In defense of the lung: surfactant protein A and surfactant protein D

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.

The role of protein corona on nanodrugs for organ-targeting and its prospects of application

Nowadays, nanodrugs become a hotspot in the high-end medical field. They have the ability to deliver drugs to reach their destination more effectively due to their unique properties and flexible functionalization. However, the fate of nanodrugs in vivo is not the same as those presented in vitro, which indeed influenced their therapeutic efficacy in vivo. When entering the biological organism, nanodrugs will first come into contact with biological fluids and then be covered by some biomacromolecules, especially proteins. The proteins adsorbed on the surface of nanodrugs are known as protein corona (PC), which causes the loss of prospective organ-targeting abilities. Fortunately, the reasonable utilization of PC may determine the organ-targeting efficiency of systemically administered nanodrugs based on the diverse expression of receptors on cells in different organs. In addition, the nanodrugs for local administration targeting diverse lesion sites will also form unique PC, which plays an important role in the therapeutic effect of nanodrugs. This article introduced the formation of PC on the surface of nanodrugs and summarized the recent studies about the roles of diversified proteins adsorbed on nanodrugs and relevant protein for organ-targeting receptor through different administration pathways, which may deepen our understanding of the role that PC played on organ-targeting and improve the therapeutic efficacy of nanodrugs to promote their clinical translation.

A Biomolecular Toolbox for Precision Nanomotors

The application of nanomotors for cancer diagnosis and therapy is a new and exciting area of research, which when combined with precision nanomedicine, promises to solve many of the issues encountered by previous development of passive nanoparticles. The goal of this article is to introduce nanomotor and nanomedicine researchers to the deep pool of knowledge available regarding cancer cell biology and biochemistry, as well as provide a greater appreciation of the complexity of cell membrane compositions, extracellular surfaces, and their functional consequences. A short description of the nanomotor state-of-art for cancer therapy and diagnosis is first provided, as well as recommendations for future directions of the field. Then, a biomolecular targeting toolbox has been collated for researchers looking to apply their nanomaterial of choice to a biological setting, as well as providing a glimpse into currently available clinical therapies and technologies. This toolbox contains an overview of different classes of targeting molecules available for high affinity and specific targeting and cell surface targets to aid researchers in the selection of a clinical disease model and targeting methodology. It is hoped that this review will provide biological context, inspiration, and direction to future nanomotor and nanomedicine research.

Sigmar1 ablation leads to lung pathological changes associated with pulmonary fibrosis, inflammation, and altered surfactant proteins levels

Sigma1 receptor protein (Sigmar1) is a small, multifunctional molecular chaperone protein ubiquitously expressed in almost all body tissues. This protein has previously shown its cardioprotective roles in rodent models of cardiac hypertrophy, heart failure, and ischemia-reperfusion injury. Extensive literature also suggested its protective functions in several central nervous system disorders. Sigmar1's molecular functions in the pulmonary system remained unknown. Therefore, we aimed to determine the expression of Sigmar1 in the lungs. We also examined whether Sigmar1 ablation results in histological, ultrastructural, and biochemical changes associated with lung pathology over aging in mice. In the current study, we first confirmed the presence of Sigmar1 protein in human and mouse lungs using immunohistochemistry and immunostaining. We used the Sigmar1 global knockout mouse (Sigmar1-/-) to determine the pathophysiological role of Sigmar1 in lungs over aging. The histological staining of lung sections showed altered alveolar structures, higher immune cells infiltration, and upregulation of inflammatory markers (such as pNFκB) in Sigmar1-/- mice compared to wildtype (Wt) littermate control mice (Wt). This indicates higher pulmonary inflammation resulting from Sigmar1 deficiency in mice, which was associated with increased pulmonary fibrosis. The protein levels of some fibrotic markers, fibronectin, and pSMAD2 Ser 245/250/255 and Ser 465/467, were also elevated in mice lungs in the absence of Sigmar1 compared to Wt. The ultrastructural analysis of lungs in Wt mice showed numerous multilamellar bodies of different sizes with densely packed lipid lamellae and mitochondria with a dark matrix and dense cristae. In contrast, the Sigmar1-/- mice lung tissues showed altered multilamellar body structures in alveolar epithelial type-II pneumocytes with partial loss of lipid lamellae structures in the lamellar bodies. This was further associated with higher protein levels of all four surfactant proteins, SFTP-A, SFTP-B, SFTP-C, and SFTP-D, in the Sigmar1-/- mice lungs. This is the first study showing Sigmar1's expression pattern in human and mouse lungs and its association with lung pathophysiology. Our findings suggest that Sigmar1 deficiency leads to increased pulmonary inflammation, higher pulmonary fibrosis, alterations of the multilamellar body stuructures, and elevated levels of lung surfactant proteins.

Avian surfactant protein (SP)-A2 first arose in an early tetrapod before the divergence of amphibians and gradually lost the collagen domain

The air-liquid interface of the mammalian lung is lined with pulmonary surfactants, a mixture of specific proteins and lipids that serve a dual purpose-enabling air-breathing and protection against pathogens. In mammals, surfactant proteins A (SP-A) and D (SP -D) are involved in innate defence of the lung. Birds seem to lack the SP-D gene, but possess SP-A2, an additional SP-A-like gene. Here we investigated the evolution of the SP-A and SP-D genes using computational gene prediction, homology, simulation modelling and phylogeny with published avian and other vertebrate genomes. PCR was used to confirm the identity and expression of SP-A analogues in various tissue homogenates of zebra finch and turkey. In silico analysis confirmed the absence of SP-D-like genes in all 47 published avian genomes. Zebra finch and turkey SP-A1 and SP-A2 sequences, confirmed by PCR of lung homogenates, were compared with sequenced and in silico predicted vertebrate homologs to construct a phylogenetic tree. The collagen domain of avian SP-A1, especially that of zebra finch, was dramatically shorter than that of mammalian SP-A. Amphibian and reptilian genomes also contain avian-like SP-A2 protein sequences with a collagen domain. NCBI Gnomon-predicted avian and alligator SP-A2 proteins all lacked the collagen domain completely. Both avian SP-A1 and SP-A2 sequences form separate clades, which are most closely related to their closest relatives, the alligators. The C-terminal carbohydrate recognition domain (CRD) of zebra finch SP-A1 was structurally almost identical to that of rat SP-A. In fact, the CRD of SP-A is highly conserved among all the vertebrates. Birds retained a truncated version of mammalian type SP-A1 as well as a non-collagenous C-type lectin, designated SP-A2, while losing the large collagenous SP-D lectin, reflecting their evolutionary trajectory towards a unidirectional respiratory system. In the context of zoonotic infections, how these evolutionary changes affect avian pulmonary surface protection is not clear.

Lung surfactant as a biophysical assay for inhalation toxicology

Lung surfactant (LS) is a mixture of lipids and proteins that forms a thin film at the gas-exchange surfaces of the alveoli. The components and ultrastructure of LS contribute to its biophysical and biochemical functions in the respiratory system, most notably the lowering of surface tension to facilitate breathing mechanics. LS inhibition can be caused by metabolic deficiencies or the intrusion of endogenous or exogenous substances. While LS has been sourced from animals or synthesized for clinical therapeutics, the biofluid mixture has also gained recent interest as a biophysical model for inhalation toxicity. Various methods can be used to evaluate LS function quantitatively or qualitatively after exposure to potential toxicants. A narrative review of the recent literature was conducted. Studies focused whether LS was inhibited by various environmental contaminants, nanoparticles, or manufactured products. A review is also conducted on synthetic lung surfactants (SLS), which have emerged as a promising alternative to conventional animal-sourced LS. The intrinsic advantages and recent advances of SLS make a strong case for more widespread usage in LS-based toxicological assays.

