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

Advancements in cyclodextrin-based controlled drug delivery: Insights into pharmacokinetic and pharmacodynamic profiles

This article discusses and summarizes some fascinating outcomes and applications of cyclodextrins (CDs) and their derivatives in drug delivery. These applications include the administration of protein, peptide medications, and gene delivery. Several innovative drug delivery systems, including NPs, microspheres, microcapsules, and liposomes, are designed with the help of CD, which is highlighted in this article. The use of these compounds as excipients in medicine formulation is reviewed, in addition to their well-known effects on drug solubility and dissolution, as well as their bioavailability, safety, and stability. Furthermore, the article focuses on many factors that influence the development of inclusion complexes, as having this information is necessary to manage these diverse materials effectively. An overview of the commercial availability, regulatory status, and patent status of CDs for pharmaceutical formulation is also presented. Due to the fact that CDs can discover new uses in drug delivery consistently, it is predicted that they will solve a wide range of issues related to the distribution of a variety of unique medications through various delivery channels.

Aqueous eye drops containing drug/cyclodextrin nanoparticles deliver therapeutic drug concentrations to both anterior and posterior segment

Using topical application to deliver therapeutic concentrations of drugs to the posterior segment of the eye remains very challenging. As a result, posterior segment diseases are usually treated by intravitreal injection or implant. While topical treatments are commonly used for anterior segment conditions, they sometimes require frequent applications. Eye drop formulations based on γ-cyclodextrin (γCD)-based nanoparticle aggregates were developed, which in animal models and clinical studies deliver therapeutic concentrations of drugs (dorzolamide and dexamethasone) to both anterior and posterior segments of the eye. An early study in humans showed dorzolamide/γCD eye drops could achieve comparable intraocular pressure decreases to commercial dorzolamide eye drops, but with less frequent application. Pilot studies with dexamethasone/γCD eye drops suggested that they could be effective in a range of conditions, including diabetic macular oedema, cystoid macular oedema and vitritis secondary to uveitis, postcataract surgery inflammation and postoperative treatment in trabeculectomy. Phase II studies with similar dexamethasone/γCD nanoparticle eye drops in diabetic macular oedema and postcataract surgery inflammation have recently been completed. This technology has the potential to be used with other classes of drug molecules and to replace or complement invasive treatments, providing safer, non-invasive therapies, particularly for posterior segment conditions, that can be self-administered as eye drops by patients.

Cyclodextrins: structure, physicochemical properties and pharmaceutical applications

Since their discovery over 100 years ago cyclodextrins (CDs) have been the subject of numerous scientific publications. In 2016 alone CDs were the subject of over 2200 research articles published in peer-reviewed journals and mentioned in over 2300 patents and patent applications, many of which were on pharmaceutical applications. Natural CDs and their derivatives are used as enabling pharmaceutical excipients that enhance aqueous solubility of poorly soluble drugs, increase drug permeability through biological membranes and improve drug bioavailability. Unlike conventional penetration enhancers, their hydrophilic structure and high molecular weight prevents them from penetrate into lipophilic membranes leaving biological membranes intact. The natural CDs and some of their derivatives have monographs in pharmacopeias and are also commonly used as food additives and in toiletry products. CDs form inclusion complexes with lipophilic moieties of hydrophobic drugs. Furthermore, CDs are able to form non-inclusion complexes and self-assembled aggregates; small and large complex aggregates with micellar-like structures that can enhance drug solubility. Excipients commonly used in pharmaceutical formulations may have additive or inhibiting effect on the CD solubilization. Here various methods used to investigate CD aggregate formation are reviewed as well as techniques that are used to increase the solubilizing effects of CDs; methods that enhance the apparent intrinsic solubility of drugs and/or the complexation efficacy and decrease the amount of CD needed to develop CD-containing pharmaceutical formulations. It will be explained how too much or too little CD can hamper drug bioavailability, and the role of CDs in solid dosage forms and parenteral formulations, and examples given on how CDs can enhance drug delivery after ocular, nasal and pulmonary administration.

