Possible enhancing mechanism of the cutaneous permeation of 4-biphenylylacetic acid by beta-cyclodextrin derivatives in hydrophilic ointment

The enhancing effects of heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD) and 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) on the percutaneous absorption of 4-biphenylylacetic acid (BPAA), a nonsteroidal anti-inflammatory drug, in hydrophilic ointment were studied and compared with the parent beta-cyclodextrin (beta-CyD). 13C-NMR measurements suggested that the biphenyl group of BPAA is preferably included within the cavity of three beta-CyDs. The three beta-CyDs remarkably enhanced the release of BPAA from the hydrophilic ointment base and the in vitro cutaneous permeation, depending on the increase in solubility of BPAA in the ointment base. Pretreatment of the ointment containing DM-beta-CyD or HP-beta-CyD onto the isolated skin of hairless mice, however, provided no effects on the skin permeation of BPAA. When propylene glycol was used as a vehicle, both the release rate and cutaneous permeation parameters showed no appreciable difference between BPAA alone and its HP-beta-CyD complex, because the solubilities of BPAA and its HP-beta-CyD complex were almost comparable in the vehicle. The present results suggested that the enhancing effect of beta-CyDs on the percutaneous absorption of BPAA can be mainly ascribed to an increase in the solubility of BPAA in the hydrophilic ointment.

The interaction of charged and uncharged drugs with neutral (HP-beta-CD) and anionically charged (SBE7-beta-CD) beta-cyclodextrins

PURPOSE

The objective of this work was to determine the role that charge might play in the interaction of charged and uncharged drugs with neutral (2-hydroxypropyl-beta-cyclodextrin, HP-beta-CD) and anionically charged (SBE7-beta-CD) modified beta-cyclodextrins. SBE7-beta-CD is a sulfobutyl ether, sodium salt, derivative variably substituted on the 2-, 3- and the 6-positions of beta-cyclodextrin. The number seven refers to the average degree of substitution.

METHODS

The binding of the acidic drugs, indomethacin, naproxen and warfarin and the basic drugs, papaverine, thiabendazole, miconazole and cinnarizine with the two cyclodextrins was determined at 25 degrees C as a function of pH and cyclodextrin concentration by the phase-solubility method.

RESULTS

Except for miconazole and cinnarizine (Ap-type diagrams), all other materials studied displayed AL-type diagrams. By comparing the binding constants of both the charged and uncharged forms of the same drugs to both HP-beta-CD and SBE7-beta-CD, the following conclusions could be drawn. The binding constants for the neutral forms of the drugs were always greater with SBE7-beta-CD than with HP-beta-CD. For the anionic agents, the binding constants between SBE7-beta-CD and HP-beta-CD were similar while the binding constants for the cationic agents with SBE7-beta-CD were superior to those of HP-beta-CD, especially when compared with the neutral form of the same drug.

CONCLUSIONS

A clear charge effect on complexation, attraction in the case of cationic drugs and perhaps inhibition in the case of anionic drugs, was seen with the SBE7-beta-CD.

Combination effects of alpha-cyclodextrin and xanthan gum on rectal absorption and metabolism of morphine from hollow-type suppositories in rabbits

Pharmacokinetics of morphine and its glucuronides in plasma were studied after rectal administration of hollow-type oleaginous suppositories containing kneading mixtures of morphine hydrochloride, alpha-cyclodextrin, and/or xanthan gum in rabbits. In combination with xanthan gum, alpha-cyclodextrin reduced the first-pass metabolism of morphine in the rectal mucosa and by the liver and improved the apparent rectal bioavailability of the opioid about 4 fold. In vitro permeation studies using an isolated rectal mucosal preparation of rabbits revealed that alpha-cyclodextrin increased the transepithelial conductance and facilitated the transport of morphine through the rectal mucosa. Furthermore, alpha-cyclodextrin facilitated its own mucosal permeation and reduced the glucuronidation of morphine during the passage through the rectal mucosa, probably through restricting the formation of a catalytic complex of morphine with glucuronyltransferases, rather than because of the enzyme saturation. The present data suggest that alpha-cyclodextrin in combination with xanthan gum is particularly effective in improving the rectal bioavailability of morphine from hollow-type suppositories.

In-vitro evaluation of biphenylyl acetic acid-beta-cyclodextrin conjugates as colon-targeting prodrugs: drug release behaviour in rat biological media

Biphenylyl acetic acid was selectively conjugated to one of the primary hydroxyl groups of beta-cyclodextrin through an ester- or amide-linkage, and the physicochemical properties (aqueous solubility and hydrolysis) were investigated. Aqueous solubility of the conjugates was lower than those of either drug or parent beta-cyclodextrin. The amide conjugate was stable in aqueous solution and in rat biological fluids and gastrointestinal contents. The ester conjugate was hydrolysed to beta-cyclodextrin and biphenylyl acetic acid at moderate rates resulting in a V-shaped rate-pH profile in aqueous solution. The ester conjugate released the drug preferentially when incubated with the contents of caecum or colon, whereas no appreciable drug release was observed on incubation with contents of stomach or intestine, nor on incubation with intestinal or liver homogenates, nor on incubation with rat blood. The present results suggest that the ester-type drug conjugate of beta-cyclodextrin may serve as a colon-targeting prodrug.

