AMP is an adenosine A 1 receptor agonist

Department of Cell and Molecular Physiology, University of North Carolina Neuroscience Center, Chapel Hill, North Carolina 27599, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 01/2012; 287(8):5301-9. DOI: 10.1074/jbc.M111.291666
Source: PubMed

ABSTRACT Numerous receptors for ATP, ADP, and adenosine exist; however, it is currently unknown whether a receptor for the related
nucleotide adenosine 5′-monophosphate (AMP) exists. Using a novel cell-based assay to visualize adenosine receptor activation
in real time, we found that AMP and a non-hydrolyzable AMP analog (deoxyadenosine 5′-monophosphonate, ACP) directly activated
the adenosine A1 receptor (A1R). In contrast, AMP only activated the adenosine A2B receptor (A2BR) after hydrolysis to adenosine by ecto-5′-nucleotidase (NT5E, CD73) or prostatic acid phosphatase (PAP, ACPP). Adenosine
and AMP were equipotent human A1R agonists in our real-time assay and in a cAMP accumulation assay. ACP also depressed cAMP levels in mouse cortical neurons
through activation of endogenous A1R. Non-selective purinergic receptor antagonists (pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid and suramin) did not
block adenosine- or AMP-evoked activation. Moreover, mutation of His-251 in the human A1R ligand binding pocket reduced AMP potency without affecting adenosine potency. In contrast, mutation of a different binding
pocket residue (His-278) eliminated responses to AMP and to adenosine. Taken together, our study indicates that the physiologically
relevant nucleotide AMP is a full agonist of A1R. In addition, our study suggests that some of the physiological effects of AMP may be direct, and not indirect through ectonucleotidases
that hydrolyze this nucleotide to adenosine.

