Non-selective Adenosine Receptor Antagonist Research Articles

Abstract 18147: Role of Adenosine Receptor Engagement in Ectonucleotide Triphosphate Diphosphohydrolase-1 Mediated Resistance to Conduit Arterial Thrombosis in Mice

Background: Ectonucleoside Triphosphate Diphosphohydrolase-1 (ENTPD-1/CD39) plays a key role in regulating platelet reactivity; it converts prothrombotic ATP and ADP to AMP which is further degraded by ecto-5’-nucleotidase (CD73) to adenosine, an anti-thrombotic mediator. The objective was to determine role of adenosine receptor engagement in ENTPDase-1 mediated resistance to in vivo arterial thrombosis in mice. Methods: Transgenic mice expressing human ENTPD-1 and littermate controls (WT) were subjected to FeCl 3 -induced carotid artery thrombosis. Results: ENTPD-1 mice displayed marked resistance to thrombosis (WT: 13.7 ± 0.9 min vs. ENTPD-1: 281.5 ± 57.3 min; P <0.001; n=6/group; Figure). Treatment of mice with α-β-methylene-ADP (APCP; 2 mg/kg 15 minute prior to injury), a specific ecto-5’-nucleotidase antagonist, completely abrogated the protection from thrombosis mediated by ENTPD-1 overexpression (APCP-treated WT: 11.9 ± 1.0min vs. APCP-treated ENTPD-1: 26.5 ± 11.1 min; n=6/group; Figure), suggesting that ecto-5’-nucleotidase-mediated generation of adenosine is required for ENTPD-1 mediated resistance to in vivo thrombosis. Furthermore, in mice treated with the non-selective adenosine receptor antagonist 8-(p-Sulfophenyl) theophylline (8-SPT; 20 mg /kg 15 minutes prior to injury) the resistance to thrombosis observed in ENTPDase-1 overexpresssing mice was abrogated (8-SPT Treated WT (n=8): 10.5 ± 1.4 min vs. 8-SPT Treated ENTPD-1 (n=9): 14.3 ± 1.6 min; Figure). Conclusions: Adenosine receptor engagement contributes to the resistance to thrombosis mediated by ENTPDase-1 overexpression.

SCH58261 the Selective Adenosine A2A Receptor Blocker Modulates Ischemia Reperfusion Injury Following Bilateral Carotid Occlusion: Role of Inflammatory Mediators

In the present study, the effects of SCH58261, a selective adenosine A(2A) receptor antagonist that crosses the blood brain barrier (BBB) and 8-(4-sulfophenyl) theophylline (8-SPT), a non-selective adenosine receptor antagonist that acts peripherally, were investigated on cerebral ischemia reperfusion injury (IR). Male Wistar rats (200-250 g) were divided into four groups: (1) sham-operated (SO), IR pretreated with either (2) vehicle (DMSO); (3) SCH58261 (0.01 mg/kg); (4) 8-SPT (2.5 mg/kg). Animals were anesthetized and submitted to occlusion of both carotid arteries for 45 min. All treatments were administered intraperitoneally (i.p.) post carotid occlusion prior to exposure to a 24 h reperfusion period. Ischemic rats showed increased infarct size compared to their control counterparts that corroborated with histopathological changes as well as increased lactate dehydrogenase (LDH) activity in the hippocampus. Moreover, ischemic animals showed habituation deficit, increased anxiety and locomotor activity. IR increased hippocampal glutamate (Glu), GABA, glycine (Gly) and aspartate (ASP). SCH58261 significantly reversed these effects while 8-SPT elicited minimal change. IR raised myeloperoxidase (MPO), tumor necrosis factor-alpha (TNF-α), nitric oxide (NO), prostaglandin E₂ (PGE₂) accompanied by a decrease in interleukin-10 (IL-10), effects that were again reversed by SCH58261, but 8-SPT elicited less changes. Results from the present study point towards the importance of central blockade of adenosine A(2A) receptor in ameliorating hippocampal damage following IR injury by halting inflammatory cascades as well as modulating excitotoxicity.

