Abstract: BACKGROUND: Rheumatoid arthritis is an autoimmune disease that causes joint inflammation and pain, which is categorized as arthralgia in traditional Chinese medicine. Coix seed-based prescription is the classic prescription for relieving arthralgia, but the active components and their mechanisms are still unclear.
OBJECTIVE: To investigate the anti-inflammatory effect and mechanism of coix seed and its components in adjuvant arthritis rats and to find the key anti-inflammatory components of coix seed. 
METHODS: Sixty-four SPF Wistar rats were randomly divided into normal group, model group, dexamethasone group, coix seed decoction group, coix seed volatile oil group, coix seed protein group, coix seed polysaccharide group, and coix seed starch group. In addition to the normal group, animal models were successfully established in the other groups by subcutaneous injection of 0.2 mL of Freund’s complete adjuvant into the planta pedis of the right hindfoot. Drug administration by gavage began on the 14th day after modeling and lasted for 18 days. The control and model groups were given the same volume of normal saline. General conditions and body mass changes in rats were observed. The swelling degree of the feet was measured by perimeter method. Thymus and spleen indexes were detected. Levels of interleukin-1, interleukin-6, and tumor necrosis factor α in the cartilage were detected by enzyme-linked immunosorbent assay. Histopathological changes of rat knee joint were observed by hematoxylin-eosin staining. 
RESULTS AND CONCLUSION: Compared with the normal group, the degree of joint swelling in each group reached the peak after modeling (14 days), and the body mass was significantly increased (P < 0.05). Compared with the model group, the body mass of rats in coix seed decoction group and coix seed volatile oil group decreased significantly (P < 0.05). Compared with the model group, the joint circumference of rats in the dexamethasone group and coix seed volatile oil group decreased significantly, and the degree of joint swelling decreased (both P < 0.05). Compared with the normal control group, the thymus index and spleen index increased significantly in the model group (P < 0.05 and P < 0.01). Compared with the model group, the thymus and spleen indexes in the dexamethasone group decreased significantly (P < 0.05, P < 0.01). Coix seed protein could significantly decrease the spleen index (P < 0.05). Compared with the normal control group, the levels of interleukin-1, interleukin-6, and tumor necrosis factor α in serum were significantly downregulated in the dexamethasone group, coix seed volatile oil group, and coix seed protein group (P < 0.01). To conclude, coix seed protein and coix seed volatile oil have significant effects on rheumatoid arthritis in rats, which may reduce the serum levels of interleukin-1, interleukin-6, and tumor necrosis factor α, thereby alleviating joint redness and swelling in adjuvant arthritis rats.

Key words: coix seed, effective component, adjuvant arthritis, animal model, inflammatory factor, rat