Adenosine inhibits collagen and protein synthesis in cardiac fibroblasts: role of A2B receptors

Blockage of the adenosine A2B receptor prevents cardiac fibroblasts overgrowth in rats with pulmonary arterial hypertension

Sustained pressure overload and fibrosis of the right ventricle (RV) are the leading causes of mortality in pulmonary arterial hypertension (PAH). Although the role of adenosine in PAH has been attributed to the control of pulmonary vascular tone, cardiac reserve, and inflammatory processes, the involvement of the nucleoside in RV remodelling remains poorly understood. Conflicting results exist on targeting the low-affinity adenosine A2B receptor (A2BAR) for the treatment of PAH mostly because it displays dual roles in acute vs. chronic lung diseases. Herein, we investigated the role of the A2BAR in the viability/proliferation and collagen production by cardiac fibroblasts (CFs) isolated from RVs of rats with monocrotaline (MCT)-induced PAH. CFs from MCT-treated rats display higher cell viability/proliferation capacity and overexpress A2BAR compared to the cells from healthy littermates. The enzymatically stable adenosine analogue, 5'-N-ethylcarboxamidoadenosine (NECA, 1-30 μM), concentration-dependently increased growth, and type I collagen production by CFs originated from control and PAH rats, but its effects were more prominent in cells from rats with PAH. Blockage of the A2BAR with PSB603 (100 nM), but not of the A2AAR with SCH442416 (100 nM), attenuated the proliferative effect of NECA in CFs from PAH rats. The A2AAR agonist, CGS21680 (3 and 10 nM), was virtually devoid of effect. Overall, data suggest that adenosine signalling via A2BAR may contribute to RV overgrowth secondary to PAH. Therefore, blockage of the A2AAR may be a valuable therapeutic alternative to mitigate cardiac remodelling and prevent right heart failure in PAH patients.

Primary cardiac fibroblast cell culture: methodological considerations for physiologically relevant conditions

Primary cardiac fibroblast (CF) tissue culture is a necessary tool for interrogating specific signaling mechanisms that dictate the phenotypic heterogeneity observed in vivo in different disease states. Traditional approaches that use tissue culture plastic and nutrient-rich medium have been shown to induce CF activation and, therefore, alter CF subpopulation composition. This shift away from in vivo phenotypes complicate the interpretation of results through the lens of the animal model. As the field works to identify CF diversity, these methodological flaws have begun to be addressed and more studies are focused on the dynamic interaction of CFs with their environment. This review focuses on the aspects of tissue culture that impact CF activation and, therefore, require consideration when designing in vitro experiments. The complexity of CF biology overlaid onto diverse model systems highlight the need for study-specific optimization and validation.

Adenosine and Adenosine Receptors: Advances in Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the world. Because the key to developing innovative therapies that limit the onset and the progression of AF is to fully understand the underlying molecular mechanisms of AF, the aim of the present narrative review is to report the most recent advances in the potential role of the adenosinergic system in the pathophysiology of AF. After a comprehensive approach describing adenosinergic system signaling and the mechanisms of the initiation and maintenance of AF, we address the interactions of the adenosinergic system's signaling with AF. Indeed, adenosine release can activate four G-coupled membrane receptors, named A₁, A_2A, A_2B and A₃. Activation of the A_2A receptors can promote the occurrence of delayed depolarization, while activation of the A₁ receptors can shorten the action potential's duration and induce the resting membrane's potential hyperpolarization, which promote pulmonary vein firing, stabilize the AF rotors and allow for functional reentry. Moreover, the A_2B receptors have been associated with atrial fibrosis homeostasis. Finally, the adenosinergic system can modulate the autonomous nervous system and is associated with AF risk factors. A question remains regarding adenosine release and the adenosine receptors' activation and whether this would be a cause or consequence of AF.

Adenosine Receptors Profile in Fibromuscular Dysplasia

Fibromuscular dysplasia (FMD) is a non-inflammatory vascular disease that is characterized by unexplained systemic hypertension occurring in young people, associated with arterial stenosis, aneurysm rupture, intracranial/renal infarction, and stroke. Although the gold standard for the diagnosis remains catheter-angiography, biological markers would be helpful due to the delay from first symptom to diagnosis. Adenosine is an ATP derivative, that may be implicated in FMD pathophysiology. We hypothesized that changes in adenosine blood level (ABL) and production of adenosine receptors may be associated with FMD. Using peripheral blood mononuclear cells, we evaluated A1, A2A, and A2B receptor production by Western blot, in 67 patients (17 men and 50 women, mean (range) age 55 (29−77) years and 40 controls, 10 men and 30 women, mean (range) age 56 (37−70)). ABL was evaluated by liquid chromatography, mass spectrometry. ABL was significantly higher in patients vs. controls, mean (range): 1.7 (0.7−3) µmol/L vs. controls 0.6 (0.4−0.8) µmol/L (+180%) p < 0.001. While A1R and A2AR production did not differ in patients and controls, we found an over-production of A2BR in patients: 1.70 (0.90−2.40; arbitrary units) vs. controls = 1.03 (0.70−1.40), mean + 65% (p < 0.001). A2BR production with a cut off of 1.3 arbitrary units, gives a good sensitivity and specificity for the diagnosis. Production measurement of A2BR on monocytes and ABL could help in the diagnosis, especially in atypical or with poor symptoms.

Brown Adipocyte ADRB3 Mediates Cardioprotection via Suppressing Exosomal iNOS

BACKGROUND

The ADRB3 (β3-adrenergic receptors), which is predominantly expressed in brown adipose tissue (BAT), can activate BAT and improve metabolic health. Previous studies indicate that the endocrine function of BAT is associated with cardiac homeostasis and diseases. Here, we investigate the role of ADRB3 activation-mediated BAT function in cardiac remodeling.

METHODS

BKO (brown adipocyte-specific ADRB3 knockout) and littermate control mice were subjected to Ang II (angiotensin II) for 28 days. Exosomes from ADRB3 antagonist SR59230A (SR-exo) or agonist mirabegron (MR-exo) treated brown adipocytes were intravenously injected to Ang II-infused mice.

RESULTS

BKO markedly accelerated cardiac hypertrophy and fibrosis compared with control mice after Ang II infusion. In vitro, ADRB3 KO rather than control brown adipocytes aggravated expression of fibrotic genes in cardiac fibroblasts, and this difference was not detected after exosome inhibitor treatment. Consistently, BKO brown adipocyte-derived exosomes accelerated Ang II-induced cardiac fibroblast dysfunction compared with control exosomes. Furthermore, SR-exo significantly aggravated Ang II-induced cardiac remodeling, whereas MR-exo attenuated cardiac dysfunction. Mechanistically, ADRB3 KO or SR59230A treatment in brown adipocytes resulted an increase of iNOS (inducible nitric oxide synthase) in exosomes. Knockdown of iNOS in brown adipocytes reversed SR-exo-aggravated cardiac remodeling.

CONCLUSIONS

Our data illustrated a new endocrine pattern of BAT in regulating cardiac remodeling, suggesting that activation of ADRB3 in brown adipocytes offers cardiac protection through suppressing exosomal iNOS.

Involvement of β-adrenoceptors in the cardiovascular responses induced by selective adenosine A2A and A2B receptor agonists

A_2A and A_2B adenosine receptors produce regionally selective regulation of vascular tone and elicit differing effects on mean arterial pressure (MAP), whilst inducing tachycardia. The tachycardia induced by the stimulation of A_2A or A_2B receptors has been suggested to be mediated by a reflex increase in sympathetic activity. Here, we have investigated the role of β₁ - and β₂ -adrenoceptors in mediating the different cardiovascular responses to selective A_2A and A_2B receptor stimulation. Hemodynamic variables were measured in conscious male Sprague-Dawley rats (350-450 g) via pulsed Doppler flowmetry. The effect of intravenous infusion (3 min per dose) of the A_2A -selective agonist CGS 21680 (0.1, 0.3, 1.0 µg.kg^-1 .min^-1 ) or the A_2B -selective agonist BAY 60-6583 (4.0, 13.3, 40.0 µg.kg^-1 .min^-1 ) in the absence or following pre-treatment with the non-selective β-antagonist propranolol (1.0 mg.kg^-1 ), the selective β₁ -antagonist CGP 20712A (200 µg.kg^-1 ), or the selective β₂ -antagonist ICI 118,551 (2.0 mg.kg^-1 ) was investigated (maintenance doses also administered). CGP 20712A and propranolol significantly reduced the tachycardic response to CGS 21680, with no change in the effect on MAP. ICI 118,551 increased BAY 60-6583-mediated renal and mesenteric flows, but did not affect the heart rate response. CGP 20712A attenuated the BAY 60-6583-induced tachycardia. These data imply a direct stimulation of the sympathetic activity via cardiac β₁ -adrenoceptors as a mechanism for the A_2A - and A_2B -induced tachycardia. However, the regionally selective effects of A_2B agonists on vascular conductance were independent of sympathetic activity and may be exploitable for the treatment of acute kidney injury and mesenteric ischemia.

