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ABSTRACT: Particulate matter (PM) is an important risk factor for asthma. Generation of oxidative stress by PM is a major mechanism of its health effects. Transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) mediates antioxidant and phase II enzymes and is essential in protecting against oxidative stress and lung inflammation. We have previously shown that ambient ultrafine particles (UFP) could exert a potent adjuvant effect on allergic sensitization to ovalbumin (OVA) in mice. We hypothesized that Nrf2 deficiency in dendritic cells (DC) could enhance the adjuvant potential of UFP on allergic sensitization. We show that the adjuvant effect of intranasally instilled UFP is significantly enhanced in Nrf2 knockout (Nrf2(-/-)) mice compared with their wild-type (Nrf2(+/+)) counterparts. Under resting conditions, Nrf2(-/-) DC displayed an intrinsic predilection to a T helper 2-favoring cytokine profile characterized by a low level of IL-12p70 and a high level of IL-6 as compared to Nrf2(+/+) DC. Adoptive transfer of OVA/UFP-treated Nrf2(-/-) DC provoked a more severe allergic inflammation in the lung than Nrf2(+/+) DC in the same treatment group. We conclude that Nrf2 deficiency in DC may promote a constitutive immune-polarizing cytokine milieu, which we propose may have contributed to the augmented adjuvant effect of UFP on allergic sensitization.
Journal of Innate Immunity 04/2013; · 4.21 Impact Factor
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Ruibin Li,
Xiang Wang,
Zhaoxia Ji,
Bingbing Sun,
Haiyuan Zhang,
Chong Hyun Chang,
Sijie Lin,
Huan Meng,
Yu-Pei Liao, Meiying Wang,
Zongxi Li,
Angela A Hwang,
Tze-Bin Song,
Run Xu,
Yang Yang,
Jeffrey I Zink,
André E Nel,
Tian Xia
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ABSTRACT: Functionalized carbon nanotubes (f-CNTs) are being produced in increased volume because of the ease of dispersion and maintenance of the pristine material physicochemical properties when used in composite materials as well as for other commercial applications. However, the potential adverse effects of f-CNTs have not been quantitatively or systematically explored. In this study, we used a library of covalently functionalized multiwall carbon nanotubes (f-MWCNTs), established from the same starting material, to assess the impact of surface charge in a predictive toxicological model that relates the tubes' pro-inflammatory and pro-fibrogenic effects at cellular level to the development of pulmonary fibrosis. Carboxylate (COOH), polyethylene glycol (PEG), amine (NH2), sidewall amine (sw-NH2), and polyetherimide (PEI)-modified MWCNTs were successfully established from raw or as-prepared (AP-) MWCNTs and comprehensively characterized by TEM, XPS, FTIR, and DLS to obtain information about morphology, length, degree of functionalization, hydrodynamic size, and surface charge. Cellular screening in BEAS-2B and THP-1 cells showed that, compared to AP-MWCNTs, anionic functionalization (COOH and PEG) decreased the production of pro-fibrogenic cytokines and growth factors (including IL-1β, TGF-β1, and PDGF-AA), while neutral and weak cationic functionalization (NH2 and sw-NH2) showed intermediary effects. In contrast, the strongly cationic PEI-functionalized tubes induced robust biological effects. These differences could be attributed to differences in cellular uptake and NLRP3 inflammasome activation, which depends on the propensity toward lysosomal damage and cathepsin B release in macrophages. Moreover, the in vitro hazard ranking was validated by the pro-fibrogenic potential of the tubes in vivo. Compared to pristine MWCNTs, strong cationic PEI-MWCNTs induced significant lung fibrosis, while carboxylation significantly decreased the extent of pulmonary fibrosis. These results demonstrate that surface charge plays an important role in the structure-activity relationships that determine the pro-fibrogenic potential of f-CNTs in the lung.
