TUDCA and the Quiet Rise of Bile Acid Therapy

New research positions TUDCA beyond liver care into neurodegeneration, metabolic disease, and retinal protection. Here's where the science stands.

Molecular research into bile acid therapies and TUDCA neuroprotection

For most of its pharmaceutical history, tauroursodeoxycholic acid occupied a narrow clinical lane. TUDCA, as researchers abbreviate it, is the taurine-conjugated form of ursodeoxycholic acid (UDCA), and doctors have prescribed it primarily for cholestatic liver diseases, conditions where bile flow from the liver is impaired or blocked. It worked. It was safe. And for decades, that was more or less the whole story. But over the past five years, a different kind of evidence has been accumulating in journals that don’t typically concern themselves with bile ducts: Nature Medicine, Translational Neurodegeneration, Cell Death & Disease. Researchers studying neurodegenerative disease, metabolic syndrome, and retinal degeneration keep circling back to this same molecule, and their findings are starting to tell a coherent story about what bile acids actually do in the human body beyond digesting fat.

The Molecule That Refused to Stay in Its Lane

Understanding why TUDCA keeps appearing in such disparate research requires a quick detour into how bile acids work as signaling molecules. The old textbook view treated bile acids as biological detergents, synthesized in the liver, secreted into the gut, and recycled through enterohepatic circulation. That view isn’t wrong, but it’s incomplete in ways that matter enormously. Bile acids activate at least two major receptor systems: the farnesoid X receptor (FXR), a nuclear receptor that regulates bile acid synthesis, glucose metabolism, and lipid homeostasis; and TGR5 (also called GPBAR1), a G protein-coupled receptor expressed in tissues ranging from the intestinal epithelium to the brain. A 2024 review in Frontiers in Nutrition documented how FXR activation reduces hepatic gluconeogenesis and triglyceride synthesis while improving insulin sensitivity, and how TGR5 signaling stimulates GLP-1 release from intestinal L-cells and promotes thermogenesis in brown adipose tissue (1). These aren’t marginal effects. They sit at the center of metabolic regulation, and TUDCA, being fully ionized and water-soluble across a wide pH range, reaches these receptors more efficiently than its unconjugated parent compound UDCA (2).

What has made TUDCA especially interesting to cell biologists, though, is a property that has nothing to do with bile acid receptors. TUDCA functions as a chemical chaperone, a small molecule that stabilizes protein folding inside the endoplasmic reticulum (ER). When cells are stressed by inflammation, metabolic dysfunction, or genetic mutations that produce misfolded proteins, the ER triggers what’s called the unfolded protein response, or UPR. The UPR is a survival mechanism, but when it stays activated chronically, it drives cells toward apoptosis. TUDCA appears to dampen this destructive cycle by assisting protein folding and activating the ATF6 arm of the UPR, which promotes adaptive rather than apoptotic signaling (3). A 2024 study from Janelia Research Campus complicated this picture somewhat by showing that in yeast models, TUDCA’s protective effect against the ER stressor tunicamycin came partly from reducing the drug’s bioavailability through micelle formation rather than pure chaperone activity (4). The finding doesn’t invalidate years of mammalian cell data, but it does suggest the mechanism is more complex than “TUDCA helps proteins fold better,” and that’s probably a good thing to keep in mind as the clinical story unfolds.

The ALS Disappointment and What It Actually Means

No discussion of TUDCA’s therapeutic trajectory can avoid the ALS data, because it illustrates both the promise and the peril of translating preclinical excitement into human benefit. The backstory looked encouraging. A phase IIb proof-of-concept trial had shown that patients receiving TUDCA alongside riluzole experienced roughly seven fewer points of annual decline on the ALSFRS-R scale compared to riluzole alone, corresponding to an estimated four to five months of prolonged median survival (5). A retrospective population-based cohort study published in eClinicalMedicine in 2023 supported the signal (6). So when a multinational phase III trial launched across 25 European centers, expectations ran high.

