Publications by authors named "Kenneth G Sexton"

23 Publications

  • Page 1 of 1

Identifying the Transcriptional Response of Cancer and Inflammation-Related Genes in Lung Cells in Relation to Ambient Air Chemical Mixtures in Houston, Texas.

Environ Sci Technol 2020 11 16;54(21):13807-13816. Epub 2020 Oct 16.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.

Atmospheric pollution represents a complex mixture of air chemicals that continually interact and transform, making it difficult to accurately evaluate associated toxicity responses representative of real-world exposure. This study leveraged data from a previously published article and reevaluated lung cell transcriptional response induced by outdoor atmospheric pollution mixtures using field-based exposure conditions in the industrialized Houston Ship Channel. The tested hypothesis was that individual and co-occurring chemicals in the atmosphere relate to altered expression of critical genes involved in inflammation and cancer-related processes in lung cells. Human lung cells were exposed at an air-liquid interface to ambient air mixtures for 4 h, with experiments replicated across 5 days. Real-time monitoring of primary and secondary gas-phase pollutants, as well as other atmospheric conditions, was simultaneously conducted. Transcriptional analysis of exposed cells identified critical genes showing differential expression associated with both individual and chemical mixtures. The individual pollutant identified with the largest amount of associated transcriptional response was benzene. Tumor necrosis factor () and interferon regulatory factor 1 () were identified as key upstream transcription factor regulators of the cellular response to benzene. This study is among the first to measure lung cell transcriptional responses in relation to real-world, gas-phase air mixtures.
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http://dx.doi.org/10.1021/acs.est.0c02250DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7757424PMC
November 2020

Cardiovascular effects of diesel exhaust inhalation: photochemically altered versus freshly emitted in mice.

J Toxicol Environ Health A 2019 29;82(17):944-955. Epub 2019 Sep 29.

Department of Environmental Sciences and Engineering, Gilling's School of Global Public Health, University of North Carolina at Chapel Hill , Chapel Hill , NC , USA.

This study was designed to compare the cardiovascular effects of inhaled photochemically altered diesel exhaust (aged DE) to freshly emitted DE (fresh DE) in female C57Bl/6 mice. Mice were exposed to either fresh DE, aged DE, or filtered air (FA) for 4 hr using an environmental irradiation chamber. Cardiac responses were assessed 8 hr after exposure utilizing Langendorff preparation with a protocol consisting of 20 min of perfusion and 20 min of ischemia followed by 2 hr of reperfusion. Cardiac function was measured by indices of left-ventricular-developed pressure (LVDP) and contractility (dP/dt) prior to ischemia. Recovery of post-ischemic LVDP was examined on reperfusion following ischemia. Fresh DE contained 460 µg/m of particulate matter (PM), 0.29 ppm of nitrogen dioxide (NO) and no ozone (O), while aged DE consisted of 330 µg/m of PM, 0.23 ppm O and no NO. Fresh DE significantly decreased LVDP, dP/dt, and dP/dt compared to FA. Aged DE also significantly reduced LVDP and dP/dt. Data demonstrated that acute inhalation to either fresh or aged DE lowered LVDP and dP/dt, with a greater fall noted with fresh DE, suggesting that the composition of DE may play a key role in DE-induced adverse cardiovascular effects in female C57Bl/6 mice.
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http://dx.doi.org/10.1080/15287394.2019.1671278DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7308149PMC
May 2020

Photochemical Cloud Processing of Primary Wildfire Emissions as a Potential Source of Secondary Organic Aerosol.

Environ Sci Technol 2018 10 11;52(19):11027-11037. Epub 2018 Sep 11.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States.

We investigated the gas-phase chemical composition of biomass burning (BB) emissions and their role in aqueous secondary organic aerosol (aqSOA) formation through photochemical cloud processing. A high-resolution time-of-flight chemical ionization mass spectrometer using iodide reagent ion chemistry detected more than 100 gas-phase compounds from the emissions of 30 different controlled burns during the 2016 Fire Influence on Regional and Global Environments Experiment (FIREX) at the Fire Science Laboratory. Compounds likely to partition to cloudwater were selected based on high atomic oxygen-to-carbon ratio and abundance. Water solubility was confirmed by detection of these compounds in water after mist chamber collection during controlled burns and analysis using ion chromatography and electrospray ionization interfaced to high-resolution time-of-flight mass spectrometry. Known precursors of aqSOA were found in the primary gaseous BB emissions (e.g., phenols, acetate, and pyruvate). Aqueous OH oxidation of the complex biomass burning mixtures led to rapid depletion of many compounds (e.g., catechol, levoglucosan, methoxyphenol) and formation of others (e.g., oxalate, malonate, mesoxalate). After 150 min of oxidation (approximatively 1 day of cloud processing), oxalate accounted for 13-16% of total dissolved organic carbon. Formation of known SOA components suggests that cloud processing of primary BB emissions forms SOA.
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http://dx.doi.org/10.1021/acs.est.8b03293DOI Listing
October 2018

Occurrence of Staphylococcus aureus in swine and swine workplace environments on industrial and antibiotic-free hog operations in North Carolina, USA: A One Health pilot study.

Environ Res 2018 05 22;163:88-96. Epub 2018 Feb 22.

