Camouflaged angiogenic BMP-2 functions exposed by pico-paracrine biohybrids.

The constant release of human bone morphogenetic protein 2 (rhBMP-2) in the picomolar range (Pico-Stat) from PDLLA-biohybrids led to the detection of intrinsic novel pro- and anti-angiogenic functions of this cytokine. As integrant part in this perspective of previous work, first evidence for the binding of rhBMP-2, as an inverse agonist, to allosteric angiogenic receptors in cocultures of human endothelial cells is reported.

Intrasurgical Protein Layer on Titanium Arthroplasty Explants: From the Big Twelve to the Implant Proteome.

PURPOSE: Aseptic loosening in total joint replacement due to insufficient osteointegration is an unsolved problem in orthopaedics. The purpose of the study is to obtain a picture of the initial protein adsorption layer on femoral endoprosthetic surfaces as the key to the initiation of osseointegration. EXPERIMENTAL DESIGN: The paper describes the first study of femoral stem explants from patients for proteome analysis of the primary protein layer. After 2 min in situ, the stems are explanted and frozen in liquid nitrogen. Proteins are eluted under reducing conditions and analyzed by LC-MS/MS. RESULTS: After exclusion of proteins identified by a single peptide, the implant proteome is found to consist of 2802 unique proteins. Of these, 77% are of intracellular origin, 9% are derived from the plasma proteome, 8% from the bone proteome, and four proteins with highest specificity score could be assigned to the bone marrow proteome (transcriptome). The most abundant protein in the adsorbed total protein layer is hemoglobin (8-11%) followed by serum albumin (3.6-6%). CONCLUSIONS: A detailed knowledge of the initial protein film deposited onto the implants, as demonstrated here for the first time, may help to understand and predict the response of the osseous microenvironment to implant surfaces.

Antimicrobial and Osseointegration Properties of Nanostructured Titanium Orthopaedic Implants.

The surface design of titanium implants influences not only the local biological reactions but also affects at least the clinical result in orthopaedic application. During the last decades, strong efforts have been made to improve osteointegration and prevent bacterial adhesion to these surfaces. Following the rule of "smaller, faster, cheaper", nanotechnology has encountered clinical application. It is evident that the hierarchical implant surface micro- and nanotopography orchestrate the biological cascades of early peri-implant endosseous healing or implant loosening. This review of the literature gives a brief overview of nanostructured titanium-base biomaterials designed to improve osteointegration and prevent from bacterial infection.

Synthesis of novel tricalcium phosphate-bioactive glass composite and functionalization with rhBMP-2.

A functionalization is required for calcium phosphate-based bone substitute materials to achieve an entire bone remodeling. In this study it was hypothesized that a tailored composite of tricalcium phosphate and a bioactive glass can be loaded sufficiently with rhBMP-2 for functionalization. A composite of 40 wt% tricalcium phosphate and 60 wt% bioactive glass resulted in two crystalline phases, wollastonite and rhenanite after sintering. SEM analysis of the composite's surface revealed a spongious bone-like morphology after treatment with different acids. RhBMP-2 was immobilized non-covalently by treating with chrome sulfuric acid (CSA) and 3-aminopropyltriethoxysilane (APS) and covalently by treating with CSA/APS, and additionally with 1,1'-carbonyldiimidazole. It was proved that samples containing non-covalently immobilized rhBMP-2 on the surface exhibit significant biological activity in contrast to the samples with covalently bound protein on the surface. We conclude that a tailored composite of tricalcium phosphate and bioactive glass can be loaded sufficiently with BMP-2.

Chick ex ovo culture and ex ovo CAM assay: how it really works.

Chicken eggs in the early phase of breeding are between in vitro and in vivo systems and provide a vascular test environment not only to study angiogenesis but also to study tumorigenesis. After the chick chorioallantoic membrane (CAM) has developed, its blood vessel network can be easily accessed, manipulated and observed and therefore provides an optimal setting for angiogenesis assays. Since the lymphoid system is not fully developed until late stages of incubation, the chick embryo serves as a naturally immunodeficient host capable of sustaining grafted tissues and cells without species-specific restrictions. In addition to nurturing developing allo- and xenografts, the CAM blood vessel network provides a uniquely supportive environment for tumor cell intravasation, dissemination, and vascular arrest and a repository where arrested cells extravasate to form micro metastatic foci. For experimental purposes, in most of the recent studies the CAM was exposed by cutting a window through the egg shell and experiments were carried out in ovo, resulting in significant limitations in the accessibility of the CAM and possibilities for observation and photo documentation of effects. When shell-less cultures of the chick embryo were used(1-4), no experimental details were provided and, if published at all, the survival rates of these cultures were low. We refined the method of ex ovo culture of chick embryos significantly by introducing a rationally controlled extrusion of the egg content. These ex ovo cultures enhance the accessibility of the CAM and chick embryo, enabling easy in vivo documentation of effects and facilitating experimental manipulation of the embryo. This allows the successful application to a large number of scientific questions: (1) As an improved angiogenesis assay(5,6), (2) an experimental set up for facilitated injections in the vitreous of the chick embryo eye(7-9), (3) as a test environment for dissemination and intravasation of dispersed tumor cells from established cell lines inoculated on the CAM(10-12), (4) as an improved sustaining system for successful transplantation and culture of limb buds of chicken and mice(13) as well as (5) for grafting, propagation, and re-grafting of solid primary tumor tissue obtained from biopsies on the surface of the CAM(14). In this video article we describe the establishment of a refined chick ex ovo culture and CAM assay with survival rates over 50%. Besides we provide a step by step demonstration of the successful application of the ex ovo culture for a large number of scientific applications.

