Analysis of soy isoflavone conjugation in vitro and in human blood using liquid chromatography-mass spectrometry.
(33/1619)
Soybean products containing isoflavones are widely consumed in Western and Asian diets for putative health benefits, but adverse effects are also possible. The conjugated forms of isoflavones present in a soy nutritional supplement (predominately acetyl glucosides) and in blood from two human volunteers after consuming the supplement (7- and 4'-glucuronides and sulfates) were identified using liquid chromatography coupled with electrospray/tandem mass spectrometry. Circulating conjugates of genistein and daidzein were quantified using selective enzymatic hydrolysis and deuterated internal standards for liquid chromatography-electrospray/mass spectrometry. The levels of isoflavone glucuronides were much greater than the corresponding sulfates or aglycones. The substrate activities of genistein and daidzein were evaluated with recombinant human UDP glucuronosyl transferase (UGT) and sulfotransferase (SULT) by using enzyme kinetics. The SULTs 1A1*2, 1E, and 2A1 catalyzed formation of a single genistein sulfate; however, SULTs 1A2*1 and 1A3 had no observed activity. None of the SULTs showed activity with daidzein. Although several UGTs (1A1, 1A4, 1A6, 1A7, 1A9, and 1A10) catalyzed 7- and 4'-glucuronidation of genistein or daidzein, the UGT 1A10 isoform, which is found in human colon but not liver, was found to be specific for genistein. Glucuronidation of only genistein was observed in human colon microsomes, although nearly equal activity was observed for daidzein in human liver and kidney microsomes. These findings suggest a prominent role for glucuronidation of genistein in the intestine concomitant with absorption, although hepatic glucuronidation of absorbed genistein and daidzein aglycones is also likely. (+info)
Dietary flavonoid and isoflavone glycosides are hydrolysed by the lactase site of lactase phlorizin hydrolase.
(34/1619)
Lactase phlorizin hydrolase (LPH; EC 3.2.1.62) is a membrane-bound, family 1 beta-glycosidase found on the brush border of the mammalian small intestine. LPH, purified from sheep small intestine, was capable of hydrolysing a range of flavonol and isoflavone glycosides. The catalytic efficiency (k(cat)/K(m)) for the hydrolysis of quercetin-4'-glucoside, quercetin-3-glucoside, genistein-7-glucoside and daidzein-7-glucoside was 170, 137, 77 and 14 (mM(-1) s(-1)) respectively. The majority of the activity occurred at the lactase and not phlorizin hydrolase site. The ability of LPH to deglycosylate dietary (iso)flavonoid glycosides suggests a possible role for this enzyme in the metabolism of these biologically active compounds. (+info)
Evaluation of soy phytoestrogens for the treatment of hot flashes in breast cancer survivors: A North Central Cancer Treatment Group Trial.
(35/1619)
PURPOSE: Hot flashes represent a significant clinical problem for some breast cancer survivors. Safe, effective treatment is needed for this prominent clinical problem. Although it has been shown that estrogen or progesterone replacement therapy can alleviate this problem, there are continued safety concerns regarding the use of hormonal therapies in these women. Based on anecdotal information, we hypothesized that soy-derived phytoestrogens, weak estrogen-like substances in the soybean that demonstrate estrogen agonist and/or antagonist effects when they bind to estrogen receptors, could alleviate hot flashes. This current trial was designed to investigate this hypothesis. PATIENTS AND METHODS: This double-blind clinical trial involved breast cancer survivors with substantial hot flashes. After randomization, patients underwent a 1-week baseline period with no therapy. This was followed by 4 weeks of either soy tablets or placebo. The patients then crossed over to the opposite arm in a double-blind manner for the last 4 weeks. Patients completed a daily questionnaire documenting hot flash frequency, intensity, and perceived side effects. RESULTS: Of the 177 women who were randomized and started the study substance, 155 (88%) provided useable data over the first 5 weeks; 149 provided usable data over the entire 9 weeks. There was no suggestion that the soy product was more effective in reducing hot flashes than the placebo. At study completion, patients preferred the soy product 33% of the time, the placebo 37% of the time, and neither substance 31% of the time. No toxicity was observed. CONCLUSION: The soy product did not alleviate hot flashes in breast cancer survivors. (+info)
Differential inhibition of multiple cAMP phosphodiesterase isozymes by isoflavones and tyrphostins.
