Methotrexate inhibits rheumatoid synovitis by inducing apoptosis

Area of Science:

• Rheumatology
• Immunology
• Pharmacology

Background:

• Rheumatoid arthritis (RA) is a chronic inflammatory disease affecting the synovium.
• Methotrexate (MTX) is a primary therapeutic agent for RA, but its precise mechanism on synovial tissue requires further elucidation.
• Severe combined immunodeficient (SCID) mice engrafted with human RA synovial tissue (SCID-HuRAg) provide a model to study RA pathogenesis and drug effects.

Purpose of the Study:

• To investigate the pharmacological action of methotrexate (MTX) on human rheumatoid arthritis (RA) synovium in a SCID-HuRAg mouse model.
• To determine if MTX induces apoptosis in RA synovial tissue and cells.
• To compare the effects of MTX with other disease-modifying antirheumatic drugs (DMARDs) and a nonsteroidal anti-inflammatory drug (NSAID).

Main Methods:

• Human RA synovial tissue was grafted into SCID mice (SCID-HuRAg model).
• MTX was administered orally, and apoptosis in grafted tissue was assessed using TUNEL staining and electron microscopy.
• Synovial cells were cultured to evaluate MTX-induced apoptotic changes via gel electrophoresis and flow cytometry; histological comparisons were made with other DMARDs and an NSAID.

Main Results:

• MTX treatment led to a significant reduction in inflammatory cells within the grafted RA synovial tissue.
• MTX induced apoptosis in the synovial tissue and cultured synovial cells, an effect not observed with other tested DMARDs or the NSAID.
• Histological examination confirmed MTX's unique anti-inflammatory and pro-apoptotic effects compared to other agents.

Conclusions:

• Methotrexate demonstrably induces apoptosis in the rheumatoid arthritis synovium.
• The induction of apoptosis by MTX is a key mechanism contributing to its anti-inflammatory effects in RA synovitis.
• The SCID-HuRAg model is effective for evaluating the direct impact of drugs on human RA synovial tissue.