New developments in aerosol dosimetry

Nicotine flux and pharmacokinetics-based considerations for early assessment of nicotine delivery systems

In the past few years, technological advancements enabled the development of novel electronic nicotine delivery systems (ENDS). Several empirical measures such as "nicotine flux" are being proposed to evaluate the abuse liability potential of these products. We explored the applicability of nicotine flux for clinical nicotine pharmacokinetics (PK) and 52-week quit success from cigarettes for a wide range of existing nicotine delivery systems. We found that the differences in nicotine flux for various nicotine delivery systems are not related to changes in PK, as nicotine flux does not capture key physiological properties such as nicotine absorption rate. Further, the 52-week quit success and abuse liability potential of nicotine nasal sprays (high nicotine flux product), and nicotine inhalers (nicotine flux similar to ENDS) are low, suggesting that nicotine flux is a poor metric for the assessment of nicotine delivery systems. PK indices are more dependable for characterizing nicotine delivery systems, and a nicotine plasmaC max T max > 1 could improve 52-week quit success from cigarettes. However, a single metric may be inadequate to fully assess the abuse liability potential of nicotine delivery systems and needs to be further studied. A combination of in vitro and in silico approaches could potentially address the factors influencing the inhaled aerosol dosimetry and resulting PK of nicotine to provide early insights for ENDS assessments. Further research is required to understand nicotine dosimetry and PK for ad libitum product use, and abuse liability indicators of nicotine delivery systems. This commentary is intended to (1) highlight the need to think beyond a single empirical metric such as nicotine flux, (2) suggest potential PK-based metrics, (3) suggest the use of in vitro and in silico tools to obtain early insights into inhaled aerosol dosimetry for ENDS, and (4) emphasize the importance of considering comprehensive clinical pharmacology outcomes to evaluate nicotine delivery systems.

Monitoring and apportioning sources of indoor air quality using low-cost particulate matter sensors

Air quality is one of the most important factors in public health. While outdoor air quality is widely studied, the indoor environment has been less scrutinised, even though time spent indoors is typically much greater than outdoors. The emergence of low-cost sensors can help assess indoor air quality. This study provides a new methodology, utilizing low-cost sensors and source apportionment techniques, to understand the relative importance of indoor and outdoor air pollution sources upon indoor air quality. The methodology is tested with three sensors placed in different rooms inside an exemplar house (bedroom, kitchen and office) and one outdoors. When the family was present, the bedroom had the highest average concentrations for PM_2.5 and PM₁₀ (3.9 ± 6.8 ug/m³ and 9.6 ± 12.7 μg/m³ respectively), due to the activities undertaken there and the presence of softer furniture and carpeting. The kitchen, while presenting the lowest PM concentrations for both size ranges (2.8 ± 5.9 ug/m³ and 4.2 ± 6.9 μg/m³ respectively), presented the highest PM spikes, especially during cooking times. Increased ventilation in the office resulted in the highest PM₁ concentration (1.6 ± 1.9 μg/m³), highlighting the strong effect of infiltration of outdoor air for the smallest particles. Source apportionment, via positive matrix factorisation (PMF), showed that up to 95 % of the PM₁ was found to be of outdoor sources in all the rooms. This effect was reduced as particle size increased, with outdoor sources contributing >65 % of the PM_2.5, and up to 50 % of the PM₁₀, depending on the room studied. The new approach to elucidate the contributions of different sources to total indoor air pollution exposure, described in this paper, is easily scalable and translatable to different indoor locations.

Air Pollution: Possible Interaction between the Immune and Nervous System?

Exposure to environmental pollutants is a serious and common public health concern associated with growing morbidity and mortality worldwide, as well as economic burden. In recent years, the toxic effects associated with air pollution have been intensively studied, with a particular focus on the lung and cardiovascular system, mainly associated with particulate matter exposure. However, epidemiological and mechanistic studies suggest that air pollution can also influence skin integrity and may have a significant adverse impact on the immune and nervous system. Air pollution exposure already starts in utero before birth, potentially causing delayed chronic diseases arising later in life. There are, indeed, time windows during the life of individuals who are more susceptible to air pollution exposure, which may result in more severe outcomes. In this review paper, we provide an overview of findings that have established the effects of air pollutants on the immune and nervous system, and speculate on the possible interaction between them, based on mechanistic data.

Susceptibility of individuals with lung dysfunction to systemic inflammation associated with ambient fine particle exposure: A panel study in Beijing

BACKGROUND

The underlying mechanism on the susceptibility of chronic obstructive pulmonary disease (COPD) patients to air pollution has yet to be clarified.

