Thyroid Hormones and Derivatives: Endogenous Thyroid Hormones and Their Targets

Area of Science:

• Endocrinology
• Molecular Biology
• Biochemistry

Background:

• L-Thyroxine is the primary thyroid hormone, with numerous identified metabolites crucial for vertebrate development and regulation.
• These metabolites include 3,3',5-Triiodo-L-thyronine (T3), reverse-T3, thyronamines, and thyroacetic acids, each with specific functions.

Purpose of the Study:

• To provide a comprehensive overview of thyroid hormone metabolites.
• To elucidate their transport mechanisms, cellular actions, and inactivation pathways.

Main Methods:

• Literature review of identified thyroid hormone metabolites.
• Analysis of their binding proteins, cellular transporters, and receptor interactions.
• Examination of enzymatic pathways involved in their metabolism and inactivation.

Main Results:

• Thyroid hormone metabolites are transported in blood bound to proteins like TBG and TTR.
• Cellular uptake involves transporters such as MCT8, MCT10, OATP, and LAT families.
• Metabolites act via cell membrane receptors and nuclear receptors (TRs), with local availability controlled by deiodinases and other enzymes.

Conclusions:

• Thyroid hormone metabolites exhibit diverse functions and require complex transport and signaling systems.
• Understanding these pathways is essential for comprehending thyroid hormone action and regulation.
• Inactivation primarily occurs through deiodination, sulfation, or glucuronidation for elimination.