Distinct and complementary metabolic effects of GLP-1 and glucagon receptor agonism in diet-induced obese mice

Glucagon-like peptide-1 (GLP-1) and glucagon receptor co-agonism is an emerging therapeutic strategy for obesity and metabolic dysfunction-associated steatotic liver disease (MASLD). To examine their distinct and combined metabolic actions in a model reflecting chronic disease, we used diet-induced obese mice that had been maintained on high-fat diet from early adulthood, allowing obesity and hepatic steatosis to develop gradually and remain stable before initiating treatment. Mice received a long-acting GLP-1 receptor agonist (NNC2220), a long-acting glucagon receptor agonist (NNC9204-0043), or both for 28 days, and a calorie-restricted weight-matched group was included to separate drug-specific from weight-dependent effects. Monotherapy with either agonist produced similar weight loss of approximately 24 %, whereas combined treatment resulted in a substantially greater reduction of 37 %. GLP-1 agonism decreased food intake, whereas glucagon agonism did not; however, glucagon agonism produced a larger reduction in hepatic triglycerides than GLP-1 agonism or weight matching, indicating hepatic effects not explained solely by weight loss. Chronic glucagon receptor activation also increased hepatic glycogen content, both alone and in combination therapy, without corresponding changes in glycogen synthase or phosphorylase activities, suggesting regulation upstream of these enzymatic pathways. These data show that combined GLP-1 and glucagon receptor agonism enhances weight loss and reduces hepatic lipid content beyond GLP-1 agonism alone. Because energy expenditure and dynamic glucose tolerance were not directly assessed, mechanistic interpretation is limited. Glucagon receptor signaling may be a key contributor to hepatic lipid metabolism and support its therapeutic potential-alone or combined with GLP-1 agonism-for improving liver health in MASLD.