Multiwalled carbon nanotubes activate NF-κB and AP-1 signaling pathways to induce apoptosis in rat lung epithelial cells

Modified toxic potential of multi-walled carbon nanotubes to zebrafish (Danio rerio) following a two-year incubation in water

Multi-walled carbon nanotubes (MWCNTs), widely used in several industrial fields, are not readily degradable thus, persist in environmental matrices, serving as a source of environmental toxicity to organisms. However, the effects of environmental weathering on nanomaterial toxicity remain unclear. Herein, we prepared aged-MWCNTs (a-CNTs) by incubating commercial pristine-MWCNTs (p-CNTs) for two years and compared their changes in physicochemical properties and toxic effects on zebrafish. The characterization of a-CNTs by transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and Fourier-transform infrared spectroscopy showed an increased surface area, pore size, structural defects, and surface oxidation than those of p-CNTs. Zebrafish were exposed to 100 mg/L p-CNT and a-CNT for four days. Subsequently, the mRNA expression of antioxidant enzymes, including cat, gst, and sod, in a-CNT group increased by 1.5- to 1.7-fold, consistent with increased expression of genes associated with inflammation (interleukin-8) and apoptosis (p53) compared to control. The higher toxicity of a-CNTs to zebrafish than p-CNT might be due to the increased oxidative potential by altered physicochemical properties. These findings provide new insights into the risk assessment and environmental management of MWCNTs in the aquatic environment. However, further testing at environmentally relevant doses, different exposure durations, and diverse weathering parameters is warranted.

In vitro toxicity of carbon nanotubes: a systematic review

Carbon nanotube (CNT) toxicity-related issues provoke many debates in the scientific community. The controversial and disputable data about toxicity doses, proposed hazard effects, and human health concerns significantly restrict CNT applications in biomedical studies, laboratory practices, and industry, creating a barrier for mankind in the way of understanding how exactly the material behaves in contact with living systems. Raising the toxicity question again, many research groups conclude low toxicity of the material and its potential safeness at some doses for contact with biological systems. To get new momentum for researchers working on the intersection of the biological field and nanomaterials, i.e., CNT materials, we systematically reviewed existing studies with in vitro toxicological data to propose exact doses that yield toxic effects, summarize studied cell types for a more thorough comparison, the impact of incubation time, and applied toxicity tests. Using several criteria and different scientific databases, we identified and analyzed nearly 200 original publications forming a "golden core" of the field to propose safe doses of the material based on a statistical analysis of retrieved data. We also differentiated the impact of various forms of CNTs: on a substrate and in the form of dispersion because in both cases, some studies demonstrated good biocompatibility of CNTs. We revealed that CNTs located on a substrate had negligible impact, i.e., 90% of studies report good viability and cell behavior similar to control, therefore CNTs could be considered as a prospective conductive substrate for cell cultivation. In the case of dispersions, our analysis revealed mean values of dose/incubation time to be 4-5 μg mL-1 h-1, which suggested the material to be a suitable candidate for further studies to get a more in-depth understanding of its properties in biointerfaces and offer CNTs as a promising platform for fundamental studies in targeted drug delivery, chemotherapy, tissue engineering, biosensing fields, etc. We hope that the present systematic review will shed light on the current knowledge about CNT toxicity, indicate "dark" spots and offer possible directions for the subsequent studies based on the demonstrated here tabulated and statistical data of doses, cell models, toxicity tests, viability, etc.

Do Carbon Nanotubes and Asbestos Fibers Exhibit Common Toxicity Mechanisms?

During the last two decades several nanoscale materials were engineered for industrial and medical applications. Among them carbon nanotubes (CNTs) are the most exploited nanomaterials with global production of around 1000 tons/year. Besides several commercial benefits of CNTs, the fiber-like structures and their bio-persistency in lung tissues raise serious concerns about the possible adverse human health effects resembling those of asbestos fibers. In this review, we present a comparative analysis between CNTs and asbestos fibers using the following four parameters: (1) fibrous needle-like shape, (2) bio-persistent nature, (3) high surface to volume ratio and (4) capacity to adsorb toxicants/pollutants on the surface. We also compare mechanisms underlying the toxicity caused by certain diameters and lengths of CNTs and asbestos fibers using downstream pathways associated with altered gene expression data from both asbestos and CNT exposure. Our results suggest that indeed certain types of CNTs are emulating asbestos fiber as far as associated toxicity is concerned.

Signaling Pathways Implicated in Carbon Nanotube-Induced Lung Inflammation

Inflammation is a tissue response to a variety of harmful stimuli, such as pathogens, irritants, and injuries, and can eliminate insults and limit tissue damage. However, dysregulated inflammation is recognized as a cause of many human diseases, exemplified by organ fibrosis and cancer. In this regard, inflammation-promoted fibrosis is commonly observed in human lung diseases, such as idiopathic pulmonary fibrosis and pneumoconiosis. Carbon nanotubes (CNTs) are a type of nanomaterials with unique properties and various industrial and commercial applications. On the other hand, certain forms of CNTs are potent inducers of inflammation and fibrosis in animal lungs. Notably, acute inflammation is a remarkable phenotype elicited by CNTs in the lung during the early acute phase post-exposure; whereas a type 2 immune response is evidently activated and dominates during the late acute and chronic phases, leading to type 2 inflammation and lung fibrosis. Numerous studies demonstrate that these immune responses involve distinct immune cells, various pathologic factors, and specific functions and play crucial roles in the initiation and progression of inflammation and fibrosis in the lung exposed to CNTs. Thus, the mechanistic understanding of the immune responses activated by CNTs has drawn great attention in recent years. This article reviews the major findings on the cell signaling pathways that are activated in immune cells and exert functions in promoting immune responses in CNT-exposed lungs, which would provide new insights into the understanding of CNT-induced lung inflammation and inflammation-driven fibrosis, the application of CNT-induced lung inflammation and fibrosis as a new disease model, and the potential of targeting immune cells as a therapeutic strategy for relevant human lung diseases.

Multi-walled carbon nanotubes induce oxidative stress, apoptosis, and dysfunction in isolated rat heart mitochondria: protective effect of naringin

Multi-walled carbon nanotubes (MWCNTs) are material with exclusive features that can be applied in different fields including industrial and medicine. It has been determined that the accumulation of MWCNTs in the organs is along with genotoxic and cytotoxic injuries. Previous studies have shown mitochondrial dysfunction in MWCNTs exposure with cell lines, but their exact mechanisms with isolated mitochondria have remained unclear. The present study evaluated toxicity induced by MWCNTs in isolated rat heart mitochondria and protective effect of naringin. Our results showed that MWCNTs toxicity caused the prevention of heart mitochondrial complex II activity. Treatment of isolated heart mitochondria with MWCNTs led to an increase in mitochondrial reactive oxygen species (ROS) generation, mitochondrial membrane potential (MMP) collapse, and mitochondrial malondialdehyde (MDA) and a decrease in mitochondrial glutathione (GSH) level and mitochondrial catalase (CAT) activity. Pretreatment of isolated heart mitochondria with naringin decreased mitochondrial oxidative damage through decreasing lipid peroxidation, returned mitochondrial complex II changes, decreasing MMP collapse and ROS production, and restoration of GSH level and CAT activity. Our findings indicated that MWCNTs had toxic effects on isolated heart mitochondria by inducing oxidative stress and possibly apoptosis pathway. The protection effects of naringin may be accompanied by mitochondrial conservation by its antioxidant property or due to its free radical scavenging. Our findings indicated that naringin had a possible role in preventing the mitochondria complaints in the heart.

