Biochemical and physiological effects from exhaust emissions. A review of the relevant literature

Low-vacuum SEM imaging and viability test of L929 cells exposed to a Euro 6 diesel exhaust gas mixture in a BAT-CELL chamber in comparison with hydrocarbons emission

Exhaust emissions, which count among the most common causes of premature death worldwide, can cause irreversible changes in cells, leading to their damage or degeneration. In this research, L929 line cells were observed after exposure in the BAT-CELL chamber to exhaust gases emitted from a Euro 6 compression-ignition engine. Real road traffic conditions were simulated, taking into account air resistance while driving at speeds of 50 km/h, 120 km/h and idling engine. Morphological analysis of the cells was performed using an environmental scanning electron microscope. It has been observed that diesel exhaust fumes can cause inflammation, which can induce apoptosis or leads to necrotic cell death. The impact of the vehicle exhaust gases can inhibit cell proliferation by almost three times. Moreover, a correlation has been observed between the speed of the inflammatory reaction in cells and the presence of specific hydrocarbon compounds that determine the toxicity of exhaust gases. Research has shown that the toxicity of the emitted exhaust gases has been the highest at the driving speed of 120 km/h. In order to reduce the harmful effects of exhaust emissions, ecological alternatives and the supplementation of legal provisions regarding the compounds subject to limitation are necessary.

In vitro neurotoxicity of particles from diesel and biodiesel fueled engines following direct and simulated inhalation exposure

Combustion-derived particulate matter (PM) is a major source of air pollution. Efforts to reduce diesel engine emission include the application of biodiesel. However, while urban PM exposure has been linked to adverse brain effects, little is known about the direct effects of PM from regular fossil diesel (PMDEP) and biodiesel (PMBIO) on neuronal function. Furthermore, it is unknown to what extent the PM-induced effects in the lung (e.g., inflammation) affect the brain. This in vitro study investigates direct and indirect toxicity of PMDEP and PMBIO on the lung and brain and compared it with effects of clean carbon particles (CP). PM were generated using a common rail diesel engine. CP was sampled from a spark generator. First, effects of 48 h exposure to PM and CP (1.2-3.9 µg/cm2) were assessed in an in vitro lung model (air-liquid interface co-culture of Calu-3 and THP1 cells) by measuring cell viability, cytotoxicity, barrier function, inflammation, and oxidative and cell stress. None of the exposures caused clear adverse effects and only minor changes in gene expression were observed. Next, the basal medium was collected for subsequent simulated inhalation exposure of rat primary cortical cells. Neuronal activity, recorded using microelectrode arrays (MEA), was increased after acute (0.5 h) simulated inhalation exposure. In contrast, direct exposure to PMDEP and PMBIO (1-100 µg/mL; 1.2-119 µg/cm2) reduced neuronal activity after 24 h with lowest observed effect levels of respectively 10 µg/mL and 30 µg/mL, indicating higher neurotoxic potency of PMDEP, whereas neuronal activity remained unaffected following CP exposure. These findings indicate that combustion-derived PM potently inhibit neuronal function following direct exposure, while the lung serves as a protective barrier. Furthermore, PMDEP exhibit a higher direct neurotoxic potency than PMBIO, and the data suggest that the neurotoxic effects is caused by adsorbed chemicals rather than the pure carbon core.

Role of different mechanisms in pro-inflammatory responses triggered by traffic-derived particulate matter in human bronchiolar epithelial cells

BACKGROUND

Traffic-derived particles are important contributors to the adverse health effects of ambient particulate matter (PM). In Nordic countries, mineral particles from road pavement and diesel exhaust particles (DEP) are important constituents of traffic-derived PM. In the present study we compared the pro-inflammatory responses of mineral particles and DEP to PM from two road tunnels, and examined the mechanisms involved.

METHODS

The pro-inflammatory potential of 100 µg/mL coarse (PM10-2.5), fine (PM2.5-0.18) and ultrafine PM (PM0.18) sampled in two road tunnels paved with different stone materials was assessed in human bronchial epithelial cells (HBEC3-KT), and compared to DEP and particles derived from the respective stone materials. Release of pro-inflammatory cytokines (CXCL8, IL-1α, IL-1β) was measured by ELISA, while the expression of genes related to inflammation (COX2, CXCL8, IL-1α, IL-1β, TNF-α), redox responses (HO-1) and metabolism (CYP1A1, CYP1B1, PAI-2) was determined by qPCR. The roles of the aryl hydrocarbon receptor (AhR) and reactive oxygen species (ROS) were examined by treatment with the AhR-inhibitor CH223191 and the anti-oxidant N-acetyl cysteine (NAC).

