Effect of dispersants of multi-walled carbon nanotubes on cellular uptake and biological responses

Disruption of phosphofructokinase activity and aerobic glycolysis in human bronchial epithelial cells by atmospheric ultrafine particulate matter

Exposure to ambient ultrafine particulate matter (UPM) causes respiratory disorders; however, the underlying molecular mechanisms remain unclear. In this study, we synthesized simulated UPM (sUPM) with controlled physicochemical properties using the spark-discharge method. Subsequently, we investigated the biological effects of sUPM using BEAS-2B human bronchial epithelial cells (HBECs) and a mouse intratracheal instillation model. High throughput RNA-sequencing and bioinformatics analyses revealed that dysregulation of the glycolytic metabolism is involved in the inhibited proliferation and survival of HBECs by sUPM treatment. Furthermore, signaling pathway and enzymatic analyses showed that the treatment of BEAS-2B cells with sUPM induces the inactivation of extracellular signal-regulated kinase (ERK) and protein kinase B (PKB, also known as AKT), resulting in the downregulation of phosphofructokinase 2 (PFK2) S483 phosphorylation, PFK enzyme activity, and aerobic glycolysis in HBECs in an oxidative stress-independent manner. Additionally, intratracheal instillation of sUPM reduced the phosphorylation of ERK, AKT, and PFK2, decreased proliferation, and increased the apoptosis of bronchial epithelial cells in mice. The findings of this study imply that UPM induces pulmonary toxicity by disrupting aerobic glycolytic metabolism in lung epithelial cells, which can provide novel insights into the toxicity mechanisms of UPM and strategies to prevent their toxic effects.

Three-Dimensional Modeling with Osteoblast-like Cells under External Magnetic Field Conditions Using Magnetic Nano-Ferrite Particles for the Development of Cell-Derived Artificial Bone

The progress in artificial bone research is crucial for addressing fractures and bone defects in the aging population. However, challenges persist in terms of biocompatibility and structural complexity. Nanotechnology provides a promising avenue by which to overcome these challenges, with nano-ferrite particles (NFPs) exhibiting superparamagnetic properties. The ability to control cell positioning using a magnetic field opens up new possibilities for customizing artificial bones with specific shapes. This study explores the biological effects of NFPs on osteoblast-like cell lines (MC3T3-E1), including key analyses, such as cell viability, cellular uptake of NFPs, calcification processes, cell migration under external magnetic field conditions, and three-dimensional modeling. The results indicate that the impact of NFPs on cell proliferation is negligible. Fluorescence and transmission electron microscopy validated the cellular uptake of NFPs, demonstrating the potential for precise cell positioning through an external magnetic field. Under calcification-inducing conditions, the cells exhibited sustained calcification ability even in the presence of NFPs. The cell movement analysis observed the controlled movement of NFP-absorbing cells under an external magnetic field. Applying a magnetic field along the z-axis induced the three-dimensional shaping of cells incorporating NFPs, resulting in well-arranged z-axis directional patterns. In this study, NFPs demonstrated excellent biocompatibility and controllability under an external magnetic field, laying the foundation for innovative treatment strategies for customizing artificial bones.

Recent advances in nanobiosensors for sustainable healthcare applications: A systematic literature review

The need for novel healthcare treatments and drugs has increased due to the expanding human population, detection of newer diseases, and looming pandemics. The development of nanotechnology offers a platform for cutting-edge in vivo non-invasive monitoring and point-of-care-testing (POCT) for rehabilitative disease detection and management. The advancement and uses of nanobiosensors are currently becoming more common in a variety of scientific fields, such as environmental monitoring, food safety, biomedical, clinical, and sustainable healthcare sciences, since the advent of nanotechnology. The identification and detection of biological patterns connected to any type of disease (communicable or not) have been made possible in recent years by several sensing techniques utilizing nanotechnology concerning biosensors and nanobiosensors. In this work, 2218 articles are drawn and screened from six digital databases out of which 17 were shortlisted for this review by using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) technique. As a result, this study uses a systematic methodology to review some recently developed extremely sensitive nanobiosensors, along with their biomedical, point-of-care diagnostics (POCD), or healthcare applications and their capabilities, particularly for the prediction of some fatal diseases based on a few of the most recent publications. The potential of nanobiosensors for medicinal, therapeutic, or other sustainable healthcare applications, notably for ailments diagnostics, is also recognized as a way forward in the manifestation of future trends.

Future Prospects for Clinical Applications of Nanocarbons Focusing on Carbon Nanotubes

Over the past 15 years, numerous studies have been conducted on the use of nanocarbons as biomaterials towards such applications as drug delivery systems, cancer therapy, and regenerative medicine. However, the clinical use of nanocarbons remains elusive, primarily due to short- and long-term safety concerns. It is essential that the biosafety of each therapeutic modality be demonstrated in logical and well-conducted experiments. Accordingly, the fundamental techniques for assessing nanocarbon biomaterial safety have become more advanced. Optimal controls are being established, nanocarbon dispersal techniques are being refined, the array of biokinetic evaluation methods has increased, and carcinogenicity examinations under strict conditions have been developed. The medical implementation of nanocarbons as a biomaterial is in sight. With a particular focus on carbon nanotubes, these perspectives aim to summarize the contributions to date on nanocarbon applications and biosafety, introduce the recent achievements in evaluation techniques, and clarify the future prospects and systematic introduction of carbon nanomaterials for clinical use through practical yet sophisticated assessment methods.

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.

