Lipid emulsions as vehicles for enhanced nasal delivery of insulin

A comprehensive review of advanced nasal delivery: Specially insulin and calcitonin

Peptide drugs through nasal mucous membrane, such as insulin and calcitonin have been widely used in the medical field. There are always two sides to a coin. One side, intranasal drug delivery can imitate the secretion pattern in human body, having advantages of physiological structure and convenient use. Another side, the low permeability of nasal mucosa, protease environment and clearance effect of nasal cilia hinder the intranasal absorption of peptide drugs. Researchers have taken multiple means to achieve faster therapeutic concentration, lower management dose, and fewer side effects for better nasal preparations. To improve the peptide drugs absorption, various strategies had been explored via the nasal mucosa route. In this paper, we reviewed the achievements of 18 peptide drugs in the past decade about the perspectives of the efficacy, mechanism of enhancing intranasal absorption and safety. The most studies were insulin and calcitonin. As a result, absorption enhancers, nanoparticles (NPs) and bio-adhesive system are the most widely used. Among them, chitosan (CS), cell penetrating peptides (CPPs), tight junction modulators (TJMs), soft NPs and gel/hydrogel are the most promising strategies. Moreover, two or three strategies can be combined to prepare drug vectors. In addition, spray freeze dried (SFD), self-emulsifying nano-system (SEN), and intelligent glucose reaction drug delivery system are new research directions in the future.

Versatile Oral Insulin Delivery Nanosystems: From Materials to Nanostructures

Diabetes is a chronic metabolic disease characterized by lack of insulin in the body leading to failure of blood glucose regulation. Diabetes patients usually need frequent insulin injections to maintain normal blood glucose levels, which is a painful administration manner. Long-term drug injection brings great physical and psychological burden to diabetic patients. In order to improve the adaptability of patients to use insulin and reduce the pain caused by injection, the development of oral insulin formulations is currently a hot and difficult topic in the field of medicine and pharmacy. Thus, oral insulin delivery is a promising and convenient administration method to relieve the patients. However, insulin as a peptide drug is prone to be degraded by digestive enzymes. In addition, insulin has strong hydrophilicity and large molecular weight and extremely low oral bioavailability. To solve these problems in clinical practice, the oral insulin delivery nanosystems were designed and constructed by rational combination of various nanomaterials and nanotechnology. Such oral nanosystems have the advantages of strong adaptability, small size, convenient processing, long-lasting pharmaceutical activity, and drug controlled-release, so it can effectively improve the oral bioavailability and efficacy of insulin. This review summarizes the basic principles and recent progress in oral delivery nanosystems for insulin, including physiological absorption barrier of oral insulin and the development of materials to nanostructures for oral insulin delivery nanosystems.

Preparation and Evaluation of Mebendazole Microemulsion for Intranasal Delivery: an Alternative Approach for Glioblastoma Treatment

Although mebendazole (MBZ) has demonstrated antitumor activity in glioblastoma models, the drug has low aqueous solubility and therefore is poorly absorbed. Considering that other strategies are needed to improve its bioavailability, the current study was aimed to develop and evaluate novel microemulsions of MBZ (MBZ-NaH ME) for intranasal administration. MBZ raw materials were characterized by FTIR, DSC, and XDP. Subsequently, the raw material that contained mainly polymorph C was selected to prepare microemulsions. Two different oleic acid (OA) systems were selected. Formulation A was composed of OA and docosahexaenoic acid (3:1% w/w), while formulation B was composed of OA and Labrafil M2125 (1:1% w/w). Sodium hyaluronate (NaH) at 0.1% was selected as a mucoadhesive agent. MBZ MEs showed a particle size of 209 nm and 145 nm, respectively, and the pH was suitable for nasal formulations (4.5-6.5). Formulation B, which showed the best solubility and rheological behavior, was selected for intranasal evaluation. The nasal toxicity study revealed no damage in the epithelium. Furthermore, formulation B improved significantly the median survival time in the orthotopic C6 rat model compared to the control group. Moreover, NIRF signal intensity revealed a decrease in tumor growth in the treated group with MBZ-MaH ME, which was confirmed by histologic examinations. Results suggest that the intranasal administration of mebendazole-loaded microemulsion might be appropriated for glioblastoma treatment. Graphical abstract.

