The Importance of Redox Status in the Frame of Lifestyle Approaches and the Genetics of the Lung Innate Immune Molecules, SP-A1 and SP-A2, on Differential Outcomes of COVID-19 Infection

Estimation of Redox Status in Military Pilots during Hypoxic Flight-Simulation Conditions—A Pilot Study

At high altitude conditions, the low-pressure atmospheric oxygen reduces the generation of energy, thus inducing a decrease in oxygen availability. As a result, endurance flights evoke imbalance in redox signaling, posing a safety risk for the pilots involved. The aim of the present study was to assess changes in the redox status of military pilots during flight simulation conditions according to their flight hours (experts vs. novice). A total of seven expert pilots and an equal number of novice pilots (trainees) were recruited from the Center for Airforce Medicine of the Greek Military Airforce. Glutathione (GSH) levels, catalase activity (CAT), total antioxidant capacity (TAC), lipid peroxidation through the thiobarbituric acid-reactive substances (TBARS), and protein oxidative damage through the assay of protein carbonyls (PCs) levels were assessed at two time points, once prior to and once immediately post a scheduled flight simulation. In the experienced pilots’ arms, GSH was significantly increased post-flight simulation, with TAC being simultaneously reduced. On the other hand, in the trainees’ arms, CAT and TAC were both increased post-flight. No differences were noted with regard to the TBARS and PCs post-simulation. When the two groups were compared, TAC and PCs were significantly lower in the trainees compared to the experienced pilots. The present study provides useful insight into the physiological redox status adaptations to hypobaric hypoxic flight conditions among pilots. In a further detail, an increase in GSH response post-flight simulation is being evoked in more experienced pilots, indicating an adaptation to the extreme flight conditions, as they battle oxidative stress.

Elevated plasma levels of epithelial and endothelial cell markers in COVID-19 survivors with reduced lung diffusing capacity six months after hospital discharge

Background

Some COVID-19 survivors present lung function abnormalities during follow-up, particularly reduced carbon monoxide lung diffusing capacity (DLCO). To investigate risk factors and underlying pathophysiology, we compared the clinical characteristics and levels of circulating pulmonary epithelial and endothelial markers in COVID-19 survivors with normal or reduced DLCO 6 months after discharge.

Methods

Prospective, observational study. Clinical characteristics during hospitalization, and spirometry, DLCO and plasma levels of epithelial (surfactant protein (SP) A (SP-A), SP-D, Club cell secretory protein-16 (CC16) and secretory leukocyte protease inhibitor (SLPI)), and endothelial (soluble intercellular adhesion molecule 1 (sICAM-1), soluble E-selectin and Angiopoietin-2) 6 months after hospital discharge were determined in 215 COVID-19 survivors.

Results

DLCO was < 80% ref. in 125 (58%) of patients, who were older, more frequently smokers, had hypertension, suffered more severe COVID-19 during hospitalization and refer persistent dyspnoea 6 months after discharge. Multivariate regression analysis showed that age ≥ 60 years and severity score of the acute episode ≥ 6 were independent risk factors of reduced DLCO 6 months after discharge. Levels of epithelial (SP-A, SP-D and SLPI) and endothelial (sICAM-1 and angiopoietin-2) markers were higher in patients with reduced DLCO, particularly in those with DLCO ≤ 50% ref. Circulating SP-A levels were associated with the occurrence of acute respiratory distress syndrome (ARDS), organizing pneumonia and pulmonary embolisms during hospitalization.

Conclusions

Reduced DLCO is common in COVID-19 survivors 6 months after hospital discharge, especially in those older than 60 years with very severe acute disease. In these individuals, elevated levels of epithelial and endothelial markers suggest persistent lung damage.

