Enhancing effects of cyclodextrins on nasal absorption of insulin in rats

Cytotoxicity of β-Cyclodextrins in Retinal Explants for Intravitreal Drug Formulations

Cyclodextrins (CDs) have been widely used as pharmaceutical excipients for formulation purposes for different delivery systems. Recent studies have shown that CDs are able to form complexes with a variety of biomolecules, such as cholesterol. This has subsequently paved the way for the possibility of using CDs as drugs in certain retinal diseases, such as Stargardt disease and retinal artery occlusion, where CDs could absorb cholesterol lumps. However, studies on the retinal toxicity of CDs are limited. The purpose of this study was to examine the retinal toxicity of different beta-(β)CD derivatives and their localization within retinal tissues. To this end, we performed cytotoxicity studies with two different CDs—2-hydroxypropyl-βCD (HPβCD) and randomly methylated β-cyclodextrin (RMβCD)—using wild-type mouse retinal explants, the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, and fluorescence microscopy. RMβCD was found to be more toxic to retinal explants when compared to HPβCD, which the retina can safely tolerate at levels as high as 10 mM. Additionally, studies conducted with fluorescent forms of the same CDs showed that both CDs can penetrate deep into the inner nuclear layer of the retina, with some uptake by Müller cells. These results suggest that HPβCD is a safer option than RMβCD for retinal drug delivery and may advance the use of CDs in the development of drugs designed for intravitreal administration.

In Vitro and Ex Vivo Evaluation of Tablets Containing Piroxicam-Cyclodextrin Complexes for Buccal Delivery

In the current study, the development of mucoadhesive tablets for buccal delivery of a non-steroidal anti-inflammatory drug was investigated. Binary complexes with piroxicam and cyclodextrins (β-cyclodextrin (β-CD), methylated-β-cyclodextrin (Me-β-CD), and hydroxypropyl-β-cyclodextrin (HP-β-CD)) were prepared by the co-evaporation method. All formulations were characterized by means of differential scanning calorimetry, infrared spectroscopy and powder X-ray diffractometry. Mucoadhesive tablets of binary systems were formulated by direct compression using chitosan as mucoadhesive polymer. The in vitro release profiles of tablets were conducted in simulated saliva and, the drug permeation studies, across porcine buccal mucosa. The results suggest that the rank order effect of cyclodextrins for the drug release was Me-β-CD > HP-β-CD > β-CD, whereas the ex vivo studies showed that the tablets containing chitosan significantly increased the transport of the drug compared to their free complexes. Finally, histological assessment revealed loss of the superficial cell layers, which might be attributed to the presence of cyclodextrins.

Overview of intranasally delivered peptides: key considerations for pharmaceutical development

INTRODUCTION

Intranasal (IN) delivery for peptides provides unique advantages compared to other invasive systemic delivery routes. However, there still lacks a clear understanding on how to evaluate the potential of the peptides for nasal delivery and key considerations for the nasal formulation development.

AREAS COVERED

A retrospective analysis of intranasally delivered peptides was conducted. The goals of this undertaking were 1) to build a database of the key physicochemical and pharmacokinetic properties of peptides delivered by the nasal route, 2) to evaluate formulation attributes applied to IN peptide delivery systems, and 3) to provide key considerations for IN delivery of peptides.

EXPERT OPINION/COMMENTARY

Extensive data mining showed that peptides with molecular weights up to 6000 Da have been delivered intranasally. The high solubility of some peptides highlighted the possibility of delivering sufficient amounts of peptide in the limited volume available for nasal sprays. Permeation enhancers and mucoadhesives have shown promise in improving the IN bioavailability of peptides. Other formulation considerations, such as the type of formulation, pH, osmolality, as well as drug deposition, are reviewed herein. Based on this retrospective analysis, key considerations for nasal peptides formulations were proposed to guide drug discovery and development for IN delivery of peptides.

