The effects of fine particulate matter (SRM 2786) on three different 3D lung models exposed at the air-liquid interface - A comparative study

3D cell culture models exposed at the air-liquid interface (ALI) represent a potential alternative to animal experiments for hazard and risk assessment of inhaled compounds. This study compares cocultures composed of either Calu-3, A549 or HBEC3-KT lung epithelial cells, cultured together with THP-1-derived macrophages and EA.hy926 endothelial cells, in terms of barrier capacity and responses to a standard reference sample of fine particulate matter (SRM 2786). High-content imaging analysis revealed a similar cellular composition between the different cell models. The 3D cell cultures with Calu-3 cells showed the greatest barrier capacity, as measured by transepithelial electrical resistance and permeability to Na-fluorescein. Mucus production was detected in 3D cell cultures based on Calu-3 and A549 cells. Exposure to SRM 2786 at ALI increased cytokine release and expression of genes associated with inflammation and xenobiotic metabolism. Moreover, the presence of THP-1-derived macrophages was central to the cytokine responses in all cell models. While the different 3D cell culture models produced qualitatively similar responses, more pronounced pro-inflammatory responses were observed in the basolateral compartment of the A549 and HBEC3-KT models compared to the Calu-3 model, likely due to their reduced barrier capacity and lower retention of secreted mediators in the apical compartment.

Role of different mechanisms in pro-inflammatory responses triggered by traffic-derived particulate matter in human bronchiolar epithelial cells

BACKGROUND

Traffic-derived particles are important contributors to the adverse health effects of ambient particulate matter (PM). In Nordic countries, mineral particles from road pavement and diesel exhaust particles (DEP) are important constituents of traffic-derived PM. In the present study we compared the pro-inflammatory responses of mineral particles and DEP to PM from two road tunnels, and examined the mechanisms involved.

METHODS

The pro-inflammatory potential of 100 µg/mL coarse (PM10-2.5), fine (PM2.5-0.18) and ultrafine PM (PM0.18) sampled in two road tunnels paved with different stone materials was assessed in human bronchial epithelial cells (HBEC3-KT), and compared to DEP and particles derived from the respective stone materials. Release of pro-inflammatory cytokines (CXCL8, IL-1α, IL-1β) was measured by ELISA, while the expression of genes related to inflammation (COX2, CXCL8, IL-1α, IL-1β, TNF-α), redox responses (HO-1) and metabolism (CYP1A1, CYP1B1, PAI-2) was determined by qPCR. The roles of the aryl hydrocarbon receptor (AhR) and reactive oxygen species (ROS) were examined by treatment with the AhR-inhibitor CH223191 and the anti-oxidant N-acetyl cysteine (NAC).

RESULTS

Road tunnel PM caused time-dependent increases in expression of CXCL8, COX2, IL-1α, IL-1β, TNF-α, COX2, PAI-2, CYP1A1, CYP1B1 and HO-1, with fine PM as more potent than coarse PM at early time-points. The stone particle samples and DEP induced lower cytokine release than all size-fractionated PM samples for one tunnel, and versus fine PM for the other tunnel. CH223191 partially reduced release and expression of IL-1α and CXCL8, and expression of COX2, for fine and coarse PM, depending on tunnel, response and time-point. Whereas expression of CYP1A1 was markedly reduced by CH223191, HO-1 expression was not affected. NAC reduced the release and expression of IL-1α and CXCL8, and COX2 expression, but augmented expression of CYP1A1 and HO-1.

CONCLUSIONS

The results indicate that the pro-inflammatory responses of road tunnel PM in HBEC3-KT cells are not attributed to the mineral particles or DEP alone. The pro-inflammatory responses seem to involve AhR-dependent mechanisms, suggesting a role for organic constituents. ROS-mediated mechanisms were also involved, probably through AhR-independent pathways. DEP may be a contributor to the AhR-dependent responses, although other sources may be of importance.

Characterization of elements, PAHs, AhR-activity and pro-inflammatory responses of road tunnel-derived particulate matter in human hepatocyte-like and bronchial epithelial cells

The aims were to characterize the content of elements and polycyclic aromatic hydrocarbons (PAHs) in size-separated particulate matter (PM) sampled in a road tunnel, estimate the contribution of PAHs to the toxic potential, and measure the pro-inflammatory potential of PM samples and extracts with increasing polarity. Several elements/metals previously associated with cytokine responses were found. Based on PAHs levels and published PAHs potency, the calculated mutagenic and carcinogenic activities of size-separated samples were somewhat lower for coarse than fine and ultrafine PM. The AhR-activity of the corresponding PM extracts measured in an AhR-luciferase reporter model (human hepatocytes) were more similar. The highest AhR-activity was found in the neutral (parent and alkylated PAHs) and polar (oxy-PAHs) fractions, while the semi-polar fractions (mono-nitrated-PAHs) had only weak activity. The neutral and polar aromatic fractions from coarse and fine PM were also found to induce higher pro-inflammatory responses and CYP1A1 expression in human bronchial epithelial cells (HBEC3-KT) than the semi-polar fractions. Fine PM induced higher pro-inflammatory responses than coarse PM. AhR-inhibition reduced cytokine responses induced by parent PM and extracts of both size fractions. Contributors to the toxic potentials include PAHs and oxy-PAHs, but substantial contributions from other organic compounds and/or metals are likely.

The importance of mineralogical composition for the cytotoxic and pro-inflammatory effects of mineral dust

Background

Respirable mineral particles represent a potential health hazard in occupational settings and ambient air. Previous studies show that mineral particles may induce cytotoxicity and inflammatory reactions in vitro and in vivo and that the potency varies between samples of different composition. However, the reason for these differences is largely unknown and the impact of mineralogical composition on the biological effects of mineral dust remains to be determined.

Methods

We have assessed the cytotoxic and pro-inflammatory effects of ten mineral particle samples of different composition in human bronchial epithelial cells (HBEC3-KT) and THP-1-derived macrophages, as well as their membranolytic properties in erythrocytes. Moreover, the results were compiled with the results of recently published experiments on the effects of stone particle exposure and analysed using linear regression models to elucidate which mineral components contribute most to the toxicity of mineral dust.

Results

While all mineral particle samples were more cytotoxic to HBEC3-KT cells than THP-1 macrophages, biotite and quartz were among the most cytotoxic in both cell models. In HBEC3-KT cells, biotite and quartz also appeared to be the most potent inducers of pro-inflammatory cytokines, while the quartz, Ca-feldspar, Na-feldspar and biotite samples were the most potent in THP-1 macrophages. All particle samples except quartz induced low levels of membranolysis. The regression analyses revealed associations between particle bioactivity and the content of quartz, muscovite, plagioclase, biotite, anorthite, albite, microcline, calcite, chlorite, orthopyroxene, actinolite and epidote, depending on the cell model and endpoint. However, muscovite was the only mineral consistently associated with increased cytotoxicity and cytokine release in both cell models.

Conclusions

The present study provides further evidence that mineral particles may induce cytotoxicity and inflammation in cells of the human airways and that particle samples of different mineralogical composition differ in potency. The results show that quartz, while being among the most potent samples, does not fully predict the toxicity of mineral dust, highlighting the importance of other particle constituents. Moreover, the results indicate that the phyllosilicates muscovite and biotite may be more potent than other minerals assessed in the study, suggesting that this group of sheet-like minerals may warrant further attention.

Road tunnel-derived coarse, fine and ultrafine particulate matter: physical and chemical characterization and pro-inflammatory responses in human bronchial epithelial cells

BACKGROUND

Traffic particulate matter (PM) comprises a mixture of particles from fuel combustion and wear of road pavement, tires and brakes. In countries with low winter temperatures the relative contribution of mineral-rich PM from road abrasion may be especially high due to use of studded tires during winter season. The aim of the present study was to sample and characterize size-fractioned PM from two road tunnels paved with different stone materials in the asphalt, and to compare the pro-inflammatory potential of these fractions in human bronchial epithelial cells (HBEC3-KT) in relation to physicochemical characteristics.

