Cyclodextrin Inclusion Complexes Loaded in Particles as Drug Carrier Systems

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Binary and ternary inclusion complexes of dapsone in cyclodextrins and polymers: preparation, characterization and evaluation

Dapsone (DAP) is a synthetic sulfone drug with bacteriostatic activity, mainly against Mycobacterium leprae. In this study we have investigated the interactions of DAP with cyclodextrins, 2-hydroxypropyl-beta-cyclodextrin (HP beta CD) and beta-cyclodextrin (beta CD), in the presence and absence of water-soluble polymers, in order to improve its solubility and bioavailability. Solid systems DAP/HP beta CD and DAP/beta CD, in the presence or absence of polyvinylpyrrolidone (PVP K30) or hydroxypropyl methylcellulose (HPMC), were prepared. The binary and ternary systems were evaluated and characterized by SEM, DSC, XRD and NMR analysis as well as phase solubility assays, in order to investigate the interactions between DAP and the excipients in aqueous solution. This study revealed that inclusion complexes of DAP and cyclodextrins (HP beta CD and beta CD) can be produced in order to improve DAP solubility and bioavailability in the presence or absence of polymers (PVP K30 and HPMC). The more stable inclusion complex was obtained with HP beta CD, and consequently HP beta CD was more efficient in improving DAP solubility than beta CD, and the addition of polymers had no influence on DAP solubility or on the stability of the DAP/CDs complexes.

Pluronic F127-modified liposome-containing tacrolimus-cyclodextrin inclusion complexes:improved solubility, cellular uptake and intestinal penetration

Objective The aim of this study was to investigate Pluronic F127-modified liposome-containing cyclodextrin (CD) inclusion complex (FLIC) for improving the solubility, cellular uptake and intestinal penetration of tacrolimus (FK 506) in the gastrointestinal (GI) tract. Methods Molecular modelling was performed to screen the optimal CD for the solubilization of FK 506. FLIC was prepared by thin-lipid film hydration with the inclusion complex solutions followed by membrane extrusion. Dilution tests were conducted in simulated gastric fluids and phosphate-buffered solution of sodium taurocholate to investigate the solubility improvement of FK506. The cellular uptake of nanocarriers was studied in Caco-2 cells, and intestinal mucous membrane penetration in the GI tract was evaluated in Sprague-Dawley rats. Key findings The results showed that β-CD had the strongest binding energy with the guest molecule among the CDs. The prepared FLIC has an average diameter of 180.8 ± 8.1 nm with a spherical shape. The solubility and cellular uptake of FK 506 was greatly improved by the incorporation of CD complexes in the Pluronic F127-modified liposomes. Intestinal mucous membrane penetration was also significantly improved by the preparation of FLIC. Conclusion With improved drug solubility and intestinal mucous membrane penetration, FLIC shows a promising oral delivery system for FK 506. © 2013 Royal Pharmaceutical Society.

Repellent effects of Melaleuca alternifolia (tea tree) oil against cattle tick larvae (Rhipicephalus australis) when formulated as emulsions and in β-cyclodextrin inclusion complexes

Rhipicephalus australis (formerly Boophilus microplus) is a one host tick responsible for major economic loss in tropical and subtropical cattle production enterprises. Control is largely dependent on the application of acaricides but resistance has developed to most currently registered chemical groups. Repellent compounds that prevent initial attachment of tick larvae offer a potential alternative to control with chemical toxicants. The repellent effects of Melaleuca alternifolia oil (TTO) emulsions and two β-cyclodextrin complex formulations, a slow release form (SR) and a modified faster release form (FR), were examined in a series of laboratory studies. Emulsions containing 4% and 5% TTO applied to cattle hair in laboratory studies completely repelled ascending tick larvae for 24 h whereas 2% and 3% formulations provided 80% protection. At 48 h, 5% TTO provided 78% repellency but lower concentrations repelled less than 60% of larvae. In a study conducted over 15 days, 3% TTO emulsion applied to cattle hair provided close to 100% repellency for 2 days, but then protection fell to 23% by day 15. The FR formulation gave significantly greater repellency than the emulsion and the SR formulation from day 3 until the end of the study (P < 0.05), providing almost complete repellency at day 3 (99.5%), then decreasing over the period of the study to 49% repellency at day 15. Proof of concept is established for the use of appropriately designed controlled-release formulations to extend the period of repellency provided by TTO against R. australis larvae.

