Intercellular gap formation induced by TNF and the effect of antioxidants on TNF-induced TER. Live, unfixed HUVECs (original magnification, × 100) mounted on a heated stage were infected with Ad-VE-cadherin GFP and exposed to vehicle (A) or TNF (B) and were observed under fluorescence confocal microscopy for 30 minutes. Ad-VE-cadherin GFP localized to adherens junctions similar to endogenous VE-cadherin. Compared with vehicle controls (A), TNF caused early separation of cell-cell junctions (B, arrows). In parallel, intercellular gap formation was associated with loss of VE-cadherin GFP from adherens junctions. (C-D) Confluent HUVEC monolayers exposed to the antioxidants (C) NAC (20 mM) or (D) MnTBAP (10 mM) for 30 minutes before TNF exposure. Both NAC and MnTBAP prevented TNF-induced intercellular gap formation and VE-cadherin redistribution. (E-F) Effect of antioxidants on TNF-induced reduction in transmonolayer resistance, TER, and intercellular gap formation. (E) Early and persistent decrease in TER induced by TNF (▪) compared with vehicle controls (□). NAC (▵) prevented TNF-induced decreased TER, whereas NAC alone (×) had no effect on TER. (F) Similar effects were observed with MnTBAP. *P < .05; n > 6 per group.