Parallel-plate Flow Chamber Assay Research Articles

Receptor-ligand non-equilibrium kinetics (RLNEK) 1.0: An integrated Trackmate laminar flow chamber analysis

Although parallel plate flow chamber assays are widely performed, extraction of kinetic parameters is limited to specialized labs with mathematical expertise and customized video-microscopy tracking tools. The recent development of Trackmate has increased researcher accessibility to tracking particles in video-microscopy experiments; however, there is a lack of tools that analyze this tracking information. We report a software tool, compatible with Trackmate, that extracts Receptor Ligand Non-Equilibrium Kinetic (RLNEK) parameters from video-microscopy data. This software should be of particular interest to the community of researchers and scientists interrogating the target-specific binding and release of immune cells.

Structural characterization and antagonistic effect against P-selectin-mediated function of SFF-32, a fucoidan fraction from Sargassum fusiforme

Ethnopharmacological relevanceSargassum fusiforme (Harvey) Setchell, or Haizao, has been used in traditional Chinese medicine (TCM) since at least the eighth century a.d. S. fusiforme is an essential component of several Chinese formulas, including Haizao Yuhu Decoction, used to treat goiter, and Neixiao Lei Li Wan used to treat scrofuloderma. The pharmacological efficacy of S. fusiforme may be related to its anti-inflammatory effect. Aim of the studyTo determine the structural characteristics of SFF-32, a fucoidan fraction from S. fusiforme, and its antagonistic effect against P-selectin mediated function. Materials and methodsThe primary structure of SFF-32 was determined using methylation/GC–MS and NMR analysis. Surface morphology and solution conformation of SFF-32 were determined by scanning electron microscopy (SEM), Congo red test, and circular dichroic (CD) chromatography, respectively. The inhibitory effects of SFF-32 against the binding of P-selectin to HL-60 cells were evaluated using flow cytometry, static adhesion assay, and parallel-plate flow chamber assay. Furthermore, the blocking effect of SFF-32 on the interaction between P-selectin and PSGL-1 was evaluated using an in vitro protein binding assay. ResultsThe main linkage types of SFF-32 were proven to →[3)-α-l-Fucp-(1→3,4)-α-l-Fucp-(1]2→[4)-β-d-Manp-(1→3)-d-GlcAp-(1]2→4)-β-d-Manp-(1→3)-β-d-Glcp-(1→4)-β-d-Manp-(1→2,3)-β-d-Galp-(1→4)-β-d-Manp-(1→[4)-α-l-Rhap-(1]3→. The sulfated unit or terminal xylose residues were attached to the backbone through the C-3 of some fucose residues and terminal xylose residues were attached to C-3 of galactose residues. Moreover, SFF-32 disrupted P-selectin-mediated cell adhesion and rolling as well as blocked the interaction between P-selectin and its physiological ligand PSGL-1 in a dose-dependent manner. ConclusionsBlocking the binding between P-selectin and PSGL-1 is the possible underlying mechanism by which SFF-32 inhibits P-selectin-mediated function, which demonstrated that SFF-32 may be a potential anti-inflammatory lead compound.

Carbon Nanotube/Poly(dimethylsiloxane) Composite Materials to Reduce Bacterial Adhesion.

Different studies have shown that the incorporation of carbon nanotubes (CNTs) into poly(dimethylsiloxane) (PDMS) enables the production of composite materials with enhanced properties, which can find important applications in the biomedical field. In the present work, CNT/PDMS composite materials have been prepared to evaluate the effects of pristine and chemically functionalized CNT incorporation into PDMS on the composite’s thermal, electrical, and surface properties on bacterial adhesion in dynamic conditions. Initial bacterial adhesion was studied using a parallel-plate flow chamber assay performed in conditions prevailing in urinary tract devices (catheters and stents) using Escherichia coli as a model organism and PDMS as a control due to its relevance in these applications. The results indicated that the introduction of the CNTs in the PDMS matrix yielded, in general, less bacterial adhesion than the PDMS alone and that the reduction could be dependent on the surface chemistry of CNTs, with less adhesion obtained on the composites with pristine rather than functionalized CNTs. It was also shown CNT pre-treatment and incorporation by different methods affected the electrical properties of the composites when compared to PDMS. Composites enabling a 60% reduction in cell adhesion were obtained by CNT treatment by ball-milling, whereas an increase in electrical conductivity of seven orders of magnitude was obtained after solvent-mediated incorporation. The results suggest even at low CNT loading values (1%), these treatments may be beneficial for the production of CNT composites with application in biomedical devices for the urinary tract and for other applications where electrical conductance is required.

