Mechanisms of pulmonary toxicity and medical applications of carbon nanotubes: Two faces of Janus?

Occupational nanosafety considerations for carbon nanotubes and carbon nanofibers

Carbon nanotubes (CNTs) are carbon atoms arranged in a crystalline graphene lattice with a tubular morphology. CNTs exhibit high tensile strength, possess unique electrical properties, are durable, and can be functionalized. These properties allow applications as structural materials, in electronics, as heating elements, in batteries, in the production of stain-resistant fabric, for bone grafting and dental implants, and for targeted drug delivery. Carbon nanofibers (CNFs) are strong, flexible fibers that are currently used to produce composite materials. Agitation can lead to aerosolized CNTs and CNFs, and peak airborne particulate concentrations are associated with workplace activities such as weighing, transferring, mixing, blending, or sonication. Most airborne CNTs or CNFs found in workplaces are loose agglomerates of micrometer diameter. However, due to their low density, they linger in workplace air for a considerable time, and a large fraction of these structures are respirable. In rat and mouse models, pulmonary exposure to single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or CNFs causes the following pulmonary reactions: acute pulmonary inflammation and injury, rapid and persistent formation of granulomatous lesions at deposition sites of large CNT agglomerates, and rapid and progressive alveolar interstitial fibrosis at deposition sites of more dispersed CNT or CNF structures. Pulmonary exposure to SWCNTs can induce oxidant stress in aortic tissue and increases plaque formation in an atherosclerotic mouse model. Pulmonary exposure to MWCNTs depresses the ability of coronary arterioles to respond to dilators. These cardiovascular effects may result from neurogenic signals from sensory irritant receptors in the lung. Pulmonary exposure to MWCNTs also upregulates mRNA for inflammatory mediators in selected brain regions, and pulmonary exposure to SWCNTs upregulates the baroreceptor reflex. In addition, pulmonary exposure to MWCNTs may induce levels of inflammatory mediators in the blood, which may affect the cardiovascular system. Intraperitoneal instillation of MWCNTs in mice has been associated with abdominal mesothelioma. MWCNTs deposited in the distal alveoli can migrate to the intrapleural space, and MWCNTs injected in the intrapleural space can cause lesions at the parietal pleura. However, further studies are required to determine whether pulmonary exposure to MWCNTs can induce pleural lesions or mesothelioma. In light of the anticipated growth in the production and use of CNTs and CNFs, worker exposure is possible. Because pulmonary exposure to CNTs and CNFs causes inflammatory and fibrotic reactions in the rodent lung, adverse health effects in workers represent a concern. NIOSH has conducted a risk assessment using available animal exposure-response data and is developing a recommended exposure limit for CNTs and CNFs. Evidence indicates that engineering controls and personal protective equipment can significantly decrease workplace exposure to CNTs and CNFs. Considering the available data on health risks, it appears prudent to develop prevention strategies to minimize workplace exposure. These strategies would include engineering controls (enclosure, exhaust ventilation), worker training, administrative controls, implementation of good handling practices, and the use of personal protective equipment (such as respirators) when necessary. NIOSH has published a document containing recommendations for the safe handling of nanomaterials.

Systematic safety evaluation on photoluminescent carbon dots

Photoluminescent carbon dots (C-dots) were prepared using the improved nitric acid oxidation method. The C-dots were characterized by tapping-mode atomic force microscopy, and UV-vis absorption spectroscopy. The C-dots were subjected to systematic safety evaluation via acute toxicity, subacute toxicity, and genotoxicity experiments (including mouse bone marrow micronuclear test and Salmonella typhimurium mutagenicity test). The results showed that the C-dots were successfully prepared with good stability, high dispersibility, and water solubility. At all studied C-dot dosages, no significant toxic effect, i.e., no abnormality or lesion, was observed in the organs of the animals. Therefore, the C-dots are non-toxic to mice under any dose and have potential use in fluorescence imaging in vivo, tumor cell tracking, and others.

Stimulation of production of reactive oxygen and nitrogen species in endothelial cells by unmodified and Fenton-modified ultradisperse detonation diamond

In recent years, the development of nanotechnology opens up new prospects for biomedical applications of unmodified and chemically modified diamond nanoparticles (DNPs). The problem of biocompatibility of DNPs is thus of primary importance. The first step in the modification of DNPs is usually the introduction of -OH groups, which can bind other functional groups. One of the basic methods to introduce -OH groups onto DNPs is the Fenton reaction. The aim of this study was to compare the effect of unmodified DNPs and nanoparticles modified by the Fenton reaction on human endothelial cells. Ultradisperse diamond (UDD) was modified by the Fenton reaction introducing surface -OH groups. Immortalized human umbilical cord endothelial cells (HUVEC-ST) were incubated with 2-100 µg/mL nanopowders in the opti-MEM medium. For comparison, graphite powder (GRAF and GRAF+OH) was also employed. UDD and GRAF augmented generation of reactive oxygen species in the cells after 24 H incubation, estimated by oxidation of 2',7'-dichlorofluorescin diacetate (H2DCF-DA). Cellular production of nitric oxide, estimated with DAF-FM-DA (3-amino-4-aminomethyl 2',7'-dichlorofluorescein diacetate), was also affected by UDD and GRAF after 24 H. Fenton-modified OH, in contrast to unmodified diamond, decreased NO production. Detonation nanoparticles also affected the cellular content of glutathione and activities of main antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione S-transferase). This article was published online on 5 February 2013. Errors in the byline and affiliation line were subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected 18 April 2013.

Deriving TC50 values of nanoparticles from electrochemical monitoring of lactate dehydrogenase activity indirectly

Nanotoxicity assessment methods for nanoparticles (NPs) such as carbon nanotubes (CNTs), nano-Al(2)O(3), and tridecameric aluminum polycation or nanopolynuclear (nano-Al(13)), particularly lactate dehydrogenase (LDH) assays are reviewed. Our researches on electrochemically monitoring the variations of LDH activity indirectly in the presence of multiwalled carbon nanotubes (MWCNTs), nano-Al(13), and nano-Al(2)O(3) separately to derive toxic concentrations of NPs altering LDH activity by 50% (TC(50)) values are discussed. TC(50) values indicated that the toxicity order was Al (III)> MWCNTs > nano-Al(13) > nano-Al(2)O(3). Zeta potentials (ζ) data of these NPs in the literature proved that the surfaces of these NPs are charged negatively. Negatively charged surfaces might be a main cause in the reduction of LDH activity. Therefore, the classic LDH assays are doubtful to underestimate the nanotoxicities when they are applied to those NPs with negatively charged surfaces. These observations highlight and reconcile some contradictory results at present such as medium-dependent toxicity of NPs among the literature and develop novel analytical methods for evaluation of toxicities of NPs.

