Dipeptide Uptake and Transport Characteristics in Rabbit Tracheal Epithelial Cell Layers Cultured at an Air Interface

Purpose. To determine the functional presence of a H⁺/peptide cotransport process in rabbit tracheal epithelial cell layers cultured at an air-interface and its contribution to transepithelial dipeptide transport. Methods. Rabbit tracheocytes were isolated, plated on Transwells, and cultured at an air-interface. After 5 or 6 days in culture, uptake and transepithelial transport of carnosine were examined. Results. Carnosine uptake by tracheocytes was pH-dependent and was saturable with a Michaelis-Menten constant of 170 M. Moreover, carnosine uptake was inhibited 94% by Gly-L-Phe, 28% by (-Ala-Gly, but not at all by Gly-D-Phe or by the amino acids -Ala and L-His. Unexpectedly, transepithelial carnosine transport at pH 7.4 (i.e., in the absence of a transepithelial pH gradient) was similar in both the apical-to-basolateral (ab) and basolateral-to-apical (ba) directions. Lowering the apical fluid pH to 6.5 reduced abtransport 1.6 times without affecting ba transport, consistent with predominantly paracellular diffusion of carnosine under an electrochemical potential gradient. Conclusions. The kinetic behavior of carnosine uptake into cultured tracheal epithelial cell layers is characteristic of a H⁺-coupled dipeptide transport process known to exist in the small intestine and the kidney. Such a process does not appear to be rate-limiting in the transport of carnosine across the tracheal epithelial barrier.     

β2-Adrenergic Receptor Genotype-Related Changes in cAMP Levels in Peripheral Blood Mononuclear Cells After Multiple-Dose Oral Procaterol

Purpose. To evaluate the ₂-adrenergic receptor (₂AR) genotype frequency in the Japanese population and the relationship between ₂AR genotype at amino acid position 16 (₂AR-16) and desensitization to ₂-agonist ex vivo. Methods. The ₂AR genotypes at amino acid positions 16, 27, and 164 of 92 healthy Japanese subjects were determined by polymerase chain reaction-restriction fragment-length polymorphism. The relationship between the ₂AR-16 genotype and the desensitization to ₂-agonist was examined in 10 male subjects ex vivo. Procaterol tablet (HCl salt, 50g, Meptin®) was given orally for 5 days, and peripheral blood was obtained before and after 5 days of consecutive medications followed by the assessment of the intracellular cAMP levels in peripheral blood mononuclear cells after incubation with or without procaterol hydrochloride (0-1000 ng/mL). Results. Allele frequency was Arg16:Gly16 = 46%:54%, Gln27:Glu27 = 92%:8%, and Thr164:Ile164 = 100%:0%, respectively. The cAMP levels were increased by incubation with procaterol hydrochloride, and the increase was suppressed after 5 days of consecutive medications. The suppression was more significant in the homozygote for Gly16 than the homozygote for Arg16. Conclusions. The desensitization to ₂-agonist was associated more frequently with the mutation at ₂AR-16 (Gly16).     

Controlled Systemic Absorption and Increased Anesthetic Effect of Bupivacaine Following Epidural Administration of Bupivacaine-Hydroxypropyl-β-Cyclodextrin Complex

Purpose. To investigate the influence of complexation between bupivacaine and hydroxypropyl--cyclodextrin (HP--CD) on the systemic absorption and on the pharmacodynamic effect of bupivacaine following epidural administration in a rabbit model. Methods. Bupivacaine and bupivacaine-HP--CD complex were administered according to a randomized and cross-over design in six rabbits chronically instrumented with an epidural catheter. The plasma concentrations of bupivacaine and the duration and intensity of the motor blockade were evaluated. Results. Complexation with HP--CD led to a decrease in the maximum plasma concentration of bupivacaine. Individual absorption kinetics evaluated by Loo-Riegelman absorption analysis indicated that systemic absorption resulted from two parallel first-order processes. Only the faster absorption phase was slowed by complexation with HP--CD. The duration of the motor blockade was increased almost twice but the intensity was not modified. Conclusions. Complexation with HP--CD could be a promising drug delivery system to improve the therapeutic index of bupivacaine.     

