Abstract 217: Vitamin E forms induce apoptosis, necrosis, and autophagy and caused accumulation of sphingolipid intermediates in human colon cancer cells

Abstract

Abstract Emerging evidence by us and others suggests that certain forms of vitamin E may be promising chemoprevention agents. Here we systemically investigated the effect and mechanism of different forms of vitamin E on the growth and death of human colon cancer HT29 and HCT116 cells. γ-tocopherol (γT), δ-tocopherol (δT), and γ-tocotrienol (γTE) inhibited the proliferation of HT29 and HCT116 cells in a time- and dose-dependent manner, with the potency of γTE > δT > γT. HCT116 cells appeared to be more sensitive to the treatment than HT29 cells. Studies using annexin V and propidium iodide staining revealed that γT (50 µM) and γTE (20 µM) induced externalization of phosphatidylserine and enhanced permeability of the plasma membrane, indicating apoptosis and necrosis. On the other hand, none of the treatments activate caspase-3 and PARP except in HCT116 by γTE at 20 µM. Interestingly, γT, δT and γTE enhanced expression of microtubule-associated protein light chain-3 II (LC3 II) in both HT29 and HCT116 cells, suggesting that these vitamin E forms may induce autophagy. Consistently, electromicroscopic results showed that after 14-h treatment, γTE (20 µM) induced extensive formation of autophagic vacuoles with intact cytoplasmic membrane and little induction of chromatin condensation in HCT116. Myriocin, a specific inhibitor of serine palmitoyltransferase, a key enzyme in de novo synthesis of sphingolipids, partially protected HT29 and HCT116 cells from γTE-induced cell death. Importantly, γTE caused marked accumulation of dihydrosphingosine and dihydroceramide but not ceramide or sphingosine as early as after 8-hour incubation. Because dihydrosphingosine is shown to be a potent inducer of cell death, these findings demonstrated that vitamin E may induce apoptosis, autophagy and necrosis in colon cancer cells by modulation of sphingolipid synthesis pathway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 217.