Lung surfactant and neonatal respiratory distress syndrome

New experiments and models to describe soluble surfactant adsorption above and below the critical micelle concentration

HYPOTHESIS

Lysopalmitoylphosphatidylcholine (LysoPC) is a soluble single-chain surfactant product of the innate immune system degradation of double-chain phospholipids. LysoPC adsorption to the air-water interface in lung alveoli can be modeled using alveolar-sized bubbles of constant surface area in a capillary pressure microtensiometer to show that adsorption is diffusion limited both below and above the critical micelle concentration (CMC). Above the CMC, a local equilibrium model is proposed in which depletion of the local monomer concentration drives dissociation of micelles in a region near the bubble surface.

EXPERIMENTAL

A capillary pressure microtensiometer in which a feedback loop maintains a constant bubble radius and surface area is used to measure dynamic surface tension during LysoPC adsorption. Direct numerical solution of the spherical diffusion equations, a new three parameter virial equation of state for interface thermodynamics, and a local equilibrium model of micellization above the CMC are used to accurately model the dynamic surface tension experiments both below and above the LysoPC CMC.

FINDINGS

LysoPC adsorption is shown to be diffusion-limited over concentrations ranging from below to well above the CMC, and to be well described by a local equilibrium model at concentrations above the CMC. Modelling the dynamic surface tension provides a reliable estimate of the micelle diffusivity near the CMC that is difficult to obtain by other methods in systems with low CMCs.

Mechanosensitive channels TMEM63A and TMEM63B mediate lung inflation-induced surfactant secretion

Pulmonary surfactant is a lipoprotein complex lining the alveolar surface to decrease the surface tension and facilitate inspiration. Surfactant deficiency is often seen in premature infants and in children and adults with respiratory distress syndrome. Mechanical stretch of alveolar type 2 epithelial (AT2) cells during lung expansion is the primary physiological factor that stimulates surfactant secretion; however, it is unclear whether there is a mechanosensor dedicated to this process. Here, we show that loss of the mechanosensitive channels TMEM63A and TMEM63B (TMEM63A/B) resulted in atelectasis and respiratory failure in mice due to a deficit of surfactant secretion. TMEM63A/B were predominantly localized at the limiting membrane of the lamellar body (LB), a lysosome-related organelle that stores pulmonary surfactant and ATP in AT2 cells. Activation of TMEM63A/B channels during cell stretch facilitated the release of surfactant and ATP from LBs fused with the plasma membrane. The released ATP evoked Ca2+ signaling in AT2 cells and potentiated exocytic fusion of more LBs. Our study uncovered a vital physiological function of TMEM63 mechanosensitive channels in preparing the lungs for the first breath at birth and maintaining respiration throughout life.

Comparative biophysical study of clinical surfactants using constrained drop surfactometry

Surfactant replacement therapy is crucial in managing neonatal respiratory distress syndrome (RDS). Currently licensed clinical surfactants in the United States and Europe, including Survanta, Infasurf, Curosurf, and Alveofact, are all derived from bovine or porcine sources. We conducted a comprehensive examination of the biophysical properties of these four clinical surfactant preparations under physiologically relevant conditions, using constrained drop surfactometry (CDS). The assessed biophysical properties included the adsorption rate, quasi-static and dynamic surface activity, resistance to surfactant inhibition by meconium, and the morphology of the adsorbed surfactant films. This comparative study unveiled distinct in vitro biophysical properties of these clinical surfactants and revealed correlations between their chemical composition, lateral film structure, and biophysical functionality. Notably, at 1 mg/mL, Survanta exhibited a significantly lower adsorption rate compared with the other preparations at the same surfactant concentration. At 10 mg/mL, Infasurf, Curosurf, and Survanta all demonstrated excellent dynamic surface activity, whereas Alveofact exhibited the poorest quasi-static and dynamic surface activity. The suboptimal surface activity of Alveofact is found to be correlated with its unique monolayer-predominant morphology, in contrast to other surfactants forming multilayers. Curosurf, in particular, showcased superior resistance to biophysical inhibition by meconium compared with other preparations. Understanding the diverse biophysical behaviors of clinical surfactants provides crucial insights for precision and personalized design in treating RDS and other respiratory conditions. The findings from this study contribute valuable perspectives for the development of more efficacious and fully synthetic surfactant preparations.NEW & NOTEWORTHY A thorough investigation into the biophysical properties of four animal-derived clinical surfactant preparations was conducted through constrained drop surfactometry under physiologically relevant conditions. This comparative study unveiled unique in vitro biophysical characteristics among these clinical surfactants, establishing correlations between their chemical composition, lateral film structure, and biophysical functionality. The acquired knowledge offers essential insights for the precise and personalized design of clinical surfactant for the treatment of respiratory distress syndrome and other respiratory conditions.

Life-saving effect of pulmonary surfactant in premature babies

The discovery and replacement of lung surfactant have helped increase survival rates for neonatal respiratory distress syndrome in extremely premature infants.

Evolution of interfacial mechanics of lung surfactant mimics progression of acute respiratory distress syndrome

How acute respiratory distress syndrome progresses from underlying disease or trauma is poorly understood, and there are no generally accepted treatments resulting in a 40% mortality rate. However, during the inflammation that accompanies this disease, the phospholipase A2 concentration increases in the alveolar fluids leading to the hydrolysis of bacterial, viral, and lung surfactant phospholipids into soluble lysolipids. We show that if the lysolipid concentration in the subphase reaches or exceeds its critical micelle concentration, the surface tension, γ, of dipalmitoyl phosphatidylcholine (DPPC) or Curosurf monolayers increases and the dilatational modulus, [Formula: see text], decreases to that of a pure lysolipid interface. This is consistent with DPPC being solubilized in lysolipid micelles and being replaced by lysolipid at the interface. These changes lead to [Formula: see text] which is the criterion for the Laplace instability that can lead to mechanical instabilities during lung inflation, potentially causing alveolar collapse. These findings provide a mechanism behind the alveolar collapse and uneven lung inflation during ARDS.

