Exposure to carbon nanotube material: assessment of nanotube cytotoxicity using human keratinocyte cells

Conductive interpenetrating networks of polypyrrole and polycaprolactone encourage electrophysiological development of cardiac cells

Conductive and electroactive polymers have the potential to enhance engineered cardiac tissue function. In this study, an interpenetrating network of the electrically-conductive polymer polypyrrole (PPy) was grown within a matrix of flexible polycaprolactone (PCL) and evaluated as a platform for directing the formation of functional cardiac cell sheets. PCL films were either treated with sodium hydroxide to render them more hydrophilic and enhance cell adhesion or rendered electroactive with PPy grown via chemical polymerization yielding PPy-PCL that had a resistivity of 1.0 ± 0.4 kΩ cm, which is similar to native cardiac tissue. Both PCL and PPy-PCL films supported cardiomyocyte attachment; increasing the duration of PCL pre-treatment with NaOH resulted in higher numbers of adherent cardiomyocytes per unit area, generating cell densities which were more similar to those on PPy-PCL films (1568 ± 126 cells mm(-2), 2880 ± 439 cells mm(-2), 3623 ± 456 cells mm(-2) for PCL with 0, 24, 48 h of NaOH pretreatment, respectively; 2434 ± 166 cells mm(-2) for PPy-PCL). When cardiomyocytes were cultured on the electrically-conductive PPy-PCL, more cells were observed to have peripheral localization of the gap junction protein connexin-43 (Cx43) as compared to cells on NaOH-treated PCL (60.3 ± 4.3% vs. 46.6 ± 5.7%). Cx43 gene expression remained unchanged between materials. Importantly, the velocity of calcium wave propagation was faster and calcium transient duration was shorter for cardiomyocyte monolayers on PPy-PCL (1612 ± 143 μm/s, 910 ± 63 ms) relative to cells on PCL (1129 ± 247 μm/s, 1130 ± 20 ms). In summary, PPy-PCL has demonstrated suitability as an electrically-conductive substrate for culture of cardiomyocytes, yielding enhanced functional properties; results encourage further development of conductive substrates for use in differentiation of stem cell-derived cardiomyocytes and cardiac tissue engineering applications.

STATEMENT OF SIGNIFICANCE

Current conductive materials for use in cardiac regeneration are limited by cytotoxicity or cost in implementation. In this manuscript, we demonstrate for the first time the application of a biocompatible, conductive polypyrrole-polycaprolactone film as a platform for culturing cardiomyocytes for cardiac regeneration. This study shows that the novel conductive film is capable of enhancing cell-cell communication through the formation of connexin-43, leading to higher velocities for calcium wave propagation and reduced calcium transient durations among cultured cardiomyocyte monolayers. Furthermore, it was demonstrated that chemical modification of polycaprolactone through alkaline-mediated hydrolysis increased overall cardiomyocyte adhesion. The results of this study provide insight into how cardiomyocytes interact with conductive substrates and will inform future research efforts to enhance the functional properties of cardiomyocytes, which is critical for their use in pharmaceutical testing and cell therapy.

Differentiation of chemical reaction activity of various carbon nanotubes using redox potential: Classification by physical and chemical structures

The present study systematically examined the kinetics of a hydroxyl radical scavenging reaction of various carbon nanotubes (CNTs) including double-walled and multi-walled carbon nanotubes (DWCNTs and MWCNTs), and carbon nano peapods (AuCl₃@DWCNT). The theoretical model that we recently proposed based on the redox potential of CNTs was used to analyze the experimental results. The reaction kinetics for DWCNTs and thin MWCNTs agreed well with the theoretical model and was consistent with each other. On the other hand, thin and thick MWCNTs behaved differently, which was consistent with the theory. Additionally, surface morphology of CNTs substantially influenced the reaction kinetics, while the doped particles in the center hollow parts of CNTs (AuCl₃@DWCNT) shifted the redox potential in a different direction. These findings make it possible to predict the chemical and biological reactivity of CNTs based on the structural and chemical nature and their influence on the redox potential.

