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.

OBJECTIVE: Weekly low-dose methotrexate (MTX) remains the mainstay of second-line therapy for rheumatoid 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 adenosine A3 receptors are not blocked by theophylline, selective A1, A2A, and A2B 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 hindpaw ankylosis. Radiographic and histologic analyses confirmed these observations. Neither A1, A2A, nor A2B 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.

Anticonvulsant actions of LY 367385 ((+)-2-methyl-4-carboxyphenylglycine) and AIDA ((RS)-1-aminoindan-1,5-dicarboxylic acid).

We have studied the effects in three rodent models of generalised convulsive or absence epilepsy of two antagonists of group I metabotropic glutamate receptors that are selective for the mGlu1 receptor. LY 367385 ((+)-2-methyl-4-carboxyphenylglycine) and AIDA ((RS)-1-aminoindan-1,5-dicarboxylic acid) have been administered intracerebroventricularly (i.c.v.) to DBA/2 mice and lethargic mice (lh/lh), and focally into the inferior colliculus of genetically epilepsy prone rats (GEPR). In DBA/2 mice both compounds produce a rapid, transient suppression of sound-induced clonic seizures (LY 367385: ED50 = 12 nmol, i.c.v., 5 min; AIDA: ED50 = 79 nmol, i.c.v., 15 min). In lethargic mice both compounds significantly reduce the incidence of spontaneous spike and wave discharges on the electroencephalogram, from <30 to >150 min after the administration of AIDA, 500 nmol, i.c.v., and from 30 to >150 min after the administration of LY 367385, 250 nmol, i.c.v. LY 367385, 50 nmol, suppresses spontaneous spike and wave discharges from 30 to 60 min. In genetically epilepsy prone rats both compounds reduce sound-induced clonic seizures. LY 367385, 160 nmol bilaterally, fully suppresses clonic seizures after 2-4 h. AIDA is fully effective 30 min after 100 nmol bilaterally. It is concluded that antagonists of mGlu1 receptors are potential anticonvulsant agents and that activation of mGlu1 receptors probably contributes to a variety of epileptic syndromes.