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evue des Maladies Respiratoires (2011) 28, e66—e75
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espiratory effects of manufactured nanoparticles�
P. Andujara,b,c,∗,1, S. Lanonea,b,c,1, P. Brochardd,e,2,J. Boczkowskia,b,1
a Inserm, U955, 94000 Créteil, Franceb Faculté de médecine, université Paris-Est Créteil, 94000 Créteil, Francec Service de pneumologie et pathologie professionnelle, centre hospitalier intercommunal deCréteil, 40, avenue de Verdun, 94000 Créteil, Franced EA 3672, IFR 99, laboratoire santé-travail-environnement, 33076 Bordeaux, Francee Faculté de médecine, université Bordeaux-2, 33076 Bordeaux, France
Available online 20 October 2011
KEYWORDSNanomaterials;Nanoparticles;Nanotubes;Lung;Toxicity
Summary Nanotechnology is the set of techniques used to engineer, characterize, and pro-duce materials that have at least one dimension within the nanoscale. These nanomaterials, ornanoobjects, include nanoparticles and nanotubes. As dictated by the laws of quantum physics,a size within the nanoscale results in unique physicochemical properties and distinctive behav-iors. Nanotechnology has a host of applications in fields ranging from cosmetology to the industryand medicine. The production and use of nanomaterials are expanding at a brisk pace. How-ever, concerns are emerging about the potential health effects of nanoparticles in the shortand long terms. These concerns are rooted in data on the harmful health effects of micrometricairborne particulate matter. Conceivably, these adverse effects might be amplified when theparticles are within the nanoscale. This article is a nonexhaustive overview of current dataon the penetration, deposition, translocation, and elimination of inhaled nanoparticles and onthe respiratory effects of metallic nanoparticles (with special attention to titanium dioxide)and carbon nanotubes. Both in vivo and in vitro studies consistently found biological effectsof nanoparticles on the respiratory system, including oxidative stress generation, proinflamma-tory and prothrombotic effects, pulmonary fibrosis and emphysema, and DNA damage. Improved
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knowledge of the potential strategies for the workplace and© 2011 SPLF. Published by Elsevi� This article is the English translation of the following manuscript, whevue des Maladies Respiratoires. Please cite this article as: ‘‘Andujar Panoparticules manufacturées. Rev Mal Respir 2009;26:625—37’’.∗ Corresponding author.
E-mail address: [email protected] (P. Andujar).1 Contribution: manuscript drafting.2 Contribution: manuscript revision.
761-8425/$ — see front matter © 2011 SPLF. Published by Elsevier Massoi:10.1016/j.rmr.2011.09.008
ogical effects of nanoparticles is needed to guide preventive
/or general population if needed.er Masson SAS. All rights reserved.ich was originally published in French in, Lanone S, Brochard P, Boczkowski J. Effets respiratoires des
on SAS. All rights reserved.
e67
• A size within the nanoscale is associated withan increase in the proportion of surface atoms,which enhances surface reactivity and produces newproperties.
• Although extremely promising, nanotechnology isgenerating major concern about potential harmfuleffects on human health (at the workplace and in
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Respiratory effects of manufactured nanoparticles
Introduction
The term ‘‘nanotechnology’’ holds connotations of innova-tion and technological progress. Nanotechnology is the setof techniques required to engineer, characterize, produceand use nanostructures, nanodevices, and nanosystems.Nanotechnology is now viewed as the highest point ofminiaturization achieved by integrating technology, biology,chemistry, and physics. Nanoscience is the study of phe-nomena generated by nanomaterials. As dictated by thelaws of quantum physics, particles within the nanoscaleexhibit unique properties compared to larger particles hav-ing the same chemical composition. Thus, a characteristicinherent in the nanoscale is a large proportion of surfaceatoms, which may result in high surface reactivity, highresistance, and modified electrical properties. Nanoparti-cles have a broad range of applications, particularly ininnovative sectors such as the cosmetic industry (e.g.,sunscreens, lipstick, and toothpastes) [1,2], automotiveindustry (e.g., paints, tires, lubricants, and windshields)[3,4], and healthcare industry (e.g., drug pharmacokinet-ics and bioavailability, prosthetic materials, and molecularimaging) [5,6].
Nanotechnology has a major impact on the world econ-omy. Thus, public funding for nanoresearch has increasedfrom slightly less than 500 million US dollars in 1997 to3.5 billion in 2004 [7]. The National Science Foundationhad estimated that by 2015 nanotechnology will gener-ate an income of about 1000 billion US dollars worldwide[8].
The rapidly growing place occupied by these newand promising technologies in our everyday life is rais-ing many issues regarding potential effects on humanhealth (at the workplace and in the general population)and on the environment. Concern has been voiced aboutthe very properties responsible for the appealing char-acteristics of nanomaterials (e.g., high surface reactivityand ability to cross cell membranes). This concern isrooted in data on the harmful health effects of micro-metric airborne pollutant particles [9—15]. Conceivably,these adverse effects might be amplified when the par-ticles are within the nanoscale. Robust research effortsare focusing on the toxicology of nanomaterials and ontheir potential effects on human health and the environ-ment. Nevertheless, many questions are still unanswered.Thus, insufficient data are available on situations associatedwith nanoparticle exposure (e.g., nanoparticle manufac-turing, use, and application) and levels of exposure tomanufactured nanoparticles. Furthermore, risk evaluationsmust assess not only the potential effects of native nano-materials, but also their behavior throughout their lifecycle (manufacturing method, use, aging, and biodegrad-ability). Most of the currently available information onadverse health effects of nanoparticle comes from in vitrostudies and in vivo animal studies. Given the complexityof the topic, this article is a detailed but nonexhaustiveoverview of current data on the penetration, deposition,translocation, and elimination of inhaled nanoparticles and
on the respiratory effects of metallic nanoparticles (withspecial attention to titanium dioxide [TiO2]) and carbon nan-otubes.amd[
the general population) and on the environment.
ackground
efinitions
anomaterials, or nanoobjects, have at least one dimensionithin the nanometric range (1—100 nm). Nanomaterialsaving a single nanometric dimension are nanosheets (e.g.,ade of graphite). Two nanometric dimensions define nan-
tubes and nanowires, of which the most extensively studiedre carbon nanotubes, first described in 1991 [16]. Carbonanotubes measure a few nanometers in diameter and up toeveral micrometers in length. Finally, nanoparticles havell three dimensions within the nanometric range.
anoparticle sources
anoparticles are either produced naturally (e.g., byolcanic eruptions, wildfires, or marine pollution) or man-factured. Manufactured nanoparticles may be generatednintentionally (that is, as pollutants, produced for instancey manufacturing processes, diesel engines, various forms ofombustion, and building materials) or intentionally (e.g.,y the industry or by research laboratories).
