Adenosine signaling pathways as potential therapeutic targets in respiratory disease

Berberine attenuates epithelial mesenchymal transition in bleomycin-induced pulmonary fibrosis in mice via activating A2aR and mitigating the SDF-1/CXCR4 signaling

AIMS

Berberine is endowed with anti-oxidant, anti-inflammatory and anti-fibrotic effects. This study explored the role of adenosine A_2a receptor (A_2aR) activation and SDF-1/CXCR4 signaling suppression in the protective effects of berberine in bleomycin-induced pulmonary fibrosis in mice.

MAIN METHODS

Pulmonary fibrosis was generated in mice by injecting bleomycin (40 U/kg, i.p.) on days 0, 3, 7, 10 and 14. Mice were treated with berberine (5 mg/kg, i.p.) from day 15 to day 28.

KEY FINDINGS

Severe lung fibrosis and increased collagen content were observed in the bleomycin-challenged mice. Pulmonary A_2aR downregulation was documented in bleomycin-induced pulmonary fibrosis animals and was accompanied by enhanced expression of SDF-1/CXCR4. Moreover, TGF-β1elevation and pSmad2/3 overexpression were reported in parallel with enhanced epithelial mesenchymal transition (EMT) markers expression, vimentin and α-SMA. Besides, bleomycin significantly elevated the inflammatory and pro-fibrogenic mediator NF-κB p65, TNF-α and IL-6. Furthermore, bleomycin administration induced oxidative stress as depicted by decreased Nrf2, SOD, GSH and catalase levels. Interestingly, berberine administration markedly ameliorated the fibrotic changes in lungs by modulating the purinergic system through the inhibition of A_2aR downregulation, mitigating EMT and effectively suppressing inflammation and oxidative stress. Strikingly, A_2aR blockade by SCH 58261, impeded the pulmonary protective effect of berberine.

SIGNIFICANCE

These findings indicated that berberine could attenuate the pathological processes of bleomycin-induced pulmonary fibrosis at least partially via upregulating A_2aR and mitigating the SDF-1/CXCR4 related pathway, suggesting A_2aR as a potential therapeutic target for the management of pulmonary fibrosis.

Update on the recent development of allosteric modulators for adenosine receptors and their therapeutic applications

Adenosine receptors (ARs) have been identified as promising therapeutic targets for countless pathological conditions, spanning from inflammatory diseases to central nervous system disorders, from cancer to metabolic diseases, from cardiovascular pathologies to respiratory diseases, and beyond. This extraordinary therapeutic potential is mainly due to the plurality of pathophysiological actions of adenosine and the ubiquitous expression of its receptors. This is, however, a double-edged sword that makes the clinical development of effective ligands with tolerable side effects difficult. Evidence of this is the low number of AR agonists or antagonists that have reached the market. An alternative approach is to target allosteric sites via allosteric modulators, compounds endowed with several advantages over orthosteric ligands. In addition to the typical advantages of allosteric modulators, those acting on ARs could benefit from the fact that adenosine levels are elevated in pathological tissues, thus potentially having negligible effects on normal tissues where adenosine levels are maintained low. Several A1 and various A3AR allosteric modulators have been identified so far, and some of them have been validated in different preclinical settings, achieving promising results. Less fruitful, instead, has been the discovery of A2A and A2BAR allosteric modulators, although the results obtained up to now are encouraging. Collectively, data in the literature suggests that allosteric modulators of ARs could represent valuable pharmacological tools, potentially able to overcome the limitations of orthosteric ligands.

Extracellular metabolism of 3',5'-cyclic AMP as a source of interstitial adenosine in the rat airways