METHODS

The road tunnel PM was collected with a vacuum pump and a high-volume cascade impactor sampler. PM was sampled during winter, both during humid and dry road surface conditions, and before and after cleaning the tunnels. Samples were analysed for hydrodynamic size distribution, content of elemental carbon (EC), organic carbon (OC) and endotoxin, and the capacity for acellular generation of reactive oxygen species. Cytotoxicity and pro-inflammatory responses were assessed in HBEC3-KT cells after exposure to coarse (2.5-10 μm), fine (0.18-2.5 μm) and ultrafine PM (≤ 0.18 μm), as well as particles from the respective stone materials used in the pavement.

RESULTS

The pro-inflammatory potency of the PM samples varied between road tunnels and size fractions, but showed more marked responses than for the stone materials used in asphalt of the respective tunnels. In particular, fine samples showed significant increases as low as 25 µg/mL (2.6 µg/cm²) and were more potent than coarse samples, while ultrafine samples showed more variable responses between tunnels, sampling conditions and endpoints. The most marked responses were observed for fine PM sampled during humid road surface conditions. Linear correlation analysis showed that particle-induced cytokine responses were correlated to OC levels, while no correlations were observed for other PM characteristics.

CONCLUSIONS

The pro-inflammatory potential of fine road tunnel PM sampled during winter season was high compared to coarse PM. The differences between the PM-induced cytokine responses were not related to stone materials in the asphalt. However, the ratio of OC to total PM mass was associated with the pro-inflammatory potential.

Short-term exposure to stone minerals used in asphalt affect lung function and promote pulmonary inflammation among healthy adults

Objective

Stone minerals are a partially ignored environmental challenge but a significant contributor to urban air pollution. We examined if short-term exposure to two stone minerals – quartz diorite and rhomb porphyry – commonly used in asphalt pavement would affect lung function, promote pulmonary inflammation, and affect bronchial reactivity differently.

Methods

Our randomized crossover study included 24 healthy, non-smoking young adults exposed to the stone minerals quartz diorite, rhomb porphyry, and control dust (lactose). Exposure occurred in an exposure chamber, in three separate 4-hour exposure sessions. Fractional exhaled nitric oxide (FeNO) and lung function were monitored before exposure, then immediately following exposure, and 4 and 24 hours after exposure. In addition, methacholine was administered 4 hours following exposure, and exhaled breath condensate (EBC) was collected before exposure, then immediately and 4 hours after exposure. EBC was analyzed for pH, thiobarbituric acid reactive substances (TBARS), intercellular adhesion molecule 1 (ICAM-1), interleukin-6 (IL-6), IL-10, P-Selectin, surfactant protein D (SP-D), and tumor necrosis factor-α (TNF-α).

Results

Our results showed significantly elevated concentrations of FeNO after exposure to quartz diorite compared to rhomb porphyry, suggesting that quartz diorite is more likely to trigger pulmonary inflammation after short-term exposure. Moreover, short-term exposure to rhomb porphyry was associated with a modest but statistically significant decline in forced vital capacity (FVC) compared to quartz diorite.

Conclusion

These results emphasize that using stone material in asphalt road construction should be reconsidered as it may affect lung inflammation and lung function in exposed subjects.

The pro-inflammatory effects of combined exposure to diesel exhaust particles and mineral particles in human bronchial epithelial cells

Background

People are exposed to ambient particulate matter (PM) from multiple sources simultaneously in both environmental and occupational settings. However, combinatory effects of particles from different sources have received little attention in experimental studies. In the present study, the pro-inflammatory effects of combined exposure to diesel exhaust particles (DEP) and mineral particles, two common PM constituents, were explored in human lung epithelial cells.

Methods

Particle-induced secretion of pro-inflammatory cytokines (CXCL8 and IL-1β) and changes in expression of genes related to inflammation (CXCL8, IL-1α, IL-1β and COX-2), redox responses (HO-1) and xenobiotic metabolism (CYP1A1 and CYP1B1) were assessed in human bronchial epithelial cells (HBEC3-KT) after combined exposure to different samples of DEP and mineral particles. Combined exposure was also conducted using lipophilic organic extracts of DEP to assess the contribution of soluble organic chemicals. Moreover, the role of the aryl hydrocarbon receptor (AhR) pathway was assessed using an AhR-specific inhibitor (CH223191).

Results

Combined exposure to DEP and mineral particles induced increases in pro-inflammatory cytokines and expression of genes related to inflammation and redox responses in HBEC3-KT cells that were greater than either particle sample alone. Moreover, robust increases in the expression of CYP1A1 and CYP1B1 were observed. The effects were most pronounced after combined exposure to α-quartz and DEP from an older fossil diesel, but enhanced responses were also observed using DEP generated from a modern biodiesel blend and several stone particle samples of mixed mineral composition. Moreover, the effect of combined exposure on cytokine secretion could also be induced by lipophilic organic extracts of DEP. Pre-incubation with an AhR-specific inhibitor reduced the particle-induced cytokine responses, suggesting that the effects were at least partially dependent on AhR.

Conclusions

Exposure to DEP and mineral particles in combination induces enhanced pro-inflammatory responses in human bronchial epithelial cells compared with exposure to the individual particle samples. The effects are partly mediated through an AhR-dependent pathway and lipophilic organic chemicals in DEP appear to play a central role. These possible combinatory effects between different sources and components of PM warrant further attention and should also be considered when assessing measures to reduce PM-induced health effects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00455-0.

Role of scavenger receptors in silica nanoparticle-induced cytokine responses in bronchial epithelial cells

A major challenge in nanoparticle (NP) research is to elucidate how NPs activate initial targets in cells, leading to cytotoxicity and inflammation. We have previously shown that silica (Si)NPs induce pro-inflammatory responses in bronchial epithelial cells (BEAS-2B) via mechanisms involving transforming growth factor (TGF)-α release, and activation of MAP-kinase p38 and JNK besides NF-κB (p65). In the present study, the roles of scavenger receptors (SRs) in SiNP-induced cytokine responses in BEAS-2B cells were examined by siRNA silencing. Cells exposed to Si10 and Si50 (nominal sizes 10 and 50 nm) showed marked interleukin (IL)-6, CXCL8, IL-1α, IL-1β responses. Transient knockdown of SR-B1, LOX-1 and CXCL16 reduced the Si10- and Si50-induced cytokine responses, to a different magnitude dependent on the particle size, SR and cytokine. Si10-induced TGF-α responses were also markedly reduced by knockdown of SR-B1 and CXCL16. Furthermore, the role of SR-B1 in Si10-induced phosphorylations of p65 and MAP-kinases p38 and JNK were examined, and no significant reductions were observed upon knockdown of SR-B1. In conclusion, LOX-1 and CXCL16 and especially SR-B1 seem to have important roles in mediating cytokine responses and TGF-α release due to SiNP exposure in BEAS-2B cells, without a down-stream role of MAP-kinase and NF-κB.

Respirable stone particles differ in their ability to induce cytotoxicity and pro-inflammatory responses in cell models of the human airways

Background

Respirable stone- and mineral particles may be a major constituent in occupational and ambient air pollution and represent a possible health hazard. However, with exception of quartz and asbestos, little is known about the toxic properties of mineral particles. In the present study, the pro-inflammatory and cytotoxic responses to six stone particle samples of different composition and with diameter below 10 μm were assessed in human bronchial epithelial cells (HBEC3-KT), THP-1 macrophages and a HBEC3-KT/THP-1 co-culture. Moreover, particle-induced lysis of human erythrocytes was assessed to determine the ability of the particles to lyse biological membranes. Finally, the role of the NLRP3 inflammasome was assessed using a NLRP3-specific inhibitor and detection of ASC oligomers and cleaved caspase-1 and IL-1β. A reference sample of pure α-quartz was included for comparison.

