(1/50) Brief, repeated, oxygen-glucose deprivation episodes protect neurotransmission from a longer ischemic episode in the in vitro hippocampus: role of adenosine receptors.

1. Ischemic preconditioning in the brain consists of reducing the sensitivity of neuronal tissue to further, more severe, ischemic insults. We recorded field epsps (fepsps) extracellularly from hippocampal slices to develop a model of in vitro ischemic preconditioning and to evaluate the role of A1, A2A and A3 adenosine receptors in this phenomenon. 2. The application of an ischemic insult, obtained by glucose and oxygen deprivation for 7 min, produced an irreversible depression of synaptic transmission. Ischemic preconditioning was induced by four ischemic insults (2 min each) separated by 13 min of normoxic conditions. After 30 min, an ischemic insult of 7 min was applied. This protocol substantially protected the tissue from the irreversible depression of synaptic activity. 3. The selective adenosine A1 receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 100 nm), completely prevented the protective effect of preconditioning. The selective adenosine A2A receptor antagonist 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phe nol (ZM 241385, 100 nm) did not modify the magnitude of fepsp recovery compared to control slices. The selective A3 adenosine receptor antagonists, 3-propyl-6-ethyl-5[ethyl(thio)carbonyl]-2-phenyl-4-propyl-3-pyridinecarboxylate (MRS 1523, 100 nm) significantly improved the recovery of fepsps after 7 min of ischemia. 4. Our results show that in vitro ischemic preconditioning allows CA1 hippocampal neurons to become resistant to prolonged exposure to ischemia. Adenosine, by stimulating A1 receptors, plays a crucial role in eliciting the cell mechanisms underlying preconditioning; A2A receptors are not involved in this phenomenon, whereas A3 receptor activation is harmful to ischemic preconditioning.  (+info)

(2/50) Pharmacological preconditioning with resveratrol: role of CREB-dependent Bcl-2 signaling via adenosine A3 receptor activation.

Recent studies demonstrated that resveratrol, a grape-derived polyphenolic phytoalexin, provides pharmacological preconditioning (PC) of the heart through a NO-dependent mechanism. Because adenosine receptors play a role in PC, we examined whether they play any role in resveratrol PC. Rats were randomly assigned to groups perfused for 15 min with 1) Krebs-Henseleit bicarbonate buffer (KHB) only; 2) KHB containing 10 microM resveratrol; 3) 10 microM resveratrol + 1 microM 8-cyclopentyl-1,3-dimethylxanthine (CPT; adenosine A(1) receptor blocker); 4) 10 microM resveratrol + 1 microM 8-(3-chlorostyryl)caffeine (CSC; adenosine A(2a) receptor blocker); 5) 10 microM resveratrol + 1 microM 3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5- dicarboxylate (MRS-1191; adenosine A(3) receptor blocker); or 6) 10 microM resveratrol + 3 microM 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride [LY-294002, phosphatidylinositol (PI)3-kinase inhibitor], and groups perfused with adenosine receptor blockers alone. Hearts were then subjected to 30-min ischemia followed by 2-h reperfusion. The results demonstrated significant cardioprotection with resveratrol evidenced by improved ventricular recovery and reduced infarct size and cardiomyocyte apoptosis. CPT and MRS 1191, but not CSC, abrogated the cardioprotective abilities of resveratrol, suggesting a role of adenosine A(1) and A(3) receptors in resveratrol PC. Resveratrol induced expression of Bcl-2 and caused its phosphorylation along with phosphorylation of cAMP response element-binding protein (CREB), Akt, and Bad. CPT blocked phosphorylation of Akt and Bad without affecting CREB, whereas MRS 1191 blocked phosphorylation of all compounds, including CREB. LY-294002 partially blocked the cardioprotective abilities of resveratrol. The results indicate that resveratrol preconditions the heart through activation of adenosine A(1) and A(3) receptors, the former transmitting a survival signal through PI3-kinase-Akt-Bcl-2 signaling pathway and the latter protecting the heart through a CREB-dependent Bcl-2 pathway in addition to an Akt-Bcl-2 pathway.  (+info)

(3/50) Activation of A3 adenosine receptors attenuates lung injury after in vivo reperfusion.

