Associations of 24 h urinary excretions of α- and γ-carboxyethyl hydroxychroman with plasma α- and γ-tocopherol and dietary vitamin E intake in older adults: the Lifelines-MINUTHE Study

BACKGROUND

Urinary metabolites of vitamin E, i.e., α- and γ-carboxyethyl hydroxychroman (α- and γ-CEHC), have gained increasing attention and have been proposed as novel biomarkers of vitamin E intake and status. However, there are insufficient data on the relationship of plasma α-tocopherol and γ-tocopherol and dietary vitamin E intake with 24 h urinary excretions of α- and γ-CEHC.

OBJECTIVES

We aimed to (1) investigate the associations of urinary α- and γ-CEHC/creatinine ratios and 24 h urinary excretions of α- and γ-CEHC with plasma α- and γ-tocopherol, respectively; (2) investigate the associations of urinary α- and γ-CEHC/creatinine ratios and 24 h urinary excretions of α- and γ-CEHC with dietary vitamin E intake, and we hypothesize that 24 h urinary excretions of α- and γ-CEHC will better correlate with vitamin E intake than urinary α- and γ-CEHC/creatinine ratios.

DESIGN

24 h Urine and plasma samples were collected from 1519 participants (60-75 years, male: 50%) included in the Lifelines-MINUTHE Study for the assessments of urinary α- and γ-CEHC/creatinine ratios and 24 h urinary excretions of α- and γ-CEHC, and plasma α- and γ-tocopherol. Among those participants, dietary vitamin E intake data from 387 participants were available from an externally validated Flower-Food Frequency Questionnaire (FFQ). The associations of plasma α- and γ-tocopherol, dietary vitamin E intake, with urinary α- and γ-CEHC were assessed using multivariate linear regressions.

RESULTS

24 h Urinary excretion of α-CEHC (median (IQR): 0.9 (0.3-2.4) µmol) was less than that of γ-CEHC (median (IQR): 1.5 (0.5-3.5) µmol). After adjustment for covariates, we found that 24 h urinary α-CEHC excretion and urinary α-CEHC/creatinine ratio were both positively associated with plasma α-tocopherol (std.beta: 0.06, p = 0.02; std.beta: 0.06, p = 0.01, respectively). Furthermore, the sum of 24 h urinary α- and γ-CEHC excretions was positively associated with dietary vitamin E intake (std.beta: 0.08; p = 0.03), whereas there was no relation between urinary α- and γ-CEHC/creatinine ratios and vitamin E intake. No association was observed neither between plasma α- and γ-tocopherol and dietary vitamin E intake, nor between urinary γ-CEHC and plasma γ-tocopherol.

CONCLUSION

Our study confirmed our hypothesis that 24 h urinary α- and γ-CEHC excretions would be a better marker for dietary vitamin E intake than urinary α- and γ-CEHC/creatinine ratios. Considering that both 24 h urinary α- and γ-CEHC excretions and α- and γ-CEHC/creatinine ratios were also associated with plasma α-tocopherol status, we suggest that 24 h urinary α- and γ-CEHC excretions could be used to assess overall vitamin E status.

γ-Tocopherol-rich supplementation additively improves vascular endothelial function during smoking cessation

Oxidative stress and inflammation persist years after smoking cessation thereby limiting the restoration of vascular endothelial function (VEF). Although short-term smoking cessation improves VEF, no studies have examined co-therapy of antioxidants in combination with smoking cessation to improve VEF. We hypothesized that improvements in γ-tocopherol (γ-T) status during smoking cessation would improve VEF beyond that from smoking cessation alone by decreasing oxidative stress and proinflammatory responses. A randomized, double-blind, placebo-controlled study was conducted in otherwise healthy smokers (22 ± 1 years; mean ± SEM) who quit smoking for 7 days with placebo (n=14) or γ-T-rich supplementation (n=16; 500 mg γ-T/day). Brachial artery flow-mediated dilation (FMD), cotinine, and biomarkers of antioxidant status, oxidative stress, and inflammation were measured before and after 7 days of smoking cessation. Smoking cessation regardless of supplementation similarly decreased plasma cotinine, whereas γ-T-rich supplementation increased plasma γ-T by seven times and its urinary metabolite γ-carboxyethyl hydroxychroman by nine times (P<0.05). Smoking cessation with γ-T-rich supplementation increased FMD responses by 1.3% (P<0.05) beyond smoking cessation alone (4.1 ± 0.6% vs 2.8 ± 0.3%; mean ± SEM). Although plasma malondialdehyde decreased similarly in both groups (P<0.05), plasma oxidized LDL and urinary F2-isoprostanes were unaffected by smoking cessation or γ-T-rich supplementation. Plasma TNF-α and myeloperoxidase decreased (P<0.05) only in those receiving γ-T-rich supplements and these were inversely related to FMD (P<0.05; R=-0.46 and -0.37, respectively). These findings demonstrate that short-term γ-T-rich supplementation in combination with smoking cessation improved VEF beyond that from smoking cessation alone in young smokers, probably by decreasing the proinflammatory mediators TNF-α and myeloperoxidase.

Association between 24 hour urinary α-tocopherol catabolite, 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (α-CEHC) and α-tocopherol intake in intervention and cross-sectional studies

The objective is to determine the association between the 24 hour urinary α-tocopherol catabolite, 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (α-CEHC) and α-tocopherol intake in an intervention and a cross-sectional studies. In the 4-weeks intervention study, Japanese men (n = 10) consumed the test diet in week 1, and the test diet plus varying amounts of α-tocopherol in the three subsequent weeks: 21 μmol/d α-tocopherol in week 2, 63 μmol/d in week 3, and 125 μmol/d in week 4. A significant association between α-tocopherol intake and urinary α-CEHC was observed in this strictly controlled experiment (r = 0.99, p<0.001). In the cross-sectional study, all foods consumed over 4 consecutive days were recorded in 76 free-living young subjects (18-33 years). The association was weak, but a significant relationship was observed (r = 0.29, p<0.05) even in the cross-sectional study. In the cross-sectional study adults, mean estimated α-tocopherol intake calculated by urinary α-CEHC and the excretory ratio was 91% of their mean intake over the 4 days. The results show that urinary α-CEHC level reflected recent α-tocopherol intake in free-living young Japanese adults, and could be used as a measure of intake during the previous few days, both for group means and for individual rankings within a group.

Isolation and identification of alpha-CEHC sulfate in rat urine and an improved method for the determination of conjugated alpha-CEHC

2,5,7,8-Tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), the water-soluble metabolite of alpha-tocopherol (alpha-TOH) with a shortened side chain but an intact hydroxychroman structure, has been identified in human urine and are thought to be produced in significant amount at excess intake of alpha-TOH. In previous studies, CEHCs in biological specimens were measured by HPLC, GC-MS or LC-MS, preceded by a hydrolysis procedure using either enzyme or methanolic HCl. In an attempt to analyze alpha-CEHC in rat urine accordingly, we observed that enzyme hydrolysis was relatively inefficient in releasing alpha-CEHC compared to high concentrations of HCl. The HCl releasable alpha-CEHC conjugate was isolated and chemically identified as 6-O-sulfated alpha-CEHC (alpha-CEHC sulfate). Using the synthetic alpha-CEHC sulfate standard, it was found that sulfatase could not hydrolyze to a significant extent. On the other hand, pretreatment with HCl at 60 degrees C in the presence of ascorbate, followed by a one-step ether extraction, not only hydrolyzed the sulfate conjugate completely but also extracted alpha-CEHC with high recovery. The inclusion of ascorbate minimized the conversion of alpha-CEHC to alpha-tocopheronolactone in the HCl pretreatment. A complete procedure for the quantitative analysis of alpha-CEHC including HCl hydrolysis, ether extraction and reverse phase isocratic HPLC-ECD was thus established. In conclusion, alpha-CEHC sulfate was isolated and identified as the HCl-releasable conjugate of alpha-CEHC in rat urine. A rapid and sensitive method with high reproducibility for the determination of free, conjugated and total alpha-CEHC is then established.

Pregnenolone and dexamethasone, modulators of cytochrome P450-3A, not increase but reduce urinary alpha-CEHC excretion in rats

In this study, the CYP3A inducer pregnenolone-16alpha-carbonitrile (PCN) and the CYP3A inhibitor ketoconazole (KCZ) were used to investigate whether the metabolism of alpha-tocopherol to its metabolite, alpha-carboxyethyl hydroxychroman (alpha-CEHC), is CYP3A-dependent in rats. In experiment 1, two groups of Wistar rats were fed for 3 wk with either a basal diet (containing 50 ppm of alpha-tocopherol) or the same diet containing 10-fold more alpha-tocopherol. In the last 3 days, each group was divided into 2 subgroups which were given a single i.p. injection of either PCN at 75 mg/kg/d (P50 & P500 groups) or DMSO (D50 & D500 groups). The liver TBARS concentration was highest in the P50 group. Two-way ANOVA analysis showed that alpha-tocopherol levels in the plasma and liver were both significantly decreased by PCN (p < 0.0001), as were alpha-CEHC levels in the urine (p = 0.0004). In experiment 2, alpha-tocopherol levels in the liver were increased and alpha-CEHC excretion in the urine decreased in the Wistar rats fed with KCZ containing diet. In experiment 3, Wistar rats administered with dexamethasone (DEX) significantly decreased alpha-tocopherol levels in the plasma and liver and alpha-CEHC levels in the urine. These data showed CYP3A is not a major contributor of the metabolism of alpha-tocopherol to alpha-CEHC. Nevertheless, vitamin E status was markedly reduced by CYP3A inducers due to increased lipid peroxidation and this would increase the consumption of alpha-tocopherol in the liver.

