Systematic Assessment of Exposure Variations on Observed Bioactivity in Zebrafish Chemical Screening

Abstract

The embryonic zebrafish is a powerful tool for high-throughput screening of chemicals. While this model has significant potential for use in safety assessments and chemical prioritization, a lack of exposure protocol harmonized across laboratories has limited full model adoption. To assess the potential that exposure protocols alter chemical bioactivity, we screened a set of eight chemicals and one 2D nanomaterial across four different regimens: (1) the current Tanguay laboratory’s standard protocol of dechorionated embryos and static exposure in darkness; (2) exposure with chorion intact; (3) exposure under a 14 h light: 10 h dark cycle; and (4) exposure with daily chemical renewal. The latter three regimens altered the concentrations, resulting in bioactivity of the test agents compared to that observed with the Tanguay laboratory’s standard regimen, though not directionally the same for each chemical. The results of this study indicate that with the exception for the 2D nanomaterial, the screening design did not change the conclusion regarding chemical bioactivity, just the nominal concentrations producing the observed activity. Since the goal of tier one chemical screening often is to differentiate active from non-active chemicals, researchers could consider the trade-offs regarding cost, labor, and sensitivity in their study design without altering hit rates. Taken further, these results suggest that it is reasonably feasible to reach agreement on a standardized exposure regiment, which will promote data sharing without sacrificing data content.

A Comparative Multi-System Approach to Characterizing Bioactivity of Commonly Occurring Chemicals

“…Multiple studies suggest BHT is toxic, with a 96-h LC50 ranging from ~20–60 µM and larval behavior being affected at as low as 1 µM [ 57 , 61 ]; however, a separate study did not find significant lethality up to 200 µM, though physical malformations were observed below 100 µM [ 58 ]. The inconsistency between our findings and those of previous studies may be attributed to variable exposure conditions, including chorion status and exposure in pools versus individual wells, both of which can affect the actual internal dose of a chemical [ 62 , 63 , 64 ]. Additionally, while the developmental zebrafish model is highly sensitive to detecting bioactive chemicals, whole-animal bioactivity screening does not provide mechanistic information about a chemical.…”

Predictive Capability of QSAR Models Based on the CompTox Zebrafish Embryo Assays: An Imbalanced Classification Problem

“…Furthermore, zebrafish dechorionated embryos (CompTox ZF; [ 18 ]) are more sensitive to chemicals exposure in comparison to chorionated embryos. The presence [ 51 , 52 , 53 ] or absence [ 18 , 21 , 54 , 55 ] of the chorion is important because it acts as a moderator of chemicals’ contact to embryos and their biological response. Chorion removal increases embryos sensitivity, which is an important trait for chemicals hazard identification using this assay [ 21 ].…”

Comparison of the Zebrafish Embryo Toxicity Assay and the General and Behavioral Embryo Toxicity Assay as New Approach Methods for Chemical Screening

“…These differences relate to initial exposure time (6–24 hpf), the length of exposure time (48–120 h), chorionated versus dechorionated embryos, and static exposure versus media replacement at multiple time points during the test. A recent study compared some of these different protocols and found that they can and do have an effect on the concentration response pattern of the chemicals tested [ 24 ]. However, since the phenotypes produced by the chemicals were similar regardless of the exposure paradigm, the study concluded that the concentration response differences did not affect the conclusions made regarding the bioactivity and potential toxicity of the chemicals tested.…”