Effects of Surfactant Lavage Combined With Intratracheal Budesonide Instillation on Meconium-Injured Piglet Lungs

Surfactant replacement therapy as promising treatment for COVID-19: an updated narrative review

Patients with COVID-19 exhibit similar symptoms to neonatal respiratory distress syndrome. SARS-CoV-2 spike protein has been shown to target alveolar type 2 lung cells which synthesize and secrete endogenous surfactants leading to acute respiratory distress syndrome in some patients. This was proven by post-mortem histopathological findings revealing desquamated alveolar type 2 cells. Surfactant use in patients with COVID-19 respiratory distress syndrome results in marked improvement in respiratory parameters but not mortality which needs further clinical trials comparing surfactant formulas and modes of administration to decrease the mortality. In addition, surfactants could be a promising vehicle for specific drug delivery as a liposomal carrier, which requires more and more challenging efforts. In this review, we highlight the current reviews and two clinical trials on exogenous surfactant therapy in COVID-19-associated respiratory distress in adults, and how surfactant could be a promising drug to help fight the COVID-19 infection.

Efficacy of intratracheal budesonide-surfactant combined therapy in surfactant-insufficient rat lungs with lipopolysaccharide insult

BACKGROUND

Intratracheal steroid therapy for lipopolysaccharide (LPS)-induced acute lung injury (ALI) remains challenging particularly in surfactant-insufficient lungs, a common problem of neonatal or pediatric ALI. Surfactant has been used as a vehicle for intratracheal steroid in the treatment of other types of ALI. This study investigated the efficacy of intratracheal budesonide (BUD) delivered by two concentrations of surfactant in the treatment of LPS-induced ALI in surfactant-insufficient rat lungs.

METHODS

Male adult rats were anesthetized and ventilated. Our ALI model was established by repeated saline lavage to produce surfactant insufficiency, followed by intratracheal LPS instillation. Five study groups (n = 5 for each) with different intratracheal treatments following ALI were used: control (no treatment), BUD (NS-BUD; BUD in saline), DS-BUD (BUD in diluted surfactant), FS-BUD (BUD in full-strength surfactant), FS (full-strength surfactant). Cardiopulmonary variables were monitored 4 hours post injury. Histological and immunohistochemical assessments of the lungs were performed.

RESULTS

The FS-BUD and FS groups presented better gas exchange, less metabolic acidosis, less oxygen index, and more stable hemodynamic changes than the DS-BUD, NS-BUD, and control groups. The total lung injury scores assessed by histological examination were ordered as follows: FS-BUD < DS-BUD or FS < NS-BUD < control. The immunostaining intensities of lung myeloperoxidase showed the following order: NS-BUD, DS-BUD, or FS-BUD < control or FS. Only the FS-BUD group displayed a smaller immunostaining intensity of lung tumor necrosis factor (TNF)-α than the control group.

CONCLUSION

Among our therapeutic strategies, intratracheal BUD delivered by full-strength surfactant confers an optimal protection against LPS-induced ALI in surfactant-insufficient rat lungs.

Meconium Aspiration Syndrome: A Narrative Review

Meconium aspiration syndrome is a clinical condition characterized by respiratory failure occurring in neonates born through meconium-stained amniotic fluid. Worldwide, the incidence has declined in developed countries thanks to improved obstetric practices and perinatal care while challenges persist in developing countries. Despite the improved survival rate over the last decades, long-term morbidity among survivors remains a major concern. Since the 1960s, relevant changes have occurred in the perinatal and postnatal management of such patients but the most appropriate approach is still a matter of debate. This review offers an updated overview of the epidemiology, etiopathogenesis, diagnosis, management and prognosis of infants with meconium aspiration syndrome.

Pathophysiological effects of intravenous phosphodiesterase type 4 inhibitor in addition to surfactant lavage in meconium-injured newborn piglet lungs

BACKGROUND

Nonsteroidal anti-inflammatory drugs, such as selective phosphodiesterase type 4 (PDE4) inhibitors have potential anti-inflammatory and respiratory smooth muscle relaxation effects. This study aimed to investigate the pathophysiological effects of an intravenous PDE4 inhibitor (rolipram) and surfactant lavage (SL) in a newborn piglet model of meconium aspiration syndrome (MAS).

