In vitro Fourier transform infrared spectroscopic study of the effect of glycerol on the uptake of beclomethasone dipropionate in living respiratory cells

The quantification of drug in living cells is of increasing interest in pharmaceutical research because of its importance in understanding drug efficacy and toxicity. Label-free in situ measurement methods are advantageous for their ability to obtain chemical and time profiles without the need of labelling or extraction steps. We have previously shown that Fourier transform infrared (FTIR) spectroscopy has the potential to quantify drug in situ within living cells at micromolar level when a simple solution of drug was added to the medium. The purpose of this study was to demonstrate that the approach can evaluate more complex systems such as the effect of membrane modification by a formulation on drug uptakes. The inhaled corticosteroid, beclomethasone dipropionate (BDP), in Calu-3 respiratory epithelial cells in the absence and presence of glycerol, an excipient in some inhaled medicines was used as the model system. The FTIR method was first validated for limit of detection (LOD) and quantification (LOQ) according to published guidelines and the LOQ was found to be ∼ 20 μM, good enough to quantify BDP in the living cell. The uptake of BDP by living Calu-3 cells was found to be reduced in the presence of glycerol as expected due to the stiffening of the cell membrane by the presence of glycerol in the formulation. This study demonstrates the valuable analytical capability of live-cell FTIR to study the effect of formulation on drug transport in lungs and to evaluate drug availability to intracellular targets. We conclude that FTIR has potential to contribute widely at the frontier of live-cell studies.

Fluticasone Particles Bind to Motile Respiratory Cilia: A Mechanism for Enhanced Lung and Systemic Exposure?

Background: Inhaled corticosteroids (ICSs) are the main prophylactic treatment for asthma and are used in other diseases, including chronic pulmonary obstructive disease, yet the interaction of ICS particles with the ciliated epithelium remains unclear. The aim of this study was to investigate the earliest interaction of aerosolized fluticasone propionate (FP) particles with human ciliated respiratory epithelium. Methods: A bespoke system was developed to allow aerosolized FP particles to be delivered to ciliated epithelial cultures by nebulization and from a pressurized metered-dose inhaler (pMDI) through a spacer with interactions observed in real time using high-speed video microscopy. Interaction with nonrespiratory cilia was investigated using steroids on brain ependymal ciliary cultures. The dissolution rate of steroid particles was determined. Results: FP particles delivered by aerosol attached to the tips of rapidly beating cilia. Within 2 hours, 8.7% ± 1.8% (nebulization) and 12.1% ± 2.1% (pMDI through spacer) of ciliated cells had one or more particles attached to motile cilia. These levels decreased to 5.8% ± 1.6% (p = 0.59; nebulization) and 5.3% ± 2.2% (p = 0.14; pMDI through spacer) at 24 hours. Particle attachment did not affect ciliary beat frequency (p > 0.05) but significantly (p < 0.001) reduced ciliary beat amplitude. Steroid particles also attached to the tips of motile ependymal brain cilia and also reduced beat amplitude (24 hours: >2 particles bound p < 0.001). Dissolution of FP particles was slow with only 22.8% ± 1.3% of nebulized and 12.8% ± 0.5% of pMDI-delivered drug dissolving by 24 hours. Conclusions: FP particles adhere to the tips of rapidly moving cilia with significant numbers remaining bound at 24 hours, resisting the shear stress generated by ciliary beating. In vivo, this mechanism may predispose to high local drug concentrations and enhance respiratory and systemic corticosteroid exposure.

A novel method for studying airway hyperresponsiveness in allergic guinea pigs in vivo using the PreciseInhale system for delivery of dry powder aerosols

Inhaled adenosine receptor agonists induce bronchoconstriction and inflammation in asthma and are used as bronchial challenge agents for the diagnosis of asthma and in respiratory drug development. Recently developed dry powder aerosols of adenosine have several advantages over nebulised adenosine 5′-monophosphate (AMP) as bronchial challenge agents. However, reverse translation of this bronchial challenge technique to pre-clinical drug development is limited by the difficulty of administering powder aerosols to animals. The aim of the current study was to develop methods for delivering powder aerosols of adenosine receptor agonists to sensitised guinea pigs (as a model of allergic asthma) and evaluate their effect as challenge agents for the measurement of airway responsiveness. The PreciseInhale system delivered micronised AMP and adenosine powders, with mass median aerodynamic diameters of 1.81 and 3.21 μm and deposition fractions of 31 and 48% in the lungs, respectively. Bronchoconstrictor responses in passively sensitised, anaesthetised, spontaneously breathing guinea pigs were compared to responses to nebulised and intravenously administered AMP and adenosine. AMP- and adenosine-induced bronchoconstriction following all routes of administration with the magnitude of response ranking intravenous > dry powder > nebulisation, probably reflecting differences in exposure to the adenosine agonists delivered by the different routes. In conclusion, the PreciseInhale system delivered AMP and adenosine dry powder aerosols accurately into the lungs, suggesting this method can be used to investigate drug effects on airway responsiveness.

Glycerol Solvates DPPC Headgroups and Localizes in the Interfacial Regions of Model Pulmonary Interfaces Altering Bilayer Structure

The inclusion of glycerol in formulations for pulmonary drug delivery may affect the bioavailability of inhaled steroids by retarding their transport across the lung epithelium. The aim of this study was to evaluate whether the molecular interactions of glycerol with model pulmonary interfaces provide a biophysical basis for glycerol modifying inhaled drug transport. Dipalmitoylphosphatidylcholine (DPPC) monolayers and liposomes were used as model pulmonary interfaces, in order to examine the effects of bulk glycerol (0-30% w/w) on their structures and dynamics using complementary biophysical measurements and molecular dynamics (MD) simulations. Glycerol was found to preferentially interact with the carbonyl groups in the interfacial region of DPPC and with phosphate and choline in the headgroup, thus causing an increase in the size of the headgroup solvation shell, as evidenced by an expansion of DPPC monolayers (molecular area increased from 52 to 68 Ų) and bilayers seen in both Langmuir isotherms and MD simulations. Both small angle neutron scattering and MD simulations indicated a reduction in gel phase DPPC bilayer thickness by ∼3 Å in 30% w/w glycerol, a phenomenon consistent with the observation from FTIR data, that glycerol caused the lipid headgroup to remain oriented parallel to the membrane plane in contrast to its more perpendicular conformation adopted in pure water. Furthermore, FTIR measurements suggested that the terminal methyl groups of the DPPC acyl chains were constrained in the presence of glycerol. This observation is supported by MD simulations, which predict bridging between adjacent DPPC headgroups by glycerol as a possible source of its putative membrane stiffening effect. Collectively, these data indicate that glycerol preferentially solvates DPPC headgroups and localizes in specific areas of the interfacial region, resulting in structural changes to DPPC bilayers which may influence cell permeability to drugs.