Pathogenesis of pneumonia and acute lung injury

Pneumonia and its sequelae, acute lung injury, present unique challenges for pulmonary and critical care healthcare professionals, and these challenges have recently garnered global attention due to the ongoing Sars-CoV-2 pandemic. One limitation to translational investigation of acute lung injury, including its most severe manifestation (acute respiratory distress syndrome, ARDS) has been heterogeneity resulting from the clinical and physiologic diagnosis that represents a wide variety of etiologies. Recent efforts have improved our understanding and approach to heterogeneity by defining sub-phenotypes of ARDS although significant gaps in knowledge remain. Improving our mechanistic understanding of acute lung injury and its most common cause, infectious pneumonia, can advance our approach to precision targeted clinical interventions. Here, we review the pathogenesis of pneumonia and acute lung injury, including how respiratory infections and lung injury disrupt lung homoeostasis, and provide an overview of respiratory microbial pathogenesis, the lung microbiome, and interventions that have been demonstrated to improve outcomes-or not-in human clinical trials.

A New Homotetramer Hemoglobin in the Pulmonary Surfactant of Plateau Zokors (Myospalax Baileyi)

The plateau zokor (Myospalax baileyi) is a native species to the Qinghai-Tibetan Plateau, inhabiting hypoxia and hypercapnia sealed subterranean burrows that pose several unique physiological challenges. In this study, we observed a novel heme-containing protein in the pulmonary surfactant (PS) of plateau zokor, identified the encoding gene of the protein, predicted its origination and structure, verified its expression in alveolar epithelial cells, and determined the protein’s affinity to oxygen and its effect on the oxygen-dissolving capability in the PS of plateau zokors. The protein is an unusual homotetramer hemoglobin consisting of four γ-like subunits, and the subunit is encoded by a paralog gene of γ, that is γ-like. The divergence time of γ-like from γ is estimated by the molecular clock to be about 2.45 Mya. The generation of γ-like in plateau zokors might well relate to long-time stress of the high land hypoxia. Unlike γ, the γ-like has a hypoxia response element (HRE) and a lung tissue-specific enhancer in its upstream region, and it is expressed specifically in lung tissues and up-regulated by hypoxia. The protein is named as γ₄-like which is expressed specifically in Alveolar epithelial type II (ATII) cells and secreted into the alveolar cavities through the osmiophilic multilamellar body (LBs). The γ₄-like has a higher affinity to oxygen, and that increases significantly oxygen-dissolving capability in the PS of plateau zokors by its oxygenation function, which might be beneficial for the plateau zokors to obtain oxygen from the severe hypoxia environments by facilitating oxygen diffusion from alveoli to blood.

Full-Length Recombinant hSP-D Binds and Inhibits SARS-CoV-2

SARS-CoV-2 infection of host cells is driven by binding of the SARS-CoV-2 spike-(S)-protein to lung type II pneumocytes, followed by virus replication. Surfactant protein SP-D, member of the front-line immune defense of the lungs, binds glycosylated structures on invading pathogens such as viruses to induce their clearance from the lungs. The objective of this study is to measure the pulmonary SP-D levels in COVID-19 patients and demonstrate the activity of SP-D against SARS-CoV-2, opening the possibility of using SP-D as potential therapy for COVID-19 patients. Pulmonary SP-D concentrations were measured in bronchoalveolar lavage samples from patients with corona virus disease 2019 (COVID-19) by anti-SP-D ELISA. Binding assays were performed by ELISAs. Protein bridge and aggregation assays were performed by gel electrophoresis followed by silver staining and band densitometry. Viral replication was evaluated in vitro using epithelial Caco-2 cells. Results indicate that COVID-19 patients (n = 12) show decreased pulmonary levels of SP-D (median = 68.9 ng/mL) when compared to levels reported for healthy controls in literature. Binding assays demonstrate that SP-D binds the SARS-CoV-2 glycosylated spike-(S)-protein of different emerging clinical variants. Binding induces the formation of protein bridges, the critical step of viral aggregation to facilitate its clearance. SP-D inhibits SARS-CoV-2 replication in Caco-2 cells (EC90 = 3.7 μg/mL). Therefore, SP-D recognizes and binds to the spike-(S)-protein of SARS-CoV-2 in vitro, initiates the aggregation, and inhibits viral replication in cells. Combined with the low levels of SP-D observed in COVID-19 patients, these results suggest that SP-D is important in the immune response to SARS-CoV-2 and that rhSP-D supplementation has the potential to be a novel class of anti-viral that will target SARS-CoV-2 infection.

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.

Neutrophils and IL-1α Regulate Surfactant Homeostasis during Cigarette Smoking

Cigarette smoke exposure induces inflammation marked by rapid and sustained neutrophil infiltration, IL-1α, release and altered surfactant homeostasis. However, the extent to which neutrophils and IL-1α contribute to the maintenance of pulmonary surfactant homeostasis is not well understood. We sought to investigate whether neutrophils play a role in surfactant clearance as well as the effect of neutrophil depletion and IL-1α blockade on the response to cigarette smoke exposure. In vitro and in vivo administration of fluorescently labeled surfactant phosphatidylcholine was used to assess internalization of surfactant by lung neutrophils and macrophages during or following cigarette smoke exposure in mice. We also depleted neutrophils using anti-Ly-6G or anti-Gr-1 Abs, or we neutralized IL-1α using a blocking Ab to determine their respective roles in regulating surfactant homeostasis during cigarette smoke exposure. We observed that neutrophils actively internalize labeled surfactant both in vitro and in vivo and that IL-1α is required for smoke-induced elevation of surfactant protein (SP)-A and SP-D levels. Neutrophil depletion during cigarette smoke exposure led to a further increase in SP-A levels in the bronchoalveolar lavage and increased IL-1α, CCL2, GM-CSF, and G-CSF release. Finally, macrophage expression of Mmp12, a protease linked to emphysema, was increased in neutrophil-depleted groups and decreased following IL-1α blockade. Taken together, our results indicate that neutrophils and IL-1α signaling are actively involved in surfactant homeostasis and that the absence of neutrophils in the lungs during cigarette smoke exposure leads to an IL-1α-dependent exacerbation of the inflammatory response.

Molecular Mechanisms of Maternal Diabetes Effects on Fetal and Neonatal Surfactant

Respiratory distress is a significant contributor to newborn morbidity and mortality. An association between infants of diabetic mothers (IDMs) and respiratory distress syndrome (RDS) has been well recognized for decades. As obesity and diabetes prevalence have increased over the past several decades, more women are overweight and diabetic in the first trimester, and many more pregnant women are diagnosed with gestational diabetes. Glycemic control during pregnancy can be challenging due to the maternal need for higher caloric intake and higher insulin resistance. Surfactant is a complex molecule at the alveolar air–liquid interface that reduces surface tension. Impaired surfactant synthesis is the primary etiology of RDS. In vitro cell line studies, in vivo animal studies with diabetic rat offspring, and clinical studies suggest hyperglycemia and hyperinsulinemia can disrupt surfactant lipid and protein synthesis, causing delayed maturation in surfactant in IDMs. A better understanding of the molecular mechanisms responsible for surfactant dysfunction in IDMs may improve clinical strategies to prevent diabetes-related complications and improve neonatal outcomes.

