Progress 10/01/03 to 05/01/09
Outputs
OUTPUTS: The interaction of alpha tocopherol (AT) with both monmeric (quercetin, catechin, epicatechin) and a polymeric polyphenol (lignin) has been examined under in vitro and in vivo conditions. Using both the oxidative stability index, OSI, (hydrophobic medium), and the oxygen radical absorbance capacity assay, ORAC, (hydrophobic medium) the interactions of AT with monomeric compounds gave inhibitory activity with th OSI while being additive with the ORAC. AT-lignin interaction was also additive with the OSI. ORAC was not tested. The overall data demonstrated that both the concentration of compounds and the medium in which reactants are dissolved or dispersed influences the results. The effect of monomeric (0.5% by wt of diet) and the polymeric polyphenol (1% & 5% by wt of diet) on tocopherol status in rats has been examined. All treatment resulted in a statistically significant (p <0.05)increase in liver tocopherol compared to controls. Since monomeric polyphenols are poorly absorbed and the polymeric polyphenol is not absorbed, these data suggest that the phenolic compounds tested might be exerting their effects intraluminally during digestion and absorption. A group of rats fed 1% and 5% cellulose a non absorbable, non-digestible, non phenolic polymer showed no change in tocopherol status. Furthermore, since lignin is a nonfermentable dietary component, it seems less likely that secondary enteric microbial metabolites might be causing the observed changes in tocopherol status. Thus, it is possible that polyphenolics protect AT from intraluminal oxidation during digestion. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
These results demonstrated that none of the in vitro tests predicted in vivo results. In vivo results indicate a positive effect of polyphenols on tocopherol status, but that the additional tocopherol offered no additional antioxidant protection. These data suggest that polyphenols spare tocopherol possibly at the digestion/absorption level and could be useful in future assessment of a DRI or similar estimate for polyphenols.
Publications
- No publications reported this period
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Progress 10/01/06 to 09/30/07
Outputs
Preliminary work from this laboratory has demonstrated that lignin, an insoluble fiber comprised of polymeric phenolic compounds, has antioxidant properties. To further test this hypothesis tocopherol stripped corn oil(SCO) was tested alone or in the presence of 2.5% lignin(SCOL) or 0.03% alpha tocopherol(SCOT). In addition, SCO in the presence of 2.5% cellulose(SCOC), an insoluble fiber comprised of polymeric glucose, was included as a control for the presence of particulates suspended in the oil. Both fibers were 200-400 mesh. Using an accelerated oxidation test, 400g samples were heated at 100C and aerated at 180mL per minute in 500mL gas washing bottles for seven hours. Primary and secondary oxidation products were measured by peroxide value(PV) and malonaldehyde by thiobarbituric acid(TBA) respectively. The following results were obtained:PV for SCO, SCOL, SCOC, and SCOT were 161.8, 40.7, 219.2, and 26.7(meq peroxide per kg. oil);TBA for the same samples were 8.9,
1.6, 9.8,and 1.0(mg malonaldehyde per kg.oil). Only the oil with lignin and alpha tocopherol had significantly lower PV and TBA values compared to controls(P<0.01).
Impacts
These studies demonstrate that lignin exhibits antioxidant properties in oil.
Publications
- No publications reported this period
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Progress 10/01/05 to 09/30/06
Outputs
Previous research from this laboratory indicated that flavonoids had a sparing effect on tocopherol levels of plasma and tissues of rats. Flavonoids offered no additional antioxidant activity when measured as F2 isoprostanes. The objective of this project is to study the interactions of tocopherols with flavonoids under two antioxidant quantifying methods to determine if either would be a useful tool for predicting in vivo action when two or more antioxidants are present. Quercetin, (+) catechin, and (-) epicatechin were selected for investigation due to their predominance in the human diet. The first quantification test investigated was the Oxidative Stability Index (OSI), a lipid based system. Previously completed results indicated that combining the alpha tocopherol with flavonoids inhibited the flavonoids antioxidant activity due to the pro-oxidant nature of the tocopherol under the experimental conditions. The second quantification test under investigation is the
Oxygen Radical Absorbance Capacity Assay (ORAC), a phosphate buffer based system. Alpha tocopherol and the flavonoids were prepared by in a 1:10 acetone: phosphate buffer solution. Concentrations tested ranged from 0.10μM to 100μM for tocopherol, 0.10μM to 6μM for (-) epicatechin and 0.05μM to 3μM for (+) catechin and quercetin. Samples were pipetted into 96-well plates with fluorescein indicator solution and 2,2'-Azobis(2-amidinopropane) dihydrochloride (AAPH), a free radical generator. Results are compared against a standard curve generated from trolox (a water soluble vitamin E analog) standards ranging from 1.56μM to 50μM. Results indicated that antioxidant activity of individual compounds increased as concentration increased , producing a dose response. In the range of 0.05μM to 1μM individual antioxidant activity results were as follows: quercetin> (-) epicatechin > (+) catechin > alpha tocopherol. Quercetin reached concentration
limits of the assay at 1μM, (+) catechin at 3μM, and (-) epicatechin at 5μM. Alpha tocopherol exhibited no antioxidant activity from 0.1 to 10μM, but showed activity in a dose dependent manner from 10μM through the 100μM sample, the highest concentration in this experiment. When adding tocopherol at a level of 25μM to each of the flavonoids results indicated an overall additive effect. Quercetin was additive between 0.2μM and 0.8μM, (+) catechin between 0.9μM to 3μM and (-) epicatechin between 0.5μM and 4μM. These results indicate that neither in vitro test mimics the results seen in vivo.
