Carbon nanotubes elicit DNA damage and inflammatory response relative to their size and shape

A cohesive effort to assess the suitability and disparity of carbon nanotubes for water treatment

Population growth, industrialization, and the extensive use of chemicals in daily life have all contributed to an increase in waste generation and an intensified release of organic pollutants into the aquatic environment. To ensure the quality of water (including natural resources), the removal of these pollutants from wastewater has become a challenging task for scientific community. Conventional physical, chemical, and biological treatment methods are commonly used in combinations and are not very effective. Recently, carbon nanotubes (CNTs) emerged as the most reliable and adaptable choice for efficient water treatment due to their extraordinary material properties appearing as a single-step solution for water treatment. High surface area, exceptional porosities, hollow and layered structures, and ease of chemical activation and functionalization are some properties which makes it excellent adsorption material. Hence, this review paper discusses the recent advances in the synthesis, purification, and functionalization of CNTs for water and wastewater treatment. In addition, this study also also provides a quick overview of CNTs-based advance technologies employed in water treatment and carefully assesses the benefits versus risks during large-scale water treatment. Furthermore, it concludes that identified risks to the environment and human health cannot be easily ignored and strict regulatory requirements are a must for producing low-cost innoxious CNTs.

Recent advances in nanoantibiotics against multidrug-resistant bacteria

Multidrug-resistant (MDR) bacteria-caused infections have been a major threat to human health. The abuse of conventional antibiotics accelerates the generation of MDR bacteria and makes the situation worse. The emergence of nanomaterials holds great promise for solving this tricky problem due to their multiple antibacterial mechanisms, tunable antibacterial spectra, and low probabilities of inducing drug resistance. In this review, we summarize the mechanism of the generation of drug resistance, and introduce the recently developed nanomaterials for dealing with MDR bacteria via various antibacterial mechanisms. Considering that biosafety and mass production are the major bottlenecks hurdling the commercialization of nanoantibiotics, we introduce the related development in these two aspects. We discuss urgent challenges in this field and future perspectives to promote the development and translation of nanoantibiotics as alternatives against MDR pathogens to traditional antibiotics-based approaches.

Carbon Nanomaterials: Emerging Roles in Immuno-Oncology

Cancer immunotherapy has made breakthrough progress in cancer treatment. However, only a subset of patients benefits from immunotherapy. Given their unique structure, composition, and interactions with the immune system, carbon nanomaterials have recently attracted tremendous interest in their roles as modulators of antitumor immunity. Here, we focused on the latest advances in the immunological effects of carbon nanomaterials. We also reviewed the current preclinical applications of these materials in cancer therapy. Finally, we discussed the challenges to be overcome before the full potential of carbon nanomaterials can be utilized in cancer therapies to ultimately improve patient outcomes.

Comparing the Toxicological Responses of Pulmonary Air-Liquid Interface Models upon Exposure to Differentially Treated Carbon Fibers

In recent years, the use of carbon fibers (CFs) in various sectors of industry has been increasing. Despite the similarity of CF degradation products to other toxicologically relevant materials such as asbestos fibers and carbon nanotubes, a detailed toxicological evaluation of this class of material has yet to be performed. In this work, we exposed advanced air-liquid interface cell culture models of the human lung to CF. To simulate different stresses applied to CF throughout their life cycle, they were either mechanically (mCF) or thermo-mechanically pre-treated (tmCF). Different aspects of inhalation toxicity as well as their possible time-dependency were monitored. mCFs were found to induce a moderate inflammatory response, whereas tmCF elicited stronger inflammatory as well as apoptotic effects. Furthermore, thermal treatment changed the surface properties of the CF resulting in a presumed adhesion of the cells to the fiber fragments and subsequent cell loss. Triple-cultures encompassing epithelial, macrophage, and fibroblast cells stood out with an exceptionally high inflammatory response. Only a weak genotoxic effect was detected in the form of DNA strand breaks in mono- and co-cultures, with triple-cultures presenting a possible secondary genotoxicity. This work establishes CF fragments as a potentially harmful material and emphasizes the necessity of further toxicological assessment of existing and upcoming advanced CF-containing materials.

In vitro-in vivo correlations of pulmonary inflammogenicity and genotoxicity of MWCNT

Background

Multi-walled carbon nanotubes (MWCNT) have received attention due to extraordinary properties, resulting in concerns for occupational health and safety. Costs and ethical concerns of animal testing drive a need for in vitro models with predictive power in respiratory toxicity. The aim of this study was to assess pro-inflammatory response (Interleukin-8 expression, IL-8) and genotoxicity (DNA strand breaks) caused by MWCNT with different physicochemical properties in different pulmonary cell models and correlate these to previously published in vivo data. Seven MWCNT were selected; two long/thick (NRCWE-006/Mitsui-7 and NM-401), two short/thin (NM-400 and NM-403), a pristine (NRCWE-040) and two surface modified; hydroxylated (NRCWE-041) and carboxylated (NRCWE-042). Carbon black Printex90 (CB) was included as benchmark material. Human alveolar epithelial cells (A549) and monocyte-derived macrophages (THP-1a) were exposed to nanomaterials (NM) in submerged conditions, and two materials (NM-400 and NM-401) in co-cultures of A549/THP-1a and lung fibroblasts (WI-38) in an air-liquid interface (ALI) system. Effective doses were quantified by thermo-gravimetric-mass spectrometry analysis (TGA-MS). To compare genotoxicity in vitro and in vivo, we developed a scoring system based on a categorization of effects into standard deviation (SD) units (< 1, 1, 2, 3 or 4 standard deviation increases) for the increasing genotoxicity.

Results

Effective doses were shown to be 25 to 53%, and 21 to 57% of the doses administered to A549 and THP-1a, respectively. In submerged conditions (A549 and THP-1a cells), all NM induced dose-dependent IL-8 expression. NM-401 and NRCWE-006 caused the strongest pro-inflammatory response. In the ALI-exposed co-culture, only NM-401 caused increased IL-8 expression, and no DNA strand breaks were observed. Strong correlations were found between in vitro and in vivo inflammation when doses were normalized by surface area (also proxy for diameter and length). Significantly increased DNA damage was found for all MWCNT in THP-1a cells, and for short MWCNT in A549 cells. A concordance in genotoxicity of 83% was obtained between THP-1a cells and broncho-alveolar lavaged (BAL) cells.

Conclusion

This study shows correlations of pro-inflammatory potential in A549 and THP-1a cells with neutrophil influx in mice, and concordance in genotoxic response between THP-1a cells and BAL cells, for seven MWCNT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00413-2.