Ex vivo buccal drug delivery of ropinirole hydrochloride in the presence of permeation enhancers: the effect of charge

In the current study, the ex vivo permeation of ropinirole hydrochloride (RH) across porcine buccal mucosa in the presence of three permeation enhancers, namely N-trimethyl chitosan (TMC) (positively charged) a chitosan derivative, sulfobutyl ether-β-cyclodextrin (SBE-β-CD) (negatively charged) and hydroxypropyl-β-cyclodextrin (HP-β-CD) (neutral), was investigated. Buccal permeation studies were conducted using Franz diffusion cells. Cumulative amounts of RH were plotted versus time. The presence of the permeation enhancers significantly increased the transport of the drug across the porcine buccal epithelium compared to its plain congener (RH solution). The rank order effect of the permeation enhancers for the transport of RH across buccal epithelium was TMC ≥ SBE-β-CD > HP-β-CD > RH solution. The presence of TMC increased 1.34-fold the transport of RH across buccal epithelium, whereas an increase of 1.23- and 1.28-fold was reported in the presence of HP-β-CD and SBE-β-CD, respectively. Infrared spectroscopy (IR) was employed to investigate the interaction of permeation enhancers with the epithelial lipids of porcine buccal mucosa corroborating the permeation results. Finally, light microscopy was performed to assess the histological changes in the porcine epithelium. Formation of vacuoles, spongiosis and acantholysis linear detachment and destruction of the epithelium resulted from the presence of the permeation enhancers. The data suggest that all enhancers tested, and particularly TMC, increase the transport of RH across buccal epithelium.

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

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

Bioavailability of phytochemicals and its enhancement by drug delivery systems

Issues of poor oral bioavailability of cancer chemopreventives have hindered progress in cancer prevention. Novel delivery systems that modulate the pharmacokinetics of existing drugs, such as nanoparticles, cyclodextrins, niosomes, liposomes and implants, could be used to enhance the delivery of chemopreventive agents to target sites. The development of new approaches in prevention and treatment of cancer could encompass new delivery systems for approved and newly investigated compounds. In this review, we discuss some of the delivery approaches that have already made an impact by either delivering a drug to target tissue or increasing its bioavailability by many fold.

Intranasal drug delivery: an efficient and non-invasive route for systemic administration: focus on opioids

Intranasal administration is a non-invasive route for drug delivery, which is widely used for the local treatment of rhinitis or nasal polyposis. Since drugs can be absorbed into the systemic circulation through the nasal mucosa, this route may also be used in a range of acute or chronic conditions requiring considerable systemic exposure. Indeed, it offers advantages such as ease of administration, rapid onset of action, and avoidance of first-pass metabolism, which consequently offers for example an interesting alternative to intravenous, subcutaneous, oral transmucosal, oral or rectal administration in the management of pain with opioids. Given these indisputable interests, fentanyl-containing formulations have been recently approved and marketed for the treatment of breakthrough cancer pain. This review will outline the relevant aspects of the therapeutic interest and limits of intranasal delivery of drugs, with a special focus on opioids, together with an in-depth discussion of the physiological characteristics of the nasal cavity as well as physicochemical properties (lipophilicity, molecular weight, ionisation) and pharmaceutical factors (absorption enhancers, devices for application) that should be considered for the development of nasal drugs.

Pharmaceutical applications of cyclodextrins: effects on drug permeation through biological membranes

Objectives

Cyclodextrins are useful solubilizing excipients that have gained currency in the formulator's armamentarium based on their ability to temporarily camouflage undesirable physicochemical properties. In this context cyclodextrins can increase oral bioavailability, stabilize compounds to chemical and enzymatic degradation and can affect permeability through biological membranes under certain circumstances. This latter property is examined herein as a function of the published literature as well as work completed in our laboratories.

