Do interactions with phospholipids contribute to the prolonged retention of polypeptides within the lung?

Protein and peptide delivery to lungs by using advanced targeted drug delivery

The challenges and difficulties associated with conventional drug delivery systems have led to the emergence of novel, advanced targeted drug delivery systems. Therapeutic drug delivery of proteins and peptides to the lungs is complicated owing to the large size and polar characteristics of the latter. Nevertheless, the pulmonary route has attracted great interest today among formulation scientists, as it has evolved into one of the important targeted drug delivery platforms for the delivery of peptides, and related compounds effectively to the lungs, primarily for the management and treatment of chronic lung diseases. In this review, we have discussed and summarized the current scenario and recent developments in targeted delivery of proteins and peptide-based drugs to the lungs. Moreover, we have also highlighted the advantages of pulmonary drug delivery over conventional drug delivery approaches for peptide-based drugs, in terms of efficacy, retention time and other important pharmacokinetic parameters. The review also highlights the future perspectives and the impact of targeted drug delivery on peptide-based drugs in the coming decade.

Delivery of Dry Powders to the Lungs: Influence of Particle Attributes from a Biological and Technological Point of View

Dry powder inhalers are medical devices used to deliver powder formulations of active pharmaceutical ingredients via oral inhalation to the lungs. Drug particles, from a biological perspective, should reach the targeted site, dissolve and permeate through the epithelial cell layer in order to deliver a therapeutic effect. However, drug particle attributes that lead to a biological activity are not always consistent with the technical requirements necessary for formulation design. For example, small cohesive drug particles may interact with neighbouring particles, resulting in large aggregates or even agglomerates that show poor flowability, solubility and permeability. To circumvent these hurdles, most dry powder inhalers currently on the market are carrier-based formulations. These formulations comprise drug particles, which are blended with larger carrier particles that need to detach again from the carrier during inhalation. Apart from blending process parameters, inhaler type used and patient's inspiratory force, drug detachment strongly depends on the drug and carrier particle characteristics such as size, shape, solid-state and morphology as well as their interdependency. This review discusses critical particle characteristics. We consider size of the drug (1-5 µm in order to reach the lung), solid-state (crystalline to guarantee stability versus amorphous to improve dissolution), shape (spherical drug particles to avoid macrophage clearance) and surface morphology of the carrier (regular shaped smooth or nano-rough carrier surfaces for improved drug detachment.) that need to be considered in dry powder inhaler development taking into account the lung as biological barrier.

The influence of lung surfactant liquid crystalline nanostructures on respiratory drug delivery

The respiratory route increasingly has been used for both local and systemic drug delivery. Although drug is absorbed rapidly after respiratory delivery, the role of lung surfactant in drug delivery is not well understood. The human lung contains only around 15mL of surface lining fluid spread over ∼100m² surface. The fluid contains lung surfactant at a concentration of 8-24mg/kg/body weight; the lung surfactant which is lipo-protein in nature can form different liquid crystalline nanostructures. After a brief overview of the anatomy of respiratory system, the review has focused on the current understanding of lung surface lining fluid, lung surfactants and their composition and possible self-assembled nanostructures. The role of lung surfactant in drug delivery and drug dissolution has been briefly considered. Lung surfactant may form different liquid crystalline phases which can have an active role in drug delivery. The hypotheses developed in this review focuses on the potential roles of surface epithelial fluid containing liquid crystalline nanostructures in defining the dissolution mechanism and rate. The hypotheses also focus an understanding how liquid crystalline nanostructures can be used to control dissolution rate and how the nanostructures might be changed to influence delivery and induce toxicity.

Pegylation of antimicrobial peptides maintains the active peptide conformation, model membrane interactions, and antimicrobial activity while improving lung tissue biocompatibility following airway delivery

Antimicrobial peptides (AMPs) have therapeutic potential, particularly for localized infections such as those of the lung. Here we show that airway administration of a pegylated AMP minimizes lung tissue toxicity while nevertheless maintaining antimicrobial activity. CaLL, a potent synthetic AMP (KWKLFKKIFKRIVQRIKDFLR) comprising fragments of LL-37 and cecropin A peptides, was N-terminally pegylated (PEG-CaLL). PEG-CaLL derivatives retained significant antimicrobial activity (50% inhibitory concentrations [IC(50)s] 2- to 3-fold higher than those of CaLL) against bacterial lung pathogens even in the presence of lung lining fluid. Circular dichroism and fluorescence spectroscopy confirmed that conformational changes associated with the binding of CaLL to model microbial membranes were not disrupted by pegylation. Pegylation of CaLL reduced AMP-elicited cell toxicity as measured using in vitro lung epithelial primary cell cultures. Further, in a fully intact ex vivo isolated perfused rat lung (IPRL) model, airway-administered PEG-CaLL did not result in disruption of the pulmonary epithelial barrier, whereas CaLL caused an immediate loss of membrane integrity leading to pulmonary edema. All AMPs (CaLL, PEG-CaLL, LL-37, cecropin A) delivered to the lung by airway administration showed limited (<3%) pulmonary absorption in the IPRL with extensive AMP accumulation in lung tissue itself, a characteristic anticipated to be beneficial for the treatment of pulmonary infections. We conclude that pegylation may present a means of improving the lung biocompatibility of AMPs designed for the treatment of pulmonary infections.

