Effect Of Silica Nanoparticles On The Morphology And Phase Of Model Cell Membranes

Silica nanoparticles?SiO₂ NPs?have wide application in medication and biotechnology owing to its superior chemical stability.Thus SiO₂ NPs become one of the most commonly used nanomaterials,which increases the possibility of their exposure to organisms.Previous studies indicate that SiO₂ NPs have pathogenicity such as pneumoconiosis.However,the mechanisms of the toxic effects are unclear.Direct contact of SiO₂ NPs with cell membrane may cause the risk of membrane rupture and cytotoxicity.Therefore,the interaction between SiO₂ NPs and cell membranes should be further studied.The membrane integrity and fluidity are essential to cell physiological activities.This study was designed to investigate the effects of the SiO₂ NPs on membrane integrity and fluidity.However,the cellular activities make the difficulties to evaluate the interaction between SiO₂ NPs and membranes.Therefore,giant unilamellar vesicles?GUVs?and small unilamellar vesicles?SUVs?were used as model cell membranes.SiO₂ NPs with different surface coating and colloidal stability were selected to study their effects on membrane integrity and fluidity in this study.In addition,giant plasma membrane vesicles?GPMVs?were prepared from RBL-2H3 cells,to explore how the lipid components affect the SiO₂ NPs inducing membrane gelation.The study provides better understanding of the interaction between SiO₂ NPs and membranes,and provides important information for nanomaterial design and safe application.1.Effect of SiO₂ NPs and other oxide nanoparticles on membrane morphology and fluidityThe effects of Al₂O₃,Fe₂O₃,SiO₂,TiO₂ and ZnO NPs on membrane integrity and fluidity were investigated in this study to explore the differences of the interactions between nano oxides and membranes.Al₂O₃ and SiO₂ NPs disrupted the oppositely charged membranes,indicating the important role of electrostatic attraction.However,Fe₂O₃,TiO₂ and ZnO NPs did not cause serious membrane disruption as Al₂O₃ and SiO₂ NPs.Membrane fluidity was introduced by the fluorescent emission of Laurdan labeled vesicles.SiO₂ NPs induces the membrane gelation of both positively and negatively charged membranes.Al₂O₃ and ZnO NPs induced the gelation of the oppositely charged membrane,but did not cause obvious membrane gelation to the like charged membrane.The phospholipid molecular structural changes after NP exposure were analyzed by Fourier transform infrared?FT-IR?spectroscopy.FTIR spectra revealed the hydrogen bond formation between Al₂O₃/SiO₂ NPs and the carbonyl/phosphate groups of phospholipids.The hydrogen bond was more obvious between SiO₂ NPs and phospholipid.Therefore,hydrogen bonding makes Al₂O₃ and SiO₂ NPs disrupt membrane.2.Effect of Silica nanoparticles with various stability and surface coating on phospholipid membraneDue to the most serious membrane damage induced by SiO₂ NPs,SiO₂ NPs with different surface coatings and colloidal stability were selected,to further study their effects on the membrane integrity and phase of GUVs.Result showed that SiO₂ NPs caused more serious damage to oppositely-charged membrane because electrostatic attraction favored the hydrogen bonding to the phospholipids.Increase in NP exposure dose and time aggravated the membrane damage.Powder nanopaticles present faster damage to the oppositely-charged GUVs than colloids nanoparticles because the interaction between NPs and membrane increase during the sedimentation.The membrane phases were evaluated applying the fluorescent probe Laurdan.Anionic SiO₂ NPs induced membrane gelation.Cationic SiO₂ NPs did not change the phase of positively-charged GUV and pure DOPC vesicles,but induced the gelation of negatively-charged GUV.3.Role of bovine serum albumin and humic acid in the interaction between SiO₂ NPs and model cell membranesSilica nanoparticles adsorb the widely existent natural organic matter?NOM?after their release into natural waters or soils,and interacts with biomolecules in interstitial fluid after the uptake by organisms.Adsorption of natural organic matter and biomolecules on SiO₂ NPs alters their surface properties and cytotoxicity.In this study,SiO₂ NP was treated by bovine serum albumin?BSA?and humic acid?HA?to study their effects on the integrity and fluidity of model cell membranes.The microscopic observation revealed that the BSA/HA treated?BSA-/HA-?SiO₂ NP took more time to disrupt membrane than untreated-SiO₂ NP,because BSA/HA adsorption covered then surface SiOH/SiO-groups and weakened the interaction between NP and phospholipids.The deposition of SiO₂ NP on membrane was monitored by a quartz crystal microbalance with dissipation?QCM-D?.Untreated-and HA-SiO₂ NPs quickly disrupted the SUV layer on QCM-D sensor;BSA-SiO₂ NP attached on the membranes but only caused slow vesicle disruption.Untreated-,BSA-and HA-SiO₂ NP all caused the gelation of the positively-charged membrane,which was evaluated by the generalized polarity values.HA-SiO₂ NP caused most serious gelation,and BSA-SiO₂ NP caused the least.It is expected that the design of novel SiO₂ NP in future.4.Effect of SiO₂ NPs on the phase of giant plasma membrane vesiclesDue to the different components between artificial model membranes and the real cell membranes,GPMVs were prepared from RBL-2H3 cells,which is the intermediate model membrane between real cell membranes and the artificial biomembranes.GPMVs were used to study the role of lipid components in the SiO₂ NP induced membrane phase change.After cholesterols in GPMVs were erased by methyl-?-cyclodextrin?M?CD?,SiO₂ NPs cause more serious membrane gelation.RBL-2H3 cells were treated by PFA/DTT or NEM to obtain GPMVs with different lipid composition.PFA/DTT treatment deplet phosphatidyl the ethanolamine?PE?and phosphoinositides?PI?in GPMV,but NEM treatment obtains the GPMVs with similar components to the original cell membranes.The membrane gelation is more remarkable for the GPMVs depleting phosphatidyl ethanolamine?PE?and phosphatidylinositol?PI?when exposing to SiO₂ NPs.In addition,SiO₂ NPs induce more serious membrane gelation in higher temperature.Break of membrane integrity and change in membrane phase are possible mechanisms of cytotoxicity because cellular physiological activities require a separated intracellular environment and a fluid membrane phase to support proteins and regulate molecular transport.Understanding the interaction between SiO₂ NP and membrane will be helpful to design safe nanomaterials.