Eleutheroside E Attenuates Hypobaric Hypoxia-Induced High Altitude Pulmonary Edema by Regulating Ferritinophagy-Mediated Ferroptosis via Keap1-Nrf2 Regulatory Axis

Background: Eleutheroside E is a natural lignan and high-altitude pulmonary edema (HAPE) is a noncardiogenic pulmonary edema induced by exposure to a high-altitude environment. The present study is designed to investigate the therapeutic effects of eleutheroside E against HAPE in rats. Methods: In this study, Sprague-Dawley rats were placed in a hypobaric hypoxia chamber (simulated altitude of 6,000 m; partial pressure of oxygen: 9.6 kPa) for 48 h of continuous exposure and treated with varying doses of eleutheroside E to evaluate its therapeutic effects against HAPE. To investigate the mechanism by which eleutheroside E regulates ferritinophagy and ferroptosis via the Keap1-Nrf2 axis, rescue experiments were performed using the autophagy inhibitor 3-MA, the ferroptosis agonist RSL3, and the Nrf2 inhibitor ML385. The therapeutic effects were validated by utilizing hematoxylin and eosin (H&E) staining, arterial blood gas analysis, lung wet/dry weight ratio, and inflammation cytokines. Furthermore, ferritinophagy-mediated ferroptosis was detected by transmission electron microscope, immunofluorescence staining, and Western blotting. Oxidative stress was detected by associated kits and reactive oxygen species levels. Results: The administration of eleutheroside E alleviated HAPE in rats, and it could correct hypoxia and suppress lipid oxidation induced by hypobaric hypoxia. Moreover, it decreased the levels of inflammation cytokines, VEGF, and total proteins in the bronchoalveolar lavage fluid of rats. Autophagy was found to be involved in the pathological process of HAPE, specifically in the form of ferritinophagy, which represents a novel type of autophagy. The anti-ferritinophagy-mediated ferroptosis effects of eleutheroside E were confirmed by using transmission electron microscopy and Western blotting. The involvement of the Keap1-Nrf2 axis in eleutheroside E-mediated inhibition of ferritinophagy-driven ferroptosis was confirmed by rescue experiments. Conclusion: In summary, eleutheroside E exhibits therapeutic effects against HAPE in rats by suppressing ferritinophagy-mediated ferroptosis via the Keap1-Nrf2 axis. This study indicated a prospective role of eleutheroside E as a functional component in preventing HAPE.