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Researchers identify threshold length for nanoparticle-induced lung inflammation


New research shows that carbon nanoparticles longer than four micrometers in length cause acute pleural inflammation in laboratory mice, findings that suggest a connection between the synthetic fibers and mesothelioma, a deadly cancer of the lining of the lungs.

In an earlier study, in 2008, researchers at Queen's Medical Research Institute at the University of Edinburgh’s MRC Centre for Inflammation Research found that injecting carbon nanotubes  — straw-like cylinders of pure carbon used to manufacture a growing number of consumer products — into the abdominal cavity of mice had the same effect as asbestos fibers.

Last year, the same research team, led by Ken Donaldson, professor of respiratory toxicology at the University of Edinburgh, tested the toxicity of the particles in cavities of mice. They discovered that short carbon nanotubes are relatively harmless, but that longer particles were more likely to become lodged in the lung lining.

However, until the recent study, published online last week in the journal Toxicological Sciences, the threshold length beyond which ingestion of the material can damage the lungs was unknown.

First discovered in 1991, nanotubes are about 1/50,000th the width of a human hair and resemble asbestos fibers in size and shape. Used to make everything from electronics to building materials to sports equipment to medical devices, they are among the strongest materials known. Nanotubes were found in four of seven first responders to the 2001 World Trade Center attacks who developed severe respiratory impairment.

The current study involved the intrapleural injection of nanofibers in female mice. The researchers than used an electron microscope to scan sections of the chest wall for lesions and other signs of an inflammatory response.

The researchers concluded “the identification of the threshold length for nanofiber induced pathogenicity in the pleura has important implications for understanding the structure-toxicity relationship for asbestos-induced mesothelioma …”

They said the study underscores the need for “a benign-by-design approach” to engineering nanofibers that are long enough to be useful but short enough to avoid causing disease.