Skin and wound delivery systems for antimicrobial peptides

Non-healing wounds cause hundreds of thousands of deaths every year, and result in large costs for society. A key reason for this is the prevalence of challenging bacterial infections, which may dramatically hinder wound healing. With resistance development among bacteria against antibiotics, this situation has deteriorated during the last couple of decades, pointing to an urgent need for new wound treatments. In particular, this applies to wound dressings able to combat bacterial infection locally in wounds and impaired skin, including those formed by bacteria resistant to conventional antibiotics. Within this context, antimicrobial peptides (AMPs) are currently receiving intense interest. AMPs are amphiphilic peptides, frequently net positively charged, and with a sizable fraction of hydrophobic amino acids. Through destabilization of bacterial membranes, neutralization of inflammatory lipopolysaccharides, and other mechanisms, AMPs can be designed for potent antimicrobial effects, also against antibiotics-resistant strains, and to provide immunomodulatory effects while simultaneously displaying low toxicity. While considerable attention has been placed on AMP optimization and clarification of their mode(s)-of-action, much less attention has been paid on efficient AMP delivery. Considering that AMPs are large molecules, net positively charged, amphiphilic, and susceptible to infection-mediated proteolytic degradation, efficient in vivo delivery of such peptides is, however, challenging and delivery systems needed for the realization of AMP-based therapeutics. In the present work, recent developments regarding AMP delivery systems for treatment of wounds and skin infections are discussed, with the aim to link results from physicochemical studies on, e.g., peptide loading/release, membrane interactions, and self-assembly, with those on the biological functional performance of AMP delivery systems in terms of antimicrobial effects, cell toxicity, inflammation, and wound healing.     

Interaction between amphiphilic peptides and phospholipid membranes

This brief review aims at providing some illustrative examples on the interaction between amphiphilic peptides and phospholipid membranes, an area of significant current interest. Focusing on antimicrobial peptides, factors affecting peptide–membrane interactions are addressed, including effects of peptide length, charge, hydrophobicity, secondary structure, and topology. Effects of membrane composition are also illustrated, including effects of membrane charge, nature of the polar headgroup, and presence of cholesterol and other sterols. Throughout, novel insights on the importance of peptide adsorption density on membrane stability are emphasized, as is the correlation between peptide adsorption, peptide-induced leakage in model liposome systems, peptide-induced lysis of bacteria, and bacteria killing.     

Effect of hydrophobic modifications in antimicrobial peptides

With increasing resistance development against conventional antibiotics, there is an urgent need to identify novel approaches for infection treatment. Antimicrobial peptides may offer opportunities in this context, hence there has been considerable interest in identification and optimization of such peptides during the last decade in particular, with the long-term aim of developing these to potent and safe therapeutics. In the present overview, focus is placed on hydrophobic modifications of antimicrobial peptides, and how these may provide opportunities to combat also more demanding pathogens, including multi-resistant strains, yet not provoking unacceptable toxic responses. In doing so, physicochemical factors affecting peptide interactions with bacterial and eukaryotic cell membranes are discussed. Throughout, an attempt is made to illustrate how physicochemical studies on model lipid membranes can be correlated to result from bacterial and cell assays, and knowledge from this translated into therapeutic considerations.     

Loading of gold nanoparticles inside the DPPC bilayers of liposome and their effects on membrane fluidities

Gold nanoparticles were loaded in the bilayer of dipalmitoylphosphatidylcholine (DPPC) liposomes, named as gold-loaded liposomes. Above the gel to liquid-crystalline phase transition temperature, membrane fluidities of DPPC liposomes were changed by loading the gold nanoparticles. Compared with liposomes without loading the gold nanoparticles, gold-loaded liposomes showed the lower fluorescence anisotropy values. That is, the membrane fluidities of DPPC bilayer were increased by loading the gold nanoparticles. The membrane fluidities were increased as the amount of gold nanoparticles increased. The existence of gold nanoparticles in the DPPC bilayer was observed by transmission electron microscopy. Through the energy dispersive X-ray spectrometer, the particles in DPPC bilayer were confirmed to be gold nanoparticles.     

A perspective on general direction and challenges facing antimicrobial peptides

The emergence of drug resistant bacterium threatens the global public healthcare systems.The urgent need to obtain new antimicrobials has driven antimicrobial peptides(AMPs)research into spotlight.Here we give a brief introduction of the recent progress of AMPs regarding their structures,properties, production and modification,and antimicrobial mechanism.Thereby,this review will give an insight into the trends and challenges facing on this particular kind of antimicrobial materials.     

