Inhibition of tumor promoter-induced hydrogen peroxide formation in vitro and in vivo by genistein

Effects of phytoestrogens genistein and daidzein on production of human chorionic gonadotropin in term trophoblast cells in vitro

BACKGROUND

Phytoestrogens are a diverse group of non-steroidal compounds that occur naturally in many plants. Because they possess a ring system similar to estrogens they are able to bind to estrogen receptors in humans. In the present study we tested the effects of the phytoestrogens genistein and daidzein on the production of human chorionic gondaotropin (hCG) in isolated trophoblast cells of term placentas in vitro.

METHODS

Genistein and daidzein were incubated at different concentrations with trophoblast cells. Untreated cells were used as controls. At designated times aliquots were removed and tested for hCG production.

RESULTS

Production of the protein hormone hCG was influenced by the phytoestrogens genistein and daidzein in trophoblast cells. We found a significant decrease of hCG production in genistein- and daidzein-treated trophoblast cells that was concentration-dependent. Compared with daidzein, genistein seems to be a more efficient inhibitor of the production of hCG.

CONCLUSION

The phytoestrogens genistein and daidzein can reduce hCG production in human term trophoblasts. Both phytoestrogens belong to the group of isoflavones, which are enriched in soy-containing foods and are widely consumed by humans for putative beneficial health effects. Because both phytoestrogens have inhibitory effects on hCG production during pregnancy, exposure to these estrogen-like compounds during sensitive periods of development may have the capacity to alter the function of the reproductive system and thereby influence fertility.

Glycoprotein Isolated fromSolanum nigrumL. Kills HT-29 Cells Through Apoptosis

Solanum nigrum L. (SNL) has been used in folk medicine for its anti-inflammatory activity. We previously isolated glycoprotein from SNL and observed that it decreased viable HT-29 cell numbers at a low concentration (60 microg/mL). This study investigated the apoptotic signal pathway triggered by glycoprotein isolated from SNL in HT-29 cells. Treatment of HT-29 cells with SNL glycoprotein (60 microg/mL) for 4 hours resulted in a cytotoxic effect of more than 60%, compared with the control. To explain the apoptotic effects of SNL glycoprotein, we investigated its effects on 12-O-tetradecanoylphorbol 13-acetate (TPA)-stimulated protein kinase C (PKC) alpha activity and DNA-binding activity of nuclear factor (NF) kappaB in HT-29 cells, using western blot analysis and electrophoretic mobility shift assays. Results from these experiments showed that SNL glycoprotein has remarkable inhibitory effects on the activities of TPA (100 nM)-stimulated PKCalpha and NF-kappaB in HT-29 cells. They also substantiated that PKCalpha is a part of the TPA-activated upstream signal pathway of NF-kappaB, since NF-kappaB activity was inhibited by staurosporine (a PKC inhibitor) and pyrrolidine dithiocarbamate (an NF-kappaB inhibitor) in a western blot analysis. Furthermore, to verify the triggering of apoptosis by the SNL glycoprotein, we performed DNA fragmentation, nuclear staining, and protein expression assays of apoptotic-related proteins. The amount of DNA fragmentation and apoptotic cell numbers increased in a dose-dependent manner after treatment with SNL glycoprotein. Apoptosis-related protein assays demonstrated that SNL glycoprotein-induced apoptosis is associated with the regulation of bcl-2 and Bax expression. Taken together, the results of this study showed that the activation of PKCalpha, NF-kappaB, and Bax expression by SNL glycoprotein is possibly involved in the apoptotic process. Consequently, these results indicate that SNL glycoprotein causes HT-29 cell death through apoptosis by its ability to modulate anti-apoptotic signals. We suggest that SNL glycoprotein is a natural anti-cancer agent due to its potential to induce apoptosis in HT-29 cells.

Comparison between daidzein and genistein antioxidant activity in primary and cancer lymphocytes

The main objective of this study was to compare the protective effect of daidzein and genistein against induced oxidative damage in Jurkat T-cell line and in peripheral blood lymphocytes of healthy subjects. After supplementation of cells with isoflavones (from 2.5 to 20micromol/L in Jurkat T-cell and from 0.01 to 2.5micromol/L in primary lymphocytes, 24h), we determined DNA damage induced by hydrogen peroxide using the comet assay and lipid peroxidation evaluating malondialdehyde (MDA) production after ferrous ion treatment. Supplementation of Jurkat cells and primary lymphocytes with both isoflavones significantly increased DNA protection from oxidative damage at concentrations between 0.1 and 5micromol/L (P<0.05), and with just daidzein, at concentrations higher than 2.5micromol/L, there was a decrease in the production of MDA (P<0.05). Our results seem to support that daidzein is just as effective as genistein in protecting cells against oxidative damage especially with respect to DNA. Moreover, since the protective effect was found at concentrations reachable in plasma after soy consumption (less than 2micromol/L), it can be assumed that the antioxidant activity of isoflavones could really contribute to the healthy properties of soy.

Modulatory effect of gentisic acid on the augmentation of biochemical events of tumor promotion stage by benzoyl peroxide and ultraviolet radiation in Swiss albino mice

The present study was carried out to study the effect of gentisic acid (2,5-dihydroxybenzoic acid (2,5-DHBA)) on the tumor promotion related events of carcinogenesis in murine skin. Benzoyl peroxide (BPO) (20 mg/0.2 ml/animal) and ultraviolet radiations (UVR) (0.420 J/m2/s) were used to induce tumor promotion response and oxidative stress and caused significant depletion in the detoxification and antioxidant enzyme armory with concomitant elevation in malondialdehyde (MDA) formation, hydrogen peroxide (H2O2) generation, ornithine decarboxylase (ODC) activity and unscheduled DNA synthesis. However, gentisic acid pretreatment at two different doses restored the levels of the above said parameters (P < 0.05) in a dose-dependent manner except in the case of ODC activity. Therefore, we propose that it might suppress the promotion stage via inhibition of oxidative stress but may not affect the polyamine biosynthetic pathway.

The soy isoflavone, genistein, protects human cortical neuronal cells from oxidative stress

Genistein, a soy isoflavone, has been shown to mimic the pharmacological actions of the endogenous steroid estrogen with which it has structural similarities. There is now evidence that the genistein can prevent disorders-like heart diseases, cancer and diabetes as well. However, very few studies have looked at the effect of genistein on the central nervous system. Published studies also show conflicting conclusions regarding the effects of genistein in the brain. The current study was conducted in the human cortical cell lines HCN1-A and HCN2 in order to determine the neuroprotective efficacy of genistein. It was observed that pre-treatment with 50 or 10 microM genistein was able to protect HCN1-A and HCN2 cells from the cell death induced by 100 microM or 1 mM tertiary butylhydroperoxide (t-BuOOH; a free radical generating toxin). The morphological disruption caused by t-BuOOH was also prevented by genistein in HCN2 cells. Moreover, genistein was able to prevent the down-regulation of the anti-apoptotic protein bcl-2 that was caused by t-BuOOH treatment. These results indicate that genistein may have neuroprotective effect in cortical cells, which may be mediated by its regulation of the anti-apoptotic protein bcl-2.