Pulmonary Surfactant and Drug Delivery: An Interface-Assisted Carrier to Deliver Surfactant Protein SP-D Into the Airways

This work is focused on the potential use of pulmonary surfactant to deliver full-length recombinant human surfactant protein SP-D (rhSP-D) using the respiratory air-liquid interface as a shuttle. Surfactant protein D (SP-D) is a collectin protein present in the pulmonary surfactant (PS) system, involved in innate immune defense and surfactant homeostasis. It has been recently suggested as a potential therapeutic to alleviate inflammatory responses and lung diseases in preterm infants suffering from respiratory distress syndrome (RDS) or bronchopulmonary dysplasia (BPD). However, none of the current clinical surfactants used for surfactant replacement therapy (SRT) to treat RDS contain SP-D. The interaction of SP-D with surfactant components, the potential of PS as a respiratory drug delivery system and the possibility to produce recombinant versions of human SP-D, brings the possibility of delivering clinical surfactants supplemented with SP-D. Here, we used an in vitro setup that somehow emulates the respiratory air-liquid interface to explore this novel approach. It consists in two different compartments connected with a hydrated paper bridge forming a continuous interface. We firstly analyzed the adsorption and spreading of rhSP-D alone from one compartment to another over the air-liquid interface, observing low interfacial activity. Then, we studied the interfacial spreading of the protein co-administered with PS, both at different time periods or as a mixed formulation, and which oligomeric forms of rhSP-D better traveled associated with PS. The results presented here demonstrated that PS may transport rhSP-D long distances over air-liquid interfaces, either as a mixed formulation or separately in a close window time, opening the doors to empower the current clinical surfactants and SRT.

Non-Reflex Defense Mechanisms of Upper Airway Mucosa: Possible Clinical Application

The sinonasal mucosa has an essential role in defense mechanisms of the upper respiratory tract. The innate immune system presents the primary defense against noxious microorganisms followed by induction of the adaptive immune mechanisms as a consequence of the presence of pathogens. This well-known activation of adaptive immune system in response to presence of the antigen on mucosal surfaces is now broadly applicated in vaccinology research. Prevention of infectious diseases belongs to substantial challenges in maintaining the population health. Non-invasive, easily applicable mucosal vaccination purposes various research opportunities that could be usable in daily practice. However, the existence of multiple limitations such as rapid clearance of vaccine from nasal mucosa by means of mucociliary transport represents a great challenge in development of safe and efficient vaccines. Here we give an updated view on nasal functions with focus on nasal mucosal immunity and its potential application in vaccination in nearly future.

Protective effects of pulmonary surfactant on decompression sickness in rats

Decompression sickness (DCS) is a systemic pathophysiological process featured by bubble load. Lung dysfunction plays a harmful effect on off-gassing, which contributes to bubble load and subsequent DCS occurrence. This study aimed to investigate the effects of pulmonary surfactant on DCS as it possesses multiple advantages on the lung. Rats were divided into three groups: the normal (n = 10), the surfactant (n = 36), and the saline (n = 36) group. Animals in surfactant or saline group were administered aerosol surfactant or saline 12 h before a stimulated diving, respectively. Signs of DCS were recorded and bubble load was detected. The contents of phospholipid and surfactant protein A (SPA), protein, IL-1 and IL-6 in bronchoalveolar lavage fluid (BALF), and lung wet/dry (W/D) ratio were determined. Serum levels of IL-6, ICAM-1, E-selectin, GSH, and GSSG were detected. In surfactant-treated rats, the morbidity and mortality of DCS markedly decreased (P < 0.01 and P < 0.05, respectively). Survival time prolonged and the latency to DCS dramatically delayed (P < 0.01). More importantly, bubble load markedly decreased (P < 0.01). The increases of protein, IL-1 and IL-6 in BALF, and lung W/D ratio were alleviated. Restoration of total phospholipid and SPA in BALF and ICAM-1 and E-selectin in serum was observed. The inflammation and oxidation were attenuated (P < 0.01). In conclusion, prediving administrating exogenous surfactant by aerosolization is an efficient, simple, and safe method for DCS prevention in rats.NEW & NOTEWORTHY This is the first study exploring the effects of aerosol surfactant on DCS prevention and it was proven to be an efficient and simple method. The role of surfactant in facilitating off-gassing was thought to be the critical mechanism in bubble degrading and subsequent DCS prevention.

Pulmonary and systemic toxicity in rats following inhalation exposure of 3-D printer emissions from acrylonitrile butadiene styrene (ABS) filament

BACKGROUND

Fused filament fabrication 3-D printing with acrylonitrile butadiene styrene (ABS) filament emits ultrafine particulates (UFPs) and volatile organic compounds (VOCs). However, the toxicological implications of the emissions generated during 3-D printing have not been fully elucidated.

AIM AND METHODS

The goal of this study was to investigate the in vivo toxicity of ABS-emissions from a commercial desktop 3-D printer. Male Sprague Dawley rats were exposed to a single concentration of ABS-emissions or air for 4 hours/day, 4 days/week for five exposure durations (1, 4, 8, 15, and 30 days). At 24 hours after the last exposure, rats were assessed for pulmonary injury, inflammation, and oxidative stress as well as systemic toxicity.

RESULTS AND DISCUSSION

3-D printing generated particulate with average particle mass concentration of 240 ± 90 µg/m³, with an average geometric mean particle mobility diameter of 85 nm (geometric standard deviation = 1.6). The number of macrophages increased significantly at day 15. In bronchoalveolar lavage, IFN-γ and IL-10 were significantly higher at days 1 and 4, with IL-10 levels reaching a peak at day 15 in ABS-exposed rats. Neither pulmonary oxidative stress responses nor histopathological changes of the lungs and nasal passages were found among the treatments. There was an increase in platelets and monocytes in the circulation at day 15. Several serum biomarkers of hepatic and kidney functions were significantly higher at day 1.

CONCLUSIONS

At the current experimental conditions applied, it was concluded that the emissions from ABS filament caused minimal transient pulmonary and systemic toxicity.

An internal amino-terminal FLAG-tag octapeptide alters oligomerization of expressed surfactant protein-A

Pulmonary surfactant protein-A (SP-A) is expressed by lung alveolar and bronchiolar epithelial cells and plays a critical role in innate immunity of the lung. Exposure of the lung to various environmental insults alters SP-A homeostasis. To investigate the cellular mechanisms involved in these alterations, we added the FLAG octapeptide (DYKDDDDK) to the carboxy-terminus (SP-A/C-FLAG) or near the amino-terminus (SP-A/N-FLAG) of mouse SP-A (WT-SP-A) to tag specific pools of protein. We hypothesized that addition of FLAG would have negligible effects on SP-A expression, oligomerization and secretion. Analysis of Chinese hamster ovary cells expressing these proteins indicated that tagged SP-A mRNA could be distinguished from WT-SP-A by northern analysis and RT-PCR using sequence-specific oligonucleotides. Tagged SP-A protein could be differentiated from WT-SP-A by western analysis using antibodies specific for the FLAG epitope. Subcellular fractionation and immunocytochemistry indicated the majority of each protein was present in punctuate (presumably endocytic) vesicles, and all forms of SP-A protein were secreted. These results suggest that a FLAG epitope added to the carboxy-terminus or inserted into the amino-terminus of the mature SP-A protein has little effect on its expression and cellular processing. However, disruptions of the amino-terminal end of SP-A prevents proper oligomerization, suggesting that this region of mature SP-A is critical in proper oligomeric assembly and is not useful for studies intended to define mechanisms underlying SP-A homeostasis.

