Respiratory Effects and Systemic Stress Response Following Acute Acrolein Inhalation in Rats

Countermeasures against Pulmonary Threat Agents

Inhaled toxicants are used for diverse purposes, ranging from industrial applications such as agriculture, sanitation, and fumigation to crowd control and chemical warfare, and acute exposure can induce lasting respiratory complications. The intentional release of chemical warfare agents (CWAs) during World War I caused life-long damage for survivors, and CWA use is outlawed by international treaties. However, in the past two decades, chemical warfare use has surged in the Middle East and Eastern Europe, with a shift toward lung toxicants. The potential use of industrial and agricultural chemicals in rogue activities is a major concern as they are often stored and transported near populated areas, where intentional or accidental release can cause severe injuries and fatalities. Despite laws and regulatory agencies that regulate use, storage, transport, emissions, and disposal, inhalational exposures continue to cause lasting lung injury. Industrial irritants (e.g., ammonia) aggravate the upper respiratory tract, causing pneumonitis, bronchoconstriction, and dyspnea. Irritant gases (e.g., acrolein, chloropicrin) affect epithelial barrier integrity and cause tissue damage through reactive intermediates or by direct adduction of cysteine-rich proteins. Symptoms of CWAs (e.g., chlorine gas, phosgene, sulfur mustard) progress from airway obstruction and pulmonary edema to acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), which results in respiratory depression days later. Emergency treatment is limited to supportive care using bronchodilators to control airway constriction and rescue with mechanical ventilation to improve gas exchange. Complications from acute exposure can promote obstructive lung disease and/or pulmonary fibrosis, which require long-term clinical care. SIGNIFICANCE STATEMENT: Inhaled chemical threats are of growing concern in both civilian and military settings, and there is an increased need to reduce acute lung injury and delayed clinical complications from exposures. This minireview highlights our current understanding of acute toxicity and pathophysiology of a select number of chemicals of concern. It discusses potential early-stage therapeutic development as well as challenges in developing countermeasures applicable for administration in mass casualty situations.

Serum metabolome and liver transcriptome reveal acrolein inhalation-induced sex-specific homeostatic dysfunction

Acrolein, a respiratory irritant, induces systemic neuroendocrine stress. However, peripheral metabolic effects have not been examined. Male and female WKY rats were exposed to air (0 ppm) or acrolein (3.16 ppm) for 4 h, followed by immediate serum and liver tissue collection. Serum metabolomics in both sexes and liver transcriptomics in males were evaluated to characterize the systemic metabolic response. Of 887 identified metabolites, > 400 differed between sexes at baseline. An acrolein biomarker, 3-hydroxypropyl mercapturic acid, increased 18-fold in males and 33-fold in females, indicating greater metabolic detoxification in females than males. Acrolein exposure changed 174 metabolites in males but only 50 in females. Metabolic process assessment identified higher circulating free-fatty acids, glycerols, and other lipids in male but not female rats exposed to acrolein. In males, acrolein also increased branched-chain amino acids, which was linked with metabolites of nitrogen imbalance within the gut microbiome. The contribution of neuroendocrine stress was evident by increased corticosterone in males but not females. Male liver transcriptomics revealed acrolein-induced over-representation of lipid and protein metabolic processes, and pathway alterations including Sirtuin, insulin-receptor, acute-phase, and glucocorticoid signaling. In sum, acute acrolein inhalation resulted in sex-specific serum metabolomic and liver transcriptomic derangement, which may have connections to chronic metabolic-related diseases.

Multimodal Diagnostics of Changes in Rat Lungs after Vaping

(1) Background: The use of electronic cigarettes has become widespread in recent years. The use of e-cigarettes leads to milder pathological conditions compared to traditional cigarette smoking. Nevertheless, e-liquid vaping can cause morphological changes in lung tissue, which affects and impairs gas exchange. This work studied the changes in morphological and optical properties of lung tissue under the action of an e-liquid aerosol. To do this, we implemented the "passive smoking" model and created the specified concentration of aerosol of the glycerol/propylene glycol mixture in the chamber with the animal. (2) Methods: In ex vivo studies, the lungs of Wistar rats are placed in the e-liquid for 1 h. For in vivo studies, Wistar rats were exposed to the e-liquid vapor in an aerosol administration chamber. After that, lung tissue samples were examined ex vivo using optical coherence tomography (OCT) and spectrometry with an integrating sphere. Absorption and reduced scattering coefficients were estimated for the control and experimental groups. Histological sections were made according to the standard protocol, followed by hematoxylin and eosin staining. (3) Results: Exposure to e-liquid in ex vivo and aerosol in in vivo studies was found to result in the optical clearing of lung tissue. Histological examination of the lung samples showed areas of emphysematous expansion of the alveoli, thickening of the alveolar septa, and the phenomenon of plasma permeation, which is less pronounced in in vivo studies than for the exposure of e-liquid ex vivo. E-liquid aerosol application allows for an increased resolution and improved imaging of lung tissues using OCT. Spectral studies showed significant differences between the control group and the ex vivo group in the spectral range of water absorption. It can be associated with dehydration of lung tissue owing to the hyperosmotic properties of glycerol and propylene glycol, which are the main components of e-liquids. (4) Conclusions: A decrease in the volume of air in lung tissue and higher packing of its structure under e-liquid vaping causes a better contrast of OCT images compared to intact lung tissue.

