Colloidal Carrier Systems Research Articles

Asymmetrical flow field-flow fractionation and multiangle light scattering for analysis of gelatin nanoparticle drug carrier systems.

The physicochemical properties of nanosized colloidal drug carrier systems are of great influence on drug efficacy. Consequently, a broad spectrum of analytical techniques is applied for comprehensive drug carrier characterization. It is the primary objective of this paper to present asymmetrical flow field-flow fractionation (AF4), coupled online with multiangle light scattering detection, for the characterization of gelatin nanoparticles. Size and size distribution of drug-loaded and unloaded nanoparticles were determined, and data were correlated with results of state-of-the-art methods, such as scanning electron microscopy and photon correlation spectroscopy. Moreover, the AF4 fractionation of gelatin nanoparticulate carriers from a protein model drug is demonstrated for the first time, proposing a feasible way to assess the amount of loaded drug in situ without sample preparation. This hypothesis was set into practice by monitoring the drug loading of nanoparticles with oligonucleotide payloads. In this realm, various fractions of gelatin bulk material were analyzed via AF4 and size-exclusion high-pressure liquid chromatography. Mass distributions and high-molecular-weight fraction ratios of the gelatin samples varied, depending on the separation method applied. In general, the AF4 method demonstrated the ability to comprehensively characterize polymeric gelatin bulk material as well as drug-loaded and unloaded nanoparticles in terms of size, size distribution, molecular weight, and loading efficiency.

Preparation and characterization of solid lipid nanoparticles containing peptide

Solid lipid nanoparticles (SLN) are an alternative colloidal carrier system for controlled drug delivery. However, only a few have been studied regarding the incorporation of peptides into SLN, due to the hydrophilic peptide not easy to enter the lipophilic matrix of SLN. In the present report, peptide-loaded solid lipid nanoparticles were prepared by a novel solvent diffusion method in an aqueous system. The model peptide gonadorelin was incorporated to study the entrapment efficiency, size, zeta potential (charge) and drug delivery characterization. Gonadorelin and monostearin were dissolved in acetone and ethanol at 50 °C in water bath, the resultant organic solution was poured into an aqueous containing 1% polyvinyl alcohol (PVA) under mechanical agitation. The peptide-loaded solid lipid nanoparticles were quickly produced and separated by centrifugation. The average volume diameter of gonadorelin-loaded SLN is 421.7 nm and the zeta potential of SLN is −21.1 mV dispersed in distilled water. Up to 69.4% of gonadorelin can be incorporated. In vitro release of gonadorelin from SLN is slow. In the test solution of a 0.1N hydrochloric acid for 2 h and then transferred in a pH 6.8 phosphate buffer (simulative gastrointestinal fluid), the drug-release behavior from SLN suspension exhibited a biphasic pattern. After burst drug-release at the first 6 h at a percentage of 24.4% of loaded gonadorelin, a distinctly prolonged release over a monitored period of 12 days was observed and nearly 3.81% of drug was released in each day. In the test solution of a pH 6.8 phosphate buffer (simulative intestinal fluid), the drug-release rate from SLN was similar to that in the simulative gastrointestinal fluid. Further, a novel preparation method in the present research for peptide-loaded SLN was established. These results also demonstrate the principle suitability of SLN as a prolonged release formulation for hydrophilic peptide drugs.

Effect of colloidal carriers on ascorbyl palmitate stability.

Active compounds can be protected against degradation by incorporation into colloidal carrier systems. The stabilizing effect of carrier systems for ascorbyl palmitate (AP) was investigated using microemulsions (ME), liposomes and solid lipid nanoparticles (SLN). Analysis of chemical stability by HPLC showed that AP is most resistant against oxidation in non-hydrogenated soybean lecithin liposomes, followed by SLN, w/o and o/w ME, and hydrogenated soybean lecithin liposomes. The molecular environment of the AP-like nitroxide probe (C(16)-Tempo) in colloidal carriers was characterized using electron paramagnetic resonance (EPR) spectroscopy. We have found that the nitroxide groups are located in environments with different polarity and mobility. The hydrophilic part of AP is the reactive moiety, and high stability is obtained in systems in which this part is exposed to a less polar environment. Additionally, the determined accessibility of nitroxide groups to reduction correlated well with the chemical stability of AP. It is more deeply immersed in the interface when entrapped in a liquid-state carrier than when applied in gel-state particles. Encapsulation of AP in SLN core leads to greater stability. We conclude that the location of the sensitive group of the drug-molecule in a carrier system is crucial for its stability.

