Adenosine Antagonists Research Articles

Citrulline activates adenosine receptors: New insight into metabolic pathways interaction

Citrulline is a non-proteinogenic amino acid that forms as by-product in nitric oxide (NO) synthesis from arginine and may act in concert with NO as an independent signaling molecule that involves in the mechanism of vascular smooth muscle vasodilation.In this study we examined the effects of citrulline on pulmonary artery smooth muscles. Experimental design comprised outward potassium currents measurements in enzymatically isolated rat pulmonary artery smooth muscle (PASMc) cells using whole-cell patch clamp technique, isometric contractile force recordings on rat pulmonary artery rings and method of molecular docking simulation.Citrulline in a concentration 10−9-10−5 M relaxed phenylephrine (PHE)-preactivated SM of rat pulmonary artery in a dose-dependent manner (EC50 0,67 μM). This citrulline-induced relaxation was dependent on an intact endothelium. Bath application of citrulline (10-8-10-5 M) on isolated PASMc induced a significant increase in the amplitude of outward potassium current (Ik). The adenosine antagonist caffeine (10-6 M) effectively blocked both the citrulline-induced relaxation response and Ik increment. Molecular docking modeling suggests that caffeine blocking the potent activity of citrulline results from competitive interactions at the A2 adenosine receptor binding site.In summary, our data suggest that citrulline, released with NO at low concentrations, can effectively interact with adenosine receptors in smooth muscle cells, causing their relaxation, indicating surprising interaction between NO and adenosine pathways.

Protective Effects of Early Neonatal Methylxanthine Treatment on Cognitive and Language Outcomes in Premature Infants with and without High-Risk Perinatal Factors.

Caffeine and theophylline are methylxanthines and nonselective adenosine antagonists commonly used to treat apnea of prematurity. Both human and animal data suggest that xanthines also have clinically important long-term neuroprotective effects in the presence of inflammation in the perinatal period as seen following hypoxic-ischemic brain insults. Moreover, these protective effects appear to be more robust when administered shortly (<48 h) after preterm birth. To evaluate the importance of the postdelivery therapeutic window, we collected and analyzed medical data from preterm infants meeting criteria (23-30 weeks' gestational age [GA]), born at the University of Connecticut Health Center (UCHC), and cared for at the UCHC/Connecticut Children's Medical Center (CCMC) NICU from 1991 to 2017 (n = 858). Eighteen-month follow-up data included cognitive and language scores from the Neonatal Neurodevelopmental Follow-Up Clinic records, with a retention of 81% of subjects (n = 696). Differences were analyzed via multivariate ANOVA and ANCOVA. Analyses showed that infants who received xanthine treatment within the first 48 h after preterm birth showed significantly better 18-month behavioral outcomes than those treated later than 48 h, despite a lack of a priori differences in GA, birth, or length of stay. The positive effect of early xanthine therapy was particularly robust for infants exposed prenatally to the inflammatory conditions of chorioamnionitis and/or preeclampsia. Current findings are consistent with human and animal data, showing that caffeine exerts protective effects, at least in part via attenuation of inflammation. Results add to the evidence supporting routine immediate prophylactic neuroprotective xanthine therapy (i.e., caffeine) in preterm infants. Findings also add important new evidence of the augmented value of caffeine for infants with inflammatory exposure due to mothers with preeclampsia or chorioamnionitis.

Sex Dependence in Control of Renal Haemodynamics and Excretion in Streptozotocin Diabetic Rats-Role of Adenosine System and Nitric Oxide.

