The influence of absorption enhancers on intranasal insulin absorption in normal and diabetic subjects

Cyclodextrin-induced release of drug-entrapping liposomes associated with the solation of liposome gels

In this work, we demonstrate that liposome gels in which liposomes are connected by polyethylene glycol terminated by cholesterol groups at both ends can store hydrophilic and hydrophobic drugs in the gel interiors, inner aqueous phases, and lipid membranes. The addition of cyclodextrins (CDxs) as extrinsic stimuli led to the release of drug-entrapping liposomes due to the interactions between CDxs and cholesteryl groups and/or the alkyl chains of lipids. The addition of aqueous solutions of β-CDx, dimethyl-β-CDx, trimethyl-β-CDx, and γ-CDx (final concentration: 7.5 mM) induced the solation of liposome gels and the release of liposomes accompanying the solation. Furthermore, the addition of β-CDx led to the partial release of hydrophilic drugs encapsulated in the liposomes, although the drug release was scarcely observed in other CDxs. In particular, the addition of trimethyl-β-CDx, which has low cytotoxicity, accelerated solation, and cationic liposomes released from the gels were effectively taken up by murine colon cancer (Colon26) cells. Thus, we propose that liposomes released from liposome gels can function as drug carriers.

The solation of liposome gels owing to the addition of trimethyl-β-cyclodextrin (TMe-β-CDx) and the uptake of cationic liposomes released from liposome gels by Colon26 cells are demonstrated.

Non-invasive ways of administering insulin

BACKGROUND AND AIMS

Insulin is crucial in the management of diabetes. However, requires injection which itself comes with some challenges. Alternative delivery routes have been investigated that are needle-free, with enhanced absorption and bioavailability. This review presents novel non-invasive insulin administration approaches that overcome some hurdles, as well as delineating their advantages and disadvantages.

METHODS

Information was primarily gathered by employing various PubMed scholarly articles for real-world examples in addition to data extraction from supplementary manuscripts. Articles were evaluated between 1958 and 2022. An introductive approach was used to identify matters related to the concept of different ways of administering insulin.

RESULTS

Approaches aim to administer insulin in a safe, stable, and easy to use form, whether via oral, buccal, intranasal, oral inhalation, transdermal, ocular, rectal, or vaginal routes. Some have been shown to clinically improve blood glucose levels, while others are still in the investigational stage.

CONCLUSION

Many approaches have been taken in an attempt to overcome physical barriers of insulin delivery. Some of these systems discussed may reach the market in the future and assist the millions of people who currently take subcutaneous injections of insulin.

Spray Freeze Dried Lyospheres® for Nasal Administration of Insulin

Pharmacologically active macromolecules, such as peptides, are still a major challenge in terms of designing a delivery system for their transport across absorption barriers and at the same time provide sufficiently high long-term stability. Spray freeze dried (SFD) lyospheres^® are proposed here as an alternative for the preparation of fast dissolving porous particles for nasal administration of insulin. Insulin solutions containing mannitol and polyvinylpyrrolidone complemented with permeation enhancing excipients (sodium taurocholate or cyclodextrins) were sprayed into a cooled spray tower, followed by vacuum freeze drying. Final porous particles were highly spherical and mean diameters ranged from 190 to 250 µm, depending on the excipient composition. Based on the low density, lyospheres resulted in a nasal deposition rates of 90% or higher. When tested in vivo for their glycemic potential in rats, an insulin-taurocholate combination revealed a nasal bioavailability of insulin of 7.0 ± 2.8%. A complementary study with fluorescently labeled-dextrans of various molecular weights confirmed these observations, leading to nasal absorption ranging from 0.7 ± 0.3% (70 kDa) to 10.0 ± 3.1% (4 kDa). The low density facilitated nasal administration in general, while the high porosity ensured immediate dissolution of the particles. Additionally, due to their stability, lyospheres provide an extremely promising platform for nasal peptide delivery.

