Host defense peptide mimicking cyclic peptoid polymers exerting strong activity against drug-resistant bacteria.

Extensive use of antibiotics accelerates the emergence of drug-resistant bacteria and related infections. Host defense peptides (HDPs) have been studied as promising and potential therapeutic candidates. However, their clinical applications of HDPs are limited due to their high cost of synthesis and low stability upon proteolysis. Therefore, HDP mimics have become a new approach to address the challenge of bacterial resistance. In this work, we design the amphiphilic peptoid polymers by mimicking the positively charged and hydrophobic structures of HDPs and synthesize a series of cyclic peptoid polymers efficiently via the polymerization on α-amino acid N-substituted glycine N-carboxyanhydrides (α-NNCAs) using 1,8-diazabicycloundec-7-ene (DBU) as the initiator. The optimal cyclic peptoid polymer, poly(Naeg0.7Npfbg0.3)20, displays strong antibacterial activities against drug-resistant bacteria, but low hemolysis and cytotoxicity. In addition, the mode-of-action study indicates that the antibacterial mechanism is associated with bacterial membrane interaction. Our study implies that HDP mimicking cyclic peptoid polymers have potential application in treating drug-resistant bacterial infections.

Structural design and antimicrobial properties of polypeptides and saccharide-polypeptide conjugates.

The problems of microbial infections and the emergence of drug-resistant microbes are increasingly serious, causing countless loss of lives and economic loss. The discovery and study of host defense peptides opened a new avenue in developing antimicrobial regents, and have attracted a lot of attention in recent years. Compared with natural host defense peptides, synthetic antimicrobial polypeptides can be conveniently synthesized in large scale and with low cost. Furthermore, saccharide-polypeptide conjugates have been valued for their optimal effect on antimicrobial properties and biocompatibility. In this review article, we provide an overview of the development and progress of antimicrobial polypeptides and saccharide-polypeptide conjugates regarding their structural design, biological functions and antimicrobial mechanism. By pointing out the challenges, we also provide future prospects of this research field from our perspectives.

Preparation of a novel asymmetric wettable chitosan-based sponge and its role in promoting chronic wound healing.

Cutaneous chronic wounds are characterized by an impaired wound healing which may lead to infection. To surmount this problem, a novel quaternary ammonium chitosan nanoparticles (TMC NPs)/chitosan (CS)composite sponge with asymmetric wettability surfaces was successfully prepared. The optimum concentrations of TMC NPs and CS were 0.2 mg/mL and 2.0%, respectively. The incorporated TMC NPs could improve the antibacterial activity of the CS sponge. Asymmetric modification enables the CS sponge to have hydrophobic outer surface and hydrophilic inner surface. The hydrophobic surface of the sponge shows waterproof and anti-adhesion contaminant properties, whereas the hydrophilic surface preserves water-absorbing capability and efficiently inhibits the growth of bacteria. More importantly, in vivo chronic wound healing model evaluation reveals that TMC NPs/CS composite sponge promotes the wound healing and accelerates re-epithelialization and angiogenesis. And in vivo anti-infection test shows the TMC NPs/CS composite sponge could effectively prevent wound infection. These findings demonstrate that TMC NPs/CS composite sponge is a promising dressing material for chronic wounds.

Striatisporolide A, a butenolide metabolite from Athyrium multidentatum (Doll.) Ching, as a potential antibacterial agent.

The present study aimed to investigate the antibacterial activity of striatisporolide A (SA) against Escherichia coli (E. coli) and the underlying mechanism. Antibacterial activity was evaluated according to the inhibitory rate and zone of inhibition. The antibacterial mechanism was investigated by analyzing alkaline phosphatase (AKP) activity and ATP leakage, protein expression, cell morphology and intracellular alterations in E. coli. The results demonstrated that SA exerted bacteriostatic effects on E. coli in vitro. AKP activity and ATP leakage analysis revealed that SA damaged the cell wall and cell membrane of E. coli. SDS­PAGE analysis indicated that SA notably altered the level of 10 and 35 kDa proteins. Scanning electron microscopy and transmission electron microscopy analyses revealed marked alterations in the morphology and ultrastructure of E. coli following treatment with SA. The mechanism underlying the antimicrobial effects of SA against E. coli may be attributed to its actions of disrupting the cell membrane and cell wall and regulation of protein level. The findings of the present study provide novel insight into the antimicrobial activity of SA as a potential natural antibacterial agent.