Enantioseparation of Flobufen with Cyclodextrins Studied by Capillary Electrophoresis and NMR

Purpose. The aim of this study was to obtain the resolution of flobufen enantiomers, an antiinflammatory active substance, by capillary electrophoresis with cyclodextrins. The mechanism of com- plexation and determination of the stoichiometry of the complexes were studied by NMR and the analytical method was developed and validated. Methods. Zone capillary electrophoresis coupled to direct ultraviolet detection was selected. The interaction between flobufen and the chiral selector was studied by NMR. Optimization of the separation was performed using a Box-Wilson Central Composite Design for three factors related to the composition of the electrolyte. Results. Heptakis (2,3,6-tri-O-methyl)--cyclodextrin (TM--CD) was found to be the most efficient selector via the formation of a 1:1 complex proved by NMR. Constants of complexation of flobufen enantiomers were determined by NMR and capillary electrophoresis. Optimal values for the critical factors of the analytical system were: pH (5.50), content in methanol (10% v/v), and TM--CD (30 mM). The ability of capillary electrophoresis to quantify as low as 0.1% (w/w) of R in S-flobufen or vice-versa was established. Conclusions. Capillary electrophoresis was shown to be a valuable method to control the enantiocomposition of flobufen by use of a chiral selector whose interactions with the analytes could be explored by NMR.     

Drug Delivery Studies in Caco-2 Monolayers. IV. Absorption Enhancer Effects of Cyclodextrins

Purpose. The purpose of the present study was to use the human colorectal carcinoma cell line, Caco-2, as a human intestinal epithelial model for studying the effects of cyclodextrins as absorption enhancers. Methods. Cyclodextrins of varying sizes and physico-chemical characters were investigated. The effects of the cyclodextrins were evaluated by means of staining of the cytoplasma and determination of the mitochondrial dehydrogenase activity as well as by transport enhancement of the macromolecular pore marker polyethylene glycol 4000 (PEG-4000) across the Caco-2 monolayers. Results. The transport enhancing properties of the cyclodextrins were found to follow the lipophilicity of the core in their cyclic structure. Dimethyl--cyclodextrin was the most powerful in all aspects and caused an increase in the permeability of the cytoplasma membrane in a concentration dependent manner. It was possible to increase the overall transport of PEG-4000 10-fold by the use of dimethyl--cyclodextrin in low concentrations where the toxic effects on the monolayers were insignificant. It was further observed that the basolateral membrane was significantly more sensitive to cyclodextrins than the apical membrane. Conclusions. Since dimethyl--cyclodextrin was able to produce an absorption enhancing effect on PEG-4000 in concentrations where the toxic effects on Caco-2 monolayers were low it is worth to pursue the compound as an absorption enhancer.     

Design and Evaluation of an Osmotic Pump Tablet (OPT) for Chlorpromazine Using (SBE)7m-β-CD

Purpose. The purpose of this study was to develop a controlled-porosity osmotic pump tablet (OPT) which exhibits pH-independent release profiles for a basic drug using a sulfobutyl ether--cyclodextrin, (SBE)_7m--CD, which acts as both a solubilizer and as an osmotic agent. Methods. Chlorpromazine free base (CLP) was chosen as a model drug for this study. The release of CLP from osmotic pump tablets was studied in vitro. In vivo absorption of CLP from the OPT was evaluated in male beagle dogs. Results. The CLP release profile from an OPT prepared from a core tablet composed of a 1:10 molar ratio of CLP to (SBE)_7m--CD was pH-independent, and was controlled by modulating the membrane thickness of the OPT. Another cyclodextrin, hydroxypropyl--cyclodextrin (HP--CD), and a sugar mixture of lactose and fructose resulted in pH-dependent release at the same molar ratio. An in vivo absorption study in dogs with an OPT containing (SBE)_7m--CD correlated very well with the in vitro release profiles using the Japanese Pharmacopoeia dissolution method. Conclusions. In addition to serving as a solubilizer and osmotic agent, (SBE)_7m--CD can also serve as the controlling agent for pH independent release of CLP from OPTs. This system successfully modified the in vivo input rate of CLP without compromising oral bioavailability.     

