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American Journal of Clinical Nutrition, Vol. 87, No. 6, 1723-1729, June 2008
© 2008 American Society for Nutrition

ORIGINAL RESEARCH COMMUNICATION

Sex differences in the inhibition of {gamma}-tocopherol metabolism by a single dose of dietary sesame oil in healthy subjects1,2,3

Jan Frank, Sangeun Lee, Scott W Leonard, Jeffrey K Atkinson, Afaf Kamal-Eldin and Maret G Traber

1 From the Department of Food Science, Swedish University of Agricultural Sciences, Uppsala, Sweden (JF and AK-E); the Department of Nutrition and Exercise Sciences (SL and MGT), and the Linus Pauling Institute (SWL and MGT), Oregon State University, Corvallis, OR; and the Department of Chemistry, Brock University, St Catharines, ON, Canada (JKA)

2 Supported by NIH grant DK 67930 (to MGT) and Swedish Research Council grant, Vetenskapsrådet, project no. 621-2003-4746 (to AK-E). JF was supported by a travel stipend from the Swedish University of Agricultural Sciences (Dnr 12.23-3272/02).

3 Address reprint requests and correspondence to MG Traber, Linus Pauling Institute, Oregon State University, Corvallis, OR 97331. E-mail: maret.traber{at}oregonstate.edu.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: {gamma}-Tocopherol has unique properties that may be beneficial in sustaining optimal human health, but hepatic vitamin E metabolism enhances {gamma}-tocopherol turnover.

Objective: Our aim was to determine the extent to which dietary sesame lignans alter human {alpha}- and {gamma}-tocopherol metabolism and elimination as carboxyethyl hydroxychromanols (CEHCs).

Design: Healthy participants (n = 5 women and 5 men) in a randomized, crossover study (with 4-wk washout) consumed muffins prepared with either corn oil or unrefined sesame oil (sesamin, 94 mg; sesamolin, 42 mg), along with a capsule containing a 1:1 molar ratio of deuterium-labeled d6-{alpha}- and d2-{gamma}-tocopherol acetates ({approx}50 mg each). Plasma and urine were collected up to 72 h; unlabeled and labeled tocopherol and CEHC concentrations were determined by liquid chromatography–mass spectrometry.

Results: Sesame oil muffin consumption in men, but not in women, decreased (P < 0.05) areas under plasma d2-{gamma}-CEHC concentration-time curves (area under the curve) and maximum concentrations. However, in both sexes urinary d2-{gamma}-CEHCs were decreased for 24 h following sesame oil muffin consumption.

Conclusions: In humans, {gamma}-tocopherol metabolism can be inhibited by the simultaneous consumption of {gamma}-tocopherol and sesame lignans. The observed differences between men and women with respect to vitamin E metabolism warrant further investigation.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
{gamma}-Tocopherol has unique properties that may be beneficial in sustaining optimal human health and preventing disease (1). For example, {gamma}-tocopherol as a result of the unsubstituted 5-position on the chromanol ring can scavenge reactive nitrogen species (RNS) (2). RNS damage in humans has been substantiated by the detection of higher 5-nitro-{gamma}-tocopherol concentrations in smokers (3) and Alzheimer's disease patients (4). {gamma}-Tocopherol reportedly inhibits thrombogenesis (5), decreases inflammation (6), as well as reduces cancer cell proliferation (7, 8). Moreover, {gamma}-tocopherol, but not {alpha}-tocopherol, levels were reduced in coronary heart disease patients (9-11), suggesting that there may be benefits in raising plasma {gamma}-tocopherol concentrations (5, 12).

Although the liver expresses the {alpha}-tocopherol transfer protein, which is responsible for salvaging {alpha}-tocopherol from the excretory pathway and returning it to the liver, hepatic metabolism appears to be a key factor in the discrimination between tocopherols (13). In the fruit fly Drosophila melanogaster, because the fly lacks {alpha}-tocopherol transfer protein, the selective accumulation of {alpha}-tocopherol has been attributed to metabolism of non-{alpha}-tocopherols (14). Vitamin E forms are metabolized to side chain–truncated, water-soluble carboxyethyl hydroxychromans (CEHCs) (15-18) and are excreted in urine (19-21) and bile (22, 23). Cytochrome P450 (CYP) enzymes catalyze the initial {omega}-hydroxylation of the side chain before its shortening by enzymes of the β-oxidation pathway (17, 18). Importantly, these processes have a higher catalytic activity toward the non-{alpha}-vitamers (15, 17).

