Lung inflammatory and oxidative alterations after exogenous surfactant therapy fortified with budesonide in rabbit model of meconium aspiration syndrome

Intratracheal instillation of budesonide suspension versus normal saline on oxidative stress in neonates with meconium aspiration syndrome

BACKGROUND

Presently, the efficacy of neonatal resuscitation techniques via interventions such as oral, nasal, and endotracheal suction for preventing meconium aspiration syndrome (MAS) after delivery has not been satisfactory.

OBJECTIVE

This study aimed to investigate the role of intratracheal instillation of budesonide on oxidative stress in MAS.

METHODS

Sixty-two neonates with MAS admitted to Huai'an Maternity and Child Healthcare Hospital from January 2018 to June 2020 were divided into a study group (intratracheal instillation of 2 ml budesonide suspension; n = 31) and a control group (intratracheal instillation of 2 ml normal saline; n = 31). Collect data from two groups of patients and evaluate clinical outcomes, including oxygenation index (OI), as well as serum total oxidant status (TOS), total antioxidant capacity (TAC), oxidative stress index (OSI) and 8-Isoprostane before treatment and 72h after admission.

RESULTS

We found no statistical differences in mortality, complication rate, total oxygen inhalation time, OI before treatment and 72h after admission between the two groups of neonates with MAS, while the duration of invasive respiratory support in the study group was significantly shorter than in the control group. Also, serum TAC, TOS, OSI and 8-isoprostane levels were not statistically different before treatment between the two groups. After 72h of admission, OSI and 8-Isoprostane in neonates with MAS in the study group were much lower than those in the control group. TOS, OSI, 8-Isoprostane in the control group and 8-Isoprostane in the study group were significantly higher than those before treatment. As for TAC and TOS, no significant differences were observed between the two groups.

CONCLUSION

Intratracheal instillation of budesonide was shown to alleviate oxidative stress and shorten invasive ventilation time in neonates with MAS.

Thermodynamic and Structural Study of Budesonide-Exogenous Lung Surfactant System

The clinical benefits of using exogenous pulmonary surfactant (EPS) as a carrier of budesonide (BUD), a non-halogenated corticosteroid with a broad anti-inflammatory effect, have been established. Using various experimental techniques (differential scanning calorimetry DSC, small- and wide- angle X-ray scattering SAXS/WAXS, small- angle neutron scattering SANS, fluorescence spectroscopy, dynamic light scattering DLS, and zeta potential), we investigated the effect of BUD on the thermodynamics and structure of the clinically used EPS, Curosurf®. We show that BUD facilitates the Curosurf® phase transition from the gel to the fluid state, resulting in a decrease in the temperature of the main phase transition (Tm) and enthalpy (ΔH). The morphology of the Curosurf® dispersion is maintained for BUD < 10 wt% of the Curosurf® mass; BUD slightly increases the repeat distance d of the fluid lamellar phase in multilamellar vesicles (MLVs) resulting from the thickening of the lipid bilayer. The bilayer thickening (~0.23 nm) was derived from SANS data. The presence of ~2 mmol/L of Ca2+ maintains the effect and structure of the MLVs. The changes in the lateral pressure of the Curosurf® bilayer revealed that the intercalated BUD between the acyl chains of the surfactant's lipid molecules resides deeper in the hydrophobic region when its content exceeds ~6 wt%. Our studies support the concept of a combined therapy utilising budesonide-enriched Curosurf®.

The effect of budesonide delivered by high-frequency oscillatory ventilation on acute inflammatory response in severe lung injury in adult rabbits

