Activated estrogens and antiestrogens: a 30-year journey with David Kupfer

David Kupfer had a passion for drug metabolism and used his talents to understand the putative metabolic activation of the insecticides o, p'DDT and methoxychlor to estrogens. His research helped to create a scientific foundation for the current interest in endocrine disruption. With the increasing clinical significance of tamoxifen in the late 1980s, and the proposal to test tamoxifen as a breast cancer chemopreventive in healthy women, David initiated laboratory studies on the mechanisms of tamoxifen metabolism. He was the first to note that tamoxifen is metabolically activated to alkylating species. Tamoxifen and insecticides covalently bind to microsomal proteins. His contribution presaged worldwide studies of the induction of rat liver carcinogenesis by tamoxifen.     

Isolation and quantitative analysis of cryptotanshinone,an active quinoid diterpene formed in callus of Salvia miltiorrhiza BUNGE

Effect of N(6)-benzyladenine (BA) on tanshinone formation in callus cultures of Salvia miltiorrhiza was examined in an attempt to increase the productivity of the medicinal compound, cryptotanshinone. Primary callus was induced by culturing leaf explants on Murashige and Skoog's (MS) basal medium supplemented with 1.0 mg l(-1) of 2,4-dichlorophenoxyacetic acid (2,4-D) in darkness. The callus proliferated further on MS basal medium containing 1.0 mg l(-1) 2,4-D and 0.5 mg l(-1) BA and was analyzed for cryptotanshinone by high performance liquid chromatography (HPLC). The HPLC results indicated that it contained small amounts of cryptotanshinone (0.26+/-0.05 mg/g dry wt). Omission of 2,4-D from the medium resulted in a marked increase in the content of cryptotanshinone in callus. The HPLC analysis revealed that the content of cryptotanshinone in the callus cultured on the MS basal medium supplemented with 0.1, 0.2, 0.5, 1.0, and 2.0 mg l(-1) of BA was significantly higher than the marketed crude drug (processed underground parts of S. miltiorrhiza). Maximum yield of cryptotanshinone (4.59+/-0.09 mg/g dry wt) was observed in the callus cultured on MS basal medium supplemented with 0.2 mg l(-1) BA for 60 d. Cryptotanshinone was isolated from callus through silica gel column chromatography followed by preparative TLC and characterized based on NMR and mass spectral data.     

Prooxidant activity and cellular effects of the phenoxyl radicals of dietary flavonoids and other polyphenolics

Dietary polyphenolics in fruits, vegetables, wines, spices and herbal medicines have beneficial antioxidant, anti-inflammatory and anticancer effects. However, we have observed that dietary polyphenolics with phenol rings were metabolized by peroxidase to form prooxidant phenoxyl radicals which, in some cases were sufficiently reactive to cooxidize GSH or NADH accompanied by extensive oxygen uptake and reactive oxygen species formation. The order of catalytic effectiveness found for oxygen activation when polyphenolics were metabolized by peroxidase in the presence of GSH was phloretin>phloridzin>4,2'-dihydroxy chalcone>p-coumaric acid>naringenin>apigenin>curcumin>resveratrol>isoliquiritigenin>capsaicin>kaempferol. Ascorbate was also cooxidized by the phenoxyl radicals but without oxygen activation. Polyphenolics with catechol rings also cooxidized ascorbate, likely mediated by semiquinone radicals. The order of catalytic effectiveness found for ascorbate cooxidation was fisetin luteolin, quercetin, >eriodictyol, caffeic acid, nordihydroguaiaretic acid>catechin>taxifolin, catechol. NADH was stoichiometrically oxidized without oxygen uptake which, suggests that o-quinone metabolites were responsible. GSH was not cooxidized and GSH conjugates were formed, likely mediated by the o-quinone metabolites. Incubation of hepatocytes with dietary polyphenolics containing phenol rings was found to partially oxidize hepatocyte GSH to GSSG while polyphenolics with a catechol ring were found to deplete GSH through formation of GSH conjugates. Dietary polyphenolics with phenol rings also oxidized human erythrocyte oxyhemoglobin and caused erythrocyte hemolysis more readily than polyphenolics with catechol rings. It is concluded that polyphenolics containing a phenol ring are generally more prooxidant than polyphenolics containing a catechol ring.     