A new compound-specific pleiotropic effect of statins: modification of plasma gamma-tocopherol levels

Gamma tocopherol (gamma-T) is a recognized peroxynitrite scavenger, reputedly metabolized via the cytochrome P450 3A4 (CYP3A4). In this study, we assessed whether equipotent LDL-lowering doses of statins with or without inhibitory activity on CYP3A4 differently affect gamma-T metabolism. Patients with ATP III criteria for statin use (n=35) were randomly allocated to treatment with simvastatin 20mg/day or pravastatin 40 mg/day. Plasma lipids, alpha-tocopherol (alpha-T), gamma-T as well as the urinary excretion of the gamma-T metabolite 2,7,8-trimethyl-2-(2'carboxyethyl)-6-hydroxychroman (gamma-CEHC), were determined at baseline and after 6 weeks of treatment. Pravastatin and simvastatin equally reduced LDL-C (-42.8+/-2.9 and -42.1+/-3.0%) and alpha-T levels (-17.5+/-4.2 and -12.2+/-4.1%), and increased the alpha-T/LDL-C ratios (51.4+/-14.6 and 60.4+/-15%). Conversely, pravastatin did not affect whereas simvastatin significantly augmented plasma gamma-T levels (22+/-7.9%, p=0.009, between groups p=0.0045). Moreover, the gamma-T/LDL-C ratio increased significantly more with simvastatin than with pravastatin (124+/-23 versus 61.3+/-22.1%, p=0.05 between groups). In addition, pravastatin but not simvastatin increased the urinary excretion of gamma-CEHC (34.3+/-17.3%, p=0.056; between groups p=0.046). In conclusion, simvastatin and pravastatin produced distinct effects on gamma-T metabolism, presumably as a result of different statin-CYP interactions.

Cigarette smokers differ in their handling of natural (RRR) and synthetic (all rac) alpha-tocopherol: a biokinetic study in apoE4 male subjects

We have compared the biokinetics of deuterated natural (RRR) and synthetic (all rac) alpha-tocopherol in male apoE4-carrying smokers and nonsmokers. In a randomized, crossover study subjects underwent two 4-week treatments (400 mg/day) with undeuterated RRR- and all rac-alpha-tocopheryl acetate around a 12-week washout. Before and after each supplementation period subjects underwent a biokinetic protocol (48 h) with 150 mg deuterated RRR- or all rac-alpha-tocopheryl acetate. During the biokinetic protocols, the elimination of endogenous plasma alpha-tocopherol was significantly faster in smokers (P < 0.05). However, smokers had a lower uptake of deuterated RRR than nonsmokers, but there was no difference in uptake of deuterated all rac. The supplementation regimes significantly raised plasma alpha-tocopherol (P < 0.001) with no differences in response between smokers and nonsmokers or between alpha-tocopherol forms. Smokers had significantly lower excretion of alpha-carboxyethyl-hydroxychroman than nonsmokers following supplementation (P < 0.05). Nonsmokers excreted more alpha-carboxyethyl-hydroxychroman following RRR than all rac; however, smokers did not differ in excretion between forms. At baseline, smokers had significantly lower ascorbate (P < 0.01) and higher F(2)-isoprostanes (P < 0.05). F(2)-isoprostanes in smokers remained unchanged during the study, but increased in nonsmokers following alpha-tocopherol supplementation. These data suggest that apoE4-carrying smokers and nonsmokers differ in their handling of natural and synthetic alpha-tocopherol.

Supplementation with mixed tocopherols increases serum and blood cell gamma-tocopherol but does not alter biomarkers of platelet activation in subjects with type 2 diabetes

BACKGROUND

Some studies have shown potential benefit of vitamin E on platelet function, but several clinical trials failed to show improved cardiovascular outcome with alpha-tocopherol supplementation. Gamma-tocopherol, a major dietary form of vitamin E, may have protective properties different from those of alpha-tocopherol.

OBJECTIVE

We compared the effects of supplementation with alpha-tocopherol (500 mg) and a gamma-tocopherol-rich compound (500 mg, containing 60% gamma-tocopherol) on serum and cellular tocopherol concentrations, urinary tocopherol metabolite excretion, and in vivo platelet activation in subjects with type 2 diabetes.

DESIGN

Fifty-eight subjects were randomly assigned to receive either 500 mg alpha-tocopherol/d, 500 mg mixed tocopherols/d, or matching placebo. Serum, erythrocyte, and platelet tocopherol and urinary metabolite concentrations were measured at baseline and after the 6-wk intervention. Soluble CD40 ligand, urinary 11-dehydro-thromboxane B2, serum thromboxane B2, soluble P-selectin, and von Willebrand factor were measured as biomarkers of in vivo platelet activation.

RESULTS

Serum alpha-tocopherol increased with both tocopherol treatments. Serum and cellular gamma-tocopherol increased 4-fold (P < 0.001) in the mixed tocopherol group, whereas red blood cell gamma-tocopherol decreased significantly after alpha-tocopherol supplementation. Excretion of alpha-carboxyethyl-hydroxychroman increased significantly after supplementation with alpha-tocopherol and mixed tocopherols. Excretion of gamma-carboxyethyl-hydroxychroman increased significantly after supplementation with mixed tocopherols and after that with alpha-tocopherol, which may reflect the displacement of gamma-tocopherol by alpha-tocopherol due to incorporation of the latter into lipoproteins in the liver. Neither treatment had any significant effect on markers of platelet activation.

CONCLUSIONS

Supplementation with alpha-tocopherol decreased red blood cell gamma-tocopherol, whereas mixed tocopherols increased both serum alpha-tocopherol and serum and cellular gamma-tocopherol. Changes in serum tocopherol closely reflect changes in cellular concentrations of tocopherols after supplementation.

Nitration of gamma-tocopherol prevents its oxidative metabolism by HepG2 cells

Gamma-tocopherol (gammaT) is one of the major forms of vitamin E consumed in the diet. Previous reports have suggested increased levels of nitrated gamma-tocopherol (5-NO2-gammaT) in smokers and individuals with conditions associated with elevated nitrative stress. The monitoring of 5-NO2-gammaT and its possible metabolite(s) may be a useful marker of reactive nitrogen species generation in vivo. The major pathway for the metabolism of gammaT is the cytochrome P450 dependent oxidation to its water-soluble metabolite gamma-CEHC, which is excreted in urine. In order to determine if 5-NO2-gammaT could be metabolised via the same route and detected in urine we developed a sensitive gas chromatography-mass spectrometry assay for 5-NO2-gamma-CEHC. 5-NO2-gamma-CEHC was synthesised and its structure confirmed by proton nuclear magnetic resonance and mass spectrometry. While gamma-CEHC was abundant in urine from healthy volunteers, as well as patients with coronary heart disease and type 2 diabetes, 5-NO2-gamma-CEHC was undetectable (limit of detection of 5 nM). To understand this observation we examined the uptake and metabolism of gammaT and 5-NO2-gammaT by HepG2 cells. gammaT was readily incorporated into cells and metabolised to gamma-CEHC over a period of 48 hours. In contrast, 5-NO2-gammaT was poorly incorporated into HepG2 cells and not metabolised to 5-NO2-gamma-CEHC over the same time period. We conclude that nitration of gammaT prevents its incorporation into liver cells and therefore its metabolism to the water-soluble metabolite. Whether 5-NO2-gammaT could be metabolised via other pathways in vivo requires further investigation.

Cigarette smoking increases human vitamin E requirements as estimated by plasma deuterium-labeled CEHC

Cigarette smoking (CS) is a well-described oxidant burden in humans. We hypothesized that CS would accelerate alpha-tocopherol (alpha-T) utilization leaving less for metabolite (CEHC) production. After labeled alpha-T consumption (75 mg each of d(3)-RRR-alpha-TAc and d(6)-all-rac-alpha-TAc) by smokers and nonsmokers (n = 10/group), CS increased alpha-T disappearance and decreased plasma and urinary CEHCs. Plasma d(3)/d(6)-alpha-T ratios were approximately 1.4 during supplementation and approximately 2 from days 5 to 17. d(3)/d(6)-alpha-CEHC ratios were on average 0.29 +/- 0.05, confirming that all-rac-alpha-tocopherol is metabolized more efficiently. CEHC may be a good marker of vitamin E status, and smokers may have an increased vitamin E requirement.

