaking.
"During scanning, these labeled cells disturb the magnetic field created by the MRI machine, causing water molecules that pass by to get 'out of phase,'" he explains. "When this happens, the imaging scanner loses the signal,
Contact: Joanna Downer
Johns Hopkins Medical Institutions