Prenylflavonoids: a new class of non-steroidal phytoestrogen (Part 2). Estrogenic effects of 8-isopentenylnaringenin on bone metabolism

An Overview of Bioactive Phenolic Molecules and Antioxidant Properties of Beer: Emerging Trends

Beer is one of the oldest and most common beverages worldwide. The phenolic contents and antioxidant properties of beer are crucial factors in evaluating its nutritional quality. Special beers brewed with the addition of adjuncts are gaining in consumer preference, in response to demands for healthy food and new gustatory and olfactory stimuli. Many studies recently dealt with functional beers brewed with the addition of adjuncts. This review focuses on bioactive molecules, particularly the composition of phenolic compounds, and the antioxidant activity of beer. The current knowledge concerning the effect of the addition of adjuncts in the form of fruit, vegetables, herbs, and natural foods on the polyphenol content, antioxidant properties, and phenolic profile of beer is reviewed, with an outline of the emerging trends in brewing processes. Future studies need to complete the identification and characterization of the bioactive molecules in beer, as well as studying their absorption and metabolic fate in humans.

The Potent Phytoestrogen 8-Prenylnaringenin: A Friend or a Foe?

8-prenylnaringenin (8-PN) is a prenylated flavonoid, occurring, in particular, in hop, but also in other plants. It has proven to be one of the most potent phytoestrogens in vitro known to date, and in the past 20 years, research has unveiled new effects triggered by it in biological systems. These findings have aroused the hopes, expectations, and enthusiasm of a “wonder-drug” for a host of human diseases. However, the majority of 8-PN effects require such high concentrations that they cannot be reached by normal dietary exposure, only pharmacologically; thus, adverse impacts may also emerge. Here, we provide a comprehensive and up-to-date review on this fascinating compound, with special reference to the range of beneficial and untoward health consequences that may ensue from exposure to it.

Absorption, metabolism, and pharmacokinetic profile of xanthohumol in rats as determined via UPLC-MS/MS

Xanthohumol, a natural isoflavone from Humulus lupulus L., possesses biological activities. However, the biological fate of xanthohumol in vivo remains unclear. The aim of this study was to investigate the absorption and metabolism of xanthohumol in rats through UPLC-MS/MS. The plasma, urine and fecal samples were collected after oral administration of xanthohumol (25, 50, 100 mg/kg) in SD rats. The contents of xanthohumol and its metabolites were determined by UPLC-MS/MS. A total of 6 metabolites of xanthohumol were identified in rats, including methylated, glucuronidated, acid-catalyzed cyclization and oxidation, indicating xanthohumol underwent phase I and II metabolism. Besides, isoxanthohumol was the major metabolites of xanthohumol. Xanthohumol was rapidly absorbed, metabolized, and eliminated in rats. The pharmacokinetics results showed the T_max of xanthohumol and isoxanthohumol were 3 and 2.33 h, respectively. The AUC_0-t of xanthohumol and isoxanthohumol were 138.83 ± 6.03 and 38.77 ± 4.46 ng/ml·h, respectively. Furthermore, xanthohumol was mainly excreted in the form of prototype through feces and a small amount of xanthohumol was excreted through urine. These results illustrated the absorption, metabolism, and pharmacokinetics process of xanthohumol in rats, and provided a reference for the further rational applications.

Flavonoids as Phytoestrogenic Components of Hops and Beer

The value of hops (Humulus lupulus L.) in beer production has been undisputed for centuries. Hops is rich in humulones and lupulones which gives the characteristic aroma and bitter taste, and preserves this golden drink against growing bacteria and molds. Besides α- and β-acids, the lupulin glands of hop cones excrete prenylated flavonoids, which exhibit a broad spectrum of biological activities and therefore has therapeutic potential in humans. Recently, interest in hops was raised due to hop prenylated flavanones which show extraordinary estrogen activities. The strongest known phytoestrogen so far is 8-prenylnaringenin (8-PN), which along with 6-prenylanaringenin (6-PN), 6,8-diprenylnaringenin (6,8-DPN) and 8-geranylnaringenin (8-GN) are fundamental for the potent estrogen activity of hops. This review provides insight into the unusual hop phytoestrogens and shows numerous health benefits associated with their wide spectrum of biological activities including estrogenic, anticancer, neuropreventive, antinflamatory, and antimicrobial properties, which were intensively studied, and potential applications of these compounds such as, as an alternative to hormone replacement therapy (HRT).

Effect of alendronate or 8-prenylnaringenin applied as a single therapy or in combination with vibration on muscle structure and bone healing in ovariectomized rats

Bisphosphonate alendronate (ALN), phytoestrogen 8-prenylnaringenin (8-PN) and the whole body vibration exert a favorable effect on osteoporotic bone. However, the impact of these treatments and the combination of pharmacological therapies with biomechanical stimulation on muscle and bone has not yet been explored in detail. The effect of ALN and 8-PN and their combination with the vibration (Vib) on skeletal muscle and bone healing was investigated in ovariectomized (Ovx) rats.

Three-month old rats were Ovx (n = 78), or left intact (Non-Ovx; n = 12). Five weeks after Ovx, all rats were treated according to the group assignment (n = 12/13): 1) Non-Ovx; 2) Ovx; 3) Ovx + Vib; 4) Ovx + ALN; 5) Ovx + ALN + Vib; 6): Ovx + 8-PN; 7) Ovx + 8-PN + Vib. Treatments with ALN (0.58 mg/kg BW, in food), 8-PN (1.77 mg/kg BW, daily s.c. injections) and/or with vertical vibration (0.5 mm, 35 Hz, 1 g, 15 min, 2×/day, 5×/week) were conducted for ten weeks. Nine weeks after Ovx, all rats underwent bilateral tibia osteotomy with plate osteosynthesis and were sacrificed six weeks later.