The inflammation present in acute respiratory distress syndrome (ARDS) and thereby associated injury to the alveolar-capillary membrane and pulmonary surfactant can potentiate respiratory failure. Even considering the high mortality rate of severe ARDS, glucocorticoids appear to be a reasonable treatment option along with an appropriate route of delivery to the distal lung. This study aimed to investigate the effect of budesonide therapy delivered intratracheally by high-frequency oscillatory ventilation (HFOV) on lung function and inflammation in severe ARDS. Adult New Zealand rabbits with respiratory failure (P/F<13.3 kPa) induced by intratracheal instillation of hydrochloric acid (HCl, 3 ml/kg, pH 1.5) followed by high tidal ventilation (VT 20 ml/kg) to mimic ventilator-induced lung injury (VILI) were treated with intratracheal bolus of budesonide (0.25 mg/kg, Pulmicort) delivered by HFOV (frequency 8 Hz, MAP 1 kPa, deltaP 0.9 kPa). Saline instead of HCl without VILI with HFOV delivered air bolus instead of therapy served as healthy control. All animals were subjected to lung-protective ventilation for 4 h, and respiratory parameters were monitored regularly. Postmortem, lung injury, wet-to-dry weight ratio, leukocyte shifts, and levels of cytokines in plasma and lung were evaluated. Budesonide therapy improved the lung function (P/F ratio, oxygenation index, and compliance), decreased the cytokine levels, reduced lung edema and neutrophils influx into the lung, and improved lung architecture in interstitial congestion, hyaline membrane, and atelectasis formation compared to untreated animals. This study indicates that HFOV delivered budesonide effectively ameliorated respiratory function, and attenuated acid-induced lung injury in a rabbit model of severe ARDS.

Time-Dependent Oxidative Alterations in Plasma and Lung Tissue after Meconium Aspiration in a Rabbit Model

Aspirated meconium into a newborn's airways induces the transcription of pro-oxidative mediators that cooperate in the pathogenesis of inflammatory changes and may negatively affect the commonly used exogenous surfactant therapy. However, inflammation is not treated at present, nor is the time dependence of oxidative damage known. The aim of our study was to describe the time course of oxidative stress marker production during meconium aspiration syndrome (MAS) and its relationship to leukocyte infiltration. New Zealand rabbits were instilled with saline or meconium suspension and ventilated for 5.5 h. Respiratory parameters were recorded and blood samples were taken before meconium application and in time intervals of 15 and 30 min, 1.0, 1.5, 3.5 and 5.5 h after application to evaluate oxidative markers and differential leukocytes count. Meconium aspiration led to a worsening of respiratory parameters and a decrease in leukocytes in the first 15 min. Changes in leukocytes were correlated both with nitrotyrosine (3NT) levels and thiobarbituric acid reactive substance (TBARS) levels, with the latter also related to changes in neutrophil count. The production of 3NT and TBARS increased in 1.5 and 3.5 h, respectively, in different ways, suggesting more than one source of oxidative agents and a potential risk of exogenous surfactant inactivation in a short time. We observed that MAS triggered neutrophil migration to the alveolar space and activation, as shown by the increased expression of pro-inflammatory cytokines and generation of indicators of oxidative damage to proteins and lipids during the time period when iNOS and NO metabolites were released.

Glycyrrhizic acid alleviates the meconium-induced acute lung injury in neonatal rats by inhibiting oxidative stress through mediating the Keap1/Nrf2/HO-1 signal pathway

Meconium aspiration syndrome (MAS) is a disease closely related to inflammation and oxidative stress. Glycyrrhizic acid (GA) is a triterpenoid isolated from licorice with multiple bioprotective properties. In the present study, impacts of GA against MAS rats, as well as the potential mechanism, will be investigated. MAS model was established on newborn rats, followed by the treatment of 12.5, 25, and 50 mg/kg GA. The wet/dry weight ratio of lung tissues was calculated. The production of IL-6, IL-1β, TNF-α, malonaldehyde (MDA), superoxide dismutase (SOD), glutathione (GSH) was measured using ELISA assay. HE staining was used to evaluate the pathological state of lung tissues and TUNEL assay was used to detect the apoptotic state. The protein expression of Nrf2, Keap1, HO-1, Bcl-2, Bax, and cleaved-Caspase3 was measured by Western blotting assay. The elevated W/D ratio, release of inflammatory factors, lung injury score, and apoptotic index, as well as the activated oxidative stress and suppressed Keap1/Nrf2/HO-1 pathway, in MAS rats were significantly alleviated by GA. After introducing the inhibitor of Nrf2, ML385, the protective property of GA on the pathological state, apoptotic index, and oxidative stress in MAS rats was pronouncedly abolished. Taken together, glycyrrhizin alleviated GAH in rats by suppressing Keap1/Nrf2/HO-1 signaling mediated oxidative stress.

