The prenylflavonoid isoxanthohumol from hops (Humulus lupulus L.) is activated into the potent phytoestrogen 8-prenylnaringenin in vitro and in the human intestine

Interaction between phenolics and gut microbiota: role in human health

Dietary phenolic compounds are often transformed before absorption. This transformation modulates their biological activity. Different studies have been carried out to understand gut microbiota transformations of particular polyphenol types and identify the responsible microorganisms. Although there are potentially thousands of different phenolic compounds in the diet, they are typically transformed to a much smaller number of metabolites. The aim of this review was to discuss the current information about the microbial degradation metabolites obtained from different phenolics and their formation pathways, identifying their differences and similarities. The modulation of gut microbial population by phenolics was also reviewed in order to understand the two-way phenolic-microbiota interaction. Clostridium and Eubacterium genera, which are phylogenetically associated, are other common elements involved in the metabolism of many phenolics. The health benefits from phenolic consumption should be attributed to their bioactive metabolites and also to the modulation of the intestinal bacterial population.

Comparison of prebiotic effects of arabinoxylan oligosaccharides and inulin in a simulator of the human intestinal microbial ecosystem

In this study, the prebiotic potential of arabinoxylan oligosaccharides (AXOS) was compared with inulin in two simulators of the human intestinal microbial ecosystem. Microbial breakdown of both oligosaccharides and short-chain fatty acid production was colon compartment specific, with ascending and transverse colon being the predominant site of inulin and AXOS degradation, respectively. Lactate levels (+5.5 mM) increased in the ascending colon during AXOS supplementation, while propionate levels (+5.1 mM) increased in the transverse colon. The concomitant decrease in lactate in the transverse colon suggests that propionate was partially formed over the acrylate pathway. Furthermore, AXOS supplementation strongly decreased butyrate in the ascending colon, this in parallel with a decrease in Roseburia spp. and Bacteroides/Prevotella/Porphyromonas (-1.4 and -2.0 log CFU) levels. Inulin treatment had moderate effects on lactate, propionate and butyrate levels. Denaturing gradient gel electrophoresis analysis revealed that inulin changed microbial metabolism by modulating the microbial community composition. In contrast, AXOS primarily affected microbial metabolism by 'switching on' AXOS-degrading enzymes (xylanase, arabinofuranosidase and xylosidase), without significantly affecting microbial community composition. Our results demonstrate that AXOS has a higher potency than inulin to shift part of the sugar fermentation toward the distal colon parts. Furthermore, due to its stronger propionate-stimulating effect, AXOS is a candidate prebiotic capable of lowering cholesterol and beneficially affecting fat metabolism of the host.

Oestrogenicity of prenylflavonoids from hops: activation of pro-oestrogens by intestinal bacteria

For many centuries, hops (Humulus lupulus L.) have been used as essential ingredient in beers, providing the typical bitterness and hoppy flavour. However, the last few years the plant has gained increasing attention as a source of prenylflavonoids and in 1999, 8-prenylnaringenin (8-PN) was identified as the most potent phyto-oestrogen known so far. Hop extracts are therefore now marketed to reduce menopausal complaints. However, 8-PN concentrations in hops are very low, and variable efficiency of these extracts was observed. Yet, hops also contain isoxanthohumol (IX) in much higher amounts (IX/8-PN ratio in hop extracts is typically 10-20). This article reviews our recent findings on how the human intestinal microbiota may activate IX. Depending on inter-individual differences in the intestinal transformation potential, this conversion could easily increase the 8-PN exposure 10-fold. The variability in efficacy of hop extracts may therefore be explained by variable intestinal metabolism. Based on this scientific knowledge, an innovative strategy was developed to decrease this variability. First, Eubacterium limosum, capable of rapidly metabolizing all IX into 8-PN, was isolated from the complex intestinal ecosystem. This bacterium was then used to develop a new generation of hop products with increased reliability in effect. This strategy involves the use of the bacterium as probiotic, in which the bacterium is administered in combination with the original hop extract. This leads to efficient intestinal 8-PN production, also in individuals who originally did not harbour the appropriate bacteria. The findings presented in this review can therefore be considered as a typical example that good insight in the specific metabolic potential of complex microbial communities and individual bacterial species may offer important opportunities for the management and modulation of the microbial organization towards a certain metabolic function.

