Gregory J. Smith

This review aims to summarize the effects of per- and poly-fluoroalkyl substances (PFAS) exposures on the lung, emphasizing data coverage across steps of human health risk assessments. There is expansive literature characterizing PFAS contamination in water, but recent studies have identified PFAS as a component of air pollution, thus impacts on the lung have been an increasing point of inquiry. Mounting evidence from human clinical/epidemiological, animal, and in vitro investigations supports relationships between PFAS exposures and adverse pulmonary outcomes including asthma, allergies, infections, and cancer. Focusing on toxicology studies using animal and in vitro lung cell models, exposures to PFAS modulated inflammation/immune responses, oxidative stress, mucus production, surfactant properties, and epithelial barrier integrity, representing important mechanisms impacting pulmonary health. There are expanding datasets linking PFAS exposures to adverse pulmonary outcomes; however, these data originated from mostly oral/ingestion exposure and not from volatilized or aerosolized PFAS exposure designs. Furthermore, there is a general lack of data informing dose-response modeling and risk characterization, representing gaps needed to characterize pulmonary health risks. The online version contains supplementary material available at 10.1007/s11882-026-01273-6.

Vitamin D aerosols have the potential to protect against exposure to ozone and other inhaled oxidants and prevent the development and exacerbation of lung disease. Here, we show that aerosolized vitamin D treatment decreased ozone-induced oxidative stress and inflammatory responses, as well as decreased production of an oxysterol, β-epoxycholesterol, indicating vitamin D may act as a membrane antioxidant in the airway epithelium.

Acute exposure to ozone (O3) causes pulmonary inflammation and injury in humans and animal models. In rodents, acute O3-induced inflammation and injury can be mitigated by pre-exposure to relatively low concentrations of O3, a phenomenon referred to as tolerance. Although tolerance was first described long ago, the underlying mechanisms are not known. We hypothesized that alveolar macrophages (AMs) play a key role in tolerance to O3 based on prior studies with other exposures. To enable our studies, we first generated a mouse model in which female C57BL6/NJ mice were pre-exposed to filtered air or 0.8 ppm O3 for 4 days (4 h/day), then challenged with 2 ppm O3 (3 h) 2 days later, and phenotyped for airway inflammation and injury 6 or 24 h thereafter. As expected, pre-exposure to O3 resulted in significantly reduced airway inflammation and injury 24 h following O3 challenge. Tolerance was associated with regenerative hyperplasia in the terminal bronchioles and changes in the frequency of proliferating alveolar type 2 cells. O3 pre-exposure altered the expression of ∼1,500 genes in AMs, most notably downregulation of Toll-like receptor and proinflammatory cytokine signaling pathways, suggesting AMs had become hypo-responsive. Depletion of tolerized AMs prior to acute O3 challenge did not, however, alter inflammation and injury. Additionally, adoptive transfer of tolerized AM to naïve recipient mice failed to alter responses to acute O3 challenge. In total, our results argue against an important role for AMs in tolerance to ozone and suggest that other cell types are involved.

As the public health burden of air pollution continues to increase, new strategies to mitigate harmful health effects are needed. Dietary antioxidants have previously been explored to protect against air pollution-induced lung injury producing inconclusive results. Inhaled (pulmonary or nasal) administration of antioxidants presents a more promising approach as it could directly increase antioxidant levels in the airway surface liquid (ASL), providing protection against oxidative damage from air pollution. Several antioxidants have been shown to exhibit antioxidant, anti-inflammatory, and anti-microbial properties in in vitro and in vivo models of air pollution exposure; however, little work has been done to translate these basic research findings into practice. This narrative review summarizes these findings and data from human studies using inhaled antioxidants in response to air pollution, which have produced positive results, indicating further investigation is warranted. In addition to human studies, cell and murine studies should be conducted using more relevant models of exposure such as air–liquid interface (ALI) cultures of primary cells and non-aqueous apical delivery of antioxidants and pollutants. Inhalation of antioxidants shows promise as a protective intervention to prevent air pollution-induced lung injury and exacerbation of existing lung disease.Graphical Abstract

