Toxicity of Multiwalled Carbon Nanotubes with End Defects Critically Depends on Their Functionalization Density

Lung Microtissue Array to Screen the Fibrogenic Potential of Carbon Nanotubes

Due to their excellent physical and chemical characteristics, multi-wall carbon nanotubes (MWCNT) have the potential to be used in structural composites, conductive materials, sensors, drug delivery and medical imaging. However, because of their small-size and light-weight, the applications of MWCNT also raise health concerns. In vivo animal studies have shown that MWCNT cause biomechanical and genetic alterations in the lung tissue which lead to lung fibrosis. To screen the fibrogenic risk factor of specific types of MWCNT, we developed a human lung microtissue array device that allows real-time and in-situ readout of the biomechanical properties of the engineered lung microtissue upon MWCNT insult. We showed that the higher the MWCNT concentration, the more severe cytotoxicity was observed. More importantly, short type MWCNT at low concentration of 50 ng/ml stimulated microtissue formation and contraction force generation, and caused substantial increase in the fibrogenic marker miR-21 expression, indicating the high fibrogenic potential of this specific carbon nanotube type and concentration. The presented microtissue array system provides a powerful tool for high-throughput examination of the therapeutic and toxicological effects of target compounds in realistic tissue environment.

Multi-walled carbon nanotube physicochemical properties predict pulmonary inflammation and genotoxicity

Lung deposition of multi-walled carbon nanotubes (MWCNT) induces pulmonary toxicity. Commercial MWCNT vary greatly in physicochemical properties and consequently in biological effects. To identify determinants of MWCNT-induced toxicity, we analyzed the effects of pulmonary exposure to 10 commercial MWCNT (supplied in three groups of different dimensions, with one pristine and two/three surface modified in each group). We characterized morphology, chemical composition, surface area and functionalization levels. MWCNT were deposited in lungs of female C57BL/6J mice by intratracheal instillation of 0, 6, 18 or 54 μg/mouse. Pulmonary inflammation (neutrophil influx in bronchoalveolar lavage (BAL)) and genotoxicity were determined on day 1, 28 or 92. Histopathology of the lungs was performed on day 28 and 92. All MWCNT induced similar histological changes. Lymphocytic aggregates were detected for all MWCNT on day 28 and 92. Using adjusted, multiple regression analyses, inflammation and genotoxicity were related to dose, time and physicochemical properties. The specific surface area (BET) was identified as a positive predictor of pulmonary inflammation on all post-exposure days. In addition, length significantly predicted pulmonary inflammation, whereas surface oxidation (–OH and –COOH) was predictor of lowered inflammation on day 28. BET surface area, and therefore diameter, significantly predicted genotoxicity in BAL fluid cells and lung tissue such that lower BET surface area or correspondingly larger diameter was associated with increased genotoxicity. This study provides information on possible toxicity-driving physicochemical properties of MWCNT. The results may contribute to safe-by-design manufacturing of MWCNT, thereby minimizing adverse effects.

Responses of testis, epididymis, and sperm of pubertal rats exposed to functionalized multiwalled carbon nanotubes

The present study investigated the response of testes, epididymides and sperm in pubertal Wistar rats following exposure to 0, 0.25, 0.5, 0.75, and 1.0 mg kg(-1) functionalized multi-walled carbon nanotubes (f-MWCNTs) for 5 days. The results showed that administration of (f-MWCNTs) significantly increased the activities of superoxide dismutase, catalase, and glutathione peroxidase in a dose-dependent manner in both testes and sperm compared with control group. Moreover, the significant decrease in the activity of glutathione-S-transferase and glutathione level was accompanied with significant elevation in the levels of hydrogen peroxide and malondialdehyde in both testes and sperm of (f-MWCNTs)-treated rats. The spermiogram of (f-MWCNTs)-treated rats indicated significant decrease in epididymal sperm number, sperm progressive motility, testicular sperm number and daily sperm production with elevated sperm abnormalities when compared with the control. Exposure to (f-MWCNTs) decreased plasma testosterone level and produced marked morphological changes including decreased geminal epithelium, edema, congestion, reduced spermatogenic cells and focal areas of tubular degeneration in the testes. The lumen of the epididymides contained reduced sperm cells and there was mild to severe hyperplasia epithelial cells lining the duct of the epididymis. Collectively, pubertal exposure of male rats to (f-MWCNTs) elicited oxidative stress response resulting in marked testicular and epididymides dysfunction.

Influence of purified multiwalled carbon nanotubes on the mechanical and morphological behavior in poly (L-lactic acid) matrix

Poly (L-latic acid) (PLLA) is a bioresorbable polymer widely used as a biomaterial, but its fragility can limit its use. An alternative is to produce polymer nanocomposites, which can enhance the mechanical properties of polymeric matrix, resulting in a material with differentiated properties. In this work, PLLA based nanocomposites containing 0.25, 0.5 and 1.0wt% of purified multiwalled carbon nanotubes (p-MWCNTs) were prepared by the solvent casting method. The morphology and mechanical properties results show an improvement in strain at break for 0.25 and 0.5wt% p-MWCNTs and an increase in stiffness and elastic modulus for all compositions. Nanocomposites presented a p-MWCNTs agglomeration; however, there was a good stress transfer between PLLA and p-MWCNTs, which was confirmed by the increase in the hardness and elastic modulus. Atomic force microscopy analysis indicated an increase in roughness after nanotube addition. The in vitro biological study showed that PLLA/p-MWCNTs nanocomposites are cytocompatible with osteoblasts cells. The capacity of PLLA nanocomposites to stimulate osteogenesis was investigated by alkaline phosphatase (ALP) activity assay. Higher ALP activity was found on osteoblasts cultured on nanocomposites with 0.25 and 0.5wt% p-MWCNT compared to neat PLLA, confirming that PLLA cytocompatibility was improved on these compositions. Finally, our results showed that by a simple and inexpensive solvent casting method, it is possible to manufacture biofunctional nanocomposites devices with potential for orthopedic applications.

