Potential Use of Fluorocarbons in Lung Surfactant Therapy

Structure of Langmuir Monolayers of Perfluorinated Fatty Acids: Evidence of a New 2D Smectic C Phase

Due to the characteristic chain rigidity and weak intermolecular interactions of perfluorinated substances, the phase diagram of Langmuir monolayer formed by perfluorinated molecules has been interpreted so far as displaying only two phases, a 2D gas (G) and a liquid condensed (LC). However, in this work, we presented Grazing Incidence X-ray Diffraction measurements, which exhibit two diffraction peaks on the transition plateau: One is the signature of the hexagonal structure of the LC phase, the second one is associated to the low-density fluid phase and is thus more ordered than expected for a 2D gas or a typical fluid phase. Atomistic molecular dynamics simulations, performed on the transition plateau, revealed the existence of clusters in which domains of vertical molecules organized in a hexagonal lattice coexist with domains of parallel lines formed by tilted molecules, a new structure that could be described as a “2D smectic C” phase. Moreover, the diffraction spectrum calculated from the simulation trajectories compared favorably with the experimental spectra, fully validating the simulations and the proposed interpretation. The results were also in agreement with the thermodynamic analysis of the fluid phase and X-ray Reflectivity experiments performed before and after the transition between these two phases.

The role of surfactant in respiratory distress syndrome

The key feature of respiratory distress syndrome (RDS) is the insufficient production of surfactant in the lungs of preterm infants. As a result, researchers have looked into the possibility of surfactant replacement therapy as a means of preventing and treating RDS. We sought to identify the role of surfactant in the prevention and management of RDS, comparing the various types, doses, and modes of administration, and the recent development. A PubMed search was carried out up to March 2012 using phrases: surfactant, respiratory distress syndrome, protein-containing surfactant, protein-free surfactant, natural surfactant, animal-derived surfactant, synthetic surfactant, lucinactant, surfaxin, surfactant protein-B, surfactant protein-C.Natural, or animal-derived, surfactant is currently the surfactant of choice in comparison to protein-free synthetic surfactant. However, it is hoped that the development of protein-containing synthetic surfactant, such as lucinactant, will rival the efficacy of natural surfactants, but without the risks of their possible side effects. Administration techniques have also been developed with nasal continuous positive airway pressure (nCPAP) and selective surfactant administration now recommended; multiple surfactant doses have also reported better outcomes. An aerosolised form of surfactant is being trialled in the hope that surfactant can be administered in a non-invasive way. Overall, the advancement, concerning the structure of surfactant and its mode of administration, offers an encouraging future in the management of RDS.

Pilot study of vaporization of perfluorohexane during high-frequency oscillatory ventilation in experimental acute lung injury

Inhalation of perfluorohexane vapor (PFH) and high-frequency oscillatory ventilation (HFOV) both have been shown to improve lung function in acute lung injury (ALI). Their combination implies synergistic action. The authors investigated technical aspects of PFH vaporization during HFOV and effects on gas exchange in a pilot study of experimental ALI. Eighteen anesthetized sheep were randomly assigned to HFOV or HFOV with PFH inhalation after oleic acid-induced ALI. HFOV was set to a continuous distending pressure of 25 cm H₂O, and an oscillation of 80 to 100 cm H₂O at a frequency of 5 Hz. PFH vapor was delivered by means of bypassed high-flow oxygen through a thin endotracheal tube. PFH concentration was measured by infrared absorption. Blood gases and hemodynamic data were taken. PaO₂ significantly increased from 9.1 ± 0.9 to 32.7 ± 9.5 kPa (mean ± SEM) in the HFOV group and from 12.5 ± 1.1 to 27.0 ± 6.8 kPa in the HFOV PFH group. PaCO₂ significantly decreased from 6.3 ± 0.3 to 5.5 ± 0.5 kPa in the HFOV group and from 5.7 ± 0.4 to 4.9 ± 0.5 kPa in the HFOV PFH group. Changes in gas exchange were not different between groups. These results show that the inhalation of PFH during HFOV is technically feasible, but did not enhance gas exchange in a 210-minute observation period of experimental ALI.

Comparison of surfactants used to prepare aqueous perfluoropentane emulsions for pharmaceutical applications

Perfluoropentane (PFP), a very hydrophobic, nontoxic, noncarcinogenic fluoroalkane, has generated much interest in biomedical applications, including occlusion therapy and controlled drug delivery. For most of these applications, the dispersion within aqueous media of a large quantity of PFP droplets of the proper size is critically important. Surprisingly, the interfacial tension of PFP against water in the presence of surfactants used to stabilize the emulsion has rarely, if ever, been measured. In this study, we report the interfacial tension of PFP in the presence of surfactants used in previous studies to produce emulsions for biomedical applications: polyethylene oxide-co-polylactic acid (PEO-PLA) and polyethylene oxide-co-poly-epsilon-caprolactone (PEO-PCL). Because both of these surfactants are uncharged diblock copolymers that rely on the mechanism of steric stabilization, we also investigate for comparison's sake the use of the small-molecule cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and the much larger protein surfactant bovine serum albumin (BSA). The results presented here complement previous reports of the PFP droplet size distribution and will be useful for determining to what extent the interfacial tension value can be used to control the mean PFP droplet size.

Exploiting lipid raft transport with membrane targeted nanoparticles: a strategy for cytosolic drug delivery

The ability to specifically deliver therapeutic agents to selected cell types while minimizing systemic toxicity is a principal goal of nanoparticle-based drug delivery approaches. Numerous cellular portals exist for cargo uptake and transport, but after targeting, intact nanoparticles typically are internalized via endocytosis prior to drug release. However, in this work, we show that certain classes of nanoparticles, namely lipid-coated liquid perfluorocarbon emulsions, undergo unique interactions with cells to deliver lipophilic substances to target cells without the need for entire nanoparticle internalization. To define the delivery mechanisms, fluorescently-labeled nanoparticles complexed with alphav beta 3-integrin targeting ligands were incubated with alphav beta 3-integrin expressing cells (C32 melanoma) under selected inhibitory conditions that revealed specific nanoparticle-to-cell interactions. We observed that the predominant mechanism of lipophilic delivery entailed direct delivery of lipophilic substances to the target cell plasma membrane via lipid mixing and subsequent intracellular trafficking through lipid raft-dependent processes. We suggest that local drug delivery to selected cell types could be facilitated by employing targeted nanoparticles designed specifically to utilize alternative membrane transport mechanisms.