Pulmonary surfactant: a unique biomaterial with life-saving therapeutic applications

Pulmonary surfactant is a complex lipoprotein mixture secreted into the alveolar lumen by type 2 pneumocytes, which is composed by tens of different lipids (approximately 90% of its entire mass) and surfactant proteins (approximately 10% of the mass). It is crucially involved in maintaining lung homeostasis by reducing the values of alveolar liquid surface tension close to zero at end-expiration, thereby avoiding the alveolar collapse, and assembling a chemical and physical barrier against inhaled pathogens. A deficient amount of surfactant or its functional inactivation is directly linked to a wide range of lung pathologies, including the neonatal respiratory distress syndrome. This paper reviews the main biophysical concepts of surfactant activity and its inactivation mechanisms, and describes the past, present and future roles of surfactant replacement therapy, focusing on the exogenous surfactant preparations marketed worldwide and new formulations under development. The closing section describes the pulmonary surfactant in the context of drug delivery. Thanks to its peculiar composition, biocompatibility, and alveolar spreading capability, the surfactant may work not only as a shuttle to the branched anatomy of the lung for other drugs but also as a modulator for their release, opening to innovative therapeutic avenues for the treatment of several respiratory diseases.

Acute lung injury - from pathophysiology to treatment

Acute lung injury is characterized by acute respiratory insufficiency with tachypnea, cyanosis refractory to oxygen, decreased lung compliance, and diffuse alveolar infiltrates on chest X-ray. The 1994 American-European Consensus Conference defined "acute respiratory distress syndrome, ARDS" by acute onset after a known trigger, severe hypoxemia defined by PaO2/FiO2</=200 mm Hg, bilateral infiltrates on chest X-ray, and absence of cardiogenic edema. Milder form of the syndrome with PaO2/FiO2 between 200-300 mm Hg was named "acute lung injury, ALI". Berlin Classification in 2012 defined three categories of ARDS according to hypoxemia (mild, moderate, and severe), and the term "acute lung injury" was assigned for general description or for animal models. ALI/ARDS can originate from direct lung triggers such as pneumonia or aspiration, or from extrapulmonary reasons such as sepsis or trauma. Despite growing understanding the ARDS pathophysiology, efficacy of standard treatments, such as lung protective ventilation, prone positioning, and neuromuscular blockers, is often limited. However, there is an increasing evidence that direct and indirect forms of ARDS may differ not only in the manifestations of alterations, but also in the response to treatment. Thus, individualized treatment according to ARDS subtypes may enhance the efficacy of given treatment and improve the survival of patients.

Effects of PDE3 Inhibitor Olprinone on the Respiratory Parameters, Inflammation, and Apoptosis in an Experimental Model of Acute Respiratory Distress Syndrome

This study aimed to investigate whether a selective phosphodiesterase-3 (PDE3) inhibitor olprinone can positively influence the inflammation, apoptosis, and respiratory parameters in animals with acute respiratory distress syndrome (ARDS) model induced by repetitive saline lung lavage. Adult rabbits were divided into 3 groups: ARDS without therapy (ARDS), ARDS treated with olprinone i.v. (1 mg/kg; ARDS/PDE3), and healthy ventilated controls (Control), and were oxygen-ventilated for the following 4 h. Dynamic lung-thorax compliance (Cdyn), mean airway pressure (MAP), arterial oxygen saturation (SaO2), alveolar-arterial gradient (AAG), ratio between partial pressure of oxygen in arterial blood to a fraction of inspired oxygen (PaO2/FiO2), oxygenation index (OI), and ventilation efficiency index (VEI) were evaluated every hour. Post mortem, inflammatory and oxidative markers (interleukin (IL)-6, IL-1β, a receptor for advanced glycation end products (RAGE), IL-10, total antioxidant capacity (TAC), 3-nitrotyrosine (3NT), and malondialdehyde (MDA) and apoptosis (apoptotic index and caspase-3) were assessed in the lung tissue. Treatment with olprinone reduced the release of inflammatory mediators and markers of oxidative damage decreased apoptosis of epithelial cells and improved respiratory parameters. The results indicate a future potential of PDE3 inhibitors also in the therapy of ARDS.

Meconium "aspiration" (or respiratory distress associated with meconium-stained amniotic fluid?)

