Improvement of nasal bioavailability of luteinizing hormone-releasing hormone agonist, buserelin, by cyclodextrin derivatives in rats

Factors affecting nasal drug delivery and design strategies for intranasal drug delivery

Intranasal drug delivery system is a non-invasive drug delivery route with the advantages of no first-pass effect, rapid effect and brain targeting. It is a feasible alternative to drug delivery via injection, and a potential drug delivery route for the central nervous system. However, the nasal physiological environment is complex, and the nasal delivery system requires "integration of medicine and device". Its delivery efficiency is affected by many factors such as the features and formulations of drug, delivery devices and nasal cavity physiology. Some strategies have been designed to improve the solubility, stability, membrane permeability and nasal retention time of drugs. These include the use of prodrugs, adding enzyme inhibitors and absorption enhancers to preparations, and new drug carriers, which can eventually improve the efficiency of intranasal drug delivery. This article reviews recent publications and describes the above mentioned aspects and design strategies for nasal intranasal drug delivery systems to provide insights for the development of intranasal drug delivery systems.

The pharmacokinetics of buserelin after intramuscular administration in pigs and cows

BACKGROUND

Buserelin is a luteinizing hormone releasing hormone (LHRH) agonist used for the treatment of hormone-dependent diseases in males and females. However, the pharmacokinetics of buserelin in pigs and cows are not fully understood. This study was designed to develop a sensitive method to determine the concentration of buserelin in blood plasma and to investigate the pharmacokinetic parameters after intramuscular (i.m.) administration in pigs and cows.

RESULTS

A sensitive and rapid stability method based on ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) was developed. The pharmacokinetic parameters of buserelin after i.m. administration were studied in five pigs and five cows at a single dose of 1 mg per pig and 3 mg per cow. The plasma kinetics were analyzed by WinNonlin 8.1.0 software using a non-compartmental model. The mean concentration area under the curve (AUC0-t) was 25.02 ± 6.93 h × ng/mL for pigs and 5.63 ± 1.86 h × ng/mL for cows. The maximum plasma concentration (Cmax) and time to reach the maximum concentration (tmax) were 10.99 ± 2.04 ng/mL and 0.57 ± 0.18 h for pigs and 2.68 ± 0.36 ng/mL and 1.05 ± 0.27 h for cows, respectively. The apparent volume of distribution (Vz) in pigs and cows was 80.49 ± 43.88 L and 839.88 ± 174.77 L, respectively. The elimination half-time (t1/2), and clearance (CL) were 1.29 ± 0.40 h and 41.15 ± 11.18 L/h for pigs and 1.13 ± 0.3 h and 545.04 ± 166.40 L/h for cows, respectively. No adverse effects were observed in any of the animals.

CONCLUSION

This study extends previous studies describing the pharmacokinetics of buserelin following i.m. administration in pigs and cows. Further studies investigating other factors were needed to establish therapeutic protocol in pigs and cows and to extrapolate these parameters to others economic animals.

Preparation and evaluation of fast-dissolving films of etilefrine hydrochloride for practical buccal dosing

Etilefrine hydrochloride (ET) is an important drug in the treatment of hypotension, and parenteral injections and oral tablets are the conventional dosage forms. However, parenteral injections may cause abnormally high plasma levels as well as pain and necrosis, and oral tablets undergo first-pass metabolism. Although fast-dissolving buccal tablets were previously reported, the initial absorption rate was a little slow and the plasma levels were varied extensively. Recently, many films have been developed as novel dosage forms. Therefore, in the present study, film dosage forms containing ET were produced using water-soluble polymers and glycerin (GLY) as excipients to obtain a practical buccal dosage form. Films composed of ET, GLY, and sodium alginate (AL) exhibited good physical characteristics and rapid release in vitro (more than 70% at 2 min). The compacted AL film containing 2 mg ET (1 × 1 cm) exhibited rapid absorption (>19 ng/mL at 0.5 h), maintained an effective plasma level (>7 ng/mL) for a long time period (0.5-4 h), and had an adequate plasma concentration-time profile with a smaller standard error (<15.3 ng/mL). These results suggest that the present compacted buccal film is a superior dosage form of ET for practical use.

Cyclodextrins: structure, physicochemical properties and pharmaceutical applications

Since their discovery over 100 years ago cyclodextrins (CDs) have been the subject of numerous scientific publications. In 2016 alone CDs were the subject of over 2200 research articles published in peer-reviewed journals and mentioned in over 2300 patents and patent applications, many of which were on pharmaceutical applications. Natural CDs and their derivatives are used as enabling pharmaceutical excipients that enhance aqueous solubility of poorly soluble drugs, increase drug permeability through biological membranes and improve drug bioavailability. Unlike conventional penetration enhancers, their hydrophilic structure and high molecular weight prevents them from penetrate into lipophilic membranes leaving biological membranes intact. The natural CDs and some of their derivatives have monographs in pharmacopeias and are also commonly used as food additives and in toiletry products. CDs form inclusion complexes with lipophilic moieties of hydrophobic drugs. Furthermore, CDs are able to form non-inclusion complexes and self-assembled aggregates; small and large complex aggregates with micellar-like structures that can enhance drug solubility. Excipients commonly used in pharmaceutical formulations may have additive or inhibiting effect on the CD solubilization. Here various methods used to investigate CD aggregate formation are reviewed as well as techniques that are used to increase the solubilizing effects of CDs; methods that enhance the apparent intrinsic solubility of drugs and/or the complexation efficacy and decrease the amount of CD needed to develop CD-containing pharmaceutical formulations. It will be explained how too much or too little CD can hamper drug bioavailability, and the role of CDs in solid dosage forms and parenteral formulations, and examples given on how CDs can enhance drug delivery after ocular, nasal and pulmonary administration.

