Abstract: OBJECTIVE: To explore whether the intraperitoneal administration of Cionbufagin has an analgesic effect on cancer-induced bone pain (BICP) rats,and to assess whether the inhibition of astrocytic and microglia activation is involved in the analgesic effects of Cionbufagin. METHODS: A total of 48 adult female Sprague-Dawley (SD) rats were divided into the following groups with 12 rats per group:Control,Sham,CIBP,and Cionbufagin. The groups of CIBP and Cionbufagin rats were prepared by injection of 20 μL Walker 256 breast cancer cell suspension into the tibial bone marrow cavity. For the sham-operated group,20 μL PBS was used to replace the tumor cells injected into the tibia. Cionbufagin was injected intraperitoneally on the seventh day post-operation and once daily for 7 days whereas normal saline was used for the other groups. Mechanical withdrawal threshold and radiant heat threshold of hind paws of rats were measured to evaluate analgesic effects of Cionbufagin. Moreover,tibia was detected by X-ray assay on the seventh day after operation. Immunofluorescence staining was used to determine the expression of spinal astrocytes and microglial activation. Enzyme-linked immunosorbent assay (ELISA) was used to detect expression of pro-inflammatory cytokines[interleukin (IL)-1β and tumor necrosis factor (TNF)-α]. RESULTS: After operation,mechanical pain and thermal pain threshold decreased in the BICP group,and the differences were statistically significant compared with the control and sham groups on the 7th day (P < 0.01). After injected with Cinobufagin,the pain threshold of the Cinobufagin group was increased and the difference was statistically significant compared with the CIBP group (P < 0.01). X-ray assay showed tibia were obviously broken,suggesting that model was successful. The activation of microglia and astrocytes in the spinal cord in BICP group were higher than that of the sham group (P < 0.05),the activation of microglia and astrocytes of the Cinobufagin group was significantly lower than that of the CIBP group (P < 0.05). The concentration of TNF-α and IL-1β in peripheral blood and spinal cord in BICP group were increased when compared with the sham rats,but there were low on the Cionbufagin group when compared with the BICP group (P < 0.05). CONCLUSION: The study showed that Cionbufagin has an analgesic effect on CIBP rats,the analgesic effects were mainly mediated through inhibition of activation of microglia and astrocytes in the spinal cord.

Key words: cancer-induced bone pain, cionbufagin, glial cells, inflammatory cytoki, analgesic effect