Fluorescent Multiplex Cell Rolling Assay: Simultaneous Capturing up to Seven Samples in Real-Time Using Spectral Confocal Microscopy.

The parallel plate flow chamber assay is widely utilized to study physiological cell-cell adhesive interactions under dynamic flow that mimics the bloodstream. In this technique, the cells are perfused under defined shear stresses over a monolayer of endothelial cells (expressing homing molecules, e.g., selectins) or a surface (expressing recombinant homing molecules). However, with the need to study multiple samples and multiple parameters per sample, using a traditional bright-field microscope-based flow assay allows only one sample at a time to be analyzed, resulting in high interexperiment variability, the need for normalization, waste of materials, and significant consumption of time. We developed a multiplexing approach using a three-color fluorescence staining method, which allowed for up to seven different combination signatures to be run at one time. Using this fluorescent multiplex cell rolling (FMCR) assay, each sample is labeled with a different signature of emission wavelengths and mixed with other samples just minutes before the flow run. Subsequently, real-time images are acquired in a single pass using a line-scanning spectral confocal microscope. To illustrate the glycan-dependent binding of E-selectin, a central molecule in cell migration, to its glycosylated ligands expressed on myeloid-leukemic cells in flow, the FMCR assay was used to analyze E-selectin-ligand interactions following the addition (fucosyltransferase-treatment) or removal (deglycosylation) of key glycans on the flowing cells. The FMCR assay allowed us to analyze the cell-adhesion events from these different treatment conditions simultaneously in a competitive manner and to calculate differences in rolling frequency, velocity, and tethering capability of cells under study.

Fluorometric Quantification of Single-Cell Velocities to Investigate Cancer Metastasis.

Hematogenous metastasis is a multistep, selectin-regulated process whose mechanisms remain poorly understood. To investigate this biological pathway of cancer dissemination and better understand circulating cancer cells, we developed a high-throughput methodology that integrates organ-on-chip-like microfluidic and photoconvertible protein technologies. Our approach can ascribe single-cell velocity as a traceable cell property for off-chip analysis of the direct relationships between cell molecular profiles and adhesive phenotypes in the context of physiologically relevant fluid flow. We interrogate how natively expressed selectin ligands relate to colon cancer cell rolling frequencies and velocities and provide context for previously reported disparities in invitro and invivo models of selectin-mediated adhesion and metastasis. This integrated methodology represents a versatile approach for the development of anti-metastatic therapeutics as well as to generate and test mechanistic hypotheses regarding spatiotemporal processes that occur over timescales of seconds to hours with single-cell resolution.

Wdr1-Mediated Actin Reorganization Is Essential for Integrin αIIbβ3 Activation in Platelets