Comparison of the toxicological potential of two JUUL ENDS products to reference cigarette 3R4F and filtered air in a 90-day nose-only inhalation toxicity study

Electronic nicotine delivery systems (ENDS) are generally recognized as less harmful alternatives for those who would otherwise continue to smoke cigarettes. The potential toxicity of aerosols generated from JUUL Device and Virginia Tobacco (VT3) or Menthol (ME3) JUULpods at 3.0% nicotine concentration was assessed in rats exposed at target aerosol concentrations of 1400 μg/L for up to 6 h/day on a 5 day/week basis for at least 90 days (general accordance with OECD 413). 3R4F reference cigarette smoke (250 μg/L) and Filtered Air were used as comparators. JUUL ENDS product aerosol exposures at >5x the 3R4F cigarette smoke level resulted in greater plasma nicotine and cotinine levels (up to 2x). Notable cigarette smoke related effects included pronounced body weight reductions in male rats, pulmonary inflammation evidenced by elevated lactate dehydrogenase, pro-inflammatory cytokines and neutrophils in bronchoalveolar lavage fluid, increased heart and lung weights, and minimal to marked respiratory tract histopathology. In contrast, ENDS aerosol exposed animals had minimal body weight changes, no measurable inflammatory changes and minimal to mild laryngeal squamous metaplasia. Despite the higher exposure levels, VT3 and ME3 did not result in significant toxicity or appreciable respiratory histopathology relative to 3R4F cigarette smoke following 90 days administration.

Sex-specific respiratory and systemic endocrine effects of acute acrolein and trichloroethylene inhalation

Acrolein and trichloroethylene (TCE) are priority hazardous air pollutants due to environmental prevalence and adverse health effects; however, neuroendocrine stress-related systemic effects are not characterized. Comparing acrolein, an airway irritant, and TCE with low irritancy, we hypothesized that airway injury would be linked to neuroendocrine-mediated systemic alterations. Male and female Wistar-Kyoto rats were exposed nose-only to air, acrolein or TCE in incremental concentrations over 30 min, followed by 3.5-hr exposure to the highest concentration (acrolein - 0.0, 0.1, 0.316, 1, 3.16 ppm; TCE - 0.0, 3.16, 10, 31.6, 100 ppm). Real-time head-out plethysmography revealed acrolein decreased minute volume and increased inspiratory-time (males>females), while TCE reduced tidal-volume. Acrolein, but not TCE, inhalation increased nasal-lavage-fluid protein, lactate-dehydrogenase activity, and inflammatory cell influx (males>females). Neither acrolein nor TCE increased bronchoalveolar-lavage-fluid injury markers, although macrophages and neutrophils increased in acrolein-exposed males and females. Systemic neuroendocrine stress response assessment indicated acrolein, but not TCE, increased circulating adrenocorticotrophic hormone, and consequently corticosterone, and caused lymphopenia, but only in males. Acrolein also reduced circulating thyroid-stimulating hormone, prolactin, and testosterone in males. In conclusion, acute acrolein inhalation resulted in sex-specific upper respiratory irritation/inflammation and systemic neuroendocrine alterations linked to hypothalamic-pituitary-adrenal axes activation, which is critical in mediating extra-respiratory effects.

Acrolein Exposure Impaired Glucose Homeostasis and Increased Risk of Type 2 Diabetes: An Urban Adult Population-Based Cohort Study with Repeated Measures

Acrolein is an identified high-priority hazardous air pollutant ubiquitous in daily life and associated with cardiometabolic risk that attracts worldwide attention. However, the etiology role of acrolein exposure in glucose dyshomeostasis and type 2 diabetes (T2D) is unclear. This repeated-measurement prospective cohort study included 3522 urban adults. Urine/blood samples were repeatedly collected for determinations of acrolein metabolites (N-acetyl-S-(3-hydroxypropyl)-l-cysteine, N-acetyl-S-(2-carboxyethyl)-l-cysteine; acrolein exposure biomarkers), glucose homeostasis, and T2D at baseline and a three-year follow-up. We found that each 3-fold increment in acrolein metabolites was cross-sectionally associated with 5.91-6.52% decrement in homeostasis model assessment-insulin sensitivity (HOMA-IS) and 0.07-0.14 mmol/L, 4.02-4.57, 5.91-6.52, 19-20, 18-19, and 23-31% increments in fasting glucose (FPG), fasting insulin (FPI), HOMA-insulin resistance (HOMA-IR), risks of prevalent IR, impaired fasting glucose (IFG), and T2D, respectively; longitudinally, participants with sustained-high acrolein metabolite levels had increased risks of incident IR, IFG, and T2D by 63-80, 87-99, and 120-154%, respectively (P < 0.05). In addition, biomarkers of heme oxygenase-1 activity (exhaled carbon monoxide), lipid peroxidation (8-iso-prostaglandin-F2α), protein carbonylation (protein carbonyls), and oxidative DNA damage (8-hydroxy-deoxyguanosine) mediated 5.00-38.96% of these associations. Our study revealed that acrolein exposure may impair glucose homeostasis and increase T2D risk via mediating mechanisms of heme oxygenase-1 activation, lipid peroxidation, protein carbonylation, and oxidative DNA damage.

Intratracheal instillation of respirable particulate matter elicits neuroendocrine activation

OBJECTIVE

Inhalation of ozone activates central sympathetic-adrenal-medullary and hypothalamic-pituitary-adrenal stress axes. While airway neural networks are known to communicate noxious stimuli to higher brain centers, it is not known to what extent responses generated from pulmonary airways contribute to neuroendocrine activation.

MATERIALS AND METHODS

Unlike inhalational exposures that involve the entire respiratory tract, we employed intratracheal (IT) instillations to expose only pulmonary airways to either soluble metal-rich residual oil fly ash (ROFA) or compressor-generated diesel exhaust particles (C-DEP). Male Wistar-Kyoto rats (12-13 weeks) were IT instilled with either saline, C-DEP or ROFA (5 mg/kg) and necropsied at 4 or 24 hr to assess temporal effects.