AmyloLipid Nanovesicles: A self-assembled lipid-modified starch hybrid system constructed for direct nose-to-brain delivery of curcumin

AmyloLipid nanovesicles (ALNs) are new lipid-modified starch complex nanoparticles developed and presented as nanocarriers of curcumin for targeting the CNS via the intranasal route. Curcumin has been indicated as a promising active agent with a variety of pharmacological activities, including a potential ability to treat brain tumors, traumatic brain injury, and CNS disorders, such as Alzheimer's disease, as it may inhibit amyloid-β-protein (Aβ) aggregation and Aβ-induced inflammation. Although curcumin has a tremendous potential as a therapeutic agent for CNS disorders, its low bioavailability and its rapid total body clearance reduce any chance for therapeutic levels to reach the brain. By using an optimized (2% crosslinked starch) curcumin-loaded ALNs, which was fabricated from a microemulsion as a precursor, an average of 141.5 ± 55.9 ng/g brain levels and 11.9 ± 12.0 ng/ml plasma concentrations were detected, one hour following intranasal administration of 160 μg/kg dose of curcumin. In comparison, 1 h after IV administration of the same dose, no CUR was detected in the brain and the mean plasma level was approximately one half of the level monitored after intranasal ALNs, i.e., 7.25 ± 0.20 ng/ml. It has been clearly demonstrated, therefore, that a well-designed ALN formulation proved itself as a promising carrier for intranasal delivery and brain targeting of curcumin.

Nasal formulations for drug administration and characterization of nasal preparations in drug delivery

This special report gives an insight in the rationale of utilizing the nasal cavity for drug administration and the formulation as well as characterization of nasal preparations. As the nose is an easy-to-access, noninvasive and versatile location for absorption, this route of delivery will play an increasingly important role in future drug product development both for new and repurposed drugs. The nose can be utilized for local and systemic delivery including drug delivery to the central nervous system and the immune system. Typical formulation strategies and future developments are reviewed, which nowadays mostly comprise liquid formulations. Although they are straight forward to develop, a number of aspects from choice of solvent, osmolarity, pH, viscosity and more need to be considered, which determine formulation characteristics, not at least nasal deposition. Nasal powders offer higher stability and, along with more sophisticated nasal devices, may play a major role in the future.

Metal Nanoparticles as Targeted Carriers Circumventing the Blood-Brain Barrier

Metal nanoparticles have been proposed as a carrier and a therapeutic agent in biomedical field because of their unique physiochemical properties. Due to these physicochemical properties, they can be used in different fields of biomedicine. In relation to this, plasmonic nanoparticles can be used for detection and photothermal destruction of tumor cells or toxic protein aggregates, and magnetic iron nanoparticles can be used for imaging and for hyperthermia of tumor cells. In addition, both therapy and imaging can be combined in one nanoparticle system, in a process called theranostics. Metal nanoparticles can be synthesized to modulate their size and shape, and conjugated with different ligands, which allow their application in drug delivery, diagnostics, and treatment of central nervous system diseases. This review is focused on the potential applications of metal nanoparticles and their capability to circumvent the blood-brain barrier (BBB). Although many articles have demonstrated delivery of metal nanoparticles to the brain by crossing the BBB after systemic administration, the percentage of the injected dose that reaches this organ is low in comparison to others, especially the liver and spleen. In connection with this drawback, we elaborate the architecture of the BBB and review possible mechanisms to cross this barrier by engineered nanoparticles. The potential uses of metal nanoparticles for treatment of disorders as well as related neurotoxicological considerations are also discussed. Finally, we bring up for discussion a direct and relatively simpler solution to the problem. We discuss this in detail after having proposed the use of the intranasal administration route as a way to circumvent the BBB. This route has not been extensively studied yet for metal nanoparticles, although it could be used as a research tool for mechanistic understanding and toxicity as well as an added value for medical practice.

