Inhibition of bacterial and leukocyte adhesion under shear stress conditions by material surface chemistry

Biomaterial-centered infections, initiated by bacterial adhesion, persist due to a compromised host immune response. Altering implant materials with surface modifying endgroups (SMEs) may enhance their biocompatibility by reducing bacterial and inflammatory cell adhesion. A rotating disc model, which generates shear stress within physiological ranges, was used to characterize adhesion of leukocytes and Staphylococcus epidermidis on polycarbonate-urethanes and polyetherurethanes modified with SMEs (polyethylene oxide, fluorocarbon and dimethylsiloxane) under dynamic flow conditions. Bacterial adhesion in the absence of serum was found to be mediated by shear stress and surface chemistry, with reduced adhesion exhibited on materials modified with polydimethylsiloxane and polyethylene oxide SMEs. In contrast, bacterial adhesion was enhanced on materials modified with fluorocarbon SMEs. In the presence of serum, bacterial adhesion was primarily neither material nor shear dependent. However, bacterial adhesion in serum was significantly reduced to < or = 10% compared to adhesion in serum-free media. Leukocyte adhesion in serum exhibited a shear dependency with increased adhesion occurring in regions exposed to lower shear-stress levels of < or = 7 dyne/cm2. Additionally, polydimethylsiloxane and polyethylene oxide SMEs reduced leukocyte adhesion on polyether-urethanes. In conclusion, these results suggest that surface chemistry and shear stress can mediate bacterial and cellular adhesion. Furthermore, materials modified with polyethylene oxide SMEs are capable of inhibiting bacterial adhesion, consequently minimizing the probability of biomaterial-centered infections.     

Quantification of initial adhesion of Enterococcus faecalis to medical grade polymers using a DNA-based fluorescence assay

This paper reports on the use of a DNA-based fluorescence assay to study and quantify the initial interactions of the uropathogen Enterococcus faecalis with different polymers commonly used for the fabrication of medical devices and implants, including polyurethane (PU), silicone (SI), high-density polyethylene (HDPE), polyamide (PA), poly(methyl methacrylate) (PMMA) and polytetrafluoroethylene (PTFE). To follow the kinetics of E. faecalis adhesion, polymer samples were incubated in bacterial solution for various times and the relative concentration of adhered bacteria was obtained using two methods: commonly used CFU plate counting and a DNA quantification assay. Results obtained from DNA-based fluorescence assays showed that E. faecalis adhesion on PU is 3-times higher than that on PTFE following exposure to bacteria for 180 min. Neither surface wettability nor surface roughness of the studied polymers was found to correlate with E. faecalis adhesion, suggesting the involvement of much more complex adhesion mechanisms of bacteria onto surfaces. SEM micrographs of adhered bacteria illustrated that adhesion was different depending on the type of polymeric substrate: adhesion on PU samples was characterized by the aggregation of bacterial cells in dense clusters, as well as by the presence of fimbriae between cells and the substrate, which could explain the high adhesion to PU compared to the other polymers. This work demonstrated that the bacterial adhesion to polymers occurs at an early stage of the contact and suggests that the initial adhesion stage should be controlled, in order to prevent subsequent biofilm formation and, thus, reduce the risk of implant-associated infections.     

In vitro study of blood-contacting properties and effect on bacterial adhesion of a polymeric surface with immobilized heparin and sulphated hyaluronic acid

The blood-contacting properties and the effect on bacterial adhesion of a material based on polyurethane and poly(amido-amine) (PUPA), both in its native form and with the anticoagulant molecules heparin or sulphated hyaluronic acid (HyalS3.5) electrostatically bonded to its surface, were evaluated and compared in vitro. The presence of the biological molecules on the surface was revealed by a dye test and ATR/FTIR analysis. Bound heparin was found to maintain its physiological action, in terms of thrombin inactivation, as well as did free heparin. Moreover, it reduced the degree of platelet adhesion. On the contrary, bound HyalS3.5 lost its anticoagulant activity, though it reduced platelet adhesion. The number of platelets on both modified surfaces was low. Their shape distribution, as determined by SEM, did not differ significantly on the two modified surfaces or with respect to the bare PUPA surface. HyalS3.5 and heparin also inhibited adhesion of Staphylococcus epidermidis to the material. A possible relationship between the platelet and bacterial adhesion is ascribed to the mediating role of plasma proteins.     

