The role of glycolipids in mediating cell adhesion: a flow chamber study

In silico design and fabrication of an SFI chip-based microspheroid culture system

The emergence of microfluidic devices and computational fluid dynamics (CFD) has propelled the need for next-generation biomimetic cell culture platforms that are flexible for monitoring and regulation. Therefore, this study evaluated a CFD application in an in silico-designed and spheroid-based flow integration 3D cell culture chip (SFI chip) to illustrate cell culture, drug screening, cytokine delivery, and differentiation of cells in a platform that partially recapitulates the natural environment. Our results show that a flow rate of 0.05 mL h^-1 or less induced no physical stress in the SFI chip (15 mm), and uniform cell spheroids (approximately 200 μm) were formed across the platform. The cultured cells were tested in several experimental contexts (co-culture, drug screening, cytokine delivery, and differentiation), demonstrating the usefulness of computational simulation in expediting discovery and simple and effective means to scale the production of standardized cell spheroids cultured under dynamic and natural conditions. Advanced cell culture technologies can be used to accelerate research and discovery and the preclinical and clinical development of cell and cell-free therapies for urgent medical needs.

Modulating Macrophage Polarization through CCR2 Inhibition and Multivalent Engagement

Excessive or prolonged recruitment of inflammatory monocytes to damaged tissue can significantly worsen patient outcomes. Monocytes migrate to sites of tissue inflammation in response to high local concentrations of CCL2, a chemokine that binds to and signals through the CCR2 receptor. While the role of CCR2 in cellular migration is well studied, it is unclear how CCR2 inhibition affects macrophage polarization and if multivalency can increase downstream signaling effects. Using affinity selection with a phage library, we identified a novel single-chain variable fragment (scFv) (58C) that binds specifically and with high affinity to the N-terminal domain of CCR2 ( KD = 59.8 nM). The newly identified 58C-scFv bound to native CCR2 expressed on macrophages and MDA-MB-231 cells, inhibited migration, and induced a pro-inflammatory M1-phenotype in macrophages. The M1/M2 macrophage phenotype ratio for monomeric 58C-scFv was significantly increased over the negative control by 1.0 × 104-fold (iNOS/Arg-1), 5.1 × 104-fold (iNOS/Mgl2), 3.4 × 105-fold (IL-6/Arg-1), and 1.7 × 106-fold (IL-6/Mgl2). The multivalent display of 58C-scFv on liposomes further reduced migration of both cell types by 25-40% and enhanced M1 polarization by 200% over monomeric 58C-scFv. These studies demonstrate that CCR2 inhibition polarizes macrophages toward an inflammatory M1 phenotype, and that multivalent engagement of CCR2 increases the effects of 58C-scFv on polarization and migration. These data provide important insights into the role of multivalency in modulating binding, downstream signaling, and cellular fate.

Precision engineering of targeted nanocarriers

Since their introduction in 1980, the number of advanced targeted nanocarrier systems has grown considerably. Nanocarriers capable of targeting single receptors, multiple receptors, or multiple epitopes have all been used to enhance delivery efficiency and selectivity. Despite tremendous progress, preclinical studies and clinically translatable nanotechnology remain disconnected. The disconnect in targeting efficacy may stem from poorly-understood factors such as receptor clustering, spatial control of targeting ligands, ligand mobility, and ligand architecture. Further, the relationship between receptor distribution and ligand architecture remains elusive. Traditionally, targeted nanocarriers were engineered assuming a "static" target. However, it is becoming increasingly clear that receptor expression patterns change in response to external stimuli and disease progression. Here, we discuss how cutting-edge technologies will enable a better characterization of the spatiotemporal distribution of membrane receptors and their clustering. We further describe how this will enable the design of new nanocarriers that selectively target the site of disease. Ultimately, we explore how the precision engineering of targeted nanocarriers that adapt to receptor dynamics will have the potential to drive nanotechnology to the forefront of therapy and make targeted nanomedicine a clinical reality. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Lipid-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

