The stimulation of cell proliferation by quercetin is mediated by the estrogen receptor

Molecular Targets Underlying the Anticancer Effects of Quercetin: An Update

Quercetin, a medicinally important member of the flavonoid family, is one of the most prominent dietary antioxidants. It is present in a variety of foods—including fruits, vegetables, tea, wine, as well as other dietary supplements—and is responsible for various health benefits. Numerous pharmacological effects of quercetin include protection against diseases, such as osteoporosis, certain forms of malignant tumors, and pulmonary and cardiovascular disorders. Quercetin has the special ability of scavenging highly reactive species, such as hydrogen peroxide, superoxide anion, and hydroxyl radicals. These oxygen radicals are called reactive oxygen species, which can cause oxidative damage to cellular components, such as proteins, lipids, and deoxyribonucleic acid. Various oxygen radicals play important roles in pathophysiological and degenerative processes, such as aging. Subsequently, several studies have been performed to evaluate possible advantageous health effects of quercetin and to collect scientific evidence for these beneficial health claims. These studies also gather data in order to evaluate the exact mechanism(s) of action and toxicological effects of quercetin. The purpose of this review is to present and critically analyze molecular pathways underlying the anticancer effects of quercetin. Current limitations and future directions of research on this bioactive dietary polyphenol are also critically discussed.

The metabolite 3,4,3',4'-tetrachloroazobenzene (TCAB) exerts a higher ecotoxicity than the parent compounds 3,4-dichloroaniline (3,4-DCA) and propanil

3,4,3',4'-tetrachloroazobenzene (TCAB) is not commercially manufactured but formed as an unwanted by-product in the manufacturing of 3,4-dichloroaniline (3,4-DCA) or metabolized from the degradation of chloranilide herbicides, like propanil. While a considerable amount of research has been done concerning the toxicological and ecotoxicological effects of propanil and 3,4-DCA, limited information is available on TCAB. Our study examined the toxicity of TCAB in comparison to its parent compounds propanil and 3,4-DCA, using a battery of bioassays including in vitro with aryl hydrocarbon receptor (AhR) mediated activity by the 7-ethoxyresorufin-O-deethylase (EROD) assay and micro-EROD, endocrine-disrupting activity with chemically activated luciferase gene expression (CALUX) as well as in vivo with fish embryo toxicity (FET) assays with Danio rerio. Moreover, the quantitative structure activity response (QSAR) concepts were applied to simulate the binding affinity of TCAB to certain human receptors. It was shown that TCAB has a strong binding affinity to the AhR in EROD and micro-EROD induction assay, with the toxic equivalency factor (TEF) of 8.7×10(-4) and 1.2×10(-5), respectively. TCAB presented to be a weak endocrine disrupting compound with a value of estradiol equivalence factor (EEF) of 6.4×10(-9) and dihydrotestosterone equivalency factor (DEF) of 1.1×10(-10). No acute lethal effects of TCAB were discovered in FET test after 96h of exposure. Major sub-lethal effects detected were heart oedema, yolk malformation, as well as absence of blood flow and tail deformation. QSAR modelling suggested an elevated risk to environment, particularly with respect to binding to the AhR. An adverse effect potentially triggering ERβ, mineralocorticoid, glucocorticoid and progesterone receptor activities might be expected. Altogether, the results obtained suggest that TCAB exerts a higher toxicity than both propanil and 3,4-DCA. This should be considered when assessing the impact of these compounds for the environment and also for regulatory decisions.

Mechanisms of Neuroprotection by Quercetin: Counteracting Oxidative Stress and More

Increasing interest has recently focused on determining whether several natural compounds, collectively referred to as nutraceuticals, may exert neuroprotective actions in the developing, adult, and aging nervous system. Quercetin, a polyphenol widely present in nature, has received the most attention in this regard. Several studies in vitro, in experimental animals and in humans, have provided supportive evidence for neuroprotective effects of quercetin, either against neurotoxic chemicals or in various models of neuronal injury and neurodegenerative diseases. The exact mechanisms of such protective effects remain elusive, though many hypotheses have been formulated. In addition to a possible direct antioxidant effect, quercetin may also act by stimulating cellular defenses against oxidative stress. Two such pathways include the induction of Nrf2-ARE and induction of the antioxidant/anti-inflammatory enzyme paraoxonase 2 (PON2). In addition, quercetin has been shown to activate sirtuins (SIRT1), to induce autophagy, and to act as a phytoestrogen, all mechanisms by which quercetin may provide its neuroprotection.

Protective effect of porcine placenta in a menopausal ovariectomized mouse

Menopause is a significant physiological phase that occurs as women's ovaries stop producing ovum and the production of estrogen declines. Human placenta and some amino acids are known to improve menopausal symptoms. In this study, we investigated that porcine placenta extract (PPE) and arginine (Arg), a main amino acid of PPE, would have estrogenic activities in ovariectomized (OVX) mice as a menopause mouse model, human breast cancer cell line (MCF-7) cells, and human osteoblast cell line (MG-63) cells. PPE or Arg significantly inhibited the body weight and increased the vagina weight compared to the OVX mice. PPE or Arg ameliorated the vaginal atrophy in the OVX mice. The levels of 17β-estradiol and the activities of alkaline phosphatase (ALP) were significantly increased by PPE or Arg in the serum of OVX mice. Trabecular bone parameters such as bone mineral density and porosity were also improved by PPE or Arg in the OVX mice. In the MCF-7 and MG-63 cells, PPE or Arg significantly increased the cell proliferation, estrogen receptor β mRNA expression, and estrogen-response elements luciferase activity. Finally, PPE or Arg increased the activations of ALP and extracellular signal-regulated kinase 1/2 in the MG-63 cells. These results indicate that PPE or Arg would have estrogenic and osteoblastic activity. Therefore, PPE or Arg may be useful as new pharmacological tools for treating menopausal symptoms including osteoporosis. Free Korean abstract: A Korean translation of this abstract is freely available at http://www.reproduction-online.org/content/150/3/173/suppl/DC1.

Deconjugation of soy isoflavone glucuronides needed for estrogenic activity

Soy isoflavones (SIF) are present in the systemic circulation as conjugated forms of which the estrogenic potency is not yet clear. The present study provides evidence that the major SIF glucuronide metabolites in blood, genistein-7-O-glucuronide (GG) and daidzein-7-O-glucuronide (DG), only become estrogenic after deconjugation. The estrogenic potencies of genistein (Ge), daidzein (Da), GG and DG were determined using stably transfected U2OS-ERα, U2OS-ERβ reporter gene cells and proliferation was tested in T47D-ERβ cells mimicking the ERα/ERβ ratio of healthy breast cells and inT47D breast cancer cells. In all assays applied, the estrogenic potency of the aglycones was significantly higher than that of their corresponding glucuronides. UPLC analysis revealed that in U2OS and T47D cells, 0.2-1.6% of the glucuronides were deconjugated to their corresponding aglycones. The resulting aglycone concentrations can account for the estrogenicity observed upon glucuronide exposure. Interestingly, under similar experimental conditions, rat breast tissue S9 fraction was about 30 times more potent in deconjugating these glucuronides than human breast tissue S9 fraction. Our study confirms that SIF glucuronides are not estrogenic as such, and that the small % of deconjugation in the cell is enough to explain the slight bioactivity observed for the SIF-glucuronides. Species differences in deconjugation capacity should be taken into account when basing risk-benefit assessment of these SIF for the human population on animal data.