Enhanced nasal delivery of luteinizing hormone releasing hormone agonist buserelin by oleic acid solubilized and stabilized in hydroxypropyl-beta-cyclodextrin

The potential use of three 2-hydroxypropyl ether derivatives of cyclodextrins (HP-alpha-, HP-beta- and HP-gamma-CyDs) as biocompatible solubilizers and stabilizers for oleic acid, a lipophilic absorption enhancer, was assessed in the nasal absorption of buserelin, an agonist of luteinizing hormone-releasing hormone, in rats. HP-CyDs increased the aqueous solubility of oleic acid and protected it against oxidation through the formation of inclusion complexes with the efficacy increasing in the order: HP-gamma-CyD << HP-alpha-CyD < HP-beta- CyD. The bend structure due to a cis-double bond halfway along the acyl chain of oleic acid provided a better fit into the cavity of HP-beta-CyD, in which the double bond appears to be buried, and hence becomes less susceptible to oxidation. The rate and extent of nasal bioavailability of buserelin were remarkably increased by coadministration of oleic acid and HP-beta-CyD, compared with the sole use of the enhancer. This enhancement was ascribable to the lowering of both the enzymatic and physical barriers of the nasal epithelium to the peptide, probably through the facilitated transmucosal penetration of oleic acid solubilized in HP-beta-CyD.

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

The effects of chemically modified cyclodextrins on the nasal absorption of buserelin, an agonist of luteinizing hormone-releasing hormone, were investigated in anesthetized rats. Of the cyclodextrins tested, dimethyl-beta-cyclodextrin (DM-beta-CyD) was the most effective in improving the rate and extent of the nasal bioavailability of buserelin. Fluorescence spectroscopic studies indicated that the cyclodextrins formed inclusion complexes with buserelin, which may reduce the diffusibility of buserelin across the nasal epithelium and may participate in the protection of the peptide against enzymatic degradation in the nasal mucosa. Additionally, the cyclodextrins increased the permeability of the nasal mucosa, which was the primary determinant based on the multiple regression analysis of the nasal absorption enhancement of buserelin. Scanning electron microscopic observations revealed that DM-beta-CyD induced no remarkable changes in the surface morphology of the nasal mucosa at a minimal concentration necessary to achieve substantial absorption enhancement. The present results suggest that DM-beta-CyD could improve the nasal bioavailability of buserelin and is well-tolerated by the nasal mucosa of the rat.

Direct measurement of high-density lipoprotein cholesterol in serum with polyethylene glycol-modified enzymes and sulfated alpha-cyclodextrin

We have developed an automated method for measuring high-density lipoprotein (HDL)-cholesterol in serum without prior separation, using polyethylene glycol (PEG)-modified enzymes and sulfated alpha-cyclodextrin. When cholesterol esterase and cholesterol oxidase enzymes were modified with PEG, they showed selective catalytic activities towards lipoprotein fractions, with the reactivity increasing in the order: low-density lipoprotein < very-low-density lipoprotein approximately chylomicron < HDL. In the presence of magnesium ions, alpha-cyclodextrin sulfate reduced the reactivity of cholesterol, especially in chylomicrons and very-low-density lipoprotein, without the need for precipitation of those lipoprotein fractions. The combination of PEG-modified enzymes with alpha-cyclodextrin sulfate provided selectivity for the determination of HDL-cholesterol in serum in the presence of a small amount of dextran sulfate without the need for precipitation of lipoprotein aggregates. The results of the HDL-cholesterol assayed in serum by this direct method correlated well with those obtained by precipitation-based methods and also that by an ultracentrifugation method.

Direct measurement of high-density lipoprotein cholesterol in serum with polyethylene glycol-modified enzymes and sulfated alpha-cyclodextrin

We have developed an automated method for measuring high-density lipoprotein (HDL)-cholesterol in serum without prior separation, using polyethylene glycol (PEG)-modified enzymes and sulfated alpha-cyclodextrin. When cholesterol esterase and cholesterol oxidase enzymes were modified with PEG, they showed selective catalytic activities towards lipoprotein fractions, with the reactivity increasing in the order: low-density lipoprotein &lt; very-low-density lipoprotein approximately chylomicron &lt; HDL. In the presence of magnesium ions, alpha-cyclodextrin sulfate reduced the reactivity of cholesterol, especially in chylomicrons and very-low-density lipoprotein, without the need for precipitation of those lipoprotein fractions. The combination of PEG-modified enzymes with alpha-cyclodextrin sulfate provided selectivity for the determination of HDL-cholesterol in serum in the presence of a small amount of dextran sulfate without the need for precipitation of lipoprotein aggregates. The results of the HDL-cholesterol assayed in serum by this direct method correlated well with those obtained by precipitation-based methods and also that by an ultracentrifugation method.

In-vivo and in-vitro correlation for delayed-release behaviour of a molsidomine/O-carboxymethyl-O-ethyl-beta-cyclodextrin complex in gastric acidity-controlled dogs

The in-vivo absorption behaviour of molsidomine from the delayed-release tablets of an O-carboxymethyl-O-ethyl-beta-cyclodextrin complex was investigated using gastric acidity-controlled dogs under fasted and non-fasted conditions. The in-vitro release profiles were generated by changing the pH of the dissolution medium at different rotation paddle speeds. The absorptivity of molsidomine in the high acidity dog was correlated with the pH-changed release profile (pH 1.2 to 7.0 after 2 h), whereas that in the low acidity dog was correlated with the release profile at a constant pH of 7.0. The absorption in fasted dogs was well correlated with the in-vitro release at the low-rotation paddle speed (< 5 rev min-1), whereas that in the non-fasted dogs was correlated with that of high rotation (100 rev min-1). The present results suggested that the in-vivo delayed-release behaviour of the complex is predictable from the in-vitro release profiles generated using pH-variable dissolution testing apparatus at different rotation speeds of the paddle.

