Diacetyl exposure disrupts iron homeostasis in animals and cells.

OBJECTIVE: Several mechanisms have been proposed for the biological effect of diacetyl. We tested the postulate that animal and cell exposures to diacetyl are associated with a disruption in iron homeostasis. MATERIALS AND METHODS: Male, Sprague-Dawley rats were intratracheally-instilled with either distilled water or diacetyl. Seven days after treatment, animals were euthanized and the lungs removed, fixed, and embedded. Sections were cut and stained for iron, collagen, and ferritin. Human epithelial (BEAS-2B) and monocytic (THP-1) cells were exposed in vitro to ferric ammonium citrate (FAC), diacetyl, and both FAC and diacetyl. Cell non-heme iron concentrations and ferritin levels were quantified using inductively coupled plasma optical emission spectroscopy and an immunoassay respectively. RESULTS: After exposure of animals to diacetyl, there were airway polypoid lesions which stained positively for both iron and the intracellular storage protein ferritin. Trichrome stain showed a deposition of collagen immediately adjacent to accumulated metal following diacetyl exposure. In in vitro cell exposures, FAC increased non-heme iron concentration but co-incubations of FAC and diacetyl elevated levels to significantly greater values. Levels of ferritin were increased with exposures of BEAS-2B and THP-1 cells to FAC but were similarly greater after co-exposure with FAC and diacetyl. CONCLUSIONS: Results of animal and cell studies support a disruption of iron homeostasis by diacetyl. It is proposed that, following internalization, diacetyl complexes intracellular sources of iron. The cell recognizes a loss of its requisite iron to diacetyl and imports greater concentrations of the metal.

Ozone Reacts With Carbon Black to Produce a Fulvic Acid-Like Substance and Increase an Inflammatory Effect.

Exposure to ambient ozone has been associated with increased human mortality. Ozone exposure can introduce oxygen-containing functional groups in particulate matter (PM) effecting a greater capacity of the particle for metal complexation and inflammatory effect. We tested the postulate that (1) a fulvic acid-like substance can be produced through a reaction of a carbonaceous particle with high concentrations of ozone and (2) such a fulvic acid-like substance included in the PM can initiate inflammatory effects following exposure of respiratory epithelial (BEAS-2B) cells and an animal model (male Wistar Kyoto rats). Carbon black (CB) was exposed for 72 hours to either filtered air (CB-Air) or approximately 100 ppm ozone (CB-O3). Carbon black exposure to high levels of ozone produced water-soluble, fluorescent organic material. Iron import by BEAS-2B cells at 4 and 24 hours was not induced by incubations with CB-Air but was increased following coexposures of CB-O3 with ferric ammonium citrate. In contrast to CB-Air, exposure of BEAS-2B cells and rats to CB-O3 for 24 hours increased expression of pro-inflammatory cytokines and lung injury, respectively. It is concluded that inflammatory effects of carbonaceous particles on cells can potentially result from (1) an inclusion of a fulvic acid-like substance after reaction with ozone and (2) changes in iron homeostasis following such exposure.

A new cell culture exposure system for studying the toxicity of volatile chemicals at the air-liquid interface.

A cell culture exposure system (CCES) was developed to expose cells established at an air-liquid interface (ALI) to volatile chemicals. We characterized the CCES by exposing indigo dye-impregnated filter inserts inside culture wells to 125 ppb ozone (O3) for 1 h at flow rates of 5 and 25 mL/min/well; the reaction of O3 with an indigo dye produces a fluorescent product. A 5-fold increase in fluorescence at 25 mL/min/well versus 5 mL/min/well was observed, suggesting higher flows were more effective. We then exposed primary human bronchial epithelial cells (HBECs) to 0.3 ppm acrolein for 2 h at 3, 5, and 25 mL/min/well and compared our results against well-established in vitro exposure chambers at the U.S. EPA's Human Studies Facility (HSF Chambers). We measured transcript changes of heme oxygenase-1 (HMOX1) and interleukin-8 (IL-8), as well as lactate dehydrogenase (LDH) release, at 0, 1, and 24 h post-exposure. Comparing responses from HSF Chambers to the CCES, differences were only observed at 1 h post-exposure for HMOX1. Here, the HSF Chamber produced a ∼6-fold increase while the CCES at 3 and 5 mL/min/well produced a ∼1.7-fold increase. Operating the CCES at 25 mL/min/well produced a ∼4.5-fold increase; slightly lower than the HSF Chamber. Our biological results, supported by our comparison against the HSF Chambers, agree with our fluorescence results, suggesting that higher flows through the CCES are more effective at delivering volatile chemicals to cells. This new CCES will be deployed to screen the toxicity of volatile chemicals in EPA's chemical inventories.