Effects of estrogens and antiestrogens on gene expression of fathead minnow (Pimephales promelas) early life stages

Endocrine disrupting chemicals (EDCs) are known to contaminate aquatic environments and alter the growth and reproduction of organisms. The objective of this study was to evaluate the sensitivity and utility of fathead minnow (Pimephales promelas) early life‐stages as a model to measure effects of estrogenic and antiestrogenic EDCs on physiological and gene expression endpoints relative to growth and reproduction. Embryos (<24‐h postfertilization, hpf) were exposed to a potent estrogen (17α‐ethinyl estradiol, EE₂, 2, 10, and 50 ng L^?1); a weak estrogen (mycotoxin zearalenone, ZEAR, same concentrations as above); an antiestrogen (ZM 189, 154; 40, 250, and 1000 ng L^?1); and to mixtures of EE₂ and ZM until swim‐up stage (～170 hpf). Exposure to all concentrations of ZEAR and to the lowest concentration of ZM resulted in increased body sizes, whereas high concentrations of EE₂ decreased body sizes. There was a significant increase in the frequency of abnormalities (mostly edema) in larvae exposed to all concentrations of EE₂, and high ZEAR, and EE₂ + ZM mixture groups. Expression of growth hormone was upregulated by most of the conditions tested. Exposure to 50 ng L^?1 ZEAR caused an induction of insulin‐like growth factor 1, whereas exposure to 40 ng L^?1 ZM caused a downregulation of this gene. Expression of steroidogenic acute regulatory protein gene was significantly upregulated after exposure to all concentrations of EE₂ and luteinizing hormone expression increased significantly in response to all treatments tested. As expected, EE₂ induced vitellogenin expression; however, ZEAR also induced expression of this gene to similar levels compared to EE₂. Overall, exposure to EE₂ + ZM mixture resulted in a different expression pattern compared to single exposures. The results of this study suggest that an early life stage 7‐day exposure is sufficient to recognize and evaluate effects of estrogenic compounds on gene expression in this fish model. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2009.     

Leptin, estrogens and cancer

Obesity is a state of leptin resistance in which the membrane leptin receptor and the JAK-STAT pathway are blocked. This leads to increased intracellular concentrations of lipid metabolites, increased non-oxidative metabolism by adipocytes, and stimulation of the cell estrogen cycle. These factors are potentially oncogenic via the shared mitogen-activated protein kinase (MAPK), mitogen/extracellular signal-regulated kinase (MEK) and extracellular signal-regulated kinase (ERK) cellular pathways.     

Estrogens and antiestrogens activate hPXR

The pregnane X receptor (PXR, NR1I2) and the estrogen receptors (ERalpha, NR3A1 and ERbeta, NR3A2) bind a large number of compounds, including environmental pollutants and drugs, which exhibit remarkably diverse structural features. This prompted us to investigate if ER ligands could be PXR activators. We focused our attention on known estrogens from various chemical classes: physiological and synthetic estrogens and antiestrogens, plant and fungus estrogens, and other man-made chemicals belonging to phthalate plasticizers, surfactant-derived alkylphenols and cosmetics. Altogether, nearly 50 compounds were thus analyzed for their ability to activate human PXR in stably transfected cells, HGPXR cells, derived from HeLa cells and expressing luciferase under the control of a chimeric hPXR. Some of the newly identified hPXR activators were also checked for their ability to induce cytochrome P450 3A4 and 2B6 expressions in a primary culture of human hepatocytes. A significant proportion (54%) of compounds with estrogenic activity or able to bind ER were found to be hPXR activators: in particular, antiestrogens, mycoestrogens and phthalates. An even greater proportion is observed if estrogenic pesticides are included. Altogether, these results raise the question of the meaning and consequences of compounds with double PXR/ER activation ability.     

An oxygen-bonded c8-deoxyguanosine nucleoside adduct of pentachlorophenol by peroxidase activation: evidence for ambident c8 reactivity by phenoxyl radicals

