Membrane outer leaflet is the primary regulator of membrane damage induced by silica nanoparticles in vesicles and erythrocytes

Abstract

Plasma membrane damage is one of the primary mechanisms through which engineered nanoparticles induce cell toxicity. Over the past decade, a number of mechanistic studies have used membrane models to examine how nanoparticles alter membrane structure and integrity. However, the role of membrane lipid asymmetry, considering that the plasma membrane has a different lipid composition in the exofacial leaflet compared to the cytofacial leaflet, in regulating nanoparticle–membrane interactions has remained obscure. In the current study, the role of individual membrane leaflets in regulating the interactions of membrane models and erythrocytes with engineered silica nanoparticles (50 and 100 nm) was examined. It was found that silica nanoparticles bind to and disrupt synthetic vesicles mimicking the exofacial leaflet but not those mimicking the cytofacial leaflet of the erythrocyte plasma membrane. Förster resonance energy transfer (FRET) studies revealed that nanoparticles disrupted vesicle integrity by inducing pore formation in vesicles. Imaging giant unilamellar vesicles and further FRET experiments revealed that nanoparticles that disrupt membrane integrity show significant localization at the vesicle surface. Nanoparticles that disrupted vesicles mimicking the exofacial leaflet also induced hemolysis in erythrocytes, suggesting that the exofacial leaflet is the primary regulator of nanoparticle-induced membrane damage. This was confirmed by demonstrating that nanoparticles caused a similar disruptive behavior in symmetric and asymmetric vesicles, which had similar outer leaflet, but different inner leaflet lipid compositions. Together, these studies reveal that membrane lipid asymmetry plays a minor role in nanoparticle-induced membrane disruption with the exofacial leaflet being the primary regulator of interactions.