Three widely used GLP-1 weight-loss drugs—semaglutide, tirzepatide, and retatrutide—have demonstrated effectiveness in a rare, genetically-driven form of obesity, according to a novel study conducted on mice. Over a three-week period, the drugs reduced food intake, improved liver health, and lowered cholesterol levels, with tirzepatide exhibiting the most significant weight loss.
For individuals grappling with genetic mutations affecting the hypothalamus, the prospect of treatment is offering a glimmer of hope. These mutations can disrupt the body’s natural ability to regulate appetite and weight, creating a sensation akin to having failing brakes while descending a steep hill.
The MC4R receptor, located in the hypothalamus, plays a crucial role in controlling food intake and body weight. Mutations within the pathways leading to this receptor can result in a loss of control over these vital functions. Children born with these mutations often experience early-onset obesity, a condition that proves remarkably resistant to intervention even into adulthood.
Published in the International Journal of Obesity, the study tested the three GLP-1 drugs on mice genetically engineered to lack the MC4R gene entirely. The results indicated that all three drugs had a significant impact. Semaglutide led to an average body weight reduction of 19.7 percent, retatrutide reduced weight by 24.1 percent, and tirzepatide, which targets two receptors, achieved the most substantial result—a 31.6 percent decrease in body weight.
Despite the absence of a functioning MC4R receptor in the mice, the drugs proved effective. Food consumption decreased across all groups, liver injury markers declined, and levels of cholesterol and triglycerides were lowered. Genes within the liver responsible for fat production were deactivated.
“Our findings demonstrate that all three GLP-1 analogs exhibit significant anti-obesity effects in MC4R KO mice,” the study authors wrote.
The body typically regulates hunger through a series of signals transmitted along the POMC-MC4R and leptin-MC4R pathways as the stomach approaches fullness. Mutations along these pathways can contribute to some of the most challenging forms of obesity to treat. GLP-1 drugs, including those containing semaglutide and tirzepatide, function by relaying messages to receptors throughout the brain, pancreas, and vagus nerve—a nerve extending from the brainstem to the abdomen.
Researchers sought to determine whether these drugs would remain effective even in the complete absence of the MC4R receptor. Mice lacking the MC4R receptor exhibited increased appetite, rapid weight gain, fatty livers, elevated cholesterol, and early insulin resistance—characteristics mirroring those observed in patients with MC4R pathway deficiencies.
The study similarly revealed that all three drugs reduced not only fat mass but also lean mass. The authors cautioned that prolonged treatment could lead to sarcopenia—loss of muscle mass and strength—and suggested that combining these drugs with agents that preserve or increase muscle mass might mitigate this risk. Rhythm Pharmaceuticals is currently conducting trials related to these conditions, with preliminary data expected to be announced, according to GlobeNewswire.
The study, which lasted three weeks, involved only male mice and resulted in the loss of two animals from the tirzepatide group before completion. No human trials have yet been conducted to assess the effectiveness of these drugs in patients with MC4R mutations. The findings from the mice serve as a proof of concept, but do not constitute a prescription.
“This study provides the first demonstration that GLP-1 analogs can be effective in treating obesity associated with MC4R deficiency,” the authors concluded.
