Adenosine: an old drug newly discovered

Attenuation of HIV-Specific T Cell Responses Among People with HIV on art Following Dipyridamole Treatment

Twelve weeks of dipyridamole increased extracellular adenosine levels and decreased T cell activation in people with HIV. In this analysis, we investigated the effect of dipyridamole on HIV-specific T cell responses. We compared changes in Gag- and Env-specific T cell responses using intracellular cytokine staining, following 12 weeks of dipyridamole treatment vs placebo. We evaluated whether frequencies of polyfunctional HIV-specific T cells were associated with purines in the adenosine pathway and with measures of HIV persistence and chronic inflammation. There was a significant decrease in CD4+ polyfunctional T cell responses to Gag (-62.6% vs -23.0%; p<0.001) and Env (-56.1% vs -6.0%; p<0.001) in the dipyridamole arm. In the dipyridamole group, lower frequencies of polyfunctional Env-specific CD4+ T cells were associated with higher plasma levels of adenosine (r= -0.85; p<0.01) and inosine (r= -0.70; p=0.04). Higher adenosine levels induced by dipyridamole treatment is associated with decreased HIV-specific CD4+ T cell polyfunctional responses in people with HIV on antiretroviral therapy.

Fludarabine-induced bradycardia in allogeneic hematopoietic stem cell transplantation: A retrospective study

INTRODUCTION

Fludarabine, a purine analog, is getting more attention with the increasing use of reduced intensive conditioning regimens in allogeneic hematopoietic stem cell transplantation (allo-HSCT). The side effect of bradycardia was observed in only a few cases reported in the literature. In clinical practice, bradycardia can be asymptomatic or cause syncope and cardiac arrest. This study aimed to evaluate the bradycardia side effect of fludarabine used in the conditioning regimen in allo-HSCT recipients and to increase awareness of this issue.

METHODS

This retrospective study included 73 patients who received fludarabine in the allo-HSCT conditioning regimen between January 2015 and January 2021. Patients with and without bradycardia were compared regarding demographic data, allo-HSCT characteristics, electrolyte values, fludarabine administration dose and duration, and survival. Univariate and multivariate analyzes were performed to evaluate independent predictors for fludarabine-induced bradycardia.

RESULTS

Fludarabine administration doses and days were higher in the bradycardia group, but no statistically significant difference was observed. In the multivariate analysis, age was the only independent predictor of fludarabine-induced bradycardia (odds ratio (OR) 0.93, 95% confidence interval (CI): 0.89-0.98, p = 0.007). The median age in the group with bradycardia was 19 years younger than those without bradycardia (34 (19-49) vs 53 (19-69), p = 0.005). In 11 (84.6%) of the patients who had bradycardia, bradycardia improved with the discontinuation of fludarabine alone, but atropine was administered in 2 (15.4%) patients.

CONCLUSION

Age was the only independent predictor of fludarabine-induced bradycardia; therefore, close heart rate monitoring is recommended during fludarabine administration, especially in younger patients.

CD73 polymorphisms are associated with schizophrenia

Ecto-5'-nucleotidase/CD73 enzyme plays a key role in the regulation of extracellular adenosine levels, thereby exerting influence on adenosine homeostasis. Emerging evidence suggests that perturbations in purines and ecto-5'-nucleotidase activity are associated with an augmented susceptibility to schizophrenia. However, the precise impact of genetic variations in CD73 on individuals with schizophrenia remains poorly understood. Here, our study demonstrated that rs3734442 allele and rs4431401 heterozygote were conferred a significant risk of schizophrenia disease (rs3734442: odds ratio, 0.556; 95% CI, 0.375 to 0.825; p = 0.004; rs4431401: odds ratio, 1.881, 95% CI, 1.117 to 3.166; p = 0.020). Comparing different genders, we observed a significant association between rs3734442 genotypes and male cases (rs3734442: odds ratio, 0.452; 95% CI, 0.257 to 0.796; p = 0.007). Likewise, there was a significant association between rs4431401 genotypes and male patients (rs4431401: odds ratio, 2.570; 95% CI, 1.196 to 5.522; p = 0.015). Based on family history and antipsychotics medication usage, our data reveals that the rs9444348 allele exhibits the most significant association with familial susceptibility to schizophrenia (odds ratio, 1.541; 95% CI, 1.009 to 2.353; p = 0.048 for A vs G). Moreover, individuals carrying variants of rs6922, rs2229523, and rs2065114 while being treated with clozapine demonstrate a higher frequency proportion compared to those receiving risperidone treatment (p = 0.035; p = 0.049; p = 0.027 respectively). Additionally, our results indicate that patients with GG genotype of rs9444348 had significantly higher likelihood of using clozapine instead of sulpiride (p = 0.048). Overall, our data strongly suggest that genetic variations in CD73 are significantly associated with schizophrenia risk and may serve as valuable resources for identifying therapeutic targets.

Integration of metabolomics and transcriptomics reveals the therapeutic mechanism underlying Chelidonium majus L. in the treatment of allergic asthma

BACKGROUND

Chelidonium majus is a well-known traditional Chinese medicine, and has been reported of the effect in relieving cough and asthma. However, the mechanism of action is still unknown.

METHODS

Asthmatic SD rats were first sensitized and established through ovalbumin (OVA) motivation. Subsequently, Hematoxylin and eosin (H&E) staining, Masson's trichrome (Masson) staining, Periodic acid-Schiff (PAS) staining and inflammatory cytokines assay of interleukin (IL)-4, IL-6, IL-17 were implemented to evaluate the protective effects of Chelidonium majus on asthma. Then, the effects of Chelidonium majus and their molecular mechanisms of action on asthma were detected based on the integration of transcriptomics and metabolomics analyses.

RESULTS

After administration with Chelidonium majus, the histological injuries of inflammation, collagen deposition and mucus secretion in lungs were attenuated and the serum inflammatory cytokines perturbations were also converted. Furthermore, integrated analysis revealed that after Chelidonium majus treatment, 7 different expression genes (DEGs) (Alox15, P4ha1, Pla2g16, Pde3a, Nme1, Entpd8 and Adcy9) and 9 metabolic biomarkers (ADP, Xanthosine, Hypoxanthine, Inosine, prostaglandin E2 (PGE2), prostaglandin F2a (PGF2a), phosphatidylserine, Creatine and LysoPC (10:0)) were discovered to be connected with the enrichment metabolic pathways, including Purine metabolism, Arachidonic acid metabolism, Arginine and proline metabolism and Glycerophospholipid metabolism. The obtained metabolic biomarkers and DEGs were mainly related to energy metabolism and inflammation, and may be potential therapeutic targets.

CONCLUSION

Chelidonium majus relieved OVA-induced asthma in rats by regulating the Alox15, P4ha1, Pla2g16, Pde3a, Nme1, Entpd8 and Adcy9 genes expression to restore the disorders in energy metabolism and inflammation.

Torsades de pointes and myocardial infarction following reversal of supraventricular tachycardia with adenosine: a case report

Adenosine is an antiarrhythmic drug that slows conduction through the atrioventricular node and acts as a coronary blood vessel dilator. This case report highlights two unusual life-threatening events following the use of adenosine to revert supraventricular tachycardia in a structurally normal heart: non-sustained polymorphic ventricular tachycardia and myocardial infarction. A 46-year-old woman presented to the emergency department with a two-hour history of palpitations and was diagnosed with supraventricular tachycardia. Vagal maneuvers were ineffective, and after intravenous adenosine administration, the patient presented with chest pain and hypotension. The rhythm degenerated into non-sustained polymorphic ventricular tachycardia and spontaneously reverted to sinus rhythm with ST elevation in lead aVR and ST depression in the inferior and anterolateral leads. The patient spontaneously recovered within a few minutes. Despite successful arrhythmia reversal, the patient was admitted to the intensive care unit because of an infarction without obstructive atherosclerosis. This report aims to alert emergency physicians about the potential complications associated with supraventricular tachycardia and its reversal with adenosine.

Circadian Influences on Myocardial Ischemia-Reperfusion Injury and Heart Failure

The impact of circadian rhythms on cardiovascular function and disease development is well established, with numerous studies in genetically modified animals emphasizing the circadian molecular clock's significance in the pathogenesis and pathophysiology of myocardial ischemia and heart failure progression. However, translational preclinical studies targeting the heart's circadian biology are just now emerging and are leading to the development of a novel field of medicine termed circadian medicine. In this review, we explore circadian molecular mechanisms and novel therapies, including (1) intense light, (2) small molecules modulating the circadian mechanism, and (3) chronotherapies such as cardiovascular drugs and meal timings. These promise significant clinical translation in circadian medicine for cardiovascular disease. (4) Additionally, we address the differential functioning of the circadian mechanism in males versus females, emphasizing the consideration of biological sex, gender, and aging in circadian therapies for cardiovascular disease.