Viscoelasticity of Anionic Polymers and Their Mucociliary Transport on the Frog Palate

The influence of formulation variables on the rheology of polyanionic formulations and the relationships between viscoelastic properties and mucociliary transport rate were investigated. Polymeric samples were oscillated from 0.001 to 5 Hz using either a "cone and plate or a "coaxial cylinder measuring system. The mucociliary transport rates of polymeric samples were determined and compared movement of charcoal powder on the frog palate. For the linear polymeric solutions, sodium carboxymethylcellulose and sodium alginate, the elastic modulus (G) increased with increasing amplitudes during frequency scan. However, the G or viscous modulus (G) of partially cross-linked polyacrylic acid (cPAA) samples did not change significantly under oscillation. Both G and G of cPAA samples were significantly influenced by the amount of salt present in the formulation. The rheology of 2% (w/w) cPAA in 90:10 (w/w) propylene glycol:alcohol changed from a viscous fluid to a coarse suspension after neutralization. The pH increased gradually when the nonaqueous formulation reacted with water and the maximum dynamic moduli were obtained after incorporating 20% (w/w) water in the formulation. A negative correlation was found between the G of linear polyanionic samples and the relative transport rate. However, the lowest mucociliary transport rate was observed when the loss tangent (G/G) was around 0.4–0.5.     

Delivery of Nasal Powders of β-Cyclodextrin by Insufflation

Purpose. Delivery of nasal powders of granulated -cyclodextrin by insufflation was studied in order to find the relationship between powder properties and delivery behavior. Methods. Three nasal powder formulations, prepared by granulating -cyclodextrin with different binders, were delivered from a powder insufflation device, in which the dose to be emitted was loaded in a gelatin capsule. The delivery sequence of powder was recorded and characterized using an image analysis program. Results. Particle size was the main parameter affecting nasal powder delivery, both as to the amount of dose sprayed and the aspect of cloud produced. Between 50–150 µm of particle size a substantial change in delivery behavior of powders was observed. Powder of around 100 µm in size showed useful insufflation characteristics for nasal delivery. Bioavailability of nasal formulations of progesterone/-cyclodextrin powders was discussed in term of delivery behavior. Conclusions. The formulation approaches for improving nasal delivery of powders require the use of size optimized carriers. Insufflation of powders over 50 µm can favour the particle deposition by impaction, whereas for powders below 50 µm, deposition by sedimentation is moved. -cyclodextrin is a suitable carrier for achieving high systemic availability following nasal administration of powder formulations.     

Enhancement of the Antiinflammatory Effect of Ethyl 4-Biphenylyl Acetate in Ointment by β-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 -cyclodextrin (-CyD), heptakis(2,6-di-O-methyl)--cyclodextrin (DM--CyD), and 2-hydroxypropyl--cyclodextrin (HP--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 -CyD < DM--CyD HP--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 -CyD < DM--CyD < HP--CyD. HP--CyD may be a particularly useful cyclodextrin derivative since it improves the topical availability and does not irritate tissues.     

Efficacy,Safety and Mechanism of Cyclodextrins as Absorption Enhancers in Nasal Delivery of Peptide and Protein Drugs

Abstract

Cyclodextrins are used in nasal drug delivery as absorption enhancing compounds to increase the intranasal bioavailability of peptide and protein drugs. The most effective cyclodextrins in animal experiments are the methylated derivatives, dimethyl-β-cyclo-dextrin and randomly methylated β-cyclodextrin, which are active at low concentrations ranging between 2% and 5%. However, large species differences between rats, rabbits and humans exist for the nasal absorption enhancement by cyclodextrins.