Preclinical evaluation of tacrolimus colloidal dispersion for inhalation

Substantial improvements in transplant therapy have been made in the past four decades resulting in the acceptance of organ transplantation as a viable treatment for late-stage disease and organ failure. More recently, lung transplantation has gained acceptance; however, high incidence of chronic rejection and opportunistic infections has limited success rates in comparison with other transplant procedures. To achieve more targeted therapy, pulmonary administration of nebulized tacrolimus (TAC) colloidal dispersion once daily for 28 consecutive days in Sprague Dawley (SD) rats has been investigated for safety and systemic elimination. A liquid dispersion of colloidal TAC and lactose (1:1 ratio by weight) was aerosolized using a vibrating mesh nebulizer and administered via a nose-only dosing chamber. Blood chemistry and histological comparisons to saline-dosed animals showed no clinically significant differences in liver and kidney function or lung tissue damage. Maximum blood and lung concentrations sampled 1h after the final dose showed TAC concentrations of 10.1 ± 1.4 ng/mL and 1758.7 ± 80.0 ng/g, respectively. Twenty-four hours after the final dose, systemic TAC concentrations measured 1.0 ± 0.5 ng/mL, which is well below clinically accepted trough concentrations (5-15 ng/mL) for maintenance therapy, and therefore, would not be expected to induce toxic side effects. The propensity for pulmonary retention seen when compared to single dose lung levels may be due to macrophage uptake and the lipophilic nature of TAC. Additionally, three month stability testing of TAC powder for reconstitution showed no changes in amorphous nature or drug potency when stored at ambient conditions. TAC colloidal dispersion proved to be non-toxic when administered by pulmonary inhalation to SD rats over 28 days while providing therapeutic concentrations locally. This delivery strategy may prove safe and effective for the prevention of lung allograft rejection in lung transplant recipients.

Evaluation of metered dose inhaler (MDI) formulations of ciclosporin

Our purpose was to evaluate metered dose inhaler (MDI) formulations of ciclosporin (cyclosporine) for aerodynamic properties, chemical stability and bioactivity. Ciclosporin formulations (0.1, 0.5 and 1.0% w/w) were prepared in hydrofluoroalkane (HFA) propellants (134a and 227) containing 3 and 6% ethanol. Aerodynamic properties of the MDI formulations were analysed using an eight-stage Andersen cascade impactor and respirable mass and non-respirable mass, mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) were determined from the impaction profiles. The chemical stability of 0.1% ciclosporin in HFA 227 containing 3% ethanol formulation stored at room temperature and 40°C was evaluated by HPLC at 0, 14, 30 and 90 days. The bioactivity of ciclosporin MDI formulations was evaluated by determining the ciclosporin-mediated inhibition of interleukin-2 (IL-2) release from human Jurkat cells stimulated with phorbol 12-myristate 13-acetate (PMA). As ethanol concentration increased from 3 to 6%, respirable mass decreased from 2.3 mg per five actuations to 0.04 mg per five actuations for HFA 227 formulations, and from 1.5 mg to 0.09 mg per five actuations for HFA 134a formulations. The MMAD for both HFA 134a and 227 formulations increased with an increase in ciclosporin concentration. HPLC analysis showed ciclosporin to be extremely stable in HFA 227 at room temperature and 40°C. Stimulation of Jurkat cells with PMA released significant amounts of IL-2, which was inhibited by ciclosporin in a dose-dependent manner. This study shows the feasibility of developing chemically stable and bioactive HFA-based MDI formulations of ciclosporin.

