Time-resolved transcriptomic profiling of the developing rabbit's lungs: impact of premature birth and implications for modelling bronchopulmonary dysplasia.

BACKGROUND: Premature birth, perinatal inflammation, and life-saving therapies such as postnatal oxygen and mechanical ventilation are strongly associated with the development of bronchopulmonary dysplasia (BPD); these risk factors, alone or combined, cause lung inflammation and alter programmed molecular patterns of normal lung development. The current knowledge on the molecular regulation of lung development mainly derives from mechanistic studies conducted in newborn rodents exposed to postnatal hyperoxia, which have been proven useful but have some limitations. METHODS: Here, we used the rabbit model of BPD as a cost-effective alternative model that mirrors human lung development and, in addition, enables investigating the impact of premature birth per se on the pathophysiology of BPD without further perinatal insults (e.g., hyperoxia, LPS-induced inflammation). First, we characterized the rabbit's normal lung development along the distinct stages (i.e., pseudoglandular, canalicular, saccular, and alveolar phases) using histological, transcriptomic and proteomic analyses. Then, the impact of premature birth was investigated, comparing the sequential transcriptomic profiles of preterm rabbits obtained at different time intervals during their first week of postnatal life with those from age-matched term pups. RESULTS: Histological findings showed stage-specific morphological features of the developing rabbit's lung and validated the selected time intervals for the transcriptomic profiling. Cell cycle and embryo development, oxidative phosphorylation, and WNT signaling, among others, showed high gene expression in the pseudoglandular phase. Autophagy, epithelial morphogenesis, response to transforming growth factor ß, angiogenesis, epithelium/endothelial cells development, and epithelium/endothelial cells migration pathways appeared upregulated from the 28th day of gestation (early saccular phase), which represents the starting point of the premature rabbit model. Premature birth caused a significant dysregulation of the inflammatory response. TNF-responsive, NF-κB regulated genes were significantly upregulated at premature delivery and triggered downstream inflammatory pathways such as leukocyte activation and cytokine signaling, which persisted upregulated during the first week of life. Preterm birth also dysregulated relevant pathways for normal lung development, such as blood vessel morphogenesis and epithelial-mesenchymal transition. CONCLUSION: These findings establish the 28-day gestation premature rabbit as a suitable model for mechanistic and pharmacological studies in the context of BPD.

Efficacy of synthetic surfactant (CHF5633) bolus and/or lavage in meconium-induced lung injury in ventilated newborn rabbits.

BACKGROUND: The pathogenesis of neonatal meconium aspiration syndrome (MAS) involves meconium-induced lung inflammation and surfactant inactivation. Bronchoalveolar lavage (BAL) with diluted surfactant facilitates the removal of meconium. CHF5633, one of the most promising synthetic surfactants, is effective in neonatal respiratory distress syndrome. Here we investigated its efficacy via BAL in an experimental MAS model. METHODS: Experimental MAS was induced at birth in near-term newborn rabbits by intratracheal instillation of reconstituted human meconium. First, undiluted CHF5633 was compared with a porcine-derived surfactant (Poractant alfa) via intratracheal bolus (200 mg/kg). Second, the efficacy of BAL with diluted CHF5633 (5 mg/mL, 20 ml/kg) alone, or followed by undiluted boluses (100 or 300 mg/kg), was investigated. RESULTS: Meconium instillation caused severe lung injury, reduced endogenous surfactant pool, and poor survival. CHF5633 had similar benefits in improving survival and alleviating lung injury as Poractant alfa. CHF5633 BAL plus higher boluses exerted better effects than BAL or bolus alone in lung injury alleviation by reversing phospholipid pools and mitigating proinflammatory cytokine mRNA expression, without fluid retention and function deterioration. CONCLUSIONS: CHF5633 improved survival and alleviated meconium-induced lung injury, the same as Poractant alfa. CHF5633 BAL plus boluses was the optimal modality, which warrants further clinical investigation. IMPACT: To explore the efficacy of a synthetic surfactant, CHF5633, in neonatal lung protection comparing with Poractant alfa in a near-term newborn rabbit model with meconium-induced lung injury. Similar effects on improving survival and alleviating lung injury were found between CHF5633 and Poractant alfa. Optimal therapeutic effects were identified from the diluted CHF5633 bronchoalveolar lavage followed by its undiluted bolus instillation compared to the lavage or bolus alone regimens. Animals with CHF5633 lavage plus bolus regimen exerted neither substantial lung fluid retention nor lung mechanics deterioration but a trend of higher pulmonary surfactant-associated phospholipid pools.

