The role of adenosine A2A and A2B receptors in the regulation of TNF-alpha production by human monocytes.
Adenosine is an endogenous nucleoside that regulates many physiological processes through the activation of its four receptors: A(1), A(2A), A(2B) and A(3). Previous studies have identified the involvement of A(2) receptors in the inhibitory activity of adenosine analogues on tumor necrosis factor-alpha (TNF-alpha) production by lipopolysaccharide (LPS) activated monocytes, but the relative contributions of A(2A) versus A(2B) receptors have not been determined in human primary monocytes. Nor has the role of A(1) and A(3) been clearly identified in the system. The lack of such information impacts on the selection of adenosine receptor agonists for disease intervention. Using LPS-stimulated human primary monocytes, we found that the adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA) or the A(2A) receptor agonist, 4-[2-[[6-amino-9-(N-ethyl-b-d-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS21680) produced a concentration-dependent inhibition of TNF-alpha production, with IC(50)s of 58.4nM (32.7-104.5nM, 95% confidence interval) and 49.2nM (22.7-105.9nM, 95% confidence interval), respectively. The selective A(2A) receptor blocker, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylaminso]ethyl)phenol (ZM241385, 30nM), antagonized the effects of NECA and CGS21680 (pK(B) estimates were 8.7+/-0.1 and 8.9+/-0.1, respectively), while the selective A(2B) antagonist, N-(4-cyano-phenyl)-2-[4-(2,6-dioxo-1,3-dipropyl-2,3,4,5,6,7-hexahydro-1H-purin-8-yl)-phenoxy]-acetamide (MRS1754, 100nM), failed to antagonize the effects of either agonist. Furthermore, neither the A(1) receptor agonist, 2-chloro-N(6)-cyclopentyladenosine (CCPA) nor the A(3) receptor agonist, 1-[2-chloro-6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-b-d-ribofuranuronamide (2-Cl-IB-MECA) showed significant inhibitory activity at concentrations that effectively bind to their respective receptors. We conclude that A(2A) receptor activation is predominantly responsible for the inhibitory effects of adenosine receptor agonists on TNF-alpha production from LPS-stimulated monocytes.
Zhang
Jian G
JG
Pharmagene Laboratories Limited, 2 Orchard Road, Royston SG8 5HD, UK. Jian.Zhang@Pharmagene.com <Jian.Zhang@Pharmagene.com>
Hepburn
Lucy
L
Cruz
Gabriela
G
Borman
Richard A
RA
Clark
Kenneth L
KL
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D010627:Phenethylamines / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D043705:Receptor, Adenosine A2A / Q000502:physiology*; D043704:Receptor, Adenosine A2B / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*
D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D010627:Phenethylamines; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D014409:Tumor Necrosis Factor-alpha; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D019830:Adenosine-5'-(N-ethylcarboxamide); D000241:Adenosine