A Gut Enzyme Fueled by Microbiota May Drive Fatty Liver Disease in Mice

If you've been told your fatty liver disease is "just about diet" and it keeps getting worse anyway, a new mouse study points to a culprit hiding in the gut wall itself. Researchers report that an intestinal enzyme called neutral ceramidase reshapes gut bacteria and their chemical byproducts in ways that erode the gut's protective lining, worsening liver scarring in MASH (metabolic dysfunction-associated steatohepatitis, the more severe, inflamed form of fatty liver disease). Deleting that one enzyme in mice's intestinal cells reversed much of the liver damage, even though it left the underlying fat buildup untouched, pointing to a narrow, targetable mechanism rather than a blanket fix.

Key takeaways

• The gut enzyme neutral ceramidase (Asah2) reshapes gut bacteria in ways that raise a bacterial byproduct, 2-HHA, which blocks a gut-protective signaling pathway; more 2-HHA means a weaker gut barrier and worse liver scarring.
• In mice, deleting this enzyme only in intestinal cells cut liver fibrosis and inflammation after a year on a Western-style diet, without changing how much fat built up in the liver.
• Deleting the receptor this pathway relies on, AhR, had the opposite effect and worsened liver and lung inflammation, while a seaweed-derived fiber called fucoidan partly reversed the damage.
• Caveat: this is entirely mouse and cell-line evidence with small group sizes (4 to 5 animals per group); none of it has been tested in people yet.

Neutral Ceramidase in Gut Cells Fuels MASH Progression

A gut enzyme called neutral ceramidase (made from the Asah2 gene, normally involved in breaking down a fatty molecule called ceramide) drives progression of MASH by disrupting the chemical conversation between gut bacteria and the intestinal lining, according to a study published in eGastroenterology. Researchers deleted Asah2 only in intestinal epithelial cells (the single layer of cells lining the gut) of mice, rather than throughout the body, then fed the animals a Western-style, high-fat diet for 12 months to trigger MASH. That targeted deletion shifted the mix of gut bacteria and lowered a bacteria-linked metabolite called 2-hydroxyhippuric acid (2-HHA, also known as salicyluric acid). The researchers show that 2-HHA blocks a receptor called AhR (the aryl hydrocarbon receptor, a protein that senses gut molecules and normally tells intestinal cells to build a protective sugar coating). With less 2-HHA circulating, AhR signaling switched back on, restoring fucosylation (attaching fucose sugar molecules onto the gut's mucus and cells), which helps seal the barrier. Mice missing intestinal neutral ceramidase had a lower liver-to-body-weight ratio, less liver collagen buildup, and lower blood ALT and AST (liver-damage markers) than normal mice after a year on the diet, despite similar liver fat and body-weight gain.

Fatty Liver Disease Patients Face a Hidden Gut Culprit

MASH is already among the most common causes of serious chronic liver disease worldwide, and 20 to 30% of the broader condition it stems from, metabolic dysfunction-associated steatotic liver disease (MASLD), can progress to this more damaging, scarring stage, per background cited in the study and the NIDDK's overview of fatty liver disease. What makes this relevant to that population is where the damage appears to originate: not only the liver, but the gut lining and the bacteria living against it. Gut-driven protection traveled with the microbes themselves: germ-free mice given a stool transplant from ceramidase-deficient donor mice developed less liver inflammation and lower liver collagen than germ-free mice given normal donor stool, after both groups were fed a MASH-inducing diet. The same axis reached beyond the liver: mice lacking intestinal neutral ceramidase had less lung inflammation, while mice lacking AhR had more, echoing the gut-liver-lung connections researchers increasingly see in metabolic disease.

