Interaction of phytoestrogens and other environmental estrogens with prostaglandin synthase in vitro

Phytoestrogens in postmenopausal indications: A theoretical perspective

This review discusses plant-derived compounds with estrogenic activity. The authors rightly emphasize the need for the intake of foods containing phytoestrogens in view of their positive effects on postmenopausal indications. This is particularly significant in the light of the current wave of enthusiasm for vegetarian food, in general, and phytoestrogens, in particular. Phytoestrogens are plant-derived hormone-like diphenolic compounds of dietary origin. These compounds are weakly estrogenic and could play a role in the prevention of other estrogen-related conditions, namely, cardiovascular diseases, menopausal symptoms, postmenopausal osteoporosis, neuroprotective effects, and hormone-dependent cancers (breast and endometrium cancer).

Effect of serum metabolites ofPueraria lobata in rats on peripheral nerve regeneration:In vitro andin vivo studies

This study provides in vitro and in vivo evaluation of rat serum metabolites of the Pueraria lobata (SMP) on peripheral nerve regeneration. In the in vitro study, we found that the SMP caused a marked enhancement of the nerve growth factor (NGF)-mediated neurite outgrowth and the expression of synapsin I from PC12 cells. In the in vivo study, silicone rubber chambers filled with the SMP were used to bridge a 10-mm sciatic nerve defect in rats. At the conclusion of 8 weeks, animals from the groups treated with the SMP had a relatively more mature structure with larger mean values of myelinated axon number, endoneurial area, and total nerve area when compared with those in the controls receiving the saline only. These results suggest that the serum metabolites of Pueraria lobata can be a potential nerve growth-promoting factor.

Inhibition of 17beta-hydroxysteroid dehydrogenases by phytoestrogens: comparison with other steroid metabolizing enzymes

Effects of phytoestrogens on human health have been reported for decades. These include not only beneficial action in cancer prevention but also endocrine disruption in males. Since then many molecular mechanisms underlying these effects have been identified. Targets of phytoestrogens comprise steroid receptors, steroid metabolising enzymes, elements of signal transduction and apoptosis pathways, and even the DNA processing machinery. Understanding the specific versus pleiotropic effects of selected phytoestrogens will be crucial for their biomedical application. This review will concentrate on the influence of phytoestrogens on 17beta-hydroxysteroid dehydrogenases from a comparative perspective with other steroid metabolizing enzymes.

Phytoestrogens as modulators of steroid action in target cells

Although numerous reports exist on the potential beneficial role of nutritional phytoestrogens in human health, their molecular mechanism in target cells is still not completely understood. Phytoestrogens promote estrogen and antiestrogen effects by interacting with numerous molecules, carrier proteins, enzymes and membrane and nuclear receptors, directly or indirectly involved in the transfer of estrogen signals. The hypothesis that the ER beta subtype plays a key role in antiproliferative effect of phytoestrogens, especially in breast cancer, is examined here. This review focus on the effects of phytoestrogens in developmental processes such as those linked to reproductive function, tumorigenesis and angiogenesis.

Sexual dimorphism in prostanoid-potentiated vascular contraction: roles of endothelium and ovarian steroids

The effects of constrictor prostanoid (CP) pathway inhibitors on vascular reactivity to vasopressin (VP) and phenylephrine (PE) were examined in thoracic aortas of male, female, and ovariectomized (OVX) female Sprague-Dawley rats. Maximal contractile response of control (Cont) aortas to VP was markedly higher in females (3,885 +/- 332 mg/mg ring wt) than in males (810 +/- 148 mg). Indomethacin (Indo; 10 microM) attenuated maximal response to VP in females (3,043 +/- 277 mg) but not in males. SQ-29,548 (SQ; 1 microM) attenuated maximal response to VP in females (3,042 +/- 290 mg) to a similar extent as Indo. Dazoxiben (Daz; 10 microM) alone had no effect, but Daz + SQ attenuated maximal contractile response to VP to a similar extent as SQ alone. Removal of the endothelium in female aortas attenuated contractile responses to VP in Cont aortas. OVX attenuated maximal contractile response to VP in Cont aortas (2,093 +/- 329 mg) and abolished the attenuating effects of Indo. Indo, SQ, and Daz exerted identical effects on contractile responses of male, female, and OVX female aortas to PE. These findings establish the following in the rat aorta: 1) CP, probably thromboxane and/or endoperoxide, is responsible for approximately 25-30% of contractile responses of females, but not males, to VP and PE; 2) CP production by the female aorta is primarily endothelial in origin; and 3) ovarian steroids modulate production and/or actions of CP in female aortas.

