Manual acupuncture ameliorates inflammatory pain by upregulating adenosine A₃ receptor in complete Freund's adjuvant-induced arthritis rats

Adenosine A₃ receptor (A₃R) exerts analgesic, anti-inflammatory, and anti-nociceptive effects. In this study, we determined the analgesic mechanism of manual acupuncture (MA) in rats with complete Freund's adjuvant (CFA)-induced arthritis and explored whether MA ameliorates inflammation in these rats by upregulating A₃R.

Sixty Sprague Dawley (SD) rats were randomly divided into the following groups: Control, CFA, CFA + MA, CFA + sham MA, CFA + MA + DMSO, CFA + MA + IB-MECA, and CFA + MA + Reversine groups. The arthritis rat model was induced by injecting CFA into the left ankle joints. Thereafter, the rats were subjected to MA (ST36 acupoint) for 3 days. The clinical indicators paw withdrawal latency (PWL), paw withdrawal threshold (PWT), and open field test (OFT) were used to determine the analgesic effect of MA. In addition, to explore the effect of A₃R on inflammation after subjecting arthritis rats to MA, IB-MECA (A₃R agonist) and Reversine (A₃R antagonist) were injected into ST36 before MA.

MA ameliorated the pathological symptoms of CFA-induced arthritis, including the pain indicators PWL and PWT, number of rearing, total ambulatory distance, and activity trajectory. Furthermore, after MA, the mRNA and protein expression of A₃R was upregulated in CFA-induced arthritis rats. In contrast, the protein levels of TNF-α, IL-1β, Rap1, and p-p65 were downregulated after MA. Interestingly, the A₃R agonist and antagonist further downregulated and upregulated inflammatory cytokine expression, respectively, after MA. Furthermore, the A₃R antagonist increased the degree of ankle swelling after MA.

MA can alleviate inflammatory pain by inhibiting the NF-κB signaling pathway via upregulating A₃R expression of the superficial fascia of the ST36 acupoint site in CFA-induced arthritis rats.