Directing carbon nanotubes from aqueous phase to o/w interface for heavy metal uptaking

Separation and reuse of dispersed nanoparticles are major obstacles to the extensive application of nano-sized absorbents in wastewater treatment. Herein, we demonstrate the capability of directing acid-oxidized carbon nanotubes (CNTs) as the transfer vehicles of heavy metal ions from simulated wastewater. The heavy metal-loaded CNTs can be readily separated from the aqueous phase via the aggregation process at an oil/water (o/w) interface. The minimum surfactant amount to achieve 99 % transfer ratio (Tr) of 100 mg/L CNTs from water phase to o/w interface was ∼0.01 mM. The adsorption experiments showed that the removal efficiency of the divalent lead ions increased with an increase in CNT mass, and the subsequent addition of cetyltrimethylammonium bromide (CTAB) surfactant did not negatively impact the removal of soluble divalent lead species (Pb(II)). In a wide region of pH and ionic strength, both the decontamination of Pb(II) and the transfer of CNTs from water phase to o/w interface can be accomplished successively. The method presented in this study may be developed as a generic one for collecting or recycling the pollutant-loaded nano-sized absorbents.

Multiwall Carbon Nanotube-Induced DNA Damage and Cytotoxicity in Male Human Peripheral Blood Lymphocytes

Carbon nanotubes (CNTs) have been introduced recently as a novel carrier system for both small and large therapeutic molecules. Biotin-functionalized single-wall CNTs have been conjugated with the anticancer agent taxoid using a cleavable linker, and multiwall carbon nanotubes (MWCNTs) conjugated with iron nanoparticles have been efficiently loaded with doxorubicin. The MWCNTs are effective transporters for biological macromolecules and drugs to target cells and tissues, thereby attracting the attention of the biomedical industry. Administrating MWCNTs for medical application invariably involves intravenous administration and ultimate contact with human peripheral blood lymphocytes (HPBLs), yet toxicological studies on the effect of MWCNTs on HPBLs are lacking. Accordingly, this study evaluated the cytotoxic and genotoxic effects of MWCNTs on healthy male HPBLs. Healthy male HPBLs were treated with MWCNTs at 3 different concentrations (12.5, 25, and 50 μg/mL) for 48 hours. Under these conditions, the MWCNTs induced significant cell growth retardation, DNA damage, and cytotoxicity. The MWCNT-treated HPBLs also exhibited an increased intracellular reactive oxygen species level during the experimental period, which leads to cell damage and death, proliferation inhibition, DNA damage, and an inflammatory response.

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

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

Cytotoxicity of BSA-Stabilized Gold Nanoclusters: In Vitro and In Vivo Study

Gold nanoclusters (Au NCs) are one of the most promising fluorescent nanomaterials for bioimaging, targeting, and cancer therapy due to their tunable optical properties, yet their biocompatibility still remains unclear. Herein, the cytotoxicity of bovine serum albumin (BSA)-stabilized Au NCs is studied by using three tumor cell lines and two normal cell lines. The results indicate that Au NCs induce the decline of cell viabilities of different cell lines to varying degrees in a dose- and time-dependent manner, and umbilical vein endothelial cells which had a higher intake of Au NCs than melanoma cells show more toxicity. Addition of free BSA to BSA-Au NCs solutions can relieve the cytotoxicity, implying that BSA can prevent cell damage. Moreover, Au NCs increase intracellular reactive oxygen species (ROS) production, further causing cell apoptosis. Furthermore, N-acetylcysteine, a ROS scavenger, partially reverses Au NCs-induced cell apoptosis and cytotoxicity, indicating that ROS might be one of the primary reasons for the toxicity of BSA-Au NCs. Surprisingly, Au NCs with concentrations of 5 and 20 nM significantly inhibit tumor growth in the xenograft mice model of human liver cancer, which might provide a new avenue for the design of anti-cancer drug delivery vehicles.

Diels-Alder functionalized carbon nanotubes for bone tissue engineering: in vitro/in vivo biocompatibility and biodegradability

The risk-benefit balance for carbon nanotubes (CNTs) dictates their clinical fate. To take a step forward at this crossroad it is compulsory to modulate the CNT in vivo biocompatibility and biodegradability via e.g. chemical functionalization. CNT membranes were functionalised combining a Diels-Alder cycloaddition reaction to generate cyclohexene (-C6H10) followed by a mild oxidisation to yield carboxylic acid groups (-COOH). In vitro proliferation and osteogenic differentiation of human osteoblastic cells were maximized on functionalized CNT membranes (p,f-CNTs). The in vivo subcutaneously implanted materials showed a higher biological reactivity, thus inducing a slighter intense inflammatory response compared to non-functionalized CNT membranes (p-CNTs), but still showing a reduced cytotoxicity profile. Moreover, the in vivo biodegradation of CNTs was superior for p,f-CNT membranes, likely mediated by the oxidation-induced myeloperoxidase (MPO) in neutrophil and macrophage inflammatory milieus. This proves the biodegradability faculty of functionalized CNTs, which potentially avoids long-term tissue accumulation and triggering of acute toxicity. On the whole, the proposed Diels-Alder functionalization accounts for the improved CNT biological response in terms of the biocompatibility and biodegradability profiles. Therefore, CNTs can be considered for use in bone tissue engineering without notable toxicological threats.