Biochemical evaluation and ligand binding studies on glycerophosphodiester phosphodiesterase from Staphylococcus aureus using STD-NMR spectroscopy and molecular docking analysis

Glycerophosphodiester phosphodiesterase (GDPD) is a highly conserved enzyme in both prokaryotic and eukaryotic organisms. It catalyses the hydrolysis of various glycerophosphodiesters into glycerol-3-phosphate and corresponding alcohols, which serve as building blocks in several biosynthetic pathways. This enzyme is a well-known virulence factor in many pathogenic bacteria, including Staphylococcus aureus, and is thus considered a potential drug target. In this study, competent E. coli BL21(DE3)pLysS expression cells were used to express the GDPD enzyme from vancomycin-resistant Staphylococcus aureus (VRSA), which was then purified using size exclusion and anion exchange chromatography. The hydrolytic activity of GDPD was evaluated on the non-physiological substrate bis(p-nitrophenyl) phosphate (BpNPP), which indicated functional activity of the enzyme. 79 drugs were evaluated for their inhibitory potential against GDPD enzyme by the colorimetric assay. Out of 79 drugs, 13 drugs, including tenofovir (1), adenosine (2), clioquinol (11), bromazepam (12), lamotrigine (13), sulfadiazine (14), azathioprine (15), nicotine (16), sitagliptin PO4 (17), doxofylline (18), clindamycin phosphate (19), gentamycin sulphate (20), and ceftriaxone sodium (21) revealed varying degrees of inhibitory potential with IC50 values in the range of 400 ± 0.007-951 ± 0.016 µM. All drugs were also evaluated for their binding interactions with the target enzyme by saturation transfer difference (STD-NMR) spectroscopy. 10 drugs demonstrated STD interactions and hence, showed binding affinity with the enzyme. Exceptionally, tenofovir (1) was identified to be a better inhibitor with an IC50 value of 400 ± 0.007 µM, as compared to the standard EDTA (ethylenediaminetetraacetic acid) (IC50 = 470 ± 0.008 µM). Moreover, molecular docking studies have identified key interactions of the ligand (tenofovir) with the binding site residues of the enzyme.

Therapeutic potency of A1 adenosine receptor antagonists in the treatment of cardiovascular diseases, current status and perspectives

BACKGROUND

Cardiomyocytes form, transport, and metabolize the omnipresent metabolite adenosine. Depending upon the adenosine concentrations and the pharmacological properties of receptor subtypes, adenosine exerts (patho)physiological responses in the cardiovascular system. The objective of this review is to present different protective mechanisms of A1-adenosine receptor inhibitors in cardiovascular diseases.

METHODS AND RESULTS

Literature references were collected and sorted using relevant keywords and key phrases as search terms in scientific databases such as Web of Science, PubMed and Google Scholar. A1 adenosine receptor regulates free fatty acid metabolism, lipolysis, heart rate, blood pressure, and cardiovascular toxicity. The evidence clearly supporting the therapeutic potency of pharmacological A1 adenosine receptors agonists and antagonists in modulating cardiovascular risk factor parameters and treatment of cardiovascular diseases.

CONCLUSION

This review summarizes the protective role of pharmacological A1-adenosine receptor regulators in the pathogenesis of cardiovascular diseases for a better management of cardiovascular diseases.

Pathomechanisms of Prenatally Programmed Adult Diseases

Based on epidemiological observations Barker et al. put forward the hypothesis/concept that an adverse intrauterine environment (involving an insufficient nutrient supply, chronic hypoxia, stress, and toxic substances) is an important risk factor for the development of chronic diseases later in life. The fetus responds to the unfavorable environment with adaptive reactions, which ensure survival in the short run, but at the expense of initiating pathological processes leading to adult diseases. In this review, the major mechanisms (including telomere dysfunction, epigenetic modifications, and cardiovascular-renal-endocrine-metabolic reactions) will be outlined, with a particular emphasis on the role of oxidative stress in the fetal origin of adult diseases.

Assessment of Squalene-Adenosine Nanoparticles in Two Rodent Models of Cardiac Ischemia-Reperfusion

Reperfusion injuries after a period of cardiac ischemia are known to lead to pathological modifications or even death. Among the different therapeutic options proposed, adenosine, a small molecule with platelet anti-aggregate and anti-inflammatory properties, has shown encouraging results in clinical trials. However, its clinical use is severely limited because of its very short half-life in the bloodstream. To overcome this limitation, we have proposed a strategy to encapsulate adenosine in squalene-based nanoparticles (NPs), a biocompatible and biodegradable lipid. Thus, the aim of this study was to assess, whether squalene-based nanoparticles loaded with adenosine (SQAd NPs) were cardioprotective in a preclinical cardiac ischemia/reperfusion model. Obtained SQAd NPs were characterized in depth and further evaluated in vitro. The NPs were formulated with a size of about 90 nm and remained stable up to 14 days at both 4 °C and room temperature. Moreover, these NPs did not show any signs of toxicity, neither on HL-1, H9c2 cardiac cell lines, nor on human PBMC and, further retained their inhibitory platelet aggregation properties. In a mouse model with experimental cardiac ischemia-reperfusion, treatment with SQAd NPs showed a reduction of the area at risk, as well as of the infarct area, although not statistically significant. However, we noted a significant reduction of apoptotic cells on cardiac tissue from animals treated with the NPs. Further studies would be interesting to understand how and through which mechanisms these nanoparticles act on cardiac cells.

Targeting myocardial equilibrative nucleoside transporter ENT1 provides cardioprotection by enhancing myeloid Adora2b signaling

Previous studies implicate extracellular adenosine signaling in attenuating myocardial ischemia and reperfusion injury (IRI). This extracellular adenosine signaling is terminated by its uptake into cells by equilibrative nucleoside transporters (ENTs). Thus, we hypothesized that targeting ENTs would function to increase cardiac adenosine signaling and concomitant cardioprotection against IRI. Mice were exposed to myocardial ischemia and reperfusion injury. Myocardial injury was attenuated in mice treated with the nonspecific ENT inhibitor dipyridamole. A comparison of mice with global Ent1 or Ent2 deletion showed cardioprotection only in Ent1-/- mice. Moreover, studies with tissue-specific Ent deletion revealed that mice with myocyte-specific Ent1 deletion (Ent1loxP/loxP Myosin Cre+ mice) experienced smaller infarct sizes. Measurements of cardiac adenosine levels demonstrated that postischemic elevations of adenosine persisted during reperfusion after targeting ENTs. Finally, studies in mice with global or myeloid-specific deletion of the Adora2b adenosine receptor (Adora2bloxP/loxP LysM Cre+ mice) implied that Adora2b signaling on myeloid-inflammatory cells in cardioprotection provided by ENT inhibition. These studies reveal a previously unrecognized role for myocyte-specific ENT1 in cardioprotection by enhancing myeloid-dependent Adora2b signaling during reperfusion. Extension of these findings implicates adenosine transporter inhibitors in cardioprotection against ischemia and reperfusion injury.

The resurgence of the Adora2b receptor as an immunotherapeutic target in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense desmoplastic stroma that impedes drug delivery, reduces parenchymal blood flow, and suppresses the anti-tumor immune response. The extracellular matrix and abundance of stromal cells result in severe hypoxia within the tumor microenvironment (TME), and emerging publications evaluating PDAC tumorigenesis have shown the adenosine signaling pathway promotes an immunosuppressive TME and contributes to the overall low survival rate. Hypoxia increases many elements of the adenosine signaling pathway, resulting in higher adenosine levels in the TME, further contributing to immune suppression. Extracellular adenosine signals through 4 adenosine receptors (Adora1, Adora2a, Adora2b, Adora3). Of the 4 receptors, Adora2b has the lowest affinity for adenosine and thus, has important consequences when stimulated by adenosine binding in the hypoxic TME. We and others have shown that Adora2b is present in normal pancreas tissue, and in injured or diseased pancreatic tissue, Adora2b levels are significantly elevated. The Adora2b receptor is present on many immune cells, including macrophages, dendritic cells, natural killer cells, natural killer T cells, γδ T cells, B cells, T cells, CD4+ T cells, and CD8+ T cells. In these immune cell types, adenosine signaling through Adora2b can reduce the adaptive anti-tumor response, augmenting immune suppression, or may contribute to transformation and changes in fibrosis, perineural invasion, or the vasculature by binding the Adora2b receptor on neoplastic epithelial cells, cancer-associated fibroblasts, blood vessels, lymphatic vessels, and nerves. In this review, we discuss the mechanistic consequences of Adora2b activation on cell types in the tumor microenvironment. As the cell-autonomous role of adenosine signaling through Adora2b has not been comprehensively studied in pancreatic cancer cells, we will also discuss published data from other malignancies to infer emerging therapeutic considerations for targeting the Adora2b adenosine receptor to reduce the proliferative, invasive, and metastatic potential of PDAC cells.

