New poly-(3-hydroxybutyrate)-based systems for controlled release of dipyridamole and indomethacin

New poly-(3-hydroxybutyrate)-based systems for controlled release of anti-inflammatory and antithrombogenic drugs have been studied. The release occurs via two mechanisms (diffusion and degradation) operating simultaneously. Dipyridamole and indomethacin diffusion processes determine the rate of the release at the early stages of the contact of the system with the environment (the first 6-8 days). The coefficient of the release diffusion of a drug depends on its nature, the thickness of the poly-(3-hydroxybutyrate) films containing the drug, the concentrations of dipyridamole and indomethacin, and the molecular weight of the poly-(3-hydroxybutyrate). The results obtained are critical for developing systems of release of diverse drugs, thus, enabling the attainment of the requisite physiological effects on tissues and organs of humans.     

Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate)-based biopolymer systems

Biodegradable biopolymers attract much attention in biology and medicine due to its wide application. The present review considers a biodegradable and biocompatible polymer of bacterial origin, poly(3-hydroxybutyrate), which has wide perspectives in medicine and pharmaceutics. It highlights basic properties of biopolymer (biodegradability and biocompatibility) and also biopolymer systems: various materials, devices and compositions based on the biopolymer. Application of poly(3-hydroxybutyrate)-based biopolymer systems in medicine as surgical implants, in bioengineering as cell culture scaffolds, and in pharmacy as novel drug dosage forms and drug systems are also considered.     

Sustained release of the antitumor drug paclitaxel from poly(3-hydroxybutyrate)-based microspheres

The development of sustained release formulations based on biodegradable polymers is a promising trend in modern pharmacology. Polyhydroxyalkanoates (PHA) attract increasing attention due to their biodegradability and high biocompatibility, which make them suitable for the development of novel drug dosage forms. We have produced poly(3-hydroxybutyrate) (PHB)-based microspheres loaded with the antitumor drug paclitaxel and investigated morphology, drug release kinetics and the effect of these microspheres on tumor cells in vitro. The data on the kinetics of drug release, biocompatibility and biological activity of the biopolymer microspheres in vitro have demonstrated that the studied system of prolonged drug release had lower toxicity and higher efficiency compared to the traditional dosage forms of paclitaxel.     

Poly(3-hydroxybutyrate)/chitosan/ketoprofen or piroxicam composite microparticles: Preparation and controlled drug release evaluation

Poly(3-hydroxybutyrate)/chitosan/piroxicam or ketoprofen composite microparticles were prepared by the solid-in-water-in-oil emulsion-solvent evaporation technique with the aim of reducing the burst effect and controlling the drug release. Reservoir-type microparticles, composed of poly(3-hydroxybutyrate) microspheres embedded in a chitosan matrix were prepared. The size and morphological characteristics of the composite microparticles were evaluated in relation to the chitosan concentration and cross-linking with glutaraldehyde. Reservoir-type composite microparticles were obtained using 2.0% and 3.0% w/v chitosan solutions. A significant reduction in the burst effect and prolonged drug release were observed, particularly when higher chitosan and glutaraldehyde concentrations were used.     

Doxorubicin and beta-lapachone release and interaction with micellar core materials: experiment and modeling

Polymer micelles with two different core-forming blocks, poly(d,l -lactide) (PLA) and poly(epsilon-caprolactone) (PCL), but the same coronal material, poly(ethylene glycol) (PEG), were investigated in this study as nanoscopic drug carriers. The release of two different drugs, doxorubicin (DOX) and beta-lapachone (beta-lap), from PEG(5k)-b-PCL(5k) and PEG(5k)-b-PLA(5k) micelles was studied at pH 5.0 and 7.4. Mathematical solutions of both Higuchi's model and Fickian diffusion equations were utilized to elucidate the differences between the micelle core materials for the two drugs. The neutral and smaller of the two drugs tested, beta-lap, demonstrated faster, pH-independent release, suggesting that no substantial changes occurred in either micelle core at lower pH. In contrast, the release rate of DOX was found to noticeably increase at lower pH with a larger cumulative amount of drug released. Different core materials were shown to have considerable influence on the release kinetics of both drugs: in both cases, the more hydrophobic PCL core showed slower drug release rates compared with the less hydrophobic PLA core.     