Emerging micro- and nanotechnology based synthetic approaches for insulin delivery

Insulin is essential for type 1 and advanced type 2 diabetics to maintain blood glucose levels and prolong lives. The traditional administration requires frequent subcutaneous insulin injections that are associated with poor patient compliance, including pain, local tissue necrosis, infection, and nerve damage. Taking advantage of emerging micro- and nanotechnologies, numerous alternative strategies integrated with chemical approaches for insulin delivery have been investigated. This review outlines recent developments in the controlled delivery of insulin, including oral, nasal, pulmonary, transdermal, subcutaneous and closed-loop insulin delivery. Perspectives from new materials, formulations and devices at the micro- or nano-scales are specifically surveyed. Advantages and limitations of current delivery methods, as well as future opportunities and challenges are also discussed.

Formulation of intranasal mucoadhesive temperature-mediated in situ gel containing ropinirole and evaluation of brain targeting efficiency in rats

Mucoadhesive temperature-mediated in situ gel formulations using chitosan and hydroxyl propyl methyl cellulose were used to enhance intranasal (i.n.) delivery of the dopamine D2 agonist ropinirole to the brain. Formulations were tested for gelation time, thermosensitivity, mucoadhesion, in vitro release and permeation, in vitro cytotoxicity, nasal clearance, in vivo bioavailability and brain uptake. In vivo bioavailability and brain uptake of ropinirole were assessed in albino rats following intranasal administration of 99mTc-ropinirole in situ gel, intranasal ropinirole solution and intravenous (i.v.) ropinirole solution. Radiolabeled ropinirole uptake was calculated as a fraction of administered dose. The absolute bioavailabilty of ropinirole from the temperature-mediated in situ gelling nasal formulation was 82%. The AUC (0-480 min) in brain after nasal administration of ropinirole in situ gel was 8.5 times (869 +/- 250% x min/g versus 102 +/- 20% x min/g) that obtained following i.v. administration, this value was also considerably higher (869 +/- 250% x min/g versus 281 +/- 52% x min/g) than that achieved with intranasal ropinirole solution. High brain direct drug transport percentage (DTP; 90.36%) and drug targeting index (DTI) > 1 confirms direct nose to brain transport of the intranasal in situ gel formulation of ropinirole.

Nasal delivery of high molecular weight drugs

Nasal drug delivery may be used for either local or systemic effects. Low molecular weight drugs with are rapidly absorbed through nasal mucosa. The main reasons for this are the high permeability, fairly wide absorption area, porous and thin endothelial basement membrane of the nasal epithelium. Despite the many advantages of the nasal route, limitations such as the high molecular weight (HMW) of drugs may impede drug absorption through the nasal mucosa. Recent studies have focused particularly on the nasal application of HMW therapeutic agents such as peptide-protein drugs and vaccines intended for systemic effects. Due to their hydrophilic structure, the nasal bioavailability of peptide and protein drugs is normally less than 1%. Besides their weak mucosal membrane permeability and enzymatic degradation in nasal mucosa, these drugs are rapidly cleared from the nasal cavity after administration because of mucociliary clearance. There are many approaches for increasing the residence time of drug formulations in the nasal cavity resulting in enhanced drug absorption. In this review article, nasal route and transport mechanisms across the nasal mucosa will be briefly presented. In the second part, current studies regarding the nasal application of macromolecular drugs and vaccines with nano- and micro-particulate carrier systems will be summarised.