A 20-Mer Peptide Derived from the Lectin Domain of SP-A2 Decreases Tumor Necrosis Factor Alpha Production during Mycoplasma pneumoniae Infection

Human surfactant protein-A2 (hSP-A2) is a component of pulmonary surfactant that plays an important role in the lung's immune system by interacting with viruses, bacteria, and fungi to facilitate pathogen clearance and by downregulating inflammatory responses after an allergic challenge. Genetic variation in SP-A2 at position Gln223Lys is present in up to ∼30% of the population and has been associated with several lung diseases, such as asthma, pulmonary fibrosis, and lung cancer (M. M. Pettigrew, J. F. Gent, Y. Zhu, E. W. Triche, et al., BMC Med Genet 8:15, 2007, https://bmcmedgenet.biomedcentral.com/articles/10.1186/1471-2350-8-15; Y. Wang, P. J. Kuan, C. Zing, J. T. Cronkhite, et al., Am J Hum Genet 84:52-59, 2009, https://www.cell.com/ajhg/fulltext/S0002-9297(08)00595-8). Previous work performed by our group showed differences in levels of SP-A binding to non-live mycoplasma membrane fractions that were dependent on the presence of a lysine (K) or a glutamine (Q) at amino acid position 223 in the carbohydrate region of SP-A2. On the basis of these differences, we have derived 20-amino-acid peptides flanking this region of interest in order to test the ability of each to regulate various immune responses to live Mycoplasma pneumoniae in SP-A knockout mice and RAW 264.7 cells. In both models, the 20-mer containing 223Q significantly decreased both tumor necrosis factor alpha (TNF-α) mRNA levels and protein levels in comparison to the 20-mer containing 223K during M. pneumoniae infection. While neither of the 20-mer peptides (223Q and 223K) had an effect on p38 phosphorylation during M. pneumoniae infection, the 223Q-20mer peptide significantly reduced NF-κB p65 phosphorylation in both models. Taken together, our data suggest that small peptides derived from the lectin domain of SP-A2 that contain the major allelic variant (223Q) maintain activity in reducing TNF-α induction during M. pneumoniae infection.

Food-Derived Nanoscopic Drug Delivery Systems for Treatment of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a severe systemic inflammatory disease with no cure at present. Recent developments in the understanding of inflammation and nanomaterial science have led to increased applications of nanostructured drug delivery systems in the treatment of RA. The present review summarizes novel fabrications of nanoscale drug carriers using food components as either the delivered drugs or carrier structures, in order to achieve safe, effective and convenient drug administration. Polyphenols and flavonoids are among the most frequently carried anti-RA therapeutics in the nanosystems. Fatty substances, polysaccharides, and peptides/proteins can function as structuring agents of the nanocarriers. Frequently used nanostructures include nanoemulsions, nanocapsules, liposomes, and various nanoparticles. Using these nanostructures has improved drug solubility, absorption, biodistribution, stability, targeted accumulation, and release. Joint vectorization, i.e., using a combination of bioactive molecules, can bring elevated therapeutic outcomes. Utilization of anti-arthritic chemicals that can self-assemble into nanostructures is a promising research orientation in this field.

The gallbladder and vermiform appendix influence the assemblage of intestinal microorganisms

Surgical procedures for the symptomatic removal of the gallbladder and the vermiform appendix have been posited to adversely shift the assemblage of the intestinal microbiome increasing the risk of disease. The associated mechanisms have been linked with dysbiosis of the gut microbiota. Cholecystectomy causes changes of bile acid compositions and bile secretion patterns as bile acids interact with the intestinal microbiota in a bidirectional capacity. An appendectomy precludes the further recolonization of the proximal colon with a commensal biofilm that could maintain a stable intestinal microbiome. Epidemiological studies indicate that there is an increased risk of disease rather than causality following a cholecystectomy and appendectomy. This narrative review summarizes studies that report on the role that bile salts and the appendix, contribute to the assemblage of the intestinal microbiome in health and disease.

On Top of the Alveolar Epithelium: Surfactant and the Glycocalyx

Gas exchange in the lung takes place via the air-blood barrier in the septal walls of alveoli. The tissue elements that oxygen molecules have to cross are the alveolar epithelium, the interstitium and the capillary endothelium. The epithelium that lines the alveolar surface is covered by a thin and continuous liquid lining layer. Pulmonary surfactant acts at this air-liquid interface. By virtue of its biophysical and immunomodulatory functions, surfactant keeps alveoli open, dry and clean. What needs to be added to this picture is the glycocalyx of the alveolar epithelium. Here, we briefly review what is known about this glycocalyx and how it can be visualized using electron microscopy. The application of colloidal thorium dioxide as a staining agent reveals differences in the staining pattern between type I and type II alveolar epithelial cells and shows close associations of the glycocalyx with intraalveolar surfactant subtypes such as tubular myelin. These morphological findings indicate that specific spatial interactions between components of the surfactant system and those of the alveolar epithelial glycocalyx exist which may contribute to the maintenance of alveolar homeostasis, in particular to alveolar micromechanics, to the functional integrity of the air-blood barrier, to the regulation of the thickness and viscosity of the alveolar lining layer, and to the defence against inhaled pathogens. Exploring the alveolar epithelial glycocalyx in conjunction with the surfactant system opens novel physiological perspectives of potential clinical relevance for future research.

Functional characterization of the different oligomeric forms of human surfactant protein SP-D

Surfactant Protein D (SP-D) is a collectin protein that participates in the innate immune defense of the lungs. SP-D mediates the clearance of invading microorganisms by opsonization, aggregation or direct killing, which are lately removed by macrophages. SP-D is found as a mixture of trimers, hexamers, dodecamers and higher order oligomers, "fuzzy balls". However, it is unknown whether there are differences between these oligomeric forms in functions, activity or potency. In the present work, we have obtained fractions enriched in trimers, hexamers and fuzzy balls of full-length recombinant human (rh) SP-D by size exclusion chromatography, in a sufficient amount to perform functional assays. We have evaluated the differences in protein lectin-dependent activity relative to aggregation and binding to E. coli, one of the ligands of SP-D in vivo. Fuzzy balls are the most active oligomeric form in terms of binding and aggregation of bacteria, achieving 2-fold binding higher than hexamers and 50% bacteria aggregation at very short times. Hexamers, recently described as a defined oligomeric form of the protein, have never been isolated or tested in terms of protein activity. rhSP-D hexamers efficiently bind and aggregate bacteria, achieving 50-60% aggregation at final time point and high protein concentrations. Nevertheless, trimers are not able to aggregate bacteria, although they bind to them. Therefore, SP-D potency, in functions that relay on the C-lectin activity of the protein, is proportional to the oligomeric state of the protein.

Irreversible disruption of the cytoskeleton as induced by non-cytotoxic exposure to titanium dioxide nanoparticles in lung epithelial cells

Exposure to TiO₂ NPs induces several cellular alterations after NPs uptake including disruption of cytoskeleton that is crucial for lung physiology but is not considered as a footprint of cell damage. We aimed to investigate cytoskeleton disturbances and the impact on cell migration induced by an acute TiO₂ NPs exposure (24 h) and the recovery capability after 6 days of NPs-free treatment, which allowed investigating if cytoskeleton damage was reversible. Exposure to TiO₂ NPs (10 μg/cm²) for 24 h induced a decrease 20.2% and 25.1% in tubulin and actin polymerization. Exposure to TiO₂ NPs (10 μg/cm²) for 24 h followed by 6 days of NPs-free had a decrease of 26.6% and 21.3% in tubulin and actin polymerization, respectively. The sustained exposure for 7 days to 1 μg/cm² and 10 μg/cm² induced a decrease of 22.4% and 30.7% of tubulin polymerization respectively, and 28.7% and 46.2% in actin polymerization. In addition, 24 h followed 6 days of NPs-free exposure of TiO₂ NPs (1 μg/cm² and 10 μg/cm²) decreased cell migration 40.7% and 59.2%, respectively. Cells exposed (10 μg/cm²) for 7 days had a decrease of 65.5% in cell migration. Ki67, protein surfactant B (SFTPB) and matrix metalloprotease 2 (MMP2) were analyzed as genes related to lung epithelial function. The results showed a 20% of Ki67 upregulation in cells exposed for 24 h to 10 μg/cm² TiO₂ NPs while a downregulation of 20% and 25.8% in cells exposed to 1 μg/cm² and 10 μg/cm² for 24 h followed by 6 days of NPs-free exposure. Exposure to 1 μg/cm² and 10 μg/cm² for 24 h and 7 days upregulates SFTPB expression in 53% and 59% respectively, MMP2 expression remain unchanged. In conclusion, exposure of TiO₂ NPs affected cytoskeleton of lung epithelial cells irreversibly but this damage was not cumulative.

