Gut Bacteria Compound May Protect the Liver During Long-Term IV Nutrition

If you or someone you love depends on intravenous (IV) feeding because your gut can no longer absorb enough nutrients on its own, you have probably already heard that this life-sustaining treatment carries a hidden cost: it can quietly damage the liver over time. A new study offers one of the clearest mechanistic explanations yet for why, and points to a specific gut bacteria byproduct that might prevent it.

Key takeaways:

• A compound called indole-3-acetic acid (IAA), made by the gut bacterium Lactobacillus reuteri, protected mice from liver damage caused by long-term IV nutrition.
• IAA worked by dialing down a small RNA molecule called miR-216a-5p, which in turn allowed a liver-protective gene, LRH-1, to do its job.
• The researchers also measured this same microRNA in blood from a real patient cohort with intestinal failure-associated liver disease (IFALD), not just in mice.
• This is early-stage mouse and cell-line research; L. reuteri or IAA supplements are not an established treatment for IFALD in people.

Indole-3-Acetic Acid Blocks Liver Damage Tied to IV Feeding

Researchers at Jinling Hospital, affiliated with Nanjing University in China, found that a tryptophan-derived metabolite called indole-3-acetic acid, or IAA (a molecule gut bacteria make by breaking down the amino acid tryptophan), protected the liver in a mouse model of intestinal failure-associated liver disease, largely by suppressing a single microRNA. The study, published in the Journal of Nutritional Biochemistry, found that mice given long-term total parenteral nutrition (TPN, meaning virtually all their nutrition delivered directly into a vein rather than through the gut) developed reduced levels of the gut bacterium Lactobacillus reuteri and, correspondingly, lower IAA. Supplementing either live L. reuteri or IAA itself eased the hepatic steatosis (fat buildup in the liver) and the abnormal blood liver-function markers that TPN otherwise caused.

Who Faces Intestinal Failure-Associated Liver Disease

Intestinal failure-associated liver disease, or IFALD, affects people whose intestines can no longer absorb enough nutrients or fluids on their own, forcing them onto long-term parenteral (IV) nutrition. That group includes patients with short bowel syndrome, severe inflammatory bowel disease complications, or other conditions that have damaged large stretches of the gut. Prior research on IFALD has estimated it develops in a large share of patients on long-term home parenteral nutrition, and it is a leading reason some of these patients eventually need a liver or combined liver-intestine transplant, so a mechanism that could be targeted with a drug or supplement would matter enormously to this population. Researchers have long suspected the gut-liver axis (the biological communication loop between gut bacteria and the liver, connected via the bloodstream) plays a central role in IFALD, but the exact molecular steps have been unclear.

How the Researchers Traced the Mechanism Step by Step

This was a preclinical mechanistic study, not a clinical trial. The team built a TPN model in male mice by surgically implanting a catheter into a vein and infusing nutrition solution continuously for 14 days, which reproduced the liver injury and gut bacteria disruption seen in IFALD. Separately, they enrolled 80 people in a clinical cohort (31 healthy controls, 33 people with intestinal failure but no liver disease, and 16 with confirmed IFALD) and measured the same candidate microRNA in blood, to check whether the mouse mechanism had a human counterpart. To confirm causation rather than mere correlation in the animal work, the researchers used fecal microbiota transplants between chow-fed and TPN-fed donor mice, supplemented TPN mice directly with live or heat-killed L. reuteri or with IAA itself, and then used genetic tools (viral vectors) to overexpress or knock down the microRNA miR-216a-5p and its downstream target gene in mouse liver and in both mouse and human liver cell lines. A luciferase reporter assay (a lab test that confirms whether one molecule directly binds and regulates another) verified that miR-216a-5p binds directly to the messenger RNA of the gene LRH-1 (also called Nr5a2), a liver receptor known to help regulate fat and bile metabolism.