METHODS

MAS was induced in 25 newborn piglets, which were randomly divided into control and four SL treatment groups administered with different doses of intravenous rolipram (0, 0.1, 0.5, and 1 mg/kg). Cardiopulmonary variables were monitored and recorded. The experimental time was 4 hours. Serial blood was drawn for blood gas and biomarker analyses. Lung tissue was examined for histological analysis.

RESULTS

All SL-treated groups revealed improved oxygenation during the 4-hour experiments and had significantly lower peak inspiratory pressure levels than the control group at the end of experiments. All SL plus rolipram-treated groups exhibited significantly higher lung compliance than the control group. However, the animals receiving high-dose (0.5 and 1.0 mg/kg) rolipram demonstrated significantly elevated heart rates. Lung histology of the nondependent sites revealed significantly lower lung injury scores in all SL-treated groups compared with that in the control group, but there were no differences among the rolipram-treated groups.

CONCLUSIONS

In addition to SL, intravenous PDE4 inhibitors may further improve lung compliance in treating MAS; however, it is necessary to consider cardiovascular adverse effects, primarily tachycardia. Further investigations are required before the clinical application of intravenous PDE4 inhibitor as an anti-inflammatory agent to treat severe MAS.

An Unsettled Promise: The Newborn Piglet Model of Neonatal Acute Respiratory Distress Syndrome (NARDS). Physiologic Data and Systematic Review

Despite great advances in mechanical ventilation and surfactant administration for the newborn infant with life-threatening respiratory failure no specific therapies are currently established to tackle major pro-inflammatory pathways. The susceptibility of the newborn infant with neonatal acute respiratory distress syndrome (NARDS) to exogenous surfactant is linked with a suppression of most of the immunologic responses by the innate immune system, however, additional corticosteroids applied in any severe pediatric lung disease with inflammatory background do not reduce morbidity or mortality and may even cause harm. Thus, the neonatal piglet model of acute lung injury serves as an excellent model to study respiratory failure and is the preferred animal model for reasons of availability, body size, similarities of porcine and human lung, robustness, and costs. In addition, similarities to the human toll-like receptor 4, the existence of intraalveolar macrophages, the sensitivity to lipopolysaccharide, and the production of nitric oxide make the piglet indispensable in anti-inflammatory research. Here we present the physiologic and immunologic data of newborn piglets from three trials involving acute lung injury secondary to repeated airway lavage (and others), mechanical ventilation, and a specific anti-inflammatory intervention via the intratracheal route using surfactant as a carrier substance. The physiologic data from many organ systems of the newborn piglet—but with preference on the lung—are presented here differentiating between baseline data from the uninjured piglet, the impact of acute lung injury on various parameters (24 h), and the follow up data after 72 h of mechanical ventilation. Data from the control group and the intervention groups are listed separately or combined. A systematic review of the newborn piglet meconium aspiration model and the repeated airway lavage model is finally presented. While many studies assessed lung injury scores, leukocyte infiltration, and protein/cytokine concentrations in bronchoalveolar fluid, a systematic approach to tackle major upstream pro-inflammatory pathways of the innate immune system is still in the fledgling stages. For the sake of newborn infants with life-threatening NARDS the newborn piglet model still is an unsettled promise offering many options to conquer neonatal physiology/immunology and to establish potent treatment modalities.

Effects of intravenous phosphodiesterase inhibitors and corticosteroids on severe meconium aspiration syndrome

BACKGROUND

Meconium aspiration syndrome (MAS) is a major cause of severe respiratory failure in near- and full-term neonates. Alleviating inflammation is key to successfully treating severe MAS. Phosphodiesterase (PDE) inhibitors are known to play a role in airway smooth muscle relaxation and alveolar inflammation inhibition. This study aimed to investigate the effects of various intravenous (IV) PDE inhibitors and corticosteroids on MAS.

