Analgesic effect of "Zhibian" (BL54)-toward-"Shuidao" (ST28) needling technique of acupuncture on primary dysmenorrhea based on NOD1/RIP2/NF-κB signaling pathway in the rats

Objective: To observe the effect of "Zhibian" (BL54)-toward-"Shuidao" (ST28) needling technique on the relative protein expression of the signaling pathway of nucleotide-binding oligomerization domain-containing protein 1 (NOD1)/ receptor-interacting protein 2 (RIP2)/nuclear factor kappa-B (NF-κB) and the expression of proinflammatory cytokines in the rats with primary dysmenorrhea (PD), so as to explore the underlying mechanism of this acupuncture technique for pain alleviation in PD.

Methods: Thirty female SD rats of SPF grade with normal estrous cycle were randomized into a blank group, a model group and an acupuncture group, 10 rats in each one. Using the intraperitoneal injection with estradiol benzoate combined with oxytocin, PD model was prepared in the model group and the acupuncture group. In the acupuncture group, during model preparation, the intervention with "Zhibian" (BL54)-toward-"Shuidao" (ST28) needling technique was delivered simultaneously, 20 min each time, once daily for consecutive 10 days. On day 11, within 30 min after the intraperitoneal injection with oxytocin, the writhing reaction (latency, frequency and score) was recorded; the morphology of uterine tissue was observed with HE staining, the contents of prostaglandin E2 (PGE2), prostaglandin F2α (PGF2α), interleukin (IL)-1β, IL-18, cyclooxygenase-2 (COX-2), and tumor necrosis factor-α(TNF-α) in the serum were detected using ELISA method; the relative protein expression of NOD1, RIP2, NF-κB p65, phosphorylation-NF-κB p65 (p-NF-κB p65) was detected in the uterine tissue using Western blot method; and the mRNA expression of NOD1, RIP2 and NF-κB p65 was detected with the quantitative real-time PCR employed.

Results: Compared with the blank group, in the model group, the writhing latency was prolonged (P<0.01), the writhing frequency and score increased (P<0.01) in the rats; the endometrial epithelial cells showed massive degeneration and necrosis, with severe endometrial edema and widespread shedding, combined with neutrophil infiltration; the serum PGE2 content was dropped (P<0.01), while those of PGF2α, IL-1β, IL-18, COX-2, and TNF-α elevated (P<0.01); the protein expression of NOD1, RIP2, NF-κB p65 and p-NF-κB p65, and the mRNA expression of NOD1, RIP2 and NF-κB p65 in uterine tissue increased (P<0.01). In comparison with the model group, in the acupuncture group, the writhing latency was prolonged (P<0.01), the writhing frequency and score were reduced (P<0.01) in the rats; there was less degeneration and necrosis of endometrial epithelial cells, with mild endometrial edema and very little neutrophil infiltration; the serum PGE2 content increased (P<0.01), while those of PGF2α, IL-1β, IL-18, COX-2, and TNF-α decreased (P<0.01); the protein expression of NOD1, RIP2, NF-κB p65 and p-NF-κB p65 and the mRNA expression of NOD1, RIP2 and NF-κB p65 in uterine tissue were dropped (P<0.05, P<0.01).

Conclusions: "Zhibian" (BL54)-toward-"Shuidao" (ST28) needling technique can alleviate the pain symptom of PD rats, and its action mechanism may be related to inhibiting the active expression of NOD1/RIP2/NF-κB signaling pathway in the uterine tissue, thereby reducing the inflammatory response.