Design principles for bacteria-responsive antimicrobial nanomaterials

Despite advancements in biomedical sciences and medicine, bacterial infection remains a leading cause of death globally. The conventional treatment of bacterial infections through general administration of antibiotics has been challenged by the emergence of antibiotics resistance. An exciting direction to solve current challenges that attracted enormous interest in the last decade is focused on designing stimuli-responsive systems incorporating a wide range of antimicrobial nanomaterials. The aim of this review is to highlight fundamental principles involved in the design of bacteria-responsive nanosystems that release their antibacterial load in response only to the specific environment and factors produced endogenously by bacteria. Such specific changes to the micro-environment include changes in pH, reactive oxygen species, and production of enzymes specific to bacteria. We provide examples and a critical review of such systems and finish with the authors’ perspective for the future of the field.     

Analytical characterization of chitosan nanoparticles for peptide drug delivery applications

Chitosan-cyclodextrin hybrid nanoparticles (NPs) were obtained by the ionic gelation process in the presence of glutathione (GSH), chosen as a model drug. NPs were characterized by means of transmission electron microscopy and zeta-potential measurements. Furthermore, a detailed X-ray photoelectron spectroscopy study was carried out in both conventional and depth-profile modes. The combination of controlled ion-erosion experiments and a scrupulous curve-fitting approach allowed for the first time the quantitative study of the GSH in-depth distribution in the NPs. NPs were proven to efficiently encapsulate GSH in their inner cores, thus showing promising perspectives as drug carriers.     

Criterion for amino acid composition of defensins and antimicrobial peptides based on geometry of membrane destabilization

Defensins comprise a potent class of membrane disruptive antimicrobial peptides (AMPs) with well-characterized broad spectrum and selective microbicidal effects. By using high-resolution synchrotron small-angle X-ray scattering to investigate interactions between heterogeneous membranes and members of the defensin subfamilies, α-defensins (Crp-4), β-defensins (HBD-2, HBD-3), and θ-defensins (RTD-1, BTD-7), we show how these peptides all permeabilize model bacterial membranes but not model eukaryotic membranes: defensins selectively generate saddle-splay ("negative Gaussian") membrane curvature in model membranes rich in negative curvature lipids such as those with phosphoethanolamine (PE) headgroups. These results are shown to be consistent with vesicle leakage assays. A mechanism of action based on saddle-splay membrane curvature generation is broadly enabling, because it is a necessary condition for processes such as pore formation, blebbing, budding, and vesicularization, all of which destabilize the barrier function of cell membranes. Importantly, saddle-splay membrane curvature generation places constraints on the amino acid composition of membrane disruptive peptides. For example, we show that the requirement for generating saddle-splay curvature implies that a decrease in arginine content in an AMP can be offset by an increase in both lysine and hydrophobic content. This "design rule" is consistent with the amino acid compositions of 1080 known cationic AMPs.     

Rationalizing the membrane interactions of cationic amphipathic antimicrobial peptides by their molecular shape

Biophysical and structural studies of cationic amphipathic antimicrobial peptides have revealed new mechanistic details concerning their membrane interactions. In interfacial environments the peptides adopt amphipathic conformations and the resulting distribution of polar, charged and hydrophobic residues allows them to partition into the bilayer interface. For several helical peptides it was found that their long axis is oriented parallel to the membrane surface, an arrangement which results in considerable perturbations in the packing of the lipid bilayer. Within the molecular shape concept the peptides act as wedge-like structures which impose positive curvature strain on the membrane. As a consequence a wide variety of morphologies are observed of peptide–lipid mixtures which strongly depend on the detailed peptide sequence, the membrane lipid composition, buffer, temperature and other environmental parameters. Therefore, the peptide–lipid systems are best described by phase diagrams, similar to the ones of detergent–lipid mixtures, encompassing on the one extreme regions where the peptide stabilizes the bilayer and on the other extreme regions where membrane lysis occurs. The effects of peptide sequence, membrane penetration depth, lipid composition and membrane surface charge density on membrane-association, -morphology and the resulting phase boundaries are discussed.     