Different stabilities of liposomes containing saturated and unsaturated lipids toward the addition of cyclodextrins

The liposomal collapse resulting from the addition of heptakis(2,6-di-O-methyl)cyclodextrin was more difficult to observe in the presence of unsaturated lipids compared to saturated lipids.

Absorption-Enhancing Effects of Bile Salts

Bile salts are ionic amphiphilic compounds with a steroid skeleton. Among the most important physiological properties of bile salts are lipid transport by solubilization and transport of some drugs through hydrophobic barriers. Bile salts have been extensively studied to enhance transepithelial permeability for different marker molecules and drugs. They readily agglomerate at concentrations above their critical micelle concentration (CMC). The mechanism of absorption enhancement by bile salts appears to be complex. The aim of the present article was to review bile salt structure and their application as absorption enhancers and the probable mechanism for increasing permeation based on previous studies.

Liposome collapse resulting from an allosteric interaction between 2,6-dimethyl-β-cyclodextrins and lipids

The addition of a large excess of heptakis(2,6-di-O-methyl)-β-cyclodextrin (DMe-β-CDx) led to the collapse of several liposomes via the formation of water-soluble lipid–DMe-β-CDx complex with allosteric interactions.

Enhancing effect of natural borneol on the absorption of geniposide in rat via intranasal administration

Both geniposide (Ge) and natural borneol (NB) are bioactive substances derived from traditional Chinese herbs. The effect of NB on the pharmacokinetics of Ge in rat via intranasal administration was investigated. The concentrations of Ge in plasma were determined by reversed-phase high-performance liquid chromatography (HPLC) after intranasal administration of Ge (4 mg/kg) alone and combined with different doses (0.08, 0.8, and 8 mg/kg) of NB. The intravenous administration was given as a reference (4 mg/kg of Ge and 8 mg/kg of NB). Compared with the intravenous administration, the absolute bioavailability of Ge was 76.14% through intranasal administration combined with NB. Compared with the intranasal administration of Ge alone, Ge could be absorbed rapidly in the nasal cavity combined with NB; the peak time of Ge in the plasma became shorter (3-5 min vs. 40 min); the peak concentration became higher (1.32-4.25 μg/ml vs. 0.67 μg/ml); and, the relative bioavailability of Ge combined with NB was 90.3%-237.8%. The enhancing effect was attenuated as the dose of NB decreased. The results indicated that NB can accelerate the absorption of Ge dose-dependently in the nasal cavity.

Dry powder vaccines for mucosal administration: critical factors in manufacture and delivery

Dry powder vaccine formulations have proved effective for induction of systemic and mucosal immune responses. Here we review the use of dry vaccines for immunization in the respiratory tract. We discuss techniques for powder formulation, manufacture, characterization and delivery in addition to methods used for evaluation of stability and safety. We review the immunogenicity and protective efficacy of dry powder vaccines as compared to liquid vaccines delivered by mucosal or parenteral routes. Included is information on mucosal adjuvants and mucoadhesives that can be used to enhance nasal or pulmonary dry vaccines. Mucosal immunization with dry powder vaccines offers the potential to provide a needle-free and cold chain-independent vaccination strategy for the induction of protective immunity against either systemic or mucosal pathogens.

Systemic delivery of insulin via the nasal route using a new microemulsion system: In vitro and in vivo studies