Effects of nickel-oxide nanoparticle pre-exposure dispersion status on bioactivity in the mouse lung

Nanotechnology is emerging as one of the world's most promising new technologies. From a toxicology perspective, nanoparticles possess two features that promote their bioactivity. The first involves physical-chemical characteristics of the nanoparticle, which include the surface area of the nanoparticle. The second feature is the ability of the nanoparticle to traverse cell membranes. These two important nanoparticle characteristics are greatly influenced by placing nanoparticles in liquid medium prior to animal exposure. Nanoparticles tend to agglomerate and clump in suspension, making it difficult to reproducibly deliver them for in vivo or in vitro experiments, possibly affecting experimental variability. Thus, we hypothesize that nanoparticle dispersion status will correlate with the in vivo bioactivity/toxicity of the particle. To test our hypothesis, nano-sized nickel oxide was suspended in four different dispersion media (phosphate-buffered saline (PBS), dispersion medium (DM), a combination of dipalmitoyl-phosphatidyl choline (DPPC) and albumin in concentrations that mimic diluted alveolar lining fluid), Survanta®, or pluronic (Pluronic F-68). Well-dispersed and poorly dispersed suspensions were generated in each media by varying sonication time on ice utilizing a Branson Sonifer 450 (25W continuous output, 20 min or 5 min, respectively). Mice (male, C57BL/6J, 7-weeks-old) were given 0-80 µg/mouse of nano-sized nickel oxide in the different states of dispersion via pharyngeal aspiration. At 1 and 7 d post-exposure, mice underwent whole lung lavage to assess pulmonary inflammation and injury as a function of dispersion status, dose and time. The results show that pre-exposure dispersion status correlates with pulmonary inflammation and injury. These results indicate that a greater degree of pre-exposure dispersion increases pulmonary inflammation and cytotoxicity, as well as decreases in the integrity of the blood-gas barrier in the lung.

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

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

The past, present and future in scaffold-based tendon treatments

Tendon injuries represent a significant clinical burden on healthcare systems worldwide. As the human population ages and the life expectancy increases, tendon injuries will become more prevalent, especially among young individuals with long life ahead of them. Advancements in engineering, chemistry and biology have made available an array of three-dimensional scaffold-based intervention strategies, natural or synthetic in origin. Further, functionalisation strategies, based on biophysical, biochemical and biological cues, offer control over cellular functions; localisation and sustained release of therapeutics/biologics; and the ability to positively interact with the host to promote repair and regeneration. Herein, we critically discuss current therapies and emerging technologies that aim to transform tendon treatments in the years to come.

Impact of nanoparticles on human and environment: review of toxicity factors, exposures, control strategies, and future prospects

Nanotechnology has revolutionized the world through introduction of a unique class of materials and consumer products in many arenas. It has led to production of innovative materials and devices. Despite of their unique advantages and applications in domestic and industrial sectors, use of materials with dimensions in nanometers has raised the issue of safety for workers, consumers, and human environment. Because of their small size and other unique characteristics, nanoparticles have ability to harm human and wildlife by interacting through various mechanisms. We have reviewed the characteristics of nanoparticles which form the basis of their toxicity. This paper also reviews possible routes of exposure of nanoparticles to human body. Dermal contact, inhalation, and ingestion have been discussed in detail. As very limited data is available for long-term human exposures, there is a pressing need to develop the methods which can determine short and long-term effects of nanoparticles on human and environment. We also discuss in brief the strategies which can help to control human exposures to toxic nanoparticles. We have outlined the current status of toxicological studies dealing with nanoparticles, accomplishments, weaknesses, and future challenges.

Carbon nanotubes: Properties, biomedical applications, advantages and risks in patients and occupationally-exposed workers

Since the beginning of the 21st century, carbon-based nanomaterials (CNTs) have been introduced in pharmacy and medicine for drug delivery system in therapeutics. CNTs have proved able to transport a wide range of molecules across membranes and into living cells; therefore, they have attracted great interest in biomedical applications such as advanced imaging, tissue regeneration, and drug or gene delivery. Although there are many data on the advantages in terms of higher efficacy and less adverse effects, several recent findings have reported unexpected toxicities induced by CNTs. The dose, shape, surface chemistry, exposure route, and purity play important roles in these differential toxicities. Mapping these risks as well as understanding their molecular mechanisms is a crucial step in the development of any CNT-containing nanopharmaceuticals. This paper seeks to provide a comprehensive review of all articles published on cellular response to CNTs, underlining their therapeutic applications and possible toxicity in patients and occupationally exposed workers.

