Controlled Release of Insulin from Injectable Biodegradable Triblock Copolymer

Pharmaceutical Research -     

Controlled Release of Liposomes from Biodegradable Dextran Microspheres: A Novel Delivery Concept

Purpose. Previous experimental work suggests that convection maybe important in determining the biodistribution of drugs implanted orinjected in the vitreous humor. To develop accurate biodistributionmodels, the relative importance of diffusion and convection inintravitreal transport must be assessed. This requires knowledge of both thediffusivity of candidate drugs and the hydraulic conductivity of thevitreous humor. Methods. Hydraulic conductivity of cadaveric bovine vitreous humorwas measured by confined compression tests at constant loads of 0.15and 0.2 N and analyzed numerically using a two-phase model. Diffusioncoefficient of acid orange 8, a model compound, in the same mediumwas measured in a custom-built diffusion cell. Results. Acid orange 8 diffusivity within vitreous humor is about halfthat in free solution. When viscous effects are properly accounted for,the hydraulic conductivity of bovine vitreous humor is 8.4 ± 4.5 ×10^–7 cm²/Pa s. Conclusions. We predict that convection does not contributesignificantly to transport in the mouse eye, particularly forlow-molecular-weight compounds. For delivery to larger animals, such as humanswe conclude that convection accounts for roughly 30% of the totalintravitreal drug transport. This effect should be magnified forhigher-molecular-weight compounds, which diffuse more slowly, and inglaucoma, which involves higher intraocular pressure and thus potentiallyfaster convective flow. Thus, caution should be exercised in theextrapolation of small-animal-model biodistribution data to human scale.     

Biodegradable Triblock Copolymer Microspheres Based on Thermosensitive Sol-Gel Transition

PURPOSE: The purpose of this study is to design microspheres for sustained protein delivery using thermosensitive, biodegradable tri-block copolymer, poly (D,L-lactide-co-glycolide)-b-poly (ethylene glycol)-b-poly (D,L-lactide-co-glycolide) (PLGA-PEG-PLGA) without using organic solvent. METHODS: Microspheres of the triblock copolymer PLGA-PEG-PLGA were prepared in an aqueous-based method without using methylene chloride (Msp A). This method used the sol-gel transition property of the polymer. The size and morphology of the microspheres were examined by optical microscopy and scanning electron microscopy (SEM). Zinc crystalline recombinant human insulin was incorporated in Msp A as well as in the microspheres of the same polymer prepared by the conventional water-in-oil-in-water (w/o/w) double emulsion method using methylene chloride (Msp B). Insulin release from both microspheres was carried out using high-performance liquid chromatography (HPLC) as well as circular dichroism (CD) spectroscopy of released insulin. FITC-insulin-loaded Msp A and Msp B were observed under confocal microscopy. Both microspheres were injected subcutaneously to SD rats with diabetes induced by streptozotocin. Blood glucose and plasma insulin levels were monitored. RESULTS: Although the insulin release from Msp B exhibited initial burst and incomplete release, Msp A showed significant reduction of initial burst and continuous release over 3 weeks (>85%). CD spectra of released insulin showed that insulin from Msp A preserved its secondary structural integrity, whereas that from Msp B indicated changes in conformation. Confocal microscopy of FITC-insulin-loaded microspheres (both A and B) showed that the observed release profile may be attributed to homogeneous distribution of FITC-insulin within Msp A but inhomogeneiety in Msp B. Both microspheres were injected s.c. to diabetic rats. Whereas Msp B caused a burst effect (hypoglycemia) followed by quick change in blood glucose and insulin level, Msp A exhibited relatively sustained release of insulin and blood glucose level for at least 10 days. CONCLUSIONS: The PLGA-PEG-PLGA microspheres (Msp A) demonstrated continuous release of insulin in vitro and in vivo without serious burst effect and incomplete release, as shown by Msp B.     