The main purpose of this study was to investigate the nasal absorption of insulin from a new microemulsion spray preparation in rabbits. The bioavailability of insulin lispro via the nasal route using a W/O microemulsion was found to reach 21.5% relative to subcutaneous administration, whereas the use of an inverse microemulsion as well as a plain solution yielded less than 1% bioavailability. The profile of plasma glucose levels obtained after nasal spray application of the microemulsion (1IU/kg lispro) was similar to the subcutaneous profile of 0.5IU/kg at the first 90min after application and resulted in a 30-40% drop in glucose levels. The microemulsion system was characterized by DLS, TEM, viscosity measurements, and by construction of pseudo-ternary phase diagram. The average droplet size of an insulin-unloaded and insulin-loaded microemulsions containing 20% aqueous phase (surfactants-to-oil ratio=87:13) was 2nm and 2.26nm in diameter, respectively. In addition, the effect of the microemulsion on FITC-labeled insulin permeation was examined across the porcine nasal mucosa in vitro. The permeability coefficient of FITC-insulin via the microemulsion was 0.210±0.048cm/h with a lag time of 10.9±6.5min, whereas the permeability coefficient from a plain solution was 0.082±0.043cm/h with a lag time of 36.3±10.1min. In view of the absorption differences of insulin between 20%, 50% water-containing microemulsions and an aqueous solution obtained in vitro and in vivo, it has been concluded that the acceleration in the intramucosal transport process is the result of encapsulating insulin within the nano-droplet clusters of a W/O microemulsion, while the microemulsion ingredients seems to have no direct role.

The in situ and in vivo study on enhancing effect of borneol in nasal absorption of Geniposide in rats

The objective of this research was to study the in situ and in vivo nasal absorption of Geniposide (Ge) co-administered with borneol. A rat in situ nasal perfusion technique with a novel volumeadjusted calculation was used to examine the absorption rate and extent of Ge. The influence of different experimental conditions such as purity of extract, drug concentration, co-administration with synthetic borneol or natural borneol were also investigated. Results indicated nasal absorption of Ge was primarily by passive diffusion that resembled first order kinetics. Following co-administration with borenol, the drug absorption was increased by 1.4 and 1.7 folds for natural borneol and synthetic borneol, respectively. However, the effect of other factors on drug absorption was not significant. In addition, it was also observed that there is a positive correlation between the absorption of water and Ge by the nasal route. In vivo studies carried out in rats where Ge was co-administered with NB and the pharmacokinetic profile obtained following intranasal administration were compared with those after intravenous administration. The bioavailability of Ge by intranasal was 101.5% and T(max) was 2.04 +/- 0.64 min. MRT was 218.7 +/- 74.1 min and 44.4 +/- 8.9 min for intranasal and intravenous, respectively. Combined with the borneol, Ge can be promptly and thoroughly absorbed intranasally in rats.

Air-Liquid Interface Culture of Serially Passaged Human Nasal Epithelial Cell Monolayer forIn VitroDrug Transport Studies

The objective of this study was to establish a drug transport study using human nasal epithelial (HNE) cell monolayers cultured by the air-liquid interface (ALI) method using serum-free medium (BEGM:DME/F12, 50:50). The cells were developed and characterized in comparison to those that have been previously cultured by the liquid-covered culture (LCC) method. The epithelial cell monolayer cultured by the ALI method resulted in a significantly higher transepithelial electrical resistance value (3,453 +/- 302 ohm x cm(2)) that was maintained (>1,000 ohm x cm(2)) for up to 20 days compared with that cultured by the LCC method. Observation by scanning electron microscopy revealed mature cilia after 2 weeks in the ALI culture, while flatten unhealthy ciliated cells were observed in the LCC method. After 21 days, higher level of MUC5AC and 8 mRNA were expressed in ALI culture which confirmed the secretory differentiation of HNE monolayers in vitro. No significant difference in the permeability coefficients of a model hydrophilic marker ((14)C-mannitol) and a lipophilic drug (budesonide) was observed between the two conditions on day 7. The passage 2-3 of the HNE monolayer using ALI condition retained the morphology and differentiated features of normal epithelium. Thus it would be a suitable model for in vitro nasal drug delivery studies.

