Age-related differences in pulmonary effects of acute and subchronic episodic ozone exposures in Brown Norway rats

The bidirectional lung brain-axis of amyloid-β pathology: ozone dysregulates the peri-plaque microenvironment

The mechanisms underlying how urban air pollution affects Alzheimer's disease (AD) are largely unknown. Ozone (O3) is a reactive gas component of air pollution linked to increased AD risk, but is confined to the respiratory tract after inhalation, implicating the peripheral immune response to air pollution in AD neuropathology. Here, we demonstrate that O3 exposure impaired the ability of microglia, the brain's parenchymal immune cells, to associate with and form a protective barrier around Aβ plaques, leading to augmented dystrophic neurites and increased Aβ plaque load. Spatial proteomic profiling analysis of peri-plaque proteins revealed a microenvironment-specific signature of dysregulated disease-associated microglia protein expression and increased pathogenic molecule levels with O3 exposure. Unexpectedly, 5xFAD mice exhibited an augmented pulmonary cell and humoral immune response to O3, supporting that ongoing neuropathology may regulate the peripheral O3 response. Circulating HMGB1 was one factor upregulated in only 5xFAD mice, and peripheral HMGB1 was separately shown to regulate brain Trem2 mRNA expression. These findings demonstrate a bidirectional lung-brain axis regulating the central and peripheral AD immune response and highlight this interaction as a potential novel therapeutic target in AD.

The contribution of the neuroendocrine system to adaption after repeated daily ozone exposure in rats

Ozone-induced lung injury/inflammation dissipates despite continued exposure for 3 or more days; however, the mechanisms of adaptation/habituation remain unclear. Since ozone effects are mediated through adrenal-derived stress hormones, which also regulate longevity of centrally-mediated stress response, we hypothesized that ozone-adaptation is linked to diminution of neuroendocrine stress-axes activation and glucocorticoid levels. Male Wistar-Kyoto-rats (12-week-old) were injected with vehicle or a therapeutically-relevant dexamethasone dose (0.01-mg/kg/day; intraperitoneal) for 1-month to determine if suppression of glucocorticoid signaling was linked to adaptation. Vehicle- and dexamethasone-treated rats were exposed to air or 0.8-ppm ozone, 4 h/day × 2 or 4 days to assess the impacts of acute exposure and adaptation, respectively. Dexamethasone reduced thymus and spleen weights, circulating lymphocytes, corticosterone and increased insulin. Ozone increased lavage-fluid protein and neutrophils and decreased circulating lymphocytes at day-2 but not day-4. Ozone-induced hyperglycemia, glucose intolerance and inhibition of beta-cell insulin release occurred at day-1 but not day-3. Ozone depleted circulating prolactin, thyroid-stimulating hormone, and luteinizing-hormone at day-2 but not day-4, suggesting central mediation of adaptation. Adrenal epinephrine biosynthesis gene, Pnmt, was up-regulated after ozone exposure at both timepoints. However, genes involved in glucocorticoid biosynthesis were up-regulated after day-2 but not day-4, suggesting that acute 1- or 2-day ozone-mediated glucocorticoid increase elicits feedback inhibition to dampen hypothalamic stimulation of ACTH release in response to repeated subsequent ozone exposures. Although dexamethasone pretreatment affected circulating insulin, lymphocytes and adrenal genes, it had modest effect on ozone adaptation. In conclusion, ozone adaptation likely involves lack of hypothalamic response due to reduced availability of circulating glucocorticoids.

Ozone-induced changes in oxidative stress parameters in brain regions of adult, middle-age, and senescent Brown Norway rats

A critical part of community based human health risk assessment following chemical exposure is identifying sources of susceptibility. Life stage is one such susceptibility. A prototypic air pollutant, ozone (O3) induces dysfunction of the pulmonary, cardiac, and nervous systems. Long-term exposure may cause oxidative stress (OS). The current study explored age-related and subchronic O3-induced changes in OS in brain regions of rats. To build a comprehensive assessment of OS-related effects of O3, a tripartite approach was implemented focusing on 1) the production of reactive oxygen species (ROS) [NADPH Quinone oxidoreductase 1, NADH Ubiquinone reductase] 2) antioxidant homeostasis [total antioxidant substances, superoxide dismutase, γ-glutamylcysteine synthetase] and 3) an assessment of oxidative damage [total aconitase and protein carbonyls]. Additionally, a neurobehavioral evaluation of motor activity was compared to these OS measures. Male Brown Norway rats (4, 12, and 24 months of age) were exposed to air or O3 (0.25 or 1 ppm) via inhalation for 6 h/day, 2 days per week for 13 weeks. A significant decrease in horizontal motor activity was noted only in 4-month old rats. Results on OS measures in frontal cortex (FC), cerebellum (CB), striatum (STR), and hippocampus (HIP) indicated life stage-related increases in ROS production, small decreases in antioxidant homeostatic mechanisms, a decrease in aconitase activity, and an increase in protein carbonyls. The effects of O3 exposure were brain area-specific, with the STR being more sensitive. Regarding life stage, the effects of O3 were greater in 4-month-old rats, which correlated with horizontal motor activity. These results indicate that OS may be increased in specific brain regions after subchronic O3 exposure, but the interactions between age and exposure along with their consequences on the brain require further investigation.