Department of Environmental Health and Engineering, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA; Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA; Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA. Electronic address:

Occupational exposure to swine has been associated with increased Staphylococcus aureus carriage, including antimicrobial-resistant strains, and increased risk of infections. To characterize animal and environmental routes of worker exposure, we optimized methods to identify S. aureus on operations that raise swine in confinement with antibiotics (industrial hog operation: IHO) versus on pasture without antibiotics (antibiotic-free hog operation: AFHO). We associated findings from tested swine and environmental samples with those from personal inhalable air samplers on worker surrogates at one IHO and three AFHOs in North Carolina using a new One Health approach. We determined swine S. aureus carriage status by collecting swab samples from multiple anatomical sites, and we determined environmental positivity for airborne bioaerosols with inhalable and impinger samplers and a single-stage impactor (ambient air) cross-sectionally. All samples were analyzed for S. aureus, and isolates were tested for antimicrobial susceptibility, absence of scn (livestock marker), and spa type. Seventeen of twenty (85%) swine sampled at the one IHO carried S. aureus at >1 anatomical sites compared to none of 30 (0%) swine sampled at the three AFHOs. All S. aureus isolates recovered from IHO swine and air samples were scn negative and spa type t337; almost all isolates (62/63) were multidrug resistant. S. aureus was recovered from eight of 14 (67%) ambient air and two (100%) worker surrogate personal air samples at the one IHO, whereas no S. aureus isolates were recovered from 19 ambient and six personal air samples at the three AFHOs. Personal worker surrogate inhalable sample findings were consistent with both swine and ambient air data, indicating the potential for workplace exposure. IHO swine and the one IHO environment could be a source of potential pathogen exposure to workers, as supported by the detection of multidrug-resistant S. aureus (MDRSA) with livestock-associated spa type t337 among swine, worker surrogate personal air samplers and environmental air samples at the one IHO but none of the three AFHOs sampled in this study. Concurrent sampling of swine, personal swine worker surrogate air, and ambient airborne dust demonstrated that IHO workers may be exposed through both direct (animal contact) and indirect (airborne) routes of transmission. Investigation of the effectiveness of contact and respiratory protections is warranted to prevent IHO worker exposure to multidrug-resistant livestock-associated S. aureus and other pathogens.
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http://dx.doi.org/10.1016/j.envres.2017.12.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6292733PMC
May 2018

Effect of secondary organic aerosol from isoprene-derived hydroxyhydroperoxides on the expression of oxidative stress response genes in human bronchial epithelial cells.

Environ Sci Process Impacts 2018 Feb;20(2):332-339

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.

Isoprene-derived secondary organic aerosol (SOA), which comprise a large portion of atmospheric fine particulate matter (PM), can be formed through various gaseous precursors, including isoprene epoxydiols (IEPOX), methacrylic acid epoxide (MAE), and isoprene hydroxyhydroperoxides (ISOPOOH). The composition of the isoprene-derived SOA affects its reactive oxygen species (ROS) generation potential and its ability to alter oxidative stress-related gene expression. In this study we assess effects of isoprene SOA derived solely from ISOPOOH oxidation on human bronchial epithelial cells by measuring the gene expression changes in 84 oxidative stress-related genes. In addition, the thiol reactivity of ISOPOOH-derived SOA was measured through the dithiothreitol (DTT) assay. Our findings show that ISOPOOH-derived SOA alter more oxidative-stress related genes than IEPOX-derived SOA but not as many as MAE-derived SOA on a mass basis exposure. More importantly, we found that the different types of SOA derived from the various gaseous precursors (MAE, IEPOX, and ISOPOOH) have unique contributions to changes in oxidative stress-related genes that do not total all gene expression changes seen in exposures to atmospherically relevant compositions of total isoprene-derived SOA mixtures. This study suggests that amongst the different types of known isoprene-derived SOA, MAE-derived SOA are the most potent inducer of oxidative stress-related gene changes but highlights the importance of considering isoprene-derived SOA as a total mixture for pollution controls and exposure studies.
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http://dx.doi.org/10.1039/c7em00439gDOI Listing
February 2018

Variation in DNA-Damage Responses to an Inhalational Carcinogen (1,3-Butadiene) in Relation to Strain-Specific Differences in Chromatin Accessibility and Gene Transcription Profiles in C57BL/6J and CAST/EiJ Mice.

Environ Health Perspect 2017 10 16;125(10):107006. Epub 2017 Oct 16.

Department of Genetics, University of North Carolina , Chapel Hill, North Carolina, USA.

Background: The damaging effects of exposure to environmental toxicants differentially affect genetically distinct individuals, but the mechanisms contributing to these differences are poorly understood. Genetic variation affects the establishment of the gene regulatory landscape and thus gene expression, and we hypothesized that this contributes to the observed heterogeneity in individual responses to exogenous cellular insults.

Objectives: We performed an study of how genetic variation and chromatin organization may dictate susceptibility to DNA damage, and influence the cellular response to such damage, caused by an environmental toxicant.

Materials And Methods: We measured DNA damage, messenger RNA (mRNA) and microRNA (miRNA) expression, and genome-wide chromatin accessibility in lung tissue from two genetically divergent inbred mouse strains, C57BL/6J and CAST/EiJ, both in unexposed mice and in mice exposed to a model DNA-damaging chemical, 1,3-butadiene.