Sesamin, an abundant lignan in sesame seeds and oils, when fed to rats, substantially increased plasma {gamma}-tocopherol, but not {alpha}-tocopherol concentrations (24, 25). In human hepatocellular liver carcinoma (HepG2) cell line and primary rat hepatocytes, sesamin inhibited the degradation of non-{alpha}-tocopherols to their corresponding CEHC metabolites (18, 26). Consistently, dietary sesame seeds or sesame lignans (sesamin and sesaminol) reduced the urinary excretion of {gamma}-CEHC in rats (21). Increased blood {gamma}-tocopherol concentrations in response to sesame lignan intake have also been reported in 2 controlled human studies (27, 28). Thus, the lack of {gamma}-tocopherol retention in blood is greatly influenced by hepatic metabolism.

Our previous studies using deuterium-labeled {alpha}- and {gamma}-tocopherols demonstrated that not only does {gamma}-tocopherol turn over faster than does {alpha}-tocopherol but that {gamma}-CEHC and {gamma}-tocopherol disappear from the plasma at the same rates (29). Moreover, women had a faster {gamma}-tocopherol disappearance rate than did men. These data suggest that vitamin E metabolism is critical in regulating plasma {gamma}-tocopherol concentrations in humans. To evaluate the hypothesis that the simultaneous consumption of vitamin E with sesame oil containing sesame lignans could decrease vitamin E metabolism and thus increase plasma {gamma}-tocopherol concentrations, a randomized, crossover study was carried out in both women and men. The participants consumed deuterium-labeled {alpha}- and {gamma}-tocopheryl acetates along with a breakfast containing either sesame or corn oil muffins; after a 4-wk washout, the subjects repeated the study with the opposite muffin.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Materials
{alpha}-5,7-(C2H3)2 tocopheryl acetate (d6-{alpha}-TAc) was a gift from Dr. James Clark of Cognis Nutrition and Health (LaGrange, IL). {gamma}-3,4-(2H) tocopheryl acetate (d2-{gamma}-TAc) was prepared from {gamma}-tocopherol as described (30). The d6-{alpha}- and d2-{gamma}-TAc were diluted in tocopherol-stripped corn oil at a 1:1 molar mixture, and gelatin capsules containing ~50 mg of each {alpha}- and {gamma}-TAc were prepared. The d6-{alpha}- to d2-{gamma}-tocopherol molar ratio was determined by liquid chromatography–mass spectrometry (LC-MS) to be 0.98. The internal standard, {alpha}-5,7,8-(C2H3)3 tocopheryl acetate (d9-{alpha}-TAc), was provided by Carolyn Good of The Bell Institute of Health and Nutrition (Minneapolis, MN) and was synthesized by Isotec, Inc (Miamisburg, OH). Cold-pressed, unrefined sesame oil (a gift from Henry Lamotte GmbH, Bremen, Germany) contained sesamin, 607 mg/100 g oil and sesamolin, 269 mg/100 g oil. For use as standards, 2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman ({alpha}-CEHC) and 2,7,8-trimethyl-2-(β-carboxyethyl)-6-hydroxychroman ({gamma}-CEHC) were gifts from WJ Wechter of Loma Linda University (Loma Linda, CA). Trolox, {gamma}-tocopherol, ascorbic acid, butylated hydroxy toluene (BHT), potassium hydroxide (KOH), lithium perchlorate, and β-glucuronidase (type H-1, contains minimum 300,000 U/g β-glucuronidase activity and minimum 10 000 U/g sulfatase activity) were obtained from Sigma-Aldrich (St. Louis, MO). Diethyl ether was obtained from Mallinckrodt Baker, Inc (Phillipsburg, NJ), and high-pressure liquid chromatography–grade methanol, ethanol, hexane, and glacial acetic acid were from Fisher (Fair Lawn, NJ).