RESULTS

IT-instillation of particulate matter (PM) induced hyperglycemia as early as 30-min and glucose intolerance when measured at 2 hr post-exposure. We observed PM- and time-specific effects on markers of pulmonary injury/inflammation (ROFA>C-DEP; 24 hr>4hr) as corroborated by increases in lavage fluid injury markers, neutrophils (ROFA>C-DEP), and lymphocytes (ROFA). Increases in lavage fluid pro-inflammatory cytokines differed between C-DEP and ROFA in that C-DEP caused larger increases in TNF-α whereas ROFA caused larger increases in IL-6. No increases in circulating cytokines occurred. At 4 hr, PM impacts on neuroendocrine activation were observed through depletion of circulating leukocytes, increases in adrenaline (ROFA), and decreases in thyroid-stimulating-hormone, T3, prolactin, luteinizing-hormone, and testosterone. C-DEP and ROFA both increased lung expression of genes involved in acute stress and inflammatory processes. Moreover, small increases occurred in hypothalamic Fkbp5, a glucocorticoid-sensitive gene.

CONCLUSION

Respiratory alterations differed between C-DEP and ROFA, with ROFA inducing greater overall lung injury/inflammation; however, both PM induced a similar degree of neuroendocrine activation. These findings demonstrate neuroendocrine activation after pulmonary-only PM exposure, and suggest the involvement of pituitary- and adrenal-derived hormones.

Air Pollutant impacts on the brain and neuroendocrine system with implications for peripheral organs: a perspective

Air pollutants are being increasingly linked to extrapulmonary multi-organ effects. Specifically, recent studies associate air pollutants with brain disorders including psychiatric conditions, neuroinflammation and chronic diseases. Current evidence of the linkages between neuropsychiatric conditions and chronic peripheral immune and metabolic diseases provides insights on the potential role of the neuroendocrine system in mediating neural and systemic effects of inhaled pollutants (reactive particulates and gases). Autonomically-driven stress responses, involving sympathetic-adrenal-medullary and hypothalamus-pituitary-adrenal axes regulate cellular physiological processes through adrenal-derived hormones and diverse receptor systems. Recent experimental evidence demonstrates the contribution of the very stress system responding to non-chemical stressors, in mediating systemic and neural effects of reactive air pollutants. The assessment of how respiratory encounter of air pollutants induce lung and peripheral responses through brain and neuroendocrine system, and how the impairment of these stress pathways could be linked to chronic diseases will improve understanding of the causes of individual variations in susceptibility and the contribution of habituation/learning and resiliency. This review highlights effects of air pollution in the respiratory tract that impact the brain and neuroendocrine system, including the role of autonomic sensory nervous system in triggering neural stress response, the likely contribution of translocated nano particles or metal components, and biological mediators released systemically in causing effects remote to the respiratory tract. The perspective on the use of systems approaches that incorporate multiple chemical and non-chemical stressors, including environmental, physiological and psychosocial, with the assessment of interactive neural mechanisms and peripheral networks are emphasized.

Impact of sub-acute acrolein inhalation on the molecular regulation of mitochondrial metabolism in rat lung

Nowadays, mitochondria are recognized as key players in the pathogenesis of a variety of smoking-associated lung diseases. Acrolein, a component of cigarette smoke, is a known driver of biological mechanisms underlying smoking-induced respiratory toxicity. The impact of sub-acute acrolein inhalation in vivo on key processes controlling mitochondrial homeostasis in cells of the airways however is unknown. In this study, we investigated the activity/abundance of a myriad of molecules critically involved in mitochondrial metabolic pathways and mitochondrial quality control processes (mitochondrial biogenesis and mitophagy) in the lungs of Sprague-Dawley rats that were sub-acutely exposed to filtered air or 3 ppm acrolein by whole-body inhalation (5 h/day, 5 days/week for 4 weeks). Acrolein exposure induced a general inflammatory response in the lung as gene expression analysis revealed an increased expression of Icam1 and Cinc1 (p < 0.1; p < 0.05). Acrolein significantly decreased enzyme activity of hydroxyacyl-Coenzyme A dehydrogenase (p < 0.01), and decreased Pdk4 transcript levels (p < 0.05), suggestive of acrolein-induced changes in metabolic processes. Investigation of constituents of the mitochondrial biogenesis pathways and mitophagy machinery revealed no pronounced alterations. In conclusion, sub-acute inhalation of acrolein did not affect the regulation of mitochondrial metabolism and quality control, which is in contrast to more profound changes after acute exposure in other studies.

Association of volatile organic compounds co-exposure with bone health indicators and potential mediators

Limited evidence was found in the associations of volatile organic compound (VOC) exposure with bone health indicators. This study aimed to explore the associations of individual and combined metabolites of VOCs (mVOCs) in urine, a representative of the internal exposure level of VOCs, with bone mineral density (BMD), osteoporosis (OP) and fracture, and potential mediators. Data of the National Health Examination and Nutrition Survey 2005-2006 and 2013-2014 was used. Multiple linear and logistic regression modeling were performed to analyze the associations of individual mVOC with bone health indicators. The least absolute shrinkage and selection operator (LASSO) regression was adopted to select mVOCs that were more relevant to bone health indicators for further weight quantile sum (WQS) analysis used for analyzing the associations between multiple VOC co-exposure and bone health indicators. Mediation analysis was used to identify potential mediators. Seventeen mVOC members with detection rate of >50% in urine of all 3478 participants aged ≥20 years (1829 females) were involved. Levels of most mVOCs were higher in women than men. Eight mVOCs were negatively associated with BMDs, and two and four mVOCs were positively associated with OP and fracture risks, respectively. WQS regression revealed decreased femoral neck BMD (β = -0.010 g/cm², 95% CI: -0.020, -0.0001) and total spine BMD (β = -0.015 g/cm², 95% CI: -0.028, -0.002) in response to increasing mVOC mixture levels. And alkaline phosphatase (ALP), body mass index (BMI), fasting insulin (FI) and high-density lipoprotein (HDL), were mediators in the associations with proportions of mediating effect ranging from 4.6% to 10.2%. Individual and combined VOC (co-)exposure were associated with reduced BMDs in American adults. ALP, BMI, FI and HDL were demonstrated to be mediators in the association of multiple VOC co-exposure with BMD.

