Iron Treatment Makes Stem Cells Visible

Orthopedic surgeons perform about 700, 000 knee replacements in the U.S. every year—a number that is expected to quintuple within the next 20 years. Not all of those implants are successful. Some implants come loose; others result in fractures of adjoining bone. They wear out. The average lifetime of a knee implant is about ten years.

In a study reported by Bruce Goldman published in Stanford Medicine, Stanford pediatric radiologist Heike Daldrup-Link, M.D. has developed a class of adult stem cells that have the potential to repair worn-out knees. They are the mesenchymal stem cells (MSCs) found in bone marrow. While the cells have been known to initiate the growth of tumors, they usually generate only bone, cartilage, muscle and fat. On the positive side, they are easy to extract from a patient’s bone marrow.

For some time doctors have experimented with injecting these cells into damaged knees in the hope they could lead to the regeneration of tissue. Unfortunately, there has been no way to track the location of the injected cells. Some cells move away, others die; some create scar tissue instead of cartilage or bone. Once injected, the location of the stem cells was unknown.

Daldrup-Link found that loading the cells with iron before injecting them into a joint makes them visible to an MRI machine. The problem was that the cells did not take up iron when they were mixed with iron in a lab dish. But they did take it up when they were placed in some bone marrow together with iron. Daldrup-Link and colleagues gave rats an “injected snack of ferumoxytol, an FDA-approved supplement composed of iron-oxide nanoparticles. When they later harvested MCSs from those rats’ bone marrow and infused them into other rats’ injured knees, they could track the iron-stuffed MSCs for weeks afterward because they gave off a powerful MRI signal, ” Goldman wrote.

Encouraged by this ability to track the location of the injected stem cells, Stanford orthopedic surgeon Jason Dragoo, M.D. is planning a clinical trial in which he will use the new MSC-labeling method. He plans to deliver MSCs extracted from feroxytol-supplemented knee-damaged patients’ own bone marrow in a single procedure. Stay tuned.