ACS Nano 02/2013; · 10.77 Impact Factor
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Xiang Wang,
Tian Xia,
Matthew C Duch,
Zhaoxia Ji,
Haiyuan Zhang,
Ruibin Li,
Bingbing Sun,
Sijie Lin,
Huan Meng,
Yu-Pei Liao, Meiying Wang,
Tze-Bin Song,
Yang Yang,
Mark C Hersam,
André E Nel
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ABSTRACT: We compared the use of bovine serum albumin (BSA) and pluronic F108 (PF108) as dispersants for multiwalled carbon nanotubes (MWCNTs) in terms of tube stability as well as profibrogenic effects in vitro and in vivo. While BSA-dispersed tubes were a potent inducer of pulmonary fibrosis, PF108 coating protected the tubes from damaging the lysosomal membrane and initiating a sequence of cooperative cellular events that play a role in the pathogenesis of pulmonary fibrosis. Our results suggest that PF108 coating could serve as a safer design approach for MWCNTs.
Nano Letters 04/2012; 12(6):3050-61. · 13.20 Impact Factor
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Haiyuan Zhang,
Zhaoxia Ji,
Tian Xia,
Huan Meng,
Cecile Low-Kam,
Rong Liu,
Suman Pokhrel,
Sijie Lin,
Xiang Wang,
Yu-Pei Liao, Meiying Wang,
Linjiang Li,
Robert Rallo,
Robert Damoiseaux,
Donatello Telesca,
Lutz Mädler,
Yoram Cohen,
Jeffrey I Zink,
Andre E Nel
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ABSTRACT: We demonstrate for 24 metal oxide (MOx) nanoparticles that it is possible to use conduction band energy levels to delineate their toxicological potential at cellular and whole animal levels. Among the materials, the overlap of conduction band energy (E(c)) levels with the cellular redox potential (-4.12 to -4.84 eV) was strongly correlated to the ability of Co(3)O(4), Cr(2)O(3), Ni(2)O(3), Mn(2)O(3), and CoO nanoparticles to induce oxygen radicals, oxidative stress, and inflammation. This outcome is premised on permissible electron transfers from the biological redox couples that maintain the cellular redox equilibrium to the conduction band of the semiconductor particles. Both single-parameter cytotoxic as well as multi-parameter oxidative stress assays in cells showed excellent correlation to the generation of acute neutrophilic inflammation and cytokine responses in the lungs of C57 BL/6 mice. Co(3)O(4), Ni(2)O(3), Mn(2)O(3), and CoO nanoparticles could also oxidize cytochrome c as a representative redox couple involved in redox homeostasis. While CuO and ZnO generated oxidative stress and acute pulmonary inflammation that is not predicted by E(c) levels, the adverse biological effects of these materials could be explained by their solubility, as demonstrated by ICP-MS analysis. These results demonstrate that it is possible to predict the toxicity of a large series of MOx nanoparticles in the lung premised on semiconductor properties and an integrated in vitro/in vivo hazard ranking model premised on oxidative stress. This establishes a robust platform for modeling of MOx structure-activity relationships based on band gap energy levels and particle dissolution. This predictive toxicological paradigm is also of considerable importance for regulatory decision-making about this important class of engineered nanomaterials.
ACS Nano 04/2012; 6(5):4349-68. · 10.77 Impact Factor
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Xiang Wang,
Tian Xia,
Susana Addo Ntim,
Zhaoxia Ji,
Sijie Lin,
Huan Meng,
Choong-Heui Chung,
Saji George,
Haiyuan Zhang, Meiying Wang,
Ning Li,
Yang Yang,
Vincent Castranova,
Somenath Mitra,
James C Bonner,
André E Nel
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ABSTRACT: We developed a dispersal method for multiwalled carbon nanotubes (MWCNTs) that allows quantitative assessment of dispersion on profibrogenic responses in tissue culture cells and in mouse lung. We demonstrate that the dispersal of as-prepared (AP), purified (PD), and carboxylated (COOH) MWCNTs by bovine serum albumin (BSA) and dipalmitoylphosphatidylcholine (DPPC) influences TGF-β1, PDGF-AA, and IL-1β production in vitro and in vivo. These biomarkers were chosen based on their synergy in promoting fibrogenesis and cellular communication in the epithelial-mesenchymal cell trophic unit in the lung. The effect of dispersal was most noticeable in AP- and PD-MWCNTs, which are more hydrophobic and unstable in aqueous buffers than hydrophilic COOH-MWCNTs. Well-dispersed AP- and PD-MWCNTs were readily taken up by BEAS-2B, THP-1 cells, and alveolar macrophages (AM) and induced more prominent TGF-β1 and IL-1β production in vitro and TGF-β1, IL-1β, and PDGF-AA production in vivo than nondispersed tubes. Moreover, there was good agreement between the profibrogenic responses in vitro and in vivo as well as the ability of dispersed tubes to generate granulomatous inflammation and fibrosis in airways. Tube dispersal also elicited more robust IL-1β production in THP-1 cells. While COOH-MWCNTs were poorly taken up in BEAS-2B and induced little TGF-β1 production, they were bioprocessed by AM and induced less prominent collagen deposition at sites of nongranulomatous inflammation in the alveolar region. Taken together, these results indicate that the dispersal state of MWCNTs affects profibrogenic cellular responses that correlate with the extent of pulmonary fibrosis and are of potential use to predict pulmonary toxicity.
