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This article is from Diabetes , volume 60 . Abstract OBJECTIVE: To determine the mechanisms by which blockade of adenosine A2B receptors (A2BRs) reduces insulin resistance. RESEARCH DESIGN AND METHODS: We investigated the effects of deleting or blocking the A2BR on insulin sensitivity using glucose tolerance tests (GTTs) and hyperinsulinemic-euglycemic clamps in mouse models of type 2 diabetes. The effects of diabetes on A2BR transcription and signaling were measured in human and mouse macrophages and mouse endothelial cells. In addition, tag single nucleotide polymorphisms (SNPs) in ∼42 kb encompassing the A2BR gene, ADORA2B, were evaluated for associations with markers of diabetes and inflammation. RESULTS: Treatment of mice with the nonselective adenosine receptor agonist 5′-N-ethylcarboxamidoadensoine (NECA) increased fasting blood glucose and slowed glucose disposal during GTTs. These responses were inhibited by A2BR deletion or blockade and minimally affected by deletion of A1Rs or A2ARs. During hyperinsulinemic-euglycemic clamp of diabetic KKAY mice, A2BR antagonism increased glucose infusion rate, reduced hepatic glucose production, and increased glucose uptake into skeletal muscle and brown adipose tissue. Diabetes caused a four- to sixfold increase in A2BR mRNA in endothelial cells and macrophages and resulted in enhanced interleukin (IL)-6 production in response to NECA due to activation of protein kinases A and C. Five consecutive tag SNPs in ADORA2B were highly correlated with IL-6 and C-reactive protein (CRP). Diabetes had a highly significant independent effect on variation in inflammatory markers. The strength of associations between several ADORA2B SNPs and inflammatory markers was increased when accounting for diabetes status. CONCLUSIONS: Diabetes affects the production of adenosine and the expression of A2BRs that stimulate IL-6 and CRP production, insulin resistance, and the association between ADORA2B SNPs and inflammatory markers. We hypothesize that increased A2BR signaling in diabetes increases insulin resistance in part by elevating proinflammatory mediators. Selective A2BR blockers may be useful to treat insulin resistance.

This article is from Diabetes , volume 60 . Abstract OBJECTIVE: To determine the mechanisms by which blockade of adenosine A2B receptors (A2BRs) reduces insulin resistance. RESEARCH DESIGN AND METHODS: We investigated the effects of deleting or blocking the A2BR on insulin sensitivity using glucose tolerance tests (GTTs) and hyperinsulinemic-euglycemic clamps in mouse models of type 2 diabetes. The effects of diabetes on A2BR transcription and signaling were measured in human and mouse macrophages and mouse endothelial cells. In addition, tag single nucleotide polymorphisms (SNPs) in ∼42 kb encompassing the A2BR gene, ADORA2B, were evaluated for associations with markers of diabetes and inflammation. RESULTS: Treatment of mice with the nonselective adenosine receptor agonist 5′-N-ethylcarboxamidoadensoine (NECA) increased fasting blood glucose and slowed glucose disposal during GTTs. These responses were inhibited by A2BR deletion or blockade and minimally affected by deletion of A1Rs or A2ARs. During hyperinsulinemic-euglycemic clamp of diabetic KKAY mice, A2BR antagonism increased glucose infusion rate, reduced hepatic glucose production, and increased glucose uptake into skeletal muscle and brown adipose tissue. Diabetes caused a four- to sixfold increase in A2BR mRNA in endothelial cells and macrophages and resulted in enhanced interleukin (IL)-6 production in response to NECA due to activation of protein kinases A and C. Five consecutive tag SNPs in ADORA2B were highly correlated with IL-6 and C-reactive protein (CRP). Diabetes had a highly significant independent effect on variation in inflammatory markers. The strength of associations between several ADORA2B SNPs and inflammatory markers was increased when accounting for diabetes status. CONCLUSIONS: Diabetes affects the production of adenosine and the expression of A2BRs that stimulate IL-6 and CRP production, insulin resistance, and the association between ADORA2B SNPs and inflammatory markers. We hypothesize that increased A2BR signaling in diabetes increases insulin resistance in part by elevating proinflammatory mediators. Selective A2BR blockers may be useful to treat insulin resistance.