Stress Drivers of Glucose Dynamics during Ozone Exposure Measured Using Radiotelemetry in Rats

BACKGROUND

Inhaled irritant air pollutants may trigger stress-related metabolic dysfunction associated with altered circulating adrenal-derived hormones.

OBJECTIVES

We used implantable telemetry in rats to assess real-time changes in circulating glucose during and after exposure to ozone and mechanistically linked responses to neuroendocrine stress hormones.

METHODS

First, using a cross-over design, we monitored glucose during ozone exposures (0.0, 0.2, 0.4, and 0.8 ppm) and nonexposure periods in male Wistar Kyoto rats implanted with glucose telemeters. A second cohort of unimplanted rats was exposed to ozone (0.0, 0.4 or 0.8 ppm) for 30 min, 1 h, 2 h, or 4 h with hormones measured immediately post exposure. We assessed glucose metabolism in sham and adrenalectomized rats, with or without supplementation of adrenergic/glucocorticoid receptor agonists, and in a separate cohort, antagonists.

RESULTS

Ozone (0.8 ppm) was associated with significantly higher blood glucose and lower core body temperature beginning 90 min into exposure, with reversal of effects 4-6 h post exposure. Glucose monitoring during four daily 4-h ozone exposures revealed duration of glucose increases, adaptation, and diurnal variations. Ozone-induced glucose changes were preceded by higher levels of adrenocorticotropic hormone, corticosterone, and epinephrine but lower levels of thyroid-stimulating hormone, prolactin, and luteinizing hormones. Higher glucose and glucose intolerance were inhibited in rats that were adrenalectomized or treated with adrenergic plus glucocorticoid receptor antagonists but exacerbated by agonists.

DISCUSSION

We demonstrated the temporality of neuroendocrine-stress-mediated biological sequalae responsible for ozone-induced glucose metabolic dysfunction and mechanism in a rodent model. Stress hormones assessment with real-time glucose monitoring may be useful in identifying interactions among irritant pollutants and stress-related illnesses. https://doi.org/10.1289/EHP11088.

Acrolein inhalation acutely affects the regulation of mitochondrial metabolism in rat lung

Exposure of the airways to cigarette smoke (CS) is the primary risk factor for developing several lung diseases such as Chronic Obstructive Pulmonary Disease (COPD). CS consists of a complex mixture of over 6000 chemicals including the highly reactive α,β-unsaturated aldehyde acrolein. Acrolein is thought to be responsible for a large proportion of the non-cancer disease risk associated with smoking. Emerging evidence suggest a key role for CS-induced abnormalities in mitochondrial morphology and function in airway epithelial cells in COPD pathogenesis. Although in vitro studies suggest acrolein-induced mitochondrial dysfunction in airway epithelial cells, it is unknown if in vivo inhalation of acrolein affects mitochondrial content or the pathways controlling this. In this study, rats were acutely exposed to acrolein by inhalation (nose-only; 0-4 ppm), 4 h/day for 1 or 2 consecutive days (n = 6/group). Subsequently, the activity and abundance of key constituents of mitochondrial metabolic pathways as well as expression of critical proteins and genes controlling mitochondrial biogenesis and mitophagy were investigated in lung homogenates. A transient decreasing response in protein and transcript abundance of subunits of the electron transport chain complexes was observed following acrolein inhalation. Moreover, acrolein inhalation caused a decreased abundance of key regulators associated with mitochondrial biogenesis, respectively a differential response on day 1 versus day 2. Abundance of components of the mitophagy machinery was in general unaltered in response to acrolein exposure in rat lung. Collectively, this study demonstrates that acrolein inhalation acutely and dose-dependently disrupts the molecular regulation of mitochondrial metabolism in rat lung. Hence, understanding the effect of acrolein on mitochondrial function will provide a scientifically supported reasoning to shortlist aldehydes regulation in tobacco smoke.

Serum branched-chain amino acids modifies the associations between air pollutants and insulin resistance

Growing evidence supports that air pollution exposure has become a risk factor of type II diabetes mellitus through the induction of insulin resistance (IR), but the presented findings did not provide a consistent relationship between air pollution exposure and IR in the temporal scale and the magnitude. Reported associated with IR and air pollution exposure, branched-chain amino acids (BCAAs) in blood might modify the association between air pollution exposure and IR. We took advantage of an existing panel study on elderly people who were healthy or with pre-diabetes. Amino acids were analyzed from the serum samples using a UPLC-QQQ-MS, and the homeostasis model assessment of insulin resistance (HOMA-IR) values were calculated to represent the levels of IR in each visit. Exposures to PM_2.5, NO₂, SO₂, CO, O₃, and black carbon (BC) were estimated using data from a monitoring station. Linear mixed-effects models were applied to estimate the associations between the air pollution and HOMA-IR, as well as the modifying effects of BCAAs. We found significantly higher concentrations of BCAAs in the pre-diabetic subjects than healthy ones. The concentrations of BCAAs were all significantly associated with HOMA-IR. For subjects with high-level BCAAs, HOMA-IR was positively associated with an IQR increase in PM_2.5, NO₂, BC, and CO at lag day 2 and in PM_2.5, SO₂, NO₂, BC, and CO at lag day 7. While for subjects with low-level BCAAs, there was no significant association observed at any lag day except for CO at lag day 5. The study provided evidence that circulating BCAAs may modify the relationship between air pollution exposure and the level of insulin resistance in humans.

