Properties of liposomes coated with hydrophobically modified chitosan in oral liposomal drug delivery

Chitosan (CS) has been widely used as an adhesive coating polymer for oral liposomal drug delivery systems because of its adhesive properties on mucous layers. The coating mechanism or interaction of chitosan and liposomes or mucin mainly depends on electrostatic forces. Thus, to enhance the adhesive properties of chitosan, a hydrophobically modified chitosan, i.e., dodecylated chitosan (DC), was synthesized. BIACORE results showed that both CS and DC could interact with mucin. Differences in sensorgram patterns between chitosan-mucin and dodecylated chitosan-mucin were observed and tentatively attributed to differences in binding kinetics. The zeta potential of dodecylated chitosan-coated liposomes (DC-Lip) showed positive values in both liposomal formulations, i.e., negatively charged and neutral-charge liposomes. These results indicated that DC could be considered a more suitable polymer for coating neutral-charge liposomes than CS because the hydrophobic side chain of DC inserts itself into the lipid bilayer of liposomes. Moreover, CS seemed to be less effective in the coating of a neutral-charge liposome because of the low positive values of its zeta potential. CS provided solely electrostatic forces when used for coating liposomes while DC provided electrostatic and hydrophobic forces due to the long alkyl chain in its backbone. Confocal Laser Scanning Microscopy (CLSM) images indicated that both chitosan-coated liposomes (CS-Lip) and DC-Lip could adhere to and penetrate through the small intestine of rats after oral administration. The pharmacological results showed that DC-Lip had a greater effect in decreasing blood calcium concentration during the first 12 h compared with CS-Lip. Therefore, it can be concluded that dodecylated chitosan can be useful in designing oral liposomal drug delivery systems.     

Mucoadhesive nanoparticulate systems for peptide drug delivery

This chapter describes the preparation of and methods for evaluating mucoadhesive nanoparticulate systems, including liposomes and polymeric nanoparticles. Mucoadhesive ability is conferred on the particulate systems by coating their surface with mucoadhesive polymers such as chitosan and Carbopol. The feasibility of this surface modification was confirmed by measuring the zeta potential. Several methods of evaluating the mucoadhesive properties of particulate systems have been reported in the literature. We have also developed some novel evaluation procedures including a particle counting method using a Coulter counter for polymer-coated liposomes. The mucoadhesive properties of the polymer-coated liposomes and polymeric nanoparticles were confirmed by means of these mucoadhesion tests. In applying these mucoadhesive nanoparticles to the oral and pulmonary administration of peptide drugs, more effective and prolonged action was observed in comparison with non-coated systems, thereby confirming the usefulness of mucoadhesive nanoparticulate systems for the delivery of peptide drugs.     

The use of chitosan-6-mercaptonicotinic acid nanoparticles for oral peptide drug delivery

The aim of this study was to develop a novel nanoparticulate formulation and test its potential for oral peptide drug delivery. Chitosan-6-mercaptonicotinic acid is a novel thiolated chitosan with strong mucoadhesive properties. Nanoparticles were developed by an ionic gellation method. The obtained particles were characterized in terms of mucoadhesion, stability, toxicity, and in vitro release. Human insulin (HI) was chosen as a model peptide drug, incorporated in the particles and orally administered to rats. Human insulin was quantified in the blood by means of ELISA. The size of the obtained particles was in the range of 200–300?nm and the zeta potential was determined to be +8?+23 depending on the amount of thiol groups attached on the polymer. After 3?h of incubation up to 60% of the thiolated chitosan nanoparticles remained attached to the mucosa in contrast to 20% of unmodified chitosan particles. The AUC of HI after oral administration of thiolated chitosan nanoparticles was 4-fold improved compared to unmodified chitosan nanoparticles. Due to these improvements, chitosan-6-mercaptonicotinic acid nanoparticles are promising vehicles for oral delivery of peptide drugs.     

Poly(4-vinylpyridine)-coated liposomes: stability studies and release of acetylsalicylic acid.

