Conjugation of proteins and enzymes with hydrophilic polymers and their applications.

The efficacy of a number of therapeutically active proteins and peptides is severely limited due to their instability in circulation. Of the various approaches used to stabilise these proteins, the one more successful is covalent modification of the protein or enzyme with some hydrophilic polymers such as dextran or PEG. These conjugates are more stable than the native protein both in vitro as well as in vivo. They exhibit enhanced resistant to proteolytic degradation, have a long-life in circulation and exhibit reduced immunogenicity. The therapeutic efficacy of these conjugates is also greatly enhanced compared to the native protein or enzyme.     

Biomedical applications of nisin

Nisin is a bacteriocin produced by a group of Gram‐positive bacteria that belongs to Lactococcus and Streptococcus species. Nisin is classified as a Type A (I) lantibiotic that is synthesized from mRNA and the translated peptide contains several unusual amino acids due to post‐translational modifications. Over the past few decades, nisin has been used widely as a food biopreservative. Since then, many natural and genetically modified variants of nisin have been identified and studied for their unique antimicrobial properties. Nisin is FDA approved and generally regarded as a safe peptide with recognized potential for clinical use. Over the past two decades the application of nisin has been extended to biomedical fields. Studies have reported that nisin can prevent the growth of drug‐resistant bacterial strains, such as methicillin‐resistant Staphylococcus aureus, Streptococcus pneumoniae, Enterococci and Clostridium difficile. Nisin has now been shown to have antimicrobial activity against both Gram‐positive and Gram‐negative disease‐associated pathogens. Nisin has been reported to have anti‐biofilm properties and can work synergistically in combination with conventional therapeutic drugs. In addition, like host‐defence peptides, nisin may activate the adaptive immune response and have an immunomodulatory role. Increasing evidence indicates that nisin can influence the growth of tumours and exhibit selective cytotoxicity towards cancer cells. Collectively, the application of nisin has advanced beyond its role as a food biopreservative. Thus, this review will describe and compare studies on nisin and provide insight into its future biomedical applications.     

Biomedical applications of protein chips

The development of microchips involving proteins has accelerated within the past few years. Although DNA chip technologies formed the precedent, many different strategies and technologies have been used because proteins are inherently a more complex type of molecule. This review covers the various biomedical applications of protein chips in diagnostics, drug screening and testing, disease monitoring, drug discovery (proteomics), and medical research. The proteomics and drug discovery section is further subdivided to cover drug discovery tools (on-chip separations, expression profiling, and antibody arrays), molecular interactions and signaling pathways, the identification of protein function, and the identification of novel therapeutic compounds. Although largely focused on protein chips, this review includes chips involving cells and tissues as a logical extension of the type of data that can be generated from these microchips.     

Well-defined DNA-mimic brush polymers bearing adenine moieties: synthesis, layer-by-layer self-assembly, and biocompatibility

Two new DNA-mimicking brush polymers were synthesized: poly[oxy(11-(3-(9-adeninyl)propionato)-undecanyl-1-thiomethyl)ethylene] (PECH-AP) and poly[oxy(11-(5-(9-adenylethyloxy)-4-oxopentanoato)undecanyl-1-thiomethyl)ethylene] (PECH-AS). These polymers were found to be thermally stable up to 220 °C and could be applied easily by conventional coating processes to produce good quality films. Interestingly, both brush polymers formed molecular multibilayer structures to provide an adenine-rich surface. Despite the structural similarities, PECH-AS surprisingly exhibited higher hydrophilicity and better water sorption properties than PECH-AP. These differences were attributed to the chemical structures in the bristles of the polymers. The adenine-rich surfaces of the polymer films demonstrated selective protein adsorption, suppressed bacterial adherence, facilitated HEp-2 cell adhesion, and exhibited good biocompatibility in mice. However, the high hydrophilicity and good water sorption characteristics of the PECH-AS film suggest that this brush polymer is better suited to applications requiring good biocompatibility and reduced chance of bacterial infection compared with the PECH-AP film.     

Biomedical applications of degradable polyphosphazenes

This article describes the synthesis of biodegradable polyphosphazenes. The rate of degradation can be varied in a controllable manner by the introduction of hydrolysis-sensitive amino acid ester side groups or by blending of polymers. Biodegradable polyphosphazenes can be used for the preparation of drug-containing implants and this is illustrated for devices containing the cytostatic agent mitomycin C. This article reviews data about the degradation characteristics of poly[(amino acid ester)phosphazene] derivatives that have been discussed previously. Some new data about MMC-containing poly[(organo)phosphazene] devices are discussed as well. (c) 1996 John Wiley & Sons, Inc.     