Carbon nanotube-based multi electrode arrays for neuronal interfacing: progress and prospects

Carbon nanotube (CNT) coatings have been demonstrated over the past several years as a promising material for neuronal interfacing applications. In particular, in the realm of neuronal implants, CNTs have major advantages owing to their unique mechanical and electrical properties. Here we review recent investigations utilizing CNTs in neuro-interfacing applications. Cell adhesion, neuronal engineering and multi electrode recordings with CNTs are described. We also highlight prospective advances in this field, in particular, progress toward flexible, bio-compatible CNT-based technology.

Nanoparticle filtration performance of filtering facepiece respirators and canister/cartridge filters

Respiratory protection offered by a particulate respirator is a function of the filter efficiency and face seal leakage. A previous study in our laboratory measured the filter penetration and total inward leakage (TIL) of 20-1000 nm size particles for N95 filtering facepiece respirators (FFRs) using a breathing manikin. The results showed relatively higher filter penetration and TIL value under different leak sizes and flow rates at the most penetrating particle size (MPPS), ∼45 nm for electrostatic FFRs,and ∼150 nm for the same FFRs after charge removal. This indicates an advantage of mechanical filters over electrostatic filters rated for similar filter efficiencies in providing respiratory protection in nanoparticle workplaces. To better understand the influence of the MPPS, the filtration performance of commonly used one N95 and one N100 FFR models, and four P100 canister/cartridge models were measured with monodisperse NaCl aerosols, and polydisperse NaCl aerosols employed in the National Institute for Occupational Safety and Health (NIOSH) certification test method. As expected, the polydisperse aerosol penetration was below 5% for the N95 FFR, and below 0.03% for the N100 FFR and P100 canister/cartridge filters. Monodisperse aerosol penetration results showed a MPPS of ∼40 nm for both the N95 and N100 FFRs. All four P100 canister/cartridge filters had a MPPS of ≥150 nm, similar to expectations for mechanical filters. The P100 canister/cartridge filters showed lower penetration values for different size nanoparticles than the N100 FFRs. The results indicate that a mechanical filter would offer a relatively higher filtration performance for nanoparticles than an electrostatic counterpart rated for the same filter efficiency. Overall, the results obtained in the study suggest that MPPS should be considered as a key factor in the development of respirator standards and recommendations for protection against nanoparticles.

Toxicity of novel nanosized formulations used in medicine

Nanotechnology involves the creation and manipulation of materials at nanoscale levels (1-100 nm) to create products that exhibit novel properties. While this motivation has driven nanoscience and technology in physics and engineering, it is not the main reason that nanoparticles are useful for systemic applications in the human body. The application of nanotechnology to medicine, known as nanomedicine, concerns the use of precisely engineered materials at this length scale to develop novel therapeutic and diagnostic modalities. A number of nanotherapeutic formulations are already approved for medical use and more are in the approval pipeline currently. This chapter is intended to provide an overview of the toxicity of these therapeutic nanoparticles and to summarize the current state of the field. We begin with background on the sources of exposure to nanoparticles, followed by reviewing different forms of nanosized therapeutic tools as quantum dots, nanoshells, nanocapsules, echogenic bubble, and "nanoshuttles." Moreover, cytotoxic effects of nanoparticles on cell membrane, mitochondrial function, prooxidant/antioxidant status, enzyme leakage, DNA, and other biochemical endpoints were elucidated. We highlight the need for caution during the use and disposal of such manufactured nanomaterials to prevent unintended environmental impacts. Moreover, different strategies which could be used to minimize or eliminate nanotoxicity were also discussed in detail. Understanding of how to tune size and surface properties to provide safety will permit the creation of new, more effective nanomedicines for systemic use.

Synthesis of Isatin Derivative on the Short Multiwalled Carbon Nanotubes and Their Effect on the MKN-45 and SW742 Cancer Cells

The carboxylated short multiwalled carbon nanotubes (Sh-MWCNT-COOH) were first modified by isatin derivative to form Sh-MWCNT-Amide and then by hydrazine to produce Sh-MWCNT-Spiro. All products were characterized by the Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscope, elemental analysis, thermogravimetric analysis, derivative thermogravimetric, solubility test, and cellular investigations. This functionalization has been chosen due to active sites of OH and carbonyl groups in Sh-MWCNT-Amide which might be used as functional materials in the future. Toxicity of these samples was evaluated with human gastric and colon cancer cells, and killed cell numbers were measured by reduction of living cells with 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide. Cellular results showed high toxicity of Sh-MWCNT-Amide in all samples investigated.

Combined effects of direct current stimulation and immobilized BMP-2 for enhancement of osteogenesis

Direct current (DC) stimulation has been used to promote bone repair and osteogenesis, but problems associated with the implanted metal electrodes may limit its application and compromise the therapeutic results. The replacement of the metal electrodes with a biodegradable conductive polymer film can potentially overcome these problems. In our work, polypyrrole/chitosan films comprising polypyrrole nanoparticles dispersed in a chitosan matrix were prepared. The polypyrrole/chitosan film meets the requirements for DC delivery, as indicated by its electrical conductivity, biodegradability, and mechanical properties. The film supports osteoblast growth to the same degree as dentine discs (a bone-like mineralized substrate), confirming that it is non-cytotoxic. Our results showed that optimal DC stimulation was achieved with 200 µA for 4 h per day, and under this condition, osteoblast metabolic activity on Day 7 increased by 1.8-fold over that without DC stimulation. To further improve osteogenesis on the polypyrrole/chitosan film, bone morphogenetic protein-2 (BMP-2) was covalently immobilized on the film surface. Osteoblasts cultured on the BMP-2-functionalized polypyrrole/chitosan film and subjected to the optimal DC stimulation exhibited a significant increase in cellular metabolic activity (2.3-fold on Day 7), ALP activity (1.7-fold on Day 21) and mineralization (twofold on Day 21) over those cultured on polypyrrole/chitosan film without DC stimulation. Osteogenic gene expression results showed that BMP-2 and DC stimulation by itself enhanced osteoblast differentiation, and a combination of these two factors resulted in synergistic effects on osteoblast differentiation and maturation.

