| Osteosarcoma (OSA) is a devastating form of musculoskeletal cancer that most commonly results in death due to pulmonary metastatic disease. It is a rapidly growing, aggressive bone neoplasm, which accounts for up to 85% of all malignant bone tumors in small animals and about 400 new cases per year in humans. Clinically, acupuncture and electroacupuncture (EA) have been used in human and veterinary medicine mainly as adjunct therapies. The anti-inflammatory, immune-boosting, and analgesic effects of electroacupuncture (EA) are well-documented in a variety of animal models and human patients. A number of studies suggest that females have lower pain thresholds than males. In this regard, central c-fos expression was higher in females with chronic pain syndromes, and recent experiments in our lab suggest a trend toward differential spinal cord c-fos expression in tumor-bearing females versus males. However, males are more predisposed to developing OSA, and because of this susceptibility, it is to be expected that they exhibit faster growing, larger, and more painful tumors than females. To date, there are no studies investigating the gender effects of EA on OSA pain and tumor growth. Moreover, EA has never been investigated as sole therapy in a mouse model of bone cancer.;We studied the effects of EA in Balb-C mice, by implanting K7M2 osteosarcoma cells into the calcaneus bone of the left hind paw. Electroacupuncture (4 Hz) was applied to the Zusanli (ST-36) acupuncture point at different time intervals. EA+1: once, 24 hours after tumor implantation. EA+: once weekly for 3 weeks. EA++: twice weekly for 3 weeks, starting on day 3 post-implantation. EA+5: twice weekly for 3 weeks, starting on day 5 post-implantation. EA+7: twice weekly, starting on day 7 post-implantation. PxEA+: 3 treatments prior to implantation. Each group was accompanied by a sham treatment group (no current). Primary hyperalgesia was evaluated using von Frey filaments. Spinal samples underwent avitin-biotin/DAB immunohistochemistry to quantify c-fos expression using light microscopy. Tumor size was measured using calipers. Tumor tissue innervation and vascularization were also analyzed using confocal microscopy. Statistical comparisons between groups were carried out using a Repeated Measures ANOVA (p ≤ 0.05) followed by post-hoc Bonferroni analysis where necessary. Primary hyperalgesia was evaluated using von Frey filaments applied to the plantar surface of each paw. Tumor size was measured using calipers. Vaginal swabs were carried out in female mice to determine the stage of the estrous cycle during treatments.;Tumors in control animals showed a 30.23% growth increase from baseline, while EA+ animals exhibited an average tumor growth increase of 100% or more. Significant reductions in tumor size were seen in mice undergoing early and frequent EA treatments (EA++). Hyperalgesia consistently increased with tumor growth, although less so in EA-treated mice. Hyperalgesia dropped slightly in both males and females on the days EA was performed, but rose again 24 hours later. Estrous cycles in female mice varied greatly and were not synchronized within groups. They showed no correlation to EA or behavioral testing, indicating no direct hormonal influence. Tumors tended to grow slightly larger in males and resulted in higher von Frey scores and c-fos expression across the groups. With few exceptions, there were no significant gender differences in tumor growth or von Frey scores.;The results of this study indicate that early EA treatment has inhibitory effects on nociception and tumor growth that are not influenced by gender, while late EA treatment actually increases tumor growth. |
