Adenosine A1 Agonist Research Articles

Identification of hypothermia-inducing neurons in the preoptic area and activation of them by isoflurane anesthesia and central injection of adenosine

Hibernation and torpor are not passive responses caused by external temperature drops and fasting but are active brain functions that lower body temperature. A population of neurons in the preoptic area was recently identified as such active torpor-regulating neurons. We hypothesized that the other hypothermia-inducing maneuvers would also activate these neurons. To test our hypothesis, we first refined the previous observations, examined the brain regions explicitly activated during the falling phase of body temperature using c-Fos expression, and confirmed the preoptic area. Next, we observed long-lasting hypothermia by reactivating torpor-tagged Gq-expressing neurons using the activity tagging and DREADD systems. Finally, we found that about 40–60% of torpor-tagged neurons were activated by succeeding isoflurane anesthesia and by icv administration of an adenosine A1 agonist. Isoflurane-induced and central adenosine-induced hypothermia is, at least in part, an active process mediated by the torpor-regulating neurons in the preoptic area.Graphical abstract

DDEL-11. DETERMINING THE DOSE OF REGADENOSON MOST LIKELY TO TRANSIENTLY ALTER THE INTEGRITY OF THE BLOOD-BRAIN BARRIER IN PATIENTS WITH GLIOMAS

Abstract BACKGROUND The blood brain barrier (BBB) is a major obstacle to the delivery of chemotherapy to the CNS. Regadenoson is an FDA approved adenosine A2 agonist used for cardiac stress tests. In murine models, it transiently increases BBB permeability to a 70KD dextran. This multi-institutional, NIH funded, Adult Brain Tumor Consortium trial was designed to discover a dose of regadenoson that substantially increases vascular permeability in normal appearing white matter (NAWM) where drug delivery is particularly challenging. METHODS Adults ages 18-45 with supratentorial gliomas at low-risk for regadenoson complications were recruited (n = 7). One patient was treated at each of seven dose levels (from 0.05 to 1.4 mg) that are known to be safe in humans. The primary outcome measure is change in vascular permeability via dynamic contrast enhanced (DCE) perfusion MRI estimates of Ktrans. The primary outcome measure was a 10-fold higher Ktrans in NAWM than reported in literature (Ktrans > 0.04 min-1). Contrast-enhanced T1 subtraction map estimates of change in contrast enhancement and other measurements in normal brain and non-enhancing tumor were quantified. RESULTS Ktrans measures in NAWM averaged 1.13x10-3 ± 0.44x10-3 (SEM) min-1, lower than the target of 0.04 min-1. Normalized, contrast enhanced T1-weighted MR signal intensity in NAWM increased an average of 74.0 ± 22.4% min-1 (SEM) min-1, which was significantly higher than zero (P = 0.0163). Data available from this limited sample failed to meet the target goal in Ktrans increase or change in contrast enhancing signal intensity. CONCLUSION Administration of regadenoson at seven different doses did not significantly elevate Ktrans for gadolinium in NAWM. This data suggests that single doses of regadenoson are unlikely to substantially increase the delivery of therapeutic agents in non-enhancing brain tissue. This trial design is appropriate for further human testing of other regadenoson schedules and other novel approaches aimed at transiently modifying BBB permeability.

Guanine-Based Purines as an Innovative Target to Treat Major Depressive Disorder.

Guanine-Based Purines as an Innovative Target to Treat Major Depressive Disorder.

Activation of central adenosine A2B receptors mediate brain ghrelin-induced improvement of intestinal barrier function through the vagus nerve in rats

