Evaluation of dermal and eye irritation and skin sensitization due to carbon nanotubes

The present paper summarizes the results of our studies on dermal and eye irritation and skin sensitization due to carbon nanotubes (CNTs), whose potential applications and uses are wide and varied, including CNT-enhanced plastics, electromagnetic interference/radio-frequency (EMI/RFI) shielding, antistatic material, flexible fibers and advanced polymers, medical and health applications, and scanning probe microscopy. Skin and eyes have the highest risk of exposure to nanomaterials, because deposition of nanomaterials to the surficial organs has the potential to be a major route of exposure during the manufacturing, use, and disposal of nanomaterials. Two products composed of single-walled carbon nanotubes (SWCNTs) and two products composed of multi-walled carbon nanotubes (MWCNTs) were tested regarding acute dermal and acute eye irritation using rabbits, and skin sensitization using guinea pigs. The concentrations of the CNTs in the substances were the maximum allowable for administration. The two products of SWCNTs and one of the products of MWCNTs were not irritants to the skin or eyes. The other product of MWCNTs caused very slight erythema at 24 h, but not at 72 h, after patch removal in the dermal irritation experiments and conjunctival redness and blood vessel hyperemia at 1 h, but not at 24 h, in eye irritation experiments. These findings showed that one product of MWCNTs was a very weak acute irritant to the skin and eyes. No products of SWCNTs and MWCNTs exhibited skin-sensitization effects. Our knowledge of the toxicological effects of CNTs is still limited. Further information is needed to clarify the potential for irritation and sensitization given the complex nature of CNTs.     

Evaluation of dermal and eye irritation and skin sensitization due to carbon nanotubes

The present paper summarizes the results of our studies on dermal and eye irritation and skin sensitization due to carbon nanotubes (CNTs), whose potential applications and uses are wide and varied, including CNT-enhanced plastics, electromagnetic interference/radio-frequency (EMI/RFI) shielding, antistatic material, flexible fibers and advanced polymers, medical and health applications, and scanning probe microscopy. Skin and eyes have the highest risk of exposure to nanomaterials, because deposition of nanomaterials to the surficial organs has the potential to be a major route of exposure during the manufacturing, use, and disposal of nanomaterials. Two products composed of single-walled carbon nanotubes (SWCNTs) and two products composed of multi-walled carbon nanotubes (MWCNTs) were tested regarding acute dermal and acute eye irritation using rabbits, and skin sensitization using guinea pigs. The concentrations of the CNTs in the substances were the maximum allowable for administration. The two products of SWCNTs and one of the products of MWCNTs were not irritants to the skin or eyes. The other product of MWCNTs caused very slight erythema at 24 h, but not at 72 h, after patch removal in the dermal irritation experiments and conjunctival redness and blood vessel hyperemia at 1 h, but not at 24 h, in eye irritation experiments. These findings showed that one product of MWCNTs was a very weak acute irritant to the skin and eyes. No products of SWCNTs and MWCNTs exhibited skin-sensitization effects. Our knowledge of the toxicological effects of CNTs is still limited. Further information is needed to clarify the potential for irritation and sensitization given the complex nature of CNTs.     

Lack of mutagenic effect by multi-walled functionalized carbon nanotubes in the somatic cells of Drosophila melanogaster

Carbon nanotubes (CNTs) are formed by rolling up a single graphite sheet into a tube. Among the different types of CNTs, the multi-walled carbon nanotubes (MWCNTs) comprise a set of concentric nanotubes with perfect structures. Several uses for MWCNTs have been suggested to be included in biological applications such as manufacturing of biosensors, carriers of drugs. However, before these materials can be put on the market, it is necessary to know their genotoxic effects. Thus, this study aims to evaluate the mutagenicity of multi-walled carbon nanotubes (MWCNTs) functionalized in somatic cells of Drosophila melanogaster, using the somatic mutation and recombination test (SMART). This assay detects the loss of heterozygosity of marker genes expressed phenotypically on the wings of the fly. Larvae of three days were used, resulting from ST cross, with basal levels of the cytochrome P450 and larvae of high metabolic bioactivity capacity (HB cross). They were treated with different concentrations of MWCNTs functionalized. The MH descendants, analyzed in both ST and HB crosses, had no significant effects on the frequency of mutant. Based on the results and on the experimental conditions mentioned in this study, it was concluded that MWCNTs were not mutagenic in D. melanogaster.     

