RESUMO
Hydrogen peroxide (H2O2) plays an important role physiologically as the second messenger and pathologically as an inducer of oxidative stress in injury, ischemia and other conditions. However, it is unclear how H2O2 influences various cellular functions in health and disease differentially, particularly in the blood-brain barrier (BBB). We hypothesized that the change in cellular concentrations of H2O2 is a major contributor in regulation of angiogenesis, barrier integrity/permeability and cell death/apoptosis in BBB endothelial cells. Rat brain microvascular endothelial cells were exposed to various concentrations of H2O2 (1 nM to 25 mM). BBB tight junction protein (zonula ocludens-1; ZO-1) localization and expression, cytoskeletal organization, monolayer permeability, angiogenesis, cell viability and apoptosis were evaluated. H2O2 at low concentrations (0.001 µM to 1 µM) increased endothelial cell tube formation indicating enhanced angiogenesis. H2O2 at 100 µM and above induced monolayer hyperpermeability significantly (p < 0.05). H2O2 at 10 mM and above decreased cell viability and induced apoptosis (p < 0.05). There was a decrease of ZO-1 tight junction localization with 100 µm H2O2, but had no effect on protein expression. Cytoskeletal disorganizations were observed starting at 1 µm. In conclusion H2O2 influences angiogenesis, permeability, and cell death/apoptosis in a tri-phasic and concentration-dependent manner in microvascular endothelial cells of the blood-brain barrier.