Polyethylenimine-coated albumin nanoparticles for BMP-2 delivery.

Nanoparticle (NP)-based delivery has gained importance for improving the potency of therapeutic agents. The bovine serum albumin (BSA) NPs, obtained by a coacervation process, was modified by electrostatic adsorption of cationic polyethylenimine (PEI) to NP surfaces for delivery of bone-inducing growth factor, bone morphogenetic protein-2 (BMP-2). Different concentrations of PEI were utilized for coating BSA NPs to stabilize the colloidal system and to control the release of BMP-2. The NPs were characterized by size and zeta potential measurements, as well as by Scanning Electron Microscopy and Atomic Force Microscopy. The encapsulation efficiency was typically >90% in all NP preparations. In vitro release kinetics showed that the PEI concentration used for coating the NPs efficiently controlled the release of BMP-2, demonstrating a gradual slowing, sustained release pattern during a 10-day study period. The bioactivity of the encapsulated BMP-2 and the toxicity of the NPs were examined by the alkaline phosphatase (ALP) induction assay and the MTT assay, respectively, using C2C12 cells. The results indicated that PEI was the primary determinant of NP toxicities, and BSA NPs coated with 0.1 mg/mL PEI demonstrated tolerable toxicity, retained the bioactivity of BMP-2, and efficiently slowed the release rate of BMP-2. We conclude that BMP-2 encapsulated in BSA NPs might be an efficient way to deliver the protein for in vivo bone induction.

Extracellular proteasome in the human alveolar space: a new housekeeping enzyme?

We hypothesized that 20S proteasome is present and functional in the extracellular alveolar space in humans. Proteasomal activity was measured in bronchoalveolar lavage (BAL) supernatant from eight humans using specific proteasomal fluorogenic substrates and I(125)-albumin with and without specific proteasome inhibitors. Furthermore, gelfiltration, Western blot technique, and mass spectrometry were applied for proteasome characterization. All proteasomal fluorogenic substrates were hydrolyzed by BAL supernatant, with hydrolysis inhibited by epoxomicin (P = 0.024) and other proteasome inhibitors as well. E64, a lysosomal inhibitor, did not inhibit enzyme activity. The majority of proteolytic activity was detected in BAL supernatant rather than in the cell pellet. No correlation was found between proteasomal hydrolysis in BAL supernatant and lactate dehydrogenase activity, the total cell count in the cell pellet, and the fraction of avital cells in the cell pellet, ruling out cell lysis as a major source of proteasomal activity. Gelfiltration revealed hydrolyzing activity in the supernatant at 660 kDa and proteasome core proteins after analysis by ESI-QqTOF mass spectrometry. Furthermore, Western blots using a polyclonal antibody against proteasomal alpha-/beta-subunits detected proteasomal proteins in the typical 20- to 30-kDa range in BAL supernatant. Incubation of BAL supernatant with I(125)-albumin showed a high mean cleavage rate (101.8 microg/ml x h lavage +/- 46 SD) that was inhibited by epoxomicin (P = 0.013) and was ATP and ubiquitin independent. We identified for the first time extracellular, biologically active, ATP- and ubiquitin-independent 20S proteasome in the human alveolar space, with a high albumin cleavage rate. Possibly, the proteasome assists in maintenance of a low intra-alveolar oncotic pressure and/or alveolar protein degradation.

Bone apposition to titanium implants biocoated with recombinant human bone morphogenetic protein-2 (rhBMP-2). A pilot study in dogs.