Vibration increased fiber size and capillary density in muscle, enlarged callus area and width, and decreased callus density in tibia, and elevated alkaline phosphatase in serum. ALN and ALN + Vib enhanced capillarization and lactate dehydrogenase activity in muscle. In tibia, ALN slowed bone healing, ALN + Vib increased callus width and density, enhanced callus formation rate and expression of osteogenic genes. 8-PN and 8-PN + Vib decreased fiber size and increased capillary density in muscle; callus density and cortical width were reduced in tibia. Vibration worsened 8-PN effect on bone healing decreasing the callus width and area.

Our data suggest that Vib, ALN, 8-PN, or 8-PN + Vib do not appear to aid bone healing. ALN + Vib improved bone healing; however application is questionable since single treatments impaired bone healing. Muscle responds to the anti-osteoporosis treatments and should be included in the evaluation of the drugs.

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Vibration (Vib) was beneficial for muscle structure, it tended to interfere with early bone healing.

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Alendronate (ALN) enhanced capillary density and metabolism in muscle, slowed bone healing.

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8-Prenylnaringenin (8-PN) had favorable effects on muscle, for bone healing it was disadvantageous.

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8PN + Vib further worsened 8-PN effect on bone, ALN + Vib improved bone healing.

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Muscles respond to anti-osteoporosis treatments, their analysis should be included in the evaluation of drugs.

Reductive Metabolism of Xanthohumol and 8-Prenylnaringenin by the Intestinal Bacterium Eubacterium ramulus

SCOPE

The intestinal microbiota transforms a wide range of available substrates, including polyphenols. Microbial catabolites of polyphenols can contribute in significant ways to the health-promoting properties of their parent polyphenols. This work aims to identify intestinal metabolites of xanthohumol (XN), a prenylated flavonoid found in hops (Humulus lupulus) and beer, as well as to identify pathways of metabolism of XN in the gut.

METHODS AND RESULTS

To investigate intestinal metabolism, XN and related prenylated flavonoids, isoxanthohumol (IX), and 8-prenylnaringenin (8PN) were added to growing cultures of intestinal bacteria, Eubacterium ramulus and E. limosum. Liquid chromatography coupled with mass spectrometry was used to identify metabolites of the flavonoids from the cultures. The metabolic capacity of E. limosum appears to be limited to O-demethylation. Evidence from the study indicates that E. ramulus hydrogenates XN to form α,β-dihydroxanthohumol (DXN) and metabolizes the potent phytoestrogen 8PN into the chalcones, O-desmethylxanthohumol (DMX) and O-desmethyl-α,β-dihydroxanthohumol (DDXN).

CONCLUSION

Microbial metabolism is likely to affect both activity and toxicity of XN and derivatives. This study along with others highlights that attention should be focused on metabolites, in particular, products of intestinal microbial metabolism.

Estrogenic Activities of Food Supplements and Beers as Assessed by a Yeast Bioreporter Assay

Mounting evidence of the effects of endocrine-disrupting chemicals (EDCs) in humans has led to assaying a vast array of food items (processed or packaged) as possible sources of human exposure to estrogens. In this study, we investigated the current situation in this respect of different food supplements and beer brands. Eleven food supplements and 24 beer brands were obtained from Helsinki, Finland. Sample preparation was carried out by established methods while estrogenic activities were assessed by a yeast bioluminescent assay, using two recombinant yeast strains (Saccharomyces cerevisiae BMAEREluc/ERα and S. cerevisiae BMA64/luc). All the food supplements as well as 81% of the beer samples tested were found to be estrogenic, with estradiol equivalent concentrations of food supplements and beer brands ranging from 7.5 to 11.5 µg/ml and from below detection limits to 43.6 ng/ml, respectively. The estrogenic activities detected in beer samples were not dependent on the beer's alcoholic content, the country of production, or the size of the production brewery. The results of our study imply that both food supplements and beers can be a significant source of human exposure to estrogens. Therefore, further studies and regular surveillance are warranted.

A standardized Humulus lupulus (L.) ethanol extract partially prevents ovariectomy-induced bone loss in the rat without induction of adverse effects in the uterus

BACKGROUND

Hops (Humulus lupulus (L.)) dietary supplements are of interest as herbal remedies to alleviate menopausal symptoms, such as hot flushes, depression and anxiety. So far, the evidence regarding estrogenic and related properties of hops preparations has been considered insufficient for a market authorization for menopausal indications.

PURPOSE

The study aims to investigate a chemically standardized hops extract regarding its safety in the uterus, as wells as its efficacy to prevent bone loss in the ovariectomized rat model.

STUDY DESIGN/METHODS

Female Wistar rats were ovariectomized and divided into a control group receiving phytoestrogen-free diet, a group treated with E₂benzoate (0.93 mg/kg body weight/d) and a group treated with the standardized hops extract (60 mg/kg body weight/d) for 8 weeks. Micro-computed tomography of the tibiae and vertebrae, as wells as histological changes in the uterus and tibia were analyzed.

RESULTS

Neither uterotrophic nor proliferative effects were observed in the endometrium in response to the oral 8-week administration of the hops extract. However, site-dependent skeletal effects were observed. The hops extract significantly decreased the number of osteoclasts in the tibial metaphysis and prevented reduction of the trabecular thickness that resulted from estradiol depletion. In contrast, the hops extract did not prevent the ovariectomy-induced micro-architectural changes in the lumbar vertebra. Certain parameters (e.g. thickness and number of trabeculae) were even found to be below the values determined in the ovariectomized control group.

CONCLUSION

Taken together, the results provide evidence for the safety of the standardized hops extract and point to a weak bone type-specific, protective effect on bone loss following estradiol depletion.