In resting platelets, the heterodimeric integrin αIIbβ3 is present in a low-affinity state. During platelet activation, the intracytoplasmic signals induce conformational changes that results in a swung-out conformation of the extracellular domain competent to bind ligands such as fibrinogen with high affinity to mediate platelet aggregation. Actin turnover is essential for this process and dynamic assembly and disassembly of actin filaments regulate it. We have identified Wdr1, a cofilin and actin binding protein containing WD40 repeats, as an essential component of the machinery that orchestrates actin fiber reorganization that leads to integrin αIIbβ3 activation.Methods: Wdr1-deficient mouse strain, Wdr1rd/rd. was obtained through an N-ethyl-N-nitrosourea mutagenesis screen in Baylor College of Medicine. The mutant mouse has a T>A transversion in the second dinucleotide of the intron 9 splice donor site and it produces a mutant transcript containing a 6-bp in-frame deletion that results in a incorrectly folded, nonfunctional protein. Normal splicing produces a small amount of Wdr1 protein (~2%) resulting in a hypomorphic allele. Wdr1-deficient mice are moderately thrombocytopenic (85± 11 x 106 ml Wdr1 deficient versus 427± 52 x 106/ml for wild-type). Platelets were isolated from Wdr1-deficient and control mice. Platelet aggregation was carried out by standard turbidometric methods. Calcium mobilization was measured by incubating Wdr1-deficient and WT (wild-type) platelets with Fura 2 AM and measuring the Fura 2 fluorescence after collagen treatment. Conformational change in αIIbβ3 was determined by flow cytometry with a conformation-specific anti-αIIbβ3 antibody JON/A. In vivo hemostasis was assessed by tail bleeding time and FeCl3-induced endothelial carotid injury/thrombosis model was used to assess the occlusion in carotid artery of mice.Results: Aggregation response of Wdr1-deficient platelets to different doses of collagen was significantly impaired compared to WT platelets. Under similar conditions, the calcium response was similar to the WT. In a parallel-plate flow chamber assay, WT platelets stably adhered to collagen surface and formed stable thrombus. On the other hand, significantly less number of Wdr1 deficient platelets were stably attach to the collagen surface and it did not form stable thrombus. As expected the tail bleeding time of Wdr1 deficient mice is significantly prolonged (> 10 minutes) compared to WT mice (<2 min). In vivo, in FeCl3 induced carotid artery thrombosis model, vessel occlusion in Wdr1 deficient was prolonged significantly compared wild type mice (15.8 ± 12.6 minutes versus 9.0 ± 10.5 minutes (p=0.041, Mann-Whitney non parametric comparison).To examine directly the activation of αIIbβ3, we used JON/A antibody, which selectively binds to activated αIIbβ3 integrins on mouse platelets. Binding of collagen treated Wdr1-deficient platelets to JON/A as determined by flow cytometry, is significantly less compared to WT platelets (6.1±0.3 fluorescence units (FU) versus 17.4±0.6 FU, p≤0.05) indicating impaired inside-out activation of αIIbβ3. Since, Wdr1 promotes actin disassembly, which is essential for the rearrangement of the actin fibers that occurs during platelet activation, we measured actin turn over by measuring F-actin and G-actin ratios of collagen treated platelets at various time points. Actin turnover is highly impaired in Wdr1 deficient platelets compared to WT platelets. Furthermore, integrin αIIbβ3 association with actin cytoskeleton was markedly impaired in Wdr1 deficient mice compared to their WT controls.These studies show that Wdr1 mediated actin cytoskeleton reorganization is essential for integrin αIIbβ3 activation. DisclosuresNo relevant conflicts of interest to declare.

Effect of variation in hemorheology between human and animal blood on the binding efficacy of vascular-targeted carriers.

Animal models are extensively used to evaluate the in vivo functionality of novel drug delivery systems (DDS). However, many variations likely exist in vivo between the animals and human physiological environment that significantly alter results obtained with animal models relative to human system. To date, it is not clear if the variation in hemorheology and hemodynamics between common animal and human models affect the functionality of DDS. This study investigates the role of hemorheology of humans and various animal models in dictating the binding efficiency of model vascular-targeted carriers (VTCs) to the wall in physiological blood flows. Specifically, the adhesion of sLeA-coated nano- and micro-spheres to inflamed endothelial cells monolayers were conducted via a parallel plate flow chamber assay with steady and disturbed red blood cells (RBCs)-in-buffer and whole blood flows of common animal models. Our results suggest that the ratio of carrier size to RBC size dictate particle binding in blood flow. Additionally, the presence of white blood cells affects the trend of particle adhesion depending on the animal species. Overall, this work sheds light on some deviation in VTC vascular wall interaction results obtained with in vivo animal experimentation from expected outcome and efficiency in vivo in human.

Glycosyltransferases involved in the synthesis of MUC-associated metastasis-promoting selectin ligands.

The sialyl Lewis a and x (sLe(a/x)) antigens frequently displayed on the surface of tumor cells are involved in metastasis. Their synthesis has been attributed to altered expression of selective glycosyltransferases. Identification of these glycosyltransferases and the glycoproteins that carry these carbohydrate antigens should help advance our understanding of selectin-mediated cancer metastasis. In this study, quantitative real-time polymerase chain reaction analysis coupled with in situ proximity ligation assay and small interference RNA treatment shows involvement of β3galactosyltransferase-V in the synthesis of MUC16-associated sLe(a) in H292 cells. Also, α3fucosyltransferase-V, which is absent in BEAS-2B human immortalized bronchial epithelial cells and A549 lung carcinoma cells, participates in the synthesis of MUC1-associated sLe(x) in CFT1 human immortalized bronchial epithelial cells and H292 lung carcinoma cells. Neither selectin ligand is found on MUC1 in BEAS-2B and A549 cells. Knockdown of either enzyme suppresses migration, and selectin tethering and rolling properties of H292 cells under dynamic flow as determined by wound healing and parallel plate flow chamber assays, respectively. These results provide insights into how the synthesis of mucin-associated selectin ligands and the metastatic properties of cancer cells can be regulated by selective glycosyltransferases that work on mucins. They may help develop novel anticancer drugs.