Poly(hydroxyethylaspartamide) derivatives as colloidal drug carrier systems

Poly(hydroxyethylaspartamide) (PHEA) derivatives bearing at the polyaminoacidic backbone poly(ethyleneglycol) (2000 or 5000 Da) or both poly(ethyleneglycol) and hexadecylalkylamine as pendant moieties were investigated as polymeric colloidal drug carriers. The ability of the PHEA derivatives to solubilize hydrophobic drugs was investigated using paclitaxel, amphotericin B and methotrexate. The results demonstrated that the drug solubility depends on both macromolecule composition and drug physicochemical properties. In particular, PEG/hexadecylalkylamine co-grafting increased significantly the solubilization properties of PHEA for the considered drugs while the conjugation of PEG only did not endow PHEA with drug carrier properties. A stability study carried out with paclitaxel/PHEA–PEG 5000–hexadecylalkylamine demonstrated that the drug/carrier system is characterized by physicochemical instability, which is strictly related to the incubation pH. However, the carrier was found to partially prevent drug degradation. Investigations performed using murine myeloid leukaemia NFS-60 cell line showed that paclitaxel loaded PHEA–PEG 5000–hexadecylalkylamine possesses high pharmacological activity with IC 50 value of 22.3 ng/ml. Pharmacokinetic studies carried out by intravenous administration of paclitaxel loaded PHEA–PEG 5000–hexadecylalkylamine to Balb/c mice demonstrated that the carrier modifies the in vivo paclitaxel fate. In particular, PHEA–PEG 5000–hexadecylalkylamine prolonged the drug distribution and elimination phase of 6 and 17 times, respectively; in addition, it increased the systemic availability (AUC) by about 30 times.

Preparation of solid lipid nanoparticles with clobetasol propionate by a novel solvent diffusion method in aqueous system and physicochemical characterization

Solid lipid nanoparticles (SLN) are a colloidal carrier system for controlled drug delivery. Monostearin SLN were prepared by a novel solvent diffusion method in an acidic aqueous system in order to improve the recovery of the method. The lipophilic model drug clobetasol propionate was incorporated to study the recovery of nanoparticles, entrapment efficacy, zeta potential (charge) and drug delivery characterization. The drug and monostearin were dissolved in acetone and ethanol at 50 °C in water bath, the resultant organic solution was poured into an acidic aqueous (pH 1.10) containing 1% polyvinyl alcohol (PVA) under mechanical agitate at room temperature. The drug loaded SLN was quickly produced with an aggregation state and easily separated by centrifugation. The recovery of nanoparticles was markedly increased compared to using a usual aqueous (pH 5.73) containing the same concentration of PVA. After burst drug release at the first 3 h, a distinctly prolonged release over a monitored period of 4 days was observed and nearly 6% drug was released in each day. Further, a novel preparation method and the optimized separation parameters in the present research for SLN were established. These results also demonstrate the principle suitability of SLN as a prolonged release formulation for lipophilic drugs.

Lectin-mediated Drug Delivery: Discrimination Between Cytoadhesion and Cytoinvasion and Evidence for Lysosomal Accumulation of Wheat Germ Agglutinin in the Caco-2 Model

Lectin-mediated drug delivery may become a promising strategy to improve the efficacy of poorly permeable drugs by utilising active high-capacity transport pathways of epithelial tissues. This requires the elucidation of the basic mechanisms of lectin uptake prior to their practical use. We studied the interaction between the dietary lectin wheat germ agglutinin (WGA) and Caco-2 cells (single cells and monolayers) by a newly established assay design that is able to discriminate between cellular binding and uptake as well as by confocal microscopy: (i) All binding sites available for WGA at the cell membrane were occupied within 10 min of incubation. (ii) Cytoadhesion was followed by immediate uptake. After 20 min, 60% (single cells) or 30% (monolayers) of the membrane bound lectin were internalised. However, regardless of cell arrangement, 80% of the surface bound lectin was taken up into the cells during the course of the experiment. (iii) About 50% of the internalised lectin accumulated within the lysosomes after 1 h. This was confirmed by assays in the presence of monensin, an inhibitor of endosomal acidification, and by colocalisation with lysosomal cathepsin followed by semiquantitative image analysis. Further analysis by immunocytochemistry suggested that the trans-Golgi complex and the caveoli were not involved. Due to cytoadhesion, cytoinvasion and partial lysosomal accumulation, WGA-mediated drug delivery may provide for improved intracellular availability of conjugated drugs or colloidal carrier systems.

