Evaluation of the effect of z-VAD-fmk, inhibitor of effector caspases, and of L-NAME, inhibitor of NOS, on the TRAIL-mediated cytotoxicity.

At 6 and 24 hours after TRAIL treatment, viable cells were counted by trypan blue dye exclusion (A, data are expressed as percentage of His peptide–treated controls) and the percentage of apoptosis was quantitatively evaluated by flow cytometry after PI staining (B). Data represent the means ± SDs of 5 independent experiments performed in duplicate. Panel C shows the percentage of cells incorporating BrdU, evaluated by flow cytometry, in samples treated for 16 hours with TRAIL or His peptide in the presence or absence (vehicle) of the indicated inhibitors. In panel D, NOS activity was evaluated in cells treated with TRAIL or His peptide in the absence or presence of z-VAD-fmk. In panels C and D, data represent the means ± SDs of 3 separate experiments performed in duplicate.