Biomedical subjects

Roger E Marchant

Publications and source records attributed to Roger E Marchant.

At least 19 recordsLinked to original sources

PubMed2006

Surface-dependent expression in the platelet GPIb binding domain within human von Willebrand factor studied by atomic force microscopy.

Adsorption of plasma proteins such as von Willebrand factor (vWF) on thrombogenic surfaces can induce conformational changes in tertiary structure so that the prothrombotic functional epitopes are exposed for interactions with platelets, resulting in platelet adhesion and thrombus formation. Thus, understanding platelet binding following changes in the structure of vWF is critical in understanding the mechanisms of thrombogenesis. The present study examined the accessibility of platelet binding epitopes within vWF adsorbed on two different thrombogenic surfaces, a hydrophobic synthetic surface and collagen VI coated substrates, under physiological buffer conditions using atomic force microscopy (AFM) in combination with immunogold labeling. Our results demonstrated that the glycoprotein Ib (GPIb) binding domain in vWF undergoes changes when adsorbed on collagen VI compared to vWF on a hydrophobic synthetic surface. This study provides a basis for a novel approach to understand the molecular mechanisms of surface-induced thrombosis by directly examining the structure-function relationships of plasma proteins involved in the thrombus formation.

Adsorption↗

PubMed2006

Effects of biomaterial surface chemistry on the adhesion and biofilm formation of Staphylococcus epidermidis in vitro.

The formation of biofilm, a structured community of bacteria enclosed in slime, is a significant virulence factor in medical-device-centered infection. The development of cardiovascular device infection can be separated into two phases: initial bacterial adhesion and aggregation, followed by proliferation and production of slime. It is possible to modulate the adhesion and biofilm formation of Staphylococcus epidermidis, a commensal skin bacterium commonly found on infected medical devices, through biomaterial surface chemistry. This study examines bacterial adhesion and biofilm formation on surface-modified polyethylene terephthalate (PET), including surfaces with varying hydrophilic, hydrophobic, and ionic character. Bacterial adhesion and biofilm formation were observed over 48 hours in phosphate-buffered saline (PBS) and 20% pooled human serum. The hydrophilic surface (PAAm) had significantly less nonspecific adhesion of bacteria than that in the control (PET) and other surfaces, when cultured in PBS (P < 0.0001). Charged surfaces, both anionic and cationic, had increased adhesion and aggregation of bacteria in comparison with the control (PET) in the presence of serum proteins over 24 hours (P < 0.0001). Bacteria cultured in serum on the charged surfaces did not have significantly different amounts of biofilm formation compared with that of the control (PET) surface after 48 hours. This study showed that biomaterial surface chemistry characteristics impact initial adhesion and aggregation of S. epidermidis on biomaterials.

Bacterial Adhesion↗

PubMed2006

The effect of RGD fluorosurfactant polymer modification of ePTFE on endothelial cell adhesion, growth, and function.

We have synthesized and characterized a novel peptide fluorosurfactant polymer (PFSP) modification that facilitates the adhesion and growth of endothelial cells on expanded polytetrafluoroetheylene (ePTFE) vascular graft material. This PFSP consists of a poly(vinyl amine) (PVAm) backbone with integrin binding Arg-Gly-Asp (RGD) peptides and perfluorocarbon pendant branches for adsorption and stable adhesion to underlying ePTFE. Aqueous PFSP solution was used to modify the surface of fluorocarbon substrates. Following subconfluent seeding, endothelial cell (EC) adhesion and growth on PFSP was assessed by determining cell population at different time points. Spectroscopic results indicated successful synthesis of PFSP. PFSP modification of ePTFE reduced the receding water contact angle measurement from 120 degrees to 6 degrees , indicating successful surface modification. Quantification of cell population demonstrated reduced EC attachment efficiency but increased growth rate on RGD PFSP compared with fibronectin (FN). Actin staining revealed a well-developed cytoskeleton for ECs on RGD PFSP indicative of stable adhesion. Uptake of acetylated low-density lipoprotein and positive staining for VE-Cadherin confirm EC phenotype for adherent cells. Production of prostacyclin, a potent antiplatelet agent, was equivalent between ECs on FN and RGD PFSP surfaces. Our results indicate successful synthesis and surface modification with PFSP; this is a simple, quantitative, and effective approach to modifying ePTFE to encourage endothelial cell attachment, growth, and function.