Pulmonary Surfactant: A Mighty Thin Film

Pulmonary surfactant is a critical component of lung function in healthy individuals. It functions in part by lowering surface tension in the alveoli, thereby allowing for breathing with minimal effort. The prevailing thinking is that low surface tension is attained by a compression-driven squeeze-out of unsaturated phospholipids during exhalation, forming a film enriched in saturated phospholipids that achieves surface tensions close to zero. A thorough review of past and recent literature suggests that the compression-driven squeeze-out mechanism may be erroneous. Here, we posit that a surfactant film enriched in saturated lipids is formed shortly after birth by an adsorption-driven sorting process and that its composition does not change during normal breathing. We provide biophysical evidence for the rapid formation of an enriched film at high surfactant concentrations, facilitated by adsorption structures containing hydrophobic surfactant proteins. We examine biophysical evidence for and against the compression-driven squeeze-out mechanism and propose a new model for surfactant function. The proposed model is tested against existing physiological and pathophysiological evidence in neonatal and adult lungs, leading to ideas for biophysical research, that should be addressed to establish the physiological relevance of this new perspective on the function of the mighty thin film that surfactant provides.

Constrained drop surfactometry for studying adsorbed pulmonary surfactant at physiologically relevant high concentrations

Exogenous surfactant therapy has been used as a standard clinical intervention for treating premature newborns with respiratory distress syndrome. The phospholipid concentrations of exogenous surfactants used in clinical practice are consistently higher than 25 mg/mL; while it was estimated that the phospholipid concentration of endogenous surfactant is approximately in the range between 15 and 50 mg/mL. However, most in vitro biophysical simulations of pulmonary surfactants were only capable of studying surfactant concentrations up to 3 mg/mL, one order of magnitude lower than the physiologically relevant concentration. Using a new in vitro biophysical model, called constrained drop surfactometry, in conjunction with atomic force microscopy and other technological advances, we have investigated the biophysical properties, ultrastructure, and topography of the pulmonary surfactant film adsorbed from the subphase at physiologically relevant high surfactant concentrations of 10-35 mg/mL. It was found that the effect of surfactant concentration on the dynamic surface activity of the surfactant film was only important when the surface area of the surfactant film varied no more than 15%, mimicking normal tidal breathing. The adsorbed surfactant film depicts a multilayer conformation consisting of a layer-by-layer assembly of stacked bilayers with the height of the multilayers proportional to the surfactant concentration. Our experimental data suggest that the biophysical function of these multilayer structures formed after de novo adsorption is to act as a buffer zone to store surface-active materials ejected from the interfacial monolayer under extreme conditions such as deep breathing.NEW & NOTEWORTHY An in vitro biophysical model, called constrained drop surfactometry, was developed to study the biophysical properties, ultrastructure, and topography of the pulmonary surfactant film adsorbed from the subphase at physiologically relevant high surfactant concentrations of 10-35 mg/mL. These results suggest that the biophysical function of multilayers formed after de novo adsorption is to act as a buffer zone to store surface-active materials ejected from the interfacial monolayer under extreme conditions such as deep breathing.

Synergism of Surfactant Mixture in Lowering Vapor-Liquid Interfacial Tension

Through employing molecular dynamics, in this work, we study how a two-component surfactant mixture cooperatively reduces the interfacial tension of a flat vapor-liquid interface. Our simulation results show that in the presence of a given insoluble surfactant, adding a secondary surfactant would either further reduce interfacial tension, indicating a positive synergistic effect, or increase the interfacial tension instead, indicating a negative synergistic effect. The synergism of the surfactant mixture in lowering surface tension is found to depend strongly on the structure complementary effect between different surfactant components. The synergistic mechanisms are then interpreted with minimization of the bending free energy of the composite surfactant monolayer via cooperatively changing the monolayer spontaneous curvature. By roughly describing the monolayer spontaneous curvature with the balanced distribution of surfactant heads and tails, we confirm that the positive synergistic effect in lowering surface tension is featured with the increasingly symmetric head-tail distributions, while the negative synergistic effect is featured with the increasingly asymmetric head-tail distributions. Furthermore, our simulation results indicate that minimal interfacial tension can only be observed when the spontaneous curvature is nearly zero.

Dilatational and shear rheology of soluble and insoluble monolayers with a Langmuir trough

HYPOTHESIS

The surface dilatational and shear moduli of surfactant and protein interfacial layers can be derived from surface pressures measured with a Wilhelmy plate parallel, ΔΠpar and perpendicular ΔΠperp to the barriers in a Langmuir trough.

EXPERIMENTAL

Applying area oscillations, A0+ ΔAeiωt, in a rectangular Langmuir trough induces changes in surface pressure, ΔΠpar and ΔΠperp for monolayers of soluble palmitoyl-lysophosphatidylcholine (LysoPC), insoluble dipalmitoylphosphatidylcholine (DPPC), and the protein β-lactoglobulin to evaluate Es∗+Gs∗=A0ΔΠparΔA and Es∗-Gs∗=A0ΔΠperpΔA. Gs∗ was independently measured with a double-wall ring apparatus (DWR) and Es∗ by area oscillations of hemispherical bubbles in a capillary pressure microtensiometer (CPM) and the results were compared to the trough measurements.

FINDINGS

For LysoPC and DPPC, A0ΔΠparΔA≅A0ΔΠperpΔA meaning Es∗≫Gs∗ and Es∗≅A0ΔΠparΔA≅A0ΔΠperpΔA. Trough values for Es∗ were quantitatively similar to CPM when corrected for interfacial curvature. DWR showed G∗ was 4 orders of magnitude smaller than Es∗ for both LysoPC and DPPC. For β-lactoglobulin films, A0ΔΠparΔA>A0ΔΠperpΔA and Es∗ and Gs∗ were in qualitative agreement with independent CPM and DWR measurements. For β-lactoglobulin, both Es∗ and Gs∗ varied with film age and history on the trough, suggesting the evolution of the protein structure.

