Endoluminal graft repair of abdominal aortic aneurysms by vascular surgeons at a nonclinical trial center

The purpose of this study was to compare the early results and complication rates of commercially available endoluminal grafts (ELG) for abdominal aortic aneurysm (AAA) by a team of vascular surgeons at a nontrial center with those of published results from trial centers. A retrospective chart review of all patients undergoing endoluminal graft repair of AAA was made at the medical center. From October 1, 1999, to December 31, 2000, a team of vascular surgeons electively repaired AAAs in 100 patients at a regional referral center. Of these patients, 49 underwent repair with a commercially available ELG (35 AneuRx, 14 Ancure) whereas the remaining were repaired with an open operation. In the ELG group, the primary technical success rate was 100% with a 30-day mortality rate of 2.0%. The average hospital length of stay was 3.28 days with ICU stay of 1.20 days. The average operative estimated blood loss was 501 mL (100-2,500) with average transfusions of 0.49 unit packed red blood cells (prbc) (0-6). Eighty-eight percent of ELG patients left the hospital without complication. Seven patients (14%) required 11 follow-up procedures for complications including endoleak, limb or graft thrombosis, graft stenosis, distal embolization, or wound complications. Three of 26 patients (11%) with 6-month computed tomography follow-up had evidence of endoleak (2 have subsequently undergone lumbar embolization). Only 1 6-month follow-up patient had shown increased aneurysm size before endoleak treatment. A team of board-certified vascular surgeons at a nonclinical trial center can safely perform ELG for AAA with results similar to those of published series from trial centers.

Protein A is the von Willebrand factor binding protein on Staphylococcus aureus

Endovascular infection is a highly critical complication of invasive Staphylococcus aureus disease. For colonization, staphylococci must first adhere to adhesive endovascular foci. Von Willebrand factor (vWF) is a large, multimeric glycoprotein mediating platelet adhesion at sites of endothelial damage. Earlier it was demonstrated that vWF binds to and promotes the surface adhesion of S. aureus, prompting this effort to identify the vWF adhesin. In Western ligand assays of S. aureus lysates, staphylococcal protein A (SPA) was recognized by purified vWF. Surface plasmon resonance demonstrated the binding of soluble vWF to immobilized recombinant protein A with a K(d) of 1.49 x 10(-8) mol/L. Using flow cytometry, the binding of fluorescein isothiocyanate-labeled vWF to S. aureus was found to be saturable and inhibitable by unlabeled vWF, antiprotein-A antibodies, or IgG. Isogenic Deltaspa::Tc(r) mutants were constructed by the insertion of a tetracycline resistance cassette into spa using allelic replacement, and it exhibited decreased binding of soluble vWF and decreased adhesion to vWF-adsorbed surfaces. The interaction was restored on complementation of the mutants with spa-containing plasmid pSPA7235. In conclusion, protein A confers interaction of S. aureus with soluble and immobilized vWF in a newly discovered function characterizing protein A as a novel member of the staphylococcal surface protein adhesin superfamily and suggesting its potential role in the pathogenesis of endovascular staphylococcal disease.

Modification of the adhesive properties of collagen by covalent grafting with RGD peptides

Collagen, either alone or in combination with other materials, is an important natural biomaterial that is used in a variety of tissue-engineering applications. Cell adhesion and migration of cells within collagen-based biomaterials may be controlled by modifying the adhesive properties of collagen. Furthermore, spatially controlling the adhesiveness of the collagen may allow controlled localization or redistribution of cells. A method is presented for covalently coupling peptides that contain the well-characterized arginine-glycine-aspartic acid adhesion sequence directly to type I collagen monomers prior to fibrillogenesis. A heterobifunctional coupling agent was used to create stable amide and disulfide bonds with the lysine residues of the collagen monomers and the cysteine termini of the peptide molecules, respectively. The degree of conjugation could be controlled by changing the reaction conditions (ratios of reactants added and the length of incubation). The microstructure and gelation times of gels composed of covalently modified collagen were similar to those of unmodified gels. Cell adhesion on adsorbed monolayers of modified collagen was quantified using a well-established clonal cell line (K1735 murine melanoma). Cell adhesion was found to increase with both increasing degree of conjugation and increasing ratio of modified to unmodified collagen.