Prenylation of flavonoids by biotransformation of yeast expressing plant membrane-bound prenyltransferase SfN8DT-1

Prenylated flavonoids are natural products that exhibit diverse biological effects and often represent the active components of various medicinal plants. This study demonstrated the production of prenylated naringenin by biotransformation using transgenic yeast expressing naringenin 8-dimethylallyltransferase, a membrane-bound enzyme, without feeding of prenyl donors. This method provides the possibility of generating prenylated flavonoids that occur rarely in nature.

Validity and reproducibility of a self-administered semi-quantitative food-frequency questionnaire for estimating usual daily fat, fibre, alcohol, caffeine and theobromine intakes among Belgian post-menopausal women

A novel food-frequency questionnaire (FFQ) was developed and validated to assess the usual daily fat, saturated, mono-unsaturated and poly-unsaturated fatty acid, fibre, alcohol, caffeine, and theobromine intakes among Belgian post-menopausal women participating in dietary intervention trials with phyto-oestrogens. The relative validity of the FFQ was estimated by comparison with 7 day (d) estimated diet records (EDR, n 64) and its reproducibility was evaluated by repeated administrations 6 weeks apart (n 79). Although the questionnaire underestimated significantly all intakes compared to the 7 d EDR, it had a good ranking ability (r 0.47-0.94; weighted kappa 0.25-0.66) and it could reliably distinguish extreme intakes for all the estimated nutrients, except for saturated fatty acids. Furthermore, the correlation between repeated administrations was high (r 0.71-0.87) with a maximal misclassification of 7% (weighted kappa 0.33-0.80). In conclusion, these results compare favourably with those reported by others and indicate that the FFQ is a satisfactorily reliable and valid instrument for ranking individuals within this study population.

Arabinoxylan-oligosaccharides (AXOS) affect the protein/carbohydrate fermentation balance and microbial population dynamics of the Simulator of Human Intestinal Microbial Ecosystem

Arabinoxylan‐oligosaccharides (AXOS) are a recently newly discovered class of candidate prebiotics as – depending on their structure – they are fermented in different regions of gastrointestinal tract. This can have an impact on the protein/carbohydrate fermentation balance in the large intestine and, thus, affect the generation of potentially toxic metabolites in the colon originating from proteolytic activity. In this study, we screened different AXOS preparations for their impact on the in vitro intestinal fermentation activity and microbial community structure. Short‐term fermentation experiments with AXOS with an average degree of polymerization (avDP) of 29 allowed part of the oligosaccharides to reach the distal colon, and decreased the concentration of proteolytic markers, whereas AXOS with lower avDP were primarily fermented in the proximal colon. Additionally, prolonged supplementation of AXOS with avDP 29 to the Simulator of Human Intestinal Microbial Ecosystem (SHIME) reactor decreased levels of the toxic proteolytic markers phenol and p‐cresol in the two distal colon compartments and increased concentrations of beneficial short‐chain fatty acids (SCFA) in all colon vessels (25–48%). Denaturant gradient gel electrophoresis (DGGE) analysis indicated that AXOS supplementation only slightly modified the total microbial community, implying that the observed effects on fermentation markers are mainly caused by changes in fermentation activity. Finally, specific quantitative PCR (qPCR) analysis showed that AXOS supplementation significantly increased the amount of health‐promoting lactobacilli as well as of Bacteroides–Prevotella and Clostridium coccoides–Eubacterium rectale groups. These data allow concluding that AXOS are promising candidates to modulate the microbial metabolism in the distal colon.

DNA sequence and expression variation of hop (Humulus lupulus) valerophenone synthase (VPS), a key gene in bitter acid biosynthesis

BACKGROUND

The hop plant (Humulus lupulus) is a source of many secondary metabolites, with bitter acids essential in the beer brewing industry and others having potential applications for human health. This study investigated variation in DNA sequence and gene expression of valerophenone synthase (VPS), a key gene in the bitter acid biosynthesis pathway of hop.

METHODS

Sequence variation was studied in 12 varieties, and expression was analysed in four of the 12 varieties in a series across the development of the hop cone.

RESULTS

Nine single nucleotide polymorphisms (SNPs) were detected in VPS, seven of which were synonymous. The two non-synonymous polymorphisms did not appear to be related to typical bitter acid profiles of the varieties studied. However, real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis of VPS expression during hop cone development showed a clear link with the bitter acid content. The highest levels of VPS expression were observed in two triploid varieties, 'Symphony' and 'Ember', which typically have high bitter acid levels.

CONCLUSIONS

In all hop varieties studied, VPS expression was lowest in the leaves and an increase in expression was consistently observed during the early stages of cone development.