Cyclodextrins and topical drug delivery to the anterior and posterior segments of the eye

It is generally believed that it is virtually impossible to obtain therapeutic drug concentrations in the posterior segment of the eye after topical application of aqueous, low viscosity eye drops. Thus, intravitreal drug injections and drug implants are currently used to treat diseases in the posterior segment such as macular edema. Here it is described how, through proper analysis of the drug permeation barriers and application of well-known pharmaceutical excipients, aqueous eye drops are designed that can deliver lipophilic drugs to the posterior segment as well as how such eye drops can maintain high drug concentrations in the anterior segment. Through stepwise optimization, eye drops containing solid drug/cyclodextrin complex microparticles with a mean diameter of 2-4μm, dissolved drug/cyclodextrin complex nanoparticles and dissolved drug molecules in an aqueous eye drop media of low viscosity were designed. After administration of the eye drops the microparticles slowly dissolved and maintained close to saturated drug concentrations in the aqueous tear fluid for several hours. Studies in rabbits and clinical evaluations in humans, using dorzolamide and dexamethasone as sample drugs, show that the eye drops deliver significant amounts of drugs to both the posterior segment and anterior segment of the eye. Clinical studies indicate that the eye drops can replace intravitreal injections and implants that are currently used to treat ophthalmic diseases and decrease frequency of drug administration, both of which can improve patient compliance.

Thermosensitive PLA based nanodispersion for targeting brain tumor via intranasal route

Delivery of drugs to the brain via nasal route has been studied by many researchers. However, low residence time, mucociliary clearance and enzymatically active environment of nasal cavity pose many challenges to successful nasal delivery of drugs. We aim to deliver methotrexate by designing thermosensitive nanodispersion exhibiting enhanced residence time in nasal cavity and bypassing the blood brain barrier (BBB). PLA nanoparticles were developed using solvent evaporation technique. The developed nanoparticles were further dispersed in prepared thermosensitive vehicle of poloxamer 188 and Carbopol 934 to impart the property of increased residence time. The formulated nanoparticles demonstrated no interaction with the simulated nasal fluids (SNF), mucin, serum proteins and erythrocytes which demonstrate the safety of developed formulation for nasal administration. The penetration property of nanoparticles though the nasal mucosa was higher than the pure drug due to low mucociliary clearance. The developed nanoparticles diffused though the membrane pores and rapidly distributed into the brain portions compared to the pure drug. There was detectable and quantifiable amount of drug seen in the brain as demonstrated by in vivo brain distribution studies with considerably low amount of drug deposition in the lungs. The pharmacokinetic parameters demonstrated the enhancement in circulation half life, area under curve (AUC) and Cmax of the drug when administered intranasal in encapsulated form. Thus, the thermosensitive nanodispersions are surely promising delivery systems for delivering anticancer agents though the nasal route for potential treatment of brain tumors.

Cyclodextrins, blood-brain barrier, and treatment of neurological diseases

Biological barriers are the main defense systems of the homeostasis of the organism and protected organs. The blood-brain barrier (BBB), formed by the endothelial cells of brain capillaries, not only provides nutrients and protection to the central nervous system but also restricts the entry of drugs, emphasizing its importance in the treatment of neurological diseases. Cyclodextrins are increasingly used in human pharmacotherapy. Due to their favorable profile to form hydrophilic inclusion complexes with poorly soluble active pharmaceutical ingredients, they are present as excipients in many marketed drugs. Application of cyclodextrins is widespread in formulations for oral, parenteral, nasal, pulmonary, and skin delivery of drugs. Experimental and clinical data suggest that cyclodextrins can be used not only as excipients for centrally acting marketed drugs like antiepileptics, but also as active pharmaceutical ingredients to treat neurological diseases. Hydroxypropyl-β-cyclodextrin received orphan drug designation for the treatment of Niemann-Pick type C disease. In addition to this rare lysosomal storage disease with neurological symptoms, experimental research revealed the potential therapeutic use of cyclodextrins and cyclodextrin nanoparticles in neurodegenerative diseases, stroke, neuroinfections and brain tumors. In this context, the biological effects of cyclodextrins, their interaction with plasma membranes and extraction of different lipids are highly relevant at the level of the BBB.

Strategic approaches for enhancement of in vivo transbuccal peptide drug delivery in rabbits using iontophoresis and chemical enhancers

PURPOSE

To evaluate the feasibility of iontophoresis and the combination effects with chemical enhancers on in vivo hypocalcemic effect of transbuccally delivered salmon calcitonin (sCT).