Characterization and pharmacokinetic analysis of tacrolimus dispersion for nebulization in a lung transplanted rodent model

Lung transplantation animal models have been well established and enabled the investigation of a variety of new pharmacotherapeutic strategies for prevention of lung allograft rejection. Direct administration of immunosuppressive agents to the lung is a commonly investigated approach; however, can prove challenging due to the poor solubility of the drug molecule, the tortuous pathways of the lung periphery, and the limited number of excipients approved for inhalation. In this study, we aimed to evaluate a solubility enhancing formulation of tacrolimus for localized therapy in a lung transplanted rat model and determine the extent of drug absorption into systemic circulation. Characterization of the nebulized tacrolimus dispersion for nebulization showed a fine particle fraction (FPF) of 46.1% and a mass median aerodynamic diameter (MMAD) of 4.06 microm. After single dose administration to transplanted and non-transplanted rats, a mean peak transplanted lung concentration of 399.8+/-29.2 ng/g and mean peak blood concentration of 4.88+/-1.6 ng/mL were achieved. It is theorized that enhanced lung retention of tacrolimus is due to lipophilic associations with bronchial tissue and phospholipid surfactants in lung fluid. These findings indicate that tacrolimus dispersion for nebulization can achieve highly localized therapy for lung transplant recipients.

Mucosal delivery of liposome-chitosan nanoparticle complexes

Designing adequate drug carriers has long been a major challenge for those working in drug delivery. Since drug delivery strategies have evolved for mucosal delivery as the outstanding alternative to parenteral administration, many new drug delivery systems have been developed which evidence promising properties to address specific issues. Colloidal carriers, such as nanoparticles and liposomes, have been referred to as the most valuable approaches, but still have some limitations that can become more inconvenient as a function of the specific characteristics of administration routes. To overcome these limitations, we developed a new drug delivery system that results from the combination of chitosan nanoparticles and liposomes, in an approach of combining their advantages, while avoiding their individual limitations. These lipid/chitosan nanoparticle complexes are, thus, expected to protect the encapsulated drug from harsh environmental conditions, while concomitantly providing its controlled release. To prepare these assemblies, two different strategies have been applied: one focusing on the simple hydration of a previously formed dry lipid film with a suspension of chitosan nanoparticles, and the other relying on the lyophilization of both basic structures (nanoparticles and liposomes) with a subsequent step of hydration with water. The developed systems are able to provide a controlled release of the encapsulated model peptide, insulin, evidencing release profiles that are dependent on their lipid composition. Moreover, satisfactory in vivo results have been obtained, confirming the potential of these newly developed drug delivery systems as drug carriers through distinct mucosal routes.

Dimeric Zanamivir Conjugates with Various Linking Groups Are Potent, Long-Lasting Inhibitors of Influenza Neuraminidase Including H5N1 Avian Influenza

The synthesis, antiviral and pharmacokinetic properties of zanamivir (ZMV) dimers 8 and 13 are described. The compounds are highly potent neuraminidase (NA) inhibitors which, along with dimer 3, are being investigated as potential second generation inhaled therapies both for the treatment of influenza and for prophylactic use. They show outstanding activity in a 1 week mouse influenza prophylaxis assay, and compared with ZMV, high concentrations of 8 and 13 are found in rat lung tissue after 1 week. Retention of compounds in rat lung tissue correlated both with molecular weight (excluding 3 and 15) and with a capacity factor K' derived from immobilized artificial membrane (IAM) chromatography (including 3 and 15). Pharmacokinetic parameters for 3, 8 and 13 in rats show the compounds have short to moderate plasma half-lives, low clearances and low volumes of distribution. Dimer 3 shows NA inhibitory activity against N1 viruses including the recent highly pathogenic H5N1 A/Chicken/Vietnam/8/2004. In plaque reduction assays, 3, 8 and 13 show good to outstanding potency against a panel of nine flu A and B virus strains. Consistent with its shorter and more rigid linking group, dimer 8 has been successfully crystallized.

Note: dissolution of aerosol particles of budesonide in Survanta, a model lung surfactant

The effect of a pulmonary surfactant extract from bovine lung, Survanta, on the dissolution rate of aerosol particles of budesonide was determined. Aerosol particles of budesonide were generated from an ethanol solution, dried, and collected by a cascade impactor for characterization or by a liquid impinger for dissolution experiments. Powder x-ray diffraction, differential scanning calorimetry, differential thermal analysis, and scanning electron microscopy were used to characterize the aerosol particles and starting material. No change in phase was detected, although the aerosol particles appeared to contain residual solvent. The dissolution rate of the aerosol particles in saline was low and variable. Survanta increased the extent of dissolution of budesonide in proportion to the added concentration, which was also verified by equilibrium solubilization studies. Survanta also increased rate of dissolution, in a manner similar to sodium dodecyl sulfate. Analysis of the concentration of budesonide following ultracentrifugation indicated that there is rapid equilibration of budesonide between the Survanta and aqueous phase. These results show that lung surfactant has the potential of enhancing the rate and extent of dissolution of drugs administered to the lung.