METHODS

MAS was induced in newborn piglets by instilling human meconium in them. The piglets were randomly divided into five groups (n = 5 in each group): (1) control (sham treatment); (2) dexamethasone (Dex) (IV 0.6 mg/kg of dexamethasone); (3) aminophylline (Ami) (IV 6 mg/kg of aminophylline, followed by continuous infusion of 0.5 mg/kg/h of aminophylline; (4) milrinone (Mil) (IV 50 μg/kg of milrinone, followed by continuous infusion of 0.75 μg/kg/h of milrinone); and (5) rolipram (Rol) (IV 0.8 mg/kg of rolipram). The duration of the experimental period was 4 hours.

RESULTS

Compared to the control group, all the four treatment groups revealed better oxygenation 3 hours and more after the start of treatment. The Rol group had a significantly elevated heart beat (p < 0.05) and relatively lower blood pressure compared to the other groups during the first 2 hours of the experiment. The Dex group had significantly lower interleukin (IL)-1β levels in the lung tissue compared to the other groups (p < 0.05) and significantly lower IL-6 levels compared to the Ami and Mil groups (p < 0.05). Lung histology showed slightly less inflammation and atelectasis in the Dex group compared to the other groups, but lung injury scores showed no significant between-group differences.

CONCLUSION

Using IV corticosteroids or any type of PDE inhibitors has some beneficial effects in improving oxygenation in MAS. PDE inhibitors are not superior to IV corticosteroids; in fact, adverse cardiovascular effects occur with the phosphodiesterase type 4 (PDE4) inhibitor. Further investigations are required before using IV corticosteroids and PDE inhibitors in future clinical application.

Effects of intratracheal captopril on severely meconium-injured piglet lungs

BACKGROUND

Severe meconium aspiration syndrome (MAS) may cause intractable respiratory failure in neonates. Targeting the renin-angiotensin system may be an effective way to treat such pulmonary dysfunction. Captopril has the potential to mitigate the severity of lung injury by inhibiting angiotensin-converting enzyme.

METHODS

Twelve newborn piglets were intratracheally instilled with human meconium to induce severe MAS and were randomly treated with IT administration of captopril (0.5 mg/kg) (IT-Cap group, n = 6), or sham air instillation (Control group, n = 6). Cardiopulmonary profiles were monitored for a total of 5 hours. Pulmonary history was examined to compare lung injury severity between groups.

RESULTS

There were no significant differences between the two study groups in gas exchange and lung compliance, peak inspiratory pressure, heart rate, and mean arterial blood pressure over the 5-h experimental period, but there were trends toward lower blood pressure and pH in the IT-Cap group. Histopathological examinations revealed significantly higher lung injury scores in the dependent site of the control group than in the nondependent site of the control group and both sites of the IT-Cap group.

CONCLUSION

Intratracheal captopril did not present significant beneficial effects on severe meconium-injured lungs within 5 hours after injury. Further studies with different disease severities and dosing strategies are required.

Selective inhibition of NF-kappaB and surfactant therapy in experimental meconium-induced lung injury

Meconium aspiration syndrome (MAS) in newborns is characterized mainly by respiratory failure due to surfactant dysfunction and inflammation. Previous meta-analyses did not prove any effect of exogenous surfactant treatment nor glucocorticoid administration on final outcome of children with MAS despite oxygenation improvement. As we supposed there is the need to intervene in both these fields simultaneously, we evaluated therapeutic effect of combination of exogenous surfactant and selective inhibitor of NF-kappaB (IKK-NBD peptide). Young New Zealand rabbits were instilled by meconium suspension and treated by surfactant alone or surfactant in combination with IKK-NBD, and oxygen-ventilated for 5 h. PaO(2)/FiO(2), oxygenation index, oxygen saturation and ventilation efficiency index were evaluated every hour; post mortem, total and differential leukocyte counts were investigated in bronchoalveolar lavage fluid (BALF) and inflammatory, oxidative and apoptotic markers were assessed in lung tissue homogenates. Exogenous surfactant combined with IKK-NBD improved oxygenation, reduced neutrophil count in BALF and levels of IL-1beta, IL-6, p38 MAPK and caspase 3 in comparison with surfactant-only therapy. It seems that inhibition of inflammation may be strong supporting factor in surfactant treatment of MAS.