The results, announced in March 2024, were unambiguous. After 18 months, TUDCA showed no statistically significant difference from placebo on the primary endpoint, defined as a greater-than-20% reduction in the slope of ALSFRS-R decline. Secondary endpoints, including survival time and neurofilament light protein biomarker changes, also came up empty (7). The trial had enrolled 336 patients rather than the planned 440 due to COVID-related recruitment disruptions, which weakened its statistical power, but the investigators themselves acknowledged that the effect signal simply wasn’t there. TUDCA was well tolerated, with only mild gastrointestinal side effects in both arms, so safety wasn’t the issue. Efficacy was.

The parallel story of Relyvrio makes this even more instructive. Amylyx Pharmaceuticals had developed AMX0035, a combination of sodium phenylbutyrate and taurursodiol (a form of TUDCA), which received FDA approval for ALS in September 2022 on the basis of a small phase II trial. The company charged $163,000 per year and generated $381 million in sales in 2023. Then the phase III PHOENIX trial reported in April 2024 that AMX0035 failed to meet its primary or secondary endpoints (8). Amylyx announced in September 2024 it would withdraw Relyvrio from the market, and the FDA formally revoked approval in August 2025 (9). The Relyvrio episode carries a specific lesson about TUDCA: the compound’s genuine biological activity against ER stress, mitochondrial dysfunction, and neuroinflammation in preclinical ALS models did not translate into measurable clinical benefit in large controlled trials. This doesn’t mean the biology was wrong. It may mean that by the time ALS patients present clinically, the neurodegenerative cascade has progressed past the point where modulating ER stress can slow it meaningfully.

Where the Metabolic Evidence Is Stronger

The metabolic data, by contrast, has a sturdier foundation in human physiology. A clinical study published in Diabetes by Kars and colleagues demonstrated that oral TUDCA administration improved hepatic and muscle insulin sensitivity by approximately 30% in obese men and women, measured by hyperinsulinemic-euglycemic clamp, the gold standard for assessing insulin action (10). The effect was mediated through increased phosphorylation of insulin receptor substrate 1 (IRS-1) and Akt activation in muscle tissue, providing a clear mechanistic link between ER stress reduction and improved insulin signaling. Adipose tissue insulin sensitivity didn’t budge, which is a useful reminder that TUDCA’s effects are tissue-specific rather than systemic.

Mouse studies have pushed this further. A 2022 paper in Scientific Reports showed that TUDCA reduced age-related hyperinsulinemia by increasing expression of insulin-degrading enzyme in the liver, improving insulin clearance alongside reduced adiposity and increased energy expenditure (11). Another 2022 study in Redox Biology identified TUDCA as a critical downstream effector of metformin’s insulin-sensitizing action, suggesting the world’s most widely prescribed diabetes drug may work partly through bile acid signaling pathways that nobody was looking at when metformin was approved in the 1990s (12). A 2023 review in Frontiers in Endocrinology compiled evidence that TUDCA activates both FXR and TGR5 to improve glucose homeostasis and lipid metabolism, while simultaneously alleviating ER stress in dysfunctional adipose tissue (13). The convergence of receptor-mediated and chaperone-mediated mechanisms in the same molecule makes TUDCA a genuinely unusual pharmacological tool for studying metabolic disease, even if clinical trials in type 2 diabetes haven’t yet matured past early phases.

The Retinal Protection Puzzle

Perhaps the most intriguing thread in TUDCA research is its consistent neuroprotective effect in the retina, a tissue where ER stress, oxidative damage, and inflammation converge in diseases ranging from retinitis pigmentosa to diabetic retinopathy. A 2024 systematic review in Current Neuropharmacology evaluated 24 studies meeting inclusion criteria and found that TUDCA delayed retinal neuron degeneration and preserved retinal structure and function across multiple disease models (14). The mechanisms involved inhibiting apoptosis, suppressing ER stress, reducing oxidative damage, and attenuating neuroinflammation. A 2025 study published in Pharmaceuticals confirmed that TUDCA protected retinal ganglion cells after optic nerve crush injury in mice, reducing both cell death and expression of pro-inflammatory genes as measured by digital droplet PCR (15). Another 2025 paper demonstrated that TUDCA induced protective autophagy in retinal pigment epithelial cells via mTORC1/mTORC2-independent pathways, suggesting the compound can activate cellular self-cleaning mechanisms that are critical for long-term retinal health (16).