RESULTS

Road tunnel PM caused time-dependent increases in expression of CXCL8, COX2, IL-1α, IL-1β, TNF-α, COX2, PAI-2, CYP1A1, CYP1B1 and HO-1, with fine PM as more potent than coarse PM at early time-points. The stone particle samples and DEP induced lower cytokine release than all size-fractionated PM samples for one tunnel, and versus fine PM for the other tunnel. CH223191 partially reduced release and expression of IL-1α and CXCL8, and expression of COX2, for fine and coarse PM, depending on tunnel, response and time-point. Whereas expression of CYP1A1 was markedly reduced by CH223191, HO-1 expression was not affected. NAC reduced the release and expression of IL-1α and CXCL8, and COX2 expression, but augmented expression of CYP1A1 and HO-1.

CONCLUSIONS

The results indicate that the pro-inflammatory responses of road tunnel PM in HBEC3-KT cells are not attributed to the mineral particles or DEP alone. The pro-inflammatory responses seem to involve AhR-dependent mechanisms, suggesting a role for organic constituents. ROS-mediated mechanisms were also involved, probably through AhR-independent pathways. DEP may be a contributor to the AhR-dependent responses, although other sources may be of importance.

The Actual Toxicity of Engine Exhaust Gases Emitted from Vehicles: The Development and Perspectives of Biological and Chemical Measurement Methods

Most of the current studies on vehicle engine exhaust emissions are focused on qualitative and quantitative measurements. Approval tests for admitting vehicles to traffic and tests performed at vehicle inspection stations are limited to measuring the concentrations of individual compounds or selected groups of compounds. For vehicles with compression-ignition engines, the annual emission control comprises only an exhaust gas opacity test, performed with an opacimeter. This approach does not consider very harmful groups of compounds that determine the toxicity of exhaust gases but are not directly covered by the emission standards, such as polycyclic aromatic hydrocarbons and volatile organic compounds. Also, it does not provide a clear answer to the question of the actual toxicity of exhaust gases, understood as the harmful effect that a given substance causes on living organisms or biological processes. Studies on the actual toxicity of engine exhaust gases present a new area of interest, increasingly more discussed but still not approached in a comprehensive way. The studies include experiments using in vitro biological methods and chemical analyses of gas mixtures. In this Review, I present an overview of current research and a critical comparison of commonly used methods of testing engine exhaust emissions and methods that might supplement them in a significant manner. The development of in vitro biological methods, including methods of microscopic analysis of cells in the assessment of exhaust gas toxicity, provides an innovative approach to the problem of air pollution. This type of research presents the opportunity to indisputably answer the question of the actual toxicity of a given gas mixture and to make a new contribution to science in the field of molecular biology. Current data show that the survival of cells exposed to engine exhaust emissions from older generation vehicles is higher compared to that of newer generation vehicles.

Markers of lipid oxidation and inflammation in bronchial cells exposed to complete gasoline emissions and their organic extracts

Road traffic emissions consist of gaseous components, particles of various sizes, and chemical compounds that are bound to them. Exposure to vehicle emissions is implicated in the etiology of inflammatory respiratory disorders. We investigated the inflammation-related markers in human bronchial epithelial cells (BEAS-2B) and a 3D model of the human airways (MucilAir™), after exposure to complete emissions and extractable organic matter (EOM) from particles generated by ordinary gasoline (E5), and a gasoline-ethanol blend (E20; ethanol content 20% v/v). The production of 22 lipid oxidation products (derivatives of linoleic and arachidonic acid, AA) and 45 inflammatory molecules (cytokines, chemokines, growth factors) was assessed after days 1 and 5 of exposure, using LC-MS/MS and a multiplex immunoassay, respectively. The response observed in MucilAir™ exposed to E5 gasoline emissions, characterized by elevated levels of pro-inflammatory AA metabolites (prostaglandins) and inflammatory markers, was the most pronounced. E20 EOM exposure was associated with increased levels of AA metabolites with anti-inflammatory effects in this cell model. The exposure of BEAS-2B cells to complete emissions reduced lipid oxidation, while E20 EOM tended to increase concentrations of AA metabolite and chemokine production; the impacts on other inflammatory markers were limited. In summary, complete E5 emission exposure of MucilAir™ induces the processes associated with the pro-inflammatory response. This observation highlights the potential negative health impacts of ordinary gasoline, while the effects of alternative fuel are relatively weak.