Modification of rectal absorption of morphine from hollow-type suppositories with a combination of alpha-cyclodextrin and viscosity-enhancing polysaccharide

An attempt was made to optimize the rectal delivery of morphine, using cyclodextrins as an absorption enhancer and polysaccharides as a swelling hydrogel in Witepsol H-15 hollow-type suppositories, and this was tested in rabbits. alpha- and beta-cyclodextrins enhanced the rate and extent of bioavailability, the former being more effective; gamma-cyclodextrin decreased the absorption of morphine. The in-vitro membrane permeation studies using excised rectal sacs revealed that alpha-cyclodextrin enhanced the permeation of morphine through the rectal membranes. In contrast, viscous polysaccharides such as xanthan gum retarded the plasma morphine levels after the rectal administration, reflecting in-vitro slow release characteristics. A combination of alpha-cyclodextrin and xanthan gum produced sustained plasma profiles of morphine along with an increased rectal bioavailability (more than 4 times). From the observation of the distribution behavior of suppositories in rabbit rectum and colon after the rectal administration, xanthan gum was found to prevent the upward spread of the drug. Gross and microscopic observations suggested that this preparation was less irritating to the rectal mucosa.

Differential effects of sulfate and sulfobutyl ether of beta-cyclodextrin on erythrocyte membranes in vitro

The hemolytic activity of beta-cyclodextrin (beta-CyD) on rabbit erythrocytes was reduced by the introduction of negatively-charged groups onto the hydroxyls of beta-CyD; the membrane disrupting abilities decreased in the order of beta-CyD > 2-hydroxypropyl-beta-CyD (HP-beta-CyD) > sulfobutyl-beta-CyD (SB-beta-CyD) >> beta-CyD sulfate (S-beta-CyD). Under pre-hemolytic concentrations, both beta-CyD and SB-beta-CyD induced shape changes of membrane invagination on the erythrocytes. In sharp contrast, S-beta-CyD showed biphasic effect on the shape of the erythrocytes; i.e. the crenation at relatively low concentrations and the invagination at higher concentrations. The S-beta-CyD-induced membrane crenation arose from a direct action on the membranes rather than cell metabolism-mediated effects. Unlike beta-CyD, S-beta-CyD was found to bind to the erythrocytes and may be confined to the outer surface of the membrane bilayer, which may expand the exterior layer relative to the cytoplasmic half, thereby inducing the cells to crenate. On the other hand, the membrane invagination mediated by the three beta-CyDs was initiated by extracting specific membrane lipids from the cells, depending upon their inclusion abilities, subsequently leading to the lysis of the cells. These results indicate that SB-beta-CyD and S-beta-CyD interact with the erythrocyte membranes in a differential manner and possess lower membrane disrupting abilities than the parent beta-CyD and HP-beta-CyD.

Effect of 2-hydroxypropyl-beta-cyclodextrin on crystallization and polymorphic transition of nifedipine in solid state

The glassy state of nifedipine (NP) was prepared in the absence and presence of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD), and its crystallization and polymorphic transition behavior was investigated by differential scanning calorimetry (DSC) and powder X-ray diffractometry. In DSC thermograms, the glassy NP exhibited an endothermic peak at 48 degrees C representing the glass transition of NP, an exothermic peak at 105 degrees C for the crystallization to a metastable form of NP (Form B), an exothermic peak at 125 degrees C for the polymorphic transition of Form B to a stable form of NP (Form A), and an endothermic peak at 171 degrees C for the melting of Form A. The powder X-ray diffractogram of Form B was apparently different from that of Form A. In the presence of HP-beta-CyD, the exothermic peak at 125 degrees C for the Form B to A transition disappeared and a new endothermic peak appeared at 163 degrees C. This new peak was ascribed to the melting of Form B, and the conversion of Form B to Form A was significantly suppressed in HP-beta-CyD matrix. Upon storage at 60 degrees C, the glassy NP was converted to Form A with an activation energy of 18 kcal/mol. The apparent dissolution rate of the NP/HP-beta-CyD (molar ratio 1:1) increased in the order of glassy NP < Form A < Form B, because the glassy NP was readily converted to Form A upon contact with water, resulting in a lower dissolution rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the inclusion mode of beta-cyclodextrin sulfate and its effect on the chlorpromazine-induced hemolysis of rabbit erythrocytes

The inclusion mode of beta-cyclodextrin sulfate (beta-CyD-sul) with a cationic drug, chlorpromazine, was investigated, and the effect of beta-CyD-sul on the hemolytic activity of chlorpromazine was compared with that of parent beta-CyD. The interaction of beta-CyD-sul with chlorpromazine was weaker than that of parent beta-CyD, probably because of the steric or electrostatic repulsion between anionic sulfate groups and hydrophobic phenothiazine moiety. Spectroscopic studies, including pH- and salt-effects, as well as thermodynamic parameters, suggested that both electrostatic and hydrophobic interactions are operative in the inclusion complexation of beta-CyD-sul with chlorpromazine. The inhibiting effect of parent beta-CyD on the chlorpromazine-induced hemolysis of rabbit erythrocytes was accounted for by the decreased fraction of free drug through the complexation. In the case of beta-CyD-sul, the hemolysis and binding of the drug to the erythrocyte membrane was higher than those estimated from the fraction of free drug, probably due to the increased hydrophobicity of the drug through the complexation. However, the chlorpromazine-induced shape change of the erythrocytes was significantly suppressed by beta-CyD-sul, and its inhibiting effect was greater than that of beta-CyD, because of the counterbalance of the opposite effects, i.e., internalization and externalization induced by chlorpromazine and beta-CyD-sul, respectively.