Results

Several stone particle samples induced a concentration-dependent increase in cytotoxicity and secretion of the pro-inflammatory cytokines CXCL8, IL-1α, IL-1β and TNFα. In HBEC3-KT, quartzite and anorthosite were the most cytotoxic stone particle samples and induced the highest levels of cytokines. Quartzite and anorthosite were also the most cytotoxic samples in THP-1 macrophages, while anorthosite and hornfels induced the highest cytokine responses. In comparison, few significant differences between particle samples were detected in the co-culture. Adjusting responses for differences in surface area concentrations did not fully account for the differences between particle samples. Moreover, the stone particles had low hemolytic potential, indicating that the effects were not driven by membrane lysis. Pre-incubation with a NLRP3-specific inhibitor reduced stone particle-induced cytokine responses in THP-1 macrophages, but not in HBEC3-KT cells, suggesting that the effects are mediated through different mechanisms in epithelial cells and macrophages. Particle exposure also induced an increase in ASC oligomers and cleaved caspase-1 and IL-1β in THP-1 macrophages, confirming the involvement of the NLRP3 inflammasome.

Conclusions

The present study indicates that stone particles induce cytotoxicity and pro-inflammatory responses in human bronchial epithelial cells and macrophages, acting through NLRP3-independent and -dependent mechanisms, respectively. Moreover, some particle samples induced cytotoxicity and cytokine release to a similar or greater extent than α-quartz. Thus, these minerals warrant further attention in future research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00409-y.

Pro-inflammatory effects of crystalline- and nano-sized non-crystalline silica particles in a 3D alveolar model

BACKGROUND

Silica nanoparticles (SiNPs) are among the most widely manufactured and used nanoparticles. Concerns about potential health effects of SiNPs have therefore risen. Using a 3D tri-culture model of the alveolar lung barrier we examined effects of exposure to SiNPs (Si10) and crystalline silica (quartz; Min-U-Sil) in the apical compartment consisting of human alveolar epithelial A549 cells and THP-1-derived macrophages, as well as in the basolateral compartment with Ea.hy926 endothelial cells. Inflammation-related responses were measured by ELISA and gene expression.

RESULTS

Exposure to both Si10 and Min-U-Sil induced gene expression and release of CXCL8, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interleukin-1α (IL-1α) and interleukin-1β (IL-1β) in a concentration-dependent manner. Cytokine/chemokine expression and protein levels were highest in the apical compartment. Si10 and Min-U-Sil also induced expression of adhesion molecules ICAM-1 and E-selectin in the apical compartment. In the basolateral endothelial compartment we observed marked, but postponed effects on expression of all these genes, but only at the highest particle concentrations. Geneexpressions of heme oxygenase-1 (HO-1) and the metalloproteases (MMP-1 and MMP-9) were less affected. The IL-1 receptor antagonist (IL-1RA), markedly reduced effects of Si10 and Min-U-Sil exposures on gene expression of cytokines and adhesion molecules, as well as cytokine-release in both compartments.

CONCLUSIONS

Si10 and Min-U-Sil induced gene expression and release of pro-inflammatory cytokines/adhesion molecules at both the epithelial/macrophage and endothelial side of a 3D tri-culture. Responses in the basolateral endothelial cells were only induced at high concentrations, and seemed to be mediated by IL-1α/β released from the apical epithelial cells and macrophages.

Synthetic hydrosilicate nanotubes induce low pro-inflammatory and cytotoxic responses compared to natural chrysotile in lung cell cultures

Asbestos (Mg-hydrosilicate; chrysotile) is known to cause pleural diseases, pulmonary fibrosis and lung cancers, via mechanisms strongly depending on diameter-length ratio and possibly metal content. A critical question is whether synthetic hydrosilicate nanotubes (NTs) of short length possess little toxic potential compared to chrysotile. Five Mg- and two NiNTs of different lengths were assessed for cytotoxicity and pro-inflammatory responses in THP-1 macrophages and human bronchial epithelial lung cells (HBEC3-KT), in comparison with chrysotile. NT lengths/diameters were characterized by TEM, surface areas by BET- and BJH analysis, and chemical composition by XRD. The different Mg- and NiNTs induced little cytotoxicity in both cell models, in contrast to chrysotile that induced marked cytotoxicity. The two longest synthetic MgNTs, with median lengths of 3 and 5 µm, induced increased levels of pro-inflammatory cytokines in THP-1 macrophages, but much less than chrysotile (median length 15 µm) and silica nanoparticles (Si10). The shortest NTs did not induce any increase in cytokines. In HBEC3-KT cells, all synthetic NTs induced no or only small changes in cytokine responses, in contrast to chrysotile and Si10. The synthetic NTs induced lower TGF-β responses than chrysotile in both cell models. In conclusion, the pro-inflammatory responses were associated with the length of synthetic hydrosilicate NTs in THP-1 macrophages, but not in HBEC3-KT cells. Notably, the shortest NTs showed no or little pro-inflammatory activity or cytotoxicity in both cell models. Such a safety by design approach is important for development of new materials being candidates for various new products.

Potential role of polycyclic aromatic hydrocarbons as mediators of cardiovascular effects from combustion particles

Air pollution is the most important environmental risk factor for disease and premature death, and exposure to combustion particles from vehicles is a major contributor. Human epidemiological studies combined with experimental studies strongly suggest that exposure to combustion particles may enhance the risk of cardiovascular disease (CVD), including atherosclerosis, hypertension, thrombosis and myocardial infarction.In this review we hypothesize that adhered organic chemicals like polycyclic aromatic hydrocarbons (PAHs), contribute to development or exacerbation of CVD from combustion particles exposure. We summarize present knowledge from existing human epidemiological and clinical studies as well as experimental studies in animals and relevant in vitro studies. The available evidence suggests that organic compounds attached to these particles are significant triggers of CVD. Furthermore, their effects seem to be mediated at least in part by the aryl hydrocarbon receptor (AhR). The mechanisms include AhR-induced changes in gene expression as well as formation of reactive oxygen species (ROS) and/or reactive electrophilic metabolites. This is in accordance with a role of PAHs, as they seem to be the major chemical group on combustion particles, which bind AhR and/or is metabolically activated by CYP-enzymes. In some experimental models however, it seems as PAHs may induce an inflammatory atherosclerotic plaque phenotype irrespective of DNA- and/or AhR-ligand binding properties. Thus, various components and several signalling mechanisms/pathways are likely involved in CVD induced by combustion particles.We still need to expand our knowledge about the role of PAHs in CVD and in particular the relative importance of the different PAH species. This warrants further studies as enhanced knowledge on this issue may amend risk assessment of CVD caused by combustion particles and selection of efficient measures to reduce the health effects of particular matters (PM).

Lipophilic components of diesel exhaust particles induce pro-inflammatory responses in human endothelial cells through AhR dependent pathway(s)

Background

Exposure to traffic-derived particulate matter (PM), such as diesel exhaust particles (DEP), is a leading environmental cause of cardiovascular disease (CVD), and may contribute to endothelial dysfunction and development of atherosclerosis. It is still debated how DEP and other inhaled PM can contribute to CVD. However, organic chemicals (OC) adhered to the particle surface, are considered central to many of the biological effects. In the present study, we have explored the ability of OC from DEP to reach the endothelium and trigger pro-inflammatory reactions, a central step on the path to atherosclerosis.

Results

Exposure-relevant concentrations of DEP (0.12 μg/cm²) applied on the epithelial side of an alveolar 3D tri-culture, rapidly induced pro-inflammatory and aryl hydrocarbon receptor (AhR)-regulated genes in the basolateral endothelial cells. These effects seem to be due to soluble lipophilic constituents rather than particle translocation. Extractable organic material of DEP (DEP-EOM) was next fractionated with increasing polarity, chemically characterized, and examined for direct effects on pro-inflammatory and AhR-regulated genes in human microvascular endothelial (HMEC-1) cells and primary human endothelial cells (PHEC) from four healthy donors. Exposure-relevant concentrations of lipophilic DEP-EOM (0.15 μg/cm²) induced low to moderate increases in IL-1α, IL-1β, COX2 and MMP-1 gene expression, and the MMP-1 secretion was increased. By contrast, the more polar EOM had negligible effects, even at higher concentrations. Use of pharmacological inhibitors indicated that AhR and protease-activated receptor-2 (PAR-2) were central in regulation of EOM-induced gene expression. Some effects also seemed to be attributed to redox-responses, at least at the highest exposure concentrations tested. Although the most lipophilic EOM, that contained the majority of PAHs and aliphatics, had the clearest low-concentration effects, there was no straight-forward link between chemical composition and biological effects.

