Antioxidant action of vitamin E in vivo as assessed from its reaction products with multiple biological oxidants

Vitamin E acts as essential antioxidant against detrimental oxidation of biological molecules induced by multiple reactive species. To gain more insight into the physiological role of vitamin E, the levels of its oxidation products in humans under normal and pathological conditions were compared. alpha-Tocopherol quinone (alpha-TQ) and 5-nitro-gamma-tocopherol (5-NgT) were focused. alpha-TQ is produced by multiple oxidants including oxygen radicals, peroxynitrite, hypochlorite, singlet oxygen, and ozone, while 5-NgT is produced by nitrogen dioxide radical derived from peroxynitrite and the reaction of nitrite and hypochlorite. The reported concentrations of alpha-TQ and 5-NgT in healthy human plasma are highly variable ranging from 15 to 360 and 4 to 170 nM, respectively. In general, the molar ratio 5-NgT/gamma-tocopherol was higher than the ratio alpha-TQ/alpha-tocopherol. Both absolute concentrations of alpha-TQ and 5-NgT and the molar ratios to the parent tocopherols were elevated significantly in the plasma of patients with various diseases compared with healthy subjects except neurological diseases. The molar ratios of the products to the respective parent compounds decreased in the order of 5-NgT/gamma-tocopherol > alpha-TQ/alpha-tocopherol > hydroxyoctadecadienoate/linoleate > 3-nitrotyrosine/tyrosine > isoprostane/arachidonate. The molar ratios of nitrated products to the respective parent compounds in human plasma are approximately 10(-2) for 5-NgT and 10(-5) for 3-nitrotyrosine, nitro-oleic acid, and 8-nitroguaine. These data indicate that vitamin E acts as an important physiological antioxidant and that alpha-TQ and 5-NgT represent biomarker for oxidative stress and nitrative stress respectively.

Automated summary

Vitamin E acts as an important physiological antioxidant, with alpha-TQ and 5-NgT serving as biomarkers for oxidative stress and nitrative stress respectively. The concentrations of these oxidation products in human plasma vary under different health conditions, indicating their potential role in disease diagnosis and treatment.