Air pollution particles and iron homeostasis.

BACKGROUND: The mechanism underlying biological effects, including pro-inflammatory outcomes, of particles deposited in the lung has not been defined. MAJOR CONCLUSIONS: A disruption in iron homeostasis follows exposure of cells to all particulate matter including air pollution particles. Following endocytosis, functional groups at the surface of retained particle complex iron available in the cell. In response to a reduction in concentrations of requisite iron, a functional deficiency can result intracellularly. Superoxide production by the cell exposed to a particle increases ferrireduction which facilitates import of iron with the objective being the reversal of the metal deficiency. Failure to resolve the functional iron deficiency following cell exposure to particles activates kinases and transcription factors resulting in a release of inflammatory mediators and inflammation. Tissue injury is the end product of this disruption in iron homeostasis initiated by the particle exposure. Elevation of available iron to the cell precludes deficiency of the metal and either diminishes or eliminates biological effects. GENERAL SIGNIFICANCE: Recognition of the pathway for biological effects after particle exposure to involve a functional deficiency of iron suggests novel therapies such as metal supplementation (e.g. inhaled and oral). In addition, the demonstration of a shared mechanism of biological effects allows understanding the common clinical, physiological, and pathological presentation following exposure to disparate particles. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Differential expression of pro-inflammatory and oxidative stress mediators induced by nitrogen dioxide and ozone in primary human bronchial epithelial cells.

CONTEXT: NO2 and O3 are ubiquitous air toxicants capable of inducing lung damage to the respiratory epithelium. Due to their oxidizing capabilities, these pollutants have been proposed to target specific biological pathways, but few publications have compared the pathways activated. OBJECTIVE: This work will test the premise that NO2 and O3 induce toxicity by activating similar cellular pathways. METHODS: Primary human bronchial epithelial cells (HBECs, n = 3 donors) were exposed for 2 h at an air-liquid interface to 3 ppm NO2, 0.75 ppm O3, or filtered air and harvested 1 h post-exposure. To give an overview of pathways that may be influenced by each exposure, gene expression was measured using PCR arrays for toxicity and oxidative stress. Based on the results, genes were selected to quantify whether expression changes were changed in a dose- and time-response manner using NO2 (1, 2, 3, or 5 ppm), O3 (0.25, 0.50, 0.75, or 1.00 ppm), or filtered air and harvesting 0, 1, 4 and 24 h post-exposure. RESULTS: Using the arrays, genes related to oxidative stress were highly induced with NO2 while expression of pro-inflammatory and vascular function genes was found subsequent to O3. NO2 elicited the greatest HMOX1 response, whereas O3 more greatly induced IL-6, IL-8 and PTGS2 expression. Additionally, O3 elicited a greater response 1 h post-exposure and NO2 produced a maximal response after 4 h. CONCLUSION: We have demonstrated that these two oxidant gases stimulate differing mechanistic responses in vitro and these responses occur at dissimilar times.

The biological effect of asbestos exposure is dependent on changes in iron homeostasis.

Functional groups on the surface of fibrous silicates can complex iron. We tested the postulate that (1) asbestos complexes and sequesters host cell iron resulting in a disruption of metal homeostasis and (2) this loss of essential metal results in an oxidative stress and biological effect in respiratory epithelial cells. Exposure of BEAS-2B cells to 50 µg/mL chrysotile resulted in diminished concentrations of mitochondrial iron. Preincubation of these cells with 200 µM ferric ammonium citrate (FAC) prevented significant mitochondrial iron loss following the same exposure. The host response to chrysotile included increased expression of the importer divalent metal transporter-1 (DMT1) supporting a functional iron deficiency. Incubation of BEAS-2B cells with both 200 µM FAC and 50 µg/mL chrysotile was associated with a greater cell accumulation of iron relative to either iron or chrysotile alone reflecting increased import to correct metal deficiency immediately following fiber exposure. Cellular oxidant generation was elevated after chrysotile exposure and this signal was diminished by co-incubation with 200 µM FAC. Similarly, exposure of BEAS-2B cells to 50 µg/mL chrysotile was associated with release of the proinflammatory mediators interleukin (IL)-6 and IL-8, and these changes were diminished by co-incubation with 200 µM FAC. We conclude that (1) the biological response following exposure to chrysotile is associated with complexation and sequestration of cell iron and (2) increasing available iron in the cell diminished the effects of asbestos exposure.

