Reversal of the antiinflammatory effects of methotrexate by the nonselective adenosine receptor antagonists theophylline and caffeine: Evidence that the antiinflammatory effects of methotrexate are mediated via multiple adenosine receptors in rat adjuvant arthritis

Abstract

Objective. Weekly low-dose methotrexate (MTX) remains the mainstay of second-line therapy for rheu-matoid arthritis (RA). We have previously reported that adenosine, acting at specific receptors on inflammatory cells, mediates the antiinflammatory effects of MTX in both in vitro and in vivo models of acute inflammation, but the mechanism by which MTX suppresses the chronic inflammation of arthritis remains controversial. The present study was undertaken to further investigate the means by which adenosine mediates the antiinflammatory effects of MTX. Methods. The effects of 2 nonselective adenosine receptor antagonists, theophylline and caffeine, were examined, using the rat adjuvant arthritis model of RA. These agents were given alone and in conjunction with MTX, and arthritis severity was assessed clinically, radiologically, and histologically. Since rodent adeno-sine A 3 receptors are not blocked by theophylline, selective A 1 , A 2A , and A 2B receptor antagonists were tested as well. Results. Control animals developed severe arthritis , which was markedly attenuated by weekly treatment with MTX (0.75 mg/kg/week). Neither theophylline alone nor caffeine alone (each at 10 mg/kg/day) significantly affected the severity of the arthritis, but both agents markedly reversed the effect of MTX as measured by a severity index, hindpaw swelling, and hind-paw ankylosis. Radiographic and histologic analyses confirmed these observations. Neither A 1 , A 2A , nor A 2B receptor antagonists affected the capacity of MTX to ameliorate inflammation in adjuvant arthritis. Conclusion. These results provide strong evidence that adenosine mediates the antiinflammatory effects of MTX in this model of RA. Moreover, the findings suggest that abstinence from caffeine, a ubiquitous food additive and medication, may enhance the therapeutic effects of MTX in RA. Low-dose, intermittently administered metho-trexate (MTX) is among the most widely used forms of therapy for inflammatory arthritis (particularly rheuma-toid arthritis [RA]), psoriasis, and inflammatory bowel disease. MTX was introduced for the treatment of inflammatory diseases, with very little understanding of its mechanism of action. We, and subsequently others, have reported that the antiinflammatory actions of MTX are mediated by its capacity to increase extracellular adenosine concentrations (1-4). However, the studies reported to date have demonstrated that adenosine is responsible for the antiinflammatory actions of MTX only in acute inflammation; the mechanism of action of MTX in the treatment of chronic inflammation has not been fully explored.

Adenosine A1 receptor regulates osteoclast formation by altering TRAF6/TAK1 signaling

“…It is also interesting to note that it is likely that the inhibitory effects of methotrexate on osteoclast-mediated bone destruction are mediated by the higher levels of adenosine released by methotrexate-treated cells and tissues which interact with A 2A and A 3 receptors [53]. Indeed, in the adjuvant arthritis model studied by Teramachi and colleagues, the adenosine receptor antagonists theophylline and caffeine reverse the anti-inflammatory effects of methotrexate [54].…”

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.…”

Pleural fluid from tuberculous pleurisy inhibits the functions of T cells and the differentiation of Th1 cells via immunosuppressive factors

“…27 At the height of inflammation, the destruction of host tissue combined with damaged microcirculation and hypoxia leads to elevation of extracellular adenosine. 28 Animal models of asthma, 29 arthritis, 30 sepsis, 31 inflammatory bowel disease 32 and wound healing 33 have helped to elucidate the regulatory roles of adenosine in dictating the development and progression of disease. Adenosine potently inhibits a wide range of T-cell responses, including cell proliferation, 34 synthesis of IL-2 and proinflammatory cytokines, such as IFN-c and TNF-a, 35 and some of the earliest steps of T-cell activation, which were reported to be mediated mainly by the adenosine A 2A receptor.…”