|Lai, Chao Qiang|
Submitted to: Journal of Free Radical Biology and Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2010
Publication Date: 12/1/2010
Citation: Zingg, J., Libinaki, R., Lai, C., Meydani, M., Gianello, R., Ogru, E., Azzi, A. 2010. Modulation of gene expression by alpha-tocopherol and alpha-tocopheryl phosphate in thp-1 monocytes. Journal of Free Radical Biology and Medicine. 49:1989-2000. Interpretive Summary: In this study we compared the cellular effects of vitamin E (alpha-tocopherol, alphaT) with that of a recently discovered variation of vitamin E (alpha-tocopheryl phosphate, alphaTP). alphaTP can be isolated from food and animal tissues in small amounts and is formed in small amounts from alphaT in cultured cells and animal tissues. The molecular function of alphaTP is not yet clear but it could have an important impact on the cellular effects of alphaT. We reported on the measurements of alphaTP in the blood of rats, minipigs and humans. To assess a possible function of alphaT and alphaTP in modifying cell reactions, we have compared their effects on cell growth and gene expression. As assessed by gene expression microarrays, more genes are regulated by alphaTP than by alphaT. The expression of one gene, the vascular endothelial growth factor (VEGF), is induced by alphaTP due to activation of protein kinase B (PKB/Akt). In the body, alphaTP may be relevant for cell survival, wound repair and tissue stability in several physiological conditions; higher concentrations of alphaTP could be used to normalize several pathological conditions in the nervous system and heart and reduce pathological angiogenesis.
Technical Abstract: The naturally occurring vitamin E analogue, alpha-tocopheryl phosphate (alphaTP), has been reported to be more potent than the un-phosphorylated alpha alpha-tocopherol (alphaT). We have now measured plasma levels of alphaTP and compared the cellular effects of alphaTP and gamma-tocopheryl phosphate (gammaTP) in THP-1 monocytic leukaemia cells. alphaT slightly increases cell proliferation, whereas alpha'TP and more potently gammaTP inhibit it. The inhibitory effect requires cellular uptake of alphaTP and gammaTP, as determined by using the transport inhibitor, glybenclamide. In contrast, CD36 surface expression is inhibited by alphaTP in a glybenclamide-insensitive manner and occurs within hours, suggesting that alphaTP, as other anionic lipids, may bind to CD36 and/or trigger its internalization. As assessed by gene expression microarrays, more genes are regulated by alphaTP than by alphaT, and only for some genes the expression levels of alphaT-regulated genes correlated with the ones of alphaTP. Among a set of genes that was confirmed by quantitative real time RT-PCR, the expression of the vascular endothelial growth factor (VEGF) is induced by alphaTP as a result of activation of protein kinase B (PKB/Akt) and is associated with increased levels of reactive oxygen species (ROS). Increased Akt(Ser473) phosphorylation and induction of ROS by alphaTP occur in a wortmannin-sensitive manner indicating the involvement of phosphatidylinositol kinases. The level of Akt(Ser473) phosphorylation and ROS production is determined by the ratio between alpha T and alpha TP. Thus, alpha TP and alpha T influence cell proliferation, ROS production and the level of Akt(Ser473) phosphorylation in an antagonistic manner most likely by modulating phosphatidylinositol kinases.