Inter- and intra-individual vitamin E uptake in healthy subjects is highly repeatable across a wide supplementation dose range

Vitamin E uptake after supplementation varies widely in the healthy population, and preliminary studies have indicated that individual responses are relatively stable over periods in excess of 1 year. This phenotypic stability suggests a genetic basis to this observed variation. To examine this issue further, we examined the repeatability of both baseline plasma alpha-tocopherol and urinary alpha-tocopherol metabolite concentrations, as well as individual responses of these parameters after vitamin E supplementation. In the first study, 65 subjects (33 males, 32 females, aged 30.7 +/- 7.4 years) provided three plasma and urine samples for alpha-tocopherol and metabolite analysis with each collection separated by at least 2 weeks. Plasma alpha-tocopherol concentrations were found to be highly repeatable over this short interval (intra-class correlation coefficient [ICC] = 0.85), although the association deteriorated once values were corrected for plasma cholesterol (ICC = 0.64). Similarly, urinary alpha-tocopherol metabolites 2(2'-carboxyethyl)-6-hydroxychroman acid (alpha-CEHC) and quinone lactone (QL) concentration were found to display a moderate degree of intra-subject repeatability: ICC = 0.65 and 0.58, respectively. In a second study, plasma alpha-tocopherol and urinary metabolite responses were investigated in 18 healthy, nonsmoking subjects (12 males, 6 females, aged 33.1 +/- 9.1 years) after successive 6-week periods of vitamin E (RRR-alpha-tocopherol acetate) supplementation at 15, 100, 200, and 400 mg/day. Plasma and urine samples were obtained on days 0, 7, 14, 21, and 28 (7 days after the final supplement) of each dosing period and the strength of the underlying association between responses determined using Kendall's tau_b test. Individual plasma alpha-tocopherol responses at the 100, 200, and 400 mg/day doses were found to be highly associated: tau, 0.51, P = 0.02 [100 vs. 200] and tau, 0.49, P = 0.03 [100 vs. 400] and tau, 0.56, P = 0.005 [200 vs. 400]. Together these data support the contention that alpha-tocopherol uptake is a stable individual phenotype under genetic regulation.

Studies in humans using deuterium-labeled alpha- and gamma-tocopherols demonstrate faster plasma gamma-tocopherol disappearance and greater gamma-metabolite production

We hypothesized that human plasma alpha- and gamma-tocopherol concentrations reflect differences in their kinetics, especially influenced by gamma-tocopherol metabolism. Vitamin E kinetics were evaluated in humans (n=14) using approximately 50 mg each of an equimolar ratio of d6-alpha- and d2-gamma-tocopheryl acetates administered orally. Mass spectrometry was used to measure deuterated plasma tocopherols, as well as plasma and urinary vitamin E metabolites, alpha- and gamma-carboxyethylhydroxychromans (CEHCs). Plasma d2-gamma-tocopherol fractional disappearance rates (FDR; 1.39+/-0.44 pools/day, mean+/-SD) were more than three times greater than those of d6-alpha-tocopherol (0.33+/-0.11, p<0.001). The d2-gamma-tocopherol half-life was 13+/-4 h compared with 57+/-19 for d6-alpha-tocopherol. Whereas neither plasma nor urinary d6-alpha-CEHC was detectable (limit of detection 1 nmol/L), gamma-CEHC (labeled plus unlabeled) increased from 129+/-20 to 258+/-40 nmol/L by 12 h and returned to baseline by 48 h; at 12 h d2-gamma-CEHC represented 54+/-4% of plasma gamma-CEHC. Women compared with men had a greater d2-gamma-tocopherol FDR (p<0.004) and a greater maximal plasma d2-gamma-CEHC concentration (p<0.02) and CEHC FDR (p<0.007), as well as excreting four times as much d2-gamma-CEHC (p<0.04) in urine. Thus, gamma-tocopherol is rapidly metabolized to gamma-CEHC, and to a greater degree in women than in men, whereas alpha-tocopherol is maintained in the plasma and little is metabolized to alpha-CEHC.

Cigarette smokers have decreased lymphocyte and platelet alpha-tocopherol levels and increased excretion of the gamma-tocopherol metabolite gamma-carboxyethyl-hydroxychroman (gamma-CEHC)

Cigarette smoking is associated with increased oxidative stress and increased risk of degenerative disease. As the major lipophilic antioxidant, requirements for vitamin E may be higher in smokers due to increased utilisation. In this observational study we have compared vitamin E status in smokers and non-smokers using a holistic approach by measuring plasma, erythrocyte, lymphocyte and platelet alpha- and gamma-tocopherol, as well as the specific urinary vitamin E metabolites alpha- and gamma-carboxyethyl-hydroxychroman (CEHC). Fifteen smokers (average age 27 years, smoking time 7.5 years) and non-smokers of comparable age, gender and body mass index (BMI) were recruited. Subjects completed a 7-day food diary and on the final day they provided a 24 h urine collection and a 20 ml blood sample for measurement of urinary vitamin E metabolites and total vitamin E in blood components, respectively. No significant differences were found between plasma and erythrocyte alpha- and gamma-tocopherol in smokers and non-smokers. However, smokers had significantly lower alpha-tocopherol (mean+/-SD, 1.34+/-0.31 micromol/g protein compared with 1.94+/-0.54, P = 0.001) and gamma-tocopherol (0.19+/-0.04 micromol/g protein compared with 0.26+/-0.08, P = 0.026) levels in their lymphocytes, as well as significantly lower alpha-tocopherol levels in platelets (1.09+/-0.49 micromol/g protein compared with 1.60+/-0.55, P = 0.014; gamma-tocopherol levels were similar). Interestingly smokers also had significantly higher excretion of the urinary gamma-tocopherol metabolite, gamma-CEHC (0.49+/-0.25mg/g creatinine compared with 0.32+/-0.16, P = 0.036) compared to non-smokers, while their alpha-CEHC (metabolite of alpha-tocopherol) levels were similar. There was no significant difference between plasma ascorbate, urate and F2-isoprostane levels. Therefore in this population of cigarette smokers (mean age 27 years, mean smoking duration 7.5 years), alterations to vitamin E status can be observed even without the more characteristic changes to ascorbate and F2-isoprostanes. We suggest that the measurement of lymphocyte and platelet vitamin E may represent a valuable biomarker of vitamin E status in relation to oxidative stress conditions.

{alpha}-Tocopherol disappearance is faster in cigarette smokers and is inversely related to their ascorbic acid status

BACKGROUND

Cigarette smokers have enhanced oxidative stress from cigarette smoke exposure and from their increased inflammatory responses.

OBJECTIVE

The objective of this study was to determine whether cigarette smoking increases plasma alpha-tocopherol disappearance in otherwise healthy humans.

DESIGN

Smokers and nonsmokers (n = 10/group) were supplemented with deuterium-labeled alpha-tocopheryl acetates (75 mg each of d(3)-RRR-alpha-tocopheryl acetate and d(6)-all-rac-alpha-tocopherols acetate) for 6 evenings (days -6 to -1). Plasma alpha-tocopherols, ascorbic acid, uric acid, and F(2alpha)-isoprostanes were measured in blood samples collected on days -6 through 17. The urinary alpha-tocopherol metabolite, alpha-carboxy-ethyl-hydroxy-chroman (alpha-CEHC), was measured on days -6, 0, and 17 in 24-h urine samples.

RESULTS

F(2alpha)-isoprostanes were, on average, approximately 40% higher in smokers than in nonsmokers. On day 0, plasma labeled and unlabeled alpha-tocopherol concentrations were not significantly different between groups. Smoking resulted in faster fractional disappearance of plasma alpha-tocopherol (0.215 +/- 0.011 compared with 0.191 +/- 0.009 pools/d; P < 0.05). Fractional disappearance rates of alpha-tocopherol correlated with plasma ascorbic acid concentrations in smokers (P = 0.021) but not in nonsmokers despite plasma ascorbic acid concentrations that were not significantly different between groups. By day 17, cigarette smoking resulted in lower plasma alpha-tocopherol concentrations and urinary excretion of labeled and unlabeled alpha-CEHC (P < 0.05).

CONCLUSIONS

Cigarette smoking increased alpha-tocopherol disappearance. Greater rates of alpha-tocopherol disappearance in smokers appear to be related to increased oxidative stress accompanied by lower plasma ascorbic acid concentrations. Thus, smokers have an increased requirement for both alpha-tocopherol and ascorbic acid.

The Effect of Age on Vitamin E Status, Metabolism, and Function: Metabolism as Assessed by Labeled Tocopherols

The effects of age on vitamin E metabolism were studied in 97 healthy 20-75-year-old male nonsmoking Austrian volunteers of the VITAGE project. After a single oral intake of 30 mg d(6)-RRR-alpha- and d(2)-RRR-gamma-tocopheryl acetate, blood and 24-hour urine was collected. Deuterated tocopherols in plasma and deuterated urinary metabolites were analyzed by GC-MS. A first evaluation revealed a similar uptake of d(6)-alpha- and d(2)-gamma-tocopherol during the first 6 hours, and then d(2)-gamma-tocopherol started to decrease. Urinary d(2)-gamma- carboxyethyl hydroxychroman metabolites (CEHCs) exceeded those of d(6)-alpha-CEHCs by about 10 times. There was no effect of age. Thus, there might be no need for a higher vitamin E intake for healthy elderly nonsmoking men.

Consumption of Sesame Oil Muffins Decreases the Urinary Excretion of γ-Tocopherol Metabolites in Humans

Sesame seed and oil consumption previously increased human plasma gamma-tocopherol (gamma-T) concentrations. This was attributed to the sesame lignans sesamin and sesamolin. Here, we studied the inhibition of vitamin E metabolism by a single dose of sesame oil lignans coingested with deuterated alpha- and gamma-tocopherols in human volunteers. The urinary excretion of gamma-T metabolites was significantly lower in sesame oil treated than in control subjects. Concentrations of tocopherols in blood were not affected by the treatment. In conclusion, a single dose of sesame oil, containing 136 mg sesame lignans (sesamin and sesamolin), reduces the urinary excretion of co-administered gamma-T in humans.