METHODS

N-acetyl-L-cysteine (NAC), sodium deoxyglycocholate (SDGC), and ethanol were used as chemical enhancers; and 0.5 mA/cm(2) fixed electric current was employed as a physical enhancer. sCT hydrogel was applied to rabbit buccal mucosa, and blood samples were obtained via the central auricular artery. Blood calcium level was measured by calcium kit and the conformational changes of buccal mucosa were investigated with FT-IR spectroscopy. Hematoxylin/eosin staining was used for the histological evaluation of buccal mucosa.

RESULTS

Iontophoresis groups except iontophoresis-NAC group showed significant hypocalcemic effect compared to negative control, in particular iontophoresis-SDGC combination group showed fast onset of action as well as sustained hypocalcemic effect (p < 0.05). FT-IR result demonstrated the reduction of buccal barrier function, and the histological study showed a decrease in buccal thickness as well as minor damage to the dermal-epidermal junctions in the enhancing method groups; however, the damaged tissues virtually recovered within 24 h after the removal of electrodes.

CONCLUSIONS

Iontophoresis and combination with SDGC were found to be safe and potential strategies for transbuccal peptide delivery in vivo.

Enhancement of nasal absorption of calcitonin loaded in liposomes

Intranasal administration of calcitonin-containing liposomes in rabbits was investigated to evaluate the in vivo calcitonin absorption performance. Plasma calcitonin concentrations and calcium levels were measured and pharmacokinetic parameters were calculated. The bioavailability of calcitonin resulted from the intranasal delivery formulations demonstrated an order of calcitonin-containing positively charged liposomes > calcitonin-containing negatively charged liposomes > calcitonin solution. The significant enhancement of bioavailability of calcitonin for positively charged liposomes may be due to the charge interaction of positively charged liposomes with the negatively charged mucosa surface. Marked accumulation of positively charged liposomes was found on the negatively charged nasal mucosa surface. The retention of positively charged liposomes on the nasal mucosa resulted in an increase of residence time with high local concentration of calcitonin for increase of absorption.

Comparison of different absorption enhancers on the intranasal absorption of isosorbide dinitrate in rats

The objective of this work was to study the influence of different absorption enhancers on the intranasal absorption of isosorbide dinitrate (ISDN). First of all, an in situ nasal perfusion technique in rats was used to investigate the effect of pH, concentration of drug solution and different absorption enhancers on the intranasal absorption of ISDN. The absorption enhancers investigated include hydroxypropyl-beta-cyclodextrin (HP-beta-CD), chitosans (CS) of different molecular weight, and poloxamer 188. All of them enhanced the intranasal absorption of ISDN remarkably. It was found that poloxamer 188 had better permeation enhancing effect than that of HP-beta-CD and CS of the same concentration. Thereafter, in vivo behaviors of the selected formulations were studied in rats and the pharmacokinetic parameters were calculated and compared with that of intravenous injection. Both in situ and in vivo studies demonstrated that poloxamer 188 played a key role in promoting intranasal absorption of ISDN. In nasal ciliotoxicity test, all the absorption enhancers investigated showed good safety profiles. Taking both enhancing effect and safety into account, we suggest poloxamer 188 is the most promising as an intranasal absorption enhancer.

Influence of fillers in powder formulations containing N-acetyl-L-cysteine on nasal peptide absorption

We examined the influence of filler species on the nasal absorbability of peptide drugs via a newly developed powdery formulation system containing N-acetyl-l-cysteine (NAC) as an absorption enhancer. Using salmon calcitonin (SCT) as the principal model drug, we tested the effects of various formulations with different powder materials as fillers on the nasal absorption of SCT in rats. An intranasal administration experiment revealed that the use of less wettable powders provided better nasal absorbability, and the highest absolute bioavailability (30.0% +/- 8.6%) was obtained when ethylcellulose was used as a filler. All these results were readily explicable in terms of our hypothetical enhancing mechanism. Furthermore, human parathyroid hormone and insulin were applied to this ethylcellulose formulation system, giving nasal bioavailabilities of 28.2% +/- 6.5% and 23.4% +/- 10.6%, respectively, thus suggesting that this formulation system is widely applicable to peptide drugs.

