Predicted structures of agonist and antagonist bound complexes of adenosine A_3 receptor

We used the GEnSeMBLE Monte Carlo method to predict ensemble of the 20 best packings (helix rotations and tilts) based on the neutral total energy (E) from a vast number (10 trillion) of potential packings for each of the four subtypes of the adenosine G protein-coupled receptors (GPCRs), which are involved in many cytoprotective functions. We then used the DarwinDock Monte Carlo methods to predict the binding pose for the human A_3 adenosine receptor (hAA_3R) for subtype selective agonists and antagonists. We found that all four A_3 agonists stabilize the 15th lowest conformation of apo-hAA_3R while also binding strongly to the 1st and 3rd. In contrast the four A_3 antagonists stabilize the 2nd or 3rd lowest conformation. These results show that different ligands can stabilize different GPCR conformations, which will likely affect function, complicating the design of functionally unique ligands. Interestingly all agonists lead to a trans χ1 angle for W6.48 that experiments on other GPCRs associate with G-protein activation while all 20 apo-AA_3R conformations have a W6.48 gauche+ χ1 angle associated experimentally with inactive GPCRs for other systems. Thus docking calculations have identified critical ligand-GPCR structures involved with activation. We found that the predicted binding site for selective agonist Cl-IB-MECA to the predicted structure of hAA_3R shows favorable interactions to three subtype variable residues, I253^(6.58), V169^(EL2), and Q167^(EL2), while the predicted structure for hAA_(2A)R shows weakened to the corresponding amino acids: T256^(6.58), E169^(EL2), and L167^(EL2), explaining the observed subtype selectivity

Editorial: Purinergic Pharmacology

The purine nucleotides and nucleosides constitute important extracellular signaling molecules acting as neurotransmitters and neuromodulators. Indeed, extracellular adenosine 5′-triphosphate (ATP) and adenosine, tightly controlled by nucleotidases, ribokinases, deaminases, and transporters, signal through a rich array of purinergic receptors. These receptors, which emerged early in evolution, are among the most abundant in living organisms controlling many physiological actions, thus becoming promising therapeutic targets in a wide range of pathological conditions. Thus, while P1 receptors are selective for adenosine, a breakdown product of ATP, P2 receptors are activated by purine nucleotides, as well as P2Y receptors being activated by pyrimidine nucleotides. Interestingly, purinergic receptors, both G protein-coupled (i.e., P1 and P2Y) and ligand-gated ion channel (i.e., P2X) receptors, are involved in many neuronal and non-neuronal mechanisms, including pain, immune responses, exocrine and endocrine secretion, platelet aggregation, endothelial-mediated vasodilatation and inflammation, among others

Optical control of adenosine A3 receptor signaling: Towards a multimodal phototherapy in psoriasis?

Psoriasis is a long-lasting inflammatory disease primarily characterized by cutaneous and systemic manifestations but also showing multiple comorbidities (i.e., psoriatic arthritis, cardiometabolic diseases, psychological illnesses, inflammatory bowel diseases), which affect patients’ quality of life. Its global prevalence score fluctuates around 2% of the population, from which 70% to 80% show a mild variant (i.e., less than 3% to 5% of affected body surface area), and is equally present in both sexes (1). Current treatments of psoriasis show excellent clinical efficacy for many patients but are not curative and eventually remain deficient or inefficient for many others. Thus, despite the therapeutic arsenal for psoriasis being considered first-rate, some unmet clinical conditions will require further pharmacotherapeutic development. In that context, novel orally active drugs for the management of moderate-to-severe psoriasis are under development (2), including Piclidenoson (CF101), an adenosine A3 receptor (A3R) agonist. Indeed, A3R has emerged as novel, promising therapeutic target and biologically predictive marker not only for psoriasis but also for other inflammatory diseases (i.e., rheumatoid arthritis) (3)

Synthesis and evaluation of N⁶-substituted apioadenosines as potential adenosine A₃ receptor modulators