The impact of multi-walled carbon nanotubes with different amount of metallic impurities on immunometabolic parameters in healthy volunteers

The impact of two types of multi-walled carbon nanotubes (MWCNTs) (12–14 nm) with different content of metallic impurities (purified and unpurified nanotubes) on peroxidation processes, the status of immune cells in healthy volunteers and gene expression combined to pathway analysis was studied in vitro. From the study it was shown that the main mechanism of action for both types of MWCNTs is induction of oxidative stress, the intensity of which is directly related to the amount of metallic impurities. Unpurified MWCNTs produced twice as high levels of oxidation than the purified CNTs inducing thus more intense mitochondrial dysfunction. All the above were also verified by gene expression analysis of 2 different human cellular cultures (lung epithelium and keratinoma cells) and the respective pathway analysis; modulation of genes activating the NFkB pathway is associated to inflammatory responses. This may cause a perturbation in the IL-6 signaling pathway in order to regulate inflammatory processes and compensate for apoptotic changes. A plausible hypothesis for the immunological effects observed in vivo, are considered as the result of the synergistic effect of systemic (mediated by cells of the routes of exposure) and local inflammation (blood cells).     

Acute and long-term effects after single loading of functionalized multi-walled carbon nanotubes into zebrafish (Danio rerio)

Carbon nanotubes (CNTs) are widely explored for biomedical applications, but there is very limited information regarding their in vivo biodistribution and biocompatibility. Here, we report the in vivo biodistribution and long-term effects of functionalized multi-walled carbon nanotubes (MWCNTs) in developing zebrafish. The fluorescent-labeled MWCNTs were introduced into zebrafish embryos at 1-cell stage and at 72 h post fertilization through microinjection. After single injection, both acute and long-term interactions between zebrafish and functionalized MWCNTs were studied. The injected FITC-BSA-MWCNTs (at 1-cell stage) were allocated to all blastoderm cells of the embryos through proliferation, and were distinctively excluded from the yolk cell. When introduced into the circulation system, FITC-BSA-MWCNTs moved easily in the compartments and finally were cleaned out by the body at 96 h after the loading. At early stages, the treated zebrafish embryos generated immune response by accumulating circulating white blood cells at the trunk region. Under transmission electron microscope, many lysosome-like vesicles were observed in the blastoderm cells of the treated embryos. The zebrafish loaded with MWCNTs had normal primordial germ cells at early stage and produced second generation later on. However, the larvae of the second generation had obviously lower survival rates as compared to the untreated groups, suggesting a negative effect on the reproduction potential. These results suggest that extensive purification and functionalization processes can help improve the biocompatibility of CNTs. This study also indicates that purified CNTs may have long-term toxicity effects when they were delivered into the body.     