PDMS-based polyurethanes with MPEG grafts: Mechanical properties,bacterial repellency,and release behavior of rifampicin

PDMS-based polyurethanes (PUs) grafted with monomethoxy poly(ethylene glycol) (MPEG) were synthesized to develop a coating material for urinary catheters with a silicone surface for minimizing urinary tract infections. MPEG was grafted on PDMS-based PUs by two methods depending on the PU synthetic routes: esterification and allophanate reactions. It was confirmed from mechanical characterization that an increase of the hard segment amount enhanced the ultimate strength and Young's modulus, while reducing elongation at the end-points. The incorporation of MPEG in PDMS-based PUs induced a decrease in tensile strength and Young's modulus, and increased elongation at the break point due to its high flexibility. When hydrated in distilled water, mechanical properties of all PUs synthesized in this study deteriorated due to water absorption. It was evident from the bacterial adhesion test that PDMS-based PUs showed moderate resistance to adhesion of E. coli on their surfaces compared to Pellethane®, while the incorporation of MPEG significantly enhanced repellency to bacteria, including E. coli and S. epidermidis. We also studied the release behavior of an antibiotic drug, rifampicin, from the polymeric devices fabricated by solvent evaporation. Although rifampicin is hydrophilic and soluble in pH 7.4 phosphate buffer, it showed a sustained release over 45 days from PDMS-based PUs with MPEG that were grafted on ethylene glycol residues by allophanate reaction. This release characteristic was predominantly influenced by a hydrogen bond interaction between the polymers and rifampicin, which was confirmed through an ATR-IR study. This may imply that the specific interaction is responsible for the delayed release. Considering the mechanical properties, morphologies of drug-incorporated polymeric matrices, and drug release behaviors, PDMS-based PU with MPEG that were grafted on ethylene glycol (a chain extender) residues by allophanate reaction showed better material properties for uretharal catheter coating pusposes in order to minimize urinary tract infections.     

Inhibition of bacterial adhesion by subinhibitory concentrations of antibiotics

Background: Urinary Tract Infections (UTIs) due to Escherichia coli is one of the most common diseases encountered in clinical practice. Most common recognised pathogenic factor in E.coli is adhesion. There is accumulating evidence that through subinhibitory concentrations (sub – MICs) of many antibiotics do not kill bacteria, they are able to interfere with some important aspects of bacterial cell function. Materials and Methods: A study was conducted to investigate the effect of sub MICs (1/2–1/8 MIC) of ciprofloxacin, ceftazidime, gentamicin, ampicillin and co - trimoxazole on E. coli adhesiveness to human vaginal epithelial cells using three strains ATCC 25922, MTCC 729 and U 105. Results: The 1/2 MIC of all the antibiotics tested produced the greatest inhibition of bacterial adhesion. Morphological changes were observed with ciprofloxacin, ceftazidime and ampicillin at 1/2 MIC and to a lesser extent at 1/4 and 1/8 MIC. Co-trimoxazole caused the greatest suppression of adhesion at 1/2 MIC of E. coli strain MTCC 729 when compared with the controls, followed by ceftazidime. Conclusion: These results suggest that co - trimoxazole is the most effective antibiotic in the treatment of urinary tract infections caused by uropathogenic E. coli.     

Effect of surface chemistry on bacterial adhesion, viability, and morphology

Helicobacter pylori (H. pylori) is one of the most common infectious agents in the world and it is thought to colonize the gastric mucosa of about half of the world's population causing several gastric diseases. In this work, the effect of surface chemistry on H. pylori nonspecific adhesion, viability, and morphology was evaluated using three H. pylori strains with different adhesins expression profile. Self-assembled monolayers (SAMs) of alkanethiols on gold were used to obtain surfaces exposing different functional groups: OH, CH3, and ethylene glycol (EG4). Bacterial adhesion onto the surfaces reached a plateau at 2 h. There was a correlation between adhesion and the exposed surface group, with bacterial cells adhering preferentially to CH3-SAMs while EG4-SAMs prevented H. pylori adhesion during the entire adhesion test (24 h). Surfaces that presented the EG4 group were also the only ones that significantly reduced the viability of adhered bacteria. Surface chemistry also influenced the morphology of adhered bacteria. The H. pylori rod shape observed in the control (Tissue Culture Polyethylene-TCPE) was only retrieved on CH3-SAMs. This work demonstrates that surface chemistry, namely specific functional groups on the material, influence the nonspecific adsorption of H. pylori. Moreover, the features of the bacterial strain and the surface chemistry can alter the adhesion kinetics, as well as the morphology and viability of attached bacteria.     

