Colon-specific drug delivery based on a cyclodextrin prodrug: release behavior of biphenylylacetic acid from its cyclodextrin conjugates in rat intestinal tracts after oral administration

Therapeutic efficacy and gastrointestinal biodistribution of polycationic nanoparticles for oral camptothecin delivery in early and late-stage colorectal tumor-bearing animal model

Colorectal cancer (CRC) is the third most commonly diagnosed cancer in the world and is the second leading cause of cancer related deaths. New cases are increasingly diagnosed every day, but current therapeutic options are still insufficient for an effective treatment. In CRC treatment, there is a significant need for alternative treatment approaches that can both prevent relapse and provide strong antimetastatic effects as the intestines and colon are prone to metastasis to neighboring organs and tissues as well as the liver and the lung. In this study, optimized polycationic cyclodextrin (CD) nanoparticles for oral Camptothecin (CPT) delivery were comprehensively examined for in vivo performance in early and late stage tumor bearing mouse model in terms of antitumoral and antimetastatic efficacy of CPT bound to polycationic CD nanoparticles in comparison to free CPT. In addition, the gastrointestinal localization of a single administration of fluorescent dye loaded polycationic CD nanoparticles in the gastrointestinal tract at the end of 24 hours after oral administration was also imaged and evaluated by in vivo imaging system against fluorescent dye intensity. Results showed that survival percentage was significantly improved in CRC-bearing mice compared to oral CPT solution, with significantly reduced colorectal tumor masses and number of liver metastatic foci (p<0.05). It was also possible to differentiate between the effectiveness of nanoparticles in early or late stages of CRC. In vivo imaging studies have also confirmed that polycationic CD nanoparticles are able to deliver the therapeutic load up to the colon and tend to accumulate especially in tumor foci, indicating an effective local treatment strategy. In addition number of liver metastases were significantly decreased with the CPT-loaded polycationic CD nanoparticle formulation in both early and late stage tumor models. These findings indicated that CPT-loaded polycationic CD nanoparticles could be an efficient oral nanocarrier formulation for anticancer molecules that have limited application because of oral bioavailability and stability problems.

Oral delivery of natural active small molecules by polymeric nanoparticles for the treatment of inflammatory bowel diseases

The incidence of inflammatory bowel disease (IBD) is rapidly rising throughout the world. Although tremendous efforts have been made, limited therapeutics are available for IBD management. Natural active small molecules (NASMs), which are a gift of nature to humanity, have been widely used in the prevention and alleviation of IBD; they have numerous advantageous features, including excellent biocompatibility, pharmacological activity, and mass production potential. Oral route is the most common and acceptable approach for drug administration, but the clinical application of NASMs in IBD treatment via oral route has been seriously restricted by their inherent limitations such as high hydrophobicity, instability, and poor bioavailability. With the development of nanotechnology, polymeric nanoparticles (NPs) have provided a promising platform that can efficiently encapsulate versatile NASMs, overcome multiple drug delivery barriers, and orally deliver the loaded NASMs to targeted tissues or cells while enhancing their stability and bioavailability. Thus, NPs can enhance the preventive and therapeutic effects of NASMs against IBD. Herein, we summarize the recent knowledge about polymeric matrix-based carriers, targeting ligands for drug delivery, and NASMs. We also discuss the current challenges and future developmental directions.

Commensal flora triggered target anti-inflammation of alginate-curcumin micelle for ulcerative colitis treatment

Ulcerative colitis (UC) is a chronic, idiopathic inflammatory bowel disease characterized by dysregulation of colon immune response. Curcumin (Cur) has strong anti-inflammatory activities, but the application is severely hindered by the extremely hydrophobicity and pitiful bioavailability. Alginate (Alg), a natural polysaccharide with ideal solubility and biosafety, was introduced to prepare the esterified alginate-curcumin conjugate (Alg-Cur) and constructed stable Alg-Cur micelle in physiological solutions. Compared with crystalline Cur, the target anti-inflammatory activities of Alg-Cur were systematically investigated. The results showed that Alg-Cur exerted effective anti-inflammatory effects in Raw 264.7 cells. After oral administration, 92.32 % of Alg-Cur reached colon, and the ester bonds were quickly sheared by abundant esterase produced by commensal anaerobic flora. The released Cur was quickly absorbed in-situ in monomolecular state, and effectively ameliorated the colonic inflammation and tissue damage by inhibiting the TLR4 expression in colonic epithelial cell, reducing the transcription and expression of the pro-inflammation cytokines downstream, as well as the infiltration of lymphocytes, macrophages and neutrophils. The Alg-Cur micelle effectively enhanced the hydrophilicity and bioavailability of Cur, and the commensal flora triggered Cur release showed great potential for UC treatment.