Electric Field-Controlled Benzoic Acid and Sulphanilamide Delivery from Poly(Vinyl Alcohol) Hydrogel

The controlled release of benzoic acid (3.31 Å) and sulphanilamide (3.47 Å) from poly(vinyl alcohol), PVA, hydrogels fabricated by solution casting at various cross-linking ratios, were investigated. The PVA hydrogels were characterized in terms of the degree of swelling, the molecular weight between cross-links, and the mesh size. The drug release experiment was carried out using a modified Franz diffusion cell, at a pH value of 5.5 and at temperature of 37°C. The amount of drug release and the diffusion coefficients of the drugs from the PVA hydrogels increased with decreasing cross-linking ratio, as a larger mesh size was obtained with lower cross-linking ratios. With the application of an electric field, the amount of drug release and the diffusion coefficient increased monotonically with increasing electric field strength, since the resultant electrostatic force drove the ionic drugs from the PVA matrix. The drug size, matrix pore size, electrode polarity, and applied electric field were shown to be influential controlling factors for the drug release rate.KEY WORDS: electrophoresis force, ionic drug delivery, iontophoresis, poly(vinyl alcohol)     

The effect of storage and active ingredient properties on the drug release profile of poly(ethylene oxide) matrix tablets

Different molecular weight forms of poly(ethylene oxide) can be used successfully in controlled release drug delivery due to their excellent matrix forming properties. Drug release of these materials follows nearly zero order kinetics, and is mainly governed by polymer swelling and erosion and diffusion of drug molecules. Because of its partly amorphous structure, poly(ethylene oxide) undergoes structural changes caused by elevated temperature and relative humidity of the storage medium resulting in an increased drug release. This physical process can be highly influenced by the structure of different drug molecules, such as polymer-binding ability and hydration tendency. These properties of two basic drugs embedded into poly(ethylene oxide) matrices were characterized by molecular modelling and an attempt was made to reveal their effect on the change of drug release stability, a prerequisite of the marketing authorization of dosage forms. The findings suggest that both the hydration properties of the active ingredient and the molecular weight of the polymer influence the effect of physical ageing of poly(ethylene oxide) on the drug release properties of the matrix.     

Prolonged release of chlorambucil and etoposide from poly-3-oxybutyrate-based microspheres

Microspheres were obtained on the basis of poly(3-oxibutyrate) (POB) with the inclusion of the Chlorambucil and Etoposide cytostatic drugs in a polymer matrix, and the morphology, kinetics of drug release from microspheres, and the interaction between microspheres and tumor cells in vitro were studied. Data on the kinetics of drug release suggests that a prolonged release occurs by drug diffusion from the polymer matrix at the initial stage and at the expense of hydrolytic degradation of the polymer at a later stage. A study of the biocompatibility and biological activity of biopolymeric microspheres showed that chlorambucil operates actively and strongly inhibits the growth of cultured cells for a short time (24 h). Etoposide acts weaker (the percentage of cell growth suppression during 48 h does not exceed 50%), but subsequently it has a basis for the creation of new dosage forms with prolonged action of Etoposide and chlorambucil for cancer therapy.     