[Advantages and challenges of carbon nanotubes as bone repair materials]

With the in-depth research on bone repair process, and the progress in bone repair materials preparation and characterization, a variety of artificial bone substitutes have been fully developed in the treatment of bone related diseases such as bone defects. However, the current various natural or synthetic biomaterials are still unable to achieve the structure and properties of natural bone. Carbon nanotubes (CNTs) have provided a new direction for the development of new materials in the field of bone repair due to their excellent structural stability, mechanical properties, and functional group modifiability. Moreover, CNTs and their composites have broad prospects in the design of bone repair materials and as drug delivery carriers. This paper describes the advantages of CNTs related to bone tissue regeneration from the aspects of morphology, chemistry, mechanics, electromagnetism, and biosafety, as well as the application of CNTs in drug delivery carriers and reinforcement components of scaffold materials. In addition, the potential problems and prospects of CNTs in bone regenerative medicine are discussed.

Cellular Responses of Human Lymphatic Endothelial Cells to Carbon Nanomaterials

One of the greatest challenges to overcome in the pursuit of the medical application of carbon nanomaterials (CNMs) is safety. Particularly, when considering the use of CNMs in drug delivery systems (DDSs), evaluation of safety at the accumulation site is an essential step. In this study, we evaluated the toxicity of carbon nanohorns (CNHs), which are potential DDSs, using human lymph node endothelial cells that have been reported to accumulate CNMs, as a comparison to fibrous, multi-walled carbon nanotubes (MWCNTs) and particulate carbon black (CB). The effect of different surface characteristics was also evaluated using two types of CNHs (untreated and oxidized). In the fibrous MWCNT, cell growth suppression, as well as expression of inflammatory cytokine genes was observed, as in previous reports. In contrast, no significant toxicity was observed for particulate CB and CNHs, which was different from the report of CB cytotoxicity in vascular endothelial cells. These results show that (1) lymph endothelial cells need to be tested separately from other endothelial cells for safety evaluation of nanomaterials, and (2) the potential of CNHs as DDSs.

Applications of Carbon Nanotubes in Bone Regenerative Medicine

Scaffolds are essential for bone regeneration due to their ability to maintain a sustained release of growth factors and to provide a place where cells that form new bone can enter and proliferate. In recent years, scaffolds made of various materials have been developed and evaluated. Functionally effective scaffolds require excellent cell affinity, chemical properties, mechanical properties, and safety. Carbon nanotubes (CNTs) are fibrous nanoparticles with a nano-size diameter and have excellent strength and chemical stability. In the industrial field, they are used as fillers to improve the performance of materials. Because of their excellent physicochemical properties, CNTs are studied for their promising clinical applications as biomaterials. In this review article, we focused on the results of our research on CNT scaffolds for bone regeneration, introduced the promising properties of scaffolds for bone regeneration, and described the potential of CNT scaffolds.

Biocompatibility and Carcinogenicity of Carbon Nanotubes as Biomaterials

With the development of nanotechnology in recent years, there have been concerns about the health effects of nanoparticles. Carbon nanotubes (CNTs) are fibrous nanoparticles with a micro-sized length and nano-sized diameter, which exhibit excellent physical properties and are widely studied for their potential application in medicine. However, asbestos has been historically shown to cause pleural malignant mesothelioma and lung cancer by inhalation exposure. Because carbon nanotubes are also fibrous nanotubes, some have raised concerns about its possible carcinogenicity. We have reported that there is no clear evidence of carcinogenicity by local and intravenous administration of multi-walled CNTs to cancer mice models. We firmly believe that CNTs can be a safe, new, and high-performance biomaterials by controlling its type, site of administration, and dosage.

Carbon nanotube-based biomaterials for orthopaedic applications

Carbon nanotubes can enhance the functionality of orthopedic applications.

Different aggregation and shape characteristics of carbon materials affect biological responses in RAW264 cells

Introduction

Carbon nanotubes (CNTs) have various shapes, including needle-like shapes and curled shapes, and the cytotoxicity and carcinogenicity of CNTs differ depending on their shapes and surface modifications. However, the biological responses induced by CNTs and related mechanisms according to the dispersion state of CNTs have not been extensively studied.

Materials and methods

We prepared multiwalled CNTs (MWCNTs) showing different dispersions and evaluated these MWCNTs in RAW264 cells to determine cytotoxicity, cellular uptake, and immune responses. Furthermore, RAW264 cells were also used to compare the cellular uptake and cytotoxicity of fibrous MWCNTs and spherical carbon nanohorns (CNHs) exhibiting the same degree of dispersion.

Results

Our analysis showed that the cellular uptake, localization, and inflammatory responses of MWCNTs differed depending on the dispersion state. Moreover, there were differences in uptake between MWCNTs and CNHs, even showing the same degree of dispersion. These findings suggested that receptors related to cytotoxicity and immune responses differed depending on the aggregated state of MWCNTs and surface modification with a dispersant. Furthermore, our results suggested that the receptors recognized by the cells differed depending on the particle shape.

Conclusion

Therefore, to apply MWCNTs as a biomaterial, it is important to determine the carcinogenicity and toxicity of the CNTs and to examine different biological responses induced by varying shapes, dispersion states, and surface modifications of particles.

Carbon Nanotubes and Other Engineered Nanoparticles Induced Pathophysiology on Mesothelial Cells and Mesothelial Membranes

Nanoparticles have great potential for numerous applications due to their unique physicochemical properties. However, concerns have been raised that they may induce deleterious effects on biological systems. There is accumulating evidence that, like asbestos, inhaled nanomaterials of >5 μm and high aspect ratio (3:1), particularly rod-like carbon nanotubes, may inflict pleural disease including mesothelioma. Additionally, a recent set of case reports suggests that inhalation of polyacrylate/nanosilica could in part be associated with inflammation and fibrosis of the pleura of factory workers. However, the adverse outcomes of nanoparticle exposure to mesothelial tissues are still largely unexplored. In that context, the present review aims to provide an overview of the relevant pathophysiological implications involving toxicological studies describing effects of engineered nanoparticles on mesothelial cells and membranes. In vitro studies primarily emphasize on simulating cellular uptake and toxicity of nanotubes on benign or malignant cell lines. On the other hand, in vivo studies focus on illustrating endpoints of serosal pathology in rodent animal models. From a molecular aspect, some nanoparticle categories are shown to be cytotoxic and genotoxic after acute treatment, whereas chronic incubation may lead to malignant-like transformation. At an organism level, a number of fibrous shaped nanotubes are related with features of chronic inflammation and MWCNT-7 is the only type to consistently inflict mesothelioma.