Bioresponsive drug delivery systems in intestinal inflammation: State-of-the-art and future perspectives

Oral colon-specific delivery systems emerged as the main therapeutic cargos by making a significant impact in the field of modern medicine for local drug delivery in intestinal inflammation. The site-specific delivery of therapeutics (aminosalicylates, glucocorticoids, biologics) to the ulcerative mucus tissue can provide prominent advantages in mucosal healing (MH). Attaining gut mucosal healing and anti-fibrosis are main treatment outcomes in inflammatory bowel disease (IBD). The pharmaceutical strategies that are commonly used to achieve a colon-specific drug delivery system include time, pH-dependent polymer coating, prodrug, colonic microbiota-activated delivery systems and a combination of these approaches. Amongst the different approaches reported, the use of biodegradable polysaccharide coated systems holds great promise in delivering drugs to the ulcerative regions. The present review focuses on major physiological gastro-intestinal tract challenges involved in altering the pharmacokinetics of delivery systems, pathophysiology of MH and fibrosis, reported drug-polysaccharide cargos and focusing on conventional to advanced disease responsive delivery strategies, highlighting their limitations and future perspectives in intestinal inflammation therapy.

Functionalization of Lipid-Based Nutrient Supplement with β-Cyclodextrin Inclusions of Oregano Essential Oil

Intestinal parasitic infection is one of the main causes of acute undernutrition in children. Oral consumption of oregano essential oil (OEO) can reduce intestinal parasitic infections, however, its addition to therapeutic and supplementary foods is hampered by its undesirable flavor. The objective of this study was to develop a functional lipid-based nutrient supplement (LNS) containing OEO, which is stable, acceptable and provides targeted intestinal delivery of bioactive. β-cyclodextrin (β-CyD) inclusion complexes of OEO (β-CyD-OEO), and carvacrol (β-CyD-CV) (1:1 molar) were prepared using slurry complexation (-20 °C) method and characterized based on encapsulation efficiency, moisture content, morphology, and 2-phase in vitro digestion stability. Carvacrol (CV) content was measured using reverse phase HPLC-UV. LNS containing β-CyD-OEO (27.2 mg encapsulate/20 g LNS) was formulated using Indian staples and ingredients. Discriminatory sensory tests (triangle) were performed with college students (n = 58) and low-income women (n = 25), with young children at home (1 to 6 years), living in Mehsana, India to evaluate differences between LNS with and without bioactive ingredient (β-CyD-OEO only). Moisture of dried complexes ranged 9.1% to 9.7% d.b., whereas water activity 0.35 to 0.412. The complex size and encapsulation efficiency of β-CyD-OEO and β-CyD-CV were 1.5 to 7 μm and 4 to 20 μm, and 86.04 ± 4.48% and 81.39 ± 3.34%, respectively. The bioactive complexes were stable through the gastric and intestinal phases. Bioaccessibility of encapsulated CV ranged 6.0% to 7.7%. Sensory tests revealed no differences (P > 0.05) in color, aroma, and taste between LNS with and without β-CyD-OEO complexes. Functionalization of LNS with β-CyD-OEO is feasible based on in vitro stability and sensory studies.

PRACTICAL APPLICATION

Despite its antiparasitic activities, the addition of oregano essential oil into foods is limited due to its strong flavor and volatility. In this study, we evaluated the encapsulation of oregano essential oil with β-cyclodextrin and its addition into lipid-based nutrition supplements. The results revealed that complex encapsulation efficiency was above 80%. Also, the bioactive complexes were stable under in vitro gastrointestinal conditions. Sensory evaluation of LNS with and without encapsulated essential oil showed no difference in terms of color, aroma, and taste. The functional LNS can both address nutrient insufficiency as well as parasitic infection among malnourished populations in low-resource settings.

Safety, pharmacokinetics and pharmacogenetics of a single ascending dose of pradefovir, a novel liver-targeting, anti-hepatitis B virus drug, in healthy Chinese subjects

BACKGROUND

Pradefovir is efficiently converted to adefovir [9-(2-phosphonylmethoxyethyl) adenine (PMEA)], producing high hepatic PMEA concentration but low levels in the systemic circulation and kidney. The aim of this study is to evaluate the tolerability, adverse effect (AEs), pharmacokinetics and pharmacogenetics of a single ascending dose of pradefovir.

METHODS

Fifty healthy subjects were divided into five groups and randomized within each group at a ratio of 3:1:1 to receive a single ascending dose of pradefovir (10, 30, 60, 90, or 120 mg), and 10 mg adefovir dipivoxil (ADP) or placebo. Blood and urine samples were collected and analyzed. A total of 1930 polymorphic loci were analyzed in 6 blood samples collected from the 90 mg pradefovir group.

