Diameter size and aspect ratio as critical determinants of uptake, stress response, global metabolomics and epigenetic alterations in multi-wall carbon nanotubes

The present study aimed to refurbish the fact of size and aspect ratio specific biological response of MWCNT in different cell systems. The bioactivities of three MWCNTs, differing in length/diameter [10–30 μm/20–30 nm (LW); 10–30 μm/8–15 nm (LN); 0.5–2.0 μm/8–15 nm (SN)], were then evaluated in terms of uptake and various toxicological end points (anti-proliferative, oxidative stress, inflammatory, DNA damage-repair and differential mode of marker gene expressions) in two different cell types - human bronchial epithelial (BEAS-2B) and human hepatoma (HepG2) cell lines. The surface enhanced Raman scattering (SERS) with dark-field microscopy attested the intracellular uptake of SN, but not the LW/LN, supports length dependency. The MWCNTs showed size specific stress responses (greatest in short sized one, SN) in both type of cells and aspect ratio dependent pro-fibrogenic potentiality, the LN with highest aspect ratio exhibited highest fibrogenicity in lung cells. Furthermore, alterations in global metabolomics and global DNA methylation status (DNMT3B dependent hypo-methylation in BEAS-2B cells and hyper-methylation in HepG2 cells) were also evident. Taken together, our findings provide evidence of variations in stress response, epigenetic modifications and global metabolomics alterations in association with differential size and aspect ratio of MWCNT which might be translated to the safe-by-design concept as well as risk assessment.