Role of sulfhydryl groups in transfection? A case study with chitosan-NAC nanoparticles

Thiolated α-cyclodextrin: The likely smallest drug carrier providing enhanced cellular uptake and endosomal escape

This study aimed to evaluate the effect of thiolated α-cyclodextrin (α-CD-SH) on the cellular uptake of its payload. For this purpose, α-CD was thiolated using phosphorous pentasulfide. Thiolated α-CD was characterized by FT-IR and ¹H NMR spectroscopy, differential scanning calorimetry (DSC), and powder X-ray diffractometry (PXRD). Cytotoxicity of α-CD-SH was evaluated on Caco-2, HEK 293, and MC3T3 cells. Dilauryl fluorescein (DLF) and coumarin-6 (Cou) serving as surrogates for a pharmaceutical payload were incorporated in α-CD-SH, and cellular uptake was analyzed by flow cytometry and confocal microscopy. Endosomal escape was investigated by confocal microscopy and hemolysis assay. Results showed no cytotoxic effect within 3 h, while dose-dependent cytotoxicity was observed within 24 h. The cellular uptake of DLF and Cou was up to 20- and 11-fold enhanced by α-CD-SH compared to native α-CD, respectively. Furthermore, α-CD-SH provided an endosomal escape. According to these results, α-CD-SH is a promising carrier to shuttle drugs into the cytoplasm of target cells.

Recent advances in the intracellular delivery of macromolecule therapeutics

This review summarizes the uptake pathway of intracellular delivery vehicles for macromolecule therapeutics, and provides in-depth discussions and prospects about intracellular delivery of macromolecule therapeutics.

Biodegradable Harmonophores for Targeted High-Resolution In Vivo Tumor Imaging

Optical imaging probes have played a major role in detecting and monitoring a variety of diseases. In particular, nonlinear optical imaging probes, such as second harmonic generating (SHG) nanoprobes, hold great promise as clinical contrast agents, as they can be imaged with little background signal and unmatched long-term photostability. As their chemical composition often includes transition metals, the use of inorganic SHG nanoprobes can raise long-term health concerns. Ideally, contrast agents for biomedical applications should be degraded in vivo without any long-term toxicological consequences to the organism. Here, we developed biodegradable harmonophores (bioharmonophores) that consist of polymer-encapsulated, self-assembling peptides that generate a strong SHG signal. When functionalized with tumor cell surface markers, these reporters can target single cancer cells with high detection sensitivity in zebrafish embryos in vivo. Thus, bioharmonophores will enable an innovative approach to cancer treatment using targeted high-resolution optical imaging for diagnostics and therapy.

The Influence of Nanoparticle Properties on Oral Bioavailability of Drugs

Oral administration has been the most common therapeutic regimen in various diseases because of its high safety, convenience, lower costs, and high compliance of patients. However, susceptible in hostile gastrointestinal (GI) environment, many drugs show poor permeability across GI tract mucus and intestinal epithelium with poor oral absorption and limited therapeutic efficacy. In recent years, nanoparticulate drug delivery systems (NDDS) have become a hot research spot because of their unique advantages including protecting drug from premature degrading and interacting with the physiological environment, increasing intracellular penetration, and enhancing drug absorption. However, a slight change in physicochemistry of nanoparticles can significantly impact their interaction with biological pathways and alter the oral bioavailability of drugs. Hence, this review focuses on the factors affecting oral bioavailability from two aspects. On the one hand, the factors are the biochemical and physiological barriers in oral drugs delivery. On the other hand, the factors are the nanoparticle properties including size, surface properties, and shape of nanoparticles.

In Vitro and In Vivo Osteogenesis Induced by Icariin and Bone Morphogenetic Protein-2: A Dynamic Observation