Biodegradation of Single-Walled Carbon Nanotubes in Macrophages through Respiratory Burst Modulation

The biodegradation of carbon nanotubes (CNTs) may be one of major determinants of the toxic outcomes in exposed individuals. In this study, we employed a macrophage/monocyte model, Raw264.7, to investigate the feasibility of regulating the biodegradation of three types of single-walled carbon nanotubes (SWCNTs) (pristine, ox-, and OH-SWCNTs) by respiratory burst modulation. An artificial fluid mimicking the enzymatic reactions of respiratory burst was constituted to reveal the role of respiratory burst played in SWCNT biodegradation. The biodegradation of SWCNTs were characterized by Raman, ultraviolet-visible-near-infrared spectroscopy, and transmission electron microscopy. Our results showed significantly accelerated biodegradation of ox-SWCNTs and OH-SWCNTs in macrophages activated by phorbol myristate acetate (PMA), which could be prevented by N-acetyl-l-cysteine (NAC), whereas p-SWCNTs were resistant to biodegradation. Similar tendencies were observed by using the in vitro enzymatic system, and the degradation rates of these SWCNTs are in the order of OH-SWCNTs > ox-SWCNTs >> p-SWCNTs, suggesting a pivotal role of respiratory burst in accelerating the biodegradation of SWCNTs and that defect sites on SWCNTs might be a prerequisite for the biodegradation to occur. Our findings might provide invaluable clues on the development of intervention measurements for relieving the side effects of SWCNTs and would help to design safer SWCNT products with higher biodegradability and less toxicity.

Toxicity determinants of multi-walled carbon nanotubes: The relationship between functionalization and agglomeration

The elucidation of toxicity determinants of multi-walled carbon nanotubes (MWCNT) is still incomplete. Functionalization with carboxyl groups is, however, commonly used to mitigate MWCNT toxicity, although the rationale for the mitigating effect has not been fully clarified yet. In this work, two optimized chemical vapor deposition methods were employed to obtain MWCNT of comparable length but different diameter, which were subsequently functionalized. For MWCNT of diameter larger than 40 nm, no detrimental effects on cell viability of macrophages were observed, while mild cytotoxicity was recorded for diameters between 15 and 40 nm, with a mitigating effect of functionalization. To investigate the factors responsible for the mitigation, we used the thinnest MWCNT preparation on different cell models, evaluating several endpoints, such as viability, production of nitric oxide (NO), expression of pro-inflammatory markers, the Trans-Epithelial Electrical Resistance (TEER), and clonogenic activity. Substantial mitigation of the changes caused by pristine MWCNT was observed not only with carboxyl- but also with amino-functionalized MWCNT, suggesting that negative or positive surface charge was not the main factor responsible for the effect. Instead, either functionalized preparation exhibited a stronger tendency to agglomerate that was strictly dependent on the presence of proteins. Moreover, we found that either carboxyl- or amino-functionalized MWCNT adsorbed a larger amount of serum proteins than pristine counterparts, with a distinctive pattern for each type of MWCNT. We propose, therefore, that the formation of larger agglomerates, dependent upon different protein coronae, contributes to mitigate the biological effects of functionalized MWCNT in protein-rich biological media.

Effects of multiwalled carbon nanotube surface modification and purification on bovine serum albumin binding and biological responses

The potential diagnostic and therapeutic applications such as drug delivery of multi-walled carbon nanotubes (MWCNTs) are being increasingly explored due to their unique mechanical, chemical and biological properties. Carboxylation of MWCNTs has been widely used to improve the solubility in aqueous systems, and for further functionalization with biologically active moieties. Purity of carboxylated MWCNTs is of great importance in nanomedicine. An important consideration is that oxidation debris is generated during the process of carboxylation, which can be removed by base washing. We hypothesized that surface modification as well as further purification by debris removal may alter physicochemical properties of MWCNTs and their ability to bind proteins. In this study, we utilized pristine MWCNT carboxylated MWCNTs (F-MWCNTs) and base-washed carboxylated MWCNTs (BW-F-MWCNTs) to examine formation of a bovine serum albumin (BSA) protein corona and impact on biological responses. We found that carboxylation increased the capability of F-MWCNTs to bind BSA, and base washing further increased this binding by 41% implying that purification of F-MWCNTs is an important consideration in biological applications. The BSA protein corona decreased the hydrodynamic size of MWCNTs by nearly 50% because the coating improved colloidal behavior. The effect was significantly less pronounced for F-MWCNTs and BW-F-MWCNTs because they were highly dispersible to begin with. Functionalization increased cellular uptake by both rat aortic endothelial cells (RAEC) and macrophage-like murine cells (RAW264.7), while base washing showed results similar to the functionalized analog. Interestingly, BSA binding downregulated mRNA levels of interleukin-6 (IL-6) and heme oxygenase 1 (Hmox1) in RAEC cells but upregulated the expression of IL-6 and Hmox1 in RAW264.7 cells, indicating the dependence of cell types in biological responses to MWCNTs. Overall, our study demonstrated that surface modification as well as further purification impacted the interaction of MWCNTs with proteins and subsequent cellular responses. Interestingly, while the corona associated with the F-MWCNTs and BW-F-MWCNTs were significantly different, their respective cellular uptake and biological responses were similar. This implied that surface functionalization played a more important role than surface corona.

Estradiol functionalized multi-walled carbon nanotubes as renovated strategy for efficient gene delivery

The present work focuses on the development and characterization of the estradiol functionalized CNTs for efficient gene delivery applications.

