Microscopic Fibers String Spinal Cord Back Together
With plans just approved for the first trial to treat spinal cord injuries in humans with embryonic stem cells, a team of Northwestern scientists is tackling the problem from a different angle: through microscopic messenger molecules that can tell the disconnected nerve cells to re-grow.
The molecules are called nanofibers, and scientists at Northwestern’s Institute for BioNanotechnology in Medicine are exploring their potential to treat problems ranging from severed spinal cords to Parkinson’s disease.
Researchers have made nanofibers before with materials such as collagen, but most have to be constructed outside the body and implanted. The ones being researched at Northwestern can spontaneously create themselves from smaller molecules called peptide amphiphiles, allowing scientists to insert them with a simple liquid injection.
“Because they form through self-assembly, we can create therapies that are non-invasive,” said Ramille Capito, assistant director of research at the Institute who presented the team’s findings at the annual meeting of the American Association for the Advancement of Science in Chicago Saturday.
Spinal cord injuries present a two-fold problem for the patient: First, the nerve cells are disconnected, cutting off messages from the brain that tell the body how to move. Second, shortly after the injury a scar tissue begins to form, blocking nerve cells from growing back.
Messages from nanofibers might be able to stop the process.
According to Capito, the cylinder-shaped nanofibers work by binding to a specific group of amino acids, the tiny molecules that form proteins. Nanofibers carry the amino acids to the injured area. The amino acids then bind to receptors on the cell surface, promoting the growth of nerve cells and inhibiting the growth of scar tissue.
Northwestern scientists tried the technique on rats with severed spines and found that five weeks after the injury, rats injected with nanofibers regained significantly more motion in their hind legs than a control group injected with glucose sugar.
Capito said when they tested the nanofibers on rats with Parkinson’s symptoms, 83 percent of the rats injected with them recovered.
After a few weeks the nanofibers spontaneously disintegrate into harmless amino acids.
“The nice thing about those nanomaterials is that they are completely biodegradable. They break down into amino acids, and so we don’t think there’s going to be any toxicity from them,” said Douglas Losordo, director of the Program in Cardiovascular Regenerative Medicine at Northwestern’s Feinberg School of Medicine, who hopes to apply the nanofibers to his own research with adult stem cells.
Losordo is exploring the use of adult stem cells to treat ischemic heart disease, an illness in which blood is cut off from the heart. He found that special stem cells from the bone marrow called endothelial progenitor cells could enter the blood-deprived area and stimulate the growth of new blood vessels.
Losordo said he is collaborating with Capito’s team to find ways nanofibers and stem cells can work together. For example, the low blood supply in the areas he wants to regenerate makes it hard for the stem cells to take effect. The job might be easier if nanofibers could shelter them.
“It’s a challenging environment for the cells to survive,” Losordo said. “We thought, if we could provide the cells with some survival cues, or a matrix or a soil, if you will, that they’re happier in, maybe we’ll have better luck with retention, survival, proliferation, differentiation of those cells into the target organ.”
by Kristen Minogue