Intranasal Bioavailability of Insulin from Carbopol-Based Gel Spray in Rabbits

The purpose of this study was to investigate the nasal absorption of insulin from a carbopol-based nasal gel spray in rabbits. An insulin nasal gel was prepared by dispersing carbopol in distilled water, followed by the addition of insulin solution, then neutralization and viscosity adjustment. The nasal absorption of insulin from the gel, in conscious rabbits, was evaluated in comparison with absorption from an insulin solution. The absolute bioavailability of insulin from the nasal gel was studied using blood glucose level in comparison to intravenous injection. The insulin gel formulation produced a significant hypoglycemic response in rabbits, whereas no response was seen following administration of the insulin solution formulation. The bioavailability of insulin from the nasal gel formulation was 20.6% compared with the intravenous injection. The results of the present study suggest that the carbopol gel promotes the nasal absorption of insulin in rabbit model and due to its sprayability with commercially available spray pumps, could be considered as a preferred platform in nasal drug administration.

Permeation studies and histological examination of sheep nasal mucosa following administration of different nasal formulations with or without absorption enhancers

This study was designed to investigate the possible histological effects of different intranasal (IN) formulations of indomethacin (IND) on nasal mucosa in sheep. For this purpose, oil-in-water (O/W) emulsion (E) and solution (S) formulations including 3 mg/mL of IND were prepared. Penetration enhancers such as polyvinylpyrolidone (PVP), citric acid (CA) and sodium taurocholate (NaT) were added to emulsion (1%) at the final step into the formulations. First, the effect of penetration enhancers on permeation of IND was evaluated by in vitro permeation studies in which sheep nasal mucosa was used. According to the permeation studies PVP showed the highest enhancing effect on the permeation rate of IND from sheep nasal mucosa. Furthermore, the IND permeation from E containing PVP (1.624 +/- 0.045 mg) was significantly higher than that obtained from E (0.234 +/- 0.012 mg) (p < 0.05). For the histological studies, white Karaman sheep of approximately 20 +/- 5 kg, aged 4 to 8 months were used. They were randomly divided into eight groups, each including three sheep. Five experimental groups received different formulations of IND emulsion without/ with penetration enhancers (E-PVP, E-CA, E-NaT, E) and IND solution (S), respectively. Parallel controls were composed of either untreated groups and were given blank emulsion or isotonic sodium chloride solution (0.31 mg/kg). 2 mL of each experimental formulation was applied to both nostrils of sheep, and 1/3 central and lower regions of the nose were dissected and prepared for light microscopy. Specimens stained with hematoxylin and eosin and Gomori's trichrome were examined by light microscopy. No signs of inflammation or erosion were noticed in the nasal mucosa of the control groups. Widened epithelial intercellular spaces were noticed in E-CA, E-NaT, and E-PVP groups as well with the E-PVP group showing the largest intraepithelial separations. E-CA and E-NaT groups showed significant decrease in the amount of goblet cells, while hypoplasia was considerably moderate in the E-PVP group. Finally, intranasal administration of IND emulsion with PVP may be considered as an alternative to intravenous and per oral administrations of IND to overcome their adverse effects.

The release and analgesic activities of morphine and its ester prodrug, morphine propionate, formulated by water-in-oil nanoemulsions

In this study, we examined the feasibility of water-in-oil (w/o) nanoemulsions as sustained-release systems for morphine, following subcutaneous administration in rats. The ester prodrug of morphine, morphine propionate (MPR), was also utilized in this study. A variety of nanoemulsions were prepared using soybean oil or sesame oil as the external phase. Span 80, Tween 80, Plurol diisostearique and Brij 98 were used as surfactants in the w/o interface. The effects of the formulation variables on the characteristics of the nanoemulsions, such as inner droplet size, zeta potential, viscosity, drug partitioning, drug release and pharmacological effect, were evaluated. Mean sizes of nanoemulsions of 50-200 nm were obtained. The initial surface charge of the emulsions was found to be around - 3 to - 4 mV, except that the Plurol-containing vehicle showed a highly negative charge of - 23 mV. The loading of morphine and MPR into the nanoemulsions resulted in slower sustained-release behavior as compared with the drug/prodrug in aqueous solution. The rate of morphine released across the membrane was found to be highly dependent on the choice of oil and surfactant types. On the other hand, discrepancies in MPR release rates among the various formulations were minimal. The in vivo analgesic duration of morphine by targeting the drug to central nerve system could be prolonged from 1 to 3 h by incorporating the drug into nanoemulsions using Span 80 or Tween 80 as the surfactant. These results suggest that w/o nanoemulsions are well suited to provide sustained morphine delivery for therapeutic purposes.

