Protective effects of adenosine A2A receptor agonist in ventilator-induced lung injury in rats

Camellia sinensis L. Alleviates Pulmonary Inflammation Induced by Porcine Pancreas Elastase and Cigarette Smoke Extract

Cigarette smoke (CS) is the major factor in the development of chronic obstructive pulmonary disease (COPD), the third leading cause of death worldwide. Furthermore, although Camellia sinensis (CN) has been known as an anti-inflammatory material, the effect of CN has not yet been known on pulmonary inflammation in COPD. Thus, we investigated the protective effects of Camellia sinensis L. extract (CLE) against pulmonary inflammation in porcine pancreas elastase (PPE) and a cigarette smoke extract (CSE)-induced COPD mouse model. Oral administration of CLE suppressed the symptoms such as infiltration of immune cells, cytokines/chemokines secretion, mucus hypersecretion, and injuries of the lung parenchyma. Increased inflammatory responses in COPD are mediated by various immune cells such as airway epithelial cells, neutrophils, and alveolar macrophages. Thus, we investigated the effect and mechanisms of CLE in H292, HL-60, and MH-S cells. The CLE inhibited the expression of IL-6, IL-8, MUC5AC and MUC5B on CSE/LPS-stimulated H292 cells and also suppressed the formation of neutrophil extracellular traps and secretion of neutrophil elastase by inhibiting reactive oxygen species in PMA-induced HL-60 cells. In particular, the CLE suppressed the release of cytokines and chemokines caused by activating the nuclear factor kappa-light-chain-enhancer of activated B via the activation of nuclear factor erythroid-2-related factor 2 and the heme oxygenase-1 pathway in CSE/LPS-stimulated MH-S cells. Therefore, we suggest that the CLE administration be the effective approach for treating or preventing chronic pulmonary diseases such as COPD induced by CS.

Emerging pharmacological therapies for ARDS: COVID-19 and beyond

ARDS, first described in 1967, is the commonest form of acute severe hypoxemic respiratory failure. Despite considerable advances in our knowledge regarding the pathophysiology of ARDS, insights into the biologic mechanisms of lung injury and repair, and advances in supportive care, particularly ventilatory management, there remains no effective pharmacological therapy for this syndrome. Hospital mortality at 40% remains unacceptably high underlining the need to continue to develop and test therapies for this devastating clinical condition. The purpose of the review is to critically appraise the current status of promising emerging pharmacological therapies for patients with ARDS and potential impact of these and other emerging therapies for COVID-19-induced ARDS. We focus on drugs that: (1) modulate the immune response, both via pleiotropic mechanisms and via specific pathway blockade effects, (2) modify epithelial and channel function, (3) target endothelial and vascular dysfunction, (4) have anticoagulant effects, and (5) enhance ARDS resolution. We also critically assess drugs that demonstrate potential in emerging reports from clinical studies in patients with COVID-19-induced ARDS. Several therapies show promise in earlier and later phase clinical testing, while a growing pipeline of therapies is in preclinical testing. The history of unsuccessful clinical trials of promising therapies underlines the challenges to successful translation. Given this, attention has been focused on the potential to identify biologically homogenous subtypes within ARDS, to enable us to target more specific therapies ‘precision medicines.’ It is hoped that the substantial number of studies globally investigating potential therapies for COVID-19 will lead to the rapid identification of effective therapies to reduce the mortality and morbidity of this devastating form of ARDS.

Mechanistic actions of oxygen and methylxanthines on respiratory neural control and for the treatment of neonatal apnea

Apnea remains one of the most concerning and prevalent respiratory disorders spanning all ages from infants (particularly those born preterm) to adults. Although the pathophysiological consequences of apnea are fairly well described, the neural mechanisms underlying the etiology of the different types of apnea (central, obstructive, and mixed) still remain incompletely understood. From a developmental perspective, however, research into the respiratory neural control system of immature animals has shed light on both central and peripheral neural pathways underlying apnea of prematurity (AOP), a highly prevalent respiratory disorder of preterm infants. Animal studies have also been fundamental in furthering our understanding of how clinical interventions (e.g. pharmacological and mechanical) exert their beneficial effects in the clinical treatment of apnea. Although current clinical interventions such as supplemental O₂ and positive pressure respiratory support are critically important for the infant in respiratory distress, they are not fully effective and can also come with unfortunate, unintended (and long-term) side-effects. In this review, we have chosen AOP as one of the most common clinical scenarios involving apnea to highlight the mechanistic basis behind how some of the interventions could be both beneficial and also deleterious to the respiratory neural control system. We have included a section on infants with critical congenital heart diseases (CCHD), in whom apnea can be a clinical concern due to treatment with prostaglandin, and who may benefit from some of the treatments used for AOP.