Cytotoxicity of single-walled carbon nanotubes on PC12 cells

The increasing use of carbon nanotubes (CNTs) in biomedical applications underlines the importance of its potential toxic effects to human health. In the present study, we first exposed PC12 cells, a commonly used in vitro model for neurotoxicity study, to two kinds of commercially available single-walled carbon nanotubes (SWCNTs), to investigate the effect of SWCNTs on nervous system in vitro. The decrease of PC12 cells viability was time and dose-dependent with exposure to SWCNTs demonstrated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, lactate dehydrogenase (LDH) release and morphological observation. Flow cytometry analysis showed that the PC12 cells’ cycle was arrested in the G2/M phase, and their apoptotic rate induced by SWCNTs was dose-dependent. Further studies revealed SWCNTs decreased mitochondrial membrane potential (MMP), induced the formation of reactive oxygen species (ROS) and increased the level of lipid peroxide and decreased the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and the content of glutathione (GSH) in a time and dose-dependent manner. These findings reveal that SWCNTs may induce oxidative stress to nervous system in vivo, causing the occurrence of diseases related to cellular injuries of neuronal cells, such as neurodegenerative disorders, and demonstrating the necessity of further research in vivo.     

Carbon nanotubes for biomedical imaging: The recent advances

This article reviews the latest progresses regarding the applications of carbon nanotubes (CNTs), including single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs), as multifunctional nano-probes for biomedical imaging. Utilizing the intrinsic band-gap fluorescence of semi-conducting single-walled carbon nanotubes (SWNTs), fluorescence imaging in the near infrared II (NIR-II) region with enhanced tissue penetration and spatial resolution has shown great promise in recent years. Raman imaging based on the resonance Raman scattering of SWNTs has also been explored by a number of groups for in vitro and in vivo imaging of biological samples. The strong absorbance of CNTs in the NIR region can be used for photoacoustic imaging, and their photoacoustic signals can be dramatically enhanced by adding organic dyes, or coating with gold shells. Taking advantages of metal nanoparticle impurities attached to nanotubes, CNTs can also serve as a T2-contrast agent in magnetic resonance (MR) imaging. In addition, when labeled with radioactive isotopes, many groups have developed nuclear imaging with functionalized CNTs. Therefore CNTs are unique imaging probes with great potential in biomedical multimodal imaging.     

Effects of water-soluble functionalized multi-walled carbon nanotubes examined by different cytotoxicity methods in human astrocyte D384 and lung A549 cells

The widespread projected use of functionalized carbon nanotubes (CNTs) makes it important to understand their potential harmful effects. Two cell culture systems, human A549 pneumocytes and D384 astrocytoma cells, were used to assess cytotoxicity of multi-walled CNTs (MWCNTs) with varying degrees of functionalization. Laboratory-made highly functionalized hf-MW-NH₂ and less functionalized CNTs (MW-COOH and MW-NH₂) were tested in comparison with pristine MWCNTs, carbon black (CB) and silica (SiO₂) by MTT assay and calcein/propidium iodide (PI) staining. Purity and physicochemical properties of the test nanomaterials were also determined.     

Toxicity of carboxylated carbon nanotubes in endothelial cells is attenuated by stimulation of the autophagic flux with the release of nanomaterial in autophagic vesicles

Carbon nanotubes (CNTs) exhibit a number of unique properties that make them attractive for various nanomedicine applications including their intravascular use. Therefore, the vascular toxicity of CNTs is a critical safety concern and methods of CNTs toxicity modulation are of great interest. Here, we report that carboxylated multiwalled carbon nanotubes (MWCNTs) induce a decrease in viability of cultured human umbilical vein endothelial cells (HUVECs) associated with the profound accumulation of autophagosomes. This autophagosome accumulation was mTOR kinase independent and was caused by blockade of the autophagic flux rather than by activation of autophagy. Stimulation of the autophagic flux with 1 nmol/L bafilomycin A1 attenuated the cytotoxicity of carboxylated MWCNTs in HUVECs and was associated with the extracellular release of the nanomaterial in autophagic microvesicles. Thus, pharmacological stimulation of the autophagic flux may represent a new method of cytoprotection against toxic effects of nanomaterials.From the Clinical EditorThis study investigates the mechanisms of toxicity of multiwalled carbon nanutubes on human endothelial cells, concluding that pharmacological stimulation of autophagic flux may represent a new method of cytoprotection against the toxic effects of these nanomaterials.     

