Mazdutide Ameliorates Metabolic Dysfunction-Associated Steatotic Liver Disease by Modulating Endoplasmic Reticulum Stress, Improving Lipid Metabolism and Alleviating Inflammation

<b>Background:</b> Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is the most prevalent chronic liver disorder globally. Mazdutide has shown clinical benefits in weight management and metabolic regulation, indicating its potential as a therapeutic agent for MASLD. This study aimed to investigate the efficacy and mechanism of action of Mazdutide against early-stage MASLD. <b>Methods:</b> A MASLD mouse model was induced by a 12-week high-fat diet, followed by a 4-week treatment with subcutaneous Mazdutide (100, 200, or 400 μg/kg). In vitro, a cellular MASLD model was established by treating hepatocytes with 1 mM free fatty acids for 24 h, followed by co-treatment with Mazdutide (10, 20, or 50 nM) or the endoplasmic reticulum (ER) stress inhibitor 4-phenylbutyric acid (4-PBA). Serum and hepatic lipid profiles, liver injury markers, and pro-inflammatory cytokines were quantified. Liver histopathology was assessed by hematoxylin and eosin and Oil Red O staining. Protein expression related to ER stress, inflammation, and lipid metabolism was analyzed by immunohistochemistry and Western blot. <b>Results:</b> Compared with the MASLD model group, Mazdutide treatment significantly ameliorated systemic and hepatic lipid metabolism disorders, reduced liver injury markers and hepatic steatosis, and mitigated inflammation and oxidative stress in MASLD mice and hepatocytes (<i>p</i> < 0.05). Mechanistically, Mazdutide alleviated ER stress by modulating the protein kinase R-like endoplasmic reticulum kinase (PERK) pathway, suppressed the nuclear Factor kappa B (NF-κB)-mediated inflammatory response, and downregulated the expression of key lipogenic regulators including sterol regulatory element-binding protein 1 (SREBP-1), CCAAT/enhancer-binding protein beta (C/EBPβ), and peroxisome proliferator-activated receptor gamma (PPARγ) in both models (<i>p</i> < 0.05). <b>Conclusions:</b> Our findings demonstrate that Mazdutide alleviates hepatic ER stress in MASLD, suppresses inflammatory responses and improved lipid metabolism, which ultimately attenuates disease progression.