Molecular dynamics simulation of crystalline beta-cyclodextrin dodecahydrate at 293 K and 120 K

Molecular dynamics (MD) simulations for crystalline beta-cyclodextrin dodecahydrate (beta-CD) at two different temperatures, 293 K and 120 K, have been performed using the GROMOS program package. The calculated structural properties are compared to those obtained from neutron diffraction studies of this system at the quoted temperatures. The simulation was carried out over a period of 20 ps on four unit cells containing 8 beta-CD molecules and 96 water molecules, whereby all atoms were allowed to move. At room temperature, the experimental positions of the (non-hydrogen) glucose atoms are reproduced within 0.034 nm, a value which is smaller than the experimental (0.041 nm) or simulated (0.049 nm) overall root mean square (rms) positional fluctuation. The corresponding numbers for the low temperature study are 0.046 nm, 0.019 nm and 0.022 nm. At both temperatures the experimentally observed degree of anisotropy of the atomic motions is also found in the simulations. The comparison of a variety of structural properties leads to the conclusion that the molecular model and force field used are able to simulate the cyclodextrin system very well. Experimentally observed differences in properties as a function of number of glucose units in the CD molecule (alpha-CD, 6 versus beta-CD, 7) and as a function of temperature are qualitatively reproduced by the simulations.

Inhibition of experimental and spontaneous pulmonary metastasis of murine RCT (+) sarcoma by beta-cyclodextrin-benzaldehyde

The effect of beta-cyclodextrin-benzaldehyde (CDBA) on pulmonary metastasis in C3H/He mice was examined. In experimental metastasis that was induced by iv injection of 1 X 10(6) RCT (+) cells, the highest inhibition was observed in the mice that were treated daily with CDBA (5 mg/day) for 1 week before tumor cell inoculation and further treated for 3 weeks after inoculation, when compared with those in other experimental groups that were given only pretreatment or posttreatment. The inhibitory effect was dose-dependent. In spontaneous metastasis that was induced by sc injection of 3 X 10(6) RCT (+) cells, the inhibition of metastasis was also observed in the mice treated with CDBA (5 mg/day) in the same manner as described above. However, the development of the primary tumor was not inhibited. CDBA-treated tumor-bearing mice showed almost as much NK activity as normal mice. Furthermore, although injection of 5-fluorouracil suppressed this activity to about 50% of that in normal mice, the combined treatment with CDBA could maintain the NK cell activity at the normal level. The results suggested that the inhibition of pulmonary metastasis might be induced by a combined effect of CDBA; that is, the direct inhibition of tumors and the maintenance of NK cell activity.

The use of beta-cyclodextrin-containing culture medium for in vitro evaluation of immunomodulating agents

We have devised a new culture medium that is made of RPMI-1640 medium, 500 micrograms/ml beta-cyclodextrin (beta-CD) and 1% fetal calf serum (FCS) (beta-CD medium). Murine lymphocytes stimulated with sheep erythrocytes in vitro developed antibody-forming cells in beta-CD medium as efficiently as in 10% FCS-containing RPMI-1640 medium (10F medium). Immunostimulating agents (SA96 and levamisole) and immunosuppressive agents (hydrocortisone and D-penicillamine) showed similar immunomodulating effects on the antibody responses in both media. In addition, the enhancing effect of levamisole varied drastically depending on the lot of FCS used in 10F medium, but a clear enhancement was always observed in beta-CD medium containing any lot of FCS tested.

Enhanced percutaneous absorption of homogenized tolnaftate/beta-cyclodextrin polymer ground mixture

The absorption of tolnaftate after external application of tolnaftate-cyclodextrin polymer homogenized ground mixtures was investigated in comparison with that of tolnaftate alone and non-homogenized mixtures. To evaluate their percutaneous absorption, samples were applied to the shaved back skin of mice. It was found that homogenized ground mixture samples showed the highest level of percutaneous absorption, and also resulted in the highest blood level concentrations.