A Review of Cell Adhesion Studies for Biomedical and Biological Applications

Cell adhesion is essential in cell communication and regulation, and is of fundamental importance in the development and maintenance of tissues. The mechanical interactions between a cell and its extracellular matrix (ECM) can influence and control cell behavior and function. The essential function of cell adhesion has created tremendous interests in developing methods for measuring and studying cell adhesion properties. The study of cell adhesion could be categorized into cell adhesion attachment and detachment events. The study of cell adhesion has been widely explored via both events for many important purposes in cellular biology, biomedical, and engineering fields. Cell adhesion attachment and detachment events could be further grouped into the cell population and single cell approach. Various techniques to measure cell adhesion have been applied to many fields of study in order to gain understanding of cell signaling pathways, biomaterial studies for implantable sensors, artificial bone and tooth replacement, the development of tissue-on-a-chip and organ-on-a-chip in tissue engineering, the effects of biochemical treatments and environmental stimuli to the cell adhesion, the potential of drug treatments, cancer metastasis study, and the determination of the adhesion properties of normal and cancerous cells. This review discussed the overview of the available methods to study cell adhesion through attachment and detachment events.

Bis-triazologlycolipid mimetics – low molecular weight organogelators

A facile regioselective synthesis of bis-triazologlycolipids, a class of organogelators, has been accomplished by “Click reaction”. The morphology and self-assembly of the gelators were examined by FESEM and HRTEM analysis.

Microfluidic devices modulate tumor cell line susceptibility to NK cell recognition

This study aims to adoptively reduce the major histocompatibility complex class I (MHC-I) molecule surface expression of cancer cells by exposure to microfluid shear stress and a monoclonal antibody. A microfluidic system is developed and tumor cells are injected at different flow rates. The bottom surface of the microfluidic system is biofunctionalized with antibodies (W6/32) specific for the MHC-I molecules with a simple method based on microfluidic protocols. The antibodies promote binding between the bottom surface and the MHC-I molecules on the tumor cell membrane. The cells are injected at an optimized flow rate, then roll on the bottom surface and are subjected to shear stress. The stress is localized and enhanced on the part of the membrane where MHC-I proteins are expressed, since they stick to the antibodies of the system. The localized stress allows a stripping effect and consequent reduction of the MHC-I expression. It is shown that it is possible to specifically treat and recover eukaryotic cells without damaging the biological samples. MHC-I molecule expression on treated and control cell surfaces is measured on tumor and healthy cells. After the cell rolling treatment a clear reduction of MHC-I levels on the tumor cell membrane is observed, whereas no changes are observed on healthy cells (monocytes). The MHC-I reduction is investigated and the possibility that the developed system could induce a loss of these molecules from the tumor cell surface is addressed. The percentage of living tumor cells (viability) that remain after the treatment is measured. The changes induced by the microfluidic system are analyzed by fluorescence-activated cell sorting and confocal microscopy. Cytotoxicity tests show a relevant increased susceptibility of natural killer (NK) cells on microchip-treated tumor cells.

Simultaneous nanoplasmonic and quartz crystal microbalance sensing: analysis of biomolecular conformational changes and quantification of the bound molecular mass

This paper presents a study of supported lipid bilayer (SLB) formation and subsequent protein binding using a sensor that combines localized surface plasmon resonance (LSPR) and quartz crystal microbalance with dissipation (QCM-D) monitoring. The LSPR activity arises from silicon oxide (SiO x ) coated nanometric apertures in a thin gold film, which also serves as the active electrode of a QCM-D crystal. Both transducer principles provide signatures for the formation of a SLB upon adsorption and subsequent rupture of adsorbed lipid vesicles. However, the two techniques are sensitive over different regions of the sample: LSPR primarily inside and on the rim of the holes and QCM-D primarily on the planar areas between the holes. Although the dimension of the lipid vesicles is on the same order as the dimension of the nanoholes, it is concluded from the response of the combined system that vesicle rupture in the nanoholes and on the planar region between the holes is synchronized. Furthermore, by determining the thickness of the SLB from the QCM-D response, the characteristic decay length of the LSPR field intensity could be determined. This made it possible not only to determine the mass and refractive index of the homogeneous SLB but also to postulate a generic means to quantify the LSPR response in terms of mass-uptake also for nonhomogeneous films. This is exemplified by measuring the adsorbed lipid mass during vesicle adsorption, yielding the critical lipid vesicle coverage at which spontaneous rupture into a planar bilayer occurs. The generic applicability and versatility of the method is demonstrated from specific protein binding to a functionalized SLB. From the absolute refractive index of the protein, provided from the LSPR data alone, it was possible to determine both the effective thickness of the protein film and the molecular mass (or number) of bound protein.