Regional differences in the effect of oestrogen on vascular tone in isolated rabbit arteries

The aim of the study was to assess how oestrogen acutely affects the tone of isolated artery segments from different vascular beds in rabbit. Cumulative concentrations of 17beta-oestradiol were added to ring segments of thoracic aorta, pulmonary artery, ear artery and coronary arteries from adult male rabbits. Coronary arteries precontracted with potassium or the thromboxane agonist, U46619, relaxed to oestrogen (10(-7) to 10(-4) M), whereas oestrogen (10(-8) to 10(-4) M) only caused additional contraction in segments of thoracic aorta and pulmonary artery precontracted with phenylephrine. In the thoracic aorta both the phospholipase C inhibitor NCDC (10(-4) M) and the cyclooxygenase inhibitor indomethacin (10(-5) M) almost completely blocked the contractile effect of oestrogen. In segments of the ear artery, oestrogen caused relaxation only at higher concentrations of oestrogen (10(-5) to 10(-4) M). In conclusion, oestrogen may cause both relaxation and vasoconstriction in different vascular beds, and in the thoracic aorta the contractile effects of oestrogen may be mediated via inositol phosphate-dependent pathways and release of prostaglandins.

Characterization of the estrogenic response to genistein in Japanese medaka (Oryzias latipes)

This study was designed to determine the estrogenic effect of the phytoestrogen genistein on several measures of endocrine function in adult Japanese medaka (Oryzias latipes) relative to 17-beta-estradiol. Adult animals of both sexes were exposed to 75, 750 and 30,000 ng/fish (average fish weight equals 0.26 g) of genistein by i.p. injection, with a positive control group treated with 300 ng/fish of 17-beta-estradiol, while a negative control group received a vehicle-only (corn oil) injection. Content of vitellogenin, the yolk glycoprotein made in the liver in response to estradiol stimulation, was measured using Western blots. Circulating estradiol and testosterone levels were measured using a steroid-enzyme immunosorbant assay. The ability of ovaries and testes to synthesize and release estradiol and testosterone was determined by ex vivo incubation of gonads with 25-hydroxycholesterol. Vitellogenin, while induced by 17-beta-estradiol, was not increased in the liver of individuals treated with genistein. In females, genistein treatment at 750 and 30,000 ng increased the estradiol production of ovaries more than the 17-beta-estradiol treatment. In males, genistein treatment resulted in decreased testosterone production from ex vivo testis and a comparable reduction in circulating testosterone level. The changes in vitellogenin, circulating steroids and ex vivo steroidogenesis in medaka in response to genistein are similar to that of 17-beta-estradiol. However, some endpoints are more sensitive to estradiol treatment (vitellogenin), while others are more sensitive to genistein (male testosterone and ovarian estrogenesis).

Estrogenic isoflavones in rodent diets

Many rodent diets contain components such as soy isoflavones (daidzein and genistein) known to have estrogenic properties. The dietary background of phytoestrogens may modulate some responses to environmental estrogens when these compounds are tested in rodent bioassays. Thus, and since only few data were available on the phytoestrogen content of rodent diets commonly used in European laboratories, it was of interest to analyze the daidzein and genistein contents of our standard animal feeds. Isoflavone contents were determined in seven batches of rodent chow (from two suppliers in Germany, Altromin and Ssniff) by high-performance liquid chromatography, and also analyzed in six rodent diets from the United States. The soy-based rodent diets from Germany contained isoflavone (daidzein plus genistein) concentrations in the range of 0.3-0.55 mg/g feed. These isoflavone contents are similar to those analyzed in the US rodent diets, and similar to values reported by others, including one particular lot of feed (with 0.35 mg isoflavones per g) which produced a large uterotrophic response in immature ovariectomized rats [Environ. Health Perspect., 106 (1998) 369]. Coumestrol was found in a sample of commercial rabbit food at rather high levels (0.27 mg/g), but, this phytoestrogen was not detected (<1 microg/g feed) in any of the other samples we analyzed. The soy components in our rodent diet produce a measurable background of daidzein and genistein in blood of female DA/Han rats, total isoflavones (aglycone plus conjugates) ranging between 90 and 290 ng/ml plasma. The ovariectomized animals kept on this chow, showed no signs of estrogenization of the reproductive tract (uterus, vagina), and responded normally to (xeno-)estrogen administration in a uterotrophic assay [J. Steroid Biochem. Mol. Biol., 73 (2000) 1]. Moreover, ovariectomized Wistar rats on our standard rodent diet (Ssniff R/M H) had lower uterine weights than animals kept on the isoflavone-free (solvent extracted) chow; both groups of rats responded to genistein administration with an increase in uterine weights. These results suggest that--albeit the sensitivity of the rodent uterotrophic assay is not reduced by the use of a diet containing soy isoflavones at commonly encountered levels--attention should be given to a variable dietary phytoestrogen background.

