Surfactant protein D protects against acute hyperoxic lung injury

A Review on Investigating the Interactions between Nanoparticles and the Pulmonary Surfactant Monolayer with Coarse-Grained Molecular Dynamics Method

Pulmonary drug delivery has garnered significant attention due to its targeted local lung action, minimal toxic side effects, and high drug utilization. However, the physicochemical properties of inhaled nanoparticles (NPs) used as drug carriers can influence their interactions with the pulmonary surfactant (PS) monolayer, potentially altering the fate of the NPs and impairing the biophysical function of the PS monolayer. Thus, the objective of this review is to summarize how the physicochemical properties of NPs affect their interactions with the PS monolayer. Initially, the definition and properties of NPs, as well as the composition and characteristics of the PS monolayer, are introduced. Subsequently, the coarse-grained molecular dynamics (CGMD) simulation method for studying the interactions between NPs and the PS monolayer is presented. Finally, the implications of the hydrophobicity, size, shape, surface charge, surface modification, and aggregation of NPs on their interactions with the PS monolayer and on the composition of biomolecular corona are discussed. In conclusion, gaining a deeper understanding of the effects of the physicochemical properties of NPs on their interactions with the PS monolayer will contribute to the development of safer and more effective nanomedicines for pulmonary drug delivery.

Alveolar Hyperoxia and Exacerbation of Lung Injury in Critically Ill SARS-CoV-2 Pneumonia

Acute hypoxic respiratory failure (AHRF) is a prominent feature of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) critical illness. The severity of gas exchange impairment correlates with worse prognosis, and AHRF requiring mechanical ventilation is associated with substantial mortality. Persistent impaired gas exchange leading to hypoxemia often warrants the prolonged administration of a high fraction of inspired oxygen (FiO2). In SARS-CoV-2 AHRF, systemic vasculopathy with lung microthrombosis and microangiopathy further exacerbates poor gas exchange due to alveolar inflammation and oedema. Capillary congestion with microthrombosis is a common autopsy finding in the lungs of patients who die with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome. The need for a high FiO2 to normalise arterial hypoxemia and tissue hypoxia can result in alveolar hyperoxia. This in turn can lead to local alveolar oxidative stress with associated inflammation, alveolar epithelial cell apoptosis, surfactant dysfunction, pulmonary vascular abnormalities, resorption atelectasis, and impairment of innate immunity predisposing to secondary bacterial infections. While oxygen is a life-saving treatment, alveolar hyperoxia may exacerbate pre-existing lung injury. In this review, we provide a summary of oxygen toxicity mechanisms, evaluating the consequences of alveolar hyperoxia in COVID-19 and propose established and potential exploratory treatment pathways to minimise alveolar hyperoxia.

Chitosan/Calcium-Alginate Encapsulated Flaxseed Oil on Dairy Cattle Diet: In Vitro Fermentation and Fatty Acid Biohydrogenation

The aim of this study was to investigate the effect of using chitosan nanoparticles and calcium alginate in the encapsulation of flaxseed oil on the biohydrogenation of unsaturated fatty acids and in vitro fermentation. The experiments were performed in a completely randomized design with 7 treatments. The experimental treatments included: diets without oil additive (control), diet containing 7% flaxseed oil, diet containing 14% flaxseed oil, diet containing 7% oil encapsulated with 500 ppm chitosan nanocapsules, diet containing 14% flaxseed oil encapsulated with 1000 ppm chitosan nanocapsules, diet containing 7% of flaxseed oil encapsulated with 500 ppm of calcium alginate nanocapsules, diet containing 14% flaxseed oil encapsulated with 1000 ppm calcium alginate nanocapsules. The results showed that encapsulation of flaxseed oil with calcium alginate (14%) had a significant effect on gas production (p < 0.05). The treatment containing calcium alginate (14%) increased the digestibility of dry matter compared to the control treatment, but the treatments containing chitosan caused a significant reduction (p < 0.05). The results indicated that the percentage of ruminal saturated fatty acids decreased by encapsulation of flaxseed oil with chitosan (14% and 7%). The percentage of oleic unsaturated fatty acid by encapsulating flaxseed oil with chitosan (14%) had a significant increase compared to the control treatment (p < 0.05). As a result, encapsulating flaxseed oil with chitosan (14%) reduced the unsaturated fatty acids generated during ruminal biohydrogenation.

Construction of a potential microRNA and messenger RNA regulatory network of acute lung injury in mice

Acute lung injury (ALI) is a life-threatening clinical condition associated with critically ill patients, and the construction of potential microRNA (miRNA) and messenger RNA (mRNA) regulatory networks will help to fully elucidate its underlying molecular mechanisms. First, we screened fifteen upregulated differentially expressed miRNAs (DE-miRNAs) and six downregulated DE-miRNAs from the Gene Expression Omnibus (GEO) database. Then, the predicted target genes of the upregulated and downregulated DE-miRNAs were identified from the miRNet database. Subsequently, differentially expressed mRNAs (DE-mRNAs) were identified from the GEO database and subjected to combined analysis with the predicted DE-miRNA target genes. Eleven target genes of the upregulated DE-miRNAs and one target gene of the downregulated DE-miRNAs were screened out. To further validate the prediction results, we randomly selected a dataset for subsequent analysis and found some accurate potential miRNA-mRNA regulatory axes, including mmu-mir-7b-5p-Gria1, mmu-mir-486a-5p-Shc4 and mmu-mir-486b-5p-Shc4 pairs. Finally, mir-7b and its target gene Gria1 and mir-486b and its target gene Shc4 were further validated in a bleomycin-induced ALI mouse model. We established a potential miRNA-mRNA regulatory network of ALI in mice, which may provide a basis for basic and clinical research on ALI and advance the available treatment options.

Surfactant protein D and bronchopulmonary dysplasia: a new way to approach an old problem

Surfactant protein D (SP-D) is a collectin protein synthesized by alveolar type II cells in the lungs. SP-D participates in the innate immune defense of the lungs by helping to clear infectious pathogens and modulating the immune response. SP-D has shown an anti-inflammatory role by down-regulating the release of pro-inflammatory mediators in different signaling pathways such as the TLR4, decreasing the recruitment of inflammatory cells to the lung, and modulating the oxidative metabolism in the lungs. Recombinant human SP-D (rhSP-D) has been successfully produced mimicking the structure and functions of native SP-D. Several in vitro and in vivo experiments using different animal models have shown that treatment with rhSP-D reduces the lung inflammation originated by different insults, and that rhSP-D could be a potential treatment for bronchopulmonary dysplasia (BPD), a rare disease for which there is no effective therapy up to date. BPD is a complex disease in preterm infants whose incidence increases with decreasing gestational age at birth. Lung inflammation, which is caused by different prenatal and postnatal factors like infections, lung hyperoxia and mechanical ventilation, among others, is the key player in BPD. Exacerbated inflammation causes lung tissue injury that results in a deficient gas exchange in the lungs of preterm infants and frequently leads to long-term chronic lung dysfunction during childhood and adulthood. In addition, low SP-D levels and activity in the first days of life in preterm infants have been correlated with a worse pulmonary outcome in BPD. Thus, SP-D mediated functions in the innate immune response could be critical aspects of the pathogenesis in BPD and SP-D could inhibit lung tissue injury in this preterm population. Therefore, administration of rhSP-D has been proposed as promising therapy that could prevent BPD.