Key findings

Cyclodextrins can increase the uptake of drugs through biological barriers if the limiting barrier component is the unstirred water layer (UWL) that exists between the membrane and bulk water. This means that cyclodextrins are most useful when they interact with lipophiles in systems where such an UWL is present and contributes significantly to the barrier properties of the membrane. Furthermore, these principles are used to direct the optimal formulation of drugs in cyclodextrins. A second related critical success factor in the formulation of cyclodextrin-based drug product is an understanding of the kinetics and thermodynamics of complexation and the need to optimize the cyclodextrin amount and drug-to-cyclodextrin ratios. Drug formulations, especially those targeting compartments associated with limited dissolution (i.e. the eye, subcutaneous space, etc.), should be carefully designed such that the thermodynamic activity of the drug in the formulation is optimal meaning that there is sufficient cyclodextrin to solubilize the drug but not more than that. Increasing the cyclodextrin concentration decreases the formulation ‘push’ and may reduce the bioavailability of the system.

Conclusions

A mechanism-based understanding of cyclodextrin complexation is essential for the appropriate formulation of contemporary drug candidates.

A comprehensive development strategy in buccal drug delivery

This work combines several methods in an integrated strategy to develop a matrix for buccal administration. For this purpose, tablets containing selected mucoadhesive polymers loaded with a model drug (omeprazole), free or in a complexed form with cyclodextrins, and in the absence and presence of alkali agents were subjected to a battery of tests. Mucoadhesion studies, including simple factorial analysis, in vitro release studies with both model-dependent and model-independent analysis, and permeation studies were performed. Mucoadhesive profiles indicated that the presence of the drug decreases the mucoadhesion profile, probably due its hydrophobic character. In tablets loaded with the drug complexed with β-cyclodextrin or methyl-β-cyclodextrin, better results were obtained with the methylated derivative. This effect was attributed to the fact that in the case of β-cyclodextrin, more hydroxyl groups are available to interact with the mucoadhesive polymers, thus decreasing the mucoadhesion performance. The same result was observed in presence of the alkali agent (L: -arginine), in this case due to the excessive hydrophilic character of L: -arginine. Drug release from tablets was also evaluated, and results suggested that the dissolution profile with best characteristics was observed in the matrix loaded with omeprazole complexed with methyl-β-cyclodextrin in the presence of L: -arginine. Several mathematical models were applied to the dissolution curves, indicating that the release of the drug, in free or in complexed state, from the mucoadhesive matrices followed a super case II transport, as established on the basis of the Korsmeyer-Peppas function. The feasibility of drug buccal administration was assessed by permeation experiments on porcine buccal mucosa. The amount of drug permeated from mucoadhesive tablets presented a maximum value for the system containing drug complexed with the methylated cyclodextrin derivative in presence of L: -arginine. According to these results, the system containing the selected polymer mixture and the drug complexed with methyl-β-cyclodextrin in presence of L: -arginine showed a great potential as a buccal drug delivery formulation, in which a good compromise among mucoadhesion, dissolution, and permeation properties was achieved.

Nasal administration of metoclopramide from different dosage forms: in vitro, ex vivo, and in vivo evaluation

Nasal drug delivery is an interesting route of administration for metoclopramide hydrochloride (MTC) in preventing different kind of emesis. Currently, the routes of administration of antiemetics are oral or intravenous, although patient compliance is often impaired by the difficulties associated with acute emesis or invasiveness of parenteral administration. In this perspective, nasal dosage forms (solution, gel, and lyophilized powder) of MTC were prepared by using a mucoadhesive polymer sodium carboxymethylcellulose (NaCMC). In vitro and ex vivo drug release studies were performed in a modified horizontal diffusion chamber with cellulose membrane and excised cattle nasal mucosa as diffusion barriers. The tolerance of nasal mucosa to the formulation and its components were investigated using light microscopy. In vivo studies were carried out for the optimized formulations in sheep and the pharmacokinetics parameters were compared with oral solution and IV dosage form. The release of MTC from solution and powder formulations was found to be higher than gel formulation (p < 0.05). Histopathological examination did not detect any severe damage. Hydroxypropyl-beta-cyclodextrin (HPbetaCD) used in powder formulations was found to be effective for enhancing the release and absorption of MTC. In contrast to in vitro and ex vivo experiments nasal bioavailability of gel is higher than those of solution and powder (p < 0.05). In conclusion, the NaCMC gel formulation of MTC with mucoadhesive properties with increased permeation rate is promising for prolonging nasal residence time and thereby nasal absorption.