Results: Our results showed that unexposed CAST/EiJ and C57BL/6J mice have very different chromatin organization and transcription profiles in the lung. Importantly, in unexposed CAST/EiJ mice, which acquired relatively less 1,3-butadiene-induced DNA damage, we observed increased transcription and a more accessible chromatin landscape around genes involved in detoxification pathways. Upon chemical exposure, chromatin was significantly remodeled in the lung of C57BL/6J mice, a strain that acquired higher levels of 1,3-butadiene-induced DNA damage, around the same genes, ultimately resembling the molecular profile of CAST/EiJ.

Conclusions: These results suggest that strain-specific changes in chromatin and transcription in response to chemical exposure lead to a "compensation" for underlying genetic-driven interindividual differences in the baseline chromatin and transcriptional state. This work represents an example of how chemical and environmental exposures can be evaluated to better understand gene-by-environment interactions, and it demonstrates the important role of chromatin response in transcriptomic changes and, potentially, in deleterious effects of exposure. https://doi.org/10.1289/EHP1937.
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http://dx.doi.org/10.1289/EHP1937DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5944832PMC
October 2017

Gene Expression Profiling in Human Lung Cells Exposed to Isoprene-Derived Secondary Organic Aerosol.

Environ Sci Technol 2017 Jul 5;51(14):8166-8175. Epub 2017 Jul 5.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, ‡Center for Environmental Medicine, Asthma and Lung Biology, School of Medicine, and §Department of Pediatrics, School of Medicine, The University of North Carolina , Chapel Hill, North Carolina 27599, United States.

Secondary organic aerosol (SOA) derived from the photochemical oxidation of isoprene contributes a substantial mass fraction to atmospheric fine particulate matter (PM). The formation of isoprene SOA is influenced largely by anthropogenic emissions through multiphase chemistry of its multigenerational oxidation products. Considering the abundance of isoprene SOA in the troposphere, understanding mechanisms of adverse health effects through inhalation exposure is critical to mitigating its potential impact on public health. In this study, we assessed the effects of isoprene SOA on gene expression in human airway epithelial cells (BEAS-2B) through an air-liquid interface exposure. Gene expression profiling of 84 oxidative stress and 249 inflammation-associated human genes was performed. Our results show that the expression levels of 29 genes were significantly altered upon isoprene SOA exposure under noncytotoxic conditions (p < 0.05), with the majority (22/29) of genes passing a false discovery rate threshold of 0.3. The most significantly affected genes belong to the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) transcription factor network. The Nrf2 function is confirmed through a reporter cell line. Together with detailed characterization of SOA constituents, this study reveals the impact of isoprene SOA exposure on lung responses and highlights the importance of further understanding its potential health outcomes.
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http://dx.doi.org/10.1021/acs.est.7b01967DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5610912PMC
July 2017

Assessment of biological responses of EpiAirway 3-D cell constructs versus A549 cells for determining toxicity of ambient air pollution.

Inhal Toxicol 2016 ;28(6):251-9

a Department of Environmental Sciences & Engineering , University of North Carolina at Chapel Hill , Chapel Hill , NC, USA .

Context: EpiAirway™ 3-D constructs are human-derived cell cultures of differentiated airway epithelial cells that may represent a more biologically relevant model of the human lung. However, limited information is available on their utility for exposures to air pollutants at the air-liquid interface (ALI).

Objective: To assess the biological responses of EpiAirway™ cells in comparison to the responses of A549 human alveolar epithelial cells after exposure to air pollutants at ALI.

Methods: Cells were exposed to filtered air, 400 ppb of ozone (O3) or a photochemically aged Synthetic Urban Mixture (SynUrb54) consisting of hydrocarbons, nitrogen oxides, O3 and other secondary oxidation products for 4 h. Basolateral supernatants and apical washes were collected at 9 and 24 h post-exposure. We assessed cytotoxicity by measuring lactate dehydrogenase (LDH) release into the culture medium and apical surface. Interleukin 6 (IL-6) and interleukin 8 (IL-8) proteins were measured in the culture medium and in the apical washes to determine the inflammatory response after exposure.

Results: Both O3 and SynUrb54 significantly increased basolateral levels of LDH and IL-8 in A549 cells. No significant changes in LDH and IL-8 levels were observed in the EpiAirway™ cells, however, IL-6 in the apical surface was significantly elevated at 24 h after O3 exposure.

Conclusion: LDH and IL-8 are robust endpoints for assessing toxicity in A549 cells. The EpiAirway™ cells show minimal adverse effects after exposure suggesting that they are more toxicologically resistant compared to A549 cells. Higher concentrations or longer exposure times are needed to induce effects on EpiAirway™ cells.
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http://dx.doi.org/10.3109/08958378.2016.1157227DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4913276PMC
January 2017

From the Field to the Laboratory: Air Pollutant-Induced Genomic Effects in Lung Cells.

Environ Health Insights 2015 18;9(Suppl 4):15-23. Epub 2016 Feb 18.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.

Current in vitro studies do not typically assess cellular impacts in relation to real-world atmospheric mixtures of gases. In this study, we set out to examine the feasibility of measuring biological responses at the level of gene expression in human lung cells upon direct exposures to air in the field. This study describes the successful deployment of lung cells in the heavily industrialized Houston Ship Channel. By examining messenger RNA (mRNA) levels from exposed lung cells, we identified changes in genes that play a role as inflammatory responders in the cell. The results show anticipated responses from negative and positive controls, confirming the integrity of the experimental protocol and the successful deployment of the in vitro instrument. Furthermore, exposures to ambient conditions displayed robust changes in gene expression. These results demonstrate a methodology that can produce gas-phase toxicity data in the field.
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http://dx.doi.org/10.4137/EHI.S15656DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4760675PMC
February 2016

Cellular RNA is chemically modified by exposure to air pollution mixtures.