Carboxylation of multiwalled carbon nanotube attenuated the cytotoxicity by limiting the oxidative stress initiated cell membrane integrity damage, cell cycle arrestment, and death receptor mediated apoptotic pathway

In this study, the effects of carboxylated multiwalled carbon nanotubes (MWCNTs-COOH) on human normal liver cell line L02 was compared with that of pristine multiwalled carbon nanotubes (p-MWCNTs). It was shown that compared with MWCNTs-COOH, p-MWCNTs induced apoptosis, reduced the level of intracellular antioxidant glutathione more significantly, and caused severer cell membrane damage as demonstrated by lactate dehydrogenase leakage. Cell cycles were arrested by both MWCNTs, while p-MWCNTs induced higher ratio of G0/G1 phase arrestment as compared with MWCNTs-COOH. Caspase-8 was also activated after both MWCNTs exposure, indicating extrinsic apoptotic pathway was involved in the apoptosis induced by MWCNTs exposure, more importantly, MWCNTs-COOH significantly reduced the activation of caspase-8 as compared with p-MWCNTs. All these results suggested that MWCNTs-COOH might be safer for in vivo application as compared with p-MWCNTs.

The effects of carbon nanotubes on lung and dermal cellular behaviors

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

Using hollow carbon nanospheres as a light-induced free radical generator to overcome chemotherapy resistance

Under evolutionary pressure from chemotherapy, cancer cells develop resistance characteristics such as a low redox state, which eventually leads to treatment failures. An attractive option for combatting resistance is producing a high concentration of produced free radicals in situ. Here, we report the production and use of dispersible hollow carbon nanospheres (HCSs) as a novel platform for delivering the drug doxorubicine (DOX) and generating additional cellular reactive oxygen species using near-infrared laser irradiation. These irradiated HCSs catalyzed sufficiently persistent free radicals to produce a large number of heat shock factor-1 protein homotrimers, thereby suppressing the activation and function of resistance-related genes. Laser irradiation also promoted the release of DOX from lysosomal DOX@HCSs into the cytoplasm so that it could enter cell nuclei. As a result, DOX@HCSs reduced the resistance of human breast cancer cells (MCF-7/ADR) to DOX through the synergy among photothermal effects, increased generation of free radicals, and chemotherapy with the aid of laser irradiation. HCSs can provide a unique and versatile platform for combatting chemotherapy-resistant cancer cells. These findings provide new clinical strategies and insights for the treatment of resistant cancers.

The redox-active nanomaterial toolbox for cancer therapy

Advances in nanomaterials science contributed in recent years to develop new devices and systems in the micro and nanoscale for improving the diagnosis and treatment of cancer. Substantial evidences associate cancer cells and tumor microenvironment with reactive oxygen species (ROS), while conventional cancer treatments and particularly radiotherapy, are often mediated by ROS increase. However, the poor selectivity and the toxicity of these therapies encourage researchers to focus efforts in order to enhance delivery and to decrease side effects. Thus, the development of redox-active nanomaterials is an interesting approach to improve selectivity and outcome of cancer treatments. Herein, we describe an overview of recent advances in redox nanomaterials in the context of current and emerging strategies for cancer therapy based on ROS modulation.

Non-contact acoustic radiation force impulse microscopy via photoacoustic detection for probing breast cancer cell mechanics

We demonstrate a novel non-contact method: acoustic radiation force impulse microscopy via photoacoustic detection (PA-ARFI), capable of probing cell mechanics. A 30 MHz lithium niobate ultrasound transducer is utilized for both detection of phatoacoustic signals and generation of acoustic radiation force. To track cell membrane displacements by acoustic radiation force, functionalized single-walled carbon nanotubes are attached to cell membrane. Using the developed microscopy evaluated with agar phantoms, the mechanics of highly- and weakly-metastatic breast cancer cells are quantified. These results clearly show that the PA-ARFI microscopy may serve as a novel tool to probe mechanics of single breast cancer cells.

