Attenuation of caspase-3-dependent apoptosis by Trolox post-treatment of X-irradiated MOLT-4 cells

Purpose: The relationship between post-irradiation treatment with Trolox, a n antioxidant that inhibits lipid peroxidation, and X-ray-induced apoptosis , with regard to signal transduction pathways, was examined in MOLT-4, a hu man leukaemia cell line. Materials and methods: In MOLT-4 cells treated with Trolox after X-irradiat ion, viability, DNA fragmentation, expression of p53 BCL-2, BAX, active SAP K/JNK, active caspase-3 and the cleavage of PARP were measured by the trypa n blue exclusion test, agarose pel electrophoresis and Western blotting. Results: Stained cells and ladder-like DNA cleavage were observed after X-i rradiation. Cell death and DNA fragmentation were significantly inhibited b y the post-irradiation treatment with Trolox. The expression of p53 and act ive SAPK/JNK was increased after X-irradiation, and fragments of PARP and t he activated fragment of caspase-3 were produced. Post-irradiation treatmen t with Trolox attenuated the X-irradiation-induced expression, fragmentatio n or activation of these apoptosis-related biomolecules. The expression of BCL-2 and BAX, which would occur downstream from p53, was not changed by ir radiation and Trolox treatment. Furthermore, cell death was associated with caspase-3 because the ladder-like DNA cleavage was completely inhibited by Ac-DEVD-CHO but not Ac-YVAD-CHO, TLCK and PMSF. Conclusion. Post-irradiation events such as membrane damage induce caspase- 3-dependent apoptosis, which might be mediated by the activation of SAPK/JN K and be independent of p53.