Toxicological Aspects of Carbon Nanotubes, Fullerenes and Graphenes

Nanomedicines exhibit unbelievable capability in overcoming the hurdles faced in biological applications. Carbon nanotubes (CNTs), graphene-family nanomaterials and fullerenes are a class of engineered nanoparticles that have emerged as a new option for possible use in drug/gene delivery for life-threatening diseases. Their adaptability to pharmaceutical applications has opened new vistas for biomedical applications. Successful applications of this family of engineered nanoparticles in various fields may not support their use in medicine due to inconsistent data on toxicity as well as the lack of a centralized toxicity database. Inconsistent toxicological studies and lack of mechanistic understanding have been the reasons for limited understanding of their toxicological aspects. These nanoparticles, when underivatized or pristine, are considered as safe, however less reactive. The derivatized forms or functionalization changes their chemistry significantly to modify their biological effects including toxicity. They can cause acute and long term injuries in tissues by penetration through the the blood-air barrier, blood-alveolus barrier, blood-brain barrier, and blood-placenta barrier. and by accumulating in the lung, liver, and spleen . The toxicological effects are manifested through inflammatory response, DNA damage, apoptosis, autophagy and necrosis. Other factors that largely influence the toxicity of carbon nanotubes, graphenes and fullerenes are the concentration, functionalization, dimensional and surface topographical factors. Thus, a better understanding of the toxicity profile of CNTs, graphene-family nanomaterials and fullerenes in humans, animals and the environment is of significant importance, to improve their biological safety, to facilitate their wide biological application and for the successful commercial application. The exploration of appropriate cell lines to investigate specific receptors and intracellular targets as well as chronic toxicity beyond the proof-of-concept is required.

Electrospun polyurethane/carbon nanotube composites with different amounts of carbon nanotubes and almost the same fiber diameter for biomedical applications

The aim of this study was to investigate the net effect of raw carbon nanotube (CNTs) on the final properties of polyurethane (PU)/CNT composites considering their biomedical applications. So, neat PU and PU/CNT composites containing different amounts of CNTs (0.05%, 0.1%, 0.5%, and 1%) were prepared by electrospinning. Electrospinning parameters optimized to have a bead-free structure with no significant difference between their mean fiber diameter and porosity percentage. The results showed adding CNTs caused an increase in crystallinity percentage, water absorption ratio, young modulus, toughness, conductivity, degradation time in an accelerated medium, clotting time, and human umbilical vein endothelial cells adhesion. But a direct relationship between CNT percentage and the calcium adsorption was not detected. Moreover, no significant cytotoxicity was observed for 7-day extracts of all samples. These nanocomposites have a vast range of properties which make them a good candidate as neural, cardiovascular, osseous biomaterials or tendon, and ligament substitute.

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

Background

Inhalation 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).

Methods

MWCNTs 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.

Results

At 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.

Conclusions

These data demonstrate that the purification method is an important determinant of lung toxicity induced by carboxyl- and amine-functionalized MWCNTs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-020-00390-y.

Pleural translocation and lesions by pulmonary exposed multi-walled carbon nanotubes

Carbon nanotubes (CNTs) are recently developed tubular nanomaterials, with diameters ranging from a few nanometers to tens of nanometers, and the length reaching up to several micrometers. They can be either single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs). Due to their nano-scaled structure, CNTs have a unique set of mechanical, electrical, and chemical properties that make them useful in information technologies, optoelectronics, energy technologies, material sciences, medical technologies, and other fields. However, with the wide application and increasing production of CNTs, their potential risks have led to concerns regarding their impact on environment and health. The shape of some types of CNTs is similar to asbestos fibers, which suggests that these CNTs may cause characteristic pleural diseases similar to those found in asbestos-exposed humans, such as pleural plaques and malignant mesothelioma. Experimental data indicate that CNTs can induce lung and pleural lesions, inflammation, pleural fibrosis, lung tumors, and malignant mesothelioma upon inhalation in the experimental animals. In this review, we focus on the potential of MWCNTs to induce diseases similar to those by asbestos, molecular and cellular mechanisms associated with these diseases, and we discuss a method for evaluating the pleural toxicity of MWCNTs.

The Rational Design and Biological Mechanisms of Nanoradiosensitizers

Radiotherapy (RT) has been widely used for cancer treatment. However, the intrinsic drawbacks of RT, such as radiotoxicity in normal tissues and tumor radioresistance, promoted the development of radiosensitizers. To date, various kinds of nanoparticles have been found to act as radiosensitizers in cancer radiotherapy. This review focuses on the current state of nanoradiosensitizers, especially the related biological mechanisms, and the key design strategies for generating nanoradiosensitizers. The regulation of oxidative stress, DNA damage, the cell cycle, autophagy and apoptosis by nanoradiosensitizers in vitro and in vivo is highlighted, which may guide the rational design of therapeutics for tumor radiosensitization.

Quantitative Flow Cytometric Evaluation of Oxidative Stress and Mitochondrial Impairment in RAW 264.7 Macrophages after Exposure to Pristine, Acid Functionalized, or Annealed Carbon Nanotubes

Conventional nanotoxicological assays are subjected to various interferences with nanoparticles and especially carbon nanotubes. A multiparametric flow cytometry (FCM) methodology was developed here as an alternative to quantify oxidative stress, mitochondrial impairment, and later cytotoxic and genotoxic events. The experiments were conducted on RAW264.7 macrophages, exposed for 90 min or 24 h-exposure with three types of multiwalled carbon nanotubes (MWCNTs): pristine (Nanocyl™ CNT), acid functionalized (CNTf), or annealed treatment (CNTa). An original combination of reactive oxygen species (ROS) probes allowed the simultaneous quantifications of broad-spectrum ROS, superoxide anion (O₂^•-), and hydroxyl radical (•OH). All MWCNTs types induced a slight increase of broad ROS levels regardless of earlier antioxidant catalase activity. CNTf strongly stimulated the O₂^•- production. The •OH production was downregulated for all MWCNTs due to their scavenging capacity. The latter was quantified in a cell-free system by electron paramagnetic resonance spectroscopy (EPR). Further FCM-based assessment revealed early biological damages with a mitochondrial membrane potential collapse, followed by late cytotoxicity with chromatin decondensation. The combined evaluation by FCM analysis and cell-free techniques led to a better understanding of the impacts of MWCNTs surface treatments on the oxidative stress and related biological response.