Nebulization of High-Dose Poractant Alfa in Newborn Piglets on Nasal Continuous Positive Airway Pressure Yields Therapeutic Lung Doses of Phospholipids.

OBJECTIVE: It is not known how much surfactant must be nebulized to reach a lung dose of phospholipids equivalent to that obtained by the instillation of 200 mg/kg of surfactant. We aimed to assess the feasibility of nebulizing a high-dose of poractant alfa with the eFlow-Neos investigational vibrating-membrane nebulizer in newborn piglets on nasal continuous positive airway pressure (nCPAP) and to determine whether this intervention would yield therapeutic lung doses of phospholipids. STUDY DESIGN: Twelve 1-day-old piglets on nCPAP received 600 mg/kg of poractant alfa admixed with technetium-99m via nebulization. Six piglets receiving 200 mg/kg of instilled synthetic surfactant served as controls. Lung deposition (percentage of the nominal dose) was determined by gamma scintigraphy, and the phospholipids' lung dose was calculated. RESULTS: The lung dose of phospholipids (mean ± standard deviation [SD]) was 138 ± 96 mg/kg with nebulization, and 172 ± 24 mg/kg with instillation (p = 0.42). Nebulization took 58 ± 12 minutes. The arterial partial pressure of carbon dioxide increased from 6.7 ± 1.1 to 7.2 ± 1.1 kPa during nebulization (p = 0.04). Cerebral oximetry remained stable, and there was no hemodynamic instability. CONCLUSION: Nebulization was well tolerated, and the mean lung dose of phospholipids was above 100 mg/kg, that is, not different from the instillation group. These experimental findings suggest that it may be feasible to reach therapeutic lung doses of phospholipids by surfactant nebulization during nCPAP. KEY POINTS: · It is not known if effective lung doses of surfactant can be delivered by nebulization.. · Nebulization of high-dose surfactant in newborn piglets on nCPAP was well tolerated.. · A high-dose of nebulized poractant alfa yielded therapeutic lung doses of phospholipids..

A new anesthesia protocol enabling longitudinal lung-function measurements in neonatal rabbits by micro-CT.

Micro-computed tomography (micro-CT) imaging is an emerging technology with many applications in small animals, for example, the study of pulmonary diseases, although clear guidelines and critical mass of evidence are still missing in the preclinical literature. The neonatal rabbit is a valuable model for studying pulmonary development. However, the longitudinal monitoring of lung function by micro-CT can be challenging. Distinctive datasets corresponding to the end-inspiration and end-expiration phases need to be generated and analyzed to derive lung-functional parameters. The quality of CT scans and the reliability of parameters obtained remain highly dependent on the anesthesia protocol used. Three different anesthetic protocols were tested. The combination of dexmedetomidine 0.25 mg/kg injected intraperitoneally followed by 1% isoflurane was found to facilitate CT imaging at 4 and 11 days after birth. Contrarily, isoflurane and ketamine-xylazine were found unsuitable and thus not investigated further. Total lung volumes significantly increased at day 11 compared with baseline in both respiratory phases, whereas lung tissue remained constant. As expected, functional residual capacity, air-to-tissue ratio, and minute ventilation were significantly increased at day 11 in each animal. Those parameters were correlated with inspiratory capacity, compliance, elastance, and resistance of both respiratory system and tissue component, as measured by flexiVent. Lung development was also evaluated by histomorphometric analyses. In conclusion, we have identified a safe and suitable anesthesia protocol for micro-CT imaging in neonatal rabbits. Moreover, the possibility to longitudinally measure lung function in the same subject dramatically reduced the intraexperimental variability.

Aerosol drug delivery to spontaneously-breathing preterm neonates: lessons learned.