In Vivo Activation and Pro-Fibrotic Function of NF-κB in Fibroblastic Cells During Pulmonary Inflammation and Fibrosis Induced by Carbon Nanotubes

Exposure to insoluble particles in the lung elicits inflammatory responses that eliminate deposited particulates and repair damaged tissue. Overzealous or prolonged responses lead to chronic conditions, such as fibrosis and malignancy, which are frequently progressive and refractory to drug therapy leading to high rates of disability and mortality. The molecular events underlying the progression of lung inflammation to chronic pathology, in particular, the conversion to fibrosis, remain poorly understood. Fibrogenic multi-walled carbon nanotubes (MWCNTs) have been shown to stimulate prominent acute inflammation that evolves into chronic lesions characterized by chronic inflammation, interstitial fibrosis, and granulomas in mouse lungs. In this communication, we examined the in vivo activation of nuclear factor-κB (NF-κB) signaling in fibroblastic cells during the inflammatory and fibrotic progression induced by MWCNTs. Wild-type C57BL/6J male mice were exposed to two fibrogenic MWCNTs (Mitsui XNRI MWNT-7 and long MWCNTs) by pharyngeal aspiration. Both MWCNTs strongly stimulated the nuclear translocation of NF-κB p65 in lung fibroblasts and myofibroblasts during the acute and chronic responses. Phosphorylated NF-κB p65 at serine 276, a marker of NF-κB activation, was markedly induced by MWCNTs in the nucleus of fibroblastic cells. Moreover, two NF-κB-regulated genes encoding pro-fibrotic mediators, tissue inhibitor of metalloproteinase 1 (TIMP1), and osteopontin (OPN), respectively, were significantly induced in lung fibroblasts and myofibroblasts. These results demonstrate that NF-κB is activated to mediate transactivation of pro-fibrotic genes in fibroblastic cells during pulmonary acute and chronic responses to CNTs, providing a mechanistic framework for analyzing gene regulation in pulmonary fibrotic progression through NF-κB signaling.

Toxicity of carbon-based nanomaterials: Reviewing recent reports in medical and biological systems

Application of nanomaterials in our daily life is increasing, day in day out and concerns have raised about their toxicity for human and other organisms. In this manner, carbon-based nanomaterials have been applied to different products due to their unique physicochemical, electrical, mechanical properties, and biological compatibility. But, there are several reports about the negative effects of these materials on biological systems and cellular compartments. This review article describes the various types of carbon-based nanomaterials and methods that use for determining these toxic effects that are reported recently in the papers. Then, extensively discussed the toxic effects of these materials on the human and other living organisms and also their toxicity routs including Neurotoxicity, Hepatotoxicity, Nephrotoxicity, Immunotoxicity, Cardiotoxicity, Genotoxicity and epigenetic toxicity, Dermatotoxicity, and Carcinogenicity.

Mangiferin alleviates arsenic induced oxidative lung injury via upregulation of the Nrf2-HO1 axis

Arsenic contaminated drinking water consumption is a serious health issue around the world. Chronic inorganic arsenic exposure has been associated with respiratory dysfunctions. It exerts various detrimental effects, disrupting normal cellular homeostasis and turning on severe pulmonary complications. This study elucidated the role of mangiferin, a natural xanthone, against arsenic induced lung toxicity. Chronic exposure of sodium arsenite (NaAsO2) at 10 mg/kg bw for 3 months abruptly increased the LDH release in broncho-alveolar lavage fluid, generated reactive oxygen species (ROS), impaired the antioxidant defense and distorted the alveoli architecture. It caused significant inflammatory outburst and promoted the apoptotic mode of cell death via upregulating the expressions of various proapoptotic molecules related to mitochondrial, extra-mitochondrial and ER stress mediated apoptotic pathway. Activation of inflammatory cascade led to disruption of alveolar capillary barrier and impaired Na+/K+-ATPase function that led to detaining of alveolar fluid clearance activity. Mangiferin due to its anti-inflammatory activity suppressed this inflammation and reduced inflammatory cell infiltration in lung tissue. It significantly restored the antioxidant balance and inhibited apoptosis in lung via upregulating Nrf2-HO1 axis.

Single wall and multiwall carbon nanotubes induce different toxicological responses in rat alveolar macrophages

Human exposure to airborne carbon nanotubes (CNT) is increasing because of their applications in different sectors; therefore, they constitute a biological hazard. Consequently, developing studies on CNT toxicity become a necessity. CNTs can have different properties in term of length, size and charge. Here, we compared the cellular effect of multiwall (MWCNTs) and single wall CNTs (SWCNTs). MWCNTs consist of multiple layers of graphene, while SWCNTs are monolayers. The effects of MWCNTs and SWCNTs were evaluated by the water-soluble tetrazolium salt cell proliferation assay on NR8383 cells, rat alveolar macrophage cell line (NR8383). After 24 hours of exposure, MWCNTs showed higher toxicity (50% inhibitory concentration [IC₅₀ ] = 3.2 cm² /cm² ) than SWCNTs (IC₅₀  = 44 cm² /cm² ). Only SWCNTs have induced NR8383 cells apoptosis as assayed by flow cytometry using the annexin V/IP staining test. The expression of genes involved in oxidative burst (Ncf1), inflammation (Nfκb, Tnf-α, Il-6 and Il-1β), mitochondrial damage (Opa) and apoptotic balance (Pdcd4, Bcl-2 and Casp-8) was determined. We found that MWCNT exposure predominantly induce inflammation, while SWCNTs induce apoptosis and impaired mitochondrial function. Our results clearly suggest that MWCNTs are ideal candidates for acute inflammation induction. In vivo studies are required to confirm this hypothesis. However, we conclude that toxicity of CNTs is dependent on their physical and chemical characteristics.