Purinergic receptors modulators: An emerging pharmacological tool for disease management

Purinergic signaling is mediated through extracellular nucleotides (adenosine 5'-triphosphate, uridine-5'-triphosphate, adenosine diphosphate, uridine-5'-diphosphate, and adenosine) that serve as signaling molecules. In the early 1990s, purines and pyrimidine receptors were cloned and characterized drawing the attention of scientists toward this aspect of cellular signaling. This signaling pathway is comprised of four subtypes of adenosine receptors (P1), eight subtypes of G-coupled protein receptors (P2YRs), and seven subtypes of ligand-gated ionotropic receptors (P2XRs). In current studies, the pathophysiology and therapeutic potentials of these receptors have been focused on. Various ligands, modulating the functions of purinergic receptors, are in current clinical practices for the treatment of various neurodegenerative disorders and cardiovascular diseases. Moreover, several purinergic receptors ligands are in advanced phases of clinical trials as a remedy for depression, epilepsy, autism, osteoporosis, atherosclerosis, myocardial infarction, diabetes, irritable bowel syndrome, and cancers. In the present study, agonists and antagonists of purinergic receptors have been summarized that may serve as pharmacological tools for drug design and development.

Serum collected from rats with myocardial infarction increases extracellular matrix accumulation by myofibroblasts isolated from myocardial infarction scar

The effect on extracellular matrix content is believed to be an average of several serum derived compounds acting in opposition. The aim of the study is to determine whether whole serum of rats with myocardial infarction may modify the accumulation of extracellular matrix in cultures of myofibroblasts isolated from the myocardial infarction scar. A second aim is to determine whether the tested serum can also degranulate the mast cells. Serum was collected from rats with sham myocardial infarction, rats with myocardial infarction induced by coronary artery ligation and control animals. The experiments were carried out on myocardial infarction scar myofibroblasts or mast cells from the peritoneal cavity. The cultures were divided into three groups containing eight cultures each: one treated with serum from control rats, from animals after sham operation or from those after myocardial infarction. In all groups, the serum was used at concentrations of 10%, 20% or 30%. The total collagen content (Woesner method) glycosaminoglycan level (Farandale method), cell proliferation (BrdU), histamine secretion from mast cells (spectrofluorymetry), β1 integrin and α-smooth muscle actin expression (flow cytometry) were evaluated. Isolated cells were α-smooth muscle actin positive and identified as myofibroblasts. Serum derived from rats with myocardial infarction increased collagen and glycosaminoglycan content in the cultures and modified myofibroblast proliferation in a concentration-dependent manner. The serum also results in an imbalance between collagen and glycosaminoglycan levels. The content of β1 integrin was not influenced by myocardial infarction serum. The serum of rats with myocardial infarction is involved in regulation of collagen and glycosaminoglycan content in myofibroblast cultures, as well as the modification of their proliferation. These changes were not accompanied with integrin β1 density variations. The serum of the myocardial infarction rats did not influence the mast cell degranulation.

PDGF-D activation by macrophage-derived uPA promotes AngII-induced cardiac remodeling in obese mice

Obesity-induced secretory disorder of adipose tissue-derived factors is important for cardiac damage. However, whether platelet-derived growth factor-D (PDGF-D), a newly identified adipokine, regulates cardiac remodeling in angiotensin II (AngII)-infused obese mice is unclear. Here, we found obesity induced PDGF-D expression in adipose tissue as well as more severe cardiac remodeling compared with control lean mice after AngII infusion. Adipocyte-specific PDGF-D knockout attenuated hypertensive cardiac remodeling in obese mice. Consistently, adipocyte-specific PDGF-D overexpression transgenic mice (PA-Tg) showed exacerbated cardiac remodeling after AngII infusion without high-fat diet treatment. Mechanistic studies indicated that AngII-stimulated macrophages produce urokinase plasminogen activator (uPA) that activates PDGF-D by splicing full-length PDGF-D into the active PDGF-DD. Moreover, bone marrow-specific uPA knockdown decreased active PDGF-DD levels in the heart and improved cardiac remodeling in HFD hypertensive mice. Together, our data provide for the first time a new interaction pattern between macrophage and adipocyte: that macrophage-derived uPA activates adipocyte-secreted PDGF-D, which finally accelerates AngII-induced cardiac remodeling in obese mice.

Cardiac Fibroblast-Specific Knockout of PGC-1α Accelerates AngII-Induced Cardiac Remodeling

Cardiac remodeling consisted of ventricular hypertrophy and interstitial fibrosis is the pathological process of many heart diseases. Fibroblasts as one of the major cells in the myocardium regulate the balance of the generation and degeneration of collagen, and these cells transform toward myofibroblasts in pathological state, contributing to the remodeling of the heart. Peroxisome proliferator-activated receptor-γ (PPAR-γ) coactivator-1α (PGC-1α) is vital to the function of mitochondria, which contributes to the energy production and reactive oxidative species (ROS)-scavenging activity in the heart. In this study, we found that fibroblast-specific PGC-1α KO induced cardiac remodeling especially fibrosis, and Angiotensin II (AngII) aggravated cardiac fibrosis, accompanied with a high level of oxidative stress response and inflammation.

Collagen triple helix repeat containing-1 exerts antifibrotic effects on human skin fibroblast and bleomycin-induced dermal fibrosis models

Background

Systemic scleroderma (SSc) is an acquired disorder characterized by excessive deposition of extracellular matrix in the skin and internal organs. So far, the molecular mechanisms underpinning the pathogenesis of SSc have remained unknown. Collagen triple helix repeat containing-1 (CTHRC1) has been indicated to be a cell type-specific inhibitor of transforming growth factor-β (TGF-β), which could have the potential for extensive clinical application owing to its ability to reduce collagen deposition. Our previous studies showed that CTHRC1 inhibited TGF-β1-induced collagen type I synthesis in keloid fibroblasts. In our present research, we attempted to probe the role of CTHRC1 in dermal fibrosis in bleomycin (BLM)-treated mice.

Methods

CTHRC1 and TGF-β1 expression was detected in dermal tissues from patients with SSc and BLM-treated mice by immunohistochemistry. A 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay was used to assess TGF-β1-induced proliferation of human dermal fibroblasts. Collagen expression and fibroblast synthesis were evaluated by quantitative real-time polymerase chain reaction and the 3H-proline incorporation. Masson’s trichrome staining and western blotting were carried out to analyze the deposits and protein levels of type I collagen, respectively.

Results

Compared with those in normal tissues, the levels of CTHRC1 and TGF-β1 were elevated in dermal tissues from patients with SSc and in skin tissues from BLM-treated mice, respectively. Furthermore, recombinant CTHRC1 was found to inhibit TGF-β1-stimulated collagen deposition by fibroblasts. Finally, the in vivo experiments showed that CTHRC1 alleviated BLM-induced dermal fibrotic changes.

Conclusions

CTHRC1 can inhibit human dermal fibroblast collagen deposition and can also exert protective effects against BLM-induced dermal fibrosis in mice. This research provides an indication that CTHRC1 may be a promising treatment choice for dermal fibrosis in SSc patients.

Biomimetic microsystems for cardiovascular studies

Traditional tissue culture platforms have been around for several decades and have enabled key findings in the cardiovascular field. However, these platforms failed to recreate the mechanical and dynamic features found within the body. Organs-on-chips (OOCs) are cellularized microfluidic-based devices that can mimic the basic structure, function, and responses of organs. These systems have been successfully utilized in disease, development, and drug studies. OOCs are designed to recapitulate the mechanical, electrical, chemical, and structural features of the in vivo microenvironment. Here, we review cardiovascular-themed OOC studies, design considerations, and techniques used to generate these cellularized devices. Furthermore, we will highlight the advantages of OOC models over traditional cell culture vessels, discuss implementation challenges, and provide perspectives on the state of the field.