A dietary pattern rich in lignans, quercetin and resveratrol decreases the risk of oesophageal cancer

Dietary lignans, quercetin and resveratrol have oestrogenic properties, and animal studies suggest that they synergistically decrease cancer risk. A protective effect of lignans on the development of oesophageal cancer in humans has recently been demonstrated, and the present study aimed to test whether these three phytochemicals synergistically decrease the risk of oesophageal cancer. Data from a Swedish nationwide population-based case-control study that recruited 181 cases of oesophageal adenocarcinoma (OAC), 158 cases of oesophageal squamous-cell carcinoma (OSCC), 255 cases of gastro-oesophageal junctional adenocarcinoma (JAC) and 806 controls were analysed. Exposure data were collected through face-to-face interviews and questionnaires. The intake of lignans, quercetin and resveratrol was assessed using a sixty-three-item FFQ. Reduced-rank regression was used to assess a dietary pattern, and a simplified dietary pattern score was categorised into quintiles on the basis of the distribution among the control subjects. Unconditional multivariable logistic regression provided OR with 95% CI, adjusted for all the potential risk factors. A dietary pattern rich in lignans, quercetin and resveratrol was mainly characterised by a high intake of tea, wine, lettuce, mixed vegetables, tomatoes, and whole-grain bread and a low intake of milk. There were dose-dependent associations between simplified dietary pattern scores and all types of oesophageal cancer (all P for trend < 0.05). On comparing the highest quintiles with the lowest, the adjusted OR were found to be 0.24 (95% CI 0.12, 0.49) for OAC, 0.31 (95% CI 0.15, 0.65) for OSCC, and 0.49 (95% CI 0.28, 0.84) for JAC. The results of the present study indicate that a dietary pattern characterised by the intake of lignans, quercetin and resveratrol may play a protective role in the development of oesophageal cancer in the Swedish population.

Er-xian Decoction exerts estrogen-like osteoprotective effects in vivo and in vitro

Er-xian Decoction (EXD), containing Herba epimedii Maxim (HEP) and Curculigo orchioides Gaertn (XM) as principal drugs, is a traditional Chinese medicine (TCM) formula prescribed for the treatment of postmenopausal osteoporosis. In the present study, the in vivo anti-osteoporosis effects of EXD, HEP and XM on four-month-old ovariectomized (OVX) Sprague-Dawley rats were investigated. Micro-computed tomography analysis showed that EXD could significantly improve the micro-architectural parameters (BMD, BV/TV, Tb.N, Tb.Th, and Tb.Sp) of trabecular bone in the distal femur and proximal tibia in OVX rats (p < 0.05). The biomechanical parameters of the distal femur in rats treated with EXD were also improved significantly (p < 0.05 vs. OVX group). The in vivo efficacy of EXD was found to be superior to HEP or XM alone in improving the bone properties of OVX rats. Treatment of rat osteoblastic-like UMR-106 cells with EXD, HEP, and XM significantly promoted the cell proliferation rate (p < 0.05) with the most promising effects observed in cells treated with EXD (p < 0.001). The proliferative effect in UMR-106 cells induced by EXD, HEP, and XM were abolished in the presence of the estrogen antagonist, ICI182780, suggesting that their effects were mediated by estrogen receptor (ER). Additionally, EXD could activate ER-α and ER-β mediated estrogen-response element (ERE)-dependent luciferase activity as well as phosphorylate ER-α at serine 118 in UMR-106 cells. Taken together, EXD offered better osteoprotective effects than its single principal herb, and the beneficial effects of EXD in preventing bone deteriorations are, at least partially, through the ER signaling pathway.

Association between dietary intake of flavonoid and bone mineral density in middle aged and elderly Chinese women and men

SUMMARY

This large cross-sectional study examined the associations of dietary intakes of total flavonoids and their subtypes with bone density in women and men. We found that greater flavonoid intake was associated with higher bone density in women but not in men.

INTRODUCTION

Studies in vitro and in animal models suggest a potential effect of flavonoids on bone health. Few studies have examined the association between the habitual intake of flavonoids and bone mineral density (BMD) in humans.

METHODS

The cross-sectional study recruited 2,239 women and 1,078 men. A semiquantitative food frequency questionnaire was administered in face-to-face interviews to assess habitual dietary flavonoid intake using food composition databases. BMD was measured over the whole body (WB) and in the femoral neck (FN) and lumbar spine (LS) by dual-energy X-ray absorptiometry (DXA).

RESULTS

After adjusting for covariates, women who consumed higher total flavonoids, and the subtypes of flavonols, flavan-3-ols, flavones, and proanthocyanidins tended to have greater BMD at the WB, LS, and FN (all P-trend < 0.05). Women in the highest (vs. the lowest) quartile of total flavonoids intake had 0.020 (1.91 %), 0.021 (2.51 %), and 0.013 (1.99 %) g/cm(2) greater BMD at the whole body, LS, and FN, respectively. For the subtypes of flavonoids, the corresponding differences in BMD (in g/cm(2)) were 0.012-0.021 (flavan-3-ols), 0.013-0.020 (flavonols), 0.016-0.019 (flavones), and 0.014-0.016 (proanthocyanidins), respectively. A higher intake of flavonones was associated with a greater BMD at the whole body (P-trend 0.041) and the FN (P-trend 0.022). In men, there were no significant positive associations between the consumption of total flavonoids and the subclasses and BMD at any sites.

CONCLUSION

Dietary flavonoids intake was positively associated with BMD in women. Further large studies are needed to clarify this issue in men.

Flavonoids from Herba epimedii selectively activate estrogen receptor alpha (ERα) and stimulate ER-dependent osteoblastic functions in UMR-106 cells

Total flavonoids in Herba epimedii (HEP) have been demonstrated to protect against bone loss and bone deterioration associated with estrogen deficiency without exerting any uterotrophic effects. However, it is unclear how flavonoids in HEP exert their protective effects on bone and if different flavonoids exert estrogenic actions in bone cells via similar mechanism of actions. The present study aims to investigate the bone anabolic effects of four major flavonoids isolated from HEP, namely icariin, baohuoside-I, epimedin B and sagittatoside A as well as the mechanism involved in mediating their estrogenic actions in rat osteoblastic-like UMR-106 cells. All tested compounds significantly stimulated the cell proliferation rate, alkaline phosphate (ALP) activity and osteoprotegerin (OPG)/receptor activator of nuclear factor κ-B ligand (RANKL) mRNA expression in UMR-106 cells and their effects could be abolished by co-incubation with 10(-6)M ICI 182,780. None of the flavonoids exhibited binding affinities toward ERα and ERβ. However, sagittatoside A selectively activated estrogen response element (ERE)-luciferase activity via ERα. In addition, icariin and sagittatoside A induced ERα phosphorylation at serine 118 residue. Taken together, our results indicated that all four flavonoids from HEP stimulated ER-dependent osteoblastic functions in UMR-106 cells, but only two of them appeared to exert their actions by ligand-independent activation of ERα. Our study provides evidence to support the hypothesis that the estrogen-like protective effects on bone by flavonoids are mediated via mechanisms that are distinct from the classical actions of estrogen.

Wild Saccharomyces cerevisiae strains display biofilm-like morphology in contact with polyphenols from grapes and wine

Polyphenols are a major component of wine grapes, and contribute to color and flavor, but their influence upon yeast growth forms has not been investigated. In this work we have studied the effect of polyphenols on the ability of natural isolates of wine-related Saccharomyces cerevisiae strains to form biofilms attaching to plastic surfaces, to grow as mat colonies, to invade media, and to display filamentous growth. The use of carbon- and nitrogen-rich or deficient media simulated grape juice fermentation conditions. The addition of wine polyphenols to these media affected biofilm formation, and cells exhibited a wide variety of invasiveness and mat formation ability with associated different growth and footprint patterns. Microscopic observation revealed that some strains switched to filamentous phenotypes which were able to invade media. The wide range of phenotypic expression observed could have a role in selection of strains suitable for inoculated wine fermentations and may explain the persistence of yeast strains in vineyard and winery environments.

