2 research outputs found
Estrogenic Mechanisms and Cardiac Responses Following Early Life Exposure to Bisphenol A (BPA) and Its Metabolite 4‑Methyl-2,4-bis(<i>p</i>‑hydroxyphenyl)pent-1-ene (MBP) in Zebrafish
Environmental
exposure to Bisphenol A (BPA) has been associated
with a range of adverse health effects, including on the cardiovascular
system in humans. Lack of agreement on its mechanism(s) of action
likely stem from comparisons between in vivo and in vitro test systems
and potential multiple effects pathways. In rodents, in vivo, metabolic
activation of BPA produces 4-methyl-2,4-bisÂ(4-hydroxyphenyl)Âpent-1-ene
(MBP), which is reported to be up to 1000 times more potent as an
estrogen than BPA. We investigated the estrogenic effects and estrogen
receptor signaling pathway(s) of BPA and MBP following early life
exposure using a transgenic, estrogen responsive (ERE-TG) zebrafish
and a targeted morpholino approach to knockdown the three fish estrogen
receptor (ER) subtypes. The functional consequences of BPA exposure
on the cardiovascular system of zebrafish larvae were also examined.
The heart atrioventricular valves and the <i>bulbus arteriosus</i> were primary target tissues for both BPA and MBP in the ERE-TG zebrafish,
and MBP was approximately 1000-fold more potent than BPA as an estrogen
in these tissues. Estrogen receptor knockdown with morpholinos indicated
that the estrogenic responses in the heart for both BPA and MBP were
mediated via an estrogen receptor 1 (esr1) dependent pathway. At the
highest BPA concentration tested (2500 ÎĽg/L), alterations in
the atrial:ventricular beat ratio indicated a functional impact on
the heart of 5 days post fertilization (dpf) larvae, and there was
also a significantly reduced heart rate in these larvae at 14 dpf.
Our findings indicate that some of the reported adverse effects on
heart function associated with BPA exposure (in mammals) may act through
an estrogenic mechanism, but that fish are unlikely to be susceptible
to adverse effects on heart development for environmentally relevant
exposures
High-Content and Semi-Automated Quantification of Responses to Estrogenic Chemicals Using a Novel Translucent Transgenic Zebrafish
Rapid
embryogenesis, together with genetic similarities with mammals,
and the desire to reduce mammalian testing, are major incentives for
using the zebrafish model in chemical screening and testing. Transgenic
zebrafish, engineered for identifying target gene expression through
expression of fluorophores, have considerable potential for both high-content
and high-throughput testing of chemicals for endocrine activity. Here
we generated an estrogen responsive transgenic zebrafish model in
a pigment-free “Casper” phenotype, facilitating identification
of target tissues and quantification of these responses in whole intact
fish. Using the ERE-GFP-Casper model we show chemical type and concentration
dependence for green fluorescent protein (GFP) induction and both
spatial and temporal responses for different environmental estrogens
tested. We also developed a semiautomated (ArrayScan) imaging and
image analysis system that we applied to quantify whole body fluorescence
responses for a range of different estrogenic chemicals in the new
transgenic zebrafish model. The zebrafish model developed provides
a sensitive and highly integrative system for identifying estrogenic
chemicals, their target tissues and effect concentrations for exposures
in real time and across different life stages. It thus has application
for chemical screening to better direct health effects analysis of
environmental estrogens and for investigating the functional roles
of estrogens in vertebrates