Understanding metabolic alterations after SARS-CoV-2 infection: insights from the patients' oral microenvironmental metabolites

BACKGROUND

Coronavirus disease 2019 is a type of acute infectious pneumonia and frequently confused with influenza since the initial symptoms. When the virus colonized the patient's mouth, it will cause changes of the oral microenvironment. However, few studies on the alterations of metabolism of the oral microenvironment affected by SARS-CoV-2 infection have been reported. In this study, we explored metabolic alterations of oral microenvironment after SARS-CoV-2 infection.

METHODS

Untargeted metabolomics (UPLC-MS) was used to investigate the metabolic changes between oral secretion samples of 25 COVID-19 and 30 control participants. To obtain the specific metabolic changes of COVID-19, we selected 25 influenza patients to exclude the metabolic changes caused by the stress response of the immune system to the virus. Multivariate analysis (PCA and PLS-DA plots) and univariate analysis (students' t-test) were used to compare the differences between COVID-19 patients and the controls. Online hiplot tool was used to perform heatmap analysis. Metabolic pathway analysis was conducted by using the MetaboAnalyst 5.0 web application.

RESULTS

PLS-DA plots showed significant separation of COVID-19 patients and the controls. A total of 45 differential metabolites between COVID-19 and control group were identified. Among them, 35 metabolites were defined as SARS-CoV-2 specific differential metabolites. Especially, the levels of cis-5,8,11,14,17-eicosapentaenoic acid and hexanoic acid changed dramatically based on the FC values. Pathway enrichment found the most significant pathways were tyrosine-related metabolism. Further, we found 10 differential metabolites caused by the virus indicating the body's metabolism changes after viral stimulation. Moreover, adenine and adenosine were defined as influenza virus-specific differential metabolites.

CONCLUSIONS

This study revealed that 35 metabolites and tyrosine-related metabolism pathways were significantly changed after SARS-CoV-2 infection. The metabolic alterations of oral microenvironment in COVID-19 provided new insights into its molecular mechanisms for research and prognostic treatment.

Endless Journey of Adenosine Signaling in Cardioprotective Mechanism of Conditioning Techniques: Clinical Evidence

Myocardial ischemic injury is a primary cause of death among various cardiovascular disorders. The condition occurs due to an interrupted supply of blood and vital nutrients (necessary for normal cellular activities and viability) to the myocardium, eventually leading to damage. Restoration of blood supply to ischemic tissue is noted to cause even more lethal reperfusion injury. Various strategies, including some conditioning techniques, like preconditioning and postconditioning, have been developed to check the detrimental effects of reperfusion injury. Many endogenous substances have been proposed to act as initiators, mediators, and end effectors of these conditioning techniques. Substances, like adenosine, bradykinin, acetylcholine, angiotensin, norepinephrine, opioids, etc., have been reported to mediate cardioprotective activity. Among these agents, adenosine has been widely studied and suggested to have the most pronounced cardioprotective effects. The current review article highlights the role of adenosine signaling in the cardioprotective mechanism of conditioning techniques. The article also provides an insight into various clinical studies that substantiate the applicability of adenosine as a cardioprotective agent in myocardial reperfusion injury.

Discovery of Hepatotoxic Equivalent Markers and Mechanism of Polygonum multiflorum Thunb. by Metabolomics Coupled with Molecular Docking

Polygonum multiflorum Thunb. (PMT), a commonly used Chinese herbal medicine for treating diseases such as poisoning and white hair, has attracted constant attention due to the frequent occurrence of liver injury incidents. To date, its hepatotoxic equivalent markers (HEMs) and potential hepatotoxic mechanisms are still unclear. In order to clarify the HEMs of PMT and further explore the potential mechanisms of hepatotoxicity, firstly, the chemical constituents in PMT extract were globally characterized, and the fingerprints of PMT extracts were established along with the detection of their hepatotoxicity in vivo. Then, the correlations between hepatotoxic features and component contents were modeled by chemometrics to screen HEMs of PMT, which were then further evaluated. Finally, the hepatotoxic mechanisms of PMT were investigated using liver metabolomics and molecular docking. The results show that the chemical combination of 2,3,5,4-tetrahydroxystilbene-2-O-β-D-glucoside (TSG) and emodin-8-O-glucoside (EG) was discovered as the HEMs of PMT through pre-screening and verifying process. Liver metabolomics revealed that PMT caused liver injury by interfering with purine metabolism, which might be related to mitochondrial function disorder and oxidative injury via the up-regulations of xanthosine and xanthine, and the down-regulation of 5' nucleotidase (NT5E) and adenylate kinase 2 (AK2). This study not only found that the HEMs of PMT were TSG and EG, but also clarified that PMT might affect purine metabolism to induce liver injury, which contributed to our understanding of the underlying mechanisms of PMT hepatotoxicity.

Nucleoside transporters and immunosuppressive adenosine signaling in the tumor microenvironment: Potential therapeutic opportunities

Adenosine compartmentalization has a profound impact on immune cell function by regulating adenosine localization and, therefore, extracellular signaling capabilities, which suppresses immune cell function in the tumor microenvironment. Nucleoside transporters, responsible for the translocation and cellular compartmentalization of hydrophilic adenosine, represent an understudied yet crucial component of adenosine disposition in the tumor microenvironment. In this review article, we will summarize what is known regarding nucleoside transporter's function within the purinome in relation to currently devised points of intervention (i.e., ectonucleotidases, adenosine receptors) for cancer immunotherapy, alterations in nucleoside transporter expression reported in cancer, and potential avenues for targeting of nucleoside transporters for the desired modulation of adenosine compartmentalization and action. Further, we put forward that nucleoside transporters are an unexplored therapeutic opportunity, and modulation of nucleoside transport processes could attenuate the pathogenic buildup of immunosuppressive adenosine in solid tumors, particularly those enriched with nucleoside transport proteins.

Discovery and Structure-Activity Relationship Studies of Novel Adenosine A1 Receptor-Selective Agonists

A series of benzyloxy and phenoxy derivatives of the adenosine receptor agonists N6-cyclopentyl adenosine (CPA) and N6-cyclopentyl 5'-N-ethylcarboxamidoadenosine (CP-NECA) were synthesized, and their potency and selectivity were assessed. We observed that the most potent were the compounds with a halogen in the meta position on the aromatic ring of the benzyloxy- or phenoxycyclopentyl substituent. In general, the NECA-based compounds displayed greater A1R selectivity than the adenosine-based compounds, with N6-2-(3-bromobenzyloxy)cyclopentyl-NECA and N6-2-(3-methoxyphenoxy)cyclopentyl-NECA showing ∼1500-fold improved A1R selectivity compared to NECA. In addition, we quantified the compounds' affinity and kinetics of binding at both human and rat A1R using a NanoBRET binding assay and found that the halogen substituent in the benzyloxy- or phenoxycyclopentyl moiety seems to confer high affinity for the A1R. Molecular modeling studies suggested a hydrophobic subpocket as contributing to the A1R selectivity displayed. We believe that the identified selective potent A1R agonists are valuable tool compounds for adenosine receptor research.

Serum adenosine deaminase activity and acute cerebral infarction: a retrospective case-control study based on 7913 participants

BACKGROUND

Adenosine deaminase (ADA) is a key enzyme that catalyzes the deamination of adenosine into inosine, which eventually decomposes into uric acid (UA). A body of papers have reported that adenosine and UA are closely related to cerebrovascular events. However, the association between serum ADA activity and acute cerebral infarction (ACI) remains unclear.

METHODS

7913 subjects were enrolled, including 3968 ACI patients and 3945 controls, in this study. An automatic biochemistry analyzer was used to determine serum activity.

RESULTS

Serum ADA activity was found that was significantly decreased in patients with ACI (10.10 ± 3.72 U/L) compared to those without ACI (11.07 ± 2.85 U/L, p < 0.001). After Logistic regression analysis, ADA concentrations were negatively correlated with ACI (OR = 1.161, 95% CI: 1.140-1.183, p < 0.001). Smoking and alcohol consumption decreased serum ADA concentrations in patients with ACI, whereas diabetes and hypertension had the opposite effect.