Estrogen and related compounds: biphasic dose responses

This article documents and quantitatively assesses the capacity of estrogen, phytoestrogens, and antiestrogens to affect biphasic dose-response relationships in animal/human models and across a broad range of cell types, affecting multiple endpoints. The range of endpoints displaying such biphasic dose responses includes plasminogen activation, oxytocin secretion, angiogenesis, cell proliferation, bone growth, monocyte chemotaxis, secretion of various cytokines, and other effects. The quantitative features of the dose response relationships revealed that the magnitude of the stimulatory responses was typically less than twofold, whereas the stimulatory responses were markedly variable ranging from about 5- to 10(6)-fold. Mechanistic explanations of the biphasic responses are addressed.

Effect of genistein-enriched diets on the endocrine process of gametogenesis and on reproduction efficiency of the rainbow trout Oncorhynchus mykiss

Three practical diets were formulated to contain 0, 500, or 1000 ppm genistein. The three diets were distributed for 1 year to groups of rainbow trout undergoing their first gametogenesis and until spawning. Growth performance of rainbow trout was not affected by dietary treatments. Plasma cholesterol levels were equivalent between groups. In males, a slight but constant induction of vitellogenin (VTG) synthesis and a decrease in testosterone levels were observed. A slight decrease in plasma levels of betaFSH and betaLH was noticed at the end of spermatogenesis in the male fish fed a diet with 500 ppm (genistein) (from 2.16 +/- 0.39 to 1.47 +/- 0.23 for betaFSH and from 0.44 +/- 0.09 to 0.31 +/- 0.09 for betaLH). There was a significantly reduced 17alpha,20beta(OH)(2)-progesterone (from 10.93 +/- 0.88 in control to 5.46 +/- 0.92 in males and from 251.22 +/- 21.40 to 183.22 +/- 13.48 in females). Testicular development was accelerated in genistein-fed fish, and sperm motility and concentration were decreased in a dose-dependent manner at spawning. In females, a significant increase in plasma VTG occurred only at the beginning and at the end of oogenesis. Testosterone levels were decreased at the beginning of oogenesis. Both betaFSH and betaLH were decreased by genistein (from 6.38 +/- 1.55 to 3.44 +/- 0.82 for betaFSH and from 15.18 +/- 3.00 to 6.93 +/- 0.99 for betaLH in females), whereas spawning was delayed only in females fed the diet with 500 ppm of genistein. Gamete quality was impaired only in this group, as underlined by a lower percentage of ovulating females (from 100 to 79% at the end of the trial), a lower fertilization rate, and a lower viability of fry. These results may be explained by the agonistic/antagonistic effect of genistein on estrogen function related to the tissue ratio between endogenous estrogens/genistein.

Dietary phytoestrogens and their role in hormonally dependent disease

Epidemiological studies suggest that diets rich in phytoestrogens (plant estrogens), particularly soy and unrefined grain products, may be associated with low risk of breast and prostate cancer. It has also been proposed that dietary phytoestrogens could play a role in the prevention of other estrogen-related conditions, namely cardiovascular disease, menopausal symptoms and post-menopausal osteoporosis. However, there is no direct evidence for the beneficial effects of phytoestrogens in humans. All information is based on consumption of phytoestrogen-rich diets, and the causal relationship and the mechanisms of phytoestrogen action in humans still remain to be demonstrated. In addition, the possible adverse effects of phytoestrogens have not been evaluated. It is plausible that phytoestrogens, as any exogenous hormonally active agent, might also cause adverse effects in the endocrine system, i.e. act as endocrine disrupters.

