Modulation of the glutathione redox cycle may influence tumor necrosis
factor-alpha (TNF)-mediated disturbances of endothelial integrity. To
test this hypothesis, normal endothelial cells or cells with either i
ncreased or decreased glutathione levels were exposed to 100 ng (500 U
) TNF/ml. Increased glutathione levels were achieved by exposure to 0.
2 mM N-acetyl-L-cysteine (NAG) and decreased glutathione levels by exp
osure to 25 mu M buthionine sulfoximine (BSO). Several components of t
he glutathione redox cycle as well as markers of endothelial integrity
, such as cytoplasmic free calcium and transendothelial albumin transf
er, were measured in the treated cells. Exposure to TNF for 3 and 6 h
decreased total glutathione levels, which was followed by an increase
at later time points. Moreover, treatment with TNF resulted in an incr
ease in the ratio of oxidized to reduced glutathione, intracellular fr
ee calcium, albumin transfer across endothelial monolayers and lipid h
ydroperoxides. However, an increase in lipid hydroperoxides was seen o
nly when endothelial cell cultures were supplemented with iron. BSO tr
eatment increased susceptibility of endothelial cells to TNF-mediated
metabolic disturbances. On the other hand, NAC partially protected aga
inst TNF-induced injury to endothelial monolayers. Our results demonst
rate the important role of the glutathione redox cycle in TNF-mediated
disturbances of the vascular endothelium and indicate that modulation
of glutathione levels may potentiate the injurious effects of this in
flammatory cytokine.