ACS Nano 11/2011; 5(12):9772-87. · 10.77 Impact Factor
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Haiyuan Zhang,
Tian Xia,
Huan Meng,
Min Xue,
Saji George,
Zhaoxia Ji,
Xiang Wang,
Rong Liu, Meiying Wang,
Bryan France,
Robert Rallo,
Robert Damoiseaux,
Yoram Cohen,
Kenneth A Bradley,
Jeffrey I Zink,
Andre E Nel
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ABSTRACT: Most in vitro toxicity studies on engineered nanomaterials (ENMs) use transformed rather than primary cells for logistical reasons. However, primary cells may provide a more appropriate connection to in vivo toxicity because these cells maintain their phenotypic fidelity and are also capable of differentiating into lineages that may be differently affected by potentially hazardous ENMs. Few studies to date have focused on the role of cellular differentiation in determining ENM toxicity. We compared the response of undifferentiated and differentiated primary human bronchial epithelial (NHBE) cells to cationic mesoporous silica nanoparticles (MSNPs) that are coated with polyethyleneimine (PEI) since this polymer is known to exert differential cytotoxicity depending on its molecular weight and cationic density. The attachment of cationic PEI polymers to the MSNP surface was used to assess these materials' toxicological potential in undifferentiated and differentiated human bronchial epithelial cells, using a multiparametric assay that screens for an integrated set of sublethal and lethal response outcomes. MSNPs coated with high molecular weight (10 and 25 kD) polymers were more toxic in differentiated cells than particles coated with shorter length polymers. The increased susceptibility of the differentiated cells is in agreement with more abundant expression of a proteoglycan, syndecan-1, which contains copious heparin sulfate side chains. Pretreatment with heparinase to remove the negatively charged sulfates decreased MSNP-PEI binding to the cell surface and lowered the cytotoxic potential of the cationic particles. These data demonstrate the importance of studying cellular differentiation as an important variable in the response of primary cells to toxic ENM properties.
ACS Nano 03/2011; 5(4):2756-69. · 10.77 Impact Factor
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Tian Xia,
Yan Zhao,
Tina Sager,
Saji George,
Suman Pokhrel,
Ning Li,
David Schoenfeld,
Huan Meng,
Sijie Lin,
Xiang Wang, Meiying Wang,
Zhaoxia Ji,
Jeffrey I Zink,
Lutz Mädler,
Vincent Castranova,
Shuo Lin,
Andre E Nel
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ABSTRACT: We have recently shown that the dissolution of ZnO nanoparticles and Zn(2+) shedding leads to a series of sublethal and lethal toxicological responses at the cellular level that can be alleviated by iron doping. Iron doping changes the particle matrix and slows the rate of particle dissolution. To determine whether iron doping of ZnO also leads to lesser toxic effects in vivo, toxicity studies were performed in rodent and zebrafish models. First, we synthesized a fresh batch of ZnO nanoparticles doped with 1-10 wt % of Fe. These particles were extensively characterized to confirm their doping status, reduced rate of dissolution in an exposure medium, and reduced toxicity in a cellular screen. Subsequent studies compared the effects of undoped to doped particles in the rat lung, mouse lung, and the zebrafish embryo. The zebrafish studies looked at embryo hatching and mortality rates as well as the generation of morphological defects, while the endpoints in the rodent lung included an assessment of inflammatory cell infiltrates, LDH release, and cytokine levels in the bronchoalveolar lavage fluid. Iron doping, similar to the effect of the metal chelator, DTPA, interfered in the inhibitory effects of Zn(2+) on zebrafish hatching. In the oropharyngeal aspiration model in the mouse, iron doping was associated with decreased polymorphonuclear cell counts and IL-6 mRNA production. Doped particles also elicited decreased heme oxygenase 1 expression in the murine lung. In the intratracheal instillation studies in the rat, Fe doping was associated with decreased polymorphonuclear cell counts, LDH, and albumin levels. All considered, the above data show that Fe doping is a possible safe design strategy for preventing ZnO toxicity in animals and the environment.