Liposomes of dimyristoylphosphatidylcholine (DMPC) and dicetylphosphate (DCP) reacted with 4-vinylpyridine (4-VP) to form a salt and, subsequently, autopolymerized for form poly(4-vinylpyridine) (poly(4-VP))-coated liposomes. The conditions for optimization of polymer coating have been determined; also, the effects of polymer coating on liposome stability, the encapsulation of ASA and its release kinetics have been measured. The coating efficiency was maximum at a DMPC:DCP 1:1 mole ratio, at pH 4.0 in acetate buffer, and a polymerization time of 40 min. The polymer-coated liposomes were stable in 2 mM sodium cholate and 4 per cent isopropanol solutions, as determined from turbidity measurements, versus a 20-25% decrease in stability of uncoated liposomes. The encapsulation efficiency of ASA reached a maximum of 9 per cent at DMPC:DCP 1:1 mole ratio. The release of ASA at 37 degrees C, pH 7.0 was characterized by an initial fast release (85 and 63 per cent in 20 min from uncoated and polymer-coated liposomes, respectively) followed by a slow, constant release rate up to 140 min. Thus, autopolymerization of a polymerizable monomer at liposome surfaces represents a potentially feasible stabilization approach for liposomes exposed to sodium cholate solutions with greater retention of solute than uncoated liposomes.     

Liposome surface charge influence on skin penetration behaviour

Vesicular systems have shown their ability to increase dermal and transdermal drug delivery. Their mechanism of drug transport into and through the skin has been investigated but remains a much debated question. Several researchers have outlined that drug penetration can be influenced by modifying the surface charge of liposomes. In the present work we study the influence of particle surface charge on skin penetration. The final purpose is the development of a carrier system which is able to enhance the skin delivery of two model drugs, betamethasone and betamethasone dipropionate. Liposomes were characterised by their size, morphology, zeta potential, encapsulation efficiency and stability. Ex vivo diffusion studies using Franz diffusion cells were performed. Confocal microscopy was performed to visualise the penetration of fluorescently labelled liposomes into the skin. This study showed the potential of negatively charged liposomes to enhance the skin penetration of betamethasone and betamethasone dipropionate.     

Physicochemical properties of liposomes incorporating hydrochlorothiazide and chlorothiazide

In an attempt to study the effect of hydrophobic drugs on liposome properties, multilamellar liposomes (MLV) consisting of phosphatidylcholine (PC) and incorporating chlorothiazide (CT) or hydrochlorothiazide (HCT), were prepared and characterized. Liposome size, surface charge, stability (in buffer, plasma and sodium cholate) and calcium-induced aggregation were studied for drug-incorporating liposomes and empty liposomes for comparison. Results show that drug incorporation affects liposome size, z-potential and stability in presence of buffer and plasma proteins. Indeed, drug-incorporating liposomes are slightly larger and have a negative surface charge, which increases with the amount of drug incorporated in the lipid membrane. The membrane integrity of drug incorporating liposomes (in absence and presence of plasma proteins) is significantly higher when compared with that of empty liposomes (for both drugs studied). On the contrary, vesicle membrane integrity in presence of sodium cholate and calcium induced vesicle aggregation, are not affected by drug incorporation. Leakage of thiazides from liposomes was demonstrated to be induced by dilution. Low amounts of thiazides (around 10-15%) are released when lipid concentration is over 0.1 mM, while further dilution increased drug leakage exponentially. Concluding, results demonstrate that the presence of HCT or CT in liposome membranes has a significant effect on main vesicle properties, which are known to influence vesicle targeting ability. Thereby, it is very interesting to continue studies in this respect, especially with more lipophilic drugs.     

Acacia-Gelatin Microencapsulated Liposomes: Preparation,Stability, and Release of Acetylsalicylic Acid

Liposomes of dipalmitoylphosphatidylcholine (DPPC) containing acetylsalicylic acid (ASA) have been microencapsulated by acacia-gelatin using the complex coacervation technique as a potential oral drug delivery system. The encapsulation efficiency of ASA was unaltered by the microencapsulation process. The stability of the microencapsulated liposomes in sodium cholate solutions at pH 5.6 was much greater than the corresponding liposomes. The optimum composition and conditions for stability and ASA release were 3.0% acacia-gelatin and a 1- to 2-hr formaldehyde hardening time. Approximately 25% ASA was released in the first 6 hr from microencapsulated liposomes at 23°C and the kinetics followed matrix-controlled release (Q t ^l/2). At 37°C, this increased to 75% released in 30 min followed by a slow constant release, likely due to lowering of the phase transition temperature of DPPC by the acacia-gelatin to near 37°C. At both temperatures, the release from control liposomes was even more rapid. Hardening times of 4 hr and an acacia-gelatin concentration of 5% resulted in a lower stability of liposomes and a faster release of ASA. It is concluded that under appropriate conditions the microencapsulation of liposomes by acacia-gelatin may increase their potential as an oral drug delivery system.     