Aqueous stability of leuprolide acetate: effect of temperature, dissolved oxygen, pH and complexation with β-cyclodextrin

In the present research, the aqueous stability of leuprolide acetate (LA) in phosphate buffered saline (PBS) medium was studied (pH = 2.0-7.4). For this purpose, the effect of temperature, dissolved oxygen and pH on the stability of LA during 35 days was investigated. Results showed that the aqueous stability of LA was higher at low temperatures. Degassing of the PBS medium partially increased the stability of LA at 4 °C, while did not change at 37 °C. The degradation of LA was accelerated at lower pH values. In addition, complexes of LA with different portions of β-cyclodextrin (β-CD) were prepared through freeze-drying procedure and characterized by Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) analyses. Studying their aqueous stability at various pH values (2.0-7.4) showed LA/β-CD complexes exhibited higher stability when compared with LA at all pH values. The stability of complexes was also improved by increasing the portion of LA/β-CD up to 1/10.

Chitosan and cyclodextrin in intranasal microemulsion for improved brain buspirone hydrochloride pharmacokinetics in rats

The aim of this study was to develop buspirone hydrochloride microemulsion formulations for intranasal administration to improve the drug bioavailability and provide high drug brain levels. For the purpose, chitosan aspartate, and hydroxypropyl-β-cyclodextrin were incorporated in the microemulsions. The prepared formulations were characterized. Biological investigations including pharmacokinetic studies, brain drug targeting efficiency determinations and histopathological examinations were performed on rats. The results showed that safe and stable mucoadhesive microemulsion suitable for nasal administration were successfully prepared. Ex vivo drug permeation revealed high drug permeation from microemulsions. Absolute bioavailability after intranasal administration of buspirone mucoadhesive microemulsion increased significantly and plasma concentration peaked at 15 min. The AUC0-360(brain) was 3 times that obtained after intravenous administration. A high brain targeting efficiency (86.6%) and a direct nose to brain transport (88%) confirmed the direct nose to brain transport of buspirone following nasal administration of the microemulsions.

Confocal laser scanning microscopy (CLSM) based evidence for cell permeation by mono-4-(N-6-deoxy-6-amino-β-cyclodextrin)-7-nitrobenzofuran (NBD-β-CyD)

Beta-cyclodextrin (β-CyD), amantadine and glucose were fluorescently tagged with 4-chloro-7-nitrobenz-2-oxa-1,3-diazole (NBD chloride) to afford NBD-β-CyD, NBD-amantadine and NBD-glucose, respectively. NBD-β-CyD/amantadine and β-CyD/NBD-amantadine inclusion complexes were prepared. Fluorescence emission maxima (λ(max) 544nm) and relative fluorescence intensities for NBD-β-CyD and NBD-β-CyD/amantadine were virtually identical, precluding the use of emission spectrum shifts for distinguishing free NBD-β-CyD from the complex. Intracellular accumulation of NBD-β-CyD was studied in HepG2 and SK-MEL-24 cells using confocal laser scanning microscopy (CLSM). No major differences were observed between uptake of NBD-β-CyD and NBD-β-CyD/amantadine. Serum proteins did not perturb uptake, whereas temperature-dependent uptake, indicative of cell entry via diffusion, was observed. Intracellular distribution favoured mitochondria, with less fluorescent material present in cytoplasm and none in cell nuclei. No experimental evidence of NBD-β-CyD breakdown to NBD-glucose was found upon chromatographic analysis of incubation mixtures, providing additional evidence of intact NBD-β-CyD entry into these cells. Endocytosis and/or cholesterol-independent membrane modulation are discussed as possible mechanisms for the transmembrane passage of NBD-β-CyD.

Effects of polyamidoamine (PAMAM) dendrimers on the nasal absorption of poorly absorbable drugs in rats

The absorption enhancing effects of polyamidoamine (PAMAM) dendrimers with various concentrations and generations on the nasal absorption of fluorescein isothiocyanate-labeled dextran with an average molecular weight of 4400 (FD4) were initially studied in rats. PAMAM dendrimers with different generations improved the nasal absorption of FD4 and the absorption enhancing effects of PAMAM dendrimers were generation dependent. The rank order of absorption enhancement effects of PAMAM dendrimers was G3>G2>G1>G0. The absorption enhancing effects of PAMAM dendrimers were shown to be concentration dependent for the same generation of PAMAM dendrimers. The nasal membrane toxicity of these PAMAM dendrimers was evaluated by measuring the release of protein and lactate dehydrogenase (LDH) in nasal cavity lavage fluid. PAMAM dendrimers with higher generations and concentrations caused some membrane damage to the nasal tissues, but it was much less than the damage caused by sodium deoxycholate as a positive control. Based on the consideration between the efficacy and safety of PAMAM dendrimers, 1% (w/v) G3 dendrimer with high effectiveness and low toxicity was considered to be a best absorption enhancer for improving the nasal absorption of FD4. 1% (w/v) G3 dendrimer also improved the nasal absorption of macromolecular compounds and drugs including FD10, FD70, insulin and calcitonin. Finally, we measured the zeta potentials of drug solutions with or without PAMAM dendrimers to elucidate their absorption enhancing mechanisms. The zeta potentials of model drug solutions changed to positive by the addition of 1% (w/v) G3 dendrimer. This changing might trigger the absorption enhancing effects of PAMAM dendrimers on the nasal absorption of FDs, insulin and calcitonin, as the first step of mechanisms. In conclusion, 1% (w/v) G3 dendrimer is a promising absorption enhancer for improving the nasal absorption of FDs, insulin and calcitonin without any membrane damage to the nasal tissues.

