January 2008: "Assessing the Effect of Surface Chemistry on Gold Nanorod Uptake, Toxicity, and Gene Expression in Mammalian Cells", Tanya S. Hauck et al.
Small 4(1) (2008) 153-159 [doi: 10.1002/smll.200700217]
February 2008: "Induction of mesothelioma in p53+/- mouse by intraperitoneal application of multi-wall carbon nanotube", Atsuya Takagi et al.
The Journal of Toxicological Sciences 33 (1) (2008) 105-116 [doi:10.2131/jts.33.105]
April 2008: "Nano titanium dioxide photocatalytic protein tyrosine nitration: A potential hazard of TiO2 on skin", Naihao Lu et al.
Biochemical and Biophysical Research Communications 370(4) (2008) 675–680 [doi:10.1016/j.bbrc.2008.04.010]
May 2008: "Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study", C.A. Poland et al.
Nature Nanotechnology 3 (2008) 423-428 [doi:10.1038/nnano.2008.111]
June 2008: "Single walled carbon nanotubes induce indirect cytotoxicity by medium depletion in A549 lung cells", A. Casey et al.
Toxicological Letters 179 (2008) 78-84 [doi:10.1016/j.toxlet.2008.04.006]
July 2008: "Nominal and effective dosimetry of silica nanoparticles in cytotoxicity assays", D. Lison et al.
Toxicol Sci. 104(1) (2008) 155-162 [doi:10.1093/toxsci/kfn072]
August 2008a: "Long-term accumulation and low toxicity of single-walled carbon nanotubes in intravenously exposed mice", ST Yang et al.
Toxicological Letters 181(3) (2008) 182-189 [doi:10.1016/j.toxlet.2008.07.020]
August 2008b: "Comparative study of cytotoxicity, oxidative stress and genotoxicity induced by four typical nanomaterials: the role of particle size, shape and composition", C Liu et al.
J.of Applied Toxicology 29(1) (2008) 69-78 [doi: 10.1002/jat.1385]
September 2008a: "Structural Defects Play a Major Role in the Acute Lung Toxicity of Multiwall Carbon Nanotubes: Physicochemical Aspects", I. Fenoglio et al.
Chem Res Toxicol. 21(9) (2008) 1690-1697 [doi: 10.1021/tx800100s]
September 2008b: "Structural Defects Play a Major Role in the Acute Lung Toxicity of Multiwall Carbon Nanotubes: Toxicological Aspects", J. Muller et al.
Chem Res Toxicol. 21(9) (2008) 1698-1705 [doi: 10.1021/tx800101p]
October 2008: "Inhalation vs. aspiration of single-walled carbon nanotubes in C57BL/6 mice: inflammation, fibrosis, oxidative stress and mutagenesis", AA Shvedova et al.
Am J Physiol Lung Cell Mol Physiol 295 (2008) L552 [doi: 10.1152/ajplung.90287.2008]
November 2008: "Subchronic inhalation toxicity of silver nanoparticles", JH Sung et al.
Toxicol Sci. 108(2) (2009) 452-461 [doi:10.1093/toxsci/kfn246]
December 2008: "Biodistribution and clearance of instilled carbon nanotubes in rat lung", D. Elgrabli
Part Fibre Toxicol. (2008) 5:20 [doi:10.1186/1743-8977-5-20]
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 January 2008: "Assessing the Effect of Surface Chemistry on Gold Nanorod Uptake, Toxicity, and Gene Expression in Mammalian Cells", Tanya S. Hauck et al.
Small 4(1) (2008) 153-159 [doi: 10.1002/smll.200700217] |
General comments
This fascinating study shows the importance of the coating of nanomaterials (surface charge and functional groups) and shows convincingly that biocompatibility can be tuned, which will help to develop nanomaterials’ medical applications. We are eager to see what the effects of nanoparticle coating will be in long term studies and in animal models.
The only small drawback in this study is the use of trypan blue exclusion as a viability marker, since this dye is not considered a very reliable assay.
Methods
Material: Gold nanorods, synthesized by the authors. The rods were coated with polyelectrolytes (PE) using established procedures.
Specific material characterization is found in supplement (http://www.wiley-vch.de/contents/jc_2296/2008/f700217_s.pdf).