Amino Acid Sequence↗

PubMed2006

Dendritic saccharide surfactant polymers as antifouling interface materials to reduce platelet adhesion.

Here, we report on the synthesis of dendritic saccharide surfactant polymers as antifouling interface materials to reduce platelet adhesion. An acetal-protected poly(amidoamine) (PAMAM) dendron (5, G = 2) was first synthesized by using aminoacetaldehyde dimethyl acetal (1) as the starting material to provide a monovalent focal structure with dimethyl acetal-protected aldehyde functionality. Maltose dendron (M4, 6) was obtained by reacting the peripheral amine groups of acetal-dendron (5) with maltonolactone. The dendritic surfactant polymers (9) were then synthesized via a two-step method by sequential addition of maltose dendron and hexanal to react with the amine groups on the poly(vinylamine) (PVAm) backbone. Surface activity of the amphiphilic glycopolymers at the air/water interface was demonstrated by reduction in water surface tension. Adsorption of the amphiphilic glycopolymers at the solid/water interface was examined on octadecyltrichlorosilane (OTS)-coated coverslips by water contact angle measurements. A nanoscale understanding of surface-induced self-assembly of the dendritic surfactant polymer on highly oriented pyrolytic graphite (HOPG) was gained using AFM operated in fluid tapping mode. A lateral ordering of adsorbing surfactant polymer was visualized with a pattern in strands 60 degrees out of alignment. The static platelet adhesion tests show that the hexyl side chains can facilitate adsorption of the surfactant polymers onto hydrophobic substrates, while the maltose dendron side chains can provide a dense canopy of protective glycocalyx-like layer as an antifouling interface to reduce platelet adhesion.

Adsorption↗

PubMed2005

Surface modification of liposomes by saccharides: vesicle size and stability of lactosyl liposomes studied by photon correlation spectroscopy.

The cell glycocalyx is an attractive model for surface modification of liposomes, because its hydrated oligosaccharide layer inhibits nonspecific protein adsorption and can provide specificity towards desired sites. Here, we report on the use of lactose as a model saccharide to modify the liposome surface and examine the vesicle size and stability. Two kinds of lactosyl lipids, including lactosyl ether-lipid (6a) and lactosyl ester-lipid (6b), which contain octadecyl and octadecanoyl as the lipid tails, respectively, were synthesized and their liposomes were prepared by the extrusion method. The effects of glycolipid structure, concentration, and the pore size of the extrusion membrane on vesicle size and stability were investigated at room temperature by photon correlation spectroscopy (PCS). All liposomes with 5 or 10 mol% of lactosyl lipids had a narrow size distribution and remained stable at room temperature for at least one month, which is comparable to 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)- and poly(ethylene glycol) (PEG)-liposomes. The maximum incorporation of lactosyl ester-lipid into liposomes was 15 mol%, compared with only 10 mol% for the lactosyl ether-lipid. The lactosyl ester-liposomes had better stability and exhibited less size change than the lactosyl ether-liposomes at 15 or 20 mol% of lactosyl lipids incorporated. This may be attributed to the better structural compatibility of lactosyl ester-lipid with DSPC. The PCS results show that the glycolipid structure and concentrations are major factors that affect vesicle stability, while the pore size of extrusion membranes has no influence.

Carbohydrate Conformation↗

PubMed2005

Pentaerythritol as the core of multivalent glycolipids: synthesis of a glycolipid with three SO3Lea ligands.

A glycolipid containing three SO(3)Le(a) ligands was synthesized with pentaerythritol as the core. The glycolipid was used to prepare glycoliposomes that showed stability similar to that of DSPC liposomes without glycolipid. The easily prepared derivatives of pentaerythritol proved to be useful scaffolds for multivalent displaying of carbohydrates in the form of glycolipids and clustered glycoliposomes. [structure: see text]

Carbohydrate Sequence↗

PubMed2005

RGD-modified liposomes targeted to activated platelets as a potential vascular drug delivery system.

