Drug delivery studies in Caco-2 monolayers. IV. Absorption enhancer effects of cyclodextrins

Influence of permeability enhancers on the paracellular permeability of metformin hydrochloride and furosemide across Caco-2 cells

Permeability enhancers can affect absorption of paracellularly transported drugs. This study aims to evaluate effects of permeability enhancers (chitosan, methyl-β -cyclodextrin, sodium caprate, sodium lauryl sulfate, etc.) on the permeability of paracellularly absorbed furosemide and metformin hydrochloride. Methyl thiazole tetrazolium bromide test was carried out to determine the drug concentrations in permeability study. Trans-epithelial electrical resistance (TEER) values determined to assess the integrity of tight junctions. Permeability enhancers were applied at different concentrations alone, in dual/triple combinations. Permeability was determined using human colorectal adenocarcinoma (Caco-2) cells (TEER > 400 Ω·cm²). Permeability enhancers have no significant effect (<2-fold; p > 0.05) on the permeability of furosemide (1.80 × 10^-5 ± 4.55 × 10^-7 cm/s); however, metformin permeability (1.36 × 10^-5 ± 1.25 × 10^-6 cm/s) increased significantly (p < 0.05) with 0.3% and 0.5% (w/v) chitosan (2.0- and 2.7-fold, respectively), 1% methyl-β -cyclodextrin (w/v) (3.5-fold), 10 and 20 µmol/L sodium caprate (2.2- and 2.8-fold, respectively), and 0.012% sodium lauryl sulfate (w/v) (1.9-fold). Furosemide permeability increased significantly (p < 0.05) with chitosan-sodium lauryl sulfate combination (1.7-fold), and all triple combinations (1.4- to 1.9-fold). Chitosan containing dual/triple combinations resulted in significant increase (p < 0.05) in metformin permeability (1.7 to 2.8-fold). All results indicated that absorption of furosemide and metformin can be improved by the combination of permeability enhancers. Therefore, it can be evaluated for the formulation of development strategies containing furosemide and metformin by the pharmaceutical industry.

Effects of alpha-cyclodextrin on water transport, cell hydration and longevity

Among parent cyclodextrins (CDs), alpha-CD (a-CD) has been utilized in a number of nutraceutical products, and approved as a dietary fiber to affect glycemic response and reduce dietary fat absorption. To extend our current knowledge on the biology of this natural carbohydrate, here we investigated its potential effects on cellular water uptake and aging. Two independent in vivo biological test systems were used, a single cell Xenopus oocyte with expressed human aquaporin for cell hydration studies and the nematode Caenorhabditis elegans for testing life span in the treated animals. a-CD was found to enhance water uptake through aquaporins of oocytes. Furthermore, the compound promoted longevity in C. elegans. Together, these results raise a rational for assaying a-CD as a potent drug candidate in treating various age-related diseases.

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.

Improvement of intestinal absorption of curcumin by cyclodextrins and the mechanisms underlying absorption enhancement

Curcumin is known to possess a wide range of pharmacological activities for the treatment of chronic or inflammatory diseases, Alzheimer's disease, and various cancers. However, the therapeutic efficacy of curcumin is restricted by its poor bioavailability after oral administration. In this study, the effects of various cyclodextrins on the intestinal absorption of curcumin were evaluated in rat intestine by an in situ closed-loop method. Among the tested cyclodextrins, 50 mM α-cyclodextrin significantly enhanced the absorption of curcumin without inducing any intestinal toxicity. The analysis of cellular transport across Caco-2 cell monolayers showed that 50 mM α-cyclodextrin reduced the transepithelial electrical resistance value of cell monolayers and improved the permeability of 5(6)-carboxyfluorescein, a poorly absorbable drug, which is mainly transported via a paracellular pathway. Furthermore, the western blotting analysis showed that α-cyclodextrin decreased the expression of claudin-4, a tight junction-associated protein, in brush border membrane vesicles. Additionally, α-cyclodextrin increased the membrane fluidity of lipid bilayers in brush border membrane vesicles and may also have promoted the permeation of drug molecules via a transcellular pathway. These results suggested that α-cyclodextrin might enhance the intestinal absorption of curcumin via both paracellular and transcellular pathways.

Buccal Dosage Forms: General Considerations for Pediatric Patients

The development of an appropriate dosage form for pediatric patients needs to take into account several aspects, since adult drug biodistribution differs from that of pediatrics. In recent years, buccal administration has become an attractive route, having different dosage forms under development including tablets, lozenges, films, and solutions among others. Furthermore, the buccal epithelium can allow quick access to systemic circulation, which could be used for a rapid onset of action. For pediatric patients, dosage forms to be placed in the oral cavity have higher requirements for palatability to increase acceptance and therapy compliance. Therefore, an understanding of the excipients required and their functions and properties needs to be particularly addressed. This review is focused on the differences and requirements relevant to buccal administration for pediatric patients (compared to adults) and how novel dosage forms can be less invasive and more acceptable alternatives.

Cyclodextrins as Emerging Therapeutic Tools in the Treatment of Cholesterol-Associated Vascular and Neurodegenerative Diseases

Cardiovascular diseases, like atherosclerosis, and neurodegenerative diseases affecting the central nervous system (CNS) are closely linked to alterations of cholesterol metabolism. Therefore, innovative pharmacological approaches aiming at counteracting cholesterol imbalance display promising therapeutic potential. However, these approaches need to take into account the existence of biological barriers such as intestinal and blood-brain barriers which participate in the organ homeostasis and are major defense systems against xenobiotics. Interest in cyclodextrins (CDs) as medicinal agents has increased continuously based on their ability to actively extract lipids from cell membranes and to provide suitable carrier system for drug delivery. Many novel CD derivatives are constantly generated with the objective to improve CD bioavailability, biocompatibility and therapeutic outcomes. Newly designed drug formulation complexes incorporating CDs as drug carriers have demonstrated better efficiency in treating cardiovascular and neurodegenerative diseases. CD-based therapies as cholesterol-sequestrating agent have recently demonstrated promising advances with KLEPTOSE® CRYSMEB in atherosclerosis as well as with the 2-hydroxypropyl-β-cyclodextrin (HPβCD) in clinical trials for Niemann-Pick type C disease. Based on this success, many investigations evaluating the therapeutical beneficial of CDs in Alzheimer's, Parkinson's and Huntington's diseases are currently on-going.