Delivery of medications to preterm neonates receiving non-invasive ventilation (NIV) represents one of the most challenging scenarios for aerosol medicine. This challenge is highlighted by the undersized anatomy and the complex (patho)physiological characteristics of the lungs in such infants. Key physiological restraints include low lung volumes, low compliance, and irregular respiratory rates, which significantly reduce lung deposition. Such factors are inherent to premature birth and thus can be regarded to as the intrinsic factors that affect lung deposition. However, there are a number of extrinsic factors that also impact lung deposition: such factors include the choice of aerosol generator and its configuration within the ventilation circuit, the drug formulation, the aerosol particle size distribution, the choice of NIV type, and the patient interface between the delivery system and the patient. Together, these extrinsic factors provide an opportunity to optimize the lung deposition of therapeutic aerosols and, ultimately, the efficacy of the therapy.In this review, we first provide a comprehensive characterization of both the intrinsic and extrinsic factors affecting lung deposition in premature infants, followed by a revision of the clinical attempts to deliver therapeutic aerosols to premature neonates during NIV, which are almost exclusively related to the non-invasive delivery of surfactant aerosols. In this review, we provide clues to the interpretation of existing experimental and clinical data on neonatal aerosol delivery and we also describe a frame of measurable variables and available tools, including in vitro and in vivo models, that should be considered when developing a drug for inhalation in this important but under-served patient population.

Budesonide with surfactant decreases systemic responses in mechanically ventilated preterm lambs exposed to fetal intra-amniotic lipopolysaccharide.

BACKGROUND: Chorioamnionitis is associated with increased rates of bronchopulmonary dysplasia (BPD) in ventilated preterm infants. Budesonide when added to surfactant decreased lung and systemic inflammation from mechanical ventilation in preterm lambs and decreased the rates and severity of BPD in preterm infants. We hypothesized that the addition of budesonide to surfactant will decrease the injury from mechanical ventilation in preterm lambs exposed to intra-amniotic (IA) lipopolysaccharide (LPS). METHODS: Lambs at 126 ± 1 day GA received LPS 10 mg IA 48 h prior to injurious mechanical ventilation. After 15 min, lambs received either surfactant mixed with: (1) saline or (2) Budesonide 0.25 mg/kg, then ventilated with normal tidal volumes for 4 h. Injury markers in the lung, liver, and brain were compared. RESULTS: Compared with surfactant alone, the addition of budesonide improved blood pressures, dynamic compliance, and ventilation, while decreasing mRNA for pro-inflammatory cytokines in the lung, liver, and multiple areas of the brain. LPS caused neuronal activation and structural changes in the brain that were not altered by budesonide. Budesonide was not retained within the lung beyond 4 h. CONCLUSIONS: In preterm lambs exposed to IA LPS, the addition of budesonide to surfactant improved physiology and markers of lung and systemic inflammation. IMPACT: The addition of budesonide to surfactant decreases the lung and systemic responses to injurious mechanical ventilation preterm lambs exposed to fetal LPS. Budesonide was present in the plasma by 15 min and the majority of the budesonide is no longer in the lung at 4 h of ventilation. IA LPS and mechanical ventilation caused structural changes in the brain that were not altered by short-term exposure to budesonide. The budesonide dose of 0.25 mg/kg being used clinically seems likely to decrease lung inflammation in preterm infants with chorioamnionitis.

Surfactant lung delivery with LISA and InSurE in adult rabbits with respiratory distress.

BACKGROUND: In preterm infants, InSurE (Intubation-Surfactant-Extubation) and LISA (less invasive surfactant administration) techniques allow for exogenous surfactant administration while reducing lung injury associated with mechanical ventilation. We compared the acute pulmonary response and lung deposition of surfactant by LISA and InSurE in surfactant-depleted adult rabbits. METHODS: Twenty-six spontaneously breathing surfactant-depleted adult rabbits (6-7 weeks old) with moderate RDS and managed with nasal continuous positive airway pressure were randomized to 3 groups: (1) 200 mg/kg of surfactant by InSurE; (2) 200 mg/kg of surfactant by LISA; (3) no surfactant treatment (Control). Gas exchange and lung mechanics were monitored for 180 min. After that, surfactant lung deposition and distribution were evaluated monitoring disaturated-phosphatidylcholine (DSPC) and surfactant protein C (SP-C), respectively. RESULTS: No signs of recovery were found in the untreated animals. After InSurE, oxygenation improved more rapidly compared to LISA. However, at 180' LISA and InSurE showed comparable outcomes in terms of gas exchange, ventilation parameters, and lung mechanics. Neither DSPC in the alveolar pool nor SP-C signal distributions in a frontal lung section were significantly different between InSurE and LISA groups. CONCLUSIONS: In an acute setting, LISA demonstrated efficacy and surfactant lung delivery similar to that of InSurE in surfactant-depleted adult rabbits. IMPACT: Although LISA technique is gaining popularity, there are still several questions to address. This is the first study comparing LISA and InSurE in terms of gas exchange, ventilation parameters, and lung mechanics as well as surfactant deposition and distribution. In our animal study, three hours post-treatment, LISA method seems to be as effective as InSurE and showed similar surfactant lung delivery. Our findings provide some clarifications on a fair comparison between LISA and InSurE techniques, particularly in terms of surfactant delivery. They should reassure some of the concerns raised by the clinical community on LISA adoption in neonatal units.