Permeation studies of indomethacin from different emulsions for nasal delivery and their possible anti-inflammatory effects

The purpose of this research was to develop an emulsion formulation of indomethacin (IND) suitable for nasal delivery. IND was incorporated into the oil phases of oil in water (O/W) and water in oil (W/O) emulsions. For this purpose, different emulsifying agents (Tween 80, Span 80 and Brij 58) were used in two emulsion formulations. When the effects of several synthetic membranes (nylon, cellulose, cellulose nitrate) were compared with the sheep nasal mucosa, the cellulose membrane and sheep nasal mucosa showed similar permeation properties for O/W emulsion (P > 0.05). To examine the absorption characteristics of IND, the anti-inflammatory properties of intravenous solution of IND, intranasal O/W emulsions of IND (with or without enhancers) and intranasal solution of IND (IND-Sol) were investigated in rats with carrageenan-induced paw edema. When citric acid was added to the nasal emulsion, the anti-inflammatory activity was similar to that of intravenous solution (P > 0.05). Finally, it was concluded that, intranasal administration of IND emulsion with citric acid may be considered as an alternative to intravenous and per oral administrations of IND to overcome their adverse effects.

Current challenges in non-invasive insulin delivery systems: a comparative review

The quest to eliminate the needle from insulin delivery and to replace it with non- or less-invasive alternative routes has driven rigorous pharmaceutical research to replace the injectable forms of insulin. Recently, various approaches have been studied involving many strategies using various technologies that have shown success in delivering insulin, which are designed to overcome the inherent barriers for insulin uptake across the gastrointestinal tract, mucosal membranes and skin. This review examines some of the many attempts made to develop alternative, more convenient routes for insulin delivery to avoid existing long-term dependence on multiple subcutaneous injections and to improve the pharmacodynamic properties of insulin. In addition, this article concentrates on the successes in this new millennium in developing potential non-invasive technologies and devices, and on major new milestones in modern insulin delivery for the effective treatment of diabetes.

Intranasal delivery: physicochemical and therapeutic aspects

Interest in intranasal (IN) administration as a non-invasive route for drug delivery continues to grow rapidly. The nasal mucosa offers numerous benefits as a target issue for drug delivery, such as a large surface area for delivery, rapid drug onset, potential for central nervous system delivery, and no first-pass metabolism. A wide variety of therapeutic compounds can be delivered IN, including relatively large molecules such as peptides and proteins, particularly in the presence of permeation enhancers. The current review provides an in-depth discussion of therapeutic aspects of IN delivery including consideration of the intended indication, regimen, and patient population, as well as physicochemical properties of the drug itself. Case examples are provided to illustrate the utility of IN dosing. It is anticipated that the present review will prove useful for formulation scientists considering IN delivery as a delivery route.

A thermosensitive hydrogel based on quaternized chitosan and poly(ethylene glycol) for nasal drug delivery system