Carboxymethyl chitosan nanoparticles loaded with bioactive peptide OH-CATH30 benefit nonscar wound healing.

BACKGROUND: Nonscar wound healing is a desirable treatment for cutaneous wounds worldwide. Peptide OH-CATH30 (OH30) from king cobra can selectively regulate the innate immunity and create an anti-inflammatory micro-environment which might benefit nonscar wound healing. PURPOSE: To overcome the enzymatic digestion and control release of OH30, OH30 encapsulated in carboxymethyl chitosan nanoparticles (CMCS-OH30 NP) were prepared and their effects on wound healing were evaluated. METHODS: CMCS-OH30 NP were prepared by mild ionic gelation method and properties of the prepared CMCS-OH30 NP were determined by dynamic light scattering. Encapsulation efficiency, stability and release profile of OH30 from prepared CMCS-OH30 NP were determined by HPLC. Cytotoxicity, cell migration and cellular uptake of CMCS-OH30 NP were determined by conventional methods. The effects of prepared CMCS-OH30 NP on the wound healing was investigated by full-thickness excision animal models. RESULTS: The release of encapsulated OH30 from prepared CMCS-OH30 NP was maintained for at least 24 h in a controlled manner. CMCSOH30 NP enhanced the cell migration but had no effects on the metabolism and proliferation of keratinocytes. In the full-thickness excision animal models, the CMCS-OH30 NP treatment significantly accelerated the wound healing compared with CMCS or OH30 administration alone. Histopathological examination suggested that CMCS-OH30 NP promoted wound healing by enhancing the granulation tissue formation through the re-epithelialized and neovascularized composition. CMCS-OH30 NP induced a steady anti-inflammatory cytokine IL10 expression but downregulated the expressions of several pro-inflammatory cytokines. CONCLUSION: The prepared biodegradable drug delivery system accelerates the healing and shows better prognosis because of the combined effects of OH30 released from the nanoparticles.

Preparation and characterization of mucosal adhesive and two-step drug releasing cetirizine-chitosan nanoparticle.

To develop a functional nanosized mucosal drug delivery system, a series of amphiphilic cetirizine-chitosan polymer (CTZ-CSs) were constructed. CTZ-CSs could self-assemble into nanoparticles (NPs) which gradually evolved from irregular aggregates to spherical particles with an increasing substitution degree (DS) in CTZ group. The average particle size of CTZ-CSs-NPs with nano ZS90 Zetasizer varied from 153.92nm to 184.48nm and their zeta potential varied between +19.14mV and +22.93mV. Biocompatibility assay exhibited CTZ-CS-NPs had few adverse effects within a certain concentration range. Cetirizine dihydrochloride(CedH):CTZ-CS-NPs displayed burst and sustained drug release profiles in the presence of lysozyme. CedH showed a burst release during the first 6h, after which the release rate slowed down significantly. The release of CedH totally sustained for 72h. Ex vivo mucosal adhesion indicated CedH:CTZ-CS-NPs were able to prolong the residence time in the entire small intestine mucosa.

Systematic investigation of fabrication conditions of nanocarrier based on carboxymethyl chitosan for sustained release of insulin.

pH-responsive nanoparticles (NPs) comprised of degradable carboxymethyl chitosan (CMCS) crosslinked with CaCl2 were simply prepared via ionic gelation. Fabrication conditions including insulin dosage, CMCS concentration, and crosslinking density were systematically investigated for insulin loading and release in vitro. The encapsulation efficiencies (EE), loading capacity (LC) and average size of the NPs decreased with the increasing insulin concentrations (<0.192mg/mL), while they notably increased as the insulin dosage was above 0.192mg/mL. When the concentration of CMCS increased from 0.5 to 2.0mg/mL, the EE of the NPs reduced while the size of the NPs increased. We further demonstrated that crosslinking density offered a simple method for tuning the properties of the NPs towards various insulin concentrations. The mass ratio 10:5 of CMCS to CaCl2 exhibited the optimal performance at higher insulin concentration, whereas a higher crosslinking density of 10:7 (m:m) gave the optimal performance at low insulin concentration. The cumulative release of insulin from insulin loaded NPs decreased with the elevating crosslinking density. These findings not only provided a better understanding of the synthesis of CMCS NPs but also contributed to the practical applications of insulin loading and release.