Biphasic effect of daidzein on cell growth of human colon cancer cells

Colorectal cancer is one of the most common cancers in the world, poorly responding to available chemotherapeutic agents. To investigate whether natural molecules can inhibit colon cancer progression, we investigated a principle phytoestrogen found in soybean known as daidzein, and determined its effects on the human colon cancer cell line LoVo. LoVo cells were treated with 0.1, 1, 5, 10, 50 and 100 microM daidzein for 2, 3, 4 or 5 d. The results indicated that daidzein stimulated the growth of LoVo cells at 0.1 and 1 microM whereas at higher concentrations (10, 50 and 100 microM) cell growth was inhibited in a dose-dependent manner. Treatment of daidzein at 10, 50 and 100 microM resulted in cell cycle arrest at G0/G1 phase, DNA fragmentation and increases in caspase-3 activity. There were no changes in alkaline phosphatase activity (ALP), an indicator of cell differentiation, upon treatment with daidzein when compared to controls. These results indicate that daidzein has a biphasic effect on LoVo cell growth and its tumor suppressive effect is by means of cell cycle arrest and apoptosis but not through cell differentiation.

Phyto-oestrogens, their mechanism of action: current evidence for a role in breast and prostate cancer

The incidence of hormone-dependent cancers, such as those of the breast and prostate, is much lower in Eastern countries such as China and Japan in comparison with the Western world. Diet is believed to have a major effect on disease risk and one group of compounds, the phyto-oestrogens, which are consumed in large amounts in Asian populations, have been implicated in cancer protection. This view follows the finding that plasma and urinary levels of phyto-oestrogens are much higher in areas where cancer incidence is low in comparison with areas of high cancer incidence. The phyto-oestrogens are comprised of two main groups; the isoflavones and lignans. Of the isoflavones, genistein and daidzein have been the most widely studied. These compounds have been shown to possess anticancer properties; however their precise mechanism of action remains to be elucidated. In comparison, few studies have investigated the effects of lignans in breast and prostate cancer. In vitro studies have shown that genistein exerts biphasic effects on cancer cell growth, stimulating growth at low concentrations (<10 microm) and inhibiting growth at high concentrations (>10 microm), which suggests that low phyto-oestrogen levels may stimulate cancer growth in vivo. Plasma phyto-oestrogen concentrations of >10 microm cannot be achieved by dietary intake and therefore the timing of exposure to phyto-oestrogens may be of the utmost importance in determining their chemopreventive effects. The present paper reviews the effects of phyto-oestrogens on breast and prostate cancer in vivo and in vitro and discusses possible mechanisms of action via which these compounds may exert their effects.

Effects of daidzein on estrogen-receptor-positive and negative pancreatic cancer cells in vitro

AIM: To study the effects of daidzein on human pancreatic cancer cells in vitro.

METHODS: Human estrogen-receptor (ER)-positive pancreatic cancer cells MiaPaCa-2 and ER-negative pancreatic cancer cells PANC-1 were treated by 0.1 μmol/L, 1 μmol/L, 10 μmol/L, 25 μmol/L, 50 μmol/L, 75 μmol/L and 100 μmol/L of daidzein, respectively. Its antiproliferative effect was studied by MTT assay.

RESULTS: Daidzein inhibited the growth of MiaPaCa-2 and PANC-1 cells at the concentrations from 0.1 μmol/L to 100 μmol/L. A dose- and time-dependent manner was found. The IC₅₀ of daidzein on MiaPaCa-2 and PANC-1 cells was 45 μmol/L and 75 μmol/L, respectively. After MiaPaCa-2 cells were treated by daidzein for 3 d and at the concentrations more than IC₅₀, the inhibitory manner was identical and the inhibition appeared a saturation phenomenon, but the inhibitory manner of daidzein on PANC-1 cells was different from that of MiaPaCa-2 cells.

CONCLUSION: Daidzein has antiproliferative effects on human estrogen-receptor-positive and negative pancreatic cancer cells, but their mechanisms may be different.

The selective effect of genistein on the toxicity of bleomycin in normal lymphocytes and HL-60 cells

This study was carried out to find whether genistein might enhance bleomycin induced cytotoxicity in human leukemia (HL-60) while protecting normal blood lymphocytes. Despite the excellent chemotherapeutic effect of bleomycin, its cytotoxicity and genotoxicity in normal cells remains a major problem in chemotherapy. Genistein, one of the major Soy isoflavones, is particularly effective in quenching free radicals generated by toxic agents. In this study, the protective and enhancement effects of genistein on bleomycin induced cytotoxicity in HL-60 cells and blood lymphocytes were demonstrated. HL-60 cells were treated with various concentrations of genistein for 3 h followed by treatment with various concentrations of bleomycin during the G1 phase. Pretreatment of genistein increased micronuclei (MN) frequency and DNA damage as a result of bleomycin treatment. However, when human lymphocytes were pretreated with genistein prior to bleomycin treatment during the G2 or G0 phase, the frequencies of bleomycin induced MN was decreased. Although the extent of bleomycin induced DNA damage determined by single cell gel electrophoresis was increased through the pretreatment of genistein in HL-60 cells, it was decreased in normal lymphocytes. The result of this study may therefore provide great impact on the potential activity of genistein as a therapeutic agent.

Dietary constituents as novel therapies for pain

The use of complementary and alternative medicine has dramatically increased in the United States. The effects of select dietary constituents in animal models and clinical pain states are reviewed. Specifically, the antinociceptive and analgesic properties of soybeans, sucrose, and tart cherries are discussed. The potential actions of dietary constituents as antiinflammatory and antioxidant agents are presented.

Soy isoflavones and cancer prevention

Epidemiological studies have shown a significant difference in cancer incidence among different ethnic groups, which is believed to be partly attributed to dietary habits. The incidences of breast and prostate cancers are much higher in the United States and European countries compared with Asian countries such as Japan and China. One of the major differences in diet between these populations is that the Japanese and the Chinese consume a traditional diet high in soy products. Soy isoflavones have been identified as dietary components having an important role in reducing the incidence of breast and prostate cancers. Genistein, the predominant isoflavones found in soy, has been shown to inhibit the carcinogenesis in animal models. There are growing body of experimental evidence that show the inhibition of human cancer cells by genistein through the modulation of genes that are related to the control of cell cycle and apoptosis. Moreover, it has been shown that genistein inhibits the activation of NF-kappa B and Akt signaling pathways, both of which are known to maintain a homeostatic balance between cell survival and apoptosis. Genistein is commonly known as phytoestrogen, which targets estrogen- and androgen-mediated signaling pathways in the processes of carcinogenesis. Furthermore, genistein has been found to have antioxidant property, and shown to be a potent inhibitor of angiogenesis and metastasis. Taken together, both in vivo and in vitro studies have clearly shown that genistein, one of the major soy isoflavones, is a promising reagent for cancer chemoprevention and/or treatment. In this article, we attempt to provide evidence for these effects of genistein in a succinct manner to provide comprehensive state-of-the-art knowledge of the biological and molecular effects of the isoflavone genistein in cancer cells.