Inactivation of sarin and soman by cyclodextrins in vitro

Cyclodextrins catalyzed the inactivation of sarin and soman but did not inactivate tabun and VX. Furthermore, sarin and soman showed greater affinity for beta-cyclodextrin than for alpha- or gamma-cyclodextrins. Thus beta-cyclodextrin appears to be an attractive starting material for the preparation of a catalyst able to inactivate sarin and soman more effectively. Such a catalyst might contribute to improving the therapy of poisoning caused by these two nerve agents.

Colorimetric determination of beta-cyclodextrin: two assay modifications based on molecular complexation of phenolphtalein

The decolorization of phenolphtalein upon complexation to cyclodextrins was studied to measure beta-cyclodextrin concentrations. Several factors possibly affecting the self-life of the dye were tested. By making the assays in 0.1 M NaCO3 solution beta-cyclodextrin concentrations down to 6 microM (SNR = 2) could be determined while the practical assay range reached up to 0.06 mM. In this form the method was unaffected by acyclic oligosaccharides and directly applicable to cyclodextrin assays in complex starch hydrolyzates. The method was further modified to be used in a flow-injection analyzator and the results were comparable to those obtained by HPLC analyses after prepurification of the samples.

Thermal and pH stability of "beta-benzyme"

The thermal and pH stability of "beta-benzyme", an artificial chymotrypsin based on beta-cyclodextrin, has been studied and compared with the stability of real chymotrypsin. Artificial chymotrypsin is vastly superior to real chymotrypsin with regard to both temperature and pH stability. The reasons for this increased stability are discussed.

The binding of fluorescent 4,6,8(14)-triene-3-one steroids to cyclodextrins as a model for steroid-protein interactions

The 4,6,8(14)-triene-3-one steroids, highly fluorescent in aqueous solutions, lose their fluorescence power when binding occurs to hydrophobic regions of other molecules, such as the hydrophobic cavity in the ring system of cyclodextrins. The fluorescence intensity decreases almost completely when beta- and gamma-cyclodextrins are present in the solution. Scatchard plots derived from fluorescence titrations show that one or two molecules of steroid bind to one cyclodextrin molecule with KD,F-values of about 10(-4)-10(-5) mol/liter. Temperature-jump experiments show a single relaxation process, with rate constants for the decay of the beta-cyclodextrin-steroid complexes of about 10(4)-10(5) per s. For alpha- and gamma-cyclodextrins such relaxation processes are not observed.

beta-Cyclodextrin as a substitute for fetal calf serum in the primary antibody response in vitro

Fetal calf serum (FCS) must be present at 10% in the culture medium for optimally eliciting the primary antibody response to sheep erythrocytes (SRBC) in murine lymphocytes. The response was no longer observed when FCS was reduced to less than 1%. However, we found that the addition of 250-500 micrograms/ml beta-cyclodextrin (beta-CD) to RPMI 1640 medium containing 1% FCS restored the immune response to a level comparable to that observed in 10% FCS-containing medium. beta-CD did not further augment the response in the presence of 10% FCS. The order of effectiveness of various cyclodextrin compounds tested was as follows: beta-CD (100) greater than alpha-CD(30) greater than gamma-CD(10) greater than heptakis (2,6-O-dimethyl)beta-CD (less than 1). The in vitro antibody response varied drastically depending on the lot of FCS added to the culture medium. The important observation was that even a deficient lot of FCS could elicit the antibody response as efficiently as a good lot if it was added to the culture medium at 1% in combination with beta-CD. beta-CD was also effective in inducing the primary antibody responses to both SRBC and dinitrophenylated Ficoll in serum-free RPMI 1640 medium containing bovine serum albumin, insulin and transferrin. In serum-free conditions, the responses were 40-50% of those in serum-containing medium. beta-CD did not increase the number of antibody-forming cells nonspecifically, nor did it show a significant mitogenic activity and cytotoxicity. These data suggest that beta-CD is a useful material as a serum substitute in inducing primary antibody response in vitro.

