Multi-ion-crosslinked nanoparticles with pH-responsive characteristics for oral delivery of protein drugs

pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates

Titratable polyanions, and more particularly polymers bearing carboxylate groups, have been used in recent years to produce a variety of pH-sensitive colloids. These polymers undergo a coil-to-globule conformational change upon a variation in pH of the surrounding environment. This conformational change can be exploited to trigger the release of a drug from a drug delivery system in a pH-dependent fashion. This review describes the current status of pH-sensitive vesicles, polymeric micelles, and nanospheres prepared with polycarboxylates and their performance as nano-scale drug delivery systems, with emphasis on our recent contribution to this field.

Strategies for non-invasive delivery of biologics

Macromolecular therapeutics, in particular, many biologics, is the most advancing category of drugs over conventional chemical drugs. The potency and specificity of the biologics for curing certain disease made them to be a leading compound in the pharmaceutical industry. However, due to their intrinsic nature, including high molecular weight, hydrophilicity and instability, they are difficult to be administered via non-invasive route. This is a major quest especially in biologics, as they are frequently used clinically for chronic disorders, which requires long-term administration. Therefore, many efforts have been made to develop formulation for non-invasive administration, in attempt to improve patient compliance and convenience. In this review, strategies for non-invasive delivery, in particular, oral, pulmonary and nasal delivery, that are recently adopted for delivery of biologics are discussed. Insulin, calcitonin and heparin were mainly focused for the discussion as they could represent protein, polypeptide and polysaccharide drugs, respectively. Many recent attempts for non-invasive delivery of biologics are compared to provide an insight of developing successful delivery system.

Oral drug delivery with polymeric nanoparticles: the gastrointestinal mucus barriers

Oral delivery is the most common method for drug administration. However, poor solubility, stability, and bioavailability of many drugs make achieving therapeutic levels via the gastrointestinal (GI) tract challenging. Drug delivery must overcome numerous hurdles, including the acidic gastric environment and the continuous secretion of mucus that protects the GI tract. Nanoparticle drug carriers that can shield drugs from degradation and deliver them to intended sites within the GI tract may enable more efficient and sustained drug delivery. However, the rapid secretion and shedding of GI tract mucus can significantly limit the effectiveness of nanoparticle drug delivery systems. Many types of nanoparticles are efficiently trapped in and rapidly removed by mucus, making controlled release in the GI tract difficult. This review addresses the protective barrier properties of mucus secretions, how mucus affects the fate of orally administered nanoparticles, and recent developments in nanoparticles engineered to penetrate the mucus barrier.

pH-responsive nanoparticles shelled with chitosan for oral delivery of insulin: from mechanism to therapeutic applications

Despite advances in drug-delivery technologies, successful oral administration of protein drugs remains an elusive challenge. When protein drugs are administered orally, they can rapidly denature or degrade before they reach their targets. Such drugs also may not absorb adequately within the small intestine. As a protein drug for treating diabetes, insulin is conventionally administered via subcutaneous (SC) injection, yet often fails to achieve the glucose homeostasis observed in nondiabetic subjects. Some of this difference may relate to insulin transport: normally, endogenously secreted insulin moves to the liver via portal circulation. When administered subcutaneously, insulin moves through the body via peripheral circulation, which can produce a peripheral hyperinsulinemia. In addition, because SC treatment requires multiple daily injections of insulin, patients often do not fully comply with treatment. Oral administration of exogenous insulin would deliver the drug directly into the liver through portal circulation, mimicking the physiological fate of endogenously secreted insulin. This characteristic may offer the needed hepatic activation, while avoiding hyperinsulinemia and its associated long-term complications. This Account demonstrates the feasibility of using chitosan nanoparticles for oral insulin delivery. Nanoparticle (NP) delivery systems may provide an alternative means of orally administering protein drugs. In addition to protecting the drugs against a harmful gastric environment, the encapsulation of protein drugs in particulate carriers can avert enzymatic degradation, while controlling the drug release and enhancing their absorption in the small intestine. Our recent study described a pH-responsive NP system composed of chitosan (CS) and poly(γ-glutamic acid) for oral delivery of insulin. As a nontoxic, soft-tissue compatible, cationic polysaccharide, CS also adheres to the mucosal surface and transiently opens the tight junctions (TJs) between contiguous epithelial cells. Therefore, drugs made with CS NPs would have delivery advantages over traditional tablet or powder formulations. This Account focuses on the premise that these CS NPs can adhere to and infiltrate the mucus layer in the small intestine. Subsequently, the infiltrated CS NPs transiently open the TJs between epithelial cells. Because they are pH-sensitive, the nanoparticles become less stable and disintegrate, releasing the loaded insulin. The insulin then permeates through the opened paracellular pathway and moves into the systemic circulation.

