Protein conformational stability in the hydrofluoroalkane propellants tetrafluoroethane and heptafluoropropane analysed by Fourier transform Raman spectroscopy

In Vitro Evaluation of Colistin Conjugated with Chitosan-Capped Gold Nanoparticles as a Possible Formulation Applied in a Metered-Dose Inhaler

Inhaled colistin is used to treat pneumonia and respiratory infections through nebulization or dry powder inhalers. Nevertheless, the development of a metered-dose inhaler (MDI) for colistin, which could enhance patient convenience and treatment efficacy, has not yet been developed. Colistin is known for its ability to induce cellular toxicity. Gold nanoparticles (AuNPs) can potentially mitigate colistin toxicity. Therefore, this study aimed to evaluate the antimicrobial effectiveness of colistin conjugated with chitosan-capped gold nanoparticles (Col-CS-AuNPs) and their potential formulation for use with MDIs to deliver the aerosol directly to the deep lung. Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and elemental analysis were used to characterize the synthesized Col-CS-AuNPs. Drug release profiles fitted with the most suitable release kinetic model were evaluated. An MDI formulation containing 100 µg of colistin per puff was prepared. The aerosol properties used to determine the MDI performance included the fine particle fraction, mass median aerodynamic diameter, and geometric standard deviation, which were evaluated using the Andersen Cascade Impactor. The delivered dose uniformity was also determined. The antimicrobial efficacy of the Col-CS-AuNP formulation in the MDI was assessed. The chitosan-capped gold nanoparticles (CS-AuNPs) and Col-CS-AuNPs had particle sizes of 44.34 ± 1.02 and 174.50 ± 4.46 nm, respectively. CS-AuNPs effectively entrapped 76.4% of colistin. Col-CS-AuNPs exhibited an initial burst release of up to 60% colistin within the first 6 h. The release mechanism was accurately described by the Korsmeyer-Peppas model, with an R2 > 0.95. The aerosol properties of the Col-CS-AuNP formulation in the MDI revealed a high fine particle fraction of 61.08%, mass median aerodynamic diameter of 2.34 µm, and geometric standard deviation of 0.21, with a delivered dose uniformity within 75-125% of the labeled claim. The Col-CS-AuNP MDI formulation completely killed Escherichia coli at 5× and 10× minimum inhibitory concentrations after 6 and 12 h of incubation, respectively. The toxicity of CS-AuNP and Col-CS-AuNP MDI formulations in upper and lower respiratory tract cell lines was lower than that of free colistin. The stability of the Col-CS-AuNP MDI formulation was maintained for at least 3 months. The Col-CS-AuNP MDI formulation effectively eradicated bacteria over a 12-h period, showing promise for advancing lung infection treatments.

Lecithin Reverse Micelle System is Promising in Constructing Carrier Particles for Protein Drugs Encapsulated Pressurized Metered‐Dose Inhalers

Protein drugs contained within pressurized metered dose inhalers (pMDIs) show immense potential for fundamental research and industrial applications, owing to their high bioavailability, convenient administration, and cost‐effectiveness. To deliver protein drugs efficiently, researchers have reached a consensus on the use of carrier particles. However, the main obstacle impeding the commercial availability of pMDI carrier particles is their low stability. This instability is primarily attributed to particle aggregation caused by the Ostwald ripening phenomenon and chemical degradation by water sensitivity of protein drugs. This study proposes the utilization of lecithin, a carrier material possessing an amphiphilic structure, to overcome this bottleneck. By constructing lecithin‐based reverse micelle systems with protein drugs encapsulated within the high‐polarity microdomain, this work anticipates an improvement in the stability of carrier particles within pMDIs. Specifically, the formation of crystalline phases in the reverse micelle systems can control carrier particle size through crystalline self‐limiting effect, preventing particle aggregation. Additionally, the low‐polarity microdomain of the carrier serves as a hydrophobic barrier, shielding protein drugs from water and preventing chemical degradation. Consequently, this work believes that the lecithin‐based reverse micelle system holds significant potential in providing new theoretical insights and experimental support for the advancement of pMDIs containing protein drugs.