Effects of 8-Prenylnaringenin and Whole-Body Vibration Therapy on a Rat Model of Osteopenia

Background. 8-Prenylnaringenin (8-PN) is the phytoestrogen with the highest affinity for estrogen receptor-α (ER-α), which is required to maintain BMD. The osteoprotective properties of 8-PN have been demonstrated previously in tibiae. We used a rat osteopenia model to perform the first investigation of 8-PN with whole-body vertical vibration (WBVV). Study Design. Ovariectomy was performed on 52 of 64 Sprague-Dawley rats. Five weeks after ovariectomy, one group received daily injections (sc) of 8-PN (1.77 mg/kg) for 10 weeks; a second group was treated with both 8-PN and WBVV (twice a day, 15 min, 35 Hz, amplitude 0.47 mm). Other groups received either only WBVV or no treatment. Methods. The rats were sacrificed 15 weeks after ovariectomy. Lumbar vertebrae and femora were removed for biomechanical and morphological assessment. Results. 8-PN at a cancer-safe dose did not cause fundamental improvements in osteoporotic bones. Treatment with 8-PN caused a slight increase in uterine wet weight. Combined therapy using WBVV and 8-PN showed no significant improvements in bone structure and biomechanical properties. Conclusion. We cannot confirm the osteoprotective effects of 8-PN at a cancer-safe dose in primary affected osteoporotic bones. Higher concentrations of 8-PN are not advisable for safety reasons. Adjunctive therapy with WBVV demonstrates no convincing effects on bones.

Assessment of the effects of naringenin-type flavanones in uterus and vagina

The potential utilization of plant secondary metabolites possessing estrogenic properties as alternatives to the classical hormone replacement therapy (HRT) for the relief of postmenopausal complaints asks for an evaluation regarding the safety in reproductive organs. In order to contribute to the estimation of the safety profile of the flavanones naringenin (Nar), 8‑prenylnaringenin (8PN) and 6‑(1,1‑dimethylally) naringenin (6DMAN), we investigated uterus and vagina derived from a three‑day uterotrophic assay in rats. Also, we investigated the metabolite profile resulting from the incubation of the three substances with liver microsomes. While no metabolites were detectable for naringenin, hydroxylation products were observed for 8PN and 6DMAN after incubation with human as well as rat liver microsomes. The parent compound naringenin did not evoke any estrogenic responses in the investigated parameters. A significant increase of the uterine wet weight, uterine epithelial thickness and proliferating vaginal cells was observed in response to 8PN, questioning the safety of 8PN if applied in the human situation. In contrast, no estrogenic effects on the reproductive organs were observed for 6DMAN in the conducted study, rendering it the compound with a more promising safety profile, therefore justifying further investigations into its efficacy to alleviate postmenopausal discomforts.

Premature T cell senescence in Ovx mice is inhibited by repletion of estrogen and medicarpin: a possible mechanism for alleviating bone loss

Presently the relationship between CD28, biological marker of senescence, and ovariectomy is not well understood. We show that ovariectomy leads to CD28 loss on T cells and estrogen (E2) repletion and medicarpin (Med) inhibits this effect. We thus propose that Med/E2 prevents bone loss by delaying premature T cell senescence.

INTRODUCTION

Estrogen deficiency triggers reproductive aging by accelerating the amplification of TNF-α-producing T cells, thereby leading to bone loss. To date, no study has been carried out to explain the relationship between CD4(+)CD28null T cells and ovariectomy or osteoporosis. We aim to determine the effect of Ovx on CD28 expression on T cells and effects of E2 and medicarpin (a pterocarpan phytoalexin) with proven osteoprotective effect on altered T cell responses.

METHODS

Adult, female Balb/c mice were taken for the study. The groups were: sham, Ovx, Ovx + Med or E2. Treatments were given daily by oral gavage. At autopsy bone marrow and spleen were flushed out and cells labelled with antibodies for FACS analysis. Serum was collected for ELISA.

RESULTS

In Ovx mice, Med/E2 at their respective osteoprotective doses resulted in thymus involution and lowered Ovx-induced increase in serum TNF-α level and its mRNA levels in the BM T cells. Med/E2 reduced BM and spleen CD4(+) T cell proliferation and prevented CD28 loss on CD4(+) T cells. Further, Med abrogated TNF-α-induced loss of CD28 expression in the BM T cells.

CONCLUSIONS

To our knowledge this is the first report to determine the mechanism of CD28 loss on T cells as a result of ovariectomy. Our study demonstrates that Ovx leads to the generation of premature senescent CD4(+)CD28null T cells, an effect inhibited by E2 and Med. We propose that one of the mechanisms by which Med/E2 alleviates Ovx-induced bone loss is by delaying T cell senescence and enhancing CD28 expression.

Production of 8-prenylnaringenin from isoxanthohumol through biotransformation by fungi cells

8-Prenylnaringenin (8PN), which presents in hop, enjoys fame as the most potential phytoestrogen. Although a number of health effects are attributed to 8PN, few reports are available about the production of it. In this work, screening of fungi to efficiently transform isoxanthohumol (IXN) into 8PN was designed. The biotransformation of IXN was significantly observed in Eupenicillium javanicum, Cunninghamella blakesleana, and Ceriporiopsis subvermispora under five kinds of transformation conditions. As a comparative result of IXN transformation, E. javanicum was the optimal biocatalyst to produce 8PN. Transformation caused by growing precultured fungal mycelia, a process designated as G2, was a favorable condition for IXN transformation in view of the yield of 8PN. The possible transformation pathway of 8PN bioproduction is postulated in this work. The construction of fungus and transformation mode derived from the current work is viable and an alternative procedure for 8PN formation.