Abstract 653: Endothelial ASC Modulates Early Atherosclerosis by Limiting Monocyte Recruitment

The inflammasome consists of an innate immune receptor, the adaptor molecule ASC, and the effector Caspase-1 that is responsible for processing signature cytokines such as IL-1beta. The exact role of the inflammasome in atherosclerosis is not clear since both pathogenic and dispensable roles have been reported. Notably, ASC has functions that may impact atherosclerosis but are unrelated to the inflammasome, for example the induction of apoptosis and the regulation of pro-inflammatory transcription factors. The various roles of ASC (i.e. IL-1beta processing, cell death, NF-kappaB and AP-1 regulation) may modulate the progression of atherosclerosis depending on lesion stage and explain the divergent findings highlighted above. To examine the role of ASC in lesion progression, we bred ASC -deficient mice onto the Ldlr -/- background and initiated a cholesterol-rich diet (CRD). In the early stages of atherogenesis (2 weeks of CRD), ASC -/- Ldlr -/- mice had a significantly increased lesion surface area, leukocyte content, and rate of Ly6C hi monocyte recruitment in the ascending aorta. Bone marrow transplant experiments suggested that ASC deficiency in the vessel wall was responsible for this phenotype. Knockdown of ASC by siRNA in cultured human umbilical vein endothelial cells lead to increased TNF-alpha-induced expression of VCAM1 and monocyte adhesion in parallel-plate flow chamber assays. Monocyte adhesion was not affected by silencing Caspase-1, suggesting that the effect of ASC was independent of the inflammasome. Preliminary findings implicate MAPK family members in ASC-mediated regulation of endothelial adhesion molecules. At 16 weeks of a CRD ASC -/- Ldlr -/- mice had a significantly decreased lesion size compared with controls. Lesions from ASC -/- Ldlr -/- mice had a smaller necrotic core area accompanied by decreased numbers of apoptotic leukocytes as determined by active Caspase-3 and TUNEL positivity. These data are in accordance with the pro-atherogenic role of ASC in later stages of atherosclerosis. However our findings demonstrate a novel protective role for ASC in the early stage, which represents a non-inflammasome function via modulation of endothelial-associated adhesion molecules.

Ultrasound Molecular Imaging of E-Selectin in Tumor Vessels Using Poly n-Butyl Cyanoacrylate Microbubbles Covalently Coupled to a Short Targeting Peptide

The purposes of this study were the development and preclinical evaluation of clinically translatable E-selectin-specific ultrasound contrast agents based on a peptide ligand with the recognition sequence IELLQAR. The E-selectin-specific peptide was synthesized through solid phase peptide synthesis and covalently attached to poly n-butylcyanoacrylate-stabilized microbubbles with an air core. Quantification of the microbubble surface coverage with peptides was performed through flow cytometry. Targeted adhesion of peptide-coated microbubbles was investigated in vitro using parallel plate flow chamber assays on tumor necrosis factor-α-stimulated human umbilical vein endothelial cells. In vivo imaging was performed in nude mice bearing human ovarian carcinoma xenografts (MLS), followed by ex vivo immunohistochemistry validation of E-selectin expression. Success of peptide synthesis was validated through preparative reverse phase high-pressure liquid chromatography and electronspray ionization-mass spectrometry. Results of the flow cytometry revealed approximately 4000 E-selectin-specific peptides/microbubble surface. Results of the in vitro experiments demonstrated the specificity of peptide-coated microbubbles to E-selectin (1.10 ± 0.48 vs 0.19 ± 0.09 bound microbubbles per cell, before and after competition respectively; P < 0.01). The in vivo imaging enabled specific assessment of E-selectin expression in MLS carcinoma xenografts (5.21 ± 3.41 vs 1.37 ± 0.67 contrast intensity before and after competition, respectively; P < 0.05). Clinically translatable microbubbles that were covalently coupled to the short E-selectin-specific peptide (IELLQAR) enabled specific imaging of the E-selectin expression in tumor vessels in vivo.

Simultaneously Capturing Real-time Images in Two Emission Channels Using a Dual Camera Emission Splitting System: Applications to Cell Adhesion

Multi-color immunofluorescence microscopy to detect specific molecules in the cell membrane can be coupled with parallel plate flow chamber assays to investigate mechanisms governing cell adhesion under dynamic flow conditions. For instance, cancer cells labeled with multiple fluorophores can be perfused over a potentially reactive substrate to model mechanisms of cancer metastasis. However, multi-channel single camera systems and color cameras exhibit shortcomings in image acquisition for real-time live cell analysis. To overcome these limitations, we used a dual camera emission splitting system to simultaneously capture real-time image sequences of fluorescently labeled cells in the flow chamber. Dual camera emission splitting systems filter defined wavelength ranges into two monochrome CCD cameras, thereby simultaneously capturing two spatially identical but fluorophore-specific images. Subsequently, psuedocolored one-channel images are combined into a single real-time merged sequence that can reveal multiple target molecules on cells moving rapidly across a region of interest.

