Ozone-dependent increases in lung glucocorticoids and macrophage response: Effect modification by innate stress axis function

Toxicological inhalation studies in rats to substantiate grouping of zinc oxide nanoforms

BACKGROUND

Significant variations exist in the forms of ZnO, making it impossible to test all forms in in vivo inhalation studies. Hence, grouping and read-across is a common approach under REACH to evaluate the toxicological profile of familiar substances. The objective of this paper is to investigate the potential role of dissolution, size, or coating in grouping ZnO (nano)forms for the purpose of hazard assessment. We performed a 90-day inhalation study (OECD test guideline no. (TG) 413) in rats combined with a reproduction/developmental (neuro)toxicity screening test (TG 421/424/426) with coated and uncoated ZnO nanoforms in comparison with microscale ZnO particles and soluble zinc sulfate. In addition, genotoxicity in the nasal cavity, lungs, liver, and bone marrow was examined via comet assay (TG 489) after 14-day inhalation exposure.

RESULTS

ZnO nanoparticles caused local toxicity in the respiratory tract. Systemic effects that were not related to the local irritation were not observed. There was no indication of impaired fertility, developmental toxicity, or developmental neurotoxicity. No indication for genotoxicity of any of the test substances was observed. Local effects were similar across the different ZnO test substances and were reversible after the end of the exposure.

CONCLUSION

With exception of local toxicity, this study could not confirm the occasional findings in some of the previous studies regarding the above-mentioned toxicological endpoints. The two representative ZnO nanoforms and the microscale particles showed similar local effects. The ZnO nanoforms most likely exhibit their effects by zinc ions as no particles could be detected after the end of the exposure, and exposure to rapidly soluble zinc sulfate had similar effects. Obviously, material differences between the ZnO particles do not substantially alter their toxicokinetics and toxicodynamics. The grouping of ZnO nanoforms into a set of similar nanoforms is justified by these observations.

Impact of climate change on immune responses and barrier defense

Climate change is not just jeopardizing the health of our planet but is also increasingly affecting our immune health. There is an expanding body of evidence that climate-related exposures such as air pollution, heat, wildfires, extreme weather events, and biodiversity loss significantly disrupt the functioning of the human immune system. These exposures manifest in a broad range of stimuli, including antigens, allergens, heat stress, pollutants, microbiota changes, and other toxic substances. Such exposures pose a direct and indirect threat to our body's primary line of defense, the epithelial barrier, affecting its physical integrity and functional efficacy. Furthermore, these climate-related environmental stressors can hyperstimulate the innate immune system and influence adaptive immunity-notably, in terms of developing and preserving immune tolerance. The loss or failure of immune tolerance can instigate a wide spectrum of noncommunicable diseases such as autoimmune conditions, allergy, respiratory illnesses, metabolic diseases, obesity, and others. As new evidence unfolds, there is a need for additional research in climate change and immunology that covers diverse environments in different global settings and uses modern biologic and epidemiologic tools.

Plasma sterols and vitamin D are correlates and predictors of ozone-induced inflammation in the lung: A pilot study

BACKGROUND

Ozone (O3) exposure causes respiratory effects including lung function decrements, increased lung permeability, and airway inflammation. Additionally, baseline metabolic state can predispose individuals to adverse health effects from O3. For this reason, we conducted an exploratory study to examine the effect of O3 exposure on derivatives of cholesterol biosynthesis: sterols, oxysterols, and secosteroid (25-hydroxyvitamin D) not only in the lung, but also in circulation.

METHODS

We obtained plasma and induced sputum samples from non-asthmatic (n = 12) and asthmatic (n = 12) adult volunteers 6 hours following exposure to 0.4ppm O3 for 2 hours. We quantified the concentrations of 24 cholesterol precursors and derivatives by UPLC-MS and 30 cytokines by ELISA. We use computational analyses including machine learning to determine whether baseline plasma sterols are predictive of O3 responsiveness.

