Objective: To observe the effect of electroacupuncture (EA) on the expression of high mobility group box 1 (HMGB 1) and its receptor CD 24 proteins and β-endorphin (β-EP) content in "Zusanli" (ST 36) region in rats with chronic constriction injury (CCI), so as to explore its mechanisms underlying pain relief.
Methods: Thirty male Wistar rats were rando-mized into control, CCI model and EA groups (n＝ 10 rats in each). The neuropathic pain model was established by ligature of the left sciatic nerve to induce CCI in the model and EA groups, and sham operation was performed in rats of the control group. Paw with drawal latency (PWL, thermal pain threshold) of the bilateral hind-limbs was detected by using an algesia-detector. Eight days after CCI operation, EA was applied to bilateral "Zusanli" (ST 36) and "Yanglingquan" (GB 34) for 30 min, once daily for 5 days. The acetylated-HMGB 1 expression was determined by immunoprecipitation, and the expression of HMGB 1 and toll like receptor 4 (TLR 4) proteins and CD 24 mRNA were detected using Western blot and fluorescent quantitative real time-PCR, respectively, and the content of β-EP in the acupoint region was assayed by enzyme linked immunosorbent assay (ELISA). Anti-CD 24 neutralizing antibody (200 µL, 100 µg/mL) was injected into ST 36 region once daily for 3 days for verifying the involvement of HMGB 1/CD 24 signaling in EA analgesia.
Results: Compared with the control group, the bilateral PWL difference values in the other two groups were significantly increased (P<0.05), meaning an occurrence of hyperalgesia after CCI. In comparison with the CCI model group, the hyperalgesia in the EA group was obviously decreased (P<0.05). After CCI, the expression levels of HMGB 1 and TLR 4 proteins were considerably increased compared with those in the control group (P<0.05). After 5-times' EA, the acetylated-HMGB 1, the expression of CD 24 mRNA, and the content of β-EP were notably up-regulated (P<0.05), and there were no obvious changes in the expression levels of HMGB 1 and TLR 4 proteins (P>0.05). After local injection of anti-CD 24 antibody, EA-induced increases of β-EP content and reduction of thermal pain threshold were significantly suppressed (P<0.05).
Conclusion: EA of ST 36 and GB 34 can alleviate neuropathic pain in CCI rats, which is associated with its effects in up-regulating β-EP content, and HMGB 1 protein and CD 24 mRNA expression levels in ST 36 region. The activated HMGB 1/CD 24/β-EP signaling contributes to EA-ST 36 induced analgesia.
Keywords: Acupuncture analgesia; CD 24; Chronic neuropathic pain; High mobility group box 1; Toll like receptor 4; β-endorphinβ.