Air Pollution-Induced Autonomic Modulation

Air pollutants pose a serious worldwide health hazard, causing respiratory and cardiovascular morbidity and mortality. Pollutants perturb the autonomic nervous system, whose function is critical to cardiopulmonary homeostasis. Recent studies suggest that pollutants can stimulate defensive sensory nerves within the cardiopulmonary system, thus providing a possible mechanism for pollutant-induced autonomic dysfunction. A better understanding of the mechanisms involved would likely improve the management and treatment of pollution-related disease.

P53 in the impaired lungs

Our laboratory is focused on investigating the supportive role of P53 towards the maintenance of lung homeostasis. Acute lung injury, acute respiratory distress syndrome, chronic obstructive pulmonary disease, pulmonary fibrosis, bronchial asthma, pulmonary arterial hypertension, pneumonia and tuberculosis are respiratory pathologies, associated with dysfunctions of this endothelium defender (P53). Herein we review the evolving role of P53 towards the aforementioned inflammatory disorders, to potentially reveal new therapeutic possibilities in pulmonary disease.

Transcriptional Effects of Ozone and Impact on Airway Inflammation

Epidemiological and challenge studies in healthy subjects and in individuals with asthma highlight the health impact of environmental ozone even at levels considered safe. Acute ozone exposure in man results in sputum neutrophilia in 30% of subjects particularly young children, females, and those with ongoing cardiopulmonary disease. This may be associated with systemic inflammation although not in all cases. Chronic exposure amplifies these effects and can result in the formation of asthma-like symptoms and immunopathology. Asthmatic patients who respond to ozone (responders) induce a greater number of genes in bronchoalveolar (BAL) macrophages than healthy responders with up-regulation of inflammatory and immune pathways under the control of cytokines and chemokines and the enhanced expression of remodeling and repair programmes including those associated with protease imbalances and cell-cell adhesion. These pathways are under the control of several key transcription regulatory factors including nuclear factor (NF)-κB, anti-oxidant factors such as nuclear factor (erythroid-derived 2)-like 2 NRF2, the p38 mitogen activated protein kinase (MAPK), and priming of the immune system by up-regulating toll-like receptor (TLR) expression. Murine and cellular models of acute and chronic ozone exposure recapitulate the inflammatory effects seen in humans and enable the elucidation of key transcriptional pathways. These studies emphasize the importance of distinct transcriptional networks in driving the detrimental effects of ozone. Studies indicate the critical role of mediators including IL-1, IL-17, and IL-33 in driving ozone effects on airway inflammation, remodeling and hyperresponsiveness. Transcription analysis and proof of mechanisms studies will enable the development of drugs to ameliorate the effects of ozone exposure in susceptible individuals.

The influence of maternal and perinatal high-fat diet on ozone-induced pulmonary responses in offspring

There is growing interest in understanding how maternal diet might affect the sensitivity of offspring to environmental exposures. Previous studies demonstrated that adult rat offspring (approximately 6-months-old) from dams given a high-fat diet (HFD) prior to, during, and after pregnancy displayed elevated pulmonary responses to an acute ozone (O3) exposure. The aim of this study was to examine the influence of maternal and perinatal HFD on pulmonary and metabolic responses to O3 in male and female young-adult offspring (approximately 3-month old). One-month-old F0 female Long-Evans rats commenced HFD (60% kcal from fat) or control diet (CD; 10.5% kcal from fat) and were bred on PND 72. Offspring were maintained on respective HFD or CD until PND 29 when all groups were switched to CD. The 3-months-old female and male offspring (n = 10/group) were exposed to air or 0.8 ppm O3 for 5hr/day for 2 consecutive days. Maternal and perinatal HFD significantly increased body weight and body fat % in offspring regardless of gender. Ozone exposure, but not maternal and perinatal diet, induced hyperglycemia and glucose intolerance in the offspring. Ozone-induced alterations in pulmonary function were exacerbated by maternal and perinatal HFD in both offspring genders. Pulmonary injury/inflammation markers in response to O3 exposure such as bronchoalveolar lavage fluid total protein, lactate dehydrogenase, total cells, and neutrophils were further augmented in offspring (males>females) from dams fed the HFD. Data suggest that maternal and perinatal HFD may enhance the susceptibility of offspring to O3-induced pulmonary injury and that these effects may be sex-specific.

