Adenosine, Adenosine Receptors and Neurohumoral Syncope: From Molecular Basis to Personalized Treatment

Screening and toxicity evaluation of natural compounds as adenosine 2a and 2b receptor ligands: insights from molecular docking, dynamics, and ADMET analysis

Recent studies suggest that immunological and inflammatory responses in cardiovascular disorders, such as hypertension, myocardial infarction, ischemia injury, heart failure, arrhythmias, and atherosclerosis, may be affected by changes in the adenosine system. Pharmacological modulation of adenosine occurs through its receptor subtypes. In numerous preclinical studies, the activation of adenosine receptor 2A (A2AR) or the blockade of adenosine receptor 2B (A2BR) has shown promising results against cardiovascular diseases. This in silico study aimed to identify potential natural compounds that can activate A2AR or block A2BR without causing toxicity. Natural compounds were screened using COlleCtion of Open Natural ProdUcTs (COCONUT) or Natural Product Activity and Species Source Database (NPASS) databases to find agonists for A2AR or an antagonists/inverse agonists for A2BR. These compounds were then pre-filtered based on their toxicity profiles. The remaining compounds were subjected to molecular docking against A2AR and A2BR followed by molecular dynamics simulations were conducted. Finally, selected compounds' ADMET properties were determined using ADMETlab 2.0 web tool. Ultimately, one novel natural compound with potential agonistic activity (COCONUT IDs: CNP0450901) for A2AR and one antagonist/inverse agonist (rauwolscine) for A2BR were identified.

The Brain-Heart Network of Syncope

Observed and recorded in various forms since ancient times, 'syncope' is often popularly called 'fainting', such that the two terms are used synonymously. Syncope/fainting can be caused by a variety of conditions, including but not limited to head injuries, vertigo, and oxygen deficiency. Here, we draw on a large body of literature on syncope, including the role of a recently discovered set of specialized mammalian neurons. Although the etiology of syncope still remains a mystery, we have attempted to provide a comprehensive account of what is known and what still needs to be performed. Much of our understanding of syncope is owing to studies in the laboratory mouse, whereas evidence from human patients remains scarce. Interestingly, the cardioinhibitory Bezold-Jarisch reflex, recognized in the early 1900s, has an intriguing similarity to-and forms the basis of-syncope. In this review, we have integrated this minimal model into the modern view of the brain-neuron-heart signaling loop of syncope, to which several signaling events contribute. Molecular signaling is our major focus here, presented in terms of a normal heart, and thus, syncope due to abnormal or weak heart activity is not discussed in detail. In addition, we have offered possible directions for clinical intervention based on this model. Overall, this article is expected to generate interest in chronic vertigo and syncope/fainting, an enigmatic condition that affects most humans at some point in life; it is also hoped that this may lead to a mechanism-based clinical intervention in the future.

cAMP-PKA/EPAC signaling and cancer: the interplay in tumor microenvironment

Cancer is a complex disease resulting from abnormal cell growth that is induced by a number of genetic and environmental factors. The tumor microenvironment (TME), which involves extracellular matrix, cancer-associated fibroblasts (CAF), tumor-infiltrating immune cells and angiogenesis, plays a critical role in tumor progression. Cyclic adenosine monophosphate (cAMP) is a second messenger that has pleiotropic effects on the TME. The downstream effectors of cAMP include cAMP-dependent protein kinase (PKA), exchange protein activated by cAMP (EPAC) and ion channels. While cAMP can activate PKA or EPAC and promote cancer cell growth, it can also inhibit cell proliferation and survival in context- and cancer type-dependent manner. Tumor-associated stromal cells, such as CAF and immune cells, can release cytokines and growth factors that either stimulate or inhibit cAMP production within the TME. Recent studies have shown that targeting cAMP signaling in the TME has therapeutic benefits in cancer. Small-molecule agents that inhibit adenylate cyclase and PKA have been shown to inhibit tumor growth. In addition, cAMP-elevating agents, such as forskolin, can not only induce cancer cell death, but also directly inhibit cell proliferation in some cancer types. In this review, we summarize current understanding of cAMP signaling in cancer biology and immunology and discuss the basis for its context-dependent dual role in oncogenesis. Understanding the precise mechanisms by which cAMP and the TME interact in cancer will be critical for the development of effective therapies. Future studies aimed at investigating the cAMP-cancer axis and its regulation in the TME may provide new insights into the underlying mechanisms of tumorigenesis and lead to the development of novel therapeutic strategies.