Combined effects of urinary phytoestrogens metabolites and polymorphisms in metabolic enzyme gene on idiopathic male infertility

Phytoestrogens are plant-derived compounds that may interact with estrogen receptors and mimic estrogenic effects. It remains unclear whether the individual variability in metabolizing phytoestrogens contributes to phytoestrogens-induced beneficial or detrimental effects. Our aim was to determine whether there is any interaction between metabolic rates (MR) of phytoestrogens and genetic polymorphisms in related xenobiotic metabolizing enzyme genes. MR was used to assess phytoestrogen exposure and individual metabolic ability. The amount of phytoestrogens in urine was measured by ultra-high performance liquid chromatography-tandem mass spectrometry in 600 idiopathic infertile male patients and 401 controls. Polymorphisms were genotyped using the SNPstream platform combined with the Taqman method. Prototypes and metabolites of secoisolariciresinol (SEC) have inverse effects on male reproduction. It was found that low MR of SEC increased the risk of male infertility (OR 2.49, 95 % CI 1.78, 3.48, P trend = 8.00 × 10(-8)). Novel interactions were also observed between the MR of SEC and rs1042389 in CYP2B6, rs1048943 in CYP1A1, and rs1799931 in NAT2 on male infertility (P inter = 1.06 × 10(-4), 1.14 × 10(-3), 3.55 × 10(-3), respectively). By analyzing the relationships between urinary phytoestrogen concentrations, their metabolites and male infertility, we found that individual variability in metabolizing SEC contributed to the interpersonal differences in SEC's effects on male reproduction.

A targeted approach for evaluating preclinical activity of botanical extracts for support of bone health

Using a sequential in vitro/in vivo approach, we tested the ability of botanical extracts to influence biomarkers associated with bone resorption and bone formation. Pomegranate fruit and grape seed extracts were found to exhibit anti-resorptive activity by inhibiting receptor activator of nuclear factor-κB ligand (RANKL) expression in MG-63 cells and to reduce IL-1β-stimulated calvarial ⁴⁵Ca loss. A combination of pomegranate fruit and grape seed extracts were shown to be effective at inhibiting bone loss in ovariectomised rats as demonstrated by standard histomorphometry, biomechanical and bone mineral density measurements. Quercetin and licorice extract exhibited bone formation activity as measured by bone morphogenetic protein-2 (BMP-2) promoter activation, increased expression of BMP-2 mRNA and protein levels, and promotion of bone growth in cultured mouse calvariae. A combination of quercetin and licorice extract demonstrated a potential for increasing bone mineral density in an intact female rat model as compared with controls. The results from this sequential in vitro/in vivo research model yielded botanical extract formulas that demonstrate significant potential benefits for bone health.

Glucuronidation does not suppress the estrogenic activity of quercetin in yeast and human breast cancer cell model systems

Several plant-derived molecules, referred to as phytoestrogens, are thought to mimic the actions of endogenous estrogens. Among these, quercetin, one of the most widespread flavonoids in the plant kingdom, has been reported as estrogenic in some occasions. However, quercetin occurs in substantial amounts as glycosides such as quercetin-3-O-glucoside (isoquercitrin) and quercetin-3-O-rutinoside (rutin) in dietary sources. It is now well established that quercetin undergoes substantial phase II metabolism after ingestion by humans, with plasma metabolites after a normal dietary intake rarely exceeding nmol/L concentrations. Therefore, attributing phytoestrogenic activity to flavonoids without taking into account the fact that it is their phase II metabolites that enter the circulatory system, will almost certainly lead to misleading conclusions. With the aim of clarifying the above issue, the goal of the present study was to determine if plant-associated quercetin glycosides and human phase II quercetin metabolites, actually found in human biological fluids after intake of quercetin containing foods, are capable of interacting with the estrogen receptors (ER). To this end, we used a yeast-based two-hybrid system and an estrogen response element-luciferase reporter assay in an ER-positive human cell line (MCF-7) to probe the ER interaction capacities of quercetin and its derivatives. Our results show that quercetin-3-O-glucuronide, one of the main human phase II metabolites produced after intake of dietary quercetin, displays ERα- and ERβ-dependent estrogenic activity, the functional consequences of which might be related to the protective activity of diets rich in quercetin glycosides.

Site-specific anticancer effects of dietary flavonoid quercetin

Food-derived flavonoid quercetin, widely distributed in onions, apples, and tea, is able to inhibit growth of various cancer cells indicating that this compound can be considered as a good candidate for anticancer therapy. Although the exact mechanism of this action is not thoroughly understood, behaving as antioxidant and/or prooxidant as well as modulating different intracellular signalling cascades may all play a certain role. Such inhibitory activity of quercetin has been shown to depend first of all on cell lines and cancer types; however, no comprehensive site-specific analysis of this effect has been published. In this review article, cytotoxicity constants of quercetin measured in various human malignant cell lines of different origin were compiled from literature and a clear cancer selective action was demonstrated. The most sensitive malignant sites for quercetin revealed to be cancers of blood, brain, lung, uterine, and salivary gland as well as melanoma whereas cytotoxic activity was higher in more aggressive cells compared to the slowly growing cells showing that the most harmful cells for the organism are probably targeted. More research is needed to overcome the issues of poor water solubility and relatively low bioavailability of quercetin as the major obstacles limiting its clinical use.

Phytoestrogens induce apoptosis through a mitochondria/caspase pathway in human breast cancer cells

OBJECTIVE

To explore the effect and pathway of phytoestrogens on the growth of breast cancer cell line MCF-7.

METHODS

MCF-7 cells (human estrogen receptor-positive and progesterone receptor-positive breast cancer cells) were cultured in serum-free medium for 24 h and then treated with genistein, resveratrol, and quercetin (10(-10)-10(-4) mol/l). After further incubation for 24, 48, 72, and 92 h, the cells were harvested and extracted for 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. According to the above results, the proteins involving proliferative and apoptotic pathways were evaluated by Western blot analysis.

RESULTS

Genistein, resveratrol, and quercetin significantly inhibited cellular proliferation in a dose- and time-dependent manner. Significantly elevated caspase-3 activity was noted after treatment with genistein (10(-9)-10(-7) mol/l), as well as with resveratrol and quercetin (10(-9)-10(-5) mol/l). Significant reduction of PI3K and AKT protein and significant increase of Fas ligand, Fas-associated protein with death domain, cytochrome C, truncated Bid, caspase-9, and caspase-3 were all noted after genistein, resveratrol, and quercetin treatment. 17β-Estradiol induced completely opposite results. Estrogen receptor (ER) α expression was significantly increased with 17β-estradiol, whereas ERβ expression was significantly elevated in the cultures with genistein, resveratrol, and quercetin.

CONCLUSIONS

These data demonstrate that genistein, resveratrol, and quercetin have antiproliferative effects on breast cancer cells. Their induction of apoptosis involves the activation of both the intrinsic and extrinsic apoptotic pathways, which may be related to the differential affinity to ERα and ERβ. Whether phytoestrogens have similar effects on normal breast cells remains to be examined.

Endocrine disrupting activities of the flavonoid nutraceuticals luteolin and quercetin

Dietary plant flavonoids have been proposed to contribute to cancer prevention, neuroprotection, and cardiovascular health through their anti-oxidant, anti-inflammatory, pro-apoptotic, and antiproliferative activities. As a consequence, flavonoid supplements are aggressively marketed by the nutraceutical industry for many purposes, including pediatric applications, despite inadequate understanding of their value and drawbacks. We show that two flavonoids, luteolin and quercetin, are promiscuous endocrine disruptors. These flavonoids display progesterone antagonist activity beneficial in a breast cancer model but deleterious in an endometrial cancer model. Concurrently, luteolin possesses potent estrogen agonist activity while quercetin is considerably less effective. These results highlight the promise and peril of flavonoid nutraceuticals and suggest caution in supplementation beyond levels attained in a healthy, plant-rich diet.

