The Role of Membrane Asymmetry in Nanoparticle-Induced Plasma Membrane Damage

Abstract

Over the past decade, there has been increasing interest in understanding the interactions between nanomaterials and the cell plasma membrane. However, despite a number of studies, the structural complexities of the plasma membrane including lipid asymmetry between the cytofacial and exofacial leaflets have been largely overlooked. The present study focused on the role of individual membrane leaflets in regulating nanoparticle-plasma membrane interactions. Specifically, the effects of amine, hydroxyl, and polyethylene glycol(PEG)-modified silica nanoparticles (105 ± 4 nm) on the integrity of vesicles mimicking the exofacial (Vexo) and cytofacial leaflets (Vcyto) of the plasma membrane of erythrocytes was examined and compared with nanoparticle-induced hemolysis in erythrocytes. Vesicle integrity was studied by encapsulating the self-quenching fluorescent probe, carboxyfluorescein, in vesicles and studying its leakage after exposure to 0.0001-0.01 g/L of nanoparticles at 37 °C. Confocal microscopy on giant unilamellar vesicles was used to monitor nanoparticle effects on vesicle morphology. Nanoparticle-induced hemolysis was evaluated by measuring the absorbance of hemoglobin released from erythrocytes after incubation with 0.01 g/L of nanoparticles at 37 °C. Nanoparticle interactions with Vexo and Vcyto vesicles were drastically different. Vexo vesicles showed significant leakage after exposure to hydroxyl- and amine-modified nanoparticles, but were not disrupted by PEGylated nanoparticles. Conversely, none of the particles caused significant leakage in Vcyto vesicles. GUV images indicated visual disruption of Vexo vesicles by nanoparticles. Interestingly, hemolysis of erythrocytes by nanoparticles was consistent with leakage assays using Vexo vesicles. Hemolysis was observed after erythrocyte incubation with hydroxyl- and amine-modified particles, but not after incubation with PEGylated particles. In conclusion, these results suggest that artificial vesicles mimicking the lipid composition of the exofacial leaflet of the cell plasma membrane might be a useful tool in predicting nanoparticle-induced membrane damage in cells.