A new thermosensitive hydrogel was designed and prepared by simply mixing N-[(2-hydroxy-3-trimethylammonium) propyl] chitosan chloride (HTCC) and poly(ethylene glycol) (PEG) with a small amount of alpha-beta-glycerophosphate (alpha-beta-GP). The optimum preparative condition was investigated, and the obtained formulation underwent thermal transition from solution below or at room temperature to non-flowing hydrogel around 37 degrees C in several minutes. As a new formulation, its potential use as nasal drug delivery system was studied. It can be dropped or sprayed easily into nasal cavity and spread on the nasal mucosa in solution state. After being administered into nasal cavity, the solution transformed into viscous hydrogel at body temperature, which decreased nasal mucociliary clearance rate and released drug slowly. Morever, quaternized chitosan as absorption enhancer has been studied extensively in several reports and proved its non-toxicity, mucoadhesivity and the capacity to open the tight junctions between epithelial cells. Therefore, in this study insulin as a model drug was entrapped in this formulation and its release behavior in vitro was also investigated. The enhancement of absorption of fluorescein isothiocyanate (FITC)-labeled insulin in rat nasal cavity by this formulation was proved by confocal laser scanning microscopy (CLSM). The cytoxicity and the change of the blood glucose concentration after nasal administration of this hydrogel were also investigated. The hydrogel formulation decreased the blood glucose concentration apparently (40-50% of initial blood glucose concentration) for at least 4-5h after administration, and no apparent cytoxicity was found after application. These results showed that HTCC-PEG-GP formulation can be used as nasal drug delivery system to improve the absorption of hydrophilic macromolecular drugs.

In vitro formulation optimization of intranasal galantamine leading to enhanced bioavailability and reduced emetic response in vivo

The purpose of the current investigation was to optimize an intranasal (IN) galantamine (an acetylcholinesterase inhibitor used for treatment of Alzheimer's disease) formulation using an in vitro tissue model, to correlate those results to in vivo bioavailability, and to compare emetic response to oral dosing. A design-of-experiments (DOE) based formulation screening employing an in vitro tissue model of human nasal epithelium was used to assess drug permeability, tight junction modulation, and cellular toxicity. In vivo studies in rats compared pharmacokinetic (PK) profiles of different formulations dosed intranasally. Finally, studies in ferrets evaluated PK and gastrointestinal (GI) related side effects of oral compared to nasal dosage forms. Galantamine permeation was enhanced without increasing cytotoxicity. Pharmacokinetic testing in rats confirmed the improved drug bioavailability and demonstrated an in vitro-in vivo correlation. Compared to oral dosing, IN galantamine resulted in a dramatically lowered incidence of GI-related side effects, e.g., retching and emesis. These findings illustrate that IN delivery represents an attractive alternative to oral dosing for this important Alzheimer's disease therapeutic. To our knowledge, the data herein represent the first direct confirmation of reducing GI-related side effects for IN galantamine compared to oral dosing.

Therapeutic utility of a novel tight junction modulating peptide for enhancing intranasal drug delivery

Previously, a novel tight junction modulating (TJM) peptide was described affording a transient, reversible lowering of transepithelial electrical resistance (TER) in an in vitro model of nasal epithelial tissue. In the current report, this peptide has been further evaluated for utility as an excipient in transepithelial drug formulations. Chemical stability was optimal at neutral to acidic pH when stored at or below room temperature, conditions relevant to therapeutic formulations. The TJM peptide was tested in the in vitro tissue model for potential to enhance permeation of a low-molecular-weight (LMW) drug, namely the acetylcholinesterase inhibitor galantamine, as well as three peptides, salmon calcitonin, parathyroid hormone 1-34 (PTH(1-34)), and peptide YY 3-36 (PYY(3-36)). In all cases, the TJM peptide afforded a dramatic improvement in drug permeation across epithelial tissue. In addition, a formulation containing PYY(3-36) and TJM peptide was dosed intranasally in rabbits, resulting in a dramatic increase in bioavailability. The TJM peptide was as or more effective in enhancing PYY(3-36) permeation in vivo at a 1000-fold lower molar concentration compared to using LMW enhancers. Based on these in vitro and in vivo data, the novel TJM peptide represents a promising advancement in intranasal formulation development.

