The preventive effects of electro-acupuncture stimulation on acute and chronic radiation-induced masseter contractile dysfunction-animal study

Background: Previous study has found that the off-target low dose irradiation could cause muscle contractile dysfunction which was related to radiation-induced oxidative damage to muscle protein. However, the effect of radiation related chronic oxidative stress on muscle contractile function was not clear. Electro-acupuncture (EA) stimulation has been used to decrease oxidative damage in various injury models but whether EA prior to radiation could ameliorate radiation related muscle contractile dysfunction remains to be determined. Purpose: The aims of this study were to investigate the acute and chronic effect of EA prior to radiation on radiation-induced masseter contractile dysfunction and exploring the potential underlying mechanism in animal model. Methods: Sprague-Dawley rats aged 7-to-8 week-old were used in this study. Whole study was divided into acute phase and chronic phase. In acute phase, rats were randomized into 6 groups (n=4 per group): Ctrl, IR, EA2, EA100, EA2-IR, and EA100-IR. EA stimulation was applied at the masseter muscle belly and temporomandibular joint, 20 minutes per section, for a total of 3 sections in one week (EA2, EA100, EA2-IR, and EA100-IR). Upon the completion of EA interventions, a single dose of 10 Gy radiation was delivered to bilateral masseter muscles (IR, EA2-IR, and EA100-IR). All rats were sacrificed 24 hours post-irradiation and bilateral masseter muscles were removed and analyzed for contractile function, oxidative injury (protein carbonyl), and antioxidant capacity (CuZnSOD and MnSOD mRNA expression). In chronic phase, rats were randomized into 4 groups (n=4 per group):cCtrl, cIR, cEA2-IR, and cEA100-IR. All interventions and assessments were performed identically as those described in acute phase, expect the time points for sacrificing animals were 3-week- post-irradiation. H&E stain, Masson trichrome stain, and TGF-β1 mRNA expression were used to assess fibrotic response. Results: In acute phase, compared to Ctrl, the contractility of masseter muscle was significantly lower (p<0.05), the force-frequency curve showed significant downward shift (p<0.05), and the protein carbonyl concentration was significantly increased in IR (p<0.01). In rats received EA stimulation, the SOD mRNA expression of masseter muscle was upregulation after EA intervention. In rats received EA stimulation before irradiation showed less contractility decline and lower concentration of protein carbonyl of masseter muscle (both p<0.05), compare to no EA group. In chronic phase, compare to cCtrl, the contractility of masseter muscle remained lower and protein carbonyl concentration remained higher in cIR (both p<0.05). The beneficial effects of EA prior to radiation on masseter muscle persisted in chronic phase, including better contractile function and less protein carbonyl concentration. In groups receiving IR (cIR, cEA2-IR, and cEA100-IR), TGF-β1 mRNA was significantly upregulated (all p<0.05) with no apparent evidence of deposition of collagen Conclusion: The present study showed that irradiation could induce acute and chronic masseter muscle contractile dysfunction and EA pre-treatment could attenuate this harmful radiation-induced effect through upregulation muscle’s antioxidant capacity and its role on prevention of fibrosis is inconclusive.