H. Süheyla Kaş

Chitosan: Properties, preparations and application to microparticulate systems

Chitosan, a hydrophilic biopolymer, is obtained industrially by hydrolysing the aminoacetyl groups of chitin. It is a natural, non-toxic, biodegradable polysaccharide available as solution, flake, fine powder, bead and fibre. The sources, biochemical aspects, structure and chemical modification, physico-chemical and functional properties, and applications of chitosan have been investigated extensively in the literature. In this paper, the attractive properties and broad applications of chitosan-based microparticles, their versatile properties, different preparation methods, and pharmaceutical and biopharmaceutical applications are reviewed.

Preparation, characterization and in vivo distribution of terbutaline sulfate loaded albumin microspheres

Terbutaline sulfate is widely used as a bronchodilator for the treatment of bronchial asthma, chronic bronchitis and emphysema. As it has a short biological half-life, a long acting terbutaline sulfate formulation is desirable to improve patient compliance. Bovine serum albumin microspheres were prepared by an emulsion polymerization method using glutaraldehyde as the crosslinking agent. All microspheres were spherical and smooth with the mean particle size in the range of 22-30 microm. Drug release from the BSA microspheres displayed a biphasic pattern characterized by an initial fast release, followed by a slower release. The released amount was decreased with an increase in the glutaraldehyde concentration. In the absence of trypsin, the time required for complete degradation of microspheres was increased from 144 to 264 h when the glutaraldehyde concentration increased from 0.1 to 0.7 ml. In the presence of trypsin, a linear relationship was obtained between the degradation rates and trypsin concentrations, indicating that saturation was not reached under the experimental conditions. Biodistribution studies indicated that the degree of uptake by the lungs was higher than that of the other organs. All these results demonstrated that terbutaline sulfate loaded microspheres can be used for passive lung targeting.

Influence of irradiation sterilization on poly(lactide-co-glycolide) microspheres containing anti-inflammatory drugs

Gamma-irradiation is finding increasing use in the sterilization of pharmaceutical products. However, irradiation might also affect the performance of drug delivery systems. In this study, the influence of gamma-irradiation on the physicochemical properties of two commonly used non-steroidal anti-inflammatory drugs (NSAIDs) [naproxen sodium (NS) and diclofenac sodium (DS)] was investigated. The drugs were incorporated in poly(lactide-co-glycolide) (PLGA, 50:50; molecular weight 34000 or 88000 Da) microspheres. The biodegradable microspheres were irradiated at doses of 5, 15, 25 kGy using a 60Co source. Drug loading of irradiated and non-irradiated microspheres with both 34000 and 88000 Da polymers were essentially the same. A significant difference was noticed in the particle sizes of the irradiated as compared to the non-irradiated formulations. Notably, in release studies, the amount of active substance released from PLGA microspheres showed an increase with increasing irradiation dose. In DSC, the glass transition temperatures (Tg) of microspheres exhibited a slow increase with irradiation dose.

In vitro and in vivo evaluation of PLAGA (50/50) microspheres containing 5-fluorouracil prepared by a solvent evaporation method

Poly (DL-lactide-co-glycolide) PLAGA (50/50) microspheres containing an antineoplastic drug, 5-fluorouracil (5-FU) were prepared by a solvent evaporation process in order to passively target liver carcinomas. The microspheres were spherical with diameters 2–5 μm and encapsulated more than 70% (w/w) of the 5-FU. In vitro release patterns of 5-FU from microspheres were determined for various systems. It was found that drug release depended upon the amount of entrapped drug, the polymer molecular weight and pH of the dissolution medium. The in vitro release mechanism was diffusion controlled and followed a square-root of time relationship. In vivo distribution of 99mTc labeled microspheres after intravenous injection into mice was characterized by an initially high uptake by organs of the mononuclear phagocyte system (MPS). Following i.v. administration of fluorescein-labeled PLAGA microspheres, accumulation was into the MPS, mainly the Kupffer cells cytoplasm and near the liver sinusoids.

Solid tumor chemotherapy and in vivo distribution of fluorouracil following administration in poly(L-lactic acid) microspheres.

The physicochemical properties and in vivo distribution of poly(L-lactide) (L-PLA) microspheres containing 5-fluorouracil (5-FU) prepared by a solvent evaporation method were evaluated for potential use in the treatment of liver cancers. Two different molecular weight polymers of L-PLA [L-PLA1 (152,500 Da) and L-PLA2 (52,000 Da)] were used to prepare 5-FU-loaded microspheres. The mean particle size of the microspheres was 3-6 microns, and there was a direct relationship between the mean particle size and the molecular weight of the polymers. The drug release behavior from microspheres exhibited a diffusion mechanism in different dissolution media, with the molecular weight of the polymer being a major factor in controlling the drug release and degradation rates. Following intravenous injection of 99mTc-labeled L-PLA microspheres, with or without 5-FU, or free 5-FU into mice, L-PLA2 microspheres localized mainly in the liver. The disappearance rate of radioactivity from the tissue was very slow in comparison to that of free 5-FU. The results were confirmed by histological examination of liver tissue following administration of fluorescein particles. In addition, growth of a human liver tumor as first transplant generation under the renal capsule of immunocompetent rats and antitumor activity of L-PLA2 microspheres were investigated. Histological examination by optical microscopy showed that there was no neoplastic tissue of the kidney or in other tissues examined after treatment.

