Does Membrane Asymmetry Affect Nanoparticle-Membrane Interactions

Abstract

Plasma membrane damage is one of the primary mechanisms through which engineered nanomaterials cause cytotoxicity. Despite a number of studies, the role of the structural features of the plasma membrane, in particular membrane phospholipid asymmetry in regulating nanoparticle-membrane interactions has remained obscure. In the current study, the role of membrane phospholipid asymmetry, differences in the lipid composition of exofacial and cytofacial leaflet of the plasma membrane in regulating nanoparticle-membrane interactions was investigated. Vesicles mimicking the exofacial (Vexo) and cytofacial leaflets (Vcyto) of the plasma membrane of erythrocytes were exposed to silica nanoparticles (50 nm), with different surface functional groups, plain, or carboxyl-, amine-, and polyethylene glycol (PEG)-modified and the effect of particles on vesicle integrity was examined. Symmetric and asymmetric vesicles with similar outer leaflet, but different inner leaflet lipid compositions, as well as live erythrocytes, were also used to elucidate the role of membrane asymmetry and individual leaflets in regulating nanoparticle-membrane interaction. Vexo and Vcyto vesicles showed significant difference in their interactions with nanoparticles. Vexo vesicles showed drastic leakage of intravesicular content after exposure to plain and amine-modified particles while none of the particles caused significant leakage in Vcyto vesicles. FRET experiments revealed that nanoparticle-induced disruption by plain and amine-modified particles occurs via pore formation. In agreement, FRET assay and GUV images revealed significant localization of plain and amine-modified particles at the surface of the Vexo vesicles. However, no localization was observed with the Vcyto vesicles. Interestingly, symmetric and asymmetric vesicles were disrupted similarly by plain and amine-modified particles. Importantly, hemolysis was observed after the incubation of erythrocytes with plain and amine-modified particles, consistent with leakage assays using Vexo vesicles. In conclusion, these results suggest that the exofacial leaflet of the plasma membrane is the primary regulator of nanoparticle-induced membrane damage in erythrocytes.