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.

Comparison of different dosing strategies of intratracheally instilled budesonide on meconium injured piglet lungs

BACKGROUND

Severe inflammation plays a vital role in the pathogenesis of meconium aspiration syndrome (MAS). Intratracheal (IT) instillation of corticosteroids may be beneficial for MAS in optimizing local effect and reducing systemic adverse effects, but the optimum dosing course remains open to question.

METHODS

Thirty meconium-injured newborn piglets were enrolled into six study groups. The first four groups consisted of the IT instillation of 0.25/0.5 mg/kg using either one (IT-B251/IT-B501) or two (IT-B252/IT-B502) doses of budesonide, while the other two groups were the intravenous (IV) dexamethasone (0.5 mg/kg) (IV-Dex) group and the control group (Ctrl). Vital signs and cardiopulmonary functions were monitored throughout the experiments. Pulmonary histology was examined after completing the experiments.

RESULTS

Both the IV-Dex and IT-B501 groups got significant improvement in oxygenation (P < 0.05). Lung compliance became worse after one dose of 0.25 mg/kg of IT budesonide. Pulmonary histology revealed that there were significantly lower lung injury scores for all treatment groups compared to control group, especially at the non-dependent sites of both the IT-B501 and IT-B502 groups. There was no significant difference between double- and single-dose groups, no matter whether 0.25 or 0.5 mg/kg of budesonide was used.

CONCLUSIONS

IT instillation of one dose of 0.5 mg/kg budesonide is beneficial in treating meconium-injured piglet lungs during the first 8 h of injury, but a second dose at an interval of 4 h does not have a superior beneficial effect compared to one dose.

Update on Postnatal Steroids

Antenatal steroid treatment to enhance fetal lung maturity and surfactant treatment to prevent or treat respiratory distress syndrome have been major advances in perinatal medicine in the past 40 years contributing to improved outcomes for preterm infants. Use of postnatal steroids to prevent or treat chronic lung disease in preterm infants has been less successful and associated with adverse neurodevelopmental outcomes. Although early (in the first week of life) postnatal steroid treatment facilitates earlier extubation and reduces the risk of chronic lung disease, it is associated with adverse effects, such as hyperglycemia, hypertension, gastrointestinal bleeding and perforation, hypertrophic cardiomyopathy, growth failure, and cerebral palsy, and cannot be recommended. Early treatment with hydrocortisone may also improve survival without chronic lung disease, but concerns remain about possible adverse effects such as gastrointestinal perforation and sepsis, particularly in very preterm infants. Early inhaled budesonide also reduces the incidence of chronic lung disease but there are concerns that this may occur at the expense of increased risk of death. More studies of early low-dose steroids with adequate long-term follow-up are needed before they can be recommended for the prevention of chronic lung disease. Late (after the first week of life) postnatal steroids may have a better benefit-to-harm ratio than early steroids. A Cochrane Review shows that late steroid treatment reduces chronic lung disease, the combination of death and chronic lung disease at both 28 days and 36 weeks' corrected age, and the need for later rescue dexamethasone. Adverse effects include hyperglycemia, hypertension, hypertrophic cardiomyopathy, and severe retinopathy of prematurity but without an increase in blindness. Long-term neurodevelopmental effects are not significantly increased by late postnatal steroid treatment. Current recommendations are that postnatal steroid treatment should be reserved for preterm infants who are ventilator-dependent after the first 7-14 days of life and any course should be low dose and of short duration to facilitate endotracheal extubation. Budesonide/surfactant mixtures show some promise as a means of reducing chronic lung disease in preterm infants with severe respiratory distress syndrome, but further larger studies with long-term follow-up are needed before this treatment can be recommended as a routine intervention.