A generalized transport model for biased cell migration in an anisotropic environment

A generalized transport model is derived for cell migration in an anisotropic environment and is applied to the specific cases of biased cell migration in a gradient of a stimulus (taxis; e.g., chemotaxis or haptotaxis) or along an axis of anisotropy (e.g., contact guidance). The model accounts for spatial or directional dependence of cell speed and cell turning behavior to predict a constitutive cell flux equation with drift velocity and diffusivity tensor (termed random motility tensor) that are explicit functions of the parameters of the underlying random walk model. This model provides the connection between cell locomotion and the resulting persistent random walk behavior to the observed cell migration on longer time scales, thus it provides a framework for interpreting cell migration data in terms of underlying motility mechanisms.

Quantitative analysis of adhesion-mediated cell migration in three-dimensional gels of RGD-grafted collagen

Adhesion-mediated migration is required in a number of physiological and pathological processes. A further quantitative understanding of the relationship between cell migration and cell-substratum adhesiveness may aid in therapeutic or tissue engineering applications. The aim of this work was to quantify three-dimensional cell migration as a function of increasing cell-substratum adhesiveness within reconstituted collagen gels. Cell-substratum adhesiveness was controlled by grafting additional adhesive peptides containing the well-characterized arginine-glycine-aspartic acid sequence to collagen. The three-dimensional migration of multiple individual cells was tracked in real time in an automated fashion for extended periods. Cell displacements were statistically analyzed and fit to a correlated persistent random walk model to estimate root-mean-square speed, directional persistence time, and random motility coefficient. Based on model parameter estimates, cell speed was found to be a monotonically decreasing function of increasing substratum adhesiveness, while the directional persistence time and random motility coefficient exhibited a biphasic dependence, with maximum values at approximately intermediate concentrations of grafted adhesive peptide and hence intermediate cell-substratum adhesiveness. In conclusion, these studies suggest an optimal adhesiveness for three-dimensional random migration, consistent with previous studies on two-dimensional surfaces. However, the maximum in random motility corresponded to a maximum in directional persistence, not in cell speed.

Analysis of Bacterial Deposition on Metal (Hydr)oxide-Coated Sand Filter Media

The aim of this study was to investigate the importance of surface potential in microbial deposition onto modified granular surfaces. Recent experimental and theoretical work has indicated that surfaces coated with metal oxides and hydroxide rich oxide/hydroxide mixtures ((hydr)oxides) have the potential to increase the capture efficiencies of commercial filtration systems. This study quantitatively compared different metal (hydr)oxide coatings in their abilities to enhance bacterial deposition. Specifically, the deposition rates of bacterial strains Streptococcus faecalis, Staphylococcus aureus, Salmonella typhimurium, and Escherichia coli were compared for Ottawa sand and surface coatings consisting of aluminum (hydr)oxide, iron (hydr)oxide, and mixed iron and aluminum (hydr)oxide. The metal-(hydr)oxide-modified granular media enhanced bacterial deposition relative to the noncoated Ottawa sand. The electropositive surfaces, the aluminum and the mixed (hydr)oxides, had similar average kinetic rate constants, five times larger than the rate constants observed for the untreated Ottawa sand. The measured kinetic rate constants for the positively charged systems of aluminum (hydr)oxide and mixed (hydr)oxide collectors suggested that the overall rate of deposition was limited by the transport of bacteria to the granular surface rather than the rate of attachment. For systems where the collector surfaces were negatively charged, as in the cases of Ottawa sand and the iron (hydr)oxide coating, large energy barriers to attachment were predicted from DLVO theory but these barriers did not totally inhibit bacterial deposition. The deposition results could not be fully explained by DLVO theory and suggested the importance of other factors such as collector charge heterogeneity, motility, and bacterial surface appendages in enhanced deposition. Copyright 1998 Academic Press.

