Screening the ToxCast Chemical Libraries for Binding to Transthyretin

Area of Science:

• Endocrinology
• Toxicology
• Biochemistry

Background:

• Transthyretin (TTR) is a key serum binding protein for thyroid hormone (TH) transport.
• Chemicals disrupting TH balance can bind to and displace TH from TTR.
• Limited data exists on chemicals interacting with TTR.

Purpose of the Study:

• To develop and optimize an in vitro assay for screening chemical binding to human TTR.
• To screen a large library of chemicals for their potential to bind to TTR.
• To identify chemicals that may disrupt thyroid hormone homeostasis.

Main Methods:

• An in vitro assay using fluorescent probe 8-anilino-1-napthalenesulfonic acid (ANSA) and human TTR was optimized.
• Over 1500 chemicals from U.S. EPA ToxCast libraries were screened using a tiered approach.
• Chemicals showing significant ANSA displacement were further tested in concentration-response studies.

Main Results:

• 888 out of 1500+ chemicals showed ≥20% activity in displacing ANSA from TTR at 100 μM.
• 282 chemicals exhibited ≥85% activity and proceeded to concentration-response testing.
• EC50 values were determined for 276 of these 301 chemicals.

Conclusions:

• This study presents the largest dataset to date of chemicals screened for TTR binding.
• The developed assay is a valuable tool for identifying potential thyroid disruptors.
• This work contributes to expanding in vitro assays for assessing thyroid hormone homeostasis disruption.