Opening of epithelial tight junctions and enhancement of paracellular permeation by chitosan: microscopic, ultrastructural, and computed-tomographic observations

This study investigates the effects of chitosan (CS) on the opening of epithelial tight junctions (TJs) and paracellular transport at microscopic, ultrastructural, and computed-tomographic levels in Caco-2 cell monolayers and animal models. Using immunofluorescence staining, CS treatment was observed to be associated with the translocation of JAM-1 (a trans-membrane TJ protein), resulting in the disruption of TJs; the removal of CS was accompanied by the recovery of JAM-1. Ultrastructural observations by TEM reveal that CS treatment slightly opened the apical intercellular space, allowing lanthanum (an electron-dense tracer) to stain the intercellular surface immediately beneath the TJs, suggesting the opening of TJs. Following the removal of CS, the TJs were completely recovered. Similar microscopic and ultrastructural findings were obtained in animal studies. CS nanoparticles were prepared as an insulin carrier. The in vivo fluorescence-microscopic results demonstrate that insulin could be absorbed into the systemic circulation, while most CS was retained in the microvilli scaffolds. These observations were verified in a biodistribution study following the oral administration of isotope-labeled nanoparticles by single-photon emission computed tomography. Above results reveal that CS is a safe permeation enhancer and is an effective carrier for oral protein delivery.

Chitosan-tripolyphosphate submicron particles as the carrier of entrapped rutin

Chitosan (CH)-tripolyphosphate (TPP) submicron particles were formed as carriers of entrapped rutin, and the release properties characterized using simulated gastric juices and fluids of the small intestine. Particle size, charge and entrapment efficiencies were investigated as a function of the CH:TPP molar ratio (2.0:1.0-5.0:1.0). Size was found to decrease from ~814 nm for the 2.0:1:0 mass ratio to ~528 nm for the ratios between 2.5:1.0 and 4.0:1.0, and then again to ~322 nm for the 5:0:1.0 mass ratio, whereas all particles carried a positive surface charge, increasing from +21 to +59 mV as the ratio increased from 2.0:1.0 to 5.0:1.0. The percent entrapment was found to rise from 3.68% to 57.6% as the ratios increased from 2.0:1:0 to 4.0:1:0, before reaching a plateau. Submicron particles (4.0:1.0 mass ratio only) were found to retain rutin in simulated gastric fluids, whereas in conditions which simulated fluids from the small intestine, only 20% of the entrapped rutin was released and 80% remained absorbed to the CH:TPP carriers. Such particles have applications for the delivery of phenolics in food and natural health products.

Cellular uptake and cytotoxicity of chitosan-caseinophosphopeptides nanocomplexes loaded with epigallocatechin gallate

