Methotrexate sodium, an inhibitor of tetrahydrofolate dehydrogenase, is an antineoplastic antimetabolite with immunosuppressant properties.
Methotrexate (0.1-10 mM) induces apoptosis of in vitro activated T cells from human peripheral blood. Methotrexate achieves clonal deletion of activated T cells in mixed lymphocyte reactions. Methotrexate can selectively delete activated peripheral blood T cells by a CD95-independent pathway. [1] Methotrexate is taken up by cells via the reduced folate carrier and then is converted within the cells to polyglutamates. Methotrexate leads to diminished production of leukotriene B4 by neutrophils stimulated ex vivo. Methotrexate polyglutamates inhibit the enzyme aminoimidazolecarboxamidoadenosineribonucleotide (AICAR) transformylase more potently than the other enzymes involved in purine biosynthesis. Methotrexate is also known to suppress TNF activity by suppressing TNF-induced nuclear factor-κB activation in vitro, in part related to a reduction in the degradation and inactivation of an inhibitor of this factor, IκBα, and probably related to the release of adenosine. Methotrexate suppresses the production of both TNF and IFN-γ by T-cell-receptor-primed T lymphocytes from both healthy human donors and RA patients. Methotrexate treatment is associated with a significant decrease of TNF-α-positive CD4+ T cells, while the number of T cells expressing the anti-inflammatory cytokine IL-10 increased. [2]
Methotrexate increases splenocyte AICAR content, raised adenosine concentrations in exudates from carrageenan-inflamed air pouches, and markedly inhibits leukocyte accumulation in inflamed air pouches in mice. Methotrexate-mediated reduction in leukocyte accumulation is partially reversed by injection of adenosine deaminase (ADA) into the air pouch, completely reverses by a specific adenosine A2 receptor antagonist, 3,7-dimethyl-1-propargylxanthine (DMPX), but not affected by an adenosine A1 receptor antagonist, 8-cyclopentyl-dipropylxanthine in mice. [3]
[1] Genestier L, et al. J Clin Invest, 1998, 102(2), 322-328. [2] Chan ES, et al. Arthritis Res, 2002, 4(4), 266-273. [3] Cronstein BN, et al. J Clin Invest, 1993, 92(6), 2675-2682.