In the present study, we aimed to compare the effects of icariin (ICA) and bone morphogenetic protein-2 (BMP-2) on osteoblast proliferation and osteogenesis in bone defects. We found that in vitro ICA or BMP-2 treatment is able to increase osteoblast proliferation, which was detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Specifically, ICA at a concentration of 30 µg/ml had the strongest ability to promote cell proliferation, which is equivalent with the effect of BMP-2 at a concentration of 50 µg/ml. Furthermore, Western blot and RT-qPCR analyses showed that treatment with ICA (20–30 µg/ml) had similar increase effect with BMP-2 (50 µg/ml) on the protein and mRNA levels of BMP-2, osteoprotegerin (OPG), and alkaline phosphatase (ALP) mRNAs. In addition, the animal model of bone defects was successfully prepared. The in vivo data showed that compared with the control group, highest osteogenesis in the ICA or BMP-2 groups was observed at different observational times. Four weeks after surgery, osteogenesis in the BMP-2 group was slightly higher than that in the ICA group, but there was no significant difference between the two groups until the eighth week. ICA promotes osteoblast proliferation by stimulating the expression of BMP-2 and OPG proteins and upregulating the expression of BMP-2, OPG, and ALP mRNAs. ICA at a certain concentration has the same osteogenic effect as BMP-2. ICA or BMP-2 composite nanomaterials can be used as a framework to guide bone regeneration and promote osteogenesis. In addition, the combined use of hematoxylin-eosin and Goldner’s trichrome staining techniques contributes to acquiring better bone morphometric information about bone defects.

Thiolated Chitosans: A Multi-talented Class of Polymers for Various Applications

Various properties of chitosan can be customized by thiolation for very specific needs in a wide range of application areas. Since the discovery of thiolated chitosans, many studies have proven their advantageous characteristics, such as adhesion to biological surfaces, adjustable cross-linking and swelling behavior, controllable drug release, permeation as well as cellular uptake enhancement, inhibition of efflux pumps and enzymes, complexation of metal ions, antioxidative properties, and radical scavenging activity. Simultaneously, these polymers remain biodegradable without increased toxicity. Within this Review, an overview about the different possibilities to covalently attach sulfhydryl ligands to the polymeric backbone of chitosan is given, and the resulting versatile physiochemical properties are discussed in detail. Furthermore, the broad spectrum of applications for thiolated chitosans in science and industry, ranging from their most advanced use in pharmaceutical and medical science over wastewater treatment to the impregnation of textiles, is addressed.

Improving cellular uptake of therapeutic entities through interaction with components of cell membrane

Efficient cellular delivery of biologically active molecules is one of the key factors that affect the discovery and development of novel drugs. The plasma membrane is the first barrier that prevents direct translocation of chemic entities, and thus obstructs their efficient intracellular delivery. Generally, hydrophilic small molecule drugs are poor permeability that reduce bioavailability and thus limit the clinic application. The cellular uptake of macromolecules and drug carriers is very inefficient without external assistance. Therefore, it is desirable to develop potent delivery systems for achieving effective intracellular delivery of chemic entities. Apart from of the types of delivery strategies, the composition of the cell membrane is critical for delivery efficiency due to the fact that cellular uptake is affected by the interaction between the chemical entity and the plasma membrane. In this review, we aimed to develop a profound understanding of the interactions between delivery systems and components of the plasma membrane. For the purpose, we attempt to present a broad overview of what delivery systems can be used to enhance the intracellular delivery of poorly permeable chemic entities, and how various delivery strategies are applied according to the components of plasma membrane.

S-preactivated thiolated glycol chitosan useful to combine mucoadhesion and drug delivery

This work describes S-preactivated N-acetylcysteine (NAC)- and glutathione (GSH)-glycol chitosan (GC) polymer conjugates engineered as potential mucoadhesive platform. Preactivated thiomers (GC-NAC-MNA, GC-GSH-MNA) were synthesized by bond formation between GC-NAC or GC-GSH and 2-mercaptonicotinic acid (MNA) used as ligand. The presence of protected thiol moieties on this new class of thiolated GC made them not subject to oxidation. The structural modifications of the resulting derivatives were confirmed by proton Nuclear Magnetic Resonance (¹H NMR) and Size Exclusion Chromatography (SEC). The conjugates displayed 91.2% and 90.1% of S-preactivation for GC-NAC-MNA and GC-GSH-MNA, respectively. The polymers were tested in ex-vivo and in vitro for their mucoadhesive properties and toxicity. The results showed that the preactivation of GC-NAC and GC-GSH increased their mucoadhesive abilities compared to their thiolated precursors by 1.4-, 4.4-fold in time of adhesion evaluated using rotating cylinder method, 1.6-, 1.5-fold in total work of adhesion (TWA) and 2.0-, 1.3-fold in maximum detachment force (MDA) determined using tensile studies, respectively. Moreover, water-uptake studies showed an improved in weight indicating water-uptake strongly dependent on derivations, before erosion occurred, whereas disintegration took place for the thiolated polymers within the first hour. The S-preactivated modification did not affect the cell viability of Caco2 cells exposed to the polymers. The release of the model drug sodium naproxen from tablets prepared with a lyophilized mixture of drug and polymer was studied via dissolution apparatus revealing that the preactivation on GC-GSH and GC-NAC involves a slowdown in the drug release rate. The results shown that the novel preactivated thiolated GC-derivatives can be considered promising excipients for the development of mucoadhesive drug delivery systems.

