AFM of the Ultrastructural and Mechanical Properties of Lipid-Raft-Disrupted and/or Cold-Treated Endothelial Cells

Dynamized ultra-low dilution of Ruta graveolens disrupts plasma membrane organization and decreases migration of melanoma cancer cell

Cutaneous melanoma is a cancer with a very poor prognosis mainly because of metastatic dissemination and therefore a deregulation of cell migration. Current therapies can benefit from complementary medicines as supportive care in oncology. In our study, we show that a dynamized ultra-low dilution of Ruta Graveolens leads to an in vitro inhibition of migration on fibronectin of B16F10 melanoma cells, as well as a decrease in metastatic dissemination in vivo. These effects appear to be due to a disruption of plasma membrane organization, with a change in cell and membrane stiffness, associated with a disorganization of the actin cytoskeleton and a modification of the lipid composition of the plasma membrane. Together, these results demonstrate, in in vitro and in vivo models of cutaneous melanoma, an anti-cancer and anti-metastatic activity of ultra-low dynamized dilution of Ruta graveolens and reinforce its interest as complementary medicine in oncology.

β-cyclodextrin microencapsulation enhanced antioxidant and antihyperlipidemic properties of Tunisian Periploca angustifolia roots condensed tannins in rats

This study aimed to investigate the microencapsulation of novel condensed tannins isolated from Periploca angustifolia roots, using β-cyclodextrin macrocyclic oligosaccharides, in order to enhance their antioxidant and antihyperlipidemic potentials. Scanning electron microscopy and Fourier transform infrared spectroscopy results revealed that tannin fraction was successfully included into β-cyclodextrin cavities proved with an encapsulation efficacy of 70%. Our in vitro findings highlighted that both pure and encapsulated tannins have efficient inhibition capacities of pancreatic lipase activity. However, the inclusion complex has the greatest, in vivo, antioxidant, and antihyperlipidemic effects. In fact, results showed that complexed tannins had markedly restored serum lipid biomarkers, lipid peroxidation, protein carbonyl oxidation, and antioxidant enzyme defense. These findings were additionally confirmed by aortic and myocardial muscle sections of histological examination. Consequently, β-cyclodextrin microencapsulation may be considered as an effective and promising technique for tannin delivery with improved antioxidant and antihyperlipidemic activities.

Dynamic single-vesicle tracking of cell-bound membrane vesicles on resting, activated, and cytoskeleton-disrupted cells

The composition, structure, production, motion, fate, and functions of cell-bound membrane vesicles pre-existing in the plasma membrane of cells are poorly understood. Here, single-vesicle tracking of individual cell-bound membrane vesicles in the plasma membrane of endothelial cells treated with or without various reagents was performed to investigate the motion of cell-bound membrane vesicles. The efficacy of each of these reagents was confirmed prior to single-vesicle tracking. Via single-vesicle tracking, we found that oxLDL, TNF-α, and VEGFα significantly increased the average number of cell-bound membrane vesicles per cell, implying that cell activation by oxLDL, TNF-α, and VEGFα could trigger the production of cell-bound membrane vesicles. It was also found that oxLDL, TNF-α, VEGFα, LPS, and MβCD but not LDL could significantly affect the motion speed of cell-bound membrane whereas none of them could significantly influence the displacement (moving range) of cell-bound membrane vesicles. The single-vesicle tracking further revealed that the average number of cell-bound membrane vesicles per cell and the mean speed/displacement of individual cell-bound membrane vesicles could be dramatically altered by the cytoskeleton-disrupting reagents (cytochalasin D and nocodazole). The data imply that the production and movement of cell-bound membrane vesicles are probably controlled by intracellular cytoskeletons and capable of being affected by multiple conditions e.g. cell activation, membrane fluidity alteration, and others.