Based on toxicological studies of the local effects of cyclodextrins on the nasal mucosa dimethyl-β-cyclodextrin and randomly methylated β-cyclodextrin are considered safe nasal absorption enhancers. Their effects were quite similar to controls (physiological saline), but smaller than those of the preservative benzalkonium chloride in histological and ciliary beat frequency studies. In these studies, and in a study of the release of marker compounds after nasal administration, methylated β-cyclodextrins were less toxic than sodium glycocholate, sodium taurodihydrofusidate, laureth-9 and L-α-phosphatidylcholine. Systemic toxicity after nasal cyclodextrin administration is not expected, because very low doses of cyclodextrins are administered and only very small amounts are absorbed.

The mechanism of action of cyclodextrins may be explained by their interaction with the nasal epithelial membranes and their ability to transiently open tight junctions.     

Enhancement of Solubility and Bioavailability of β-Lapachone Using Cyclodextrin Inclusion Complexes

Purpose. To explore the use of cyclodextrins (CD) to form inclusion complexes with -lapachone (-lap) to overcome solubility and bioavailability problems previously noted with this drug. Methods. Inclusion complexes between -lap and four cyclodextrins (-, -, -, and HP-CD) in aqueous solution were investigated by phase solubility studies, fluorescence, and ¹H-NMR spectroscopy. Biologic activity and bioavailability of -lap inclusion complexes were investigated by in vitro cytotoxicity studies with MCF-7 cells and by in vivo lethality studies with C57Blk/6 mice (18-20 g). Results. Phase solubility studies showed that -lap solubility increased in a linear fashion as a function of -, -, or HP-CD concentrations but not -CD. Maximum solubility of -lap was achieved at 16.0 mg/ml or 66.0 mM with HP-CD. Fluorescence and ¹H-NMR spectroscopy proved the formation of 1:1 inclusion complexes between -CD and HP-CD with -lap. Cytotoxicity assays with MCF-7 cells showed similar biologic activities of -lap in -CD or HP-CD inclusion complexes (TD₅₀ = 2.1 M). Animal studies in mice showed that the LD₅₀ value of -lap in an HP-CD inclusion complex is between 50 and 60 mg/kg. Conclusions. Complexation of -lap with HP-CD offers a major improvement in drug solubility and bioavailability.     

Effects of Absorption Enhancers on Rat Nasal Epithelium in Vivo: Release of Marker Compounds in the Nasal Cavity

Purpose. The assessment of the effects of nasal absorption enhancers on the rat nasal epithelium and membrane permeability in vivo after a single nasal dose of the enhancers. Methods. The release of marker compounds (protein, cholesterol and acid phosphatase) from the nasal epithelium was measured using a lavage technique. The nasal membrane permeability was determined after intravenous administration of a systemic tracer (FITC-albumin). Results. The effects of the absorption enhancers could be classified into four categories. The first consisted of HPCD (5%), DMCD (2%) and RAMEB (2%) and was not different from the control (physiological saline). For the second category, DMCD (5%), effects were significantly higher than for the control. The third category, SGC (1%), was more active than DMCD (5%) but less active than the last group. The fourth, most membrane damaging, category consisted of STDHF (1%), laureth-9 (1%) and LPC (1%). Administration of these three enhancers also resulted in release of acid phosphatase, indicating that severe membrane damage occurred. The release of cholesterol from nasal epithelium was largely dependent on the cholesterol solubilisation of the absorption enhancers. The amount of cholesterol released by laureth-9 and LPC was the largest. Conclusions. The results of this in vivo study are in agreement (i.e. similarity in rank order) with morphological and ciliotoxicity studies of nasal absorption enhancers, demonstrating that this in vivo model is a valuable tool to classify nasal absorption enhancers according to their effects on the rat nasal epithelium.     

