Thyroid hormones exert their effects by stimulation of thyroid hormone receptors that have different tissue distribution and metabolic targets. TRβ is predominant in liver and mainly responsible for effects on cholesterol and lipoprotein metabolism, whereas TRα is most important in fat, muscle and heart. Thyroid hormone analogs (thyromimetics, tiromes) have been developed that activate TRβ are selectively taken up and/or activated by the liver. Such compounds stimulate hepatic LDL receptors, cholesterol elimination as bile acids and cholesterol and presumably promote reverse cholesterol transport. In animals, they retard atherosclerosis progression. In humans, eprotirome exerts favourable lipid-modulating effects while lacking thyroid hormone-related side-effects and maintaining normal hypothalamicpituitarythyroid feedback. When added to statins, it reduces LDL and non-HDL cholesterol, apolipoprotein B, and triglycerides as well as lipoprotein (a).
Conclusion: Liver-specific and β-selective thyroid hormone analogs activate a spectrum of favourable thyroid hormone actions that optimize lipid metabolism and promote cholesterol elimination. Further studies should establish long-term safety and potential clinical usefulness of thyromimetics.