Peracylated beta-cyclodextrins as novel sustained-release carriers for a water-soluble drug, molsidomine

Peracylated beta-cyclodextrins with different alkyl chains (acetyl-octanoyl) were prepared by acylating all hydroxyl groups of beta-cyclodextrin (beta-CyD), and their physical properties were evaluated. These hydrophobic beta-CyDs decreased the release rate of molsidomine, a peripheral vasodilator, in proportion to the lengthening of alkyl chain and suppressed a peak plasma level of molsidomine following oral administration of peracylated beta-CyD complexes to dogs. Among the peracylated beta-CyDs tested, perbutanoyl-beta-CyD maintained sufficient plasma drug levels for a long period of time, while other peracylated beta-CyDs having shorter or longer chains were inappropriate to control the in-vivo release behaviour of molsidomine. The prominent retarding effect of perbutanoyl-beta-CyD was ascribable to the appropriate mucoadhesive property and hydrophobicity, compared with other peracylated beta-CyDs. The present results suggest that perbutanoyl-beta-CyD is particularly useful in modifying the release rate of water-soluble drugs as a novel slow-release carrier.

In-vivo and in-vitro evaluations of a modified-release oral dosage form of nifedipine by hybridization of hydroxypropyl-beta-cyclodextrin and hydroxypropylcelluloses in dogs

To maintain a suitable blood level of nifedipine for a long period of time, double-layer tablets consisting of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and 3% nonionic surfactant (HCO-60) as a fast-release portion and hydroxypropylcelluloses (HPCs) with different viscosity grades (low, medium and high) as a slow-release portion were prepared, and their in-vitro and in-vivo release behaviours were investigated. Among the seven formulations, the tablet having the mean dissolution time of 0.8-1.3 h gave prolonged plasma nifedipine levels without decrease of AUC after oral administration to dogs. Consequently, the double-layer tablet consisting of HP-beta-CyD with 3% HCO-60/(HPC-low:HPC-medium) in a weight ratio 1/(1.5:1.5) was selected as an appropriate modified-release formulation because it elicited almost comparable retarding effects with superior oral bioavailability compared with those of a commercially available slow-release nifedipine product.

Aluminium beta-cyclodextrin sulphate as a stabilizer and sustained-release carrier for basic fibroblast growth factor

The water-insoluble aluminium salt of beta-cyclodextrin sulphate (Al.beta-CyD-Sul) was used as a stabilizer and sustained-release carrier for recombinant human basic fibroblast growth factor (bFGF). An adsorbate of bFGF with Al.beta-CyD-Sul was prepared by incubating the protein with a suspension of Al.beta-CyD-Sul in water. The mitogenic activity of bFGF released from the adsorbate, as indicated by the proliferation of kidney cells of baby hamster (BHK-21), was almost comparable with that of the intact bFGF. Al.beta-CyD-Sul significantly protected bFGF from proteolytic degradation by pepsin and alpha-chymotrypsin, compared with the water-soluble sodium salt. The in-vitro release of bFGF from the adsorbate was sustained in proportion to a rise in the ratio of Al.beta-CyD-Sul to the protein in the adsorbate. Of the bFGF preparations evaluated, the adsorbate of bFGF with Al.beta-CyD-Sul, when given subcutaneously to the rat, showed the most prominent increase in the formation of granulation tissues, due to the stabilization and slow-release of the mitogen. The limited data presented here suggest that the adsorbate of bFGF with Al.beta-CyD-Sul has a potent therapeutic efficacy for wound healing, and may be applicable to oral protein formulations for the treatment of intestinal mucosal erosions.

Design and in-vitro evaluation of a modified-release oral dosage form of nifedipine by hybridization of hydroxypropyl-beta-cyclodextrin and hydroxypropylcellulose

To modify the release rate of nifedipine, a potent calcium channel antagonist, a double-layer tablet was designed, anticipating a more balanced oral bioavailability and a prolonged efficacy than the simple plain tablet. Amorphous nifedipine powders prepared by spray-drying with 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and nonionic surfactant HCO-60 were employed as a fast-release portion to attain an initial rapid dissolution of nifedipine. Hydroxypropylcelluloses (HPCs) with different viscosity grades (type L, M, and H) were used for a slow-release portion to provide an appropriate sustained-release. Taking into account the physiological conditions of the gastrointestinal tract (pH and motility), an optimal formulation of the double-layer tablet was obtained by changing the mixing ratios of each component. For example, the tablet consisting of HP-beta-CyD with 3% HCO-60/(HPC-L:HPC-M) in the weight ratio 1/2(1:1) provided a sufficient slow release of the drug over a wide pH region following an initial rapid dissolution. The release of nifedipine from the double-layer tablets was little affected by pH of the medium and rotation speed of paddle after accelerated storage conditions (60 degrees C, 75% r.h.). The present results suggest that a combination of HP-beta-CyD, HCO-60 and HPCs can serve as a modified-release carrier for poorly water-soluble nifedipine.