Eubacterium limosum activates isoxanthohumol from hops (Humulus lupulus L.) into the potent phytoestrogen 8-prenylnaringenin in vitro and in rat intestine

Recently, it was shown that the exposure to the potent hop phytoestrogen 8-prenylnaringenin (8-PN) depends on intestinal bacterial activation of isoxanthohumol (IX), but this occurs in only one-third of tested individuals. As the butyrate-producing Eubacterium limosum can produce 8-PN from IX, a probiotic strategy was applied to investigate whether 8-PN production could be increased in low 8-PN producers, thus balancing phytoestrogen exposure. Using fecal samples from high (Hop +) and low (Hop -) 8-PN-producing individuals, a Hop + and Hop - dynamic intestinal model was developed. In parallel, Hop + and Hop - human microbiota-associated rats were developed, germ-free (GF) rats acting as negative controls. IX and then IX + E. limosum were administered in the intestinal model and to the rats, and changes in 8-PN production and exposure were assessed. After dosing IX, 80% was converted into 8-PN in the Hop + model and highest 8-PN production, plasma concentrations, and urinary and fecal excretion occurred in the Hop + rats. Administration of the bacterium triggered 8-PN production in the GF rats and increased 8-PN production in the Hop - model and Hop - rats. 8-PN excretion was similar in the feces (294.1 +/- 132.2 nmol/d) and urine (8.5 +/- 1.1 nmol/d ) of all rats (n = 18). In addition, butyrate production increased in all rats. In conclusion, intestinal microbiota determined 8-PN production and exposure after IX intake. Moreover, E. limosum administration increased 8-PN production in low producers, resulting in similar 8-PN production in all rats.

Metabolism of the lignan macromolecule into enterolignans in the gastrointestinal lumen as determined in the simulator of the human intestinal microbial ecosystem

Estrogenic plant compounds from the human diet such as the lignan secoisolariciresinol diglucoside (SDG, 1) can exert biological activity in the human body upon ingestion and bioactivation to enterodiol (END, 5) and enterolactone (ENL, 6). Bioavailability of lignans is influenced by the food matrix and gut microbial action, of which the latter is subject to a large interindividual variation. In this study, the fate of the lignan precursor SDG, present in the lignan macromolecule of flax seed ( Linum usitatissimum), was determined during an artificial stomach and small intestinal digestion and during metabolism by two different enterolignan phenotypes in a TWINSHIME environment (TWIN Simulator of the Human Intestinal Microbial Ecosystem). The lignan macromolecule acted as a delivery system of SDG in the large intestine. SDG was only hydrolyzed into secoisolariciresinol (SECO, 2) through microbial action in the ascending colon, after which it was bioactivated into enterolignans from the transverse colon onward. Single demethylation was a first step in the bioactivation, followed by dehydroxylation. Enterolignan phenotypes remained stable throughout the experimental period. The establishment of END and ENL production equilibria reflected the subdominance of ENL-producing bacteria in the gastrointestinal tract.

Pharmacognostic and pharmacological profile of Humulus lupulus L

The present review describes the morphological, phytochemical and ethnopharmacological aspects of Humulus lupulus L. (Cannabinaceae) and summarizes the most interesting findings obtained in the preclinical and clinical research related to the plant. The female inflorescences of Humulus lupulus (hops), well-known as bittering agent in brewing industry, have long been used in traditional medicine mainly to treat sleep disturbances. However the sedative activity is still under investigation in order to recognize the active principles responsible for the neuropharmacological effects observed in laboratory animals, and their mechanism of action. Here we report the data from our experiments as well as those obtained from other researchers, focusing on the variability of the results. Other traditional applications of hops as stomachic, antibacterial and antifungal remedy have been supported by in vivo and/or in vitro investigations. In recent years some prenylated chalcones present in hops have received much attention for their biological effects: in particular, xanthohumol has been shown to exert cancer chemopreventive activity in in vitro experiments, while 8-prenylnaringenin has been characterized as one of the most potent phytoestrogens isolated until now. Nevertheless much additional work is needed to open up new biomedical application of these compounds.