How to design the surface of peptide-loaded nanoparticles for efficient oral bioavailability?

The oral administration of proteins is a current challenge to be faced in the field of therapeutics. There is currently much interest in nanocarriers since they can enhance oral bioavailability. For lack of a clear definition, the key characteristics of nanoparticles have been highlighted. Specific surface area is one of these characteristics and represents a huge source of energy that can be used to control the biological fate of the carrier. The review discusses nanocarrier stability, mucus interaction and absorption through the intestinal epithelium. The protein corona, which has raised interest over the last decade, is also discussed. The universal ideal surface is a myth and over-coated carriers are not a solution either. Besides, common excipients can be useful on several targets. The suitable design should rather take into account the composition, structure and behavior of unmodified nanomaterials.

Spray-dried mucoadhesives for intravesical drug delivery using N-acetylcysteine- and glutathione-glycol chitosan conjugates

This work describes N-acetylcysteine (NAC)- and glutathione (GSH)-glycol chitosan (GC) polymer conjugates engineered as potential platform useful to formulate micro-(MP) and nano-(NP) particles via spray-drying techniques. These conjugates are mucoadhesive over the range of urine pH, 5.0-7.0, which makes them advantageous for intravesical drug delivery and treatment of local bladder diseases. NAC- and GSH-GC conjugates were generated with a synthetic approach optimizing reaction times and purification in order to minimize the oxidation of thiol groups. In this way, the resulting amount of free thiol groups immobilized per gram of NAC- and GSH-GC conjugates was 6.3 and 3.6mmol, respectively. These polymers were completely characterized by molecular weight, surface sulfur content, solubility at different pH values, substitution and swelling degree. Mucoadhesion properties were evaluated in artificial urine by turbidimetric and zeta (ζ)-potential measurements demonstrating good mucoadhesion properties, in particular for NAC-GC at pH 5.0. Starting from the thiolated polymers, MP and NP were prepared using both the Büchi B-191 and Nano Büchi B-90 spray dryers, respectively. The resulting two formulations were evaluated for yield, size, oxidation of thiol groups and ex-vivo mucoadhesion. The new spray drying technique provided NP of suitable size (<1μm) for catheter administration, low degree of oxidation, and sufficient mucoadhesion property with 9% and 18% of GSH- and NAC-GC based NP retained on pig mucosa bladder after 3h of exposure, respectively.

STATEMENT OF SIGNIFICANCE

The aim of the present study was first to optimize the synthesis of NAC-GC and GSH-GC, and preserve the oxidation state of the thiol moieties by introducing several optimizations of the already reported synthetic procedures that increase the mucoadhesive properties and avoid pH-dependent aggregation. Second, starting from these optimized thiomers, we studied the feasibility of manufacturing MP and NP by spray-drying techniques. The aim of this second step was to produce mucoadhesive drug delivery systems of adequate size for vesical administration by catheter, and comparable mucoadhesive properties with respect to the processed polymers, avoiding thiolic oxidation during the formulation. MP with acceptable size produced by spray-dryer Büchi B-191 were compared with NP made with the apparatus Nano Büchi B-90.

Mucoadhesive vs. mucopenetrating particulate drug delivery

Mucus layer is a hydrophilic absorption barrier found in various regions of the body. The use of particulate delivery systems showed potential in drug delivery to mucosal membranes by either prolonging drug residence time at the absorption or target membrane or promoting permeation of particles across mucus gel layer to directly reach underlying epithelium. Mucoadhesive particles (MAP) are advantageous for delivering drug molecules to various mucosal membranes including eyes, oral cavity, bladder and vagina by prolonging drug residence time on those membranes. In contrast, a broader particle distribution and deeper penetration of the mucus gel layer are accomplished by mucopenetrating particles (MPP) especially in the gastrointestinal tract. Based on the available literature in particular dealing with in vivo results none of both systems (MAP and MPP) seems to be advantageous over the other. The choice of system primarily depends on the therapeutic target and peculiar properties of the target mucosa including thickness of the mucus gel layer, mucus turnover rate and water movement within the mucus. Future trends are heading in the direction of combining both systems to one i.e. mucoadhesive and mucopenetrating properties on the same particles.