A Review of Carbon Nanotube Toxicity and Assessment of Potential Occupational and Environmental Health Risks

Nanotechnology has emerged at the forefront of science research and technology development. Carbon nanotubes (CNTs) are major building blocks of this new technology. They possess unique electrical, mechanical, and thermal properties, with potential wide applications in the electronics, computer, aerospace, and other industries. CNTs exist in two forms, single-wall (SWCNTs) and multi-wall (MWCNTs). They are manufactured predominately by electrical arc discharge, laser ablation and chemical vapor deposition processes; these processes involve thermally stripping carbon atoms off from carbon-bearing compounds. SWCNT formation requires catalytic metals. There has been a great concern that if CNTs, which are very light, enter the working environment as suspended particulate matter (PM) of respirable sizes, they could pose an occupational inhalation exposure hazard. Very recently, MWCNTs and other carbonaceous nanoparticles in fine (<2.5 μm) PM aggregates have been found in combustion streams of methane, propane, and natural-gas flames of typical stoves; indoor and outdoor fine PM samples were reported to contain significant fractions of MWCNTs. Here we review several rodent studies in which test dusts were administered intratracheally or intrapharyngeally to assess the pulmonary toxicity of manufactured CNTs, and a few in vitro studies to assess biomarkers of toxicity released in CNT-treated skin cell cultures. The results of the rodent studies collectively showed that regardless of the process by which CNTs were synthesized and the types and amounts of metals they contained, CNTs were capable of producing inflammation, epithelioid granulomas (microscopic nodules), fibrosis, and biochemical/toxicological changes in the lungs. Comparative toxicity studies in which mice were given equal weights of test materials showed that SWCNTs were more toxic than quartz, which is considered a serious occupational health hazard if it is chronically inhaled; ultrafine carbon black was shown to produce minimal lung responses. The differences in opinions of the investigators about the potential hazards of exposures to CNTs are discussed here. Presented here are also the possible mechanisms of CNT pathogenesis in the lung and the impact of residual metals and other impurities on the toxicological manifestations. The toxicological hazard assessment of potential human exposures to airborne CNTs and occupational exposure limits for these novel compounds are discussed in detail. Environmental fine PM is known to form mainly from combustion of fuels, and has been reported to be a major contributor to the induction of cardiopulmonary diseases by pollutants. Given that manufactured SWCNTs and MWCNTs were found to elicit pathological changes in the lungs, and SWCNTs (administered to the lungs of mice) were further shown to produce respiratory function impairments, retard bacterial clearance after bacterial inoculation, damage the mitochondrial DNA in aorta, increase the percent of aortic plaque, and induce atherosclerotic lesions in the brachiocephalic artery of the heart, it is speculated that exposure to combustion-generated MWCNTs in fine PM may play a significant role in air pollution-related cardiopulmonary diseases. Therefore, CNTs from manufactured and combustion sources in the environment could have adverse effects on human health.     

Toxicogenomic comparison of multi-wall carbon nanotubes (MWCNTs) and asbestos

Carbon nanotubes (CNTs) have specific properties, including electrical and thermal conductivity, great strength, and rigidity, that allow them to be used in many fields. However, this increasing contact with humans and the environment is also raising health and safety concerns. Thus, research on the safety of CNTs has attracted much interest, including a comparison of the toxic effects of asbestos and carbon nanotubes, due to their physical similarity of a high aspect ratio (length/diameter). Nonetheless, there has not yet been a toxicogenomic comparison. Therefore, to examine toxicogenomic effects, the 50% growth inhibition (GI₅₀) concentration was determined for multi-wall carbon nanotubes (MWCNTs) and asbestos (crocidolite) and found to be approximately 0.0135 and 0.066%, respectively, in the case of 24-h treatment of normal human bronchial epithelia (NHBE) cells. Using these GI₅₀ concentrations, NHBE cells were then treated with MWCNTs and asbestos for 6 and 24 h, followed by a DNA microarray analysis. Among 31,647 genes, 1,201 and 1,252 were up-regulated by both asbestos and MWCNTs after 6 and 24 h of exposure, respectively. Meanwhile, 1,977 and 1,542 genes were down-regulated by both asbestos and MWNCTs after 6 and 24 h of exposure, respectively. In particular, the asbestos and MWCNTs both induced an over twofold up- and down-regulated expression of 12 mesothelioma-related genes and 22 lung cancer-related genes when compared with the negative control. Plus, the genes induced by the MWCNT exposure were expressed in the brain, lungs, epithelium, liver, and colon.     