Pharmacokinetic Advantage of an Intranasal Preparation of a Novel Anti-osteoporosis Drug, L-Asp-Hexapeptide-Conjugated Estradiol

We examined the usefulness of intranasal (i.n.) administration of a novel osteotropic prodrug of estradiol, estradiol-17beta-succinate-(L-aspartate)6 (E2.17D6), for selective drug delivery to bone. E2.17D6 alone or with 5% 2,6-di-O-methyl-beta-cyclodextrin (DMbetaCD), 5% beta-cyclodextrin (betaCD), or 10% hydroxypropyl cellulose (HPC) as an absorption enhancer was administered to ovariectomized (OVX) mice via the i.n. route. The oral and nasal bioavailability after p.o. or i.n. administration of E2.17D6 (3.7 micromol/kg) in mice amounted to 9.9 and 23.0% of the dose, respectively. The values of nasal bioavailability of E2.17D6 administered with DMbetaCD, betaCD, and HPC were 74.9, 55.8, and 49.1%, respectively. The plasma concentration of E2.17D6 after i.n. administration of E2.17D6-DMbetaCD decreased rapidly to the endogenous level by 6 h, but the concentration in the bone was about 200 times higher than that in plasma, and decreased slowly over a period of about a week. When E2 (total dose 4.4 micromol/kg, i.n., every 3rd day) was administered to OVX mice for 35 d, bone mineral density (BMD), liver weight, and uterus weight increased, whereas E2.17D6-DMbetaCD (total dose 0.44 to 8.8 micromol/kg, i.n., every 7th day) increased only BMD in a dose-dependent manner. In conclusion, intranasally administered E2.17D6-DMbetaCD has a potent antiosteoporotic effect without side effects, and has potential to provide an improved quality of life for patients with osteoporosis.

Absorption enhancers for nasal drug delivery

This paper describes the basic concepts for the transmucosal delivery of drugs, and in particular the use of the nasal route for delivery of challenging drugs such as polar low-molecular-weight drugs and peptides and proteins. Strategies for the exploitation of absorption enhancers for the improvement of nasal delivery are discussed, including consideration of mechanisms of action and the correlation between toxic effect and absorption enhancement. Selected enhancer systems, such as cyclodextrins, phospholipids, bioadhesive powder systems and chitosan, are discussed in detail. Examples of the use of these enhancers in preclinical and clinical studies are given. Methods for assessing irritancy and damage to the nasal membrane from the use of absorption enhancers are also described. Finally, the mucosal use of absorption enhancers (chitosan) for the improved nasal delivery of vaccines is reported with reference to recent phase I/II clinical studies.

Enhanced bioavailability of calcitonin formulated with alkylglycosides following nasal and ocular administration in rats

PURPOSE

The purpose of this study was to characterize the effects of alkylglycosides on the bioavailability of calcitonin following nasal and ocular administration.

METHODS

A salmon calcitonin specific radioimmunoassay kit was used to measure calcitonin levels in anesthetized rats at various times after nasal or ocular administration of calcitonin formulated with saline or with octylmaltoside, a medium chain length alkylglycoside or tetradecylmaltoside, a long chain alkylglycoside. The extent of calcitonin absorption was determined directly from the plasma calcitonin level-time curve and the bioavailability of calcitonin was determined from the area under the plasma calcium level-time curve. The calcium level was determined using a colorimetric method.

RESULTS

When the nasal formulation contained calcitonin plus saline or 0.125% octylmaltoside, little or no calcitonin was absorbed. However, plasma calcitonin levels were increased and plasma calcium levels were decreased when the nasal formulation contained calcitonin plus 0.125% or 0.25% tetradecylmaltoside. Maximal calcitonin levels were observed 7.5-10 min after nasal administration of the formulation. Ocular administration of calcitonin formulated with tetradecylmaltoside also resulted in calcitonin absorption, but less calcitonin absorption was found after ocular administration than after nasal administration.

CONCLUSION

The experimental data indicate that tetradecylmaltoside, but not octylmaltoside. can be effectively used to enhance the bioavailability of nasally and ocularly administered calcitonin.

