Technique Allows Noninvasive Tracking, Imaging of Stem Cells in the Brain

A new technique using quantum dot technology generated through nanotechnology is a promising new tool for monitoring the effects of stem cell therapies for stroke and other types of brain damage.

The study's findings were published in the April 2011 issue of the journal Neurosurgery, the journal of the Congress of Neurological Surgeons. The researchers reported the successful use of near-infrared fluorescence labeling to track the behavior of injected stem cells in brain-injured rats. "The results open up new opportunities to develop noninvasive near-infrared fluorescence imaging...to track bone marrow stem cells transplanted into the human brain,” wrote Dr. Taku Sugiyama and colleagues of Hokkaido University Graduate School of Medicine (Sapporo, Japan).

The researchers utilized bone marrow stem cells to treat induced brain injuries, similar to stroke, in rats. Before injection, the stem cells were labeled with quantum dots, a biocompatible, fluorescent semiconductor created using nanotechnology.

Other fluorescence techniques used to label stem cells have an important limitation their comparatively short wavelengths do not easily penetrate through bone and skin. The quantum dots emit near infrared light, with much longer wavelengths that can easily penetrate tissues. This allowed the researchers to monitor the behavior of stem cells within the brain after transplantation using a computer-assisted, three-dimensional (3D) imaging system.

Using this technology, Dr. Sugiyama and colleagues were able to detect near-infrared fluorescence from the stem cells as they moved to and incorporated themselves into the area around the injured area of the brain. Reflecting the stem cells' behavior, the fluorescence increased gradually, peaking at four weeks after injection. The fluorescence remained detectable for up to eight weeks. The results were validated by direct examination of the brains.

Stem cell transplantation is a potentially beneficial treatment for stroke and other central nervous system disorders. The use of stem cells developed from the patient's own bone marrow is a particularly promising approach. For example, a study in the March 2011 issue of the journal Neurosurgery reported that bone marrow stem cell transplantation was a "logistically feasible and safe” approach to treatment of severe traumatic brain injury in children.

However, some sort of imaging system is needed to track the activity of stem cells as they travel to the injured area and develop into new brain cells. "Such techniques would be crucial to validate the therapeutic benefits of bone marrow stem cell transplantation for central nervous system disorders,” Dr. Sugiyama and coauthors wrote in their article.

Near-infrared fluorescence labeling using quantum dots appears to provide a noninvasive technique for monitoring the effects of stem cell transplantation in the rat brain. Additional studies will be needed to see if similar techniques can be developed and used in humans, according to the researchers. If so, this technology would be an important part of experimental stem cell therapies to enhance functional recovery of the brain after stroke or other types of injury.

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Hokkaido University Graduate School of Medicine