Incomplete lung recovery following sub-acute inhalation of combustion-derived ultrafine particles in mice

Noël et al. Particle and Fibre Toxicology (2016) 13:10 DOI 10.1186/s12989-016-0122-z RESEARCH Open Access Incomplete lung recovery following sub-acute inhalation of combustion-derived ultrafine particles in mice A. Noël1, R. Xiao3, Z. Perveen1, H. M. Zaman1, R. L. Rouse4, D. B. Paulsen2 and A. L. Penn1* Abstract Background: Particulate matter (PM) is one of the six criteria pollutant classes for which National Ambient Air Quality Standards have been set by the United States Environmental Protection Agency. Exposures to PM have been correlated with increased cardio-pulmonary morbidity and mortality. Butadiene soot (BDS), generated from the incomplete combustion of 1,3-butadiene (BD), is both a model PM mixture and a real-life example of a petrochemical product of incomplete combustion. There are numerous events, including wildfires, accidents at refineries and tank car explosions that result in sub-acute exposure to high levels of airborne particles, with the people exposed facing serious health problems. These real-life events highlight the need to investigate the health effects induced by short-term exposure to elevated levels of PM, as well as to assess whether, and if so, how well these adverse effects are resolved over time. In the present study, we investigated the extent of recovery of mouse lungs 10 days after inhalation exposures to environmentally-relevant levels of BDS aerosols had ended. Methods: Female BALB/c mice exposed to either HEPA-filtered air or to BDS (5 mg/m3 in HEPA filtered air, 4 h/day, 21 consecutive days) were sacrificed immediately, or 10 days after the final BDS exposure. Bronchoalveolar lavage fluid (BALF) was collected for cytology and cytokine analysis. Lung proteins and RNA were extracted for protein and gene expression analysis. Lung histopathology evaluation also was performed. Results: Sub-acute exposures of mice to hydrocarbon-rich ultrafine particles induced: (1) BALF neutrophil elevation; (2) lung mucosal inflammation, and (3) increased BALF IL-1β concentration; with all three outcomes returning to baseline levels 10 days post-exposure. In contrast, (4) lung connective tissue inflammation persisted 10 days post-exposure; (5) we detected time-dependent up-regulation of biotransformation and oxidative stress genes, with incomplete return to baseline levels; and (6) we observed persistent particle alveolar load following 10 days of recovery. Conclusion: These data show that 10 days after a 21-day exposure to 5 mg/m3 of BDS has ended, incomplete lung recovery promotes a pro-biotransformation, pro-oxidant, and pro-inflammatory milieu, which may be a starting point for potential long-term cardio-pulmonary effects. Keywords: Inhalation, Particulate matter, Combustion-derived ultrafine particles, Lung recovery, Inflammation, Oxidative stress, Biotransformation, Gene expression, Particle-laden macrophage biomarker * Correspondence: 1 Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Dr., Baton Rouge, LA 70803, USA Full list of author information is available at the end of the article © 2016 Noël et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Noël et al. Particle and Fibre Toxicology (2016) 13:10 Background Particulate matter (PM) is one of the six criteria pollutant classes for which National Ambient Air Quality Standards have been set by the United States Environmental Protection Agency [1]. PM is ubiquitous in outdoor air and contributes significantly to air pollution, especially in urban areas [2, 3]. PM are composed of ambient coarse (PM10, < 10 μm), fine (PM2.5, < 2.5 μm) and ultrafine (PM0.1, < 0.1 μm) particles. PM are found in multiple physicochemical forms, due to environmental as well as meteorological factors, and arise from diverse emission sources, both natural and anthropogenic [2, 4, 5]. Petroleum refineries, chemical plants and diesel engines release combustion-derived PM into the atmosphere following incomplete combustion of volatile hydrocarbons. The PM-rich soots produced during incomplete combustion of fuels are complex and may contain, in addition to polynuclear aromatic hydrocarbons (PAHs), a variety of oxygen radical-generating quinones and metal species [6–8]. PAHs, many of which are carcinogenic, are present in combustion-derived PM and thereby may increase considerably the potency of PM to induce adverse health effects [9]. Combustion-derived PM, particularly those resulting from traffic exhaust, are known health risk factors and are responsible for about 80 % of the human PM exposures [2]. Populations living in urban communities near heavily traveled highways potentially have a higher risk of exposure and consequently, of diseases related to air pollution [10]. In 2012, the World Health Organization estimated that outdoor air pollution accounted for 3.7 million premature deaths worldwide [11]. Thus, inhalation of outdoor air pollutants remains a leading public health concern [11]. Extended, high PM exposures result in sharp increases in morbidity and mortality. The Great London Smog of 1952 lasted 4 days, with peak particle concentrations reaching 0.4 mg/m3, and resulted in an estimated 12,000 deaths [2, 12]. In 1991, five months after the start of the fires at Kuwaiti oil depots and refineries, the concentration of ambient PM2.5 20 km from the fire site still exceeded 830 μg/m3 [13]. In the 2001 World Trade Center (WTC) attack, people were exposed to complex particle mixtures from the destroyed towers and the burning aviation fuel. PM concentration levels remained above 1 mg/m3 more than one week after the attack [14]. Within a year of the WTC attack, a report on aggravated morbidity and mortality among ‘first responders’ was published [15]. PM-exposed firefighters also are a vulnerable sub-population of workers acutely exposed to very high concentrations of dust, fumes and gas mixtures. During the six days of the October 2003 Southern California wildfires, the maximum daily averaged PM2.5 concentration was 270 μg/m3 [16]. Furthermore, as in cases of pipeline sabotage, attacks on Page 2 of 20 refineries (Gulf War I), accidents at refineries/oil storage depots (Texas City, TX, March 23rd 2005; Buncefield, UK, December 13th 2005) and routine flaring of volatiles at refineries, incomplete combustion of petrochemicals results in production of large particle-rich soot clouds. Although these sporadic ev (...truncated)