ACS Nano 02/2011; 5(2):1223-35. · 10.77 Impact Factor
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ABSTRACT: We have previously demonstrated that intranasal administration of ambient ultrafine particles (UFP) acts as an adjuvant for primary allergic sensitization to ovalbumin (OVA) in Balb/c mice. It is important to find out whether inhaled UFP exert the same effect on the secondary immune response as a way of explaining asthma flares in already-sensitized individuals due to traffic exposure near a freeway. The objective of this study is to determine whether inhalation exposure to ambient UFP near an urban freeway could enhance the secondary immune response to OVA in already-sensitized mice. Prior OVA-sensitized animals were exposed to concentrated ambient UFP at the time of secondary OVA challenge in our mobile animal laboratory in Los Angeles. OVA-specific antibody production, airway morphometry, allergic airway inflammation, cytokine gene expression, and oxidative stress marker were assessed. As few as five ambient UFP exposures were sufficient to promote the OVA recall immune response, including generating allergic airway inflammation in smaller and more distal airways compared with the adjuvant effect of intranasally instilled UFP on the primary immune response. The secondary immune response was characterized by the T helper 2 and IL-17 cytokine gene expression in the lung. In summary, our results demonstrated that inhalation of prooxidative ambient UFP could effectively boost the secondary immune response to an experimental allergen, indicating that vehicular traffic exposure could exacerbate allergic inflammation in already-sensitized subjects.
AJP Lung Cellular and Molecular Physiology 09/2010; 299(3):L374-83. · 3.66 Impact Factor
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ABSTRACT: Ambient particulate matter (PM) from air pollution is associated with exacerbation of asthma. The immunological basis for the adjuvant effects of PM is still not well understood. The generation of ROS and the resulting oxidative stress has been identified as one of the major mechanisms. Using a new intranasal sensitization model in which ambient PM is used as an adjuvant to enhance allergic inflammation (Li et al., Environ. Health Perspect. 2009, 117, 1116-1123), a proteomics approach was applied to study the adjuvant effects of ambient PM. The enhanced in vivo adjuvant effect of ultrafine particles correlates with a higher in vitro oxidant potential and a higher content of redox-cycling organic chemicals. Bronchoalveolar lavage fluid proteins from normal and sensitized mice were resolved by 2-DE, and identified by MS. Polymeric immunoglobulin receptor, complement C3, neutrophil gelatinase-associated lipocalin, chitinase 3-like protein 3, chitinase 3-like protein 4, and acidic mammalian chitinase demonstrated significantly enhanced up-regulation by UFP with a polycyclic aromatic hydrocarbon content and a higher oxidant potential. These proteins may be the important specific elements targeted by PM in air pollution through the ability to generate ROS in the immune system, and may be involved in allergen sensitization and asthma pathogenesis.
Proteomics 02/2010; 10(3):520-31. · 4.43 Impact Factor
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ABSTRACT: It has been demonstrated that ambient particulate matter (PM) can act as an adjuvant for allergic sensitization. Redox-active organic chemicals on the particle surface play an important role in PM adverse health effects and may determine the adjuvant effect of different particle types according to their potential to perturb redox equilibrium in the immune system.
We determined whether the adjuvant effect of ambient fine particles versus ultrafine particles (UFPs) is correlated to their prooxidant potential.
We have established an intranasal sensitization model that uses ambient PM as a potential adjuvant for sensitization to ovalbumin (OVA), which enhances the capacity for secondary OVA challenge to induce allergic airway inflammation.