Nasal residence of insulin containing lyophilised nasal insert formulations, using gamma scintigraphy

Bioadhesive dosage forms are a potential method for overcoming rapid mucociliary transport in the nose. A lyophilised nasal insert formulation previously investigated in sheep demonstrated prolonged absorption of nicotine hydrogen tartrate suggestive of extended nasal residence, and increased bioavailability. The current study was performed to quantify nasal residence of the formulations using gamma scintigraphy, and to investigate the absorption of a larger molecule, namely insulin. A four-way crossover study was conducted in six healthy male volunteers, comparing a conventional nasal spray solution with three lyophilised nasal insert formulations (1-3% hydroxypropylmethylcellulose (HPMC)). The conventional nasal spray deposited in the posterior nasal cavity in only one instance, with a rapid clearance half-life of 9.2 min. The nasal insert formulations did not enhance nasal absorption of insulin, however an extended nasal residence time of 4-5 h was observed for the 2% HPMC formulation. The 1% HPMC insert initially showed good spreading behaviour; however, clearance was faster than for the 2% formulation. The 3% HPMC nasal insert showed no spreading, and was usually cleared intact from the nasal cavity within 90 min. In conclusion, the 2% HPMC lyophilised insert formulation achieved extended nasal residence, demonstrating an optimum combination of rapid adhesion without over hydration.

Study of the relationship between lipid binding properties of cyclodextrins and their effect on the integrity of liposomes

It is well known that cyclodextrins are able to extract lipids constituting membranes, increasing their fluidity and permeability. This behaviour towards biological membranes is directly linked to the toxicological effects of methylated cyclodextrins. However, confusion is currently made in the literature between the different methylated cyclodextrin derivatives. Moreover, a new methylated cyclodextrin derivative recently occurred in the market, the Crysmeb. We wanted to compare and understand the effect of the most currently used cyclodextrins on a model membrane. We studied the influence of natural cyclodextrins (betaCD and gammaCD), methylated derivatives (2,6-dimethyl-betaCD (Dimeb), 2,3,6-trimethyl-betaCD (Trimeb) and randomly methylated-betaCD (Rameb), as well as the new derivative Crysmeb), hydroxypropylated derivatives (HPbetaCD of different substitution degrees and HPgammaCD) and the sulfobutylated derivative (SBEbetaCD) on the release of a fluorescent marker encapsulated in the inner cavity of liposomes. It was shown that the observed effect on calcein release can be directly related to the affinity of cyclodextrins for both lipid components of liposomes, cholesterol and phosphatidylcholine. From this relationship, we were able to determine, for each cyclodextrin, a theoretical concentration giving rise to 50% or 100% calcein release. This theoretical concentration was confirmed experimentally. We have also showed that cyclodextrins which provoke calcein release also induce large structure modifications of liposomes.

Preparation, characterization and nasal delivery of alpha-cobrotoxin-loaded poly(lactide-co-glycolide)/polyanhydride microspheres

In this study, alpha-cobrotoxin was incorporated into the microspheres composed of poly(lactide-co-glycolide) (PLGA) and poly[1,3-bis(p-carboxy-phenoxy) propane-co-p-(carboxyethylformamido) benzoic anhydride] (P(CPP:CEFB)) and intranasally delivered to model rats in order to improve its analgesic activity. The microspheres with high entrapment efficiency (>80%) and average diameter of about 25 microm could be prepared by a modified water-in-oil-in-oil (w/o/o) emulsion solvent evaporation method. Scanning electron micrograph (SEM) study indicated that P(CPP:CEFB) content played a considerable role on the morphology and degradation of the microspheres. The presence of P(CPP:CEFB) in the microspheres increased their residence time at the surface of the nasal rat mucosa. The toxicity of the composite microspheres to nasal mucosa was proved to be mild and reversible. A tail flick assay was used to evaluate the antinociceptive activity of the microspheres after nasal administration. Compared with the free alpha-cobrotoxin and PLGA microspheres, PLGA/P(CPP:CEFB) microspheres showed an apparent increase in the strength and duration of the antinociceptive effect at the same dose of alpha-cobrotoxin (80 microg/kg body weight).