Innate immune humoral factors, C1q and factor H, with differential pattern recognition properties, alter macrophage response to carbon nanotubes

Interaction between the complement system and carbon nanotubes (CNTs) can modify their intended biomedical applications. Pristine and derivatised CNTs can activate complement primarily via the classical pathway which enhances uptake of CNTs and suppresses pro-inflammatory response by immune cells. Here, we report that the interaction of C1q, the classical pathway recognition molecule, with CNTs involves charge pattern and classical pathway activation that is partly inhibited by factor H, a complement regulator. C1q and its globular modules, but not factor H, enhanced uptake of CNTs by macrophages and modulated the pro-inflammatory immune response. Thus, soluble complement factors can interact differentially with CNTs and alter the immune response even without complement activation. Coating CNTs with recombinant C1q globular heads offers a novel way of controlling classical pathway activation in nanotherapeutics. Surprisingly, the globular heads also enhance clearance by phagocytes and down-regulate inflammation, suggesting unexpected complexity in receptor interaction.

FROM THE CLINICAL EDITOR

Carbon nanotubes (CNTs) maybe useful in the clinical setting as targeting drug carriers. However, it is also well known that they can interact and activate the complement system, which may have a negative impact on the applicability of CNTs. In this study, the authors functionalized multi-walled CNT (MWNT), and investigated the interaction with the complement pathway. These studies are important so as to gain further understanding of the underlying mechanism in preparation for future use of CNTs in the clinical setting.

Evaluation of uptake, cytotoxicity and inflammatory effects in respiratory cells exposed to pristine and -OH and -COOH functionalized multi-wall carbon nanotubes

Toxic effects were reported for pristine-multi-wall carbon nanotubes (p-MWCNTs) while the role of the functionalization on MWCNT-induced toxicity is not yet well defined. We evaluated on human alveolar (A549) epithelial cells and normal bronchial (BEAS-2B) cells exposed to p-MWCNTs, MWCNTs-OH and MWCNTs-COOH: uptake by TEM, cell viability by different assays, membrane damage by the LDH assay and cytokine release by ELISA. The aims of the present study were to: (i) confirm MWCNT cytotoxicity mechanisms hypothesized in our previous studies; (ii) identify the most reliable viability assay to screen MWCNT toxicity; and (iii) to test our model to clarify the role of functionalization on MWCNT-induced toxicity. In A549 cells, p-MWCNTs and MWCNTs-OH were localized free in the cytoplasm and inside vacuoles whereas MWCNTs-COOH were confined inside filled cytoplasmic vesicles. WST-1 and Trypan blue assays showed in A549 cells a similar slight viability reduction for all MWCNTs whereas in BEAS-2B cells WST1 showed a high viability reduction at the highest concentrations, particularly for MWCNTs-COOH. The MTT assay showed a false cytotoxicity as a result of MWCNTs-interference. Pristine and MWCNTs-COOH induced membrane damage, particularly in BEAS-2B cells. MWCNTs-COOH induced interleukin-6 (IL-6) and IL-8 release in A549 cells whereas p-MWCNTs induced IL-8 release in BEAS-2B cells. MWCNTs intracellular localization in A549 cells confirms the toxicity mechanisms previously hypothesized, with p-MWCNTs disrupting the membrane and vesicle-confined MWCNTs-COOH inducing inflammation. WST-1 was more reliable than MTT to test MWCNT-toxicity. BEAS-2B cells were more susceptible then A549 cells, particularly to MWCNT-COOH cytotoxicity. Our results confirm the toxicity of p-MWCNTs and demonstrate, also for the two kinds of tested functionalized MWCNTs toxic effects with a different mechanism of action.

Multifunctional hybrid-carbon nanotubes: new horizon in drug delivery and targeting

Carbon nanotubes (CNTs) have emerged as an intriguing nanotechnological tool for numerous biomedical applications including biocompatible modules for the bioactives delivery ascribed to their unique properties, such as greater loading efficiency, biocompatibility, non-immunogenicity, high surface area and photoluminescence, that make them ideal candidate in pharmaceutical and biomedical science. The design of multifunctional hybrid-CNTs for drug delivery and targeting may differ from the conventional drug delivery system. The conventional nanocarriers have few limitations, such as inappropriate availability of surface-chemical functional groups for conjugation, low entrapment/loading efficiency as well as stability as per ICH guidelines with generally regarded as safe (GRAS) prominences. The multifunctional hybrid-CNTs will sparked and open a new door for researchers, scientist of the pharmaceutical and biomedical arena. This review summarizes the vivid aspects of CNTs like characterization, supramolecular chemistry of CNTs-dendrimer, CNTs-nanoparticles, CNTs-quantum dots conjugate for delivery of bioactives, not discussed so far.

High dispersity of carbon nanotubes diminishes immunotoxicity in spleen

BACKGROUND

From the various physiochemical material properties, the chemical functionalization order of single-walled carbon nanotubes (swCNTs) has not been considered as a critical factor for modulating immunological responses and toxicological aspects in drug delivery applications. Although most nanomaterials, including carbon nanotubes, are specifically accumulated in spleen, few studies have focused on spleen immunotoxicity. For this reason, this study demonstrated that the dispersity of swCNTs significantly influenced immunotoxicity in vitro and in vivo.

MATERIALS AND METHODS

For cytotoxicity of swCNTs, MTT assay, reactive oxygen species production, superoxide dismutase activity, cellular uptake, and confocal microscopy were used in macrophages. In the in vivo study, female BALB/c mice were intravenously administered with 1 mg/kg/day of swCNTs for 2 weeks. The body weight, organ weight, hematological change, reverse-transcription polymerase chain reaction, and lymphocyte population were evaluated.

RESULTS

Different orders of chemical functionalization of swCNTs controlled immunotoxicity. In short, less-dispersed swCNTs caused cytotoxicity in macrophages and abnormalities in immune organs such as spleen, whereas highly dispersed swCNTs did not result in immunotoxicity.