PEG/RGD-modified magnetic polymeric liposomes for controlled drug release and tumor cell targeting

Polymeric liposomes (PEG/RGD-MPLs), composed of amphiphilic polymer octadecyl-quaternized modified poly (γ-glutamic acid) (OQPGA), PEGylated OQPGA, RGD peptide grafted OQPGA and magnetic nanoparticles, was prepared successfully. These PEG/RGD-MPLs could be used as a multifunctional platform for targeted drug delivery. The results showed that PEG/RGD-MPLs were multilamellar spheres with nano-size (50-70 nm) and positive surface charge (28-42 mV). Compared with magnetic conventional liposomes (MCLs), PEG/RGD-MPLs exhibited sufficient size and zeta potential stability, low initial burst release and less magnetic nanoparticles leakage. The cell uptake results suggested that the PEG/RGD-MPLs (with RGD and magnetic particles) exhibited more drug cellular uptake than non RGD and non magnetism carriers in MCF-7 cells. MTT assay revealed that PEG/RGD-MPLs showed lower in vitro cytotoxicity to GES-1cells at ≤ 100 μg/mL. These data indicated that the multifunctional PEG/RGD-MPLs may be an alternative formulation for drug delivery system.     

The use of chitosan-6-mercaptonicotinic acid nanoparticles for oral peptide drug delivery

The aim of this study was to develop a novel nanoparticulate formulation and test its potential for oral peptide drug delivery. Chitosan-6-mercaptonicotinic acid is a novel thiolated chitosan with strong mucoadhesive properties. Nanoparticles were developed by an ionic gellation method. The obtained particles were characterized in terms of mucoadhesion, stability, toxicity, and in vitro release. Human insulin (HI) was chosen as a model peptide drug, incorporated in the particles and orally administered to rats. Human insulin was quantified in the blood by means of ELISA. The size of the obtained particles was in the range of 200-300?nm and the zeta potential was determined to be +8-+23 depending on the amount of thiol groups attached on the polymer. After 3?h of incubation up to 60% of the thiolated chitosan nanoparticles remained attached to the mucosa in contrast to 20% of unmodified chitosan particles. The AUC of HI after oral administration of thiolated chitosan nanoparticles was 4-fold improved compared to unmodified chitosan nanoparticles. Due to these improvements, chitosan-6-mercaptonicotinic acid nanoparticles are promising vehicles for oral delivery of peptide drugs.     

Application of surface‐coated liposomes for oral delivery of peptide: Effects of coating the liposome's surface on the GI transit of insulin

We prepared two kinds of surface‐coated liposomes and investigated their potencies as oral dosage forms for peptide drugs by focusing on their effects on the gastrointestinal (GI) transit of drugs. The surface of the liposomes was coated with poly(ethylene glycol) 2000 (PEG‐Lip) or the sugar chain of mucin (Mucin‐Lip). As a model peptide drug, insulin was encapsulated in these liposomes. Coating the surface with poly(ethylene glycol) was found to reduce the transit rate of liposomes in the small intestine after oral administration to rats in vivo. Mucin‐Lip was retained in the stomach longer than PEG‐Lip or uncoated liposomes. The effect of surface coating on the intestinal transit of liposomes was determined by means of in situ single pass perfusion in the rat small intestine. Statistical moment analysis was applied to the outflow pattern of both liposomes and encapsulated insulin. The mean transit time (MTT) and deviation of transit time (DTT) in the intestinal tract were calculated. The MTT of PEG‐Lip was much longer than those of uncoated liposomes and Mucin‐Lip and was significantly shortened after removal of the intestinal mucous layer. These results indicated that PEG‐Lip interacts strongly with the intestinal mucous layer, leading to its slow transit in the intestine. In contrast, coating the liposome's surface with mucin did not affect either the MTT or DTT of liposomes in the intestine. This result is in accordance with the in vivo observation that Mucin‐Lip was highly retained in the stomach, but not in any region of the small intestine in vivo. Both the MTT and DTT values of insulin encapsulated in PEG‐Lip and Mucin‐Lip were almost the same as those of liposomes themselves, suggesting that surface‐coated liposomes retained insulin in the intestinal tract. However, MTT and DTT of insulin were significantly shorter than those of uncoated liposomes because these liposomes degraded and released significant amounts of insulin during single pass perfusion. The ability of surface‐coated liposomes, especially of PEG‐Lip, to interact with the mucus layer and slow the transit rate in the GI tract is considered desirable for oral delivery of peptide drugs. Modification of the liposomal surface with appropriate materials, therefore, should be an effective method by which to achieve the oral delivery of peptide drugs.     

