Effects of tocotrienols on caspase-8 activities of A549 and U87MG cells. (A) Alpha-, (B) gamma- and (C) delta-tocotrienols show distinguished effects on caspase-8 activities of untreated and treated A549 and U87MG cells for 1 h treatment period at the concentrations of IC50, IC80 and ICmax with or without caspase-8 inhibitor, z-IETD-fmk (10 μM and 30 μM). Generally, alpha-, gamma- and delta-tocotrienols are able to trigger caspase-8 activities in both treated A549 and U87MG cells. All tocotrienol isomers induced approximately 2 times greater caspase-8 activation in U87MG cells as compared to A549 cells. α-T3: alpha-tocotrienol; γ-T3: gamma-tocotrienol; δ-T3: delta-tocotrienol.