This article is from Diabetes , volume 60 . Abstract OBJECTIVE: To determine the mechanisms by which blockade of adenosine A2B receptors (A2BRs) reduces insulin resistance. RESEARCH DESIGN AND METHODS: We investigated the effects of deleting or blocking the A2BR on insulin sensitivity using glucose tolerance tests (GTTs) and hyperinsulinemic-euglycemic clamps in mouse models of type 2 diabetes. The effects of diabetes on A2BR transcription and signaling were measured in human and mouse macrophages and mouse endothelial cells. In addition, tag single nucleotide polymorphisms (SNPs) in ∼42 kb encompassing the A2BR gene, ADORA2B, were evaluated for associations with markers of diabetes and inflammation. RESULTS: Treatment of mice with the nonselective adenosine receptor agonist 5′-N-ethylcarboxamidoadensoine (NECA) increased fasting blood glucose and slowed glucose disposal during GTTs. These responses were inhibited by A2BR deletion or blockade and minimally affected by deletion of A1Rs or A2ARs. During hyperinsulinemic-euglycemic clamp of diabetic KKAY mice, A2BR antagonism increased glucose infusion rate, reduced hepatic glucose production, and increased glucose uptake into skeletal muscle and brown adipose tissue. Diabetes caused a four- to sixfold increase in A2BR mRNA in endothelial cells and macrophages and resulted in enhanced interleukin (IL)-6 production in response to NECA due to activation of protein kinases A and C. Five consecutive tag SNPs in ADORA2B were highly correlated with IL-6 and C-reactive protein (CRP). Diabetes had a highly significant independent effect on variation in inflammatory markers. The strength of associations between several ADORA2B SNPs and inflammatory markers was increased when accounting for diabetes status. CONCLUSIONS: Diabetes affects the production of adenosine and the expression of A2BRs that stimulate IL-6 and CRP production, insulin resistance, and the association between ADORA2B SNPs and inflammatory markers. We hypothesize that increased A2BR signaling in diabetes increases insulin resistance in part by elevating proinflammatory mediators. Selective A2BR blockers may be useful to treat insulin resistance.

Continued progress has been made toward each of the 3 Specific Aims (SAs) of our research project, Caffeine, adenosine receptors and estrogen in toxin models of Parkinson's disease (PD) . The overarching hypothesis of the project is that multiple environmental protectants and toxins interact to influence of the health of the dopaminergic neurons lost in PD. To that end we are characterizing the interplay between several environmental agents (pesticides, caffeine and estrogen) that are leading candidate modulators of PD risk. Main accomplishments during the Year 3 of the project: 1)Demonstration that neuronal forebrain A2A receptors can play a critical role in dopaminergic neuron injury in the MPTP model of neurodegeneration in Parkinson s disease. 2) Using a powerful newly Cre/LoxP conditional knockout system, we have obtained evidence that it is the neuronal forebrain A2A receptors in the striatum that are responsible for this toxicity. Thus it is through these receptors that caffeine and more specific antagonists of the adenosine A2A receptor may offer neuroprotection against the development or progression of PD. 3) Demonstration for the first time that caffeine s neuroprotective effect extends to the dual pesticide parequat plus maneb model of PD, a chronic, potentially more environmentally relevant model of the disease. 4) Demonstration for the first time that urate -- a caffeine analog and antioxidant linked to slower PD progression and risk -- can be neuroprotective in an in vivo model of PD. This finding may have a particularly rapid translational impact as urate-elevating therapy is now being pursued as potential neuroprotectant for PD patients. 5) Methodological advances were achieved with a viral vector-based Cre/LoxP conditional knockout system. It will allow us to dissect caffeine and A2A receptor involvement in neurotoxin models of PD with an unprecedented combination of anatomical and molecular precision in different brain structures.

This article is from Frontiers in Psychiatry , volume 5 . Abstract Adenosine A2A receptors (A2AR) are a sub-type of receptors enriched in basal ganglia, activated by the neuromodulator adenosine, which interact with dopamine D2 receptors. Although this reciprocal antagonistic interaction is well-established in motor function, the outcome in dopamine-related behaviors remains uncertain, in particular in depression and anxiety. We have demonstrated an upsurge of A2AR associated to aging and chronic stress. Furthermore, Alzheimer’s disease patients present A2AR accumulation in cortical areas together with depressive signs. We now tested the impact of overexpressing A2AR in forebrain neurons on dopamine-related behavior, namely depression. Adult male rats overexpressing human A2AR under the control of CaMKII promoter [Tg(CaMKII-hA2AR)] and aged-matched wild-types (WT) of the same strain (Sprague-Dawley) were studied. The forced swimming test (FST), sucrose preference test (SPT), and the open-field test (OFT) were performed to evaluate behavioral despair, anhedonia, locomotion, and anxiety. Tg(CaMKII-hA2AR) animals spent more time floating and less time swimming in the FST and presented a decreased sucrose preference at 48 h in the SPT. They also covered higher distances in the OFT and spent more time in the central zone than the WT. The results indicate that Tg(CaMKII-hA2AR) rats exhibit depressive-like behavior, hyperlocomotion, and altered exploratory behavior. This A2AR overexpression may explain the depressive signs found in aging, chronic stress, and Alzheimer’s disease.

This article is from Frontiers in Endocrinology , volume 3 . Abstract Bone is continually being remodeled and defects in the processes involved lead to bone diseases. Many regulatory factors are known to influence remodeling but other mechanisms, hitherto unknown, may also be involved. Importantly, our understanding of these currently unknown mechanisms may lead to important new therapies for bone disease. It is accepted that purinergic signaling is involved in bone, and our knowledge of this area has increased significantly over the last 15 years, although most of the published work has studied the role of ATP and other signaling molecules via the P2 family of purinergic receptors. During the last few years, however, there has been increased interest within the bone field in the role of P1 receptors where adenosine is the primary signaling molecule. This review will bring together the current information available in relation to this expanding area of research.