Immunotoxicity of silicon dioxide nanoparticles with different sizes and electrostatic charge

Silicon dioxide (SiO2) nanoparticles (NPs) have been widely used in the biomedical field, such as in drug delivery and gene therapy. However, little is known about the biological effects and potential hazards of SiO2. Herein, the colloidal SiO2 NPs with two different sizes (20 nm and 100 nm) and different charges (L-arginine modified: SiO2 (EN20[R]), SiO2 (EN100[R]); and negative: SiO2 (EN20[-]), SiO2 (EN100[-]) were orally administered (750 mg/kg/day) in female C57BL/6 mice for 14 days. Assessments of immunotoxicity include hematology profiling, reactive oxygen species generation and their antioxidant effect, stimulation assays for B- and T-lymphocytes, the activity of natural killer (NK) cells, and cytokine profiling. In vitro toxicity was also investigated in the RAW 264.7 cell line. When the cellularity of mouse spleen was evaluated, there was an overall decrease in the proliferation of B- and T-cells for all the groups fed with SiO2 NPs. Specifically, the SiO2 (EN20(-)) NPs showed the most pronounced reduction. In addition, the nitric oxide production and NK cell activity in SiO2 NP-fed mice were significantly suppressed. Moreover, there was a decrease in the serum concentration of inflammatory cytokines such as interleukin (IL)-1β, IL-12 (p70), IL-6, tumor necrosis factor-α, and interferon-γ. To elucidate the cytotoxicity mechanism of SiO2 in vivo, an in vitro study using the RAW 264.7 cell line was performed. Both the size and charge of SiO2 using murine macrophage RAW 264.7 cells decreased cell viability dose-dependently. Collectively, our data indicate that different sized and charged SiO2 NPs would cause differential immunotoxicity. Interestingly, the small-sized and negatively charged SiO2 NPs showed the most potent in vivo immunotoxicity by way of suppressing the proliferation of lymphocytes, depressing the killing activity of NK cells, and decreasing proinflammatory cytokine production, thus leading to immunosuppression.

Molybdenum nanoparticles-induced cytotoxicity, oxidative stress, G2/M arrest, and DNA damage in mouse skin fibroblast cells (L929)

The present investigation was aimed to study the cytotoxicity, oxidative stress, and genotoxicity induced by molybdenum nanoparticles (Mo-NPs) in mouse skin fibroblast cells (L929). Cells were exposed to different concentrations (1-100 μg/ml) of Mo-NPs (size 40 nm) for 24 and 48 h. After the exposure, different cytotoxicity assays (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide, MTT; neutral red uptake, NRU; and cellular morphology) and oxidative stress markers (lipid peroxidation, LPO; glutathione, GSH; and catalase) were studied. Further, Mo-NPs-induced intracellular reactive oxygen species (ROS) generation, mitochondrial membrane potential (MMP), cell cycle arrest, and DNA damage were also studied. L929 cells treated with Mo-NPs showed a concentration- and time-dependent decrease in cell viability and a loss of the normal cell morphology. The percentage cell viability was recorded as 25%, 42%, and 58% by MTT assay and 24%, 46%, and 56% by NRU assay at 25, 50, and 100 μg/ml of Mo-NPs, respectively after 48 h exposure. Furthermore, the cells showed a significant induction of oxidative stress. This was confirmed by the increase in LPO and ROS generation, as well as the decrease in the GSH and catalase levels. The decrease in MMP also confirms the impaired mitochondrial membrane. The cell cycle analysis and comet assay data revealed that Mo-NPs induced G2/M arrest and DNA damage in a concentration-dependent manner. Our results demonstrated, for the first time, Mo-NPs induced cytotoxicity, oxidative stress and genotoxicity in L929 cells. Thus, data suggest the potential hazardous nature of Mo-NPs.

In vivo genotoxicity evaluation of lung cells from Fischer 344 rats following 28 days of inhalation exposure to MWCNTs, plus 28 days and 90 days post-exposure

