Interacting effects of tributyltin and 17β‐estradiol in male Chinese loach (Misgurnus anguillicaudatus)

In this study, male Chinese loaches in a semistatic waterborne exposure system were used to study the effects of tributyltin (TBT) on vitellogenin (Vtg) production induced by 17β‐estradiol (E2), TBT accumulation and distribution in tissues, and the effects of E2 on the distribution of TBT. The results demonstrate that TBT does not induce the synthesis of Vtg in male Chinese loach and that TBT could significantly inhibit Vtg production induced by E2, after exposure to binary mixtures of E2 and TBT for 14 days. TBT was found to accumulate in the liver, kidney, gills, intestines, and muscles of male Chinese loach, wherein the liver, kidney, gills, and intestines were found to have the most TBT accumulation. The existence of E2 did not significantly affect tissue distribution of TBT. © 2008 Wiley Periodicals, Inc. Environ Toxicol, 2009.     

Induction of the estrogen‐responsive genes encoding choriogenin H and L in the liver of male medaka (Oryzias latipes) upon exposure to estrogen receptor subtype‐selective ligands

Choriogenin (Chg) H and L are estrogen‐induced chorion precursors. We measured the induction of ChgH and ChgL mRNA in the livers of male medaka fish treated with Orthoester‐2k, a selective ligand for estrogen receptor (ER) α, and 2‐(4‐h ydroxyp henyl)‐5‐h ydroxy‐1,3‐b enzoxazole (HPHB), a selective ligand of ERβ. Although both ChgH and ChgL mRNA were induced by treatment with Orthoester‐2k or HPHB separately, their combination induced much greater expression of each Chg. ChgH expression correlated more closely with Orthoester‐2k dosage when combined with a small fixed dose of HPHB (1 μm ), whereas ChgL mRNA expression was more responsive to HPHB dose when combined with a fixed dose of Orthoester‐2k (2.8 nm ). Moreover, upon long‐term treatment with Orthoester‐2k, ChgH mRNA and ERα mRNA expression showed similar patterns with peak expression between days 6 and 10. These results imply that ERβ primarily regulates ChgL mRNA expression and ERα action primarily regulates ChgH mRNA expression. Thus, it is necessary to develop screening methods for fish ER subtype‐specific ligands. Copyright © 2014 John Wiley & Sons, Ltd.     

Validation of a new yeast‐based reporter assay consisting of human estrogen receptors α/β and coactivator SRC‐1: Application for detection of estrogenic activity in environmental samples

Endocrine disruptors are exogenous substances that act like hormones in the endocrine system and disrupt the physiologic function of endogenous hormones. In the present study, we established reporter yeast strains (Saccharomyces cerevisiae) expressing human estrogen receptors, ERα or ERβ. These strains contain a reporter plasmid carrying an estrogen responsive element (ERE) upstream of the β‐galactosidase gene, and a plasmid expressing a steroid receptor coactivator, SRC‐1e. Using these reporter strains, we demonstrated dose‐dependent estrogenic activities of different categories of ligands, a natural hormone, 17β‐estradiol (E2); a synthetic drug, diethylstilbestrol (DES); phytoestrogens, genistein, daizein and emodin; and an environmental endocrine disrupter, bisphenol A. EC₅₀ values of E2 for ERα and ERβ are 5.31 × 10^?10 and 5.85 × 10^?10 M, respectively. We also demonstrated that these yeasts were applicable for measuring estrogenic activities of environmental water samples. Most downstream sites of a river showed similar activity in both ERα and ERβ assays. These yeast strains are useful and convenient for detecting and comparing the estrogenic ligand activities of environmental samples in response to ERα and ERβ. © 2009 Wiley Periodicals, Inc. Environ Toxicol, 2009.     

Review of the effects of 17α‐estradiol in humans: a less feminizing estrogen with neuroprotective potential

17α‐Estradiol is a less feminizing isomer of the potent hormonal estrogen, 17β‐estradiol. 17α‐Estradiol is an orally active small molecule with conflicting reports of efficacy in preclinical models of degenerative diseases. A number of studies suggest neuroprotective potential in human neurodegenerative disorders, including Alzheimer's disease (AD) and Parkinson's disease. Several studies have established an antioxidant effect of 17α‐estradiol in humans. The sodium salt of 17α‐estradiol 3‐sulfate is a minor component (2.5–9.5%) of several widely marketed estrogen hormone replacement products, such as Premarin^®, that are approved by the U.S. Food and Drug Administration and have been prescribed and studied in women and men for more than 65 years. Most of the more than 100 published reports on the neurological effects of feminizing estrogens found positive responses in at least one measure relating to cognition or prevention and treatment of AD, notwithstanding the negative results in the Women's Health Initiative studies. Whether these limited, and often not statistically significant, findings are clinically meaningful remains unknown. In many in vitro and in vivo preclinical neuroprotection and related studies, 17α‐estradiol and 17β‐estradiol are active at similar concentrations and doses. However, 17α‐estradiol is less pleiotropic than 17β‐estradiol, and thus its potential toxicity might be lower. Given decades of mixed reports regarding the potential efficacy and safety of strongly feminizing hormones in neurodegenerative diseases, the weakly feminizing 17α‐estradiol might be a suitable candidate for clinical testing of the neuroprotective potential of this chemical class because it avoids, or significantly reduces, the adverse effects of potent hormonal compounds. Drug Dev Res 70:1–21, 2009. © 2009 Wiley‐Liss, Inc.     

