Mechanisms underlying the radioprotective properties of γ-tocotrienol: comparative gene expression profiling in tocol-treated endothelial cells

Among the eight naturally occurring vitamin E analogs, gamma-tocotrienol (GT3) is a particularly potent radioprophylactic agent in vivo. Moreover, GT3 protects endothelial cells from radiation injury not only by virtue of its antioxidant properties but also by inhibition of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase and by improving the availability of the nitric oxide synthase cofactor tetrahydrobiopterin. Nevertheless, the precise mechanisms underlying the superior radioprotective properties of GT3 compared with other tocols are not known. This study, therefore, examined the differences in gene expression profiles between GT3 and its tocopherol counterpart, gamma-tocopherol, as well as between GT3 and alpha-tocopherol in human endothelial cells. Cells were treated with vehicle or the appropriate tocol for 24 h, after which total RNA was isolated and genome-wide gene expression profiles were obtained using the Illumina platform. GT3 was far more potent in inducing gene-expression changes than alpha-tocopherol or gamma-tocopherol. In particular, GT3 induced multiple changes in pathways known to be of importance in the cellular response to radiation exposure. Affected GO functional clusters included response to oxidative stress, response to DNA damage stimuli, cell cycle phase, regulation of cell death, regulation of cell proliferation, hematopoiesis, and blood vessel development. These results form the basis for further studies to determine the exact importance of differentially affected GO functional clusters in endothelial radioprotection by GT3.