RGD modified polymers: biomaterials for stimulated cell adhesion and beyond

Since RGD peptides (R: arginine; G: glycine; D: aspartic acid) have been found to promote cell adhesion in 1984 (Cell attachment activity of fibronectin can be duplicated by small synthetic fragments of the molecule, Nature 309 (1984) 30), numerous materials have been RGD functionalized for academic studies or medical applications. This review gives an overview of RGD modified polymers, that have been used for cell adhesion, and provides information about technical aspects of RGD immobilization on polymers. The impacts of RGD peptide surface density, spatial arrangement as well as integrin affinity and selectivity on cell responses like adhesion and migration are discussed.     

« Les biomatériaux inhibiteurs de l'adhérence et de la prolifération bactérienne : un enjeu pour la prévention des infections sur matériel prothétique »

Bacterial infections on implanted prosthetic materials represent one of the major problems of public health and one of the first causes of nosocomial infections. Infections on implanted devices are extremely resistant to antibiotics as well as to host defences and frequently persist until the removal of the implant which remains the standard therapy. In order to prevent infection, several strategies are proposed and/or developed; amongst them heparin or antibiotic impregnations were extensively studied and gave interesting results nevertheless the most promising solutions consists in synthesizing and/or grafting bioactive polymers able to inhibit bacterial adhesion.     

Intérêt de la coopération ostéoendothéliale en ingénierie du tissu osseux

The techniques of bone tissue engineering, associating autologous repairing cells with a bioactive materials must to take into account of the mechanisms of communication which can exist between the cells requested on the level of a site of repair. Among these phenomenons of interaction, vascularization remains closely related to an osseous regeneration. In vitro studies of co-cultures between endothelials cells and osteoblastic cells of various origins let predict existence of different factors (growth factors, peptides natriuretic, nitric oxyde) but also of junction communication responsible for the regulation of the bone formation activity of the osteogenic cells. In addition, the existence of such cooperation could be demonstrated using experimental models of osseous reconstruction. Finally, the contribution of the nanotechnologies of the biomaterials offers very promising prospects to promote these cellular cooperations and these heterotopic communications.     

Extracellular matrix cell adhesion peptides: functional applications in orthopedic materials

This review describes research on selected peptide sequences that affect cell adhesion as it applies in orthopedic applications. Of particular interest are the integrin-binding RGD peptides and heparin-binding peptides. The influence of these peptides on cell adhesion is described. Cell adhesion is defined as a sequence of four steps: cell attachment, cell spreading, organization of an actin cytoskeleton, and formation of focal adhesions. RGD sequences clearly influence cell attachment and spreading, whereas heparin-binding sequences appear to be less efficient. Collectively, these sequences appear to promote all steps of cell adhesion in certain cell types. This review also addresses issues related to peptide immobilization, as well as potential complexities that may develop as a result of using these versatile cell-binding sequences. Also described are future directions in the field concerning use of existing and more sophisticated peptide substrata.     

L'adhérence des érythrocytes à l'endothélium vasculaire

Blood cells are in continuous contact with the vascular endothelium. Endothelial cell culture, intravital videomicroscopy allowed the investigation of blood cell-endothelium interactions in dynamic conditions.In the various diseases, diabetes mellitus, sickle cell anemia and malaria, erythrocytes have an increased adhesion to endothelial cells. The presence of advanced glycation end products (AGE) on erythrocytes of diabetics is responsible for their binding to the receptor RAGE present on the endothelium. The AGE-RAGE binding provokes an oxidant stress and induces the expression of the adhesion molecule. Furthermore, erythrocyte AGE induce an increase in vascular permeability. In sickle cell anemia, the increased adhesiveness and the sickling of red blood cells are responsible for thrombosis. Plasmodium falciparum infestation of erythrocytes induces knob formation at the cell surface and the P. falciparum protein binding to CD36, ICAM-1 and thrombospondin present on the endothelium, and facilitates the parasite dissemination. © 2999 Éditions scientifiques et médicales Elsevier SAS     

Development of RGD peptides grafted onto silica surfaces: XPS characterization and human endothelial cell interactions.