Accumulation mode particles and LPS exposure induce TLR-4 dependent and independent inflammatory responses in the lung

Background

Accumulation mode particles (AMP) are formed from engine combustion and make up the inhalable vapour cloud of ambient particulate matter pollution. Their small size facilitates dispersal and subsequent exposure far from their original source, as well as the ability to penetrate alveolar spaces and capillary walls of the lung when inhaled. A significant immuno-stimulatory component of AMP is lipopolysaccharide (LPS), a product of Gram negative bacteria breakdown. As LPS is implicated in the onset and exacerbation of asthma, the presence or absence of LPS in ambient particulate matter (PM) may explain the onset of asthmatic exacerbations to PM exposure.

This study aimed to delineate the effects of LPS and AMP on airway inflammation, and potential contribution to airways disease by measuring airway inflammatory responses induced via activation of the LPS cellular receptor, Toll-like receptor 4 (TLR-4).

Methods

The effects of nebulized AMP, LPS and AMP administered with LPS on lung function, cellular inflammatory infiltrate and cytokine responses were compared between wildtype mice and mice not expressing TLR-4.

Results

The presence of LPS administered with AMP appeared to drive elevated airway resistance and sensitivity via TLR-4. Augmented TLR4 driven eosinophilia and greater TNF-α responses observed in AMP-LPS treated mice independent of TLR-4 expression, suggests activation of allergic responses by TLR4 and non-TLR4 pathways larger than those induced by LPS administered alone. Treatment with AMP induced macrophage recruitment independent of TLR-4 expression.

Conclusions

These findings suggest AMP-LPS as a stronger stimulus for allergic inflammation in the airways then LPS alone.

Electronic supplementary material

The online version of this article (10.1186/s12931-017-0701-z) contains supplementary material, which is available to authorized users.

Interactions of the innate immune system with carbon nanotubes

The therapeutic application of nanomaterials requires that they are biocompatible and can reach the desired target. The innate immune system is likely to be the first defence machinery that would recognise the nanomaterials as 'non-self'. A number of studies have addressed the issue of how carbon nanotubes (CNTs) interact with phagocytic cells and their surface receptors that can impact on their intracellular processing and subsequent immune response. In addition, soluble innate immune factors also get involved in the recognition and clearance of CNTs. The interaction of CNTs with the complement system, the most potent and versatile innate immune mechanism, has shed interesting light on how complement activation on the surface of CNTs can modulate their phagocytosis and effector cytokine response. The charge or altered molecular pattern on the surface of CNTs due to functionalization and derivatization can also dictate the level of complement activation and subsequent inflammatory response. It is becoming evident that complement deposition may facilitate phagocytic uptake of CNTs through receptor routes that leads to dampening of pro-inflammatory response by complement-receptor bearing macrophages and B cells. Thus, recombinant complement regulators decorated on the CNT surface can constructively influence the therapeutic strategies involving CNTs and other nanoparticles.

In Vitro and In Vivo Evaluation of a Three-Dimensional Porous Multi-Walled Carbon Nanotube Scaffold for Bone Regeneration

Carbon nanotubes (CNTs) have attracted a great deal of attention for the biological and medical science fields because of their characteristic physical and biological properties. In this study, we investigated the capacity of the 3D porous CNT scaffold (CNT porous block; CNTp) for bone regenerative medicine. Surface observations using a scanning electron microscope (SEM), crystal depositions on the surface of CNTps immersed in simulated body fluid (SBF), and evaluations of protein adsorption and controlled releasing were conducted to assess physical properties. The cell proliferation and cell morphology were observed using SEM and fluorescent microscopy. CNTps were implanted into critical-size mouse calvarial defects and evaluated for their osteoconductive ability and in vivo controlled release of recombinant human BMP-2 (rhBMP-2). Interconnected porous HA ceramics (IP-CHAs) were used for comparison. CNTps have multiporous structures with interporous connections with networks of multiwalled CNTs. Crystals containing calcium and phosphate were deposited in CNTps and on the surface of the CNT networks by immersing CNTps in SBF. CNTps adsorbed more significantly and released protein more gradually than IP-CHAs. Preosteoblasts seeded onto CNTps filled pores with stretched actin filaments and filopodia. Compared with IP-CHAs, CNTps showed significantly higher cell proliferation, better osteoconduction, and more bone generation with rhBMP-2. In this study, CNTps demonstrated good osteoconductive ability, cell attachment and proliferation capacity, and growth factor retaining ability. CNTps have the potential not only as artificial bones for the treatment of bone defects, but also as scaffolds for regenerative medicine using tissue engineering approaches.