Impacts
Data will be useful for establishing dietary estimates for optimal plant phytochemical intakes.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
The function of antioxidants and flavonoids in human health are becoming increasingly important and may play a role in preventing heart disease and cancer. Therefore, it is important to understand how they interact. Previous research from this laboratory indicated that flavonoids produced a sparing effect of the tocopherol concentration in rat plasma and tissues. The three flavonoids that were chosen for this study are quercetin, (+) catechin, and (-) epicatechin because they are among the most commonly consumed. The objective of this project was to study the interactions of alpha tocopherol with flavonoids under three in vitro antioxidant quantifying methods for the purpose of comparison to the in vivo data. The first quantification test investigated was the Oxidative Stability Index (OSI), a lipid based system. Temperature was set at 100C. Tocopherol and flavonoids were added to 5ml of tocopherol stripped corn oil and stirred for 30 minutes at room temperature.
Alpha tocopherol readily dissolved in the oil, while the three flavonoids were suspended throughout the sample by the dry air bubbled into the sample. Concentrations for each ranged from 0.2 to 20mM. Results indicated that antioxidant activity of individual compounds increased as follows: (-) epicatechin, alpha tocopherol, quercetin, (+) catechin. Antioxidant activity increases with concentration to 5mM. At concentrations above 5mM, no significant increase is noted. In contrast to in vivo data, an inhibitory effect was observed for two of the tocopherol-flavonoid combinations. A 5mM concentration of each flavonoid plus 5mM alpha tocopherol resulted in inhibition of 47% for quercetin and 43% for (+) catechin when compared to alpha tocopherol alone. (-) Epicatechin was not inhibitory. Under the conditions for the OSI, a pro-oxidant activity for either tocopherol or flavonoid is being investigated. The second quantification test under investigation is the Oxygen Radical Absorbance
Capacity Assay (ORAC), a phosphate buffer based system. Alpha tocopherol and the flavonoids are prepared by dissolving in ethanol at 1% of total sample volume. Samples are then homogenized to incorporate the ethanol into the buffer solution. Concentrations range from 0.005mM to 0.5mM for the tocopherol and flavonoids. Preliminary results indicate that there is an inhibitory effect when combining alpha tocopherol with each of the three flavonoids.
Impacts
Studies of this nature should provide useful information to help establish a suggested or recommended intake of both vitamins and flavonoids. If interactions exist, one group of compounds could spare the other, thus changing existing dietary intake values.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
A previous report described the use of the oxidative stability index (OSI) to assess the antioxidant activity of various classes of flavonoids. The data correlated well with peroxide values and thus provided a rapid and facile method for measuring peroxidation. We have initiated studies to determine whether various nutrient antioxidants (vitamin E and vitamin C) interact with the non-nutrient flavonoids using the OSI.
Impacts
Studies of this nature should provide useful information to help establish a suggested or recommended intake of both vitamins and flavonoids. If interactions exist, one group of compounds could spare the other, thus changing existing dietary intake values.
Publications
- Harris, G. K., Willcox J. K. and Catignani G. L. 2004. Application of the oxidative stability index for assessing the antioxidant properties of flavonoids. Journal of Food Biochemistry, 28, 337-349.
- Willcox, J. K., Ash S. L. and Catignani G. L. 2004. Antioxidants and prevention of chronic diseases. Critical Reviews in Food Science and Nutrition, 44, 275-295.
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