Recently, we compared an interplay of the adenosine system and nitric oxide (NO) in the regulation of renal function between male normoglycaemic (NG) and streptozotocin-induced diabetic rats (DM). Considering the between-sex functional differences, e.g., in the NO status, we present similar studies performed in female rats. We examined if the theophylline effects (non-selective adenosine antagonist) in NG and DM females with or without active NO synthases differed from the earlier findings. In anaesthetised female Sprague Dawley rats, both NG and DM, untreated or after NO synthesis blockade with L-NAME, theophylline effects, on blood pressure, renal hemodynamics and excretion, and renal tissue NO were investigated. Renal artery blood flow (Transonic probe), cortical, outer-, and inner-medullary flows (laser-Doppler technique), and renal tissue NO signal (selective electrode) were measured. In contrast to males, in female NG and DM rats, theophylline induced renal vasodilation. In NO-deficient females, theophylline induced comparable renal vasodilatation, confirming the vasoconstrictor influence of the renal adenosine. In NG and DM females with intact NO synthesis, adenosine inhibition diminished kidney tissue NO, contrasting with an increase reported in males. Lowered baseline renal excretion in DM females suggested stimulation of renal tubular reabsorption due to the prevalence of antinatriuretic over natriuretic tubular action of adenosine receptors. An opposite inter-receptor balance pattern emerged previously from male studies. The study exposed between-sex functional differences in the interrelation of adenosine and NO in rats with normoglycaemia and streptozotocin diabetes. The findings also suggest that in diabetes mellitus, the abundance of individual receptor types can distinctly differ between females and males.

Effect of adenosinergic manipulations on amygdala-kindled seizures in mice: Implications for sudden unexpected death in epilepsy.

Sudden unexpected death in epilepsy (SUDEP) results in more years of potential life lost than any neurological condition with the exception of stroke. It is generally agreed that SUDEP happens due to some form of respiratory, cardiac, and electrocerebral dysfunction following a seizure; however, the mechanistic cause of these perturbations is unclear. One possible explanation lies with adenosinergic signaling. Extracellular levels of the inhibitory neuromodulator adenosine rapidly rise during seizures, a countermeasure that is necessary for seizure termination. Previous evidence has suggested that excessive adenosinergic inhibition could increase the risk of SUDEP by silencing brain areas necessary for life, such as the respiratory nuclei of the brainstem. The goal of this investigation was to further clarify the role of adenosine in seizure-induced respiratory and electrocerebral dysfunction. To determine the role of adenosine in postictal physiological dysregulation, we pharmacologically manipulated adenosine signaling prior to amygdala-kindled seizures in mice while recording electroencephalogram (EEG), electromyogram, and breathing using whole body plethysmography. The adenosinergic drugs used in this study included selective and nonselective adenosine receptor antagonists and inhibitors of adenosine metabolism. We found that high doses of adenosine receptor antagonists caused some seizures to result in seizure-induced death; however, counterintuitively, animals in these conditions that did not experience seizure-induced death had little or no postictal generalized EEG suppression. Inhibitors of adenosine metabolism had no effect on postictal breathing but did worsen some postictal electrocerebral outcomes. The unexpected effect of high doses of adenosine antagonists on seizure-induced death observed in this study may be due to the increase in seizure severity, vasoconstriction, or phosphodiesterase inhibition caused by these drugs at high doses. These findings further clarify the role of adenosine in seizure-induced death and may have implications for the consumption of caffeine in epilepsy patients and the prevention of SUDEP.

Role of 7-methylxanthine in myopia prevention and control: a mini-review.

Myopia is becoming increasingly common. By 2050 around 10% of the world's population is expected to be highly myopic (<-5 diopters) and therefore particularly at risk of suffering from sight-threatening complications. Currently used myopia control treatments, such as multifocal soft contact lenses or spectacle lenses, orthokeratology, and atropine eyedrops, either do not completely arrest myopia progression or are associated with significant ocular and possibly systemic side effects. A new candidate for pharmaceutical control of myopia progression and excessive eye elongation, the non-selective adenosine antagonist 7-methylxanthine (7-MX), appears to be non-toxic and effective in reducing myopia progression and axial eye growth in experimental and clinical studies. The latest findings regarding 7-MX for myopia control and evaluate its potential as a supplement to existing treatment options were reviewed.