Local drug delivery has become an important treatment modality for the prevention of thrombotic events following coronary angioplasty. In this study, we investigate the ability of liposomes bearing surface conjugated linear Arg-Gly-Asp (RGD) peptide (GSSSGRGDSPA) moieties to target and bind activated platelets, and the effect of such RGD-modified liposomes on platelet activation and aggregation. The binding of RGD-liposomes to human platelets was assessed by fluorescence microscopy, phase contrast microscopy and flow cytometry. The effect of RGD-modified liposomes on platelet activation and aggregation was investigated in vitro, with and without platelet agonists. RGD-liposomes were found to bind activated platelets at levels significantly greater than the control RGE-liposomes. The RGD-liposomes did not exhibit any statistically significant effect on platelet activation or aggregation. The results demonstrate the ability of the RGD-modified liposomes to target and bind activated platelets without causing significant platelet aggregation and suggests a feasible way for the development of a platelet-targeted anti-thrombogenic drug delivery system. Furthermore, the approach can be extended to the development of liposomes for other vascular targets, for application in drug delivery or gene therapy.

Blood Platelets↗

PubMed2004

Extracellular matrix-like surfactant polymers containing arginine-glycine-aspartic acid (RGD) peptides.

We report on a novel series of biomimetic polymers exhibiting interfacial properties similar to the extracellular matrix. A series of well-defined surfactant polymers were synthesized by simultaneously incorporating arginine-glycine-aspartic acid (RGD) peptide, dextran oligosaccharide, and hexyl ligands with controlled feed ratios onto a poly(vinyl amine) (PVAm) backbone. The peptide sequence was H-GSSSGRGDSPA-NH(2) (Pep) having a hydrophilic extender at the amino terminus and capped carboxy terminus. The peptide-to-dextran (Pep:Dex) ratios were varied to create surfactants having 0, 25, 50, 75, and 100 mol-% peptide relative to dextran. The surfactants were characterized by IR, NMR and atomic force microscopy (AFM) for composition and surface active properties. AFM confirmed full surface coverage of PVAm(Pep)(100%) on graphite, and supported the mechanism of interdigitation of hexyl ligands between surfactant molecules within a specified range of hexyl chain densities. the attachment and growth of human pulmonary artery endothelial cells on the PVAm(Pep)(100%) surface was identical to the fibronectin positive control. Cell adhesion decreased dramatically with decreasing peptide density on the surfactant polymers. Molecular model of a peptide surfactant polymer, consisting of poly(vinyl amine) backbone with peptide, dextran oligosaccharide and hexyl branches coupled to the polymer chain.

Absorption↗

PubMed2004

Biomaterial surface-dependent neutrophil mobility.

Compromised neutrophil function in the presence of an implanted biomaterial may represent an important mechanism that allows for the development of implant-associated infections. Here, human neutrophil mobility has been investigated on a polyurethane (ChronoFlex AR), a hydrophobic surface consisting of an octadecyltrichlorosilane (OTS) self-assembled monolayer, and a glass reference material. Neutrophil mobility was quantified, based on cell movement speed and persistence time obtained from time-lapse optical microscopy, while neutrophil cytoskeletal structures and morphology were visualized using confocal microscopy and atomic force microscopy. Our results show that material surface properties affect neutrophil-surface interactions, as reflected by morphological changes, and the mobility of neutrophils stimulated by N-formylmethionyl-leucyl-phenylalanine (fMLP). In the absence of adsorbed plasma proteins, the mobility of stimulated neutrophils increased with increasing material hydrophobicity from glass, to polyurethane, to OTS. The opposite trend was observed in the presence of adsorbed plasma proteins, such that neutrophil mobility increased with decreasing material hydrophobicity. Analysis of the results showed that the mobility of fMLP-stimulated neutrophils cells was inversely related to the extent of cell spreading on the materials.