Mammalian cells (HeLa cells) were used to study: cellular uptake of gold nanorods, toxicity (Trypan Blue exclusion), gene-expression analysis (mRNA microarray)
Results
The cellular uptake of gold nanorods could be tuned by manipulating the surface charge and functional groups of the polyelectrolytes on the nanoparticle surfaces. Positively charged gold nanorods demonstrated the highest cellular uptake. The presence of serum in the cell media also influenced uptake.
The PE coatings are independently toxic, but the toxicity of nanorods with the coatings was low (viability greater than 90%) at relative high concentrations of rods.
Molecular indicators of cell stress such as the expression of heat-shock proteins were analyzed. No significantly up- or down regulation was found. Furthermore, no general change in gene expression was observed upon exposure (0.35% of genes examined).
Conclusions
The reported results show that surface chemistry and the use of surface modifiers such as PEs and surfactants can be used to manipulate the uptake of nanorods. The studied rods show only limited cytotoxicity and microarray analysis shows that heat-shock proteins are not upregulated during the uptake of large quantities of gold nanorods.
The authors indicate that their future work will focus on better understanding the interrelationship between the physico-chemical properties of nanoparticles and their cellular effects (function, morphology, …). The authors believe that these specific properties (surface charge and functional groups) can be used to tune cellular uptake and therefore to be used in medical applications e.g. optimization of nanorod dosage for hyperthermia therapy or passive targeting to tissues in cancer therapy. |
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February 2008: "Induction of mesothelioma in p53+/- mouse by intraperitoneal application of multi-wall carbon nanotube", Atsuya Takagi et al.
The Journal of Toxicological Sciences 33 (1) (2008) 105-116 [doi:10.2131/jts.33.105] |
General comments
This study shows that MWCNT, behaving as aggregates in solution, induce peritoneal mesothelioma in susceptible mice. This phenomenon was also observed when mice received with similar amounts of crocidolite.
Although the intraperitoneal way of administration of materials does not reflect human exposure, this experimental model has been extensively used to investigate carcinogenic potential of asbestos fibers. The study is of valuable physiopathological interest. However, a major limitation, from a mechanistic point of vue, is the lack of extensive physico-chemical characterization of the MWCNT. The authors state that shape similarities between MWCNT and crocidolite probably explain that both materials induced mesothelioma. However, the lack of extensive physico-chemical characterization of the MWCNT does not allow a deep analysis of the mechanisms involved in MWCNT-induced mesothelioma.
Furthermore, other studies are needed to confirm the present results with other types of CNT.
Materials and Methods
The materials analyzed in the present study were : MWCNTs (MITSUI MWCNT-7, Lot NO. 060125-O1k), UICC-grade Crocidolite (NIHS material stock), and fullerene (C60, Nanon purple,, Frontier Carbon Corporation, Tokyo, Japan). These materials were suspended in a 0.5% methyl cellulose solution containing 1.0% of Tween 80.
MWCNT’s length, width and aggregates formation in solution were provided in the study. Aggregates formation was also analyzed in the case of crocidolite and fullerenes.
P53 +/- mice received a single i.p. injection of 3 mg of the different materials in 1 ml suspension. Control animals received 1 ml of the vehicle solution alone. Animals were observed until one of the groups reached 100% mortality. These animals were subject to autopsy and alive animals of the other groups were sacrificed at this time point and also subjected to autopsy.
Results
Materials characterization.
MWCNT width distribution showed a pick at 90 nm, and length distribution showed a pick 1-3 microns. The 3 materials form micrometer aggregates in suspension.
The highest mortality was observed in the MWCNT group followed by the crocidolite group, and the study terminated at week 25. Cumulative mortality attributed to large/invasive mesothelioma at week 25 was 90%, 50% and 0% in MWCNT, crocidolite and control groups respectively.
Histological analysis
Peritoneal mesothelioma was observed in MWCNT and crocidolite groups. The overall incidence of mesothelioma at day 84 was 87.5% and 77.8% in the MWCNT and crocidolite groups respectively. Neither mesothelioma nor interim death was observed in the Fullerene and vehicle groups except for one moribund mouse by chronic pyelonephritis at day 152. |
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April 2008: "Nano titanium dioxide photocatalytic protein tyrosine nitration: A potential hazard of TiO2 on skin", Naihao Lu et al.
Biochemical and Biophysical Research Communications 370(4) (2008) 675–680 [doi:10.1016/j.bbrc.2008.04.010] |
Introduction & Aim
The nitration of protein tyrosine is a common modification of proteins. The nitration is the result of which of oxidative and nitrative stress and it is possibly involved in the onset or progression of diseases.