Wood Smoke Particle Sequesters Cell Iron to Impact a Biological Effect.

The biological effect of an inorganic particle (i.e., silica) can be associated with a disruption in cell iron homeostasis. Organic compounds included in particles originating from combustion processes can also complex sources of host cell iron to disrupt metal homeostasis. We tested the postulate that (1) wood smoke particle (WSP) sequesters host cell iron resulting in a disruption of metal homeostasis, (2) this loss of essential metal results in both an oxidative stress and biological effect in respiratory epithelial cells, and (3) humic-like substances (HULIS), a component of WSP, have a capacity to appropriate cell iron and initiate a biological effect. BEAS-2B cells exposed to WSP resulted in diminished concentrations of mitochondrial (57)Fe, whereas preincubation with ferric ammonium citrate (FAC) prevented significant mitochondrial iron loss after such exposure. Cellular oxidant generation was increased after WSP exposure, but this signal was diminished by coincubation with FAC. Similarly, exposure of BEAS-2B cells to 100 µg/mL WSP activated mitogen-activated protein (MAP) kinases, elevated NF-E2-related factor 2/antioxidant responsive element (Nrf2 ARE) expression, and provoked interleukin (IL)-6 and IL-8 release, but all these changes were diminished by coincubation with FAC. The biological response to WSP was reproduced by exposure to 100 µg/mL humic acid, a polyphenol comparable to HULIS included in the WSP that complexes iron. We conclude that (1) the biological response following exposure to WSP is associated with sequestration of cell iron by the particle, (2) increasing available iron in the cell diminished the biological effects after particle exposure, and (3) HULIS included in WSP can sequester the metal initiating the cell response.

Particle retention by respiratory epithelial cells is associated with persistent biological effect.

The biological effect of particles on respiratory epithelial cells involves, in part, the generation of an oxidative stress and a consequent cascade of reactions culminating in inflammatory mediator release. Whether there is either an immediate, transitory activation or a persistent response of the cells to the particles has not been established. We tested the postulate that respiratory epithelial cells exposed to wood smoke particle (WSP) would demonstrate increased oxidative stress and mediator release following re-seeding and propagation of the cells for two generations post-initial exposure. BEAS-2B cells grown to confluence (G0) in 75 cm(2) flasks were treated for 18 h with the WSP at 0, 25, 50 and 100 µg/ml. The flasks were then used to seed another set of flasks as well as 12- and 96-well plates (G1). These flasks were similarly grown to confluence and the process repeated (G2). Cell viability was assayed using trypan blue dye exclusion and was >85%. Dichlorohydrofluorescein fluorescence after exposure of BEAS-2B cells to 50 and 100 µg/ml WSP increased in all three generations when expressed as a ratio to unexposed cells. Similarly, IL-6 and IL-8 release following the initial exposure of cells to 100 µg/ml WSP increased in all three generations when expressed as a ratio to unexposed cells. The persistence of oxidative stress and inflammatory mediator release for two generations of cells beyond the initial exposure supports a postulate of continued cell response to retained particle.

Ozone induces a proinflammatory response in primary human bronchial epithelial cells through mitogen-activated protein kinase activation without nuclear factor-κB activation.

Ground-level ozone (O3) is a ubiquitous environmental air pollutant that is a potent inducer of airway inflammation and has been linked with respiratory and cardiovascular morbidity and mortality. Some studies using transformed or immortalized cells have attributed O3-mediated expression of inflammatory cytokines with activation of the canonical NF-κB pathway. In this study, we sought to characterize the O3-mediated activation of cellular signaling pathways using primary human bronchial epithelial cells obtained from a panel of donors. We demonstrate that the O3-induced expression of proinflammatory cytokines requires the activation of the epidermal growth factor receptor/MEK/ERK and MKK4/p38 mitogen-activated signaling pathways but does not appear to involve activation of canonical NF-κB signaling. In addition to providing a novel mechanistic model for the O3-mediated induction of proinflammatory cytokines, these findings highlight the importance of using primary cells over cell lines in mechanistic studies.