Biomedical and agricultural applications of animal transgenesis

Additive transgenesis by pronuclear injection of the mouse zygote has been in use for more than 20 yr and gene targeting in mouse embryonic stem cells for almost as long. Together, these techniques have revolutionized animal biology by helping to unravel much of what we now know about gene function. Both additive transgenics and targeting can also be performed in livestock species but the impact has not yet been substantial. In part, this has been the result of the inefficiency of the techniques but—at least in agriculture—also to a lack of obvious practicality. This review assesses the extent to which this situation is changing, with particular reference to applications in biopharming, xenotransplantation, and large animal models.     

Biomedical applications of photon-induced X-ray fluorescence

An X-ray fluorescence method for in vitro analysis of trace elements is presented. The method is characterized by the use of an X-ray tube with secondary targets as a quasimonoenergetic radiation source, and by “infinitely thin” specimens. Different aspects have been examined in order to optimize the sensitivity of the method. It is extremely important to use secondary targets as pure as possible and collimators internally covered by the same element as the secondary target. It is also important to reduce the contribution at the XRF spectrum of photons scattered by the sample, by the sample support, and by the air. Preconcentration techniques can conveniently also be used to this purpose. In this work, biological samples are preconcentrated by reducing them to ash. Typical sensitivities obtained are in the order of 1–5 ng/cm² in a counting time of 10³ s for elements with atomic number ranging from 24 (chromium) to 40 (zirconium).     

Biomedical applications of multifunctional gold-based nanocomposites

Active application of gold nanoparticles for various diagnostic and therapeutic purposes started in recent decades due to the emergence of new data on their unique optical and physicochemical properties. In addition to colloidal gold conjugates, growth in the number of publications devoted to the synthesis and application of multifunctional nanocomposites has occurred in recent years. This review considers the application in biomedicine of multifunctional nanoparticles that can be produced in three different ways. The first method involves design of composite nanostructures with various components intended for either diagnostic or therapeutic functions. The second approach uses new bioconjugation techniques that allow functionalization of gold nanoparticles with various molecules, thus combining diagnostic and therapeutic functions in one medical procedure. Finally, the third method for production of multifunctional nanoparticles combines the first two approaches, in which a composite nanoparticle is additionally functionalized by molecules having different properties.     

Biomedical applications of fluorescence imaging in vivo

Optical imaging can advance knowledge of cellular biology and disease at the molecular level in vitro and, more recently, in vivo. In vivo optical imaging has enabled real-time study to track cell movement, cell growth, and even some cell functions. Thus, it can be used in intact animals for disease detection, screening, diagnosis, drug development, and treatment evaluation. This review includes a brief introduction to fluorescence imaging, fluorescent probes, imaging devices, and in vivo applications in animal models. It also describes a quantitative fluorescence detection method with a reconstruction algorithm for determining the location of fluorophores in tissue and addresses future applications of in vivo fluorescence imaging.     

Comments on diffusive and electrostatic effects with immobilized enzymes

Shuler, Aris &; Tsuchiya (1972) have recently considered the combined effects of diffusive resistance and electrostatic field on the rate of reaction catalyzed by an enzyme immobilized on a non-porous surface. They employed a potential distribution for the electrical double layer which is asymptotically valid when surface potential is small.The complete Gouy-Chapman solution, which is valid for higher surface potential, is employed here. Numerical values of the effectiveness factor calculated with this potential distribution agree very closely with the results of Shuler et al. for most cases. It is shown that the effectiveness factor can (i) attain magnitudes much greater than unity in physically realizable systems, (ii) approach the solution for “infinite” surface potential at reasonable values of surface charge density, and (iii) pass through a maximum as bulk substrate concentration is varied. This behavior leads to the existence of an optimum surface concentration for enzyme immobilized on a highly charged non-porous support such that the most effective catalytic action on a charged substrate is ensured. Finally, it is established that significant electrical and/or diffusive effects result in non-linear Lineweaver-Burk plots of reciprocal observed reaction velocity against reciprocal bulk substrate concentration. These non-linear plots cannot be interpreted in the same way as linear plots obtained when enzyme is unbound.     

Relationship between catalytic properties, fixed charge concentration and electrostatic potential of polyelectrolyte-bound enzymes

An equation for the calculation of the electrostatic potentials of polyelectrolyte-enzyme supports from electrostatic parameters has been derived by relating two different theories which describe the catalytic behaviour of polyelectrolyte-bound enzymes. The electrostatic potentials of polyionic supports have been determined by use of experimental results, on the one hand, from the fixed charge concentration and the ionic strength, on the other hand, from pH- and Km-shifts of immobilized enzymes. The accordance of potentials calculated from electrostatic and kinetic parameters confirms the macroscopic carrier-enzyme model.     

