Magnetised carriers help steer stem cells to therapy sites

By feeding stem cells particles made of magnetised iron oxide, scientists at Emory University and the Georgia Institute of Technology believe they can then use magnets to attract the cells to a particular location in the body after intravenous injection.

The results are published online in the journal Small and will appear in an upcoming issue. The paper was a result of collaboration between the laboratories of W. Robert Taylor of Emory, and Gang Bao of Georgia Tech. Taylor is professor of medicine and biomedical engineering and Bao is professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University.

The study used mesenchymal stem cells that can be obtained from adult tissues such as bone marrow or fat and are capable of becoming bone, fat and cartilage cells, but not other types of cell such as muscle or brain. They secrete a variety of nourishing and anti-inflammatory factors, which could make them valuable tools for treating conditions such as cardiovascular disease or autoimmune disorders.

Magnetized iron oxide nanoparticles are already US Food and Drug Administration (FDA) approved for diagnostic purposes with magnetic resonance imaging (MRI). Other scientists have tried to load stem cells with similar particles, but found that the coating on the particles was toxic or changed the cells’ properties.

The nanoparticles used in this study have a polyethylene glycol coating that protects the cell from damage. Another feature is that the Emory/Georgia Tech team used a magnetic field to push the particles into the cells, rather than chemical agents used previously.

‘We were able to load the cells with a lot of these nanoparticles and we showed clearly that the cells were not harmed,’ Taylor said in a statement. ‘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 non-toxic polymer polyethylene glycol, and have an iron oxide core that is about 15 nanometres across. For comparison, a DNA molecule is two nanometres wide and a single influenza virus is at least 100 nanometres wide.

The particles appear to become stuck in cells’ lysosomes, which are parts of the cell that break down waste. The particles stay in one place 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 team tested the ability of magnets to move the cells in cell culture and in living animals. In mice, a bar-shaped rare earth magnet could attract injected stem cells to the tail. 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 labelled the cells with a fluorescent dye. They calculated that the bar magnet made the stem cells six times more abundant in the tail. In addition, the iron oxide particles themselves could potentially be used to follow cells’ progress through the body.

‘Next, we plan to focus on therapeutic applications in animal models where we will use magnets to direct these cells to the precise site need to affect repair and regeneration of new blood vessels,’ Taylor said.

Co-first authors of the paper in Small are postdoctoral fellows Natalia Landazuri and Sheng Tong. Landazuri is now at the Karolinska Institute in Sweden.