(180q) Lipid Headgroup Regulates the Disruption of Lipid Membranes By Silica Nanoparticles

The increasing application of nanomaterials in industrial and biomedical applications has raised concerns about their potential adverse effects on mammalian cells. The cell plasma membrane, a lipid bilayer that separates the cell cytoplasm from the extracellular environment, is the first cellular entity that comes into direct contact with exogenous particles. Plasma membrane damage by engineered nanomaterials is one of the primary mechanisms by which nanoparticles induce cytotoxicity. Mechanistic studies on nanoparticle-membrane interactions have used membrane models, primarily lipid vesicles, to examine the mechanisms of nanoparticle-induced membrane damage. Previous studies on nanoparticle-membrane interactions have reported that electrostatic attraction between oppositely-charged particles and lipids in the membrane is the primary mechanism through which nanoparticles bind to and disrupt lipid membranes. However, our results, using silica nanoparticles of similar charge, but with different lipid headgroups have challenged the idea that electrostatic interactions alone are responsible for nanoparticle-induced membrane damage and suggest that specific interactions between nanomaterials and lipid headgroups are involved. The present study uses plain silica nanoparticles (50 nm) and phospholipids with various headgroups to examine how the lipid chemical structure regulates nanoparticle-induced disruption of lipid membranes.

A number of lipids were used to examine the effect of lipid headgroup structure in regulating lipid-nanoparticle interactions. The role of the trimethylammonium in phospholipids was examined by comparing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC, 18:1), which contains trimethylammonium in its headgroup, and 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS), which contains ammonium in its headgroup. The role of the orientation of the trimethylammonium and phosphate groups with respect to nanoparticles were examined by comparing DOPC and 2-((2,3-bis (oleoyloxy)propyl)dimethylammonio) ethyl hydrogen phosphate (DOCP, 18:1) , which have different sequences of trimethylammonium and phosphate groups. The role of lipid backbone was examined by comparing the disruptive effects of nanoparticles on DOPC, which has a glycerol backbone, compared to N-stearoyl-D-erythro-sphingosylphosphorylcholine (SM d18:1/18:0), which has a sphingosine backbone. Vesicle integrity in all cases was studied by encapsulating the self-quenching fluorescent probe, carboxyfluorescein, in vesicles and studying its leakage before and after exposure to nanoparticles at 37 °C.

Nanoparticle interactions with lipids were significantly affected by the DOPC and DOCP vesicles were drastically different. Silica nanoparticles (0.01 g/L) induced significant (~70 %) leakage in DOPC vesicles, but only (~20 %) leakage in DOCP, showing that replacing the trimethylammonium and phosphate group significantly diminished the disruptive effects of the particles. Replacing the trimethylammonium (DOPC) with an ammonium group (DOPS) completely abrogated the disruptive effects of the particles. Nanoparticles also disrupted DOPC significantly more than sphingomyelin, demonstrating the importance of the glycerol backbone in the disruptive properties of silica nanoparticles. These results show the important role of lipid chemical composition in regulating nanoparticle-induced membrane damage. Future work is focused on changing the acyl chain structure of lipids and examination of nanoparticle binding to lipids using confocal microscopy and fluorescence spectroscopy.