Substance P and beta endorphin mediate electroacupuncture induced analgesic activity in mouse cancer pain model

Cancer pain impairs the quality of life of cancer patients, but opioid analgesics can not only cause inhibition of respiratory function, and constipation, but also other significant side effects such as addiction and tolerance that further decrease quality of life. Thus, in the present study, the effects of electro-acupuncture treatment (EA) on mechanical allodynia were examined in cancer pain mouse model. In order to induce neuropathic cancer pain model, S-180 sarcoma cells were inoculated around the sciatic nerve of left legs of Balb/c mice. The mass of S-180 cancer cells embedded around sciatic nerve in a time course was confirmed by Magnetic Resonance Imaging (MRI) scanning. Mechanical allodynia was most consistently induced in mouse sarcoma cell line S-180 (2 x 10(6) sarcoma cells) treated group among all groups. EA stimulation (2Hz) was daily given to ST36 (Zusanli) of S-180 bearing mice for 30 min for 9 days after S-180 inoculation. EA treatment significantly prolonged paw withdrawal latency from 5 days after inoculation as well as shortened cumulative lifting duration from 7 days after inoculation compared with tumor control. In addition, the overexpressions of pain peptide substance P in dorsal horn of spinal cord were significantly decreased in EA treated group compared with tumor control on Day 9 after inoculation. Furthermore, EA treatment effectively increased the concentration of beta endorphin in blood and brain of mice more than tumor control as well as normal group. The concentration of beta-endorphin for EA treatment group increased by 51.457% in blood 12.6% in brain respectively, compared with tumor control group. These findings suggest that S-180 cancer pain model can be a consistent and short time animal model and also EA treatment can be an alternative therapeutic method for cancer pain via decreased substance P and increased beta endorphin.