Adenosine receptors in COPD and asymptomatic smokers: effects of smoking cessation

Analysis of the Clinical Efficacy and Molecular Mechanism of Xuefu Zhuyu Decoction in the Treatment of COPD Based on Meta-Analysis and Network Pharmacology

Background

Chronic obstructive pulmonary disease (COPD) is becoming a major public health burden worldwide. It is urgent to explore more effective and safer treatment strategy for COPD. Notably, Xuefu Zhuyu Decoction (XFZYD) is widely used to treat respiratory system diseases, including COPD, in China.

Objective

This study is aimed at comprehensively evaluating the therapeutic effects and molecular mechanism of XFZYD on COPD.

Methods

Original clinical studies were searched from eight literature databases. Meta-analysis was conducted using the Review Manager software (version 5.4.1). Network pharmacology and molecular docking experiments were utilized to explore the mechanisms of action of XFZYD.

Results

XFZYD significantly enhanced the efficacy of clinical treatment and improved the pulmonary function and hypoventilation of COPD patients. In addition, XFZYD significantly improved the hypercoagulability of COPD patients. The subgroup analysis suggested that XFZYD exhibited therapeutic effects on both stable and acute exacerbation of COPD. XFZYD exerted its therapeutic effects on COPD through multicomponent, multitarget, and multipathway characteristics. The intervention of the PI3K-AKT pathway may be the critical mechanism.

Conclusion

The application of XFZYD based on symptomatic relief and supportive treatment is a promising clinical decision. More preclinical and clinical studies are still needed to evaluate the safety and therapeutic effects of long-term use of XFZYD on COPD.

Evaluation of Plasma Adenosine as a Marker of Cardiovascular Risk: Analytical and Biological Considerations

Background

Adenosine is a ubiquitous regulatory molecule known to modulate signaling in many cells and processes vital to vascular homeostasis. While studies of adenosine receptors have dominated research in the field, quantification of adenosine systemically and locally remains limited owing largely to technical restrictions. Given the potential clinical implications of adenosine biology, there is a need for adequately powered studies examining the role of plasma adenosine in vascular health. We sought to describe the analytical and biological factors that affect quantification of adenosine in humans in a large, real‐world cohort of patients undergoing evaluation for coronary artery disease.

Methods and Results

Between November 2016 and April 2018, we assessed 1141 patients undergoing angiography for evaluation of coronary artery disease. High‐performance liquid chromatography was used for quantification of plasma adenosine concentration, yielding an analytical coefficient of variance (CV_a) of 3.2%, intra‐subject variance (CV_i) 35.8% and inter‐subject variance (CV_g) 56.7%. Traditional cardiovascular risk factors, medications, and clinical presentation had no significant impact on adenosine levels. Conversely, increasing age (P=0.027) and the presence of obstructive coronary artery disease (P=0.026) were associated with lower adenosine levels. Adjusted multivariable analysis supported only age being inversely associated with adenosine levels (P=0.039).

Conclusions

Plasma adenosine is not significantly impacted by traditional cardiovascular risk factors; however, advancing age and presence of obstructive coronary artery disease may be associated with lower adenosine levels. The degree of intra‐ and inter‐subject variance of adenosine has important implications for biomarker use as a prognosticator of cardiovascular outcomes and as an end point in clinical studies.

Roflumilast combined with adenosine increases mucosal hydration in human airway epithelial cultures after cigarette smoke exposure

Chronic obstructive pulmonary disease (COPD) is a growing cause of morbidity and mortality worldwide. Recent studies have shown that cigarette smoke (CS) induces cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction, which leads to airway-surface liquid (ASL) dehydration. This in turn contributes to the mucus dehydration and impaired mucociliary clearance that are seen in the chronic bronchitis form of COPD. Roflumilast is a phosphodiesterase 4 inhibitor that may improve lung function and reduce the frequency of exacerbations in patients with COPD. Although roflumilast can affect cAMP metabolism, little is known about the downstream pharmacological effects in the airways. We hypothesized that roflumilast would increase ASL rehydration in human bronchial epithelial cultures (HBECs) after chronic CS exposure. cAMP production was measured by Förster resonance energy transfer in HEK293T cells and by ELISA in HBECs. ASL height was measured by xz-confocal microscopy after air exposure or following HBEC exposure to freshly produced CS. Roflumilast had little effect on cAMP or ASL height when applied on its own; however, roflumilast significantly potentiated adenosine-induced increases in cAMP and ASL height in CS-exposed HBECs. Roflumilast increased the rate of ASL height recovery in cultures after CS exposure compared with controls. In contrast, the β2-adrenergic receptor agonists isoproterenol and salmeterol failed to increase ASL height after CS exposure. Our data suggest that roflumilast can increase ASL hydration in CS-exposed HBECs, which is predicted to be beneficial for the treatment of mucus dehydration/mucus stasis in patients with COPD chronic bronchitis.

Transient and persistent metabolomic changes in plasma following chronic cigarette smoke exposure in a mouse model

Cigarette smoke exposure is linked to the development of a variety of chronic lung and systemic diseases in susceptible individuals. Metabolomics approaches may aid in defining disease phenotypes, may help predict responses to treatment, and could identify biomarkers of risk for developing disease. Using a mouse model of chronic cigarette smoke exposure sufficient to cause mild emphysema, we investigated whether cigarette smoke induces distinct metabolic profiles and determined their persistence following smoking cessation. Metabolites were extracted from plasma and fractionated based on chemical class using liquid-liquid and solid-phase extraction prior to performing liquid chromatography mass spectrometry-based metabolomics. Metabolites were evaluated for statistically significant differences among group means (p-value≤0.05) and fold change ≥1.5). Cigarette smoke exposure was associated with significant differences in amino acid, purine, lipid, fatty acid, and steroid metabolite levels compared to air exposed animals. Whereas 60% of the metabolite changes were reversible, 40% of metabolites remained persistently altered even following 2 months of smoking cessation, including nicotine metabolites. Validation of metabolite species and translation of these findings to human plasma metabolite signatures induced by cigarette smoking may lead to the discovery of biomarkers or pathogenic pathways of smoking-induced disease.