OBJECTIVES

Based on the COPD in Beijing (COPDB) study, we examined whether lung dysfunction contributed to pollutant-associated systemic inflammation in COPD patients.

METHODS

Proinflammatory biomarkers including interleukin-8 (IL-8) and tumor necrosis factor α (TNFα) were measured in serum samples collected from 53 COPD and 82 healthy participants. Concentrations of particulate matter with aerodynamic diameter ≤ 2.5 μm (PM_2.5), carbonaceous components in PM_2.5, and PM size distribution were continuously monitored. Linear mixed effects models were used to examine the associations of biomarker differences with particle exposure, between COPD and healthy participants, and across subgroups with different levels of lung dysfunction.

RESULTS

COPD patients showed higher differences in IL-8 and TNFα levels associated with exposure to measured pollutants, comparing to healthy controls. In advanced analysis, particle-associated differences in IL-8 and TNFα levels were higher in participants with poorer lung ventilation and diffusion capacity, and higher ratio of residual volume. For example, an interquartile range increase in average PM_2.5 concentration 2 weeks before visits was associated with a 15.7% difference in IL-8 level in participants with the lowest ratio of measured value to predicted value of forced expiratory volume in 1 s (FEV1%pred) (65.2%), and the association decreased monotonically with increasing FEV1%pred. Associations between differences in TNFα level and average ultrafine particle concentration 1 week before visits increased gradually with increasing ratio of measured value to predicted value of residual volume/total lung capacity.

CONCLUSIONS

COPD patients, especially those with poorer lung function, are more susceptible to systemic inflammation associated with fine particle exposure.

Investigation of the Dynamism of Nanosized SOA Particle Formation in Indoor Air by a Scanning Mobility Particle Sizer and Proton-Transfer-Reaction Mass Spectrometry

Terpenes are VOCs of particular importance, since they are emitted from a wide range of indoor sources and are considered to be precursors of Secondary Organic Aerosol (SOA) formation. It has been proven that SOA particles, especially nanosized ones, pose a threat to human health. In this research, experiments with the application of an environmental chamber and real-time measurement techniques were carried out to investigate in a complimentary way the formation of monoterpene oxidation products and nanosized SOA particles initiated by monoterpene ozonolysis. Proton-Transfer-Reaction Mass Spectrometry with a Time-Of-Flight analyzer (PTR-TOF-MS) and a Scanning Mobility Particle Sizer (SMPS) were applied to determine in real time the dynamism of the formation of the corresponding terpene ozonolysis products and submicron SOA particles. Results proved that firstly, oxidation products were formed, and then, they underwent nucleation and condensation, forming particles whose diameters grew with time. The oxidation products formed were different depending on the type of terpenes applied. The comparison of the results obtained during the experiments with gaseous standard mixtures and real samples commonly present and used in indoor air revealed that the diversified chemical composition of the emission source had implications for both the particle formation initiated by the oxidation of essential oil components and the chemical reactions occurring via the oxidation process. With the instrumentation utilized, the concentration changes at the level of a few ppbv could be monitored.

Endogenous doesn't always mean innocuous: a scoping review of iron toxicity by inhalation

Ambient air pollution is a leading risk factor for the global burden of disease. One possible pathway of particulate matter (PM)-induced toxicity is through iron (Fe), the most abundant metal in the atmosphere. The aim of the review was to consider the complexity of Fe-mediated toxicity following inhalation exposure focusing on the chemical and surface reactivity of Fe as a transition metal and possible pathways of toxicity via reactive oxygen species (ROS) generation as well as considerations of size, morphology, and source of PM. A broad term search of 4 databases identified 2189 journal articles and reports examining exposure to Fe via inhalation in the past 10 years. These were sequentially analyzed by title, abstract and full-text to identify 87 articles publishing results on the toxicity of Fe-containing PM by inhalation or instillation to the respiratory system. The remaining 87 papers were examined to summarize research dealing with in vitro, in vivo and epidemiological studies involving PM containing Fe or iron oxide following inhalation or instillation. The major findings from these investigations are summarized and tabulated. Epidemiological studies showed that exposure to Fe oxide is correlated with an increased incidence of cancer, cardiovascular diseases, and several respiratory diseases. Iron PM was found to induce inflammatory effects in vitro and in vivo and to translocate to remote locations including the brain following inhalation. A potential pathway for the PM-containing Fe-mediated toxicity by inhalation is via the generation of ROS which leads to lipid peroxidation and DNA and protein oxidation. Our recommendations include an expansion of epidemiological, in vivo and in vitro studies, integrating research improvements outlined in this review, such as the method of particle preparation, cell line type, and animal model, to enhance our understanding of the complex biological interactions of these particles.