Subjects
Healthy participants (5 women, 5 men) were recruited, and written informed consent was obtained before inclusion in the trial. Participants were not smokers, did not take any dietary supplements at least 3 wk before and during the study, and restricted their physical activity to <5 h/wk. Routine blood serum chemistry assays were performed at Good Samaritan Hospital (Corvallis, OR) and were within the normal limits for all subjects. For subject characteristics, see Table 1Go. The study protocol was approved by the Institutional Review Board at Oregon State University.


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  		TABLE 1. Subject characteristics and blood lipids at screening1

 
Experimental diets and study design
Corn and sesame oils used for the preparation of the muffins were equalized with respect to concentrations of {alpha}-tocopherol (17.9 mg/100 g corn oil; 15.6 mg/100 g sesame oil) and of {gamma}-tocopherol (84.9 mg/100 g corn oil; 84.0 mg/100 g sesame oil). The 2 muffins made with either oil contained {approx}13.0 mg {alpha}-tocopherol and 2.5 mg {gamma}-tocopherol. The 2 sesame oil muffins provided 135.4 mg sesame lignans (sesamin, 93.8 mg; sesamolin, 41.6 mg). Sesame oil or corn oil (with equalized vitamin E concentrations in each oil) was used to prepare muffins from 650 g wheat flour, 250 g sugar, 25 g baking powder, 10 g salt, 130 g whole egg, 440 g milk, and 275 g oil by mixing all ingredients and weighing 50 g of the resulting batter into each paper baking cup. Muffins were baked for 25 min at 205 °C and stored at –20 °C until used in the trials.

Subjects were randomly assigned to one of 2 treatments in a crossover design with a 4-wk washout period between treatments. A standard dinner was provided at 1800 on the evening before the trial, and subjects were instructed to abstain from all food and beverages, with the exception of water, overnight. In the morning, blood samples were drawn from the antecubital arm vein into tubes containing 0.05 mL 15% K3 EDTA (Vacutainer; Becton Dickinson, Franklin Lakes, NJ). Subsequently, a standardized breakfast was served, including 2 sesame oil or corn oil (control) muffins and a capsule containing {approx}50 mg each deuterated d6-{alpha}- and d2-{gamma}-tocopheryl acetates.

Blood samples were drawn 3, 6, 9, 12, 24, 36, 48, and 72 h after treatment. Meals were standardized during the period of 12 h before to 12 h after the dietary intervention, and the subjects recorded their food consumption during the 2 consecutive days. For separation of blood plasma, samples were centrifuged (500 x g, 15 min, 4 °C), the plasma snap frozen in liquid nitrogen, and stored at –80 °C until analyzed. Urine was collected 1 h before treatment on the first day of the trial; the urine bottles were exchanged at 0, 6, 12, 24, 36, 48, and 72 h after treatment. Urine volumes were recorded and 15 mL aliquots for each period were stored at –20 °C until analyzed. After a 4-wk washout period, treatments (sesame or corn oil muffins) were switched and the above procedures repeated.

Quantification of labeled and unlabeled plasma tocopherols
Tocopherols were extracted from plasma according to the method of Podda et al (31). Briefly, plasma was saponified with saturated alcoholic KOH and the tocopherols extracted with hexane. An appropriate aliquot was dried under N2-gas, the residue resuspended in MeOH:EtOH (1:1, by vol) containing d9-{alpha}-tocopherol as internal standard and injected into the LC system. For LC-MS analysis of labeled and unlabeled tocopherols, a Waters (Milford, MA) 2690 Separations Module equipped with a Symmetry LC-18 column (Waters; 4.6 x 75 mm, 3.5-µm particle size; mobile phase, 100% methanol; flow rate, 1 mL/min) and a negative atmospheric pressure chemical ionization probe was used as previously described (32).