Despite their useful physico-chemical properties, carbon nanotubes (CNTs) continue to cause concern over occupational and human health due to their structural similarity to asbestos. Thus, to evaluate the toxic and genotoxic effect of multi-wall carbon nanotubes (MWCNTs) on lung cells in vivo, eight-week-old rats were divided into four groups (each group = 25 animals), a fresh air control (0 mg/m(3)), low (0.17 mg/m(3)), middle (0.49 mg/m(3)), and high (0.96 mg/m(3)) dose group, and exposed to MWCNTs via nose-only inhalation 6 h per day, 5 days per week for 28 days. The count median length and geometric standard deviation for the MWCNTs determined by TEM were 330.18 and 1.72 nm, respectively, and the MWCNT diameters ranged from 10 to 15 nm. Lung cells were isolated from five male and five female rats in each group on day 0, day 28 (only from males) and day 90 following the 28-day exposure. The total number of animals used was 15 male and 10 female rats for each concentration group. To determine the genotoxicity of the MWCNTs, a single cell gel electrophoresis assay (Comet assay) was conducted on the rat lung cells. As a result of the exposure, the olive tail moments were found to be significantly higher (p < 0.05) in the male and female rats from all the exposed groups when compared with the fresh air control. In addition, the high-dose exposed male and middle and high-dose exposed female rats retained DNA damage, even 90 days post-exposure (p < 0.05). To investigate the mode of genotoxicity, the intracellular reactive oxygen species (ROS) levels and inflammatory cytokine levels (TNF-α, TGF- β, IL-1, IL-2, IL-4, IL-5, IL-10, IL-12 and IFN-γ) were also measured. For the male rats, the H2O2 levels were significantly higher in the middle (0 days post-exposure) and high- (0 days and 28 days post-exposure) dose groups (p < 0.05). Conversely, the female rats showed no changes in the H2O2 levels. The inflammatory cytokine levels in the bronchoalveolar lavage (BAL) fluid did not show any statistically significant difference. Interestingly, the short-length MWCNTs deposited in the lung cells were persistent at 90 days post-exposure. Thus, exposing lung cells to MWCNTs with a short tube length may induce genotoxicity.

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

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

Carboxyl-modified single-wall carbon nanotubes improve bone tissue formation in vitro and repair in an in vivo rat model

The clinical management of bone defects caused by trauma or nonunion fractures remains a challenge in orthopedic practice due to the poor integration and biocompatibility properties of the scaffold or implant material. In the current work, the osteogenic properties of carboxyl-modified single-walled carbon nanotubes (COOH-SWCNTs) were investigated in vivo and in vitro. When human preosteoblasts and murine embryonic stem cells were cultured on coverslips sprayed with COOH-SWCNTs, accelerated osteogenic differentiation was manifested by increased expression of classical bone marker genes and an increase in the secretion of osteocalcin, in addition to prior mineralization of the extracellular matrix. These results predicated COOH-SWCNTs' use to further promote osteogenic differentiation in vivo. In contrast, both cell lines had difficulties adhering to multi-walled carbon nanotube-based scaffolds, as shown by scanning electron microscopy. While a suspension of SWCNTs caused cytotoxicity in both cell lines at levels >20 μg/mL, these levels were never achieved by release from sprayed SWCNTs, warranting the approach taken. In vivo, human allografts formed by the combination of demineralized bone matrix or cartilage particles with SWCNTs were implanted into nude rats, and ectopic bone formation was analyzed. Histological analysis of both types of implants showed high permeability and pore connectivity of the carbon nanotube-soaked implants. Numerous vascularization channels appeared in the formed tissue, additional progenitor cells were recruited, and areas of de novo ossification were found 4 weeks post-implantation. Induction of the expression of bone-related genes and the presence of secreted osteopontin protein were also confirmed by quantitative polymerase chain reaction analysis and immunofluorescence, respectively. In summary, these results are in line with prior contributions that highlight the suitability of SWCNTs as scaffolds with high bone-inducing capabilities both in vitro and in vivo, confirming them as alternatives to current bone-repair therapies.

Effects of multiwalled carbon nanotubes and triclocarban on several eukaryotic cell lines: elucidating cytotoxicity, endocrine disruption, and reactive oxygen species generation

To date, only a few reports about studies on toxic effects of carbon nanotubes (CNT) are available, and their results are often controversial. Three different cell lines (rainbow trout liver cells (RTL-W1), human adrenocortical carcinoma cells (T47Dluc), and human adrenocarcinoma cells (H295R)) were exposed to multiwalled carbon nanotubes, the antimicrobial agent triclocarban (TCC) as well as the mixture of both substances in a concentration range of 3.13 to 50 mg CNT/L, 31.25 to 500 μg TCC/L, and 3.13 to 50 mg CNT/L + 1% TCC (percentage relative to carbon nanotubes concentration), respectively. Triclocarban is a high-production volume chemical that is widely used as an antimicrobial compound and is known for its toxicity, hydrophobicity, endocrine disruption, bioaccumulation potential, and environmental persistence. Carbon nanotubes are known to interact with hydrophobic organic compounds. Therefore, triclocarban was selected as a model substance to examine mixture toxicity in this study. The influence of multiwalled carbon nanotubes and triclocarban on various toxicological endpoints was specified: neither cytotoxicity nor endocrine disruption could be observed after exposure of the three cell lines to carbon nanotubes, but the nanomaterial caused intracellular generation of reactive oxygen species in all cell types. For TCC on the other hand, cell vitality of 80% could be observed at a concentration of 2.1 mg/L for treated RTL-W1 cells. A decrease of luciferase activity in the ER Calux assay at a triclocarban concentration of 125 μg/L and higher was observed. This effect was less pronounced when multiwalled carbon nanotubes were present in the medium. Taken together, these results demonstrate that multiwalled carbon nanotubes induce the production of reactive oxygen species in RTL-W1, T47Dluc, and H295R cells, reveal no cytotoxicity, and reduce the bioavailability and toxicity of the biocide triclocarban.