RESULTS

We observed an overall decrease in the concentration of cholesterol precursors and derivatives (e.g. 27-hydroxycholesterol) and an increase in concentration of autooxidation products (e.g. secosterol-B) in sputum samples. In plasma, we saw a significant increase in the concentration of secosterol-B after O3 exposure. Machine learning algorithms showed that plasma cholesterol was a top predictor of O3 responder status based on decrease in FEV1 (>5%). Further, 25-hydroxyvitamin D was positively associated with lung function in non-asthmatic subjects and with sputum uteroglobin, whereas it was inversely associated with sputum myeloperoxidase and neutrophil counts.

CONCLUSION

This study highlights alterations in sterol metabolites in the airway and circulation as potential contributors to systemic health outcomes and predictors of pulmonary and inflammatory responsiveness following O3 exposure.

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.

Ozone exposure and blood transcriptome: A randomized, controlled, crossover trial among healthy adults

RATIONALE

Transcriptome-wide analysis is powerful in studying systemic RNA changes following environmental exposures. However, impacts of ozone inhalation on circulating transcriptome have not yet been examined.

OBJECTIVES

To explore the impact of acute ozone exposure on circulating transcriptome using RNA sequencing (RNA-seq).

METHODS

We recruited 32 healthy young adults in a randomized, crossover, controlled exposure trial. Each participant completed two 2-h exposure sessions of ozone (200 ppb) and clean air, respectively. Blood samples were collected at the end of each session and were used for RNA-seq. The differentially expressed genes associated with ozone exposure were assessed using Bayesian adjusted statistics from linear models in the limma R package.

RESULTS

A total of 29 participants finished this trial and donated their blood samples for transcriptome analysis. The average concentration of ozone was 7.8 ± 2.6 ppb under clean air and 201.1 ± 1.7 ppb under ozone exposure session. A total of 1899 genes were significantly changed (1067 up-regulated and 832 down-regulated) by ozone exposure at a false discovery rate < 0.05, in which 403 genes had a fold change of > 1.2 or < 0.8. The top 10 terms of biological processes showed that most of the differentially expressed genes were related to various functions, such as neutrophil degranulation, immune response, and neutrophil activation. Pathway enrichment analysis showed dozens of pathways were dysregulated after ozone exposure, including mitochondrial dysfunction, and glucocorticoid receptor signaling.

CONCLUSION

For the first time this trial characterized the genome-wide changes of mRNA in response to ozone exposure. We identified a range of differentially expressed genes that were involved in dozens of biological processes and pathways, providing novel biological insights into the systemic health effects of ozone.

Modulation by Ozone of Glucocorticoid-Regulating Factors in the Lungs in Relation to Stress Axis Reactivity

Exposure to air pollutants increases levels of circulating glucocorticoid stress hormones that exert profound effects relevant to health and disease. However, the nature and magnitude of tissue-level effects are modulated by factors that regulate local glucocorticoid activity; accordingly, inter-individual differences could contribute to susceptibility. In the present study, we characterized effects of ozone (O₃) inhalation on glucocorticoid-regulating factors in the lungs of rat strains with contrasting hypothalamic–pituitary–adrenal stress axis responses. Hyper-responsive Fischer (F344) and less responsive Lewis (LEW) rats were exposed to air or 0.8 ppm O₃ for 4 h by nose-only inhalation. Levels of the high-specificity and -affinity corticosteroid-binding globulin protein increased in the lungs of both strains proportional to the rise in corticosterone levels following O₃ exposure. Ozone reduced the ratio of 11β-hydroxysteroid dehydrogenase type 1 (HSDB1)/HSDB2 mRNA in the lungs of F344 but not LEW, indicating strain-specific transcriptional regulation of the major glucocorticoid metabolism factors that control tissue-level action. Intercellular adhesion molecule (ICAM)-1 and total elastase activity were increased by O₃ in both strains, consistent with extravasation and tissue remodeling processes following injury. However, mRNA levels of inflammatory markers were significantly higher in the lungs of O₃-exposed LEW compared to F344. The data show that strain differences in the glucocorticoid response to O₃ are accompanied by corresponding changes in regulatory factors, and that these effects are collectively associated with a differential inflammatory response to O₃. Innate differences in glucocorticoid regulatory factors may modulate the pulmonary effects of inhaled pollutants, thereby contributing to differential susceptibility.

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.