Pharmacological Insights Into Safety and Efficacy Determinants for the Development of Adenosine Receptor Biased Agonists in the Treatment of Heart Failure

Adenosine A₁ receptors (A₁R) are a potential target for cardiac injury treatment due to their cardioprotective/antihypertrophic actions, but drug development has been hampered by on-target side effects such as bradycardia and altered renal hemodynamics. Biased agonism has emerged as an attractive mechanism for A₁R-mediated cardioprotection that is haemodynamically safe. Here we investigate the pre-clinical pharmacology, efficacy and side-effect profile of the A₁R agonist neladenoson, shown to be safe but ineffective in phase IIb trials for the treatment of heart failure. We compare this agent with the well-characterized, pan-adenosine receptor (AR) agonist NECA, capadenoson, and the A₁R biased agonist VCP746, previously shown to be safe and cardioprotective in pre-clinical models of heart failure. We show that like VCP746, neladenoson is biased away from Ca²⁺ influx relative to NECA and the cAMP pathway at the A₁R, a profile predictive of a lack of adenosine-like side effects. Additionally, neladenoson was also biased away from the MAPK pathway at the A₁R. In contrast to VCP746, which displays more 'adenosine-like' signaling at the A_2BR, neladenoson was a highly selective A₁R agonist, with biased, weak agonism at the A_2BR. Together these results show that unwanted hemodynamic effects of A₁R agonists can be avoided by compounds biased away from Ca²⁺ influx relative to cAMP, relative to NECA. The failure of neladenoson to reach primary endpoints in clinical trials suggests that A₁R-mediated cAMP inhibition may be a poor indicator of effectiveness in chronic heart failure. This study provides additional information that can aid future screening and/or design of improved AR agonists that are safe and efficacious in treating heart failure in patients.

Role of Adenosine and Purinergic Receptors in Myocardial Infarction: Focus on Different Signal Transduction Pathways

Myocardial infarction (MI) is a dramatic event often caused by atherosclerotic plaque erosion or rupture and subsequent thrombotic occlusion of a coronary vessel. The low supply of oxygen and nutrients in the infarcted area may result in cardiomyocytes necrosis, replacement of intact myocardium with non-contractile fibrous tissue and left ventricular (LV) function impairment if blood flow is not quickly restored. In this review, we summarized the possible correlation between adenosine system, purinergic system and Wnt/β-catenin pathway and their role in the pathogenesis of cardiac damage following MI. In this context, several pathways are involved and, in particular, the adenosine receptors system shows different interactions between its members and purinergic receptors: their modulation might be effective not only for a normal functional recovery but also for the treatment of heart diseases, thus avoiding fibrosis, reducing infarcted area and limiting scaring. Similarly, it has been shown that Wnt/β catenin pathway is activated following myocardial injury and its unbalanced activation might promote cardiac fibrosis and, consequently, LV systolic function impairment. In this regard, the therapeutic benefits of Wnt inhibitors use were highlighted, thus demonstrating that Wnt/β-catenin pathway might be considered as a therapeutic target to prevent adverse LV remodeling and heart failure following MI.

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.

Adenosine A2A receptor activation prevents DOCA-salt induced hypertensive cardiac remodeling via iBAT

Hypertensive cardiac remodeling is a constellation of abnormalities that includes cardiomyocyte hypertrophy and death and tissue fibrosis. Adenosine is a long-known vasodilator, through interacting with its four cell surface receptor subtypes in cardiovascular system. However, it is unclear that whether adenosine A2A receptor (A2AR) activation is involved in the cardiac remodeling in hypertension. WT mice were utilized to induce DOCA-salt sensitive hypertension and received A2AR agonist CGS21680 or antagonist KW6002 treatment. Cardiac functional phenotyping measurement by echocardiography showed that CGS21680 improved cardiac dysfunction in DOCA-salt mice. Moreover, CGS21680 reduced cardiomyocyte hypertrophy, cardiac inflammation and fibrosis. However, iBAT depletion surgery induces dramatic cardiac remodeling in DOCA-salt mice, and the protective function of CGS21680 was blocked without intact iBAT. Mechanistically, A2AR agonist CGS21680 increased iBAT-derived fibroblast growth factor 21 (FGF21). Our data suggest that activation of A2AR could be a potential therapeutic strategy in preventing heart damage in hypertension.

The Role of Cyclic AMP Signaling in Cardiac Fibrosis

Myocardial stress and injury invariably promote remodeling of the cardiac tissue, which is associated with cardiomyocyte death and development of fibrosis. The fibrotic process is initially triggered by the differentiation of resident cardiac fibroblasts into myofibroblasts. These activated fibroblasts display increased proliferative capacity and secrete large amounts of extracellular matrix. Uncontrolled myofibroblast activation can thus promote heart stiffness, cardiac dysfunction, arrhythmias, and progression to heart failure. Despite the well-established role of myofibroblasts in mediating cardiac disease, our current knowledge on how signaling pathways promoting fibrosis are regulated and coordinated in this cell type is largely incomplete. In this respect, cyclic adenosine monophosphate (cAMP) signaling acts as a major modulator of fibrotic responses activated in fibroblasts of injured or stressed hearts. In particular, accumulating evidence now suggests that upstream cAMP modulators including G protein-coupled receptors, adenylyl cyclases (ACs), and phosphodiesterases (PDEs); downstream cAMP effectors such as protein kinase A (PKA) and the guanine nucleotide exchange factor Epac; and cAMP signaling organizers such as A-kinase anchoring proteins (AKAPs) modulate a variety of fundamental cellular processes involved in myocardial fibrosis including myofibroblast differentiation, proliferation, collagen secretion, and invasiveness. The current review will discuss recent advances highlighting the role of cAMP and AKAP-mediated signaling in regulating pathophysiological responses controlling cardiac fibrosis.

Metabolomics study of serum and urine samples reveals metabolic pathways and biomarkers associated with pelvic organ prolapse

Pelvic organ prolapse (POP) is a common medical condition among women and involves complicated diagnostics and controversial surgical management. The exact molecular mechanism underlying POP is poorly understood, especially at the metabolism level. To explore the metabolic mechanism underlying POP and discover potential biomarkers for POP diagnosis, we applied a non-targeted metabolomics approach using ultra-high performance liquid chromatography coupled with quadrupole-time-of-flight mass spectrometry (UHPLC-Q-TOF-MS). Metabolomics study of serum samples from patients with POP (n = 24) and controls (n = 22) revealed a total of 59 metabolites that are significantly different (VIP ≥ 1 and p ≤ 0.05) between the two groups. Between urine samples from POP patients (n = 45) and controls (n = 59), 33 metabolites differed significantly (VIP ≥ 1 and p ≤ 0.05). Metabolic pathways affected by these differentially expressed metabolites were analyzed. In both serum and urine samples, three pathways including arginine biosynthesis and purine metabolism were found to be significantly related to POP. Six metabolites including GPC, 1-methyladenosine, maleic acid, L-pyroglutamic acid, inosine, and citrate are significantly changed (VIP ≥ 1 and p ≤ 0.05) in both serum and urine samples from patients with POP. Receiver operating characteristics (ROC) curve analysis showed that using these six metabolites as a biomarker could distinguish patients with POP from controls with good accuracy in both serum (AUC = 1) and urine samples (AUC = 0.854). Collectively, these results further extended our understanding of key regulatory metabolic pathways involved in the pathophysiology of POP, as well as provided some promising biomarkers for effective POP diagnosis.

PET Imaging of Adenosine Receptors in Diseases

Adenosine receptors (ARs) are a class of purinergic G-protein-coupled receptors (GPCRs). Extracellular adenosine is a pivotal regulation molecule that adjusts physiological function through the interaction with four ARs: A1R, A2AR, A2BR, and A3R. Alterations of ARs function and expression have been studied in neurological diseases (epilepsy, Alzheimer's disease, and Parkinson's disease), cardiovascular diseases, cancer, and inflammation and autoimmune diseases. A series of Positron Emission Tomography (PET) probes for imaging ARs have been developed. The PET imaging probes have provided valuable information for diagnosis and therapy of diseases related to alterations of ARs expression. This review presents a concise overview of various ARs-targeted radioligands for PET imaging in diseases. The most recent advances in PET imaging studies by using ARs-targeted probes are briefly summarized.