Beyond nylon 6: polyamides via ring opening polymerization of designer lactam monomers for biomedical applications

Ring opening polymerization (ROP) of lactams is a highly efficient and versatile method to synthesize polyamides. Within the last ten years, significant advances in polymerization methodology and monomer diversity are ushering in a new era of polyamide chemistry. We begin with a discussion of polymerization techniques including the most widely used anionic ring opening polymerization (AROP), and less prevalent cationic ROP and enzyme-catalyzed ROP. Next, we describe new monomers being explored for ROP with increased functionality and stereochemistry. We emphasize the relationships between composition, structure, and properties, and how chemists can control composition and structure to dictate a desired property or performance. Finally, we discuss biomedical applications of the synthesized polyamides, specifically as biomaterials and pharmaceuticals, with examples to include as antimicrobial agents, cell adhesion substrates, and drug delivery scaffolds.

Computational lung modelling in respiratory medicine

Computational modelling of the lungs is an active field of study that integrates computational advances with lung biophysics, biomechanics, physiology and medical imaging to promote individualized diagnosis, prognosis and therapy evaluation in lung diseases. The complex and hierarchical architecture of the lung offers a rich, but also challenging, research area demanding a cross-scale understanding of lung mechanics and advanced computational tools to effectively model lung biomechanics in both health and disease. Various approaches have been proposed to study different aspects of respiration, ranging from compartmental to discrete micromechanical and continuum representations of the lungs. This article reviews several developments in computational lung modelling and how they are integrated with preclinical and clinical data. We begin with a description of lung anatomy and how different tissue components across multiple length scales affect lung mechanics at the organ level. We then review common physiological and imaging data acquisition methods used to inform modelling efforts. Building on these reviews, we next present a selection of model-based paradigms that integrate data acquisitions with modelling to understand, simulate and predict lung dynamics in health and disease. Finally, we highlight possible future directions where computational modelling can improve our understanding of the structure-function relationship in the lung.

Spontaneous evolution of equilibrium morphology in phospholipid-cholesterol monolayers

Competition between intradomain electrostatic repulsions and interdomain line tension leads to domain shape transitions in phase-separating lipid monolayers. The question remains if these morphologies are energy minima or are kinetically trapped metastable states. We show the reversible evolution of uniform width stripe domains from polydisperse semicircular domains in monolayers of dipalmitoylphosphatidylcholine (DPPC), hexadecanol (HD) or palmitic acid (PA), and dihydrocholesterol (DChol). The initial semicircular domains grow at a fixed 2:1 DPPC:HD (or PA) stoichiometry, depleting the liquid phase of HD, leaving behind a liquid enriched in DPPC and DChol. At higher surface pressures, the remaining DPPC precipitates onto existing domains, decreasing the ratio of line tension to the square of the dipole density difference, λ/μ2. Theory predicts that, as λ/μ2 decreases, circular domains reversibly transform to uniform width stripes as the minimum energy structure. Measuring the stripe width provides the first estimates of λ/μ2 at liquid condensed-liquid expanded phase coexistence.

Energy-Efficient Respiratory Anomaly Detection in Premature Newborn Infants

Precise monitoring of respiratory rate in premature newborn infants is essential to initiating medical interventions as required. Wired technologies can be invasive and obtrusive to the patients. We propose a deep-learning-enabled wearable monitoring system for premature newborn infants, where respiratory cessation is predicted using signals that are collected wirelessly from a non-invasive wearable Bellypatch put on the infant’s body. We propose a five-stage design pipeline involving data collection and labeling, feature scaling, deep learning model selection with hyperparameter tuning, model training and validation, and model testing and deployment. The model used is a 1-D convolutional neural network (1DCNN) architecture with one convolution layer, one pooling layer, and three fully-connected layers, achieving 97.15% classification accuracy. To address the energy limitations of wearable processing, several quantization techniques are explored, and their performance and energy consumption are analyzed for the respiratory classification task. Results demonstrate a reduction of energy footprints and model storage overhead with a considerable degradation of the classification accuracy, meaning that quantization and other model compression techniques are not the best solution for respiratory classification problem on wearable devices. To improve accuracy while reducing the energy consumption, we propose a novel spiking neural network (SNN)-based respiratory classification solution, which can be implemented on event-driven neuromorphic hardware platforms. To this end, we propose an approach to convert the analog operations of our baseline trained 1DCNN to their spiking equivalent. We perform a design-space exploration using the parameters of the converted SNN to generate inference solutions having different accuracy and energy footprints. We select a solution that achieves an accuracy of 93.33% with 18× lower energy compared to the baseline 1DCNN model. Additionally, the proposed SNN solution achieves similar accuracy as the quantized model with a 4× lower energy.

Bilayer aggregate microstructure determines viscoelasticity of lung surfactant suspensions

Neonatal respiratory distress syndrome (NRDS) is treated by intratracheal delivery of suspensions of animal-derived lung surfactant in saline. Lung surfactants are extracted via organic solvents from animal lung lavage, followed by solvent removal and surfactant re-hydration to form multi-bilayer particles suspended in saline. Following intra-tracheal administration, the surfactant suspension spreads throughout the lungs by surface tension gradient induced flow; the spreading rate is limited by suspension viscoelasticity. Here we examine the rheology of three clinical lung surfactant suspensions: Survanta (bovine lung), Curosurf (porcine lung), and Infasurf (calf lung). These surfactants have widely different rheological properties that depend on the lipid composition and bilayer organization. The steady shear viscosity is related to the bilayer particle volume fraction as for a suspension of hard spheres, but the lipid volume fraction is not simply related to the mass loading. Optical and electron microscopy and small angle X-ray scattering show that the viscosity variation is due to the temperature and composition dependent bilayer aggregate shapes and internal particle organization. Survanta forms crystalline bilayers at 37 °C, resulting in high aspect ratio asymmetric particles. Infasurf forms aggregates of unilamellar vesicles containing water pockets, while Curosurf forms onion-like multi-layered liposomes. While the mass loading of the three clinical surfactants is different, the different bilayer organization causes the particle volume fractions to be similar. Adding polyethylene glycol dehydrates and partially flocculates the bilayer aggregates in all suspensions, leading to smaller particle volume fractions and a reduced suspension viscosity even though the solvent viscosity increases almost six-fold.

