Near–infrared photodynamic inactivation of S. pneumoniae and its interaction with RAW 264.7 macrophages

Abstract

Pneumonia is the main cause of children mortality worldwide, and its major treatment obstacle stems from the microorganisms increasing development of resistance to several antibiotics. Photodynamic therapy has been presenting, for the last decades, promising results for some subtypes of cancer and infections. In this work we aimed to develop a safe and efficient in vitro protocol for photodynamic inactivation of Streptococcus pneumoniae, one of the most commonly found bacteria in pneumonia cases, using two near‐infrared light sources and indocyanine green, a FDA approved dye. Photodynamic inactivation experiments with bacteria alone allowed to determine the best parameters for microbial inactivation. Cytotoxicity assays with RAW 264.7 macrophages evaluated the safety of the PDI. To determine if the photodynamic inactivation had a positive or negative effect on the natural killing action of macrophages, we selected and tested fewer indocyanine green concentrations and 10 J/cm2 on macrophage‐S. pneumoniae co‐cultures. We concluded that ICG has potential as a photosensitizer for near‐infrared photodynamic inactivation of S. pneumoniae, producing minimum negative impact on RAW 264.7 macrophages and having a positive interaction with the immune cell's microbicidal action.

Nebulization as a tool for photosensitizer delivery to the respiratory tract

“…Finally, due to its prominent results in the treatment of bacterial pneumonia , we chose ICG as a model to demonstrate the delivery of the photosensitizer to the lungs in vivo. The difference in the fluorescence detected by the fiber is related to a difference in ICG concentration over time (Figure ).…”

“…Three photosensitizers were chosen based on their activity against microorganisms: indocyanine green (ICG) is a fluorescent dye used in diagnostics, and it is active against Streptococcus pneumoniae both in vitro and in vivo ; Photodithazine (PDZ) is a chlorin e6 derivative that successfully reduced the viability of a multispecies biofilm ; and Photogem (PTG) is a hematoporphyrin derivative with activity against Candida species . The critical attributes (droplet size and delivery rate), the extent of nebulization and the stability of the photosensitizers to the process were assessed to ensure that they were compatible with the jet nebulization.…”

Nebulization as a tool for the delivery of photosensitizers in the photodynamic inactivation of respiratory diseases

“…In these conditions, the treatment was safe for RAW 264.7 macrophages, and seemed to enhance their ability to fight the bacteria. 5 The in vivo investigation found a reduction in the bacterial burden and an increase in the survival rate of SKH-1 hairless mice infected with S. pneumoniae after a single PDI session using ICG 100 μM and 120 J/cm² of light at 780 nm. 6 In this study, the light exposure did not seem to be harmful to the animals.…”

“…The initial in vitro studies showed that it was possible to eliminate S. pneumoniae using doses of ICG and light that were unharmful to macrophages. 5 Moreover, there was evidence that the PDI could potentialize the antimicrobial activity of such macrophages during the infection. 5 In the in vivo studies, a single session of PDI was enough to reduce the bacterial burden and increase the survival rate of previously infected mice.…”

“…5 Moreover, there was evidence that the PDI could potentialize the antimicrobial activity of such macrophages during the infection. 5 In the in vivo studies, a single session of PDI was enough to reduce the bacterial burden and increase the survival rate of previously infected mice. 6 However, ICG was delivered to the mice using instillation, which has the benefits of being local, but is uncomfortable and not well accepted in the clinical practice.…”