Metformin Mitigates Radiation-Induced Endothelial Cell Damage by Attenuating Oxidative Stress, DNA Damage, and Apoptosis

Background and Objectives: Radiation-induced endothelial injury is a major contributor to cardiovascular complications among cancer survivors.Metformin, an antidiabetic drug with well-established pleiotropic effects, has been reported to exert protective actions beyond glucose regulation.This study aimed to investigate whether metformin mitigates radiationinduced cytotoxicity in human endothelial cells.Methods: EA.hy926 endothelial cells were pretreated with metformin (0.1, 0.2, 0.5, or 1 mM) for 24 hours prior to exposure to 5 Gy of ionizing radiation.Cell viability was assessed using the Cell Counting Kit assay, and Western blot analysis was performed to evaluate phosphorylated and total levels of DNA-dependent protein kinase catalytic subunit (DNA-PKcs), ataxia-telangiectasia mutated (ATM), and H2AX-key proteins involved in DNA double-strand break repair.Results: Radiation significantly decreased cell viability and increased phosphorylation of DNA-PKcs, ATM, and H2AX.Metformin pretreatment significantly improved viability at 0.5 and 1 mM in a dose-dependent manner, while lower concentrations (0.1 and 0.2 mM) showed a non-significant upward trend.Metformin also markedly reduced phosphorylation of DNA damage response proteins at 0.5 and 1 mM, whereas total protein levels of DNA-PKcs, ATM, and H2AX remained unchanged, indicating selective inhibition of protein activation.Conclusions: Metformin exerts a radioprotective effect in human endothelial cells by enhancing cell viability and attenuating radiation-induced DNA damage signaling.These findings suggest the potential clinical utility of metformin in preventing radiation-induced vascular injury.