The retinal data sits in an interesting evidential position. No human clinical trials have specifically tested TUDCA for retinal degeneration, so these findings remain preclinical. But the consistency across models and mechanisms is striking, and the retina offers certain advantages as a clinical target. It’s accessible to imaging, allowing researchers to measure structural changes with optical coherence tomography (OCT) in real time. Functional endpoints like visual acuity and electroretinography are well-validated. And because retinal degenerative diseases progress relatively slowly compared to ALS, a therapeutic window for ER stress modulation may actually exist in a way it doesn’t for motor neuron disease. If TUDCA clinical trials in ophthalmology happen, and given the preclinical consistency they should, the retina could become the tissue where TUDCA’s chaperone biology finally proves itself in humans.

The Alzheimer’s Question Mark

TUDCA’s preclinical Alzheimer’s data is promising but earlier-stage. In transgenic mouse models, TUDCA diets initiated before significant amyloid deposition prevented deficits in spatial, recognition, and contextual memory over six months of treatment. The mechanistic picture involves multiple pathways: TUDCA decreased amyloid-beta-induced activation of caspase-3 and subsequent tau cleavage, while promoting PI3K/Akt signaling to inhibit GSK3-beta activity and reduce tau hyperphosphorylation (17). A phase II trial called Pegasus (NCT03533257) completed enrollment of 96 participants testing the AMX0035 combination (TUDCA plus sodium phenylbutyrate) in Alzheimer’s disease, but the withdrawal of Relyvrio from the ALS market has cast a shadow over the broader AMX0035 program (18). Amylyx also discontinued its AMX0035 program in progressive supranuclear palsy after disappointing phase IIb results. Whether TUDCA alone, separated from the phenylbutyrate combination, might perform differently in Alzheimer’s remains an open and testable question. The preclinical data specifically on TUDCA’s anti-amyloid and anti-tau effects is strong enough to warrant dedicated investigation, but nobody appears to be running that trial yet.

Bile Acids as a Class: What Comes Next

The broader context for TUDCA’s research trajectory is a fundamental reassessment of bile acids as signaling molecules rather than digestive chemicals. The discovery that FXR and TGR5 regulate glucose metabolism, lipid storage, inflammation, and even intestinal barrier integrity has created an entire therapeutic class that pharmaceutical companies are only beginning to exploit. Obeticholic acid, an FXR agonist, already has approval for primary biliary cholangitis, and multiple TGR5 agonists are in preclinical development for obesity and type 2 diabetes. TUDCA occupies a unique position in this space because it activates both receptor systems while simultaneously functioning as a chaperone. That dual mechanism gives it a pharmacological profile that purely receptor-targeted drugs can’t replicate.

The honest assessment of where TUDCA stands in early 2026 requires holding two realities at once. The ALS and Relyvrio failures demonstrate that preclinical promise in neurodegeneration doesn’t automatically translate to clinical efficacy, and the field should be chastened by that. The compound didn’t work where patients most desperately needed it to work. At the same time, the metabolic data in humans is real: 30% improvements in hepatic and muscle insulin sensitivity aren’t trivial, and the mechanistic explanations for those improvements are well-characterized. The retinal neuroprotection data is preclinically consistent in ways that demand proper clinical testing. And the broader bile acid signaling field keeps producing findings that make TUDCA’s multi-target pharmacology more interesting, not less, as our understanding of metabolic disease deepens. TUDCA’s story isn’t one of a wonder molecule that fixes everything. It’s the story of a compound whose biology keeps revealing new connections between systems we used to study separately, and the clinical work of figuring out where those connections actually matter for patients is still very much in progress.