자생식물 혼합 추출물이 SD 흰쥐에서의 행동양상 및 항산화 체계에 미치는 영향

Caffeine, a psychoactive stimulant, has been implicated in the modulation of learning and memory functions due to its action as a non-selective adenosine receptors antagonist. On the contrary, some side effects of caffeine have been reported, such as an increased energy loss and metabolic rate, decrease DNA synthesis in the spleen, and increased oxidative damage to exerted on LDL particles. Therefore, the aim of this study was to develop a safe stimulant from natural plants mixture (Aralia elata, Acori graminei Rhizoma, Chrysanthemum, Dandleion, Guarana, Shepherd’s purse) that can be used as a substitute for caffeine. Thirty SD rats were divided into three groups; control group, caffeine group (15.0 mg/kg, i.p.), and natural plants mixture group (NP, 1 mL/kg, p.o.). The effect of NP extract on stimulant activity was evaluated with open-field test (OFT) and plus maze test for measurement of behavioral profiles. Plasma lipid profiles, lipid peroxidation in LDL (conjugated dienes), total antioxidant capacity (TRAP) and DNA damage in white blood, liver, and brain cells were measured. In the OFT, immobility time was increased significantly by acute (once) and chronic (3 weeks) supplementation of NP and showed a similar effect to caffeine treatment. Three weeks of caffeine treatment caused plasma lipid peroxidation and DNA damage in liver cells, whereas there were no changes in the NP group. NP group showed a higher plasma HDL cholesterol concentration compared to the caffeine group. The results indicate that the natural plants mixture had a stimulant effect without inducing oxidative stress.

Transgenic over expression of ectonucleotide triphosphate diphosphohydrolase-1 protects against murine myocardial ischemic injury

Modulation of purinergic signaling is critical to myocardial homeostasis. Ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD-1; CD39) which converts the proinflammatory molecules ATP or ADP to AMP is a key regulator of purinergic modulation. However, the salutary effects of transgenic over expression of ENTPD-1 on myocardial response to ischemic injury have not been tested to date. Therefore we hypothesized that ENTPD-1 over expression affords myocardial protection from ischemia–reperfusion injury via specific cell signaling pathways. ENTPD-1 transgenic mice, which over express human ENTPDase-1, and wild-type (WT) littermates were subjected to either ex vivo or in vivo ischemia–reperfusion injury. Infarct size, inflammatory cell infiltrate and intracellular signaling molecule activation were evaluated. Infarct size was significantly reduced in ENTPD-1 versus WT hearts in both ex vivo and in vivo studies. Following ischemia–reperfusion injury, ENTPD-1 cardiac tissues demonstrated an increase in the phosphorylation of the cellular signaling molecule extracellular signal-regulated kinases 1/2 (ERK 1/2) and glycogen synthase kinase-3β (GSK-3β). Resistance to myocardial injury was abrogated by treatment with a non-selective adenosine receptor antagonist, 8-SPT or the more selective A2B adenosine receptor antagonist, MRS 1754, but not the A1 selective antagonists, DPCPX. Additionally, treatment with the ERK 1/2 inhibitor PD98059 or the mitochondrial permeability transition pore opener, atractyloside, abrogated the cardiac protection provided by ENTPDase-1 expression. These results suggest that transgenic ENTPDase-1 expression preferentially conveys myocardial protection from ischemic injury via adenosine A2B receptor engagement and associated phosphorylation of the cellular protective signaling molecules, Akt, ERK 1/2 and GSK-3β that prevents detrimental opening of the mitochondrial permeability transition pore.