State of knowledge on the occupational exposure to carbon nanotubes

Carbon nanotubes (CNT) trigger fascination as well as anxiety, given their unique physical and chemical properties, and continuing concerns around their possible health effects. CNT exposure assessment is an integral component of occupational and environmental epidemiology, risk assessment, and management. We conducted a systematic review to analyze the quality of CNT occupational exposure assessments in field studies and to assess the relevance of available quantitative data from occupational hygiene and epidemiological perspectives. PubMed and Scopus databases were searched for the period 2000-2018. To grade the quality of each study, we used a standardized grid of seven criteria. The first criterion addressed 12 items deemed most relevant CNT physical-chemical properties with respect to their in vitro and in vivo toxicity. We included 27 studies from 11 countries in the review and graded them high (n = 2), moderate (n = 15) and low quality (n = 10). Half of the studies measured elemental carbon mass concentration (EC) using different methods and aerosol fractions. In 85% of studies, the observed values exceed the US National Institute for Occupational Safety and Health Recommended Exposure Limit. The quantification of CNT agglomerates and/or CNT contained fibers becomes increasingly common although lacking methodological standardization. Work activities with the greatest mean CNT mass concentrations were non-enclosed and included sieving, harvesting, packaging, reactor cleaning, extrusion and pelletizing. Some of the large studies defined standardized job titles according to exposure estimates at corresponding workstations and classified them by decreasing CNT exposure level: technicians > engineers > chemists. The already initiated harmonization of CNT exposure assessment and result reporting need to continue to favor not only studies in the field, but also to identify companies and workers using CNTs to characterize their exposures as well as monitor their health. This will enable an objective and realistic evaluation of risks associated with CNT applications and an appropriate risk management.

A Safe-by-Design Strategy towards Safer Nanomaterials in Nanomedicines

The marriage of nanotechnology and medicine offers new opportunities to fight against human diseases. Benefiting from their unique optical, thermal, magnetic, or redox properties, a wide range of nanomaterials have shown potential in applications such as diagnosis, drug delivery, or tissue repair and regeneration. Despite the considerable success achieved over the past decades, the newly emerging nanomedicines still suffer from an incomplete understanding of their safety risks, and of the relationships between their physicochemical characteristics and safety profiles. Herein, the most important categories of nanomaterials with clinical potential and their toxicological mechanisms are summarized, and then, based on this available information, an overview of the principles in developing safe-by-design nanomaterials for medical applications and of the recent progress in this field is provided. These principles may serve as a starting point to guide the development of more effective safe-by-design strategies and to help identify the major knowledge and skill gaps.

Mitsui-7, heat-treated, and nitrogen-doped multi-walled carbon nanotubes elicit genotoxicity in human lung epithelial cells

Background

The unique physicochemical properties of multi-walled carbon nanotubes (MWCNT) have led to many industrial applications. Due to their low density and small size, MWCNT are easily aerosolized in the workplace making respiratory exposures likely in workers. The International Agency for Research on Cancer designated the pristine Mitsui-7 MWCNT (MWCNT-7) as a Group 2B carcinogen, but there was insufficient data to classify all other MWCNT. Previously, MWCNT exposed to high temperature (MWCNT-HT) or synthesized with nitrogen (MWCNT-ND) have been found to elicit attenuated toxicity; however, their genotoxic and carcinogenic potential are not known. Our aim was to measure the genotoxicity of MWCNT-7 compared to these two physicochemically-altered MWCNTs in human lung epithelial cells (BEAS-2B & SAEC).

Results

Dose-dependent partitioning of individual nanotubes in the cell nuclei was observed for each MWCNT material and was greatest for MWCNT-7. Exposure to each MWCNT led to significantly increased mitotic aberrations with multi- and monopolar spindle morphologies and fragmented centrosomes. Quantitative analysis of the spindle pole demonstrated significantly increased centrosome fragmentation from 0.024–2.4 μg/mL of each MWCNT. Significant aneuploidy was measured in a dose-response from each MWCNT-7, HT, and ND; the highest dose of 24 μg/mL produced 67, 61, and 55%, respectively. Chromosome analysis demonstrated significantly increased centromere fragmentation and translocations from each MWCNT at each dose. Following 24 h of exposure to MWCNT-7, ND and/or HT in BEAS-2B a significant arrest in the G1/S phase in the cell cycle occurred, whereas the MWCNT-ND also induced a G2 arrest. Primary SAEC exposed for 24 h to each MWCNT elicited a significantly greater arrest in the G1 and G2 phases. However, SAEC arrested in the G1/S phase after 72 h of exposure. Lastly, a significant increase in clonal growth was observed one month after exposure to 0.024 μg/mL MWCNT-HT & ND.

Conclusions

Although MWCNT-HT & ND cause a lower incidence of genotoxicity, all three MWCNTs cause the same type of mitotic and chromosomal disruptions. Chromosomal fragmentation and translocations have not been observed with other nanomaterials. Because in vitro genotoxicity is correlated with in vivo genotoxic response, these studies in primary human lung cells may predict the genotoxic potency in exposed human populations.

Electronic supplementary material

The online version of this article (10.1186/s12989-019-0318-0) contains supplementary material, which is available to authorized users.

Organ accumulation and carcinogenicity of highly dispersed multi-walled carbon nanotubes administered intravenously in transgenic rasH2 mice

PURPOSE

Multiwalled carbon nanotubes (MWCNTs) have been known to enter the circulatory system via the lungs from inhalation exposure; however, its carcinogenicity and subsequent accumulation in other organs have not been adequately reported in the literature. Moreover, the safety of MWCNTs as a biomaterial has remained a matter of debate, particularly when the material enters the circulatory system. To address these problems, we used carcinogenic rasH2 transgenic mice to intravenously administer highly dispersed MWCNTs and to evaluate their carcinogenicity and accumulation in the organs.

METHODS

Two types of MWCNTs (thin- and thick-MWCNTs) were intravenously administered at a high dose (approximately 0.7 mg per kg body weight) and low dose (approximately 0.07 mg per kg body weight).

RESULTS

MWCNTs showed pancreatic accumulation in 3.2% of mice administered with MWCNTs, but there was no accumulation in other organs. In addition, there was no significant difference in the incidence of tumor among the four MWCNTs-administered groups compared to the vehicle group without MWCNTs administration. Blood tests revealed elevated levels in mean red blood cell volume and mean red blood cell hemoglobin level for the MWCNTs-administered group, in addition to an increase in eotaxin.

CONCLUSION

The present study demonstrated that the use of current technology to sufficiently disperse MWCNTs resulted in minimal organ accumulation with no evidence of carcinogenicity.

A holistic study on potential toxic effects of carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) on zebrafish (Danio rerio) embryos/larvae

Multi-walled carbon nanotubes (MWCNTs) have widespread use in industrial and consumer products and great potential in biomedical applications. This leads to inevitably their release into the environment and the formation of their toxic effects on organisms. These effects can change depending on their physicochemical characteristics. Therefore, the toxicological findings of MWCNTs are inconsistent. Their toxicities related to surface modification have not been elucidated in a holistic manner. Hence, this study was conducted to clarify their potential toxic effects on zebrafish embryos/larvae in a comprehensive approach using morphologic, biochemical and molecular parameters. Zebrafish embryos were exposed to 5, 10, 20 mg/L doses of MWCNTs-COOH at 4 h after fertilization and grown until 96 hpf. Physiological findings demonstrated that they induced a concentration-dependent increase in the mortality rate, delayed hatching and decrease in the heartbeat rate. Moreover, it caused abnormalities including yolk sac edema, pericardial edema, head, tail malformations, and vertebral deformities. These effects may be due to the alterations in antioxidant and immune system related gene expressions after their entry into zebrafish embryo/larvae. The entry was confirmed from the evaluation of Raman spectra collected from the head, yolk sac, and tail of control and the nanotube treated groups. The gene expression analysis indicated the changes in the expression of oxidative stress (mtf-1, hsp70, and nfkb) and innate immune system (il-1β, tlr-4, tlr-22, trf, and cebp) related genes, especially an increased in the expression of the hsp70 and il-1β. These findings proved the developmental toxicities of MWCNTs-COOH on the zebrafish embryos/larvae.