Leaky gut that is a condition reflecting intestinal barrier dysfunction has been attracting attention for its relations with many diseases such as irritable bowel syndrome or Alzheimer dementia. We have recently demonstrated that ghrelin acts in the brain to improve leaky gut via the vagus nerve. In the present study, we tried to clarify the precise central mechanisms by which ghrelin improves intestinal barrier function through the vagus nerve. Colonic permeability was estimated in vivo by quantifying the absorbed Evans blue in colonic tissue in rats. Adenosine receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), blocked the intracisternal ghrelin-induced improvement of intestinal hyperpermeability while dopamine, cannabinoid or opioid receptor antagonist failed to prevent it. Since DPCPX can block adenosine A1 and adenosine A2B receptors, we examined which subtype is involved in the mechanism. Intracisternal injection of adenosine A2B agonist but not adenosine A1 agonist improved colonic hyperpermeability, while peripheral injection of adenosine A2B agonist failed to improve it. Intracisternal adenosine A2B agonist-induced improvement of colonic hyperpermeability was blocked by vagotomy. Adenosine A2B specific antagonist, alloxazine blocked the ghrelin- or central vagal stimulation by 2-deoxy-d-glucose-induced improvement of intestinal hyperpermeability. These results suggest that activation of adenosine A2B receptors in the central nervous system is capable of improving intestinal barrier function through the vagal pathway, and the adenosine A2B receptors may mediate the ghrelin-induced improvement of leaky gut in a vagal dependent fashion. These findings may help us understand the pathophysiology in not only gastrointestinal diseases but also non-gastrointestinal diseases associated with the altered intestinal permeability.

Topical Trabodenoson Is Neuroprotective in a Rodent Model of Anterior Ischemic Optic Neuropathy (rNAION).

PurposeNonarteritic anterior ischemic optic neuropathy (NAION) is the leading cause of sudden optic nerve–related vision loss currently without effective treatment. We evaluated the neuroprotective potential of ocular (topical) delivery of trabodenoson, a selective A1 receptor mimetic, in a rodent model of NAION (rNAION).MethodsDaily topical delivery of 3% trabodenoson or vehicle administered in both eyes 3 days prior to rNAION induction and for 21 days post induction. Retinal appearance and optic nerve head (ONH) edema was evaluated using spectral-domain optical coherence tomography (SD-OCT). Retinal function was evaluated before and after induction by ganzfeld electroretinography (ERG). Brn3a(+) retinal ganglion cells (RGCs) were quantified by stereology. Axonal ultrastructure was evaluated by electron microscopy.ResultsTrabodenoson-treated eyes had significantly reduced optic nerve (ON) edema compared with vehicle-treated eyes (ANOVA, P < 0.05). Electrophysiologically, there was a nonsignificant trend toward b-wave and oscillatory potential (OP) preservation in the trabodenoson-treated eyes. RGC counts were higher in trabodenoson-treated eyes compared to vehicle (74% versus 47% of the contralateral eye; two-tailed t-test; P = 0.01), as were ON axons. No overt morphologic differences in cell inflammation were observed between vehicle- and trabodenoson-treated ONHs, but trabodenoson-treated ONHs revealed increased expression of astrocyte-related neuroprotective responses.ConclusionsTrabodenoson preserves RGCs in the rodent NAION model. While previous clinical trials focused on trabodenoson's ocular antihypertensive effect, our data suggest trabodenoson's primary target may be both the retina and ONH. Selective adenosine A1 agonists may prove an appropriate neuroprotective adjunctive for ischemia-related ON diseases such as NAION and glaucoma.Translational RelevanceRGC and ON neuroprotection in ischemic neuropathies may be achievable by topical administration of A1 adenosine agonists rather than by simply relying on intraocular pressure reduction.

THER-04. THE USE OF AN ADENOSINE A2 AGONIST TO IMPROVE THE PREVENTION AND TREATMENT OF BRAIN METASTASES

As systemic therapies for cancer become increasingly effective, there is generally a rise in the incidence of brain metastases as a site of first recurrence. This occurs because most antineoplastic agents do not reach the brain in therapeutic concentrations. Many approaches have been studied to improve drug distribution to the central nervous system (CNS) such as intra-arterial administration, osmotic blood-brain barrier (BBB) disruption, focused ultrasound, convection-enhanced delivery, development of CNS penetrant pro-drugs, and the use of vasoactive peptides to transiently disrupt the BBB. However, none of these has improved the prevention or treatment of CNS metastases. Regadenoson is an adenosine A2 agonist that is FDA approved for use in cardiac stress tests. In animals, it has been shown to transiently increase BBB permeability allowing high molecular weight dextran and chemotherapy to enter brain in higher concentrations. A clinical study designed to determine if regadenoson will perform similarly in humans has been CTEP approved and will soon be accruing patients through the Adult Brain Tumor Consortium. If the results are encouraging, future studies will focus on administering regadenoson concurrently with systemically administered chemotherapy in an effort to reduce the incidence of CNS metastases and to improve CNS drug delivery in patients with known brain metastases. This presentation will focus on the available pre-clinical and clinical data supporting this approach and the potential advantages and risks associated with transient BBB disruption in this setting.

