Gut bacterial metabolism of the soy isoflavone daidzein: exploring the relevance to human health

The indigenous intestinal microflora are involved in a variety of processes within the human body, and are important for maintaining host health. As such, interindividual differences in the ability to harbor certain intestinal bacteria might be associated with interindividual differences in health and/or disease susceptibility. In the last decade there has been considerable interest in phytoestrogen intakes in relation to human health. Daidzein, an isoflavone phytoestrogen found in soy, is metabolized to equol and O-desmethylangolensin (O-DMA) by intestinal bacteria. The specific bacterium/bacteria responsible for equol and O-DMA production in humans have yet to be identified definitively, but in vitro and animal studies have suggested that equol and O-DMA are more biologically active than their precursor daidzein. Interestingly, substantial interindividual differences in daidzein metabolism exist; following soy or daidzein consumption, approximately 30%-50% of the human population produce equol, and approximately 80%-90% produce O-DMA. Observational and intervention studies in humans have suggested that the ability to produce equol and O-DMA may be associated with reduced risk of certain diseases including breast and prostate cancers. However, relatively few studies have been conducted to date. In this review, we discuss the available evidence for a relationship between daidzeinmetabolizing phenotypes and human health, and suggest potential mechanisms for some of the reported relationships.     

Mammalian phytoestrogens: enterodiol and enterolactone

The mammalian phytoestrogens enterodiol (END) and enterolactone (ENL) are produced in the colon by the action of bacteria on the plant precursors matairesinol (MAT), secoisolariciresinol (SECO), their glycosides, and other precursors in the diet. Both END and ENL have been shown to possess weakly estrogenic and antiestrogenic activities, and it has been suggested that the high production of these antiestrogenic mammalian lignans in the gut may serve to protect against breast cancer in women and prostate cancer in men. Various in vitro experiments suggested END and ENL significantly inhibited the growth of human colon tumor cells, and the E2-induced proliferation of MCF-7 breast cancer cells was inhibited by ENL. The protective effects of mammalian lignans may be due to their ability to compete with E2 for the type II estrogen receptor, to induce sex hormone binding globulin (SHBG), to inhibit placental aromatase, and to act as antioxidants. This review mainly deals with the chemistry, quantitative analysis, biological properties and health effects of END and ENL.     

Variations in metabolism of the soy isoflavonoid daidzein by human intestinal microfloras from different individuals

Isoflavonoids found in legumes, such as soybeans, are converted by intestinal bacteria to metabolites that might have increased or decreased estrogenic activity. Variation in the effects of dietary isoflavonoids among individuals has been attributed to differences in their metabolism by intestinal bacteria. To investigate this variation, the metabolism of the isoflavonoid daidzein by bacteria from ten fecal samples, provided at different times by six individuals on soy-containing diets, was compared. After anaerobic incubation of bacteria with daidzein for 2 weeks, four samples had metabolized daidzein and six samples had not. Three of the positive samples were from individuals whose microflora had not metabolized daidzein in previous samples. Dihydrodaidzein was observed in one sample, dihydrodaidzein and equol in another sample, and equol and O-desmethylangolensin in two other samples. These results corroborate the hypothesis that the microflora of the gastrointestinal tract of an individual influences the particular isoflavone metabolites produced following consumption.     

Effect of dietary components, including lignans and phytoestrogens, on enterohepatic circulation and liver metabolism of estrogens and on sex hormone binding globulin (SHBG)

A brief account of our present knowledge on the enterohepatic metabolism of estrogens and on the origin, metabolism and biological effects of mammalian lignans and phytoestrogens is undertaken. Furthermore, recently published results on the effects of dietary fiber, fat and carbohydrates on estrogen metabolism are reviewed. New preliminary results are presented on quantitative assays of lignans and phytoestrogens in urine of women belonging to various dietary and population groups and in a group of chimpanzees. The highest values of lignans and phytoestrogens were found in the non-human primates, and in macrobiotic, lactovegetarian and Japanese women, all groups considered having a low risk for the development of breast and other hormone-dependent cancer. New results on correlations between intake of various fibers, lignan and phytoestrogen excretion and plasma levels of estrogens, free testosterone and SHBG in women are presented. There is a significant positive correlation between the intake of fiber and urinary excretion of lignans and phytoestrogens, and the concentration of plasma SHBG. Fiber intake and urinary excretion of lignans and equol correlated negatively with plasma percentage free estradiol. Enterolactone excretion correlated negatively with plasma free testosterone. It is concluded that dietary macro- and micronutrients seem to play an important role in estrogen metabolism.     