可生物降解长效注射给药系统的研究进展

可生物降解长效注射给药系统具有局部注射给药一次后能持续几天甚至几个月释药的特点,日益受到生命科学研究者和临床医生的重视.本文介绍了长效注射给药系统的研发历程、生物降解聚合物的类型与特性以及该剂型的临床应用现况,同时客观评价了可生物降解注射剂的应用前景和存在问题.     

利培酮生物可降解注射型植入剂的制备及体外释放特性的研究

目的:制备利培酮生物可降解注射型植入剂并考察其体外释放特性。方法:选用聚乳酸乙醇酸共聚物(PLGA)为载体和N-甲基吡咯烷酮(NMP)为溶剂,制备利培酮生物可降解注射型植入剂。考察制剂在30d内累积释药率、PLGA在降解过程中分子量的变化情况以及固体聚合物在降解过程表面孔径的变化情况。结果:所制制剂30d内释药曲线平稳,累积释药率为89.01%,前24h突释量较小,为13.8%。聚合物降解30d后分子量从43000减少到10000左右,表面孔径逐渐变大。结论:利培酮生物可降解注射型植入剂可在体外30d持续稳定释药。     

Control of Blood Glucose by Novel GLP-1 Delivery Using Biodegradable Triblock Copolymer of PLGA-PEG-PLGA in Type 2 Diabetic Rats

PURPOSE: The incretin hormone glucagon-like peptide-1 (GLP-1) is a promising candidate for treatment of type 2 diabetes mellitus. However, plasma half-life of GLP-1 is extremely short, thus multiple injections or continuous infusion is required for therapeutic use of GLP-1. Therefore, we investigated a new delivery system as a feasible approach to achieve sustained GLP-1 release for a 2-week period. METHODS: A water-soluble, biodegradable triblock copolymer of poly [(DL-lactide-co-glycolide)-b-ethylene glycol-b-(DL-lactide-coglycolide)] (ReGel) was used in this study as an injectable formulation for controlled release of GLP-1. GLP-1 was formulated into ReGel as insoluble zinc complex to stabilize GLP-1 against aggregation and slow down release. The GLP-1 release profile was monitored in vitro and in vivo. Zucker Diabetic Fatty rats were administered subcutaneously with the GLP-1 formulation. The concentration of GLP-1, insulin, and glucose was monitored every day after the GLP-1 administration. RESULTS: The GLP-1 release from ReGel formulation in vitro and in vivo showed no initial burst and constant release for 2 weeks. Animal study demonstrated that the plasma insulin level was increased, and the blood glucose level was controlled for 2 weeks by one injection of ReGel/ ZnGLP-1 formulation. CONCLUSIONS: It is concluded that one injection of zinc-complexed GLP-1 loaded ReGel can be used for delivery of bioactive GLP-1 during a 2-week period. Because this new delivery system is biocompatible and requires twice-a-month injection, it can improve patient compliance and cost-effectiveness.     

Biodegradable polymers: an update on drug delivery in bone and cartilage diseases

ABSTRACT

Introduction: The unique structure of bone and cartilage makes the systemic delivery of free drugs to those connective tissues very challenging. Consequently, effective and targeted delivery for bone and cartilage is of utmost importance. Engineered biodegradable polymers enable designing carriers for a targeted and temporal controlled release of one or more drugs in concentrations within the therapeutic range. Also, tissue engineering strategies can allow drug delivery to advantageously promote the in situ tissue repair.

Areas covered: This review article highlights various drug delivery systems (DDS) based on biodegradable biomaterials to treat bone and/or cartilage diseases. We will review their applications in osteoporosis, inflammatory arthritis (namely osteoarthritis and rheumatoid arthritis), cancer and bone and cartilage tissue engineering.