Evaluation of γ-cyclodextrin effect on permeation of lipophilic drugs: application of cellophane/fused octanol membrane

According to the Biopharmaceutics Classification System, oral bioavailability of drugs is determined by their aqueous solubility and the ability of the dissolved drug molecules to permeate lipophilic biological membranes. Similarly topical bioavailability of ophthalmic drugs is determined by their solubility in the aqueous tear fluid and their ability to permeate the lipophilic cornea. Enabling pharmaceutical excipients such as cyclodextrins can have profound effect on the drug bioavailability. However, to fully appreciate such enabling excipients, the relationship between their effects and the physicochemical properties of the permeating drug needs to be known. In this study, the permeation enhancing effect of γ-cyclodextrin (γCD) on saturated drug solutions containing hydrocortisone (HC), irbesartan (IBS), or telmisartan (TEL) was evaluated using cellophane and fused cellulose-octanol membranes in a conventional Franz diffusion cell system. The flux (J), the flux ratio (J_R) and the apparent permeability coefficients (P_app) demonstrate that γCD increases drug permeability. However, its efficacy depends on the drug properties. Addition of γCD increased P_app of HC (unionized) and IBS (partially ionized) through the dual membrane but decreased the P_app of TEL (fully ionized) that displays low complexation efficacy. The dual cellophane-octanol membrane system was simple to use and gave reproducible results.

Effect of permeability enhancers on paracellular permeability of acyclovir

Objectives

According to Biopharmaceutics Classification System (BCS), acyclovir is a class III (high solubility, low permeability) compound, and it is transported through paracellular route by passive diffusion. The aim of this study was to investigate the effect of various pharmaceutical excipients on the intestinal permeability of acyclovir.

Methods

The single-pass in-situ intestinal perfusion (SPIP) method was used to estimate the permeability values of acyclovir and metoprolol across different intestinal segments (jejunum, ileum and colon). Permeability coefficient (Peff) of acyclovir was determined in the absence and presence of a permeation enhancer such as dimethyl β-cyclodextrin (DM-β-CD), sodium lauryl sulfate (SLS), sodium caprate (Cap-Na) and chitosan chloride.

Key findings

All enhancers increased the permeability of paracellularly transported acyclovir. Although Cap-Na has the highest permeability-enhancing effect in all segments, permeation-enhancing effect of chitosan and SLS was only significant in ileum. On the other hand, DM-β-CD slightly decreased the permeability in all intestinal segments.

Conclusions

These findings have potential implication concerning the enhancement of absorption of paracellularly transported compounds with limited oral bioavailability. In the case of acyclovir, Cap-Na either alone or in combination with SLS or chitosan has the potential to improve its absorption and bioavailability and has yet to be explored.

Combinational enhancing effects of formulation and encapsulation on digestive stability and intestinal transport of green tea catechins

The hypothesis was that green tea catechins (GTCs) formulated with vitamin C and xylitol followed by enteric coating with hydroxypropyl methyl cellulose phthalate (HPMCP) or encapsulated into γ-cyclodextrin (γ-CD) could enhance intestinal absorption of GTCs. Surface morphology and size obtained by SEM were different. Digestive stability of GTCs encapsulated into γ-CD or coated with HPMCP was enhanced up to 65.56% or 57.63%, respectively. When GTCs were formulated, the digestive stability was greater than the one not formulated. Formulated GTCs followed by encapsulation into γ-CD significantly increased intestinal transport. Absorption of GTCs was 2.8%, 9.64%, 11.97%, 8.41% and 14.36% for only GTCs, GTCs encapsulated into γ-CD, formulated GTCs encapsulated into γ-CD, GTCs coated with HPMCP and formulated GTCs coated with HPMCP, respectively. This study suggests that GTCs, formulated with vitamin C and xylitol followed by γ-CD encapsulation or HPMCP enteric coating, provide combinational effect to increase bioavailability of GTCs.

Development of rectal delivered thermo-reversible gelling film encapsulating a 5-fluorouracil hydroxypropyl-β-cyclodextrin complex

We have developed a novel 5-Fluorouracil (5FU) formulation for rectal application to improve its therapeutic efficiency in colorectal cancer. The results indicated that 5FU formed an inclusion complex with Hydroxypropyl-β-Cyclodextrin (HP-β-CD). The stoichiometry of the complex was 1:1, with apparent stability constant of 100.4M(-1). After investigating physicochemical properties of the 5FU-HP-β-CD complex encapsulated with thermo-reversible gelling film, the optimized formulation P407/P188/HPMC/5FU-HP-β-CD (18.5/2.5/0.2/15%) was selected and evaluated. The result showed that the 5FU-HP-β-CD complex increased the solubility of 5FU, prolonged and enhanced its releasing. As compared to the raw drug, the transport efficiency of the 5FU-HP-β-CD complex itself or entrapped in thermo-reversible gelling film were respectively 7.3- and 6.8-fold increased, and the cellular uptake of 5-FU 4.9- and 5.4-fold elevated. There was no irritation or damage to rectal sites in the 10h treatment period. Therefore, this HP-β-CD based formulation might improve the therapeutic effect of 5FU on colon-rectal cancer.

A novel oral preparation of hydroxysafflor yellow A base on a chitosan complex: a strategy to enhance the oral bioavailability

Hydroxysafflor yellow A (HSYA), the main active pharmaceutical ingredient of the safflower plant (Carthamus tinctorius L.), is a hydrophilic drug with low oral bioavailability (BA). The objective of the present study was to improve the oral BA of HSYA by formulation design. The effect of several pharmaceutical excipients on enhancing BA, including Poloxamer 188 (P188), sodium caprate (SC), sodium deoxycholate, and β-cyclodextrin (β-CD), was investigated through animal models. Sodium caprate, with a relative BA of 284.2%, was able to improve the oral BA of HSYA. Furthermore, HSYA can bind with chitosan (CS) by Coulomb attraction and form a HSYA-CS complex. The preparation process was optimized, and the binding rate reached 99.4%. HSYA granules were prepared using a HSYA-CS complex and SC. The results of the pharmacokinetics showed that the relative BA of HSYA granules was 476%, much higher than HSYA/SC.

Cholesterol depletion by methyl-β-cyclodextrin augments tamoxifen induced cell death by enhancing its uptake in melanoma

BACKGROUND

Despite modern advances in treatment, skin cancer is still one of the most common causes of death in the western countries. Chemotherapy plays an important role in melanoma management. Tamoxifen has been used either alone or in- combination with other chemotherapeutic agents to treat melanoma. However, response rate of tamoxifen as a single agent has been comparatively low. In the present study, we investigated whether treatment with methyl-β-cyclodextrin (MCD), a cholesterol depleting agent, increases the efficacy of tamoxifen in melanoma cells.

METHODS

This was a two-part study that incorporated in vitro effects of tamoxifen and MCD combination by analyzing cell survival, apoptosis and cell cycle analysis and in vivo antitumor efficacy on tumor isografts in C57BL/6J mice.

RESULTS

MCD potentiated tamoxifen induced anticancer effects by causing cell cycle arrest and induction of apoptosis. Sensitization to tamoxifen was associated with down regulation of antiapoptotic protein Bcl-2, up-regulation of proapoptotic protein Bax, reduced caveolin-1 (Cav-1) and decreased pAkt/pERK levels. Co-administration of tamoxifen and MCD caused significant reduction in tumor volume and tumor weight in mice due to enhancement of drug uptake in the tumor. Supplementation with cholesterol abrogated combined effect of tamoxifen and MCD.

CONCLUSION

Our results emphasize a potential synergistic effect of tamoxifen with MCD, and therefore, may provide a unique therapeutic window for improvement in melanoma treatment.