The chemical nature of nanoparticles varies in com-lexity. Nanomaterials may be composed of minerals (e.g.,raphite, hematite, and silica sol), metals (silicon dioxideSiO2] and TiO2), or organic compounds (carbon compoundsuch as buckminsterfullerene [C60], single-wall carbonanotubes [SWCNTs], and multiple-wall carbon nanotubesMWCNTs]; and polymers such as polystyrene, nylon, andextrane). Nanoparticles may also be mixtures of variableomplexity depending on the method used to generatehem (heating of polytetrafluoroethylene [PTFE or Teflon],elding fumes, and soot produced by the combustion ofydrocarbons or polymers). Furthermore, a nanoparticleay have a particulate core surrounded by a shell of
dsorbed pollutants such as transition metals, hydrocarbons,r biological substances (e.g., endotoxins).
eterminants of harmful health effects ofanoparticles
ata about ultrafine airborne pollutants suggests that theealth effects of nanomaterials may depend on a numberf frequently intercorrelated factors including size, number
nd/or surface, shape, chemical composition, surface treat-ent, and potential for aggregation/agglomeration. Fewata are available on the toxicity of nanoparticles to humans17—19].
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anoparticle size
1994 model of discrete inhaled particles of well-definedize, with no aggregates suggests that nanoparticle deposi-ion in each of the three regions of the airway (nasopharynx,racheobronchial tree, and alveolar region) may dependhiefly on nanoparticle size, which may therefore influenceotential effects [20]. This point is discussed in detail in theection entitled ‘‘Inhalation, penetration, and deposition ofanoparticles in the respiratory system’’. Nanoparticle sizes also intrinsically related to relative surface, at least forolid nanoparticles.
anoparticle shape
he biological effects depend on the shape of the nanopar-icles. Manufactured nanoparticles come in many differenthapes (e.g., spheres, fibers, tubes, rings, and disks). Exper-mental in vitro and in vivo studies of micrometric sphericalnd fibrous materials have convincingly demonstrated thatbers, whether occurring naturally (e.g., asbestos) or man-factured (e.g., fiberglass), have greater cytotoxic andenotoxic potential and generate higher risks of lung fibro-is and lung cancer [21,22]. The critical parameters are theose, size, and biopersistence of the fibers. Biopersistencef fibrous materials is an important characteristic, becauseonger material-cell contact times are associated withtronger biological effects [22]. Biopersistence is greaterith fibers than with spherical particles. Toxicological stud-
es of TiO2 have shown greater toxicity with fibers than withpheres. In a study of rat alveolar macrophages exposedo similar concentrations of fibrous and particulate TiO2
1—2 �m), electron microscopy showed vacuolar changesnd cell surface damage with the fibrous form but no signifi-ant changes with the particulate form [23]. In keeping withhis finding, LDH release into the medium, used as a cytotox-city index, increased significantly after exposure to fibrousiO2 but not to particulate TiO2 [23]. These data indicatehat the cytotoxic potential of TiO2 depends on the shape ofhe material. Although they were obtained with TiO2 fibersnd particles larger than 100 nm, they strongly suggest annfluence of shape on the biological effects of nanoparticles.
anoparticle surface characteristics andurface reactivity
everal in vivo animal studies of ultrafine airborne pollutantshowed that total particle surface area correlated with var-ous parameters including neutrophil influx into the lungs,hanges in lung epithelium permeability, and accumulationithin the lymph nodes [21,24,25]. The small size and corre-
pondingly large specific surface area of solid nanoparticlesroduce specific properties such as the ability to catalyzehemical reactions. The atoms and molecules at the sur-ace play a crucial role in determining the physicochemicalroperties of nanomaterials [19]. The ratio of particle sur-ace area over total number of atoms or molecules increasesxponentially as particle size decreases. Given that chemi-
al reactions occur at the particle surface, nanomaterialsre expected to show greater reactivity than larger par-icles of identical chemical composition. For instance, inn inhaled volume of 10 �g/m3 of air, the number of 5-�matsa
P. Andujar et al.
articles is 0.15/mL but the number of 5-nm nanoparticless 109 times higher (153 × 106/mL). However, the total sur-ace areas are 12 �m2/mL for 5-�m particles and 1000 timesigher (12,000 �m2/mL) for nanoparticles. This far greaterurface area available for contact with cells and biologi-al molecules explains the greater biological reactivity ofanoparticles compared to the same mass concentrationf larger particles. Thus, nanoparticles are associated withreater free oxygen radical production, oxidative stress,nd proinflammatory potential compared to larger particles26].
hemical composition of nanoparticles
he chemical composition of nanoparticles also influencesheir biological effects. Thus, one determinant of biologi-al activity is the presence of metals in the composition ofhe nanoparticles or of transition metals produced as impu-ities during the manufacturing process. Transition metalsn naturally occurring nanoparticles are involved in the pro-uction of free oxygen radicals, which are highly reactiveolecules capable of modulating various biological pro-
esses and causing cell damage [19]. For instance, ironontributes to the harmful effects of particulate matter inrban air pollution [27,28]. The bioavailability of iron fromarticles that contact epithelial cells decreases as parti-le size increases [29]. Iron can induce the proinflammatoryytokine interleukin-8. Similarly, data suggest that the redoxroperties of iron may be involved in the cytotoxicity ofarbon nanotubes for human keratinocytes [30].
egree of nanoparticleggregation/agglomeration
anoparticles tend to aggregate and/or agglomerate toarying degrees. Nanoparticles subjected to Van der Waalsorces, electrostatic forces, or surface tension forces tend togglomerate [31]. Aggregates form when nanoparticles areubjected to stronger forces and are therefore more diffi-ult to separate. Nanoparticle agglomerates or aggregates,hich may reach the microscale, exhibit complex shapesnd are difficult to characterize. Agglomeration or aggre-ation changes the aerodynamic properties of nanoparticlesnd therefore probably influences airway deposition. Databtained in mice suggest that gastrointestinal toxicity maye influenced by aggregation [32]. Thus, oral administrationf zinc nanoparticles caused the death of some of the ani-als, in which nanoparticle aggregation was found, whereasicroscale zinc particles caused no death [32].Interestingly, the ability of nanoparticles to form aggre-
ates via the adsorption of proteins has a major impact onlearance of the nanoparticles and on their immunologicalnd toxicological effects. When carbon black nanoparticles25 to 100 nm) subjected to different surface treatmentsere placed with dipalmitoylphosphatidylcholine (DPPC) inulture medium, agglomeration occurred within 1 hour [33].he size distribution of the immersed nanoparticles differedignificantly from that obtained with phosphate buffer used
s a control. DPPC concentrations decreased in a nanopar-icle surface- and size-dependent manner, indicating thaturface adsorption was responsible for the agglomerationnd decrease in phospholipids concentrations [33]. The
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Respiratory effects of manufactured nanoparticles
occurrence of similar interactions within the alveolar sur-factant, which contains phospholipids crucial to normal lungmechanical properties, may contribute to the toxicity ofnanoparticles for the respiratory system.
