Local Multiple-site Injections of a Plasmid Harboring Human MnSOD Mitigate Radiation-induced Skin Injury by Inhibiting Ferroptosis

Background: Most patients who undergo radiotherapy develop radiation skin injury, for which effective treatment is urgently needed. MnSOD defends against reactive oxygen species (ROS) damage and may be valuable for treating radiation-induced injury. Here, we (i) investigated the therapeutic and preventive effects of local multiple-site injections of a plasmid, encoding human MnSOD, on radiation-induced skin injury in rats and (ii) explored the mechanism underlying the protective effects of pMnSOD. Methods: The recombinant plasmid (pMnSOD) was constructed with human cytomegalovirus (CMV) promoter and pUC-ori. The protective effects of pMnSOD against 20-Gy X-ray irradiation were evaluated in human keratinocytes (HaCaT cells) by determining cell viability, ROS levels, and ferroptosisrelated gene expression. In therapeutic treatment, rats received local multiple-site injections of pMnSOD on days 12, 19, and 21 after 40-Gy γ-ray irradiation. In preventive treatment, rats received pMnSOD injections on day -3 pre-irradiation and on day 4 post-irradiation. The skin injuries were evaluated based on the injury score and pathological examination, and ferroptosis-related gene expression was determined. Results: In irradiated HaCaT cells, pMnSOD transfection resulted in an increased SOD2 expression, reduced intracellular ROS levels, and increased cell viability. Moreover, GPX4 and SLC7A11 expression was significantly upregulated, and erastin-induced ferroptosis was inhibited in HaCaT cells. In the therapeutic and prevention treatment experiments, pMnSOD administration produced local SOD protein expression and evidently promoted the healing of radiation-induced skin injury. In the therapeutic treatment experiments, the injury score in the high-dose pMnSOD group was significantly lower than in the PBS group on day 33 post-irradiation (1.50 vs. 2.80, P < 0.05). In the prevention treatment experiments, the skin injury scores were much lower in the pMnSOD administration groups than in the PBS group from day 21 to day 34. GPX4, SLC7A11, and Bcl-2 were upregulated in irradiated skin tissues after pMnSOD treatment, while ACSL4 was downregulated. Conclusion: The present study provides evidence that the protective effects of MnSOD in irradiated HaCaT cells may be related to the inhibition of ferroptosis. The multi-site injections of pMnSOD had clear therapeutic and preventive effects on radiation-induced skin injury in rats. pMnSOD may have therapeutic value for the treatment of radiation-induced skin injury.