Triple Agonist Zabopegdutide Achieves 62.5% MASH Resolution in Phase 2 — Highest Rate Published to Date

Metabolic-associated steatohepatitis (MASH) — previously called NASH — is the progressive inflammatory form of metabolic fatty liver disease. It affects an estimated 16–20 million Americans, and roughly 20% of those with MASH will develop cirrhosis within 20 years. Until 2024, no pharmacologic therapy had received FDA approval for MASH — the disease was managed with weight loss, exercise, and treatment of metabolic comorbidities. The GLP-1 receptor agonists semaglutide and liraglutide, initially developed for type 2 diabetes and obesity, showed MASH resolution rates of approximately 40–59% in Phase 2 trials, but fibrosis improvement remained modest. Resmetirom (a thyroid hormone receptor-β agonist) received FDA approval in 2024 specifically for MASH with fibrosis, with a MASH resolution rate around 26%. Into this competitive landscape, zabopegdutide enters with 62.5%.[1, 2]

Zabopegdutide is a tri-agonist: it activates GLP-1 receptors (reducing appetite, slowing gastric emptying, improving insulin secretion), GIP receptors (potentiating GLP-1 effects, reducing bone fat), and glucagon receptors (stimulating hepatic fat oxidation and fatty acid β-oxidation in the liver — the mechanistic element most directly relevant to MASH). The glucagon receptor agonism is the key differentiator from GLP-1/GIP dual agonists like tirzepatide. In the liver, glucagon receptor activation drives triglyceride breakdown and export, directly targeting the steatosis that initiates the MASH cascade.[1, 3]

The Phase 2 trial randomized adults with biopsy-confirmed MASH (NAS ≥4) and fibrosis stage F2–F3 to once-weekly zabopegdutide subcutaneous injection or placebo for 48 weeks, with repeat liver biopsy at week 48. The primary endpoint — histologic MASH resolution with no worsening of fibrosis — was met by 62.5% of zabopegdutide-treated patients versus approximately 10% with placebo. A secondary endpoint, fibrosis improvement by at least one stage with no worsening of MASH activity, was achieved in approximately 45% of treated patients. Mean body weight declined by approximately 14% in the active arm. GI adverse events (nausea, vomiting, diarrhea) were the most common side effects, consistent with GLP-1 class effects, and led to dose reduction or discontinuation in a minority.[1]

Clinical Context

The pharmacological treatment of MASH moved from a field of repeated failures to one of approved therapies in 2024, when the FDA approved resmetirom (Rezdiffra) — a thyroid hormone receptor beta agonist — for MASH with moderate-to-advanced fibrosis. The MAESTRO-NASH trial (NEJM 2024) demonstrated that resmetirom 100 mg daily achieved MASH resolution without worsening fibrosis in 25.9% of patients (vs 9.7% placebo) and fibrosis improvement ≥1 stage in 24.2% (vs 14.2% placebo) at 52 weeks.[2] Semaglutide, the GLP-1 receptor agonist, showed impressive MASH resolution rates in the phase 2 NASH trial (59% at 1.0 mg weekly) and is being tested in the ongoing ESSENCE phase 3 trial. GLP-1 agonism reduces hepatic steatosis through appetite suppression, reduced hepatic lipogenesis, and possibly direct hepatocyte signaling.

The rationale for triple receptor agonism in MASH is mechanistic: MASH involves metabolic dysfunction (excess hepatic lipid deposition), inflammatory injury, and progressive fibrosis driven by stellate cell activation. GLP-1 receptor agonism reduces steatosis. GIP receptor agonism (as in tirzepatide) enhances lipid clearance and adipose tissue function. Glucagon receptor agonism drives fatty acid oxidation in the liver, directly reducing hepatic lipid content through a pathway complementary to insulin sensitization. Zabopegdutide combines all three signals in a once-weekly pegylated peptide. Phase 2 trials for multi-agonists in MASH have consistently shown higher histological response rates than any single-mechanism agent — but the key questions are fibrosis outcomes (steatosis does not equal fibrosis), durability, and hepatic safety.[3]

Why It Matters Clinically

The 62.5% MASH resolution figure deserves context. Histologic MASH resolution requires normalization of lobular inflammation and hepatocyte ballooning without worsening fibrosis — it is a meaningful biopsy endpoint, not a surrogate marker. The separation between 62.5% (zabopegdutide) and approximately 59% (semaglutide Phase 2) or approximately 45% (tirzepatide Phase 3 interim) is notable but must be interpreted cautiously across different Phase 2 populations and trial designs. The confirmatory question — whether the fibrosis improvement seen in this trial translates into reduced risk of cirrhosis and liver-related mortality — will require longer-term Phase 3 data.[1, 2, 3]

Limitations

Phase 2 trials in MASH are notoriously difficult to interpret — placebo MASH resolution rates of 10–20% reflect the impact of trial participation (improved diet, weight loss) on biopsy outcomes. The trial enrolled F2–F3 fibrosis; the most clinically urgent question is whether zabopegdutide works in F4 (compensated cirrhosis). Full Phase 3 data are required before regulatory approval, and the comparison to existing approved therapies will require head-to-head trials.