Detection of nano- and micro-sized particles in routine biopsy material - pilot study

BACKGROUND

Nanotechnology is receiving enormous funding. Very little however is known about the health dangers of this technology so far. Chronic tonsillitis is one of a number of diseases called idiopathic. Among other factors, the tonsils are exposed to suspended particles in inhaled air including nano particles. The objective of this study was to detect and evaluate metallic particles in human tonsil tissue diagnosed with chronic tonsillitis and in amniotic fluid as a comparison.

METHODS

. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) was used for identification of solid particles in a total of 64 samples of routinely analyzed biopsy and cytologic material.

RESULTS

Almost all samples were found to contain solid particles of various metals. The most frequent, regardless of diagnosis, were iron, chromium, nickel and aluminium. The size, determined using SEM, varied from around 500 nm to 25 µm. The majority formed aggregates of several micrometers in size but there were a significant number of smaller (sub-micrometer or nano-sized) particles present. The incidence of metallic particles was similar in child and adult tissues. The difference was in composition: the presence of several metals in adults was due to occupational exposure.

CONCLUSIONS

The presence of metallic particles in pathologically altered tissues may signal an alternative causation of some diseases. The ethiopathogenic explanation of these diseases associated with the presence of nano-sized particles in the organism has emerged into a new field of pathology, nanopathology.

Spatiotemporal visualization of subcellular dynamics of carbon nanotubes

To date, there is no consensus on the relationship between the physicochemical characteristics of carbon nanotubes (CNTs) and their biological behavior; however, there is growing evidence that the versatile characteristics make their biological fate largely unpredictable and remain an issue of limited knowledge. Here we introduce an experimental methodology for tracking and visualization of postuptake behavior and the intracellular fate of CNTs based on the spatial distribution of diffusion values throughout the plant cell. By using raster scan image correlation spectroscopy (RICS), we were able to generate highly quantitative spatial maps of CNTs diffusion in different cell compartments. The spatial map of diffusion values revealed that the uptake of CNTs is associated with important subcellular events such as carrier-mediated vacuolar transport and autophagy. These results show that RICS is a useful methodology to elucidate the intracellular behavior mechanisms of carbon nanotubes and potentially other fluorescently labeled nanoparticles, which is of relevance for the important issues related to the environmental impact and health hazards.

Respiratory toxicities of nanomaterials -- a focus on carbon nanotubes

Carbon nanotubes (CNT) are emblematic nanomaterials, presenting unique physico-chemical properties, such as mechanical, thermal, or electrical conductivity, that have led to a large number of actual applications and uses, as well as (future) developments in aerospace, automobiles, nanoelectronic, or nanomedicine. CNT are currently used in many devices (computers, aircraft airframe, and sporting goods such as tennis rackets, bicycles, golf irons) and have also emerged as efficient drug delivery carriers in the biomedical and drug delivery fields[1]. Because of these actual and future applications, there's an increasing concern regarding the consequences that could result from human exposure to CNT, particularly at the respiratory level, since it represents a major route of exposure to nanomaterials. This review will highlight the advancement in the actual knowledge on lung toxicities of CNT, and try to better understand the underlying biological mechanisms, as well as the importance of physico-chemical determinants directly related to CNT characteristics.

Critical role of surface chemical modifications induced by length shortening on multi-walled carbon nanotubes-induced toxicity

Given the increasing use of carbon nanotubes (CNT) in composite materials and their possible expansion to new areas such as nanomedicine which will both lead to higher human exposure, a better understanding of their potential to cause adverse effects on human health is needed. Like other nanomaterials, the biological reactivity and toxicity of CNT were shown to depend on various physicochemical characteristics, and length has been suggested to play a critical role. We therefore designed a comprehensive study that aimed at comparing the effects on murine macrophages of two samples of multi-walled CNT (MWCNT) specifically synthesized following a similar production process (aerosol-assisted CVD), and used a soft ultrasonic treatment in water to modify the length of one of them. We showed that modification of the length of MWCNT leads, unavoidably, to accompanying structural (i.e. defects) and chemical (i.e. oxidation) modifications that affect both surface and residual catalyst iron nanoparticle content of CNT. The biological response of murine macrophages to the two different MWCNT samples was evaluated in terms of cell viability, pro-inflammatory cytokines secretion and oxidative stress. We showed that structural defects and oxidation both induced by the length reduction process are at least as responsible as the length reduction itself for the enhanced pro-inflammatory and pro-oxidative response observed with short (oxidized) compared to long (pristine) MWCNT. In conclusion, our results stress that surface properties should be considered, alongside the length, as essential parameters in CNT-induced inflammation, especially when dealing with a safe design of CNT, for application in nanomedicine for example.

Multi walled carbon nano tubes induced hepatotoxicity in Swiss albino mice

In the present study, multi walled carbon nano tubes (MWCNTs) were synthesized using chemical vapour deposition (CVD) technique. Swiss albino mice were orally administered with single dose of 60 and 100 mg/kg body weight of purified and functionalized MWCNTs suspended in water. The mice were autopsied on 7, 14, 21 and 28 days post exposure. Liver was taken out and part of it fixed in Bouin's solution for histopathological examinations. The remaining part was immersed in cold saline, blotted dry, weighed quickly and homogenized in ice cold buffer. The activity of superoxide dismutase (SOD) and catalase (CAT) was immediately measured in the supernatant. The MWCNTs in liver led to pathological changes, including injury to macrophages, cellular swelling, unspecific inflammation, spot necrosis and blood coagulation. Estimation of SOD and CAT showed altered levels in the experimental groups as compared to controls. Therefore, MWCNTs from manufactured and combustion sources in the environment can have adverse effects on human health.

Carcinogenicity evaluation for the application of carbon nanotubes as biomaterials in rasH2 mice

The application of carbon nanotubes (CNTs) as biomaterials is of wide interest, and studies examining their application in medicine have had considerable significance. Biological safety is the most important factor when considering the clinical application of CNTs as biomaterials, and various toxicity evaluations are required. Among these evaluations, carcinogenicity should be examined with the highest priority; however, no report using transgenic mice to evaluate the carcinogenicity of CNTs has been published to date. Here, we performed a carcinogenicity test by implanting multi-walled CNTs (MWCNTs) into the subcutaneous tissue of rasH2 mice, using the carbon black present in black tattoo ink as a reference material for safety. The rasH2 mice did not develop neoplasms after being injected with MWCNTs; instead, MWCNTs showed lower carcinogenicity than carbon black. Such evaluations should facilitate the clinical application and development of CNTs for use in important medical fields.

