The pulmonary toxicity of carboxylated or aminated multi-walled carbon nanotubes in mice is determined by the prior purification method

Alexia J Taylor-Just,James C Bonner,Adriana Vulpoi,Otto Creutzenberg,Ho Young Lee,Salik Hussain,Flaviu Turcu,Dorothy J You,Monica Potara,Christina Ziemann,Milica Todea,Sybille Van Den Brule,Dominique Lison,Katherine S Duke,Mark D Ihrie,Vamsi K Kodali

doi:10.1186/s12989-020-00390-y

Abstract

BackgroundInhalation of multi-walled carbon nanotubes (MWCNTs) poses a potential risk to human health. In order to safeguard workers and consumers, the toxic properties of MWCNTs need to be identified. Functionalization has been shown to either decrease or increase MWCNT-related pulmonary injury, depending on the type of modification. We, therefore, investigated both acute and chronic pulmonary toxicity of a library of MWCNTs derived from a common pristine parent compound (NC7000).MethodsMWCNTs were thermally or chemically purified and subsequently surface functionalized by carboxylation or amination. To evaluate pulmonary toxicity, male C57BL6 mice were dosed via oropharyngeal aspiration with either 1.6 or 4 mg/kg of each MWCNT type. Mitsui-7 MWCNT was used as a positive control. Necropsy was performed at days 3 and 60 post-exposure to collect bronchoalveolar lavage fluid (BALF) and lungs.ResultsAt day 3 all MWCNTs increased the number of neutrophils in BALF. Chemical purification had a greater effect on pro-inflammatory cytokines (IL-1β, IL-6, CXCL1) in BALF, while thermal purification had a greater effect on pro-fibrotic cytokines (CCL2, OPN, TGF-β1). At day 60, thermally purified, carboxylated MWCNTs had the strongest effect on lymphocyte numbers in BALF. Thermally purified MWCNTs caused the greatest increase in LDH and total protein in BALF. Furthermore, the thermally purified and carboxyl- or amine-functionalized MWCNTs caused the greatest number of granulomatous lesions in the lungs. The physicochemical characteristics mainly associated with increased toxicity of the thermally purified derivatives were decreased surface defects and decreased amorphous content as indicated by Raman spectroscopy.ConclusionsThese data demonstrate that the purification method is an important determinant of lung toxicity induced by carboxyl- and amine-functionalized MWCNTs.

Highlights

With advancements in nanotechnology, the application of carbon nanotubes (CNTs) in commercial products has been increasing since their discovery in 1991 [1]
Characterization of the Multiwalled carbon nanotube (MWCNT) library The custom synthesized library of MWCNTs shown in Fig. 1a was thoroughly characterized as described in the Methods and Materials section
The key finding of this study was that thermal purification of MWCNTs followed by carboxyl or amine functionalization caused a greater increase in pro-fibrotic cytokines in bronchoalveolar lavage fluid (BALF) (OPN, CC chemokine ligand 2 (CCL2)) at day 3 post-exposure and more severe chronic lung injury (LDH and total protein in BALF) with increased number of granulomatous lesions in the lungs of mice at day 60 post-exposure

Summary

Introduction

The application of carbon nanotubes (CNTs) in commercial products has been increasing since their discovery in 1991 [1]. Both single-walled (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) have emerged as important classes of engineered nanomaterials. Their outstanding stability, tensile strength, electric conductivity, and thermal resistance [2, 3] have prompted their use in various industrial applications, including composite materials, nanoelectronics, fieldeffect emitters, and hydrogen storage [4]. Functionalization has been shown to either decrease or increase MWCNT-related pulmonary injury, depending on the type of modification. We investigated both acute and chronic pulmonary toxicity of a library of MWCNTs derived from a common pristine parent compound (NC7000)

Methods

Results

Discussion

Conclusion