Intracellular fate of carbon nanotubes inside murine macrophages: pH-dependent detachment of iron catalyst nanoparticles

Abstract

BackgroundCarbon nanotubes (CNT) are a family of materials featuring a large range of length, diameter, numbers of walls and, quite often metallic impurities coming from the catalyst used for their synthesis. They exhibit unique physical properties, which have already led to an extensive development of CNT for numerous applications. Because of this development and the resulting potential increase of human exposure, an important body of literature has been published with the aim to evaluate the health impact of CNT. However, despite evidences of uptake and long-term persistence of CNT within macrophages and the central role of those cells in the CNT-induced pulmonary inflammatory response, a limited amount of data is available so far on the CNT fate inside macrophages. Therefore, the overall aim of our study was to investigate the fate of pristine single walled CNT (SWCNT) after their internalization by macrophages.MethodsTo achieve our aim, we used a broad range of techniques that aimed at getting a comprehensive characterization of the SWCNT and their catalyst residues before and after exposure of murine macrophages: X-ray diffraction (XRD), High Resolution (HR) Transmission Electron Microscopy (TEM), High Angle Annular Dark Field-Scanning TEM (HAADF-STEM) coupled to Electron Energy Loss Spectroscopy (EELS), as well as micro-X-ray fluorescence mapping (μXRF), using synchrotron radiation.ResultsWe showed 1) the rapid detachment of part of the iron nanoparticles initially attached to SWCNT which appeared as free iron nanoparticles in the cytoplasm and nucleus of CNT-exposed murine macrophages, and 2) that blockade of intracellular lysosomal acidification prevented iron nanoparticles detachment from CNT bundles and protected cells from CNT downstream toxicity.ConclusionsThe present results, while obtained with pristine SWCNT, could likely be extended to other catalyst-containing nanomaterials and surely open new ways in the interpretation and understanding of CNT toxicity.

The role of p53 in lung macrophages following exposure to a panel of manufactured nanomaterials

“…Although this dose might be high with regards to the lung burden which might be reached after inhalation exposure (Basich et al 2014;gangwal et al 2011;landsiedel et al 2010), it is a relatively low dose in the context of an in vitro study required to understand the role of p53 following NM exposure. Furthermore, it has been shown that in vitro studies can be a good indicative of in vivo response dependant on the NM and the investigated specific outcome (cho et al 2013;gaiser et al 2012;Kermanizadeh et al 2013).…”

“…The MNM granularity and aggregation status were evaluated in material suspensions via photon correlation spectroscopy (PcS) and zeta potential measurements, respectively (Zetasizer 300HS, Malvern, UK). In order to calculate the purity of the MWcNT a TgA analysis was performed (Bussy et al 2013). The main physicochemical characteristics are summarised in Table 1.…”

Analytical approaches to support current understanding of exposure, uptake and distributions of engineered nanoparticles by aquatic and terrestrial organisms

“…This later study, like others discussed previously with respect to cellular targeting following assimilation, highlighted the potential importance of the lysosome in the internal fate of assimilated ENPs. In particular it was noted that blockage of intracellular lysosomal acidification prevented the Fe 3 C ENPs detachment from CNT bundles and protected cells from CNT downstream toxicity (Bussy et al 2013).…”

Early signs of multi-walled carbon nanotbues degradation in macrophages, via an intracellular pH-dependent biological mechanism; importance of length and functionalization

“…To achieve our aim, we synthesized, following a dedicated initial process, four MWCNT specifically devoted to our study and differing in length, and that were functionalized to concomitantly modify their surface chemistry and/or iron content (Additional file 1: Figure S1): S-CNT (short), SF-CNT (short and functionalized), L-CNT (long) and LF-CNT (long and functionalized), functionalized CNT (SF- and LF-CNT) having a different iron content from their non-functionalized counterpart (S- and L-CNT) (Table 1). The biodegradation of these CNT was addressed in RAW 264.7 murine macrophages in vitro, by the mean of Raman spectroscopy performed on CNT recovered in cells, after 3 different exposure time points; 6, 24 or 48 h. Moreover, as we recently demonstrated that pH could be an important player in the fate of CNT inside cells [19], we also investigated the role of pH in CNT biodegradation process. Our results demonstrate that MWCNT can be biodegraded inside macrophages, in a time-dependent manner, via an intracellular pH-dependent biological mechanism.…”