Hypoxic Preconditioning Alleviates Ethanol Neurotoxicity: The Involvement of Autophagy

Abstract

Ethanol is a neuroteratogen and neurodegeneration is the most devastating consequence of developmental exposure to ethanol. A sublethal preconditioning has been proposed as a neuroprotective strategy against several central nervous system neurodegenerative diseases. We have recently demonstrated that autophagy is a protective response to alleviate ethanol toxicity. A modest hypoxic preconditioning (1% oxygen) did not cause neurotoxicity but induced autophagy (Tzeng et al. Free Radic Biol Med 49: 839-846, 2010). We, therefore, hypothesize that the modest hypoxic preconditioning may offer a protection against ethanol-induced neurotoxicity. We showed here that the modest hypoxic preconditioning (1% oxygen) for 8h significantly alleviated ethanol-induced death of SH-SY5Y neuroblastoma cells. Under the normoxia condition, cell viability in ethanol-exposed cultures (316mg/dl for 48h) was 49±6% of untreated controls; however, with hypoxic preconditioning, cell viability in the ethanol-exposed group increased to 78±7% of the controls (p<0.05; n=3). Bafilomycin A1, an inhibitor of autophagosome and lysosome fusion, blocked hypoxic preconditioning-mediated protection. Similarly, inhibition of autophagic initiation by wortmannin also eliminated hypoxic preconditioning-mediated protection. In contrast, activation of autophagy by rapamycin further enhanced neuroprotection caused by hypoxic preconditioning. Taken together, the results confirm that autophagy is a protective response against ethanol neurotoxicity and the modest hypoxic preconditioning can offer neuroprotection by activating autophagic pathways.