Oxidation-sensitive polymeric nanoparticles

Polymers and Sulfur: what are Organic Polysulfides Good For? Preparative Strategies and Biological Applications

Sulfur(II)-containing polymers (polysulfides) combine flexible synthetic and processing techniques with a unique responsiveness to oxidants. Here, the polysulfide oxidative sensitivity is put into the biological context of the development of new anti-inflammatory therapies - the development of new anti-inflammatory methodologies, adopted interactions and the minimisation of foreign-body reactions - through the review of 50 years of research on polysulfide synthetic methodologies. Attention is paid to the identification of the most flexible and robust preparative techniques.

Probing (macro)molecular transport through cell walls

We here report a study on the passive permeability of hydrophobic probes through the cell wall of Saccharomyces cerevisiae. In this study we have prepared a series of fluorescent probes with similar chemical composition and molecular weight ranging from a few hundreds to a few thousands of g mol(-1). Their permeation into the cell body exhibits a clear MW cut-off and the underlying mechanism is governed by the permeation of individual molecules rather than aggregates. We also show that it is possible to reversibly alter the cell wall permeation properties without compromising the essence of its structure, by modifying the polarity/dielectric constant of the wall through solvent exchange.

PEG-b-PPS diblock copolymer aggregates for hydrophobic drug solubilization and release: cyclosporin A as an example

Micelles formed from amphiphilic block copolymers have been explored in recent years as carriers for hydrophobic drugs. In an aqueous environment, the hydrophobic blocks form the core of the micelle, which can host lipophilic drugs, while the hydrophilic blocks form the corona or outer shell and stabilize the interface between the hydrophobic core and the external medium. In the present work, mesophase behavior and drug encapsulation were explored in the AB block copolymeric amphiphile composed of poly(ethylene glycol) (PEG) as a hydrophile and poly(propylene sulfide) PPS as a hydrophobe, using the immunosuppressive drug cyclosporin A (CsA) as an example of a highly hydrophobic drug. Block copolymers with a degree of polymerization of 44 on the PEG and of 10, 20 and 40 on the PPS respectively (abbreviated as PEG44-b-PPS10, PEG44-b-PPS20, PEG44-b-PPS40) were synthesized and characterized. Drug-loaded polymeric micelles were obtained by the cosolvent displacement method as well as the remarkably simple method of dispersing the warm polymer melt, with drug dissolved therein, in warm water. Effective drug solubility up to 2 mg/mL in aqueous media was facilitated by the PEG- b-PPS micelles, with loading levels up to 19% w/w being achieved. Release was burst-free and sustained over periods of 9-12 days. These micelles demonstrate interesting solubilization characteristics, due to the low glass transition temperature, highly hydrophobic nature, and good solvent properties of the PPS block.

Biofunctional polymer nanoparticles for intra-articular targeting and retention in cartilage

The extracellular matrix of dense, avascular tissues presents a barrier to entry for polymer-based therapeutics, such as drugs encapsulated within polymeric particles. Here, we present an approach by which polymer nanoparticles, sufficiently small to enter the matrix of the targeted tissue, here articular cartilage, are further modified with a biomolecular ligand for matrix binding. This combination of ultrasmall size and biomolecular binding converts the matrix from a barrier into a reservoir, resisting rapid release of the nanoparticles and clearance from the tissue site. Phage display of a peptide library was used to discover appropriate targeting ligands by biopanning on denuded cartilage. The ligand WYRGRL was selected in 94 of 96 clones sequenced after five rounds of biopanning and was demonstrated to bind to collagen II alpha1. Peptide-functionalized nanoparticles targeted articular cartilage up to 72-fold more than nanoparticles displaying a scrambled peptide sequence following intra-articular injection in the mouse.

Oxidation-responsiveness of nanomaterials for targeting inflammatory reactions

Oxidation is an almost ubiquitous feature of inflammatory reactions. We discuss the development of nanocarriers that respond to the presence of oxidants with profound physical reorganization, which could in perspective allow their use for delivering anti-inflammatory principles in an inflammation-responsive fashion. We also present a study demonstrating that the response of polysulfide nanoparticles has a bulk character, i.e., the odixation reactions happen homogeneously throughout the nanoparticles, and not interfacially.

