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

Cyclodextrins as Anti-inflammatory Agents: Basis, Drugs and Perspectives

Inflammation is a biological response of the immune system to harmful stimuli. Importantly, inflammation is also a hallmark of several human diseases such as cancer or diabetes. Novel drugs to treat this response are constantly researched, but the formulation is usually forgotten. Cyclodextrins (CDs) are a well-known excipient for complexing and drug delivery. Anti-inflammatory drugs and bioactive compounds with similar activities have been favored from these CD processes. CDs also illustrate anti-inflammatory activity per se. This review tried to describe the capacities of CDs in this field, and is divided into two parts: Firstly, a short description of the inflammation disease (causes, symptoms, treatment) is explained; secondly, the effects of different CDs alone or forming inclusion complexes with drugs or bioactive compounds are discussed.

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.

Selectively functionalized cyclodextrins and their metal complexes

Cyclodextrins (CDs) are cyclic oligomers of alpha-1,4-linked D-glucopyranose. Due to their unique structure, marked by a chiral and hydrophobic cavity, CDs have been extensively used as chiral selectors and drug delivery systems. The functionalization both improve the CD applications and widen their use in many other fields, such as molecular recognition and enzyme mimicking. Moreover, the functionalization highly increases the metal binding properties of the CDs. This critical review is a report of recent applications concerning the CD derivatives and their metal complexes. The metal ion assists the host-guest interaction often increasing the properties of CDs to act as chiral receptors. Furthermore, it can act as a catalytic center in the mimicking of metalloenzymes based on functionalized CDs (164 references).

Alternative drug delivery approaches for the therapy of inflammatory bowel disease

This article shall give an overview on drug delivery systems for new therapeutic strategies in the treatment of inflammatory bowel disease. The various features of the different approaches allowing locally restricted drug delivery to the inflamed colon are discussed including the main physiological and pathophysiological limitations for the different systems. Conventional drug delivery systems are tightly adapted from developments for colonic delivery by oral administration triggered by release mechanisms owing to the physiological environment that these systems encounter in the colonic region. The newer developments in this context aim for an increased selectivity of drug delivery by targeting mechanisms which have a closer relation to pathophysiological particularities of the disease. Therefore, we were focused especially on new strategies for such treatment including liposomal formulations, cyclodextrins, micro- or nanoparticles, viral gene therapy approaches, and others. Effective and selective delivery even of an otherwise nonspecifically acting drug could provide new therapeutic pathways in the treatment of inflammatory bowel disease.

Synthesis and in vitro properties of dexamethasone 21-sulfate sodium as a colon-specific prodrug of dexamethasone

We synthesized dexamethasone 21-sulfate sodium (DS) as a colon-specific prodrug of dexamethasone and investigated its properties. Introduction of a sulfate group to dexamethasone lowered the apparent partition coefficient from 52.5 to 0.27 in 1-octanol/pH 6.8 phosphate buffer at 37 degrees C. DS was stable on incubation with buffer solutions of varied pH or with the upper intestinal contents of rats at 37 degrees C for 24 h. On incubation with the cecal contents, DS was hydrolyzed by producing dexamethasone over 80% of the dose at 10 h. When DS was incubated with the cecal contents collected from trinitrobenzenesulfonic acid (TNBS)-induced colitic rats, the degree of prodrug hydrolysis and production of dexamethasone amounted to 70% of healthy rats. In comparison with prednisolone, hydrocortisone, and cortisone, dexamethasone was stable against bioinactivation by the cecal contents, a desirable property for the development of a colon-specific prodrug. These results demonstrated that DS might be delivered specifically to the colon as an intact form to produce dexamethasone in high yield, suggesting DS as a potential colon-specific prodrug of dexamethasone.

Preparation and Pharmaceutical Evaluation of Liposomes Entrapping Salicylic Acid/.GAMMA.-Cyclodextrin Conjugate