Ozone (O3)-induced respiratory toxicity varies considerably within the human population and across inbred mouse strains, indicative of gene-environment interactions (GxE). Though previous studies have identified several quantitative trait loci (QTL) and candidate genes underlying responses to O3 exposure, precise mechanisms of susceptibility remain incompletely described. We sought to update our understanding of the genetic architecture of O3 responsiveness using the Collaborative Cross (CC) recombinant inbred mouse panel. We evaluated hallmark O3-induced inflammation and injury phenotypes in 56 CC strains after exposure to filtered air or 2 ppm O3, and performed focused genetic analysis of variation in lung injury, as reflected by protein in lung lavage fluid. Strain-dependent responses to O3 were clear, and QTL mapping revealed two novel loci on Chr (Chromosomes) 10 (peak, 26.2 Mb; 80% confidence interval [CI], 24.6–43.6 Mb) and 15 (peak, 47.1 Mb; 80% CI, 40.2–54.9 Mb), the latter surpassing the 95% significance threshold. At the Chr 15 locus, C57BL/6J and CAST/EiJ founder haplotypes were associated with higher lung injury responses compared with all other CC founder haplotypes. With further statistical analysis and a weight of evidence approach, we delimited the Chr 15 QTL to an ∼2 Mb region containing 21 genes (10 protein coding) and nominated three candidate genes, namely Oxr1, Rspo2, and Angpt1. Gene and protein expression data further supported Oxr1 and Angpt1 as priority candidate genes. In summary, we have shown that O3-induced lung injury is modulated by genetic variation, identified two high priority candidate genes, and demonstrated the value of the CC for detecting GxE.

Acute ozone (O₃) exposure is associated with multiple adverse cardiorespiratory outcomes, the severity of which varies across individuals in human populations and inbred mouse strains. However, molecular determinants of response, including susceptibility biomarkers that distinguish who will develop severe injury and inflammation, are not well characterized. We and others have demonstrated that airway macrophages (AMs) are an important resident immune cell type that are functionally and transcriptionally responsive to O₃ inhalation. Here, we sought to explore influences of strain, exposure, and strain-by-O₃ exposure interactions on AM gene expression and identify transcriptional correlates of O₃-induced inflammation and injury across six mouse strains, including five Collaborative Cross (CC) strains. We exposed adult mice of both sexes to filtered air (FA) or 2 ppm O₃ for 3 h and measured inflammatory and injury parameters 21 h later. Mice exposed to O₃ developed airway neutrophilia and lung injury with strain-dependent severity. In AMs, we identified a common core O₃ transcriptional response signature across all strains, as well as a set of genes exhibiting strain-by-O₃ exposure interactions. In particular, a prominent gene expression contrast emerged between a low- (CC017/Unc) and high-responding (CC003/Unc) strain, as reflected by cellular inflammation and injury. Further inspection indicated that differences in their baseline gene expression and chromatin accessibility profiles likely contribute to their divergent post-O₃ exposure transcriptional responses. Together, these results suggest that aspects of O₃-induced respiratory responses are mediated through altered AM transcriptional signatures and further confirm the importance of gene-environment interactions in mediating differential responsiveness to environmental agents.

Ozone is a highly reactive environmental pollutant with well-recognized adverse effects on lung health. Bronchial hyperresponsiveness (BHR) is one consequence of ozone exposure, particularly for individuals with underlying lung disease. Our data demonstrated that ozone induced substantial ATP release from human airway epithelia in vitro and into the airways of mice in vivo and that ATP served as a potent inducer of mast cell degranulation and BHR, acting through P2X7 receptors on mast cells. Both mast cell–deficient and P2X7 receptor–deficient ( P2X7 ^–/– ) mice demonstrated markedly attenuated BHR to ozone. Reconstitution of mast cell–deficient mice with WT mast cells and P2X7 ^–/– mast cells restored ozone-induced BHR. Despite equal numbers of mast cells in reconstituted mouse lungs, mice reconstituted with P2X7 ^–/– mast cells demonstrated significantly less robust BHR than mice reconstituted with WT mast cells. These results support a model where P2X7 on mast cells and other cell types contribute to ozone-induced BHR.