Iodothyronines as lipid-lowering agents

It is a common notion that thyroid status is linked to energy expenditure and body weight, and thyroid hormones (THs) have always deserved attention for their potential use as pharmacological agents to counteract obesity and lipid metabolism-related disorders. Besides 3,5,3′,5′-tetraiodo-l-thyronine (thyroxine or T4) and 3,3′,5,-triiodo-l-thyronine (T3), other iodothyronines can be produced in the thyroid or in peripheral tissues through the process of stepwise deiodination. Among these TH metabolites, 3,5-diodo-l-thyronine (T2) is of particular interest for its effects on energy metabolism. After a brief overview of TH production and actions at the cellular level, this chapter will focus on the mechanisms underlying the lipid-lowering effects of the iodothyronines T3 and T2, with particular regard to the regulation of lipid metabolism in the liver.