Pulmonary exposure to single-walled carbon nanotubes does not affect the early immune response against Toxoplasma gondii

Background

Single-walled carbon nanotubes (SWCNT) trigger pronounced inflammation and fibrosis in the lungs of mice following administration via pharyngeal aspiration or inhalation. Human exposure to SWCNT in an occupational setting may occur in conjunction with infections and this could yield enhanced or suppressed responses to the offending agent. Here, we studied whether the sequential exposure to SWCNT via pharyngeal aspiration and infection of mice with the ubiquitous intracellular parasite Toxoplasma gondii would impact on the immune response of the host against the parasite.

Methods

C57BL/6 mice were pre-exposed by pharyngeal administration of SWCNT (80 + 80 μg/mouse) for two consecutive days followed by intravenous injection with either 1x10³ or 1x10⁴ green fluorescence protein and luciferase-expressing T. gondii tachyzoites. The dissemination of T. gondii was monitored by in vivo bioluminescence imaging in real time for 7 days and by plaque formation. The inflammatory response was analysed in bronchoalveolar lavage (BAL) fluid, and by assessment of morphological changes and immune responses in lung and spleen.

Results

There were no differences in parasite distribution between mice only inoculated with T. gondii or those mice pre-exposed for 2 days to SWCNT before parasite inoculum. Lung and spleen histology and inflammation markers in BAL fluid reflected the effects of SWCNT exposure and T. gondii injection, respectively. We also noted that CD11c positive dendritic cells but not F4/80 positive macrophages retained SWCNT in the lungs 9 days after pharyngeal aspiration. However, co-localization of T. gondii with CD11c or F4/80 positive cells could not be observed in lungs or spleen. Pre-exposure to SWCNT did not affect the splenocyte response to T. gondii.

Conclusions

Taken together, our data indicate that pre-exposure to SWCNT does not enhance or suppress the early immune response to T. gondii in mice.

Adsorption of ofloxacin on carbon nanotubes: solubility, pH and cosolvent effects

The adsorption of ofloxacin (OFL) on carbon nanotubes (CNTs) has been investigated using the solubility, pH and cocolvent effects. In this work, solubilities of OFL and sorption of OFL on three multi-walled CNTs at different pHs and different methanol volume fractions (f(c)) of methanol/water mixture solutions were systematically measured. The solubilities of different OFL species were obtained based on the analysis of pH-dependent solubility. Cationic and anionic OFL showed much higher solubilities than zwitterionic OFL. The highest sorption was not observed at the pH with lowest OFL solubility, indicating hydrophobic interaction was not the dominant sorption mechanism. The sorption decreasing in pH range of 5-8 was consistent with cationic OFL species distribution, suggesting cation exchange may play an important role. With the increased methanol fraction, both OFL solubility and sorption decreased, which was different from hydrophobic organic contaminants (HOCs). Analysis of methanol-fraction-dependent OFL sorption suggested that cosolvent-sorbent (methanol-CNTs) interactions were much stronger than solute-cosolvent (OFL-methanol) interactions. This statement was also confirmed in sorption isotherm study as evidenced by decreased sorption and increased linearity of the isotherms in methanol than those in water.

Mechanisms of carbon nanotube-induced toxicity: focus on oxidative stress

Nanotechnologies are emerging as highly promising technologies in many sectors in the society. However, the increasing use of engineered nanomaterials also raises concerns about inadvertent exposure to these materials and the potential for adverse effects on human health and the environment. Despite several years of intensive investigations, a common paradigm for the understanding of nanoparticle-induced toxicity remains to be firmly established. Here, the so-called oxidative stress paradigm is scrutinized. Does oxidative stress represent a secondary event resulting inevitably from disruption of biochemical processes and the demise of the cell, or a specific, non-random event that plays a role in the induction of cellular damage e.g. apoptosis? The answer to this question will have important ramifications for the development of strategies for mitigation of adverse effects of nanoparticles. Recent examples of global lipidomics studies of nanoparticle-induced tissue damage are discussed along with proteomics and transcriptomics approaches to achieve a comprehensive understanding of the complex and interrelated molecular changes in cells and tissues exposed to nanoparticles. We also discuss instances of non-oxidative stress-mediated cellular damage resulting from direct physical interference of nanomaterials with cellular structures.

Functionalized nanostructures with application in regenerative medicine

In the last decade, both regenerative medicine and nanotechnology have been broadly developed leading important advances in biomedical research as well as in clinical practice. The manipulation on the molecular level and the use of several functionalized nanoscaled materials has application in various fields of regenerative medicine including tissue engineering, cell therapy, diagnosis and drug and gene delivery. The themes covered in this review include nanoparticle systems for tracking transplanted stem cells, self-assembling peptides, nanoparticles for gene delivery into stem cells and biomimetic scaffolds useful for 2D and 3D tissue cell cultures, transplantation and clinical application.

Biosafety of non-surface modified carbon nanocapsules as a potential alternative to carbon nanotubes for drug delivery purposes

Background

Carbon nanotubes (CNTs) have found wide success in circuitry, photovoltaics, and other applications. In contrast, several hurdles exist in using CNTs towards applications in drug delivery. Raw, non-modified CNTs are widely known for their toxicity. As such, many have attempted to reduce CNT toxicity for intravenous drug delivery purposes by post-process surface modification. Alternatively, a novel sphere-like carbon nanocapsule (CNC) developed by the arc-discharge method holds similar electric and thermal conductivities, as well as high strength. This study investigated the systemic toxicity and biocompatibility of different non-surface modified carbon nanomaterials in mice, including multi-walled carbon nanotubes (MWCNTs), single-walled carbon nanotubes (SWCNTs), carbon nanocapsules (CNCs), and C₆₀ fullerene (C₆₀). The retention of the nanomaterials and systemic effects after intravenous injections were studied.