The designation meconium aspiration syndrome (MAS) reflects a spectrum of disorders in infants born with meconium-stained amniotic fluid, ranging from mild tachypnea to severe respiratory distress and significant mortality. The frequency of MAS is highest among infants with post-term gestation, thick meconium, and birth asphyxia. Pulmonary hypertension is an important component in severe cases. Prenatal hypopharyngeal suctioning and postnatal endotracheal intubation and suctioning of vigorous infants are not effective. Intubation and suctioning of non-breathing infants is controversial and needs more investigation. Oxygen, mechanical ventilation, and inhaled nitric oxide are the mainstays of treatment. Surfactant is often used in infants with severe parenchymal involvement. High-frequency ventilation and extracorporeal membrane oxygenation are usually considered rescue therapies.

Effects of Conventional Mechanical Ventilation Performed by Two Neonatal Ventilators on the Lung Functions of Rabbits with Meconium-Induced Acute Lung Injury

Severe meconium aspiration syndrome (MAS) in the neonates often requires a ventilatory support. As a method of choice, a conventional mechanical ventilation with small tidal volumes (VT<6 ml/kg) and appropriate ventilatory pressures is used. The purpose of this study was to assess the short-term effects of the small-volume CMV performed by two neonatal ventilators: Aura V (Chirana Stara Tura a.s., Slovakia) and SLE5000 (SLE Ltd., UK) on the lung functions of rabbits with experimentally-induced MAS and to estimate whether the newly developed neonatal version of the ventilator Aura V is suitable for ventilation of the animals with MAS.

In the young rabbits, a model of MAS was induced by an intratracheal instillation of a suspension of neonatal meconium (4 ml/kg, 25 mg/ml). After creating the model of MAS, the animals were ventilated with small-volume CMV (frequency 50/min, VT <6 ml/kg, inspiration time 50 %, fraction of inspired oxygen 1.0, positive end-expiratory pressure 0.5 kPa, mean airway pressure 1.1 kPa) performed by ventilator Aura V (Aura group, n=7) or ventilator SLE5000 (SLE group, n=7) for additional 4 hours. One group of animals served as healthy non-ventilated controls (n=6). Blood gases, oxygenation indexes, ventilatory pressures, lung compliance, oxygen saturation and total and differential white blood cell (WBC) count were regularly determined. After euthanizing the animals, a left lung was saline-lavaged and total and differential counts of cells in the bronchoalveolar lavage (BAL) fluid were determined. A right lung was used for estimation of lung edema formation (expressed as a wet/dry weight ratio) and for analysis of concentrations of pro-inflammatory cytokines (IL-1β, IL-8, TNF). The cytokines were measured also in the blood plasma taken at the end of experiment.

Meconium instillation seriously worsened the gas exchange and induced inflammation and lung edema formation. In the Aura group, slightly lower concentrations of cytokines were found and better gas exchange early after creating the MAS model was observed. However, there were no significant differences in the respiratory parameters between the ventilated groups at the end of experiment (P>0.05).

Concluding, the newly developed neonatal version of the ventilator Aura V was found to be fully comparable to widely used neonatal ventilator SLE5000. Results provided by Aura V in CMV ventilation of rabbits with meconium-induced acute lung injury suggest its great potential also for future clinical use, i.e. for ventilation of the neonates with MAS.

N-acetylcysteine advancement of surfactant therapy in experimental meconium aspiration syndrome: possible mechanisms

Meconium aspiration syndrome (MAS) is meconium-induced respiratory failure of newborns associated with activation of inflammatory and oxidative pathways. For severe MAS, exogenous surfactant treatment is used which improves respiratory functions but does not treat the inflammation. Oxidative process can lead to later surfactant inactivation; hence, surfactant combination with antioxidative agent may enhance the therapeutic effect. Young New Zealand rabbits were instilled by meconium suspension and treated by surfactant alone, N-acetylcysteine (NAC) alone or by their combination and oxygen-ventilated for 5 h. Blood samples were taken before and 30 min after meconium application and 30 min, 1, 3 and 5 h after the treatment for evaluating of oxidative damage, total leukocyte count, leukocyte differential count and respiratory parameters. Leukocyte differential was assessed also in bronchoalveolar lavage fluid. NAC alone had only mild therapeutic effect on MAS. However, the combination of NAC and surfactant facilitated rapid onset of therapeutic effect in respiratory parameters (oxygenation index, PaO(2)/FiO(2)) compared to surfactant alone and was the only treatment which prevented neutrophil migration into the lungs, oxidative damage and lung edema. Moreover, NAC suppressed IL-8 and IL-beta formation and thus seems to be favorable agent for improving surfactant therapy in MAS.