The attachment of human umbilical vein endothelial cells (HUVECs) on substrates that had been covalently grafted with the cell adhesion peptides Arg-Gly-Asp (RGD) was investigated. This approach was used to provide substrates that are adhesive to cells even in the absence of serum proteins and to cells that have had no prior treatment of the surface with proteins that promote cell adhesion. We wanted to improve control of cellular interactions with cell-adhesive materials by providing fixedly bound adhesion ligands. Silica was examined as a model surface. The peptides were grafted using three different steps: grafting of aminosilane molecules; reaction with a maleimide molecule; and immobilization of cell-binding peptides containing the RGD sequence. The RGD-grafted surface was characterized by X-ray photoelectron spectroscopy (XPS) and contact-angle measurements.     

Human endothelial cell interaction with biomimetic surfactant polymers containing Peptide ligands from the heparin binding domain of fibronectin

Biomimetic materials that mimic the extracellular matrix (ECM) provide a means to control cellular functions such as adhesion and growth, which are vital to successful engineering of tissue-incorporated biomaterials. Novel "ECM-like" biomimetic surfactant polymers consisting of a poly(vinyl amine) backbone with pendant cell-adhesive peptides derived from one of the heparin-binding domains of fibronectin were developed to improve endothelial cell adhesion and growth on vascular biomaterials. Heparin-binding peptide (HBP) sequences, alone and in combination with RGD peptides, were examined for their ability to promote human pulmonary artery endothelial cell (HPAEC) adhesion and growth (HBP1, WQPPRARI; HBP2, SPPRRARVT; HBP1:RGD; and HBP2:RGD) and compared with cell adhesion and growth on fibronectin and on negative control polymer surfaces in which alanines were substituted for the positively charged arginine residues in the two peptides. The results showed that HPAECs adhered and spread equally well on all HBP-containing polymers and the positive fibronectin control, showing similar stress fiber and focal adhesion formation. However, the HBP alone was unable to support long-term HPAEC growth and survival, showing a loss of focal adhesions and cytoskeletal disorganization by 24 h after seeding. With the addition of RGD, the surfaces behaved similarly or better than fibronectin. The negative control polymers showed little to no initial cell attachment, and the addition of soluble heparin to the medium reduced initial cell adhesion on both the HBP2 and HBP2:RGD surfaces. These results indicate that the HBP surfaces promote initial HPAEC adhesion and spreading, but not long-term survival.     

Évaluation par PIXE dans des coupes minces de la migration de certains éléments relargués par des implants métalliques

Migration evaluation in thin samples by PIXE of some metallic elements displaced from prosthesis.The metallic prosthesis used in orthopaedic surgery undergo degradations some years after their implantation. This phenomenon induces metallic element transfers in surrounding tissues. From an anatomical body, we have taken out implanted hip prosthesis and the surrounding tissues; we have determined the composition of the implanted prosthesis by spark spectrometry. Using a protocol adapted for each sample, we manufacture slides parallel to the femur axis. We determine the concentration of the displaced metallic elements versus depth. We have used the so-called PIXE method (Particle Induced X-rays Emission), based on the X-rays spectroscopy, to analyse our samples. The inducing particles were 3 MeV proton, the beam was 50 μm in diameter and had an intensity of 3 nA. Preliminary results show the migration of metallic elements from prosthesis to soft tissues.     

Cellular recognition of synthetic peptide amphiphiles in self-assembled monolayer films

The incorporation of lipidated cell adhesion peptides into self-assembled structures such as films provides the opportunity to develop unique biomimetic materials with well-organized interfaces. Synthetic dialkyl tails have been linked to the amino-terminus, carboxyl-terminus, and both termini of the cell recognition sequence Arg-Gly-Asp (RGD) to produce amino-coupled, carboxyl-coupled, and looped RGD peptide amphiphiles. All three amphiphilic RGD versions self-assembled into fairly stable mixed monolayers that deposited well as Langmuir-Blodgett films on surfaces, except for films containing amino-coupled RGD amphiphiles at high peptide concentrations. FT-IR studies showed that amino-coupled RGD head groups formed the strongest lateral hydrogen bonds. Melanoma cells spread on looped RGD amphiphiles in a concentration-dependent manner, spread indiscriminately on carboxyl-coupled RGD amphiphiles, and did not spread on amino-coupled RGD amphiphiles. Looped RGD amphiphiles promoted the adhesion, spreading, and cytoskeletal reorganization of melanoma and endothelial cells while control looped Arg-Gly-Glu (RGE) amphiphiles inhibited them. Antibody inhibition of the integrin receptor alpha3beta1 blocked melanoma cell adhesion to looped RGD amphiphiles. These results confirm that novel biomolecular materials containing synthetic peptide amphiphiles have the potential to control cellular behavior in a specific manner.     