Simulated vehicle exhaust exposure induces sex-dependent behavioral deficits in rats

Chronic exposure to vehicle exhaust emissions are known to cause several adverse health effects. In this study, we examined the impact of several parameters of behavioral, cardiovascular and biochemical functions upon exposure of pro-oxidants CO2, NO2 and CO (simulated vehicle exhaust exposure: SVEE) in male and female rats. Adult rats were subjected to SVEE or ambient air in whole body chambers (5 h/day, 2 weeks). Male, but not female, rats developed memory deficits, and exhibited anxiety- and depression-like behavior, accompanied with significantly high levels of serum corticosterone, oxidative stress, and inflammatory markers (CRP and TNFα), associated with lower levels of total antioxidant capacity, glutathione, glyoxalase and superoxide dismutase (SOD) activities. Brain region-specific downregulation of Cu/Zn SOD, Mn SOD, GSR, PKCα, ERK1/2, CaMKIV, CREB, BDNF and NMDAR subunit protein expression were also observed in male, but not female, rats. Blood pressure, heart rate and eGFR were not negatively impacted by SVEE. Our results suggest that SVEE, through its pro-oxidant content, induces oxido-inflammation in susceptible brain regions in a sex-dependent manner.

Analysis of inflammatory markers in apparently healthy automobile vehicle drivers in response to exposure to traffic pollution fumes

Objective:

This study aimed to evaluate pattern of markers of inflammation in apparently healthy drivers who exposed to traffic fumes.

Methods:

This cross-sectional study was conducted from June 2016 to January 2017 at Liaquat University of Medical & Health Sciences (LUMHS), Jamshoro. It looked into the effects of traffic pollutants on markers of inflammation including CRP, Leukocytes count, IL-6, TNF-α, TNF-β of healthy human volunteers. Eighty-seven, apparently healthy, non-smoking automobile vehicle drivers, having daily contact of traffic exhaust for at least six hours, aged between 18-40 years recruited for this study. Levels of traffic-generated pollutants P.M_2.5, P.M_10, NO_x were recorded in different areas of Hyderabad City.

Results:

P.M_2.5 found to be positively correlated with markers of inflammation including IL-6 (r_s = 0.99), TNF-α (r_s = 0.41), CRP mg/dl (r_s = 0.99) , neutrophils (r_s = 0.29), lymphocytes (r_s = 0.31), eosinophils (r_s = 0.20), monocytes (r_s = 0.42) and basophils (r_s = 0.16). Positive correlation present among IL-6 (r_s = 0.21), TNF-α (r_s = 0.49) and CRP mg/dl (r_s = 0.22) % (r_s = -0.31), Leukocytes (r_s = 0.14) neutrophils (r_s = 0.31), lymphocytes (r_s = 0.21), monocytes (r_s = 0.50), basophils (r_s = 0.17) with P.M₁₀. NO_x showed positive correlation with IL-6 (r_s = 0.22), TNF-α (r_s = 0.48), CRP (r_s = 0.22), neutrophils (r_s = 0.31), lymphocytes (r_s = 0.13), basophils (r_s = 0.17) and monocytes (r_s = 0.48).

Conclusion:

Findings of our study suggest that almost all markers of inflammation are positively correlated with traffic pollutants and this condition might raise the risk of systemic diseases.

Association Between Metabolic and Hormonal Derangements and Professional Exposure to Urban Pollution in a High Intensity Traffic Area

Rationale: Studies suggest a relation between exposure to air particulate matter (PM)_2.5 pollution and greater cardiovascular morbidity, as well as increased risk for obesity and diabetes. We aimed to identify association(s) between nutritional and metabolic status and exposure to environmental pollution in a cohort of policemen exposed to high levels of air pollution. Methods: We considered adult municipal policemen, working in an urban area at high-traffic density with documented high levels of air PM_2.5 (exposed group) compared to non-exposed policemen. Clinical characteristics, including the presence/absence of metabolic syndrome, were recorded, and serum biomarkers, including adiponectin, leptin, and ghrelin, were assessed. Results: One hundred ninety-nine participants were enrolled, 100 in the exposed group and 99 in the non-exposed group. Metabolic syndrome was documented in 32% of exposed group and in 52.5% of non-exposed group (P = 0.008). In the exposed group, we found a positive correlation between body mass index and serum leptin as well as in the non-exposed group (P < 0.0001). Within the exposed group, subjects with metabolic syndrome showed lower serum adiponectin (P < 0.0001) and higher leptin (P = 0.002) levels with respect to those without metabolic syndrome, whereas in the non-exposed group, subjects with metabolic syndrome showed only higher leptin levels when compared to those without metabolic syndrome (P = 0.01). Among the participants with metabolic syndrome, we found lower adiponectin levels in those of the exposed group with respect to the non-exposed ones (P = 0.007). When comparing the exposed and non-exposed groups, after stratifying participants for Homeostatic Model Assessment for Insulin Resistance >2.5, we found lower adiponectin levels in those of the exposed group with respect to the non-exposed ones (P = 0.038). Conclusions: Exposure to air PM pollution was associated with lower levels of adiponectin in adult males with metabolic syndrome.