GAMMA.-Tocopherol Enhances Sodium Excretion as a Natriuretic Hormone Precursor

Endogenous natriuretic factors are believed to be responsible for extracellular fluid homeostasis in mammals. A new endogenous natriuretic factor, Loma Linda University-alpha (LLU-alpha) has recently been proven to be a 2,7,8-trimethyl-2-(2'-carboxyethyl)-6-hydroxychroman (gamma-CEHC), which is a metabolite of gamma-tocopherol (gamma-Toc). The purpose of this study was to investigate whether gamma-Toc could accelerate sodium excretion into rat urine as a natriuretic hormone precursor. Male SD strain rats were divided into two groups; one was a control diet group, while the other was a high NaCl group (50 g/kg diet). Next, the two groups were each subdivided into two groups consisting of a placebo group and a gamma-Toc group. After the oral administration of one experimental dose of 20 mg gamma-Toc or placebo, rat urine was collected at 6 h intervals for 24 h, and then the urine volume, sodium and potassium and gamma-CEHC content were determined. gamma-Toc increased in the urine volume of the high-NaCl intake group. The sodium excretion in the high-NaCl group given gamma-Toc was 8.29+/-2.20 g, while in the control group given gamma-Toc it was 6.24+/-1.49 g from 12-18 h. In contrast, the potassium excretion in the rat urine did not change in any of the groups. Our findings suggested that gamma-Toc accelerates the degree of sodium excretion in rats with a high sodium intake.

Gamma-tocotrienol, a vitamin E homolog, is a natriuretic hormone precursor

2,7,8-Trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (gamma-CEHC), a metabolite of gamma-tocopherol and gamma-tocotrienol, was identified as a new endogenous natriuretic factor. However, gamma-tocopherol and gamma-tocotrienol, both precursors of gamma-CEHC, have never directly been observed to have natriuretic potency. Thus, we investigated whether gamma-tocotrienol could cause natriuresis and diuresis in rats. The rats were divided into two groups that were given a control or a high-sodium diet for 4 weeks, and then subdivided into placebo and gamma-tocotrienol subgroups given only corn oil-removed vitamin E and oil supplemented with gamma-tocotrienol, respectively. After oral administration of three experimental doses, rat urine was collected and gamma-CEHC, urine volume, sodium, and potassium content were determined. Only in rats given a high-NaCl diet did gamma-tocotrienol accelerate and increase sodium excretion, showing no effect on potassium excretion. Sodium excretion in the high-NaCl group given gamma-tocotrienol was 5.06 +/- 2.70 g/day, and in the control group given gamma-tocotrienol, 0.11 +/- 0.06 g/day. Furthermore, gamma-tocotrienol affected urine volume in the specific condition of high-NaCl body stores and gamma-tocotrienol supplementation. In this study, we found that gamma-tocotrienol, one of the natural vitamin E homologs, stimulates sodium excretion in vivo, suggesting that gamma-tocotrienol possesses a hormone-like natriuretic function.

Urinary equol excretion in relation to 2-hydroxyestrone and 16alpha-hydroxyestrone concentrations: an observational study of young to middle-aged women

Approximately one-third to one-half of individuals harbor the colonic bacteria that are capable of metabolizing the soy isoflavone daidzein to equol. Results of prior studies suggest beneficial effects of producing equol in relation to breast cancer risk, potentially through effects on endogenous hormones. High urinary excretion of 2-hydroxyestrone (2-OH E(1)) relative to 16alpha-hydroxyestrone (16alpha-OH E(1)) has been associated with a reduced risk of breast cancer. In this pilot study we examined associations between urinary excretion of equol and 2-OH E(1), 16alpha-OH E(1), and their ratio, and investigated whether excretion of these estrogen metabolites differed between two samples collected 48h apart. Isoflavones (genistein, daidzein, O-desmethylangolensin (ODMA), and equol) were measured in two overnight urines from 126 women. Excretion of 2-OH E(1) and 16alpha-OH E(1) were measured in the first overnight urine from all 126 women and in the second overnight urine from 30 of these women; there were no significant differences between samples collected 48h apart in excretion of 2-OH E(1) or 16alpha-OH E(1) (P=0.75 and 0.17, respectively). Among all women, correlations between total isoflavone excretion (sum of genistein, daidzein, ODMA, and equol) and estrogen metabolites were non-significant (P>0.05). Among women with detectable levels of equol, total isoflavone excretion was significantly positively correlated with 16alpha-OH E(1) (r=0.32, P=0.02), but was not correlated with 2-OH E(1) or 2-OH E(1):16alpha-OH E(1) ratio (r=0.21, P=0.14, and r=-0.05, P=0.70, respectively). Equol excretion (adjusted for other isoflavone excretion) was significantly positively correlated with 2-OH E(1):16alpha-OH E(1) ratio (r=0.38, P=0.005), but was not correlated with 2-OH E(1) or 16alpha-OH E(1) (r=0.15, P=0.29, and r=-0.17, P=0.24, respectively). The finding that equol excretion, but not total isoflavone excretion, correlated positively with the 2-OH E(1):16alpha-OH E(1) ratio suggests that the colonic bacterial profile associated with equol production may be involved in estrogen metabolism, and may therefore possibly influence breast cancer risk.

Metabolism of isoflavones and lignans by the gut microflora: a study in germ-free and human flora associated rats

We have investigated the metabolism of isoflavones and lignans in germ-free (GF) rats and rats associated with human faecal bacteria (human flora associated [HFA] rats), in order to provide unequivocal evidence for the role of the gut microflora in the absorption and metabolism of these phytoestrogens. Furthermore, we have investigated whether certain metabolic characteristics (high equol-producing and low equol-producing status) of human intestinal floras can be transferred to GF rats. Germ-free rats fed a soy-isoflavone containing diet excreted large quantities of daidzein and genistein in urine indicating that the gut microflora is not required for the absorption of isoflavones. The isoflavone metabolites equol, O-desmethylangolensin and the lignan enterolactone were not detectable in urine from the GF rats, but were present in HFA rat urine, indicating that they were products of gut microflora activity. Colonization of GF rats with a faecal flora from a human subject with the capacity to convert daidzein to equol, resulted in the rats excreting substantial amounts of the metabolite. In contrast, equol was undetectable in urine of HFA rats associated with a faecal flora from a low equol-producing subject. The results therefore show that the inability of some subjects to produce equol is a consequence of the lack of specific components of the gut microflora.

Time-resolved fluoroimmunoassay for equol in plasma and urine

We present a method for the determination of the isoflavan equol in plasma and urine. This estrogenic isoflavan, which is formed by the action of the intestinal microflora, may have higher biological activity than its precursor daidzein. High urinary excretion of equol has been suggested to be associated with a reduction in breast cancer risk. The method is based on time-resolved fluoroimmunoassay, using a europium chelate as a label. After synthesis of 4'-O-carboxymethylequol the compound is coupled to bovine serum albumin (BSA), then used as antigen to immunize rabbits. The tracer with the europium chelate is synthesized using the same 4'-O-derivative of equol. After enzymatic hydrolysis (urine) or enzymatic hydrolysis and ether extraction (plasma) the immunoassay is carried out. The antiserum cross-reacted to variable extent with some isoflavonoids. For the plasma method the cross-reactivity does not seem to influence the results, which were highly specific. The overestimation of the values using the urine method (164%) compared to the results obtained by a gas chromatography-mass spectrometry (GC-MS) method is probably due to some influence of the matrix on the signal, and interference of structurally related compounds. It is suggested that plasma assays are used but if urine samples are measured a formula has to be used to correct the values making them comparable to the GC-MS results. The correlation coefficients between the time-resolved fluoroimmunoassay (TR-FIA) methods and GC-MS methods were high; r-values for the plasma and urine method, were 0.98 and 0.91, respectively. The intra-assay coefficient of variation (CV%) for the TR-FIA plasma and urine results at three different concentrations vary between 5.5-6.5 and 3.4-6.9, respectively. The inter-assay CV% varies between 5.4-9.7 and 7.4-7.7, respectively. The working ranges of the plasma and urine assay are 1.27-512 and 1.9-512nmol/l, respectively.

Measurement of vitamin E metabolites by high-performance liquid chromatography during high-dose administration of alpha-tocopherol

METHOD

alpha-Tocopherol and gamma-tocopherol are metabolized into 2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC) and 2,7,8-trimethyl-2-(2'-carboxyethyl)-6-hydroxychroman (gamma-CEHC), respectively. We analyzed alpha- and gamma-CEHC concentrations in human serum and urine by high-performance liquid chromatography during administration of alpha-tocopherol. Fourteen healthy adult male volunteers received 1,200 IU per day of RRR-alpha-tocopherol for 28 days. Blood and urine samples were obtained on days 0, 14, 28, and 56.

RESULTS

During alpha-tocopherol administration, the plasma gamma-tocopherol concentration decreased significantly, but there was marked elevation of the alpha-tocopherol concentration. Increased concentration of alpha-CEHC and gamma-CEHC in both serum and urine indicated the acceleration of vitamin E metabolism.

CONCLUSION

High-dose administration of alpha-tocopherol caused an increase of gamma-tocopherol metabolism, which might have caused a decrease of the plasma gamma-tocopherol concentration.

Comparing the pharmacokinetics of daidzein and genistein with the use of 13C-labeled tracers in premenopausal women

BACKGROUND

Despite significant interest in the risks and benefits of phytoestrogens to human health, few data exist on their pharmacokinetics in humans.

OBJECTIVE

We investigated the pharmacokinetics of the (13)C isotopic forms of daidzein and genistein in healthy humans, specifically addressing intraindividual variability, effect of increasing intake, and influence of prolonged exposure to a soy food diet.

