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-, γ- and 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-, γ- and 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 Ca2+, 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 Ca2+ 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 Ca2+ chelator, none of the isomers were able to induce redox changes. Altogether, our data indicate that an elevation in cytoplasmic Ca2+ is necessary for the development of a tocopherol-induced antioxidant impact on the cytoplasm of Caco-2 cells reported by HyPer biosensor.
Highlights
Vitamin E is a term that groups tocopherols and tocotrienols
Intestinal cells represent one of the first host barriers that interact with dietary compounds and are exposed to the potential antioxidant effect that some molecules possess, like tocopherol isomers, which, according to their relative abundance in food, are mainly represented by α- and γ-tocopherols followed by δ-tocopherol
We monitored the impact of short-term exposure of these three isomers on the cytoplasmic calcium level and redox status in living Caco-2 cells with a time resolution of seconds to minutes in order to visualize the first contact of these compounds with a cellular model for intestinal wall
Summary
Vitamin E is a term that groups tocopherols and tocotrienols. the concept has evolved to refer mainly to α-tocopherol, likely due to its high relative abundance in plasma and blood cells [1].This notion is changing ; the pharmacokinetics of the β, γ and δ isomers in the plasma of healthy individuals who were subjected to a single dose of a preparation enriched with one of the tocopherol isomers indicated that all the isomers reached circulation 8 h after intake of the respective isomer [2].Other studies performed in healthy individuals [3,4], as well as in patients diagnosed with diabetes mellitus type 2 [5] who followed a daily regimen of a realistic mixture of tocopherols for weeks, showed significant increases in the concentration of α- and γ-tocopherol in circulating blood cells and serum compared to a placebo group.On the other hand, the relative abundance of tocopherol isomers in food is quite diverse.Using electroanalytical techniques, Robledo et al compared the content of tocopherol isomers in edible oils such as corn, soybean and canola, among others. The concept has evolved to refer mainly to α-tocopherol, likely due to its high relative abundance in plasma and blood cells [1]. This notion is changing ; the pharmacokinetics of the β, γ and δ isomers in the plasma of healthy individuals who were subjected to a single dose of a preparation enriched with one of the tocopherol isomers indicated that all the isomers reached circulation 8 h after intake of the respective isomer [2]. Γ-tocopherol represented more than 65% of the total Vitamin E content [6]. This pattern of abundance for non-α-tocopherols is Antioxidants 2020, 9, 155; doi:10.3390/antiox9020155 www.mdpi.com/journal/antioxidants
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