The ability of the carcinogenic environmental toxin pentachlorophenol (PCP, 1) to react with DNA bases has been assessed using MS and NMR. Treatment of PCP (100 microM) with horseradish peroxidase (HRP/H(2)O(2)) or myeloperoxidase (MPx/H(2)O(2), from human leukocytes) in the presence of excess deoxyguanosine (dG, 2 mM) led to the isolation and identification of the oxygen-bonded C8-dG nucleoside adduct 4. The reaction was absolutely specific for dG; no detectable adduct(s) was observed from HRP/H(2)O(2) and PCP in the presence of deoxyadenosine, deoxycytidine, or thymidine. Formation of 4 was also specific for peroxidase activation that is known to oxidize PCP into the phenoxyl radical. Treatment of PCP/dG with rat liver microsomes (RLM) failed to generate 4; instead, an adduct derived from the benzoquinone electrophile tetrachloro-1,4-benzoquinone (chloranil) was observed in the extracted ion chromatogram from the RLM/NADPH-treated PCP/dG sample. The adduct 4 is the first structurally characterized O-bonded phenolic DNA nucleoside adduct and highlights the ambident electrophilicity of phenoxyl radicals (O- vs C-) in reaction at C8 of dG, as we have previously demonstrated that the para-chlorophenolic toxin, ochratoxin A (2), reacts at C8 of dG to give the C-bonded adduct 3 via the intermediacy of the OTA phenoxyl radical. Given that PCP is known to induce DNA adduct formation in vivo and human exposure has been linked to incidences of leukemia, the adduct 4 could play a key role in PCP-mediated carcinogenesis.     

Transdermal delivery of highly lipophilic drugs: in vitro fluxes of antiestrogens,permeation enhancers,and solvents from liquid formulations

Purpose. Highly lipophilic basic drugs, the antiestrogens AE 1 (log P = 5.82) and AE 2 (log P = 7.8) shall be delivered transdermally. Methods. Transdermal permeation of drugs, enhancers, and solvents from various fluid formulations were characterized by in-vitro permeation studies through excised skin of hairless mice. Furthermore, differential scanning calorimetry (DSC) measurements of skin lipid phase transition temperatures were conducted. Results. Transdermal flux of highly lipophilic drugs was extraordinarily enhanced by the unique permeation enhancer combination propylene glycol-lauric acid (9 + 1): steady-state fluxes of AE 1 and AE 2 were as high as 5.8 g·cm^–2·h^–1 and 3.2 g·cm^–2·h^–1, respectively. This dual enhancer formulation also resulted in a marked increase in the transdermal fluxes of the enhancers. Furthermore, skin lipid phase transition temperatures were significantly reduced by treatment with this formulation. Conclusion. Transdermal delivery of highly lipophilic drugs can be realized by using the permeation enhancer combination propylene glycol-lauric acid. The extraordinary permeation enhancement for highly lipophilic drugs by this formulation is due to mutual permeation enhancement of these two enhancers and their synergistic lipid-fluidising activity in the stratum corneum.     

Synthesis and biological activity of new halo-steroidal antiestrogens

Antiestrogen therapy is the most widely used endocrine manipulation for the treatment of breast cancer, especially in postmenopausal women. Unfortunately, the compounds presently available possess mixed agonistic/antagonistic activity, thus potentially limiting their therapeutic efficacy. Following the observations that an aliphatic chain at the 7 alpha-position of 17 beta-estradiol does not prevent binding to the estrogen receptor while halogenation of estradiol can increase the affinity of its binding (expressed as RBA) to the estrogen receptor, we have synthesized a series of new steroidal antiestrogens (6-10) which possess both an 7 alpha-undecanamide group and an halogen atom (Cl, Br, or I) at the 16 alpha-position. The stereochemistry of these compounds was unambiguously established by high-field (400-MHz) nuclear magnetic resonance. Some of the compounds obtained possess potent in vivo antiestrogenic activity. At the low twice daily 3-micrograms dose, 16 alpha-chloro 3,17 beta-diol amide, 16 alpha-iodo 3,17 beta-diol amide, 16 alpha-bromo 3,17 beta-diol amide, 16 alpha-chloro 3,17 alpha-diol amide, and 16 alpha-bromo 3,17 alpha-diol amide inhibit by 74, 63, 52, 35, and 60%, respectively, the estradiol-induced stimulation of uterine weight in ovariectomized Balb/c mice while 78-99% blockade of estradiol action is achieved at the 20-micrograms dose. These new antiestrogens show no estrogenic activity on uterine weight at the doses used while tamoxifen (2-[4-(1,2-diphenyl-1-butenyl)phenoxy]-N,N- dimethylethanamine) shows full estrogenic activity and is only a weak partial antiestrogen in the same assay.     