Inclusion complexation of p-hydroxybenzoic acid esters with 2-hydroxypropyl-beta-cyclodextrins. On changes in solubility and antimicrobial activity

To obtain a transparent and effective solution of p-hydroxybenzoic acid esters (parabens), the use of 2-hydroxypropyl-beta-cyclodextrins (2-HP-beta-CyDs) as solubilizers with different degrees of substitution (D.S.) was surveyed. 2-HP-beta-CyDs significantly increased the aqueous solubility of four kinds of parabens (methyl < ethyl < propyl < butyl esters), where the solubilizing ability decreased with an increase in the D.S. of the 2-hydroxypropyl group in beta-CyD. The antimicrobial activity of the parabens tended to decrease by complexation with 2-HP-beta-CyDs. However, the activity could be maintained by lengthening the alkyl chain of the parabens. 1H- and 13C-nuclear magnetic resonance and circular dichroism spectroscopic studies suggest that the hydrophobic alkyl moiety of butyl paraben is preferably included in the cavity, and the phenol group extrudes from the cavity. The present results suggest that a suitable combination of 2-HP-beta-CyDs and hydrophobic, longer alkyl parabens is useful for the preservation of liquid formulations.

Protective effects of cyclodextrin sulphates against gentamicin-induced nephrotoxicity in the rat

The effects of cyclodextrin sulphates on the development of rat renal dysfunction induced with gentamicin, an aminoglycoside antibiotic, were studied. Daily subcutaneous injection of gentamicin (100 mg kg-1, 14 days) developed nephrotoxicity in the rat as assessed by an increase in serum urea nitrogen and histopathological changes in the renal cortex. When cyclodextrin sulphates were given intraperitoneally at 300 mg kg-1 at 6 h intervals after gentamicin administration, they protected the rat against the drug-induced renal impairment, while the parent cyclodextrins were ineffective. Since post-administration of cyclodextrin sulphates did not reduce the total amount of gentamicin accumulated in the kidney, the protection may occur through interference with intracellular events leading from the drug accumulation to nephrotoxicity. These results suggest that cyclodextrin sulphates are particularly effective in preventing renal failure associated with aminoglycoside treatment.

Preparation of heptakis(2,6-di-O-ethyl)-beta-cyclodextrin and its nuclear magnetic resonance spectroscopic characterization

Heptakis(2,6-di-O-ethyl)-beta-cyclodextrin (DE-beta-CyD) was prepared and its 1H and 13C nuclear magnetic resonance (NMR) signals in DMSO-d6 were unequivocally assigned by two-dimensional COSY and ROESY. The results on 1H coupling constants indicated that all ethylated glucose units are in a 4C1 chair conformation. The average spin-lattice relaxation times (T1) of ring carbons of DE-beta-CyD were only slightly shorter, and their standard deviations from the mean T1 value were larger, than those of beta-cyclodextrin (beta-CyD) and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD), suggesting the presence of slightly irregular internal motion in the ethylated glucose units. The temperature dependence of chemical shift of DE-beta-CyD in DMSO-d6 suggested that the C3 hydroxyl protons may participate as proton donor in the intramolecular hydrogen bond to the C2 ethoxyl groups of neighboring glucose, and the intramolecular hydrogen bond of DE- and DM-beta-CyDs is much stronger than that of beta-CyD, suggesting the stable macrocyclic ring structure of DE-beta-CyD.

Inhibitory effect of prostaglandin E1 on laurate-induced peripheral vascular occlusive sequelae in rabbits: optimized topical formulation with beta-cyclodextrin derivative and penetration enhancer HPE-101

Prostaglandin E1 (PGE1) and its inclusion complexes with beta-cyclodextrin (beta-CyD) and O-carboxymethyl-O-ethyl-beta-cyclodextrin (CME-beta-CyD) were made as topical preparations. The PGE1 preparations, when applied with a penetration enhancer, 1-[2-(decylthio)ethyl]azacyclopentane-2-one (HPE-101), markedly increased the regional blood flow in the ear of rabbits and were longer acting than when administered by the intravenous route. Topical application of the PGE1 preparations significantly protected rabbits against laurate-induced peripheral vascular occlusive sequelae; the protective potency increased in the order of PGE1 alone = beta-CyD complex < CME-beta-CyD complex preparation. The PGE1 preparations elicited skin reactions such as erythema and oedema depending on their vasodilating actions. These reactions disappeared gradually after removal of the preparations, and hence may not be serious obstacles for their safe use. These results suggest that combinations of CME-beta-CyD and HPE-101 work synergistically to facilitate the entry of PGE1 into the skin, and consequently enhance the therapeutic potential of PGE1 in the topical preparation tested.

Enhanced rectal absorption and reduced local irritation of the anti-inflammatory drug ethyl 4-biphenylylacetate in rats by complexation with water-soluble beta-cyclodextrin derivatives and formulation as oleaginous suppository

To improve the rectal delivery of ethyl 4-biphenylylacetate (EBA), a prodrug of the anti-inflammatory drug 4-biphenylylacetic acid (BPAA), the use of highly water-soluble 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD) was investigated and compared with the use of the parent beta-cyclodextrin (beta-CyD). Among the three beta-CyDs, HP-beta-CyD was best at improving the rectal bioavailability of EBA in rats after single and multiple administrations of oleaginous suppositories (Witepsol H-5) containing the complexes. To gain insight into the enhancing effect of beta-CyDs, the absorption behaviors of EBA (observed by monitoring BPAA as an active metabolite of EBA) and beta-CyDs themselves were examined in vitro, in situ, and in vivo. The in situ recirculation study revealed that the complexed form of EBA was less absorbable from the rectal lumen in the solution state, but this disadvantageous effect of beta-CyDs was compensated in part by the inhibition of the bioconversion of EBA to BPAA. When beta-CyDs were coadministered with EBA in vivo, however, rather high amounts of HP-beta-CyD (approximately 26% of dose) and DM-beta-CyD (approximately 21% of dose), compared with beta-CyD (approximately 5% of dose), were absorbed from the rat rectum. Thus, the enhancement of rectal absorption of EBA in vivo can be explained by the facts that the hydrophilic beta-CyDs increased the release rate of EBA from the vehicle and stabilized EBA in the rectal lumen and that the drug was partly absorbed in the form of the complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-catalyzed hydrolysis of maltosyl-beta-cyclodextrin

