Adenosine A_2A or A₃ receptors are required for inhibition of inflammation by methotrexate and its analog MX‐68

Abstract

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 ( Results. Low-dose weekly methotrexate treatment increased the adenosine concentration in the exudates of all mice studied and reduced leukocyte and tumor necrosis factor ␣ accumulation in the exudates of wildtype 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.Conclusion. 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.Low-dose weekly methotrexate is the "gold standard" of therapy in rheumatoid arthritis and other inflammatory diseases. Methotrexate's mechanism of action in the treatment of inflammatory diseases has been the subject of some controversy, although in previous studies, investigators in our group have demonstrated that adenosine mediates the antiinflammatory effects of methotrexate treatment in models of acute and chronic inflammation (1,2). Adenosine, whether released from injured cells or tissues or applied exogenously, regulates inflammation via interaction with one or more of the 4 known receptors for adenosine (A 1 , A 2A , A 2B , and A 3 ), as demonstrated by many in vitro and in vivo pharmacologic studies (for review, see ref.3). The demonstration that adenosine mediates the antiinflammatory effects of methotrexate in in vivo models of acute inflammation rests upon reversal of the antiinflammatory effects of methotrexate, either by enzymatic hydrolysis of adenosine by adenosine deaminase or by administration of adenosine receptor antagonists to reverse the antiinflammatory effects of methotrexate treatment (1,2). Although the antiinflammatory effects of methotrexate are mediated by multiple adenosine receptors in the adjuvant arthritis model of inflammation (2), the identity of the receptor(s) involved in the suppression of inflammation in models of acute inflammation has not been so well characterized.

Adenosine abolishes MTX-induced suppression of osteoclastogenesis and inflammatory bone destruction in adjuvant-induced arthritis

“…Their findings showed a possible involvement of A 1 AR in normal osteoclastogenesis. Montesinos et al 28,29 has reported that adenosine acts as the suppressive factor in inflammation. In their model, MTX administration induced a significant level of adenosine; however, its level is o170 nM, which concentration are able to activate only the high-affinity receptors.…”

Polyglutamation of methotrexate with common polymorphisms in reduced folate carrier, aminoimidazole carboxamide ribonucleotide transformylase, and thymidylate synthase are associated with methotrexate effects in rheumatoid arthritis

“…MTXPGs are inhibitors of ATIC, a bifunctional enzyme that catalyzes the final steps in the de novo purine nucleotide biosynthetic pathway (45). The result is accumulation of AICAR and release of the antiinflammatory agent, adenosine (18)(19)(20). In the present study, we investigated the contribution of a threonine-to-serine substitution at position 116 of ATIC (C347G) to the effects of MTX, and our data suggest that patients carrying a homozygous variant genotype (347GG) may have an increased likelihood of response to MTX compared with those carrying a 347CC or 347CG genotype.…”

“…This inhibition by MTXPGs promotes the accumulation of AICAR ribotide, a potent inhibitor of adenosine deaminase (17). The consequence is the buildup of adenosine, a potent antiinflammatory agent (18)(19)(20). Furthermore, MTXPGs are inhibitors of thymidylate synthase (TS) (21), which methylates deoxyuridine monophosphate to produce deoxythymidylate, the unique de novo source of thymidylate in the cell.…”

Adenosine receptors as therapeutic targets

“…Knockout of the A 2A AR in mice showed that no other mechanism for inflammation could compensate fully for the loss of the A 2A AR (which has been referred to as a brake for inflammation 183 ) on immune cells. Interestingly, in knockout mouse models, the A 2A AR together with the A 3 AR mediated the antiinflammatory effect of methotrexate, which is used as a treatment of arthritis 184 . ATL-146e, a selective agonist of the A 2A AR, profoundly protects mouse liver from reperfusion injury, and the protection is blocked by the A 2A AR antagonist ZM241385.…”