P175 PARADOXICAL RESPONSE DURING DOBUTAMINE STRESS ECHOCARDIOGRAPHY: A CASE REPORT

Abstract Background Dobutamine Stress Echo (DSE) is a test widely used in the diagnosis of ischemic heart disease. The purpose of the following work is to describe a clinical case with uncommon behaviour. Case Description: 63–year–old female with dyspnoea on mild exertion, and history of NSTEMI–ACS 5 years prior with Coronary Angiography (CA) finding of 3–vessel coronary artery disease, treated with PCI + stent (DES) of right coronary artery (CDX), untreated disease sub–occlusion of the first marginal obtuse (OM1), and chronic occlusion of the anterior interventricular artery (IVA). We decide for DSE. During 20 mcg/kg/min infusion, the patient reported dyspnoea and paradoxical bradycardia (BP) was documented on the ECG, in the absence of ST changes, with the appearance of akinesia of the basal and mid posterolateral segments and worsening of the inferior hypokinesia, present in basal conditions on Echocardiograms (EC). The BP and the alterations of the ventricular motion (VCA) did not respond to the administration of Atropine (1+1 mg) while the administration of 240 mg of Aminophylline (AM) restored the HR and the VCA to baseline values. The CA demonstrated patency of the CDX with the presence of collateral circulation for IVA and occluded OM1. Discussion This case is characterized by the presence of a double paradox: the BP and the Atropine–Resistance (AR). BP during DEB, as demonstrated in previous studies, occurred in 8% of cases, with signs of significant coronary artery disease in 57% of cases. The BP is an expression of ischemia only in just over half of the patients, in the rest of the cases it appeared referable to the Bezold–Jarish reflex, a vagal reflex determined by the stimulation of the intracardiac mechanoreceptors. In our case, the presence of AR seems to exclude the possibility that bradycardia is due to this reflex. The appearance of paradoxical bradycardia during DSE is a rare complication and can lead to premature termination of the test with inconclusive results. In our case, the BP and the AR confirm the positivity of the test also in consideration of the response to the AM antagonist of Adenosine, which accumulates during ischemia. Conclusions This uncommon response to DSE, where AR and AM response in addition to BP could identify patients with severe coronary artery disease in whom the ischemic response is driven by adenosine accumulation, rather than a vagal reflex responding to atropine administration.

Prophylactic Intravenous Aminophylline for Preventing Bradyarrhythmias During Coronary Atherectomy: A 10-Year Single-Center Experience.

Aminophylline, an adenosine antagonist, can be used to prevent adenosine-mediated bradyarrhythmias. Retrospective, observational, descriptive analysis of patients undergoing rotational atherectomy with intravenous (IV) aminophylline pretreatment during a 10-year period (2010-2020). The primary composite outcome was the occurrence of a documented bradyarrhythmia requiring pharmacologic intervention and/or temporary pacemaker (TPM) implantation. A total of 296 patients received IV aminophylline pretreatment. The primary composite outcome occurred in 1.7% (n = 5) of patients. None of the patients required rescue TPM. Bradyarrhythmias were documented in 2.4% (n = 7) of patients. Pharmacologic interventions, typically with IV atropine, were used in 15% (n = 43) of patients. Per-vessel analyses demonstrated that patients undergoing atherectomy to the circumflex and right coronary arteries were more likely than those undergoing atherectomy to other vessels to have bradyarrhythmias requiring pharmacologic intervention (3.4% vs 0%, P = .01). In this 10-year single-center experience using IV aminophylline pretreatment to prevent major bradyarrhythmias in patients undergoing coronary atherectomy, none of the patients required rescue TPM implantation. These data demonstrate that coronary atherectomy can be performed safely without prophylactic TPM, with aminophylline pretreatment and selective use of atropine representing an effective noninvasive approach.

An Overview on Synthetic and Medicinal Perspectives of [1,2,4]Triazolo[1,5-a]pyrimidine Scaffold.

