adenosine-5--(n-ethylcarboxamide) and 8-(3-chlorostyryl)caffeine

The adenosine A1/A2 adenosine agonist 5'-(N-ethylcarboxamido) adenosine (NECA) and bradykinin both limit infarction when administered at reperfusion in rabbits. This study compares the signal transduction pathways responsible for their anti-infarct effect. Receptor agonists were administered to isolated rabbit hearts starting 25 min after the onset of a 30-min period of ischemia and continued into the 2-h reperfusion period. Infarct size was measured. Both NECA and bradykinin decreased infarction from 31.5 +/- 2.4% of the risk zone in untreated hearts to 11.8 +/- 2.0% and 15.4 +/- 2.4%, respectively (P<0.05). Protection from both agents was blocked by PD98059, wortmannin, and Nomega-nitro-L-arginine methyl ester (L-NAME), thus demonstrating dependence on activation of extracellular regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3K) and stimulation of nitric oxide synthase (NOS). Both wortmannin and PD98059 prevented phosphorylation of ERK 1/2 in NECA-treated hearts, whereas only wortmannin and not PD98059 blocked Akt phosphorylation. These data suggest Akt is upstream of ERK 1/2. In addition, 8-(3-chlorostyryl) caffeine blocked NECA's protection indicating that A2 adenosine receptors trigger NECA's anti-infarct effect. Of note, both bradykinin and acetylcholine (ACh) administered before ischemia to trigger preconditioning's cardioprotection use PI3K and NOS in their signaling pathway. Curiously, however, ACh, unlike bradykinin, was not protective when administered at reperfusion. Hence, both NECA and bradykinin administered at reperfusion protect through a common signaling pathway that includes PI3K, NO, and ERK.

Topics: Adenosine A2 Receptor Antagonists; Adenosine-5'-(N-ethylcarboxamide); Androstadienes; Animals; Bradykinin; Caffeine; Enzyme Inhibitors; Flavonoids; In Vitro Techniques; Infarction; Mitogen-Activated Protein Kinases; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Rabbits; Receptors, Adenosine A2; Reperfusion; Signal Transduction; Vasodilator Agents; Wortmannin

Adenosine (ADO) exerts potent anti-inflammatory and immunosuppressive effects. In this paper we address the possibility that these effects are partly mediated by inhibition of the secretion of IL-12, a proinflammatory cytokine and a major inducer of Th1 responses. We demonstrate that 5'-N-ethylcarboxamidoadenosine (NECA), a nonspecific ADO analogue, and 2-p-(2-carbonyl-ethyl)phenylethylamino-5'-N-ethylcarboxamidoadenos ine (CGS-21680), a specific A2a receptor agonist, dose-dependently inhibited, in whole blood ex vivo and monocyte cultures, the production of human IL-12 induced by LPS and Stapholococcus aureus Cowan strain 1. However, the A1 receptor agonist 2-Chloro-N6-cyclopentyladenosine and the A3 receptor agonists N6-Benzyl-NECA and 1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-be ta-d -ribofuranuronamide expressed only weak inhibitory effects. On the other hand, NECA and CGS-21680 dose-dependently potentiated the production of IL-10. The differential effect of these drugs on monocyte IL-12 and IL-10 production implies that these effects are mediated by A2a receptor signaling rather than by intracellular toxicity of ADO analogue's metabolites. Moreover, CGS-21680 inhibited IL-12 production independently of endogenous IL-10 induction, because anti-IL-10 Abs failed to prevent its effect. The selective A2a antagonist 8-(3-Chlorostyryl) caffeine prevented the inhibitory effect of CGS-21680 on IL-12 production. The phosphodiesterase inhibitor Ro 20-1724 dose-dependently potentiated the inhibitory effect of CGS-21680 and, furthermore, Rp-cAMPS, a protein kinase A inhibitor, reversed the inhibitory effect of CGS-21680, implicating a cAMP/protein kinase A pathway in its action. Thus, ligand activation of A2a receptors simultaneously inhibits IL-12 and stimulates IL-10 production by human monocytes. Through this mechanism, ADO released in excess during inflammatory and ischemic conditions, or tissue injury, may contribute to selective suppression of Th1 responses and cellular immunity.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Caffeine; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Dose-Response Relationship, Immunologic; Female; Humans; Immunosuppressive Agents; Interleukin-10; Interleukin-12; Ligands; Lipopolysaccharides; Male; Monocytes; Phenethylamines; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Receptor, Adenosine A2A; Receptor, Adenosine A3; Receptors, Purinergic P1; Signal Transduction