In Vivo Evaluation of A1 Adenosine Agonists as Novel Anticonvulsant Medical Countermeasures to Nerve Agent Intoxication in a Rat Soman Seizure Model.

Organophosphorus nerve agents (NAs) irreversibly inhibit acetylcholinesterase, which results in the accumulation of acetylcholine and widespread excitotoxic seizure activity. Because current medical countermeasures (anticholinergics, AChE reactivators, and benzodiazepines) lack sufficient anti-seizure efficacy when treatment is delayed, those intoxicated are at risk for severe brain damage or death if treatment is not immediately available. Toward developing a more effective anti-seizure treatment for NA intoxication, this study evaluated the efficacy of A1 adenosine (ADO) receptor (A1AR) agonists in a rat soman seizure model. One minute after exposure to soman (1.6 × LD50, subcutaneous), rats were treated intraperitoneally with one of the following agonists at increasing dose levels until anti-seizure efficacy was achieved: N6-cyclopentaladenosine (CPA), 2-chloro-N6-cyclopentyladenosine (CCPA), and (±)-5'-chloro-5'-deoxy-ENBA (ENBA). All A1AR agonists were efficacious in preventing seizure and promoting survival. The effective doses for the A1AR agonists were 60mg/kg CPA, 36mg/kg CCPA, and 62mg/kg ENBA. Whereas vehicle-treated rats experienced 100% seizure and 21% survival (N = 28), ADO treatments reduced seizure occurrence and improved survival rates: 8% seizure and 83% survival with CPA (60mg/kg, N = 12), 17% seizure and 75% survival with CCPA (36mg/kg, N = 12), and 8% seizure, 83% survival with ENBA (62mg/kg, N = 12). The brains of ADO-treated rats were also protected from damage as indicated by neurohistopathological analysis. While all ADO agonists provided neuroprotection, rats receiving CCPA and ENBA experienced less severe ADO-induced side effects (e.g., sedation, hypothermia, bradycardia) than with CPA. The data from this study suggest that the ADO signaling pathway is a promising mechanism for countering seizure activity induced by NAs.

Role of dopamine D2-like receptors and their modulation by adenosine receptor stimulation in the reinstatement of methamphetamine seeking.

Previous work has demonstrated that dopamine and adenosine receptors are involved in drug-seeking behaviors, yet the pharmacological interactions between these receptors in methamphetamine (MA) seeking are not well characterized. The present studies examined the role of the dopamine D2-like receptors in MA seeking and identified the interactive effects of adenosine receptor stimulation. Adult male Sprague-Dawley rats were trained to lever press for MA in daily 2-h self-administration sessions on a fixed-ratio 1 schedule for 10 consecutive days. After 1day of abstinence, lever pressing was extinguished in six daily extinction sessions. Treatments were administered systemically prior to a 2-h reinstatement test session. An increase in MA seeking was observed following the administration of the dopamine D2-like agonist, quinpirole, or the D3 receptor agonist, 7-OH-DPAT. Stimulation of D2 or D4 receptors was ineffective at inducing MA seeking. Quinpirole-induced MA seeking was inhibited by D3 receptor antagonism (SB-77011A or PG01037), an adenosine A1 agonist, CPA, and an adenosine A2A agonist, CGS 21680. MA seeking induced by a MA priming injection or D3 receptor stimulation was inhibited by a pretreatment with the adenosine A1 agonist, CPA, but not the adenosine A2A agonist, CGS 21680. These results demonstrate the sufficiency of dopamine D3 receptors to reinstate MA seeking that is inhibited when combined with adenosine A1 receptor stimulation.

Regulation of Matrix Metalloproteinase 2 Expression by an Adenosine A1 Agonist in Trabecular Meshwork Cells

Regulation of Matrix Metalloproteinase 2 Expression by an Adenosine A1 Agonist in Trabecular Meshwork Cells

Induction of hibernation-like hypothermia by central activation of the A1 adenosine receptor in a non-hibernator, the rat.

