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New selenium containing compounds which act as mimics of glutathione peroxidase (GPx) protect vascular endothelial cells (HUVEC) from the toxicity of 140 microM hydrogen peroxide. In the absence of GPx mimic, hydrogen peroxide destroys the tightness of the cellular monolayer and transforms the actin network into compact stress fibers. The pre-treatment of the cells by 4 microM of the lead-compound BXT-51072 for 1 hours inhibits the morphological modifications induced by hydrogen peroxide. This GPx mimic can also prevent the alterations of the endothelial cytoskeleton which are induced by Tumor Necrosis Factor-alpha (TNF-alpha) and which consist in a reorganization of actin filaments with the formation of stress fibers. Fluorescent labeling of polymerized actin has been performed by means of phalloidine coupled with rhodamine. The protective effect of this antioxidant catalyst against the toxicity of hydrogen peroxide and TNF-alpha includes the maintenance of a structural configuration of the cytoskeleton which is required for the function of endothelial barrier.

New selenium-containing compounds behave as GPx mimics and protect endothelial cells (HUVEC) from damage upon exposure to 55 microM linoleic acid hydroperoxide or to 200 microM hydrogen peroxide. The simultaneous presence of the GPx mimic and the hydroperoxyde is not necessary, since a pre-treatment of endothelial monolayers with 1 to 10 microM of such compounds, preserves their morphology, their cell density and their longer-term viability. The compounds which are most efficient in this model of oxidative stress also protect endothelial monolayers which have been incubated with an excess (10:1) of polymorphonuclear neutrophils (PMN) and with 1 ng/ml of TNF-alpha, if such monolayers are pre- and co-treated (10 microM). They inhibit the adhesion of activated neutrophils which show-up as polymorphous and very dense particles, in the vicinity of which endothelial alterations can be seen. The inhibition of leucocyte adhesion and that of endothelial activation/alteration have been quantified by means of immunoassays of myeloperoxidase and von Willebrand factor (vWf). The lead-compound BXT-51072 is not a direct inhibitor of the NADPH oxidase of PMN. TNF-alpha alone induces the endothelial release of Interleukin-8 (Il-8) as well as the expression of P- and E-selectin. The extent and the kinetics of inhibition of such processes by compound BXT-51072 would explain several of the effects observed in the presence of PMN. The GPx mimics also inhibit the endothelial production of Il-8 which is induced by Interleukin-1 alpha. Finally, compound BXT-51072 inhibits the endothelial expression of the adhesion factor VCAM-1 which is more slowly induced by TNF-alpha. Such antioxidant catalysts therefore protect endothelial cells from the toxic effects of TNF-alpha through mechanisms which include a down-regulation of cytokines and cell-adhesion factors.