Polysaccharides for Colon Targeted Drug Delivery

Targeted delivery of low molecular drugs using chitosan and its derivatives

Chitosan has prompted the continuous impetus for the development of safe and effective drug delivery systems because of its unique physicochemical and biological characteristics. The primary hydroxyl and amine groups located on the backbone of chitosan allow for chemical modification to control its physical properties. When the hydrophobic moiety is conjugated to a chitosan molecule, the resulting amphiphile may form self-assembled nanoparticles that can encapsulate a quantity of drugs and deliver them to a specific site of action. Chemical attachment of the drug to the chitosan throughout the functional linker may produce useful prodrugs, exhibiting the appropriate biological activity at the target site. Mucoadhesive and absorption enhancement properties of chitosan increase the in vivo residence time of the dosage form in the gastrointestinal tract and improve the bioavailability of various drugs. The main objective of this review is to provide an insight into various target-specific carriers, based on chitosan and its derivatives, towards low molecular weight drug delivery. The first part of the review is concerned with the organ-specific delivery of low molecular drugs using chitosan and its derivatives. The subsequent section considers the recent developments of drug delivery carriers for cancer therapy with special focus on various targeting strategies.

Pectin/Kollicoat SR30D isolated films for colonic delivery [I]: a comparison of normal and colitis-induced models to assess the efficiency of microbially triggered drug delivery

Objectives

The purpose of the study was to evaluate digestion of pectin/Kollicoat SR30D free films for colonic delivery in vitro and in vivo.

Methods

Free films containing different ratios of pectin to Kollicoat SR30D were prepared by casting/solvent evaporation method. An in-vitro comparison of swelling, degradation and permeability of the free films was carried out in simulated colon fluids containing caecal contents from normal rats with colitis induced by 2,4,6-trinitrobenzene sulfonic acid (TNBS) or oxazolone. A comparative in-vivo evaluation of degradation was also conducted in normal and colitis-induced model rats.

Key findings

The pectin within the mixed films was susceptible to rat colonic bacterial enzymes. The extent of digestion correlated with the amount of pectin present within the film. In vitro, the swelling index, drug permeability and extent of film digestion in simulated colon fluids with caecal contents obtained from normal rats were higher than from TNBS- or oxazolone-induced model rats, whereas in-vivo degradation was similar in the three groups of rats. The pectin/Kollicoat SR30D free films were completely degraded in the colitis-induced rats.

Conclusions

Pectic/Kollicoat SR30D films may be useful as coatings to target delivery of drugs to the colon.

Organotin Polyethers as Biomaterials

Organotin polyethers are easily synthesized employing interfacial polymerization systems involving the reaction of hydroxyl-containing Lewis bases and organotin halides. A wide variety of organotin-containing polymeric products have been synthesized including those derived from natural and synthetic polymers such as lignin, xylan, cellulose, dextran, and poly(vinyl alcohol). Others have been synthesized employing known drug diols such as dicumarol, DES, and dienestrol and a wide variety of synthetic diols. Included in these materials are the first water soluble organotin polymers. The organotin polyethers exhibit a wide range of biological activities. Some selectively inhibit a number of unwanted bacteria, including Staph. MRSA, and unwanted yeasts such as Candida albicans. Some also inhibit a variety of viruses including those responsible for herpes infections and smallpox. Others show good inhibition of a wide variety of cancer cell lines including cell lines associated with ovarian, colon, lung, prostrate, pancreatic and breast cancer. The synthesis, structural characterization, and biological characterization of these materials is described in this review.

Polymeric plant-derived excipients in drug delivery

Drug dosage forms contain many components in addition to the active pharmaceutical ingredient(s) to assist in the manufacturing process as well as to optimise drug delivery. Due to advances in drug delivery technology, excipients are currently included in novel dosage forms to fulfil specific functions and in some cases they directly or indirectly influence the extent and/or rate of drug release and absorption. Since plant polysaccharides comply with many requirements expected of pharmaceutical excipients such as non-toxicity, stability, availability and renewability they are extensively investigated for use in the development of solid oral dosage forms. Furthermore, polysaccharides with varying physicochemical properties can be extracted from plants at relatively low cost and can be chemically modified to suit specific needs. As an example, many polysaccharide-rich plant materials are successfully used as matrix formers in modified release dosage forms. Some natural polysaccharides have even shown environmental-responsive gelation characteristics with the potential to control drug release according to specific therapeutic needs. This review discusses some of the most important plant-derived polymeric compounds that are used or investigated as excipients in drug delivery systems.