Histone H4 potentiates neutrophil inflammatory responses to influenza A virus: Down-modulation by H4 binding to C-reactive protein and Surfactant protein D

Neutrophils participate in the early phase of the innate response to uncomplicated influenza A virus (IAV) infection but also are a major component in later stages of severe IAV or COVID 19 infection where neutrophil extracellular traps (NETs) and associated cell free histones are highly pro-inflammatory. It is likely that IAV interacts with histones during infection. We show that histone H4 binds to IAV and aggregates viral particles. In addition, histone H4 markedly potentiates IAV induced neutrophil respiratory burst responses. Prior studies have shown reactive oxidants to be detrimental during severe IAV infection. C reactive protein (CRP) and surfactant protein D (SP-D) rise during IAV infection. We now show that both of these innate immune proteins bind to histone H4 and significantly down regulate respiratory burst and other responses to histone H4. Isolated constructs composed only of the neck and carbohydrate recognition domain of SP-D also bind to histone H4 and partially limit neutrophil responses to it. These studies indicate that complexes formed of histones and IAV are a potent neutrophil activating stimulus. This finding could account for excess inflammation during IAV or other severe viral infections. The ability of CRP and SP-D to bind to histone H4 may be part of a protective response against excessive inflammation in vivo.

Alda-1 Attenuates Hyperoxia-Induced Acute Lung Injury in Mice

Acute lung injury (ALI), a milder form of acute respiratory distress syndrome (ARDS), is a leading cause of mortality in older adults with an increasing prevalence. Oxygen therapy, is a common treatment for ALI, involving exposure to a high concentration of oxygen. Unfortunately, hyperoxia induces the formation of reactive oxygen species which can cause an increase in 4-HNE (4-hydroxy 2 nonenal), a toxic byproduct of lipid peroxidation. Mitochondrial aldehyde dehydrogenase 2 (ALDH2) serves as an endogenous shield against oxidative stress-mediated damage by clearing 4-HNE. Alda-1 [(N-(1, 3 benzodioxol-5-ylmethyl)-2, 6- dichloro-benzamide)], a small molecular activator of ALDH2, protects against reactive oxygen species-mediated oxidative stress by promoting ALDH2 activity. As a result, Alda-1 shields against ischemic reperfusion injury, heart failure, stroke, and myocardial infarction. However, the mechanisms of Alda-1 in hyperoxia-induced ALI remains unclear. C57BL/6 mice implanted with Alzet pumps received Alda-1 in a sustained fashion while being exposed to hyperoxia for 48 h. The mice displayed suppressed immune cell infiltration, decreased protein leakage and alveolar permeability compared to controls. Mechanistic analysis shows that mice pretreated with Alda-1 also experience decreased oxidative stress and enhanced levels of p-Akt and mTOR pathway associated proteins. These results show that continuous delivery of Alda-1 protects against hyperoxia-induced lung injury in mice.

Reduction of hyperoxic acute lung injury in mice by Formononetin

Background

The antioxidant and anti-inflammatory features of Formononetin, an isoflavone constituent extracted from traditional Chinese medicine, have been reported. The present study investigated that whether Formononetin plays a benefit on hyperoxic ALI.

Methods

C57BL/6 mice were exposed to hyperoxia for 72 h to produce experimental hyperoxic ALI model. Formononetin or vehicle was administrated intraperitoneally. Samples from the lung were collected at 72 h post hyperoxia exposure for further study. Pulmonary microvascular endothelial cells isolated from the lung of C57BL/6 mice were used for in vitro study.

Results

Formononetin pretreatment notably attenuated hyperoxia-induced elevating pulmonary water content, upregulation of proinflammatory cytokine levels and increasing infiltration of neutrophil in the lung. Western blot analyses showed that Formononetin enhanced the expression of nuclear factor erythroid-2-related factor 2 (Nrf2) which is a key transcription factor regulating the expression of heme oxygenase-1 (HO-1). Formononetin increased HO-1 expression and activity compared with vehicle-treated animals. Moreover, Formononetin reversed hyperoxia-caused the reduction of M2 macrophage polarization. However, pretreatment of a HO-1 inhibitor reduced the protective effect of Formononetin on hyperoxic ALI. Cell study showed that the Formononetin-induced upregulation of HO-1 was abolished when the Nrf2 was silenced.

Conclusions

Formononetin pretreatment reduces hyperoxia-induced ALI via Nrf2/HO-1-mediated antioxidant and anti-inflammatory effects.

Innate Immunity and Influenza A Virus Pathogenesis: Lessons for COVID-19

There is abundant evidence that the innate immune response to influenza A virus (IAV) is highly complex and plays a key role in protection against IAV induced infection and illness. Unfortunately it also clear that aspects of innate immunity can lead to severe morbidity or mortality from IAV, including inflammatory lung injury, bacterial superinfection, and exacerbation of reactive airways disease. We review broadly the virus and host factors that result in adverse outcomes from IAV and show evidence that inflammatory responses can become damaging even apart from changes in viral replication per se, with special focus on the positive and adverse effects of neutrophils and monocytes. We then evaluate in detail the role of soluble innate inhibitors including surfactant protein D and antimicrobial peptides that have a potential dual capacity for down-regulating viral replication and also inhibiting excessive inflammatory responses and how these innate host factors could possibly be harnessed to treat IAV infection. Where appropriate we draw comparisons and contrasts the SARS-CoV viruses and IAV in an effort to point out where the extensive knowledge existing regarding severe IAV infection could help guide research into severe COVID 19 illness or vice versa.

The NRF2 Signaling Network Defines Clinical Biomarkers and Therapeutic Opportunity in Friedreich's Ataxia

Friedreich’s ataxia (FA) is a trinucleotide repeats expansion neurodegenerative disorder, for which no cure or approved therapies are present. In most cases, GAA trinucleotide repetitions in the first intron of the FXN gene are the genetic trigger of FA, determining a strong reduction of frataxin, a mitochondrial protein involved in iron homeostasis. Frataxin depletion impairs iron–sulfur cluster biosynthesis and determines iron accumulation in the mitochondria. Mounting evidence suggests that these defects increase oxidative stress susceptibility and reactive oxygen species production in FA, where the pathologic picture is worsened by a defective regulation of the expression and signaling pathway modulation of the transcription factor NF-E2 p45-related factor 2 (NRF2), one of the fundamental mediators of the cellular antioxidant response. NRF2 protein downregulation and impairment of its nuclear translocation can compromise the adequate cellular response to the frataxin depletion-dependent redox imbalance. As NRF2 stability, expression, and activation can be modulated by diverse natural and synthetic compounds, efforts have been made in recent years to understand if regulating NRF2 signaling might ameliorate the pathologic defects in FA. Here we provide an analysis of the pharmaceutical interventions aimed at restoring the NRF2 signaling network in FA, elucidating specific biomarkers useful for monitoring therapeutic effectiveness, and developing new therapeutic tools.

