BACKGROUND: beta-Amyloid protein (A beta) accumulation, caspase activation, apoptosis, and hypoxia-induced neurotoxicity have been suggested to be involved in Alzheimer disease neuropathogenesis. A beta is produced from amyloid precursor protein through proteolytic processing by the aspartyl protease beta-site amyloid precursor protein-cleaving enzyme (BACE) and gamma-secretase. Inhaled anesthetics have long been considered to protect against neurotoxicity. However, recent studies have suggested that the inhaled anesthetic isoflurane may promote neurotoxicity by inducing caspase activation and apoptosis, and by increasing levels of BACE and A beta. We therefore sought to determine whether isoflurane can induce concentration-dependent dual effects on hypoxia-induced caspase-3 activation and increases in BACE levels: protection versus promotion. METHODS: H4 human neuroglioma cells were treated with hypoxia (3% O-2) alone, different concentrations of isoflurane (0.5% and 2%), and the combination of hypoxia and 0.5% or 2% isoflurane. The levels of caspase-3 cleavage (activation), BACE, and Bcl-2 were determined by Western blot analysis. RESULTS: We show for the first time that treatment with 0.5% isoflurane for 8 hours attenuated, whereas treatment with 2% isoflurane for 8 hours enhanced, hypoxia-induced caspase-3 activation and increases in BACE levels. The 2% isoflurane treatment also enhanced a hypoxia-induced decrease in Bcl-2 levels. CONCLUSIONS: These results suggest a potential concept that isoflurane has dual effects (protection versus promotion) on hypoxia-induced toxicity, which may act through Bcl-2 family proteins. These findings could lead to more systematic studies to determine the potential dual effects of anesthetics on Alzheimer disease-associated neurotoxicity. (Anesth Analg 2011;113:145-52)