Daidzein prevents the increase in CD4+CD28null T cells and B lymphopoesis in ovariectomized mice: a key mechanism for anti-osteoclastogenic effect

Estrogen deficiency leads to an upregulation of TNF-α producing T cells and B-lymphopoesis which augments osteoclastogenesis. Estrogen deficiency also increases the population of premature senescent CD4⁺ CD28null T cells which secrete a higher amount of TNF-α thus leading to enhanced osteoclastogenesis. Isoflavonoids like daidzein and genistein are found mostly in soybeans, legumes, and peas. These share structural similarity with 17β-stradiol (E2) and have osteoprotective role. This study explores the effect of daidzein (Daid) on the proliferation of TNF-α producing T cells, premature senescent T cells and B cell lymphopoesis under estrogen deficient conditions. For this study adult Balb/c mice were treated with Daid at 10 mg/kg body weight dose by oral gavage daily post ovariectomy (Ovx). After six weeks animals were autopsied and bone marrow and spleen cells were collected for FACS analysis. Blood serum was collected for ELISA. It was observed that Ovx mice treated with Daid for six weeks show reduction in Ovx induced expansion of CD4⁺ T cells in bone marrow and spleen when analysed by flow cytometry. Estrogen deficiency led to increased prevalence of TNF-α secreting CD4⁺CD28null T cells, however, treatment with Daid increased the percentage of CD4⁺CD28⁺ T cells. Co-culture of CD4⁺CD28null T cells and bone marrow resulted in enhanced osteoclastogenesis as evident by increased tartarate resistant acid phosphatase (TRAP) expression, an osteoclast marker. However, treatment with Daid resulted in reduced osteoclastogenesis in CD4⁺CD28null T cells and bone marrow cell co-culture. Daid also regulated B lymphopoesis and decreased mRNA levels of RANKL in B220⁺ cells. Taken together, we propose that one of the mechanisms by which Daid prevents bone loss is by reversing the detrimental immune changes as a result of estrogen deficiency.

Flavonoid-induced autophagy in hormone sensitive breast cancer cells

The activity of 8-prenylapigenin (8-PA) and its 3'-methoxylated analogue isocannflavin B (IsoB) was investigated in estrogen-dependent T47-D and estrogen-independent MDA-MB-231 human breast cancer cell lines. 8-PA showed a biphasic effect on T47-D cell proliferation, while no significant effect was observed on MDA-MB-231 cells. Conversely, IsoB exhibited only an inhibitory effect on T47-D cell proliferation, accompanied by the appearance of an intense intracytoplasmic vacuolization of autophagic origin. Moreover, biochemical analysis showed that IsoB reduced Akt phosphorylation and p21(Cip1) expression in T47-D cells. These data show that the prenylflavone moiety is a versatile platform for the induction and modulation of bioactivity.

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.

Effects of isometric strength training followed by no exercise and Humulus lupulus L-enriched diet on bone metabolism in old female rats

We investigated in female rats the effects on bone metabolism of a prolonged no-training period, subsequent to an isometric exercise program, performed during young adulthood and those of a long-term consumption of Humulus lupulus L-enriched diet (genistein 1.92 and daidzein 1.24 mg/kg diet) combined or not with isometric training. Forty-eight rats (4 weeks old) were randomly divided into 4 groups: trained (C-Tr) or nontrained rats (C-NTr) fed with control diet and trained (H-Tr) or nontrained rats (H-NTr) fed with Humulus lupulus L-enriched diet. The diets lasted 100 weeks. Training was followed over a 25-week period. Bone parameters were measured at week 100. Our results showed that no significant difference was observed among the 4 groups in uterine relative weight, calcium (Ca) intake, fecal Ca, urinary Ca excretion, net Ca absorption, plasma Ca, and bone Ca content. Calcium balance was significantly enhanced in H-NTr rats in comparison with C-NTr and C-Tr rats. Isometric strength training led to a significant increase in total bone mineral density (BMD), diaphyseal BMD, and osteocalcin-deoxypyridinoline ratio in C-Tr rats compared with the other groups. The main findings of the present study indicate that in female rats, a 25-week isometric strength training performed during young adulthood followed by a prolonged no-training period increases BMD values and osteocalcin-deoxypyridinoline ratio, whereas long-term consumption of Humulus lupulus L-enriched diet does not improve bone parameters. It suggests that bone gains induced by exercise do not decrease immediately after cessation of training and also confirms the importance of the practice of physical activity during puberty and young adulthood to maximize the achieved peak bone density.

Effects of the chemically synthesized flavanone 7-(O-prenyl)naringenin-4'-acetate on the estrogen signaling pathway in vivo and in vitro

The flavanone naringenin is known to possess only weak estrogenic properties, but some of its derivatives such as 8-prenylnaringenin are potent phytoestrogens. The aim of this study was to further clarify structure-function relationships of flavanones regarding their estrogenic or antiestrogenic properties by characterizing the new chemically synthesized naringenin derivative 7-(O-prenyl)naringenin-4'-acetate (7-O-PN). A yeast based reporter gene assay and MVLN cells, a MCF-7-derived cell line that possesses a luciferase reporter gene under the control of a vitellogenin estrogen responsive element, were used to investigate estrogenic actions of 7-O-PN in vitro. Estradiol (E2) has been used as a positive control. Subsequently a 3-day rat uterotrophic assay was performed to test for estrogenic effects. In addition, mRNA expression of estrogen sensitive genes in the uteri of these rats was measured using real time rtPCR. While E2 leads to a strong dose dependent signal in the yeast based reporter gene assay and in MVLN cells, 7-O-PN shows mild E2 antagonistic properties at concentrations 10(-8) and 10(-7)M, E2 agonistic properties at 10(-6) and 10(-5)M in MVLN cells and no effects on the yeast based system. In contrast to E2 treatment, 7-O-PN treatment did not increase uterus wet weight compared to the negative control. These findings are supported by mRNA expression studies of proliferation markers. Additionally, mRNA expression studies of estrogen regulated genes revealed very strong antiestrogenic properties of 7-O-PN regarding regulation of complement C3 expression while some estrogenic effects could be observed on the expression of estrogen receptor beta, clusterin and possibly on progesterone receptor and vascular endothelial growth factor.