Oxidative Stress and Anti-Oxidant Markers in Premature Infants with Respiratory Distress Syndrome

BACKGROUND

Neonatal respiratory distress syndrome (RDS) caused by decreased surfactant and structural lung immaturity. The imbalance between oxidative status and antioxidant defence system was suggested to be an important trigger for lung affection with RDS.

AIM

The goal of the current research was to elucidate the significance of the oxidant/ antioxidant status in the pathogenesis of RDS in preterm infants.

PATIENTS AND METHODS

This controlled study included 31 preterm neonates with RDS and 36 healthy preterm neonates. Quantification level of oxidative stress biomarkers; malondialdehyde (MDA) & hydrogen peroxide (H₂O₂) along with antioxidant enzymes activity; catalase (CAT) & superoxide dismutase (SOD) in plasma of healthy premature neonates compared with those with RDS.

RESULTS

status of oxidative stress markers (MDA & H₂O₂) showed a significant increase with decreased levels of antioxidant enzymes activity (CAT & SOD) in neonates with RDS when compared to healthy prematures.

CONCLUSION

The results obtained in this study indicate that the increased oxidative stress accompanied by reduced antioxidant defences may play a significant role in the pathogenesis of respiratory distress in preterm newborns.

Surfactant protein-D modulation of pulmonary macrophage phenotype is controlled by S-nitrosylation

Surfactant protein-D (SP-D) is a regulator of pulmonary innate immunity whose oligomeric state can be altered through S-nitrosylation to regulate its signaling function in macrophages. Here, we examined how nitrosylation of SP-D alters the phenotypic response of macrophages to stimuli both in vivo and in vitro. Bronchoalveolar lavage (BAL) from C57BL6/J and SP-D-overexpressing (SP-D OE) mice was incubated with RAW264.7 cells ± LPS. LPS induces the expression of the inflammatory genes Il1b and Nos2, which is reduced 10-fold by SP-D OE-BAL. S-nitrosylation of the SP-D OE-BAL (SNO-SP-D OE-BAL) abrogated this inhibition. SNO-SP-D OE-BAL alone induced Il1b and Nos2 expression. PCR array analysis of macrophages incubated with SP-D OE-BAL (±LPS) shows increased expression of repair genes, Ccl20, Cxcl1, and Vcam1, that was accentuated by LPS. LPS increases inflammatory gene expression, Il1a, Nos2, Tnf, and Ptgs2, which was accentuated by SNO-SP-D OE-BAL but inhibited by SP-D OE-BAL. The transcription factor NF-κB was identified as a target for SNO-SP-D by IPA, which was confirmed by Trans-AM ELISA in vitro. In vivo, SP-D overexpression increases the burden of infection in a Pneumocystis model while increasing cellular recruitment. Expression of iNOS and the production of NO metabolites were significantly reduced in SP-D OE mice relative to C57BL6/J. Inflammatory gene expression was increased in infected C57BL6/J mice but decreased in SP-D OE. SP-D oligomeric structure was disrupted in C57BL6/J infected mice but unaltered within SP-D OE. Thus SP-D modulates macrophage phenotype and the balance of multimeric to trimeric SP-D is critical to this regulation.

Exogenous surfactant prevents hyperoxia-induced lung injury in adult mice

Background

In addition to the risk of developing ventilator-induced lung injury, patients with ARDS are at risk of developing hyperoxic injury due the supra-physiological oxygen supplementation clinically required to reverse hypoxemia. Alterations of endogenous surfactant system participate in the pulmonary dysfunction observed in ARDS. Administration of exogenous surfactant could have protective effects during hyperoxia.

Methods

Male BALB/c mice (8–10 weeks), a strain highly sensitive to hyperoxia, received the exogenous surfactant-containing protein SP-B and SP-C by intranasal instillation 12 h before starting 24 h of exposure to hyperoxia in an inhalation chamber and were compared to mice receiving hyperoxia alone and to controls subjected to normoxia.

Results

Compared to the hyperoxia group, the administration of exogenous surfactant was able to reduce lung inflammation through a reduction in the influx of neutrophils and inflammatory biomarkers such as TNF, IL-17, and HMGB1 expression. The antioxidant activity prevented oxidative damage by reducing lipid peroxidation and protein carbonylation and increasing superoxide dismutase activity when compared to the hyperoxia group.

Conclusion

Our results offer new perspectives on the effects and the mechanism of exogenous surfactant in protecting the airway and lungs, in oxygen-rich lung microenvironment, against oxidative damage and aggravation of acute inflammation induced by hyperoxia.

Oxidative stress diseases unique to the perinatal period: A window into the developing innate immune response

The innate immune system has evolved to play an integral role in the normally developing lung and brain. However, in response to oxidative stress, innate immunity, mediated by specific cellular and molecular programs and signaling, contributes to pathology in these same organ systems. Despite opposing drivers of oxidative stress, namely hyperoxia in neonatal lung injury and hypoxia/ischemia in neonatal brain injury, similar pathways-including toll-like receptors, NFκB and MAPK cascades-have been implicated in tissue damage. In this review, we consider recent insights into the innate immune response to oxidative stress in both neonatal and adult models to better understand hyperoxic lung injury and hypoxic-ischemic brain injury across development and aging. These insights support the development of targeted immunotherapeutic strategies to address the challenge of harnessing the innate immune system in oxidative stress diseases of the neonate.

A pilot clinical trial of recombinant human angiotensin-converting enzyme 2 in acute respiratory distress syndrome

Background

Renin-angiotensin system (RAS) signaling and angiotensin-converting enzyme 2 (ACE2) have been implicated in the pathogenesis of acute respiratory distress syndrome (ARDS). We postulated that repleting ACE2 using GSK2586881, a recombinant form of human angiotensin-converting enzyme 2 (rhACE2), could attenuate acute lung injury.

Methods

We conducted a two-part phase II trial comprising an open-label intrapatient dose escalation and a randomized, double-blind, placebo-controlled phase in ten intensive care units in North America. Patients were between the ages of 18 and 80 years, had an American-European Consensus Criteria consensus diagnosis of ARDS, and had been mechanically ventilated for less than 72 h. In part A, open-label GSK2586881 was administered at doses from 0.1 mg/kg to 0.8 mg/kg to assess safety, pharmacokinetics, and pharmacodynamics. Following review of data from part A, a randomized, double-blind, placebo-controlled investigation of twice-daily doses of GSK2586881 (0.4 mg/kg) for 3 days was conducted (part B). Biomarkers, physiological assessments, and clinical endpoints were collected over the dosing period and during follow-up.

