Adenosine deaminase levels in premature infants with respiratory distress syndrome and bronchopulmonary dysplasia

Prevention of Oxygen-Induced Inflammatory Lung Injury by Caffeine in Neonatal Rats

Background

Preterm birth implies an array of respiratory diseases including apnea of prematurity and bronchopulmonary dysplasia (BPD). Caffeine has been introduced to treat apneas but also appears to reduce rates of BPD. Oxygen is essential when treating preterm infants with respiratory problems but high oxygen exposure aggravates BPD. This experimental study is aimed at investigating the action of caffeine on inflammatory response and cell death in pulmonary tissue in a hyperoxia-based model of BPD in the newborn rat. Material/Methods. Lung injury was induced by hyperoxic exposure with 80% oxygen for three (P3) or five (P5) postnatal days with or without recovery in ambient air until postnatal day 15 (P15). Newborn Wistar rats were treated with PBS or caffeine (10 mg/kg) every two days beginning at the day of birth. The effects of caffeine on hyperoxic-induced pulmonary inflammatory response were examined at P3 and P5 immediately after oxygen exposure or after recovery in ambient air (P15) by immunohistological staining and analysis of lung homogenates by ELISA and qPCR.

Results

Treatment with caffeine significantly attenuated changes in hyperoxia-induced cell death and apoptosis-associated factors. There was a significant decrease in proinflammatory mediators and redox-sensitive transcription factor NFκB in the hyperoxia-exposed lung tissue of the caffeine-treated group compared to the nontreated group. Moreover, treatment with caffeine under hyperoxia modulated the transcription of the adenosine receptor (Adora)1. Caffeine induced pulmonary chemokine and cytokine transcription followed by immune cell infiltration of alveolar macrophages as well as increased adenosine receptor (Adora1, 2a, and 2b) expression.

Conclusions

The present study investigating the impact of caffeine on the inflammatory response, pulmonary cell degeneration and modulation of adenosine receptor expression, provides further evidence that caffeine acts as an antioxidative and anti-inflammatory drug for experimental oxygen-mediated lung injury. Experimental studies may broaden the understanding of therapeutic use of caffeine in modulating detrimental mechanisms involved in BPD development.

Loss of CD73-mediated extracellular adenosine production exacerbates inflammation and abnormal alveolar development in newborn mice exposed to prolonged hyperoxia

BackgroundHyperoxic lung injury is characterized by cellular damage from high oxygen concentrations that lead to an inflammatory response and it disrupts normal alveolarization in the developing newborn lung. Adenosine is a signaling molecule that is generated extracellularly by ecto-5'-nucleotidase (CD73) in response to injury. Extracellular adenosine signals through cell surface receptors and has been found to have a protective role in acute injury situations; however, chronic elevations have been associated with detrimental changes in chronic lung diseases. We hypothesized that hyperoxia-induced lung injury leads to CD73-mediated increases in extracellular adenosine, which are detrimental to the newborn lung.MethodsC57Bl/6 and CD73-/- mice were exposed to 95% oxygen, 70% oxygen, or room air. Adenosine concentration and markers of pulmonary inflammation and lung development were measured.ResultsExposure to hyperoxia caused pulmonary inflammation and disrupted normal alveolar development in association with increased pulmonary adenosine levels. Loss of CD73-mediated extracellular adenosine production led to decreased survival with exposure to 95% oxygen, and exacerbated pulmonary inflammation and worsened lung development with 70% oxygen exposure.ConclusionExposure to hyperoxia causes lung injury associated with an increase in adenosine concentration, and loss of CD73-mediated adenosine production leads to worsening of hyperoxic lung injury.Pediatric Research advance online publication, 23 August 2017; doi:10.1038/pr.2017.176.

Postnatal development and LPS responsiveness of pulmonary adenosine receptor expression and of adenosine-metabolizing enzymes in mice

BACKGROUND

Adenosine levels are regulated by ecto-5'-nucleotidase/CD73 and adenosine deaminase (ADA). Adenosine regulates endothelial permeability and anti-inflammatory responses via adenosine receptors. Here, the adenosine receptors and purine-converting enzymes were studied during postnatal development and inflammation.

