ALTERED EXPRESSION AND FUNCTIONALITY OF A2A ADENOSINE RECEPTORS IN HUNTINGTON’S DISEASE AND OTHER POLYGLUTAMINE DISORDERS

Several studies have suggested the possible involvement of A2A adenosine receptors in the pathogenesis of neuronal disorders, including Huntington’s disease. Huntington’s disease is an inherited neurodegenerative disease clinically characterized by motor, cognitive and behavioural impairments. The genetic cause of the disease is the expanded CAG triplet in a gene coding for huntingtin, a protein involved in several physiological processes. Huntington’s disease affects primarly GABAergic neurons in the basal ganglia that express adenosine A2A and dopamine D2 receptors. The present study describes a functional alteration of A2A adenosine receptor in striatal cells engineerized to express full length or truncated, wild type or mutant huntingtin. The data obtained demonstrate that the presence of mutant huntingtin induce an amplification of the transduction signal mediated by adenylyl cyclase and an aberrant coupling of A2A receptor to this transduction pathway. The expression and functionality of A2A adenosine receptor were subsequently evaluated in transgenic mice R6/2, an animal model of Huntington’s disease that express exon 1 of the human huntingtin gene. Saturation binding experiments revealed an increase of A2A receptor levels in striatum of R6/2 mice until 14 post natal days. In addition, also the potency of a typical A2A agonist was increased in striatal membranes of R6/2 mice when compared to wild type mice. The subsequent study aimed the evaluation of the presence and functionality of A2A adenosine receptors in peripheral blood cells from patients affected by Huntington’s disease compared with control subjects. The results revealed a statistically significant increase of the A2A receptor density in platelets, lymphocytes and neutrophils of Huntington’s disease patients and presymptomatic carriers of the mutation when compared to control subjects. In order to verify the specificity of A2A receptor alteration in polyglutamine disease, the same study was conducted in blood cells from patients affected by Spinocerebellar ataxia, characterized by an expanded CAG triplet in the ataxin gene and in patients affected by Friedreich’s ataxia, characterized by an expansion of the GAA triplet. Saturation binding experiments in peripheral blood cells from Spinocerebellar ataxia showed altered A2A binding parameters similar to those obtained in Huntington’s disease patients. In addition, data obtained in Friedreich’s ataxia patients showed affinity and density values for A2A receptors similar to those obtained from control subjects, demonstrating the involvement of the CAG but not of the GAA triplet. Overall these data demonstrate that an aberrant A2A receptor phenotype is present in polyglutamine disorders and this seems to be related with the expanded CAG triplet. The amplification of the signal transduction system of A2A receptors suggests that the use of selective A2A antagonists could be beneficial in the treatment of Huntington’s disease as well as in other related polyglutamine diseases. In addition, the alteration of A2A receptors in peripheral blood cells of patients with polyglutamine diseases suggests that this receptor could be an easily accessible biomarker for the evaluation of the efficacy of potential new therapies

Update on the recent development of allosteric modulators for adenosine receptors and their therapeutic applications

Adenosine receptors (ARs) have been identified as promising therapeutic targets for countless pathological conditions, spanning from inflammatory diseases to central nervous system disorders, from cancer to metabolic diseases, from cardiovascular pathologies to respiratory diseases, and beyond. This extraordinary therapeutic potential is mainly due to the plurality of pathophysiological actions of adenosine and the ubiquitous expression of its receptors. This is, however, a double-edged sword that makes the clinical development of effective ligands with tolerable side effects difficult. Evidence of this is the low number of AR agonists or antagonists that have reached the market. An alternative approach is to target allosteric sites via allosteric modulators, compounds endowed with several advantages over orthosteric ligands. In addition to the typical advantages of allosteric modulators, those acting on ARs could benefit from the fact that adenosine levels are elevated in pathological tissues, thus potentially having negligible effects on normal tissues where adenosine levels are maintained low. Several A(1) and various A(3)AR allosteric modulators have been identified so far, and some of them have been validated in different preclinical settings, achieving promising results. Less fruitful, instead, has been the discovery of A(2A) and A(2B)AR allosteric modulators, although the results obtained up to now are encouraging. Collectively, data in the literature suggests that allosteric modulators of ARs could represent valuable pharmacological tools, potentially able to overcome the limitations of orthosteric ligands

Chapter Alexander von Humboldt, da 250 anni il teorizzatore dello studio interdisciplinare dell’ambiente

In 19th century birth of the term scientist led to beginning of Sciences professionalization and end of Nature eclectic scholar, of which Humboldt was the last exponent. Humboldt managed to connect all disciplines in a holistic vision of the world: organic and inorganic nature form a single system of active forces; all the organisms of Earth are linked as a family sharing same home. Today, given the anthropogenic damage caused to Nature, it needs to reconsider his unified vision, establishing connections between scholars of various disciplines, for an organic and global vision of Environment

A2A and A3 adenosine receptor expression in rheumatoid arthritis: upregulation, inverse correlation with disease activity score and suppression of inflammatory cytokine and metalloproteinase release