Migration of enzymes on linear polymers

We present a simple model based on the kinetics of DNA-dependent ATPases where the probability for enzyme migration on the linear activating polymer depends on the rate equations at the steady state. It is shown how the chemical velocity of the reaction is correlated to the average kinematic velocity along the polymer. The implications of this result are discussed.     

Photoelectrochemical, photophysical and morphological studies of electrostatic layer-by-layer thin films based on poly(p-phenylenevinylene) and single-walled carbon nanotubes

The preparation of multilayer films based on poly(p-phenylenevinylene) (PPV) and carboxylic-functionalized single-walled carbon nanotubes (SWNT-COOH) by electrostatic interaction using the layer-by-layer (LbL) deposition method is reported herein. The multilayer build-up, monitored by UV-Vis and photoluminescence (PL) spectroscopies, displayed a linear behavior with the number of PPV and SWNT-COOH layers deposited that undergo deviation and spectral changes for thicker films. Film morphology was evaluated by AFM and epifluorescence microscopies showing remarkable changes after incorporation of SWNT-COOH layers. Films without SWNT show roughness and present dispersed grains; films with SWNT-COOH layers are flatter and some carbon nanotube bundles can be visualized. The photoinduced charge transfer from the conducting polymer to SWNT-COOH was analyzed by PL quenching either by the decrease of the emission intensity or by the presence of dark domains in the epifluorescence micrographs. Photoelectrochemical characterization was performed under white light and the films containing SWNT-COOH displayed photocurrent values between 2.0 μA cm(-2) and 7.5 μA cm(-2), as the amount of these materials increases in the film. No photocurrent was observed for the film without carbon nanotubes. Photocurrent generation was enhanced and became more stable when an intermediate layer of PEDOT:PSS was interposed between the active layer and the ITO electrode, indicating an improvement in hole transfer to the contacts. Our results indicate that these multilayer films are promising candidates as active layers for organic photovoltaic cells.     

Antimicrobial polymers: mechanism of action,factors of activity,and applications

Complex epidemiological situation, nosocomial infections, microbial contamination, and infection risks in hospital and dental equipment have led to an ever-growing need for prevention of microbial infection in these various areas. Macromolecular systems, due to their properties, allow one to efficiently use them in various fields, including the creation of polymers with the antimicrobial activity. In the past decade, the intensive development of a large class of antimicrobial macromolecular systems, polymers, and copolymers, either quaternized or functionalized with bioactive groups, has been continued, and they have been successfully used as biocides. Various permanent microbicidal surfaces with non-leaching polymer antimicrobial coatings have been designed. Along with these trends, new moderately hydrophobic polymer structures have been synthesized and studied, which contain protonated primary or secondary/tertiary amine groups that exhibited rather high antimicrobial activity, often unlike their quaternary analogues. This mini-review briefly highlights and summarizes the results of studies during the past decade and especially in recent years, which concern the mechanism of action of different antimicrobial polymers and non-leaching microbicidal surfaces, and factors influencing their activity and toxicity, as well as major applications of antimicrobial polymers.     

Biomedical applications of glyconanoparticles based on quantum dots

Background

Quantum dots (QDs) are outstanding nanomaterials of great interest to life sciences. Their conjugation versatility added to unique optical properties, highlight these nanocrystals as very promising fluorescent probes. Among uncountable new nanosystems, in the last years, QDs conjugated to glycans or lectins have aroused a growing attention and their application as a tool to study biological and functional properties has increased.

Biomedical applications of the ESRF synchrotron-based microspectroscopy platform

Very little is known about the sub-cellular distribution of metal ions in cells. Some metals such as zinc, copper and iron are essential and play an important role in the cell metabolism. Dysfunctions in this delicate housekeeping may be at the origin of major diseases. There is also a prevalent use of metals in a wide range of diagnostic agents and drugs for the diagnosis or treatment of a variety of disorders. This is becoming more and more of a concern in the field of nanomedicine with the increasing development and use of nanoparticles, which are suspected of causing adverse effects on cells and organ tissues. Synchrotron-based X-ray and Fourier-transformed infrared microspectroscopies are developing into well-suited sub-micrometer analytical tools for addressing new problems when studying the role of metals in biology. As a complementary tool to optical and electron microscopes, developments and studies have demonstrated the unique capabilities of multi-keV microscopy: namely, an ultra-low detection limit, large penetration depth, chemical sensitivity and three-dimensional imaging capabilities. More recently, the capabilities have been extended towards sub-100nm lateral resolutions, thus enabling sub-cellular chemical imaging. Possibilities offered by these techniques in the biomedical field are described through examples of applications performed at the ESRF synchrotron-based microspectroscopy platform (ID21 and ID22 beamlines).