Differences between therapeutic mechanisms of resmetirom and semaglutide against MASH in western diet-fed MC4R-knockout mice

Metabolic dysfunction-associated steatotic liver disease (MASLD) can progress to steatohepatitis (MASH), which is closely associated with obesity and insulin resistance. Resmetirom, and semaglutide, have been shown to have therapeutic effects in clinical studies. We compared these mechanisms in western diet (WD)-fed melanocortin 4 receptor knockout (MC4R-KO) mice, a human MASH pathology model. Male MC4R-KO mice were fed WD for 6 weeks starting from 22 weeks of age for disease induction and were administered drugs for 7 weeks with WD feeding, for a total duration of 13 weeks. Both resmetirom and semaglutide treatments for 7 weeks substantially improved these parameters. Although resmetirome and semaglutide improved liver hydroxyproline deposition and total fat mass, semaglutide markedly suppressed total lean mass. Moreover, resmetirom enhanced oxygen consumption, whereas semaglutide reduced energy expenditure. Histopathological evaluation showed that resmetirom significantly and semaglutide tended to improve liver steatosis score. On the fibrosis score, semaglutide significantly reduced it. Resmetirom and semaglutide have different mechanisms of action against MASH. Similar to clinical evidence, semaglutide treatment, might cause muscle mass reduction due to food intake suppression. This is the first study to simultaneously compare the effects of resmetirom and semaglutide on MASH phenotypes and reveal the differences on their mechanisms of action in WD-fed MC4R-KO mice.