CONCLUSION

This study clarified that increasing carboxyl groups on swCNTs significantly mitigated immunotoxicity in vitro and in vivo. Our findings clarified the effective immunotoxicological factors of swCNTs by increasing dispersity of swCNTs and provided useful guidelines for the effective use of nanomaterials.

In vitro and in vivo study of hazardous effects of Ag nanoparticles and Arginine-treated multi walled carbon nanotubes on blood cells: application in hemodialysis membranes

One of the novel applications of the nanostructures is the modification and development of membranes for hemocompatibility of hemodialysis. The toxicity and hemocompatibility of Ag nanoparticles and arginine-treated multiwalled carbon nanotubes (MWNT-Arg) and possibility of their application in membrane technology are investigated here. MWNT-Arg is prepared by amidation reactions, followed by characterization by FTIR spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The results showed a good hemocompatibility and the hemolytic rates in the presence of both MWNT-Arg and Ag nanoparticles. The hemolytic rate of Ag nanoparticles was lower than that of MWNT-Arg. In vivo study revealed that Ag nanoparticle and MWNT-Arg decreased Hematocrit and mean number of red blood cells (RBC) statistically at concentration of 100 µg mL(-1) . The mean decrease of RBC and Hematocrit for Ag nanoparticles (18% for Hematocrit and 5.8 × 1,000,000/µL) was more than MWNT-Arg (20% for Hematocrit and 6 × 1000000/µL). In addition, MWNT-Arg and Ag nanoparticles had a direct influence on the White Blood Cell (WBC) drop. Regarding both nanostructures, although the number of WBC increased in initial concentration, it decreased significantly at the concentration of 100 µg mL(-1) . It is worth mentioning that the toxicity of Ag nanoparticle on WBC was higher than that of MWNT-Arg. Because of potent antimicrobial activity and relative hemocompatibility, MWNT-Arg could be considered as a new candidate for biomedical applications in the future especially for hemodialysis membranes.

Biodegradation of carbon nanohorns in macrophage cells

With the rapid developments in the medical applications of carbon nanomaterials such as carbon nanohorns (CNHs), carbon nanotubes, and graphene based nanomaterials, understanding the long-term fate, health impact, excretion, and degradation of these materials has become crucial. Herein, the in vitro biodegradation of CNHs was determined using a non-cellular enzymatic oxidation method and two types of macrophage cell lines. Approximately 60% of the CNHs was degraded within 24 h in a phosphate buffer solution containing myeloperoxidase. Furthermore, approximately 30% of the CNHs was degraded by both RAW 264.7 and THP-1 macrophage cells within 9 days. Inflammation markers such as pro-inflammatory cytokines interleukin 6 and tumor necrosis factor α were not induced by exposure to CNHs. However, reactive oxygen species were generated by the macrophage cells after uptake of CNHs, suggesting that these species were actively involved in the degradation of the nanomaterials rather than in an inflammatory pathway induction.

PEGylated carbon nanotubes impair retrieval of contextual fear memory and alter oxidative stress parameters in the rat hippocampus

Carbon nanotubes (CNT) are promising materials for biomedical applications, especially in the field of neuroscience; therefore, it is essential to evaluate the neurotoxicity of these nanomaterials. The present work assessed the effects of single-walled CNT functionalized with polyethylene glycol (SWCNT-PEG) on the consolidation and retrieval of contextual fear memory in rats and on oxidative stress parameters in the hippocampus. SWCNT-PEG were dispersed in water at concentrations of 0.5, 1.0, and 2.1 mg/mL and infused into the rat hippocampus. The infusion was completed immediately after training and 30 min before testing of a contextual fear conditioning task, resulting in exposure times of 24 h and 30 min, respectively. The results showed that a short exposure to SWCNT-PEG impaired fear memory retrieval and caused lipid peroxidation in the hippocampus. This response was transient and overcome by the mobilization of antioxidant defenses at 24 h. These effects occurred at low and intermediate but not high concentration of SWCNT-PEG, suggesting that the observed biological response may be related to the concentration-dependent increase in particle size in SWCNT-PEG dispersions.

Effect of aspect ratio on the uptake and toxicity of hydroxylated-multi walled carbon nanotubes in the nematode, Caenorhabditis elegans

OBJECTIVES

In this study, the effect of tube length and outer diameter (OD) size of hydroxylated-multi walled carbon nanotubes (OH-MWCNTs) on their uptake and toxicity was investigated in the nematode Caenorhabditis elegans using a functional mutant analysis.

METHODS

The physicochemical properties of three different OH-MWCNTs were characterized. Uptake and toxicity were subsequently investigated on C. elegans exposed to MWCNTs with different ODs and tube lengths.

RESULTS

The results of mutant analysis suggest that ingestion is the main route of MWCNTs uptake. We found that OH-MWCNTs with smaller ODs were more toxic than those with larger ODs, and OH-MWCNTs with shorter tube lengths were more toxic than longer counterparts to C. elegans.

CONCLUSIONS

Overall the results suggest the aspect ratio affects the toxicity of MWCNTs in C. elegans. Further thorough study on the relationship between physicochemical properties and toxicity needs to be conducted for more comprehensive understanding of the uptake and toxicity of MWCNTs.

Carbon nanotubes: potential medical applications and safety concerns

Carbon nanotubes (CNTs) have unique atomic structure, as well as outstanding thermal, mechanical, and electronic properties, making them extremely attractive materials for several different applications. Many research groups are focusing on biomedical applications of carbon-based nanomaterials, however the application of CNTs to the biomedical field is not developing as fast as in other areas. While CNTs-based products are already being used in textiles, polymer matrices to strengthen materials, sports articles, microelectronics, energy storage, etc., medicinal products and medical devices for in vivo application based on CNTs have not been commercialized yet. However, CNTs for biomedical application, i.e., CNTs conjugated to siRNA for cancer therapy, or CNTs for imaging of colorectal cancer and many other products may enter clinical trials in the next years. Concerns related to the toxicity of CNTs must be overcome in order to have these products commercialized in a near future. This article reviews emerging biomedical applications of CNTs, specifically for therapy. It also deals with challenges associated with possible medical applications of CNTs, such as their not fully understood toxicological profile in the human body.