METHODS

Newborn, 1-, 10-, 14-d-old and adult C57BL/6 mice were challenged intraperitoneally (i.p.) with lipopolysaccharide (LPS) for 6 h. The inflammatory response was evaluated by histochemistry. Expression levels of adenosine receptors (A1, A2A, A2B, and A3), CD73, and ADA were measured by quantitative reverse transcription polymerase chain reaction. A1 was studied by immunohistochemistry, and enzyme activities were analyzed by thin-layer chromatography.

RESULTS

LPS caused respiratory distress in newborns within 24 h. LPS induced neutrophils at the basal stage and alveolar congestion. Low activity and expression of CD73 increased after birth. Expression of ADA after LPS increased 16-fold in adults and 2-fold in newborns (P < 0.05). A1 expression was high in newborns and increased after LPS (P < 0.05). A1 was localized to endothelial membranes. A2A decreased after LPS in newborns and increased in adults (P < 0.05). The expression of A3 increased in newborns and adults after LPS.

CONCLUSION

Low pulmonary CD73 expression, LPS-induced suppression of A2A, LPS-induced increase of A1 expression, and severe respiratory distress were distinguishing responses in the newborns from those in the adults.

Caffeine induces alveolar apoptosis in the hyperoxia-exposed developing mouse lung

BACKGROUND

Caffeine is a nonspecific adenosine receptor antagonist used in premature neonates to treat apnea of prematurity. While its use may reduce the incidence of bronchopulmonary dysplasia (BPD), the precise mechanisms remain unknown. Evidence of increased adenosine levels are noted in chronic lung diseases including tracheal aspirates of infants with BPD. Utilizing a well-characterized newborn mouse model of alveolar hypoplasia, we hypothesized that hyperoxia-induced alveolar inflammation and hypoplasia is associated with alterations in the adenosine signaling pathway.

METHODS

Newborn murine pups were exposed to a 14-d period of hyperoxia and daily caffeine administration followed by a 14-d recovery period in room air. Lungs were collected at both time points for bronchoalveolar lavage (BAL) analysis as well as histopathology and mRNA and protein expression.

RESULTS

Caffeine treatment increased inflammation and worsened alveolar hypoplasia in hyperoxia-exposed newborn mice. These changes were associated with decreased alveolar type II (ATII) cell numbers, increased cell apoptosis, and decreased expression of A2A receptors. Following discontinuation of caffeine and hyperoxia, lung histology returned to baseline levels comparable to hyperoxia exposure alone.

CONCLUSION

Results of this study suggest a potentially adverse role of caffeine on alveolar development in a murine model of hyperoxia-induced alveolar hypoplasia.

A new way of thinking about complications of prematurity

The morbidity and mortality of preterm infants are impacted by their ability to maintain physiologic homeostasis using metabolic, endocrine, and immunologic mechanisms independent of the mother's placenta. Exploring McEwen's allostatic load model in preterm infants provides a new way to understand the altered physiologic processes associated with frequently occurring complications of prematurity such as bronchopulmonary dysplasia, intraventricular hemorrhage, necrotizing enterocolitis, and retinopathy of prematurity. The purpose of this article is to present a new model to enhance understanding of the altered physiologic processes associated with complications of prematurity. The model of allostatic load and complications of prematurity was derived to explore the relationship between general stress of prematurity and complications of prematurity. The proposed model uses the concepts of general stress of prematurity, allostasis, physiologic response patterns (adaptive-maladaptive), allostatic load, and complications of prematurity. These concepts are defined and theoretical relationships in the proposed model are interpreted using the four maladaptive response patterns of repeated hits, lack of adaptation, prolonged response, and inadequate response. Empirical evidence for cortisol, inflammation, and oxidative stress responses are used to support the theoretical relationships. The proposed model provides a new way of thinking about physiologic dysregulation in preterm infants. The ability to describe and understand complex physiologic mechanisms involved in complications of prematurity is essential for research. Advancing the knowledge of complications of prematurity will advance clinical practice and research and lead to testing of interventions to reduce negative outcomes in preterm infants.