Abstract: BACKGROUND: Rheumatoid arthritis is an inflammatory disease with a circadian variation of symptoms. Moxibustion has achieved remarkable efficacy in the treatment of rheumatoid arthritis, but it is unclear whether the specific mechanism is related to the regulation of the clock gene and the inhibition of pyroptosis.
OBJECTIVE: To explore the effects of moxibustion at different time points on core clock genes Clock, Bmal1 and pyroptosis in rats with rheumatoid arthritis. 
METHODS: Forty adult Sprague-Dawley rats of both sexes were randomized into a control group, a model group, a moxibustion at 7:00-9:00 A.M. group and a moxibustion at 5:00-7:00 P.M. group, with 10 rats in each group. To establish the rheumatoid arthritis model, the rats were injected with Freund’s Complete Adjuvant at the right foot. Rats in the control group were given the normal saline at the right foot. At the 7th after modeling, the two moxibustion groups began to be treated with moxibustion at Zusanli and Shenshu acupoints at 7:00-9:00 A.M. or 5:00-7:00 P.M., once a day, for total 18 treatments with a 1-day break every 6 days. We measured the right foot volume of rats using drainage method before model establishment, after model establishment and after treatment. The hypothalamus and the synovium of the right knee joint were collected from the rats after treatment. The expressions of Clock, Bmal1, Nod-like receptor family pyrin domain-containing 3 (NLRP3), Caspase-1, and Gasdermin D (GSDMD) in the hypothalamus or knee synovium were tested by real-time fluorescence quantitative PCR and western blot. 
RESULTS AND CONCLUSION: The mRNA expreession of Clock and BMAL1 in the hypothalamus had no obvious change among the four groups (P > 0.05). The relative mRNA expression of Clock and Bmal in the hypothalamus was higher than that in the synovium (P < 0.01). The expression of Clock and Bmal1 in the synovium was significantly down-regulated in the model group compared with the control group (P < 0.01). Moxibustion significantly increased the mRNA and protein expression of Clock and Bmal1 in the synoviums compared with the model group (P < 0.05). Compared with the moxibustion at 7:00-9:00 A.M. group, the mRNA and protein expressions of Clock and Bmal1 in the moxibustion at 5:00-7:00 P.M. group were slightly but insignificantly up-regulated (P > 0.05). The mRNA expressions of NLRP3, Caspase-1 and GSDMD in the synovium were significantly increased in the model group compared with the control group (P < 0.01). Compared with the model group, moxibustion at 5:00-7:00 P.M. could significantly reduce the relative mRNA expression of NLRP3, Caspase-1 and GSDMD in the synovium (P < 0.01). Compared with the moxibustion at 7:00-9:00 A.M. group, the relative mRNA expressions of NLRP3 and Caspase-1 were significantly lowered in the moxibustion at 5:00-7:00 P.M. group (P < 0.05, P < 0.01). All these findings indicate that moxibustion can treat rheumatoid arthritis rats by up-regulating the expression of Clock and Bmal1 mRNA and protein in different tissues, down-regulating the mRNA expression of NLRP3, Caspase-1 and GSDMD in the classical signal pathway of pyroptosis, and reducing synovitis and pyroptosis. The anti-inflammatory mechanism of core clock genes Clock and BMAL1 in rheumatoid arthritis may be related to the inhibition of pyrolytic effectors.

Key words: rheumatoid arthritis, moxibustion, Clock, Bmal1, pyroptosis, rat