Olfactory cell cultures to investigate health effects of air pollution exposure: Implications for neurodegeneration

Air pollution is a major, global public health concern. A growing body of evidence shows that exposure to air pollutants may impair the brain. Living in highly polluted areas has been linked to several neurodegenerative diseases, where exposure to complex mixtures of air pollutants in urban environments may have harmful effects on brain function. These harmful effects are thought to originate from elevated inflammation and oxidative stress. The olfactory epithelium is a key entry site of air pollutants into the brain as the particles are deposited in the upper airways and the nasal region. A potential source of patient-derived cells for study of air pollutant effects is the olfactory mucosa, which constitutes a central part of the olfactory epithelium. This review first summarizes the current literature on the available in vitro models of the olfactory epithelium. It then describes how alterations of the olfactory mucosa are linked to neurodegeneration and discusses potential therapeutic applications of these cells for neurodegenerative diseases. Finally, it reviews the research performed on the effects of air pollutant exposure in cells of the olfactory epithelium. Patient-derived olfactory epithelial models hold great promise for not only elucidating the molecular and cellular pathophysiology of neurodegenerative disorders, but for providing key understanding about air pollutant particle entry and effects at this key brain entry site.

State-of-the-art methods and devices for the generation, exposure, and collection of aerosols from heat-not-burn tobacco products

Tobacco harm reduction is increasingly recognized as a promising approach to accelerate the decline in smoking prevalence and smoking-related population harm. Potential modified risk tobacco products (MRTPs) must undergo a rigorous premarket toxicological risk assessment. The ability to reproducibly generate, collect, and use aerosols is critical for the characterization, and preclinical assessment of aerosol-based candidate MRTPs (cMRTPs), such as noncombusted cigarettes, also referred to as heated tobacco products, tobacco heating products, or heat-not-burn (HNB) tobacco products. HNB tobacco products generate a nicotine-containing aerosol by heating tobacco instead of burning it. The aerosols generated by HNB products are qualitatively and quantitatively highly different from cigarette smoke (CS). This constitutes technical and experimental challenges comparing the toxicity of HNB aerosols with CS. The methods and experimental setups that have been developed for the study of CS cannot be directly transposed to the study of HNB aerosols. Significant research efforts are dedicated to the development, characterization, and validation of experimental setups and methods suitable for HNB aerosols. They are described in this review, with a particular focus on the Tobacco Heating System version 2.2. This is intended to support further studies, the objective evaluation and verification of existing evidence, and the development of scientifically substantiated HNB MRTPs.

Bridging inhaled aerosol dosimetry to physiologically based pharmacokinetic modeling for toxicological assessment: nicotine delivery systems and beyond

One of the challenges for toxicological assessment of inhaled aerosols is to accurately predict their deposited and absorbed dose. Transport, evolution, and deposition of liquid aerosols are driven by complex processes dominated by convection-diffusion that depend on various factors related to physics and chemistry. These factors include the physicochemical properties of the pure substance of interest and associated mixtures, the physical and chemical properties of the aerosols generated, the interplay between different factors during transportation and deposition, and the subject-specific inhalation topography. Several inhalation-based physiologically based pharmacokinetic (PBPK) models have been developed, but the applicability of these models for aerosols has yet to be verified. Nicotine is among several substances that are often delivered via the pulmonary route, with varied kinetics depending upon the route of exposure. This was used as an opportunity to review and discuss the current knowledge and state-of-the-art tools combining aerosol dosimetry predictions with PBPK modeling efforts. A validated tool could then be used to perform for toxicological assessment of other inhaled therapeutic substances. The Science Panel from the Alliance of Risk Assessment have convened at the "Beyond Science and Decisions: From Problem Formulation to Dose-Response Assessment" workshop to evaluate modeling approaches and address derivation of exposure-internal dose estimations for inhaled aerosols containing nicotine or other substances. The discussion involved PBPK model evaluation criteria, challenges, and choices that arise in such a model design, development, and application as a computational tool for use in human toxicological assessments.