This article is from PLoS ONE , volume 9 . Abstract Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease leading to motor neuron dysfunction resulting in impairment of neuromuscular transmission. A2A adenosine receptors have already been considered as a potential therapeutical target for ALS but their neuromodulatory role at the neuromuscular junction in ALS remains to be clarified. In the present work, we evaluated the effects of A2A receptors on neuromuscular transmission of an animal model of ALS: SOD1(G93A) mice either in the pre-symptomatic (4–6 weeks old) or in the symptomatic (12–14 weeks old) stage. Electrophysiological experiments were performed obtaining intracellular recordings in Mg2+ paralyzed phrenic nerve-hemidiaphragm preparations. Endplate potentials (EPPs), quantal content (q. c.) of EPPs, miniature endplate potentials (MEPPs) and giant miniature endplate potential (GMEPPs) were recorded. In the pre-symptomatic phase of the disease (4–6 weeks old mice), the selective A2A receptor agonist, CGS 21680, significantly enhanced (p

This article is from PLoS ONE , volume 9 . Abstract Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease leading to motor neuron dysfunction resulting in impairment of neuromuscular transmission. A2A adenosine receptors have already been considered as a potential therapeutical target for ALS but their neuromodulatory role at the neuromuscular junction in ALS remains to be clarified. In the present work, we evaluated the effects of A2A receptors on neuromuscular transmission of an animal model of ALS: SOD1(G93A) mice either in the pre-symptomatic (4–6 weeks old) or in the symptomatic (12–14 weeks old) stage. Electrophysiological experiments were performed obtaining intracellular recordings in Mg2+ paralyzed phrenic nerve-hemidiaphragm preparations. Endplate potentials (EPPs), quantal content (q. c.) of EPPs, miniature endplate potentials (MEPPs) and giant miniature endplate potential (GMEPPs) were recorded. In the pre-symptomatic phase of the disease (4–6 weeks old mice), the selective A2A receptor agonist, CGS 21680, significantly enhanced (p

This article is from PLoS ONE , volume 9 . Abstract Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease leading to motor neuron dysfunction resulting in impairment of neuromuscular transmission. A2A adenosine receptors have already been considered as a potential therapeutical target for ALS but their neuromodulatory role at the neuromuscular junction in ALS remains to be clarified. In the present work, we evaluated the effects of A2A receptors on neuromuscular transmission of an animal model of ALS: SOD1(G93A) mice either in the pre-symptomatic (4–6 weeks old) or in the symptomatic (12–14 weeks old) stage. Electrophysiological experiments were performed obtaining intracellular recordings in Mg2+ paralyzed phrenic nerve-hemidiaphragm preparations. Endplate potentials (EPPs), quantal content (q. c.) of EPPs, miniature endplate potentials (MEPPs) and giant miniature endplate potential (GMEPPs) were recorded. In the pre-symptomatic phase of the disease (4–6 weeks old mice), the selective A2A receptor agonist, CGS 21680, significantly enhanced (p

This article is from Journal of Nanobiotechnology , volume 12 . Abstract Background: Glutamate, the main excitatory neurotransmitter, is involved in learning and memory processes but at higher concentration results excitotoxic causing degeneration and neuronal death. Adenosine is a nucleoside that exhibit neuroprotective effects by modulating of glutamate release. Hypoxic and related oxidative conditions, in which adenosine and metabotropic glutamate receptors are involved, have been demonstrated to contribute to neurodegenerative processes occurring in certain human pathologies. Results: Human neuroblastoma cells (SH-SY5Y) were used to evaluate the long time (24, 48 and 72 hours) effects of a [60]fullerene hydrosoluble derivative (t3ss) as potential inhibitor of hypoxic insult. Low oxygen concentration (5% O2) caused cell death, which was avoided by t3ss exposure in a concentration dependent manner. In addition, gene expression analysis by real time PCR of adenosine A1, A2A and A2B and metabotropic glutamate 1 and 5 receptors revealed that t3ss significantly increased A1 and mGlu1 expression in hypoxic conditions. Moreover, t3ss prevented the hypoxia-induced increase in A2A mRNA expression. Conclusions: As t3ss causes overexpression of adenosine A1 and metabotropic glutamate receptors which have been shown to be neuroprotective, our results point to a radical scavenger protective effect of t3ss through the enhancement of these neuroprotective receptors expression. Therefore, the utility of these nanoparticles as therapeutic target to avoid degeneration and cell death of neurodegenerative diseases is suggested.