Sampling Techniques on Collecting Fine Carbon Nanotube Fibers for Exposure Assessment

Carbon nanotube (CNT) sampling using an open-faced 25 mm cassette fiber sampling method and a newly developed direct sampling device was evaluated for the size fractioned analysis of collected airborne CNT fibers to improve the sampling and analytical methods. The open-faced 25 mm cassette fiber sampling method primarily collected large agglomerates, with the majority of collected particles being larger than two micrometer in size. Most of CNT structures collected by the new direct sampling device were individual fibers and clusters smaller than one micrometer with a high particle number concentration discrepancy compared to the open-faced 25 mm cassette method raising the concern of this sampling method to representatively characterize the respirable size fraction of CNT aerosols. This work demonstrates that a specialized technique is needed for collecting small fibers to provide a more representative estimate of exposure. It is recommended that an additional sampler be used to directly collect and analyze small fibers in addition to the widely accepted sampling method which utilizes an open-faced 25 mm cassette.

Pulmonary toxicity of two different multi-walled carbon nanotubes in rat: Comparison between intratracheal instillation and inhalation exposure

Multi-walled carbon nanotubes (MWCNTs), which vary in length, diameter, functionalization and specific surface area, are used in diverse industrial processes. Since these nanomaterials have a high aspect ratio and are biopersistant in the lung, there is a need for a rapid identification of their potential health hazard. We assessed in Sprague-Dawley rats the pulmonary toxicity of two pristine MWCNTs (the "long and thick" NM-401 and the "short and thin" NM-403) following either intratracheal instillation or 4-week inhalation in order to gain insights into the predictability and intercomparability of the two methods. The deposited doses following inhalation were lower than the instilled doses. Both types of carbon nanotube induced pulmonary neutrophil influx using both exposure methods. This influx correlated with deposited surface area across MWCNT types and means of exposure at two different time points, 1-3 days and 28-30 days post-exposure. Increased levels of DNA damage were observed across doses and time points for both exposure methods, but no dose-response relationship was observed. Intratracheal instillation of NM-401 induced fibrosis at the highest dose while lower lung deposited doses obtained by inhalation did not induce such lung pathology. No fibrosis was observed following NM-403 exposure. When the deposited dose was taken into account, sub-acute inhalation and a single instillation of NM-401 and NM-403 produced very similar inflammation and DNA damage responses. Our data suggest that the dose-dependent inflammatory responses observed after intratracheal instillation and inhalation of MWCNTs are similar and were predicted by the deposited surface area.

Toxicity of nanoparticles_ challenges and opportunities

Nanomaterials (NMs) find widespread use in different industries that range from agriculture, food, medicine, pharmaceuticals, and electronics to cosmetics. It is the exceptional properties of these materials at the nanoscale, which make them successful as growth promoters, drug carriers, catalysts, filters and fillers, but a price must be paid via the potential toxity of these materials. The harmful effects of nanoparticles (NPs) to environment, human and animal health needs to be investigated and critically examined, to find appropriate solutions and lower the risks involved in the manufacture and use of these exotic materials.The vast number and complex interaction of NM/NPs with different biological systems implies that there is no universal toxicity mechanism or assessment method. The various challenges need to be overcome and a number of research studies have been conducted during the past decade on different NMs to explore the possible mechanisms of uptake, concentrations/dosage and toxicity levels. This review article examines critically the recent reports in this field to summarize and present opportunities for safer design using case studies from published literature.

Effect of iron overload from multi walled carbon nanotubes on neutrophil-like differentiated HL-60 cells

Multi walled carbon nanotubes (MWCNTs) are one of the most intensively explored nanomaterials because of their unique physical and chemical properties. Due to the widespread use of MWCNTs, it is important to investigate their effects on human health. The precise mechanism of MWCNT toxicity has not been fully elucidated. The present study was designed to examine the mechanisms of MWCNT toxicity toward human promyelocytic leukemia HL-60 cells. First, we found that MWCNTs decreased the viability of neutrophil-like differentiated HL-60 cells but not undifferentiated HL-60 cells. Because neutrophil-like differentiated HL-60 cells exhibit enhanced phagocytic activity, the cytotoxicity of MWCNTs is dependent on the intracellularly localized MWCNTs. Next, we revealed that the cytotoxicity of MWCNTs is correlated with the intracellular accumulation of iron that is released from the engulfed MWCNTs in an acidic lysosomal environment. The intracellular accumulation of iron was repressed by treatment with cytochalasin D, a phagocytosis inhibitor. In addition, our results indicated that iron overload enhanced the release of interleukin-8 (IL-8), a chemokine that activates neutrophils, and subsequently elevated intracellular calcium concentration ([Ca²⁺]_i). Finally, we found that the sustained [Ca²⁺]_i elevation resulted in the loss of mitochondrial membrane potential and the increase of caspase-3 activity, thereby inducing apoptotic cell death. These findings suggest that the iron overload caused by engulfed MWCNTs results in the increase of IL-8 production and the elevation of [Ca²⁺]_i, thereby activating the mitochondria-mediated apoptotic pathway.

Anticancer effect of novel platinum nanocomposite beads on oral squamous cell carcinoma cells

Nanoparticles are used in industry and medicine, because of their physiochemical properties, such as size, charge, large surface area and surface reactivity. Recently, metal nanoparticles were reported to show cell toxicity on cancer cells. In this study, we focused novel platinum nanoparticles-conjugated latex beads (P2VPs), platinum nanocomposite (PtNCP) beads, and investigated the possibility to incorporate novel anti-cancer effect of these combined nanoparticles. Oral squamous cell carcinoma cell lines, HSC-3-M3 cells were injected subcutaneously into the back of nude mice to produce a xenograft model. PtNCP beads were injected locally and examined by measuring tumor volume and comparing pathological histology. PtNCP beads treatment suppressed tumor growth and identified increasing pathological necrotic areas, in vivo. PtNCP beads inhibited the cell viability of HSC-3-M3 cells in dose-dependent manner and induced the cytotoxicity with extracellular LDH value, in vitro. Furthermore, SEM images were morphologically observed in PtNCP beads-treated HSC-3-M3 cells. The aggregation of the PtNCP beads on the cell membrane, the destructions of the cell membrane and globular structures were observed in the SEM image. Our results indicated that a potential anti-cancer effect of the PtNCP beads, suggesting the possibility as a therapeutic tool for cancer cell-targeted therapy. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2281-2287, 2019.