Expert opinion: The increased knowledge about biomaterials science and of the pathophysiology of diseases, biomarkers, and targets as well as the development of innovative tools has led to the design of high value-added DDS. However, some challenges persist and are mainly related to an appropriate residence time and a controlled and sustained release over a prolonged period of time of the therapeutic agents. Additionally, the poor prediction value of some preclinical animal models hinders the translation of many formulations into the clinical practice.     

Porous Biodegradable Microspheres for Controlled Drug Delivery. I. Assessment of Processing Conditions and Solvent Removal Techniques

Microspheres containing methylene blue and prednisolone acetate were prepared by one of three methods: freeze-drying, evaporation, and solvent-extraction-precipitation. An extremely porous structure was obtained by the freeze-dry and solvent-extraction-precipitation procedures. The specific surface area of 6.33-µm particles was 20.6 m²/g, or 35 times that of a particle devoid of pores, and the void space was 59–61%. The sphericity, size, and yields of the microspheres were influenced by the preparation procedure, surfactant type and concentration, temperature of the continuous phase, polymer concentration in the dispersed phase, and ratio of marker to polymer. The most suitable processing conditions were a polymer concentration of 5–10%, a marker loading of 10%, 0.1% sorbitan sesquioleate as the surfactant, and temperature adjustment of the continuous phase from 15 to 50°C following the addition of the dispersed phase. Complete release of the highly water soluble methylene blue occurred within 72 hr, while the less soluble prednisolone acetate released much more slowly, i.e., 90% after 7 days. The microspheres remained relatively intact during the in vitro release of methylene blue, confirming that the incorporated agent was confined to the walls of the porous network. Collapse of the polymer structure was evident after 7 days. The release therefore was believed to be governed principally by the solubility of the drug and the porosity of the matrix.     

Controlled Release of Contraceptive Steroids from Biodegradable and Injectable Gel Formulations: In Vivo Evaluation

Purpose. The purpose of this study was to investigate in vivo biocompatibility, biodegradability and biological effects of contraceptive steroids, such as levonorgestrel and ethinyl estradiol, released from gels prepared with a combination of derivatized vegetable oil (Labrafil 1944 CS) and glyceryl ester of fatty acids (Precirol ATO 5). Methods. Biocompatibility, biodegradability, and in vivo effects of levonorgestrel and ethinyl estradiol were studied by histologic evaluation of rat tissue, visual estimate of changes in gel size, and assessment of drug effects on reproductive cyclicity of female rats, respectively, following subcutaneous injection of gel formulations. Results. Histological evaluation of the tissue samples following an injection of the gel revealed an inflammatory reaction for about 7 days, after which the tissues did not show any inflammatory response. Complete degradation of the gels containing 10% wax was observed between 5 and 6 weeks. Normal rat estrous cycles were completely blocked by the contraceptive steroids released from the gels. Gel formulations containing 0.25% w/w levonorgestrel were more effective in blocking the estrous cycle of female rats compared to the oil formulations containing an identical drug loading. The duration of the biological effect induced by levonorgestrel appears to be dose-related. The gel formulation containing 2.00% ethinyl estradiol was superior to oil formulation containing an identical drug loading in terms of controlling drug release and toxicity. Conclusions. These observations suggest that Labrafil-Precirol gels are biocompatible and biodegradable. Moreover, controlled release of steroids is possible in vivo for a prolonged period of time.     

Controlled Release of Plasmid DNA from a Genetically Engineered Silk-Elastinlike Hydrogel