CONCLUSIONS

Serum ADA concentrations in patients with ACI are markedly decreased, suggesting that the decreased ADA concentrations may be involved in the pathogenesis of ACI. We hypothesized that decreased ADA activity may be an adaptive mechanism to maintain adenosine levels and protect against ischemic brain injury.

Alternative adenosine Receptor activation: The netrin-Adora2b link

During hypoxia or inflammation, extracellular adenosine levels are elevated. Studies using pharmacologic approaches or genetic animal models pertinent to extracellular adenosine signaling implicate this pathway in attenuating hypoxia-associated inflammation. There are four distinct adenosine receptors. Of these, it is not surprising that the Adora2b adenosine receptor functions as an endogenous feedback loop to control hypoxia-associated inflammation. First, Adora2b activation requires higher adenosine concentrations compared to other adenosine receptors, similar to those achieved during hypoxic inflammation. Second, Adora2b is transcriptionally induced during hypoxia or inflammation by hypoxia-inducible transcription factor HIF1A. Studies seeking an alternative adenosine receptor activation mechanism have linked netrin-1 with Adora2b. Netrin-1 was originally discovered as a neuronal guidance molecule but also functions as an immune-modulatory signaling molecule. Similar to Adora2b, netrin-1 is induced by HIF1A, and has been shown to enhance Adora2b signaling. Studies of acute respiratory distress syndrome (ARDS), intestinal inflammation, myocardial or hepatic ischemia and reperfusion implicate the netrin-Adora2b link in tissue protection. In this review, we will discuss the potential molecular linkage between netrin-1 and Adora2b, and explore studies demonstrating interactions between netrin-1 and Adora2b in attenuating tissue inflammation.

Plants with Therapeutic Potential for Ischemic Acute Kidney Injury: A Systematic Review

Acute kidney injury (AKI) is a complex condition which has an intricate pathology mostly involving hemodynamic, inflammatory, and direct toxic effects at the cellular level with high morbidity and mortality ratios. Renal ischemic reperfusion injury (RIRI) is the main factor responsible for AKI, most often observed in different types of shock, kidney transplantation, sepsis, and postoperative procedures. The RIRI-induced AKI is accompanied by increased reactive oxygen species generation together with the activation of various inflammatory pathways. In this context, plant-derived medicines have shown encouraging nephroprotective properties. Evidence provided in this systemic review leads to the conclusion that plant-derived extracts and compounds exhibit nephroprotective action against renal ischemic reperfusion induced-AKI by increasing endogenous antioxidants and decreasing anti-inflammatory cytokines. However, there is no defined biomarker or target which can be used for treating AKI completely. These plant-derived extracts and compounds are only tested in selected transgenic animal models. To develop the results obtained into a therapeutic entity, one should apply them in proper vertebrate multitransgenic animal models prior to further validation in humans.

Repurposing Dipyridamole in Niemann Pick Type C Disease: A Proof of Concept Study

Niemann Pick type C disease (NPC) is a rare disorder characterized by lysosomal lipid accumulation that damages peripheral organs and the central nervous system. Currently, only miglustat is authorized for NPC treatment in Europe, and thus the identification of new therapies is necessary. The hypothesis addressed in this study is that increasing adenosine levels may represent a new therapeutic approach for NPC. In fact, a reduced level of adenosine has been shown in the brain of animal models of NPC; moreover, the compound T1-11, which is able to weakly stimulate A_2A receptor and to increase adenosine levels by blocking the equilibrative nucleoside transporter ENT1, significantly ameliorated the pathological phenotype and extended the survival in a mouse model of the disease. To test our hypothesis, fibroblasts from NPC1 patients were treated with dipyridamole, a clinically-approved drug with inhibitory activity towards ENT1. Dipyridamole significantly reduced cholesterol accumulation in fibroblasts and rescued mitochondrial deficits; the mechanism elicited by dipyridamole relies on activation of the adenosine A_2AR subtype subsequent to the increased levels of extracellular adenosine due to the inhibition of ENT1. In conclusion, our results provide the proof of concept that targeting adenosine tone could be beneficial in NPC.

Inosine as a Tool to Understand and Treat Central Nervous System Disorders: A Neglected Actor?

Since the 1970s, when ATP was identified as a co-transmitter in sympathetic and parasympathetic nerves, it and its active metabolite adenosine have been considered relevant signaling molecules in biological and pathological processes in the central nervous system (CNS). Meanwhile, inosine, a naturally occurring purine nucleoside formed by adenosine breakdown, was considered an inert adenosine metabolite and remained a neglected actor on the purinergic signaling scene in the CNS. However, this scenario began to change in the 1980s. In the last four decades, an extensive group of shreds of evidence has supported the importance of mediated effects by inosine in the CNS. Also, inosine was identified as a natural trigger of adenosine receptors. This evidence has shed light on the therapeutic potential of inosine on disease processes involved in neurological and psychiatric disorders. Here, we highlight the clinical and preclinical studies investigating the involvement of inosine in chronic pain, schizophrenia, epilepsy, depression, anxiety, and in neural regeneration and neurodegenerative diseases, such as Parkinson and Alzheimer. Thus, we hope that this review will strengthen the knowledge and stimulate more studies about the effects promoted by inosine in neurological and psychiatric disorders.

Targeting circadian PER2 as therapy in myocardial ischemia and reperfusion injury

The cycle of day and night dominates life on earth. Therefore, almost all living organisms adopted a molecular clock linked to the light-dark cycles. It is now well established that this molecular clock is crucial for human health and wellbeing. Disruption of the molecular clockwork directly results in a myriad of disorders, including cardiovascular diseases. Further, the onset of many cardiovascular diseases such as acute myocardial infarction exhibits a circadian periodicity with worse outcomes in the early morning hours. Based on these observations, the research community became interested in manipulating the molecular clock to treat cardiovascular diseases. In recent years, several exciting discoveries of pharmacological agents or molecular mechanisms targeting the molecular clockwork have paved the way for circadian medicine's arrival in cardiovascular diseases. The current review will outline the most recent circadian therapeutic advances related to the circadian rhythm protein Period2 (PER2) to treat myocardial ischemia and summarize future research in the respective field.

Tackling retinal ganglion cell apoptosis in glaucoma: role of adenosine receptors

INTRODUCTION

The role of adenosine receptors as therapeutic targets for neuroprotection is now widely recognized. Their role, however, in protection against retinal ganglion cell (RGC) apoptosis in glaucoma needs further investigation. Hence, in this review, we look into the possibility of adenosine receptors as potential therapeutic targets by exploring their role in modulating various pathophysiological mechanisms underlying glaucomatous RGC loss.

AREAS COVERED

This review presents a summary of the adenosine receptor distribution in retina and the cellular functions mediated by them. The major pathophysiological mechanisms such as excitotoxicity, vascular dysregulation, loss of neurotrophic signaling, and inflammatory responses involved in glaucomatous RGC loss are discussed. The literature showing the role of adenosine receptors in modulating these pathophysiological mechanisms is discussed. The literature search was conducted using Pubmed search engine using key words such as 'RGC apoptosis,' 'adenosine,' adenosine receptors' 'retina' 'excitotoxicity,' 'neurotrophins,' 'ischemia', and 'cytokines' individually and in various combinations.

EXPERT OPINION

Use of adenosine receptor agonists and antagonists, for preservation of the RGCs in glaucomatous eyes independent of the level of intraocular pressure seems a very useful strategy. Future application of this strategy would require appropriate designing of drug formulation for tissue and disease-specific receptor targeting. Furthermore, the modulation of physiological functions and potential adverse effects need further investigations.

Dual Actions of A2A and A3 Adenosine Receptor Ligand Prevents Obstruction-Induced Kidney Fibrosis in Mice

Kidney fibrosis is the final outcome of chronic kidney disease (CKD). Adenosine plays a significant role in protection against cellular damage by activating four subtypes of adenosine receptors (ARs), A₁AR, A_2AAR, A_2BAR, and A₃AR. A_2AAR agonists protect against inflammation, and A₃AR antagonists effectively inhibit the formation of fibrosis. Here, we showed for the first time that LJ-4459, a newly synthesized dual-acting ligand that is an A_2AAR agonist and an A₃AR antagonist, prevents the progression of tubulointerstitial fibrosis. Unilateral ureteral obstruction (UUO) surgery was performed on 6-week-old male C57BL/6 mice. LJ-4459 (1 and 10 mg/kg) was orally administered for 7 days, started at 1 day before UUO surgery. Pretreatment with LJ-4459 improved kidney morphology and prevented the progression of tubular injury as shown by decreases in urinary kidney injury molecular-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) excretion. Obstruction-induced tubulointerstitial fibrosis was attenuated by LJ-4459, as shown by a decrease in fibrotic protein expression in the kidney. LJ-4459 also inhibited inflammation and oxidative stress in the obstructed kidney, with reduced macrophage infiltration, reduced levels of pro-inflammatory cytokines, as well as reduced levels of reactive oxygen species (ROS). These data demonstrate that LJ-4459 has potential as a therapeutic agent against the progression of tubulointerstitial fibrosis.