Central adenosine A1-receptor (A1AR)-mediated signals play a role in the induction of hibernation. We determined whether activation of the central A1AR enables rats to maintain normal sinus rhythm even after their body temperature has decreased to less than 20°C. Intracerebroventricular injection of an adenosine A1 agonist, N6-cyclohexyladenosine (CHA), followed by cooling decreased the body temperature of rats to less than 20°C. Normal sinus rhythm was fundamentally maintained during the extreme hypothermia. In contrast, forced induction of hypothermia by cooling anesthetized rats caused cardiac arrest. Additional administration of pentobarbital to rats in which hypothermia was induced by CHA also caused cardiac arrest, suggesting that the operation of some beneficial mechanisms that are not activated under anesthesia may be essential to keep heart beat under the hypothermia. These results suggest that central A1AR-mediated signals in the absence of anesthetics would provide an appropriate condition for maintaining normal sinus rhythm during extreme hypothermia.

Safety and Tolerability of Neladenoson Bialanate, a Novel Oral Partial Adenosine A1 Receptor Agonist, in Patients With Chronic Heart Failure.

We studied safety and tolerability of neladenoson bialanate, a novel oral selective partial adenosine A1 receptor agonist that maintains the cardioprotective effects of adenosine without the undesired side effects of a full agonist, in 2 pilot studies in patients with heart failure with reduced ejection fraction (HFrEF). The β-blocker interaction study was a single-blind, placebo-controlled study on the effects of a 30-mg single dose of neladenoson bialanate on atrioventricular (AV) conduction in 11 patients with HFrEF treated with β-blockers. The PARSiFAL pilot study was a double-blind, placebo-controlled study on the effects of a 7-day treatment with 10 or 20 mg neladenoson bialanate or placebo in 31 patients with HFrEF on β-blocker therapy. In the β-blocker interaction study with 11 HFrEF patients, no second- or third-degree AV block was detected on 48-hour Holter monitoring. In the 31 HFrEF patients included in the PARSiFAL pilot study, no second- or third-degree AV blocks were observed during 24-hour Holter monitoring, and no effects were seen on heart rate and blood pressure. Median absolute changes in LVEF, measured by cardiac magnetic resonance, were 1.9% (interquartile range -1.1 to 4.3), 0.3% (-1.4 to 2.7), and 2.2% (0.4 to 4.5), in the placebo, 10-mg, and 20-mg groups, respectively. Treatment of HFrEF patients with the novel partial adenosine A1 agonist neladenoson bialanate appeared to be safe in 2 small pilot studies, and no atrioventricular conduction disorders or neurological side effects were observed. No significant early changes in cardiac function were detected.

Would calcium or potassium channels be responsible for cardiac arrest produced by adenosine and ATP in the right atria of Wistar rats?

Autonomic nerves release ATP, which is processed into adenosine in the synaptic cleft. Adenosine and ATP exert a negative chronotropic effect in the heart. This study aims to evaluate adenosine and P2 receptors and cellular signalling in cardiac arrest produced by purines in the heart. Right atria of adult Wistar rats were used to evaluate the effects of adenosine, ATP and CPA (an adenosine A1 receptor agonist), in the presence and absence of DPCPX, an adenosine A1 receptor antagonist. Effects of adenosine A2 and A3 receptors agonists and antagonists were also investigated. Finally, involvement of calcium and potassium channels in these responses was assessed using BayK 8644 and 4-Aminopyridine. Cumulative concentration–effect curves of adenosine and CPA resulted in a negative chronotropic effect culminating in cardiac arrest at 1000μM (adenosine) and 1µM (CPA). Furthermore, ATP produced a negative chronotropic effect at 1–300µM and cardiac arrest at 1000μM in the right atrium. ATPγS (a non-hydrolysable analogue of ATP) reduced chronotropism only. The effects of adenosine, CPA and ATP were inhibited by DPCPX, a selective adenosine A1 receptor antagonist. The selective adenosine A2 and A3 receptors antagonists did not alter the chronotropic response of adenosine. 4-Aminopyridine, a blocker of potassium channels at 10mM, prevented the cardiac arrest produced by adenosine and ATP, while BayK 8644, activator of calcium channels, did not prevent cardiac arrest. Adenosine A1 receptor activation by adenosine and ATP produces cardiac arrest in the right atrium of Wistar rats predominantly through activation of potassium channels.