Inhal Toxicol 2015 Jan;27(1):74-82

McKetta Department of Chemical Engineering, The University of Texas at Austin , Austin TX , USA and.

RNAs are more susceptible to modifications than DNA, and chemical modifications in RNA have an effect on their structure and function. This study aimed to characterize chemical effects on total RNA in human A549 lung cells after exposure to elevated levels of major secondary air pollutants commonly found in urban locations, including ozone (O3), acrolein (ACR) and methacrolein (MACR). Enzyme-linked immunosorbent assays (ELISA) were used to measure levels of interleukin (IL)-8 in the growth media and 8-oxoguanine (8OG) levels in total cellular RNA, and lactate dehydrogenase (LDH) in the growth media was measured by a coupled enzymatic assay. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to measure levels of microRNA 10b (miR-10b). The study found that 1-h exposure to all tested pollutant mixtures consistently caused significant increases in the levels of 8OG in total RNA. In the case of 4 ppm O3 exposures, measured levels of IL-8, LDH and miR-10b each showed consistent trends between two independent trials, but varied among these three targets. After 1-h exposures to an ACR+MACR mixture, measured levels of IL-8, LDH and miR-10b showed variable results. For mixtures of O3+ACR+MACR, IL-8 measurements showed no change; miR-10b and LDH showed variable results. The results indicate that short-term high-concentration exposures to air pollution can cause RNA chemical modifications. Chemical modifications in RNAs could represent more consistent markers of cellular stress relative to other inflammation markers, such as IL-8 and LDH, and provide a new biomarker endpoint for mechanistic studies in toxicity of air pollution exposure.
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http://dx.doi.org/10.3109/08958378.2014.987361DOI Listing
January 2015

Application of chemical vapor generation systems to deliver constant gas concentrations for in vitro exposure to volatile organic compounds.

Environ Sci Process Impacts 2014 Dec;16(12):2703-10

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

Exposure to volatile organic compounds from outdoor air pollution is a major public health concern; however, there is scant information about the health effects induced by inhalation exposure to photochemical transformed products of primary emissions. In this study, we present a stable and reproducible exposure method to deliver ppm-ppb levels of gaseous standards in a humidified air stream for in vitro cell exposure through a direct air-liquid interface. Gaseous species were generated from a diffusion vial, and coupled to a gas-phase in vitro exposure system. Acrolein and methacrolein, which are major first-generation photochemical transformation products of 1,3-butadiene and isoprene, respectively, were selected as model compounds. A series of vapor concentrations (0.23-2.37 ppmv for acrolein and 0.68-10.7 ppmv for methacrolein) were investigated to characterize the exposure dose-response relationships. Temperature and the inner diameter of the diffusion vials are key parameters to control the evaporation rates and diffusion rates for the delivery of target vapor concentrations. Our findings suggest that this exposure method can be used for testing a wide range of atmospheric volatile organic compounds, and permits both single compound and multiple compound sources to generate mixtures in air. The relative standard deviations (%RSD) of output concentrations were within 10% during the 4-hour exposure time. The comparative exposure-response data allow us to prioritize numerous hazardous gas phase air pollutants. These identified pollutants can be further incorporated into air quality simulation models to better characterize the environmental health risks arising from inhalation of the photochemical transformed products.
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http://dx.doi.org/10.1039/c4em00465eDOI Listing
December 2014

Epigenetic events determine tissue-specific toxicity of inhalational exposure to the genotoxic chemical 1,3-butadiene in male C57BL/6J mice.

Toxicol Sci 2014 Dec 18;142(2):375-84. Epub 2014 Sep 18.

*Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina 27599, Division of Biochemical Toxicology, National Center for Toxicological Research, FDA, Jefferson, Arkansas 72079 and Department of Medicinal Chemistry, University of Minnesota, Minneapolis, Minnesota 55455

1,3-Butadiene (BD), a widely used industrial chemical and a ubiquitous environmental pollutant, is a known human carcinogen. Although genotoxicity is an established mechanism of the tumorigenicity of BD, epigenetic effects have also been observed in livers of mice exposed to the chemical. To better characterize the diverse molecular mechanisms of BD tumorigenicity, we evaluated genotoxic and epigenotoxic effects of BD exposure in mouse tissues that are target (lung and liver) and non-target (kidney) for BD-induced tumors. We hypothesized that epigenetic alterations may explain, at least in part, the tissue-specific differences in BD tumorigenicity in mice. We evaluated the level of N-7-(2,3,4-trihydroxybut-1-yl)guanine adducts and 1,4-bis-(guan-7-yl)-2,3-butanediol crosslinks, DNA methylation, and histone modifications in male C57BL/6 mice exposed to filtered air or 425 ppm of BD by inhalation (6 h/day, 5 days/week) for 2 weeks. Although DNA damage was observed in all three tissues of BD-exposed mice, variation in epigenetic effects clearly existed between the kidneys, liver, and lungs. Epigenetic alterations indicative of genomic instability, including demethylation of repetitive DNA sequences and alterations in histone-lysine acetylation, were evident in the liver and lung tissues of BD-exposed mice. Changes in DNA methylation were insignificant in the kidneys of treated mice, whereas marks of condensed heterochromatin and transcriptional silencing (histone-lysine trimethylation) were increased. These modifications may represent a potential mechanistic explanation for the lack of tumorigenesis in the kidney. Our results indicate that differential tissue susceptibility to chemical-induced tumorigenesis may be attributed to tissue-specific epigenetic alterations.
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http://dx.doi.org/10.1093/toxsci/kfu191DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4250847PMC
December 2014

The Gillings Sampler--an electrostatic air sampler as an alternative method for aerosol in vitro exposure studies.