Protective effects of ghrelin in ventilator-induced lung injury in rats

Ghrelin has exhibited potent anti-inflammatory effects on various inflammatory diseases. The aim of this study was to investigate the potential effects of ghrelin on a model of ventilator-induced lung injury (VILI) established in rats. Male Sprague-Dawley rats were randomly divided into three groups: low volume ventilation (LV, Vt=8ml/kg) group, a VILI group (Vt=30ml/kg), and a VILI group pretreated with ghrelin (GH+VILI). For the LV group, for the VILI and GH+VILI groups, the same parameters were applied except the tidal volume was increased to 40ml/kg. After 4h of MV, blood gas, lung elastance, and levels of inflammatory mediators, including tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, and (MIP)-2 and total protein in bronchoalveolar lavage fluid (BALF) were analyzed. Myeloperoxidase (MPO), (TLR)-4, and NF-κB, were detected in lung tissues. Water content (wet-to-dry ratio) and lung morphology were also evaluated. The VILI group had a higher acute lung injury (ALI) score, wet weight to dry ratio, MPO activity, and concentrations of inflammatory mediators (TNF-α, IL-6, IL-1β, and MIP-2) in BALF, as well as higher levels of TLR4 and NF-κB expression than the LV group (P<0.05). All histopathologic ALI, the inflammatory profile, and pulmonary dynamics have been improved by ghrelin pretreatment (P<0.05). Ghrelin pretreatment also decreased TLR4 expression and NF-κB activity compared with the VILI group (P<0.05). Ghrelin pretreatment attenuated VILI in rats by reducing MV-induced pulmonary inflammation and might represent a novel therapeutic candidate for protection against VILI.

Adenosine signalling mediates the anti-inflammatory effects of the COX-2 inhibitor nimesulide

Extracellular adenosine formation from ATP is controlled by ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase/CD39) and ecto-5'-nucleotidase (e-5NT/CD73); the latter converts AMP to adenosine and inorganic phosphate, representing the rate limiting step controlling the ratio between extracellular ATP and adenosine. Evidence that cellular expression and activity of CD39 and CD73 may be subject to changes under pathophysiological conditions has identified this pathway as an endogenous modulator in several diseases and was shown to be involved in the molecular mechanism of drugs, such as methotrexate, salicylates , interferon-β. We evaluated whether CD73/adenosine/A2A signalling pathway is involved in nimesulide anti-inflammatory effect, in vivo and in vitro. We found that the adenosine A2A agonist, 4-[2-[[6-amino-9-(N-ethyl-β-d-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS21680, 2mg/kg ip.), inhibited carrageenan-induced rat paw oedema and the effect was reversed by co-administration of the A2A antagonist -(2-[7-amino-2-[2-furyl][1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol (ZM241385; 3mg/kg i.p.). Nimesulide (5mg/kg i.p.) anti-inflammatory effect was inhibited by pre-treatment with ZM241385 (3mg/kg i.p.) and by local administration of the CD73 inhibitor, adenosine 5'-(α,β-methylene)diphosphate (APCP; 400μg/paw). Furthermore, we found increased activity of 5'-nucleotidase/CD73 in paws and plasma of nimesulide treated rats, 4h following oedema induction. In vitro, the inhibitory effect of nimesulide on nitrite and prostaglandin E2 production by lipopolysaccharide-activated J774 cell line was reversed by ZM241385 and APCP. Furthermore, nimesulide increased CD73 activity in J774 macrophages while it did not inhibit nitrite accumulation by lipopolysaccharide-activated SiRNA CD73 silenced J774 macrophages. Our data demonstrate that the anti-inflammatory effect of nimesulide in part is mediated by CD73-derived adenosine acting on A2A receptors.