Effects of MβCD on Lipoxygenase-Induced LDL Oxidation

Beta-cyclodextrin (β-CD) has been applied as drug/food carriers or potential drugs for treating some diseases. Most recently, some evidence indicated that methyl-β-cyclodextrin (MβCD) and 2-hydroxypropyl-β-cyclodextrin (2-HPβCD), two major derivatives of β-CD, may inhibit atherogenesis, implying that cyclodextrins also can be potential drugs for treating atherosclerosis. It is well known that modification (e.g. oxidation) of low-density lipoprotein (LDL) is one of the most critical steps of atherogenesis. Lipoxygenase, an enzyme able to be expressed by atherosclerosis-related vascular cells, is generally regarded as a possible in vivo agent of LDL oxidation. In this study, the effects of MβCD on LDL oxidation induced by lipoxygenase were investigated by measuring the electrophoretic mobility, conjugated diene formation, malondialdehyde (MDA) production, and amino group blockage of LDL. We found that the lipids depleted from LDL by MβCD could be oxygenated more readily by lipoxygenase whereas the lipoxygenase-induced oxidation of the remaining lipid-depleted LDL decreased. The data imply that MβCD has an inhibitory effect on lipoxygenase-induced LDL oxidation and probably helps to inhibit atherogenesis.

Methyl-β-Cyclodextrin Impairs the Monocyte-Adhering Ability of Endothelial Cells by Down-Regulating Adhesion Molecules and Caveolae and Reorganizing the Actin Cytoskeleton

Due to its powerful ability to deplete cholesterol from the plasma membrane of cells, methyl-β-cyclodextrin (MβCD) has been widely used as a putative research tool in cell biology. Recently, recruiting MβCD as an effective drug (e.g., antitumor drugs) has been developed. However, it remains unclear whether MβCD, when it enters the blood circulation as a drug, influences the functions of the endothelium, e.g., the adhesion of leukocytes to the endothelium. In this study, we found that MβCD can impair the adhesion of monocytes to the monolayer of endothelial cells by lowering the cell-surface adhesive force and expression of adhesion molecules and caveolae-related molecules on/in endothelial cells, and reorganizing the actin cytoskeleton of endothelial cells. The data imply that MβCD, when recruited as a drug, potentially helps to inhibit inflammation or initiation/progression of atherosclerosis since its important early step is the adhesion of circulating leukocytes (e.g., monocytes) to the endothelium.

Double-stranded DNA-scaffolded fluorescent probes for fluorescence imaging of cell-surface molecules

Double-stranded DNA-scaffolded fluorescent probes were developed for fluorescence imaging of molecules on cell surfaces.

Effects of cyclodextrins on the structure of LDL and its susceptibility to copper-induced oxidation

Cyclodextrins (CDs) have long been widely used as drug/food carriers and were recently developed as drugs for the treatment of diseases (e.g. Niemann-Pick C1 and cancers). It is unknown whether cyclodextrins may influence the structure of low-density lipoprotein (LDL), its susceptibility to oxidation, and atherogenesis. In this study, four widely used cyclodextrins including α-CD, γ-CD, and two derivatives of β-CD (HPβCD and MβCD) were recruited. Interestingly, agarose gel electrophoresis (staining lipid and protein components of LDL with Sudan Black B and Coomassie brilliant blue, respectively but simultaneously) shows that cyclodextrins at relatively high concentrations caused disappearance of the LDL band and/or appearance of an additional protein-free lipid band, implying that cyclodextrins at relatively high concentrations can induce significant electrophoresis-detectable lipid depletion of LDL. Atomic force microscopy (AFM) detected that MβCD (as a representative of cyclodextrins) induced size decrease of LDL particles in a dose-dependent manner, further confirming the lipid depletion effects of cyclodextrins. Moreover, the data from agarose gel electrophoresis, conjugated diene formation, MDA production, and amino group blockage of copper-oxidized LDL show that cyclodextrins can impair LDL susceptibility to oxidation. It implies that cyclodextrins probably help to inhibit atherogenesis by lowering LDL oxidation.

The structure and function of cell membranes examined by atomic force microscopy and single-molecule force spectroscopy

The cell membrane is one of the most complicated biological complexes, and long-term fierce debates regarding the cell membrane persist because of technical hurdles. With the rapid development of nanotechnology and single-molecule techniques, our understanding of cell membranes has substantially increased. Atomic force microscopy (AFM) has provided several unprecedented advances (e.g., high resolution, three-dimensional and in situ measurements) in the study of cell membranes and has been used to systematically dissect the membrane structure in situ from both sides of membranes; as a result, novel models of cell membranes have recently been proposed. This review summarizes the new progress regarding membrane structure using in situ AFM and single-molecule force spectroscopy (SMFS), which may shed light on the study of the structure and functions of cell membranes.