Applications of immobilized stationary-phase liquid chromatography: a potential in vitro technique

Immobilized artificial-membrane chromatography is a potential in vitro technique for determining lipophilicity and studying drug transport and membrane interactions. It is reproducible, efficient and simple. Several other and newer applications of immobilized stationary-phase liquid chromatography have been reported, including the purification of membrane proteins, the synthesis of biomolecules and the simultaneous determination of enzyme activity and enantioselectivity. This article describes the immobilized artificial-membrane concept and provides an overview of the applications, advantages and limitations, in general, of immobilized stationary-phase chromatography.

The ascent of pulmonary drug delivery

The origins of inhalation therapy can be traced back to the early civilizations but this route of administration was relatively uncommon until recently. Direct delivery of drugs to the lung by inhalation for the treatment of respiratory disease grew rapidly in the second half of the 20th century as a result of the availability of effective asthma drugs in convenient, portable delivery systems. In the search for non-invasive delivery of biologics, it was discovered that the large highly absorptive surface area of the lung could be used for systemic delivery of proteins such as insulin. New delivery systems with efficiency and reproducibility to match the high cost and therapeutic constraints of biologics are currently in late stage clinical trials. Even small molecular weight drugs previously administered by injection are tested via the inhalation route either to provide non-invasively rapid onset of action, or to improve the therapeutic ratio for drugs acting in the lung. Gene therapy of pulmonary disease is still in its infancy but could provide valuable solutions to currently unmet medical needs. The beginning of the new millennium is therefore likely to witness development of many valuable therapeutic products delivered by inhalation.

Relating the phagocytosis of microparticles by alveolar macrophages to surface chemistry: the effect of 1,2-dipalmitoylphosphatidylcholine

This study examines the potential of 1,2-dipalmitoylphosphatidylcholine (DPPC), a major component of lung surfactant, to reduce the phagocytosis of microspheres by altering the cellular interactions occurring in the alveoli. These microspheres could be designed to act as a controlled delivery system for small molecules, peptides or proteins for pulmonary administration. Microspheres were prepared using poly (lactic-co-glycolic acid) (PLGA, 50/50 and encapsulated peroxidase as a model protein. DPPC was included in some formulations. The interaction of PLGA and DPPC-PLGA microspheres with phagocytic cells was evaluated using lung macrophages in culture. X-ray Photoelectron Spectra (XPS) results indicate that the inclusion of DPPC in the microspheres alters the microsphere surface chemistry, with the DPPC covering a large portion of the microsphere surface. The dominance of DPPC on the microsphere surface is highly beneficial in moderating the interaction occurring between the microspheres and phagocytic cells in the lung. Fluorescent confocal microscopy indicates that only 25% of cells internalized DPPC-coated particles, whereas 70% of those cells exposed to particles without the DPPC coating internalized particles after one hour of incubation.

Disposition of aerosolized liposomal amphotericin B

Amphotericin B (AmB) is an important drug for the treatment of fungal infection, but toxicity limits the lung tissue doses which may be achieved through intravenous administration. Although incorporation of AmB in liposomes reduces these effects and increases the therapeutic index for intravenous administration, targeted delivery to lung tissues via inhaled liposomal AmB aerosol may be a more effective approach. Aerosolization of liposomal amphotericin B targets the lungs, the organs first infested by many fungi. Development of optimal aerosolized liposomal AmB therapies requires a better understanding of the effect that liposome surface charge has on lung clearance kinetics. In this work we evaluated the clearance kinetics and organ distribution of inhaled liposomal AmB in male Balb/C mice. Mice were exposed via nose only to AmB-containing liposomal aerosols having positive, negative, or neutral surface charge characteristics. The formulations were aerosolized using a Collison nebulizer. Groups of animals were euthanized at predetermined times and the lungs and other organs were analyzed for AmB. AmB was not detected in serum and other organs such as kidneys, liver, and brain. The disposition of neutral and positive liposomal amphotericin B in lungs followed biexponential kinetics. The alpha and beta phase half-lives for positive liposomes were 1.3 and 15.1 days, respectively, and 2.3 and 22 days for neutral liposomes. AmB delivered via negative liposomes exhibited monoexponential clearance with a half-life of 4.5 days. These results suggest that toxic side effects in nontarget tissues are minimal and may indicate a potential for long term protection against fungal infections.