Boron nitride nanotubes chemically functionalized with glycol chitosan for gene transfection in eukaryotic cell lines

Nanostructured materials have been widely studied concerning their potential biomedical applications, primarily to selectively carry specific drugs or molecules within a tissue or organ. In this context, boron nitride nanotubes (BNNTs) have generated considerable interest in the scientific community because of their unique properties, presenting good chemical inertness and high thermal stability. Among the many applications proposed for BNNTs in the biomedical field in recent years, the most important include their use as biosensors, nanovectors for the delivery of proteins, drugs, and genes. In the present study, BNNTs were synthesized, purified, and functionalized with glycol chitosan through a chemical process, yielding the BNNT-GC. The size of BNNT-GC was reduced using an ultrasound probe. Two samples with different sizes were selected for in vitro assays. The nanostructures were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA), and dynamic light scattering (DLS). The in vitro assays MTT and neutral red (NR) were performed with NIH-3T3 and A549 cell lines and demonstrated that this material is not cytotoxic. Furthermore, the BNNT-GC was applied in gene transfection of plasmid pIRES containing a gene region that express a green fluorescent protein (GFP) in NIH-3T3 and A549 cell lines. The gene transfection was characterized by fluorescent protein produced in the cells and pictured by fluorescent microscopy. Our results suggest that BNNT-GC has moderate stability and presents great potential as a gene carrier agent in nonviral-based therapy, with low cytotoxicity and good transfection efficiency.

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.

The relationship between the diameter of chemically-functionalized multi-walled carbon nanotubes and their organ biodistribution profiles in vivo

Carbon nanotubes (CNTs) exhibit unique properties which have led to their applications in the biomedical field as novel delivery systems for diagnosis and therapy purposes. We have previously reported that the degree of functionalization of CNTs is a key factor determining their biological behaviour. The present study broadens the spectrum by investigating the impact of the diameter of CNTs using two series of multi-walled CNTs (MWNTs) with distinct differences in their diameters. Both MWNTs were doubly functionalized by 1,3-dipolar cycloaddition and amidation reactions, allowing the appended functional groups to be further conjugated with radionuclide chelating moieties and antibodies or antibody fragments. All constructs possessed comparable degree of functionalization and were characterized by thermogravimetric analysis, transmission electron microscopy, gel electrophoresis and surface plasmon resonance. The MWNT conjugates were radio-labelled with indium-111, which thereby enabled in vivo single photon emission computed tomography/computed tomography (SPECT/CT) imaging and organ biodistribution study using γ-scintigraphy. The narrow MWNTs (average diameter: 9.2 nm) demonstrated enhanced tissue affinity including non-reticular endothelial tissues compared to the wider MWNTs (average diameter: 39.5 nm). The results indicate that the higher aspect ratio of narrow MWNTs may be beneficial for their future biological applications due to higher tissue accumulation.

Croix CM, Watkins SC, Kisin ER, Kotchey GP, Balasubramanian K, Vlasova II, Yu J, Kim K, Seo W, Mallampalli RK, Star A, Shvedova AA. Lung macrophages "digest" carbon nanotubes using a superoxide/peroxynitrite oxidative pathway

In contrast to short-lived neutrophils, macrophages display persistent presence in the lung of animals after pulmonary exposure to carbon nanotubes. While effective in the clearance of bacterial pathogens and injured host cells, the ability of macrophages to "digest" carbonaceous nanoparticles has not been documented. Here, we used chemical, biochemical, and cell and animal models and demonstrated oxidative biodegradation of oxidatively functionalized single-walled carbon nanotubes via superoxide/NO* → peroxynitrite-driven oxidative pathways of activated macrophages facilitating clearance of nanoparticles from the lung.

Sparking connections: toward better linkages between research and human health policy-an example with multiwalled carbon nanotubes

Risk assessment and subsequent risk management of environmental contaminants can benefit from early collaboration among researchers, risk assessors, and risk managers. The benefits of collaboration in research planning are particularly evident in light of (1) increasing calls to expand upon the risk assessment paradigm to include a greater focus on problem formulation and consideration of potential tradeoffs between risk management options, and (2) decreasing research budgets. Strategically connecting research planning to future decision making may be most critical in areas of emerging science for which data are often insufficient to clearly direct targeted research to support future risk assessment and management efforts. This article illustrates an application of the comprehensive environmental assessment approach to inform research planning for future risk assessment and management of one emerging material, multiwalled carbon nanotubes (MWCNTs). High-priority research areas identified for MWCNTs in flame-retardant coatings applied to upholstery textiles included the following: release across the product life cycle; environmental transport, transformation and fate in air, wastewater and sediment; exposure in human occupational and consumer groups; kinetics in the human body; impacts on human health and aquatic populations; and impacts on economic, social, and environmental resources. This article focuses on specific research questions related to human health and how these may connect to future risk assessments and risk management efforts. Such connections will support more effective collaborations across the scientific community and may inform the prioritization of research funding opportunities for emerging materials like MWCNTs.