DESIGN

Premenopausal women (n = 16) were administered 0.4 mg [(13)C]daidzein or [(13)C]genistein/kg body wt orally on 3 occasions, including once after eating soy foods for 7 d. On a further occasion the dose was doubled. Plasma and urinary [(13)C]isoflavone concentrations were measured by mass spectrometry.

RESULTS

Serum concentrations of [(13)C]genistein and [(13)C]daidzein peaked after 5.5 and 7.4 h, respectively. The systemic bioavailability and maximum serum concentration of [(13)C]genistein were significantly greater than those of [(13)C]daidzein. The bioavailability of both isoflavones did not increase linearly when the dietary intake was doubled. The mean volume of distribution normalized to bioavailability (V(d)/F), clearance rate, and half-life of [(13)C]daidzein were 336.25 L, 30.09 L/h, and 7.75 h, respectively; the corresponding values for [(13)C]genistein were 258.76 L, 21.85 L/h, and 7.77 h. The average recovery of [(13)C]daidzein and [(13)C]genistein in urine was 30.1% and 9.0% of the dose ingested, respectively.

CONCLUSIONS

The serum pharmacokinetics of [(13)C]daidzein and [(13)C]genistein were reproducible among healthy women, and genistein was more bioavailable than was daidzein. Pharmacokinetics were unaffected by chronic exposure to soy foods. Urinary isoflavone concentrations correlated poorly with maximal serum concentrations, indicating the limitations of urine measurements as a predictor of systemic bioavailability. The bioavailability of both isoflavones was nonlinear at higher intakes, suggesting that uptake is rate-limiting and saturable.

Synthesis and analysis of conjugates of the major vitamin E metabolite, alpha-CEHC

Glucuronide and sulphate conjugates of 2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), the major metabolite of alpha-tocopherol (vitamin E), have been synthesized and used for the first direct analysis of conjugated urinary vitamin E metabolites. The metabolites of vitamin E (alpha-tocopherol) could be useful as markers of the function(s) of vitamin E in vivo. A number of methods have been described for the analysis of urinary vitamin E metabolites but these have relied on either acid or enzymatic deconjugation of the metabolites prior to analysis by high performance liquid chromatography or gas chromatography/mass spectrometry. These methods have provided useful information about the amount and types of metabolites excreted in the urine but suffer from a number of disadvantages. Deconjugation has been shown to produce artifacts as a result of the conversion of alpha-CEHC to alpha-tocopheronolactone and the efficiency of deconjugation is also difficult to assess. Methods that allow the direct measurement of the conjugated metabolites would overcome these problems and would also substantially reduce the preparation and analysis time. Here we describe the use of conjugated standards to characterize alpha-CEHC conjugates in human urine by tandem mass spectrometry (MS-MS). The future use of MS-MS to measure urinary vitamin E metabolites is also discussed.

Quantitative analysis of urinary daidzein and equol by gas chromatography after solid-phase extraction and high-performance liquid chromatography

Daidzein and its main metabolite equol are isoflavone phytoestrogens. Several studies have suggested that intake of an isoflavone-rich diet may prevent hormone-related cancer and estrogen-related disorders (cardiovascular disease, osteoporosis and menopausal symptoms). To better understand the role of isoflavones in preventing such severe disease, several methods have been developed to measure these compounds in biological fluids. However, the analytical procedures to measure isoflavones are often time-consuming and require highly skilled technicians. In this paper we describe a method for urinary daidzein and equol measurement that combines solid phase extraction and HPLC purification before gas chromatographic determination. The specificity of the method was confirmed by the gas chromatography-mass spectrometry technique. The mean recovery of daidzein and equol was 94.6% and 97.0%, respectively. The repeatability of the method was in the range of 2.0-7.4% for daidzein and 1.3-4.9% for equol. A linear relationship between observed and expected values was found in the dilution (r2=0.9983 for daidzein; r2=0.9982 for equol) and addition (r2=0.9984 for daidzein; r2=0.9989 for equol) assays. The method is suitable to measure changes in the urinary excretion of isoflavones and to investigate urinary isoflavonoids as biomarkers of isoflavone exposure.

Dietary sesame seed and its lignans inhibit 2,7,8-trimethyl- 2(2'-carboxyethyl)-6-hydroxychroman excretion into urine of rats fed gamma-tocopherol

We showed previously that dietary sesame seed and its lignans elevate the tocopherol concentration in rats. To clarify their effect on tocopherol metabolism, we determined in this study the urinary excretion of 2,7,8-trimethyl-2(2'-carboxyethyl)-6-hydroxychroman (gamma-CEHC), a gamma-tocopherol metabolite, in rats fed sesame seed or its lignans. Rats were fed diets with or without sesame seed for 28 d in Experiment 1, and for 1, 3 and 7 d in Experiment 2. On d 28, dietary sesame seed elevated (P < 0.05) gamma-tocopherol concentrations in liver, kidney, brain and serum, and decreased (P < 0.05) urinary excretion of gamma-CEHC. The excretion was completely inhibited by feeding sesame seed on d 1 and 3. In Experiment 3, the effects of dietary sesamin and sesaminol (major lignans in sesame seed) or ketoconazole (a selective inhibitor of cytochrome P(450) (CYP)3A on urinary excretion of gamma-CEHC in rats fed gamma-tocopherol were examined. The urinary gamma-CEHC in rats fed sesamin or sesaminol was markedly lower than in rats fed gamma-tocopherol alone (P < 0.05). Dietary ketoconazole also inhibited (P < 0.05) urinary excretion of gamma-CEHC, and elevated (P < 0.05) gamma-tocopherol concentrations in tissues and serum of rats fed gamma-tocopherol. These data suggest that sesame seed and its lignans elevate gamma-tocopherol concentration due to the inhibition of CYP3A-dependent metabolism of gamma-tocopherol.

gamma-tocopherol, the major form of vitamin E in the US diet, deserves more attention

gamma-tocopherol is the major form of vitamin E in many plant seeds and in the US diet, but has drawn little attention compared with alpha-tocopherol, the predominant form of vitamin E in tissues and the primary form in supplements. However, recent studies indicate that gamma-tocopherol may be important to human health and that it possesses unique features that distinguish it from alpha-tocopherol. gamma-Tocopherol appears to be a more effective trap for lipophilic electrophiles than is alpha-tocopherol. gamma-Tocopherol is well absorbed and accumulates to a significant degree in some human tissues; it is metabolized, however, largely to 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (gamma-CEHC), which is mainly excreted in the urine. gamma-CEHC, but not the corresponding metabolite derived from alpha-tocopherol, has natriuretic activity that may be of physiologic importance. Both gamma-tocopherol and gamma-CEHC, but not alpha-tocopherol, inhibit cyclooxygenase activity and, thus, possess antiinflammatory properties. Some human and animal studies indicate that plasma concentrations of gamma-tocopherol are inversely associated with the incidence of cardiovascular disease and prostate cancer. These distinguishing features of gamma-tocopherol and its metabolite suggest that gamma-tocopherol may contribute significantly to human health in ways not recognized previously. This possibility should be further evaluated, especially considering that high doses of alpha-tocopherol deplete plasma and tissue gamma-tocopherol, in contrast with supplementation with gamma-tocopherol, which increases both. We review current information on the bioavailability, metabolism, chemistry, and nonantioxidant activities of gamma-tocopherol and epidemiologic data concerning the relation between gamma-tocopherol and cardiovascular disease and cancer.

Synthesis and application of a novel, crystalline phosphoramidite monomer with thiol terminus, suitable for the synthesis of DNA conjugates

A new, crystalline 5'-thiol modifier phosphoramidite monomer (3), suitable for DNA synthesis, has been prepared. This monomer has been built into an oligonucleotide using the standard protocol. After cleavage, purification and removal of the trityl group with Ag(+), a free 5'-thiol terminal oligonucleotide (15) has been obtained which was subsequently coupled to a cysteine derivative via a disulfide bridge to afford conjugate 16.

Alpha-tocopherol affects the urinary and biliary excretion of 2,7,8-trimethyl-2 (2'-carboxyethyl)-6-hydroxychroman, gamma-tocopherol metabolite, in rats

In this study, we investigated a change in the excretory content of 2,7,8-trimethyl-2(2'-carboxyethyl)-6-hydroxychroman (gamma-CEHC), a gamma-tocopherol (gamma-Toc) metabolite, in rat urine and bile by using a new high-performance liquid chromatography-electrochemical detection (HPLC-ECD) method. In this determination, CEHC [alpha- and gamma-CEHC, where alpha-CEHC = 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman] in the biological specimens were treated with 3 N methanolic HCl to hydrolyze conjugates and to promote esterification. The methylated samples were extracted by n-hexane/water (1:2). The analyses of the methyl esters of alpha-CEHC and gamma-CEHC were performed by an HPLC-ECD using an ODS-3 column at 35 degrees C. The mobile phase was acetonitrile/water (45:55, vol/vol) containing 50 mM sodium perchlorate. After rat urine and bile samples, respectively, were methylated as described above, methylated biliary metabolites were identified by liquid chromatography-mass spectrometry as methyl esters of gamma-CEHC. Furthermore, we examined the differences in the excretion of gamma-CEHC between rat urine and bile after an oral administration of gamma-Toc or alpha- + gamma-Toc by the above HPLC method. In the gamma-Toc group, each vitamin E-deficient rat was given 0.5 mL of a stripped corn oil preparation containing 10 mg of gamma-Toc. In the alpha- + gamma-Toc group, the rat was given 10 mg of alpha-Toc and 10 mg of gamma-Toc. The content of gamma-CEHC in rat urine from the alpha- + gamma-Toc group was increased more in comparison to the gamma-Toc group at 18-36 h after oral administration. Moreover, the content of gamma-CEHC in rat bile in the alpha- + gamma-Toc group was increased more in comparison to the gamma-Toc group at 6-18 h after oral administration. Therefore, we have suggested that gamma-CEHC was shifted mainly to urinary excretion after gamma-CEHC had been excreted into the bile. Furthermore, we assume that alpha-Toc may affect the metabolism of gamma-Toc to gamma-CEHC in the body.