Evaluation of a novel, natural oligosaccharide gum as a sustained-release and mucoadhesive component of calcitonin buccal tablets

The objective of this study was to evaluate the gum from Hakea gibbosa (hakea) as a sustained-release and mucoadhesive component in buccal tablets for a model peptide, namely, salmon calcitonin. Flat-faced core tablets containing either 12 or 32 mg of hakea and 40 microg (200 IU) of salmon calcitonin (sCT) per tablet were formulated using a direct compression technique and were coated with Cutina on all but one face. The in vitro release profiles were sigmoidal in nature and according to a mathematical model indicated super Case II transport as the primary mechanism of release. The resulting plasma sCT and calcium concentrations were determined following both intravenous administration and buccal application of mucoadhesive tablets in rabbits. Following intravenous administration, the mean values determined for t(1/2) (alpha), t(1/2) (beta), V(d), and CL for sCT were 0.76 +/- 0.06 min, 67 +/- 18 min, 1484 +/- 454 mL/kg, and 19 +/- 2 mL/min.kg, respectively. Following the application of the mucoadhesive buccal tablets which contained 40 microg of sCT and either 12 or 32 mg of hakea, the calculated apparent bioavailability (F) and clearance (CL) were 37 +/- 6% and 19 +/- 3.3 mL/min.kg and 16 +/- 8% and 18 +/- 0.4 mL/min. kg, respectively. Serum calcium concentrations indicated that biologically active sCT was delivered across the rabbit buccal mucosa. The strength of mucoadhesion of the tablets was also quantitated in terms of the force of detachment as a function of time. The force of detachment for the mucoadhesive buccal tablets containing either 12 or 32 mg of hakea and 40 microg of sCT increased from 4.47 +/- 0.68 to 8.41 +/- 1.0 N and 8.23 +/- 1.62 to 14.98 +/- 1.63 N, respectively, from 5 to 90 min following application to excised rabbit intestinal mucosa. These results demonstrate that the novel, natural gum from Hakea gibbosa may be used to sustain the release of sCT from a unidirectional-release buccal tablet. The mechanism of in vitro release is likely to involve peptide diffusion/polymer dissolution. The mucoadhesive strength, as measured by the force of detachment, can be modulated by altering the amount of hakea in the tablet. The mucoadhesive buccal tablets described in this paper represent an improved transbuccal delivery system for therapeutic polypeptides.

Cyclodextrins as permeation enhancers: some theoretical evaluations and in vitro testing

It is well known that cyclodextrins can enhance the permeation of poorly soluble drugs through biological membranes. However, the permeability will decrease if cyclodextrin is added in excess of the concentration needed to solvate the drug. The mechanism of cyclodextrin effect on drug permeability has not been fully explained. The effect of cyclodextrins can not be explained as solely due to increased solubility of the drug in the aqueous donor phase nor can it be explained by assuming that cyclodextrins act as classical permeation enhancers, i.e. by decreasing the barrier function of the lipophilic membrane. In the present work we have modeled the effect of cyclodextrins in terms of mixed barrier consisting of both diffusion and membrane controlled diffusion, where the diffusion of the drug in the aqueous diffusion layer is significantly slower than in the bulk of the donor. This diffusion model is described by simple mathematical equation where the properties of the system are expressed in terms of two constants P(M)/Kd and M1/2. Data for the permeation of hydrocortisone through hairless mouse skin in the presence of various cyclodextrins, and cyclodextrin polymer mixtures, were fitted to obtain values for these two constants. The rise in flux with increased cyclodextrin complex concentration and fall with excess cyclodextrin was accurately predicted. Data for the permeation of drugs through semi-permeable cellophane membrane could also be fitted to the equation. It was concluded that cyclodextrins act as permeation enhancers carrying the drug through the aqueous barrier, from the bulk solution towards the lipophilic surface of biological membranes, where the drug molecules partition from the complex into the lipophilic membrane.

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.

Nasal mucociliary clearance as a factor in nasal drug delivery

The nasal mucociliary clearance system transports the mucus layer that covers the nasal epithelium towards the nasopharynx by ciliary beating. Its function is to protect the respiratory system from damage by inhaled substances. Impairment of nasal mucociliary clearance can result in diseases of the upper airways. Therefore, it is important to study the effects of drugs and drug excipients on nasal mucociliary clearance. A large number of methods are used to assess mucociliary clearance. These methods study the effects of drug and excipients on the mucociliary system in vitro or in vivo in animals and humans. In some cases, the results of different in vitro and in vivo measurements do not correlate well. In vitro methods, especially ciliary beat frequency measurements, have been demonstrated to be valuable tools for toxicity screening. However, in vivo studies are essential to confirm the safety of nasal drug formulations. Nasal mucociliary clearance also has implications for nasal drug absorption. Drugs are cleared rapidly from the nasal cavity after intranasal administration, resulting in fast systemic drug absorption. Several approaches are discussed to increase the residence time of drug formulations in the nasal cavity, resulting in improved nasal drug absorption. However, more experimental evidence is needed to support the conclusion that this improved absorption is caused by a longer residence time of the nasal drug formulation.

