Polyglutamation of antifolates is not required for induction of extracellular release of adenosine or expression of their anti-inflammatory effects

Abstract

Methotrexate (MTX) exerts an anti-inflammatory effect, reportedly by enhancing the release of adenosine, through an accumulation of 5-amino-4-imidazolecarboxamide ribonucleotide (AICAR). To examine the role of polyglutamation in promoting anti-inflammatory effects by antifolates, we tested whether a new antifolate designed to be resistant to intracellular polyglutamation (MX-68) exhibited anti-inflammatory effects and stimulated adenosine release. Both MX-68 and MTX (at concentrations greater than 0.1 μM) increased the release of adenosine from Daudi cells in vitro. Inhibition of AICAR synthesis suppressed adenosine release by MX-68 and MTX. The anti-inflammatory effects of antifolates were estimated using the murine air pouch model, in which a BALB/c mouse was intraperitoneally injected with MX-68 or MTX once a week for 3 weeks. MX-68 (0.5 mg kg−1 week−1), as well as MTX, inhibited infiltration of leukocytes into the air pouch. This inhibitory effect was suppressed in the presence of an adenosine A2 receptor antagonist, 3,7-dimethyl-1-propargylxanthine (DMPX). These results suggest that MX-68, like MTX, exerts anti-inflammatory effects through the accumulation of AICAR and release of adenosine. These results suggest that polyglutamation of antifolate is not required for expression of anti-inflammatory effects.