Insulin loaded eudragit L100 microspheres for oral delivery: preliminary in vitro studies

Eudragit L100 microspheres were prepared using water-in-oil-in water (w/o/w) emulsion-solvent evaporation with polysorbate 20 as dispersing agent in the internal aqueous phase, and PVA/PVP as stabilizer in the external aqueous phase. Smaller internal and external aqueous phases provided higher drug encapsulation. The PVA-stabilized microspheres having maximum drug encapsulation (84.5 2.8%) released 7% insulin at pH 1.0 in 2 h. In phosphate buffer (pH 7.4), microspheres showed an initial burst release of 21% in 1 h with additional 35% release in the next 5 h. The smaller the volumes of internal and external aqueous phases, the lower the initial burst release. The release of drug from microspheres followed Higuchi kinetics. Scanning electron microscopy of PVA stabilized microspheres demonstrated spherical particles with smooth surface and laser diffractometry revealed a mean particle size (V(m)) of 59.11 30 m.

Eudragit S100 entrapped insulin microspheres for oral delivery

The purpose of this research was to investigate whether Eudragit S100 microspheres have the potential to serve as an oral carrier for peptide drugs like insulin. Microspheres were prepared using water-in oil-in water emulsion solvent evaporation technique with polysorbate 20 as a dispersing agent in the internal aqueous phase and polyvinyl alcohol (PVA)/polyvinyl pyrrolidone as a stabilizer in the external aqueous phase. The use of smaller internal aqueous-phase volume (50 microL) and external aqueous-phase volume (25 mL) containing PVA in the manufacturing process resulted in maximum encapsulation efficiency (81.8% +/- 0.9%). PVA-stabilized microspheres having maximum drug encapsulation released 2.5% insulin at pH 1.0 in 2 hours. In phosphate buffer (pH 7.4), microspheres showed an initial burst release of 22% in 1 hour with an additional 28% release in the next 5 hours. The smaller the volumes of internal and external aqueous phase, the lower the initial burst release. The release of drug from microspheres followed Higuchi kinetics. Scanning electron microscopy of PVA-stabilized microspheres demonstrated spherical particles with smooth surface, and laser diffractometry revealed a mean particle size of 32.51 +/- 20 microm. Oral administration of PVA stabilized microspheres in normal albino rabbits (equivalent to 6.6 IU insulin/kg of animal weight) demonstrated a 24% reduction in blood glucose level, with maximum plasma glucose reduction of 76 +/- 3.0% in 2 hours and effect continuing up to 6 hours. The area under the percentage glucose reduction-time curve was 93.75%. Thus, our results indicate that Eudragit S100 microspheres on oral administration can protect insulin from proteolytic degradation in the gastrointestinal tract and produce hypoglycemic effect.

In vivo evaluation of a reverse water-in-fluorocarbon emulsion stabilized with a semifluorinated amphiphile as a drug delivery system through the pulmonary route

The potential of a reverse water-in-fluorocarbon (w-in-FC) emulsion stabilized with a semifluorinated amphiphile, namely C8F17(CH2)11OP(O)[N(CH2CH2)2O]2 (F8H11DMP) for drug delivery through intrapulmonary administration was investigated in the mouse. This study involved assessment of the effect of single or repeated intranasal instillations of a plain emulsion on lung tissue integrity, and evaluation of blood glucose levels in mice treated with an insulin-loaded emulsion. When instilled intranasally to mice, the plain emulsion did not alter lung tissue integrity, as demonstrated by histological staining, and did not induce any airway inflammatory reaction. Treated mice exhibited decreased body weight within the 3-4 days that followed the first emulsion administration, but this decrease was reversible within few days. Mice instilled intranasally with the insulin-loaded emulsion displayed decreased blood glucose levels within the 20 min that followed the administration, thus demonstrating the potential of the reverse w-in-FC emulsion stabilized with F8H11DMP to systemically deliver drugs, including peptides, upon lung administration.

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.

