Passive membrane penetration by ZnO nanoparticles is driven by the interplay of electrostatic and phase boundary conditions

Spontaneous unbinding transition of nanoparticles adsorbing onto biomembranes: interplay of electrostatics and crowding

Cellular membranes are constantly bombarded with biomolecules and nanoscale particles, and cell functionality depends on the fraction of the bound/internalized entities. Understanding the biophysical parameters underlying this complex process is very difficult in live cells. Model membranes provide an ideal platform to obtain insight into the minimal and essential parameters involved in determining cell membrane-nanoparticle (NP) interaction. Here we report spontaneous binding and unbinding of semiconductor NPs, carrying different net charges and interacting with model biomembranes, using in situ neutron reflectivity (NR) and fluorescence microscopy studies. We observe a critical concentration of NPs above which they spontaneously unbind along with lipids from lipid monolayer membranes, leaving behind fewer bound NPs. This critical concentration varies depending on whether the NPs carry a net charge or are neutral, and is also governed by the extent of NP crowding for a fixed NP charge. The observations suggest a subtle interplay between electrostatics, membrane fluidity, and NP crowding effects, which eventually determines the adsorbed concentration for unbinding transition. Our study provides valuable microscopic insight into the parameters that could determine the biophysical process underlying NP uptake and ejection by cells which, in turn, can be utilized for their potential applications in bioimaging and drug delivery.

“Interplay of lipid-head group and packing defects in driving Amyloid-beta mediated myelin-like model membrane deformation”

Accumulating evidence suggests that amyloid plaque associated myelin lipid loss as a result of elevated amyloid burden might also contribute to Alzheimer's disease. The amyloid fibrils though closely associated with lipids under physiological conditions, however, the progression of membrane remodeling events leading to lipid-fibril assembly remains unknown. Here we first reconstitute the interaction of Aβ-40 with myelin-like model membrane and show that the binding of Aβ-40 induces extensive tubulation. To look into the mechanism of membrane tubulation we chose a set of membrane conditions varying in lipid packing density and net charge that allows us to dissect the contribution of lipid specificity of Aβ-40 binding, aggregation kinetics, and subsequent changes in membrane parameters such as fluidity, diffusion, and compressibility modulus. We show that the binding of Aβ-40 depends predominantly on the lipid packing defect densities and electrostatic interactions and results in rigidification of the myelin-like model membrane during the early phase of amyloid aggregation. Furthermore, elongation of Aβ-40 into higher oligomeric and fibrillar species leads to eventual fluidization of the model membrane followed by extensive lipid membrane tubulation observed in the late phase. Taken together, our results capture mechanistic insights into snapshots of temporal dynamics of Aβ-40 - myelin-like model membrane interaction and demonstrate how short timescale, local phenomena of binding, and fibril-mediated load generation results in the consequent association of lipids with growing amyloid fibrils.

Effect of silica nanoparticles on cell membrane fluidity: The role of temperature and membrane composition

The increasing production and application of silica nanoparticles (SiO₂ NPs) raise public concern regarding their environmental and health risks. The fluidity of the cell membrane is essential for supporting membrane proteins and regulating membrane transport. Changes in membrane fluidity inevitably influence the physiological activities of cells and even cause biological effects. In this study, the effect of SiO₂ NPs on membrane fluidity was studied at 25 °C and 37 °C, and the role of membrane components in SiO₂ NP-membrane interactions was investigated using giant plasma membrane vesicles (GPMVs) isolated from RBL-2H3 cells. SiO₂ NPs cause a more serious membrane fluidity decrease at 37 °C than at 25 °C, which is revealed by the shift of Laurdan fluorescence emission and further quantified via forster resonance energy transfer (FRET) experiments. In addition, after the removal of 75 % cholesterol from the membrane, SiO₂ NPs caused a greater extent of membrane gelation. These results indicate that SiO₂ NPs prefer to interact with membranes that are more dynamic and less densely packed. Moreover, fluorescent experiments confirmed that the existence of phosphatidyl ethanolamine (PE) and phosphoinositide (PI) can mitigate NP-induced membrane gelation. Molecular dynamics simulation further demonstrated that SiO₂ NPs form hydrogen bonds with the terminal of PE or PI but with the -PO₄^-- group in the middle of phosphatidylcholine (PC). The bonding that occurs in the terminal gives less restriction of phospholipid movement and a weaker effect on membrane fluidity. This research provides both evidence and mechanisms of SiO₂ NP-induced membrane fluidity changes, which are helpful for understanding cell membrane damage and the biological effects of NPs.