To evaluate the potential use of a drug/cyclodextrin (CyD) conjugate for efficient entrapment in liposomes and prolonged residence of a drug in tissues, we synthesized a salicylic acid (SA) conjugate bound covalently with gamma-cyclodextrin (SA/gamma-CyD conjugate), a model drug/CyD conjugate, and then liposomes entrapping the conjugate (conjugate-in-liposome) were prepared by a freezing-thawing method. The chemical and physicochemical properties of the SA/gamma-CyD conjugate in solution and solid state were investigated and then the physicochemical properties of conjugate-in-liposome, in vitro cellular uptake/release and in vivo disposition of SA/gamma-CyD conjugate after intravenous administration of aqueous suspension containing conjugate-in-liposome in rats, were evaluated, comparing with those of the liposome-entrapped SA alone (SA-in-liposome) or the liposome-entrapped noncovalent SA/gamma-CyD complex (complex-in-liposome). As a result, it was found that the conjugate was amorphous powder and the release of SA from the conjugate in phosphate-buffered saline (PBS) was tolerated to chemical and enzymatic degradation. Meanwhile, the particle sizes and stability of these liposomes were almost identical, and the entrapment ratio of SA/gamma-CyD conjugate in liposomes was higher than those of SA alone and SA/gamma-CyD complex. The cellular uptake of these liposomes was almost equivalent, but the release of SA/gamma-CyD conjugate from RAW264.7 cells was markedly slower, compared with that of SA from cells following cellular uptake of the SA-in-liposome and complex-in-liposome. The disposition of SA or SA/gamma-CyD conjugate following intravenous administration of aqueous suspensions containing each liposome system in rats was comparable, but the residence time of the conjugate in tissues significantly prolonged, compared with that of the SA-in-liposome and complex-in-liposome systems. These results suggest the potential use of SA/gamma-CyD conjugate for efficient entrapment in liposomes as well as of liposomes containing SA/gamma-CyD conjugates for prolonged residence of drugs in tissues.

Novel drug delivery strategies for the treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) encompasses two idiopathic inflammatory diseases of the intestinal tract: Crohn's disease and ulcerative colitis. Existing therapy for IBD consists mainly of orally or rectally administered small drug molecules, such as 5-aminosalicylates and corticosteroids, or potent systemic immune suppressants. IBD presents a challenging target for drug delivery, particularly by the oral route, as, contrary to most therapeutic regimens, minimal systemic absorption and maximal intestinal wall drug levels are desired. Several delivery strategies are employed to achieve this goal, including the chemical modification of the drug molecules, the use of controlled- and delayed-release formulations and the use of bioadhesive particles. The goal of this review is to summarise existing IBD therapy and examine novel approaches in intestinal drug delivery.

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.

New oral delivery systems for treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) is often localized to specific sites in the gastrointestinal tract (GIT). As a result, this disease can be treated with oral site-specific (targeted) drug delivery systems. Targeted delivery systems for treatment of IBD are designed to increase local tissue concentrations of antiinflammatory drugs from lower doses compared with systemic administration. This review addresses the impact disease has or may have on oral targeted delivery for treatment of IBD as well as a number of delivery approaches currently used in marketed products or under investigation. Delivery systems reviewed rely on temporal control, changes in pH along the GIT, the action of local enzymes to trigger drug release, and changes in intraluminal pressure. Dissolution of enteric polymer coatings due to a change in local pH and reduction of azo-bonds to release an active agent are both used in commercially marketed products. Newer approaches showing promise in treating IBD are based on polysaccharides. These materials are most effective when used as compression coatings around core tablets, which contain the active agent. More complex polymeric prodrugs systems are also under investigation. If the dose of the drug is sufficiently low, this approach may also prove useful in improving treatment of IBD.

A potent human C5a receptor antagonist protects against disease pathology in a rat model of inflammatory bowel disease

The complement system is implicated in the pathogenesis of human inflammatory bowel disease, but the specific role of C5a has never been examined. We have compared the efficacy of an orally active human C5a receptor antagonist (AcPhe[Orn-Pro-D-cyclohexylalanine-Trp-Arg]), prednisolone, and infliximab against trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats. The drugs were administered either 2 days before or 24 h after TNBS instillation, and rats were then examined after 8 days. Drug-free colitis control rats showed severe disease pathology with significant mortality (39%). Rats pre or posttreated with the C5a antagonist (10 mg/kg/day peroral, 0.3 mg/kg/day s.c.) had reduced mortality and significantly improved macroscopic scores, colon edema, colon myeloperoxidase levels, reduced concentrations of TNF-alpha levels in the colon and serum, and had greater food intake resulting in greater weight gains than colitis-only rats. Rats pretreated with prednisolone (1 mg/kg/day s.c.) displayed significant improvement in parameters measured, but posttreatment was ineffective. Single dose pretreatment with the TNF-alpha inhibitor infliximab (3 mg/kg i.v.) also had significant improvements in the parameters measured. Rats pretreated with a combination of the C5a antagonist and prednisolone showed no greater improvements than either drug alone. These findings suggest a central role for complement, particularly C5a, in the pathology of TNBS-induced colitis in rats, indicating a possible therapeutic role for C5a antagonists in inflammatory bowel disease.

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.