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Towards understanding particle-protein complexes: Physicochemical, structural, and cellbiological characterization of β-lactoglobulin interactions with silica, polylactic acid, and polyethylene terephthalate nanoparticles
Summary
This study examined how protein molecules in food coat the surfaces of nanoplastic particles — a process called protein corona formation — and what effect those coated particles have on human gut cells. Using three different nanoparticle types (silica, PLA, and PET), the researchers found that PET nanoplastics bound the least protein and were not taken up by simulated intestinal cells, while silica-protein complexes were internalized and impaired cell growth. The findings suggest that the protein corona around nanoplastics changes their behavior in the gut in ways that depend heavily on the particle's surface chemistry. This is relevant to understanding how nanoplastics interact with human digestive tissue after ingestion.
Nanoplastic particles and their additives are increasingly present in the food chain, interacting with biomacromolecules with not yet known consequences. A protein corona forms around the particles in these usually complex matrices, primarily with a first contact at surface-active proteins. However, systematic studies on the interactions between the particles and proteins -especially regarding protein affinity and structural changes due to surface properties like polarity - are limited. It is also unclear whether the protein corona can "mask" the particles, mimic protein properties, and induce cytotoxic effects when internalized by mammalian cells. This study aimed at investigating the physicochemical properties of model particle-protein complexes, the structural changes of adsorbed proteins, and their effects on Caco-2 cells. Whey protein β-lactoglobulin (β-Lg) was used as a well-characterized model protein and studied in a mixture with nanoparticles of varying polarity, specifically silica, polylactic acid (PLA), and polyethylene terephthalate (PET). The physicochemical analyses included measurements of the hydrodynamic diameter and the zeta potential, while the protein conformational changes were analyzed using Fourier-transform-infrared spectroscopy (FTIR) and intrinsic fluorescence. Cellular uptake in Caco-2 cells was assessed through flow cytometry, cell viability was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide (MTT) assay, and cellular impedance was analyzed with xCELLigence® technology. The results indicated that β-Lg had the highest affinity for hydrophilic silica particles, forming silica-β-Lg complexes and large aggregates through electrostatic interactions. The affinity decreased for PLA and was lowest for hydrophobic PET, which formed smaller complexes. Adsorption onto silica caused partial unfolding and refolding of β-Lg. The silica-β-Lg complexes were internalized by Caco-2 cells, impairing cell proliferation. In contrast, PLA- and PET-protein complexes were not internalized, though PLA complexes slightly reduced cell viability. This study enhances our understanding of protein adsorption on nanoparticles and its potential biological effects.
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