Search

BACKGROUND: The global obesity epidemic has sobering consequences to human health. Especially concerning is obesity-associated hepato-steatosis (HS), a common cause of chronic liver disease in the Americas and Western Europe that precedes non-alcoholic steatohepatitis (NASH). Maintenance of normal body weight is the only current means to prevent HS and NASH. We hypothesized that excess liver fat in obesity-associated HS could act as a pathophysiologic chemical depot for fat-soluble vitamins and alter normal physiology. Because clinical trials with Vitamin E (α-T) have shown that NASH partially responds to this supplement, we selected α-T as a model vitamin to test the sequestration hypothesis. INTERVENTIONS: Under an IND and IRB-approved protocol, two deuterium-labeled α-tocopherols (d3-α-T and d6-α-T) were administered orally and intravenously, respectively, to 10 healthy women and 6 women with HS. Serial blood samples obtained over 72 h were analyzed by LC-MS/MS. In parallel, we performed studies in hepatocytes in cell culture and mouse model. RESULTS: In healthy women who received oral d3- and intravenous d6-α-T, 85% of the initial plasma peak d6-α-T disappeared within 20 minute and reappeared in the plasma peaking between 6-8 h. Compared to healthy subjects, subjects with HS had similar d6-α-T entry rates into liver, but reduced release rates into plasma (p CONCLUSION: These findings suggest the unique role of the liver in vitamin E physiology which is dysregulated by excess liver fat (measured by magnetic resonance spectroscopy). Considered together, the findings imply that obesity-associated HS may produce unrecognized hepatic α-T sequestration, which might subsequently drive liver disease. The data here raise the intriguing possibility that timely α-T supplementation might attenuate progression of HS to NASH, perhaps by correcting an unrecognized fat-induced, localized, hepatic vitamin E deficiency prior to onset of inflammation, hepatitis, and fibrosis. Additionally, our findings raise the possibility that HS may similarly alter hepatic physiology of other fat-soluble vitamins.

Vitamin E disappearance is accelerated in cigarette smokers due to their increased oxidative stress and is inversely correlated with plasma vitamin C concentrations. Therefore, we hypothesized that ascorbic acid supplementation (500 mg, twice daily; 2 weeks) would normalize smokers' plasma alpha- and gamma-tocopherol disappearance rates and conducted a double-blind, placebo-controlled, randomized crossover investigation in smokers (n=11) and nonsmokers (n=13) given a single dose of deuterium-labeled alpha- and gamma-tocopherols (50 mg each d6-RRR-alpha and d2-RRR-gamma-tocopheryl acetate). During the placebo trial, smokers, compared with nonsmokers, had significantly (P0.05) greater alpha- and gamma-tocopherol fractional disappearance rates and shorter half-lives. Ascorbic acid supplementation doubled (P0.0001) plasma ascorbic acid concentrations in both groups and attenuated smokers', but not nonsmokers', plasma alpha- and gamma-tocopherol (P0.05) fractional disappearance rates by 25% and 45%, respectively. Likewise, smokers' plasma deuterium-labeled alpha- and gamma-tocopherol concentrations were significantly higher (P0.05) at 72 h during ascorbic acid supplementation compared with placebo. Ascorbic acid supplementation did not significantly change (P0.05) time of maximal or maximal-labeled alpha- and gamma-tocopherol concentrations. Smokers' plasma F2alpha-isoprostanes were approximately 26% higher than nonsmokers (P0.05) and were not affected by ascorbic acid supplementation in either group (P0.05). In summary, cigarette smoking increased plasma alpha- and gamma-tocopherol fractional disappearance rates, suggesting that the oxidative stress from smoking oxidizes tocopherols and that plasma ascorbic acid reduces alpha- and gamma-tocopheroxyl radicals to nonoxidized forms, thereby decreasing vitamin E disappearance in humans.

We hypothesized that the high concentrations of reactive nitrogen species in cigarette smoke and the known stimulatory effects of cigarette smoke on the inflammatory immune systems would lead to the formation of 5-nitro-gamma-tocopherol (NGT). In order to assess gamma-tocopherol nitration, human plasma was exposed in vitro to gas phase cigarette smoke (GPCS) or air for up to 6 h. A liquid chromatography-mass spectrometry (LC-MS) method was developed to quantitate NGT. Detector response was linear from 0.1 to 3 pmol NGT, with a detection limit of 20 fmol. After a 1 h lag time, 6 h plasma exposure to GPCS depleted approximately 75% of alpha-T, approximately 60% of gamma-T and increased NGT from 3 to 134 nmol/l. The increase in NGT accounted for approximately 20% of the gamma-T decrease. NGT also correlated (R2 = 0.9043) with nitrate concentrations in GPCS-exposed plasma. The physiologic relevance of NGT was evaluated in a group of healthy humans. Smokers (n = 15) had plasma NGT concentrations double those of nonsmokers (n = 19), regardless of corrections using lipids or gamma-T; plasma alpha-T and gamma-T concentrations were similar between the groups. Our results show that LC-MS can be successfully used for NGT quantitation in biologic samples. Importantly, NGT in smokers' plasma suggests that cigarette smoking causes increased nitrosative stress.