Temporal Dynamics of Simulated Microgravity-induced Endothelial Stress Response and Redox Balance: Indicators of the Onset of Cellular Adaptation

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Background: Simulated microgravity (SMG) can perturb endothelial redox regulation, but the temporal development of these responses during early exposure remains insufficiently characterised. Aim: To elucidate whether simulated microgravity-induced redox modulation in endothelial cells initiates adaptive responses towards redox homeostasis. Study Design: The 3D clinostat provides a useful and cost-effective platform for generating SMG. EA.hy926 cells were exposed to SMG for 6, 12, and 24 h, while static control (SC) cells were maintained under normal gravity (1 × g). Place and Duration of Study: The study was conducted in the Department of Biotechnology, The University of Burdwan, West Bengal, India, between August 2022 and January 2024. Methodology: The human endothelial cell line EA.hy926 was used as the experimental model. Simulated microgravity was generated using a three-dimensional (3D) clinostat. Following treatment, cell viability, intracellular reactive oxygen species (ROS), catalase activity, superoxide dismutase (SOD) activity, lipid peroxidation, and the GSH/GSSG ratio were evaluated using standard biochemical assays. Data were analysed using one-way analysis of variance (ANOVA) followed by an appropriate post hoc test and expressed as the mean ± SEM (P < 0.05). Results: Cell viability remained unaffected following SMG exposure for 6, 12, and 24 h. Intracellular ROS generation increased significantly after 6 h and declined progressively at 12 h and 24 h, although it remained elevated compared with the corresponding static controls. Catalase and SOD activities were significantly reduced at 6 h and gradually increased with increasing exposure duration. Lipid peroxidation was markedly elevated at 6 h and progressively decreased at 12 h and 24 h. The GSH/GSSG ratio was significantly reduced after 6 h and gradually increased at 12 h and 24 h. Conclusion: SMG induced an early oxidative stress response without compromising cell viability, followed by the initiation of antioxidant-mediated restoration of redox balance. Although longer exposure durations are required to confirm complete redox homeostasis, these findings improve our understanding of the early endothelial response to SMG and its potential implications for managing vascular dysfunction during prolonged microgravity exposure.