Adenosine

Adenosine, Adenosine receptors,

1. denosine denosine receptors Dr . Jervin Mano, MD A

2. Overview Introduction Adenosine Purinergic receptors Adenosine receptors Classification Therapeutic targets Drugs in clinic Drugs under CT Summary

3. Purinergic receptors Present in most organ systems Extracellular purines (Adenosine, ADP, ATP) Extracellular pyrimidines ( Uridine , UDP, UTP) Mediate biological effects via P rs Classification :

4. Purinergic receptors GPCR Ligand gated ion channel

5. Adenosine Metabolite of ATP Naturally occurring endogenous purine nucleoside Adenosine is made up of adenine attached to a ribose. Chemical name: 6-amino-9-beta-D-ribofuranosyl-9-H-purine. Plasma adenosine level : 0.04 - 0.2 µmol. Short t 1/2 : 10s Functions of adenosine: Neuromodulator, cellular energy transfer, signal of inflammation, ischaemic preconditioning.

6. Adenosine-Neurotransmitter ?? It is neither stored in synaptic vesicles nor it acts exclusively on synapses Release & uptake: mediated by bidirectional nucleoside transporter Neuromodulator: Presynaptic: controls NT release Postsynaptic: hyper/depolarizes the neurons Non synaptic: regulates the effect on glial cells Characteristics of NT: Adenosine producing enzymes present in synapse Actions via interaction with Rs Actions can be blocked by specific antagonist Actions can be terminated by reuptake and metabolic syndrome

7. Metabolism

8. Adenosine receptors (P1) GPCR Endogenous ligand – Adenosine Classification: A 1 A 2A A 2B A 3

9. A1 receptors Distribution: Brain, SC, atria Superclass: GPCR – Gi Effector mechanism: Inhibition of cAMP Increased K+ permeability Inhibition of Ca2+ channels A ctivation of phospholipase C Agonist: N6-Cyclopentyladenosine, N(6)- cyclohexyladenosine Antagonist: Non-specific: Caffeine, Theophylline Specific : Bamifylline , Rolofylline

10. Effects of the receptors CVS: Negative dromotropy Negative chronotropy Negative inotropy Inhibits pacemaker and L-type calcium currents CNS: Decrease neurotransmitter release Sedation Anticonvulsant effects

11. Effects of the receptors RENAL: Inhibits renin release Increase Na reabsorption in PCT Vasoconstriction of afferent arteriole-reduces GFR Metabolic: Inhibits lipolysis Increases insulin sensitivity

12. A 2A receptors Distribution : Brain, Heart, Blood. Superclass: GPCR – Gs Effector mechanisms: Activates adenylate cyclase → ↑ cAMP Activates phospholipases C ↓Intracellular Ca levels Agonist : Regadenoson , Limonene Antagonist : Preladenant , Istradefylline , Vipadenant

13. Effects of the receptors CVS: Coronary and peripheral vasodilation Inhibits platelet aggregation CNS: Modulate the neurotransmission of GABA, Ach, glutamate → Motor activity

14. A 2 B receptors Distribution: GIT, GUT, lungs Superclass : GPCR – Gs Effector mechanisms : Activates adenylate cyclase → ↑ cAMP ↑ Intracellular Ca levels Adenosine has low affinity Agonist : N- ethylcarboxamidoadenosine , Antagonist : MRS-1706

15. Pulmonary: Vasodilation Mast cell release of IL-8

16. A3 receptors Distribution: Kidney, testis, mast cells, eosinophills Superclass: GPCR – Gi / Gq Effector mechanisms : Inhibits adenylate cyclase → cAMP Activates phospholipases C&D Influx of Ca & release from stores Agonist : N methyl adenosine, IB-MECA, Inosine Antagonist: Theophylline, KF- 26777

