Lung surfactant negatively affects the photodynamic inactivation of bacteria—in vitro and molecular dynamic simulation analyses

Abstract

In the context of the rapid increase of antibiotic-resistant infections, in particular of pneumonia, antimicrobial photodynamic therapy (aPDT), the microbiological application of photodynamic therapy (PDT), comes in as a promising treatment alternative since the induced damage and resultant death are not dependent on a specific biomolecule or cellular pathway. The applicability of aPDT using the photosensitizer indocyanine green with infrared light has been successfully demonstrated for different bacterial agents in vitro, and the combination of pulmonary delivery using nebulization and external light activation has been shown to be feasible. However, there has been little progress in obtaining sufficient in vivo efficacy results. This study reports the lung surfactant as a significant suppressor of aPDT in the lungs. In vitro, the clinical surfactant Survanta® reduced the aPDT effect of indocyanine green, Photodithazine®, bacteriochlorin-trizma, and protoporphyrin IX against Streptococcus pneumoniae . The absorbance and fluorescence spectra, as well as the photobleaching profile, suggested that the decrease in efficacy is not a result of singlet oxygen quenching, while a molecular dynamics simulation showed an affinity for the polar head groups of the surfactant phospholipids that likely impacts uptake of the photosensitizers by the bacteria. Methylene blue is the exception, likely because its high water solubility confers a higher mobility when interacting with the surfactant layer. We propose that the interaction between lung surfactant and photosensitizer must be taken into account when developing pulmonary aPDT protocols.

Pulmonary antimicrobial photodynamic therapy and the role of the lung surfactant

“…100 Thus, a collaboration was formed to investigate the interaction using molecular dynamics simulations, in particular to bring more information regarding the mobility of the photosensitizer in the presence of the lung surfactant, that correlates to its availability to interact with the target (in this case, the bacteria). The results of such simulation have been published by Kassab et al 122 Overall, the simulation shows that all photosensitizers interact with the phospholipid mixture. Each molecule preferably interacts with specific phospholipids in the surfactant layer.…”

“…The estimated diffusion coefficient and radius of gyration (from Kassab et al) are probably more significant for the overall effect. 122 The radius of gyration of each photosensitizer molecule is similar in magnitude to the hydrodynamic radius. The mobility of non-spherical particles may be described by the hydrodynamic radius that is related to the frictional force of particle with the solvent.…”

“…Besides the specific interaction with less abundant phospholipids, another result that separates MB from the other photosensitizers is the Z-profile (see Kassab et al 122 ). MB interacts and is released from the surfactant multiple times over the course of the simulation, and even interacts with both the upper and lower layers.…”

“…The light would go through the layers of biological tissue and activate the photosensitizer in the lungs, killing the infective agent. Source: KASSAB et al 61 The combination of the photosensitizer indocyanine green (ICG) and external activation with infrared light has been initially proposed for the treatment of pulmonary infections by our research group in 2014 (as described in Figure 5). [63][64] In 2017, Leite et al showed that it was possible to eliminate S. pneumoniae using doses of ICG and light that were unharmful to macrophages.…”

“…The lung surfactant (Survanta®, AbbVie, USA) was diluted in experiment solutions to achieve a final concentration of 5%, which was sufficient to observe inhibition effects in a similar study. 82 Source: KASSAB et al 122 The light exposure was performed using custom-made devices developed by LAT (Laboratório de Suporte Técnico, IFSC-USP, Brazil). For ICG, laser devices were used, with peak emission at 808 nm (80 mW/cm² for the PDI experiment and 60 mW/cm² for the photobleaching assay).…”