In vitro modulation of doxorubicin and docetaxel antitumoral activity by methyl-beta-cyclodextrin

Methyl-beta-cyclodextrin (MEBCD) was investigated for its effect on the antitumoral activity of various antineoplastic agents (doxorubicin (DOX), docetaxel (DXL), 5-fluorouracil (5-FU) and cisplatin (CDDP)) in three different human parental sensitive cancer cell lines (K562 S, MCF7 S and A2780 S) and their multidrug resistant variant sublines (K562 R, MCF7 R and A2780 R). At non-cytotoxic concentrations, MEBCD was able to increase significantly DOX and DXL cytotoxic activity in all the cell lines tested. The sensitisation ratios (IC50 drug control/IC50 drug-MEBCD treated) ranged from 3l1 to 14.3. Moreover, intracellular DOX accumulation, determined by high-performance liquid chromatography, was also increased when cells were treated with MEBCD combined with DOX (approximately 2-3 fold). The effects of MEBCD in resistant sublines were greater than in their parental sensitive cell lines. Other experiments demonstrated that the action of the MEBCD was independent of DOX. These data provided a basis for the potential therapeutic application of MEBCD in cancer therapy.

High-performance liquid chromatographic assay for methyl-beta-cyclodextrin in plasma and cell lysate

This paper describes a high-performance liquid chromatographic method with fluorescence detection for the analysis of methyl-beta-cyclodextrin (MEBCD) in plasma and cell lysate, after in situ complexation with 1-naphthol. The size-exclusion HPLC column packed with TSK 3000 SW gel, was equilibrated with an eluent mixture composed of methanol and purified water (2:98, v/v) containing 10(-4) M 1-naphthol as a fluorophore. The detection is based on fluorescence enhancement caused by the formation of inclusion complexes and was performed at 290 and 360 nm for excitation and emission, respectively. The method involved a simple treatment of the samples with chloroform. Daunorubicin was used as internal standard. Limits of quantitation were 0.8 microM in plasma and 0.5 microM in cell lysate. Detection limits of 0.5 microM (50 pmol) and 0.3 microM (30 pmol) were obtained for MEBCD in the two media, respectively. Linear detection response was obtained for concentrations ranging from 1 to 100 microM in plasma and cell lysate. Recovery from plasma proved to be more than 40%. Precision, expressed as C.V. was in the range of 4 to 11%. Accuracy ranged from 89 to 105%.

Confocal laser scanning microscopic visualization of the transport of dextrans after nasal administration to rats: effects of absorption enhancers

PURPOSE

To visualize the transport pathway(s) of high molecular weight model compounds across rat nasal epithelium in vivo using confocal laser scanning microscopy. Furthermore, the influence of nasal absorption enhancers (randomly methylated beta-cyclodextrin and sodium taurodihydrofusidate) on this transport was studied.

METHODS

Fluorescein isothiocyanate (FITC)-labelled dextrans with a molecular weight of 3,000 or 10,000 Da were administered intranasally to rats. Fifteen minutes after administration the tissue was fixed with Bouin. The nasal septum was surgically removed and stained with Evans Blue protein stain or DiIC18(5) lipid stain prior to visualization with the confocal laser scanning microscope.

RESULTS

Transport of FITC-dextran 3,000 across nasal epithelium occurred via the paracellular pathway. Endocytosis of FITC-dextran 3,000 was also shown. In the presence of randomly methylated beta-cyclodextrin 2% (w/v) similar transport pathways for FITC-dextran 3,000 were observed. With sodium taurodihydrofusidate 1% (w/v) the transport route was also paracellular with endocytosis, but cells were swollen and mucus was extruded into the nasal cavity. For FITC-dextran 10,000 hardly any transport was observed without enhancer, or after co-administration with randomly methylated beta-cyclodextrin 2% (w/v). Co-administration with sodium taurodihydrofusidate 1% (w/v) resulted in paracellular transport of FITC-dextran 10,000, but morphological changes, i.e. swelling of cells and mucus extrusion, were observed.

CONCLUSIONS

Confocal laser scanning microscopy is a suitable approach to visualize the transport pathways of high molecular weight hydrophilic compounds across nasal epithelium, and to study the effects of absorption enhancers on drug transport and cell morphology.