Purpose. The purpose of this study was to evaluate the potential of a genetically engineered silk-elastinlike polymer (SELP) as a matrix for the controlled release of plasmid DNA. Methods. The influences of SELP concentration, DNA concentration, SELP cure time, and buffer ionic strength on the release of DNA from SELP hydrogels were investigated. To calculate the average effective diffusivity of DNA within the hydrogels, the release data were fitted to a known equation. Results. DNA was released from SELP hydrogels by an ion-exchange mechanism. Under the conditions studied, the release rate was influenced by buffer ionic strength, SELP concentration, and SELP cure time but not DNA concentration. The apparent diffusivity of pRL-CMV plasmid DNA in SELP hydrogels ranged from 3.78 ± 0.37 × 10^-10 cm²/s (for hydrogels containing 12% w/w SELP and cured for 4 h) to 4.69 ± 2.81 × 10^-9 cm²/s (for hydrogels containing 8% w/w SELP and cured for 1 h). Conclusions. The ability to precisely customize the structure and physicochemical properties of SELPs using recombinant techniques, coupled with their ability to form injectable, in situ hydrogel depots that release DNA, renders this class of polymers an interesting candidate for further evaluation in controlled gene delivery.     

Controlled Release of a Contraceptive Steroid from Biodegradable and Injectable Gel Formulations: In Vitro Evaluation

Purpose. The purpose of this study was to investigate the effects of formulation factors including varying wax concentration, drug loading and drug particle size, on drug release characteristics from both pure oil and gel formulations prepared with a combination of derivatized vegetable oil (Labrafil 1944 CS) and glyceryl palmitostearate (Precirol ATO 5), using levonorgestrel as a model drug. Methods. The effects of varying drug loadings, different drug particle sizes, and wax (Precirol) concentrations on in-vitro drug release rates were evaluated, and the mechanisms of drug release from the gels were determined. Results. Zero-order drug release rates from the 10% Precirol gel formulations containing 0.25, 0.50 and 2.00% w/v drug loadings were lower than those observed for oil formulations containing identical drug loadings. Higher zero-order release rates were observed from formulations containing smaller drug particles suspended in both oil and gel formulations. The mechanism of drug release from gels containing less than 0.25% w/w drug was diffusion-controlled. Increasing the wax concentrations in the gels from 5% w/w to 20% w/w significantly decreased the diffusivity of the drug through the gel formulations and markedly increased the force required to inject the gels from two different sizes of needles. Conclusions. This study shows how modification of the physicochemical properties of the gel formulations by changing the drug particle size, wax concentration and drug loading, affects drug release characteristics from the system.     

注射用胰岛素缓释纳米囊的研究

以聚氰基丙烯酸丁酯纳米囊为载体制备注射用胰岛素纳米囊。通过均匀设计优选实验,以乳化聚合法得到了包封率为９３．７５％,平均粒径１０１ｎｍ,跨距为１．１４的胰岛素纳米囊。初步实验表明,注射用胰岛素纳米囊在４￣２５℃较稳定,含量,包封率,平均粒径等无明显变化;体外释药符合双指数模型;单次给药表明大鼠经皮下注射后,其降糖作用可持续一周,在药物的吸收相具良好的量效关系,药效优于相同剂量的胰岛素注射剂（Ｐ〈０     

In Vivo Evaluation of a Colon-Specific Drug Delivery System: An Absorption Study of Theophylline from Capsules Coated with Azo Polymers in Rats

Azo polymers based upon 2-hydroxyethyl methacrylate, methyl methacrylate, and methacrylic acid, and containing N,N-bis [(methacryloyloxyethyl)oxy(carbonylamino)]azobenzene as azo aromatic agent were evaluated in vivo as coatings for colon-specific drug delivery. The gastrointestinal absorption of theophylline from capsules coated with the azo polymers was examined in the proximal part of the small intestine and the cecum of male Wistar rats. The capsules were surgically inserted in the region of interest. The plasma concentration of the drug was higher when the capsules were inserted in the cecum as compared to the small intestine. The appearance of theophylline in the plasma when capsules were administered in the small intestine can be attributed to simple diffusion of the drug through the swollen polymer coating. Release and absorption from the cecum is the combined result of diffusion and degradation of the azo polymer coatings by bacterial azo reductase.     

