NUS Engineers Gut Bacteria to Block Liver Toxins from Reaching the Brain in Breakthrough Study

Singapore's National University of Singapore (NUS) has made a remarkable advance in synthetic biology with researchers engineering beneficial gut bacteria to combat a devastating complication of liver failure. This innovation targets hepatic encephalopathy (HE), a condition where toxins like ammonia build up in the blood due to impaired liver function and cross into the brain, causing cognitive impairment, anxiety, confusion, and even coma. The programmable 'living medicines' offer a multi-pronged approach that could transform treatment for patients worldwide, particularly in regions like Singapore where liver diseases are on the rise.

The breakthrough comes from Professor Matthew Chang and his team at NUS's Synthetic Biology for Clinical and Technological Innovation (SynCTI) programme, housed within the Yong Loo Lin School of Medicine. Over an intensive eight-year effort, they redesigned strains of the safe, naturally occurring gut bacterium Lactobacillus plantarum WCFS1. This common probiotic was modified using genetic engineering techniques to address the root causes of HE simultaneously: excess ammonia production and depletion of essential nutrients.

The Gut-Liver-Brain Axis: Understanding the Problem

The gut-liver-brain axis refers to the bidirectional communication between these organs, heavily influenced by the gut microbiome—the trillions of microorganisms residing in our intestines. In liver cirrhosis or acute failure, the liver's detoxification capacity falters, allowing ammonia and other neurotoxins produced by gut bacteria to enter the bloodstream. These toxins disrupt brain function, leading to HE, which affects up to 30-40% of cirrhosis patients globally and is a frequent cause of hospitalization.

In Singapore, non-alcoholic fatty liver disease (NAFLD) prevalence has climbed to around 30% in adults, driven by rising obesity and diabetes rates, according to Ministry of Health data. Chronic hepatitis B remains significant, with a seroprevalence of about 3.6%. HE not only worsens quality of life but also imposes a heavy economic burden, with repeated hospital admissions and limited effective therapies. Current standard treatment, the antibiotic rifaximin, reduces ammonia-producing bacteria but often disrupts the overall microbiome, leading to resistance and incomplete symptom relief.

Engineering 'Living Medicines': How NUS Did It

SynCTI researchers created two complementary bacterial strains:

• Lp-NH3: This strain absorbs excess ammonia from the gut and converts it into branched-chain amino acids (BCAAs) like valine—nutrients often deficient in HE patients and crucial for liver repair and brain health.
• Lp-Q: Targets L-glutamine, a major ammonia precursor, breaking it down into usable metabolites while preventing further toxin buildup.

Administered orally as a cocktail, the bacteria colonize the gut transiently, acting precisely where needed before clearing naturally within 72 hours. This modularity allows future tweaks for other diseases, positioning NUS at the forefront of microbiome engineering.

Rigorous Testing in Mouse Models

The study employed two preclinical models mimicking human HE: a hyperammonemic diet-induced model and bile duct ligation (BDL), simulating cirrhosis. Mice received daily oral doses of the bacterial cocktail for weeks, with outcomes measured via blood/brain ammonia levels, metabolomics, behavioral tests, transcriptomics, and microbiome sequencing.

Results were striking: the cocktail slashed serum ammonia up to 10-fold—far surpassing rifaximin—and normalized brain levels to healthy baselines. It restored BCAA deficits and curbed glutamine excess, leading to:

• Improved short-term memory in novel object recognition tests.
• Reduced anxiety-like behaviors in open-field and elevated zero maze assays.
• Normalized neuronal signaling (e.g., dopamine/serotonin pathways) and lowered neuroinflammation (fewer cytokines like IL-1β).

Photo by Danist Soh on Unsplash

Superior to Standard Care: A Game-Changer

Compared to rifaximin, NUS's approach multitasks—tackling ammonia absorption, production blockade, and nutrient restoration—while safeguarding the microbiome. Rifaximin broadly kills bacteria, risking dysbiosis and resistance. The engineered strains' precision could reduce hospitalization rates, a boon for Singapore's ageing population facing rising liver burdens.

Singapore's Higher Education Edge in Biotech

This achievement underscores NUS's leadership in synthetic biology, bolstered by SynCTI's interdisciplinary ecosystem. Launched to bridge lab-to-clinic gaps, SynCTI integrates engineering, medicine, and data science, attracting top talent and funding. For aspiring researchers, NUS offers robust PhD programmes in microbiome engineering, with opportunities in the National Centre for Engineering Biology (NCEB).

Singapore's ecosystem—home to A*STAR and strong IP frameworks—accelerates translation. A patent is filed, paving for clinical trials, potentially positioning local universities as hubs for microbial therapeutics.

Global Implications and Broader Research Landscape

HE affects millions; globally, liver cirrhosis claims 1.3 million lives yearly (WHO). This platform could extend to urea cycle disorders or kidney failure hyperammonemia. Related NUS work includes probiotics for leaky gut and antimicrobial resistance mitigation, highlighting microbiome's therapeutic potential.

In Singapore, where NAFLD surges with metabolic syndrome, such innovations align with national health goals. Experts hail it as a 'paradigm shift' toward living drugs.

Careers in Synthetic Biology at Singapore Universities

NUS's success fuels demand for experts in genetic engineering and microbiology. Roles span faculty positions, research associates, and biotech startups. With Singapore's R&D investments, graduates enjoy competitive salaries—median S$80,000 for PhDs—and global impact.

Photo by Paras Kapoor on Unsplash

• Skills needed: CRISPR, metabolomics, animal models.
• Opportunities: NUS, NTU, A*STAR labs.

Challenges and the Road to Clinic

While promising, human trials must confirm efficacy and safety. Scalability, dosing, and patient variability pose hurdles. Prof Chang notes: 'Our goal is a new class of therapies.' Regulatory nods from HSA could fast-track, given Singapore's biotech friendliness.

Future Outlook: Programmable Microbes Revolution

This NUS milestone heralds an era of designer microbiomes for chronic ills. As liver diseases climb—projected 30% NAFLD rise by 2030 in Asia—such innovations offer hope, reducing reliance on transplants. For higher ed, it inspires curricula blending biology and engineering, preparing Singapore's next innovators.

For more on NUS research excellence, explore opportunities in synthetic biology.