Adenosine kinase attenuates cardiomyocyte microtubule stabilization and protects against pressure overload-induced hypertrophy and LV dysfunction

Adenosine exerts numerous protective actions in the heart, including attenuation of cardiac hypertrophy. Adenosine kinase (ADK) converts adenosine to adenosine monophosphate (AMP) and is the major route of myocardial adenosine metabolism, however, the impact of ADK activity on cardiac structure and function is unknown. To examine the role of ADK in cardiac homeostasis and adaptation to stress, conditional cardiomyocyte specific ADK knockout mice (cADK-/-) were produced using the MerCreMer-lox-P system. Within 4 weeks of ADK disruption, cADK-/- mice developed spontaneous hypertrophy and increased β-Myosin Heavy Chain expression without observable LV dysfunction. In response to 6 weeks moderate left ventricular pressure overload (transverse aortic constriction;TAC), wild type mice (WT) exhibited ~60% increase in ventricular ADK expression and developed LV hypertrophy with preserved LV function. In contrast, cADK-/- mice exhibited significantly greater LV hypertrophy and cardiac stress marker expression (atrial natrurietic peptide and β-Myosin Heavy Chain), LV dilation, reduced LV ejection fraction and increased pulmonary congestion. ADK disruption did not decrease protein methylation, inhibit AMPK, or worsen fibrosis, but was associated with persistently elevated mTORC1 and p44/42 ERK MAP kinase signaling and a striking increase in microtubule (MT) stabilization/detyrosination. In neonatal cardiomyocytes exposed to hypertrophic stress, 2-chloroadenosine (CADO) or adenosine treatment suppressed MT detyrosination, which was reversed by ADK inhibition with iodotubercidin or ABT-702. Conversely, adenoviral over-expression of ADK augmented CADO destabilization of MTs and potentiated CADO attenuation of cardiomyocyte hypertrophy. Together, these findings indicate a novel adenosine receptor-independent role for ADK-mediated adenosine metabolism in cardiomyocyte microtubule dynamics and protection against maladaptive hypertrophy.

The adenosine A2B G protein-coupled receptor: Recent advances and therapeutic implications

The adenosine A_2B receptor (A_2BAR) is one of four adenosine receptor subtypes belonging to the Class A family of G protein-coupled receptors (GPCRs). Until recently, the A_2BAR remained poorly characterised, in part due to its relatively low affinity for the endogenous agonist adenosine and therefore presumed minor physiological significance. However, the substantial increase in extracellular adenosine concentration, the sensitisation of the receptor and the upregulation of A_2BAR expression under conditions of hypoxia and inflammation, suggest the A_2BAR as an exciting therapeutic target in a variety of pathological disease states. Here we discuss the pharmacology of the A_2BAR and outline its role in pathophysiology including ischaemia-reperfusion injury, fibrosis, inflammation and cancer.

Aspirin causes endothelium-dependent vasodilation of resistance arteries from non-gravid and gravid rats

OBJECTIVE

The objective of this study was to understand the effect of acetylsalicylic acid (aspirin) on resistance arteries from mesentery and uterus. During pregnancy, the uterine vasculature undergoes consistent growth to provide sufficient uteroplacental blood flow, a process whose failure is associated with pregnancy complications characterized by high uterine vascular resistance.

METHODS

Uterine arcuate (UA) and mesenteric arteries (MA; diameter <300 µm) isolated from non-gravid, mid-gravid (day 14), and late-gravid rats (day 20) were exposed to aspirin (10^-12 to 10^-5 M). Further, in UA from late-gravid rats, aspirin was evaluated in presence of inhibitors of nitric oxide synthases, cyclooxygenase, cyclic nucleotides (cAMP, cGMP) and BK channels, and also on endothelium-denuded vessels.

RESULTS

Aspirin dilated both UA and MA in a dose dependent manner. Pregnancy increased aspirin vasodilation in MA and UA from mid-gravid rats, an effect that was reduced in vessels from late gravid animals at concentrations >10^-7 M. Further, uterine vasodilation was significantly reduced when the endothelium was removed (p < 0.001), and by inhibitors of nitric oxide synthase (p < 0.001), cyclooxygenase synthase (p < 0.05), cyclic nucleotides cGMP/cAMP and BK channels.

CONCLUSION

This is the first study to show a direct vasodilatory effect of aspirin on rat uterine artery that is mediated by a combination of cellular - primarily endothelial - mechanisms. Our results in UA suggest that the use of aspirin may be effective in enhancing uteroplacental blood flow, while its vasodilation effect on MA may lower peripheral resistance.

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.

A2A Receptor Activation Attenuates Hypertensive Cardiac Remodeling via Promoting Brown Adipose Tissue-Derived FGF21

Adipocytes play important roles in regulating cardiovascular health and disease. However, the molecular mechanism underlying the endocrine role of brown adipose tissue (BAT) in pathological cardiac remodeling remains unknown. Herein we show that adenosine A_2A receptor (A_2AR) knockout (A_2ARKO) causes interscapular BAT (iBAT) dysfunction, leading to accelerated cardiac remodeling in hypertension compared with wild-type (WT) mice. Surgical iBAT depletion induces dramatic cardiac remodeling in WT but not in A_2ARKO hypertensive mice. AMPK/PGC1α signaling-induced fibroblast growth factor 21 (FGF21) in brown adipocytes is required for A_2AR-mediated inhibition of hypertensive cardiac remodeling. Recombinant FGF21 administration improves cardiac remodeling in iBAT-depleted hypertensive mice. More importantly, brown adipocyte-specific A_2ARKO inhibits FGF21 production and accelerates cardiac damage in hypertension. Consistently, brown adipocyte-specific FGF21 knockout abolishes the effects of A_2AR agonism in attenuating hypertensive cardiac remodeling. Our findings reveal a distinctive endocrine role of BAT in hypertensive cardiac remodeling via activating A_2AR/FGF21 pathway.

Adenosine receptor distribution in Rhesus monkey ocular tissue

Adenosine receptor (ADOR) antagonists, such as 7-methylxanthine (7-MX), have been shown to slow myopia progression in humans and animal models. Adenosine receptors are found throughout the body, and regulate the release of neurotransmitters such as dopamine and glutamate. However, the role of adenosine in eye growth is unclear. Evidence suggests that 7-MX increases scleral collagen fibril diameter, hence preventing axial elongation. This study used immunohistochemistry (IHC) and reverse-transcription quantitative polymerase chain reaction (RT-qPCR) to examine the distribution of the four ADORs in the normal monkey eye to help elucidate potential mechanisms of action. Eyes were enucleated from six Rhesus monkeys. Anterior segments and eyecups were separated into components and flash-frozen for RNA extraction or fixed in 4% paraformaldehyde and processed for immunohistochemistry against ADORA1, ADORA2a, ADORA2b, and ADORA3. RNA was reverse-transcribed, and qPCR was performed using custom primers. Relative gene expression was calculated using the ΔΔCt method normalizing to liver expression, and statistical analysis was performed using Relative Expression Software Tool. ADORA1 immunostaining was highest in the iris sphincter muscle, trabecular meshwork, ciliary epithelium, and retinal nerve fiber layer. ADORA2a immunostaining was highest in the corneal epithelium, trabecular meshwork, ciliary epithelium, retinal nerve fiber layer, and scleral fibroblasts. ADORA2b immunostaining was highest in corneal basal epithelium, limbal stem cells, iris sphincter, ciliary muscle, ciliary epithelium, choroid, isolated retinal ganglion cells and scattered scleral fibroblasts. ADORA3 immunostaining was highest in the iris sphincter, ciliary muscle, ciliary epithelium, choroid, isolated retinal ganglion cells, and scleral fibroblasts. Compared to liver mRNA, ADORA1 mRNA was significantly higher in the brain, retina and choroid, and significantly lower in the iris/ciliary body. ADORA2a expression was higher in brain and retina, ADORA2b expression was higher in retina, and ADORA3 was higher in the choroid. In conclusion, immunohistochemistry and RT-qPCR indicated differential patterns of expression of the four adenosine receptors in the ocular tissues of the normal non-human primate. The presence of ADORs in scleral fibroblasts and the choroid may support mechanisms by which ADOR antagonists prevent myopia. The potential effects of ADOR inhibition on both anterior and posterior ocular structures warrant investigation.

Caffeine intake reduces incident atrial fibrillation at a population level

Background

The general belief is that caffeine increases the risk of hyperkinetic arrhythmias, including atrial fibrillation. The aim of this study is to investigate the effect of chronic caffeine intake on incident atrial fibrillation in general population.