Current Perspectives of Solubilization: Potential for Improved Bioavailability

This review focuses on the recent techniques of solubilization for the attainment of effective absorption and improved bioavailability. Solubilization may be affected due to cosolvent water interaction or altered crystal structure by cosolvent addition. Micellar solubilization could be affected by both ionic strength and pH. Addition of cosolvents to the surfactant solutions offers only a small advantage because of the decrease in the solubilization capacity of the micelles. Polymorphism is known to influence dissolution and bioavailability of the drugs. Molecular modeling study of cyclodextrin inclusion complexations can predict the inclusion modes, stoichiometry of the complex, and the relative complexing efficiency of cyclodextrins with various drug molecules.

Effect of cell-penetrating peptides on the nasal absorption of insulin

The goal of this study was to evaluate whether cell-penetrating peptides (CPPs) affect the nasal absorption of insulin. L- or D-forms of penetratin, or the L- or D-forms of octaarginine (L- or D-R8), was used as first time for nasal insulin delivery. Furthermore, the concentration of lactate dehydrogenase (LDH) in nasal lavage fluid was determined and a histopathological study of nasal respiratory epithelium was conducted. CPPs dramatically increased nasal insulin absorption, and it was more pronounced for L- and D-penetratin than L- or D-R8. L-penetratin was the most effective promoter of insulin absorption compared with others CPPs. A dose-dependent relationship of L-penetratin and insulin bioavailability was statically significant. The pharmacological availability and bioavailability of nasally administered insulin was up to 76.7% and 50.7% relative to the subcutaneous route, respectively. In contrast, increasing the D-penetratin concentration decreased the efficiency of nasal insulin absorption. There was no significant difference in the release of LDH in nasal lavage fluid and the integrity of nasal respiratory epithelium when L-penetratin was present. In conclusion, these data demonstrate that L-penetratin markedly increased the permeability of insulin across the nasal membrane without causing detectable damage to the integrity of cells in the nasal respiratory mucosa.

Effects of Cyclodextrins on Drug Delivery Through Biological Membranes

Cyclodextrins have proven themselves to be useful functional excipients. Cyclodextrin derivatives can be hydrophilic or relatively lipophilic based on their substitution and these properties can give insight into their ability to act as permeability enhancers. Lipophilic cyclodextrins such as the methylated derivatives are thought to increase drug flux by altering barrier properties of the membrane through component extraction or fluidization. The hydrophilic cyclodextrin family also modulate drug flux through membranes but via different mechanisms. The current effort seeks to provide various explanations for these observations based on interactions of hydrophilic cyclodextrins with the unstirred water layer that separates the bulk media from biological membranes such as the gastric mucosa, cornea and reproductive tract. Theories on the serial nature of resistances to drug flux are used to explain why hydrophilic cyclodextrins can enhance drug uptake in some situation (i.e., for lipophilic material) but not in others. In addition, the nature of secondary equilibria and competition between cyclodextrins and rheologically important biopolymers such as mucin are assessed to give a complete picture of the effect of these starch derivatives. This information can be useful not only in understanding the actions of cyclodextrin but also in expanding their application and uses.