Protective Properties of Intestinal Alkaline Phosphatase Supplementation on the Intestinal Barrier: Interactions and Effects

The intestinal barrier is critical for maintaining intestinal homeostasis, and its dysfunction is associated with various diseases. Recent findings have revealed the multifunctional role of intestinal alkaline phosphatase (IAP) in diverse biological processes, including gut health maintenance and function. This review summarizes the protective effects of IAP on intestinal barrier integrity, encompassing the physical, chemical, microbial, and immune barriers. We discuss the results and insights from in vitro, animal model, and clinical studies as well as the available evidence regarding the impact of diet on IAP activity and expression. IAP can also be used as an indicator to assess intestinal-barrier-related diseases. Further research into the mechanisms of action and long-term health effects of IAP in maintaining overall intestinal health is essential for its future use as a dietary supplement or functional component in medical foods.

AI-based identification of therapeutic agents targeting GPCRs: introducing ligand type classifiers and systems biology

Identifying ligands targeting G protein coupled receptors (GPCRs) with novel chemotypes other than the physiological ligands is a challenge for in silico screening campaigns. Here we present an approach that identifies novel chemotype ligands by combining structural data with a random forest agonist/antagonist classifier and a signal-transduction kinetic model. As a test case, we apply this approach to identify novel antagonists of the human adenosine transmembrane receptor type 2A, an attractive target against Parkinson's disease and cancer. The identified antagonists were tested here in a radio ligand binding assay. Among those, we found a promising ligand whose chemotype differs significantly from all so-far reported antagonists, with a binding affinity of 310 ± 23.4 nM. Thus, our protocol emerges as a powerful approach to identify promising ligand candidates with novel chemotypes while preserving antagonistic potential and affinity in the nanomolar range.

Adenosinergic System and Neuroendocrine Syncope: What Is the Link?

Although very common, the precise mechanisms that explain the symptomatology of neuroendocrine syncope (NES) remain poorly understood. This disease, which can be very incapacitating, manifests itself as a drop in blood pressure secondary to vasodilation and/or extreme slowing of heart rate. As studies continue, the involvement of the adenosinergic system is becoming increasingly evident. Adenosine, which is an ATP derivative, may be involved in a large number of cases. Adenosine acts on G protein-coupled receptors with seven transmembrane domains. A1 and A2A adenosine receptor dysfunction seem to be particularly implicated since the activation leads to severe bradycardia or vasodilation, respectively, two cardinal symptoms of NES. This mini-review aims to shed light on the links between dysfunction of the adenosinergic system and NHS. In particular, signal transduction pathways through the modulation of cAMP production and ion channels in relation to effects on the cardiovascular system are addressed. A better understanding of these mechanisms could guide the pharmacological development of new therapeutic approaches.

Sex Related Differences in the Complex Relationship between Coffee, Caffeine and Atrial Fibrillation

This literature review aims to explore the data of articles published on the association between coffee, caffeine and atrial fibrillation and to analyze any differences between the two sexes. Several factors influence this complex relationship; genetic, environmental and psychosocial factors come into play in the pathophysiology of atrial fibrillation. These factors are expressed differently in women and men. However, the analysis of the literature has shown that comparison works between the two sexes are extremely rare. Most population-based and prospective studies either analyze aggregated data or focus on exclusively male or female populations. This results in a lack of information that could be useful in the prevention of and treatment approach to atrial fibrillation. It is necessary to deepen this issue with dedicated studies.

The Role of Adenosine and Its Degradation Enzymes - Adenosinedeaminase and Adenosinekinase in Pathogenesis of Vasovagal Syncope

INTRODUCTION

Adenosine is mediator regulating physiological and pathological processes in organism. It probably plays a role in pathogenesis of vasovagal syncopes (VVS), too. Adenosine, its receptors and degradation enzymes- adenosinedeaminase (ADA) and adenosinekinase (ADK), are called the adenosinergic system.

AIM

We aimed to evaluate serum levels of adenosine, ADA and ADK in patients with tilt-induced VVS and compare them to tlit-negative controls. Secondary aim was to compare the levels between the types of VVS and correlate them with hemodynamic parameters.

SUBJECTS AND METHODS

Altogether 132 individuals were involved in this study (age 39,88±15,64 years, 51 males). All patients underwent head up tilt test (HUTT) in differential diagnosis of syncope. Blood sampling was performed before and after HUTT. Baseline and stimulated serum levels of adenosine, ADA and ADK were evaluated by ELISA method.

RESULTS

HUTT was positive in 91 patients (HUTT+), 41 individuals were negative (HUTT-). HUTT+ patients had higher baseline and stimulated adenosine levels, when compared to HUTT- population. The rise in adenosine was higher in HUTT+ group. On the other hand, the increase of ADA was significantly higher in HUTT- subjects. Among HUTT+ group, the highest adenosine was found during vasodepressoric VVS.

CONCLUSION

Adenosinergic system may play role in pathogenesis of VVS. Patients with VVS have higher adenosine levels, that may be caused by attenuated degradation. Adenosine seems to be involved predominantly in vasodepressoric type of VVS. Further research evaluating complex function of adenosinergic system in these patients is needed.