Nanopharmacology in translational hematology and oncology

Nanoparticles have displayed considerable promise for safely delivering therapeutic agents with miscellaneous therapeutic properties. Current progress in nanotechnology has put forward, in the last few years, several therapeutic strategies that could be integrated into clinical use by using constructs for molecular diagnosis, disease detection, cytostatic drug delivery, and nanoscale immunotherapy. In the hope of bringing the concept of nanopharmacology toward a viable and feasible clinical reality in a cancer center, the present report attempts to present the grounds for the use of cell-free nanoscale structures for molecular therapy in experimental hematology and oncology.

Stem cells and nanomaterials

Because of their ability to self-renew and differentiate into many cell types, stem cells offer the potential to be used for tissue regeneration and engineering. Much progress has recently been made in our understanding of the biology of stem cells and our ability to manipulate their proliferation and differentiation to obtain functional tissues. Similarly, nanomaterials have been recently developed that will accelerate discovery of mechanisms driving stem cell fate and their utilization in medicine. Nanoparticles have been developed that allow the labeling and tracking of stem cells and their differentiated phenotype within an organism. Nanosurfaces are engineered that mimic the extracellular matrix to which stem cells adhere and migrate. Scaffolds made of functionalized nanofibers can now be used to grow stem cells and regenerate damaged tissues and organs. However, the small scale of nanomaterials induces changes in their chemical and physical properties that might modify their interactions with cells and tissues, and render them toxic to stem cells. Therefore a thorough understanding of stem cell-nanomaterial interactions is still necessary not only to accelerate the success of medical treatments but also to ensure the safety of the tools provided by these novel technologies.

Principal component and causal analysis of structural and acute in vitro toxicity data for nanoparticles

Structure toxicity relationship analysis was conducted using principal component analysis (PCA) for a panel of nanoparticles that included dry powders of oxides of titanium, zinc, cerium and silicon, dry powders of silvers, suspensions of polystyrene latex beads and dry particles of carbon black, nanotubes and fullerene, as well as diesel exhaust particles. Acute in vitro toxicity was assessed by different measures of cell viability, apoptosis and necrosis, haemolytic effects and the impact on cell morphology, while structural properties were characterised by particle size and size distribution, surface area, morphology, metal content, reactivity, free radical generation and zeta potential. Different acute toxicity measures were processed using PCA that classified the particles and identified four materials with an acute toxicity profile: zinc oxide, polystyrene latex amine, nanotubes and nickel oxide. PCA and contribution plot analysis then focused on identifying the structural properties that could determine the acute cytotoxicity of these four materials. It was found that metal content was an explanatory variable for acute toxicity associated with zinc oxide and nickel oxide, while high aspect ratio appeared the most important feature in nanotubes. Particle charge was considered as a determinant for high toxicity of polystyrene latex amine.

Enhancement of radiosensitization by metal-based nanoparticles in cancer radiation therapy

Radiation therapy performs an important function in cancer treatment. However, resistance of tumor cells to radiation therapy still remains a serious concern, so the study of radiosensitizers has emerged as a persistent hotspot in radiation oncology. Along with the rapid advancement of nanotechnology in recent years, the potential value of nanoparticles as novel radiosensitizers has been discovered. This review summarizes the latest experimental findings both in vitro and in vivo and attempts to highlight the underlying mechanisms of response in nanoparticle radiosensitization.