In the respiratory tract, intracellular 3',5'-cAMP mediates smooth muscle relaxation triggered by the β₂-adrenoceptor/Gs protein/adenylyl cyclase axis. More recently, we have shown that β₂-adrenoceptor agonists also increase extracellular 3',5'-cAMP levels in isolated rat trachea, which leads to contraction of airway smooth muscle. In many other tissues, extracellular 3',5'-cAMP is metabolized by ectoenzymes to extracellular adenosine, a catabolic pathway that has never been addressed in airways. In order to evaluate the possible extracellular degradation of 3',5'-cAMP into 5'-AMP and adenosine in the airways, isolated rat tracheas were incubated with exogenous 3',5'-cAMP and the amount of 5'-AMP, adenosine and inosine (adenosine metabolite) produced was evaluated using ultraperformance liquid chromatography-tandem mass spectrometry. Incubation of tracheal tissue with 3',5'-cAMP induced a time- and concentration-dependent increase in 5'-AMP, adenosine and inosine in the medium. Importantly, IBMX (non-selective phosphodiesterase (PDE) inhibitor) and DPSPX (selective ecto-PDE inhibitor) reduced the extracellular conversion of 3',5'-cAMP to 5'-AMP. In addition, incubation of 3',5'-cAMP in the presence of AMPCP (inhibitor of ecto-5'-nucleotidase) increased extracellular levels of 5'-AMP while drastically reducing extracellular levels of adenosine and inosine. These results indicate that airways express an extracellular enzymatic system (ecto-phosphodiesterase, ecto-5'-nucleotidase and adenosine deaminase) that sequentially converts 3',5'-cAMP into 5'-AMP, adenosine and inosine. The observation that extracellular 3',5'-cAMP is a source of interstitial adenosine supports the idea that the extrusion and extracellular metabolism of 3',5'-cAMP has a role in respiratory physiology and pathophysiology.

Adenosine Signaling in Mast Cells and Allergic Diseases

Adenosine is a nucleoside involved in the pathogenesis of allergic diseases. Its effects are mediated through its binding to G protein-coupled receptors: A1, A2a, A2b and A3. The receptors differ in the type of G protein they recruit, in the effect on adenylyl cyclase (AC) activity and the downstream signaling pathway triggered. Adenosine can produce both an enhancement and an inhibition of mast cell degranulation, indicating that adenosine effects on these receptors is controversial and remains to be clarified. Depending on the study model, A1, A2b, and A3 receptors have shown anti- or pro-inflammatory activity. However, most studies reported an anti-inflammatory activity of A2a receptor. The precise knowledge of the adenosine mechanism of action may allow to develop more efficient therapies for allergic diseases by using selective agonist and antagonist against specific receptor subtypes.

Medicinal Chemistry and Therapeutic Potential of Agonists, Antagonists and Allosteric Modulators of A1 Adenosine Receptor: Current Status and Perspectives

Adenosine is a purine nucleoside, responsible for the regulation of a wide range of physiological and pathophysiological conditions by binding with four G-protein-coupled receptors (GPCRs), namely A1, A2A, A2B and A3 adenosine receptors (ARs). In particular, A1 AR is ubiquitously present, mediating a variety of physiological processes throughout the body, thus represents a promising drug target for the management of various pathological conditions. Agonists of A1 AR are found to be useful for the treatment of atrial arrhythmia, angina, type-2 diabetes, glaucoma, neuropathic pain, epilepsy, depression and Huntington's disease, whereas antagonists are being investigated for the treatment of diuresis, congestive heart failure, asthma, COPD, anxiety and dementia. However, treatment with full A1 AR agonists has been associated with numerous challenges like cardiovascular side effects, off-target activation as well as desensitization of A1 AR leading to tachyphylaxis. In this regard, partial agonists of A1 AR have been found to be beneficial in enhancing insulin sensitivity and subsequently reducing blood glucose level, while avoiding severe CVS side effects and tachyphylaxis. Allosteric enhancer of A1 AR is found to be potent for the treatment of neuropathic pain, culminating the side effects related to off-target tissue activation of A1 AR. This review provides an overview of the medicinal chemistry and therapeutic potential of various agonists/partial agonists, antagonists and allosteric modulators of A1 AR, with a particular emphasis on their current status and future perspectives in clinical settings.

