Ethoxylated copolymersurfactants for the HFA134a- interface: interfacial activity, aggregate microstructure and biomolecule uptake

Enhancing Stability of Exenatide-Containing Pressurized Metered-Dose Inhaler Via Reverse Microemulsion System

The dispersibility and stability issues of peptide drugs during preparation and storage hinder the widespread adoption of pressurized metered-dose inhaler (pMDI). This study aimed to develop a reverse microemulsion (RM) of exenatide (EXE) pMDI through a liquid-based bottom-up method, thus to overcome the stability issue of peptide drugs encountered in traditional top-down methods, such as milling down and high-pressure homogenization. In this study, Pluronic® L64 (L64) was chosen as a surfactant to prepare the EXE-RM pMDI formulations with the assistance of ethanol. The results showed RM possessed a particle size of 123.80 ± 2.91 nm with 0.121 ± 0.024 PdI and a satisfied fine-particle fraction of 41.30 ± 3.73% measured by a next-generation impactor. In addition, the dispersion stability of RM pMDI was maintained after storage at 4 °C for 50 days. The secondary structure of EXE was maintained during the preparation process. Moreover, the results indicated that L64 was compatible with cells and could improve the penetration of EXE through cell monolayers. Through the liquid-based bottom-up method, EXE-RM pMDI was successfully prepared and exhibited favorable stability and aerodynamic performance. This study offers a preparation strategy to enhance the stability of peptides in pMDIs.

Reverse aqueous microemulsions in hydrofluoroalkane propellants and their aerosol characteristics

In this work we describe the structure and environment of reverse aqueous microemulsions formed in 1,1,1,2-tetrafluoroethane (HFA134a) propellant in the presence of a non-ionic ethoxylated copolymer, and the aerosol characteristics of the corresponding pressurized metered dose inhaler (pMDI) formulations. The activity of selected polypropylene oxide-polyethylene oxide-polypropylene oxide (PO(m)EO(n)PO(m)) amphiphiles at the HFA134a-water interface was studied using in situ high-pressure tensiometry, and those results were used as a guide in the selection of the most appropriate candidate surfactant for the formation of microemulsions in the compressed HFA134a. The environment and structure of the aggregates formed with the selected surfactant candidate, PO(22)EO(14)PO(22), was probed via UV-vis spectroscopy (molecular probe), and small angle neutron scattering (SANS), respectively. High water loading capacity in the core of the nanoaggregates was achieved in the presence of ethanol. At a water-to-surfactant molar ratio of 21 and 10% ethanol, cylindrical aggregates with a radius of 18Å, and length of 254Å were confirmed with SANS. Anderson Cascade Impactor (ACI) results reveal that the concentration of the excipients (C(exp), including surfactant, water and ethanol) has a strong effect on the aerosol characteristics of the formulations, including the respirable fraction, and the mass mean aerodynamic diameter (MMAD), and that the trend in MMAD can be predicted as a function of the C(exp) following similar correlations to those proposed to common non-volatile excipients, indicating that the nanodroplets of water dispersed in the propellant behave similarly to molecularly solubilized compounds. Cytotoxicity studies of PO(22)EO(14)PO(22) were performed in A549 cells, an alveolar type II epithelial cell line, and indicate that, within the concentration range of interest, the surfactant in question decreases cell viability only lightly. The relevance of this work stems from the fact that aqueous-based HFA-pMDIs are expected to be versatile formulations, with the ability to carry a range of medically relevant hydrophilic compounds within the nanocontainers, including high potency drugs, drug combinations and biomacromolecules.

Nanoparticle-stabilized colloids in compressible hydrofluoroalkanes

In this work, we show that nanoparticles (NPs) dispersed in compressible hydrofluoroalkanes (HFAs) at small volume fractions are capable of stabilizing micrometer-sized particle colloids, which otherwise flocculate due to strong van der Waals forces. Water-soluble, biodegradable NPs with a chitosan (CS) core, grafted with highly HFA-philic moieties, can be readily dispersed in the low dielectric HFAs and are capable of imparting stability to a wide range of therapeutic particles having different chemistries (polar or hydrophobic; small and large molecular weight, including peptides and proteins) and morphologies (micronized crystals or amorphous). These NP systems thus serve as a broadly applicable platform for the noninvasive delivery of therapeutics to and through the lungs using propellant-based, portable inhalers, and are also of potential relevance in other industries where HFAs are employed as solvents or propellants. This concept may also be applicable to other compressible solvents.

Swellable hydrogel particles for controlled release pulmonary administration using propellant-driven metered dose inhalers

BACKGROUND

Swellable hydrogel microparticle-based pressurized metered dose inhaler (pMDI) formulations allow delivery of small respirable sized particles (1-5 microns), which swell upon the deposition in the deep lung and therefore can elude alveolar macrophage uptake via their larger geometric sizes. In addition, optimized surface chemistry may allow for sustained release of drug for multiple days.