Methodology and Principal Findings

MWCNTs, SWCNTs, CNCs, and C₆₀ were injected intravenously into FVB mice and then sacrificed for tissue section examination. Inflammatory cytokine levels were evaluated with ELISA. Mice receiving injection of MWCNTs or SWCNTs at 50 µg/g b.w. died while C₆₀ injected group survived at a 50% rate. Surprisingly, mortality rate of mice injected with CNCs was only at 10%. Tissue sections revealed that most carbon nanomaterials retained in the lung. Furthermore, serum and lung-tissue cytokine levels did not reveal any inflammatory response compared to those in mice receiving normal saline injection.

Conclusion

Carbon nanocapsules are more biocompatible than other carbon nanomaterials and are more suitable for intravenous drug delivery. These results indicate potential biomedical use of non-surface modified carbon allotrope. Additionally, functionalization of the carbon nanocapsules could further enhance dispersion and biocompatibility for intravenous injection.

Carbon nanotubes as delivery systems for respiratory disease: do the dangers outweigh the potential benefits?

Nanoparticle drug-delivery systems offer the potential for improved efficacy of treatment, and yet there are also potential risks associated with these novel therapeutic strategies. An attractive property of carbon nanotubes (CNTs) is that the tube- or fiber-like structure allows for extensive functionalization and loading of cargo. However, a large body of evidence indicates that CNTs may have adverse effects if used in drug delivery as they have been shown to cause pulmonary fibrosis and exacerbate lung disease in rodents with pre-existing lung diseases. Major factors that cause these toxic effects are the high aspect ratio, durability and residual metal content that generate reactive oxygen species. Therefore, careful consideration should be given to the possibility that lung inflammation or fibrosis could be significant side effects caused by a CNT-based drug-delivery system, thereby outweighing any potential beneficial effects of therapeutic treatment. However, functionalization of CNTs to modulate aspect ratio, biodegradability and to remove residual metals could allow for safe design of CNTs for use in drug delivery in certain circumstances.

Fatigue and biocompatibility properties of a poly(methyl methacrylate) bone cement with multi-walled carbon nanotubes

Composites of multi-walled carbon nanotubes (MWCNT) of varied functionality (unfunctionalised and carboxyl and amine functionalised) with polymethyl methacrylate (PMMA) were prepared for use as a bone cement. The MWCNT loadings ranged from 0.1 to 1.0 wt.%. The fatigue properties of these MWCNT-PMMA bone cements were characterised at MWCNT loading levels of 0.1 and 0.25 wt.% with the type and wt.% loading of MWCNT used having a strong influence on the number of cycles to failure. The morphology and degree of dispersion of the MWCNT in the PMMA matrix at different length scales were examined using field emission scanning electron microscopy. Improvements in the fatigue properties were attributed to the MWCNT arresting/retarding crack propagation through the cement through a bridging effect and hindering crack propagation. MWCNT agglomerates were evident within the cement microstructure and the degree of agglomeration was dependent on the level of loading and functionality of the MWCNT. The biocompatibility of the MWCNT-PMMA cements at MWCNT loading levels upto 1.0 wt.% was determined by means of established biological cell culture assays using MG-63 cells. Cell attachment after 4h was determined using the crystal violet staining assay. Cell viability was determined over 7 days in vitro using the standard colorimetric MTT assay. Confocal scanning laser microscopy and SEM analysis was also used to assess cell morphology on the various substrates.

Nitrative DNA damage induced by multi-walled carbon nanotube via endocytosis in human lung epithelial cells

Carbon nanotube (CNT) has a promising usage in the field of material science for industrial purposes because of its unique physicochemical property. However, intraperitoneal administration of CNT was reported to cause mesothelioma in experimental animals. Chronic inflammation may contribute to carcinogenesis induced by fibrous materials. 8-Nitroguanine is a mutagenic DNA lesion formed during inflammation and may play a role in CNT-induced carcinogenesis. In this study, we examined 8-nitroguanine formation in A549 human lung alveolar epithelial cells treated with multi-walled CNT (MWCNT) by fluorescent immunocytochemistry. Both MWCNTs with diameter of 20-30 nm (CNT20) and 40-70 nm (CNT40) significantly induced 8-nitroguanine formation at 5 and 10 μg/ml (p<0.05), which persisted for 24h, although there was no significant difference in DNA-damaging abilities of these MWCNTs. MWCNTs significantly induced the expression of inducible nitric oxide synthase (iNOS) for 24 h (p<0.05). MWCNTs also significantly increased the level of nitrite, a hydrolysis product of oxidized NO, in the culture supernatant at 4 and 8 h (p<0.05). MWCNT-induced 8-nitroguanine formation and iNOS expression were largely suppressed by inhibitors of iNOS (1400 W), nuclear factor-κB (Bay11-7082), actin polymerization (cytochalasin D), caveolae-mediated endocytosis (methyl-β-cyclodextrin, MBCD) and clathrin-mediated endocytosis (monodansylcadaverine, MDC). Electron microscopy revealed that MWCNT was mainly located in vesicular structures in the cytoplasm, and its cellular internalization was reduced by MBCD and MDC. These results suggest that MWCNT is internalized into cells via clathrin- and caveolae-mediated endocytosis, leading to inflammatory reactions including iNOS expression and resulting nitrative DNA damage, which may contribute to carcinogenesis.

Nanoparticle penetration through filter media and leakage through face seal interface of N95 filtering facepiece respirators