A dynamical overview of droplets in the transmission of respiratory infectious diseases

The outbreak of the coronavirus disease has drawn public attention to the transmission of infectious pathogens, and as major carriers of those pathogens, respiratory droplets play an important role in the process of transmission. This Review describes respiratory droplets from a physical and mechanical perspective, especially their correlation with the transmission of infectious pathogens. It covers the important aspects of (i) the generation and expulsion of droplets during respiratory activities, (ii) the transport and evolution of respiratory droplets in the ambient environment, and (iii) the inhalation and deposition of droplets in the human respiratory tract. State-of-the-art experimental, computational, and theoretical models and results are presented, and the corresponding knowledge gaps are identified. This Review stresses the multidisciplinary nature of its subject and appeals for collaboration among different fields to fight the present pandemic.

Role of inositol to improve surfactant functions and reduce IL-6 levels: A potential adjuvant strategy for SARS-CoV-2 pneumonia?

To date, the spread of SARS-CoV-2 infection is increasing worldwide and represents a primary healthcare emergency. Although the infection can be asymptomatic, several cases develop severe pneumonia and acute respiratory distress syndrome (ARDS) characterized by high levels of pro-inflammatory cytokines, primarily interleukin (IL)-6. Based on available data, the severity of ARDS and serum levels of IL-6 are key determinants for the prognosis. In this scenario, available in vitro and in vivo data suggested that myo-inositol is able to increase the synthesis and function of the surfactant phosphatidylinositol, acting on the phosphoinositide 3-kinase (PI3K)-regulated signaling, with amelioration of both immune system and oxygenation at the bronchoalveolar level. In addition, myo-inositol has been found able to decrease the levels of IL-6 in several experimental settings, due to an effect on the inositol-requiring enzyme 1 (IRE1)-X-box-binding protein 1 (XBP1) and on the signal transducer and activator of transcription 3 (STAT3) pathways. In this scenario, treatment with myo-inositol may be able to reduce IL-6 dependent inflammatory response and improve oxygenation in patients with severe ARDS by SARS-CoV-2. In addition, the action of myo-inositol on IRE1 endonuclease activity may also inhibit the replication of SARS-CoV-2, as was reported for the respiratory syncytial virus. Since the available data are extremely limited, if this potential therapeutic approach will be considered valid in the clinical practice, the necessary future investigations should aim to identify the best dose, administration route (oral, intravenous and/or aerosol nebulization), and cluster(s) of patients which may get beneficial effects from this treatment.

Systematic review found that using thin catheters to deliver surfactant to preterm neonates was associated with reduced bronchopulmonary dysplasia and mechanical ventilation

AIM

Surfactant delivery is a cornerstone for managing respiratory distress in preterm neonates, but data on the best surfactant delivery methods have been conflicting.

METHODS

A systematic literature review using the PubMed, Embase, Cochrane Library and Web of Science databases identified papers published up to November 5, 2019. Additional studies were identified from trial registries, conference proceedings and the reference lists of the selected papers.

RESULTS

We identified 15 studies covering 4926 preterm infants. The randomised controlled trials (RCTs) and observational studies both showed significant reductions in early intubation rates with use of thin catheters. The relative risk (RR) was 0.63 and the 95% confidence interval (95% CI) was 0.55-0.72 (P < .01), with an odds ratio (OR) of 0.40 and 95% CI of 0.35-0.45 (P < .0001). The collective results from the RCTs revealed a significant decrease in bronchopulmonary dysplasia (BPD) rates in the thin catheter group (RR, 0.47; 95% CI 0.33-0.66; P < .01). These findings were consistent with the observational studies (OR 0.47; 95% CI 0.43-0.52; P < .01).

CONCLUSION

Using thin catheters to deliver surfactant in comparison with intubate-surfactant-extubate (INSURE) to newborn preterm infants with respiratory distress was associated with a reduced incidence of BPD and less need for mechanical ventilation.

Bronchopulmonary Dysplasia: Then, Now, and Next

Bronchopulmonary dysplasia (BPD) has evolved considerably since its first description over 50 years ago. This review aims to provide a historical framework for conceptualizing BPD and a current understanding of the changing definition, epidemiology, pathophysiology, treatment, and outcomes of BPD. The transdisciplinary approach that led to the initial phenotypic description of BPD continues to hold promise today. Investigators are refining the definition of BPD in light of changes in clinical care and increasing survival rates of very preterm infants. Despite improvements in perinatal care the incidence of BPD continues to increase. There is growing recognition that antenatal risk factors play a key role in the development of BPD. Strategies designed to prevent or limit neonatal lung injury continue to evolve. Defining the phenotype of infants with BPD can meaningfully direct treatment. Infants with BPD benefit from an interdisciplinary approach to longitudinal care with a focus on growth and neurocognitive development. While the ultimate impact of BPD on long-term pulmonary morbidity remains an active area of investigation, current data indicate that most children and adolescents with a history of BPD have a quality of life comparable to that of other preterm infants.

Inflammation product effects on dilatational mechanics can trigger the Laplace instability and acute respiratory distress syndrome

In the lungs, the Laplace pressure, ΔP = 2γ/R, would be higher in smaller alveoli than larger alveoli unless the surface tension, γ decreases with alveolar interfacial area, A, such that 2ε > γ in which ε = A(dγ/dA) is the dilatational modulus. In Acute Respiratory Distress Syndrome (ARDS), lipase activity due to the immune response to an underlying trauma or disease causes single chain lysolipid concentrations to increase in the alveolar fluids via hydrolysis of double-chain phospholpids in bacterial, viral, and normal cell membranes. Increasing lysolipid concentrations decrease the dilatational modulus dramatically at breathing frequencies if the soluble lysolipid has sufficient time to diffuse off the interface, causing 2ε < γ, thereby potentially inducing the "Laplace Instability", in which larger alveoli have a lower internal pressure than smaller alveoli. This can lead to uneven lung inflation, alveolar flooding, and poor gas exchange, typical symptoms of ARDS. While the ARDS lung contains a number of lipid and protein species in the alveolar fluid in addition to lysolipids, the surface activity and frequency dependent dilatational modulus of lysolipid suggest how inflammation may lead to the lung instabilities associated with ARDS. At high frequencies, even at high lysolipid concentrations, 2ε - γ > 0, which may explain the benefits ARDS patients receive from high frequency oscillatory ventilation.

