Sustained release drug delivery to the lungs: an option for the future

OR2AT4 and OR1A2 counterregulate molecular pathophysiological processes of steroid-resistant inflammatory lung diseases in human alveolar macrophages

BACKGROUND

Therapeutic options for steroid-resistant non-type 2 inflammation in obstructive lung diseases are lacking. Alveolar macrophages are central in the progression of these diseases by releasing proinflammatory cytokines, making them promising targets for new therapeutic approaches. Extra nasal expressed olfactory receptors (ORs) mediate various cellular processes, but clinical data are lacking. This work investigates whether ORs in human primary alveolar macrophages could impact pathophysiological processes and could be considered as therapeutic targets.

METHODS

Human primary alveolar macrophages were isolated from bronchoalveolar lavages of 50 patients with pulmonary diseases. The expression of ORs was validated using RT-PCR, immunocytochemical staining, and Western blot. Changes in intracellular calcium levels were analyzed in real-time by calcium imaging. A luminescent assay was used to measure the cAMP concentration after OR stimulation. Cytokine secretion was measured in cell supernatants 24 h after stimulation by ELISA. Phagocytic ability was measured by the uptake of fluorescent-labeled beads by flow cytometry.

RESULTS

We demonstrated the expression of functional OR2AT4 and OR1A2 on mRNA and protein levels. Both ORs were primarily located in the plasma membrane. Stimulation with Sandalore, the ligand of OR2AT4, and Citronellal, the ligand of OR1A2, triggered a transient increase of intracellular calcium and cAMP. In the case of Sandalore, this calcium increase was based on a cAMP-dependent signaling pathway. Stimulation of alveolar macrophages with Sandalore and Citronellal reduced phagocytic capacity and release of proinflammatory cytokines.

CONCLUSION

These are the first indications for utilizing olfactory receptors as therapeutic target molecules in treating steroid-resistant lung diseases with non-type 2 inflammation.

Pharmaceutical strategies to extend pulmonary exposure of inhaled medicines

Pulmonary administration route has been extensively exploited for the treatment of local lung diseases such as asthma, chronic obstructive pulmonary diseases and respiratory infections, and systemic diseases such as diabetes. Most inhaled medicines could be cleared rapidly from the lungs and their therapeutic effects are transit. The inhaled medicines with extended pulmonary exposure may not only improve the patient compliance by reducing the frequency of drug administration, but also enhance the clinical benefits to the patients with improved therapeutic outcomes. This article systematically reviews the physical and chemical strategies to extend the pulmonary exposure of the inhaled medicines. It starts with an introduction of various physiological and pathophysiological barriers for designing inhaled medicines with extended lung exposure, which is followed by recent advances in various strategies to overcome these barriers. Finally, the applications of the inhaled medicines with extended lung exposure for the treatment of various diseases and the safety concerns associated to various strategies to extend the pulmonary exposure of the inhaled medicines are summarized.

Recent applications and strategies in nanotechnology for lung diseases

Lung diseases, including COVID-19 and lung cancers, is a huge threat to human health. However, for the treatment and diagnosis of various lung diseases, such as pneumonia, asthma, cancer, and pulmonary tuberculosis, are becoming increasingly challenging. Currently, several types of treatments and/or diagnostic methods are used to treat lung diseases; however, the occurrence of adverse reactions to chemotherapy, drug-resistant bacteria, side effects that can be significantly toxic, and poor drug delivery necessitates the development of more promising treatments. Nanotechnology, as an emerging technology, has been extensively studied in medicine. Several studies have shown that nano-delivery systems can significantly enhance the targeting of drug delivery. When compared to traditional delivery methods, several nanoparticle delivery strategies are used to improve the detection methods and drug treatment efficacy. Transporting nanoparticles to the lungs, loading appropriate therapeutic drugs, and the incorporation of intelligent functions to overcome various lung barriers have broad prospects as they can aid in locating target tissues and can enhance the therapeutic effect while minimizing systemic side effects. In addition, as a new and highly contagious respiratory infection disease, COVID-19 is spreading worldwide. However, there is no specific drug for COVID-19. Clinical trials are being conducted in several countries to develop antiviral drugs or vaccines. In recent years, nanotechnology has provided a feasible platform for improving the diagnosis and treatment of diseases, nanotechnology-based strategies may have broad prospects in the diagnosis and treatment of COVID-19. This article reviews the latest developments in nanotechnology drug delivery strategies in the lungs in recent years and studies the clinical application value of nanomedicine in the drug delivery strategy pertaining to the lung.