Results

Dose escalation in part A was well-tolerated without clinically significant hemodynamic changes. Part B was terminated after 39 of the planned 60 patients following a planned futility analysis. Angiotensin II levels decreased rapidly following infusion of GSK2586881, whereas angiotensin-(1–7) and angiotensin-(1–5) levels increased and remained elevated for 48 h. Surfactant protein D concentrations were increased, whereas there was a trend for a decrease in interleukin-6 concentrations in rhACE2-treated subjects compared with placebo. No significant differences were noted in ratio of partial pressure of arterial oxygen to fraction of inspired oxygen, oxygenation index, or Sequential Organ Failure Assessment score.

Conclusions

GSK2586881 was well-tolerated in patients with ARDS, and the rapid modulation of RAS peptides suggests target engagement, although the study was not powered to detect changes in acute physiology or clinical outcomes.

Trial registration

ClinicalTrials.gov, NCT01597635. Registered on 26 January 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1823-x) contains supplementary material, which is available to authorized users.

Lung protection by inhalation of exogenous solubilized extracellular matrix

Decellularized extracellular matrix (ECM) contains complex tissue-specific components that work in concert to promote tissue repair and constructive remodeling and has been used experimentally and clinically to accelerate epithelial wound repair, leading us to hypothesize that lung-derived ECM could mitigate acute lung injury. To explore the therapeutic potential of ECM for noninvasive delivery to the lung, we decellularized and solubilized porcine lung ECM, then characterized the composition, concentration, particle size and stability of the preparation. The ECM preparation at 3.2 mg/mL with average particle size <3 μm was tested in vitro on human A549 lung epithelial cells exposed to 95% O2 for 24 hours, and in vivo by tracheal instillation or nebulization into the lungs of rats exposed intermittently or continuously to 90% O2 for a cumulative 72 hours. Our results showed that the preparation was enriched in collagen, reduced in glycosaminoglycans, and contained various bioactive molecules. Particle size was concentration-dependent. Compared to the respective controls treated with cell culture medium in vitro or saline in vivo, ECM inhalation normalized cell survival and alveolar morphology, and reduced hyperoxia-induced apoptosis and oxidative damage. This proof-of-concept study established the methodology, feasibility and therapeutic potential of exogenous solubilized ECM for pulmonary cytoprotection, possibly as an adjunct or potentiator of conventional therapy.

Cartilage rings contribute to the proper embryonic tracheal epithelial differentiation, metabolism, and expression of inflammatory genes

The signaling cross talk between the tracheal mesenchyme and epithelium has not been researched extensively, leaving a substantial gap of knowledge in the mechanisms dictating embryonic development of the proximal airways by the adjacent mesenchyme. Recently, we reported that embryos lacking mesenchymal expression of Sox9 did not develop tracheal cartilage rings and showed aberrant differentiation of the tracheal epithelium. Here, we propose that tracheal cartilage provides local inductive signals responsible for the proper differentiation, metabolism, and inflammatory status regulation of the tracheal epithelium. The tracheal epithelium of mesenchyme-specific Sox9^Δ/Δ mutant embryos showed altered mRNA expression of various epithelial markers such as Pb1fa1, surfactant protein B (Sftpb), secretoglobulin, family 1A, member 1 (Scgb1a1), and trefoil factor 1 (Tff1). In vitro tracheal epithelial cell cultures confirmed that tracheal chondrocytes secrete factors that inhibit club cell differentiation. Whole gene expression profiling and ingenuity pathway analysis showed that the tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), and transforming growth factor-β (TGF-β) signaling pathways were significantly altered in the Sox9 mutant trachea. TNF-α and IFN-γ interfered with the differentiation of tracheal epithelial progenitor cells into mature epithelial cell types in vitro. Mesenchymal knockout of Tgf-β1 in vivo resulted in altered differentiation of the tracheal epithelium. Finally, mitochondrial enzymes involved in fat and glycogen metabolism, cytochrome c oxidase subunit VIIIb (Cox8b) and cytochrome c oxidase subunit VIIa polypeptide 1 (Cox7a1), were strongly upregulated in the Sox9 mutant trachea, resulting in increases in the number and size of glycogen storage vacuoles. Our results support a role for tracheal cartilage in modulation of the differentiation and metabolism and the expression of inflammatory-related genes in the tracheal epithelium by feeding into the TNF-α, IFN-γ, and TGF-β signaling pathways.

Prediction of non-recovery from ventilator-demanding acute respiratory failure, ARDS and death using lung damage biomarkers: data from a 1200-patient critical care randomized trial

Background

It is unclear whether biomarkers of alveolar damage (surfactant protein D, SPD) or conductive airway damage (club cell secretory protein 16, CC16) measured early after intensive care admittance are associated with one-month clinical respiratory prognosis. If patients who do not recover respiratory function within one month can be identified early, future experimental lung interventions can be aimed toward this high-risk group. We aimed to determine, in a heterogenous critically ill population, whether baseline profound alveolar damage or conductive airway damage has clinical respiratory impact one month after intensive care admittance.

Methods

Biobank study of biomarkers of alveolar and conductive airway damage in intensive care patients was conducted. This was a sub-study of 758 intubated patients from a 1200-patient randomized trial. We split the cohort into a “learning cohort” and “validating cohort” based on geographical criteria: northern sites (learning) and southern sites (validating).

Results

Baseline SPD above the 85th percentile in the “learning cohort” predicted low chance of successful weaning from ventilator within 28 days (adjusted hazard ratio 0.6 [95% CI 0.4–0.9], p = 0.005); this was confirmed in the validating cohort. CC16 did not predict the endpoint. The absolute risk of not being successfully weaned within the first month was 48/106 (45.3%) vs. 175/652 (26.8%), p < 0.0001 (high SPD vs. low SPD). The chance of being “alive and without ventilator ≥20 days within the first month” was lower among patients with high SPD (adjusted OR 0.2 [95% CI 0.2–0.4], p < 0.0001), confirmed in the validating cohort, and the risk of ARDS was higher among patients with high SPD (adjusted OR 3.4 [95% CI 1.0–11.4], p = 0.04)—also confirmed in the validating cohort.

Conclusion

Early profound alveolar damage in intubated patients can be identified by SPD blood measurement at intensive care admission, and high SPD level is a strong independent predictor that the patient suffers from ARDS and will not recover independent respiratory function within one month. This knowledge can be used to improve diagnostic and prognostic models and to identify the patients who most likely will benefit from experimental interventions aiming to preserve alveolar tissue and therefore respiratory function.

Trial registration This is a sub-study to the Procalcitonin And Survival Study (PASS), Clinicaltrials.gov ID: NCT00271752, first registered January 1, 2006

Electronic supplementary material

The online version of this article (doi:10.1186/s13613-016-0212-y) contains supplementary material, which is available to authorized users.