Antioxidant activity of a Schiff base of pyridoxal and aminoguanidine

We recently reported that PL-AG, a Schiff base of pyridoxal and aminoguanidine, was more effective than aminoguanidine (AG), a well-known anti-diabetic-complication compound, in preventing nephropathy in diabetic mice and presented brief data indicating the antioxidant activity of the adduct. In the present study, we additionally investigated the inhibitory activity of PL-AG in comparison with that of AG against in vitro and in vivo oxidation. PL-AG was more potent than AG and reference compounds such as pyridoxal and pyridoxamine in any of the five antioxidant activities examined in vitro, i.e., hydrogen peroxide-scavenging, hydroxyl radical-scavenging, superoxide radical-scavenging, ascorbic acid-autoxidation inhibitory, and low-density lipoprotein (LDL)-oxidation inhibitory activities, the last two of which were assessed in the presence of Cu(2+). Unlike AG, PL-AG did not show the pro-oxidant activity. The inhibitory activity of PL-AG against lipid peroxidation in diabetic rats was higher than that of AG, for example, the amounts of malondialdehyde in erythrocytes (nmol/g hemoglobin; mean +/- SD) in normal, untreated diabetic, AG-treated diabetic, and PL-AG-treated diabetic rats were 3.53 +/- 0.35, 4.99 +/- 0.23, 4.65 +/- 0.45, and 4.06 +/- 0.35, respectively. A fluorescent substance different from PL-AG was found in the plasma and urine of rats treated with PL-AG. The chemical structure of this substance, i.e., oxidized PL-AG, was determined by a combination of nuclear magnetic resonance, mass, and infrared spectrometry. AG dramatically decreased the pyridoxal phosphate level in the diabetic rat liver, whereas PL-AG only moderately affected it. Our results indicate that the antioxidant activity of PL-AG is due to its chelation with transition metal ions and to scavenging of reactive oxygen species. They also suggest that PL-AG is more promising for the treatment of diabetic complications than AG.

Metabolism of the soy isoflavones daidzein, genistein and glycitein in human subjects. Identification of new metabolites having an intact isoflavonoid skeleton

Epidemiological studies have associated high soy intake with a lowered risk for certain hormone-dependent diseases. Soy and soy foods are rich sources of isoflavones, which have been shown to possess several biological activities. In this study, the metabolism of soy isoflavones daidzein, genistein and glycitein was investigated in human subjects. The aim was to find and identify urinary phase I metabolites of isoflavones, which have an intact isoflavonoid skeleton, and which might possess some bioactivity. Six volunteers included three soy bars per day into their normal western diet for a 2-week period. Daily urine samples were collected before, and after the supplementation period. Urine samples were hydrolyzed with Helix pomatia, extracted with diethyl ether, purified with Sephadex LH-20 chromatography, and analyzed as trimethylsilyl derivatives using gas chromatography-mass spectrometry (GC-MS). The structures of the isoflavone metabolites were identified using authentic reference compounds. The metabolites, for which authentic reference compounds were not available, were identified by the interpretation of mass spectra. Several new isoflavone metabolites were identified, and the presence of previously reported metabolites confirmed. The metabolic pathways of daidzein, genistein and glycitein are presented on the basis of the identification of the metabolites in human urine after soy supplementation.

Isoflavone genistein: photoprotection and clinical implications in dermatology

Genistein is a soybean isoflavone with diverse biological activities. It is a potent antioxidant, a specific inhibitor of protein tyrosine kinase, and a phytoestrogen. In recent years, increasing evidence has accumulated that this natural ingredient shows preventative and therapeutic effects for breast and prostate cancers, postmenopausal syndrome, osteoporosis, and cardiovascular diseases in animals and humans. In the past decade we have conducted a series of studies and demonstrated that genistein has significant antiphotocarcinogenic and antiphotoaging effects. Genistein substantially inhibits skin carcinogenesis and cutaneous aging induced by ultraviolet (UV) light in mice, and photodamage in humans. The mechanisms of action involve protection of oxidative and photodynamically damaged DNA, downregulation of UVB-activated signal transduction cascades, and antioxidant activities. In this article, we review the biological activities of genistein, as well as published and unpublished research from our laboratory. In addition, we discuss the potential application of genistein to clinical dermatology.

[Medical value of isoflavones]

Isoflavones as a kind of phytoestrogen exist in soy plant widely. With the advantages of estrogen, they can regulate endocrine function of the human body, reduce blood cholesterol, decrease the incidence of coronary heart disease, prevent osteoporosis, inhibit tumor growth, and relieve pain. This article summarized the investigations on the medical value of isoflavones in recent years.

Inhibition of the proteasome activity, a novel mechanism associated with the tumor cell apoptosis-inducing ability of genistein

Epidemiological studies have suggested that increased soy consumption is associated with reduced cancer occurrence. Genistein, a soy isoflavone, has been reported to inhibit the growth of human tumor cells although the involved molecular mechanisms are not clearly defined. Here we report that genistein inhibits the proteasomal chymotrypsin-like activity in vitro and in vivo. Computational docking studies suggest that the interaction of genistein with the proteasomal beta 5 subunit is responsible for inhibition of the chymotrypsin-like activity. Inhibition of the proteasome by genistein in prostate cancer LNCaP and breast cancer MCF-7 cells is associated with accumulation of ubiquitinated proteins and three known proteasome target proteins, the cyclin-dependent kinase inhibitor p27(Kip1), inhibitor of nuclear factor-kappa B (I kappa B-alpha), and the pro-apoptotic protein Bax. Genistein-mediated proteasome inhibition was accompanied by induction of apoptosis in these solid tumor cells. Finally, genistein induced proteasome inhibition and apoptosis selectively in simian virus 40-transformed human fibroblasts, but not in their parental normal counterpart. Our results suggest that the proteasome is a potential target of genistein in human tumor cells and that inhibition of the proteasome activity by genistein might contribute to its cancer-preventive properties.