Doxycycline delivery from PLGA microspheres prepared by a modified solvent removal method

We report on the development of a modified solvent removal method for the encapsulation of hydrophilic drugs within poly(lactic-co-glycolic acid) (PLGA). Using a water/oil/oil double emulsion, hydrophilic doxycycline was encapsulated within PLGA spheres with particle diameters ranging from approximately 600?nm to 19?µm. Encapsulation efficiencies of up to 74% were achieved for theoretical loadings from 1% to 10% (w/w), with biphasic release over 85 days with nearly complete release at the end of this time course. About 1% salt was added to the formulations to examine its effects on doxycycline release; salt modulated release only by increasing the magnitude of initial release without altering kinetics. Fourier transform infrared spectroscopy indicated no characteristic differences between doxycycline-loaded and control spheres. Differential scanning calorimetry and X-ray diffraction suggest that there may be a molecular dispersion of the doxycycline within the spheres and the doxycycline may be in an amorphous state, which could explain the slow, prolonged release of the drug.     

Ultrasound Mediated Transdermal Insulin Delivery in Pigs Using a Lightweight Transducer

Purpose In previous studies, ultrasound mediated transdermal drug delivery has shown a promising potential as a method for noninvasive drug administration. For prospective future human application, this study was designed to determine the feasibility of lightweight cymbal transducer array as a practical device for noninvasive transdermal insulin delivery in large pigs. Materials and Methods Six Yorkshire pigs (100–140 lbs) were divided into two groups. As the control (n = 3), the first group did not receive any ultrasound exposure with the insulin. The second group (n = 3) was treated with ultrasound and insulin at 20 kHz with an I_sptp = 100 mW/cm² at a 20% duty cycle for 60 min. With the pigs in lateral recumbency after anesthesia, the ultrasound transducer with insulin was placed on the axillary area of the pig. At the beginning and every 15 min up to 90 min, the blood glucose level was determined using a glucose monitoring system. To compare the results of individual animals, the change of blood glucose level was normalized to each animal’s initial glucose value at the start of the experiment. Results Although each animal had a different initial glucose level, the mean and standard error for the six animals was 146 ± 13 mg/dl. For the control group, the blood glucose level increased to 31 ± 21 mg/dl compared to the initial baseline over the 90 min experiment. However for the ultrasound with insulin treated group, the glucose level decreased to −72 ± 5 mg/dl at 60 min (p <  0.05) and continued to decrease to −91 ± 23 mg/dl in 90 min (p < 0.05). Conclusion The results indicate the feasibility of ultrasound mediated transdermal insulin delivery using the cymbal transducer array in animal with a similar size and weight to a human. Based on these result, the cymbal array has potential as a practical ultrasound system for noninvasive transdermal insulin delivery for diabetes management.     

Controlled release systems for insulin delivery

Diabetes mellitus is a major cause of mortality in industrialised countries, and insulin has remained indispensable in the treatment of diabetes mellitus since its discovery. Generally, patients with diabetes mellitus need a relatively constant basal insulin supply to mimic a near-normal physiological pattern of insulin secretion. However, as a consequence of very short in vivo half-lifes, poor oral bioavailability and current lack of alternative delivery routes, insulin requires single or multiple daily subcutaneous injections to achieve the desired therapeutic effect, which is inconvenient and painful and with poor patient compliance. Therefore, there is a need for insulin delivery systems that have the capability of releasing the loaded insulin at a controlled and sustained rate for a prolonged period. This review examines recent (2000 – 2004) patents on the controlled release systems for insulin delivery, including those for injectable, oral, pulmonary and transdermal delivery, and the glucose-responsive controlled-release systems.     