Application of Supercritical Carbon Dioxide for the Preparation of a Piroxicam-β-Cyclodextrin Inclusion Compound

Purpose. Piroxicam is a poorly soluble NSAID, whose solubility is enhanced when included into -cyclodextrin. The preparation of a piroxicam--cyclodextrin inclusion compound using supercritical CO₂ was investigated. Methods. The solubility and the stability of piroxicam in supercritical CO₂ were determined. Then, the influence of the temperature, the pressure and the time of exposure on the inclusion rate was studied. Results. The solubility of piroxicam varied over a wide range depending on the temperature and pressure (from 0.006 to 1.500 mg/g of CO₂). The temperature and the time of exposure had a great influence on the inclusion yield, while pressure did not and a complete inclusion was achieved by keeping a physical mixture of piroxicam and -cyclodextrin (1:2.5 mol/mol) for 6 hours at 150°C and 15 MPa of CO₂. This complex was characterized by Differential Scanning Calorimetry, differential solubility and Fourier Transform Infrared Spectrometry. Conclusions. Supercritical carbon dioxide may prove to be a novel useful complexation method of drugs into -cyclodextrin.     

Plasma insulin levels and β-adrenoceptor antagonists

Summary The effect of -adrenoceptor antagonists on the intravenous glucose tolerance test was investigated in conscious dogs. dl-Celiprolol (cardioselective with ISA=intrinsic sympathomimetic activity) 200 and 1000 g/kg i.v., dl-metoprolol (cardio-selective without ISA) 200 and 1000 g/kg i.v., dl-pindolol (non-selective with ISA) 5 and 25 g i.v. and l-bupranolol (non-selective without ISA) 10 and 50 g/kg i.v. were used in the study. The influence of -adrenoceptor antagonists on the plasma glucose and immunoreactive insulin following the intravenous glucose tolerance test were evaluated by calculating the respective areas under the plasma curve.The present investigtion clearly demonstrates the marked difference between the various -adrenoceptor antagonists on heart rate and, especially on metabolic parameters. dl-Metoprolol, a -adrenoceptor antagonist with cardioselectivity and without ISA can be assumed not to alter plasma insulin level and glucose assimilation. l-Bupranolol, a non-selective -adrenoceptor antagonist without ISA reduces plasma insulin level and probably enhances peripheral glucose uptake, resulting in an unchanged glucose tolerance. dl-Celiprolol or dl-pindolol, -adrenoceptor antagonists with ISA, but cardioselective or non-selective enhance both, basal insulin level and insulin level after glucose stimulation but must be assumed to decrease peripheral glucose uptake since here too glucose tolerance was unchanged.     

In Vitro Evaluation of Microparticles and Polymer Gels for Use as Nasal Platforms for Protein Delivery

Purpose. Nasal delivery of protein therapeutics can be compromised by the brief residence time at this mucosal surface. Some bioadhesive polymers have been suggested to extend residence time and improve protein uptake across the nasal mucosa. We examined several potential polymer platforms for their in vitro protein release, relative bioadhesive properties and induction of cytokine release from respiratory epithelium. Methods. Starch, alginate, chitosan or Carbopol^® microparticles, containing the test protein bovine serum albumin (BSA), were prepared by spray-drying and characterized by laser diffraction and scanning electron microscopy. An open-membrane system was used to determine protein release profiles and confluent, polarized Calu-3 cell sheets were used to evaluate relative bioadhesion, enhancement of protein transport and induction of cytokine release in vitro. Results. All spray-dried microparticles averaged 2–4 m in diameter. Loaded BSA was not covalently aggregated or degraded. Starch and alginate microparticles released protein more rapidly but were less adhesive to polarized Calu-3 cells than chitosan and Carbopol^® microparticles. Protein transport across polarized Calu-3 cells was enhanced from Carbopol^® gels and chitosan microparticles. A mixture of chitosan microparticles with lysophosphatidylcholine increased protein transport further. Microparticles prepared from either chitosan or starch microparticles, applied apically, induced the basolateral release of IL-6 and IL-8 from polarized Calu-3 cells. Release of other cytokines, such as IL-l, TNF-, GM-CSF and TGF-, were not affected by an apical exposure to polymer formulations. Conclusions. We have described two systems for the in vitro assessment of potential nasal platforms for protein delivery. Based upon these assessments, Carbopol^® gels and chitosan microparticles provided the most desirable characteristics for protein therapeutic and protein antigen delivery, respectively, of the formulations examined.     