[1,2,4]Triazolo[1,5-a]pyrimidine is an important heterocyclic scaffold known to have a wide range of pharmacological activities such as anticancer, antimicrobial, anti-tubercular, CB2 cannabinoid agonists, feticide, and adenosine antagonists. Several clinical trials and marketed drugs such as Trapidil, Essramycin, Pyroxsulam, DSM-265, Flumetsulam, GNF-6702, and Cevipabulin indicate the potential of [1,2,4]triazolo[1,5-a]pyrimidine moiety with various functional groups in medicinal chemistry. Herein, we represent a concise report focusing on the synthetic strategies used for diversely substituted [1,2,4]triazolo[1,5-a]pyrimidine analogs and their pharmacological applications. To the best of our knowledge, since 1980, we are the first to write a review on this emerging scaffold, which reveals the synthetic strategies, and pharmacological activities of differently substituted [1,2,4]triazolo[1,5-a]pyrimidine with special emphasis on structure-activity relationship studies.

Metabolic reprogramming by adenosine antagonism and implications in non-small cell lung cancer therapy

Non-small cell lung cancer (NSCLC) is a heterogeneous disease with genetic and environmental parameters that influence cell metabolism. Because of the complex interplay of environmental factors within the tumor microenvironment (TME) and the profound impact of these factors on the metabolic activities of tumor and immune cells, there is an emerging interest to advance the understanding of these diverse metabolic phenotypes in the TME. High levels of adenosine are characteristic of the TME, and adenosine can have a significant impact on both tumor cell growth and the immune response. Consistent with this, we showed in NSCLC data from TCGA that high expression of the A2BR leads to worse outcome and that expression of A2BR may be different for different mutation backgrounds. We then investigated the metabolic reprogramming of tumor cells and immune cells (T and dendritic cells) by adenosine. We used A2AR and A2BR antagonism or agonism as well as receptor knockout animals to explore whether these treatments altered specific immune compartments or conferred specific therapeutic vulnerabilities. Using the seahorse assay, we found that an A2BR antagonist modulates oxidative stress homeostasis in NSCLC cell lines. In addition, we found distinct metabolic roles of A2AR and A2BR receptors in T cell activation and dendritic cell maturation. These data suggest potential mechanisms and therapeutic benefits of A2 receptor antagonist therapy in NSCLC.

Blood-brain barrier permeability in response to caffeine challenge.

Caffeine is known to alter brain perfusion by acting as an adenosine antagonist, but its effect on blood-brain barrier (BBB) permeability is not fully elucidated. This study aimed to dynamically monitor BBB permeability to water after a single dose of caffeine tablet using a non-contrast MRI technique. Ten young healthy volunteers who were not regular coffee drinkers were studied. The experiment began with a pre-caffeine measurement, followed by four measurements at the post-caffeine stage. Water-extraction-with-phase-contrast-arterial-spin-tagging (WEPCAST) MRI was used to assess the time dependence of BBB permeability to water following the ingestion of 200 mg caffeine. Other cerebral physiological parameters including cerebral blood flow (CBF), venous oxygenation (Yv ), and cerebral metabolic rate of oxygen (CMRO2 ) were also examined. The relationships between cerebral physiological parameters and time were studied with mixed-effect models. It was found that, after caffeine ingestion, CBF and Yv showed a time-dependent decrease (p < 0.001), while CMRO2 did not change significantly. The fraction of arterial water crossing the BBB (E) showed a significant increase (p < 0.001). In contrast, the permeability-surface-area product (PS), i.e., BBB permeability to water, remained constant (p = 0.94). Additionally, it was observed that changes in physiological parameters were non-linear with regard to time and occurred at as early as 9min after caffeine tablet ingestion. These results suggest an unchanged BBB permeability despite alterations in perfusion during a vasoconstrictive caffeine challenge.