Sample preparation strategy for the detection of steroid-like compounds using MALDI mass spectrometry imaging: pulmonary distribution of budesonide as a case study.

Corticosteroids as budesonide can be effective in reducing topic inflammation processes in different organs. Therapeutic use of budesonide in respiratory diseases, like asthma, chronic obstructive pulmonary disease, and allergic rhinitis is well known. However, the pulmonary distribution of budesonide is not well understood, mainly due to the difficulties in tracing the molecule in lung samples without the addition of a label. In this paper, we present a matrix-assisted laser desorption/ionization mass spectrometry imaging protocol that can be used to visualize the pulmonary distribution of budesonide administered to a surfactant-depleted adult rabbit. Considering that budesonide is not easily ionized by MALDI, we developed an on-tissue derivatization method with Girard's reagent P followed by ferulic acid deposition as MALDI matrix. Interestingly, this sample preparation protocol results as a very effective strategy to raise the sensitivity towards not only budesonide but also other corticosteroids, allowing us to track its distribution and quantify the drug inside lung samples.

Surfactant Injury in the Early Phase of Severe Meconium Aspiration Syndrome.

No in vivo data are available regarding the effect of meconium on human surfactant in the early stages of severe meconium aspiration syndrome (MAS). In the present study, we sought to characterize the changes in surfactant composition, function, and structure during the early phase of meconium injury. We designed a translational prospective cohort study of nonbronchoscopic BAL of neonates with severe MAS (n = 14) or no lung disease (n = 18). Surfactant lipids were analyzed by liquid chromatography-high-resolution mass spectrometry. Secretory phospholipase A2 subtypes IB, V, and X and SP-A (surfactant protein A) were assayed by ELISA. SP-B and SP-C were analyzed by Western blotting under both nonreducing and reducing conditions. Surfactant function was assessed by adsorption test and captive bubble surfactometry, and lung aeration was evaluated by semiquantitative lung ultrasound. Surfactant nanostructure was studied using cryo-EM and atomic force microscopy. Several changes in phospholipid subclasses were detected during MAS. Lysophosphatidylcholine species released by phospholipase A2 hydrolysis were increased. SP-B and SP-C were significantly increased together with some shorter immature forms of SP-B. Surfactant function was impaired and correlated with poor lung aeration. Surfactant nanostructure was significantly damaged in terms of vesicle size, tridimensional complexity, and compactness. Various alterations of surfactant phospholipids and proteins were detected in the early phase of severe meconium aspiration and were due to hydrolysis and inflammation and a defensive response. This impairs both surfactant structure and function, finally resulting in reduced lung aeration. These findings support the development of new surfactant protection and antiinflammatory strategies for severe MAS.

Intratracheal budesonide/surfactant attenuates hyperoxia-induced lung injury in preterm rabbits.

