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-co-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.
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