THROMBIN IMMOBILIZATION TO METHACRYLIC ACID GRAFTED POLY(3-HYDROXYBUTYRATE) AND ITS IN VITRO APPLICATION

Poly(3-hydroxybutyrate) is nontoxic and biodegradable, with good biocompatibility and potential support for long-term implants. For this reason, it is a good support for enzyme immobilization. Enzyme immobilization could not be done directly because poly(3-hydroxybutyrate) has no functional groups. Therefore, modification should be done for enzyme immobilization. In this study, methacrylic acid was graft polymerized to poly(3-hydroxybutyrate) and thrombin was immobilized to polymethacrylic acid grafted poly(3-hydroxybutyrate). In fact, graft polymerization of methacrylic acid to poly(3-hydroxybutyrate) and thrombin immobilization was a model study. Biomolecule immobilized poly(3-hydroxybutyrate) could be used as an implant. Thrombin was selected as a biomolecule for this model study and it was immobilized to methacrylic acid grafted poly(3-hydroxybutyrate). Then the developed product was used to stop bleeding.     

β-Cyclodextrin hydrogels as potential drug delivery systems

β-cyclodextrins (βCD) are cyclic oligosaccharides which have been widely employed for pharmaceutical applications. Discs of insoluble polymers were synthesized by crosslinking β-cyclodextrins with the reagent epichlorohydrin. In this work, the possibility of employing a polymer containing 60 ± 3% βCD for drug delivery of two antiinflammatory (naproxen and nabumetone) and two antifungal drugs (naftifine and terbinafine) has been investigated. The interaction of Naproxen with the polymers was evidenced by X-ray diffractometry, FTIR spectroscopy and differential thermal analysis. Drug release kinetics were carried out at physiological conditions of pH and temperature, and kinetic and diffusion constants were calculated by fitting 60% of the release profile according to the Korsmeyer-Peppas equation. Also, diffusion coefficients were calculated according to the simplified Higuchi model. The drug release followed a simple Fickian diffusion mechanism for all the model drugs. This study suggests that these hydrogel matrices are potentially suitable as sustained release systems.     

Polymer micelles for delayed release of therapeutics from drug-releasing surfaces with nanotubular structures

A new approach to engineer a local drug delivery system with delayed release using nanostructured surface with nanotube arrays is presented. TNT arrays electrochemically generated on a titanium surface are used as a model substrate. Polymer micelles as drug carriers encapsulated with drug are loaded at the bottom of the TNT structure and their delayed release is obtained by loading blank micelles (without drug) on the top. The delayed and time-controlled drug release is successfully demonstrated by controlling the ratio of blank and drug loaded-micelles. The concept is verified using four different polymer micelles (regular and inverted) loaded with water-insoluble (indomethacin) and water-soluble drugs (gentamicin).     

Influence of phosphated cross-linked high amylose on in vitro release of different drugs

The influence of structural characteristics of high amylose cross-linked at different degrees on the release of drugs with important molecular differences, namely sodium diclophenac (SD) and nicotinamide (NI), was assessed in vitro from non-compacted systems. The release profiles were related with classical kinetic mathematical models for better understanding of the release mechanism. An increase in polymer cross-linking degree resulted in longer release time for both drugs, although SD generally was released slower than NI. SD release from samples cross-linked at 2% of basis was driven mainly by Fickian diffusion, while from samples cross-linked at 4% of basis follows anomalous mechanism. Inversely, anomalous mechanism was responsible for NI release from 2% samples and Fickian diffusion from 4% samples. Results suggest that the performance of cross-linked high amylose as excipient for controlled drug release not only depends on cross-linking degree but also is highly influenced by structural characteristics of the drug.     

Design of an Inflammation-Sensitive Polyelectrolyte-Based Topical Drug Delivery System for Arthritis

