Physical properties of single-wall carbon nanotubes in cell culture and their dispersal due to alveolar epithelial cell response

The Impact of Background-Level Carboxylated Single-Walled Carbon Nanotubes (SWCNTs−COOH) on Induced Toxicity in Caenorhabditis elegans and Human Cells

Single-walled carbon nanotubes (SWCNTs) are widely utilized for industrial, biomedical, and environmental purposes. The toxicity of Carboxylated SWCNTs (SWCNTs−COOH) in in vivo models, particularly Caenorhabditis elegans (C. elegans), and in vitro human cells is still unclear. In this study, C. elegans was used to study the effects of SWCNTs−COOH on lethality, lifespan, growth, reproduction, locomotion, reactive oxygen species (ROS) generation, and the antioxidant system. Our data show that exposure to ≥1 μg·L⁻¹ SWCNTs−COOH could induce toxicity in nematodes that affects lifespan, growth, reproduction, and locomotion behavior. Moreover, the exposure of nematodes to SWCNTs−COOH induced ROS generation and the alteration of antioxidant gene expression. SWCNTs−COOH induced nanotoxic effects at low dose of 0.100 or 1.00 μg·L⁻¹, particularly for the expression of antioxidants (SOD-3, CTL-2 and CYP-35A2). Similar nanotoxic effects were found in human cells. A low dose of SWCNTs−COOH induced ROS generation and increased the expression of catalase, MnSOD, CuZnSOD, and SOD-2 mRNA but decreased the expression of GPX-2 and GPX-3 mRNA in human monocytes. These findings reveal that background-level SWCNTs−COOH exerts obvious adverse effects, and C. elegans is a sensitive in vivo model that can be used for the biological evaluation of the toxicity of nanomaterials.

Pulmonary toxicity, cytotoxicity, and genotoxicity of submicron-diameter carbon fibers with different diameters and lengths

Submicron-diameter carbon fibers (SCFs) are a type of fine-diameter fibrous carbon material that can be used in various applications. To accelerate their practical application, a hazard assessment of SCFs must be undertaken. This study demonstrated the pulmonary toxicity, cytotoxicity, and genotoxicity of three types of SCFs with different diameters and lengths. The average diameter and length of SCFs were 259.2 nm and 11.7 μm in SCF1 suspensions, 248.5 nm and 6.7 μm in SCF2 suspensions, and 183.0 nm and 13.7 μm in SCF3 suspensions, respectively. The results of pulmonary inflammation and recovery following intratracheal instillation with SCFs at doses of 0.25, 0.5, or 1.0 mg/kg showed that the pulmonary toxicity of SCFs was SCF3 > SCF1 > SCF2. These results suggest that SCF diameter and length are most likely important contributing factors associated with lung SCF clearance, pulmonary inflammation, and recovery. Furthermore, SCFs are less pulmonary toxic than bent multi-walled carbon nanotubes. Cell viability, pro-inflammatory cytokine and intracellular reactive oxygen species productions, morphological changes, gene expression profiling in NR8383 rat alveolar macrophage cells showed that the cytotoxic potency of SCFs is: SCF3 > SCF1 > SCF2. These results showed that SCFs with small diameters had high cytotoxicity, and SCFs with short lengths had low cytotoxicity. We conclude that pulmonary toxicity and cytotoxicity are associated with the diameter and length distributions of SCFs. In addition, a standard battery for genotoxicity testing, namely the Ames test, an in vitro chromosomal aberration test, and a mammalian erythrocyte micronucleus test, demonstrated that the three types of SCFs did not induce genotoxicity. Our findings provide new evidence for evaluating the potential toxicity of not only SCFs used in this study but also various SCFs which differ depending on the manufacturing processes or physicochemical properties.

