Carbon nanotubes may pose asbestos-style cancer risk

As well as highlighting potential exposure risks, their findings have also given new insights into how mesothelioma develops – a type of cancer that stems from the thin layer of tissue that covers many of the internal organs, and for which there is currently no cure. Often remaining undiagnosed for decades, knowing more about its very early stages could one day lead to earlier diagnosis and more effective therapies. 

Carbon nanotubes (CNTs) have a long, hollow structure a few nanometers wide (10,000 times smaller than the diameter of a human hair) and several centimetres long. They are used in the manufacture of incredibly strong, lightweight materials for use in products such as bicycle frames, aircraft and sports cars.

Some CNTs are similar in size and shape to asbestos fibres, leading researchers to question whether they might have the same harmful effect on our lungs.

Previous studies have looked at the effect of introducing the fibres directly into the abdominal cavity of mice. In this new study, the researchers placed either long carbon nanotubes or asbestos fibres directly into the pleural space (which separates the lungs and chest wall), where mesothelioma usually develops in humans. This more closely mimics occupational exposure, where free fibres might be inhaled during the manufacturing process. There is no evidence of risk from finished products which incorporate CNTs.

The researchers studied the resultant changes in the cells lining the pleural space over a number of months. The mesothelioma which developed in the mice after asbestos or CNT exposure was similar to that from patients exposed to asbestos.

Just as with asbestos fibres, they found that long nanotubes caused long-term inflammation in the pleural space. Over time, this inflammation leads to inactivation and loss of the specific genes that suppress the formation of tumours.

Professor Marion MacFarlane from the MRC Toxicology Unit, and the study’s senior author, said:

Unlike previously reported short-term studies, this is the first time the mesothelioma-causing effects of long and thin carbon nanotubes have been monitored in mice over many months. Because it is diagnosed in humans when it’s quite advanced, we don’t know much about how or why it forms. This research could help us define key indicators for early detection as well as provide information for developing targeted therapies for this devastating disease.

Importantly, the new study found that it was only CNTs which were long, thin and bio-persistent (those which aren’t broken down and expelled by the immune system) which posed a hazard.

Dr Craig Poland, Senior Research Fellow at the MRC Centre for Inflammation Research, said:

New advanced materials such as carbon nanotubes offer an exciting frontier for innovation but safety is imperative. Prior to understanding the risks posed by exposure to asbestos, it was considered a wonder material with numerous applications yet a tragic legacy arose from its widespread use. Knowledge of the sequence of events from exposure to asbestos to the formation of mesothelioma is vital for identifying any risks posed by new fibers such as certain forms of carbon nanotubes. We have demonstrated the potential risks posed by long carbon nanotubes. These findings open up the possibility of more effective and efficient screening of advanced fibres to better identify risks and ensure safety.

Dr Nathan Richardson, Head of Molecular and Cellular Medicine at the MRC, which funded the research, said:

Asbestos-related mesothelioma diagnoses have risen significantly since the 1990s, but are projected to fall steadily in the UK over the next couple of decades – thanks to greater awareness of the dangers, banning much of its use and improved health and safety measures where people can become exposed. As products using CNTs become more popular, we need to make sure that safety regulators are informed about any possible dangers.

Published article on Current Biology website

MRC Toxicology Unit website

MRC Molecular & Cellular Medicine website