National Institute for Occupational Safety and Health recommends the use of particulate respirators for protection against nanoparticles (<100 nm size). Protection afforded by a filtering facepiece particulate respirator is a function of the filter efficiency and the leakage through the face-to-facepiece seal. The combination of particle penetration through filter media and particle leakage through face seal and any component interfaces is considered as total inward leakage (TIL). Although the mechanisms and extent of nanoparticle penetration through filter media have been well documented, information concerning nanoparticle leakage through face seal is lacking. A previous study in our laboratory measured filter penetration and TIL for specific size particles. The results showed higher filter penetration and TIL for 50 nm size particles, i.e. the most penetrating particle size (MPPS) than for 8 and 400 nm size particles. To better understand the significance of particle penetration through filter media and through face seal leakage, this study was expanded to measure filter penetration at sealed condition and TIL with artificially introduced leaks for 20-800 nm particles at 8-40 l minute volumes for four N95 models of filtering facepiece respirators (FFRs) using a breathing manikin. Results showed that the MPPS was ~45 nm for all four respirator models. Filter penetration for 45 nm size particles was significantly (P < 0.05) higher than the values for 400 nm size particles. A consistent increase in filter penetrations for 45 and 400 nm size particles was obtained with increasing breathing minute volumes. Artificial leakage of test aerosols (mode size ~75 nm) through increasing size holes near the sealing area of FFRs showed higher TIL values for 45 nm size particles at different minute volumes, indicating that the induced leakage allows the test aerosols, regardless of particle size, inside the FFR, while filter penetration determines the TIL for different size particles. TIL values obtained for 45 nm size particles were significantly (P < 0.05) higher than the values obtained for 400 nm size particles for all four models. Models with relatively small filter penetration values showed lower TIL values than the models with higher filter penetrations at smaller leak sizes indicating the dependence of TIL values on filter penetration. When the electrostatic charge was removed, the FFRs showed a shift in the MPPS to ~150 nm with the same test aerosols (mode size ~75 nm) at different hole sizes and breathing minute volumes, confirming the interaction between filter penetration and face seal leakage processes. The shift in the MPPS from 45 to 150 nm for the charge removed filters indicates that mechanical filters may perform better against nanoparticles than electrostatic filters rated for the same filter efficiency. The results suggest that among the different size particles that enter inside the N95 respirators, relatively high concentration of the MPPS particles in the breathing zone of respirators can be expected in workplaces with high concentration of nanoparticles. Overall, the data obtained in the study suggest that good fitting respirators with lower filter penetration values would provide better protection against nanoparticles.

Dilemmas in the reliable estimation of the in-vitro cell viability in magnetic nanoparticle engineering: which tests and what protocols?

Magnetic nanoparticles [MNPs] made from iron oxides have many applications in biomedicine. Full understanding of the interactions between MNPs and mammalian cells is a critical issue for their applications. In this study, MNPs were coated with poly(ethylenimine) [MNP-PEI] and poly(ethylene glycol) [MNP-PEI-PEG] to provide a subtle difference in their surface charge and their cytotoxicity which were analysed by three standard cell viability assays: 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium [MTS], CellTiter-Blue and CellTiter-Glo (Promega, Southampton, UK) in SH-SY5Y and RAW 264.7 cells The data were validated by traditional trypan blue exclusion. In comparison to trypan blue manual counting, the MTS and Titer-Blue assays appeared to have consistently overestimated the viability. The Titer-Glo also experienced a small overestimation. We hypothesise that interactions were occurring between the assay systems and the nanoparticles, resulting in incorrect cell viability evaluation. To further understand the cytotoxic effect of the nanoparticles on these cells, reactive oxygen species production, lipid peroxidation and cell membrane integrity were investigated. After pegylation, the MNP-PEI-PEG possessed a lower positive surface charge and exhibited much improved biocompatibility compared to MNP-PEI, as demonstrated not only by a higher cell viability, but also by a markedly reduced oxidative stress and cell membrane damage. These findings highlight the importance of assay selection and of dissection of different cellular responses in in-vitro characterisation of nanostructures.

Nanoparticle filtration performance of NIOSH-certified particulate air-purifying filtering facepiece respirators: evaluation by light scattering photometric and particle number-based test methods

National Institute for Occupational Safety and Health (NIOSH) certification test methods employ charge neutralized NaCl or dioctyl phthalate (DOP) aerosols to measure filter penetration levels of air-purifying particulate respirators photometrically using a TSI 8130 automated filter tester at 85 L/min. A previous study in our laboratory found that widely different filter penetration levels were measured for nanoparticles depending on whether a particle number (count)-based detector or a photometric detector was used. The purpose of this study was to better understand the influence of key test parameters, including filter media type, challenge aerosol size range, and detector system. Initial penetration levels for 17 models of NIOSH-approved N-, R-, and P-series filtering facepiece respirators were measured using the TSI 8130 photometric method and compared with the particle number-based penetration (obtained using two ultrafine condensation particle counters) for the same challenge aerosols generated by the TSI 8130. In general, the penetration obtained by the photometric method was less than the penetration obtained with the number-based method. Filter penetration was also measured for ambient room aerosols. Penetration measured by the TSI 8130 photometric method was lower than the number-based ambient aerosol penetration values. Number-based monodisperse NaCl aerosol penetration measurements showed that the most penetrating particle size was in the 50 nm range for all respirator models tested, with the exception of one model at ~200 nm size. Respirator models containing electrostatic filter media also showed lower penetration values with the TSI 8130 photometric method than the number-based penetration obtained for the most penetrating monodisperse particles. Results suggest that to provide a more challenging respirator filter test method than what is currently used for respirators containing electrostatic media, the test method should utilize a sufficient number of particles <100 nm and a count (particle number)-based detector.

[DNA damage in human pleural mesothelial cells induced by exposure to carbon nanotubes]

OBJECTIVES

Nanomaterials are currently used in electronics, industrial materials, cosmetics, and medicine because they have useful physicochemical properties, such as strength, conductivity, durability, and chemical stability. As these materials have become widespread, many questions have arisen regarding their effects on health and the environment. In particular, recent studies have demonstrated that carbon nanotubes (CNTs) cause significant inflammation and mesothelioma in vivo. In this study, we investigated the potential risk posed by singlewalled carbon nanotube (SWCNT) and multiwalled carbon nanotube (MWCNT) exposure in human pleural mesothelial cells.

METHODS

CNT cytotoxicity was determined by a trypan blue exclusion assay, and DNA damage was detected by an alkaline comet assay. The concentration of 8-oxodeoxyguanosine (8-OHdG) in DNA was measured by high perhormance liquid chromatography with electrochemical detection. The expression of base excision repair enzymes in the cell was estimated by immunoblot analysis.

RESULTS

We observed inhibitory effects on cell proliferation and the induction of DNA damage following exposure of cells to purified CNTs that were suspended in dispersion medium. However, accumulation of 8-OHdG in DNA was not found. In addition, the expression levels of base excision enzymes that are involved in hOGG1, hMTH1, and MYH in MeT-5A cells remained unchanged for 24 h after carbon nanotube exposure.

CONCLUSIONS

CNTs significantly inhibit cell proliferation and decrease DNA damage in human pleural mesothelial cells. Our results indicate that the mechanism of CNT-induced genotoxicity is different from that following exposure to reactive oxygen species, which causes oxidative DNA modifications and 8-OHdG production. Further investigation is required to characterize the specific DNA mutations that occur following CNT exposure.

