Mechanisms and consequences of oxidative stress in lung disease: therapeutic implications for an aging populace

Oxidative stress and macrophages: driving forces behind exacerbations of asthma and chronic obstructive pulmonary disease?

Oxidative stress is a common feature of obstructive airway diseases like asthma and chronic obstructive pulmonary disease (COPD). Lung macrophages are key innate immune cells that can generate oxidants and are known to display aberrant polarization patterns and defective phagocytic responses in these diseases. Whether these characteristics are linked in one way or another and whether they contribute to the onset and severity of exacerbations in asthma and COPD remain poorly understood. Insight into oxidative stress, macrophages, and their interactions may be important in fully understanding acute worsening of lung disease. This review therefore highlights the current state of the art regarding the role of oxidative stress and macrophages in exacerbations of asthma and COPD. It shows that oxidative stress can attenuate macrophage function, which may result in impaired responses toward exacerbating triggers and may contribute to exaggerated inflammation in the airways.

The mitochondria in lung fibrosis: friend or foe?

Idiopathic pulmonary fibrosis (IPF) and other forms of lung fibrosis are age-associated diseases with increased deposition of mesenchymal collagen that promotes respiratory malfunction and eventual death from respiratory failure. Our understanding of the pathobiology underlying pulmonary fibrosis is incomplete and current therapies available to slow or treat lung fibrosis are limited. Evidence reviewed herein demonstrates key involvement of mitochondrial dysfunction in diverse pulmonary cell populations, including alveolar epithelial cells (AEC), fibroblasts, and macrophages and/or immune cells that collectively advances the development of pulmonary fibrosis. The mitochondria have an important role in regulating whether fibrogenic stimuli results in the return of normal healthy function ("friend") or the development of pulmonary fibrosis ("foe"). In particular, we summarize the evidence suggesting that AEC mitochondrial dysfunction is important in mediating lung fibrosis signaling via mechanisms involving imbalances in the levels of reactive oxygen species, endoplasmic reticulum stress response, mitophagy, apoptosis and/or senescence, and inflammatory signaling. Further, we review the emerging evidence suggesting that dysfunctional mitochondria in AECs and other cell types play crucial roles in modulating nearly all aspects of the 9 hallmarks of aging in the context of pulmonary fibrosis as well as some novel molecular pathways that have recently been identified. Finally, we discuss the potential translational aspects of these studies as well as the key knowledge gaps necessary for better informing our understanding of the pathobiology of the mitochondria in mediating pulmonary fibrosis. We reason that targeting deficient mitochondria-derived pathways may provide innovative future treatment strategies that are urgently needed for lung fibrosis.

Cell Death in the Lung: The Apoptosis-Necroptosis Axis

Regulated cell death is a major mechanism to eliminate damaged, infected, or superfluous cells. Previously, apoptosis was thought to be the only regulated cell death mechanism; however, new modalities of caspase-independent regulated cell death have been identified, including necroptosis, pyroptosis, and autophagic cell death. As an understanding of the cellular mechanisms that mediate regulated cell death continues to grow, there is increasing evidence that these pathways are implicated in the pathogenesis of many pulmonary disorders. This review summarizes our understanding of regulated cell death as it pertains to the pathogenesis of chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis, acute respiratory distress syndrome, and pulmonary arterial hypertension.

Oxidative stress associated with aging activates protein kinase Cε, leading to cilia slowing

Older people are four times more likely to develop pneumonia than younger people. As we age, many components of pulmonary innate immunity are impaired, including slowing of mucociliary clearance. Ciliary beat frequency (CBF) is a major determinant of mucociliary clearance, and it slows as we age. We hypothesized that CBF is slowed in aging because of increased oxidative stress, which activates PKCε signaling. We pharmacologically inhibited PKCε in ex vivo mouse models of aging. We measured a slowing of CBF with aging that was reversed with inhibition using the novel PKC inhibitor, Ro-31-8220, as well as the PKCε inhibitor, PKCe141. Inhibition of PKCε using siRNA in mouse trachea also returned CBF to normal. In addition, antioxidants decrease PKCε activity and speed cilia. We also aged wild-type and PKCε KO mice and measured CBF. The PKCε KO mice were spared from the CBF slowing of aging. Using human airway epithelial cells from younger and older donors at air-liquid interface (ALI), we inhibited PKCε with siRNA. We measured a slowing of CBF with aging that was reversed with siRNA inhibition of PKCε. In addition, we measured bead clearance speeds in human ALI, which demonstrated a decrease in bead velocity with aging and a return to baseline after inhibition of PKCε. In summary, in human and mouse models, aging is associated with increased oxidant stress, which activates PKCε and slows CBF.

Clinical differences between pulmonary and extrapulmonary acute respiratory distress syndrome: a retrospective cohort study of prospectively collected data in Japan

Background

Although acute respiratory distress syndrome (ARDS) reportedly shows various clinical phenotypes with different risk and prognostic factors, few studies have assessed the clinical features and prognosis of pulmonary and extrapulmonary ARDS. The aim of the present study was to investigate clinical differences between pulmonary and extrapulmonary ARDS.

Methods

In total, 200 patients who met the Berlin criteria and were diagnosed with ARDS between October 2004 and September 2017 were included. We classified the patients into pulmonary and extrapulmonary ARDS groups. Both groups were assessed for 60-day mortality, duration of ventilation, and other clinical features.

Results

There were 150 and 50 patients in the pulmonary and extrapulmonary ARDS groups, respectively. The two groups showed no significant differences in any assessment parameters except the serum lactate dehydrogenase (LDH) level, which was higher in the extrapulmonary ARDS group (P=0.01). After adjustment for potentially confounding covariates, there were no significant differences in 60-day mortality (P=0.99) and the duration of ventilation (P=0.45) between the two groups. Mortality was significantly associated with the disseminated intravascular coagulation (DIC) score, high-resolution computed tomography (HRCT) score, and serum LDH level in the pulmonary ARDS group and the DIC score and HRCT score in the extrapulmonary ARDS group.

Conclusions

Pulmonary and extrapulmonary ARDS may be comparable in terms of the prognosis and duration of ventilation. DIC and HRCT scores may be common clinical predictors of mortality with ARDS.