Lymphoblast Oxidative Stress Genes as Potential Biomarkers of Disease Severity and Drug Effect in Friedreich's Ataxia

There is no current approved therapy for the ultimately lethal neuro- and cardio-degenerative disease Friedreich's ataxia (FA). Finding minimally-invasive molecular biomarkers of disease progression and drug effect could support smaller, shorter clinical trials. Since we and others have noted a deficient oxidative stress response in FA, we investigated the expression of 84 genes involved in oxidative stress, signaling, and protection in control and FA lymphoblasts ranging from 460 to 1122 GAA repeats. Several antioxidant genes responded in a dose-dependent manner to frataxin expression at the mRNA and protein levels, which is inversely correlated with disease progression and severity. We tested the effect of experimental Friedreich's ataxia therapies dimethyl fumarate (DMF) and type 1 histone deacetylase inhibitor (HDACi) on biomarker mRNA expression. We observed that exposure of lymphoblasts to DMF and HDACi dose-dependently unsilenced frataxin expression and restored the potential biomarkers NCF2 and PDLIM1 expression to control levels. We suggest that in addition to frataxin expression, blood lymphoblast levels of NCF2 and PDLIM1 could be useful biomarkers for disease progression and drug effect in future clinical trials of Friedreich's ataxia.

Ventilation strategies for preventing oxidative stress-induced injury in preterm infants with respiratory disease: an update

Reactive oxygen and nitrogen species are produced by several inflammatory and structural cells of the airways. The lungs of preterm newborns are susceptible to oxidative injury induced by both reactive oxygen and nitrogen species. Increased oxidative stress and imbalance in antioxidant enzymes may play a role in the pathogenesis of inflammatory pulmonary diseases. Preterm infants are frequently exposed to high oxygen concentrations, infections or inflammation; they have reduced antioxidant defense and high free iron levels which enhance toxic radical generation. Multiple ventilation strategies have been studied to reduce injury and improve outcomes in preterm infants. Using lung protective strategies, there is the need to reach a compromise between satisfaction of gas exchange and potential toxicities related to over-distension, derecruitment of lung units and high oxygen concentrations. In this review, the authors summarize scientific evidence concerning oxidative stress as it relates to resuscitation in the delivery room and to the strategies of ventilation.

Endogeous sulfur dioxide protects against oleic acid-induced acute lung injury in association with inhibition of oxidative stress in rats

The role of endogenous sulfur dioxide (SO2), an efficient gasotransmitter maintaining homeostasis, in the development of acute lung injury (ALI) remains unidentified. We aimed to investigate the role of endogenous SO2 in the pathogenesis of ALI. An oleic acid (OA)-induced ALI rat model was established. Endogenous SO2 levels, lung injury, oxidative stress markers and apoptosis were examined. OA-induced ALI rats showed a markedly downregulated endogenous SO2/aspartate aminotransferase 1 (AAT1)/AAT2 pathway and severe lung injury. Chemical colorimetry assays demonstrated upregulated reactive oxygen species generation and downregulated antioxidant capacity in OA-induced ALI rats. However, SO2 increased endogenous SO2 levels, protected against oxidative stress and alleviated ALI. Moreover, compared with OA-treated cells, in human alveolar epithelial cells SO2 downregulated O2(-) and OH(-) generation. In contrast, L-aspartic acid-β-hydroxamate (HDX, Sigma-Aldrich Corporation), an inhibitor of endogenous SO2 generating enzyme, promoted free radical generation, upregulated poly (ADP-ribose) polymerase expression, activated caspase-3, as well as promoted cell apoptosis. Importantly, apoptosis could be inhibited by the free radical scavengers glutathione (GSH) and N-acetyl-L-cysteine (NAC). The results suggest that SO2/AAT1/AAT2 pathway might protect against the development of OA-induced ALI by inhibiting oxidative stress.

Radiation-induced lung injury and inflammation in mice: role of inducible nitric oxide synthase and surfactant protein D

Reactive nitrogen species (RNS) generated after exposure to radiation have been implicated in lung injury. Surfactant protein D (SP-D) is a pulmonary collectin that suppresses inducible nitric oxide synthase (iNOS)-mediated RNS production. Herein, we analyzed the role of iNOS and SP-D in radiation-induced lung injury. Exposure of wild-type (WT) mice to γ-radiation (8 Gy) caused acute lung injury and inflammation, as measured by increases in bronchoalveolar lavage (BAL) protein and cell content at 24 h. Radiation also caused alterations in SP-D structure at 24 h and 4 weeks post exposure. These responses were blunted in iNOS(-/-) mice. Conversely, loss of iNOS had no effect on radiation-induced expression of phospho-H2A.X or tumor necrosis factor (TNF)-α. Additionally, at 24 h post radiation, cyclooxygenase expression and BAL lipocalin-2 levels were increased in iNOS(-/-) mice, and heme oxygenase (HO)-1(+) and Ym1(+) macrophages were evident. Loss of SP-D resulted in increased numbers of enlarged HO-1(+) macrophages in the lung following radiation, along with upregulation of TNF-α, CCL2, and CXCL2, whereas expression of phospho-H2A.X was diminished. To determine if RNS play a role in the altered sensitivity of SP-D(-/-) mice to radiation, iNOS(-/-)/SP-D(-/-) mice were used. Radiation-induced injury, oxidative stress, and tissue repair were generally similar in iNOS(-/-)/SP-D(-/-) and SP-D(-/-) mice. In contrast, TNF-α, CCL2, and CXCL2 expression was attenuated. These data indicate that although iNOS is involved in radiation-induced injury and altered SP-D structure, in the absence of SP-D, it functions to promote proinflammatory signaling. Thus, multiple inflammatory pathways contribute to the pathogenic response to radiation.

NLRP3 protein deficiency exacerbates hyperoxia-induced lethality through Stat3 protein signaling independent of interleukin-1β

Supplemental oxygen inhalation is frequently used to treat severe respiratory failure; however, prolonged exposure to hyperoxia causes hyperoxic acute lung injury (HALI), which induces acute respiratory distress syndrome and leads to high mortality rates. Recent investigations suggest the possible role of NLRP3 inflammasomes, which regulate IL-1β production and lead to inflammatory responses, in the pathophysiology of HALI; however, their role is not fully understood. In this study, we investigated the role of NLRP3 inflammasomes in mice with HALI. Under hyperoxic conditions, NLRP3(-/-) mice died at a higher rate compared with wild-type and IL-1β(-/-) mice, and there was no difference in IL-1β production in their lungs. Under hyperoxic conditions, the lungs of NLRP3(-/-) mice exhibited reduced inflammatory responses, such as inflammatory cell infiltration and cytokine expression, as well as increased and decreased expression of MMP-9 and Bcl-2, respectively. NLRP3(-/-) mice exhibited diminished expression and activation of Stat3, which regulates MMP-9 and Bcl-2, in addition to increased numbers of apoptotic alveolar epithelial cells. In vitro experiments revealed that alveolar macrophages and neutrophils promoted Stat3 activation in alveolar epithelial cells. Furthermore, NLRP3 deficiency impaired the migration of neutrophils and chemokine expression by macrophages. These findings demonstrate that NLRP3 regulates Stat3 signaling in alveolar epithelial cells by affecting macrophage and neutrophil function independent of IL-1β production and contributes to the pathophysiology of HALI.

Deficiency of melanoma differentiation-associated protein 5 results in exacerbated chronic postviral lung inflammation

RATIONALE

Respiratory viral infections can result in the establishment of chronic lung diseases. Understanding the early innate immune mechanisms that participate in the development of chronic postviral lung disease may reveal new targets for therapeutic intervention. The intracellular viral sensor protein melanoma differentiation-associated protein 5 (MDA5) sustains the acute immune response to Sendai virus, a mouse pathogen that causes chronic lung inflammation, but its role in the development of postviral chronic lung disease is unknown.