The Dispersion State of Tangled Multi-Walled Carbon Nanotubes Affects Their Cytotoxicity

The medical applications of carbon nanotubes (CNTs) have garnered much attention. However, evaluating the safety of CNTs remains difficult, and no consensus has been reached. Moreover, assessing the biosafety of multi-walled CNTs (MWCNTs), which can become tangled during manufacturing, is challenging because they do not readily disperse. We studied how the dispersion state of tangled MWCNTs affects their cytotoxicity, using three sonicators. Flotube 9110 (FT9110), tangled MWCNTs, were dispersed in two dispersants (fetal bovine serum and polysorbate 80) using a new type of sonicator (PR-1) and two conventional sonicators. The size and cytotoxicity of the dispersed FT9110 were measured using the BEAS-2B human bronchial epithelial cell line. The PR-1 dispersed the FT9110 to agglomerates <200 nm in diameter; FT9110 dispersed with the PR-1 did not show cytotoxicity regardless of dispersant. The other sonicators dispersed the FT9110 to particles >1000 nm in diameter, and cytotoxicity depended on the dispersant. We found that excluding cells adhered to agglomerated FT9110 before evaluating cytotoxicity can lead to false-positive results. The PR-1 sonicator dispersed tangled FT9110 to many single fibers, which showed lower cytotoxicity than conventionally-sonicated MWCNTs. We suggest that dispersion state should be accounted for when evaluating the cytotoxicity of MWCNTs.

Deagglomeration of multi-walled carbon nanotubes via an organic modifier: structure and mechanism

We have investigated the agglomeration behaviour of two types of multi-walled carbon nanotubes (MWNTs; N-MWNTs and D-MWNTs), which have different chemical functionalities, average diameter, varying extent of agglomeration and agglomerations. The properties were altered by varying the agglomerated structure. The strength of the MWNT agglomerates was estimated via nanoindentation. The work done to indent D-MWNT agglomerates (3910.3 × 10(-8) erg) was higher than for N-MWNTs agglomerates (2316.4 × 10(-8) erg). An organic modifier, the Li salt of 6-aminohexanoic acid (Li-AHA), was used to deagglomerate the MWNTs in an aqueous medium. The stability of the aqueous dispersion of Li-AHA-modified MWNTs was analyzed by UV-vis spectroscopy and zeta potential measurements. An increase in Li-AHA concentration increased the dispersion of MWNTs in the aqueous medium. Furthermore, the mechanism of dispersion of the two types of MWNTs in the aqueous medium in the presence of Li-AHA was determined based on the electrostatic charge repulsion between the negatively charged species. A fluorescence-activated cell sorting technique was used to assess the debundling of MWNT agglomerates in the aqueous medium. We examined the morphology-property relationship in Li-AHA-modified MWNTs.

Endocytosis of Multiwalled Carbon Nanotubes in Bronchial Epithelial and Mesothelial Cells

Bronchial epithelial cells and mesothelial cells are crucial targets for the safety assessment of inhalation of carbon nanotubes (CNTs), which resemble asbestos particles in shape. Intrinsic properties of multiwalled CNTs (MWCNTs) are known to cause potentially hazardous effects on intracellular and extracellular pathways. These interactions alter cellular signaling and affect major cell functions, resulting in cell death, lysosome injury, reactive oxygen species production, apoptosis, and cytokine release. Furthermore, CNTs are emerging as a novel class of autophagy inducers. Thus, in this study, we focused on the mechanisms of MWCNT uptake into the human bronchial epithelial cells (HBECs) and human mesothelial cells (HMCs). We verified that MWCNTs are actively internalized into HBECs and HMCs and were accumulated in the lysosomes of the cells after 24-hour treatment. Next, we determined which endocytosis pathways (clathrin-mediated, caveolae-mediated, and macropinocytosis) were associated with MWCNT internalization by using corresponding endocytosis inhibitors, in two nonphagocytic cell lines derived from bronchial epithelial cells and mesothelioma cells. Clathrin-mediated endocytosis inhibitors significantly suppressed MWCNT uptake, whereas caveolae-mediated endocytosis and macropinocytosis were also found to be involved in MWCNT uptake. Thus, MWCNTs were positively taken up by nonphagocytic cells, and their cytotoxicity was closely related to these three endocytosis pathways.

Toxicology of wear particles of cobalt-chromium alloy metal-on-metal hip implants Part II: Importance of physicochemical properties and dose in animal and in vitro studies as a basis for risk assessment

The objective of the Part II analysis was to evaluate animal and in vitro toxicology studies of CoCr particles with respect to their physicochemistry and dose relevance to metal-on-metal (MoM) implant patients as derived from Part I. In the various toxicology studies, physicochemical characteristics were infrequently considered and administered doses were orders of magnitude higher than what occurs in patients. Co was consistently shown to rapidly release from CoCr particles for distribution and elimination from the body. CoCr micron sized particles appear more biopersistent in vivo resulting in inflammatory responses that are not seen with similar mass concentrations of nanoparticles. We conclude, that in an attempt to obtain data for a complete risk assessment, future studies need to focus on physicochemical characteristics of nano and micron sized particles and on doses and dose metrics relevant to those generated in patients or in properly conducted hip simulator studies.

Inhalation Exposure to Carbon Nanotubes (CNT) and Carbon Nanofibers (CNF): Methodology and Dosimetry

Carbon nanotubes (CNT) and nanofibers (CNF) are used increasingly in a broad array of commercial products. Given current understandings, the most significant life-cycle exposures to CNT/CNF occur from inhalation when they become airborne at different stages of their life cycle, including workplace, use, and disposal. Increasing awareness of the importance of physicochemical properties as determinants of toxicity of CNT/CNF and existing difficulties in interpreting results of mostly acute rodent inhalation studies to date necessitate a reexamination of standardized inhalation testing guidelines. The current literature on pulmonary exposure to CNT/CNF and associated effects is summarized; recommendations and conclusions are provided that address test guideline modifications for rodent inhalation studies that will improve dosimetric extrapolation modeling for hazard and risk characterization based on the analysis of exposure-dose-response relationships. Several physicochemical parameters for CNT/CNF, including shape, state of agglomeration/aggregation, surface properties, impurities, and density, influence toxicity. This requires an evaluation of the correlation between structure and pulmonary responses. Inhalation, using whole-body exposures of rodents, is recommended for acute to chronic pulmonary exposure studies. Dry powder generator methods for producing CNT/CNF aerosols are preferred, and specific instrumentation to measure mass, particle size and number distribution, and morphology in the exposure chambers are identified. Methods are discussed for establishing experimental exposure concentrations that correlate with realistic human exposures, such that unrealistically high experimental concentrations need to be identified that induce effects under mechanisms that are not relevant for workplace exposures. Recommendations for anchoring data to results seen for positive and negative benchmark materials are included, as well as periods for postexposure observation. A minimum data set of specific bronchoalveolar lavage parameters is recommended. Retained lung burden data need to be gathered such that exposure-dose-response correlations may be analyzed and potency comparisons between materials and mammalian species are obtained considering dose metric parameters for interpretation of results. Finally, a list of research needs is presented to fill data gaps for further improving design, analysis, and interpretation and extrapolation of results of rodent inhalation studies to refine meaningful risk assessments for humans.