Influence of alkyl chain ramification on estradiol receptor binding affinity and intrinsic activity of 1,2-dialkylated 1,2-bis(4- or 3-hydroxyphenyl)ethane estrogens and antiestrogens

The influence of a symmetrical introduction of CH3 substituents in the alpha or beta positions of the 1,2-dialkyl-1,2-bis(4-hydroxyphenyl)ethane estrogens hexestrol (ethyl, HES) and octestrol (n-propyl, OCES) [isopropyl (1), tert-butyl (2), sec-butyl (3), isobutyl (4)] and the 1,2-dialkyl-1,2-bis(3-hydroxyphenyl)ethane antiestrogens metahexestrol (ethyl, MetaHES) and metaoctestrol (n-propyl, MetaOCES) [isopropyl (5), tert-butyl (6), sec-butyl (7), isobutyl (8)] on estradiol receptor (E2R) binding affinity and intrinsic activity is described. The synthesis of compounds 1-8 was accomplished by reductive coupling of (a) the corresponding alpha-alkylbenzyl alcohols with TiCl3/LiAlH4 and separation of the meso diastereoisomers (compounds 2-4, 7, and 8), (b) alpha-tert-butyl-3-methoxybenzyl chloride with CoCl2/EtMgCl and isolation of the meso configurated isomer (6), and (c) the isopropyl phenyl ketones with TiCl4/Zn and subsequent hydrogenation of the corresponding cis-hex-3-enes (compounds 1 and 5). The binding affinity of 1-8 to the calf uterine E2R was measured relative to that of [3H]E2 by a competitive binding assay. Compounds 1 and 5 showed relative binding affinity (RBA) values exceeding those of HES and MetaHES, respectively. All other derivatives showed RBA values smaller than the corresponding parent compounds. The intrinsic activity was monitored in terms of uterotrophic and antiuterotrophic activity. It is striking that the introduction of a CH3 group in the alpha positions of MetaHES and MetaOCES led to compounds with full intrinsic activity (5-7), i.e., estrogens without antiestrogenic properties. No correlation between E2R binding affinity and intrinsic activity was found.     

Detection of free radicals formed by in vitro metabolism of fluoride using EPR spectroscopy

In many parts of the globe, where water contains large amount of fluoride, fluorosis is a serious public health problem. It is accompanied by many changes, not only in the bones, but practically in all organs of the body. Since it was discovered that oxidation stress, together with the peroxidation of lipids which accompanies it, results in many diseases, research has been carried out on this aspect of fluorosis. The findings, however, are incomplete and divergent. The aim of our study was to determine the presence of free radicals in hepatocytes exposed to fluoride in concentrations which do not lead to changes in the concentrations of calcium and magnesium ions.Free radical properties of hepatocytes incubated with fluoride were studied by an X-band electron paramagnetic resonance (EPR) spectroscopy. Hepatocytes are paramagnetic and broad unsymmetrical EPR spectra were obtained for them. Oxygen free radicals with g-factor of 2.0032 exist in hepatocytes. The effect of fluoride concentration and the time of incubation on free radicals amount in cells were examined. The amount of free radicals in hepatocytes increases with the increase of fluoride concentration for all the incubation times (10, 30, and 60 min). The amount of free radicals in hepatocytes decreases with the increase of time of incubation for all the used fluoride concentrations (0.002, 0.082, and 0.164 mmol/l). EPR spectra of the studied cells are homogeneously broadened. Continuous microwave saturation of EPR lines indicates that slow spin–lattice relaxation processes exist in the studied cells. Strong dipolar interactions responsible for the broadening (ΔB_pp: 1.45–1.87 mT) of the EPR spectra exist in the hepatocytes.     

Maternal and developmental toxicity in mice by aminophenylnorharman,formed from norharman and aniline

9-(4'-Aminophenyl)-9H-pyrido [3,4-b] indole (aminophenylnorharman, APNH) is a novel mutagenic heterocyclic amine, produced by the reaction of norharman with aniline in the presence of S9 mix. In the present study, the maternal and developmental toxicity of APNH were investigated in ICR mice administered oral doses of 0, 0.625, 1.25, 2.5 or 5 mg/kg/day on gestational days (GD) 6 through 15 or 0, 5, 10, or 20 mg/kg on GD 12. Maternal and foetal parameters were evaluated on day 18 of gestation. Foetuses of dams treated on GD 6-15 were examined for external and skeletal malformations and variations, and foetuses of dams treated on GD 12 were inspected for cleft palate. Maternal death occurred when APNH was administered at 5 mg/kg/day on GD 6-15. No significant decrease in body weight gain during the administration period was observed at doses of 2.5 mg/kg/day or less when applied on GD 6-15. Adverse changes in general condition of dams were observed in the groups treated at doses of 2.5 mg/kg/day and above on GD 6-15, whereas no adverse effects on dams were noted even when APNH was applied at a fairly high dose on GD 12. Intracytoplasmic vacuolation in hepatocytes, necrosis of proximal tubular epithelial cells and desquamation of necrotic epithelial cells in the tubular lumen were observed in dams treated with APNH at 2.5 or 5 mg/kg/day on GD 6-15. Increased preimplantation loss was observed at 5 mg/kg/day and post-implantation loss was observed at 2.5 mg/kg/day and above when applied on GD 6-15, or at 20 mg/kg when applied on GD 12. Foetal body weight was decreased by APNH in a dose-dependent manner. The frequency of external malformations (cleft palate) was significantly increased in the group treated with APNH at 2.5 mg/kg/ day on GD 6-15 compared to the controls. However, there were no foetuses with cleft palate even when APNH was given at 20 mg/kg on GD 12. No significant increases in skeletally malformed foetuses were found in any APNH-treated group. The frequency of lumbar ribs was increased dose dependently. This study demonstrated the developmental toxicity of a mutagenic compound, APNH, in mice at maternally toxic doses, and that cleft palate observed in term foetuses resulted from the adverse effect of APNH on the maternal environment during organogenesis. More detailed studies are warranted to assess the possible risks to pregnant women from exposure to APNH.     

