Nanoplastics Alter Lateral and Transverse Distributions of Cholesterol in Model Cell Membranes

Microplastics, tiny fragments resulting from the degradation of plastic waste, are abundant in water, air, and soil and are currently recognized as a global environmental problem. There is also growing evidence that nanosized microplastics (nanoplastics) can be hazardous to living species. Unlike most experimental methods, computer modeling is particularly well suited to studying the effects of such nanoplastics. Here we use atomic-scale computer simulations to explore for the first time the impact of polypropylene and polystyrene nanoparticles on model cell membranes containing cholesterol, an essential component of membranes of eukaryotic cells. Our findings clearly show that, once a polymer nanoparticle (∼4.0-4.5 nm in diameter) partitions into the membrane interior, it alters both the lateral and transverse distributions of cholesterol. Nanoplastics induce the formation of domains depleted in cholesterol and also promote cholesterol flip-flops. These changes could have severe consequences for living cells as they affect the fluidity and the phase behavior of membranes, the transmembrane cholesterol distribution, and the ability of membranes to balance the stress.