RESULTS

The single oral dose of pradefovir up to 120 mg was well tolerated. A total of 29 dose-limited mild AEs were reported in 17 subjects. The peak plasma concentration (C _max) and area under the curve (AUC)_0-48 of serum pradefovir ranged from (21.41 ± 12.98) to (447.33 ± 79.34) ng/mL and (46.10 ± 29.45) to (748.18 ± 134.15) ng h/mL across the dose range, respectively. The C _max and AUC_0-48 of serum PMEA ranged from 18.10 ± 4.96 to 312.33 ± 114.19 ng/mL and 72.65 ± 28.25 to 1095.48 ± 248.47 ng h/mL. Generally, no kidney impairment was observed. Pharmacogenetic analysis identified three metabolism-related single nucleotide polymorphism (SNP) locis, P450 (cytochrome) oxidoreductase [POR (rs6965343)], arylamine N-acetyltransferases [NAT1 (rs4986993)] and CYP2F1 (rs305968)], and one distribution-related loci, orosomucoid 2 [ORM2 (rs12685968)].

CONCLUSIONS

The single oral dose of pradefovir 10-120 mg was well tolerated. SNPs may be associated with variable rates of adverse events.

TRIAL REGISTRATION NUMBER

CTR20140341.

Inclusion of terpenes in cyclodextrins: Preparation, characterization and pharmacological approaches

Terpenes constitute the largest class of natural products and are important resources for the pharmaceutical, food and cosmetics industries. However, due to their low water solubility and poor bioavailability there has been a search for compounds that could improve their physicochemical properties. Cyclodextrins (natural and derived) have been proposed for this role and have been complexed with different types of terpenes. This complexation has been demonstrated by using analytical techniques for characterizing complexes such as DSC, NMR, XRD, FTIR, and TGA. The formation of inclusion complexes has been able to improve drug characteristics such as bioavailability, solubility and stability; and to enhance biological activity and efficacy. This review shows strong experimental evidence that cyclodextrins improve the pharmacological properties of terpenes, and therefore need to be recognized as being possible targets for clinical use.

Diclofenac-β-cyclodextrin for colonic drug targeting: In vivo performance in rats

The aim of this in vivo study was to assess the ability of the prodrug conjugate diclofenac-β-cyclodextrin to release diclofenac in the colon following oral administration, using sulfapyridine (a metabolite of sulfasalazine) as a marker of colonic absorption. Two groups of rats were used; the test rats received a suspension containing the two prodrugs, diclofenac-β-cyclodextrin and sulfasalazine, while the control rats received a suspension containing the corresponding free drugs, sodium diclofenac and sulfapyridine. The rats were fasted overnight with free access to water before and throughout the first 12h of the study. Blood was collected from the tail vein at pre-determined time points and the plasma analyzed for the concentrations of diclofenac and sulfapyridine. Following the oral administration of the two prodrugs, a more extended absorption profile was observed and Cmax was achieved 10h post-dose, in contrast to rapid absorption of the free drugs (tmax of diclofenac being 1.3h, and that of sulfapyridine being 2.1h). In addition to a later tmax, conjugation of diclofenac to β-cyclodextrin also resulted in a reduced Cmax and a reduced AUC. The same tmax for diclofenac-β-cyclodextrin as for sulfasalazine confirms the colonic metabolism of diclofenac-β-cyclodextrin. This study shows the potential of this new cyclodextrin-based prodrug to target and release diclofenac specifically in the colon following oral administration.

Qualitative and quantitative analysis of felbinac and its major metabolites in human plasma and urine by liquid chromatography tandem mass spectrometry and its application after intravenous administration of felbinac trometamol injection

We present a method for the qualitative and quantitative analysis of felbinac and its major metabolites in human plasma and urine by HPLC-MS/MS and its application. Qualitative analysis through LC-Triple-TOF-MS/MS indicated that oxidization was the main phase-I metabolic pathway of felbinac in human, conjugation with sulfate and glucuronide groups produced at least 7 phase-II metabolites. Quantitative analysis through HPLC-MS/MS in MRM mode was developed and validated for the quantification of felbinac and its major metabolite (4'-hydroxyfelbinac) in human plasma and urine. Linear calibration curves were obtained for felbinac and 4'-hydroxyfelbinac in plasma and urine (r>0.996); intra- and inter-day precision values (RSD%) obtained were ranged from 1.13 to 6.49%, and the accuracy were between 95.9% and 108.6% for the two analytes. The pharmacokinetics and excretion analysis showed that the t1/2 of 4'-hydroxyfelbinac (8.25 ± 4.15 h) is a litter longer than that of felbinac (6.13 ± 2.01 h), but the mean AUC(0-t) value of felbinac was about 20 times higher than that of 4'-hydroxyfelbinac; excretion of felbinac and 4'-hydroxyfelbinac reached their peak values at about 3-6h after intravenous administration of felbinac trometamol in human.