Surface treatments of nanoparticles
Surface treatment is a major parameter that is proba-bly more relevant than particle type to the effects ofhuman exposure. Surface treatments may either increase ordecrease the toxicity of nanoparticles. Nanoobjects knownas quantum dots, composed of cadmium selenide, are cyto-toxic for primary hepatocytes under specific conditions[34]. The cytotoxicity of quantum boxes, which are three-dimensional nanoobjects, is modulated by a number ofproduction parameters including ultraviolet radiation expo-sure and coating. Cytotoxicity correlates with the releaseof free Cd2+ ions related to deterioration of the cadmiumselenide structure. However, appropriately treated cad-mium selenide quantum dots are no longer cytotoxic. Thesequantum dots are currently used in biomedical research tomonitor in vitro cell migration and reorganization.
The coating may influence nanoparticle penetration intocells. Albumin, the most abundant protein in the plasma andinterstitial compartment, may promote endocytosis of nano-materials. Similarly, polystyrene particles (240 nm) coatedwith the membrane phospholipid lecithin can cross throughthe alveolar-capillary barrier, in contrast to the uncoatedparticles [35]. In rabbits, intravenously injected colloidalgold particles coated with rabbit serum albumin underwenttranscytosis mediated by receptors (albumin binding pro-teins) via the caveolae [36]. Thus, the presence in thealveolar epithelial lining fluid of albumin and phospholipidsmakes a major contribution to epithelial absorption of nano-materials deposited in the alveolar spaces.
• Among nanoparticles, some occur naturally whileothers are produced by human activity, eitherintentionally or unintentionally.
• Factors that influence nanoparticle toxicity includesize, number, surface characteristics, shape,chemical composition, surface treatment, andpotential for aggregation/agglomeration.
Inhalation, penetration, and deposition ofnanoparticles in the respiratory system
The airways constitute the main route by which nanopar-ticles enter the body. In general, the penetration anddeposition of inhaled particles into the respiratory systemcan occur via five mechanisms: gravitational sedimentation,inertial impaction, interception (particle-surface contact),
diffusion, and electrostatic deposition. The predominantmechanism depends on the size of the particles. Threeother factors with major effects on particle deposition areairway geometry and branching pattern, breathing rate,nPoe
e69
nd predominant breathing pattern through the mouth orhrough the nose.
Deposition of inhaled nanoparticles on the airway wallsccurs chiefly via diffusional displacement by the thermalotion of inhaled and exhaled air molecules in contactith the nanoparticles. Importantly, nanoparticles can
orm aggregates and/or agglomerates, thus increasing inize from the nanoscale to the microscale. In contrasto microscale particles, nanoparticles exhibit increasingasopharyngeal and tracheobronchial deposition as theirize diminishes [17,37—42]. Mathematical models have beeneveloped to predict particle deposition in the human air-ays. The model developed by the International Commissionn Radiobiological Protection (ICRP) can be used to computehe proportions, by mass, of inhaled nanoparticles depositedn the airways of an individual breathing through the nose.anoparticles 1 nm in diameter are predicted to show about0% deposition in the nasopharynx, 10% in the tracheo-ronchial tree, and 0% in the alveolar spaces; correspondingroportions for 5-nm particles are 30%, 30%, and 30%; andor 20-nm particles, 15%, 15%, and 50%. With 20-nm parti-les, the distribution of deposition according to lung surfaceoncentration indicates that alveolar space deposition is 100imes greater than nasopharyngeal deposition and 10 timesreater than tracheobronchial deposition [40,41].
ate of nanoparticles in the respiratoryystem
etention of nanoparticles within the lung
anoparticle lung retention depends chiefly on particleize and clearance capacity. Compared to larger-sizedarticles having the same chemical composition, inhaledanoparticles show greater lung retention. In rats, identicaloncentrations of TiO2 seems to have been intratracheallynstilled led to greater lung retention with 20-nm nanopar-icles compared to 250-nm particles [43]. Nanoparticle lungetention is increased in patients with obstructive airwayiseases such as asthma and chronic obstructive pulmonaryisease [44,45].
anoparticle clearance from the airways
articles deposited in the airways can be cleared via twoechanisms, namely, physical processes, which vary across
he three regions of the respiratory system; and chemicalrocesses capable of eliminating more or less soluble parti-les, which are identical throughout the respiratory system.
Physical clearance of inhaled nanoparticles is via theucociliary escalator that sweeps the particles up to
he pharynx where they are swallowed, phagocytosis byacrophages, and translocation through the epithelium.his last mechanism will be discussed later on. The mucocil-
ary escalator clears particles from the tracheobronchialnd nasopharyngeal airways, within 24—48 hours, as showny a study in rats exposed intratracheally for 1 hour to
anoparticles of radiolabeled iridium (15 and 80 nm) [46].hagocytosis of insoluble nanoparticles by macrophagesccurs in the tracheobronchial tree and alveolar spaces. Thefficacy of this mechanism depends largely on nanoparticle
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ize and shape and on whether aggregation occurs. Theacrophages are then cleared via the mucociliary escalator
hat pushes them into the gastrointestinal tract. The half-ife of these particles is extremely long, about 700 days inumans [40].
Chemical mechanisms include dissolution of solublearticles, lixiviation, and binding to proteins. Thus, the par-icles or their compounds undergo absorption, diffusion, orinding to proteins or other subcellular structures, afterhich they are eliminated into the bloodstream or lymph.
The main clearance mechanism in the alveolar spacess phagocytosis by macrophages. Most particles undergohagocytosis within only 6 to 12 hours, although markedifferences occur according to particle size. Several exper-mental studies in rats showed that nonagglomeratedanoparticles were less efficiently cleared by macrophagehagocytosis compared to microscale particles, the resulteing substantial accumulation of the nanoparticles withinhe alveoli [47,48]. When human alveolar macrophagesrom bronchoalveolar lavage fluids were exposed to a TiO2
anoparticle (20 nm) aerosol for 1 hour, increasing nanopar-icle accumulation within the cells was seen [49].
ranslocation and distribution of nanoparticlesn the body
onflicting results have been reported regarding the translo-ation of inhaled nanoparticles [50]. Several studies supportpithelial, interstitial and neuronal translocation of insolu-le or nearly insoluble nanoparticles to other compartmentsn the body [51—53].