Mice-to-men comparison of inhaled drug-aerosol deposition and clearance

Part of the effective prediction of the pharmacokinetics of drugs (or toxic particles) requires extrapolation of experimental data sets from animal studies to humans. As the respiratory tracts of rodents and humans are anatomically very different, there is a need to study airflow and drug-aerosol deposition patterns in lung airways of these laboratory animals and compare them to those of human lungs. As a first step, interspecies computational comparison modeling of inhaled nano-to-micron size drugs (50 nm < d<15μm) was performed using mouse and human upper airway models under realistic breathing conditions. Critical species-specific differences in lung physiology of the upper airways and subsequently in local drug deposition were simulated and analyzed. In addition, a hybrid modeling methodology, combining Computational Fluid-Particle Dynamics (CF-PD) simulations with deterministic lung deposition models, was developed and predicted total and regional drug-aerosol depositions in lung airways of both mouse and man were compared, accounting for the geometric, kinematic and dynamic differences. Interestingly, our results indicate that the total particle deposition fractions, especially for submicron particles, are comparable in rodent and human respiratory models for corresponding breathing conditions. However, care must be taken when extrapolating a given dosage as considerable differences were noted in the regional particle deposition pattern. Combined with the deposition model, the particle retention and clearance kinetics of deposited nanoparticles indicates that the clearance rate from the mouse lung is higher than that in the human lung. In summary, the presented computer simulation models provide detailed fluid-particle dynamics results for upper lung airways of representative human and mouse models with a comparative analysis of particle lung deposition data, including a novel mice-to-men correlation as well as a particle-clearance analysis both useful for pharmacokinetic and toxicokinetic studies.

Insulation fiber deposition in the airways of men and rats. A review of experimental and computational studies

The typical insulation rock, slag and glass wool fibers are high volume materials. Current exposure levels in industry (generally ≤ 1 fiber/cm³ with a median diameter ∼1 μm and length ≥10 μm) are not considered carcinogenic or causing other types of severe lung effects. However, epidemiological studies are not informative on effects in humans at fiber levels >1 fiber/cm³. Effects may be inferred from valid rat studies, conducted with rat respirable fibers (diameter ≤ 1.5 μm). Therefore, we estimate delivery and deposition in human and rat airways of the industrial fibers. The deposition fractions in humans head regions by nasal (∼0.20) and by mouth breathing (≤0.08) are lower than in rats (0.50). The delivered dose into the lungs per unit lung surface area during a 1-day exposure at a similar air concentration is estimated to be about two times higher in humans than in rats. The deposition fractions in human lungs by nasal (∼0.20) and by mouth breathing (∼0.40) are higher than in rats (∼0.04). The human lung deposition may be up to three times by nasal breathing and up to six times higher by oral breathing than in rats, qualifying assessment factor setting for deposition.

Exposure to elemental composition of outdoor PM2.5 at birth and cognitive and psychomotor function in childhood in four European birth cohorts

BACKGROUND

Little is known about developmental neurotoxicity of particulate matter composition. We aimed to investigate associations between exposure to elemental composition of outdoor PM_2.5 at birth and cognitive and psychomotor functions in childhood.

METHODS

We analyzed data from 4 European population-based birth cohorts in the Netherlands, Germany, Italy and Spain, with recruitment in 2000-2006. Elemental composition of PM_2.5 measurements were performed in each region in 2008-2011 and land use regression models were used to predict concentrations at participants' residential addresses at birth. We selected 8 elements (copper, iron, potassium, nickel, sulfur, silicon, vanadium and zinc) and used principal component analysis to combine elements from the same sources. Cognitive (general, verbal, and non-verbal) and psychomotor (fine and gross) functions were assessed between 1 and 9years of age. Adjusted cohort-specific effect estimates were combined using random-effects meta-analysis.

RESULTS

7246 children were included in this analysis. Single element analysis resulted in negative association between estimated airborne iron and fine motor function (-1.25 points [95% CI -2.45 to -0.06] per 100ng/m³ increase of iron). Association between the motorized traffic component, derived from principal component analysis, and fine motor function was not significant (-0.29 points [95% CI -0.64 to 0.06] per unit increase). None of the elements were associated with gross motor function or cognitive function, although the latter estimates were predominantly negative.

CONCLUSION

Our results suggest that iron, a highly prevalent element in motorized traffic pollution, may be a neurotoxic compound. This raises concern given the ubiquity of motorized traffic air pollution.

INHALED AEROSOL DOSIMETRY: SOME CURRENT RESEARCH NEEDS

After the presentation of 60 papers at the conference "Advancing Aerosol Dosimetry Research" (October 24-25, 2014 in Irvine, CA, USA), attendees submitted written descriptions of needed research. About 40 research needs were submitted. The suggestions fell into six broad categories: 1) Access to detailed anatomic data; 2) Access to subject-specific aerosol deposition datasets; 3) Improving current inhaled aerosol deposition models; 4) Some current experimental data needs and hot topics; 5) Linking exposure and deposition modeling to health endpoints; and 6) Developing guidelines for appropriate validation of dosimetry and risk assessment models. Summaries of suggestions are provided here as an update on research needs related to inhaled aerosol dosimetry modeling. Taken together, the recommendations support the overarching need for increased collaborations between dose modelers and those that use the models for risk assessments, aerosol medicine applications, design of toxicology experiments, and extrapolation across species. This paper is only a snapshot in time of perceived research needs from the conference attendees; it does not carry the approval of any agency or other group that plans research priorities or that funds research.