Preparation and properties of a pH sensitive carrier based on three kinds of polymer blend to control the release of 5-amino salicylic acid

CONTEXT

High concentration of 5-amino salicylic acid (5-ASA) in the distal ileum and colon is necessary for the treatment of inflammatory bowel disease (IBD). The control of small molecules, drugs, released from a polymeric matrix remains a great challenge.

OBJECTIVE

To study the preparation and properties of a pH-sensitive carrier for targeting delivery of 5-ASA.

MATERIALS AND METHODS

The carrier was prepared by ternary blends method based on polyvinyl alcohol (PVA), sodium alginate (SA) and polylactic acid. It was characterized by infrared spectrometry and scanning electronic microscopy. The adsorption and release of 5-ASA in different pH media were investigated.

RESULTS

We found out the best ratio of the materials for synthetic carrier. The vector exhibited good performance by the controlled release of the target drug experiment. The adsorption capacity of the carrier for 5-ASA was 70.34% in phosphate buffer saline at pH 1.00, and the release rate was 100.49% in phosphate buffer solution at pH 6.80.

DISCUSSION AND CONCLUSION

PVA is vector backbone of the carrier, and SA plays key role in its pH performance. It is a promising material to effectively deliver 5-ASA to the specific sites of IBD.

Carrier-linked mutual prodrugs of biphenylacetic acid as a promising alternative to bioprecursor fenbufen: design, kinetics, and pharmacological studies

Novel mutual prodrugs of biphenylacetic acid were designed as a promising gastro-protective alternative to fenbufen. Biphenyacetic acid was covalently linked with two non-essential amino acids (D-phenylalanine and glycine) possessing wound healing, analgesic, and anti-inflammatory properties. The prodrugs exhibited good stability in stomach homogenates while hydrolytic release of biphenylacetic acid was observed in phosphate buffer, small intestinal homogenates, and 80% human plasma. In vivo behavior of prodrugs on oral administration to Wistar rats demonstrated 33-45% release of biphenylacetic acid in blood over a period of 24 h indicating passage of intact prodrugs to colon, colonic release of parent drug followed by its absorption through colonic mucosa into systemic circulation. Prodrugs were extensively evaluated for analgesic, anti-inflammatory, anti-arthritic, and ulcerogenic activities. Biochemical, haemetological, histopathological, and radiological studies were also performed. Conversion of bioprecusor fenbufen into mutual carrier-linked prodrugs proved to be promising alternative in terms of reduced ulcerogenic propensity, longer duration of analgesia, enhanced/prolonged anti-inflammatory activity, and superior anti-arthritic effect. These prodrugs could be developed further for chronotherapy of rheumatoid arthritis.

Biological activity of some derivatives of β-cyclodextrin

New compounds of β-cyclodextrin containing covalently bound (conjugated) residues of acetylsalicylic and 1-(4-isobutylphenyl)-propionic acids were synthesized in the reaction of chlorides of the corresponding acids with β-cyclodextrin. We studied antiplatelet and antiphlogistic properties of these substances. It was shown that new compounds are comparable and in some cases are superior to the reference drugs acetylsalicylic acid and ibuprofen by anti-inflammatory and antiaggregant activities.

Advanced technologies for oral controlled release: cyclodextrins for oral controlled release

Cyclodextrins (CDs) are used in oral pharmaceutical formulations, by means of inclusion complexes formation, with the following advantages for the drugs: (1) solubility, dissolution rate, stability, and bioavailability enhancement; (2) to modify the drug release site and/or time profile; and (3) to reduce or prevent gastrointestinal side effects and unpleasant smell or taste, to prevent drug-drug or drug-additive interactions, or even to convert oil and liquid drugs into microcrystalline or amorphous powders. A more recent trend focuses on the use of CDs as nanocarriers, a strategy that aims to design versatile delivery systems that can encapsulate drugs with better physicochemical properties for oral delivery. Thus, the aim of this work was to review the applications of the CDs and their hydrophilic derivatives on the solubility enhancement of poorly water-soluble drugs in order to increase their dissolution rate and get immediate release, as well as their ability to control (to prolong or to delay) the release of drugs from solid dosage forms, either as complexes with the hydrophilic (e.g., as osmotic pumps) and/or hydrophobic CDs. New controlled delivery systems based on nanotechnology carriers (nanoparticles and conjugates) have also been reviewed.

Polymers for colon targeted drug delivery

The colon targeted drug delivery has a number of important implications in the field of pharmacotherapy. Oral colon targeted drug delivery systems have recently gained importance for delivering a variety of therapeutic agents for both local and systemic administration. Targeting of drugs to the colon via oral administration protect the drug from degradation or release in the stomach and small intestine. It also ensures abrupt or controlled release of the drug in the proximal colon. Various drug delivery systems have been designed that deliver the drug quantitatively to the colon and then trigger the release of drug. This review will cover different types of polymers which can be used in formulation of colon targeted drug delivery systems.