Epigallocatechin gallate (EGCG) was successfully encapsulated in novel nanocomplexes assembled from bioactive peptides, caseinophosphopeptides (CPPs), and chitosan (CS), a natural cationic polymer. Their particle sizes and surface charges were determined to be in the range of 150.0±4.3 nm and 32.2±3.3 mV respectively. Crosslinking between the -NH3+ groups of CS with the -P=O- and -COO- groups of CPP, as well as the hydrogen bonding were confirmed from the FTIR results. Atomic force microscopy (AFM) images showed that EGCG loaded CS-CPP nanocomplexes were spherical in shape. Maintaining the surface charge as high as +32.2 mV, crosslinking CS with peptides reduced the cytotoxicity of CS nanoparticles. In addition, cellular internalization of EGCG-loaded CS-CPP nanoparticles was confirmed from green fluorescence inside the Caco-2 cells. The process of nanoparticle uptake was dose and time dependent in the range of time and concentration studied. Furthermore, the intestinal permeability of EGCG using Caco-2 monolayer was enhanced significantly as delivered by nanoparticles, which indicated the promising elevation of EGCG bioavailability.

Mobilization of mesenchymal stem cells by stromal cell-derived factor-1 released from chitosan/tripolyphosphate/fucoidan nanoparticles

Stromal cell-derived factor 1 (SDF-1) is an important chemokine in stem cell mobilization, and plays a critical role in the biological and physiological functions of mesenchymal stem cells (MSC). However, the use of SDF-1 in tissue regeneration is limited by two drawbacks, which are its short half-life and ready degradation by enzymes. This study investigates the release of SDF-1 from chitosan-based nanoparticles (NP) and evaluates the effect of released SDF-1 on the migration of MSC. Among the prepared chitosan-based NP a chitosan/tripolyphosphate/fucoidan (CS/TPP/F) NP is the most effective carrier for SDF-1 release. CS/TPP/F NP are spherical and effectively encapsulate SDF-1. The CS/TPP/F NP protected SDF-1 against proteolysis and heat treatment and controlled its release for up to 7 days. The concentration of released SDF-1 reached 23 ng ml(-1). According to in vitro experiments on cells the released SDF-1 retained its mitogenic activity, promoted the migration of MSC and enhanced PI3K expression. Biocompatible CS/TPP/F NP may be effective as carriers for the delivery and controlled release of SDF-1 to mobilize stem cells in tissue engineering applications.

Hypoglycemic activity and oral bioavailability of insulin-loaded liposomes containing bile salts in rats: the effect of cholate type, particle size and administered dose

Oral delivery of protein or polypeptide drugs remains a challenge due to gastric and enzymatic degradation as well as poor permeation across the intestinal epithelia. In this study, liposomes containing bile salts were developed as a new oral insulin delivery system. The primary goal was to investigate the effect of cholate type, particle size and dosage of the liposomes on the hypoglycemic activity and oral bioavailability. Liposomes containing sodium glycocholate (SGC), sodium taurocholate (STC) or sodium deoxycholate (SDC) were prepared by a reversed-phase evaporation method. After oral administration, all liposomes elicited a certain degree of hypoglycemic effect in parallel with an increase in blood insulin level. The highest oral bioavailability of approximately 8.5% and 11.0% could be observed with subcutaneous insulin as reference for SGC-liposomes in non-diabetic and diabetic rats, respectively. Insulin-loaded liposomes showed slower and sustained action over a period of over 20 h with peak time around 8-12h. SGC-liposomes showed higher oral bioavailability than liposomes containing STC or SDC and conventional liposomes. The hypoglycemic effect was size-dependent with the highest at 150 nm or 400 nm and was proportionally correlated to the administered dose. The results supported the hypothesis of insulin absorption as intact liposomes.

Nanochemoprevention by encapsulation of (-)-epigallocatechin-3-gallate with bioactive peptides/chitosan nanoparticles for enhancement of its bioavailability

Nanochemoprevention by oral consumption was developed by the encapsulation of (-)-epigallocatechin-3-gallate (EGCG) with nanoparticles that were electrostatically assembled from bioactive caseinophosphopeptides and chitosan, which was highly biocompatible and able to enhance the bioavailability of EGCG.

