Adenosine is a ubiquitous signaling nucleoside molecule, released from different cells within the body to act on vasculature and immunoescape. The physiological action on the proliferation of tumour cell has been reported by the presence of high concentration of adenosine within the tumour microenvironment, which results in the progression of the tumour, even leading to metastases. The activity of adenosine exclusively depends upon the interaction with four subtypes of heterodimeric G-protein-coupled adenosine receptors (AR), A1, A2A, A2B, and A3-ARs on the cell surface. Research evidence supports that the activation of those receptors via specific agonist or antagonist can modulate the proliferation of tumour cells. The first category of AR, A1 is known to play an antitumour activity via tumour-associated microglial cells to prevent the development of glioblastomas. A2AAR are found in melanoma, lung, and breast cancer cells, where tumour proliferation is stimulated due to inhibition of the immune response via inhibition of natural killer cells cytotoxicity, T cell activity, and tumourspecific CD4+/CD8+ activity. Alternatively, A2BAR helps in the development of tumour upon activation via upregulation of angiogenin factor in the microvascular endothelial cells, inhibition of MAPK and ERK 1/2 phosphorylation activity. Lastly, A3AR is expressed in low levels in normal cells whereas the expression is upregulated in tumour cells, however, agonists to this receptor inhibit tumour proliferation through modulation of Wnt and NF-κB signaling pathways. Several researchers are in search for potential agents to modulate the overexpressed ARs to control cancer. Active components of A2AAR antagonists and A3AR agonists have already entered in Phase-I clinical research to prove their safety in human. This review focused on novel research targets towards the prevention of cancer progression through stimulation of the overexpressed ARs with the hope to protect lives and advance human health.
The ubiquitous signaling nucleoside molecule, adenosine is found in different cells of the human body to provide its numerous pharmacological role. The associated actions of endogenous adenosine are largely dependent on conformational change of the widely expressed heterodimeric G-protein-coupled A1, A2A, A2B, and A3 adenosine receptors (ARs). These receptors are well conserved on the surface of specific cells, where potent neuromodulatory properties of this bioactive molecule reflected by its easy passage through the rigid blood-brainbarrier, to simultaneously act on the central nervous system (CNS). The minimal concentration of adenosine in body fluids (30-300 nM) is adequate to exert its neuromodulatory action in the CNS, whereas the modulatory effect of adenosine on ARs is the consequence of several neurodegenerative diseases. Modulatory action concerning the activation of such receptors in the CNS could be facilitated towards neuroprotective action against such CNS disorders. Our aim herein is to discuss briefly pathophysiological roles of adenosine on ARs in the modulation of different CNS disorders, which could be focused towards the identification of potential drug targets in recovering accompanying CNS disorders. Researches with active components with AR modulatory action have been extended and already reached to the bedside of the patients through clinical research in the improvement of CNS disorders. Therefore, this review consist of recent findings in literatures concerning the impact of ARs on diverse CNS disease pathways with the possible relevance to neurodegeneration.
BACKGROUND: Steroid-induced ocular hypertension is currently treated in the same way as primary open-angle glaucoma. However, the treatment is often suboptimal and is associated with adverse effects. We evaluated the oculohypotensive effects of topical trans-resveratrol in rats with steroid-induced ocular hypertension and involvement of adenosine receptors (AR) in intraocular pressure (IOP) lowering effect of trans-resveratrol.
METHODS: The oculohypotensive effect of unilateral single-drop application of various concentrations of trans-resveratrol was first studied in oculonormotensive rats. Concentration with maximum effect was similarly studied in rats with steroid-induced ocular hypertension. Involvement of AR was studied by observing the alterations of IOP in response to trans-resveratrol after pretreating animals with AR subtype-specific antagonists. Additionally, we used computational methods, including 3D modelling, 3D structure generation and protein-ligand interaction, to determine the AR-trans-resveratrol interaction.
RESULTS: All concentrations of trans-resveratrol produced significant IOP reduction in normotensive rat eyes. Maximum mean IOP reduction of 15.1% was achieved with trans-resveratrol 0.2%. In oculohypertensive rats, trans-resveratrol 0.2% produced peak IOP reduction of 25.2%. Pretreatment with A₁ antagonist abolished the oculohypotensive effect of trans-resveratrol. Pretreatment with A₃ and A₂A AR antagonists produced significant IOP reduction in both treated and control eyes, which was further augmented by trans-resveratrol application in treated eyes. Computational studies showed that trans-resveratrol has highest affinity for A₂B and A₁, followed by A2A and A₃ AR.
CONCLUSION: Topically applied trans-resveratrol reduces IOP in rats with steroid-induced ocular hypertension. Trans-resveratrol-induced oculohypotension involves its agonistic activity at the A₁ AR.
KEYWORDS: adenosine receptors; docking simulation; intraocular pressure; resveratrol; topical
The homeostatic role of adenosine in regulating intraocular pressure (IOP) is now widely recognized, and hence, the drugs targeting adenosine receptors have become the focus of investigation. In this review, we summarize the adenosine receptor signaling pathways, which could be potential therapeutic targets for the management of glaucoma.