Quantitative comparison of shear-dependent Staphylococcus aureus adhesion to three polyurethane ionomer analogs with distinct surface properties

Bacterial adhesion is a central step in infection on biomaterial surfaces; however, the relation between biomaterial surface properties and adhesion remains poorly understood. To quantitatively determine the relationship among polyurethane surface properties, protein coating, and adhesion, we have compared attachment and detachment kinetics of Staphylococcus aureus on three different novel polyurethanes with different protein coatings. Rate constants for attachment or detachment were measured as a function of shear rate in a well-defined laminar flow field. The tested polyurethanes included a relatively hydrophobic-base polyether urethane and hydrophilic anionomer and cationomer analogs of the base material. Materials were tested bare, or coated with human fibrinogen, plasma, or albumin. The results suggest that the presence of fibrinogen or plasma greatly enhance the attachment rate constants and decrease the detachment rate constants on all materials. The most extreme differences among the different materials were observed on the bare materials, with the base polyurethane being most resistant to both attachment and detachment. However, except for a reduced attachment rate constant on the plasma-coated sulfonated polyurethane, few differences in the rate constants were observed among protein-coated materials, suggesting the primary role of surface properties is masked by the presence of the adsorbed protein layer.

A Dynamic Model for the Attachment of a Brownian Particle Mediated by Discrete Macromolecular Bonds

A model is presented for the attachment of a Brownian particle to a surface mediated by both the conservative colloidal forces and the formation of macromolecular bonds. By considering Brownian motion and bond formation as coupled stochastic processes, the model derives a governing equation for the time-dependent probability density of having a given number of bonds and separation distance from the surface. The model predicts the deposition rate of particles to a surface as a function of the physicochemical parameters of the binding molecules, including the density, interaction length, stiffness, and formation and dissociation kinetic rate constants. Furthermore, two limiting simplifications of the full model are explored which correspond to particle attachment rate limited by the rate of Brownian motion or by the rate of bond formation.

Bacterial adhesion to polyurethane surfaces in the presence of pre-adsorbed high molecular weight kininogen

The factors which affect the adherence of a bacteria cell to the surface of a biomaterial include the surface chemistry of the cell and material, as well as the composition of the adsorbed protein layer when the biomaterial is exposed to circulating blood. In an effort to better understand the mechanisms by which bacteria adhere to such surfaces, and specifically to determine the effects of high molecular weight kininogen on bacterial adhesion, experiments were performed in which the attachment of Staphylococcus aureus was directly observed on glass and on a series of functionalized polyurethanes. These surfaces had been pre-adsorbed with various concentrations of high molecular weight kininogen and fibrinogen. Attachment was observed using a radial flow chamber, in which shear stress varied inversely with radial distance. Protein adsorption studies were also performed using 125I labeled fibrinogen to investigate the relationship between surface chemistry, protein adsorption, and bacterial attachment. Bacterial attachment was significantly decreased when the glass surface was pre-adsorbed with high molecular weight kininogen--either alone, or following adsorption of fibrinogen. High molecular weight kininogen thus exhibited anti-adhesive effects. On polyurethane surfaces pre-adsorbed with fibrinogen, kininogen, and albumin, the highest bacterial attachment was found on the base polyurethane, while significant decreases were seen on the hydrophilic polyurethanes. In addition, it was found that the surface with the least bacterial attachment and fibrinogen deposition was the polyurethane with pendant phosphonate groups.