Intranasal delivery: physicochemical and therapeutic aspects

Interest in intranasal (IN) administration as a non-invasive route for drug delivery continues to grow rapidly. The nasal mucosa offers numerous benefits as a target issue for drug delivery, such as a large surface area for delivery, rapid drug onset, potential for central nervous system delivery, and no first-pass metabolism. A wide variety of therapeutic compounds can be delivered IN, including relatively large molecules such as peptides and proteins, particularly in the presence of permeation enhancers. The current review provides an in-depth discussion of therapeutic aspects of IN delivery including consideration of the intended indication, regimen, and patient population, as well as physicochemical properties of the drug itself. Case examples are provided to illustrate the utility of IN dosing. It is anticipated that the present review will prove useful for formulation scientists considering IN delivery as a delivery route.

A supramolecular complex between proteinases and beta-cyclodextrin that preserves enzymatic activity: physicochemical characterization

BACKGROUND

Cyclodextrins are suitable drug delivery systems because of their ability to subtly modify the physical, chemical, and biological properties of guest molecules through labile interactions by formation of inclusion and/or association complexes. Plant cysteine proteinases from Caricaceae and Bromeliaceae are the subject of therapeutic interest, because of their anti-inflammatory, antitumoral, immunogenic, and wound-healing properties.

METHODS

In this study, we analyzed the association between beta-cyclodextrin (betaCD) and fraction P1G10 containing the bioactive proteinases from Carica candamarcensis, and described the physicochemical nature of the solid-state self-assembled complexes by Fourier transform infrared (FTIR) spectroscopy, thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), and nuclear magnetic resonance (NMR), as well as in solution by circular dichroism (CD), isothermal titration calorimetry (ITC), and amidase activity.

RESULTS AND DISCUSSION

The physicochemical analyses suggest the formation of a complex between P1G10 and betaCD. Higher secondary interactions, namely hydrophobic interactions, hydrogen bonding and van der Waals forces were observed at higher P1G10 : betaCD mass ratios. These results provide evidence of the occurrence of strong solid-state supramolecular non-covalent interactions between P1G10 and betaCD. Microcalorimetric analysis demonstrates that complexation results in a favorable enthalpic contribution, as has already been described during formation of similar betaCD inclusion compounds. The amidase activity of the complex shows that the enzyme activity is not readily available at 24 hours after dissolution of the complex in aqueous buffer; the proteinase becomes biologically active by the second day and remains stable until day 16, when a gradual decrease occurs, with basal activity attained by day 29.

CONCLUSION

The reported results underscore the potential for betaCDs as candidates for complexing cysteine proteinases, resulting in supramolecular arrays with sustained proteolytic activity.

In vitro formulation optimization of intranasal galantamine leading to enhanced bioavailability and reduced emetic response in vivo

The purpose of the current investigation was to optimize an intranasal (IN) galantamine (an acetylcholinesterase inhibitor used for treatment of Alzheimer's disease) formulation using an in vitro tissue model, to correlate those results to in vivo bioavailability, and to compare emetic response to oral dosing. A design-of-experiments (DOE) based formulation screening employing an in vitro tissue model of human nasal epithelium was used to assess drug permeability, tight junction modulation, and cellular toxicity. In vivo studies in rats compared pharmacokinetic (PK) profiles of different formulations dosed intranasally. Finally, studies in ferrets evaluated PK and gastrointestinal (GI) related side effects of oral compared to nasal dosage forms. Galantamine permeation was enhanced without increasing cytotoxicity. Pharmacokinetic testing in rats confirmed the improved drug bioavailability and demonstrated an in vitro-in vivo correlation. Compared to oral dosing, IN galantamine resulted in a dramatically lowered incidence of GI-related side effects, e.g., retching and emesis. These findings illustrate that IN delivery represents an attractive alternative to oral dosing for this important Alzheimer's disease therapeutic. To our knowledge, the data herein represent the first direct confirmation of reducing GI-related side effects for IN galantamine compared to oral dosing.

Therapeutic utility of a novel tight junction modulating peptide for enhancing intranasal drug delivery

Previously, a novel tight junction modulating (TJM) peptide was described affording a transient, reversible lowering of transepithelial electrical resistance (TER) in an in vitro model of nasal epithelial tissue. In the current report, this peptide has been further evaluated for utility as an excipient in transepithelial drug formulations. Chemical stability was optimal at neutral to acidic pH when stored at or below room temperature, conditions relevant to therapeutic formulations. The TJM peptide was tested in the in vitro tissue model for potential to enhance permeation of a low-molecular-weight (LMW) drug, namely the acetylcholinesterase inhibitor galantamine, as well as three peptides, salmon calcitonin, parathyroid hormone 1-34 (PTH(1-34)), and peptide YY 3-36 (PYY(3-36)). In all cases, the TJM peptide afforded a dramatic improvement in drug permeation across epithelial tissue. In addition, a formulation containing PYY(3-36) and TJM peptide was dosed intranasally in rabbits, resulting in a dramatic increase in bioavailability. The TJM peptide was as or more effective in enhancing PYY(3-36) permeation in vivo at a 1000-fold lower molar concentration compared to using LMW enhancers. Based on these in vitro and in vivo data, the novel TJM peptide represents a promising advancement in intranasal formulation development.

Rectal and vaginal administration of insulin-chitosan formulations: an experimental study in rabbits

Insulin is a polypeptide drug and it is degraded by gastrointestinal enzymes, therefore, it cannot be used via oral route readily. There are only parenteral forms available in the market. The aim of this study was to investigate the effect of rectal and vaginal administration of various insulin gel formulations on the blood glucose level as alternative routes in rabbits. Chitosan gel (CH-gel) was used as a carrier; the penetration enhancing effect of sodium taurocholate and dimethyl-beta-cyclodextrin (DM-betaCD) was also investigated. CH-gel provided longer insulin release. The maximum decreasing effect on blood glucose level was observed with insulin-CH-gel containing 5% DM-betaCD. In conclusion, our results indicate that insulin may penetrate well through the rectal and vaginal mucosae from the CH-gel. DM-betaCD was also found to be a useful agent to enhance the penetration of insulin through rectal and vaginal membranes.