Evaluation of leukocyte adhesion on polyurethanes: the effects of shear stress and blood proteins

Leukocytes are a central cell type in directing host inflammatory and immune processes; thus, its response to biomaterials is extremely important in understanding material-host interaction. Blood contacting biomaterials may activate the complement cascade, thus promote leukocyte adhesion and activation to the biomaterial surface. We hypothesize that the extent of complement-mediated leukocyte activation is modulated by the material chemical formulation and the presence of fluid shear stress. Medical-grade polyurethanes with or without 4,4'-butyldiene bis(6-tert-butyl-m-cresol) antioxidant additives and a rotating disk system were utilized to study cell adhesion under a well-characterized shear stress field. Radioimmunoassay and ELISA were employed to assess the extent of complement activity. The results showed that adherent leukocyte densities decreased with increasing shear stress and that leukocyte adhesion was decreased significantly further by the presence of the antioxidant in the polyurethanes. Cell adhesion under flow conditions was abolished when complement C3 protein was depleted from the test medium. An increase in complement Factor H adsorption was observed at high shear region; however, no change in the complete complement activation was observed in the presence of shear stress as indicated by the protein S-terminal complement complex level. Based on these results, oligopeptides designed from C3a, C5a, and fibronectin were grafted onto a cell-nonadhesive polymer surface to probe the molecular mechanisms of leukocyte adhesion as mediated by protein-receptor complexation. The results showed that C3a-derived peptides mediated higher adherent macrophage density when compared to that mediated by C5a- and fibronectin-derived peptides.     

Leukocyte adhesion on model surfaces under flow: effects of surface chemistry, protein adsorption, and shear rate

The effect of specific chemical functionalities on the adhesion of polymorphonuclear leukocytes (PMNs) under flow was investigated using a set of well-characterized, chemically functionalized surfaces prepared by self-assembly of alkanethiolate monolayers on gold surfaces. Terminal functionalities included CH(3), CH(2)OH, COOH, and (OCH(2)CH(2))(3)OH groups. A new surface modification was used to incorporate a phosphorylcholine moiety on the hydroxyl-terminated monolayer. Surface modification was verified using contact-angle measurements, ellipsometry, and X-ray photoelectron spectroscopy. Adhesion on the surfaces was studied in the presence and absence of pre-adsorbed fibrinogen. Fibrinogen adsorption on self-assembled monolayers (SAMs) was quantified using radioisotope detection. PMN adhesion was found to be dependent on the monolayer's terminal functionality. Adhesion was higher on the hydrophobic CH(3) surface and the polar COOH monolayer. Leukocyte adhesion was least on the phosphorylcholine-rich surface, followed by the ethylene-oxide-containing monolayer. Cell adhesion also was low on the hydrophilic OH monolayer. Attachment was decreased with increasing shear rate, exhibiting a three-fold decrease between 20 and 100 s(-1). Fibrinogen adsorption was higher on the CH(3) monolayer but comparable for the other four SAMs. Preincubation of the surfaces with fibrinogen decreased adhesion on all SAMs examined.     

Human fractalkine mediates leukocyte adhesion but not capture under physiological shear conditions; a mechanism for selective monocyte recruitment

Fractalkine is a unique chemokine possessing a long mucin-like stalk and a transmembrane region that has been proposed to act as an adhesion molecule. We investigated the ability of fractalkine to recruit leukocytes from whole blood, using an immobilized fractalkine fusion protein in the parallel-plate flow-chamber assay. Significant adhesion of leukocytes to fractalkine peaked at 2 dynes/cm(2) but was minimal at 10 dynes/cm(2). In contrast, VCAM-1 could recruit cells from whole blood at 10 dynes/cm(2). Co-immobilization of fractalkine and VCAM-1 at 10 dynes/cm(2) resulted in a twofold increase in adherent cells compared with VCAM-1 alone, suggesting that fractalkine can mediate adhesion at high shear if combined with a molecule that can mediate leukocyte tethering. Pretreatment of blood with pertussis toxin eliminated this increase in adhesion, implicating intracellular signaling in fractalkine-mediated mechanisms of adhesion to co-immobilized fractalkine/VCAM-1. Analysis of the cell types recruited to fractalkine alone at low shear, or to fractalkine and VCAM-1 at 10 dynes/cm(2), revealed that monocytes were recruited to fractalkine with the highest specificity. In conclusion, fractalkine is unlikely to act alone at shear forces found in most vascular beds where it most likely co-operates with tethering molecules, e.g. VCAM-1, in the recruitment of monocytes.     