Measurement of the Raman spectra and hygroscopicity of four pharmaceutical aerosols as they travel from pressurised metered dose inhalers (pMDI) to a model lung

Particle inhalation is an effective and rapid delivery method for a variety of pharmaceuticals, particularly bronchodilation drugs used for treating asthma and COPD. Conditions of relative humidity and temperature inside the lungs are generally very different from the outside ambient air, with the lung typically being warmer and more humid. Changes in humidity, from inhaler to lung, can cause hygroscopic phase transitions and particle growth. Increasing particle size and mass can negatively affect particle deposition within the lung leading to inefficient treatment, while deliquescence prior to impaction is liable to accelerate drug uptake. To better understand the hygroscopic properties of four pharmaceutical aerosol particles; pharmaceutical particles from four commercially available pressurised metered dose inhalers (pMDIs) were stably captured in an optical trap, and their composition was examined online via Raman spectroscopy. Micron-sized particles of salbutamol sulfate, salmeterol xinafoate, fluticasone propionate and ciclesonide were levitated and examined over a range of relative humidity values inside a chamber designed to mimic conditions within the respiratory tract. The effect of temperature upon hygroscopicity was also investigated for salbutamol sulfate particles. Salbutamol sulfate was found to have significant hygroscopicity, salmeterol xinafoate showed some hygroscopic interactions, whilst fluticasone propionate and ciclesonide revealed no observable hygroscopicity. Thermodynamic and structural modelling is used to explain the observed experimental results.

Preparation of large porous deslorelin-PLGA microparticles with reduced residual solvent and cellular uptake using a supercritical carbon dioxide process

PURPOSE

The purpose of this study was to prepare large-porous peptide-encapsulating polymeric particles with low residual solvent that retain deslorelin integrity, sustain drug release, and exhibit reduced epithelial and macrophage uptake. We hypothesized that supercritical carbon dioxide (SC CO2) pressure-quench treatment of microparticles prepared using conventional approach expands these particles and extracts the residual organic solvent.

METHODS

Initial studies with crystalline L-lactide (L-PLA) and amorphous copolymers of lactide-co-glycolide (PLGA) 50:50, 65:35, and 75:25 indicated that PLGA 50:50 was the most amenable to morphological changes upon SC CO2 treatment. Therefore, we prepared deslorelin-PLGA (50:50) microparticles using the conventional emulsion-solvent evaporation method, and in a second step equilibrated with SC CO2 at various temperatures (33-37 degrees C) and pressures (1200-2000 psi) for discrete intervals followed by rapid isothermal depressurization. The particles were then characterized for morphology, polymer thermal properties, particle size, porosity, bulk density, and residual solvent content. Also, deslorelin integrity, conformation, release, and cellular uptake before and after SC CO2 treatment was determined.

RESULTS

Upon SC CO2 treatment (1200 psi, 33 degrees C for 30 min), the mean particle size of the deslorelin PLGA microparticles increased from 2.2 to 13.8 microm, the mean porosity increased from 39 to 92.38% the mean pore diameter increased from 90 to 190 nm, the mean bulk density reduced from 0.7 to 0.082 g/cc, mass spectrometry indicated structural integrity of released deslorelin, the circular dichroism spectrum indicated stabilization of beta-turn conformation, and the scanning electron microscopy confirmed increased particle size and pore formation. The deslorelin release was sustained during the 7-day study period. Also, the peak Tg of PLGA decreased from 51 to 45 degrees C, and the residual solvent content was reduced from 4500 ppm to below detection limit (< 25 ppm). The accumulation of drug from SC CO2 treated particles in cell layers of Calu-3, A549, and rat alveolar macrophages was reduced by 87, 91 and 50%, respectively, compared to untreated particles.