The authors hypothesized that nano titanium dioxide (TiO2) on the skin (from the environment or from sunscreen) together with nitrite in sweat in the presence of the UV-light may offer a suitable milieu for the photosensitized skin damage.
Material & Methods
In the present paper three commercially available nano-TiO2 products were used to test the tyrosine nitration of bovine serum albumin (BSA) during UV-irradiation in the presence of 0.25–1.0 mM NO2.
Results
It was found that anatase TiO2 and Degussa P25 TiO2 (containing a mixture of anatase and rutile TiO2) promoted the formation of protein tyrosine nitration and therefore showed strong photocatalytic activity (compared to rutile TiO2). Similar results were found for mouse skin homogenates.
In the BSA-model, the optimum condition for the protein tyrosine nitration reaction was around physiological pH and both oxidants (H2O2) as anti-oxidants (Glutathion) reduced in a dose-related manner the nitration.
Conclusion & Remarks
The present results demonstrate that protein nitration can take place when nano TiO2 is applied to the skin in the presence of UV-light. The mechanism described in this paper can also be important in other (not necessarily involving skin) in vivo and in vitro model whenever photo-biological activity is present.
Although, from this data it can be concluded that protein nitration can present a risk to skin more research is needed to show the relationship between photocatalytic protein tyrosine nitration and cutaneous diseases. |
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May 2008: "Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study", C.A. Poland et al.
Nature Nanotechnology 3 (2008) 423-428 [doi:10.1038/nnano.2008.111] |
General comments
This study, in extension to an other recent study (Takagi et al., 2008), shows that a single injection of long MWCNTs into the peritoneal cavity of mice induced inflammatory responses, including granuloma formation, similar to those of long fiber asbestos. This study provides preliminary data for the fiber effects of long MWCNTs. However, no mesothelioma was induced; this study didn’t last long enough and was not designed for that. This is not an in vivo carcinogenicity study.
As mentioned in the title, this study is a “pilot study” with some notable study limitations and uncertainties:
- the number of mice used in this study is very low, even if the differences between long and short MWCNT responses are statistically significant;
- the dose administrated to the mice by intraperitoneal injection is highly elevated, considering that only a minimal fraction of inhalated MWCNT depositing in the deep lung is likely to translocate to pleural sites. Moreover, there is an important uncertainty regarding whether, for a realistic inhalation exposure scenario, such a threshold dose of MWCNTs could migrate to the mesothelium of the pulmonary pleura in humans and induce the effects seen here in mice;
- it would have been useful to express the dose of MWCNT and asbestos as number of fibers, based on fiber regulations;
- the experimental model of intraperitoneal injection in mice has been extensively used to investigate carcinogenic potential of asbestos fibers, considering that the peritoneal cavity is lined with the same cell type as the pleural cavity and that, in in vivo studies, inhaled asbestos fibers migrate to the pleural space and can induce mesothelia. However, in the case of MWCNTs, it is still unknown whether inhalated CNT have a sufficient level of biopersistence to allow migration to the pleura in humans; additional well-defined studies are needed;
- the lack of extensive physico-chemical characterization of the MWCNT does not allow a deep analysis of the mechanisms involved in MWCNT-induced toxicity, as pointed out by the authors.
Materials and Methods
A panel of four MWCNT samples was used: two samples with a large proportion of long straight fibers longer than 20 µm and two curled/tangled CNT samples either cut to form predominantly short fibres or with their original length. Two samples of asbestos, including a long-fibre amosite (LFA) and a short-fibre amosite (LFA) were also used as positive and negative controls, respectively, while a nanoparticulate carbon black (NPCB) sample served as a non-fibrous graphene control.
Female C57Bl/6 mice received a single intraperitoneal injection of 50 µg of each material in 0.5 ml suspension. After 24 h and 7 days post-exposure, the mice were killed and the peritoneal cavity washed. Protein levels and cell populations were measured in the lavageate of the peritoneal cavity at 24 hours to assess the inflammatory. After 7 days, histological quantification of granulomas on the peritoneal side of the diaphragm and foreign body giant cells (FBGCs) was carried out.