Familial correlations, segregation analysis, and nongenetic correlates of soy isoflavone-metabolizing phenotypes

Particular intestinal bacteria metabolize the soy isoflavone daidzein to equol and O-desmethylangolensin (O-DMA), metabolites that can be identified in urine. Individuals that harbor bacteria capable of producing equol or O-DMA are known as equol producers (approximately 30%-50% of the population) and O-DMA producers (approximately 80%-90% of the population), respectively. The equol-producer phenotype has been associated with sex hormone-related outcomes in several studies. However, the bacteria responsible for these phenotypes have not yet been identified and factors that influence the manifestation of these phenotypes are not well understood. To evaluate familial clustering of and nongenetic factors associated with these phenotypes, 410 individuals from 112 families participated in phenotyping (3-day soy challenge and Day 4 spot urine collection). In segregation analyses of the equol-producer phenotype, the Mendelian dominant model provided the most parsimonious fit to the data, suggesting that the pattern of inheritance of the equol-producer phenotype is consistent with an autosomal dominant trait. This phenotype was positively associated with education (p trend = 0.01), but not with sex, smoking, or several dietary factors. Results of the segregation analyses of the O-DMA-producer phenotype were inconclusive; no other models provided a more parsimonious fit to the data than the general model. This phenotype was inversely associated with age in a nonlinear model (p = 0.01), positively associated with age- and sex-adjusted height (odds ratio [OR] 10-cm increase = 0.38, 95% confidence interval [CI] = 0.15, 0.95) and body mass index (kg/m(2)) (OR = 0.91, 95% CI = 0.85, 0.96), but not with sex, education, smoking, or several dietary factors. These results suggest the equol-producer phenotype may be under some degree of genetic control and that there are likely other environmental factors not evaluated in the present analysis that contribute to both of these phenotypes. These results provide a foundation for further work to refine our understanding of heritable and environmental determinants of daidzein-metabolizing phenotypes.     

Phytoestrogens and Their Metabolites in Bulk-Tank Milk: Effects of Farm Management and Season

Phytoestrogens have structures similar to endogenous steroids and may induce or inhibit the response of hormone receptors. The objectives of the present study were to compare the effects of long-term vs. short-term grassland management in organic and conventional dairy production systems, compare organic and conventional production systems and assess seasonal variation on phytoestrogen concentrations in bulk-tank milk. The concentrations of phytoestrogens were analyzed in bulk-tank milk sampled three times in two subsequent years from 28 dairy farms: Fourteen organic (ORG) dairy farms with either short-term or long-term grassland management were paired with 14 conventional (CON) farms with respect to grassland management. Grassland management varied in terms of time since establishment. Short-term grassland management (SG) was defined as establishment or reseeding every fourth year or more often, and long-term grassland management (LG) was defined as less frequent establishment or reseeding. The proportion of red clover (Trifolium pretense L.) in the herbage was positively correlated with milk concentrations of the mammalian isoflavone equol. Therefore, organically produced bulk-tank milk contained more equol than conventionally produced milk, and milk from ORG-SG farms had more equol than milk from ORG-LG farms. Milk produced during the indoor-feeding periods had more equol than milk produced during the outdoor feeding period, because pastures contained less red clover than fields intended for silage production. Organically produced milk had also higher concentrations of the mammalian lignan enterolactone, but in contrast to equol, concentrations increased in the outdoor-feeding periods compared to the indoor-feeding periods. There were no indications of fertility problems on ORG-SG farms who had the highest red clover proportions in the herbage. This study shows that production system, grassland management, and season affect milk concentrations of phytoestrogens. However, compared to soy products, milk concentrations of phytoestrogens are low and future studies are required to investigate if the intake of phytoestrogens from dairy products has physiological effects in humans.     