Chem Biol Interact 2014 Sep 7;220:158-68. Epub 2014 Jul 7.

Department of Environmental Sciences & Engineering, University of North Carolina at Chapel Hill, United States. Electronic address:

There is growing interest in studying the toxicity and health risk of exposure to multi-pollutant mixtures found in ambient air, and the U.S. Environmental Protection Agency (EPA) is moving towards setting standards for these types of mixtures. Additionally, the Health Effects Institute's strategic plan aims to develop and apply next-generation multi-pollutant approaches to understanding the health effects of air pollutants. There's increasing concern that conventional in vitro exposure methods are not adequate to meet EPA's strategic plan to demonstrate a direct link between air pollution and health effects. To meet the demand for new in vitro technology that better represents direct air-to-cell inhalation exposures, a new system that exposes cells at the air-liquid interface was developed. This new system, named the Gillings Sampler, is a modified two-stage electrostatic precipitator that provides a viable environment for cultured cells. Polystyrene latex spheres were used to determine deposition efficiencies (38-45%), while microscopy and imaging techniques were used to confirm uniform particle deposition. Negative control A549 cell exposures indicated the sampler can be operated for up to 4h without inducing any significant toxic effects on cells, as measured by lactate dehydrogenase (LDH) and interleukin-8 (IL-8). A novel positive aerosol control exposure method, consisting of a p-tolualdehyde (TOLALD) impregnated mineral oil aerosol (MOA), was developed to test this system. Exposures to the toxic MOA at a 1 ng/cm(2) dose of TOLALD yielded a reproducible 1.4 and 2-fold increase in LDH and IL-8 mRNA levels over controls. This new system is intended to be used as an alternative research tool for aerosol in vitro exposure studies. While further testing and optimization is still required to produce a "commercially ready" system, it serves as a stepping-stone in the development of cost-effective in vitro technology that can be made accessible to researchers in the near future.
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http://dx.doi.org/10.1016/j.cbi.2014.06.026DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4252865PMC
September 2014

Photochemically altered air pollution mixtures and contractile parameters in isolated murine hearts before and after ischemia.

Environ Health Perspect 2013 Nov-Dec;121(11-12):1344-8. Epub 2013 Oct 22.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.

Background: The cardiopulmonary effects of the individual criteria air pollutants have been well investigated, but little is known about the cardiopulmonary effects of inhaled multipollutant mixtures that more realistically represent environmental exposures.

Objectives: We assessed the cardiopulmonary effects of exposure to photochemically altered particle-free multipollutant mixtures.

Methods: We exposed mice to filtered air (FA), multipollutant mixtures, or ozone (O3) for 4 hr in a photochemical reaction chamber. Eight hours after exposure, we assessed cardiac responses using a Langendorff preparation in a protocol consisting of 20 min of global ischemia followed by 2 hr of reperfusion. Cardiac function was assessed by measuring the index of left-ventricular developed pressure (LVDP) and contractility (dP/dt) before ischemia. On reperfusion after ischemia, recovery of postischemic LVDP and size of infarct were examined. We used bronchoalveolar lavage (BAL) cell counts to assess lung inflammation.

Results: Exposure to the multipollutant mixtures decreased LVDP, baseline rate of left ventricular contraction (dP/dtmaximum), and baseline rate of left ventricular relaxation (dP/dtminimum) compared with exposure to FA. Exposure to O3 also decreased heart rate and dP/dtminimum. Time to ischemic contracture was prolonged in the multipollutant-mixture group relative to that in the FA group. Mice in the multipollutant-mixture group had better recovery of postischemic LVDP and smaller infarct size. Exposure to multipollutant mixtures and to O3 exposure increased numbers of macrophages in the BAL fluid.

Conclusions: Exposure to photochemically altered urban air pollution appears to affect cardiac mechanics in isolated perfused hearts. Inhalation of acute multipollutant mixtures decreases LVDP and cardiac contractility in isolated non-ischemic murine hearts, prolongs ischemic contracture, increases postischemic recovery of LVDP, and reduces infarct size.
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http://dx.doi.org/10.1289/ehp.1306609DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3855513PMC
July 2014

Hazard assessment of United Arab Emirates (UAE) incense smoke.

Sci Total Environ 2013 Aug 4;458-460:176-86. Epub 2013 May 4.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7431, USA.

