Evidence for the nitration of γ-tocopherol in vivo: 5-nitro-γ-tocopherol is elevated in the plasma of subjects with coronary heart disease

Abstract

This study investigated the hypothesis that nitration of gamma-tocopherol may be an important mechanism for the detoxification of reactive nitrogen oxide species in vivo. Using liquid chromatography-tandem MS we have shown that gamma-tocopherol can be nitrated in vivo to form 5-nitro-gamma-tocopherol and that concentrations of this compound are elevated in the plasma of subjects with coronary heart disease. In addition, we demonstrate in carotid-artery atherosclerotic plaque that nitration of gamma-tocopherol is also evident at levels similar to that seen in the plasma of subjects with coronary heart disease.

Analysis of plasma tocopherols α, γ, and 5-nitro-γ in rats with inflammation by HPLC coulometric detection

“…Possible artefactual nitration of ␥T during analysis was excluded by appropriate in vitro experiments. Compared to the analysis of NGT using LC-MS (18) or CoulArray detection (29), the present method requires somewhat less expensive equipment and, at the same time, offers an at least 50-fold higher sensitivity.…”

“…Also, a CoulArray system is considerably more expensive. More recently, an LC-MS/MS method was described and used for the measurement of NGT in plasma of normal human subjects and subjects with coronary heart disease (18). The advantage of this method is that NGT is unambiguously analyzed by specific detection of the nitrated chomanol ring fragment.…”

“…␤ -tocopherol is not separated from ␥ T under reversed-phase conditions, but constitutes only a minor fraction ( Ͻ 10%) in blood plasma and other tissues of rats (16) and humans (17). Also, 7-nitro-␤ -tocopherol elutes before NGT under reversed- (18). After the first 20 min, non-polar lipids and other interfering substances were washed off the column by running a linear gradient from the initial mobile phase to tertbutanol-methanol (50:50, v/v) within 20 min.…”

Reaction Products of γ-Tocopherol with (E)-4-Oxo-2-nonenal in Acidic Acetonitrile

“…14) 5-Nitro--tocopherol has been detected in human plasma and in plant tissues, and is considered to be a biomarker for oxidative stress. 15,16,26) -Tocopherol has also reacted with hypochlorous acid, a potential biological oxidant and electrophile, to form 5-chloro--tocopherol and other chlorinated products.…”

“…14) It has been demonstrated that -tocopherol was a target for nitration in vivo since the concentration of 5-nitro--tocopherol was elevated in the plasma of subjects with coronary heart disease 15) and in the plasma of smokers. 16) Supplementation with -tocopherol resulted in a significant reduction of urinary nitrotyrosine, a biomarker of nitrosative stress, in subjects with metabolic syndrome.…”