Antioxidant activities of chitobiose and chitotriose

Chitooligosaccharides, the oligomers made up of beta-1,4-linked D-glucosamine, are obtained by partial hydrolysis of chitosan, a deacetylation product of chitin. The antioxidant activity of various chitooligosaccharides was tested in vitro with aminoguanidine, pyridoxamine, and Trolox as reference compounds. Hydroxylation of benzoate to salicylate by H2O2 in the presence of Cu(2+) was effectively inhibited by chitobiose, chitotriose, aminoguanidine, pyridoxamine, and Trolox (their IC(50) values=18, 80, 85, 10, and 95 microM, respectively), whereas glucosamine and N-acetylchito-oligosaccharides (di-N-acetylchitobiose and tri-N-acetylchitotriose) did not show any inhibitory activity. Chitobiose and chitotriose were more potent than the 3 reference compounds in scavenging hydroxyl radicals produced by photolysis of zinc oxide: IC(50) values of the 2 oligomers were 30 and 55 microM, respectively. Such a scavenging activity of these 2 chitooligomers was also shown by the use of another system, a mixture of Fe(3+)/EDTA/ascorbate/H2O2, for producing hydroxyl radicals. Only chitobiose and Trolox, of the 10 compounds tested, had the ability to scavenge superoxide radicals generated by a non-enzymatic system using phenazine methosulfate and NADH. Taken together with our unpublished observation that chitobiose and chitotriose are appreciably absorbed from the intestine of rats, the present results suggest that these 2 chitooligosaccharides would act as effective antioxidants in vivo when orally ingested.

Inactivation of NF-kappaB by genistein is mediated via Akt signaling pathway in breast cancer cells

Genistein, a natural isoflavonoid found in soybean products, has been proposed to be associated with a lower rate of breast cancer in Asian women. Studies from our laboratory and others have shown that genistein can induce apoptosis by regulating the expression of apoptosis-related genes in breast cancer cells. However, the precise molecular mechanism(s) by which genistein induces apoptotic cell death is not clear. In order to investigate such mechanism, we tested the role of Akt and NF-kappaB in genistein-treated MDA-MB-231 breast cancer cells. We found that inhibition of cell growth and induction of apoptosis by genistein are partly mediated through the downregulation of Akt and NF-kappaB pathways. Gel shift assay showed that NF-kappaB DNA-binding activity in MDA-MB-231 cells transfected with Akt cDNA was induced, suggesting that there is a cross-talk between NF-kappaB and Akt signaling pathway. Moreover, we found that genistein could abrogate EGF and Akt induced NF-kappaB activation. From these results, we conclude that the inactivation of NF-kappaB by genistein in MDA-MB-231 breast cancer cells is partly mediated via Akt pathway, which could be useful for rational design of strategies for the prevention and/or treatment of breast cancer.

Photochemoprevention of skin cancer by botanical agents

Photochemoprevention has become an important armamentarium in the fight against ultraviolet radiation (UVR)-induced damage to the skin. Among many UVR-induced damages, skin cancer is of the greatest concern as its rates have been steadily increasing in recent years and the same trend is expected to continue in the future. Ultra-violet radiation increases oxidative stress in skin cells by causing excessive generation of reactive oxygen species (ROS), leading to cancer initiation and promotion. Antioxidants have the capability to quench these ROS and much recent work shows that some of these can inhibit many UVR-induced signal transduction pathways. Thus, identifying nontoxic strong antioxidants--capable of preventing UVR-induced skin cancer--has become an important area of research. The use of botanical antioxidants in skin care products is growing in popularity. A wide range of such agents has been shown to prevent skin cancer in animal model systems. New agents are constantly being investigated; however, only a few have been tested for their efficacy in humans. Animal model and cell culture studies have clarified that antioxidants act by several mechanisms at various stages of skin carcinogenesis. This review focuses on skin cancer photochemopreventive effects of selected botanical antioxidants.

Dietary compounds in relation to dietary diversity and human health

The human diet contains numerous endocrine-active compounds that influence mammalian physiology. The effects of these dietary compounds may be mediated by interaction with well-characterized intracellular hormone receptors or by other effects on patterns of endogenous hormone production, metabolism, target tissue signaling, growth, or differentiation. Because humans evolved as omnivores, the spectrum of dietary compounds that can be tolerated at modest levels of intake without frank toxicity is broad. Modest intake of these diverse nonnutritive endocrine-active compounds offers potential human health benefits through modulation of metabolic and hormonal responses, especially in sedentary individuals consuming a highly refined diet.

Effects of soy isoflavones on apoptosis induction and G2-M arrest in human hepatoma cells involvement of caspase-3 activation, Bcl-2 and Bcl-XL downregulation, and Cdc2 kinase activity

Genistein, biochanin-A, and daidzein, the predominant soy isoflavones, have been reported to lower the risk of cancer, but it is not known whether they protect against human hepatoma cancer. This study was designed to investigate their effects on cell growth, the cell cycle, and apoptosis induction in the human hepatoma cell lines, HepG2, Hep3B, Huh7, PLC, and HA22T. Genistein, biochanin-A, and daidzein inhibited growth of all five lines in a dose-dependent manner. DNA fragmentation studies and the TUNEL assay demonstrated that isoflavones caused tumor cell death by induction of apoptosis. Activation of caspase-3 and cleavage of the caspase-3 substrate, poly(ADP-ribose)polymerase, was seen in hepatoma cells after 24 hours' exposure to isoflavones. In addition, isoflavone cytotoxicity correlated with downregulation of Bcl-2 and Bcl-XL expression. Synergistic effects of the three isoflavones were observed on cell growth inhibition, apoptosis induction, and anti-apoptotic protein expression. Flow cytometry showed that genistein, but not biochanin-A or daidzein, induced progressive and sustained accumulation of hepatoma cancer cells in the G2/M phase as a result of inhibition of Cdc2 kinase activity. Coapplication of caffeine prevented this cell cycle arrest, but not apoptosis, showing that cell cycle arrest was not necessary for apoptosis. Furthermore, the isoflavones combination also had a significant tumor-suppressive effect in nude mice. These results suggest that isoflavones might be promising agents for the treatment of human hepatoma.