How Mouse Models And Germ-Free Transplants Revealed The Mechanism

To isolate the enzyme's role, researchers engineered mice with Asah2 deleted only in intestinal epithelial cells (Asah2-ΔIEC), rather than body-wide, and compared them with normal littermates on a Western-style diet for 3, 10 or 12 months, or a faster-acting hydrogenated-oil, sucrose, palmitate and cholesterol (HSPC) diet for 4 to 6 months. A separate line had AhR deleted only in intestinal cells (AhR-ΔIEC), to test what happens when the pathway is removed rather than restored. To confirm gut bacteria, not just the missing gene, were doing the work, they transplanted stool from ceramidase-deficient or normal donor mice into germ-free mice and fed them the HSPC diet for 4 months. In parallel, they tested the mechanism directly in mouse colon cell lines, exposing cells with and without AhR to 2-HHA alongside a receptor-activating chemical. Group sizes throughout were small, typically 4 to 5 animals per group.

What Fatty Liver Patients Can Take From This Study

This is not a signal to buy a supplement. The one intervention tested beyond genetics, dietary fucoidan (a fiber-like compound from brown seaweed, given at 50 milligrams per kilogram every 3 days for 4 months), partly reversed liver damage in AhR-deficient mice. But that result comes from genetically altered mice on a controlled lab diet, not a clinical trial, and no commercial fucoidan supplement has been tested this way. What the study does offer is a concrete way to think about the disease: MASH may progress not just because fat builds up in the liver, but because a gut-barrier defense breaks down under pressure from gut bacteria and their byproducts, a reasonable question to raise with a doctor managing fatty liver disease, not grounds for any specific dietary fix.

The Study's Key Limitations And Unanswered Questions

Every finding here comes from mice and mouse cell lines; none has been confirmed in human patients with MASH. The researchers flag an open question about 2-HHA itself: producing it appears to involve gut bacteria and the host's own liver and intestinal chemistry working together, so it isn't yet clear how much of the effect is microbial versus something the body does on its own. They also acknowledge that other gut-derived metabolites likely contribute to the gut-liver-lung inflammation observed, so this is unlikely to be a single-molecule story once tested further.

What Comes Next For This Fatty Liver Research

The researchers say next steps include dosing germ-free mice directly with 2-HHA to test its role without a full microbiome present, and building mouse models where AhR is deleted only in specific cell types, such as immune cells versus gut epithelial cells, to separate their individual contributions. They also want work that measures precursor availability and how the liver and gut conjugate 2-HHA, to sort out its microbial versus host origin. No timeline for human research was given, and no drug candidate targeting this pathway currently exists.

Common Questions

Is this gut enzyme finding relevant to people, or only mice? So far, only mice and mouse cell lines have been tested. The gut enzyme, bacterial metabolite and AhR receptor involved all exist in humans too, but no human study has confirmed this pathway drives MASH in people.

Does this mean fucoidan supplements can treat fatty liver disease? No. Fucoidan reduced liver-damage markers in genetically altered mice given a specific, researcher-administered dose on a controlled diet. That is not evidence that over-the-counter fucoidan supplements help human fatty liver disease, which was not tested here.

What is 2-hydroxyhippuric acid (2-HHA) and where does it come from? 2-HHA, also called salicyluric acid, is a metabolite the study ties to gut bacteria acting together with the body's own liver and intestinal chemistry. Bacteria including Alistipes and Lachnospiraceae species correlated with 2-HHA levels in the mice studied.

What is fucosylation and why does it matter for gut health? Fucosylation is the attachment of a sugar called fucose onto the mucus and cells lining the gut. It helps maintain the gut barrier and a healthy bacterial balance; when it drops, as happened here once AhR signaling was blocked, the barrier weakens and lets more bacterial products leak into the bloodstream.

References

1. Ting Wang, Liang Chen, Chao Lei, et al. (2026). Intestinal neutral ceramidase exacerbates MASH pathogenesis. eGastroenterology. https://doi.org/10.1136/egastro-2026-100417
2. Fangcong Dong, Gary H. Perdew (2020). The aryl hydrocarbon receptor as a mediator of host-microbiota interplay. Gut Microbes. https://doi.org/10.1080/19490976.2020.1859812
3. Lifen Zhao, Nianzhu Zhang (2026). FUT2-mediated intestinal fucosylation: a master regulator of host-microbiota symbiosis in health and disease. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2026.1926158
4. Definition & Facts of NAFLD & NASH – NIDDK. NIH. https://www.niddk.nih.gov/health-information/liver-disease/nafld-nash/definition-facts