Evaluation of Buccal Methyl-β-Cyclodextrin Toxicity on Human Oral Epithelial Cell Culture Model

Cyclodextrins, especially methylated beta-cyclodextrins offer several advantages for drug delivery which include improved drug solubilization, protection against physicochemical and enzymatic degradation, as well as a potential for absorption improvement. However, little or no data are available for their use as drug penetration enhancer via the buccal route. This study focuses on the toxicity of randomly methylated beta-cyclodextrin (RAMEB) on buccal mucosa using a reconstituted human oral epithelium model composed of TR 146 cells. Toxicity of RAMEB on TR 146 cells was evaluated by measuring cell viability (MTT assay) and membrane damages followed by LDH release after single and repeated exposures to RAMEB solutions. Inflammatory effects of RAMEB are also considered by measuring expression of interleukin-1alpha and are supported by histological examination. The present results indicate that 10% RAMEB results in cytotoxic and inflammatory effects depending on time exposure, whereas 2% and 5% RAMEB do not induce tissue damages even after 5 days of repeated exposures. Therefore, the highly water-soluble RAMEB is thought to be a safe candidate as an excipient for buccal mucosal drug delivery.

Cyclodextrins in drug delivery

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

Design and evaluation of cyclodextrin-based drug formulation

The pharmaceutically useful cyclodextrins (CyDs) are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in design and evaluation of CyD-based drug formulation, focusing on their ability to enhance the drug absorption across biological barriers, the ability to control the rate and time profiles of drug release, and the ability to deliver a drug to a targeted site.

[Pharmaceutical application of cyclodextrins as multi-functional drug carriers]

Owing to the increasingly globalized nature of the cyclodextrin (CyD)-related science and technology, development of the CyD-based pharmaceutical formulation is rapidly progressing. The pharmaceutically useful CyDs are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in drug delivery and pharmaceutical formulation, focusing on the following evidences. 1) The hydrophilic CyDs enhance the rate and extent of bioavailability of poorly water-soluble drugs. 2) The amorphous CyDs such as 2-hydroxypropyl-beta-CyD are useful for inhibition of polymorphic transition and crystallization rates of drugs during storage. 3) The delayed release formulation can be obtained by the use of enteric type CyDs such as O-carboxymethyl-O-ethyl-beta-CyD. 4) The hydrophobic CyDs are useful for modification of the release site and/or time profile of water-soluble drugs with prolonged therapeutic effects. 5) The branched CyDs are particularly effective in inhibiting the adsorption to hydrophobic surface of containers and aggregation of polypeptide and protein drugs. 6) The combined use of different CyDs and/or pharmaceutical additives can serve as more functional drug carriers, improving efficacy and reducing side effects. 7) The CyD/drug conjugates may provide a versatile means for the constructions of not only colonic delivery system but also site-specific drug release system, including gene delivery. On the basis of the above-mentioned knowledge, the advantages and limitations of CyDs in the design of advanced dosage forms will be discussed.

Kinetic degradation study of insulin complexed with methyl-beta cyclodextrin. Confirmation of complexation with electrospray mass spectrometry and (1)H NMR

Hydrolysis of insulin has been studied during storage of various preparations at different temperatures. Deamidation is the predominant degradation process in acid solution resulting in a desamido product. The current study examines whether the interaction of insulin with methyl-beta cyclodextrin (met beta CD) improves its stability. Hydrolysis of insulin was monitored by an HPLC assay with ultraviolet detection. The stability constant of insulin-met beta CD complex was calculated by Lineweaver-Burke linear equation. Furthermore, the complexation of insulin with met beta CD was characterized by (1)H NMR and Electrospray Mass Spectrometry (ESI-MS). Met beta CD had a stabilizing effect on insulin degradation according to the kinetic parameters, leading to a decreased chemical deterioration. Furthermore, the stability constant K(st) and the activation energy E(a) were calculated by fitting the kinetic results to Lineweaver-Burke and to Arrhenius linear equations, respectively. Finally, the complexation of insulin with met beta CD was characterized in aqueous media by (1)H NMR chemical shift displacements of assignable aromatic protons of specific amino acids upon the addition of the cyclodextrin, as well as by ESI-MS, since additional m/z peaks, which were attributed to insulin-met beta CD complex, were detected. It is concluded that addition of met beta CD resulted in a significant increase in the stability of complexed insulin compared with free insulin.

