International audienceSynthetic amorphous silica nanoparticles (SAS) are among the most widely produced and used nanomaterials, but little is known about their carcinogenic potential. This study aims to evaluate the ability of four different SAS, two precipitated, NM-200 and NM-201, and two pyrogenic, NM-202 and NM-203, to induce the transformation process. For this, we used the recently developed in vitro Bhas 42 cell transformation assay (CTA). The genome of the transgenic Bhas 42 cells contains several copies of the v-Ha-ras gene, making them particularly sensitive to tumor-promoter agents. The Bhas 42 CTA, which includes an initiation assay and a promotion assay, was validated in our laboratory using known soluble carcinogenic substances. Its suitability for particle-type substances was verified by using quartz Min-U-Sil 5 (Min-U-Sil) and diatomaceous earth (DE) microparticles. As expected given their known transforming properties, Min-U-Sil responded positively in the Bhas 42 CTA and DE responded negatively. Transformation assays were performed with SAS at concentrations ranging from 2 µg/cm 2 to 80 µg/cm 2. Results showed that all SAS have the capacity to induce transformed foci, interestingly only in the promotion assay, suggesting a mode of action similar to tumor-promoter substances. NM-203 exhibited transforming activity at a lower concentration than the other SAS. In conclusion, this study showed for the first time the transforming potential of different SAS, which act as tumor-promoter substances in the Bhas 42 model of cell transformation.Les nanoparticules de silice amorphes de synthèse (SAS) sont les nanomatériaux les plus produits et les plus utilisés dans le monde, mais leur potentiel cancérogène est peu étudié. Cette étude avait pour but d’évaluer la capacité de quatre différentes SAS, deux sous forme précipitée, NM-200 et NM-201 et deux sous forme pyrogénée, NM-202 et NM-203, d’induire des processus de cancérogénèse. Pour cela, nous avons utilisé l’essai de transformation sur les cellules Bhas 42 (Bhas 42 CTA) qui a été récemment développé. Le génome des cellules Bhas 42 transgéniques contient plusieurs copies du gène v-Ha-ras, ce qui leur confère les caractéristiques de cellules « initiées » et les rend particulièrement sensibles aux agents promoteurs de tumeur. Le Bhas 42 CTA, qui inclut un essai d’initiation et un essai de promotion, a été validé dans notre laboratoire en utilisant des agents cancérogènes solubles connus. Son adaptabilité pour des substances de type particule a été vérifié en utilisant des microparticules de quartz Min-U-Sil 5 (Min-U-Sil) et de terre de diatomée (DE). Comme attendu d’après leur propriété transformante connue, le Min-U-Sil a répondu positivement et la DE négativement au Bhas 42 CTA. Les essais de transformation ont été réalisés à des concentrations de SAS s’étalant de 2 µg/cm2 à 80 µg/cm2. Les résultats montrent que toutes les SAS ont la capacité d’induire des foyers de transformation et de manière intéressante, uniquement dans l’essai de promotion, suggérant...

The increasing use of nanomaterials in numerous domains has led to growing concern about their potential toxicological properties, and the potential risk to human health posed by silica nanoparticles remains under debate. Recent studies proposed that these particles could alter gene expression through the modulation of epigenetic marks, and the possible relationship between particle exposure and these mechanisms could represent a critical factor in carcinogenicity. In this study, using the Bhas 42 cell model, we compare the effects of exposure to two transforming particles, a pyrogenic amorphous silica nanoparticle NM-203 to those of the crystalline silica particle Min-U-Sil 5. Short-term treatment by Min-U-Sil 5 decreased global DNA methylation and increased the expression of the two de novo DNMTs, DNMT3a and DNMT3b. NM-203 treatment affected neither the expression of these enzymes nor DNA methylation. Moreover, modified global histone H4 acetylation status and HDAC protein levels were observed only in the Min-U-Sil 5-treated cells. Finally, both types of particle treatment induced strong c-Myc expression in the early stage of cell transformation and this correlated with enrichment in RNA polymerase II as well as histone active marks on its promoter. Lastly, almost all parameters that were modulated in the early stage were restored in transformed cells suggesting their involvement mainly in the first steps of cell transformation.

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Highlights • Synthetic amorphous silica nanomaterials induce transformation of Bhas 42 cells • Early modulated signaling pathways are linked to cell adhesion and proliferation • Twelve genes were selected based on their potential role in cell transformation • These genes may serve as early markers of Bhas 42 cell transformation induced by SAS