Background\r\nDown syndrome (DS) neurons are more susceptible to oxidative stress and previous studies have shown that vitamin E was able to reduce oxidative stress and improve DS neurons'' viability. Therefore, this study was done to investigate the protective role of ?-tocotrienol (?T3) in DS neurons from hydrogen peroxide (H2O2) -induced oxidative stress. The pro-apoptosis tendency of ?T3 was compared to a-tocopherol (aT) in non-stress condition as well.\r\nMethods\r\nPrimary culture of DS and euploid neurons were divided into six groups of treatment: control, H2O2, ?T3 pre-treatment with H2O2, ?T3 only, aT pre-treatment with H2O2 and aT only. The treatments were assessed by MTS assay and apoptosis assay by single-stranded DNA (ssDNA) apoptosis ELISA assay, Hoechst and Neu-N immunofluorescence staining. The cellular uptake of ?T3 and aT was determined by HPLC while protein expressions were determined by Western blot. Comparison between groups was made by the Student''s t test, one-way ANOVA and Bonferroni adjustment as well as two-way ANOVA for multiple comparisons.\r\nResults\r\nOne day incubation of ?T3 was able to reduced apoptosis of DS neurons by 10%, however ?T3 was cytotoxic at longer incubation period (14 days) and at concentrations = 100 �µM. Pre-treatment of aT and ?T3 only attenuate apoptosis and increase cell viability in H2O2-treated DS and euploid neurons by 10% in which the effects were minimal to maintain most of the DS cells'' morphology. ?T3 act as a free radical scavenger by reducing ROS generated by H2O2. In untreated controls, DS neurons showed lower Bcl-2/Bax ratio and p53 expression compared to normal neurons, while cPKC and PKC-d expressions were higher in DS neurons. On the other hand, pre-treatment of ?T3 in H2O2-treated DS neurons have reduced Bcl-2/Bax ratio, which was not shown in euploid neurons. This suggests that pre-treatment of ?T3 did not promote DS cell survival. Meanwhile ?T3 and aT treatments without H2O2 as well as pre-treatment of ?T3 and aT induced changes in cPKC and PKC-d expression in DS neurons suggesting interaction of ?T3 and aT with PKC activity.\r\nConclusion\r\nOur study suggests that ?T3 pre-treatment are not sufficient to protect DS neurons from H2O2-induced oxidative assault, instead induced the apoptosis process.
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