This article is from PLoS ONE , volume 8 . Abstract Adenosine A2A receptors (A2AR) are located postsynaptically in striatopallidal GABAergic neurons, antagonizing dopamine D2 receptor functions, and are also located presynaptically at corticostriatal terminals, facilitating glutamate release. To address the hypothesis that these two A2AR populations differently control the action of psychostimulants, we characterized A2AR modulation of cocaine-induced effects at the level of DARPP-32 phosphorylation at Thr-34 and Thr-75, c-Fos expression, and psychomotor activity using two lines of cell-type selective A2AR knockout (KO) mice with selective A2AR deletion in GABAergic neurons (striatum-A2AR-KO mice), or with A2AR deletion in both striatal GABAergic neurons and projecting cortical glutamatergic neurons (forebrain-A2AR-KO mice). We demonstrated that striatum-A2AR KO mice lacked A2ARs exclusively in striatal GABAergic terminals whereas forebrain-A2AR KO mice lacked A2ARs in both striatal GABAergic and glutamatergic terminals leading to a blunted A2AR-mediated facilitation of synaptosomal glutamate release. The inactivation of A2ARs in GABAergic neurons reduced striatal DARPP-32 phosphorylation at Thr-34 and increased its phosphorylation at Thr-75. Conversely, the additional deletion of corticostriatal glutamatergic A2ARs produced opposite effects on DARPP-32 phosphorylation at Thr-34 and Thr-75. This distinct modulation of DARPP-32 phosphorylation was associated with opposite responses to cocaine-induced striatal c-Fos expression and psychomotor activity in striatum-A2AR KO (enhanced) and forebrain-A2AR KO mice (reduced). Thus, A2ARs in glutamatergic corticostriatal terminals and in GABAergic striatal neurons modulate the action of psychostimulants and DARPP-32 phosphorylation in opposite ways. We conclude that A2ARs in glutamatergic terminals prominently control the action of psychostimulants and define a novel mechanism by which A2ARs fine-tune striatal activity by integrating GABAergic, dopaminergic and glutamatergic signaling.

Adenosine receptors (AR) are member of the G-protein Coupled Receptors (GPCR) superfamily, with four subtypes currently recognised, A1, A2A, A2B and A3 receptors. Because of various potential physiological implications of stimulating AR

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Artykuł w: Annales Universitatis Mariae Curie-Skłodowska. Sectio D, Medicina Vol. 57, N 1, nr 33 (2002), strony 245-256 ; Streszczenia w językach angielskim i polskim.

This article is from EMBO Reports , volume 14 . Abstract These study shows that A3ARs aggregate in polarized immunomodulatory microdomains on human neutrophils and induce filipodia-like projections that tether and 'reel-in' pathogens, increasing phagocytic efficiency.

This article is from EMBO Reports , volume 14 . Abstract These study shows that A3ARs aggregate in polarized immunomodulatory microdomains on human neutrophils and induce filipodia-like projections that tether and 'reel-in' pathogens, increasing phagocytic efficiency.

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This article is from Indian Journal of Pharmacology , volume 46 . Abstract Aim:: We investigated the role of adenosine in citalopram-induced cardiotoxicity. Materials and Methods:: Protocol 1: Rats were randomized into four groups. Sodium cromoglycate was administered to rats. Citalopram was infused after the 5% dextrose, 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX; A1 receptor antagonist), 8-(-3-chlorostyryl)-caffeine (CSC; A2a receptor antagonist), or dimethyl sulfoxide (DMSO) administrations. Protocol 2: First group received 5% dextrose intraperitoneally 1 hour prior to citalopram. Other rats were pretreated with erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA; inhibitor of adenosine deaminase) and S-(4-Nitrobenzyl)-6-thioinosine (NBTI; inhibitor of facilitated adenosine transport). After pretreatment, group 2 received 5% dextrose and group 3 received citalopram. Adenosine concentrations, mean arterial pressure (MAP), heart rate (HR), QRS duration and QT interval were evaluated. Results:: In the dextrose group, citalopram infusion caused a significant decrease in MAP and HR and caused a significant prolongation in QRS and QT. DPCPX infusion significantly prevented the prolongation of the QT interval when compared to control. In the second protocol, citalopram infusion did not cause a significant change in plasma adenosine concentrations, but a significant increase observed in EHNA/NBTI groups. In EHNA/NBTI groups, citalopram-induced MAP and HR reductions, QRS and QT prolongations were more significant than the dextrose group. Conclusions:: Citalopram may lead to QT prolongation by stimulating adenosine A1 receptors without affecting the release of adenosine.

The current regimen for treating nerve agent poisoning does not sufficiently suppress the excitotoxic activity that causes severe brain damage, especially in cases where treatment is delayed and nerve agent-induced status epilepticus develops. New therapeutic targets are required to improve survivability and minimize neuropathology after irreversible acetylcholinesterase inactivation. Earlier studies have shown that systemic delivery of adenosine agonists decreases nerve agent lethality; however, the mechanism of protection remains to be understood. The primary aim of this study was to investigate the role of central adenosine receptor (AR) stimulation in neuroprotection by directly injecting (6)-cyclopentyladenosine (CPA), an adenosine agonist specific to the A1 receptor subtype (A1R), into the brain intracerebroventricularly (ICV) in a soman seizure rat model. In addition to general A1R stimulation, we hypothesized that bilateral micro-injection of CPA into the cholinergic basal forebrain (BF) could also suppress excitotoxic activity. The results from these studies demonstrated that centrally administered adenosine agonists are anti-seizure and neuroprotective. CPA-delivered ICV prevented seizure and convulsion in 100% of the animals. Moreover, neuropathological evaluation indicated that adenosine treatments reduced brain damage from severe to minimal. Inhibition of the BF via CPA had varied results. Some animals were protected by treatment; however, others displayed similar pathology to the control. Overall, these data suggest that stimulating central ARs could be an effective target for the next generation countermeasures for nerve agent intoxication.

