Metals in Carbon Nanotubes Impede Neural Functions

Severe disorders such as epilepsy, Parkinson's disease and perhaps even paralysis could be cured with nanoparticle-based treatments in the future. The tiny structures were recently proven to be able to assist human nervous tissue in regrowing, following accidents, and also showed a remarkable ability to carry drugs to places in the brain where they were needed, so as to accelerate healing. But studies have revealed that the small tubes interfere with a critical signaling transaction in neurons, a fact that has thrown doubt over their future in the field of medicine. No one knew what the root cause of the problem was, until a recently published study, which threw light on the issue.

According to experts from the Brown University, who spent a good deal of time trying to figure out this puzzle, it may be that the carbon nanotubes (CNT) themselves are not to blame at all. The scientists propose that one of the catalysts used in their production process, a chemical known as yttrium, may in fact remain on the CNT in trace amounts, but sufficiently large to affect neural communications. The new theory is detailed in the latest issue of the journal Biomaterials. BU investigators believe that nanotubes made without the catalyst could be applied to brain tissue without concerns.

“We can purify the nanotubes by removing the metals. So, it's a problem we can fix,” the lead author of the new study, BU PhD candidate in biomedical engineering Lorin Jakubek, says. While studying single-walled carbon nanotubes (SWCNT), in a simulated environment inside BU neuroscientist Diane Lipscombe's laboratory at the university, Jakubek discovered that metals such as yttrium and nickel, which is also used in producing CNT, interfered with calcium ions.

This may not seem like much until we take a closer look at how neurons transmit their electrical impulses to one another. At the end of the axon, the body of the neuron, small dendrites connect to dendrites from the next neuron. They do not actually connect, as a small space exists between them. This space is laden with chemical receptors, which are thrown in or collected via chemical ion channels, which are sensitive to calcium and other elements.

When metals are thrown in the mix, things go awry. Yttrium “gets stuck and prevents calcium from entering and passing through. It's an ion pore blocker,” Lipscombe, who is also a corresponding author of the new paper, explains. She specializes in neuronal ion channels. At a concentration of less than one microgram per milliliter of water, the yttrium was able to interfere with normal neuron functioning, the team reports.