The Tri-phasic Role of Hydrogen Peroxide in Blood-Brain Barrier Endothelial cells

Hydrogen peroxide (H(2)O(2)) 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 H(2)O(2) 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 H(2)O(2) 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 H(2)O(2) (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. H(2)O(2) at low concentrations (0.001 μM to 1 μM) increased endothelial cell tube formation indicating enhanced angiogenesis. H(2)O(2) at 100 μM and above induced monolayer hyperpermeability significantly (p < 0.05). H(2)O(2) 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 H(2)O(2), but had no effect on protein expression. Cytoskeletal disorganizations were observed starting at 1 μm. In conclusion H(2)O(2) influences angiogenesis, permeability, and cell death/apoptosis in a tri-phasic and concentration-dependent manner in microvascular endothelial cells of the blood-brain barrier.