Wheat bran and soy protein feeding do not alter urinary excretion of the isoflavan equol in premenopausal women

The capacity to convert the soy isoflavone daidzein to equol in vivo is presumably determined by an individual's intestinal microfloral populations; however, diet may also influence this conversion. The objectives of the present study were to determine whether a 1-mo supplementation of dietary fiber as wheat bran increases urinary equol excretion in equol excreters and stimulates equol production in nonexcreters and whether longer-term soy isoflavone intake increases equol production or alters overall urinary isoflavone excretion. First, we screened 74 women, ages 20-40 y, and determined their equol-excreter status. In these women, health and lifestyle patterns and habitual dietary intake did not differ according to equol-excreter status. Next, 26 of the women (13 equol excreters and 13 nonexcreters) were assigned (blocked on equol-excreter status) to either longer-term (1 mo) or short-term (4 d) soy protein supplementation. Within each soy treatment group, women participated in two 1-mo intervention periods (the exact length was determined by each woman's menstrual cycle) during which they consumed their usual diets supplemented daily with either 0 or 16 g dietary fiber in a randomized crossover design. A 1-mo washout period separated the two diet periods. Among the 19 women who completed both periods, fiber supplementation did not increase equol production in equol excreters or nonexcreters. In addition, isoflavonoid excretion did not differ by fiber dose or length of soy intervention. These results suggest that a daily 16 g-fiber dose as wheat bran and the addition of soy protein do not alter significantly the capacity of colonic microflora to produce equol.

Alpha- and gamma-tocotrienols are metabolized to carboxyethyl-hydroxychroman derivatives and excreted in human urine

Limited information is available regarding metabolism of vitamin E forms, especially the tocotrienols. Carboxyethyl-hydroxychromans (alpha- and gamma-CEHC) are human urinary metabolites of alpha- and gamma-tocopherols, respectively. To evaluate whether tocotrienols are also metabolized and excreted as urinary CEHC, urine was monitored following tocotrienol supplementation. Complete (24 h) urine collections were obtained for 2 d prior to (baseline), the day of, and 2 d after human subjects (n = 6) ingested tocotrienol supplements. The subjects consumed 125 mg gamma-tocotrienyl acetate the first week, then the next week 500 mg; then 125 mg alpha-tocotrienyl acetate was administered the third week, followed by 500 mg the fourth week. Urinary alpha- and gamma-CEHC were measured by high-performance liquid chromatography with electrochemical detection. Urinary gamma-CEHC levels rose about four- to sixfold in response to the two doses of gamma-tocotrienol and then returned to baseline the following day. Significant (P < 0.0001) increases in urinary alpha-CEHC were observed only following ingestion of 500 mg alpha-tocotrienyl acetate. Typically, 1-2% of alpha-tocotrienyl acetates or 4-6% of gamma-tocotrienyl acetates were recovered as their respective urinary CEHC metabolites. A gamma-CEHC excretion time course showed an increase in urinary gamma-CEHC at 6 h and a peak at 9 h following ingestion of 125 mg gamma-tocotrienyl acetate. In summary, tocotrienols, like tocopherols, are metabolized to CEHC; however, the quantities excreted in human urine are small in relation to dose size.

Urinary alpha-tocopherol metabolites in alpha-tocopherol transfer protein-deficient patients

Patients with alpha-tocopherol transfer protein (alpha-TTP) defects experience neurological symptoms characteristic of vitamin E deficiency and depend on continuous high alpha-tocopherol supplements. We investigated the excretion of 2,5,7, 8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), a urinary metabolite of alpha-tocopherol, as a putative marker for the alpha-tocopherol status of alpha-TTP-deficient patients and control subjects. In three patients vitamin E supplementation was stopped for short periods of time, during which plasma alpha-tocopherol concentrations and urinary alpha-CEHC excretion were measured. In the patients, plasma alpha-tocopherol decreased below normal (<5 micromol/l) but alpha-CEHC excretion remained above the range of unsupplemented control subjects (0.118-0.306 mg/day, n = 6). In healthy subjects, however, alpha-CEHC excretion was increased only after surpassing a plasma alpha-tocopherol threshold of 30-40 micromol/l. Such a threshold did not exist in patients. The general mechanism of alpha-tocopherol degradation did not appear to differ between patients and control subjects. The presumed mechanism of omega- and subsequent beta-oxidation was supported by the detection of alpha- CPHC, an alpha -CEHC homolog with a side chain longer by 3 carbon atoms, both in supplemented patients and in control subjects.

A new method for the analysis of urinary vitamin E metabolites and the tentative identification of a novel group of compounds

There is currently interest in measuring urinary metabolites of vitamin E. It has been suggested that alpha-to-copheronolactone (alphaTL), with an oxidized chroman ring, may be an indicator of in vivo oxidative stress and 2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman (alpha-CEHC), with a shortened side chain but intact hydroxychroman ring, may provide a measure of adequate or excess vitamin E status. To date, methods in the literature have tended to concentrate on the estimation of single metabolites. We describe the establishment and validation of a relatively simple and reproducible method to extract and quantitate a range of vitamin E metabolites using 0.5 ml of human urine. The vitamin E metabolites were extracted from urine using solid phase extraction cartridges, deconjugated enzymatically, and analyzed using gas chromatography-mass spectrometry. Using this method we have identified alphaTL and the CEHC metabolites derived from alpha-, delta-, and gamma-tocopherol. In addition we have tentatively identified a novel group of vitamin E metabolites, which are related to the CEHCs but have three extra carbons in the side chain. The possibility of the artifactual oxidation of alpha-CEHC to alphaTL during the assay procedure is also discussed.

Interindividual variation in metabolism of soy isoflavones and lignans: influence of habitual diet on equol production by the gut microflora

The soy isoflavones, daidzein and genistein, and the lignans, matairesinol and secoisolariciresinol, are phytoestrogens metabolized extensively by the intestinal microflora. Considerable important evidence is already available that shows extensive interindividual variation in isoflavone metabolism, and we have investigated the extent of this variation in a crossover study of a soy-containing food low or high in isoflavones (each treatment period lasted for 17 days, and the 2 treatment periods were separated by a 25-day washout period) in 24 healthy subjects [19 women and 5 men, mean age 30 yr, range 19-40, mean body mass index 22.5 +/- 3.5 (SD) kg/m2]. There was a 16-fold variation in total isoflavonoid excretion in urine after the high-isoflavone treatment period. The variation in urinary equol excretion was greatest (664-fold), and subjects fell into two groups: poor equol excretors and good equol excretors (36%). A significant negative correlation was found between the proportion of energy from fat in the habitual diet and urinary equol excretion (r = -0.55; p = 0.012). Good equol excretors consumed less fat as percentage of energy than poor excretors (26 +/- 2.3% compared with 35 +/- 1.6%, p < 0.01) and more carbohydrate as percentage of energy than poor excretors (55 +/- 2.9% compared with 47 +/- 1.7%, p < 0.05). Interindividual variation in the urinary excretion of O-desmethyl-angolensin (O-DMA) was also apparent (76-fold after the high-isoflavone treatment period), but there was no relationship between equol excretion and O-DMA excretion. Enterolactone was the major lignan metabolite in urine and plasma but showed less interindividual variation than equol and O-DMA. It is suggested that the dietary fat intake decreases the capacity of gut microbial flora to synthesize equol.

Estrogenic activity of flavonoids in mice. The importance of estrogen receptor distribution, metabolism and bioavailability

The in vivo estrogenic potential of the flavonoids apigenin, kaempferol, genistein and equol was investigated in immature female mice. Genistein and equol, administered by gavage for 4 consecutive days [post-natal day (PND) 17-20, 100 mg/kg body weight], was found to significantly increase uterine weights and the overall uterine concentration of estrogen receptor alpha (ERalpha). In kaempferol- and equol-exposed mice the cytosolic ERalpha concentration was significantly increased as compared to the solvent control, which is speculated to result in an increased sensitivity of the uterus to subsequently encountered estrogens. Oral administration of equol, genistein, biochanin A and daidzein to 6-week-old female mice revealed a great variation in their systemic bioavailability. The urinary recovery of equol was thus over 90% of a single gavage administered dose, whereas the urinary recoveries of biochanin A, genistein and daidzein were 16, 11 and 3%, respectively. Most of the metabolites were either hydroxylated or dehydrogenated forms of the parent compounds. The in vitro estrogenic potency of some of the metabolites was greater than that of the parent compounds, whereas others were of similar or lower potency. Bioavailability, metabolism, the ability to alter ERalpha distribution in the uterus and the estrogenic potential of parent compound and metabolites may thus contribute to the differences in in vivo estrogenicity of dietary flavonoids.