Conclusion

Lipophilic and semi-lipophilic chemicals seemed to detach from DEP, translocate through alveolar epithelial cells and trigger pro-inflammatory reactions in endothelial cells at exposure-relevant concentrations. These effects appeared to be triggered by AhR agonists, and involve PAR-2 signaling.

Electronic supplementary material

The online version of this article (10.1186/s12989-018-0257-1) contains supplementary material, which is available to authorized users.

Early life exposure to air pollution particulate matter (PM) as risk factor for attention deficit/hyperactivity disorder (ADHD): Need for novel strategies for mechanisms and causalities

Epidemiological studies have demonstrated that air pollution particulate matter (PM) and adsorbed toxicants (organic compounds and trace metals) may affect child development already in utero. Recent studies have also indicated that PM may be a risk factor for neurodevelopmental disorders (NDDs). A pattern of increasing prevalence of attention deficit/hyperactivity disorder (ADHD) has been suggested to partly be linked to environmental pollutants exposure, including PM. Epidemiological studies suggest associations between pre- or postnatal exposure to air pollution components and ADHD symptoms. However, many studies are cross-sectional without possibility to reveal causality. Cohort studies are often small with poor exposure characterization, and confounded by traffic noise and socioeconomic factors, possibly overestimating the study associations. Furthermore, the mechanistic knowledge how exposure to PM during early brain development may contribute to increased risk of ADHD symptoms or cognitive deficits is limited. The closure of this knowledge gap requires the combined use of well-designed longitudinal cohort studies, supported by mechanistic in vitro studies. As ADHD has profound consequences for the children affected and their families, the identification of preventable risk factors such as air pollution exposure should be of high priority.

Silica Nanoparticle-induced Cytokine Responses in BEAS-2B and HBEC3-KT Cells: Significance of Particle Size and Signalling Pathways in Different Lung Cell Cultures

We have previously reported that silica nanoparticles (SiNPs) of nominal size 50 nm (Si50) induce the pro-inflammatory cytokines CXCL8 and IL-6 in BEAS-2B cells, via mechanisms involving MAPK p38, TACE-mediated TGF-α release and the NF-κB pathway. In this study, we examined whether these findings are cell specific or might be extended to another epithelial lung cell model, HBEC3-KT, and also to SiNPs of a smaller size (nominal size of 10 nm; Si10). The TEM average size of Si10 and Si50 was 10.9 and 34.7 nm, respectively. The surface area (BET) of Si10 was three times higher than for Si50 per mass unit. With respect to hydrodynamic size (DLS), Si10 in exposure medium showed a higher z-average for the main peak than Si50, indicating more excessive agglomeration. Si10 strongly induced CXCL8 and IL-6, as assessed by ELISA and RT-PCR, and was markedly more potent than Si50, even when adjusted to equal surface area. Furthermore, Si10 was far more cytotoxic, measured as lactate dehydrogenase (LDH) release, than Si50 in both epithelial cell cultures. With respect to signalling pathways, Western analysis and experiments with and without inhibition of MAPK, TACE and NF-κB (synthetic inhibitors) revealed that p38-phosphorylation, TACE-mediated TGF-α release and NF-κB activation seem to be important triggering mechanisms for both Si50 and Si10 in the two different lung epithelial cell cultures. In conclusion, the identified signalling pathways are suggested to be important in inducing cytokine responses in different epithelial cell types and also for various sizes of silica nanoparticles.

Triggering Mechanisms and Inflammatory Effects of Combustion Exhaust Particles with Implication for Carcinogenesis

A number of biological responses may contribute to the carcinogenic effects of combustion-derived particulate matter (CPM). Here, we focus on mechanisms that trigger CPM-induced pro-inflammatory responses. Inflammation has both genotoxic and non-genotoxic implications and is considered to play a central role in development of various health outcome associated with CPM exposure, including cancer. Chronic, low-grade inflammation may cause DNA damage through a persistent increased level of reactive oxygen species (ROS) produced and released by activated immune cells. Moreover, a number of pro-inflammatory cytokines and chemokines display mitogenic, motogenic, morphogenic and/or angiogenic properties and may therefore contribute to tumour growth and metastasis. The key triggering events involved in activation of pro-inflammatory responses by CPM and soluble CPM components can be categorized into (i) formation of ROS and oxidative stress, (ii) interaction with the lipid layer of cellular membranes, (iii) activation of receptors, ion channels and transporters on the cell surface and (iv) interactions with intracellular molecular targets including receptors such as the aryl hydrocarbon receptor (AhR). In particular, we will elucidate the effects of diesel exhaust particles (DEP) using human lung epithelial cells as a model system.

Air pollution-related metals induce differential cytokine responses in bronchial epithelial cells

Different transition metals have been shown to induce inflammatory responses in lung. We have compared eight different metal ions with regard to cytokine responses, cytotoxicity and signalling mechanisms in a human lung epithelial cell model (BEAS-2B). Among the metal ions tested, there were large differences with respect to pro-inflammatory potential. Exposure to Cd(2+), Zn(2+) and As(3+) induced CXCL8 and IL-6 release at concentrations below 100μM, and Mn(2+) and Ni(2+) at concentrations above 200μM. In contrast, VO4(3-), Cu(2+) and Fe(2+) did not induce any significant increase of these cytokines. An expression array of 20 inflammatory relevant genes also showed a marked up-regulation of CXCL10, IL-10, IL-13 and CSF2 by one or more of the metal ions. The most potent metals, Cd(2+), Zn(2+) and As(3+) induced highest levels of oxidative activity, and ROS appeared to be central in their CXCL8 and IL-6 responses. Activation of the MAPK p38 seemed to be a critical mediator. However, the NF-κB pathway appeared predominately to be involved only in Zn(2+)- and As(3+)-induced CXCL8 and IL-6 responses. Thus, the most potent metals Cd(2+), Zn(2+) and As(3+) seemed to induce a similar pattern for the cytokine responses, and with some exceptions, via similar signalling mechanisms.

Particulate matter properties and health effects: consistency of epidemiological and toxicological studies

Identifying the ambient particulate matter (PM) fractions or constituents, critically involved in eliciting adverse health effects, is crucial to the implementation of more cost-efficient abatement strategies to improve air quality. This review focuses on the importance of different particle properties for PM-induced effects, and whether there is consistency in the results from epidemiological and experimental studies. An evident problem for such comparisons is that epidemiological and experimental data on the effects of specific components of ambient PM are limited. Despite this, some conclusions can be drawn. With respect to the importance of the PM size-fractions, experimental and epidemiological studies are somewhat conflicting, but there seems to be a certain consistency in that the coarse fraction (PM10-2.5) has an effect that should not be neglected. Better exposure characterization may improve the consistency between the results from experimental and epidemiological studies, in particular for ultrafine particles. Experimental data indicate that surface area is an important metric, but composition may play an even greater role in eliciting effects. The consistency between epidemiological and experimental findings for specific PM-components appears most convincing for metals, which seem to be important for the development of both pulmonary and cardiovascular disease. Metals may also be involved in PM-induced allergic sensitization, but the epidemiological evidence for this is scarce. Soluble organic compounds appear to be implicated in PM-induced allergy and cancer, but the data from epidemiological studies are insufficient for any conclusions. The present review suggests that there may be a need for improvements in research designs. In particular, there is a need for better exposure assessments in epidemiological investigations, whereas experimental data would benefit from an improved comparability of studies. Combined experimental and epidemiological investigations may also help answer some of the unresolved issues.