The prevention of prostate cancer

From our better understanding of the natural history of prostate cancer, it is not unreasonable to believe that the disease is preventable. Prostate cancer has become a major healthcare problem worldwide, as life expectancy increases. Moreover, the cancer is slow growing, with a period of about 20-25 years from initiation to the stage when the clinically detectable phenotype can be identified. This review provides a simple overview of the endocrinology of prostate cancer and discusses some of the pharmaceutical agents that have been or are being tested to restrain, possibly arrest, the progression of this slowly growing cancer. Also discussed are many of the dietary factors that may influence the molecular or endocrine events implicated in its development. Dietary factors are considered responsible for the geographical differences in prostate cancer incidence and mortality. Since about 50% of all men worldwide, from both East and West, show evidence of microscopic cancer by 50 years of age, growth restraint would appear to be the pragmatic option to the possibility of preventing initiation.

Moderate alcohol consumption and increased bone mineral density: potential ethanol and non-ethanol mechanisms

Mounting epidemiological evidence indicates an association between the moderate ingestion of alcoholic beverages and higher bone mineral density (v. abstainers). More limited findings provide some evidence for translation of this association into reduced fracture risk, but further studies are required. Here, these data are reviewed and caveats in their assimilation, comparison and interpretation as well as in the use and application of bone health indices are discussed. Whilst it is concluded that evidence is now strong for the moderate alcohol-bone health association, at least in relation to bone mineral density, mechanisms are less clear. Both ethanol and non-ethanol components have been implicated as factors that positively affect bone health in the light of moderate consumption of alcoholic beverages, and four particular areas are discussed. First, recent findings suggest that moderate ethanol consumption acutely inhibits bone resorption, in a non-parathyroid hormone- and non-calcitonin-dependent fashion, which can only partly be attributed to an energy effect. Second, critical review of the literature does not support a role for moderate ethanol consumption affecting oestrogen status and leading to a knock-on effect on bone. Third, Si is present at high levels in certain alcoholic beverages, especially beer, and may have a measurable role in promoting bone formation. Fourth, a large body of work indicates that phytochemicals (e.g. polyphenols) from alcoholic beverages could influence bone health, but human data are lacking. With further work it is hoped to be able to model epidemiological observations and provide a clear pathway between the magnitude of association and the relative contribution of these mechanisms for the major classes of alcoholic beverage.

Effects of natural prenylated flavones in the phenotypical ER (+) MCF-7 and ER (−) MDA-MB-231 human breast cancer cells

The effect of seven natural prenylated flavones in DNA synthesis of two human breast cancer cell lines, the estrogen-dependent ER (+) MCF-7 and the estrogen-independent ER (-) MDA-MB-231 cells, was evaluated. Flavones with an isopentenyl group at C-8 and a ring linking C-3 and C-2' presented a biphasic effect in DNA synthesis of ER (+) MCF-7 and displayed a stimulation at low concentrations (0.02-0.78 microM) whilst at higher concentrations (> 3.12 microM) inhibition was observed. No stimulation was observed in ER (-) MDA-MB-231. In contrast, all the flavones exhibited an antiproliferative effect in both ER (-) and ER (+). Curiously, the inhibition of DNA synthesis was accompanied by a high capacity of these cells to reduce MTT, which was concurrent with the appearance of an intense intracytoplasmic vacuolization. The accumulation of the formazan product in these vacuoles could justify the enhancements of MTT reduction. The characterization of these vacuoles with the autophagic marker monodansylcadaverine (MDC) is consistent with autophagic vacuoles, which led to the suggestion that these flavones could induce autophagy in both ER (+) and ER (-) breast cancer cell lines.

A first prospective, randomized, double-blind, placebo-controlled study on the use of a standardized hop extract to alleviate menopausal discomforts

OBJECTIVES

To examine the efficacy of a hop extract enriched in 8-prenylnaringenin (8-PN, the phytoestrogen in hops, Humulus lupulus L.) on relief of menopausal discomforts.

METHODS

A prospective, randomized, double-blind, placebo-controlled study over 12 weeks with 67 menopausal women, who were administered a hop extract standardized on 8-PN (100 or 250 microg). The responses were determined by means of a modified Kupperman index (KI) and a patients' questionnaire.

RESULTS

All groups, including placebo, showed a significant reduction of the KI both after 6 weeks and after 12 weeks. The hop extract at 100 microg 8-PN was significantly superior to placebo after 6 weeks (P=0.023) but not after 12 weeks (P=0.086). No dose-response relationship could be established, as the higher dose (250 microg) was less active than the lower dose both after 6 weeks and after 12 weeks. Still, a trend for a more rapid decrease of KI was noticed for both active groups as compared to placebo. In particular, the decrease in hot flush score (isolated from the KI) was found significant for both treatment groups after 6 weeks (P<0.01) with respect to placebo. Results of the patients' questionnaire were consistent with those of the KI, with the most pronounced effects being observed for the 100-microg treatment.

CONCLUSIONS

Daily intake of a hop extract, standardized on 8-PN as a potent phytoestrogen, exerted favorable effects on vasomotor symptoms and other menopausal discomforts. Hop-derived prenylated flavonoids may provide an attractive addition to the alternative treatments available for relief of hot flushes and other menopausal discomforts.

Beer constituents as potential cancer chemopreventive agents

Beer is a complex alcoholic beverage made from barley (malt), hop, water and yeast. Phenolic constituents of beer are derived from malt (70-80%) and hop (20-30%). Structural classes include simple phenols, benzoic- and cinnamic acid derivatives, coumarins, catechins, di-, tri- and oligomeric proanthocyanidins, (prenylated) chalcones and flavonoids as well as alpha- and iso-alpha-acids derived from hop. Compounds belonging to different structural classes have distinct profiles of biological activity in in vitro test systems, and in combination might lead to enhanced effects. Scientific evidence has accumulated over the past 10 years pointing to the cancer preventive potential of selected hop-derived beer constituents, i.e., prenylflavonoids including xanthohumol and isoxanthohumol, and hop bitter acids. Chemopreventive activities observed with these compounds relevant to inhibition of carcinogenesis at the initiation, promotion and progression phases, as well as results from in vivo studies on metabolism, bioavailability and efficacy are summarised in this review.