The Alexipharmic Mechanisms of Five Licorice Ingredients Involved in CYP450 and Nrf2 Pathways in Paraquat-Induced Mice Acute Lung Injury

Oxidative stress is an important mechanism in acute lung injury (ALI) induced by paraquat (PQ), one of the most widely used herbicides in developing countries. In clinical prophylaxis and treatment, licorice is a widely used herbal medicine in China due to its strong alexipharmic characteristics. However, the corresponding biochemical mechanism of antioxidation and detoxification enzymes induced by licorice's ingredients is still not fully demonstrated. In this study, the detoxification effect of licorice was evaluated in vivo and in vitro. The detoxification and antioxidation effect of its active ingredients involved in the treatment was screened systematically according to Absorption, Distribution, Metabolism, and Excretion (ADME): predictions and evidence-based literature mining methods in silico approach. Data shows that licorice alleviate pulmonary edema and fibrosis, decrease Malondialdehyde (MDA) contents and increase Superoxide Dismutase (SOD) activity in PQ-induced ALI mice, protect the morphologic appearance of lung tissues, induce cytochrome 3A4 (CYA3A4) and Nuclear factor erythroid 2-related factor 2 (Nrf2) expression to active detoxification pathways, reduce the accumulation of PQ in vivo, protect or improve the liver and renal function of mice, and increase the survival rate. The 104 genes of PPI network contained all targets of licorice ingredients and PQ, which displayed the two redox regulatory enzymatic group modules cytochrome P450 (CYP450) and Nrf2 via a score-related graphic theoretic clustering algorithm in silico. According to ADME properties, glycyrol, isolicoflavonol, licochalcone A, 18beta-glycyrrhetinic acid, and licoisoflavone A were employed due to their oral bioavailability (OB) ≥ 30%, drug-likeness (DL) ≥ 0.1, and being highly associated with CYP450 and Nrf2 pathways, as potential activators to halt PQ-induced cells death in vitro. Both 3A4 inhibitor and silenced Nrf2 gene decreased the alexipharmic effects of those ingredients significantly. All these disclosed the detoxification and antioxidation effects of licorice on acute lung injury induced by PQ, and glycyrol, isolicoflavonol, licochalcone A, 18beta-glycyrrhetinic acid, and licoisoflavone A upregulated CYP450 and Nrf2 pathways underlying the alexipharmic mechanisms of licorice.

Pharmacology of Adenosine Receptors: The State of the Art

Adenosine is a ubiquitous endogenous autacoid whose effects are triggered through the enrollment of four G protein-coupled receptors: A₁, A_2A, A_2B, and A₃. Due to the rapid generation of adenosine from cellular metabolism, and the widespread distribution of its receptor subtypes in almost all organs and tissues, this nucleoside induces a multitude of physiopathological effects, regulating central nervous, cardiovascular, peripheral, and immune systems. It is becoming clear that the expression patterns of adenosine receptors vary among cell types, lending weight to the idea that they may be both markers of pathologies and useful targets for novel drugs. This review offers an overview of current knowledge on adenosine receptors, including their characteristic structural features, molecular interactions and cellular functions, as well as their essential roles in pain, cancer, and neurodegenerative, inflammatory, and autoimmune diseases. Finally, we highlight the latest findings on molecules capable of targeting adenosine receptors and report which stage of drug development they have reached.

Proteases and Their Inhibitors in Chronic Obstructive Pulmonary Disease

In the context of respiratory disease, chronic obstructive pulmonary disease (COPD) is the leading cause of mortality worldwide. Despite much development in the area of drug development, currently there are no effective medicines available for the treatment of this disease. An imbalance in the protease: Antiprotease ratio in the COPD lung remains an important aspect of COPD pathophysiology and several studies have shown the efficacy of antiprotease therapy in both in vitro and in vivo COPD models. However more in-depth studies will be required to validate the efficacy of lead drug molecules targeting these proteases. This review discusses the current status of protease-directed drugs used for treating COPD and explores the future prospects of utilizing the potential of antiprotease-based therapeutics as a treatment for this disease.

Toll-Like Receptor 7/8 Ligand, S28463, Suppresses Ascaris suum-induced Allergic Asthma in Nonhuman Primates