Glutamine attenuates acute lung injury caused by acid aspiration

Inadequate ventilator settings may cause overwhelming inflammatory responses associated with ventilator-induced lung injury (VILI) in patients with acute respiratory distress syndrome (ARDS). Here, we examined potential benefits of glutamine (GLN) on a two-hit model for VILI after acid aspiration-induced lung injury in rats. Rats were intratracheally challenged with hydrochloric acid as a first hit to induce lung inflammation, then randomly received intravenous GLN or lactated Ringer's solution (vehicle control) thirty min before different ventilator strategies. Rats were then randomized to receive mechanical ventilation as a second hit with a high tidal volume (TV) of 15 mL/kg and zero positive end-expiratory pressure (PEEP) or a low TV of 6 mL/kg with PEEP of 5 cm H2O. We evaluated lung oxygenation, inflammation, mechanics, and histology. After ventilator use for 4 h, high TV resulted in greater lung injury physiologic and biologic indices. Compared with vehicle treated rats, GLN administration attenuated lung injury, with improved oxygenation and static compliance, and decreased respiratory elastance, lung edema, extended lung destruction (lung injury scores and lung histology), neutrophil recruitment in the lung, and cytokine production. Thus, GLN administration improved the physiologic and biologic profiles of this experimental model of VILI based on the two-hit theory.

Anti-inflammatory effect of caffeine is associated with improved lung function after lipopolysaccharide-induced amnionitis

BACKGROUND

Although caffeine enhances respiratory control and decreases the need for mechanical ventilation and resultant bronchopulmonary dysplasia, it may also have anti-inflammatory properties in protecting lung function.

OBJECTIVE

We hypothesized that caffeine improves respiratory function via an anti-inflammatory effect in lungs of a lipopolysaccharide (LPS)-induced pro-inflammatory amnionitis rat pup model.

METHODS

Caffeine was given orally (10 mg/kg/day) from postnatal day (p)1 to p14 to pups exposed to intra-amniotic LPS or normal saline. Expression of IL-1β was assessed in lung homogenates at p8 and p14, and respiratory system resistance (Rrs) and compliance (Crs) as well as CD68 cell counts and radial alveolar counts were assessed at p8.

RESULTS

In LPS-exposed rats, IL-1β and CD68 cell counts both increased at p8 compared to normal saline controls. These increases in pro-inflammatory markers were no longer present in caffeine-treated LPS-exposed pups. Rrs was higher in LPS-exposed pups (4.7 ± 0.9 cm H2O/ml·s) at p8 versus controls (1.6 ± 0.3 cm H2O/ml·s, p < 0.01). LPS-exposed pups no longer exhibited a significant increase in Rrs (2.8 ± 0.5 cm H2O/ml·s) after caffeine. Crs did not differ significantly between groups, although radial alveolar counts were lower in both groups of LPS-exposed pups.

CONCLUSIONS

Caffeine promotes anti-inflammatory effects in the immature lung of prenatal LPS-exposed rat pups associated with improvement of Rrs, suggesting a protective effect of caffeine on respiratory function via an anti-inflammatory mechanism.

Ventilation-induced lung injury

Mechanical ventilation (MV) is, by definition, the application of external forces to the lungs. Depending on their magnitude, these forces can cause a continuum of pathophysiological alterations ranging from the stimulation of inflammation to the disruption of cell-cell contacts and cell membranes. These side effects of MV are particularly relevant for patients with inhomogeneously injured lungs such as in acute lung injury (ALI). These patients require supraphysiological ventilation pressures to guarantee even the most modest gas exchange. In this situation, ventilation causes additional strain by overdistension of the yet non-injured region, and additional stress that forms because of the interdependence between intact and atelectatic areas. Cells are equipped with elaborate mechanotransduction machineries that respond to strain and stress by the activation of inflammation and repair mechanisms. Inflammation is the fundamental response of the host to external assaults, be they of mechanical or of microbial origin and can, if excessive, injure the parenchymal tissue leading to ALI. Here, we will discuss the forces generated by MV and how they may injure the lungs mechanically and through inflammation. We will give an overview of the mechanotransduction and how it leads to inflammation and review studies demonstrating that ventilator-induced lung injury can be prevented by blocking pathways of mechanotransduction or inflammation.