Simultaneously Capturing Real-time Images in Two Emission Channels Using a Dual Camera Emission Splitting System: Applications to Cell Adhesion

Multi-color immunofluorescence microscopy to detect specific molecules in the cell membrane can be coupled with parallel plate flow chamber assays to investigate mechanisms governing cell adhesion under dynamic flow conditions. For instance, cancer cells labeled with multiple fluorophores can be perfused over a potentially reactive substrate to model mechanisms of cancer metastasis. However, multi-channel single camera systems and color cameras exhibit shortcomings in image acquisition for real-time live cell analysis. To overcome these limitations, we used a dual camera emission splitting system to simultaneously capture real-time image sequences of fluorescently labeled cells in the flow chamber. Dual camera emission splitting systems filter defined wavelength ranges into two monochrome CCD cameras, thereby simultaneously capturing two spatially identical but fluorophore-specific images. Subsequently, psuedocolored one-channel images are combined into a single real-time merged sequence that can reveal multiple target molecules on cells moving rapidly across a region of interest.

Repairing of Homing Defect in Cord Blood Hematopoietic Stem Cell Transplantation–Comparison of Fucosyltransferase VII with Fucosyltransferase VI.

AbstractAbstract 2988 Objective:Relatively slower speed of engraftment in bone marrow of recipients makes cord blood (CB) transplantation (CBT) more difficult in a clinical setting. Selectins and their ligands are known to play a role in the homing of hematopoietic stem/progenitor cell (HSPC) to the bone marrow. Fucosyltransferase VI (FTVI) mediated ex vivo fucosylation improves human CB engraftment in NOD-SCID IL-2Rγnull (NSG) mice. FTVI is expressed in many cell types, while fucosyltransferase VII (FTVII) is primarily expressed in hematopoietic cells. FTVII deficient leukocytes do not bind the P- and E-selectins and are not recruited to sites of inflammation. We hypothesize that FTVII is more efficient than FTVI in surface fucosylation of CB-HSPC and thus enhances homing and engraftment of CB-HSPC (CD34+) in NSG mice. Method:Purified CB CD34+ cells were obtained from fresh CB in healthy full-term newborns by immunomagnetic microbeads sorting. CD34+ cells were treated with FTVI or FTVII respectively, the expression level of sLex (HECA-452) and binding to P- or E-selectin were detected by flow cytometry. Interactions of FTVI-, FTVII- or combined FTVI/FTVII-fucosylated CB CD34+cells with P- or E-selectin were measured under physiological flow conditions using a parallel-plate flow chamber assay. CBT was performed in NSG mice of 5 groups (negative control, sham-control, FTVI-treated, FTVII-treated, and FTVI/FTVII-treated). From 2 weeks post transplantation, mice were bled every 2 weeks for anti-human CD45 screening by flow cytometry. We used this method to evaluate the engraftment progress of CB-HSPC with different treatments. Ten weeks after transplantation, all mice were sacrificed and peripheral blood and bone marrow cells were isolated. Hematopoiesis reconstitution of CB cells was analyzed by flow cytometry after staining the cells with antibodies to various human hematopoietic subset markers, which included CD45 for total leukocytes, CD19 for B-cells, CD33 for myeloid cells, CD41 for megakaryocytes, CD3 for T-cells, and CD34 for HSPCs. Result:Under in vitro conditions, surface fucosylation with FTVI or FTVII results in an enhanced expression of HECA-452 epitopes on CD34+ cells from fresh CB. Increased P- and E-selectin binding to fresh CB CD34+ cells after either FTVI or FTVII treatment compared to sham-treated. However, FTVII-treated fresh CB CD34+ cells had a much higher binding to P-selectin than that of FTVI-treated fresh CB CD34+ cells. FTVI/FTVII-fucosylated CD34+ cells isolated from fresh CB accumulated more on P- or E-selectin coated plates than that of single enzyme fucosylated CD34+ cells under flow conditions. Although it is not statistically significant, more FTVII-treated fresh CB CD34+ cells rolled on both P- and E-selectin surface than FTVI-treated fresh CB CD34+ cells did. FTVII- or FTVI/FTVII-treated CD34+cells from fresh CB engrafted significantly better in NSG mice than the FTVI-treated cells at 4 and 6 weeks. Ten weeks after transplantation, the bone marrows of mice that received FTVII-treated cells had significantly improved engraftment of human hematopoietic progenitors of some lineages (CD3, CD33, and CD41) compared to that of mice that received FTVI-treated cells. Conclusion:FTVII-treated CB-HSPCs have greater engraftment progress during early time after transplantation compared to FTVI. FTVII mediated fucosylation did not affect self-renewal of CB-HSPC. Hematopoiesis reconstitution of T-lymphocytes, myeloid cells, and megakaryocytes of FTVII is better than FTVI. Finally, FTVI and FTVII may have a cooperative effect on CB-HSPC homing to bone marrow. Disclosures:Miyaji:Kyowa Hakko Kirin Co., Ltd.: Research Funding. Sato:Kyowa Hakko Kirin Co., Ltd.: Research Funding. Miller:Kyowa Hakko Kirin Co., Ltd.: Research Funding. Xia:Kyowa Hakko Kirin Co., Ltd.: Research Funding.

