Microplastics Reduce Lipid Digestion in Simulated Human Gastrointestinal System

Microplastics (MPs) are unavoidably ingested by humans, and their gastrointestinal processes and impact on lipid digestion are unknown. In the present work, all five MP types used, including polystyrene (PS), polyethylene terephthalate, polyethylene, polyvinyl chloride, and poly(lactic-<i>co</i>-glycolic acid) (80 mg/L in small intestine), significantly reduced lipid digestion in the in vitro gastrointestinal system. PS MPs exhibited the highest inhibition (12.7%) among the five MPs. Lipid digestion decreased with increasing PS concentration, but independent of PS size (50 nm, 1 μm, 10 μm). PS MPs after photoaging by simulated sunlight also significantly decreased lipid digestion. Confocal imaging shows that PS MPs could interact with both lipid droplets and lipases. Two mechanisms underlying the PS-induced digestion inhibition were revealed using both experimental and molecular dynamics simulation approaches: (1) PS MPs decreased the bioavailability of lipid droplets via forming large lipid-MPs heteroaggregates due to the high MP hydrophobicity; and (2) PS MPs adsorbed lipase, and reduced its activity by changing the secondary structure and disturbing the essential open conformation. The first mechanism (MP-lipid interaction) played a more important role in lipid digestion reduction based on interaction energy calculation. These findings reveal potential risk of MPs to human digestion health and nutrient assimilation.