EFFECTS OF METHOTREXATE ON HUMAN OSTEOBLASTS IN-VITRO - MODULATION BY1,25-DIHYDROXYVITAMIN D-3

This study was designed to investigate whether methotrexate (MTX), use d in the treatment of rheumatoid arthritis (RA), affects proliferation and differentiation of human osteoblasts in culture, The effects of M TX were assessed by analyzing markers of proliferation and differentia tion of human trabecular bone-derived osteoblast-like cells cultured i n the presence or absence of 1,25-dihydroxyvitamin D-3 (1,25 [OH]D-2(3 )). Treatment of the osteoblastic cells with MTX resulted in a strong dose-dependent inhibition of cell proliferation with half maximal resp onse at a dose of 30 nM. MTX did not interfere with cellular alkaline phosphatase (AP) activity, the number of cells expressing cytochemical AP, or basal osteocalcin production. Addition of 1,25(OH)(2)D-3 to th e cultures caused an enhanced AP expression and osteocalcin production coinciding with a decreased osteoblast proliferation, Coincubation of 1,25(OH)(2)D-3 with MTX in doses greater than or equal to 100 nM furt her inhibited osteoblast growth and induced a significant stimulation of AP expression and activity, and production of osteocalcin above the values reached in the 1,25(OH)(2)D-3 cultures, In conclusion, MTX pro ved to be a potent inhibitor of osteoblast proliferation but did not a ffect basal osteoblastic phenotypic expression, In the presence of the osteoblast differentiation-promotor, 1,25(OH)(2)D-3, MTX further inhi bited cell growth which was associated with enhanced AP activity and o steocalcin production, Thus, MTX may have profound effects on bone met abolism and remodeling by interfering with bone cell turnover.