Reducing the cytotoxicity of ZnO nanoparticles by a pre-formed protein corona in a supplemented cell culture medium

The safety of zinc oxide (ZnO) nanoparticles (NPs) remains a critical concern considering that they are a common constituent in cosmetics and sunscreen formulation.

The role of autophagy as a mechanism of toxicity induced by multi-walled carbon nanotubes in human lung cells

Carbon nanotubes (CNTs) are promising nanomaterials having unique physical and chemical properties, with applications in a variety of fields. In this review, we briefly summarize the intrinsic properties of highly purified multi-walled CNTs (MWCNTs, HTT2800) and their potential hazardous effects on intracellular and extracellular pathways, which alter cellular signaling and impact major cell functions such as differentiation, reactive oxygen species (ROS) production, apoptosis, and autophagy. A recent study suggested that the induction of autophagy by CNTs causes nanotoxicity. Autophagy was recently recognized as a critical cell death pathway, and autophagosome accumulation has been found to be associated with exposure to CNTs. Although autophagy is considered as a cytoprotective process, it is often observed in association with cell death, and the relationship between autophagy and cell death remains unclear. Our recent study suggests that the levels of autophagy-related genes (LC3B) and autophagosome formation are clearly up-regulated, along with an increase in numbers of autophagosome vacuoles. This review highlights the importance of autophagy as an emerging mechanism of CNT toxicity.

Pulmonary toxicity of nanomaterials: a critical comparison of published in vitro assays and in vivo inhalation or instillation studies

To date, guidance on how to incorporate in vitro assays into integrated approaches for testing and assessment of nanomaterials is unavailable. In addressing this shortage, this review compares data from in vitro studies to results from in vivo inhalation or intratracheal instillation studies. Globular nanomaterials (ion-shedding silver and zinc oxide, poorly soluble titanium dioxide and cerium dioxide, and partly soluble amorphous silicon dioxide) and nanomaterials with higher aspect ratios (multiwalled carbon nanotubes) were assessed focusing on the Organisation for Economic Co-Operation and Development (OECD) reference nanomaterials for these substances. If in vitro assays are performed with dosages that reflect effective in vivo dosages, the mechanisms of nanomaterial toxicity can be assessed. In early tiers of integrated approaches for testing and assessment, knowledge on mechanisms of toxicity serves to group nanomaterials thereby reducing the need for animal testing.

Instillation versus inhalation of multiwalled carbon nanotubes: exposure-related health effects, clearance, and the role of particle characteristics

Inhaled multiwalled carbon nanotubes (MWCNTs) may cause adverse pulmonary responses due to their nanoscale, fibrous morphology and/or biopersistance. This study tested multiple factors (dose, time, physicochemical characteristics, and administration method) shown to affect MWCNT toxicity with the hypothesis that these factors will influence significantly different responses upon MWCNT exposure. The study is unique in that (1) multiple administration methods were tested using particles from the same stock; (2) bulk MWCNT formulations had few differences (metal content, surface area/functionalization); and (3) MWCNT retention was quantified using a specialized approach for measuring unlabeled MWCNTs in rodent lungs. Male Sprague-Dawley rats were exposed to original (O), purified (P), and carboxylic acid functionalized (F) MWCNTs via intratracheal instillation and inhalation. Blood, bronchoalveolar lavage fluid (BALF), and lung tissues were collected at postexposure days 1 and 21 for quantifying biological responses and MWCNTs in lung tissues by programmed thermal analysis. At day 1, MWCNT instillation produced significant BALF neutrophilia and MWCNT-positive macrophages. Instilled O- and P-MWCNTs produced significant inflammation in lung tissues, which resolved by day 21 despite MWCNT retention. MWCNT inhalation produced no BALF neutrophilia and no significant histopathology past day 1. However, on days 1 and 21 postinhalation of nebulized MWCNTs, significantly increased numbers of MWCNT-positive macrophages were observed in BALF. Results suggest (1) MWCNTs produce transient inflammation if any despite persistence in the lungs; (2) instilled O-MWCNTs cause more inflammation than P- or F-MWCNTs; and (3) MWCNT suspension media produce strikingly different effects on physicochemical particle characteristics and pulmonary responses.