Intestinal absorption and excretion of troglitazone sulphate, a major biliary metabolite of troglitazone

1. Deconjugation by sulphate transfer and intestinal absorption of troglitazone sulphate (M1), the major metabolite of a thiazolidinedione antidiabetic drug, troglitazone, were studied in the male F344 rat using 14C-troglitazone, 4C-M1 and 35S-M1. 2. Some part of M1, produced in the liver and excreted mostly in the bile, was deconjugated in the intestine to the parent compound, troglitazone, by arylsulphate sulphotransferase originated from intestinal flora. However, deconjugation of M1 was not catalyzed by arylsulphatases. Caecal injection of M1 led to the appearance of troglitazone and M1 in plasma. 3. Biliary excretion mostly as M1, and, following absorption, as M1 and troglitazone after deconjugation, were indicated as the basis for the enterohepatic circulation of troglitazone. 4. Enterohepatic circulation may prolong the pharmacological effects of troglitazone.

Pharmacokinetics of the insulin-sensitizing agent troglitazone in cats

OBJECTIVE

To determine pharmacokinetics of troglitazone in healthy cats after i.v. and oral administration of a single dose of the drug.

ANIMALS

5 healthy ovariohysterectomized adult cats.

PROCEDURE

Using a randomized crossover design, cats were given 5 mg of troglitazone/kg of body weight i.v. and 40 mg of troglitazone/kg orally. Blood and urine samples were collected after drug administration, and concentrations of troglitazone in plasma and urine were determined by use of high-performance liquid chromatography.

RESULTS

Area-moment analysis was used to calculate pharmacokinetic variables. Terminal phase half-life was 1.1 +/- 0.1 hours. Steady-state volume of distribution was 0.23 +/- 0.15 L/kg. After i.v. administration, clearance was 0.33 +/- 0.04 L/h/kg. Drug was not detected in urine samples. Mean bioavailability of orally administered troglitazone was 6.9%.

CONCLUSIONS AND CLINICAL RELEVANCE

The overall disposition of troglitazone in cats was similar to that reported in other species, including humans. Troglitazone has low and variable oral bioavailability. Clearance of the compound is moderate. Little if any unchanged troglitazone is excreted in urine; thus, metabolism and biliary excretion play predominant roles in elimination of the drug. On the basis of troglitazone pharmacokinetics in healthy cats, as well as on the basis of pharmacodynamics of the drug in humans and other animals, a regimen that uses a dosage of 20 to 40 mg/kg administered orally once or twice per day to cats will produce plasma concentrations of the insulin-sensitizing agent that have been documented to be effective in humans.

Occurrence and determination of a natriuretic hormone, 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxy chroman, in rat plasma, urine, and bile

The occurrence of a new natriuretic hormone, 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxy chroman (LLU-alpha, gamma-CEHC) in rat plasma was demonstrated and its concentration was determined using a coupled-column HPLC with a fluorometric derivatization with 4-N,N-dimethylaminosulfonyl-7-piperazino-2,1,3-benzoxadiazol e (DBD-PZ) followed by O-acetylation. The concentration of LLU-alpha was 328 +/- 113 nM in rat plasma (N = 5). LLU-alpha was found in not only urine, but also bile, suggesting an enterohepatic circulation in body. We also assigned the configuration at C-2 of LLU-alpha in these biological fluids as (S)-form by an HPLC with a chiral column. The LLU-alpha concentration decreased significantly by fasting for 3 days (P < 0.01). These results support the possibility that LLU-alpha is produced from gamma-tocopherol in diet via oxidative metabolism without racemization.

Premenopausal equol excretors show plasma hormone profiles associated with lowered risk of breast cancer

Increased urinary excretion of equol, a metabolite of the isoflavone daidzein, has been associated with a reduced risk of breast cancer. This risk reduction has generally been presumed to be a consequence of increased isoflavone consumption. However, only 30-40% of the population excretes more than trace amounts of equol, regardless of isoflavone intake. Accordingly, we hypothesized that the observed apparent protective effect of equol is at least in part attributable to hormonal differences between equol excretors and non-excretors, and that these differences are largely independent of isoflavone intake. We measured plasma hormone and sex hormone binding globulin (SHBG) concentrations in 14 normally cycling premenopausal women during each of three diet periods in which they consumed differing isoflavone doses (0.15, 1.0, and 2.0 mg/kg of body weight/day) as a component of soy protein isolate. The plasma hormone and SHBG concentrations of equol excretors (n = 5) were then compared with those of the non-excretors (n = 9). Results showed that even at the lowest dose, urinary equol excretion values for excretors far exceeded those for non-excretors consuming the highest dose. At all doses, equol excretors generally had lower concentrations of estrone, estrone-sulfate, testosterone, androstenedione, dehydroepiandrosterone (DHEA), DHEA-sulfate, and cortisol and higher concentrations of SHBG and midluteal progesterone, a hormonal pattern overall consistent with lowered breast cancer risk. In conclusion, the association of equol excretion and lowered breast cancer risk may largely reflect the tendency of equol excretors to have more favorable hormonal profiles, as opposed to merely reflecting increased isoflavone intake. Equol may be a marker for the presence of colonic bacterial enzymatic activity that increases fecal steroid excretion. Alternatively, equol itself, even with very modest isoflavone intake, may exert beneficial effects on the regulation of endogenous hormones.

Comparison of isoflavones among dietary intake, plasma concentration and urinary excretion for accurate estimation of phytoestrogen intake

Biological effects of dietary isoflavones, such as daidzein and genistein are of interest in preventive medicine. We estimated the dietary intake of isoflavones from dietary records and compared the values with the plasma concentrations and urinary excretions in Japanese middle-aged women. The dietary intake of daidzein and genistein was 64.6 and 111.6 mumol /day/capita (16.4 and 30.1 mg/day/capita), respectively. The isoflavones intake was mostly attributable to tofu, natto and miso. The median of plasma daidzein and genistein concentration was 72.46 and 206.09 nmol/L, respectively. The median of urinary excretion was 20.54 mumol /day for daidzein, 10.79 for genistein, 15.74 for equol and 1.64 for O-desmethylangolensin (O-DMA). Equol and O-DMA were excreted by 50% and 84% of all participants, respectively. Equol metabolizers were significantly lower the plasma and urinary daidzein and urinary O-DMA. The dietary intake of daidzein and genistein after the adjustment for total energy intake was significantly correlated with the urinary excretion (r = 0.365 for daidzein and r = 0.346 for genistein) and plasma concentration (r = 0.335 for daidzein and r = 0.429 for genistein). The plasma concentration of isoflavones was also significantly correlated with the urinary excretion. We conclude that in epidemiological studies measurements of plasma concentration or urinary excretion of these isoflavones are useful biomarkers of dietary intake and important for studies on their relation to human health.

Urinary excretion of 2,7, 8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman is a major route of elimination of gamma-tocopherol in humans

Little is known of the post-absorptive, metabolic fate of gamma-tocopherol, the major form of vitamin E in North American diets. The objective of this study was to determine the extent of urinary excretion of 2,7, 8-trimethyl-2-(beta-carboxyethyl)-6-hydroxychroman (gamma-CEHC), a recently identified metabolite of gamma-tocopherol. A method for measurement of urinary gamma-CEHC was developed, using gas chromatography-mass spectrometry (GC-MS) with a deuterated internal standard, 2,7,8-trimethyl-2-(beta-carboxyethyl)-(3, 4-2H2)-6-hydroxychroman (d2-gamma-CEHC). This standard was synthesized by dehydrogenation of 6-acetyl-gamma-CEHC followed by deuteration of the resulting 3,4-double bond. The use of d2-gamma-CEHC resulted in accurate determinations of the concentration of d0-gamma-CEHC in human urine. Urine samples containing added d2-gamma-CEHC were treated with beta-glucuronidase, extracted with an organic solvent, and analyzed by GC-MS. Analysis of 24-h urine pools from healthy subjects revealed gamma-CEHC concentrations, normalized against creatinine, ranging from 2.5 to 31.5 micromol/g creatinine, or a total of 4.6 to 29.8 micromol per day. These results correspond to 2-12 mg gamma-tocopherol excreted daily as gamma-CEHC in the urine. Given an estimated mean intake of gamma-tocopherol of 20 mg/day, catabolism of gamma-tocopherol to gamma-CEHC, followed by glucuronide conjugation and urinary excretion, is a major pathway for elimination of gamma-tocopherol in humans.

Urinary excretion of isoflavonoids and the risk of breast cancer

Isoflavonoids are a group of biologically active phytochemicals that humans are exposed to mainly through soy food intake. Because of the similar chemical structure of these compounds and estradiol, it has been hypothesized that isoflavonoids may be related to the risk of breast cancer. Overnight urine samples from 60 incident breast cancer cases and their individually matched controls were assayed for urinary excretion rates of five major isoflavonoids (daidzein, genistein, glycitein, equol, and O-desmethylangolensin) and total phenols. These subjects were from a large population-based case-control study conducted in Shanghai, and urine samples from breast cancer cases were collected before any cancer therapy to minimize the potential influence of the disease and its sequelae on study results. Urinary excretion of total phenols and all individual isoflavonoids, particularly glycitein, was substantially lower in breast cancer cases than controls. For total isoflavonoids, the mean excretion was 13.95 nmol/mg creatinine (SD, 20.76 nmol/mg creatinine) for cases and 19.52 nmol/mg creatinine (SD, 25.36 nmol/mg creatinine) for controls (P for difference = 0.04). The case-control difference was more evident when median levels of these compounds were compared, with the median excretion of all major isoflavonoids being 50-65% lower in cases than in controls. Individuals in the highest tertile of daidzein, glycitein, and total isoflavonoids had about half the cancer risk of those in the lowest tertile. The adjusted odds ratio for breast cancer was 0.14 (95% confidence interval, 0.02-0.88) for women whose urinary excretion of both phenol and total isoflavonoids was in the upper 50% compared with those in the lower 50%. The results from this study support the hypothesis that a high intake of soy foods may reduce the risk of breast cancer.