Quantification of labeled and unlabeled plasm and urine CEHC metabolites
Plasma and urinary CEHCs were extracted using a modified method of Lodge et al (33). In brief, a known amount of trolox (internal standard) was added to either 0.5 mL plasma or 1 mL urine, before incubation for 30 min at 37 °C with 100 µL β-glucuronidase (10 mg/mL dissolved in 0.01 mol/L potassium phosphate buffer, pH 6.8), and 20 µL H2O containing 1% ascorbic acid. After incubation, the samples were acidified by the addition of 10 µL 12 mol/L HCl. CEHCs were extracted with 5 mL of diethyl ether, dried under nitrogen gas, and resuspended in H2O:MeOH (1:1, by vol) containing 0.1% (by vol) acetic acid, with 10 µL injected into the LC system described above equipped with a SymmetryShield RP-18 column (Waters; 3.0 x 150 mm, 3.5-µm particle size), and the solvent was delivered by a modified gradient method of Himmelfarb et al (34). The system was first equilibrated with 50:50 H2O:MeOH (both containing 0.1% acetic acid) for 1 min, followed by a linear gradient to 80% MeOH at 6 min at a flow rate of 0.25 mL/min. These conditions were maintained for 15 min, followed by a 5-min wash period with 95% MeOH, at which time original conditions were returned to and run for 5 min before injection of the proceeding sample. Samples were detected using a Micromass (Manchester, UK) ZQ 2000 single-quadrupole mass spectrometer with an electrospray ionization source [capillary voltage, 2.5 V; sample cone voltage, –30 V; desolvation temperature, 150 °C; desolvation gas (nitrogen) flow, 160 L/h; nebulizer gas (nitrogen) pressure, 80 psi; cone gas (nitrogen) flow, 50 L/h], dwell time per compound, 0.20 s. Single-ion recording mass-to-charge (m/z) ratios for molecular ions were as follows: d0-{alpha}-CEHC, m/z 277; d6-{alpha}-CEHC, m/z 283; d0-{gamma}-CEHC, m/z 263; d2-{gamma}-CEHC, m/z 265, and trolox, m/z 249. Sample CEHC concentrations were calculated from the ratio of the peak area of the corresponding ion to that of the internal standard trolox peak; deuterated CEHCs were calculated using the corresponding nondeuterated CEHC standards.

Quantification of plasma triacylglycerols and cholesterol and urinary creatinine
Plasma triacylglycerols and cholesterol were determined using the respective ThermoDMA Kits (Louisville, CO). Urinary creatinine was quantified spectrophotometrically at a wavelength of 500 nm after reaction with picric acid according to the Jaffé reaction (35).

Statistical analyses
The maximal concentrations (Cmax) and the time to reach maximal concentrations (Tmax) were identified by visual inspection of each individual's plasma concentration data. Areas under the curve (AUC) were calculated using the trapezoidal rule. Fractional disappearance rates (FDRs) of d6-{alpha}- and d2-{gamma}-tocopherols and d6-{alpha}- and d2-{gamma}-CEHCs were calculated separately for each individual as described previously (36). Repeated measures multivariate analysis of variance was performed using JMP Statistical Discovery software (version 5.0.1a; SAS Institute, Cary, NC) to evaluate effects attributed to oil type and to sex. When significant interactions were found, then an unpaired Student's t test for between-sex comparisons or a one-tailed, paired Student's t test for comparisons of the 2 treatments within the same subjects was carried out. Differences were considered significant at a P < 0.05 level. Data are expressed as means ± SEM unless otherwise noted.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Participant characteristics
All participants had normal blood levels of analytes measured in routine chemistry panels (data not shown) and were within the normal range for body mass index and blood lipids (Table 1Go). Men, compared with women, had significantly higher plasma {gamma}-tocopherol concentrations as well as serum total and LDL cholesterol at the time of screening; plasma {alpha}-tocopherol concentrations were similar in all subjects (Table 1Go). Neither plasma {alpha}-tocopherol nor {gamma}-tocopherol concentrations were different between men and women when expressed per serum total lipids (sum of cholesterol and triacylglycerols) because total lipid concentrations were lower in women than in men (P < 0.05).

No significant differences in the dietary intakes of macro- and micronutrients, including vitamin E, were observed between treatment groups or between men and women throughout the trials (data not shown).

