Aerosolization of perfluorocarbons during mechanical ventilation: an in vitro study

Aerosol drug delivery to spontaneously-breathing preterm neonates: lessons learned

Delivery of medications to preterm neonates receiving non-invasive ventilation (NIV) represents one of the most challenging scenarios for aerosol medicine. This challenge is highlighted by the undersized anatomy and the complex (patho)physiological characteristics of the lungs in such infants. Key physiological restraints include low lung volumes, low compliance, and irregular respiratory rates, which significantly reduce lung deposition. Such factors are inherent to premature birth and thus can be regarded to as the intrinsic factors that affect lung deposition. However, there are a number of extrinsic factors that also impact lung deposition: such factors include the choice of aerosol generator and its configuration within the ventilation circuit, the drug formulation, the aerosol particle size distribution, the choice of NIV type, and the patient interface between the delivery system and the patient. Together, these extrinsic factors provide an opportunity to optimize the lung deposition of therapeutic aerosols and, ultimately, the efficacy of the therapy.In this review, we first provide a comprehensive characterization of both the intrinsic and extrinsic factors affecting lung deposition in premature infants, followed by a revision of the clinical attempts to deliver therapeutic aerosols to premature neonates during NIV, which are almost exclusively related to the non-invasive delivery of surfactant aerosols. In this review, we provide clues to the interpretation of existing experimental and clinical data on neonatal aerosol delivery and we also describe a frame of measurable variables and available tools, including in vitro and in vivo models, that should be considered when developing a drug for inhalation in this important but under-served patient population.

Aerosolized perfluorocarbon improves gas exchange and pulmonary mechanics in preterm lambs with severe respiratory distress syndrome

BACKGROUND

Aerosolized perfluorocarbon (PFC) has been proposed as an alternative method of PFC administration; however, the efficacy of aerosolized PFC in a preterm animal model has not yet been demonstrated.

METHODS

Twelve preterm lambs were randomized to two groups: a perfluorodecalin (PFD) aerosol group (n = 6) receiving 10 ml/kg/h of PFD delivered by an intratracheal inhalation catheter followed by 4 h of mechanical ventilation (MV) or the control group, in which animals (n = 6) were managed for 6 h with MV. Gas exchange, pulmonary mechanics, cardiovascular parameters, and cerebral blood flow (CBF) were measured.

RESULTS

Both groups developed hypoxia, hypercarbia, and acidosis at baseline. Aerosolized PFD improved oxygenation (P < 0.0001) and pulmonary mechanics (P < 0.0001) and changed carbon dioxide values to normal physiological levels, unlike the treatment given to the controls (P < 0.0003). The time course of mean arterial blood pressure and CBF were significantly affected by PFD aerosolization, especially during the first hour of life. CBF gradually decreased during the first hour in the PFD aerosol group and remained stable until the end of the follow-up, whereas CBF remained higher in the control group (P < 0.0028).

CONCLUSION

Aerosolized PFD improves pulmonary function in preterm lambs and should be further investigated as an alternative mode of PFC administration.

Vaporized Perfluorocarbon Confers Protection against Acute Lung Injury by Inhibiting MMP-9 Expression without Protective Effects in other Organs

OBJECTIVE: Vaporized perfluorocarbon (PFC) is a treatment for lung injury; this study investigated its mode of action and potential protective effects on other organs, which are unclear. METHODS: Acute lung injury was induced by lung lavage with artificial seawater in 32 female New Zealand White rabbits. Animals received either conventional mechanical ventilation (CMV), positive end-expiratory pressure under CMV (PEEP), vaporized PFC ventilation, or positive end-expiratory pressure with vaporized PFC ventilation (PEEP + PFC). Histopathology of the lung, small intestine, liver and kidney were investigated. Matrix metalloproteinase (MMP)-9 mRNA levels in the lung were analysed. RESULTS: Pathological injury of the lung was significantly alleviated in the PEEP, PFC and PEEP + PFC groups compared with the CMV group. Tissue damage in the liver, kidney and small intestine was similar between all groups. MMP-9 mRNA levels in the PEEP, PFC and PEEP + PFC groups were significantly lower than those in the CMV group. CONCLUSIONS: Vaporized PFC ventilation can significantly alleviate lung injury but has no significant protective effect on other organs. Alleviation of lung injury may be associated with MMP-9 inhibition.