The current regimen for treating nerve agent poisoning does not sufficiently suppress the excitotoxic activity that causes severe brain damage, especially in cases where treatment is delayed and nerve agent-induced status epilepticus develops. New therapeutic targets are required to improve survivability and minimize neuropathology after irreversible acetylcholinesterase inactivation. Earlier studies have shown that systemic delivery of adenosine agonists decreases nerve agent lethality; however, the mechanism of protection remains to be understood. The primary aim of this study was to investigate the role of central adenosine receptor (AR) stimulation in neuroprotection by directly injecting (6)-cyclopentyladenosine (CPA), an adenosine agonist specific to the A1 receptor subtype (A1R), into the brain intracerebroventricularly (ICV) in a soman seizure rat model. In addition to general A1R stimulation, we hypothesized that bilateral micro-injection of CPA into the cholinergic basal forebrain (BF) could also suppress excitotoxic activity. The results from these studies demonstrated that centrally administered adenosine agonists are anti-seizure and neuroprotective. CPA-delivered ICV prevented seizure and convulsion in 100% of the animals. Moreover, neuropathological evaluation indicated that adenosine treatments reduced brain damage from severe to minimal. Inhibition of the BF via CPA had varied results. Some animals were protected by treatment; however, others displayed similar pathology to the control. Overall, these data suggest that stimulating central ARs could be an effective target for the next generation countermeasures for nerve agent intoxication.

This article is from Journal of Young Pharmacists : JYP , volume 4 . Abstract Monoamine oxidase B (MAO-B) inhibitory potential of adenosine A2A receptor (AA2AR) antagonists has raised the possibility of designing dual-target–directed drugs that may provide enhanced symptomatic relief and that may also slow the progression of Parkinson's disease (PD) by protecting against further neurodegeneration. To explain the dual inhibition of MAO-B and AA2AR at the molecular level, molecular docking technique was employed. Lamarckian genetic algorithm methodology was used for flexible ligand docking studies. A good correlation (R2= 0.524 and 0.627 for MAO-B and AA2AR, respectively) was established between docking predicted and experimental Ki values, which confirms that the molecular docking approach is reliable to study the mechanism of dual interaction of caffeinyl analogs with MAO-B and AA2AR. Parameters for Lipinski's “Rule-of-Five” were also calculated to estimate the pharmacokinetic properties of dual-target–directed drugs where both MAO-B inhibition and AA2AR antagonism exhibited a positive correlation with calculated LogP having a correlation coefficient R2 of 0.535 and 0.607, respectively. These results provide some beneficial clues in structural modification for designing new inhibitors as dual-target–directed drugs with desired pharmacokinetic properties for the treatment of PD.

This article is from International Journal of Molecular Sciences , volume 15 . Abstract Adenosine receptors (ARs) comprise a group of G protein-coupled receptors (GPCR) which mediate the physiological actions of adenosine. To date, four AR subtypes have been cloned and identified in different tissues. These receptors have distinct localization, signal transduction pathways and different means of regulation upon exposure to agonists. This review will describe the biochemical characteristics and signaling cascade associated with each receptor and provide insight into how these receptors are regulated in response to agonists. A key property of some of these receptors is their ability to serve as sensors of cellular oxidative stress, which is transmitted by transcription factors, such as nuclear factor (NF)-κB, to regulate the expression of ARs. Recent observations of oligomerization of these receptors into homo- and heterodimers will be discussed. In addition, the importance of these receptors in the regulation of normal and pathological processes such as sleep, the development of cancers and in protection against hearing loss will be examined.