The influence of absorption enhancers on nasal absorption of acyclovir

The objective of this work was to increase the nasal absorption of acyclovir by using absorption enhancers. Acyclovir was selected as a model drug. A rat in situ nasal perfusion technique was utilized in the investigation to examine the rate and extent of absorption of acyclovir. In vitro enzymatic drug degradation study was carried out with rat nasal washings. Various experimental conditions such as nasal perfusion rate, pH of the perfusion medium and concentrations of absorption enhancers such as sodium deoxycholate, hydroxypropyl beta-cyclodextrin, sodium caprate, sodium tauroglycocholate and EDTA were optimized. Nasal absorption of acyclovir was pH dependent. Initial absorption rate constants were determined by the plot of log% remaining amount of drug in perfusate vs time. It was found maximum at pH 7.4 and decreased at lower and higher pH conditions. In in vitro enzymatic degradation study, no measurable degradation was observed during first week. The extent of drug absorption was increased via absorption enhancers. In vivo studies were carried out for the optimized formulation in rabbits and the pharmacokinetics parameters of nasal solution were compared with oral solution. Hydroxypropyl beta-cyclodextrin appeared to be more effective for enhancing the nasal absorption of acyclovir than the other absorption enhancers. The order of increasing absorption of acyclovir caused by the enhancers was hydroxypropyl beta-cyclodextrin>sodium deoxycholate>sodium caprate>sodium tauroglycocholate>EDTA.

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.

Alternative routes of insulin delivery

Attempts at replicating physiological insulin secretion, as a means of restoring the normal metabolic milieu and thereby minimizing the risk of diabetic complications, has become an essential feature of insulin treatment. However, despite advances in the production, purification, formulation and methods of delivery of insulin which have occurred in recent years, this has met with limited success. The current advocacy of intensive insulin therapy regimens involving multiple daily subcutaneous injection places a heavy burden of compliance on patients and has prompted interest in developing alternative, less invasive routes of delivery. To date, attempts to exploit the nasal, oral, gastrointestinal and transdermal routes have been mainly unsuccessful. The respiratory tree, with a large surface area, offers the greatest potential for the delivery of polypeptide drugs and there is renewed interest in administrating insulin by the intrapulmonary route. Current pulmonary drug delivery systems include a variety of pressurized metered dose inhalers, dry powder inhalers, nebulizers and aqueous mist inhalers. Recent clinical studies suggest a possible role for inhaled insulin in fulfilling meal-related insulin requirements in persons with Type 1 and Type 2 diabetes. Most experience with inhaled insulin has been obtained using either dry powder formulation in the Nektar Pulmonary Inhaler/Exubera device (Nektar Therapeutics Inc., San Carlos, CA, Aventis, Bridgewater, NJ, Pfizer, NY) or a liquid aerosol formulation in the AERx Insulin Diabetes Management System (Aradigm Corp., Hayward, CA, NovoNordisk A/S, Copenhagen, Denmark). If long-term safety and efficacy is confirmed, inhalation may become the first non-subcutaneous route of insulin administration for widespread clinical use. Despite overwhelming interest and investment in administering insulin via the oral route, success is not expected in the short term. Attempts at utilizing the buccal mucosa and skin are also continuing. Pancreatic transplantation will remain limited to those patients receiving a kidney transplant and immunotherapy. Islet cell transplantation is at an early though encouraging stage following the availability of new less toxic immunosuppressive agents. True insulin independence will require further advances in the combined fields of cell biology and genetics to ensure freedom from both the need for lifelong administration of insulin and the complications of diabetes.