Inhalation Study of Mycobacteriophage D29 Aerosol for Mice by Endotracheal Route and Nose-Only Exposure

BACKGROUND

Lytic mycobacteriophage D29 has the potential for tuberculosis treatment including multidrug-resistant strains. The aims of this study are to investigate deposition and distribution of aerosolized phage D29 particles in naive Balb/C mice, together with pharmacokinetics and evaluation of acute lung injury.

METHODS

Pharmacokinetics and BALF (bronchoalveolar lavage fluids) were analyzed after administration of phage D29 aerosols by endotracheal route using Penn-century aerosolizer; Collison 6-jet and Spinning top aerosol nebulizers (STAG) were used to generate phage aerosols with different particle size distributions in nose-only inhalation experiments. After exposure, deposited amounts of phage D29 particles in respiratory tracts were measured, and deposition efficiencies were calculated. A typical path deposition model for mice was developed, and then comparisons were made between predictions and experimentally measured results.

RESULTS

Approximately 10% of aerosolized phages D29 reached lung of mouse for pulmonary delivery, and were completely eliminated until 72 h after administration. In contrast, about 0.1% of intraperitoneal injected phages reached the lung, and were almost eliminated at 12 h time point. The inflammation was hardly observed in lung according to the results of BALF analysis. The CMADs (count median aerodynamic diameters) of generated aerosol by Collison and STAG nebulizer were 0.8 μm and 1.5 μm, respectively. After nose-only exposure, measured deposition efficiencies in whole respiratory tract for 0.8 and 1.5 μm phage particles were below 1% and 10%, respectively. Predictions of the computer deposition model compared fairly well with experimentally measured results.

CONCLUSIONS

This is the first systematic study of phage D29 aerosol respiratory challenge in laboratory animals. It provides evidence that aerosol delivery of phage D29 is an effective way for treating pulmonary infections caused by Mycobacterium tuberculosis. This research will also provide important data for future inhalation experiments.

Gaining a Critical Mass: A Dose Metric Conversion Case Study Using Silver Nanoparticles

Mass concentration is the standard convention to express exposure in ecotoxicology for dissolved substances. However, nanotoxicology has challenged the suitability of the mass concentration dose metric. Alternative metrics often discussed in the literature include particle number, surface area, and ion release (kinetics, equilibrium). It is unlikely that any single metric is universally applicable to all types of nanoparticles. However, determining the optimal metric for a specific type of nanoparticle requires novel studies to generate supportive data and employ methods to compensate for current analytical capability gaps. This investigation generated acute toxicity data for two standard species (Ceriodaphnia dubia, Pimephales promelas) exposed to five sizes (10, 20, 30, 60, 100 nm) of monodispersed citrate- and polyvinylpyrrolidone-coated silver nanoparticles. Particles were sized by various techniques to populate available models for expressing the particle number, surface area, and dissolved fraction. Results indicate that the acute toxicity of the tested silver nanoparticles is best expressed by ion release, and is relatable to total exposed surface area. Particle number was not relatable to the observed acute silver nanoparticle effects.

Progress and future of in vitro models to study translocation of nanoparticles

The increasing use of nanoparticles in products likely results in increased exposure of both workers and consumers. Because of their small size, there are concerns that nanoparticles unintentionally cross the barriers of the human body. Several in vivo rodent studies show that, dependent on the exposure route, time, and concentration, and their characteristics, nanoparticles can cross the lung, gut, skin, and placental barrier. This review aims to evaluate the performance of in vitro models that mimic the barriers of the human body, with a focus on the lung, gut, skin, and placental barrier. For these barriers, in vitro models of varying complexity are available, ranging from single-cell-type monolayer to multi-cell (3D) models. Only a few studies are available that allow comparison of the in vitro translocation to in vivo data. This situation could change since the availability of analytical detection techniques is no longer a limiting factor for this comparison. We conclude that to further develop in vitro models to be used in risk assessment, the current strategy to improve the models to more closely mimic the human situation by using co-cultures of different cell types and microfluidic approaches to better control the tissue microenvironments are essential. At the current state of the art, the in vitro models do not yet allow prediction of absolute transfer rates but they do support the definition of relative transfer rates and can thus help to reduce animal testing by setting priorities for subsequent in vivo testing.