Association between maternal caffeine intake during pregnancy and child development at 6 and 12 months: The Japan Environment and Children's Study

BackgroundCaffeine intake by pregnant women may have neurodevelopmental effects on the fetus due to adenosine antagonism. However, there are insufficient data and inconsistent results from epidemiological studies on the effect of maternal caffeine intake on child development. AimsThis study examined the association between mothers' estimated caffeine intake during pregnancy and their children's score on the Japanese version of the Ages & Stages Questionnaires™ (J-ASQ) at 6 and 12 months of age. Study designThe study is a part of nationwide prospective birth-cohort study: the Japan Environment and Children's Study. SubjectsIn total, 87,106 participants with the Food Frequency Questionnaire (FFQ) data and J-ASQ at 6 or 12 months of age were included in the study. Outcome measuresThe data were analyzed by logistic regression analysis to determine whether the scores of the five subscales on the J-ASQ were below the cutoff point as the dependent variable. ResultsThe results showed that children born to mothers who consumed >300 mg caffeine per day had a 1.11-fold increased odds of gross motor developmental delay at 12 months of age (adjusted odds ratio [AOR] = 1.114 [95 % CI: 1.013–1.226]). ConclusionsIssues in gross motor development can emerge prior to future developmental issues. Therefore, further studies on developmental outcomes in older children, including the future outcomes of the children who participated in this study, are needed.

Abstract 4150: Enriching for adenosine antagonist patient responses through deep learning

Abstract Background: Adenosine signaling is a key metabolic pathway regulating tumor immunity. The conversion of inflammatory extracellular ATP into immunosuppressive adenosine invokes signaling of the A2a receptor (A2AR) in the tumor microenvironment. This dampens immune responses and creates a pro-tumor niche. A number of novel IO drugs targeting the adenosine pathway through inhibition of the ectonucleotidases CD39 and CD73 or the A2AR/BR are in clinical trials, including our non-CNS penetrant A2AR-selective antagonist, EXS21546 (NCT04727138). While early clinical results from other adenosine receptor-inhibitors (A2ARi) have shown modest monotherapy activity in nonspecific patient populations, we believe greater success can be achieved by leveraging methods that enable the evaluation of single-cell effects in patient samples preclinically. Using our deep learning driven image analysis platform, we define an adenosine-induced, tumor protective immunosuppression biomarker to augment A2AR antagonist responder identification. Here we describe efforts to transcriptionally and functionally map the adenosine suppressed immune potential and activation by inhibition of A2AR with EXS21546 in primary material. The goal is to reveal gene signatures indicative of adenosine immunosuppression deployable in clinical studies, increasing the likelihood of trial success by identifying patients that have the highest efficiency potential for A2AR targeted therapy. Methods: Leveraging patient material as disease relevant model systems, and collecting baseline and treatment condition transcriptomics, we model the patient specific anti-cancer immune repertoire and validate patient selection methods functionally with a translatable high content imaging platform amenable to primary human material supported by end-to-end deep learning driven image analysis. Results: Combining single cell transcriptomic and functional response data, we demonstrate preclinical mechanistic studies of A2AR antagonism on infiltrating immune cells, with the ultimate aim of discovering predictive algorithms to enrich patients more likely respond to adenosine pathway inhibitors. Patient selection gene signatures are functionally validated using a high content imaging platform with proven translational capabilities (Kornauth et al, Cancer Disc., 2021), demonstrating the association of anti-cancer immune activity with inhibition of adenosine signaling by EXS21546. Signatures and patient selection algorithms are cross-validated with publicly available data. Discussion: Gathering multiple layers of data from primary tumor tissues, we reveal and map the association of immune response potential to A2AR inhibition in cancer. Patient stratification gene signatures identified have the aim to be implemented in future studies of our candidate A2ARi EXS21546, to deliver the right drug at the right time in the right patients. Citation Format: Isabella Alt, Robert Shelke, Anna Lobley, Claudia Baumgaertler, Maja Stulic, Pierre Fons, Mark Whittaker, Klaus Hackner, Lucia Dzurillova, Edga Petru, Laudia Hadjari, Judith Lafleur, Josef Singer, Nikolaus Krall, Lukas Hefler, Thorsten Füreder, Christina Taubert, Christophe Boudesco, Andrew Payne, Gregory Ian Vladimer. Enriching for adenosine antagonist patient responses through deep learning [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4150.