Biocompatible Materials↗

PubMed2004

Fluorocarbon Surfactant Polymers: Effect of Perfluorocarbon Branch Density on Surface Active Properties.

We describe a series of fluorocarbon surfactant polymers designed for modifying fluorocarbon surfaces such as poly(tetrafluoroethylene). Novel fluorocarbon surfactant polymers poly(N-vinyldextranaldonamide-co-N-vinylperfluoroundecanamide), in which hydrophilic dextran oligosaccharides and hydrophobic perfluoroundecanoyl groups were incorporated sequentially onto a poly(vinylamine) backbone, were synthesized and characterized by FT-IR, NMR, and XPS spectroscopy. By adjusting the feed ratio of dextran to fluorocarbon branches, surfactant polymers with different hydrophilic/hydrophobic balances were prepared. The surface activity of the surfactants at the air/water interface was demonstrated by significant reductions in water surface tension. Surfactant adsorption and adhesion at the solid PTFE/aqueous interface were examined under well-defined dynamic flow conditions, using a rotating disk system. The surface activity at the air/water interface and adhesion stability on PTFE under an applied shear stress both increase with increasing density of fluorocarbon branches on the polymer backbone. The results show that stable surfactant adhesion on PTFE can be achieved by adjusting the hydrophilic dextran to hydrophobic fluorocarbon branch ratio.

Journal Article↗

PubMed2004

ABri peptide associated with familial British dementia forms annular and ring-like protofibrillar structures.

Amyloid plaque deposition involves the aggregation of normally soluble proteins into insoluble amyloid fibrils (fibrillization) and proceeds through intermediates with distinct morphologies, including spherical aggregates, protofibrils, and mature fibrils. Recently, a novel annular protofibril-like intermediate with unique pore-like properties was produced by alpha-synuclein, A beta-Arctic and amylin, which are proteins associated with Parkinson's disease, Alzheimer's disease, and type-II diabetes. The observation of annular structures coupled with size selective channel-like activity by these proteins suggests that these structures may be responsible for vesicle permeability by ion-channel formation. Using atomic force spectroscopy, we report here that the ABri peptide associated with familial British dementia produces similar annular and ring-like protofibril structures during the following sequence of events: spherical aggregates (0.4-1.5 nm height)-->chain-like protofibrils (1.5-2.3 nm height)-->ring-like protofibrils and annular protofibrils (1.5-2.3 nm height). This suggests that ABri fibrillization occurs in a similar fashion to other amyloidogenic proteins and that the annular protofibrillar structures may represent a common amyloid intermediate.

Alzheimer Disease↗

PubMed2004

Poly(ethylene oxide) surfactant polymers.

We report on a series of structurally well-defined surfactant polymers that undergo surface-induced self-assembly on hydrophobic biomaterial surfaces. The surfactant polymers consist of a poly(vinyl amine) backbone with poly(ethylene oxide) and hexanal pendant groups. The poly(vinyl amine) (PVAm) was synthesized by hydrolysis of poly(N-vinyl formamide) following free radical polymerization of N-vinyl formamide. Hexanal and aldehyde-terminated poly(ethylene oxide) (PEO) were simultaneously attached to PVAm via reductive amination. Surfactant polymers with different PEO:hexanal ratios and hydrophilic/hydrophobic balances were prepared, and characterized by FT-IR, 1H-NMR and XPS spectroscopies. Surface active properties at the air/water interface were determined by surface tension measurements. Surface activity at a solid surface/water interface was demonstrated by atomic force microscopy, showing epitaxially molecular alignment for surfactant polymers adsorbed on highly oriented pyrolytic graphite. The surfactant polymers described in this report can be adapted for simple non-covalent surface modification of biomaterials and hydrophobic surfaces to provide highly hydrated interfaces.

Aldehydes↗

PubMed2003

Biometric surfactant polymers designed for shear-stable endothelialization on biomaterials.

