Human cell line-dependent WC-Co nanoparticle cytotoxicity and genotoxicity: a key role of ROS production

Although tungsten carbide-cobalt (WC-Co) nanoparticles (NPs) have been widely used because of their robustness, their risk to human health remains poorly studied, despite the International Agency for Research on Cancer (IARC) classifying them as "probably carcinogenic" for humans (Group 2A) in 2006. Our current study aimed at defining the cytotoxicity and genotoxicity of one set of commercially available 60-nm diameter WC-Co NPs on three human cell lines representative of potential target organs: A549 (lung), Hep3B (liver), and Caki-1 (kidney). The cytotoxicity of WC-Co NPs was determined by evaluating cell impedance (xCELLigence), cell survival/death, and cell cycle checkpoints. Flow cytometry was used to not only evaluate cell cycle checkpoints, but to also estimate reactive oxygen species (ROS) generation. In addition, γ-H2Ax foci detection (confocal microscopy), considered to be the most sensitive technique for studying DNA double-strand breaks, was utilized to evaluate genotoxicity. As a final part of this study, we assessed the cellular incorporation of WC-Co NPs, first byflow cytometry (side scatter), and then by confocal microscopy (light reflection) to ensure that the NPs had entered cells. Overall, our current findings demonstrate that WC-Co NPs induce cell mortality, DNA double-strand breaks, and cell cycle arrest in human renal (Caki-1) and liver (Hep3B) cell lines, but do not induce significant cytotoxic effects in A549 lung cells. Interestingly, although WC-Co NPs effectively entered the cells in all 3 lines tested, ROS were detected in Caki-1 and Hep3B, but not in A549. This may explain the great differences in the cytotoxic and genotoxic effects we observed between these lines.