HP55-coated capsule containing PLGA/RS nanoparticles for oral delivery of insulin

In this work, we designed and developed a two-stage delivery system composed of enteric capsule and cationic nanoparticles for oral delivery of insulin. The enteric capsule was coated with pH-sensitive hydroxypropyl methylcellulose phthalate (HP55), which could selectively release insulin from nanoparticles in the intestinal tract, instead of stomach. The biodegradable poly(lactic-co-glycolic acid) (PLGA) was selected as the matrix for loading insulin. Eurdragit(®) RS (RS) was also introduced to the nanoparticles for enhancing the penetration of insulin across the mucosal surface in the intestine. The nanoparticles were prepared with the multiple emulsions solvent evaporation method via ultrasonic emulsification. The optimized nanoparticles have a mean size of 285nm, a positive zeta potential of 42mV. The encapsulation efficiency was up to 73.9%. In vitro results revealed that the initial burst release of insulin from nanoparticles was markedly reduced at pH 1.2, which mimics the stomach environment. In vivo effects of the capsule containing insulin PLGA/RS nanoparticles were also investigated in diabetic rat models. The oral delivered capsules induced a prolonged reduction in blood glucose levels. The pharmacological availability was found to be approximately 9.2%. All the results indicated that the integration of HP55-coated capsule with cationic nanoparticles may be a promising platform for oral delivery of insulin with high bioavailability.

Mechanism and consequence of chitosan-mediated reversible epithelial tight junction opening

In order to increase the absorption of hydrophilic macromolecules in the small intestine, permeation enhancers such as chitosan (CS) and its derivatives have been evaluated. The aim of the current work was to investigate, on molecular levels, the effect of CS on tight junction (TJ) integrity in Caco-2 cells. The observed changes in transepithelial-electrical-resistance measurements and the staining patterns of the monolayer Caco-2 cells demonstrate that CS can transiently and reversibly open the TJs between cells, thus enhancing the paracellular permeability. TJ ultra-structures examined by transmission electron microscopy support the concept that CS did induce transient opening of TJs. We then assessed TJ disruption at the gene and protein expression levels. Our data indicate that exposure to CS followed by recovery resulted in a significant increase in claudin-4 (Cldn4) gene transcription. Additionally, CS treatment induced redistribution of the TJ protein CLDN4 intracellularly following by its degradation in lysosomes, which represented an important contributing factor in TJ weakening, leading to the opening of TJs. The recovery of TJ after CS disruption required CLDN4 protein synthesis. These results suggest that CS regulates TJs by inducing changes in transmembrane CLDN4 protein. Understanding the mechanism of interaction between CS and epithelial cells is of paramount importance and needs to be established to aid further development in the use of CS to mediate the trans-epithelial drug delivery.

Surface-modified solid lipid nanoparticulate formulation for ifosfamide: development and characterization

Aims: The present research focuses on the development of the surface modified solid lipid nanoparticulate (SLN) system for enhancing the stability and sustaining the release of a model hydrophilic drug ifosfamide. Materials & Methods: SLNs consisting of glyceryl monooleate (GMO) and chitosan were prepared by double emulsion technique, crosslinked with sodium tripolyphosphate, followed by lyophilization under two different vacuum conditions. The physicochemical characterization of SLNs included evaluation of surface morphology, particle size and surface charge, moisture content and physical state of the drug in the delivery system. The in vitro drug release and the stability were evaluated using high-performance liquid chromatography and liquid chromatography/mass spectrometry, respectively. Cellular permeability and subcellular localization studies were performed using Caco-2 cells. Results: Different chamber pressures during lyophilization produced SLNs with different morphologies and moisture contents. SLNs demonstrated high encapsulation efficiency, sustained release, and enhanced stability of ifosfamide with a high cellular uptake and permeability for Caco-2 cells. Conclusion: GMO and chitosan SLNs could be successfully used for enhancing the stability, sustaining the release, enhancing the targeting and permeability characteristics of ifosfamide.