Translocation into the epithelium and interstitium mayllow nanoparticles to penetrate the blood and lymph and,herefore, to distribute throughout the body. Endocytosis ofanoparticles has been extensively studied in various cellypes. Endocytosis by airway epithelial cells may occur atll three levels of the airway tree, providing nanoparti-les with direct entry into the blood and lymph [17,52,53].ther nanoparticle translocation mechanisms are generat-
ng debate, such as luminal vesicular transport via caveolaet the surface of epithelial and endothelial cells. Caveo-ar openings range from 40 to 100 nm, which should allowanoparticles to cross the alveolar-capillary barrier into theystemic circulation [38]. Several studies have evaluatedhe potential systemic translocation of various nanoparti-les administered by inhalation or intratracheal instillation38,53,54].
Studies in animals have shown rapid translocation of sev-ral nanoparticle types from the lung to the bloodstream17,40,43,46,53,54]. This mechanism can redistribute theanoparticles in the organs. In a rat study, nanoparti-les generated by heating PTFE were detected in theronchial submucosa and juxta-pleural lung interstitiumnly 15 minutes after inhalation [55]. In other rat studies,nly a small proportion of 192iridium-labeled nanoparticlesdministered by inhalation penetrated into the bloodstream46]. Rats exposed in inhalation chambers to insoluble 13C
anoparticles (20—29 nm) for 18—24 hours exhibited markedadioactivity of the liver and lungs starting only 30 minutesfter exposure initiation [53]. These findings indicate sys-emic translocation of the inhaled nanoparticles. Afters
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P. Andujar et al.
4 hours’ exposure, no radioactivity was detected in theeart, olfactory bulb, brain, or kidneys. The discrepanciescross studies may be ascribable to differences in adminis-ration modalities or in the nanomaterials used. In a studynvolving exposure of rats to inhaled TiO2 nanoparticles20 nm) and fine particles (250 nm), nanoparticles showedreater accumulation within the lymph nodes, indicatingenetration of the nanoparticles into the interstitial spaces43]. However, in rats exposed to nanoparticles (15—20 nm)adiolabeled with iridium, fewer than 1% of the nanoparti-les entered the bloodstream and reached the liver, spleen,idneys, brain, and heart [46]. A study of hamsters givenntratracheal colloidal nanoparticles of denatured serumlbumin radiolabeled with 99m-technetium (99mTc) (< 80 nm)howed marked pulmonary radioactivity within 5 minutesoncomitantly with very small amounts of radioactivity inhe blood, kidneys, spleen, and brain [54]. The size ofhe translocated fraction may vary with the physicochem-cal properties of the nanoparticles [56]. In a hamsterodel, physicochemical parameters such as bipolar charge
t the nanoparticle surface markedly affected translocationhrough the airway epithelium to the bloodstream [54].
Whether nanoparticles undergo translocation to theloodstream in humans is debated. An experimental studyuggests that nanoparticles may readily cross the alveolar-apillary barrier into the pulmonary bloodstream [57]. Fiveealthy volunteers inhaled 5- to 10-nm carbon nanoparticlesadiolabeled with 99mTc. Radioactivity was rapidly detectedn the blood, indicating passage across the alveolar-capillaryembrane to the pulmonary and systemic circulations, andto 5% of the total dose was found in various organs
liver, heart, spleen, and brain) [57]. In contrast, twother studies involving inhalation of 99mTc-labeled carbonanoparticles showed no evidence of translocation, theadioactivity detection limit being 1% of the inhaled dose39,58]. Nevertheless, it is reasonable to expect that inhaledanomaterials may reach various organs in the body.
Neuronal translocation of nanoparticles has been sug-ested. In rats exposed in an inhalation chamber to insoluble13 nanoparticles for 6 hours, radioactivity counts on the firstay indicated translocation of the nanoparticles to the cere-rum, cerebellum, and olfactory bulb, with persistence ofhe radioactivity until day 7 in the olfactory bulb [59]. Theuthors of this study put forward two hypotheses, namely,ranslocation from the lungs to the systemic circulationith passage across the blood-brain barrier, and neuronal
ranslocation via the olfactory bulb followed by retrogradeigration along the axons to the central nervous system.
tudies in animals suggest that neuronal translocation to theentral nervous system can occur via the sensory neurons inhe airway epithelium [21,40,60]. However, it is worth not-ng that the olfactory mucosa in humans represents only 5%f the total nasal mucosal surface area, compared to 50% inats.
ffects of nanoparticles on the respiratory
ystemhe results of experimental studies of nanoparticle effectshould be interpreted with circumspection, for a number
Respiratory effects of manufactured nanoparticles
• Particle clearance from the tracheobronchial andnasopharyngeal airways occurs chiefly via themucociliary escalator.
• Insoluble nanoparticles are cleared by macrophagephagocytosis in the tracheobronchial tree andalveolar spaces.
• Chemical mechanisms of nanoparticle clearanceconsist mainly of dissolution of soluble particles,lixiviation, and binding to proteins.
• Whether nanoparticle translocation from therespiratory system to other tissues occurs in humans
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of reasons: the number of studies is small, nanoparti-cles only recently became a focus of concern, the testednanoparticles vary widely, and the nanoparticle concentra-tions used in vitro are usually higher than those encounteredin vivo. This section emphasizes the respiratory effects oftwo types of manufactured nanoparticles, carbon nanotubesand metallic nanoparticles, most notably those composed ofTiO2.
In vitro experimental studies
Reactive oxygen species and oxidative stressCarbon nanotubesOxidative stress is among the chief mechanisms underlyingnanomaterial cytotoxicity. There is general agreement that,among carbon nanotubes, only the unpurified forms containiron, which induces oxidative stress. This point is importantwhen considering the toxic potential of SWCNTs. SWCNTswith high iron contents induce greater oxidative stress thando purified SWCNTs with low iron contents [61]. It was shownrecently that oxidative stress in cells incubated with SWCNTssecondarily weakens the antioxidant response, diminishingthe levels of glutathione and antioxidant enzymes (super-oxide dismutases 1 and 2) [62]. This interesting findingcompletes the above-described mechanism.
Metallic nanoparticlesTiO2 nanoparticles can produce reactive oxygen species insolution under abiotic conditions when exposed to ultravio-let radiation [19]. Studies in several models have establishedthat various metallic and nonmetallic nanomaterials caninduce intracellular oxidative stress [63—65]. A recent studyhighlighted the influence of particle size on the pro-oxidantand proinflammatory effects of metallic nanoparticles [66].In vitro, human A549 cells exhibited a stronger proinflam-matory response and greater oxidative stress when exposedto TiO2 and carbon black nanoparticles than when exposedto the same mass dose of larger particles having the samechemical composition. This result suggests that the totalparticle surface area normalized for the total exposed cellsurface area may be a better means of measuring the dosethan particle mass. The dose-response relationships in thisin vitro study seem consistent with the dose-response rela-
tionships found in vivo after dose standardization.Several studies indicate that oxidative stress is among themechanisms involved in the cytotoxic effects of nanopar-ticles [19]. Among them, one used a particularly elegant
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pproach. The cytotoxic effects of various nanomaterialsere compared based on correlations with intracellular oxi-ation caused by oxidative stress [23]. The results showlearly that cytotoxic nanoparticles consistently inducexidative stress, whereas nanoparticles devoid of cytotox-city produce no oxidative stress. The ability of a givenanoparticle to produce reactive oxygen species in solution,ithout cell contact, did not predict nanoparticle cytotoxi-ity in this study [23].