Sickle red cell adhesion: Many issues and some answers

Among multiple pathologies associated with sickle cell disease, sickle red cell-endothelial interaction has been implicated as a potential initiating mechanism in vaso-occlusive events that characterize this disease. Vast literature exists on various aspects of sickle red cell adhesion, but many issues remain unresolved, especially pertaining to the role of sickle red cell heterogeneity, the relative role of multiple adhesion mechanisms and targets of antiadhesive therapy. This review briefly analyzes these issues.     

RGD肽在肿瘤诊断与治疗中的应用

RGD( Arg - Gly- Asp)肽存在于多种生物细胞外基质中,能特异性识别肿瘤细胞表面的整合素并与之结合,可作为体内RGD肽类物质的竞争性抑制剂,从而能抑制肿瘤细胞与细胞外基质的黏附与迁移、抑制肿瘤血管形成、诱导肿瘤细胞凋亡.RGD肽可以作为载体在肿瘤靶向治疗中发挥重要作用,且在肿瘤显像及肿瘤治疗有潜在应用价值.该文主要介绍RGD肽在肿瘤显像中的应用、在肿瘤治疗中作为载体的应用、对肿瘤的直接抑制作用、在抗栓药物中的应用、对血小板功能的影响、诱导骨组织再生的应用研究与新进展.     

Adhesion of sickle red cells to endothelium: Myths and future directions

Sickle RBC are abnormally adherent to vascular endothelial cells. We briefly review the mechanisms that underlie this type of cell/cell adhesion, expose a number of extant myths about RBC adhesion, and discuss some aspects that need consideration via future experimentation. The relationship of this phenomenon of RBC-endothelial adhesion to the cytoadherence of parasitized sickle RBC is not yet clear.     

Outcome and perspectives in bioactive coatings: What''s new, what''s coming

The main interest of calcium phosphate (CaP) coating is osteoconduction and faster and better osteogenic cells spreading and bone ingrowth onto the dental or orthopaedic surface implant. CaP coating are bioactive materials that have been shown to promote early bone apposition at the surface of metallic implants. However, every CaP is more or less resorbable; in this way, new technologies are developed to promote and/or induce osteogenic activity. These evolutions tend to control the chemical nature of CaP ceramic, the porosity and the thickness of the coating; and/or to integrate in the coating osteoinductive or therapeutic agents (biphosphonates, antibiotics); and/or to immobilize constitutional elements of bone on implants surface (growth factors (BMP, TGF-β), adhesion proteins (collagen, fibronectin, laminin, vitronectin) or peptides (RGD sequence). All these technological and biologic progress should be evaluated compared to possible side effects and the long-term benefit for the patients.     

Immobilization of RGD to < 1 1 1 > silicon surfaces for enhanced cell adhesion and proliferation

The ability of biomaterial surfaces to regulate cell behavior requires control over surface chemistry and microstructure. One of the greatest challenges with silicon-based biomedical microdevices such as those recently developed for neural stimulation, implantable encapsulation, biosensors, and drug delivery, is to improve biocompatibility and tissue integration. This may be achieved by modifying the exposed silicon surface with bioactive peptides. In this study, Arg-Gly-Asp (RGD) peptide conjugated surfaces were prepared and characterized. The effect of these surfaces on fibroblast adhesion and proliferation was examined over 4 days. Silicon surfaces coupled with a synthetic RGD peptide, as characterized with X-ray photoelectron spectroscopy and atomic force microscopy, display enhanced cell proliferation and bioactivity. Results demonstrate an almost three-fold greater cell attachment! proliferation on RGD immobilized surfaces compared to unmodified (control) silicon surfaces. Modulating the biological response of inorganic materials such as silicon will allow us to design more appropriate interfaces for implantable diagnostic and therapeutic silicon-based microdevices.     