Effect of chemical composition and state of the surface on the toxic response to high aspect ratio nanomaterials

Nanomaterials often act as a double sword. On the one hand they offer exceptional new properties, but on the other hand show signs of toxicity. High aspect ratio nanomaterials (HARNs) cause more concern than isometric nanoparticles owing to their physical similarity with asbestos. Many compounds may be prepared in fibrous shape with nano-sized diameter differing one from the other in various ways. This article reports a comparative picture of the chemical features and related toxic responses to a variety of HARNs, namely carbon nanotubes, asbestos, carbon nanofibers, oxide and metal wires and rods. In spite of similarities in form, durability and several biological responses elicited in vitro and in vivo, carbon nanotubes - opposite to asbestos - quench radicals, are hydrophobic and may be fully purified from metal impurities. Most of the other HARNs produced so far are metal or metal oxide compounds, less biopersistent than carbon nanotubes.

Theranostic applications of nanomaterials in cancer: drug delivery, image-guided therapy, and multifunctional platforms

Successful cancer management depends on accurate diagnostics along with specific treatment protocols. Current diagnostic techniques need to be improved to provide earlier detection capabilities, and traditional chemotherapy approaches to cancer treatment are limited by lack of specificity and systemic toxicity. This review highlights advances in nanotechnology that have allowed the development of multifunctional platforms for cancer detection, therapy, and monitoring. Nanomaterials can be used as MRI, optical imaging, and photoacoustic imaging contrast agents. When used as drug carriers, nanoformulations can increase tumor exposure to therapeutic agents and result in improved treatment effects by prolonging circulation times, protecting entrapped drugs from degradation, and enhancing tumor uptake through the enhanced permeability and retention effect as well as receptor-mediated endocytosis. Multiple therapeutic agents such as chemotherapy, antiangiogenic, or gene therapy agents can be simultaneously delivered by nanocarriers to tumor sites to enhance the effectiveness of therapy. Additionally, imaging and therapy agents can be co-delivered to provide seamless integration of diagnostics, therapy, and follow-up, and different therapeutic modalities such as chemotherapy and hyperthermia can be co-administered to take advantage of synergistic effects. Liposomes, metallic nanoparticles, polymeric nanoparticles, dendrimers, carbon nanotubes, and quantum dots are examples of nanoformulations that can be used as multifunctional platforms for cancer theranostics. Nanomedicine approaches in cancer have great potential for clinically translatable advances that can positively impact the overall diagnostic and therapeutic process and result in enhanced quality of life for cancer patients. However, a concerted scientific effort is still necessary to fully explore long-term risks, effects, and precautions for safe human use.

Mapping the surface adsorption forces of nanomaterials in biological systems

The biological surface adsorption index (BSAI) is a novel approach to characterize surface adsorption energy of nanomaterials that is the primary force behind nanoparticle aggregation, protein corona formation, and other complex interactions of nanomaterials within biological systems. Five quantitative nanodescriptors were obtained to represent the surface adsorption forces (hydrophobicity, hydrogen bond, polarity/polarizability, and lone-pair electrons) of the nanomaterial interaction with biological components. We have mapped the surface adsorption forces over 16 different nanomaterials. When the five-dimensional information of the nanodescriptors was reduced to two dimensions, the 16 nanomaterials were classified into distinct clusters according their surface adsorption properties. BSAI nanodescriptors are intrinsic properties of nanomaterials useful for quantitative structure-activity relationship (QSAR) model development. This is the first success in quantitative characterization of the surface adsorption forces of nanomaterials in biological conditions, which could open a quantitative avenue in predictive nanomedicine development, risk assessment, and safety evaluation of nanomaterials.

Influence of surface charge on the potential toxicity of PLGA nanoparticles towards Calu-3 cells

Background

Because of the described hazards related to inhalation of manufactured nanoparticles, we investigated the lung toxicity of biodegradable poly (lactide-co-glycolide) (PLGA) nanoparticles displaying various surface properties on human bronchial Calu-3 cells.

Methods

Positively and negatively charged as well as neutral nanoparticles were tailored by coating their surface with chitosan, Poloxamer, or poly (vinyl alcohol), respectively. Nanoparticles were characterized in terms of size, zeta potential, and surface chemical composition, confirming modifications provided by hydrophilic polymers.

Results

Although nanoparticle internalization by lung cells was clearly demonstrated, the cytotoxicity of the nanoparticles was very limited, with an absence of inflammatory response, regardless of the surface properties of the PLGA nanoparticles.

Conclusion

These in vitro results highlight the safety of biodegradable PLGA nanoparticles in the bronchial epithelium and provide initial data on their potential effects and the risks associated with their use as nanomedicines.

Pulmonary and systemic responses of highly pure and well-dispersed single-wall carbon nanotubes after intratracheal instillation in rats

The present study was conducted to assess the pulmonary and systemic responses in rats after intratracheal instillation of highly pure, well-dispersed, and well-characterized SWCNTs. Exposure to SWCNTs up to 2 mg/kg did not produce mortality, changes in clinical signs, or body weights during the observation period. Dose-dependent changes were observed in the lung weight, BALF inflammatory cells, and biochemical parameters such as LDH value, protein content, IL-1β and IL-6 activity, and histopathology. In the 0.04 mg/kg SWCNT-exposed group, almost no changes were observed during the observation period. In the 0.2 mg/kg SWCNT-exposed group, pulmonary inflammatory responses were observed after instillation. In the 1 mg/kg and 2 mg/kg SWCNT-exposed group, acute lung inflammation and subsequent granuloma accompanied by increased lung weights were observed. Furthermore, the histopathological findings in the lungs of rats exposed to SWCNTs showed inflammatory responses related with the vital reaction to the foreign substance that was instilled intratracheally, and there were no fibrosis, atypical lesion, or tumor-related findings even at the highest dose (2 mg/kg) of SWCNT-exposed groups up to 6 months after instillation. For all groups, histopathological changes due to the instillation exposure of SWCNTs were observed only in the lungs and lung-associated lymph nodes and not in the other tissues examined (i.e. the liver, kidney, spleen, and cerebrum).