Stealth nanotubes: strategies of shielding carbon nanotubes to evade opsonization and improve biodistribution

Carbon nanotubes (CNTs) have recently been in the limelight for their potential role in disease diagnostics and therapeutics, as well as in tissue engineering. Before these medical applications can be realized, there is a need to address issues like opsonization, phagocytosis by macrophages, and sequestration to the liver and spleen for eventual elimination from the body; along with equally important issues such as aqueous solubility, dispersion, biocompatibility, and biofunctionalization. CNTs have not been shown to be able to evade such biological obstacles, which include their nonspecific attachments to cells and other biological components in the bloodstream, before reaching target tissues and cells in vivo. This will eventually determine their longevity in circulation and clearance rate from the body. This review article discusses the current status, challenges, practical strategies, and implementations of coating CNTs with biocompatible and opsonin-resistant moieties, rendering CNTs transparent to opsonins and deceiving the innate immune response to make believe that the CNTs are not foreign. A holistic approach to the development of such "stealth" CNTs is presented, which encompasses not only several biophysicochemical factors that are not limited to surface treatment of CNTs, but also extraneous biological factors such as the protein corona formation that inevitably controls the in vivo fate of the particles. This review also discusses the present and potential applications, along with the future directions, of CNTs and their hybrid-based nanotheranostic agents for multiplex, multimodal molecular imaging and therapy, as well as in other applications, such as drug delivery and tissue engineering.

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

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

Hydroxylation of multi-walled carbon nanotubes reduces their cytotoxicity by limiting the activation of mitochondrial mediated apoptotic pathway

Hydroxylation of carbon nanotubes (CNTs) can enhance their dispersibility in water, and allows the capability to conjugate with other molecules for the expected applications. However, the cytotoxicity of hydroxylated CNTs has not been thoroughly investigated. Here, we compared the cytotoxicity of hydroxylated multi-walled carbon nanotubes (MWCNTs-OH) on a human cell line with that of pristine multi-walled carbon nanotubes (p-MWCNTs). We showed that while both MWCNTs-OH and p-MWCNTs induced apoptosis in a time- and dose-dependent manner, MWCNTs-OH triggered a significantly milder cytotoxic response than that of p-MWCNTs. We further showed that such attenuated response could be attributed to a reduced disruption of the mitochondrial membrane potential (MMP), leading to the attenuation of both cytochrome c (cyt-c) release and activation of caspases. These findings suggest that MWCNTs-OH, could be more biocompatible for in vivo applications than that of p-MWCNTs by limiting the activation of the mitochondrial mediated apoptotic pathway.

The cancer targeting potential of D-α-tocopheryl polyethylene glycol 1000 succinate tethered multi walled carbon nanotubes

Our main aim in the present investigation was to explore the in vitro and in vivo cancer targeting potential of the doxorubicin (DOX) laden d-α-tocopheryl polyethylene glycol 1000 succinate (vitamin E TPGS) tethered surface engineered MWCNTs nanoformulation (DOX/TPGS-MWCNTs) and compare it with pristine MWCNTs and free doxorubicin solution. The developed MWCNTs nanoformulations were extensively characterized by Fourier-transform infrared, Raman spectroscopy, x-ray diffraction, electron microscopy, and in vitro and in vivo studies using MCF-7 cancer cell line. The entrapment efficiency was determined to be 97.2 ± 2.50% (DOX/TPGS-MWCNTs) and 92.5 ± 2.62% (DOX/MWCNTs) ascribed to π-π stacking interactions. The developed formulations depicted the sustained release pattern at the lysosomal pH (pH 5.3). The DOX/TPGS-MWCNTs showed enhanced cytotoxicity, cellular uptake and were most preferentially taken up by the cancerous cells via endocytosis mechanism. The DOX/TPGS-MWCNTs nanoconjugate depicted the significantly longer survival span (44 days, p < 0.001) than DOX/MWCNTs (23 days), free DOX (18 days) and control group (12 days). The obtained results also support the extended residence time and sustained release profile of the drug loaded surface engineered nanotubes formulations in body as compared to DOX solution. Overall we can conclude that the developed MWCNTs nanoconjugate have higher cancer targeting potential on tumor bearing Balb/c mice.

Potential Occupational Risks Associated with Pulmonary Toxicity of Carbon Nanotubes

Given their remarkable properties, carbon nanotubes (CNTs) have made their way through various industrial and medicinal applications and the overall production of CNTs is expected to grow rapidly in the next few years, thus requiring an additional recruitment of workers. However, their unique applications and desirable properties are fraught with concerns regarding occupational exposure. The concern about worker exposure to CNTs arises from the results of recent animal studies. Short-term and sub-chronic exposure studies in rodents have shown consistent adverse health effects such as pulmonary inflammation, granulomas, fibrosis, genotoxicity and mesothelioma after inhalation or instillation of several types of CNTs. Furthermore, physicochemical properties of CNTs such as dispersion, functionalization and particle size can significantly affect their pulmonary toxicity. Risk estimates from animal studies necessitate implementation of protective measures to limit worker exposure to CNTs. Information on workplace exposure is very limited, however, studies have reported that CNTs can be aerosolized and attain respirable airborne levels during synthesis and processing activities in the workplace. Quantitative risk assessments from sub-chronic animal studies recommend the health-based need to reduce exposures below the recommended exposure limit of 1 µg/m³. Practice of prevention measures including the use of engineering controls, personal protective equipment, health surveillance program, safe handling and use, as well as worker training can significantly minimize worker exposure and improve worker health and safety.

Pharmacology of carbon nanotubes: toxicokinetics, excretion and tissue accumulation

Carbon nanotubes (CNT) are increasingly being investigated for their use in biomedical applications and nanomedicine. An emergent need for the understanding of their in vivo biodistribution and pharmacokinetics is therefore needed to establish the essential properties and criteria for their further development as targeted CNT delivery systems to specific tissues for diagnostics and therapeutic purposes. Until their biodistribution and toxicoketic profiles are fully understood, their translation into the clinic will be hindered. This review will highlight the important factors affecting the biodistribution and pharmacokinetic profile of CNT and address their toxicokinetics following systemic, pulmonary and dermal exposure.