Recent clinical trials have shown improvements in neonatal outcomes after intratracheal administration of a combination of budesonide/surfactant (ITBS) in infants at risk of bronchopulmonary dysplasia. However, the effect of ITBS on lung function and alveolar structure is not known. We aimed to determine the effect of ITBS on lung function, parenchymal structure, and inflammatory cytokine expression in a relevant preterm animal model for bronchopulmonary dysplasia. Premature neonatal rabbits were administered a single dose of ITBS on the day of delivery and exposed to 95% oxygen. Following 7 days of hyperoxia, in vivo forced oscillation and pressure-volume maneuvers were performed to examine pulmonary function. Histological and molecular analysis was performed to assess alveolar and extracellular matrix (ECM) morphology, along with gene expression of connective tissue growth factor (CTGF), IL-8, and CCL-2. ITBS attenuated the functional effect of hyperoxia-induced lung injury and limited the change to respiratory system impedance, measured using the forced oscillation technique. Treatment effects were most obvious in the small airways, with significant effects on small airway resistance and small airway reactance. In addition, ITBS mitigated the decrease in inspiratory capacity and static compliance. ITBS restricted alveolar septal thickening without altering the mean linear intercept and mitigated hyperoxia-induced remodeling of the ECM. These structural changes were associated with improved inspiratory capacity and lung compliance. Gene expression of CTGF, IL-8, and CCL-2 was significantly downregulated in the lung. Treatment with ITBS shortly after delivery attenuated the functional and structural consequences of hyperoxia-induced lung injury to day 7 of life in the preterm rabbit.

Surfactant plus budesonide decreases lung and systemic responses to injurious ventilation in preterm sheep.

Mechanical ventilation from birth with normal tidal volumes (VT) causes lung injury and systemic responses in preterm sheep. The addition of budesonide to surfactant therapy decreases these injury markers. Budesonide and surfactant will decrease the injury from injurious VT ventilation in preterm sheep. Lambs at 126 ± 1 day gestational age were ventilated from birth with either: 1) Normal VT [surfactant 200 mg/kg before ventilation, positive end expiratory pressure (PEEP) 5 cmH2O, VT 8 mL/kg] or 2) Injury VT (high pressure, 100% oxygen, no PEEP) for 15 min, then further randomized to surfactant + saline or surfactant + 0.25 mg/kg budesonide with Normal VT for 6 h. Lung function and lung, liver, and brain tissues were evaluated for indicators of injury. Injury VT + saline caused significant injury and systemic responses, and Injury VT + budesonide improved lung physiology. Budesonide decreased lung inflammation and decreased pro-inflammatory cytokine mRNA in the lung, liver, and brain to levels similar to Normal VT + saline. Budesonide was present in plasma within 15 min of treatment in both ventilation groups, and less than 5% of the budesonide remained in the lung at 6 h. mRNA sequencing of liver and periventricular white matter demonstrated multiple pathways altered by both Injury VT and budesonide and the combination exposure. In lambs receiving Injury VT, the addition of budesonide to surfactant improved lung physiology and decreased pro-inflammatory cytokine responses in the lung, liver, and brain to levels similar to lambs receiving Normal VT.

Nebulized Poractant Alfa Reduces the Risk of Respiratory Failure at 72 Hours in Spontaneously Breathing Surfactant-Deficient Newborn Piglets.

OBJECTIVES: We have setup for the first time a long-term (72 hr) respiratory distress syndrome model in spontaneously breathing surfactant-deficient newborn piglets to investigate the continuous positive airway pressure failure rate with nebulized poractant alfa compared with that with the intubation surfactant extubation technique or continuous positive airway pressure only. DESIGN: Prospective randomized animal study. SETTING: Biocruces-Bizkaia Health Research Institute Animal Facility. SUBJECTS-INTERVENTIONS: Eighteen newborn piglets (n = 6/group) with surfactant-deficient respiratory distress syndrome were randomized to three continuous positive airway pressure-ventilated groups: 1) nebulized surfactant (poractant alfa 400 mg/kg) via a customized investigational eFlow-Neos vibrating membrane nebulizer system, 2) bolus administration using the Intubation Surfactant Extubation method (200 mg/kg), or 3) continuous positive airway pressure alone. MEASUREMENTS AND MAIN RESULTS: Pulmonary and hemodynamic variables were assessed at 6-hour intervals for 72 hours. Lung and brain histological analyses were performed. After bronchoalveolar lavages, piglets developed respiratory distress syndrome. Over the follow-up, both surfactant-treated groups had significantly better pulmonary outcomes than the continuous positive airway pressure alone group. Furthermore, unlike in the continuous positive airway pressure group, there were no cases of respiratory failure in either of the surfactant-treated groups. CONCLUSIONS: In newborn piglets with respiratory distress syndrome, the nebulization of 400 mg/kg of poractant alfa using a customized investigational eFlow-Neos nebulizer was found to be safe and effective in reducing the risk of respiratory failure in the 72 hours after treatment.