Quantitative comparison of clumping factor- and coagulase-mediated Staphylococcus aureus adhesion to surface-bound fibrinogen under flow

The contributions of clumping factor and coagulase in mediating Staphylococcus aureus adhesion to surface-adsorbed fibrinogen have been quantified by using a new methodology and analysis. The attachment or detachment kinetics of bacteria were directly observed in a radial flow chamber with a well-defined laminar flow field and a spatially varying shear rate and were quantified by recursively scanning the chamber surface and counting cells via automated video microscopy and image analysis with a motorized stage and focus control. Intrinsic rate constants for attachment or detachment were estimated as functions of shear rate for the wild-type Newman strain of S. aureus and for mutants lacking clumping factor, coagulase, or both proteins on surfaces coated with plasma, fibrinogen, or albumin. Clumping factor, but not coagulase, increased the probability of attachment and decreased the probability of detachment of S. aureus on plasma-coated surfaces; however, both clumping factor and, to a lesser extent, coagulase increased the probability of attachment on the purified-fibrinogen-coated surface. All mutants were resistant to detachment on the purified-fibrinogen-coated surface, suggesting the possibility of an additional adhesion mechanism which was independent of coagulase or clumping factor and effective only for fully attached cells. Together, these results suggest that the presence of clumping factor plays the primary role in enhancing adhesion to surfaces with adsorbed fibrinogen, not only by enhancing the probability of cell attachment but also by increasing the strength of the resulting adhesion.

Biased cell migration of fibroblasts exhibiting contact guidance in oriented collagen gels

We present here the first quantitative correlation for cell contact guidance in an oriented fibrillar network in terms of biased cell migration. The correlation is between the anisotropic cell diffusion parameter, DA = Dx/Dy, and the collagen gel birefringence, delta n, a measure of axially biased collagen fibril orientation in the x-direction. The cell diffusion coefficients, Dx and Dy, measure the dispersal of cells in the directions coincident with and normal to the axis of fibril orientation, respectively. Three essential methodological components are involved: (i) exploiting the orienting effect of a magnetic field on collagen fibrils during fibrillogenesis to systematically prepare uniform axially oriented collagen gels; (ii) using a microscope/image analysis workstation with precise, computer-controlled rotating and translating stages to automate birefringence measurement and, along with rapid "coarse optical sectioning" via digital image processing, to enable 3-D cell tracking of many cells in multiple samples simultaneously; and (iii) employing a rigorous statistical analysis of the cell tracks to estimate the magnitude and precision of the direction-dependent cell diffusion coefficients, Dx and Dy, that define DA. We find that this measure of biased migration in contact guidance (DA) increases with increasing collagen fibril orientation (delta n) due mainly to a rapid enhancement of migration along the axis of fibril orientation at low levels of fibril orientation, and to a continued suppression of migration normal to the axis of fibril orientation at high levels of fibril orientation.

Quantitative characterization of cell invasion in vitro: formulation and validation of a mathematical model of the collagen gel invasion assay

An in vitro assay proposed to systematically characterize and compare cell invasion under different conditions is the collagen gel invasion assay where cells, initially seeded onto the surface of a type I collagen gel, penetrate the surface and migrate within the gel over time. Using simplifying assumptions about cell transport across the gel surface and migration within the gel, we formulate and solve a mathematical model of this assay which predicts the resulting cell distribution based on three phenomenological parameters characterizing the ability of cells to penetrate the gel surface interface, migrate randomly within the gel, and return to the gel surface. An index of cell invasiveness is defined based on these parameters that reflects the overall ability of cells to transport across the gel surface interface, that is, invade the gel. Cell concentration profiles predicted by the model correspond well to measured profiles for murine melanoma cells invading gels supplemented with extracellular matrix proteins fibronectin and type IV collagen as well as unsupplemented gels, allowing these parameters to be estimated by a nonlinear regression fit of the model solution to the measured profiles. Our analysis suggests that type IV collagen and fibronectin primarily modulate cell transport across the gel surface interface rather than migration within the gel. Further, we validate the key model assumptions and obtain independent, direct estimates of model parameters by time-lapse video microscopy and digital image analysis of cell penetration of the gel surface and migration within the gel during the assay.