Permeability issues in nasal drug delivery

The nasal route is one of the most permeable and highly vascularized site for drug administration ensuring rapid absorption and onset of therapeutic action. It has been potentially explored as an alternative route for drugs with poor bioavailability and for the delivery of biosensitive and high molecular weight (MW) compounds such as proteins, peptides, steroids, vaccines, and so on. This review discusses the major factors affecting the permeability of drugs or biomolecules through the nasal mucosa, including biological, formulation and device-related factors. This information could potentially help to achieve desired plasma concentrations of drugs without compromising or altering the normal physiology of the nasal cavity.

Elucidation of the mechanism of incorporation of insulin in controlled release systems based on complexation polymers

The objective of this study was to investigate the insulin incorporation and release properties of poly(methacrylic acid-g-ethylene glycol) P(MAA-g-EG) microparticles as a function of copolymer composition. These microparticles exhibited unique pH-responsive characteristics in which interpolymer complexes were formed in acidic media and dissociated in neutral/basic environments. The microparticles containing equimolar amounts of MAA and PEG were capable of efficient insulin loading using equilibrium partitioning (>90%). Additionally, insulin release from the gel was significantly retarded in acidic media while rapid release occurred under neutral/basic conditions. In contrast, as the amount of MAA of the polymer was increased, the entrapment efficiency of insulin within the gel greatly reduced and the insulin was readily released from the polymer network in the acidic and neutral/basic media. In addition, in order to evaluate the potential application of the microparticles to other drugs, theophylline, vancomycin, fluorescein-isothiocyanate-labeled dextrans (FITC-Ds) with average molecular weights of 4400 (FITC-D-4), 12,000 (FITC-D-10) and 19,500 (FITC-D-20) were utilized as model hydrophilic drugs. The incorporation profiles showed that the uptake of theophylline and vancomycin to the microparticles was lower than that of insulin. Additionally, polymer microparticles loaded with theophylline and vancomycin exhibited pH-sensitive release behavior, however, the oscillatory behavior is less pronounced than those of insulin. The values of drug incorporation ratio showed that the microparticles were capable of incorporating almost 90% of insulin and 15% of vancomycin from solution. On the other hand, the other hydrophilic drugs showed very low incorporation efficiency to the microparticles. These data suggest that gels containing equimolar amounts of MAA:EG have the potential to be used as an oral carrier of peptide drugs, especially for insulin.

Insulin aggregation and asymmetric transport across human bronchial epithelial cell monolayers (Calu-3)

The purpose of this work was to elucidate the transport pathways of zinc insulin across the Calu-3 cell monolayer, an in vitro model of the human airway epithelium. Calu-3 cells grown in liquid-covered conditions formed a confluent monolayer with a high transepithelial electrical resistance value of 1000 +/- 150 Omega small middle dot cm(2). The cell monolayer was characterized by a low mannitol permeability of 4.7 +/- 0.5 10(-7)cm/s. Transport of zinc insulin (donor concentration 1 U/mL) in Dulbecco's modified phosphate buffer saline at 37 degrees C was found to be higher in the basolateral (BL) to apical (AP) (P(app) = 3.0 +/- 0.2 10(-8) cm/s), than in the AP to BL direction (P(app) = 0.41 +/- 0.02 10(-8) cm/s). P-glycoprotein efflux or specific enzymatic degradation did not appear to contribute toward this asymmetric transport. Insulin receptors, though apparently more abundant on the BL side than on the AP side of Calu-3 cells, did not mediate the direction-dependent transport of insulin. However, transport of a monomeric human insulin analog, Asp(B10)des(B28-30), across the Calu-3 cell monolayer was similar in both directions (BL to AP and AP to BL). The corresponding permeability, P(app) = 2.9 +/- 0.2 10(-8) cm/s, was not significantly different from the permeability of zinc insulin in the BL to AP direction. The paracellular pathway seems to play a major role in the insulin transport across the Calu-3 cell monolayers. We hypothesize that the transport of zinc insulin oligomers is restricted at the AP surface by the presence of the tight junctional complexes. From the BL side, oligomers may undergo dissociation in the intercellular space and diffuse readily as monomers to the AP surface of the membrane.