Lymphocyte Dynamics on Aligned Endothelial Cells

Immune cells circulating blood vessels recognize the signatures of tissue inflammation in blood vessels and undergo multiple cascades of interactions with inflamed endothelium to eventually leave out the vessels. Parallel plate flow chamber assay has been extensively used to investigate detailed mechanisms of lymphocyte-endothelial cell (ECs) interactions. However, orientation of ECs, which may play significant roles in lymphocyte dynamics on inflamed endothelium, has not been considered in these assays yet. Indeed, healthy blood vessels are composed of endothelium aligned in parallel with the direction of blood flow. To address the importance of ECs alignment on lymphocyte dynamics, we firstly aligned ECs on the substrates containing nanoscale grooves and ridges. Then, dynamics of T cells on the aligned endothelial layers (either parallel or perpendicular to the direction of flow) and randomly oriented ECs were monitored by video microscopy. Firstly, we quantitatively analyzed the direction of T cell crawling under the conditions stated above. Interestingly, the direction of T cell crawling was not significantly affected by the flow direction, but rather biased toward the direction of EC alignment. Indeed, when junctions and nuclei of ECs were visualized, T cells preferentially migrated along the EC the junctions, while avoided crawling on top of EC nucleus. Based on this observation, we hypothesized that topographical structures and mechanical properties of ECs guided crawling of T cells and performed a number of experiments to test the hypothesis. Secondly, we investigated the effect of EC alignment on transendothelial migration (TEM) of T cells. T cells on poorly-aligned ECs underwent TEM more quickly and frequently than T cells on well-aligned ECs. Further analysis revealed that local alignment of EC junctions surrounded by more than three ECs form preferential sites for TEM of T cells.

Spreading of human neutrophils on an ICAM-1-immobilized substrate under shear flow

Neutrophil (PMN) spreading on endothelium, mediated by the interactions between surface-bound β2 integrin and intercellular adhesion molecule-1 (ICAM-1) in the inflammatory cascade, is crucial for PMN post-adhesion and trans-migration in blood flow. The underlying mechanisms by which shear flow regulates PMN spreading dynamics are not well understood. Here, a parallel-plate flow chamber assay was applied to quantify the time course of PMN adhesion and spreading on an ICAM-1-immobilized substrate. Two types of shear flow, steady flows at shear stresses of 0.2, 0.5, and 1 dyne/cm2 and stepwise flows at 0, 1, and 10 dyne/cm2, were used to elucidate the impact of shear flow on cell adhesion and spreading. The number of adhered PMNs, the fraction of spreading PMNs and the projected area of spread PMNs were determined and were found to correlate with the distribution of surface-bound β2 integrin subunit (CD11a, CD11b, or CD18). The results indicate that PMN spreading on an ICAM-1 substrate is bi-directionally regulated under shear flow. CD11a, CD11b and CD18 subunits of β2 integrin contribute distinctly to PMN spreading on ICAM-1 substrates. This work provides new insights into understanding PMN spreading on the endothelium, mediated by β2 integrin and ICAM-1 under shear flow.

Synthesis and evaluation of an anti-MLC1 × anti-CD90 bispecific antibody for targeting and retaining bone-marrow-derived multipotent stromal cells in infarcted myocardium.