Mobile phase effects on the separations of substituted anilines with a beta-cyclodextrin-bonded column

The capacity factors of several substituted anilines were measured on a beta-cyclodextrin (beta-CD)-bonded column with mobile phases varying from the classical, normal-phase condition, e.g. n-heptane-2-propanol, to the classical, reversed-phase condition, e.g. water-2-propanol. Different modifiers, such as acetonitrile, methanol, and tetrahydrofuran and a Partisil PXS-ODS column were also used for comparison. In general, it was found that the beta-CD column, having the ability to form inclusion complexes with certain substrates is better and more selective in the reversed-phase separation of many aromatic compounds than the Partisil PXS-ODS column. The normal-phase separation on beta-CD was even more efficient, owing to the presence of large number of hydroxy groups on the surface of beta-CD molecules and the more rapid mass transfer in the column. In the present case, alcohols were found to be better modifiers than aprotic solvents. The effects of organic solvents on both normal-and reversed-phase separations are also discussed. The minima observed for the log k' vs. percent organic solvent plots for a number of substituted anilines are reasoned to originate from solute-solvent competition, which interacts with the stationary phase, as well as from the "relative solubility" of solutes in the stationary and mobile phases.

Interaction of soman with beta-cyclodextrin

Of the following neurotoxic agents, pinacolyl methylphosphonofluoridate (soman), isopropyl methylphosphonofluoridate (sarin) and ethyl N,N-dimethylphosphoramidocyanidate (tabun), only soman was inactivated appreciably at pH 7.40 by beta-cyclodextrin. The interaction of soman, a mixture of four stereoisomers designated as C(+)P(-), C(-)P(-), C(+)P(+), and C(-)P(+), with cyclodextrins was revealed by methods based on the irreversible inhibition of acetylcholinesterase (AChE) that is phosphonylated chiefly by P(-)-isomers of racemic soman and continuous titration of fluoride ions released by soman using a fluoride-specific electrode. Soman and beta-cyclodextrin form a 1:1 complex. At pH 7.40 and 25 degrees C the dissociation constant Kd of this complex and the rate constant k2 of cleavage of soman by beta-cyclodextrin are (0.53 +/- 0.05) mM and (5.9 +/- 0.6) X 10(-2) min-1, respectively. The rate constant k2 max for the cleavage of soman by monoionized beta-cyclodextrin has a value of 2.8 X 10(3) min-1 and the second order rate constant k2 max/kd is 5.3 X 10(6) M-1 min-1. Consequently, soman is hydrolyzed about 2500 times faster by the monoanion of beta-cyclodextrin, than by the hydroxide ion. The cleavage of P(-)-soman by beta-cyclodextrin as estimated by AChE inhibition proceeds apparently at the same rate for the C(-)P(-)-and C(+)P(-)-isomers. However, the release of fluoride ions indicated a stereospecific rate of reaction, the P(-)-isomers reacting faster than the P(+)-isomers. At pH 7.40, the inactivation rate of soman by beta-cyclodextrin was as fast in human plasma in vitro as in Tris buffer. This interaction between soman and beta-cyclodextrin, and other data from the literature, suggests that the introduction of catalytic or noncatalytic groups on beta-cyclodextrin might possibly make it a better catalyst for soman inactivation through improvement in the catalytic or in the binding process.