The effects of solution structure on the surface conformation and orientation of a cysteine-terminated antimicrobial peptide cecropin P1

The surface structure of an antimicrobial peptide, cecropin P1, immobilized to a gold surface via a terminal cysteine residue was investigated. Using reflection-absorption infrared spectroscopy, surface plasmon resonance, and X-ray photoelectron spectroscopy, the effects of pH, solution conformation, and concentration on the immobilized peptide conformation, average orientation, and surface density were determined. Under all conditions investigated, the immobilized peptides were α-helical in a predominately flat, random orientation. The addition of the reducing agent Tris(2-carboxyethyl) phosphine hydrochloride to the buffer resulted in a twofold increase in immobilized peptide surface density.     

An efficient method for the solid-phase synthesis of fluorescently labelled peptides

Fluorescent labelling of peptides is necessary in a wide range of cell biological applications. In the last decade, the application of cell-penetrating molecules has been advanced by the use of peptides, which have proven efficient in aiding nonpermeant molecules to cross the cell membrane. Currently, the development of new cell-penetrating peptides based on the design and synthesis of labelled peptide libraries is becoming critically important. Here we report an improved method for the solid-phase labelling of peptides, mediated by the activation of 5(6)-carboxyfluorescein with PyAOP/ HOAt.     

Antibiotic enhanced dopamine polymerization for engineering antifouling and antimicrobial membranes

In this work,we adopt a new tobramycin(TOB)-dopamine coating system to endow thin film composite membranes with excellent antifouling and antimicrobial properties.Combining the hydrophilic and antibiofouling properties of both TOB and polydopamine,the TOB-dopamine modified membrane exhibits improved antifouling and antimicrobial properties compared with the conventional dopamine modified and unmodified membranes.The TOB-dopamine system has two advantages over the conventional modification with dopamine and tris buffer solution.First,TOB-dopamine modification is more efficient than the conventional dopamine modification due to the accelerating effect of TOB on dopamine polymerization.Second,the TOB-dopamine modified membranes exhibit better hydrophilicity,and enhanced antifouling and antimicrobial properties than the conventional dopamine modified membrane.Beyond engineering membranes,the proposed TOB-dopamine system can also be extended for wider surface hydrophilic and antimicrobial modifications.     

A supramolecular co-delivery strategy for combined breast cancer treatment and metastasis prevention

We herein propose a co-delivery approach where small interference RNA(siRNA) and anticancer chemotherapeutic drug are simultaneously loaded into a single delivery carrier for the combined treatment of breast cancer and metastasis prevention.The co-delivery vector is composed of chondroitin sulfate(CS)-coated β-cyclodextrin-polyethylenemine polymer,which is capable of loading paclitaxel(PTX) and siRNA simultaneously to form therapeutic nanocomplexes.The nanocomplex,termed as CPPTX-siCD146-CS,is d...     

Synthesis,characterization and effects of arm number on properties of amphiphilic polyurethanes as drug delivery carriers

Amphiphilic polyurethanes based on methoxy poly(ethylene glycol) (mPEG) and poly(?-caprolactone) diol (PCL) with different arm numbers such as two, three and four were successfully synthesized. Their structures were confirmed by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (¹H NMR) and gel permeation chromatography (GPC). The effects of arm number on properties of amphiphilic polyurethanes were studied. Pyrene fluorescence probe technique and dynamic light scattering (DLS) analyses showed that the CMC value and the micellar size of the resultant amphiphilic polyurethanes decreased and the micellar stability against dilution enhanced with increasing the arm number of polyurethane. Using indometacin (IMC) as a model drug, the results indicated that the drug loading capacity and in vitro drug sustained release effect of polyurethane with four arms were better than those of polyurethanes with two and three arms.     

Self-assembled fluorescent tripeptide nanoparticles for bioimaging and drug delivery applications

Peptide self-assembled nanomaterials have attracted more and more attention due to their wide applications such as drug delivery, cell imaging, and real-time drug monitoring. However, the application of the peptide is still limited by its inherent optical properties. Here we proposed and prepared a series of fluorescent tripeptide nanoparticles (TPNPs) through π-π stacking and zinc coordination. The experimental results show that the nanoparticles (TPNPs1) formed by the self-assembly of the tripeptide tryptophan-tryptophan-tryptophan have the highest fluorescence intensity, uniform and appropriate size, and low cytotoxicity. Furthermore, there was fluorescence resonance between TPNPs1 and doxorubicin, which has been successfully applied for real-time cell imaging and drug release monitoring.     