Autophagy as a Possible Underlying Mechanism of Nanomaterial Toxicity

The rapid development of nanotechnologies is raising safety concerns because of the potential effects of engineered nanomaterials on human health, particularly at the respiratory level. Since the last decades, many in vivo studies have been interested in the pulmonary effects of different classes of nanomaterials. It has been shown that some of them can induce toxic effects, essentially depending on their physico-chemical characteristics, but other studies did not identify such effects. Inflammation and oxidative stress are currently the two main mechanisms described to explain the observed toxicity. However, the exact underlying mechanism(s) still remain(s) unknown and autophagy could represent an interesting candidate. Autophagy is a physiological process in which cytoplasmic components are digested via a lysosomal pathway. It has been shown that autophagy is involved in the pathogenesis and the progression of human diseases, and is able to modulate the oxidative stress and pro-inflammatory responses. A growing amount of literature suggests that a link between nanomaterial toxicity and autophagy impairment could exist. In this review, we will first summarize what is known about the respiratory effects of nanomaterials and we will then discuss the possible involvement of autophagy in this toxicity. This review should help understand why autophagy impairment could be taken as a promising candidate to fully understand nanomaterials toxicity.

Poly(ethyleneimine) functionalized carbon nanotubes as efficient nano-vector for transfecting mesenchymal stem cells

For gene and drug delivery applications, carbon nanotubes (CNTs) have to be functionalized in order to become compatible with aqueous media and bind with genetic materials. In this study, combination of polyethyleneimine (PEI) grafted multi-walled carbon nanotubes (PEI-g-MWCNTs) and chitosan substrate is used as an efficient gene delivery system for transfection of hard-to-transfect bone marrow mesenchymal stem cells (BMSCs) with enhanced green fluorescent protein (EGFP) gene. Fourier transform infrared (FT-IR) spectra, dynamic light scattering (DLS) analysis and zeta potential measurements are used to characterize binding of PEI, particle size distribution and colloidal stability of the functionalized CNTs, respectively. DNA binding affinity, cellular uptake, transfection efficiency and possible cytotoxicity are also tested by agarose gel electrophoresis, flow cytometry, cytochemisty and MTT assay. The results demonstrate that cytotoxic effect of PEI-g-MWCNTs is negligible under optimal transfection condition. In consistency with high cellular uptake (>82%), PEI-g-MWCNTs give higher delivery of EGFP into the BMSCs which results in a more sustained expression of the model gene (EGFP) in short-term culture. These results suggest that PEI-g-MWCNTs in corporation with chitosan substrates would be a promising delivery system for BMSCs, a cell type with relevancy in the regenerative medicine and clinical applications.

Drug delivery: lessons to be learnt from Leishmania studies

Background Leishmaniasis is a disease caused by infection with the protozoan parasite Leishmania, which is responsible for three main types of disease: cutaneous leishmaniasis, visceral leishmaniasis and mucocutaneous leishmaniasis based to the site of infection for the particular species. This presents a major challenge to successful drug treatment, as a drug must not only reach antileishmanial concentrations in infected macrophages, the parasites' host cell, but also reach infected cells in locations specific to the type of disease. In this paper we discuss how studies using Leishmania have contributed to our knowledge on how drug delivery systems can be used to improve drug efficacy and delivery.

In vitro and in vivo biocompatibility of multi-walled carbon nanotube/biodegradable polymer nanocomposite for bone defects repair

Biomaterials are extensively used in bone defect recovery caused by bone diseases. Multi-walled carbon nanotubes have been reported to reinforce synthetic polymeric materials. The aim of the study is to test poly(3-hydroxybutyrate- co-3-hydroxyvalerate) loaded with different amounts of multi-walled carbon nanotubes to fabricate nanocomposites. Mechanical, mineralization, and degradation properties were studied in vitro. The proliferation and differentiation of rat bone marrow stem cells were studied to determine biocompatibility in vivo. The incorporation of multi-walled carbon nanotubes greatly increased the mechanical properties of poly(3-hydroxybutyrate- co-3-hydroxyvalerate) and the strongest composite obtained was at 2% multi-walled carbon nanotubes. The 2% nanocomposite also had higher rat bone marrow stem cell adhesion, proliferation, and differentiation characteristics compared to the pure poly(3-hydroxybutyrate- co-3-hydroxyvalerate). The apoptosis in the later stage of rat bone marrow stem cells decreased in the 2% nanocomposites group at different time points. Based on histology and micro-computed tomography tests 6 weeks after in vivo implantation, the 2% multi-walled carbon nanotubes/poly(3-hydroxybutyrate- co-3-hydroxyvalerate) treated animals had a higher volume of bone formation compared to the pure poly(3-hydroxybutyrate- co-3-hydroxyvalerate) group. Thus, the presence of multi-walled carbon nanotubes has an apparent positive effect on poly(3-hydroxybutyrate- co-3-hydroxyvalerate) in assisting osteogenesis.