Necrotic, apoptotic and autophagic cell fates triggered by nanoparticles

Nanomaterials have gained a rapid increase in use in a variety of applications that pertain to many aspects of human life. The majority of these innovations are centered on medical applications and a range of industrial and environmental uses ranging from electronics to environmental remediation. Despite the advantages of NPs, the knowledge of their toxicological behavior and their interactions with the cellular machinery that determines cell fate is extremely limited. This review is an attempt to summarize and increase our understanding of the mechanistic basis of nanomaterial interactions with the cellular machinery that governs cell fate and activity. We review the mechanisms of NP-induced necrosis, apoptosis and autophagy and potential implications of these pathways in nanomaterial-induced outcomes. Abbreviations: Ag, silver; CdTe, cadmium telluride; CNTs, carbon nanotubes; EC, endothelial cell; GFP, green fluorescent protein; GO, graphene oxide; GSH, glutathione; HUVECs, human umbilical vein endothelial cells; NP, nanoparticle; PEI, polyethylenimine; PVP, polyvinylpyrrolidone; QD, quantum dot; ROS, reactive oxygen species; SiO2, silicon dioxide; SPIONs, superparamagnetic iron oxide nanoparticles; SWCNT, single-walled carbon nanotubes; TiO2, titanium dioxide; USPION, ultra-small super paramagnetic iron oxide; ZnO, zinc oxide.

Long-term polarization of alveolar macrophages to a profibrotic phenotype after inhalation exposure to multi-wall carbon nanotubes

Background

Nanomaterials are widely used in various fields. Although the toxicity of carbon nanotubes (CNTs) in pulmonary tissues has been demonstrated, the toxicological effect of CNTs on the immune system in the lung remains unclear.

Methods and finding

In this study, exposure to Taquann-treated multi-walled CNTs (T-CNTs) was performed using aerosols generated in an inhalation chamber. At 12 months after T-CNT exposure, alveolar inflammation with macrophage accumulation and hypertrophy of the alveolar walls were observed. In addition, fibrotic lesions were enhanced by T-CNT exposure. The macrophages in the bronchoalveolar lavage fluid of T-CNT-exposed mice were not largely shifted to any particular population, and were a mixed phenotype with M1 and M2 polarization. Moreover, the alveolar macrophages of T-CNT-exposed mice produced matrix metalloprotinase-12.

Conclusions

These results suggest that T-CNT exposure promoted chronic inflammation and fibrotic lesion formation in profibrotic macrophages for prolonged periods.

Effects of exposure of adult mice to multi-walled carbon nanotubes on the liver lipid metabolism of their offspring

Objective: To explore the toxicity of multi-walled carbon nanotubes (MWCNTs) on the liver lipid metabolism of offspring mice and the possible mechanisms involved. Method: Virgin female (16-18 g) and male (18-20 g) C57BL/6 mice were randomly divided into two groups: Control group and Test group. After anesthesia with chloral hydrate, the mice were administered 50 μL saline or dust solution by intratracheal instillation (Control group: 50 μL saline; Test group: 15 mg kg-1 MWCNTs). Mice were injected with these doses once a week for 13 weeks. Then, male and female mice in the same group were allowed to mate to produce offspring. The pups were fed with normal diet until the end of the experiment (12 weeks old). The offspring mice were sacrificed by decapitation to detect the blood biochemistry and the expression of genes and proteins. Results: Compared with the Control group, MWCNTs significantly reduced the weight of offspring mice (male and female) and led to histopathological changes in the liver tissues. The expression of liver fat synthesis gene significantly increased (P < 0.05 or P < 0.01). The expression of genes and proteins involved in the inflammatory reactions appeared to be abnormal (P < 0.05 or P < 0.01). Conclusion: Exposure of adult mice to MWCNTs can affect the expression of fatty acid synthesis genes in the liver tissues of offspring mice, leading to disruption of liver function and accumulation of lipid droplets in the hepatocytes. The imbalance between M1 and M2 liver macrophage phenotypes may be one of the underlying mechanisms of action of MWCNTs leading to disordered fatty acid synthesis in offspring mice.

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

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

Single-walled and multi-walled carbon nanotubes induce sequence-specific epigenetic alterations in 16 HBE cells

Recent studies have identified carbon nanotube (CNT)-induced epigenetic changes as one of the key players in patho-physiological response. In the present study, we investigated whether CNT exposure is associated with epigenetic changes in human bronchial epithelial cells (16 HBE), in vitro. We focused on global DNA methylation, methylation of LINE-1 elements and promoter sequence of twelve functionally important genes (SKI, DNMT1, HDAC4, NPAT, ATM, BCL2L11, MAP3K10, PIK3R2, MYO1C, TCF3, FGFR 1 and AGRN). Additionally, we studied the influence of CNT exposure on miRNA expression. Using a LC-MS/MS method and pyrosequencing for LINE-1, we observed no significant changes in global DNA methylation (%) between the concentrations of multi-walled and single-walled CNT (MWCNT and SWCNT, respectively). Significant changes in sequence-specific methylation was observed in at least one CpG site for DNMT1 (SWCNT), HDAC4 (MWCNT), NPAT/ATM (MWCNT and SWCNT), MAP3K10 (MWCNT), PIK3R2 (MWCNT and SWCNT) and MYO1C (SWCNT). While changes in DNA methylation of the genes were relatively small, these changes were associated with changes in RNA expression, especially for MWCNT. However, the study did not reveal any significant alteration in the miRNA expression, associated with MWCNT and SWCNT exposure. Based on our results, mainly MWCNT influence DNA methylation and expression of the studied genes and could have significant impact on several critical cellular processes.

Cross-linkable graphene oxide embedded nanocomposite hydrogel with enhanced mechanics and cytocompatibility for tissue engineering

Graphene oxide (GO) is an attractive material that can be utilized to enhance the modulus and conductivities of substrates and hydrogels. To covalently cross-link graphene oxide sheets into hydrogels, abundant cross-linkable double bonds were introduced to synthesize the graphene-oxide-tris-acrylate sheet (GO-TrisA). Polyacrylamide (PAM) nanocomposite hydrogels were then fabricated with inherent covalently and permanently cross-linked GO-TrisA sheets. Results showed that the covalently cross-linked GO-TrisA/PAM nanocomposite hydrogel had enhanced mechanical strength, thermo stability compared with GO/PAM hydrogel maintained mainly by hydrogen bonding between PAM chains and GO sheets. In vitro cell study showed that the covalently cross-linked rGO-TrisA/PAM nanocomposite hydrogel had excellent cytocompatibility after in situ reduction. These results suggest that rGO-TrisA/PAM nanocomposite hydrogel holds great potential for tissue engineering applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1247-1257, 2018.