Adenosine receptors (ARs) trigger signal transduction pathways inside the cell when activated by extracellular adenosine. Selective modulation of the A(3)AR subtype may be beneficial in controlling diseases such as colorectal cancer and rheumatoid arthritis. Here, we report the synthesis and evaluation of beta-D-apio-D-furano- and alpha-D-apio-L-furanoadenosines and derivatives thereof. Introduction of a 2-methoxy-5-chlorobenzyl group at N-6 of beta-D-apio-D-furanoadenosine afforded an A(3)AR antagonist (10c, K = 0.98 mu M), while a similar modification of an alpha-D-apio-L-furanoadenosine gave rise to a partial agonist (11c, K-i = 3.07 mu M). The structural basis for this difference was examined by docking to an A(3)AR model; the antagonist lacked a crucial interaction with Thr94

Lighting up G protein-coupled purinergic receptors with engineered fluorescent ligands

The use of G protein-coupled receptors fluorescent ligands is undergoing continuous expansion. In line with this, fluorescent agonists and antagonists of high affinity for G protein-coupled adenosine and P2Y receptors have been shown to be useful pharmacological probe compounds. Fluorescent ligands for A1R, A2AR, and A3R (adenosine receptors) and P2Y2R, P2Y4R, P2Y6R, and P2Y14R (nucleotide receptors) have been reported. Such ligands have been successfully applied to drug discovery and to GPCR characterization by flow cytometry, fluorescence correlation spectroscopy, fluorescence microscopy, fluorescence polarization, fluorescence resonance energy transfer and scanning confocal microscopy. Here we summarize recently reported and readily available representative fluorescent ligands of purinergic receptors. In addition, we pay special attention on the use of this family of fluorescent ligands revealing two main aspects of purinergic receptor biology, namely ligand binding and receptor oligomerization

Evidence for the possible involvement of the P2Y6 receptor in Ca2+ mobilization and insulin secretion in mouse pancreatic islets

Subtypes of purinergic receptors involved in modulation of cytoplasmic calcium ion concentration ([Ca2+]i) and insulin release in mouse pancreatic β-cells were examined in two systems, pancreatic islets in primary culture and beta-TC6 insulinoma cells. Both systems exhibited some physiological responses such as acetylcholine-stimulated [Ca2+]i rise via cytoplasmic Ca2+ mobilization. Addition of ATP, ADP, and 2-MeSADP (each 100 µM) transiently increased [Ca2+]i in single islets cultured in the presence of 5.5 mM (normal) glucose. The potent P2Y1 receptor agonist 2-MeSADP reduced insulin secretion significantly in islets cultured in the presence of high glucose (16.7 mM), whereas a slight stimulation occurred at 5.5 mM glucose. The selective P2Y6 receptor agonist UDP (200 µM) transiently increased [Ca2+]i and reduced insulin secretion at high glucose, whereas the P2Y2/4 receptor agonist UTP and adenosine receptor agonist NECA were inactive. [Ca2+]i transients induced by 2-MeSADP and UDP were antagonized by suramin (100 µM), U73122 (2 µM, PLC inhibitor), and 2-APB (10 or 30 µM, IP3 receptor antagonist), but neither by staurosporine (1 µM, PKC inhibitor) nor depletion of extracellular Ca2+. The effect of 2-MeSADP on [Ca2+]i was also significantly inhibited by MRS2500, a P2Y1 receptor antagonist. These results suggested that P2Y1 and P2Y6 receptor subtypes are involved in Ca2+ mobilization from intracellular stores and insulin release in mouse islets. In beta-TC6 cells, ATP, ADP, 2-MeSADP, and UDP transiently elevated [Ca2+]i and slightly decreased insulin secretion at normal glucose, while UTP and NECA were inactive. RT-PCR analysis detected mRNAs of P2Y1 and P2Y6, but not P2Y2 and P2Y4 receptors

Ultrasound Findings of Delayed‐Onset Muscle Soreness

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135570/1/jum201635112517.pd