Biophysical investigations using atomic force microscopy can elucidate the link between mouthfeel and flavour perception.

Food texture, along with taste and odour, is an important factor in determining food flavour. However, the physiological properties of oral texture perception require greater examination and definition. Here we explore recent trends and perspectives related to mouthfeel and its relevance in food flavour perception, with an emphasis on the biophysical point of view and methods. We propose that atomic force microscopy, combined with other biophysical techniques and more traditional food science approaches, offers a unique opportunity to study the mechanisms of mouthfeel at cellular and molecular levels. With this knowledge, food composition could be modified to develop healthier products by limiting salt, sugar, fat and calories while maintaining sensory qualities and consumer acceptance.

Interaction of Polystyrene Nanoparticles with Supported Lipid Bilayers: Impact of Nanoparticle Size and Protein Corona.

Polystyrene is one of the most widely used plastics. This article reports on the interaction of 50 and 210 nm polystyrene nanoparticles (PSNPs) with human serum albumin (HSA) and transferrin (Tf), as well as their effect on supported lipid bilayers (SLBs), using experimental and theoretical approaches. Dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements show that the increase in diameter for the PSNP-protein bioconjugates depends on nanoparticle size and type of proteins. The circular dichroism (CD) spectroscopy results demonstrate that the proteins preserve their structures when they interact with PSNPs at physiological temperatures. The quartz crystal microbalance (QCM) technique reveals that PSNPs and their bioconjugates show no strong interactions with SLBs. On the contrary, the molecular dynamics simulations (MDS) show that both proteins bind strongly to the lipid bilayer (SLBs) when compared to their binding to a polystyrene surface model. The interaction is strongly dependent on the protein and lipid bilayer composition. Both the PSNPs and their bioconjugates show no toxicity in human umbilical vein endothelial (HUVEC) cells; however, bare 210 nm PSNPs and 50 nm PSNP-Tf bioconjugates show an increase in reactive oxygen species production. This study may be relevant for assessing the impact of plastics on health.

Identification of a critical lipid ratio in raft-like phases exposed to nitric oxide: An AFM study.

Lipid rafts are discrete, heterogeneous domains of phospholipids, sphingolipids, and sterols that are present in the cell membrane. They are responsible for conducting cell signaling and maintaining lipid-protein functionality. Redox-stress-induced modifications to any of their components can severely alter the mechanics and dynamics of the membrane causing impairment to the lipid-protein functionality. Here, we report on the effect of sphingomyelin (SM) in controlling membrane permeability and its role as a regulatory lipid in the presence of nitric oxide (NO). Force spectroscopy and atomic force microscopy imaging of raft-like phases (referring here to the coexistence of "liquid-ordered" and "liquid-disordered" phases in model bilayer membranes) prepared from lipids: 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC):SM:cholesterol (CH) (at three ratios) showed that the adhesion forces to pull the tip out of the membrane increased with increasing SM concentration, indicating decreased membrane permeability. However, in the presence of NO radical (1 and 5 µM), the adhesion forces decreased depending on SM concentration. The membrane was found to be stable at the ratio POPC:SM:CH (2:1:1) even when exposed to 1 µM NO. We believe that this is a critical ratio needed by the raft-like phases to maintain homeostasis under stress conditions. The stability could be due to an interplay existing between SM and CH. However, at 5 µM NO, membrane deteriorations were detected. For POPC:SM:CH (2:2:1) ratio, NO displayed a pro-oxidant behavior and damaged the membrane at both radical concentrations. These changes were reflected by the differences in the height profiles of the raft-like phases observed by atomic force microscopy imaging. Malondialdehyde (a peroxidation product) detection suggests that lipids may have undergone lipid nitroxidation. The changes were instantaneous and independent of radical concentration and incubation time. Our study underlines the need for identifying appropriate ratios in the lipid rafts of the cell membranes to withstand redox imbalances caused by radicals such as NO.

Changing surface properties of artificial lipid membranes at the interface with biopolymer coated gold nanoparticles under normal and redox conditions.

Gold nanoparticles (NPs) functionalized with biopolymers are increasingly effective in drug-delivery applications. Here, we investigated how chitosan coated NPs and dextran-10 coated NPs regulate their action on DMPC bilayer under normal and stress conditions. We found that chitosan-coated NPs interact with lipid membrane in an intermittent manner, causing lipid loss and partial membrane rupture, while dextran-10 coated NPs mostly induced complete rupture as observed by quartz crystal microbalance. In-situ atomic force microscopy imaging showed that chitosan-treated membranes have a higher surface roughness than those treated with dextran-10. Treatment with 1 µM nitric oxide (NO) radical caused the release of chitosan ligand from the surface of gold NPs (reduced stability) and its aggregation, but the functionality seemed less influenced. Dextran-10 ligand showed no such behavior, while its action was only delayed. Our findings give insights into possible challenges faced by NPs in-situ and show environment dependent effects of NPs on membranes.

Biopolymer-coated gold nanoparticles inhibit human insulin amyloid fibrillation.

Deposits of protein misfolding and/or aggregates are a pathological hallmark of amyloid-related diseases. For instance, insulin amyloid fibril deposits have been observed in patients with insulin-dependent diabetes mellitus after insulin administration. Here, we report on the use of AuNPs functionalized with linear- (i.e. dextrin and chitosan) and branched- (i.e. dextran-40 and dextran-10) biopolymers as potential agents to inhibit insulin fibril formation. Our dynamic light scattering analyses showed a size decrease of the amyloid fibrils in the presence of functionalized AuNPs. Circular dichroism spectroscopy as well as enzyme-linked immunosorbent assay data demonstrated that the secondary structural transition from α-helix to ß-sheet (which is characteristic for insulin amyloid fibril formation) was significantly suppressed by all biopolymer-coated AuNPs, and in particular, by those functionalized with linear biopolymers. Both transmission electron microscopy and atomic force microscopy analyses showed that the long thick amyloid fibrils formed by insulin alone become shorter, thinner or cluster when incubated with biopolymer-coated AuNPs. Dextrin- and chitosan-coated AuNPs were found to be the best inhibitors of the fibril formation. Based on these results, we propose a mechanism for the inhibition of insulin amyloid fibrils: biopolymer-coated AuNPsstrongly interact with the insulin monomers and inhibit the oligomer formation as well as elongation of the protofibrils.Moreover, cytotoxicity experiments showed that AuNP-insulin amyloid fibrils are less toxic compared to insulin amyloid fibrils alone. Our results suggest that both dextrin- and chitosan-AuNPs could be used as therapeutic agents for the treatment of amyloid-related disorders.

Nitrosative stress affects the interaction of integrin alphaIIbbeta3 with its ligands.

Binding of integrin alphaIIbbeta3 (αiibß3) to its ligands is a highly restricted and regulated mechanism. Any modification of the protein structure yields a dysfunctional role, especially in a redox environment. Here, we examine the effect of nitrosative stress on the αiibß3 reconstituted into nanodiscs. Using single molecule force spectroscopy, we measured the interaction between αiibß3 and its ligand RGD and found that in the presence of exogenous nitric oxide (NO) two force regimes are generated: a low force regime of ~100pN indicating the presence of integrin in a normal status, and a broad spectrum of high force regime (~210-450pN) suggesting the protein modification/aggregation. By high resolution atomic force microscopy imaging, we demonstrate that both NO and nitrite (a stable product formed from NO) are involved in destabilizing the transmembrane protein complex leading to release of αiibß3 from the lipid bilayer and protein aggregation. Our experimental setup opens new ways for testing in a membrane environment the effect of radical species on integrins under clinically relevant conditions.