The Effects of Varying Degree of MWCNT Carboxylation on Bioactivity in Various In Vivo and In Vitro Exposure Models

Abstract

Functionalization has been shown to alter toxicity of multi-walled carbon nanotube (MWCNT) in several studies. This study varied the degree of functionalization (viz., amount of MWCNT surface carboxylation) to define the relationship between the extent of carboxylation and effects in a variety of in vitro cell models and short-term ex vivo/in vivo particle exposures. Studies with vitamin D3 plus phorbol ester transformed THP-1 macrophages demonstrated that functionalization, regardless of amount, corresponded with profoundly decreased NLRP3 inflammasome activation. However, all MWCNT variants were slightly toxic in this model. Alternatively, studies with A549 epithelial cells showed some varied effects. For example, IL-33 and TNF-α release were related to varying amounts of functionalization. For in vivo particle exposures, autophagy of alveolar macrophages, measured using green fluorescent protein (GFP)- fused-LC3 transgenic mice, increased for all MWCNT tested three days after exposure, but, by Day 7, autophagy was clearly dependent on the amount of carboxylation. The instilled source MWCNT continued to produce cellular injury in alveolar macrophages over seven days. In contrast, the more functionalized MWCNT initially showed similar effects, but reduced over time. Dark-field imaging showed the more functionalized MWCNTs were distributed more uniformly throughout the lung and not isolated to macrophages. Taken together, the results indicated that in vitro and in vivo bioactivity of MWCNT decreased with increased carboxylation. Functionalization by carboxylation eliminated the bioactive potential of the MWCNT in the exposure models tested. The observation that maximally functionalized MWCNT distribute more freely throughout the lung with the absence of cellular damage, and extended deposition, may establish a practical use for these particles as a safer alternative for unmodified MWCNT.

The Importance of Evaluating the Lot-to-Lot Batch Consistency of Commercial Multi-Walled Carbon Nanotube Products

“…Herein, the BET-determined SSAs of the 2015-pMWNT and 2015-cMWNT powders were 91 and 145 m 2 /g, respectively, corresponding to a SSA-increase of ~60%; and, the BET-determined SSAs of the 2018-pMWNT and 2018-cMWNT powders were 191 and 286 m 2 /g, respectively, corresponding to a SSA-increase of ~50%. While the exact reaction conditions of the oxidative treatment performed by the manufacturer are not known, the increases in SSAs measured by the BET measurement for the 2015- and 2018-MWNT product pairs are consistent with the 11–62% increases in BET-SSAs measured by others who evaluated CVD-synthesized pMWNTs and cMWNTs [ 26 , 42 , 70 , 82 , 88 ]. However, it is noteworthy that both of the 2018 products had significantly higher BET-SSAs than the 2015 products.…”

Effect of Carbon Nanotube-Metal Hybrid Particle Exposure to Freshwater Algae Chlamydomonas reinhardtii

“…The resulting solids were thoroughly washed with Milli-Q water to a neutral pH and then dried in a vacuum oven at 50 °C for 24 h. The degree of carboxylation was quantified based on the C:O molar ratio which was found to be 11:1 and in line with EDX data which showed 14.3% by weight. This C:O ratio was in line with our previous publications 62 , 63 .…”

Lung deposition patterns of MWCNT vary with degree of carboxylation

“…The synthesis of the functionalized MWCNT was described in greater detail in a previously published manuscript (Wu et al, 2017). Additional information on characterization and relative bioactivity can be found in a recent publication (Hamilton Jr. et al, 2018). In addition, an abbreviated characterization table (Table 1) is shown here for convenience, as a much more comprehensive characterization of f-MWCNT is available in reference stated above (Hamilton Jr. et al, 2018).…”