Modulation of paraoxonase 2 (PON2) in mouse brain by the polyphenol quercetin: a mechanism of neuroprotection?

Quercetin is a common flavonoid polyphenol which has been shown to exert neuroprotective actions in vitro and in vivo. Though quercetin has antioxidant properties, it has been suggested that neuroprotection may be ascribed to its ability of inducing the cell's own defense mechanisms. The present study investigated whether quercetin could increase the levels of paraoxonase 2 (PON2), a mitochondrial enzyme expressed in brain cells, which has been shown to have potent antioxidant properties. PON2 protein, mRNA, and lactonase activity were highest in mouse striatal astrocytes. Quercetin increased PON2 levels, possibly by activating the JNK/AP-1 pathway. The increased PON2 levels induced by quercetin resulted in decreased oxidative stress and ensuing toxicity induced by two oxidants. The neuroprotective effect of quercetin was significantly diminished in cells from PON2 knockout mice. These findings suggest that induction of PON2 by quercetin represents an important mechanism by which this polyphenol may exert its neuroprotective action.

Trigger values for investigation of hormonal activity in drinking water and its sources using CALUX bioassays

To screen for hormonal activity in water samples, highly sensitive in vitro CALUX bioassays are available which allow detection of estrogenic (ERα), androgenic (AR), progestagenic (PR), and glucocorticoid (GR) activities. This paper presents trigger values for the ERα, AR, PR, and GR CALUX bioassays for agonistic hormonal activities in (drinking) water, which define a level above which human health risk cannot be waived a priori and additional examination of specific endocrine activity may be warranted. The trigger values are based on 1) acceptable or tolerable daily intake (ADI/TDI) values of specific compounds, 2) pharmacokinetic factors defining their bioavailability, 3) estimations of the bioavailability of unknown compounds with equivalent hormonal activity, 4) relative endocrine potencies, and 5) physiological, and drinking water allocation factors. As a result, trigger values of 3.8ng 17β-estradiol (E2)-equivalents (eq)/L, 11ng dihydrotestosterone (DHT)-eq/L, 21ng dexamethasone (DEX)-eq/L, and 333ng Org2058-eq/L were derived. Benchmark Quotient (BQ) values were derived by dividing hormonal activity in water samples by the derived trigger using the highest concentrations detected in a recent, limited screening of Dutch water samples, and were in the order of (value) AR (0.41)>ERα (0.13)>GR (0.06)>PR (0.04). The application of trigger values derived in the present study can help to judge measured agonistic hormonal activities in water samples using the CALUX bioassays and help to decide whether further examination of specific endocrine activity followed by a subsequent safety evaluation may be warranted, or whether concentrations of such activity are of low priority with respect to health concerns in the human population. For instance, at one specific drinking water production site ERα and AR (but no GR and PR) activities were detected in drinking water, however, these levels are at least a factor 83 smaller than the respective trigger values, and therefore no human health risks are to be expected from hormonal activity in Dutch drinking water from this site.

Additive mixture effects of estrogenic chemicals in human cell-based assays can be influenced by inclusion of chemicals with differing effect profiles

A growing body of experimental evidence indicates that the in vitro effects of mixtures of estrogenic chemicals can be well predicted from the estrogenicity of their components by the concentration addition (CA) concept. However, some studies have observed small deviations from CA. Factors affecting the presence or observation of deviations could include: the type of chemical tested; number of mixture components; mixture design; and assay choice. We designed mixture experiments that address these factors, using mixtures with high numbers of components, chemicals from diverse chemical groups, assays with different in vitro endpoints and different mixture designs and ratios. Firstly, the effects of mixtures composed of up to 17 estrogenic chemicals were examined using estrogenicity assays with reporter-gene (ERLUX) and cell proliferation (ESCREEN) endpoints. Two mixture designs were used: 1) a ‘balanced’ design with components present in proportion to a common effect concentration (e.g. an EC₁₀) and 2) a ‘non-balanced’ design with components in proportion to potential human tissue concentrations. Secondly, the individual and simultaneous ability of 16 potential modulator chemicals (each with minimal estrogenicity) to influence the assay outcome produced by a reference mixture of estrogenic chemicals was examined. Test chemicals included plasticizers, phthalates, metals, PCBs, phytoestrogens, PAHs, heterocyclic amines, antioxidants, UV filters, musks, PBDEs and parabens. In all the scenarios tested, the CA concept provided a good prediction of mixture effects. Modulation studies revealed that chemicals possessing minimal estrogenicity themselves could reduce (negatively modulate) the effect of a mixture of estrogenic chemicals. Whether the type of modulation we observed occurs in practice most likely depends on the chemical concentrations involved, and better information is required on likely human tissue concentrations of estrogens and of potential modulators. Successful prediction of the effects of diverse chemical combinations might be more likely if chemical profiling included consideration of effect modulation.

Susceptibility of estrogen receptor rapid responses to xenoestrogens: Physiological outcomes

17β-Estradiol (E2) binding induces rapid modification in the conformation of its cognate receptors (i.e., ERα and ERβ). These allosteric changes allow the association of ERs with cell specific transcriptional cofactors, thus determining cellular contexts specific variations in gene expression. In addition, E2-ER complexes could also interact with membrane and cytosolic signal molecules triggering extra-nuclear signalling pathways. The synergy between these mechanisms is necessary for E2-induced pleiotropic actions in target tissues. Besides E2, the ER ligand binding domains can accommodate many other natural and synthetic ligands. Several of these compounds act as agonist or antagonist of ER transcriptional activity due to their ability to modify the interactions between ERs and transcriptional co-regulators. However, the ability of natural or manmade ER ligands to affect the extra-nuclear interactions of the ERs has been rarely evaluated. Here, the ability of two diet-derived flavonoids (i.e., naringenin and quercetin) and of the synthetic food-contaminant bisphenol A to modulate specifically ER extra-nuclear signalling pathways will be reported. All the tested compounds bind to both ER subtypes even if lesser than E2 activating divergent signal transduction pathways. In fact, in the presence of ERα, both naringenin and quercetin decouple ERα activities by specifically interfering with ERα membrane initiating signals. On the other hand, bisphenol A, but not flavonoids, maintains ERβ at the membrane thus impairing the activation of the downstream kinases. As a whole, extra-nuclear ER signals are highly susceptible to different ligands that, by unbalancing E2-induced cell functions drive cells to different functional endpoints.

Influence of berry polyphenols on receptor signaling and cell-death pathways: implications for breast cancer prevention

Breast cancer is the most commonly diagnosed cancer among women worldwide. Many women have become more aware of the benefits of increasing fruit consumption, as part of a healthy lifestyle, for the prevention of cancer. The mechanisms by which fruits, including berries, prevent breast cancer can be partially explained by exploring their interactions with pathways known to influence cell proliferation and evasion of cell-death. Two receptor pathways, estrogen receptor (ER) and tyrosine kinase receptors, especially the epidermal growth factor receptor (EGFR) family, are drivers of cell proliferation and play a significant role in the development of both primary and recurrent breast cancer. There is strong evidence to show that several phytochemicals present in berries such as cyanidin, delphinidin, quercetin, kaempferol, ellagic acid, resveratrol, and pterostilbene interact with and alter the effects of these pathways. Furthermore, they also induce cell death (apoptosis and autophagy) via their influence on kinase signaling. This review summarizes in vitro data regarding the interaction of berry polyphenols with the specific receptors and the mechanisms by which they induce cell death. This paper also presents in vivo data of primary breast cancer prevention by individual compounds and whole berries. Finally, a possible role for berries and berry compounds in the prevention of breast cancer and a perspective on the areas that require further research are presented.