17. Effects of the receptors Pulmonary: Mast cell release of allergic mediators

18. Distribution and expression of P1 receptors Expression level A1 receptors A2A receptors A2B receptors A3 receptors High expression Brain (cortex, hippocampus, cerebellum), spinal cord, eye, adrenal gland, atria Blood platelets, olfactory bulb Spleen, thymus, leukocytes Cecum, colon, bladder Testis (rat), mast cells (rat) Intermediate expression Other brain regions, skeletal muscles, liver, kidney, adipose tissue Heart, lung, blood vessels, peripheral nerves Lung, blood vessels, eye, mast cells Cerebellum, hippocampus Low expression Lungs (but probably higher in bronchi), pancreas Other brain regions Adipose tissue, adrenal gland, brain, kidney Thyroid, most of brain adrenal gland, spleen, liver, kidney, heart

19. Adenosine receptors RECEPTOR GENE MECHANISM AGONIST ANTAGONIST A 1 ADORA 1 G i - ↓ cAMP N 6 Cyclopentoadenosine Caffeine, theophylline A 2 a ADORA 2 a G s - ↑ cAMP Regadenoson Caffeine, theophylline , istradefylline A 2 b ADORA 2 b G s - ↑ cAMP 5 N Ethylcarboxamidoadenosine Theophylline , CVT-6883, MRS-1706 A 3 ADORA 3 G i - ↓ cAMP N methyl adenosine, IB-MECA Theophylline , MRS-1191, 1220,1334

20. Adenosine reuptake inhibitors 5-AICAR – Protective for MI

21. Therapeutic interventions

22. Respiratory system Bronchial asthma: Stable form of adenosine – AMP - broncho constriction Adenosine levels increased in BAL fluid and cause hyperresponsiveness in airways Adenosine receptor antagonist-theophylline & selective A1 receptor antagonist- bamiphylline

23. Respiratory system Refractory primary pulmonary hypertension: Routine treatment Adenosine infusion for refractory cases Mechanism-Pulmonary vasodilation by A2 receptors Increase AMP-vascular smooth muscle relaxation Stimulation of K+ ATPase channel

24. CNS Anaesthesia and intensive care: Adenosine blocks nociceptive transmission IV adenosine infusion-analgesia at 50-70 mg/kg/min Reduces ischaemic pain Adenosine infusion during GA- good recovery and sustained post op pain relief Superior to remifentanil

25. CNS Epilepsy: Astrogliosis - hallmark of epileptogenesis Adenosine-inhibitory modulator of brain activity Activation of A1 receptors Adenosine kinase- major metabolic enzyme predominantly expressed in adult brain ADK inhibitor GP 515 tested-reduced kindled seizures in rats

26. CNS Parkinsons disease: A2a receptor antagonist- Istradefylline in phase III trial KF 17837 KW 6002

27. CVS Ischaemia /reperfusion injury: Ischaemic preconditioning(IPC) Adenosine theory- After 5 min of cardiac ischaemia interstitial adenosine rises double the time Adenosine receptor stimulation reduces myocardial damage following ischaemia Adenosine reduces ischaemia by- Improved tissue perfusion Anti inflammatory action Direct intracellular effect

28. CVS Hypolipidemic agent: Elevated TG levels-independent risk factor of CAD RPR 749-potent and selective A1 agonist for hypertriglyceridemia

29. Platelet Platelets are rich in A2A receptors Adenosine -> increases cAMP -> decreased plt aggregation Dipyridamole inhibits adenosine reuptake – increased levels – decreased plt aggregation, vasodilation

30. GIT Inflammatory bowel disease: Role of adenosine in inflammation A2a and A3 receptors Reduces leucocyte infiltration and proinflammatory cytokines IB-MECA - A3 agonist tested in DNBS induced colitis in mice

31. Bacterial Sepsis: Acadesine , adenosine precursor injected iv in mongrel pigs following soft tissue injury and shock 72 hrs later E.coli 0111:B4 endotoxin given, effects observed were: Reduction in endotoxin induced hypoxia and pulmonary hypertension Reduction in fluid requirement Reduction in mortality and prolonged survival time

32. Immunity Adenosine accumulation and stimulation of (?A2) receptors has been implicated in the immunosuppression seen in critical illness A3 receptor stimulation may inhibit tumour growth, perhaps melanomas, colon or prostate carcinoma, and lymphomas. Peripheral blood monocytes produce G-CSF when stimulated by adenosine