Evaluation of amylose used as a drug delivery carrier

The enzyme-dependent conjugates of indomethacin and amylose (Am-IND) were synthesized at room temperature using N,N'-dicyclohexylcarbodiimide (DCC) as a coupling agent and 4-(N,N'-dimethylamino) pyridine (DMAP) as a catalyst. Their structures were characterized by FTIR and (1)H NMR analyses, and the results indicated that the IND residues were conjugated with amylose backbones through ester bonds. For the conjugate with a lower IND content, the better water absorption property was advantageous for enzymes diffusing into the swollen conjugate, resulting in biodegradation of the conjugates and release of IND. In vitro biodegradation evaluation indicated that the Am-IND conjugates were biodegraded in the simulated media of the intestines. In vitro drug release experiments showed that the Am-IND conjugates exhibited a sustained release behavior in the simulated media of the intestines, while IND was hardly released in the simulated gastric fluid. These features provide a great opportunity to use the conjugates as a prodrug for intestinally targeted and controlled release of IND through oral administration. This study may lead to the development of effective methods for utilizing amylose as a new drug delivery carrier.

5-Fluorouracil acetic acid/beta-cyclodextrin conjugates: drug release behavior in enzymatic and rat cecal media

5-Fluorouracil-1-acetic acid (5-FUA) was prepared and covalently conjugated to beta-cyclodextrin (beta-CyD) through ester or amide linkage, and the drug release behavior of the conjugates in enzymatic solutions and rat cecal contents were investigated. The 5-FUA/beta-CyD ester conjugate was slowly hydrolyzed to 5-FUA in aqueous solutions (half lives (t(1/2))=38 and 17h at pH 6.8 and 7.4, respectively, at 37 degrees C), whereas the amide conjugate was hardly hydrolyzed at these physiological conditions, but hydrolyzed only in strong alkaline solutions (>0.1M NaOH) at 60 degrees C. Both ester and amide conjugates were degraded in solutions of a sugar-degrading enzyme, alpha-amylase, to 5-FUA/maltose and triose conjugates, but the release of 5-FUA was only slight in alpha-amylase solutions. In solutions of an ester-hydrolyzing enzyme, carboxylic esterase, the ester conjugate was hydrolyzed to 5-FUA at the same rate as that in the absence of the enzyme, whereas the amide conjugate was not hydrolyzed by the enzyme. On the other hand, 5-FUA was rapidly released when the ester conjugate was firstly hydrolyzed by alpha-amylase, followed secondly by carboxylic esterase. The results indicated that the ester conjugate was hydrolyzed to 5-FUA in a consecutive manner, i.e. it was firstly hydrolyzed to the small saccharide conjugates, such as the maltose conjugate, by alpha-amylase, and the resulting small saccharide conjugates having less steric hindrance was susceptible to the action of carboxylic esterase, giving 5-FUA. The in vitro release behavior of the ester conjugate was clearly reflected in the hydrolysis in rat cecal contents and in the in vivo release after oral administration to rats.

Polysaccharides for Colon Targeted Drug Delivery

Colon targeted drug delivery has the potential to deliver bioactive agents for the treatment of a variety of colonic diseases and to deliver proteins and peptides to the colon for their systemic absorption. Various strategies, currently available to target the release of drugs to colon, include formation of prodrug, coating of pH-sensitive polymers, use of colon-specific biodegradable polymers, timed released systems, osmotic systems, and pressure controlled drug delivery systems. Among the different approaches to achieve targeted drug release to the colon, the use of polymers especially biodegradable by colonic bacteria holds great promise. Polysaccharidases are bacterial enzymes that are available in sufficient quantity to be exploited in colon targeting of drugs. Based on this approach, various polysaccharides have been investigated for colon-specific drug release. These polysaccharides include pectin, guar gum, amylose, inulin, dextran, chitosan, and chondroitin sulphate. This family of natural polymers has an appeal to drug delivery as it is comprised of polymers with a large number of derivatizable groups, a wide range of molecular weights, varying chemical compositions, and, for the most part, low toxicity and biodegradability yet high stability. The most favorable property of these materials is their approval as pharmaceutical excipients.

In-vitroandIn-vivoEvaluation of Mesalazine–Guar Gum Matrix Tablets for Colonic Drug Delivery

The aim of this study was to develop colon-specific delivery systems for mesalazine (5-ASA) using guar gum as a carrier. A colon specific matrix tablet of mesalazine with guar gum was evaluated by in vitro and in vivo X-ray studies in humans. Two different types of guar gum were used in the experiments. Tablets were prepared by the slugging method. The physical properties of tablets were tested and in vitro release studies were performed by a flow-through cell apparatus with and without galactomannanase enzyme. The type and the amount of guar gum affected the in vitro release of drug from the matrix tablets. High viscosity guar gum, in the form of a matrix tablet was capable of protecting the drug from being released in the upper region of gastrointestinal (GI) system, i.e. stomach and small intestine. X-ray imaging technique was used to monitor the tablets throughout the GI system on 8 healthy volunteers. Barium sulphate was used as a marker in the tablets for in vivo studies. These results showed that, the matrix tablets reached the colon; not being subjected to disintegration in the upper region of the GI system in all the subjects.