NA damagearbon nanotubeswo recently published studies show that DNA damageccurs when differentiated cells (V79 hamster fibroblasts,67]) or undifferentiated cells (murine embryonic stemells, [68]) are incubated with carbon nanotubes. These arehe first studies reporting nanotube-induced DNA damage.enetic alterations occurred in the murine stem cells, ineeping with the marked sensitivity of stem cells to agentsapable of causing DNA damage. In addition, although MWC-Ts were found in the nuclei of the murine stem cells [68],either study involved a detailed evaluation to determinehether the DNA damage was related to nuclear transloca-
ion of the carbon nanotubes. Although the ability of carbonanotubes to induce DNA damage needs to be confirmednd further evaluated, these two studies indicate a needor attention to DNA damage when evaluating the effects ofarbon nanotubes.
etallic nanoparticlesetallic and nonmetallic nanoparticles with limited sol-bility in water have also been shown to induce DNAamage. A literature review on the genotoxicity of poorlyydrosoluble particles, such as TiO2, shed light on the mech-nisms involved [69]. The available data indicate only thathe genotoxic effects of poorly hydrosoluble particles areelated to DNA oxidation by reactive oxygen species anditrogen. There is an urgent need for further evaluationf this effect. Whether a causal link exists between lungnflammation and genotoxic effects remains unknown. Inddition, little information is available on the impact ofnflammation on DNA alterations associated with mutagenicnd carcinogenic effects (cell cycle arrest, DNA repair, cellroliferation, and apoptosis).
n vivo experimental studies
arbon nanotubesam et al. [70] were among the first groups to investigatehe pulmonary effects of intratracheal instillation of carbonanotube suspensions. Mice received intratracheal instilla-ions of raw SWCNTs, SWCNTs treated to remove metallicesidues, carbon black nanoparticles, and quartz nanopar-icles. Histological examination of the lungs 90 days laterhowed the presence of these nanomaterials in the alveoli70]. SWCNTs (with or without metallic residues) inducedn inflammatory response with granulomas surrounding theanotubes, indicating toxicity [71]. Similar granulomas were
ound in rats intratracheally instilled with SWCNTs, althoughhe inflammation resolved within 3 months [72].Subsequent studies established that inflammationccurred chiefly with poorly dispersed carbon nanotubes
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hat aggregated into microscale particles. A dispersedreparation of SWCNTs given by pharyngeal aspiration toice caused alveolar and interstitial fibrosis, whereas lessell-dispersed SWCNTs produced a granulomatous reaction
72]. These findings were confirmed by two very recenttudies in mice exposed to aerosolized MWCNTs (6 hourser day for 24 days). These are the first two studies of theffects of inhaled carbon nanotubes [73,74]. The pulmonaryesions ranged from absent to moderate (alveolar fibrosisithout granuloma formation). Nevertheless, one of these
tudies [73], in which no lung inflammation or tissue damageas found, showed evidence of systemic immunosuppres-
ion after 14 days after inhalation for 6 hours/24 hours ofWCNTs in doses of 0.3 to 5 mg/m3. There was a decrease
n the T-cell-dependent antibody response and increasedxpression of interleukin-10 messenger RNA in spleenomogenates [73].
In ApoE−/− transgenic mice given a single intratrachealnstillation of SWCNTs, examination of the aorta after 7,8, and 60 days showed mitochondrial DNA damage andxidative stress [75]. When the SWCNTs were instilledntratracheally once a week for 8 weeks, acceleration oftheroma plaque formation in the aorta was noted [75].he fibrotic response of the lung to carbon nanotubes may
nvolve oxidative stress, as it is exaggerated in mice defi-ient in vitamin E, which has antioxidant properties [76]. Aecent study by the same group found evidence of anotherystemic effect: SWCNTs given by pharyngeal aspiration ledo a substantial increase in the severity of experimentallynduced Listeria monocytogenes pneumonia. Decreases initric oxide production and bacterial phagocytosis by alve-lar macrophages were noted [77].
MWCNTs induced malignant mesothelioma in p53+/−
ransgenic mice [78]. MWCNTs or crocidolite (asbestos) fibersdministered as a single intraperitoneal injection inducedesothelioma in 15.8% (3/19) and 31.6% (6/19) p53+/− ani-als, respectively. In contrast, no cases of mesotheliomaere seen among p53+/− mice exposed to fullerene nanopar-
icles or unexposed p53+/− mice [78].Another experimental study found a fiber-like effect of
WCNTs injected intraperitoneally to mice [79]. Each ani-al received a single injection of 100 �g/mL of short or
ong amosite (asbestos) fibers or of short or long MWC-Ts. Compared to the short fibers, long amosite fibers and
ong MWCNTs, respectively, induced a stronger inflammatoryesponse and larger numbers of inflammatory granulomas79].
etallic nanoparticlesn general, TiO2 nanoparticles administered into the lungsroduce an inflammatory response with increased totalronchoalveolar lavage fluid cell counts and a predomi-ance of macrophages and neutrophils [49,80—83]. Thisnflammatory response was often described as transient,ccurring 24 hours after inhalation or intratracheal instil-ation of the nanoparticles and usually resolving withinweeks [49,81]. As mentioned above, several physicochemi-
al parameters seem involved in the inflammatory response,ncluding dose, size, and crystalline structure. In mice,erosols of TiO2 nanoparticles having a primary size of 2o 5 nm induced an exaggerated inflammatory response onlyiomb
P. Andujar et al.
hen given in the highest dose of 8.88 mg/m3; lower doses0.77 or 7.22 mg/m3) had little effect [81]. The inflam-atory response was detected after 2 weeks but not afterweeks. Several studies suggest that nanoparticle size mayave a major influence on biological effects. When adminis-ered intranasally to mice, TiO2 generates an inflammatoryesponse only within the nanoscale (29 and 14 nm), nonflammation being seen with fine particles (250 nm) [82].n this study, the nanoparticles but not the fine particles ofiO2 acted as adjuvants to allergic sensitization [82]. Com-ared to the same mass of fine particles (250 nm) of TiO2
natase, 20-nm particles instilled intratracheally in rats andice induced a considerably stronger inflammatory response
with increased neutrophil counts in bronchoalveolar lavageuid 24 hours after the administration) [20]. However, whenhe dose was expressed as the surface area of retained par-icles, the dose-effect curve of the inflammatory responseas not significantly different between the two particle
izes. Thus, surface area may be a more relevant metric thanass or particle count when investigating biological effects
20]. Finally, a major impact of crystalline structure haseen reported. In rats given intratracheal fine or ultrafineutile TiO2 particles or ultrafine anatase/rutile (80/20) parti-les, the rutile crystalline structure was associated with onlyransient inflammation regardless of particle size, whereashe lung inflammation induced by the anatase/rutile mixtureas still present 3 months after the exposure [80].