Inhibition of mouse and human CYP 1A- and 2E1-dependent substrate metabolism by the isoflavonoids genistein and equol

The inhibitory effect of the isoflavonoids genistein and equol on cytochrome P450 activities has been investigated. Genistein and equol inhibited the high capacity component of p-nitrophenol (CYP2E1 substrate) metabolism in liver microsomes from acetone-induced mice with IC50 values of approximately 10 mM and 560 microM, respectively (cf. diethyldithiocarbamate, IC50, 69 microM). Using human CYP2E1 from a specific expression system (which overcame multienzyme involvement in the rodent system), non-competitive inhibition was also seen with both isoflavonoids. Genistein and equol also inhibited the high capacity component of ethoxyresorufin (CYP1A substrate) metabolism in liver microsomes from beta-naphthoflavone-induced mice with IC50 values of 5.6 mM and 1.7 mM, respectively (cf. alpha-naphthoflavone, IC50 0.8 microM). Using human CYPIA2 from a specific expression system, noncompetitive inhibition was seen with both isoflavonoids. CYP1A1 inhibition offers a possible explanation for the chemopreventative effect of genistein against, for example, dimethylbenz[a]anthracene genotoxicity reported in animals but the IC50 values negate the relevance of this specific chemopreventative action at the levels likely to be achieved from the human diet.

Salidiuretic action by genistein in the isolated, perfused rat kidney

The urinary isoflavonoid genistein inhibits membrane Na-K-Cl cotransporters at similar concentrations as furosemide, but the significance of this action is unknown. Genistein was therefore investigated in rats for its potential salidiuretic actions. In the isolated, perfused rat kidney, genistein induced a maximal salidiuretic action similar to that of furosemide but was 3 to 5 times less potent than furosemide in terms of active doses (natriuresis EC50, 237+/-92 versus 56+/-20 micromol/L for genistein and furosemide, respectively). Genistein and furosemide had no additive salidiuretic actions. Genistein had no significant effect on glomerular filtration rate but was able to significantly reduce renal vascular resistance with respect to vehicle isolated perfused kidney. Indomethacin (10 micromol/L), a blocker of prostaglandin biosynthesis, reduced salidiuresis and renal vasorelaxation by genistein. Subcutaneous genistein (15 mg/kg) induced a statistically significant increase in diuresis and natriuresis with respect to vehicle during the first 6 hours of administration in rats. In conclusion, genistein compares well with furosemide in vitro for its salidiuretic profile and potency in the isolated perfused rat kidney and is also natriuretic by the subcutaneous route in the rat. Further studies are required to investigate potential natriuretic and perhaps hypotensive actions of dietary genistein.

Transcriptional mechanisms involved in the relaxant effect of zeranol on isolated rat uterus

1. The effect of zeranol (3-100 microM) on rat uterus contractions induced by KCl (60 mM) and CaCl2 (30 microM-10 mM) has been assayed. 2. Zeranol relaxed the tonic contraction induced by KCl in a concentration-dependent manner (IC50 15.62 +/- 2.66 microM). CaCl2 (0.1-10 mM) did not counteract the relaxing effect of zeranol. 3. CaCl2 (30 microM -10 mM) produced a concentration-dependent contraction of rauuterus in medium lacking calcium plus KCl (60 mM) (EC50 0.34 +/- 0.03 mM). Zeranol (8 microM) displaced the CaCl2 concentration-response curve to the right and increased the EC50 to 1.27 +/- 0.57 mM (P < 0.05) without modifying the Emax. 4. The antiestrogen tamoxifen (1 microM) and the inhibitor of cAMP-dependent protein kinase TPCK (3 microM) did not modify the effect of zeranol. However, the inhibitors of transcription (actinomycin D, 4 microM), protein synthesis (cycloheximide, 100 microM), and ornithine-decarboxilase (alpha-difluoromethyl-ornithine, 10 mM)) antagonized the effect of zeranol, increasing the IC50 to 50.2 +/- 6.2 microM, 122 +/- 6.9 microM, and 23.51 +/- 1.14 microM, respectively. 5. Our results suggest that the relaxing effect of zeranol on rat uterus smooth muscle is produced by mechanisms unrelated to cAMP and estrogen receptors, but involves transcriptional effects and polyamine synthesis.