The Role of Hepatic Vagal Tone in Ozone-Induced Metabolic Dysfunction in the Liver

Air pollution has been associated with metabolic diseases and hepatic steatosis-like changes. We have shown that ozone alters liver gene expression for metabolic processes through neuroendocrine activation. This study aimed to further characterize ozone-induced changes and to determine the impact of hepatic vagotomy (HV) which reduces parasympathetic influence. Twelve-week-old male Wistar-Kyoto rats underwent HV or sham surgery 5-6 days before air or ozone exposure (0 or 1 ppm; 4 h/day for 1 or 2 days). Ozone-induced lung injury, hyperglycemia, glucose intolerance, and increases in circulating cholesterol, triglycerides, and leptin were similar in rats with HV and sham surgery. However, decreases in circulating insulin and increased HDL and LDL were observed only in ozone-exposed HV rats. Ozone exposure resulted in changed liver gene expression in both sham and HV rats (sham > HV), however, HV did not change expression in air-exposed rats. Upstream target analysis revealed that ozone-induced transcriptomic changes were similar to responses induced by glucocorticoid-mediated processes in both sham and HV rats. The directionality of ozone-induced changes reflecting cellular response to stress, metabolic pathways, and immune surveillance was similar in sham and HV rats. However, pathways regulating cell-cycle, regeneration, proliferation, cell growth, and survival were enriched by ozone in a directionally opposing manner between sham and HV rats. In conclusion, parasympathetic innervation modulated ozone-induced liver transcriptional responses for cell growth and regeneration without affecting stress-mediated metabolic changes. Thus, impaired neuroendocrine axes and parasympathetic innervation could collectively contribute to adverse effects of air pollutants on the liver.

Adrenergic and Glucocorticoid Receptors in the Pulmonary Health Effects of Air Pollution

Adrenergic receptors (ARs) and glucocorticoid receptors (GRs) are activated by circulating catecholamines and glucocorticoids, respectively. These receptors regulate the homeostasis of physiological processes with specificity via multiple receptor subtypes, wide tissue-specific distribution, and interactions with other receptors and signaling processes. Based on their physiological roles, ARs and GRs are widely manipulated therapeutically for chronic diseases. Although these receptors play key roles in inflammatory and cellular homeostatic processes, little research has addressed their involvement in the health effects of air pollution. We have recently demonstrated that ozone, a prototypic air pollutant, mediates pulmonary and systemic effects through the activation of these receptors. A single exposure to ozone induces the sympathetic–adrenal–medullary and hypothalamic–pituitary–adrenal axes, resulting in the release of epinephrine and corticosterone into the circulation. These hormones act as ligands for ARs and GRs. The roles of beta AR (βARs) and GRs in ozone-induced pulmonary injury and inflammation were confirmed in a number of studies using interventional approaches. Accordingly, the activation status of ARs and GRs is critical in mediating the health effects of inhaled irritants. In this paper, we review the cellular distribution and functions of ARs and GRs, their lung-specific localization, and their involvement in ozone-induced health effects, in order to capture attention for future research.

Exposure to volatile organic compounds - acrolein, 1,3-butadiene, and crotonaldehyde - is associated with vascular dysfunction

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Exposure to air pollution, specifically particulate matter of diameter ≤2.5 μm (PM2.5), is a well-established risk factor for CVD. However, the contribution of gaseous pollutant exposure to CVD risk is less clear.

OBJECTIVE

To examine the vascular effects of exposure to individual volatile organic compounds (VOCs) and mixtures of VOCs.

METHODS

We measured urinary metabolites of acrolein (CEMA and 3HPMA), 1,3-butadiene (DHBMA and MHBMA3), and crotonaldehyde (HPMMA) in 346 nonsmokers with varying levels of CVD risk. On the day of enrollment, we measured blood pressure (BP), reactive hyperemia index (RHI - a measure of endothelial function), and urinary levels of catecholamines and their metabolites. We used generalized linear models for evaluating the association between individual VOC metabolites and BP, RHI, and catecholamines, and we used Bayesian Kernel Machine Regression (BKMR) to assess exposure to VOC metabolite mixtures and BP.

RESULTS

We found that the levels of 3HPMA were positively associated with systolic BP (0.98 mmHg per interquartile range (IQR) of 3HPMA; CI: 0.06, 1.91; P = 0.04). Stratified analysis revealed an increased association with systolic BP in Black participants despite lower levels of urinary 3HPMA. This association was independent of PM2.5 exposure and BP medications. BKMR analysis confirmed that 3HPMA was the major metabolite associated with higher BP in the presence of other metabolites. We also found that 3HPMA and DHBMA were associated with decreased endothelial function. For each IQR of 3HPMA or DHBMA, there was a -4.4% (CI: -7.2, -0.0; P = 0.03) and a -3.9% (CI: -9.4, -0.0; P = 0.04) difference in RHI, respectively. Although in the entire cohort the levels of several urinary VOC metabolites were weakly associated with urinary catecholamines and their metabolites, in Black participants, DHBMA levels showed strong associations with urinary norepinephrine and normetanephrine levels.

DISCUSSION

Exposure to acrolein and 1,3-butadiene is associated with endothelial dysfunction and may contribute to elevated risk of hypertension in participants with increased sympathetic tone, particularly in Black individuals.