Dose of budesonide with surfactant affects lung and systemic inflammation after normal and injurious ventilation in preterm lambs.

BACKGROUND: The addition of budesonide (Bud) 0.25 mg/kg to surfactant decreased the lung and systemic responses to mechanical ventilation in preterm sheep and the rates and severity of bronchopulmonary dysplasia (BPD) in preterm infants. We hypothesized that lower budesonide concentrations in surfactant will decrease injury while decreasing systemic corticosteroid exposure. METHODS: Preterm lambs received either (1) protective tidal volume (VT) ventilation with surfactant from birth or (2) injurious VT ventilation for 15 min and then surfactant treatment. Lambs were further assigned to surfactant mixed with (i) Saline, (ii) Bud 0.25 mg/kg, (iii) Bud 0.1 mg/kg, or (iv) Bud 0.04 mg/kg. All lambs were then ventilated with protective VT for 6 h. RESULTS: Plasma Bud levels were proportional to the dose received and decreased throughout ventilation. In both protective and injurious VT ventilation, <4% of Bud remained in the lung at 6 h. Some of the improvements in physiology and markers of injury with Bud 0.25 mg/kg were also found with 0.1 mg/kg, whereas 0.04 mg/kg had only minimal effects. CONCLUSIONS: Lower doses of Bud were less effective at decreasing lung and systemic inflammation from mechanical ventilation. The plasma Bud levels were proportional to dose given and the majority left the lung.

Dose-Response Study on Surfactant Nebulization Therapy During Nasal Continuous Positive Airway Pressure Ventilation in Spontaneously Breathing Surfactant-Deficient Newborn Piglets.

OBJECTIVES: The current clinical treatment of neonates with respiratory distress syndrome includes endotracheal intubation and intratracheal instillation of exogenous surfactant. Nebulization of surfactant offers an attractive alternative. The aims of this study were to test nebulization as a noninvasive method of administering surfactant and determine the optimal dose for the treatment of respiratory distress syndrome-associated pathophysiology of the neonatal lungs. DESIGN: Prospective, randomized, animal model study. SETTING: An experimental laboratory. SUBJECTS: Thirty-six newborn piglets. INTERVENTIONS: Different doses (100, 200, 400, and 600 mg/kg) of poractant alfa were administered via a vibrating membrane nebulizer (eFlow-Neos; Pari Pharma GmbH, Starnberg, Germany) or a bolus administration using the intubation-surfactant-extubation (Insure) technique (200 mg/kg) to spontaneously breathing newborn piglets (n = 6/group) with bronchoalveolar lavage-induced respiratory distress syndrome during nasal continuous positive airway pressure (180 min). MEASUREMENTS AND MAIN RESULTS: Pulmonary, hemodynamic, and cerebral effects were assessed. Histologic analysis of lung and brain tissue was also performed. After repeated bronchoalveolar lavage, newborn piglets developed severe respiratory distress syndrome. Rapid improvement in pulmonary status was observed in the Insure group, whereas a dose-response effect was observed in nebulized surfactant groups. Nebulized poractant alfa was more effective at doses higher than 100 mg/kg and was associated with similar pulmonary, hemodynamic, and cerebral behavior to that in the Insure group, but improved lung injury scores. CONCLUSIONS: In newborn piglets with severe bronchoalveolar lavage-induced respiratory distress syndrome, our results demonstrate that the administration of nebulized poractant alfa using an investigational customized eFlow-Neos nebulizer is an effective and safe noninvasive surfactant administration technique.

Local pulmonary drug delivery in the preterm rabbit: feasibility and efficacy of daily intratracheal injections.