Evaluation of P2-purinoceptor antagonists at two relaxation-mediating P2-purinoceptors in guinea-pig taenia coli

The guinea-pig taenia coli possesses two relaxation-mediating receptors for nucleotides: a prototypic P_2Y-purinoceptor, which is activated by adenosine 5-O-(2-thiodiphosphate) (ADPßS), and a separate receptor for ,-methylene ATP (,-MeATP). Effects of several as yet incompletely characterized P₂-purinoceptor antagonists at these receptors were examined.The concentration-relaxation curve of ADPßS was shifted to the right by reactive blue 2, suramin, 8-(3,5-dinitro-phenylenecarbonylimino)-1,3,5-naphthalenetrisulphonic acid (XAMR0721; at 1000 M only), pyridoxalphosphate-6-azophenyl-2,5-disulphonic acid (iso-PPADS), pyridoxal 5-phosphate, trypan blue and Evans blue (at 320 M only). Schild plots for the antagonism of reactive blue 2, suramin, iso-PPADS and pyridoxal 5-phosphate against ADPßS had slopes <1. The concentration-relaxation curve of ,-MeATP was shifted to the right by reactive blue 2, suramin, XAMR0721, iso-PPADS, pyridoxal 5-phosphate and trypan blue but not by Evans blue (320 M). Schild plots for the antagonism of suramin, XAMR0721 and iso-PPADS against ,-MeATP had slopes >1. Only XAMR0721 differed clearly in potency against the two nucleotides: it was considerably more potent against ,-MeATP than against ADPßS. 2-Methylthio ATP (MeSATP; 1 M) and ATP (100 M) were degraded by pieces of taenia coli. All antagonists except trypan blue attenuated the degradation of either or one of the two nucleotides.The selective effect of XAMR0721 against ,-MeATP confirms the existence of two relaxation-mediating P₂-purinoceptors in guinea-pig taenia coli. Comparison of the apparent affinities of the antagonists for the two taenia coli receptors with affinities for the P_2X-purinoceptor of the rat vas deferens shows that reactive blue 2, suramin, iso-PPADS, pyridoxal 5-phosphate and trypan blue have little selectivity for any of the three receptors. XAMR0721, which has been shown to possess relatively high affinity for the P_2Y-purinoceptor in turkey erythrocytes, was very weak at the P_2Y-receptor of the taenia, thus supporting the existence of pharmacologic P_2Y-receptor subtypes. Evans blue, with little effect in the taenia coli but a marked effect in the rat vas deferens, is the most selective P_2X-(versus P_2Y-) purinoceptor antagonist presently known, although its effect on the degradation of nucleotides must be kept in mind.     

Synthesis and Cytotoxic Evaluation of a Series of γ-Substituted γ-Aryloxymethyl-α-methylene-γ-butyrolactones Against Cancer Cells

Purpose. The main objective of this investigation was to explore thecytotoxic structure-activity relationships of -substituted -aryloxymethyl--methylene--butyrolactones against cancer cells. Methods. The target compounds were synthesized in two stepscommencing with aryl-OH which was treated with a bromomethyl ketonefollowed by the Reformatsky-type condensation. Results. Seven types of -methylene--butyrolactones were evaluatedin vitro against 60 human cancer cell lines derived from nine cancercell types. The average values of log G₅₀ indicated that for thearylportion, potencies of these -methylene--butyrolactones are in adecreasing order of quinolin-2(1H)-one (or 2-hydroxyquinoline, 21,–5.89) > quinoline (19, –5.79) > 2-methylquinoline (20, –5.69)> 8-hydroxyquinoline (17, –5.64) > 2-naphthalene (16, –5.59)> benzene (15, –4.90). The same order was obtained for both log TGIand log LC₅₀. However, for the -substituent, the potencies are in adecreasing order of biphenyl (16f–21f) > phenyl and4-substituted phenyl (16b-e–21b-e) > methyl (16a–21a). Conclusions. Unlike cardiovascular activities of -methylene--butyrolactones in which a -methyl substituent is necessary for vasorelaxingeffect while a phenyl or a halogen-substituted phenyl is prefer for theantiplatelet activities, a -biphenyl substituent proved to be the bestfor their cytotoxicities against various cancer cell lines tested.     

