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Nanoparticle research propelled by the comet assay

Professor Elke Dopp is the Chief Scientist and Head of the Division of in vitro & Molecular Toxicology at the Institute of Hygiene and Environmental Medicine in Germany.  The main focus of her research is the genotoxicity of environmental pollutants in water, airborne particles and nanoparticles. She has chosen Perceptive Instrument’s Comet Assay IV as the scoring system to use in her comet assay studies for its speed, reproducibility and ease of use.

…human cells were exposed to titanium dioxide nanoparticles, followed by comet assay analysis…

Here, an investigation into the genotoxicity of titanium dioxide nanoparticles (TDNPs) to humans is described.  Occupational exposure to TDNPs can occur during manufacturing or use of these particles as pigments for paints, varnishes, enamels, lacquers and paper coatings to impart whiteness, opacity and brightness (Hext, 2005).  In this study, human lung fibroblasts (cells that synthesises extracellular matrix and collagen) and lung epithelial cells were exposed to TDNPs or iron containing nanoparticles (ICNPs) to analyse their cyto- and geno-toxic potential.  The study also investigated their ability to generate reactive oxygen species and to form DNA-adducts.   The comet assay illustrated that TDNPs did not induce DNA-breakage in the human cells.  In contrast, exposure of these cells to ICNPs induced significant DNA-damage.  Image analysis was performed using Comet Assay IV software; values of the olive tail moment (OTM) were automatically calculated by the software.  TDNPs were reported to not cause any cytotoxicity in the lung epithelial cells, but a significant loss of cell viability in lung fibroblasts was demonstrated, especially at longer exposure times.  Previously, Professor Dopp’s group had found that the native TDNPs were non-cyto- and geno-toxic in Chinese hamster lung fibroblasts (Bhattacharya, 2008).  

Comet Assay IV was the scoring system of choice for its speed, reproducibility and ease of use…

In addition to the comet assay, the micronucleus assay was used to detect both chromosome breakage and aneuploidy.  However, micronucleus formation was not observed in during this investigation.  This study demonstrates different modes of action for TDNPs and ICNPs: TDNPs were able to generate elevated amounts of free radicals, which induced indirect genotoxicity mainly by DNA-adduct formation, whereas ICNPs were clastogenic (induction of DNA-breakage) and required reducing conditions for radical formation.

This case study is based on:

Titanium dioxide nanoparticles induce oxidative stress and DNA-adduct formation but not DNA-breakage in human lung cells.
Bhattacharya K, Davoren M, Boertz J, Schins RP, Hoffmann E, Dopp E. Part Fibre Toxicol. 2009 Jun 21;6:17.
Institut für Hygiene und Arbeitsmedizin, Universität Duisburg-Essen, Germany.

Further references:
Hext PM, Tomenson JA, Thompson P. Titanium dioxide: inhalation toxicology and epidemiology. Ann Occup Hyg. 2005;49:461–472
Bhattacharya K, Cramer H, Albrecht C, Schins R, Rahman Q, Zimmermann U, Dopp E. Vanadium pentoxide-coated ultrafine titanium dioxide particles induce cellular damage and micronucleus formation in V79 cells. J Toxicol Environ Health A. 2008;71:976–980