Absorption enhancers in pulmonary protein delivery

Enhancement of insulin transport across primary rat alveolar epithelial cell monolayers by endogenous cellular factor(s)

PURPOSE

To characterize factor(s) contained in apical medium of primary cultured rat alveolar epithelial type II cell-like monolayers (RAECM-II) that enhance insulin absorption across alveolar epithelial cells.

MATERIALS AND METHODS

Primary rat alveolar epithelial cell monolayers cultured on Transwells in the presence and absence of 10 ng/ml keratinocyte growth factor for 6 days were dosed from the apical compartment with radiolabeled insulin in: newborn bovine serum-containing medium (SM), conditioned medium from apical compartment of rat alveolar epithelial type I cell-like monolayers (RAECM-I) (CMI), or conditioned medium from apical compartment of RAECM-II (CMII). At the end of 2 h incubation, basolateral medium was collected and amounts of transported radiolabeled insulin were determined using a gamma counter. In order to determine the molecular size range of the enhancing factor(s), CMII was centrifuged in 50 kDa molecular weight cut-off Centricon tubes, and both retentate and filtrate were used as separate dosing solutions. Heat denaturation and ammonium sulphate precipitation were used to determine if the involved factor(s) represent proteins or other smaller soluble factors. Transalveolar transport rates of a paracellular marker, (14)C-mannitol, and fluid-phase marker, horseradish peroxidase, were determined in the presence and absence of the factors. Effects of temperature (4, 16 and 37 degrees C) on radiolabeled insulin fluxes were also measured.

RESULTS

Conditioned medium obtained from the apical compartment of RAECM-II, CMII, increased transport of insulin across the monolayers when compared to SM or CMI. The enhancing effect of CMII was retained in the precipitate following ammonium sulfate treatment and in the retentate after Centricon filtration. The enhancing effect of CMII was significantly decreased when heated at 80 degrees C for 15 min. CMII did not affect the transport of (14)C-mannitol or HRP, while its effect on insulin transport was decreased by 87% when temperature was lowered to 4 degrees C from 37 degrees C.

CONCLUSIONS

Conditioned medium from type II cell-like monolayer cultures appears to contain protein factor(s) which seem to be involved in facilitating active transcellular transport of insulin across primary cultured RAECM-II.

The use of absorption enhancers to enhance the dispersibility of spray-dried powders for pulmonary gene therapy

BACKGROUND

Pulmonary gene therapy requires aerosolisation of the gene vectors to the target region of the lower respiratory tract. Pulmonary absorption enhancers have been shown to improve the penetration of pharmaceutically active ingredients in the airway. In this study, we investigate whether certain absorption enhancers may also enhance the aerosolisation properties of spray-dried powders containing non-viral gene vectors.

METHODS

Spray-drying was used to prepare potentially respirable trehalose-based dry powders containing lipid-polycation-pDNA (LPD) vectors and absorption enhancers. Powder morphology and particle size were characterised using scanning electron microscopy and laser diffraction, respectively, with gel electrophoresis used to assess the structural integrity of the pDNA. The biological functionality of the powders was quantified using in vitro cell (A549) transfection. Aerosolisation from a Spinhaler dry powder inhaler into a multistage liquid impinger (MSLI) was used to assess the in vitro dispersibility and deposition of the powders.

RESULTS

Spray-dried powder containing dimethyl-beta-cyclodextrin (DMC) demonstrated substantially altered particle morphology and an optimal particle size distribution for pulmonary delivery. The inclusion of DMC did not adversely affect the structural integrity of the LPD complex and the powder displayed significantly greater transfection efficiency as compared to unmodified powder. All absorption enhancers proffered enhanced powder deposition characteristics, with the DMC-modified powder facilitating high deposition in the lower stages of the MSLI.

CONCLUSIONS

Incorporation of absorption enhancers into non-viral gene therapy formulations prior to spray-drying can significantly enhance the aerosolisation properties of the resultant powder and increase biological functionality at the site of deposition in an in vitro model.

Absorption enhancement of poorly absorbed hydrophilic compounds from various mucosal sites by combination of mucolytic agent and non-ionic surfactant

Absorption enhancement of poorly absorbed hydrophilic compounds from various mucosal sites by co-administration of a mucolytic agent and a non-ionic surfactant was examined in rats. Fluorescein isothiocyanate-labeled dextran with average molecular weight of ca. 4.4kDa (FD-4), and salmon calcitonin (SCT) were used as model compounds. N-acetylcysteine (NAC) and p-t-octyl phenol polyoxyethylene-9.5 (Triton X-100, TX-100) were selected as a mucolytic agent and a non-ionic surfactant, respectively. Dosing solutions containing these agents were administered into various mucosal sites including the nose, the lung and the large intestine, and the bioavailabilities were determined. The combination of 5% NAC and 5% TX-100 significantly enhanced the nasal, the pulmonary and the large intestinal absorption of FD-4 compared to the control, and the enhancement ratios relative to the control were 7.2-, 2.8- and 4.5-fold, respectively. The different enhancement ratio among the administration sites explored indicates that the absorption enhancing effect of the combination of NAC and TX-100 is site-dependent. This combination also improved the nasal and the pulmonary absorption of SCT, and the enhancement ratios relative to the control were 6.1- and 8.1-fold, respectively. All these results suggest that the combination strategy of a mucolytic agent and a non-ionic surfactant may be widely applicable to various mucosal deliveries of poorly absorbed hydrophilic compounds.