Study on the Relationship Between Respiratory Distress Syndrome and SP-A1 (rs1059057) Gene Polymorphism in Mongolian Very Premature Infants

Aim: To study the relationship between rs1059057 polymorphism of pulmonary surfactant protein A1 (SP-A1) and respiratory distress syndrome (RDS) in Mongolian very premature infants. Methods: Applying the strategy of case-control study, 120 Mongolian RDS very premature infants (58 males and 62 females) in the western part of Inner Mongolia were selected as the case group, and 120 subjects of non-RDS very premature infants (56 males and 64 females) with the same nationality, same sex and similar gestational age were used as the control group. The single nucleotide polymorphism (SNP) site rs1059057 of SP-A1 was genotyped using polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP). Results: Two genotypes, A/G and A/A, were detected at the SP-A1 rs1059057 locus in the western part of Inner Mongolia. In the case group, the frequencies of two genotypes were 53 and 47%, and the frequencies of A allele and G allele were 73 and 27%, respectively. In the control group, the frequencies of the two genotypes were 42 and 58%, and the frequencies of A allele and G allele were 79 and 21%, respectively. There was no significant difference in the genotype frequency of SP-A1 (rs1059057) locus between the case group and the control group (X 2 = 3.275, P > 0.05), and no significant difference in allele frequency between the case group and the control group (X 2 = 2.255, P > 0.05). Conclusion: The genotypes and allele frequencies of SP-A1 (rs1059057) locus were not associated with the incidence of RDS in Mongolian very premature infants in western Inner Mongolia.

A Comparative Study to Explore the Effect of Different Compounds in Immune Proteins of Human Beings Against Tuberculosis: An In-silico Approach

Background:

The lungs are directly exposed to pollutants, pathogens, allergens, and chemicals, which might lead to physiological disorders. During the Bhopal gas disaster, the lungs of the victims were exposed to various chemicals. Here, using molecular modelling studies, we describe the effects of these chemicals (Dimethyl urea, Trimethyl urea, Trimethyl isocyanurate, Alphanaphthol, Butylated hydroxytoluene and Carbaryl) on pulmonary immune proteins.

Objective:

In the current study, we performed molecular modelling methods like molecular docking and molecular dynamics simulation studies to identify the effects of hydrolytic products of MIC and dumped residues on the pulmonary immune proteins.

Methods:

Molecular docking studies of (Dimethyl urea, Trimethyl urea, Trimethyl isocyanurate, Alphanaphthol, Butylated hydroxytoluene and Carbaryl) on pulmonary immune proteins was performed using the Autodock 4.0 tool, and gromacs was used for the molecular dynamics simulation studies to get an insight into the possible mode of protein-ligand interactions. Further, in silico ADMET studies was performed using the TOPKAT protocol of discovery studio.

Results:

From docking studies, we found that surfactant protein-D is inhibited most by the chemicals alphanaphthol (dock score, -5.41Kcal/mole), butylated hydroxytoluene (dock score,-6.86 Kcal/mole), and carbaryl (dock score,-6.1 Kcal/mole). To test their stability, the obtained dock poses were placed in a lipid bilayer model system mimicking the pulmonary surface. Molecular dynamics simulations suggest a stable interaction between surfactant protein-D and carbaryl.

Conclusion:

This, study concludes that functioning of surfactant protein-D is directly or indirectly affected by the carbaryl chemical, which might account for the increased susceptibility of Bhopal gas disaster survivors to pulmonary tuberculosis.

Altered Surfactant Protein Expression in Primary Acquired Nasolacrimal Duct Obstruction

PURPOSE

To investigate the presence and distribution patterns of 6 surfactant proteins in lacrimal drainage tissues of patients with primary acquired nasolacrimal duct (NLD) obstruction.

METHODS

The presence and distribution of surfactant proteins (SP)-G and SP-H was first assessed in normal cadaveric lacrimal systems. The study was then performed in 10 samples of lacrimal sac and the respective NLDs obtained from patients suffering from primary acquired NLD obstruction who underwent either a dacryocystorhinostomy or a dacryocystectomy. The lacrimal sac samples were further divided into fundus and body, soon after their removal. Immunohistochemical labeling was performed for assessing the presence and distribution of SPs: SP-A, SP-B, SP-C, SP-D, SP-G/SFTA2, and SP-H/SFTA3. The results were then scored as positive or negative and the distribution pattern, if any, within the lacrimal sac and NLDs was assessed. Human lung tissues were used as controls.

RESULTS

SP-H was demonstrated in the lining epithelia of the normal lacrimal drainage systems, whereas SP-G was uniformly negative. Immunohistochemical labeling revealed wide variations in the staining patterns of different SPs in different regions of the lacrimal sac and the NLD. SP-D and SP-G revealed uniformly negative immunoreactivity. Variable staining patterns were also noted between the superficial and basal layers of the lining epithelia. However, the goblet cells and intraepithelial mucous glands did not express any of the SPs.

CONCLUSIONS

This study provides a proof of principle for the presence of SP-H and absence of SP-G in the normal lacrimal drainage systems. In cases of primary acquired nasolacrimal duct obstruction, there were alterations or loss of SP expression in the lining epithelia of the lacrimal sac and NLDs, reflecting their possible role in the etiopathogenesis of primary acquired nasolacrimal duct obstruction.In cases of primary-acquired nasolacrimal duct obstruction, the expression of multiple surfactant proteins was either deranged or lost in the lining epithelium of the lacrimal sac and nasolacrimal ducts.

The Lord of the Lungs: The essential role of pulmonary surfactant upon inhalation of nanoparticles

The rapid development of nanotechnology is opening a huge world of promising possibilities in healthcare, but this is also increasing the necessity to study the potential risk of nanoparticles on public health and the environment. Since the main route for airborne particles to enter into our organism is through the lungs, it has become essential to prove that the nanoparticles generated by human activities do not compromise the respiratory function. This review explains the key role of pulmonary surfactant to sustain the normal function of breathing, as well as the stability and immunity of lungs. Particular emphasis is made on the importance of analysing the features of nanoparticles, defining their interactions with surfactant and unravelling the mutual effects. The implication of the nanoparticle-surfactant interaction on the function and fate of both structures is described, as well as the main in vitro methodologies used to evaluate this interaction. Finally, the incorporation of pulmonary surfactant in appropriate in vitro models is used in order to obtain an extensive understanding of how nanoparticles may act in the context of the lung. The main goal of this review is to offer a general view on inhaled nanoparticles and their effects on the structure and function of lungs derived from their interaction with the pulmonary surfactant system.

Formulation Strategies for Folate-Targeted Liposomes and Their Biomedical Applications

The folate receptor (FR) is a tumor-associated antigen that can bind with folic acid (FA) and its conjugates with high affinity and ingests the bound molecules inside the cell via the endocytic mechanism. A wide variety of payloads can be delivered to FR-overexpressed cells using folate as the ligand, ranging from small drug molecules to large DNA-containing macromolecules. A broad range of folate attached liposomes have been proven to be highly effective as the targeted delivery system. For the rational design of folate-targeted liposomes, an intense conceptual understanding combining chemical and biomedical points of view is necessary because of the interdisciplinary nature of the field. The fabrication of the folate-conjugated liposomes basically involves the attachment of FA with phospholipids, cholesterol or peptides before liposomal formulation. The present review aims to provide detailed information about the design and fabrication of folate-conjugated liposomes using FA attached uncleavable/cleavable phospholipids, cholesterol or peptides. Advances in the area of folate-targeted liposomes and their biomedical applications have also been discussed.