A-44 | Intravenous aminophylline for preventing bradyarrhythmias during coronary atherectomy

Aminophylline, an adenosine antagonist, can be used to prevent adenosine-mediated bradyarrhythmias. No robust data exist on its use to prevent bradyarrhythmias in patients undergoing coronary atherectomy.

Using Caffeine to Enhance the Therapeutic Effects of Respiratory Training After Cervical Spinal Cord Injury

Cervical spinal cord injury (SCI) often leads to damage of the phrenic motor circuit that innervates the diaphragm, resulting in life‐threatening respiratory deficits. While there is some limited spontaneous plasticity after a cervical SCI, severe respiratory deficits persist. Previous research has shown that non‐invasive respiratory training with intermittent hypoxia (IH) can enhance respiratory plasticity after SCI. There are two prominent plasticity promoting pathways associated with IH training, dependent on serotonin or adenosine. Prior work suggests there is greater activation of the serotonergic plasticity‐promoting pathway after inhibiting the adenosine pathway. Therefore, this work aims to use a clinically relevant adenosine antagonist – caffeine – in combination with IH respiratory training to further enhance the respiratory plasticity and diaphragm recovery of adult female rats after a mid‐cervical (C3/4) contusion injury. We hypothesized that 4 weeks of daily IH training primed with 8mg of caffeine, delivered 30 minutes before the training, will enhance the serotonergic plasticity‐promoting pathway to stimulate both anatomical and functional phrenic plasticity and improve respiration post‐SCI. To label phrenic circuitry, 72 hours before terminal experiments, animals were traced with a retrograde, transsynaptic tracer, pseudorabies virus (PRV), applied to the ipsilateral hemidiaphragm to label phrenic moto‐ and interneurons. Anatomical plasticity was assessed using immunohistochemistry to quantify interneuronal connectivity and density of descending serotonergic input to the phrenic motor network. Specifically, this study also investigated the connectivity of a cholinergic interneuron subpopulation within phrenic circuitry after IH training and caffeine delivery. Functional plasticity and respiratory recovery after IH training primed with caffeine were assessed with weekly whole‐body plethysmography and terminal diaphragm electromyography. The results of this study using caffeine as a primer for respiratory training can be easily translated to improve training outcomes and promote greater plasticity and recovery after SCI.

Caffeine, chocolate, and adenosine antagonism in Parkinson’s disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder. It is generally accepted that dopamine replacement therapy substantially improves motor symptoms; however, there is a worldwide tendency to include nutrients in treatment strategies. In the present review, caffeine and chocolate are discussed. Caffeine use seems to postpone the occurrence of PD in men, and perhaps also in women who do not take postmenopausal hormone replacement therapy. There are contradictory data concerning possible caffeine-induced improvements in PD symptoms. Given that the basic action of caffeine is the antagonism of adenosine receptors, adenosine antagonists may be a new option for treating PD patients. Furthermore, PD patients tend to have increased chocolate consumption; this may be causally related to ingredients such as phenylethylamine. Thus, nutrients such as caffeine and chocolate may play an important role in postponing and/or improving symptoms in PD.

Abstract 14180: RyR2 Hyperactivity Contributes to Arrhythmogenic Triggers in the ex vivo Human Right Ventricle