Biomembrane model interaction and percutaneous absorption of papaverine through rat skin: effects of cyclodextrins as penetration enhancers

The effects of different concentrations of beta-cyclodextrin (beta-CyD), hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) and 2,6-di-O-methyl-beta-cyclodextrin (DM-beta-CyD) on percutaneous absorption of papaverine hydrochloride (PAP) were investigated. Abdominal rat skin mounted in Franz cells was used for in vitro experiments. To evaluate CyD interaction with a bilayer structure model, dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and DPPC-Chol (8:2 mole ratio) vesicles were used. CyD vesicle interaction was evaluated by differential scanning calorimetry. Permeation through rat skin and calorimetric experiments demonstrated that at low concentrations DM-beta-CyD shows higher enhancer activity as a possible result of a perturbing action on the skin by a complexation of its lipid components, but at higher concentrations HP-beta-CyD is the most effective. By considering that HP-beta-CyD presents a very moderate destabilizing action on the skin, we conclude that a 10% aqueous solution of this macrocycle appears to be the most suitable transdermal absorption enhancer for PAP.

Pharmacokinetics and pharmacodynamics of human chorionic gonadotropin (hCG) after rectal administration of hollow-type suppositories containing hCG

To determine the effectiveness of human chorionic gonadotropin (hCG) administered rectally, we studied the pharmacokinetics and pharmacodynamics of hCG using a hollow-type suppository. HCG was not detected in plasma when only hCG was administered rectally, even at a higher dose (4,000 IU/kg body weight) than intravenous injection, because of its low bioavailability due to high molecular weight or degradation by proteolytic activity. To enhance the rectal absorption of hCG, the effectiveness of its coadministration with alpha-cyclodextrin (alpha-CyD), an absorption-enhancing agent, was investigated in male rabbits. HCG was detected in plasma following coadministration of hCG and alpha-CyD (10 mg/kg body weight) into the rectum. The plasma hCG concentration increased with increasing dose of alpha-CyD. The AUC(0-48) observed after coadministration of hCG and alpha-CyD at 30 mg/kg body weight was approximately four times higher than that of hCG and alpha-CyD at 10mg/kg body weight. HCG at a high concentration induced a rapid increase in the plasma testosterone concentration (74.2 +/- 3.4 ng/ml) 2 h after intravenous administration. However, the testosterone concentration 24 h after intravenous administration decreased to the physiological level (approximately 20 ng/ml) which had been observed before such administration. On the other hand, the maximum level of testosterone concentration (40.0 +/- 12.6 ng/ml) was observed 24 h after rectal administration of hCG (400 IU/kg body weight) in combination with alpha-CyD (30 mg/kg body weight). Moreover, the plasma testosterone concentration (31.0 +/- 11.4 ng/ml) obtained 72 h after rectal administration tended to be maintained at a higher level than that (14.4 +/- 0.9ng/ml) observed before the administration. These results suggest that the hollow-type suppository as a rectal delivery system of hCG is promising as a new mode of hCG therapy.

Cyclodextrins in oligonucleotide delivery

The aim of this contribution is to summarize recent findings on the potential use of cyclodextrins and their derivatives as carriers for oligonucleotide agents. Their peculiar properties could be exploited in such an emerging therapeutic area by virtue of their capability of interacting with cellular membranes, thus giving rise to improved cellular uptake. In particular, some specific derivatives could be considered as promising future excipients for the delivery of "naked" antisense and/or decoy oligonucleotides which are difficult to formulate with existing pharmaceutical excipients.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Intranasal insulin delivery and therapy

Intranasal insulin delivery has been widely investigated as an alternative to subcutaneous injection for the treatment of diabetes. The pharmacokinetic profile of intranasal insulin is similar to that obtained by intravenous injection and, in contrast to subcutaneous insulin delivery, bears close resemblance to the 'pulsatile' pattern of endogenous insulin secretion during meal-times. The literature suggests that intranasal insulin therapy has considerable potential for controlling post-prandial hyperglycaemia in the treatment of both IDDM and NIDDM. However, effective insulin absorption via the nasal route is unlikely without employing the help of absorption enhancers or promoters which are able to modulate nasal epithelial permeability to insulin and/or prolong the residence time of the drug formulation in the nasal cavity. This article discusses the structure and function of the nasal cavity, the barriers which prevent nasal insulin absorption and through the use of absorption enhancers or promoters methods by which these barriers may be overcome.