CONCLUSION

An SCF-derived process could be successfully applied to prepare large porous deslorelin-PLGA particles with reduced residual solvent content, which retained deslorelin integrity, sustained deslorelin release, and reduced cellular uptake.

A novel approach for lung delivery of rifampicin-loaded liposomes in dry powder form for the treatment of tuberculosis

Background:

Lung administration of antibiotics by nebulization is promising for improved treatment efficiency for pulmonary infections, as it increases drug concentration at sites of infection while minimizing systemic side effects. For poorly soluble molecules like rifampicin, lipid particulate system may improve lung delivery.

Materials and Methods:

We investigated rifampicin-loaded freeze-dried liposomes. Various formulations were prepared with different drug lipid ratios and one formulation was optimized. Optimized colloidal liposome formulation was freeze-dried and subsequently subjected for various evaluation and characterization parameters such as in-vitro dissolution, in-vitro antitubercular activity, aerodynamic characters, surface morphology, and thermal behavior. The optimized formulation of rifampicin-loaded freeze-dried liposome and free rifampicin was subjected for the in-vivo drug disposition study in Wister rat model by intra-tracheal instillation in comparison with an oral route of administration.

Results:

The results of pharmacokinetic study for both free drug and the formulation suggested that liposomes released the drug in a controlled manner for a longer period of time. The enhanced efficiency of drug incorporated into liposomes suggested that the delivery of encapsulated drugs to macrophages was more rapid than that of free drug.

Conclusion:

Therefore, the pharmacokinetic and drug disposition studies provided a sound basis for predicting the successful treatment for tuberculosis.

Newer glucocorticosteroids and corticosteroid resistance reversal in asthma

Inflammation is the hallmark of asthma. Glucocorticosteroids inhibit this inflammation and are the mainstay of therapy in asthma, however, they suffer from their own drawbacks. They possess high potency but their continued use has a negative influence on health. Hence, quest for a steroid with good potency but without the undesirable effects is ongoing. Besides, steroid resistance is a problem in a substantial proportion of severe asthmatics. Deeper insight into the molecular mechanism of this refractoriness has led to the successful trial of certain drugs to overcome this problem. This review attempts to discuss some of the patents related to improved glucocorticoids and those agents that have the potential to restore steroid sensitivity in severe asthmatics.

Formulation of inhalable lipid-based salbutamol sulfate microparticles by spray drying technique

Background

The aim of this work was to develop dry powder inhaler (DPI) formulations of salbutamol sulfate (SS) by the aid of solid lipid microparticles (SLmPs), composed of biocompatible phospholipids or cholesterol.

Methods

The SLmPs were prepared by using two different solvent systems (ethanol and water-ethanol) and lipid carriers (dipalmitoylphosphatidylcholine (DPPC) and cholesterol) with/without L-leucine in the spray drying process. The spray-dried microparticles were physically-mixed with coarse lactose monohydrate in order to make our final DPI formulations and were investigated in terms of physical characteristics as well as in vitro drug release profile and aerosolization behavior.

Results

We observed significant differences in the sizes, morphologies, and in vitro pulmonary depositions between the formulations. In particular, the SS-containing SLmPs prepared with water-ethanol (30:70 v/v) solution of DPPC and L-leucine which had then been blended with coarse lactose (1:9 w/w) exhibited the highest emitted dose (87.9%) and fine particle fraction (42.7%) among the formulations. In vitro drug release study indicated that despite of having a significant initial burst release for both cholesterol and DPPC-based microparticles, the remained drug released more slowly than the pure drug.