Design and methods

A population cohort of 1475 unselected men and women observed for 12 years and left free to intake food or beverages containing caffeine was studied. Subjects were stratified into tertiles of caffeine intake both in the whole cohort and after genotyping for the –163C > A polymorphism of the CYP1A2 gene, regulating caffeine metabolism.

Results

In the whole cohort, the 12-year incidence of atrial fibrillation was significantly lower in the third (2.2%) than in the first (10.2%) or second (5.7%) tertile of caffeine intake ( P < 0.001). The same trend was observed in all genotypes; the apparently steeper reduction of atrial fibrillation in slow caffeine metabolisers found at univariate analysis was proved wrong by multivariate Cox analysis. Age, chronic pulmonary disease, history of heart failure and of coronary artery disease, and systolic blood pressure − but not the genotype or the caffeine ×  CYP1A2 interaction term − were significant confounders of the association between incident atrial fibrillation and being in the third tertile of caffeine intake (hazard ratio 0.249, 95% confidence intervals 0.161–0.458, P < 0.01).

Conclusions

A higher caffeine intake (>165 mmol/day or > 320 mg/day) is associated with a lower incidence of atrial fibrillation in the 12-year epidemiological prospective setting based on the general population.

Epac is required for exogenous and endogenous stimulation of adenosine A2B receptor for inhibition of angiotensin II-induced collagen synthesis and myofibroblast differentiation

Angiotensin II (Ang II) plays an important role on the pathogenesis of cardiac fibrosis. Prolong and overstimulation of angiotensin II type 1 receptor with Ang II-induced collagen synthesis and myofibroblast differentiation in cardiac fibroblasts, leading to cardiac fibrosis. Although adenosine and its analogues are known to have cardioprotective effects, the mechanistic by which adenosine A₂ receptors (A₂Rs) inhibit Ang II-induced cardiac fibrosis is not clearly understood. In the present study, we examined the effects of exogenous adenosine and endogenous adenosine on Ang II-induced collagen and myofibroblast differentiation determined by α-smooth muscle action (α-SMA) overexpression and their underlying signal transduction. Elevation of endogenous adenosine levels resulted in the inhibition of Ang II-induced collagen type I and III and α-SMA synthesis in cardiac fibroblasts. Moreover, treatment with exogenous adenosine which selectively stimulated A₂Rs also suppressed Ang II-induced collagen synthesis and α-SMA production. These antifibrotic effects of both endogenous and exogenous adenosines are mediated through the A_2B receptor (A_2BR) subtype. Stimulation of A_2BR exhibited antifibrotic effects via the cAMP-dependent and Epac-dependent pathways. Our results provide new mechanistic insights regarding the role for cAMP and Epac on A_2BR-mediated antifibrotic effects. Thus, A_2BR is one of the potential therapeutic targets against cardiac fibrosis.

Stimulation of Adenosine A2B Receptor Inhibits Endothelin-1-Induced Cardiac Fibroblast Proliferation and α-Smooth Muscle Actin Synthesis Through the cAMP/Epac/PI3K/Akt-Signaling Pathway

Background and Purpose: Cardiac fibrosis is characterized by an increase in fibroblast proliferation, overproduction of extracellular matrix proteins, and the formation of myofibroblast that express α-smooth muscle actin (α-SMA). Endothelin-1 (ET-1) is involved in the pathogenesis of cardiac fibrosis. Overstimulation of endothelin receptors induced cell proliferation, collagen synthesis, and α-SMA expression in cardiac fibroblasts. Although adenosine was shown to have cardioprotective effects, the molecular mechanisms by which adenosine A₂ receptor inhibit ET-1-induced fibroblast proliferation and α-SMA expression in cardiac fibroblasts are not clearly identified.

Experimental Approach: This study aimed at evaluating the mechanisms of cardioprotective effects of adenosine receptor agonist in rat cardiac fibroblast by measurement of cell proliferation, and mRNA and protein levels of α-SMA.

Key results: Stimulation of adenosine subtype 2B (A_2B) receptor resulted in the inhibition of ET-1-induced fibroblast proliferation, and a reduction of ET-1-induced α-SMA expression that is dependent on cAMP/Epac/PI3K/Akt signaling pathways in cardiac fibroblasts. The data in this study confirm a critical role for Epac signaling on A_2B receptor-mediated inhibition of ET-1-induced cardiac fibrosis via PI3K and Akt activation.

Conclusion and Implications: This is the first work reporting a novel signaling pathway for the inhibition of ET-1-induced cardiac fibrosis mediated through the A_2B receptor. Thus, A_2B receptor agonists represent a promising perspective as therapeutic targets for the prevention of cardiac fibrosis.

Energy Drinks and the Risk of Cardiovascular Disease: A Review of Current Literature

Energy drinks (EDs) are commonly used as a dietary supplement by young adolescents and adults. They are often used as a source of energy in order to enhance physical and mental performance. EDs contain a variety of substances, but caffeine is the main component. Safety has been the biggest concern associated with consuming EDs. Case reports, observational studies, and meta-analyses have been done in order to determine the effects of EDs on cardiovascular changes. The detrimental effects of EDs are cardiac arrhythmias, myocardial infarction, prolonged QT interval, aortic dissection, and death. In this article, we review case reports, observational studies, and meta-analyses of EDs and the risk of cardiovascular events and mortality. We also review active ingredients, pharmacokinetics, and the mechanism of action of EDs.

Targeting Adenosine Receptors for the Treatment of Cardiac Fibrosis

Adenosine is a ubiquitous molecule with key regulatory and cytoprotective mechanisms at times of metabolic imbalance in the body. Among a plethora of physiological actions, adenosine has an important role in attenuating ischaemia-reperfusion injury and modulating the ensuing fibrosis and tissue remodeling following myocardial damage. Adenosine exerts these actions through interaction with four adenosine G protein-coupled receptors expressed in the heart. The adenosine A_2B receptor (A_2BAR) is the most abundant adenosine receptor (AR) in cardiac fibroblasts and is largely responsible for the influence of adenosine on cardiac fibrosis. In vitro and in vivo studies demonstrate that acute A_2BAR stimulation can decrease fibrosis through the inhibition of fibroblast proliferation and reduction in collagen synthesis. However, in contrast, there is also evidence that chronic A_2BAR antagonism reduces tissue fibrosis. This review explores the opposing pro- and anti-fibrotic activity attributed to the activation of cardiac ARs and investigates the therapeutic potential of targeting ARs for the treatment of cardiac fibrosis.

The hybrid molecule, VCP746, is a potent adenosine A2B receptor agonist that stimulates anti-fibrotic signalling

We have recently described the rationally-designed adenosine receptor agonist, 4-(5-amino-4-benzoyl-3-(3-(trifluoromethyl)phenyl)thiophen-2-yl)-N-(6-(9-((2R,3R,4S,5R)-3,4-dihydroxy-5-(hydroxylmethyl)tetrahydro-furan-2-yl)-9H-purin-6-ylamino)hexyl)benzamide (VCP746), a hybrid molecule consisting of an adenosine moiety linked to an adenosine A1 receptor (A1AR) allosteric modulator moiety. At the A1AR, VCP746 mediated cardioprotection in the absence of haemodynamic side effects such as bradycardia. The current study has now identified VCP746 as an important pharmacological tool for the adenosine A2B receptor (A2BAR). The binding and function of VCP746 at the A2BAR was rigorously characterised in a heterologous expression system, in addition to examination of its anti-fibrotic signalling in cardiac- and renal-derived cells. In FlpInCHO cells stably expressing the human A2BAR, VCP746 was a high affinity, high potency A2BAR agonist that stimulated Gs- and Gq-mediated signal transduction, with an apparent lack of system bias relative to prototypical A2BAR agonists. The distinct agonist profile may result from an atypical binding mode of VCP746 at the A2BAR, which was consistent with a bivalent mechanism of receptor interaction. In isolated neonatal rat cardiac fibroblasts (NCF), VCP746 stimulated potent inhibition of both TGF-β1- and angiotensin II-mediated collagen synthesis. Similar attenuation of TGF-β1-mediated collagen synthesis was observed in renal mesangial cells (RMC). The anti-fibrotic signalling mediated by VCP746 in NCF and RMC was selectively reversed in the presence of an A2BAR antagonist. Thus, we believe, VCP746 represents an important tool to further investigate the role of the A2BAR in cardiac (patho)physiology.