Effect of phytoestrogens on gene expression of carbonic anhydrase II in rat uterus and liver

The aim of this study was to characterize carbonic anhydrase II (CA2), as novel estrogen responsive gene, towards its usefulness to elucidate the molecular mechanisms of phytoestrogen action. Effects of estradiol-17beta (E2), and the phytoestrogens genistein (Gen), daidzein (Dai), as well as 8-prenylnaringenin (8PN) on CA2 mRNA expression were investigated in vivo in the uterus and liver of Wistar rats, and in vitro in Fe33 hepatoma cells. Relative amounts of mRNA levels of CA2 were measured by real-time RT-PCR. In vivo CA2 expression in uterus and liver is down-regulated by estrogen in time dependent manner with the most pronounced effect detectable 72 h after treatment. Treatment with Gen results in a slight down-regulation of CA2 expression in the uterus. In liver a response to Gen is detectable only after 7 h, where the expression of the gene is down-regulated to 60%. Treatment with Dai and 8PN for 72 h results in a slight down-regulation of CA2 in both tissues. In contrast in Fe 33 cells CA2 gene expression was up-regulated in response to the treatment with E2 for 7 h. In summary, we could demonstrate that the modulation of CA2 gene expression following treatment with E2 and Gen in rat uterus is comparable to the uterotrophic response of these substances, but with an inverted pattern. Remarkably, of all phytoestrogens 8PN exhibited the strongest uterotrophic response but only induced a very faint decrease of CA2 expression. In addition, we provide the first pieces of evidence that 8PN, like Gen and Dai, cannot be considered as a pure agonist. In conclusion, CA2 shows estrogen sensitivity not only in both tissues studied, but also in many others. Further, it exhibits a differential sensitivity thereby being capable to discriminate between different molecular qualities of phytoestrogens, like demonstrated for Gen and 8PN.

Tissue specificity of 8-prenylnaringenin: protection from ovariectomy induced bone loss with minimal trophic effects on the uterus

Plant secondary metabolites with estrogenic activity (phyto-estrogens) have been studied in the past as a potential alternative to classical hormone-replacement therapy (HRT) in menopausal women. No final verdict on the efficacy of soy or red clover based pharmaceutical preparations has been reached despite numerous clinical studies. We have studied the novel and most potent phyto-estrogen 8-prenylnaringenin (8-PN) in adult ovariectomized rats, an established animal model to mimic hormone dependent osteoporosis in menopausal women. Our results demonstrate that 8-PN can completely protect from ovariectomy induced bone-loss while exhibiting minimal, (dose independent) trophic effects on uterus and endometrium. It is estimated that at equivalent bone protective doses of 17beta-estradiol and 8-PN, the phyto-estrogen has a 10-fold lower stimulatory effect on uterus and endometrium. The bone tissue specific effect of 8-PN was confirmed in a transgenic reporter mouse model (ERE-Luc mice). Here we also found pronounced estrogenic activity in prostate. Present results add important aspects to the pharmacological profile of 8-PN and position this compound as an interesting alternative new candidate for treatment of peri- and postmenopausal symptoms.

Regulation of osteoblastic phenotype and gene expression by hop-derived phytoestrogens

Certain plant-derived compounds show selective estrogen receptor modulator (SERM) activity and may therefore be an alternative to the conventional hormone replacement therapy, which prevents osteoporosis but is also associated with an increased risk of breast and endometrial cancers. In the current study, we tested the effects of the hop-derived compounds 8-prenylnaringenin, 6-prenylnaringenin, xanthohumol and isoxanthohumol (1) to modulate markers of differentiation and gene expression in osteoblasts and (2) to regulate proliferation in MCF-7 breast cancer cells. Additionally, we analyzed the ER-binding affinities of these hop compounds as well as the ER-mediation of their effects. Bone-forming activity and ER-subtype specificity were investigated by measuring alkaline phosphatase (AP) activity in hFOB/ERalpha cells and regulation of gene transcription for AP, interleukin-6, pS2 and von Willebrand factor (VWF) in U-2 OS/ERalpha and U-2 OS/ERbeta cells. Our results demonstrate that AP, pS2 and VWF mRNA levels are significantly increased by the compounds in an estrogen-like manner via both ERalpha and ERbeta, while IL-6 is down-regulated in U-2 OS/ERalpha cells. Consistently, AP enzymatic activity is up-regulated by all compounds in hFOB/ERalpha9 cells. Depending on their concentration, all compounds show proliferative effects in MCF-7 cells. Except for 8-PN the hop constituents display an ERbeta-preference. Reversal of estrogen-specific AP-induction in Ishikawa cells indicates an ER-regulated mechanism. Finally, the flavonoids display cytotoxic effects only at high concentrations (> or =10(-4)M). In summary, we have demonstrated for the first time that specific phytoestrogen compounds found in hop extracts exert estrogen-like activities on bone metabolism. Regarding a potential for use in osteoporosis-prevention therapy, the dosage of a phytoestrogen, which is taken, will play an important role concerning a desired in vivo profile.