Incense burning inside the home, a common practice in Arabian Gulf countries, has been recognized as a potentially modifiable source of indoor air pollution. To better understand potential adverse effects of incense burning in exposed individuals, we conducted a hazard assessment of incense smoke exposure. The goals of this study were first to characterize the particles and gases emitted from Arabian incense over time when burned, and secondly to examine in vitro human lung cells responses to incense smoke. Two types of incense (from the United Arab Emirates) were burned in a specially designed indoor environmental chamber (22 m(3)) to simulate the smoke concentration in a typical living room and the chamber air was analyzed. Both particulate (PM) concentrations and sizes were measured, as were gases carbon monoxide (CO), sulfur dioxide (SO2), oxides of nitrogen (NOx), formaldehyde (HCHO), and carbonyls. During the burn, peak concentrations were recorded for PM (1.42 mg/m(3)), CO (122 pm), NOx (0.3 ppm), and HCHO (85 ppb) along with pentanal (71.9 μg/m(3)), glyoxal (84.8 μg/m(3)), and several other carbonyls. Particle sizes ranged from 20 to 300 nm with count median diameters ranging from 65 to 92 nm depending on time post burn-out. PM, CO, and NOx time-weighted averages exceeded current government regulation values and emissions seen previously from environmental tobacco smoke. Charcoal emissions were the main contributor to both the high CO and NOx concentrations. A significant cell inflammatory response was observed in response to smoke components formed from incense burning. Our hazard evaluation suggests that incense burning contributes to indoor air pollution and could be harmful to human health.
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http://dx.doi.org/10.1016/j.scitotenv.2013.03.101DOI Listing
August 2013

Epoxide as a precursor to secondary organic aerosol formation from isoprene photooxidation in the presence of nitrogen oxides.

Proc Natl Acad Sci U S A 2013 Apr 3;110(17):6718-23. Epub 2013 Apr 3.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

Isoprene is a substantial contributor to the global secondary organic aerosol (SOA) burden, with implications for public health and the climate system. The mechanism by which isoprene-derived SOA is formed and the influence of environmental conditions, however, remain unclear. We present evidence from controlled smog chamber experiments and field measurements that in the presence of high levels of nitrogen oxides (NO(x) = NO + NO2) typical of urban atmospheres, 2-methyloxirane-2-carboxylic acid (methacrylic acid epoxide, MAE) is a precursor to known isoprene-derived SOA tracers, and ultimately to SOA. We propose that MAE arises from decomposition of the OH adduct of methacryloylperoxynitrate (MPAN). This hypothesis is supported by the similarity of SOA constituents derived from MAE to those from photooxidation of isoprene, methacrolein, and MPAN under high-NOx conditions. Strong support is further derived from computational chemistry calculations and Community Multiscale Air Quality model simulations, yielding predictions consistent with field observations. Field measurements taken in Chapel Hill, North Carolina, considered along with the modeling results indicate the atmospheric significance and relevance of MAE chemistry across the United States, especially in urban areas heavily impacted by isoprene emissions. Identification of MAE implies a major role of atmospheric epoxides in forming SOA from isoprene photooxidation. Updating current atmospheric modeling frameworks with MAE chemistry could improve the way that SOA has been attributed to isoprene based on ambient tracer measurements, and lead to SOA parameterizations that better capture the dependency of yield on NO(x).
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http://dx.doi.org/10.1073/pnas.1221150110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637755PMC
April 2013

In vitro exposures in diesel exhaust atmospheres: resuspension of PM from filters versus direct deposition of PM from air.

Environ Sci Technol 2012 Aug 9;46(16):9062-70. Epub 2012 Aug 9.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States.

One of the most widely used in vitro particulate matter (PM) exposures methods is the collection of PM on filters, followed by resuspension in a liquid medium, with subsequent addition onto a cell culture. To avoid disruption of equilibria between gases and PM, we have developed a direct in vitro sampling and exposure method (DSEM) capable of PM-only exposures. We hypothesize that the separation of phases and post-treatment of filter-collected PM significantly modifies the toxicity of the PM compared to direct deposition, resulting in a distorted view of the potential PM health effects. Controlled test environments were created in a chamber that combined diesel exhaust with an urban-like mixture. The complex mixture was analyzed using both the DSEM and concurrently collected filter samples. The DSEM showed that PM from test atmospheres produced significant inflammatory response, while the resuspension exposures at the same exposure concentration did not. Increasing the concentration of resuspended PM sixteen times was required to yield measurable IL-8 expression. Chemical analysis of the resuspended PM indicated a total absence of carbonyl compounds compared to the test atmosphere during the direct-exposures. Therefore, collection and resuspension of PM into liquid modifies its toxicity and likely leads to underestimating toxicity.
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http://dx.doi.org/10.1021/es301431sDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3424394PMC
August 2012

A toxicogenomic comparison of primary and photochemically altered air pollutant mixtures.

Environ Health Perspect 2011 Nov 14;119(11):1583-9. Epub 2011 Jul 14.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.

Background: Air pollution contributes significantly to global increases in mortality, particularly within urban environments. Limited knowledge exists on the mechanisms underlying health effects resulting from exposure to pollutant mixtures similar to those occurring in ambient air. In order to clarify the mechanisms underlying exposure effects, toxicogenomic analyses are used to evaluate genomewide transcript responses and map these responses to molecular networks.

Objectives: We compared responses induced by exposure to primary pollutants and photochemically altered (PCA) pollutant mixtures representing urban atmospheres to test our hypothesis that exposures to PCA pollutants would show increased modulation of inflammation-associated genes and pathways relative to primary air pollutants.

Methods: We used an outdoor environmental irradiation chamber to expose human lung epithelial cells to mixtures representing either primary or PCA pollutants for 4 hr. Transcriptional changes were assessed using microarrays and confirmed using quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) on a subset of genes.

