Fig 3. In vivo conversion of α-tocopherol to its quinone metabolite and quantification of intracellular concentrations of vitamin E and its metabolites in cells in vitro.

(A) To assess the in vivo conversion of αT to its quinone metabolite, stable deuterium-labelled α-tocopherol (d₄-αT) was dosed orally to Sprague-Dawley male rats. Four hours after the final dose, plasma and tissues were collected for bioanalytical quantification of d₄-αT and d₄-αTQ by LC-MS/MS. While <1% of deuterium-labeled αT was detected as the quinone in the plasma fraction, varying levels of quinone conversion were observed in the tissues assessed, ranging from ~2% (liver) to ~50% (small intestine). (B) Vitamin E (αT) and its metabolites, vitamin E quinone (αTQ) and vitamin E hydroquinone (αTHQ), were detected simultaneously in Q7 striatal cells under basal growth conditions or supplementation with αT or αTQ (10 μM, 24 h). Results displayed are mean ± SD, n = 6; results from 1 experiment representative of 3 similar experiments. (C) Stacked bar graphs showing the mean proportions of αT, αTQ, and αTHQ quantified simultaneously under basal, αT- or αTQ-supplemented conditions using the succinate capping methodology described in Methods.