Airborne particulate matter with a diameter of 2.5 µm or less (PM_2.5) has often been reported to be associated with the cardiovascular toxic effects of air pollution mixtures and ozone (O₃) with respiratory illness.^1,2 However, there is increasing evidence that O₃, independent of PM_2.5, is also associated with cardiovascular mortality.^3,4 For example, O₃ has been associated with increases in mortality due to embolism and thrombosis,⁵ ischemic heart disease,³ heart failure,⁴ and stroke.⁶ However, not all studies reporting associations of O₃ with cardiovascular outcomes found that the associations were independent from particulate matter and other gaseous pollutants, such as nitrogen dioxide (NO₂) and sulfur dioxide (SO₂).^7,8 Other studies have found nonsignificant or seemingly “beneficial” associations between O₃ and cardiovascular outcomes.^9,10 The uncertainty in epidemiologic findings of O₃ cardiovascular effects is further enhanced by the limited understanding of biological mechanisms underlying the epidemiologic associations.¹¹

Transient receptor potential protein (TRP) ion channels TRPA1 and TRPV1 may be important in mediating airway tissue injury and inflammation. This study was designed to clarify the role of TRPA1 and TRPV1 channels in cigarette smoke extract (CSE)-induced damage to bronchial and alveolar epithelial cells. Alveolar epithelial (A549) cells and bronchial epithelial (Beas-2B) cells were treated with CSE in the presence and absence of a TRPA1 inhibitor (100 μM, A967079), a TRPV1 inhibitor (100 μM, AMG9810) or both. DCFH-DA and MitoSOX Red probes were used to assay intracellular and mitochondrial oxidative stress, respectively. The mRNA levels of inflammatory mediators (IL-1β, IL-8, IL-18, IL-33) and antioxidants (HO-1, NQO1, MnSOD, catalase) and the protein expression levels of mitochondrial and inflammasome factors (MFN2, OPA1, DRP1, MFF, NLRP3,caspase-1) were respectively detected by RT-PCR and Western Blot. The results were validated in TRPA1 shRNA and TRPV1 shRNA cells. In both cell types, 10% CSE increased intracellular and mitochondrial oxidative stress, induced Ca2+ influx, increased inflammatory gene expression, reduced antioxidant gene expression and inhibited the activities of mitochondrial respiratory chain (MRC) complexes. 10% CSE increased the expression of mitochondrial fission proteins (MFF and DRP1), Caspase-1 and NLRP3 protein expression and decreased that of mitochondrial fusion proteins (MFN2 and OPA1). Both inhibitors and gene-knockout of TRPA1 and TRPV1 reduced oxidative stress, blocked Ca2+ influx, and inhibited inflammatory and increased antioxidant gene expression. They also prevented the changes in mitochondrial fission and fusion proteins and in MRC complexes activities induced by CSE. Both TRPA1 and TRPV1 mediate CSE-induced damage of bronchial and alveolar epithelial cells via modulation of oxidative stress, inflammation and mitochondrial damage and their inhibition should be considered as potential therapy for COPD.

Mitochondrial damage leading to oxidant stress may play an important role in the pathogenesis of airflow obstruction and emphysema. NLPR3 inflammasome can be activated by mitochondrial ROS (mtROS) and other stimuli. We examined the importance of mtROS and NLRP3 inflammasome and their interactions in multiple ozone-induced lung inflammation and emphysema. C57/BL6 mice were exposed to ozone (2.5 ppm, 3 h) or filtered air twice a week over 6 weeks. MitoTEMPO (20 mg/kg), an inhibitor of mtROS, and VX765 (100 mg/kg), an inhibitor of caspase-1 activity, were administered by intraperitoneal or intragastric injection respectively 1 h prior to each ozone exposure for 6 weeks. Ozone-exposed mice had increased bronchoalveolar lavage (BAL) total cells and levels of IL-1β, KC and IL-6, augmented lung tissue inflammation scores, enhanced oxidative stress with higher serum 8-OHdG concentrations, emphysema with greater mean linear intercept (Lm), airway remodeling with increased airway smooth muscle mass and airflow limitation as indicated by a reduction in the ratio of forced expiratory volume at 25 and 50 milliseconds to forced vital capacity (FEV25/FVC, FEV50/FVC). Both MitoTEMPO and VX765 reduced lung inflammation scores, cytokine levels, oxidative stress and increased mitochondrial fission proteins. VX765 also attenuated emphysema, airway remodeling and airflow limitation. MitoTEMPO inhibited the increased expression of mitochondrial complex II and IV and of NLPR3 while VX765 inhibited the expression and activity of NLRP3 and caspase-1 pathway in the lung. Both mtROS and NLRP3 inflammasome play a role in ozone-induced lung inflammation while only NLRP3 is involved in ozone-induced emphysema.