The pro-apoptotic effect of quercetin in cancer cell lines requires ERβ-dependent signals

Quercetin has potentially beneficial effects on disease prevention, including cancer. An intriguing issue regarding the mechanisms of action of quercetin is the ability of this drug to modulate estrogen receptor (ER) activities. In a previous study, we demonstrated that quercetin elicited apoptosis through an ERα-dependent mechanism. However, the contribution of ERβ in quercetin-induced apoptosis remains elusive. Here, we report that quercetin, at nutritionally relevant concentrations, mimicked the 17β-estradiol (E2)-induced apoptotic effect in both ERβ1-transfected HeLa and in ERβ1-containing DLD-1 colon cancer cell lines by inducing the activation of p38. p38 activation is responsible for pro-apoptotic activation of caspase-3 and the cleavage of poly(ADP-ribose) polymerase. Notably, no inactivation or downregulation of the survival kinases (i.e., AKT and ERK1/2) or the antiapoptotic protein Bcl-2 was observed after quercetin stimulation. On the contrary, quercetin acted similarly to E2 by increasing the levels of the oncosuppressor protein PTEN and by impeding ERβ-dependent cyclin D1 promoter activity, which subsequently resulted in the transcription of the estrogen-responsive element remaining unchanged. As a whole, these data indicate that quercetin mimics the E2 effects in the presence of ERβ1, thus maintaining its anti-carcinogenic potential. In addition, the quercetin pro-apoptotic action in the presence of ERα may render it as a dual-sided protective agent against E2-related cancer in the reduction of tumour growth in organs that express ERα and/or ERβ.

Hormesis, resveratrol and plant-derived polyphenols: some comments

Hormesis is a dose–response phenomenon, usually present in plants and animals, characterized by a low-dose stimulation and high-dose inhibition, often resulting in typical U-shaped or J-shaped curves. Hormesis has become an interesting model for toxicology and risk assessment, as it has been described for several nature-derived phytochemicals but also because this adaptive response to stressors might hide an underlying more general behaviour of cell towards low doses.

Aqueous leaf extracts display endocrine activities in vitro and disrupt sexual differentiation of male Xenopus laevis tadpoles in vivo

The occurrence of natural substances acting as endocrine disrupting compounds (EDC) in the environment is to date poorly understood. Therefore, (anti)androgenic and (anti)estrogenic activities of three different aqueous leaf extracts (beech, reed and oak) were analyzed in vitro using yeast androgen and estrogen screen. The most potent extract was selected for in vivo exposure of Xenopus laevis tadpoles to analyze the potential effects on development and reproductive biology of amphibians. Tadpoles were exposed from stage 48 to stage 66 (end of metamorphosis) to aqueous oak leaf extracts covering natural occurring environmental concentrations of dissolved organic carbon. Gene expression analyses of selected genes of the hypothalamus-pituitary-gonad and of the hypothalamus-pituitary-thyroid axis as well as histological investigation of gonads and thyroid glands were used to evaluate endocrine disrupting effects on the reproductive biology and development. Female tadpoles remained unaffected by the exposure whereas males showed severe significant histological alterations of testes at the two highest oak leaf extract concentrations demonstrated by the occurrence of lacunae and oogonia. In addition, a significant elevation of luteinizing hormone beta mRNA expression with increasing extract concentration in male tadpoles indicates an involvement of hypothalamus-pituitary-gonad axis mainly via antiandrogenic activity. These results suggest that antiandrogenic EDC of oak leaf extract are responsible for inducing the observed effects in male tadpoles. The present study demonstrates for the first time that in surface waters, natural occurring oak leaf compounds at environmentally relevant concentrations display antiandrogenic activities and have considerable effects on the endocrine system of anurans affecting sexual differentiation of male tadpoles.

Dietary quercetin exacerbates the development of estrogen-induced breast tumors in female ACI rats

Phytoestrogens are plant compounds that structurally mimic the endogenous estrogen 17beta-estradiol (E(2)). Despite intense investigation, the net effect of phytoestrogen exposure on the breast remains unclear. The objective of the current study was to examine the effects of quercetin on E(2)-induced breast cancer in vivo. Female ACI rats were given quercetin (2.5 g/kg food) for 8 months. Animals were monitored weekly for palpable tumors, and at the end of the experiment, rats were euthanized, breast tumor and different tissues excised so that they could be examined for histopathologic changes, estrogen metabolic activity and oxidant stress. Quercetin alone did not induce mammary tumors in female ACI rats. However, in rats implanted with E(2) pellets, co-exposure to quercetin did not protect rats from E(2)-induced breast tumor development with 100% of the animals developing breast tumors within 8 months of treatment. No changes in serum quercetin levels were observed in quercetin and quercetin+E(2)-treated groups at the end of the experiment. Tumor latency was significantly decreased among rats from the quercetin+E(2) group relative to those in the E(2) group. Catechol-O-methyltransferase (COMT) activity was significantly downregulated in quercetin-exposed mammary tissue. Analysis of 8-isoprostane F(2alpha) (8-iso-PGF(2alpha)) levels as a marker of oxidant stress showed that quercetin did not decrease E(2)-induced oxidant stress. These results indicate that quercetin (2.5 g/kg food) does not confer protection against breast cancer, does not inhibit E(2)-induced oxidant stress and may exacerbate breast carcinogenesis in E(2)-treated ACI rats. Inhibition of COMT activity by quercetin may expose breast cells chronically to E(2) and catechol estrogens. This would permit longer exposure times to the carcinogenic metabolites of E(2) and chronic exposure to oxidant stress as a result of metabolic redox cycling to estrogen metabolites, and thus quercetin may exacerbate E(2)-induced breast tumors in female ACI rats.

Functional genomics of endothelial cells treated with anti-angiogenic or angiopreventive drugs

Angiogenesis is a highly regulated physiological process that has been studied in considerable detail given its importance in several chronic pathologies. Many endogenous factors and hormones intervene in the regulation of angiogensis and classical as well as targeted drugs have been developed for its control. Angiogenesis inhibition has come off the bench and entered into clinical application for cancer therapy, particularly for metastatic disease. While the clinical benefit is currently in terms of months, preclinical data suggest that novel drugs and drug combinations could lead to substantial improvement. The many targets of endogenous angiogenesis inhibitors reflect the complexity of the process; in contrast, current clinical therapies mainly target the vascular endothelial growth factor system. Cancer chemopreventive compounds can retard tumor insurgence and delay or prevent metastasis and many of these molecules hinder angiogenesis, a mechanism that we termed angioprevention. Angiopreventive drugs appear to prevalently act through the inhibition of the pro-inflammatory and anti-apoptotic player NFkappaB, thus contrasting inflammation dependent angiogenesis. Relatively little is known concerning the effects of these angiogenesis inhibitors on gene expression of endothelial cells, the main target of many of these molecules. Here we provide an exhaustive list of anti-angiogenic molecules, and summarize their effects, where known, on the transcriptome and functional genomics of endothelial cells. The regulation of specific genes can be crucial to preventive or therapeutic intervention. Further, novel targets might help to circumvent resistance to anti-angiogenic therapy. The studies we review are relevant not only to cancer but also to other chronic degenerative diseases involving endothelial cells, such as cardiovascular disorders, diabetes, rheumatoid arthritis and retinopaties, as well as vessel aging.

The phytoestrogen quercetin impairs steroidogenesis and angiogenesis in swine granulosa cells in vitro

Experimental evidence documents that nutritional phytoestrogens may interact with reproductive functions but the exact mechanism of action is still controversial. Since quercetin is one of the main flavonoids in livestock nutrition, we evaluated its possible effects on cultured swine granulosa cell proliferation, steroidogenesis, and redox status. Moreover, since angiogenesis is essential for follicle development, the effect of the flavonoid on Vascular Endothelial Growth Factor output by granulosa cells was also taken into account. Our data evidence that quercetin does not affect granulosa cell growth while it inhibits progesterone production and modifies estradiol 17beta production in a dose-related manner. Additionally, the flavonoid interferes with the angiogenic process by inhibiting VEGF production as well as by altering redox status. Since steroidogenesis and angiogenesis are strictly involved in follicular development, these findings appear particularly relevant, pointing out a possible negative influence of quercetin on ovarian physiology. Therefore, the possible reproductive impact of the flavonoid should be carefully considered in animal nutrition.