Microbial and dietary factors associated with the 8-prenylnaringenin producer phenotype: a dietary intervention trial with fifty healthy post-menopausal Caucasian women

Hop-derived food supplements and beers contain the prenylflavonoids xanthohumol (X), isoxanthohumol (IX) and the very potent phyto-oestrogen (plant-derived oestrogen mimic) 8-prenylnaringenin (8-PN). The weakly oestrogenic IX can be bioactivated via O-demethylation to 8-PN. Since IX usually predominates over 8-PN, human subjects may be exposed to increased doses of 8-PN. A dietary intervention trial with fifty healthy post-menopausal Caucasian women was undertaken. After a 4 d washout period, participants delivered faeces, blank urine and breath samples. Next, they started a 5 d treatment with hop-based supplements that were administered three times per d and on the last day, a 24 h urine sample was collected. A semi-quantitative FFQ was used to estimate fat, fibre, alcohol, caffeine and theobromine intakes. The recoveries of IX, 8-PN and X in the urine were low and considerable inter-individual variations were observed. A five-fold increase in the dosage of IX without change in 8-PN concentration resulted in a significant lower IX recovery and a higher 8-PN recovery. Classification of the subjects into poor (60%), moderate (25%) and strong (15%) 8-PN producers based on either urinary excretion or microbial bioactivation capacity gave comparable results. Recent antibiotic therapy seemed to affect the 8-PN production negatively. A positive trend between methane excretion and 8-PN production was observed. Strong 8-PN producers consumed less alcohol and had a higher theobromine intake. From this study we conclude that in vivo O-demethylation of IX increases the oestrogenic potency of hop-derived products.

Metabolism of isoflavones, lignans and prenylflavonoids by intestinal bacteria: producer phenotyping and relation with intestinal community

Many studies have investigated the importance of the intestinal bacterial activation of individual phytoestrogens. However, human nutrition contains different phytoestrogens and the final exposure depends on the microbial potential to activate all different groups within each individual. In this work, interindividual variations in the bacterial activation of the different phytoestrogens were assessed. Incubation of feces from 100 individuals using SoyLife EXTRA, LinumLife EXTRA and isoxanthohumol suggested that individuals could be separated into high, moderate and low O-desmethylangolensin (O-DMA), equol, enterodiol (END), enterolactone (ENL) or 8-prenylnaringenin producers, but that the metabolism of isoflavones, lignans and prenylflavonoids follows separate, independent pathways. However, O-DMA and equol production correlated negatively, whereas a positive correlation was found between END and ENL production. In addition, END production correlated negatively with Clostridium coccoides-Eubacterium rectale counts. Furthermore, O-DMA production was correlated with the abundance of methanogens, whereas equol production correlated with sulfate-reducing bacteria, indicating that the metabolic fate of daidzein may be related to intestinal H(2) metabolism.

Interindividual differences in phytochemical metabolism and disposition

Many phytochemicals, the bioactive nonnutrient compounds found in plant foods, possess biologic effects associated with reduced risk of various diseases such as cancer. Genetic variation in pathways affecting absorption, metabolism, and distribution of phytochemicals is likely to influence exposure at the tissue level, thus modifying disease risk in individuals. Few studies have examined these gene-phytochemical interactions in humans. In this review, we discuss the sources of variation in metabolism and disposition of phytochemicals, and focus on two aspects of phytochemical handling that have received some attention: the impact of intestinal bacteria and genetically polymorphic phase II, conjugating enzymes.

Resolution of diastereomeric flavonoid (1S)-(-)-camphanic acid esters via reversed-phase HPLC

Prenylflavonoids are an unique class of phytochemicals found in the inflorescences of the hop plant (Humulus lupulus). These flavonoids have demonstrated a wide range of biological activities, which may be influenced by their stereochemical configuration. Additionally, recent studies suggest that hop prenylflavonoids are subject to biotransformations which could alter or enrich their stereochemistry. In order to facilitate studies of the stereoisomers of flavanones, a facile method was developed for resolving the diastereomeric esters of flavanones via reversed-phase HPLC. Herein, a method for forming the tri-(1S)-(-)-camphanic acid esters of the 4',5,7-trihydroxy flavanones naringenin, 8-prenylnaringenin and 6-prenylnaringenin, is described. The respective diastereomers were separated using analytical reversed-phase HPLC. Diastereomeric esters were isolated by preparative HPLC to >98% d.e. based on HPLC, with their absolute configurations established by application of CD spectrometry.

Models for intestinal fermentation: association between food components, delivery systems, bioavailability and functional interactions in the gut

There is increasing interest in the human colonic microbiota and in the way its metabolic activities impact on host health and well-being. For most practical purposes, however, the large bowel is inaccessible for routine investigation, and a variety of animal and in vitro model systems have been developed to study the microbiota. In vitro models range from simple closed systems using pure or defined mixed populations of bacteria, or faecal material, to more sophisticated complex multistage continuous cultures that are able to simulate many of the spatial, temporal and environmental attributes that characterize microbiological events in different regions of the large gut. Recent developments using these systems have enabled modelling of surface colonisation and biofilm development, a hitherto neglected area of study.