Enhanced insulin absorption in the rabbit airways and lung by sodium dioctyl sulfosuccinate

The objective of this investigation was to study regional absorption of inhaled insulin together with an enhancer (sodium di-octyl-sulfosuccinate [DOSS]) in the rabbit airways and lung. Insulin was administered with or without DOSS by aerosol inhalation, intratracheal infusion, intranasally, sublingually, and without DOSS intravenously. Blood glucose and plasma levels of insulin were measured during 100 min from the start of administration. Inhalation of insulin (3 U) with 0.25% or 1% DOSS decreased average blood glucose levels significantly more than inhalation of insulin (3 U) without DOSS. Intratracheal administration of 1.5 U of insulin with 0.25% DOSS in 0.3 mL of vehicle decreased the average blood glucose level significantly compared with intratracheal administration of 1.5 U of insulin and no DOSS in 0.3 mL of vehicle and compared with 1.5 U of insulin with 0.25% DOSS in 0.15 mL of vehicle. Intravenous insulin (1.5 U) and inhaled (1.5 U) insulin in 0.25% DOSS decreased average blood glucose levels significantly compared with intratracheal (0.15 mL), intranasal, and sublingual administration of 1.5 U of insulin with 0.25% DOSS. The bioavailability of inhaled insulin (1.5 U) with 0.25% DOSS was estimated to be 16% in comparison with 7% for intratracheally (0.15 mL), 1% intranasally, and 0.8% sublingually administered insulin (1.5 U with 0.25% DOSS), respectively. Inhaled insulin together with the absorption enhancer DOSS decreased the blood glucose level more effectively than insulin given intratracheally, intranasally, or sublingually. The effect on blood glucose reflected the difference in plasma insulin concentration for the different routes of administration.

Comparison of vaginal aminopeptidase enzymatic activities in various animals and in humans

The specific enzymatic activity of four different aminopeptidases (aminopeptidase N, leucine aminopeptidase, aminopeptidase A and aminopeptidase B) in vaginal homogenates from rabbit, rat, guinea-pig, sheep and humans was compared. The purpose of the study was to find an appropriate animal model that can be used in degradation studies of protein and peptide drugs. Different substrates were used as the relative specific substrates for the determination of aminopeptidase enzymatic activity: 4-methoxy-2-naphthylamide of L-alanine for aminopeptidase N, 4-methoxy-2-naphthylamide of L-leucine for leucine aminopeptidase, 4-methoxy-2-naphthylamide of L-glutamic acid for aminopeptidase A and 4-methoxy-2-naphthylamide of L-arginine for aminopeptidase B. The vaginal aminopeptidase enzymatic activity of different species was determined spectrofluorometrically. The inhibition of aminopeptidase activity in the presence of bestatin and puromycin inhibitors was also investigated. The results showed the presence of aminopeptidase enzymatic activity in all vaginal homogenates in the order: sheep > guinea-pig > rabbit > or = human > or = rat. Based on the results of the hydrolysis and inhibition of the 4-methoxy-2-naphthylamide substrates, it was difficult to have an exact decision on the aminopeptidase type in the vaginal homogenates from the species studied. It was found that the aminopeptidase activity in rat, rabbit and humans was not statistically different. Therefore, we suggest that rats and rabbits could be used as model animals for vaginal enzymatic activity studies and for determination of the degradation of protein and peptide drugs in the vagina.

Intranasal bioavailability of buprenorphine in rabbit correlated to sheep and man

The purpose of the present study of buprenorphine is to add information about the correlation between various animal models and nasal bioavailabilities in man. PEG 300 was added to one formulation to study whether the addition of the co-solvent results in the same absorption pattern as seen for sheep. The bioavailability of intranasal buprenorphine 0.6 mg in PEG 300 and 5% dextrose was assessed in a cross-over study in six rabbits. The mean bioavailabilities, Tmax and Cmax were 46% (S.D. +/-13) and 53% (S.D. +/-17), 8 and 12 min, 28 and 27 ng/ml for 30% PEG 300 and 5% dextrose, respectively. No significant differences were found between the nasal buprenorphine formulations. The bioavailabilities in rabbit and sheep, respectively, were approximately 2.5 and four times higher than for man. The absorption rate was faster for rabbit and sheep than for man. It appears that rabbit and sheep bioavailability differ from humans, especially with respect to rate. PEG 300 do not increase the bioavailability of buprenorphine.