Lung burdens and kinetics of multi-walled carbon nanotubes (Baytubes) are highly dependent on the disaggregation of aerosolized MWCNT

Previous repeated inhalation exposure studies on rats with multi-walled carbon nanotubes (MWCNT, Baytubes®) suggested that their pulmonary toxicity was predominated by the morphology and density of the aggregated structure. Evidence of any disintegration of these structures in the lung did not exist. The objective of this study was to study as to which extent the formulation of pristine MWCNT as wet-dispersion changes the morphology of assemblage structures in the presence of disintegrated sub-structures. The focus was on the comparative inhalation dosimetry and kinetics of dry- and wet-dispersed Baytubes to better understand the cause of putative differences in pulmonary toxicity originating from pristine and rigorously formulated MWCNT. Rats were nose-only exposed to dry-dispersed and wet-dispersed Baytubes for 6-h at 25-30 mg/m(3). Aerodynamic particle size measurements demonstrate substantial differences in the particle size of dry- (MMAD 2.6 µm) and wet-dispersed (MMAD 0.8 µm) MWCNT. Time-course changes of MWCNT retained in the lung were examined during a post-exposure period of 3 months. Lung burdens were analytically determined in digested lungs using the EC/OC total carbon method. Dosimetry was complemented by light and transmission electron microscopy (TEM) of MWCNT retained in alveolar macrophages (AM). As a result, the initially deposited pulmonary dose of MWCNT was three times higher following wet-dispersed MWCNT at essentially similar inhalation chamber concentrations. The elimination half-time of dry- and wet-dispersed MWCNT was 87 and 46 d, respectively. TEM provided evidence that wet-dispersed MWCNT were inhaled as disintegrated structures with distribution-patterns within the cytoplasm of AMs that differed appreciably from those of dry-dust exposed animals. In summary, this study shows that specialized technical processes to formulate MWCNT may have dramatic consequences on their pulmonary fate and associated toxicity. Such properties can only be revealed by the comparison of pulmonary toxicity with pulmonary (micro-)dosimetry and kinetics.

Range-finding risk assessment of inhalation exposure to nanodiamonds in a laboratory environment

This study considers fundamental methods in occupational risk assessment of exposure to airborne engineered nanomaterials. We discuss characterization of particle emissions, exposure assessment, hazard assessment with in vitro studies, and risk range characterization using calculated inhaled doses and dose-response translated to humans from in vitro studies. Here, the methods were utilized to assess workers' risk range of inhalation exposure to nanodiamonds (NDs) during handling and sieving of ND powder. NDs were agglomerated to over 500 nm particles, and mean exposure levels of different work tasks varied from 0.24 to 4.96 µg·m(-3) (0.08 to 0.74 cm(-3)). In vitro-experiments suggested that ND exposure may cause a risk for activation of inflammatory cascade. However, risk range characterization based on in vitro dose-response was not performed because accurate assessment of delivered (settled) dose on the cells was not possible. Comparison of ND exposure with common pollutants revealed that ND exposure was below 5 μg·m(-3), which is one of the proposed exposure limits for diesel particulate matter, and the workers' calculated dose of NDs during the measurement day was 74 ng which corresponded to 0.02% of the modeled daily (24 h) dose of submicrometer urban air particles.

Vascular Tissue Contractility Changes Following Late Gestational Exposure to Multi-Walled Carbon Nanotubes or their Dispersing Vehicle in Sprague Dawley Rats

Multi-walled carbon nanotubes (MWCNTs) are increasingly used in industry and in nanomedicine raising safety concerns, especially during unique life-stages such as pregnancy. We hypothesized that MWCNT exposure during pregnancy will increase vascular tissue contractile responses by increasing Rho kinase signaling. Pregnant (17-19 gestational days) and non-pregnant Sprague Dawley rats were exposed to 100 μg/kg of MWCNTs by intratracheal instillation or intravenous administration. Vasoactive responses of uterine, mesenteric, aortic and umbilical vessels were studied 24 hours post-exposure by wire myography. The contractile responses of the vessel segments were different between the pregnant and non-pregnant rats, following MWCNT exposure. Maximum stress generation in the uterine artery segments from the pregnant rats following pulmonary MWCNT exposure was increased in response to angiotensin II by 4.9 mN/mm² (+118%), as compared to the naïve response and by 2.6 mN/mm² (+40.7%) as compared to the vehicle exposed group. Following MWCNT exposure, serotonin induced approximately 4 mN/mm² increase in stress generation of the mesenteric artery from both pregnant and non-pregnant rats as compared to the vehicle response. A significant contribution of the dispersion medium was identified as inducing changes in the contractile properties following both pulmonary and intravenous exposure to MWCNTs. Wire myographic studies in the presence of a Rho kinase inhibitor and RhoA and Rho kinase mRNA/protein expression of rat aortic endothelial cells were unaltered following exposure to MWCNTs, suggesting absent/minimal contribution of Rho kinase to the enhanced contractile responses following MWCNT exposure. The reactivity of the umbilical vein was not changed; however, mean fetal weight gain was reduced with dispersion media and MWCNT exposure by both routes. These results suggest a susceptibility of the vasculature during gestation to MWCNT and their dispersion media-induced vasoconstriction, predisposing reduced fetal growth during pregnancy.

Biological responses according to the shape and size of carbon nanotubes in BEAS-2B and MESO-1 cells

This study aimed to investigate the influence of the shape and size of multi-walled carbon nanotubes (MWCNTs) and cup-stacked carbon nanotubes (CSCNTs) on biological responses in vitro. Three types of MWCNTs – VGCF^®-X, VGCF^®-S, and VGCF^® (vapor grown carbon fibers; with diameters of 15, 80, and 150 nm, respectively) – and three CSCNTs of different lengths (CS-L, 20–80 μm; CS-S, 0.5–20 μm; and CS-M, of intermediate length) were tested. Human bronchial epithelial (BEAS-2B) and malignant pleural mesothelioma cells were exposed to the CNTs (1–50 μg/mL), and cell viability, permeability, uptake, total reactive oxygen species/superoxide production, and intracellular acidity were measured. CSCNTs were less toxic than MWCNTs in both cell types over a 24-hour exposure period. The cytotoxicity of endocytosed MWCNTs varied according to cell type/size, while that of CSCNTs depended on tube length irrespective of cell type. CNT diameter and length influenced cell aggregation and injury extent. Intracellular acidity increased independently of lysosomal activity along with the number of vacuoles in BEAS-2B cells exposed for 24 hours to either CNT (concentration, 10 μg/mL). However, total reactive oxygen species/superoxide generation did not contribute to cytotoxicity. The results demonstrate that CSCNTs could be suitable for biological applications and that CNT shape and size can have differential effects depending on cell type, which can be exploited in the development of highly specialized, biocompatible CNTs.