Grape and wine polyphenols down-regulate the expression of signal transduction genes and inhibit the growth of estrogen receptor-negative MDA-MB231 tumors in nu/nu mouse xenografts

The antitumor properties of the Merlot grape (and Merlot wine) polyphenols were evaluated in relation to their ability to modulate gene expression in developing tumors using an athymic nude mouse model transplanted with the estrogen receptor-negative MDA-MB231 cells. Groups of mice were fed a modified AIN 93G diet (Research Diets Inc, New Brunswick, NJ) with the experimental groups receiving 100 mg/kg body weight equivalent of polyphenols by gavage 3 times per week. After 1 week of acclimation and another week of polyphenol supplementation, MDA-MB231 cells were transplanted and the growth patterns of the tumors monitored. After 33 days of tumor growth, the animals were euthanized, the tumors isolated, and gene expression profiles analyzed using signal transduction and cell cycle arrays. The development of tumors was almost totally arrested in grape polyphenol-treated mice. Total polyphenols isolated from the wine were more effective in reducing tumor growth as compared with a hydrophobic polyphenol fraction isolated from the wine, showing a 50% and 60% reduction in tumor growth on day 33, respectively. Analysis of gene expression showed that genes such as CDK2, FAS, LEF1, PRKCE, and PTGS2, belonging to the NFkappaB, phospholipase C, and calcium signaling pathways, were down-regulated in tumors that developed in grape polyphenol-treated mice. Several genes related to cell cycle regulation, such as CDK5RAP1, RBBP8, and SERTAD1, were up-regulated in these tumors. Changes in the expression of these genes were less pronounced in tumors of wine polyphenol-treated mice. The study highlights the potential influences of dietary polyphenolic components on gene expression in estrogen receptor-negative tumors and its relation to inhibition of tumor growth.

Phytoestrogen-mediated inhibition of proliferation of the human T47D breast cancer cells depends on the ERalpha/ERbeta ratio

This study investigates the importance of the intracellular ratio of the two estrogen receptors ERalpha and ERbeta for the ultimate potential of the phytoestrogens genistein and quercetin to stimulate or inhibit cancer cell proliferation. This is of importance because (i) ERbeta has been postulated to play a role in modulating ERalpha-mediated cell proliferation, (ii) genistein and quercetin may be agonists for both receptor types and (iii) the ratio of ERalpha to ERbeta is known to vary between tissues. Using human osteosarcoma (U2OS) ERalpha or ERbeta reporter cells it was shown that compared to estradiol (E2), genistein and quercetin have not only a relatively greater preference for ERbeta but also a higher maximal potential for activating ERbeta-mediated gene expression. Using the human T47D breast cancer cell line with tetracycline-dependent ERbeta expression (T47D-ERbeta), the effect of a varying intracellular ERalpha/ERbeta ratio on E2- or pythoestrogen-induced cell proliferation was characterised. E2-induced proliferation of cells in which ERbeta expression was inhibited was similar to that of the T47D wild type cells, whereas this E2-induced cell proliferation was no longer observed when ERbeta expression was increased. With increased expression of ERbeta the phytoestrogen-induced cell proliferation was also reduced. These results point at the importance of the cellular ERalpha/ERbeta ratio for the ultimate effect of (phyto)estrogens on cell proliferation.

Quercetin: potentials in the prevention and therapy of disease

PURPOSE OF REVIEW

Quercetin is discussed since several decades as a multipotent bioflavonoid with great potential for the prevention and treatment of disease. In the current review, we present the most recent findings on quercetin with regard to the pharmacology, the in-vitro and in-vivo effects in different cell systems and animal models, and the clinical effects in humans.

RECENT FINDINGS

Quercetin bioavailability has been underestimated in the past and can be improved by food matrix components or particular delivery forms. Among the biological effects of particular relevance, the antihypertensive effects of quercetin in humans and the improvement of endothelial function should be emphasized. Together with its antithrombotic and anti-inflammatory effects, the latter mainly mediated through the inhibition of cytokines and nitric oxide, quercetin is a candidate for preventing obesity-related diseases. Most exiting are the findings that quercetin enhances physical power by yet unclear mechanisms. The anti-infectious and immunomodulatory activities of quercetin might be related to this effect.

SUMMARY

Quercetin is a most promising compound for disease prevention and therapy; however, many of the effects still need confirmation by human intervention trials.

Phytoestrogens induce differential estrogen receptor beta-mediated responses in transfected MG-63 cells

Phytoestrogens may function as partial agonists or antagonists of estrogen in many tissues including bone. Five phytoestrogens, belonging to the isoflavones and the flavonoids groups, were assayed in the human MG-63 osteoblastic cell line for their ability to stimulate transcriptional activity of an estrogen-response element (ERE)-luciferase reporter gene via the estrogen receptor beta (ERbeta). Although MG-63 cells were shown to express endogenous estrogen receptors, estradiol (E2) did not affect transcriptional activity of an ERE reporter in these cells. However, E2 did activate the ERE-reporter significantly in MG-63 cells where ERbeta was overexpressed. The isoflavones, genistein and daidzein, caused a dose-dependent increase in the ERE-reporter activity in MG-63 cells overexpressing ERbeta. Among the flavonoids, kaempferol activated ERE-reporter activity, whereas puerarin inhibited ERE-reporter transcription in cells overexpressing ERbeta. Quercetin had no effect on ERE-reporter activity over a concentration range of 10(-10)-10(-6) mol/l. The ERE-reporter activity induced by daidzein, genistein, and kaempferol was blocked by both ICI 182780 and 4-hydroxytamoxifen and partly blocked by puerarin. Our results demonstrated that different phytoestrogens exhibited differential transcription activity of an ERE-reporter via ERbeta-mediated mechanisms in MG-63 cells.

Influence of cellular ERalpha/ERbeta ratio on the ERalpha-agonist induced proliferation of human T47D breast cancer cells

Breast cancer cells show overexpression of estrogen receptor (ER) alpha relative to ERbeta compared to normal breast tissues. This observation has lead to the hypothesis that ERbeta may modulate the proliferative effect of ERalpha. This study investigated how variable cellular expression ratios of the ERalpha and ERbeta modulate the effects on cell proliferation induced by ERalpha or ERbeta agonists, respectively. Using human osteosarcoma (U2OS) ERalpha or ERbeta reporter cells, propyl-pyrazole-triol (PPT) was shown to be a selective ERalpha and diarylpropionitrile (DPN) a preferential ERbeta modulator. The effects of these selective estrogen receptor modulators (SERMs) and of the model compound E2 on the proliferation of T47D human breast cancer cells with tetracycline-dependent expression of ERbeta (T47D-ERbeta) were characterized. E2-induced cell proliferation of cells in which ERbeta expression was inhibited was similar to that of the T47D wild-type cells, whereas this E2-induced cell proliferation was no longer observed when ERbeta expression in the T47D-ERbeta cells was increased. In the T47D-ERbeta cell line, DPN also appeared to be able to suppress cell proliferation when levels of ERbeta expression were high. In the T47D-ERbeta cell line, PPT was unable to suppress cell proliferation at all ratios of ERalpha/ERbeta expression, reflecting its ability to activate only ERalpha and not ERbeta. It is concluded that effects of estrogen-like compounds on cell proliferation are dependent on the actual ERalpha/ERbeta expression levels in these cells or tissues and the potential of the estrogen agonists to activate ERalpha and/or ERbeta.

