In vitro effects of dexamethasone on hypoxia-induced hyperpermeability and expression of vascular endothelial growth factor.

Clinically, dexamethasone is known to reduce cerebral edema. To further investigate the mechanism of this neuroprotection, an in vitro model of brain-derived microvessel endothelial cells (BME cells) was used to investigate the effect of dexamethasone on hypoxia-induced hyperpermeability. Furthermore, the expression of vascular endothelial growth factor (VEGF), which is known to be the mediator of hypoxia-induced hyperpermeability, was evaluated. Dexamethasone (40 microg/ml=100 microM) decreased hypoxia-induced permeability and VEGF expression significantly during time periods of more than 3 h. The time dependence of the dexamethasone effect correlated with a changed mechanism by which hypoxia induced VEGF expression. This was deduced because hypoxia-induced hyperpermeability and VEGF mRNA level were decreased in the presence of an antisense oligonucleotide coding for a region which binds a mRNA stabilizing protein, but only up to 3 h of hypoxia. Furthermore, during this time period the half-life of VEGF mRNA was increased. Results suggest that dexamethasone only decreases transcriptional-induced VEGF expression and that this may be related to the efficacy of dexamethasone to treat brain edema.