Recent clinical trials in newborns have successfully used surfactant as a drug carrier for an active compound, to minimize systemic exposure. To investigate the translational potential of surfactant-compound mixtures and other local therapeutics, a relevant animal model is required in which intratracheal administration for maximal local deposition is technically possible and well tolerated. Preterm rabbit pups (born at 28 days of gestation) were exposed to either hyperoxia or normoxia and randomized to receive daily intratracheal surfactant, daily intratracheal saline, or no injections for 7 days. At day 7, the overall lung function and morphology were assessed. Efficacy in terms of distribution was assessed by micro-PET-CT on both day 0 and day 7. Lung function as well as parenchymal and vascular structure were altered by hyperoxia, thereby reproducing a phenotype reminiscent of bronchopulmonary dysplasia (BPD). Neither intratracheal surfactant nor saline affected the survival or the hyperoxia-induced BPD phenotype of the pups. Using PET-CT, we demonstrate that 82.5% of the injected radioactive tracer goes and remains in the lungs, with a decrease of only 4% after 150 min. Surfactant and saline can safely and effectively be administered in spontaneously breathing preterm rabbits. The described model and method enable researchers to evaluate intratracheal pharmacological interventions for the treatment of BPD.

Surfactant plus budesonide decreases lung and systemic inflammation in mechanically ventilated preterm sheep.

Mechanical ventilation with normal tidal volumes (VT) causes lung and systemic inflammation in preterm sheep. Mechanical ventilation is associated with bronchopulmonary dysplasia (BPD) in preterm infants, and the addition of budesonide to surfactant decreases BPD in clinical trials. Budesonide with surfactant will decrease the lung injury from mechanical ventilation for 24 h in preterm sheep. Lambs at 126 ± 1 day gestational age were delivered and randomized to either: 1) surfactant (200 mg/kg) or 2) surfactant mixed with budesonide (0.25 mg/kg) before mechanical ventilation with VT of 7-8 ml/kg for 2, 6, or 24 h (n = 6 or 7/group). Lung physiology and budesonide levels in the plasma and the lung were measured. Lung tissue, bronchoalveolar lavage fluid (BALF), liver, and brain tissues were evaluated for indicators of injury. High initial budesonide plasma levels of 170 ng/ml decreased to 3 ng/ml at 24 h. Lung tissue budesonide levels were less than 1% of initial dose by 24 h. Although physiological variables were generally similar, budesonide-exposed lambs required lower mean airway pressures, had higher hyperoxia responses, and had more stable blood pressures. Budesonide decreased proinflammatory mRNA in the lung, liver, and brain. Budesonide also decreased total protein and proinflammatory cytokines in BALF, and decreased inducible nitric oxide synthase activation at 24 h. In ventilated preterm lambs, most of the budesonide left the lung within 24 h. The addition of budesonide to surfactant improved physiology, decreased markers of lung injury, and decreased systemic responses in liver and brain.

Tracing exogenous surfactant in vivo in rabbits by the natural variation of 13C.

BACKGROUND: Respiratory Distress Syndrome (RDS) is a prematurity-related breathing disorder caused by a quantitative deficiency of pulmonary surfactant. Surfactant replacement therapy is effective for RDS newborns, although treatment failure has been reported. The aim of this study is to trace exogenous surfactant by 13C variation and estimate the amount reaching the lungs at different doses of the drug. METHODS: Forty-four surfactant-depleted rabbits were obtained by serial bronchoalveolar lavages (BALs), that were merged into a pool (BAL pool) for each animal. Rabbits were in nasal continuous positive airway pressure and treated with 0, 25, 50, 100 or 200 mg/kg of poractant alfa by InSurE. After 90 min, rabbits were depleted again and a new pool (BAL end experiment) was collected. Disaturated-phosphatidylcholine (DSPC) was measured by gas chromatography. DSPC-Palmitic acid (PA) 13C/12C was analyzed by isotope ratio mass spectrometry. One-way non-parametric ANOVA and post-hoc Dunn's multiple comparison were used to assess differences among experimental groups. RESULTS: Based on DSPC-PA 13C/12C in BAL pool and BAL end experiment, the estimated amount of exogenous surfactant ranged from 61 to 87% in dose-dependent way (p < 0.0001) in animals treated with 25 up to 200 mg/kg. Surfactant administration stimulated endogenous surfactant secretion. The percentage of drug recovered from lungs did not depend on the administered dose and accounted for 31% [24-40] of dose. CONCLUSIONS: We reported a risk-free method to trace exogenous surfactant in vivo. It could be a valuable tool for assessing, alongside the physiological response, the delivery efficiency of surfactant administration techniques.

Mass spectrometry imaging as a tool for evaluating the pulmonary distribution of exogenous surfactant in premature lambs.