Enhancement of immune function in mice fed high doses of soy daidzein

High soy consumption leading to high exposures of soy isoflavones has been associated with a reduced risk of cancers at many sites. As part of a study focusing on the chemopreventive mechanisms, we have investigated the modulating effects of daidzein, a prominent and more bioavailable isoflavone in soy foods, on murine immune function. Swiss mice were fed daidzein at various doses daily for seven consecutive days. At high doses (20 and 40 mg/kg), daidzein exerted a stimulatory effect on nonspecific immunity, as shown by increases in the phagocytic response of peritoneal macrophages and thymus weight, in a dose-dependent manner. Augmentation of spleen immunoglobulin M-producing cells against sheep red blood cells demonstrated an-activation of humoral immunity. Enhanced cell-mediated immunity was also observed as increases in lymphocyte proportion of peripheral blood. However, no significant immunoregulatory effect was found when mice were fed 10 mg/kg daidzein. These results demonstrate for the first time that daidzein at high doses enhances several immunologic functions and suggest a novel approach to understanding the mechanism(s) by which soy foods may contribute to observed cancer prevention.

Interactions between phytoestrogens and human sex steroid binding protein

The interactions of human Sex steroid binding protein (SBP) and the lignans [Nordihydrogaiaretic acid (NDGA) enterolactone (Ent), enterodiol (End)] and isoflavonoid phytoestrogens [Equol (Eq), diazein Dad), genistein (Gen)] were studied. The phytoestrogens had different dose-dependent inhibitory effects on steroid binding by SBP. Their relative efficiencies were: Ent> or = NDGA = Eq > Gen for displacing E2 and Eq > Ent > NDGA > Gen for displacing T. End and Dad were much less active. Scatchard analysis suggested that NDGA had similar non- competitive effects on T and E2 binding by reducing the number of binding sites without changing the association constants. But Eq seemed to inhibit E2 binding non-competitively and T binding competitively. NDGA binding to SBP reduced the immunorecognition of SBP by monospecific anti-SBP antibodies, suggesting that NDGA changed SBP immunoreactivity. Unlike NDGA, Eq binding to SBP caused no immunological changes in SBP, indicating qualitative differences in the effects of the lignan and isoflavonoid. Our results indicate that phytoestrogens may modulate the SBP activity and so influence the role of this protein in the delivery of hormonal information to sex steroid-dependent cells.

Sequence analysis of steroid- and prostaglandin-metabolizing enzymes: application to understanding catalysis

Amino acid sequence comparisons have revealed that mammalian 11 beta-hydroxysteroid and 17 beta-hydroxysteroid dehydrogenases and bacterial 3 alpha, 20 beta- and 3 beta-hydroxysteroid dehydrogenases are homologs; that is, these enzymes are descended from a common ancestor. These steroid dehydrogenases are also homologous to human 15-hydroxyprostaglandin dehydrogenase and to proteins found in Rhizobia, bacteria that form nitrogen-fixing nodules in the roots of legumes. We constructed a multiple sequence alignment of these proteins, which, when combined with the recently determined tertiary structure of Streptomyces hydrogenans 3 alpha, 20 beta-hydroxysteroid dehydrogenase and a homologous enzyme, rat dihydropteridine reductase, identifies segments and residues that are likely to be structurally important in the functioning of these enzymes especially regarding specificity for NADPH and NADH.

In vitro bioassays of non-steroidal phytoestrogens

Some of the isoflavonoids present in human diet as well as in urine are expected to exert biologic effects as they have been reported to bind to estrogen receptors and to be estrogenic in other species. This report describes the in vitro assessment of estrogenic effects of isoflavonoids using human endometrial cells and tissue. The relative estrogenic potencies (EC50 values) of estradiol, 3 dietary isoflavonoids (coumestrol, genistein and daidzein) and one of their metabolites (equol), were estimated by using a recently developed multiwell plate in vitro bioassay based on the estrogen-specific enhancement of alkaline phosphatase (AlkP) activity in human endometrial adenocarcinoma cells of the Ishikawa-Var I line. The maximal AlkP activity elicited by the isoflavonoids tested was as high as that achieved with estradiol and their effects were suppressed by the antiestrogens 4-hydroxytamoxifen and ICI 164,384. These results indicate that estradiol and the isoflavonoids exert their effects on AlkP by similar interactions with the estrogen receptor, with potencies depending on binding affinities. The estrogenic effect of equol was confirmed by another in vitro bioassay, based on the estrogen-stimulated enhancement of prostaglandin F2 alpha output by fragments of human secretory endometrium.