Enhancing Extracellular Adenosine Levels Restores Barrier Function in Acute Lung Injury Through Expression of Focal Adhesion Proteins

Background: Acute respiratory distress syndrome (ARDS) is a clinical presentation of acute lung injury (ALI) with often fatal lung complication. Adenosine, a nucleoside generated following cellular stress provides protective effects in acute injury. The levels of extracellular adenosine can be depleted by equilibrative nucleoside transporters (ENTs). ENT inhibition by pharmaceutical agent dipyridamole promotes extracellular adenosine accumulation and is protective in ARDS. However, the therapeutic potential of dipyridamole in acute lung injury has not yet been evaluated. Methods: Adenosine acts on three adenosine receptors, the adenosine A1 (Adora1), A2a (Adora2a), the A2b (Adora2b) or the adenosine A3 (Adora 3) receptor. Accumulation of adenosine is usually required to stimulate the low-affinity Adora2b receptor. In order to investigate the effect of adenosine accumulation and the contribution of epithelial-specific ENT2 or adora2b expression in experimental ALI, dipyridamole, and epithelial specific ENT2 or Adora2b deficient mice were utilized. MLE12 cells were used to probe downstream Adora2b signaling. Adenosine receptors, transporters, and targets were determined in ARDS lungs. Results: ENT2 is mainly expressed in alveolar epithelial cells and is negatively regulated by hypoxia following tissue injury. Enhancing adenosine levels with ENT1/ENT2 inhibitor dipyridamole at a time when bleomycin-induced ALI was present, reduced further injury. Mice pretreated with the ADORA2B agonist BAY 60-6583 were protected from bleomycin-induced ALI by reducing vascular leakage (558.6 ± 50.4 vs. 379.9 ± 70.4, p < 0.05), total bronchoalveolar lavage fluid cell numbers (17.9 ± 1.8 to 13.4 ± 1.4 e4, p < 0.05), and neutrophil infiltration (6.42 ± 0.25 vs. 3.94 ± 0.29, p < 0.05). While mice lacking Adora2b in AECs were no longer protected by dipyridamole. We also identified occludin and focal adhesion kinase as downstream targets of ADORA2B, thus providing a novel mechanism for adenosine-mediated barrier protection. Similarly, we also observed similar enhanced ADORA2B (3.33 ± 0.67 to 16.12 ± 5.89, p < 0.05) and decreased occludin (81.2 ± 0.3 to 13.3 ± 0.4, p < 0.05) levels in human Acute respiratory distress syndrome lungs. Conclusion: We have highlighted a role of dipyridamole and adenosine signaling in preventing or treating ALI and identified Ent2 and Adora2b as key mediators in important for the resolution of ALI.

Purinergic Regulation of Endothelial Barrier Function

Increased vascular permeability is a hallmark of several cardiovascular anomalies, including ischaemia/reperfusion injury and inflammation. During both ischaemia/reperfusion and inflammation, massive amounts of various nucleotides, particularly adenosine 5'-triphosphate (ATP) and adenosine, are released that can induce a plethora of signalling pathways via activation of several purinergic receptors and may affect endothelial barrier properties. The nature of the effects on endothelial barrier function may depend on the prevalence and type of purinergic receptors activated in a particular tissue. In this review, we discuss the influence of the activation of various purinergic receptors and downstream signalling pathways on vascular permeability during pathological conditions.

Accelerating Post-SELEX Aptamer Engineering Using Exonuclease Digestion

The systematic evolution of ligands by exponential enrichment (SELEX) process enables the isolation of aptamers from random oligonucleotide libraries. However, it is generally difficult to identify the best aptamer from the resulting sequences, and the selected aptamers often exhibit suboptimal affinity and specificity. Post-SELEX aptamer engineering can improve aptamer performance, but current methods exhibit inherent bias and variable rates of success or require specialized instruments. Here, we describe a generalizable method that utilizes exonuclease III and exonuclease I to interrogate the binding properties of small-molecule-binding aptamers in a rapid, label-free assay. By analyzing an ochratoxin-binding DNA aptamer and six of its mutants, we determined that ligand binding alters the exonuclease digestion kinetics to an extent that closely correlates with the aptamer's ligand affinity. We then utilized this assay to enhance the binding characteristics of a DNA aptamer which binds indiscriminately to ATP, ADP, AMP, and adenosine. We screened 13 mutants derived from this aptamer against all these analogues and identified two new high-affinity aptamers that solely bind to adenosine. We incorporated these two aptamers directly into an electrochemical aptamer-based sensor, which achieved a detection limit of 1 μM adenosine in 50% serum. We also confirmed the generality of our method to characterize target-binding affinities of protein-binding aptamers. We believe our approach is generalizable for DNA aptamers regardless of sequence, structure, and length and could be readily adapted into an automated format for high-throughput engineering of small-molecule-binding aptamers to acquire those with improved binding properties suitable for various applications.

N6-methyladenosine (m6A) is an endogenous A3 adenosine receptor ligand

About 150 post-transcriptional RNA modifications have been identified in all kingdoms of life. During RNA catabolism, most modified nucleosides are resistant to degradation and are released into the extracellular space. In this study, we explored the physiological role of these extracellular modified nucleosides and found that N⁶-methyladenosine (m⁶A), widely recognized as an epigenetic mark in RNA, acts as a ligand for the human adenosine A3 receptor, for which it has greater affinity than unmodified adenosine. We used structural modeling to define the amino acids required for specific binding of m⁶A to the human A3 receptor. We also demonstrated that m⁶A was dynamically released in response to cytotoxic stimuli and facilitated type I allergy in vivo. Our findings implicate m⁶A as a signaling molecule capable of activating G protein-coupled receptors (GPCRs) and triggering pathophysiological responses, a previously unreported property of RNA modifications.

Decreased expression of adenosine receptor 2B confers cardiac protection against ischemia via restoring autophagic flux

Adora2B (adenosine receptor 2B) has been reported as one of the key modulators during cardiac remodeling after acute myocardial infarction (AMI). However, the molecular mechanism involved has not been well investigated. Thus, our study aims to investigate whether Adora2B contributes to cardiac remodeling after AMI and its underlying mechanisms. Adenovirus harboring Adora2B or shAdora2B was injected in the border zone in a mouse model of AMI experimentally produced by permanent ligation of left anterior descending (LAD) coronary artery. Decreased Adora2B expression protected the cardiomyocytes from MI-induced autophagic flux obstacle, improved cardiac function, and reduced fibrosis after MI. Adora2B downregulation attenuated the accumulation of LC3-II and p62, which are autophagy substrate proteins. An adenovirus containing mRFP-GFP-LC3 showed that decreased expression of Adora2B restored the autophagic flux by enhancing autophagosome conversion to autophagolysosome. Also, Adora2B knockdown improved cardiomyocytes' survival and protected mitochondrial function of cardiomyocytes insulted with hypoxia. Notably, the effect of Adora2B on autophagy flux and cardiomyocyte protection could be mitigated by autophagy inhibitor chloroquine. Our results demonstrate that decreased expression of Adora2B protected cardiomyocytes from impaired autophagy flux induced by MI. Modulation Adora2B expression plays a significant role in blunting the worsening of heart function and reducing scar formation, suggesting therapeutic potential by targeting Adora2B in AMI for the infarct healing.

A1 and A2A Receptors Modulate Spontaneous Adenosine but Not Mechanically Stimulated Adenosine in the Caudate

Adenosine is a neuromodulator, and rapid increases in adenosine in the brain occur spontaneously or after mechanical stimulation. However, the regulation of rapid adenosine by adenosine receptors is unclear, and understanding it would allow better manipulation of neuromodulation. The two main adenosine receptors in the brain are A₁ receptors, which are inhibitory, and A_2A receptors, which are excitatory. Here, we investigated the regulation of spontaneous adenosine and mechanically stimulated adenosine by adenosine receptors, using global A₁ or A_2A knockout mice. Results were compared in vivo and in brain slices' models. A₁ KO mice have increased frequency of spontaneous adenosine events, but no change in the average concentration of an event, while A_2A KO mice had no change in frequency but increased average event concentration. Thus, both A₁ and A_2A self-regulate spontaneous adenosine release; however, A₁ acts on the frequency of events, while A_2A receptors regulate concentration. The trends are similar both in vivo and slices, so brain slices are a good model system to study spontaneous adenosine release. For mechanically stimulated adenosine, there was no effect of A₁ or A_2A KO in vivo, but in brain slices, there was a significant increase in concentration evoked in A₁KO mice. Mechanically stimulated release was largely unregulated by A₁ and A_2A receptors, likely because of a different release mechanism than spontaneous adenosine. Thus, A₁ receptors affect the frequency of spontaneous adenosine transients, and A_2A receptors affect the concentration. Therefore, future studies could probe drug treatments targeting A₁ and A_2A receptors to increase rapid adenosine neuromodulation.