Isolation and characterisation of an equol-producing mixed microbial culture from a human faecal sample and its activity under gastrointestinal conditions

Only about one third of humans possess a microbiota capable of transforming the dietary isoflavone daidzein into equol. Little is known about the dietary and physiological factors determining this ecological feature. In this study, the in vitro metabolism of daidzein by faecal samples from four human individuals was investigated. One culture produced the metabolites dihydrodaidzein and O-desmethylangolensin, another produced dihydrodaidzein and equol. From the latter, a stable and transferable mixed culture transforming daidzein into equol was obtained. Molecular fingerprinting analysis (denaturing gradient gel electrophoresis) showed the presence of four bacterial species of which only the first three strains could be brought into pure culture. These strains were identified as Lactobacillus mucosae EPI2, Enterococcus faecium EPI1 and Finegoldia magna EPI3, and did not produce equol in pure culture. The fourth species was tentatively identified as Veillonella sp strain EP. It was found that hydrogen gas in particular, but also butyrate and propionate, which are all colonic fermentation products from poorly digestible carbohydrates, stimulated equol production by the mixed culture. However, when fructo-oligosaccharides were added, equol production was inhibited. Furthermore, the equol-producing capacity of the isolated culture was maintained upon its addition to a faecal culture originating from a non-equol-producing individual.     

Soybean-derived phytoestrogens regulate prostaglandin secretion in endometrium during cattle estrous cycle and early pregnancy

Phytoestrogens acting as endocrine disruptors may induce various pathologies in the female reproductive tract. The purpose of this study was to determine whether phytoestrogens present in the soybean and/or their metabolites are detectable in the plasma of cows fed a diet rich in soy and whether these phytoestrogens influence reproductive efficiency and prostaglandin (PG) synthesis during the estrous cycle and early pregnancy in the bovine endometrium. In in vivo Experiment 1, we found significant levels of daidzein and genistein in the fodder and their metabolites (equol and p-ethyl-phenol) in bovine serum and urine. The mean number of artificial inseminations (AIs) and pregnancy rates in two kinds of herds, control and experimental (cows fed with soybean 2.5 kg/day), were almost double in the soy-diet herd in comparison with the control animals. In in vivo Experiment 2, three out of five heifers fed soybean (2.5 kg/day) became pregnant whereas four out of five heifers in the control group became pregnant. The concentrations of a metabolite of PGF2alpha (PGFM) were significantly higher in the blood plasma of heifers fed a diet rich in soybean than those in the control heifers throughout the first 21 days after ovulation and AI. The higher levels of PGFM were positively correlated with equol and p-ethyl phenol concentrations in the blood. In in vitro experiments, the influence of isoflavones on PG secretion in different stages of the estrous cycle was studied. Although all phytoestrogens augmented the output of both PGs throughout the estrous cycle, equol and p-ethyl-phenol preferentially stimulated PGF2alpha output. The results obtained lead to the conclusion that soy-derived phytoestrogens and their metabolites disrupt reproductive efficiency and uterus function by modulating the ratio of PGF2alpha to PGE2, which leads to high, nonphysiological production of luteolytic PGF2alpha in cattle during the estrous cycle and early pregnancy.     

Structural determinants of plant lignans for the formation of enterolactone in vivo

The quantity of mammalian lignans enterolactone (ENL) and enterodiol (END) and of plant lignans secoisolariciresinol (SECO) and 7-hydroxymatairesinol (HMR) excreted in a 24-h rat urine sample was measured after a single p.o. dose of an equivalent quantity of secoisolariciresinol diglycoside (SDG), secoisolariciresinol (SECO), matairesinol (MR), 7-hydroxymatairesinol (HMR) and ENL. Plant lignans (SECO and HMR) were partially absorbed as such. The aglycone form of SECO was more efficiently converted into mammalian lignans END and ENL than the glycosylated form, SDG. Of plant lignans, MR produced the highest quantities of ENL: the quantity was over twofold compared with HMR or SDG. The majority of the animals, which had been given SECO, excreted higher quantities of END than ENL into urine, but ENL was the main lignan metabolite after SDG. The highest quantities of ENL in urine were measured after the administration of ENL as such. The (-)SECO isolated from Araucaria angustifolia was converted into (-)ENL only. The administration of (-)SDG, which was shown to produce (+)SECO, resulted in excretion of (+)ENL only and (-)HMR was converted into (-)ENL only. This confirmed that the absolute configurations at C8 and C8' are not changed during the microbial metabolism. Whether the biological effects are enantiomer-specific, remains to be resolved.     