S28463 (S28), a ligand for Toll-like receptor 7/8, has been shown to have antiinflammatory properties in rodent models of allergic asthma. The principle goal of this study was to assess whether these antiinflammatory effects can also be observed in a nonhuman primate (NHP) model of allergic asthma. NHPs were sensitized then challenged with natural allergen, Ascaris suum extract. The animals were treated with S28 orally before each allergen challenge. The protective effect of S28 in NHPs was assessed by measuring various asthma-related phenotypes. We also characterized the metabolomic and proteomic signatures of the lung environment and plasma to identify markers associated with the disease and treatment. Our data demonstrate that clinically relevant parameters, such as wheal and flare response, blood IgE levels, recruitment of white blood cells to the bronchoalveolar space, and lung responsiveness, are decreased in the S28-treated allergic NHPs compared with nontreated allergic NHPs. Furthermore, we also identified markers that can distinguish allergic from nonallergic or allergic and drug-treated NHPs, such as metabolites, phosphocreatine and glutathione, in the plasma and BAL fluid, respectively; and inflammatory cytokines, IL-5 and IL-13, in the bronchoalveolar lavage fluid. Our preclinical study demonstrates that S28 has potential as a treatment for allergic asthma in primate species closely related to humans. Combined with our previous findings, we demonstrate that S28 is effective in different models of asthma and in different species, and has the antiinflammatory properties clinically relevant for the treatment of allergic asthma.

Prediction of consensus binding mode geometries for related chemical series of positive allosteric modulators of adenosine and muscarinic acetylcholine receptors

Following insights from recent crystal structures of the muscarinic acetylcholine receptor, binding modes of Positive Allosteric Modulators (PAMs) were predicted under the assumption that PAMs should bind to the extracellular surface of the active state. A series of well-characterized PAMs for adenosine (A1 R, A2A R, A3 R) and muscarinic acetylcholine (M1 R, M5 R) receptors were modeled using both rigid and flexible receptor CHARMM-based molecular docking. Studies of adenosine receptors investigated the molecular basis of the probe-dependence of PAM activity by modeling in complex with specific agonist radioligands. Consensus binding modes map common pharmacophore features of several chemical series to specific binding interactions. These models provide a rationalization of how PAM binding slows agonist radioligand dissociation kinetics. M1 R PAMs were predicted to bind in the analogous M2 R PAM LY2119620 binding site. The M5 R NAM (ML-375) was predicted to bind in the PAM (ML-380) binding site with a unique induced-fit receptor conformation. © 2017 Wiley Periodicals, Inc.

Evaluation of Serum Adenosine Deaminase in Cystic Fibrosis Patients in an Iranian Referral Hospital

BACKGROUND

Adenosine, a signaling nucleoside, is controlled in part by the enzyme adenosine deaminase (ADA). There are rare reports on the role of adenosine levels and ADA in cystic fibrosis (CF) patients.

OBJECTIVES

The aim of this study was to assess serum ADA in CF patients in order to find whether the severity of lung disease in CF is related to significant changes of ADA or not.

PATIENTS AND METHODS

Venous blood serum ADA was measured in CF patients (3-15 years) and 49 healthy children (3-15 years) referred to Children's Medical Center. Classification of respiratory and gastrointestinal disease severity in CF patients as well as Body Mass Index (BMI) was performed. The results were compared with values obtained from healthy children matched for age and gender.

RESULTS

This study included 49 children of both genders (20 females and 29 males) with CF (mean age: 6.36 ± 2.22 years). Mean serum ADA in CF patients group and control group was 9.38 ± 2.72 and 16.04 ± 1.27, respectively (P value = 0.001). Mean serum ADA in CF patients with normal BMI was higher than in patients with low BMI (P value = 0.002).

CONCLUSIONS

In this study the lower serum level of ADA was seen in CF patients compared to control group. The clinical symptoms, especially respiratory symptoms, in CF patients might be associated with reduction of serum ADA and rising serum adenosine; therefore, further studies on the use of ADA enzyme therapy in CF patients are highly recommended.

Ecto-5'-nucleotidase CD73 modulates the innate immune response to influenza infection but is not required for development of influenza-induced acute lung injury