Transcription-independent Induction of ERBB1 through Hypoxia-inducible Factor 2A Provides Cardioprotection during Ischemia and Reperfusion

BACKGROUND

During myocardial ischemia, hypoxia-inducible factors are stabilized and provide protection from ischemia and reperfusion injury. Recent studies show that myocyte-specific hypoxia-inducible factor 2A promotes myocardial ischemia tolerance through induction of epidermal growth factor, amphiregulin. Here, the authors hypothesized that hypoxia-inducible factor 2A may enhance epidermal growth factor receptor 1 (ERBB1) expression in the myocardium that could interface between growth factors and its effect on providing tolerance to ischemia and reperfusion injury.

METHODS

Human myocardial tissues were obtained from ischemic heart disease patients and normal control patients to compare ERBB1 expression. Myocyte-specific Hif2a or ErbB1 knockout mice were generated to observe the effect of Hif2a knockdown in regulating ERBB1 expression and to examine the role of ERBB1 during myocardial ischemia and reperfusion injury.

RESULTS

Initial studies of myocardial tissues from patients with ischemic heart disease showed increased ERBB1 protein (1.12 ± 0.24 vs. 13.01 ± 2.20, P < 0.001). In contrast, ERBB1 transcript was unchanged. Studies using short hairpin RNA repression of Hif2A or Hif2a Myosin Cre+ mice directly implicated hypoxia-inducible factor 2A in ERBB1 protein induction during hypoxia or after myocardial ischemia, respectively. Repression of RNA-binding protein 4 abolished hypoxia-inducible factor 2A-dependent induction of ERBB1 protein. Moreover, ErbB1 Myosin Cre+ mice experienced larger infarct sizes (22.46 ± 4.06 vs. 46.14 ± 1.81, P < 0.001) and could not be rescued via amphiregulin treatment.

CONCLUSIONS

These findings suggest that hypoxia-inducible factor 2A promotes transcription-independent induction of ERBB1 protein and implicates epidermal growth factor signaling in protection from myocardial ischemia and reperfusion injury.

Inosine, an endogenous purine nucleoside, avoids early stages of atherosclerosis development associated to eNOS activation and p38 MAPK/NF-kB inhibition in rats

Atherosclerosis is a multifactorial chronic disease, initiated by an endothelial dysfunction. Adenosine and its analogs can change a variety of inflammatory diseases and has shown important effects at different disease models. Inosine is a stable analogous of adenosine, but its effects in inflammatory diseases, like atherosclerosis, have not yet been studied. The aim of this study was to evaluate the pharmacological properties of inosine, administered sub chronically in a hypercholesterolemic model. Male Wistar rats were divided into four groups: control group (C) and control + inosine (C + INO) received standard chow, hypercholesterolemic diet group (HCD) and HCD + inosine (HCD + INO) were fed a hypercholesterolemic diet. At 31st experimentation day, the treatment with inosine was performed for C + INO and HCD + INO groups once daily in the last 15 days. We observed that the hypercholesterolemic diet promoted an increase in lipid levels and inflammatory cytokines production, while inosine treatment strongly decreased these effects. Additionally, HCD group presented a decrease in maximum relaxation acetylcholine induced and an increase in contractile response phenylephrine induced when compared to the control group, as well as it has presented an enhancement in collagen and ADP-induced platelet aggregation. On the other hand, inosine treatment promoted a decrease in contractile response to phenylephrine, evoked an improvement in endothelium-dependent vasorelaxant response and presented antiplatelet properties. Moreover, inosine activated eNOS and reduced p38 MAPK/NF-κB pathway in aortic tissues. Taken together, the present results indicate inosine as a potential drug for the treatment of cardiovascular disorders such as atherosclerosis.

A Randomized, Placebo-Controlled, Pilot Clinical Trial of Dipyridamole to Decrease Human Immunodeficiency Virus-Associated Chronic Inflammation

BACKGROUND

Adenosine is a potent immunoregulatory nucleoside produced during inflammatory states to limit tissue damage. We hypothesized that dipyridamole, which inhibits cellular adenosine uptake, could raise the extracellular adenosine concentration and dampen chronic inflammation associated with human immunodeficiency virus (HIV) type 1.

METHODS

Virally suppressed participants receiving antiretroviral therapy were randomized 1:1 for 12 weeks of dipyridamole (100 mg 4 times a day) versus placebo capsules. All participants took open-label dipyridamole during weeks 12-24. Study end points included changes in markers of systemic inflammation (soluble CD163 and CD14, and interleukin 6) and levels of T-cell immune activation (HLA-DR+CD38+).

RESULTS

Of 40 participants who were randomized, 17 dipyridamole and 18 placebo recipients had baseline and week 12 data available for analyses. There were no significant changes in soluble markers, apart from a trend toward decreased levels of soluble CD163 levels (P = .09). There was a modest decrease in CD8+ T-cell activation (-17.53% change for dipyridamole vs +13.31% for placebo; P = .03), but the significance was lost in the pooled analyses (P = .058). Dipyridamole also reduced CD4+ T-cell activation (-11.11% change; P = .006) in the pooled analyses. In post hoc analysis, detectable plasma dipyridamole levels were associated with higher levels of inosine, an adenosine surrogate, and of cyclic adenosine monophosphate.

CONCLUSION

Dipyridamole increased extracellular adenosine levels and decreased T-cell activation significantly among persons with HIV-1 infection receiving virally suppressive therapy.

Focusing on Adenosine Receptors as a Potential Targeted Therapy in Human Diseases

Adenosine is involved in a range of physiological and pathological effects through membrane-bound receptors linked to G proteins. There are four subtypes of adenosine receptors, described as A1AR, A2AAR, A2BAR, and A3AR, which are the center of cAMP signal pathway-based drug development. Several types of agonists, partial agonists or antagonists, and allosteric substances have been synthesized from these receptors as new therapeutic drug candidates. Research efforts surrounding A1AR and A2AAR are perhaps the most enticing because of their concentration and affinity; however, as a consequence of distressing conditions, both A2BAR and A3AR levels might accumulate. This review focuses on the biological features of each adenosine receptor as the basis of ligand production and describes clinical studies of adenosine receptor-associated pharmaceuticals in human diseases.

Adenosine A2B receptor activation stimulates alveolar fluid clearance through alveolar epithelial sodium channel via cAMP pathway in endotoxin-induced lung injury

Clinical studies have established that the capacity of removing excess fluid from alveoli is impaired in most patients with acute respiratory distress syndrome. Impaired alveolar fluid clearance (AFC) correlates with poor outcomes. Adenosine A_2B receptor (A_2BAR) has the lowest affinity with adenosine among four adenosine receptors. It is documented that A_2BAR can activate adenylyl cyclase (AC) resulting in elevated cAMP. Based on the understanding that cAMP is a key regulator of epithelial sodium channel (ENaC), which is the limited step in sodium transport, we hypothesized that A_2BAR signaling may affect AFC in acute lung injury (ALI) through regulating ENaC via cAMP, thus attenuating pulmonary edema. To address this, we utilized pharmacological approaches to determine the role of A_2BAR in AFC in rats with endotoxin-induced lung injury and further focused on the mechanisms in vitro. We observed elevated pulmonary A_2BAR level in rats with ALI and the similar upregulation in alveolar epithelial cells exposed to LPS. A_2BAR stimulation significantly attenuated pulmonary edema during ALI, an effect that was associated with enhanced AFC and increased ENaC expression. The regulatory effects of A_2BAR on ENaC-α expression were further verified in cultured alveolar epithelial type II (ATII) cells. More importantly, activation of A_2BAR dramatically increased amiloride-sensitive Na⁺ currents in ATII cells. Moreover, we observed that A_2BAR activation stimulated cAMP accumulation, whereas the cAMP inhibitor abolished the regulatory effect of A_2BAR on ENaC-α expression, suggesting that A_2BAR activation regulates ENaC-α expression via cAMP-dependent mechanism. Together, these findings suggest that signaling through alveolar epithelial A_2BAR promotes alveolar fluid balance during endotoxin-induced ALI by regulating ENaC via cAMP pathway, raising the hopes for treatment of pulmonary edema due to ALI.