Site specific delivery of microencapsulated fish oil to the gastrointestinal tract of the rat

The aim of this study was to design food grade matrices to deliver microencapsulated fish oil to the large bowel of the rat where the potential exists to retard inflammation and cancer development. Digestion in simulated gastric fluid and intestinal fluid demonstrated that only 4-6% of oil was released from the following dried emulsion formulations: 50% fish oil encapsulated in heated casein-glucose-dried glucose syrup (1:1:1) (Cas-Glu-DGS-50); 25% fish oil in casein-modified resistant starch (Hylon VII) (1:1) (Cas-Hylon-25); or 25% fish oil in Cas-Glu-Hylon (1:1:1) (Cas-Glu-Hylon-25). A short-term gavage study (0-12 h) with fish oil and Cas-Glu-DGS-50 demonstrated the appearance of fish oil long chain (LC) n-3 polyunsaturated fatty acids (PUFA) into the plasma indicating specific small intestinal absorption with little LC n-3 PUFA reaching the large bowel. In a 2-week-long term, daily gavage study, the bioavailability of fish oil and fish oil in Cas-Glu-DGS-50 or Cas-Hylon-25 demonstrated that fish oil and Cas-Glu-DGS-50 LC n-3 PUFA were incorporated into the tissue of the small intestine and colon, whereas Cas-Hylon-25 was resistant to degradation in the small intestine. The use of modified Hylon VII for targeted colonic delivery was confirmed in the final short-term gavage study (0-14 h) using Cas-Glu-Hylon-25 with [(14)C]-trilinolenin as a marker incorporated into the microcapsules, where up to 60% of the labeled oil reached the large bowel. Depending on the microencapsulating matrix employed, fish oil can be delivered selectively to the small intestine or to a high degree to the large bowel.

Synthesis, Characterization, and Evaluation of Phosphated Cross-Linked Konjac Glucomannan Hydrogels for Colon-Targeted Drug Delivery

Hydrogel systems of konjac glucomannan (KGM) cross-linked with trisodium trimetaphosphate (STMP) were prepared for colon-targeting drug delivery. Swelling degrees of the hydrogels were measured in artificial gastrointestinal fluids and in sodium chloride solution with different concentrations to study their dependence on the cross-linking density and the ionic strength. The absorption of methylene blue was used to characterize the degree of the KGM cross-linking. In vitro release of model drug hydrocortisone was studied in presence and absence of beta -mannanase. KGM cross-linked with STMP was able to retard the release of the poorly water-soluble drug and could be biodegraded enzymatically. Hydrocortisone release was cross-linking density dependent and controlled by degradation of the hydrogles.

Bovine Serum Albumin–Loaded Pectinate Beads as Colonic Peptide Delivery System: Preparation and In Vitro Characterization

Objective of this study was to prepare a drug delivery system for therapeutic peptides that are degraded in the upper part of the gastrointestinal tract due to degradation activity of the enzymes. Delivering peptide to the colon in which enzymatic activity is low is next hope for absorption of these agents. Pectin, a naturally occurring water soluble polysaccharide, as a matrix for peptide delivery was studied. Degradation of pectin by the colonic enzymes makes it suitable for colon-specific delivery of drugs. Bovine serum albumin (BSA) was used as a model peptide. Calcium pectinate beads were prepared by extruding BSA-loaded pectin solution to an agitating calcium chloride solution, and gelled spheres were formed instantaneously by an ionotropic gelation reaction. The effect of several factors such as concentration of pectin, concentration of calcium chloride, and total drug loading on the pattern of drug release in the dissolution medium was studied. Prepared beads showed good resistance in the release medium. The entrapment efficiency of the beads was high (between 63% and 99%). Entrapment efficiency of BSA was reversely dependent to the amount of the drug loaded in the beads. The amount of BSA loaded on the beads affects pattern of drug release. The concentration of the pectin showed the highest impact on the rate of drug release. Presence of the pectiolytic enzymes facilitated the drug release from the beads.

