Partial protection of rat parotid glands from irradiation-induced hyposalivation by manganese superoxide dismutase

Head-and-neck irradiation in rats often results in reduction of water and food intake, weight loss, hyposalivation, and suppression of the white blood cell (WBC) count. Oxygen free radicals are believed to be involved in this deleterious process. Superoxide dismutase (SOD) is known to act as a first line of antioxidant defence against oxygen free radicals. Here, the protective effect of manganese SOD (MnSOD) and copper/zinc SOD (Cu/ZnSOD) against irradiation-induced injuries to the head and neck in rats was investigated. Wistar rats were irradiated with 15 Gy X-rays delivered to the head-and-neck region. MnSOD (50 mg/kg) or Cu/ZnSOD (100 mg/kg) were administered before and after irradiation. Body weight, food and water intake, WBC counts, and parotid and submandibular salivary functions were examined. Irradiation of 15 Gy resulted in a significant reduction of the parotid flow rate by 73% compared with non-irradiated controls (p<0.05). MnSOD but not Cu/ZnSOD partially reduced this effect on the parotid gland by 25% (p<0.05). Both MnSOD and Cu/ZnSOD demonstrated a protective effect against irradiation-induced WBC suppression, by 35% and 25%, respectively (p<0.05). Treatment with SOD did not protect the animals against irradiation-induced reduction in oral intake and weight loss, or against submandibular hypofunction. These results suggest that SOD partially protects against head-and-neck irradiation-induced injury. Both MnSOD and Cu/ZnSOD partially protect against irradiation-induced WBC loss. The parotid gland is partially protected by MnSOD but not Cu/ZnSOD, while the submandibular gland is not protected by either MnSOD or Cu/ZnSOD.