Resmetirom is a selective thyroid hormone receptor beta (THR-β) agonist. THR-β is particularly important in the liver, where thyroid-hormone signaling influences lipid metabolism.
Simple explanation
MASH involves excessive liver fat together with inflammation and liver injury. Over time, these processes can contribute to fibrosis, or scarring.
Resmetirom activates THR-β in liver cells. This increases signaling involved in lipid metabolism and promotes processes that reduce excess liver fat. The intended therapeutic effect is to improve pathological features of MASH and liver fibrosis.
Molecular mechanism
Resmetirom is designed to preferentially activate THR-β rather than THR-α. This liver-directed selectivity is a central feature of its pharmacology.
Thyroid hormone receptor signaling regulates genes involved in lipid synthesis, oxidation and cholesterol metabolism. Activation of THR-β can therefore influence hepatic lipid handling.
Why liver selectivity matters
Thyroid hormone receptors have different physiological roles in different tissues. Resmetirom was developed to preferentially target the beta receptor in the liver while reducing exposure to effects associated with broader thyroid-hormone receptor activation.
Clinical effect
The clinical goal is not simply to reduce liver fat. Regulatory studies evaluated histologic endpoints involving MASH activity and fibrosis. FDA’s approval was based on improvement in NASH and fibrosis under accelerated approval, while confirmatory research continues to assess clinical outcomes.