A key issue regarding the use of stem cells in cardiovascular regenerative medicine is their retention in target tissues. Here, we have generated and assessed a bispecific antibody heterodimer designed to improve the retention of bone-marrow-derived multipotent stromal cells (BMMSC) in cardiac tissue damaged by myocardial infarction. The heterodimer comprises an anti-human CD90 monoclonal antibody (mAb) (clone 5E10) and an anti-myosin light chain 1 (MLC1) mAb (clone MLM508) covalently cross-linked by a bis-arylhydrazone. We modified the anti-CD90 antibody with a pegylated-4-formylbenzamide moiety to a molar substitution ratio (MSR) of 2.6 and the anti-MLC1 antibody with a 6-hydrazinonicotinamide moiety to a MSR of 0.9. The covalent modifications had no significant deleterious effect on mAb epitope binding. Furthermore, the binding of anti-CD90 antibody to BMMSCs did not prevent their differentiation into adipo-, chondro-, or osteogenic lineages. Modified antibodies were combined under mild conditions (room temperature, pH 6, 1 h) in the presence of a catalyst (aniline) to allow for rapid generation of the covalent bis-arylhydrazone, which was monitored at A(354). We evaluated epitope immunoreactivity for each mAb in the construct. Flow cytometry demonstrated binding of the bispecific construct to BMMSCs that was competed by free anti-CD90 mAb, verifying that modification and cross-linking were not detrimental to the anti-CD90 complementarity-determining region. Similarly, ELISA-based assays demonstrated bispecific antibody binding to plastic-immobilized recombinant MLC1. Excess anti-MLC1 mAb competed for bispecific antibody binding. Finally, the anti-CD90 × anti-MLC1 bispecific antibody construct induced BMMSC adhesion to plastic-immobilized MLC1 that was resistant to shear stress, as measured in parallel-plate flow chamber assays. We used mAbs that bind both human antigens and the respective pig homologues. Thus, the anti-CD90 × anti-MLC1 bispecific antibody may be used in large animal studies of acute myocardial infarction and may provide a starting point for clinical studies.

Sequential Binding of αvβ3 and ICAM-1 Determines Fibrin-Mediated Melanoma Capture and Stable Adhesion to CD11b/CD18 on Neutrophils

Fibrin (Fn) deposition defines several type 1 immune responses, including delayed-type hypersensitivity and autoimmunity in which polymorphonuclear leukocytes (PMNs) are involved. Fn monomer and fibrinogen are multivalent ligands for a variety of cell receptors during cell adhesion. These cell receptors provide critical linkage among thrombosis, inflammation, and cancer metastasis under venous flow conditions. However, the mechanisms of Fn-mediated interactions among immune cells and circulating tumor cells remain elusive. By using a cone-plate viscometer shear assay and dual-color flow cytometry, we demonstrated that soluble fibrinogen and Fn had different abilities to enhance heterotypic aggregation between PMNs and Lu1205 melanoma cells in a shear flow, regulated by thrombin levels. In addition, the involvement of integrin α(v)β(3), ICAM-1, and CD11b/CD18 (Mac-1) in fibrin(ogen)-mediated melanoma-PMN aggregations was explored. Kinetic studies provided evidence that ICAM-1 mediated initial capture of melanoma cells by PMNs, whereas α(v)β(3) played a role in sustained adhesion of the two cell types at a shear rate of 62.5 s(-1). Quantitative analysis of the melanoma-PMN interactions conducted by a parallel-plate flow chamber assay further revealed that at a shear rate of 20 s(-1), α(v)β(3) had enough contact time to form bonds with Mac-1 via Fn, which could not otherwise occur at a shear rate higher than 62.5 s(-1). Our studies have captured a novel finding that leukocytes could be recruited to tumor cells via thrombin-mediated Fn formation within a tumor microenvironment, and α(v)β(3) and ICAM-1 may participate in multistep fibrin(ogen)-mediated melanoma cell adhesion within the circulation.

