The antiproliferative effect of mizoribine on rheumatoid synovial fibroblast mediated by induction of apoptosis.

In order to investigate the mechanism of anti-rheumatic action of mizoribine (MZR), antiproliferative effect of MZR on synovial fibroblasts obtained from rheumatoid arthritis (RA) patients were examined. To examine the effect of MZR on DNA synthesis, total radioactivity of 3H-thymidine (3H-TdR) incorporated into the synovial fibroblasts was measured. Also quantification of DNA fragmentation of synovial fibroblasts in the cultured supernatant and cell associated Bcl-2 protein, which is suspected of interfering with apoptosis, were performed with enzyme-linked immunosorbent assay. MZR suppressed 3H-TdR incorporation into synovial fibroblasts in a dose dependent fashion. Significant inhibition (P < 0.01) was attained at the concentration of more than 1 microgram/ml of MZR. However, induction of DNA fragmentation which is characteristic of apoptosis, were observed at only 10 micrograms/ml of MZR over 72 h-incubation significantly. In terms of the Bcl-2 expression of synovial fibroblasts, up to 10 micrograms/ml of MZR has no effect on the expression of this protooncogene bcl-2 expression. These results suggest that MZR might suppress the growth of rheumatoid pannus by inhibition of synovial fibroblast proliferation partially through the induction of apoptosis of synovial fibroblast without modulating Bcl-2 expression.