Interaction of Diet and Ozone Exposure on Oxidative Stress Parameters within Specific Brain Regions of Male Brown Norway Rats

Oxidative stress (OS) contributes to the neurological and cardio/pulmonary effects caused by adverse metabolic states and air pollutants such as ozone (O₃). This study explores the interactive effects of O₃ and diet (high-fructose (FRUC) or high–fat (FAT)) on OS in different rat brain regions. In acute exposure, there was a decrease in markers of reactive oxygen species (ROS) production in some brain regions by diet and not by O₃. Total antioxidant substances (TAS) were increased in the cerebellum (CER) and frontal cortex (FC) and decreased in the striatum (STR) by both diets irrespective of O₃ exposure. Protein carbonyls (PC) and total aconitase decreased in some brain regions irrespective of exposure. Following subacute exposure, an increase in markers of ROS was observed in both diet groups. TAS was increased in the FC (FAT only) and there was a clear O₃ effect where TAS was increased in the FC and STR. Diet increased PC formation within the CER in the FAT group, while the hippocampus showed a decrease in PC after O₃ exposure in controls. In general, these results indicate that diet/O₃ did not have a global effect on brain OS parameters, but showed some brain region- and OS parameter-specific effects by diets.

Noncardiogenic pulmonary edema associated with ozone exposure in three kittens

CASE DESCRIPTION Three 21-week-old sexually intact female sibling domestic shorthair cats were brought to an emergency clinic because of signs of sudden respiratory distress that were noted by the owner after the cats had been confined for approximately 10 hours in a room with an operating ozone-generating air purifier. No other potential toxicant exposures were reported. CLINICAL FINDINGS On initial examination, the 3 cats were severely dyspneic and tachypneic. Pulmonary crackles were audible on thoracic auscultation. Thoracic radiography revealed a marked peribronchial, unstructured interstitial pulmonary pattern that coalesced to a patchy alveolar pattern, consistent with noncardiogenic pulmonary edema. TREATMENT AND OUTCOME A diuretic (furosemide, 2 mg/kg [0.9 mg/lb], IV) and bronchodilator (terbutaline sulfate, 0.01 mg/kg [0.005 mg/lb], IM) were administered, and supplemental oxygen was provided by placing the cats in an oxygen cage at 80% oxygen saturation. By 24 hours after placement in the oxygen cage, all cats had unremarkable respiratory rates and thoracic auscultation findings. Complete resolution of the respiratory signs and radiographic pulmonary lesions was achieved within 48 to 72 hours after initial evaluation. At a recheck examination performed 3 months after initial evaluation, the cats remained free of respiratory signs, and no radiographic pulmonary lesions were detected. CLINICAL RELEVANCE To the authors' knowledge, this was the first reported case of pulmonary toxicosis believed to have been caused by ozone exposure in cats. Associated respiratory signs were successfully and rapidly reversed following oxygen supplementation and medical treatment.

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.

Effects of maternal high-fat diet and sedentary lifestyle on susceptibility of adult offspring to ozone exposure in rats

Epidemiological and experimental data suggest that obesity exacerbates the health effects of air pollutants such as ozone (O₃). Maternal inactivity and calorically rich diets lead to offspring that show signs of obesity. Exacerbated O₃ susceptibility of offspring could thus be manifested by maternal obesity. Thirty-day-old female Long-Evans rats were fed a control (CD) or high-fat (HF) (60% calories) diet for 6 wks and then bred. GD1 rats were then housed with a running wheel (RW) or without a wheel (SED) until parturition, creating four groups of offspring: CD-SED, CD-RW, HF-SED and HF-RW. HF diet was terminated at PND 35 and all offspring were placed on CD. Body weight and %fat of dams were greatest in order; HF-SED > HF-RW > CD-SED > CD-RW. Adult offspring were exposed to O₃ for two consecutive days (0.8 ppm, 4 h/day). Glucose tolerance tests (GTT), ventilatory parameters (plethysmography), and bronchoalveolar fluid (BALF) cell counts and protein biomarkers were performed to assess response to O₃. Exercise and diet altered body weight and %fat of young offspring. GTT, ventilation and BALF cell counts were exacerbated by O₃ with responses markedly exacerbated in males. HF diet and O₃ led to significant exacerbation of several BALF parameters: total cell count, neutrophils and lymphocytes were increased in male HF-SED versus CD-SED. Males were hyperglycemic after O₃ exposure and exhibited exacerbated GTT responses. Ventilatory dysfunction was also exacerbated in males. Maternal exercise had minimal effects on O₃ response. The results of this exploratory study suggest a link between maternal obesity and susceptibility to O₃ in their adult offspring in a sex-specific manner.

