Effect of methotrexate and folinic acid on skeletal growth in mice

To investigate whether chronic administration of medium doses of methotrexate (MTX) causes suppression of skeletal growth in young mice and to determine whether folinic acid supplementation could reverse this effect.

Four equal groups of Balb/c young male mice (6 animals in each group; mean body weight 11.9 +/- 0.25 g, in their rapid growth phase) were subjected to the following drug treatment for a period of 3 wk. Group 1 was given intraperitoneal MTX (3.5 mg kg(-1) body weight) every second day. Group 2 received folinic acid (7.0 mg kg(-1) body weight) intraperitoneally every second day. Group 3 was given both drugs (MTX every second day and folinic acid 8 h post-MTX injection). Group 4 was injected with physiological saline every other day to serve as a control group. Total body weight of the animals in each group was monitored every second day for the entire study period. The animals were sacrificed, the bilateral femurs and tibias of each animal were harvested and X-rays of the bones were taken. The length of each femur and tibia was measured using a micrometer. Measurements from the radiographs were also recorded using image analysis software. The MTX concentrations in the plasma and the folate levels in erythrocytes were determined. The heights of the distal femoral and the proximal tibial growth plate for each animal were measured on histological tissue sections.

Mean lengths of both the tibia and femur of animals were compared in the four treatment groups. A significant decrease in the mean lengths (one-way ANOVA, p < 0.005) was observed in the group receiving MTX alone. Similarly, there was a significant decrease (p < 0.001) in the height of the femoral and tibial growth plate in this group when compared with the other groups. The main effect of MTX seemed to be on the hypertrophic proliferative zone of chondrocytes in the growth plate. Furthermore, animals in this MTX-treated group also showed increased levels of MTX in plasma and low levels of erythrocyte folate.

These data show that chronic administration of MTX induces suppression of skeletal growth in mice, possibly through the inhibition of the pathway of de novo DNA synthesis. Folinic acid treatment following MTX administration appears to reverse this growth inhibition. Based on these observations, children suffering from juvenile rheumatoid arthritis, osteosarcoma or acute lymphoblastic leukaemia and receiving MTX over long periods of time could be at risk of short-term suppression of skeletal growth. If this is the case, it is possible that they could benefit from dietary supplementation with folinic acid.