The most successful treatment strategy for arthritis is intra-articular injections that are costly and have reduced patient compliance. The purpose of the current study was to develop an inflammation-sensitive system for topical drug administration. Multi-macromolecular alginate-hyaluronic acid-chitosan (A-H-C) polyelectrolyte complex nanoparticles, loaded with indomethacin were developed employing pre-gel and post-gel techniques in the presence of dodecyl-l-pyroglutamate (DLP). In addition to in vitro studies, in silico simulations were performed to affirm and associate the molecular interactions inherent to the formulation of core all-natural multi-component biopolymeric architectures composed of an anionic (alginate), a cationic (chitosan), and an amphi-ionic polyelectrolytic (hyaluronic acid) macromolecule. The results demonstrated that DLP significantly influenced the size of the synthesized nanoparticles. Drug-content analysis revealed higher encapsulation efficiency (77.3%) in the presence of DLP, irrespective of the techniques used. Moreover, in vitro drug release studies showed that indomethacin release from the nanosystem was significantly improved (98%) in Fenton’s reagent. Drug permeation across a cellulose membrane using a Franz diffusion cell system showed an initial surge flux (0.125 mg/cm^?2/h), followed by sustained release of indomethacin for the post-gel nanoparticles revealing its effective skin permeation efficiency. In conclusion, the study presents novel nanoparticles which could effectively encapsulate and deliver hydrophobic drugs to the target site, particularly for arthritis.     

Matrix metalloprotease triggered delivery of cancer chemotherapeutics from hydrogel matrixes

Glioblastoma multiforme (GBM) is a highly advanced and invasive brain tumor due to which current treatments cannot completely treat GBM or prevent recurrence. Therefore, adjunctive treatments are required. As part of the invasive and angiogenic nature of GBM, it has been well established that matrix metalloprotease-2 (MMP-2) and MMP-9 are overactive. To better treat GBM using chemotherapy, we have designed a hydrogel-based delivery system that can control the release of drugs based on the activity of MMPs. A model chemotherapeutic agent, cisplatin (CDDP), complexed to an MMP substrate (peptide-linker) was incorporated into poly(ethylene glycol) diacrylate hydrogel wafers having different poly(ethylene glycol) chain lengths (M(n) approximately 574 and 4000). Hydrogel wafers were studied for physical characteristics and drug release in the presence and absence of MMPs. There was a substantial increase in CDDP release for the poly(ethylene glycol) 4000 hydrogel indicating that this chain length provides a mesh size that is sufficient to permit MMP activity within the hydrogel. CDDP bioactivity increased when the cell media was spiked with MMPs (0% cell survival) in case of the longer chain length as compared to in the absence of MMPs (approximately 50% cell survival). The results suggest that this system can be used for selective, local delivery of drugs where higher amounts of the drug are released in response to metastasis, angiogenesis, and invasion-promoting proteases. This strategy may prove to be a novel and effective method to overcome inadequacies in current controlled drug release systems.     

Controlled release from triple layer,donut-shaped tablets with enteric polymers

The purpose of this research was to evaluate triple layer, donut-shaped tablets (TLDSTs) for extended release dosage forms. TLDSTs were prepared by layering 3 powders sequentially after pressing them with a punch. The core tablet consisted of enteric polymers, mainly hydroxypropyl methylcellulose acetate succinate, and the bottom and top layers were made of a water-insoluble polymer, ethyl cellulose. Drug release kinetics were dependent on the pH of the dissolution medium and the drug properties, such as solubility, salt forms of weak acid and weak base drugs, and drug loading. At a 10% drug loading level, all drugs, regardless of their type or solubility, yielded the same release profiles within an acceptable level of experimental error. As drug loading increased from 10% to 30%, the drug release rate of neutral drugs increased for all except sulfathiazole, which retained the same kinetics as at 10% loading. HCl salts of weak base drugs had much slower release rates than did those of neutral drugs (eg, theophylline) as drug loading increased. The release of labetalol HCl retarded as drug loading increased from 10% to 30%. On the other hand, Na salts of weak acid drugs had much higher release rates than did those of neutral drugs (eg, theophylline). Drug release kinetics were governed by the ionization/erosion process with slight drug diffusion, observing no perfect straight line. A mathematical expression for drug release kinetics (erosion-controlled system) of TLDSTs is presented. In summary, a TLDST is a good design to obtain zero-order or nearly zero-order release kinetics for a wide range of drug solubilities.     