A Study on the Preparation and Anti-Tumor Efficacy of Bovine Serum Albumin Nanospheres Containing 5-Fluorouracil

ABSTRACTThe therapeutic profile of many anti-cancer drugs has been improved by their modified distribution through a colloidal carrier system. Hence, bovine serum albumin nanospheres containing 5-fluorouracil were prepared by pH-coacervation methods. To select the most suitable cryoprotector for the formulated nanosphere system, a study on the effect of cryoprotectors in the prevention of particle agglomeration was done. Using glucose and mannitol at various concentrations during freeze drying, glucose at a concentration of 5% was observed to be relatively more effective in the prevention of particle agglomeration than the other cryoprotectors. The carrier capacity was determined through the drug-to-albumin ratio. The particle size of all the drug-loaded batches was analyzed before and after freeze drying. The batch of nanospheres with uniform size distribution, and highest drug loading, was used for other subsequent studies. The effect of surfactant in drug loading was estimated through various concentrations of sodium lauryl sulfate, and it was observed that the surfactant has no influence on drug loading at the selected concentrations. The batch of nanospheres with highest drug loading was evaluated for its in-vitro release, and the drug release was found to be in a bi-phasic pattern. To evaluate the efficacy of 5-fluorouracil-loaded nanospheres against cancer cells, an in vitro cytotoxicity study was carried out using HEp-2 cell lines. The nanosphere-bound drug was observed to produce a better cytotoxic effect than the free drug. The anti-tumor efficacy of drug-loaded nanosphere was investigated in DLA tumor-induced mice models, and the percentage tumor inhibition was relatively higher in animals treated with nanosphere-bound drug than with free drug.

Nanocapsule technology: a review.

Nanocapsules are submicroscopic colloidal drug carrier systems composed of an oily or an aqueous core surrounded by a thin polymer membrane. Two technologies can be used to obtain such nanocapsules: the interfacial polymerization of a monomer or the interfacial nanodeposition of a preformed polymer. This article is an extended review of these nanocapsule technologies and their applications for the treatment of various diseases (including cancer and infections).

Production of solid lipid nanoparticles (SLN): scaling up feasibilities

Solid lipid nanoparticles (SLN/Lipopearls) are widely discussed as a new colloidal drug carrier system. In contrast to polymeric systems, such as Polylactic copolyol microcapsules, these systems show with a good biocompatibility, if applied parenterally. The solid lipid matrices can be comprised of fats or waxes, and allow protection of incorporated active ingredients against chemical and physical degradation. The SLN can either be produced by 'hot homogenization' of melted lipids at elevated temperatures or by a 'cold homogenization' process. This paper deals with production technologies for SLN formulations, based on non-ethoxylated fat components for topical application and high pressure homogenization. Based on the chosen fat components, a novel and easy manufacturing and scaling-up method was developed to maintain chemical and physical integrity of the encapsulated active ingredients in the carrier.

Block copolymer micelles for drug delivery: design, characterization and biological significance

Recently, colloidal carrier systems have been receiving much attention in the field of drug targeting because of their high loading capacity for drugs as well as their unique disposition characteristics in the body. This paper highlights the utility of polymeric micelles formed through the multimolecular assembly of block copolymers as novel core–shell typed colloidal carriers for drug and gene targeting. The process of micellization in aqueous milieu is described in detail based on differences in the driving force of core segregation, including hydrophobic interaction, electrostatic interaction, metal complexation, and hydrogen bonding of constituent block copolymers. The segregated core embedded in the hydrophilic palisade is shown to function as a reservoir for genes, enzymes, and a variety of drugs with diverse characteristics. Functionalization of the outer surface of the polymeric micelle to modify its physicochemical and biological properties is reviewed from the standpoint of designing micellar carrier systems for receptor-mediated drug delivery. Further, the distribution of polymeric micelles is described to demonstrate their long-circulating characteristics and significant tumor accumulation, emphasizing their promising utility in tumor-targeting therapy. As an important perspective on carrier systems based on polymeric micelles, their feasibility as non-viral gene vectors is also summarized in this review article.