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Available from: Ilia Korboukh, Mar 30, 2015
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    • "Benzodiazepines are reported to potentiate the depressant actions of AMP and adenosine on cerebral cortical neurons (Phillis 1979). Studies have demonstrated that AMP and adenosine are equipotent agonists for human A 1 receptors (Rittiner et al. 2012). Hawkins et al. (1988) evaluated, by radioligand, the effects of subcutaneous administration of chronic diazepam (5 mg/kg/day) for 10 and 20 days on adenosine receptors in different brain areas. "
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    ABSTRACT: Anxiety is characterized by unpleasant bodily sensations, such as pounding heart and intense fear. The therapy involves the administration of benzodiazepine drugs. Purinergic signaling participates in the induction of several behavioral patterns and their actions are inactivated by ectonucleotidases and adenosine deaminase (ADA). Since there is evidence about the involvement of purinergic system in the actions mediated by benzodiazepines, we evaluated the effects in vitro and in vivo of administration of diazepam and midazolam on nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, and ADA activities in zebrafish brain, followed by the analysis of gene expression pattern of these enzymes and adenosine receptors (A1, A2a1, A2a2, A2b). The in vitro studies demonstrated that diazepam decreased ATP (66 % for 500 µM) and ADP hydrolysis (40-54 % for 10-500 µM, respectively). Midazolam decreased ATP (16-71 % for 10-500 µM, respectively) and ADP (48-73.5 % for 250-500 µM, respectively) hydrolysis as well as the ecto-ADA activity (26-27.5 % for 10-500 µM, respectively). AMP hydrolysis was decreased in animals treated with of 0.5 and 1 mg/L midazolam (32 and 36 %, respectively). Diazepam and midazolam decreased the ecto-ADA activity at 1.25 mg/L and 1 mg/L (31 and 33 %, respectively), but only 0.1 mg/L midazolam induced an increase (40 %) in cytosolic ADA. The gene expression analysis demonstrated changes on ecto-5'-nucleotidase, A1, A2a1, A2a2, and A2b mRNA transcript levels after acute treatment with benzodiazepines. These findings demonstrated that benzodiazepine exposure induces a modulation of extracellular nucleotide and nucleoside metabolism, suggesting the purinergic signaling may be, at least in part, related to benzodiazepine effects.
    Journal of Neural Transmission 03/2015; 122(8). DOI:10.1007/s00702-015-1390-8 · 2.40 Impact Factor
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    • "Other natural product aaRS inhibitors consist of reveromycin A (targets IleRS), borrelidin (targets ThrRS), indolmycin (targets TrpRS), ochratoxin (targets PheRS), cispentacin (targets ProRS), and granaticin (targets LeuRS) [1] [3]. Besides, some synthetic aaRS inhibitors are also developed as variants of the natural substrate or as non-hydrolyzable aa-AMP mimics [4], most of which act through competitive binding to the aaRSs. Although the aa-AMP mimics demonstrated low nanomolar binding affinities against their corresponding aaRSs, the lack of selectivity and poor bacterial cell permeability are the most prominent problems for this new potential class of antibiotics. "
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    ABSTRACT: Borrelidin exhibits a wide spectrum of biological activities and has been considered as a non-competitive inhibitor of Threonyl-tRNA synthetase (ThrRS). However, the detailed mechanisms of borrelidin against ThrRS, especially borrelidin binding site on ThrRS, are still unclear, which limits the development of novel borrelidin derivatives and rational design of structure-based ThrRS inhibitors. In this study, the binding site of borrelidin on E. coli ThrRS was predicted by molecular docking. To validate our speculations, the ThrRS mutants of E. coli (P424K, E458Δ, and G459Δ) were constructed and their sensitivity to borrelidin was compared to that of the wild-type ThrRS by enzyme kinetics and stopped-flow fluorescence analysis. The docking results showed that borrelidin binds the pocket outside but adjacent to the active site of ThrRS, consisting of residue Y313, R363, R375, P424, E458, G459, and K465. Site-directed mutagenesis results showed that sensitivities of P424K, E458Δ, and G459Δ ThrRSs to borrelidin were reduced markedly. All the results showed that residue Y313, P424, E458, and G459 play vital roles in the binding of borrelidin to ThrRS. It indicated that borrelidin may induce the cleft closure, which blocks the release of Thr-AMP and PPi, to inhibit activity of ThrRS rather than inhibit the binding of ATP and threonine. This study provides new insight into inhibitory mechanisms of borrelidin against ThrRS, and paves the way for development of novel borrelidin derivatives and rational design of structure-based ThrRS inhibitors.
    Biochemical and Biophysical Research Communications 09/2014; 451(4). DOI:10.1016/j.bbrc.2014.07.100 · 2.30 Impact Factor
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    • "Induced torpor acts via A1 receptors in Syrian hamster, ground squirrel and rat [49]–[51]. 5′-AMP has been shown to be a true A1 receptor agonist [52]. These studies, however, did not measure platelet count. "
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    ABSTRACT: Hibernation is an energy-conserving behavior in winter characterized by two phases: torpor and arousal. During torpor, markedly reduced metabolic activity results in inactivity and decreased body temperature. Arousal periods intersperse the torpor bouts and feature increased metabolism and euthermic body temperature. Alterations in physiological parameters, such as suppression of hemostasis, are thought to allow hibernators to survive periods of torpor and arousal without organ injury. While the state of torpor is potentially procoagulant, due to low blood flow, increased viscosity, immobility, hypoxia, and low body temperature, organ injury due to thromboembolism is absent. To investigate platelet dynamics during hibernation, we measured platelet count and function during and after natural torpor, pharmacologically induced torpor and forced hypothermia. Splenectomies were performed to unravel potential storage sites of platelets during torpor. Here we show that decreasing body temperature drives thrombocytopenia during torpor in hamster with maintained functionality of circulating platelets. Interestingly, hamster platelets during torpor do not express P-selectin, but expression is induced by treatment with ADP. Platelet count rapidly restores during arousal and rewarming. Platelet dynamics in hibernation are not affected by splenectomy before or during torpor. Reversible thrombocytopenia was also induced by forced hypothermia in both hibernating (hamster) and non-hibernating (rat and mouse) species without changing platelet function. Pharmacological torpor induced by injection of 5'-AMP in mice did not induce thrombocytopenia, possibly because 5'-AMP inhibits platelet function. The rapidness of changes in the numbers of circulating platelets, as well as marginal changes in immature platelet fractions upon arousal, strongly suggest that storage-and-release underlies the reversible thrombocytopenia during natural torpor. Possibly, margination of platelets, dependent on intrinsic platelet functionality, governs clearance of circulating platelets during torpor.
    PLoS ONE 04/2014; 9(4):e93218. DOI:10.1371/journal.pone.0093218 · 3.23 Impact Factor
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