A prothrombotic effect was reported recently in ratsntratracheally instilled with TiO2 rutile nanoparticles inoses of 1 and 5 mg/kg [84]. Findings after 24 hours includedncreased alveolar macrophage and neutrophil counts inronchoalveolar lavage fluid, pulmonary and cardiac edema,nd systemic inflammation with increased monocyte andranulocyte counts and platelet aggregation.
Finally, an emphysema-like condition was described inCR mice only 2 weeks after a single intratracheal instillationf TiO2 nanoparticles (19—21 nm) [83]. The histopathologicalxamination of the lungs showed disrupted alveolar septa,ype II pneumocyte hyperplasia, epithelial cell apoptosis,nd inflammation with increased macrophage counts. Thiss the first evidence to date of an emphysema-like effect.nterestingly, the induction of emphysema-like lesions con-rasts with the predominantly fibrotic lesions seen withicroscale TiO2 particles.
onclusions
vailable in vivo and in vitro studies consistently showed bio-ogical effects of nanomaterials (including carbon nanotubesnd TiO2) on the respiratory system. These effects includedxidative stress generation, proinflammatory effects, pro-hrombotic effects, lung fibrosis, emphysema-like lungisease, and DNA damage. However, the amount of pub-ished scientific information remains scant. The expandingse of nanoparticles, most notably in the industry andn medicine, together with the industrial-scale productionf nanoparticles, indicates an urgent need for additional
nformation on the potential and established health effectsf nanoparticles. The underlying pathogenic mechanismsust be elucidated. Improved knowledge of the potentialiological effects of nanoparticles is required to develop
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Respiratory effects of manufactured nanoparticles
appropriate preventive methods for workers and for thegeneral population if needed.
Disclosure of interest
The authors declare that they have no conflicts of interestconcerning this article.
KEY POINTS
• Whether nanoparticles generate meaningful toxiceffects remains unclear.
• Few data are available on nanoparticle toxicity inhumans. Factors that affect nanoparticle toxicityinclude size, shape, total surface area, chemicalcomposition, degree of aggregation/agglomeration,and surface coating.
• The smaller size of nanoparticles compared tomicroscale particles is responsible for differences indeposition patterns within the respiratory system.
• Nanoparticle retention within the lungs dependschiefly on particle size, physical clearancemechanisms (mucociliary escalator, macrophagephagocytosis, and epithelial translocation), andchemical clearance mechanisms (dissolution ofsoluble particles, lixiviation, and protein binding).
• Whether nanoparticles can translocate from therespiratory system to other tissues in humans is stilla matter of debate.
• The biological effects of nanoparticles on therespiratory system may include oxidative stress,proinflammatory effects, prothrombotic effects, andDNA damage. Lung fibrosis and emphysema maydevelop.
References
[1] Somasundaran P, Chakraborty S, Qiang Q, et al. Surfactants,polymers and their nanoparticles for personal care applica-tions. J Cosmet Sci 2004;55:S1—17.
[2] Cross SE, Innes B, Roberts MS, et al. Human skin penetra-tion of sunscreen nanoparticles: in-vitro assessment of a novelmicronized zinc oxide formulation. Skin Pharmacol Physiol2007;20:148—54.
[3] Chen W, Zhang JZ, Joly AG. Optical properties and potentialapplications of doped semiconductor nanoparticles. J NanosciNanotechnol 2004;4:919—47.
[4] Murphy CJ, Sau TK, Gole AM, et al. Anisotropic metal nanoparti-cles: synthesis, assembly, and optical applications. J Phys ChemB 2005;109:13857—70.
[5] Nair LS, Laurencin CT. Nanofibers and nanoparticles fororthopaedic surgery applications. J Bone Joint Surg Am2008;90:128—31.
[6] le Masne de Chermont Q, Chanéac C, Seguin J, et al.
Nanoprobes with near-infrared persistent luminescence forin vivo imaging. Proc Natl Acad Sci U S A 2007;104:9266—71.[7] Service R. Nanotechnology grows up. Science2004;304:1732—4.
[
e73
[8] Roco M, Bainbridge WS. Societal implications of nanoscienceand nanotechnology. NSET workshop report. Arlington, Virg.NSET: National Science Foundation; 2001, 272 p.
[9] Sorensen M, Autrup H, Moller P, et al. Linking exposure toenvironmental pollutants with biological effects. Mutat Res2003;544:255—71.
10] Künzli N, Kaiser R, Medina S, et al. Public-health impact of out-door and traffic-related air pollution: a European assessment.Lancet 2000;356:795—801.
11] Peters A, Wichmann HE, Tuch T, et al. Respiratory effects areassociated with the number of ultrafine particles. Am J RespirCrit Care Med 1997;155:1376—83.
12] Pope 3rd CA, Burnett RT, Thun MJ, et al. Lung cancer, cardiopul-monary mortality, and long-term exposure to fine particulateair pollution. JAMA 2002;287:1132—41.
13] Timonen KL, Vanninen E, de Hartog J, et al. Effects of ultra-fine and fine particulate and gaseous air pollution on cardiacautonomic control in subjects with coronary artery disease: theULTRA study. J Expo Sci Environ Epidemiol 2006;16:332—41.
14] de Hartog JJ, Hoek G, Peters A, et al. Effects of fine and ultra-fine particles on cardiorespiratory symptoms in elderly subjectswith coronary heart disease: the ULTRA study. Am J Epidemiol2003;157:613—23.
15] Pekkanen J, Timonen KL, Ruuskanen J, et al. Effects ofultrafine and fine particles in urban air on peak expiratoryflow among children with asthmatic symptoms. Environ Res1997;74:24—33.
16] Iijima S. Helical microtubules of graphitic carbon. Nature1991;354:56—8.
17] Oberdörster G, Oberdörster E, Oberdörster J. Nanotechnology:an emerging discipline evolving from studies of ultrafine parti-cles. Environ Health Perspect 2005;113:823—39.
18] Lanone S, Boczkowski J. Biomedical applications and potentialhealth risks of nanomaterials: molecular mechanisms. Curr MolMed 2006;6:651—63.
19] Nel A, Xia T, Mädler L, et al. Toxic potential of materials at thenanolevel. Science 2006;311:622—7.
20] Oberdörster G, Ferin J, Lehnert BE. Correlation between par-ticle size, in vivo particle persistence, and lung injury. EnvironHealth Perspect 1994;102:173—9.