Activation of proestrogens from hops (Humulus lupulus L.) by intestinal microbiota; conversion of isoxanthohumol into 8-prenylnaringenin

Hop, an essential ingredient in most beers, contains a number of prenylflavonoids, among which 8-prenylnaringenin (8-PN) would be the most potent phytoestrogen currently known. Although a number of health effects are attributed to these compounds, only a few reports are available about the bioavailability of prenylflavonoids and the transformation potency of the intestinal microbial community. To test these transformations, four fecal samples were incubated with xanthohumol, isoxanthohumol (IX), and 8-PN. Upon incubation with IX, present in strong ales up to 4 mg/L, 36% was converted into 8-PN in one fecal sample and the estrogenic properties of the sample drastically increased. In an experiment with 12 fecal cultures, this conversion was observed in one-third of the samples, indicating the importance of interindividual variability in the intestinal microbial community. Eubacterium limosum was identified to be capable of this conversion (O-demethylation) of IX into 8-PN, and after strain selection, a conversion efficiency of 90% was achieved. Finally, strain supplementation to a nonconverting fecal sample led to rapid and high 8-PN production at only 1% (v/v) addition. Up to now, the concentration of 8-PN in beer was considered too low to affect human health. However, these results show that the activity of the intestinal microbial community could more than 10-fold increase the exposure concentration. Because prenylflavonoids are present in many beers with IX being the major constituent, the results raise the question whether moderate beer consumption might contribute to increased in vivo levels of 8-PN and even influence human health.

Artelastin is a cytotoxic prenylated flavone that disturbs microtubules and interferes with DNA replication in MCF-7 human breast cancer cells

Artelastin, a novel prenylated flavone, previously isolated from the wood bark of Artocarpus elasticus, was evaluated for its capacity to inhibit the growth of fifty-two human tumor cell lines, representing nine different tumor types. A pronounced dose-dependent growth inhibitory effect was detected in all the cell lines, with GI50 values ranging from 0.8-20.8 microM. Studies to elucidate the basis of the growth inhibitory activity of artelastin were performed in the MCF-7 human breast cancer cell line (GI50 = 6.0 microM). We show that artelastin exerts a biphasic effect in the DNA synthesis of MCF-7 cells, a stimulatory effect at low concentrations (below GI50) for short times of exposition (6 h and 24 h), and an inhibitory effect at high concentrations (above GI50). Remarkably, treated cells that have DNA synthesis affected could be viable and metabolically active. Furthermore, artelastin acts as a cytotoxic rather than a cytostatic compound. Massive cytoplasmatic vacuoles were detected in cells after artelastin treatment. Together with these morphological alterations, cells show the presence of abnormal nuclear morphologies, and occasionally nuclear condensation, which were identified as apoptotic by TUNEL assay. Moreover, artelastin was shown to disturb the microtubule network while no effect was observed on the kinetochores. Flow cytometry analysis of cells treated with artelastin reveal an accumulation in S phase that interferes with the cell cycle progression. Additionally, according to BrdU patterns, studies with synchronized cells at G0 and at G1/S transition also suggest that artelastin delays DNA replication since progression of cells trough S-phase is perturbed.

Naringenin-type flavonoids show different estrogenic effects in mammalian and teleost test systems

The estrogenic activity of several intermediary plant compounds has raised concern about possible risks of unwanted interference with endocrine regulation, but on the other hand there are potential medical benefits, in particular in treatment of menopausal symptoms or cancer. In the present study, we compare the estrogenic effects of phytoestrogens naringenin, 8-prenylnaringenin, 6-(1,1-dimethylallyl)naringenin, and the synthetic 4'-acetyl-7-prenyloxynaringenin. Two mammalian in vitro systems and a fish in vivo system were used to study the estrogenic properties with reference to genistein, 17-beta-estradiol or ethynylestradiol. Strong differences were observed between the mammalian in vitro and the fish in vivo test system. In the medaka sex reversal/vtg gene expression assay no estrogenic effects of the naringenin-type flavonoids were observed, while mammalian in vitro systems showed a similar and graded response to the test compounds.

Two major metabolites of 8-prenylnaringenin are estrogenic in vitro

8-prenylnaringenin (8-PN) and preparations containing 8-prenylnaringenin have been suggested for use in medicinal and cosmetic applications like hormone replacement or bust enhancement. However, the safety of application is still under considerable debate. Recently it has been shown that human liver microsomes are converting 8-prenylnaringenin to 12 metabolites, with (E)-8-(4''-hydroxyisopentenyl)naringenin (8-PN-OH) and (E)-8-(4''-oxoisopentenyl)naringenin (8-PN=O) being among the most abundant. Applying two independent in vitro test systems we demonstrate that these two metabolites of 8-prenylnaringenin are estrogenic in vitro. These results represent an important piece of information towards the discussion of safety of use of preparations containing 8-prenylnaringenin.

Phytoestrogens

Collectively, plants contain several different families of natural products among which are compounds with weak estrogenic or antiestrogenic activity toward mammals. These compounds, termed phytoestrogens, include certain isoflavonoids, flavonoids, stilbenes, and lignans. The best-studied dietary phytoestrogens are the soy isoflavones and the flaxseed lignans. Their perceived health beneficial properties extend beyond hormone-dependent breast and prostate cancers and osteoporosis to include cognitive function, cardiovascular disease, immunity and inflammation, and reproduction and fertility. In the future, metabolic engineering of plants could generate novel and exquisitely controlled dietary sources with which to better assess the potential health beneficial effects of phytoestrogens.

Estrogenic and Antiestrogenic Activities of the Roots of Moghania philippinensis and Their Constituents

In the course of our search for natural estrogenic compounds from medicinal plants, we found that the methanolic extract from the roots of Moghania philippinensis (Fabaceae) showed significant effects on the proliferation of MCF-7 cells (human breast cancer) and induction of beta-galactosidase activity in a yeast two-hybrid assay. Through estrogenic activity-guided fractionation, we isolated several active flavonoids including prenylated ones. The CHCl(3) fraction and its new constituent, 8-(1,1-dimethylallyl)genistein (9), appreciably increased the uterine weight in ovariectomized rats when administered orally for 14 consecutive days, in which compound 9 showed stronger estrogenic activity than genistein. Antiestrogenic activities were also examined based on the inhibition of MCF-7 cell proliferation and beta-galactosidase activity in the yeast two-hybrid assay, mediated by 17beta-estradiol. 5,7,3',4'-Tetrahydroxy-6,8-diprenylisoflavone (6) showed the strongest antiestrogenic activity.