Multitargeted cancer prevention by quercetin

Quercetin is an anti-oxidative flavonoid widely distributed in the plant kingdom. Phenolic hydroxyl groups at the B-ring and the 3-position are responsible for its free radical-scavenging activity. Quercetin is commonly present as a glycoside and is converted to glucuronide/sulfate conjugates during intestinal absorption and only conjugated metabolites are therefore found in circulating blood. Although metabolic conversion attenuates its biological effects, active aglycone may be generated from the glucuronide conjugates by enhanced beta-glucuronidase activity during inflammation. With respect to its relationship with molecular targets relevant to cancer prevention, quercetin aglycone has been shown to interact with some receptors, particularly an aryl hydrocarbon receptor, which is involved in the development of cancers induced by certain chemicals. Quercetin aglycone has also been shown to modulate several signal transduction pathways involving MEK/ERK and Nrf2/keap1, which are associated with the processes of inflammation and carcinogenesis. Rodent studies have demonstrated that dietary administration of this flavonol prevents chemically induced carcinogenesis, especially in the colon, whilst epidemiological studies have indicated that an intake of quercetin may be associated with the prevention of lung cancer. Dietary quercetin is, therefore, a promising agent for cancer prevention and further research is warranted.

Phytoestrogens and breast cancer prevention: possible mechanisms of action

OBJECTIVE

Phytoestrogens display an array of pharmacologic properties, and in recent years investigation of their potential as anticancer agents has increased dramatically. In this article we review the published literature related to phytoestrogens and breast cancer as well as suggest the possible mechanisms that may underlie the relationship between phytoestrogens and breast cancer.

DATA SOURCES

Electronic searches on phytoestrogens and breast cancer were performed on MEDLINE and EMBASE in June 2007. No date restriction was placed on the electronic search.

DATA EXTRACTION

We focused on experimental data from published studies that examined the characteristics of phytoestrogens using in vivo or in vitro models. We also include human intervention studies in this review.

DATA SYNTHESIS

We evaluated evidence regarding the possible mechanisms of phytoestrogen action. Discussions of these mechanisms were organized into those activities related to the estrogen receptor, cell growth and proliferation, tumor development, signaling pathways, and estrogen-metabolizing enzymes.

CONCLUSIONS

We suggest that despite numerous investigations, the mechanisms of phytoestrogen action in breast cancer have yet to be elucidated. It remains uncertain whether these plant compounds are chemoprotective or whether they may produce adverse outcomes related to breast carcinogenesis.

Dietary quercetin does not affect pituitary lutenizing hormone (LH) expression and has no uterotropic effects in ovariectomized Sprague–Dawley rats

INTRODUCTION

The aim of this study was to investigate the potency of LH suppression and the uterotrophic effects of quercetin, a flavonoid widely present in our diet which in vitro has been shown to posses estrogenic properties.

METHODS

Fifty-nine female Sprague-Dawley (SD) rats were ovariectomized (ovx) and fed with soy-free rodent chow with the addition of quercetin or estradiol-3 benzoate (E2B). Quercetin was added to the rodent chow at the dose of 200mg/kg (n=12) and 1000 mg/kg (n=11) which on average corresponded to 3.55 mg and 18.42 mg per animal per day, respectively, and E2B at the dose of 4.3mg/kg (n=12) or 17.3mg/kg (n=12) which corresponded to 0.07 mg and 0.20 mg per animal per day, respectively. The control group (n=12) received soy-free chow only. After three months of treatment, animals were sacrificed and using real time RT-PCR, pituitary LHbeta and uterine insulin like growth factor (IGF)-1, progesterone receptor (PR) and complement 3 protein (C3) mRNA levels were measured. Additionally, the in vitro binding capacity of quercetin with a porcine cytosolic ER preparation was evaluated.

RESULTS

In contrast to E2B, dietary quercetin did not decrease pituitary LH expression, had no effects on uterine weight and uterine expression of estrogen regulated genes. The binding capacity of quercetin with the ERs was also 35000-fold lower compared with 17beta-estradiol (E2).

CONCLUSION

Our study shows that quercetin does not show any estrogenic effects in the pituitary and the uterus of the ovx SD rats.

(Anti)estrogenic effects of phytochemicals on human primary mammary fibroblasts, MCF-7 cells and their co-culture

In the public opinion, phytochemicals (PCs) present in the human diet are often considered beneficial (e.g. by preventing breast cancer). Two possible mechanisms that could modulate tumor growth are via interaction with the estrogen receptor (ER) and inhibition of aromatase (CYP19). Multiple in vitro studies confirmed that these compounds act estrogenic, thus potentially induce tumor growth, as well as aromatase inhibitory, thus potentially reduce tumor growth. It is thought that in the in vivo situation breast epithelial (tumor) cells communicate with surrounding connective tissue by means of cytokines, prostaglandins and estradiol forming a complex feedback mechanism. Recently our laboratory developed an in vitro co-culture model of healthy mammary fibroblasts and MCF-7 cells that (at least partly) simulated this feedback mechanism (M. Heneweer et al., TAAP vol. 202(1): 50-58, 2005). In the present study biochanin A, chrysin, naringenin, apigenin, genistein and quercetin were studied for their estrogenic properties (cell proliferation, pS2 mRNA) and aromatase inhibition in MCF-7 breast tumor cells, healthy mammary fibroblasts and their co-culture. The proliferative potency of these compounds in the MCF-7 cells derived from their EC(50)s decreased in the following order: estadiol (4*10(-3) nM)>biochanin A (9 nM)>genistein (32 nM)>testosterone (46 nM)>naringenin (287 nM)>apigenin (440 nM)>chrysin (4 microM). The potency to inhibit aromatase derived from their IC(50)s decreased in the following order: chrysin (1.5 microM)>naringenin (2.2 microM)>genistein (3.6 microM)>apigenin (4.1 microM)>biochanin A (25 microM)>quercetin (30 microM). The results of these studies show that these PCs can induce cell proliferation or inhibit aromatase in the same concentration range (1-10 microM). Results from co-cultures did not elucidate the dominant effect of these compounds. MCF-7 cell proliferation occurs at concentrations that are not uncommon in blood of individuals using food supplements. Results also indicate that estrogenicity of these PCs is quantitatively more sensitive than aromatase inhibition. It is suggested that perhaps a more cautionary approach should be taken for these PCs before taken as food supplements.

Evaluation of estrogenic/antiestrogenic activity of Onobrychis ebenoides extract – Interaction with estrogen receptor subtypes ERα and ERβ

A protective effect of plant extract from Onobrychis ebenoides on ovariectomy-induced bone loss in rats has been shown. To investigate the molecular mechanisms that underly the beneficial effect of O. ebenoides (Onb) on bone loss, we studied its potential to activate ER subtypes (ERalpha and ERbeta) on transiently transfected HeLa cells with HO-hERalpha or pSG5-hERbeta and 3xERE-TATA-Luc expression vectors. Its impact to stimulate differentiation and mineralization of osteoblasts (KS483 cell line) by Alizarin Red-S staining was also examined. Furthermore we sought to induce for its potential the IGFBP3, a known estrogen-dependent marker in MCF7 breast cancer cells. 17beta-Estradiol and the pure antiestrogen ICI182780 were included to serve as control samples of the estrogenic and antiestrogenic activity respectively. Our data revealed: (1) Onb extract displayed a significant estrogenic activity on both ERalpha and ERbeta subtypes. (2) It exhibited direct action on osteoblasts by inducing mineralization. (3) It showed estrogenic activity in MCF7 cells. These findings suggest that the beneficial effect of Onb extract on bone loss is mediated through an estrogen-like action via activation of ERalpha-ERE and ERbeta-ERE pathways and via direct action on the mineralization process of osteoblasts.

