M. Ian Gilmour

How Exposure to Environmental Tobacco Smoke, Outdoor Air Pollutants, and Increased Pollen Burdens Influences the Incidence of Asthma

Asthma is a multifactorial airway disease that arises from a relatively common genetic background interphased with exposures to allergens and airborne irritants. The rapid rise in asthma over the past three decades in Western societies has been attributed to numerous diverse factors, including increased awareness of the disease, altered lifestyle and activity patterns, and ill-defined changes in environmental exposures. It is well accepted that persons with asthma are more sensitive than persons without asthma to air pollutants such as cigarette smoke, traffic emissions, and photochemical smog components. It has also been demonstrated that exposure to a mix of allergens and irritants can at times promote the development phase (induction) of the disease. Experimental evidence suggests that complex organic molecules from diesel exhaust may act as allergic adjuvants through the production of oxidative stress in airway cells. It also seems that climate change is increasing the abundance of aeroallergens such as pollen, which may result in greater incidence or severity of allergic diseases. In this review we illustrate how environmental tobacco smoke, outdoor air pollution, and climate change may act as environmental risk factors for the development of asthma and provide mechanistic explanations for how some of these effects can occur.

Prenatal air pollution exposure induces neuroinflammation and predisposes offspring to weight gain in adulthood in a sex-specific manner

Emerging evidence suggests environmental chemical exposures during critical windows of development may contribute to the escalating prevalence of obesity. We tested the hypothesis that prenatal air pollution exposure would predispose the offspring to weight gain in adulthood. Pregnant mice were exposed to filtered air (FA) or diesel exhaust (DE) on embryonic days (E) 9‐17. Prenatal DE induced a significant fetal brain cytokine response at E18 (46–390% over FA). As adults, offspring were fed either a low‐fat diet (LFD) or high‐fat diet (HFD) for 6 wk. Adult DE male offspring weighed 12% more and were 35% less active than FA male offspring at baseline, whereas there were no differences in females. Following HFD, DE males gained weight at the same rate as FA males, whereas DE females gained 340% more weight than FA females. DE‐HFD males had 450% higher endpoint insulin levels than FA‐HFD males, and all males on HFD showed decreased activity and increased anxiety, whereas females showed no differences. Finally, both DE males and females fed HFD showed increased microglial activation (30–66%) within several brain regions. Thus, prenatal air pollution exposure can “program” offspring for increased susceptibility to diet‐induced weight gain and neuroinflammation in adulthood in a sex‐specific manner.—Bolton, J. L., Smith, S. H., Huff, N. C., Gilmour, M. I., Foster, W. M., Auten, R. L., Bilbo, S. D. Prenatal air pollution exposure induces neuroinflammation and predisposes offspring to weight gain in adulthood in a sex‐specific manner. FASEB J. 26, 4743–4754 (2012). www.fasebj.org

Influence of acid functionalization on the cardiopulmonary toxicity of carbon nanotubes and carbon black particles in mice

Engineered carbon nanotubes are being developed for a wide range of industrial and medical applications. Because of their unique properties, nanotubes can impose potentially toxic effects, particularly if they have been modified to express functionally reactive chemical groups on their surface. The present study was designed to evaluate whether acid functionalization (AF) enhanced the cardiopulmonary toxicity of single-walled carbon nanotubes (SWCNT) as well as control carbon black particles. Mice were exposed by oropharyngeal aspiration to 10 or 40 microg of saline-suspended single-walled carbon nanotubes (SWCNTs), acid-functionalized SWCNTs (AF-SWCNTs), ultrafine carbon black (UFCB), AF-UFCB, or 2 microg LPS. 24 hours later, pulmonary inflammatory responses and cardiac effects were assessed by bronchoalveolar lavage and isolated cardiac perfusion respectively, and compared to saline or LPS-instilled animals. Additional mice were assessed for histological changes in lung and heart. Instillation of 40 microg of AF-SWCNTs, UFCB and AF-UFCB increased percentage of pulmonary neutrophils. No significant effects were observed at the lower particle concentration. Sporadic clumps of particles from each treatment group were observed in the small airways and interstitial areas of the lungs according to particle dose. Patches of cellular infiltration and edema in both the small airways and in the interstitium were also observed in the high dose group. Isolated perfused hearts from mice exposed to 40 microg of AF-SWCNTs had significantly lower cardiac functional recovery, greater infarct size, and higher coronary flow rate than other particle-exposed animals and controls, and also exhibited signs of focal cardiac myofiber degeneration. No particles were detected in heart tissue under light microscopy. This study indicates that while acid functionalization increases the pulmonary toxicity of both UFCB and SWCNTs, this treatment caused cardiac effects only with the AF-carbon nanotubes. Further experiments are needed to understand the physico-chemical processes involved in this phenomenon.