Inhibition of experimental pulmonary metastasis in mice by beta-cyclodextrin-benzaldehyde

The effect of beta-cyclodextrin-benzaldehyde (CDBA) on experimental pulmonary metastasis in C3H/He mice was examined. In an in vitro assay, the growth of RCT(+) cells was inhibited by 1200 micrograms/ml CDBA using unrenewed media, and by 600 micrograms/ml CDBA in that using daily renewed media. When mice were treated daily with CDBA, 3 weeks later the number of lung nodules developing after i.v. injection of 1 X 10(6) RCT(+) cells was significantly decreased in a dose-dependent manner, i.e., 73.8%, 85.6%, and 95.7% inhibition was observed following 0.5, 5, and 25 mg CDBA/mouse per day p.o. administration, respectively. The same mice showed almost as much natural killer (NK) activity as normal mice. Therefore, experiments were designed to evaluate the effect of CDBA on the NK activity of tumor-free mice whose immunity had been suppressed by 5-fluorouracil (5FU). Injections of 5FU only suppressed this activity to about 50% of normal mice, but the combined treatment with CDBA negated the suppressive effect of 5FU on NK activity. The results suggested that the inhibition of experimental pulmonary metastasis might be induced by the possible combined effects of CDBA; that is, the direct inhibition of tumors and the augmentation of NK cell activity.

Normal-phase high-performance liquid chromatographic separations of positional isomers of substituted benzoic acids with amine and beta-cyclodextrin bonded-phase columns

The separation of positional isomers of several substituted benzoic acids was studied using two different columns, i.e. amine and beta-cyclodextrin bonded silicas, at appropriate normal-phase conditions. Although some other columns do separate substituted benzoic acids, particularly the octadecylsilica column in a reversed-phase mode, the present separation under simple normal-phase, isocratic conditions is unique. In particular, the retention order of these acids for the amino bonded-phase column can be roughly predicted using the pKa values of the analytes. On the other hand, due to the strong interaction between substituted benzoic acids and the beta-cyclodextrin bonded phase, a small amount of acetic acid has to be added into the mobile phase to overcome band broadening and tailing problems. Possible retention mechanisms are also discussed.

Comparison of blood-free medium (cyclodextrin solid medium) with Bordet-Gengou medium for clinical isolation of Bordetella pertussis

Cyclodextrin solid medium (CSM) developed by us was evaluated to be a suitable synthetic medium for the clinical isolation of Bordetella pertussis when compared with Bordet-Gengou (BG) medium. The addition of 5 micrograms of cephalexin (CEX) per ml to CSM not only supported the good growth of B. pertussis but also sufficiently suppressed the growth of nasopharyngeal flora. During period 1 of this study, nasopharyngeal specimens from 60 patients with clinical pertussis were inoculated on CSM supplemented with 5 micrograms of CEX per ml. The isolation rate was 70% (42 of 60). To confirm the efficacy of CSM, another study was performed. During period 2 of this study, nasopharyngeal specimens were cultured on both CSM and BG medium, each with 5 micrograms of CEX per ml. The comparative isolation rates were 100% (40 of 40 specimens from 29 patients) on CSM with 5 micrograms of CEX and 65% (26 out of 40) on BG medium with 5 micrograms of CEX. The excellent efficacy of CSM as measured by the isolation rate was thought to be due to the poor nutrition of this medium for the growth of nasopharyngeal bacteria. CSM retained its efficacy in clinical isolations even after 3 months of storage in a refrigerator. These data led us to conclude that CSM with 5 micrograms of CEX was much better than BG medium with 5 micrograms of CEX, determined by both the isolation rate and preservativity considerations, and that CSM with 5 micrograms of CEX per ml can be successfully used instead of BG medium as a medium for the clinical isolation of B. pertussis.

Separation of drug stereoisomers by the formation of beta-cyclodextrin inclusion complexes

For many drugs, only racemic mixtures are available for clinical use. Because different stereoisomers of drugs often cause different physiological responses, the use of pure isomers could elicit more exact therapeutic effects. Differential complexation of a variety of drug stereoisomers by immobilized beta-cyclodextrin was investigated. Chiral recognition and racemic resolution were observed with a number of compounds from such clinically useful classes as beta-blockers, calcium-channel blockers, sedative hypnotics, antihistamines, anticonvulsants, diuretics, and synthetic opiates. Separation of the diastereomers of the cardioactive and antimalarial cinchona alkaloids and of two antiestrogens was demonstrated as well. Three dimensional projections of beta-cyclodextrin complexes of propanolol, which is resolved by this technique, and warfarin, which is not, are compared. These studies have improved the understanding and application of the chiral interactions of beta-cyclodextrin, and they have demonstrated a means to measure optical purity and to isolate or produce pure enantiomers of drugs. In addition, this highly specific technique could also be used in the pharmacological evaluation of enantiomeric drugs.