Characterization of the proteome and lipidome profiles of human lung cells after low dose and chronic exposure to multiwalled carbon nanotubes

The effects of long-term chronic exposure of human lung cells to multi-walled carbon nanotubes (MWCNT) and their impact upon cellular proteins and lipids were investigated. Since the lung is the major target organ, an in vitro normal bronchial epithelial cell line model was used. Additionally, to better mimic exposure to manufactured nanomaterials at occupational settings, cells were continuously exposed to two non-toxic and low doses of a MWCNT for 13-weeks. MWCNT-treatment increased ROS levels in cells without increasing oxidative DNA damage and resulted in differential expression of multiple anti- and pro-apoptotic proteins. The proteomic analysis of the MWCNT-exposed cells showed that among more than 5000 identified proteins; more than 200 were differentially expressed in the treated cells. Functional analyses revealed association of these differentially regulated proteins to cellular processes such as cell death and survival, cellular assembly, and organization. Similarly, shotgun lipidomic profiling revealed accumulation of multiple lipid classes. Our results indicate that long-term MWCNT-exposure of human normal lung cells at occupationally relevant low-doses may alter both the proteome and the lipidome profiles of the target epithelial cells in the lung.

Immunotoxicological impact and biodistribution assessment of bismuth selenide (Bi2Se3) nanoparticles following intratracheal instillation in mice

Variously synthesized and fabricated Bi2Se3 nanoparticles (NPs) have recently been explored for their theranostic properties. Herein, we investigated the long term in-vivo biodistribution of Bi2Se3 NPs and systematically screened its immune-toxic potential over lungs and other secondary organs post intratracheal instillation. X-Ray CT scan and ICP MS results revealed significant particle localization and retention in lungs monitored for 1 h and 6 months time period respectively. Subsequent particle trafficking was observed in liver, the major reticuloendothelial organ followed by gradual but incomplete renal clearance. Pulmonary cytotoxicity was also found to be associated with persistent neutrophilic and ROS generation at all time points following NP exposure. The inflammatory markers along with ROS generation further promoted oxidative stress and exaggerated additional inflammatory pathways leading to cell death. The present study, therefore, raises serious concern about the hazardous effects of Bi2Se3 NPs and calls for further toxicity assessments through different administration routes and doses as well.

Cellular responses induced by multi-walled carbon nanotubes: in vivo and in vitro studies on the medicinal leech macrophages

The core characteristics of multi-wall carbon nanotubes (MWCNTs) are impressive and attractive for technology however, since their production and use is steadily increasing, their environmental dispersion could be potentially hazardous to animal and human health. For this reason, the identification of new methods and of reliable models to better understand MWCNT effects is essential. Here we propose the medicinal leech as an alternative model to assess the effects of MWCNTs on immune system. Our previous studies have already demonstrated that in vivo MWCNT treatment induces the activation of leech’s macrophages. Here we will focus on the direct effects of MWCNTs on these cells by isolating and culturing leech's macrophages by means of the consolidated Matrigel technique, followed by MWCNT in vitro treatment. Our results indicate that MWCNT administration causes both the decrease of cell proliferation rate and the increase of the apoptotic rate. Furthermore, since oxidative stress is linked with inflammation, reactive oxygen species has been evaluated confirming that their production rate increases after MWCNT treatment. Our experimental approaches demonstrate the ability of MWCNTs inducing a powerful inflammatory response and confirm that the medicinal leech is a good alternative model to study the possible harmful effects of any nanomaterial.

Current applications and future prospects of nanomaterials in tumor therapy

Tumors are one of the most serious human diseases and cause numerous global deaths per year. In spite of many strategies applied in tumor therapy, such as radiation therapy, chemotherapy, surgery, and a combination of these treatments, tumors are still the foremost killer worldwide among human diseases, due to their specific limitations, such as multidrug resistance and side effects. Therefore, it is urgent and necessary to develop new strategies for tumor therapy. Recently, the fast development of nanoscience has paved the way for designing new strategies to treat tumors. Nanomaterials have shown great potential in tumor therapy, due to their unique properties, including passive targeting, hyperthermia effects, and tumor-specific inhibition. This review summarizes the recent progress using the innate antitumor properties of metallic and nonmetallic nanomaterials to treat tumors, and related challenges and prospects are discussed.

Polydatin ameliorates Staphylococcus aureus-induced mastitis in mice via inhibiting TLR2-mediated activation of the p38 MAPK/NF-κB pathway

Recent studies show that Polydatin (PD) extracted from the roots of Polygonum cuspidatum Sieb, a widely used traditional Chinese remedies, possesses anti-inflammatory activity in several experimental models. In this study, we investigated the anti-inflammatory effects of PD on Staphylococcus aureus-induced mastitis in mice and elucidated the potential mechanisms. In mice with S aureus-induced mastitis, administration of PD (15, 30, 45 mg/kg, ip) or dexamethasone (Dex, 5 mg/kg, ip) significantly suppressed the infiltration of inflammatory cells, ameliorated the mammary structural damage, and inhibited the activity of myeloperoxidase, a biomarker of neutrophils accumulation. Furthermore, PD treatment dose-dependently decreased the levels of TNF-α, IL-1β, IL-6 and IL-8 in the mammary gland tissues. PD treatment also dose-dependently decreased the expression of TLR2, MyD88, IRAK1, IRAK4 and TRAF6 as well as the phosphorylation of TAK1, MKK3/6, p38 MAPK, IκB-α and NF-κB in the mammary gland tissues. In mouse mammary epithelial cells (mMECs) infected by S aureus in vitro, pretreatment with PD dose-dependently suppressed the upregulated pro-inflammatory cytokines and signaling proteins, and the nuclear translocation of NF-κB p65 and AP-1. A TLR2-neutralizing antibody mimicked PD in its suppression on S aureus-induced upregulation of MyD88, p-p38 and p-p65 levels in mMECs. PD (50, 100 μg/mL) affected neither the growth of S aureus in vitro, nor the viability of mMECs. In conclusion, PD does not exhibit antibacterial activity against S aureus, its therapeutic effects in mouse S aureus-induced mastitis depend on its ability to down-regulate pro-inflammatory cytokine levels via inhibiting TLR2-mediated activation of the p38 MAPK/NF-κB signaling pathway.

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

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

TIMP1 promotes multi-walled carbon nanotube-induced lung fibrosis by stimulating fibroblast activation and proliferation

Pulmonary exposure to multi-walled carbon nanotubes (MWCNTs) may cause fibrosing lesions in animal lungs, raising health concerns about such exposure in humans. The mechanisms underlying fibrosis development remain unclear, but they are believed to involve the dysfunction of fibroblasts and myofibroblasts. Using a mouse model of MWCNT exposure, we found that the tissue inhibitor of metalloproteinase 1 (Timp1) gene was rapidly and highly induced in the lungs by MWCNTs in a time- and dose-dependent manner. Concomitantly, a pronounced elevation of secreted TIMP1 was observed in the bronchoalveolar lavage (BAL) fluid and serum. Knockout (KO) of Timp1 in mice caused a significant reduction in fibrotic focus formation, collagen fiber deposition, recruitment of fibroblasts and differentiation of fibroblasts into myofibroblasts in the lungs, indicating that TIMP1 plays a critical role in the pulmonary fibrotic response to MWCNTs. At the molecular level, MWCNT exposure significantly increased the expression of the cell proliferation markers Ki-67 and PCNA and a panel of cell cycle-controlling genes in the lungs in a TIMP1-dependent manner. MWCNT-stimulated cell proliferation was most prominent in fibroblasts but not myofibroblasts. Furthermore, MWCNTs elicited a significant induction of CD63 and integrin β1 in lung fibroblasts, leading to the formation of a TIMP1/CD63/integrin β1 complex on the surface of fibroblasts in vivo and in vitro, which triggered the phosphorylation and activation of Erk1/2. Our study uncovers a new pathway through which induced TIMP1 critically modulates the pulmonary fibrotic response to MWCNTs by promoting fibroblast activation and proliferation via the TIMP1/CD63/integrin β1 axis and ERK signaling.