Apnea of prematurity--perfect storm

With increased survival of preterm infants as young as 23 weeks gestation, maintaining adequate respiration and corresponding oxygenation represents a clinical challenge in this unique patient cohort. Respiratory instability characterized by apnea and periodic breathing occurs in premature infants because of immature development of the respiratory network. While short respiratory pauses and apnea may be of minimal consequence if oxygenation is maintained, they can be problematic if accompanied by chronic intermittent hypoxemia. Underdevelopment of the lung and the resultant lung injury that occurs in this population concurrent with respiratory instability creates the perfect storm leading to frequent episodes of profound and recurrent hypoxemia. Chronic intermittent hypoxemia contributes to the immediate and long term co-morbidities that occur in this population. In this review we discuss the pathophysiology leading to the perfect storm, diagnostic assessment of breathing instability in this unique population and therapeutic interventions that aim to stabilize breathing without contributing to tissue injury.

Design and application of locally delivered agonists of the adenosine A(2A) receptor

The broad spectrum anti-inflammatory actions of adenosine A(2A) receptor agonists are well described. The wide distribution of this receptor, however, suggests that the therapeutic potential of these agents is likely to reside in topical treatments to avoid systemic side effects associated with oral administration. Adenosine A(2A) receptor agonists have been assessed as topical agents: GW328267X (GSK; allergic rhinitis and asthma), UK-432097 (Pfizer; chronic obstructive pulmonary disease [COPD]) and Sonedenoson (MRE0094, King Pharmaceuticals; wound healing). All trials failed to achieve effects against the desired clinical end points. This broad-based review will discuss general principles of chemical design of topically applied agents and potential therapeutic topical applications of current adenosine A(2A) receptor agonists. Potential factors contributing to the lack of efficacy in the above clinical trials will be discussed together with design principles, which may influence efficacy in disease states. Our analysis suggests that adenosine A(2A) receptor agonists have a wide therapeutic potential as topical agents in a wide variety of diseases, such as neutrophil-dependent lung diseases (acute lung injury, exacerbations in asthma and COPD), allergic rhinitis, glaucoma and wound repair. Factors that will influence topical activity include formulation, tissue retention, compound potency, receptor kinetics and pharmacokinetics.

Lung regional metabolic activity and gas volume changes induced by tidal ventilation in patients with acute lung injury

RATIONALE

During acute lung injury (ALI), mechanical ventilation can aggravate inflammation by promoting alveolar distension and cyclic recruitment-derecruitment. As an estimate of the intensity of inflammation, metabolic activity can be measured by positron emission tomography imaging of [(18)F]fluoro-2-deoxy-D-glucose.

OBJECTIVES

To assess the relationship between gas volume changes induced by tidal ventilation and pulmonary metabolic activity in patients with ALI.

METHODS

In 13 mechanically ventilated patients with ALI and relatively high positive end-expiratory pressure, we performed a positron emission tomography scan of the chest and three computed tomography scans: at mean airway pressure, end-expiration, and end-inspiration. Metabolic activity was measured from the [(18)F]fluoro-2-deoxy-D-glucose uptake rate. The computed tomography scans were used to classify lung regions as derecruited throughout the respiratory cycle, undergoing recruitment-derecruitment, and normally aerated.

MEASUREMENTS AND MAIN RESULTS

Metabolic activity of normally aerated lung was positively correlated both with plateau pressure, showing a pronounced increase above 26 to 27 cm H(2)O, and with regional Vt normalized by end-expiratory lung gas volume. This relationship did not appear to be caused by a higher underlying parenchymal metabolic activity in patients with higher plateau pressure. Regions undergoing cyclic recruitment-derecruitment did not have higher metabolic activity than those collapsed throughout the respiratory cycle.

CONCLUSIONS

In patients with ALI managed with relatively high end-expiratory pressure, metabolic activity of aerated regions was associated with both plateau pressure and regional Vt normalized by end-expiratory lung gas volume, whereas no association was found between cyclic recruitment-derecruitment and increased metabolic activity.