Cell adhesion behavior of chitosan surface modified by bonding 2-methacryloyloxyethyl phosphorylcholine

2-Methacryloyloxyethyl phosphorylcholine (MPC)-bonded chitosan was prepared by Michael addition of MPC to the amino groups of chitosan. The modified surfaces were characterized by static contact angle and electron spectroscopy for chemical analysis (ESCA). The water contact angle of chitosan decreased with the MPC bonding and the rate of decrease depended on the amount of MPC bonding. ESCA analysis results proved that MPC had been bonded on the chitosan surface and the chitosan modified directly by MPC had a much higher concentration of MPC on the surface compared with that of MPC on chitosan modified indirectly by MPC. Cell adhesion tests indicated that a low concentration of MPC bonded chitosan was more favorable to cell adhesion while a high concentration of MPC bonded chitosan inhibited cell attachment.     

Role of actin filaments in endothelial cell-cell adhesion and membrane stability under fluid shear stress

Clostridium botulinum C2 toxin (C2 toxin) and purified ADP-ribosylated-alpha-actin (ADP-r-alpha-actin) cause specific actin depolymerisation in living cells. This effect was used to investigate the actin microfilament system with particular emphasis on cell-cell adhesion and plasma membrane integrity in endothelial cells. C2 toxin caused time- and dose-dependent (15-100 ng/ml) changes in endothelial surface morphology (investigated by atomic force microscopy), intercellular gap formation and cell detachment under shear stress. Low concentrations of C2 toxin (1.5 ng/ml), however, did not induce cell detachment but inhibited shear stress-dependent cell alignment. Gap formation as well as cell loss under shear stress was also observed in cells microinjected with purified ADP-r-alpha-actin. Intercellular gap formation was mediated by increased alpha-catenin solubility (40%) due to actin filament depolymerisation. Disintegration of plasma membranes (measured by LDH release) and cell fragmentation during simultaneous exposure to shear stress and C2 toxin were due to a loss of more than 50% of membrane-associated actin. These data show that small disturbances in actin dynamics inhibit shear stress-dependent cell alignment; that depolymerisation of actin filaments increases the solubility of alpha-catenin, thus resulting in cell dissociation and that actin filaments of the membrane cytoskeleton are required to protect the cells from haemodynamic injury such as shear stress. Together, the study shows a heterogeneous regulation of actin filament dynamics at subcellular locations. Junction-associated actin filaments displayed the highest sensitivity whereas stress fibres were far more stable.     

Influence of nanopatterns on endothelial cell adhesion: Enhanced cell retention under shear stress

In this study, nanopatterned crosslinked films of collagen Type I were seeded with human microvascular endothelial cells and tested for their suitability for vascular tissue engineering. Since the films will be rolled into tubes with concentric layers of collagen, nutrient transfer through the collagen films is quite crucial. Molecular diffusivity through the collagen films, cell viability, cell proliferation and cell retention following shear stress were studied. Cells were seeded onto linearly nanogrooved films (groove widths of 332.5, 500 and 650 nm), with the grooves aligned in the direction of flow. The nanopatterns did not affect cell proliferation or initial cell alignment; however, they significantly affected cell retention under fluid flow. While cell retention on unpatterned films was 35 ± 10%, it was 75 ± 4% on 332.5 nm patterned films and even higher, 91 ± 5%, on 650 nm patterned films. The films were found to have diffusion coefficients of ca. 10⁻⁶ cm² s⁻¹ for O₂ and 4-acetaminophenol, which is comparable to that observed in natural tissues. This constitutes another positive asset of these films for consideration as a scaffold material for vascular tissue engineering.     

