Richard Denison, Ph.D., is a Senior Scientist.
Some months ago, my colleague John Balbus posted here about studies finding that when multi-walled carbon nanotubes (MWCNTs) are injected into the abdominal cavities of mice, they induce inflammation and mesothelioma-like reactions similar to those caused by asbestos. He appropriately cautioned that – among other critical questions – these studies had not demonstrated that inhaled MWCNTs could actually move out of the lung and into the tissues where asbestos gives rise to its effects. Well, that particular dot now appears to have been connected.
We learned about the new findings via a blog post by Liz Borkowski at The Pump Handle. She noted a disturbing item on the NIOSH blog posted by Vince Castranova and his colleagues late last week, in which they are seeking to share more broadly results they first presented at the recently-concluded Society of Toxicology meeting in Baltimore.
The NIOSH researchers reported new data showing for the first time that MWCNTs can migrate intact from the alveoli out of the lungs of mice and into the pleura, the tissue surrounding the lungs. And it is in the pleura (as well as the abdominal cavity) where asbestos induces its signature form of cancer, mesothelioma.
In this case, the MWCNTs were introduced into the lungs using pharyngeal aspiration, a procedure by which mice are induced to inhale a droplet of liquid in which the MWCNTs are suspended. While this procedure is thought to mimic direct inhalation, the NIOSH researchers note this and other limitations of the study, and caution that the results are preliminary and have not yet been peer-reviewed.
They also note that it's possible that the mice used in the study are unique and may not accurately portray what would happen in people, say, workers exposed to MWCNTs. And, as my colleague pointed out in his earlier post, whether sufficient material could or would be suspended in the air to result in inhalation exposure also remains an open question.
Nonetheless, these new findings strongly suggest that, like asbestos, MWCNTs behave as stable fibers capable of penetrating and migrating through the lung. And together with the earlier studies showing that introducing MWCNTs into the tissues surrounding the lung induces mesothelioma-like reactions, it's fair to say the alert level on MWCNTs just went up significantly.