Nano-carrier systems: Strategies to overcome the mucus gel barrier

The present review provides an overview of nanotechnology-based strategies to overcome various mucus gel barriers including the intestinal, nasal, ocular, vaginal, buccal and pulmonary mucus layer without destroying them. It focuses on the one hand on strategies to improve the mucus permeation behavior of particles and on the other hand on systems avoiding the back-diffusion of particles out of the mucus gel layer. Nanocarriers with improved mucus permeation behavior either exhibit a high density of positive and negative charges, bearing mucolytic enzymes such as papain and bromelain on their surface or display a slippery surface due to PEG-ylation. Furthermore, self-nanoemulsifying-drug-delivery-systems (SNEDDS) turned out to exhibit comparatively high mucus permeating properties. Strategies in order to avoid back-diffusion are based on thiolated polymers reacting to a higher extent with cysteine subunits of the mucus at pH 7 in deeper mucus regions than at pH 5 being prevalent in luminal mucus regions of the intestinal and vaginal mucosa. Furthermore, particles changing their zeta potential from negative to positive once they have reached the epithelium seem to be promising carriers. The summarized knowledge should provide a good starting point for further developments in this field.

The sustained-release behavior and in vitro and in vivo transfection of pEGFP-loaded core-shell-structured chitosan-based composite particles

Novel submicron core-shell-structured chitosan-based composite particles encapsulated with enhanced green fluorescent protein plasmids (pEGFP) were prepared by complex coacervation method. The core was pEGFP-loaded thiolated N-alkylated chitosan (TACS) and the shell was pH- and temperature-responsive hydroxybutyl chitosan (HBC). pEGFP-loaded TACS-HBC composite particles were spherical, and had a mean diameter of approximately 120 nm, as measured by transmission electron microscopy and particle size analyzer. pEGFP showed sustained release in vitro for >15 days. Furthermore, in vitro transfection in human embryonic kidney 293T and human cervix epithelial cells, and in vivo transfection in mice skeletal muscle of loaded pEGFP, were investigated. Results showed that the expression of loaded pEGFP, both in vitro and in vivo, was slow but could be sustained over a long period. pEGFP expression in mice skeletal muscle was sustained for >60 days. This work indicates that these submicron core-shell-structured chitosan-based composite particles could potentially be used as a gene vector for in vivo controlled gene transfection.

Thiomers and thiomer-based nanoparticles in protein and DNA drug delivery

INTRODUCTION

Thanks to advances in biotechnology, more and more highly efficient protein- and DNA-based drugs have been developed. Unfortunately, these kinds of drugs underlie poor non-parental bioavailability. To overcome hindrances like low mucosal permeability and enzymatic degradation polymeric excipients are utilized as drug carrier whereat thiolated excipients showed several promising qualities in comparison to the analogical unmodified polymer.

AREAS COVERED

The article deals with the comparatively easy modification of well-established polymers like chitosan or poly(acrylates) to synthesize thiomers. Further, the recently developed "next generation" thiomers e.g. preactivated or S-protected thiomers are introduced. Designative properties like mucoadhesion, uptake and permeation enhancement, efflux pump inhibition and protection against enzymatic degradation will be discussed and differences between first and next generation thiomers will be pointed out. Additionally, nanoparticles prepared with thiomers will be dealt with regarding to protein and DNA drug delivery as thiomers seem to be a promising approach to avoid parenteral application.

EXPERT OPINION

Properties of thiomers per se and results of in vivo studies carried out so far for peptide and DNA drugs demonstrate their potential as multifunctional excipients. However, further investigations and optimizations have to be done before establishing a carrier system ready for clinical approval.

Exploiting cell surface thiols to enhance cellular uptake

Efficient cellular delivery is one of the key issues that has hampered the therapeutic development of novel synthetic biomolecules such as oligonucleotides, peptides and nanoparticles. The highly specialized cellular plasma membrane specifically internalizes compounds through tightly regulated mechanisms. It is possible to exploit these natural mechanisms of cellular uptake with rationally designed reagents. Here, we discuss how thiol groups (-SH) naturally present on the cell surface (exofacial thiols) can be used to enhance cellular association and internalization of various materials bearing thiol-reactive groups in their structure. We propose that such thiol modifications should be considered in future design of synthetic biomolecules for optimized cellular delivery.

