Thyroid hormone deiodination in target tissues--a regulatory role for the trace element selenium?

Area of Science:

• Biochemistry
• Endocrinology
• Molecular Biology

Background:

• Thyroid hormones (TH) are crucial for development and metabolism.
• Deiodinase enzymes regulate TH bioavailability by converting thyroxine (T4) to triiodothyronine (T3) or inactivating T3.
• These enzymes act as gatekeepers to TH receptors, controlling tissue-specific TH action.

Purpose of the Study:

• To review the physiological, biochemical, and pharmacological properties of the three deiodinase isozymes.
• To highlight the role of selenium in regulating deiodinase expression, particularly type I 5 -deiodinase.
• To discuss the contribution of each deiodinase isozyme to TH activation and inactivation.

Main Methods:

• Literature review of existing studies on deiodinase isozymes.
• Analysis of the regulation of deiodinase expression by hormonal, nutritional, and neural factors.
• Examination of the role of trace elements, iodine and selenium, in TH metabolism.

Main Results:

• Deiodinase isozymes control tissue-specific TH action by modulating T4 to T3 conversion and T3 degradation.
• Strict regulation of deiodinase expression ensures coordinated TH action for growth, differentiation, and metabolism.
• Selenium is essential for TH synthesis, activation, metabolism, and action, with iodine supplementation being a prerequisite.

Conclusions:

• Deiodinase isozymes are critical regulators of thyroid hormone homeostasis.
• Selenium plays a vital role in deiodinase function and overall thyroid hormone economy.
• Adequate iodine and selenium supply is essential for optimal thyroid hormone action, particularly in regions with deficiencies.