33. Renal

34. Disease susceptibility Single nucleotide polymorphisms in the A1: Aspirin intolerant asthma Alterations in ADORA1 gene: Change in infarct size in patients with ischaemic infarct size SNPs in ADORA2A gene: Anxiety disoroders SNPs in ADORA2A gene: Stopping Mtx Rx for RhA due to ADR(GIT) but not efficacy High expression of A2A Rs : Pts with unexplained syncope Up regulation of A2A Rs in endothelial cells: Lung cancer Dysfunctional A2B Rs : impotence

35. Drugs in clinic

36. Acupuncture Mechanical deformation of the skin by acupuncture needles appears to result in the release of adenosine . A 2014 Nature Reviews Cancer review journal found that the key mouse studies that suggested acupuncture relieves pain via the local release of adenosine, which then triggered close-by A1 receptors . The anti-nociceptive effect of acupuncture may be mediated by the adenosine A1 receptor.

37. Methotrexate Methotrexate, which has strong anti-inflammatory properties, inhibits the action of dihydrofolate reductase, leading to an accumulation of adenosine. Adenosine-receptor antagonist caffeine reverses the anti-inflammatory effects of methotrexate.

38. Adenosine Marked hyperpolarization and suppression of calcium-dependent action potentials inhibits AV nodal conduction and increases the AV nodal refractory period Use: paroxysmal supraventricular tachycardia Half life: 10 seconds ADR: Metallic taste, flushing, rashes, apprehension

39. Dipyridamole Dipyridamole inhibits the phosphodiesterase Adenosine reuptake inhibitor Uses: adjunct to coumarin anticoagulants in the prevention of postoperative thromboembolic complications of cardiac valve replacement Pulmonary hypertension Overdose: Rx – Xanthine derivatives

40. Caffeine Nonspecific adenosine Rs antagonist competitive nonselective phosphodiesterase inhibitor B ronchodilator, CNS stimulant, c ardiac muscle stimulant and a diuretic. Ischemic preconditioning Caffeine for apnoea of prematurity

41. Aminophylline N onselective adenosine receptor antagonist. Competitive nonselective phosphodiesterase inhibitor Uses: Bronchodilator, Dipyrimadole overdose, anaphylactic shock.

42. Drugs in trial

43. A1 partial agonists A1 agonists: Heart block, reduce pain, lipolysis Partial agonists: without heart block DRUGs: GW493838 – Peripheral neuropathic pain GS9667 – hypertriglyceridemia ass with DM Capadenoson – Phase II – AF

44. A2A agonists Vasodilation, reduce inflammation DRUGS Regadenoson : FDA 2008, Apadenoson BVT.115959: diabetic neuropathic pain

45. A3 agonists CF 101 (IB-MECA) Rheumatoid arthritis Glaucoma: phase II Dry eye disease: Phase III CF102 Advanced HCC Chronic hepatitis C genotype 1 Phase1-2

46. Selective A1 antagonists Rolofylline : PROTECT-2 : Heart failure Tonafylline KFM-19: Dementia, cognitive deficits 8-cyclopentyl-1,3-dipropylxanthine(CFX) : Diuresis (K sparing)

47. Selective A2a antagonists Parkinson’s disease, drug addiction Stimulate D2 receptors Istradefylline : Phase III Vipadenant : Parkinson’s : Monotherapy, adjunct: { reclinical toxicological studies issues: Phase I Preladenant : phase II

48. Selective A2B antagonists Reversal insulin resistance in Type II DM Inhibition of degranulation of human mast cells, release of cytokines Under development

49. Adenosine modulators Allosteric modulators for adenosine receptors may have potential therapeutic advantage. A1 Allosteric enhancers - Antiarrhythmic and antilipolytic activity. A2 Not yet been developed Amiloride and analogues were demonstrated to be allosteric inhibitors at A 2A  receptor A3   Allosteric enhancers are -useful against ischemic conditions or as antitumor agents .

50. Adenosine precursors 5-AICAR Precursor of adenosine Protective effects in myocardial infarction Acadesine - adenosine precursor