3'-Monoiodothyronine

3'-Monoiodothyronine zwitterion 3D ball

3'-Monoiodothyronine (3'-MIT), also known as reverse triiodothyronine or rT3, is a thyroid hormone metabolite. It is one of the compounds produced by the thyroid gland and is a derivative of thyroxine (T4), which is the primary hormone secreted by the gland. Unlike thyroxine and triiodothyronine (T3), which are active thyroid hormones involved in regulating various physiological processes, 3'-Monoiodothyronine is considered an inactive metabolite. Its role in human physiology and its exact effects on the body are less understood compared to T3 and T4.

Production and Metabolism

3'-Monoiodothyronine is produced through the deiodination process of thyroxine. Deiodination involves the removal of an iodine atom from the outer or inner ring of the thyroxine molecule. The deiodination of thyroxine can lead to the production of either 3'-Monoiodothyronine or the biologically active hormone triiodothyronine (T3), depending on which iodine atom is removed. The enzyme responsible for this process is called deiodinase. There are three types of deiodinase enzymes, and their activity determines whether T4 is converted into T3, which is the active form of the hormone that can exert its effects on the body, or into rT3 (3'-MIT), which is considered inactive.

Function

The precise physiological role of 3'-Monoiodothyronine remains a subject of research. It is generally considered an inactive metabolite because it does not bind effectively to thyroid hormone receptors and, therefore, does not activate the gene transcription processes that the active thyroid hormones do. However, its presence in the body and its production process suggest it may have some regulatory functions, possibly in modulating the activity of T3 or in the process of thyroid hormone metabolism and clearance.

Clinical Significance

The measurement of 3'-Monoiodothyronine levels, along with other thyroid hormones, can be used in the diagnosis and management of thyroid disorders. Elevated levels of rT3 may be seen in conditions such as non-thyroidal illness syndrome (NTIS), also known as euthyroid sick syndrome, where there is a disruption in thyroid hormone metabolism during non-thyroidal illness without an inherent dysfunction of the thyroid gland itself. In this condition, the conversion of T4 to T3 is decreased, and the conversion to rT3 is increased, which may reflect the body's attempt to decrease energy expenditure during critical illness.

Research Directions

Research into 3'-Monoiodothyronine and its role in human health and disease is ongoing. Understanding the precise functions of this metabolite, its interaction with other thyroid hormones, and its potential effects on the body could lead to new insights into thyroid hormone metabolism and the management of thyroid-related disorders.