Increase in fluidity in the membrane of MT3 breast cancer cells correlates with enhanced cell adhesion in vitro and increased lung metastasis in NOD/SCID mice

To study whether membrane fluidity of tumor cells have an influence on metastasis, MT3 breast cancer cells harvested during exponential growth and under confluent conditions were compared. Electron paramagnetic resonance (EPR) data revealed that, in comparison to growing cells, confluent cells have a significant higher fluidity in their membrane related to a higher relative portion of disordered domains and a reduced portion of the most ordered domains. Further, sialyl Lewis X and/or A ligand-mediated adhesion of these cells was 2-fold enhanced. Confocal laser scanning microscopy further demonstrated a higher motility of ligands in the membrane of confluent cells, together with an accumulation of these ligands in distinct areas. Both facts are suggested to be responsible for an enhanced cell adhesion observed. Finally, an increased number of large distinct metastatic foci was registered in lungs of mice after i.v. inoculation of confluent cells. The results indicate that domain organization and fluidity of the cell membrane affect tumor cell adhesion and can have in this way also an impact on the malignancy of breast cancer cells.

Human milk oligosaccharides affect P-selectin binding capacities: In vitro investigation

OBJECTIVE

In the initial phase of cellular immune response, selectins mediate the emigration of leukocytes from the blood stream into inflammatory regions. Human milk oligosaccharides (HMOs) possess binding epitopes of selectin ligands such as sialyl Lewis(x) and sialyl Lewis(a) and therefore might impair the interaction of selectins with cellular ligands. Neutral, acidic, sialylated, or fucosylated HMO fractions with polymerization degrees of 3 to 50 were investigated regarding this interaction in a dynamic flow chamber model that considers physiologic shear stress conditions.

METHODS

Human milk oligosaccharides were compared with kappa-carrageenans and pectin oligosaccharides to deduce structure-activity relations. Fucoidan and sialyl Lewis(x) served as positive controls.

RESULTS

All HMO fractions affected P-selectin ligand binding capacity but were not comparable to fucoidan. The activity of the acidic HMO fraction resembled sialyl Lewis(x) in decreasing the binding of the ligand to P-selectin.

CONCLUSION

Human milk oligosaccharides modulate rather than block the function of P-selectin.

Carbohydrate−Protein Interactions by “Clicked” Carbohydrate Self-Assembled Monolayers

A Huisgen 1,3-dipolar cycloaddition "click chemistry" was employed to immobilize azido sugars (mannose, lactose, alpha-Gal) to fabricate carbohydrate self-assembled monolayers (SAMs) on gold. This fabrication was based on preformed SAM templates incorporated with alkyne terminal groups, which could further anchor the azido sugars to form well-packed, stable, and rigid sugar SAMs. The clicked mannose, lactose, and alpha-Gal trisaccharide SAMs were used in the analysis of specific carbohydrate-protein interactions (i.e., mannose-Con A; ECL-lactose, alpha-Gal-anti-Gal). The apparent affinity constant of Con A binding to mannose was (8.7 +/- 2.8) x 10(5) and (3.9 +/- 0.2) x 10(6) M(-1) measured by QCM and SPR, respectively. The apparent affinity constants of lactose binding with ECL and alpha-Gal binding with polyclonal anti-Gal antibody were determined to be (4.6 +/- 2.4) x 10(6) and (6.7 +/- 3.3) x 10(6) M(-1), respectively by QCM. SPR, QCM, AFM, and electrochemistry studies confirmed that the carbohydrate SAM sensors maintained the specificity to their corresponding lectins and nonspecific adsorption on the clicked carbohydrate surface was negligible. This study showed that the clicked carbohydrate SAMs in concert with nonlabel QCM or SPR offered a potent platform for high-throughput characterization of carbohydrate-protein interactions. Such a combination should complement other methods such as ITC and ELISA in a favorable manner and provide insightful knowledge for the corresponding complex glycobiological processes.

Selectins-an emerging target for drug delivery

Selectins are multifunctional adhesion molecules that mediate the initial interactions between circulating leukocytes and cells of the endothelium. First identified over a decade ago, selectins have provided insight into areas as diverse as normal lymphocyte homing, leukocyte recruitment during inflammatory responses, carbohydrate ligand biosynthesis and adhesion-mediated signalling. Of late, selectins were introduced as targets for drug delivery in the development of new anti-inflammatory therapeutics and in anti-cancer therapy. This review will examine the selectins and their ligands with a focus on recent findings on their role in physiology and pathophysiology as well as the emerging role of selectins as targets in controlled drug delivery.