The influence of surface micro-structure on endothelialization under supraphysiological wall shear stress

Interaction between platelets and artificial materials within cardiovascular devices triggers blood coagulation and represents a frequent adverse response to implant deployment. Avoidance of this interaction is obtained through the generation and sustenance under flow of a confluent and stable endothelial monolayer covering the luminal device surface, altogether defined as the process of endothelialization. Supraphysiological wall shear stress (WSS) levels generated within vascular assist devices (VADs) constitute a major challenge toward endothelialization. Here we report the experimental demonstration that stable endothelialization can be achieved at supraphysiological WSS levels by pure means of appropriate surface micro-structuring. Using a custom-designed flow bioreactor we exposed endothelial monolayers to physiological and supraphysiological WSS levels and investigated the resulting integrity of cell-to-cell junctions, the cell density and the cell polarization. At physiological WSS levels, optimal endothelialization was obtained independently from surface topography. However, at higher WSS levels, only monolayers grown on appropriately micro-structured surfaces preserved optimal integrity. Under these flow conditions, endothelial cells polarized by the contact with the micro-structure and, interestingly, oriented themselves in the direction perpendicular to flow. Such endothelial layers withstood WSS levels exceeding of 100% or more the thresholds detected on flat substrates.     

The control of endothelial cell adhesion and migration by shear stress and matrix-substrate anchorage

Endothelial cells constitute the natural inner lining of blood vessels and possess anti-thrombogenic properties. This characteristic is frequently used by seeding endothelial cells on vascular prostheses. As the type of anchorage of adhesion ligands to materials surfaces is known to determine the mechanical balance of adherent cells, we investigated herein the behaviour of endothelial cells under physiological shear stress conditions. The adhesion ligand fibronectin was anchored to polymer surfaces of four physicochemical characteristics exhibiting covalent and non-covalent attachment as well as high and low hydrophobicity. The in situ analysis combined with cell tracking of shear stress-induced effects on cultured isolated cells and monolayers under venous (0.5 dyn/cm²) and arterial (12 dyn/cm²) shear stress over a time period of 24 h revealed distinct differences in their morphological and migratory features. Most pronounced, unidirectional and bimodal migration patterns of endothelial cells in or against flow direction were found in dependence on the type of substrate-matrix anchorage. Combined by an immunofluorescent analysis of the actin cytoskeleton, cell-cell junctions, cell-matrix adhesions, and matrix reorganization these results revealed a distinct balance of laminar shear stress, cell-cell contacts and substrate-matrix anchorage in affecting endothelial cell fate under flow conditions. This analysis underlines the importance of materials surface parameters as well as primary and secondary adhesion ligand anchorage in the context of artificial blood vessels for future therapeutic devices.     

Modification of gold surface by grafting of poly(ethylene glycol) for reduction in protein adsorption and platelet adhesion

Gold surfaces were first treated in an alkanethiol solution to form self-assembled monolayers (SAMs). The thiolated Au surface was then subjected to Ar plasma pretreatment, followed by air exposure and UV-induced graft polymerization of poly(ethylene glycol) methacrylate (PEGMA) macromonomer. In comparison with the 3-mercaptopropionic acid-2-ethylhexyl ester (MPAEE) SAM, the (3-mercaptoproply)trimethoxysilane (MPTMS) SAM on Au exhibited higher stability under the conditions of Ar plasma pretreatment. The graft concentration of the PEGMA polymer on SAMmodified Au surface increased with increasing PEGMA macromonomer concentration and UV-graft polymerization time. The modified-Au surfaces were characterized by X-ray spectroscopy (XPS), atomic force microscopy (AFM), and water contact angle measurement. The Au surface with a high concentration of grafted PEGMA polymer could completely repel protein adsorption and platelet adhesion.     

Inhibition of bacterial adherence by nitroxoline on cellular adhesion and on urinary catheter surfaces

Nitroxolin or 5-nitro-8-hydroxyquinoline, used in the treatment of acute or recurrent uncomplicated urinary tract infection (UTI), has been investigated to demonstrate inhibitory effect on bacterial adherence to epithelial cells or solid surfaces. Nitroxolin in vitro and in urine inhibits bacterial adherence of E. coli 38 (MS/MS) on HeLa cells and epithelial cells from human bladder mucosa. In the same conditions, norfloxacin has no effect. Nitroxolin (MIC/8) decreases with a statistically significant difference (p less than 0.001) the bacterial attachment to a urinary catheter surface made in siliconated latex. These results justify the performance of a clinical trial in the prophylaxis of recurrent UTI and the outcome of a bacteriuria associated with indwelling or intermittent bladder catheter.     