A review of carbon nanotube toxicity and assessment of potential occupational and environmental health risks

Nanotechnology has emerged at the forefront of science research and technology development. Carbon nanotubes (CNTs) are major building blocks of this new technology. They possess unique electrical, mechanical, and thermal properties, with potential wide applications in the electronics, computer, aerospace, and other industries. CNTs exist in two forms, single-wall (SWCNTs) and multi-wall (MWCNTs). They are manufactured predominately by electrical arc discharge, laser ablation and chemical vapor deposition processes; these processes involve thermally stripping carbon atoms off from carbon-bearing compounds. SWCNT formation requires catalytic metals. There has been a great concern that if CNTs, which are very light, enter the working environment as suspended particulate matter (PM) of respirable sizes, they could pose an occupational inhalation exposure hazard. Very recently, MWCNTs and other carbonaceous nanoparticles in fine (<2.5 microm) PM aggregates have been found in combustion streams of methane, propane, and natural-gas flames of typical stoves; indoor and outdoor fine PM samples were reported to contain significant fractions of MWCNTs. Here we review several rodent studies in which test dusts were administered intratracheally or intrapharyngeally to assess the pulmonary toxicity of manufactured CNTs, and a few in vitro studies to assess biomarkers of toxicity released in CNT-treated skin cell cultures. The results of the rodent studies collectively showed that regardless of the process by which CNTs were synthesized and the types and amounts of metals they contained, CNTs were capable of producing inflammation, epithelioid granulomas (microscopic nodules), fibrosis, and biochemical/toxicological changes in the lungs. Comparative toxicity studies in which mice were given equal weights of test materials showed that SWCNTs were more toxic than quartz, which is considered a serious occupational health hazard if it is chronically inhaled; ultrafine carbon black was shown to produce minimal lung responses. The differences in opinions of the investigators about the potential hazards of exposures to CNTs are discussed here. Presented here are also the possible mechanisms of CNT pathogenesis in the lung and the impact of residual metals and other impurities on the toxicological manifestations. The toxicological hazard assessment of potential human exposures to airborne CNTs and occupational exposure limits for these novel compounds are discussed in detail. Environmental fine PM is known to form mainly from combustion of fuels, and has been reported to be a major contributor to the induction of cardiopulmonary diseases by pollutants. Given that manufactured SWCNTs and MWCNTs were found to elicit pathological changes in the lungs, and SWCNTs (administered to the lungs of mice) were further shown to produce respiratory function impairments, retard bacterial clearance after bacterial inoculation, damage the mitochondrial DNA in aorta, increase the percent of aortic plaque, and induce atherosclerotic lesions in the brachiocephalic artery of the heart, it is speculated that exposure to combustion-generated MWCNTs in fine PM may play a significant role in air pollution-related cardiopulmonary diseases. Therefore, CNTs from manufactured and combustion sources in the environment could have adverse effects on human health.     