AFM visualization of cortical filaments/network under cell-bound membrane vesicles

While circulating/plasma membrane vesicles have been extensively characterized, due to the lack of effective methods cell-bound membrane vesicles are poorly understood including their shape and correlation with the intracellular cytoskeleton. In this study, we focused on cell-bound membrane vesicles and individual vesicle-derived pits on endothelial cells by using confocal microscopy and atomic force microscopy (AFM). For the first time, we found that cell-bound membrane vesicles are hemisphere-shaped and that the actin cortical filaments/network lies at the cytosolic opening of a vesicle instead of being closely attached to the inner side of the vesicle membrane. This structure of cell-bound membrane vesicles may be beneficial to their movement in, or release from, the plasma membrane of cells due to less membrane-cytoskeleton coupling to be broken therefore probably minimizing energy consumption and time usage. Further study indicates that TNF-α activation induced a significant increase in average number/size of cell-bound vesicles and the local disruption of the actin network at the cytosolic opening of cell-bound vesicles.

An AFM-based pit-measuring method for indirect measurements of cell-surface membrane vesicles

Circulating membrane vesicles, which are shed from many cell types, have multiple functions and have been correlated with many diseases. Although circulating membrane vesicles have been extensively characterized, the status of cell-surface membrane vesicles prior to their release is less understood due to the lack of effective measurement methods. Recently, as a powerful, micro- or nano-scale imaging tool, atomic force microscopy (AFM) has been applied in measuring circulating membrane vesicles. However, it seems very difficult for AFM to directly image/identify and measure cell-bound membrane vesicles due to the similarity of surface morphology between membrane vesicles and cell surfaces. Therefore, until now no AFM studies on cell-surface membrane vesicles have been reported. In this study, we found that air drying can induce the transformation of most cell-surface membrane vesicles into pits that are more readily detectable by AFM. Based on this, we developed an AFM-based pit-measuring method and, for the first time, used AFM to indirectly measure cell-surface membrane vesicles on cultured endothelial cells. Using this approach, we observed and quantitatively measured at least two populations of cell-surface membrane vesicles, a nanoscale population (<500 nm in diameter peaking at ∼250 nm) and a microscale population (from 500 nm to ∼2 μm peaking at ∼0.8 μm), whereas confocal microscopy only detected the microscale population. The AFM-based pit-measuring method is potentially useful for studying cell-surface membrane vesicles and for investigating the mechanisms of membrane vesicle formation/release.

Fixation-induced cell blebbing on spread cells inversely correlates with phosphatidylinositol 4,5-bisphosphate level in the plasma membrane

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Protein- but not lipid-stabilizing fixatives induce cell blebbing of spread cells.

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Asymmetric distribution of fixation-induced blebs coincides with that of PIP₂.

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Fixation less readily induces blebbing on spread cells with elevated PIP₂ levels.

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Fixation more readily induces blebbing on spread cells with lower PIP₂ levels.

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Disruption of lipid rafts enhances fixation-induced blebbing of spread cells.

While most attention has been focused on physiologically generated blebs, the molecular mechanisms for fixation-induced cell blebbing are less investigated. We show that protein-fixing (e.g. aldehydes and picric acid) but not lipid-stabilizing (e.g. OsO₄ and KMnO₄) fixatives induce blebbing on spread cells. We also show that aldehyde fixation may induce the loss or delocalization of phosphatidylinositol 4,5-bisphosphate (PIP₂) in the plasma membrane and that the asymmetric distribution of fixation-induced blebs on spread/migrating cells coincides with that of PIP₂ on the cells prefixed by lipid-stabilizing fixatives (e.g., OsO₄). Moreover, fixation induces blebbing less readily on PIP₂-elevated spread cells but more readily on PIP₂-lowered or lipid raft-disrupted spread cells. Our data suggest that fixation-induced lowering of PIP₂ level at cytoskeleton-attaching membrane sites causes bleb formation via local breakdown of the membrane–cytoskeleton coupling.