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

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

Absorption enhancers as tools to determine the route of nasal absorption of peptides

The nasal absorption of a series of peptides was studied in order to examine the relationship between extent of absorption and lipophilicity and absorption enhancers were used to probe the mechanism of peptide absorption. An in situ rat nasal perfusion technique was employed to assess the nasal absorption of a series of peptides, D-FGGGGG (D-FG5), D-FD-FGGGG (D-F2G4) and D-FD-FD-FGGG (D-F3G3), [D-ala2, D-leu5]enkephalin (YD-AGFD-L) and thyrotrophin releasing hormone (TRH). The enhancers sodium tauro-24,25 dihydrofusidate (STDHF), ethylene diamine tetraacetic acid (EDTA and dimethyl-beta-cyclodextrin (DMbetaCD) were utilized to improve and elucidate the mechanisms of peptide absorption. There was no significant relationship between extent of peptide absorption and lipophilicity as determined by C log P values. STDHF was a potent absorption enhancer but demonstrated overt toxicity. Conversely, EDTA did not demonstrate extensive toxicity but was found to be a poor absorption enhancer. DMbetaCD displayed some toxicity and was also found to inhibit the absorption of D-FG5,D-F2G4 and D-F3G3. This reduction is likely to be a result of the peptide/DMbetaCD complex formation. The peptides studied appear to be predominantly absorbed by a passive paracellular mechanism.

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

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

Intestinal safety of water-soluble beta-cyclodextrins in paediatric oral solutions of spironolactone: effects on human intestinal epithelial Caco-2 cells

Effects of water-soluble beta-cyclodextrins (beta CDs) on intestinal epithelial integrity were investigated, to establish the safe use of these beta CDs as solubilizers of spironolactone in paediatric enteral solutions. Mannitol permeability and transepithelial resistance (TER) of human intestinal epithelial Caco-2 cell monolayers during exposure to dimethyl-beta-cyclodextrin (DM beta CD), hydroxypropyl-beta-cyclodextrin (HP beta CD) and sulphobutyl ether beta-cyclodextrin (SBE beta CD) were followed. Staining methods were used to discern cells with damaged membranes and to study the integrity of cytoskeletal actin and tight junctions. Cytotoxicity of the beta CDs was tested by effects on intracellular dehydrogenase activity. Exposure to HP beta CD and SBE beta CD solutions had only minor effects on the integrity of Caco-2 cell monolayers. In contrast, DM beta CD clearly increased the epithelial permeability for the hydrophilic marker [14C]mannitol across Caco-2 monolayers, decreased TER and showed a dose-dependent cytotoxicity. According to staining, DM beta CD increased the permeability of the apical cell membrane without discernable effects on cytoskeletal actin. HP beta CD and SBE beta CD appear to be safe additives for use in enteral spironolactone preparations with respect to their acute local effects on epithelial integrity.

Pharmaceutical applications of cyclodextrins. 2. In vivo drug delivery

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

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.