Early adenosine release contributes to hypoxia-induced disruption of stimulus-induced sharp wave-ripple complexes in rat hippocampal area CA3.

We investigated the effects of hypoxia on sharp wave-ripple complex (SPW-R) activity and recurrent epileptiform discharges in rat hippocampal slices, and the mechanisms underlying block of this activity. Oxygen levels were measured using Clark-style oxygen sensor microelectrodes. In contrast to recurrent epileptiform discharges, oxygen consumption was negligible during SPW-R activity. These network activities were reversibly blocked when oxygen levels were reduced to 20% or less for 3min. The prolongation of hypoxic periods to 6min caused reversible block of SPW-Rs during 20% oxygen and irreversible block when 0% oxygen (anoxia) was applied. In contrast, recurrent epileptiform discharges were more resistant to prolonged anoxia and almost fully recovered after 6min of anoxia. SPW-Rs were unaffected by the application of 1-butyl-3-(4-methylphenylsulfonyl) urea, a blocker of KATP channels, but they were blocked by activation of adenosine A1 receptors. In support of a modulatory function of adenosine, the amplitude and incidence of SPW-Rs were increased during application of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Interestingly, hypoxia decreased the frequency of miniature excitatory post-synaptic currents in CA3 pyramidal cells, an effect that was converted into increased frequency by the adenosine A1 agonist DPCPX. In addition, DPCPX also delayed the onset of hypoxia-mediated block of SPW-Rs. Our data suggest that early adenosine release during hypoxia induces a decrease in pre-synaptic glutamate release and that both might contribute to transient block of SPW-Rs during hypoxia/anoxia in area CA3.

The Yin and Yan of Adenosine A1 and A2A Receptors in Global Cerebral Ischemia Reperfusion Injury

Global cerebral ischemia reperfusion (IR) following cardiac arrest, shock and asphyxia can affect wide brain areas where new therapies are imperative. Moreover, many intracellular pathways mediating tissue response to IR are still elusive. Adenosine is a neuromodulator that greatly impacts IR through the inhibitory A1 and excitatory A2 receptors. Studies indicate that both adenosine A1 agonists and A2A antagonists are neuroprotective during ischemic insults. However, many of the signaling pathways affecting such responses are largely unknown. In the current study, bilateral carotid occlusion for 45 min. followed by 24h reperfusion period resulted in histopathological damage as well as memory impairment, motor incoordination and increased locomotor activity. Such events were attenuated by unilateral intra‐hippocampal injection of both the selective A1 agonist N6‐cyclohexyl adenosine (CHA) and the A2A antagonist 7‐(2‐phenylethyl)‐5‐amino‐2‐(2‐furyl)‐pyrazolo‐[4,3‐e]‐1,2,4‐triazolo[1,5‐c]pyrimidine (SCH58261). On the cellular level, IR increased glutamate, pERK1/2, c‐Fos, NF‐kB, TNF‐α, cytochrome c, caspase‐3, BDNF, Nrf2 and IL‐10 contents. Both CHA and SCH58261signifiantly reduced glutamate, c‐Fos, TNF‐α, cytochrome c, caspase‐3 and increased Nrf‐2 and IL‐10 contents. While only SCH58261 reduced pERK1/2, NF‐kB and BDNF contents. By the same token, iNOS and TBARS levels were increased following IR and attenuated by both CHA and SCH58261 treatments. Accordingly, these results lend insight to the neuroprotective effects of A1 and A2A agonists and antagonists respectively where pERK1/2 and NF‐kB pathways might be involved in adenosine mediated attenuation of inflammation, apoptosis and oxidative stress.

Caffeine ameliorates hemodynamic derangements and portosystemic collaterals in cirrhotic rats.