(36/1619)
A series of isoflavone and tyrphostin compounds were found to inhibit the degradation of cAMP by several cyclic nucleotide phosphodiesterase (PDE) isozymes. Specific hydroxyl groups on the isoflavone structure were critical for PDE isozyme-selective inhibition. Replacement of the C-7 hydroxyl group of the isoflavone with a methoxy group raised the IC(50) for PDE1, PDE3, and PDE4. The absence of the C-5 hydroxyl group raised the IC(50) from 5 to >100 microM for PDE4, but actually lowered the IC(50) for PDE3 and PDE1. Replacement of the C-4' hydroxyl group with a methoxy group raised the IC(50) for PDE3 and PDE1, yet only slightly changed the IC(50) for PDE4. Various tyrphostins were also potent inhibitors of PDE1, PDE3, and PDE4. The four-carbon side chained tyrphostins were much less potent; however, a very interesting pattern was observed in which removal of phenolic hydroxyls on the tyrphostin structure increased the potency for PDE1 and PDE3, but not PDE4. These results may help to explain some of the therapeutic and intracellular signaling effects of isoflavones and tyrphostins. Moreover, the isozyme selectivity demonstrated by the isoflavones and tyrphostins can serve as a pharmacophore for the design of specific PDE inhibitors. (+info)
Increased urinary excretion of 2-hydroxyestrone but not 16alpha-hydroxyestrone in premenopausal women during a soya diet containing isoflavones.
(37/1619)
Asian diets high in soy are associated with lower risk for breast cancer compared with Western diets. Moreover, higher levels of two putative carcinogenic metabolites of 17beta-estradiol, 4- and 16alpha-hydroxyestrogen, and lower amounts of anticarcinogenic metabolites, 2-hydroxyestrogens, have been associated with greater breast cancer risk. In this study, we tested the hypothesis that consumption of a soya diet containing the weakly estrogenic isoflavones genistein and daidzein may alter the metabolism of 17beta-estradiol to 2- and 16alpha-hydroxylated products. Eight pre-menopausal women were placed on a soya-containing, constant diet in a metabolic unit. The diet provided 400 kilocalories from soymilk and 113-202 mg/day (158 +/- 26 mg/day, mean +/- SD) isoflavones daily for a complete menstrual cycle. After a washout period of 4 months, the subjects consumed the same diet, but with soymilk that contained <4.5 mg/day isoflavones ("isoflavone-free"). Urine samples were collected for 24 h daily for the entire cycle during each soya diet period for the analysis of daidzein, genistein, and 2- and 16alpha-hydroxyestrone. Subjects excreted measurable amounts of daidzein (11.6-39.2 mg/day) and genistein (2.9-18.2 mg/day) during the isoflavone-rich soya diet but not during the isoflavone-free soya diet. The diet rich in isoflavones increased the cycle mean daily urinary excretion of 2-hydroxyestrone (averaged over the entire cycle) from 11.6 +/- 2.06 to 17.0 +/- 2.96 nmol/12-h (P = 0.03), a 47% increase. However, the mean daily excretion of 16alpha-hydroxyestrone did not change (7.0 +/- 1.14 nmol/12-h during the isoflavone-free and 7.7 +/- 1.25 nmol/12-h during the isoflavone-rich diet; P = 0.36). The ratio of 2-hydroxyestrone to 16alpha-hydroxyestrone was higher during the isoflavone-rich soya diet (2.6 +/- 0.34) than during the isoflavone-free diet (2.0 +/- 0.32; P = 0.01), a 27% increase. These results suggest that soya isoflavones increase the metabolism of endogenous estrogens to the protective 2-hydroxylated estrogens in women, and this may play an important role in lowering 17beta-estradiol levels and the long-term risk for breast cancer. (+info)
Neither background diet nor type of soy food affects short-term isoflavone bioavailability in women.
(38/1619)
To characterize bioavailability of soybean isoflavones, proposed anticarcinogenic food components, eight women, ages 20-41 y, were fed 0.9 mg isoflavones/kg body wt from soymilk at 0730, 1230 and 1730 h for 1 d. Subjects consumed three background diets in random order: a diet prepared for them (basic foods diet) or a self-selected diet at the specified times, or a self-selected diet eaten ad libitum. In a second study, women were fed single isoflavone doses of 0.8-1.4 mg/kg in breakfast casseroles containing tofu, tempeh, cooked soybeans or texturized vegetable protein. Both studies were conducted in randomized, cross-over designs. Plasma, urine and fecal isoflavones were measured by reverse-phase HPLC. After consumption of background diets, 48-h urinary recovery of daidzein (D) was 26-27%, and of genistein (G), 18-20% of the dose given with each diet. At 24 h after consumption of different background diets, plasma D and G concentrations were similar (1.4 +/- 0.7 mmol/L) and were not affected by diet selection. Urinary recoveries of D over 24 h from the various soy foods were 38-51%, and of G, 9-16% of the dose given. In both studies, urinary recovery of D was significantly greater than that of G. Only a few percentage of the total isoflavone dose was recovered in feces, probably due to bacterial breakdown of these compounds. Therefore, isoflavone bioavailability may not be affected by choice of background diet or food source of isoflavones. (+info)
Consumption of soy protein reduces cholesterol absorption compared to casein protein alone or supplemented with an isoflavone extract or conjugated equine estrogen in ovariectomized cynomolgus monkeys.
