Zalfermin Plus Semaglutide Delivers Additive Liver and Weight Benefits in MASH

Metabolic dysfunction–associated steatohepatitis (MASH) is a progressive liver disease closely linked to obesity and metabolic syndrome, and it remains an area of high unmet medical need. FGF21 analogs show meaningful effects on liver fat and fibrosis in clinical trials but produce limited body weight reduction. GLP-1 receptor agonists like semaglutide are established for weight loss and are in late-stage development for MASH. This study tested whether combining these two mechanistically distinct agents could produce additive or synergistic benefits.

Male C57BL/6J mice were fed the AMLN diet (high fat, trans-fat, fructose, cholesterol) for 36 weeks to induce diet-confirmed MASH with fibrosis. A liver biopsy was performed at baseline to confirm moderate-to-severe steatosis (score ≥2) and fibrosis (stage ≥F1). Animals were then randomized to 8 weeks of subcutaneous daily dosing with vehicle, low-dose zalfermin (0.05 mg/kg), high-dose zalfermin (0.2 mg/kg), low-dose semaglutide (3 µg/kg), high-dose semaglutide (120 µg/kg), or a low-dose combination (zalfermin 0.05 mg/kg + semaglutide 3 µg/kg). Endpoints included body weight, plasma and liver biochemistry, histopathological scoring (NAS and fibrosis stage), quantitative histology, and liver RNA sequencing.

The combination of low-dose zalfermin and semaglutide produced approximately 18% body weight loss—a super-additive effect compared to ~6% for low-dose zalfermin alone and ~4% for low-dose semaglutide alone, and comparable to high-dose monotherapies (~15–16%). The combination also outperformed each individual low-dose monotherapy on plasma ALT, AST, total cholesterol, triglycerides, NAFLD Activity Score (NAS), steatosis, and inflammation scores. High-dose zalfermin was broadly as effective as the low-dose combination across most endpoints. Both the combination and high-dose zalfermin significantly reduced liver weight and liver index relative to vehicle-treated MASH mice.

Liver transcriptomics via RNA sequencing revealed that combination therapy suppressed fibrosis-related gene expression—including collagen and stellate cell activation markers—to a greater extent than either monotherapy alone. This suggests the two agents act through complementary pathways: FGF21 primarily targets adipose tissue and hepatic lipid metabolism via β-klotho/FGFR complexes, while GLP-1 reduces appetite, body weight, and systemic metabolic stress, together amplifying hepatic benefit.

This study has limitations inherent to preclinical rodent models: the AMLN DIO-MASH mouse, while translational, does not fully recapitulate human MASH progression or treatment response timelines. Drug doses, particularly semaglutide's 120 µg/kg daily regimen, are extrapolated from human pharmacokinetics and may not perfectly mirror clinical exposures. Nevertheless, findings strongly support the rationale for an ongoing phase 2b clinical trial (NCT05016882) evaluating zalfermin plus semaglutide in patients with MASH.