Results
Only the samples that contained long fibres caused inflammatory response, with significant polymorphonuclear leukocyte (PMN) or protein exudation. FBGCs and granulomas on the peritoneal side of the diaphragm were also seen with the long-fibre-containing samples. The mesothelial lining on the pleural side of the diaphragm was normal in every case.
In contrast, particle samples that did not contain detectable long fibres failed to cause any significant inflammation at 1 day or giant cell formation at 7 days. A small non-significant granuloma response was seen in one of three of the NTtang2-treated mice.
The authors indicated that neither soluble metals nor endotoxin contamination were correlated with the greater inflammogenicity and granuloma formation seen with the long-fiber MWCNT samples. |
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June 2008: "Single walled carbon nanotubes induce indirect cytotoxicity by medium depletion in A549 lung cells", A. Casey et al.
Toxicological Letters 179 (2008) 78-84 [doi:10.1016/j.toxlet.2008.04.006] |
In this paper the hypothesis of an indirect toxicity – due to medium depletion in vitro - of two types of single walled carbon nanotubes (SWCNT) (Arc Discharge (AD) and HiPco SWCNT) was investigated.
The (indirect) cytotoxicity in A549 lung cells cultures was measured using two endpoints, namely the Alamar Blue (AB) and the Clonogenic assay
Based on observations in the literature reporting that SWCNT can absorb organic compounds the authors have posed the hypothesis that that SWCNT probably can absorb essential nutrients from the culture medium and therefore induce cytotoxicity.
The nanotubes were dispersed in a common, commercial available cell culture medium and subsequently removed by centrifugation and filtration. Thereafter, the presence (or better the removal of) SWCNT was confirmed spectroscopicly. In this analysis it was shown that with the nanotubes the composition of the medium was altered. The SWCNT “conditioned medium” was then used as culture medium to grow A549 cells and the viability was assessed.
Exposure of the A549 cells to the depleted medium which had previously contained SWCNT, revealed significant cytotoxicity for both endpoints. These results suggest that SWCNT can in vitro induce an indirect cytotoxicity by alteration of cell culture medium.
Therefore, researcher have to take care to when studying cytotoxicity because the toxic response reported here is probably typical for in vitro studies and it is to be expected that the absorption plays a less in vivo (although this should be proven). A word of criticism to this paper is removal of the SWCNT from the conditioned medium (which could not be avoided to prove the hypothesis), it is to our opinion possible that with time some absorbed molecules would de-sorb and provide essential nutrients to the growing cells. Such an experiment could maybe be done using an insert in which the SWCNT remain separated from the growing cells but allows nutrients to be exchanged. |
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July 2008: "Nominal and effective dosimetry of silica nanoparticles in cytotoxicity assays", D. Lison et al.
Toxicol Sci. 104(1) (2008) 155-162 [doi:10.1093/toxsci/kfn072] |
In 2007, Teeguarden et al (Toxicol. Sci. 95, 300-312) raised, based on the small mass and large surface area (SA) of nanoparticles, their concern to adequately characterize the dose of nanoparticles in vitro. As it is generally known that nanoparticles due to their small size and large specific SA, insoluble nanoparticles are almost not (or not strongly) affected by the gravitational force and are generally formulated in stable suspensions or sols it can be questioned how in vitro assay systems, in which cells adhering to the bottom of a culture vessel, may (or may not) be exposed to the majority of nanoparticles in suspension.
In a theoretical model (based on sedimentation and gravitation forces) it was calculated that the effective dose (mass or number or SA dose of particles that affect the cells) might only represent a very small fraction of the nominal dose.
In this paper the authors hypothesized that due to (of a third force) convection forces that usually develop in sols, the majority of the particles may reach the target cells. They have designed different experiments to try and prove their position.
They exposed three different cell lines (A549 epithelial cells, EAHY926 endothelial cells, and J774 monocyte-macrophages) to a monodisperse suspension (no aggregates present) of Stöber silica nanoparticles (SNP). Four different end points for cytotoxicity were used: lacticodehydrogenase [LDH] release, LDH cell content, tetrazolium salt (MTT), and crystal violet staining.
The dose, in all cell lines and for all end points, in the paper was presented in different ways: mass, number or SA.
The authors could conclude that the nominal dose remains the most appropriate metric for in vitro toxicity testing of insoluble SNP dispersed in aqueous medium. The importance of this observation is very important for the experimental design and the interpretation of in vitro toxicological studies with nanoparticles.