We have developed a series of extracellular matrix (ECM)-like biomimetic surfactant polymers to improve endothelial cell adhesion and growth on vascular biomaterials. These polymers provide a single-step procedure for modifying the surface of existing biomaterials and consist of a poly(vinyl amine) (PVAm) backbone with varying ratios of cell-binding peptide (RGD) to carbohydrate (maltose), ranging from 100% RGD:0% maltose to 50% RGD:50% maltose. Three biomimetic surfaces, as well as a fibronectin (FN)-coated glass surface were seeded at confluence with human pulmonary artery endothelial cells (HPAECs) and exposed to shear stresses ranging from 0-40.6 dyn/cm2 for periods of 2 h and 6 h. Surfaces were examined for HPAEC coverage and cytoskeletal arrangement as a function of time and shear stress. In general, after 6 h of shear exposure, EC retention on 100% RGD > FN > 75% RGD > 50% RGD. The 100% RGD surface maintained more than 50% of its initial EC monolayer at low to moderate shear stresses whereas all other surfaces dropped to approximately 40% or less in the same shear stress range. The most stable surface, 100% RGD, showed a significant increase in cytoskeletal organization at all shear stresses greater than 2.5 dyn/cm2. In contrast, there was no real change in cytoskeletal organization on the FN surface, and there was a decrease on the 75% RGD surface over time. These results indicate that increasing surface peptide density can control EC shear stability. Furthermore, improved shear stability increases with increasing peptide density and is related to the EC's ability to reorganize its cytoskeleton.

Biocompatible Materials↗

PubMed2003

pH-dependent amyloid and protofibril formation by the ABri peptide of familial British dementia.

The ABri is a 34 residue peptide that is the major component of amyloid deposits in familial British dementia. In the amyloid deposits, the ABri peptide adopts aggregated beta-pleated sheet structures, similar to those formed by the Abeta peptide of Alzheimer's disease and other amyloid forming proteins. As a first step toward elucidating the molecular mechanisms of the beta-amyloidosis, we explored the ability of the environmental variables (pH and peptide concentration) to promote beta-sheet fibril structures for synthetic ABri peptides. The secondary structures and fibril morphology were characterized in parallel using circular dichroism, atomic force microscopy, negative stain electron microscopy, Congo red, and thioflavin-T fluorescence spectroscopic techniques. As seen with other amyloid proteins, the ABri fibrils had characteristic binding with Congo red and thioflavin-T, and the relative amounts of beta-sheet and amyloid fibril-like structures are influenced strongly by pH. In the acidic pH range 3.1-4.3, the ABri peptide adopts almost exclusively random structure and a predominantly monomeric aggregation state, on the basis of analytical ultracentrifugation measurements. At neutral pH, 7.1-7.3, the ABri peptide had limited solubility and produced spherical and amorphous aggregates with predominantly beta-sheet secondary structure, whereas at slightly acidic pH, 4.9, spherical aggregates, intermediate-sized protofibrils, and larger-sized mature amyloid fibrils were detected by atomic force microscopy. With aging at pH 4.9, the protofibrils underwent further association and eventually formed mature fibrils. The presence of small amounts of aggregated peptide material or seeds encourage fibril formation at neutral pH, suggesting that generation of such seeds in vivo could promote amyloid formation. At slightly basic pH, 9.0, scrambling of the Cys5-Cys22 disulfide bond occurred, which could lead to the formation of covalently linked aggregates. The presence of the protofibrils and the enhanced aggregation at slightly acidic pH is consistent with the behavior of other amyloid-forming proteins, which supports the premise that a common mechanism may be involved in protein misfolding and beta-amyloidosis.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Methionine 35 oxidation reduces fibril assembly of the amyloid abeta-(1-42) peptide of Alzheimer's disease.

The major component of amyloid plaques in Alzheimer's disease (AD) is Abeta, a small peptide that has high propensity to assemble as aggregated beta-sheet structures. Using three well established techniques for studying amyloid structure, namely circular dichroism, thioflavin-T fluorescence, and atomic force microscopy, we demonstrate that oxidation of the Met-35 side chain to a methionine sulfoxide (Met-35(ox)) significantly hinders the rate of fibril formation for the 42-residue Abeta-(1-42) at physiological pH. Met-35(ox) also alters the characteristic Abeta fibril morphology and prevents formation of the protofibril, which is a key intermediate in beta-amyloidosis and the associated neurotoxicity. The implications of these results for the biological function and role of Abeta with oxidative stress in AD are discussed.

