Vitellogenin-inducing activities of natural, synthetic, and environmental estrogens in primary cultured Xenopus laevis hepatocytes

Endocrine disrupting effect and reproductive toxicity of the separate exposure and co-exposure of nano-polystyrene and diethylstilbestrol to zebrafish

The co-occurrence of nanoplastics and other pollutants in the environment has gotten a lot of attention, but information on the biological toxicity of their co-exposure was limited. This study aims to reveal the endocrine disrupting effect and reproductive toxicity of nano-polystyrene (NPS) and diethylstilbestrol (DES) to zebrafish under separate and combined exposure. Results indicated that NPS and DES exposure in isolation reduced the hepatosomatic index and gonadosomatic index, and altered the cell maturity in gonads in both cases. Even worse, the co-exposure of NPS and DES exacerbated the damage to the liver and gonads of fish. The two pollutants individually inhibited the secretion of sex hormones and vitellogenin. The inhibition effect of DES was especially dose-dependent, while NPS had weaker effect than DES. Their combined action on the secretion of sex hormones and vitellogenin exhibited additive effect. However, NPS did not affect the content of thyroid hormones in fish, and also had no significant effect on the reduction of thyroid hormone caused by DES exposure. Furthermore, their co-exposure decreased the cumulative eggs from 1031 to 306, and the spawning number from 12 to 8. The fertilization rate and hatchability rete of eggs were reduced by 30.9% and 40.4%, respectively. The abnormality rate of embryos was 65.0%, significantly higher than in separate DES and NPS groups (55.7% and 30.8% respectively). The abnormal development of offspring was mainly pericardial cyst, spinal curvature, and growth retardation.

Occurrence, sorption, and transformation of free and conjugated natural steroid estrogens in the environment

Natural steroid estrogens (NSEs), including free estrogens (FEs) and conjugated estrogens (CEs), are of emerging concern globally among public and scientific community due to their recognized adverse effects on human and wildlife endocrine systems in recent years. In this review, the properties, occurrence, sorption process, and transformation pathways of NSEs are clarified in the environment. The work comprehensively summarizes the occurrence of both free and conjugated estrogens in different natural and built environments (e.g., river, WWTPs, CAFOs, soil, and sediment). The sorption process of NSEs can be impacted by organic compounds, colloids, composition of clay minerals, specific surface area (SSA), cation exchange capacity (CEC), and pH value. The degradation and transformation of free and conjugated estrogens in the environment primarily involves oxidation, reduction, deconjugation, and esterification reactions. Elaboration about the major, subordinate, and minor transformation pathways of both biotic and abiotic processes among NSEs is highlighted. The moiety types and binding sites also would affect deconjugation degree and preferential transformation pathways of CEs. Notably, some intermediate products of NSEs still remain estrogenic potency during transformation process; the elimination of total estrogenic activity needs to be addressed in further studies. The in-depth researches regarding the behavior of both free and conjugated estrogens are further required to tackle their contamination problem in the ecosystem. Graphical abstract ᅟ.

Environmental Effects of BPA: Focus on Aquatic Species

Research on bisphenol A (BPA) as an environmental contaminant has now major regulatory implications toward the ecosystem health, and hence it is incumbent on scientists to do their research to the highest standards possible, in order that the most appropriate decisions are made to mitigate the impacts to aquatic wildlife. However, the contribution given so far appears rather fragmented. The present overview aims to collect available information on the effects of BPA on aquatic vertebrates and invertebrates to provide a general scenario and to suggest future developments toward more comprehensive approaches useful for aquatic species protection.

Vitellogenin of the northern leopard frog (Rana pipiens): development of an ELISA assay and evaluation of induction after immersion in xenobiotic estrogens

An immunoassay for leopard frog (Rana pipiens) vitellogenin was developed for studying endocrine disruption. Male frogs were injected with estradiol-17β to stimulate vitellogenin for purification. SDS-PAGE revealed high amounts of a 170-180 kDa protein, which was confirmed to be vitellogenin by Western blotting. Vitellogenin was purified by DEAE chromatography and used to generate a polyclonal antibody. A competitive ELISA was developed for leopard frog vitellogenin with a detection limit of 6.0 ng mL(-1) and a working range of 20-1000 ng mL(-1). The intra-assay coefficient of variation averaged 5.47% for control sera and 9.71% for estrogen-treated sera. The inter-assay coefficient of variation averaged 8.21% for control sera and 9.93% for estrogen-treated sera. Recovery of purified vitellogenin averaged 95.2%. Vitellogenin was measured in male frogs immersed in the estrogenic compound diethylstilbestrol (DES) for various times and doses. Serum vitellogenin was detected within five days after immersion in 1.0 mg L(-1) DES and levels continued to increase through 20 d. In a 20-day dose-response experiment, serum vitellogenin was detected in frogs immersed in 0.01 mg L(-1) DES and vitellogenin concentration increased with dose. Immersion of frogs in one of several xenobiotic estrogens (nonylphenol, octylphenol, bisphenol-A) for 20 d did not increase vitellogenin for any treatment, suggesting that this frog may be less sensitive than fish to endocrine disruptors. Vitellogenin induction in R.pipiens may be a useful amphibian model system for field studies of endocrine disruption, due to its broad geographic range.