21] IARC. IARC monographs on the evaluation of carcinogenic risksto humans. Man-made vitreous fibres. Lyon, France: IARC;2002, 81:418 pages.
22] Stanton MF, Laynard M, Tegeris A, et al. Carcinogenicity offibrous glass: pleural response in the rat in relation to fiberdimension. J Natl Cancer Inst 1977;58:587—603.
23] Watanabe M, Okada M, Kudo Y, et al. Differences in theeffects of fibrous and particulate titanium dioxide on alveo-lar macrophages of Fischer 344 rats. J Toxicol Environ HealthA 2002;65:1047—60.
24] Oberdörster G, Ferin J, Gelein R, et al. Role of the alveo-lar macrophage in lung injury: studies with ultrafine particles.Environ Health Perspect 1992;97:193—9.
25] Hohr D, Steinfartz Y, Schins RP, et al. The surface area ratherthan the surface coating determines the acute inflammatoryresponse after instillation of fine and ultrafine TiO2 in the rat.Int J Hyg Environ Health 2002;205:239—44.
26] Donaldson K, Stone V, Clouter A, et al. Ultrafine particles.Occup Environ Med 2001;58:211—6.
27] Park S, Nam H, Chung N, et al. The role of iron in reactive oxy-gen species generation from diesel exhaust particles. ToxicolIn Vitro 2006;20:851—7.
28] Bachoual R, Boczkowski J, Goven D, et al. Biological effectsof particles from the Paris subway system. Chem Res Toxicol
2007;20:1426—33.29] Ball BR, Smith KR, Veranth JM, et al. Bioavailability of ironfrom coal fly ash: mechanisms of mobilization and of biologicaleffects. Inhal Toxicol 2000;12:209—25.
e
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
[
74
30] Shvedova AA, Castranova V, Kisin ER, et al. Exposure to car-bon nanotube material: assessment of nanotube cytotoxicityusing human keratinocyte cells. J Toxicol Environ Health A2003;66:1909—26.
31] Patnaik A. Structure and dynamics in self-organized C60fullerenes. J Nanosci Nanotechnol 2007;7:1111—50.
32] Wang B, Feng WY, Wang TC, et al. Acute toxicity of nano- andmicro-scale zinc powder in healthy adult mice. Toxicol Lett2006;161:115—23.
33] Kendall M, Brown L, Trought K. Molecular adsorption at parti-cle surfaces: a PM toxicity mediation mechanism. Inhal Toxicol2004;16:99—105.
34] Derfus AM, Chan WCW, Bhatia SN. Probing the cytotoxicity ofsemiconductor quantum dots. Nano Lett 2004;4:11—8.
35] Kato T, Yashiro T, Murata Y, et al. Evidence that exoge-nous substances can be phagocytized by alveolar epithelialcells and transported into blood capillaries. Cell Tissue Res2003;311:47—51.
36] Heckel K, Kiefmann R, Dorger M, et al. Colloidal gold particlesas a new in vivo marker of early acute lung injury. Am J PhysiolLung Cell Mol Physiol 2004;287:867—78.
37] Daigle CC, Chalupa DC, Gibb FR, et al. Ultrafine particledeposition in humans during rest and exercise. Inhal Toxicol2003;15:539—52.
38] Takenaka S, Karg E, Kreyling WG, et al. Distribution patternof inhaled ultrafine gold particles in the rat lung. Inhal Toxicol2006;18:733—40.
39] Brown JS, Zeman KL, Bennett WD. Ultrafine particle depositionand clearance in the healthy and obstructed lung. Am J RespirCrit Care Med 2002;166:1240—7.
40] Oberdörster G. Inhaled nano-sized particles: potential effectsand mechanisms. Report of the First International Sym-posium on Occupational Health Implications of Nano-materials, 12—14 October 2004, Buxton, UK, p. 35—46.Ed. Health and Safety Executive-National Institute forOccupational Safety and Health (http://www.hsl.gov.uk/capabilities/nanosymrep final.pdf).
41] Witschger O, Fabries JF. Particules ultrafines et santé au tra-vail : caractéristiques et effets potentiels sur la santé. Hygièneet sécurité du travail. Cahiers de notes documentaires. INRS2005;199:21—35.
42] Witschger O, Fabries JF. Particules ultrafines et santé au tra-vail : sources et caractérisation de l’exposition. Hygiène etsécurité du travail. Cahiers de notes documentaires. INRS2005;199:37—54.
43] Oberdörster G, Finkelstein JN, Johnston C, et al. Acute pul-monary effects of ultrafine particles in rats and mice. Res RepHealth Eff Inst 2000;96:5—74.
44] Pietropaoli AP, Frampton MW, Hyde RW, et al. Pulmonaryfunction, diffusing capacity, and inflammation in healthy andasthmatic subjects exposed to ultrafine particles. Inhal Toxicol2004;16:59—72.
45] Kim CS, Kang TC. Comparative measurement of lung deposi-tion of inhaled fine particles in normal subjects and patientswith obstructive airway disease. Am J Respir Crit Care Med1997;155:899—905.
46] Kreyling WG, Semmler M, Erbe F, et al. Translocation ofultrafine insoluble iridium particles from lung epithelium toextrapulmonary organs is size dependent but very low. J ToxicolEnviron Health 2002;65:1513—30.
47] Tabata Y, Ikada Y. Effect of the size and surface charge ofpolymer microspheres on their phagocytosis by macrophages.Biomaterials 1988;9:356—62.
48] Green TR, Fisher J, Stone MH, et al. Polyethylene parti-
cles of a ‘critical size’ are necessary for the induction ofcytokines by macrophages in vitro. Biomaterials 1998;19:2297—302.[
P. Andujar et al.
49] Geiser M, Casaulta M, Kupferschmid B, et al. The roleof macrophages in the clearance of inhaled ultrafine tita-nium dioxide particles. Am J Respir Cell Mol Biol 2008;38:371—6.
50] Borm PJ, Kreyling W. Toxicological hazards of inhaled nanopar-ticles, potential implications for drug delivery. J NanosciNanotechnol 2004;4:521—31.
51] Semmler-Behnke M, Takenaka S, Fertsch S, et al. Effi-cient elimination of inhaled nanoparticles from the alveolarregion: evidence for interstitial uptake and subsequent reen-trainment onto airways epithelium. Environ Health Perspect2007;115:728—33.
52] Möller W, Felten K, Sommerer K, et al. Deposition, reten-tion, and translocation of ultrafine particles from the centralairways and lung periphery. Am J Respir Crit Care Med2008;177:426—32.
53] Oberdörster G, Sharp Z, Atudorei V, et al. Extrapulmonarytranslocation of ultrafine carbon particles following whole-body inhalation exposure of rats. J Toxicol Environ Health2002;65:1531—43.