Formulation, Device, and Clinical Factors Influencing the Targeted Delivery of COVID-19 Vaccines to the Lungs

The COVID-19 pandemic has proven to be an unprecedented health crisis in the human history with more than 5 million deaths worldwide caused to the SARS-CoV-2 and its variants ( https://www.who.int/emergencies/diseases/novel-coronavirus-2019 ). The currently authorized lipid nanoparticle (LNP)-encapsulated mRNA vaccines have been shown to have more than 90% vaccine efficacy at preventing COVID-19 illness (Baden et al. New England J Med 384(5):403-416, 2021; Thomas et al., 2021). In addition to vaccines, other small molecules belonging to the class of anti-viral and anti-inflammatory compounds have also been prescribed to reduce the viral proliferation and the associated cytokine storm. These anti-viral and anti-inflammatory compounds have also been shown to be effective in reducing COVID-19 exacerbations especially in reducing the host inflammatory response to SARS-CoV-2. However, all of the currently FDA-authorized vaccines for COVID-19 are meant for intramuscular injection directly into the systemic circulation. Also, most of the small molecules investigated for their anti-COVID-19 efficacy have also been explored using the intravenous route with a few of them explored for the inhalation route (Ramakrishnan et al. Lancet Respir Med 9:763-772, 2021; Horby et al. N Engl J Med 384(8):693-704, 2021). The fact that the SARS-CoV-2 enters the human body mainly via the nasal and airway route resulting in the lungs being the primary organs of infection as characterized by acute respiratory distress syndrome (ARDS)-mediated cytokine storm in the alveolar region has made the inhalation route gain significant attention for the purposes of targeting both vaccines and small molecules to the lungs (Mitchell et al., J Aerosol Med Pulm Drug Deliv 33(4):235-8, 2020). While there have been many studies reporting the safety and efficacy of targeting various therapeutics to the lungs to treat COVID-19, there is still a need to match the choice of inhalation formulation and the delivery device platform itself with the patient-related factors like breathing pattern and respiratory rate as seen in a clinical setting. In that perspective, this review aims to describe the various formulation and patient-related clinical factors that can play an important role in the judicious choice of the inhalation delivery platforms or devices for the development of inhaled COVID-19 vaccines.

Developing inhaled protein therapeutics for lung diseases

Biologic therapeutics such as protein/polypeptide drugs are conventionally administered systemically via intravenous injection for the treatment of diseases including lung diseases, although this approach leads to low target site accumulation and the potential risk for systemic side effects. In comparison, topical delivery of protein drugs to the lung via inhalation is deemed to be a more effective approach for lung diseases, as proteins would directly reach the target in the lung while exhibiting poor diffusion into the systemic circulation, leading to higher lung drug retention and efficacy while minimising toxicity to other organs. This review examines the important considerations and challenges in designing an inhaled protein therapeutics for local lung delivery: the choice of inhalation device, structural changes affecting drug deposition in diseased lungs, clearance mechanisms affecting an inhaled protein drug’s lung accumulation, protein stability, and immunogenicity. Possible approaches to overcoming these issues will also be discussed.

Pulmonary Delivery of Biological Drugs

In the last decade, biological drugs have rapidly proliferated and have now become an important therapeutic modality. This is because of their high potency, high specificity and desirable safety profile. The majority of biological drugs are peptide- and protein-based therapeutics with poor oral bioavailability. They are normally administered by parenteral injection (with a very few exceptions). Pulmonary delivery is an attractive non-invasive alternative route of administration for local and systemic delivery of biologics with immense potential to treat various diseases, including diabetes, cystic fibrosis, respiratory viral infection and asthma, etc. The massive surface area and extensive vascularisation in the lungs enable rapid absorption and fast onset of action. Despite the benefits of pulmonary delivery, development of inhalable biological drug is a challenging task. There are various anatomical, physiological and immunological barriers that affect the therapeutic efficacy of inhaled formulations. This review assesses the characteristics of biological drugs and the barriers to pulmonary drug delivery. The main challenges in the formulation and inhalation devices are discussed, together with the possible strategies that can be applied to address these challenges. Current clinical developments in inhaled biological drugs for both local and systemic applications are also discussed to provide an insight for further research.