Future of toxicology--low-dose toxicology and risk--benefit analysis

Toxicology historically has been directed at studying the mechanisms of adverse effects of isolated compounds on living organisms at high levels of exposure, forming the basis for risk and safety assessment. One way to refocus and mobilize new research funds would be to better match the priorities in regulatory issues and direct the research within the field of toxicology more to low-dose toxicology and risk--benefit analysis. Low-dose toxicology can only be developed when taking into account mechanistic insight and will require risk-benefit analysis and a definition of interactions between compounds at realistic doses of exposure, especially in the case of dietary constituents. This is because the biological effects at low levels of exposure not only may be adverse but also can be beneficial depending on the target organ, the actual end point studied, the receptors activated, and/or the gene expression, protein, and metabolite patterns affected. Toxicologists have the tools and knowledge to study mechanisms of biological effects of chemicals on living organisms, and they should redirect their focus from looking only at adverse effects at high levels of exposure to characterizing the complex biological effects, both adverse and beneficial, at low levels of exposure. This may even result in the notion that beneficial effects can be the result of reaction pathways that are generally considered adverse and vice versa. Low-dose toxicology not only will provide a significant research challenge for the years ahead but also should contribute to better methods for low-dose risk assessment for complex mixtures of chemical compounds. This refocusing from high- to low-dose effects turns the field from a science focusing on adverse effects into a science studying the biological effects of chemical compounds on living organisms, taking into account the realization that the ultimate biological effect of a chemical may vary with its dose, the end point or target organ considered, and/or the combined exposure with other chemicals. By defining the effects of chemicals on living organisms at physiologically relevant exposure levels, toxicologists may contribute not only to better risk and safety assessment but also to preventive medicine, generating knowledge on possible adverse and also beneficial effects of chemicals. In addition, it will result in an approach for food safety assessment more in line with that for drug safety assessment taking the risk-benefit balance into consideration.

Estrogenic potency of food-packaging-associated plasticizers and antioxidants as detected in ERalpha and ERbeta reporter gene cell lines

This study presents the estrogenic potency of 21 food-packaging-associated compounds determined for the first time, using two transfected U2-OS (human osteoblasts devoid of endogenous estrogen receptors) estrogen receptor (ER) alpha and beta cell lines. Six plasticizers and three antioxidants were slightly estrogenic in the ERalpha cells. The model compounds bisphenol A and nonylphenol, one plasticizer [tris(2-ethylhexyl)trimellitate (TEHTM)], and two antioxidants (propyl gallate and butylated hydroxyanisole) were estrogenic in both ERalpha and ERbeta cells. Compared to estradiol (E2), these compounds appeared to be relatively more estrogenic in the ERbeta cells than in the ERalpha cells. Three sorbitol-based plasticizers activated neither ERalpha nor ERbeta and may be good replacements of existing plasticizers. All responses were additive with the response of E2. This indicates that they may contribute to the total effects of the pool of estrogenic compounds humans are exposed to. The estrogenic potencies of these compounds, together with the suggested beneficial effect of ERbeta-mediated responses and adverse ERalpha-mediated effects, support the importance of detecting characteristics for ERalpha and ERbeta response separately in independent models, as done in the present study.

Quercetin reduces chromosome aberrations induced by atrazine in the Allium cepa test

Quercetin is a widely distributed plant flavonoid possessing a variety of chemical and biological activities, including chelation, free-radical scavenging, and antioxidant activity. Atrazine is a selective triazine herbicide that has been the subject of an international revision program for human and ecological health risks because of its persistence in the environment. In a previous study, we demonstrated that atrazine was clastogenic in the Allium cepa test. In this present study, we investigated whether quercetin affords protection from the chromosome breaks induced by atrazine. In a preliminary assay, 0.1-20 microg/ml quercetin produced no toxicity or clastogenic activity in the Allium cepa test. Subsequently, we evaluated the effects of 0.5 and 5 microg/ml quercetin on the clastogenicity of 2.5, 5.0, and 7.5 microg/l atrazine. Quercetin (0.5 microg/ml) significantly reduced the frequency of total aberrations induced by 7.5 microg/l atrazine, while both concentrations of quercetin significantly decreased the frequency of fragments induced by 7.5 microg/l atrazine. The results of this study indicate that plant flavonoids such as quercetin may protect against the genotoxic effects of atrazine. Efforts to understand the extent to which plant flavonoids influence the biological activities of genotoxicants and the mechanisms involved in the interactions could help to better discern the advantages and disadvantages of their use and to clarify their possible protective role against pollutants.

SIRT1 stimulation by polyphenols is affected by their stability and metabolism

Silent information regulator two ortholog 1 (SIRT1) is the human ortholog of the yeast sir2 protein; one of the most important regulators of lifespan extension by caloric restriction in several organisms. Dietary polyphenols, abundant in vegetables, fruits, cereals, wine and tea, were reported to stimulate the deacetylase activity of recombinant SIRT1 protein and could therefore be potential regulators of aging associated processes. However, inconsistent data between effects of polyphenols on the recombinant SIRT1 and on in vivo SIRT1, led us to investigate the influence of (1) stability of polyphenols under experimental conditions and (2) metabolism of polyphenols in human HT29 cells, on stimulation of SIRT1. With an improved SIRT1 deacetylation assay we found three new polyphenolic stimulators. Epigallocatechin galate (EGCg, 1.76-fold), epicatechin galate (ECg, 1.85-fold) and myricetin (3.19-fold) stimulated SIRT1 under stabilizing conditions, whereas without stabilization, these polyphenols strongly inhibited SIRT1, probably due to H2O2 formation. Using metabolically active HT29 cells we were able to show that quercetin (a stimulator of recombinant SIRT1) could not stimulate intracellular SIRT1. The major quercetin metabolite in humans, quercetin 3-O-glucuronide, slightly inhibited the recombinant SIRT1 activity which explains the lack of stimulatory action of quercetin in HT29 cells. This study shows that the stimulation of SIRT1 is strongly affected by polyphenol stability and metabolism, therefore extrapolation of in vitro SIRT1 stimulation results to physiological effects should be done with caution.

Consequences of quercetin methylation for its covalent glutathione and DNA adduct formation

This study investigates the pro-oxidant activity of 3'- and 4'-O-methylquercetin, two relevant phase II metabolites of quercetin without a functional catechol moiety, which is generally thought to be important for the pro-oxidant activity of quercetin. Oxidation of 3'- and 4'-O-methylquercetin with horseradish peroxidase in the presence of glutathione yielded two major metabolites for each compound, identified as the 6- and 8-glutathionyl conjugates of 3'- and 4'-O-methylquercetin. Thus, catechol-O-methylation of quercetin does not eliminate its pro-oxidant chemistry. Furthermore, the formation of these A-ring glutathione conjugates of 3'- and 4'-O-methylquercetin indicates that quercetin o-quinone may not be an intermediate in the formation of covalent quercetin adducts with glutathione, protein and/or DNA. In additional studies, it was demonstrated that covalent DNA adduct formation by a mixture of [4-(14)C]-3'- and 4'-O-methylquercetin in HepG2 cells amounted to only 42% of the level of covalent adducts formed by a similar amount of [4-(14)C]-quercetin. Altogether, these results reveal the effect of methylation of the catechol moiety of quercetin on its pro-oxidant behavior. Methylation of quercetin does not eliminate but considerably attenuates the cellular implications of the pro-oxidant activity of quercetin, which might add to the mechanisms underlying the apparent lack of in vivo carcinogenicity of this genotoxic compound. The paper also presents a new mechanism for the pro-oxidant chemistry of quercetin, eliminating the requirement for formation of an o-quinone, and explaining why methylation of the catechol moiety does not fully abolish formation of reactive DNA binding metabolites.