Emulsion macromonomer cross-linking. A preparative method for oxidation-responsive nanoparticles with a controlled network structure

We here report on a preparative, template-based method for oxidation-responsive, poly(propylene sulfide) cross-linked nanoparticles. In this study we demonstrate that preformed, narrow polydispersity, and end-functional polysulfides can be dispersed to yield stable emulsions, which can then be converted into stable nanoparticles through photochemically initiated cross-linking. The nanoparticle size is substantially templated on that of the precursor emulsions; the nanoparticles bulk is an elastomeric material with a homogeneous cross-linking density. The nanoparticles show a peculiar, two-stage behavior upon exposure to oxidants, which is likely composed of a first agglomeration phase followed by swelling.

Controlled release drug coatings on flexible neural probes

We present the development, characterization and in vivo validation of a novel drug eluting coating that has been applied to flexible neural probes. The coating consists of drug eluting nanoparticles loaded with an anti-inflammatory drug embedded in a biodegradable polymer. The drug eluting coating is applied to flexible polymer neural probes with platinum electrodes. The drug eluting device is implanted in one hemisphere of a rat, while a control device is implanted in the opposite hemisphere. Impedance measurements are performed to determine the effect of the drug eluting coating on the tissue reaction surrounding the probe and the electrical characteristics of the devices. Probes that are coated with drug eluting coatings show better long term impedance characteristics over control probes. These coatings can be used to increase the reliability and long term success of neural prostheses.

Chemical modification of therapeutic drugs or drug vector systems to achieve targeted therapy: looking for the grail

Most therapeutic drugs distribute to the whole body, which results in general toxicity and poor acceptance of the treatments by patients. The targeted delivery of chemotherapeutics to defined cells, either stromal or cancer cells in cancer lesions, or defined inflammatory cells in immunological disorders, is one of the main challenges and a very active field of research in the development of treatment strategies to minimize side-effects of drugs. Disease-associated cells express molecules, including proteases, receptors, or adhesion molecules, that are different or differently expressed than their normal counterparts. Therefore one goal in the field of targeted therapies is to develop chemically derivatized drugs or drug vectors able to target defined cells via specific recognition mechanisms and also able to overcome biological barriers. This article will review the approaches which have been explored to achieve these goals and will discuss in more detail three examples (i) the use of nanostructures to take advantage of increased vascular permeability in some human diseases, (ii) the targeting of therapeutic drugs to an organ, the brain, protected against foreign molecules by the blood-brain barrier, and (iii) the use of the folate receptor to target either tumor cells or activated macrophages.

Exploiting lymphatic transport and complement activation in nanoparticle vaccines

Antigen targeting and adjuvancy schemes that respectively facilitate delivery of antigen to dendritic cells and elicit their activation have been explored in vaccine development. Here we investigate whether nanoparticles can be used as a vaccine platform by targeting lymph node-residing dendritic cells via interstitial flow and activating these cells by in situ complement activation. After intradermal injection, interstitial flow transported ultra-small nanoparticles (25 nm) highly efficiently into lymphatic capillaries and their draining lymph nodes, targeting half of the lymph node-residing dendritic cells, whereas 100-nm nanoparticles were only 10% as efficient. The surface chemistry of these nanoparticles activated the complement cascade, generating a danger signal in situ and potently activating dendritic cells. Using nanoparticles conjugated to the model antigen ovalbumin, we demonstrate generation of humoral and cellular immunity in mice in a size- and complement-dependent manner.

Synthesis and Properties of Amphiphilic Star Polysulfides

We here present the synthesis and characterisation of linear and star-shaped amphiphilic block copolymers based on hydrophobic polysulfides (poly(propylene sulfide), PPS) and hydrophilic polyethers (poly(ethylene glycol), PEG). We also discuss the proof of the principle of their responsiveness to oxidising conditions. In a water environment, these polymers aggregate in the form of sub-micron carriers that, due to the sensitivity to oxidation reactions typical of PPS, can be used for responsive drug delivery. In this first study we have focused on the study of large aggregates, which do not apparently show dramatic differences in behaviour when polymer chains with different degrees of branching are studied.