Introduction: Sudden cardiac death (SCD) caused by VT/VF is a major cause of mortality and morbidity, accounting for up to 20% of all deaths in the United States. Novel antiarrhythmic targets and relevant translational models of SCD are urgently needed for basic and translational arrhythmia research, and ex vivo donor human hearts are invaluable resources for such pharmacological studies. It was the goal of this study to investigate the occurrence of VT/VF in excised human hearts and to test a novel pharmacological agent to suppress arrhythmias. Hypothesis: We assessed the hypothesis that RyR2 hyperactivity contributes to arrhythmogenic triggers and substrates in the human RV, and we analyzed the antiarrhythmic effects of pharmacological RyR2 suppression. Methods: Adult human hearts (n = 10; 3F, 7M) were procured from the Washington Regional Transplant Community. The entire RV free wall was isolated, coronary perfused, and placed in an oxygenated, 37°C bath of Tyrode’s solution for optical mapping with the addition of Di-4-ANBDQBS and blebbistatin. Pseduo ECGs were recorded, and action potentials (APs) were spatiotemporally mapped using high-speed CMOS cameras. Optical recordings were taken at baseline and after exposure to the adrenergic agonist isoproterenol (ISO, 250 nM) and the adenosine antagonist caffeine (CAF, 200 μM) to elicit RyR2 hyperactivity. We also evaluated pharmacological RyR2 suppression (2 μM dantrolene) on arrhythmia inhibition. Results: ISO and ISO+CAF significantly shortened tissue APDs. ISO+CAF increased the incidence of PVCs at low pacing frequencies as well as increased the incidence of VT/VF at high pacing frequencies. We observed non-sustained arrhythmias in roughly a third of the hearts examined. No significant differences in conduction velocities were observed. While dantrolene did not return APDs to baseline conditions, it did significantly reverse the effect of caffeine on inducing PVCs. Conclusions: In conclusion, caffeine contributes to arrhythmogenic triggers in the ex vivo human right ventricle, and dantrolene may be used as a pharmacological tool to suppress RyR2 hyperactivity and thus prevent SCD.

Discovery of Highly Potent Adenosine A1 Receptor Agonists: Targeting Positron Emission Tomography Probes.

Adenosine receptor (AR) radiotracers for positron emission tomography (PET) have provided knowledge on the in vivo biodistribution of ARs in the central nervous system (CNS), which is of therapeutic interest for various neuropsychiatric disorders. Additionally, radioligands that can image changes in endogenous adenosine levels in different physiological and pathological conditions are still lacking. The binding of known antagonist adenosine A1 receptor (A1R) radiotracer, [11C]MDPX, failed to be inhibited by elevated endogenous adenosine in a rodent PET study. Since most of the known AR PET radiotracers were antagonists, we propose that an A1R agonist radioligand may possess higher sensitivity to measure changes in endogenous adenosine concentration. Herein, we report our latest findings toward the development of a full agonist adenosine A1 radioligand for PET. Based on a 3,5-dicyanopyridine template, 16 new derivatives were designed and synthesized to optimize both binding affinity and functional activity, resulting in two full agonists (compounds 27 and 29) with single-digit nanomolar affinities and good subtype selectivity (A1/A2A selectivity of ∼1000-fold for compound 27 and 29-fold for compound 29). Rapid O-[11C]methylation provided [11C]27 and [11C]29 in high radiochemical yields and radiochemical purity. However, subsequent brain PET imaging in rodents showed poor brain permeability for both radioligands. An in vivo PET study using knockout mice for MDR 1a/a, BCRP, and MRP1 indicated that these compounds might be substrates for brain efflux pumps. In addition, in silico evaluation using multiparameter optimization identified high molecular weight and high polar surface area as the main molecular descriptors responsible for low brain penetration. These results will provide further insight toward development of full agonist adenosine A1 radioligands and also highly potent CNS A1AR drugs.

Adenosine A2AR/A1R Antagonists Enabling Additional H3R Antagonism for the Treatment of Parkinson's Disease.