Physical and chemical properties of carbon nanotubes in view of mechanistic neuroscience investigations. Some outlook from condensed matter, materials science and physical chemistry

The open border between non-living and living matter, suggested by increasingly emerging fields of nanoscience interfaced to biological systems, requires a detailed knowledge of nanomaterials properties. An account of the wide spectrum of phenomena, belonging to physical chemistry of interfaces, materials science, solid state physics at the nanoscale and bioelectrochemistry, thus is acquainted for a comprehensive application of carbon nanotubes interphased with neuron cells. This review points out a number of conceptual tools to further address the ongoing advances in coupling neuronal networks with (carbon) nanotube meshworks, and to deepen the basic issues that govern a biological cell or tissue interacting with a nanomaterial. Emphasis is given here to the properties and roles of carbon nanotube systems at relevant spatiotemporal scales of individual molecules, junctions and molecular layers, as well as to the point of view of a condensed matter or materials scientist. Carbon nanotube interactions with blood-brain barrier, drug delivery, biocompatibility and functionalization issues are also regarded.

Comparative assessments of the biodistribution and toxicity of oxidized single-walled carbon nanotubes dispersed with two different reagents after intravenous injection

The present study compared the effects of two commonly-used dispersants, bovine serum albumin (BSA) and polyethylene glycol (PEG), on the biodistribution and toxicity of oxidized super-growth single-wall carbon nanotubes (oxSG) injected intravenously into mice over 3 months. About 1-2% of the injected dose (ID) of oxSG dispersed in BSA (oxSG-BSA) was present in the lungs at all time points. By contrast, about 15% of the ID of oxSG dispersed in PEG (oxSG-PEG) was present in the lungs at 1 day (D1), with accumulation decreasing to about 5% of the ID at 90 days (D90). About 70-80% of the IDs of both oxSG-BSA and oxSG-PEG were present in the liver at D1; by D90, about 15% of the IDs were cleared slowly (oxSG-BSA) or rapidly (oxSG-PEG). In the spleen, about 7% of the IDs of both oxSG-BSA and oxSG-PEG were present at all time points. The toxicities of oxSG-BSA and oxSG-PEG were comparable: no obvious signs of inflammation were observed on histological assessments of the lungs, liver, and spleen and on measurements of cytokine activity in blood plasma and tissue lysates. Concentrations of aspartate transaminase slightly increased at some time points in blood plasma, suggesting that oxSG-BSA and oxSG-PEG were slightly hepatoxic. Taken together, these results indicated that the dispersants had limited effect on the biodistribution and toxicity of oxSGs.

Clearance of single-wall carbon nanotubes from the mouse lung: a quantitative evaluation

Based on the characteristics of carbon nanotubes (CNTs) that absorb light in the near-infrared region, we have developed a method to quantify the biodistribution of CNTs in mouse tissues such as the liver, lungs and spleen. By using this method, the kinetic biodistribution of single-walled CNTs (SWNTs) after intravenous injection into mice for 60 days has been successfully investigated. The results show that the biodistribution of CNTs was diameter-dependent by comparing two different diameters of SWNTs. The SWNTs with larger diameters (1-5 nm) accumulated more in the liver or spleen but less in the lungs than those with smaller diameters (0.7-0.9 nm). The quantities of both SWNTs in the liver and lungs decreased with time and showed no significant change in the spleen, which is also confirmed by histological analysis. In particular, the results have demonstrated that both SWNTs are cleared from the lungs almost completely within 60 days, suggesting that the pulmonary toxicity of SWNTs would be low when low amounts of CNTs (<70 μg g^-1 of tissue) enter inside the lungs. In addition, no obvious inflammatory responses are found from the measurement of the cytokines TGF-β1, IL-6, INF-γ, and TNF-α in the plasma and organs after the injection of both SWNTs into mice.

A Simple Method for Removal of Carbon Nanotubes from Wastewater Using Hypochlorite

Carbon nanotubes (CNTs) have been applied in a wide range of fields, such as materials, electronics, energy storages, and biomedicine. With the rapid increase in CNTs industrialization, more and more CNT-containing wastewater is being produced. Since concerns about the toxic effects of CNTs on human health persist, CNT-containing wastewater should not be released into the environment without purification, but no effective methods have been reported. In the present study, we report a simple method to eliminate CNTs from industrial or laboratorial wastewater using sodium hypochlorite. Direct treatment of aqueous dispersions with sodium hypochlorite solution completely degraded CNTs into carbon oxides or carbonates ions. Since hypochlorite is environmentally friendly and frequently used as a disinfectant or bleaching agent in domestic cleaning, this method is practical for purification of CNT-contaminated industrial wastewater.