Poly(ethylene glycol) methacrylate/dimethacrylate hydrogels for controlled release of hydrophobic drugs

Hydrogels have been successfully used to entrap hydrophilic drugs and release them in a controlled fashion; however, the entrapment and release of hydrophobic drugs has not been well studied. We report on the release characteristics of a model hydrophobic drug, the steroid hormone estradiol, entrapped in low (MW 360/MW 550) and high (MW 526/MW 1000) molecular weight poly(ethylene glycol) methacrylate (PEG-MA)/dimethacrylate (PEG-DMA) hydrogels. The cross-linking ratio, temperature, and pH ranged from 10:1 to 10:3, from 33 to 41 degrees C, and from 2 to 12, respectively. The gelation of the PEG-MA/PEG-DMA hydrogel was initiated with UV irradiation. The absence of poly(glutamic acid) in the hydrogel formulation resulted in a loss of pH sensitivity in the acidic range, which was displayed by the hydrogels' similarities in swelling ratios in the pH buffers of pH 2, 4, and 7. Use of high molecular weight polymers resulted in a higher hydrogel swelling (300%) in comparison to the low molecular weight polymers. Drug size was found to be a significant factor. In comparison to 100% estradiol (MW 272) release, the fractional release of insulin (MW 5733) was 12 and 24% in low and high molecular weight gels at pH 2, respectively, and 17% in low molecular weight gels at pH 7. On the release kinetics of the estradiol drug, the hydrogels displayed a non-Fickian diffusion mechanism, which indicated that the media penetration rate is in the same range as the drug diffusion. The synthesis, entrapment, and release of estradiol by the PEG-MA/PEG-DMA hydrogels proved to be successful, but the use of ethanol in the buffers to promote the hydrophobic release of the estradiol in the in vitro environment caused complications, attributed to the process of transesterification.     

The release dynamics of salicylic acid and tetracycline hydrochloride from the psyllium and polyacrylamide based hydrogels (II)

Psyllium, a medicinally active natural polysaccharide, has been modified with polyacrylamide to develop the hydrogels; those can act as the potential candidate for novel drug delivery systems. In the present studies, the release dynamics of model drugs (salicylic acid and tetracycline hydrochloride) from the drug-loaded hydrogels have been discussed, for the evaluation of the drug release mechanism and diffusion coefficients. It has been observed that diffusion exponent ‘n’ have 0.68 and 0.74 values and gel characteristic constant ‘k’ have 1.625 × 10⁻² and 1.272 × 10⁻² values, respectively, for the release of salicylic acid and tetracycline hydrochloride in distilled water from the drug loaded hydrogels. Therefore, drug release from the drug loaded hydrogels through Non-Fickian or Anomalous diffusion mechanism where the rate of drug diffusion and rate of polymer relaxation were comparable. The effect of pH on the release pattern of tetracycline has been studied by varying the pH of the release medium. However, in each release medium, the Initial diffusion coefficient was observed to be more than the late time diffusion coefficient.     