Plasma tocopherols and CEHCs
With respect to plasma d6-{alpha}-tocopherol concentrations and calculated kinetic parameters, sesame oil compared with corn oil-containing muffins had no significant effects on any of these parameters (Figure 1Go A and Table 2Go). Specifically, plasma d6-{alpha}-tocopherol AUC, Cmax, and Tmax values did not differ between the treatments (Table 2Go). Participants' plasma unlabeled (d0)-{alpha}-tocopherol and d0-{gamma}-tocopherol concentrations were unresponsive to the type of muffin consumed (data not shown).


Figure 1
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  		FIGURE 1.. Mean (±SEM) plasma d6-{alpha}- and d2-{gamma}-tocopherol and d2-{gamma}-carboxyethyl hydrochromanols (CEHC) concentrations. Plasma d6-{alpha}-tocopherol (A), d2-{gamma}-tocopherol (B), and d2-{gamma}-CEHC (C) concentrations (µmol/L) following ingestion of muffins prepared from unrefined sesame oil (squares, dotted lines) or corn oil (triangles, solid lines) simultaneously with a capsule containing 50 mg each d6-{alpha}- and d2-{gamma}-tocophenyl acetates in men (n = 5, filled symbols) and in women (n = 5, open symbols). Plasma samples were collected periodically for 72 h. By 72 h, the d2-{gamma}- tocopherol (B) concentrations were below levels of detection for many subjects, and thus the means are not shown.

 

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  		TABLE 2. Kinetic parameters calculated from plasma d6-{alpha}-tocopherol, d2-{gamma}-tocopherol, and d2-{gamma}-carboxyethyl hydrochromanol (CEHC) concentrations in subjects consuming d6-{alpha}-tocophenyl acetate (TAc) and d2-{gamma}-TAc together with sesame oil or corn oil muffins, respectively1

 
In contrast, consumption of sesame oil compared with corn oil muffins delayed the time of the peak (Tmax) in the plasma kinetics of concurrently ingested d2-{gamma}-tocopherol in both men and women (Figure 1BGo and Table 2Go). The dietary treatments did not significantly alter any of the other parameters of d2-{gamma}-tocopherol kinetics (Table 2Go).

Differences between plasma {alpha}- and {gamma}-tocopherol concentrations have been attributed in part to increased {gamma}-tocopherol metabolism (13). Therefore, we sought to evaluate the efficacy with which sesame oil might alter vitamin E metabolism by measuring plasma CEHCs derived from the administered deuterated {alpha}- and {gamma}-tocopherols. Similar to our previous studies, no d6-{alpha}-CEHC was detected in plasma or urine (29), suggesting that the dose of d6-{alpha}-tocopherol was insufficient to be metabolized and detectable as plasma d6-{alpha}-CEHC.

In the present study, differences in d2-{gamma}-CEHC concentrations were observed with respect to the sesame oil treatment in men, but not in women (significant interactions between oil type and sex, for Cmax and AUC). Sesame oil consumption significantly (P < 0.05) decreased both plasma Cmax and d2-{gamma}-CEHC AUCs (Figure 1CGo and Table 2Go). Thus, sesame oil consumption in men not only delayed the Tmax of plasma d2-{gamma}-tocopherol concentrations (discussed above), it also halved the maximum plasma d2-{gamma}-CEHC concentrations and the AUCs. Remarkably, sesame oil consumption also decreased (P < 0.05) mean concentrations over 72 h of both plasma d0-{alpha}- and d0-{gamma}-CEHCs in men, but not in women (Figure 2Go).


Figure 2
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  		FIGURE 2.. Mean (±SEM) sesame oil consumption in men decreased plasma d0-{alpha} and d0-{gamma}-carboxyethyl hydrochromanol (CEHC) concentrations. Plasma d0-{alpha}-CEHC (A) and d0-{gamma}-CEHC (B) concentrations (nmol/L) from all samples from 3 to 72 h were averaged for each subject (n = 5 women, 5 men) following ingestion of corn oil (solid bar) or sesame oil (hatched bar) muffins. Repeated-measures multivariate ANOVA was performed using JMP Statistical Discovery software (SAS Institute, Cary, NC) to evaluate effects attributed to oil type and to sex. *Sesame oil consumption decreased plasma d0-{alpha}-CEHC concentrations (interaction P < 0.01: only in men, P < 0.05). There was a main effect of oil type on plasma d0-{gamma}-CEHC concentrations (P < 0.05).