Efficient gene carriers composed of 2-hydroxypropyl-β-cyclodextrin, ethanolamine-functionalized poly(glycidyl methacrylate), and poly((2-dimethyl amino)ethyl methacrylate) by combination of ATRP and click chemistry

In this work, a simple one-step method is first employed to produce the bromoisobutyryl-terminated 2-hydroxypropyl-β-cyclodextrin (HPCD-Br). The pendant epoxy groups of poly(glycidyl methacrylate) block prepared via ATRP from HPCD-Br can be reacted with ethanolamine to produce HPCD-PGEA which exhibits much lower cytotoxicity and better gene transfection yield than polyethylenimine (25 kDa) in COS7 and HepG2 cell lines. Moreover, poly((2-dimethyl amino)ethyl methacrylate) blocks can be incorporated into low-molecular-weight HPCD-PGEA via "click" reaction to further enhance the gene transfection efficiency in HepG2 cell lines.

Polymeric penetration enhancers promote humoral immune responses to mucosal vaccines

Protective mucosal immune responses are thought best induced by trans-mucosal vaccination, providing greater potential to generate potent local immune responses than conventional parenteral vaccination. However, poor trans-mucosal permeability of large macromolecular antigens limits bioavailability to local inductive immune cells. This study explores the utility of polymeric penetration enhancers to promote trans-mucosal bioavailability of insulin, as a biomarker of mucosal absorption, and two vaccine candidates: recombinant HIV-1 envelope glycoprotein (CN54gp140) and tetanus toxoid (TT). Responses to vaccinating antigens were assessed by measurement of serum and the vaginal humoral responses. Polyethyleneimine (PEI), Dimethyl-β-cyclodextrin (DM-β-CD) and Chitosan enhanced the bioavailability of insulin following intranasal (IN), sublingual (SL), intravaginal (I.Vag) and intrarectal (IR) administration. The same penetration enhancers also increased antigen-specific IgG and IgA antibody responses to the model vaccine antigens in serum and vaginal secretions following IN and SL application. Co-delivery of both antigens with PEI or Chitosan showed the highest increase in systemic IgG and IgA responses following IN or SL administration. However the highest IgA titres in vaginal secretions were achieved after IN immunisations with PEI and Chitosan. None of the penetration enhancers were able to increase antibody responses to gp140 after I.Vag immunisations, while in contrast PEI and Chitosan were able to induce TT-specific systemic IgG levels following I.Vag administration. In summary, we present supporting data that suggest appropriate co-formulation of vaccine antigens with excipients known to influence mucosal barrier functions can increase the bioavailability of mucosally applied antigens promoting the induction of mucosal and systemic antibody responses.

Improvement of oxaprozin solubility and permeability by the combined use of cyclodextrin, chitosan, and bile components

The effect of the combined use of randomly methylated β-cyclodextrin (RAMEB), chitosan (CS), and bile components (dehydrocholic (DHCA) or ursodeoxycholic (UDCA) acids and their sodium salts) on solubility and permeability through Caco-2 cells of oxaprozin (a very poorly water-soluble non-steroidal anti-inflammatory drug) has been investigated. Addition of CS, bile acids, and their sodium salts increased the RAMEB solubilizing power of 4, 2, and 5 times, respectively. Drug-RAMEB-CS co-ground systems showed very higher dissolution rate than corresponding drug-RAMEB systems. Addition of bile components further improved drug dissolution rate. The CS presence enabled a significant increase in drug permeability through Caco-2 cells with respect to drug-RAMEB systems. Moreover, CS and NaDHC showed a synergistic enhancer effect, enabling a 1.4-fold permeability increase in comparison with systems without bile salt. However, unexpectedly, no significant differences were found between physical mixtures and co-ground products, indicating that drug permeation improvement was due to the intrinsic enhancer effect of the carriers and not to drug-carrier interactions brought about by co-grinding, as instead found in dissolution rate studies. The combined use of RAMEB, CS, and NaDHC could be exploited to develop effective oral dosage forms of oxaprozin, with increased drug solubility and permeability, and then improved bioavailability.

Confocal laser scanning microscopy (CLSM) based evidence for cell permeation by mono-4-(N-6-deoxy-6-amino-β-cyclodextrin)-7-nitrobenzofuran (NBD-β-CyD)

Beta-cyclodextrin (β-CyD), amantadine and glucose were fluorescently tagged with 4-chloro-7-nitrobenz-2-oxa-1,3-diazole (NBD chloride) to afford NBD-β-CyD, NBD-amantadine and NBD-glucose, respectively. NBD-β-CyD/amantadine and β-CyD/NBD-amantadine inclusion complexes were prepared. Fluorescence emission maxima (λ(max) 544nm) and relative fluorescence intensities for NBD-β-CyD and NBD-β-CyD/amantadine were virtually identical, precluding the use of emission spectrum shifts for distinguishing free NBD-β-CyD from the complex. Intracellular accumulation of NBD-β-CyD was studied in HepG2 and SK-MEL-24 cells using confocal laser scanning microscopy (CLSM). No major differences were observed between uptake of NBD-β-CyD and NBD-β-CyD/amantadine. Serum proteins did not perturb uptake, whereas temperature-dependent uptake, indicative of cell entry via diffusion, was observed. Intracellular distribution favoured mitochondria, with less fluorescent material present in cytoplasm and none in cell nuclei. No experimental evidence of NBD-β-CyD breakdown to NBD-glucose was found upon chromatographic analysis of incubation mixtures, providing additional evidence of intact NBD-β-CyD entry into these cells. Endocytosis and/or cholesterol-independent membrane modulation are discussed as possible mechanisms for the transmembrane passage of NBD-β-CyD.

Effect of cyclodextrins on the complexation and nasal permeation of melatonin

The inclusion complexation of melatonin (MT) with modified cyclodextrins (CDs) was studied with an objective of improving the solubility and nasal absorption of MT. The formation of inclusion complex of MT with Hydroxypropyl beta CD (HPbeta CD) and randomly methylated beta CD (RMbeta CD) was characterized in solution and solid states by phase solubility and differential scanning calorimetry analyses. The phase solubility data indicate a linear increase in the solubility of MT with CDs demonstrating Higuchi's A(L)-type phase solubility profiles. The effect of CDs on the permeation of MT across EpiAirway(TM)-100 cultures was studied using a modified nonstatic diffusion setup. CDs were employed at different concentrations with 1% w/v micronized MT suspension in hydroxypropyl methyl cellulose (HPMC) vehicle. At low CD concentrations (1% w/v), the permeation of MT from HPMC formulation was significantly increased (125%,p < .001). However, the permeation was significantly reduced when CDs were used at relatively high concentrations (5 to 10% w/v concentration for HPbetaCD and 10% w/v concentration for RMbetaCD,p < .001). All the tissues were viable with good tissue integrity at the end of permeation experiments, as measured by methylthiazoletetrazolium assay and transepithelial electrical resistance measurements. In conclusion, formation of inclusion complex of MT with HPbetaCD and RMbetaCD was demonstrated in solution and solid state. Both HPbetaCD and RM betaCD at 1% w/v concentration were found to improve the nasal permeability of MT from HPMC gel formulations.