Adenosine A1/A2A receptors (A1R/A2AR) represent targets in nondopaminergic treatment of motor disorders such as Parkinson's disease (PD). As an innovative strategy, multitargeting ligands (MTLs) were developed to achieve comprehensive PD therapies simultaneously addressing comorbid symptoms such as sleep disruption. Recognizing the wake-promoting capacity of histamine H3 receptor (H3R) antagonists in combination with the "caffeine-like effects" of A1R/A2AR antagonists, we designed A1R/A2AR/H3R MTLs, where a piperidino-/pyrrolidino(propyloxy)phenyl H3R pharmacophore was introduced with overlap into an adenosine antagonist arylindenopyrimidine core. These MTLs showed distinct receptor binding profiles with overall nanomolar H3R affinities (Ki < 55 nM). Compound 4 (ST-2001, Ki (A1R) = 11.5 nM, Ki (A2AR) = 7.25 nM) and 12 (ST-1992, Ki (A1R) = 11.2 nM, Ki (A2AR) = 4.01 nM) were evaluated in vivo. l-DOPA-induced dyskinesia was improved after administration of compound 4 (1 mg kg-1, i.p. rats). Compound 12 (2 mg kg-1, p.o. mice) increased wakefulness representing novel pharmacological tools for PD therapy.

“The path is smooth that leadeth on to danger”: caffeine and psychosis

AimsTo review literature on the importance of caffeine intake with regard to psychosis. The need for intervention with regard to caffeine intake hinges on effectively recognizing potential risks.BackgroundCaffeine is the most widely consumed psychoactive substance worldwide and as such is generally considered acceptable but as a competitive adenosine antagonist, it affects dopamine transmission. Patients with serious mental illness are known to have higher caffeine intakes than the general population. The hierarchy of needs for this patient population is complex, frequently leaving the intake of caffeine under the radar of clinical priorities.MethodPubMed and Google Scholar search for caffeine/coffee and psychosis/schizophreniaResultOf the 43 articles that were considered relevant for clinical practice, caffeine consumption was associated with 1) appearance of psychotic symptoms and episodes (caffeine-induced psychosis) and chronic psychosis in high intake 2) exacerbation of psychosis in schizophrenic patients even in lower intakes, 3) treatment resistance possibly due to interference with antipsychotics (ex. clozapine), 4) abuse and addiction, 5) comorbidity with tobacco smoking and other addictions. Caffeine in low doses was associated with ameliorating cognitive and extrapyramidal side-effects of medication and as a potential treatment strategy for treatment-resistant schizophrenia.ConclusionCaffeine consumption may have a greater impact on psychotic symptoms and episodes than is recognized with negative effects outweighing any potential benefits. Greater awareness of the necessity to quantify caffeine intake and implementation of interventions to curb intake may contribute to better quality of care of serious mental illness. Further research is warranted.

Adenosine 5’-monophosphate induces hypothermia and alters gene expressions in the brain and liver of chicks

The adenosine A1 receptor is important for body temperature regulation in mammals; however, little is known about its function in avian species. In this study, we investigated the effects of the adenosine A1 receptor agonist and antagonist (adenosine 5′-monophosphate [5′-AMP] and 8 p-sulfophenyl theophylline [8-SPT], respectively) on thermoregulation in chickens. Male chicks were used in this study. After administration of 5′-AMP and 8-SPT, the rectal temperature, plasma metabolites, and gene expressions in the hypothalamus and liver were measured. The rectal temperature was reduced by peripheral administration of 5′-AMP, and the hypothermic effect of 5′-AMP was attenuated by central injection of 8-SPT in chicks. In the hypothalamus, the mRNA level of the agouti-related protein (AgRP) was increased by 5′-AMP administration, whereas it was suppressed by 8-SPT. The plasma levels of free fatty acid were elevated in 5′-AMP-treated chicks and that elevation was suppressed by the 8-SPT treatment. The gene expression of proopiomelanocortin in the hypothalamus was affected by 8-SPT. Nevertheless, the gene expressions of the thermoregulation-related genes, such as the thyrotropin-releasing hormone, were not affected by 5′-AMP and 8-SPT. Hepatic gene expressions related to lipid intake and metabolism were suppressed by 5′-AMP. However, the gene expression of the uncoupling protein was upregulated by 5′-AMP. Based on these results, birds, like mammals, will undergo adenosine A1 receptor-induced hypothermia. In conclusion, it is suggested that 5′-AMP-mediated hypothermia via the adenosine A1 receptor may affect the central melanocortin system and suppress hepatic lipid metabolism in chickens.