(39/1619)
Dietary intake of soy protein is associated with reductions in plasma cholesterol. Isoflavones are thought to be active components of soy and responsible for the beneficial effects because of their structural similarities to estrogen. The purposes of this study were to determine if i) soy protein or a semipurified soy extract, rich in isoflavones, is responsible for improving the lipid profile and ii) altered intestinal cholesterol metabolism is one mechanism for hypocholesterolemic effects. Ovariectomized adult female cynomolgus monkeys (40) were assigned to groups fed diets containing i) casein-lactalbumin (CAS) ii) intact soy protein (SOY), iii) CAS plus an isoflavone-rich semipurified soy extract similar in isoflavone content as SOY (ISO) or iv) CAS plus conjugated equine estrogen (CEE) for 20 wk. Cholesterol absorption was determined using the fecal isotope ratio method. Bile acid excretion was measured using the 3alpha-hydroxysteroid dehydrogenase assay. The SOY group had significantly lower total- and VLDL + LDL-cholesterol compared to the other three groups and significantly higher HDL-cholesterol compared to the CAS and CEE groups. Cholesterol absorption was significantly lower in the SOY group compared to the other groups, but bile acid excretion was not significantly affected. The hypocholesterolemic effect of soy protein appears to be mediated in part by decreased cholesterol absorption. The semipurified soy extract, rich in isoflavones, added to casein protein did not have lipid-lowering effects. Other components of soy such as saponins, phytic acid or the amino acid composition may be involved in the hypocholesterolemic effects seen in this study. (+info)
Urinary isoflavonoid and lignan excretion on a Western diet: relation to soy, vegetable, and fruit intake.
(40/1619)
Dietary isoflavone and lignan phytoestrogens are potential chemopreventive agents. This has led to a need to monitor exposure to these compounds in human populations and to determine which components of a mixed diet contribute to the exposure. Typically, urinary isoflavonoid excretion is associated with soy consumption and that of lignans is associated with whole grains. However, other plant foods are known to contain phytoestrogen precursors. The purpose of this study was to examine the association between urinary isoflavonoid and lignan excretion and intakes of vegetables and fruits (V&F). Isoflavonoids (genistein, daidzein, O-desmethylangolensin, and equol) and lignans (enterolactone, enterodiol, and matairesinol) were measured in urine collected for 3 days from 49 male and 49 female volunteers (age, 18-37 years) reporting a wide range of habitual V&F intakes. Dietary intakes were assessed using 5-day diet records and a food frequency questionnaire. V&F groupings (total V&F, total V, total F, soyfoods, and V&F grouped by botanical families) were used to assess the relationship between V&F intake and urinary isoflavonoid and lignan excretion. Pearson correlations were performed. Intake of soyfoods was correlated significantly with urinary genistein (r = 0.40; P = 0.0001), O-desmethylangolensin (r = 0.37; P = 0.0002), daidzein (r = 034; P = 0.0007), and the sum of isoflavonoids (r = 0.39; P = 0.0001). There was no association between equol excretion and soy intake or between the isoflavonoids and any other V&F groupings. In addition, isoflavonoid excretion was correlated positively with intake of high-fat and processed meats, particularly among men who did not consume soy. This suggests that, even in the United States, on a Western diet, soyfoods are the primary contributors to isoflavone intake; however, additional "hidden sources" of soy may also contribute to exposure. In contrast, a variety of fiber-containing foods contributed to lignan excretion; the sum of the urinary lignans, enterodiol, enterolactone, and matairesinol, was associated with intake of total F (r = 0.27; P = 0.008), total V&F (r = 0.25; P = 0.01), soyfoods (r = 0.28; P = 0.006), and dietary fiber (r = 0.36; P = 0.0003). Overall, urinary phytoestrogens (isoflavonoids + lignans) were significantly higher in "high" compared with "low" V&F consumers. Compared with the "low" V&F group, the "high" group consumed diets that were, on average, higher in fiber and carbohydrate and soyfoods and lower in fat; thus, the urinary phytoestrogens may also be a useful marker of healthier dietary patterns. (+info)