Extracellular nucleotide regulation and signaling in cardiac fibrosis

Following myocardial infarction, purinergic nucleotides and nucleosides are released via non-specific and specific mechanisms in response to cellular activation, stress, or injury. These extracellular nucleotides are potent mediators of physiologic and pathologic responses, contributing to the inflammatory and fibrotic milieu within the injured myocardium. Via autocrine or paracrine signaling, cell-specific effects occur through differentially expressed purinergic receptors of the P2X, P2Y, and P1 families. Nucleotide activation of the ionotropic (ligand-gated) purine receptors (P2X) and several of the metabotropic (G-protein-coupled) purine receptors (P2Y) or adenosine activation of the P1 receptors can have profound effects on inflammatory cell function, fibroblast function, and cardiomyocyte function. Extracellular nucleotidases that hydrolyze released nucleotides regulate the magnitude and duration of purinergic signaling. While there are numerous studies on the role of the purinergic signaling pathway in cardiovascular disease, the extent to which the purinergic signaling pathway modulates cardiac fibrosis is incompletely understood. Here we provide an overview of the current understanding of how the purinergic signaling pathway modulates cardiac fibroblast function and myocardial fibrosis.

Dual A1/A2B Receptor Blockade Improves Cardiac and Renal Outcomes in a Rat Model of Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is prevalent and often accompanied by metabolic syndrome. Current treatment options are limited. Here, we test the hypothesis that combined A1/A2B adenosine receptor blockade is beneficial in obese ZSF1 rats, an animal model of HFpEF with metabolic syndrome. The combined A1/A2B receptor antagonist 3-[4-(2,6-dioxo-1,3-dipropyl-7H-purin-8-yl)-1-bicyclo[2.2.2]octanyl]propanoic acid (BG9928) was administered orally (10 mg/kg/day) to obese ZSF1 rats (n = 10) for 24 weeks (from 20 to 44 weeks of age). Untreated ZSF1 rats (n = 9) served as controls. After 24 weeks of administration, BG9928 significantly lowered plasma triglycerides (in mg/dl: control group, 4351 ± 550; BG9928 group, 2900 ± 551) without adversely affecting plasma cholesterol or activating renin release. BG9928 significantly decreased 24-hour urinary glucose excretion (in mg/kg/day: control group, 823 ± 179; BG9928 group, 196 ± 80) and improved oral glucose tolerance, polydipsia, and polyuria. BG9928 significantly augmented left ventricular diastolic function in association with a reduction in cardiac vasculitis and cardiac necrosis. BG9928 significantly reduced 24-hour urinary protein excretion (in mg/kg/day: control group, 1702 ± 263; BG9928 group, 1076 ± 238), and this was associated with a reduction in focal segmental glomerulosclerosis, tubular atrophy, tubular dilation, and deposition of proteinaceous material in the tubules. These findings show that, in a model of HFpEF with metabolic syndrome, A1/A2B receptor inhibition improves hyperlipidemia, exerts antidiabetic actions, reduces HFpEF, improves cardiac histopathology, and affords renal protection. We conclude that chronic administration of combined A1/A2B receptor antagonists could be beneficial in patients with HFpEF, in particular those with comorbidities such as obesity, diabetes, and dyslipidemias.

Adenosine Attenuates Human Coronary Artery Smooth Muscle Cell Proliferation by Inhibiting Multiple Signaling Pathways That Converge on Cyclin D

The goal of this study was to determine whether and how adenosine affects the proliferation of human coronary artery smooth muscle cells (HCASMCs). In HCASMCs, 2-chloroadenosine (stable adenosine analogue), but not N(6)-cyclopentyladenosine, CGS21680, or N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide, inhibited HCASMC proliferation (A2B receptor profile). 2-Chloroadenosine increased cAMP, reduced phosphorylation (activation) of ERK and Akt (protein kinases known to increase cyclin D expression and activity, respectively), and reduced levels of cyclin D1 (cyclin that promotes cell-cycle progression in G1). Moreover, 2-chloroadenosine inhibited expression of S-phase kinase-associated protein-2 (Skp2; promotes proteolysis of p27(Kip1)) and upregulated levels of p27(Kip1) (cell-cycle regulator that impairs cyclin D function). 2-Chloroadenosine also inhibited signaling downstream of cyclin D, including hyperphosphorylation of retinoblastoma protein and expression of cyclin A (S phase cyclin). Knockdown of A2B receptors prevented the effects of 2-chloroadenosine on ERK1/2, Akt, Skp2, p27(Kip1), cyclin D1, cyclin A, and proliferation. Likewise, inhibition of adenylyl cyclase and protein kinase A abrogated 2-chloroadenosine's inhibitory effects on Skp2 and stimulatory effects on p27(Kip1) and rescued HCASMCs from 2-chloroadenosine-mediated inhibition. Knockdown of p27(Kip1) also reversed the inhibitory effects of 2-chloroadenosine on HCASMC proliferation. In vivo, peri-arterial (rat carotid artery) 2-chloroadenosine (20 μmol/L for 7 days) downregulated vascular expression of Skp2, upregulated vascular expression of p27(Kip1), and reduced neointima hyperplasia by 71% (P<0.05; neointimal thickness: control, 37 424±18 371 pixels; treated, 10 352±2824 pixels). In conclusion, the adenosine/A2B receptor/cAMP/protein kinase A axis inhibits HCASMC proliferation by blocking multiple signaling pathways (ERK1/2, Akt, and Skp2) that converge at cyclin D, a key G1 cyclin that controls cell-cycle progression.

Adenosine A2A receptor plays an important role in radiation-induced dermal injury

Ionizing radiation is a common therapeutic modality and following irradiation dermal changes, including fibrosis and atrophy, may lead to permanent changes. We have previously demonstrated that occupancy of A2A receptor (A2AR) stimulates collagen production, so we determined whether blockade or deletion of A2AR could prevent radiation-induced fibrosis. After targeted irradiation (40 Gy) of the skin of wild-type (WT) or A2AR knockout (A2ARKO) mice, the A2AR antagonist ZM241385 was applied daily for 28 d. In irradiated WT mice treated with the A2AR antagonist, there was a marked reduction in collagen content and skin thickness, and ZM241385 treatment reduced the number of myofibroblasts and angiogenesis. After irradiation, there is an increase in loosely packed collagen fibrils, which is significantly diminished by ZM241385. Irradiation also induced an increase in epidermal thickness, prevented by ZM241385, by increasing the number of proliferating keratinocytes. Similarly, in A2ARKO mice, the changes in collagen alignment, skin thickness, myofibroblast content, angiogenesis, and epidermal hyperplasia were markedly reduced following irradiation. Radiation-induced changes in the dermis and epidermis were accompanied by an infiltrate of T cells, which was prevented in both ZM241385-treated and A2ARKO mice. Radiation therapy is administered to a significant number of patients with cancer, and radiation reactions may limit this therapeutic modality. Our findings suggest that topical application of an A2AR antagonist prevents radiation dermatitis and may be useful in the prevention or amelioration of radiation changes in the skin.

Activation of A2b adenosine receptor regulates ovarian cancer cell growth: involvement of Bax/Bcl-2 and caspase-3

A2b adenosine receptor (A2bAR) acts as a potent regulator of cell growth in various cell lines. The present study was designed to understand the controlling mechanism of A2bAR agonist (NECA)-induced apoptosis in ovarian cancer cells. Real-time PCR and western blotting assays were used to evaluate the gene and protein expression profiles of A2bAR, respectively. MTT assay was used to study the cell proliferation effect of A2bAR agonist (NECA). Detection of apoptosis was conducted using annexin V-FITC/PI staining, caspase-3 activation assay, and the expression of Bax and Bcl-2 proteins analysis. The mitochondrial membrane potential (ΔΨM) was analyzed by employing JC-1 prob. The mRNA and protein expression levels of A2bAR in ovarian cancer cells were detected. NECA significantly reduced cell viability in a dose-dependent manner in OVCAR-3 and Caov-4 cell lines. The growth inhibition effect of NECA was related to the induction of cell apoptosis, which was manifested by annexin V-FITC staining, activation of caspase-3, and loss of mitochondrial membrane potentials (ΔΨm). In addition, downregulation of the regulatory protein Bcl-2 and upregulation of Bax protein by NECA were also observed. These findings demonstrated that NECA induces apoptosis via the mitochondrial signaling pathway. Thus, A2bAR agonists may be a potential agent for induction of apoptosis in ovarian cancer cells.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

Commonly consumed beverages in daily life: do they cause atrial fibrillation?