Coupled beta-cyclodextrin and reverse-phase high-performance liquid chromatography for assessing biphenyl hydroxylase activity in hepatic 9000g supernatant

Coupled beta-cyclodextrin bonded-phase and reverse-phase high-performance liquid chromatography with fluorescence detection has been employed to detect the major hydroxylated metabolites of biphenyl following in vitro incubation with hepatic 9000g supernatant. The method requires only 0.3 mg of protein and its sensitivity was as low as 0.36 nmol metabolite formed/mg protein/h (0.32 pmol injected) for 2-, 3-, and 4-hydroxybiphenyl. Microsomes need not be purified and no organic extraction or derivatization was required. The method was employed successfully with samples from rats and mice treated with Aroclor, beta-naphthoflavone, or phenobarbital; from monkeys dosed with Aroclor; and from untreated dogs.

Enhancement of bioavailability of cinnarizine from its beta-cyclodextrin complex on oral administration with DL-phenylalanine as a competing agent

The present investigation is concerned with an improvement of the bioavailability of cinnarizine by administering its beta-cyclodextrin complex together with another compound which competes with the beta-cyclodextrin molecule in complex formation in aqueous solution (competing agent). The bioavailability of cinnarizine on oral administration of the cinnarizine-beta-cyclodextrin inclusion complex was enhanced by the simultaneous administration of DL-phenylalanine as a competing agent, e.g., the AUC was 1.9 and 2.7 times as large as those of the cinnarizine-beta-cyclodextrin complex alone and cinnarizine alone, respectively. The enhancement of AUC and Cmax completely depended on the dose of DL-phenylalanine. It was found from these results that DL-phenylalanine acted as a competing agent in the GI tract and the minimum effective dose required of DL-phenylalanine might be 1 g for 50 mg of cinnarizine in the cinnarizine-beta-cyclodextrin complex. Evaluating the competing effect of DL-phenylalanine in vitro using an absorption simulator, it was found that the decreased penetration rate of cinnarizine through the artificial lipid barrier with addition of beta-cyclodextrin was restored with the addition of DL-phenylalanine.

Liquid chromatographic retention behavior of organometallic compounds and ligands with amine-, octadecylsilica- and beta-cyclodextrin-bonded phase columns

Effects of solvent composition and ligand variation on the retention of organometallic compounds have been studied using an amino, an octadecylsilica (ODS) and a beta-cyclodextrin (beta-CD) bonded phase column in either a normal-phase or a reversed-phase mode. The retention behavior for the organometallic compounds with the amino column can be rationalized using the displacement model. The "apparent" molecular areas are greater for compounds capable of strong hydrogen bonding. The retention in the ODS column roughly follows an argument based on the expected solubility behavior while mixed retention mechanisms are involved for the solubility behavior while mixed retention mechanisms are involved for the beta-CD column, i.e. both inclusion process and solubility or solvophobic interactions are possibly operative.

Improvement of dissolution and suppository release characteristics of flurbiprofen by inclusion complexation with heptakis(2,6-di-O-methyl)-beta-cyclodextrin

The inclusion behavior of methylated beta-cyclodextrins, heptakis(2,6-di-O-methyl)-beta-cyclodextrin and heptakis-(2,3,6-tri-O-methyl)-beta-cyclodextrin in solution and the solid state was compared with that of natural beta-cyclodextrin using an anti-inflammatory drug, flurbiprofen, as a guest molecule. Stability constants were determined by the solubility method at various temperatures, and the thermodynamic parameters were calculated for inclusion complex formation in aqueous solution. The solid complexes were obtained in a molar ratio of 1:1, and their dissolution behavior and release from suppository bases were examined. The data suggest that the inclusion mode of the complex with 3 is somewhat different from that of the complexes with 1 and 2. From a practical point of view, 2 seems to be particularly useful for improving the pharmaceutical properties of flurbiprofen in various dosage forms.

