DHA induced caspase-3 activation in ASTC-a-1 cells. Cells were incubated with 1 μM STS for 12 h, 20 μg/m1 DHA for 48 h and co-treatment with 20 μg/m1 DHA and 10 μM Z-VAD.fmk for 48 h, and then were analyzed by caspase-3 activity and Western Blot assay. a Caspase-3 activity was measured using the fluorescence substrate Ac-DEVD-AFC as described in Materials and Methods. The activation index was determined as the ratio between the activity in treated cells and untreated cells. Data analyzed with SPSS10.0 software is representative of three identical experiments. **P < 0.01, compared with control cells; ##P < 0.01, compared with only DHA-treated cells. b The cells were treated with STS as a positive control showed the decreased proform and the increased cleavage of caspase-3. DHA-treated cells also showed the loss of the proform and appearance of cleaved caspase-3 compared with control. Moreover, DHA-induced caspase-3 activation was blocked under the co-treatment with DHA and Z-VAD.fmk.