Reciprocal modulation of anti‐IgE induced histamine release from human mast cells by A1 and A2B adenosine receptors

Adenosine is believed to participate in the pathological development of asthma through a mast cell-dependent mechanism. Our study aimed to pharmacologically characterize the functions of adenosine receptor (AR) subtypes (A₁, A(2A) , A(2B) and A₃) in primary human cultured mast cells (HCMC). HCMC were derived from progenitor stem cells in buffy coat and the effects of adenosine receptor ligands on basal and IgE-dependent histamine release were evaluated. Adenosine and analogues alone did not induce HCMC degranulation. When HCMC were activated by anti-IgE after 10 min pre-incubation with adenosine, a biphasic effect on histamine release was observed with enhancement of HCMC activation at low concentrations of adenosine (10⁻⁹-10⁻⁷ mol·L⁻¹) and inhibition at higher concentrations (10⁻⁶-10⁻⁴ mol·L⁻¹). The potentiating action was mimicked by A₁ AR agonists CCPA and 2'MeCCPA, and inhibited by the A₁ AR antagonist PSB36. In contrast, the inhibitory action of adenosine was mimicked by the non-specific A₂ AR agonist CV1808 and attenuated by A(2B) AR antagonists PSB1115 and MRS1760. The non-selective AR antagonist CGS15943 attenuated both the potentiating and inhibitory actions. We have defined for the first time the contribution of A₁ and A(2B) ARs, respectively, to the potentiating and inhibitory action of adenosine on human mast cell activation. With reference to the current trend of developing novel anti-asthmatic agents from AR ligands, our results suggest that inhibition of human mast cell activation would be a mechanism for A₁ AR antagonists, but not A(2B) AR antagonists.

Linalool from Rosewood (Aniba rosaeodora Ducke) Oil Inhibits Adenylate Cyclase in the Retina, Contributing to Understanding its Biological Activity

Rosewood oil (RO) (Aniba rosaeodora Ducke) is rich in linalool, a monoterpene alcohol, which has well studied anxiolytic, sedative and anticonvulsant effects. The inhibition of the increases in cAMP protects against seizures in a diversity of models of epilepsy. In this paper, the principal aim was to investigate the effects of RO, (±)-linalool and (-)-linalool) on adenylate cyclase. They were tested in chick retinas and forskolin was used to stimulate the enzyme target. The phosphodiesterase inhibitor, 4-(3-butoxy-4-methoxybenzyl)-imidazolidin-2-one, and the non-selective adenosine receptor antagonist 3-isobutyl-methyl-xanthine (IBMX), were used to control the participation of phosphodiesterase and adenosine receptors in the resulting effects, respectively. The cAMP accumulation was measured by enzyme immune assay (EIA). Rosewood oil, (-)-linalool and (±)-linalool inhibited exclusively the cAMP accumulation stimulated by forskolin, even when adenosine receptors were blocked with IBMX. The IC(50) values (in μ m concentration range) calculated from their concentration response-curves were not statistically different, however, the compounds presented a different relative efficacy. These results extend the range of subcellular mechanisms underlying the relaxant action of linalool on the central nervous system.

Role of adenosine A 2A receptor signaling in the nicotine-evoked attenuation of reflex cardiac sympathetic control

Baroreflex dysfunction contributes to increased cardiovascular risk in cigarette smokers. Given the importance of adenosinergic pathways in baroreflex control, the hypothesis was tested that defective central adenosinergic modulation of cardiac autonomic activity mediates the nicotine–baroreflex interaction. Baroreflex curves relating changes in heart rate (HR) to increases or decreases in blood pressure (BP) evoked by i.v. doses (1–16 μg/kg) of phenylephrine (PE) and sodium nitroprusside (SNP), respectively, were constructed in conscious rats; slopes of the curves were taken as measures of baroreflex sensitivity (BRS). Nicotine (25 and 100 μg/kg i.v.) dose-dependently reduced BRS SNP in contrast to no effect on BRS PE. BRS SNP was also attenuated after intracisternal (i.c.) administration of nicotine. Similar reductions in BRS SNP were observed in rats pretreated with atropine or propranolol. The combined treatment with nicotine and atropine produced additive inhibitory effects on BRS, an effect that was not demonstrated upon concurrent exposure to nicotine and propranolol. BRS SNP was reduced in preparations treated with i.c. 8-phenyltheophylline (8-PT, nonselective adenosine receptor antagonist), 8-(3-Chlorostyryl) caffeine (CSC, A 2A antagonist), or VUF5574 (A 3 antagonist). In contrast, BRS SNP was preserved after blockade of A 1 (DPCPX) or A 2B (alloxazine) receptors or inhibition of adenosine uptake by dipyridamole. CSC or 8-PT abrogated the BRS SNP depressant effect of nicotine whereas other adenosinergic antagonists were without effect. Together, nicotine preferentially impairs reflex tachycardia via disruption of adenosine A 2A receptor-mediated facilitation of reflex cardiac sympathoexcitation. Clinically, the attenuation by nicotine of compensatory sympathoexcitation may be detrimental in conditions such as hypothalamic defense response, posture changes, and ventricular rhythms.