Manipulation of bacterial adhesion and proliferation by surface charges of electrically polarized hydroxyapatite

The manipulation of bacterial adhesion and proliferation by surface charges built onto the surfaces of electrically polarized bioceramic hydroxyapatite (HAp) was investigated. The gram-positive bacteria Staphylococcus aureus (S. aureus) and the gram-negative bacteria Escherichia coli (E. coli) were cultivated on negatively charged, positively charged, and non-charged HAp surfaces (denoted as N-, P-, and 0-surface, respectively). The electrostatic force caused by the surface charges experimentally was proven to affect both adhesion and proliferation. Compared with the 0-surface of HAp ceramics over a 3-h cultivation, the population of adhered bacteria rapidly multiplied on the N-surface whereas it multiplied quite slowly on the P-surface. Compared with the 0-surface over a cultivation period of 12 to 72 h, the proliferation rate of the bacterial cell density per colony was accelerated on the N-surface and decelerated on the P-surface. The above results are attributed (1) to the electrostatic interaction between the cell surfaces and the charged surfaces of the polarized HAp, (2) to the stimulus of the electrostatic force for bacterial cells, and (3) to the concentration of the nutrient for the bacteria.     

体外反搏对血管剪切分力频率分量的影响

目的研究体外反搏治疗心肌缺血时血管对剪切应力各频率分量的影响。方法对17条开胸犬实时测节其正常情况下、缺血1h、缺血1h后反搏1h、反博2h以及正常情况时不同反搏压力下头臂干处的血流量，计算出此处剪切应力的频率分最变化。结果体外反搏使头臂干处剪切应力的频率分量发生了明显的变化。急性心肌缺血和体外反搏可以使剪切应力的各频率分量发生明显的改变。结论反搏压力大于一定程度时休外反搏可以明显改变体内血管剪切应力的低频分量。     

Fluid shear induced endothelial cell detachment from glass - influence of adhesion time and shear stress

In this study, human umbilical vein and human saphenous vein endothelial cells were seeded on glass and exposed to fluid shear in a parallel-plate flow chamber. Cell retention, morphology and migration were studied as a function of shear stress and of adhesion time prior to exposure to shear. Three-hour and 24-h adhesion times gave rise to comparable cell retention values after 2 h of flow for both cell types. Cell retention decreased from 85 to 20% as shear stress increased from 88 to 264 dynes cm⁻² (8.8 to 26 Pa). Mean spreading areas decreased after the onset of flow, but subsequently stabilized to plateau values, which were smaller at higher shear stresses. Shape factors increased faster to higher values as cells were exposed to higher shear stresses, without any obvious preference in orientation of the cells with respect to the direction of flow. Migration was unidirectional with flow and linear with time. Migration was faster for cells which had adhered for 24 h than for cells which had adhered for 3 h and was accompanied by the presence of fibrillar structures left behind on the surface upstream of migrating cells. It is concluded that after 3 h adhesion to glass, cells have adhered with an adhesion strength that does not substantially increase during the next 21 h. However, during this time changes in cell-substratum interactions seem to occur judging by the differences in, e.g., migration rates.     

A peptide inhibitor of vascular adhesion protein-1 (VAP-1) blocks leukocyte-endothelium interactions under shear stress

Vascular adhesion protein-1 (VAP-1) is an endothelial adhesion molecule mediating leukocyte interactions with blood vessels during leukocyte extravasation. Molecularly VAP-1 is a cell-surface-expressed ecto-enzyme belonging to the group of semicarbazide-sensitive amine oxidases (SSAO; EC 2.4.6.3), which deaminate primary amines. Here we asked whether peptides displaying a suitable free amine group could be a substrate or inhibitor of SSAO and thus regulate VAP-1-mediated leukocyte adhesion. On the basis of a molecular model of VAP-1, we designed synthetic peptides that fit to the substrate channel of VAP-1. One of these lysine-containing peptides effectively inhibits VAP-1-dependent lymphocyte rolling and firm adhesion to primary endothelial cells under physiologically relevant shear conditions. The same peptide inhibits the SSAO activity of endothelial and recombinant VAP-1 in a selective and long-lasting manner. We also show that all enzymatically active VAP-1 is displayed on the cell surface. Our results suggest that, in addition to soluble amines, specific cell-surface-bound molecules containing free NH(2) groups in a suitable position may modulate the enzymatic activity of SSAO. Moreover, the inhibitory peptide diminishes leukocyte interactions with endothelial cells under conditions of shear, and thus it may be useful to treat inflammatory conditions.