Simulation of fusion-mediated nanoemulsion interactions with model lipid bilayers

Perfluorocarbon-based nanoemulsion particles have become promising platforms for the delivery of therapeutic and diagnostic agents to specific target cells in a non-invasive manner. A "contact-facilitated" delivery mechanism has been proposed wherein the emulsifying phospholipid monolayer on the nanoemulsion surface contacts and forms a lipid complex with the outer monolayer of target cell plasma membrane, allowing cargo to diffuse to the surface of target cell. While this mechanism is supported by experimental evidence, its molecular details are unknown. The present study develops a coarse-grained model of nanoemulsion particles that are compatible with the MARTINI force field. Simulations using this coarse-grained model have demonstrated multiple fusion events between the particles and a model vesicular lipid bilayer. The fusion proceeds in the following sequence: dehydration at the interface, close apposition of the particles, protrusion of hydrophobic molecules to the particle surface, transient lipid complex formation, absorption of nanoemulsion into the liposome. The initial monolayer disruption acts as a rate-limiting step and is strongly influenced by particle size as well as by the presence of phospholipids supporting negative spontaneous curvature. The core-forming perfluorocarbons play critical roles in initiating the fusion process by facilitating protrusion of hydrophobic moieties into the interface between the two particles. This study directly supports the hypothesized nanoemulsion delivery mechanism and provides the underlying molecular details that enable engineering of nanoemulsions for a variety of medical applications.

Surfactant and perfluorocarbon aerosolization during different mechanical ventilation strategies by means of inhalation catheters: an in vitro study

BACKGROUND

Aerosol delivery of surfactant and perfluorocarbon (PFC) is a desirable therapeutic approach for the treatment of various lung diseases in patients undergoing mechanical ventilation. However, the behavior of these substances during aerosolization differs significantly from that of aqueous solutions. In particular, the high vapor pressure of many PFCs tends to result in greater evaporation during mechanical ventilation.

METHODS

Three PFCs and surfactant were aerosolized during mechanical ventilation by means of three intratracheal inhalation catheters (IC) with different air flow rates (IC-1.23, IC-1.1, and IC-1.4), with their aerosol generating tip placed at the distal end of the endotracheal tube (i.d. 4 mm). The influence of four different ventilation strategies on aerosol production rate and PFC and surfactant recovery was studied. The changes in intrapulmonary pressure produced by the air jets of each IC were measured.

RESULTS

With IC-1.23 and IC-1.1, the highest rates of aerosol production were achieved using FC75 (2.27±0.18 and 0.76±0.01, respectively) followed by PFOB (1.74±0.06 and 0.56±0.04), PFD (0.82±0.01 and 0.21±0.01), and surfactant (0.42±0.05 and 0.092±0.01). With IC-1.4 modest aerosol production was obtained irrespective of the aerosolized compound. Mechanical ventilation influenced aerosol recovery, with the trend being toward recovering higher percentages of the compounds with lower peak inspiratory pressure (PIP) and lower respiratory rate (RR) settings. The highest percentages of the initial volume were recovered with IC-1.23 (between 65.43%±4.2 FC75 and 90.21%±4.71 surfactant) followed by IC-1.1 (between 46.48%±4.46 FC75 and 73.19%±2.82 PFOB) and IC-1.4 (between 4.65%±4.36 FC75 and 63.24%±9.71 surfactant). Each of three of the ICs were found to increase the intrapulmonary pressure by about 2-3 cmH₂O during mechanical ventilation.

CONCLUSIONS

Despite of mechanical ventilation, IC-1.23 and IC-1.1 were able to deliver significant amounts of surfactant and perfluorocarbon to the lung model. Changes in PIP and RR directly influence the percentage of surfactant and perfluorocarbon recovered.

Surfactant and perfluorocarbon aerosolization by means of inhalation catheters for the treatment of respiratory distress syndrome: an in vitro study

BACKGROUND

The aerosolization of perfluorocarbons or surfactant has emerged as a feasible alternative to instillation, for the treatment of experimental respiratory distress syndrome. However, the biophysical properties that make these compounds useful in such therapies, significantly affect the performance of nebulizers. Therefore, in vitro studies are required to assess the suitability of new aerosolization technologies for use with these compounds.

METHODS

The aim of the present in vitro study was to investigate the influence of the biophysical properties of perfluorocarbons (PFD, FC75, and PFOB) and a natural porcine surfactant, Curosurf®; on aerosolization and to assess the suitability of three intratracheal inhalation catheters (IC) with different air flow rates (IC-1.23, IC-1.1, IC-1.4) coupled to a jet nebulizer, for aerosol delivery of these compounds.

RESULTS

With IC-1.23 significantly higher aerosol production rates were achieved (p < 0.0001), ranging between 6.05 ± 0.17 mL/min (FC75) and 1.94 ± 0.09 mL/min (Curosurf®), and lower percentage losses of the compound (5-21%), compared to IC-1.1 and IC-1.4 catheters. The lowest aerosolization rates were produced with IC-1.4 ranging from 0.58 ± 0.02 mL/min (FC75) to 0.14 ± 0.01 mL/min (Curosurf®), and this catheter also resulted in the highest percentage losses (25-60%). The mass median aerodynamic diameter (MMAD) ranged between 0.77 μm (PFD) and 8.29 μm (Curosurf®) with IC-1.1, whereas higher MMAD values, of between 4.84 μm (FC75) and 13.42 μm (PFOB), were observed with IC-1.23. Regardless of the catheter used during aerosolization, the perfluorocarbon with the highest kinematic viscosity showed the lowest aerosolization and emission rates and vice versa, which reveals the substantial contribution of this parameter that should accordingly be considered in the design of perfluorocarbon aerosol drug delivery systems.