Irremovable Blood Stain in Lung: Air-to-Interface Transport of Albumin and Its Mechanical Response to Biaxial Compression/Expansion

Serum proteins are believed to trigger a sudden failure of lung function, but to date the mechanism remains elusive. Most studies have focused on the transport of the proteins from the subphase to the lung surfactant interface, although the opposite direction of transport, i.e., from air-to-interface, could be equally important. Here, we report that physiological concentrations of serum droplets can rapidly form a film upon exposure to air, and the entire film can be transferred to the lung surfactant interface upon coalescence, displacing it. This film was mechanically stable and remains intact even for multiple biaxial compression/expansion cycles. Our findings provide a mechanism of lung surfactant replacement by serum proteins that is fundamentally different from the subphase-to-interface transport and demonstrate that it is nearly impossible to remove the film from the interface where the lung surfactant should be, thus impairing the lung in a permanent way.

Fisioterapia respiratória não altera agudamente os parâmetros fisiológicos ou os níveis de dor em prematuros com síndrome do desconforto respiratório internados em unidade de terapia intensiva

RESUMO Objetivo: avaliar a ocorrência de alterações fisiológicas adversas agudas e a presença de dor em recém-nascidos prematuros com síndrome do desconforto respiratório internados em uma unidade de terapia intensiva neonatal após a fisioterapia respiratória. Métodos: estudo transversal que avaliou 30 neonatos prematuros em três momentos, sendo eles Momento um (M1), antes da fisioterapia, Momento dois (M2), imediatamente após a fisioterapia, e Momento três (M3), 15 minutos após. Consideraram-se alterações fisiológicas as variações da frequência cardíaca (FC), da frequência respiratória (FR), da saturação periférica de oxigênio (SpO2) e da temperatura corporal. A presença de dor foi avaliada pelas escalas neonatal infant pain scale e neonatal facial coding system. Resultados: houve aumento estatisticamente significativo na FC no M2 quando comparados os três momentos, porém com retorno aos valores basais 15 minutos após a fisioterapia. Outras variáveis fisiológicas (FR, SpO2 e temperatura) e a avaliação da dor não apresentaram alterações significativas. Conclusão: parâmetros fisiológicos e comportamentais permaneceram estáveis após a realização da fisioterapia respiratória, com discretas alterações imediatamente após o procedimento, mas com retorno aos valores basais, indicando que a fisioterapia respiratória não alterou agudamente os sinais vitais e os níveis de dor dos neonatos.

Interfacial rheology and direct imaging reveal domain-templated network formation in phospholipid monolayers penetrated by fibrinogen

Phospholipids are found throughout the natural world, including the lung surfactant (LS) layer that reduces pulmonary surface tension and enables breathing. Fibrinogen, a protein involved in the blood clotting process, is implicated in LS inactivation and the progression of disorders such as acute respiratory distress syndrome. However, the interaction between fibrinogen and LS at the air-water interface is poorly understood. Through a combined microrheological, confocal and epifluorescence microscopy approach we quantify the interfacial shear response and directly image the morphological evolution when a model LS monolayer is penetrated by fibrinogen. When injected into the subphase beneath a monolayer of the phospholipid dipalmitoylphosphatidylcholine (DPPC, the majority component of LS), fibrinogen preferentially penetrates disordered liquid expanded (LE) regions and accumulates on the boundaries between LE DPPC and liquid condensed (LC) DPPC domains. Thus, fibrinogen is line active. Aggregates grow from the LC domain boundaries, ultimately forming a percolating network. This network stiffens the interface compared to pure DPPC and imparts the penetrated monolayer with a viscoelastic character reminiscent of a weak gel. When the DPPC monolayer is initially compressed beyond LE-LC coexistence, stiffening is significantly more modest and the penetrated monolayer retains a viscous-dominated, DPPC-like character.

Evolution and mechanics of mixed phospholipid fibrinogen monolayers

All mammals depend on lung surfactant (LS) to reduce surface tension at the alveolar interface and facilitate respiration. The inactivation of LS in acute respiratory distress syndrome (ARDS) is generally accompanied by elevated levels of fibrinogen and other blood plasma proteins in the alveolar space. Motivated by the mechanical role fibrinogen may play in LS inactivation, we measure the interfacial rheology of mixed monolayers of fibrinogen and dipalmitoylphosphatidylcholine (DPPC), the main constituent of LS, and compare these to the single species monolayers. We find DPPC to be ineffective at displacing preadsorbed fibrinogen, which gives the resulting mixed monolayer a strongly elastic shear response. By contrast, how effectively a pre-existing DPPC monolayer prevents fibrinogen adsorption depends upon its surface pressure. At low DPPC surface pressures, fibrinogen penetrates DPPC monolayers, imparting a mixed viscoelastic shear response. At higher initial DPPC surface pressures, this response becomes increasingly viscous-dominated, and the monolayer retains a more fluid, DPPC-like character. Fluorescence microscopy reveals that the mixed monolayers exhibit qualitatively different morphologies. Fibrinogen has a strong, albeit preparation-dependent, mechanical effect on phospholipid monolayers, which may contribute to LS inactivation and disorders such as ARDS.

Improving pregnancy outcomes in humans through studies in sheep

Experimental studies that are relevant to human pregnancy rely on the selection of appropriate animal models as an important element in experimental design. Consideration of the strengths and weaknesses of any animal model of human disease is fundamental to effective and meaningful translation of preclinical research. Studies in sheep have made significant contributions to our understanding of the normal and abnormal development of the fetus. As a model of human pregnancy, studies in sheep have enabled scientists and clinicians to answer questions about the etiology and treatment of poor maternal, placental, and fetal health and to provide an evidence base for translation of interventions to the clinic. The aim of this review is to highlight the advances in perinatal human medicine that have been achieved following translation of research using the pregnant sheep and fetus.

