Ischemic alterations in the
glutathione (GSH) redox system of the blood-brain barrier (BBB) may facilitate oxidative injury and formation of
vasogenic brain edema. In this study, both the intra- and extracellular GSH contents of human cerebromicrovascular endothelial cells (
HCEC) were reduced by 35% after exposing the cells to 4 h in vitro
ischemia and 24 h-recovery. The intracellular/extracellular GSH ratio was not affected, indicating a constant rate of GSH efflux. The activities of the
peroxide detoxifying
enzymes,
glutathione peroxidase and
glutathione S-transferase, increased by 35%-50%, whereas the GSH regenerating
enzyme,
glutathione reductase, remained unchanged in ischemic
HCEC.
gamma-glutamyl transpeptidase (
GGTP), a GSH catabolizing
enzyme enriched in brain capillaries, was reduced by 30-50% in ischemic
HCEC. The effect of in vitro
ischemia on
HCEC permeability was assessed by measuring
sodium fluorescein clearance across a compartmentalized in vitro BBB model.
Sodium fluorescein clearance across
HCEC monolayers exposed to
leukotriene C4 in the presence of the
GGTP inhibitor,
acivicin (1 microM), or after in vitro
ischemia was increased by 60% and 30%, respectively, suggesting that oxidative stress and loss of
GGTP may 'unmask' BBB permeabilizing actions of
leukotrienes. These results indicate that oxidative stress and loss of
GGTP activity in
HCEC contribute to ischemic BBB disruption and
vasogenic brain edema.