Abstract 1746: Modulation of ABCG2 mediated multidrug resistance by xanthine derivatives

Abstract ABCG2 is an ATP-binding-cassette (ABC) transporter that confers multidrug resistance (MDR) in tumor cells by extruding a broad variety of chemotherapeutic agents, ultimately leading to failure of cancer therapy. Accordingly, the downregulation of ABCG2 expression and/or function has been proposed as part of a regimen to improve cancer therapeutic efficacy. Adenosine receptors (ARs), belong to the G-protein coupled receptor superfamily, and play important roles in stimulating neuronal cells, regulating cell proliferation and controlling immune responses. Adenosine receptor antagonists, a large collection of small molecules mainly composed of methylxanthines and other xanthine derivatives, have been used or implicated in many therapeutic applications, such as treatment of asthma, chronic bronchitis, emphysema and neural degenerative diseases. Previously, we have shown that the non-selective AR antagonist 1,3,7-methyxanthine (caffeine) can dramatically downregulate ABCG2 expression levels in cancer cell lines, increasing the intracellular retention of the ABCG2 specific substrate Mitoxantrone (MX) and markedly sensitizing cells to this chemotherapeutic agent. In order to find more potent and specific modulators of ABCG2 expression, we recently tested other ARs antagonists. Among the compounds we have examined, the non-selective antagonists theophylline, theobromine, paraxanthine, and the A2R selective antagonists 8-(3-chlorostyryl), caffeine (CSC) and 3,7-dimethyl-1-propargylxanthine (DMPX), were capable of downregulating ABCG2 protein levels to varying degrees. An A1R selective antagonist, 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX), currently in clinical trials, also decreased the expression of ABCG2 significantly at physiologically- relevant concentrations. In addition, the natural ligand of the ARs, adenosine, completely blocked the downregulation of ABCG2 by caffeine, suggesting that adenosine receptors and their downstream signaling pathways are involved in the regulation of ABCG2 gene expression. These findings suggest that xanthine adenosine receptor antagonists could be developed as combination therapy to improve the efficacy of drugs that are ABCG2 substrates. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1746. doi:10.1158/1538-7445.AM2011-1746

Central Adenosine Receptors Differentially Contribute To The Nicotine‐Induced Attenuation Of Reflex Tachycardic Responses To Baroreceptor Unloading

Nicotine impairs reflex cardiac sympathoexcitatory responses to baroreceptor unloading. The role of central adenosine receptors in the nicotine-baroreflex interaction was investigated. Baroreflex curves relating reflex heart rate (HR) responses to decreases in blood pressure (BP) evoked by i.v. doses (1–16 μg/kg) of sodium nitroprusside (SNP) was constructed in conscious male rats. Slopes of the curves were taken as a measure of baroreflex sensitivity (BRSSNP). Whether administered i.v. (25 or 100 μg/kg) or intracis-ternally (2 or 5 μg/rat), nicotine caused dose-dependent downward shifts in SNP curves and reductions in BRSSNP. BRSSNP was also reduced in rats treated intracisternally with 8-phenyltheophylline (8-PT, nonselective adenosine receptor antagonist), 8-(3-Chlorostyryl) caffeine (CSC, A2A antagonist), or VUF5574 (A3 antagonist) in contrast to no effect for DPCPX (A1 antagonist), alloxazine (A2B antagonist), or dipyridamole (adenosine uptake inhibitor). Pretreatment with 8-PT or CSC abrogated the BRSSNP depressant effect of nicotine whereas other adenosine receptor antagonists were without effect. It is concluded that central pathways of A2A or A3 receptors tonically facilitate reflex cardiac sympathoexcitation. Further, disruption of central A2A receptor signaling mediates the nicotine-baroreflex interaction. Supported by Faculty of Pharmacy, Alexandria University, Egypt.

