Assessing the Toxicity of 17α-Ethinylestradiol in Rainbow Trout Using a 4‑Day Transcriptomics Benchmark Dose (BMD) Embryo Assay

There
is an urgent demand for more efficient and ethical approaches
in ecological risk assessment. Using 17α-ethinylestradiol (EE2)
as a model compound, this study established an embryo benchmark dose
(BMD) assay for rainbow trout (RBT; Oncorhynchus mykiss) to derive transcriptomic points-of-departure (tPODs) as an alternative
to live-animal tests. Embryos were exposed to graded concentrations
of EE2 (measured: 0, 1.13, 1.57, 6.22, 16.3, 55.1, and 169 ng/L) from
hatch to 4 and up to 60 days post-hatch (dph) to assess molecular
and apical responses, respectively. Whole proteome analyses of alevins
did not show clear estrogenic effects. In contrast, transcriptomics
revealed responses that were in agreement with apical effects, including
excessive accumulation of intravascular and hepatic proteinaceous
fluid and significant increases in mortality at 55.1 and 169 ng/L
EE2 at later time points. Transcriptomic BMD analysis estimated the
median of the 20th lowest geneBMD to be 0.18 ng/L, the most sensitive
tPOD. Other estimates (0.78, 3.64, and 1.63 ng/L for the 10th percentile
geneBMD, first peak geneBMD distribution, and median geneBMD of the
most sensitive over-represented pathway, respectively) were within
the same order of magnitude as empirically derived apical PODs for
EE2 in the literature. This 4-day alternative RBT embryonic assay
was effective in deriving tPODs that are protective of chronic effects
of EE2.