Ex vivo chemical cytometric analysis of protein tyrosine phosphatase activity in single human airway epithelial cells.

We describe a novel method for the measurement of protein tyrosine phosphatase (PTP) activity in single human airway epithelial cells (hAECs) using capillary electrophoresis. This technique involved the microinjection of a fluorescent phosphopeptide that is hydrolyzed specifically by PTPs. Analyses in BEAS-2B immortalized bronchial epithelial cells showed rapid PTP-mediated dephosphorylation of the substrate (2.2 pmol min(-1) mg(-1)) that was blocked by pretreatment of the cells with the PTP inhibitors pervanadate, Zn(2+), and 1,2-naphthoquinone (76%, 69%, and 100% inhibition relative to PTP activity in untreated controls, respectively). These studies were then extended to a more physiologically relevant model system: primary hAECs cultured from bronchial brushings of living human subjects. In primary hAECs, dephosphorylation of the substrate occurred at a rate of 2.2 pmol min(-1) mg(-1) and was also effectively inhibited by preincubation of the cells with the inhibitors pervanadate, Zn(2+), and 1,2-naphthoquinone (91%, 88%, and 87% median PTP inhibition, respectively). Reporter proteolysis in single BEAS-2B cells occurred at a median rate of 43 fmol min(-1) mg(-1) resulting in a mean half-life of 20 min. The reporter displayed a similar median half-life of 28 min in these single primary cells. Finally, single viable epithelial cells (which were assayed for PTP activity immediately after collection by bronchial brushing of a human volunteer) showed dephosphorylation rates ranging from 0.34 to 36 pmol min(-1) mg(-1) (n = 6). These results demonstrate the utility and applicability of this technique for the ex vivo quantification of PTP activity in small, heterogeneous, human cells and tissues.

In vitro determinants of asbestos fiber toxicity: effect on the relative toxicity of Libby amphibole in primary human airway epithelial cells.

BACKGROUND: An abnormally high incidence of lung disease has been observed in the residents of Libby, Montana, which has been attributed to occupational and environmental exposure to fibrous amphiboles originating from a nearby contaminated vermiculite mine. The composition of Libby amphibole (LA) is complex and minimal toxicity data are available. In this study, we conduct a comparative particle toxicity analysis of LA compared with standard reference asbestiform amphibole samples. METHODS: Primary human airway epithelial cells (HAEC) were exposed to two different LA samples as well as standard amphibole reference samples. Analysis of the samples included a complete particle size distribution analysis, calculation of surface area by electron microscopy and by gas adsorption and quantification of surface-conjugated iron and hydroxyl radical production by the fibers. Interleukin-8 mRNA levels were quantified by qRT-PCR to measure relative pro-inflammatory response induced in HAEC in response to amphibole fiber exposure. The relative contribution of key physicochemical determinants on the observed pro-inflammatory response were also evaluated. RESULTS: The RTI amosite reference sample contained the longest fibers and demonstrated the greatest potency at increasing IL-8 transcript levels when evaluated on an equal mass basis. The two LA samples and the UICC amosite reference sample consisted of similar particle numbers per milligram as well as similar particle size distributions and induced comparable levels of IL-8 mRNA. A strong correlation was observed between the elongated particle (aspect ratio ≥3:1) dose metrics of length and external surface area. Expression of the IL-8 data with respect to either of these metrics eliminated the differential response between the RTI amosite sample and the other samples that was observed when HAEC were exposed on an equal mass basis. CONCLUSIONS: On an equal mass basis, LA is as potent as the UICC amosite reference sample at inducing a pro-inflammatory response in HAEC but is less potent than the RTI amosite sample. The results of this study show that the particle length and particle surface area are highly correlated metrics that contribute significantly to the toxicological potential of these amphibole samples with respect to the inflammogenic response induced in airway epithelial cells.

Iron decreases biological effects of ozone exposure.