UFPs with a greater polycyclic aromatic hydrocarbon (PAH) content and higher oxidant potential enhanced OVA sensitization more readily than did fine particles. This manifests as enhanced allergic inflammation upon secondary OVA challenge, leading to eosinophilic inflammation and mucoid hyperplasia starting at the nasal turbinates all the way down to the small pulmonary airways. The thiol antioxidant N-acetyl cysteine was able to suppress some of these sensitization events.
The adjuvant effects of ambient UFP is determined by their oxidant potential, which likely plays a role in changing the redox equilibrium in the mucosal immune system.
Environmental Health Perspectives 08/2009; 117(7):1116-23. · 7.04 Impact Factor
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ABSTRACT: Oxidative stress plays an important role in the development of airway inflammation and hyperreactivity in asthma. The identification of oxidative stress markers in bronchoalveolar lavage fluid (BALF) and lung tissue from ovalbumin (OVA) sensitized mice could provide new insight into disease pathogenesis and possible use of antioxidants to alleviate disease severity. We used two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to determine the impact of the thiol antioxidant, N-acetylcysteine (NAC), on protein expression in a murine OVA model. At least six proteins or protein families were found to be significantly increased in BALF from OVA-challenged mice compared to a control group: Chitinase 3-like protein 3 (Yml), Chitinase 3-like protein 4 (Ym2), acidic mammalian Chitinase (AMCase), pulmonary surfactant-associated protein D (SP-D), resistin-like molecule alpha (RELMalpha) or "found in inflammatory 1" (FIZZ1), and haptoglobin alpha-subunit. A total of nine proteins were significantly increased in lung tissue from the murine asthma model, including Yml, Ym2, FIZZ1, and other lung remodeling-related proteins. Western blotting confirmed increased Yml/Ym2, SP-D, and FIZZ1 expression measured from BAL fluid and lung tissue from OVA-challenged mice. Intraperitoneal NAC administration prior to the final OVA challenge inhibited Yml/Ym2, SP-D, and FIZZ1 expression in BALF and lung tissue. The oxidative stress proteins, Ym1/Ym2, FIZZ1, and SP-D, could play an important role in the pathogenesis of asthma and may be useful oxidative stress markers.
Journal of Proteome Research 05/2009; 8(4):1631-8. · 5.11 Impact Factor
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ABSTRACT: The decrease in cellular immunity with aging is of considerable public health importance. Recent studies suggest that the redox equilibrium of dendritic cells (DCs) is a key factor in maintaining protective cellular immunity and that a disturbance of this homeostatic mechanism could contribute to immune senescence.
We sought (1) to elucidate the role of DC redox equilibrium in the decrease of contact hypersensitivity (CHS) and T(H)1 immunity during aging and (2) to determine how restoration of glutathione (GSH) levels by the Nrf2-mediated antioxidant defense pathway affects this decrease.
We assessed the effect of Nrf2 deficiency and boosting of GSH levels by the Nrf2 agonist sulforaphane or the thiol precursor N-acetyl cysteine (NAC) on the CHS response to contact antigens in old mice. We studied the effect of SFN and NAC on restoring T(H)1 immunity by treating DCs ex vivo before adoptive transfer and in vivo challenge.
Aging was associated with a decreased CHS response that was accentuated by Nrf2 deficiency. Systemic SFN treatment reversed this decrease through Nrf2-mediated antioxidant enzyme expression and GSH synthesis. Adoptive transfer of DCs from old animals induced a weakened CHS response in recipient animals. Treatment of DCs from old animals with SFN or NAC ex vivo restored the in vivo challenge response.
SFN and NAC upregulate T(H)1 immunity in aging through a restoration of redox equilibrium.