Effects of chitosan-nanoparticle-mediated tight junction opening on the oral absorption of endotoxins

Recently, we reported a pH-responsive nanoparticle (NP) system shelled with chitosan (CS), which could effectively increase the oral absorption of insulin and produce a hypoglycemic effect, presumably due to the CS-mediated tight junction (TJ) opening. It has been often questioned whether CS can also enhance the absorption of endotoxins present in the small intestine. To address this concern, we studied the effect of CS NPs on the absorption of lipopolysaccharide (LPS), the most commonly found toxin in the gastrointestinal tract. To follow their biodistribution by the single-photon emission computed tomography/computed tomography, LPS and insulin were labeled with (99m)Tc-pertechnetate ((99m)Tc-LPS) and (123)iodine ((123)I-insulin), respectively. The (99m)Tc-LPS was ingested 1 h prior to the administration of the (123)I-insulin-loaded NPs to mimic the physiological conditions. The confocal and TEM micrographs show that the orally administered CS NPs were able to adhere and infiltrate through the mucus layer, approach the epithelial cells and mediate to open their TJs. The radioactivity associated with LPS was mainly restricted to the gastrointestinal tract, whereas (123)I-insulin started to appear in the urinary bladder at 3 h post administration. This observation indicates that the insulin-loaded in CS NPs can traverse across the intestinal epithelium and enter the systemic circulation, whereas LPS was unable to do so, probably because of the charge repulsion between the anionic LPS in the form of micelles and the negatively charged mucus layer. Our in vivo toxicity study further confirms that the enhancement of paracellular permeation by CS NPs did not promote the absorption of LPS. These results suggest that CS NPs can be used as a safe carrier for oral delivery of protein drugs.

A galactosamine-mediated drug delivery carrier for targeted liver cancer therapy

In order to minimize the side effect of cancer chemotherapy, a novel galactosamine-mediated drug delivery carrier, galactosamine-conjugated albumin nanoparticles (GAL-AN), was developed for targeted liver cancer therapy. The albumin nanoparticles (AN) and doxorubicin-loaded AN (DOX-AN) were prepared by the desolvation of albumin in the presence of glutaraldehyde crosslinker. Morphological study indicated the spherical structure of these synthesized particles with an average diameter of around 200 nm. The functional ligand of galactosamine (GAL) was introduced onto the surfaces of AN and DOX-AN via carbodiimide chemistry to obtain GAL-AN and GAL-DOX-AN. Cellular uptake and kinetic studies showed that GAL-AN is able to be selectively incorporated into the HepG2 cells rather than AoSMC cells due to the existence of asialoglycoprotein receptors on HepG2 cell surface. The cytotoxicity, measured by MTT test, indicated that AN and GAL-AN are non-toxic and GAL-DOX-AN is more effective in HepG2 cell killing than that of DOX-AN. As such, our results implied that GAL-AN and GAL-DOX-AN have specific interaction with HepG2 cells via the recognition of GAL and asialoglycoprotein receptor, which renders GAL-AN a promising anticancer drug delivery carrier for liver cancer therapy.

Liposomes containing glycocholate as potential oral insulin delivery systems: preparation, in vitro characterization, and improved protection against enzymatic degradation

Background:

Oral delivery of insulin is challenging and must overcome the barriers of gastric and enzymatic degradation as well as low permeation across the intestinal epithelium. The present study aimed to develop a liposomal delivery system containing glycocholate as an enzyme inhibitor and permeation enhancer for oral insulin delivery.

Methods:

Liposomes containing sodium glycocholate were prepared by a reversed-phase evaporation method followed by homogenization. The particle size and entrapment efficiency of recombinant human insulin (rhINS)-loaded sodium glycocholate liposomes can be easily adjusted by tuning the homogenization parameters, phospholipid:sodium glycocholate ratio, insulin:phospholipid ratio, water:ether volume ratio, interior water phase pH, and the hydration buffer pH.

Results:

The optimal formulation showed an insulin entrapment efficiency of 30% ± 2% and a particle size of 154 ± 18 nm. A conformational study by circular dichroism spectroscopy and a bioactivity study confirmed the preserved integrity of rhINS against preparative stress. Transmission electron micrographs revealed a nearly spherical and deformed structure with discernable lamella for sodium glycocholate liposomes. Sodium glycocholate liposomes showed better protection of insulin against enzymatic degradation by pepsin, trypsin, and α-chymotrypsin than liposomes containing the bile salt counterparts of sodium taurocholate and sodium deoxycholate.

