CarboTox

CarboTox – Development of screening methods to analyse cancerogenous potential of carbon nano tubes

As part of the joint project CarboTox, tailor-made multi-walled carbon nanotubes (MWCNT) with different lengths, diameters and shapes, produced by our cooperation partner (IFW, Dresden), were tested both in vivo and in vitro for their toxic and carcinogenic potential.

A carcinogenicity study was performed to evaluate the carcinogenic potential of multi-walled CNT over a test duration of 2 years. To this end, rats were treated once with the test item (2 dose groups with 50 animals/group: 1 x 109 and 5 x 109 WHO fibers*/rat, amosite as reference fiber, dose: 0.1 x 109 WHO fibers*/rat) by intraperitoneal injection. In parallel, a screening test was developed with the aim to identify markers for chronic adverse effects detectable already after shorter observation periods. All multi-walled carbon nanotubes, independent of their length and diameter, caused tumors (mesothelioma) typically associated with fibers after intraperitoneal injection, but multi-walled carbon nanotubes with more needle-like morphology showed a stronger tumorigenic effect than the coiled carbon nanotubes.

*WHO fibers: length > 5 µm, diameter < 3 µm; length/diameter ratio > 3/1

Measuring the thickness of the diaphragm covering the peritoneum was found to be a well suited endpoint for an in vivo screening test with observation periods of 3 and 6 months. Equally valid is the determination of the ratio of proliferated cells compared to non-proliferated cells in the peritoneum using the BrdU method (chem. Bromodeoxyuridine). An increase in proliferated cells indicates the beginning of possibly uncontrolled cell division. A simultaneously performed subchronic inhalation test with the same multi-walled carbon nanotubes is aimed at detecting and quantifying the migration of multi-walled CNT to the pleura. With the currently available results, however, it is not yet possible to answer these questions

In vitro assays with primary mesothelial cell cultures showed that multi-walled CNT, depending on their morphology, inhibit cell proliferation, lead to damage of membranes, cytoskeleton and DNA, and cause cellular senescence. The strongest biological effects were induced by multi-walled carbon nanotubes with needle-like morphology.

Interestingly, the effects of different multi-walled carbon nanotubes observed in cell cultures correlated with tumor development in rats, so that certain cell culture methods might be suitable for use as screening tests to assess the adverse, carcinogenic potential of new multi-walled CNT.