Potential of Guar Gum Microspheres for Target Specific Drug Release to Colon

Various approaches for colon targeted drug delivery have been studied over the last decade including, pro-drugs, timed-released systems, coating of pH-dependant polymer and the use of polysaccharides. In the present work, a novel formulation consisting of cross-linked microspheres of guar gum has been investigated for colon-targeted delivery of metronidazole. An emulsification method involving the dispersion of aqueous solution of guar gum in castor oil was used to prepare spherical microspheres. Process parameters were analyzed in order to optimize the formulation. Shape and surface morphology of the microspheres were examined using scanning electron microscopy. Placebo microspheres exhibited a smooth surface while the incorporation of drug imparted a slight roughness to the surface texture. Particle size of the microspheres was determined using laser diffraction particle size analyzer. The in vitro drug release studies were performed in simulated gastric fluid for 2 h and intestinal fluid for 3 h, which revealed that the drug was retained comfortably inside the microspheres and that only 15.27+/-0.56% of the drug was released in 5 h. In vitro release rate studies were also carried out in simulated colonic fluid (SCF) in the presence of rat cecal contents, which showed improved drug release. Moreover, to induce the enzymes that specifically act on guar gum, the rats were treated with 1 ml of 1% w/v dispersion of guar gum for 2, 4 and 6 days and release rate studies were repeated in SCF in the presence of 2 and 4% w/v of cecal matter. A marked improvement in the drug release was observed in presence of cecal matter obtained after induction when compared to those without induction. In vitro release studies exhibited 31.23+/-1.49% drug release in 24 h in dissolution medium without rat cecal matter. However, the incorporation of 4% w/v cecal matter obtained after 6 days of enzymes induction increased the drug release to 96.24+/-4.77%.

Degradation Kinetics of Fluorouracil-Acetic-Acid-Dextran Conjugate in Aqueous Solution

The degradation kinetics of fluorouracil-acetic-acid-dextran conjugate (FUAC-dextran) was investigated in various buffer solutions with different pH value and physiological saline solution at 60 degrees C and 37 degrees C, respectively. The hydrolytic reaction displayed pseudo-first-order degradation kinetics. Hydrolytic rate constant obtained was the function of pH value and independent of species of buffering agents. The smallest rate constant was observed at pH round 3.00. The activation energy of the hydrolytic reaction was estimated from Arrhenius equation as 88.73 +/- 6.00 kJ.mol-1. The special base catalytic degradation of the conjugate was observed from acidic to slight alkaline condition and the special base catalytic rate constants were calculated. The conjugate was more stable in physiological saline than that in buffer solution at pH 7.00 or 9.00 at 37 degrees C. The results revealed that the conjugate was stable in acidic condition and will degrade in alkaline condition.

In vitro release dynamics of model drugs from psyllium and acrylic acid based hydrogels for the use in colon specific drug delivery

Psyllium is medicinally important gel forming polysaccharides. Keeping in view, the pharmacological importance of psyllium and drug delivery devices based on hydrogels, psyllium, if suitably tailored to prepare the hydrogels, can act as the double potential candidates for the novel drug delivery systems. Therefore, it is an attempt to prepared psyllium and acrylic acid based pH sensitive novel hydrogels by using N,N'-methylenebisacrylamide (N,N-MBAAm) as crosslinker and ammonium persulfate (APS) as initiator for the use in colon specific drug delivery. The present paper discusses the swelling kinetics of the hydrogels and release dynamics of model drugs (tetracycline hydrochloride, insulin and tyrosine) from drug-loaded hydrogels, for the evaluation of the swelling mechanism and drug release mechanism from the polymeric networks .The effect of pH on the swelling kinetics and release pattern of drugs have been studied by varying the pH of the release medium. It has been observed that swelling and release of drugs from the hydrogels occurred through non-Fickian or anomalous diffusion mechanism in distilled water and pH 7.4 buffer. It shows that the rate of polymer chain relaxation and the rate of drug diffusion from these hydrogels are comparable.

