ABSTRACT
BACKGROUND: The blood-brain barrier (BBB) forms a selective barrier between blood and brain and regulates the passage of most molecules. Pathological conditions such as ischemia lead to breakdown of the BBB. Vascular endothelial growth factor (VEGF) has been shown to be responsible for hypoxia-induced hyperpermeability of the BBB in vivo as well as in vitro. To eliminate factors which alter the permeability of the BBB in vivo, an in vitro model was used to test the effects of intravenous and volatile anesthetics on the permeability and on VEGF expression during normoxia and hypoxia. METHODS: The in vitro model of the BBB consisted of primary cultures of porcine brain microvascular endothelial cells (BMEC). The permeability was measured by the paracellular passage of [3H]inulin across the BMEC monolayer and the expression of VEGF was determined by northern blot analysis. RESULTS: All intravenous and volatile anesthetics tested (etomidate, ketamine, fentanyl, propofol, midazolam, sodium-gamma-hydroxybutyrate as well as halothane, enflurane, isoflurane, sevoflurane, desflurane) did not alter the permeability of the BBB or the expression of VEGF in vitro. Hypoxia (2 vol%) increased the permeability and the VEGF expression significantly which was not altered in the presence of the anesthetics. CONCLUSION: The in vitro model represents a suitable model of the BBB to investigate direct effects of anesthetics on functions of the BBB independent of hemodynamic factors.
Subject(s)
Anesthetics/pharmacology , Blood-Brain Barrier/drug effects , Anesthetics, Inhalation/pharmacology , Anesthetics, Intravenous/pharmacology , Animals , Blotting, Northern , Cell Membrane Permeability/drug effects , Cell Survival/drug effects , Cells, Cultured , Endothelial Cells/drug effects , Endothelial Cells/metabolism , Hypoxia/metabolism , Swine , Vascular Endothelial Growth Factor A/biosynthesisABSTRACT
An in vitro model of the blood-brain barrier (BBB), consisting of porcine brain-derived microvascular endothelial cells (PBMEC), was used to evaluate the effect of astrocytes in the BBB disruption during hypoxia. Hypoxia-induced hyperpermeability was decreased significantly in a coculture model of astroglia cells, either astrocytes or C6 glioma cells, with PBMEC and, to the same extent, when glia cell-conditioned medium was used. Corresponding to effects on hypoxia-induced hyperpermeability, astrocyte- and C6 cell-conditioned medium diminished hypoxia-induced vascular endothelial growth factor (VEGF) mRNA and protein expression, which recently was shown to be responsible for hypoxia-induced permeability changes in vitro. The effect on hypoxia-induced hyperpermeability and VEGF expression was specific for astroglia cells because conditioned medium from bovine smooth muscle cells (BSMC) did not show any effect. Immunocytochemistry revealed that 24 h of hypoxia disrupted the continuity of the tight junction protein, zonula occludens-1 (ZO-1), which lines the cytoplasmic face of intact tight junctions. These changes were prevented when hypoxia was performed in glia cell-conditioned medium. Results suggest that astrocytes protect the BBB from hypoxia-induced paracellular permeability changes by decreasing hypoxia-induced VEGF expression in microvascular endothelial cells.