Non-inclusion complexes between riboflavin and cyclodextrins

Objectives To investigate the molecular interaction between beta-cyclodextrin (beta CD) or hydroxypropyl-beta-cyclodextrin (HP beta CD) and riboflavin (RF), and to test the anticancer potential of these formulations. Methods The physicochemical characterization of the association between RF and CDs was performed by UV-vis absorption, fluorescence, differential scanning calorimetry and NMR techniques. Molecular dynamics simulation was used to shed light on the mechanism of interaction of RF and CDs. Additionally, in-vitro cell culture tests were performed to evaluate the cytotoxicity of the RFCD complexes against prostate cancer cells. Key findings Neither beta CD nor HP beta CD led to substantial changes in the physicochemical properties of RF (with the exception of solubility). Additionally, rotating frame Overhauser effect spectroscopy experiments detected no spatial correlations between hydrogens from the internal cavity of CDs and RF, while molecular dynamics simulations revealed out-of-ring RFCD interactions. Notwithstanding, both RF beta CD and RFHP beta CD complexes were cytotoxic to PC3 prostate cancer cells. Conclusions The interaction between RF and either beta CD or HP beta CD, at low concentrations, seems to be made through hydrogen bonding between the flavonoid and the external rim of both CDs. Regardless of the mechanism of complexation, our findings indicate that RFCD complexes significantly increase RF solubility and potentiate its antitumour effect.

Characterization, inclusion mode, phase-solubility and in vitro release studies of inclusion binary complexes with cyclodextrins and meglumine using sulfamerazine as model drug

In order to investigate the effect on the aqueous solubility and release rate of sulfamerazine (SMR) as model drug, inclusion complexes with beta-cyclodextrin (beta CD), methyl-beta-cyclodextrin (M beta CD) and hydroxypropyl-beta-cyclodextrin (HP beta CD) and a binary system with meglumine (MEG) were developed. The formation of 1: 1 inclusion complexes of SMR with the CDs and a SMR: MEG binary system in solution and in solid state was revealed by phase solubility studies (PSS), nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR), thermal analysis and X-Ray diffractometry (XRD) studies. The CDs solubilization of SMR could be improved by ionization of the drug molecule through pH adjustments. The higher apparent stability constants of SMR:CDs complexes were obtained in pH 2.00, demonstrating that CDs present more affinity for the unionized drug. The best approach for SMR solubility enhancement results from the combination of MEG and pH adjustment, with a 34-fold increment and a S-max of 54.8 mg/ml. The permeability of the drug was reduced due to the presence of beta CD, M beta CD, HP beta CD and MEG when used as solubilizers. The study then suggests interesting applications of CD or MEG complexes for modulating the release rate of SMR through semipermeable membranes.

Controlled release of ethylene gas from the ethylene-α-cyclodextrin inclusion complex powder with deliquescent salts

Deliquescent calcium chloride (CaCl2) and magnesium chloride (MgCl2) were investigated for their practical application to release ethylene gas from an ethylene-α-cyclodextrin inclusion complexes (CD IC) powder at relative humidities (RHs) between 11.2 and 93.6 % at 18 °C. The IC powder and deliquescent salts were mixed at a ratio of 1:5, respectively. CaCl2 and MgCl2 started to deliquesce at 32.7 % RH. The IC powder dissolved in the concentrated salt solutions to release ethylene gas. Increasing the RH accelerated the release rate. Maximum release of ethylene gas was achieved after 24 h at 75.5 and 93.6 % RH for both IC powder-deliquescent salts mixture. The deliquescent salts proved to be a simple option for releasing ethylene gas from the IC powder.

