Tumor necrosis factor (TNF) and its related ligands TNF-related apoptosis inducing ligand (TRAIL) and Fas ligand (FasL) play roles in the regulation of vascular responses, but their effect on the formation of new blood vessels (angiogenesis) is unclear Therefore, we have examined the effects of these ligands on angiogenesis modeled with primary Cultures of human umbilical vein endothelial cells (HUVEC). To examine angiogenesis in the context of the central nervous system. we have also modeled cerebral angiogenesis with the human brain endothelial cell line hCMEC/D3. Parameters Studied were bromodeoxyuridine (BrdU) incorporation and cell number (MTT) assay (to assess endothelial proliferation), scratch assay (migration) and networks on Matrigel (tube formation). In Our hands, neither TRAIL nor FasL (1, 10, and 100 ng/ml) had an effect on parameters of angiogenesis in the HUVEC model In hCMEC/D3 cells by contrast, TRAIL inhibited all parameters (10-100 ng/ml, 24 h) This was due to apoptosis, since its action was blocked by the pan-caspase inhibitor zVADfmk (5 x 10(-5) mol/l) and TRAIL increased caspase-3 activity 1 h after application. However FasL (100 ng/ml) increased BrdU uptake without other effects We conclude that TRAIL has different effects on in vitro angiogenesis depending on which model is used, but that FasL is generally ineffective when applied in vitro The data suggest that TRAIL primarily influences angiogenesis by the induction of vascular endothelial apoptosis, leading to vessel regression. (C) 2009 Elsevier Inc All rights reserved.