This article is from Upsala Journal of Medical Sciences , volume 119 . Abstract Background: Diabetes and hypertension independently contribute to renal injury, and the major mechanisms involved are increased reactive oxygen species (ROS) bioavailability and renin-angiotensin system (RAS) activation. We investigated the role of adenosine in controlling ROS production and RAS activation associated with renal dysfunction in hypertension and diabetes. Methods: Fourteen days after induction of diabetes with streptozotocin in 12-week-old male Wistar and spontaneously hypertensive (SHR) rats, animals were treated during 7 days with 2-chloroadenosine (CADO group, 5 mg/kg/d), a stable analogue of adenosine, or underwent a sham operation procedure. At the end of the study (day 21), intra-arterial systolic blood pressure (SBP) was measured, and 24-h urine and plasma samples and renal tissue were collected. Results: CADO treatment decreased the plasma glucose concentration and glucose and protein excretion by more than 30% in both strains. CADO treatment decreased SBP in diabetic SHR rats (143 ± 8 versus 114 ± 4 mmHg, p < 0.05), but not in diabetic Wistar rats. The hypotensive effect of CADO was associated to a ∼70% increase in plasma angiotensinogen (AGT) concentration and a ∼50% decrease in urinary AGT excretion. CADO also caused a decrease in medullary and cortical hydrogen peroxide production of about 40%, which was associated with a proportional increase in glutathione peroxidase (GPx) activity in diabetic Wistar but not in diabetic SHR animals. Conclusions: These results suggest that activation of adenosine receptors improves renal antioxidant capacity in diabetic Wistar but not SHR rats, although it improves glucose metabolism in both strains. Furthermore, activation of adenosine receptors does not seem to be directly influencing AGT production.

This article is from Sensors (Basel, Switzerland) , volume 8 . Abstract In the striatum many neurotransmitters including GABA, glutamate, acetylcholine, dopamine, nitric oxide and adenosine interact to regulate synaptic transmission. Dopamine release in the striatum is regulated by a number of pre- and post-synaptic receptors including adenosine. We have recently shown using isolated rat striatal slices, and the technique of fast cyclic voltammetry, that adenosine A1 receptor-mediated inhibition of dopamine release is modulated by dopamine D1 receptors. In the present study we have investigated the influence of NMDA and GABA receptor activation on the modulation of electrically stimulated dopamine release by adenosine. Application of the adenosine A1 receptor agonist, N6-cyclopentyladenosine (CPA), concentration-dependently inhibited dopamine release to a maxiumum of 50%. Perfusion of the glutamate receptor agonist, NMDA, in low magnesium, caused a rapid and concentration-dependent inhibition of dopamine release. Prior perfusion with the adenosine A1 receptor antagonist, DPCPX, significantly reduced the effect of 5 μM and 10 μM NMDA on dopamine release. The GABAA receptor agonist, isoguvacine, had a significant concentration-dependent inhibitory effect on dopamine release which was reversed by prior application of the GABAA receptor antagonist, picrotoxin, but not DPCPX. Finally inhibition of dopamine release by CPA (1μM) was significantly enhanced by prior perfusion with picrotoxin. These data demonstrate an important role for GABA, NMDA and adenosine in the modulation of dopamine release.

In pursuit of an improved understanding and treatment of Parkinson's disease (PD) and related neuropsychiatric disease we have held a translational research conference entitled, Targeting Adenosine A2A Receptors in ParkThson's Disease and other CNS Disorders in Boston, May 17-19, 2006. Recent insights into the ONS functions of the adenosine A2A receptor, A2A receptor neurotoxicology, and intriguing environmental clues have all converged to markedly enhance the potential of A2A antagonists as a therapeutic strategy for PD. The goal of this conference was to facilitate the translation of advances in A2A receptor biology into improved therapy for PD by promoting the exchange of ideas on the basic science and clinical study of this molecular target.

This article is from Arthritis Research & Therapy , volume 15 . Abstract Introduction: Adenosine, acting through the A2A receptor, promotes tissue matrix production in the skin and the liver and induces the development of dermal fibrosis and cirrhosis in murine models. Since expression of A2A receptors is increased in scleroderma fibroblasts, we examined the mechanisms by which the A2A receptor produces its fibrogenic effects. Methods: The effects of A2A receptor ligation on the expression of the transcription factor, Fli1, a constitutive repressor for the synthesis of matrix proteins, such as collagen, is studied in dermal fibroblasts. Fli1 is also known to repress the transcription of CTGF/CCN2, and the effects of A2A receptor stimulation on CTGF and TGF-β1 expression are also examined. Results: A2A receptor occupancy suppresses the expression of Fli1 by dermal fibroblasts. A2A receptor activation induces the secretion of CTGF by dermal fibroblasts, and neutralization of CTGF abrogates the A2A receptor-mediated enhancement of collagen type I production. A2AR activation, however, resulted in a decrease in TGF-β1 protein release. Conclusions: Our results suggest that Fli1 and CTGF are important mediators of the fibrogenic actions of adenosine and the use of small molecules such as adenosine A2A receptor antagonists may be useful in the therapy of dermal fibrosis in diseases such as scleroderma.