OBJECTIVES

To establish the role of MDA5 in the development of chronic lung disease.

METHODS

MDA5-deficient or control mice were infected with Sendai virus. The acute inflammatory response was evaluated by profiling chemokine and cytokine expression and by characterizing the composition of the cellular infiltrate. The impact of MDA5 on chronic lung pathology and function was evaluated through histological studies, degree of oxygen saturation, and responsiveness to carbachol.

MEASUREMENTS AND MAIN RESULTS

MDA5 deficiency resulted in normal virus replication and in a distinct profile of chemokines and cytokines that associated with acute lung neutropenia and enhanced accumulation of alternatively activated macrophages. Diminished expression of neutrophil-recruiting chemokines was also observed in cells infected with influenza virus, suggesting a key role of MDA5 in driving the early accumulation of neutrophils at the infection site. The biased acute inflammatory response of MDA5-deficient mice led to an enhanced chronic lung inflammation, epithelial cell hyperplasia, airway hyperreactivity, and diminished blood oxygen saturation.

CONCLUSIONS

MDA5 modulates the development of chronic lung inflammation by regulating the early inflammatory response in the lung.

NLRP3 deletion protects from hyperoxia-induced acute lung injury

Inspiration of a high concentration of oxygen, a therapy for acute lung injury (ALI), could unexpectedly lead to reactive oxygen species (ROS) production and hyperoxia-induced acute lung injury (HALI). Nucleotide-binding domain and leucine-rich repeat PYD-containing protein 3 (NLRP3) senses the ROS, triggering inflammasome activation and interleukin-1β (IL-1β) production and secretion. However, the role of NLRP3 inflammasome in HALI is unclear. The main aim of this study is to determine the effect of NLRP3 gene deletion on inflammatory response and lung epithelial cell death. Wild-type (WT) and NLRP3(-/-) mice were exposed to 100% O2 for 48-72 h. Bronchoalveolar lavage fluid and lung tissues were examined for proinflammatory cytokine production and lung inflammation. Hyperoxia-induced lung pathological score was suppressed in NLRP3(-/-) mice compared with WT mice. Hyperoxia-induced recruitment of inflammatory cells and elevation of IL-1β, TNFα, macrophage inflammatory protein-2, and monocyte chemoattractant protein-1 were attenuated in NLRP3(-/-) mice. NLRP3 deletion decreased lung epithelial cell death and caspase-3 levels and a suppressed NF-κB levels compared with WT controls. Taken together, this research demonstrates for the first time that NLRP3-deficient mice have suppressed inflammatory response and blunted lung epithelial cell apoptosis to HALI.

Lifespan extension in the spontaneous dwarf rat and enhanced resistance to hyperoxia-induced mortality

Lifespan extension has been demonstrated in dwarfism mouse models relative to their wild-type. The spontaneous dwarf rat (SDR) was isolated from a closed colony of Sprague-Dawley (SD) rats. Growth hormone deficiencies have been indicated to be responsible for dwarfism in SDR. Survival time, the markers of oxidative stress, antioxidant enzymes, and resistance to hyperoxia were compared between SDR and SD rats, to investigate whether SDR, a dwarfism rat model, also extends lifespan and has an enhanced resistance to oxidative stress. SDRs lived 38% longer than SD rats on average. This is the first report to show that dwarf rats exhibit lifespan extensions similar to Ames and Snell mice. Decreased 8-oxo-2'-deoxyguanosine (8-oxodG) content, a marker of oxidative DNA damage, indicated suppressed oxidative stress in the liver, kidney, and lung of SDRs. Increased glutathione peroxidase enzyme activity was consistent with decreased 8-oxodG content in the same tissues. The heart and brain showed a similar tendency, but this was not significant. However, the catalase and superoxide dismutase enzyme activities of SDRs were not different from those of SD rats in any tissue. This was not what the original null hypothesis predicted. SDRs had potent resistance to the toxicity associated with high O2 (85%) exposure. The mean survival time in SDRs was more than 147% that of SD rats with 168h O2 exposure. These results suggest that the enhanced resistance to oxidative stress of SDRs associated with enhanced hydrogen peroxide elimination may support its potential role in lifespan extension.

Differential response of primary alveolar type I and type II cells to LPS stimulation

The alveolar epithelium serves as a barrier between organism and environment and functions as the first line of protection against potential respiratory pathogens. Alveolar type II (TII) cells have traditionally been considered the immune cells of the alveolar epithelium, as they possess immunomodulatory functions; however, the precise role of alveolar type I (TI) cells, which comprise ∼95% of the alveolar epithelial surface area, in lung immunity is not clear. We sought to determine if there was a difference in the response of TI and TII cells to lung injury and if TI cells could actively participate in the alveolar immune response. TI cells isolated via fluorescence activated cell sorting (FACS) from LPS-injured rats demonstrated greater fold-induction of multiple inflammatory mediators than TII cells isolated in the same manner from the same animals. Levels of the cytokines TNF-α, IL-6 and IL-1β from cultured primary rat TI cells after LPS stimulation were significantly increased compared to similarly studied primary rat TII cells. We found that contrary to published reports, cultured TII cells produce relatively small amounts of TNF-α, IL-6 and IL-1β after LPS treatment; the higher levels of cytokine expression from cultured TII cells reported in the literature were likely from macrophage contamination due to traditional non-FACS TII cell isolation methods. Co-culture of TII cells with macrophages prior to LPS stimulation increased TNF-α and IL-6 production to levels reported by other investigators for TII cells, however, co-culture of TI cells and macrophages prior to LPS treatment resulted in marked increases in TNF-α and IL-6 production. Finally, exogenous surfactant blunted the IL-6 response to LPS in cultured TI cells. Taken together, these findings advocate a role for TI cells in the innate immune response and suggest that both TI and TII cells are active players in host defense mechanisms in the lung.

Metallothionein-induced zinc partitioning exacerbates hyperoxic acute lung injury

Hypozincemia, with hepatic zinc accumulation at the expense of other organs, occurs in infection, inflammation, and aseptic lung injury. Mechanisms underlying zinc partitioning or its impact on extrahepatic organs are unclear. Here we show that the major zinc-binding protein, metallothionein (MT), is critical for zinc transmigration from lung to liver during hyperoxia and preservation of intrapulmonary zinc during hyperoxia is associated with an injury-resistant phenotype in MT-null mice. Particularly, lung-to-liver zinc ratios decreased in wild-type (WT) and increased significantly in MT-null mice breathing 95% oxygen for 72 h. Compared with female adult WT mice, MT-null mice were significantly protected against hyperoxic lung injury indicated by reduced inflammation and interstitial edema, fewer necrotic changes to distal airway epithelium, and sustained lung function at 72 h hyperoxia. Lungs of MT-null mice showed decreased levels of immunoreactive LC3, an autophagy marker, compared with WT mice. Analysis of superoxide dismutase (SOD) activity in the lungs revealed similar levels of manganese-SOD activity between strains under normoxia and hyperoxia. Lung extracellular SOD activity decreased significantly in both strains at 72 h of hyperoxia, although there was no difference between strains. Copper-zinc-SOD activity was ~4× higher under normoxic conditions in MT-null compared with WT mice but was not affected in either group by hyperoxia. Collectively the data suggest that genetic deletion of MT-I/II in mice is associated with compensatory increase in copper-zinc-SOD activity, prevention of hyperoxia-induced zinc transmigration from lung to liver, and hyperoxia-resistant phenotype strongly associated with differences in zinc homeostasis during hyperoxic acute lung injury.