Phytoestrogens: dietary intake and excretion in postmenopausal Chinese women

OBJECTIVES

The aims of this study were to estimate the dietary intake of phytoestrogens and to measure urinary phytoestrogen excretion in postmenopausal Chinese women.

METHODS

Postmenopausal Chinese women were recruited from the hormone replacement clinic of the Prince of Wales Hospital. Dietary intake of phytoestrogen-rich foods was estimated using a food frequency questionnaire. Urinary output of the isoflavonoids daidzein and genistein and the metabolite of daidzein, equol, was measured using high-performance liquid chromatography.

RESULTS

The mean daily excretion of daidzein, genistein and equol was 3.24 (+/- 3.63), 1.47 (+/- 1.75) and 0.64 (+/- 1.53) mumol, respectively. The total mean daily isoflavonoid excretion was 5.36 (+/- 5.27) mumol.

CONCLUSIONS

Urinary excretion of isoflavonoid phytoestrogens in this Chinese population was lower than that reported in Japanese subjects. This may be due to the higher consumption of legumes, especially soy products, in the Japanese compared to the Chinese diet. The intake of green vegetables was higher in the Chinese subjects, and this food group may be the main contributor to their total phytoestrogen intake.

Daidzein conjugates are more bioavailable than genistein conjugates in rats

This study compared the bioavailability of conjugates of the soy isoflavones genistein and daidzein in rats. Rats were given a single oral dose of a soy extract that provided 74 micromol genistein and 77 micromol daidzein/kg body wt (as conjugates). Plasma samples were obtained from treated and untreated rats; urine and fecal samples were obtained before and after treatment. Isoflavones, equol (the main end product of bacterial degradation of daidzein), and 4-ethyl phenol (the main end product from genistein) were measured by HPLC. The plasma daidzein concentration was maximal at 2 h (9.5 +/- 0.71 micromol/L) and was almost double that of genistein (P = 0.009). Between 2 and 15 h, the plasma daidzein concentration declined by 32%, but the concentration of genistein changed little. At 15 h, the concentrations of daidzein and genistein were not significantly different. Urinary excretion of daidzein over the 48-h postdose period was 17.4 +/- 1.2% of the dose, but only 11.9 +/- 1.1% of the genistein dose was excreted in urine. Equol excretion was 5.0 +/- 1.5% of the daidzein dose, but 41.9 +/- 5.0% of the genistein dose was excreted as 4-ethyl phenol. Fecal daidzein accounted for 2.3 +/- 0.5% and fecal genistein for 3.4 +/- 0.4% of the respective doses. It is concluded that conjugates of daidzein are more bioavailable than those of genistein, probably because of the greater resistance of the former to degradation by gut bacteria.

Phyto-oestrogen excretion and rate of bone loss in postmenopausal women

OBJECTIVE

The hypothesis was tested that the rate of postmenopausal bone loss is inversely associated with long-term urinary excretion of phyto-oestrogens, as a marker of habitual dietary intake.

DESIGN

Secondary analysis of a 10-year follow-up study (1979 1989) among postmenopausal women in the Netherlands.

SUBJECTS

From the original population of 154 women, 32 women were selected with an annual rate of radial bone loss of < or = 0.5% over the first 5 years of the study and 35 women with a rate of > or = 2.5% per year.

METHODS

The isoflavonoids genistein, daidzein and equol, and the lignan enterolactone were determined by gas chromatography mass spectrometry in aggregate samples from annually collected urine samples. Cortical bone density of the radius had previously been measured annually by single-photon absorptiometry.

RESULTS

Excretion of isoflavonoids did not differ between both groups, although in multivariate analysis equol excretion was weakly positively associated with rate of bone loss in the 5 years after the menopause. Enterolactone excretion was significantly higher in the group with high rate of bone loss. This positive association remained in multivariate linear regression analysis after adjustment for age, years since menopause, body mass index and intake of calcium, vegetable protein and dietary fibre.

CONCLUSIONS

Enterolactone excretion is likely to be an indicator of consumption of grains and legumes; it is not clear whether the observed positive association with rate of bone loss is a causal one. Our results do not support a preventive effect of low, unsupplemented dietary intake of phyto-oestrogens on postmenopausal cortical bone loss. However, no conclusions can be drawn about effects of higher doses of phyto-oestrogens.

Synthetic as compared with natural vitamin E is preferentially excreted as alpha-CEHC in human urine: studies using deuterated alpha-tocopheryl acetates

Alpha-CEHC (2,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman) is a urinary vitamin E metabolite with a truncated phytyl tail. To test whether natural and synthetic vitamin E are similarly converted to alpha-CEHC, 6 humans consumed 150 mg each RRR-alpha-[5-(C2H3)]- and all rac-alpha-[5,7(C2H3)2]-tocopheryl acetates (d3RRR-alpha- and d6all rac-alpha-tocopheryl acetates, respectively). Plasma was collected at 0, 6, 12 and 24 h; urine (24 h) at 0, 1, 2, 3, 4 and 8 days. Following dosing, plasma was enriched with d3RRR-alpha-tocopherol, while urine was enriched with alpha-CEHC derived from d6all rac-alpha-tocopherol. Thus, synthetic compared with natural vitamin E is preferentially metabolized to alpha-CEHC and excreted.

Urinary metabolites of daidzin orally administered in rats

In a study on the metabolism of flavonoids, the isoflavone glycoside daidzin was orally administered to rats. Urine samples were collected and treated with beta-glucuronidase and arylsulfatase. Aglycone daidzein (M3) and other three metabolites, 3',4',7-trihydroxyisoflavone (M1), 4',7-dihydroxyisoflavanone (M2) and 4',7-dihydroxyisoflavan (M4) were isolated from the urine following treatment with enzymes. The structures of M1, M2 and M4 were determined on the basis of chemical and spectral data.

Plasma and urinary kinetics of the isoflavones daidzein and genistein after a single soy meal in humans

The aim of this study was to determine the pharmacokinetics and urinary excretion patterns of the soy isoflavones daidzein and genistein in humans. Six healthy men with a mean age of 37 y and a mean body mass index (in kg/m2) of 24 consumed a soybean flour-based meal on two occasions approximately 6 d apart. Blood samples and total urine were collected at intervals for the measurement of daidzein and genistein with HPLC. Isoflavone concentrations rose slowly and reached maximum values of 3.14 +/- 0.36 micromol/L at 7.42 +/- 0.74 h for daidzein and 4.09 +/- 0.94 micromol/L at 8.42 +/- 0.69 h for genistein. Elimination half-lives were 4.7 +/- 1.1 and 5.7 +/- 1.3 h for daidzein and genistein, respectively. The slow increase in plasma concentrations is consistent with the facilitation of absorption by hydrolysis in the small and large intestines of the glycosidic forms of the isoflavones present in soybean-containing foods to their corresponding aglycones. The rate of urinary excretion of daidzein was greater than that of genistein throughout the postmeal period, with mean recoveries of 62 +/- 6% and 22 +/- 4% (P < 0.001) for daidzein and genistein, respectively. However, the ratio of the areas under the plasma concentration versus time curves for genistein and daidzein was equal to the ratio of the concentrations of the respective isoflavones in the soy meal. It is concluded that the bioavailabilities of daidzein and genistein are similar, not withstanding the difference in urinary excretion.

Urinary equol excretion with a soy challenge: influence of habitual diet

Equol is an isoflavonoid phytoestrogen produced from the soy isoflavone daidzein by gut microflora. Not all humans produce equol from daidzein, presumably due to differences in colonic bacterial populations among individuals. Previously, smaller studies reported that approximately 30% of participants excreted equol when consuming soy. The purpose of our study was to determine the prevalence of equol excreters in a larger sample and to examine what dietary components might influence the tendency to be an equol excreter. Thirty men and thirty women consumed a soy protein beverage containing 22 mg genistein and 8 mg daidzein for 4 days as a supplement to their habitual diets. The mean daily nutrient content of their habitual intakes was determined from 4-day food records. On Day 4, participants provided a 24-hour urine collection. Urinary isoflavonoid (genistein, daidzein, equol, and O-desmethylangolensin) excretion was measured by gas chromatography-mass spectrometry. Twenty-one of the 60 participants (35%) excreted equol (> 2000 nmol/day) after 3 days of consuming the soy supplement. Daily equol excretion ranged from 2,134-20,301 nmol/day in the excreters and 21-233 nmol/day in the nonexcreters. There was no difference in equol excreter prevalence between men (43%) and women (27%). Daily excretion of daidzein, genistein, and O-desmethylangolensin was similar between equol excreters and nonexcreters and between men and women. Among the women, equol excreters consumed a significantly higher percentage of energy as carbohydrate and greater amounts of plant protein and dietary fiber, both as soluble and insoluble fiber compared to nonexcreters. Such differences were not observed in the men, who overall had significantly higher fiber intakes than the women. These data suggest that, among women, dietary fiber or other components of a high-fiber diet may promote the growth and/or the activity of bacterial populations responsible for equol production in the colon.