Cytokine responses induced by diesel exhaust particles are suppressed by PAR-2 silencing and antioxidant treatment, and driven by polar and non-polar soluble constituents

Adsorbed soluble organics seem to be the main drivers of inflammatory responses induced by diesel exhaust particles (DEP). The specific compounds contributing to this process and the cellular mechanisms behind DEP-induced inflammation are not well known. We have assessed pro-inflammatory effects of DEP and various soluble DEP fractions, in human bronchial epithelial cells (BEAS-2B). DEP increased the expression of interleukin (IL)-6 and CXCL8. Silencing of the aryl hydrocarbon receptor (AhR) by siRNA or pretreatment with AhR-antagonists did not attenuate DEP-induced IL-6 and CXCL8 responses. However, the halogenated aromatic hydrocarbon (HAH)-selective AhR antagonist CH223191 caused a considerable reduction in DEP-induced CYP1A1 expression indicating that this response may be due to dioxin or dioxin-like constituents in DEP. Knock-down of protease activated receptor (PAR)-2 attenuated IL-6 responses without affecting CXCL8. Antioxidants did not affect IL-6 expression after 4h DEP-exposure and only partly reduced CXCL8 expression. However, after 24h exposure antioxidant treatment partly suppressed IL-6 protein release and completely blocked CXCL8 release. Furthermore, a heptane-soluble (non-polar) extract of DEP induced both IL-6 and CXCL8 release, whereas a PBS-soluble (highly polar) extract induced only IL-6. Thus, pro-inflammatory responses in DEP-exposed epithelial cells appear to be the result of both reactive oxygen species and receptor signaling, mediated through combinatorial effects between both non-polar and polar constituents adhered to the particle surface.

Activation of Proinflammatory Responses in Cells of the Airway Mucosa by Particulate Matter: Oxidant- and Non-Oxidant-Mediated Triggering Mechanisms

Inflammation is considered to play a central role in a diverse range of disease outcomes associated with exposure to various types of inhalable particulates. The initial mechanisms through which particles trigger cellular responses leading to activation of inflammatory responses are crucial to clarify in order to understand what physico-chemical characteristics govern the inflammogenic activity of particulate matter and why some particles are more harmful than others. Recent research suggests that molecular triggering mechanisms involved in activation of proinflammatory genes and onset of inflammatory reactions by particles or soluble particle components can be categorized into direct formation of reactive oxygen species (ROS) with subsequent oxidative stress, interaction with the lipid layer of cellular membranes, activation of cell surface receptors, and direct interactions with intracellular molecular targets. The present review focuses on the immediate effects and responses in cells exposed to particles and central down-stream signaling mechanisms involved in regulation of proinflammatory genes, with special emphasis on the role of oxidant and non-oxidant triggering mechanisms. Importantly, ROS act as a central second-messenger in a variety of signaling pathways. Even non-oxidant mediated triggering mechanisms are therefore also likely to activate downstream redox-regulated events.

Differential proinflammatory responses induced by diesel exhaust particles with contrasting PAH and metal content

Exposure to diesel engine exhaust particles (DEPs), representing a complex and variable mixture of components, has been linked with cellular production and release of several types of mediators related to pulmonary inflammation. A key challenge is to identify the specific components, which may be responsible for these effects. The aim of this study was to compare the proinflammatory potential of two DEP-samples with contrasting contents of polycyclic aromatic hydrocarbons (PAHs) and metals. The DEP-samples were compared with respect to their ability to induce cytotoxicity, expression and release of proinflammatory mediators (IL-6, IL-8), activation of mitogen-activated protein kinases (MAPKs) and expression of CYP1A1 and heme oxygenase-1 (HO-1) in human bronchial epithelial (BEAS-2B) cells. In addition, dithiothreitol and ascorbic acid assays were performed in order to examine the oxidative potential of the PM samples. The DEP-sample with the highest PAH and lowest metal content was more potent with respect to cytotoxicity and expression and release of proinflammatory mediators, CYP1A1 and HO-1 expression and MAPK activation, than the DEP-sample with lower PAH and higher metal content. The DEP-sample with the highest PAH and lowest metal content also possessed a greater oxidative potential. The present results indicate that the content of organic components may be determinant for the proinflammatory effects of DEP. The findings underscore the importance of considering the chemical composition of particulate matter-emissions, when evaluating the potential health impact and implementation of air pollution regulations.

Differential NF-κB and MAPK activation underlies fluoride- and TPA-mediated CXCL8 (IL-8) induction in lung epithelial cells

Different toxic agents have a varying potential to induce the production of the proinflammatory chemokine, CXCL8 (interleukin [IL]-8), in lung cells. A critical question is which mechanisms determine the magnitude and persistence of the CXCL8 responses to different stimuli. To approach this, we compared the potential of the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), and sodium fluoride (NaF) to induce CXCL8 responses in A549 cells, with emphasis on the importance of nuclear factor kappa B (NF-κB)- and mitogen-activated protein kinase (MAPK) signaling. Notably, TPA induced a greater release of CXCL8 than did NaF. Furthermore, TPA induced a strong, rapid, but transient upregulation of CXCL8 messenger (m)RNA, whereas NaF induced a weaker, more delayed, but persistent upregulation. With respect to signaling, TPA led to an early, strong, and relatively transient extracellular signal-regulated kinase (ERK)1/2 phosphorylation, and a less marked and even more transient phosphorylation of c-jun-N-terminal kinases (JNK1/2) and p38. In contrast, NaF elicited a lower, but relatively sustained increase in phosphorylation of ERK1/2, and a marked phosphorylation of p38 and JNK1/2, with the JNK1/2 response as most transient. Only ERK1/2 inhibition affected the TPA response, whereas inhibition of all the three MAPK cascades reduced NaF-induced CXCL8 release. TPA also induced an early, marked phosphorylation/translocation of p65 (NF-κB), whereas NaF induced slower, less pronounced effects on p65. The CXCL8 responses by TPA and NaF were reduced by p65-siRNA. In conclusion, all MAPK cascades were involved in NaF-induced CXCL8 release, whereas only ERK1/2 activation was involved in response to TPA. Furthermore, NF-κB activation appeared to be indispensable for CXCL8 induction. The early response, magnitude, and persistency of MAPK and NF-κB signaling seemed to be critical determinants for the potential to induce CXCL8. These findings underscore that a strong, rapid, and relatively transient activation of ERK1/2 in combination with NF-kB may be sufficient for a strong induction of CXCL8, which may exceed the effects of a more moderate ERK1/2 activation in combination with activation of p38, JNK1/2, and NF-κB.

Mechanisms linked to differences in the mutagenic potential of 1,3-dinitropyrene and 1,8-dinitropyrene

This study explores and characterizes the toxicity of two closely related carcinogenic dinitro-pyrenes (DNPs), 1,3-DNP and 1,8-DNP, in human bronchial epithelial BEAS-2B cells and mouse hepatoma Hepa1c1c7 cells. Neither 1,3-DNP nor 1,8-DNP (3–30 μM) induced cell death in BEAS-2B cells. In Hepa1c1c7 cells only 1,3-DNP (10–30 μM) induced a mixture of apoptotic and necrotic cell death after 24 h. Both compounds increased the level of reactive oxygen species (ROS) in BEAS-2B as measured by CM-H₂DCFDA-fluorescence. A corresponding increase in oxidative damage to DNA was revealed by the formamidopyrimidine-DNA glycosylase (fpg)-modified comet assay. Without fpg, DNP-induced DNA damage detected by the comet assay was only found in Hepa1c1c7 cells. Only 1,8-DNP formed DNA adduct measured by ³²P-postlabelling. In Hepa1c1c cells, 1,8-DNP induced phosphorylation of H2AX (γH2AX) and p53 at a lower concentration than 1,3-DNP and there was no direct correlation between DNA damage/DNA damage response (DR) and induced cytotoxicity. On the other hand, 1,3-DNP-induced apoptosis was inhibited by pifithrin-α, an inhibitor of p53 transcriptional activity. Furthermore, 1,3-DNP triggered an unfolded protein response (UPR), as measured by an increased expression of CHOP, ATF4 and XBP1. Thus, other types of damage possibly linked to endoplasmic reticulum (ER)-stress and/or UPR could be involved in the induced apoptosis. Our results suggest that the stronger carcinogenic potency of 1,8-DNP compared to 1,3-DNP is linked to its higher genotoxic effects. This in combination with its lower potency to induce cell death may increase the probability of causing mutations.

