Genotoxicity of multi-walled carbon nanotubes at occupationally relevant doses

Abstract

Carbon nanotubes are commercially-important products of nanotechnology; however, their low density and small size makes carbon nanotube respiratory exposures likely during their production or processing. We have previously shown mitotic spindle aberrations in cultured primary and immortalized human airway epithelial cells exposed to single-walled carbon nanotubes (SWCNT). In this study, we examined whether multi-walled carbon nanotubes (MWCNT) cause mitotic spindle damage in cultured cells at doses equivalent to 34 years of exposure at the NIOSH Recommended Exposure Limit (REL). MWCNT induced a dose responsive increase in disrupted centrosomes, abnormal mitotic spindles and aneuploid chromosome number 24 hours after exposure to 0.024, 0.24, 2.4 and 24 μg/cm2 MWCNT. Monopolar mitotic spindles comprised 95% of disrupted mitoses. Three-dimensional reconstructions of 0.1 μm optical sections showed carbon nanotubes integrated with microtubules, DNA and within the centrosome structure. Cell cycle analysis demonstrated a greater number of cells in S-phase and fewer cells in the G2 phase in MWCNT-treated compared to diluent control, indicating a G1/S block in the cell cycle. The monopolar phenotype of the disrupted mitotic spindles and the G1/S block in the cell cycle is in sharp contrast to the multi-polar spindle and G2 block in the cell cycle previously observed following exposure to SWCNT. One month following exposure to MWCNT there was a dramatic increase in both size and number of colonies compared to diluent control cultures, indicating a potential to pass the genetic damage to daughter cells. Our results demonstrate significant disruption of the mitotic spindle by MWCNT at occupationally relevant exposure levels.

In vivo activation of a T helper 2-driven innate immune response in lung fibrosis induced by multi-walled carbon nanotubes

“…2B, middle panel, indicated by #). This finding is consistent with previous reports that exposure to MWCNT caused a G1/S block in cultured cells (Han et al 2012; Siegrist et al 2014). …”

Repeated exposure to carbon nanotube-based aerosols does not affect the functional properties of a 3D human epithelial airway model

“…The deposited doses for the current study were selected to be in the range of 0.24-2.4 mg/cm 2 for occupationally relevant doses recently reported in studies in accordance to the permissible exposure limit of 1 mg/m 3 suggested by NIOSH (NIOSH, 2013;Porter et al, 2010;Siegrist et al, 2014). Sargent et al (2014) have performed an inhalation study with mice and exposed them with 5 mg/m 3 MWCNTs for 5 h per day, 5 d a week for 15 d and calculated a total deposited material concentration in the lungs to 0.06 mg/cm 2 mimicking a two week human occupational exposure scenario.…”

Multi-walled carbon nanotube-induced gene expression in vitro: Concordance with in vivo studies

“…A recent study concerning the potential toxicity of MWCNT showed that, although pathway-level cellular functions were similar between in vivo and in vitro experiments, microarray analysis determined different gene expression profiles between in vivo and in vitro models (Sos Poulsen et al 2013). MWCNT induce numerous deleterious effects in mouse lungs after both aspiration and inhalation exposures (Mercer et al 2011; Mercer et al 2013; Porter et al 2013; Porter et al 2010; Sargent et al 2014; Siegrist et al 2014), and the ability to reflect these effects in vitro with an accurate transcriptomic profile remains difficult. Although in vitro global gene expression and microarray analysis may be useful for providing a generic overview of responses, cellular signaling from chronic exposure in vivo and acute signaling in vitro may produce different expression results (Klaper et al 2014).…”