The effects of subacute inhaled multi-walled carbon nanotube exposure on signaling pathways associated with cholesterol transport and inflammatory markers in the vasculature of wild-type mice

Exposure to multi-walled carbon nanotubes (MWCNTs) has been associated with detrimental cardiovascular outcomes; however, underlying mechanisms have not yet been fully elucidated. Thus, we investigated alterations in proatherogenic and proinflammatory signaling pathways in C57Bl6/ mice exposed to MWCNTs (1 mg/m³) or filtered air (FA-Controls), via inhalation, for 6 h/day, 14d. Expression of mediators of cholesterol transport, namely the lectin-like oxidized low-density lipoprotein receptor (LOX)-1 and ATP-binding cassette transporter (ABCA)-1, inflammatory markers tumor necrosis factor (TNF)-α and interleukin (IL)-1β/IL-6, nuclear-factor kappa-light-chain-enhancer of activated B cells (NF-κB), intracellular/vascular adhesion molecule(s) (VCAM-1, ICAM-1), and miRNAs (miR-221/-21/-1), associated with cardiovascular disease (CVD), were analyzed in cardiac tissue and coronary vasculature. Cardiac fibrotic deposition, matrix-metalloproteinases (MMP)-2/9, and reactive oxygen species (ROS) were also assessed. MWCNT-exposure resulted in increased coronary ROS production with concurrent increases in expression of LOX-1, VCAM-1, TNF-α, and MMP-2/9 activity; while ABCA-1 expression was downregulated, compared to FA-Controls. Additionally, trends in fibrotic deposition and induction of cardiac TNF-α, MMP-9, IκB Kinase (IKK)-α/β, and miR-221 mRNA expression were observed. Analysis using inhibitors for nitric oxide synthase or NADPH oxidase resulted in attenuated coronary ROS production. These findings suggest that subacute inhalation MWCNT-exposure alters expression of cholesterol transporter/receptors, and induces signaling pathways associated with inflammation, oxidative stress, and CVD in wild-type mice.

Changes in DNA methylation induced by multi-walled carbon nanotube exposure in the workplace

This study was designed to assess the epigenetic alterations in blood cells, induced by occupational exposure to multi-wall carbon nanotubes (MWCNT). The study population comprised of MWCNT-exposed workers (n=24) and unexposed controls (n=43) from the same workplace. We measured global DNA methylation/hydroxymethylation levels on the 5th cytosine residues using a validated liquid chromatography tandem-mass spectrometry (LC-MS/MS) method. Sequence-specific methylation of LINE1 retrotransposable element 1 (L1RE1) elements, and promoter regions of functionally important genes associated with epigenetic regulation [DNA methyltransferase-1 (DNMT1) and histone deacetylase 4 (HDAC4)], DNA damage/repair and cell cycle pathways [nuclear protein, coactivator of histone transcription/ATM serine/threonine kinase (NPAT/ATM)], and a potential transforming growth factor beta (TGF-β) repressor [SKI proto-oncogene (SKI)] were studied using bisulfite pyrosequencing. Analysis of global DNA methylation levels and hydroxymethylation did not reveal significant difference between the MWCNT-exposed and control groups. No significant changes in Cytosine-phosphate-Guanine (CpG) site methylation were observed for the LINE1 (L1RE1) elements. Further analysis of gene-specific DNA methylation showed a significant change in methylation for DNMT1, ATM, SKI, and HDAC4 promoter CpGs in MWCNT-exposed workers. Since DNA methylation plays an important role in silencing/regulation of the genes, and many of these genes have been associated with occupational and smoking-induced diseases and cancer (risk), aberrant methylation of these genes might have a potential effect in MWCNT-exposed workers.

Perturbation of the pulmonary surfactant monolayer by single-walled carbon nanotubes: a molecular dynamics study

Single-walled carbon nanotubes (SWCNTs) are at present synthesized on a large scale with a variety of applications. The increasing likelihood of exposure to SWCNTs, however, puts human health at a high risk. As the front line of the innate host defense system, the pulmonary surfactant monolayer (PSM) at the air-water interface of the lungs interacts with the inhaled SWCNTs, which in turn inevitably perturb the ultrastructure of the PSM and affect its biophysical functions. Here, using molecular dynamics simulations, we demonstrate how the diameter and length of SWCNTs critically regulate their interactions with the PSM. Compared to their diameters, the inhalation toxicity of SWCNTs was found to be largely affected by their lengths. Short SWCNTs with lengths comparable to the monolayer thickness are found to vertically insert into the PSM with no indication of translocation, possibly leading to accumulation of SWCNTs in the PSM with prolonged retention and increased inflammation potentials. The perturbation also comes from the forming water pores across the PSM. Longer SWCNTs are found to horizontally insert into the PSM during inspiration, and they can be wrapped by the PSM during deep expiration via a tube diameter-dependent self-rotation. The potential toxicity of longer SWCNTs comes from severe lipid depletion and the PSM-rigidifying effect. Our findings could help reveal the inhalation toxicity of SWCNTs, and pave the way for the safe use of SWCNTs as vehicles for pulmonary drug delivery.

Toward the suppression of cellular toxicity from single-walled carbon nanotubes

In the multidisciplinary fields of nanobiology and nanomedicine, single-walled carbon nanotubes (SWCNTs) have shown great promise due to their unique morphological, physical and chemical properties. However, understanding and suppressing their cellular toxicity is a mandatory step before promoting their biomedical applications. In light of the flourishing recent literature, we provide here an extensive review on SWCNT cellular toxicity and an attempt to identify the key parameters to be considered in order to obtain SWCNT samples with minimal or no cellular toxicity.

Evaluating the mechanistic evidence and key data gaps in assessing the potential carcinogenicity of carbon nanotubes and nanofibers in humans

In an evaluation of carbon nanotubes (CNTs) for the IARC Monograph 111, the Mechanisms Subgroup was tasked with assessing the strength of evidence on the potential carcinogenicity of CNTs in humans. The mechanistic evidence was considered to be not strong enough to alter the evaluations based on the animal data. In this paper, we provide an extended, in-depth examination of the in vivo and in vitro experimental studies according to current hypotheses on the carcinogenicity of inhaled particles and fibers. We cite additional studies of CNTs that were not available at the time of the IARC meeting in October 2014, and extend our evaluation to include carbon nanofibers (CNFs). Finally, we identify key data gaps and suggest research needs to reduce uncertainty. The focus of this review is on the cancer risk to workers exposed to airborne CNT or CNF during the production and use of these materials. The findings of this review, in general, affirm those of the original evaluation on the inadequate or limited evidence of carcinogenicity for most types of CNTs and CNFs at this time, and possible carcinogenicity of one type of CNT (MWCNT-7). The key evidence gaps to be filled by research include: investigation of possible associations between in vitro and early-stage in vivo events that may be predictive of lung cancer or mesothelioma, and systematic analysis of dose-response relationships across materials, including evaluation of the influence of physico-chemical properties and experimental factors on the observation of nonmalignant and malignant endpoints.