Results: We found a large difference in the cellular responses to the two pollutant exposures: Primary air pollutants altered the expression levels of 19 genes, whereas PCA pollutants altered 709 genes. Functional and molecular analyses of the altered genes revealed novel pathways, such as hepatocyte nuclear factor 4α, potentially regulating the pollutant responses. Chemical component analysis characterized and confirmed the photochemical transformation of primary air pollutants into PCA air pollutants.

Conclusions: Our study shows that the photochemical transformation of primary air pollutants produces altered mixtures that cause significantly greater biological effects than the primary pollutants themselves. These findings suggest that studying individual air pollutants or primary pollutant mixtures may greatly underestimate the adverse health effects caused by air pollution.
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http://dx.doi.org/10.1289/ehp.1003323DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3226493PMC
November 2011

Epigenetic changes induced by air toxics: formaldehyde exposure alters miRNA expression profiles in human lung cells.

Environ Health Perspect 2011 Apr 9;119(4):494-500. Epub 2010 Dec 9.

Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina 27599, USA.

Background: Exposure to formaldehyde, a known air toxic, is associated with cancer and lung disease. Despite the adverse health effects of formaldehyde, the mechanisms underlying formaldehyde-induced disease remain largely unknown. Research has uncovered microRNAs (miRNAs) as key posttranscriptional regulators of gene expression that may influence cellular disease state. Although studies have compared different miRNA expression patterns between diseased and healthy tissue, this is the first study to examine perturbations in global miRNA levels resulting from formaldehyde exposure.

Objectives: We investigated whether cellular miRNA expression profiles are modified by formaldehyde exposure to test the hypothesis that formaldehyde exposure disrupts miRNA expression levels within lung cells, representing a novel epigenetic mechanism through which formaldehyde may induce disease.

Methods: Human lung epithelial cells were grown at air-liquid interface and exposed to gaseous formaldehyde at 1 ppm for 4 hr. Small RNAs and protein were collected and analyzed for miRNA expression using microarray analysis and for interleukin (IL-8) protein levels by enzyme-linked immunosorbent assay (ELISA).

Results: Gaseous formaldehyde exposure altered the miRNA expression profiles in human lung cells. Specifically, 89 miRNAs were significantly down-regulated in formaldehyde-exposed samples versus controls. Functional and molecular network analysis of the predicted miRNA transcript targets revealed that formaldehyde exposure potentially alters signaling pathways associated with cancer, inflammatory response, and endocrine system regulation. IL-8 release increased in cells exposed to formaldehyde, and results were confirmed by real-time polymerase chain reaction.

Conclusions: Formaldehyde alters miRNA patterns that regulate gene expression, potentially leading to the initiation of a variety of diseases.
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http://dx.doi.org/10.1289/ehp.1002614DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3080931PMC
April 2011

Development and testing of a chemical mechanism for atmospheric photochemical transformations of 1,3-butadiene.

Chem Biol Interact 2007 Mar 10;166(1-3):156-62. Epub 2007 Jan 10.

CB7431, Environmental Sciences and Engineering, School of Public Health, Columbia Street, University of North Carolina, Chapel Hill, NC 27599, USA.

1,3-Butadiene (BD) in the atmosphere is a highly reactive hazardous air pollutant, which has a short lifetime and is quickly transformed to reaction products, some of which are also toxic. The ability to predict exposure to BD and its' products requires models with chemical mechanisms which can simulate these transformations. The atmospheric photochemical reactions of BD have been studied in the University of North Carolina Outdoor smog chamber, which has been used for over 30 years to test photochemical mechanisms for air quality simulation models for ozone. Experiments have been conducted under conditions of real sunlight and realistic temperature and humidity to study the transformations of BD and to develop and test chemical mechanisms for the simulation of these processes. Experimental observation of time-concentration data of BD decay and the formation of many products is compared to simulation results. This chemical mechanism can be incorporated into air quality simulation models which can be used to estimate ambient concentrations needed for exposure estimates.
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http://dx.doi.org/10.1016/j.cbi.2007.01.002DOI Listing
March 2007

Atmospheric photochemical transformations enhance 1,3-butadiene-induced inflammatory responses in human epithelial cells: The role of ozone and other photochemical degradation products.

Chem Biol Interact 2007 Mar 3;166(1-3):163-9. Epub 2006 Jun 3.

Department of Environmental Sciences and Engineering, University of North Carolina-Chapel Hill, CB #7431, Chapel Hill, NC 27599, USA.