Site‐Specific Drug Delivery to the Middle Region of the Small Intestine by Application of Enteric Coating with Hypromellose Acetate Succinate (HPMCAS)

Enteric coatings that deliver drugs to specific regions of the small intestine were examined. Hypromellose acetate succinate (HPMCAS) with different values of succinoyl group contents was used. Decreasing the succinoyl group content resulted in an increase in the pH at which HPMCAS started to dissolve. Drug-containing granules with or without enteric coating were prepared and their in vitro dissolution in a simulated intestinal fluid of pH 6.8 was examined. Granules coated with HPMCAS having the succinoyl group content of 6.2% showed a lag time of about 30 min, although drug release from granules without coating was completed within 20 min. The time lag and dissolution rate were extended and reduced, respectively, as the succinoyl group content was decreased. Rat experiments indicated that enteric-coated granules disintegrated and the bulk of the drugs was immediately released when the granules reached a specific site of the small intestine where the pH corresponded to the pH at which the enteric coating agent started to dissolve. Similar results were observed in monkey experiments. It was suggested that HPMCAS with the succinoyl group content of about 5% was suitable as an enteric coating agent for delivering drugs to the middle-to-lower region of the small intestine.

In-vitro and in-vivo studies of pectin/ethylcellulosefilm-coated pellets of 5-fluorouracil for colonic targeting

The aim of the present study was to define in-vitro and in-vivo characteristics of pectin/ethylcellulose-film-coated pellets of 5-fluorouracil (5-FU) for colonic targeting. The pellet cores were coated to different film thicknesses with three different pectin/ethylcellulose formulations using a fluidized bed coater. The gastrointestinal (GI) transit of coated pellets was determined by counting the percentage of coated pellets in the GI lumen by celiotomy at certain times after oral administration. 5FU was administered to rats at a dose of 15 mg kg(-1). The toxicity of 5-FU in the GI tract was evaluated using histological examination. The 1:2 ratio pectin:ethylcellulose-coated pellets with 30% total weight gain (TWG-30%) produced more satisfactory drug-release profiles in the simulated gastric, intestinal and colonic fluids. Most of the coated pellets were eliminated from the stomach in 2 h, moved into the small intestine after 2-4 h, and reached the large intestine after 4 h. After oral administration of coated pellets, 5-FU started appearing in the plasma at 7 h, and reached peak plasma concentration (Cmax) of 3.21+/-2.01 microg mL(-1) at 16 h (Tmax); the Cmax for uncoated pellets was 22.21+/-2.60 microg mL(-1) at Tmax 0.75 h. The TWG-30% formulation showed delayed Tmax, decreased Cmax and prolonged mean residence time compared with uncoated pellets. Marked pathological features in the colon were seen in rats given coated pellets, but no injuries were observed in the upper GI tract. The formulation of TWG-30% could deliver 5-FU to the colon for local action.

Konjac glucomannan/xanthan gum enzyme sensitive binary mixtures for colonic drug delivery

The polysaccharide konjac glucomannan (KGM) is degraded in the colon but not the small intestine, which makes it potentially useful as an excipient for colonic drug delivery. With xanthan gum (XG) KGM forms thermoreversible gels with hitherto unexplored biodegradation properties. In this work, rheological measurements of KGM and KGM/XG systems incubated with and without Aspergillus niger beta-mannanase (used to mimic colonic enzymes) showed that KGM was degraded by the enzyme even when interacting with XG. Tablets with KGM/XG/sucrose matrices that varied in accordance with a simplex design and bore diltiazem as a typical highly soluble drug load were prepared by wet granulation, and in most cases were found to possess satisfactory mechanical strength and exhibit slow, nearly zero-order drug release. Drug release from these tablets remained zero-order, but was accelerated (presumably due to degradation of KGM), in the presence of A. niger beta-mannanase at concentrations equivalent to human colonic conditions. However, marked differences between Japanese and American varieties of KGM as regards degree of acetylation and particle size led to significant differences in swelling rate and drug release between formulations prepared with one and the other KGM: whereas a formulation with Japanese KGM released its entire drug load within 24h in the presence of beta-mannanase, only 60% release was achieved under the same conditions by the corresponding formulation with American KGM, suggesting that with this KGM it will be necessary to optimize technological variables such as compression pressure in order to achieve suitable porosity, swelling rate, and drug release. To sum up, the results of this study suggest that sustained release of water-soluble drugs in the colon from orally administered tablets may be achieved using simple, inexpensive formulations based on combinations of KGM and XG that take the variability of KGM characteristics into account.