Peripheral metabolic effects of ozone exposure in healthy and diabetic rats on normal or high-cholesterol diet

Epidemiological studies show that individuals with underlying diabetes and diet-associated ailments are more susceptible than healthy individuals to adverse health effects of air pollution. Exposure to air pollutants can induce metabolic stress and increase cardiometabolic disease risk. Using male Wistar and Wistar-derived Goto-Kakizaki (GK) rats, which exhibit a non-obese type-2 diabetes phenotype, we investigated whether two key metabolic stressors, type-2 diabetes and a high-cholesterol atherogenic diet, exacerbate ozone-induced metabolic effects. Rats were fed a normal control diet (ND) or high-cholesterol diet (HCD) for 12 weeks and then exposed to filtered air or 1.0-ppm ozone (6 h/day) for 1 or 2 days. Metabolic responses were analyzed at the end of each day and after an 18-h recovery period following the 2-day exposure. In GK rats, baseline hyperglycemia and glucose intolerance were exacerbated by HCD vs. ND and by ozone vs. air. HCD also resulted in higher insulin in ozone-exposed GK rats and circulating lipase, aspartate transaminase, and alanine transaminase in all groups (Wistar>GK). Histopathological effects induced by HCD in the liver, which included macrovesicular vacuolation and hepatocellular necrosis, were more severe in Wistar vs. GK rats. Liver gene expression in Wistar and GK rats fed ND showed numerous strain differences, including evidence of increased lipid metabolizing activity and ozone-induced alterations in glucose and lipid transporters, specifically in GK rats. Collectively, these findings indicate that peripheral metabolic alterations induced by diabetes and high-cholesterol diet can enhance susceptibility to the metabolic effects of inhaled pollutants.

Pulmonary and vascular effects of acute ozone exposure in diabetic rats fed an atherogenic diet

Air pollutants may increase risk for cardiopulmonary disease, particularly in susceptible populations with metabolic stressors such as diabetes and unhealthy diet. We investigated effects of inhaled ozone exposure and high-cholesterol diet (HCD) in healthy Wistar and Wistar-derived Goto-Kakizaki (GK) rats, a non-obese model of type 2 diabetes. Male rats (4-week old) were fed normal diet (ND) or HCD for 12 weeks and then exposed to filtered air or 1.0 ppm ozone (6 h/day) for 1 or 2 days. We examined pulmonary, vascular, hematology, and inflammatory responses after each exposure plus an 18-h recovery period. In both strains, ozone induced acute bronchiolar epithelial necrosis and inflammation on histopathology and pulmonary protein leakage and neutrophilia; the protein leakage was more rapid and persistent in GK compared to Wistar rats. Ozone also decreased lymphocytes after day 1 in both strains consuming ND (~50%), while HCD increased circulating leukocytes. Ozone increased plasma thrombin/antithrombin complexes and platelet disaggregation in Wistar rats on HCD and exacerbated diet effects on serum IFN-γ, IL-6, KC-GRO, IL-13, and TNF-α, which were higher with HCD (Wistar>GK). Ex vivo aortic contractility to phenylephrine was lower in GK versus Wistar rats at baseline(~30%); ozone enhanced this effect in Wistar rats on ND. GK rats on HCD had higher aortic e-NOS and tPA expression compared to Wistar rats. Ozone increased e-NOS in GK rats on ND (~3-fold) and Wistar rats on HCD (~2-fold). These findings demonstrate ways in which underlying diabetes and HCD may exacerbate pulmonary, systemic, and vascular effects of inhaled pollutants.

The Impacts of Illegal Toxic Waste Dumping on Children's Health: A Review and Case Study from Pasir Gudang, Malaysia

Poor management of hazardous waste can lead to environmental pollution, injuries, and adverse health risks. Children’s exposure to hazardous waste may cause serious acute and chronic health problems due to their higher vulnerability to the toxic effects of chemicals. This study examines an incident of illegal chemical dumping in Pasir Gudang, Malaysia and its potential health impacts on children. The study introduced a risk assessment of possible health-related effects due to chemical contamination based on a real case scenario where quantification of the contamination was not feasible. A literature review and spatial analysis were used as research methods. On 6th March 2019, tons of hazardous waste were illegally disposed into Kim Kim River, Pasir Gudang, Malaysia. They were identified as benzene, acrolein, acrylonitrile, hydrogen chloride, methane, toluene, xylene, ethylbenzene, and d-limonene. As a result, 975 students in the vicinity developed signs and symptoms of respiratory disease due to the chemical poisoning. The findings of this study indicate that more effective policies and preventive actions are urgently needed to protect human health, especially children from improper hazardous waste management.

Offspring susceptibility to metabolic alterations due to maternal high-fat diet and the impact of inhaled ozone used as a stressor

The influence of maternal high-fat diet (HFD) on metabolic response to ozone was examined in Long-Evans rat offspring. F0 females were fed control diet (CD; 10%kcal from fat) or HFD (60%kcal from fat) starting at post-natal day (PND) 30. Rats were bred on PND 72. Dietary regimen was maintained until PND 30 when all offspring were switched to CD. On PND 40, F1 offspring (n = 10/group/sex) were exposed to air or 0.8 ppm ozone for 5 h. Serum samples were collected for global metabolomic analysis (n = 8/group/sex). Offspring from HFD dams had increased body fat and weight relative to CD. Metabolomic analysis revealed significant sex-, diet-, and exposure-related changes. Maternal HFD increased free fatty acids and decreased phospholipids (male > female) in air-exposed rats. Microbiome-associated histidine and tyrosine metabolites were increased in both sexes, while 1,5-anhydroglucitol levels decreased in males indicating susceptibility to insulin resistance. Ozone decreased monohydroxy fatty acids and acyl carnitines and increased pyruvate along with TCA cycle intermediates in females (HFD > CD). Ozone increased various amino acids, polyamines, and metabolites of gut microbiota in HFD female offspring indicating gut microbiome alterations. Collectively, these data suggest that maternal HFD increases offspring susceptibility to metabolic alterations in a sex-specific manner when challenged with environmental stressors.