Atrial fibrillation (AF) is the most prevalent cardiac arrhythmia in the United States and worldwide. Caffeine, alcohol, and, more recently, energy drinks are the most commonly consumed beverages in daily living, especially by young individuals. Several questions have been raised about the implications of caffeine, alcohol, and energy drinks in cardiovascular health, especially in triggering AF. This review focuses on the role of these commonly consumed beverages as a cause of AF, with special emphasis of potential mechanisms and studies addressing this issue.

Role of adenosine A2B receptor signaling in contribution of cardiac mesenchymal stem-like cells to myocardial scar formation

Adenosine levels increase in ischemic hearts and contribute to the modulation of that pathological environment. We previously showed that A2B adenosine receptors on mouse cardiac Sca1(+)CD31(-) mesenchymal stromal cells upregulate secretion of paracrine factors that may contribute to the improvement in cardiac recovery seen when these cells are transplanted in infarcted hearts. In this study, we tested the hypothesis that A2B receptor signaling regulates the transition of Sca1(+)CD31(-) cells, which occurs after myocardial injury, into a myofibroblast phenotype that promotes myocardial repair and remodeling. In vitro, TGFβ1 induced the expression of the myofibroblast marker α-smooth muscle actin (αSMA) and increased collagen I generation in Sca1(+)CD31(-) cells. Stimulation of A2B receptors attenuated TGFβ1-induced collagen I secretion but had no effect on αSMA expression. In vivo, myocardial infarction resulted in a rapid increase in the numbers of αSMA-positive cardiac stromal cells by day 5 followed by a gradual decline. Genetic deletion of A2B receptors had no effect on the initial accumulation of αSMA-expressing stromal cells but hastened their subsequent decline; the numbers of αSMA-positive cells including Sca1(+)CD31(-) cells remained significantly higher in wild type compared with A2B knockout hearts. Thus, our study revealed a significant contribution of cardiac Sca1(+)CD31(-) cells to the accumulation of αSMA-expressing cells after infarction and implicated A2B receptor signaling in regulation of myocardial repair and remodeling by delaying deactivation of these cells. It is plausible that this phenomenon may contribute to the beneficial effects of transplantation of these cells to the injured heart.

A novel adenosine precursor 2',3'-cyclic adenosine monophosphate inhibits formation of post-surgical adhesions

BACKGROUND

Intraperitoneal adenosine reduces abdominal adhesions. However, because of the ultra-short half-life and low solubility of adenosine, optimal efficacy requires multiple dosing.

AIM

Here, we compared the ability of potential adenosine prodrugs to inhibit post-surgical abdominal adhesions after a single intraperitoneal dose.

METHODS

Abdominal adhesions were induced in mice using an electric toothbrush to damage the cecum. Also, 20 μL of 95 % ethanol was applied to the cecum to cause chemically induced injury. After injury, mice received intraperitoneally either saline (n = 18) or near-solubility limit of adenosine (23 mmol/L; n = 12); 5'-adenosine monophosphate (75 mmol/L; n = 11); 3'-adenosine monophosphate (75 mmol/L; n = 12); 2'-adenosine monophosphate (75 mmol/L; n = 12); 3',5'-cyclic adenosine monophosphate (75 mmol/L; n = 19); or 2',3'-cyclic adenosine monophosphate (75 mmol/L; n = 20). After 2 weeks, adhesion formation was scored by an observer blinded to the treatments. In a second study, intraperitoneal adenosine levels were measured using tandem mass spectrometry for 3 h after instillation of 2',3'-cyclic adenosine monophosphate (75 mmol/L) into the abdomen.

RESULTS

The order of efficacy for attenuating adhesion formation was: 2',3'-cyclic adenosine monophosphate > 3',5'-cyclic adenosine monophosphate ≈ adenosine > 5'-adenosine monophosphate ≈ 3'-adenosine monophosphate ≈ 2'-adenosine monophosphate. The groups were compared using a one-factor analysis of variance, and the overall p value for differences between groups was p < 0.000001. Intraperitoneal administration of 2',3'-cAMP yielded pharmacologically relevant levels of adenosine in the abdominal cavity for >3 h.

CONCLUSION

Administration of 2',3'-cyclic adenosine monophosphate into the surgical field is a unique, convenient and effective method of preventing post-surgical adhesions by acting as an adenosine prodrug.

Blockade of A2B adenosine receptor reduces left ventricular dysfunction and ventricular arrhythmias 1 week after myocardial infarction in the rat model

BACKGROUND

Remodeling occurs after myocardial infarction (MI), leading to fibrosis, dysfunction, and ventricular tachycardias (VTs). Adenosine via the A2B adenosine receptor (A2BAdoR) has been implicated in promoting fibrosis.

OBJECTIVE

To determine the effects of GS-6201, a potent antagonist of the A2BAdoR, on arrhythmogenic and functional cardiac remodeling after MI.

METHODS

Rats underwent ischemia-reperfusion MI and were randomized into 4 groups: control (treated with vehicle), angiotensin-converting enzyme inhibitor (treated with enalapril 1 day after MI), GS-6201-1d (treated with GS-6201 1 day after MI), GS-6201-1w (treated with GS-6201 administered 1 week after MI) . Echocardiography was performed at baseline and 1 and 5 weeks after MI. Optical mapping, VT inducibility, and histologic analysis were conducted at follow-up.

RESULTS

Treatment with the angiotensin-converting enzyme inhibitor improved ejection fraction (57.8% ± 2.5% vs 43.3% ± 1.7% in control; P < .01), but had no effect on VT inducibility. Treatment with GS-6201 improved ejection fraction (55.6% ± 2.6% vs 43.3% ± 1.7% in control; P < .01) and decreased VT inducibility (9.1% vs 68.4% in control; P < .05). Conduction velocities were significantly higher at border and infarct zones in hearts of rats treated with GS-6201 than in those of other groups. The conduction heterogeneity index was also significantly lower in hearts of rats treated with GS-6201. Histologic analysis showed that while both GS-6201 and enalapril decreased fibrosis in the noninfarct zone, only GS-6201 reduced the heterogeneity of fibrosis at the border, which is consistent with its effect on VT reduction.

CONCLUSIONS

Treatment with an A2BAdoR antagonist at 1 week results in the improvement in cardiac function and decreased substrate for VT. The inhibition of fibrogenesis by A2BAdoR antagonists may be a new target for the prevention of adverse remodeling after MI.

Bradykinin-induced Ca2+ signaling in human subcutaneous fibroblasts involves ATP release via hemichannels leading to P2Y12 receptors activation

Background

Chronic musculoskeletal pain involves connective tissue remodeling triggered by inflammatory mediators, such as bradykinin. Fibroblast cells signaling involve changes in intracellular Ca²⁺ ([Ca²⁺]_i). ATP has been related to connective tissue mechanotransduction, remodeling and chronic inflammatory pain, via P2 purinoceptors activation. Here, we investigated the involvement of ATP in bradykinin-induced Ca²⁺ signals in human subcutaneous fibroblasts.

Results

Bradykinin, via B₂ receptors, caused an abrupt rise in [Ca²⁺]_i to a peak that declined to a plateau, which concentration remained constant until washout. The plateau phase was absent in Ca²⁺-free medium; [Ca²⁺]_i signal was substantially reduced after depleting intracellular Ca²⁺ stores with thapsigargin. Extracellular ATP inactivation with apyrase decreased the [Ca²⁺]_i plateau. Human subcutaneous fibroblasts respond to bradykinin by releasing ATP via connexin and pannexin hemichannels, since blockade of connexins, with 2-octanol or carbenoxolone, and pannexin-1, with ¹⁰Panx, attenuated bradykinin-induced [Ca²⁺]_i plateau, whereas inhibitors of vesicular exocytosis, such as brefeldin A and bafilomycin A1, were inactive. The kinetics of extracellular ATP catabolism favors ADP accumulation in human fibroblast cultures. Inhibition of ectonucleotidase activity and, thus, ADP formation from released ATP with POM-1 or by Mg²⁺ removal from media reduced bradykinin-induced [Ca²⁺]_i plateau. Selective blockade of the ADP-sensitive P2Y₁₂ receptor with AR-C66096 attenuated bradykinin [Ca²⁺]_i plateau, whereas the P2Y₁ and P2Y₁₃ receptor antagonists, respectively MRS 2179 and MRS 2211, were inactive. Human fibroblasts exhibited immunoreactivity against connexin-43, pannexin-1 and P2Y₁₂ receptor.