CONTEXT: Ozone (O3) exposure is associated with a disruption of iron homeostasis and increased availability of this metal which potentially contributes to an oxidative stress and biological effects. OBJECTIVE: We tested the postulate that increased concentrations of iron in cells, an animal model and human subjects would significantly impact the biological effects of O3 exposure. RESULTS: Exposure to 0.4 ppm O3 for 5 h increased mRNA for both Superoxide Dismutase-1 (SOD1) and Cyclooxygenase-2 (COX2) in normal human bronchial epithelial (NHBE) cells. Pre-treatment of NHBE cells with 200 µM ferric ammonium citrate (FAC) for 4 h diminished changes in both SOD1 and COX2 following O3 exposure. mRNA transcript levels and associated protein release of the pro-inflammatory mediators IL-6 and IL-8 were increased by O3 exposure of NHBE cells; changes in these endpoints after O3 exposure were significantly decreased by FAC pre-treatment of the cells. Exposure of CD-1 mice to 2 ppm O3 for 3 h significantly increased lavage indices of inflammation and airflow limitation. Pre-treatment of the animals with pharyngeal aspiration of FAC diminished the same endpoints. Finally, the mean loss of pulmonary function in 19 healthy volunteers exposed to 0.3 ppm O3 for 2 h demonstrated significant correlations with either their pre-exposure plasma ferritin or iron concentrations. DISCUSSION AND CONCLUSION: We conclude that greater availability of iron after O3 exposure does not augment biological effects. On the contrary, increased available iron decreases the biological effects of O3 exposure in cells, animals and humans.

Biological effects of desert dust in respiratory epithelial cells and a murine model.

As a result of the challenge of recent dust storms to public health, we tested the postulate that desert dust collected in the southwestern United States imparts a biological effect in respiratory epithelial cells and an animal model. Two samples of surface sediment were collected from separate dust sources in northeastern Arizona. Analysis of the PM20 fraction demonstrated that the majority of both dust samples were quartz and clay minerals (total SiO2 of 52 and 57%). Using respiratory epithelial and monocytic cell lines, the two desert dusts increased oxidant generation, measured by Amplex Red fluorescence, along with carbon black (a control particle), silica, and NIST 1649 (an ambient air pollution particle). Cell oxidant generation was greatest following exposures to silica and the desert dusts. Similarly, changes in RNA for superoxide dismutase-1, heme oxygenase-1, and cyclooxygenase-2 were also greatest after silica and the desert dusts supporting an oxidative stress after cell exposure. Silica, desert dusts, and the ambient air pollution particle NIST 1649 demonstrated a capacity to activate the p38 and ERK1/2 pathways and release pro-inflammatory mediators. Mice, instilled with the same particles, showed the greatest lavage concentrations of pro-inflammatory mediators, neutrophils, and lung injury following silica and desert dusts. We conclude that, comparable to other particles, desert dusts have a capacity to (1) influence oxidative stress and release of pro-inflammatory mediators in respiratory epithelial cells and (2) provoke an inflammatory injury in the lower respiratory tract of an animal model. The biological effects of desert dusts approximated those of silica.

Sequestration of mitochondrial iron by silica particle initiates a biological effect.

Inhalation of particulate matter has presented a challenge to human health for thousands of years. The underlying mechanism for biological effect following particle exposure is incompletely understood. We tested the postulate that particle sequestration of cell and mitochondrial iron is a pivotal event mediating oxidant generation and biological effect. In vitro exposure of human bronchial epithelial cells to silica reduced intracellular iron, which resulted in increases in both the importer divalent metal transporter 1 expression and metal uptake. Diminished mitochondrial (57)Fe concentrations following silica exposure confirmed particle sequestration of cell iron. Preincubation of cells with excess ferric ammonium citrate increased cell, nuclear, and mitochondrial metal concentrations and prevented significant iron loss from mitochondria following silica exposure. Cell and mitochondrial oxidant generation increased after silica incubation, but pretreatment with iron diminished this generation of reactive oxygen species. Silica exposure activated MAP kinases (ERK and p38) and altered the expression of transcription factors (nF-κB and NF-E2-related factor 2), proinflammatory cytokines (interleukin-8 and -6), and apoptotic proteins. All of these changes in indexes of biological effect were either diminished or inhibited by cell pretreatment with iron. Finally, percentage of neutrophils and total protein concentrations in an animal model instilled with silica were decreased by concurrent exposure to iron. We conclude that an initiating event in the response to particulate matter is a sequestration of cell and mitochondrial iron by endocytosed particle. The resultant oxidative stress and biological response after particle exposure are either diminished or inhibited by increasing the cell iron concentration.

Growth of human bronchial epithelial cells at an air-liquid interface alters the response to particle exposure.