CONCLUSIONS

Jet aerosolization of perfluorocarbons or surfactant with the intratracheal inhalation catheters seems to be a suitable method for treating experimental respiratory distress syndrome, because it delivers relatively high doses of perfluorocarbons and surfactant to the lungs in a respirable size droplets.

Characterization of perfluorooctylbromide-based nanoemulsion particles using atomistic molecular dynamics simulations

Perfluorocarbon-based nanoemulsion particles have arisen as promising platforms for the cellular delivery of imaging and therapeutic agents to specific targets. However, current knowledge of the agent delivery mechanism is limited to qualitative and phenomenological models. Lack of detail at the molecular level has hence delayed optimizing or customizing nanoemulsion particles for therapeutic and imaging applications. Here we report the first atomistic structural details of a perfluorooctylbromide-based (PFOB-based) nanoemulsion particle (NEP) with a 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) lipid emulsifier. Newly developed PFOB force-field parameters were used in molecular dynamics simulations to model the PFOB-NEP interface in a planar configuration. These PFOB force field parameters were developed and tested to reproduce the characteristics of bulk PFOB as well as PFOB at interfaces with water and emulsifying phospholipids. The modeled PFOB-NEP interface demonstrated significant intercalation of PFOB into the emulsifying lipid monolayer and consequent changes in the structural, electrostatic, and mechanical properties of the POPC monolayer and PFOB. This intercalation provides an explanation for experimental data demonstrating melittin tryptophan fluorescence quenching upon binding to the nanoemulsion particles through the observation of direct contact between the melittin tryptophan and the PFOB bromine. Additionally, the atomistic details of the PFOB-NEP interface structure provided by our simulations are used to suggest the influence of each component on PFOB-NEP delivery function which will be tested in future coarse-grained simulations.

Perfluorocarbon species and nebulizer type influence aerosolization rate and particle size of perfluorocarbon aerosol

PURPOSE

Aerosolization of perfluorocarbons (PFC) has been proven beneficial in vivo. The present in vitro study was performed to investigate, how PFC-aerosolization is affected by type of nebulizer and PFC properties.

MATERIALS AND METHODS

Aerosolization rate was studied of 4 different PFC that were nebulized using 3 different jet nebulizers (operating at different flows: 4.1; 7.1; 13 l/min) and one ultrasonic nebulizer. Distribution of aerosol particle size was determined with a laser diffraction device.

RESULTS

Between the studied nebulizers, considerable differences in the aerosolization rate were found. Aerosolization rate was significantly lower for PFOB (0.48-1.24 mL/min), when compared with PF 5080, RM 101 and FC 77 (1.33-4.75 mL/min). The ultrasonic nebulizer did not generate an aerosol but rather PFC vapor. Lowest mass median diameter (MMD) was found for PFOB and varied between the jet nebulizers from 2.2 and 3.7 microm, with a small range in particle size (maximum of 7.3 microm). FC 77 had highest MMD (3.5 to 9.2 microm) and greatest range of particle size of up to 13 microm.

CONCLUSIONS

Our in vitro data show that aerosolization rate depends mainly on density of PFC and the flow of nebulizer. Particle size distribution is affected by PFC properties. Our result may explain controversial results of published in vivo studies.

Breathing gas perfluorocarbon measurements using an absorber filled with zeolites

BACKGROUND

Perfluorocarbon (PFC) has been widely used in the treatment of respiratory diseases; however, PFC content of the breathing gases remains unknown. Therefore, we developed an absorber using PFC selective zeolites for PFC measurement in gases and investigated its accuracy.

METHODS

To generate a breathing gas with different PFC contents a heated flask was rinsed with a constant air flow of 4 litre x min(-1) and 1, 5, 10, and 20 ml of PFC were infused over 20 min using an infusor. The absorber was placed on an electronic scale and the total PFC volume was calculated from the weight gain.

RESULTS

Steady-state increase in weight was achieved 3.5 min after stopping the infusion. The calculated PFC volume was slightly underestimated but the measuring error did not exceed -1% for PFC less than 1 ml. The measurement error decreased with increasing PFC volume.

CONCLUSIONS

This zeolite absorber is an accurate method to quantitatively determine PFC in breathing gases and can be used as a reference method to validate other PFC sensors.