Purification of guar gum for biological applications

Commercial guar gum (GG) was purified by four different methods and characterized by gel permeation chromatography (GPC), thermogravimetric analysis and the determination of monosaccharides composition, protein and copper content, turbidity, intrinsic viscosity and rheological parameters. The first method was based on enzymatic hydrolysis with porcine pancreatin. In the second method successive gum dissolution, centrifugation and precipitation with acetone and ethanol were carried out. Precipitation with Fehling solution was employed in the third method. In the fourth method, the gum was purified by method 2 and then by method 3. All methods led to a reduction in protein content, arabinose and glucose residues, considered as sugar contaminants, and also in intrinsic viscosity and molar mass. Total elimination of protein was only achieved by method 4. Using methods 3 and 4, the gum was contaminated with small amounts of Cu(II) from the Fehling solution. Methods 2 and 4 apparently provided purer guar gum. If the amount of protein is a crucial parameter in the biological application and the guar will be taken in low amounts, method 4 is recommended. Taking into account the purity, thermal stability, rheological parameters of the purified gum and also the cost and simplicity of the procedure, method 2 has wider biological application.

Cerium complexes of cyclodextrin dimers as efficient catalysts for luminol chemiluminescence reactions

The chemiluminescence of a luminol-H(2)O(2) system is found to be remarkably enhanced by the Ce(IV) complexes of EDTA-bridged cyclodextrin dimers. The dimers were proved to work much more efficiently than the corresponding monomer. The cavity shape of cyclodextrin moieties and their cooperation displayed an important role in amplifying the chemiluminescence. Further modification of either the cyclodextrin rims or the EDTA linker altered significantly the catalytic abilities of the cyclodextrin dimers, and the examination of the effect of substituents on the chemiluminescence outputs suggested that the proximity between the cyclodextrin cavity and the metallic center might account for the amelioration of the chemiluminescence output.

Cross-linked guar gum microspheres: a viable approach for improved delivery of anticancer drugs for the treatment of colorectal cancer

In the present work, guar gum microspheres containing methotrexate (MTX) were prepared and characterized for local release of drug in the colon, which is a prerequisite for the effective treatment of colorectal cancer. Guar gum microspheres were prepared by the emulsification method using glutaraldehyde as a cross-linking agent. Surface morphological characteristics were investigated using scanning electron microscopy. Particle size, shape, and surface morphology were significantly affected by guar gum concentration, glutaraldehyde concentration, emulsifier concentration (Span 80), stirring rate, stirring time, and operating temperature. MTX-loaded microspheres demonstrated high entrapment efficiency (75.7%). The in vitro drug release was investigated using a US Pharmacopeia paddle type (type II) dissolution rate test apparatus in different media (phosphate-buffered saline [PBS], gastrointestinal fluid of different pH, and rat cecal content release medium), which was found to be affected by a change to the guar gum concentration and glutaraldehyde concentration. The drug release in PBS (pH 7.4) and simulated gastric fluids followed a similar pattern and had a similar release rate, while a significant increase in percent cumulative drug release (91.0%) was observed in the medium containing rat cecal content. In in vivo studies, guar gum microspheres delivered most of their drug load (79.0%) to the colon, whereas plain drug suspensions could deliver only 23% of their total dose to the target site. Guar gum microspheres showed adequate potential in achieving local release of drug in in vitro release studies, and this finding was further endorsed with in vivo studies.

Study of gamma-irradiation effects on chitosan microparticles

Gamma (gamma)-irradiation is finding increasing use in the sterilization of pharmaceutical products. However, irradiation also might affect the performance of drug delivery systems. In this study, the influence of gamma-irradiation on the characteristics of chitosan microparticles was investigated. The diclofenac sodium was incorporated into chitosan microparticles by spray-drying method. The chitosan microparticles (placebo and drug-loaded) were irradiated at doses of 5, 15, and 25 kGy using a (60)Co source. Later, the microparticles were characterized by Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and atomic force microscopy. In addition, microparticles also were evaluated for their sizes, drug content, swelling, and drug release behavior. Encapsulation efficiency of irradiated and nonirradiated microparticles was essentially the same. Notably, surface roughness (rms) of placebo microparticles decreased significantly after gamma-irradiation when compared with nonirradiated placebo microparticles. FTIR spectroscopy revealed that gamma-irradiation of chitosan microparticles induced neither cross-linking nor formation of new group in the chitosan matrix. EPR spectroscopy results showed that the gamma rays induced only one kind of free radical in the chitosan matrix. Size, crystallinity, and thermal properties of the chitosan microparticles did not change much after gamma-irradiation. gamma-irradiated microparticles, exhibited a slightly higher drug release rate and low swelling capacity than the nonirradiated microparticles.