In vitro heterogeneous degradation of alginate and its validation of different molecular weight on blood bio-compatibility.

In the present work, sodium alginate (ALG) was degraded by heterogeneous phase acid degradation. The molecular weight distribution of ALG after degradation was close to homogenization. Then the blood bio-compatibility of ALG with different molecular weights (ALG-0h 50,075, ALG-0.5h 20,680, ALG-2h 13,170 and ALG-96h 1170 kDa) was evaluated in vitro and vivo. The human umbilical vein endothelial cells were used to assess the cytotoxicity of ALGs, ALG-0.5h and ALG-2h exhibited greater increment in percentage of cell viability comparing with ALG-0h and ALG-96h. With increasing of molecular weight of ALG, the blood clotting time was shortened and the hemolysis rate was slightly decreased. The different degree aggregation of red blood cells (RBCs) was observed in the ALG with different molecular groups and ALG-0h caused a severe aggregation of RBCs. Hematology analysis in vivo behavior after intraperitoneal (i.p.) injection indicated ALG-0h could cause blood solidification. Above results provided a reference for molecular weight selection in different applications.

Nanoparticles/thermosensitive hydrogel reinforced with chitin whiskers as a wound dressing for treating chronic wounds.

Cutaneous chronic wounds are characterized by impaired wound healing which may lead to infection and even amputation. To surmount this problem, we developed a chitin whisker (CW)/carboxymethyl chitosan nanoparticles (CMCS NPs)/thermosensitive hydroxybutyl chitosan (HBC) composite hydrogel (CW/NPs/HBC-HG) as a wound dressing for treating chronic wounds. Upon introduction of CWs, the composite hydrogel exhibited a significant decrease in gelation temperature and enhanced mechanical properties. The storage modulus (G') of the CW/NPs/HBC-HG was 3.6 times that of the NPs/HBC-HG at 37 °C and the ex vivo rat skin test also showed that the mechanical properties were significantly improved. Linezolid, a wide-spectrum antibiotic, was dissolved directly in the water phase of the composite hydrogel, and the antibacterial activity of the composite hydrogel against Escherichia coli and Staphylococcus aureus was up to 99% until 7 days. When recombinant human epidermal growth factor (rhEGF) was encapsulated into the NPs, the CW/NPs/HBC-HG offered prolonged cell proliferation activity up to 5 days. More importantly, the in vivo chronic wound healing model evaluation in diabetic rats revealed that the CW/NPs/HBC-HG dressing promoted wound healing and accelerated reepithelialization, collagen deposition and angiogenesis. These findings demonstrated that CW/NPs/HBC-HG is a promising dressing for chronic wounds.

Influence of the graft density of hydrophobic groups on thermo-responsive nanoparticles for anti-cancer drugs delivery.

A series of deoxycholate-chitosan-hydroxybutyl (DAHBCs) with different degrees of substitution (DS) of hydrophobic deoxycholate (DOCA) were successfully synthesized. The lower critical solution temperature (LCST) of various DAHBCs could be adjusted from 35.4°C to 42.1°C by controlling the graft density of DOCA. DAHBCs could self-assemble into nanoparticles (NPs) which gradually evolved from irregular aggregates to spherical particles with the decrease of the DS of DOCA groups. The size of DAHBCs NPs ranged from 100nm to 250nm and their zeta potential varied between 3.85 and 12.37mV. Hemolysis tests and protein adsorption assay exhibited DAHBCs NPs had few adverse effects on the blood components even at a concentration as high as 1mg/mL. DAHBCs NPs showed high curcumin (CUR) encapsulation efficiency up to 80%. CUR-loaded DAHBCs NPs displayed thermal-dependent drug release profiles, and the release rate of CUR (∼75%) was significantly (p<0.05) accelerated at a temperature above the LCST compared with that (∼40%) below the LCST. Cytotoxicity analysis identified no toxicity associated with DAHBCs NPs at a concentration up to 0.5mg/mL. However, when the cells were incubated with the CUR-loaded NPs, their growth was significantly inhibited at 43°C (>LCST), demonstrating the thermal-responsive release of encapsulated cargoes from the NPs. With the capacity to control the LCST of DAHBCs NPs at specific temperatures, it could be speculated that DAHBCs NPs might serve as a promising thermo-responsive nanoplatform for the delivery of antitumor drugs.