Endowing carbon nanotubes with biological and biomedical properties by chemical modifications

The scope of nanotechnology is gaining importance in biology and medicine. Carbon nanotubes (CNTs) have emerged as a promising tool due to their unique properties, high specific surface area, and capacity to cross biological barriers. These properties offer a variety of opportunities for applications in nanomedicine, such as diagnosis, disease treatment, imaging, and tissue engineering. Nevertheless, pristine CNTs are insoluble in water and in most organic solvents; thereby functionalization of their surface is necessary to increase biocompatibility. Derivatization of CNTs also gives the possibility to conjugate different biological and bioactive molecules including drugs, proteins, and targeting ligands. This review focuses on the chemical modifications of CNTs that have been developed to impart specific properties for biological and medical purposes. Biomolecules can be covalently grafted or non-covalently adsorbed on the nanotube surface. In addition, the inner core of CNTs can be exploited to encapsulate drugs, nanoparticles, or radioactive elements.

Effect of MWCNT size, carboxylation, and purification on in vitro and in vivo toxicity, inflammation and lung pathology

Background

Several properties of multi-walled carbon nanotubes (MWCNT) have the potential to affect their bioactivity. This study examined the in vitro and in vivo outcomes of the influence of diameter, length, purification and carboxylation (in vitro testing only) of MWCNT.

Methods

Three original ‘as received’ MWCNT that varied in size (diameter and length) were purified and functionalized by carboxylation. The resulting MWCNT were characterized and examined for cytotoxicity and inflammasome activation in vitro using THP-1 cells and primary alveolar macrophages from C57BL/6 mice. Oropharyngeal aspiration administration was used to deliver original MWCNT and in vivo bioactivity and lung retention was examined at 1 and 7 days.

Results

Studies with THP-1 macrophages demonstrated that increased length or diameter corresponded with increased bioactivity as measured by inflammasome activation. Purification had little effect on the original MWCNT, and functionalization completely eliminated bioactivity. Similar results were obtained using alveolar macrophages isolated from C57BL/6 mice. The in vivo studies demonstrated that all three original MWCNT caused similar neutrophil influx at one day, but increasing length or diameter resulted in the lavaged cells to release more inflammatory cytokines (IL-6, TNF-α, and IL-1β) ex vivo. Seven-day histology revealed that, consistent with the in vitro results, increasing width or length of MWCNT caused more severe pathology with the longest MWCNT causing the most severe inflammation. In addition, the same two larger MWCNT were retained more in the lung at 7 days.

Conclusions

Taken together, the results indicated that in vitro and in vivo bioactivity of MWCNT increased with diameter and length. Purification had no significant modifying effect from the original MWCNT. Functionalization by carboxylation completely eliminated the bioactive potential of the MWCNT regardless of size in in vitro testing.

Fucosylated multiwalled carbon nanotubes for Kupffer cells targeting for the treatment of cytokine-induced liver damage

PURPOSE

To develop, characterize and exploring the sulfasalazine loaded fucoyslated multi walled carbon nanotubes for Kupffer cell targeting for effective management of cytokine-induce liver damage.

METHODS

Sulfasalazine was loaded into the fucosylated MWCNTs after subsequential functionalization (carboxylation, acylation and amidation) using dialysis membrane technique. The in vitro, in vivo studies were performed on macrophages J 774 cell line for Kupffer cells targeting for the treatment of cytokine-induced liver damage.

RESULTS

The loading of SSZ into SSZ-FUCO-MWCNTs was 87.77 ± 0.11% (n = 3). Sustained release was obtained from SSZ-FUCO-MWCNTs, with 89.12 ± 0.71% of SSZ released into medium at 48th hr. SSZ-FUCO-MWCNTs showed the 9.0  ± 0.23% hemolysis was drastically reduced from 21.62 ± 0.24% SSZMWCNTs 21.62 ± 0.24%. In SRB assay, SSZ-FUCO-MWCNTs showed more cytotoxicity than raw and SSZ-MWCNTs. In cytokine assay, SSZ- FUCO-MWCNTs exhibited significantly higher inhibition of IL-12 p40 secretion. In Western blot assay, SSZ-FUCO-MWCNTs significantly inhibit NF-κB activation.

CONCLUSION

The results suggested that the SSZ-FUCO-MWCNTs may be useful nano-carriers for targeted delivery to Kupffer cells in the treatment of cytokine-induced liver damage.

Purification and sidewall functionalization of multiwalled carbon nanotubes and resulting bioactivity in two macrophage models

This study examined the consequences of surface carboxylation of multiwalled carbon nanotubes (MWCNT) on bioactivity. Since commercial raw MWCNT contain impurities that may affect their bioactivity, HCl refluxing was exploited to purify raw "as-received" MWCNT by removing the amorphous carbon layer on the MWCNT surface and reducing the metal impurities (e.g. Ni). The removal of amorphous carbon layer was confirmed by Raman spectroscopy and thermogravimetric analysis. Furthermore, the HCl-purified MWCNT provided more available reaction sites, leading to enhanced sidewall functionalization. The sidewall of HCl-purified MWCNT was further functionalized with the -COOH moiety by HNO(3) oxidation. This process resulted in four distinct MWCNT: raw, purified, -COOH-terminated raw MWCNT, and -COOH-terminated purified MWCNT. Freshly isolated alveolar macrophages from C57Bl/6 mice were exposed to these nanomaterials to determine the effects of the surface chemistry on the bioactivity in terms of cell viability and inflammasome activation. Inflammasome activation was confirmed using inhibitors of cathepsin B and Caspase-1. Purification reduced the cell toxicity and inflammasome activation slightly compared to raw MWCNT. In contrast, functionalization of MWCNT with the -COOH group dramatically reduced the cytotoxicity and inflammasome activation. Similar results were seen using THP-1 cells supporting their potential use for high-throughput screening. This study demonstrated that the toxicity and bioactivity of MWCNT were diminished by removal of the Ni contamination and/or addition of -COOH groups to the sidewalls.