Grafting of terbium(iii) complexes onto layered rare-earth hydroxide nanosheets to fabricate novel optical fiber temperature sensors

Optical sensors of temperature possess the unique advantages of contactless measurement and large-scale imaging. Developments have been rapidly made in optical fiber sensors due to their high sensitivity, short response time, and electromagnetic immunity, and being easy to handle and light weight. Therefore, novel optical sensors of temperature based on optical fibers were fabricated to explore their application in special environments, such as poisonous, sparkless, currentless, and gelid ones. The present study is the first report of successful intercalation of neutral Y(iii) complexes in situ into the gallery of Y/Eu binary layered rare-earth hydroxides by hydrothermal processing without replacing the nitrate ions. The swollen layered rare-earth hydroxides were then exfoliated into ultrathin nanosheets ∼2 nm thick through dispersion in formamide. Grafting of Tb(iii) complexes onto the exfoliated nanosheets yielded novel temperature sensor films <100 nm thick, which exhibited color emissions from green to pink tunable through temperatures ranging from 77 to 360 K under ultraviolet excitation. Due to the highly sensitive and temperature-dependent emission, an optical fiber-based temperature sensor was fabricated by employing these novel allochroic films, which showed luminescence that could reversibly undergo repeated thermocycles. These optical fiber sensors have the potential to open up new fields in material functionalities via nanostructure manipulation and functionalized optical fiber engineering.

Determination of physical and chemical stability in pressurised metered dose inhalers: potential new techniques

INTRODUCTION

Pressurised metered dose inhalers (pMDIs) are subject to rigorous physical and chemical stability tests during formulation. Due to the time and cost associated with product development studies, there is a need for online techniques to fast screen new formulations in terms of physical and chemical (physico-chemical) stability. The problem with achieving this is that pMDIs are by their definition, pressurised, making the direct observation of physico-chemical properties in situ difficult.

AREAS COVERED

This review highlights the characterisation tools that can enhance the product development process for pMDIs. Techniques investigated include: laser diffraction, Raman spectroscopy, isothermal ampoule calorimetry, titration calorimetry and gas perfusion calorimetry. The operational principles behind each technique are discussed and complemented with examples from the literature.

EXPERT OPINION

Laser diffraction is well placed to analyse real-time physical stability as a function of particle size; however, its use is restricted to suspension pMDIs. Raman spectroscopy can be potentially used to attain both suspension and solution pMDI spectra in real time; however, the majority of experiments are ex-valve chemical composition mapping. Calorimetry is an effective technique in capturing both chemical and physical degradations of APIs in real time but requires redevelopment to withstand pressure for the purposes of pMDI screening.

A novel bottom-up process to produce nanoparticles containing protein and peptide for suspension in hydrofluoroalkane propellants

To overcome the disadvantages of microemulsion and nanoprecipitation methods to produce protein-containing nanoparticles, a novel bottom-up process was developed to produce nanoparticles containing the model protein lysozyme. The nanoparticles were generated by freeze-drying a solution of lysozyme, lecithin and lactose in tert-butyl alcohol (TBA)/water co-solvent system and washing off excess lecithin in lyophilizate by centrifugation. Formulation parameters such as lecithin concentration in organic phase, water content in TBA/water co-solvent, and lactose concentration in water were optimized so as to obtain desired nanoparticles with retention of the bioactivity of lysozyme. Based on the results, 24.0% (w/v) of lecithin, 37.5% (v/v) of water content, and 0.56% (w/v) of lactose concentration were selected to generate spherical nanoparticles with approximately 200 nm in mean size, 0.1 in polydispersity index (PI), and 99% retained bioactivity of lysozyme. These nanoparticles rinsed with ethanol containing dipalmitoylphosphatidylcholine (DPPC), Span 85 or oleic acid (3%, w/v) could readily be dispersed in HFA 134a to form a stable suspension with good redispersibility and 98% retained bioactivity of lysozyme. The study indicates there is a potential to produce pressed metered dose inhaler (pMDI) formulations containing therapeutic protein and peptide nanoparticles.