Maltosyl-beta-cyclodextrin was hydrolyzed via two pathways in acidic solution: (1) ring opening to give noncyclic oligosaccharides and (2) cleavage of maltose in the branched residue to give glucosyl-beta-CyD and glucose. Ring opening was approximately 2-3 times faster than maltose cleavage because of the multiple hydrolysis sites of the beta-cyclodextrin (beta-CyD) ring (seven glycosidic linkages) compared with only one reaction site of the maltose residue in the branch. Values of the enthalpy and entropy of activation of the hydrolyses were positive and in the range reported for maltose, a result indicating that the hydrolyses proceeded according to the A-1 mechanism (i.e., unimolecular decomposition). The alpha-1,6-glycosidic bond of branched beta-CyDs connecting beta-CyD and branched sugar moieties resisted hydrolysis; this property is a potential pharmaceutical advantage because the parent beta-CyD, which has low aqueous solubility, would not precipitate after hydrolysis.

Prominent inclusion effect of dimethyl-beta-cyclodextrin on photoisomerization of the thromboxane synthetase inhibitor (E)-4-(1-imidazoylmethyl)cinnamic acid

The direct photoisomerization of (E)-4-(1-imidazoylmethyl)-cinnamic acid (IMC), a thromboxane synthetase inhibitor, to its (Z)-isomer at pH 2.0 was decelerated by beta-cyclodextrin (beta-CyD) and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD). The photostationary composition [(Z)-isomer:IMC ratio] was shifted in favor of IMC. These effects were much greater with DM-beta-CyD than with the parent beta-CyD. The quantum yield of the photoisomerization was significantly decreased by complex formation with beta-CyDs, whereas the extinction coefficient of the guest was only slightly decreased. This situation was in sharp contrast to those observed in less polar solvents and suggests that the suppressing mechanism with beta-CyD is different from that with less polar solvent systems. Spectroscopic studies (ultraviolet, circular dichroism, and nuclear magnetic resonance) indicated that IMC is tightly included in an axial mode in the cavity of DM-beta-CyD and that the rotation of the photoreactive site is sterically hindered. The results suggest that the suppressing effect of beta-CyDs on the photoisomerization of IMC results mainly from a steric origin.

[Use of water-soluble beta-cyclodextrin derivatives as carriers of anti-inflammatory drug biphenylylacetic acid in rectal delivery]

To improve the rectal delivery of an anti-inflammatory drug, biphenylylacetic acid (BPAA), the use of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and heptakis (2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD) was investigated. Inclusion complex formations of BPAA with both beta-CyDs in a molar ratio of 1:1 in water were ascertained, and their stability constants were determined. The dissolution of BPAA in water and the release of BPAA from an oleaginous suppository (Witepsol H-5) were significantly increased by beta-CyDs, depending on the magnitude of the stability constants of the water-soluble complexes. However, the serum levels of BPAA after rectal administration of the suppositories containing BPAA or its beta-CyDs complexes in rats increased in the order of BPAA alone much less than DM-beta-CyD less than or equal to HP-beta-CyD complex. The in situ recirculation study revealed that the greater the stability constant of the complex, the lesser was the absorption of BPAA from the rectal lumen of rats under the solution state. Both in vivo and in situ studies demonstrated that rather high amount of HP-beta-CyD (about 20% of dose) was absorbable from the rat's rectum, compared with DM-beta-CyD (less than 5% of dose), suggesting the possibility of the permeation of BPAA through the rectal membrane in the form of HP-beta-CyD complex. Furthermore, DM-beta-CyD and HP-beta-CyD significantly reduced the irritation of the rectal mucosa caused by BPAA after the administration of the suppositories to rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystal structure of 2-O-[(S)-2-hydroxypropyl]cyclomaltoheptaose

2-O-[(S)-2-Hydroxypropyl]cyclomaltoheptaose crystallises in the monoclinic space group P2(1) with unit-cell dimensions a = 15.072(1), b = 10.409(1), c = 20.623(2) A, and beta = 108.52(1) degrees. The structure was solved by X-ray diffraction and refined to an R-value of 0.096. The macrocyclic ring of the cyclomaltoheptaose moiety is less symmetrical than that in cyclomaltoheptaose. The glucose residue that carries the hydroxypropyl group inclines much more with its primary hydroxyl side towards the inside of the macrocycle than the other glucose residues. The molecules are arranged in a herring-bone fashion to form a cage-type packing structure. The hydroxypropyl group is inserted into the cavity of an adjacent molecule related by a two-fold screw axis, and the hydroxyl group is linked to an HO-6 via OH...water...OH hydrogen bonds. The crystal contains 8.5 water molecules which occupy 11 sites. Two water molecules are included at the primary hydroxyl side of the cyclomaltoheptaose cavity.

[Improvement of stability and bioavailability of 1-hexylcarbamoyl-5-fluorouracil (HCFU) by O-carboxymethyl-O-ethyl-beta- cyclodextrin]

The possible utility of O-carboxymethyl-O-ethyl-beta-cyclodextrin (CME-beta-CyD) as a novel drug carrier was studied in vitro and in vivo, by using 1-hexylcarbamoyl-5-fluorouracil (HCFU) as a model drug. The chemical instability of HCFU in solution and solid state was improved by CME-beta-CyD complexation. The in vitro release of HCFU from the CME-beta-CyD complex was decelerated in acidic solution, while accelerated at neutral pH regions, showing a typical delayed-release pattern. This pattern was clearly reflected in the blood levels after the oral administration of the complex to dogs, increasing the bioavailability. The present results suggested that CME-beta-CyD is useful as a delayed-release-type carrier for the oral administration of chemically labile HCFU.

