Avaliação in vivo da inativação fotodinâmica para tratamento de pneumonia

Abstract

Infectious pneumonia is a major cause of morbidity/mortality, mainly due to the increasing rate of microorganisms resistant to antibiotics. Photodynamic Inactivation (PDI) is emerging as a promising approach, as effects are based on oxidative stress, preventing the emergence of resistant microorganism strains. In previous studies, the in vitro inactivation of Streptococcus pneumoniae using indocyanine green (ICG) and infrared light source was successful, and achieved reduction of 5 log10 colony-forming units (CFU/mL) with concentration as low as 10 μM ICG. In the present study, a proof-of-principle protocol was designed to treat lung infections by PDI using extracorporeal illumination with a 780 nm laser device and ICG as photosensitizer. In a first row of experiments, hairless mice were infected with S. pneumoniae and PDI was performed two days after infection. For control groups, CFU recovery ranged between 103-104 CFU/mL/mouse. For PDT group, however, no bacteria were recovered in 80% of the animals. Animal survival was evaluated separately over 50 days. No deaths occurred in PDT group, whereas 60% of the control did not survive. Lung injury analyses were performed in BALB/c mice, the bacteria reduction were 2 and 4 log10 in 2 mice (5 in total) and the wet-to-dry ratio showed that PDI did not increase the edema in lungs. The bronchoalveolar lavage data indicated a larger absolute number of cells (mononuclear and polymorphonuclear) in the PDI group in contrast to control group, meaning that the technique could increase the immune system response. In vitro results showed the irradiated ICG could generate aggregates or photoproducts that help PDI to inactivate the bacteria. Our results indicate that extracorporeal PDI has potential for pneumonia treatment, and pulmonary decontamination with PDI may be used as a single therapy or as an antibiotics adjuvant.