BACKGROUND: We tested the hypothesis that normal human bronchial epithelial (NHBE) cells 1) grown submerged in media and 2) allowed to differentiate at air-liquid interface (ALI) demonstrate disparities in the response to particle exposure. RESULTS: Following exposure of submerged NHBE cells to ambient air pollution particle collected in Chapel Hill, NC, RNA for IL-8, IL-6, heme oxygenase 1 (HOX1) and cyclooxygenase 2 (COX2) increased. The same cells allowed to differentiate over 3, 10, and 21 days at ALI demonstrated no such changes following particle exposure. Similarly, BEAS-2B cells grown submerged in media demonstrated a significant increase in IL-8 and HOX1 RNA after exposure to NIST 1648 particle relative to the same cells exposed after growth at ALI. Subsequently, it was not possible to attribute the observed decreases in the response of NHBE cells to differentiation alone since BEAS-2B cells, which do not differentiate, showed similar changes when grown at ALI. With no exposure to particles, differentiation of NHBE cells at ALI over 3 to 21 days demonstrated significant decrements in baseline levels of RNA for the same proteins (i.e. IL-8, IL-6, HOX1, and COX2). With no exposure to particles, BEAS-2B cells grown at ALI showed comparable changes in RNA for IL-8 and HOX1. After the same particle exposure, NHBE cells grown at ALI on a transwell in 95% N2-5% CO2 and exposed to NIST 1648 particle demonstrated significantly greater changes in IL-8 and HOX1 relative to cells grown in 95% air-5% CO2. CONCLUSIONS: We conclude that growth of NHBE cells at ALI is associated with a diminished biological effect following particle exposure relative to cells submerged in media. This decreased response showed an association with increased oxygen availability.

Liquid Application Dosing Alters the Physiology of Air-Liquid Interface Primary Bronchial Epithelial Cultures and In vitro Testing Relevant Endpoints.

Differentiated Primary human bronchial epithelial cell (dpHBEC) cultures grown under air-liquid interface (ALI) conditions exhibit key features of the human respiratory tract and are thus critical for respiratory research as well as efficacy and toxicity testing of inhaled substances (e.g., consumer products, industrial chemicals, and pharmaceuticals). Many inhalable substances (e.g., particles, aerosols, hydrophobic substances, reactive substances) have physiochemical properties that challenge their evaluation under ALI conditions in vitro. Evaluation of the effects of these methodologically challenging chemicals (MCCs) in vitro is typically conducted by "liquid application," involving the direct application of a solution containing the test substance to the apical, air-exposed surface of dpHBEC-ALI cultures. We report that the application of liquid to the apical surface of a dpHBEC-ALI co-culture model results in significant reprogramming of the dpHBEC transcriptome and biological pathway activity, alternative regulation of cellular signaling pathways, increased secretion of pro-inflammatory cytokines and growth factors, and decreased epithelial barrier integrity. Given the prevalence of liquid application in the delivery of test substances to ALI systems, understanding its effects provides critical infrastructure for the use of in vitro systems in respiratory research as well as in the safety and efficacy testing of inhalable substances.

Mucus increases cell iron uptake to impact the release of pro-inflammatory mediators after particle exposure.

We tested the hypothesis that (1) mucus production can be included in the cell response to iron deficiency; (2) mucus binds iron and increases cell metal uptake; and subsequently (3) mucus impacts the inflammatory response to particle exposure. Using quantitative PCR, RNA for both MUC5B and MUC5AC in normal human bronchial epithelial (NHBE) cells decreased following exposures to ferric ammonium citrate (FAC). Incubation of mucus-containing material collected from the apical surface of NHBE cells grown at air-liquid interface (NHBE-MUC) and a commercially available mucin from porcine stomach (PORC-MUC) with iron demonstrated an in vitro capacity to bind metal. Inclusion of either NHBE-MUC or PORC-MUC in incubations of both BEAS-2B cells and THP1 cells increased iron uptake. Exposure to sugar acids (N-acetyl neuraminic acid, sodium alginate, sodium guluronate, and sodium hyaluronate) similarly increased cell iron uptake. Finally, increased metal transport associated with mucus was associated with a decreased release of interleukin-6 and -8, an anti-inflammatory effect, following silica exposure. We conclude that mucus production can be involved in the response to a functional iron deficiency following particle exposure and mucus can bind metal, increase cell uptake to subsequently diminish or reverse a functional iron deficiency and inflammatory response following particle exposure.