Extracellular nucleotides and nucleosides are important signaling molecules in the lung. Nucleotide and nucleoside concentrations in alveolar lining fluid are controlled by a complex network of surface ectonucleotidases. Previously, we demonstrated that influenza A/WSN/33 (H1N1) virus resulted in increased levels of the nucleotide ATP and the nucleoside adenosine in bronchoalveolar lavage fluid (BALF) of wild-type (WT) C57BL/6 mice. Influenza-induced acute lung injury (ALI) was highly attenuated in A1-adenosine receptor-knockout mice. Because AMP hydrolysis by the ecto-5'-nucleotidase (CD73) plays a central role in and is rate-limiting for generation of adenosine in the normal lung, we hypothesized that ALI would be attenuated in C57BL/6-congenic CD73-knockout (CD73-KO) mice. Infection-induced hypoxemia, bradycardia, viral replication, and bronchoconstriction were moderately increased in CD73-KO mice relative to WT controls. However, postinfection weight loss, pulmonary edema, and parenchymal dysfunction were not altered. Treatment of WT mice with the CD73 inhibitor 5'-(α,β-methylene) diphosphate (APCP) also had no effect on infection-induced pulmonary edema but modestly attenuated hypoxemia. BALF from CD73-KO and APCP-treated WT mice contained more IL-6 and CXCL-10/IFN-γ-induced protein 10, less CXCL-1/keratinocyte chemoattractant, and fewer neutrophils than BALF from untreated WT controls. BALF from APCP-treated WT mice also contained fewer alveolar macrophages and more transforming growth factor-β than BALF from untreated WT mice. These results indicate that CD73 is not necessary for development of ALI following influenza A virus infection and suggest that tissue-nonspecific alkaline phosphatase may be responsible for increased adenosine generation in the infected lung. However, they do suggest that CD73 has a previously unrecognized immunomodulatory role in influenza.

The discovery of a selective and potent A2a agonist with extended lung retention

Although the anti-inflammatory role of the A2a receptor is well established, controversy remains with regard to the therapeutic value for A2a agonists in treatment of inflammatory lung diseases, also as a result of unwanted A2a-mediated cardiovascular effects. In this paper, we describe the discovery and characterization of a new, potent and selective A2a agonist (compound 2) with prolonged lung retention and limited systemic exposure following local administration. To support the lead optimization chemistry program with compound selection and profiling, multiple in vitro and in vivo assays were used, characterizing compound properties, pharmacodynamics (PD), and drug concentrations. Particularly, pharmacokinetic-PD modeling was applied to quantify the effects on the cardiovascular system, and an investigative toxicology study in rats was performed to explore potential myocardial toxicities. Compound 2, in comparison to a reference A2a agonist, UK-432,097, demonstrated higher solubility, lower lipophilicity, lower plasma protein binding, high rat lung retention (28% remaining after 24 h), and was efficacious in a lung inflammatory rat model following intratracheal dosing. Despite these properties, compound 2 did not provide a sufficient therapeutic index, that is, separation of local anti-inflammatory efficacy in the lung from systemic side effects in the cardiovascular system. The plasma concentration that resulted in induction of hypotension (half maximal effective concentration; EC50 0.5 nmol/L) correlated to the in vitro A2a potency (rIC50 0.6 nmol/L). Histopathological lesions in the heart were observed at a dose level which is threefold above the efficacious dose level in the inflammatory rat lung model. In conclusion, compound 2 is a highly potent and selective A2a agonist with significant lung retention after intratracheal administration. Despite its local anti-inflammatory efficacy in rat lung, small margins to the cardiovascular effects suggested limited therapeutic value of this compound for treatment of inflammatory lung disease by the inhaled route.

The role of the adenosinergic system in lung fibrosis

Adenosine (ADO) is a retaliatory metabolite that is expressed in conditions of injury or stress. During these conditions ATP is released at the extracellular level and is metabolized to adenosine. For this reason, adenosine is defined as a "danger signal" for cells and organs, in addition to its important role as homeostatic regulator. Its physiological functions are mediated through interaction with four specific transmembrane receptors called ADORA1, ADORA2A, ADORA2B and ADORA3. In the lungs of mice and humans all four adenosine receptors are expressed with different roles, having pro- and anti-inflammatory roles, determining bronchoconstriction and regulating lung inflammation and airway remodeling. Adenosine receptors can also promote differentiation of lung fibroblasts into myofibroblasts, typical of the fibrotic event. This last function suggests a potential involvement of adenosine in the fibrotic lung disease processes, which are characterized by different degrees of inflammation and fibrosis. Idiopathic pulmonary fibrosis (IPF) is the pathology with the highest degree of fibrosis and is of unknown etiology and burdened by lack of effective treatments in humans.