Disulfide-crosslinked heparin-pluronic nanogels as a redox-sensitive nanocarrier for intracellular protein delivery

Improving the efficacy of drug delivery via nanocarriers has been a major issue in the field of intravenous delivery. In this study, a polymeric nanogel was developed to enhance the stability, redox responsiveness, and the efficacy for intracellular protein delivery. The thiolated heparin-Pluronic conjugate was self-assembled and oxidized to form a disulfide-crosslinked nanogel network under a diluted aqueous condition. The disulfide-crosslinked heparin-Pluronic (DHP) nanogels with encapsulated RNase A were characterized by in vitro release and cytotoxicity tests depending on the existence of glutathione (GSH). The DHP nanogels exhibited reduced hydrodynamic size, higher encapsulation degree, and augmentable release responding to the GSH concentration. The ctotoxicity data confirmed that DHP nanogels were more effective for the intracellular delivery of RNase A compared to non-crosslinked nanogel.

Chitosan-based gene delivery vectors targeted to the peripheral nervous system

A non-toxic, targeted, simple and efficient system that can specifically transfect peripheral sensorial neurons can pave the way towards the development of new therapeutics for the treatment of peripheral neuropathies. In this study chitosan (CH), a biodegradable polymer, was used as the starting material in the design of a multicomponent vector targeted to the peripheral nervous system (PNS). Polycation-DNA complexes were optimized using imidazole- and thiol-grafted CH (CHimiSH), in order to increase transfection efficiency and allow the formation of ligand conjugated nanocomplexes, respectively. The 50 kDa non-toxic fragment from the tetanus toxin (HC), shown to interact specifically with peripheral neurons and undergo retrograde transport, was grafted to the binary complex via a bi-functional poly(ethylene glycol) (HC-PEG) reactive for the thiol moieties present in the complex surface. The targeting of the developed nanocomplexes was assessed by means of internalization and transfection studies in the ND7/23 (neuronal) vs. NIH 3T3 (fibroblast) cell lines. Targeted transfection was further confirmed in dorsal root ganglion dissociated primary cultures. A versatile, multi-component nanoparticle system that successfully targets and transfects neuronal cell lines, as well as dorsal root ganglia (DRG) primary neuron cultures was obtained for the 1.0 (w/w) HC-PEG/DNA formulation.

Leukocyte nicotinamide adenine dinucleotide phosphate-reduced oxidase is required for isocyanate-induced lung inflammation

BACKGROUND

Isocyanates are low-molecular-weight compounds noted for inducing occupational and environmental asthma. Isocyanate-induced lung disease, an oxidant stress-dependent pulmonary inflammation, is the leading cause of occupational asthma.

OBJECTIVES

To address the role of leukocyte-produced oxidants in airway inflammation induced by toluene diisocyanate (TDI), and to elucidate the role of leukocyte nicotinamide adenine dinucleotide phosphate-reduced (NADPH) oxidase in pathogenesis by TDI.

METHODS

Wild-type mice and NADPH oxidase-deficient mice (neutrophil cytosolic factor 1 mutant, Ncf1(-/-)) were intranasally injected, challenged with inhalatory TDI, and then investigated for lung inflammation.

RESULTS

Cell infiltration in lung tissue and leukocytes in bronchoalveolar lavage, airway reactivity to a methacholine challenge, and TDI-induced inflammatory cytokine expression and nuclear factor activation in the lung tissue were all markedly lower in Ncf1(-/-) mice. Wild-type mice treated with blocking antibodies against CD4 and IL-17 showed markedly lower TDI-induced airway hyperresponsiveness.

CONCLUSION

Leukocyte NADPH oxidase is an essential regulator in TDI-induced airway inflammation through redox modification of immune responses.

Gene silencing activity of siRNA polyplexes based on thiolated N,N,N-trimethylated chitosan

N,N,N-Trimethylated chitosan (TMC) is a biodegradable polymer emerging as a promising nonviral vector for nucleic acid and protein delivery. In the present study, we investigated whether the introduction of thiol groups in TMC enhances the extracellular stability of the complexes based on this polymer and promotes the intracellular release of siRNA. The gene silencing activity and the cellular cytotoxicity of polyplexes based on thiolated TMC were compared with those based on the nonthiolated counterpart and the regularly used lipidic transfection agent Lipofectamine. Incubation of H1299 human lung cancer cells expressing firefly luciferase with siRNA/thiolated TMC polyplexes resulted in 60-80% gene silencing activity, whereas complexes based on nonthiolated TMC showed less silencing (40%). The silencing activity of the complexes based on Lipofectamine 2000 was about 60-70%. Importantly, the TMC-SH polyplexes retained their silencing activity in the presence of hyaluronic acid, while nonthiolated TMC polyplexes hardly showed any silencing activity, demonstrating their stability against competing anionic macromolecules. Under the experimental conditions tested, the cytotoxicity of the thiolated and nonthiolated siRNA complexes was lower than those based on Lipofectamine. Given the good extracellular stability and good silencing activity, it is concluded that polyplexes based on TMC-SH are attractive systems for further in vivo evaluations.