Novel drug nanocarriers combining hydrophilic cyclodextrins and chitosan

The aim of this study was to explore the possibility of obtaining nanoparticles (NPs) containing high amounts of cyclodextrin (CD) derivatives such as carboxymethyl-β-CD and sulphobutyl ether-β-CD. The rationale used was to combine the drug solubilizing and stabilizing properties of cyclodextrins (CDs) with the mucoadhesive properties of chitosan (CS) in a unique nanoparticulate drug delivery system. The size of the resulting NPs was affected by the nature of the CDs, ranging between 275 and 550 nm, whereas the zeta potential of the NPs was always positive and close to +35 mV. The positive zeta values, together with the results from NMR studies, suggest that CS is the major compound on the surface of the NPs, while CD molecules are strongly associated with the NP matrix. The empirical composition of the NPs was quantified by elemental analysis and the results indicated that the amount of CD associated with the NPs was strictly dependent on its electrostatic charge. Finally, in vitro stability studies indicated that the presence of CDs in the NP structure can prevent the aggregation of this nanometric carrier system in simulated intestinal fluid. Overall, this new type of NP represents an attractive drug delivery platform of particular interest for the oral administration of drugs with low bioavailability.

In situ intestinal absorption behaviors of tanshinone IIA from its inclusion complex with hydroxypropyl-beta-cyclodextrin

In this paper, the intestinal permeability of the inclusion complex of tanshinone IIA (TS IIA) with 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was investigated. The corresponding complexation of TS IIA-HP-beta-CD was obtained by coevaporation and characterized by differential scanning calorimetry and X-ray diffraction. The recirculation intestinal perfusion technique in rats was used to study the absorption behavior of free and complexed TS IIA. The change of concentration of TS IIA was separately calculated according to Michaelis-Menten and the Fick's equation to investigate its absorption rate-limiting step. Using the mathematical models above, it was concluded that the limit step to absorption of TS IIA was the dissolution process. Different concentrations of complexed TS IIA were administrated to three intestinal segments, with the intestinal permeability ranging from 3.16x10(-5) cm.s(-1) in the duodenum (50 microg.ml(-1)) to 4.11x10(-5) cm.s(-1) in the jejunum (100 microg.ml(-1)). With the increase of dosage of complex, TS IIA's absorption did not show saturated phenomenon, suggesting its transport mechanism in vivo might primary be passive transport. Besides, the permeability of TS IIA was not apparently influenced by the perfusion section studied, which indicated that there might not exist specific absorption site for TS IIA.

Investigation of the improved effects of 2-hydroxypropyl-beta-cyclodextrin on solubility, dissolution rate, and intestinal absorptive profile of tanshinone IIA in rats

In this paper, the effect of the chemically modified cyclodextrin [namely, 2-hydroxypropyl-beta-cyclodextrin, (HP-beta-CD)] on the aqueous solubility, dissolution rate, and intestinal permeability of the tanshinone IIA (TS) was investigated. The corresponding inclusion complex of TS-HP-beta-CD at the molar ratio of 1:1 was obtained by coevaporation. The solubility of complexed TS in water at 37+/-0.1 centi-degree was 17 times greater than that for the uncomplexed drug. The dissolution rate of TS was significantly increased by the complexation with HP-beta-CD, due to its solubilizing activity. The everted intestinal sac technique in rats was used to study the absorption behavior studies of TS and this complexation through the intestinal tissues. The permeability rates of TS across the intestinal epithelial membrane were enhanced by the formation of inclusion complex with HP-beta-CD about 89, 97 and 82 times of the uncomplexed TS in duodenum, jejunum and ileum, respectively. It was revealed that the absorption rate-limiting step of TS might be the dissolution process. The present results indicated the potential use of HP-beta-CD to improve the gastrointestinal tract absorption of TS.

Modulation of Ganciclovir Intestinal Absorption in Presence of Absorption Enhancers

The purpose of this investigation was to study the influences of absorption enhancers in increasing oral bioavailability of Ganciclovir (GAN) by assessing the transepithelial permeation across cell monolayers in vitro and bioavailability in rats in vivo. The permeation of GAN across Caco-2 and MDCK cell monolayers in the absence/presence of dimethyl-beta-cyclodextrin (DMbetaCD), chitosan hydrochloride (CH), sodium lauryl sulphate (SLS), and their combinations was studied for a 2-h period. GAN was administered to rats in absence/presence of absorption enhancers and drug contents in plasma were estimated. We found that the apparent permeability coefficient (Papp) of GAN in absence of absorption enhancers (control) were 0.261 +/- 0.072 x 10(-6) and 0.486 +/- 0.063 x 10(-6) cm/s in Caco-2 and MDCK cell monolayers, respectively, whereas in the presence of DMbetaCD, CH, SLS, and their combinations, Papp of GAN increased by 5- to 25-fold and 7- to 33-fold as compared to control in Caco-2 and MDCK cell monolayers, respectively. However, in rats, the maximum enhancement in bioavailability of GAN during coadministration of these absorption enhancers was only fivefold compared to GAN control. To conclude, the absorption enhancers-DMbetaCD, CH, SLS, and their combinations demonstrated significant improvement in transepithelial permeation and bioavailability of GAN.

Complexation of tanshinone IIA with 2-hydroxypropyl-beta-cyclodextrin: effect on aqueous solubility, dissolution rate, and intestinal absorption behavior in rats

In this paper, the effect of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the aqueous solubility, dissolution rate, and intestinal permeability of the tanshinone IIA (TS IIA) was investigated. The corresponding inclusion complex of TS IIA/HP-beta-CD at the molar ratio of 1:1 was obtained by coevaporation and characterized by differential scanning calorimetry, and X-ray diffraction. The solubility of complexed TS IIA in water at 37+/-0.1 degrees C was 17 times greater than that for the uncomplexed drug. The dissolution rate of TS IIA was significantly increased by the complexation with HP-beta-CD, due to its solubilizing activity. The everted intestinal sac technique in rats was used to study the absorption behavior of TS IIA and this complexation through the intestinal tissues. The permeability rates of TS IIA across the intestinal epithelial membrane were enhanced by the formation of inclusion complex with HP-beta-CD about 5.2, 5.8 and 4.8 times of the uncomplexed TS IIA in duodenum, jejunum and ileum, respectively. It was revealed that the absorption rate-limiting step of TS IIA might be the dissolution process. The present results indicate the potential use of HP-beta-CD to improve the gastrointestinal tract absorption of TS IIA.