Inhibition of ultraviolet light-induced oxidative events in the skin and internal organs of hairless mice by isoflavone genistein

We have previously demonstrated that soybean isoflavone genistein inhibits ultraviolet-B (UVB)-induced skin tumorigenesis in hairless mice. In the present study, we further investigated the possible mechanism(s) of action whereby genistein inhibits photocarcinogenesis with focuses on UVB-induced oxidative events, including hydrogen peroxide (H(2)O(2)) production, lipid peroxidation (as represented by malondialdehyde, MDA), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in vivo. We demonstrated that subacute exposure to UVB substantially increased the level of H(2)O(2), lipid peroxides, and 8-OHdG in skin of hairless mice. In addition, chronic exposure to low-dose UVB (0.9-1.2 kJ/m(2) for 20 weeks) substantially increased the levels of 8-OHdG not only in the epidermis, but also in the internal organs such as liver, brain, and spleen of mice with exception of kidney. However, genistein did not affect the level of UVB-induced pyrimidine dimmers in the same UVB exposed mouse skin, indicating selective inhibition of oxidative DNA damage by genistein. Induction of H(2)O(2) was independent of UVB fluences whereas the levels of MDA and 8-OHdG were induced in an UVB fluence-dependent manner. The results suggest that H(2)O(2) be generated as an acute cutaneous response to UVB irradiation, while MDA and 8-OHdG are accumulated with increasing UVB exposure and more closely related to chronic effects of UVB radiation. Pre-treatment of animals with 10 micromol of genistein 1 h prior to UVB exposure significantly inhibited UVB-induced H(2)O(2) and MDA in skin and 8-OHdG in epidermis as well as internal organs. Suppression of 8-OHdG formation by genistein has been corroborated in purified DNA irradiated with UVA and B. In summary, our results suggest that UVB irradiation elicit a series of oxidative events, which can be substantially inhibited by isoflavonoid genistein through either direct quenching of reactive oxygen species or indirect antiinflammatory effects. Thus, the antioxidative properties of genistein may explain for the mechanisms of anti-photocarcinogenic action of genistein.

The mutant androgen receptor T877A mediates the proliferative but not the cytotoxic dose-dependent effects of genistein and quercetin on human LNCaP prostate cancer cells

High consumption of soybean products, such as phytoestrogens, has been hypothesized to contribute to a reduced incidence of prostate cancer in Southeast Asian people, although there have been inconsistent results among studies. Human LNCaP cells, extensively used as a model for androgen-dependent prostate tumor, express the androgen receptor (AR) mutant T877A promiscuously transactivated by estrogens and other ligands, which may further facilitate cancer progression. Here, for the first time to our knowledge, we demonstrate that genistein and quercetin, two phytoestrogens abundantly present in soybeans, activate either the AR mutant T877A in LNCaP or in transfected Chinese hamster ovary cells. This observation is supported by their capability to induce AR accumulation in the nuclear compartment of LNCaP together with mRNA down-regulation of the androgen target genes AR and PAP, and PSA up-regulation. Of interest, at concentrations eliciting transcriptional activity, both genistein and quercetin stimulate LNCaP cell growth, whereas at high levels, they become cytotoxic independently of AR expression, as ascertained in steroid receptor-negative Hela cells. The results of our study provide evidence that phytoestrogens may regulate several signaling processes in LNCaP cells; however, further studies are needed to assess their potential capability to restrain prostate tumor progression.

Estrogenic and antiproliferative activities of isoliquiritigenin in MCF7 breast cancer cells

Licorice root contains chemically diverse compounds that exhibit estrogenic effects in vitro and in vivo. The chalcone isoliquiritigenin (ISL) is a component of licorice extract exhibiting either antitumorigenic activity or estrogen receptor (ER) alpha-dependent growth promoting effects on breast cancer cells. In order to contribute to a better understanding of this apparent paradox, we synthesized and ascertained the estrogenic properties of ISL using, as model systems, the hormone-sensitive MCF7 breast cancer cells and the steroid-independent HeLa cells. Transfection experiments reveal that ISL is able to transactivate the endogenous ER alpha in MCF7 cells and this is supported by the capability to induce down-regulation of ER alpha protein levels and up-regulation of pS2 mRNA. Moreover, by using chimeric proteins consisting of the hormone binding domains of ER alpha and ER beta fused to the Gal4 DNA binding domain, we have determined that ISL is an estrogenic agonist of both ER isoforms. As a biological counterpart, low and intermediate ISL concentrations that induce substantial transcriptional activity stimulate the proliferation of MCF7 cells. However, high levels of ISL become cytotoxic even in steroid-receptor negative HeLa cells. Thus, the activity of ISL and the balance between risk or chemopreventive factor for estrogen-dependent breast cancer may depend on dietary intake.

Different action of IBMX, isoproterenol and rutin on orthovanadate-induced nitric oxide release in mouse macrophage cells

The effects of cAMP-elevating compounds IBMX (3-isobutyl-1-methylxanthine) and isoproterenol, and that of rutin (an effective superoxide scavenger) were studied on orthovanadate--(a putative protein-phosphotyrosine phosphatase inhibitor) induced nitric oxide (NO) production in J774A.1 mouse macrophage cells. As we previously reported (Koncz and Horváth, 2000), rutin and sodium orthovanadate act synergistically to induce production of high amount of NO in J774A.1 cells. IBMX, an agent that can elevate cAMP level in the cells, can reduce the production of both the LPS- and rutin + orthovanadate-induced NO in macrophages. In contrast, isoproterenol, a non-selective beta-adrenergic receptor agonist, that reduced the LPS-induced NO production in macrophage cells, was unable to reduce the rutin + orthovanadate-induced NO production without negatively affecting cell viability. Moreover, isoproterenol dramatically enhanced the orthovanadate-induced NO synthesis in J774A.1 cells. Our previous study clarified that rutin and orthovanadate, in a specific concentration ratio of both, were able to produce hydrogen peroxide (H2O2). Using 2',7'-dichlorofluorescein-diacetate as a marker for H2O2, isoproterenol alone induced its oxidation but the rutin plus orthovanadate-induced H2O2 production was reduced by isoproterenol. These observations have revealed that, in some cases, H2O2 and superoxide (O2-) scavengers can act in a reverse mode on macrophage cells depending on the presence or absence of orthovanadate.

ESR and cell culture studies on free radical-scavenging and antioxidant activities of isoflavonoids

Isoflavonoids are thought to be the biologically active components in soy that play a role in the prevention of coronary heart disease and breast and prostate cancer. Mechanisms to explain how isoflavonoids mediate beneficial effects have not yet been clearly established. This study was undertaken to investigate the free radical-scavenging and antioxidant activities of various structure-related isoflavonoids including genistein, daidzein, biochanin A, and genistin in a cell-free and an endothelial cell model system. Electron spin resonance spectroscopy and spin trapping techniques were applied to evaluate the ability of isoflavonoids to scavenge hydroxyl, superoxide, nitric oxide, diphenylpicrylhydrazyl, galvinoxyl, and lipid-derived radicals. All isoflavonoids tested had no significant scavenging effects on the aforementioned radicals in concentrations up to 1.0 mM. However, at a physiologically achievable concentration of 5 nM, both genistein and daidzein slightly increased intracellular-reduced glutathione levels approximately by 10 and 30%, respectively, in human endothelial cells, whereas cellular alpha-tocopherol and uric acid remained unchanged by the isoflavonoid treatments. Present data indicate that free radical-scavenging activities of the isoflavonoids tested probably do not substantially contribute to their antioxidant properties. The ability of genistein and daidzein to increase cellular GSH (reduced glutathione) might be important for their action in biological system.