Novel pMDI formulations for pulmonary delivery of proteins

In this paper, we demonstrate that co-spray-drying a model protein with sodium carboxymethylcellulose (NaCMC) protects protein integrity during spray-drying, and that the resultant spray-dried powders can be successfully dispersed in hydrofluoroalkane (HFA) propellant to prepare pressurised metered dose (pMDI) formulations that exhibit high respirable fractions. The spray-dried powders were formulated as HFA-134a pMDI suspensions in the absence of any other excipients (e.g. surfactants) or co-solvents (e.g. ethanol). The in vitro aerosolisation profile of these systems was assessed using the twin stage impinger; fine particle fractions (FPF) > or = 50% of the recovered dose were obtained. Following storage for five months, the aerosolisation performance was reassessed; the NaCMC-free formulation demonstrated a significant decrease in FPF, whereas the performance of the NaCMC-modified formulations was statistically equivalent to their initial performance. Thus, formulation of pMDI suspensions using NaCMC-based spray-dried powders is a promising approach for the pulmonary delivery of proteins and peptides.

Raman characterization and chemical imaging of biocolloidal self-assemblies, drug delivery systems, and pulmonary inhalation aerosols: a review

This review presents an introduction to Raman scattering and describes the various Raman spectroscopy, Raman microscopy, and chemical imaging techniques that have demonstrated utility in biocolloidal self-assemblies, pharmaceutical drug delivery systems, and pulmonary research applications. Recent Raman applications to pharmaceutical aerosols in the context of pulmonary inhalation aerosol delivery are discussed. The "molecular fingerprint" insight that Raman applications provide includes molecular structure, drug-carrier/excipient interactions, intramolecular and intermolecular bonding, surface structure, surface and interfacial interactions, and the functional groups involved therein. The molecular, surface, and interfacial properties that Raman characterization can provide are particularly important in respirable pharmaceutical powders, as these particles possess a higher surface-area-to-volume ratio; hence, understanding the nature of these solid surfaces can enable their manipulation and tailoring for functionality at the nanometer level for targeted pulmonary delivery and deposition. Moreover, Raman mapping of aerosols at the micro- and nanometer level of resolution is achievable with new, sophisticated, commercially available Raman microspectroscopy techniques. This noninvasive, highly versatile analytical and imaging technique exhibits vast potential for in vitro and in vivo molecular investigations of pulmonary aerosol delivery, lung deposition, and pulmonary cellular drug uptake and disposition in unfixed living pulmonary cells.

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.

Stabilisation of deoxyribonuclease in hydrofluoroalkanes using miscible vinyl polymers

A mix of biocompatible macromolecules (poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP)) has been shown previously to enhance the physical stability of non-aqueous pharmaceutical suspensions. The aim of this work was to assess the feasibility of employing such a combination to facilitate the formulation of deoxyribonuclease I (DNase I) in a metered dose inhaler (MDI) using hydrofluoroalkane (HFA) propellants. DNase I was combined with the selected excipients and formed into an inhalable microparticle by spray-drying. When spray-dried alone DNase I lost almost 40% of its original biological activity, but stabilising DNase I with trehalose and PVA (DTPVA) retained 85% biological activity and trehalose, PVA and PVP (DTPVAPVP) retained 100%. Suspending the DTPVAPVP microparticles within a HFA pMDI for 24 weeks led to no further reduction in the biological activity of DNase I and the formulation delivered almost 60% of the dose expelled to the second stage of a twin-stage impinger. The solubility of PVP in HFA propellants suggests that the enhanced physical stability observed with PVA and PVP may partially be as a result of steric stabilisation. However, the large zeta potential associated with the suspensions suggested that charge stabilisation may also influence the pMDI physical stability.

Prospects of formulating proteins/peptides as aerosols for pulmonary drug delivery

Formulation of proteins/peptides for therapeutic uses has often posed some challenges to drug formulators. The main problem is the relatively weak forces involved in the native conformation of these proteins and so making them quite labile. Furthermore, their susceptibility to proteolytic enzymes in the gut makes oral administration quite challenging. While various routes like, ocular, transdermal, nasal and buccal have been tried, none of these routes has proved to be a potential alternative to the invasive injection. However, various studies have been performed on the formulation of these proteins as aerosols for pulmonary delivery and promising results have been obtained. This article looks at the prospects of inhaled proteins as a delivery route for systemic activity.

