Expression of methotrexate transporters and metabolizing enzymes in rheumatoid synovial tissue.

Objective: To determine whether methotrexate (MTX) affects the expression of genes involved in the transport [SLC19A1 (RFC1), ABCB1 (MDR1), ABCC1 (multidrug resistance proteins 1), ABCG2 (BCRP)], metabolism [γ-glutamyl hydrolase (GGH), folylpolyglutamate synthetase (FPGS)], and mechanism of action of MTX [thymidylate synthase, MTR, MTRR] in rheumatoid synovium.

Methods: Synovial tissue samples were obtained from 20 patients with rheumatoid arthritis (RA). Gene expression was undertaken using quantitative real-time PCR.

Results: All the genes examined were expressed in all samples. Expression of SLC19A1, GGH, FPGS, ABCC1, and MTRR was significantly higher in patients receiving MTX compared to those not receiving MTX (p < 0.05). The ratio of FPGS:GGH gene expression was 2.7 ± 0.51 ng/ml GAPDH (range 0.67-9.58).

Conclusion: Genes involved in the transport, metabolism, and mechanism of action of MTX are expressed in rheumatoid joint synovium. These data provide evidence that MTX has the potential to be polyglutamated within the joint. The higher expression of FPGS compared to GGH in synovial tissue might favor production of long-chain MTX polyglutamates. Thus MTX has the potential to exert its therapeutic effects at the primary site of the inflammatory process in RA.