The aim of the present study was to investigate bone formation to recombinant human bone morphogenetic protein-2 (rhBMP-2)-biocoated and rhBMP-2-nonbiocoated titanium implants after implantation in dogs. Implantation of sand-blasted and acid-etched (C), chromosulfuric acid surface-enhanced (CSA), and rhBMP-2-biocoated CSA [BMP-A: noncovalently immobilized rhBMP-2 (596 ng/cm(2)), BMP-B: covalently immobilized rhBMP-2 (819 ng/cm(2))] implants was performed in both the mandible and tibia of dogs. After 4 weeks of healing, the percentage of direct bone to implant contact (BIC) and the induced bone density (BD) at a distance of less than and greater than 1 mm adjacent to each implant was assessed. Histomorphometric analysis of implants inserted in the mandible and tibia revealed that BIC values appeared to be highest in the BMP-B group, followed by BMP-A, CSA, and C. BD as measured at a distance of <1 mm revealed obvious differences between groups: BMP-B>BMP-A>CSA>C. However, no differences between groups were observed at a distance of >1 mm. Within the limits of the present study, it may be concluded that rhBMP-2 immobilized by covalent and noncovalent methods on CSA-treated implant surfaces seemed to be stable and promoted direct bone apposition in a concentration-dependent manner.

Interaction of fibrinogen with n-alkylagaroses and its purification by critical hydrophobicity hydrophobic interaction chromatograpy.

A rational application of hydrophobic interaction chromatography (HIC) to the purification of proteins has remained an enigma in spite of over 30 years of research. The critical hydrophobicity parameter, which can be determined from a concentration series of n-alkyl Sepharose 4B (Seph-Cn) offers the possibility of adapting the HIC gel to the needs of purification. To this end a library of HIC gels (Seph-C4 to Seph-C6) of different immobilized alkyl residue concentrations was synthesized and tested with purified bovine fibrinogen. Binding of fibrinogen to such a concentration series resulted in sigmoidal binding curves. Analysis of the Seph-C5 data according to the lattices-site binding model yielded adsorption coefficients (nS) between 5 and 10 indicating that 5-10 lattice-sites (alkyl residues) interact multivalently with a fibrinogen molecule for adsorption at low ionic strength. The apparent lattice-site half-saturation constant of dissociation lies between 21 and 25 micromol/ml packed gel. For each alkyl chain length a critical hydrophobicity could be determined. For fibrinogen purification the critical hydrohobicity gel, Seph-C5 (13 micromol/ml packed gel), was selected. With the help of the cosolvents NaCl or glycine a fully reversible adsorption of fibrinogen could be facilitated on the critical hydrophobicity gel. Application of the method to human and bovine blood plasma resulted in a single step purification of fibrinogen in high yields. A comparison of the classical purification of fibrinogen with the critical hydrophobicity HIC (CHIC) method demonstrates a reduction in preparation time from several days to ca. 1 h. The subunit structure of HIC-purified human fibrinogen is identical to the classically purified protein. In the case of bovine fibrinogen however HIC-purified fibrinogen displayed a different subunit structure in that the Aalpha chain of fibrinogen had a ca. 5 kDa higher molecular mass. This may be due to the rapidity of the new one-step method and an avoidance of proteolysis.

Hydrophobic interaction chromatography: harnessing multivalent protein-surface interactions for purification procedures.

Hydrophobic interaction chromatography (HIC) is one of the basic purification procedures in the biosciences. However, because of its complexity, it has not gained the same foothold in the methodological repertoire of protein chemistry as has affinity chromatography or ion exchange chromatography. This is mainly a result of the lack of a general optimization procedure for the reversible adsorption and elution of a novel protein to be purified. Further problems arise from the fact that most commercial hydrophobic adsorbents are inadequate for an ideal performance in downstream processing procedures, because these media are too hydrophobic and elution of proteins in their native state is often impossible. Therefore, as in the 1970s, a bioscientist of today has to be capable of synthesizing a small library of hydrophobic gels from which he or she can then select and optimize the ideal matrix for their special needs. In addition, a general optimization method employing the critical hydrophobicity concept has now been devised that should allow the application of HIC methodology to many hitherto unpurified proteins. In this chapter, the reader is first introduced to the theoretical background (multivalence, negative cooperativity, adsorption hysteresis) of the binding of protein ligands to hydrophobic supports, so that they will be capable of independently adapting HIC to a novel protein. Then a simple nontoxic method is described for the synthesis of HIC-gel libraries consisting of a homologous series of uncharged alkyl-Sepharoses of three chain lengths (butyl, pentyl, and hexyl Sepharose) prepared with different degrees of separation. From this series a critical hydrophobicity gel can then be selected and employed for critical hydrophobicity HIC. A detailed example for the chromatography of human fibrinogen is given that has been employed as a one-step procedure for the purification of fibrinogen from human plasma.

Accelerated and improved osteointegration of implants biocoated with bone morphogenetic protein 2 (BMP-2).

A concept and methodology are presented for the direct biocoating of implantable metals like titanium and stainless steel with bone morphogenetic protein 2 (BMP-2) for future applications as cementless bone or dental prostheses. Such bioactive surfaces can influence cells and tissues by chemotactic as well as juxtacrine mechanisms. Reference is made to first experiments in sheep and rabbits in which BMP-2 coatings impressively increased the osteoinductive potential of titanium implants.