The Journal of allergy and clinical immunology 06/2008; 121(5):1255-1261.e7. · 9.17 Impact Factor
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ABSTRACT: The aim of this study is to identify candidate factors which may be responsible for the functional inactivation and depletion of NK cells by tumor cells. Inhibition of NFkappaB activity by an IkappaB super-repressor in HEp2 cells, a cell line commonly used as an oral tumor model, blocked tumor-induced NK cell death, and increased the function of NK cells significantly. Increased expression of CD69 early activation antigen on NK cells as well as augmented proliferation and secretion of IFN-gamma by NK cells were observed when these cells were co-incubated with IkappaB super-repressor transfected HEp2 cells (HEp2-IkappaB((S32AS36A))). More importantly, the secretion of IL-6 was significantly inhibited when NK cells were co-cultured with HEp2-IkappaB((S32AS36A)) cells. In addition, the survival and function of cytotoxic effector cells remained significantly elevated in the presence of IFN-gamma-treated HEp2-IkappaB((S32AS36A)) cells when compared to either untreated or IFN-gamma-treated vector-alone transfected HEp2 cells. Similar findings to those obtained using purified peripheral blood NK cells were also observed when non-fractionated peripheral blood mononuclear cells were used in the co-cultures of immune effectors with HEp2 cell transfectants. Addition of recombinant human IL-6 to the co-cultures of immune effectors with the NFkappaB knockdown HEp2 tumor cells substantially decreased the levels of secreted IFN-gamma. Thus, the results presented in this paper suggest that the inhibition of NFkappaB function in oral tumors may serve to activate and expand the function and numbers of NK cells. Moreover, NFkappaB-mediated increase in IL-6 secretion by oral tumors may in part be responsible for the observed inactivation and death of the immune effectors.
Cancer Immunology and Immunotherapy 10/2006; 55(9):1052-63. · 3.70 Impact Factor
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ABSTRACT: Epidemiologic studies show that exposure to ambient particulate matter leads to asthma exacerbation. Diesel exhaust particles (DEPs), a model pollutant, act as an adjuvant for allergic sensitization. Increasing evidence shows that this effect could be mediated by an effect on dendritic cells (DCs).
Our aim was to elucidate the mechanism by which pro-oxidative DEP chemicals change DC function so that these antigen-presenting cells strengthen the immune response to an experimental allergen.
We exposed murine bone marrow-derived DCs and a homogeneous myeloid DC line, BC1, to DEPs and organic extracts made from these particles to determine how the induction of oxidative stress affects cellular maturation, cytokine production, and activation of antigen-specific T cells.
DEP extracts induced oxidative stress in DCs. This change in redox equilibrium interfered in the ability of Toll-like receptor agonists to induce the expression of maturation receptors (eg, CD86, CD54, and I-A(d)) and IL-12 production. This perturbation of DC function was accompanied by decreased IFN-gamma and increased IL-10 induction in antigen-specific T cells. The molecular basis for the perturbation of DC function is the activation of a nuclear factor-erythroid 2 (NF-E2)-related factor 2-mediated signaling pathway that suppresses IL-12 production. NF-E2-related factor 2 deficiency abrogates the perturbation of DC function by DEPs.
These data provide the first report that pro-oxidative DEP chemicals can interfere in T(H)1-promoting response pathways in a homogeneous DC population and provide a novel explanation for the adjuvant effect of DEPs on allergic inflammation.
These data clarify the adjuvant effect of particulate air pollutants in allergic inflammatory disease.
Journal of Allergy and Clinical Immunology 09/2006; 118(2):455-65. · 11.00 Impact Factor
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ABSTRACT: A large body of evidence has shown that exposure to ambient particulate matter (PM) leads to asthma exacerbation through an excitation of allergic inflammation. Utilizing diesel exhaust particles (DEPs) as a model air pollutant, we and others have demonstrated that PM contains redox-active chemicals that generate inflammation through an oxidative stress mechanism. Recently, the strengths of proteomics have enabled us to demonstrate that organic DEP extracts induce a hierarchical expression pattern of oxidative stress-induced proteins in macrophages and epithelial cells. As a further extension of this work, we now employ a new phosphosensor fluorescent dye, Pro-Q Diamond, to elucidate the induction of phosphoproteins and intracellular signaling cascades that may play a role in DEP-induced inflammation. We demonstrate that DEPs induced the phosphorylation of several phosphoproteins that belong to a number of signaling pathways as well as other oxidative stress pathways. In combination with cytokine array, phosphoproteome analysis using Pro-Q Diamond allowed us to characterize the aromatic and polar chemicals of DEPs that are involved in the activation of three different mitogen-activated protein (MAP) kinase signaling pathways.