Portal hypertension (PH), a pathophysiological derangement of liver cirrhosis, is characterized by hyperdynamic circulation, angiogenesis, and portosystemic collaterals. These may lead to lethal complications, such as variceal bleeding. Caffeine has been noted for its effects on liver inflammation, fibrogenesis, and vasoreactiveness. However, the relevant influences of caffeine in cirrhosis and PH have not been addressed. Spraque-Dawley rats with common bile duct ligation-induced cirrhosis or sham operation received prophylactic or therapeutic caffeine treatment (50 mg/kg/day, the first or 15th day since operation, respectively) for 28 days. Compared to vehicle (distilled water), caffeine decreased cardiac index, increased systemic vascular resistance, reduced portal pressure (PP), superior mesenteric artery flow, mesenteric vascular density, portosystemic shunting (PSS), intrahepatic angiogenesis, and fibrosis without affecting liver and renal biochemistry. The beneficial effects were reversed by selective adenosine A1 agonist N6-cyclopentyladenosine (CPA) or A2A agonist GCS21680. Both prophylactic and therapeutic caffeine treatment decreased portal resistance and PP in thioacetamide (200mg/kg, thrice-weekly for 8 weeks)-induced cirrhotic rats. Caffeine down-regulated endothelial nitric oxide synthase, vascular endothelial growth factor (VEGF), phospho-VEGFR2, and phospho-Akt mesenteric protein expression. Caffeine adversely affected viability of hepatic stellate and sinusoidal endothelial cells, which was reversed by CPA and GCS21680. On the other hand, caffeine did not modify vascular response to vasoconstrictors in splanchnic, hepatic, and collateral vascular beds. Caffeine decreased PP, ameliorated hyperdynamic circulation, PSS, mesenteric angiogenesis, hepatic angiogenesis, and fibrosis in cirrhotic rats. Caffeine may be a feasible candidate to ameliorate PH-related complications in cirrhosis.

Cannabinoid receptor-interacting protein 1a modulates CB1 receptor signaling and regulation.

Cannabinoid CB1 receptors (CB1Rs) mediate the presynaptic effects of endocannabinoids in the central nervous system (CNS) and most behavioral effects of exogenous cannabinoids. Cannabinoid receptor-interacting protein 1a (CRIP1a) binds to the CB1R C-terminus and can attenuate constitutive CB1R-mediated inhibition of Ca(2+) channel activity. We now demonstrate cellular colocalization of CRIP1a at neuronal elements in the CNS and show that CRIP1a inhibits both constitutive and agonist-stimulated CB1R-mediated guanine nucleotide-binding regulatory protein (G-protein) activity. Stable overexpression of CRIP1a in human embryonic kidney (HEK)-293 cells stably expressing CB1Rs (CB1-HEK), or in N18TG2 cells endogenously expressing CB1Rs, decreased CB1R-mediated G-protein activation (measured by agonist-stimulated [(35)S]GTPγS (guanylyl-5'-[O-thio]-triphosphate) binding) in both cell lines and attenuated inverse agonism by rimonabant in CB1-HEK cells. Conversely, small-interfering RNA-mediated knockdown of CRIP1a in N18TG2 cells enhanced CB1R-mediated G-protein activation. These effects were not attributable to differences in CB1R expression or endocannabinoid tone because CB1R levels did not differ between cell lines varying in CRIP1a expression, and endocannabinoid levels were undetectable (CB1-HEK) or unchanged (N18TG2) by CRIP1a overexpression. In CB1-HEK cells, 4-hour pretreatment with cannabinoid agonists downregulated CB1Rs and desensitized agonist-stimulated [(35)S]GTPγS binding. CRIP1a overexpression attenuated CB1R downregulation without altering CB1R desensitization. Finally, in cultured autaptic hippocampal neurons, CRIP1a overexpression attenuated both depolarization-induced suppression of excitation and inhibition of excitatory synaptic activity induced by exogenous application of cannabinoid but not by adenosine A1 agonists. These results confirm that CRIP1a inhibits constitutive CB1R activity and demonstrate that CRIP1a can also inhibit agonist-stimulated CB1R signaling and downregulation of CB1Rs. Thus, CRIP1a appears to act as a broad negative regulator of CB1R function.