Biotransformation of soy isoflavone-glycosides in laying hens: intestinal absorption and preferential accumulation into egg yolk of equol, a more estrogenic metabolite of daidzein

Dietary soy-isoflavones have recently been noted as phytoestrogens with potentially beneficial effects on human health, and they are biologically transformed in the intestinal tract into aglycones and further into several specific metabolites. Here we report that in laying hens daidzin, a soy isoflavone-glycoside, in the diet was transformed into equol, absorbed, transported in circulating peripheral blood, and preferentially accumulated into egg yolk in its conjugated form. Laying hens were fed experimental diets containing two levels of soy isoflavone-glycosides (177 or 528 mg per 100 g diet) for 21 or 42 days, and blood and eggs were collected at 1- to 9-day intervals. HPLC analyses revealed that most of the isoflavones (daidzein, glycitein, and genistein) and a metabolite, equol, were present in blood and egg yolk in conjugated form. The concentration of equol-conjugates in blood plasma and egg yolk was higher than any of the other three isoflavone-conjugates analyzed and, especially in egg yolk, the equol-conjugates comprised no less than 60% of the total isoflavone-conjugates. The isoflavones, including equol, distributed mostly (95%) in the high-density fraction of blood serum, and more (65%) in the granule fraction of egg yolk. These results raise the possibility that feeding domestic animals soy-based fodder produces animal-based foods rich in a more active form of phytoestrogens.     

Novel metabolites of the mammalian lignans enterolactone and enterodiol in human urine

Enterolactone (ENL) and enterodiol (END) are found in high concentrations in human body fluids after ingestion of flaxseed and whole-grain products. Although much interest is presently focused on these mammalian lignans because of their putative beneficial health effects, little is known about their metabolic fate in humans. We have now identified nine novel metabolites of ENL and END in the urine of female and male humans ingesting flaxseed for five days. The chemical structures of six ENL metabolites and of three END metabolites were elucidated by GC/MS analysis and comparison with authentic reference compounds obtained by chemical synthesis. The six identified metabolites of ENL were the products of monohydroxylation at the para-position and at both ortho-positions of the parent hydroxy group of either aromatic ring. Likewise, the three END metabolites were formed through aromatic monohydroxylation at the para- and ortho-positions. The biological significance of these metabolites remains to be established.     

Identification of phytoestrogens in the urine of male dogs

It is becoming increasingly apparent that dietary factors may play a role in the etiology of hormone dependent neoplasias. It has been hypothesized that estrogens play some role in the etiology of benign prostatic hyperplasia (BPH) in the canine. The presence of estrogen receptor binding activity in a fraction of canine urine purified by high performance liquid chromatography (HPLC) that did not correspond to estriol, estradiol, estrone or any of their primary metabolites was observed in the present study. We used thermospray-mass spectrometry and GC-MS to identify the phytoestrogens daidzein, equol, formononetin and genistein in HPLC purified fractions of urine obtained from male beagles. Using the same techniques we also confirmed the presence of daidzein and genistein in the commercial diet fed to these same dogs. Using the immature rat uterine cytosol estrogen receptor assay, relative binding affinities of 0.08, 1.1, less than 0.01 and 3.9% were obtained for daidzein, equol, formononetin and genistein, respectively when compared to estradiol (100%). In conclusion, phytoestrogens are present in urine of male beagles. Moreover, the commercial diet fed to these dogs contains isoflavones which can be converted to equol by intestinal microflora. These results suggest the need for investigations of phytoestrogens (e.g. equol) excreted into the urine daily and its relationship to the incidence and severity of BPH in the dog.     

Microbial equol production attenuates colonic methanogenesis and sulphidogenesis in vitro

Hydrogen gas produced during colonic fermentation is excreted in breath and flatus, or removed by hydrogen-consuming bacteria such as methanogens and sulphate-reducing bacteria. However, recent research has shown that H₂ is also consumed by equol-producing bacteria during the reduction of daidzein into equol. In this study, the interactions between methanogens, sulphate-reducing, and equol-producing bacteria were investigated under in vitro simulated intestinal conditions. In the presence of daidzein, the equol-producing bacterial consortium EPC4 gave rise to equol production in cultures of Methanobrevibacter smithii or Desulfovibrio sp. as well as in faecal samples with methanogenic or sulphate-reducing abilities. Moreover, this supplementation significantly (P < 0.001) decreased the methanogenesis and sulphidogenesis. The attenuation did not occur in the absence of a daidzein source. Additionally, there was no influence of soy germ powder, daidzein or equol as such, excluding a possible inhibition by these compounds. Finally, a stronger decrease was observed with increasing amounts of EPC4 and a constant equol production, suggesting that the observed effect was only partly caused by the action of daidzein as a hydrogen sink. These findings are of relevance since abdominal discomfort such as bloating and flatulence, are related to colonic gas production, whereas equol has potential health benefits.     

