Several studies have documented increased levels of polyamines in rheumatoid arthritis (RA). We have suggested that one of the mechanisms of action of methotrexate (MTX) involves the inhibition of polyamine synthesis in lymphocytes. In this study, we sought to establish the inhibitory effect of MTX on polyamine synthesis and its specificity.
Polyamine levels were determined in stimulated RA lymphocytes incubated in vitro with MTX and compared to levels in lymphocytes incubated with hydrocortisone, D-penicillamine, or medium alone. Lymphocyte polyamine levels were correlated with IgM-rheumatoid factor (RF) synthesis.
Incubation with MTX resulted in concentration-dependent decreased intracellular levels of spermidine and spermine, while putrescine levels were not affected. Addition of folinic acid or S-adenosyl-methionine (SAM) prevented this MTX-induced inhibition. Incubation with D-penicillamine or hydrocortisone had no significant effect on polyamine levels. There was a positive correlation between intracellular polyamine levels and the inhibition of IgM-RF synthesis by MTX.
These data suggest that MTX inhibits the synthesis of spermidine and spermine in stimulated RA lymphocytes through inhibition of the SAM-dependent pathway. This inhibition may be related to the immune-modulating properties of MTX.