It should be noted that, although the point made by these authors is clearly shown, the presented endpoints are “only” viability endpoints. More subtle toxicological changes have not been taken into account, but it is not to be expected that this would change the outcome of the investigation. |
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August 2008a: "Long-term accumulation and low toxicity of single-walled carbon nanotubes in intravenously exposed mice", ST Yang et al.
Toxicological Letters 181(3) (2008) 182-189 [doi:10.1016/j.toxlet.2008.07.020] |
The expected beneficial (biomedical) use of single-walled carbon nanotubes (SWCNTs) in drug delivery and cancer treatment raises many questions especially in view of their fate (biodistribution) and toxicity after intravenous administration.
In the current study the authors have investigated in vivo the effect of intravenously injected (tail vein) SWCNTs the distribution and the toxicity in the main organs (such as liver, lung and spleen) in mice.
The SWCNTs were synthesized by arc-discharge and purified to a carbonaceous purity of 95%. The main metal impurities are 0.4 % Fe, 3.0 % Ni and 1.3 % Y. It was reported that the remaining metals were mainly attributed to the encapsulation by carbon, which prevents the solubilization The purified SWCNTs were suspended in 1.0 wt% Tween® 80 aqueous solution by sonication.
By using Raman spectroscopy and TEM technique it was shown that SWCNT were still present in the studied organs 3 months after exposure.
The serum biochemical parameters (LDH, ALT and AST), which were elevated, are a sign of hepatic damage being present at 90 days post exposure. were observed. The histological observations demonstrate a slight inflammation and cell infiltration in the lung, In lung and liver a decreasing glutathione (GSH) level and an increasing malondialdehyde (MDA) level was found, suggestive for oxidative damage.
This study clearly reveals SWCNT related toxicity 90 days after dosing. Unfortunately, no blood samples were taken at earlier timepoint (to follow changes over time). Concerning the dose it has to be noted that 1 mg SWCNT in a 25 g mouse is the equivalent of 2.8 g in a 70 kg human, which is a relative high dose. |
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August 2008b: "Comparative study of cytotoxicity, oxidative stress and genotoxicity induced by four typical nanomaterials: the role of particle size, shape and composition", C Liu et al.
J.of Applied Toxicology 29(1) (2008) 69-78 [doi: 10.1002/jat.1385] |
Our General comments
This study address a timely question: what is the role of particle composition and shape on toxicological effects ?
The study was well-performed and the results are interesting and agree with accumulating evidence about a role of oxidative stress on nanoparticles-induced cytotoxicity. The genotoxic effect of CNT was not associated with a high oxidative stress, as compared to the other particles, suggesting an oxidant-independent mechanism.
The limitations of the study are the lack of extensive physico-chemical characterization of the materials (chemical composition of the CNT, quantitative analysis of materials aggregation and charge in solution), the lack of microscopic analysis of particles internalization in cells (were CNT localized in the nucleus ?), as well as mechanistic experiments demonstrating the responsibility of oxidative stress in cytotoxicity (for example studies using antioxidant strategies).
Aim
The objectives of this study was to analyze the effects of four different nanomaterials that are characterized by different particle size, shape and chemical composition (carbon black (CB) ; single wall carbon nanotubes (CNT) ; silicon dioxide (SiO2) ; and zinc oxide (ZnO) nanoparticles) on cellular viability, oxidative stress and genotoxicity in primary mouse embryo fibroblasts (PMEF).
Materials and Methods
Manufactured nanoparticles of CB, CNTs, SiO2 and ZnO were purchased from commercial suppliers. The particles were sterilized by heating for 4 h at 180°C in the oven, and then suspended in fetal bovine serum. All particle samples were sonicated six times intermittently (30 s every 2 min) and characterized using TEM.
The size and shape of nanoparticles in suspensions was provided. CB nanoparticles had a sphere shape with an average size of 12.3 nm. CNTs were rope-shaped with lengths less than 5 µm and diameters of approximate 8 nm. SiO2 and ZnO nanoparticles exhibited a crystal structure with an average size of 20.2 and 19.6 nm, respectively. The chemical composition was quantitatively analyzed by Raman spectroscopic technique and the results show that the purity of four nanomaterials are all more than 99.0%.
Particle suspensions were freshly prepared before the cells were exposed, and diluted to appropriate concentrations (5, 10, 20, 50 and 100 mg ml-1) with the culture medium, then immediately applied to the cells. Cells not treated with particles served as controls in each experiment.