Keep an eye on adenosine: Its role in retinal inflammation

Adenosine is an endogenous purine nucleoside ubiquitously distributed throughout the body that interacts with G protein-coupled receptors, classified in four subtypes: A₁R, A_2AR, A_2BR and A₃R. Among the plethora of functions of adenosine, it has been increasingly recognized as a key mediator of the immune response. Neuroinflammation is a feature of chronic neurodegenerative diseases and contributes to the pathophysiology of several retinal degenerative diseases. Animal models of retinal diseases are helping to elucidate the regulatory roles of adenosine receptors in the development and progression of those diseases. Mounting evidence demonstrates that the adenosinergic system is altered in the retina during pathological conditions, compromising retinal physiology. This review focuses on the roles played by adenosine and the elements of the adenosinergic system (receptors, enzymes, transporters) in the neuroinflammatory processes occurring in the retina. An improved understanding of the molecular and cellular mechanisms of the signalling pathways mediated by adenosine underlying the onset and progression of retinal diseases will pave the way towards the identification of new therapeutic approaches.

Nucleotide ecto-enzyme metabolic pattern and spatial distribution in calcific aortic valve disease; its relation to pathological changes and clinical presentation

BACKGROUND

Extracellular nucleotide metabolism contributes to chronic inflammation, cell differentiation, and tissue mineralization by controlling nucleotide and adenosine concentrations and hence its purinergic effects. This study investigated location-specific changes of extracellular nucleotide metabolism in aortic valves of patients with calcific aortic valve disease (CAVD). Individual ecto-enzymes and adenosine receptors involved were analyzed together with correlation with CAVD severity and risk factors.

RESULTS

Nucleotide and adenosine degradation rates were adversely modified on the aortic surface of stenotic valve as compared to ventricular side, including decreased ATP removal (1.25 ± 0.35 vs. 2.24 ± 0.61 nmol/min/cm2) and adenosine production (1.32 ± 0.12 vs. 2.49 ± 0.28 nmol/min/cm2) as well as increased adenosine deamination (1.28 ± 0.31 vs. 0.67 ± 0.11 nmol/min/cm2). The rates of nucleotide to adenosine conversions were lower, while adenosine deamination was higher on the aortic sides of stenotic vs. non-stenotic valve. There were no differences in extracellular nucleotide metabolism between aortic and ventricular sides of non-stenotic valves. Furthermore, nucleotide degradation rates, measured on aortic side in CAVD (n = 62), negatively correlated with echocardiographic and biochemical parameters of disease severity (aortic jet velocity vs. ATP hydrolysis: r = - 0.30, p < 0.05; vs. AMP hydrolysis: r = - 0.44, p < 0.001; valvular phosphate concentration vs. ATP hydrolysis: r = - 0.26, p < 0.05; vs. AMP hydrolysis: r = - 0.25, p = 0.05) while adenosine deamination showed positive correlation trend with valvular phosphate deposits (r = 0.23, p = 0.07). Nucleotide and adenosine conversion rates also correlated with CAVD risk factors, including hyperlipidemia (AMP hydrolysis vs. serum LDL cholesterol: r = - 0.28, p = 0.05; adenosine deamination vs. total cholesterol: r = 0.25, p = 0.05; LDL cholesterol: r = 0.28, p < 0.05; triglycerides: r = 0.32, p < 0.05), hypertension (adenosine deamination vs. systolic blood pressure: r = 0.28, p < 0.05) and thrombosis (ATP hydrolysis vs. prothrombin time: r = - 0.35, p < 0.01). Functional assays as well as histological and immunofluorescence, flow cytometry and RT-PCR studies identified all major ecto-enzymes engaged in nucleotide metabolism in aortic valves that included ecto-nucleotidases, alkaline phosphatase, and ecto-adenosine deaminase. We have shown that changes in nucleotide-converting ecto-enzymes were derived from their altered activities on valve cells and immune cell infiltrate. We have also demonstrated a presence of A1, A2a and A2b adenosine receptors with diminished expression of A2a and A2b in stenotic vs. non-stenotic valves. Finally, we revealed that augmenting adenosine effects by blocking adenosine deamination with deoxycoformycin decreased aortic valve thickness and reduced markers of calcification via adenosine-dependent pathways in a mouse model of CAVD.

CONCLUSIONS

This work highlights profound changes in extracellular nucleotide and adenosine metabolism in CAVD. Altered extracellular nucleotide hydrolysis and degradation of adenosine in stenotic valves may affect purinergic responses to support a pro-stenotic milieu and valve calcification. This emphasizes a potential mechanism and target for prevention and therapy. .

Exploring the binding modes of cordycepin to human adenosine deaminase 1 (ADA1) compared to adenosine and 2'-deoxyadenosine

Cordycepin (3'-deoxyadenosine, abbreviated as COR) from Cordyceps shows a wide range of pharmacological activities, including antioxidant and anticancer effects, therefore representing a potential alternative medicine. However, COR has a short half-life in the human body, where it is metabolized by adenosine deaminase 1 (ADA1). ADA1 helps regulate adenosine levels by deaminating excess adenosine (ADE) and its derivatives, such as 2'-deoxyadenosine (DEO). Understanding binding mechanisms of ADA1 with COR in comparison with its other substrates will play a vital role in improving the bioactivity and lifetime of COR for commercial medicinal use. Recently, the first structure of human ADA1 in complex with DEO was solved. We therefore employed molecular dynamics (MD) simulations to predict structures and dynamics of ADA1 complexing with ADE, DEO, and COR in comparison to a ligand-free (LF) structure. Our data reveal that a large and highly water-exposed binding pocket of ADA1 is responsible for ligand translocation and reorientation. Two possible binding locations (site1 and site2) are identified. The binding affinities of the ligands are ADE > COR > DEO. Furthermore, the movements of two loop regions at the binding pocket entrance, residues 183-193 and 215-230, contribute to gating activity.

Perioperative Acute Kidney Injury

Perioperative organ injury is among the leading causes of morbidity and mortality of surgical patients. Among different types of perioperative organ injury, acute kidney injury occurs particularly frequently and has an exceptionally detrimental effect on surgical outcomes. Currently, acute kidney injury is most commonly diagnosed by assessing increases in serum creatinine concentration or decreased urine output. Recently, novel biomarkers have become a focus of translational research for improving timely detection and prognosis for acute kidney injury. However, specificity and timing of biomarker release continue to present challenges to their integration into existing diagnostic regimens. Despite many clinical trials using various pharmacologic or nonpharmacologic interventions, reliable means to prevent or reverse acute kidney injury are still lacking. Nevertheless, several recent randomized multicenter trials provide new insights into renal replacement strategies, composition of intravenous fluid replacement, goal-directed fluid therapy, or remote ischemic preconditioning in their impact on perioperative acute kidney injury. This review provides an update on the latest progress toward the understanding of disease mechanism, diagnosis, and managing perioperative acute kidney injury, as well as highlights areas of ongoing research efforts for preventing and treating acute kidney injury in surgical patients.

Blockade of equilibrative nucleoside transporter 1/2 protects against Pseudomonas aeruginosa-induced acute lung injury and NLRP3 inflammasome activation

Pseudomonas aeruginosa infections are increasingly multidrug resistant and cause healthcare-associated pneumonia, a major risk factor for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Adenosine is a signaling nucleoside with potential opposing effects; adenosine can either protect against acute lung injury via adenosine receptors or cause lung injury via adenosine receptors or equilibrative nucleoside transporter (ENT)-dependent intracellular adenosine uptake. We hypothesized that blockade of intracellular adenosine uptake by inhibition of ENT1/2 would increase adenosine receptor signaling and protect against P. aeruginosa-induced acute lung injury. We observed that P. aeruginosa (strain: PA103) infection induced acute lung injury in C57BL/6 mice in a dose- and time-dependent manner. Using ENT1/2 pharmacological inhibitor, nitrobenzylthioinosine (NBTI), and ENT1-null mice, we demonstrated that ENT blockade elevated lung adenosine levels and significantly attenuated P. aeruginosa-induced acute lung injury, as assessed by lung wet-to-dry weight ratio, BAL protein levels, BAL inflammatory cell counts, pro-inflammatory cytokines, and pulmonary function (total lung volume, static lung compliance, tissue damping, and tissue elastance). Using both agonists and antagonists directed against adenosine receptors A2AR and A2BR, we further demonstrated that ENT1/2 blockade protected against P. aeruginosa -induced acute lung injury via activation of A2AR and A2BR. Additionally, ENT1/2 chemical inhibition and ENT1 knockout prevented P. aeruginosa-induced lung NLRP3 inflammasome activation. Finally, inhibition of inflammasome prevented P. aeruginosa-induced acute lung injury. Our results suggest that targeting ENT1/2 and NLRP3 inflammasome may be novel strategies for prevention and treatment of P. aeruginosa-induced pneumonia and subsequent ARDS.