Increased surfactant protein D fails to improve bacterial clearance and inflammation in serpinB1-/- mice

Previously, we described the protective role of the neutrophil serine protease inhibitor serpinB1 in preventing early mortality of Pseudomonas aeruginosa lung infection by fostering bacterial clearance and limiting inflammatory cytokines and proteolytic damage. Surfactant protein D (SP-D), which maintains the antiinflammatory pulmonary environment and mediates bacterial removal, was degraded in infected serpinB1-deficient mice. Based on the hypothesis that increased SP-D would rescue or mitigate the pathological effects of serpinB1 deletion, we generated two serpinB1(-/-) lines overexpressing lung-specific rat SP-D and inoculated the mice with P. aeruginosa. Contrary to predictions, bacterial counts in the lungs of SP-D(low)serpinB1(-/-) and SP-D(high) serpinB1(-/-) mice were 4 logs higher than wild-type and not different from serpinB1(-/-) mice. SP-D overexpression also failed to mitigate inflammation (TNF-α), lung injury (free protein, albumin), or excess neutrophil death (free myeloperoxidase, elastase). These pathological markers were higher for infected SP-D(high)serpinB1(-/-) mice than for serpinB1(-/-) mice, although the differences were not significant after controlling for multiple comparisons. The failure of transgenic SP-D to rescue antibacterial defense of serpinB1-deficient mice occurred despite 5-fold or 20-fold increased expression levels, largely normal structure, and dose-dependent bacteria-aggregating activity. SP-D of infected wild-type mice was intact in 43-kD monomers by reducing SDS-PAGE. By contrast, proteolytic fragments of 35, 17, and 8 kD were found in infected SP-D(low)serpinB1(-/-), SP-D(high) serpinB1(-/-) mice, and serpinB1(-/-) mice. Thus, although therapies to increase lung concentration of SP-D may have beneficial applications, the findings suggest that therapy with SP-D may not be beneficial for lung inflammation or infection if the underlying clinical condition includes excess proteolysis.

Differential modulation of surfactant protein D under acute and persistent hypoxia in acute lung injury

Hypoxia contributes to the development of fibrosis with epithelial-mesenchymal transition (EMT) via stimulation of hypoxia-inducible factor 1α (HIF-1α) and de novo twist expression. Although hypoxemia is associated with increasing levels of surfactant protein D (SP-D) in acute lung injury (ALI), the longitudinal effects of hypoxia on SP-D expression in lung tissue injury/fibrosis have not been fully evaluated. Here, the involvement of hypoxia and SP-D modulation was evaluated in a model of bleomycin-induced lung injury. We also investigated the molecular mechanisms by which hypoxia might modulate SP-D expression in alveolar cells, by using a doxycycline (Dox)-dependent HIF-1α expression system. Tissue hypoxia and altered SP-D levels were present in bleomycin-induced fibrotic lesions. Acute hypoxia induced SP-D expression, supported by the finding that Dox-induced expression of HIF-1α increased SP-D expression. In contrast, persistent hypoxia repressed SP-D expression coupled with an EMT phenotype and twist expression. Long-term expression of HIF-1α caused SP-D repression with twist expression. Ectopic twist expression repressed SP-D expression. The longitudinal observation of hypoxia and SP-D levels in ALI in vivo was supported by the finding that HIF-1α expression stabilized by acute hypoxia induced increasing SP-D expression in alveolar cells, whereas persistent hypoxia induced de novo twist expression in these cells, causing repression of SP-D and acquisition of an EMT phenotype. Thus this is the first study to demonstrate the molecular mechanisms, in which SP-D expression under acute and persistent hypoxia in acute lung injury might be differentially modulated by stabilized HIF-1α expression and de novo twist expression.

Granulocyte colony-stimulating factor protects mice during respiratory virus infections

A burst in the production of pro-inflammatory molecules characterizes the beginning of the host response to infection. Cytokines, chemokines, and growth factors work in concert to control pathogen replication and activate innate and adaptive immune responses. Granulocyte colony-stimulating factor (G-CSF) mobilizes and activates hematopoietic cells from the bone marrow, and it has been shown to mediate the generation of effective immunity against bacterial and fungal infections. G-CSF is produced at high levels in the lungs during infection with influenza and parainfluenza viruses, but its role during these infections is unknown. Here we show that during infection of mice with a non-lethal dose of influenza or Sendai virus, G-CSF promotes the accumulation of activated Ly6G⁺ granulocytes that control the extent of the lung pro-inflammatory response. Remarkably, these G-CSF-mediated effects facilitate viral clearance and sustain mouse survival.

S-nitrosylation of surfactant protein D as a modulator of pulmonary inflammation

BACKGROUND

Surfactant protein D (SP-D) is a member of the family of proteins termed collagen-like lectins or "collectins" that play a role in non-antibody-mediated innate immune responses [1]. The primary function of SP-D is the modulation of host defense and inflammation [2].

SCOPE OF REVIEW

This review will discuss recent findings on the physiological importance of SP-D S-nitrosylation in biological systems and potential mechanisms that govern SP-D mediated signaling.

MAJOR CONCLUSIONS

SP-D appears to have both pro- and anti-inflammatory signaling functions. SP-D multimerization is a critical feature of its function and plays an important role in efficient innate host defense. Under baseline conditions, SP-D forms a multimer in which the N-termini are hidden in the center and the C-termini are on the surface. This multimeric form of SP-D is limited in its ability to activate inflammation. However, NO can modify key cysteine residues in the hydrophobic tail domain of SP-D resulting in a dissociation of SP-D multimers into trimers, exposing the S-nitrosylated N-termini. The exposed S-nitrosylated tail domain binds to the calreticulin/CD91 receptor complex and initiates a pro-inflammatory response through phosphorylation of p38 and NF-κB activation [3,4]. In addition, the disassembled SP-D loses its ability to block TLR4, which also results in activation of NF-κB.

GENERAL SIGNIFICANCE

Recent studies have highlighted the capability of NO to modify SP-D through S-nitrosylation, causing the activation of a pro-inflammatory role for SP-D [3]. This represents a novel mechanism both for the regulation of SP-D function and NO's role in innate immunity, but also demonstrates that the S-nitrosylation can control protein function by regulating quaternary structure. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.

