Efficacy of GLP-1 analog peptides, semaglutide, tirzepatide, and retatrutide on MC4R deficient obesity and their comparison.
This animal study investigated the anti-obesity effects of three GLP-1 receptor agonist peptides — semaglutide, tirzepatide, and retatrutide — in melanocortin 4 receptor knockout (MC4R KO) mice, a model of genetically driven obesity caused by disruption of the POMC-MC4R signaling pathway. All three compounds were administered for 21 days, after which body weight, body composition, metabolic markers, liver health, and gene expression were assessed. The study found that all three GLP-1 analogs produced statistically significant reductions in body weight, with tirzepatide showing the greatest effect (approximately 31.6%), followed by retatrutide (approximately 24.1%) and semaglutide (approximately 19.7%). All three agents reduced both fat and lean mass, improved plasma insulin levels and insulin resistance (HOMA-IR), lowered cholesterol, and reduced markers of liver damage (AST and ALT) as well as liver hypertrophy. Gene expression analysis showed suppression of fatty acid synthesis genes, but no significant effect on inflammatory gene expression. Energy expenditure was reduced by all agents; only tirzepatide significantly decreased the respiratory quotient. A key limitation is that this is a mouse model study, and findings may not directly translate to humans. The authors suggest MC4R KO mice are a valid model for studying obesity-related drug efficacy.
Why this grade: All experimental work was conducted exclusively in MC4R knockout mice; no human subjects or clinical data were included, limiting direct translation of findings to humans.
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.
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