What This Could Mean if You Rely on IV Nutrition

For someone managing long-term parenteral nutrition, or caring for a child who is, this study does not change today's treatment plan, but it does sharpen the picture of what is likely happening inside the liver and why. The fact that the researchers went to the trouble of measuring miR-216a-5p in the blood of actual IFALD patients, not just mice, strengthens the case that this pathway is relevant to human disease and could eventually be developed into a blood-based marker to flag liver damage earlier, before it shows up on standard liver tests, which the researchers note are notoriously insensitive for catching IFALD early. It is reasonable to ask your medical team whether gut microbiome health or tryptophan metabolism come up in discussions about your nutrition plan, but no one should start taking probiotics or IAA supplements based on this study; the doses and delivery methods used in mice have not been tested for safety or effectiveness in people.

What This Study Cannot Yet Tell Us

This is animal and cell-line evidence for a specific molecular pathway, plus a correlational blood measurement in a modest human sample of just 16 IFALD patients; it is not evidence that giving people L. reuteri or IAA will prevent or reverse their liver disease. The mouse TPN model, however carefully constructed, cannot fully capture the variety of underlying conditions and health complications real IFALD patients have. The study also does not report how IAA or L. reuteri would perform against IFALD that has already progressed to fibrosis or cirrhosis, only the earlier stages of steatosis and metabolic disruption the researchers modeled.

What Comes Next

The authors frame their results as evidence for the diagnosis and treatment potential of the miR-216a-5p/LRH-1 axis, which suggests the next logical steps are validating miR-216a-5p as a blood biomarker in larger patient cohorts and testing whether IAA or engineered L. reuteri strains are safe and effective in human trials. Similar tryptophan-derived compounds have shown protective effects against fatty liver disease in other mouse models, and other L. reuteri strains have shown broader liver-protective effects across several disease models, so this fits a growing pattern researchers are trying to translate into actual therapies.

Common Questions

What is indole-3-acetic acid and is it the same as the plant hormone? Indole-3-acetic acid is best known as a plant growth hormone (auxin), but the same molecule is also produced by certain gut bacteria, including Lactobacillus reuteri, as a byproduct of breaking down the amino acid tryptophan; this study concerns the bacterial, gut-derived version.

Can I take Lactobacillus reuteri probiotics to protect my liver on IV nutrition? Not based on this study alone. The protective effects were shown in mice given specific doses of live bacteria or purified IAA under controlled conditions, and there is no human clinical trial evidence yet that over-the-counter probiotics containing L. reuteri prevent or treat IFALD.

What is LRH-1 and why does it matter here? LRH-1 (liver receptor homolog-1, gene name Nr5a2) is a protein in liver cells that helps regulate fat and bile metabolism; this study found that suppressing the microRNA miR-216a-5p frees up LRH-1 to work normally, which appears to protect the liver from IV-nutrition-related damage.

Is this the same thing as fatty liver disease from diet? No. IFALD is triggered specifically by long-term intravenous feeding in people whose intestines cannot absorb nutrients, which is a different clinical situation from diet-related nonalcoholic fatty liver disease, though the two conditions share some overlapping biology in the gut-liver axis.

References

1. Shuai Liu, Longchang Huang, Sirui Liu, Xin Qi, Gulisudumu Maitiabula, Xinying Wang (2026). Indole-3-acetic acid alleviates intestinal failure associated liver disease via the miR-216a-5p/LRH-1 axis. The Journal of Nutritional Biochemistry. https://doi.org/10.1016/j.jnutbio.2026.110488
2. Sasha-Jane Abi-Aad, Mark Lovell, Racha T. Khalaf, Ronald J. Sokol (2025). Pathogenesis and Management of Intestinal Failure-Associated Liver Disease. Seminars in Liver Disease. https://doi.org/10.1055/a-2545-7370
3. Yufang Ding, Karin Yanagi, Fang Yang, et al. (2023). Oral supplementation of gut microbial metabolite indole-3-acetate alleviates diet-induced steatosis and inflammation in mice. https://doi.org/10.7554/elife.87458.2
4. Yijing Peng, Yizhe Ma, Zichen Luo, Yifan Jiang, Zhimin Xu, Renqiang Yu (2023). Lactobacillus reuteri in digestive system diseases: focus on clinical trials and mechanisms. Frontiers in Cellular and Infection Microbiology. https://doi.org/10.3389/fcimb.2023.1254198