Comparison of the Effects of Genistein and Daidzein with Dexamethasone and Soy Protein on Rheumatoid Arthritis in Rats

We have already shown the protective effects of soy protein on rheumatoid arthritis in rats. In this study, the effects of genistein and daidzein, two isoflavones from soy on rheumatoid arthritis prognosis and prevention in rats have been investigated. Rheumatoid arthritis was induced in female Sprague-Dawley rats using collagen type II plus adjuvant. Rats were then treated with soy protein (7 g/kg), dexamethasone (1 mg/kg), genistein (20 mg/kg genistein), daidzein (20 mg/kg genistein) and casein (in control groups) by daily gavage feedings for 50 days. Scores of arthritis were recorded every day for each paw of animal. Serum concentrations of TNF-α, IL-6, adiponectin and leptin were characterized. Tibiotarsal tissue was used for histopathologic analyses. Treatment with genistein and daidzein resulted in not only a reduction in disease symptoms but also a delay in the onset of symptoms. Results from delayed-type hypersensitivity test demonstrated that the ear thickness in treated rats was significantly lower than that in the control group (p<0.05). There was a reduction in TNF-α, IL-6, adiponectin and leptin serum concentrations after treatment with genistein and daidzein. Dexamethasone reduced the serum concentrations of TNF-α, IL-6 and adiponectin but increased leptin serum level. Prevention of the tissue damage and joint inflammation was also observed following treatment with two soy isoflavones. soy isoflavones, daidzein and especially genistein, could significantly improve rheumatoid arthritis symptoms in rats. The structural similarity of isoflavones to estrogen could be the possible underlying mechanism involved in the function.