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

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.

Phosphodiesterase Inhibitors in Acute Lung Injury: What Are the Perspectives?

Despite progress in understanding the pathophysiology of acute lung damage, currently approved treatment possibilities are limited to lung-protective ventilation, prone positioning, and supportive interventions. Various pharmacological approaches have also been tested, with neuromuscular blockers and corticosteroids considered as the most promising. However, inhibitors of phosphodiesterases (PDEs) also exert a broad spectrum of favorable effects potentially beneficial in acute lung damage. This article reviews pharmacological action and therapeutical potential of nonselective and selective PDE inhibitors and summarizes the results from available studies focused on the use of PDE inhibitors in animal models and clinical studies, including their adverse effects. The data suggest that xanthines as representatives of nonselective PDE inhibitors may reduce acute lung damage, and decrease mortality and length of hospital stay. Various (selective) PDE3, PDE4, and PDE5 inhibitors have also demonstrated stabilization of the pulmonary epithelial-endothelial barrier and reduction the sepsis- and inflammation-increased microvascular permeability, and suppression of the production of inflammatory mediators, which finally resulted in improved oxygenation and ventilatory parameters. However, the current lack of sufficient clinical evidence limits their recommendation for a broader use. A separate chapter focuses on involvement of cyclic adenosine monophosphate (cAMP) and PDE-related changes in its metabolism in association with coronavirus disease 2019 (COVID-19). The chapter illuminates perspectives of the use of PDE inhibitors as an add-on treatment based on actual experimental and clinical trials with preliminary data suggesting their potential benefit.

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.

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.