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.
Because of the deleterious effects of phthalates, regulations have been taken to decrease their use, and the needs for alternatives are increasing. Due to the concerns about the endocrine-disrupting properties of phthalates, it was deemed necessary to particularly investigate these effects for potential substitutes. In this study, we compared the in vitro endocrine activity of several already used potential alternative plasticizers (DEHT, DINCH, and TOTM) or new substitutes (POLYSORB® isosorbide and POLYSORB® ID 46) to one of 2 phthalates, DEHP and DINP. Effects of these chemicals on 3 common mechanisms of endocrine disruption, i.e., interaction with estrogen receptors (ER), androgen receptors (AR), or steroidogenesis, were studied using extensively used in vitro methods. In the E-Screen assay, only DEHP moderately induced MCF-7 cell proliferation; none of the other tested substances were estrogenic or antiestrogenic. No androgenic or antiandrogenic activity in MDA-kb2 cells was shown for any of the tested phthalates or alternatives. On the other hand, both DEHP and DINP, as well as DEHT, DINCH, and TOTM, disrupted steroidogenesis in the H295R assay, mainly by inducing an increase in estradiol synthesis; no such effect was observed for POLYSORB® isosorbide and POLYSORB® ID 46.
With the increasing human exposure to nanoparticles (NP), the evaluation of their genotoxic potential is of significant importance. However, relevance for NP of the routinely used in vitro genotoxicity assays is often questioned, and a nanoparticulate reference positive control would therefore constitute an important step to a better testing of NP, ensuring that test systems are really appropriate. In this study, we investigated the possibility of using tungsten carbide-cobalt (WC-Co) NP as reference positive control in in vitro genotoxicity assays, including 2 regulatory assays, the mouse lymphoma assay and the micronucleus assay, and in the Comet assay, recommended for the toxicological evaluation of nanomedicines by the French Agency of Human Health Products (Afssaps). Through these assays, we were able to study different genetic endpoints in 2 cell types commonly used in regulatory genotoxicity assays: the L5178Y mouse lymphoma cell line and primary cultures of human lymphocytes. Our results showed that the use of WC-Co NP as positive control in in vitro genotoxicity assays was conceivable, but that different parameters have to be considered, such as cell type and treatment schedule. L5178Y mouse lymphoma cells did not provide satisfactory results in the 3 performed tests. However, human lymphocytes were more sensitive to genotoxic effects induced by WC-Co NP, particularly after a 24-h treatment in the in vitro micronucleus assay and after a 4-h treatment in the in vitro Comet assay. Under such conditions, WC-Co could be used as a nanoparticulate reference positive control in these assays.
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