Electrophoresis 07/2005; 26(11):2092-108. · 3.30 Impact Factor
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Ning Li,
Jawed Alam,
M Indira Venkatesan,
Arantza Eiguren-Fernandez,
Debra Schmitz,
Emma Di Stefano,
Ndaisha Slaughter,
Erin Killeen,
Xiaorong Wang,
Aaron Huang, Meiying Wang,
Antonio H Miguel,
Arthur Cho,
Constantinos Sioutas,
Andre E Nel
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ABSTRACT: The proinflammatory effects of particulate pollutants, including diesel exhaust particles (DEP), are related to their content of redox cycling chemicals and their ability to generate oxidative stress in the respiratory tract. An antioxidant defense pathway, which involves phase II enzyme expression, protects against the pro-oxidative and proinflammatory effects of DEP. The expression of enzymes, including heme oxygenase-1 (HO-1) and GST, is dependent on the activity of a genetic antioxidant response element in their promoters. In this study we investigated the mechanism by which redox cycling organic chemicals, prepared from DEP, induce phase II enzyme expression as a protective response. We demonstrate that aromatic and polar DEP fractions, which are enriched in polycyclic aromatic hydrocarbons and quinones, respectively, induce the expression of HO-1, GST, and other phase II enzymes in macrophages and epithelial cells. We show that HO-1 expression is mediated through accumulation of the bZIP transcription factor, Nrf2, in the nucleus, and that Nrf2 gene targeting significantly weakens this response. Nrf2 accumulation and subsequent activation of the antioxidant response element is regulated by the proteasomal degradation of Nrf2. This pathway is sensitive to pro-oxidative and electrophilic DEP chemicals and is also activated by ambient ultrafine particles. We propose that Nrf2-mediated phase II enzyme expression protects against the proinflammatory effects of particulate pollutants in the setting of allergic inflammation and asthma.
The Journal of Immunology 10/2004; 173(5):3467-81. · 5.79 Impact Factor
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ABSTRACT: Epidemiological studies demonstrate an association between short term exposure to ambient particulate matter (PM) and cardiorespiratory morbidity and mortality. Although the biological mechanisms of these adverse effects are unknown, emerging data suggest a key role for oxidative stress. Ambient PM and diesel exhaust particles (DEP) contain redox cycling organic chemicals that induce pro-oxidative and pro-inflammatory effects in the lung. These responses are suppressed by N-acetylcysteine (NAC), which directly complexes to electrophilic DEP chemicals and exert additional antioxidant effects at the cellular level. A proteomics approach was used to study DEP-induced responses in the macrophage cell line, RAW 264.7. We demonstrate that in the dose range 10-100 microg/ml, organic DEP extracts induce a progressive decline in the cellular GSH/GSSG ratio, in parallel with a linear increase in newly expressed proteins on the two-dimensional gel. Using matrix-assisted laser desorption ionization time-of-flight mass spectrometry and electrospray ionization-liquid chromatography/mass spectrometry/mass spectrometry analysis, 32 newly induced/NAC-suppressed proteins were identified. These include antioxidant enzymes (e.g. heme oxygenase-1 and catalase), pro-inflammatory components (e.g. p38MAPK and Rel A), and products of intermediary metabolism that are regulated by oxidative stress. Heme oxygenase-1 was induced at low extract dose and with minimal decline in the GSH/GSSG ratio, whereas MAP kinase activation required a higher chemical dose and incremental levels of oxidative stress. Moreover, at extract doses >50 microg/ml, there is a steep decline in cellular viability. These data suggest that DEP induce a hierarchical oxidative stress response in which some of these proteins may serve as markers for oxidative stress during PM exposures.
Journal of Biological Chemistry 12/2003; 278(50):50781-90. · 4.77 Impact Factor
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ABSTRACT: Epidemiologic studies show that sudden surges in ambient particulate matter (PM) levels can trigger acute asthma exacerbations. Although diesel exhaust particles (DEPs) act as an adjuvant for allergic sensitization, this is a delayed response and does not explain acute PM effects on airway hyperreactivity (AHR).
Our aim was to determine the acute effects of DEPs on AHR using a mouse model.