Protection against skeletal muscle hypoperfusion by adenosine and nitric oxide: together alone?

regulation of vasomotor tone in the microcirculation is essential to ensure adequate tissue oxygenation, particularly when oxygen demand is high, i.e., in skeletal or cardiac muscle during exercise and/or when supply is compromised, i.e., during hypoxia or in the presence of a flow-limiting stenosis

Effects of maternal hypoxia on muscle vasodilatation evoked by acute systemic hypoxia in adult rat offspring: changed roles of adenosine and A1receptors

Suboptimal conditions in utero can have long-lasting effects including increased risk of cardiovascular disease in adult life. Such programming effects may be induced by chronic systemic hypoxia in utero (CHU). We have investigated how CHU affects cardiovascular responses evoked by acute systemic hypoxia in adult male offspring, recognising that adenosine contributes to hypoxia-induced muscle vasodilatation and bradycardia by acting on A(1) receptors in normal (N) rats. In the present study, dams were housed in a hypoxic chamber at 12% O(2) for the second half of gestation; offspring were born and reared in air until 9-10 weeks of age. Under anaesthesia, acute systemic hypoxia (breathing 8% O(2) for 5 min) evoked similar biphasic tachycardia/bradycardia, fall in arterial pressure and increase in femoral vascular conductance (FVC) in N and CHU rats (+2.0 vs. +2.7 conductance units respectively). However, in CHU rats, neither the non-selective adenosine receptor antagonist 8-sulphophenyltheopylline (8-SPT), nor the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) affected the increase in FVC, but DPCPX attenuated the hypoxia-induced bradycardia. Further, in N and CHU rats, 5 min infusion of adenosine induced similar increases in FVC; in CHU rats, DPCPX reduced the adenosine-induced increase in FVC (by >50%) and accentuated the concomitant tachycardia. These results suggest that CHU rats have functional A(1) receptors in heart and vasculature, but the release and/or vasodilator influence of adenosine on the endothelium in acute hypoxia is attenuated and replaced by other dilator factors. Such changes from normal endothelial function may have implications for general cardiovascular regulation.

Caffeine, inflammation, and BPD

In this issue of The Journal, Chavez Valdez et al provide observations on the relationship between serum caffeine levels and cytokine concentrations in tracheal aspirates and peripheral blood. The rationale for the study was to examine the role of caffeine, a non-selective adenosine receptor antagonist, in the regulation of pro- and anti-inflammatory cytokines. The results show that serum caffeine levels were higher after more than a week of treatment than they were after the initial doses. The relationship between caffeine levels and pro-inflammatory cytokines was U-shaped, meaning that at low serum caffeine levels TNF-α, IL-1 and IL-6 were reduced in concentration but at higher caffeine levels their levels were increased. One of the touted advantages of caffeine for the treatment of apnea of prematurity was the purported absence of the “need” to monitor levels. This study suggests that there is a complex relationship between caffeine levels and pro-inflammatory cytokines, which may contribute to the severity of inflammatory conditions, such as bronchopulmonary dysplasia (BPD), in children with high caffeine levels. This has important management and therapeutic implications. We may need to monitor caffeine levels if, indeed, these studies can be corroborated and a relationship between plasma caffeine levels, evoked inflammation, and BPD is further established.Article page 38 ▸ In this issue of The Journal, Chavez Valdez et al provide observations on the relationship between serum caffeine levels and cytokine concentrations in tracheal aspirates and peripheral blood. The rationale for the study was to examine the role of caffeine, a non-selective adenosine receptor antagonist, in the regulation of pro- and anti-inflammatory cytokines. The results show that serum caffeine levels were higher after more than a week of treatment than they were after the initial doses. The relationship between caffeine levels and pro-inflammatory cytokines was U-shaped, meaning that at low serum caffeine levels TNF-α, IL-1 and IL-6 were reduced in concentration but at higher caffeine levels their levels were increased. One of the touted advantages of caffeine for the treatment of apnea of prematurity was the purported absence of the “need” to monitor levels. This study suggests that there is a complex relationship between caffeine levels and pro-inflammatory cytokines, which may contribute to the severity of inflammatory conditions, such as bronchopulmonary dysplasia (BPD), in children with high caffeine levels. This has important management and therapeutic implications. We may need to monitor caffeine levels if, indeed, these studies can be corroborated and a relationship between plasma caffeine levels, evoked inflammation, and BPD is further established. Article page 38 ▸ Correlation between Serum Caffeine Levels and Changes in Cytokine Profile in a Cohort of Preterm InfantsThe Journal of PediatricsVol. 158Issue 1PreviewTo determine changes in cytokine levels associated with caffeine treatment in a cohort of preterm infants. Full-Text PDF