Early alveolar epithelial dysfunction promotes lung inflammation in a mouse model of Hermansky-Pudlak syndrome

RATIONALE

The pulmonary phenotype of Hermansky-Pudlak syndrome (HPS) in adults includes foamy alveolar type 2 cells, inflammation, and lung remodeling, but there is no information about ontogeny or early disease mediators.

OBJECTIVES

To establish the ontogeny of HPS lung disease in an animal model, examine disease mediators, and relate them to patients with HPS1.

METHODS

Mice with mutations in both HPS1/pale ear and HPS2/AP3B1/pearl (EPPE mice) were studied longitudinally. Total lung homogenate, lung tissue sections, and bronchoalveolar lavage (BAL) were examined for phospholipid, collagen, histology, cell counts, chemokines, surfactant protein D (SP-D), and S-nitrosylated SP-D. Isolated alveolar epithelial cells were examined for expression of inflammatory mediators, and chemotaxis assays were used to assess their importance. Pulmonary function test results and BAL from patients with HPS1 and normal volunteers were examined for clinical correlation.

MEASUREMENTS AND MAIN RESULTS

EPPE mice develop increased total lung phospholipid, followed by a macrophage-predominant pulmonary inflammation, and lung remodeling including fibrosis. BAL fluid from EPPE animals exhibited early accumulation of both SP-D and S-nitrosylated SP-D. BAL fluid from patients with HPS1 exhibited similar changes in SP-D that correlated inversely with pulmonary function. Alveolar epithelial cells demonstrated expression of both monocyte chemotactic protein (MCP)-1 and inducible nitric oxide synthase in juvenile EPPE mice. Last, BAL from EPPE mice and patients with HPS1 enhanced migration of RAW267.4 cells, which was attenuated by immunodepletion of SP-D and MCP-1.

CONCLUSIONS

Inflammation is initiated from the abnormal alveolar epithelial cells in HPS, and S-nitrosylated SP-D plays a significant role in amplifying pulmonary inflammation.

Total antioxidant capacity and total oxidant status after surfactant treatment in preterm infants with respiratory distress syndrome

BACKGROUND

Oxidative damage is important in the pathogenesis of respiratory distress syndrome (RDS). However, data on the effect of surfactant therapy on oxidative stress in vivo are limited. We aimed to evaluate the oxidant/antioxidant status in preterm infants with RDS via measurement of total antioxidant capacity (TAC) and total oxidant status (TOS), to determine the effect of surfactant on oxidant/antioxidant balance and to assess the association between TAC, TOS and clinical outcomes of the patients.

METHODS

Sixty-nine infants with RDS were included. Blood samples for determining TAC and TOS were collected before and 48 h after surfactant treatment. TAC and TOS levels were analysed in serum. Patients were followed up until discharge or death.

RESULTS

Post-surfactant TAC levels were significantly higher than pre-surfactant TAC levels (P = 0.029). TAC/TOS ratio significantly increased after surfactant treatment (P = 0.018). Infants <28 weeks of gestational age had lower levels of baseline TAC than those ≥28 weeks of gestational age (P = 0.020), whereas TOS levels were similar. Baseline TAC/TOS ratio was lower in infants who died in the study period than those who survived (P = 0.023). After controlling gestational age, baseline TAC levels were significantly and inversely correlated with the duration of total respiratory support (r = -0.343; P = 0.009) and hospitalization (r = -0.341; P = 0.009). TAC or TOS levels were not associated with the development of bronchopulmonary dysplasia or other complications as determined during the investigation period.

CONCLUSIONS

Oxidant-antioxidant balance shifts in favour of the antioxidant system after surfactant treatment. Lower TAC/TOS ratio in preterm infants may be associated with increased mortality.

Deficiency of matrix metalloproteinase-13 increases inflammation after acute lung injury

Human and animal studies of acute lung injury (ALI) have shown that matrix metalloproteinases (MMPs) play an important role in disease pathogenesis, but despite being detected during ALI, the function of the collagenase MMP-13 in ALI is unknown. To evaluate this role of MMP-13, mice deficient in MMP-13 (KO) were examined after hyperoxic lung injury, and compared to wild-type (WT) mice. There was no survival difference between KO and WT mice. There was also no difference in fibrosis between WT and KO mice, as determined by hydroxyproline content and collagen expression by real-time polymerase chain reaction (PCR). Within the bronchoalveolar lavage (BAL), the KO mice exhibited a significant increase in inflammatory cells, when compared to the WT mice (5.51 × 10(5) versus 2.35 × 10(5) cells/mL; P = .001). Increased levels of the chemokine monocyte chemoattractant protein 1 (MCP-1) were observed in the lungs of the KO mice, confirmed via immunohistochemistry. In a subsequent in vitro experiment, MMP-13 was shown to cleave MCP-1. In ALI in the MMP-13 KO mice, MCP-1 could therefore remain active and potentially attract macrophages to the BAL. This study suggests a direct role for MMP-13 in modifying the inflammatory response in the lung after ALI.

Nrf2 increases survival and attenuates alveolar growth inhibition in neonatal mice exposed to hyperoxia

Increased oxidative stress is associated with perinatal asphyxia and respiratory distress in the newborn period. Induction of nuclear factor erythroid 2 p45-related factor (Nrf2) has been shown to decrease oxidative stress through the regulation of specific gene pathways. We hypothesized that Nrf2 attenuates mortality and alveolar growth inhibition in newborn mice exposed to hyperoxia. Nrf2(+/+) and Nrf2(-/-) newborn mice were exposed to hyperoxia at 24 h. Survival was significantly less in Nrf2(-/-) mice exposed to 72 h of hyperoxia and returned to room air (P < 0.0001) and in Nrf2(-/-) mice exposed to hyperoxia for 8 continuous days (P < 0.005). To determine the response of Nrf2 target genes to hyperoxia, glutathione peroxidase 2 (Gpx2) and NAD(P)H:quinone oxidoreductase (NQO1) expression was measured from lung of newborn mice using real-time PCR. In the Nrf2(+/+) mice, significant induction of lung Gpx2 and NQO1 above room air controls was found with hyperoxia. In contrast, Nrf2(-/-) mice had minimal induction of lung Gpx2 and NQO1 with hyperoxia. Expression of p21 and IL-6, genes not regulated by Nrf2, were also measured. IL-6 expression in Nrf2(-/-) lung was markedly induced by 72 h of hyperoxia in contrast to the Nrf2(+/+) mice. p21 was induced in both Nrf2(+/+) and Nrf2(-/-) lung by hyperoxia. Mean linear intercept (MLI) and mean chord length (MCL) were significantly increased in 14-day-old Nrf2(-/-) mice previously exposed to hyperoxia compared with Nrf2(+/+) mice. The percentage of surfactant protein C (Sp-c(+)) type 2 alveolar cells in 14-day-old Nrf2(-/-) mice exposed to neonatal hyperoxia was also significantly less than Nrf2(+/+) mice (P < 0.02). In summary, these findings indicate that Nrf2 increases survival in newborn mice exposed to hyperoxia and that Nrf2 may help attenuate alveolar growth inhibition caused by hyperoxia exposure.