Conclusion:

Sodium glycocholate liposomes showed promising in vitro characteristics and have the potential to be able to deliver insulin orally.

Recent advancement of chitosan-based nanoparticles for oral controlled delivery of insulin and other therapeutic agents

Nanoparticles composed of naturally occurring biodegradable polymers have emerged as potential carriers of various therapeutic agents for controlled drug delivery through the oral route. Chitosan, a cationic polysaccharide, is one of such biodegradable polymers, which has been extensively exploited for the preparation of nanoparticles for oral controlled delivery of several therapeutic agents. In recent years, the area of focus has shifted from chitosan to chitosan derivatized polymers for the preparation of oral nanoparticles due to its vastly improved properties, such as better drug retention capability, improved permeation, enhanced mucoadhesion and sustained release of therapeutic agents. Chitosan derivatized polymers are primarily the quaternized chitosan derivatives, chitosan cyclodextrin complexes, thiolated chitosan, pegylated chitosan and chitosan combined with other peptides. The current review focuses on the recent advancements in the field of oral controlled release via chitosan nanoparticles and discusses about its in vitro and in vivo implications.

pH-Responsive nanoparticles for drug delivery

First-generation nanoparticles (NPs) have been clinically translated as pharmaceutical drug delivery carriers for their ability to improve on drug tolerability, circulation half-life, and efficacy. Toward the development of the next-generation NPs, researchers have designed novel multifunctional platforms for sustained release, molecular targeting, and environmental responsiveness. This review focuses on environmentally responsive mechanisms used in NP designs, and highlights the use of pH-responsive NPs in drug delivery. Different organs, tissues, and subcellular compartments, as well as their pathophysiological states, can be characterized by their pH levels and gradients. When exposed to these pH stimuli, pH-responsive NPs respond with physicochemical changes to their material structure and surface characteristics. These include swelling, dissociating or surface charge switching, in a manner that favors drug release at the target site over surrounding tissues. The novel developments described here may revise the classical outlook that NPs are passive delivery vehicles, in favor of responsive, sensing vehicles that use environmental cues to achieve maximal drug potency.

Novel technology for the preparation of self-assembled catechin/gelatin nanoparticles and their characterization

In this study, self-assembled tea catechin/gelatin nanoparticles were prepared by directly mixing the catechins and gelatin solutions. The mean particle sizes were almost less than 200 nm, and the zeta potential values were negatively charged. FT-IR spectral analysis indicated that hydrogen bonding between aliphatic and aromatic hydroxyl groups, respectively, on gelatin and catechins is responsible for the self-assembly of nanoparticles. Free radical (DPPH* and ABTS*(+)) scavenging assays showed that tea catechins could be protected by the nanoparticles and that the antioxidant activity of tea catechins was almost retained after three weeks of storage. The tea catechin/gelatin nanoparticles exhibited 28-41% inhibition to trypsin against the degradation of gelatin. This result suggested that the tea catechin/gelatin nanoparticles might be a useful antioxidant carrier because catechins and gelatin were, respectively, protected from oxidation and enzymatic digestion.

Biopharmaceutical parameters to consider in order to alter the fate of nanocarriers after oral delivery

Oral route is the most common route for the delivery of drugs because it is simple to implement and improves patient compliance and quality of life. However, oral absorption is limited by various physiological barriers and remains a scientific challenge. Nanometric-sized drug delivery systems are being extensively studied and provide promising potential for oral drug delivery. Many different technological solutions have been proposed to enhance the bioavailability or the targeting of drug after oral administration. To reach these goals, it is important to analyze the biopharmaceutical parameters to consider in order to alter the fate of nanocarriers after oral delivery. In the present review, the gastrointestinal barrier and physiological stress factors with regard to nanocarriers' performance or integrity issues are first described. Second, the different characteristics offered by the nanocarriers (size, surface composition and properties mediated by external factors such as ligands) and their effect on the optimal transport of drug into the bloodstream are discussed. Finally, the integrity issue is discussed in function of the expected role of the nanocarriers: bioavailability enhancement or pharmacological targeting.