 
Some notable differences in vitamin E kinetics were observed that were related only to sex differences. Women had significantly (P < 0.002, main effect) greater FDRs of plasma d6-{alpha}-tocopherol concentrations than did men (Figure 1AGo and Table 2Go). Similarly, when the d2-{gamma}-tocopherol FDRs were averaged for the 2 dietary treatments for each subject, women compared with men also had greater d2-{gamma}-tocopherol FDRs (2.0 ± 0.1 compared with 1.5 ± 0.0 pools per day, P < 0.05). When concentrations were adjusted for serum total lipids at each timepoint and kinetics similarly calculated, women's plasma d6-{alpha}-tocopherol/lipids FDRs were also greater than men's (main effect, P < 0.01, not shown).

Urinary CEHC excretion
We observed that urinary d2-{gamma}-CEHC concentrations during the first 24 h of the study were significantly decreased by consumption of sesame oil muffins both in women and in men (Table 3Go). Because sesame lignans and their metabolites appear to be eliminated from the body and excreted in urine within 24 h following consumption by humans (37), any potential physiologic effects would be expected only during this interval. Thus, it is not surprising that sesame oil consumption did not have effects in the subsequent urine collections (data not shown). No d6-{alpha}-CEHC was detectable in the urine samples (data not shown).


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  		TABLE 3. Urinary excretion of d0-{alpha}-carboxyethyl hydrochromanol (CEHC), d0-{gamma}-CEHC and d2-{gamma}-CEHC (nmol/g creatinine) over 24 h in subjects consuming d6-{alpha}-tocophenyl acetate (TAc) and d2-{gamma}-tocophenyl acetate (TAc) together with sesame oil or corn oil muffins, respectively1

 
Both d0-{alpha}- and d0-{gamma}-CEHC urinary excretion were higher in women than in men, but sesame oil consumption had no significant effect on their excretion.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
This study was designed to test the hypothesis that humans consuming sesame lignans (sesamin and sesamolin) from unrefined sesame oil would have increased plasma {gamma}-tocopherol concentrations likely as a result of inhibiting the metabolism of {gamma}-tocopherol to {gamma}-CEHC. These expectations are in accordance with previously published findings from human (27, 28) and rat (24, 25, 38, 39) studies that showed markedly increased plasma {gamma}-tocopherol concentrations after dietary intervention with sesame seeds, sesame oil, or isolated sesame lignans. Although sesame oil consumption delayed the peak in d2-{gamma}-tocopherol concentrations in both men and women (Table 2Go), none of the other d2-{gamma}-tocopherol kinetic parameters were altered by sesame oil. However, we found that plasma d2-{gamma}-CEHC AUCs and Cmaxs were significantly lower in men after consuming sesame oil muffins compared with corn oil muffins (Figure 1CGo and Table 2Go), suggesting that sesame lignans interfered with d2-{gamma}-tocopherol metabolism. Surprisingly, similar decreases in response to sesame oil consumption were not found for women's plasma d2-{gamma}-CEHC concentrations, although sesame delayed the peak in the d2-{gamma}-CEHC concentrations in both men and women.

In conjunction with the significant decrease in the plasma d2-{gamma}-CEHC AUCs and Cmaxs, a reduction in urinary d2-{gamma}-CEHC excretion was observed in both sexes during the first 24 h of the sesame oil trial. It is likely that women's vitamin E metabolism was affected by sesame lignans, as observed previously (27), but did not result in differences in their plasma d2-{gamma}-CEHC concentrations. This speculation is supported by the findings that overall urinary excretion of unlabeled {alpha}- and {gamma}-CEHC and d2-{gamma}-CEHC was higher in women than in men (Table 3Go).