Inhaled Insulin is Better Absorbed When Administered as a Dry Powder Compared to Solution in the Presence or Absence of Alkylglycosides

PURPOSE

This study was performed to investigate the safety of alkylglycosides administered via the respiratory route and to compare the pulmonary absorption profiles of insulin administered as dry powder inhaler and inhaler solution.

METHODS

The safety of a series of alkylglycosides with varying alkyl chain lengths was studied by measuring the enzymatic activities in the bronchoalveolar lavage (BAL) fluid of rat lungs. Pulmonary formulations of insulin plus octylmaltoside were administered either as solution or lyophilized dry powder to anesthetized rats, and absorption of insulin was assessed by measuring plasma insulin and glucose levels. The physical characterization of the dry powder formulation was performed using scanning electron microscope (SEM) and Fourier transform infrared spectrophotometer (FTIR).

RESULTS

The BAL analysis showed that there was a gradual increase in the amount of lung injury markers released with the increase in the hydrophobic chain length of alkylglycosides. The pulmonary administration of lyophilized dry powder of insulin plus octylmaltoside or its solution counterpart showed that the bioavailability of powder formulation was about 2-fold higher than that of the formulation administered as solution. The SEM studies showed a subtle difference in the surface morphologies of formulation particles after lyophilization. FTIR data showed minor interactions between the peptide and excipients upon lyophilization.

CONCLUSIONS

Of the alkylglycosides tested, octylmaltoside was least toxic in releasing lung injury markers. Octylmaltoside-based dry powder insulin formulations were more efficacious in enhancing pulmonary insulin absorption and reducing plasma glucose levels compared with the formulations administered as a solution.

Indication of transcytotic movement of insulin across human bronchial epithelial cells

This study was performed to evaluate insulin permeability across human bronchial epithelial cell lines and investigate if insulin is transported via the paracellular or transcellular pathway. The movement of insulin across two bronchial epithelial cells, 16HBE14o- and Calu-3, was studied in the presence or absence of octylmaltoside. Mannitol and propanolol have been used as paracellular and transcellular marker, respectively, and transepithelial electrical resistance (TEER) was determined to investigate the tight junctional integrity of the monolayers. The possible endocytotic mechanism of insulin across these two cell lines was studied by confocal laser scanning microscopy after incubating the cells with fluorescent-labeled insulin. The TEER values for both cell monolayers were >400 Omega cm2 at confluency. There was a decrease in the TEER values when octylmaltoside was added to the apical side of transwells. Similarly, the apparent permeability coefficient (P(app)) values of insulin, mannitol and propanolol, showed an increase with the rise in the concentration of octylmaltoside. In the absence of octylmaltoside, the P(app) values for insulin and the markers were in the following order: propanolol > mannitol > insulin. Confocal microscopic studies revealed that the uptake of insulin by the bronchial epithelial cells perhaps occurs via translocation across the cell. The data presented in this study demonstrate that insulin perhaps moves across the bronchial cells via both paracellular and transcellular pathways.

Polymer-surfactant and protein-surfactant interactions

The phase behavior and some physicochemical properties of homopolymers (HP) and hydrophobically modified (HMP) polymers, as well as of polyelectrolytes (PE) and proteins (PR), in the presence of aqueous surfactants, or their mixtures, are discussed. Mixing the above components gives rise to the formation of organized phases, whose properties are controlled by polymer and/or surfactant content, temperature, pH, and ionic strength. Depending on the nature, concentration, and net charge of both solutes, molecular solutions, polymer-surfactant complexes, adsorption onto micelles and vesicles, gels, liquid crystalline phases, and precipitates are observed. Such rich polymorphic behavior is the result of a complex balance between electrostatic, excluded volume, van der Waals, and other contributions to overall system stability. It is also modulated by the molecular details and architecture of both the polymer and the surfactant. Different experimental methods allow investigation of the above systems and getting information on the nature of polymer-surfactant interactions (PSI). Surface adsorption and thermodynamic methods, together with investigation of the phase diagrams, give information on the forces controlling PSI and on the existence of different phases. Conductivity, QELS and viscosity allow estimating the size and shape of polymer-surfactant (protein-surfactant) complexes. Optical microscopy, cryo-TEM, AFM, NMR, fluorescence, and relaxation methods give more information on the above systems. Use of the above mixtures in controlling gelation, surface covering, preparing dielectric layers, and drug release is suggested.