Chemical modification and formulation approaches to elevated drug transport across cell membranes

Drug delivery across cellular barriers, such as intestinal, nasal, buccal, alveolar, vaginal, ocular and blood-brain, is a challenging task. Multiple physiological mechanisms, such as cellular organisation, efflux, and chemical and enzymatic degradation, as well as physicochemical properties of the drug molecule itself, determine the penetration of xenobiotics across epithelial cell layers. Limited intestinal absorption of many novel and highly potent lead compounds has stimulated an intense search for strategies that can effectively enhance permeation across these biological barriers. This review discusses some of the approaches that have been, and are currently being, investigated for transepithelial drug delivery. Transdermal drug delivery requires a separate discussion on its own and is thus outside the scope of this review article.

Methyl-β-cyclodextrin enhances the susceptibility of human breast cancer cells to carboplatin and 5-fluorouracil: Involvement of Akt, NF-κB and Bcl-2

The response rates of extensively used chemotherapeutic drugs, carboplatin (Carb) or 5-fluorouracil (5-FU) are relatively disappointing because of considerable side effects associated with their high-dose regimen. In the present study, we determined whether treatment with a cholesterol depleting agent, methyl-beta-cyclodextrin (MCD), enhances the weak efficacy of low doses of Carb or 5-FU in human breast cancer cells. Data demonstrate that pretreatment with MCD significantly potentiates the cytotoxic activity of Carb and 5-FU in both MCF-7 and MDA-MB-231. Furthermore, we explored the molecular basis of enhanced cytotoxicity, and our data revealed that low-dose treatment with these drugs in MCD pretreated cells exhibited significantly decreased Akt phosphorylation, NF-kappaB activity and down-regulation in expression of anti-apoptotic protein Bcl-2. In addition, MCD pretreated cells demonstrated an increased intracellular drug accumulation as compared to cells treated with drugs alone. Taken together, our data provide the basis for potential therapeutic application of MCD in combination with other conventional cytotoxic drugs to facilitate reduction of drug dosage that offers a better chemotherapeutic approach with low toxicity.

The effects of sinomenine on intestinal absorption of paeoniflorin by the everted rat gut sac model

Paeoniflorin and sinomenine, derived from the root of Paeonia lactiflora Pall. (family Ranunculaceae) and the stem of Sinomenium acutum Rehder & Wilson (family Menispermaceae), respectively, have been, and are currently, widely used for treatment of rheumatic and arthritic diseases in China and Japan. Our previous studies demonstrated that sinomenine could significantly improve the bioavailability of paeoniflorin in rats, but the underlying mechanisms remain unknown. The present study aims to investigate the intestinal kinetic absorptive characteristics of paeoniflorin as well as the absorptive behavior influenced by co-administration of sinomenine using an in vitro everted rat gut sac model. The results showed a good linear correlation between the paeoniflorin absorption in sac contents and the incubation time from 0 to 90 min. However, the concentration dependence showed that a non-linear correlation exists between the paeoniflorin absorption and its concentrations from 10 to 160 microM, and the absorption was saturated at about 80 microM of the drug. Sinomenine at 16 and 136 microM concentrations could significantly enhance the absorption of paeoniflorin (20 microM) by 1.5- and 2.5-fold, respectively. Moreover, two well-known P-glycoprotein inhibitors, verapamil and quinidine, could significantly elevate the absorption of paeoniflorin by 2.1- and 1.5-fold, respectively. Furthermore, sinomenine in a pattern, which influenced paeoniflorin's absorption, manifested as similar to that of P-glycoprotein inhibitors. In conclusion, sinomenine significantly enhance the intestinal absorption of paeoniflorin, subsequently improve the bioavailability of paeoniflorin. The mechanism underlying the improvement of paeoniflorin's bioavailability was proposed that sinomenine could decrease the efflux transport of paeoniflorin by P-glycoprotein.

Modulation of intestinal barrier properties by miltefosine

Miltefosine (hexadecylphosphocholine, HePC) is the first effective oral agent for the treatment of visceral leishmaniasis. This study aimed to determine whether this oral administration alters the integrity and transport capacities of the intestinal barrier. The objectives of this study were: (i) to evaluate the cytotoxicity of HePC, (ii) to investigate the effects of HePC on paracellular and transcellular transport and (iii) to investigate the influence of HePC on three major transporters of the intestinal barrier, namely, P-glycoprotein, the human intestinal peptide transporter (PepT-1) and the monocarboxylic acid transporter (MCT-1) in Caco-2 cell monolayers, used as an in vitro model of the human intestinal barrier. We show that HePC reduced the transepithelial electrical resistance and increased D-[14C]mannitol permeability in a dose-dependent manner but had no effect on [3H]testosterone permeability, demonstrating that HePC treatment enhances paracellular permeability via an opening of the tight junction complex without affecting the transcellular route. Morphological studies using confocal fluorescence microscopy showed no perturbation of the normal distribution of ZO-1, occludin or E-cadherin but revealed a redistribution of the tight junction-associated protein claudin-1 and the perijunctional actin after incubation with HePC. Finally, HePC was found to inhibit the intestinal P-glycoprotein in the Caco-2 cell model after a single short exposure. These results suggest that HePC could modify the oral bioavailability of other therapeutic compounds absorbed via the paracellular route or which are substrates of the intestinal P-glycoprotein.

Lack of effect of β-cyclodextrin and its water-soluble derivatives on in vitro drug transport across rat intestinal epithelium

The present study aimed to investigate whether beta-cyclodetxrin (beta-CD) and its water-soluble derivatives, hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and sulfobutyl ether beta-cyclodextrin (SBE-beta-CD), exert any effects on the permeation of two drug transport markers (propranolol and lucifer yellow) across rat intestinal epithelium. Rat ileum was stripped of its serosa and mounted inside an Ussing Chamber. Apparent permeability coefficients (P(app)) of the markers from the mucosal to serosal side of the tissue were determined at 37 degrees C in the presence and absence of the beta-cyclodextrins on the mucosal side. Potential difference (PD) was constantly monitored during each experiment to ensure maintenance of the viability and integrity of the tissue. Pre-incubation with 1% beta-CD, 1% HP-beta-CD or 1.48% SBE-beta-CD on the mucosal side for 30 min did not significantly alter the PD and the propranolol permeability (p>0.05). Co-incubation with 1% beta-CD or 1% HP-beta-CD exerted no significant effect on the P(app) of both propranolol and lucifer yellow (p>0.05), but co-incubation with 1.48% SBE-beta-CD lowered the P(app) of propranolol from (1.71+/-0.44)x10(-5) to (0.19+/-0.04)x10(-5)cm/s, which may be ascribed to the molecular complexation of propranolol with SBE-beta-CD. All three beta-cyclodextrins exert no apparent impact on both (passive) transcellar and paracellular drug transports.