A high isoflavone soy protein diet and intravenous genistein delay rejection of rat cardiac allografts

Genistein, a soy isoflavone, has in vitro immunosuppressive properties. We investigated whether genistein or dietary soy protein containing isoflavones could influence the outcome of rat cardiac allografts. Lewis rats were fed a diet with protein from high isoflavone soy protein fraction (HIS), casein (CAS) or casein with isoflavones added (CI) starting 1 wk before heart transplants from Wistar Furth donors, and continuing throughout the study. HIS-fed rats had significantly prolonged time to rejection compared with CAS- and CI-fed recipients (10.8 +/- 2.62 vs. 7.18 +/- 0.75 and 7.22 +/- 0.44 d, P < 0.001). Intravenous genistein [20mg/(kg. d) for 14 d] significantly prolonged heart survival compared with controls and dissolvent-treated recipients (23.2 +/- 7.4 vs. 8.4 +/- 1.3 and 11.4+/3.6 d, P < 0.0005), and had an additive effect when given to heart recipients also receiving low dose cyclosporine for 7 d (30.8 +/- 2.3 vs. 23.4 +/- 2.4 d, P < 0.005). Concanavalin A-stimulated lymphocytes, isolated from Lewis rats given intraperitoneal genistein for 7 d, had decreased production of interferon gamma compared with controls or dimethyl sulfoxide-treated groups (22.6 +/- 9.9 vs 149 +/- 105 and 154 +/- 103 micro g/L, P < 0.05). In conclusion, a high isoflavone soy diet and intravenous genistein, but not isoflavone extract alone, delay rejection of rat cardiac allografts, with an additive effect in cyclosporine-treated rats. In addition, intraperitoneal genistein has immunosuppressive properties in vivo.

Transactivation of involucrin, a marker of differentiation in keratinocytes, by lens epithelium-derived growth factor (LEDGF)

Human involucrin (hINV), first appears in the cytosol of keratinocytes and ultimately cross-linked to membrane proteins via transglutaminase and forms a protective barrier as an insoluble envelope beneath the plasma membrane. Although the function and evolution of involucrin is known, the regulation of its gene expression is not well understood. An analysis of the hINV gene sequence, upstream of the transcription start site (-534 to +1 nt) revealed the presence of potential sites for binding of lens epithelium-derived growth factor (LEDGF); stress response element (STRE; A/TGGGGA/T) and heat shock element (HSE; nGAAn). We reported earlier that LEDGF activates stress-associated genes by binding to these elements and elevates cellular resistance to various stresses. Here, gel-shift and super-shift assays confirm the binding of LEDGF to the DNA fragments containing HSEs and STREs that are present in the involucrin gene promoter. Furthermore, hINV promoter linked to CAT reporter gene, cotransfected in human corneal simian virus 40-transformed keratinocytes (HCK), was transactivated by LEDGF significantly. In contrast, the activity of hINV promoter bearing mutations at the WT1 (containing HSE and STRE), WT2 (containing STRE) and WT3 (containing STRE) binding sites was diminished. In addition, in HCK cell over-expressing LEDGF, the levels of hINV mRNA and hINV protein are increased by four to five-fold. LEDGF is inducible to oxidants. Cells treated with 12-O-tetradecanoyl-phorbol-13-acetate (TPA), known to stimulate production of H(2)O(2), showed higher levels of LEDGF mRNA. Furthermore, our immunohistochemical studies revealed that hINV protein is found in the cytoplasm of HCK cells over-expressing LEDGF, but not detectable in the normal HCK cells or HCK cells transfected with vector. This regulation appears to be physiologically important, as over-expression of HCK with LEDGF increases the expression of the endogenous hINV gene and may provide new insight to understand the molecular mechanism of transcriptional regulation of this gene. LEDGF may play an important role in establishing an important barrier in corneal keratinocytes by maintaining epidermal turn-over rate, and protecting HCKs against stress.

Genotoxicity and carcinogenicity studies of soy isoflavones

The potential cancer preventive efficacy of soy isoflavones is being investigated in preclinical and phase 1 clinical studies sponsored by the U.S. National Cancer Institute. Although 90-day oral toxicity studies with PTI G-2535 (an investigational soy isoflavone drug product) in rats and dogs, as well as teratology studies, indicated no signs of toxicity, there remains a mechanistic concern associated with the ability of isoflavones (i.e., genistein) to inhibit topoisomerase, possibly leading to DNA strand breaks. The present report describes results from two in vitro genotoxicity studies, one in vivo genotoxicity study, and a single carcinogenicity study conducted in p53 knockout mice. Bacterial mutagenesis experiments using six tester strains without metabolic activation revealed no evidence that PTI G-2535 was mutagenic. In similar experiments with exogenous metabolic activation there were statistically significant increases in revertants, but less than twofold, in a single (Salmonella typhimurium TA100) tester strain. Mouse lymphoma cell mutagenesis experiments conducted with and without metabolic activation revealed statistically significant increases in mutation frequency at PTI G-2535 concentrations > or = 0.8 and 12 microg/ml, respectively; such increases were dose related and increases in the frequency of both small and large colonies were observed. A statistically significant increase in the frequency of micronucleated polychromatic erythrocytes was also seen 24 hours after treatment in male, but not female, mice who received 500 and 1000 mg/kg body weight PTI G-2535; however,such increases were small, were not dose related, and were not observed 48 hours after treatment. In contrast, dietary genistein had no effect on survival, weight gain, or the incidence or types of tumors that developed in cancer-prone rodents lacking the p53 tumor suppressor gene, p53 knockout mice. The apparent risk/benefit of isoflavone ingestion may ultimately depend on the dose and developmental timing of exposure.

Effects of genistein and daidzein on the cell growth, cell cycle, and differentiation of human and murine melanoma cells(1)

Genistein and daidzein are two major isoflavonoids in dietary soybean that have inhibition effect on the cell growth of different tumor cell lines. We previously reported the anti-tumor activities of genistein and daidzein in human co1on tumor (HCT) cells and their different ability to enhance the activation of murine lymphocytes. In the present study, the effect of genistein and daidzein on the cell growth, cell cycle progression, and differentiation of murine K1735M2 and human WM451 cel1s was investigated. It was found that genistein could inhibit the cell growth of two metastatic melanoma cell lines, murine Kl735M2 and human WM45l in a dose-dependent manner. Flow cytometry showed that genistein could cause arrest of both Kl735M2 and WM45l at G(2)/M phase, while daidzein increased the cell numbers at S phase, decreased the cell numbers at G(1) phase. Detection of melanin and morphological observation showed that genistein can induce Kl735M2 and WM45l to produce dendrite-like structure and produce more melanin by 80%. In contrast, daidzein only retarded the growth of K1735M2 and did not induce differentiation in either K1735M2 or WM451. These results suggest that genistein and daidzein in soybean can inhibit certain malignant phenotype of melanoma via different mechanisms and be potential medical candidates for melanoma cancer therapy.