Study of serum interaction with a cationic nanoparticle: Implications for in vitro endocytosis, cytotoxicity and genotoxicity

We used well-characterized and positively charged nanoparticles (NP(+)) to investigate the importance of cell culture conditions, specifically the presence of serum and proteins, on NP(+) physicochemical characteristics, and the consequences for their endocytosis and genotoxicity in bronchial epithelial cells (16HBE14o-). NP(+) surface charge was significantly reduced, proportionally to NP(+)/serum and NP(+)/BSA ratios, while NP(+) size was not modified. Microscopy studies showed high endocytosis of NP(+) in 16HBE14o-, and serum/proteins impaired this internalization in a dose-dependent manner. Toxicity studies showed no cytotoxicity, even for very high doses of NP(+). No genotoxicity was observed with classic comet assay while primary oxidative DNA damage was observed when using the lesion-specific repair enzyme, formamidopyrimidine DNA-glycosylase (FPG). The micronucleus test showed NP(+) genotoxicity only for very high doses that cannot be attained in vivo. The low toxicity of these NP(+) might be explained by their high exocytosis from 16HBE14o- cells. Our results confirm the importance of serum and proteins on nanoparticles endocytosis and genotoxicity.

Carbon nanotubes induce malignant transformation and tumorigenesis of human lung epithelial cells

Carcinogenicity of carbon nanotubes is a major concern but has not been well addressed due to the lack of experimental models. Here, we show that chronic exposure to single-walled carbon nanotubes causes malignant transformation of human lung epithelial cells. The transformed cells induce tumorigenesis in mice and exhibit an apoptosis resistant phenotype characteristic of cancer cells. This study provides new evidence for carbon nanotube-induced carcinogenesis and indicates the potential role of p53 in the process.

Cytotoxicity screening of single-walled carbon nanotubes: detection and removal of cytotoxic contaminants from carboxylated carbon nanotubes

This study compares the cytotoxicity to cultured mammalian cells of nine different single-walled carbon nanotube (SWNT) products synthesized by a variety of methods and obtained from a cross section of vendors. A standard procedure involving sonication and centrifugation in buffered bovine serum albumin was developed to disperse all the SWNTs in a biocompatible solution to facilitate comparisons. The effect of the SWNTs on the proliferative ability of a standard cell line was then assessed. Of the nine different SWNT materials tested, only two were significantly toxic, and both were functionalized by carboxylation from different vendors. This was unexpected because carboxylation makes SWNTs more water-soluble, which would presumably correlate with better biocompatibility. However, additional purification work demonstrated that the toxic material in the carboxylated SWNT preparations could be separated from the SWNTs by filtration. The filtrate that contained the toxic activity also contained abundant small carbon fragments that had Raman signatures characteristic of amorphous carbon species, suggesting a correlation between toxicity and oxidized carbon fragments. The removal of a toxic contaminant associated with carboxylated SWNTs is important in the development of carboxylated SWNTs for pharmacological applications.

Low doses of pristine and oxidized single-wall carbon nanotubes affect mammalian embryonic development

Several in vitro and in vivo studies suggest local and systemic effects following exposure to carbon nanotubes. No data are available, however, on their possible embryotoxicity in mammals. In this study, we tested the effect of pristine and oxidized single-wall carbon nanotubes (SWCNTs) on the development of the mouse embryo. To this end, SWCNTs (from 10 ng to 30 μg/mouse) were administered to female mice soon after implantation (postcoital day 5.5); 10 days later, animals were sacrificed, and uteri, placentas, and fetuses examined. A high percentage of early miscarriages and fetal malformations was observed in females exposed to oxidized SWCNTs, while lower percentages were found in animals exposed to the pristine material. The lowest effective dose was 100 ng/mouse. Extensive vascular lesions and increased production of reactive oxygen species (ROS) were detected in placentas of malformed but not of normally developed fetuses. Increased ROS levels were likewise detected in malformed fetuses. No increased ROS production or evident morphological alterations were observed in maternal tissues. No fetal and placental abnormalities were ever observed in control animals. In parallel, SWCNT embryotoxicity was evaluated using the embryonic stem cell test (EST), a validated in vitro assay developed for predicting embryotoxicity of soluble chemical compounds, but never applied in full to nanoparticles. The EST predicted the in vivo data, identifying oxidized SWCNTs as the more toxic compound.

Length-dependent retention of carbon nanotubes in the pleural space of mice initiates sustained inflammation and progressive fibrosis on the parietal pleura

The fibrous shape of carbon nanotubes (CNTs) raises concern that they may pose an asbestos-like inhalation hazard, leading to the development of diseases, especially mesothelioma. Direct instillation of long and short CNTs into the pleural cavity, the site of mesothelioma development, produced asbestos-like length-dependent responses. The response to long CNTs and long asbestos was characterized by acute inflammation, leading to progressive fibrosis on the parietal pleura, where stomata of strictly defined size limit the egress of long, but not short, fibers. This was confirmed by demonstrating clearance of short, but not long, CNT and nickel nanowires and by visualizing the migration of short CNTs from the pleural space by single-photon emission computed tomographic imaging. Our data confirm the hypothesis that, although a proportion of all deposited particles passes through the pleura, the pathogenicity of long CNTs and other fibers arises as a result of length-dependent retention at the stomata on the parietal pleura.

In vitro investigation of the cellular toxicity of boron nitride nanotubes

Nanotubes present one of the most promising opportunities in nanotechnology with a plethora of applications in nanoelectronics, mechanical engineering, as well as in biomedical technology. Due to their structure and some physical properties, boron nitride (BN) nanotubes (BNNTs) possess several advantages over carbon nanotubes (CNTs), and they are now commercially produced and used on a large scale. The human and environmental exposure to BN nanomaterials is expected to increase in the near future, and their biological responses need to be examined. Using complementary assays, we have extensively investigated the effects of BNNTs on the viability and metabolic status of different cell types: on the one hand, the effects on cells present in the lung alveoli, and on the other hand, on human embryonic kidney (HEK) cells. Our results indicate that BNNTs are cytotoxic for all cell types studied and, in most cases, are more cytotoxic than CNTs in their pristine (p-CNT) and functionalized (f-CNT) form. However, the level of toxicity and the prominent morphological alterations in the cell populations withstanding BNNT exposure are cell-type-dependent. For instance, BNNTs induced extensive multinucleated giant cell formation in macrophages and increased levels of eosinophilia in fibroblasts. Finally, our results point the toxicity of tubular nanomaterials to be strongly correlated with the cellular accumulation enhanced for straight nanotubes.