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

Previous studies have demonstrated that exposure to the pulmonary irritant ozone causes myriad systemic metabolic and pulmonary effects attributed to sympathetic and hypothalamus-pituitary-adrenal (HPA) axis activation, which are exacerbated in metabolically impaired models. We examined respiratory and systemic effects following exposure to a sensory irritant acrolein to elucidate the systemic and pulmonary consequences in healthy and diabetic rat models. Male Wistar and Goto Kakizaki (GK) rats, a nonobese type II diabetic Wistar-derived model, were exposed by inhalation to 0, 2, or 4 ppm acrolein, 4 h/d for 1 or 2 days. Exposure at 4 ppm significantly increased pulmonary and nasal inflammation in both strains with vascular protein leakage occurring only in the nose. Acrolein exposure (4 ppm) also caused metabolic impairment by inducing hyperglycemia and glucose intolerance (GK > Wistar). Serum total cholesterol (GKs only), low-density lipoprotein (LDL) cholesterol (both strains), and free fatty acids (GK > Wistar) levels increased; however, no acrolein-induced changes were noted in branched-chain amino acid or insulin levels. These responses corresponded with a significant increase in corticosterone and modest but insignificant increases in adrenaline in both strains, suggesting activation of the HPA axis. Collectively, these data demonstrate that acrolein exposure has a profound effect on nasal and pulmonary inflammation, as well as glucose and lipid metabolism, with the systemic effects exacerbated in the metabolically impaired GKs. These results are similar to ozone-induced responses with the exception of lung protein leakage and ability to alter branched-chain amino acid and insulin levels, suggesting some differences in neuroendocrine regulation of these two air pollutants.

The perpetuation of the misconception that rats receive a 3-5 times lower lung tissue dose than humans at the same ozone concentration

This paper highlights the pervasive misconception concerning 1994 findings from Hatch et al. about ozone (O₃) tissue dose in humans versus rats. That study exposed humans to 0.4 ppm and rats to 2 ppm ¹⁸O-labeled O₃ and found comparable incorporation of ¹⁸O into bronchoalveolar lavage constituents. However, during O₃ exposure humans were exercising, which increased their ventilation rate five-fold, while rats were at rest. This resulted in similar O₃ tissue doses between the two species, and predominantly explained the comparable ¹⁸O incorporation at five-fold different concentrations. The five-times higher exercising human inhalation rate offset the five-times lower concentration, producing the same human dose expected at rest at 2 ppm (i.e. 0.4 ppm × 4686 L/2 hour ≈ 2 ppm × 998 L/2 hour). In 2013, Hatch et al. showed that resting humans and resting rats experienced fairly comparable ¹⁸O incorporation at the same O₃ exposure concentration and activity state into BALF cells. Despite these findings, we show here that in the peer-reviewed literature a substantial proportion of researchers continue to perpetuate the misunderstanding that human lung tissue doses of O₃ are simply 3-5 times greater than rat doses at the same O₃ concentration, due to interspecies differences, and not considering activity state. It is important to correct this misconception to ensure an appropriate understanding of the implications of O₃ studies by the scientific community and policy experts making regulatory decisions (e.g. the US Environmental Protection Agency's National Ambient Air Quality Standards for O₃).

Systemic metabolic derangement, pulmonary effects, and insulin insufficiency following subchronic ozone exposure in rats

Acute ozone exposure induces a classical stress response with elevated circulating stress hormones along with changes in glucose, protein and lipid metabolism in rats, with similar alterations in ozone-exposed humans. These stress-mediated changes over time have been linked to insulin resistance. We hypothesized that acute ozone-induced stress response and metabolic impairment would persist during subchronic episodic exposure and induce peripheral insulin resistance. Male Wistar Kyoto rats were exposed to air or 0.25ppm or 1.00ppm ozone, 5h/day, 3 consecutive days/week (wk) for 13wks. Pulmonary, metabolic, insulin signaling and stress endpoints were determined immediately after 13wk or following a 1wk recovery period (13wk+1wk recovery). We show that episodic ozone exposure is associated with persistent pulmonary injury and inflammation, fasting hyperglycemia, glucose intolerance, as well as, elevated circulating adrenaline and cholesterol when measured at 13wk, however, these responses were largely reversible following a 1wk recovery. Moreover, the increases noted acutely after ozone exposure in non-esterified fatty acids and branched chain amino acid levels were not apparent following a subchronic exposure. Neither peripheral or tissue specific insulin resistance nor increased hepatic gluconeogenesis were present after subchronic ozone exposure. Instead, long-term ozone exposure lowered circulating insulin and severely impaired glucose-stimulated beta-cell insulin secretion. Thus, our findings in young-adult rats provide potential insights into epidemiological studies that show a positive association between ozone exposures and type 1 diabetes. Ozone-induced beta-cell dysfunction may secondarily contribute to other tissue-specific metabolic alterations following chronic exposure due to impaired regulation of glucose, lipid, and protein metabolism.