54] Nemmar A, Vanbilloen H, Hoylaerts MF, et al. Passage of intra-tracheally instilled ultrafine particles from the lung into thesystemic circulation in hamster. Am J Respir Crit Care Med2001;164:1665—8.
55] Johnston CJ, Finkelstein JN, Gelein R, et al. Charac-terization of the early pulmonary inflammatory responseassociated with PTFE fume exposure. Toxicol Appl Pharmacol1996;140:154—63.
56] Kreyling WG, Semmler-Behnke M, Möller W. Ultrafineparticle-lung interactions: does size matter? J Aerosol Med2006;19:74—83.
57] Nemmar A, Hoet PH, Vanquickenborne B, et al. Passage ofinhaled particles into the blood circulation in humans. Circu-lation 2002;105:411—4.
58] Mills NL, Amin N, Robinson SD, et al. Do inhaled car-bon nanoparticles translocate directly into the circulation inhumans? Am J Respir Crit Care Med 2006;173:426—31.
59] Oberdörster G, Sharp Z, Atudorei V, et al. Translocationof inhaled ultrafine particles to the brain. Inhal Toxicol2004;16:437—45.
60] Katz LC, Burkhalter A, Dreyer WJ. Fluorescent latex micro-spheres as a retrograde neuronal marker for in vivo and in vitrostudies of visual cortex. Nature 1984;310:498—500.
61] Sarkar S, Sharma C, Yog R, et al. Analysis of stress responsivegenes induced by single-walled carbon nanotubes in BJ Foreskincells. J Nanosci Nanotechnol 2007;7:584—92.
62] Sharma CS, Sarkar S, Periyakaruppan A, et al. Single-walledcarbon nanotubes induces oxidative stress in rat lung epithelialcells. J Nanosci Nanotechnol 2007;7:2466—72.
63] Limbach LK, Wick P, Manser P, et al. Exposure of engineerednanoparticles to human lung epithelial cells: influence ofchemical composition and catalytic activity on oxidative stress.Environ Sci Technol 2007;41:4158—63.
64] Wilson MR, Foucaud L, Barlow PG, et al. Nanoparticle inter-actions with zinc and iron: implications for toxicology andinflammation. Toxicol Appl Pharmacol 2007;225:80—9.
65] Xia T, Kovochich M, Brant J, et al. Comparison of the abilitiesof ambient and manufactured nanoparticles to induce cellulartoxicity according to an oxidative stress paradigm. Nano Lett2006;6:1794—807.
66] Monteiller C, Tran L, MacNee W, et al. The pro-inflammatoryeffects of low-toxicity low-solubility particles, nanoparticlesand fine particles, on epithelial cells in vitro: the role of surfacearea. Occup Environ Med 2007;64:609—15.
67] Kisin ER, Murray AR, Keane MJ, et al. Single-walled carbon nan-otubes: geno- and cytotoxic effects in lung fibroblast V79 cells.J Toxicol Environ Health A 2007;70:2071—9.
[
[
[
[
[
[
[
Respiratory effects of manufactured nanoparticles
[68] Zhu L, Chang DW, Dai L, et al. DNA damage induced by multi-walled carbon nanotubes in mouse embryonic stem cells. NanoLett 2007;7:3592—7.
[69] Schins RP, Knaapen AM. Genotoxicity of poorly soluble parti-cles. Inhal Toxicol 2007;19:189—98.
[70] Lam C, James JT, McCluskey R, et al. Pulmonary toxicity ofsingle-wall carbon nanotubes in mice 7 and 90 days after intra-tracheal instillation. Toxicol Sci 2004;77:126—34.
[71] Warheit DB, Laurence BR, Reed KL, et al. Comparative pul-monary toxicity assessment of single-wall carbon nanotubes inrats. Toxicol Sci 2004;77:117—25.
[72] Mercer RR, Scabilloni J, Wang L, et al. Alteration of depositionpattern and pulmonary response as a result of improved disper-sion of aspirated single-walled carbon nanotubes in a mousemodel. Am J Physiol Lung Cell Mol Physiol 2008;294:L87—97.
[73] Mitchell LA, Gao J, Wal RV, et al. Pulmonary and systemicimmune response to inhaled multiwalled carbon nanotubes.Toxicol Sci 2007;100:203—14.
[74] Li JG, Li WX, Xu JY, et al. Comparative study of pathologi-cal lesions induced by multiwalled carbon nanotubes in lungsof mice by intratracheal instillation and inhalation. EnvironToxicol 2007;22:415—21.
[75] Li Z, Hulderman T, Salmen R, et al. Cardiovascular effects ofpulmonary exposure to single-wall carbon nanotubes. EnvironHealth Perspect 2007;115:377—82.
[76] Shvedova AA, Kisin ER, Murray AR, et al. E deficiency enhancespulmonary inflammatory response and oxidative stress inducedby single-walled carbon nanotubes in C57BL/6 mice. ToxicolAppl Pharmacol 2007;221:339—48.
[
e75
77] Shvedova AA, Fabisiak JP, Kisin ER, et al. Sequential expo-sure to carbon nanotubes and bacteria enhances pulmonaryinflammation and infectivity. Am J Respir Cell Mol Biol 2008;38:579—90.
78] Takagi A, Hirose A, Nishimura T, et al. Induction of mesothe-lioma in p53+/- mouse by intraperitoneal application ofmulti-wall carbon nanotube. J Toxicol Sci 2008;33:105—16.
79] Poland CA, Duffin R, Kinloch I, et al. Carbon nanotubes intro-duced into the abdominal cavity of mice show asbestos-likepathogenicity in a pilot study. Nat Nanotechnol 2008;3:423—8.
80] Warheit DB, Webb TR, Reed KL, et al. Pulmonary toxicitystudy in rats with three forms of ultrafine-TiO2 particles: dif-ferential responses related to surface properties. Toxicology2007;230:90—104.
81] Grassian VH, O’Shaughnessy PT, Adamcakova-Dodd A, et al.Inhalation exposure study of titanium dioxide nanoparticleswith a primary particle size of 2 to 5 nm. Environ Health Per-spect 2007;115:397—402.
82] De Haar C, Hassing I, Bol M, et al. Ultrafine but not fineparticulate matter causes airway inflammation and allergic air-way sensitization to co-administered antigen in mice. Clin ExpAllergy 2006;36:1469—79.
83] Chen HW, Su SF, Chien CT, et al. Titanium dioxide nanopar-ticles induce emphysema-like lung injury in mice. FASEB J2006;20:2393—5.
84] Nemmar A, Melghit K, Ali BH. The acute proinflammatoryand prothrombotic effects of pulmonary exposure to rutileTiO2 nanorods in rats. Exp Biol Med (Maywood) 2008;233:610—9.