Induction of Asthma and the Environment: What We Know and Need to Know

The prevalence of asthma has increased dramatically over the last 25 years in the United States and in other nations as a result of ill-defined changes in living conditions in modern society. On 18 and 19 October 2004 the U.S. Environmental Protection Agency and the National Institute of Environmental Health Sciences sponsored the workshop “Environmental Influences on the Induction and Incidence of Asthma” to review current scientific evidence with respect to factors that may contribute to the induction of asthma. Participants addressed two broad questions: a) What does the science suggest that regulatory and public health agencies could do now to reduce the incidence of asthma? and b) What research is needed to improve our understanding of the factors that contribute to the induction of asthma and our ability to manage this problem? In this article (one of four articles resulting from the workshop), we briefly characterize asthma and its public health and economic impacts, and intervention strategies that have been successfully used to prevent induction of asthma in the workplace. We conclude with the findings of seven working groups that focus on ambient air, indoor pollutants (biologics), occupational exposures, early life stages, older adults, intrinsic susceptibility, and lifestyle. These groups found strong scientific support for public health efforts to limit in utero and postnatal exposure to cigarette smoke. However, with respect to other potential types of interventions, participants noted many scientific questions, which are summarized in this article. Research to address these questions could have a significant public health and economic impact that would be well worth the investment.

Differential Pulmonary Inflammation and In Vitro Cytotoxicity of Size-Fractionated Fly Ash Particles from Pulverized Coal Combustion

Abstract Exposure to airborne particulate matter (PM) has been associated with adverse health effects in humans. Pulmonary inflammatory responses were examined in CD1 mice after intratracheal instillation of 25 or 100 μg of ultrafine (<0.2 μm), fine (<2.5 μm), and coarse (>2.5 μm) coal fly ash from a combusted Montana subbituminous coal, and of fine and coarse fractions from a combusted western Kentucky bituminous coal. After 18 hr, the lungs were lavaged and the bronchoalveolar fluid was assessed for cellular influx, biochemical markers, and pro-inflammatory cytokines. The responses were compared with saline and endotoxin as negative and positive controls, respectively. On an equal mass basis, the ultrafine particles from combusted Montana coal induced a higher degree of neutrophil inflammation and cytokine levels than did the fine or coarse PM. The western Kentucky fine PM caused a moderate degree of inflammation and protein levels in bronchoalveolar fluid that were higher than the Montana fine PM. Coarse PM did not produce any significant effects. In vitro experiments with rat alveolar macrophages showed that of the particles tested, only the Montana ultrafine displayed significant cytotoxicity. It is concluded that fly ash toxicity is inversely related with particle size and is associated with increased sulfur and trace element content.

Murine pulmonary inflammatory responses following instillation of size-fractionated ambient particulate matter

The mechanisms for increased cardiopulmonary disease in individuals exposed to particulate air pollution are associated with fine and ultrafine particles that have a high oxidative potential. Particulate matter (PM) from Research Triangle Park (NC) was collected and separated into 3 different size fractions: coarse (CO; >3.5 w m), fine (FI; 1.7-3.5 w m), and fine/ultrafine (FU; <1.7 w m) using impaction and electrostatic precipitation. Particle chemistry indicated the presence of sulfates, zinc, iron, and copper in all fractions. CD1 mice were intratracheally instilled with 10, 50, or 100 w g of each fraction. After 18 h, the lungs were lavaged and assayed for signs of inflammation. All particles produced increases in neutrophil number, and this was highest in the high-dose FU group. Biochemical analysis revealed no change in lactate dehydrogenase (LDH) activity, and increased albumin and tumor necrosis factor (TNF)- f levels were only seen with the high-dose FI particles. Interleukin 6 (IL-6) levels were increased over control levels after treatment with 100 w g of all 3 particle sizes. To determine whether oxidative stress may contribute to these effects, antioxidant levels in the lung were boosted by an intraperitoneal (ip) injection with dimethylthiourea (DMTU). This treatment resulted in a twofold increase in the total antioxidant capacity of the lung and decreased the PM-induced cytokine and neutrophil influx up to 50%. The data indicate that on an equal mass basis, ambient particles of these three size ranges produce pulmonary inflammation, and that increasing the antioxidant capacity of the lung reduces particle-induced cytokine and cellular responses.

Differential cardiopulmonary effects of size-fractionated ambient particulate matter in mice.

A growing body of evidence from epidemiological and toxicological studies provides a strong link between exposure to ambient particulate matter (PM) of varying size and increased cardiovascular and respiratory morbidity and mortality. This study was designed to evaluate the cardiopulmonary effects of ambient coarse, fine, and ultrafine particles collected in Chapel Hill, NC. Mice were exposed to each size fraction by oropharyngeal instillation. Twenty-four hours later, pulmonary inflammation was assessed by bronchoalveolar lavage and cardiac injury was measured using a Langendorff cardiac perfusion preparation. Recovery of post-ischemic left ventricular developed pressure and infarct size were measured as indeces of cardiac ischemia/reperfusion injury. Coronary flow rate was measured before, during, and after ischemia. We demonstrate that coarse PM caused the most significant pulmonary inflammatory responses. In contrast, hearts from ultrafine-exposed mice had significantly lower post-ischemic functional recovery and greater infarct size, while hearts from coarse and fine PM-exposed mice had no significant responses to ischemia/reperfusion. The coronary flow rate was significantly reduced in the ultrafine PM group. This study shows that exposure of mice to coarse PM results in significant pulmonary toxicity while ultrafine PM appears to enhance cardiac ischemia/reperfusion injury.