Smoke extract impairs adenosine wound healing: implications of smoke-generated reactive oxygen species

Adenosine concentrations are elevated in the lungs of patients with asthma and chronic obstructive pulmonary disease, where it balances between tissue repair and excessive airway remodeling. We previously demonstrated that the activation of the adenosine A2A receptor promotes epithelial wound closure. However, the mechanism by which adenosine-mediated wound healing occurs after cigarette smoke exposure has not been investigated. The present study investigates whether cigarette smoke exposure alters adenosine-mediated reparative properties via its ability to induce a shift in the oxidant/antioxidant balance. Using an in vitro wounding model, bronchial epithelial cells were exposed to 5% cigarette smoke extract, were wounded, and were then stimulated with either 10 μM adenosine or the specific A2A receptor agonist, 5'-(N-cyclopropyl)-carboxamido-adenosine (CPCA; 10 μM), and assessed for wound closure. In a subset of experiments, bronchial epithelial cells were infected with adenovirus vectors encoding human superoxide dismutase and/or catalase or control vector. In the presence of 5% smoke extract, significant delay was evident in both adenosine-mediated and CPCA-mediated wound closure. However, cells pretreated with N-acetylcysteine (NAC), a nonspecific antioxidant, reversed smoke extract-mediated inhibition. We found that cells overexpressing mitochondrial catalase repealed the smoke extract inhibition of CPCA-stimulated wound closure, whereas superoxide dismutase overexpression exerted no effect. Kinase experiments revealed that smoke extract significantly reduced the A2A-mediated activation of cyclic adenosine monophosphate-dependent protein kinase. However, pretreatment with NAC reversed this effect. In conclusion, our data suggest that cigarette smoke exposure impairs A2A-stimulated wound repair via a reactive oxygen species-dependent mechanism, thereby providing a better understanding of adenosine signaling that may direct the development of pharmacological tools for the treatment of chronic inflammatory lung disorders.

Purinergic signaling in the airways

Evidence for a significant role and impact of purinergic signaling in normal and diseased airways is now beyond dispute. The present review intends to provide the current state of knowledge of the involvement of purinergic pathways in the upper and lower airways and lungs, thereby differentiating the involvement of different tissues, such as the epithelial lining, immune cells, airway smooth muscle, vasculature, peripheral and central innervation, and neuroendocrine system. In addition to the vast number of well illustrated functions for purinergic signaling in the healthy respiratory tract, increasing data pointing to enhanced levels of ATP and/or adenosine in airway secretions of patients with airway damage and respiratory diseases corroborates the emerging view that purines act as clinically important mediators resulting in either proinflammatory or protective responses. Purinergic signaling has been implicated in lung injury and in the pathogenesis of a wide range of respiratory disorders and diseases, including asthma, chronic obstructive pulmonary disease, inflammation, cystic fibrosis, lung cancer, and pulmonary hypertension. These ostensibly enigmatic actions are based on widely different mechanisms, which are influenced by the cellular microenvironment, but especially the subtypes of purine receptors involved and the activity of distinct members of the ectonucleotidase family, the latter being potential protein targets for therapeutic implementation.

Elevated airway purines in COPD

BACKGROUND

Adenosine and related purines have established roles in inflammation, and elevated airway concentrations are predicted in patients with COPD. However, accurate airway surface purine measurements can be confounded by stimulation of purine release during collection of typical respiratory samples.

METHODS

Airway samples were collected noninvasively as exhaled breath condensate (EBC) from 36 healthy nonsmokers (NS group), 28 healthy smokers (S group), and 89 subjects with COPD (29 with GOLD [Global Initiative for Chronic Obstructive Lung Disease] stage II, 29 with GOLD stage III, and 31 with GOLD stage IV) and analyzed with mass spectrometry for adenosine, adenosine monophosphate (AMP), and phenylalanine, plus urea as a dilution marker. Variable dilution of airway secretions in EBC was controlled using ratios to urea, and airway surface concentrations were calculated using EBC to serum urea-based dilution factors.

RESULTS

EBC adenosine to urea ratios were similar in NS (0.20 ± 0.21) and S (0.22 ± 0.20) groups but elevated in those with COPD (0.32 ± 0.30, P < .01 vs NS). Adenosine to urea ratios were highest in the most severely affected cohort (GOLD IV, 0.35 ± 0.34, P < .01 vs NS) and negatively correlated with FEV(1) (r = -0.27, P < .01). Elevated AMP to urea ratios were also observed in the COPD group (0.58 ± 0.97 COPD, 0.29 ± 0.35 NS, P < .02), but phenylalanine to urea ratios were similar in all groups. Airway surface adenosine concentrations calculated in a subset of subjects were 3.2 ± 2.7 μM in those with COPD (n = 28) relative to 1.7 ± 1.5 μM in the NS group (n = 16, P < .05).

CONCLUSIONS

Airway purines are present on airway surfaces at physiologically significant concentrations, are elevated in COPD, and correlate with markers of COPD severity. Purinergic signaling pathways are potential therapeutic targets in COPD, and EBC purines are potential noninvasive biomarkers.