Formulation of RNA interference-based drugs for pulmonary delivery: challenges and opportunities

With recent advances in the field of RNAi-based therapeutics, it is possible to make any target gene 'druggable', at least in principle. The present review focuses on aspects critical for pulmonary delivery of formulations of nucleic acid-based drugs. The first part introduces the therapeutic potential of RNAi-based drugs for the treatment of lung diseases. Subsequently, we discuss opportunities for formulation-enabled pulmonary delivery of RNAi drugs in light of key physicochemical properties and physiological barriers. In the following section, an overview is included of methodologies for imparting inhalable characteristics to nucleic acid formulations. Finally, we review one of the bottlenecks in the early preclinical testing of inhalable nucleic acid-based formulations, in other words, devices suitable for pulmonary administration of powder-based formulations in rodents.

Quenching of tryptophan fluorescence in a highly scattering solution: Insights on protein localization in a lung surfactant formulation

CHF5633 (Chiesi Farmaceutici, Italy) is a synthetic surfactant developed for respiratory distress syndrome replacement therapy in pre-term newborn infants. CHF5633 contains two phospholipids (dipalmitoylphosphatidylcholine and 1-palmitoyl-2oleoyl-sn-glycero-3-phosphoglycerol sodium salt), and peptide analogues of surfactant protein C (SP-C analogue) and surfactant protein B (SP-B analogue). Both proteins are fundamental for an optimal surfactant activity in vivo and SP-B genetic deficiency causes lethal respiratory failure after birth. Fluorescence emission of the only tryptophan residue present in SP-B analogue (SP-C analogue has none) could in principle be exploited to probe SP-B analogue conformation, localization and interaction with other components of the pharmaceutical formulation. However, the high light scattering activity of the multi-lamellar vesicles suspension characterizing the pharmaceutical surfactant formulation represents a challenge for such studies. We show here that quenching of tryptophan fluorescence and Singular Value Decomposition analysis can be used to accurately calculate and subtract background scattering. The results indicate, with respect to Trp microenvironment, a conformationally homogeneous population of SP-B. Trp is highly accessible to the water phase, suggesting a surficial localization on the membrane of phospholipid vesicles, similarly to what observed for full length SP-B in natural lung surfactant, and supporting an analogous role in protein anchoring to the lipid phase.

Clinical, technological, and economic issues associated with developing new lung surfactant therapeutics

Discovery of lung surfactant deficiency as a main cause of neonatal respiratory distress syndrome (NRDS) has influenced a steep increase in lung surfactant research. Although this has yielded impactful scientific discoveries, much of the basic research on lung surfactants has failed to translate into clinical practices. This is attributed to insufficient information covering the entire lung surfactant ecosystem, from the basic science to economics surrounding the development and clinical practices. In this manuscript, developments related to improving therapeutic lung surfactant as well as the degree of unmet need are analyzed from both technical and economic perspectives. Two potential opportunities are emphasized: (1) aerosolized lung surfactants to treat NRDS infants, and (2) synthetic lung surfactants for acute respiratory distress syndrome (ARDS) patients. Each has a modestly projected US market size of $120 million and $4 billion, well enough to make up for the high development costs associated with investigational drug development. Both opportunities have been pursued in the past, but to date these attempts have met with no success mainly due to technical limitations. With the recent advancements in both fields, technology improvements have created opportunities to solve both decades-old problems.

Fungal melanin stimulates surfactant protein D-mediated opsonization of and host immune response to Aspergillus fumigatus spores

Surfactant protein D (SP-D), a C-type lectin and pattern-recognition soluble factor, plays an important role in immune surveillance to detect and eliminate human pulmonary pathogens. SP-D has been shown to protect against infections with the most ubiquitous airborne fungal pathogen, Aspergillus fumigatus, but the fungal surface component(s) interacting with SP-D is unknown. Here, we show that SP-D binds to melanin pigment on the surface of A. fumigatus dormant spores (conidia). SP-D also exhibited an affinity to two cell-wall polysaccharides of A. fumigatus, galactomannan (GM) and galactosaminogalactan (GAG). The immunolabeling pattern of SP-D was punctate on the conidial surface and was uniform on germinating conidia, in accordance with the localization of melanin, GM, and GAG. We also found that the collagen-like domain of SP-D is involved in its interaction with melanin, whereas its carbohydrate-recognition domain recognized GM and GAG. Unlike un-opsonized conidia, SP-D-opsonized conidia were phagocytosed more efficiently and stimulated the secretion of proinflammatory cytokines by human monocyte-derived macrophages. Furthermore, SP-D^-/- mice challenged intranasally with wildtype conidia or melanin ghosts (i.e. hollow melanin spheres) displayed significantly reduced proinflammatory cytokines in the lung compared with wildtype mice. In summary, SP-D binds to melanin present on the dormant A. fumigatus conidial surface, facilitates conidial phagocytosis, and stimulates the host immune response.

Pulmonary alveolar proteinosis in adults: pathophysiology and clinical approach

Pulmonary alveolar proteinosis (PAP) is a diffuse lung disease that results from the accumulation of lipoproteinaceous material in the alveoli and alveolar macrophages due to abnormal surfactant homoeostasis. Identification of the granulocyte-macrophage colony-stimulating factor (GM-CSF) as an indispensable mediator of macrophage maturation and surfactant catabolism was the key discovery leading to the current understanding of the pathogenesis of most forms of PAP. Impaired GM-CSF bioavailability due to anti-GM-CSF autoimmunity is the cause of approximately 90% of adult PAP cases. Abnormal macrophage function due to endogenous or exogenous triggers, GM-CSF receptor defects, and other genetic abnormalities of surfactant production account for the remainder of causes. The usual physiological consequence of PAP is impairment of gas exchange, which can lead to dyspnoea, hypoxaemia, or even respiratory failure and death. Pulmonary fibrosis occurs occasionally in patients with PAP. For patients with moderate to severe disease, whole lung lavage is still the first-line treatment of choice. Supplemental GM-CSF is also useful, but details about indications, choice of agent, and dosing remain unclear. Other therapies, including rituximab, plasmapheresis, and lung transplantation have been described but should be reserved for refractory cases.

Surfactant protein A down-regulates epidermal growth factor receptor by mechanisms different from those of surfactant protein D

We recently reported that the lectin surfactant protein D (SP-D) suppresses epidermal growth factor receptor (EGFR) signaling by interfering with ligand binding to EGFR through an interaction between the carbohydrate-recognition domain (CRD) of SP-D and N-glycans of EGFR. Here, we report that surfactant protein A (SP-A) also suppresses EGF signaling in A549 human lung adenocarcinoma cells and in CHOK1 cells stably expressing human EGFR and that SP-A inhibits the proliferation and motility of the A549 cells. Results with ¹²⁵I-EGF indicated that SP-A interferes with EGF binding to EGFR, and a ligand blot analysis suggested that SP-A binds EGFR in A549 cells. We also found that SP-A directly binds the recombinant extracellular domain of EGFR (soluble EGFR or sEGFR), and this binding, unlike that of SP-D, was not blocked by EDTA, excess mannose, or peptide:N-glycosidase F treatment. We prepared a collagenase-resistant fragment (CRF) of SP-A, consisting of CRD plus the neck domain of SP-A, and observed that CRF directly binds sEGFR but does not suppress EGF-induced phosphorylation of EGFR in or proliferation of A549 cells. These results indicated that SP-A binds EGFR and down-regulates EGF signaling by inhibiting ligand binding to EGFR as well as SP-D. However, unlike for SP-D, SP-A lectin activity and EGFR N-glycans were not involved in the interaction between SP-A and EGFR. Furthermore, our results suggested that oligomerization of SP-A is necessary to suppress the effects of SP-A on EGF signaling.