Formulation and Characterization of Formaldehyde Cross-linked Degradable Starch Microspheres Containing Terbutaline Sulfate

ABSTRACT Preparation of starch microspheres using epichlorohydrin is a time consuming method and requires around 18 hr for cross-linking reaction. To reduce reaction time, terbutaline sulfate (TBS) loaded degradable starch microspheres (DSM) were prepared using formaldehyde as the cross-linking agent. All microspheres were spherical in shape and had a porous, rough surface with a mean particle size of 18–24 μm. Whatever the cross-linking time, it was seen that the release of the TBS was not complete during the release experiments. The influence of enzyme on the degradation of microspheres was moderate. Following intravenous administration, initial uptake of microspheres by the lung was higher than those of other organs.

Drug delivery to Brain by Microparticulate Systems

The site specific delivery of chemotherapeutic agents allows maximum concentration of an agent at a desired body site. This area specific drug delivery decreases the unwanted systemic distribution and decreases toxicity of the administered drugs. Blood-Brain Barrier (BBB) is considered to be an obstacle in delivering large number of drugs to brain. The endothelial cells forming the tubular capillaries in the brain are cemented together by intercellular tight junctions. In this way, the BBB has an important role in providing a stable extracellular environment in the central nervous system. Lack of fenestrations, very few pinocytotic vesicles, and more mitochondria are other differences of the brain capillaries which play important role in transport of drugs to brain (Fig.1). The purpose of this paper is to summarise the methods for BBB permeability modifications and to focus on various examples in delivering drugs, especially neuroncology and neuroactive drugs, to brain by microparticulate systems.

Phenytoin Sodium Microcapsules: Bench Scale Formulation, Process Characterization and Release Kinetics

The objective of this investigation was to formulate and prepare sustained-action microcapsules of phenytoin sodium (diphenyl hydantoin sodium salt). Using ethylcellulose and methyl acrylic acid copolymers (Eudragit S-100 and L-100) as coating materials, microcapsules of phenytoin sodium were formulated by an organic phase separation and a granule coating method. The phase diagrams were used to study the phase separation in an ethylcellulose-petroleum ether-toluene system, and the effect of temperature and amount of petroleum ether on the ethylcellulose left in the organic solvent mixture was investigated. The phase diagrams showed that increase in temperature did not significantly affect the ethylcellulose residue, and 60 ml of nonsolvent was found adequate for microencapsulation. In vitro release of the formulated microcapsules and the commercially available preparations was performed in CO2-free distilled water using the USP XXIII rotating basket method, and the profiles were evaluated by Higuchi kinetics. Geometric mean diameters of the microparticles prepared by two different methods showed differences due to different core:wall ratios. A 4 x 5 factorial design was utilized and multiple regression was applied to the dependent variables (ethylcellulose content, percent dissolved) against the independent variables (amount of nonsolvent, temperature, core:wall ratio); the optimum phenytoin sodium-to-ethylcellulose ratio was 1:2.3. Utilizing second-order polynomial equations, response-surface graphs and contour plots pointed out the time necessary for 40%, 55%, and 70% release of phenytoin sodium. The desired release profiles were obtained with formulations E-5, ES-2 and ESL-2.

Evaluation and Formulation of Biodegradable Levodopa Microspheres Using 32 Factorial Design

The main neurochemial characteristic of the Parkinson’s disease is a marked degeneration of the nigrostriatal dopaminergic neurons which provide the dopaminergic striatal innervation. Due to the complex chemoarchitectiture of the Central Nervous System (CNS), drug delivery to a very restricted region of the brain is always required. The treatment of Parkinson’s disease patients with the dopamine biosynthetic precursor, levodopa in conjunction with a decarboxylase inhibitor 1 has received wide acceptance as an effective approach for the reduction of extrapyramidal symptoms in Parkinson’s disease. With the current convential medication levodopa can cause serious adverse effect reactions and its effectiveness decreases with time. However, implanted polymeric devices releasing the appropriate pharmacological agent could restore neurotransmission and lead to functional improvement.

Epidermal Growth Factor (EGF) Wound Healing in Fluorocarbon and Chitosan Gels in a Rabbit Model

Wound repair follows a general scheme, a sequence of processes taking place in an orderly way: inflammation, repair and closure, remodelling and final healing. Growth factors are produced by the cells aiding the process and are effective during replacement and reconstitution1. A wound is defined as an interruption of tissue to a greater or lesser extent, which may affect skin, mucosa or organs. The specific sequence of different processes following wounding has one common aim: repair. In every wound type, the healing process runs through three stages, which partly overlap. The first one, the exsudative or inflammatory phase, is followed by the proliferative phase and finally the regenerative phase. Characteristic for the inflammatory phase, lasting approximately 72 h, is the activation of blood coagulation system and the release of various mediators from platelets. This is followed by the coagulation of blood, within 2–4 h inflammatory cell immigration starts and after 32 h fibroblasts are present in the wound site. The second phase of wound repair is characterized by proliferation and lasts from day 1 to a maximum of 14 days. Highly vascularized granulation tissue is formed and angiogenesis and neovascularization in the wound site starts. During the last phase of wound healing the production of new connective tissue is of main importance. If all epidermal layers are effected, re-epithelialization proceeds through the following three stages: migration of basal lamina cells, mitosis of cells migrating across the wound surface and maturation of newly generated cells. The final step in epidermal wound healing is characterized by cell maturation, leading to the regeneration of a defined epidermal layer. Keratinization starts and finally desmosomes promote attachment of cells to one another. The wound is closed and covered by mature epidermis2.