References

  1. “Regulation of bile acids and their receptor FXR in metabolic diseases.” Frontiers in Nutrition, 2024. DOI: 10.3389/fnut.2024.1447878

  2. “A multicenter, randomized, double-blind trial comparing the efficacy and safety of TUDCA and UDCA in Chinese patients with primary biliary cholangitis.” Medicine, 2016. DOI: 10.1097/MD.0000000000004864

  3. “Tauroursodeoxycholate—Bile Acid with Chaperoning Activity: Molecular and Cellular Effects and Therapeutic Perspectives.” Cells, 2019. DOI: 10.3390/cells8121471

  4. “TUDCA modulates drug bioavailability to regulate resistance to acute ER stress in Saccharomyces cerevisiae.” Molecular Biology of the Cell, 2025. DOI: 10.1091/mbc.E24-04-0147

  5. “Tauroursodeoxycholic acid in the treatment of patients with amyotrophic lateral sclerosis.” European Journal of Neurology, 2016. PMID: 25664595

  6. “Effect of tauroursodeoxycholic acid on survival and safety in amyotrophic lateral sclerosis: a retrospective population-based cohort study.” eClinicalMedicine (The Lancet), 2023. DOI: 10.1016/j.eclinm.2023.102256

  7. “TUDCA-ALS Top-Line Results Announcement.” TUDCA-ALS Consortium / MND Association, March 2024. www.tudca.eu/top-line-results-announcement/

  8. “Tauroursodeoxycholic Acid Falls Short in Phase 3 Study of Amyotrophic Lateral Sclerosis.” NeurologyLive, 2024. www.neurologylive.com/view/tauroursodeoxycholic-acid-falls-short-phase-3-study-amyotrophic-lateral-sclerosis

  9. “Amylyx Pharmaceuticals, Inc.; Withdrawal of Approval of New Drug Application for RELYVRIO.” Federal Register, August 29, 2025. www.federalregister.gov/documents/2025/08/29/2025-16646/

  10. Kars M, et al. “Tauroursodeoxycholic Acid May Improve Liver and Muscle but Not Adipose Tissue Insulin Sensitivity in Obese Men and Women.” Diabetes, 2010;59(8):1899–1905. DOI: 10.2337/db10-0308

  11. “The bile acid TUDCA reduces age-related hyperinsulinemia in mice.” Scientific Reports, 2022. DOI: 10.1038/s41598-022-26915-3

  12. “Tauroursodeoxycholic acid functions as a critical effector mediating insulin sensitization of metformin in obese mice.” Redox Biology, 2022. DOI: 10.1016/j.redox.2022.102481

  13. “Insights by which TUDCA is a potential therapy against adiposity.” Frontiers in Endocrinology, 2023. DOI: 10.3389/fendo.2023.1090039

  14. Li J, et al. “Neuroprotective Effect of Tauroursodeoxycholic Acid (TUDCA) on In Vitro and In Vivo Models of Retinal Disorders: A Systematic Review.” Current Neuropharmacology, 2024;22(7):1295–1306. DOI: 10.2174/1570159X22666230904150737

  15. “Tauroursodeoxycholic Acid Protects Retinal Ganglion Cells and Reduces Inflammation in Mice Following Optic Nerve Crush.” Pharmaceuticals, 2025;18(4):569. DOI: 10.3390/ph18040569

  16. “Tauroursodeoxycholic Acid Confers Protection Against Oxidative Stress via Autophagy Induction in Retinal Pigment Epithelial Cells.” Current Issues in Molecular Biology, 2025;47(4):224. DOI: 10.3390/cimb47040224

  17. “Tauroursodeoxycholic acid: a bile acid that may be used for the prevention and treatment of Alzheimer’s disease.” Frontiers in Neuroscience, 2024. DOI: 10.3389/fnins.2024.1348844

  18. “Phase 2 Trial of Tauroursodeoxycholic Acid for Alzheimer Disease Completes Enrollment.” Practical Neurology, 2023. practicalneurology.com/news/phase-2-trial-of-tauroursodeoxycholic-acid-for-alzheimer-disease-completes-enrollment/