Alveolar type II cells and pulmonary surfactant in COVID-19 era

In this review, we discuss the role of pulmonary surfactant in the host defense against respiratory pathogens, including novel coronavirus SARS-CoV-2. In the lower respiratory system, the virus uses angiotensin-converting enzyme 2 (ACE2) receptor in conjunction with serine protease TMPRSS2, expressed by alveolar type II (ATII) cells as one of the SARS-CoV-2 target cells, to enter. ATII cells are the main source of surfactant. After their infection and the resulting damage, the consequences may be severe and may include injury to the alveolar-capillary barrier, lung edema, inflammation, ineffective gas exchange, impaired lung mechanics and reduced oxygenation, which resembles acute respiratory distress syndrome (ARDS) of other etiology. The aim of this review is to highlight the key role of ATII cells and reduced surfactant in the pathogenesis of the respiratory form of COVID-19 and to emphasize the rational basis for exogenous surfactant therapy in COVID-19 ARDS patients.

Human Surfactant Protein SP-A1 and SP-A2 Variants Differentially Affect the Alveolar Microenvironment, Surfactant Structure, Regulation and Function of the Alveolar Macrophage, and Animal and Human Survival Under Various Conditions

The human innate host defense molecules, SP-A1 and SP-A2 variants, differentially affect survival after infection in mice and in lung transplant patients. SP-A interacts with the sentinel innate immune cell in the alveolus, the alveolar macrophage (AM), and modulates its function and regulation. SP-A also plays a role in pulmonary surfactant-related aspects, including surfactant structure and reorganization. For most (if not all) pulmonary diseases there is a dysregulation of host defense and inflammatory processes and/or surfactant dysfunction or deficiency. Because SP-A plays a role in both of these general processes where one or both may become aberrant in pulmonary disease, SP-A stands to be an important molecule in health and disease. In humans (unlike in rodents) SP-A is encoded by two genes (SFTPA1 and SFTPA2) and each has been identified with extensive genetic and epigenetic complexity. In this review, we focus on functional, structural, and regulatory differences between the two SP-A gene-specific products, SP-A1 and SP-A2, and among their corresponding variants. We discuss the differential impact of these variants on the surfactant structure, the alveolar microenvironment, the regulation of epithelial type II miRNome, the regulation and function of the AM, the overall survival of the organism after infection, and others. Although there have been a number of reviews on SP-A, this is the first review that provides such a comprehensive account of the differences between human SP-A1 and SP-A2.

The Role of Pulmonary Surfactants in the Treatment of Acute Respiratory Distress Syndrome in COVID-19

Lung alveolar type-II (AT-II) cells produce pulmonary surfactant (PS), consisting of proteins and lipids. The lipids in PS are primarily responsible for reducing the air-fluid surface tension inside the alveoli of the lungs and to prevent atelectasis. The proteins are of two types: hydrophilic and hydrophobic. Hydrophilic surfactants are primarily responsible for opsonisation, thereby protecting the lungs from microbial and environmental contaminants. Hydrophobic surfactants are primarily responsible for respiratory function. Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) enters the lungs through ACE-2 receptors on lungs and replicates in AT-II cells leading to the etiology of Coronavirus disease - 2019 (COVID-19). The SARS-CoV-2 virus damages the AT-II cells and results in decreased production of PS. The clinical symptoms of acute respiratory distress syndrome (ARDS) in COVID-19 patients are like those of neonatal respiratory distress syndrome (NRDS). The PS treatment is first-line treatment option for NRDS and found to be well tolerated in ARDS patients with inconclusive efficacy. Over the past 70°years, a lot of research is underway to produce natural/synthetic PS and developing systems for delivering PS directly to the lungs, in addition to finding the association between PS levels and respiratory illnesses. In the present COVID-19 pandemic situation, the scientific community all over the world is searching for the effective therapeutic options to improve the clinical outcomes. With a strong scientific and evidence-based background on role of PS in lung homeostasis and infection, few clinical trials were initiated to evaluate the functions of PS in COVID-19. Here, we connect the data on PS with reference to pulmonary physiology and infection with its possible therapeutic benefit in COVID-19 patients.