Thiol-modified chitosan sulfate nanoparticles for protection and release of basic fibroblast growth factor

A series of chitosan (CS) derivatives, the 6-O-carboxymethylchitosan (6-O-CC), 2-N sulfated 6-O-carboxymethylchitosan (N-SOCC) and the 2-N and 3,6-O sulfated 6-O-carboxymethyl chitosan (N,O-SOCC) were synthesized in this study. The chemical structures and the degrees of substituted carboxymethyl and sulfate groups of the synthesized compounds were respectively determined by FT-IR spectra and elemental analysis. N,O-SOCC displayed the highest protective efficiency for basic fibroblast growth factor (bFGF) as examined by the L929 fibroblast culture test and docking simulation. N,O-SOCC-4-thio-butylamidine (TBA) conjugates prepared by modification of N,O-SOCC with 2-iminothiolane were in situ cross-linkable. The degrees of thiol substitution of the 2-iminothiolane modified N,O-SOCC polymers were determined to be in the ranges of 45.9 +/- 3.7 and 415.6 +/- 12.5 micromol SH/g SOCC by quantifying the amount of thiol groups on the thiolated polymers with Ellman's reagent. The 2-iminothiolane modified N,O-SOCC and CS complex could be used for preparing nanoparticles by a polyelectrolyte self-assembly method, and the release of bFGF from the nanoparticles was successfully controlled. L929 fibroblast culture tests showed that the thiol modified N,O-SOCC/CS nanoparticles could effectively protect bFGF from inactivation over a 120 h period. The results of this study suggest that the thiol modified N,O-SOCC/CS nanoparticles may be useful as novel materials for specific delivery of bFGF with mitogenic activity.

Stabilization of polyion complex nanoparticles composed of poly(amino acid) using hydrophobic interactions

We report the design and preparation of polyion complex (PIC) nanoparticles composed of anionic hydrophobically modified and cationic poly(amino acid) and the effect of hydrophobic interactions on the stability of these PIC nanoparticles under physiological conditions. We selected poly(gamma-glutamic acid) (gamma-PGA) as the biodegradable anionic polymer and poly(epsilon-lysine) (epsilon-PL) as the cationic polymer. Amphiphilic graft copolymers consisting of gamma-PGA and L-phenylalanine (L-Phe) as the hydrophobic side chain were synthesized by grafting L-Phe to gamma-PGA. The PIC nanoparticles were prepared by mixing gamma-PGA-graft-L-Phe (gamma-PGA-Phe) with epsilon-PL in phosphate buffered saline (PBS). The formation and stability of the PIC nanoparticles were investigated by dynamic light scattering (DLS) measurements. Monomodal anionic PIC nanoparticles were obtained using nonstoichiometric mixing ratios. When unmodified gamma-PGA was mixed with epsilon-PL in PBS, the formation of PIC nanoparticles was observed. However, within a few hours after the preparation, the PIC nanoparticles dissolved in the PBS. In contrast, gamma-PGA-Phe/epsilon-PL nanoparticles showed high stability for a prolonged period of time in PBS and over a wide range of pH values. The stability and size of the PIC nanoparticles depended on the gamma-PGA-Phe/epsilon-PL mixing ratio and the hydrophobicity of the gamma-PGA. The improved stability of the PIC nanoparticles was attributed to the formation of hydrophobic domains in the core of the nanoparticles. The fabrication of PIC nanoparticles using hydrophobic interactions was very useful for the stabilization of the nanoparticles. These results will provide a novel concept in the design of carrier systems composed of PIC. It is expected that the gamma-PGA-Phe/epsilon-PL nanoparticles will have great potential as multifunctional carriers for pharmaceutical and biomedical applications, such as drug and vaccine delivery systems.