Biological Redox Impact of Tocopherol Isomers Is Mediated by Fast Cytosolic Calcium Increases in Living Caco-2 Cells

Abstract

Most of the biological impacts of Vitamin E, including the redox effects, have been raised from studies with α-tocopherol only, despite the fact that tocopherol-containing foods carry mixed tocopherol isomers. Here, we investigated the cellular mechanisms involved in the immediate antioxidant responses evoked by α-, γand δ-tocopherol in Caco-2 cells. In order to track the cytosolic redox impact, we performed imaging on cells expressing HyPer, a fluorescent redox biosensor, while cytosolic calcium fluctuations were monitored by means of Fura-2 dye and imaging. With this approach, we could observe fast cellular responses evoked by the addition of α-, γand δ-tocopherol at concentrations as low as 2.5 µM. Each isomer induced rapid and consistent increases in cytosolic calcium with fast kinetics, which were affected by chelation of extracellular Ca 2+ , suggesting that tocopherols promoted a calcium entry upon the contact with the plasma membrane. In terms of redox effects, δ-tocopherol was the only isomer that evoked a significant change in the HyPer signal at 5 µM. By mimicking Ca 2+ entry with ionomycin and monensin, a decline in the HyPer signal was induced as well. Finally, by silencing calcium with 1,2-bis(o-aminophenoxy)ethane-N,N,N ,N -tetraacetic acid (BAPTA), an intracellular Ca 2+ chelator, none of the isomers were able to induce redox changes. Altogether, our data indicate that an elevation in cytoplasmic Ca 2+ is necessary for the development of a tocopherol-induced antioxidant impact on the cytoplasm of Caco-2 cells reported by HyPer biosensor.

Tocotrienol in Pre-Eclampsia Prevention: A Mechanistic Analysis in Relation to the Pathophysiological Framework

“…Vitamin E has been actively investigated for its effects in managing pre-eclampsia, because it could tackle several pathophysiological pathways of the disease, theoretically. Firstly, vitamin E is a well-established antioxidant [ 45 , 46 ] that can suppress the oxidative damage caused by repeated placental ischaemia/reperfusion. Secondly, vitamin E and its metabolites are anti-inflammatory agents [ 47 , 48 , 49 ] that could suppress systemic inflammation caused by the release of damage-associated molecules.…”

Vitamin E beyond Its Antioxidant Label

“…In colon cancer cell lines, TFs were found to exhibit an anti-inflammatory effect and promoted apoptosis (especially δ-TF) in an IFNγ/PMA model [ 87 ], suppressing the activation of NF-κB (α-TF and γ-TF) and enhancing the Nrf2 pathway (δ-TF) [ 88 ]; their overall effect on antioxidant defense also seemed to be dependent on an elevation of cytoplasmic Ca 2+ [ 89 ]. Moreover, γ-TF increased PPARγ mRNA and protein expression (more efficiently versus α-TF or troglitazone), with possibly important implications in inflammatory diseases [ 90 ].…”

Induction of Exocytosis Rescues Lysosomal GM2 Accumulation in Tay-Sachs Disease

“…Tocopherol and cyclodextrin have been reported to be used as therapeutic small drugs to alleviate lipid accumulation and recuperate enlarged lysosomes in several LSDs as they enhance lysosomal exocytosis through increment of cytosolic and lysosomal Ca 2+ level [19]. The exact mechanism of action is unclear, but it was reported that tocopherol isomers evoked fast Ca 2+ responses with an increase in cytosolic Ca 2+ [20]. It was also shown that tocopherol caused exocytosis of related vesicles, such as endocytic ones [21].…”