Adapting OECD Aquatic Toxicity Tests for Use with Manufactured Nanomaterials: Key Issues and Consensus Recommendations

The unique or enhanced properties of manufactured nanomaterials (MNs) suggest that their use in nanoenabled products will continue to increase. This will result in increased potential for human and environmental exposure to MNs during manufacturing, use, and disposal of nanoenabled products. Scientifically based risk assessment for MNs necessitates the development of reproducible, standardized hazard testing methods such as those provided by the Organisation of Economic Cooperation and Development (OECD). Currently, there is no comprehensive guidance on how best to address testing issues specific to MN particulate, fibrous, or colloidal properties. This paper summarizes the findings from an expert workshop convened to develop a guidance document that addresses the difficulties encountered when testing MNs using OECD aquatic and sediment test guidelines. Critical components were identified by workshop participants that require specific guidance for MN testing: preparation of dispersions, dose metrics, the importance and challenges associated with maintaining and monitoring exposure levels, and the need for reliable methods to quantify MNs in complex media. To facilitate a scientific advance in the consistency of nanoecotoxicology test results, we identify and discuss critical considerations where expert consensus recommendations were and were not achieved and provide specific research recommendations to resolve issues for which consensus was not reached. This process will enable the development of prescriptive testing guidance for MNs. Critically, we highlight the need to quantify and properly interpret and express exposure during the bioassays used to determine hazard values.

Particle size dependent deposition and pulmonary inflammation after short-term inhalation of silver nanoparticles

Background

Although silver nanoparticles are currently used in more than 400 consumer products, it is not clear to what extent they induce adverse effects after inhalation during production and use. In this study, we determined the lung burden, tissue distribution, and the induction and recovery of adverse effects after short-term inhalation exposure to 15 nm and 410 nm silver nanoparticles.

Methods

Rats were nose-only exposed to clean air, 15 nm silver nanoparticles (179 μg/m³) or 410 nm silver particles (167 μg/m³) 6 hours per day, for four consecutive days. Tissue distribution and the induction of pulmonary toxicity were determined at 24 hours and 7 days after exposure and compared with the internal alveolar dose. Presence of silver nanoparticles in lung cells was visualized by transmission electron microscopy (TEM).

Results

Exposure to 15 nm silver nanoparticles induced moderate pulmonary toxicity compared to the controls, indicated by a 175-fold increased influx of neutrophils in the lungs, a doubling of cellular damage markers in the lungs, a 5-fold increase in pro-inflammatory cytokines, and a 1.5-fold increase in total glutathione at 24 hours after exposure. All the observed effects disappeared at 7 days after exposure. No effects were observed after exposure to 410 nm silver particles. The internal alveolar mass dose of the 15 nm nanoparticles was 3.5 times higher compared to the 410 nm particles, which equals to a 66,000 times higher particle number. TEM analysis revealed 15 nm nanoparticles in vesicles and nuclei of lung cells, which were decreased in size to <5 nm at 24 hours after exposure. This demonstrates substantial dissolution of the silver nanoparticles.

Conclusion

The results show a clear size-dependent effect after inhalation of similar mass concentrations of 15 nm and 410 nm silver (nano)particles. This can be partially explained by the difference in the internal alveolar dose between the 15 nm and 410 nm silver (nano)particles as well as by a difference in the release rate of silver ions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-014-0049-1) contains supplementary material, which is available to authorized users.

Engineered nanoparticles. How brain friendly is this new guest?

In the last 30 years, the use of engineered nanoparticles (NPs) has progressively increased in many industrial and medical applications. In therapy, NPs may allow more effective cellular and subcellular targeting of drugs. In diagnostic applications, quantum dots are exploited for their optical characteristics, while superparamagnetic iron oxides NPs are used in magnetic resonance imaging. NPs are used in semiconductors, packaging, textiles, solar cells, batteries and plastic materials. Despite the great progress in nanotechnologies, comparatively little is known to date on the effects that exposure to NPs may have on the human body, in general and specifically on the brain. NPs can enter the human body through skin, digestive tract, airways and blood and they may cross the blood-brain barrier to reach the central nervous system. In addition to the paucity of studies describing NP effects on brain function, some of them also suffer of insufficient NPs characterization, inadequate standardization of conditions and lack of contaminant evaluation, so that results from different studies can hardly be compared. It has been shown in vitro and in vivo in rodents that NPs can impair dopaminergic and serotoninergic systems. Changes of neuronal morphology and neuronal death were reported in mice treated with NPs. NPs can also affect the respiratory chain of mitochondria and Bax protein levels, thereby causing apoptosis. Changes in expression of genes involved in redox pathways in mouse brain regions were described. NPs can induce autophagy, and accumulate in lysosomes impairing their degradation capacity. Cytoskeleton and vesicle trafficking may also be affected. NPs treated animals showed neuroinflammation with microglia activation, which could induce neurodegeneration. Considering the available data, it is important to design adequate models and experimental systems to evaluate in a reliable and controlled fashion the effects of NPs on the brain, and generate data representative of effects on the human brain, thereby useful for developing robust and valid nanosafety standards.