A preliminary study on fetal lung injury in a rat model of acute pancreatitis in pregnancy

Acute pancreatitis in pregnancy (APIP), which was thought to be rare, is becoming more frequent. In addition, high perinatal mortality among fetuses has been reported. Our research aimed to investigate and assess fetal lung injury in a rat model of APIP and its possible mechanisms. The APIP model was induced by sodium taurocholate in Sprague-Dawley rats during the third trimester. Sham-operated (SO) rats in late gestation were used as controls, and dynamic observation and detection in the SO and acute pancreatitis (AP) groups were performed at 3 time-points. Histological changes in the fetal lungs, as well as the maternal pancreas and placenta were assessed. The levels of serum amylase, lipase, TNF-α and IL-1β were detected in maternal rats, and the expression of surfactant proteins A, B, C and D as well as their mRNA were determined. In this study, fetal lung injury as well as maternal pancreas and placenta injuries occurred in a time-dependent manner. The levels of serum amylase, lipase and TNF-α were markedly increased in maternal rats, and the levels of surfactant proteins A, B, C and D in fetal lungs were significantly decreased in the fetal lungs of the AP group. Ultrastructure injuries and the dysregulated synthesis and secretion of pulmonary surfactant proteins were observed in the AP group. Our research suggests that fetal lung injury is involved in the rat model of APIP and that the dysregulated synthesis and secretion of pulmonary surfactant proteins play a critical role in fetal lung injury during APIP.

Pulmonary Surfactant and Bacterial Lipopolysaccharide: The Interaction and its Functional Consequences

The respiratory system is constantly exposed to pathogens which enter the lungs by inhalation or via blood stream. Lipopolysaccharide (LPS), also named endotoxin, can reach the airspaces as the major component of the outer membrane of Gram-negative bacteria, and lead to local inflammation and systemic toxicity. LPS affects alveolar type II (ATII) cells and pulmonary surfactant and although surfactant molecule has the effective protective mechanisms, excessive amount of LPS interacts with surfactant film and leads to its inactivation. From immunological point of view, surfactant specific proteins (SPs) SP-A and SP-D are best characterized, however, there is increasing evidence on the involvement of SP-B and SP-C and certain phospholipids in immune reactions. In animal models, the instillation of LPS to the respiratory system induces acute lung injury (ALI). It is of clinical importance that endotoxin-induced lung injury can be favorably influenced by intratracheal instillation of exogenous surfactant. The beneficial effect of this treatment was confirmed for both natural porcine and synthetic surfactants. It is believed that the surfactant preparations have anti-inflammatory properties through regulating cytokine production by inflammatory cells. The mechanism by which LPS interferes with ATII cells and surfactant layer, and its consequences are discussed below.

Genetic Polymorphisms of SP-A, SP-B, and SP-D and Risk of Respiratory Distress Syndrome in Preterm Neonates

Background

We examined selected polymorphisms in 3 pulmonary surfactant-associated proteins (SP) for their influence on serum SP levels and risk of respiratory distress syndrome (RDS) in preterm neonates.

Material/Methods

Premature infants from a Han population were enrolled, including 100 premature infants with RDS (case group) and 120 premature infants without RDS (control group). SNP genotyping for SP-A (+186A/G and +655C/T), SP-B (−18A/C and 1580C/T), and SP-D (Met11ThrT/C and Ala160ThrG/A) used polymerase chain reaction-restriction fragment length polymorphism. Haplotypes were calculated with Shesis software and serum SP-A/B/D levels were quantified by ELISA.

Results

Case and control groups exhibited significant differences in genotype and allele frequencies of SP-A (+186A/G, +655C/T) and SP-B (1580C/T). However, no statistically significant differences were observed in the allele and genotype frequencies of SP-B −18A/C, SP-D Met11ThrT/C, and SP-D Ala160ThrG/A. Importantly, serum SP-A and SP-B levels were reduced in RDS patients carrying SP-A (+186A/G, +655C/T) and SP-B (1580C/T) polymorphisms. AA genotype of +186A/G, SP-A level, and CC genotype of 1580C/T were independently correlated with increased RDS risk.

Conclusions

SP-A (+186A/G) and SP-B (1580C/T) polymorphisms are strongly associated with the risk of RDS in preterm infants. Notably, reduced serum SP-A levels were correlated with a high risk of RDS and may serve as novel biomarkers for RDS detection and monitoring.

Elucidation of Lipid Binding Sites on Lung Surfactant Protein A Using X-ray Crystallography, Mutagenesis, and Molecular Dynamics Simulations

Surfactant protein A (SP-A) is a collagenous C-type lectin (collectin) that is critical for pulmonary defense against inhaled microorganisms. Bifunctional avidity of SP-A for pathogen-associated molecular patterns (PAMPs) such as lipid A and for dipalmitoylphosphatidylcholine (DPPC), the major component of surfactant membranes lining the air-liquid interface of the lung, ensures that the protein is poised for first-line interactions with inhaled pathogens. To improve our understanding of the motifs that are required for interactions with microbes and surfactant structures, we explored the role of the tyrosine-rich binding surface on the carbohydrate recognition domain of SP-A in the interaction with DPPC and lipid A using crystallography, site-directed mutagenesis, and molecular dynamics simulations. Critical binding features for DPPC binding include a three-walled tyrosine cage that binds the choline headgroup through cation-π interactions and a positively charged cluster that binds the phosphoryl group. This basic cluster is also critical for binding of lipid A, a bacterial PAMP and target for SP-A. Molecular dynamics simulations further predict that SP-A binds lipid A more tightly than DPPC. These results suggest that the differential binding properties of SP-A favor transfer of the protein from surfactant DPPC to pathogen membranes containing appropriate lipid PAMPs to effect key host defense functions.

Surfactant Protein-D Is Essential for Immunity to Helminth Infection

Pulmonary epithelial cell responses can enhance type 2 immunity and contribute to control of nematode infections. An important epithelial product is the collectin Surfactant Protein D (SP-D). We found that SP-D concentrations increased in the lung following Nippostrongylus brasiliensis infection; this increase was dependent on key components of the type 2 immune response. We carried out loss and gain of function studies of SP-D to establish if SP-D was required for optimal immunity to the parasite. N. brasiliensis infection of SP-D-/- mice resulted in profound impairment of host innate immunity and ability to resolve infection. Raising pulmonary SP-D levels prior to infection enhanced parasite expulsion and type 2 immune responses, including increased numbers of IL-13 producing type 2 innate lymphoid cells (ILC2), elevated expression of markers of alternative activation by alveolar macrophages (alvM) and increased production of the type 2 cytokines IL-4 and IL-13. Adoptive transfer of alvM from SP-D-treated parasite infected mice into naïve recipients enhanced immunity to N. brasiliensis. Protection was associated with selective binding by the SP-D carbohydrate recognition domain (CRD) to L4 parasites to enhance their killing by alvM. These findings are the first demonstration that the collectin SP-D is an essential component of host innate immunity to helminths.

Infections by parasitic worms are very common, and controlling them is a major medical and veterinary challenge. Very few drugs exist to treat them, and the parasites can develop resistance to these. In order to find new ways to control worm infections, understanding how our immune system responds to them is essential. Many important parasitic worm infections move through the host lung. In this study we show that a major secreted protein in the lung, Surfactant Protein D (SP-D), is essential for immunity to a parasitic worm infection. We found that this protein binds to worm larvae in the lung to help the immune system kill them. Infecting mice that do not express SP-D with worms demonstrates SP-D is important in this immune response. These mice are unable to launch an effective anti-worm immune response and have many more worms in their intestine compared to mice that do express SP-D. We also show that if we increase SP-D levels in the lung the mouse has better immunity to worms. Together this shows for the first time that SP-D is very important for immunity to worm infections.