A new [2H]‐labelled α‐trichloroimidate glucuronic ester for the synthesis of deuterated drug conjugates

A new reaction pathway for the synthesis of a [²H]‐labelled trichloroacetimidate precursor for the preparation of glucuronides is described. Therewith, stable isotope‐labelled drug glucuronides become accessible on a preparative scale, which can further be used as internal standards for quantitative analysis.     

Acute spill‐mimicking exposure effect of hexavalent chromium on the pituitary‐ovarian axis of a teleost,Channa punctatus (Bloch)

Acute exposure to hexavalent chromium (as 10, 20, and 40 mg/L potassium dichromate for 96 h) adversely affected the pituitary‐ovarian axis of a teleost Channa punctatus. The toxic impact of metal exposure on fish ovary was revealed in the form of increased percentage of atretic follicles, significantly in 20 mg/L and 40 mg/L exposure groups. The follicular atresia mostly occurred in vitellogenic (stage II and stage III) oocytes. Reduction of serum level of 17β‐estradiol was also significant in 20 mg/L and 40 mg/L exposure groups. The increase of LH‐immunointensity of pituitary gonadotrophs (LHβ‐immunoreactive cells) and their hypertrophy was evident, significantly in fish of 40 mg/L exposed group. Thus, the present acute metal spill‐mimicking laboratory study clearly demonstrated that short‐term exposures to high doses of hexavalent chromium may disrupt reproduction of the fish and affect their population. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 733–739, 2014.     

Synthesis and preliminary characterization of radioiodinated benzofuran‐3‐yl‐(indol‐3‐yl)maleimide derivatives as potential SPECT imaging probes for the detection of glycogen synthase kinase‐3β (GSK‐3β) in the brain

We report on the synthesis and preliminary characterization of two radioiodinated benzofuran‐3‐yl‐(indol‐3‐yl)maleimides, 3‐(benzofuran‐3‐yl)‐4‐(5‐[¹²⁵I]iodo‐1‐methyl‐1H‐indol‐3‐yl)‐1H‐pyrrole‐2,5‐dione ([¹²⁵I]5), and 3‐(5‐[¹²⁵I]iodo‐1‐methyl‐1H‐indol‐3‐yl)‐4‐(6‐methoxybenzofuran‐3‐yl)‐1H‐pyrrole‐2,5‐dione ([¹²⁵I]6), as the first potential SPECT imaging probes targeting glycogen synthase kinase‐3β (GSK‐3β). In this study, we used ¹²⁵I as a surrogate of ¹²³I because of its ease of use. The radioiodinated ligands were prepared from the corresponding tributyltin precursors through an iododestannylation reaction using hydrogen peroxide as an oxidant with a radiochemical yield of 10–30%. In vitro binding experiments suggested that both compounds show high affinity for GSK‐3β at a level similar to a known GSK‐3β inhibitor. Biodistribution studies with normal mice revealed that the radioiodinated compounds display sufficient uptake into (1.8%ID/g at 10 min postinjection) and clearance from the brain (1.0%ID/g at 60 min postinjection). These preliminary results suggest that the further optimization of radioiodinated benzofuran‐3‐yl‐(indol‐3‐yl)maleimide derivatives may facilitate the development of clinically useful SPECT imaging probes for the in vivo detection of GSK‐3β.     

Development of the Larval Amphibian Growth and Development Assay: effects of chronic 4‐tert‐octylphenol or 17β‐trenbolone exposure in Xenopus laevis from embryo to juvenile

The Larval Amphibian Growth and Development Assay (LAGDA) is a globally harmonized test guideline developed by the U.S. Environmental Protection Agency in collaboration with Japan's Ministry of the Environment. The LAGDA was designed to evaluate apical effects of chronic chemical exposure on growth, thyroid‐mediated amphibian metamorphosis and reproductive development. During the validation phase, two well‐characterized endocrine‐disrupting chemicals were tested to evaluate the performance of the initial assay design: xenoestrogen 4‐tert‐octylphenol (tOP) and xenoandrogen 17β‐trenbolone (TB). Xenopus laevis embryos were exposed, in flow‐through conditions, to tOP (nominal concentrations: 0.0, 6.25, 12.5, 25 and 50 µg l^–1) or TB (nominal concentrations: 0.0, 12.5, 25, 50 and 100 ng l^–1) until 8 weeks post‐metamorphosis, at which time growth measurements were taken, and histopathology assessments were made of the gonads, reproductive ducts, liver and kidneys. There were no effects on growth in either study and no signs of overt toxicity, sex reversal or gonad dysgenesis. Exposure to tOP caused a treatment‐related decrease in circulating thyroxine and an increase in thyroid follicular cell hypertrophy and hyperplasia (25 and 50 µg l^–1) during metamorphosis. Müllerian duct development was affected after exposure to both chemicals; tOP exposure caused dose‐dependent maturation of oviducts in both male and female frogs, whereas TB exposure caused accelerated Müllerian duct regression in males and complete regression in >50% of the females in the 100 ng l^–1 treatment. Based on these results, the LAGDA performed adequately to evaluate apical effects of chronic exposure to two endocrine‐active compounds and is the first standardized amphibian multiple life stage toxicity test to date. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.