Other researchers have used dendrimers containing gadolinium, which is also useful as a contrast medium for MRI, but which is toxic if it stays in the body for a prolonged time. But animal cells have a process to deal with iron and a storage mechanism for the metal, making the iron-based dendrimers inherently safer, says Bulte. For instance, iron is a key part of the transporter for oxygen and carbon monoxide found in red blood cells.
He adds that while it was not easy to develop the way to make magnetic dendrimers, it is easy to label cells with them. In essence, the dendrimer and the cell do that work themselves. Dendrimers stick to cells because they are charged -- kind of like static electricity. Cells then suck them inside and lock them away in the cellular equivalent of a garbage can -- a tiny holding spot called an endosome.
Other magnetic tags have used antibodies or other molecules that recognize and bind to certain features on cells, says Bulte. Unlike those tags, the magnetic dendrimers are universal; the scientists showed that different cell types will take in dendrimers just by mixing the spheres and the cells together, without affecting the cells' behavior.
Bulte's research with magnetic dendrimers is aligned with the Johns Hopkins Institute of Cell Engineering, created in early 2001 to advance research into the biology and potential application of pluripotent stem cells (primitive cells that become any type of cell in the body) and multipotent or adult stem cells (precursor cells that are naturally limited to becoming a specific tissue's cell types).
A next step with magnetic dendrimers, Bulte says, is watching the cells' distribution when they are injected into the circulatory system instead of the brain. Bulte also wants to study white blood cells in diseases of the central nervous system, such as multiple sclerosis, as well as the behavior of embryonic stem cells an
Contact: Joanna Downer
Johns Hopkins Medical Institutions