Researchers at Karolinska Institutet have for the first time shown that carbon nanotubes can be broken down by an enzyme available in white blood cells, myeloperoxidase (MPO). The discovery was made in collaboration with American scientists.
The findings, presented in the latest issue of Nature Nanotechnology, run contrary to what was previously thought, namely that carbon nanotubes do not degrade in the body or in nature. The researchers hope that the new knowledge on how MPO converts carbon nanotubes to water and carbon dioxide will be important for possible future use in medical applications.
“Previous studies have shown that carbon nanotubes could be used to introduce drugs or other substances in the body’s cells. There has been a limitation in the fact that we have not previously known how to control the degradation of carbon nanotubes. This can result in undesirable toxicity and tissue damage. Our study shows a possible way to biologically break down carbon nanotubes to harmless constituents,” says Associate Professor Bengt Fadeel, one of the researchers behind the study.
Carbon nanotubes is a material consisting of a single layer of carbon atoms rolled into a tube with a diameter of a few nanometres (one nanometre = 1 billionth of a metre). Its length can vary from a few dozen nanometres up to several micrometres. Carbon nanotubes are both lighter and stronger than steel and has very specific thermal conductivity and electrical properties. Today, they are produced in large scale mainly for various technical applications, but also occurs in some consumer products.
Carbon nanotubes have previously been regarded as bio persistent, i.e. that they do not degrade in body tissues or in nature. Research in recent years have demonstrated significant inflammation in experimental animals exposed to carbon nanotubes via air or injection into the abdominal cavity. The inflammation and tissue transformation (fibrosis) that occurs when exposure leads to respiratory problems and can also be linked to development of cancer. For example, a few years ago, a study warned that carbon nanotubes are very similar to asbestos fibres. These are also bio persistent and can cause lung cancer (mesothelioma) in humans long after exposure.
As it clearly shows that the endogenous MPO enzyme can break down carbon nanotubes, the present study constitutes a breakthrough in both nanotechnology and nanotoxicology. The MPO enzyme is expressed in certain types of white blood cells, so-called neutrophils, and is required in order for neutrophils to be able to destroy bacteria. Researchers have now found that the enzyme also attacks carbon nanotubes, breaking them down to plain water and carbon dioxide. In addition, the researchers showed that carbon nanotubes degraded by MPO no longer give rise to inflammation in mice.
“This means that there may be a way to defuse carbon nanotubes, if there is an accident in a workplace where carbon nanotubes are produced, for example. The findings are also relevant to future use of carbon nanotubes in medical treatment,” says Bengt Fadeel.
The study was carried out by researchers at Karolinska Institutet, the University of Pittsburgh and the National Institute for Occupational Safety and Health (NIOSH) in the U.S. The study has been funded by grants from the National Institutes of Health (NIH) and the EU:s Seventh Framework Programme, among others. The work has been carried out within the framework of the NANOMMUNE project, coordinated by Professor Bengt Fadeel at the Institute of Environmental Medicine, Karolinska Institutet, which covers a total of 13 research groups in Europe and the US.