Properties of Tableted High-Amylose Corn Starch–Pectin Blend Microparticles Intended for Controlled Delivery of Diclofenac Sodium

This study reports the properties of tableted microparticles based on high-amylose corn starch (HACS)–pectin blend polymers as the controlled release system for diclofenac sodium (DS). HACS–pectin blend microparticles are prepared through a modified process by the spray drying technique, which is a widely used microencapsulation technique in the pharmaceutical industry. The mean particle size of various formulations of blend microparticles is in the range of 5.8–7.3 μm. Fourier transform infrared (FTIR) spectroscopy study reveals the absence of well-defined interaction between HACS–pectin and polymers–DS. The blend microparticles thus prepared were compressed into tablets using the directly compressible excipients. A cross-sectional view of the tablet reveals the presence of nearly spherical shaped particles in the tablet, suggesting that the system chosen is ideal for tableting. In vitro drug release study indicates that tableted microparticulate system is found to be suitable for the manipulation of release behavior for DS in the gastrointestinal tract. Release mechanism of the DS from tableted microparticles is by Fickian diffusion since the value of n approaches 0.5.

Low viscosity hydrogel of guar gum: Preparation and physicochemical characterization

Guar gum was cross-linked with glutaraldehyde and characterized by GPC, rheology, WADX, SEM and TGA. This guar gum is a galactomannan polysaccharide, that contains small amount of arabinose, glucose and uronic acid, besides galactose and mannose. The polymer has high molar mass, with Mw, Mn and Mv values of 2.0x10(6), 1.2x10(6) and 1.9x10(6)g/mol, respectively. The reticulation follows a slow process and lead to a viscosity increase of 40 times compared with the original gum solution. The final viscosity was similar to that of Hylan G-F 20, a hyaluronate derivative, commercially used in viscosupplementation treatment. The gel contains 95.6% of water and the amount of residual glutaraldehyde is much lower than the LD-50. Porous structure was detected by SEM and thermal stability was improved by the cross-linking. The low viscosity, the small amount of remained glutaraldehyde, and the thermal stability indicates that the guar hydrogel has potential to be applied as biomaterial with specific rheological requirements.

Preparation of recombinant human bone morphogenetic protein-2 loaded dextran-based microspheres and their characteristics

AIM

To prepare new pharmaceutical forms with sustained delivery properties of recombinant human bone morphogenetic protein-2 (rhBMP2) for tissue engineering and guided tissue regeneration (GTR) use.

METHODS

rhBMP2-loaded dextran-based hydrogel microspheres (rhBMP2-MPs), which aimed to keep rhBMP2 bioactivity and to achieve long-term sustained release of rhBMP2, were prepared by double-phase emulsified condensation polymerization. The physical, chemical performances and biological characteristics of those microspheres were studied both in vitro and in vivo.

RESULTS

The microspheres' average diameter was 30.33+/-4.32 microm with 75.4% ranging from 20 microm to 40 microm and the drug loading and encapsulation efficiency were 7.82% and 82.25%, respectively. The rhBMP2-releasing profiles in vitro showed that rhBMP2 release could be maintained more than 10 d. The rhBMP2-MPs, with good swelling and biodegradation behavior, could be kept for 6 months at below 4 degree without significant characteristic change or bioactivity loss. Cytology studies showed that rhBMP2-MPs could promote the proliferation of periodontal ligament cells (PDLCs) approximately 10 d, while the bioactivity of concentrated rhBMP2 solution could keep no more than 3 d. Scanning electron microscope showed that rhBMP2-MPs could be enchased into the porous structure of calcium phosphate ceremic (CPC) and the eugonic growth of PDLCs in CPC/rhBMP2-MPs scaffolds. Animal experiments indicated that using CPC/rhBMP2-MPs scaffolds could gain more periodontal tissue regeneration than using rhBMP2 compound firsthand with CPC (CPC/rhBMP2).

CONCLUSION

By encapsulating rhBMP2 into dextran-based microspheres, a small quantity of rhBMP2 could achieve equivalent effects to the concentrated rhBMP2 solution and at the same time, could prolong rhBMP2 retention both in vitro and in vivo.