Detailed investigation of a gamma-cyclodextrin inclusion complex with L-thyroxine for improved pharmaceutical formulations

Thyroxine is a naturally occurring human hormone produced by the thyroid gland. Clinical applications of thyroxine to treat several chronic disorders are limited by poor water solubility and instability under physiological conditions. An inclusion complex of levo-thyroxine (l-thyroxine), the active form of the hormone with gamma cyclodextrin (gamma-CD) has been obtained and studied with the aim of improving oral delivery rather than the injection formulation of the sodium salt. In addition to greater patient acceptability, inclusion complexes often improve aqueous solubility and bioavailability, stability, and reduce toxicity of drugs, thus providing enhanced pharmaceutical formulations. Physicochemical characterization of the inclusion complex was carried out using Fourier transform infrared spectroscopy, X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy and proton nuclear magnetic resonance spectroscopy. Intermolecular dipolar interactions for the inclusion complex were also studied using 2 dimensional ROESY experiments. Formation of the inclusion complex between the protons H3 and H5 of cyclodextrin with aromatic protons of thyroxine was confirmed by their dipolar interaction. Molecular modelling was used to understand the basis for the complex formation and predict the formation of other complexes. Interestingly, we found that l-thyroxine forms an inclusion complex only with the larger gamma-CD and not with other available alpha and beta forms.

Photoinduced DNA Cleavage by alpha-, beta-, and gamma-Cyclodextrin-Bicapped C-60 Supramolecular Complexes

Water-soluble supramolecular inclusion complexes of alpha-, beta-, and gamma-cyclodextrin-bicapped C-60 (CD/C-60) have been investigated for their photoinduced DNA cleavage activities, with the aim to assess the potential health risks of this class of compounds and to understand the effect of host cyclodextrins having different cavity dimensions. Factors such as incubation temperature, irradiation time, and concentration of NADH or CDs/C-60 supramolecular inclusion complexes have been examined. The results show that alpha-, beta-, and gamma-CDs/C-60 are all able to cleave double-stranded DNA under visible light irradiation in the presence of NADH. However, a difference in the photoinduced DNA cleavage efficiency is observed, where the cleavage efficiency increases in the order of alpha-, beta-, and gamma-CD/C-60. The difference is attributed to the different aggregation behavior of the inclusion complexes in aqueous solution, which is correlated to the cavity dimension of the host cyclodextrin molecules.

Study of alpha-, beta- and gamma-cyclodextrin/C-60 supramolecular complexes: Influence of the cavity dimension toward the host-guest complexes

Herein we report the spectroscopic, electrochemical, TEM and DLS characterizations Of C-60 supramolecular inclusion complexes with alpha-, beta- and gamma-cyclodextrins prepared using anionic C-60. The results indicate that the cyclodextrin itself has little effect on the encapsulated C-60 or on the properties of the inclusion complex. Instead, the cyclodextrin has a significant influence on the aggregation behavior of individual complex in aqueous solution, which in turn affects the property of the supramolecular complex of cyclodextrin and C-60 greatly, As the cavity dimension of cyclodextrin becomes smaller as it changes from gamma-CD to beta-CD, and finally to alpha-CD, it is observed that more aggregation occurs for the corresponding inclusion complex in aqueous solution.

Characterization of non-covalent complexes of rutin with cyclodextrins by electrospray ionization tandem mass spectrometry

