Effects of Gasoline Engine Emissions on Preexisting Allergic Airway Responses in Mice

Systematic review of preclinical studies on the neutrophil-mediated immune response to air pollutants, 1980-2020

Preclinical evidence about the neutrophil-mediated response in exposure to air pollutants is scattered and heterogeneous. This has prevented the consolidation of this research field around relevant models that could advance towards clinical research. The purpose of this study was to systematic review the studies of the neutrophils response to air pollutants, following the recommendations of the Cochrane Collaboration and the PRISMA guide, through 54 search strategies in nine databases. We include 234 studies (in vitro, and in vivo), being more frequent using primary neutrophils, Balb/C and C57BL6/J mice, and Sprague-Dawley and Wistar rats. The most frequent readouts were cell counts, cytokines and histopathology. The temporal analysis showed that in the last decade, the use of mice with histopathological and cytokine measurement have predominated. This systematic review has shown that study of the neutrophils response to air pollutants started 40 years ago, and composed of 100 different preclinical models, 10 pollutants, and 11 immunological outcomes. Mechanisms of neutrophils-mediated immunopathology include cellular activation, ROS production, and proinflammatory effects, leading to cell-death, oxidative stress, and inflammatory infiltrates in lungs. This research will allow consolidating the research efforts in this field, optimizing the study of causal processes, and facilitating the advance to clinical studies.

Health effects of carbon-containing particulate matter: focus on sources and recent research program results

Air pollution is a complex mixture of gas-, vapor-, and particulate-phase materials comprised of inorganic and organic species. Many of these components have been associated with adverse health effects in epidemiological and toxicological studies, including a broad spectrum of carbonaceous atmospheric components. This paper reviews recent literature on the health impacts of organic aerosols, with a focus on specific sources of organic material; it is not intended to be a comprehensive review of all the available literature. Specific emission sources reviewed include engine emissions, wood/biomass combustion emissions, biogenic emissions and secondary organic aerosol (SOA), resuspended road dust, tire and brake wear, and cooking emissions. In addition, recent findings from large toxicological and epidemiological research programs are reviewed in the context of organic PM, including SPHERES, NPACT, NERC, ACES, and TERESA. A review of the extant literature suggests that there are clear health impacts from emissions containing carbon-containing PM, but difficulty remains in apportioning responses to certain groupings of carbonaceous materials, such as organic and elemental carbon, condensed and gas phases, and primary and secondary material. More focused epidemiological and toxicological studies, including increased characterization of organic materials, would increase understanding of this issue.

The National Environmental Respiratory Center (NERC) experiment in multi-pollutant air quality health research: II. Comparison of responses to diesel and gasoline engine exhausts, hardwood smoke and simulated downwind coal emissions

The NERC Program conducted identically designed exposure-response studies of the respiratory and cardiovascular responses of rodents exposed by inhalation for up to 6 months to diesel and gasoline exhausts (DE, GE), wood smoke (WS) and simulated downwind coal emissions (CE). Concentrations of the four combustion-derived mixtures ranged from near upper bound plausible to common occupational and environmental hotspot levels. An "exposure effect" statistic was created to compare the strengths of exposure-response relationships and adjustments were made to minimize false positives among the large number of comparisons. All four exposures caused statistically significant effects. No exposure caused overt illness, neutrophilic lung inflammation, increased circulating micronuclei or histopathology of major organs visible by light microscopy. DE and GE caused the greatest lung cytotoxicity. WS elicited the most responses in lung lavage fluid. All exposures reduced oxidant production by unstimulated alveolar macrophages, but only GE suppressed stimulated macrophages. Only DE retarded clearance of bacteria from the lung. DE before antigen challenge suppressed responses of allergic mice. CE tended to amplify allergic responses regardless of exposure order. GE and DE induced oxidant stress and pro-atherosclerotic responses in aorta; WS and CE had no such effects. No overall ranking of toxicity was plausible. The ranking of exposures by number of significant responses varied among the response models, with each of the four causing the most responses for at least one model. Each exposure could also be deemed most or least toxic depending on the exposure metric used for comparison. The database is available for additional analyses.