Fasting enhances p-Cresol production in the rat intestinal tract.

p-Cresol is a metabolite of aromatic amino acid metabolism produced by intestinal microflora, and its formation is influenced by intestinal conditions. Fasting drastically changes intestinal conditions. However, the effect of fasting on p-cresol production is unclear. In this study, serum and cecal p-cresol levels were determined in non-fasted rats and in rats fasting for either 12 or 18 h. Serum p-cresol increased significantly with 12-h fasting (3.44 +/- 2.15 nmol/ml; P<0.05) and 18-h fasting (5.40 +/- 2.20; P<0.001) as compared to the level in the non-fasted rats (1.02 +/- 0.50). Cecal p-cresol levels of the 12-h fasted (272.6 +/- 313.2 nmol/cecum) and 18-h fasted rats (436.6 +/- 190.8; P<0.01) were higher than those in non-fasted rats (27.1 +/- 21.9). The total cecal protein in content did not change with 18-h fasting. However, the cecal protein concentration increased significantly with fasting (P<0.001), and correlated closely with total cecal p-cresol contents (P<0.001). These results indicate that fasting enhances p-cresol production in the rat cecum, resulting in accumulation of serum p-cresol. We presume that the increase in p-cresol produced by fasting is related to the enhancement of bacterial nitrogen metabolism via an increased concentration of endogenous protein in the cecum.     

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.     

Differential role of Rho GTPases in intestinal epithelial barrier regulation in vitro

Maintenance of intestinal epithelial barrier functions is crucial to prevent systemic contamination by microbes that penetrate from the gut lumen. GTPases of the Rho-family such as RhoA, Rac1, and Cdc42 are known to be critically involved in the regulation of intestinal epithelial barrier functions. However, it is still unclear whether inactivation or activation of these GTPases exerts barrier protection or not. We tested the effects of Rho GTPase activities on intestinal epithelial barrier functions by using the bacterial toxins cytotoxic necrotizing factor 1 (CNF-1), toxin B, C3 transferase (C3 TF), and lethal toxin (LT) in an in vitro model of the intestinal epithelial barrier. Incubation of cell monolayers with CNF-1 for 3 h induced exclusive activation of RhoA whereas Rac1 and Cdc42 activities were unchanged. As revealed by FITC-dextran flux and measurements of transepithelial electrical resistance (TER) intestinal epithelial permeability was significantly increased under these conditions. Inhibition of Rho kinase via Y27632 blocked barrier destabilization of CNF-1 after 3 h. In contrast, after 24 h of incubation with CNF-1 only Rac1 and Cdc42 but not RhoA were activated which resulted in intestinal epithelial barrier stabilization. Toxin B to inactivate RhoA, Rac1, and Cdc42 as well as Rac1 inhibitor LT increased intestinal epithelial permeability. Similar effects were observed after inhibition of RhoA/Rho kinase signaling by C3 TF or Y27632. Taken together, these data demonstrate that both activation and inactivation of RhoA signaling increased paracellular permeability whereas activation of Rac1 and Cdc42 correlated with stabilized barrier functions.     

雌马酚产生细菌及其雌马酚合成代谢机制

大豆食品中通常富含染料木素和大豆苷元等异黄酮素,人和动物肠道中的某些细菌具有将异黄酮素代谢转化为S-雌马酚的能力。到目前为止,S-雌马酚被认为是一种具有潜在健康调节作用的化合物。啮齿类动物均具备产雌马酚的能力,但不同人群之间存在差异,产雌马酚细菌是否存在可能是造成这种差异的重要原因;不同产雌马酚细菌的代谢机制可能不同,并影响机体最终产雌马酚的能力。本文对已知的各种产雌马酚细菌及其细菌的雌马酚合成机制进行综述,以期为进一步了解雌马酚产生个体差异、雌马酚代谢转化效率、体外雌马酚的发酵生产,以及临床产雌马酚细菌的应用等提供理论参考。     

Enantioselective synthesis of S-equol from dihydrodaidzein by a newly isolated anaerobic human intestinal bacterium

