Apitegromab preserves 55% lean mass during tirzepatide-induced weight loss in overweight/obese adults
Background
Weight loss induced by incretin mimetic therapies like tirzepatide is highly effective for obesity and overweight, but often leads to a significant loss of lean body mass alongside fat mass. This disproportionate lean mass loss can negatively impact metabolic health, physical function, and overall quality of life, especially in older adults or those with sarcopenia risk. Myostatin is a key negative regulator of skeletal muscle growth, and its inhibition offers a promising strategy to counteract muscle wasting. Targeting the myostatin pathway could mitigate this adverse effect, improving the long-term benefits of potent weight loss medications.
Study Design
The randomized, double-blind, placebo-controlled phase 2 EMBRAZE study enrolled 102 adults with overweight or obesity. Participants were randomized 1:1 to receive tirzepatide plus apitegromab (10 mg/kg) or tirzepatide plus placebo. The intervention involved co-administration of apitegromab or placebo with tirzepatide over 24 weeks. The primary endpoint was the change in lean mass, assessed by DXA scans, comparing the apitegromab arm to the placebo arm, while monitoring total body weight loss and safety profiles.
Results
At week 24, apitegromab significantly reduced lean mass loss compared to placebo. Participants receiving apitegromab experienced 1.9 kg (80% CI: 1.2-2.7 kg) less lean mass loss than the placebo group, a statistically significant difference (P=0.001). This represented a 54.9% retention of lean mass relative to placebo, despite both groups achieving similar total body weight loss. Trough concentrations of apitegromab and total latent myostatin, a pharmacodynamic marker, increased over time in the apitegromab group, reaching a plateau after approximately 16 weeks. The incidence of adverse events (AEs) was comparable: 39 of 51 (76%; 95% CI: 63-86%) in the apitegromab group and 36 of 51 (71%; 95% CI: 57-81%) in the placebo group.
Serious adverse events (SAEs) were balanced, occurring in one of 51 (2%; 95% CI: 0-10%) participants in each arm, indicating a favorable safety profile for the combination.
Key Findings
- Apitegromab reduced lean mass loss by 1.9 kg compared to placebo during tirzepatide-induced weight loss (P=0.001).
- Apitegromab led to 54.9% retention of lean mass relative to placebo, despite similar total weight loss.
- Apitegromab and total latent myostatin levels plateaued after approximately 16 weeks.
- Incidence of adverse events was similar between apitegromab (76%) and placebo (71%) groups.
- Serious adverse events were balanced, with 2% in each treatment arm.
Why It Matters
This study offers a crucial step towards optimizing weight loss therapies by addressing the often-overlooked challenge of lean mass preservation. Combining tirzepatide with a myostatin inhibitor like apitegromab could significantly improve the quality of weight loss, leading to better long-term health outcomes, enhanced physical function, and potentially reduced risks of sarcopenia or frailty associated with rapid weight reduction. For individuals using GLP-1/GIP agonists, this suggests a future where muscle mass can be actively protected, potentially altering current weight loss protocols to include muscle-preserving agents. While this is a phase 2 study, the proof-of-concept is strong, paving the way for larger trials and eventual clinical translation of combination therapies.
apitegromab
tirzepatide
lean mass
weight loss
myostatin inhibitor
glp-1 agonist