Electrospray ionization tandem mass spectrometry (ESI-MSn) and the phase solubility method were used to characterize the gas-phase and solution-phase non-covalent complexes between rutin (R) and alpha-, beta- and gamma-cyclodextrins (CDs). The direct correlation between mass spectrometric results and solution-phase behavior is thus revealed. The order of the 1:1 association constants (K-c) of the complexes between R and the three CDs in solution calculated from solubility diagrams is in good agreement with the order of their relative peak intensities and relative collision-induced dissociation (CID) energies of the complexes under the same ESI-MSn condition in both the positive and negative ion modes. Not only the binding stoichiometry but also the relative stabilities and even binding sites of the CD-R complexes can be elucidated by ESI-MSn. The diagnostic fragmentation of CD-R complexes, with a significant contribution of covalent fragmentation of rutin leaving the quercetin (Q) moiety attached to the CDs, provides convincing evidence for the formation of inclusion complexes between R and CDs. The diagnostic fragment ions can be partly confirmed by the complexes between Q and CDs. The gas-phase stability order of the deprotonated CD-R complexes is beta-CD-R > alpha-CD-R > gamma-CD/R; beta-CD seems to bind R more strongly than the other CDs.

Studies on the non-covalent complexes between oleanolic acid and cyclodextrins using electrospray ionization tandem mass spectrometry

Non-covalent inclusion complexes formed between an anti-inflammatory drug, oleanolic acid (OA), and alpha-, beta- and gamma-cyclodextrins (CDs) were investigated by means of solubility studies and electrospray ionization tandem mass spectrometry (ESI-MSn). The order of calculated association constants (K-1:1) of complexes between OA and different CDs in solution is in good agreement with the order of their relative peak intensities and the relative CID energies of the complexes under the same ESI-MSn conditions. These results indicate a direct correlation between the behaviors of solution- and gas-phase complexes. ESI-MS can thus be used to evaluate solution-phase non-covalent complexes successfully. The experimental results show that the most stable 1:1 inclusion complexes between three CDs and OA can be formed, but 2:1 CD-OA complexes can be formed with beta- and gamma-CDs. Multi-component complexes of alpha-CD-OA-beta-CD (1:1:1), alpha-CD-OA-gamma-CD (1:1:1) and beta-CD-OA-gamma-CD (1:1:1) were found in equimolar CD mixtures with excess OA. The formation of 2:1 and multi-component 1:1:1 non-covalent CD-OA complexes indicates that beta- and gamma-CD are able to form sandwich-type inclusion non-covalent complexes with OA. The above results can be partly supported by the relative sizes of OA and CD cavities by molecular modeling calculations.

Electrospray ionization mass spectrometry of cyclodextrin complexes with amino acids in incubated solutions and in eluates of gel permeation chromatography

1:1 complexes of beta-cyclodextrin (CD) with three amino acids (Gly, Phe and Trp) have been detected as ions in the gas phase using infusion positive and negative ion electrospray ionization mass spectrometry (ESI-MS). In contrast with the positive ion ESI mass spectra of simple aqueous solutions, the aggregates and adducts usually formed in the ESI process did not appear in the positive ion ESI spectra of solutions buffered with ammonium acetate (NH4Ac), even at higher analyte concentrations, These studies suggest that addition of buffer and/or use of a low analyte concentration should be used to overcome formation of aggregates and metal ion adducts in such mass spectrometry studies. Also, the deprotonated complexes are dissociated by collision induced dissociation (CID) to form an abundant product ion, the deprotonated CD, requiring transfer of a proton to the amino acid carboxyl group, To understand formation of complexes in the gas phase, gel permeation chromatography (GPC) was used to separate free amino acids (AAs) from complexes in an incubated solution. The ESI mass spectra of the GPC fractions show the presence of 1:1 complexes of both CD-aromatic amino acids and CD-aliphatic amino acids. Compared with CD-aliphatic amino acid complexes, CD-aromatic amino acid complexes appear to be destabilized in the gas phase, possibly because the hydrophobic interaction which binds the aromatic group of amino acids in the CD cavity in solution may become repulsive when solvent evaporates from the droplets during the electrospray process, whereas those complex ions formed as proton bound dimers are stabilized by electrostatic forces, the major binding force for such complexes in the gas phase. In addition, the GPC technique coupled with off-line ESI-MS can rapidly separate CD complexes by size, and provides some information on the character of the complexes in solution. (C) 1998 John Wiley & Sons, Ltd.