Length effects of single-walled carbon nanotubes on pulmonary toxicity after intratracheal instillation in rats

We aimed to evaluate the effects of the length of single-walled carbon nanotubes (SWCNTs) on pulmonary toxicity in rats. Each rat received a single intratracheal instillation of short (S-) (average length of 0.40 μm) or long (L-) (average length of 2.77 μm) SWCNTs at a dose of 1 mg/kg and was observed for the next 6 months. Neither S- nor L-SWCNTs affected clinical signs, body weight, or autopsy findings. An increase in lung weight was observed after instillation of S- or L-SWCNTs; however, lung weights were slightly higher in the rats that were administered the S-SWCNTs. Distinct differences in bronchoalveolar lavage fluid (BALF) composition were observed between the S- and L-SWCNT-treated rats as early as 7 days after the intratracheal instillations of the SWCNTs. The S-SWCNTs caused persistent lung injury and inflammation during the 6-month observational period. However, the L-SWCNTs induced minimal lung injury and inflammation. Although the S- and L-SWCNTs changed BALF parameters and histopathological features of the lung, the magnitudes of the changes observed after the S-SWCNT treatment were greater than the respective changes observed after the L-SWCNT treatment. These findings indicate that the severity of the pulmonary toxicity caused after intratracheal instillation of SWCNT depends on the length of the SWCNTs. It appears that shorter SWCNTs induce greater pulmonary toxicity than longer SWCNTs do.

Effects of Various Carbon Nanotube Suspensions on A549, THP-1, and Peritoneal Macrophage Cells

The effects of iron content, fiber length, and stability of carbon nanotube (CNT) suspension on cells were examined. Five kinds of single-wall carbon nanotube (SWCNT) suspensions were prepared: with catalytic iron, without iron, long SWCNTs (stable), short SWCNTs (stable), and short SWCNT (unstable). These suspensions were applied to A549, THP-1, and mouse peritoneal macrophage cells. After a 24-h exposure, the mitochondrial activity, cell membrane damage, intracellular oxidative stress, and expression of cytokine genes were determined. Among these properties of SWCNTs, stability of CNT suspension had the most influence on the cells, whereas the effects of iron content and fiber length were small. The unstable SWCNT suspension caused a substantial increase in intracellular ROS levels. Additionally, the cellular effects of stable multi-wall carbon nanotubes (MWCNTs) were examined. The MWCNT suspension did not show any cellular effects. Overall, influences of CNT suspension on mitochondrial activity and cell membrane damage were small. These results suggest that the physical properties of CNT suspension are important factors for their cellular effects. Thus, CNT suspensions prepared with the same material but having different physical properties would differ in the cellular effects they exert, including cytotoxicity. Therefore, physical characterization of CNT suspensions is essential to the evaluation of CNT toxicity. In particular, stability of CNT suspension notably influenced the intracellular ROS level.

Size effects of single-walled carbon nanotubes on in vivo and in vitro pulmonary toxicity