Toxicity of graphene-family nanoparticles: a general review of the origins and mechanisms

Due to their unique physicochemical properties, graphene-family nanomaterials (GFNs) are widely used in many fields, especially in biomedical applications. Currently, many studies have investigated the biocompatibility and toxicity of GFNs in vivo and in intro. Generally, GFNs may exert different degrees of toxicity in animals or cell models by following with different administration routes and penetrating through physiological barriers, subsequently being distributed in tissues or located in cells, eventually being excreted out of the bodies. This review collects studies on the toxic effects of GFNs in several organs and cell models. We also point out that various factors determine the toxicity of GFNs including the lateral size, surface structure, functionalization, charge, impurities, aggregations, and corona effect ect. In addition, several typical mechanisms underlying GFN toxicity have been revealed, for instance, physical destruction, oxidative stress, DNA damage, inflammatory response, apoptosis, autophagy, and necrosis. In these mechanisms, (toll-like receptors-) TLR-, transforming growth factor β- (TGF-β-) and tumor necrosis factor-alpha (TNF-α) dependent-pathways are involved in the signalling pathway network, and oxidative stress plays a crucial role in these pathways. In this review, we summarize the available information on regulating factors and the mechanisms of GFNs toxicity, and propose some challenges and suggestions for further investigations of GFNs, with the aim of completing the toxicology mechanisms, and providing suggestions to improve the biological safety of GFNs and facilitate their wide application.

Triggering of apoptosis in osteosarcoma cells by graphene/single-walled carbon nanotube hybrids via the ROS-mediated mitochondrial pathway

Carbon nanomaterials are increasingly significant in the biological and medical fields, especially becoming promising candidates in treating difficult and complicated disease. Graphene/single-walled carbon nanotubes (G/SWCNT) hybrids is 3D structure which has been constructed by combining 1D single-walled carbon nanotubes (SWCNTs) and 2D graphene. However, the effects of the nanomaterial on biological systems are limited. In this study, we report a systematic investigation of the cytotoxicity and in vivo biodistribution of G/SWCNT hybrids on osteosarcoma cells (HOS and U2OS). The CCK-8, neutral red, and lactic dehydrogenase assays demonstrated that the cytotoxicity of G/SWCNT hybrids exhibits a dose-dependent behavior on osteosarcoma cells. In our conditions, the hybrids were less cytotoxic than graphene and single-walled carbon nanotubes. The results also showed the apoptosis of osteosarcoma cells induced by G/SWCNT hybrids was through the increase of intracellular reactive oxygen species, the decrease of mitochondrial membrane potential, the alternation of apoptosis-related proteins, and then triggered the ROS-mediated mitochondrial pathway. Moreover, the in vivo biodistribution of G/SWCNT hybrids was observed by histological analysis of major organs in mice, and showed that organs were neither damaged nor inflammatory. This study demonstrated that G/SWCNT hybrids could serve as a potential platform in anticancer therapy. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 443-453, 2017.

Impeded repair of abasic site damaged lesions in DNA adsorbed over functionalized multiwalled carbon nanotube and graphene oxide

The processing of abasic site DNA damage lesions in extracellular DNA in the presence of engineered carbon nanomaterials (CNMs) is demonstrated. The efficacy of the apurinic-apyrimidinic endonuclease 1 (APE1) in the cleavage of abasic site lesions in the presence of carboxylated multi-walled carbon nanotubes (MWCNT-COOH) and graphene oxide (GO) are compared. The CNMs were found to perturb the incision activity of APE1. The reason for such perturbation process was anticipated to take place either by the non-specific adsorption of APE1 over the free surface of the CNMs or steric hindrance offered by the CNM-DNA complex. Accordingly, bovine serum albumin (BSA) was selectively utilized to block the free surface of the CNM-DNA hybrid material. Further treatment of the CNM-DNA-BSA complex with APE1 resulted in a marginal increase in APE1 efficiency. This indicates that APE1 in solution is unable to process the abasic sites on DNA adsorbed over the CNMs. However, the cleavage activity of APE1 was restored in the presence of non-ionic surfactant (Tween 20) that inhibits adsorption of the DNA on the surface of the CNMs. The conformational deformation of the DNA, along with steric hindrance induced by the CNMs resulted in the inhibition of abasic site DNA repair by APE1. Moreover, appreciable changes in the secondary structure of APE1 adsorbed over the CNMs were observed that contribute further to the repair refractivity of the abasic sites. From a toxicological viewpoint, these findings can be extended to the study of the effect of engineered nanoparticles in the intracellular DNA repair process.

In vivo activation of a T helper 2-driven innate immune response in lung fibrosis induced by multi-walled carbon nanotubes

Pulmonary exposure to certain forms of carbon nanotubes (CNT) induces fibrosing lesions in the lungs that manifest an acute inflammation followed by chronic interstitial fibrosis. The mechanism of CNT-induced fibrogenesis is largely unknown. The biphasic development with drastically distinct pathologic manifestations suggests a junction of acute-to-chronic transition. Here we analyzed the molecular pathways and regulators underlying the pathologic development of CNT-induced lung fibrosis. Mice were exposed to multi-walled CNT (MWCNT; XNRI MWNT-7, Mitsui; 40 μg) by pharyngeal aspiration for 7 days along with vehicle and carbonaceous controls. Genome-wide microarray analyses of the lungs identified a range of differentially expressed genes that potentially function in the acute-to-chronic transition through pathways involving immune and inflammatory regulation, responses to stress and extracellular stimuli, and cell migration and adhesion. In particular, a T helper 2 (Th2)-driven innate immune response was significantly enriched. We then demonstrated that MWCNT induced the expression of Th2 cytokines interleukin (IL)-4 and IL-13, and a panel of signature downstream genes, such as Il4i1, Chia, and Ccl11/Eotaxin, time dependently. Induction of Th2 cytokines took place in CD4+ T lymphocytes indicating activation of Th2 cells. Furthermore, induction involved activation of a Th2 cell-specific signaling pathway through phosphorylation of STAT6 and up-regulation of GATA-3 to mediate the transcription of Th2 target genes. Our study uncovers activation of a Th2-driven immune/inflammatory response during pulmonary fibrosis development induced by MWCNT. The findings provide novel insights into the molecular events that control the transition from an acute inflammatory response to chronic fibrosis through Th2 functions in CNT-exposed lungs.

