Microplastics are now turning up in human bile, and new research reveals how these tiny particles may disrupt cellular function and potentially contribute to gallstone disease.
Study: Microplastics accumulate in human bile and drive cholangiocyte senescence. Image credit: RHJPhtotos/Shutterstock.com
A recent Environmental Science and Ecotechnology study investigated microplastic accumulation and its chronic toxic effects on the human biliary system. It also explored potential therapeutic interventions against microplastic-induced cellular damage in vitro using experimental models.
Microplastics as Emerging Contaminants
Plastics are highly valued in manufacturing for their durability, affordability, and corrosion resistance. However, these same properties confer significant environmental persistence, rendering plastics resistant to natural degradation processes. The surge in plastic production has led to the accumulation of plastic waste, which reached around 350 million metric tons in 2019 and could surpass 1 billion metric tons per year by 2060.
Over time, physical wear, sunlight, and biological activity break larger plastic items into tiny fragments known as microplastics (MPs), which range in size from 1 μm to 5 mm. Multiple studies have detected MPs across atmospheric, terrestrial, and aquatic compartments. These tiny particles have infiltrated the food chain, positioning them as contaminants of significant environmental and public health concern.
MPs have been identified across multiple human biological matrices, including pulmonary tissue, placenta, feces, cerebral tissue, and semen, confirming systemic bioaccumulation. Both in vitro and in vivo evidence demonstrates that MP internalization induces oxidative stress, pro-inflammatory cascades, and histopathological lesions in the kidneys, intestines, and liver.
A key limitation, however, is that most studies use MP concentrations far above real-world levels and rely on short-term exposure models that do not accurately reflect chronic, low-dose human exposure.
Assessing MP Presence in Bile and Its Consequences
The biliary tract, which includes the gallbladder and bile ducts, is responsible for producing and transporting bile, a fluid that aids digestion and helps the body eliminate certain waste products. When the balance of bile components, such as cholesterol, bilirubin, and bile acids, is disrupted, gallstones can form. Because bile is also an excretory fluid, researchers believe that it may represent a potential route through which the body processes and eliminates MPs after ingestion.
Bile's lipid-rich composition may preferentially bind certain plastic polymers, promoting MP accumulation. It is an underexplored but potentially significant matrix for studying MP transit and clearance, and raises concern over its possible role in biliary pathologies, such as gallstone formation.
The current study employed a multimodal approach to assess and quantify the mass concentration, types, and physical characteristics of MPs in human bile. Furthermore, the chronic cytotoxic effects of MPs were assessed using in vitro cell-based models, providing novel insights into the health risks posed by MPs in the biliary system.
Bile samples were collected from Dongguan People's Hospital patients undergoing laparoscopic cholecystectomy. Patients between 18 and 80 years of age with typical upper abdominal pain and tenderness, imaging-confirmed gallstones on magnetic resonance imaging (MRI) and/or computed tomography (CT) were recruited.
Exclusion criteria comprised a history of non-calculous biliary diseases, prior biliary surgery, severe comorbidities contraindicating surgical or endoscopic intervention, and pregnancy or lactation.
Elevated MP Burden in Gallstone Bile Triggers Cellular Senescence Through Mitochondrial Impairment
The study cohort comprised five participants in the non-gallstone control group (CG) and nine participants in the gallstone group (GG). The average age of the participants was 56.29 years, with a balanced distribution of males and females. Three patients reported a history of alcohol consumption, while one patient had a history of smoking. The majority of participants resided in urban areas, and half were classified as overweight.
Liver function indices were significantly elevated in the GG group compared to the CG group, with alanine transaminase (ALT), aspartate transaminase (AST), total bilirubin, direct bilirubin, and indirect bilirubin all reaching statistical significance. No significant difference in bile acids was observed between the two groups.
Pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) analysis revealed the presence of MPs in all bile samples. Among the 11 polymer categories examined, six types of MPs were identified, with polyethylene terephthalate (PET, 68.05 %) and polyethylene (PE, 27.11 %) predominating. Other polymers detected at minor levels included polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), and polyamide 66 (PA66).
The total concentration of MPs was slightly higher in individuals under 60 years of age compared to those 60 years and older, and marginally higher in males than in females, though these differences were not statistically significant.
MP distribution was not uniform across groups. PE and PP were present in all samples, while PS and PA66 were exclusive to the gallstone bile (GB) group. PET was detected in all GB samples and in 60 % of control bile (CB) samples. The overall MP burden was markedly higher in the GB group. PP and PVC concentrations did not differ significantly between groups.
These findings indicate that bile from gallstone patients contains substantially higher MP levels, though this represents an association and does not establish that microplastics cause gallstones, and further validation in larger cohorts is warranted.
Laser direct infrared (LDIR) spectroscopy identified 32 distinct polymer types in bile MPs, with polyamide (PA, 29.57 %), acrylic polymers (ACR, 15.74 %), and chlorinated paraffins (CPE, 15.44 %) being the most prevalent, reflecting methodological differences in detection compared with Py-GC/MS. Most MPs (86.42 %) measured 20–50 μm, and SEM imaging confirmed diverse morphologies, including irregular, rod-shaped, and spherical particles.
Chronic low-dose polystyrene nanoparticle (PS-NP) exposure at 0.04 mg mL−1 for seven days induced time- and concentration-dependent cytotoxicity in HuCCT1 cholangiocytes. Proteomic analysis revealed downregulation of 425 proteins and upregulation of 197, with enrichment in metabolic, cell cycle, and cancer-related pathways. This study also identified 25 senescence-associated molecules, including upregulated BHLHE40, CDKN1B, and G6PD and downregulated AURKA.
Experimental validation confirmed senescence through elevated senescence-associated beta-galactosidase (SA-β-gal) activity, G1-phase cell cycle arrest, and upregulation of senescence-associated secretory phenotype (SASP) markers interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), an effect observed across multiple polymer types, including PE and PP.
Mechanistically, PS-NP exposure impaired mitochondrial function by reducing ATP levels, increasing ROS production, promoting Drp1 translocation, and decreasing membrane potential, all of which were partially reversed under experimental conditions by co-administration of melatonin, a mitochondrial-targeted antioxidant.
Conclusions
This study found MPs in human bile and reported an association with gallstone diseases, showing that low-dose MPs in in vitro experimental systems can trigger cholangiocyte senescence through mitochondrial dysfunction.
These findings are limited by a small sample size, a single-center design, incomplete exposure assessment, uncertainty about how experimental exposure levels compare with real-world human exposure, and a lack of long-term in vivo data. Future studies should expand the sample size, improve exposure assessment, and use animal models to confirm mechanisms and explore potential therapies.
Download your PDF copy by clicking here.
How Traditional Chinese Medicine may reshape the gut microbiome to ease insulin resistance in PCOS