Evaluation of starch-maltodextrin-Carbopol 974 P mixtures for the nasal delivery of insulin in rabbits

In this study insulin was administered nasally to rabbits as a dry powder formulation. The powders consisted of drum-dried waxy maize starch (DDWM) or maltodextrins with different DE values and Carbopol 974 P. The powders were prepared by freeze-drying a dispersion of these excipients with insulin. Bioavailabilities obtained with the powder formulations containing DDWM/Carbopol 974 P (5 and 10%) were significantly higher (p<0.05) than those containing maltodextrins-Carbopol 974 P mixtures. The bioavailability of the powder formulation containing DDWM and 10% Carbopol 974 P was significantly higher (14.4%) than the bioavailability of the same mixture containing 5% Carbopol 974 P (9.9%). The bioavailability, t(max) and C(max) values of the formulation with 5% Carbopol 974 P were significantly higher in comparison with the formulation without Carbopol 974 P. 10% Carbopol 974 P was required when maltodextrins were used in order to obtain a significantly higher bioavailability compared with the formulations without Carbopol 974 P. Freeze-drying seemed a prerequisite for a good bioavailability from the powder formulation as well as the ratio of insulin versus bioadhesive powder (1 IU and 2 IU/mg of bioadhesive powder).

Intranasal insulin delivery and therapy

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

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

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

Nasal delivery of peptides: an in vitro cell culture model for the investigation of transport and metabolism in human nasal epithelium

We investigated the transport- and metabolism properties of three peptides in monolayers of human nasal epithelial cells. The effective permeability coefficients of thyrotropin-releasing hormone, met-enkephalin and human recombinant insulin were found to be 4.5, 4.4 and 0.4 x 10(-7) cm/s, respectively. The permeability was inversely proportional to the molecular weight and one order of magnitude lower than in excised nasal mucosa of rabbits. The metabolic cleavage of thyrotropin-releasing hormone (TRH) to the free acid by cytosolic prolyl-endopeptidase was also detected in human nasal cell monolayers, suggesting that ca. 10% of the total amount of TRH is transported via a transcellular pathway. Met-enkephalin is a substrate for aminopeptidases, located on the apical membrane of nasal epithelial cells. Metabolites and enzyme activity are comparable with literature data. Our studies demonstrate that not only morphological, but also functional properties of human nasal epithelial cells are preserved under in vitro conditions. Such a cell culture model based on human nasal cells could be beneficial for the characterization of peptide transport on a cellular level and for investigation of the absorption enhancer mechanism. Further studies are necessary, however, to establish correlations between in vitro permeabilities in cell cultures and nasal drug absorption in animals and humans.

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.

Effect of Brij-78 on systemic delivery of insulin from an ocular device

An ocular insert is developed for the controlled systemic delivery of insulin. Commercially available Gelfoam absorbable gelatin sponge, USP, is used in the fabrication of the ocular insert in the form of a matrix system. Two eyedrop formulations and 13 eye device formulations were evaluated. The efficacy of insulin ocular delivery was quantitated by monitoring the changes in its pharmacological response (i.e., blood glucose lowering). The in vivo results from devices containing 0.5 or 1.0 mg of insulin with 20 micrograms of polyoxyethylene-20-stearyl ether (Brij-78) give a substantial improvement in insulin activity and a significant prolongation in its duration compared with the eyedrops. In addition, the mean blood glucose concentration returns to nearly normal levels within 60 min after the removal of the device. Overall, the application of the Gelfoam device makes it feasible to obtain a prolonged systemic delivery of insulin within the desired therapeutic levels without the risk of hypoglycemia.