Multiwall Carbon Nanotube-Induced Apoptosis and Antioxidant Gene Expression in the Gills, Liver, and Intestine of Oryzias latipes

Multiwall carbon nanotubes (MWCNTs) have many attractive properties with potential applications in various fields. Despite their usefulness, however, the associated waste can be hazardous to the environment. To examine adverse effects in aquatic environments, Oryzias latipes were exposed to MWCNTs dispersed in water for 14 days and apoptosis and antioxidant gene expression were observed. This work showed that in gills exposed to 100 mg/L MWCNTs for 4 days, there was significant p53, caspase-3 (Cas3), caspase-8 (Cas8), and caspase-9 (Cas9) gene expression relative to the controls, while catalase (CAT) and glutathione-S-transferase (GST) expression were reduced. At 14 days, CAT, GST, and metallothionein (MT) were induced significantly in the gills and Cas3, Cas8, and Cas9 were induced in the liver. No significant gene induction was seen in intestine. Intracellular reactive oxygen species (ROS) were increased significantly only at 14 days. Histologically, no apoptosis was observed with exposure to 100 mg/L MWCNTs for 21 days. The gills were more sensitive to MWCNT toxicity than the other organs. Males had higher apoptosis gene induction than females. These results demonstrated that MWCNTs could cause apoptosis in a manner influenced by tissue and gender in aqueous environments.

Advances in mechanisms and signaling pathways of carbon nanotube toxicity

Carbon nanotubes (CNT) have been developed into new materials with a variety of industrial and commercial applications. In contrast, the physicochemical properties of CNT at the nanoscale render them the potency to generate toxic effects. Indeed, the potential health impacts of CNT have drawn a great deal of attention in recent years, owing to their identified toxicological and pathological consequences including cytotoxicity, inflammation, fibrosis, genotoxicity, tumorigenesis, and immunotoxicity. Understanding the mechanisms by which CNT induce toxicity and pathology is thus urgently needed for accurate risk assessment of CNT exposure in humans, and for safe and responsible development and commercialization of nanotechnology. Here, we summarize and discuss recent advances in this area with a focus on the molecular interactions between CNT and mammalian systems, and the signaling pathways important for the development of CNT toxicity such as the NF-κB, NLRP3 inflammasome, TGF-β1, MAPK, and p53 signaling cascades. With the current mechanistic evidence summarized in this review, we expect to provide new insights into CNT toxicology at the molecular level and offer new clues to the prevention of health effects resulting from CNT exposure. Moreover, we disclose questions and issues that remain in this rapidly advancing field of nanotoxicology, which would facilitate ascertaining future research directions.

Carboxylated short single-walled carbon nanotubes but not plain and multi-walled short carbon nanotubes show in vitro genotoxicity

Long carbon nanotubes (CNTs) resemble asbestos fibers due to their high length to diameter ratio and they thus have genotoxic effects. Another parameter that might explain their genotoxic effects is contamination with heavy metal ions. On the other hand, short (1-2 µm) CNTs do not resemble asbestos fibers, and, once purified from contaminations, they might be suitable for medical applications. To identify the role of fiber thickness and surface properties on genotoxicity, well-characterized short pristine and carboxylated single-walled (SCNTs) and multi-walled (MCNTs) CNTs of different diameters were studied for cytotoxicity, the cell's response to oxidative stress (immunoreactivity against hemoxygenase 1 and glutathione levels), and in a hypoxanthine guanine phosphoribosyltransferase (HPRT) assay using V79 chinese hamster fibroblasts and human lung adenocarcinoma A549 cells. DNA repair was demonstrated by measuring immunoreactivity against activated histone H2AX protein. The number of micronuclei as well as the number of multinucleated cells was determined. CNTs acted more cytotoxic in V79 than in A549 cells. Plain and carboxylated thin (<8 nm) SCNTs and MCNTs showed greater cytotoxic potential and carboxylated CNTs showed indication for generating oxidative stress. Multi-walled CNTs did not cause HPRT mutation, micronucleus formation, DNA damage, interference with cell division, and oxidative stress. Carboxylated, but not plain, SCNTs showed indication for in vitro DNA damage according to increase of H2AX-immunoreactive cells and HPRT mutation. Although short CNTs presented a low in vitro genotoxicity, functionalization of short SCNTs can render these particles genotoxic.

Identifying contact-mediated, localized toxic effects of MWCNT aggregates on epithelial monolayers: a single-cell monitoring toxicity assay

Aggregates of multiwalled carbon nanotubes (MWCNT) impair the barrier properties of human airway cell monolayers. To resolve the mechanism of the barrier alteration, monolayers of Calu-3 human airway epithelial cells were exposed to aggregated MWCNT. At the cell-population level, trans-epithelial electrical resistance (TEER) was used as an indicator of barrier competence, caspase activity was assessed with standard biochemical assays, and cell viability was investigated by biochemical techniques and high-throughput screening (HTS) technique based on automated epifluorescence microscopy. At cell level, the response to MWCNT was investigated with confocal microscopy, by evaluating cell death (calcein/propidium iodide (PI)), proliferation (Ki-67), and apoptosis (caspase activity). At the cell-population level, exposure to aggregated MWCNT caused a decrease in TEER, which was not associated with a decrease in cell viability or onset of apoptosis even after an 8-d exposure. In contrast, confocal imaging demonstrated contact with MWCNT aggregates triggered cell death after 24 h of exposure. In the presence of a natural surfactant, both TEER decrease and contact-mediated toxicity were mitigated. With confocal imaging, increased proliferation and apoptosis were detected in Calu-3 cells next to the aggregates. Contact-mediated cytotoxicity was recorded in two additional cell lines (BEAS-2B and A549) derived from human airways. Similar results were confirmed by adopting two additional MWCNT preparations with different physico-chemical features. This indicates MWCNT caused localized damage to airway epithelial monolayers in vitro and altered the apoptotic and proliferative rate of epithelial cells in close proximity to the aggregates. These findings provide evidence on the pathway by which MWCNT aggregates impair airway barrier function, and support the use of imaging techniques as a possible regulatory-decision supporting tool to identify effects of aggregated nanomaterials not readily detected at cell population level.

