Objective: We investigated the antiproliferative and antiinflammatory effects of methotrexate (MTX) on differentiating/differentiated cells, namely cultured human monocytic myeloid cells (THP-1), and primary cultures of synovial macrophages from patients with rheumatoid arthritis (RA).
Methods: We evaluated early and late apoptosis as well as natural cytokine inhibitor production, such as the interleukin 1 (IL-1) receptor antagonist (IL-1ra) and the soluble tumor necrosis factor receptor (sTNFr).
Results: Within THP-1 cells we observed a significant (p < 0.001) dose-dependent inhibition of proliferation (at 24-48 and 72-96 h) and a significant presence of apoptosis (at 24-48 h) with MTX concentrations of 500, 100, and 75 microg/ml compared with untreated controls. No significant changes were observed with 5 microg/ml or 500 to 50, and 5 ng/ml. A significant increase of IL-1ra (p < 0.001) was observed with MTX concentrations of 5 microg (51.43 +/- 2.53 vs 16.22 +/- 5.19 pg/ml control) and 500 ng (36.43 +/- 3.3 vs 16.22 +/- 5.19 pg/ml control) at all the tested times. No significant changes were observed for the sTNFr p75. Evaluating the RA synovial macrophages, we obtained no significant effects on cell proliferation and apoptosis with MTX treatment at 24 h and at the concentration of 50 microg/ml (achievable in the serum with low dose MTX treatment in RA). No significant changes were observed for the IL-1ra and no detectable levels for the sTNFr p75 were detected after treatment with MTX.
Conclusion: This study shows that the antiproliferative and antiinflammatory effects of MTX on human cultured monocytes are dose-dependent. The antiproliferative activity seems to be mediated by cell apoptosis and the antiinflammatory activity seems to be related to cytokine inhibitor release.