Novel N-Methylated 8-Oxoisoguanines from Pacific Sponges with Diverse Neuroactivities

Marine organisms have yielded a variety of metabolites with neuropharmacological applications. Here we describe the isolation and pharmacological characterization of four novel, neurologically active purines 1-4, isolated from Haplosclerida sponges collected in the Republic of Palau. The structures were determined by analyses of spectral and X-ray data. Compound 1 induced convulsions upon intracerebroventricular injection into mice, with a CD50 value of 2.4 nmol/mouse. Purines 2-4 were active in mouse bioassays at higher doses. The seizurogenic activity of 1 was correlated with inhibition of neuronal GABAergic transmission, with only a modest impact on excitatory signaling, in electrophysiological recordings from hippocampal neurons. Despite having a purine template structure, the inhibitory activity of 1 was not prevented by a nonselective adenosine receptor antagonist. Thus, 1 represents a novel substituted purine that elicits convulsions through its actions on inhibitory neurotransmission. These 8-oxoisoguanine analogs comprise a new family of compounds closely related in structure to endogenous neurosignaling molecules and commonly used CNS stimulants.

Antinociceptive effect of butyl (2-phenylethynyl) selenide on formalin test in mice: Evidences for the involvement of serotonergic and adenosinergic systems

The present study investigated the effect of per oral (p.o.) administration of butyl (2-phenylethynyl) selenide (1–50mg/kg) on formalin-induced nociception in mice. The involvement of serotonergic, adenosinergic, muscarinic cholinergic and opioid mechanisms in the antinociceptive effect was also investigated. Butyl (2-phenylethynyl) selenide inhibited both neurogenic (at doses equal or higher than 10mg/kg) and inflammatory (at doses equal or higher than 25mg/kg) phases of the nociception caused by intraplantar (i.pl.) injection of 2.5% formalin solution (20μl), with ID50 values of 36.7 (29.28–46.0) and 20.37 (15.74–26.36) mg/kg, respectively. This compound reduced the formalin-induced paw oedema formation (55±4%) at doses equal or higher than 25mg/kg. The antinociceptive effect of compound (25mg/kg, p.o.) was reversed by ondansetron (0.5mg/kg, a 5-HT3 receptor antagonist) and caffeine (3mg/kg, a nonselective adenosine receptor antagonist), but not by atropine (0.1mg/kg, a non selective muscarinic antagonist), WAY100635 (0.1mg/kg, a selective 5-HT1A receptor antagonist), ritanserin (1mg/kg, a 5-HT2 receptor antagonist) and naloxone (1mg/kg, a non selective opioid receptor antagonist). These results indicate that butyl (2-phenylethynyl) selenide produced antinociception in the formalin test through mechanisms that involve an interaction with serotonergic (5-HT3) and adenosinergic systems.