生物降解微球的制备工艺及释药特性研究进展

综述了近年来生物降解微球在制备工艺、聚合物降解机理、药物释放等方面的研究进展。     

Preparation of Three-Month Depot Injectable Microspheres of Leuprorelin Acetate Using Biodegradable Polymers

To obtain a three-month release injection of leuprorelin acetate, microspheres were prepared with copoly(DL-lactic/glycolic acid) or poly(DL-lactic acid) (PLA) using an in-water drying method, and drug release was evaluated. The content of water-soluble oligomers in the polymers was found to strongly affect the initial burst, and reducing the content to less than 0.1% was necessary to keep the first-day release below 10%. Drug loading of more than 15% also increased the initial drug release; the acceptable maximum loading was 12%. Elevation of the glass transition temperature of the microspheres was observed with an increase in drug loading. This suggests formation of a rigid structure, possibly with arrangement of the polymer around the drug cores like in a micelle. This structure provides a hydrophobic barrier against diffusion of the hydrophilic peptide, resulting in high trapping efficiency and long-term sustained release dependent on polymer erosion. The microspheres prepared with PLA having a m.w. of 12,000 to 18,000 provided linear sustained release and persistent serum levels of the drug in rats for over 3 months.     

Biodegradable Delivery System for a Birth Control Vaccine: Immunogenicity Studies in Rats and Monkeys

Purpose. The purpose of this study was to develop a single administration delivery system for a model birth control vaccine, in order to reduce the need for multiple injections and enhance immunogenicity. Methods. The immunogen-loaded microspheres were prepared by solvent evaporation method and characterized for loading levels, size distribution and in vitro release kinetics. The microspheres were immunized intramuscularly in wistar rats and bonnet monkeys, and the antibody response was compared to that obtained with the same total dose of the immunogen on alum given at a monthly interval. Results. Results indicated that a single injection of the immunogen entrapped in the microspheres generated a response comparable to that obtained by the same immunogen on alum injected at a monthly interval. The antibodies generated by the microspheres in the monkeys also had a good bioneutralization capacity indicating immunogen integrity during the microencapsulation process. Conclusions. Biodegradable microspheres served as an effective delivery system for a model immunogen used in this study to reduce the need for frequent immunizations and enhance immunogenicity.     

Polyanhydride Mierospheres that Display Near-Constant Release of Water-Soluble Model Drug Compounds

A new method to prepare polyanhydride microspheres capable of near-constant sustained release of low molecular weight, water-soluble molecules is presented. The polyanhydrides used were poly-(fatty acid dimer) (PFAD), poly(sebacic acid) (PSA), and their co-polymers [P(FAD-SA)]. Acid orange 63 (AO), acid red 8 (AR), and p-nitroaniline, were used as model release molecules. P(FAD-SA) microspheres containing the molecules with or without gelatin were prepared by a modified solvent evaporation method using a double emulsion. The microspheres were spherical with diameters of 50–125 µm and encapsulated more than 85% of the molecule, irrespective of the compound used. Near-zero-order degradation kinetics were observed for 5 days as judged by sebacic acid (SA) release. Microsphere degradation was pH sensitive, being enhanced at high pH, and became more stable in acidic conditions, irrespective of the incorporation of gelatin in the matrix. For the gelatin-free microspheres, a close correlation of SA release and AO release was observed (2% loading), suggesting a release mechanism that was controlled dominantly by degradation. However, the incorporation of gelatin into the microsphere significantly extended the periods of molecule release from P(FAD-SA) microspheres, although the degradation profile of the microspheres themselves was quite similar to that of gelatin-free microspheres. It is possible that an interaction between FAD monomers and gelatin molecules causes continued release, even after the polymer matrix completely degrades (even after complete degradation, FAD monomers remain because of their poor water solubility). Thermal analysis of polyanhydride microspheres at different degradation stages demonstrated that a crystalline structure was formed between gelatin and the FAD monomers produced with microsphere degradation. This gelatin effect on the extended period of drug release was not observed for microspheres prepared from other polyanhydrides: poly (sebacic acid) and its co-polymer of bis(p-carboxyphenoxy) propane and sebacic acid. It is therefore likely that the crystalline structure formed between gelatin and FAD monomers may function as a reservoir for water-soluble drugs, leading to an extended period of molecule release from the gelatin-loaded P(FAD-SA) microspheres.