Influences of process parameters on nanoparticle preparation performed by a double emulsion pressure homogenization technique

The preparation of nanoparticles (NP) as an improved colloidal carrier system for proteins was investigated. Bovine serum albumin (BSA) was used as model drug. Owing to the high solubility of the protein in water, the double emulsion technique has been chosen as one of the most appropriate method. In order to both reaching submicron size as well as increasing the grade of monodispersity compared to previous preparation techniques, a microfluidizer as homogenization device was used. All experiments were performed using two biodegradable polymers, poly[d,l-lactic-co-glycolic acid] 50/50 (PLGA) and poly[ε-caprolactone] (PCL). The homogenization procedure has been optimized with regard to particle size and monodispersity by studying the influence of the homogenization time as well as the amount of polymer and surfactant in the external aqueous phase. The drug loading has been improved by varying the concentration of the protein in the inner aqueous phase. By increasing the protein concentration in the inner aqueous phase the polydispersity was slightly higher, while the particle size was not influenced significantly. The BSA encapsulation efficiency decreased with higher protein concentration in the inner aqueous phase. All release profiles were characterized by a initial burst effect, a higher release rate was obtained after 4 weeks for PLGA NP (60%) compared with PCL NP (47%).

微粒子製剤設計とＤＤＳ コアーシェル型高分子ミセルの構造設計とＤＤＳへの応用

Recently, colloidal carrier systems have been receiving much attention in the field of drug targeting because of their high loading capacity for drugs as well as of their unique disposition characteristics in the body. This paper highlights the utility of polymeric micelles formed through the multimolecular assembly of block copolymers as novel core-shell typed particulates for drug and gene targeting. The process of micellization in aqueous milieu is described in detail based on the differences in the driving force of core segregation, including hydrophobic interaction, electrostatic interaction, metal complexation, and hydrogen bonding of constituent block copolymers. The segregated core embedded in the hydrophilic palisade is shown to function as a reservoir for genes, enzymes, and a variety of drugs with diverse characteristics. Further, the body distribution of polymeric micelles is described to demonstrate their long-circulating characteristics. Focus is placed on the role of the hydrophilic shell in preventing micelles from reticular endothelial recognition, Significant tumor accumulation of polymeric micelles entrapping cytotoxic agents in the core is shown to emphasize their promising utility in tumor-targeting therapy. As an important perspective on carrier systems based on polymeric micelles, their feasibility as non-viral gene vectors is also summarized in this review article.

Evaluation of aminoalkylmethacrylate nanoparticles as colloidal drug carrier systems. Part II: characterization of antisense oligonucleotides loaded copolymer nanoparticles

Aminoalkylmethacrylate methylmethacrylate copolymer nanoparticles were evaluated for their use as potential drug carrier systems. Their cytotoxicity, as well as the loading of antisense oligonucleotides that were employed as anionic model drugs depended on the substitution of the basic aminoalkyl copolymer. Toxic influences on the integrity of cell membranes depended on aminoalkyl groups located on the particle surfaces. Toxicity was observed either by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays using African green monkey kidney (AGMK) cells or by a hemolysis test, where the efflux of haemoglobin from disrupted erythrocytes was measured. The cytotoxic effects were increased by the elongation of the N-alkyl chain by four additional methylene groups. Lipophilic polymethylmethacrylate (PMMA) homopolymer nanoparticles showed a negative surface charge and, therefore, were not suitable for the adsorption of anionic drugs. The surface charge was changed to positive values by the incorporation of basic monomers. Consequently, the loading efficacy was increased by raising the basic copolymer portion. Additionally, a pH-dependent loading behaviour of oligonucleotides was observed. Substitution of the amino nitrogen protons by methyl groups led to a decreased oligonucleotide loading and to a reduced cytotoxicity. Nanoparticles with permanent positively charged quarternary ammonium groups showed a high pH-independent loading efficacy, but also possessed a high cytotoxic potential. In this study, cationic copolymer nanoparticles containing 30% (w/w) methylaminoethyl-methacrylate (MMAEMC) were found to be optimal with regard to biocompatibility and carrier properties for hydrophilic anionic antisense oligonucleotides. A significant portion of adsorbed oligonucleotides were protected from enzymatic degradation. The cellular uptake of oligonucleotides into Vero cells was significantly enhanced by this methylaminoethyl-methacrylate derivative.