Carbon Nanostructures in Bone Tissue Engineering

BACKGROUND

Recent advances in developing biocompatible materials for treating bone loss or defects have dramatically changed clinicians' reconstructive armory. Current clinically available reconstructive options have certain advantages, but also several drawbacks that prevent them from gaining universal acceptance. A wide range of synthetic and natural biomaterials is being used to develop tissue-engineered bone. Many of these materials are currently in the clinical trial stage.

METHODS

A selective literature review was performed for carbon nanostructure composites in bone tissue engineering.

RESULTS

Incorporation of carbon nanostructures significantly improves the mechanical properties of various biomaterials to mimic that of natural bone. Recently, carbon-modified biomaterials for bone tissue engineering have been extensively investigated to potentially revolutionize biomaterials for bone regeneration.

CONCLUSION

This review summarizes the chemical and biophysical properties of carbon nanostructures and discusses their functionality in bone tissue regeneration.

Physico-chemical properties based differential toxicity of graphene oxide/reduced graphene oxide in human lung cells mediated through oxidative stress

Goraphene derivatives (GD) are currently being evaluated for technological and biomedical applications owing to their unique physico-chemical properties over other carbon allotrope such as carbon nanotubes (CNTs). But, the possible association of their properties with underlying in vitro effects have not fully examined. Here, we assessed the comparative interaction of three GD - graphene oxide (GO), thermally reduced GO (TRGO) and chemically reduced GO (CRGO), which significantly differ in their lateral size and functional groups density, with phenotypically different human lung cells; bronchial epithelial cells (BEAS-2B) and alveolar epithelial cells (A549). The cellular studies demonstrate that GD significantly ineternalize and induce oxidative stress mediated cytotoxicity in both cells. The toxicity intensity was in line with the reduced lateral size and increased functional groups revealed more toxicity potential of TRGO and GO respectively. Further, A549 cells showed more susceptibility than BEAS-2B which reflected cell type dependent differential cellular response. Molecular studies revealed that GD induced differential cell death mechanism which was efficiently prevented by their respective inhibitors. This is prior study to the best of our knowledge involving TRGO for its safety evaluation which provided invaluable information and new opportunities for GD based biomedical applications.

Efficient delivery of DNA into bovine preimplantation embryos by multiwall carbon nanotubes

The pellucid zone (PZ) is a protective embryonic cells barrier against chemical, physical or biological substances. This put, usual transfection methods are not efficient for mammal oocytes and embryos as they are exclusively for somatic cells. Carbon nanotubes have emerged as a new method for gene delivery, and they can be an alternative for embryos transfection, however its ability to cross the PZ and mediated gene transfer is unknown. Our data confirm that multiwall carbon nanotubes (MWNTs) can cross the PZ and delivery of pDNA into in vitro-fertilized bovine embryos. The degeneration rate and the expression of genes associated to cell viability were not affected in embryos exposed to MWNTs. Those embryos, however, had lower cell number and higher apoptotic cell index, but this did not impair the embryonic development. This study shows the potential utility of the MWNT for the development of new method for delivery of DNA into bovine embryos.

Multi-walled carbon nanotubes increase antibody-producing B cells in mice immunized with a tetravalent vaccine candidate for dengue virus

Background

In recent times, studies have demonstrated that carbon nanotubes are good candidates for use as vehicles for transfection of exogenous material into the cells. However, there are few studies evaluating the behavior of carbon nanotubes as DNA vectors and few of these studies have used multi-walled carbon nanotubes (MWCNTs) or carboxylated MWCNTs. Thus, this study aims to assess the MWCNTs’ (carboxylated or not) efficiency in the increase in expression of the tetravalent vaccine candidate (TVC) plasmid vector for dengue virus in vitro using Vero cells, and in vivo, through the intramuscular route, to evaluate the immunological response profile.

Results

Multi-walled carbon nanotubes internalized by Vero cells, have been found in the cytoplasm and nucleus associated with the plasmid. However, it was not efficient to increase the messenger ribonucleic acid (mRNA) compared to the pure vaccine candidate associated with Lipofectamine^® 2000. The in vivo experiments showed that the use of intramuscular injection of the TVC in combination with MWCNTs reduced the immune response compared to pure TVC, in a general way, although an increase was observed in the population of the antibody-producing B cells, as compared to pure TVC.

Conclusions

The results confirm the data found by other authors, which demonstrate the ability of nanotubes to penetrate target cells and reach both the cytoplasm and the cell nucleus. The cytotoxicity values are also in accordance with the literature, which range from 5 to 20 µg/mL. This has been found to be 10 µg/mL in this study. Although the expression levels are higher in cells that receive the pure TVC transfected using Lipofectamine^® 2000, the nanotubes show an increase in B-cells producing antibodies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-016-0196-7) contains supplementary material, which is available to authorized users.

Neurobehavioral toxicity of carbon nanotubes in mice

Objectives:

The aim of this study was to evaluate neurobehavioral toxicity of single-walled (SWNTs) and multiwalled carbon nanotubes (MWNTs) in mice.

Methods:

Male NMRI mice were randomized into 5 groups ( n = 10 each): Normal control (NC) group was injected intraperitoneally (i.p.) with phosphate-buffered saline (PBS) solution (pH 7.8; ca. 1 mL), MW80 and MW800 groups were injected with either i.p. 80 or 800 mg kg−1 MWNTs suspended in 1 mL of PBS and SW80 and SW800 groups were injected with either i.p. 80 or 800 mg kg−1 SWNTs suspended in 1 mL of PBS. After 2 weeks, five mice from each group were evaluated for brain-derived neurotrophic factor (BDNF) messenger RNA expression and protein content of brain tissues. Locomotion, anxiety, learning and memory, and depression were measured by open field test (OFT), elevated plus-maze (EPM), object recognition test (ORT), and forced swimming test (FST), respectively.

Results:

Ambulation time and center arena time in the OFT did not change among groups. In the EPM paradigm, SWNTs (800 mg kg−1) and MWNTs (80 and 800 mg kg−1) showed an anxiogenic effect. In ORT, MWNTs (80 mg kg−1) increased the discrimination ratio while in FST, MWNTs showed a depressant effect as compared to vehicle. The BDNF gene expression in mice treated with 80 and 800 mg kg−1 SWNTs or 80 mg kg−1 MWNTs decreased as compared to NC mice although BDNF gene expression increased in mice that were treated with 800 mg kg−1 MWNTs. The whole brain BDNF protein content did not change among groups.