Differential effects of cyclodextrins and derivatives on the biological behavior of the myocardial perfusion imaging agent 99mTcN-NOET

In addition to improving drug solubilization, cyclodextrins (CDs) also affect the biological behavior of the included compound. We evaluated the effects of two natural CDs beta-CD and gamma-CD, and six beta-CD derivatives, Dimeb, Trimeb, SBb, 2-HP, 6AD, and 6 MTU on the biological behavior of (99m)TcN-NOET, a technetium-99m-labeled, lipophilic compound readily detectable through radioactivity assessment. Determination of CDs' affinities for (99m)TcN-NOET indicated that the cavity size of gamma-CD was not suitable for (99m)TcN-NOET inclusion, and that beta-CD derivatization mostly resulted in decreased CDs affinities for (99m)TcN-NOET to various extents compared with the natural beta-CD. In vitro and ex vivo experiments performed on newborn rat cardiomyocytes and isolated perfused rat hearts, respectively, showed 1.7- and 2.3-fold maximal differences in (99m)TcN-NOET cellular and tissue activities. Regression analyzes indicated no significant correlation between these observed biological differences and the affinities of the eight CDs tested for (99m)TcN-NOET or for cellular membranes. In conclusion, CD derivatization often resulted in impaired affinity of the derivatives for the lipophilic compound (99m)TcN-NOET. Moreover, the in vitro and ex vivo biological behavior of (99m)TcN-NOET was greatly affected depending on the CD used for inclusion of the tracer.

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.

Validated HPLC analytical method with programmed wavelength UV detection for simultaneous determination of DRF-4367 and Phenol red in rat in situ intestinal perfusion study

A simple, precise and accurate isocratic reverse-phase liquid chromatography method with programmed wavelength detection has been validated to quantify DRF-4367 and Phenol red, simultaneously for application in rat in situ single pass intestinal perfusion study to assess intestinal permeability of DRF-4367, a novel cox-2 inhibitor. The method was validated on RP C-18 analytical column. Mobile phase consisted of sodium dihydrogen orthophosphate (pH 3.2, 0.01 M)-acetonitrile-methanol (30:50:20, v/v/v). The developed method has a short run time of 12 min with a flow rate of 1.0 ml/min. The injector volume was set to 20 microl and acquisition was carried out using a PDA detector while processing was done by timed wavelength extraction. The percentage R.S.D. and recovery in all studies indicated that the method was suitable for the intended purpose. The validated method was found to be linear and precise in the working range. Suitability of storage at cold temperature was ensured along with complete sample recovery.

Cyclodextrins in nasal delivery of low-molecular-weight heparins: in vivo and in vitro studies

PURPOSE

To test the hypothesis that cyclodextrins reversibly enhance nasal absorption of low-molecular-weight heparins (LMWHs) and to investigate the mechanisms by which cyclodextrins enhance LMWH absorption via the nose.

METHODS

Absorption of LMWHs was studied by measuring plasma anti-factor Xa activity after nasal administration of various LMWH formulations to anesthetized rats. In vivo reversibility studies were performed to investigate if the effects of cyclodextrins are reversible and diminish with time. The absorption-enhancing mechanisms of cyclodextrins were investigated in cell culture model. The transport of enoxaparin and mannitol, changes in transepithelial electrical resistance (TEER), and distribution of tight junction protein ZO-1 were investigated.

RESULTS

Formulations containing 5% dimethyl-beta-cyclodextrin (DMbetaCD) produced the highest increase in the bioavailability of LMWH preparations tested. In vivo reversibility studies with 5% DMbetaCD showed that the effect of the absorption enhancer at the site of administration diminished with time. Transport studies using 16HBE14o(-) cells demonstrated that the increase in the permeability of enoxaparin and mannitol, reduction in TEER, and the changes in the tight junction protein ZO-1 distribution produced by 5% DMbetaCD were much greater than those produced by beta-cyclodextrin (betaCD) or hydroxyl-propyl-beta-cyclodextrin (HPbetaCD).

CONCLUSIONS

Of the cyclodextrins tested, DMbetaCD was the most efficacious in enhancing absorption of LMWHs both in vivo and in vitro. The study also suggests that cyclodextrins enhance nasal drug absorption by opening of cell-cell tight junctions.

Effects of γ- and Hydroxypropyl-γ-cyclodextrins on the Transport of Doxorubicin across an in Vitro Model of Blood-Brain Barrier

Association between doxorubicin (DOX) and gamma-cyclodextrin (gamma-CD) or hydroxypropyl-gamma-CD (HP-gamma-CD) has been examined to increase the delivery of this antitumoral agent to the brain. The stoichiometry and the stability constant of gamma-CD or HP-gamma-CD and DOX complexes were determined in physiological medium by UV-visible spectroscopy. By using an in vitro model of the blood-brain barrier (BBB), endothelial permeability and toxicity toward the brain capillary endothelial cells of DOX, gamma-CD, and HP-gamma-CD were performed. For each CD, endothelial permeability was relatively low and a disruption of the BBB occurred at 20 microM, 20 mM, and 50 mM DOX, gamma-CD, and HP-gamma-CD, respectively. Increasing amounts of CDs were added to a fixed DOX concentration. Addition of gamma-CD or HP-gamma-CD, up to 15 and 35 mM, respectively, decreased the DOX delivery, probably due to the low complex penetration across the BBB and the decrease in free DOX concentration. Higher CD concentrations increased the DOX delivery to the brain, but this effect is due to a loss of BBB integrity. In contrast to what was observed on Caco-2 cell model with various drugs, CDs are not able to increase the delivery of DOX across our in vitro model of BBB.

Behavior of α-, β-, and γ-Cyclodextrins and Their Derivatives on an in Vitro Model of Blood-Brain Barrier

Cyclodextrins (CDs) can be envisaged to cure some diseases related to the brain, but the behavior of these compounds toward the blood-brain barrier (BBB) remains largely unexplored to envisage such clinical applications. To fulfill this gap, the toxicity and endothelial permeability for native, methylated, and hydroxypropylated alpha-, beta-, and gamma-CDs have been studied on an in vitro model of BBB. As shown by the endothelial permeability for sucrose and immunofluorescence stainings, the native CDs are the most toxic CDs (alpha- > beta- > gamma-CD). Whereas the chemical modification of beta-CD did not affect the toxicity of this CD, differences are observed for the alpha- and gamma-CD. To determine the origin of toxicity, lipid effluxes on the brain capillary endothelial cells were performed in the presence of native CDs. It was found that alpha-CD removed phospholipids and that beta-CD extracted phospholipids and cholesterol. gamma-CD was less lipid-selective than the other CDs. Finally, the endothelial permeability of each CD has been determined. Surprisingly, no structure/permeability relationship has been observed according to the nature and chemical modifications of CDs.

Gastrointestinal Absorption of Recombinant Hirudin-2 in Rats

To investigate the absorption of recombinant hirudin-2 (rHV2) after oral administration to rats and its possible absorption mechanism, a series of experiments were carried out. The degradation of (125)I-rHV2 in the luminal contents and variant mucosal subcellular fractions, as well as the effect of degradation inhibition of some adjuvant was investigated. The bioavailability of rHV2, with or without degradation inhibitor after oral administration to rats was estimated, whereas the in situ loop test and everted sac experiment were also conducted to understand more about the gastrointestinal absorption of rHV2 in rats. It was demonstrated that the rHV2 was not stable in the luminal contents and subfraction of the intestinal mucosa. Some enzyme inhibitor, such as bacitracin or casein, could inhibit the degradation to certain degrees. The intact rHV2 molecules were found in the rat plasma after oral administration, and the bioavailability varies obviously, dependent on the analytical method. Some of the enzyme inhibitor could enhance the rHV2 oral absorption. There is no site difference on rHV2 absorption in different segments of small intestine. The possible transport mechanism of rHV2 across the gastrointestinal tract is concerned with the endocytosis process.