To elucidate the effect of size on the pulmonary toxicity of single-wall carbon nanotubes (SWCNTs), we prepared two types of dispersed SWCNTs, namely relatively thin bundles with short linear shapes (CNT-1) and thick bundles with long linear shapes (CNT-2), and conducted rat intratracheal instillation tests and in vitro cell-based assays using NR8383 rat alveolar macrophages. Total protein levels, MIP-1α expression, cell counts in BALF, and histopathological examinations revealed that CNT-1 caused pulmonary inflammation and slower recovery and that CNT-2 elicited acute lung inflammation shortly after their instillation. Comprehensive gene expression analysis confirmed that CNT-1-induced genes were strongly associated with inflammatory responses, cell proliferation, and immune system processes at 7 or 30 d post-instillation. Numerous genes were significantly upregulated or downregulated by CNT-2 at 1 d post-instillation. In vitro assays demonstrated that CNT-1 and CNT-2 SWCNTs were phagocytized by NR8383 cells. CNT-2 treatment induced cell growth inhibition, reactive oxygen species production, MIP-1α expression, and several genes involved in response to stimulus, whereas CNT-1 treatment did not exert a significant impact in these regards. These results suggest that SWCNTs formed as relatively thin bundles with short linear shapes elicited delayed pulmonary inflammation with slower recovery. In contrast, SWCNTs with a relatively thick bundle and long linear shapes sensitively induced cellular responses in alveolar macrophages and elicited acute lung inflammation shortly after inhalation. We conclude that the pulmonary toxicity of SWCNTs is closely associated with the size of the bundles. These physical parameters are useful for risk assessment and management of SWCNTs.

Intratracheal instillation of single-wall carbon nanotubes in the rat lung induces time-dependent changes in gene expression

The use of carbon nanotubes in the industry has grown; however, little is known about their toxicological mechanism of action. Single-wall carbon nanotube (SWCNT) suspensions were administered by single intratracheal instillation in rats. Persistence of alveolar macrophage-containing granuloma was observed around the sites of SWCNT aggregation at 90 days post-instillation in 0.2-mg- or 0.4-mg-injected doses per rat. Meanwhile, gene expression profiling revealed that a large number of genes involved in the inflammatory response were markedly upregulated until 90 days or 180 days post-instillation. Subsequently, gene expression patterns were dramatically altered at 365 days post-instillation, and the number of upregulated genes involved in the inflammatory response was reduced. These results suggested that alveolar macrophage-containing granuloma reflected a characteristic of the histopathological transition period from the acute-phase to the subchronic-phase of inflammation, as well as pulmonary acute phase response persistence up to 90 or 180 days after intratracheal instillation in this experimental setting. The expression levels of the genes Ctsk, Gcgr, Gpnmb, Lilrb4, Marco, Mreg, Mt3, Padi1, Slc26a4, Spp1, Tnfsf4 and Trem2 were persistently upregulated in a dose-dependent manner until 365 days post-instillation. In addition, the expression levels of Atp6v0d2, Lpo, Mmp7, Mmp12 and Rnase9 were significantly upregulated until 754 days post-instillation. We propose that these persistently upregulated genes in the chronic-phase response following the acute-phase response act as potential biomarkers in lung tissue after SWCNT instillation. This study provides further insight into the time-dependent changes in genomic expression associated with the pulmonary toxicity of SWCNTs.

Intracellular signal modulation by nanomaterials

A thorough understanding of the interactions of nanomaterials with biological systems and the resulting activation of signal transduction pathways is essential for the development of safe and consumer friendly nanotechnology. Here we present an overview of signaling pathways induced by nanomaterial exposures and describe the possible correlation of their physicochemical characteristics with biological outcomes. In addition to the hierarchical oxidative stress model and a review of the intrinsic and cell-mediated mechanisms of reactive oxygen species (ROS) generating capacities of nanomaterials, we also discuss other oxidative stress dependent and independent cellular signaling pathways. Induction of the inflammasome, calcium signaling, and endoplasmic reticulum stress are reviewed. Furthermore, the uptake mechanisms can be of crucial importance for the cytotoxicity of nanomaterials and membrane-dependent signaling pathways have also been shown to be responsible for cellular effects of nanomaterials. Epigenetic regulation by nanomaterials, effects of nanoparticle-protein interactions on cell signaling pathways, and the induction of various cell death modalities by nanomaterials are described. We describe the common trigger mechanisms shared by various nanomaterials to induce cell death pathways and describe the interplay of different modalities in orchestrating the final outcome after nanomaterial exposures. A better understanding of signal modulations induced by nanomaterials is not only essential for the synthesis and design of safer nanomaterials but will also help to discover potential nanomedical applications of these materials. Several biomedical applications based on the different signaling pathways induced by nanomaterials are already proposed and will certainly gain a great deal of attraction in the near future.