Design and evaluation of colon specific drug delivery system containing flurbiprofen microsponges

The purpose of this study was to design novel colon specific drug delivery system containing flurbiprofen (FLB) microsponges. Microsponges containing FLB and Eudragit RS 100 were prepared by quasi-emulsion solvent diffusion method. Additionally, FLB was entrapped into a commercial Microsponge 5640 system using entrapment method. Afterwards, the effects of drug:polymer ratio, inner phase solvent amount, stirring time and speed and stirrer type on the physical characteristics of microsponges were investigated. The thermal behaviour, surface morphology, particle size and pore structure of microsponges were examined. The colon specific formulations were prepared by compression coating and also pore plugging of microsponges with pectin:hydroxypropylmethyl cellulose (HPMC) mixture followed by tabletting. In vitro dissolution studies were done on all formulations and the results were kinetically and statistically evaluated. The microsponges were spherical in shape, between 30.7 and 94.5microm in diameter and showed high porosity values (61-72%). The pore shapes of microsponges prepared by quasi-emulsion solvent diffusion method and entrapment method were found as spherical and cylindrical holes, respectively. Mechanically strong tablets prepared for colon specific drug delivery were obtained owing to the plastic deformation of sponge-like structure of microsponges. In vitro studies exhibited that compression coated colon specific tablet formulations started to release the drug at the 8th hour corresponding to the proximal colon arrival time due to the addition of enzyme, following a modified release pattern while the drug release from the colon specific formulations prepared by pore plugging the microsponges showed an increase at the 8th hour which was the time point that the enzyme addition made. This study presents a new approach based on microsponges for colon specific drug delivery.

Colon drug delivery

Oral drug delivery to the colon has attracted significant attention during the past 20 years. Colon targeting is recognised to have several therapeutic advantages, such as the oral delivery of drugs that are destroyed by the stomach acid and/or metabolised by pancreatic enzymes. Sustained colonic release of drugs can be useful in the treatment of nocturnal asthma, angina and arthritis. Local treatment of colonic pathologies, such as ulcerative colitis, colorectal cancer and Crohn's disease, is more effective with the delivery of drugs to the affected area. Likewise, colonic delivery of vermicides and colonic diagnostic agents requires smaller doses. This article aims to provide an insight into the design and manufacturing considerations, and an evaluation of colonic drug delivery systems in order to understand why there are still few delivery technologies that have reached the market, despite intensive research in this field. For this purpose, various approaches to colon-specific drug delivery are discussed.

Cyclodextrins in drug delivery: an updated review

The purpose of this review is to discuss and summarize some of the interesting findings and applications of cyclodextrins (CDs) and their derivatives in different areas of drug delivery, particularly in protein and peptide drug delivery and gene delivery. The article highlights important CD applications in the design of various novel delivery systems like liposomes, microspheres, microcapsules, and nanoparticles. In addition to their well-known effects on drug solubility and dissolution, bioavailability, safety, and stability, their use as excipients in drug formulation are also discussed in this article. The article also focuses on various factors influencing inclusion complex formation because an understanding of the same is necessary for proper handling of these versatile materials. Some important considerations in selecting CDs in drug formulation such as their commercial availability, regulatory status, and patent status are also summarized. CDs, because of their continuing ability to find several novel applications in drug delivery, are expected to solve many problems associated with the delivery of different novel drugs through different delivery routes.

Synthesis and properties of polysaccharide prodrugs of 5-aminosalicylic acid as potential colon-specific delivery systems

The drug release of the polymer prodrugs of 5-aminosalicylic acid (5-ASA) was not only dependent on the property of the polymers but also dependent on the solubility of the prodrugs. We prepared several polysaccharide prodrugs of 5-ASA to examine the effect of solubility of prodrugs on the release characteristics of 5-ASA in the gastrointestinal contents of rats. The amide prodrug, chitosan-5-ASA (ChT-5-ASA), did not release the 5-ASA in the cecal and colonic contents. The ester prodrugs, hydroxypropyl cellulose-5-ASA (HPC-5-ASA), being poor solubility in 0.05mol/l acetic acid solution also did not release the 5-ASA in any of gastrointestinal contents of rats. Whereas the 5-ASA release from cyclodextrins-5-ASA (CyDs-5-ASA) in cecal and colonic contents was significantly higher than that in stomach and small intestine contents. And furthermore, with the decrease in the degree of substitution, the solubility of CyD-5-ASA increased, and the release of 5-ASA in the gastrointestinal contents was also higher at the same time interval of incubation. When the ratio of cyclodextrin (CyD) and 5-formylaminosalicylic acid (5-fASA), a precursor of 5-ASA prodrugs, was 1:10, CyD-5-ASA was very slightly soluble, and no release of 5-ASA was observed within 48h in gastrointestinal contents. The present results suggested that the ester prodrugs of 5-ASA with certain solubility could release 5-ASA in the cecal and colonic contents of rat.

