Mechanism of analgesic effect of fire needle on peripheral sensitization in rats with neuropathic pain induced by chemotherapy.

OBJECTIVES

This study aims to explore the analgesic mechanism of fire needle on peripheral sensitization in rats with neuropathic pain(NP) induced by oxaliplatin, so as to investigate its mechanism in improving peri-pheral sensitization.

METHODS

Male SD rats aged 8 weeks were randomly divided into 4 groups：normal group(=6), model group(=6), fire needle group(=6), and medication group(=6). NP rat model was established by intraperitoneal injection of oxaliplatin(4 mg/kg) on days 1, 2, 8, 9, 15, 16, 22, and 23. For rats in the fire needle group, fire needle treatment was performed at the "Jiaji"(EX-B2) acupoints of the L4-L6 segments on days 24, 26, and 28, ie. 1 day, 3 and 5 days after modeling. The medication group received intraperitoneal injection of pregabalin(100 mg/kg). Mechanical pain thresholds of the rats were measured before modeling, after modeling and intervention. Serum contents of tumor necrosis factor-α(TNF-α), interleukin-6(IL-6) and chemokine ligand 12(CXCL12) were detected by ELISA. Skin histopathology changes in the acupoint area were observed using HE staining. The number of mast cells in the skin of the acupoints was observed using toluidine blue staining. Immunohistochemical staining was performed to detect the postive expressions of transient receptor potential vanilloid 1(TRPV1), protease-activated receptor 2(PAR2) and tryptase(TPS) in the skin of the acupoint area. Western blot was used to detect the protein expressions of TRPV1 and PAR2 in the dorsal root ganglia(DRG).

RESULTS

Compared with the normal group, the model group had decreased paw withdrawal threshold(PWT) after modeling(<0.05), increased serum contents of IL-6, TNF-α, and CXCL12(<0.05), increased number of mast cells in the acupoint area(<0.05), and increased positive protein expressions of TPS, TRPV1, and PAR2 in the skin of the acupoint area(<0.05). Compared with the model group, the fire needle group and medication group had increased PWT after intervention(<0.05), decreased serum contents of IL-6, TNF-α, and CXCL12, and postive protein expressions of TPS, TRPV1, and PAR2 in the skin of the acupoint area(<0.05)；while the medication group had decreased protein expressions of TRPV1 and PAR2 in DRG(<0.05). HE staining showed thickened epidermis, disordered cellular arrangement, significant intercellular edema, and inflammatory cell infiltration in the model group. In the medication and fire needle groups, the epidermis was thinner, cellular arrangement was clearer, and the extent of tissue edema and inflammatory cell infiltration was reduced compared to the model group.

CONCLUSIONS

Fire needle can improve mechanical pain threshold and reduce the contents of peripheral inflammatory factors in rats with oxaliplatin-induced NP. This effect may be related to the inhibition of mast cell activation and the inhibition of TPS, TRPV1 and PAR2 protein expressions, in the local areas of acupoints.