Novel pectin-4-aminothiophenole conjugate microparticles for colon-specific drug delivery

Within this study metronidazole-containing microparticles based on a pectin-4-aminothiophenol (Pec-ATP) conjugate were developed and investigated regarding their potential for colon-specific drug delivery. Microparticles were produced by spray-drying and subsequent processing. Posteriorly, they were investigated regarding their disintegration behavior, particle size, drug load, release behavior and impact on viability of Caco-2 cells. Microparticles with a mean diameter of 5.16+/-2.41 microm and a drug load of 1.15+/-0.03% metronidazole were prepared. Disintegration studies revealed that the stability of Pec-ATP microparticles was significantly improved compared to control microparticles based on unmodified pectin. In vitro release studies without potential colonic release-inducers revealed that 34.4-fold more metronidazole is retarded in Pec-ATP microparticles within 6h compared to control particles. It could be demonstrated that the retarded amount of metronidazole can be released rapidly under the influence of pectinolytic enzymes or a reducing agent, simulating the colonic environment. Cell viability studies did not reveal a significant difference between native and modified pectin, neither as a solution nor as microparticle suspension. From the improved stability, the described release features and the low toxicity of the investigated microparticles can be concluded that these particles are a promising carrier for colon-specific drug delivery.

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.

Recent developments in nanoparticle-based drug delivery and targeting systems with emphasis on protein-based nanoparticles

BACKGROUND

Drug delivery systems with nm dimensions (nanoparticles [NPs]) are attracting increasing attention because they can sequester drugs in systemic circulation, prevent non-specific biodistribution, and target to specific tissues.

OBJECTIVE

We reviewed the recent literature pertinent to NP-based drug delivery, primarily emphasizing NPs fabricated from proteins.

METHODS

A summary of common NP fabrication techniques is provided along with the range of sizes and functional properties obtained. The NP properties critical for injectable drug delivery are reviewed, as well as the attempts to design 'tissue-specific' NPs.

RESULTS/CONCLUSIONS

It has been possible to design > 100 nm NPs from different biomaterials, and further understanding of in vivo stability and interactions with physiologic systems will lead to improved drug delivery systems.

Oral delivery of peptide drugs using nanoparticles self-assembled by poly(gamma-glutamic acid) and a chitosan derivative functionalized by trimethylation

In the study, chitosan (CS) was conjugated with trimethyl groups for the synthesis of N-trimethyl chitosan (TMC) polymers with different degrees of quaternization. Nanoparticles (NPs) self-assembled by the synthesized TMC and poly(gamma-glutamic acid) (gamma-PGA, TMC/gamma-PGA NPs) were prepared for oral delivery of insulin. The loading efficiency and loading content of insulin in TMC/gamma-PGA NPs were 73.8 +/- 2.9% and 23.5 +/- 2.1%, respectively. TMC/gamma-PGA NPs had superior stability in a broader pH range to CS/gamma-PGA NPs; the in vitro release profiles of insulin from both test NPs were significantly affected by their stability at distinct pH environments. At pH 7.0, CS/gamma-PGA NPs became disintegrated, resulting in a rapid release of insulin, which failed to provide an adequate retention of loaded insulin, while the cumulative amount of insulin released from TMC/gamma-PGA NPs was significantly reduced. At pH 7.4, TMC/gamma-PGA NPs were significantly swelled and a sustained release profile of insulin was observed. Confocal microscopy confirmed that TMC40/gamma-PGA NPs opened the tight junctions of Caco-2 cells to allow the transport of insulin along the paracellular pathway. Transepithelial-electrical-resistance measurements and transport studies implied that CS/gamma-PGA NPs can be effective as an insulin carrier only in a limited area of the intestinal lumen where the pH values are close to the p K a of CS. In contrast, TMC40/gamma-PGA NPs may be a suitable carrier for transmucosal delivery of insulin within the entire intestinal tract.