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A computational study of the interaction between nanoplastic and model biological membranes

Final Report Summary - NANOPLAST (A computational study of the interaction between nanoplastic and model biological membranes)

Every year, millions of tons of plastic litter are reversed into the oceans, washed up on the shores or piled in landfills. There, plastics are degraded down to the micro and nano scale, and enter the food chain. Plastic particles can transport toxic substances, but the effects of micro and nanoplastics themselves on living organisms is still largely unknown.
When plastic nanoparticles enter in contact with living organisms, the first barrier they come in contact with is the cell membrane. The objective of the NANOPLAST project is the understanding of the mechanisms of interaction between nanoplastics and model biological membranes. Our main goal is to identify possible physical mechanisms of damage to the cell membrane induced by the interaction with plastic nanofragments. NANOPLAST is a computational project: we are using new models and cutting-edge computational tools to simulate in silico the nanoplastic-membrane interaction.
During the first half of the project we successfully developed new molecular, coarse-grained models for two common hydrophobic polymers, namely polypropylene (PP) and polyethylene (PE). We then used our new models to study the interaction of polymer nanoparticles with lipid membranes. We considered both homogeneous membranes, constituted by a single type of lipid molecules, and laterally heterogeneous membranes, made of a mixture of different lipids phase-separating into liquid-ordered and liquid-disordered phases. The latter, while posing more challenges from a technical point of view, are more realistic models of plasma membranes, whose lipid composition is extremely rich.
In the last year of the project we have fully characterized the behavior of three hydrophobic polymers in model lipid bilayers. Polyethylene, polypropylene and polystyrene (PS) are all favorably embedded by the hydrophobic core of lipid bilayers. Still, their behavior in the membrane core is not the same. When interacting with homogeneous 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) membranes, PP and PS dissolve in the core of the bilayer, while PE shows the tendency to form liquid aggregates. The behavior of the three polymers differs in laterally heterogeneous membranes, as well. In a ternary lipid mixture exhibiting phase separation between liquid-ordered and liquid-disordered states, PP disfavor lipid phase separation while PS enhances it. PE modifies the topology of the phase boundaries and causes cholesterol depletion from the liquid ordered phase.
These changes of membrane structure and lipid lateral organization are potentially dangerous for the overall functioning of the membrane in the biological environment.
Thanks to the CIG grant, the fellow, Dr. Giulia Rossi, has been able to hire a post-doc researcher (Dr. Davide Bochicchio) who will work at the project until March, 2016. The PhD application that was pending at the time of the first periodic report has been accepted. The group computational facilities have been enriched by the purchase of 4 workstations equipped with GPUs.