As observed by the methyl thiazolyl tetrazolium (MTT) and water-soluble tetrazolium (WST) assays, ZnO induced much greater cytotoxicity than non-metal nanoparticles. This was in accordance with intracellular oxidative stress levels measured by glutathione depletion, malondialdehyde production, superoxide dismutase inhibition as well as reactive oxygen species generation.
Compared with ZnO nanoparticles, carbon nanotubes were moderately cytotoxic and oxidative but induced more DNA damage determined by the comet assay. CB and SiO2 seemed to be less effective. |
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September 2008a: "Structural Defects Play a Major Role in the Acute Lung Toxicity of Multiwall Carbon Nanotubes: Physicochemical Aspects", I. Fenoglio et al.
Chem Res Toxicol. 21(9) (2008) 1690-1697 [doi: 10.1021/tx800100s] |
September 2008:
Twin papers: Structural defects play a major role in the acute lung toxicity of multiwall carbon nanotubes
Paper 1:
Studies, both in vivo and in vitro, have revealed that carbon nanotubes (CNTs) have a toxicological potential. In the lung it is e.g. shown that CNT exposure can result in alveolitis and fibrosis; in the epithelium genotoxic responses have been found.
CNT’s are relative inert materials a therefore it is not clear what makes these materials potential pulmonary toxins.
In the past, suggestions have been made: the metal contamination (catalyst), CNT length, degree of oxidation, or extent of hydrophilicity.
In the twin papers presented here the structural properties of CNT’s have been studied in relation to their toxicity.
In the first paper different the physicochemical aspects are studied. For this purpose a preparation of multiwall CNT has specially been modified (i) by grinding (introducing structural defects) and subsequently heating (reducing oxygenated carbon functionalities and reduction of metallic oxides) (ii) by heating at 2400 degrees C in an inert atmosphere and subsequently grinding the thermally treated CNT (introducing defects in a metal-deprived carbon framework).
Subsequently, the modified CNT’s were characterized in detail. The presence of framework and surface defects, metals, and oxygenated functionalities
was monitored by means of a large set of techniques.
It has reported before that CNT may quench rather than generate oxygenated free radicals. This was investigated using electron spin resonance spectroscopy (spin trapping). It was found that the original ground material exhibited a scavenging activity while after heating (2400°C) this property was lost.
It was noted that the scavenging activity, related to the presence of defects, appears to go hand in hand with the genotoxic and inflammatory potential of CNT (paper 2). |
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September 2008b: "Structural Defects Play a Major Role in the Acute Lung Toxicity of Multiwall Carbon Nanotubes: Toxicological Aspects", J. Muller et al.
Chem Res Toxicol. 21(9) (2008) 1698-1705 [doi: 10.1021/tx800101p] |
September 2008:
Twin papers: Structural defects play a major role in the acute lung toxicity of multiwall carbon nanotubes
Paper 2:
In this paper the physico-chemical determinants of the toxic responses with selectively modified CNTs (see paper 1) was investigated. The CNTs were used lung epithelial cells to assess the genotoxic potential. In vivo (in wistar rats) the pulmonary toxicity was assessed after 3 and 60 days.
The results show that the acute pulmonary toxicity and the genotoxicity of CNT were reduced upon heating but restored upon grinding, indicating that the intrinsic toxicity of CNT is mainly mediated by the presence of defective sites in their carbon framework.
Thus, structural defects may be one of the major factors governing the toxic potential of CNT.
These two papers show probably why batches of different productions can give very another toxicological outcome because subtle, microscopic, differences in the structure (not in the chemical composition) can change significantly the interaction with biological material. |
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October 2008: "Inhalation vs. aspiration of single-walled carbon nanotubes in C57BL/6 mice: inflammation, fibrosis, oxidative stress and mutagenesis", AA Shvedova et al.
Am J Physiol Lung Cell Mol Physiol 295 (2008) L552 [doi: 10.1152/ajplung.90287.2008] |
The use and production of nanomaterials, and more specific single-walled carbon nanotubes (SWCNT), raised concerns on human health upon inhalation.
It has been found that pharyngeal aspiration of purified SWCNT by C57BL/6 mice caused a dose-dependent granulomatous pneumonia, oxidative stress, acute inflammatory/cytokine responses, fibrosis, and decrease in pulmonary function. In order to avoid any possible artifactual effect (due to instillation) associated with SWCNT the same authors also conducted an experiment in which mice inhaled a uniform SWCNT dispersions.