BACKGROUND: The amount of surfactant deposited in the lungs and its overall pulmonary distribution determine the therapeutic outcome of surfactant replacement therapy. Most of the currently available methods to determine the intrapulmonary distribution of surfactant are time-consuming and require surfactant labelling. Our aim was to assess the potential of Mass Spectrometry Imaging (MSI) as a label-free technique to qualitatively and quantitatively evaluate the distribution of surfactant to the premature lamb. METHODS: Twelve preterm lambs (gestational age 126-127d, term ~150d) were allocated in two experimental groups. Seven lambs were treated with an intratracheal bolus of the synthetic surfactant CHF5633 (200 mg/kg) and 5 lambs were managed with mechanical ventilation for 120 min, as controls. The right lung lobes of all lambs were gradually frozen while inflated to 20 cmH2O pressure for lung cryo-sections for MSI analysis. The intensity signals of SP-C analog and SP-B analog, the two synthetic peptides contained in the CHF5633 surfactant, were used to locate, map and quantify the intrapulmonary exogenous surfactant. RESULTS: Surfactant treatment was associated with a significant improvement of the mean arterial oxygenation and lung compliance (p < 0.05). Nevertheless, the physiological response to surfactant treatment was not uniform across all animals. SP-C analog and SP-B analog were successfully imaged and quantified by means of MSI in the peripheral lungs of all surfactant-treated animals. The intensity of the signal was remarkably low in untreated lambs, corresponding to background noise. The signal intensity of SP-B analog in each surfactant-treated animal, which represents the surfactant distributed to the peripheral right lung, correlated well with the physiologic response as assessed by the area under the curves of the individual arterial partial oxygen pressure and dynamic lung compliance curves of the lambs. CONCLUSIONS: Applying MSI, we were able to detect, locate and quantify the amount of exogenous surfactant distributed to the lower right lung of surfactant-treated lambs. The distribution pattern of SP-B analog correlated well with the pulmonary physiological outcomes of the animals. MSI is a valuable label-free technique which is able to simultaneously evaluate qualitative and quantitative drug distribution in the lung.

Simultaneous Detection of Local Polarizability and Viscosity by a Single Fluorescent Probe in Cells.

Many intracellular reactions are dependent on the dielectric ("polarity") and viscosity properties of their milieu. Fluorescence imaging offers a convenient strategy to report on such environmental properties. Yet, concomitant and independent monitoring of polarity and viscosity in cells at submicron scale is currently hampered by the lack of fluorescence probes characterized by unmixed responses to both parameters. Here, the peculiar photophysics of a green fluorescent protein chromophore analog is exploited for quantifying and imaging polarity and viscosity independently in living cells. We show that the polarity and viscosity profile around a novel hybrid drug-delivery peptide changes dramatically upon cell internalization via endosomes, shedding light on the spatiotemporal features of the release mechanism. Accordingly, our fluorescent probe opens the way to monitor the environmental effects on several processes relevant to cell biochemistry and nanomedicine.

Metabolism of a synthetic compared with a natural therapeutic pulmonary surfactant in adult mice.

Secreted pulmonary surfactant phosphatidylcholine (PC) has a complex intra-alveolar metabolism that involves uptake and recycling by alveolar type II epithelial cells, catabolism by alveolar macrophages, and loss up the bronchial tree. We compared the in vivo metabolism of animal-derived poractant alfa (Curosurf) and a synthetic surfactant (CHF5633) in adult male C57BL/6 mice. The mice were dosed intranasally with either surfactant (80 mg/kg body weight) containing universally 13C-labeled dipalmitoyl PC (DPPC) as a tracer. The loss of [U13C]DPPC from bronchoalveolar lavage and lung parenchyma, together with the incorporation of 13C-hydrolysis fragments into new PC molecular species, was monitored by electrospray ionization tandem mass spectrometry. The catabolism of CHF5633 was considerably delayed compared with poractant alfa, the hydrolysis products of which were cleared more rapidly. There was no selective resynthesis of DPPC and, strikingly, acyl remodeling resulted in preferential synthesis of polyunsaturated PC species. In conclusion, both surfactants were metabolized by similar pathways, but the slower catabolism of CHF5633 resulted in longer residence time in the airways and enhanced recycling of its hydrolysis products into new PC species.