Development of a novel high-concentration galantamine formulation suitable for intranasal delivery

The goal of the current study was to develop an intranasal (IN) formulation of the acetylcholinesterase inhibitor galantamine, an important therapeutic for treating Alzheimer's disease. To allow for delivering a therapeutically relevant dose, it was necessary to greatly enhance drug solubility. Various approaches were examined to this end, including adding co-solvents, cyclodextrins, and counterion exchange. Of these, the latter, for example, replacement of bromide ion with lactate or gluconate, resulted in a dramatic drug solubility increase, more than 12-fold. NMR confirmed the molecular structure of new drug salt forms. An in vitro epithelial tissue model was used to assess drug permeability and cellular toxicity. In vitro, galantamine lactate formulations performed as well as or better than their hydrobromide (HBr) counterparts with respect to drug permeation across the epithelial membrane with minimal toxicity. In vivo studies in rats compared pharmacokinetic (PK) profiles of different formulations. The in vivo studies confirmed that IN galantamine achieves systemic blood levels comparable to those of conventional oral administration. Both the in vitro and in vivo data support the feasibility of IN administration of this important drug.

Evidence for LHRH-receptor expression in human airway epithelial (Calu-3) cells and its role in the transport of an LHRH agonist

PURPOSE

To determine whether LHRH-receptor is expressed in Calu-3, a human bronchial epithelial cell line, and to further determine whether this receptor plays a role in the transport of deslorelin, an LHRH agonist.

METHODS

Using cultured monolayers of Calu-3 grown at air-interface, the presence and localization of LHRH-receptors in Calu-3 cells was determined using immunochemical methods. To determine the mechanisms of deslorelin transport, the directionality [apical-basolateral (A-B) and basolateral-apical (B-A)] of deslorelin transport across Calu-3 monolayers and the effects of temperature (37 degrees C and 4 degrees C) and an energy depletor (2,4-dinitrophenol) were investigated. To determine the role of LHRH-receptor in deslorelin transport across Calu-3 monolayers, the influence of an LHRH-receptor antisense oligonucleotide on the LHRH-receptor expression and deslorelin transport was studied. Also, the effect of a competing LHRH agonist, buserelin, on deslorelin transport was determined.

RESULTS

Immunofluorescence studies indicated the predominance of LHRH-receptor in Calu-3 cells at the apical and lateral surfaces. Western blot and RT-PCR studies further confirmed the expression of LHRH-receptor in Calu-3 cells. Deslorelin transport across Calu-3 monolayers was vectorial, with the cumulative A-B transport (1.79 +/- 0.29%) at the end of 240 min being higher than the B-A transport (0.34 +/- 0.11%). Low temperature as well as 2,4-dinitrophenol abolished this directionality. LHRH-receptor antisense oligonucleotide decreased the receptor expression at the mRNA and protein level and reduced the A-B deslorelin transport by 55 +/- 4%, without affecting the B-A transport, suggesting a role for LHRH-receptor in the vectorial transport of deslorelin. In addition, buserelin reduced the A-B deslorelin transport by 56 +/- 5% without affecting the B-A transport.

CONCLUSIONS

Taken together, our results provide evidence that deslorelin is transported across the respiratory epithelium via the LHRH-receptor.

Cyclodextrin-Mediated Drug Release from Liposomes Dispersed Within a Bioadhesive Gel

PURPOSE

The aim of the present study was to design a new mucosal drug delivery system composed of liposomes dispersed within a bioadhesive hydrogel containing methyl-beta-cyclodextrin (Me(beta)CD) for controlled drug release.

METHODS

A hydrophilic model molecule, inulin, was encapsulated within positively charged and PEG-ylated liposomes and its release was measured in the presence of Me(beta)CD after vesicle dispersion within the bioadhesive Carbopol 974P gel. Freeze-fracture electron microscopy (FFEM) was used to follow liposome morphological changes when dispersed within the hydrogel. Liposome-Me(beta)CD interactions were investigated by turbidity monitoring during continuous addition of Me(beta)CD to liposomes and by FFEM.

RESULTS

Inulin diffusion within the gel was influenced by Carbopol 974P concentration since no gel erosion occurred. When dispersed within the gel, positively charged liposomes displayed a higher stability than PEG-ylated vesicles. In the presence of Me(beta)CD, higher amounts of free inulin were released from liposomes, especially in Carbopol-free system. Me(beta)CD appeared to diffuse towards lipid vesicles and permeabilized their bilayer allowing inulin leakage. Indeed, freeze-fracture experiments and liposome turbidity monitoring have shown that Me(beta)CD behaved as a detergent behavior, resulting in lipid vesicle solubilization.

CONCLUSION

is able to mediate, within a bioadhesive hydrogel, the release of a liposome-encapsulated molecule allowing further application of this delivery system for mucosal administration.

Cyclodextrins in drug delivery

Cyclodextrins are a family of cyclic oligosaccharides with a hydrophilic outer surface and a lipophilic central cavity. Cyclodextrin molecules are relatively large with a number of hydrogen donors and acceptors and, thus, in general they do not permeate lipophilic membranes. In the pharmaceutical industry cyclodextrins have mainly been used as complexing agents to increase aqueous solubility of poorly soluble drugs, and to increase their bioavailability and stability. Studies in both humans and animals have shown that cyclodextrins can be used to improve drug delivery from almost any type of drug formulation. However, the addition of cyclodextrins to existing formulations without further optimisation will seldom result in acceptable outcome. Currently there are approximately 30 different pharmaceutical products worldwide containing drug/cyclodextrin complexes on the market.