Oleic acid and derivatives affect human endothelial cell mitochondrial function and vasoactive mediator production

BACKGROUND

Inhalation of common air pollutants such as diesel and biodiesel combustion products can induce vascular changes in humans which may contribute to increased mortality and morbidity associated with fine particulate matter exposures. Diesel, biodiesel, and other combustion byproducts contain fatty acid components capable of entering the body through particulate matter inhalation. Fatty acids can also be endogenously released into circulation following a systemic stress response to some inhaled pollutants such as ozone. When in the circulation, bioactive fatty acids may interact with cells lining the blood vessels, potentially inducing endothelial dysfunction. To examine whether fatty acids could potentially be involved in human vascular responses to air pollutants, we determined the effects of fatty acids and derivatives on important vascular cell functions.

METHODS

Human umbilical vein endothelial cells (HUVEC) were exposed in vitro to oleic acid (OA) or OA metabolites for 4-48 h. Cytotoxicity, vasodilator production (by ELISA measurement), mitochondrial function (using Sea Horse assays), and iron metabolism (inferred by ICP-OES measurements) were examined, with standard statistical testing (ANOVA, t-tests) employed.

RESULTS

Dose-dependent cytotoxicity was noted at 24 h, with 12-hydroxy OA more potent than OA. Mitochondrial stress testing showed that 12-hydroxy OA and OA induce mitochondrial dysfunction. Analysis of soluble mediator release from HUVEC showed a dose-dependent increase in prostaglandin F2α, a lipid involved in control of vascular tone, at 24 h (85% above controls) after OA-BSA exposure. RT-PCR analysis revealed OA did not induce changes in gene expression at noncytotoxic concentrations in exposed HUVEC, but 12-OH OA did alter ICAM and COX2 gene expression.

CONCLUSIONS

Together, these data demonstrate that FA may be capable of inducing cytotoxic effects and altering expression of mediators of vascular function following inhalation exposure, and may be implicated in air pollutant-induced deaths and hospitalizations. (267 of max 350 words).

Susceptibility Variations in Air Pollution Health Effects: Incorporating Neuroendocrine Activation

Diverse host factors/phenotypes may exacerbate or diminish biological responses induced by air pollutant exposure. We lack an understanding of biological indicators of environmental exposures that culminate in a physiological response versus those that lead to adversity. Variations in response phenotype might arise centrally and/or at the local tissue level. In addition to genetic differences, the current evidence supports the roles of preexisting cardiopulmonary diseases, diabetes, diet, adverse prenatal environments, neurobehavioral disorders, childhood infections, microbiome, sex, and psychosocial stressors in modifying the susceptibility to air pollutant exposures. Animal models of human diseases, obesity, nutritional inadequacies, and neurobehavioral conditions have been compared with healthy controls to understand the causes of variations in susceptibility. Although psychosocial stressors have been associated with increased susceptibility to air pollutant effects, the contribution of neuroendocrine stress pathways in mediating these effects is just emerging. The new findings of neuroendocrine activation leading to systemic metabolic and immunological effects of air pollutants, and the potential contribution to allostatic load, emphasize the consideration of these mechanisms into susceptibility. Variations in susceptibility to air pollution health effects are likely to underlie host genetic and physiological conditions in concert with disrupted neuroendocrine circuitry that alters physiological stability under the influence of stressors.

Beta-2 Adrenergic and Glucocorticoid Receptor Agonists Modulate Ozone-Induced Pulmonary Protein Leakage and Inflammation in Healthy and Adrenalectomized Rats

We have shown that acute ozone inhalation activates sympathetic-adrenal-medullary and hypothalamus-pituitary-adrenal stress axes, and adrenalectomy (AD) inhibits ozone-induced lung injury and inflammation. Therefore, we hypothesized that stress hormone receptor agonists (β2 adrenergic-β2AR and glucocorticoid-GR) will restore the ozone injury phenotype in AD, while exacerbating effects in sham-surgery (SH) rats. Male Wistar Kyoto rats that underwent SH or AD were treated with vehicles (saline + corn oil) or β2AR agonist clenbuterol (CLEN, 0.2 mg/kg, i.p.) + GR agonist dexamethasone (DEX, 2 mg/kg, s.c.) for 1 day and immediately prior to each day of exposure to filtered air or ozone (0.8 ppm, 4 h/day for 1 or 2 days). Ozone-induced increases in PenH and peak-expiratory flow were exacerbated in CLEN+DEX-treated SH and AD rats. CLEN+DEX affected breath waveform in all rats. Ozone exposure in vehicle-treated SH rats increased bronchoalveolar lavage fluid (BALF) protein, N-acetyl glucosaminidase activity (macrophage activation), neutrophils, and lung cytokine expression while reducing circulating lymphocyte subpopulations. AD reduced these ozone effects in vehicle-treated rats. At the doses used herein, CLEN+DEX treatment reversed the protection offered by AD and exacerbated most ozone-induced lung effects while diminishing circulating lymphocytes. CLEN+DEX in air-exposed SH rats also induced marked protein leakage and reduced circulating lymphocytes but did not increase BALF neutrophils. In conclusion, circulating stress hormones and their receptors mediate ozone-induced vascular leakage and inflammatory cell trafficking to the lung. Those receiving β2AR and GR agonists for chronic pulmonary diseases, or with increased circulating stress hormones due to psychosocial stresses, might have altered sensitivity to air pollution.