An integrated approach for assessing the in vitro and in vivo redox-related effects of nanomaterials

Over the last few decades, nanotechnology has risen to the forefront of both the research and industrial interest, resulting in the manufacture and utilization of various nanomaterials, as well as in their integration into a wide range of fields. However, the consequent elevated exposure to such materials raises serious concerns regarding their effects on human health and safety. Existing scientific data indicate that the induction of oxidative stress, through the excessive generation of Reactive Oxygen Species (ROS), might be the principal mechanism of exerting their toxicity. Meanwhile, a number of nanomaterials exhibit antioxidant properties, either intrinsic or resulting from their functionalization with conventional antioxidants. Considering that their redox properties are implicated in the manifestation of their biological effects, we propose an integrated approach for the assessment of the redox-related activities of nanomaterials at three biological levels (in vitro-cell free systems, cell cultures, in vivo). Towards this direction, a battery of translational biomarkers is recommended, and a series of reliable protocols are presented in detail. The aim of the present approach is to acquire a better understanding with respect to the biological actions of nanomaterials in the interrelated fields of Redox Biology and Toxicology.

Detection of SARS-CoV-2 virus using an alternative molecular method and evaluation of biochemical, hematological, inflammatory, and oxidative stress in healthcare professionals

In early December 2019, an outbreak of coronavirus disease 2019 caused by a new strain of coronavirus (SARS-CoV-2), occurred in the city of Wuhan, Hubei Province, China. On January 30, 2020, the World Health Organization (WHO) declared the outbreak a public health emergency of international concern. Since then, frontline healthcare professionals have been experiencing extremely stressful situations and damage to their physical and mental health. These adverse conditions cause stress and biochemical, hematological, and inflammatory changes, as well as oxidative damage, and could be potentially detrimental to the health of the individual. The study population consisted of frontline health professionals working in BHU in a city in southern Brazil. Among the 45 participants, two were infected with the SARS-CoV-2 virus and were diagnosed using immunochromatographic tests such as salivary RT-LAMP and qRT-PCR. We also evaluated biochemical, hematological, inflammatory, and oxidative stress markers in the participants. The infected professionals (CoV-2-Prof) showed a significant increase in the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), cholesterol, lactic dehydrogenase, lymphocytes, and monocytes. In this group, the levels of uric acid, triglycerides, leukocytes, neutrophils, hemoglobin, hematocrit, and platelets decreased. In the group of uninfected professionals (NoCoV-2-Prof), significant increase in HDL levels and the percentages of eosinophils and monocytes, was observed. Further, in this group, uric acid, LDH, triglyceride, and cholesterol levels, and the hematocrit count and mean corpuscular volume were significantly reduced. Both groups showed significant inflammatory activity with changes in the levels of C-reactive protein and mucoprotein. The NoCoV-2-Prof group showed significantly elevated plasma cortisol levels. To our kowledge, this study is the first to report the use of the RT-LAMP method with the saliva samples of health professionals, to evalute of SARS-CoV-2.

Can Prophylactic High Flow of Humidified and Warmed Filtered Air Improve Survival from Bacterial Pneumonia and SARS-CoV-2 in Elderly Individuals? The Role of Surfactant Protein A

In this opinion article, we discuss a serendipitous observation we made in a study investigating survival in aged mice after bacterial infection. This observation involved a non-invasive ventilation approach that led to variable and higher survival in male and female mice with different genetic backgrounds for the innate immune molecule, surfactant protein A (SP-A). We suggest that employing the best ventilatory modality, whether that be HFNC or another method, may augment the role of other factors such as SP-A genetics and sex in a personalized approach, and may ultimately improve the outcome.