Influence of Spacer Length on the Agglutination of Glycolipid‐Incorporated Liposomes by ConA as Model Membrane

Through a systematic investigation of the agglutination of long chain mannolipid and glucolipid incorporated liposomes by concanavalin A (ConA) it was found that the agglutination was dependent on different factors. The studied factors reported here are (1) spacer length and (2) ground lipid matrix. The threshold and the relative saturating ConA binding concentration (saturation point to attain the binding saturation condition) of glycosides with varying spacer length for agglutination are dependent on the spacer length of the glycolipid. These concentrations decrease with the increasing number of in-built ethyleneoxy spacer length in the glycolipid and find its minimum with 6 spacer units; it increases then more and more with increasing number of spacer units (>6 units). This is supposed to be due to the requirement of a proper distance of the hydrophilic determinant from the liposome surface for the response by ConA (response invoking distance), which may be most favorable in case of 6 spacer units. Further increase in number of spacer units (>6) results to an increasing probability of the bending of the spacer chain along with the terminal polar head group more and more towards the liposome surface; this leads to a reduction of the factual distance of the terminal hydrophilic head group from the liposome surface, weakening the response for ConA binding. The threshold concentration or saturation point decreases also with the rigidity of the ground lipid matrix. Increased rigidity of the ground matrix leads to a phase separation and localized 'Domain' formation with the glycolipid inside the ground matrix layer due to their immiscibility, invoking better response resulting to a reduction of required incorporated glycolipid concentration.

New EPR method for cellular surface characterization

An electron paramagnetic resonance (EPR)-based membrane surface characterization method is presented to detect the properties of the carbohydrate-rich part of membrane surfaces as well as carbohydrate interaction with other membrane constituents and water-soluble molecules. The proposed method relies on the spin-labeling and spectral decomposition based on spectral simulation and optimization with EPRSIM software. In order to increase the sensitivity of characterization to the carbohydrate-rich part of the membrane surface, the sucrose-contrasting approach is introduced. With this method, which was established on model membranes with glycolipids and tested on erythrocyte membrane, we were able to characterize the surface and lipid bilayer lateral heterogeneity. Additionally, some properties of the interaction between glycocalyx and lipid bilayer as well as between glycocalyx and sucrose molecules were determined. The experiments also provided some information about the anchoring and aggregation of the glycosylated molecules. According to the results, some functions of the glycosylated surface are discussed.

Selectin-blocking semisynthetic sulfated polysaccharides as promising anti-inflammatory agents

Selectin-induced leucocytes rolling along the endothelial surface of blood vessels initiate a complex adhesion cascade, which is an essential step in the cellular immune response. Consequently, blocking the binding between the selectins and their ligands represents a promising strategy for suppressing pathological inflammatory reactions. This study describes the effects of an unfractionated heparin and a low-molecular-weight heparin and a series of structurally well-defined semisynthetic glucan sulfates on selectin-mediated cell-rolling with respect to inhibition. To simulate the blood flow characteristics of postcapillary venules, the rolling experiments were performed in a dynamic-flow-chamber system with immobilized selectins and selectin ligand-carrying U937 cells. The influence of the test compounds on cell rolling was measured by the percentage of adherent cells after a certain flow time and the velocity of the rolling cells. Whereas the test compounds displayed no inhibitory effect on E-selectin-mediated cell rolling, they efficiently blocked the rolling induced by P-selectin. The glucan sulfates were much more active than either unfractionated heparin or low-molecular-weight heparin, or the standard inhibitor Sialyl Lewis(X). Their inhibitory potency turned out to be strongly dependent on various structural parameters, such as sulfation pattern and molecular weight. In conclusion, the semisysnthetic glucan sulfates represent promising candidates in the development of selectin blocking agents.

Hydrophilic/Hydrophobic balance determines morphology of glycolipids with oligolactose headgroups

The morphology of synthetic glycolipids with lactose oligomers (Lac N, the number of lactose units, N = 1, 2, 3) was studied in lamellar phase. By a systematic combination of differential scanning calorimetry and small- and wide-angle x-ray scattering experiments, the effects of hydrophilic/hydrophobic balance on their thermotropic phase behaviors were discussed. The dispersion of Lac 1 exhibited a crystalline-fluid phase transition, dominated by the strong van der Waals interaction between dihexadecyl chains. In the case of Lac 2, the hydrophilic/hydrophobic balance between the headgroup and the alkyl chains is shifted to the hydrophilic side, resulting in a gel-fluid phase transition with a decreased transition temperature and phase transition enthalpy. Different from the first two systems, the differential scanning calorimetry trace of Lac 3 showed much less remarkable peaks. The small- and wide-angle x-ray diffraction patterns did not reveal any transition in the chain ordering, suggesting that the correlation between the hexasaccharide headgroups is so strong that the melting of the alkyl chains was not allowed. Such dominant effects of the hydrophilic/hydrophobic balance on the morphology of Lac N lipids can be attributed to the small sterical mismatch between the alkyl chains and the linear, cylindrical oligolactose groups.