FA15, a hydrophobic derivative of ferulic acid, suppresses inflammatory responses and skin tumor promotion: comparison with ferulic acid

In our previous study, FA15 (2-methyl-1-butyl ferulic acid) was chemically synthesized as a novel ferulic acid (FA) analog, and found to notably suppress phorbol ester-induced Epstein-Barr virus activation and superoxide anion generation in vitro. In this report, we demonstrated that FA15, in contrast to FA, markedly suppressed the combined lipopolysaccharide and interferon-gamma-induced protein expressions of inducible nitric oxide synthase and cyclooxygenase-2, and also inhibited the release of tumor necrosis factor-alpha accompanied by suppression of I-kappa B degradation in RAW264.7, a murine macrophage cell line. In ICR mouse skin, topical application of FA15 significantly attenuated phorbol ester-triggered hydrogen peroxide production and edema formation as well as papilloma development while that of FA did not. Our results suggest that FA15, derived from natural sources, is a novel chemopreventive agent, both structurally and functionally.

Genistein, a soy isoflavone, induces glutathione peroxidase in the human prostate cancer cell lines LNCaP and PC-3

Genistein is a major component of soybean isoflavone and has multiple functions resulting in antitumor effects. Prostate cancer is 1 of the targets for the preventive role of genistein. We examined the effect of genistein on human prostate cancer (LNCaP and PC-3) cells. Proliferation of both cell lines was inhibited by genistein treatment in a dose-dependent manner. To obtain the gene expression profile of genistein in LNCaP cells, we performed cDNA microarray analysis. The expression of many genes, including apoptosis inhibitor (survivin), DNA topoisomerase II, cell division cycle 6 (CDC6) and mitogen-activated protein kinase 6 (MAPK 6), was downregulated. Expression levels were increased more than 2-fold in only 4 genes. The glutathione peroxidase (GPx)-1 gene expression level was the most upregulated. Quantitative real-time polymerase chain reaction revealed significant elevation of transcript levels of GPx-1 in both LNCaP and PC-3 cells. Upregulation of gene expression levels accompanied elevation of GPx enzyme activities. In contrast, no significant changes were observed in the gene expression levels and enzyme activities of the other antioxidant enzymes, superoxide dismutase and catalase. GPx activation might be one of the important characteristics of the effects of genistein on prostate cancer cells.

In vitro isoflavone supplementation reduces hydrogen peroxide-induced DNA damage in sperm

Isoflavones are plant compounds, proposed to have health benefits in a variety of human diseases, including coronary heart disease and endocrine-responsive cancers. Their physiological effects include possible antioxidant activity, therefore suggesting a role for isoflavones in the prevention of male infertility. The aim of this study was to test the antioxidant effects of the isoflavones genistein and equol on sperm DNA integrity, assessed in vitro after hydrogen peroxide-mediated damage, using the comet assay. Pre-treatment with genistein or equol at doses of 0.01-100 micromol/l significantly protected sperm DNA against oxidative damage. Both ascorbic acid (10-600 micromol/l) and alpha-tocopherol (1-100 micromol/l) also protected. Compared with ascorbic acid and alpha-tocopherol, added at physiological concentrations, genistein was the most potent antioxidant, followed by equol, ascorbic acid, and alpha-tocopherol. Genistein and equol added in combination were more protective than when added singly. Based on these preliminary data, which are similar to those observed previously in lymphocytes, these compounds may have a role to play in antioxidant protection against male infertility.

Use of alternative therapies in menopause

Hormone replacement therapy has traditionally been used to treat the accompanying symptoms of oestrogen deficiency in menopause. However, not all women can, or prefer to, receive this treatment and alternatives should be considered to reduce the increased risk of osteoporosis and heart disease in menopausal women. This chapter reviews the current literature on the efficacy of phyto-oestrogens in preventing cardiovascular disease, various cancers and osteoporosis, as well as treating the vasomotor and other menopause-related symptoms. Select herbal therapies, as well as selective oestrogen receptor modulators, are also considered.

Synergistic inhibitory effects of genistein and tamoxifen on human dysplastic and malignant epithelial breast cells in vitro

OBJECTIVE

Genistein is a phytoestrogen with in vitro anticancerogenic activity. We examined in vitro the effects of genistein alone, or in combination with estradiol and tamoxifen, on the growth of human dysplastic and malignant epithelial breast cell lines.

METHODS

Dysplastic breast cell lines (MCF-10A(1), MCF-ANeoT, MCF-T(6)3B) and cell lines of breast cancer (MCF-7, MDA-231, MDA-435) were cultured as monolayers in RPMI 1640 medium supplemented with 10% fetal bovine serum, and L-glutamine. After preincubation of 20 h, genistein (1, 2.5, 5, 7.5 and 10 microg/ml) alone or in combination with estrogen or tamoxifen was added to the cultured cells. The cells were treated continuously for 72 h and then the growth rate was assessed colorimetrically. Stepwise multiple linear regression analysis was used to evaluate the effect of genistein, tamoxifen, and estradiol on cell proliferation.

RESULTS

Genistein had a significant (dose-dependent) inhibitory effect on the proliferation of both dysplastic (P<0.0001) and malignant (P<0.0001) cells. The growth inhibition was significantly higher P<0.0001 in dysplastic cells compared to the cancer cells. Addition of tamoxifen to genistein further inhibited the proliferation of both cell types, reflecting a synergistic antiproliferative effect on dysplastic cells P<0.0001 and an additive growth inhibition effect P<0.0003 on malignant cells. Estradiol significantly (P=0.005) stimulated the growth of dysplastic cell lines while a significant (P=0.003) antiproliferative effect on growth of the malignant cells was observed. The concentration of estrogen receptor (ER) had no significant effect on growth rates and did not modulate the effects of genistein or tamoxifen.

CONCLUSIONS

Genistein (1-10 microg/ml) inhibits the growth of dysplastic and malignant epithelial breast cancer cells in vitro and the addition of tamoxifen (10(-6), 10(-7)M) has a synergistic/additive inhibitory effect. These effects are not modulated by the presence of ER.

Protective effect of L-carnosine against 12-O-tetradecanoylphorbol-13-acetate- or hydrogen peroxide-induced apoptosis on v-myc transformed rat liver epithelial cells

Apoptotic processes have been associated with cancer and neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease etc. beta-Alanyl-L-histidine (L-carnosine), occurring abundantly in skeletal muscles has been suggested to possess antioxidative activity. We investigated whether L-carnosine prevents 12-O-tetradecanoylphorbol-13-acetate (TPA)- or hydrogen peroxide (H2O2)-induced apoptosis involving mitochondria in the v-myc transformed rat liver epithelial cells (WB-myc cells). L-Carnosine prevented both TPA- and H2O2-induced DNA fragmentation, the loss of mitochondrial membrane potentials and blocked the release of cytochrome c into cytosol. Subsequently, the cleavages of poly (ADP-ribose) polymerase were significantly reduced in L-carnosine-treated cells. However, western blotting analysis revealed that p53 protein level did not change for 12h after TPA- and H2O2-treatment. Therefore, these results suggested that L-carnosine, an antioxidant, protected both H2O2- and TPA-induced apoptosis through mitochondrial pathways.