Caffeine, Adenosine Receptors, and Synaptic Plasticity

Few studies to date have looked at the effects of caffeine on synaptic plasticity, and those that did used very high concentrations of caffeine, whereas the brain concentrations attained by regular coffee consumption in humans should be in the low micromolar range, where caffeine exerts pharmacological actions mainly by antagonizing adenosine receptors. Accordingly, rats drinking caffeine (1 g/L) for 3 weeks, displayed a concentration of caffeine of circa 22 microM in the hippocampus. It is known that selective adenosine A1 receptor antagonists facilitate, whereas selective adenosine A2A receptor antagonists attenuate, long term potentiation (LTP) in the hippocampus. Although caffeine is a non-selective antagonist of adenosine receptors, it attenuates frequency-induced LTP in hippocampal slices in a manner similar to selective adenosine A2A receptor antagonists. These effects of low micromolar concentration of caffeine (30 microM) are maintained in aged animals, which is important when a possible beneficial effect for caffeine in age-related cognitive decline is proposed. Future studies will still be required to confirm and detail the involvement of A1 and A2A receptors in the effects of caffeine on hippocampal synaptic plasticity, using both pharmacological and genetic approaches.

Role of the central ascending neurotransmitter systems in the psychostimulant effects of caffeine.

Caffeine is the most consumed psychoactive drug in the world. It is a non-selective adenosine receptor antagonist that in the brain targets mainly adenosine A1 and A2A receptors. The same as classical psychostimulants, caffeine produces motor-activating, reinforcing and arousing effects. This depends on the ability of caffeine to counteract multiple effects of adenosine in the central ascending neurotransmitter systems. Motor and reinforcing effects depend on the ability of caffeine to release pre- and postsynaptic brakes that adenosine imposes on the ascending dopaminergic system. By targeting A1-A2A receptor heteromers in striatal glutamatergic terminals and A1 receptors in striatal dopaminergic terminals (presynaptic brake), caffeine induces glutamate-dependent and glutamate-independent release of dopamine. These presynaptic effects of caffeine are potentiated by the release of the postsynaptic brake imposed by antagonistic interactions in the striatal A2A-D2 and A1-D1 receptor heteromers. Arousing effects of caffeine depend on the blockade of multiple inhibitory mechanisms that adenosine, as an endogenous sleep-promoting substance, exerts on the multiply interconnected ascending arousal systems. Those mechanisms include a direct A1-receptor mediated modulation of the corticopetal basal forebrain system and an indirect A2A-receptor mediated modulation of the hypothalamic histaminergic and orexinergic systems.

Adenosinergic Modulation Of The Imidazoline I1‐Receptor‐Dependent Hypotensive Effect Of Ethanol In Acute Renal Failure

We recently reported that ethanol lowers blood pressure (BP) in rats with acute renal failure (ARF) via facilitation of sympathoinhibitory pathways of central imidazoline I1‐receptors. This study investigated whether adenosine receptor subtypes modulate the ethanol‐I1‐receptor interaction. The effect of selective blockade of adenosine A1, A2A, or A2B receptors on hemodynamic responses to consecutive administration of moxonidine, I1‐receptor agonist, and ethanol was determined in the glycerol model (10 ml/kg, i.m.) of ARF. Ethanol (1 g/kg i.v.) elicited significant decreases and increases in BP and heart rate (HR), respectively, in ARF rats. Prior exposure to moxonidine abolished the hypotensive but not the tachycardic effect of ethanol. The ability of moxonidine to abolish ethanol hypotension disappeared after selective blockade of adenosine A1 or A2A receptors with 8‐Cyclopentyl‐1,3‐dipropylxanthine and 8‐(3‐chlorostyryl) caffeine, respectively. In contrast, the moxonidine‐ethanol interaction was not affected in presence of alloxazine, a selective A2B antagonist or 8‐phenyltheophylline, a nonselective adenosine receptor antagonist. These findings suggest that alterations caused by moxonidine in adenosine A1 and A2A receptor signaling function to offset the I1‐receptor‐dependent hypotensive action of ethanol in ARF rats.