Suppositories containing cyclodextrin complexes. Part 2: Dissolution and absorption studies

The dissolution and absorption of poorly water-soluble drugs from rectal suppositories can be enhanced by complexing these substances (e.g., essential oils, indomethacin) with beta-cyclodextrin. Preliminary in vivo studies showed, that the application of cyclodextrin complexes to suppositories, the same as to oral applications, resulted in an increased blood level.

Microanalyses of beta-cyclodextrin in plasma by high-performance liquid chromatography

Procedures for the micro-determination of beta-cyclodextrin (beta-CyD) in plasma were investigated by four methods using high-performance liquid chromatography (HPLC). In methods A and B, underivatized beta-CyD was detected with a refractive index detector and determined by the absolute calibration graph method. An NH2-bonded silica/acetonitrile-water system was used in A and a C18-bonded silica/methanol-water system in B. In method C, the percarbanilate of beta-CyD was separated on a C8-bonded silica column with acetonitrile-water and determined using gamma-CyD as the internal standard with a UV detector at 231 nm. In method D, the per[1-14C]acetate of beta-CyD was fractionated on a silica column with n-hexane-ethanol containing 1% of water and the radioactivity of each fraction was measured with a liquid scintillation counter. gamma-CyD was used as the internal standard. Interfering plasma proteins were removed by centrifugal ultrafiltration with an MPS-1 micro-partition system. Method B was superior to the other methods with respect to ease of sample preparation, sensitivity and time required for analysis. The cumulative amount of beta-CyD in the mesenteric vein absorbed from the rat intestinal lumen after administration of phenobarbital-beta-CyD complex in a closed loop method was determined by the use of method B.

Effects of adjuvants to local anaesthetics on their duration. II. Studies of some substituted dextrans and other macromolecules in rat infraorbital nerve block

The effects of adding various macromolecular substances to 2% prilocaine on duration of rat infraorbital nerve block were investigated. The tested substances consisted of dextrans with lipophilic or charged substituents as well as other neutral or highly charged macromolecules. Most of the adjuvants caused significant prolongations of sensory block. For substituted dextrans the duration of sensory block degree 3 amounted to between 120% (3% capryldextran II) and 350% (3% carboxymethyldextran) in comparison to prilocaine plain. The corresponding values for hydroxypropylstarch (3%) alginic acid (0.5%), beta-cyclodextrin (1.5%) and hyaluronic acid (0.25%) were about 170%, 285% and 380%, respectively. The results suggest that the increased duration of local analgesia by prilocaine is related to increased viscosity of the solution produced by the macromolecular compounds. The mechanism seems to be of a physical character, and hyaluronic acid seems to be worthy of further studies.

Quantitative structure-stability relationships among inclusion complexes of cyclodextrins. I: Barbituric acid derivatives

Quantitative structure-stability relationships (QSSRs) are formulated for the inclusion complexation of 17 barbituric acid derivatives with alpha- and beta-cyclodextrin. The variation in the complex stability constants K alpha and K beta is found to be partly accounted for by the molar refractivity or the hydrophobicity of the substituent R1 at position 5 of the barbiturate ring. In addition, K alpha also depends upon whether or not R1 is branching or cyclic, and K beta also depends upon whether the guest molecule is a barbiturate or a thiobarbiturate. The results suggest that in alpha-cyclodextrin-barbiturate complexes the cyclodextrin cavity includes only R1, while in beta-cyclodextrin complexes both R1 and (part of) the barbiturate ring are included. This complexation model is compared with those proposed by other authors.