Conclusions

Bradykinin induces ATP release from human subcutaneous fibroblasts via connexin and pannexin-1-containing hemichannels leading to [Ca²⁺]_i mobilization through the cooperation of B₂ and P2Y₁₂ receptors.

Targeting adenosine receptors in the development of cardiovascular therapeutics

Adenosine receptor stimulation has negative inotropic and dromotropic actions, reduces cardiac ischemia-reperfusion injury and remodeling, and prevents cardiac arrhythmias. In the vasculature, adenosine modulates vascular tone, reduces infiltration of inflammatory cells and generation of foam cells, and may prevent the development of atherosclerosis as a result. Modulation of insulin sensitivity may further add to the anti-atherosclerotic properties of adenosine signaling. In the kidney, adenosine plays an important role in tubuloglomerular feedback and modulates tubular sodium reabsorption. The challenge is to take advantage of the beneficial actions of adenosine signaling while preventing its potential adverse effects, such as salt retention and sympathoexcitation. Drugs that interfere with adenosine formation and elimination or drugs that allosterically enhance specific adenosine receptors seem to be most promising to meet this challenge.

Adenosine receptors and fibrosis: a translational review

Adenosine—a purine nucleoside generated extracellularly from adenine nucleotides released by cells as a result of direct stimulation, hypoxia, trauma, or metabolic stress—is a well-known physiologic and pharmacologic agent. Recent studies demonstrate that adenosine, acting at its receptors, promotes wound healing by stimulating both angiogenesis and matrix production. Subsequently, adenosine and its receptors have also been found to promote fibrosis (excess matrix production) in the skin, lungs, and liver, but to diminish cardiac fibrosis. A commonly ingested adenosine receptor antagonist, caffeine, blocks the development of hepatic fibrosis, an effect that likely explains the epidemiologic finding that coffee drinking, in a dose-dependent fashion, reduces the likelihood of death from liver disease. Accordingly, adenosine may be a good target for therapies that prevent fibrosis of the lungs, liver, and skin.

Collagen triple helix repeat containing-1 inhibits transforming growth factor-b1-induced collagen type I expression in keloid

BACKGROUND

Keloids are benign skin tumours occurring during wound healing in genetically predisposed patients. There is evidence that transforming growth factor (TGF)-b is involved in keloid formation. Collagen triple helix repeat containing- 1 (Cthrc1) was identified as a novel gene expressed in the adventitia and neointima on arterial injury. It is indicated to be a cell type-specific inhibitor of TGF-b, which functionally increases cell migration while reducing collagen type I and III deposition. However, to our knowledge expression and regulatory mechanisms of Cthrc1 and TGF-b1 in keloid and normal skin have not been studied before.

OBJECTIVES

Cthrc1 gene regulation and potential role in keloid formation were determined, and its correlation with TGF-b1 involved in keloid pathogenesis was examined in human fibroblasts of keloids and normal skin.

METHODS

The expression of Cthrc1 and TGF-b1 was investigated in fibroblasts of keloid and normal skin. Collagen type I expression and collagen synthesis in keloid fibroblasts induced by TGF-b1 were examined. Then, recombinant Cthrc1 was applied to assess its correlation with TGF-b1.

RESULTS

Increased TGF-b1 and Cthrc1 expression was examined in keloid compared with normal skin. Cthrc1 expression increased in a concentration-dependent manner induced by TGF-b1 in keloid fibroblasts. TGF-b1 stimulated collagen type I expression and collagen synthesis in keloid fibroblasts, which can be reversed by recombinant Cthrc1.

CONCLUSIONS

TGF-b1 was upregulated in keloid fibroblasts and recombinant Cthrc1 inhibited TGF-b1-stimulated collagen type I synthesis, which suggests that Cthrc1 may be a potential therapeutic option for keloids.

2',3'-cAMP, 3'-AMP, and 2'-AMP inhibit human aortic and coronary vascular smooth muscle cell proliferation via A2B receptors

Rat vascular smooth muscle cells (VSMCs) from renal microvessels metabolize 2',3'-cAMP to 2'-AMP and 3'-AMP, and these AMPs are converted to adenosine that inhibits microvascular VSMC proliferation via A(2B) receptors. The goal of this study was to test whether this mechanism also exists in VSMCs from conduit arteries and whether it is similarly expressed in human vs. rat VSMCs. Incubation of rat and human aortic VSMCs with 2',3'-cAMP concentration-dependently increased levels of 2'-AMP and 3'-AMP in the medium, with a similar absolute increase in 2'-AMP vs. 3'-AMP. In contrast, in human coronary VSMCs, 2',3'-cAMP increased 2'-AMP levels yet had little effect on 3'-AMP levels. In all cell types, 2',3'-cAMP increased levels of adenosine, but not 5'-AMP, and 2',3'-AMP inhibited cell proliferation. Antagonism of A(2B) receptors (MRS-1754), but not A(1) (1,3-dipropyl-8-cyclopentylxanthine), A(2A) (SCH-58261), or A(3) (VUF-5574) receptors, attenuated the antiproliferative effects of 2',3'-cAMP. In all cell types, 2'-AMP, 3'-AMP, and 5'-AMP increased adenosine levels, and inhibition of ecto-5'-nucleotidase blocked this effect of 5'-AMP but not that of 2'-AMP nor 3'-AMP. Also, 2'-AMP, 3'-AMP, and 5'-AMP, like 2',3'-cAMP, exerted antiproliferative effects that were abolished by antagonism of A(2B) receptors with MRS-1754. In conclusion, VSMCs from conduit arteries metabolize 2',3'-cAMP to AMPs, which are metabolized to adenosine. In rat and human aortic VSMCs, both 2'-AMP and 3'-AMP are involved in this process, whereas, in human coronary VSMCs, 2',3'-cAMP is mainly converted to 2'-AMP. Because adenosine inhibits VSMC proliferation via A(2B) receptors, local vascular production of 2',3'-cAMP may protect conduit arteries from atherosclerosis.

2'-AMP and 3'-AMP inhibit proliferation of preglomerular vascular smooth muscle cells and glomerular mesangial cells via A2B receptors

Studies show that kidneys produce 2',3'-cAMP, 2',3'-cAMP is exported and metabolized to 2'-AMP and 3'-AMP, 2'-AMP and 3'-AMP are metabolized to adenosine, 2',3'-cAMP inhibits proliferation of preglomerular vascular smooth muscle cells (PGVSMCs) and glomerular mesangial cells (GMCs), and A(2B) (not A(1), A(2A), or A(3)) adenosine receptors mediate part of the antiproliferative effects of 2',3'-cAMP. These findings suggest that extracellular 2',3'-cAMP attenuates proliferation of PGVSMCs and GMCs partly via conversion to corresponding AMPs, which are metabolized to adenosine that activates A(2B) receptors. This hypothesis predicts that extracellular 2'-AMP and 3'-AMP should exert A(2B) receptor-mediated antiproliferative effects. Therefore, we examined the antiproliferative effects (cell counts) of 2'-AMP and 3'-AMP. In PGVSMCs and GMCs, 2'-AMP and 3'-AMP exerted concentration-dependent antiproliferative effects. 3'-AMP was equipotent with and 2'-AMP was 3-fold less potent than 5'-AMP (prototypical adenosine precursor). In PGVSMCs, the effects of 2'-AMP and 3'-AMP were mimicked by adenosine, and 8-[4-[((4-cyanophenyl)carbamoylmethyl)oxy]phenyl]-1,3-di(n-propyl)xanthine (MRS-1754) (A(2B) receptor antagonist) equally blocked the antiproliferative effects of 2'-AMP, 3'-AMP, and adenosine but less effectively blocked the effects of 2',3'-cAMP. Similar results were obtained in GMCs except that MRS-1754 also incompletely blocked the effects of 3'-AMP. We conclude that in PGVSMCs, 2'-AMP and 3'-AMP are antiproliferative, the antiproliferative effects of 2'-AMP and 3'-AMP are mediated nearly entirely by adenosine/A(2B) receptors, and some of the antiproliferative effects of 2',3'-cAMP are independent of adenosine/A(2B) receptors. Similar conclusions apply to GMCs except that 3'-AMP also has actions independent of adenosine/A(2B) receptors. Because A(2B) receptors are renoprotective, 2'-AMP and 3'-AMP may provide renoprotection by generating adenosine that activates A(2B) receptors.