Free radical scavenging and formation by multi-walled carbon nanotubes in cell free conditions and in human bronchial epithelial cells.
BACKGROUND
Certain multi-walled carbon nanotubes (MWCNTs) have been shown to elicit asbestos-like toxicological effects. To reduce needs for risk assessment it has been suggested that the physicochemical characteristics or reactivity of nanomaterials could be used to predict their hazard. Fibre-shape and ability to generate reactive oxygen species (ROS) are important indicators of high hazard materials. Asbestos is a known ROS generator, while MWCNTs may either produce or scavenge ROS. However, certain biomolecules, such as albumin - used as dispersants in nanomaterial preparation for toxicological testing in vivo and in vitro - may reduce the surface reactivity of nanomaterials.


METHODS
Here, we investigated the effect of bovine serum albumin (BSA) and cell culture medium with and without BEAS 2B cells on radical formation/scavenging by five MWCNTs, Printex 90 carbon black, crocidolite asbestos, and glass wool, using electron spin resonance (ESR) spectroscopy and linked this to cytotoxic effects measured by trypan blue exclusion assay. In addition, the materials were characterized in the exposure medium (e.g. for hydrodynamic size-distribution and sedimentation rate).


RESULTS
The test materials induced highly variable cytotoxic effects which could generally be related to the abundance and characteristics of agglomerates/aggregates and to the rate of sedimentation. All carbon nanomaterials were found to scavenge hydroxyl radicals (•OH) in at least one of the solutions tested. The effect of BSA was different among the materials. Two types of long, needle-like MWCNTs (average diameter >74 and 64.2 nm, average length 5.7 and 4.0 μm, respectively) induced, in addition to a scavenging effect, a dose-dependent formation of a unique, yet unidentified radical in both absence and presence of cells, which also coincided with cytotoxicity.


CONCLUSIONS
Culture medium and BSA affects scavenging/production of •OH by MWCNTs, Printex 90 carbon black, asbestos and glass-wool. An unidentified radical is generated by two long, needle-like MWCNTs and these two CNTs were more cytotoxic than the other CNTs tested, suggesting that this radical could be related to the adverse effects of MWCNTs.
Department of Toxicogenomics, Maastricht University, Maastricht, The Netherlands. p.nymark@maastrichtuniversity.nl.
Penny
P
Nymark
Keld Alstrup
KA
Jensen
Satu
S
Suhonen
Yahia
Y
Kembouche
Minnamari
M
Vippola
Jos
J
Kleinjans
Julia
J
Catalán
Hannu
H
Norppa
Joost
J
van Delft
Jacob Jan
JJ
Briedé
D017638:Asbestos, Crocidolite / Q000494:pharmacology; D001980:Bronchi / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002474:Cell-Free System; D003470:Culture Media; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D016166:Free Radical Scavengers / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism*; D005898:Glass; D006801:Humans; D008027:Light; D046529:Microscopy, Electron, Transmission; D037742:Nanotubes, Carbon; D010316:Particle Size; D012542:Scattering, Radiation; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D053260:Soot / Q000633:toxicity
D003470:Culture Media; D016166:Free Radical Scavengers; D005609:Free Radicals; D037742:Nanotubes, Carbon; D053260:Soot; D017638:Asbestos, Crocidolite; D012710:Serum Albumin, Bovine