Die Reduktion von Oestron zu Oestradiol-17β durch das Glucose-6-phosphat-Dehydrogenasesystem

Zusammenfassung In Fortsetzung einer früheren Untersuchung wird in der vorliegenden Mitteilung nachgewiesen, daß das Glucose-6-phosphat-Dehydrogenasesystem von roten Blutzellen und Hefezellen zusammen mit einem noch unbekannten Wasserstoffüberträger Oestron zu Oestradiol-17 zu reduzieren vermag. Das Fermentsystem wird durch Oestron und Oestradiol-17 geringfügig in seiner Aktivität gehemmt.Mit 1 Textabbildung.Herrn Prof. P. Wels zum 65. Geburtstag gewidmet.     

The Transport Barrier of Epithelia: A Comparative Study on Membrane Permeability and Charge Selectivity in the Rabbit

The transport barrier of the epithelia presents one of the major problems limiting the effective use of these tissues as alternate delivery routes for macromolecules such as peptides and proteins. In the present study, two membrane transport properties, namely, the permeability and permselectivity of the shunt pathway, were investigated and compared in various tissues including the nasal, tracheal, bronchial, buccal, rectal, vaginal, corneal, epidermal, duodenal, jejunal, ileal, and colonic epithelia. Membrane permeability was evaluated using a combined method based on electrical conductance and flux measurements of a hydrophilic fluorescent probe, 6-carboxy fluorescein (CF). Membrane permselectivity or the charge discriminating ability of the membrane was evaluated by KCl diffusion potential measurements. The results indicate that all epithelia under investigation possess a relatively high degree of permeation barrier and are highly selective for the absorption of positively charged solutes. Shunt path permeability was found to vary greatly among tissues from different epithelia, whereas membrane charge selectivity was relatively constant in these tissues. A good correlation was observed between membrane electrical conductance and steady-state flux of CF, indicating a paracellular transport of the compound. The rank order of the intrinsic membrane permeability was as follows: intestinal nasal bronchial tracheal > vaginal rectal > corneal > buccal > skin. Membrane permselectivity, expressed as the ratio of transport number (positive over negative), ranges from 1.78 for the buccal to 1.33 for the rectal epithelium. These results suggest that, for effective delivery purposes, permeation enhancing methods, by either increasing tissue permeability or modifying drug-membrane charge selectivity, are generally required. The permeation data also suggest that the respiratory epithelia represent good alternate routes for drug delivery, particularly for those that are orally ineffective, i.e., due to extensive gastrointestinal tract degradation or first-pass metabolism.     

The Interaction of Charged and Uncharged Drugs with Neutral (HP-β-CD) and Anionically Charged (SBE7-β-CD) β-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--cyclodextrin, HP--CD) and anionically charged (SBE7--CD) modified -cyclodextrins. SBE7--CD is a sulfobutyl ether, sodium salt, derivative variably substituted on the 2-, 3- and the 6-positions of -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°C as a function of pH and cyclodextrin concentration by the phase-solubility method. Results. Except for miconazole and cinnarizine (A_P-type diagrams), all other materials studied displayed A_L-type diagrams. By comparing the binding constants of both the charged and uncharged forms of the same drugs to both HP--CD and SBE7--CD, the following conclusions could be drawn. The binding constants for the neutral forms of the drugs were always greater with SBE7--CD than with HP--CD. For the anionic agents, the binding constants between SBE7--CD and HP--CD were similar while the binding constants for the cationic agents with SBE7--CD were superior to those of HP--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--CD.