Suppression of type II collagen‐induced arthritis by the endogenous estrogen metabolite 2‐methoxyestradiol

OBJECTIVE: To evaluate the antiarthritic properties of 2-methoxyestradiol, an endogenous metabolite of estradiol, on type II collagen-induced arthritis (CIA) in DBA/1 mice. METHODS: The effects of treatment with 2-methoxyestradiol on the development of CIA were evaluated clinically and histologically. The in vitro effects of 2-methoxyestradiol on lymphocyte and endothelial cell proliferation and differentiation were analyzed by standard methods. RESULTS: The development of CIA was significantly suppressed by 2-methoxyestradiol. Incubation with 2-methoxyestradiol suppressed the in vitro proliferation of endothelial cells, indicating that this compound down-regulates angiogenesis. Endothelial cell production of nitric oxide (NO) was also down-regulated by 2-methoxyestradiol. In contrast to estradiol, 2-methoxyestradiol exerted neither detectable feminizing effects on the sex organs nor inhibition of leukocyte development in hematopoietic organs. CONCLUSION: The development of CIA is suppressed by 2-methoxyestradiol, possibly via inhibition of angiogenesis. Diminished NO production could be of importance in vivo because it is a potent proinflammatory mediator. Since 2-methoxyestradiol exerts only mild side effects compared with estradiol, it is an interesting candidate for therapeutic use in inflammatory diseases.