Particle engineering techniques for inhaled biopharmaceuticals

Formulation of biopharmaceuticals for pulmonary delivery is faced with the challenge of producing particles with the optimal properties for deep lung deposition without altering the native conformation of these molecules. Traditional techniques such as milling are continuously being improved while newer and more advanced techniques such as spray drying, spray freeze drying and supercritical fluid technology are being developed so as to optimize pulmonary delivery of biopharmaceuticals. While some of these techniques are quite promising, some are harsh and impracticable. Method scale up, cost-effectiveness and safety issues are important factors to be considered in the choice of a technique. This paper reviews the presently developed techniques for particle engineering biopharmaceuticals.

Pulmonary delivery of insulin by liposomal carriers

Growing attention has been given to the potential of a pulmonary route as a non-invasive administration for systemic delivery of therapeutic agents (mainly peptides and proteins). The lungs provide a large absorptive surface area, extremely thin absorptive mucosal membrane, and good blood supply. The non-invasive nature of this pathway makes it especially valuable for the delivery of large molecular protein. However, pulmonary delivery of peptides and proteins is complicated by the complexity of the anatomic structure of the human respiratory system and the effect of disposition exerted by the respiration process. In this study, novel nebulizer-compatible liposomal carrier for aerosol pulmonary drug delivery of insulin was developed and characterized. Experimental results showed that insulin could be efficiently encapsulated into liposomes by preformed vesicles and detergent dialyzing method. The optimal encapsulation efficiency was achieved when 40% ethanol was used. The particle size of liposomal aerosols from ultrasonic nebulizer approximated to 1 mum. Insulin was stable in the liposomal solution. Animal studies showed that plasma glucose level was effectively reduced when liposomal insulin was delivered by inhalation route of using aerosolized insulin-encapsulated liposomes. Including fluorescent probe (phosphatidylethanolamine-rhodamine) into liposome, we found that the liposomal carriers were effectively and homogeneously distributed in the lung aveolar. Liposome-mediated pulmonary drug delivery promotes an increase in drug retention-time in the lungs, and more importantly, a reduction in extrapulmonary side-effects which invariably results in enhanced therapeutic efficacies.

Delivery of parathyroid hormone for the treatment of osteoporosis

Parathyroid hormone (PTH), along with its fragments and analogues, potently restores bone mass and biomechanical strength in animal models of osteoporosis, and reduces fractures by up to 65% in clinical trials in osteoporotic patients. Despite this demonstrated efficacy, patient acceptance and compliance with PTH is limited by the need for daily subcutaneous injections. The development of an equally efficacious, noninjectable form of PTH would significantly expand the present market. A challenge to the development of an alternative delivery system is the requirement for low-dose, daily, intermittent pulses of PTH to induce the anabolic actions on bone. In this review, recent basic and clinical efforts to deliver PTH by oral, buccal, sublingual, transdermal, nasal and pulmonary approaches will be addressed.

Protein drug stability: a formulation challenge

The increasing use of recombinantly expressed therapeutic proteins in the pharmaceutical industry has highlighted issues such as their stability during long-term storage and means of efficacious delivery that avoid adverse immunogenic side effects. Controlled chemical modifications, such as substitutions, acylation and PEGylation, have fulfilled some but not all of their promises, while hydrogels and lipid-based formulations could well be developed into generic delivery systems. Strategies to curb the aggregation and misfolding of proteins during storage are likely to benefit from the recent surge of interest in protein fibrillation. This might in turn lead to generally accepted guidelines and tests to avoid unforeseen adverse effects in drug delivery.

Cyclodextrins as a potential carrier in drug nebulization

The inhalation route is widely studied for many drug applications focusing on either local or systemic distributions. One matter of concern is the solubilization of hydrophobic drugs. We have studied the feasibility of using different cyclodextrins (CDs) to elaborate pharmaceutical formulations for the inhalation route and tested the short-term toxicity of such formulations administered by inhalation to C57BL/6 mice. We have shown that HP-beta-CD, gamma-CD, as well as RAMEB aqueous solutions can undergo aerosolization and that the resulting droplet-size ranges are compatible with pulmonary deposition. In vivo, we have demonstrated that short-term exposure to inhaled HP-beta-CD, gamma-CD and RAMEB solutions are non-toxic after assessing bronchoalveolar lavage (BAL), lung and kidney histology, bronchial responsiveness to methacholine and blood urea. The only change noted is a slight increase in lymphocyte count in the BAL after HP-beta-CD and gamma-CD inhalation. We conclude that CDs are useful in significantly enhancing the solubility of apolar drugs with a view to inhalation therapy although an increase in lymphocyte counts in the BAL after CDs inhalations needs further investigations.