METHODS

Drug-loaded PLGA nanoparticles encapsulated in PEG/chitosan (Cs) graft copolymer-based hydrogel microparticles were synthesized and characterized. Physical stability of dispersions within Hydrofluoroalkane propellant systems was assessed. The formulations were evaluated for aerosolization performance using a Next Generation Impactor.

RESULTS

Low density PEG/chitosan (Cs) graft copolymer-based hydrogel microparticles containing drug-loaded PLGA nanoparticles has an average diameter of 1-2 μm. These dispersions showed good compatibility with HFA227ea. Suspension stability was found to vary with the concentration of hydrogel particles. It was typically between 1 to 5 min and was found to be easily redispersible. Aerosolization studies showed fine particle fraction as high as 65% could be achieved.

CONCLUSIONS

These swellable hydrogel-based microparticle pMDI formulations could be used as potential delivery vehicles for nanoparticle therapeutics.

Reverse aqueous emulsions and microemulsions in HFA227 propellant stabilized by non-ionic ethoxylated amphiphiles

In this work we use in situ high-pressure tensiometry to screen non-ionic ethoxylated surfactants at the 1,1,1,2,3,3,3-heptafluoropropane (HFA227) propellant|Water (HFA227|W) interface. The EO(n)PO( approximately )(30)EO(n) series, where EO stands for ethylene oxide and PO for propylene oxide, and n the number of repeat EO units, was selected for this study based on the favorable interactions reported between HFA propellants and the PO moiety. The surfactants used in FDA-approved pressurized metered-dose inhaler formulations were also investigated. Tension measurements provide not only information on the relative activity of the different surfactants in the series, but they also serve as a guide for selecting an appropriate candidate for the formation of reverse aggregates based on the surfactant natural curvature. Moreover, the effect of ethanol and the chemistry of the surfactant tail group on the surfactant activity were also investigated. Surfactants with hydrogenated tails are not capable of forming stable water-in-HFA227 microemulsions. This is true even at very low tensions observed when in the presence of ethanol, indicating the lack of affinity between HFA227 and hydrogenated moieties-the surfactant does not tend to curve about water. On the other hand, PO-based amphiphiles can significantly reduce the tension of the HFA227|W interface. Small angle neutron scattering (SANS) and UV-vis spectroscopy results also reveal that a selected ethoxylated amphiphile (EO(13)PO(30)EO(13) at 1mM concentration), when in the presence of ethanol, is capable of forming stable cylindrical reverse aqueous microemulsions. EO(13)PO(30)EO(13) is also capable of forming emulsions of water-in-HFA227 that are fairly stable against coalescence. Such dispersions are potential candidates for the delivery of small polar solutes and larger therapeutic biomolecules to and through the lungs in the form of pMDI formulations, and in other medical sprays.

Solvent-solute interactions in hydrofluoroalkane propellants

Understanding solvation in hydrofluoroalkane (HFA) propellants is of great importance for the development of novel pressurized metered-dose inhaler (pMDI) formulations. HFA-based pMDIs are not only the most widely used inhalation therapy devices for delivering small drug molecules to the respiratory tract, but they also hold promise as vehicles for the delivery of therapeutic biomolecules to and through the lungs. In this work we use binding energy calculations to determine the degree of interaction between HFA propellants and candidate HFA-philes, including a methyl-based tail (isohexane, ISO), and fragments of poly(ethylene oxide) (EO), poly(propylene oxide) (PO), and poly(lactide) (LA). The distinct nature of solvation forces of the two HFA propellants approved by the FDA for use in pMDIs, 1,1,1,2-tetrafluoroethane (HFA134a) and 1,1,1,2,3,3,3-heptafluoropropane (HFA227), is also studied. Binding energy (Ebst) calculations demonstrated that an increase in tail polarity through the addition of oxygen atoms in the fragment backbone provides for sites capable of interacting with the HFA propellant molecules, thus enhancing the stabilization energy of the complexes. The interaction energy between HFA227 and LA (EbHFA227-LA = -24.7 kJ.mol(-1)) is significantly more favorable than that between HFA227 and its hydrocarbon analog (EbHFA227-ISO = -10.0 kJ.mol(-1)). However, it was shown that not only the fragment polarity is of relevance in stabilizing the complexes. The accessibility of the oxygen atoms in the fragments of interest is also relevant. Cluster studies indicate that although both oxygen atoms in the LA fragment are available to form H-bonds with the propellant molecules, the ether oxygen in PO is accessible to only one propellant molecule, thus decreasing significantly the stabilization energy of the cluster. The results shown here serve as a guide for the design of novel HFA-philes for HFA-based pMDIs.