Drug-loading capacity and nuclear targeting of multiwalled carbon nanotubes grafted with anionic amphiphilic copolymers

In this study, three types of hybrid nanotubes (NTs), ie, oxidized multiwalled carbon NTs (COOH MWCNTs), heparin (Hep)-conjugated MWCNTs (Hep MWCNTs), and diblock copolymer polyglycolic acid (PGA)-co-heparin conjugated to MWCNTs (PGA MWCNTs), were synthesized with improved biocompatibility and drug-loading capacity. Hydrophilic Hep substituents on MWCNTs improved biocompatibility and acted as nucleus-sensitive segments on the CNT carrier, whereas the addition of PGA enhanced drug-loading capacity. In the PGA MWCNT system, the amphiphilic copolymer (PGA-Hep) formed micelles on the side walls of CNTs, as confirmed by electron microscopy. The PGA system encapsulated the hydrophobic drug with high efficiency compared to the COOH MWCNT and Hep MWCNT systems. This is because the drug was loaded onto the PGA MWCNTs through hydrophobic forces and onto the CNTs by π-π stacking interactions. Additionally, most of the current drug-carrier designs that target cancer cells release the drug in the lysosome or cytoplasm. However, nuclear-targeted drug release is expected to kill cancer cells more directly and efficiently. In our study, PGA MWCNT carriers effectively delivered the active anticancer drug doxorubicin into targeted nuclei. This study may provide an effective strategy for the development of carbon-based drug carriers for nuclear-targeted drug delivery.

Highly purified, multi-wall carbon nanotubes induce light-chain 3B expression in human lung cells

Bronchial epithelial cells are targets of inhalation and play a critical role in the maintenance of mucosal integrity as mechanical barriers against various particles. Our previous result suggest that vapor-grown carbon fiber, HTT2800, which is one of the most highly purified multi-wall carbon nanotubes (MWCNT) showed cellular uptake of the carbon nanotube, increased cell death, enhanced DNA damage, and induced cytokine release. Increasing evidence suggests that autophagy may critically influence vital cellular processes such as apoptosis, cell proliferation and inflammation and thereby may play a critical role in pulmonary diseases. Autophagy was recently recognized as a critical cell death pathway, and autophagosome accumulation has been found to be associated with the exposure of various nanoparticles. In this study, the authors focus on the autophagic responses of HTT2800 exposure. The HTT2800-exposed cells induced LC3B expression and induced cell growth inhibition.

Metabolic characterization of cell systems used in in vitro toxicology testing: lung cell system BEAS-2B as a working example

The bioactivation of pro-toxicants is the biological process through which some chemicals are metabolized into reactive metabolites. Therefore, in vitro toxicological evaluation should ideally be conducted in cell systems retaining adequate metabolic competency and relevant to the route of exposure. The respiratory tract is the primary route of exposure to inhaled pro-toxicants and lung-derived BEAS-2B cell line has been considered as a potentially suitable model for in vitro toxicology testing. However, its metabolic activity has not been characterized. We performed a gene expression analysis for 41 metabolism-related genes and compared the profile with liver- and lung-derived cell lines (HepaRG, HepG2 and A549). To confirm that mRNA expression was associated with the corresponding enzyme activity, we used a series of metabolic substrates of CYPs (CYP1A1/1B1, CYP1A2, CYP2A6/2A13 and CYP2E1) known to bioactivate inhaled pro-toxicants. CYP activities were compared between BEAS-2B, HepaRG, HepG2, and A549 cells and published literature on primary bronchial epithelium cells (HBEC). We found that in contrast to HBEC, BEAS-2B and A549 have limited CYP activity which was in agreement with their CYP gene expression profile. Control cell lines such as HepG2 and HepaRG were metabolically active for the tested CYPs. We recommend that similar strategies can be used to select suitable cell systems in the context of pro-toxicant assessment.

Genotoxicity of short single-wall and multi-wall carbon nanotubes in human bronchial epithelial and mesothelial cells in vitro

Although some types of carbon nanotubes (CNTs) have been described to induce mesothelioma in rodents and genotoxic effects in various cell systems, there are few previous studies on the genotoxicity of CNTs in mesothelial cells. Here, we examined in vitro DNA damage induction by short multi-wall CNTs (MWCNTs; 10-30 nm × 1-2 μm) and single-wall CNTs (SWCNTs; >50% SWCNTs, ~40% other CNTs; <2 nm × 1-5 μm) in human mesothelial (MeT-5A) cells and bronchial epithelial (BEAS 2B) cells, using the single cell gel electrophoresis (comet) assay and the immunoslot blot assay for the detection of malondialdehyde (M1dG) DNA adducts. In BEAS 2B cells, we also studied the induction of micronuclei (MN) by the CNTs using the cytokinesis-block method. The cells were exposed to the CNTs (5-200 μg/cm(2), corresponding to 19-760 μg/ml) for 24 and 48h in the comet assay and for 48 and 72 h in the MN and M1dG assays. Transmission electron microscopy (TEM) showed more MWCNT fibres and SWCNT clusters in BEAS 2B than MeT-5A cells, but no significant differences were seen in intracellular dose expressed as area of SWCNT clusters between TEM sections of the cell lines. In MeT-5A cells, both CNTs caused a dose-dependent induction of DNA damage (% DNA in comet tail) in the 48-h treatment and SWCNTs additionally in the 24-h treatment, with a statistically significant increase at 40 μg/cm(2) of SWCNTs and (after 48 h) 80 μg/cm(2) of both CNTs. SWCNTs also elevated the level of M1dG DNA adducts at 1, 5, 10 and 40 μg/cm(2) after the 48-h treatment, but both CNTs decreased M1dG adduct level at several doses after the 72-h treatment. In BEAS 2B cells, SWCNTs induced a statistically significant increase in DNA damage at 80 and 120 μg/cm(2) after the 24-h treatment and in M1dG adduct level at 5 μg/cm(2) after 48 h and 10 and 40 μg/cm(2) after 72 h; MWCNTs did not affect the level of DNA damage but produced a decrease in M1dG adducts in the 72-h treatment. The CNTs did not affect the level of MN. In conclusion, MWCNTs and SWCNTs induced DNA damage in MeT-5A cells but showed a lower (SWCNTs) or no (MWCNTs) effect in BEAS 2B cells, suggesting that MeT-5A cells were more sensitive to the DNA-damaging effect of CNTs than BEAS 2B cells, despite the fact that more CNT fibres or clusters were seen in BEAS 2B than MeT-5A cells. M1dG DNA adducts were induced by SWCNTs but decreased after a 3-day exposure to MWCNTs and (in MeT-5A cells) SWCNTs, indicating that CNTs may lead to alterations in oxidative effects within the cells. Neither of the CNTs was able to produce chromosomal damage (MN).

