Effects of tumor necrosis factor on prostacyclin production and the barrier function of human endothelial cell monolayers

The endothelium controls the influx of macromolecules into the tissues, a process that may be disturbed at sites of inflammation and in atherosclerotic plaques. In this article, we report our evaluations of the effects of the inflammatory mediator, tumor necrosis factor-alpha (TNF-alpha), on the production of prostacyclin and the barrier function of human endothelial cell monolayers in an in vitro model. TNF-alpha (500 units/ml) had no direct effect on the passage of sucrose, peroxidase, and low density lipoprotein through monolayers of human aortic endothelial cells. On the other hand, during the first hours after addition 500 units/ml TNF-alpha induced a reduction of the permeability of umbilical artery endothelial cell monolayers. Within 10 minutes TNF-alpha induced an increase in prostacyclin production by primary cultures of umbilical artery endothelial cells. However, the reduction in permeability was not caused by a change in prostacyclin production or by a change in cyclic AMP concentration because 1) the effect of TNF-alpha on permeability was not prevented by aspirin, 2) no change in the cellular cyclic AMP concentration could be observed after addition of TNF-alpha, and 3) TNF-alpha was still able to reduce the passage rate in the presence of 25-mu-M forskolin. The reduction in permeability was accompanied by a decrease of F-actin in stress fibers. With prolonged incubation with TNF-alpha, the permeability of umbilical artery endothelial cell monolayers increased, and F-actin was found again in stress fibers. However, these effects of TNF-alpha were only significant at high concentrations of TNF-alpha. Because high TNF-alpha concentrations only persist in vivo for short periods and no increase in the permeability of human aortic endothelial permeability was observed after incubation with TNF-alpha, it is unlikely that TNF-alpha plays a role in the increased permeability that has been found in human arteriosclerotic lesions

Perivenous support reduces early changes in human vein grafts:Studies in whole blood perfused human vein segments

Background: Patency of vein grafts in coronary artery bypass grafting procedures is generally less favorable than those of selected arterial grafts. However, vein grafts still are needed in cardiac operations. It would be desirable to find measures to improve the patency of vein grafts next to antithrombotic regimens. Animal studies demonstrated that arterial pressure induces overdistention of the thin-walled vein grafts and that prevention of this overdistention with extravascular support ameliorates the arterialization process with, subsequently, more favorable patency. To evaluate whether perivenous stenting of the rather muscular human vein grafts is also beneficial, we designed an in vitro model to study the early effects of perivenous support in human vein grafts. Methods: Seven paired segments of human vein graft obtained during coronary artery bypass grafting procedures were placed in a perfusion circuit and perfused simultaneously with autologous whole blood, with a pressure of 60 mm Hg (nonpulsatile flow). After 30 minutes of perfusion, one segment, and after 60 minutes of perfusion, the remaining segment were taken for histologic and immunohistochemical examination. In the next experiments 7 segments of human vein graft were placed in the circuit and supported with a polytetrafluoroethylene graft to prevent overdistention with 7 unstented segments as controls. Results: In unsupported vein grafts perfused with autologous blood under a pressure of 60 mm Hg, a complete de-endothelialization was shown after I hour of perfusion. In the study vein grafts, with a perivenous polytetrafluoroethylene graft preventing overdistention (n = 7), the endothelium remained intact. Electron microscopic investigation of the media showed severe damage in the circular smooth muscle layer in the unstented group, whereas in the stented group almost no injury was found. Conclusion: In our in vitro closed-loop model, reproducible vessel wall changes were observed in all human vein graft specimens studied. The beneficial effect of perivenous support could also be established for the human greater saphenous vein, providing a basis for clinical application