Phase 2 MASLD/MASH Substudy (Liver Fat Analysis)

Study Overview

The liver fat substudy of the Phase 2 obesity trial was a pre-specified analysis using magnetic resonance imaging-proton density fat fraction (MRI-PDFF) to quantify changes in hepatic fat content. Published by Sanyal et al. in Nature Medicine in June 2024, the results were described as “remarkable” by hepatologists, showing the most potent pharmacological liver fat reduction ever reported in a clinical trial.

Background

MASLD/MASH Epidemic

Metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD) affects approximately 25-30% of the global adult population. Its progressive form, metabolic dysfunction-associated steatohepatitis (MASH, formerly NASH), can lead to liver fibrosis, cirrhosis, and hepatocellular carcinoma. Until the March 2024 approval of resmetirom (Rezdiffra), there were no approved pharmacological treatments.

Glucagon Receptor and Liver Fat

The glucagon receptor component of retatrutide’s triple agonism is hypothesized to be a key driver of hepatic fat reduction:

• Glucagon promotes hepatic lipid oxidation (fat burning in liver cells)
• Glucagon suppresses de novo lipogenesis (new fat creation in the liver)
• Glucagon increases hepatic energy expenditure
• These direct hepatic effects augment the indirect benefits of weight loss

Results

MRI-PDFF Findings

The liver fat reductions were dose-dependent and dramatic:

Comparison with Other Therapies

The magnitude of liver fat reduction with retatrutide far exceeded other approaches:

• Resmetirom (approved for MASH): ~30-35% relative reduction
• Semaglutide 2.4 mg: ~40-50% relative reduction
• Tirzepatide 15 mg: ~50-55% relative reduction
• Retatrutide 12 mg: ~82% relative reduction

MASH Resolution Indicators

While liver biopsies were not performed in this substudy, the magnitude of fat reduction and the high rate of fat normalization strongly suggest that retatrutide would demonstrate MASH resolution in biopsy-confirmed trials.

Significance

These results directly led to the design of the SYNERGY clinical trial program — a dedicated Phase 3 initiative evaluating retatrutide specifically for MASLD/MASH with liver fibrosis. The 4,500-participant SYNERGY-Outcomes trial will assess liver histology endpoints and long-term clinical outcomes.

Publication

Sanyal AJ, Kaplan LM, Frias JP, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nature Medicine. 2024;30:2037-2048.