Design and evaluation of cyclodextrin-based drug formulation

The pharmaceutically useful cyclodextrins (CyDs) are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in design and evaluation of CyD-based drug formulation, focusing on their ability to enhance the drug absorption across biological barriers, the ability to control the rate and time profiles of drug release, and the ability to deliver a drug to a targeted site.

[Pharmaceutical application of cyclodextrins as multi-functional drug carriers]

Owing to the increasingly globalized nature of the cyclodextrin (CyD)-related science and technology, development of the CyD-based pharmaceutical formulation is rapidly progressing. The pharmaceutically useful CyDs are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in drug delivery and pharmaceutical formulation, focusing on the following evidences. 1) The hydrophilic CyDs enhance the rate and extent of bioavailability of poorly water-soluble drugs. 2) The amorphous CyDs such as 2-hydroxypropyl-beta-CyD are useful for inhibition of polymorphic transition and crystallization rates of drugs during storage. 3) The delayed release formulation can be obtained by the use of enteric type CyDs such as O-carboxymethyl-O-ethyl-beta-CyD. 4) The hydrophobic CyDs are useful for modification of the release site and/or time profile of water-soluble drugs with prolonged therapeutic effects. 5) The branched CyDs are particularly effective in inhibiting the adsorption to hydrophobic surface of containers and aggregation of polypeptide and protein drugs. 6) The combined use of different CyDs and/or pharmaceutical additives can serve as more functional drug carriers, improving efficacy and reducing side effects. 7) The CyD/drug conjugates may provide a versatile means for the constructions of not only colonic delivery system but also site-specific drug release system, including gene delivery. On the basis of the above-mentioned knowledge, the advantages and limitations of CyDs in the design of advanced dosage forms will be discussed.

Microbially triggered drug delivery to the colon

Increasing acceptance of protein- and peptide-based drugs necessitates an investigation into the suitability of various sites for their administration. Colon is being investigated for delivery of such molecules. Colon-specific drug delivery is designed to target drug molecules specifically to this area. Development of site-specific delivery systems may exploit a specific property of the target site for drug activation/release. The gastrointestinal tract is inhabited by over 400 bacterial species, each having a specific niche in the tract. Colon, the distal part of the intestine is inhabited by a large variety of gram negative microflora. This flora produces a vast number of enzymes which are being exploited for formulation of colon-specific drug delivery systems. A number of microbially activated systems for colon-specific drug delivery are being evaluated. These include prodrugs and synthetic or natural polymer-based delivery systems. This article aims at reviewing the various microbially activated drug delivery systems for colon-specific drug delivery with specific reference to the microflora of the various segments of the gastrointestinal tract and their role in targeting drug delivery to the colon.

Synthesis of an enzyme-dependent prodrug and evaluation of its potential for colon targeting

AIM: To synthesize dexamethasone-succinate-dextran (DSD) conjugate and to evaluate the potentiality of DSD for the treatment of inflammatory bowel diseases.

METHODS: Dexamethasone was attached to dextran (average molecular weight = 70400 Dalton) using succinate anhydride in an anhydrous environment catalyzed by 4-dimethylaminopyridine and 1,1’-carbonyldiimidazole. The chemical structure of DSD was identified by UV, IR and NMR, and the in vivo drug release behavior of this prodrug was investigated after oral administration of DSD suspension.

RESULTS: The DSD conjugate was obtained in two steps and the content of dexamethasone in DSD was 11.28%. The dextran prodrug was stable in rat stomach and small intestine and negligibly absorbed from these tracts. Four to nine hours after the oral administration, most of the prodrug (> 95%) had moved to the cecum and colon, and was easily hydrolyzed by an endodextranase. Recover of dexamethasone from colon and cecum after administration of DSD conjugate was 6-12 folds higher than the recovery after administration of unmodified dexamethasone (t = 2.74, P < 0.05). The preferential release of free dexamethasone in cecum and colon over that in the small intestine was statistically significant (t = 2.27, P < 0.05).

CONCLUSION: The results of this study indicate that dextran conjugates may be useful in selectively delivering glucocorticoids to the colon.