Involvement of Cx43 phosphorylation in 5′‐N‐ethylcarboxamide‐induced migration and proliferation of mouse embryonic stem cells

Despite a lot of gap junction research, the complex connection between gap junction and cell proliferation remains an exciting area of investigation. Thus, we examined the effect of connexin 43 (Cx43) on the migration and proliferation of embryonic stem (ES) cells and its related signaling pathways following stimulation with the adenosine analogue 5'-N-ethylcarboxamide (NECA). NECA increased phosphorylation of Cx43 which was blocked by caffeine, a non-selective adenosine receptor antagonist. In experiment to measure the gap junctional intercellular communication, NECA blocked transfer of Lucifer yellow to neighboring cells in a scrape loading/dye transfer (SL/DT) assay. In addition, NECA-induced phosphorylation of phosphoinositide 3-kinase (PI3K)/Akt, protein kinase C (PKC), mitogen-activated protein kinases (MAPKs), and nuclear factor-kappa B (NF-kappaB) signal pathways. Inhibition of these signaling pathways reduced NECA-induced phosphorylation of Cx43. Moreover, NECA-treated cells demonstrated phosphorylation of Src, which was blocked by caffeine. In this experiment, a disruption of Cx43 using Cx43-specific small interfering RNA (siRNA) also enhanced Src phosphorylation. In a further study, phosphorylations of integrin beta1, focal adhesion kinase (FAK), and paxillin by NECA were restrained by caffeine as well as the Src blocker, PP2. Finally, we identified that NECA-stimulated cell migration and expressions of cell-cycle regulatory proteins [cyclin D1, cyclin-dependent kinase (CDK) 4, cyclin E, and CDK2]; these increases were inhibited by caffeine, or PP2. We conclude that NECA-stimulated Cx43 phosphorylation mediated by PI3K/Akt, PKC, MAPKs, and NF-kappaB, which subsequently stimulated cell migration and proliferation through Src, integrin beta1, FAK, and paxillin signal pathways.

Mechanisms involved in the antinociception induced by systemic administration of guanosine in mice

It is well known that adenine-based purines exert multiple effects on pain transmission. However, less attention has been given to the potential effects of guanine-based purines on pain transmission. The aim of this study was to investigate the effects of intraperitoneal (i.p.) and oral (p.o.) administration of guanosine on mice pain models. Additionally, investigation into the mechanisms of action of guanosine, its potential toxicity and cerebrospinal fluid (CSF) purine levels were also assessed. Mice received an i.p. or p.o. administration of vehicle (0.1 mM NaOH) or guanosine (up to 240 mg x kg(-1)) and were evaluated in several pain models. Guanosine produced dose-dependent antinociceptive effects in the hot-plate, glutamate, capsaicin, formalin and acetic acid models, but it was ineffective in the tail-flick test. Additionally, guanosine produced a significant inhibition of biting behaviour induced by i.t. injection of glutamate, AMPA, kainate and trans-ACPD, but not against NMDA, substance P or capsaicin. The antinociceptive effects of guanosine were prevented by selective and non-selective adenosine receptor antagonists. Systemic administration of guanosine (120 mg x kg(-1)) induced an approximately sevenfold increase on CSF guanosine levels. Guanosine prevented the increase on spinal cord glutamate uptake induced by intraplantar capsaicin. This study provides new evidence on the mechanism of action of the antinociceptive effects after systemic administration of guanosine. These effects seem to be related to the modulation of adenosine A(1) and A(2A) receptors and non-NMDA glutamate receptors.

Adenosine A1 receptor blockage mediates theophylline‐associated seizures

Theophylline-associated seizures (TAS) often progress to prolonged or treatment-resistant convulsions. Theophylline is a nonselective adenosine receptor antagonist. Adenosine is an endogenous anticonvulsant that can terminate seizures. Fever and young age have been reported to be risk factors for TAS. To elucidate the mechanism of TAS, we investigated the effect of theophylline and adenosine receptor ligands on hyperthermia-induced seizures in juvenile rats. The treatment dose of theophylline or control saline was injected intraperitoneally 1 h before hyperthermia-induced seizures. The seizure threshold in the theophylline group was significantly lower and seizure duration was significantly longer than those in the control group. The addition of a selective adenosine A(1) receptor agonist and an adenosine kinase inhibitor completely counteracted the effects of theophylline. Moreover, a selective A(1) antagonist caused a significantly longer seizure duration compared with the control. These findings suggest that blockage of the adenosine A(1) receptor is the main cause of TAS.