Design of nanoparticles composed of graft copolymers for oral peptide delivery

The development of a dosage form that improves the absorption of peptide and protein drugs via the gastrointestinal tract is one of the greatest challenges in the pharmaceutical field. Many researchers have taken up the challenge, using approaches including mucoadhesive drug delivery, colon delivery, particulate drug delivery such as nanoparticles, microcapsules, liposomes, emulsions, micelles, and so on. The objective of this article is to provide the reader with outlines of novel nanoparticle technologies for oral peptide delivery based on polymer chemistry. The physicochemical properties of nanoparticles and their behavior on exposure to physiological media are greatly dominated by their chemical structures and surface characteristics. We will especially focus on the design of nanoparticles composed of novel graft copolymers having a hydrophobic backbone and hydrophilic branches as drug carriers.     

Chitosan-coated liposomes for intracellular oligonucleotides delivery: characteristics and cell uptake behavior

Surface modification of liposomes with polymer to optimize drug delivery was well developed recently. The objective of the present work was to evaluate the feasibility of chitosan-coated liposomes (CSLP) as vehicles for anti-sense oligodeoxynucleotides (ASON). CSLP was obtained by adding chitosan dropwise to liposomes under magnetic stirring. The effect of chitosan content on size, zeta potential, and coating efficiency was investigated, which showed that chitosan increased the size and zeta potential of CSLP, and the coating efficiency increased with chitosan content increasing. Agarose gel electrophoresis was employed to evaluate the loading efficiency of CSLP for ASON, from which one could see ASON was completely combined to CSLP when the mass ratio of total lipids:ASON was more than 50:1. MTT assay showed that CSLP took on very low cytotoxicity, which is much lower than chitosan. At last, cell uptake behavior was investigated by a flow cytometer, which showed that CSLP enhanced significantly the COS7 cells uptake of ASON. All the results indicated that the CSLP could be a promising non-viral ASON vehicle.     

Chitosan-coated liposomes for intracellular oligonucleotides delivery: Characteristics and cell uptake behavior

Surface modification of liposomes with polymer to optimize drug delivery was well developed recently. The objective of the present work was to evaluate the feasibility of chitosan-coated liposomes (CSLP) as vehicles for anti-sense oligodeoxynucleotides (ASON). CSLP was obtained by adding chitosan dropwise to liposomes under magnetic stirring. The effect of chitosan content on size, zeta potential, and coating efficiency was investigated, which showed that chitosan increased the size and zeta potential of CSLP, and the coating efficiency increased with chitosan content increasing. Agarose gel electrophoresis was employed to evaluate the loading efficiency of CSLP for ASON, from which one could see ASON was completely combined to CSLP when the mass ratio of total lipids:ASON was more than 50:1. MTT assay showed that CSLP took on very low cytotoxicity, which is much lower than chitosan. At last, cell uptake behavior was investigated by a flow cytometer, which showed that CSLP enhanced significantly the COS7 cells uptake of ASON. All the results indicated that the CSLP could be a promising non-viral ASON vehicle.     