Physicochemical characteristics of nanomaterials that affect pulmonary inflammation

The increasing manufacture and use of products based on nanotechnology raises concerns for both workers and consumers. Various studies report induction of pulmonary inflammation after inhalation exposure to nanoparticles, which can vary in aspects such as size, shape, charge, crystallinity, chemical composition, and dissolution rate. Each of these aspects can affect their toxicity, although it is largely unknown to what extent. The aim of the current review is to analyse published data on inhalation of nanoparticles to identify and evaluate the contribution of their physicochemical characteristics to the onset and development of pulmonary inflammation. Many physicochemical characteristics of nanoparticles affect their lung deposition, clearance, and pulmonary response that, in combination, ultimately determine whether pulmonary inflammation will occur and to what extent. Lung deposition is mainly determined by the physical properties of the aerosol (size, density, shape, hygroscopicity) in relation to airflow and the anatomy of the respiratory system, whereas clearance and translocation of nanoparticles are mainly determined by their geometry and surface characteristics. Besides size and chemical composition, other physicochemical characteristics influence the induction of pulmonary inflammation after inhalation. As some nanoparticles dissolve, they can release toxic ions that can damage the lung tissue, making dissolution rate an important characteristic that affects lung inflammation. Fibre-shaped materials are more toxic to the lungs compared to spherical shaped nanoparticles of the same chemical composition. In general, cationic nanoparticles are more cytotoxic than neutral or anionic nanoparticles. Finally, surface reactivity correlates well with observed pulmonary inflammation. With all these characteristics affecting different stages of the events leading to pulmonary inflammation, no unifying dose metric could be identified to describe pulmonary inflammation for all nanomaterials, although surface reactivity might be a useful measure. To determine the extent to which the various characteristics influence the induction of pulmonary inflammation, the effect of these characteristics on lung deposition, clearance, and pulmonary response should be systematically evaluated. The results can then be used to facilitate risk assessment by categorizing nanoparticles according to their characteristics.

Integrating health on air quality assessment--review report on health risks of two major European outdoor air pollutants: PM and NO₂

Quantifying the impact of air pollution on the public's health has become an increasingly critical component in policy discussion. Recent data indicate that more than 70% of the world population lives in cities. Several studies reported that current levels of air pollutants in urban areas are associated with adverse health risks, namely, cardiovascular diseases and lung cancer. IARC recently classified outdoor air pollution and related particulate matter (PM) as carcinogenic to humans. Despite the air quality improvements observed over the last few years, there is still continued widespread exceedance within Europe, particularly regarding PM and nitrogen oxides (NOx). The European Air Quality Directive 2008/50/EC requires Member States to design appropriate air quality plans for zones where air quality does not comply with established limit values. However, in most cases, air quality is only quantified using a combination of monitored and modeled data and no health impact assessment is carried out. An integrated approach combining the effects of several emission abatement measures on air quality, impacts on human health, and associated implementation costs enables an effective cost-benefit analysis and an added value to the decision-making process. Hence, this review describes the basic steps and tools for integrating health into air quality assessment (health indicators, exposure-response functions). In addition, consideration is given to two major outdoor pollutants: PM and NO2. A summary of the health metrics used to assess the health impact of PM and NO2 and recent epidemiologic data are also described.

The outdoor air pollution and brain health workshop

Accumulating evidence suggests that outdoor air pollution may have a significant impact on central nervous system (CNS) health and disease. To address this issue, the National Institute of Environmental Health Sciences/National Institute of Health convened a panel of research scientists that was assigned the task of identifying research gaps and priority goals essential for advancing this growing field and addressing an emerging human health concern. Here, we review recent findings that have established the effects of inhaled air pollutants in the brain, explore the potential mechanisms driving these phenomena, and discuss the recommended research priorities/approaches that were identified by the panel.

Toxicological properties of emission particles from heavy duty engines powered by conventional and bio-based diesel fuels and compressed natural gas

Background

One of the major areas for increasing the use of renewable energy is in traffic fuels e.g. bio-based fuels in diesel engines especially in commuter traffic. Exhaust emissions from fossil diesel fuelled engines are known to cause adverse effects on human health, but there is very limited information available on how the new renewable fuels may change the harmfulness of the emissions, especially particles (PM). We evaluated the PM emissions from a heavy-duty EURO IV diesel engine powered by three different fuels; the toxicological properties of the emitted PM were investigated. Conventional diesel fuel (EN590) and two biodiesels were used − rapeseed methyl ester (RME, EN14214) and hydrotreated vegetable oil (HVO) either as such or as 30% blends with EN590. EN590 and 100% HVO were also operated with or without an oxidative catalyst (DOC + POC). A bus powered by compressed natural gas (CNG) was included for comparison with the liquid fuels. However, the results from CNG powered bus cannot be directly compared to the other situations in this study.