Intranuclear drug delivery and effective in vivo cancer therapy via estradiol-PEG-appended multiwalled carbon nanotubes

Cancer cell-selective, nuclear targeting is expected to enhance the therapeutic efficacy of a myriad of antineoplastic drugs, particularly those whose pharmacodynamic site of action is the nucleus. In this study, a steroid-macromolecular bioconjugate based on PEG-linked 17β-Estradiol (E2) was appended to intrinsically cell-penetrable multiwalled carbon nanotubes (MWCNTs) for intranuclear drug delivery and effective breast cancer treatment, both in vitro and in vivo. Taking Doxorubicin (DOX) as a model anticancer agent, we tried to elucidate how E2 appendage influences the cell internalization, intracellular trafficking, and antitumor efficacy of the supramolecularly complexed drug. We observed that the combination of DOX with E2-PEG-MWCNTs not only facilitated nuclear targeting through an estrogen receptor (ER)-mediated pathway but also deciphered to a synergistic anticancer response in vivo. The antitumor efficacy of DOX@E2-PEG-MWCNTs in chemically breast cancer-induced female rats was approximately 18, 17, 5, and 2 times higher compared to the groups exposed to saline, drug-deprived E2-PEG-MWCNTs, free DOX, and DOX@m-PEG-MWCNTs, respectively. While free DOX treatment induced severe cardiotoxicity in animals, animals treated with DOX@m-PEG-MWCNTs and DOX@E2-PEG-MWCNTs were devoid of any perceivable cardiotoxicity, hepatotoxicity, and nephrotoxicity. To the best of our knowledge, this is the first instance in which cancer cell-selective, intranuclear drug delivery, and, subsequently, effective in vivo breast cancer therapy has been achieved using estrogen-appended MWCNTs as the molecular transporter.

Augmented anticancer activity of a targeted, intracellularly activatable, theranostic nanomedicine based on fluorescent and radiolabeled, methotrexate-folic Acid-multiwalled carbon nanotube conjugate

The present study reports the design, synthesis, and biological evaluation of a novel, intravenously injectable, theranostic prodrug based on multiwalled carbon nanotubes (MWCNTs) concomitantly decorated with a fluorochrome (Alexa-fluor, AF488/647), radionucleide (Technitium-99m), tumor-targeting module (folic acid, FA), and anticancer agent (methotrexate, MTX). Specifically, MTX was conjugated to MWCNTs via a serum-stable yet intracellularly hydrolyzable ester linkage to ensure minimum drug loss in circulation. Cell uptake studies corroborated the selective internalization of AF-FA-MTX-MWCNTs (1) by folate receptor (FR) positive human lung (A549) and breast (MCF 7) cancer cells through FR mediated endocytosis. Lysosomal trafficking of 1 enabled the conjugate to exert higher anticancer activity as compared to its nontargeted counterpart that was mainly restricted to cytoplasm. Tumor-specific accumulation of 1 in Ehlrich Ascites Tumor (EAT) xenografted mice was almost 19 and 8.6 times higher than free MTX and FA-deprived MWCNTs. Subsequently, the conjugate 1 was shown to arrest tumor growth more effectively in chemically breast tumor induced rats, when compared to either free MTX or nontargeted controls. Interestingly, the anticancer activities of the ester-linked CNT-MTX conjugates (including the one deprived of FA) were significantly higher than their amide-linked counterpart, suggesting that cleavability of linkers between drug and multifunctional nanotubes critically influence their therapeutic performance. The results were also supported by in silico docking and ligand similarity analysis. Toxicity studies in mice confirmed that all CNT-MTX conjugates were devoid of any perceivable hepatotoxicity, cardiotoxicity, and nephrotoxicity. Overall, the delivery property of MWCNTs, high tumor binding avidity of FA, optical detectability of AF fluorochromes, and radio-traceability of (99m)Tc could be successfully integrated and partitioned on a single CNT-platform to augment the therapeutic efficacy of MTX against FR overexpressing cancer cells while allowing a real-time monitoring of treatment response through multimodal imaging.

Intravenously delivered graphene nanosheets and multiwalled carbon nanotubes induce site-specific Th2 inflammatory responses via the IL-33/ST2 axis

Carbon-based nanomaterials (CBN), such as graphene nanosheets (GNS) and multiwalled carbon nanotubes (MWCNT), have been proposed for potential nanomedicine applications such as biomedical devices and carriers for drug delivery. However, our current understanding regarding the systemic toxicity of these CBN through intravenous (iv) injection is limited. In this study, we compare the immune response resulting from GNS and MWCNT exposure. We hypothesize that iv administration of GNS and MWCNT would result in divergent systemic inflammatory responses due to physicochemical differences between these two CBN. In the lungs of C57BL/6 mice, GNS actuate a Th2 immune response 1 day following iv administration, which consists of neutrophilic influx and a significant increase in interleukin (IL)-5, IL-13, IL-33, and its soluble receptor (sST2) in the bronchoalveolar lavage fluid. MWCNT elicited a significant increase in the messenger ribonucleic acid expression of cytokines in the spleen including IL-4 and IL-33, which are associated with an increase in splenic cell differentiation (CD)4⁺ and CD8⁺ T-cells in C57BL/6 mice following iv injection. The observed Th2 responses in both the lung and spleen are absent in ST2^−/− mice administrated GNS or MWCNT, suggesting a critical role for IL-33. In conclusion, the use of GNS or MWCNT as nanocarriers for drug delivery may result in Th2 immune responses that are mediated through the IL-33/ST2 axis and therefore may promote adverse allergic reactions.