Cyclodextrin sulfates: characterization as polydisperse and amorphous mixtures

Alpha- and beta-cyclodextrins and their hydroxypropyl derivatives were converted by the reaction with chlorosulfonic acid in pyridine to the corresponding sulfates. Cyclodextrin sulfates were shown by fast-atom bombardment mass spectrometry (negative ion mode, triethanolamine matrix) to be mixtures with nearly symmetrical distributions of degree of substitution by sulfate groups and by powder X-ray diffraction to be amorphous. Thus, in these aspects, cyclodextrin sulfates are similar to the potent drug solubilizers hydroxypropylcyclodextrins.

Enhancement of the antiinflammatory effect of ethyl 4-biphenylyl acetate in ointment by beta-cyclodextrin derivatives: increased absorption and localized activation of the prodrug in rats

Ethyl 4-biphenylyl acetate (EBA) is a prodrug of the antiinflammatory 4-biphenylyl acetic acid (BPAA). The inclusion complexes of EBA with beta-cyclodextrin (beta-CyD), heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD), and 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) at a molar ratio of 1:2 (EBA:cyclodextrin) were prepared and used to make hydrophilic antiinflammatory ointments. The in vitro release of EBA from the ointments was enhanced by complexation in the order of beta-CyD less than DM-beta-CyD less than or equal to HP-beta-CyD. The improvement correlated with the improved solubility and not with the decreased diffusibility observed to occur upon the complexation of EBA. In vivo the complexation with cyclodextrin derivatives increased both the release of EBA from the vehicle and its conversion in the underlying tissue to BPAA, but the total of EBA and BPAA in the tissue was decreased. In vitro studies confirmed that the effects of cyclodextrin derivatives on the conversion were exerted indirectly. The combination of the enhanced release and of the enhanced prodrug hydrolysis by esterases in the site where the antiinflammatory action is required resulted in increased therapeutic effects. In the model of carrageenan-induced acute edema in rat paw, the complexation improved the therapeutic effects over those of EBA alone in the order of beta-CyD less than DM-beta-CyD less than HP-beta-CyD. HP-beta-CyD may be a particularly useful cyclodextrin derivative since it improves the topical availability and does not irritate tissues.

Design and in vitro evaluation of slow-release dosage form of piretanide: utility of beta-cyclodextrin:cellulose derivative combination as a modified-release drug carrier

To modify the release rate of piretanide, a potent loop diuretic, a double-layer tablet was designed, and in vitro release was evaluated. For a rapidly releasing portion, hydrophilic beta-cyclodextrin derivatives were employed to form a water-soluble complex with piretanide. For a sustained-release portion, cellulose derivatives were used to provide appropriate hydrophobicity. The release rate of piretanide in the pH range 1.2-6.8 was automatically monitored by a pH-changeable dissolution testing apparatus. The low solubility of piretanide in acidic medium was significantly improved by complexations with dimethyl-beta-cyclodextrin (DM-beta-CyD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CyD). The pH-independent slow release was attained by use of hydroxypropylcellulose (HPC):ethylcellulose (EC) matrices. Then, an optimal formulation of a double-layer tablet was obtained by the combination of each fraction. For example, the tablet consisting of the [DM-beta-CyD/(HPC:EC)] system in the weight ratio [1/3(1:3)] provided a sufficiently slow release of the drug over a period of 8 h in a wide pH region following an initial rapid dissolution.

Slow-release characteristics of diltiazem from ethylated beta-cyclodextrin complexes

Release characteristics of two ethylated beta-cyclodextrins [heptakis(2,6-di-O-ethyl)-beta-cyclodextrin (diethyl-beta-cyclodextrin) and heptakis(2,3,6-tri-O-ethyl)-beta-cyclodextrin (triethyl-beta-cyclodextrin)] as sustained-release drug carriers were evaluated using diltiazem hydrochloride, a water-soluble calcium antagonist. The release rate of diltiazem from compressed tablets was significantly retarded by the complexation with ethylated beta-cyclodextrin. Various environmental effects (such as pH, rotating speed, and additive in the dissolution medium) on the release rate were investigated, together with a microscopic observation of the tablet surface. The water penetration rate into the tablet was measured in order to gain insight into the release mechanism. The results suggested that diltiazem is released slowly from the hydrophobic matrix consisting of diethyl-beta-cyclodextrin following water penetration. When a single dose of tablets containing diethyl-beta-cyclodextrin complex was orally administered to dogs, the sustained-release pattern of the drug, without decrease in area under the plasma concentration-time curve, was produced for a long period. The release rate of diltiazem can be controlled by combining the ethylated beta-cyclodextrin complexes with the parent beta-cyclodextrin complex in different mixing ratios.