Evaluation of aminoalkylmethacrylate nanoparticles as colloidal drug carrier systems. Part I: synthesis of monomers, dependence of the physical properties on the polymerization methods

Conventional nanoparticles based on acrylic compounds are lipophilic and possess a negative surface charge. This is due to their manufacturing process and to the chemical structure of the polymer. Hence, these particles are not suitable for the adsorption of hydrophilic anionic drugs. In the present investigation, positively charged copolymer nanoparticles prepared from aminoalkyl- and methylmethacrylates were evaluated, with regard to their physical properties. This report provides a detailed description of the synthesis of the non-commercially available monomers and their polymerization procedure. Various parameters were investigated, such as comonomer content, total amount of monomer, concentration of the radical initiator, and the composition of the polymerization medium. The resulting particle diameter and the surface charge were found to be strongly dependent on the polymerization conditions and on the pH. Optimization of the polymerization procedure yielded nanoparticles of about 200 nm exhibiting a positive surface charge. The charges of the different copolymer particles were then compared at different pH values. N-trimethylaminoethylmethacrylate (TMAEMC) nanoparticles with quaternary ammonium groups located at their surfaces, possessed a nearly constant positive zeta potential at various pH values and, consequently, pH-independent particle diameters. The physical characteristics of the other aminoalkyl copolymers correlated with the basicity of the monomers employed and were found to be strongly dependent on the pH of the dispersion medium. Aminoethylmethacrylate (AEMC), methylaminoethylmethacrylate (MMAEMC), and aminohexylmethacrylate (AHMC) as well as aminoethylmethacrylamide (AHMAC) copolymer nanoparticles exhibited a strong positively charged surface even at physiological pH and, therefore, are useful candidates for the adsorption of anionic drugs.

Solid lipid nanoparticles (SLN) for controlled drug delivery II. drug incorporation and physicochemical characterization

Solid lipid nanoparticles (SLN) are a colloidal carrier system for controlled drug delivery. The lipophilic model drugs tetracaine and etomidate were incorporated to study the maximum drug loading, entrapment efficacy, effect of drug incorporation on SLN size, zeta potential (charge) and long-term physical stability. Drug loads of up to 10% could be achieved whilst simultaneously maintaining a physically stable nanoparticle dispersion. Incorporation of drugs showed no or little effect on particle size and zeta potential compared to drug-free SLN. The optimized production parameters previously established for drug-free SLN dispersions can therefore be transferred to drug-loaded systems to facilitate product development.

Amphiphilic cyclodextrin nanospheres: particle solubilization and reconstitution by the action of a non-ionic detergent

Cyclodextrin nanospheres are a new type of colloidal carrier system that has been intensively studied in the area of pharmacotechnical aspects of drug association. However, the physical stability of this carrier has rarely been investigated, mainly towards the presence of another amphiphilic molecule in its environment. In this work, the first results relating to the action of solubilizing surfactants on nanospheres prepared from the amphiphilic 2,3-di- O-hexanoyl cyclomaltooctaose [ γCDC 6, average molar degree of substitution (MDS)=6.25] are described using n-octyl- β- d-glucopyranoside (OG) as the model. Solubilization experiments were performed by continuous addition of OG into nanosphere suspensions and it was demonstrated that, at a given critical ratio, this non-ionic detergent disrupts the spherical structure of the initial particles. The evidence of the γCDC 6–OG mixed micelle formation was provided by changes in the turbidity of suspensions with OG addition and by TEM micrographs. Reconstitution of the particles was performed by two detergent removal procedures: water dilution of micellar solutions and detergent dialysis. In both cases, the formation of new aggregates was demonstrated by changes in the turbitity of the initial mixed micelles. TEM micrographs revealed reconstituted nanoparticles. The QELS size and shape of the particles was dependent on the rate of detergent removal, but not on the initial γCDC 6 and OG concentrations: fast OG elimination led to the most regular spherical shapes. Finally, the entrapment upon detergent removal of the hydrophobic drug progesterone previously dissolved in the mixed micelles was investigated. In conclusion, all the results demonstrated that detergents can interact with nanospheres in a reversible process. These results will be very useful in stability studies, and also in the pharmacotechnical development of nanospheres constituted by amphiphilic cyclodextrins.