Liquid application dosing alters the physiology of air-liquid interface (ALI) primary human bronchial epithelial cell/lung fibroblast co-cultures and in vitro testing relevant endpoints.

Differentiated primary human bronchial epithelial cell (dpHBEC) cultures grown under air-liquid interface (ALI) conditions exhibit key features of the human respiratory tract and are thus critical for respiratory research as well as efficacy and toxicity testing of inhaled substances (e.g., consumer products, industrial chemicals, and pharmaceuticals). Many inhalable substances (e.g., particles, aerosols, hydrophobic substances, reactive substances) have physiochemical properties that challenge their evaluation under ALI conditions in vitro. Evaluation of the effects of these methodologically challenging chemicals (MCCs) in vitro is typically conducted by "liquid application," involving the direct application of a solution containing the test substance to the apical, air-exposed surface of dpHBEC-ALI cultures. We report that the application of liquid to the apical surface of a dpHBEC-ALI co-culture model results in significant reprogramming of the dpHBEC transcriptome and biological pathway activity, alternative regulation of cellular signaling pathways, increased secretion of pro-inflammatory cytokines and growth factors, and decreased epithelial barrier integrity. Given the prevalence of liquid application in the delivery of test substances to ALI systems, understanding its effects provides critical infrastructure for the use of in vitro systems in respiratory research as well as in the safety and efficacy testing of inhalable substances.

Disruption of iron homeostasis in mesothelial cells after talc pleurodesis.

The mechanism for biological effects after exposure to particles is incompletely understood. One postulate proposed to explain biological effects after exposure to particles involves altered iron homeostasis in the host. The fibro-inflammatory properties of mineral oxide particles are exploited therapeutically with the instillation of massive quantities of talc into the pleural space, to provide sclerosis. We tested the postulates that (1) in vitro exposure to talc induces a disruption in iron homeostasis, oxidative stress, and a biological effect, and (2) talc pleurodesis in humans alters iron homeostasis. In vitro exposures of both mesothelial and airway epithelial cells to 100 µg/ml talc significantly increased iron importation and concentrations of the storage protein ferritin. Using dichlorodihydrofluorescein, exposure to talc was associated with a time-dependent and concentration-dependent generation of oxidants in both cell types. The expression of proinflammatory mediators was also increased after in vitro exposures of mesothelial and airway epithelial cells to talc. Relative to control lung tissue, lung tissue from patients treated with sclerodesis demonstrated an accumulation of iron and increased expression of iron-related proteins, including ferritin, the importer divalent metal transport-1 and the exporter ferroportin-1. Talc was also observed to translocate to the parenchyma, and changes in iron homeostasis were focally distributed to sites of retention. We conclude that exposure to talc disrupts iron homeostasis, is associated with oxidative stress, and results in a biological effect (i.e., a fibro-inflammatory response). Talc pleurodesis can function as a model of the human response to mineral oxide particle exposure, albeit a massive one.

Exposure to wood smoke particles produces inflammation in healthy volunteers.

OBJECTIVES: Human exposure to wood smoke particles (WSP) impacts on human health through changes in indoor air quality, exposures from wild fires, burning of biomass and air pollution. This investigation tested the postulate that healthy volunteers exposed to WSP would demonstrate evidence of both pulmonary and systemic inflammation. METHODS: Ten volunteers were exposed to filtered air and, 3 weeks or more later, WSP. Each exposure included alternating 15 min of exercise and 15 min of rest for a total duration of 2 h. Wood smoke was generated by heating an oak log on an electric element and then delivered to the exposure chamber. Endpoints measured in the volunteers included symptoms, pulmonary function tests, measures of heart rate variability and repolarisation, blood indices and analysis of cells and fluid obtained during bronchoalveolar lavage. RESULTS: Mean particle mass for the 10 exposures to air and WSP was measured using the mass of particles collected on filters and found to be below the detectable limit and 485±84 µg/m(3), respectively (mean±SD). There was no change in either symptom prevalence or pulmonary function with exposure to WSP. At 20 h after wood smoke exposure, blood tests demonstrated an increased percentage of neutrophils, and bronchial and bronchoalveolar lavage revealed a neutrophilic influx. CONCLUSIONS: We conclude that exposure of healthy volunteers to WSP may be associated with evidence of both systemic and pulmonary inflammation.