Electrospinning and characterization of self-assembled inclusion complexies

L’électrofilage est une technique permettant de fabriquer des fibres polymériques dont le diamètre varie entre quelques nanomètres et quelques microns. Ces fibres ont donc un rapport surface/volume très élevé. Les fibres électrofilées pourraient trouver des applications dans le relargage de médicaments et le génie tissulaire, comme membranes et capteurs chimiques, ou dans les nanocomposites et dispositifs électroniques. L’électrofilage était initialement utilisé pour préparer des toiles de fibres désordonnées, mais il est maintenant possible d’aligner les fibres par l’usage de collecteurs spéciaux. Cependant, il est important de contrôler non seulement l’alignement macroscopique des fibres mais aussi leur orientation au niveau moléculaire puisque l’orientation influence les propriétés mécaniques, optiques et électriques des polymères. Les complexes moléculaires apparaissent comme une cible de choix pour produire des nanofibres fortement orientées. Dans les complexes d’inclusion d’urée, les chaînes polymères sont empilées dans des canaux unidimensionnels construits à partir d’un réseau tridimensionnel de molécules d’urée liées par des ponts hydrogène. Ainsi, les chaînes polymère sonts très allongées à l’échelle moléculaire. Des nanofibres du complexe PEO-urée ont été préparées pour la première fois par électrofilage de suspensions et de solutions. Tel qu’attendu, une orientation moléculaire inhabituellement élevée a été observée dans ces fibres. De tels complexes orientés pourraient être utilisés à la fois dans des études fondamentales et dans la préparation de matériaux hiérarchiquement structurés. La méthode d’électrofilage peut parfois aussi être utilisée pour préparer des matériaux polymériques métastables qui ne peuvent pas être préparés par des méthodes conventionnelles. Ici, l’électrofilage a été utilisé pour préparer des fibres des complexes stables (α) et "métastables" (β) entre le PEO et l’urée. La caractérisation du complexe β, qui était mal connu, révèle un rapport PEO:urée de 12:8 appartenant au système orthorhombique avec a = 1.907 nm, b = 0.862 nm et c = 0.773 nm. Les chaînes de PEO sont orientées selon l’axe de la fibre. Leur conformation est significativement affectée par les ponts hydrogène. Une structure en couches a été suggérée pour la forme β, plutôt que la structure conventionnelle en canaux adoptée par la forme α. Nos résultats indiquent que le complexe β est thermodynamiquement stable avant sa fonte et peut se transformer en forme α et en PEO liquide par un processus de fonte et recristallisation à 89 ºC. Ceci va dans le sens contraire aux observations faites avec le complexe β obtenu par trempe du complexe α fondu. En effet, le complexe β ainsi obtenu est métastable et contient des cristaux d’urée. Il peut subir une transition de phases cinétique solide-solide pour produire du complexe α dans une vaste gamme de températures. Cette transition est induite par un changement de conformation du PEO et par la formation de ponts hydrogène intermoléculaires entre l’urée et le PEO. Le diagramme de phases du système PEO-urée a été tracé sur toute la gamme de compositions, ce qui a permis d’interpréter la formation de plusieurs mélanges qui ne sont pas à l’équilibre mais qui sont été observés expérimentalement. La structure et le diagramme de phases du complexe PEO-thiourée, qui est aussi un complexe très mal connu, ont été étudiés en détail. Un rapport molaire PEO :thiourée de 3:2 a été déduit pour le complexe, et une cellule monoclinique avec a = 0.915 nm, b = 1.888 nm, c = 0.825 nm et β = 92.35º a été déterminée. Comme pour le complexe PEO-urée de forme β, une structure en couches a été suggérée pour le complexe PEO-thiourée, dans laquelle les molécules de thiourée seraient disposées en rubans intercalés entre deux couches de PEO. Cette structure en couches pourrait expliquer la température de fusion beaucoup plus faible des complexes PEO-thiourée (110 ºC) et PEO-urée de forme β (89 ºC) en comparaison aux structures en canaux du complexe PEO-urée de forme α (143 ºC).