Targeting dendritic cells with biomaterials: developing the next generation of vaccines

Current vaccine and immunotherapy technology faces ongoing challenges in both efficacy and practicality: many chronic diseases cannot yet be addressed by vaccination, and several vaccines that do function well require multiple injections, which is a substantial limitation in various parts of the world. A possible key to developing the next generation of vaccines is the ability to deliver antigen to dendritic cells (DCs) more specifically and induce the subsequent activation of T-cell immunity. However, antigen delivery to, and activation of, DCs is a complex problem, involving antigen transport to DC-rich areas, DC binding and antigen uptake, and antigen processing and presentation. Addressing these challenges requires novel and multidisciplinary approaches, for example, the application of biomaterials to immunotechnology. Here, we review the latest advances in biomaterial drug vehicles, such as polymer microparticles and nanoparticles, and liposomes, that are being used to target DCs in new strategies for vaccination.

In vivo targeting of dendritic cells in lymph nodes with poly(propylene sulfide) nanoparticles

Delivery of biodegradable nanoparticles to antigen-presenting cells (APCs), specifically dendritic cells (DCs), has potential for immunotherapy. This study investigates the delivery of 20, 45, and 100nm diameter poly(ethylene glycol)-stabilized poly(propylene sulfide) (PPS) nanoparticles to DCs in the lymph nodes. These nanoparticles consist of a cross-linked rubbery core of PPS surrounded by a hydrophilic corona of poly(ethylene glycol). The PPS domain is capable of carrying hydrophobic drugs and degrades within oxidative environments. 20 nm particles were most readily taken up into lymphatics following interstitial injection, while both 20 and 45nm nanoparticles showed significant retention in lymph nodes, displaying a consistent and strong presence at 24, 72, 96 and 120h post-injection. Nanoparticles were internalized by up to 40-50% of lymph node DCs (and APCs) without the use of a targeting ligand, and the site of internalization was in the lymph nodes rather than at the injection site. Finally, an increase in nanoparticle-containing DCs (and other APCs) was seen at 96h vs. 24h, suggesting an infiltration of these cells to lymph nodes. Thus, PPS nanoparticles of 20-45nm have the potential for immunotherapeutic applications that specifically target DCs in lymph nodes.

Synthesis and Unexpected Reactivity of Iron Tris(bipyridine) Complexes with Poly(ethylene glycol) Macroligands

High molecular weight poly(ethylene glycol) (PEG) derivatized iron tris(bipyridine) complexes, presenting hydroxyl end groups for further modification as bioconjugates, copolymers, or cross-linking agents, were synthesized via ring-opening anionic polymerization of ethylene oxide from hydroxyl-functionalized bipyridine (bpy) initiators and subsequent chelation to iron(II). Bpy-centered PEG macroligands (bpyPEG(2)) with molecular weights ranging from 4,000 to 17,000 and low polydispersity indices (<1.1) were obtained. Chelation of the bpyPEG(2) macroligands to iron(II) sulfate was studied in aqueous solution by titration and kinetics experiments, which revealed unexpected air sensitivity compared to nonpolymeric iron tris(bipyridine) complexes. Red-violet aqueous solutions of [Fe(bpyPEG(2))(3)](2+) begin to bleach within hours when exposed to air. Enhanced polymer degradation and gel formation of acrylate-modified bpyPEG(2) in the presence of Fe(2+) suggest that radicals may be involved. Under argon, the chromophores are stable. Polymeric iron complexes are slower to form and faster to degrade in air with increasing bpyPEG(2) molecular weight. These studies demonstrate the influence of molecular weight in polymeric iron tris(bipyridine) complex coordination chemistry and reactivity.

Development of a new colorimetric method determining the yield of microencapsulation of alpha-tocopherol

Microencapsulation of alpha-tocopherol effectively protects alpha-tocopherol from oxidation and produces high-value-added and long-shelf-stable foods. High-performance liquid chromatography (HPLC) has been applied to measure the yield of microencapsulated alpha-tocopherol with high accuracy; however, it takes long analysis time. An alternative method is required to determine the yield of microencapsulated alpha-tocopherol in food industry. A new, easy, and sensitive colorimetric method using 5% cupric acetate pyridine and oleic acid was developed. Correlation coefficient (r) of colorimetric method on alpha-tocopherol in microencapsulation system and of results between colorimetric method and HPLC were +0.996 and +0.989, respectively, which indicates that this novel colorimetric method can be successfully applied to evaluate the yield of microencapsulated alpha-tocopherol instead of HPLC. The optimum storage temperature and pH of microencapsulated alpha-tocopherol for 7-day storage were 25 degrees C and pH 9, respectively, determined by this new colorimetric method.