Cyclodextrins in nasal delivery of low-molecular-weight heparins: in vivo and in vitro studies

PURPOSE

To test the hypothesis that cyclodextrins reversibly enhance nasal absorption of low-molecular-weight heparins (LMWHs) and to investigate the mechanisms by which cyclodextrins enhance LMWH absorption via the nose.

METHODS

Absorption of LMWHs was studied by measuring plasma anti-factor Xa activity after nasal administration of various LMWH formulations to anesthetized rats. In vivo reversibility studies were performed to investigate if the effects of cyclodextrins are reversible and diminish with time. The absorption-enhancing mechanisms of cyclodextrins were investigated in cell culture model. The transport of enoxaparin and mannitol, changes in transepithelial electrical resistance (TEER), and distribution of tight junction protein ZO-1 were investigated.

RESULTS

Formulations containing 5% dimethyl-beta-cyclodextrin (DMbetaCD) produced the highest increase in the bioavailability of LMWH preparations tested. In vivo reversibility studies with 5% DMbetaCD showed that the effect of the absorption enhancer at the site of administration diminished with time. Transport studies using 16HBE14o(-) cells demonstrated that the increase in the permeability of enoxaparin and mannitol, reduction in TEER, and the changes in the tight junction protein ZO-1 distribution produced by 5% DMbetaCD were much greater than those produced by beta-cyclodextrin (betaCD) or hydroxyl-propyl-beta-cyclodextrin (HPbetaCD).

CONCLUSIONS

Of the cyclodextrins tested, DMbetaCD was the most efficacious in enhancing absorption of LMWHs both in vivo and in vitro. The study also suggests that cyclodextrins enhance nasal drug absorption by opening of cell-cell tight junctions.

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.

Polyfection as Nonviral Gene Transfer Method —Design of Novel Nonviral Vector Using α-Cyclodextrin—

Due to the growing concerns over the toxicity and immunogenicity of viral DNA delivery systems, DNA delivery via nonviral routes has become more desirable and advantageous. In particular, polycation complexes with DNA (polyplex) are attractive nonviral vectors. To design novel polycationic vectors, we prepared polyamidoamine starburst dendrimer (dendrimer) conjugates with three cyclodextrins (CDE conjugates) and three generations (G2, G3, and G4) of dendrimers. Of seven CDE conjugates, an alpha-CDE conjugate (G3) with an average degree of substitution (DS) of alpha-CyD of 2.4 [alpha-CDE conjugate (G3, DS 2.4)] showed greater gene transfer activity than dendrimers and other alpha-CDE conjugates with less cytotoxicity. These results suggest the potential use of alpha-CDE conjugate (G3, DS 2.4) as a polycationic vector in vitro and in vivo. Herein, I review a recent polyfection method, with special focus on alpha-CDE conjugate (G3, DS 2.4).

Absorption enhancers for nasal drug delivery

This paper describes the basic concepts for the transmucosal delivery of drugs, and in particular the use of the nasal route for delivery of challenging drugs such as polar low-molecular-weight drugs and peptides and proteins. Strategies for the exploitation of absorption enhancers for the improvement of nasal delivery are discussed, including consideration of mechanisms of action and the correlation between toxic effect and absorption enhancement. Selected enhancer systems, such as cyclodextrins, phospholipids, bioadhesive powder systems and chitosan, are discussed in detail. Examples of the use of these enhancers in preclinical and clinical studies are given. Methods for assessing irritancy and damage to the nasal membrane from the use of absorption enhancers are also described. Finally, the mucosal use of absorption enhancers (chitosan) for the improved nasal delivery of vaccines is reported with reference to recent phase I/II clinical studies.

Association complexes between ovalbumin and cyclodextrins have no effect on the immunological properties of ovalbumin

Delivery systems are designed to deliver necessary amounts of drugs without modifying their biological features. Cyclodextrins (CD) are potential candidates for such a role due to their ability to alter physical and chemical properties of guest molecules by the formation of inclusion/association complexes. They have already been used to stabilize and solubilize peptides and proteins of biological importance. However, no systematic study has been reported on their immunological effects upon coupling to such proteins. Herein, we prepared and characterized the association complexes between alpha-, beta- and hydroxypropyl-beta-cyclodextrin and ovalbumin (Ova). Afterward we tested the effect of CD coupling in the Ova antigenicity and the immunological effects of CD coupling on Ova oral and subcutaneous administration. Our results clearly show that CD-coupled Ova elicits the same immunological activities as uncoupled Ova. Therefore, we conclude that CDs are immunologically safe for use as delivery systems in animals.

Absorption enhancers in pulmonary protein delivery

Extensive research efforts have been directed towards the systemic administration of therapeutic proteins and poorly absorbed macromolecules via various nontraditional, injection-free administration sites such as the lung. As a portal for noninvasive delivery, pulmonary administration possesses several attractive features including a large surface area for drug absorption. Nevertheless, achieving substantial bioavailability of proteins and macromolecules by this route has remained a challenge, chiefly due to poor absorption across the epithelium. The lungs are relatively impermeable to most drugs when formulated without an absorption enhancer/promoter. In an attempt to circumvent this problem, many novel absorption promoters have been tested for enhancing the systemic availability of drugs from the lungs. Various protease inhibitors, surfactants, lipids, polymers and agents from other classes have been tested for their efficacy in improving the systemic availability of protein and macromolecular drugs after pulmonary administration. The purpose of this article is to provide the reader with a summary of recent advances made in the field of pulmonary protein delivery utilizing absorption enhancers. This report reviews the various agents used to increase the bioavailability of these drugs from the lungs, their mechanisms of action and effectiveness, and their potential for toxicity.