Dose-response characteristics of neonatal exposure to genistein on pituitary responsiveness to gonadotropin releasing hormone and volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) in postpubertal castrated female rats

Estrogen exposure during critical periods of development promotes androgenization of the brain, which is reflected in altered morphology, behavior, and cyclic hormone secretion in females. Previous work in our laboratory demonstrated that neonatal female rats injected with pharmaceutical or naturally occurring estrogens had decreased GnRH-induced LH secretion and increased volume of the SDN-POA as 42 day castrates. The current experiment defines the dose-response characteristics of neonatal exposure to the isoflavonoid phytoestrogen genistein (G) on pituitary sensitivity to GnRH and SDN-POA volume. Litters of rat pups received subcutaneous injections of either corn oil, 1, 10, 100, 200, 400, 500, or 1000 micrograms of G on days 1 to 10 of life. The litters were ovariectomized and weaned on day 21. On day 42 blood was drawn from right atrial catheters immediately prior to, 5, 10, 15, and 30 min following a single injection of 50 ng/kg of GnRH. Only the 10 micrograms dose of G was associated with increased pituitary response to GnRH, while progressive increases in exposure levels of G were associated with decreasing LH secretion. The SDN-POA volume was increased in only the 500 micrograms and 1000 micrograms exposure groups compared to controls. The results confirm that low doses of G have nonandrogenizing, pituitary-sensitizing effects, while higher doses of G mimic the more typical effects of estrogens. The use of both morphologic and physiologic end points more completely defines the reproductive consequences of environmental estrogen exposure during critical periods of CNS development.

Expansion of the mammalian 3 beta-hydroxysteroid dehydrogenase/plant dihydroflavonol reductase superfamily to include a bacterial cholesterol dehydrogenase, a bacterial UDP-galactose-4-epimerase, and open reading frames in vaccinia virus and fish lymphocystis disease virus

Mammalian 3 beta-hydroxysteroid dehydrogenase and plant dihydroflavonol reductases are descended from a common ancestor. Here we present evidence that Nocardia cholesterol dehydrogenase, E. coli UDP-galactose-4 epimerase, and open reading frames in vaccinia virus and fish lymphocystis disease virus are homologous to 3 beta-hydroxysteroid dehydrogenase and dihydroflavonol reductase. Analysis of a multiple alignment of these sequences indicates that viral ORFs are most closely related to the mammalian 3 beta-hydroxysteroid dehydrogenases. The ancestral protein of this superfamily is likely to be one that metabolized sugar nucleotides. The sequence similarity between 3 beta-hydroxysteroid dehydrogenase and the viral ORFs is sufficient to suggest that these ORFs have an activity that is similar to 3 beta-hydroxysteroid dehydrogenase or cholesterol dehydrogenase, although the putative substrates are not yet known.

Evolution of regulation of steroid-mediated intercellular communication in vertebrates: insights from flavonoids, signals that mediate plant-rhizobia symbiosis

Various flavonoids, such as genistein, luteolin, and coumestrol, have actions in mammals that are mediated by binding either to classical estrogen receptors or to type II receptors, which also bind estrogen. These actions are of intense interest because they may be the basis for the protective actions of plants against certain cancers, such as breast cancer. The biological activity of flavonoids in mammals raises some questions. Is the hormonal action of flavonoids "an accident" derived from their phenolic groups and general hydrophobicity, which gives them some properties in common with estrogens? Or do flavonoids regulate gene transcription in other organisms? And, if so, is there a connection between their actions in these organisms and in mammals? Some answers to these questions are provided by the actions of plant-derived flavonoids in regulating gene transcription in rhizobia, bacteria that form nitrogen-fixing nodules in the roots of legumes, which has several interesting similarities with steroid-mediated actions in vertebrates. First, there is specificity in the actions of flavonoids in rhizobia; oxidation or reduction of the flavonoid or removal of a hydroxyl group can alter its biological activity. Moreover, some flavonoids are anti-inducers functioning like steroid antagonists to negate the actions of inducers. Also there are sequence similarities between various steroid metabolizing enzymes and proteins found in rhizobia, which indicates that these proteins are derived from a common ancestor. For example, 17 beta-hydroxysteroid dehydrogenase, which catalyzes the interconversion of the alcohol and ketone a C17 on estrogens and androgens, 11 beta-hydroxysteroid dehydrogenase, which catalyzes the interconversion of the alcohol and ketone at C11 of glucocorticoids, and 3 alpha,20 beta-hydroxysteroid dehydrogenase, which catalyzes the interconversion of the alcohol and ketone at C20 of corticosteroids, are homologs of proteins found in rhizobia. Thus, the binding of flavonoids to vertebrate proteins may represent an evolutionary linkage between the actions of steroids in mammals and communication between plants and rhizobia.