The impact of smoking and the influence of other factors on lung cancer

Introduction: Smoking is the main preventable cause of lung cancer. This review summarizes preclinical and clinical data on the mechanisms of smoking-associated cancer development of the major histological lung cancer types small cell lung carcinoma squamous cell carcinoma and pulmonary adenocarcinoma (PAC) and the impact of several factors other than smoking on this process. Areas covered: The role of intracellular signaling induced by nicotinic receptors and beta-adrenergic receptors, the resulting increase in intracellular cyclic adenosine monophosphate (cAMP) as a key driver of PAC and the promoting effects of respiratory tract diseases and their therapeutics, psychological stress and global warming. Expert opinion: Smoking has deleterious effects on the regulation of lung epithelia by neurotransmitter receptors that are further enhanced by gene mutations. Sensitization of the alpha-7 nicotinic receptor (α7nAChR) by COPD enhances the carcinogenic effects of smoking and turns nicotine into a carcinogen. Nicotine vaping may, therefore, cause cancer in individuals with chronic obstructive pulmonary disease. The opposing effects of cAMP on the major lung cancer types indicate that patients with PAC of Clara cell phenotype (PAC-Cl) will benefit from treatment with cAMP reducers and suggest that global warming-induced respiratory tract diseases and their therapeutics cause the global increase in the incidence of PAC.

Neuroendocrine Regulation of Air Pollution Health Effects: Emerging Insights

Air pollutant exposures are linked to cardiopulmonary diseases, diabetes, metabolic syndrome, neurobehavioral conditions, and reproductive abnormalities. Significant effort is invested in understanding how pollutants encountered by the lung might induce effects in distant organs. The role of circulating mediators has been predicted; however, their origin and identity have not been confirmed. New evidence has emerged which implicates the role of neuroendocrine sympathetic-adrenal-medullary (SAM) and hypothalamic-pituitary-adrenal (HPA) stress axes in mediating a wide array of systemic and pulmonary effects. Our recent studies using ozone exposure as a prototypical air pollutant demonstrate that increases in circulating adrenal-derived stress hormones (epinephrine and cortisol/corticosterone) contribute to lung injury/inflammation and metabolic effects in the liver, pancreas, adipose, and muscle tissues. When stress hormones are depleted by adrenalectomy in rats, most ozone effects including lung injury/inflammation are diminished. Animals treated with antagonists for adrenergic and glucocorticoid receptors show inhibition of the pulmonary and systemic effects of ozone, whereas treatment with agonists restore and exacerbate the ozone-induced injury/inflammation phenotype, implying the role of neuroendocrine activation. The neuroendocrine system is critical for normal homeostasis and allostatic activation; however, chronic exposure to stressors may lead to increases in allostatic load. The emerging mechanisms by which circulating mediators are released and are responsible for producing multiorgan effects of air pollutants insists upon a paradigm shift in the field of air pollution and health. Moreover, since these neuroendocrine responses are linked to both chemical and nonchemical stressors, the interactive influence of air pollutants, lifestyle, and environmental factors requires further study.

Effects of Simulated Smog Atmospheres in Rodent Models of Metabolic and Immunologic Dysfunction

Air pollution is a diverse and dynamic mixture of gaseous and particulate matter, limiting our understanding of associated adverse health outcomes. The biological effects of two simulated smog atmospheres (SA) with different compositions but similar air quality health indexes were compared in a nonobese diabetic rat model (Goto-Kakizaki, GK) and three mouse immune models (house dust mite (HDM) allergy, antibody response to heat-killed pneumococcus, and resistance to influenza A infection). In GK rats, both SA-PM (high particulate matter) and SA-O3 (high ozone) decreased cholesterol levels immediately after a 4-h exposure, whereas only SA-O3 increased airflow limitation. Airway responsiveness to methacholine was increased in HDM-allergic mice compared with nonallergic mice, but exposure to SA-PM or SA-O3 did not significantly alter responsiveness. Exposure to SA-PM did not affect the IgM response to pneumococcus, and SA-O3 did not affect virus titers, although inflammatory cytokine levels were decreased in mice infected at the end of a 7-day exposure. Collectively, acute SA exposures produced limited health effects in animal models of metabolic and immune diseases. Effects of SA-O3 tended to be greater than those of SA-PM, suggesting that gas-phase components in photochemically derived multipollutant mixtures may be of greater concern than secondary organic aerosol PM.

Adrenergic and glucocorticoid receptor antagonists reduce ozone-induced lung injury and inflammation

Recent studies showed that the circulating stress hormones, epinephrine and corticosterone/cortisol, are involved in mediating ozone-induced pulmonary effects through the activation of the sympathetic-adrenal-medullary (SAM) and hypothalamus-pituitary-adrenal (HPA) axes. Hence, we examined the role of adrenergic and glucocorticoid receptor inhibition in ozone-induced pulmonary injury and inflammation. Male 12-week old Wistar-Kyoto rats were pretreated daily for 7days with propranolol (PROP; a non-selective β adrenergic receptor [AR] antagonist, 10mg/kg, i.p.), mifepristone (MIFE; a glucocorticoid receptor [GR] antagonist, 30mg/kg, s.c.), both drugs (PROP+MIFE), or respective vehicles, and then exposed to air or ozone (0.8ppm), 4h/d for 1 or 2 consecutive days while continuing drug treatment. Ozone exposure alone led to increased peak expiratory flow rates and enhanced pause (Penh); with greater increases by day 2. Receptors blockade minimally affected ventilation in either air- or ozone-exposed rats. Ozone exposure alone was also associated with marked increases in pulmonary vascular leakage, macrophage activation, neutrophilic inflammation and lymphopenia. Notably, PROP, MIFE and PROP+MIFE pretreatments significantly reduced ozone-induced pulmonary vascular leakage; whereas PROP or PROP+MIFE reduced neutrophilic inflammation. PROP also reduced ozone-induced increases in bronchoalveolar lavage fluid (BALF) IL-6 and TNF-α proteins and/or lung Il6 and Tnfα mRNA. MIFE and PROP+MIFE pretreatments reduced ozone-induced increases in BALF N-acetyl glucosaminidase activity, and lymphopenia. We conclude that stress hormones released after ozone exposure modulate pulmonary injury and inflammatory effects through AR and GR in a receptor-specific manner. Individuals with pulmonary diseases receiving AR and GR-related therapy might experience changed sensitivity to air pollution.