Stem cell-based therapies in neonatology: a new hope

Despite progress made in neonatal intensive care, complications of extreme preterm birth still contribute as the main cause of death to children below 5 years of age. Stem cell-based therapies-mesenchymal stromal cells in particular-offer a new hope in preventing and/or restoring organ damage in extreme preterm infants. Early phase clinical trials, fueled by promising preclinical studies on lung and brain injury, have begun. While the enthusiasm in the neonatal community is palpable, much more needs to be learnt about cell-based therapies. Maintaining the balance between temptation and a cautious, evidence-based approach will be critical for cell therapies to fulfil their promise in substantially improving the outcome of extreme preterm infants.

Nanoparticle Wettability Influences Nanoparticle-Phospholipid Interactions

We explored the influence of nanoparticle (NP) surface charge and hydrophobicity on NP-biomolecule interactions by measuring the composition of adsorbed phospholipids on four NPs, namely, positively charged CeO₂ and ZnO and negatively charged BaSO₄ and silica-coated CeO_2, after exposure to bronchoalveolar lavage fluid (BALf) obtained from rats, and to a mixture of neutral dipalmitoyl phosphatidylcholine (DPPC) and negatively charged dipalmitoyl phosphatidic acid (DPPA). The resulting NP-lipid interactions were examined by cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). Our data show that the amount of adsorbed lipids on NPs after incubation in BALf and the DPPC/DPPA mixture was higher in CeO₂ than in the other NPs, qualitatively consistent with their relative hydrophobicity. The relative concentrations of specific adsorbed phospholipids on NP surfaces were different from their relative concentrations in the BALf. Sphingomyelin was not detected in the extracted lipids from the NPs despite its >20% concentration in the BALf. AFM showed that the more hydrophobic CeO₂ NPs tended to be located inside lipid vesicles, whereas less hydrophobic BaSO₄ NPs appeared to be outside. In addition, cryo-TEM analysis showed that CeO₂ NPs were associated with the formation of multilamellar lipid bilayers, whereas BaSO₄ NPs with unilamellar lipid bilayers. These data suggest that the NP surface hydrophobicity predominantly controls the amounts and types of lipids adsorbed, as well as the nature of their interaction with phospholipids.

Surfactant and continuous positive airway pressure for the prevention of chronic lung disease: History, reality, and new challenges

The discovery of surfactant was one of the most significant research events to occur in the history of neonatology. Certainly, surfactant saved lives for premature infants who were otherwise considered non-viable. However, the prevention of chronic lung disease did not progress and it became clear that a significant portion of the help surfactant provides to the premature lung is counteracted by mechanical ventilation. A dilemma exists over the priorities in premature management to intubate and administer surfactant or not to intubate and support these infants non-invasively with the use of continuous positive airway pressure. A new hydrophilic surfactant preparation has been developed with the hope to enable the introduction of surfactant therapy without the need for tracheal intubation. Clinical trials on this product are currently in progress. This article provides the history and prospect of respiratory distress management in premature infants and evaluates the current evidence for non-invasive practices.

Interfacial rheology of coexisting solid and fluid monolayers

Biologically relevant monolayer and bilayer films often consist of micron-scale high viscosity domains in a continuous low viscosity matrix. Here we show that this morphology can cause the overall monolayer fluidity to vary by orders of magnitude over a limited range of monolayer compositions. Modeling the system as a two-dimensional suspension in analogy with classic three-dimensional suspensions of hard spheres in a liquid solvent explains the rheological data with no adjustable parameters. In monolayers with ordered, highly viscous domains dispersed in a continuous low viscosity matrix, the surface viscosity increases as a power law with the area fraction of viscous domains. Changing the phase of the continuous matrix from a disordered fluid phase to a more ordered, condensed phase dramatically changes the overall monolayer viscosity. Small changes in the domain density and/or continuous matrix composition can alter the monolayer viscosity by orders of magnitude.

What is the identity of fibroblast-pneumocyte factor?

Glucocorticoid induction of pulmonary surfactant involves a mesenchyme-derived protein first characterized in 1978 by Smith and termed fibroblast-pneumocyte factor (FPF). Despite a number of agents having been postulated as being FPF, its identity has remained obscure. In the past decade, three strong candidates for FPF have arisen. This review examines the evidence that keratinocyte growth factor (KGF), leptin or neuregulin-1β (NRG-1β) act as FPF or components of it. As with FPF production, glucocorticoids enhance the concentration of each of these agents in fibroblast-conditioned media. Moreover, each stimulates the synthesis of surfactant-associated phospholipids and proteins in type II pneumocytes. Further, some have unique activities, for example, KGF also minimizes lung injury through enhanced epithelial cell proliferation and NRG-1β enhances surfactant phospholipid secretion and β-adrenergic receptor activity in type II cells. However, even though these agents have attributes in common with FPF, it is inappropriate to specify any one of these agents as FPF. Rather, it appears that each contributes to separate mesenchymal-epithelial signaling mechanisms involved in different aspects of lung development. Given that the production of pulmonary surfactant is essential for postnatal survival, it is reasonable to suggest that several mechanisms independently regulate surfactant synthesis.

Metabolic Functions of the Lung, Disorders and Associated Pathologies

The primary function of the lungs is gas exchange. Approximately 400 million years ago, the Earth's atmosphere gained enough oxygen in the gas phase for the animals that emerged from the sea to breathe air. The first lungs were merely primitive air sacs with a few vessels in the walls that served as accessory organs of gas exchange to supplement the gills. Eons later, as animals grew accustomed to a solely terrestrial life, the lungs became highly compartmentalized to provide the vast air-blood surface necessary for O2 uptake and CO2 elimination, and a respiratory control system was developed to regulate breathing in accordance with metabolic demands and other needs. With the evolution and phylogenetic development, lungs were taking a variety of other specialized functions to maintain homeostasis, which we will call the non-respiratory functions of the lung and that often, and by mistake, are believed to have little or no connection with the replacement gas. In this review, we focus on the metabolic functions of the lung, perhaps the least known, and mainly, in the lipid metabolism and blood-adult lung vascular endothelium interaction. When these functions are altered, respiratory disorders or diseases appear, which are discussed concisely, emphasizing how they impact the most important function of the lungs: external respiration.