Results

High volume PM samples were collected on PTFE filters from a constant volume dilution tunnel. The PM mass emission with HVO was smaller and with RME larger than that with EN590, but both biofuels produced lower PAH contents in emission PM. The DOC + POC catalyst greatly reduced the PM emission and PAH content in PM with both HVO and EN590. Dose-dependent TNFα and MIP-2 responses to all PM samples were mostly at the low or moderate level after 24-hour exposure in a mouse macrophage cell line RAW 264.7. Emission PM from situations with the smallest mass emissions (HVO + cat and CNG) displayed the strongest potency in MIP-2 production. The catalyst slightly decreased the PM-induced TNFα responses and somewhat increased the MIP-2 responses with HVO fuel. Emission PM with EN590 and with 30% HVO blended in EN590 induced the strongest genotoxic responses, which were significantly greater than those with EN590 + cat or 100% HVO. The emission PM sample from the CNG bus possessed the weakest genotoxic potency but had the strongest oxidative potency of all the fuel and catalyst combinations. The use of 100% HVO fuel had slightly weaker and 100% RME somewhat stronger emission PM induced ROS production, when compared to EN590.

Conclusions

The harmfulness of the exhaust emissions from vehicle engines cannot be determined merely on basis of the emitted PM mass. The study conditions and the engine type significantly affect the toxicity of the emitted particles. The selected fuels and DOC + POC catalyst affected the PM emission from the heavy EURO IV engine both qualitative and quantitative ways, which influenced their toxicological characteristics. The plain HVO fuel performed very well in emission reduction and in lowering the overall toxicity of emitted PM, but the 30% blend of HVO in EN590 was no better in this respect than the plain EN590. The HVO with a DOC + POC catalyst in the EURO IV engine, performed best with regard to changes in exhaust emissions. However some of the toxicological parameters were significantly increased even with these low emissions.

In silico models of aerosol delivery to the respiratory tract - development and applications

This review discusses the application of computational models to simulate the transport and deposition of inhaled pharmaceutical aerosols from the site of particle or droplet formation to deposition within the respiratory tract. Traditional one-dimensional (1-D) whole-lung models are discussed briefly followed by a more in-depth review of three-dimensional (3-D) computational fluid dynamics (CFD) simulations. The review of CFD models is organized into sections covering transport and deposition within the inhaler device, the extrathoracic (oral and nasal) region, conducting airways, and alveolar space. For each section, a general review of significant contributions and advancements in the area of simulating pharmaceutical aerosols is provided followed by a more in-depth application or case study that highlights the challenges, utility, and benefits of in silico models. Specific applications presented include the optimization of an existing spray inhaler, development of charge-targeted delivery, specification of conditions for optimal nasal delivery, analysis of a new condensational delivery approach, and an evaluation of targeted delivery using magnetic aerosols. The review concludes with recommendations on the need for more refined model validations, use of a concurrent experimental and CFD approach for developing aerosol delivery systems, and development of a stochastic individual path (SIP) model of aerosol transport and deposition throughout the respiratory tract.

The adverse effects of air pollution on the nervous system

Exposure to ambient air pollution is a serious and common public health concern associated with growing morbidity and mortality worldwide. In the last decades, the adverse effects of air pollution on the pulmonary and cardiovascular systems have been well established in a series of major epidemiological and observational studies. In the recent past, air pollution has also been associated with diseases of the central nervous system (CNS), including stroke, Alzheimer's disease, Parkinson's disease, and neurodevelopmental disorders. It has been demonstrated that various components of air pollution, such as nanosized particles, can easily translocate to the CNS where they can activate innate immune responses. Furthermore, systemic inflammation arising from the pulmonary or cardiovascular system can affect CNS health. Despite intense studies on the health effects of ambient air pollution, the underlying molecular mechanisms of susceptibility and disease remain largely elusive. However, emerging evidence suggests that air pollution-induced neuroinflammation, oxidative stress, microglial activation, cerebrovascular dysfunction, and alterations in the blood-brain barrier contribute to CNS pathology. A better understanding of the mediators and mechanisms will enable the development of new strategies to protect individuals at risk and to reduce detrimental effects of air pollution on the nervous system and mental health.

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.