Intermittent Exposure to Hypobaric Hypoxia Increases MDA and LC3 Levels and Differentially Affects GSH Levels in Rat Brain Tissue

Abstract

BACKGROUND: Intermittent hypobaric hypoxia (IHH) induces repeated episodes of reduced oxygen availability that may elicit adaptive responses in the brain. Oxidative stress, antioxidant defences, and autophagy-related processes are interconnected during hypoxic adaptation. However, the relationship among malondialdehyde (MDA), reduced glutathione (GSH), microtubule-associated protein 1 light chain 3 (LC3), and mechanistic target of rapamycin (mTOR) during repeated IHH exposure remains incompletely characterized. This study was conducted to evaluate these biomarkers simultaneously to provide an integrated perspective on the cerebral response to repeated IHH exposure.

METHODS: Twenty-five male Sprague-Dawley rats were divided into five groups: a control group and 4 IHH groups subjected to either 1, 2, 3, or 4 exposures, respectively, to a simulated altitude of 25,000 feet for 5 minutes at one-week intervals. Brain tissues were collected one hour after the final IHH exposure, homogenized and centrifuged to obtain tissue supernatants for analysis. MDA and GSH levels were measured using colorimetric assays, while LC3 and mTOR protein levels were assessed using sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS: MDA concentrations were significantly higher in all IHH groups compared with control group (p<0.05), with the highest level observed after three exposures. GSH levels were significantly lower in groups receiving one and four exposure(s) compared with control group (p<0.05), whereas groups receiving two and three exposures did not differ significantly from the control. LC3 protein levels were significantly higher in all IHH groups than in control group (p<0.05), reaching the highest level after three exposures and remaining elevated after four exposures. In contrast, total mTOR protein levels did not differ significantly among the experimental groups (p>0.05).

CONCLUSION: Repeated IHH exposure was associated with increased oxidative stress and alterations in antioxidant and autophagy-related responses in the rat brain, as indicated by elevated MDA and LC3 expression and fluctuating GSH levels. Total mTOR protein levels remained unchanged in IHH groups, suggesting that repeated IHH may induce dynamic oxidative stress and autophagy responses without detectable changes in total mTOR.

KEYWORDS: autophagy, hypoxia, LC3, oxidative stress, mTOR