Changes in Course of Retinopathy of Prematurity from 1986 to 2013: Comparison of Three Studies in the United States

PURPOSE

To compare infant and retinopathy of prematurity (ROP) characteristics from 3 clinical studies conducted over a 27-year period in the United States.

DESIGN

Secondary analysis of results of 3 clinical studies.

PARTICIPANTS

Infants with birth weight (BW) <1251 g.

METHODS

Analysis of data from the Cryotherapy for Retinopathy of Prematurity (CRYO-ROP) and Early Treatment for Retinopathy of Prematurity (ETROP) trials and the primary data from the Telemedicine Approaches for the Evaluation of Acute-Phase Retinopathy of Prematurity (e-ROP) study.

MAIN OUTCOME MEASURES

Infant characteristics and onset, severity, and time course of ROP.

RESULTS

Across the 3 studies, mean (standard deviation) BW and mean gestational age (GA) decreased over time from CRYO-ROP (954 g [185 g], 27.9 weeks [2.2 weeks]) to ETROP (907 g [205 g], 27.4 weeks [2.2 weeks]) to e-ROP (864 g [212 g], 27.0 weeks [2.2 weeks]), with an increase in the percentage of infants enrolled weighing <750 g (15.8% CRYO, 24.9% ETROP, 33.4% e-ROP; P<0.0001). The percentage of infants who developed ROP varied only minimally (65.8% CRYO, 68.0% ETROP, 63.7% e-ROP; P = 0.003). Moderately severe ROP (defined as prethreshold or referral warranted) varied (17.8% CRYO, 12.3% ETROP, 19.4% e-ROP; P<0.0001), whereas the time of onset of any ROP did not vary (34.3 weeks CRYO, 34.1 weeks ETROP, 34.8 weeks e-ROP).

CONCLUSIONS

The BW and GA of infants enrolled in ROP studies in the United States have decreased over the past 27 years, whereas ROP prevalence and onset of disease are stable.

The role of natural processes and surface energy of inhaled engineered nanoparticles on aggregation and corona formation

The surface chemistry of engineered nanoparticles (ENPs) becomes more important as their size decreases and enters the nanometer-range. This review explains the fundamental properties of the surface chemistry of nanoparticles, and argues that their agglomeration and the formation of corona around them are natural processes that reduce surface energy. ENP agglomeration and surface corona formation are further discussed in the context of inhaled ENPs, as the lung is a major port of ENP entry to the body. The pulmonary surfactant layer, which the inhaled ENPs first encounter as they land on the lung surface, represents a unique environment with a variety of well-defined biomolecules. Many factors, such as hydrophobicity, surface charge of ENPs, protein/phospholipid concentrations of the alveolar lining fluid, etc. influence the complex processes of ENP agglomeration and corona formation in the alveolar lining fluid, and these events occur even before the ENPs reach the cells. We suggest that molecular dynamic simulations can represent a promising future direction for research of the behavior of inhaled ENPs, complementing the experimental approaches. Moreover, we want to remind biologists working on ENPs of the importance relationship between ENP surface energy and size.

Combined effect of synthetic protein, Mini-B, and cholesterol on a model lung surfactant mixture at the air-water interface

The overall goal of this work is to study the combined effects of Mini-B, a 34 residue synthetic analog of the lung surfactant protein SP-B, and cholesterol, a neutral lipid, on a model binary lipid mixture containing dipalmitolphosphatidylcholine (DPPC) and palmitoyl-oleoyl-phosphatidylglycerol (POPG), that is often used to mimic the primary phospholipid composition of lung surfactants. Using surface pressure vs. mean molecular area isotherms, fluorescence imaging and analysis of lipid domain size distributions; we report on changes in the structure, function and stability of the model lipid-protein films in the presence and absence of varying composition of cholesterol. Our results indicate that at low cholesterol concentrations, Mini-B can prevent cholesterol's tendency to lower the line tension between lipid domain boundaries, while maintaining Mini-B's ability to cause reversible collapse resulting in the formation of surface associated reservoirs. Our results also show that lowering the line tension between domains can adversely impact monolayer folding mechanisms. We propose that small amounts of cholesterol and synthetic protein Mini-B can together achieve the seemingly opposing requirements of efficient LS: fluid enough to flow at the air-water interface, while being rigid enough to oppose irreversible collapse at ultra-low surface tensions.

Mesenchymal Stem Cells in Lipogems, a Reverse Story: from Clinical Practice to Basic Science

The idea that basic science should be the starting point for modern clinical approaches has been consolidated over the years, and emerged as the cornerstone of Molecular Medicine. Nevertheless, there is increasing concern over the low efficiency and inherent costs related to the translation of achievements from the bench to the bedside. These burdens are also perceived with respect to the effectiveness of translating basic discoveries in stem cell biology to the newly developing field of advanced cell therapy or Regenerative Medicine. As an alternative paradigm, past and recent history in Medical Science provides remarkable reverse stories in which clinical observations at the patient's bedside have fed major advances in basic research which, in turn, led to consistent progression in clinical practice. Within this context, we discuss our recently developed method and device, which forms the core of a system (Lipogems) for processing of human adipose tissue solely with the aid of mild mechanical forces to yield a microfractured tissue product.

Visualizing monolayers with a water-soluble fluorophore to quantify adsorption, desorption, and the double layer

Contrast in confocal microscopy of phase-separated monolayers at the air-water interface can be generated by the selective adsorption of water-soluble fluorescent dyes to disordered monolayer phases. Optical sectioning minimizes the fluorescence signal from the subphase, whereas convolution of the measured point spread function with a simple box model of the interface provides quantitative assessment of the excess dye concentration associated with the monolayer. Coexisting liquid-expanded, liquid-condensed, and gas phases could be visualized due to differential dye adsorption in the liquid-expanded and gas phases. Dye preferentially adsorbed to the liquid-disordered phase during immiscible liquid-liquid phase coexistence, and the contrast persisted through the critical point as shown by characteristic circle-to-stripe shape transitions. The measured dye concentration in the disordered phase depended on the phase composition and surface pressure, and the dye was expelled from the film at the end of coexistence. The excess concentration of a cationic dye within the double layer adjacent to an anionic phospholipid monolayer was quantified as a function of subphase ionic strength, and the changes in measured excess agreed with those predicted by the mean-field Gouy-Chapman equations. This provided a rapid and noninvasive optical method of measuring the fractional dissociation of lipid headgroups and the monolayer surface potential.