Differential Potentiation of Allergic Lung Disease in Mice Exposed to Chemically Distinct Diesel Samples

Numerous studies have demonstrated that diesel exhaust particles (DEP) potentiate allergic immune responses, however the chemical components associated with this effect, and the underlying mechanisms are not well understood. This study characterized the composition of three chemically distinct DEP samples (N, C, and A-DEP), and compared post-sensitization and post-challenge inflammatory allergic phenotypes in BALB/c mice. Mice were instilled intranasally with saline or 150 microg of N-DEP, A-DEP, or C-DEP with or without 20 microg of ovalbumin (OVA) on days 0 and 13, and were subsequently challenged with 20 microg of OVA on days 23, 26, and 29. Mice were necropsied 18 h post-sensitization and 18 and 48 h post-challenge. N-DEP, A-DEP, and C-DEP contained 1.5, 68.6, and 18.9% extractable organic material (EOM) and 47, 431, and 522 microg of polycyclic aromatic hydrocarbons (PAHs), respectively. The post-challenge results showed that DEP given with OVA induced a gradation of adjuvancy as follows: C-DEP approximately A-DEP > N-DEP. The C- and A-DEP/OVA exposure groups had significant increases in eosinophils, OVA-specific IgG1, and airway hyperresponsiveness. In addition, the C-DEP/OVA exposure increased the T helper 2 (T(H)2) chemoattractant chemokine, thymus and activation-regulated chemokine and exhibited the most severe perivascular inflammation in the lung, whereas A-DEP/OVA increased interleukin (IL)-5 and IL-10. In contrast, N-DEP/OVA exposure only increased OVA-specific IgG1 post-challenge. Analysis of early signaling showed that C-DEP induced a greater number of T(H)2 cytokines compared with A-DEP and N-DEP. The results suggest that potentiation of allergic immune responses by DEP is associated with PAH content rather than the total amount of EOM.

Source apportionment of particulate matter in the U.S. and associations with lung inflammatory markers.

Size-fractionated particulate matter (PM) samples were collected from six U.S. cities and chemically analyzed as part of the Multiple Air Pollutant Study. Particles were administered to cultured lung cells and the production of three different proinflammatory markers was measured to explore the association between the health effect markers and PM. Ultrafine, fine, and coarse PM samples were collected between December 2003 and May 2004 over a 4-wk period in each city. Filters were pooled for each city and the PM samples were extracted then analyzed for trace metals, ions, and elemental carbon. Particle extracts were applied to cultured human primary airway epithelial cells, and the secreted levels of interleukin-8 (IL-8), heme oxygenase-1, and cyclooxygenase-2 were measured 1 and 24 h following exposure. Fine PM sources were quantified by the chemical mass balance (CMB) model. The relationship between toxicological measures, PM sources, and individual species were evaluated using linear regression. Ultrafine and fine PM mass were associated with increases in IL-8 (r2 = .80 for ultrafine and r2 = .52 for fine). Sources of fine PM and their relative contributions varied across the sampling sites and a strong linear association was observed between IL-8 and secondary sulfate from coal combustion (r2 = .79). Ultrafine vanadium, lead, copper, and sulfate were also associated with increases in IL-8. Increases in inflammatory markers were not observed for coarse PM mass and source markers. These findings suggest that certain PM size fractions and sources are associated with markers of lung injury or inflammation.

Enhanced in vitro and in vivo toxicity of poly-dispersed acid-functionalized single-wall carbon nanotubes

Many potential applications in nanotechnology envisage the use of better-dispersed and functionalized preparations of carbon nanotubes. Single-walled carbon nanotubes (SWCNTs) were treated with 1:1 mixtures of concentrated nitric and sulfuric acids for 3 min in a microwave oven under 20 psi pressure followed by extensive dialysis to remove the acids. This treatment resulted in acid functionalized SWCNTs (AF-SWCNTs) that had high negative charge (Zeta potential −40 to −60 mV) and were well dispersed (98% of the particles <150 nm) in aqueous suspensions. In vitro and in vivo toxic effects of SWCNTs and AF-SWCNTs were compared. AF-SWCNTs exerted a strong cytotoxic effect on LA4 mouse lung epithelial cells in culture that could be blocked by prior treatment of the nanotubes with poly L-lysine which neutralized the electric charge and promoted re-agglomeration. AF-SWCNT, but not the unmodified SWCNT preparations, strongly inhibited cell cycling of LA4 cells. Both SWCNTs and AF-SWCNTS were however equally effective in inducing apoptotic responses in LA4 cells as examined using an Annexin V binding assay. Oro-pharyngeal aspiration of AF-SWCNT preparation induced a strong acute inflammatory response in the lungs of CD1 mice, compared to control SWCNTs which caused only a marginal effect. Taken together the results indicate that unlike pristine SWCNTs, acid-functionalized SWCNT preparations exert strong toxic effects in vitro and in vivo and these effects can be reversed by neutralizing their surface charge.