Phytoestrogens: new ligands for rat and human alpha-fetoprotein

The binding of the lignans, enterolactone, enterodiol, nordihydroguaiaretic acid (NDGA), and the isoflavonic phytoestrogen equol, to human and rat alpha-fetoprotein (AFP) was studied. They had differential inhibitory effects (NDGA greater than equol greater than enterolactone greater than enterodiol) on the binding of estrone and estradiol to rat AFP and the binding of unsaturated fatty acid to both rat and human AFP. Inhibition was dose-dependent. The apparent dissociation constants (Kd) for phytoestrogens binding to AFP were: Kd NDGA = 5 +/- 1.2.10(-7) M, Kd equol = 6.7 +/- 0.8.10(-6) M, Kd enterolactone = 1.7 +/- 0.4.10(-5) M and Kd enterodiol = 2.2 +/- 0.6.10(-5) M. The Kd for estrone binding to rat AFP was increased by increasing concentrations of equol, but the number of esterone binding sites remained unchanged. This, plus the results of double-reciprocal plots, suggests that they compete for the same site(s). NDGA also competitively inhibited estrone binding at low NDGA concentrations (increased Kd), but high concentrations induced conformational changes in rat AFP, as both Kd and the number of binding sites (n) were altered. Both rat and human AFPs underwent changes in electrophoretic behaviour and loss of immunoreactivity with increasing NDGA, suggesting that NDGA binding induces conformational changes in the AFPs. However, equol did not alter the electrophoretic or immunological properties of either rat or human AFP, providing further evidence for qualitative differences in the effects of these diphenols. These findings indicate that phytoestrogens could play a role in AFP-dependent normal and pathological growth and development.

Bioactivation of xenobiotics by prostaglandin H synthase

Prostaglandin H synthase (PHS) catalyzes the oxidation of arachidonic acid to prostaglandin H2 in reactions which utilize two activities, a cyclooxygenase and a peroxidase. These enzymatic activities generate enzyme- and substrate-derived free radical intermediates which can oxidize xenobiotics to biologically reactive intermediates. As a consequence, in the presence of arachidonic acid or a peroxide source, PHS can bioactivate many chemical carcinogens to their ultimate mutagenic and carcinogenic forms. In general, PHS-dependent bioactivation is most important in extrahepatic tissues with low monooxygenase activity such as the urinary bladder, renal medulla, skin and lung. Mutagenicity assays are useful in the detection of compounds which are converted to genotoxic metabolites during PHS oxidation. In addition, the oxidation of xenobiotics by PHS often form metabolites or adducts to cellular macromolecules which are specific for peroxidase- or peroxyl radical-dependent reactions. These specific metabolites and/or adducts have served as biological markers of xenobiotic bioactivation by PHS in certain tissues. Evidence is presented which supports a role for PHS in the bioactivation of several polycyclic aromatic hydrocarbons and aromatic amines, two classes of carcinogens which induce extrahepatic neoplasia. It should be emphasized that the toxicities induced by PHS-dependent bioactivation of xenobiotics are not limited to carcinogenicity. Examples are given which demonstrate a role for PHS in pulmonary toxicity, teratogenicity, nephrotoxicity and myelotoxicity.

Effect of the tyrosine kinase inhibitor, genistein, on interleukin-1 stimulated PGE2 production in mesangial cells

Prostaglandin production and cAMP formation are two signaling pathways identified for IL-1, though neither adequately account for the multitude of effects of IL-1. To investigate the role of tyrosine phosphorylation in IL-1 signaling, we used the tyrosine kinase inhibitor, genistein. At 10-30 micrograms/ml, genistein blocked IL-1 stimulated prostaglandin production and induction of prostaglandin endoperoxide synthase (PES) in glomerular mesangial cells maintained in 10% serum. Addition of genistein hours after IL-1 addition also halted further PGE2 synthesis. Genistein failed to block PES activity in vitro, indicating it was not acting as a PES inhibitor. Overall these data suggest that tyrosine phosphorylation may be a required event for IL-1 stimulation of PGE2 and PES activity, either directly as part of IL-1 signaling, or indirectly as part of a serum/PDGF competence effect on mesangial cells.