ScVEGF Microbubble Ultrasound Contrast Agents

To develop a novel microbubble (MB) ultrasound contrast agent covalently coupled to a recombinant single-chain vascular endothelial growth factor construct (scVEGF) through uniform site-specific conjugation for ultrasound imaging of tumor angiogenesis. Ligand conjugation to maleimide-bearing MB by thioether bonding was first validated with a fluorophore (BODIPY-cystine), and covalently bound dye was detected by fluorometry and flow cytometry. MBs were subsequently site-specifically conjugated to cysteine-containing Cys-tag in scVEGF, and bound scVEGF was quantified by enzyme-linked immunosorbent assay. Targeted adhesion of scVEGF-MB was investigated with in vitro parallel plate flow chamber assays with recombinant murine VEGFR-2 substrates and human VEGFR-2-expressing porcine endothelial cells (PAE/KDR). A wall-less ultrasound flow phantom, with flow channels coated with immobilized VEGFR-2, was used to detect adhesion of scVEGF-MB with contrast ultrasound imaging. A murine model of colon adenocarcinoma was used to assess retention of scVEGF-MB with contrast ultrasound imaging during tumor angiogenesis in vivo. Proof-of-principle of ligand conjugation to maleimide-bearing MB was demonstrated with a BODIPY-cysteine fluorophore. Conjugation of BODIPY to MB saturated at 10-fold molar excess BODIPY relative to maleimide groups on MB surfaces. MB reacted with scVEGF and led to the conjugation of 1.2 × 10(5) molecules scVEGF per MB. Functional adhesion of sc-VEGF-MB was shown in parallel plate flow chamber assays. At a shear stress of 1.0 dynes/cm2, scVEGF-MB exhibited 5-fold higher adhesion to both recombinant VEGFR-2 substrates and VEGFR-2-expressing endothelial cells compared with nontargeted control MB. Additionally, scVEGF-MB targeted to immobilized VEGFR-2 in an ultrasound flow phantom showed an 8-fold increase in mean acoustic signal relative to casein-coated control channels. In an in vivo model of tumor angiogenesis, scVEGF MB showed significantly higher ultrasound contrast signal enhancement in tumors (8.46 ± 1.61 dB) compared with nontargeted control MB (1.58 ± 0.83 dB). These results demonstrate the functionality of a novel scVEGF-bearing MB contrast agent, which could be useful for molecular imaging of VEGFR-2 in basic science and drug discovery research.

Tumor Necrosis Factor-Induced Neutrophil Adhesion Occurs Via Sphingosine Kinase-1-Dependent Activation of Endothelial α 5β 1 Integrin

Leukocyte recruitment plays a major role in the immune response to infectious pathogens, as well as during inflammatory and autoimmune disorders. The process of leukocyte extravasation from the blood requires a complex cascade of adhesive events between the leukocytes and the endothelium, including initial leukocyte rolling, adhesion, and finally transendothelial migration. Current research in this area aims to identify the key leukocyte subsets that initiate a given disease and to identify the trafficking molecule(s) that will most specifically inhibit those cells. Herein we demonstrate that tumor necrosis factor (TNF)alpha activates the integrin alpha(5)beta(1) without altering total expression levels of beta(1) integrin on human umbilical vein endothelial cells. Moreover, our studies suggest that TNFalpha-induced beta(1) activation is dependent on sphingosine kinase-1, but independent of the sphingosine-1-phosphate family of G protein-coupled receptors. We also show, using a parallel plate flow chamber assay, that neutrophil adhesion to TNFalpha-activated endothelium can be attenuated by blocking alpha(5)beta(1) or its ligand angiopoietin-2. These observations add new complexities that broaden the accepted concept of cellular trafficking with neutrophil adhesion to TNFalpha activated endothelial cells being sphingosine kinase-1, alpha(5)beta(1), and angiopoietin-2 dependent. Moreover, this work supports the notion that sphingosine kinase-1 may be the single target required for an effective broad spectrum approach to combat inflammation and immune disorders.

Potential role of size and hemodynamics in the efficacy of vascular-targeted spherical drug carriers

Targeting of drug carriers to the vascular wall is of interest for localized delivery of therapeutics in many human diseases. Nanometer-sized spherical particles are widely proposed for use as carriers for vascular targeting, yet very little evidence has been presented as to their ability to interact with the vascular wall. Thus, this work focuses on elucidating the effect of particle size along with hemodynamics, blood rheology, and vessel size on the adhesion efficiency of targeted polymeric spheres to inflamed endothelium in vitro via parallel plate flow chamber assays. We find that the binding efficiency of spheres to the endothelium from blood flow generally increased with increasing particle size, wall shear rate and channel height for particle sizes from 100 nm up to 10 μm. However, nano-sized particles showed minimal adhesion to the endothelium from blood flow in horizontal (gravity or anti-gravity direction) and vertical channels on the order of small to medium-sized venules and arteries when compared to micron-sized spheres. Furthermore, adhesion of nanospheres was not enhanced with pulsatility in flow. Overall, the presented data suggests that spheres 2–5 μm in size are optimal for targeting the wall in medium to large vessels relevant in several cardiovascular diseases.