Introduction The reduction of the inflammatory status represents one of the most important targets in rheumatoid arthritis (RA). A central role of A2A and A3 adenosine receptors (ARs) in mechanisms of inflammation has been reported in different pathologies. The primary aim of this study was to investigate the A2A and A3ARs and their involvement in RA progression measured by Disease Activity Score in 28 or 44 joints (DAS28 or DAS). Methods ARs were analyzed by saturation binding assays, mRNA and Western blotting analysis in lymphocytes from early and established RA patients. The effect of A2A and A3AR agonists in nuclear factor kB (NF-kB) pathway was evaluated. Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) release was carried out by A2A and A3AR activation. AR pharmacological regulation in matrix metalloproteinase-1 (MMP-1) and metalloproteinase-3 (MMP-3) release was also studied. Results In lymphocytes obtained from RA patients, A2A and A3ARs were up-regulated if compared with healthy controls. A2A and A3AR activation inhibited the NF-kB pathway and diminished inflammatory cytokines such as TNF-α, IL-1β and IL-6. A2A and A3AR agonists mediated a reduction of MMP-1 and MMP-3 release. A2A and A3AR density inversely correlated with DAS28 and DAS suggesting a direct role of the endogenous activation of these receptors in the control of RA joint inflammation. Conclusions Taken together these data demonstrate that the inflammatory and clinical responses in RA are regulated by A2A and A3ARs and support the use of A2A and/or A3AR agonists as novel and effective pharmacological treatment in RA patients

4-Heteroaryl Substituted Amino-3,5-Dicyanopyridines as New Adenosine Receptor Ligands: Novel Insights on Structure-Activity Relationships and Perspectives

A new set of amino-3,5-dicyanopyridines was synthesized and biologically evaluated at the adenosine receptors (ARs). This chemical class is particularly versatile, as small structural modifications can influence not only affinity and selectivity, but also the pharmacological profile. Thus, in order to deepen the structure-activity relationships (SARs) of this series, different substituents were evaluated at the diverse positions on the dicyanopyridine scaffold. In general, the herein reported compounds show nanomolar binding affinity and interact better with both the human (h) A(1) and A(2A) ARs than with the other subtypes. Docking studies at hAR structure were performed to rationalize the observed affinity data. Of interest are compounds 1 and 5, which can be considered as pan ligands as binding all the ARs with comparable nanomolar binding affinity (A(1)AR: 1, K-i = 9.63 nM; 5, K-i = 2.50 nM; A(2A)AR: 1, K-i = 21 nM; 5, Ki = 24 nM; A(3)AR: 1, Ki = 52 nM; 5, Ki = 25 nM; A(2B)AR: 1, EC50 = 1.4 nM; 5, EC50 = 1.12 nM). Moreover, these compounds showed a partial agonist profile at all the ARs. This combined AR partial agonist activity could lead us to hypothesize a potential effect in the repair process of damaged tissue that would be beneficial in both wound healing and remodeling

Are Two Riboses Better Than One? The Case of the Recognition and Activation of Adenosine Receptors

Traditionally, molecular recognition between the orthosteric site of adenosine receptors and their endogenous ligand occurs with a 1 : 1 stoichiometry. Inspired by previous mechanistic insights derived from supervised molecular dynamics (SuMD) simulations, which suggested an alternative 2 : 1 binding stoichiometry, we synthesized BRA1, a bis-ribosyl adenosine derivative, tested its ability to bind to and activate members of the adenosine receptor family, and rationalized its activity through molecular modeling

The role of 5-arylalkylamino- and 5-piperazino- moieties on the 7-aminopyrazolo[4,3-d]pyrimidine core in affecting adenosine A1 and A2A receptor affinity and selectivity profiles

New 7-amino-2-phenylpyrazolo[4,3-d]pyrimidine derivatives, substituted at the 5-position with aryl(alkyl)amino- and 4-substituted-piperazin-1-yl- moieties, were synthesized with the aim of targeting human (h) adenosine A1 and/or A2A receptor subtypes. On the whole, the novel derivatives 1-24 shared scarce or no affinities for the off-target hA2B and hA3 ARs. The 5-(4-hydroxyphenethylamino)- derivative 12 showed both good affinity (Ki = 150 nM) and the best selectivity for the hA2A AR while the 5-benzylamino-substituted 5 displayed the best combined hA2A (Ki = 123 nM) and A1 AR affinity (Ki = 25 nM). The 5-phenethylamino moiety (compound 6) achieved nanomolar affinity (Ki = 11 nM) and good selectivity for the hA1 AR. The 5-(N4-substituted-piperazin-1-yl) derivatives 15-24 bind the hA1 AR subtype with affinities falling in the high nanomolar range. A structure-based molecular modeling study was conducted to rationalize the experimental binding data from a molecular point of view using both molecular docking studies and Interaction Energy Fingerprints (IEFs) analysis.[Formula: see text]