The occurrence of polycyclic aromatic hydrocarbons and their derivatives and the proinflammatory potential of fractionated extracts of diesel exhaust and wood smoke particles

Exposure to combustion emissions, including diesel engine exhaust and wood smoke particles (DEPs and WSPs), has been associated with inflammatory responses. To investigate the possible role of polycyclic aromatic hydrocarbons (PAHs) and PAH-derivatives, the DEPs and WSPs methanol extracts were fractionated by solid phase extraction (SPE), and the fractions were analyzed for more than ∼120 compounds. The pro-inflammatory effects of the fractionated extracts were characterized by exposure of bronchial epithelial lung cells (BEAS-2B). Both native DEPs and WSPs caused a concentration-dependent increase in IL-6 and IL-8 release and cytotoxicity. This is consistent with the finding of a rather similar total content of PAHs and PAH-derivatives. Yet, the samples differed in specific components, suggesting that different species contribute to the toxicological response in these two types of particles. The majority of the IL-6 release and cytotoxicity was induced upon exposure to the most polar (methanol) SPE fraction of extracts from both samples. In these fractions hydroxy-PAHs, carboxy-PAHs were observed along with nitro-amino-PAHs in DEP. However, the biological effects induced by the polar fractions could not be attributed only to the occurrence of PAH-derivatives. The present findings indicate a need for further characterization of organic extracts, beyond an extensive analysis of commonly suspected PAH and PAH-derivatives. Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Environmental Science and Health, Part A, to view the supplemental file.

Role of size and surface area for pro-inflammatory responses to silica nanoparticles in epithelial lung cells: importance of exposure conditions

The present study compared non-crystalline silica particles of nano (50nm)- and submicro (500nm)-size (Si50 and Si500) for the potential to induce cytokine responses in bronchial epithelial lung cells (BEAS-2B). The cell cultures were exposed to equal mass and surface area concentrations of the two particles in different exposure media; LHC-9 and DMEM:F12. The state of agglomeration was different in the two media; with marked agglomeration in LHC-9 and nearly no agglomeration in DMEM:F12. On a mass basis, Si50 was more potent than Si500 in inducing cytokine responses in both exposure media. In contrast, upon exposure to similar surface area concentrations, Si500 was more potent than Si50 in DMEM:F12. This might be due to different agglomeration/sedimentation properties of Si50 versus Si500 in the two media. However, influence of differences in particle reactivity or particle uptake cannot be excluded. The data indicated no qualitative changes in the cytokine gene-expression patterns induced by the two particles, suggesting effects through similar mechanisms. These aspects might be of importance for interpretation of in vitro studies of nanomaterials.

Cell toxicity and oxidative potential of engine exhaust particles: impact of using particulate filter or biodiesel fuel blend

The link between emissions of vehicular particulate matter (PM) and adverse health effects is well established. However, the influence of new emission control technologies and fuel types on both PM emissions and health effects has been less well investigated. We examined the health impact of PM emissions from two vehicles equipped with or without a diesel particulate filter (DPF). Both vehicles were powered either with diesel (B0) or a 50% v/v biodiesel blend (B50). The DPF effectively decreased PM mass emissions (∼85%), whereas the fuel B50 without DPF lead to less reduction (∼50%). The hazard of PM per unit distance driven was decreased for the DPF-equipped vehicle as indicated by a reduced cytotoxicity, oxidative, and pro-inflammatory potential. This was not evident and even led to an increase when the hazard was expressed on a per unit of mass basis. In general, the PM oxidative potential was similar or reduced for the B50 compared to the B0 powered vehicle. However, the use of B50 resulted in increased cytotoxicity and IL-6 release in BEAS-2B cells irrespective of the expression metric. This study shows that PM mass reduction achieved by the use of B50 will not necessarily decrease the hazard of engine emissions, while the application of a DPF has a beneficial effect on both PM mass emission and PM hazard.

Differential chemokine induction by 1-nitropyrene and 1-aminopyrene in bronchial epithelial cells: importance of the TACE/TGF-α/EGFR-pathway

1-nitropyrene (1-NP), a common PAH in diesel exhaust, and its amine metabolite 1-aminopyrene (1-AP) induce distinctly different chemokine-responses in bronchial epithelial cells (BEAS-2B) characterized by increases in CXCL8 and CCL5, respectively. Tumor necrosis factor-α converting enzyme (TACE), which cleaves membrane-bound transforming growth factor (TGF)-α, activating the epidermal growth factor receptor (EGFR), may regulate pro-inflammatory responses induced by a variety of endogenous and exogenous agents. The present results suggest that CXCL8, but not CCL5 responses in 1-NP- or 1-AP-exposed cells required TACE/TGF-α/EGFR-signaling. The findings strengthen the notion that TACE/TGF-α/EGFR-signaling is central in epithelial CXCL8-regulation upon exposure to multiple airborne pollutants.

Mechanisms of chemokine responses by polycyclic aromatic hydrocarbons in bronchial epithelial cells: sensitization through toll-like receptor-3 priming

We have previously observed that 1-nitropyrene (1-NP) and its amine metabolite 1-aminopyrene (1-AP) induce differential chemokine responses in human bronchial epithelial cells (BEAS-2B) characterized by maximum responses for CXCL8 (IL-8) and CCL5 (RANTES), respectively. In the present study, we further explored the effects of 1-NP and 1-AP on chemokine responses. The results suggest that the differential effect of 1-NP and 1-AP on CXCL8 and CCL5 in BEAS-2B cells was mainly related to effects at higher concentrations, which in the case of 1-NP seemed to be linked to ROS-formation and/or metabolic activation by CYP-enzymes. However, at a low concentration (1 μM) where neither 1-NP, 1-AP nor unsubstituted pyrene had any effect on chemokine responses, we found that all three PAHs potentiated CXCL8 and CCL5 responses induced by the TLR3 ligand polyinosinic:polycytidylic acid (Poly I:C) in BEAS-2B cells. As neither benzo[a]pyrene nor β-naphthoflavone induced a similar effect in Poly I:C-primed cells, the response seemed independent of aryl hydrocarbon receptor-mediated mechanisms. The results show that priming cells with an inflammogenic stimuli like Poly I:C sensitizes the cells toward additional pro-inflammatory effects of certain PAHs. The study underscores that testing on healthy cells or animals may not be sufficient to fully evaluate chemokine responses and the pro-inflammatory potential of organic chemicals.

Comparison of non-crystalline silica nanoparticles in IL-1β release from macrophages

BACKGROUND

Respirable crystalline silica (silicon dioxide; SiO₂, quartz) particles are known to induce chronic inflammation and lung disease upon long-term inhalation, whereas non-crystalline (amorphous) SiO₂ particles in the submicrometre range are regarded as less harmful. Several reports have demonstrated that crystalline, but also non-crystalline silica particles induce IL-1β release from macrophages via the NALP3-inflammasome complex (caspase-1, ASC and NALP3) in the presence of lipopolysaccharide (LPS) from bacteria. Our aim was to study the potential of different non-crystalline SiO₂ particles from the nano- to submicro-sized range to activate IL-1β responses in LPS-primed RAW264.7 macrophages and primary rat lung macrophages. The role of the NALP3-inflammasome and up-stream mechanisms was further explored in RAW264.7 cells.

RESULTS

In the present study, we have shown that 6 h exposure to non-crystalline SiO₂ particles in nano- (SiNPs, 5-20 nm, 50 nm) and submicro-sizes induced strong IL-1β responses in LPS-primed mouse macrophages (RAW264.7) and primary rat lung macrophages. The primary lung macrophages were more sensitive to Si-exposure than the RAW-macrophages, and responded more strongly. In the lung macrophages, crystalline silica (MinUsil 5) induced IL-1β release more potently than the non-crystalline Si50 and Si500, when adjusted to surface area. This difference was much less pronounced versus fumed SiNPs. The caspase-1 inhibitor zYVAD and RNA silencing of the NALP3 receptor reduced the particle-induced IL-1β release in the RAW264.7 macrophages. Furthermore, inhibitors of phagocytosis, endosomal acidification, and cathepsin B activity reduced the IL-1β responses to the different particles to a similar extent.