Differences of the tumour cell glycocalyx affect binding of capsaicin-loaded chitosan nanocapsules

The glycocalyx regulates the interaction of mammalian cells with extracellular molecules, such as cytokines. However, it is unknown to which extend the glycocalyx of distinct cancer cells control the binding and uptake of nanoparticles. In the present study, exome sequencing data of cancer patients and analysis of distinct melanoma and bladder cancer cell lines suggested differences in cancer cell-exposed glycocalyx components such as heparan sulphate. Our data indicate that glycocalyx differences affected the binding of cationic chitosan nanocapsules (Chi-NCs). The pronounced glycocalyx of bladder cancer cells enhanced the internalisation of nanoencapsulated capsaicin. Consequently, capsaicin induced apoptosis in the cancer cells, but not in the less glycosylated benign urothelial cells. Moreover, we measured counterion condensation on highly negatively charged heparan sulphate chains. Counterion condensation triggered a cooperative binding of Chi-NCs, characterised by a weak binding rate at low Chi-NC doses and a strongly increased binding rate at high Chi-NC concentrations. Our results indicate that the glycocalyx of tumour cells controls the binding and biological activity of nanoparticles. This has to be considered for the design of tumour cell directed nanocarriers to improve the delivery of cytotoxic drugs. Differential nanoparticle binding may also be useful to discriminate tumour cells from healthy cells.

Amphiphilic gold nanoparticles perturb phase separation in multidomain lipid membranes

Amphiphilic gold nanoparticles with diameters in the 2-4 nm range are promising as theranostic agents thanks to their spontaneous translocation through cell membranes. This study addresses the effects that these nanoparticles may have on a distinct feature of plasma membranes: lipid lateral phase separation. Atomic force microscopy, quartz crystal microbalance, and molecular dynamics are combined to study the interaction between model neuronal membranes, which spontaneously form ordered and disordered lipid domains, and amphiphilic gold nanoparticles having negatively charged surface functionalization. Nanoparticles are found to interact with the bilayer and form bilayer-embedded ordered aggregates. Nanoparticles also suppress lipid phase separation, in a concentration-dependent fashion. A general, yet simple thermodynamic model is developed to show that the change of lipid-lipid enthalpy is the dominant driving force towards the nanoparticle-induced destabilization of phase separation.

Oxidative stress generated at nickel oxide nanoparticle interface results in bacterial membrane damage leading to cell death

Metal oxide nanoparticles (NPs) have shown enhanced antibacterial effects against many bacteria. Thus, understanding the potential antibacterial effects of nickel oxide nanoparticles (NiO NPs) against Gram-positive and Gram-negative pathogenic bacteria is an urgent need to enable the exploration of NiO NP use in biomedical sciences. To this end, NiO NPs were synthesized by microwave assisted hydrothermal synthesis method. The synthesized NPs were characterized by X-ray diffraction (XRD) and Fourier Transfer Infrared (FT-IR) and UV-visible spectroscopy. The morphological features of the synthesized NiO NPs were analysed using Transmission Electron Microscopy (TEM) and FE-SEM analysis. The antibacterial activity of NiO NP was explored using different antimicrobial and biophysical studies. The obtained data reveals that the NiO NP has stronger antibacterial activity against Gram-positive bacteria compared to Gram-negative bacteria. The mechanism behind the antibacterial activity of the NiO NP was explored by evaluating the amount of ROS generation at the NiO NP interface. The effect of ROS generation on the bacterial membrane was evaluated by BacLight assay and morphological analysis of the bacterial membrane using FE-SEM. The data altogether suggested that the oxidative stress generated at the NiO NP interface resulted in membrane damage leading to bacterial cell death.

Attenuation of neuroblastoma cell growth by nisin is mediated by modulation of phase behavior and enhanced cell membrane fluidity

Antimicrobial peptide mediated fluidization of cancer membrane reduces cancer cell growth.

Insulin adsorption onto zinc oxide nanoparticle mediates conformational rearrangement into amyloid-prone structure with enhanced cytotoxic propensity

BACKGROUND

Injection localized amyloidosis is one of the most prevalent disorders in type II diabetes mellitus (TIIDM) patients relying on insulin injections. Previous studies have reported that nanoparticles can play a role in the amyloidogenic process of proteins. Hence, the present study deals with the effect of zinc oxide nanoparticles (ZnONP) on the amyloidogenicity and cytotoxicity of insulin.

METHODS

ZnONP is synthesised and characterized using XRD, Zeta Sizer, UV-Visible spectroscope and TEM. The characterization is followed by ZnONP interaction with insulin, which is studied employing fluorescence spectroscopes, isothermal titration calorimetry and molecular dynamics simulations. The interaction leads insulin conformational rearrangement into amyloid-like fibril, which is studied using thioflavin T dye binding assay, circular dichroism spectroscopy and TEM, followed by cytotoxicity propensity using Alamar Blue dye reduction assay.

RESULTS

Insulin has very weak interaction with ZnONP interface. Insulin at studied concentration forms amorphous aggregates at physiological pH, whereas in presence of ZnONP interface amyloid-like fibrils are formed. While the amyloid-like fibrils are cytotoxic to MIN6 and THP-1 cell lines, insulin and ZnONP individual solutions and their fresh mixtures enhance the cells proliferation.

CONCLUSIONS

The presence of ZnONP interface enhances insulin fibrillation at physiological pH by providing a favourable template for the nucleation and growth of insulin amyloids.

GENERAL SIGNIFICANCE

The studied protein-nanoparticle system from protein conformational dynamics point of view throws caution over nanoparticle use in biological applications, especially in vivo applications, considering the amyloidosis a very slow but non-curable degenerative disease.