Chemistry of hazardous air pollutants has been studied for many years, yet little is known about how these chemicals, once reacted within urban atmospheres, affect healthy and susceptible individuals. Once released into the atmosphere, 1,3-butadiene (BD) reacts with hydroxyl radicals and ozone (created by photochemical processes), to produce many identified and unidentified products. Once this transformation has occurred, the toxic potential of atmospheric pollutants such as BD in the ambient environment is currently unclear. During this study, environmental irradiation chambers (also called smog chambers), utilizing natural sunlight, were used to create photochemical transformations of BD. The smog chamber/in vitro exposure system was designed to investigate the toxicity of chemicals before and after photochemical reactions and to investigate interactions with the urban atmosphere using representative in vitro samples. In this study, we determined the relative toxicity and inflammatory gene expression induced by coupling smog chamber atmospheres with an in vitro system to expose human respiratory epithelial cells to BD, BDs photochemical degradation products, or the equivalent ozone generated within the photochemical mixture. Exposure to the photochemically generated products of BD (primarily acrolein, acetaldehyde, formaldehyde, furan and ozone) induced significant increases in cytotoxicity, IL-8, and IL-6 gene expression compared to a synthetic mixture of primary products that was created by injecting the correct concentrations of the detected products from the irradiation experiments. Interestingly, exposure to the equivalent levels of ozone generated during the photochemical transformation of BD did not induce the same level of inflammatory cytokine release for either exposure protocol, suggesting that the effects from ozone alone do not account for the entire response in the irradiation experiments. These results indicate that BDs full photochemical product generation and interactions, rather than ozone alone, must be carefully evaluated when investigating the possible adverse health effects to BD exposures. The research presented here takes into account that photochemical transformations of hazardous air pollutants (HAPs) does generate a dynamic exposure system and therefore provides a more realistic approach to estimate the toxicity of ambient air pollutants once they are released into the atmosphere.
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http://dx.doi.org/10.1016/j.cbi.2006.05.016DOI Listing
March 2007

Effects of 1,3-butadiene, isoprene, and their photochemical degradation products on human lung cells.

Environ Health Perspect 2004 Nov;112(15):1488-95

Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina, USA.

Because of potential exposure both in the workplace and from ambient air, the known carcinogen 1,3-butadiene (BD) is considered a priority hazardous air pollutant. BD and its 2-methyl analog, isoprene (ISO), are chemically similar but have very different toxicities, with ISO showing no significant carcinogenesis. Once released into the atmosphere, reactions with species induced by sunlight and nitrogen oxides convert BD and ISO into several photochemical reaction products. In this study, we determined the relative toxicity and inflammatory gene expression induced by exposure of A549 cells to BD, ISO, and their photochemical degradation products in the presence of nitric oxide. Gas chromatography and mass spectrometry analyses indicate the initial and major photochemical products produced during these experiments for BD are acrolein, acetaldehyde, and formaldehyde, and products for ISO are methacrolein, methyl vinyl ketone, and formaldehyde; both formed < 200 ppb of ozone. After exposure the cells were examined for cytotoxicity and interleukin-8 (IL-8) gene expression, as a marker for inflammation. These results indicate that although BD and ISO alone caused similar cytotoxicity and IL-8 responses compared with the air control, their photochemical products significantly enhanced cytotoxicity and IL-8 gene expression. This suggests that once ISO and BD are released into the environment, reactions occurring in the atmosphere transform these hydrocarbons into products that induce potentially greater adverse health effects than the emitted hydrocarbons by themselves. In addition, the data suggest that based on the carbon concentration or per carbon basis, biogenic ISO transforms into products with proinflammatory potential similar to that of BD products.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1247611PMC
http://dx.doi.org/10.1289/ehp.7022DOI Listing
November 2004

Photochemical products in urban mixtures enhance inflammatory responses in lung cells.

Inhal Toxicol 2004 ;16 Suppl 1:107-14

Department of Environmental Science and Engineering, University of North Carolina at Chapel Hill, 27599, USA.

Complex urban air mixtures that realistically mimic urban smog can be generated for investigating adverse health effects. "Smog chambers" have been used for over 30 yr to conduct experiments for developing and testing photochemical models that predict ambient ozone (O(3)) concentrations and aerosol chemistry. These chambers were used to generate photochemical and nonirradiated systems, which were interfaced with an in vitro exposure system to compare the inflammatory effects of complex air pollutant mixtures with and without sunlight-driven chemistry. These are preliminary experiments in a new project to study the health effects of particulate matter and associated gaseous copollutants. Briefly, two matched outdoor chambers capable of using real sunlight were utilized to generate two test atmospheres for simultaneous exposures to cultured lung cells. One chamber was used to produce a photochemically active system, which ran from sunrise to sunset, producing O(3) and the associated secondary products. A few hours after sunset, NO was added to titrate and remove completely the O(3), forming NO(2). In the second chamber, an equal amount of NO(2) and the same amount of the 55-component hydrocarbon mixture used to setup the photochemical system in the first side were injected. A549 cells, from an alveolar type II-like cell line grown on membranous support, were exposed to the photochemical mixture or the "original" NO(2)/hydrocarbon mixture for 5 h and analyzed for inflammatory response (IL-8 mRNA levels) 4 h postexposure. In addition, a variation of this experiment was conducted to compare the photochemical system producing O(3) and NO(2), with a simple mixture of only the O(3) and NO(2). Our data suggest that the photochemically altered mixtures that produced secondary products induced about two- to threefold more IL-8 mRNA than the mixture of NO(2) and hydrocarbons or O(3). These results indicate that secondary products generated through the photochemical reactions of NO(x) and hydrocarbons may significantly contribute to the inflammatory responses induced by exposure to urban smog. From previous experience with relevant experiments, we know that many of these gaseous organic products would contribute to the formation of significant secondary organic particle mass in the presence of seed particles (including road dust or combustion products). In the absence of such particles, these gaseous products remained mostly as gases. These experiments show that photochemically produced gaseous products do influence the toxic responses of the cells in the absence of particles.
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http://dx.doi.org/10.1080/08958370490443196DOI Listing
October 2004
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