Investigators Identify Human Enzyme that Breaks Down Nanomaterials

An international study based at the University of Pittsburgh has identified a human enzyme that can biodegrade carbon nanotubes. Laboratory tests showed that it could also offset the potentially damaging health effects of being exposed to such nanotechnology.

The scientists found that carbon nanotubes degraded with the human enzyme myeloperoxidase (hMPO) did not produce the lung inflammation that intact nanotubes have been shown to cause. Furthermore, neutrophils, the white blood cells that contain and emit hMPO to kill invading microorganisms, can be directed to attack carbon nanotubes specifically.

The research appears online in Nature Nanotechnology, and the paper is titled “Carbon nanotubes degraded by neutrophil myeloperoxidase induce less pulmonary inflammation.” The scientists hope that their findings will open the door to using carbon nanotubes as a safe drug delivery tool and lead to the development of a natural treatment for people exposed to nanotubes.

“The successful medical application of carbon nanotubes relies on their effective breakdown in the body, but carbon nanotubes also are notoriously durable,” points out lead researcher, Valerian Kagan, a professor and vice chair in the department of environmental and occupational health in Pitt's Graduate School of Public Health. “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.”

The team focused on hMPO because it works via the release of strong acids and oxidants, similar to the chemicals used to break down carbon nanotubes. They first incubated short, single-walled nanotubes in an hMPO and hydrogen peroxide solution for 24 hours; hydrogen peroxide sparks and sustains hMPO activity.

They found that the structure and bulk of the tube had completely degenerated. The nanotubes degraded even faster when sodium chloride was added to the solution to produce hypochlorite, a strong oxidizing compound known to break down nanotubes.

The team then developed a technique to prompt neutrophils to attack nanotubes by capturing them and exposing them to the enzyme. They implanted a sample of nanotubes with immunoglobulin G (IgG) antibodies, which made them specific neutrophil targets.

After 12 hours, 100% of IgG nanotubes were degraded versus 30% of those without IgG, the investigators report. They also tested the ability of macrophages to break down nanotubes, but after two days only 50% of the tubes had degenerated.

In subsequent laboratory tests, lung tissue exposed to the degraded nanotubes for seven days exhibited negligible change when compared to unexposed tissue. On the other hand, tissue exposed to untreated nanotubes developed severe inflammation.