Synthesis of dimeric lactose and dimeric (sialyl) Lewis(X) glycolipids

To investigate structural requirements for the homophilic interaction between carbohydrates on planar model membranes, divalent derivatives with enforced proximity between the two carbohydrate epitopes (lactose, Lewis(X), and sialyl Lewis(X)) were synthesized by use of a dimeric membrane anchor as scaffold.

The physical properties of glycosyl diacylglycerols. Calorimetric, X-ray diffraction and Fourier transform spectroscopic studies of a homologous series of 1,2-di-O-acyl-3-O-(beta-D-galactopyranosyl)-sn-glycerols

We have synthesized a homologous series of saturated 1,2-di-O-n-acyl-3-O-(beta-D-galactopyranosyl)-sn-glycerols with odd- and even-numbered hydrocarbon chains ranging in length from 10 to 20 carbon atoms, and have investigated their physical properties using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The DSC results show a complex pattern of phase behaviour, which in a typical preheated sample consists of a lower temperature, moderately energetic lamellar gel/lamellar liquid-crystalline (L(beta)/L(alpha)) phase transition and a higher temperature, weakly energetic lamellar/nonlamellar phase transition. On annealing at a suitable temperature below the L(beta)/L(alpha) phase transition, the L(beta) phase converts to a lamellar crystalline (L(c1)) phase which may undergo a highly energetic L(c1)/L(alpha) or L(c1)/inverted hexagonal (H(II)) phase transition at very high temperatures on subsequent heating or convert to a second L(c2) phase in certain long chain compounds on storage at or below 4 degrees C. The transition temperatures and phase assignments for these galactolipids are supported by our XRD and FTIR spectroscopic measurements. The phase transition temperatures of all of these events are higher than those of the comparable phase transitions exhibited by the corresponding diacyl alpha- and beta-D-glucosyl glycerols. In contrast, the L(beta)/L(alpha) and lamellar/nonlamellar phase transition temperatures of the beta-D-galactosyl glycerols are lower than those of the corresponding diacyl phosphatidylethanolamines (PEs) and these glycolipids form inverted cubic phases at temperatures between the lamellar and H(II) phase regions. Our FTIR measurements indicate that in the L(beta) phase, the hydrocarbon chains form a hexagonally packed structure in which the headgroup and interfacial region are undergoing rapid motion, whereas the L(c) phase consists of a more highly ordered, hydrogen-bonded phase, in which the chains are packed in an orthorhombic subcell similar to that reported for the diacyl-beta-D-glucosyl-sn-glycerols. A comparison of the DSC data presented here with our earlier studies of other diacyl glycolipids shows that the rate of conversion from the L(beta) to the L(c) phase in the beta-D-galactosyl glycerols is slightly faster than that seen in the alpha-D-glucosyl glycerols and much faster than that seen in the corresponding beta-D-glucosyl glycerols. The similarities between the FTIR spectra and the first-order spacings for the lamellar phases in both the beta-D-glucosyl and galactosyl glycerols suggest that the headgroup orientations may be similar in both beta-anomers in all of their lamellar phases. Thus, the differences in their L(beta)/L(c) conversion kinetics and the lamellar/nonlamellar phase properties of these lipids probably arise from subtly different hydration and H-bonding interactions in the headgroup and interfacial regions of these phases. In the latter case, such differences would be expected to alter the ability of the polar headgroup to counterbalance the volume of the hydrocarbon chains. This perspective is discussed in the context of the mechanism for the L(alpha)/H(II) phase transition which we recently proposed, based on our X-ray diffraction measurements of a series of PEs.

Short-range interactions between lipid bilayers measured by X-ray diffraction

Interactions between lipid bilayers are critical in many biological processes in which membrane surfaces come close together. Recent X-ray diffraction analyses of bilayers subjected to known osmotic pressures have provided critical information on the magnitude of both the repulsive and the attractive forces that exist between phospholipid and glycolipid membranes.