Utility of 2-hydroxypropyl-beta-cyclodextrin in an intramuscular injectable preparation of nimodipine

Possible utility of hydroxyalkylated beta-cyclodextrin (beta-CyD) derivatives as parenteral drug carriers was investigated, using nimodipine, a dihydropyridine derivative with calcium antagonistic action, as a model drug. The aqueous solubility of nimodipine increased linearly with increase in the concentration of hydroxyalkylated beta-CyDs, showing an AL-type phase solubility diagram. The stability constant of nimodipine--hydroxyalkylated beta-CyD complexes was in the order of 2,3-dihydroxypropyl-beta-CyD less than beta-CyD less than 2-hydroxyethyl-beta-CyD less than 3-hydroxypropyl-beta-CyD less than 2-hydroxypropyl-beta-CyD, and the solubilizing ability of the beta-CyDs was also in that order. The results of powder X-ray diffractometry and thermal analysis suggested 1:3 (guest:host) complex formation of nimodipine with 2-hydroxypropyl-beta-CyD in the solid state. The dissolution rate of nimodipine-2-hydroxypropyl-beta-CyD complex was much faster than that of the drug alone. Nimodipine-2-hydroxypropyl-beta-CyD complex gave higher plasma levels of the drug after intramuscular administration to rabbits, i.e., the area under the plasma concentration--time curve and the maximum plasma concentration of the complex were about 2.5 times higher than those of the drug alone. The muscular damage after the injection of nimodipine was reduced by the administration of the complexed form.

Differential effects of alpha-, beta- and gamma-cyclodextrins on human erythrocytes

Alpha-, beta- and gamma-cyclodextrins are cyclic hexamers, heptamers, and octamers of glucose, respectively, and thus are hydrophilic; nevertheless, they have the ability to solubilize lipids through the formation of molecular inclusion complexes. The volume of lipophilic space involved in the solubilization process increases with the number of glucose units in the cyclodextrin molecule and, consequently, cyclodextrins were found to have different effects on human erythrocytes: (a) in the induction of shape change from discocyte to spherocyte the potency was observed to be alpha greater than gamma, but with beta-cyclodextrin hemolysis occurred before the change was complete; (b) in the increase of fluorescence intensity of 1-anilinonaphthalene-8-sulfonate in cyclodextrin-pretreated membranes, the observed potency was beta much greater than gamma greater than alpha; (c) in the release of potassium and hemoglobin, the potency was beta greater than alpha greater than gamma. The potencies of cyclodextrin for solubilizing various components of erythrocytes were alpha greater than beta much greater than gamma for phospholipids, beta much greater than gamma greater than alpha for cholesterol and beta much greater than gamma greater than alpha for proteins. The solubilization potencies were derived from concentration/final-effect curves. The above processes occurred without entry of solubilizer into the membrane, since (a) beta-[14C]cyclodextrin did not bind to erythrocytes and (b) cyclodextrins did not enter the cholesterol monolayer. A study of the [3H]cholesterol in erythrocytes indicated that beta-cyclodextrin extracted this lipid from membrane into a new compartment located in the aqueous phase which could equilibrate rapidly with additional erythrocytes. Therefore, the effects of cyclodextrins differ from those of detergents which first incorporate themselves into membranes then extract membrane components into supramolecular micelles.

Sustained release of buserelin acetate, a luteinizing hormone-releasing hormone agonist, from an injectable oily preparation utilizing ethylated beta-cyclodextrin

The possible use of heptakis (2,6-di-O-ethyl)-beta-cyclodextrin (DE-beta-CyD) as a parenteral sustained-release carrier for buserelin acetate, a luteinizing hormone-releasing hormone superagonist, has been examined. The in-vitro release of buserelin from the oily suspension was significantly retarded by the complexation with DE-beta-CyD, mainly due to the poor water solubility of the complex. A single subcutaneous injection of the suspension containing the buserelin-DE-beta-CyD complex to rats provided an effective continuous plasma level of buserelin lasting for at least one month, indicating a potential therapeutic efficacy for the treatment of the endocrine-dependent diseases. These results suggest that DE-beta-CyD serves as an injectable sustained-release drug carrier suitable for chronic treatment with buserelin acetate.

Alkylation of cyclomalto-oligosaccharides (cyclodextrins) with dialkyl sulfate-barium hydroxide: heterogeneity of products and the marked effect of the size of the macrocycle

The alkylation of cyclomalto-oligosaccharides (cyclodextrins, CDs) with dialkyl sulfate-barium hydroxide has been claimed to yield 2,6-di-O-alkyl derivatives. Re-investigation by plasma desorption-m.s. of the products of laboratory methylation of alpha CD, beta CD, or gamma CD and ethylation of beta CD and several commercial preparations revealed them to be mixtures with broad and roughly symmetrical distributions of the degree of substitution. Recrystallization separated the components only partially. Analysis of the product of methylation of a mixture of CDs established the order of reactivity gamma much greater than alpha greater than or equal to beta. The reactivity of gamma CD thus resembles that of amylose.

O-carboxymethyl-O-ethylcyclomaltoheptaose as a delayed-release-type drug carrier: improvement of the oral bioavailability of diltiazem in the dog

The utility of O-carboxymethyl-O-ethylcyclomaltoheptose (carboxymethyl-ethyl-beta-cyclodextrin, CME-beta CD) as a delayed-release-type drug carrier was investigated in vitro and in vivo, using diltiazem hydrochloride as a model drug. The aqueous solubility of CME-beta CD showed a marked dependency on pH, because of the ionization of the carboxyl group (pKa 3.75). The formation of an inclusion complex between diltiazem and CME-beta CD in aqueous solution and in the solid state was assessed by a solubility method and by X-ray diffractometry, respectively. The rate of release of the drug from the compressed tablet containing the complex was significantly retarded in solutions at low pH and increased with increase in pH, and this was reflected in the blood levels in the dog after the oral administration. The results suggested that the use of CME-beta CD could improve the oral bioavailability of diltiazem and release the drug preferentially in the intestinal fluid but only slightly in the gastric fluid.