Enhanced transport of a novel anti-HIV agent--cosalane and its congeners across human intestinal epithelial (Caco-2) cell monolayers

PURPOSE

Cosalane is a potent inhibitor of HIV replication with activity against a broad range of viral targets. However, oral bioavailability of this highly lipophilic compound is extremely poor (<1%). The purpose of this study is to screen a variety of permeation enhancers (cyclodextrin derivatives, cremophor EL, bile salts and mixed micelles) for their ability to enhance the transport of cosalane and its analogs/prodrugs across Caco-2 cell monolayers.

METHODS

Cosalane and its different analogs/prodrugs were synthesized and their physicochemical properties were determined. Caco-2 cells were cultured at a density of 66,000 cells/cm(2) either on collagen coated clear polyester membranes or Transwell inserts. Side-bi-side diffusion cells and Transwell inserts were employed to study for the transport of cosalane and its analogs/prodrugs with various permeation enhancers across Caco-2 cell monolayers.

RESULTS

Permeabilities of EH-3-39, EH-3-55 and EH-3-57 significantly improved compared to that of cosalane in the presence of bile salt, sodium desoxycholate. Among the various cyclodextrins studied, hydroxypropyl beta cyclodextrin (HP-beta-CD) and dimethyl beta cyclodextrin (DM-beta-CD) exhibited 22.3-fold and 19-fold permeability enhancement of cosalane respectively across Caco-2 cell monolayers. Sodium desoxycholate (10 mM) also showed a remarkable (105-fold) enhancement on the permeability of cosalane (P(app) 11.72+/-3.31 x 10(-6) cm/s) without causing any measurable cellular damage. Cremophor EL resulted in higher transport of 14C mannitol. The mechanism of enhancement effect can be mainly attributed to the alteration of membrane fluidity by cyclodextrin and opening of tight junctions by cremophor EL.

CONCLUSIONS

Among the enhancers tested, 10 mM sodium desoxycholate and HP-beta-CD appear to be viable candidates for further development of an oral formulation of cosalane and its congeners.

Time-dependent loss of radioactivity counts associated with paracellular markers in the presence of cyclodextrin

This communication reports an unexpected phenomenon observed during the counting of radiolabeled paracellular marker solutions in the presence of 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD). The results revealed time-dependent loss of 14C-mannitol and 14C-polyethlene glycol 4000 radioactivity counts with increased percentages of HPbetaCD. However, 14C-diazepam, a transcellular marker, displayed a stable count. A hypothesis behind this phenomenon is being proposed, involving water transfer from aqueous droplets to the surfactant rich scintillation fluid. The remaining droplets, becoming more and more concentrated in cyclodextrin, entrap the hydrophilic markers and consequently exhibit an increasing quenching effect. This effect shows that careful monitoring of radiolabeled markers used in transport experiments is necessary, even with high quench resistant scintillation fluids, to prevent erroneous interpretation of the transport data.

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.

In-vitro nasal drug delivery studies: comparison of derivatised, fibrillar and polymerised collagen matrix-based human nasal primary culture systems for nasal drug delivery studies

The aim of this study was to establish a collagen matrix-based nasal primary culture system for drug delivery studies. Nasal epithelial cells were cultured on derivatised (Cellagen membrane CD-24), polymerised (Vitrogen gel) and fibrillar (Vitrogen film) collagen substrata. Cell morphology was assessed by microscopy. The cells were further characterised by measurement of ciliary beat frequency (CBF), transepithelial resistance (TER), permeation of sodium fluorescein, mitochondrial dehydrogenase (MDH) activity and lactate dehydrogenase (LDH) release upon cell exposure to sodium tauro-24, 25 dihydrofusidate (STDHF). Among the three collagen substrata investigated, the best epithelial differentiated phenotype (monolayer with columnar/cuboidal morphology) occurred in cells grown on Cellagen membrane CD-24 between day 4 and day 11. Cell culture reproducibility was better with Cellagen membrane CD-24 (90%) in comparison with Vitrogen gel (70%) and Vitrogen film (< 10%). TER was higher in cells grown on Vitrogen gel than on Cellagen membrane CD-24 and Vitrogen film. The apparent permeability coefficient (Papp x 10(-7)cm s(-1)) of sodium fluorescein in these conditions was 0.45+/-0.08 (Vitrogen gel) and 1.91+/-0.00 (Cellagen membrane CD-24). Except for LDH release, CBF and cell viability were comparable for all the substrata. Based on MDH activity, LDH release, CBF, TER and permeation studies, Cellagen membrane CD-24- and Vitrogen gel-based cells were concluded to be functionally suitable for in-vitro nasal drug studies. Vitrogen film-based cultures may be limited to metabolism and cilio-toxicity studies.

Intranasal vaccination against plague, tetanus and diphtheria

Plague is an extremely virulent and potentially lethal infection caused by the bacterium Y. pestis. The current vaccine used to immunise against plague often fails to engender solid (100%) protection against inhalational infection with Y. pestis. Similarly, logistical factors favour the development of non-parenteral immunisation protocols to counter plague. Recently an improved parenteral vaccination strategy for plague, based on the recombinant subunit approach, has entered clinical trails. The Yersinia pestis subunit antigens (F1 and V) have been successfully incorporated into novel vaccine delivery systems such as biodegradable microspheres composed of poly-L-(lactide) (PLLA). Intranasal and intratracheal administration of PLLA microencapsulated F1 and V serves to protect experimental animals from inhalational and subcutaneous challenge with virulent Y. pestis bacilli. Liposomes have also been used to improve the immunogenicity of intranasally administered Y. pestis antigens, and the effectiveness of this approach to plague immunisation has been evaluated. Tetanus and diphtheria still cause many deaths worldwide. The maintenance of protective immunity to diphtheria and tetanus requires booster injections of the currently licensed toxoid vaccines. Consequently, many people remain unprotected. Improved coverage may well result from the development of effective non-invasive vaccines that could be readily distributed and potentially self-administered. To this end, the intranasal and inhalational routes of administration have been extensively investigated. Tetanus and diphtheria toxoids have been delivered intranasally to experimental animals using a wide variety of adjuvants (enterotoxin derivatives), penetration enhancers (cyclodextrins, bile salts, surfactants, cationic polymers) and delivery systems (microspheres and liposomes). As compared with parenteral vaccination, nasal immunisation has been shown favourably effective in small animal models, and a limited number of early phase clinical trails. As a caveat to this, adjuvantisation of toxoid/subunit molecules appears to be a requisite for elicitation of appreciable immunological responses, following nasal administration of acellular immunogens. Testing in larger animal models and humans is needed to ascertain if the promising results obtained in rodents can be reciprocated without compromising safety.