Conclusion:

Our study showed that i.p. exposure to carbon nanotubes (CNTs) may result in behavioral toxicity linked with expression of depression or anxiety that depends on the type of CNTs. In addition, exposure to CNTs changed BDNF gene expression.

Meta-analysis of transcriptomic responses as a means to identify pulmonary disease outcomes for engineered nanomaterials

Background

The increasing use of engineered nanomaterials (ENMs) of varying physical and chemical characteristics poses a great challenge for screening and assessing the potential pathology induced by these materials, necessitating novel toxicological approaches. Toxicogenomics measures changes in mRNA levels in cells and tissues following exposure to toxic substances. The resulting information on altered gene expression profiles, associated pathways, and the doses at which these changes occur, are used to identify the underlying mechanisms of toxicity and to predict disease outcomes. We evaluated the applicability of toxicogenomics data in identifying potential lung-specific (genomic datasets are currently available from experiments where mice have been exposed to various ENMs through this common route of exposure) disease outcomes following exposure to ENMs.

Methods

Seven toxicogenomics studies describing mouse pulmonary responses over time following intra-tracheal exposure to increasing doses of carbon nanotubes (CNTs), carbon black, and titanium dioxide (TiO₂) nanoparticles of varying properties were examined to understand underlying mechanisms of toxicity. mRNA profiles from these studies were compared to the publicly available datasets of 15 other mouse models of lung injury/diseases induced by various agents including bleomycin, ovalbumin, TNFα, lipopolysaccharide, bacterial infection, and welding fumes to delineate the implications of ENM-perturbed biological processes to disease pathogenesis in lungs.

Results

The meta-analysis revealed two distinct clusters—one driven by TiO₂ and the other by CNTs. Unsupervised clustering of the genes showing significant expression changes revealed that CNT response clustered with bleomycin injury and bacterial infection models, both of which are known to induce lung fibrosis, in a post-exposure-time dependent manner, irrespective of the CNT’s physical-chemical properties. TiO₂ samples clustered separately from CNTs and disease models.

Conclusions

These results indicate that in the absence of apical toxicity data, a tiered strategy beginning with short term, in vivo tissue transcriptomics profiling can effectively and efficiently screen new ENMs that have a higher probability of inducing pulmonary pathogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0137-5) contains supplementary material, which is available to authorized users.

Metronomic Doses of Temozolomide Enhance the Efficacy of Carbon Nanotube CpG Immunotherapy in an Invasive Glioma Model

Even when treated with aggressive current therapies, most patients with glioblastoma survive less than two years. Rapid tumor growth, an invasive nature, and the blood-brain barrier, which limits the penetration of large molecules into the brain, all contribute to the poor tumor response associated with conventional therapies. Immunotherapy has emerged as a therapeutic approach that may overcome these challenges. We recently reported that single-walled carbon nanotubes (SWCNTs) can be used to dramatically increase the immunotherapeutic efficacy of CpG oligonucleotides in a mouse model of glioma. Following implantation in the mouse brain, the tumor cell line used in these previous studies (GL261) tends to form a spherical tumor with limited invasion into healthy brain. In order to evaluate SWCNT/CpG therapy under more clinically-relevant conditions, here we report the treatment of a more invasive mouse glioma model (K-Luc) that better recapitulates human disease. In addition, a CpG sequence previously tested in humans was used to formulate the SWCNT/CpG which was combined with temozolomide, the standard of care chemotherapy for glioblastoma patients. We found that, following two intracranial administrations, SWCNT/CpG is well-tolerated and improves the survival of mice bearing invasive gliomas. Interestingly, the efficacy of SWCNT/CpG was enhanced when combined with temozolomide. This enhanced anti-tumor efficacy was correlated to an increase of tumor-specific cytotoxic activity in splenocytes. These results reinforce the emerging understanding that immunotherapy can be enhanced by combining it with chemotherapy and support the continued development of SWCNT/CpG.

Corking Nitrogen-Doped Carbon Nanotube Cups with Gold Nanoparticles for Biodegradable Drug Delivery Applications

Carbon nanomaterials have been proposed as effective drug delivery devices; however their perceived biopersistence and toxicological profile may hinder their applications in medical therapeutics. Nitrogen doping of carbon nanotubes results in a unique "stacked-cup" structure, with cups held together through van der Waals forces. Disrupting these weak interactions yields individual and short-stacked nanocups that can subsequently be corked with gold nanoparticles, resulting in sealed containers for delivery of cargo. Peroxidase-catalyzed reactions can effectively uncork these containers, followed by complete degradation of the graphitic capsule, resulting in effective release of therapeutic cargo while minimizing harmful side effects. The protocols reported herein describe the synthesis of stacked nitrogen-doped carbon nanotube cups followed by effective separation into individual cups and gold nanoparticle cork formation resulting in loaded and sealed containers.

A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing

Some animals, such as the chameleon and cephalopod, have the remarkable capability to change their skin colour. This unique characteristic has long inspired scientists to develop materials and devices to mimic such a function. However, it requires the complex integration of stretchability, colour-changing and tactile sensing. Here we show an all-solution processed chameleon-inspired stretchable electronic skin (e-skin), in which the e-skin colour can easily be controlled through varying the applied pressure along with the applied pressure duration. As such, the e-skin's colour change can also be in turn utilized to distinguish the pressure applied. The integration of the stretchable, highly tunable resistive pressure sensor and the fully stretchable organic electrochromic device enables the demonstration of a stretchable electrochromically active e-skin with tactile-sensing control. This system will have wide range applications such as interactive wearable devices, artificial prosthetics and smart robots.

Some animals and insects can change the colour of their skin, but mimicking such function in man-made materials is complex. Here, the authors demonstrate an all-solution processed chameleon-inspired stretchable e-skin capable of interactive colour changes and tactile sensing.

Effect of nonendocytic uptake of nanoparticles on human bronchial epithelial cells

The toxicity of artificial nanoparticles is a major concern in industrial applications. Cellular uptake of hard nanoparticles could follow either endocytic or nonendocytic pathways, leading to different stimuli to the cells. Yet the cellular responses to nanoparticles following different pathways have not been compared due to the lack of an independent nonendocytic delivery method. We applied a unique delivery method, nanochannel electroporation (NEP), to produce predominantly nonendocytic uptakes of quantum dots (Q-dots) and multiwalled carbon nanotubes (MWCNTs) with different chemical modifications. NEP delivery bypassed endocytosis by electrophoretic injection of nanoparticles into human bronchial epithelial (BEAS-2B) cells at different dosages. Conventional exposure by direct nanoparticle suspending in cell culture medium was also performed as control. The dosage-dependent responses to nanoparticles under different uptake pathways were compared. Fluorescence colocalization demonstrated that nanoparticles followed both endocytic and nonendocytic pathways for cell entry in contact exposure, whereas NEP delivery of nanoparticles bypassed endocytosis. Nonendocytic entry resulted in much higher oxidation stress and, for MWCNTs, more cell death in BEAS-2B cells. Despite the observation that most nanoparticles were taken up by cells through endocytosis, the minor nonendocytic entry of nanoparticles seemed to dominate the overall cellular response in conventional contact exposure. Our finding suggests that prevention against nonendocytic uptake could help reduce the toxicity of hard nanoparticles.