Efficacité et performance des substituts osseux pour remplacer les allogreffes et autogreffes

Although bone tissue possesses the capacity for regenerative growth, the bone repair process is impaired in many clinical and pathological situations. For example massive bone loss caused by trauma and tumor resection as well as deformities require reconstructive surgery. In this context, there was a critical need to develop implant technologies to promote bone healing. Cortical and cancellous bone grafts are the materials of choice for bone filling or reconstruction, but their clinical use involves some difficulties. Septic complications, viral transmission and unavailability of native bone have therefore led to the development of synthetic bone substitutes. Allograft bone, or tissue harvested from a cadaver, while more readily available, may carry with it the risk of disease transmission and is also difficult to shape [1–3]. A significant additional limitation of allograft bone is the delayed remodeling by the host. In the case of very large defects, the allograft may remain in the implant site throughout the patient's life, creating an area more prone to fracture or infection. The development of calcium phosphate ceramics and other related biomaterials for bone graft involved a better control of the process of biomaterials resorption and bone substitution. Synthetic bone graft materials available as alternatives to autogeneous bone for repair, substitution or augmentation, in particular synthetic biomaterials include, special glass ceramics described as bioactive glasses; calcium phosphates (calcium hydroxyapatite, HA; tricalcium phosphate, TCP; and biphasic calcium phosphate, BCP). These materials differ in composition and physical properties from each other and from bone; and must be take in consideration for more efficient bone ingrowth at the expense of the biomaterials and to adapt to new development of dedicated biomaterials. In the last decade synthetic calcium phosphate materials, principally calcium hydroxyapatite (HA) ceramics, was commercially used. However the concept of bioactivity (release of ions of biological interest) well described for glass ceramic was not particularly take in account for HA and other related biomaterials(ACP Amorphous Calcium Phosphate, CdA Calcium Phosphate deficient Apatite). HA until recently was considered to be non able to be resorbed. Calcium phosphate biomaterials differ in their solubility or extent of dissolution: ACP > > α-TCP > > β-TCP > CdA > > ACP. These ceramics are osteoconductive (act as a support for new bone formation requiring the presence of porosity) and able to be resorbed (degradable through chemical and cellular processes). They are also biocompatible (do not induce adverse local tissue reaction, immunogenicity or systematically toxicity); and more recently, some papers report osteoinductive properties associated to the chemical nature (biphasic Ca P) and the microstruture. Past decade, these bioceramics have been marketed and approved for use in humans as bone substitutes. Various presentations are currently used in orthopaedic and maxillo-facial surgery such as wedges, blocks or granules. Owing to their bone substitution properties, CaP ceramics have naturally been considered as a potential matrix for tissue engineering and the development of a bioactive drug delivery system (DDS) in bone sites. The paper presents the current knowledge on Calcium phosphate bioceramics, Bone tissue engineering and Calcium Phosphate Drug Delivery.     

The effect of the addition of a polyglutamate motif to RGD on peptide tethering to hydroxyapatite and the promotion of mesenchymal stem cell adhesion

Mimicking endogenous bone-binding proteins, RGD peptides have been synthesized with polyacidic amino acid domains in order to ionically tether the peptides to bone-like synthetic biomaterials, including hydroxyapatite (HA). However, a direct comparison of unmodified RGD with polyacidic-conjugated RGD has not been performed, and thus a benefit for the acidic domain has not been established. We evaluated the peptide/HA bond of RGD peptides with and without an attached polyglutamate sequence (E(7)), as well as examined mesenchymal stem cell (MSC) adhesion and morphology as they were affected by the conjugated peptide. We found that significantly more E(7)RGD was bound to HA than RGD at all coating concentrations tested, and moreover, more E(7)RGD was retained on the HA surface even after extended washing in serum-free media. Consistent with in vitro results, higher levels of E(7)RGD than RGD remained on HA that had been implanted in vivo for 24 h, indicating that the polyacidic domain improved peptide-binding efficiency. At several peptide concentrations, E(7)RGD increased cell adhesion compared to RGD surfaces, establishing a biological benefit for the E(7) modification. In addition, HA pre-coated sequentially with low-density E(7)RGD (1-10 microg/ml) and serum (FBS) stimulated cell adhesion and spreading, compared to either coating alone, suggesting that an ionic linkage allows for the potential adsorption of serum proteins to unoccupied sites, which may be important for bone formation in vivo. Collectively, these results suggest that tethering peptides to HA via a polyglutamate domain is an effective method for improving the peptide/HA bond, as well as for enhancing MSC adhesion.     