Adenosine (Ado) is an important autocrine modulator of neutrophil functions. In this study, we determined the effects of endogenous Ado on fMet-Leu-Phe (fMLP)-induced phospholipase D (PLD) activity in neutrophils. The removal of extracellular Ado by Ado deaminase (ADA) or the blockade of its action by the A2a receptor antagonists 8-(3-chlorostyryl) caffeine (CSC) or CGS15943 markedly increased fMLP-induced PLD activation. The concentration-dependent stimulatory effects of CSC and CGS15943 were abolished by a pretreatment of neutrophil suspensionswith ADA. In contrast, the selective A2a receptor agonist CGS21680 suppressed fMLP-induced PLD activation. Furthermore, inhibition by CGS21680 of fMLP-induced PLD activity was reversed by CSC or CGS15943. The removal of Ado by ADA or the blockade of its action by CSC or CGS15943, markedly increased the membrane recruitment of cytosolic protein kinase Calpha (PKCalpha), RhoA, and ADP-ribosylation factor (ARF) in response to fMLP. As shown for PLD activity, the stimulatory effect of Ado receptor antagonists on PLD cofactors translocation was abolished by a pretreatment of the cells with ADA. Moreover, the membrane translocation of both PKCalpha, RhoA, and ARF in response to fMLP was attenuated by CGS21680 and this effect of the A2a receptor agonist was antagonized by CSC or CGS15943. These data demonstrate that Ado released by neutrophils in the extracellular milieu inhibits PLD activation by blocking membrane association of ARF, RhoA, and PKCalpha through Ado A2a receptor occupancy. (Blood. 2000;95:519-527)

Topics: Adenosine; Adenosine Deaminase; Adenosine-5'-(N-ethylcarboxamide); ADP-Ribosylation Factor 1; Adult; Caffeine; Cell Membrane; Enzyme Activation; GTP Phosphohydrolases; Humans; In Vitro Techniques; Isoenzymes; Kinetics; N-Formylmethionine Leucyl-Phenylalanine; Neutrophils; Phenethylamines; Phospholipase D; Protein Kinase C; Protein Kinase C-alpha; Purinergic P1 Receptor Antagonists; Quinazolines; Receptor, Adenosine A2A; Receptors, Purinergic P1; rhoA GTP-Binding Protein; Triazoles

The cytokine interleukin (IL)-6 has recently been demonstrated to play a role in the pathology of Alzheimer's disease (AD). The mechanisms leading to increased IL-6 levels in brains of AD patients are still unknown. Because in experimental animals ischemia increases both the levels of cytokines and the extracellular concentrations of adenosine in the brain, we hypothesized that these two phenomena may be functionally connected and that adenosine might increase IL-6 gene expression in the brain. Here we show that the mixed A1 and A2 agonist 5'-(N-ethylcarboxamido) adenosine (NECA) induces an increase in IL-6 mRNA levels and protein synthesis in the human astrocytoma cell line U373 MG. The A1-specific agonists R-phenylisopropyladenosine and cyclopentyladenosine are much less potent, and the A2a-specific agonist CGS-21860 shows only marginal effects. Increased levels of mRNA are already found within 30 min after NECA treatment. The A2a-selective antagonists 8-(3-chlorostyryl) caffeine and KF17837 [(E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxanthine] , which have also some antagonistic properties at A2b receptors, and the nonspecific adenosine antagonist 8-phenyltheophylline were equipotent at inhibiting the NECA-induced increase in IL-6 protein synthesis, whereas the specific A1 antagonist 8-cyclopentyl-1,3 dipropylxanthine is much less potent. The results indicate that adenosine A2b receptors participate in the regulation of the IL-6 gene in astrocytoma cells.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Antineoplastic Agents; Astrocytoma; Blotting, Northern; Caffeine; Dose-Response Relationship, Immunologic; Gene Expression Regulation, Neoplastic; Humans; Interleukin-6; Purinergic P1 Receptor Agonists; Receptors, Purinergic P1; RNA, Messenger; Stereoisomerism; Tumor Cells, Cultured; Xanthines