This article is from Physiological Reports , volume 1 . Abstract A recent study (American Journal of Physiology – Cell Physiology 304:C406–C421, 2013) suggests that extracellular guanosine increases extracellular adenosine by modifying the disposition of extracellular adenosine (“guanosine–adenosine mechanism”) and that the guanosine–adenosine mechanism is not mediated by classical adenosine transport systems (SLC28 and SLC29 families) nor by classical adenosine-metabolizing enzymes. The present investigation had two aims (1) to test the hypothesis that the “guanosine–adenosine mechanism” affects cell proliferation; and (2) to determine whether the transporters SLC19A1, SLC19A2, SLC19A3, or SLC22A2 (known to carrier guanosine analogs) might be responsible for the guanosine–adenosine mechanism. In the absence of added adenosine, guanosine had little effect on the proliferation of coronary artery vascular smooth muscle cells (vascular conduit cells) or preglomerular vascular smooth muscle cells (vascular resistance cells). However, in the presence of added adenosine (3 or 10 μmol/L), guanosine (10–100 μmol/L) decreased proliferation of both cell types, thus resulting in a highly significant (P < 0.000001) interaction between guanosine and adenosine on cell proliferation. The guanosine–adenosine interaction on cell proliferation was abolished by 1,3-dipropyl-8-(p-sulfophenyl)xanthine (adenosine receptor antagonist). Guanosine (30 μmol/L) increased extracellular levels of adenosine when adenosine (3 μmol/L) was added to the medium. This effect was not reproduced by high concentrations of methotrexate (100 μmol/L), thiamine (1000 μmol/L), chloroquine (1000 μmol/L), or acyclovir (10,000 μmol/L), archetypal substrates for SLC19A1, SLC19A2, SLC19A3, and SLC22A2, respectively; and guanosine still increased adenosine levels in the presence of these compounds. In conclusion, the guanosine–adenosine mechanism affects cell proliferation and is not mediated by SLC19A1, SLC19A2, SLC19A3, or SLC22A2.

This article is from Current Neuropharmacology , volume 9 . Abstract Adenosine is produced primarily by the metabolism of ATP and mediates its physiological actions by interacting primarily with adenosine receptors (ARs) on the plasma membranes of different cell types in the body. Activation of these G protein-coupled receptors promotes activation of diverse cellular signaling pathways that define their tissue-specific functions. One of the major actions of adenosine is cytoprotection, mediated primarily via two ARs - A1 (A1AR) and A3 (A3AR). These ARs protect cells exposed to oxidative stress and are also regulated by oxidative stress. Stress-mediated regulation of ARs involves two prominent transcription factors - activator protein-1 (AP-1) and nuclear factor (NF)-κB – that mediate the induction of genes important in cell survival. Mice that are genetically deficient in the p50 subunit of NF-κB (i.e., p50 knock-out mice) exhibit altered expression of A1AR and A2AAR and demonstrate distinct behavioral phenotypes under normal conditions or after drug challenges. These effects suggest an important role for NF-κB in dictating the level of expression of ARs in vivo, in regulating the cellular responses to stress, and in modifying behavior.

Continued progress has been made toward each of the Specific Aims (SAs) 1 and 2 (SA 3 completed) of our research project, Caffeine, adenosine receptors and estrogen in toxin models of Parkinson's disease (PD) . The overarching hypothesis of the project is that multiple environmental protectants and toxins interact to influence of the health of the dopaminergic neurons lost in PD. To that end we are characterizing the interplay between several environmental agents (pesticides, caffeine and estrogen) that are leading candidate modulators of PD risk. In Year 4 we have obtained and reported evidence that the adenosine receptor blocker caffeine as well as specific genetic depletion of the A2A subtype of adenosine receptor are capable of conferring neuroprotection in chronic pesticide and genetic mouse models of PD. Critical to our ability to successfully pursue the Specific Aims of our research program, we have made technical progress in assessing modification of a key conditional KO methodology developed in this project. We have presented initial data applying this method to the MPTP model of neurodegeneration in PD.

Substantial progress has been made toward each of the 3 Specific Aims (SAs) of our research project, Caffeine, adenosine receptors andestrogen in toxin models of Parkinson's disease (PD). The overarching hypothesis of the project is that multiple environmental protectants and toxins interact to influence of the health of the dopaminergic neurons lost in PD. To that end we are characterizing the interplay between several environmental agents (pesticides, caffeine and estrogen) that are leading candidate modulators of PD risk. A major finding and publication of this project (SA #3) in its first year entails our demonstration that estrogen can prevent the neuroprotective effect of caffeine in the mouse MPTP model of PD. We have obtained evidence that endogenous estrogen (in females) andexogenous estrogen (in males and in ovariectomized females) can prevent the protective effect of caffeine on MPTP- induced loss of brain dopamine. Estrogen did not alter caffeine pharmacokinetics arguing for a downstream estrogen-caffeine interaction in the modification of dopaminergic neuron injury. These findings establish an animal model of estrogen-caffeine interactions in the modification of PD risk in humans, along with the opportunity to understand its molecular mechanisms. In addition, our laboratory and human data for this interaction are now sufficiently compelling to influence the design and interpretation of neuroprotection trials of estrogen or caffeine currently underway or under consideration. Ultimately, a better understanding of the interplay between environmental factors like caffeine estrogen may suggest effective preventative as well as therapeutic strategies for this neurodegenerative disorder.

