INTRODUCTION: Melanocortin 4 receptor (MC4R) is a G-protein-coupled receptor expressed in the hypothalamus, playing a key role in regulating feeding behavior and energy homeostasis. MC4R is integral to the POMC-MC4R and leptin-MC4R pathways, which control food intake and body weight. Mutations in the POMC gene lead to severe early-onset obesity and increased food consumption. Recently, glucagon-like peptide-1 (GLP-1) analogs, including semaglutide, tirzepatide, and retatrutide, have been explored as potential anti-obesity therapies.
METHODS: This study aimed to assess and compare the efficacy of these GLP-1 analogs in MC4R knockout (KO) mice, which are deficient in the POMC-MC4R pathway. GLP-1 analogs were administered for 21 days to MC4R KO mice and compared their efficacy.
RESULTS: The percentage of body weight reduction was 19.7 ± 4.1% for semaglutide, 31.6 ± 7.6% for tirzepatide, and 24.1 ± 5.8% for retatrutide. Body composition analysis, including fat and lean mass, was performed using the Echo-MRI system, revealing significant suppression of both fat and lean mass by all three GLP-1 analogs. Furthermore, GLP-1 analogs improved plasma insulin levels, HOMA-IR, cholesterol levels, and markers of liver damage (AST and ALT), as well as reduced liver hypertrophy. While GLP-1 analogs suppressed genes related to fatty acid synthesis, they had no significant effect on inflammation-related gene expressions. Additionally, GLP-1 analogs reduced energy expenditure, with only tirzepatide showing a significant decrease in the respiratory quotient (RQ) in MC4R KO mice.
CONCLUSION: Our findings demonstrate that all three GLP-1 analogs, semaglutide, tirzepatide, and retatrutide, exhibit significant anti-obesity effects in MC4R KO mice. These results suggest that GLP-1 analogs may provide an effective treatment option for patients with MC4R-POMC pathway deficiencies. Moreover, the efficacy of these drugs in MC4R KO mice aligns with clinical studies, indicating that MC4R KO mice serve as a reliable animal model for obesity research.
