Neutrophil Enzyme Digests Carbon Nanotubes

Researchers have found that the human neutrophil enzyme myeloperoxidase (hMPO) is able to breakdown and detoxify carbon nanotubes, a finding that paves the way for their use as a drug delivery mechanism.

Investigators at the University of Pittsburgh (PA, USA) and colleagues from several other institutions exposed carbon nanotubes to myeloperoxidase in vitro, in neutrophil cultures, and in macrophage cultures. To increase the uptake of the nanotubes by neutrophils they were first coated with immunoglobulins.

Results reported in the April 4, 2010, online edition of the journal Nature Nanotechnology showed that incubation of single-walled nanotubes with hMPO and hydrogen peroxide resulted in degeneration of the nanotubes within 24 hours. This process could be accelerated by the addition of sodium chloride, which generated hypochlorite, a strong oxidizing compound known to break down nanotubes.

Native or immunoglobulin-coated nanotubes were introduced into neutrophil or macrophage cell cultures. After 12 hours in the neutrophil culture, essentially all the coated nanotubes were degraded as compared to only about 30% of the native nanotubes. In contrast, after two days in the macrophage culture only about 50% percent of the coated nanotubes had degenerated. The biodegraded nanotubes did not generate an inflammatory response when aspirated into the lungs of mice.

"The successful medical application of carbon nanotubes relies on their effective breakdown in the body, but carbon nanotubes also are notoriously durable,” said first author Dr. Valerian Kagan, professor of environmental and occupational health at the University of Pittsburgh. "The ability of hMPO to biodegrade carbon nanotubes reveals that this breakdown is part of a natural inflammatory response. The next step is to develop methods for stimulating that inflammatory response and reproducing the biodegradation process inside a living organism.”

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