Genome-wide transcriptional analysis of apoptosis-related genes and pathways regulated by H2AX in lung cancer A549 cells

Histone H2AX is a novel tumor suppressor protein and plays an important role in apoptosis of cancer cells. However, the role of H2AX in lung cancer cells is unclear. The detailed mechanism and epigenetic regulation by H2AX remain elusive in cancer cells. We showed that H2AX was involved in apoptosis of lung cancer A549 cells as in other tumor cells. Knockdown of H2AX strongly suppressed apoptosis of A549 cells. We clarified the molecular mechanisms of apoptosis regulated by H2AX based on genome-wide transcriptional analysis. Microarray data analysis demonstrated that H2AX knockdown in A549 cells affected expression of 3,461 genes, including upregulation of 1,435 and downregulation of 2,026. These differentially expressed genes were subjected to bioinformatic analysis for exploring biological processes regulated by H2AX in lung cancer cells. Gene ontology analysis showed that H2AX affected expression of many genes, through which, many important functions including response to stimuli, gene expression, and apoptosis were involved in apoptotic regulation of lung cancer cells. Pathway analysis identified the mitogen-activated protein kinase signaling pathway and apoptosis as the most important pathways targeted by H2AX. Signal transduction pathway networks analysis and chromatin immunoprecipitation assay showed that two core genes, NFKB1 and JUN, were involved in apoptosis regulated by H2AX in lung cancer cells. Taken together, these data provide compelling clues for further exploration of H2AX function in cancer cells.

A nanoengineered embolic agent for precise radiofrequency ablation

The purpose of the work is to investigate whether the electromagnetic properties of multi-walled carbon nanotubes (MWCNT) in the presence of radiofrequency (RF) energy is (1) safe, and (2) improves the precision of the therapeutic efficiency of the RF-ablation (RFA) procedure. An in vitro phantom was created for evaluating temperature near RF treated nanotubes. For the in vivo study, three baboons and six pigs were submitted for RFA procedure in superior/inferior kidney poles embolized with a non-adherent, lipophilic embolic agent (marsembol) with or without MWCNT. Tissue damage in the surrounding kill zone was assayed through caspase-3 activation. The in vitro results showed marked heat increase only in the region of the nanotubes. In vivo, necrosis/ischemic damage resulted from RFA therapy alone, RFA plus marsembol only. In marsembol + MWCNT condition, dramatic disruption of cell membranes and sub-cellular organelles was found whereas the nuclear membranes and basal cell membranes remained largely intact. The marsembol vaporized under RFA and tissue fluid filled the space. This caused the MWCNT to cluster within the new aqueous environment. RFA plus marsembol + MWCNT created a well-defined demarcation between healthy and apoptotic cells as evidenced by a marked reduction of caspase-3 expression. By contrast, there was a much less defined ablation zone in the absence of MWCNT. In conclusion, the combination of RFA plus marsembol + MWCNT embolization delineated the kill zone in vitro and in vivo. We demonstrate that MWCNTs remain in the ablation region thus minimizing their migration to the systemic circulation.

Proteomic analysis of cellular response induced by multi-walled carbon nanotubes exposure in A549 cells

The wide application of multi-walled carbon nanotubes (MWCNT) has raised serious concerns about their safety on human health and the environment. However, the potential harmful effects of MWCNT remain unclear and contradictory. To clarify the potentially toxic effects of MWCNT and to elucidate the associated underlying mechanisms, the effects of MWCNT on human lung adenocarcinoma A549 cells were examined at both the cellular and the protein level. Cytotoxicity and genotoxicity were examined, followed by a proteomic analysis (2-DE coupled with LC-MS/MS) of the cellular response to MWCNT. Our results demonstrate that MWCNT induces cytotoxicity in A549 cells only at relatively high concentrations and longer exposure time. Within a relatively low dosage range (30 µg/ml) and short time period (24 h), MWCNT treatment does not induce significant cytotoxicity, cell cycle changes, apoptosis, or DNA damage. However, at these low doses and times, MWCNT treatment causes significant changes in protein expression. A total of 106 proteins show altered expression at various time points and dosages, and of these, 52 proteins were further identified by MS. Identified proteins are involved in several cellular processes including proliferation, stress, and cellular skeleton organization. In particular, MWCNT treatment causes increases in actin expression. This increase has the potential to contribute to increased migration capacity and may be mediated by reactive oxygen species (ROS).

Understanding the toxicity of carbon nanotubes in the environment is crucial to the control of nanomaterials in producing and processing and the assessment of health risk for human: a review

With the development and application of carbon nanotubes (CNTs), the potential hazards of CNTs to biological systems and the environment are getting more and more attention. This review evaluated the effects of physicochemical properties of CNTs on toxicity and summarized the advances on the mechanism of CNTs toxicity. We also proposed the possible hazards associated with CNTs and harmful effects resulting from exposure of aquatic animals, bacteria and higher plants to CNTs in vitro and in vivo. The current knowledge and gaps on CNTs were outlined as a potential problem for the environment and human health. The current research gaps on CNTs toxicity were identified and the further studying focus was proposed, too. This essay concluded with a set of recommendations for the advancement of understanding of the role of CNTs and future challenges in environmental and ecotoxicological research.

Mechanisms of nanoparticle-induced oxidative stress and toxicity

The rapidly emerging field of nanotechnology has offered innovative discoveries in the medical, industrial, and consumer sectors. The unique physicochemical and electrical properties of engineered nanoparticles (NP) make them highly desirable in a variety of applications. However, these novel properties of NP are fraught with concerns for environmental and occupational exposure. Changes in structural and physicochemical properties of NP can lead to changes in biological activities including ROS generation, one of the most frequently reported NP-associated toxicities. Oxidative stress induced by engineered NP is due to acellular factors such as particle surface, size, composition, and presence of metals, while cellular responses such as mitochondrial respiration, NP-cell interaction, and immune cell activation are responsible for ROS-mediated damage. NP-induced oxidative stress responses are torch bearers for further pathophysiological effects including genotoxicity, inflammation, and fibrosis as demonstrated by activation of associated cell signaling pathways. Since oxidative stress is a key determinant of NP-induced injury, it is necessary to characterize the ROS response resulting from NP. Through physicochemical characterization and understanding of the multiple signaling cascades activated by NP-induced ROS, a systemic toxicity screen with oxidative stress as a predictive model for NP-induced injury can be developed.

Nanomaterials in the application of tumor vaccines: advantages and disadvantages

Tumor vaccines are a novel approach to the treatment of malignancy, and are attracting the attention of the medical profession. Nanomaterials have significant advantages in the preparation of a tumor vaccine, including their ability to penetrate and target cancer tissue and their antigenic properties. In this review, we focus on several nanomaterials, ie, carbon nanotubes, nanoemulsions, nanosized aluminum, and nanochitosan. Applications for these nanomaterials in nanovaccines and their biological characteristics, as well as their potential toxicity, are discussed.

