Adenosine A2A or A3 receptors are required for inhibition of inflammation by methotrexate and its analog MX-68.
OBJECTIVE
Low-dose weekly methotrexate therapy remains a mainstay in the treatment of inflammatory arthritis. Results of previous studies demonstrated that adenosine, acting at one or more of its receptors, mediates the antiinflammatory effects of methotrexate in animal models of both acute and chronic inflammation. We therefore sought to establish which receptor(s) is involved in the modulation of acute inflammation by methotrexate and its nonpolyglutamated analog MX-68 (N-[[4-[(2,4-diaminopteridin-6-yl)methyl]-3,4-dihydro-2H-1,4-benzothiazin-7-yl]-carbonyl]-L-homoglutamic acid).


METHODS
We studied the effects of low-dose methotrexate (0.75 mg/kg intraperitoneally [IP] every week for 5 weeks), MX-68 (2 mg/kg IP 2 days and 1 hour before induction of inflammation), dexamethasone (1.5 mg/kg IP 1 hour before induction of inflammation), or vehicle control on acute inflammation in an air-pouch model in A(2A) and A(3) receptor knockout mice.


RESULTS
Low-dose weekly methotrexate treatment increased the adenosine concentration in the exudates of all mice studied and reduced leukocyte and tumor necrosis factor alpha accumulation in the exudates of wild-type mice, but not in those of A(2A) or A(3) receptor knockout mice. Dexamethasone, an agent that suppresses inflammation by a different mechanism, was equally effective at suppressing leukocyte accumulation in A(2A) knockout, A(3) knockout, and wild-type mice, indicating that the lack of response was specific for methotrexate and MX-68.


CONCLUSIONS
These findings confirm that adenosine, acting at A(2A) and A(3) receptors, is a potent regulator of inflammation. Moreover, these results provide strong evidence that adenosine, acting at either or both of these receptors, mediates the antiinflammatory effects of methotrexate and its analog MX-68.
Montesinos
M Carmen
MC
New York University School of Medicine, New York, New York 10016, USA.
Desai
Avani
A
Delano
Dave
D
Chen
Jiang-Fan
JF
Fink
J Stephen
JS
Jacobson
Marlene A
MA
Cronstein
Bruce N
BN
D015074:2-Aminoadipic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D000208:Acute Disease; D000818:Animals; D018501:Antirheumatic Agents / Q000494:pharmacology*; D001168:Arthritis / Q000188:drug therapy* / Q000276:immunology; D008727:Methotrexate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D051379:Mice; D018345:Mice, Knockout; D043705:Receptor, Adenosine A2A; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1 / Q000235:genetics* / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology
D018501:Antirheumatic Agents; C104193:N-(1-((2,4-diamino-6-pteridinyl)methyl)-3,4-dihydro -2H-1,4-benzothiazine-7-carbonyl)-L-2-aminoadipic acid; D043705:Receptor, Adenosine A2A; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1; D014409:Tumor Necrosis Factor-alpha; D015074:2-Aminoadipic Acid; D008727:Methotrexate