Disclosing caffeine action on insulin sensitivity: Effects on rat skeletal muscle

Caffeine, a non-selective adenosine antagonist, has distinct effects on insulin sensitivity when applied acutely or chronically. Herein, we investigated the involvement of adenosine receptors on insulin resistance induced by single-dose caffeine administration. Additionally, the mechanism behind adenosine receptor-mediated caffeine effects in skeletal muscle was assessed.The effect of the administration of caffeine, 8-cycle-1,3-dipropylxanthine (DPCPX, A1 antagonist), 2-(2-Furanyl)-7-(2-phenylethyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine (SCH58261, A2A antagonist) and 8-(4-{[(4-cyanophenyl)carbamoylmethyl]-oxy}phenyl)-1,3-di(n-propyl)xanthine (MRS1754, A2B antagonist) on whole-body insulin sensitivity was tested. Skeletal muscle Glut4,5′-AMP activated protein kinase (AMPK) and adenosine receptor protein expression were also assessed. The effect of A1 and A2B adenosine agonists on skeletal muscle glucose uptake was evaluated in vitro. Sodium nitroprussiate (SNP, 10nM), a nitric oxide (NO) donor, was used to evaluate the effect of NO on insulin resistance induced by adenosine antagonists.Acute caffeine decreased insulin sensitivity in a concentration dependent manner (Emax=55.54±5.37%, IC50=11.61nM), an effect that was mediated by A1 and A2B adenosine receptors. Additionally, acute caffeine administration significantly decreased Glut4, but not AMPK expression, in skeletal muscle. We found that A1, but not A2B agonists increased glucose uptake in skeletal muscle. SNP partially reversed DPCPX and MRS1754 induced-insulin resistance.Our results suggest that insulin resistance induced by acute caffeine administration is mediated by A1 and A2B adenosine receptors. Both Glut4 and NO seem to be downstream effectors involved in insulin resistance induced by acute caffeine.

Emerging Trabecular Outflow Drugs

Emerging Trabecular Outflow Drugs

ASSA13-03-54 Adenosine A1 Agonist Inhibit the Hypertrophy of Cardiomyocyte Induced by Angiotensin II Through Calcineurin Pathway

<h3>Objective</h3> We aimed to study the mechanism and pathway of the adenosine A1 receptor agonist 2-chloro-N6 cyclopentyladenosine (CCPA) in the inhibition of the cardiomyocyte hypertrophy induced by angiotensin II (AngII) in vitro. <h3>Methods</h3> Cardiomyocytes from neonatal SD rats were treated with AngII to generate a cardiomyocyte hypertrophy model. The cell cultures were randomised into four groups: (1) control; (2) AngII; (3) AngII + cyclosporin A (CsA); and (4) AngII + CCPA. The MTT method was used to measure cardiomyocyte viability. Protein synthesis was monitored by measuring the incorporation of tritiated leucine (3H-Leu), and the expression of β-myosin heavy chain (β-MHC) and calcineurin Aβ (CnAβ) mRNA was measured by semi-quantitative RT-PCR. <h3>Results</h3> Forty-eight hours after AngII treatment, surface area, viability and 3H-Leu incorporation of the cardiomyocytes were significantly increased in a dose-dependent manner. Both CCPA and the calcineurin (CaN)-specific inhibitor CsA significantly inhibited AngII-induced cardiomyocyte 3H-Leu incorporation. These compounds also inhibited the mRNA expression of CnAβ and β-MHC in AngII-induced cardiomyocytes but had no significant effect on 3H-Leu incorporation in the control group. The inhibition by CCPA was dose-dependent within the range of 1 × 10–8 mol/L to 1 × 10–6 mol/L. <h3>Conclusions</h3> The adenosine A1 receptor agonist CCPA can significantly inhibit AngII-induced cardiomyocyte hypertrophy in a manner related to the CaN signalling pathway.

Armillaria mellea: an adenosine A1 agonist useful against dizziness and a possible anti-ischemic agent

L’Armillaria mellea (AM) est un agoniste adénosine A1 qui en théorie protège les tissus de l’ischémie. Des effets antivertigineux sont documentés par un essai randomisé en double insu. Les effets antiépileptogènes, protecteurs sur le rein, sur le coeur (antiarythmogène ou antiangineux) ou encore sur les nerfs périphériques restent théoriques. Comme de nombreux champignons, l’AM stimule l’immunité et possède des propriétés antioxydantes ou antibiotiques. Il faut tenir compte de son effet fibrinolytique lors d’une prescription: utilité pour reperfuser un tissu mais risque lorsqu’associé à un antiagrégant plaquettaire ou à un anticoagulant. On retiendra surtout son potentiel important contre les vertiges et l’ischémie.