Mechanistic insights into nanotoxicity determined by synchrotron radiation-based Fourier-transform infrared imaging and multivariate analysis

Our ability to identify the mechanisms by which carbon-based nanomaterials (CBNs) exert toxicity in cells is constrained by the lack of standardized methodologies to assay endpoint effects. Herein we describe a method of mechanistically identifying the effects of various CBN types in both prokaryotic and eukaryotic cells using multi-beam synchrotron radiation-based Fourier-transform infrared imaging (SR-FTIRI) at diffraction-limited resolution. This technique overcomes many of the inherent difficulties of assaying nanotoxicity and demonstrates exceptional sensitivity in identifying the effects of CBNs in cells at environmentally-relevant concentrations. We identify key mechanisms of nanotoxicity as the alteration of Amide and lipid biomolecules, but propose more specific bioactivity of CBNs occurs as a result of specific interactions between CBN structural conformation and cellular characteristics.

Effects of the presence or absence of a protein corona on silica nanoparticle uptake and impact on cells

Nanoparticles enter cells through active processes, thanks to their capability of interacting with the cellular machinery. The protein layer (corona) that forms on their surface once nanoparticles are in contact with biological fluids, such as the cell serum, mediates the interactions with cells in situ. As a consequence of this, here we show that the same nanomaterial can lead to very different biological outcomes, when exposed to cells in the presence or absence of a preformed corona. In particular, silica nanoparticles exposed to cells in the absence of serum have a stronger adhesion to the cell membrane and higher internalization efficiency, in comparison to what is observed in medium containing serum, when a preformed corona is present on their surface. The different exposure conditions not only affect the uptake levels but also result in differences in the intracellular nanoparticle location and impact on cells. Interestingly, we also show that after only one hour of exposure, a corona of very different nature forms on the nanoparticles exposed to cells in the absence of serum. Evidence suggests that these different outcomes can all be connected to the different adhesion and surface properties in the two conditions.

Differences and similarities between carbon nanotubes and asbestos fibers during mesothelial carcinogenesis: shedding light on fiber entry mechanism

The emergence of nanotechnology represents an important milestone, as it opens the way to a broad spectrum of applications for nanomaterials in the fields of engineering, industry and medicine. One example of nanomaterials that have the potential for widespread use is carbon nanotubes, which have a tubular structure made of graphene sheets. However, there have been concerns that they may pose a potential health risk due to their similarities to asbestos, namely their high biopersistence and needle-like structure. We recently found that despite these similarities, carbon nanotubes and asbestos differ in certain aspects, such as their mechanism of entry into mesothelial cells. In the study, we showed that non-functionalized, multi-walled carbon nanotubes enter mesothelial cells by directly piercing through the cell membrane in a diameter- and rigidity-dependent manner, whereas asbestos mainly enters these cells through the process of endocytosis, which is independent of fiber diameter. In this review, we discuss the key differences, as well as similarities, between asbestos fibers and carbon nanotubes. We also summarize previous reports regarding the mechanism of carbon nanotube entry into non-phagocytic cells. As the entry of fibers into mesothelial cells is a crucial step in mesothelial carcinogenesis, we believe that a comprehensive study on the differences by which carbon nanotubes and asbestos fibers enter into non-phagocytic cells will provide important clues for the safer manufacture of carbon nanotubes through strict regulation on fiber characteristics, such as diameter, surface properties, length and rigidity.

Elucidation mechanism of different biological responses to multi-walled carbon nanotubes using four cell lines

We examined differences in cellular responses to multi-walled carbon nanotubes (MWCNTs) using malignant pleural mesothelioma cells (MESO-1), bronchial epithelial cells (BEAS-2B), neuroblastoma cells (IMR-32), and monoblastic cells (THP-1), before and after differentiation. MESO-1, BEAS-2B and differentiated THP-1 cells actively endocytosed MWCNTs, resulting in cytotoxicity with lysosomal injury. However, cytotoxicity did not occur in IMR-32 or undifferentiated THP-1 cells. Both differentiated and undifferentiated THP-1 cells exhibited an inflammatory response. Carbon blacks were endocytosed by the same cell types without lysosomal damage and caused cytokine secretion, but they did not cause cytotoxicity. These results indicate that the cytotoxicity of MWCNTs requires not only cellular uptake but also lysosomal injury. Furthermore, it seems that membrane permeability or cytokine secretion without cytotoxicity results from several active mechanisms. Clarification of the cellular recognition mechanism for MWCNTs is important for developing safer MWCNTs.