BACKGROUND: A3 adenosine receptor (AR) activation worsens or protects against renal and cardiac ischemia-reperfusion (IR) injury, respectively. The aims of the current study were to examine in an in vivo model the effect of A3AR activation on IR lung injury and investigate the mechanism by which it exerts its effect. METHODS: The arterial branch of the left lower lung lobe in intact-chest, spontaneously breathing cats was occluded for 2 h and reperfused for 3 h (IR group). Animals were treated with the selective A3 receptor agonist IB-MECA (300 microg/kg intravenously) given 15 min before ischemia or with IB-MECA as described, with pretreatment 15 min earlier with the selective A3AR antagonist MRS-1191, the nonsulfonylurea adenosine triphosphate-sensitive potassium channel-blocking agent U-37883A, or the nitric oxide synthase inhibitor N-nitro-l-arginine benzyl ester. RESULTS: IB-MECA markedly (P < 0.01) reduced the percentage of injured alveoli (IR, 48 +/- 4%; IB-MECA, 18 +/- 2%), wet:dry weight ratio (IR, 8.2 +/- 0.4; IB-MECA, 4 +/- 2), and myeloperoxidase activity (IR, 0.52 +/- 0.06 U/g; IB-MECA, 0.17 +/- 0.04 U/g). This protective effect was completely blocked by pretreatment with the selective A3AR antagonist MRS-1191 and the adenosine triphosphate-sensitive potassium channel blocking agent U-37883A but not the nitric oxide synthase inhibitor N-nitro-l-arginine benzyl ester. CONCLUSIONS: In the feline lung, the A3AR agonist IB-MECA confers a powerful protection against IR lung injury. This effect is mediated by a nitric oxide synthase-independent pathway and involves opening of adenosine triphosphate-sensitive potassium channels. Therefore, selective activation of A3AR may be an effective means of protecting the reperfused lung.  (+info)

(4/50) A3 adenosine receptor activation inhibits cell proliferation via phosphatidylinositol 3-kinase/Akt-dependent inhibition of the extracellular signal-regulated kinase 1/2 phosphorylation in A375 human melanoma cells.

Adenosine exerts its effects through four subtypes of G-protein-coupled receptors: A(1), A(2A), A(2B), and A(3). Stimulation of the human A(3) receptor has been suggested to influence cell death and proliferation. The phosphatidylinositide-3-OH kinase (PI3K)/Akt and the Raf/mitogen-activated protein kinase (MAPK/ERK) kinase (MEK)/mitogen-activated protein kinase (MAPK) pathways have central roles in the regulation of cell survival and proliferation. Due to their importance, the cross-talk between these two pathways has been investigated. Here, we show that the A(3) adenosine receptor agonist Cl-IB-MECA stimulates PI3K-dependent phosphorylation of Akt leading to the reduction of basal levels of ERK1/2 phosphorylation, which in turn inhibits cell proliferation. The response to Cl-IB-MECA was not blocked by A(1), A(2A), or A(2B) receptor antagonists, although it was abolished by A(3) receptor antagonists. Furthermore, the response to Cl-IB-MECA was generated at the cell surface, since the inhibition of A(3) receptor expression, by using small interfering RNA, abolished agonist effects. Using A375 cells, we show that A(3) adenosine receptor stimulation results in PI3K-dependent phosphorylation of Akt, leading to the reduction of basal levels of ERK1/2 phosphorylation, which in turn inhibits cell proliferation.  (+info)

(5/50) Resveratrol-mediated activation of cAMP response element-binding protein through adenosine A3 receptor by Akt-dependent and -independent pathways.

A recent study documented a role of adenosine A(3)-Akt-cAMP response element-binding protein (CREB) survival signaling in resveratrol preconditioning of the heart. In this study, we demonstrate that resveratrol-mediated CREB activation can also occur through an Akt-independent pathway. Isolated rat hearts were perfused for 15 min with Krebs-Henseleit bicarbonate (KHB) buffer containing resveratrol in the absence or presence of adenosine A(3) receptor blocker MRS-1191 [3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5 -dicar-boxylate], phosphatidylinositol 3 (PI3)-kinase inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride], mitogen-activated extracellular signal-regulated protein kinase inhibitor PD098059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one], or a combination of LY294002 and PD098059. All hearts were subsequently subjected to 30-min ischemia followed by 2-h reperfusion. Cardioprotection was examined by determining infarct size, cardiomyocyte apoptosis, and ventricular recovery. Resveratrol phosphorylated both Akt and CREB that was blocked by MRS-1191, which also abolished cardioprotective abilities of resveratrol. LY294002 completely inhibited Akt phosphorylation but partially blocked the phosphorylation of CREB. Inhibition of PI3-kinase also partially blocked resveratrol's ability to precondition the heart. PD098059 partially blocked the phosphorylation of CREB and resveratrol-mediated cardioprotection. Preperfusing the hearts with LY294002 and PD098059 together completely abolished the phosphorylation of CREB, simultaneously inhibiting resveratrol-mediated cardioprotection. The results indicate that resveratrol preconditions the hearts through adenosine A(3) receptor signaling that triggers the phosphorylation of CREB through both Akt-dependent and -independent pathways, leading to cardioprotection.  (+info)

(6/50) Phosphatidylinositol 3-kinase and ERK1/2 are not involved in adenosine A1, A2A or A3 receptor-mediated preconditioning in rat ventricle strips.

Mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase 1 and 2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3-kinase)/protein kinase B (PKB; also known as Akt) are important antiapoptotic signalling pathways which have recently been implicated in cardioprotection. However, at present the involvement of ERK1/2 and PI3-kinase/PKB in adenosine receptor-mediated cardioprotection is poorly understood. In this study we used isolated rat right ventricular strips, contracted by electrical-field stimulation, in order to investigate the role of ERK1/2 and PI3-kinase/PKB in adenosine receptor-induced cardioprotection. Ventricle strips were pretreated for 2 min with the agonists adenosine (non-selective), CPA (A1 selective), CGS 21680 (A2A selective) and Cl-IB-MECA (A3 selective) before 30 min hypoxia followed by 30 min reoxygenation. Each agonist significantly improved posthypoxic percentage contraction recovery compared to control strips. Similarly hypoxic preconditioning (10 min hypoxia followed by 20 min reoxygenation) significantly improved posthypoxic percentage contraction recovery compared to non-preconditioned strips. The selective adenosine receptor antagonists DPCPX (A1), ZM 241385 (A2A) and MRS 1220 (A3) attenuated cardioprotection induced by CPA, CGS 21680 and Cl-IB-MECA, respectively. Pre-incubation (30 min) of ventricle strips with the MEK1 inhibitor PD 98059 (50 microM) or the PI3-kinase inhibitor wortmannin (100 nM) significantly reduced posthypoxic percentage contraction recovery induced by hypoxic preconditioning. In contrast, PD 98059 and wortmannin had no significant effect on cardioprotection induced by CPA, Cl-IB-MECA or CGS 21680. Overall these data indicate that although selective A1, A2A and A3 adenosine receptor agonists induce preconditioning in rat right ventricular strips the effects are independent of ERK1/2- and PI3-kinase-dependent pathways. In contrast ERK1/2 and PI3-kinase-dependent pathways do appear to be involved in early hypoxic preconditioning.  (+info)

(7/50) "Reversine" and its 2-substituted adenine derivatives as potent and selective A3 adenosine receptor antagonists.

The dedifferentiation agent "reversine" [2-(4-morpholinoanilino)-N(6)-cyclohexyladenine 2] was found to be a moderately potent antagonist for the human A(3) adenosine receptor (AR) with a K(i) value of 0.66 microM. This result prompted an exploration of the structure-activity relationship of related derivatives, synthesized via sequential substitution of 6-chloro-2-fluoropurine with selected nucleophiles. Optimization of substituents at these two positions identified 2-(phenylamino)-N(6)-cyclohexyladenine (12), 2-(phenylamino)-N(6)-cycloheptyladenine (19), and 2-phenylamino-N(6)-endo-norbornyladenine (21) as potent A(3) AR ligands with K(i) values of 51, 42, and 37 nM, respectively, with 30-200-fold selectivity in comparison to A(1) and A(2A) ARs. The most selective A(3) AR antagonist (>200-fold) was 2-(phenyloxy)-N(6)-cyclohexyladenine (22). 9-Methylation of 12, but not 19, was well-tolerated in A(3) AR binding. Extension of the 2-phenylamino group to 2-benzyl- and 2-(2-phenylethylamino) reduced affinity. In the series of 2-(phenylamino), 2-(phenyloxy), and 2-(phenylthio) substitutions, the order of affinity at the A(3) AR was oxy > or = amino > thio. Selected derivatives, including reversine (K(B) value of 466 nM via Schild analysis), competitively antagonized the functional effects of a selective A(3) AR agonist, i.e., inhibition of forskolin-stimulated cAMP production in stably transfected Chinese hamster ovary (CHO) cells. These results are in agreement with other studies suggesting the presence of a lipophilic pocket in the AR binding site that is filled by moderately sized cycloalkyl rings at the N(6) position of both adenine and adenosine derivatives. Thus, the compound series reported herein comprise an important new series of selective A(3) AR antagonists. We were unable to reproduce the dedifferentiation effect of reversine, previously reported, or to demonstrate any connection between A(3) AR antagonist effects and dedifferentiation.  (+info)

(8/50) The cross-species A3 adenosine-receptor antagonist MRS 1292 inhibits adenosine-triggered human nonpigmented ciliary epithelial cell fluid release and reduces mouse intraocular pressure.

PURPOSE: Antagonists to A3 adenosine receptors (ARs) lower mouse intraocular pressure (IOP), but extension to humans is limited by species variability. We tested whether the specific A3AR antagonist MRS 1292, designed to cross species, mimicks the effects of other A3AR antagonists on cultured human nonpigmented ciliary epithelial (NPE) cells and mouse IOP. METHODS: NPE cell volume was monitored by electronic cell sorting. Mouse IOP was measured with the Servo-Null Micropipette System. RESULTS: Adenosine triggered A3AR-mediated shrinkage of human NPE cells. Shrinkage was blocked by MRS 1292 (IC50 = 42 +/- 11 nM, p < 0.01) and by another A3AR antagonist effective in this system, MRS 1191. Topical application of the A3AR agonist IB-MECA increased mouse IOP. MRS 1292 reduced IOP by 4.0 +/- 0.8 mmHg at 25-microM droplet concentration (n = 10, p < 0.005). CONCLUSIONS: MRS 1292 inhibits A3AR-mediated shrinkage of human NPE cells and reduces mouse IOP, consistent with its putative action as a cross-species A3 antagonist.  (+info)