Conclusion

This study demonstrated the potential of using lipid carriers as well as L-leucine in DPI formulations of SS to improve its aerosolization behavior and retard the release profile of the drug.

Preparation of sustained release rifampicin microparticles for inhalation

Objectives

The aim of this research was to develop a novel carrier-free dry powder formulation of rifampicin for inhalation with controlled-release properties.

Methods

Rifampicin dihydrate (RFDH) microcrystals were prepared by a polymorphic transformation of rifampicin. The prepared RFDH microcrystals were coated with poly (dl-lactide-co-glycolide) or poly (dl-lactide), using a spray-dryer equipped with two different types of three-fluid (3F) spray nozzles. The physicochemical and aerodynamic properties of the coated RFDH microcrystals were compared with those of conventional matrix microparticles.

Key findings

The coated RFDH powder, encapsulating 50% of rifampicin, was successfully prepared by simple in-situ coating methods using two different types of 3F nozzles and had mass median aerodynamic diameter values of 3.5–4.5 µm. The thin flaky morphology of RFDH powders, providing good aerosolization properties, was maintained after coating. The coated RFDH formulations showed relatively low initial rifampicin release, compared with the uncoated RFDH crystals, followed by slow rifampicin release (about 70%) over 8 h in phosphate-buffered saline media (pH 7.4). Significant chemical degradations were not observed from the crystalline-structured RFDH formulations, while the amorphous-structured matrix formulations showed chemical degradation in six months.

Conclusions

These polymer coated RFDH formulations may be a valuable alternative in the treatment of tuberculosis since the carrier-free formulation offers the benefit of delivering a maximum-potency formulation of the antibiotic directly to the site of infection, and long drug residence times may be achieved by the controlled release of the drug.

Micro- and nanocarrier-mediated lung targeting

IMPORTANCE OF THE FIELD

Drug delivery to lungs appears to be an attractive proposition on account of the large surface area of the alveolar region; it provides tremendous opportunities to improve drug therapies both systemically and locally using new drug delivery systems. Administration of drugs directly to the lungs is the most appropriate route in the treatment of asthma and other pulmonary diseases such as tuberculosis, chronic obstructive pulmonary disease and lung cancer.

AREAS COVERED IN THIS REVIEW

This review focuses on the utilization of nano- and microcarriers such as microspheres, nanoparticles, liposomes, niosomes and dendrimers for targeted delivery of bioactive molecules to lungs.

WHAT THE READER WILL GAIN

This review sheds light on the current status of nano- and microcarrier-mediated lung targeting of bioactive compounds.

TAKE HOME MESSAGE

The literature review shows that carriers could supplement sustained drug delivery to the lungs, extended duration of action, reduced therapeutic dose, improved patient compliance, and reduced adverse effects of highly toxic drugs. There is still a need to identify more specific receptors that are present exclusively in the lungs. The identification of such receptors may also facilitate drug targeting to further specific parts of the lungs, such as bronchioles and alveoli.

Chitosan-based spray-dried respirable powders for sustained delivery of terbutaline sulfate

In this study, we describe the preparation of highly dispersible dry powders for pulmonary drug delivery that display sustained drug release characteristics. Powders were prepared by spray-drying 30% v/v aqueous ethanol formulations containing terbutaline sulfate as a model drug, chitosan as a drug release modifier and leucine as an aerosolisation enhancer. The influence of chitosan molecular weight on the drug release profile was investigated by using low, medium and high molecular weight chitosan or combinations thereof. Following spray-drying, resultant powders were characterised using scanning electron microscopy, laser diffraction, tapped density analysis, differential scanning calorimetry and thermogravitational analysis. The in vitro aerosolisation performance and drug release profile were investigated using Multi-Stage Liquid Impinger analysis and modified USP II dissolution apparatus, respectively. The powders generated were of a suitable aerodynamic size for inhalation, had low moisture content and were amorphous in nature. The powders were highly dispersible, with emitted doses of over 90% and fine particle fractions of up to 82% of the total loaded dose, and mass median aerodynamic diameters of less than 2.5microm. A sustained drug release profile was observed during dissolution testing; increasing the molecular weight of the chitosan in the formulation increased the duration of drug release.