Influence of purity and surface oxidation on cytotoxicity of multiwalled carbon nanotubes with human neuroblastoma cells

There are conflicting data concerning the safety and biocompatibility of carbon nanotubes (CNTs). In some reports CNTs have been used for gene delivery without significant toxicity, whereas in others various cytotoxic effects were observed, including induction of intracellular reactive oxygen species (ROS), DNA damage, and apoptosis. Although it is clear that CNT production methods, purity, and functionalization treatments impact on biocompatibility, most of the published reports lack detailed characterization of the CNT samples used. We investigated the effect of various physicochemical features of multiwalled carbon nanotubes (MWCNTs) on toxicity and biocompatibility with cultured human neuroblastoma cells by using MTT, WST-1, Hoechst, and oxidative stress assays. In vitro experiments confirm that after 3 days of incubation with three different types of CNTs dispersed in Pluronic F127 solution, 0.01% cell viability is not affected and apoptosis and ROS are not induced in the SH-SY5Y cells. With prolonged cultures and continued propagation in the presence of MWCNTs, the loss of cell viability was minimal for pure MWCNTs (99% purity), but cell proliferation decreased significantly for 97% purity MWCNTs and acid-treated MWCNTs (97% purity, surface oxidation 8%); no intracellular ROS were detected. When the concentration of CNTs increases, purity and surface oxidation seem to affect cell viability (ED₂₅ is 48, 34.4, and 18.4 μg/mL, respectively, for 99% purity MWCNTs, 97% purity MWCNTs, and acid-treated 97% purity MWCNTs. Our results indicate that concentrations of 5–10 μg/mL MWCNTs seem ideal for studies on the design and development of artificial MWCNT nanovectors for gene and drug therapy against cancer.From the Clinical EditorWith prolonged cultures, loss of cell viability was minimal for preparations with 99% purity, but significant adverse effects were detected with 97% purity and with acid-treated preparations. A concentrations of 5–10 μg/mL of MWCNTs seems ideal for gene and drug therapy against cancer.     

Toxicity of multiwalled carbon nanotubes with end defects critically depends on their functionalization density

Carboxylated carbon nanotubes stand as the most promising nanovectors for biomedical and pharmaceutical applications due to their ease of covalent conjugation with eclectic functional molecules including therapeutic drugs, proteins, and oligonucleotides. In the present study, we attempt to investigate how the toxicity of acid-oxidized multiwalled carbon nanotubes (MWCNTs) can be tweaked by altering their degree of functionalization and correlate the toxicity trend with their biodistribution profile. In line with that rationale, mice were exposed to 10 mg/kg of pristine (p) and acid-oxidized (f) MWCNTs with varying degrees of carboxylation through a single dose of intravenous injection. Thereafter, extensive toxicity studies were carried out to comprehend the short-term (7 day) and long-term (28 day) impact of p- and various f-MWCNT preparations on the physiology of healthy mice. Pristine MWCNTs with a high aspect ratio, surface hydrophobicity, and metallic impurities were found to induce significant hepatotoxicity and oxidative damage in mice, albeit the damage was recovered after 28 days of treatment. Conversely, acid-oxidized carboxylated CNTs with shorter lengths, hydrophilic surfaces, and high aqueous dispersibility proved to be less toxic and more biocompatible than their pristine counterparts. A thorough scrutiny of various biochemical parameters, inflammation indexes, and histopathological examination of liver indicated that toxicity of MWCNTs systematically decreased with the increased functionalization density. The degree of shortening and functionalization achieved by refluxing p-MWCNTs with strong mineral acids for 4 h were sufficient to render the CNTs completely hydrophilic and biocompatible, while inducing minimal hepatic accumulation and inflammation. Quantitative biodistribution studies in mice, intravenously injected with Tc-99m labeled MWCNTs, clearly designated that clearance of CNTs from reticuloendothelial system (RES) organs such as liver, spleen, and lungs was critically functionalization density dependent. Well-individualized MWCNTs with shorter lengths (<500 nm) and higher degrees of oxidation (surface carboxyl density >3 μmol/mg) were not retained in any of the RES organs and rapidly cleared out from the systematic circulation through renal excretion route without inducing any obvious nephrotoxicity. As both p- and f-MWCNT-treated groups were devoid of any obvious nephrotoxicity, CNTs with larger dimensions and lower degrees of functionalization, which fail to clear out from the body via renal excretion route, were thought to be excreted via biliary pathway in faeces.     