Three protocols were developed, 2 of which require OVA sensitization, whereas the third was OVA independent. In the mild sensitization protocol BALB/c mice receive intraperitoneal OVA without alum and are then challenged with aerosolized OVA with or without DEPs. In the postchallenge model DEPs are delivered after OVA challenge to animals sensitized by intraperitoneal OVA plus alum. In the third protocol nebulizer DEPs were also delivered to IL-5-overexpressing mice that exhibit constitutive airway inflammation. Animals were subjected to whole-body plethysmography (WBP) and then killed for performance of bronchoalveolar lavage, histology, and serology.
DEP delivery concomitant with OVA challenge or after the induction of airway inflammation with this allergen induced increased AHR in models 1 and 2, respectively. Although these animals showed DEP-induced inflammation and mucus production in the intermediary airways, there was no effect on OVA-specific IgE or T(H)2 cytokine production. In the IL-5 transgenic mice it was possible to induce similar effects with DEPs in the absence of an allergen.
We demonstrate that DEPs induced AHR independent of their adjuvant effects, suggesting the use of these models to study the mechanism or mechanisms of acute asthma exacerbation by means of PM.
Journal of Allergy and Clinical Immunology 12/2003; 112(5):905-14. · 11.00 Impact Factor
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ABSTRACT: The objectives of this study were to determine whether differences in the size and composition of coarse (2.5-10 micro m), fine (< 2.5 microm), and ultrafine (< 0.1 microm) particulate matter (PM) are related to their uptake in macrophages and epithelial cells and their ability to induce oxidative stress. The premise for this study is the increasing awareness that various PM components induce pulmonary inflammation through the generation of oxidative stress. Coarse, fine, and ultrafine particles (UFPs) were collected by ambient particle concentrators in the Los Angeles basin in California and used to study their chemical composition in parallel with assays for generation of reactive oxygen species (ROS) and ability to induce oxidative stress in macrophages and epithelial cells. UFPs were most potent toward inducing cellular heme oxygenase-1 (HO-1) expression and depleting intracellular glutathione. HO-1 expression, a sensitive marker for oxidative stress, is directly correlated with the high organic carbon and polycyclic aromatic hydrocarbon (PAH) content of UFPs. The dithiothreitol (DTT) assay, a quantitative measure of in vitro ROS formation, was correlated with PAH content and HO-1 expression. UFPs also had the highest ROS activity in the DTT assay. Because the small size of UFPs allows better tissue penetration, we used electron microscopy to study subcellular localization. UFPs and, to a lesser extent, fine particles, localize in mitochondria, where they induce major structural damage. This may contribute to oxidative stress. Our studies demonstrate that the increased biological potency of UFPs is related to the content of redox cycling organic chemicals and their ability to damage mitochondria.
Environmental Health Perspectives 05/2003; 111(4):455-60. · 7.04 Impact Factor
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ABSTRACT: Inhaled diesel exhaust particles (DEP) exert proinflammatory effects in the respiratory tract. This effect is related to the particle content of redox cycling chemicals and is involved in the adjuvant effects of DEP in atopic sensitization. We demonstrate that organic chemicals extracted from DEP induce oxidative stress in normal and transformed bronchial epithelial cells, leading to the expression of heme oxygenase 1, activation of the c-Jun N-terminal kinase cascade, IL-8 production, as well as induction of cytotoxicity. Among these effects, heme oxygenase 1 expression is the most sensitive marker for oxidative stress, while c-Jun N-terminal kinase activation and induction of apoptosis-necrosis require incremental amounts of the organic chemicals and increased levels of oxidative stress. While a macrophage cell line (THP-1) responded in similar fashion, epithelial cells produced more superoxide radicals and were more susceptible to cytotoxic effects than macrophages. Cytotoxicity is the result of mitochondrial damage, which manifests as ultramicroscopic changes in organelle morphology, a decrease in the mitochondrial membrane potential, superoxide production, and ATP depletion. Epithelial cells also differ from macrophages in not being protected by a thiol antioxidant, N-acetylcysteine, which effectively protects macrophages against cytotoxic DEP chemicals. These findings show that epithelial cells exhibit a hierarchical oxidative stress response that differs from that of macrophages by more rapid transition from cytoprotective to cytotoxic responses. Moreover, epithelial cells are not able to convert N-acetylcysteine to cytoprotective glutathione.
The Journal of Immunology 11/2002; 169(8):4531-41. · 5.79 Impact Factor