A newly isolated rod-shaped, gram-negative anaerobic bacterium from human feces, named Julong 732, was found to be capable of metabolizing the isoflavone dihydrodaidzein to S-equol under anaerobic conditions. The metabolite, equol, was identified by using electron impact ionization mass spectrometry, (1)H and (13)C nuclear magnetic resonance spectroscopy, and UV spectral analyses. However, strain Julong 732 was not able to produce equol from daidzein, and tetrahydrodaidzein and dehydroequol, which are most likely intermediates in the anaerobic metabolism of dihydrodaidzein, were not detected in bacterial culture medium containing dihydrodaidzein. Chiral stationary-phase high-performance liquid chromatography eluted only one metabolite, S-equol, which was produced from a bacterial culture containing a racemic mixture of dihydrodaidzein. Strain Julong 732 did not show racemase activity to transform R-equol to S-equol and vice versa. Its full 16S rRNA gene sequence (1,429 bp) had 92.8% similarity to that of Eggerthella hongkongenis HKU10. This is the first report of a single bacterium capable of converting a racemic mixture of dihydrodaidzein to enantiomeric pure S-equol.     

松墨天牛成虫室内外种群肠道细菌的多样性及功能分析

【目的】为明确松墨天牛Monochamus alternatus成虫中、后肠细菌群落结构,探索肠道细菌的潜在功能。【方法】分别提取室外和室内饲养的松墨天牛成虫各15头(室内和室外各15个中肠、15个后肠)的肠道DNA,利用二代测序技术对松墨天牛成虫肠道细菌的16S rDNA V3–V4区序列进行测序,统计操作分类单元(OTUs)数量,分析物种组成、Alpha多样性和Beta多样性;采用PICRUSt软件预测肠道细菌的功能。【结果】共获得544180条高质量序列,在97%相似度下将其聚类为615个OTUs,总共注释到22个门、48个纲、112个目、172个科、285个属和408个种。室内种群的OTUs数量多于室外种群,室内外种群的OTUs种类存在差异性。同一种群的中、后肠之间差异不明显。变形菌门Proteobacteria为室内外松墨天牛肠道细菌的最优势门;肠杆菌属Enterobacter为室外种群肠道细菌和室内种群后肠细菌的最优势属,沙雷氏菌属Serratia为室内种群中肠的最优势属。Alpha多样性结果表明松墨天牛成虫室内种群肠道菌群的丰度显著高于室外种群;Beta多样性结果显示室外种群肠道菌群均一性和稳定性比室内种群好。室外和室内种群的中肠与后肠之间在菌群丰度和多样性上均无显著差异。功能预测结果表明,室内外松墨天牛成虫肠道菌群中代谢通路的丰度最高,其中以糖类代谢和氨基酸代谢为主,还有降解外源化学物质、萜类和聚酮类化合物及其他次生代谢物质的能力。不同种群、不同肠段之间的功能丰度均无显著差异。【结论】明确了取食不同食料的松墨天牛成虫中、后肠的细菌群落结构及差异,了解了肠道细菌的潜在作用,为进一步探究松墨天牛肠道共生菌的功能提供了理论基础。     

Synergistic inhibition of LDL oxidation by phytoestrogens and ascorbic acid

Increasing evidence indicates that oxidative modification of low-density lipoprotein (LDL) is an important determinant in atherogenesis, and following menopause, the incidence of coronary heart disease is as prevalent in women as it is in men. Estrogen has been demonstrated to inhibit the susceptibility of LDL to be oxidized, and more recently the use of phytoestrogens has been considered for estrogen replacement therapy. In this study the antioxidant activity of the three major phytoestrogens: genistein, daidzein, and equol were measured in terms of LDL oxidative susceptibility. Increasing levels of genistein, daidzein, and equol inhibited LDL oxidation, and this inhibitory effect was further enhanced in the presence of ascorbic acid. The synergism exhibited by these compounds is of clinical importance to phytoestrogen therapy since the efficacy of phytoestrogens as effective antioxidants is evident at concentration well within the range found in the plasma of subjects consuming soy products. However, this synergism, combined with the low reactivity of the phytoestrogens with peroxyl radicals, suggests that an antioxidant mechanism other then free radical scavenging reactions account for the phytoestrogen antioxidant effect. A structural basis for inhibition of LDL oxidation involving interaction of the phytoestrogens with apoB-100 is postulated.