Cyclodextrins in topical drug formulations: theory and practice

Cyclodextrins are cyclic oligosaccharides with a hydrophilic outer surface and a somewhat lipophilic central cavity. Cyclodextrins are able to form water-soluble inclusion complexes with many lipophilic water-insoluble drugs. In aqueous solutions drug molecules located in the central cavity are in a dynamic equilibrium with free drug molecules. Furthermore, lipophilic molecules in the aqueous complexation media will compete with each other for a space in the cavity. Due to their size and hydrophilicity only insignificant amounts of cyclodextrins and drug/cyclodextrin complexes are able to penetrate into lipophilic biological barriers, such as intact skin. In general, cyclodextrins enhance topical drug delivery by increasing the drug availability at the barrier surface. At the surface the drug molecules partition from the cyclodextrin cavity into the lipophilic barrier. Thus, drug delivery from aqueous cyclodextrin solutions is both diffusion controlled and membrane controlled. It appears that cyclodextrins can only enhance topical drug delivery in the presence of water.

A moderate interaction of maltosyl-alpha-cyclodextrin with Caco-2 cells in comparison with the parent cyclodextrin

The cytotoxicity of maltosyl-alpha-cyclodextrin (G2-alpha-CyD) and maltosyl-beta-cyclodextrin (G2-beta-CyD) toward Caco-2 cells was compared with that of natural alpha-cyclodextrin (alpha-CyD), beta-cyclodextrin (beta-CyD) and gamma-cyclodextrin (gamma-CyD). The degree of increase in cytotoxicity was dependent on the CyD's type and the concentration: the cytotoxicity of CyDs at the same concentration increased in the order of gamma-CyD<G2-beta-CyD<G2-alpha-CyD<<alpha-CyD, although beta-CyD could not be compared to other CyDs because of low solubility in water. Alpha-CyD decreased transepithelial electrical resistance (TEER) and increased the apical-to-basolateral (AP-to-BL) transport of [3H]mannitol, a paracellular transport marker, in a concentration-dependent manner, suggesting that alpha-CyD decreased the integrity of Caco-2 cell monolayers. In addition, alpha-CyD increased the AP-to-BL transport of rhodamine 123, a transcellular transport marker, under the experimental conditions being independent of P-glycoprotein. In contrast, G2-alpha-CyD, G2-betaCyD and gamma-CyD had slight effect on both TEER and the transport of mannitol and rhodamine 123 even at relatively high concentrations up to 150 mM. The inability of G2-alpha-CyD and G2-beta-CyD to effect TEER and the transport of mannitol and rhodamine 123 could be explained by the findings that these maltosylated CyDs released only a small amount of membrane constituents from Caco-2 cell monolayers and interacted only weakly with monolayers composed of L-alpha-dipalmitoylphosphatidylcholine (DPPC) formed on water. These results indicate that G2-alpha-CyD has less cytotoxicity and less disturbing ability toward Caco-2 cell monolayers than alpha-CyD, and G2-beta-CyD has, at least, comparable cytotoxicity to beta-CyD toward them. Thus, from the safety point of view, highly water-soluble G2-alpha-CyD and G2-beta-CyD may be particularly useful in various pharmaceutical formulations.

Evaluation of absorption enhancement for a potent cyclopeptidic alpha(nu)beta(3)-antagonist in a human intestinal cell line (Caco-2)

Different absorption enhancing principles for a potent cyclopeptidic alpha(nu)beta(3)-antagonist (EMD 121974) were investigated in monolayers of a human intestinal cell line (Caco-2). Transepithelial transport was quantitated by reversed-phase high-performance liquid chromatography. Cytotoxic effects were characterized by determination of transepithelial electrical resistances (TEERs), propidium iodide (PI)-influx, FITC-phalloidin staining and the release of cytosolic lactate dehydrogenase (LDH). Medium chain fatty acids (MCFAs, NaC10, NaC12) and taurocholate (NaTC) were the most efficient enhancers of cyclopeptide and FITC-dextran 4400 permeability coefficients, displaying different time profiles of activity. Whereas NaTC (15 mM) showed almost a constant permeation enhancing effect from 20 min up to 120 min (ca. 12-fold), MCFA absorption enhancement was markedly dependent on incubation time (NaC10, 20 min: 1.2-fold, 120 min: 17-fold; NaC12, 20 min: 4.3-fold, 120 min: 13-fold). All cytotoxicity assays demonstrated that MCFAs were significantly more cytotoxic than NaTC. Ion pairing with hydrophobic amino acids and heptane sulfonate distinctly increased octanol-buffer partition coefficients of the cationic cyclopeptide but did not enhance its transepithelial permeability. Nanoparticles as well as beta-cyclodextrin neither affected integrity of the cells nor transport properties of the cyclopeptide. In summary, significant absorption enhancement was only observed with NaTC or MCFAs. Increase in permeability coefficients using NaTC occurred rapidly with acceptable cytotoxicities and merits further investigations.

Regulation of the intestinal epithelial paracellular barrier

Paracellular transport of orally-administered drugs, the passage of molecules between adjacent intestinal epithelial cells, is impeded by a range of structural and functional features found in the intestine. An increased knowledge of the mechanisms that govern the paracellular barrier will enable the pharmaceutical scientist to design novel and rational formulations and delivery platforms that will improve the oral bioavailability of therapeutic molecules, particularly proteins and peptides, which would be taken-up by the paracellular pathway.

Prediction of dissolution-absorption relationships from a continuous dissolution/Caco-2 system

The objectives were 1) to design a continuous dissolution/Caco-2 system to predict the dissolution-absorption relationships for fast and slow dissolving formulations of piroxicam, metoprolol tartrate, and ranitidine HCl, and compare the predicted relationships with observed relationships from clinical studies; 2) to estimate the effect of croscarmellose sodium on ranitidine dissolution-absorption relationships; and 3) to estimate the effect of solubilizing agents on piroxicam dissolution-absorption relationships. A continuous dissolution/Caco-2 system was constructed from a dissolution apparatus and a diffusion cell, such that drug dissolution and permeation across a Caco-2 monolayer would occur sequentially and simultaneously. The continuous system generally matched observed dissolution-absorption relationships from clinical studies. For example, the system successfully predicted the slow metoprolol and slow ranitidiine formulations to be permeation-rate-limited. The system predicted the slow piroxicam formulation to be dissolution-rate-limited, and the fast piroxicam formulation to be permeation-rate-limited, in spite of piroxicam's high permeability and low solubility. Additionally, the system indicated croscarmellose sodium enhanced ranitidine permeability and predicted solubilizing agents to not modulate permeability. These results suggest a dissolution/Caco-2 system to be an experimentally based tool that may predict dissolution-absorption relationships from oral solid dosage forms, and hence the relative contributions of dissolution and permeation to oral drug absorption kinetics.