Self-assembled fluorescent tripeptide nanoparticles for bioimaging and drug delivery applications

Peptide self-assembled nanomaterials have attracted more and more attention due to their wide applications such as drug delivery, cell imaging, and real-time drug monitoring. However, the application of the peptide is still limited by its inherent optical properties. Here we proposed and prepared a series of fluorescent tripeptide nanoparticles (TPNPs) through π-π stacking and zinc coordination. The experimental results show that the nanoparticles (TPNPs1) formed by the self-assembly of the tripeptide tryptophan-tryptophan-tryptophan have the highest fluorescence intensity, uniform and appropriate size, and low cytotoxicity. Furthermore, there was fluorescence resonance between TPNPs1 and doxorubicin, which has been successfully applied for real-time cell imaging and drug release monitoring.     

中孔MCM-41负载Ru纳米粒子催化剂用于超声辐射下芳烃选择氧化反应

以中孔MCM-41为载体制得均一分散的粒径约5nm的Ru纳米粒子催化剂MCM-41-Ru,采用电感耦合等离子体、透射电镜、能量散射谱、X射线衍射和N2吸附-脱附法对其进行了表征,并将其作为可重复使用高效催化剂用于超声辅助芳烃选择氧化反应.结果表明,在超声辐射和KBrO3为氧化剂条件下,MCM-41-Ru催化剂加速了氧化反应,并以较高产率得到目的产物.回收的催化剂用于下次反应时活性保持不变,但其活性中心性质发生变化.     

Co-delivery of anticancer drugs and cell penetrating peptides for improved cancer therapy

Delivery systems based on nanoparticles (NPs) have shown great potential to reduce side effects and improve the therapeutic efficacy. Herein, we report the one-pot synthesis of poly(ethylene glycol)-mediated zeolitic imidazolate framework-8 (ZIF-8) NPs for the co-delivery of an anticancer drug (i.e., doxorubicin) and a cell penetrating peptide containing histidine and arginine (i.e., H4R4) to improve the efficacy of therapeutic delivery. The cargo-encapsulated ZIF-8 NPs are pH-responsive, which are stable at neutral pH and degradable at acidic pH to release the encapsulated cargos. The released H4R4 can help for endosome/lysosome escape to enhance the cytotoxicity of the encapsulated drugs. In vivo studies demonstrate that the co-delivery of doxorubicin and H4R4 peptides can efficiently inhibit tumor growth without significant side effects. The reported strategy provides a new perspective on the design of drug delivery systems and brings more opportunities for biomedical applications.     

Self-assembled thermosensitive luminescent nanoparticles with peptide-Au conjugates for cellular imaging and drug delivery

A facile and efficient strategy has been developed to fabricate a multifunctional,theranostic anticancer drug delivery platform featuring active targeting,controlled drug release and fluorescence imaging for real-time control of delivery.To this end,thermo sensitive poly(N-isopropyl acrylamide)(PNIPAM)nanospheres are decorated with peptide-Au cluster conjugates as a smart nanomedicine platform.A sophisticated trifunctional peptide is designed to release the anticancer drug doxorubicin(DOX),target cells and reduce Au^3+ions to form luminescent Au cluste rs.Importantly,the peptide-Au cluster moieties are attached to the PNIPAM nanospheres via amide bonds rather than noncovalent interactions,significantly improving their stability in biological medium and drug release efficiency.The in vitro experiments showed that DOX was released in an efficient and controlled manner under physiological conditions.     

PEG-stabilized palladium nanoparticles： An efficient and recyclable catalyst for the selective hydrogenation of 1,5-cyclooctadiene in thermoregulated PEG biphase system

Polyethylene glycol （PEG）-stabilized palladium nanoparticles were prepared and applied to the selective hydrogenation of 1,5- cyclooctadiene （1,5-COD） in thermoregulated PEG biphase system, which allows a reaction in a single-phase at a higher temperature followed by a phase split at a lower temperature. Under the optimized reaction conditions, the conversion of 1,5-COD and the selectivity of cyclooctene （COE） were 100 and 98%, respectively. The catalyst could be easily separated from the product by phase separation and reused for 6 times without evident loss in activity and selectivity. 2007 Yan Hua Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.