Enzyme in white blood cells can break down carbon nanotubes

nanotube toxicityAn EU-funded study of carbon nanotubes by scientists in Ireland, Sweden and the US has shown that these extraordinarily strong molecules can be broken down into carbon and water by an enzyme found in white blood cells. The discovery, published in the journal Nature Nanotechnology, offers hope that this new material may be exploited safely in medicine and industry.

The findings are an outcome of the NANOMMUNE (‘Comprehensive assessment of hazardous effects of engineered nanomaterials on the immune system’) project, financed under the NMP (‘Nanosciences, nanotechnologies, materials and new production’) theme of the EU’s Seventh Framework Programme (FP7).

Carbon nanotubes are cylindrical, engineered carbon molecules that are lighter and stronger than steel and have unique electrical properties. They are used in several areas of industry, for example in the manufacture of silicon chips, electronics and sporting goods. Carbon nanotubes are produced in large quantities, which has implications for occupational health, and are also being used in the development of new drugs and other medical applications. Their behaviour in living organisms is, therefore, an intensive area of study. NANOMMUNE researchers are seeking to fill the gaps in our knowledge of the potentially hazardous effects of engineered nanomaterials on the human immune system.

‘Previous studies have shown that carbon nanotubes could be used for introducing drugs or other substances into human cells,’ explained Dr Bengt Fadeel of the Institute of Environmental Medicine at Sweden’s Karolinska Institute. ‘The problem has been not knowing how to control the breakdown of the nanotubes, which can cause unwanted toxicity and tissue damage. Our study now shows how they can be broken down biologically into harmless components.’

Recent experiments on mice have demonstrated that animals exposed to carbon nanotubes via inhalation or through injection into the abdominal cavity are not able to break down the material causing severe inflammation and changes to tissues, which in turn lead to impaired lung function and in some cases to cancer. This ‘biopersistence’ has been likened to that of asbestos; ways to neutralise the toxicity of this engineered material have been avidly sought.

The researchers examined the effects of an enzyme called myeloperoxidase (MPO), which is found in white blood cells (neutrophils), on carbon nanotubes both in vitro and in mice. They discovered that the enzyme can indeed break the nanotubes down into carbon and water. Once broken down they ceased to have an inflammatory effect in the lungs of mice.

‘This means that there might be a way to render carbon nanotubes harmless, for example in the event of an accident at a production plant,’ said Dr Fadeel. ‘But the findings are also relevant to the future use of carbon nanotubes for medical purposes.’ The researchers speculated that the lung inflammation seen in mice exposed to carbon nanotubes may have to do with the very high concentrations used, which may have overwhelmed the biodegradation capacity of the neutrophil enzymatic system. The new understanding of hMPO-mediated biodegradation of this promising material paves the way for its use in biomedical applications such as the delivery of drugs ‘when used at appropriate and readily degradable concentrations’.

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