重组大肠杆菌合成聚(3-巯基丙酸)和聚(3-羟基丁酸-3-巯基丙酸)的研究

利用Clostridium acetobutylicum的丁酸激酶基因 (buk) 和磷酸转丁酰基酶基因(ptb),以及Thiocapsa pfennigii的PHA合成酶基因,设计了一条能够合成多种聚羟基烷酸的代谢途径,用构建的质粒转化大肠杆菌,获得了重组大肠杆菌菌株.前期的研究表明,在合适的前体物条件下,该重组大肠杆菌能够合成包括聚羟基丁酸、聚(羟基丁酸-戊酸)等多种生物聚酯[Liu and Steinbüchel, Appl. Environ. Microbiol. 66739-743].利用该重组大肠杆菌,通过生物催化作用合成了3-巯基丙酸的同型共聚酯,同时利用该重组大肠杆菌还获得了含3-巯基丙酸单体的多种异型共聚物.实验首先研究了3-巯基丙酸对大肠杆菌生长的影响,在此基础上优化了培养过程中添加3-巯基丙酸的时机和浓度,结果表明,在实验的条件下,细胞合成聚(3-巯基丙酸)可达6.7%(占细胞干重),合成聚(3-羟基丁酸-3-巯基丙酸)(分子中3-巯基丙酸3-羟基丁酸=31)可达24.3%.实验进一步研究了同时或分别表达以上3个基因的重组大肠杆菌合成聚合物的能力,结果表明只有当3个基因同时表达时才能合成聚合物,说明3个基因对合成过程是必须的,从而表明了合成途径是按照设计的路线进行的.还通过GC/MS、GPC、IR等手段对合成的化合物进行了定性的研究.聚(3-巯基丙酸)或聚(3-羟基丁酸-3-巯基丙酸)等聚酯属于一类新型生物聚合物,它在分子骨架中含有硫酯键,不同于聚羟基烷酸酯的氧酯键,从而具有显著不同的物理、化学、光学等性质和具有重要的潜在应用价值.     

Fabrication of novel combinatorial drug encapsulated micelles for enhanced tumor targeting in intestinal cancer in mouse model

Hindrance to successful therapy of colon cancer is generally characterized with reduced potency of a single drug at the active site of cancer, poor drug release, and most importantly, potential toxic side effects of the drug resulting in cytotoxicity. Therefore, we investigated combinatorial drug micelles which are a potent combination of twin anticancer drugs (indomethacin and piroxicam, IND+PIR mc) for successful therapeutics of colon cancer. The novel combinatorial micelles showed improved drug encapsulation efficiency, an in vitro burst release of the dual drugs, increased cytocompatibility and increased efficacy in tumor reduction (weight and volume) than in single drug micelles (IND mc or PIR mc). The improved IND+PIR MC were to have small size 150.36 ± 15.13 nm (to avoid being taken up by liver, lungs or kidney or to sediment) with poly dispersity index (PDI) value at 0.24 ± 0.01. The PDI values suggest homogenous distribution. Encapsulation efficiency of IND+PIR mc was calculated at 86%. IND+PR mc had improved biocompatibility as demonstrated by CRL-1459™ (normal colon) cell line than IND mc or PIR mc individually. The in vivo studies in mice model clearly depict that subcutaneous tumor weight reduced by almost 75% and volume reduced drastically by 55% on administration of IND+PIR mc than IND mc or PIR mc. Furthermore, fewer side effects were found with IND+PIR mc. To conclude, IND+PIR mc may be a potential anticancer strategy to be explored more in the future.     

Intracellular degradation of poly(3-hydroxybutyrate) granules of Zoogloea ramigera I-16-M

Abstract Intracellular degradation of poly(3-hydroxybutyrate) (PHB) in bacteria is not yet clear. The properties of the autodigestion of native PHB granules from Zooglea ramigera I-16-M were examined. The release of d (−)-3-hydroxybutyrate was observed only at pH values higher than about 8.5 and at relatively high ionic strength (optimal concentration 200 mM NaCl). Triton X-100 and diisopropylfluorophosphate inhibited this reaction. Addition of the supernatant fraction of Z. ramigera did not increase the release of d (−)-3-hydroxybutyrate from the native PHB granules. On the other hand, using the protease-treated PHB granules from Alcaligenes eutrophus as a substrate, PHB depolymerase activity was detected in the supernatant fraction of Z. ramigera cells. The soluble PHB depolymerase showed similar properties to the enzyme in the PHB granules. Since PHB depolymerase activity was found in fractions containing d (−)-3-hydroxybutyrate oligomer hydrolase activity, which were separated by DEAE-Toyopearl or by Sephacryl S-100, it is possible that the intracellular PHB depolymerase is identical to the oligomer hydrolase which has been purified already.