Screening for chemicals with thyroid hormone-disrupting effects using zebrafish embryo

Area of Science:

• Environmental Toxicology
• Endocrine Disruption
• Zebrafish Models

Background:

• Thyroid disruption is a growing concern in chemical and drug development.
• Current assessment methods for thyroid disruptors are limited by cost and labor.
• New Approach Methodologies (NAMs) are needed to complement existing toxicological data.

Purpose of the Study:

• To develop and validate a medium-throughput screening approach for identifying chemical thyroid disruptors.
• To utilize zebrafish embryos as a model system for assessing thyroid-specific endocrine disruption.
• To provide a cost-effective and physiologically relevant alternative to traditional assays.

Main Methods:

• A tiered approach was used, starting with maximum tolerated concentration identification.
• Zebrafish larvae were exposed to sub-adverse effect levels of reference compounds.
• A transgenic zebrafish line (Tg(tg:mCherry)) was used to measure thyroid gland fluorescence.
• Gene expression patterns of the hypothalamus-pituitary-thyroid (HPT) axis were analyzed.
• Thyroid hormone levels (T3 and T4) were quantified using liquid chromatography-mass spectrometry (LCMS).

Main Results:

• The method successfully identified thyroid-disrupting effects of reference chemicals.
• Fluorescence levels in the thyroid gland correlated with chemical exposure.
• Altered gene expression in the HPT axis confirmed thyroid disruption.
• Changes in T3 and T4 hormone levels were detected, validating the findings.

Conclusions:

• The presented tiered approach offers a viable medium-throughput screening tool for thyroid disruptors.
• This New Approach Methodology (NAM) can enhance the assessment of endocrine disruptors in chemical safety evaluations.
• The method provides a valuable addition to the regulatory and industrial toxicologist's toolkit.