Metabolism of stilbene estrogens and steroidal estrogens in relation to carcinogenicity

The oxidative metabolism of diethylstilbestrol (DES) and 17-ethynyl estradiol, as examples of stilbene- and steroid-type estrogens, is discussed with respect to the formation of reactive intermediates. For DES, a genotoxic potential is implied by metabolic studies and positive effects in short-term tests for genetic damage. A particularly important pathway for DES carcinogenicity appears to be peroxidase-mediated oxidation. Although data for steroidal estrogens are more ambiguous, the available evidence suggests that metabolic activation by peroxidatic oxidation may also be of importance for this class of estrogens.Abbreviations DES diethylstilbestrol, 3,4-bis-(p-hydroxyphenyl)hex-3-ene - E-DES trans-diethylstilbestrol - Z-DES cis-diethylstilbestrol - DIES dienestrol, 3,4-bis-(p-hydroxyphenyl)-hexa-2,4-diene (nomenclature of DES metabolites according to the system of Metzler and McLachlan 1978a) - E₁ estrone - E₂ estradiol-17ß - EE₂ 17-ethynylestradiol - 7,8-BF 7,8-benzoflavone - GC gas chromatography - HPLC high performance liquid chromatography - MS mass spectrometry Paper presented at the Satellite Symposium of the 24th Congress of the European Society of Toxicology, Rome, March 29, 1983     

Quantification of total oxidant scavenging capacity of antioxidants for peroxynitrite, peroxyl radicals, and hydroxyl radicals

We have extended the application of our previously reported total oxidant scavenging capacity (TOSC) assay (Winston et al., Free Radical Biol. Med. 24, 480-493, 1998) to permit facile quantification of the absorbance capacity of antioxidants toward three potent oxidants, i.e., hydroxyl radicals, peroxyl radicals, and peroxynitrite. Respectively, these oxidants were generated by the iron plus ascorbate-driven Fenton reaction, thermal homolysis of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (ABAP), and 3-morpholinosydnonimine N-ethylcarbamide (SIN-1). Each of these oxidants reacts with alpha-keto-gamma-methiolbutyric acid (KMBA), which is oxidized and yields ethylene. The antioxidant capacity of the compounds tested is quantified from their ability to inhibit ethylene formation relative to a control reaction. Assay conditions were established in which control reactions give comparable yields of ethylene with each of the oxidants studied. Thus, the relative efficiency of various antioxidants could be compared under conditions of quantitatively similar KMBA oxidizing capability by the three oxidants. Reduced glutathione was an efficient scavenger of peroxyl radicals, but scavenged peroxynitrite and hydroxyl radicals relatively poorly. Uric acid, Trolox, and ascorbic acid were comparable scavengers of peroxynitrite and peroxyl radicals. Uric acid and Trolox were approximately an order of magnitude less efficient as scavengers of hydroxyl radicals. The classical hydroxyl radical scavenging agents mannitol, dimethyl sulfoxide, and benzoic acid had much higher TOSC values with hydroxyl than with peroxyl radicals or peroxynitrite. The very different chemical reactivity toward KMBA by the SIN-1- and iron-ascorbate-generated oxidants indicates that hydroxyl radical is not a major oxidant produced by the SIN-1 system. The data show that the TOSC assay is useful and robust in distinguishing the reactivity of various oxidants and the relative capacities of antioxidants to scavenge these oxidants.