Cytoprotective Effect of Alpha-Lipoic Acid on Paraquat-Exposed Human Bronchial Epithelial Cells via Activation of Nuclear Factor Erythroid Related Factor-2 Pathway

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Alpha-lipoic acid (LA), a metabolic antioxidant, is a natural compound and its biological function has been well studied in various human diseases. The present study was designed to investigate the cytoprotective effect and the molecular mechanisms of LA in paraquat (PQ)-induced oxidative stress injury using BEAS-2B human bronchial epithelial cells. LA co-treatment prevented PQ-induced BEAS-2B cell death. LA also prevented PQ-induced increases in total reactive oxygen species (ROS), lactate dehydrogenase (LDH) and malondialdehyde (MDA). LA also increased the expression of detoxifying phase II enzyme encoding genes and antioxidant genes including HO-1, NQO1, CAT, GPX3 and GPX4, resulting in the attenuation of the decreases of antioxidants during PQ-induced oxidative stress. Nuclear factor erythroid related factor 2 (Nrf2) was induced by LA. Additionally, translocation of Nrf2 from the cytoplasm to the nucleus was promoted by LA treatment. While LA was responsible for the upregulation of Nrf2, it also activated and up-regulated the downstream proteins heme oxygenase-1 (HO-1) and reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) quinone oxidoreductase 1 (NQO1). The data collectively suggest that the beneficial effect of LA involving the activation of cytoprotective antioxidant genes make LA a potential candidate in the prevention of PQ-induced oxidative stress-related bronchial cell death, pending clinically relevant studies.