Oxidative stress plays a role in the pathophysiology of emphysema through the activation of tissue proteases and apoptosis. We examined the effects of ozone exposure by exposing BALB/c mice to either a single 3-h exposure or multiple exposures over 3 or 6 wk, with two 3-h exposures per week. Compared with air-exposed mice, the increase in neutrophils in bronchoalveolar lavage fluid and lung inflammation index was greatest in mice exposed for 3 and 6 wk. Lung volumes were increased in 3- and 6-wk-exposed mice but not in single-exposed. Alveolar space and mean linear intercept were increased in 6- but not 3-wk-exposed mice. Caspase-3 and apoptosis protease activating factor-1 immunoreactivity was increased in the airway and alveolar epithelium and macrophages of 3- and 6-wk-exposed mice. Interleukin-13, keratinocyte chemoattractant, caspase-3, and IFN-γ mRNA were increased in the 6-wk-exposed group, but heme oxygenase-1 (HO-1) mRNA decreased. matrix metalloproteinase-12 (MMP-12) and caspase-3 protein expression increased in lungs of 6-wk-exposed mice. Collagen area increased and epithelial area decreased in airway wall at 3- and 6-wk exposure. Exposure of mice to ozone for 6 wk induced a chronic inflammatory process, with alveolar enlargement and damage linked to epithelial apoptosis and increased protease expression.

Ozone is an oxidizing environmental pollutant that contributes significantly to respiratory health. Exposure to increased levels of ozone has been associated with worsening of symptoms of patients with asthma and COPD (chronic obstructive pulmonary disease). In the present study, we investigated the acute and chronic effects of ozone exposure-induced oxidative stress-related inflammation mechanics in mouse lung. In particular, we investigated the oxidative stress-induced effects on HDAC2 (histone deacetylase 2) modification and activation of the Nrf2 (nuclear factor erythroid-related factor 2) and HIF-1α (hypoxia-inducible factor-1α) signalling pathways. Male C57BL/6 mice were exposed to ozone (3 p.p.m.) for 3 h a day, twice a week for a period of 1, 3 or 6 weeks. Control mice were exposed to normal air. After the last exposure, mice were killed for BAL (bronchoalveolar lavage) fluid and lung tissue collection. BAL total cell counts were elevated at all of the time points studied. This was associated with increased levels of chemokines and cytokines in all ozone-exposed groups, indicating the presence of a persistent inflammatory environment in the lung. Increased inflammation and L_m (mean linear intercept) scores were observed in chronic exposed mice, indicating emphysematous changes were present in lungs of chronic exposed mice. The antioxidative stress response was active (indicated by increased Nrf2 activity and protein) after 1 week of ozone exposure, but this ability was lost after 3 and 6 weeks of ozone exposure. The transcription factor HIF-1α was elevated in 3- and 6-week ozone-exposed mice and this was associated with increased gene expression levels of several HIF-1α target genes including Hdac2 (histone deacetylase 2), Vegf (vascular endothelial growth factor), Keap1 (kelch-like ECH-associated protein 1) and Mif (macrophage migration inhibitory factor). HDAC2 protein was found to be phosphorylated and carbonylated in nuclear and cytoplasm fractions, respectively, and was associated with a decrease in DNA-binding activity and protein expression of HDAC2. Decreased HDAC2 activity, most likely a direct result of protein modification, in combination with the loss of the antioxidative stress response and activation of the HIF-1α pathway, contribute to the inflammatory response and emphysema observed in ozone-exposed mice.