Traffic-related PM2.5 induces cytosolic [Ca²⁺] increase regulated by Orai1, alters the CaN-NFAT signaling pathway, and affects IL-2 and TNF-α cytoplasmic levels in Jurkat T-cells

The atmospheric particulate matter with a diameter less than or equal to 2.5 um (PM2.5) can result in increased immune system damage or diseases, however, the possible mechanism remains unclear. In this study, we used Jurkat T cells to determine the effects of PM2.5 on T cell-mediated adaptive immune response. Our results indicated that PM2.5 exposure increased intracellular calcium ion concentration [Ca(2+)]. In contrast, cytosolic free Ca(2+) concentration [Ca(2+)]i significantly decreased in Jurkat T cells transfected with Orai1siRNA. In addition, we detected the level of interleukin (IL)-2 and tumor-necrosis factor (TNF)-α as well as other signalling molecules, including calcineurin (CaN) and NFATc2, a gene on 20q13.2 that encodes a member of the nuclear factor of activated T cells (NFAT), in the supernatant of cells exposed to PM2.5. The expression of NFATc2 protein increased in a time-dependent manner after exposure to PM2.5, but the activity of CaN decreased. NFATc2 was not consistent with IL-2 accumulation, thus indicating the involvement of other signals in the suppression of IL-2 accumulation. Our findings demonstrate that PM2.5 exposure in immune cells results in locally increased [Ca(2+)]i generated by Orai1 and CaN-NFAT gene expression, TNF-α and IL-2 cytoplasmic concentrations may be altered.

Simulated downwind coal combustion emissions for laboratory inhalation exposure atmospheres

Exposure atmospheres for rodent inhalation toxicology studies were generated to enable the evaluation of biological responses to a simulated downwind coal combustion atmosphere. A composition representing a single test case of emissions components as they may exist tens to hundreds of miles from a coal-fired power plant was developed. The particulate matter (PM) was 99% sulfate (partially neutralized) and 1% ash. Sulfate was present in equimolar concentrations to sulfur dioxide (SO₂). Gaseous nitrogen species included nitrogen monoxide (NO), nitrogen dioxide (NO₂), and nitric acid (HNO₃). At the high-exposure level, the gaseous species target concentrations were 0.2 ppm SO₂, 0.6 ppm NO, 0.3 ppm NO₂, and 0.1 ppm HNO₃. The test atmosphere was produced by combining effluent from a laboratory coal combustor with sulfate generated through an evaporation-condensation generator. These atmospheres were used to conduct inhalation toxicology studies that have been previously reported.

Effects of simulated downwind coal combustion emissions on pre-existing allergic airway responses in mice

CONTEXT

Coal-fired power plant emissions can contribute a significant portion of the ambient air pollution in many parts of the world.

OBJECTIVE

We hypothesized that exposure to simulated downwind coal combustion emissions (SDCCE) may exacerbate pre-existing allergic airway responses.

METHODS

Mice were sensitized and challenged with ovalbumin (OVA). Parallel groups were sham-sensitized with saline. Mice were exposed 6 h/day for 3 days to air (control, C) or SDCCE containing particulate matter (PM) at low (L; 100 μg/m³), medium (M; 300 μg/m³), or high (H; 1000 μg/m³) concentrations, or to the H level with PM removed by filtration (high-filtered, HF). Immediately after SDCCE exposure, mice received another OVA challenge (pre-OVA protocol). In a second (post-OVA) protocol, mice were similarly sensitized but only challenged to OVA before air/SDCCE. Measurement of airway hyperresponsiveness (AHR), bronchoalveolar lavage (BAL), and blood collection were performed ~24 h after the last exposure.

RESULTS

SDCCE significantly increased BAL macrophages and eosinophils in OVA-sensitized mice from the post-OVA protocol. However, there was no effect of SDCCE on BAL macrophages or eosinophils in OVA-sensitized mice from the pre-OVA protocol. BAL neutrophils were elevated following SDCCE in both protocols in nonsensitized mice. These changes were not altered by filtering out the PM. In the post-OVA protocol, SDCCE decreased OVA-specific IgG₁ in OVA-sensitized mice but increased levels of total IgE, OVA-specific IgE and OVA-specific IgG₁ and IgG(2a) in non-sensitized animals. In the pre-OVA protocol, SDCCE increased OVA-specific IgE in both sensitized and non-sensitized animals. Additionally, BAL IL-4, IL-13, and IFN-γ levels were elevated in sensitized mice.

CONCLUSION

These results suggest that acute exposure to either the particulate or gaseous phase of SDCCE can exacerbate various features of allergic airway responses depending on the timing of exposure in relation to allergen challenge.