The percentage of the d2-{gamma}-tocopherol dose recovered over 72 h as urinary d2-{gamma}-CEHC in men nearly doubled during the corn oil (2.1% ± 0.6%) intervention compared with the sesame intervention (1.2% ± 0.4%), but these differences did not reach statistical significance; in women the overall percentage of dose excreted was 2.5% ± 0.7% and 2.3% ± 0.5% during the corn and sesame oil trials, respectively. Parker et al (26) previously demonstrated in cells in culture that the sesame lignan, sesamin, at very low concentrations (1 µmol/L) almost completely inhibited the formation of the side chain-truncated metabolite {gamma}-CEHC from {gamma}-tocopherol. They proposed the involvement of cytochrome P450 (CYP) enzymes in the initial {omega}-hydroxylation of the terminal methyl group of the tocopherol side chain (18) and its inhibition by sesamin (26). These findings offer a ready explanation for the pronounced decrease in plasma {gamma}-CEHCs concentrations because of sesame lignan consumption in our study. This mechanism is further supported by reports of a reduced excretion of {gamma}-CEHC in the urine of rats fed sesame seeds, isolated sesame lignans (sesamin or sesaminol), or ketoconazole (21). The data presented herein, however, show in humans that {gamma}-tocopherol metabolism can be inhibited by the simultaneous consumption of {gamma}-tocopherol and sesame lignans. It is remarkable that this {gamma}-tocopherol-sparing activity was observed after the consumption of only a single oral dose of 94 mg sesamin and 42 mg sesamolin. Repeated ingestion of sesame lignans results in an even more pronounced increase in {gamma}-tocopherol concentrations, as observed by Cooney et al (28) in subjects consuming muffins prepared with ground sesame seeds on 3 consecutive days.

The potent inhibition of CYP-mediated vitamin E metabolism by sesame lignans is of particular importance with regard to clinical nutrition. Chemicals with a methylenedioxyphenyl function, such as sesamin and sesamolin, are known to form complexes with CYPs, thereby irreversibly inactivating the enzymes (40). CYPs are centrally involved in the detoxification of xenobiotics, including many pharmaceutical agents. CYP3A4, for example, metabolizes >50% of prescription drugs (41). Thus, simultaneously ingested sesame lignans may alter the bioavailability and biopotency of drugs by altering their in vivo conversion to the bioactive forms or by slowing down their elimination from the body. Furthermore, phase I enzymes, such as CYPs, are involved in the activation, as well as the elimination, of procarcinogens; thus, sesame lignans may hypothetically interfere with cancer development. In female rats, feeding of a mixture of sesamin and episesamin at 0.2% (by weight) in the diet significantly reduced the formation of chemically induced mammary carcinomas (42).

Throughout the current investigation, we observed considerable differences in the handling, metabolism, and excretion of tocopherols and their water-soluble metabolites between men and women. The faster disappearance of both plasma d6-{alpha}-tocopherol and d2-{gamma}-tocopherol in women compared with men (Table 2Go) and increased urinary excretion of {gamma}-CEHC relative to {alpha}-CEHC is consistent with our previous results (29). In general, the production of {alpha}-CEHC from {alpha}-tocopherol is limited (17, 18). Our previous study examining the relative metabolism of {alpha}-tocopherol and {gamma}-tocopherol showed in normal individuals that plasma {alpha}-CEHC concentrations are 1/10th of those of {gamma}-CEHC (29). Additionally, Schultz et al (43) showed that {alpha}-tocopherol intakes in humans had to be over 150 mg/d to detect plasma {alpha}-CEHC. We therefore did not find it surprising that d6-{alpha}-CEHC was not detectable with a single dose of 50 mg/d.

These data suggest that further studies comparing vitamin E metabolism in men and women are warranted.


   ACKNOWLEDGMENTS
 
We express thanks to the study participants for their cooperation throughout the investigation. The skillful help of Richard Bruno and Lee Moore (Linus Pauling Institute) with the data analyses and sample collection is gratefully acknowledged.

The authors' responsibilities were as follows—JF, AK-E, and MGT: designed the study; JF: recruited and attended to the subjects and supervised the trial; JKA: synthesized the labeled tocopherols; JF and SWL: participated in the sample collection; JF, SL, and SWL: analyzed the samples; JF, SL and MGT: performed the calculations and statistical analyses; and JF, SL, AK-E, and MGT: wrote the first draft of the manuscript. All authors edited and reviewed the final manuscript. None of the authors had a known conflict of interest.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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Received for publication June 18, 2007. Accepted for publication January 28, 2008.





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