Short multiwall carbon nanotubes promote neuronal differentiation of PC12 cells via up-regulation of the neurotrophin signaling pathway

Numerous unique properties of carbon nanotubes make them attractive for applications in neurobiology such as drug delivery, tissue regeneration, and as scaffolds for neuronal growth. In this study, the critical roles of the length of multiwall carbon nanotubes (MWCNTs) on a neuronal-like model cell line PC12 cells are investiaged. Incubation of PC12 cells with carboxylated MWCNTs did not significantly affect cellular morphology and viability at lower concentrations. Short MWCNTs show higher cellular uptake and more obvious removal compared to longer ones, which can result in higher ability to promote PC12 cell differentiation. Pre-incubation of short MWCNTs can up-regulate the expression of neurotrophin signaling pathway-associated TrkA/p75 receptors and Pincher/Gap43/TH proteins, which might be the underlying mechanism for the improved differentiation in PC12 cells. The current results provide insight for future applications of MWCNTs in neuron drug delivery and neurodegenerative disease treatment.

Behavior and toxicity of graphene and its functionalized derivatives in biological systems

Graphene, as a class of 2D carbon nanomaterial, has attracted tremendous interest in different areas in recent years including biomedicine. The toxicity and behavior of graphene in biological systems are thus important fundamental issues that require significant attention. In this article, the toxicity of graphene is reviewed by describing the behavior of graphene and its derivatives in microorganisms, cells, and animals. Despite certain inconsistencies in several detailed experimental results and hypotheses of toxicity mechanisms, results from numerous reports all agree that the physicochemical properties such as surface functional groups, charges, coatings, sizes, and structural defects of graphene may affect its in vitro/in vivo behavior as well as its toxicity in biological systems. It is hoped that this review article will provide an overview understanding of the impacts, behavior, and toxicology of graphene and its derivatives in various biological systems.

Cytotoxicity and expression of genes involved in the cellular stress response and apoptosis in mammalian fibroblast exposed to cotton cellulose nanofibers

Cellulose nanofibers (CNF) have mechanical properties that make them very attractive for applications in the construction of polymeric matrices, drug delivery and tissue engineering. However, little is known about their impact on mammalian cells. The objective of this study was to evaluate the cytotoxicity of CNF and their effect on gene expression of fibroblasts cultured in vitro. The morphology of CNF was analyzed by transmission electron microscopy and the surface charge by Zeta potential. Cell viability was analyzed by flow cytometry assay and gene expression of biomarkers focused on cell stress response such as Heat shock protein 70.1 (HSP70.1) and Peroxiredoxin 1 (PRDX1) and apoptosis as B-cell leukemia (BCL-2) and BCL-2 associated X protein (BAX) by RT-PCR assay. Low concentrations of CNF (0.02-100 μg ml(-1)) did not cause cell death; however, at concentrations above 200 μg ml(-1), the nanofibers significantly decreased cell viability (86.41 ± 5.37%). The exposure to high concentrations of CNF (2000 and 5000 μg ml(-1)) resulted in increased HSP70.1, PRDX1 and BAX gene expression. The current study concludes that, under the conditions tested, high concentrations (2000 and 5000 μg ml(-1)) of CNF cause decreased cell viability and affect the expression of stress- and apoptosis-associated molecular markers.

Multi-walled carbon nanotube-induced inflammatory response and oxidative stress in a dynamic cell growth environment

BACKGROUND

Rapid increase in multi-walled carbon nanotube (MWCNT) production for their industrial and biomedical applications has led to concerns over the effects of MWCNTs on human health and the environment. Both animal and in vitro studies have provided important findings about MWCNT-induced effects on the lung cells or tissues. In vitro studies have provided a considerable amount of fundamental information on MWCNT-induced effects on the specific lung cells. However, the cell culture systems used in those studies were limited by the absence of dynamic nature of lung tissues. We hypothesized that MWCNT-induced cellular responses such as proliferation, inflammation, and oxidative stress under dynamic cell growth environment may differ from those under static cell growth environment.

RESULTS

In this study, we used a dynamic cell growth condition to mimic mechanically dynamic environment of the lung and characterized interleukin 8 (IL-8), reactive oxygen species (ROS), glutathione (GSH), and cell proliferation for three days following exposure of MWCNTs at different concentrations (5, 10, and 20 μg/ml) to A549 cell monolayer under both static and dynamic cell growth conditions. Our results demonstrated the distinct differences in the levels of inflammatory response and oxidative stress between static and dynamic cell growth conditions.

CONCLUSIONS

In conclusion, the dynamic cell growth system used in this study provided important changes in cellular responses that were not found in the static cell growth system and were similar to animal studies. The dynamic cell growth system can be considered as a viable alternative to in vivo test system in combination with existing in vitro static cell growth systems to evaluate the effect of MWCNTs on cellular responses in the respiratory system.

Multi-walled carbon nanotubes induce apoptosis via mitochondrial pathway and scavenger receptor

We have demonstrated previously that the acid-treated multi-walled carbon nanotubes (aci-MWCNTs) and taurine functionalized MWCNTs (tau-MWCNTs) induced differential pulmonary toxicity in mice after instillation exposure. In order to compare differences of cytotoxicity between the aci- and tau-MWCNTs, RAW 264.7 cells (a murine macrophage cell line) were chosen to be exposed to the aci- and tau-MWCNTs at concentrations of 0, 5, 20, 40, and 80μg/ml for 12 or 24h respectively. The results showed that although the aci- and tau-MWCNTs induced only mild decrease in cell viability to RAW 264.7 cells, the two types of MWCNTs elicited significant increase in apoptosis and decreased ability in cellular phagocytosis. Moreover, by using the specific inhibitors, we found that the scavenger receptors (SR) and caspase-9 were actively involved in the apoptosis induced by the aci- and tau-MWCNTs. The taurine functionalized MWCNTs (tau-MWCNTs) showed less cytotoxicity and apoptotic effect to RAW 264.7 cells than those of aci-MWCNTs. Taken together, the results indicated the important role of scavenger receptors and mitochondria in the apoptosis induced by MWCNTs.

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.

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.

The triggering of apoptosis in macrophages by pristine graphene through the MAPK and TGF-beta signaling pathways

With the development of nanotechnology and the wide use of graphene, it has become necessary to assess the potential biological adverse effects of graphene. However, most of the recent publications are focused on various modified graphenes. We demonstrated biological effects of commercial pristine graphene in murine RAW 264.7 macrophages, which is an important effector cells of the innate immune system. We found that the pristine graphene can induce cytotoxicity through the depletion of the mitochondrial membrane potential (MMP) and the increase of intracellular reactive oxygen species (ROS), then trigger apoptosis by activation of the mitochondrial pathway. The MAPKs (JNK, ERK and p38) as well as the TGF-beta-related signaling pathways were found to be activated in the pristine grapheme-treated cells, which activated Bim and Bax, two pro-apoptotic member of Bcl-2 protein family. Consequently, the caspase 3 and its downstream effector proteins such as PARP were activated and the execution of apoptosis was initiated. This study provides an insight for the suppression of the apoptosis induced by the graphene through the mitochondrial pathways, the MAPKs- and TGF-beta-related signaling pathways.