CONCLUSIONS

In conclusion, non-crystalline silica particles in the nano- and submicro-size ranges seemed to induce IL-1β release from LPS-primed RAW264.7 macrophages via similar mechanisms as crystalline silica, involving particle uptake, phagosomal leakage and activation of the NALP3 inflammasome. Notably, rat primary lung macrophages were more sensitive with respect to silica-induced IL-1β release. The differential response patterns obtained suggest that silica-induced IL-1β responses not only depend on the particle surface area, but on factors and/or mechanisms such as particle reactivity or particle uptake. These findings may suggest that bacterial infection via LPS may augment acute inflammatory effects of non-crystalline as well as crystalline silica particles.

Diesel exhaust particles induce CYP1A1 and pro-inflammatory responses via differential pathways in human bronchial epithelial cells

Background

Exposure to diesel engine exhaust particles (DEPs) has been associated with several adverse health outcomes in which inflammation seems to play a key role. DEPs contain a range of different inorganic and organic compounds, including polycyclic aromatic hydrocarbons (PAHs). During the metabolic activation of PAHs, CYP1A1 enzymes are known to play a critical role. In the present study we investigated the potential of a characterised sample of DEPs to induce cytotoxicity, to influence the expression of CYP1A1 and inflammation-related genes, and to activate intracellular signalling pathways, in human bronchial epithelial cells. We specifically investigated to what extent DEP-induced expression of interleukin (IL)-6, IL-8 and cyclooxygenase (COX)-2 was regulated differentially from DEP-induced expression of CYP1A1.

Results

The cytotoxicity of the DEPs was characterised by a marked time- and concentration-dependent increase in necrotic cells at 4 h and above 200 μg/ml (~ 30 μg/cm²). DEP-induced DNA-damage was only apparent at high concentrations (≥ 200 μg/ml). IL-6, IL-8 and COX-2 were the three most up-regulated genes by the DEPs in a screening of 20 selected inflammation-related genes. DEP-induced expression of CYP1A1 was detected at very low concentrations (0.025 μg/ml), compared to the expression of IL-6, IL-8 and COX-2 (50-100 μg/ml). A CYP1A1 inhibitor (α-naphthoflavone), nearly abolished the DEP-induced expression of IL-8 and COX-2. Of the investigated mitogen-activated protein kinases (MAPKs), the DEPs induced activation of p38. A p38 inhibitor (SB202190) strongly reduced DEP-induced expression of IL-6, IL-8 and COX-2, but only moderately affected the expression of CYP1A1. The DEPs also activated the nuclear factor-κB (NF-κB) pathway, and suppression by siRNA tended to reduce the DEP-induced expression of IL-8 and COX-2, but not CYP1A1.

Conclusion

The present study indicates that DEPs induce both CYP1A1 and pro-inflammatory responses in vitro, but via differential intracellular pathways. DEP-induced pro-inflammatory responses seem to occur via activation of NF-κB and p38 and are facilitated by CYP1A1. However, the DEP-induced CYP1A1 response does not seem to involve NF-κB and p38 activation. Notably, the present study also indicates that expression of CYP1A1 may represent a particular sensitive biomarker of DEP-exposure.

Differential effects of nitro-PAHs and amino-PAHs on cytokine and chemokine responses in human bronchial epithelial BEAS-2B cells

Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) are found in diesel exhaust and air pollution particles. Along with other PAHs, many nitro-PAHs possess mutagenic and carcinogenic properties, but their effects on pro-inflammatory processes and cell death are less known. In the present study we examined the effects of 1-nitropyrene (1-NP), 3-nitrofluoranthene (3-NF) and 3-nitrobenzanthrone (3-NBA) and their corresponding amino forms, 1-AP, 3-AF and 3-ABA, in human bronchial epithelial BEAS-2B cells. The effects of the different nitro- and amino-PAHs were compared to the well-characterized PAH benzo[a]pyrene (B[a]P). Expression of 17 cytokine and chemokine genes, measured by real-time PCR, showed that 1-NP and 3-NF induced a completely different cytokine/chemokine gene expression pattern to that of their amino analogues. 1-NP/3-NF-induced responses were dominated by maximum effects on CXCL8 (IL-8) and TNF-alpha expression, while 1-AP-/3-AF-induced responses were dominated by CCL5 (RANTES) and CXCL10 (IP-10) expression. 3-NBA and 3-ABA induced only marginal cytokine/chemokine responses. However, 3-NBA exposure induced considerable DNA damage resulting in accumulation of cells in S-phase and a marked increase in apoptosis. B[a]P was the only compound to induce expression of aryl hydrocarbon receptor (AhR)-regulated genes, such as CYP1A1 and CYP1B1, but did not induce cytokine/chemokine responses in BEAS-2B cells. Importantly, nitro-PAHs and amino-PAHs induced both qualitatively and quantitatively different effects on cytokine/chemokine expression, DNA damage, cell cycle alterations and cytotoxicity. The cytokine/chemokine responses appeared to be triggered, at least partly, through mechanisms separate from the other examined endpoints. These results confirm and extend previous studies indicating that certain nitro-PAHs have a considerable pro-inflammatory potential.

Helseeffekter av byluftpartikler

Svevestøv i byluft består av forbrenningspartikler og mineralpartikler med svært forskjellige størrelser og kjemiske egenskaper. Svevestøvet kan deles inn i størrelsesfraksjoner som PMAmbient particulate matter (PM) comprises particles from different combustion processes and a variety of mineral particles. The particles vary widely in size distribution and chemical/physical characteristics. PM is often divided into size fractions with different aerodynamic diameters: PM10 (PM ! 10 mm), PM2.5 (PM ! 2.5 mm) and PM0.1 (PM ! 0.1 mm). Recent population studies have found an association between an increase in mortality and morbidity due to lung and/or cardiovascular disease and short-term increases in PM. The relative risk (RR) was approximately 1.005 for an increase in 10 mg/m3 PM10, without an observed threshold even at concentrations below 10 mg/m3. Chronic exposure has been investigated to a lesser extent, but longterm exposure to PM2.5 has been found to be associated with an approximately 10-fold greater increase in RR than short-term exposures. Experimental studies with volunteers in chamber and field studies show mild lung or cardiovascular responses at concentrations of ambient particles (PM2.5/PM10: 100-200 mg/m3) that may occur during episodes of air pollution. Animal studies at higher concentrations have shown stronger responses. The experimental studies support the epidemiological evidence for an adverse health effect of PM. Both population- and experimental studies indicate the existence of vulnerable individuals. At low to average ambient concentrations there seems to exist a discrepancy between the results of population- and experimental studies that might be due to the absence of the most vulnerable individuals in the experimental studies. Together with cell culture experiments, human and animal studies indicate the importance of physical and chemical properties of the particles (size, content of metals, organics, endotoxins, etc.) for the observed effects. More knowledge about adverse health effects induced by low concentrations of PM and the critical particle characteristics, is required.10 (PM £ 10 mm), PM2,5 (PM £ 2,5 mm) og PM0,1 (PM £ 0,1 mm). Nyere befolkningsstudier viser en assosiasjon mellom økning i dødelighet og sykelighet (pga. lunge- og hjertekarsykdommer) og kortvarige økninger i svevestøvskonsentrasjoner i byluft. Den relative risikoen (RR) er rundt 1,005 ved en økning av PM10 på 10 mg/m3, uten noen observert terskelverdi, selv ved nivåer under 10 mg/m3. Kronisk eksponering for svevestøv er mindre undersøkt, men årelang eksponering for PM2,5 er assosiert med en RR som er omlag 10 ganger større enn ved korttidseksponering. Befolkningsstudiene indikerer at enkelte grupper synes å være spesielt følsomme (lungesyke, hjertesyke og barn). Hos frivillige individer i kammer- og feltstudier, fant man effekter både i luftveiene og i hjerte-karsystemet ved konsentrasjoner av svevestøv (PM2,5/PM10: 100-200 mg/m3) som kan forekomme i episoder med økt luftforurensning. Dyreforsøk med høyere konsentrasjoner ga kraftigere responser. De eksperimentelle studiene understøtter befolkningsstudiene i at byluftpartikler representerer et helseproblem. Både befolkningsstudiene og eksperimentelle studier indikerer at enkelte individer er mer sårbare enn andre. Ved lave til middels konsentrasjoner av byluftpartikler synes det å foreligge en diskrepans mellom disse studietypene som kan skyldes at de mest sårbare individene ikke er inkludert i eksperimentelle forsøk. Studier med mennesker, dyr og celler viser at fysisk/kjemiske egenskaper ved partiklene (størrelse, innhold av metaller, organiske forbindelser, endotoksiner etc.) er sentrale for de observerte effektene av svevestøvet. Mer kunnskap både om helseeffekter ved lave konsentrasjoner, samt egenskaper ved partikler, er nødvendig.