Dietary phytoestrogens and their effect on bone: evidence from in vitro and in vivo, human observational, and dietary intervention studies

Impressive data from the many studies on cultured bone cells and rat models of postmenopausal osteoporosis support a significant bone-sparing effect of the soy isoflavones genistein and daidzein. Translating this research to the clinic has been more challenging, and thus far only a few clinical studies have attempted to tease out the influence of phytoestrogens on bone from the many other components of the diet. Human studies have shown promising although variable results. Studies have been mostly of short duration and with relatively small sample sizes, making it difficult to observe significant and accurate changes in bone. Levels of intake of the soy protein and isoflavones are varied, and the optimal isoflavone intake for bone-sparing effects remains to be determined. Clinical studies thus far performed can be broadly divided into those that have assessed biochemical evidence of reduced bone turnover from measurement of surrogate markers of osteoblast and osteoclast activity, and those that have examined changes in bone mineral density. There are no studies examining effects on fracture rate. This review focuses specifically on the potential influence of phytoestrogens on bone by examining the evidence from 17 in vitro studies of cultured bone cells, 24 in vivo studies of animal models for postmenopausal osteoporosis, 15 human observational/epidemiologic studies, and 17 dietary intervention studies. On balance, the collective data suggest that diets rich in phytoestrogens have bone-sparing effects in the long term, although the magnitude of the effect and the exact mechanism(s) of action are presently elusive or speculative.

Prevention of osteopaenia by phyto-oestrogens: animal studies

Osteoporosis has become a major public health problem. Because the biggest culprit in the process of bone loss is oestrogen deficiency, hormone replacement therapy remains the mainstay for prevention, but prophylaxis by this means is limited. Phyto-oestrogens deserve special mention because emerging data support the suggestion that these weakly oestrogenic compounds, present in plants, may prevent bone loss associated with the menopause and thus represent a potential alternative therapy for a range of hormone-dependent conditions, including postmenopausal symptoms. A substantial body of work in animal models in the past few years has provided convincing data for significant improvements in bone mass and other endpoints following feeding with soya. Thus, phyto-oestrogens appear to have potential promise for maintaining or modestly improving bone mass of human subjects when consumed at optimal dosages. However, we must appreciate the limits of the information reached before extrapolating to man and we need to gather more data before health professionals can actively advocate the increased consumption of soya. Indeed, it will be important further to characterise the physiological effects of phyto-oestrogens and their margins of safety.

Overview of in vitro tools to assess the estrogenic and antiestrogenic activity of phytoestrogens

There is an intense discussion in the scientific and even more so in the public community as well as regulatory agencies about the potential benefits or detrimental effects of plant-derived compounds that may affect the endocrine system, especially estrogen signaling pathways. These so-called phytoestrogens are found in the normal western diet and predominantly in an eastern or soy-based diet and the potency of the isolated compounds to interact with the known receptors for estrogen varies tremendously. The estrogen receptors, ER alpha and ER beta, mediate the effects of endogenous estrogens, i.e. regulation of reproductive function, tissue development, cell proliferation and differentiation. In this review, in vitro test systems available to date for the screening of estrogenic and antiestrogenic activity including mechanism-based assays are described. The potency of phytoestrogens determined using these in vitro assays are compared with the potency of endogenous estrogens and results obtained in vitro are compared with effects in vivo. Finally, the impact of in vitro assays to determine estrogenicity on human hazard assessment is discussed as well as other non ER-mediated mechanisms that may contribute to potential beneficial or adverse effects of phytoestrogens in man.

Identification, quantitation and biological activity of phytoestrogens in a dietary supplement for breast enhancement

A hop-based dietary supplement, marketed for natural breast enhancement, was analysed to determine the identity and biological activity of active constituents and potential biological effects in man. Extracts of the dietary supplement were analysed by LC-MS(n) and phytoestrogens identified and quantitated by reference to appropriate standards. Only hop-associated phytoestrogens were found in the dietary supplement at significant concentrations as follows (mean+/-1 S.D.); 8-prenylnaringenin 10.9+/-0.3, 6-prenylnaringenin 27.4+/-1.2, 6,8-diprenylnaringenin 0.9+/-0.1, xanthohumol 321+/-17 and isoxanthohumol 81.1+/-1.6 microg/g of dietary supplement. The oestrogenic activity of extracts in an ERalpha reporter gene assay was equivalent to 48+/-6.3 ng 17beta-oestradiol/g supplement and consistent with the 8-prenylnaringenin content. The dietary supplement extract also inhibited reductive 17beta-hydroxysteroid oxidoreductase activity, but to a greater extent than a concentration matched reference mixture of hop phytoestrogens. However, the supplement was only weakly active in mouse uterotrophic assays following administration in feed or after subcutaneous injection of extract at doses of 8-PN up to 250 times higher than that recommended for women. These preliminary findings suggest that the dietary supplement is unlikely to produce oestrogenic effects in vivo at the level of the uterus; supporting evidence is still required to demonstrate efficacy.

Advances in flavonoid research since 1992

Some of the recent advances in flavonoid research are reviewed. The role of anthocyanins and flavones in providing stable blue flower colours in the angiosperms is outlined. The contribution of leaf flavonoids to UV-B protection in plants is critically discussed. Advances in understanding the part played by flavonoids in warding off microbial infection and protecting plants from herbivory are described. The biological properties of flavonoids are considered in an evaluation of the medicinal and nutritional values of these compounds.