Methylated beta-cyclodextrins are able to improve the nasal absorption of salmon calcitonin

The absorption enhancing effect of methylated beta-cyclodextrins on the nasal absorption of salmon calcitonin (sCT) was studied in rats and rabbits. The nasal absorption of sCT following administration without additives was low in both species. The absorption in rats could be largely improved by coadministration of cyclodextrins as apparent from the effect on serum calcium concentrations. Trimethyl-beta-cyclodextrin (TM beta CD), at a concentration of 5% (w/v), was the least potent enhancer. Randomly methylated-beta-cyclodextrin (RM beta CD) and dimethyl-beta-cyclodextrin (DM beta CD), all at a concentration of 5% (w/v), were almost equally effective in decreasing serum calcium levels, and the hypocalcemic responses were similar to those of i.v. and s.c. injected sCT. Absorption enhancement was already achieved with 1% DM beta CD added to the nasal formulations. In rabbits, only the effect of DM beta CD on the nasal sCT absorption was investigated. A total serum calcium decrement in 4 hours of 9.4 +/- 3.9% (mean +/- SD) was observed following nasal administration of 12.6 IU/kg sCT with 5% DM beta CD, comparable to that of i.v.-injected sCT. In conclusion, the methylated cyclodextrins DM beta CD and RM beta CD are suitable absorption enhancers for nasal sCT administration, which is expected to have a clinical impact on the therapy with calcitonin.

Differential effects of modified beta-cyclodextrins on pharmacological activity and bioavailability of 4-biphenylacetic acid in rats after oral administration

Gastric tolerability, absorption and pharmacological activity of the non-steroidal anti-inflammatory drug 4-biphenylacetic acid (BPAA), as an inclusion complex with beta-cyclodextrin (beta-CyD) or chemically modified beta-CyDs: 2,6-di-O-methyl-beta-CyD (DM-beta-CyD), 2,3,6-tri-O-methyl-beta-CyD (TM-beta-CyD) and 2-hydroxypropyl-beta-CyD (HP-beta-CyD), were investigated in the rat after oral administration. BPAA absorption, determined from area under the plasma concentration-time curve (AUC), was increased by complexation with all beta-CyDs in the following order: DM-beta-CyD > TM-beta-CyD > HP-beta-CyD > beta-CyD. The carrageenan paw oedema test demonstrated a significant increase in anti-inflammatory activity of BPAA and the ED50 values, compared with BPAA alone, were reduced to about a third for the BPAA-DM-beta-CyD complex and halved for the others. BPAA complexed with DM-beta-CyD, HP-beta-CyD or beta-CyD showed better gastric tolerability compared with uncomplexed drug, whereas the BPAA-TM-beta-CyD complex produced marked gastric lesions similar in extent to BPAA alone. TM-beta-CyD (500 mg kg-1) and DM-beta-CyD (1000 mg kg-1) caused gastric erosions 21 h after oral administration. The pharmacokinetic profiles of BPAA-beta-CyD complexes have shown that DM-beta-CyD is the most effective in enhancing the bioavailability of BPAA.

Pharmacokinetics and pharmacodynamics of recombinant human granulocyte colony-stimulating factor (rhG-CSF) following intranasal administration in rabbits

The objective of this study was to evaluate the pharmacokinetics and pharmacodynamics of G-CSF as well as their relationship following intranasal (i.n.) administration of aqueous rhG-CSF preparations with or without additives. In order to achieve a better understanding of the dosage regimen and the effectiveness of intranasally administered rhG-CSF in inducing leukopoiesis, we investigated rhG-CSF absorption and blood leukocyte dynamics with respect to dose in rabbits. RhG-CSF could be absorbed through the nasal cavity of rabbits when rhG-CSF aqueous preparations, especially those containing alpha-cyclodextrin (alpha-CyD) were intranasally administered. We found that serum G-CSF levels and the total count of leukocytes in peripheral blood (total blood leukocyte count) showed a dose-dependent increase with rhG-CSF. The area under the serum G-CSF concentration-time curve (AUC, a pharmacokinetic parameter) and the area under the increased total blood leukocyte count-time curve (AUL, a pharmacodynamic parameter) increased with increase of dose of rhG-CSF administered intranasally. Good agreement was observed between log AUC and AUL; thus, it is concluded that an increase of AUC leads to an increase in effectiveness of rhG-CSF in inducing leukopoiesis in rabbits. A novel rhG-CSF delivery system in the form of i.n. administration of rhG-CSF was thus achieved.