Prospects for chemoprevention of cancer

The recent progress in molecular biology and pharmacology has increased the likelihood that cancer prevention will rely increasingly on interventions collectively termed 'chemoprevention'. Cancer chemoprevention is the use of agents to inhibit, delay or reverse carcinogenesis. A number of potential targets for chemoprevention have recently been identified. Many classes of agents including antioestrogens, anti-inflammatories, antioxidants and other diet-derived agents have shown a great deal of promise. In this review, we will begin by describing the general classes of chemopreventive agents and the mechanisms by which these agents act. We will then describe the opportunities that presently exist for chemoprevention of specific cancers.

Effects of the isoflavone 4',5,7-trihydroxyisoflavone (genistein) on psoralen plus ultraviolet A radiation (PUVA)-induced photodamage

Long-term psoralen plus ultraviolet A radiation (PUVA) therapy is associated with an increased risk of squamous cell carcinoma and malignant melanoma. Genistein (4',5,7-trihydroxyisoflavone), a major isoflavone in soybeans and a specific inhibitor of protein tyrosine kinase, has been shown to inhibit UVB induced skin carcinogenesis in hairless mice. For this study we examined the protective effects of topical genistein on PUVA-induced photodamage. In two separate experiments, genistein in a dimethyl sulfoxide/acetone (1:9) solution was applied to SKH-1 female mice 1 h post 8-methoxy-psoralen dosing and 1 h prior to UVA irradiation. Application of genistein significantly decreased PUVA-induced skin thickening, and greatly diminished cutaneous erythema and ulceration in a dose-dependent manner. Histological examination showed that PUVA treatment of mouse skin induced dramatic inflammatory changes throughout the epidermis; topical genistein prevented these changes without noticeable adverse effects. Cells containing cleaved poly(ADP-ribose) polymerase (PARP) and active caspase-3 were significantly increased in PUVA-treated skin (P < 0.05 and P < 0.0001, respectively) as compared with unexposed control skin. Topical genistein completely inhibited cleavage of PARP and caspase-3. Proliferating cell nuclear antigen (PCNA) positive cells were observed in suprabasal areas of the epidermis and were significantly decreased in PUVA-treated skin compared with both control samples and samples treated with PUVA plus topical genistein (P < 0.005). These results indicate that genistein protects the skin from PUVA-induced photodamage.

Ebselen, a glutathione peroxidase mimetic seleno-organic compound, as a multifunctional antioxidant. Implication for inflammation-associated carcinogenesis

Ebselen, a seleno-organic compound showing glutathione peroxidase-like activity, is one of the promising synthetic antioxidants. In the present study, we investigated the antioxidant activities of ebselen using a 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated mouse skin model. Double pretreatments of mouse skin with ebselen significantly inhibited TPA-induced formation of thiobarbituric acid-reacting substance, known as an overall oxidative damage biomarker, in mouse epidermis, suggesting that ebselen indeed acts as an antioxidant in mouse skin. The antioxidative effect of ebselen is attributed to its selective blockade of leukocyte infiltration and activation leading to attenuation of the H(2)O(2) level. In in vitro studies, ebselen inhibited TPA-induced superoxide generation in differentiated HL-60 cells and lipopolysaccharide-induced cyclooxygenase-2 protein expression in RAW 264.7 cells. In addition, we demonstrated for the first time that ebselen potentiated phase II enzyme activities, including NAD(P)H:(quinone-acceptor) oxidoreductase1 and glutathione S-transferase in cultured hepatocytes and in mouse skin. These results strongly suggest that ebselen, a multifunctional antioxidant, is a potential chemopreventive agent in inflammation-associated carcinogenesis.

Soy isoflavonoids and cancer -- metabolism at the target site

Isoflavonoids are members of the broad class of plant polyphenols that have been shown in vivo to have benefit in the prevention of a wide variety of chronic diseases, including cancer. For genistein (5,7,4'-trihydroxyisoflavone) (GEN), the major isoflavone in soy, reported mechanisms for these biological activities are numerous and include regulation of estrogen-mediated events, inhibition of tyrosine kinase and DNA topoisomerase activities, synthesis and release of TGF beta, and modulation of apoptosis. However, the biochemical effects of GEN in cell culture occur at concentrations in the micromolar range, far above the circulating levels of the unconjugated GEN. This may point to the limitations of cell culture for the evaluation of the activity and mechanisms of potential anti-carcinogens. GEN is extensively metabolized in vivo, with only about 14-16% excreted in an unmodified form. Metabolism may also occur because of interaction between GEN (as well as other polyphenols) and oxidants produced by inflammatory cells (HOCl, HOBr and ONOO(-)). These react with GEN to form brominated, chlorinated and/or nitrated GEN. Emerging evidence indicates that these modifications may substantially increase the biological activities of the parent compound. Future investigations of GEN and other polyphenols must, therefore, take into account metabolism at the tissue site.

Isoflavonoid compounds from red clover (Trifolium pratense) protect from inflammation and immune suppression induced by UV radiation

Isoflavones derived from many edible plants have been reported to possess significant antioxidant, estrogenic and tyrosine kinase inhibitory activity. Genistein has been found previously to provide protection from oxidative damage induced by UV radiation both in vitro and following dietary administration. We have therefore examined the potential of a number of isoflavones from red clover (Trifolium pratense) and some metabolically related compounds to offer protection from UV irradiation in hairless mice by topical application after UV exposure. We show that whereas the primary isoflavones, daidzein, biochanin A and formononetin, were inactive, 20 microM lotions of genistein and the metabolites equol, isoequol and the related derivative dehydroequol had powerful potential to reduce the inflammatory edema reaction and the suppression of contact hypersensitivity induced by moderate doses of solar-simulated UV radiation. For equol the protection was concentration dependent and 5 microM equol markedly reduced the UV-induced inflammation but abrogated the UV-induced immunosuppression. Equol protected similarly from immunosuppression induced by the putative epidermal mediator, cis-urocanic acid (UCA), indicating a potential mechanism of action involving inactivation of this UV-photoproduct. Since immunosuppression induced by both UV radiation and by cis-UCA appears to be an oxidant-dependent response our observations support the actions of these topically applied isoflavones and their metabolites as antioxidants. They also indicate that lotions containing equol, unlike topical UV sunscreens, more readily protect the immune system from photosuppression than from the inflammation of the sunburn reaction, even when applied after exposure, and thus such compounds may have a future role as sun-protective cosmetic ingredients.