Abstract 11 C-SCH442416 was reported in preclinical studies with rodents and primates to be the first nonxanthine radioligand suitable for the  in vivo  imaging of adenosine A 2A  receptors with positron emission tomography (PET). The aim of the present work was to investigate the suitability of  11 C-SCH442416 for the  in vivo  quantification of A 2A  receptors in human brain. Methods:   Five male healthy subjects were scanned with 364 MBq bolus injections of  11 C-SCH442416. 90 minutes of dynamic PET emission data were acquired, and arterial blood samples were taken throughout the scan to generate an arterial plasma input function. Using the individual MR images, regions-of-interest (ROIs) were defined for cerebellum, caudate, putamen and thalamus. Spectral analysis was used to determine the frequency components of the  11 C-SCH442416 tissue response for regional and voxel time-activity curves (TACs). Results:   11 C-SCH442416 was rapidly metabolised in blood, the fraction of unmetabolised parent tracer in plasma being 41% at 15 minutes and 15% at 95 minutes, lower than that reported in rats and  macaca nemestrina . No lipophilic radiolabelled metabolites were found in human plasma. Rapid uptake of  11 C-SCH442416 was observed in all brain regions, reaching a maximum at about 3 minutes. When spectral analysis was applied to regional brain time activity curves (TACs), relatively rapid reversible region dependent and slower irreversible, region independent but subject specific components were identified. These components were further separated into irreversible nonspecific binding, reversible nonspecific binding, reversible specific binding and a blood component. Binding potentials of the nondisplaceable binding  BPND  were calculated using cerebellar volume of distribution as an estimate of the reversible nondisplaceable binding across the entire brain. Mean binding potentials  BPND  were: 2.5 (putamen), 1.6 (caudate) and 0.5 (thalamus). Conclusion:  Our study demonstrates that A 2A  receptor binding can be quantified in striatal regions of the human brain with  11 C-SCH442416 PET. Despite the complex tracer kinetics and its low specific binding, reliable binding potentials could be estimated with spectral analysis. Citation Grachev ID, Doder M, Brooks DJ, Hinz R. Quantitative  in vivo  Imaging of Adenosine A 2A  Receptors in the Human Brain Using  11 C-SCH442416 PET: A Pilot Study.  Journal of Diagnostic Imaging in Therapy . 2014; 1(1): 1-19. http://dx.doi.org/10.17229/jdit.2014-0620-001

Substantial progress has been made toward our original Specific Aims (SAs) in pursuit of the core hypothesis that multiple environmental protectants and toxins interact to influence of the health of the dopaminergic neurons lost in PD. SA#1: Using a series of global and conditional knockout mice lacking the adenosine A2A receptor, we characterized the molecular and cellular basis of caffeine s protective actions in acute toxin models of PD. Recently we showed that caffeine also confers protection in a chronic pesticide model of PD. SA#2: We have validated a powerful (AAV) virus-based (cre) gene delivery system to conditionally knock out adenosine receptors from specific brain regions, enabling us to determine in which brain region(s) A2A receptors contribute to neurotoxicity. Despite technical challenges of viral and/or cre gene toxicity, we have obtained initial evidence of striatal A2A receptor-dependence of MPTP toxicity with this system. SA#3: We systematically demonstrated that endogenous estrogen (in females) and exogenous estrogen (e.g., in ovariectomized females) can prevent the protective effect of caffeine on MPTP toxicity, without altering caffeine pharmacokinetics. The findings provide insight into epidemiological studies consistently identifying coffee and caffeine consumption as an inverse risk factor for PD in men, and only in women who have not taken estrogen replacement therapy. These data have helped substantiate that critical interactions between environmental toxicants and protectants influencing the neurodegeneration of PD. Finally, our demonstrations of adenosine A2A receptor-dependent protection by caffeine, and of the prognostic biomarker potential of another purine urate, have directly contributed to the rationale for novel clinical trials with disease-modification designs currently in progress.

During the reporting period continued progress has been made toward our original Specific Aims (1-3) through approved Modified Aims (M1 and M2) of our project, Caffeine, adenosine receptors and estrogen in toxin models of Parkinson's disease (PD). The overarching hypothesis of the project is that multiple environmental protectants and toxins interact to influence of the health of the dopaminergic neurons lost in PD. To that end we are characterizing the interplay between environmental agents (e.g., pesticides, caffeine, estrogen) that are leading candidate modulators of PD risk. In Year 5 we obtained and reported evidence that the adenosine receptor blocker caffeine as well as specific genetic depletion of the A2A subtype of adenosine receptor are capable of conferring protection against neuron degeneration in chronic pesticide and genetic mouse models of PD. Moreover, we have demonstrated and published that adenosine A2A receptors expressed in forebrain neuron are critical for neuron degeneration in toxin model of PD. We also identified CSF levels of urate (an environmentally and genetically determined antioxidant) is a predictor of progression of PD.

Identifying the mechanisnms by which caffeine and more specific A2A antagonists protect dopaminergic neurons in muttiple toxin models of Parkinson's disease (PD) will advance our knowledge of the pathophysiology epidemiology and therapeutics of PD.