Effects of methotrexate on normal articular cartilage in vitro and in vivo

Methotrexate (MTX) has become the disease modifying drug of choice for the treatment of rheumatoid arthritis (RA). Direct effects of MTX on articular cartilage in vivo and in vitro were studied to determine possible adverse effects of the drug.

For in vitro experiments, adult bovine articular cartilage explants were cultured in the presence of MTX (0 to 100 microM), and effects on DNA and matrix metabolism were studied. For in vivo studies, 48 adult female rabbits were treated with MTX (30 mg/kg/week intramuscularly) or placebo, respectively, for up to 12 weeks, and effects on the cartilage of the femoral condyles were assessed.

In vitro, MTX dose dependently increased the uptake of [3H]-thymidine, and decreased incorporation of [3H]-d-uridine into chondrocytes with a half maximal effect at 0.03 microM, suggesting inhibition of thymidylate-synthetase activity by the drug. MTX also dose dependently reduced the proportion of chondrocytes in S-phase, as determined by flow cytometry. MTX did not affect LDH release from chondrocytes or the proportion of viable cells, nor did it change the rate of protein synthesis, proteoglycan synthesis, proteoglycan breakdown, or the hydrodynamic size of newly synthesised proteoglycans. In vivo, MTX did not appreciably affect proteoglycan synthesis of the chondrocytes, proteoglycan content of the cartilage matrix, density of the chondrocyte population, or histological integrity of the cartilage.

The data suggest the absence of major adverse effects by MTX on articular cartilage proteoglycan metabolism. Chondrocyte DNA metabolism seems to be changed by MTX only in concentrations and exposition periods clearly exceeding those found in synovial fluid of RA patients receiving the commonly prescribed doses of the drug.