Preparation and characterization of liposomes encapsulating chitosan nanoparticles

Liposomes are an important colloidal carrier system for controlled drug delivery. However some highly hydrophilic small molecules are difficult to entrap into liposomes and store stably, resulting in poor encapsulation efficiency and fast leakage. In the present work, fluorescein sodium (FS) was used as a model drug that was loaded into chitosan nanoparticles and then encapsulated into liposomes by reverse-phase evaporation (RPV). The encapsulation efficiency, particle size, zeta potential, release in vitro and pharmacokinetics in rats were determined in order to characterize the novel drug delivery system. The entrapment efficiency was above 80% in nanoparticles (Np) and 95% in liposomes encapsulating the nanoparticles (Lip-Np). The Lip-Np was composed of soybean phospholipids, cholesterol and chitosan, which the average diameter was 202.6 nm and zeta potential was -34.8 mV. The release rate of fluorescein sodium from Lip-Np was slower than from Np and liposomes. FS in Lip-Np administered to rats exhibited prolonged circulation and higher bioavailability than FS in Np. The results indicated that liposomal release kinetics can be controlled by encapsulating nanoparticles and thus solid-cored liposomes can be used as a potential drug delivery system.     

表面活性剂-醇质体增强多烯紫杉醇经皮给药的渗透性研究(英文)

皮肤的屏障作用使大部分药物无法实现透皮给药。本文以改善难溶性大分子模型药物多烯紫杉醇(docetaxel,DTX)的经皮渗透性为主体思路,研制了DTX的表面活性剂-醇质体(surfactant-ethanlic liposomes,SEL)。SEL由磷脂、乙醇、胆酸钠、DTX和磷酸盐缓冲液组成,采用薄膜分散法制备。对SEL的囊泡形态(冷冻蚀刻电镜法)、粒径大小及分布进行了表征,并测定包封率和载药量。采用体外扩散池实验研究了DTX表面活性剂-醇质体的经皮渗透性。结果表明,当磷脂与表面活性剂的比例为85:15时,DTX的稳态透皮速率和累计透皮量均为最高,且优于表面活性剂脂质体、醇质体和普通脂质体。最优处方的粒径分布、形态和载药量均较为稳定。本研究表明,通过将DTX包载于SEL中可显著改善DTX的经皮渗透性。     

Preparation and evaluation of N(3)-O-toluyl-fluorouracil-loaded liposomes

This study was aimed at developing a liposome delivery system for a new and potential antitumor lipophilic prodrug of 5-fluorouracil (5-Fu)-N(3)-O-toluyl-fluorouracil (TFu), intended to improve the bioavailability and therapeutic efficacy of 5-Fu by oral and intravenous administration. TFu-loaded liposomes were prepared by a modified film dispersion-homogenization technique, the formulation and manufacture parameters were optimized concerning the drug encapsulation efficiency. TFu-loaded liposomes were characterized according to particle size, size distribution, zeta potential, drug entrapment efficiency, drug loading and physical stability, respectively. In vitro release characteristics, in vivo pharmacokinetic properties and bioavailabilities were also investigated. The formulated liposomes were found to be relatively uniform in size (400.5 +/- 9.6 nm) with a negative zeta potential (-6.4 +/- 0.8 mV). The drug entrapment efficiency and loading were (88.87 +/- 3.25%) and (8.89 +/- 0.19%), respectively. The physical stability experiments results indicated that lyophilized TFu-loaded liposomes were stable for at least 9 months at 4 degrees C. In vitro drug release profile of TFu-loaded liposomes followed the bi-exponential equation. The results of the pharmacokinetic studies in mice indicated that the bioavailability of TFu-loaded liposomes was higher than the suspension after oral administration, and was bioequivalent comparing with TFu 50% alcohol solution after intravenous (i.v.) administration. These results indicated that TFu-loaded liposomes were valued to develop as a practical preparation for oral or i.v. administration.     

Enteral Absorption of Insulin in Rats from Mucoadhesive Chitosan-Coated Liposomes

Purpose. The mucoadhesiveness of polymer-coated liposomes was evaluated to develop a novel drug carrier system for oral administration of poorly absorbed drugs such as peptide drugs. Methods. Multilamellar liposomes consisting of dipalmitoylphosphatidylcholine (DPPC) and dicetyl phosphate (DCP) (DPPC:DCP = 8:2 in molar ratio) were coated with chitosan (CS), polyvinyl alcohol having a long alkyl chain (PVA-R) and poly (acrylic acid) bearing a cholesteryl group. The adhesiveness of the resultant polymer-coated liposomes to the rat intestine was measured in vitro by a particle counting method with a Coulter counter. The CS-coated liposomes containing insulin were administered to normal rats and the blood glucose level was monitored. Results. The existence of polymer layers on the surface of liposomes was confirmed by measuring the zeta potential of liposomes. The CS-coated liposomes showed the highest mucoadhesiveness and the degree of adhesion was dependent on the amount of CS on the surface of the liposomes. The blood glucose level of rats was found to be significantly decreased after administration of the CS-coated liposomes containing insulin. The lowered glucose level was maintained for more than 12h after administration of the liposomal insulin, which suggested mucoadhesion of the CS-coated liposomes in the intestinal tract of the rats.     