Cyclodextrin conjugate-based controlled release system: repeated- and prolonged-releases of ketoprofen after oral administration in rats

6(A)-O-[2-(3-Benzoylphenyl)propinoyl]-alpha-cyclodextrin (KP-alpha-CyD conjugate), in which an anti-inflammatory drug, ketoprofen (KP), is covalently bound to one of the primary hydroxyl groups of alpha-cyclodextrin, was prepared, and its release behavior in vitro and in vivo was investigated. Further, the CyD conjugate-based repeated- and prolonged-release systems were designed by combining the conjugate (used as a delayed-release fraction) with the KP-2-hydroxypropyl-beta-CyD (HP-beta-CyD) complex (used as a fast-release fraction) or with KP-ethylcellulose (EC) solid dispersion (used as a slow-release fraction), respectively. The conjugate released KP only in rat cecum and colonic contents, whereas it was stable in other biological fluids of rats. The conjugate showed a typical delayed-release pattern after oral administration to rats, i.e., plasma levels of KP increased after a lag time of about 3 h and reached a maximum concentration at about 7 h. On the other hand, the non-covalent inclusion complex of KP with HP-beta-CyD gave a rapid increase in plasma drug levels, and the KP-EC solid dispersion retarded slightly the increase of plasma levels. The co-administration of the conjugate and the HP-beta-CyD complex gave a typical repeated release profile, i.e., double peaks were observed at about 1-2 and 8-12 h in plasma KP levels. On the other hand, the co-administration of the conjugate and the EC solid dispersion gave a typical sustained-release pattern of KP, i.e., a constant plasma KP level was maintained for at least 24 h. These repeated or long circulating release patterns in plasma KP levels after oral administration were clearly reflected in the anti-inflammatory effect using rats with carageenan-induced acute edema in paw. The results suggest that various release-controlled preparations can be designed by employing CyD conjugates in combination with other carriers with different releasing properties.

Enantioselective stabilization of inclusion complexes of metoprolol in carboxymethylated beta-cyclodextrin

The inclusion complexes of metoprolol (MT) and carboxymethyl-beta-cyclodextrin (CMCD) were prepared and the stability constants of the complexes were determined. Binding studies performed using high performance liquid chromatography (HPLC), UV spectrometry and capillary electrophoresis (CE) indicated that a complex with 1:1 stoichiometry is predominant in the solution. The enantiomers of MT possess relatively high affinity towards CMCD with stability constants of 288 and 262 per M for (R)- and (S)-MT, respectively. Through nuclear magnetic resonance (NMR) analysis, MT was predicted to be a bent structure with phenyl ring of MT inserted in the shielding cavity of CMCD during complex formation. The NMR data suggested that the chiral side chain and the methoxyethyl moiety of MT are aligned in the deshielding zone, above and below the CMCD torus ring.

Cyclodextrins in oligonucleotide delivery

The aim of this contribution is to summarize recent findings on the potential use of cyclodextrins and their derivatives as carriers for oligonucleotide agents. Their peculiar properties could be exploited in such an emerging therapeutic area by virtue of their capability of interacting with cellular membranes, thus giving rise to improved cellular uptake. In particular, some specific derivatives could be considered as promising future excipients for the delivery of "naked" antisense and/or decoy oligonucleotides which are difficult to formulate with existing pharmaceutical excipients.

Prednisolone-appended alpha-cyclodextrin: alleviation of systemic adverse effect of prednisolone after intracolonic administration in 2,4,6-trinitrobenzenesulfonic acid-induced colitis rats

The titled compound is a cyclodextrin derivative in which prednisolone 21-succinate (PDsuc) is covalently bound to one of the secondary hydroxyl groups of alpha-cyclodextrin (alpha-CyD) via an ester linkage. In this study, the PDsuc-appended alpha-CyD ester conjugate (PDsuc/alpha-CyD conjugate) was intracolonically administered to rats with 2,4,6-trinitrobenzensulfonic acid-induced colitis, and its antiinflammatory and systemic adverse effects were compared with those of prednisolone (PD) alone and the PD/2-hydroxypropyl-beta-CyD complex (PD/HP-beta-CyD complex), which is a noncovalent inclusion complex. Colonic damage score, ratio of distal colon wet weight to body weight, and myeloperoxidase activity were evaluated as measures of the therapeutic effect of PD, whereas the ratio of thymus wet weight to body weight was evaluated as a measure of the side effect of PD. The local antiinflammatory activity increased in the order of PD alone approximately PDsuc/alpha-CyD conjugate < PD/HP-beta-CyD complex. As to systemic adverse effect, the PD/HP-beta-CyD complex and PD alone caused thymolysis at doses of 5-10 mg/kg. In contrast, the PDsuc/alpha-CyD conjugate showed no clear systemic adverse effect at the same doses. The low adverse effect of the conjugate may be ascribed to the slow release of PD in the colon, which keeps the local concentration in the colon at a low but constant level. The results suggest that the PDsuc/alpha-CyD conjugate can alleviate the systemic adverse effect of PD while maintaining the therapeutic activity of PD. This kind of knowledge will be useful in the rational design of steroid prodrugs for the colon-specific drug delivery system.