Alternatives to in vivo tests to detect endocrine disrupting chemicals (EDCs) in fish and amphibians--screening for estrogen, androgen and thyroid hormone disruption

Endocrine disruption is considered a highly relevant hazard for environmental risk assessment of chemicals, plant protection products, biocides and pharmaceuticals. Therefore, screening tests with a focus on interference with estrogen, androgen, and thyroid hormone pathways in fish and amphibians have been developed. However, they use a large number of animals and short-term alternatives to animal tests would be advantageous. Therefore, the status of alternative assays for endocrine disruption in fish and frogs was assessed by a detailed literature analysis. The aim was to (i) determine the strengths and limitations of alternative assays and (ii) present conclusions regarding chemical specificity, sensitivity, and correlation with in vivo data. Data from 1995 to present were collected related to the detection/testing of estrogen-, androgen-, and thyroid-active chemicals in the following test systems: cell lines, primary cells, fish/frog embryos, yeast and cell-free systems. The review shows that the majority of alternative assays measure effects directly mediated by receptor binding or resulting from interference with hormone synthesis. Other mechanisms were rarely analysed. A database was established and used for a quantitative and comparative analysis. For example, a high correlation was observed between cell-free ligand binding and cell-based reporter cell assays, between fish and frog estrogenic data and between fish embryo tests and in vivo reproductive effects. It was concluded that there is a need for a more systematic study of the predictive capacity of alternative tests and ways to reduce inter- and intra-assay variability.

Molecular cloning and mRNA expression of the vitellogenin and nuclear receptor gene induced by 17β-estradiol in the mud carp, Cirrhinus molitorella

Vitellogenins (VTGs), the precursors of yolk proteins, are crucial for the embryonic development of teleosts, and have also been studied extensively as biomarkers for environmental estrogenic mimics. The cDNA of a VTG was isolated from the liver of male mud carp (Cirrhinus molitorella) following induction by 17β-estradiol (E(2)) using 3'- and 5'-RACE methods. It was 4,216 bp in length, and encoded a putative protein of 1,342 amino acids. This putative VTG contained complete portions of lipovitellin I (LVI) and phosvitin, but lacked the C-terminal half of LVII and was thus classed as a type I vitellogenin. In addition, the partial cDNA of estrogen receptors (ERα and ERβ) and androgen receptors (AR) were cloned. The mRNA expression of VTG, ERα, ERβ and AR were examined in the liver of juvenile mud carp exposed to E(2) (0, 5, 50 and 500 ng/l) in the water for 2, 4, 6 and 8 days. Quantitative reverse transcription PCR (RT-PCR) revealed a significant increase in transcript levels of VTG and ERα but not of ERβ and AR. VTG and ERα were expressed in a time-dose-dependent manner. Our results imply that ERα may be the principal subtype that regulates VTG, and that VTG mRNA of mud carp is an ideal biomarker to detect environmental estrogens.

Effects of 4-tert-octylphenol on Xenopus tropicalis in a long term exposure

Endocrine disrupting chemicals that activate the estrogen receptor are routinely detected in the environment and are a concern for the health of both exposed humans and indigenous wildlife. We exposed the western clawed frog (Xenopus tropicalis) to the weak estrogen octylphenol from Nieuwkoop-Faber (NF) stage 46 tadpoles through adulthood in order to document the effects of a weak estrogen on the life history of an amphibian species. Frogs were exposed to 1, 3.3, 11 and 36 μg/L octylphenol in a continuous flow-through water system. Just prior to completion of metamorphosis (NF 65), a random subsample of froglets was collected and assessed, while the remaining frogs received continued exposure through 31 weeks of exposure when the remaining animals were sampled. Significant induction of the female egg yolk protein precursor vitellogenin was observed in the high treatment at the larval subsampling for both males and females, but not at the final sampling for either sex. No significant deviation from the control sex ratio was observed for either sampling period, suggesting minimal to no effect of octylphenol exposure on gonad differentiation. No effects in the adult frogs were observed for mortality, body mass and size, liver somatic index, estradiol and testosterone serum levels, sperm counts, or oocyte counts. The development and growth of oviducts, a female-specific secondary sex characteristic, was observed in males exposed to octylphenol. These results indicate that octylphenol exposure can induce vitellogenin in immature froglets and the development of oviducts in male adult frogs. The lack of effect observed on the developing gonads suggests that in amphibians, secondary sex characteristics are more susceptible to impact from estrogenic compounds than the developing gonads.

Assessing combined toxicity of estrogen receptor agonists in a primary culture of rainbow trout (Oncorhynchus mykiss) hepatocytes

The presence of highly complex mixtures of chemicals in the environment challenges our ability to assess single chemical effects and the interaction that occurs with cellular receptor targets and regulation of endocrine processes. In this study concentration addition (CA) and independent action (IA) prediction models were used to assess the combined toxicity of mixtures of environmental relevant estrogen receptor (ER) agonists (hormones and anthropogenic pollutants) in a primary culture of rainbow trout (Oncorhynchus mykiss) hepatocytes using the ER-mediated production of vitellogenin (Vtg) as a biological marker (biomarker) for estrogenicity. Nine of the eleven tested chemicals induced the production of Vtg and the parameters from the fitted concentration-response curves were used to model four mixtures containing four (17β-estradiol, estrone, estriol and diethylstilbestrol), five (musk ketone, 4-tert-octylphenol, bisphenol A, o,p'-DDT and dibenzothiophene), seven (17β-estradiol, estrone, estriol, diethylstilbestrol, 4-tert-octylphenol, bisphenol A and o,p'-DDT) and nine compounds (17β-estradiol, estrone, estriol, diethylstilbestrol, musk ketone, 4-tert-octylphenol, bisphenol A, o,p'-DDT and dibenzothiophene). The CA and IA prediction model proved to be a good estimation for the combined effect of mixtures of ER agonists at low relative mixture concentration (e.g. relative to the maximum mixture concentrations used), but a deviation from the prediction models was observed when exposing hepatocytes to high relative mixture concentrations. The CA and IA prediction models' ability to predict the combined estrogenic effect of complex mixtures, especially in the low concentration-response range, is of ecological relevance since organisms in the environment generally encounter low concentrations of chemicals from a wide array of chemical groups that may not elicit estrogenic effects on their own.