IL-1beta differently involved in IL-8 and FGF-2 release in crystalline silica-treated lung cell co-cultures

Background

Inhalation of crystalline silica particles is in humans associated with inflammation and development of fibrosis. The aim of the present study was to investigate the effect of crystalline silica on the release of the fibrosis- and angiogenesis-related mediator FGF-2 and the pro-inflammatory mediator IL-8, and how IL-1β and TNF-α were involved in this release from various mono- and co-cultures of monocytes, pneumocytes and endothelial cells.

Results

Silica exposure induced an increase of IL-8 release from monocytes and from pneumocytes alone, and the FGF-2 level in the medium increased upon silica exposure of pneumocytes. Both the responses were enhanced in non-contact co-cultures with endothelial cells. The FGF-2 release seemed to increase with the silica-induced decrease in the number of pneumocytes. The release of IL-8 and FGF-2 was partially suppressed in cultures with pneumocytes in contact with monocytes compared to non-contact cultures. Treatment with anti-TNF-α and the IL-1 receptor antagonist revealed that release of IL-1β, and not TNF-α, from monocytes dominated the regulation of IL-8 release in co-cultures. For release of FGF-2, IL-1ra was without effect. However, exogenous IL-1β reduced the FGF-2 levels, strongly elevated the FGF-2-binding protein PTX3, and prevented the reduction in the number of pneumocytes induced by silica.

Conclusion

IL-1β seems to be differently involved in the silica-induced release of IL-8 and FGF-2 in different lung cell cultures. Whereas the silica-induced IL-8 release is regulated via an IL-1-receptor-mediated mechanism, IL-1β is suggested only indirectly to affect the silica-induced FGF-2 release by counteracting pneumocyte loss. Furthermore, the enhanced IL-8 and FGF-2 responses in co-cultures involving endothelial cells show the importance of the interaction between different cell types and may suggest that both these mediators are important in angiogenic or fibrogenic processes.

3-Nitrofluoranthene (3-NF) but not 3-aminofluoranthene (3-AF) elicits apoptosis as well as programmed necrosis in Hepa1c1c7 cells

In this study, we show that the environmental pollutant, 3-nitrofluoranthene (3-NF) but not its amine form, 3-aminofluoranthene (3-AF), induces apoptosis as well as regulated necrosis with necroptotic features in Hepa1c1c7 cells. Upon exposure to 3-NF, both typical apoptotic and necrotic cells were observed. A large number of the cells exhibited a characteristic partial nuclear chromatin condensation. Cycloheximide completely attenuated 3-NF-induced cell death. Activation of caspase-8, -9, and -3 were observed. Moreover, Z-VAD-FMK decreased the apoptotic cells, whereas the number of propidium iodide (PI)-positive cells with partial chromatin condensation was reduced by Nec-1, an inhibitor of receptor interacting protein (RIP-1). Cyp1a1, but not nitric oxide synthase (NOS), appears to be involved in activation of 3-NF to reactive metabolites. Increase in the number as well as size of lysosomes, myelinosomes, and activation of autophagy were also observed. 3-NF induced phosphorylation of ERK1/2, JNK and p38 MAPKs. Interestingly, while inhibitors of ERK1/2 and JNK reduced apoptotic as well as necrotic cell death, the p38 inhibitor, SB202190 reduced only the necrotic cell death. Taken together, 3-NF elicits both apoptosis and a caspase-independent programmed cell death (PCD) with autophagic characteristics. Conversely, with 3-AF, no apparent cytotoxic effects besides a reduction in cell proliferation was observed.

Importance of Size and Composition of Particles for Effects on Cells In Vitro

A primary goal of current research on particle-induced health effects is to reveal the critical characteristics that determine their biological effects. Experimental studies have shown that smaller particles induce stronger biological effects than larger particles of similar composition, due to their larger surface area to mass ratio. However, correlation for variations in surface area could not account for variation in biological reactivity among particles of differential composition. Hence, the importance of size and surface area does not override the importance of particle composition. Moreover, different particle characteristics appear to be involved in different biological effects in vitro. Our studies show that mineral particle-induced apoptosis mostly seems to depend on particle size, whereas composition and surface reactivity appeared to be most important for the proinflammatory potential of the particles. The ability of the particles to generate reactive oxygen species in vitro was not correlated with either inflammatory markers or apoptosis, suggesting that other mechanisms are at play. A single, specific component of the mineral particles, explaining the differences in response, has not been identified. In European-wide studies such as the Respiratory Allergy and Inflammation due to Air Pollution (RAIAP) study, particles have been sampled in different locations to study season- and site-dependent variations in responses particles, such as markers of inflammatory and allergic reactions in cells and animals. The data indicate that coarse particles can induce at least as strong inflammatory responses as fine particles. The allergic responses tended to be more associated with the organic fraction (PAH) of particles, whereas the inflammatory reactions seemed to be more associated with metals and endotoxin. Overall, coarse PM was found to have an inflammatory potential similar to fine PM on an equal mass basis. Even though one has to take into account different concentrations in ambient air as well as differences in respiratory system deposition of the size fractions, the potential of coarse particles to induce pulmonary effects should not be neglected.

IL-1β as a determinant in silica-induced cytokine responses in monocyte-endothelial cell co-cultures

Alveolar macrophages and endothelial cells are both involved in lung inflammation and remodeling of lung alveolar structures. In the present study, monocytes (precursors for macrophages) were exposed to crystalline silica and examined for pro- and anti-inflammatory cytokine responses in non-contact co-cultures with endothelial cells. The time courses for silica-induced release of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-8 both from co-cultures and monocyte mono-cultures showed an early peak at 5–10 h, almost no response at 20 h, and a strong increase at 43 h. At 43 h, co-cultures also showed strongly increased IL-6 levels. Steady-state levels of mRNA roughly exhibited the same pattern of early up-regulation and reduced levels at 20 h. Compared with monocyte mono-cultures, silica induced a strong release of IL-1β, IL-6, and IL-8, but not of TNF-α, after 43 h in co-cultures, whereas at 5 and 10 h a significant difference was only observed for the silica-induced IL-8 response. An antagonist to the IL-1 receptor strongly reduced IL-6 and IL-8 levels, whereas antibodies to TNF-α increased the levels of IL-1β and IL-8. Thus, IL-1β is suggested to be an important triggering factor that determines the silica-induced release of several of the other cytokines in this co-culture system.

Regulation of rat alveolar type 2 cell proliferation in vitro involves type II cAMP-dependent protein kinase

To elucidate the role of cAMP and different cAMP-dependent protein kinases (PKA; A-kinase) in lung cell proliferation, we investigated rat alveolar type 2 cell proliferation in relation to activation or inhibition of PKA and PKA regulatory subunits (RIIalpha and RIalpha). Both the number of proliferating type 2 cells and the level of different regulatory subunits varied during 7 days of culture. The cells exhibited a distinct peak of proliferation after 5 days of culture. This proliferation peak was preceded by a rise in RIIalpha protein level. In contrast, an inverse relationship between RIalpha and type 2 cell proliferation was noted. Activation of PKA increased type 2 cell proliferation if given at peak RIIalpha expression. Furthermore, PKA inhibitors lowered the rate of proliferation only when a high RII level was observed. An antibody against the anchoring region of RIIalpha showed cell cycle-dependent binding in contrast to antibodies against other regions, possibly related to altered binding to A-kinase anchoring protein. Following activation of PKA, relocalization of RIIalpha was confirmed by immunocytochemistry. In conclusion, it appears that activation of PKA II is important in regulation of alveolar type 2 cell proliferation.