Abstract
To date, there has not been an agreement on the best methods for the characterisation of multi-walled carbon nanotube (MWCNT) toxicity. The length of MWCNTs has been identified as a factor in in vitro and in vivo studies, in addition to their purity and biocompatible coating. Another unresolved issue relates to the variable toxicity of MWCNTs on different cell types. The present study addressed the effects of MWCNTs' length on mammalian immune and epithelial cancer cells RAW264.7 and MCF-7, respectively. Our data confirm that MWCNTs induce cytotoxicity in a length- and cell type-dependent manner. Whereas, longer (3 to 14 μm) MWCNTs exert high toxicity, especially to RAW264.7 cells, shorter (1.5 μm) MWCNTs are significantly less cytotoxic. These findings confirm that the degree of biocompatibility of MWCNTs is closely related to their length and that immune cells appear to be more susceptible to damage by MWCNTs. Our study also indicates that MWCNT nanotoxicity should be analysed for various components of cellular response, and cytotoxicity data should be validated by the use of more than one assay system. Results from chromogenic-based assays should be confirmed by trypan blue exclusion.
Highlights
Since the landmark paper on carbon nanotubes (CNTs) by Iijima in 1991 [1], extensive research has confirmed their unique physical, chemical, and electrical properties generating considerable interest in their potential biomedical applications, e.g. drug delivery [2], tumour hyperthermic ablation [3], and tissue engineering [4]
We investigated the lengthdependent effects of multi-walled carbon nanotubes (MWCNTs) in vitro on two types of cell lines: macrophage-like RAW264.7 and epithelial cancer cell line MCF-7, using highly purified and stable aqueous dispersed MWCNTs that were characterised by scanning electron microscopy (SEM)
By manually counting 50 of each of the two types of MWCNTs, S-MWCNTs were of 0.4 to 1.4 μm in length as were claimed by the manufacturer (
Summary
Since the landmark paper on carbon nanotubes (CNTs) by Iijima in 1991 [1], extensive research has confirmed their unique physical, chemical, and electrical properties generating considerable interest in their potential biomedical applications, e.g. drug delivery [2], tumour hyperthermic ablation [3], and tissue engineering [4]. As with any potential therapeutic or diagnostic agents, the safety profile (biocompatibility and potential adverse effects) of CNTs is crucial for the translation into novel clinical therapies based on these nanomaterials. Several in vitro and in vivo studies have demonstrated that short, highly purified CNTs with biocompatible polymer coating and functionalisation are essential for reduction in cytotoxicity [5,6,7,8]. For various reasons, there remain conflicting data concerning CNT toxicity: lack of characterisation of the CNTs and differences in the experimental design, materials, cell viability systems, and nanotube concentrations. Immune cells have been identified as effective vehicles for cancer therapy and in the treatment of infectious diseases when stimulated and targeted by functionalized CNTs [9,10,11]. Evaluation of CNT toxicity to immune cells is an important but overlooked component of CNT nanotoxicology
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