Like asbestos fibers, multi-walled carbon nanotubes (MWCNTs) are small enough to be inhaled or accidentally ingested as dust. Unlike asbestos, which occurs naturally and is mined for commercial use, MWCNTs are synthetic. These carbon-based molecules are shaped into concentric tubes which resist chemical corrosion and are valuable for use in electronics, optics, textiles, and other areas of manufacturing.
The goal of the new German study was to identify possible carcinogenic effects of MWCNTs and to determine how the cancer triggered by these molecules compares to mesothelioma triggered by asbestos. The team injected different shapes and sizes of MWCNTs into the abdomens of 500 lab rats. A control group of rats received injections of amosite asbestos.
All of the treated rats developed malignant peritoneal mesothelioma, which was confirmed by microscopic and immunohistochemical evaluation. Most of these MWCNT-induced mesothelioma tumors occurred not only on the peritoneum lining the abdomen, but also spread into peritoneal organs, especially the diaphragm, suggesting an aggressive malignancy.
But, even though mesothelioma developed in all cases, there were differences in the time it took for tumors to occur. The researchers theorize that the differences may lie in the shapes and sizes of the MWCNTs.
“We observed highest frequencies and earliest appearances after treatment with the rather straight MWCNT types A and B,” writes researcher Susanne Rittinghausen of the Fraunhofer Institute for Toxicology and Experimental Medicine in Hannover. Rats injected with the slightly curved C type of MWCNTs developed mesothelioma slightly later and those injected with the D type, the most curved variety, were the latest to develop mesothelioma.
The researchers report that, regardless of the cause, all of the mesotheliomas that developed in the rats were similar to each other and to human mesothelioma. The team concludes that all types of MWCNTs have the potential to cause mesothelioma, but that certain varieties are more carcinogenic than others. Mesothelioma is a highly aggressive cancer that is currently considered incurable. The new study appears in the journal Particle and Fibre Toxicology.
Rittinghausen, Susanne et al, “The carcinogenic effect of various multi-walled carbon nanotubes (MWCNTs) and intraperitoneal injection in rats”, November 20, 2014, Particle and Fibre Toxicology, EPub ahead of print