A stochastic model for adhesion-mediated cell random motility and haptotaxis

The active migration of blood and tissue cells is important in a number of physiological processes including inflammation, wound healing, embryogenesis, and tumor cell metastasis. These cells move by transmitting cytoplasmic force through membrane receptors which are bound specifically to adhesion ligands in the surrounding substratum. Recently, much research has focused on the influence of the composition of extracellular matrix and the distribution of its components on the speed and direction of cell migration. It is commonly believed that the magnitude of the adhesion influences cell speed and/or random turning behavior, whereas a gradient of adhesion may bias the net direction of the cell movement, a phenomenon known as haptotaxis. The mechanisms underlying these responses are presently not understood. A stochastic model is presented to provide a mechanistic understanding of how the magnitude and distribution of adhesion ligands in the substratum influence cell movement. The receptor-mediated cell migration is modeled as an interrelation of random processes on distinct time scales. Adhesion receptors undergo rapid binding and transport, resulting in a stochastic spatial distribution of bound receptors fluctuating about some mean distribution. This results in a fluctuating spatio-temporal pattern of forces on the cell, which in turn affects the speed and turning behavior on a longer time scale. The model equations are a system of nonlinear stochastic differential equations (SDE's) which govern the time evolution of the spatial distribution of bound and free receptors, and the orientation and position of the cell. These SDE's are integrated numerically to simulate the behavior of the model cell on both a uniform substratum, and on a gradient of adhesion ligand concentration. Furthermore, analysis of the governing SDE system and corresponding Fokker-Planck equation (FPE) yields analytical expressions for indices which characterize cell movement on multiple time scales in terms of cell cytomechanical, morphological, and receptor binding and transport parameters. For a uniform adhesion ligand concentration, this analysis provides expressions for traditional cell movement indices such as mean speed, directional persistence time, and random motility coefficient. In a small gradient of adhesion, a perturbation analysis of the FPE yields a constitutive cell flux expression which includes a drift term for haptotactic directional cell migration. The haptotactic drift contains terms identified as contributions from directional orientation bias (taxis), kinesis, and orthotaxis, of which taxis appears to be predominant given estimates of the model parameters.

Cell surface CD44-related chondroitin sulfate proteoglycan is required for transforming growth factor-beta-stimulated mouse melanoma cell motility and invasive behavior on type I collagen

Tumor cell metastasis involves a complex series of events, including the adhesion, migration and invasive behavior of tumor cells on components of the extracellular matrix. Multiple cell surface receptors mediate interactions with the surrounding extracellular matrix and thereby influence cell adhesion, motility and invasion. We have previously described a cell surface CD44-related chondroitin sulfate proteoglycan on highly metastatic melanoma cells. CD44-chondroitin sulfate proteoglycan was shown to be important in melanoma cell motility and invasive behavior on type I collagen matrices. In our current studies, the role of cell surface CD44-chondroitin sulfate proteoglycan in collagen-mediated mouse melanoma cell migration and invasive behavior is further evaluated using transforming growth factor-beta 1. We report that transforming growth factor-beta 1 stimulates the migratory and invasive behavior of mouse melanoma cells on type I collagen. Transforming growth factor-beta 1 stimulated cell surface CD44-chondroitin sulfate proteoglycan synthesis in mouse melanoma cells, specifically through an upregulation of chondroitin sulfate production, while the expression of CD44-chondroitin sulfate proteoglycan core protein was not affected. Furthermore, transforming growth factor-beta 1-mediated enhancement of cell polarity, migration and invasive behavior on type I collagen gels was markedly inhibited in the presence of beta-D-xyloside, an agent that blocks chondroitin sulfate addition to the core protein. Collectively, our findings indicate that mouse melanoma cell surface CD44-chondroitin sulfate proteoglycan is required for transforming growth factor-beta 1-enhanced cell motility and invasion, and that CD44-chondroitin sulfate proteoglycan may play a role in forming and/or maintaining a dominant leading lamella, which is required for efficient locomotion.