Advances in use of functionalized carbon nanotubes for drug design and discovery

Introduction: As a part of increasing interest in nanobiotechnology, nanoparticle-based drug discovery as well as development and drug delivery constitute an important area in nanomedicine, and it is also driven by search for new drugs by the pharmaceutical industry. Nanomaterials for pharmaceutical application include carbon nanotubes (CNTs).

Areas covered: This article describes the properties of CNTs, both single-walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs) with relevance to drug discovery and development. Pharmacokinetics of CNTs as well as CNT-based drug delivery is discussed. The article also looks at how the scope for pharmaceutical applications of CNTs is broadened by conjugation with other molecules and presents the potential therapeutic applications. Finally, the toxicology of CNTs is considered with measures under investigation for reducing it. Literature on CNTs, from the past 5 years, was reviewed and selected publications relevant to drug discovery, development, and delivery were included in the bibliography.

Expert opinion: Carbon nanotubes combine more properties relevant to drug development and delivery than any other nanomaterial. Although a tremendous amount of basic research has been done on CNTs during the past decade, little of this is nearing translation into human applications. No CNT-based medicine has reached clinical trials. Nevertheless, CNT conjugation with other molecules has extended the horizons for their potential therapeutic applications. The most promising of these is PEGylation, which extends the survival of CNTs in circulation. Potential future applications of CNTs include combination of diagnostics and therapeutic drug delivery as well as a component of multimodal therapies for tissue regeneration.     

Comparative study of the clastogenicity of functionalized and nonfunctionalized multiwalled carbon nanotubes in bone marrow cells of Swiss‐Webster mice

The development of nanotechnologies may lead to environmental release of nanomaterials that are potentially harmful to human health. Among the nanomaterials, multiwalled carbon nanotubes (MWCNTs) are already commercialized in various products which can be in direct contact with populations. However, few studies address their potential toxicity. Although a few reports on the cytotoxicity of carbon nanotubes (CNTs) have been published, very little is known about their toxicity or genotoxicity in mammalian cells. We have for the first time compared the clastogenic/genotoxic potential of functionalized and nonfunctionalized MWCNTs in bone marrow cells of Swiss‐Webster mice; using mitotic index (MI), chromosome aberrations (CA), micronuclei (MN) formation, and DNA damage in leukocytes as toxicologic endpoints. Six groups of five male mice, each weighing ～30 ± 2 g, were administered intraperitoneally, once a day for five days with doses of 0.25, 0.5, 0.75, mg/kg body weight (BW) of functionalized and nonfunctionalized MWCNTs. Four vehicle control groups (negative) and a positive control group (carbon black) were also made of 5 mice each. Chromosome and micronuclei from bone marrow cells and comet slides from leukocytes were examined following standard protocols. The results demonstrated that MWCNTs exposure significantly increased (P < 0.05) the number of structural chromosomal aberrations, the frequency of micronucleated cells and the level of DNA damage, and decreased the mitotic index in treated groups compared to control groups. MWCNTs were shown to be toxic at sufficiently high concentrations, however purified functionalized MWCNTs had a higher clastogenic/genotoxic potential compared to nonfunctionalized form of MWCNT. The results of our study suggest that exposure to MWCNT has the potential to cause genetic damage. Hence, careful monitoring should be done with respect to designing/synthesizing biocompatible carbon nanomaterials. Further characterization of their systemic toxicity, genotoxicity and carcinogenicity is also essential. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2010.     