The effects of water-soluble cyclodextrins on the histological integrity of the rat nasal mucosa

The aim of this study was to investigate the effect of highly water-soluble cyclodextrins (CDs) on the histological integrity of the nasal mucosa. In order to evaluate their effects, the in vivo single and repeated nasal exposure studies were performed using male Wistar rats. The rat nasal cavity was excised after an application of various CD solutions at different times. The morphological appearances of the rat nasal mucosae were analyzed with the light microscopic and the scanning electron microscopic studies. By utilizing 5-min exposure of each CD solution to the nasal mucosa, no tissue damage was visible for 1.5% w/v beta-CD and 5 and 20% w/v hydroxypropyl beta-CD (HP beta-CD), and the effects were quite similar to controls. However, using 20% w/v randomly methylated beta-CD (RM beta-CD) showed severe damage on the integrity of nasal mucosa. The severity was similar to 1% w/v polyoxyethylene-9-lauryl ether or l% w/v sodium deoxycholate. Meanwhile, 30 or 60 min exposure to 10% w/v HP beta-CD or RM beta-CD resulted in no obvious mucosal damage. In addition, in vivo repeated dosing of RM beta-CD did not show any toxicity up to 20% w/v. These results suggest that at least, less than 10% w/v CD solutions do not induce gross tissue damage and can keep the histological integrity of the nasal mucosa.

Interaction of [D-Trp6, Des-Gly10] LHRH ethylamide and hydroxy propyl beta-cyclodextrin (HPbetaCD): thermodynamics of interaction and protection from degradation by alpha-chymotrypsin

PURPOSE

The purpose of this study is to investigate the mechanisms and thermodynamics of the interaction between hydroxypropyl beta-cyclodextrin (HPdetaCD) and [D-Trp6, des-Gly10] LHRH ethylamide (deslorelin), a peptide drug.

METHODS

We used UV and fluorescence spectroscopy to study the interaction of HPbetaCD and deslorelin. Circular dichroism was used to study the conformational changes induced in deslorelin upon interaction with HP beta CD. The thermodynamics of the interaction of deslorelin and HPbetaCD was studied using isothermal titration calorimetry (ITC). We also determined the effect of HPbetaCD on the degradation of deslorelin by alpha-chymotrypsin.

RESULTS

UV and fluorescence spectroscopy indicated that HPbetaD induced a change in polarity of the environment surrounding the chromophores of deslorelin. Wavelength selective fluorescence indicated an increase in the fluorescence polarization of deslorelin with an increase in excitation wavelength in the presence of HPbetaCD suggesting that tryptophan is present in a media of reduced mobility. Circular dichroism studies indicated that HPbetaCD stabilizes the conformation of deslorelin. In addition, ITC indicated an exothermic reaction between deslorelin and HPbetaCD with a low enthalpy of binding of approximately -600 cal/mol and a binding affinity of approximately -1.25 x 10(2) M-1. Finally, the rate of degradation of deslorelin by alpha-chymotrypsin was decreased by 33% in the presence of HPbetaCD.

CONCLUSIONS

These results indicate that there is an interaction between HPbetaCD and deslorelin, which involves the inclusion of aromatic amino acids of deslorelin into the hydrophobic cavity of the cyclodextrin. This inclusion, providing steric hindrance, may be one of the mechanisms by which HPbetaCD reduces enzymatic hydrolysis of deslorelin.

Non-invasive treatments of luteinizing hormone-releasing hormone for inducing spermiation in American (Bufo americanus) and Gulf Coast (Bufo valliceps) toads

As many as 20% of all assessed amphibian species are threatened with extinction, and captive breeding programs are becoming important components of conservation strategies for this taxon. For some species, exogenous hormone administration has been integrated into breeding protocols to improve propagation. However, most treatments are administered by an intraperitoneal injection that can be associated with some risks. The general goal of this study was to identify a non-invasive method of applying luteinizing hormone-releasing hormone (LHRH), which reliably induces sperm release in toads. Specific objectives were to 1) test the spermiation response after topical application of different LHRH doses to the abdominal seat region, 2) evaluate the effects of adding the absorption enhancers dimethyl sulfoxide (DMSO), acetone, and glyceryl monocaprylate (GMC) to the LHRH, 3) assess the spermiation response after oral delivery of LHRH in a mealworm vehicle, and 4) compare sperm characteristics and spermiation responses to treatments in two different toad species. Male American (n = 9) and Gulf Coast (n = 7) toads were rotated systematically through a series of treatments. Urine was collected and evaluated for the presence of sperm at 0, 3, 7, 12, and 24 hours post-treatment. There were no statistical differences in spermiation induction or sperm characteristics between American and Gulf Coast toads after the treatments. Oral administration of 100 &mgr;g LHRH was occasionally successful in inducing spermiation, but results appeared largely unreliable. Ventral dermal application of 100 or 10 &mgr;g LHRH in 40% DMSO were more effective (P < 0.05) at inducing spermiation compared with the other treatments tested, eliciting sperm release in more than 70% of toads tested. In breeding programs for rare and/or fragile anurans, these non-invasive methods of exogenous hormone administration might be preferred over intraperitoneal injections. Zoo Biol 20:63-74, 2001. Copyright 2001 Wiley-Liss, Inc.