Drug release from the enzyme-degradable and pH-sensitive hydrogel composed of glycidyl methacrylate dextran and poly(acrylic acid)

Hydrogels composed of glycidyl methacrylate dextran (GMD) and poly(acrylic acid, PAA) were prepared by UV irradiation method for colon-specific drug delivery. GMD was synthesized by coupling of glycidyl methacrylate to dextran in the presence of 4-(N,N-dimethylamino)pyridine. GMD was photo-polymerized by ammonium peroxydisulfate as initiating system in phosphate-buffered solution (0.1 M, pH 7.4). And then, acrylic acid monomer was added and subsequently heat-polymerized by 2,2'-azobisisobutyronitrile as an initiator. The hydrogels exhibited high swelling ratio (about 20) at 37 degrees C, and showed a pH-dependent swelling behavior. In addition, the swelling ratio of the hydrogel was remarkably enhanced to about 45 times in the presence of dextranase at pH 7.4. The swelling-deswelling behavior proceeded reversibly for the GMD/PAA hydrogels between pH 2 and pH 7.4. Release of 5-aminosalicylic acid from the GMD/PAA hydrogels was evaluated in simulated gastrointestinal pH fluids in the absence or presence of dextranase. We concluded that the hydrogels prepared could be used as a dual-sensitive drug carrier for sequential release in gastrointestinal tract.

Pectin-based oral drug delivery to the colon

This review presents an overview of studies concerning oral formulations intended for site-specific drug delivery to the colon with pectin as the main excipient. The biological aspects covered include gastrointestinal transit and the enzymatic degradation of pectin. Scintigraphic methods demonstrating the functionality of pectin formulations are discussed. The main focus is on the various formulations reported, including matrix tablets, multiparticulate formulations as pellets and hydrogel beads, and pectin-based coatings. Also included is an evaluation of common excipients employed to improve colon specificity by crosslinking or increasing the hydrophobicity. Finally, properties of the pectin molecules that are important for successful formulations are examined. The conclusion is that the studies found in the literature provide an excellent platform for the development of pectin-based colon delivery systems.

Matrices for site-specific controlled-delivery of 5-fluorouracil to descending colon

Colon-specific controlled-delivery 5-fluorouracil (5-FU) matrices for the treatment of colorectal carcinoma were prepared and evaluated. Matrices are destined to be introduced into enteric-coated capsules and thereby carried to and liberated in the ileum. There, drug release should be prevented until matrices reach descending colon where release should occur. Matrices (50 mg, diameter 0.6 mm) were prepared by compression of powders or of granules prepared by melt granulation. The ingredients comprised 30-70% w/w 5-FU, glyceryl palmitostearate as rate-controlling material and 5% w/w Aerosil as glidant. Drug release was measured by the rotating basket method. The matrix containing 60% w/w drug, prepared by compression of powders, was appropriate to make the planned system, in virtue of its fairly high drug load and its nearly constant and reasonable release rate. This matrix was spray-coated with Eudragit S100 (EUD). Subsequently, an external layer of chitosan hydrochloride (CH-HCl) was applied by a dipping-drying technique. When transit of coated matrix through ileum (phosphate buffer (PB) pH 7.4), ascending colon (PB pH 6 containing rat cecal contents) and descending colon (PB pH 7.4) was simulated in vitro, the pH 4.7 of the CH-HCl gel layer and the pH 6 of the ascending colon prevented dissolution of the protective EUD film until descending colon was reached, then controlled release started. The present small matrices can enter size no. 00 capsules. Considering that each capsule contains 10 matrices, the maximal dose is 300 mg.

Advances in Colonic Drug Delivery

Targeting drugs and delivery systems to the colonic region of the gastrointestinal tract has received considerable interest in recent years. Scientific endeavour in this area has been driven by the need to better treat local disorders of the colon such as inflammatory bowel disease (ulcerative colitis and Crohn's disease), irritable bowel syndrome and carcinoma. The colon is also receiving significant attention as a portal for the entry of drugs into the systemic circulation. A variety of delivery strategies and systems have been proposed for colonic targeting. These generally rely on the exploitation of one or more of the following gastrointestinal features for their functionality: pH, transit time, pressure or microflora. Coated systems that utilise the pH differential in the gastrointestinal tract and prodrugs that rely on colonic bacteria for release have been commercialised. Both approaches have their own inherent limitations. Many systems in development have progressed no further than the bench, while others are expensive or complex to manufacture, or lack the desired site-specificity. The universal polysaccharide systems appear to be the most promising because of their practicality and exploitation of the most distinctive property of the colon, abundant microflora.