Modulation of methotrexate efficacy by green tea polyphenols in rat adjuvant arthritis

[Display omitted] •Co-administration of green tea extract and methotrexate (MTX) has been studied in arthritic rats.•A green tea extract gradually decreased the effectiveness of MTX on arthritic score.•A green tea extract alone and with MTX reduced MCP-1, but counteracted IL-17 only at day 14.•A green tea extract inhibited iNOS mRNA and GGT, but in a less extent compared to MTX.•Long-term administration of green tea extract may inhibit the therapeutic action of methotrexate. Green tea catechins are widely employed as dietary supplements to restore the oxidative state in adjuvant-induced arthritic rats, a model for human rheumatoid arthritis. Methotrexate is the first line antirheumatic drug. The present study aimed to investigate if a decaffeinated extract (GreenSelect®, GS) of tea polyphenols can ameliorate methotrexate treatment in rat adjuvant arthritis. The study lasted 28 days and included healthy animals administered with GS (daily dose of 200 mg/kg), untreated arthritic rats and arthritic rats treated with: GS, methotrexate in single treatment or in combination with GS. Arthritic score and changes in body weigh were measured during the treatment while inflammatory markers (monocyte chemotactic protein-1, IL-17 and inducible NO-synthase mRNA) and biochemical parameters (gamma-glutamyltransferase and heme oxygenase-1) at the end of the treatment. The association between GS and methotrexate was less efficient in ameliorating the arthritic score compared to methotrexate alone. GS did not improve the inflammatory and biochemical markers except for monocyte chemotactic protein-1 and negatively affected the body weight. GS did not increase the plasma antioxidant capacity, suggesting a pro-oxidant effect. The results suggest that long-term administration of GS may inhibit the therapeutic action of methotrexate in arthritic rats.