Enrichment of immunoregulatory proteins in the biomolecular corona of nanoparticles within human respiratory tract lining fluid

When inhaled nanoparticles deposit in the lungs, they transit through respiratory tract lining fluid (RTLF) acquiring a biomolecular corona reflecting the interaction of the RTLF with the nanomaterial surface. Label-free snapshot proteomics was used to generate semi-quantitative profiles of corona proteins formed around silica (SiO2) and poly(vinyl) acetate (PVAc) nanoparticles in RTLF, the latter employed as an archetype drug delivery vehicle. The evolved PVAc corona was significantly enriched compared to that observed on SiO2 nanoparticles (698 vs. 429 proteins identified); however both coronas contained a substantial contribution from innate immunity proteins, including surfactant protein A, napsin A and complement (C1q and C3) proteins. Functional protein classification supports the hypothesis that corona formation in RTLF constitutes opsonisation, preparing particles for phagocytosis and clearance from the lungs. These data highlight how an understanding of the evolved corona is necessary for the design of inhaled nanomedicines with acceptable safety and tailored clearance profiles.

FROM THE CLINICAL EDITOR

Inhaled nanoparticles often acquire a layer of protein corona while they go through the respiratory tract. Here, the authors investigated the identity of these proteins. The proper identification would improve the understanding of the use of inhaled nanoparticles in future therapeutics.

Surfactant Protein A in Exhaled Endogenous Particles Is Decreased in Chronic Obstructive Pulmonary Disease (COPD) Patients: A Pilot Study

Background

Exhaled, endogenous particles are formed from the epithelial lining fluid in small airways, where surfactant protein A (SP-A) plays an important role in pulmonary host defense. Based on the knowledge that chronic obstructive pulmonary disease (COPD) starts in the small airway epithelium, we hypothesized that chronic inflammation modulates peripheral exhaled particle SP-A and albumin levels. The main objective of this explorative study was to compare the SP-A and albumin contents in exhaled particles from patients with COPD and healthy subjects and to determine exhaled particle number concentrations.

Methods

Patients with stable COPD ranging from moderate to very severe (n = 13), and healthy non-smoking subjects (n = 12) were studied. Subjects performed repeated breath maneuvers allowing for airway closure and re-opening, and exhaled particles were optically counted and collected on a membrane using the novel PExA^® instrument setup. Immunoassays were used to quantify SP-A and albumin.

Results

COPD patients exhibited significantly lower SP-A mass content of the exhaled particles (2.7 vs. 3.9 weight percent, p = 0.036) and lower particle number concentration (p<0.0001) than healthy subjects. Albumin mass contents were similar for both groups.

Conclusions

Decreased levels of SP-A may lead to impaired host defense functions of surfactant in the airways, contributing to increased susceptibility to COPD exacerbations. SP-A in exhaled particles from small airways may represent a promising non-invasive biomarker of disease in COPD patients.

The clinical use of corticosteroids in pregnancy

BACKGROUND

The use of antenatal steroid therapy is common in pregnancy. In early pregnancy, steroids may be used in women for the treatment of recurrent miscarriage or fetal abnormalities such as congenital adrenal hyperplasia. In mid-late pregnancy, the antenatal administration of corticosteroids to expectant mothers in anticipation of preterm birth is one of the most important advances in perinatal medicine; antenatal corticosteroids are now standard care for pregnancies at risk of premature delivery in high- and middle-income countries. The widespread uptake of this therapy is due to a compelling body of evidence demonstrating improved neonatal outcomes following antenatal corticosteroid exposure, stemming most notably from corticosteroid-driven maturation of fetal pulmonary function. As we approach the 50th anniversary of landmark work in this area by Liggins and Howie, it is apparent that much remains to be understood with regards to how we might best apply antenatal corticosteroid therapy to improve pregnancy outcomes at both early and mid to late gestation.

METHODS

Drawing on advances in laboratory science, pre-clinical and clinical studies, we performed a narrative review of the scientific literature to provide a timely update on the benefits, risks and uncertainties regarding antenatal corticosteroid use in pregnancy. Three, well-established therapeutic uses of antenatal steroids, namely recurrent miscarriage, congenital adrenal hyperplasia and preterm birth, were selected to frame the review.

RESULTS

Even the most well-established antenatal steroid therapies lack the comprehensive pharmacokinetic and dose-response data necessary to optimize dosing regimens. New insights into complex, tissue-specific corticosteroid signalling by genomic-dependent and independent mechanisms have not been used to inform corticosteroid treatment strategies. There is growing evidence that some fetal corticosteroid treatments are either ineffective, or may result in adverse outcomes, in addition to lasting epigenetic changes in a variety of homeostatic mechanisms. Nowhere is the need to better understand the intricacies of corticosteroid therapy better conveyed than in the findings of Althabe and colleagues who recently reported an increase in overall neonatal mortality and maternal morbidity in association with antenatal corticosteroid administration in low-resource settings.

CONCLUSIONS

New research to clarify the benefits and potential risks of antenatal corticosteroid therapy is urgently needed, especially with regard to corticosteroid use in low-resource environments. We conclude that there is both significant scope and an urgent need for further research-informed refinement to the use of antenatal corticosteroids in pregnancy.

Secretoglobin 3A2 Exhibits Anti-Fibrotic Activity in Bleomycin-Induced Pulmonary Fibrosis Model Mice

OBJECTIVE

Secretoglobin (SCGB) 3A2 is a novel lung-enriched cytokine, previously shown to exhibit anti-inflammatory, growth factor, and anti-fibrotic activities. The latter activity was demonstrated using exogenously-administered recombinant SCGB3A2 in the bleomycin (BLM)-induced pulmonary fibrosis model. Whether SCGB3A2 exhibits anti-fibrotic activity in vivo is not known.

METHODS

Mice null for the Scgb3a2 gene were subjected to the BLM-induced pulmonary fibrosis model, and the severity of pulmonary fibrosis determined using histological and biochemical methods.

RESULTS

BLM treatment caused weight loss of both Scgb3a2-null and wild-type mice, however, the loss was far more pronounced in BLM-treated Scgb3a2-null than wild-type mice, and the weight of day 21 of BLM-treated Scgb3a2-null mice was about half of that of BLM-treated wild-type mice. Hematoxylin & Eosin, Masson Trichrome, and Sirius Red staining of lung sections, Ashcroft fibrosis scores, hydroxyproline contents, and the levels of mRNAs encoding various collagens demonstrated that BLM-treated Scgb3a2-null mouse lungs had more severe fibrosis than those of wild-type mouse lungs. Total and differential inflammatory cell numbers in bronchoalveolar lavage fluids, and levels of lung mRNAs including those encoding Th2 cytokines such as IL-4 and profibrotic cytokines such as TGFβ were higher in BLM-treated Scgb3a2-null mouse lungs as compared to those of wild-type mouse lungs. In contrast, mRNAs encoding surfactant proteins A, B, C, and D, and SCGB1A1 did not differ between BLM-treated Scgb3a2-null and wild-type mouse lungs.

CONCLUSION

The role of SCGB3A2 in fibrosis was revisited using Scgb3a2-null mice and littermate controls in the BLM-induced pulmonary fibrosis model. The pulmonary fibrosis in the Scgb3a2-null mice was more severe than the wild-type controls, thus establishing that SCGB3A2 has anti-fibrotic activity in vivo. Importantly, surfactant proteins and SCGB1A1 appear not to be involved in the susceptibility of Scgb3a2-null mice to BLM-induced pulmonary fibrosis.