The protective effect of hypoxic preconditioning on cortical neuronal cultures is associated with increases in the activity of several antioxidant enzymes

Preconditioning describes a variety of treatments that induce neurons to become more resistant to a subsequent ischemic insult. How preconditioned neurons adapt to subsequent ischemic stress is not fully understood, but is likely to involve multiple protective mechanisms. We hypothesized hypoxic preconditioning induces protection by a coordinated up-regulation of antioxidant enzyme activity. To test this hypothesis, we developed two in vitro models of ischemia/reperfusion, involving oxygen-glucose deprivation (OGD) where neuronal cell death was predominantly by necrosis (necrotic model) or programmed cell death (PCD model). Hypoxic preconditioning 24 h prior to OGD significantly reduced cell death from 83% to 22% in the necrotic model and 68% to 11% in the PCD model. Consistent with the hypothesis, the activity of the antioxidant enzymes glutathione peroxidase, glutathione reductase, and Mn superoxide dismutase were significantly increased by 54%, 73% and 32%, respectively, in neuronal cultures subjected to hypoxic preconditioning. Furthermore, superoxide and hydrogen peroxide concentrations following OGD were significantly lower in the PCD model that had been subjected to hypoxic preconditioning. (C) 2004 Elsevier B.V. All rights reserved.