Assessment of the potential in vivo ecotoxicity of Double-Walled Carbon Nanotubes (DWNTs) in water,using the amphibian Ambystoma mexicanum

Because of their specific properties (mechanical, electrical, etc), carbon nanotubes (CNTs) are being assessed for inclusion in many manufactured products. Due to their massive production and number of potential applications, the impact of CNTs on the environment must be taken into consideration. The present investigation evaluates the ecotoxic potential of CNTs in the amphibian larvae (Ambystoma mexicanum). Acute toxicity and genotoxicity were analysed after 12 days of exposure in laboratory conditions. The genotoxic effects were analysed by scoring the micronucleated erythrocytes in the circulating blood of the larvae according to the French standard micronucleus assay. The results obtained in the present study demonstrated that CNTs are neither acutely toxic nor genotoxic to larvae whatever the CNTs concentration in the water, although black masses of CNTs were observed inside the gut. In the increasing economical context of CNTs, complementary studies must be undertaken, especially including mechanistic and environmental investigations.     

Genotoxicity and carcinogenicity risk of carbon nanotubes

Novel materials are often commercialized without a complete assessment of the risks they pose to human health because such assessments are costly and time-consuming; additionally, sometimes the methodology needed for such an assessment does not exist. Carbon nanotubes have the potential for widespread application in engineering, materials science and medicine. However, due to the needle-like shape and high durability of multiwalled carbon nanotubes (MWCNTs), concerns have been raised that they may induce asbestos-like pathogenicity when inhaled. Indeed, experiments in rodents supported this hypothesis. Notably, the genetic alterations in MWCNT-induced rat malignant mesothelioma were similar to those induced by asbestos. Single-walled CNTs (SWCNTs) cause mitotic disturbances in cultured cells, but thus far, there has been no report that SWCNTs are carcinogenic. This review summarizes the recent noteworthy publications on the genotoxicity and carcinogenicity of CNTs and explains the possible molecular mechanisms responsible for this carcinogenicity. The nanoscale size and needle-like rigid structure of CNTs appear to be associated with their pathogenicity in mammalian cells, where carbon atoms are major components in the backbone of many biomolecules. Publishing adverse events associated with novel materials is critically important for alerting people exposed to such materials. CNTs still have a bright future with superb economic and medical merits. However, appropriate regulation of the production, distribution and secondary manufacturing processes is required, at least to protect the workers.     

Carbon nanotube exploration in cancer cell lines

Complete with extraordinary structures and properties, carbon nanotubes (CNTs) have recently emerged as a potential new option for use in cancer treatment. During recent years, cancer cell lines have also been explored as prominent experimental models for evaluating pharmacokinetic parameters, cell viability, cytotoxicity and drug efficacy in tumor cells. Thus, cell lines have emerged as the best-fit model that has been thoroughly investigated and explored. This review focuses on potential applications and a compilation of various cancer cell lines used to evaluate CNT efficacy on one platform. This is likely to aid the researchers in exploring another dimension of CNTs in cancer treatment.     

Macrophages targeting of amphotericin B through mannosylated multiwalled carbon nanotubes

The objective of the present investigation was to assess the potential of polysaccharide (mannose) conjugated engineered multiwalled carbon nanotubes (MWCNTs) bearing Amphotericin B (AmB) formulation for site-specific delivery to macrophages. The mannosylated carbon nanotubes (CNTs) were synthesized and AmB was efficiently loaded using dialysis diffusion method. The synthesized mannosylated MWCNTs were characterized by various physicochemical and physiological parameters such as fourier transform infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM & TEM), drug loading and entrapment efficiency, in-vitro release kinetics, in-vivo study and toxicological investigation. AmB loaded mannosylated MWCNTs (AmBitubes) was found to be nanometric in size (500 nm) with tubular structure and good entrapment efficiency (75.46 ± 1.40%). In-vitro AmB from AmBitubes was found to be released in a controlled manner at pH 4, 7.4 and 10, with enhanced cell uptake and higher disposition in macrophage-rich organs, thereby indicating the site-specific drug delivery. The results suggest that AmBitubes could be employed as efficient nano-carrier for antileishmanial therapy.