Abstract
Purpose: To study the curative effect of the volatile oil from Litsea cubeba (EOL) on type II collagen (CII) induced arthritic (CIA) rat.
 Methods: The chemical constituents of EOL were analyzed by gas chromatography-mass spectrometry (GC-MS). The analgesic effect of the oil was assessed by acetic acid-stimulated torsion and hot plate methods, while antiinflammatory potential was further assessed by in an ear oedema model induced by dimethylbenzene in mice. The anti-rheumatoid arthritis (RA) activity of EOL in mice was evaluated in terms of paw volume, arthritis index, thymus and spleen index, and serum inflammatory factor levels.
 Results: GC-MS showed that α-citral (26.42 %), β-citral (21.94 %), and limonene (12.79 %) were the main components of EOL. Different doses of EOL (50, 100, 200 mg/kg) exerted varying inhibitory effects on torsion in mice induced by acetic acid (p < 0.01) but had no significant effect on thermal stimulation-induced pain. EOL reduced ear oedema in mice (p < 0.01). In addition, EOL (50, 100, 200 mg/kg) reduced the mouse paw volume, arthritis index, and thymus and spleen index (p < 0.01). Furthermore, EOL reduced proinflammatory cytokines in serum but increased antiinflammatory cytokines (p < 0.01).
 Conclusion: EOL ameliorates symptoms of inflammation in CIA rats by inhibiting inflammatory reactions, suggesting it could be further developed as an anti-arthritic drug.
 Keywords: Litsea cubeba, Essential oil, Rrheumatoid arthritis, Pro-inflammatory cytokines
Highlights
Previous studies have demonstrated that rheumatoid arthritis (RA) is an intractable inflammatory polyarthritis that can result in serious damage to joints, commonly resulting in gradual cartilage and synovial bone destruction, loss of joint function, and disability [1,2,3]
After EOL treatment, paw volume and arthritis score of collagen-induced arthritis (CIA) rats were significantly reduced, as were the thymus and spleen indexes. These results demonstrate that EOL could reduce inflammation and affect immune function in CIA rats
The present findings suggested that EOL treatment for 24 days can decease the tumor necrosis factor (TNF)-α, IL-1β, -6, -8, and -17A in serum of CIA rats, whereas the IL-10 was significantly increased, suggesting that EOL may play a potential anti-RA therapeutic role by regulating these cytokines
Summary
Previous studies have demonstrated that rheumatoid arthritis (RA) is an intractable inflammatory polyarthritis that can result in serious damage to joints, commonly resulting in gradual cartilage and synovial bone destruction, loss of joint function, and disability [1,2,3]. From days 1 to 24 following the initial CII immunization, and MTX (1.0 mg/kg, thrice per week) used as the positive control, and the three EOL groups were treated with EOL (50, 100, 200 mg/kg), The normal and control groups were given with 0.5 % CMC-Na. During the experiment, paw volume was measured every 3 days using an YLS-7C paw volume meter (TECHMAN SOFT, Chengdu, China), and the arthritis score was calculated every 3 days after the first injection using the a five-point scale: (0) no redness or swelling, (1) swelling and erythema can be seen in 1 joint, (2) swelling and erythema can be seen in 2 joints, (3) swelling and erythema can be seen in 3 joints, and 4) maximal erythema and swelling can be seen in 3 joints affected.
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