A single enzyme inside liver cells drives the production of triglycerides that, in excess, fuel the inflammation and scarring behind the deadliest form of fatty liver disease. An experimental drug that silences that enzyme just showed it can reverse the damage.
In a 51-week clinical trial published in The Lancet in May 2025, patients with biopsy-confirmed metabolic dysfunction-associated steatohepatitis (MASH) and liver fibrosis who received the drug ION224 experienced significantly higher rates of disease resolution and fibrosis regression than those given a placebo. The multicenter, randomized, double-blind, placebo-controlled phase 2 trial was led by UC San Diego hepatologist Rohit Loomba and sponsored by Ionis Pharmaceuticals.
“This is the first therapy targeting a single enzyme to demonstrate resolution of steatohepatitis and improvement in fibrosis in patients with MASH,” Loomba’s team reported, a finding UC San Diego Health highlighted as a potential turning point for a disease that affects an estimated 6 to 8 million adults in the United States alone and has become the leading cause of liver transplants linked to chronic liver disease.
How the drug works and what the trial showed
ION224 is an antisense oligonucleotide, a short strand of synthetic genetic material designed to bind to the messenger RNA that encodes diacylglycerol O-acyltransferase 2, or DGAT2. This enzyme catalyzes the final step in triglyceride assembly inside hepatocytes. By intercepting the mRNA before it can produce DGAT2 protein, ION224 cuts off fat production at its source rather than trying to manage downstream consequences like inflammation or scarring.
The drug is administered by subcutaneous injection. In the trial, designated ION224-CS2, patients received either ION224 or placebo over 51 weeks, with liver biopsies taken at baseline and at the end of treatment to assess histologic changes. Biopsy endpoints remain the gold standard for evaluating MASH because imaging alone cannot reliably distinguish simple fat accumulation from the lobular inflammation and hepatocyte ballooning that define the disease and precede cirrhosis.
Patients in the ION224 group showed greater rates of MASH resolution without worsening of fibrosis and greater rates of fibrosis improvement by at least one stage compared with placebo, based on central pathology reads. The trial also measured liver fat using MRI-PDFF, a specialized imaging technique that quantifies fat content, and found substantial reductions in the treatment arm. These results built on an earlier phase 2 study by Loomba’s group that had established the biological proof of concept: blocking DGAT2 reliably lowers hepatic triglyceride stores on imaging. The new trial extended that finding to show that sustained fat reduction can also reverse the tissue-level damage that makes MASH progressive and dangerous.
For patients, the practical significance is straightforward. MASH often produces no symptoms until fibrosis is advanced, and lifestyle modification, the current first-line intervention, requires sustained weight loss that many patients struggle to achieve and maintain. A targeted therapy that addresses the metabolic root of fat overproduction in the liver offers a fundamentally different approach.
What the trial does not yet answer
Several critical questions remain open heading into potential phase 3 testing.
The Lancet publication reports prespecified endpoints and summary results, but full per-patient histologic data, including detailed fibrosis stage shifts across baseline severity levels, comorbidities, and demographic subgroups, have not been released beyond aggregate tables. Independent researchers cannot yet assess how consistently the drug worked across different patient profiles or whether certain inflammatory phenotypes responded less well to DGAT2 suppression.
Safety and tolerability data are described in aggregate terms. Antisense oligonucleotides as a drug class have a mixed track record: injection-site reactions, flu-like symptoms, platelet count changes, and liver enzyme elevations have appeared in other programs. Because ION224 targets the liver directly, the organ it treats is also the organ most likely to show off-target effects, making long-term monitoring essential. Detailed adverse-event breakdowns by dose group, dropout rates, and any signals of hepatotoxicity will be closely scrutinized before regulators greenlight a larger trial.
The 51-week treatment window, while longer than many phase 2 MASH studies, leaves durability unproven. Liver disease progresses and regresses over years. Whether patients who stop ION224 retain their histologic gains or revert to fat accumulation is unknown. So is whether continued therapy beyond one year yields further improvement, a plateau, or new safety trade-offs. Phase 3 trials with longer follow-up and off-drug observation periods would need to address these gaps before any regulatory submission.
It is also unclear how ION224 might fit alongside other emerging MASH therapies. Because DGAT2 inhibition acts upstream in triglyceride synthesis, it could theoretically complement drugs that modulate inflammation, fibrosis, or systemic metabolism. But combination regimens raise new safety and cost questions, and regulators typically require clear evidence that each component contributes independent benefit. No combination data exist yet.
Where ION224 fits in a crowded field
ION224 enters a MASH treatment landscape that has shifted rapidly. In March 2024, the FDA granted accelerated approval to resmetirom (brand name Rezdiffra), a thyroid hormone receptor beta agonist developed by Madrigal Pharmaceuticals, making it the first drug approved specifically for MASH with moderate to advanced fibrosis. That approval was based on surrogate endpoints from the phase 3 MAESTRO-NASH trial and remains contingent on confirmatory data. Tirzepatide, the dual GIP/GLP-1 receptor agonist already approved for type 2 diabetes and obesity, demonstrated histologic improvement in a phase 2 MASH trial linking weight loss and metabolic control to better liver outcomes.
Both resmetirom and tirzepatide act on broad metabolic pathways. ION224’s mechanism is narrower by design: it targets a single enzymatic step in triglyceride synthesis. That precision is both its appeal and its open question. A tightly targeted drug may produce fewer off-target effects, but it also raises the possibility that patients with MASH driven primarily by inflammation or insulin resistance rather than hepatic fat overproduction may benefit less.
No head-to-head trials comparing ION224 with resmetirom or tirzepatide exist, and cross-trial comparisons are unreliable because of differences in patient populations, endpoints, biopsy reading methods, and trial duration. What can be said is that ION224’s impact on liver fat appears substantial and that its histologic benefits are directionally consistent with those seen in other programs, even as precise effect sizes await confirmation in larger studies.
What comes next for patients and clinicians
For the millions of adults living with MASH, the ION224 results represent a proof of principle: precisely shutting down a single metabolic enzyme in the liver can translate into measurable, biopsy-confirmed reversal of a disease long considered intractable without dramatic weight loss or transplantation. That is a meaningful step, but it is not yet a treatment option.
Ionis Pharmaceuticals has not publicly announced phase 3 trial timelines as of June 2025. Before ION224 could reach patients, it would need to demonstrate efficacy and safety in a larger, longer confirmatory trial, likely enrolling thousands of participants across a broader range of disease severity and demographics. Regulatory agencies will weigh the drug’s benefits against the unmet need in MASH, but they will also demand clarity on durability, long-term safety, and whether the histologic improvements translate into reduced rates of cirrhosis, liver failure, and transplantation over time.
Until those answers arrive, the current evidence supports a clear but bounded conclusion: DGAT2 inhibition works in the short term, in a controlled setting, in patients with confirmed MASH and fibrosis. Whether that finding holds up across the years and populations that matter most is the next question Loomba’s team and Ionis will need to answer.
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*This article was researched with the help of AI, with human editors creating the final content.