Pharmaceutical particle engineering via spray drying

This review covers recent developments in the area of particle engineering via spray drying. The last decade has seen a shift from empirical formulation efforts to an engineering approach based on a better understanding of particle formation in the spray drying process. Microparticles with nanoscale substructures can now be designed and their functionality has contributed significantly to stability and efficacy of the particulate dosage form. The review provides concepts and a theoretical framework for particle design calculations. It reviews experimental research into parameters that influence particle formation. A classification based on dimensionless numbers is presented that can be used to estimate how excipient properties in combination with process parameters influence the morphology of the engineered particles. A wide range of pharmaceutical application examples—low density particles, composite particles, microencapsulation, and glass stabilization—is discussed, with specific emphasis on the underlying particle formation mechanisms and design concepts.

Design of fine particles for pulmonary drug delivery

Particle design for inhalation is characterized by advances in particle processing methods and the utilization of new excipients. Processing methods such as spray drying allow control over critical particle design features, such as particle size and distribution, surface energy, surface rugosity, particle density, surface area, porosity and microviscosity. Control of these features has enabled new classes of therapeutics to be delivered by inhalation. These include therapeutics that have a narrow therapeutic index, require a high delivered dose, and/or elicit their action systemically. Engineered particles are also being utilized for immune modulation, with exciting advances being made in the delivery of antibodies and inhaled vaccines. Continued advances are expected to result in 'smart' therapeutics capable of active targeting and intracellular trafficking.

Effervescent dry powder for respiratory drug delivery

The objective of this work was to develop a new type of respiratory drug delivery carrier particle that incorporates an active release mechanism. Spray drying was used to manufacture inhalable powders containing polybutylcyanoacrylate nanoparticles and ciprofloxacin as model substances for pulmonary delivery. The carrier particles incorporated effervescent technology, thereby adding an active release mechanism to their pulmonary route of administration. Effervescent activity of the carrier particles was observed when the carrier particles were exposed to humidity. Gas bubbles caused by the effervescent reaction were visualized by confocal laser scanning microscopy. The images showed that nanoparticles were distributed throughout the gas bubble. For the effervescent formulation the average mass median aerodynamic diameter (MMAD) was 2.17 microm+/-0.42, fine particle fraction (FPF(<=5.6 microm)) was 46.47%+/-15 and the GSD was 2.00+/-0.06. The results also showed that the effervescent carrier particles released 56+/-8% ciprofloxacin into solution compared with 32+/-3% when lactose carrier particles were used. The mean nanoparticle size did not significantly change upon release when the nanoparticles were incorporated into an effervescent formulation. However, the mean size significantly increased upon release when only lactose was used as carrier particle matrix. In conclusion, effervescent carrier particles can be synthesized with an adequate particle size for deep lung deposition. This opens the door for future research to explore this technology for delivery of a large range of substances to the lungs with possible improved release compared to conventional carrier particles.

Solid lipid microparticles as a sustained release system for pulmonary drug delivery

The controlled release of drugs for pulmonary delivery is a research field which has been so far rather unexploited but is currently becoming increasingly attractive. The introduction part of this research article first details the potential advantages of solid lipid microparticles (SLMs) as drug carrier compared to liposomes and polymeric microspheres. The aim of this work is to use SLMs to impart a sustained release profile to a model drug, salbutamol acetonide (SA). SA was synthesized from salbutamol in order to increase the lipophilicity of this molecule and thereby to increase its incorporation efficiency into SLMs. SA-loaded SLMs were then produced by a hot emulsion technique followed by high-shear homogenisation and the manufacturing parameters were optimized using the experimental design methodology in order to reach a suitable particle size for pulmonary administration. Scanning electron micrographs showed that SLMs are spherical, have a smooth surface and that SA crystallizes outside of the particles when the drug loading is higher than 20%. This was confirmed by X-ray diffraction. SA in vitro release study from SLMs showed that the release rate increased with SA loading but remained in every case lower than the dissolution rate of pure SA.

