Differences in mRNA expression, protein content, and enzyme activity of superoxide dismutases in type II pneumocytes of acute and chronic lung injury

A novel concern from two sample Mendelian randomization study: The effects of air pollution exposure on the cardiovascular, respiratory, and nervous system

BACKGROUND

Cardiovascular, respiratory, and nervous system diseases have high morbidity and mortality rates, but the causal relationship between air pollution and these diseases remains controversial.

METHODS

We conducted a large-scale genome-wide association (GWAS) study using Mendelian randomization (MR) to investigate the association between air pollution like Nitrogen dioxide (NO2), Nitrogen oxides (NOX), Particulate matter with diameter<2.5μm (PM2.5), Particulate matter with diameter<10μm (PM10) and cardiovascular, respiratory, and nervous system diseases, including acute myocardial infarction, heart failure, asthma, chronic obstructive pulmonary disease (COPD), pneumonia, stroke and Parkinson's disease. This study included 337,199 patients with acute myocardial infarction, 178,726 patients with heart failure, 463,010 patients with asthma, 462,933 patients with COPD, 486,484 patients with pneumonia, 484,598 patients with stroke, and 482,730 patients with Parkinson's disease. All genetic tools were identified from GWAS. The association effects of environmental pollution and these diseases were investigated using MR analysis, sensitivity analysis with heterogeneity, pleiotropy test, and leave-one-out test.

RESULTS

Our MR analysis showed the association between NOX and the development of COPD and stroke (Odds ratio (OR)=1.010, 95 % Confidence interval (CI): 1.000～1.020, P=0.046; OR=1.017, 95 %CI:1.003-1.031, P=0.019), the association between PM2.5 and the development of asthma, COPD and stroke (OR=1.013, 95 %CI:1.003-1.024, P=0.011; OR=1.010, 95 %CI:1.000-1.019, P=0.035; OR=1.019, 95 %CI:1.004-1.033, P=0.012). No significant associations were found between the rest of the air pollution exposures and diseases. Leave-one-out sensitivity analysis showed stable results.

CONCLUSIONS

The study clarifies the relationship between air pollution and cardiovascular, respiratory, and nervous system diseases, providing valuable evidence for environmental pollution prevention and population health monitoring, and provides a clear direction and evidence for the subsequent investigation of the association between air pollution and diseases.

Motor Cortex and Hippocampus Display Decreased Heme Oxygenase Activity 2 Weeks After Ventricular Fibrillation Cardiac Arrest in Rats

Heme oxygenase (HO) and biliverdin reductase (BVR) activities are important for neuronal function and redox homeostasis. Resuscitation from cardiac arrest (CA) frequently results in neuronal injury and delayed neurodegeneration that typically affect vulnerable brain regions, primarily hippocampus (Hc) and motor cortex (mC), but occasionally also striatum and cerebellum. We questioned whether these delayed effects are associated with changes of the HO/BVR system. We therefore analyzed the activities of HO and BVR in the brain regions Hc, mC, striatum and cerebellum of rats subjected to ventricular fibrillation CA (6 min or 8 min) after 2 weeks following resuscitation, or sham operation. From all investigated regions, only Hc and mC showed significantly decreased HO activities, while BVR activity was not affected. In order to find an explanation for the changed HO activity, we analyzed protein abundance and mRNA expression levels of HO-1, the inducible, and HO-2, the constitutively expressed isoform, in the affected regions. In both regions we found a tendency for a decreased immunoreactivity of HO-2 using immunoblots and immunohistochemistry. Additionally, we investigated the histological appearance and the expression of markers indicative for activation of microglia [tumor necrosis factor receptor type I (TNFR1) mRNA and immunoreactivity for ionized calcium-binding adapter molecule 1 (Iba1])], and activation of astrocytes [immunoreactivity for glial fibrillary acidic protein (GFAP)] in Hc and mC. Morphological changes were detected only in Hc displaying loss of neurons in the cornu ammonis 1 (CA1) region, which was most pronounced in the 8 min CA group. In this region also markers indicating inflammation and activation of pro-death pathways (expression of HO-1 and TNFR1 mRNA, as well as Iba1 and GFAP immunoreactivity) were upregulated. Since HO products are relevant for maintaining neuronal function, our data suggest that neurodegenerative processes following CA may be associated with a decreased capacity to convert heme into HO products in particularly vulnerable brain regions.