Improvement of subcutaneous bioavailability of insulin by sulphobutyl ether beta-cyclodextrin in rats

The objective of this study was to examine and compare how hydrophilic beta-cyclodextrin derivatives (beta-CyDs) improve the bioavailability of insulin following subcutaneous injection of insulin solution in rats. When insulin solutions in the absence of beta-CyDs were injected into the dorsal subcutaneous tissues of rats, the absolute bioavailability of insulin calculated from plasma immunoreactive insulin (IRI) levels was approximately 50%. When maltosyl-beta-cyclodextrin was added to the solutions, there was no change in the plasma IRI levels and hypoglycaemia compared with those of the insulin-alone solution. Dimethyl-beta-cyclodextrin decreased the bioavailability of insulin, although it increased the maximal concentration of IRI in plasma and the capillary permeability of the fluorescein isothiocyanatedextran 40, a non-degraded permeation marker. When insulin solutions containing sulphobutyl ether-beta-cyclodextrin with a degree of substitution of the sulphobutyl group of 3.9 (SBE4-beta-CyD) were injected, the IRI level rapidly increased and maintained higher IRI levels for at least 8 h. The bioavailability of the insulin/SBE4-beta-CyD system was about twice that of insulin alone and approached 96%. The enhancing effects of SBE4-beta-CyD may be in part due to the inhibitory effects of SBE4-beta-CyDs on the enzymatic degradation and/or the adsorption of insulin onto the subcutaneous tissue at the injection site, although this does not apparently facilitate capillary permeability. These results suggest that SBE4-beta-CyD in aqueous insulin injection for subcutaneous administration is useful for improving the bioavailability and the hence the pharmacological effects of insulin.

Beta-cyclodextrin(beta-CD) influence on the biotoxicities of substituted benzene compounds and pesticide intermediates

The acute toxicities of 19 substituted benzene compounds and intermediates of pesticides to Photobacterium phosphoreum in beta-CD aqueous solution (5 g/L) were studied and compared with those in water through luminescent bacteria toxicity test, and 15min-EC50 values were obtained. The presence of beta-CD significantly reduce biotoxicities of the low-polarity compounds, while for the higher-polarity compounds, such effect was slight. The differences of biotoxicities were correlated with Log10Kow (octanol/water partition coefficients). A significant linear relationship was obtained with some abnormal data picked out. Some explanations concerning molecular structure of chemicals as well as beta-CD were given for the relationship.

Efficacy, safety and mechanism of cyclodextrins as absorption enhancers in nasal delivery of peptide and protein drugs

Cyclodextrins are used in nasal drug delivery as absorption enhancing compounds to increase the intranasal bioavailability of peptide and protein drugs. The most effective cyclodextrins in animal experiments are the methylated derivatives, dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin, which are active at low concentrations ranging between 2% and 5%. However, large species differences between rats, rabbits and humans exist for the nasal absorption enhancement by cyclodextrins. Based on toxicological studies of the local effects of cyclodextrins on the nasal mucosa dimethyl-beta-cyclodextrin and randomly methylated beta-cyclodextrin are considered safe nasal absorption enhancers. Their effects were quite similar to controls (physiological saline), but smaller than those of the preservative benzalkonium chloride in histological and ciliary beat frequency studies. In these studies, and in a study of the release of marker compounds after nasal administration, methylated beta-cyclodextrins were less toxic than sodium glycocholate, sodium taurodihydrofusidate, laureth-9 and L-alpha-phosphatidylcholine. Systemic toxicity after nasal cyclodextrin administration is not expected, because very low doses of cyclodextrins are administered and only very small amounts are absorbed. The mechanism of action of cyclodextrins may be explained by their interaction with the nasal epithelial membranes and their ability to transiently open tight junctions.

Modification of the apparent lipophilicity of steroidal drugs with gamma-cyclodextrin

The interaction between 17 steroidal drugs and gamma-cyclo-dextrin (gamma-CD) was determined by charge-transfer chromatography and the relative strength of interaction was calculated. The relationship between the strength of interaction and the physico-chemical parameters of steroidal drugs was elucidated with principal component analysis. Gamma-CD interacted with each steroidal drug decreasing the apparent hydrophobicity of the guest molecules. Calculations indicated that the interaction between the drugs and gamma-CD is of mixed character: steric, hydrophobic and electronic forces are involved in the complex formation. The marked influence of gamma-CD on the apparent hydrophobicity of drugs suggests that this interaction may modify the biological properties (absorption, uptake, half-life etc.) of drug-gamma-CD complexes resulting in modified efficacy.

Nasal mucociliary clearance as a factor in nasal drug delivery

The nasal mucociliary clearance system transports the mucus layer that covers the nasal epithelium towards the nasopharynx by ciliary beating. Its function is to protect the respiratory system from damage by inhaled substances. Impairment of nasal mucociliary clearance can result in diseases of the upper airways. Therefore, it is important to study the effects of drugs and drug excipients on nasal mucociliary clearance. A large number of methods are used to assess mucociliary clearance. These methods study the effects of drug and excipients on the mucociliary system in vitro or in vivo in animals and humans. In some cases, the results of different in vitro and in vivo measurements do not correlate well. In vitro methods, especially ciliary beat frequency measurements, have been demonstrated to be valuable tools for toxicity screening. However, in vivo studies are essential to confirm the safety of nasal drug formulations. Nasal mucociliary clearance also has implications for nasal drug absorption. Drugs are cleared rapidly from the nasal cavity after intranasal administration, resulting in fast systemic drug absorption. Several approaches are discussed to increase the residence time of drug formulations in the nasal cavity, resulting in improved nasal drug absorption. However, more experimental evidence is needed to support the conclusion that this improved absorption is caused by a longer residence time of the nasal drug formulation.

Protection afforded by maltosyl-beta-cyclodextrin against alpha-chymotrypsin-catalyzed hydrolysis of a luteinizing hormone-releasing hormone agonist, buserelin acetate

PURPOSE

The present study addresses how maltosyl-beta-cyclodextrin (G2-beta-CyD) impacts upon the alpha-chymotrypsin-catalyzed hydrolysis of buserelin acetate, an agonist of luteinizing hormone-releasing hormone with emphasis upon the direct effect of G2-beta-CyD on the activity of the protease.

METHODS

Kinetic and solubility studies were performed in isotonic phosphate buffer (pH 7.4) at 25 degrees C and 37 degrees C. The interaction of alpha-chymotrypsin with G2-beta-CyD in the buffer solution was examined by differential scanning calorimetry.