In this study these authors compared these two dosing techniques using nonpurified SWCNT (Fe content = 17.7%).
In the inhalation study the nonpurified SWCNT were dosed at 5 mg/3 for 5 h/day during 4 days. In comparison the dose in the pharyngeal aspiration experiment was varied between 5 and 20 µg per mouse.
In both exposure techniques the pathological events reported as inflammation and oxidative stress synergized into the development of multifocal granulomatous pneumonia and interstitial fibrosis.
It was reported that SWCNT inhalation was more effective than aspiration in causing these responses, but overall the outcomes of inhalation exposure and pharyngeal exposure were very similar. It was suggested that because of exposure to smaller SWCNT structures by inhalation (of a dry aerosol) compared to the aspiration of a agglomerated particle suspension (micrometer-size agglomerates) leads to a more potent response.
This study is not showing many “new” toxicological data but the main massage is that the use of inhalation is to be seen as superior to aspiration but, most important, aspiration is a valid alternative to explore pulmonary toxicity of SWCNT. This conclusion is useful because most labs do not have the opportunity to run inhalation experiment. |
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November 2008: "Subchronic inhalation toxicity of silver nanoparticles", JH Sung et al.
Toxicol Sci. 108(2) (2009) 452-461 [doi:10.1093/toxsci/kfn246] |
Recently, the interest in nanosilver has increased because of its anti-bacterial properties. Therefore, nanosilver has a high commercial potential in several general applications such as washing machines and textiles. The use of high quantities of nanosilver raises the need for more profound toxicological studies.
In this study the authors have undertaken a subchronic inhalation toxicity study of silver nanoparticles.
Eight-week-old rats (Sprague-Dawley) were exposed to silver nanoparticles (average diameter 18-19 nm) for 6 h/day, 5 days/week, for 13 weeks in a whole-body inhalation chamber. Three dosing levels (and a control) were used for each sex; low dose (0.6 x 106 particle/cm3, 49 microg/m3), middle dose (1.4 x 106 particle/cm3, 133 microg/m3), and high dose (3.0 x 106 particle/cm3, 515 microg/m3).
After the dosing period, the animals underwent a full necropsy: blood was sampled and organ were taken out and fixed.
In the liver, bile-duct hyperplasia was found (dose dependently) in both the males and females. The histopathological examinations of the lung indicated a dose-dependent increases in inflammatory cell infiltrate, chronic alveolar inflammation, and small granulomatous lesions. It was concluded that the main target organs for nanosilver were the lungs and liver in both sexes. A No observable adverse effect level (NOAEL) of 100 microg/mł was suggested.
This paper was choosen not for its spectacular outcome but for its merit as a basic toxicological study. For many critical nanomaterials there is a need for such data (to many studies are concentrated on acute effects), in order to ascertain health and to build a reliable toxicological database. |
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December 2008: "Biodistribution and clearance of instilled carbon nanotubes in rat lung", D. Elgrabli
Part Fibre Toxicol. (2008) 5:20 [doi:10.1186/1743-8977-5-20] |
Carbon nanotubes (CNT), only build from carbon atoms, are hydrophobic (and therefore difficult to disperse in an aqueous solution) and hardly detectable in biological tissues. These properties render toxicological and biokinetics (biodistribution) studies more complex. During the production of CNT metal catalyst is used which remain as impurities in the final product, this metal can be quantified and used as a indication for the CNT content. In this study, Elgrabli used the traces of metal catalyst of CNT as a tracer to study the biokinetics and biopersitance of CNT.
The MWCNT used in this study contained nickel catalyst.
The results show, in rats after dosing MWCNT by intratracheal instillation, that the MWCNT do not significantly cross the pulmonary barrier but are still present in lungs 6 months after one instillation. Notwithstanding the low distribution the MWCNT are eliminated from the lung. In a separate study the authors show that MWCNT structure was also chemically modified and cleaved in the lung.
It was concluded that these MWCNT are at least persistent for 6 months in the lung but that clearance can be observed (this elimination might to be due in part to macrophages) probably due to repeated phagocytosis, cleavage and chemical modifications.
This paper carries an important messages:
- MWCNT can be bio-degradated (and probably can be designed to be degradated).
- NWCNT do not easily cross the pulmonary border. |
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POM 2008