A critical review of developmental exposure to particulate matter, autism spectrum disorder, and attention deficit hyperactivity disorder

Autism spectrum disorder (ASD) and attention deficit (hyperactivity) disorder (ADD/ADHD) are key focuses of current health research due to their increasing prevalence. The objective of this systematic literature search and critical review was to evaluate whether the human epidemiologic data indicate a pattern of association between ASD or ADD/ADHD and developmental exposure to particulate matter (PM), with a focus on exposures encountered before the age of three. A MEDLINE and EMBASE search was conducted; following preliminary and full-text screening, 14 relevant articles were identified for review. Three of the 14 studies were prospective cohort studies evaluating exposure to PM₁₀; 11 studies had a case-control design. There was no consistent association between developmental PM exposure and ASD across the three of the cohort studies. Seven of the case-control studies examined the relationship between PM_2.5 and/or PM₁₀ and ASD; four examined the relationship between developmental diesel PM exposure and ASD. Overall, there was low external consistency in results among studies of PM_2.5/PM₁₀ and ASD, with some reporting high internal consistency without significant associations, others showing associations with high internal consistency for specific exposure windows only (e.g., third trimester), and still others showing high consistency for moderate to strong associations between PM and ASD. The majority of studies reporting significant results had low effect sizes in conjunction with small sample sizes. The four studies of diesel PM and ASD also had low external consistency of results. Only one study evaluated associations with ADD/ADHD, and it found no significant associations with PM₁₀. The inconsistent findings across studies of developmental exposure to PM and ASD may be attributed to differences in the study populations, exposure assessments, outcome assessments, or chance. Further research is needed to understand the underlying biological mechanisms that lead to ASD and ADD/ADHD and how PM might be involved in those mechanisms, if at all. High-quality epidemiologic studies are also needed to conclusively determine whether developmental PM exposure is a causal factor for ASD or ADD/ADHD, with focus on a well-developed exposure assessment.

A comparative analysis of in vitro toxicity of diesel exhaust particles from combustion of 1st- and 2nd-generation biodiesel fuels in relation to their physicochemical properties-the FuelHealth project

Biodiesels represent more carbon-neutral fuels and are introduced at an increasing extent to reduce emission of greenhouse gases. However, the potential impact of different types and blend concentrations of biodiesel on the toxicity of diesel engine emissions are still relatively scarce and to some extent contradictory. The objective of the present work was to compare the toxicity of diesel exhaust particles (DEP) from combustion of two 1st-generation fuels: 7% fatty acid methyl esters (FAME; B7) and 20% FAME (B20) and a 2nd-generation 20% FAME/HVO (synthetic hydrocarbon biofuel (SHB)) fuel. Our findings indicate that particulate emissions of each type of biodiesel fuel induce cytotoxic effects in BEAS-2B and A549 cells, manifested as cell death (apoptosis or necrosis), decreased protein concentrations, intracellular ROS production, as well as increased expression of antioxidant genes and genes coding for DNA damage-response proteins. The different biodiesel blend percentages and biodiesel feedstocks led to marked differences in chemical composition of the emitted DEP. The different DEPs also displayed statistically significant differences in cytotoxicity in A549 and BEAS-2B cells, but the magnitude of these variations was limited. Overall, it seems that increasing biodiesel blend concentrations from the current 7 to 20% FAME, or substituting 1st-generation FAME biodiesel with 2nd-generation HVO biodiesel (at least below 20% blends), affects the in vitro toxicity of the emitted DEP to some extent, but the biological significance of this may be moderate.

Diesel exhaust particulate associated chemicals attenuate expression of CXCL10 in human primary bronchial epithelial cells

Air pollution affects a large proportion of the population particularly in urban areas, with diesel particulates recognised as particular causes for concern in respiratory conditions such as asthma. In this study we examined the response of human primary airway epithelial cells to diesel particulate chemical extracts (DE) and characterised gene expression alterations using RNA-SEQ. Using the antagonist CH223191, DE induced CYP1A1 and attenuation of CXCL10 among other genes were observed to be aryl hydrocarbon receptor dependent. Basal and toll like receptor dependent protein levels for CXCL10 were markedly reduced. Investigation of similar regulation in plasmacytoid dendritic GEN2.2 cells did not show DE dependent regulation of CXCL10. Instillation of DE into mice to recapitulate airway epithelial exposure to chemical extracts in an in vivo setting failed to demonstrate a reduction in CXCL10. There was however an increase in the Th2 type epithelial cell derived inflammatory mediators TSLP and SERPINB2. We also observed an increased macrophages and a decrease in the proportion of lymphocytes in bronchoalveolar lavage fluid. CXCL10 can play a role in allergic airway disease through recruitment of Th1 type CD4+ T-cells, which can act to counterbalance Th2 type allergic responses. Modulation of such chemokines within the airway epithelium may represent a mechanism through which pollutant material can modify respiratory conditions such as allergic asthma.