RESULTS

G2-beta-CyD decelerated the alpha-chymotrypsin-catalyzed hydrolysis of buserelin acetate to give the 1-3 tripeptide and the 4-9 hexapeptide fragments. This deceleration can be explained solely by a non-productive encounter between a complex of the substrate with G2-beta-CyD and the protease at relatively low CyD concentrations, while the direct inhibitory effect of G2-beta-CyD on the proteolytic activity made a considerable contribution to the overall deceleration of the hydrolysis at higher CyD concentrations. Calorimetric studies indicate the presence of intermediate states in the thermal unfolding of alpha-chymotrypsin, simultaneously accompanied by the autolysis. By contrast, a two-state thermal unfolding of alpha-chymotrypsin was observed in the presence of G2-beta-CyD, suggesting reduced proteolytic activity upon binding to G2-beta-CyD.

CONCLUSIONS

These results suggest that G2-beta-CyD at higher concentrations inhibits the proteolytic action of alpha-chymotrypsin through direct interaction with the protease, as well as through the formation of a non-productive complex with the substrate.

Confocal laser scanning microscopic visualization of the transport of dextrans after nasal administration to rats: effects of absorption enhancers

PURPOSE

To visualize the transport pathway(s) of high molecular weight model compounds across rat nasal epithelium in vivo using confocal laser scanning microscopy. Furthermore, the influence of nasal absorption enhancers (randomly methylated beta-cyclodextrin and sodium taurodihydrofusidate) on this transport was studied.

METHODS

Fluorescein isothiocyanate (FITC)-labelled dextrans with a molecular weight of 3,000 or 10,000 Da were administered intranasally to rats. Fifteen minutes after administration the tissue was fixed with Bouin. The nasal septum was surgically removed and stained with Evans Blue protein stain or DiIC18(5) lipid stain prior to visualization with the confocal laser scanning microscope.

RESULTS

Transport of FITC-dextran 3,000 across nasal epithelium occurred via the paracellular pathway. Endocytosis of FITC-dextran 3,000 was also shown. In the presence of randomly methylated beta-cyclodextrin 2% (w/v) similar transport pathways for FITC-dextran 3,000 were observed. With sodium taurodihydrofusidate 1% (w/v) the transport route was also paracellular with endocytosis, but cells were swollen and mucus was extruded into the nasal cavity. For FITC-dextran 10,000 hardly any transport was observed without enhancer, or after co-administration with randomly methylated beta-cyclodextrin 2% (w/v). Co-administration with sodium taurodihydrofusidate 1% (w/v) resulted in paracellular transport of FITC-dextran 10,000, but morphological changes, i.e. swelling of cells and mucus extrusion, were observed.

CONCLUSIONS

Confocal laser scanning microscopy is a suitable approach to visualize the transport pathways of high molecular weight hydrophilic compounds across nasal epithelium, and to study the effects of absorption enhancers on drug transport and cell morphology.

Charge-transfer chromatographic study of the complex formation of some steroidal drugs with carboxymethyl-gamma-cyclodextrin

The interaction between 15 steroidal drugs and carboxymethyl-gamma-cyclodextrin (CM-gamma-CD) was studied by reversed-phase charge-transfer thin-layer chromatography and the relative strength of interaction was calculated. CM-gamma-CD formed inclusion complexes with each compound, the complex always being less hydrophobic than the uncomplexed drug. The inclusion-forming capacity of drugs differed considerably depending on their chemical structures. The linear correlation between the hydrophobicity and specific hydrophobic surface area of anticancer drugs indicated that they can be considered as a homologous series of compounds, although their chemical structures are different. Hydrophobicity of drugs significantly influenced the strength of interaction, indicating the involvement of hydrophobic forces in the binding of drugs to CM-gamma-CD. The marked influence of CM-gamma-CD on the hydrophobicity of drugs suggests that this interaction may modify the biological properties (adsorption, uptake, half-life, etc.) of drug-CM-gamma-CD complexes drug, resulting in modified efficacy.

Pharmaceutical applications of cyclodextrins. III. Toxicological issues and safety evaluation

The objective of this review is to summarize recent findings on the safety profiles of three natural cyclodextrins (alpha-, beta- and gamma-CDs) and several chemically modified CDs. To demonstrate the potential of CDs in pharmaceutical formulations, their stability against non-enzymatic and enzymatic degradations in various body fluids and tissue homogenates and their pharmacokinetics via parenteral, oral, transmucosal, and dermal routes of administration are outlined. Furthermore, the bioadaptabilities of CDs, including in vitro cellular interactions and in vivo safety profiles, via a variety of administration routes are addressed. Finally, the therapeutic potentials of CDs are discussed on the basis of their ability to interact with various endogenous and exogenous lipophiles or, especially for sulfated CDs, their effects on cellular processes mediated by heparin binding growth factors.

Pharmaceutical applications of cyclodextrins. 2. In vivo drug delivery

The objective of this Review is to summarize and critique recent findings and applications of both unmodified and modified cyclodextrins for in vivo drug delivery. This review focuses on the use of cyclodextrins for parenteral, oral, ophthalmic, and nasal drug delivery. Other routes including dermal, rectal, and pulmonary delivery are also briefly addressed. This Review primarily focuses on newer findings concerning cyclodextrin derivatives which are likely to receive regulatory acceptance due to improved aqueous solubility and safety profiles as compared to the unmodified cyclodextrins. Many of the applications reviewed involve the use of hydroxypropyl-beta-cyclodextrins (HP-beta-CDs) and sulfobutylether-beta-cyclodextrins (SBE-beta-CDs) which show promise of greater safety while maintaining the ability to form inclusion complexes. The advantages and limitations of HP-beta-CD, SBE-beta-CD, and other cyclodextrins are addressed.