The effects of carbon nanotubes on lung and dermal cellular behaviors

Carbon nanotubes (CNTs) hold great promise to create new and better products, but their adverse health effect is a major concern. Human exposure to CNTs is primarily through inhalation and dermal contact, especially during the manufacturing and handling processes. Numerous animal studies have demonstrated the potential pulmonary and dermal hazards associated with CNT exposure, while in vitro studies have assessed the effects of CNT exposure on various cellular behaviors and have been used to perform mechanistic studies. In this review, we provide an overview of the pathological effects of CNTs and examine the acute and chronic effects of CNT exposure on lung and dermal cellular behaviors, beyond the generally discussed cytotoxicity. We then examine the linkage of cellular behaviors and disease pathogenesis, and discuss the pertinent mechanisms.

Interactions of multiwalled carbon nanotubes with algal cells: quantification of association, visualization of uptake, and measurement of alterations in the composition of cells

Carbon nanotubes (CNTs) are considered promising materials in nanotechnology. We quantified CNT accumulation by the alga Desmodesmus subspicatus. Cells were exposed to radiolabeled CNTs ((14)C-CNTs;1 mg/L) to determine uptake and association, as well as elimination and dissociation in clear media.Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used to detect effects of CNTs on algae. CNT-cell interactions were visualized by electron microscopy and related to alterations in their cell composition. A concentration factor of 5000 L/kg dry weight was calculated. Most of the material agglomerated around the cells, but single tubes were detected in the cytoplasm. Computational analyses of the ATR-FTIR data showed that CNT treated algae differed from controls at all sampling times.CNT exposure changed the biochemical composition of cells. The fact that CNTs are bioavailable for algae and that they influence the cell composition is important with regard to environmental risk assessment of this nanomaterial.

Effect of aspect ratio on the uptake and toxicity of hydroxylated-multi walled carbon nanotubes in the nematode, Caenorhabditis elegans

OBJECTIVES

In this study, the effect of tube length and outer diameter (OD) size of hydroxylated-multi walled carbon nanotubes (OH-MWCNTs) on their uptake and toxicity was investigated in the nematode Caenorhabditis elegans using a functional mutant analysis.

METHODS

The physicochemical properties of three different OH-MWCNTs were characterized. Uptake and toxicity were subsequently investigated on C. elegans exposed to MWCNTs with different ODs and tube lengths.

RESULTS

The results of mutant analysis suggest that ingestion is the main route of MWCNTs uptake. We found that OH-MWCNTs with smaller ODs were more toxic than those with larger ODs, and OH-MWCNTs with shorter tube lengths were more toxic than longer counterparts to C. elegans.

CONCLUSIONS

Overall the results suggest the aspect ratio affects the toxicity of MWCNTs in C. elegans. Further thorough study on the relationship between physicochemical properties and toxicity needs to be conducted for more comprehensive understanding of the uptake and toxicity of MWCNTs.

Gene expression profile of human lung epithelial cells chronically exposed to single-walled carbon nanotubes

A rapid increase in utility of engineered nanomaterials, including carbon nanotubes (CNTs), has raised a concern over their safety. Based on recent evidence from animal studies, pulmonary exposure of CNTs may lead to nanoparticle accumulation in the deep lung without effective clearance which could interact with local lung cells for a long period of time. Physicochemical similarities of CNTs to asbestos fibers may contribute to their asbestos-like carcinogenic potential after long-term exposure, which has not been well addressed. More studies are needed to identify and predict the carcinogenic potential and mechanisms for promoting their safe use. Our previous study reported a long-term in vitro exposure model for CNT carcinogenicity and showed that 6-month sub-chronic exposure of single-walled carbon nanotubes (SWCNT) causes malignant transformation of human lung epithelial cells. In addition, the transformed cells induced tumor formation in mice and exhibited an apoptosis resistant phenotype, a key characteristic of cancer cells. Although the potential role of p53 in the transformation process was identified, the underlying mechanisms of oncogenesis remain largely undefined. Here, we further examined the gene expression profile by using genome microarrays to profile molecular mechanisms of SWCNT oncogenesis. Based on differentially expressed genes, possible mechanisms of SWCNT-associated apoptosis resistance and oncogenesis were identified, which included activation of pAkt/p53/Bcl-2 signaling axis, increased gene expression of Ras family for cell cycle control, Dsh-mediated Notch 1, and downregulation of apoptotic genes BAX and Noxa. Activated immune responses were among the major changes of biological function. Our findings shed light on potential molecular mechanisms and signaling pathways involved in SWCNT oncogenic potential.

MWCNTs of different physicochemical properties cause similar inflammatory responses, but differences in transcriptional and histological markers of fibrosis in mouse lungs

Multi-walled carbon nanotubes (MWCNTs) are an inhomogeneous group of nanomaterials that vary in lengths, shapes and types of metal contamination, which makes hazard evaluation difficult. Here we present a toxicogenomic analysis of female C57BL/6 mouse lungs following a single intratracheal instillation of 0, 18, 54 or 162 μg/mouse of a small, curled (CNT(Small), 0.8 ± 0.1 μm in length) or large, thick MWCNT (CNT(Large), 4 ± 0.4 μm in length). The two MWCNTs were extensively characterized by SEM and TEM imaging, thermogravimetric analysis, and Brunauer-Emmett-Teller surface area analysis. Lung tissues were harvested 24h, 3 days and 28 days post-exposure. DNA microarrays were used to analyze gene expression, in parallel with analysis of bronchoalveolar lavage fluid, lung histology, DNA damage (comet assay) and the presence of reactive oxygen species (dichlorodihydrofluorescein assay), to profile and characterize related pulmonary endpoints. Overall changes in global transcription following exposure to CNT(Small) or CNT(Large) were similar. Both MWCNTs elicited strong acute phase and inflammatory responses that peaked at day 3, persisted up to 28 days, and were characterized by increased cellular influx in bronchoalveolar lavage fluid, interstitial pneumonia and gene expression changes. However, CNT(Large) elicited an earlier onset of inflammation and DNA damage, and induced more fibrosis and a unique fibrotic gene expression signature at day 28, compared to CNT(Small). The results indicate that the extent of change at the molecular level during early response phases following an acute exposure is greater in mice exposed to CNT(Large), which may eventually lead to the different responses observed at day 28.