The effects of polyvinyl alcohol on the in vitro stability and delivery of spray-dried protein particles from surfactant-free HFA 134a-based pressurised metered dose inhalers

The objective of the present study was to investigate the physical stability of spray-dried proteins within surfactant-free hydrofluoroalkane (HFA) pressurised metered dose inhalers (pMDIs) during prolonged storage. Two model proteins (lysozyme and catalase) were spray-dried and stabilised in the presence of excipients, and subsequently suspended within HFA 134a. The pMDIs were stored valve-up for 6 months at room temperature (ca. 25 degrees C). Activities of the proteins were determined using biological assays and the fine particle fraction of the pMDIs was measured using a twin-stage impinger. The biological activities of catalase and lysozyme were found to be preserved in the presence of sugars and/or 80% hydrolysed polyvinyl alcohol (PVA) during spray drying. In addition, suspending the stabilised proteins within HFA for up to 6 months had little effect on their activity. The aerosolisation performance of lysozyme or catalase formulations containing either sucrose or trehalose as stabilisers appeared to deteriorate as a function of storage time. However, those formulations containing PVA were found to generate the greatest fine particle fraction, which in some cases was up to 50%, and to possess excellent physical stability during storage. The results indicated that the presence of PVA in the spray-dried stabilised protein particles could enhance the physical stability of particles, when suspended in the surfactant-free HFA MDI formulations, without affecting the protein stability upon prolonged storage.

Stability of crystallised and spray-dried lysozyme

Moisture and temperature promote protein degradation. The stabilities of commercial, crystallised and spray-dried lysozyme, a model protein, were assessed under these stresses to explore whether a crystalline protein had better storage stability than a conventionally produced one. Samples were maintained at different relative humidities (RH) and temperatures for 20 weeks and stabilities estimated in solid and aqueous states. Differential scanning calorimetry (DSC) and thermogravimetry (TGA) characterised solid samples. Fourier transform Raman (FT-Raman) spectroscopy analysed solid material and aqueous solutions. High sensitivity differential scanning calorimetry (HSDSC) and enzymatic assays were used to monitor solutions. DSC and HSDSC data revealed that crystals maintained thermal stability at high RH; spray drying appreciably changed melting characteristics. These results correlated with enzymatic assays that demonstrated good activity retention for crystals but less so for spray-dried material (e.g. 95 and 87% relative to fresh samples after 20 weeks at 40 degrees C/75% RH). FT-Raman analysis showed that crystallised lysozyme better-maintained protein conformational integrity compared to spray-dried samples in accelerated stability studies. Based on TGA data, spray-dried protein absorbed water on storage under humid conditions, which induced instability. Thus, crystallisation enhanced storage stability of lysozyme with negligible loss of activity.

Integrity of crystalline lysozyme exceeds that of a spray-dried form

The development of proteins as therapeutic agents is challenging partly due to their inherent instabilities. Consequently, crystallisation and spray drying techniques were assessed to determine their effects on protein integrity using lysozyme as a model protein. Unprocessed, crystallised and spray-dried lysozyme were characterised by: thermal analysis using hot stage microscopy (HSM), differential scanning calorimetry (DSC), high sensitivity differential scanning calorimetry (HSDSC) and thermogravimetry (TGA); and spectroscopic analysis employing Fourier transform Raman (FT-Raman). Moisture contents were determined by TGA and Karl Fisher titration (KFT). Enzymatic assay measured biological activity. HSM showed no changes in crystals until complete melting. TGA and KFT indicated that spray-dried lysozyme contained a lower moisture content than crystals, hence the higher apparent thermal stability was shown by DSC. HSDSC revealed that crystallisation and spray drying did not affect the denaturation temperature of lysozyme in solution when compared with unprocessed material. However, in the solid state, FT-Raman spectra showed perturbation of the conformational structure of spray-dried sample, whereas crystal conformation remained intact. Enzymatic assay revealed increased activity retention of crystals compared with spray-dried powder. Hence, crystals maintained the conformational integrity and activity of lysozyme in solution.