Dermal delivery of selected hydrophilic drugs from elastic liposomes: effect of phospholipid formulation and surfactants

The effect of phospholipid formulation and choice of surfactant on skin permeation of selected hydrophilic drugs from elastic liposomes across human epidermal membrane has been studied. Sodium cholate and various concentrations of phosphatidylcholine were used for the preparation of liposomes namely hydrogenated phosphatidylcholine 90% (Phospholipon 90H), phosphatidylcholine 95% (Phospholipon 90G), phosphatidylcholine 78.6% (Phospholipon 80), and phosphatidylcholine 50% (Phosal PG). To investigate the effect of the surfactant, liposomes were prepared from 95% phosphatidylcholine (Phospholipon 90G) and various surfactants (sodium cholate, sodium deoxycholate, Span 20 (sorbitan monolaurate), Span 40 (sorbitan monopalmitate), Span 60 (sorbitan stearate) and Span 80 (sorbitan monooleate)). The vesicles were prepared by the conventional rotary evaporation technique. The film was hydrated with phosphate-buffered saline (10 mL) containing 9, 2 and 2.5 mg mL(-1) of methotrexate, idoxuridine and aciclovir, respectively. All formulations contained 7% ethanol. Homogenously-sized liposomes were produced following extrusion through 100-nm polycarbonate filters using Lipex Extruder. Particle size was characterized by transmission electron microscopy. Vertical Franz diffusion cells were used for the study of drug delivery through human epidermal membrane. For the three drugs, the highest transcutaneous fluxes were from elastic liposomes containing 95% phosphatidylcholine. In general, a higher flux value was obtained for liposomes containing sodium cholate compared with sodium deoxycholate. For the liposomes containing sorbitan monoesters, there was no clearly defined trend between alkyl chain length and flux values. Overall, transcutaneous fluxes of liposomal preparations of hydrophilic drugs were comparable with those from saturated aqueous solutions (P > 0.05).     

洛伐他汀自组装前体脂质体的制备及其理化性质的研究

目的:为研究洛伐他汀新剂型,制备洛伐他汀新型前体脂质体,并对其质量进行考察。方法:采用一种新型前体脂质体制备方法将洛伐他汀制成自组装前体脂质体,对水合后脂质体的形态、粒径、Zeta电位、包封率、自组装速度、稳定性等进行考察,验证这种新型前体脂质体制备方法用于制备洛伐他汀脂质体的可行性。结果:所形成的洛伐他汀脂质体包封率为95.4%±6.7%,平均粒径为(327.4±29.6)nm,Zeta电位值为-(22.4±1.5)mV。洛伐他汀自组装前体脂质体可在60 s内自发形成脂质体并达到分散平衡;以人工胃液为稀释介质,洛伐他汀脂质体在12 h内稳定。结论:采用新型前体脂质体制备方法可将洛伐他汀制成洛伐他汀脂质体,形成的脂质体包封率较高且具有良好的稳定性。     

Evaluation of liposomes coated with a pH responsive polymer

Liposomes have been coated with the pH responsive polymer, Eudragit S100, and the formulation's potential for lower gastrointestinal (GI) targeting following oral administration assessed. Cationic liposomes were coated with the anionic polymer through simple mixing. The evolution of a polymer coat was studied using zeta potential measurements and laser diffraction size analysis. Further evidence of an association between polymer and liposome was obtained using light and cryo scanning electron microscopy. Drug release studies were carried out at pH 1.4, pH 6.3 and pH 7.8, representing the pH conditions of the stomach, small intestine and ileocaecal junction, respectively. The polymer significantly reduced liposomal drug release at pH 1.4 and pH 6.3 but drug release was equivalent to the uncoated control at pH 7.8, indicating that the formulation displayed appropriate pH responsive release characteristics. While the coating layer was not able to withstand the additional challenge of bile salts this reinforces the importance of evaluating these types of formulations in more complex media.