Chitosan based nanoparticles as protein carriers for efficient oral antigen delivery.

This study aimed to investigate the efficacy of nanoparticles based on chitosan as a vehicle for oral antigen delivery in fish vaccination. Carboxymethyl chitosan/chitosan nanoparticles (CMCS/CS-NPs) loaded extracellular products (ECPs) of Vibrio anguillarum were successfully developed by ionic gelation method. The prepared ECPs-loaded CMCS/CS-NPs were characterized for various parameters including morphology, particle size (312±7.18nm), zeta potential (+17.4±0.38mV), loading efficiency (57.8±2.54%) and stability under the simulated gastrointestinal (GI) tract conditions in turbot. The in vitro profile showed that the cumulative release of ECPs from nanoparticles was higher in pH 7.4 (58%) than in pH 2.0 (37%) and pH 4.5 (29%) after 48h. Fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) was used as model protein antigen and encapsulated in CMCS/CS-NPs for investigating the biodistribution of antigen after oral delivery to turbot in 24h. Oral immunization of ECPs-loaded CMCS/CS-NPs group in turbot showed elevated specific antibody and higher concentrations of lysozyme activity and complement activity in fish serum than ECPs solution. CMCS/CS-NPs loaded with ECPs could enhance both adaptive and innate immune responses than the group treated with ECPs solution and suggested to be a potential antigen delivery system.

Surface fluid-swellable chitosan fiber as the wound dressing material.

The objective of this study was to develop a novel surface fluid-swellable chitosan (SFSC) fiber for potential wound dressing. The SFSC fiber was successfully prepared by surface modification of chitosan fiber with succinic anhydride, which was characterized by FTIR and solid-state (13)C NMR. The SFSC fiber exhibited better water absorption capacity (approx. 2980%) and stronger antibacterial activities (both above 90%) against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) than chitosan fiber (both below 75%). The cell viability was more than 90% after treated with the SFSC fiber extract, which demonstrated that SFSC fiber had low cytotoxicity towards mouse embryo fibroblasts (MEFs). The SFSC fiber could promote wound healing with advanced development of granulation tissue and epithelial coverage compared with the control (gauze-covered) group. The results indicated that SFSC fiber had great potential to be used as wound dressing material.

A thermosensitive hydroxybutyl chitosan hydrogel as a potential co-delivery matrix for drugs on keloid inhibition.

Keloid is a kind of unique human fibroproliferative dermal disease, and there are still no optimal treatment methods for it. In the present study, a thermosensitive hydroxybutyl chitosan (HBC) hydrogel as a co-delivery matrix for 5-fluorouracil (5-FU) and dexamethasone sodium phosphate (DEXSP) in keloid treatment was developed. The gelation temperature of the HBC hydrogel was observed to be 25.7 °C by rheology analysis. The HBC hydrogel showed sustained drug release capacity (5-FU, 89.3 ± 3.4%; DEXSP, 95.6 ± 3.9%) for drug delivery. The HBC hydrogel was shown to be cytocompatible, while the dual drug-loaded HBC hydrogel could suppress the proliferation of keloid fibroblasts (KFs). The keloid biopsies treated with the dual drug-loaded hydrogel could be inhibited through the efficient suppression of VEGF expression within 7 days. The results suggested that the HBC hydrogel could be applied as a potential co-delivery matrix for drugs in the keloid therapy field.