Human respiratory epithelial cell culture for drug delivery applications

Recent developments in delivering drugs to the lung are driving the need for in vitro methods to evaluate the fate of inhaled medicines. Constraints on experimentation using animals have promoted the use of human respiratory epithelial cell cultures to model the absorption barrier of the lung; with two airway cell lines, 16HBE14o- and Calu-3, and primary cultured human alveolar type I-like cells (hAEpC) gaining prominence. These in vitro models develop permeability properties which are comparable to those reported for native lung epithelia. This is in contrast to the high permeability of the A549 human alveolar cell line, which is unsuitable for use in drug permeability experiments. Tabulation of apparent permeability coefficients (Papp) of compounds measured in 'absorptive' and 'secretory' directions reveals that fewer compounds (< 15) have been evaluated in 16HBE14o- cells and hAEpC compared to Calu-3 cells (> 50). Vectorial (asymmetric) transport of compounds is reported in the three cell types with P-glycoprotein, the most studied transport mechanism, being reported in all. Progress is being made towards in vitro-in vivo-correlation for pulmonary absorption and in the use of cultured respiratory cells to evaluate drug metabolism, toxicity and targeting strategies. In summary, methods for the culture of human respiratory epithelial cell layers have been established and data regarding their permeability characteristics and suitability to model the lung is becoming available. Discerning the circumstances under which the use of human respiratory cell models will be essential, or offers advantages over non-organ, non-species specific cell models, is the next challenge.

Novel sustained release microspheres for pulmonary drug delivery

A novel process for generating sustained release (SR) particles for pulmonary drug delivery is described. High purity nanoparticles of a hydrophilic, ionised drug are entrapped within hydrophobic microspheres using a spray-drying approach. Sustained release of the model drug, terbutaline sulphate (TS), from the microspheres was found to be proportional to drug loading and phospholipid content. Microspheres with a 33% drug loading exhibited sustained release of 32.7% over 180 min in phosphate buffer. Release was not significantly different in simulated lung fluids. No significant burst release was observed which suggested that nanoparticles were coated effectively during spray-drying. The absence of nanoparticles at the microsphere surface was confirmed with confocal microscopy. The sustained release microspheres were formulated as a carrier-free dry powder for inhalation, and exhibited a favourable Fine Particle Fraction (FPF) of 46.5+/-1.8% and Mass Median Aerodynamic Diameter (MMAD) of 3.93+/-0.12 microm.

Droplet and particle size relationship and shell thickness of inhalable lactose particles during spray drying

To find means of controlling the size and density of particles intended for inhalation the relationship between droplet and particle size during spray drying was investigated. Lactose solutions were atomized with a two-fluid nozzle and dried in a laboratory spray drier. The effects of nozzle orifice diameter, atomization airflow and feed concentration on droplet and particle size were examined. Mass median diameter of both droplets and particles were analyzed with laser diffraction. In addition, scanning electron microscopy and transmission electron microscopy were used for studies of particle shape and morphology. It was demonstrated that nozzle orifice diameter and airflow, but not feed concentration controlled the droplet size during atomization. Increasing droplet size increased particle size but the effect was also influenced by feed concentration. Particles from solutions of a low concentration (1% w/w) were smaller than those from higher concentrations (5-20% w/w). This may be partly explained by lower yields at higher feed concentrations, but may also be related to differences in drying rate. Spray-dried lactose solutions formed hollow particles, and it was suggested that the shell thickness of the particles increased with increasing feed concentration.