Nitration of protein without allergenic potential triggers modulation of antioxidant response in type II pneumocytes

Inhalation of nitrogen and reactive oxygen species (ROS) is known to induce lung inflammation, which is prevented by enzymatic and nonenzymatic antioxidant systems. These agents form nitrated allergens that were shown to enhance allergenicity. The aim of this study was to examine the influence of nitrated proteins on inflammation and antioxidant status of the lung. Ovalbumin (OVA) in nitrated form (nOVA) was intraperitoneally (ip) injected in mice for sensitization and in nitrated or unmodified form for challenge to induce allergic bronchial inflammation. To study the allergen potential of unrelated protein and verify cross-reactivity, nitrated and unmodified keyhole limpet hemocyanin (nKLH, KLH) was used for challenge. Challenge with OVA or nOVA reduced lung function and increased eosinophilia and protein content in bronchoalveolar lavage fluid (BALF). Challenge with nitrated or native OVA or KLH elevated glutathione (GSH) ratio in type II pneumocytes. Reduced mRNA expression of glutathione peroxidase (GPX) 3, glutathione reductase (GR), superoxide dismutase (SOD) 2, and catalase (CAT) was most prominent after challenge with nitrated OVA and nitrated KLH, respectively. Challenge with nOVA enhanced SOD1 mRNA reduction. Immunostaining of GPX 3 and SOD2 increased after challenge with OVA or nOVA, while reactivity of GR and reactivity of SOD2 were reduced after challenge with KLH or nKLH. SOD1 immunostaining was diminished after challenge with nonnitrated OVA or KLH. CAT immunoreaction was similar in all groups. Nitrated proteins without allergenic potential triggered mRNA reduction of antioxidants in type II cells after sensitization with a nitrated allergen but did not induce bronchial inflammation.

Nitrogen dioxide induces apoptosis and proliferation but not emphysema in rat lungs

BACKGROUND

Apoptosis of alveolar septal cells has been linked to emphysema formation. Nitrogen dioxide, a component of cigarette smoke, has been shown to induce alveolar epithelial cell apoptosis in vitro. It is hypothesised that exposure of rats to nitrogen dioxide may result in increased alveolar septal cell apoptosis in vivo with ensuing emphysema-that is, airspace enlargement and loss of alveolar walls.

METHODS

Fischer 344 rats were exposed to 10 ppm nitrogen dioxide for 3, 7, 21 days or 21 days followed by 28 days at room air. Age-matched control rats were exposed to room air for 3, 21 or 49 days. Lungs fixed at 20 cm fluid column, embedded in paraffin wax, glycol methacrylate and araldite, were analysed by design-based stereology. Alveolar septal cell apoptosis (transferase dUTP nick end labelling assay, active caspase 3) and proliferation (Ki-67), airspace enlargement, total alveolar surface area, and absolute alveolar septal volume as well as the ultrastructural composition of the alveolar wall were quantified.

RESULTS

Nitrogen dioxide resulted in an eightfold increase in alveolar septal cell apoptosis at day 3 and a 14-fold increase in proliferation compared with age-matched controls. Airspace enlargement, indicated by a 20% increase in mean airspace chord length, was evident by day 7 but was not associated with loss of alveolar walls. By contrast, nitrogen dioxide resulted in an increase in the total surface area and absolute volume of alveolar walls comprising all compartments. The ratio of collagen to elastin, however, was reduced at day 21. Lungs exposed to nitrogen dioxide for 21 days exhibited quantitative structural characteristics as seen in control lungs on day 49.

CONCLUSIONS

Nitrogen dioxide exposure of rats results in increased alveolar septal cell turnover leading to accelerated lung growth, which is associated with an imbalance in the relative composition of the extracellular matrix, but fails to induce emphysema.

Protection against bleomycin-induced lung injury by IL-18 in mice

The role of interleukin (IL)-18 in the protection from interstitial pneumonia and pulmonary fibrosis induced by bleomycin (BLM) was investigated by comparing the severity of BLM-induced lung injuries between wild-type and C57BL/6 mice with a targeted knockout mutation of the IL-18 gene (IL-18−/− mice). IL-18−/− mice showed much worse lung injuries than wild-type mice, as assessed by the survival rate, histological images, and leukocyte infiltration in the bronchoalveolar lavage fluid and myeloperoxidase activity. In wild-type mice, administration of IL-18 before BLM instillation resulted in suppression of lung injuries, increases in the hydroxyproline content, and decreases in the granulocyte-macrophage colony-stimulating factor content in the lung. Preadministration of IL-18 also resulted in prevention of the reduction of the lung IL-10 content caused by BLM-induced damage of alveolar epithelial. BLM instillation suppressed superoxide dismutase (SOD) activity in IL-18−/− mice to a greater extent than in wild-type mice. Pretreatment of IL-18 augmented Mn-containing superoxide dismutase (Mn-SOD) messenger RNA expression and SOD activity in the lung and prevented the reduction of SOD activity caused by BLM in both wild-type and IL-18−/− mice. These results suggest that IL-18 plays a protective role against BLM-induced lung injuries by upregulating a defensive molecule, Mn-SOD.