Colloidal systems for tumor targeting.

The potential and limitations of targeted delivery of anticancer agents with colloidal particulate carriers is the subject of this contribution. Because over the years liposomes have gained the most attention as carrier system in the category of colloidal carrier systems, this paper focuses on the utility of the liposomal system for tumor targeting. It is imperative that an intended therapeutic application of liposomes should be well matched with the liposome behavior in vivo. Therefore, the in vivo fate of the first-generation liposomes and the more recently developed second-generation liposomes (surface-modified liposomes such as the immunoliposomes and long-circulating liposomes) is analyzed in terms of accessibility of target sites, time-, and site-controlled drug release and potential target sites for rational targeted delivery are discussed. A few examples of areas in cancer chemotherapy, with a strong rationale for the use of liposomes, are given. It is concluded that, although several options are available on the drawing board, issues such as tumor cell heterogeneity, access to the target site, shedding of antigens, and target site-specific release of the liposome-associated drug need to be addressed early in the development process.

Spontaneous formation of drug-containing amphiphilic β-cyclodextrin nanocapsules

A new colloidal carrier system, nanocapsules, using 2,3-diacyl- O- β-cyclodextrins is described. The nanocapsules were prepared by adding a mixture of an organic solution of 2,3-diacyl- O- β-cyclodextrins (with or without a lipophilic surfactant) and an oily phase to an aqueous solution (with or without a hydrophilic surfactant) whilst stirring. Nanocapsules with a mean size of 200 nm are formed progressively. Direct microscopic observation of the particles was carried out using transmission electron microscopy (TEM) combined with the freeze-fracture method. The influence of different constituents on the preparation process was studied: type of 2,3-diacyl- O- β-cyclodextrins (β-CD-C 6, β-CD-C 12 and β-CD-C 14), nature of the oily phase (benzyl benzoate, Miglyol 812®), and the surfactants used (Pluronic PEF68®, Span 85®). An investigation of lipophilic drug encapsulation was also carried out. The results of this study suggest that nanocapsules of 2,3-diacyl- O- β-cyclodextrins could be considered as a potential colloidal drug carrier system.

Interleukin-2 lipid microspheres. I. development and evaluation of the colloidal drug carrier

AbstractUndesirable toxic effects associated with intravenous interleukin-2 (IL2) therapy have limited its use for the treatment of cancer. Therefore, we investigated properties of a colloidal carrier system intended for the delivery of IL2. Lipid microspheres (LMS) are 10% (v/v) soybean oil emulsions stabilized with block copolymers of the poloxamer and poloxamine type. Poloxamers 238, 338, 407 or poloxamine 908 LMS were evaluated for physical stability, in vitro toxicity, and in vivo biodistribution. With the exception of 2% poloxamer 238 LMS, all preparations displayed acceptable stability when stored for 3 months at 4° or 37°C. In addition, all LMS preparations exhibited physical stability when subjected to freeze-thaw cycling and extended periods of freezing. In vitro cellular toxicity was evaluated in a murine cytotoxic T lymphocyte cell line (CTLL-2) and human peripheral blood mononuclear cells (PBMC). The calculated IC50 of LMS was approximately 30 and 10 mg/liter in CTLL-2 cells and PBMC, respect...

A novel assay to determine the hemolytic activity of drugs incorporated in colloidal carrier systems.

A novel assay to determine the hemolytic activity of drugs incorporated in colloidal carrier systems.