Adenosine deaminase inhibition

Adenosine deaminase is a critical enzyme in purine metabolism that regulates intra and extracellular adenosine concentrations by converting it to inosine. Adenosine is an important purine that regulates numerous physiological functions by interacting with its receptors. Adenosine and consequently adenosine deaminase can have pro or anti-inflammatory effects on tissues depending on how much time has passed from the start of the injury. In addition, an increase in adenosine deaminase activity has been reported for various diseases and the significant effect of deaminase inhibition on the clinical course of different diseases has been reported. However, the use of inhibitors is limited to only a few medical indications. Data on the increase of adenosine deaminase activity in different diseases and the impact of its inhibition in various cases have been collected and are discussed in this review. Overall, the evidence shows that many studies have been done to introduce inhibitors, however, in vivo studies have been much less than in vitro, and often have not been expanded for clinical use.

Pharmacologic stress cardiovascular magnetic resonance in the pediatric population: A review of the literature, proposed protocol, and two examples in patients with Kawasaki disease

Pharmacologic stress cardiovascular magnetic resonance (PSCMR) is a well-established and reliable diagnostic tool for evaluation of coronary artery disease in the adult population. Stress imaging overall and PSCMR in particular is less utilized in the pediatric population with limited reported data. In this review, we highlight the potential use of PSCMR in specific pediatric cohorts with congenital and acquired heart disease, and we review the reported experience. A suggested protocol is presented in addition to two case examples of patients with Kawasaki disease where PSCMR aided decision making.

Cell type- and tissue-specific functions of ecto-5'-nucleotidase (CD73)

Ecto-5'-nucleotidase [cluster of differentiation 73 (CD73)] is a ubiquitously expressed glycosylphosphatidylinositol-anchored glycoprotein that converts extracellular adenosine 5'-monophosphate to adenosine. Anti-CD73 inhibitory antibodies are currently undergoing clinical testing for cancer immunotherapy. However, many protective physiological functions of CD73 need to be taken into account for new targeted therapies. This review examines CD73 functions in multiple organ systems and cell types, with a particular focus on novel findings from the last 5 years. Missense loss-of-function mutations in the CD73-encoding gene NT5E cause the rare disease "arterial calcifications due to deficiency of CD73." Aside from direct human disease involvement, cellular and animal model studies have revealed key functions of CD73 in tissue homeostasis and pathology across multiple organ systems. In the context of the central nervous system, CD73 is antinociceptive and protects against inflammatory damage, while also contributing to age-dependent decline in cortical plasticity. CD73 preserves barrier function in multiple tissues, a role that is most evident in the respiratory system, where it inhibits endothelial permeability in an adenosine-dependent manner. CD73 has important cardioprotective functions during myocardial infarction and heart failure. Under ischemia-reperfusion injury conditions, rapid and sustained induction of CD73 confers protection in the liver and kidney. In some cases, the mechanism by which CD73 mediates tissue injury is less clear. For example, CD73 has a promoting role in liver fibrosis but is protective in lung fibrosis. Future studies that integrate CD73 regulation and function at the cellular level with physiological responses will improve its utility as a disease target.

Purinergic Signaling in Pulmonary Inflammation

Purine nucleotides and nucleosides are at the center of biologic reactions. In particular, adenosine triphosphate (ATP) is the fundamental energy currency of cellular activity and adenosine has been demonstrated to play essential roles in human physiology and pathophysiology. In this review, we examine the role of purinergic signaling in acute and chronic pulmonary inflammation, with emphasis on ATP and adenosine. ATP is released into extracellular space in response to cellular injury and necrosis. It is then metabolized to adenosine monophosphate (AMP) via ectonucleoside triphosphate diphosphohydrolase-1 (CD39) and further hydrolyzed to adenosine via ecto-5'-nucleotidase (CD73). Adenosine signals via one of four adenosine receptors to exert pro- or anti-inflammatory effects. Adenosine signaling is terminated by intracellular transport by concentrative or equilibrative nucleoside transporters (CNTs and ENTs), deamination to inosine by adenosine deaminase (ADA), or phosphorylation back into AMP via adenosine kinase (AK). Pulmonary inflammatory and hypoxic conditions lead to increased extracellular ATP, adenosine diphosphate (ADP) and adenosine levels, which translates to increased adenosine signaling. Adenosine signaling is central to the pulmonary injury response, leading to various effects on inflammation, repair and remodeling processes that are either tissue-protective or tissue destructive. In the acute setting, particularly through activation of adenosine 2A and 2B receptors, adenosine signaling serves an anti-inflammatory, tissue-protective role. However, excessive adenosine signaling in the chronic setting promotes pro-inflammatory, tissue destructive effects in chronic pulmonary inflammation.

mSphere of Influence: Adenosine in Host Defense against Bacterial Pneumonia-Friend or Foe?

Elsa N. Bou Ghanem works in the field of innate immune senescence, inflammation, and host defense. In this mSphere of Influence article, she reflects on how "Adenosine A2B receptor deficiency promotes host defenses against Gram-negative bacterial pneumonia" by Barletta et al. (K. E. Barletta, R. E. Cagnina, M. D. Burdick, J. Linden, and B. Mehrad, Am J Respir Crit Care Med 186:1044-1050, 2012, https://doi.org/10.1164/rccm.201204-0622OC) impacted her own work examining the role of the extracellular adenosine pathway in neutrophil responses and host defense against pneumococcal pneumonia.

CD73 Expression on Mesenchymal Stem Cells Dictates the Reparative Properties via Its Anti-Inflammatory Activity

Mesenchymal stem cells (MSC) are not universal and may be subject to dynamic changes upon local milieus in vivo and after isolation and cultivation in vitro. Here, we demonstrate that MSC derived from murine pericardial adipose tissue (pMSC) constitute two cohorts of population distinguished by the level of CD73 expression (termed as CD73high and CD73low pMSC). Transplantation of two types of cells into mouse hearts after myocardial infarction (MI) revealed that the CD73high pMSC preferentially brought about structural and functional repair in comparison to the PBS control and CD73low pMSC. Furthermore, the CD73high pMSC displayed a pronounced anti-inflammatory activity by attenuating CCR2+ macrophage infiltration and upregulating several anti-inflammatory genes 5 days after in vivo transplantation and ex vivo cocultivation with peritoneal macrophages. The immunomodulatory effect was not seen in cocultivation experiments with pMSC derived from CD73 knockout mice (CD73-/-) but was partially blocked by pretreatment of the A2b receptor antagonist, PSB603. The results highlight a heterogeneity of the CD73 expression that may be related to its catalytic products on the modulation of the local immune response and thus provide a possible explanation to the inconsistency of the regenerative results when different sources of donor cells were used in stem cell-based therapy.

Historical and Current Adenosine Receptor Agonists in Preclinical and Clinical Development

Adenosine receptors (ARs) function in the body’s response to conditions of pathology and stress associated with a functional imbalance, such as in the supply and demand of energy/oxygen/nutrients. Extracellular adenosine concentrations vary widely to raise or lower the basal activation of four subtypes of ARs. Endogenous adenosine can correct an energy imbalance during hypoxia and other stress, for example, by slowing the heart rate by A₁AR activation or increasing the blood supply to heart muscle by the A_2AAR. Moreover, exogenous AR agonists, antagonists, or allosteric modulators can be applied for therapeutic benefit, and medicinal chemists working toward that goal have reported thousands of such agents. Thus, numerous clinical trials have ensued, using promising agents to modulate adenosinergic signaling, most of which have not succeeded. Currently, short-acting, parenteral agonists, adenosine and Regadenoson, are the only AR agonists approved for human use. However, new concepts and compounds are currently being developed and applied toward preclinical and clinical evaluation, and initial results are encouraging. This review focuses on key compounds as AR agonists and positive allosteric modulators (PAMs) for disease treatment or diagnosis. AR agonists for treating inflammation, pain, cancer, non-alcoholic steatohepatitis, angina, sickle cell disease, ischemic conditions and diabetes have been under development. Multiple clinical trials with two A₃AR agonists are ongoing.