Alzheimer Disease↗

PubMed2002

Synthesis and characterization of oligomaltose-grafted lipids with application to liposomes.

Novel glycolipids, which contain 2 and 15 oligomaltose units and a phosphatidylethanolamine, were synthesized and characterized by FTIR and (1)H-NMR spectroscopies. The well-defined linear structure of the glycolipids was assured by an end-point conjugation strategy using selective oxidation of the reducing end groups of maltose oligosaccharides, followed by aminolysis with distearoylphosphatidylethanolamine. The intermediate acids react selectively with amines to form amide linkages, catalyzed by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide. Conformations of the glycolipids at the air-water interface were proposed based on the film balance measurements. The unique conformations of glycolipids at interfaces may offer advantages over traditional PEO-derived lipids in regard to their applications for sterically stabilizing liposomes. The glycolipids demonstrated the ability for sterically stabilizing liposome dispersions, as determined by turbidity measurements.

Catalysis↗

PubMed2002

Surface modification of liposomes for selective cell targeting in cardiovascular drug delivery.

Cardiovascular disease processes such as atherosclerosis, restenosis, and inflammation are typically localized to discrete regions of the vasculature, affording great opportunity for targeted pharmacological treatment. Liposomes are potentially advantageous targeted drug carriers for such intravascular applications. To facilitate their use as drug delivery vehicles, we have considered three components of liposome design: (i) identification of candidate cell surface receptors for targeting; (ii) identification of ligands that maintain binding specificity and affinity; and (iii) prevention of rapid nonspecific clearance of liposomes into the reticuloendothelial organs. In this report, we describe our work in developing liposomal surface modifications that address both targeting and clearance. An arginine-glycine-aspartic acid (RGD) containing peptide was used as a model ligand to target liposomes to the integrin GPIIb-IIIa on activated platelets. Additionally, oligodextran surfactants incorporated into liposomes provided insight into the effect of vesicle perturbations on liposome clearance, and the importance of molecular geometry in designing oligosaccharide surface modifications. Together these studies demonstrate the feasibility of using peptides to guide liposomes to desired receptors, and illustrate the influence of vesicle stability on liposome interactions in vivo. Furthermore, they underscore the importance of simultaneously considering both targeting specificity and vesicle longevity in the design of effective targeted drug delivery systems.

Animals↗

PubMed2002

Endothelial cell formation of focal adhesions on hydrophilic plasma polymers.

Endothelial cell (EC) formation and distribution of both actin stress fibers and focal contacts on hydrophilic plasma polymers derived from gamma-butyrolactone (GBL) and n-vinylpyrrolidone (NVP) were examined to determine their ability to support endothelial cell growth in comparison to fibronectin. One hour after seeding, cells adhered and spread moderately on fibronectin with the development of defined actin stress fibers and focal adhesions compared to NVP and GBL, on which the cells were spread with poorly developed stress fibers and a perinuclear localization of vinculin. At 3 h, cells continue to spread more on fibronectin and NVP than GBL, and the cells on fibronectin had well-defined stress fibers terminating with sharp spikes of vinculin, typical of focal adhesions. At this time point, paxillin, a signaling component of focal adhesion complex, was predominantly localized at the focal contacts for well-spread EC on fibronectin and NVP, whereas it was almost entirely concentrated in the perinuclear region of less-spread cells on GBL. However, by 24h, cells were much more spread on all three surfaces with defined stress fibers and focal contacts although EC expression of vinculin and paxillin was moderate on GBL compared to fibronectin and NVP. These results suggest that EC can form cytoskeletal structures necessary for cell survival on plasma polymers, especially on more hydrophilic NVP, which could be exploited as interface material for seeding endothelial cells.

4-Butyrolactone↗