DPP4 inhibitors increase differentially the expression of surfactant proteins in Fischer 344 rats

AIM

Intact surface active agent (surfactant) composed of surfactant-associated proteins (SPs) and lipids is necessary for respiration and prevents alveoli from collapsing. CD26, a transmembrane glycoprotein exerting dipeptidyl peptidase activity (DPP4), highly expressed in lung parenchyma, is involved in inflammatory processes. A pharmacological inhibition of DPP4 influenced not only the inflammation but also elevated the SPs. Thus, DPP4 inhibitors may be a novel drug for treatment of diseases with surfactant deficiency. Therefore, we tested firstly the hypothesis that DPP4 inhibitors increase the expression of SPs in healthy rats.

METHODS

SP mRNA and protein expression were determined different times after nebulization of aerosolized DPP4 inhibitors [L-isoleucine-thiazolidide (L-Ile-Thia), L-valine-pyrrolidide (L-Val-Pyrr)], budesonide, saline or stereoisomers.

RESULTS

Compared with negative controls (1) L-Ile-Thia as well as budesonide led to a significant higher and L-Val-Pyrr had the tendency to a significant higher expression of SP-A mRNA 6 h after nebulization, (2) the expression of SP-D mRNA increased significantly 6 h after nebulization with L-Ile-Thia and 3 and 6 h after nebulization with Val-pyrr, (3) SP-B mRNA levels showed significantly higher values 3 and 6 h after nebulization with L-Val-Pyrr, (4) protein levels of SP-A, SP-B and SP-C were elevated significantly 6 h after nebulization with L-Val-Pyrr as well as with budesonide, and (5) phospholipids were also increased in response to DPP4 inhibition; the minimal surface tension was comparable.

CONCLUSION

DPP4 inhibition influence differently the expression of surfactant proteins in healthy rats and may be suitable to elevate surfactant synthesis in different diseases accompanied with surfactant deficiencies.

Composition, structure and mechanical properties define performance of pulmonary surfactant membranes and films

The respiratory surface in the mammalian lung is stabilized by pulmonary surfactant, a membrane-based system composed of multiple lipids and specific proteins, the primary function of which is to minimize the surface tension at the alveolar air-liquid interface, optimizing the mechanics of breathing and avoiding alveolar collapse, especially at the end of expiration. The goal of the present review is to summarize current knowledge regarding the structure, lipid-protein interactions and mechanical features of surfactant membranes and films and how these properties correlate with surfactant biological function inside the lungs. Surfactant mechanical properties can be severely compromised by different agents, which lead to surfactant inhibition and ultimately contributes to the development of pulmonary disorders and pathologies in newborns, children and adults. A detailed comprehension of the unique mechanical and rheological properties of surfactant layers is crucial for the diagnostics and treatment of lung diseases, either by analyzing the contribution of surfactant impairment to the pathophysiology or by improving the formulations in surfactant replacement therapies. Finally, a short review is also included on the most relevant experimental techniques currently employed to evaluate lung surfactant mechanics, rheology, and inhibition and reactivation processes.

Influence of molecular coherence on surface viscosity

Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine (DPPC) monolayers by an order of magnitude per wt %. Grazing incidence X-ray diffraction shows that cholesterol at these small fractions does not mix ideally with DPPC but rather induces nanophase separated structures of an ordered, primarily DPPC phase bordered by a line-active, disordered, mixed DPPC-cholesterol phase. We propose that the free area in the classic Cohen and Turnbull model of viscosity is inversely proportional to the number of molecules in the coherence area, or product of the two coherence lengths. Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity. Using this free area collapses the surface viscosity data for all surface pressures and cholesterol fractions to a universal logarithmic relation. The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers.

Use of CPAP and surfactant therapy in newborns with respiratory distress syndrome

Respiratory distress syndrome (RDS) is a major disease burden in the developing countries. Current evidence supports early continuous positive airway pressure (CPAP) use and early selective surfactant administration as the most efficacious interventions in the management of RDS, both in developed and developing countries. In developing countries, it is recommended to increase institutional deliveries and increase the coverage of antenatal steroids in women in preterm labor as preventive measures. Establishing intervention of CPAP and surfactant therapies in the Level II special care newborn units (SCNUs) and Level III units requires focus on training nursing staff and pediatricians across the board. These approaches would pave the way in optimizing the care of the preterm infants with RDS and decrease their mortality and morbidity significantly.

Pbx1 activates Fgf10 in the mesenchyme of developing lungs

Insufficiency of surfactants is a core factor in respiratory distress syndrome, which causes apnea and neonatal death, particularly in preterm infants. Surfactant proteins are secreted by alveolar type II cells in the lung epithelium, the differentiation of which is regulated by Fgf10 elaborated by the adjacent mesenchyme. However, the molecular regulation of mesenchymal Fgf10 during lung development has not been fully understood. Here, we show that Pbx1, a homeodomain transcription factor, is required in the lung mesenchyme for the expression of Fgf10. Mouse embryos lacking Pbx1 in the lung mesenchyme show compact terminal saccules and perinatal lethality with failure of postnatal alveolar expansion. Mutant embryos had severely reduced expression of Fgf10 and surfactant genes (Spa, Spb, Spc, and Spd) that are essential for alveolar expansion for gas exchange at birth. Molecularly, Pbx1 directly binds to the Fgf10 promoter and cooperates with Meis and Hox proteins to transcriptionally activate Fgf10. Our results thus show how Pbx1 controls Fgf10 in the developing lung.