精氨酸甘氨酸天冬氨酸多肽表面修饰促进生物支架材料对骨髓来源 种子细胞的黏附

背景：精氨酸甘氨酸天冬氨酸多肽具有较强的黏附性和生物支架材料可接枝结合,且不会改变材料的表面理化性质。 目的：观察应用精氨酸甘氨酸天冬氨酸多肽表面修饰猪主动脉瓣去细胞支架材料对骨髓干细胞黏附性的影响。 方法：采用胰蛋白酶+TritonX-100法制备猪主动脉瓣去细胞支架材料,用YGRGDSP多肽(酪氨酸-甘氨酸-精氨酸-甘氨酸-天冬氨酸-丝氨酸-脯氨酸)进行处理,按照精氨酸甘氨酸天冬氨酸多肽的质量浓度(0.5,1.0,1.5,2.0 g/L)、反应时间(4,8,12,24 h)、反应pH值(7.0,7.4,8.0)分为不同实验组。 结果与结论：茚三酮显示精氨酸甘氨酸天冬氨酸多肽可很好的交联到猪主动脉瓣去细胞支架材料,最佳反应条件为：室温、1.5 g/L精氨酸甘氨酸天冬氨酸、pH 7.4、持续振荡12 h。提示利用YGRGDSP多肽对猪主动脉瓣去细胞支架材料进行表面修饰可显著改善骨髓来源种子细胞的黏附性。     

Projet Tim-Star en région Rhône-Alpes: partage d'informations médicales résumées

Chaîner les informations médicales est une question importante. La plupart des récentes réformes des systèmes de santé des pays occidentaux (y compris la France, depuis 1996), grâce aux avancées technologiques dans le domaine des réseaux d'information de santé, ont intégré cet objectif. Le contexte national social et juridique des systèmes de santé ralentit souvent le processus. Dans la région Rhône-Alpes, le projet Téle-information médicale (TIM)—Seamless Telematics Across Regions (Star) a été développé en différentes étapes permettant de déterminer différents besoins d'échanges d'informations médicales. Les données médicales nominatives non-structurées (en langage naturel) ne peuvent être échangées qu'entre les praticiens directement en charge du malade: elles doivent être cryptées. Les données, médicales structurées, résumées et codées peuvent être échangées, après anonymisation, entre les différents partenaires du système de soins (hôpital, médecins, payeurs). Une procédure d'anonymisation-chaînage des données PMSI de deux établissements hospitaliers différents a été appliquée pour tester la faisabilité du partage de données médicales structurées à l'intérieur du futur réseau de soins.     

RGD肽对内皮细胞在聚酯材料表面粘附、增殖的影响

RGD是许多粘附蛋白结构中的高度保守序列，与细胞在生物材料表面的粘附、增殖密切相关。本研究在聚酯薄膜表面分别预衬纤维粘连蛋白和共价接枝RGD三肽，然后在不同聚酯材料上种植体外培养的人脐静脉内皮细胞，结果显示RGD可明显促进细胞在材料表面的粘附和增殖，与纤维粘连蛋白相比，RGD促进细胞粘附的作用更为明显，而在细胞增殖方面，二者的作用无显著性差异。本研究为改进生物材料的表面设计，促进心血管移植物的内皮化提供了一个切实可行的思路。     

The α4β1 integrin in sickle cell disease

The α4β1 integrin is an adhesion receptor expressed on reticulocytes in sickle cell disease (SCD) and mediates the adhesion of these cells to sub-endothelial matrix proteins and the endothelium. In this review, we describe the mechanism of activation of the α4β1 integrin on sickle reticulocytes and discuss novel roles for this integrin in SCD as a result of this activation. We also illustrate novel therapies in SCD that may target the integrin and alleviate vaso-occlusion.