Surfactant Protein-A Function: Knowledge Gained From SP-A Knockout Mice

Pulmonary surfactant proteins have many roles in surfactant- related functions and innate immunity. One of these proteins is the surfactant protein A (SP-A) that plays a role in both surfactant-related processes and host defense and is the focus in this review. SP-A interacts with the sentinel host defense cell in the alveolus, the alveolar macrophage (AM), to modulate its function and expression profile under various conditions, as well as other alveolar epithelial cells such as the Type II cell. Via these interactions, SP-A has an impact on the alveolar microenvironment. SP-A is also important for surfactant structure and function. Much of what is understood of the function of SP-A and its various roles in lung health has been learned from SP-A knockout (KO) mouse experiments, as reviewed here. A vast majority of this work has been done with infection models that are bacterial, viral, and fungal in nature. Other models have also been used, including those of bleomycin-induced lung injury and ozone-induced oxidative stress either alone or in combination with an infectious agent, bone marrow transplantation, and other. In addition, models investigating the effects of SP-A on surfactant components or surfactant structure have contributed important information. SP-A also appears to play a role in pathways involved in sex differences in response to infection and/or oxidative stress, as well as at baseline conditions. To date, this is the first review to provide a comprehensive report of the functions of SP-A as learned through KO mice.

Improved strategies to counter the COVID-19 pandemic: Lockdowns vs. primary and community healthcare

COVID-19 pandemic mitigation strategies are mainly based on social distancing measures and healthcare system reinforcement. However, many countries in Europe and elsewhere implemented strict, horizontal lockdowns because of extensive viral spread in the community which challenges the capacity of the healthcare systems. However, strict lockdowns have various untintended adverse social, economic and health effects, which have yet to be fully elucidated, and have not been considered in models examining the effects of various mitigation measures. Unlike commonly suggested, the dilemma is not about health vs wealth because the economic devastation of long-lasting lockdowns will definitely have adverse health effects in the population. Furthermore, they cannot provide a lasting solution in pandemic containment, potentially resulting in a vicious cycle of consecutive lockdowns with in-between breaks. Hospital preparedness has been the main strategy used by governments. However, a major characteristic of the COVID-19 pandemic is the rapid viral transmission in populations with no immunity. Thus, even the best hospital system could not cope with the demand. Primary, community and home care are the only viable strategies that could achieve the goal of pandemic mitigation. We present the case example of Greece, a country which followed a strategy focused on hospital preparedness but failed to reinforce primary and community care. This, along with strategic mistakes in epidemiological surveillance, resulted in Greece implementing a second strict, horizontal lockdown and having one of the highest COVID-19 death rates in Europe during the second wave. We provide recommendations for measures that will reinstate primary and community care at the forefront in managing the current public health crisis by protecting hospitals from unnecessary admissions, providing primary and secondary prevention services in relation to COVID-19 and maintaining population health through treatment of non-COVID-19 conditions. This, together with more selective social distancing measures (instead of horizontal lockdowns), represents the only viable and realistic long-term strategy for COVID-19 pandemic mitigation.

Sex and SP-A2 Dependent NAD(H) Redox Alterations in Mouse Alveolar Macrophages in Response to Ozone Exposure: Potential Implications for COVID-19

Co-enzyme nicotinamide adenine dinucleotide (NAD(H)) redox plays a key role in macrophage function. Surfactant protein (SP-) A modulates the functions of alveolar macrophages (AM) and ozone (O₃) exposure in the presence or absence of SP-A and reduces mouse survival in a sex-dependent manner. It is unclear whether and how NAD(H) redox status plays a role in the innate immune response in a sex-dependent manner. We investigated the NAD(H) redox status of AM from SP-A2 and SP-A knockout (KO) mice in response to O₃ or filtered air (control) exposure using optical redox imaging technique. We found: (i) In SP-A2 mice, the redox alteration of AM in response to O₃ showed sex-dependence with AM from males being significantly more oxidized and having a higher level of mitochondrial reactive oxygen species than females; (ii) AM from KO mice were more oxidized after O₃ exposure and showed no sex differences; (iii) AM from female KO mice were more oxidized than female SP-A2 mice; and (iv) Two distinct subpopulations characterized by size and redox status were observed in a mouse AM sample. In conclusions, the NAD(H) redox balance in AM responds to O₃ in a sex-dependent manner and the innate immune molecule, SP-A2, contributes to this observed sex-specific redox response.